Recent Progress in Mesostructured Materials, Volume 165: Proceedings of the 5th International Mesostructured Materials Symposium (IMMS 2006) Shanghai, ... (Studies in Surface Science and Catalysis)

Studies in Surface Science and Catalysis 165 RECENT PROGRESS IN MESOSTRUCTURED MATERIALS

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Studies in Surface Science and Catalysis Advisory Editors: B. Delmon and J.T. Yates Series Editor: G. Centi Vol. 165

RECENT PROGRESS IN MESOSTRUCTURED MATERIALS Proceedings of the 5th International Mesostructured Materials Symposium (IMMS2006), Shanghai, P.R. China, August 5-7, 2006

Edited by Dongyuan Zhao Fudan University, Department of Chemistry, Shanghai 200433, P.R. China Shilun Qiu Jilin University, Department of Chemistry, Changchun, Jilin 130023, P.R. China Yi Tang Fudan University, Department of Chemistry, Shanghai 200433, P.R. China Chengzhong Yu Fudan University, Department of Chemistry, Shanghai 200433, P.R. China

Amsterdam – Boston – Heidelberg – London – New York – Oxford – Paris San Diego – San Francisco – Singapore – Sydney – Tokyo

Elsevier Radarweg 29, PO Box 211, 1000 AE Amsterdam, The Netherlands The Boulevard, Langford Lane, Kidlington, Oxford OX5 1GB, UK First edition 2007 Copyright © 2007 Elsevier B.V. All rights reserved No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means electronic, mechanical, photocopying, recording or otherwise without the prior written permission of the publisher Permissions may be sought directly from Elsevier’s Science & Technology Rights Department in Oxford, UK: phone (+44) (0) 1865 843830; fax (+44) (0) 1865 853333; email: [email protected]. Alternatively you can submit your request online by visiting the Elsevier web site at http://elsevier.com/locate/permissions, and selecting Obtaining permission to use Elsevier material Notice No responsibility is assumed by the publisher for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions or ideas contained in the material herein. Because of rapid advances in the medical sciences, in particular, independent verification of diagnoses and drug dosages should be made Library of Congress Cataloging-in-Publication Data A catalog record for this book is available from the Library of Congress British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library ISBN-13: 978-0-444-52178-1 ISBN-10: 0-444-52178-X ISSN: 0167-2991

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v

PREFACE

Since the first discovery in the early of 1990's, the research of mesostructured materials is continuously growing in a fast speed and has attracted more and more scientists from area to area. More than 10,000 research papers and patents have been reported, related to the fabrication of mesostructured materials. The recent progresses include extending the mesostructures ranging from hexagonal to cubic structures, accessible pore sizes, compositions for example silicates, metal oxides, carbon and polymers, surface functionalities, as well as morphologies such as powders, films and monoliths. The efforts to the applications of mesostructured materials have achieved great outcomes and breakthroughs in many fields, such as catalysis, adsorption, separation, optical and electrical devices, biological systems and so on. Many outstanding results have already exhibited the great potential of mesostructured materials to be utilized in our modern society. The International Mesostructured Materials Symposium (IMMS) organized by the International Mesostructured Materials Association (IMMA) has become a routine and fruitful meeting for scientists working on all aspects in mesostructured materials all over the world since it was firstly held in Baltimore, USA, in 1998. During all the symposiums held so far, the communications among scientists and students have connected all the researchers together and inspired them with great views and new ideas. This eventually accelerates the development of mesostructured materials community. During August 4th - 7th, 2006, the 5th International Mesostructured Materials Symposium was successfully held in Shanghai, China. Over 50 oral presentations were delivered and 400 posters were exhibited on 5 sessions as following: i) application of mesoporous materials and their devices; ii) non-siliceous mesoporous materials; iii) functional mesoporous materials and mesoporous zeolites; iv) mesoporous films and functional mesoporous materials; and v) synthesis and structural characterization of mesoporous materials. The contents of the current volume present a selection of more than 200 oral and poster papers from all submitted (more than 500 papers), which covers most of the research aspects of mesostructured materials and reflects the research level and developing trends in this area. This book is believed to be contributing to the progresses of mesostructured materials and will attract the attention of scientists from broad realms.

Dongyuan Zhao Shilun Qiu Yi Tang Chengzhong Yu December 1, 2006

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vii Vll

ORGANIZATION COMMITTEE Honorary Chairman Dongsheng Yan Shanghai Inst. Ceram, Shanghai, China Ruren Xu Jilin University, Changchun, China Mingyuan He Bejing Petroleum Science Inst., Beijing, China Chairman Dongyuan Zhao

Fudan University, Shanghai, China

Co-Chairman Shilun Qiu

Jilin University, Changchun, China

Secretary Yi Tang

Fudan University, Shanghai, China

INTERNATIONAL ADVISORY BOARD Michael W. Anderson George S. Attard Laurent Bonneviot JeffBrinker Avelino Corma Francois Fajula Daniella Goldfarb Shinji Inagaki Mietek Jaroniec Serge Kaliaguine Kazuyuki Kuroda G. Q. Max Lu Alexander V. Neimark Joel Patarin Thomas J. Pinnavaia Ryong Ryoo Clement Sanchez Ferdi Schtlth Galen D. Stucky Baolian Su Takashi Tatsumi Osamu Terasaki James C. Vartuli Jackie Y. Ying Wuzong Zhou

UMIST, UK Univ. Southampton, UK Laval Univ., Canada Sandia National Lab,USA Univ. Politecnica de Valencia, Spain ENSCM, France Weizmann Inst., Israel Toyota Central R&D Labs., Japan Kent State Univ., USA Laval Univ., Canada Waseda Univ., Japan Univ. Queensland, Australia TRI Princeton Univ. Haute Alsace, France Michigan State Univ., USA KAISY, Korea Univ. Pierre, France Max-Planck-Institute, Germany UC Santa Barbara, USA Univ. Namur, Belgium Yokohama Univ. Japan Stockholm Univ. Swenden Mobil, USA MIT, USA Univ. St Andrews, UK

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ix

Contents Preface

v

Organizing Committee

vii

International Advisory Committee

vii

I. Synthesis and structure of mesoporous materials 1.

2.

3.

4.

5.

6.

7.

Synthesis of thick-walled SBA-15 in PEO27-PPO61-PEO27 template under relative low temperature and acidity Hailan Liu, Xiuguo Cui, Sik-Won Moon and Wang-Cheol Zin

1

Synthesis of tetrakaidecahedronal SBA-16 by acidity adjusting Xiuguo Cui, Sik-Won Moon and Wang-Cheol Zin

5

In-situ x-ray diffraction study on the formation of a periodic mesoporous organosilica material Michael Tiemann, Cilâine V. Teixeira, Maximilian Cornelius, Jürgen Morell, Heinz Amenitsch, Mika Lindén and Michael Fröba

9

Is constant mean curvature a valid description for mesoporous materials? Michael W. Anderson, Philip J. Hughes, Osamu Terasaki, Yasuhiro Sakamoto and Ken Brakke

13

Salt effect in the synthesis of highly ordered, extremely hydrothermal stable SBA-15 Changlin Li, Yanqin Wang, Yanglong Guo, Xiaohui Liu, Yun Guo and Guanzhong Lu

17

Hydrocarbon templated sol-gel Synthesis and characterizations of mesoporous silica xerogel Halina Misran, Mohd Ambar Yarmo and Ramesh Singh

21

Microwave Synthesis of SBA-15 mesoporous silica material for beneficial effect on the hydrothermal stability Sang-Cheol Han, Nanzhe Jiang, Sujandi, David Raju Burri, Kwang-Min Choi, Seung-Cheol Lee and Sang-Eon Park

25

x

8.

9.

10.

11.

12.

13.

14.

15.

16.

Control of pore size of mesoporous silica utilizing noncovalent supermicelles Zhurui Shen, Yuping Liu, Pingchuan Sun, Zhongyong Yuan and Tiehong Chen

29

Synthesis of supermicro-macroporous silica with polypeptide-based triblock copolymer Yuping Liu, Liying Li, Zhurui Shen, Pingchuan Sun, Zhongyong Yuan and Tiehong Chen

33

Synthesis of silica nanostructures using synthetic block copolypeptide Yuping Liu, Liying Li, Huijing Zhou, Zhurui Shen, Pingchuan Sun, Zhongyong Yuan and Tiehong Chen

37

Synthesis of mesoporous silica materials from kenyaite Ziyu Liu, Yingxu Wei, Yue Qi, Shiyun Sang and Zhongmin Liu

41

Fluorinated surfactant with short carbon chain templating macropores in hierarchically mesoporous/macroporous silica Xiangju Meng and Takashi Tatsumi

45

Synthesis of mesostructured silica with strongly hydrophilic surfactant templates Weibin Fan, Xiangju Meng, Toshiyuki Yokoi, Yoshihiro Kubota and Takashi Tatsumi

49

Synthesis of stable colloidal suspensions of ordered mesostructured silica from sodium metasilicate using pluronic P123 and mildly acidic conditions Andreas Berggren, Krister Holmberg and Anders E.C. Palmqvist

53

Three-dimensional large pore cubic silica mesophases with tailored pore topology: developments and characterization Freddy Kleitz and Tae-Wan Kim

57

A novel method of mesostructured material architecture using DBD plasma on illite with non-expandibility Myung Hun Kim, Il Mo Kang, Kiwoong Sung, Bui Hoang Bac, Jeong Hun Kim, Yungoo Song, Hi-Soo Moon and Su Dok Yi

61

xi

17.

18.

19.

20.

21.

22.

23.

24.

25.

26.

Production of highly mesostructured SBA-15 silicas at pH around the PZC Alexandra Chaumonnot and Emmanuelle Trela

65

Three-dimensional large pore cubic niobosilicates: direct synthesis and characterization Izabela Nowak and Mietek Jaroniec

69

Synthesis under different conditions of NbMCM-48 with an epoxidation activity Izabela Nowak and Maria Ziolek

73

Composite hydroxyapatite -Na/MCM-41 for the fluoride retention in contaminated water Oscar A. Anunziata, Andrea R. Beltramone and Jorgelina Cussa

77

Direct synthesis of cerium-incorporated SBA-15 mesoporous molecular sieves Qiguang Dai, Guoping Chen, Xingyi Wang and Guanzhong Lu

81

Direct synthesis of MgO modified HMS solid basic materials Zheng Ying Wu, Xin Dong and Jian Hua Zhu

85

Nitrided BaO-MCM-41 as a new mesoporous basic material Shaoliang Jiang, Fuxiang Zhang, Qingfeng Li and Naijia Guan

91

Synthesis and characterization of SBA-15 type mesoporous silicate containing niobium and tin Izabela Nowak, Iveta Nekoksová and Jirí Cejka

95

Effect of concentration of nitric acid on transition of mesoporous silica structure Shuhua Han, Wanguo Hou, Xirong Huang, Liqiang Zheng and Youshao Wang

101

Structure characterization of mesostructured silica nanowires formed in porous alumina membranes Baodian Ya and Ning Wang

105

xii

27.

28.

29.

30.

31.

32.

33.

34.

35.

36.

CRISP and eMap: software for determining 3D pore structures of ordered mesoporous materials by electron crystallography Hong Zhang, Ting Yu, P. Oleynikov, Dongyuan Zhao, S. Hovmöller and Xiaodong Zou

109

A mechanistic study on the degradation of highly ordered, non-ionic surfactant templated aluminosilicate mesoporous materials Al-CMI-1 in boiling water Alexandre Léonard and Baolian Su

113

Tailoring the phase and texture of mesoporous silica by using tetraethylenepentamine and ethanol Ming Bo Yue, Xin Dong and Jian Hua Zhu

117

Synthesis of mesoporous aluminosilicates via recrystallisation of pure silica MCM-41: a stepwise post-synthesis alumination route Robert Mokaya

123

One-pot Synthesis of ionic liquid functionalized SBA-15 mesoporous silicas Yong Liu, Jiajian Peng, Shangru Zhai, Ningya Yu, Meijiang Li, Jianjiang Mao, Huayu Qiu, Jianxiong Jiang and Guoqiao Lai

127

Preparation of novel mesostructured titanium-pillared hydrotalcite Myung Hun Kim, Seok-Heung Jang, Youngho Lee, Il Mo Kang, Yungoo Song, Myongsoo Lee, Jin-Won Park and William Jones

131

Synthesis, characterization and catalytic activity of titania and vanadium grafted and substituted on mesoporous silicas T. Williams, J. N. Beltramini and G. Q. Lu

135

Synthesis and characterization of B- and Ti-MCM-36 Se-Young Kim, Gon Seo and Wha-Seung Ahn

139

Delamination and intercalation of layered aluminophosphate with [Al2P3O12]3- stoichiometry by a controlled two-step method Chen Wang, Ying Li, Weiming Hua, Yinghong Yue and Zi Gao

143

Novel Synthesis method of mesoporous MoSiOx Yanying Zheng, Tao Dou, Aijun Duan, Zhen Zhao and Shanjiao Kang

147

xiii

37.

38.

39.

40.

41.

42.

43.

Birch templated Synthesis of macro-mesoporous silica material for sustained drug delivery Huiming Lin, Fengyu Qu, Shiying Huang, Guangshan Zhu and Shilun Qiu

151

Synthesis of metal-doped mesoporous silica by spray drying and their adsorption properties of water vapor Akira Endo, Yuki Inagi, Satoko Fujisaki, Takuji Yamamoto, Takao Ohmori and Masaru Nakaiwa

157

Structural characterization and systematic gas adsorption studies on a series of novel ordered mesoporous silica materials with 3D cubic Ia-3d structure (KIT-6) Freddy Kleitz, Chia-Min Yang and Matthias Thommes

161

Synthesis and characterization of mesoporous MCM-41 silica with thick wall and high hydrothermal stability under mild base solution Chi-Feng Cheng, Po-Wen Cheng, Shu-Hsien Chou, Hsu-Hsuan Cheng and Hwa Kwang Yak

165

A facile Synthesis of MCM-41 by ultrasound irradiation Alina-Mihaela Hanu, Eveline Popovici, Pegie Cool and Etienne F. Vansant

169

Crystalline micro- and meso-porous materials from inorganic molecular clusters Xiaodong Zou, Tony Conradsson, Kirsten E. Christensen, Tiezhen Ren and Michael O’Keeffe

173

Aluminum incorporation into plate-like ordered mesoporous materials obtained from layered zeolite precursors Raquel García, Isabel Díaz, Carlos Márquez-Álvarez and Joaquín Pérez-Pariente

177

II. Characterization of mesoporous materials 44.

Shaping of mesoporous molecular sieves Martin Hartmann, Sebastian Kunz, G. Chandrasekar and V. Murugesan

181

xiv

45.

46.

47.

48.

49.

50.

51.

52.

53.

A new temperature-programmed calcination route to remove the organic templates from mesoporous aluminophosphate materials Jing Yu, Juan Tan, An J. Wang, Xiang Li and Yong K. Hu

185

Calcination mechanism of block-copolymer template in SBA-15 materials François Bérubé and Serge Kaliaguine

189

Evolution of mesoporosity and microporosity of SBA-15 during a treatment with sulfuric acid Anja Rumplecker, Bodo Zibrowius, Wolfgang Schmidt, Chia-Min Yang and Ferdi Schüth

195

Framework modification and acidity enhancement of zirconium-containing mesoporous materials Lifang Chen, Xiaolong Zhou, Luis E. Noreña, Guoxian Yu, Chenglie Li and Jin-An Wang

199

Pulsed field gradient NMR studies of n-hexane diffusion in MCM-41 materials Ziad Adem, Flavien Guenneau, Marie-Anne Springuel-Huet, Juliette Blanchard and Antoine Gédéon

203

TEM studies of bicontinuous cubic mesoporous crystals Yasuhiro Sakamoto, Chuanbo Gao, Shunai Che and Osamu Terasaki

207

Characterization of vesicular mesostructured silica synthesized under alkaline conditions Cheng Chi, Bo Wang, Wei Shan, Yahong Zhang and Yi Tang

211

Zirconium species created within the mesopores of MCM-41 and NbMCM-41 Joanna Goscianska and Maria Ziolek

215

Synthesis and characterization of tetrahedral aluminumspecies-containing SBA-15 and its application for selective t-butylation of naphthalene M. Selvaraj and S. Kawi

219

xv

54.

55.

Adsorption–desorption characteristics of volatile organic compounds over various zeolites and their regeneration by microwave irradiation K.-J. Kim, Y.-H. Kim, W.-J. Jeong, N.-C. Park, S.-W. Jeong and H.-G. Ahn

223

Reversible and irreversible adsorption of dye on mesoporous materials in aqueous solution Shaobin Wang and Lili Tian

227

III. Non-siliceous mesoporous materials 56.

57.

58.

59.

60.

61.

Thermal stability of mesotructured aluminas obtained from different procedures Sébastien Royer, Charles Leroux, Alexandra Chaumonnot, Renaud Revel, Stéphane Morin and Loïc Rouleau

231

Self-formation phenomenon of hierarchically meso- (micro-) macroporous zirconium oxide Aurélien Vantomme and Bao-Lian Su

235

Synthesis and characteristics of hierarchically porous zirconia-based composite oxides Hangrong Chen, Jianlin Shi and Dongsheng Yan

239

Synthesis of ordered mesoporous zinc oxide obtained by dry gel nanocasting from the mesoporous carbon CMK-3 Helwig H. Thiel, Pablo Cascales de Paza, Martin Hartmann and Stefan Ernst

243

Synthesis of mesostructured TiO2 through self-assembly of nanocrystals of rutile Wenfu Yan, Zuojiang Li and Sheng Dai

247

Synthesis of a lamellar mesostructured calcium phosphate using hexadecylamine as a structure-directing agent in the ethanol/water solvent system Nobuaki Ikawa, Yasunori Oumi, Tatsuo Kimura, Takuji Ikeda and Tsuneji Sano

253

xvi

62.

63.

64.

65.

66.

67.

68.

69.

70.

71.

Formation of pt nanowires in mesoporous materials and SiO2 nanotubes Inga Bannat and Michael Wark

257

Synthesis of Pd nanoparticles in la-doped mesoporous titania with polycrystalline framework Shuai Yuan, Qiao R. Sheng, Jin L. Zhang, Feng Chen, Masakazu Anpo and Wei L. Dai

261

Fabrication of metal oxide nanowires templated by SBA-15 with adsorption-precipitation method Renlie Bao, Kun Jiao, Heyong He, Jihua Zhuang and Bin Yue

267

Facile Synthesis of hierarchically structured titanium phosphate with bimodal wormhole-like mesopores and macropores Hailong Fei, Xiaoquan Zhou, Pingchuan Sun, Zhongyong Yuan and Tiehong Chen

271

Synthesis of mesoporous alumina using anionic, nonionic and cationic surfactants Jagadish C. Ray, Kwang-Seok You, Ji-Whan Ahn and Wha-Seung Ahn

275

Synthesis of b-SiC nanofiber using PMOs as a single precursor Jeong-Rae Ko, Ju-Won Min, Byung-Don You and Wha-Seung Ahn

279

Synthesis of porous TiO2 monolith by organic membrane template Jianxi Yao and Dan Wang

283

Template-free synthesis of hierarchical mesoporous alumina-based materials with uniform channel-like macrostructures Tiezhen Ren, Zhongyong Yuan and Baolian Su

287

Mesostructured powder of tungsten oxide-surfactant compound: influence of calcination on the material’s structure Zhimei Qi, Itaru Honma and Haoshen Zhou

291

Hydrothermal Synthesis and characterization of mesoporous zirconia templated by triethanolamine Fu Ma, Jihong Sun, Hongjian Zhao, Yun Li and Shijie Luo

301

xvii

72.

73.

74.

75.

76.

77.

78.

79.

80.

The role of triethanolamine in the synthesis of mesostructured TiO2 by sol-gel method Feng Wang, Jihong Sun and Chongfang Ma

305

Nano-replication to mesoporous metal oxides using mesoporous silica as template Byung Guk So, Jeong Kuk Shon, Ji Ae Yu, Oh-Shim Joo and Ji Man Kim

309

A novel synthesis of manganese oxide nanotubes Li Tao, Chenggao Sun, Meilian Fan, Caijuan Huang, Hesheng Zhai, Hailong Wu and Zisheng Chao

313

Synthesis of well ordered crystalline TiO2 photocatalyst with enhanced stability and photoactivity Zhenfeng Bian, Jian Zhu and Hexing Li

317

Crystallization of stable mesoporous zirconia and ceria-zirconia Anil K. Sinha and Kenichirou Suzuki

323

Synthesis of mesoporous structures zinc sulfide by assembly of nanoparticles with block-copolymer as template Hongmei Ji, Jieming Cao, Jinsong Liu, Mingbo Zheng, Yongping Chen, Yulin Cao and Nongyue He

327

Surfactant-free Synthesis of mesoporous tin oxide with a crystalline wall Jieming Cao, Haitao Hou, Xianjia Ma, Mingbo Zheng and Jinsong Liu

331

Mesoporous crystals of metal oxides and their properties Calum Dickinson, Andrew Harrison, Jim A. Anderson and Wuzong Zhou

335

Synthesis and characterization of lanthanum oxide nanotubes using dendritic surfactant Li Tao, Chenggao Sun, Meilian Fan, Qi Liu, Caijuan Huang, Hesheng Zhai, Hailong Wu and Zisheng Chao

339

xviii

81.

82.

83.

84.

85.

Nanostructured SiC from preceramic polymer via replication of hard templates Jia Yan, Hao Wang, In-Kyung Sung, Kyung-Hoon Park, Anjie Wang, Xiao-dong Li and Dong-Pyo Kim

343

Gas-sensing properties of ordered mesoporous Co3O4 synthesized by replication of SBA-15 silica Thorsten Wagner, Jan Roggenbuck, Claus-Dieter Kohl, Michael Fröba and Michael Tiemann

347

Direct Synthesis of mesoporous spinel-type Zn-Al complex oxide with a crystalline framework Lu Zou, Feng Li, Xu Xiang, David G. Evans and Xue Duan

351

Visible light activated mesoporous TiO2-xNx nanocrystalline photocatalyst Zheng Jiang, Farhan Al-Shahrani, Tsung-Wu Lin, Yingying Cui and Tiancun Xiao

355

Mesoporous metal oxides and mixed oxides nanocasted from mesoporous vinylsilica and their applications in catalysis Yanqin Wang, Yangang Wang, Yun Guo, Yanglong Guo, Xiaohui Liu and Guanzhong Lu

361

IV. Mesoporous carbons 86.

87.

88.

89.

Surface functionalization of templated porous carbon materials Dan Yu, Zhiyong Wang, Nicholas S. Ergang and Andreas Stein

365

Rational control of the micro/mesoporosity of multimodally porous carbon monoliths synthesized by nanocasting Jan-Henrik Smått, An-Hui Lu, Stefan Backlund and Mika Lindén

369

Synthesis of mesoporous carbon frameworks with graphitic walls by secondary hard template method Renyuan Zhang, Bo Tu and Dongyuan Zhao

373

Porous carbons cast from meso- or nonporous silica nanoparticles Camila Ramos da Silva, Martin Wallau, Eduardo Prado Baston, Rita Karolinny Chaves de Lima and Ernesto A. Urquieta-González

377

xix

90.

91.

92.

93.

94.

95.

96.

97.

98.

Carbon fiber-templated growth of hierarchical analcime hollow fibers Xueying Chen, Zhiying Lou, Minghua Qiao, Kangnian Fan and Heyong He

381

Synthesis of mesoporous silica and mesoporous carbon using gelatin as organic template Chun-Han Hsu, Hong-Ping Lin, Chih-Yuan Tang and Ching-Yen Lin

385

A study on the Synthesis of mesoporous silica and carbon platelets with perpendicular nanochannels Yi-Qi Yeh, Gui-Min Teo, Bi-Chang Chen, Hong-Ping Lin, Chih-Yuan Tang and Chin-Yen Lin

389

Preparation of versatile silica/carbon nanocomposites via carbonization of ethyl-bridged periodic mesoporous organosilica Zhuxian Yang, Yongde Xia and Robert Mokaya

393

Ordered mesoporous carbon as new support for direct methanol fuel cell: controlling of microporosity and graphitic character Chanho Pak, Sang Hoon Joo, Dae Jong You, Hyung Ik Lee, Ji Man Kim, Hyuk Chang and Doyoung Seung

397

Direct sulfonation of ordered mesoporous carbon for catalyst support of direct methanol fuel cell Chanho Paka, Sang Hoon Joo, Dae Jong You, Ji Man Kim, Hyuk Chang and Doyoung Seung

401

Effect of chemically surface modified MWNTs on the mechanical and electrical properties of epoxy nanocomposites Joohyuk Park and Abu Bakar Bin Sulong

405

Synthesis of uniform carbon nanotubes by chemical vapor infiltration method using SBA-15 mesoporous silica as template An-Ya Lo, Shou-Heng Liu, Shing-Jong Huang, Huang-Kai Shen, Cheng-Tzu Kuo and Shang-Bin Liu

409

Synthesis of large pore mesoporous carbon using colloidal silica template Huachun Li and Shunai Che

413

xx

V. Functional Mesoporous Materials 99.

Study of mercury(II) binding to thiol-modified ordered mesoporous silicas by analytical and electrochemical analyses: influence of the pore structure and the functionalization process Fabrice Gaslain, Cyril Delacôte, Bénédicte Lebeau, Claire Marichal, Joël Patarin and Alain Walcarius

417

100. The effect of inorganic salt on the Synthesis of large-pore PMO with aromatic moieties in the framework Sung Soo Park, Booyoun An, Yunji Kang, Mina Park, Il Kim and Chang-Sik Ha

421

101. Bovine serum albumin adsorption in large pore amine functionalized mesoporous silica S. Z. Qiao, Haiying Zhang, Xufeng Zhou, Sandy Budihartono and G. Q. Lu

425

102. Effect of various templates on the formation of mesoporous benzene-silica hybrid material K.-F. Zhou, Q.-H. Xia, H.-B. Zhu, D. Hu and Z.-M. Liu

429

103. Synthesis of layered organosilica binding with self-assembled LB film Takayuki Chujo, Yu Gonda, Yasunori Oumi, Tsuneji Sano and Hideaki Yoshitake

433

104. Synthesis of highly ordered mesoporous benzene-silicas using PEO–PLGA–PEO triblock copolymers Eun-Bum Cho, Hyojung Kim and Dukjoon Kim

437

105. Tailoring cage-like organosilicas with multifunctional bridging and surface groups Rafal M. Grudzien, Bogna E. Grabicka, Donald J. Knobloch and Mietek Jaroniec

443

106. Synthesis and morphology of functionalized mesoporous ethanesilica Yaojun Wang, Yanqin Wang, Xiaohui Liu and Guanzhong Lu

447

xxi

107. Periodic mesoporous organosilicas: thermal stability and etherification of phenol Micha Rat, M. Hassan Zahedi-Niaki, Serge Kaliaguine and Do Trong-On

451

108. Highly efficient microwave-assisted asymmetric transfer hydrogenation with SBA-15-supported TsCHDA chiral ligands Myung-Jong Jin, M. S. Sarkar and Ji-Young Jung

455

109. Preparation of bimodal MCM-41 encapsulated Co(III)-porphyrin complex and its catalytic properties in cyclohexane oxidation Shijie Luo and Jihong Sun

459

110. Synthesis of optically active monoesters via enantioselective reaction catalyzed by heterometallic chiral (salen) co complex immobilized on acid sites of A1-MCM-41 Geon-Joong Kim, Chang-Kyo Shin and Rahul B. Kawthekar

463

111. Chiral (salen) cobalt complexes encapsulated in mesoporous mordenite as an enantioselective catalyst for phenolic ring opening of terminal epoxides Kwang-Yeon Lee, Young-Hee Lee, Chang-Kyo Shin and Geon-Joong Kim

467

112. Effect of surface functional groups on adsorption and release of bovine serum albumin on SBA-15 S.-W. Song, S.-P. Zhong, K. Hidajat and S. Kawi

471

113. Microstructure understanding of organic-inorganic hybrid mesoporous silica by SAXS Yanjun Gong, Zhihong Li and Tao Dou

475

114. Surface aminosilylated mesoporous SBA-15 with rare earth metal sandwiched polyoxometalates as heterogeneous catalyst Yan Zhou, Bin Yue, Renlie Bao, Min Gu and Heyong He

479

VI. Mesoporous zeolite-like materials 115. Characterization of nickel metal distribution in Ni/y-zeolite Dul-Sun Kim, Jung-hee Yoon, Jae-Suk Shin and Dong-keun Lee

483

xxii

116. Synthesis of MCM-22/MCM-41 composites with zeolite MCM-22 as precursor Li Yuping, Zhang Wei, Wang Xiaoli, Dou Tao and Xie Kechang

487

117. Micro-mesoporous composite molecular sieves with wormlike morphology prepared from zeolite beta Ying Zhang, Tao Dou, Qiang Li and Shanjiao Kang

491

118. Steam stable mesoporous silicalite-1 with semi-crystalline framework Xiong Li, Sun-Jin Kim and Wha-Seung Ahn

495

119. Synthesis of bimodal mesoporous material with the primary/ secondary structure of ZSM-5 as building unit Yong Niu and Jihong Sun

499

120. Synthesis of meso-structured silicalite-1 by combining solid phase crystallization and carbon templating Jia Wang and Marc-Olivier Coppens

503

121. Assembly of mesocellular silica foams from colloidal zeolite nanocrystals through template free process Yuxin Jia, Wei Han, Guoxing Xiong and Weishen Yang

507

122. Microwave assisted-direct Synthesis of highly ordered large pore functionalized mesoporous SBA Sujandi, Sang-Cheol Han, Dae-Soo Han and Sang-Eon Park

511

123. Template-free sol-gel synthesis of mesoporous materials with ZSM-5 structure walls Wei Han, Yuxin Jia, Guoxing Xiong and Weishen Yang

515

124. Facile low temperature synthesis of primary amine templated super-microporous aluminosilicates Graham Rance, Yongde Xia and Robert Mokaya

519

125. Synthesis of zeolitic mesoporous titanosilicate using mesoporous carbon as a hard template Haijiao Zhang, Yueming Liu, Mingyuan He and Peng Wu

523

xxiii

126. Synthesis of micro- and mesoporous ZSM-5 composites and their catalytic application in glycerol dehydration to acrolein Chunjiao Zhou, Caijuan Huang, Wengui Zhang, Hesheng Zhai, Hailong Wu and Zisheng Chao

527

127. Comparative time-resolved luminescence studies of Tb-ZSM-5 and Tb-MFI mesoporous materials C. Tiseanu, M. U. Kumke, V.I. Parvulescu, B. C. Gagea and J. A. Martens

531

128. Acylation of fatty acids with amino-alcohols on UL-MFI type materials M. Musteata, V. Musteata, A. Dinu, V.I. Parvulescu, V.T. Hoang, D. Trong-On and S. Kaliaguine

535

129. Creating mesopores in ZSM-5 for improving catalytic cracking of hydrocarbons Yingxu Wei, Fuxiang Chang, Yanli He, Shuanghe Meng, Yue Yang, Yue Qi and Zhongmin Liu

539

VII. Mesoporous films and morphology of mesoporous materials 130. Effect of surfactant on the morphology of Ti-MMM-2 mixed-phase materials Sean M. Solberg, Dharmesh Kumar and Christopher C. Landry

543

131. Chiral mesoporous silica tubules by achiral surfactant template Jingui Wang, Wenqiu Wang, Pingchuan Sun, Zhongyong Yuan and Tiehong Chen

547

132. Aspects of a novel method for the pore size analysis of thin silica films based on krypton adsorption at liquid argon temperature (87.3 k) Matthias Thommes, Norikazu Nishiyama and Shunsuke Tanaka 551 133. Dynamics of xenon adsorbed in organically modified silica thin films using hyperpolarized 129Xe 2D- exchange NMR M. Nader, F. Guenneau, C. Boissiere, D. Grosso, C. Sanchez and A. Gédéon

555

xxiv

134. Nanocrystal-micelle: a new building block for facile self-assembly and integration of 2, 3-dimensional functional nanostructures Hongyou Fan

559

135. Direct visualization of mesoporous structures in the framework of SBA-15 mesoporous films Jinlou Gu, Hangrong Chen, Xiongping Dong, Zhicheng Liu and Jianlin Shi

563

136. Preparation, texture and electrochemical properties of TiO2 films with highly ordered mesoporosity and controlled crystallinity D. Fattakhova Rohlfing, M. Wark, J. Rathousky, T. Brezesinski and B. Smarsly

569

137. Optimization of the silylation procedure of thin mesoporous SiO2 films with cationic trimethylaminopropylammonium groups Dina Fattakhova-Rohlfing, Michael Wark and Jiri Rathousky

573

138. Synthesis of transparent mesoporous aluminum organophosphonate films through triblock copolymer templating Tatsuo Kimura and Kazumi Kato

579

139. Electrical/mechanical properties of nanoporous thin films by using various sized cyclodextrins Jin-Heong Yim, Jong-Ki Jeon and Young-Kwon Park

583

140. Synthesis of MSU-1 silica particles with spherical morphology Kalidas Biswas, Soo-Hyun Jang, Wha-Seung Ahn, Yoon-Suk Baik and Won-Jo Cheong

587

141. Proton conductivity of cubic silica-based mesostructured monolithic membranes Liangming Xiong, Yong Yang, Hangrong Chen, Jianlin Shi and Masayuki Nogami

591

142. Vapor phase preparations of mesoporous silica thin films for ultra-low-k dielectrics Shunsuke Tanaka, Takanori Maruo, Norikazu Nishiyama, Korekazu Ueyama and Hugh W. Hillhouse

595

xxv

143. Synthesis of silica nanospheres with well-ordered mesopores assisted by amino acids Toshiyuki Yokoi, Marie Iwama, Tatsuya Okubo, Yasuhiro Sakamoto, Osamu Terasaki, Yoshihiro Kubota and Takashi Tatsumi

599

144. Size and morphology control in the Synthesis of SBA-15 Huanling Xie, Ranbo Yu, Dan Wang, Jianxi Yao, Xianran Xing and Wenguo Xu

603

145. Synthesis and characterization of mesostructured silica sphere particles with core space Jung-Sik Choi, Kyung-Ku Kang and Wha-Seung Ahn

607

146. Synthesis of highly ordered large pore mesoporous silica SBA-16 spheres Hongxiao Jin, Qingyin Wu, Chao Chen, Daliang Zhang and Wenqin Pang

611

147. Effects of the different amount of phosphoric acid on the resulting morphology of SBA-15 Yun Li, Jihong Sun, Fu Ma and Shijie Luo

617

148. Morphology control of SBA-15 in chiral organic acid media Shengrong Ye, Yueming Liu, Mingyuan He and Peng Wu

621

149. Synthesis of the mesoporous TiO2 films and their application to dye-sensitized solar cells Dong-Hyun Cha, Young-Suk Kim, Jia Hong Pan, Yoon Hee Lee and Wan In Lee

625

150. Formation mechanism of monodispersed mesoporous silica spheres and its application to the synthesis of core/shell particles Hiroshi Nozaki, Noritomo Suzuki, Tadashi Nakamura, Yuusuke Akimoto and Kazuhisa Yano

629

151. Controllable synthesis of cubic MCM-48 with different morphologies by using ternary surfactant templating route Lingdong Kong, Su Liu, Yi Wang, Xuewu Yan, Heyong He and Quanzhi Li

633

xxvi

VIII. Catalysis of mesoporous materials 152. Mesoporous silica hosts for polyenzymatic catalysis Anne Galarneau, Lai Truong Phuoc, Aude Falcimaigne, Gilbert Renard and François Fajula

637

153. Mesoporous silica-supported chiral norephedrine ligands for asymmetric transfer hydrogenation Myung-Jong Jin, M. S. Sarkar and Sang-Eon Park

643

154. Facile heterogenization of homogeneous ferrocene catalyst on SBA-16 David Raju Burri, Isak Rajjak Shaikh, Sang-Cheol Han and Sang-Eon Park

647

155. Naphthalene alkylation with i-PrOH over bimodal mesoporous catalysts containing alumina Fang Liu, Jihong Sun, Quansheng Liu and Haibo Jin

651

156. Synthesis and application of MCM-41 molecular sieves modified by lanthanum in oxidation of cyclohexane Wangcheng Zhan, Yanglong Guo, Yanqin Wang, Yun Guo and Guanzhong Lu

655

157. Microwave Synthesis of Fe-SBA-16 mesoporous silica and Friedel-Crafts type reaction Dae-Soo Han, Sujandi, Jeong-Boon Koo and Sang-Eon Park

659

158. Photocatalytic oxidation of phenylsulfonephthalein by hydrogen peroxide over Ti containing SBA-15 mesoporous materials Phuong T. Dang, Tuan A. Vu, Thang C. Dinh, Yen Hoang, Thang G. Vuong, Thang V. Hoang, Hoa K.T. Tran, Lan K. Le and Phu H. Nguyen

663

159. Influence of the catalyst on the formation and structure of bimodal mesopore silica Xiaozhong Wang, Wenhuai Li, Bing Zhong and Kechang Xie

667

160. Mesoporous zirconia with different pore size for Fischer-Tropsch Synthesis Yachun Liu, Jiangang Chen, Kegong Fang and Yuhan Sun

671

xxvii

161. Catalytic phenol hydroxylation over Cu-incorporated mesoporous materials Huili Tang, Yu Ren, Bin Yue, Shirun Yan and Heyong He

675

162. Alumina-promoted sulfated mesoporous zirconia and catalytic application in butane isomerization Chi-Chau Hwang, Jung-Hui Wang, She-Tin Wong and Chung-Yuan Mou

679

163. Reducibility of cobalt oxides over SBA-15 supported cobalt catalysts for Fischer-Tropsch synthesis Dae Jung Kim, Brian C. Dunn, Min Kang, Jae Eui Yie, Seong-Hyun Kim, Jenifer Gasser, Eric Fillerup, Louisa Hope-Weeks and Edward M. Eyring

685

164. Microencapsulation of heterocyclic carbene-pd complex in SBA-15 silica for heck reactions M. S. Sarkar, Ji-Young Jung and Myung-Jong Jin

689

165. Heterogeneous asymmetric transfer hydrogenation with mesoporous silica SBA-15-supported Ru-TsCHDA catalyst Ji-Young Jung, M. S. Sarkar and Myung-Jong Jin

693

166. Mesoporous silica-SBA-15 supported n-heterocyclic carbene-Pd complex for Suzuki coupling reaction Myung-Jong Jin and M. S. Sarkar

697

167. Selective a-alkylation of ketones with alcohols catalyzed by highly active mesoporous Pd/MgO-Al2O3 type basic solid derived from pd-supported MgAl-hydrotalcite Suman K. Jana, Yoshihiro Kubota and Takashi Tatsumi

701

168. Asymmetric dihydroxylation catalyzed by SBA-15 silica-supported bis-cinchona alkaloid M. S. Sarkar, Ji-Young Jung and Myung-Jong Jin

705

169. Mesoporous silica SBA-15-supported palladium catalyst for green Sonogashira coupling reactions Myung-Jong Jin, M. S. Sarkar, Dong-Hwan Lee and Ik-Mo Lee

709

xxviii

170. VO(acac)2 incorporated in mesoporous silica SBA-15-confined ionic liquid as a catalyst for epoxidation M. S. Sarkar, Ji-Young Jung and Myung-Jong Jin

713

171. Selective photocatalytic oxidation of methane into methanol on V-MCM-41 mesoporous molecular sieves Yun Hu, Yasuhito Nagai, Masaya Matsuoka and Masakazu Anpo

717

172. Hydrodesulfurization of dibenzothiophene and 4,6-dimethyldibenzothiophene over Ni-Mo catalysts supported by siliceous SBA-15 Jing Ren, Anjie Wang, Juan Tan, Guangwei Cao, Chang Liu, Yongtai Li, Mohong Lu and Yongkan Hu

721

173. Photocatalytic preferential oxidation of Co with O2 in the presence of H2 (photo- PROX) on Mo-MCM-41 at 293 K Masaya Matsuoka, Takashi Kamegawa and Masakazu Anpo

725

174. Influence of the location of Rh(0) particles within MCM-41 materials on the selectivity of hydrogenation reactions Maya Boutros, Franck Launay, Audrey Nowicki, Thomas Onfroy, Virginie Semmer-Herledan, Alain Roucoux and Antoine Gédéon

729

175. Platinum catalysts supported on SBA-15 for the selective catalytic reduction of lean NOx with propylene Kwang-Eun Jeong, Joo-Il Park and Son-Ki Ihm

733

176. Catalytic activity of dinuclear chiral salen complexes immobilized on modified SBA-15 Chang-Kyo Shin, Chul-Heng Ahn, Wenji Li and Geon-Joong Kim

737

177. Simultaneous separation and enantioselective hydrolysis reaction of epoxides in membrane system containing chiral polymer salen catalyst immobilized on MCM-41 Young-Hee Lee, Kwang-Yeon Lee, Chang-Kyo Shin, Sang-Han Kim and Geon-Joong Kim

741

178. Mesoporous silica MCM-41-supported norephedrine and ephedrine as heterogeneous chiral ligands in asymmetric catalysis Sang Han Kim, Chang kyo Shin, Jong Hyuk Seok, Choong Young Lee and Geon Joong Kim

745

xxix

179. Catalytic performance of Cu-MCM41 with high copper content for NO reduction by CO Yan Kong, Yanhua Zhang, Xiaoshu Wa, Jun Wang, Haiqin Wan, Lin Dong and Qijie Yan

749

180. Influence of iron content on the structure and catalytic activity for the hydroxylation phenol of Fe-MCM41 Cheng Wu, Yan Kong, Xingjie Xu, Jun Wang, Fei Gao, Lin Dong and Qijie Yan

755

181. Basic catalysis by surfactant containing MCM-41 Leandro Martins and Dilson Cardoso

761

182. Growth of carbon nanotubes with different inner diameter on mesoporous silica Lingxia Zhang, Jina Yan, Jianlin Shi, Lei Li, Zile Hua and Hangrong Chen

765

183. Selective hydrogenation of benzene over Ru/SBA-15 catalyst prepared by the “double solvents” impregnation method Juan Bu, Yan Pei, Pingjun Guo, Minghua Qiao, Shirun Yan and Kangnian Fan

769

184. Mesoporous calcined Mg-Al hydrotalcites as catalysts for synthesis of propylene glycol Gongde Wu, Xiaoli Wang, Junping Li, Ning Zhao, Wei Wei and Yuhan Sun

773

185. Application of Ti-containing mesoporous silica (single-site photocatalyst) and photo-assisted deposition (PAD) method for preparation of nano-sized Pt metal catalyst Hiromi Yamashita, Toshiaki Shimizu, Naoki Mimura, Makoto Shimada, Shuai Yuan, Kohsuke Mori, Tetsutaro Ohmichi, Iwao Katayama, Takao Sakata and Hirotaro Mori

777

186. Hydroisomerization and hydrocracking of long chain n-alkane and Fischer-Tropsch wax over bifunctional Pt-promoted Al-HMS catalysts Yanyong Liu, Toshiaki Hanaoka, Kazuhisa Murata and Kinya Sakanishi

781

xxx

187. Preparation and characterization of SBA-15 supported molybdenum nitride for NH3 decomposition Hongchao Liu, Hua Wang, Zhongmin Liu, Jianghan Shen and Ying Sun

787

188. Comparative study of the catalytic activity of Al-SBA-15 and Ga-SBA-15 materials in a-pinene isomerisation and oxidative cleavage of epoxides B. Jarry, F. Launay, J. P. Nogier and J. L. Bonardet

791

189. Mesoporous silica supported Ni catalysts for CO2 reforming of methane Shaobin Wang

795

190. SBA-15 mesoporous molecular sieve as an appropriate support for highly active HDS catalysts prepared using Mo and W heteropolyacids Lilia Lizama, Juan C. Amezcua, Ramón Reséndiz, Sergio Guzmán, Gustavo A. Fuentes and Tatiana Klimova 799 191. SBA-15 mesoporous molecular sieves doped with ZrO2 or TiO2 as supports for Mo HDS catalysts Oliver Y. Gutiérrez, Fernando Pérez, Cecilia Salcedo, Gustavo A. Fuentes, Manuel Aguilar, Xim Bokhimi and Tatiana Klimova

803

192. Isopropylation of naphthalene over mesostructured aluminosilicate nanoparticles with wormhole framework structures Shang-Ru Zhai, Chang-Sik Ha, Yong Liu, Hua-Yu Qiu, Dong Wu, Yu-Han Sun, Shao-Jun Wang and Bin Zhai

807

193. Adsorption desulfurization from gasoline by silver loaded on mesoporous aluminum oxide Wenzhong Shen, Xiangping Yang, Qingjie Guo, Yihong Liu and Yanru Song

811

xxxi

IX. Applications of mesoporous materials 194. Proton conduction of ordered mesoporous silica-methanesulfonic acid hybrids Yonggang Jin, Zhi Ping Xu, Shizhang Qiao, João C. Diniz da Costa and G.Q. Max Lu

817

195. Oligodeoxynucleotide molecule delivery by organically modified SBA-15 mesoporous materials Xi-chuan Cao, Zhuo-qi Zhang, Jian R. Lu and Michael W. Anderson

821

196. Release of guest molecules from modified mesoporous silica Magdalena Stempniewicz, Michael Rohwerder and Frank Marlow

825

197. Spherical siliceous mesocellular foam particles for high-speed size exclusion chromatography Yu Han, Su Seong Lee and Jackie Y. Ying

829

198. Synthesis of meso/macroporous SBA-15 and its application to VOCs’ adsorption Ji Sun Yun, Joo-Il Park, Kwang-Eun Jeong and Son-Ki Ihm

833

199. Novel hydrophobic mesostructured materials: synthesis and application for VOCs removal Thang C. Dinh, Yen Hoang, Thanh V. Ho, Phuong T. Dang, Nam H. T. Le, Hoa K. T. Tran, Hoa V. Nguyen, Tuan A. Vu and Phu H. Nguyen

837

200. Synthesis of silver nanowire/mesoporous silica composite as a highly active antiseptic Diequing Zhang, Ying Wan, Guisheng Li, Jing Zhang and Hexing Li

841

201. Preparation and conductivity of decatungstomolybdovanadogermanic heteropoly acid supported on mesoporous silica SBA-15, SBA-16, MCM-41 and MCM-48 Qingyin Wu, Hongxiao Jin, Wenqi Feng and Wenqin Pang

847

xxxii

202. Fabrication of highly dispersed Pt nanoparticles in tubular carbon mesoporous materials for hydrogen energy applications Shou-Heng Liu, Rong-Feng Lu, Shing-Jong Huang, An-Ya Lo, Wen-Hua Chen, Wen-Yueh Yu, Shu-Hua Chien and Shang-Bin Liu

853

203. Membranes with Ni, Mn-MCM-41 mesoporous molecular sieves and their applications for waste water purification Viorica Pârvulescu, Gabriela Roman, Simona Somacescu, Isabella Dascalu, Bujor Albu and Baolian Su

857

204. Hybrid mesoporous SC/SBA as a chemosensor for recognizing Cu2+ Ling Gao, Jianqiang Wang, Liying Shi, Li Huang, Ying Wang, Xiaoxing Fan, Tao Yu, Mei Zhu and Zhigang Zou

861

205. Aluminosilicate mesoporous MCM-41 for drug famotidine delivery Qunli Tang, Yao Xu, Dong Wu and Yuhan Sun

865

206. DNA delivery using polyethyleneimine (PEI) coated iron oxide-silica mesostructured particles Stuart C. McBain, Humphrey H. P. Yiu, Alicia J. El Haj and Jon Dobson

869

207. A new highly sensitive and selective nanosensor for Mercury (II) ions Noan Nivarlet, Samuel Martinquet and Baolian Su

873

208. SBA-15 functionalized by epoxy groups for immobilization of penicillin G acylase Yongjun Lü, Qiaoling Zhao, Yanglong Guo, Yanqin Wang, Yun Guo and Guanzhong Lu

877

209. Adsorptive desulfurization of diesel using metallic Nickel supported on SBA-15 as adsorbent Chang Hyun Ko, Jung Geun Park, Sang-Sup Han, Jong-Ho Park, Soon-Haeng Cho and Jong-Nam Kim

881

210. Highly hydrophobic mesoporous materials as matrix for gas chromatography separation of water-alcohols mixtures Lianxiu Guan, Junping Li, Dongjiang Yang, Xiuzhi Wang, Ning Zhao, Wei Wei and Yuhan Sun

885

xxxiii

211. Photoluminescence study of [Eu(bpy)2]3+ supported on mesoporous materials of different pore sizes Shuxun Ge, Nongyue He, Song Li, Jiqing Wang, Libo Nie and Hong Chen

889

212. Benzene sensors based on surface photo voltage of mesoporous organo-silica hybrid thin films Brian Yuliarto, Yoko Kumai, Itaru Honma, Shinji Inagaki and Haoshen Zhou

893

213. Lipase immobilization in ordered mesoporous materials Elías Serra, Álvaro Mayoral, Yasuhiro Sakamoto, Rosa M. Blanco and Isabel Díaz

897

214. Microwave Synthesis of Zr incorporated SBA-16 mesoporous silica as a catalyst for Meerwein-Ponndorf-Verley (MPV) reduction Nanzhe Jiang, Kwang-Min Choi, Sang-Cheol Han, Jeong-Boon Koo and Sang-Eon Park

901

215. One and three dimensional mesoporous carbon nitride molecular sieves with tunable pore diameters Ajayan Vinu, Toshiyuki Mori, Sunichi Hishita, Srinivasan Anandan, Veerappan Vaithilingam Balasubramanian and Katsuhiko Ariga

905

216. Synthesis of well-ordered carboxyl group functionalized mesoporous carbon using non-toxic oxidant, (NH4)2S2O8 Ajayan Vinu, Kazi Zahir Hossain, Sunichi Hishita, Toshiyuki Mori, Narasimhan Gokulakrishnan, Veerappan Vaithilingam Balasubramanian and Katsuhiko Ariga

909

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Recent Progress in Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

1

Synthesis of thick-walled SBA-15 in PEO27-PPO6r PEO27 template under relative low temperature and acidity Hailan Liua, Xiuguo Cuia*, Sik-Won Moonb and Wang-Cheol Zinb "Key Laboratory of Organism Functional Factors of the Changbai Mountain (Education Ministry of China), College of Engineering, Yanbian University, Yanji 133002, P. R. China h Dept. of Materials Engineering, Pohang University of Science and Technology, Pohang 790-390, Korea

Thick walled (7.7 nm) SBA-15 has been synthesized by using PEO27-PPO6r PEO27 (P104) as template under relative low temperature and acidity. SAXS, nitrogen sorption experiments and TEM have been utilized to characterize resultant materials. 1. Introduction The mesostructure of porous materials grown by surfactant templated processes is well established in pioneering work of Mobil's research group [1]. In view of the some applications such as catalytic cracking process as well as preparation of inverse replica materials through mesoporous template, wall thickness of mesoporous materials is a key feature that needs to be tuned. Much effort has been taken to control wall thickness by adjusting ratio of SiO2 and surfactant [2], acidity [3] and employing surfactant with ultra-long hydrophilic chains [4]. In hexagonal mesoporous materials, wall thickness (-6.4 nm) of SBA-15 obtained by PI 23 (PEO20-PPO70-PEO20) is larger than that of MCM-41, which result in well hydrothermal stability of SBA-15 [5]. However, further thickening of wall still remains as a challenge in the study of hexagonal mesoporous materials. Here, we present an easy method for preparation of thick walled SBA-15 (TSBA-15, 7.7 nm) in the presence of triblock copolymer, PI04 (PEO27-PPO6r PEO27), at relative low synthetic temperature and acidity. To the best of our

2

knowledge, to date there has been no report on wall thickness of SBA-15 exceeds 7 nm. 2. Experimental Section In a typical synthesis of T-SBA-15, 0.33 g of P104 (EO27-PO61-EO27, Mw=5160, BASF) were dissolved in 10 g of HC1 aqueous solution (2.5 g of H2O and 7.5 g of 2.5M HC1) by stirring at 45°C. Then, 0.7 ml of tetraethyl orthosilicate (TEOS, Aldrich) was added to the homogeneous solution. White precipitate was repeatedly washed with water and air-dried at 45°C for an additional 48 h, and then was calcined at 500°C for 8 h. In characterization of TSBA-15, synchrotron small angle X-ray scattering (SAXS) pattern was obtained on 3C2 beam line with CuKa radiation (wavelength, A,=0.1542 nm) in the Pohang Accelerator Laboratory, POSTECH, Korea. Nitrogen adsorption and desorption isotherms were measured at 77K on a Micromeritics ASAP2010 having an accelerated surface area and porometry system. Surface area was determined by the BET (Brunauer-Emmett-Teller) method. The pore size distribution (PSD) was calculated by the BJH (Barrett-Joymer-Halenda) method from the isotherm of adsorption branch. Transmission electron microscopy (TEM) image was achieved using a Hitachi S-4200 microscope operating at HOkV. 3. Results and Discussion

.04nm

o . 500

100

—

210

1

2

q(nm 1 )

3

100 0.0

D(illgitrom)

0.2

0.4

0.6

0.8

1.0

Relative pressure (p/p0)

Figure 1 SAXS pattern (a), nitrogen sorption isotherm (b) and the pore size distribution (inset of Fig lb) of T-SBA-15.

3

Figure la demonstrates that T-SBA-15 exhibits three well resolved 100, 200 and 210 reflections resulting from the P6mm hexagonal symmetry, and about 10 nm of first ^/-spacing, similar to that reported for SBA-15 from PI23 in the past [4]. The nitrogen sorption isotherm and pore size distribution (determined by using BJH model) are shown in Fig. lb and its inset. A clear type IV isotherm with a small Hi-type hysteresis was obtained, which is typical of mesoporous materials and is in good agreement with SBA-15 prepared from PI23. Furthermore, T-SBA-15 has BET surface area of 884m/g and mean pore size of 3.86 nm. Thus, wall thickness of T-SBA-15 that calculated by subtracting mean pore size from aQ (=2d]Oo/^3) is 7.73 nm, which is both larger than reported SBA-15 with 6.4 nm of wall thickness from P123 [4] and that with 4.1 nm from PI04 [6].

Figure 2 TEM image of T-SBA-15 in [100] (left) and [110] direction (right).

TEM images in two directions shown in Fig. 2 further verified the results of the SAXS measurement and the nitrogen adsorption and desorption experiments. The space between pore and its adjacent pore, and the silica wall thickness are observably larger than that of usual SBA-15, which favor the improvement of hydrothermal stability mesoporous materials and the controlling pore size of the inverse replica materials such as CMK-3. Generally, in case of nonionic block copolymer template, because the surfactant PI04 used here has larger EO chains than the surfactant PI23, thicker silica wall of SBA-15 is expected and observed in our samples. Furthermore, both low synthetic temperature and certain pH value range that is nearby the

4

isoelectric point of silica result in thick silica wall of mesoporous materials [3]. The synthetic temperature of SBA-15 from P104 is in range of 55-85°C within which SBA-15 with wall thickness of 4.1 nm can be prepared [6]. Here, our synthetic temperature is 45°C that more lower than that of the past report, which induce well hydrophilic property of amphiphilic block copolymer and the formation of thick silica wall framework. At the isoelectric point of silica, hydrolysis rate is minimum and condensation rate is maximum, which is one of the reasons for T-SBA-15. Although synthetic conditions are strictly restricted, we have successfully synthesized T-SBA-15 (wall thickness of 7.73 nm) at new synthetic temperature and relative low acidity in the presence of PI 04. 4. Conclusion In summary, at relative low synthetic temperature and acidity, thick silica wall SBA-15 has been prepared in the presence of P104 (EO27-PO61-EO27). Increasing and controlling of wall thickness are significant both for hydrothermal stability of mesoporous materials and structure tailoring of the inverse replica materials. 5. Acknowledgement This work was supported by National R & D Project of Nano-Science and Technology (Grant No. Ml-0214-00-0021) in Korea, NSFC (Grant No. 20061003, 50463002), EYTP of M. O. E. and JDYSP of Jilin Prov. in P. R. China. Cui wishes to thank to the Korea-China Young Scientist Exchange Program of KOSEF. 6. References [1] C. T. Kresge, M. E. Leonowicz, W. J. Roth, J. C. Vartuli and J. S. Beck, Nature, 359 (1992) 710. [2] M. Choi, W. Heo, F. Kleitz and R. Ryoo, Chem. Comm., (2003) 1340. [3] X. Cui, W.-C. Zin, W.-J. Cho and C.-S. Ha, Mater. Lett., 59 (2005) 2257. [4] L. Wang, J. Fan, B. Tian, H. Yang, C. Yu, B. Tu and D. Zhao, Micropor. Mesopor. Mater., 67 (2004) 135. [5] D. Zhao, Q. Huo, J. Feng, B. F. Chmelka and G. D. Stucky, J. Am. Chem. Soc., 120 (1998) 6024. [6] P. Kipemboi, A. Fogden, V. Alfredsson and K. FlodstrSm, Langmuir, 17 (2001) 5398.

Recent Progress in Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

5

Synthesis of tetrakaidecahedronal SBA-16 by acidity adjusting Xiuguo Cuia*, Sik-Won Moonb and Wang-Cheol Zinb " Laboratory of Advanced Functional Materials, College of Engineering, Yanbian University, Yanji 133002, P. R. China b Dept. of Materials Engineering, Pohang University of Science and Technology, Pohang 790-390, Korea

Tetrakaidecahedronal SBA-16 (cubic Im 3 m) has been synthesized in PEO106-PPO70-PEO106 ( F127 ) template solution without inorganic salt by adjusting acidity at low temperature. Due to the pH-dependence of mesoporous silica morphology, the shapes of resultant materials show an evolution from irregular sphere —» dodecahedron —> tetrakaidecahedron —> irregular shape as the acidity increases. 1. Introduction In the past decade, A new development is the discovery of crystal morphology of mesoporous materials that reveal well order both on the mesoscopic scale of porous structures and the macroscopic scale of particle shapes. Ryoo [1] first reported on truncated rhombic dodecahedral single crystal MCM-48 (cubic, Ia3d). Subsequently, cubic mesophase crystal materials with dodecaoctahedron shape (SBA-1, Pm3n) [2, 3], a large number of facets [4], square [5], truncated-cube (SBA-1, Pm3n) [5], large hierarchical structured mesoporous built single crystals [6], and hybrid mesostructures (cubic, Pm3n) with dodecahedral crystal-like morphology [7] were synthesized by using an ionic surfactant template. Compared to the ionic surfactant method, non-ionic block copolymer synthesis of crystal or crystal-like mesophase is more difficult due to its relative weak the intensity of interaction between surfactants and inorganic species. Zhao [8] reported the first synthesis_of rhombdodecahedron shaped SBA-16 mesoporous single crystals (cubic Im 3 m) in the presence of F108 triblock copolymer and inorganic salt. In this present, a new_ faceted mesoporous material, tetrakaidecahedronal SBA-16 silica (cubic Im 3 m) has

6

been firstly synthesized by adjusting acidity of F127 template solution without auxiliary agent. 2. Experimental Section In a typical synthesis of tetrakaidecahedronal SBA-16, 0.35 g of F127 (EO106-PO70-EO106) were dissolved in 10 g of HC1 aqueous solution (9.0ml of H2O and 1.0ml of 2MHC1) by stirring at 18°C. Then, 0.7 ml of tetraethyl orthosilicate (TEOS) was added to the homogeneous solution. White precipitated was repeatedly washed with water and air-dried at 50°C for an additional 48h, and then was calcined at 500°C for 8 h. In characterization of tetrakaidecahedronal SBA-16, synchrotron small angle X-ray scattering (SAXS) pattern was obtained on 3C2 beam line with CuKa radiation (wavelength, A,=0.1542 nm) in the Pohang Accelerator Laboratory, POSTECH, Korea. Nitrogen adsorption and desorption isotherms were measured at 77K on a Micromeritics ASAP2010 having an accelerated surface area and porometry system. Surface area was determined by the BET (Brunauer-Emmett-Teller) method. The pore size distribution (PSD) was calculated by the BJH (Barrett-Joymer-Halenda) method from the isotherm of adsorption branch. Scanning electron microscopy (SEM) images were taken using a JEOL JSM-6330F operating at an accelerating voltage of 15 keV. 3. Results and Discussion

200-

rTTTrTO

dV/dr

Mean PoreS ze » B.3nm

100

I

Radius(An jstrom) 0.2

0.4

0.6

0.8

Relative pressure (p/pj

Figure 1 SAXS pattern (a) and N2 sorption isotherm (b) of tetrakaidecahedronal SBA-16

Figure la demonstrates that resultant material exhibits three well resolved 110, 200 and 211 reflections resulting from the Im3m cubic symmetry, similar to that reported for SBA-16 from F108 [5] and F127 [9]. The correlation between the mesostructure and crystal morphology of tetrakaidecahedronal

7

SBA-16 can not be fully confirmed in this present due to insufficient data from SAXS pattern and HRTEM images. The nitrogen sorption isotherm shows two condensation steps at middle and high relative pressure, respectively (Fig lb). In the set of Fig lb, pore size distribution (determined by using BJH model) is narrow and bimodal (6.3 nm and 4.1 nm of mean pore sizes). Under condition of strong acid, dodecahedron SBA-16 has been synthesized by aid of inorganic salt. In our work, SEM images of resultant materials reveal that tetrakaidecahedron consists of two hexagon facets and twelve trapezia facets. External morphologies of mesoporous materials present irregular sphere, dodecahedron (Figure 2 left), tetrakaidecahedron (Figure 2 right) and irregular shape at various acidity of template solution. These changes are related to acidity range within which assembly between inorganic precursor and polymer template is well accurate, without which it is discordant.

(a)

(b)

Figure 2 SEM images of dodecahedronal, and tetrakaidecahedronal SBA-16 at various acidity. Left: template solution (lml H2O+9ml 2MHC1). Right: template solution (9 ml H2O + lml 2M HC1).

In the absence of auxiliary agent such as electrolyte and co-solvent, it is somewhat difficult to prepare crystal-like mesoporous material from nonionic polymer template. Tetrakaidecahedronal SBA-16 can be fabricated only in a narrow range of acidity and temperature. 4. Conclusion In this work, SBA-16 with a new external morphology, tetrakaidecahedronal has been synthesized in low acidity template solution without aid of auxiliary.

8

An external morphological evolvement from irregular sphere to dodecahedron, and then to tetrakaidecahedron, final to irregular shape with increasing acidity of F127 template solution. 5. Acknowledgement This work was supported by National R & D Project of Nano-Science and Technology (Grant No. Ml-0214-00-0021) in Korea, NSFC (Grant No. 20061003, 50463002), EYTP of M. O. E. and JDYSP of Jilin Prov. in P. R. China. Cui wishes to thank to the Korea-China Young Scientist Exchange Program of KOSEF. 6. References [1] J. M. Kim, S. K. Kim and R. Ryoo, Chem. Commun., (1998) 259. [2] S. Guan, S. Inagaki, T. Ohsuna and O. Terasai, J. Am. Chem. Soc., 122 (2000) 5660. [3] Sayari, S. Hamoudi, Y. Yang, I. L. Moudrakovski and J. R. Ripmeester, Chem. Mater., 12 (2000) 3857. [4] S. Che, Y. Sakamoto, O. Terasaki and T. Tatsumi, Chem. Mater., 13 (2001) 2237. [5] M. C. Chao, D. S. Wang, H. P. Lin and C. Y. Mou, J. Mater. Chem., 13 (2003) 2853. [6] Z. R. Tian, J. Liu, J. A. Voigt, B. Mckenzie and H. Xu, Angew. Chem., Int. Ed., 42 (2003) 413. [7] M. P. Kapoor and S. Inagaki, Chem. Mater., 14 (2002) 3509. [8] Yu, B. Tian, J. Fan, G. D. Stucky and D. Zhao, J. Am. Chem. Soc., 124 (2002) 4556. [9] W. Stevens, K. Lebeau, M. Mertens, G. V. Tendeloo, P. Cool and E. F. Vansant, J. Phys. Chem. B, 110(2006)9183.

Progress in in Mesostructured Materials Materials Recent Progress S. Qiu, Y. Tang and C. Yu (Editors) (Editors) D. Zhao, S. © 2007 2007 Elsevier Elsevier B.V. B.V. All All rights reserved. reserved.

9

In-situ X-ray diffraction study on the formation of a periodic mesoporous organosilica material Michael Tiemann,a Cilaine V. Teixeira,b Maximilian Cornelius,8 Jiirgen Morell,a Heinz Amenitsch,0 Mika Lindenb and Michael Frobaa "Institute of Inorganic and Analytical Chemistry, Justus Liebig University, HeinrichBuff-Ring 58, D-35392 Giessen, Germany b Department of Physical Chemistry, Abo Akademi University, Porthansgatan 3-5, FIN-20500 Turku, Finland c Institute of Biophysics and X-ray Structure Research, Austrian Academy of Sciences, Schmiedlstrafie 6, A-8042 Graz, Austria

1. Introduction Recently the synthesis of a new periodic mesoporous organosilica (PMO) material, including the preparation of the respective organosilane precursor, l,4-bis-((E)-2-(triethoxysilyl)vinyl)benzene (BTEVB), was reported simultaneously and independently by Cornelius etal. [1] and by Wang and Sayari [2]. The organic unit consists of an aromatic and an unsaturated component conjugated to each other. The PMO material exhibits cylindrical mesopores periodically arranged in a two-dimensional hexagonal p6mm symmetry as evidenced by X-ray diffraction (see below) and TEM. Nitrogen physisorption reveals typical mean pore diameters (BJH) and specific surface areas (BET) of 2.6 nm and 730 m2g'', respectively. Within the pore walls the organic units are aligned in a crystal-like fashion, similar to those in some phenylene- [3, 4], biphenylene [5], and ethylene-bridged PMOs [6]. For further details on the synthesis and structural properties of the products see reference 1. Characterization of the PMO material by X-ray diffraction yields two pieces of information. First, the low-angle region of the diffraction pattern shows peaks which correspond to the periodic two-dimensional hexagonal order of the mesopores. Second, the wide-angle region exhibits a series of equidistant reflections which are created by the periodic, crystal-like arrangement of the organic groups within the pore walls. These two sets of information obtained from a single X-ray diffraction experiment over the entire scattering region, i.e.

10 10

low angle and wide angle, make it possible to tackle the question whether or not the formation of crystal-like ordering in the pore walls occurs simultaneously with the generation of the periodically arranged mesopores [7]. 2. Experimental Section In-situ X-ray diffraction experiments were carried out at the Austrian SAXS beamline at the ELETTRA synchrotron source in Trieste, Italy, using a 2D CCD-detector. Prior to each measurement BTEVB was dispersed in an aqueous solution of octadecyltrimethylammonium chloride (OTAC1) and NaOH (BTEVB/OTACl/NaOH/H2= 1/1.4/11.9/660) and allowed to hydrolyze at room temperature for 24 h under vigorous stirring. A fraction of the homogeneous mixture was then transferred to an X-ray capillary. The sealed capillary was mounted in the sample holder where it was heated to 95 °C under constant rotation during the measurement. These experimental conditions correspond to those of the synthesis reported in reference 1. The diffraction patterns were corrected for variations in the primary intensity as well as for a background of the solvent. Positions and integrated intensities of the reflections were obtained by fitting Lorentzian profiles to the experimental data. 3. Results and Discussion Figure 1 shows the temporal evolution of the diffraction patterns during the PMO synthesis. The generally high intensity in the low-angle region is due to diffuse scattering from various objects, such as micellar aggregates. After ca. 50 minutes a low-angle Bragg reflection (s = 0.21 nm"1) is visible, corresponding to the formation of the periodic surfactant-organosilane mesophase. About simultaneously (see below) two additional Bragg reflections in the wide-angle region (s = 0.85 nm"1 and 1.70 nm"1) are detected which correspond to the periodic, crystal-like arrangement of the organic groups within the pore walls. The low-angle peak's integrated intensity is plotted as a function of the reaction time in Figure 2a. During the first 50 minutes the peak is not unambiguously distinguishable from diffuse scattering. The broad distribution of the data, especially after longer reaction times, is presumably caused by inhomogenities of the sample in the rotating capillary. However, extrapolation of the mean peak intensity towards zero suggests that the formation of the mesophase starts approximately at the onset of the measurement, i.e. at t = 0. Figure 2b shows the temporal evolution of the second wide-angle peak's intensity. (The second wide-angle peak was chosen instead of the first one because it has a higher signal-to-noise ratio.) The peak cannot be distinguished from noise at short reaction times, but extrapolation indicates that it has its origin at approximately t = 0. These findings indicate that both the formation of the mesophase and the local ordering in the walls occur simultaneously, i.e. in a

11 11

cooperative fashion. Similar results have been reported for the synthesis of a PMO material with a different organic unit [7].

0,2

0,4

0,6

0,8

1,0

1.2

2,0

s / nm"1

Figure 1: Temporal evolution of the X-ray diffraction pattern for the formation of a periodic mesoporous organosilica material. The peak at low-angle (a) corresponds to the periodic surfactant-organosilane mesophase; the peaks in the wide-angle region (b) characterize the periodic arrangement of the organic groups within the pore walls.

The d values of all three reflections remain approximately constant during the in-situ measurement. This is in contrast to the slight subsequent decrease which is frequently observed during the formation of mesostructured silica materials from precursors which are not organically modified [8-10]. However, in the in-situ measurements the low-angle reflection is located at a slightly larger d value (4.89 nm) than in the powder diffraction pattern of the final porous material after removal of the surfactant (4.72 nm [1]). This shift in the repeat distance by ca. 4 % is attributable to a shrinkage of the mesostructure due to additional condensation of the building units in the pore walls upon removal of the surfactant. For the wide-angle reflections no such difference between the in-situ measurements and the powder diffraction pattern is observed; in both cases the d values are 1.19 nm for the first peak and 0.60 nm for the second peak, respectively, indicating that the repeat distance in the regular arrangement of the organic units is widely inflexible.

12 12

60

120 180 time I minutes

240

Figure 2: Temporal evolution of the intensities of (a) the low-angle reflection and (b) the second wide-angle reflection. Extrapolation of both plots to zero suggests that both peaks start to evolve simultaneously at / = 0.

4. References [1] [2] [3] [4] [5] [6] [7]

M. Cornelius, F. Hoffmann and M. Froba, Chem. Mater., 17 (2005) 6674. Sayari and W. Wang, J. Am. Chem. Soc, 127 (2005) 12194. S. Inagaki, S. Guan, Y. Fukushima, T. Ohsuna and O. Terasaki, Nature, 416 (2002) 304. M. P. Kapoor, Q. Yang and S. Inagaki, Chem. Mater., 16 (2004) 1209. M. P. Kapoor, Q. Yang and S. Inagaki, J. Am. Chem. Soc, 124 (2002) 15176. J. Xia, W. Wang and R. Mokaya, J. Am. Chem. Soc, 127 (2005) 790. J. Morell, C. V. Teixeira, M. Cornelius, V. Rebbin, M. Tiemann, H. Amenitsch, M. Froba and M. Linden, Chem. Mater., 16 (2004) 5564. [8] P. Agren, M. Linden, J. B. Rosenholm, R. Schwarzenbacher, M. Kriechbaum, H. Amenitsch, P. Laggner, J. Blanchard and F. Schuth, J. Phys. Chem. B, 103 (1999) 5943. [9] M. Tiemann, V. Goletto, R. Blum, F. Babonneau, H. Amenitsch and M. Linden, Langmuir, 18(2002)10053. [10] K. FlodstrOm, C. V. Teixeira, H. Amenitsch, V. Alfredsson and M. Linden, Langmuir, 20 (2004) 4885.

Recent Progress in Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Published by Elsevier B.V.

13 13

Is constant mean curvature a valid description for mesoporous materials? Michael W. Andersona, Philip J. Hughesa, Osamu Terasakib, Yasuhiro Sakamotob and Ken Brakke0 "School of Chemistry, The University of Manchester, Oxford Road, Manchester, Ml 3 9PL, UK b Structural Chemistry, Arrhenius Laboratory, Stockholm University, 10691 Stockholm, Sweden 'Mathematics Department, Susquehanna University, Selinsgrove PA 17870, USA

1. Introduction A detailed comparison is made between electrostatic potential density maps and surfaces of constant mean curvature for a variety of cubic mesoporous phases. We establish that the average iso-electron density surface near the wall of the mesoporous material is consistent, within experimental error, with a constant mean curvature surface. The deviation from zero mean curvature is different for different synthesis conditions and structures. On a short timescale surfactant mesophases in a water/surfactant system exhibit a boundary between the two phases which can be described in terms of sectional curvatures - usually either the mean curvature H= (ki+ k2)/2 or Gaussian curvature K = ki * k2, where kjand k2 are the maximum and minimum curvature at any given point on the surface. In a number of instances this surface has been considered to be minimal and periodic corresponding to zero mean curvature at every point (Luzzati et al 1996). This is similar to the surface formed by an open soap film suspended on a wire frame where the pressure is equal on both sides of the film and hence the mean curvature at every point is zero. Mesoporous inorganic phases templated by surfactant or block co-polymer mesophases make an interesting test of such theories. Although the system is more complex, and also there is some debate as to whether the structures are at thermodynamic equilibrium, there is the distinct advantage that the materials are solid and amenable to detailed investigation by electron crystallography. Consequently we have access to accurate electrostatic potential density maps which can be

14 14

matched with computed surfaces with known mean curvature (Anderson et al. 2005). The goal of this work is not only to establish the nature of the curvature but also to understand the formation mechanism. The results also have implications for natural inorganic structures which are templated by macromolecular organic assemblies. 2. Experimental section Electrostatic potential density maps were determined using electron crystallographic methods, described elsewhere (Anderson et al. 2004), which rely on data from a single particle and consequently are not contaminated by scattering from ill-formed material. Constant mean curvature surfaces are computed using a periodic lattice with pre-determined symmetry using the Surface Evolver programme (Brakke 1996). 3. Results and discussion Fig. 1 shows an example of AMS-8, synthesised with an anionic surfactant (Garcia-Bennett et al. 2004) both as an iso-electron density contour plot and as a constant mean curvature surface. The slices shown in Fig. 2 reveal that for this structure there is a very close fit at zero mean curvature. However, for SBA-1, SBA-6 and SBA-16 - all with cubic symmetry - a similar analysis reveals a constant mean curvature but not zero mean curvature. AMS-8

Equi-electrostatic potential surface

Zero mean curvature surface

Fig. 1 The structure of AMS-8 from both experimental electron crystallography and as an isomean curvature map determined using Surface Evolver.

The close approximation to a constant mean curvature surface suggests that the forces at the interface of the average silica surface with the mixed phase water/surfactant or water/polymer are relatively even. This in turn suggests a uniform interface. The four cubic mesophase systems studied all result from an

15 15

arrangement of high mean curvature micelles packed on a cubic lattice. The gaussian curvature of these micelles is positive. The resulting silica structures for three materials, SBA-1, SBA-6 and AMS-8, have constant but low mean curvature and also negative gaussian curvature. This suggests that the interface is not between the silica and organic agent but between silica and water. Only for SBA-16 does the mean curvature of the silica material become sufficiently high to suggest a closer interaction between silica and block co-polymer template.

Fig. 2 Slice of electrostatic potential density map for AMS-8, coloured contours are experimental and dotted line is computed for slices taken through the unit cell at z=0 and z=0.125.

Fig. 3 shows the gaussian curvature computed for AMS-8 and also SBA-16. The AMS-8 structure has already been shown to have constant mean curvature close to zero and as expected the gaussian curvature is negative everywhere, indicating a saddle-like surface. The gaussian curvature is most negative at the necks which join the cages. For SBA-16 the story is quite different. In this case the actual structure is far from zero mean curvature exhibiting a constant and positive mean curvature. As can be seen from Fig.3 the gaussian curvature over most of the surface is also strongly positive with negative gaussian curvature only at the rather narrow necks. This is consistent with the silica surface being much more closely bound to the block co-polymer templating agent. This is consistent with the prevailing conjecture that the end of the block co-polymer chains are embedded within the silica wall resulting in additional microporosity when the template is removed by calcination. Fig. 3 also shows the ideal zero mean curvature topology for the Im 3m structure which is often used to describe the related liquid crystal boby-centred cubic mesophase. This demonstrates how the specific interactions between the templating agent and the silica wall are crucial to define to final topology.

16 16

Fig. 3 Gaussian curvature for (a) AMS-8, (b) zero mean curvature ideal SBA-16 topology and (c) actual SBA-16 topology with positive mean curvature.

4. Summary This work demonstrates that, within experimental error, constant mean curvature is a valid description to describe the stucture of a variety of cubic mesoporous structures. The mean curvature is closest to zero for surfactant based preparations but large and positive for polymer based preparations. This indicates the difference in interfacial interactions between the two systems. 5. References [1] V. Luzzati, H. Delacroix and A.Gulik, The micellar cubic phases of lipid-containing systems: Analogies with foams, relations with the infinite periodic minimal surfaces, sharpness of the polar apolar partition. Journal De Physique II 6 (1996) 405. [2] M. W. Anderson, C. C. Egger, G. J. T. Tiddy, J. L. Casci and K. A. Brakke, A new minimal surface and the structure of mesoporous silicas. Angewandte Chemie-International Edition 44 (2005) 3243. [3] M. W. Anderson, T. Ohsuna, Y. Sakamoto, Z. Liu, A. Carlsson and O. Terasaki, Modern microscopy methods for the structural study of porous materials. Chemical Communications (2004) 907. [4] K. A. Brakke, The surface evolver and the stability of liquid surfaces. Philosophical Transactions of the Royal Society of London Series a-Mathematical Physical and Engineering Sciences 354 (1996) 2143. [5] A. E. Garcia-Bennett, O. Terasaki, S. Che and T. Tatsumi, Structural investigations of AMS-n mesoporous materials by transmission electron microscopy. Chemistry of Materials 16 (2004) 813.

Recent Progress in Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

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Salt effect in the synthesis of highly ordered, extremely hydrothermal stable SBA-15 C. L. Li, Y.Q. Wang*, Y. L. Guo, X. H. Liu, Y. Guo and G. Z. Lu Lab for Advanced Materials, Research Institute of Industrial Catalysis, East China University of Science and Technology, Shanghai 200237, P. R. China

1. Introduction Since the discovery of MCM-41 by Mobil scientists in 1992 [1], ordered mesoporous silicate materials have attracted considerable attention for their potentially applications as catalyst supports, adsorbents and etc. Up to now, a serial of ordered mesoporous silica (M41S, SBA-2, 3, MSU, SBA-15, etc.) have been successfully synthesized. However, these materials have not been widely used in industry because of their relatively poor hydrothermal stability. Hydrothermal stability of mesoporous materials is an important property for future applications and much work has done to improve it. Normally, post-treatment with organosilane, incorporation of hetero-atoms, carbon propping and assembly of zeolite precursors with template were used to enhance the hydrothermal stability. Such as post-treatment of MCM-41 with methyl-chlorosilane has been used just at the discovery of M41S family [1]. Generally, increasing the aging temperature would be a good way to enhance the hydrolysis and condensation of silicon precursors, and finally improve the hydrothermal stability. Yan Y et al [2, 3] realized it by using fluorocarbon-hydrocarbon surfactant mixtures as templates. In our work, inorganic salt (NaCl) was used to assist the formation of highly ordered, extremely hydrothermal stable SBA-15. 2. Experimental Section The synthesis was done under 1.0 M HC1 solution, using the mixture of triblock copolymer P123 and semi-fluorinated surfactant FSO-100 as the template and inorganic salt (NaCl) as an assistant agent. Samples without addition of NaCl were synthesized with the similar procedure and the normal SBA-15 was also synthesized according to literature [4] for comparison.

18 18

The hydrothermal stability was investigated by treating samples in a closed bottle at 100°C for 300 h under static conditions. High-temperature steam test was carried out by exposing the samples to water vapor in N2 steam at 600°C for 6 h. The samples were characterized with small-angle XRD, TEM, N2 sorption and solid state 29 Si MAS NMR. 3. Results and Discussion The mesoporous structures were characterized by SXRD, TEM and N2 sorption. Fig. 1A shows the SXRD patterns of SBA-15 synthesized at 160 °C with and without NaCl. It can be seen clearly that the addition of NaCl remarkably enhances the ordering of mesostructure, this phenomena have been confirmed before [5-8]. Fig. IB gives the SXRD patterns of SBA-15 synthesized at various aging temperatures in the presence of NaCl. They clearly show 3-4 well-resolved reflections that can be indexed as 100, 110, 200 and 210 diffractions associated with the p6mm hexagonal symmetry. This is an indication of good long-range hexagonal ordering. It is interesting to note that with the increase of aging temperature, the diffraction intensity decreases slightly, but the positions have no obvious shift. It is different from that synthesized at relatively low temperatures [9], which showed that the temperature had a significant influence on the structural parameters. 100

B

Intensity

Intensity

A

11

110 200 210 O

140 C O

With NaCl

160 C

Without NaCl

180 C

3 4 2 2 2-Theta(degree)

O

5

1

3 4 2 2 2-Theta(degree)

5

Fig. 1 (A)SXRD patterns of SBA-15 synthesized at 160°C with and without NaCl, (B) SXRD of SBA-15 synthesized with the addition of NaCl at different temperature (140 -180 °C).

Fig. 2A is the SXRD patterns of SBA-15 after treating in boiling water for 300 h. Three peaks indexed as 100, 110 and 200 reflections of the mesostructure are obvious. There were no significant changes of the 20 positions, intensities and linewidths of diffraction peaks compared with that of calcined SBA-15, which indicates that the highly ordered mesostructures were still maintained after hydrothermal treatment. The SXRD patterns of steaming treated SBA-15 are displayed in Fig. 2B, the patterns also show a very intense 100 reflection and two

19 19 1 100 100

Hydrothermal treatment A: Hydrothermal

110 200

O 140OC;300h 140 C; 300 h

Intensity

Intensity

100 100

B: Steaming treatment

110200

O

160 C; 300 160OC; 300 h

O

140 C;steaming 66 h 140 O

160 C;steaming C;steaming6h 160 6h

O

180 C; 300 h C;300 1

2

3

4

O 180OC;steaming6h C;steaming 6 h 180

5

1

2

2-Theta(degree)

3

4

5

2-Theta(degree)

Fig. 2 (A) SXRD patterns of SB A-15 after treating in boiling water for 300 h, (B) after steaming at 600 °C for 6 h.

additional higher order reflections with lower intensity, indicating that the mesostructures weren't destroyed even under such severe conditions. These results demonstrate that the synthesized samples have remarkably hydrothermal stability. N2 sorption measurements showed that the BET surface area reduced a little bit after hydrothermal treatment, but narrow pore size distribution still maintained (unshown here), indicating that the ordered structures undestroyed, which is in accordance with the XRD measurement. The structural properties of the samples are summarized in Table 1. All the results demonstrate that the synthesized samples have good mesostructural ordering and remarkably hydrothermal stability. The extremely high hydrothermal stability of thus-synthesized SBA-15 was due to the high aging temperature as discussed by Han Y [2, 3]; and at the same time, inorganic salt, NaCl, also played a important role in the enhancement of the hydrolysis and condensation of silicon precursor. The latter was confirmed by solid Table 1. Structural properties of calcined and treated samples Sample

dioo

/nm S-140 S-140-H S-140-600 S-160 S-160-H S-160-600 S-180 S-180-H S-180-600

10.2 10.4

9.7 10.4 10.5

9.9 10.0 10.1 10.0

a0 /nm

/m

11.8 12.0 11.2 11.9 12.1 11.4 11.5 11.7 11.5

438 320 298 422 312 313 377 294 243

SBET 2

g"1

Dp /nm 7.4 7.5 6.5 7.3 7.5 7.3 6.8 7.6 7.0+14.7*

W /nm 4.4 4.5 4.7 4.6 4.6 4.1 4.7 4.1 4.5

Vp

SBET reduction

/cmV

/%

0.983 0.848 0.738 0.941 0.832 0.764 0.851 0.797 0.821

26.9 32.0 26.0 25.8 22.0 35.5

Note: a0: cell dimension; Dp: pore diameter; W: pore wall thickness; Vp: total pore volume. * Pores come from the aggregation of particles (void space).

20

state 29Si MAS NMR (unshown here). The ratio of Q4/Q3 in thus-synthesized SBA-15 is higher than that in the sample synthesized without NaCl addition and much higher than that in normal SBA-15. The high degree of condesation plays the most important role in enhancing the hydrothermal stability. 4. Conclusion

In conclusion, highly ordered and high hydrothermal stable SBA-15 have been synthesized in a one-step simple process. After treatment in boiling water or steaming, the ordering of the mesostructures hasn't destroyed. Such materials may have potential applications in catalysis and separation. 5. Acknowledgement This project was supported financially by the National Basic Research Program of China (No. 2004CB719500) and Commission of Science and Technology of Shanghai Municipality (04ZR14036, 05PJ14032), China. 6. References [1] J. S. Beck, J. C. Vartuli, W. J. Roth, M. E. Leonowicz, C. T. Kresge, K. D. Schmitt, C. T-W. Chu, D. H. Olson, E. W. Sheppard, S. B. McCullen, J. B. Higgins and J. L. Schlenker, J. Am. Chem. Soc. 114(1992)10834. [2] Y. Han, D. F. Li, L. Zhao, J. W. Song, X. Y. Yang, N. Li, Y. Di, C. J. Li, S. Wu, X. Z. Xu, X. J. Meng, K. F. Lin and F. S. Xiao, Angew. Chem. Int. Ed. 42(2003) 3633. [3] D. F. Li, Y. Han, J. W. Song, 1. Zhao, X. Z. Xu, Y. Di and F. S. Xiao, Chem. Euro. J. 10 (2004)5911. [4] D. Y. Zhao, J. L. Feng, Q. S. Huo, N. Melosh, G. H. Fredrickson, B. F. Chmelka and G. D. Stucky, Science, 279(1998)548. [5] C. Z. Yu, B. Z. Tia, J. Fan, G. D. Stucky and D. Y. Zhao, J. Am. Chem. Soc, 124(2002) 4556. [6] K. Flodstrom, V. Alfredsson andN. Kallrot, J. Am. Chem. Soc. 125(2003) 4402. [7] B. Lee, D. L. Lu, J. N. Kondo and K. Domen, J. Am. Chem. Soc. 124(2002)11256. [8] Y. Q. Wang, B. Zibrowius, C. M. Yang, B. Spliethoff and F. Schiith, Chem. Commun., (2004) 46. [9] X. J. Meng, Y. Di, L. Zhao, D. Z. Jiang, S. G. Li and F. S. Xiao, Chem. Mater., 16(2004) 5518.

Recent Progress in Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

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Hydrocarbon templated sol-gel synthesis and characterizations of mesoporous silica xerogel Halina Misran3*, Mohd Ambar Yarmob and Ramesh Singh3 "College of Engineering, University Tenaga Nasional, Km 7, Jalan Kajang-Puchong 43009 Kajang, Selangor, Malaysia. School of Chemical Sciences and Food Technology, Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor, Malaysia.

1. Introduction Porous silica materials are widely known for various applications from adsorbents, catalysis and as template to metal oxide [1-3]. In recent years, ordered mesoporous silica xerogels had gained considerable attention in various field due to the reduced production cost and improved properties. Recently, a low-cost attempt on producing nanosized perovskite, spinels and mesoporous carbon via silica xerogel templating route where the silica xerogel used had the structural characteristics similar to mesoporous silica materials were reported [4]. Microporosity, mesoporosity or both could be introduced in the silica xerogels by using quaternary surfactant and polystyrene spheres in a "one-pot" synthesis method [5]. General method of producing mesoporous silica xerogel employed the use of expensive and toxic surfactants as structure directing agents. Thus, a low-cost and environmental-friendly approach of producing mesoporous silica xerogel would be by terminally eliminating the use of surfactants in the synthesis procedure. In this study, we report on the attempt to produce silica xerogels with similar properties as MCM type silica materials using renewable resources of palm oil derived hydrocarbons in nanometer size oil-in-water droplets emulsion. In order to study the application of the silica xerogels as silica support materials, "one-pot" functionalization method using phenol-red were carried out and the resulting materials were characterized accordingly.

22

2. Experimental Section Silica xerogels were prepared by the hydrolysis and co-condensation of TEOS as silica precursor in a surfactant-less oil-in-water emulsion. In a typical synthesis procedure, oil phase were dispersed in a continuous phase containing co-solvent by ultrasonification. Then, TEOS was added dropwise to the solution mixture containing base catalyst and subjected to acoustic emulsification followed by stirring for 24 h. The final pH of the mixture was adjusted with acid until gelation occurred [7]. The gels were washed, filtered and dried followed by calcinations to obtain xerogels, hereafter denoted as ULSF6,ULSF-8 and ULSF-9. For functionalized silica xerogel materials, phenol red (PR) was diluted in alcohol and added to the solution mixture. The gel was solvent extracted, filtered and dried to obtain ULSF-10PR. Structural characterizations were done using nitrogen sorption on a Quantachrome NOVA 1200e at 77 K, SEM using LEO 1450VP at 20 kV, TEM using Hitachi Tecnai at 200 kV. 29Si and 13C were measured using Bruker AV400. 3. Results and Discussion The 13C CP NMR of as-synthesized xerogels as shown in Figure 1 exhibited strong signals at ca. 22 to 34 ppm were assigned to the alkyl groups in saturated alkanes [6]. The peaks were attributable to the carbon atom chains in fatty alcohols. These results suggested that the fatty alcohols play the role as structure directing agents during the synthesis. The resonance peaks observed at ca. 62 and 69 ppm were assigned to the carbon atoms in the methoxy groups. These signals were observed from the residues of short-chain alcohol used in the synthesis. A representative X-ray diffraction analysis of calcined silica #

F li e : H \: 3 1 C N M \R r1

* OCH

In t e n s it y ( a .u . )

OCH33 #

Si CH2 CH2 O OSiC OCH3 OCH

## * 80 80 8 0

7 0

#

* 6050 40 60 40 Chemical shift shift (ppm) (ppm) Chemical 6 0

5 0

4 0

3 0

# #

20 2 0

Fig. 1. 13 CCP NMR of as-synthesized xerogels.

1 0

20 20

40 40

220O θ(°)

60 60

Fig. 2 A representative XRD pattern.

xerogels as shown in Figure 2, exhibited a broad peak centered at ca. 20 = 22° suggesting that the materials were of amorphous nature. The absence of pronounce peaks at lower angle also indicated that the pores were of disordered

23

wormhole-like structure. Nitrogen adsorption isotherms of calcined samples are shown in Figure 3. With the exception of ULSF-9, all samples exhibited Type IVa isotherms in the IUPAC classification with narrow HI type hysteresis loops These results suggested the successful formation of mesoporous silica xerogels with open-ended tubular pores. The surface area estimated from the BET equation applied to the monolayer region of adsorption branches were at ca. 305 m /g to 600 m2/g as shown in Table 1. Silica xerogels prepared from decyl alcohols exhibited highest surface area at ca. 600 m2/g. This result was obtained due to the stability of the nanometer sized oil droplets in the oil-in-water emulsion formed from decyl alcohol. Thus, during the synthesis, more hydrolysis and condensation-polymerizations of anionic silicate oligomers could occur on the surface of the nanosized oil droplets giving rise to the morphology of spherical agglomerates as confirmed by SEM image in Figure 4. Pore volume estimated by the t-plot method also exhibited highest value of 1.5 mL/g for ULSF-9, sample prepared from decyl alcohol. SEM image of calcined sample as shown in Figure 4 exhibited fine globular units of spherical morphology. 800

0.5 Relative Pressure (P/Po)

0.2 0.4 0.6 0.8 Relative Pressure (P/Po)

1

Fig. 3. Nitrogen adsorption isotherms with the corresponding pore size distributions a) ULSF-8 b) ULSF-6. Table 1. Pore characteristics of calcined and solvent extracted silica xerogels. Sample Name

Type of fatty alcohols

Pore size (nm)c

Surface area (m2/g)a

Total pore volume (mL/g)b

ULSF-9

Decyl

17.4d

600

1.5

ULSF-6

Octyl

12.1

305

0.9

ULSF10-PR

Octyl

8.0

545

0.8

ULSF-8

Dodecyl

19.7

a

By BET method.

b

By t-plot method.

494 c

By BJH method

1.1 d

By DFT method.

The particle sizes observed were at ca. <50 nm. These results suggested that the anionic silicate agglomerated and condensed on the nanosized oil droplets

24

giving rise to wormlike pores and slit-shaped pores of ca. 7 to 20 nm as in Table 1 estimated from the BJH method and the DFT method from the desorption branch. These pores could be observed by TEM image as shown in Figure 4. 29Si NMR spectra of calcined and solvent-extracted samples as shown in Figure 5 exhibited Q3 and Q signals at ca. -100 ppm and -110 ppm suggesting that the surface chemical structure of the materials were similar to that of MCM-type material. For functionna -lized samples, Q2 and Q3 peaks were dis-tinguished indicating that some of the hydroxyl groups in the phenol red interacted with the siloxane bond in the framework resulting in a higher resonance signals.

100 nm

50 nm

Fig. 4. SEM and TEM image of calcined silica xerogel.

4. Conclusion ULSF-6

Nanoporous silica xerogels with high surface ULSF-8 area, pore volume and fine spherical morphology with particle size from ca. 50 nm were successfully ULSF10-PR synthesized using palm oil derivatives of fatty alcohols employing acoustic emulsification. The oil droplets in the presence of co-solvent such as -50 -150 -100 -100 Chemical Chemical shift shift (ppm) (ppm) short-chain alcohols to act as dispersant behaved as template where the hydrolysis and condensation-polymerization of silica could take Fig. 5. 29Si NMR spectra. place. Thus, the applications of the materials as cheap silica support in other fields such as catalysis are in progress and will be reported in the future. 0

-1 0 0

-2 0 0

5. References [1] [2] [3] [4] [5] [6] [7]

A.B. Fuertes and J. Physics Chemistry of Solids, 66 (2005) 741. F.A. Twaiq,A.R. Mohamed and S. Bhatia,Microporous and Mesoporous Mat.,64 (2003) 95. A. Matsumoto, H. Misran and K. Tsutsumi, Langmuir, 20 (2004) 7139. T. Valdes-Solis, G .Marban and A.B. Fuertes, Chem.Mater., 17, (2005) 1919. T. Sen, G. J. T. Tiddy, J.L. Casci and M.W. Anderson, Chem. Mater., 16 (2004) 2044. S. Hamoudi, S. Royer and S. Kaliaguine, Microporous and Mesoporous Mat., 71 (2004) 17. M. Halina, S. Ramesh, M.A.Yarmo and R.A. Kamarudin, Mat. Chem and Phys., (2006), accepted, in press.

Recent Progress in Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

25 25

Microwave synthesis of SBA-15 mesoporous silica material for beneficial effect on the hydrothermal stability Sang-Cheol Han, Nanzhe Jiang, Sujandi, David Raju Burri, Kwang-Min Choi, Seung-Cheol Lee and Sang-Eon Park* Laboratory ofNano-Green Catalysis andNano Center for Fine Chemicals Fusion Technology, Department of Chemistry, Inha University, Incheon, 402-751, Korea

Hydrothermally robust mesoporous SBA-15 silica material was synthesized for the first time using microwave with out adding any other chemical ingredients. For the sake of stability comparison, mesoporous SBA-15 material was also prepared by conventional hydrothermal technique. The stability of the material was tested by boiling water method and 29Si-NMR Q4/Q3 ratios. It was observed that SBA-15 synthesized under microwave conditions exhibited higher stability than that of hydrothermally synthesized SBA-15. 1. Introduction Recently, microwave heating has been greatly applied in the synthesis of nanoporous materials. Our group including others have used microwave method for the synthesis of hexagonal and cubic mesoporous materials such as MCM41 [1], MCM-48 [2], SBA-15 [3] and SBA-16 [4]. It offers several advantages such as homogeneous heating throughout the reaction vessel, the possibility of selective heating according to the desirability of the materials, homogeneous nucleation, crystal growth processes [5] and short crystallization time so on and so forth [6,7]. We also have found that this technique could provide an efficient way to control particle size distribution and macroscopic morphology of nanostructured materials [8,9]. Besides morphology control and short crystallization time, improvement of the degree of silica condensation in the mesoporous walls could be expected in the microwave synthesis. In this study, microwave synthesis was used as the strategy for supplying higher crystallization conditions in the synthesis of mesoporous materials. Microwave synthesis is essentially different from conventional heating. In

26

microwave processes, heat is generated directly from the interaction between molecules in the heated material by the electromagnetic fields created in the microwave oven. Microwave processing can be beneficial in the processing of materials with high dielectric constants, because absorption of microwave irradiation onto substrates depends on its dielectric constants and dielectric loss factors [10]. Water absorbed microwave energy efficiently due to the high values of dielectric constant, which is a very good absorber of microwave energy at the frequency of 2.450 GHz. So, the microwave effect in the synthesis of SBA-15 silica could be expected to be significantly enhanced. Our results showed that this technique was a powerful tool to control the pore wall condensation as well as facile synthesis of SBA-15 having high hydrothermal stability. 2. Experimental Section 2.1. Synthesis of Materials The synthesis of SBA-15 was carried out as follows: 8 g of triblock copolymer PI23 (EO20PO70EO20; M.W. 5800, Aldrich) was dissolved in 205 ml of water, followed by the 17 g of tetraethylorthosilicate (TEOS, Aldrich). To this solution, 65 g of concentrated hydrochloric acid (37.6%) was quickly added with vigorous stirring to obtain gel. The mixture was stirred at 40°C for 4 h and then transferred to a microwave digestion system (CEM Corporation, MAR-5). SBA-15 microwave synthesis was performed for 1, 2, 3, 4 and 5h at 373 K, and also it was synthesized by conventional hydrothermal method for 24 and 48 h at 373 K. The surfactants were removed through the solvent extraction method using ethanol solution and then by calcination at 813 K. 2.2. Stability test The hydrothermal stability of samples was tested by treatment in boiling water (0.2 L of water per 0.4 g of Materials) for 80 hrs. 2.3. Characterization X-ray diffraction patterns (XRD) were recorded on a Rigaku multiflex diffractometer with a monochromated high-intensity Cu Ka radiation (A,=0.15418 nm). The diffraction data were collected by using a continuous scan mode with a scan speed of 0.1°/min (20 kv, 10 mA).29Si NMR spectra were recorded on a Varian unity-inova 400 spectrometer. The samples were fitted in a 7mm SiO2 rotor, spinning at 4 kHz.

27

3. Results and Discussion SBA-15 synthesized by both microwave and hydrothermal methods exhibited highly ordered mesoporosity. The microwave synthesized SBA-15 exhibited extremely higher stability, which can be seen from the Fig.l. 29Sia NMR spectra exhibited three kinds of bands centered at chemical shifts of 8 = -92, -102, and -112 ppm, which can be ascribed to Si(OSi)x(OH)4.x framework units b where x=2 (Q2), x=3 (Q3), and x=4 4 (Q ), respectively. Notably, assynthesized SBA-15-4h was made Q Q up of almost fully condensed Q4 c silica units (8 = -112ppm). Q A small contribution was resulted from incompletely cross-linked Q3 (8 = -102 ppm), as deduc -ed -5 0 -1 0 0 -1 5 0 from the very high Q4/Q3 ratio of ppm 6:1, whereas no Q2 units were observed. And the higher irradiaFigure l.29Si MAS NMR spectra of microwave 4 3 tion times gave the higher Q /Q synthesized SBA-15 : a) SBA-15-MW-4h,b) ratios. It meant that microwave irra SBA-15-MW-3h, c) SBA-15-MW-2h. -diation might contribute the cond -ensation of silicas and the dehy- droxylation of the silica surface as well. On 3

4

2

a

b SBA-15-HT 24hr

SBA-15-MW 3hr

After

O Si

Before Before

Si

Si O Si

Si Si O Si O

Amorphous Pore wall Pore wall

High crystalline Pore wall

Si HO OH

Si HO Si

Si OH HO

Si

Si Si

OH HO

Si

OH Si

High Q4/Q3 ratio 0.5

1.0 1.0

1.5 1.5

22.0 .0

2.5 2.5

33.0 .0

3.5 3.5

4.0

4.5

5.0 5.0

0.5

1.0 1.0

1.5 1.5

Low Q4/Q3 ratio ratio

2 . 5 3.0 3.03 . 0 44.5 . 5 5 5.0 .0 2.02 . 02.5 3.5. 5 44.0

Figure 2. XRD patterns of as-synthesized a) SBA-15-MW-3hr, b) SBA-15-HT-48hr before and after at boiling water treatment for 80 hrs.

the other hand, mesoporous silica material (SBA-15) having a highly ordered hexagonal mesostructure was synthesized hydrothermally at 100°C and gave

28

much lower Q4/Q3 ratios below 1.0 [11]. These results indicated that microwave syntheses were indeed favorable for promoting silica condensation on the pore walls giving more hydrophobicity. The XRD patterns of microwave synthesized SBA-15 exhibited three distinct peaks which denoted the ordered hexagonal symmetry. After treatment of SBA15-MW-3h with boiling water for 80 h, it still gave clear peaks of 100 and 110 reflections of the hexagonally ordered mesostructure. In contrast, the boiling water treated SBA-HT-24h exhibited a very broad peak assigned to the (100) reflection. These results indicated that SBA-15-MW-3h had much better hydrothermal stability than that of the hydrothermally synthesized SBA-15. The materials prepared by microwave synthesis proven to be fully condensed mesopore walls, and exhibited higher hydrothermal stability at boiling water condition, than that hydrothermally prepared SBA-15 materials. 4. Conclusion Synthesis of SBA-15 molecular sieves was performed via hydrothermal and microwave approach to compare resulting hydrothermal stability properties of these materials. In case of SBA-15 prepared by microwave irradiation exhibited a higher hydrothermal stability. 5. Acknowledgement Authors are gratefully acknowledged advanced scientist supporting program (KRF-2005-041-C00238) and BK-21 program of the Korea Ministry of Education for the financial supported. 6. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11]

C. G. Wu and T. Bein, Chem. Commun. (1996) 925. S. -E. Park, D. S. Kim, J.-S. Chang and W. Y. Kim, Catal. Today 44(1998) 301. B. L. Newlkar, S. Komarneni and H. Katsuki, Chem. Commun. (2000) 2389. Y. K. Hwang, J. -S. Chang, Y. -U. Kwon and S. -E. Park, Micro. Meso. Mater. 68(2004)21. S. L. Burkett and M.E. Davis, In Comprehensive Supramolecular Chemistry, G. Alberti and T. Bein(eds), Vol. 7(1996) 465. C. S. Cundy, R.J. Plaisted and J. P. Zhao, Chem. Commun. (1998) 1465. Arafat, J.C. Jansen, A.R. Ebaid and H. Van Bekkum. Zeolites 13(1993) 162. S. -E. Park, J.-S. Chang, Y. K. Hwang, D. S. Kim, S. H. Jhung and J. -S. Hwang, Catal. Surveys from Asia 8(2004) 91. Y. K. Hwang, J.-S. Chang, S. -E. Park, D. S. Kim, Y. -U. Kwon, S. H. Jhung, J. -S. Hwang and M. S. Park, Angew. Chem. Int. Ed. 44(2005) 556. C. Gabriel, S. Gabriel, E.H. Grant B.S.J. Halsteed and D. P. Mingos, Chem.Soc.Rev. 27(1998)213. D. Li, Y. Han, J. Song, L. Zhao, X. Xu and F. -S. Xiao, Chem. Eur. J. 10(2004) 5911.

Recent Progress in Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

29 29

Control of pore size of mesoporous silica utilizing noncovalent supermicelles Zhurui Shen, Yuping Liu, Pingchuan Sun, Zhongyong Yuan and Tiehong Chen* College of Chemistry, Department of Materials Chemistry, Key Laboratory of Functional Polymer Materials ofMOE, Nankai University, Tianjin, 300071, P.R. China

A novel approach has been developed to control the pore size of mesoporous silica materials utilizing noncovalently connected micelles (NCCMs), which is different from the traditional small molecular surfactant or block copolymer templating technique in that the supermicelles are connected through non-covalent interactions, mainly hydrogen bonding, between hydrophobic polymer and hydrophilic polymer. In the present study, we have successfully fabricated mesoporous silica materials templated by NCCMs from hydroxyl-terminated polybutadiene (HTPB) and poly(vinyl alcohol) (PVA) under acidic condition. The delicate control over pore size can be easily achieved by changing the weight ratio of PVA/HTPB. 1. Introduction The synthesis of a new family of M41S templated from surfactant micelles [1], has stimulated great interest in the mesoporous silica materials due to their fascinating structures and wide application perspective. Currently, mesoporous silica materials have been synthesized by using nonionic block copolymer surfactants [2], cationic alkyl trimethylammonium surfactants [3], mixed surface-tants [4], or polystyrene particles [5] as templates. Herein, we demonstrate a new method to prepare mesoporous silica materials with supermicelles by mixing of hydrophobic polymer and hydrophilic polymer. 2. Experimental Section Hydroxyl-terminated polybutadiene (HTPB, Mw=2200) and poly(vinyl alcohol) (PVA, Mw=70650) were used as received. Tetraethoxysilcane (TEOS,

30

98 wt %) was used as the silica source. Hydrochloric acid (5 M) was used as the catalyst for the hydrolysis and condensation of TEOS. Micellar solutions were typically prepared by adding 3 ml of HTPB/THF solution with certain concentrations (denoted as x wt%.) dropwise into 30 ml 1 wt% PVA/water solution (the ratio of HTPB/PVA denoted as x/30). The mixture was stirred for 24 h at room temperature and then kept for 3 days. 10 ml of 5 M HC1 solution was added dropwise under stirring to the above-prepared solution of micelle, followed by adding 4 ml TEOS. The reaction mixture was kept stirring for 1 h at room temperature until it became clear. The resulting mixture was transferred into a Teflon-lined autoclave and aged at 90°C for 4 days. The product was filtered and washed with ethanol and distilled water several times, then dried for 24 h at 60°C and subsequently calcined at 550°C for 5.5 h under air to remove the polymers. 3. Results and Discussion Representative SEM image and TEM image of mesoporous silica material fabricated from molar ratio of HTPB to PVA=3:30 are shown in Figure 1. It can be seen from SEM image (Fig. 1, left) that morphology of the calcined silica samples shows the normal tens-of-micrometers-sized particles with irregular shape. Disordered worm-like mesopores were observed from TEM image (Fig.l, right). Correspondingly, no low-angle reflections were observed in the XRD patterns (figure not shown) for the present materials.

Fig. 1 SEM image (left) and TEM image (right) of calcined silica sample (HTPB/PVA=3:30)

In the PVA-HTPB system, we fixed the amount of PVA and tuned the amount of HTPB, and a series of silica samples S1-S4 were obtained, corresponding to the weight ratios of HTPB/PVA from 3:30 to 12:30. The representative N2 adsorption-desorption isotherms (not shown) of calcined silica samples show type IV adsorption isotherm behavior with a type H2

31

hysteresis loop, which indicates the presence of mesopores. From the data of N2 adsorption-desorption test (Table 1) we can see that the pore size, pore volume, and BET surface area did not monotonously increase with the amount of HTPB. When the amount of HTPB increased, the pore size and pore volume increased from 3:30 to 6:30, and then decreased, when the ratios were 9:30 and 12:30. Table 1 The results obtained from N2 adsorption-desorption isotherm test Sample code

Weight ratio of HTPB/PVA

BET

Total pore volume

(mV)

(crnlg )

(nm)

SI

3:30

568

0.37

3

S2

6:30

545

0.93

8

S3

9:30

502

0.80

7

S4

12:30

583

0.75

5

1

pore size

The change of pore size with increasing amount of HTPB can be explained according to the principle of formation of noncovalently connected micelles (NCCMs). When the ratio of HTPB/PVA is 3:30, there exsits small amount of free PVA chains due to the higher concentration of PVA in the initial solution. Under stirring, these free PVA chains might interact with much more HTPB chains through hydrogen bonding between the hydroxyl groups on HTPB and PVA to form bigger micelles. With an increase of the amount of HTPB, the supermicelles become larger due to the bigger inner parts (HTPB aggregates) of supermicelles, which leads to larger pore size. However, it is not the case that, the more the amount of HTPB, the bigger the micelles. Because of the limited amount of hydroxyl groups on PVA in the solution, the amount of PVA chains wrapped on the surface of the HTPB aggregates varies with the increase of HTPB. The experimental results indicate that when the ratios of HTPB/PVA increased from 3:30 to 6:30, the HTPB aggregates might be saturated by PVA chains outside, and therefore, the size of micelles reaches the maximum in the solution. There is an optimal ratio at which the hydroxyl groups of PVA and HTPB might be properly interacted and formed micelles with minimum interfacial free energy. When the amount of HTPB continued to increase, the limited PVA chains would not be enough to stabilize the bigger micelles. The bigger micelles were unstable and tended to form smaller ones under stirring. Therefore, when the ratios of HTPB/PVA increased from 6:30 to 12:30, the pore size decreased. From this point of view, the delicate control over pore size could be facilitated.

32

4. Conclusion Under acidic condition, using the co-assembly aggregate, i.e., supermicelles, driven by hydrogen bonding between hydrophilic polymer poly(vinyl alcohol) (PVA) and hydrophobic polymer hydroxyl-terminated polybutadiene (HTPB) as a template, mesoporous silica was synthesized by sol-gel reaction. The calcined silica had higher BET surface area (S = 500-600m2/g). The pore size on nanoscale can be easily adjusted through changing the ratio of PVA/HTPB. 5. Acknowledgement This work was supported by National Science Foundation of China (Grants No. 20373029, 20233030), and joint-research fund of Nankai University and Tianjin University on Nano-sciences. 6. References [1] C.T. Kresge, C.Z. Leonow, W.J. Roth et al.Nature, 359 (1992)710. [2] D. Zhao, J. feng, Q. Huo, N. Melosh, G.H. Fredericson, B.F. Hmelkaand G.D. Stucky, Science, 279(1998)548. [3] S. M. Yang, I. Sokolov, N. Coombs, C.T. Kresge and G.A. Ozin, Adv. Mater. 11 (1999)1427. [4] B. C. Chen, H.P. Lin, M.C. Chao et al., Adv. Mater. 16 (2004)1657. [5] F. Iskandar, Mikrajuddin and K. Okuyama, Nano Lett. 1 (2001)231.

Recent Progress in Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

33 33

Synthesis of supermicro-macroporous silica with polypeptide-based triblock copolymer Yuping Liu, Liying Li, Zhurui Shen, Pingchuan Sun, Zhongyong Yuan and Tiehong Chen College of Chemistry, Department of Materials Chemistry, Key Laboratory of Functional Polymer Materials ofMOE, Nankai University, Tianjin, 300071, P.R. China

With anilino-methyl triethoxy silane (AMTS) as an intermedium, supermicro-macroporous silica was synthesized through 71-71 interaction under ambient conditions, utilizing synthetic polypeptide-based triblock copolymer poly(L-phenylalanine)-b-poly(ethylene glycol )-b-poly(L-phenylalanine) (Phe7PEGi35-Phe7) as a template . The prepared silica has mesoscale short-rangeorder and hierarchical structure with both supermicropores and interconnected macropores. It is proposed that the supermicropores are templated by the polypeptide segments, while the open 3D interconnected macroporous networks are presumably attributed to both PEG segments and organic solvent. Both polypeptide-based block copolymer and AMTS play important roles in the formation of mesoscale short-range-order and hierarchical structure. 1. Introduction Exquisite silica structures existing in the diatoms and sponges are generally controlled by specific interactions between peptides (and/or polyamines) and silicic acid derivatives under mild physiological conditions [1]. Peptides such as silaffin [2] and silicateins [3] (isolated from diatom biosilica and sponges, respectively) can induce the formation of silica from silicic acid solution at neural pH. Stucky group for the first time used self-assembly structured aggregates of synthetic poly (Cysteine)-b-poly(Lysine) block copolypeptide to synthesize transparent mesoporous silica microspheres [4]. Shantz et al. reported the fabrication of polypeptide-templated nanoporous materials by using commercially available PLL [5, 6], however, the synthesized silica did not exhibit well-defined morphology and multi-scale architecture.

34 34

Inspired by the works mentioned above, here we describe an approach to prepare hierarchically structured silica templated from synthetic polypeptidebased triblock copolymer poly(L-phenylalanine)-b-poly(ethylene glycol)i35-bpoly(L-phenylalanine) (Phe7-PEGi35-Phe7, synthesized by our lab). It is firstly reported that hierarchical silica material is successfully prepared by utilizing polypeptide-based triblock copolymer as a template, through it—% interaction under ambient conditions. In addition, control experiments without AMTS or without the triblock polymer have been performed for comparison. The mechanism on the formation of the hierarchically structured silica in the presence of polypeptide-based triblock copolymer and AMTS is discussed. 2. Experimental Section Phe7-PEGi35-Phe7 was synthesized by our lab according to our previous works[7]. Anilino-methyl triethoxy silicane (denoted as AMTS, 95%, whose chemical formula is shown in Scheme 1) was obtained from Wuhan Tianmu Co. Ltd. (China). Tetratetraethoxysilane (TEOS, Aldrich) and dioxane (Aldrich) were used without further purification. Preparation of Hierarchical silica: In a typical experiment, 40 ml of Phe7-PEGi35-Phe7 solution in dioxane organic solvent (2.5 mg/ml) was gently mixed with 120 ml benzyl alcohol under stir for 20 min. Then 5ml of AMTS was added to the solution. The mixture was heated at 80°C for 10 min. Subsequently, 3 ml of benzyl ammine (as catalyst), 3 ml of deionized water and 5 ml of TEOS were added to the mixture, respectively. The final mixture was stirred for 10 min and was sonicated (with 20 kHz frequency, 300 w power) for 20 min to obtain a clear solution. The solution was kept static in a sealed flask at room temperature for two weeks. The product (denoted as SI) was obtained by washing with methanol and deionized water for several times, and dried at 60 °C for 24 hrs. The white as-synthesized product was calcined at 550°C for 5 hrs to remove organic solvents and the copolymer. In addition, white product was also obtained under the same reaction conditions except either without AMTS (denoted as S2) or without the triblock copolymer (no product was obtained). The obtained product was charaterization by means of TEM,SEM,XRD and N2 adsorption and desorption measurement. 3. Results and Discussion From XRD pattern of calcined sample SI (unshown), one broad diffraction peak with d spacing of 3.1 nm appears, indicating the presence of disordered short-range ordering structure. No such diffraction peak appears in the lowangle region of XRD pattern for sample S2(unshown), so it is believed that anilino-methyl triethoxy silicane (AMTS) plays a significant role in the formation of the disordered mesostructure of sample SI. If the triblock copolymer was not used under same synthesis condition of sample SI, silica precipitation did not occur and the system remained an optically clear solution

35

without formation of gel. Evidently, the triblock copolymer effectively controls the nucleation and growth of silica. From the SEM images (Fig. 1 a, b), the calcined sample SI displays interesting macroporous morphology, with the macropore size of about 200-700 nm. The macroporous network is composed of layers interconnected by struts-like pillars. For sample S2, the SEM images only display irregular particles (unshown), indicating that without the addition of AMTS, the triblock copolymers were not involved in the silica precipitation to give rise to formation of the specific morphology. The results from the nitrogen adsorption-desorption test of the calcined sample SI (unshown) indicate the presence of micropores (<2 nm) and its BET surface area of calcined sample is 439 m2/g (micropore area is 389 m2/g). The Barrett-Joynes-Halenda (BJH) average pore size of sample SI is estimated to be about 1.6 nm. This supermicroporous character is also confirmed by the TEM images (Fig.lc). The N2 adsorption line of the calcined sample S2 (unshown) is a type II isotherm, indicating the presence of mesovoids resulted from the aggregation of silica particles.

Fig.l. SEM images (a, b, with different magnifications)and TEM image (c) of calcined samples SI

In this experiment, the triblock copolymer, as a template, is indispensable to the formation of silica through controlling the nucleation and growth of silicate precursors. And anilino-methyl triethoxy silane (AMTS) which contains phenyl and amine groups was used as a bridge, i.e., on the one hand it interacts with polypeptide-based triblock copolymer through template-bridge interactions (hydrogen bonding and n-n interactions) between copolymer and AMTS; on the other hand, AMTS can co-condense with tetraethoxylsilane (TEOS) through hydrolysis process. 4. Conclusion The presented results suggest a bio-inspired approach for the preparation of hierarchical silica material with both supermicropores and macropores utilizing polypeptide-based triblock copolymer Phe7-PEGi35-Phe7 as a template through n —% interaction under ambient conditions. The formation of supermicropores

36

4. Conclusion Under acidic condition, using the co-assembly aggregate, i.e., supermicelles, driven by hydrogen bonding between hydrophilic polymer poly(vinyl alcohol) (PVA) and hydrophobic polymer hydroxyl-terminated polybutadiene (HTPB) as a template, mesoporous silica was synthesized by sol-gel reaction. The calcined silica had higher BET surface area (S = 500-600m2/g). The pore size on nanoscale can be easily adjusted through changing the ratio of PVA/HTPB. 5. Acknowledgement This work was supported by National Science Foundation of China (Grants No. 20373029, 20233030), and joint-research fund of Nankai University and Tianjin University on Nano-sciences. 6. References [1] C.T. Kresge, C.Z. Leonow, W.J. Roth et al.Nature, 359 (1992)710. [2] D. Zhao, J. feng, Q. Huo, N. Melosh, G.H. Fredericson, B.F. Hmelkaand G.D. Stucky, Science, 279(1998)548. [3] S. M. Yang, I. Sokolov, N. Coombs, C.T. Kresge and G.A. Ozin, Adv. Mater. 11 (1999)1427. [4] B. C. Chen, H.P. Lin, M.C. Chao et al., Adv. Mater. 16 (2004)1657. [5] F. Iskandar, Mikrajuddin and K. Okuyama, Nano Lett. 1 (2001)231.

Recent Progress in Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

37 37

Synthesis of silica nanostructures using synthetic block copolypeptide Yuping Liu, Liying Li, Huijing Zhou, Zhurui Shen, Pingchuan Sun, Zhongyong Yuan and Tiehong Chen College of Chemistry, Department of Materials Chemistry, Key Laboratory of Functional Polymer Materials ofMOE, Nankai University, Tianjin, 300071, P.R. China

Nanoporous silica was synthesized by using synthetic block copolypeptide Phe2o-b-PBLG5o as a template under ambient conditions. Anilino-methyl triethoxy silane (AMTS) was used as an intermedium to interact with block copolypeptide Phe2o-b-PBLG5O through TE-TU interaction between the phenyl groups of block copolypeptide and AMTS. Meanwhile, AMTS co-condenses together with tetraethyl orthosilicate (TEOS) after hydrolysis. The structure of complex vesicles due to the self-assembly of block copolypeptide in the organic solvent was immobilized and transcribed by the formation of silica. The formation of micropores could be ascribed to the secondary structure of block copolypeptide and small molecular amine. Our results suggest a new avenue to synthesize porous oxide materials with novel interior structures with the aid of copolypeptide self-assembly under ambient conditions. 1. Introduction The protein and polysaccharide are involved in the formation of diverse and intricate shapes of natural silica structures existing in biological systems such as diatom and sponge. The recent study demonstrates the silaffins [1] and silicateins [2] isolated from marine diatoms and sponges can template and catalyze silica formation from silicic acid at neural pH, which have spurred much interest in biomimetic or bio-inspired approaches in synthetic polypeptide-templated synthesis of inorganic materials. Stucky et al. [3] for the first time used synthetic block copolypeptide poly(L-cysteine)-b-poly(L-lysine) to mimic the properties of silicatein and obtained ordered silica morphology. Shantz's group reported the fabrication of silica particles through the secondary structures of poly-L-lysine [4]. In this paper, under ambient conditions,

38

nanoporous silica with novel interior structures was synthesized by using synthetic block copolypeptide Phe2o-b-PBLG5O (which contains phenyl groups in both Phe and PBLG segments) as a template and Anilino-methyl triethoxy silane (AMTS, containing bifunctional groups, phenyl and amine groups) as an intermedium. 2. Experimental Section Firstly, according to ref. [4], Ncarboxyanhydrides of L-phenylalanine d=2.7nm (L-Phe-NCA) and y-benzyl-L-glutama -te (y-BLG-NCA) were prepared from L-phenylalanine and y-benzyl-L-glutamate with triphosgene in THF, respecta tively. Then, block copolypeptide Phe20 b -b-PBLG50 was synthesized using triec thylamine to initiate the polymerization 2 4 66 8 10 of NCAs. Secondly, 40 ml of block 2 Theta copolypeptide Phe20-b-PBLG50 solution Fig.1 XRD patterns of calcined in DMF (2.5 mg/ml) was gently mixed samples prepared with AMTS (a), with 120 ml of benzyl alcohol under APS (b) and PTMS (c) stirring and was heated at 80°C for 20 min. Subsequently, 5 ml of anilino-methyl triethoxy silicane (AMTS), 3 ml of benzyl ammine (as catalyst), 3ml of deionized water and 5ml of tetraethyl orthosilicate (TEOS) were added to the mixture, respectively. After heating at 80°C for 10 min, the reaction mixture was kept static in the sealed flask at room temperature for 15 days. The resultant gel product (denoted as LI) was obtained by washing with methanol and deionized water several times, and dried at 60°C for 24 h. Control experiments with (3-aminopropyl) trimethoxysilane (APS, with amine group) and phenyl trimethoxysilane (PTMS, with phenyl group) were carried out. In addition, white product was also obtained under the same reaction conditions except either without AMTS (denoted as L2). The white assynthesized product was calcined to remove organic solvents and copolymer at 550°C for 6 h. The prepared product was characterized by methods of XRD, TEM, TG/DTA, N2 adsorption-desorption test. 3. Results and Discussion XRD pattern (Figure 1 a) shows one broad diffraction peak with d spacing of 2.7 nm in the low-angle region, which indicates the presence of disordered short-range ordering structure. TGA data (unshown) reveal 51% of organic substance contained in the as-made sample LI. From the FT-IR patterns of assynthesized sample LI (unshown), the amide I and amide II bands at 1654 and

39

-1

a

140

0.40

120 100 80 60 40

0.35

1.43nm

0.30 0.25 0.20 0.15 0.10 0.05 0.00 0

20 0 0.0

500

b

3

160

Adsorbed volume/cm .g

180

dV/dD /cc.nm -1.g-1

Adsorbed volume/cm3.g-1

1542 cm"1 can be observed, which indicates that polypeptide mainly exists in the form ofa-helix conformation [4,5,6]

2

4

6

8

10

Pore Width/nm

0.2

0.4

0.6

0.8

Relative pressure (P/P ) (P/P0 0

1.0 1.0

400 300 200 100 0 0.0

0.2

0.4

0.6

0.8

1.0

Relative pressure (P/P (P/P0 Relative ) 0

Fig.2 N 2 adsorption-desorption isotherm of calcined samples (a) sample LI, inset: pore size distribution and (b) sample L2.

The nitrogen adsorption-desorption isotherm of calcined sample LI (Fig. 1) is a type I isotherm, and the BET surface area of sample LI is 506 m2/g (with micropore area of 455 m2/g), which indicates the presence of micropores (< 2 nm). Pore size distribution from DFT method centers at about 1.4nm. The formation of supermicropores might be mainly ascribed to polypeptide secondary structure [4]. Therefore, this type of micropores should be channellike. Meanwhile, the formation of part of micropores (below lnm) might be relevant to small molecular amine due to the possible hydrogen bond interaction between Si-OH and small molecular amine [7]. The N2 adsorption line of the calcined sample L2 is a type II isotherm, indicating the presence of mesovoids resulted from the aggregation of silica particles. TEM images (not shown) display that there exist a lot of interesting spindle-like nanorods with unusual interior nano-cells from. These nano-cells with thin walls are closed and the nano-cell size is between 3-10 nm. The structures of complex vesicles were also observed in the TEM images of self-assembly behavior of block copolypeptide in the organic solvent. Thus the closed complex nano-cells inside synthesized silica are the real immobilization and transcription for the structure of complex vesicles from self-assembly of block copolypeptide in the organic solvent. Novel interior structures might be ascribed to the strong interactions (hydrogen bonding and n-n interactions) between copolypeptide and AMTS, which has been verified by the control experiments with (3-aminopropyl) trimethoxysilane (APS, with amine group) and phenyl trimethoxysilane (PTMS, with phenyl group). No evident diffraction peak appears in the low-angle region of their XRD patterns (Figure 1). Both the polypeptide and AMTS play key roles in the formation of nanoporous silica with interior closed complex vesicle structures. Herein, AMTS acts as a bridge to indirectly connect water-insoluble

40

copolypetide with TEOS together, while copolypeptide as a template plays a decisive role in the formation of nano-structured silica. 4. Conclusion With the aid of 71-71 interaction between the phenyl groups of block copolypeptide and AMTS, nanoporous silica with unusual interior closed cells was prepared utilizing synthetic block copolypeptide Phe2o-b-PBLG5O as a template under ambient conditions. Here the presented results suggest a new approach for the preparation of hierarchical silica material with novel interior structures templating from polypeptide and the prepared material has certain potential applications in the encapsulation of biofluorescent materials or magnetic nanoparticles. 5. Acknowledgement This work was supported by National Science Foundation of China (Grants No. 20373029, 20233030), and joint-research fund of Nankai University and Tianjin University on Nano-sciences. 6. References [1] [2] [3] [4] [5] [6] [7]

N. Kroger, S.Lorenz, E. Brunner and M. Sumper, Science, 298(1999) 584. G. Pohnert, Angew Chem. Int. Ed., 41(2002) 3167. J. N. Cha, G. D. Stucky, D. E. Morse et al., Nature, 403(2000)289. K. M. Hawkins, S. S.-S.Wang, D. Ford M. et al., J. Am. Chem. Soc, 126(2004) 9112. M. Mttller, B. Kessler and K. Lunkwitz J. Phys. Chem. B., 107(2003) 8189. M. Muller Biomacromolecules, 2(2001) 262. T. Sun, M. S. Wong and J. Y. Ying Chem. Commun., (2000) 2057.

Recent Progress in Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

41 41

Synthesis of mesoporous silica materials from kenyaite Ziyu Liu, Yingxu Wei, Yue Qi, Shiyun Sang and Zhongmin Liu* Applied Catalysis Laboratory, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, 457 Zhongshan Road, Dalian 116023, China

Mesoporous silica materials with high BET specific surface area were synthesized from kenyaite, a layered silicate with multi-layers of SiO4 tetrahedra. Well-ordered mesostructure was obtained at pH=7, which exhibited similar framework to that of MCM-41 but with much shorter pore length. Keywords: kenyaite, MCM-41, pH, mesoporous 1. Introduction The discovery of MCM-41 [1] stimulated the synthesis of ordered mesoporous materials significantly. Siliceous sources were reported to have great influence on the synthesis of ordered mesoporous materials and layered silicates have attracted much attention as the siliceous sources [2-4]. Yanagisawa et al. [2] synthesized a mesoporous material named FSM-16 from kanemite, a layered silicate consisted of single layers of SiC>4 tetrahedra. The single layers of SiO4 tetrahedra was believed to be necessary for the synthesis while a layered silicate with multi-layers of SiC"4 tetrahedra, such as kenyaite [5], was not a suitable siliceous source. This maybe the reason why no mesoporous materials derived from kenyaite has been reported up to now except a few pillared structures with low BET specific surface area (less than 600 m2/g) and disordered pore systems [6-8]. Synthesis of ordered mesoporous materials with high BET specific surface area from kenyaite is still desirable and merits further efforts since it is a cheap natural mineral. In this paper, the precursor kenyaite was hydrothermally synthesized first and then transferred to mesoporous silica materials by a post-synthetic treatment.

42 2. Experimental Section 2.1. Synthesis The precursor kenyaite was prepared as follows: 2 g of NaOH and 2.16 g of NaCl were dissolved in 432 g of deionized water. To this solution, 32 g of fumed silica and 32 g of hexamethyleneimide were added under stirring. The mixture was heated at 423 K with 90 rpm for 192 h. The resulting solid was centrifuged, washed with deionized water and dried at 373 K overnight. For post-synthetic treatment, 3 g of kenyaite was dispersed in 315 g of deionized water containing 7.5 g of hexadecyltrimethylammonium bromide and 6.65 g of NaOH. After being refluxed at 373 K for 8 h, the obtained clear solution was cooled to room temperature, and the pH value of which was adjusted using 2 M HC1 solution to 9, 7, 5, 3, respectively. The resulting mixtures were stirred at room temperature for 12 h followed by centrifugation, washing and drying (the products were designated as MSK-n, n = 9, 7, 5, 3). For comparison, MCM-41 with similar composition was synthesized directly from TEOS by the conventional hydrothermal route [1]. 2.2. Characterization XRD patterns were recorded on a D/Max-b X-ray diffractometer with Cu Ka radiation of wavelength 1= 0.15406 nm (40 kV, 40 mA). FTIR studies were performed on a Bruker EQUINOX 55 spectrometer by KBr pellet method. TEM studies were carried out with a JEOL JEM-2000Ex electron microscopy. Nitrogen adsorption isotherms were measured at 77 K on a Micromeritics ASAP 2010 volumetric adsorption analyzer. Prior to the measurements, the samples were outgassed at 623 K for at least 4 h. 3. Results and Discussion Fig. 1A shows that the precursor is a pure kenyaite phase [9]. After the postsynthetic treatment, kenyaite is transferred to mesostructured materials (Fig. 1B-E). MSK-9 shows three diffractions corresponding to aos of 4.64, 2.64 and 2.30 nm (Fig. IB). These diffractions are similar to those of MCM-41 (Fig. IF), and such can be indexed as 100, 110 and 200 of a hexagonal mesostructure. MSK-7 also shows these diffractions and a slight increase in the (100) intensity is observed (Fig. 1C). Decreasing the pH value to 5 or 3, however, leads to an obvious decrease in 100 intensity and the vanishing of 110 and 200 diffractions (Fig. 1D-E). The structural dependence of MSK-n on the pH values may be related to the silica condensation rate [10]. The as-synthesized MSK-7 exhibits bands centred at 3500, 2917, 2846, 1640, 1477, 1240, 1070, 964, 912, 794 and 451 cm"1 in the FTIR spectra (Fig. 2A).

43

These bands are very close to those of MCM-41 (Fig. 2B), showing that these two samples possess almost identical frameworks. A A a00=4.64 =4.64 nm

A

3500

4.48 nm

1640 1477

794 912 964

B

1240 2917 1070 2846

C

451

4.35 nm D 4.33 nm 4 « n m a0=4.9 =4.94t nm

I.

B

E

F

2 2 44 66 88 10 10

20 20

30 30

40 40

50 50

2 2 Theta Theta Fig. 1 XRD patterns of as-synthesized (A) kenyaite, (B) MSK-9, (C) MSK-7, (D) MSK-5, (E) MSK-3 and (F) MCM-41.

4 000 4000

3 0 0 0 11500 500 3000

11000 000

Wave numbers

50 0 500

-1 (cm-1 )

Fig. 2 FTIR spectra of as-synthesized (A) MSK-7 and (B) MCM-41

Fig. 3 TEM images of as-synthesized (A) MSK-7 and (B) MCM-41.

Fig. 3 shows that MSK-7 and MCM-41 both exhibit arrays of parallel lines, indicating the presence of ordered mesostructures. The aoS detected by TEM are 4.42 nm for MSK-7 and 4.73 nm for MCM-41, respectively, which agree with the results from XRD. After calcination at 823 K, MCM-41 displays a type IV isotherm and shows a strong uptake of N2 in a relative pressure (p/po) range of 0.2-0.3 due to capillary condensation (Fig. 4A). The sample exhibits a BET specific surface area of 858 m2/g, a pore volume of 0.68 cm3/g and a uniform pore size distribution of 2.2 nm (Fig. 4, inset A). These textual data are comparable to those reported [1]. The isotherm of MSK-7 also shows a strong capillary condensation at p/po range of

44

4. Conclusion

700

Absorbed Volume (cm /g)

600

B

•2?

3

400

A

300

3

3

500

d V / d D (cm /g/mn)

0.2-0.3, however, a large hysteresis loop at p/p0 range of 0.4-0.9 is observed (Fig. 4B), which indicates the existence of secondary mesopores [11]. Fig. 4 (inset B) shows that MSK-7 possesses two mesoporous pore sizes centered at 2.2 and 3.6 nm, respectively. Meanwhile, a BET specific surface area of 1044 m2/g and a pore volume of 0.99 crnVg are observed for MSK-7, which are higher than the corresponding data of MCM-41.

200

0 .1 5 0 .1 0

A

0 .0 0

100 100 0.0

B

0 .0 5

0

0.2

0.4

2 4 6 8 10 P o re d ia m e te r ( n m )

0.6

0.8

1.0 1.0

Relative pressure (p/p (p/p0) 0) Fig. 4 N 2 adsorption isotherms of 823 K calcined (A) MCM-41 and (B) MSK-7. Inset is the pore size distribution of (A) and (B).

In summary, mesoporous silica materials can be synthesized from kenyaite by a post-synthetic treatment. The sample showed almost identical framework to that of MCM-41 but with higher BET specific surface area and two pore size distributions. This new method provides a possible way to prepare ordered mesoporous materials from layered silicates. 5. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11]

C.T Kresge, M.E Leonowicz, W.J Roth, J.C Vartuli and J.S Beck, Nature 359 (1992) 710. T. Yanagisawa, T. Shimizu, K. Kuroda and C. Kato, Bull. Chem. Soc. Jpn. 63 (1990) 988. S. Inagaki, Y. Fukushima and K. Kuroda, J. Chem. Soc, Chem. Commun. (1993) 680. S. Inagaki, A. Koiwai, N. Suzuki, Y. Fukushima and K. Kuroda, Bull. Chem. Soc. Jpn. 69 (1996) 1449. H.P. Eugster, Science 157 (1967) 1177. S.Y. Jeong, J.K. Suh, H. Jin, J.M. Lee and O.Y. Kwon, J. Colloid Interface Sci. 180 (1996) 269. Kwon, K.W. Park and U.H. Paek, J. Ind. Eng. Chem. 5 (1999) 93. Kwon and S.W. Choi, Bull. Korean Chem. Soc. 20 (1999) 69. Z.Y. Liu, Z.M. Liu, Y. Qi, L. Xu, Y.L. He, Y. Yang and Y.Y. Zhang, Chin. J. Catal. 25 (2004) 542. M.T. Bore, S.B. Rathod, T.L. Ward and A.K. Datye, Langmuir 19 (2003) 256. S.Z. Qiao, C.Z. Yu, Q.H. Hu, Y.G. Jin, X.F. Zhou, X.S. Zhao and G.Q. Lu, Microporous Mesoporous Mater. 91(2006) 59.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

45 45

Fluorinated surfactant with short carbon chain templating macropores in hierarchically mesoporous/macroporous silica Xiangju Meng and Takashi Tatsumi* Chemial Resources Laboratory, Tokyo Institute of Technology, Yokohama, 226-8503, Japan.

1. Introduction Hierarchical porous materials are of interest in fundamental research and for practical applications in catalysis, separation, adsorption, or electrode materials [1]. Various types of hierarchical bi- or trimodal porous materials have been reported recently, in particular, micro-macro, micro-meso, meso-macro, small meso-large meso, micro-meso-macro, and small meso-large meso-macroporous materials, in particular, using ionic liquids as templates for small mesopores. Such hierarchical pore systems are supposed to be advantageous, because they feature high pore volumes and large surface areas together with potentially larger pore sizes [1,2]. In general, templates with relatively large diameter such as polymer sphere, polymer colloid and block copolymer are used to produce macropores in the hierarchically mesoporous/macroporous silica. However, small templates for the macropores are seldom reported except the formation of some macrochannels in metal oxides by small surfactants [3]. Recently, much attention has been paid to the application of fluorinated surfactants in the synthesis of nanoporous materials, because of their special physical and chemical properties [4]. Mesoporous silica with ultrahigh hydrothermal stability have been prepared by the mixture of fluorocarbon and hydrocarbon surfactants at high temperature; mesoporous silica nanoparticles with various pore structures are also synthesized in a similar manner. Here, we show that fluorinated surfactants with short carbon chains templates macropores in heirarchically mesoporous/macroporous silica.

46

2. Experimental Section In a typical synthesis, the mixture of 0.4-0.6 g oligomer surfactant and 0.81.0 g fluorinated surfactant FC-4911 (CF3(CF2)3SO2NHCH2CH2CH2N+(CH3)3r) or FC-911 (CF3(CF2)7SO2NHCH2CH2CH2N+(CH3)3r) were dissolved in 45 gof dilute solution of HC1 (pH = 1.7). After the addition of 2.2 g TEOS, the mixture was stirred for 24 h at room temperature and then treated at 100°C in an oven for another day. Then, the product was collected by filtration, dried in air, and calcined at 600°C for 5 h to remove the surfactants. The detailed information for each sample is presented in Table 1. 3. Results and Discussion Table 1 Structural parameters of various hierarchically mesoporous/macroporous silica. Sample

Surfactants

A B C D E

Brij35+FC-911 Brij56+FC-4911 Brij56+FC-911 Brij58+FC-911 Brij76+FC-4911 Brij76+FC-911

F

Surface area (m2/g) 687 824 594 629 708 621

Pore size Pore volume (nm) (cm3/g) 2.3 0.66 2.4 1.42 3.1 0.86 2.4 0.63 2.7 2.06 3.1 0.97

Scanning electronic microscopy (SEM) images for various samples are shown in Figure 1. Obviously, they exhibit a large amount of macropores in all samples with the pore size in the range of 30-60 nm (Figure 1). N2 adsorption isotherms for various samples are given in Figure 2. The N2 adsorption isotherms for all samples basically show the IV-type curve and the capillary condensation step at a relative pressure (P/Po) of 0.25-0.4, suggesting the existence of typical mesopores. Additionally, at the relative pressure higher than 0.85, a strong increase in the adsorbed volume of N2 can be observed, evidently showing an appreciable amount of secondary porosity, i.e. the large mesopores or macropores [3], which is different from the curves for the samples prepared by the oligomer surfactants without fluorinated surfactants (curves a-d in Figure 2). As a result, it is reasonable that a very large pore volume can be obtained in the range of 0.66-2.06 cm3/g with high surface area of 594-824 m2/g. Especially, sample E gives a very large pore volume of 2.06 cmVg, indicating the existence of a large amount of macropores. Addtionally, it is interesting to note that the macropore volume of samples B and E prepared by FC-4911 are much higher than that of other samples prepared by FC-911. XRD patterns for various hierarchically mesoporous/macroporous silica samples are shown in Figure 2, which are similar to those mesoporous silica synthesized by oligomer surfactants reported previously [5]. These results

47

A

B

C

D

E

F

Figure 1 SEM images for various hierarchically mesoporous/macroporous silica.

suggest that the addition of fluorinated surfactants change the structure of mesoporous silica in agreement with the recent reports [4] about the synthesis of highly thermally stable mesoporous silica synthesized with the mixture of hydrocarbon surfactants and fluorinated surfactants. Amorphous silica materials without special structure were obtained if only fluorinated surfactants were used as templates without any oligomer surfactant, which suggests that fluorinated surfactants are essential for the formation of macropores, while oligomer surfactants template the mesostructure. It is interesting to discuss the formation of macropores templated by fluorinated surfactants

48

with short carbon chains. Fluorinated surfactants are well known for their very high surface activities and always lead to very low surface tension in aqueous 1800

600

1600 500

400

1000

d 300

800

c

F 600

200 0.0

E D C

E 200

D 400

F

Intensity (a. u.)

1200

3

Adsorbed Volume (cm /g)

1400

b

C

B

B A

100

0.2

0.4

0.6

(P/P) Relative Pressure (P/P ) 0

0.8

1.0 0.0

A

a 0.2

0.4

0.6

) Relative Pressure (P/P (P/P) 0

0.8

1.0

2

4

6

221heta Thet a

Figure 2 N 2 adsorption isotherms and XRD patterns for various samples. (Samples a-d are prepared by oligomer surfactants of Brij 35, Brij 56, Brij 58 and Brij 78 under the same condition, respectively)

solution [5]. Therefore, part or most of fluorinated surfactants probably form "supermicelle" by self-assembly, and such supermicelles would aggregate with the diameter in the range of 40-60 nm during the hydrothermal treatment at 100°C. These aggregations of supermicelles may be embedded in the silica particles and form macropores after the surfactants were removed, resulting in the formation of hierarchically mesoporous/macroporous silica, as previously reported on the preparation of hierarchically mesoporous/macroporous metal oxides templated by CI6EOio (or Ci3EO6) [3]. This work is supported by Core Research for Evolutional Science and Technology of Japan Science and Technology Corporation. Dr. X. Meng gratefully thanks Japan Society for the Promotion of Science (JSPS) for postdoctoral fellowship. 4. References [1] A. Hagfeldt and M. Gratzel Chem. Rev. 95 (1995) 49. [2] O. Zel, D. Kuang, M. Thommes and B. Smarsly, Langmuir 22 (2006) 2311. [3] J.-L. Blin, A. Leonard, Z.-Y. Yuan, L. Gigot, A. Vantomme, A. K. Cheetham and B.-L. Su, Angew. Chem. Int. Ed., 42 (2003) 2872. [4] F.-S. Xiao, Curr. Opin. Coll. Inter. Sci., 10 (2005) 94. [5] Y. Han and J. Y. Ying, Angew. Chem. Int. Ed., 424 (2005) 288.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

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Synthesis of mesostructured silica with strongly hydrophilic surfactant templates Weibin Fana, Xiangju Menga, Toshiyuki Yokof, Yoshihiro Kubotab and Takashi Tatsumi3* "Chemical Resources Laboratory, Tokyo Institute of Technology, Nagatsuda 4259, Midori-ku, Yokohama 226-8503, Japan. Department of Materials Science and Chemical Engineering, Graduate School of Engineering, Yokohama National University, 79-5 Tokiwadai, Hodogaya-ku, Yokohama 240-8501, Japan

A series of strongly hydrophilic surfactants have been examined for the synthesis of mesoporous silica under both acidic and basic conditions in the presence of different cations. This makes it possible to morphosynthesize mesostructured silica and adjust the pore openings to the border between micropore and mesopore regions. 1. Introduction Morphologenesis of mesoporous materials and synthesis of materials with a pore size intermediate between zeolite micropores and mesopores have attracted much attention [1-3]. This is because mesoporous materials with complex forms have potentials for catalysts, adsorbents and semiconductor hosts as well as medical implants [1], while the materials with a pore opening in the range of 1.3 - 2 nm could fill the gap between zeolites and mesoporous materials. In this context, a variety of peculiarly shaped, such as rope-, discoid-, gyroid- and eccentric-shaped, hexagonal mesoporous silicas have been synthesized with cetyltrimethylammonium chloride (CTAC1) surfactant under strongly acidic conditions or by using a complex template of poly(acrylic acid) and CTABr in the presence of alkaline earth cations of Mg2+ or Sr + at a pH value in the range of 5.5 - 9.0 [1,2]. However, morphologenesis of mesostructured silica at pH > 10 has not been reported yet. Ryoo et al. reported that ordered and disordered silica with uniform pores on the border between micropore and mesopore regions could be synthesized with short double-chain surfactants [3]. Here, we

50 50

report that this goal and morphologenesis could be achieved by employing strongly hydrophilic surfactants under both acidic and basic conditions. 2. Experimental Section The samples were synthesized with tetraethyl orthosilicate (TEOS), distilled water, one type of strongly hydrophilic surfactant (cetyl- or octadecyldimethylethanolammonium bromide (CDMEA or ODMEA), diethylethanolammonium bromide (CDEEA or ODEEA), dimethyl-3-propanolammonium bromide (CDMPA or ODMPA) and dimethyl-3-phenolammonium bromide (CDMPhA or ODMPhA)) and one kind of alkali (TMAOH, LiOH, NaOH, KOH and CsOH) under acidic or basic conditions. 3. Results and Discussion Figure 1 shows as an example the XRD patterns of the samples synthesized under strong acidic conditions. Clearly, well-resolved 100, 200 and 210 diffraction lines were present in both as-synthesized and calcined materials, showing a highly ordered hexagonal symmetry. This is further confirmed by the commonality of TEM images for typical hexagonal structure (not shown here for brevity). A shift to high angle of the diffraction lines after calcination is a result of the unit-cell contraction.

^ 200 1 ^ 100 2

4

2 Theta/degree

0

100 200 Pore diameter/A

0 0.4

0.8

1.2

P/P° Figure 1 (A) XRD patterns of the (a) as-synthesized and (b) calcined sample synthesized with a gel having a [CDMEA] :[SiO2] ratio of 0.18; (B) N2 adsorption/desorption isotherms of the sample prepared from a gel with a [CDMEA]:[SiO2] ratio of 0.13.

Figure 2 displays the FE-SEM images of the samples synthesized with CDMEA under quiescent aqueous acidic conditions at 0°C. It shows that the morphologies of the samples varied with the amounts of HCl and CDMEA. The crystals synthesized with a gel having a [CDMEA]:[SiO2] ratio of 0.1 showed an intriguing gyroid shape. A slight increase in the ratio to 0.13 led to the formation of particles with a rope shape with the knots weaved by entangled gyroids. A further increase in the CDMEA amount gave rise to spherical

51

crystals composed of uniform nanosized particles, indicating a potential for the hierarchical synthesis of mesoporous materials. In contrast, a decrease in the [HCl]:[SiO2] ratio from 2.5 to 1 made the particles irregular. On the other hand, when the [HCl]:[SiO2] ratio was increased to 5, partially radial patterns were observed. The N2 adsorption/desorption measurements showed that all these highly ordered materials had a surface area higher than 1000 m2/g (Figure IB). It is noteworthy that the gyroidal sample exhibited an isotherm typical of microporous materials with a pore size of 14.0 - 15.0 A, intermediate between zeolite and mesoscale pore openings. To the best of our knowledge, this is the first highly ordered mesostructured silica with such an intriguing pore size synthesized with a single-chain surfactant template. 29Si MAS NMR spectroscopy shows that the material synthesized with CDEMA possessed a higher condensation degree than that synthesized with the surfactant of cetyldimethylethylammoium bromide under the same conditions, indicating a higher hydrothermal stability. As expected, the synthesis temperature also had a strong influence on the formed samples. An increase in the temperature from 0 to 25°C resulted in the less ordered structure.

Figure 2 SEM images of the samples synthesized with a synthesis gel having a [CDMEA]:[SiO2] ratio of (A) 0.1; (B) 0.13 and (C) 0.18 at 0°C under acidic conditions.

Figure 3 SEM images of the materials synthesized with CDMPA surfactant in the presence of (A) TMAOH, (B) LiOH and (C) NaOH under basic conditions.

A replacement of the surfactant of CDMEA with CDMPA led to the formation of SBA-1 structure as a result of the decrease in the g value. Nevertheless, when CDEEA was used, the as-synthesized material showed a poorly ordered structure, as revealed by the presence of only one diffraction line.

52

A change of the surfactant head or chain length could adjust the pore size of the formed materials. Synthesis of mesostructured silica with these strongly hydrophilic surfactants was further examined under basic conditions. Attempts to synthesize ordered mesoporous materials with CDMEA, ODMEA or CDMPhA failed regardless of the amounts of the surfactants and OH" during the hydrolysis process, the pH value in the final gel, or the crystallization time. In contrast, CDMPA as a template resulted in the formation of highly ordered hexagonal structure irrespective of the alkalis used when the pH value was adjusted to higher than 10. Unexpectedly, when CDEEA served as a template, a highly ordered mesoporous material could be obtained only with TMAOH as an alkali source. A substitution of LiOH, NaOH, KOH, RbOH or CsOH for TMAOH led to the structure less ordered or layered. A striking feature in the basic synthesis system is that the morphologies and channel structures of the formed materials depended on the type of alkali. It is interesting that TMAOH as an alkali led to formation of gyroid particles (Figure 2) although part of them were not perfect. In contrast, when LiOH was used, the particles showed a shape of bundles of fibers with a circular channel structure, whereas NaOH produced arc-dendritic shaped particles. KOH, RbOH and CsOH gave particles with a shape of bundles of rods, some of which partially arced. The alkali amount and the pH value in the final gel are key factors for the synthesis of highly ordered mesoporous materials. A good match between alkali and surfactant in the amount is crucially important. The crystallization mechanism will be reported elsewhere. 4. Acknowledgment This work is supported by Core Research for Evolutional Science and Technology of Japan Science and Technology Agency (JST). W. Fan is grateful to JST for a postdoctoral fellowship. 5. References [1] H. Yang, N. Coombs and G.A Ozin, Nature, 386 (1997) 692.1. Sokolov, H. Yang, G.A. Ozin and C.T. Kresge, Adv. Mater., 11 (1999) 636. S.M. Yang, H. Yang, N. Coombs, I. Sokolov, C.T. Kresge and G.A. Ozin, Adv. Mater., 11 (1999) 52. [2] C.C. Pantazis, A.P. Katsoulidis and P.J. Pomonis, Chem. Mater., 18 (2006) 149. [3] R. Ryoo, I. Park, S. Jun, C.W. Lee, M. Kruk and M. Jaroniec, J. Am. Chem. Soc, 123 (2001) 1650.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Published by Elsevier B.V.

53 53

Synthesis of stable colloidal suspensions of ordered mesostructured silica from sodium metasilicate using pluronic P123 and mildly acidic conditions Andreas Berggren, Krister Holmberg and Anders E. C. Palmqvist Applied Surface Chemistry, Department of Chemical and Biological Engineering Chalmers University of Technology, SE-412 96 Goteborg, Sweden

Colloidal suspensions of ordered mesostructured silica with particle size of 50-200 nm have been synthesized from sodium metasilicate using mildly acidic conditions and Pluronic PI23 as structure directing agent. The suspensions form rapidly upon mixing of the reagents and are stable without sedimentation over several weeks. The synthesis yield was affected by the concentration of silica in excess of an equilibrium concentration, and the particle size increased with increasing concentration of surfactant. 1. Introduction The interest in ordered mesostructured silica (OMS) materials has increased rapidly since their discovery and syntheses have been developed focusing on properties like pore diameter, wall thickness and shape of the materials. In the mid 1990's stable suspensions of colloidal zeolites were reported [1,2] and these have now found extensive use in mechanistic studies of zeolite growth and in the preparation of zeolite membranes [3]. Fewer studies have been devoted to the control of particle size of OMS materials and very few to syntheses of stable colloidal suspensions of OMS materials [4-10]. These are mainly based on cationic surfactants, alkoxides and alkaline conditions. We have developed a method for preparation of stable colloidal suspensions of OMS materials with the SBA-15 structure [11] using mild acidic conditions and low price silicate. Partly similar syntheses previously reported result in precipitation of a mesostructured solid instead of a stable colloidal suspension [11-15].

54

2. Experimental Section A series of syntheses were performed in which sodium silicate was dissolved in milliQ-water and then pH adjusted to 3 before mixing with water solutions containing PI23. The resulting reaction mixtures had different silica/surfactant and silica/water ratios. The products obtained were washed by centrifugation and redispersion in water, then freeze-dried and calcined at 500°C. Dry samples were characterized using SAXS, SEM, TEM, andN2-sorption. Table 1 Reaction conditions and product properties Synthesis

Mass ratio (SiO2/H2O)

Mass ratio (P123/SiO2)

Mass ratio (P123/H2O)

Initial pH

BET area (m2/g)

Yield (%)

SI

1/500

2

1/250

4,1

654

37

S2

1/100

2

1/50

3,5

801

57

S3

1/100

0,5

1/200

3,3

505

60

3. Results and Discussion A colloidal suspension found stable for weeks was obtained within a second of mixing the reagents in synthesis SI described in Table 1. Also synthesis S3 gave a stable colloidal suspension, whereas with S2 the stability of the suspension decreased to hours. The lower stability of S2 is likely due to its larger particle size shown in Figure 1. However, only syntheses SI and S2 resulted in hexagonally ordered mesoporous materials as shown by TEM in Figure 2 and N2-sorption in Figure 3. These samples also exhibited the typical elongated morphology, whereas S3 gave spherical particles shown in Figure 1. Interestingly, the yield of SiO2 found in the products was similar for S2 and S3 (57 and 60 %) and lower for SI (37 %) as given in Table 1.

Figure 1. SEM micrographs of dried reaction solutions of synthesis SI (A), S2 (B) and S3 (C).

55

Figure 2. TEM micrographs of purified and calcined samples from synthesis SI (A) and S2 (B). 400

300 250 200 150

Pore V olum e (mm ³/g·Å)

Quantity Adsorbe d (cm³/g STP)

350

100 50

16 14 12 10 8 6 4 2 0

0

50

100

150

Pore Diameter (Å)

200

0 0

0,2

0,4 0,6 Relative Relative Pressure (P/Po)

0,8

1

Figure 3. N2-sorption isotherms and pore size distributions calculated using the adsorption branch and the BJH-method for the purified and calcined samples from synthesis Sl(o), S2(«) and S3(+).

56

The above observations can be explained as follows. As previously reported, a suitable surfactant/silica ratio is essential in obtaining an ordered mesostructure and for the presented system a mass ratio of 2 gives a hexagonal structure whereas 0.5 results in a disordered structure. The differences in yield can be explained by the equilibrium between silica species in the formed particles and species soluble in solution. The yield is thus higher for S2 and S3 because their higher concentrations of silica results in a larger excess concentration of silica above the equilibrium concentration in these two syntheses compared to SI. This higher concentration results in an increased amount of the silica added being accessible for particle formation. Finally, it seems that the particle size of the products is related to the surfactant concentration since this is similar for SI and S3 but higher for S2. Although this observation should be corroborated by further investigations to be fully understood, an increase in particle size when concentrating the reaction solution is in agreement with previous reports on syntheses of mesostructured silica using CTAB, TEOS and alkaline conditions [5,6]. 4. Acknowledgement AB acknowledges financial support from the Knowledge Foundation through the research school YPK. AECP thanks the Swedish Research Council for a senior researcher grant. 5. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15]

B.J. Schoeman, J. Sterte and J.-E. Otterstedt, Zeolites, 14 (1994) 110. A.E. Persson, B.J. Schoeman, J. Sterte and J.-E. Otterstedt, Zeolites, 14 (1994) 557. R.F. Lobo and A.E.C. Palmqvist, Curr. Opin. Coll. Interface Sci., 10, (2005) 185. C.E. Fowler, D. Khushalani, B. Lebeau and S. Mann, Adv. Mater., 13 (2001) 649. Q. Cai, Z.-S. Luo, W.-Q. Pang, Y.-W. Fan, X.-H. Chen and F.-Z. Cui, Chem. Mater., 13 (2001)258. R.I. Nooney, D. Thirunavukkarasu, Y. Chen, R. Josephs and A.E. Ostafin, Chem. Mater., 14 (2002)4721. J. Rathousky, M. Zukalova, P.J. Kooymanb and A. Zukal, Coll. Surf. A: Physicochem. Eng. Aspects, 241(2004)81. K. Ikari, K. Suzuki and H. Imai, Langmuir, 22 (2006) 802. Y. Han and J.Y. Ying, Angew. Chem. Int. Ed. 44 (2005) 288. W. Zhao and Q. Li, Chem Mater. 15 (2003) 4160. D. Zhao, Q. Huo, J. Feng, B.F. Chmelka and G.D. Stucky, J. Am. Chem. Soc, 120 (1998) 6024. L. Sierra and J.-L. Guth, Micropor. Mesopor. Mater., 27, 243 (1999) 243. X. Cui, W.-C. Zin, W.-J. Cho and C.-S. Ha, Mater. Lett., 59 (2005) 2257. J.M. Kim and G.D. Stucky, Chem. Commun., (2000) 1159. K. Kosuge, T. Sato, N. Kikukawa and M. Takemori, Chem. Mater., 16 (2004) 899.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserve.

57 57

Three-Dimensional large pore cubic silica mesophases with tailored pore topology: developments and characterization Freddy Kleitz* and Tae-Wan Kim Department of Chemistry, Universite Laval, Quebec G1K 7P4, Canada, 1. Introduction

Poly(alkylene oxide)-type block copolymers are ideal structure-directing agents for the preparation of ordered large pore (> 5 nm) silicas [1]. However, mesoporous silicas with cubic symmetry are generally more difficult to prepare than their two dimensional (2-D) hexagonal counterparts (e.g. SBA-15) [2], and particularly, cage-like mesophases are often synthesized in a narrow range of synthesis conditions. 3-D materials are expected to be superior to materials with 1-D channels especially for applications related to adsorption, diffusion and host-guest interactions. Despite synthetic progress [3-7], methods for synthetic tailoring of structure, pore dimensions and pore topology remain to be improved. In addition, due to the cage-like pore structure, it is challenging to accurately determine the real size of the cages and pore windows. The present contribution introduces recent developments in the preparation and characterization of 3-D silica mesostructures consisting of large interconnected cage-like pores. The results are especially concerned with the modulation of pore dimension and pore shape of mesoporous Imhm silicas (SBA-16) [8,9]. 2. Experimental Section Large pore cage-like mesoporous silicas were synthesized with Pluronic F127 (EO106PO70EO106) as the structure-directing agent and TEOS as the silica source. The reactions were performed at low HC1 concentration (0.4 M) at 45°C for 24 h, followed by aging for 24 h at a temperature ranging from 45 to 130°C. nButanol was added to the mixture to act as a co-surfactant. The molar composition of the starting mixture was varied in the range 0.0035 F127:x TEOS:^ BuOH:0.91 HC1:117 H2O with x = 0.5-3, and y = 0-3, respectively. For template removal, the as-synthesized mesophases were either extracted at room temperature with HCl/ethanol followed by calcination at 550°C for 2 h, or

58

subjected to H2SO4 treatment. Briefly on the treatment, 2 g of the as-synthesized mesophase was stirred in H2SO4 (48 wt%) at 95°C for 24 h. The powder was further heated at 250°C in air for 3 h. Materials were characterized by nitrogen physisorption measurements at 77 K, argon physisorption measurements at 87 K, and powder X-ray diffraction (XRD). Physisorption data were evaluated using the Quantachrome Autosorb 1.52 software. 3. Results and Discussion The low acid concentration conditions employed enable the introduction of nbutanol as a phase-controlling agent [4,8] into the Si02-EOio6P070EOio6-H20 system, to provide tuning of the mesophase topology. Various silica mesophases with either facecentered cubic (fee) Fm3m, body-centered cubic (bec) Im3m or 2-D hexagonal [0.91,2.08| structures are generated depending on the TEOS/BuOH mole ratio in the starting synthesis mixture [8]. For TEOS/BuOH [1.52,1.34) ratios comprised between 2.29/0.15 and 0.91/2.08, the XRD peaks observed in the [2.29, 0.15] range of 2 theta = 0.6-2.5 are indexed to the 0.5 1.0 1.5 2.0 2.5 3.0 Im3m space group, as exemplified in Fig. 1. 28 (degrees) All the N2 isotherms of these silicas are type IV isotherms with a H2-type adsorption- Fig. 1 XRD patterns for cubic Iniim desorption hysteresis loop characteristic of SBA-16 silicas, prepared at the mesoporous materials with cage-like pores molar ratio of 0.0035 F127:* [3,10]. The structural parameters of these TEOSy BuOH:0.91 HC1:117 H2O, cubic Im3m silica materials are summarized with [x, y] as shown. in Table 1. Specific surface area (SOFT), total pore volume (FDFT), and micropore volume (Vmi volume for pore diameters < 2 nm) could be estimated using non-linear density functional theory method (NLDFT). The model used for the NLDFT evaluations is the recently developped kernel of isotherms of N2 adsorbed on silica with spherical pore geometry, using the adsorption branch [11]. The primary mesopore cage diameter is denoted $DFT and was estimated using the same NLDFT method.

59 Table 1 Physicochemical parameters derived from N2 sorption measurements performed at 77 K [TEOS, BuOH]

a

SOFT 2

1

SBET 2

1

VDFT 3

1

vmi 3

1

W X. '' spheres

"cylinders

fry]

(nm)

(m g )

(m g )

(cm g )

(cm g )

(nm)

(nm)

[2.29,0.15]

15.3

753

890

0.49

0.088

7.1

4.7

[1.88,0.68]

15.5

746

860

0.51

0.092

7.9

5.1

[1.52, 1.34]

15.1

767

810

0.51

0.116

8.2

5.4

[1.27, 1.61]

15.6

909

1050

0.72

0.090

8.9

6.3

[0.91, 2.08]

16.2

930

980

0.74

0.068

10.1

7.2

for the calcined SBA-16 samples with different TEOS/BuOH molar ratios (see text).

Our investigations reveal that the structural properties of the cubic Im3m mesoporous silicas can be tailored by simply adjusting the amounts of the silica source and co-surfactant in the synthesis mixture. A pronounced increase of the mesopore volume is observed with simultaneous decrease of the TEOS amount and increase of the butanol content. This behavior is also reflected on the dimension of the cages as illustrated by the evolution of the pore size distribution (Fig. 2). The pore size increases from 7.1 nm up to 10.1 nm with concurrent increase of butanol and decrease of the quantity of TEOS. Note that pore size analysis by NLDFT calculations based on a cylindrical pore model underestimates the pore dimensions by about 30%. Three population of pores are evidenced (Fig. 2): micropores around 1.4 nm (possibly noncomnecting), connecting windows centered around 3 nm, and the main large mesocages. Cubic mesoporous silicas prepared at low HC1 concentrations also exhibit distinct textural properties when the template is removed either by calcination or by a treatment with sulfuric acid. Particularly, the acid treatment allows for tailoring of the pore topology and seems to open access to uniform synthetic tuning of pore entrances instead of producing materials with distribution of entrance sizes.

2

4

6

8

10

12

" 16 1» 2° Pore diameter [nm]

Fig. 2 PSD for SBA-16 samples, calculated from the N2 sorption isotherms at 77 K using the NLDFT model based on spherical pores (dotted line). Solid line is the FFT smoothed

60

0.2

0.4 0.6 0.8 Relative pressure (P/PJ

0.2

0.4 0.6 0.8 Relative pressure (P/Po)

Fig. 3 Argon physisorption isotherms measured at 87 K on calcined and acid-treated SBA-16 (Si02-EO,o6P07oE0106-H20-butanol): (a) aged at 100 °C and (b) aged at 60 °C.

The acid-treated materials exhibit larger unit cell parameter and larger pore volume than those observed for the same materials after conventional calcination. The applied acid treatment can produce materials with pseudocylindrical mesopores (Fig. 3) while maintaining the overall cubic symmetry. However, pore size analyses performed with the respective NLDFT pore models suggest little influence of the treatment on the large mesopore diameter. 4. References [1] G. J. A. A. Soler-Illia, E. L. Crepaldi, D. Grosso and Sanchez, C, Curr. Opin. Colloid Interface Sci., 8 (2003) 109. [2] M. Choi, W. Heo, F. Kleitz and R. Ryoo, Chem. Commun., (2003) 1340. [3] F. Kleitz, D. Liu, G. M. Anilkumar, I. S. Park, L. A. Solovyov, A. N. Shmakov and R. Ryoo, J. Phys. Chem. B, 107 (2003) 14296. [4] F. Kleitz, L. A. Solovyov, G. M. Anilkumar, S. H. Choi and R. Ryoo, Chem. Commun., (2004)1536. [5] T.-W. Kim, R. Ryoo, M. Kruk, K. P. Gierszal, M. Jaroniec, S. Kamiya and O. Terasaki, J. Phys. Chem. B, 108 (2004) 11480. [6] J. Fan, C. Yu, F. Gao, J. Lei, B. Tian, L. Wang, Q. Luo, B. Tu, W. Zhou and D. Zhao, Angew. Chem. Int. Ed., 42 (2003) 3146. [7] J. Fan, et al. J. Am. Chem. Soc, 127 (2005) 10794. [8] F. Kleitz, T.-W. Kim and R. Ryoo, Langmuir, 22 (2006) 440. [9] C. M. Yang, W. Schmidt and F. Kleitz, J. Mater. Chem., 15 (2005) 5112. [10] P. I. Ravikovitch and A.V. Neimark, Langmuir, 18 (2002) 1550. [11] M. Thommes, B. Smarsly, M. Groenewolt, P. I. Ravikovitch and A. V. Neimark, Langmuir, 22 (2006) 756.

Recent Progress in Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

61 61

A novel method of mesostructured material architecture using DBD plasma on illite with nonexpandibility Myung Hun Kima, II Mo Kangb, Kiwoong Sungc, Bui Hoang Bacc, Jeong Hun Kimd, Yungoo Songc, Hi-Soo Moon0 and Su Dok Yie "Department of Chemistry, Yonsei University, Seoul 120-749, Korea Institute of Earth Atmosphere Astronmy, Yonsei University, Seoul 120-749, Korea c Department of Earth System Sciences, Yonsei University, Seoul 120-749, Korea Department of Ophtalmology, Seoul National UniversityHospital, Seoul lqO-744, Korea e Yong Koong Illite Company, Bokwang Building, Seoul 152-080, Korea

The mesostructured material architecture using hydroxyl groups derived from DBD plasma within illite structure has been successfully accomplished by hydrothermal conditions under between 353 and 373 K and pH=6 condition. 1. Introduction Illite has a three-sheet layer structure and non-expandibility with tightly held interlayer K+ balancing a high layer charge. The surface charge of illite layers, one Al3+ octahedral sheet sandwiched between two Si4+ tetrahedral sheets, is the permanent negative charge on the basal planes due to the isomorphic substitutions, Al3+ for Si4+ and Mg2+ or Fe3+ for Al3+. Additional polar sites, mainly octahedral Al-OH and tetrahedral Si-OH groups, are situated at the broken edges. These amphoteric sites are conditionally charged, and so variable charges can develop at the edges by direct H+ or OH" transfer from aqueous phase depending pH. The hydroxyl groups are active sites which tend to react with many polar organic compounds and various functional groups [1]. However, no attempt to generate effectively hydroxyl groups in illite is mentioned in literatures and the use for the hydroxyl groups has been published a few reports. Hence, in an effort to establish the importance of these groups, we refered to a noteworth paper reported by U. Kogelschatz et. al to generate a lot of hydroxyl groups on illite [2]. The author showed the ozone generated from the

62

dielectric-barrier discharge (DBD) plasma through the discharge gap between the electrodes was transformed into the hydroxyl groups on the amorphous silica. The purpose of present work gains a better understanding of the role of hydroxyl groups molded in DBD plasma treatment process on non-expandible illite and derives the mesostructured materials using these groups. 2. Experimental Section Illite was obtained from Yong Koong Illite Company. DBD plasma was treated for 0.5 and 1.0 min on illite under oxygen atmosphere, respectively. After that, the samples were refluxed with 0.5 N HC1 for 4 h, washed and dried at RT. The chemical composition of the gel solution is 1.5 CTMAC1: 2.0 Illite: 0.5 EtOH: 5000 H2O. All reactions carried out at 353 K and 373 K under pH = 6. Also, the products were denoted M-Ili(l) and M-Ili(2). The resultant solids were characterized by means of PXRD, TGA, TEM and nitrogen adsorption. 3. Results and Discussion The X-ray patterns in Fig. 1 show mesopore phases displaying peaks in the range of 0.78-90 nm with the interplanar spacing of 7.0-8.0 nm. MIli(l) and M-Ili(2) synthesized at 353 K and 373 K with plasma-treated illites exhibit one peak, respectively, but raw illite was not appeared any peaks at low q value. The results from XRD indicate that DBD plasma treatment causes the generation of specific active sites within illite structure and it derives the formation of pores in accordance with CTMA+ induction. In order to investigate the presence of the functional groups generated after DBD plasma treatment, FTIR analyses were carred out in the range 400-4000 cm"1. The band at 3752 cm"1 is due to the free silanol groups and the band at 3671 cm"1 represents the vibration of weakly interacting vicinal silanol groups. In addition, the band at 3650 cm"1 corresponds to Si-O-H stretching of

(i)

0.4

0.8

1.2

1.6

2.0

Fig. 1. Powder XRD patterns (I) of (a) Illite, (b) M-Ili(l) and (c) M-Ili(2) (inset: FTIR spectrum (II) of samples treated by DBD plasma with different time of (a) 0 min., (b) 0.5 min., and (c) 1 min.).

63

internal silanol groups and the band at 3627 cm"1 is attributed to OH vibration mode of hydrogen bonded hydroxyl groups between inter/intra illite layers. Actually, plasma-treated samples appeared to increase the band intensity of new hydroxyl groups than raw illite. This means that oxygen radicals formed from plasma treatment lead new functional hydroxyl groups in illite basal layers. The groups play an important role of the interaction between the CTMA+ as structure directing agent and the sheets of non-expandible illite to derive mesostructure materials. Representative N2 adsorption-desorption isotherm results are displayed in Table 1. The shapes of the isotherm for M-Ili series corresponded typical behavior of mesopore solids with partial micropore contribution in the lower relative Table 1. Specific surface area, mesopore and micropore volume of illite and M-Ili series.

Materials Illite M-Ili(l)

Total N2adsb (mL/g)

Micropore vol.0 (mL/g)

65

0.056

0.056

335

0.310

0.054

BET

Mesopore vol.0 (mL/g) 0.256

400 0.405 0.058 0.347 b From the linear t-plot at low P/Po. From the isotherm at low P/P0~0.55. °Total amount adsorbed minus micropore volume. a

pressure range and with mesopore volume saturation capacity of about 0.256 and 0.347 mL/g, respectively. The estimated BET surface areas are much larger than that for the parent illite. The pore volumes for M-Ili(l) and M- Ili(2) are lower than those of typically observed mesoporous solids. The results of the presented isotherms confirmed to form a novel mesostructured material by selfassembly of induced CTMA+and illite with new generated hydroxyl groups. This is consisted with the micrograph suggested by high resolution TEM in Fig. 2. The TEM image shows representative example of the material produced, all being essentially homogeneous. From upper results, authors suggest that after disintegration of the illite layers under specific pH condition and temperature, induced CTMA+ ions are bonded on the fragments surfaces of illite layers 50 nm with new hydroxyl groups as Fig. 3. And + then CTMA ions-illites are selfassembled as spherical shape to keep Fig. 2. TEM micrograph of M-Ili(2).

64

3k. Ci6TMA +

Illite

Fig. 3. Mechanisms of the mesostruct formation of illite with hydroxyl groups generated from DBD plasma treatment. thermo-dynamical stable state. This model implies that silanol groups (Si-OH) generated after DBD plasma treatment form hydrogen bondings with CTMA+ and they derive a novel porous material going with the micropores according to mesopore evolution process such as Fig. 3. 4. Conclusion This study introduces the architecture of a novel mesostructured material from illite with non-expandibility. The pores are formed from the interaction between structure directing agent, CTMA+, and new functional groups within illite sheets due to hydroxyl groups generated by oxygen radical emitted from DBD plasma. 5. Acknowledgement Financial supports of the Ministry of Science and Technology of Korea (Grant No. R01-2005-000-11039-0) and Yong Koong Illite Company are greatly acknowledged. 6. References [1] C. C. Liu and G. E. Maciel, The Fumed Silica Surface: A Study by NMR. J. Am. Chem. Soc. 118(1996)5103-5119. [2] U. Kogelschatz, B. Eliasson and W. Egli, From Ozone Generators to Flat Television Screens: History and Future Potential of Dielectric-Barrier Discharges. Pure Appl. Chem. 71 (1999) 1819-1828.

Progress in in Mesostructured Materials Recent Progress S. Qiu, Y. Tang and C. Yu (Editors) (Editors) D. Zhao, S. © 2007 2007 Elsevier Elsevier B.V. B.V. All All rights reserved. reserved.

65 65

Production of highly mesostructured SBA-15 silicas at pH around the PZC Alexandra Chaumonnot and Emmanuelle Trela IFP-Lyon, BP 3, 69390 Vernaison, France.

1. Introduction During the last few years, an increasing amount of mesostructured oxide materials with high specific surface area have been synthesized by a cooperative self-assembly mechanism between inorganic precursors and surfactant molecules or macromolecules under hydrothermal conditions [1, 2], Among them, mesostructured aluminosilicates present an obvious interest as heterogeneous catalysts and sorbents [3]. Much effort has therefore been devoted to the introduction of aluminum into silica frameworks [4]. A usual method to obtain Al-SBA-15 materials consists in adding an aluminum precursor into the silica gel prior to hydrothermal synthesis. Contrary to the preparation of SBA-15 silica, where pH is around 0, Al-SBA-15 is produced at a higher pH (just below the point of zero charge of silica, pH ~ 1.5) in order to limit the dissolution of a fraction of the aluminum precursor [5]. In this range of pH, a decrease in the level of mesostructuration is observed, even for pure SBA15 silica materials. Moreover, the presence of aluminum species reinforces this phenomenon. In preliminary works, we have found that the loss of structural organisation for pure SBA-15 silicas is due to the presence of amorphous and partially organised phases mixed with a well-organised phase. In this study, we describe and discuss the influence of the rate of hydrolysis (r = H2O mole number/Si mole number in the initial solution) of a conventional synthesis on the percentage of non-organized phases present in pure SBA-15 silicas. In fact, it is well reported in the literature that two aspects are essential to fine-tune the selfassembly and the construction of the inorganic framework: the reactivity of the inorganic precursors (hydrolysis and polymerization rate) and their interactions with the template to generate a well-defined organic-inorganic interface [2]. The rate of hydrolysis is closely related to the kinetics of polymerization. Therefore,

66

r is obviously one of the most critical experimental parameters which need to be precisely controlled in order to induce the mesostructuration process. 2. Experimental Section SBA-15 silica was synthesized according to literature procedures and used as a reference (So sample) [6]. Practically, 4 g of triblock poly(ethylene oxide)poly(propylene oxide)-poly(ethylene oxide) (EO20PO70EO20, Aldrich) were added to 150 mL of an aqueous HC1 solution at pH = 1.5 at 313 K. After stirring for 24 h, 9 mL of tetraethylorthosilicate (TEOS) were added at 313 K. The mixture was stirred for another 24 h and then heated at 373 K for 24 h under hydrothermal conditions. The reference rate of hydrolysis r was set at 217. The samples Si to S4 were obtained using similar setups with the following respective rates of hydrolysis: 54, 79, 108 and 434. The other experimental parameters were kept constant, particularly the weight ratio TEOS/ - All products were filtered, dried at 373 K and calcined at 823 K for 4 h with a heating rate of 120 K.h"1. N2 adsorption/desorption isotherms were recorded on a Micromeritics ASAP 2405 volumetric adsorption analyzer at 77 K. Samples were dried under a vacuum of 10"5 Torr for 12 h at 723 K. The specific surface area was determined by a modified BET method adapted to microporous/mesoporous solids [7]. The mesopore size distribution (Dmeso < 50 nm) and the cumulative surface area as a function of pore size were calculated by applying the BdB method to the N2 adsorption branch [8]. XRD data were collected on a PANalytical X'Pert Pro 9/20 diffractometer equipped with a copper X-ray target and an X'Celerator fast detector. Special attention was given to the sample preparation as reflexion Bragg Brentano geometry was used at a very low angular range (0.4 to 2.0°26). TEM images were obtained on a Jeol 2010 microscope. 3. Results and Discussion Fig. 1 shows the N2 adsorption/desorption isotherm and the evolution of the cumulative surface area as a function of pore size, obtained for the reference silica sample So. For P/Po > 0.6, this isotherm is characteristic of mesostructured solids with a narrow pore size distribution centered around 8 nm (type IV according to the IUPAC classification). The organized porosity is also confirmed by the small angle XRD data (not shown) typical of a 2D hexagonal mesostructure. Nevertheless, another porosity in the range of small mesopores is observed, characterized by a large pore size distribution centered around 5 nm. TEM analyses also show that the mesostructuration process was not complete. This leads to the production of an amorphous or partially organized phase in the reference sample, yielding this second porosity.

67

500

400

350

C u m u l a t i v e S m 2 .g -1

3

Volume adsorbed cm .g

-1

* 400

300

200

S0 -o-SO

300

250

200

150

100

50

100 0

- • - SS3 3

2

4

6

8

10

12

14

Pore size nm

0 0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1

P/Po

Fig. 1 N2 adsorption/desorption isotherms at 77 K and cumulative surface area as a function of pore size (inset) calculated for the adsorption branch (BdB method) for So et S3 samples.

By varying the hydrolysis rate between 54 to 434, we have shown that only a narrow window of r values leads to the mesostructuration process. In fact all products, except for S3 sample, are characterized by an amorphous or a partially organized phase (presence of some uniform porosity with an absence of organization) (Table 1). Table 1 Properties of the So to S4 samples. Sample

r

Structure

SO

217

A/PO/O mixture

460

242

218

5,0 - 7,9

SI

54

A/PO

517

339

178

5,8

S2

79

A/PO

494

314

180

5,5

S3

108

0

577

380

197

7,3

S4

434

A

495

113

382

5,4

S B ET

m2

/g

SBdB m /g

SBET " SedB m

/g

§ (nm)

A: amorphous; PO: partially organized; O: organized.

High rates of hydrolysis lead to an entirely amorphous solid (S4 sample), which is presumably due to a lack of interaction between the silica oligomers generated and the triblock copolymer macromolecules. The medium being more diluted than in the reference sample, we may assume that it induces the formation of smaller silica oligomers with probably non-hydrolyzed OEt groups at the surface. These species might not be able to undergo enough of the weak interactions that are necessary to activate the mesostructuration process. Reversely, excessively low values of r lead to pseudo-organized materials with a high percentage of amorphous or partially organized phases (Si and S2 samples). This could be explained by an excessive rate of polymerization of the inorganic precursors which prevents either the creation of an interface with the

68

organic micelles or the formation of these micelles. Finally, only values of r around 100 lead to a highly mesostructured silica (S3 sample, Fig. 1). 4. Conclusion We have shown that, in the case of SBA-15 silicas, the percentage of amorphous and partially organized phases, mixed with a highly mesostructured 2D hexagonal phase, clearly depends on the concentration of the precursors. In fact, a complete mesostructuration process can only be obtained for values of the rate of hydrolysis around 100. These new experimental data should pave the way towards the controlled synthesis of well-ordered Al-SBA-15. 5. References [1] J. S. Beck, J. C. Vartuli, W. J. Roth, M. E. Leonowicz, C. T. Kresge, K. D. Kresge, K. D. Schmitt, C. T.-W. Chu, D. H. Olson, E. W. Sheppard, S. B. McCullen, J. B. Higgins and J. L. Schlenker, J. Am. Chem. Soc, 114 (1992) 10834. [2] G. J. de A. A. Soler-Illia, C. Sanchez, B. Lebeau and J. Patarin, Chem. Rev., 102 (2002) 4093. [3] A. Corma, Chem. Rev., 97(1997)2373. [4] Luan, M.Hartmann, D. Zhao, W. Zhou and L. Kevan, Chem. Mater., 11 (1999) 1621. [5] S. Sumiya, Y. Oumi, T. Uozumi and T. Sano, J. Mater. Chem., 11 (2001) 1111. [6] Y.-H.Yue, A. Gedeon, J. L. Bonardet, J. B. d'Espinose and J. Fraissard, Stud. Surf. Sci. Catal., 130(2000)3035. [7] D. Zhao, J. Feng, Q. Huo, N. Melosh, G. H. Fredrickson, B. F. Chmelka and G. D. Stucky, Science, 279 (1998) 548. [8] P. Schneider, Applied Catalysis A:General, 129 (1995) 157. [9] A. J. Lecloux, J. Bronckart, F. Noville and J.-P. Pirard, Stud. Surf. Sci. Catal., 39 (1988) 233.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

69 69

Three-dimensional large pore cubic niobosilicates: direct synthesis and characterization IzabelaNowak*aand Mietek Jaroniecb "Faculty of Chemistry, A. Mickiewicz University, Grunwaldzka 6, PL-60-780 Poznan, Poland b Department of Chemistry, Kent State University, Kent, OH-44240 USA 1. Introduction

Since discovery of surfactant-templated silicas the pore range of structurally ordered materials has been extended from micropores (zeolites) to mesopores (2-50 nm). Ordered mesoporous silicas are amorphous frameworks of welldefined porous structures that impart strict shape-selective properties utilized to great advantage in separations and catalysis. For many applications three dimensional molecular sieves are desired because they provide an accessible pore volume to minimize (reactant, product) diffusion constraints. To take a full advantage of these mesostructures in catalysis, one should be able to incorporate transition metal species of desired catalytic activity and to control the sizes of cages and cage entrances. The polymeric templates provide great opportunities in the pore size and pore structure engineering [1], thus three kinds of triblock copolymers that generate cubic cage-like structures: SBA-1 (Pm3n), SBA-16 (Im3m), and FDU-1 (Fm3m) were chosen for this study. A comparative study of these mesostructures containing niobium species is presented. 2. Experimental Section NbSBA-1, NbSBA-16, and NbFDU-1 materials were prepared using tetraethyl orthosilicate (TEOS) from Aldrich and ammonium tris(oxalate) complex of niobium(V) (CBMM, Brazil) as silicon and niobium sources, respectively. The Si/Nb atomic ratio was kept 64. Three different block copolymers, i.e., Pluronics P85 (EO)26(PO)39(EO)26 and F127 (EO),06(PO)7o(EO)io6 from BASF and B50-6600 (EO)39(BO)47(EO)39 from Dow Chemicals,

70

were used for the synthesis of NbSBA-1, NbSBA-16, and NbFDU-1, respectively, in order to investigate the influence of the surfactant geometry on the mesostructure. The synthesis gel was subjected to a hydrothermal treatment by transferring it into polypropylene bottles and heating at 373 K for 48 h without stirring. The product was then filtered out, washed, dried and calcined at 813 K. The synthesis of NbFDU-1 was previously reported in [2], while the NbSBAland NbSBA-16 samples were prepared by using recipes provided in [3]. The structure was confirmed by X-ray diffraction (XRD), transmission and scanning electron microscopy (SEM and TEM), and nitrogen adsorption at 77 K. In addition, the incorporation of niobium species was investigated by UV-Vis Diffuse Reflectance (UV-Vis-DR) and Infrared (FTIR) spectroscopies. 3. Results and Discussion Textural/structural properties. The powder Xray diffraction patterns for the samples prepared using J2500 s different triblock copolymers showed characteristic n low angle diffraction peaks typical for SBA-1, SBA16, and FDU-1 structures. The well-resolved diffraction peaks of NbFDU-1 were assigned to cubic Fm3m symmetry group [2]. The XRD patterns for calcined NbSBA-16 shows a strong 110 peak at 20 = Nb-SBA-1 -0.8° with small shoulders, which could be arise from 200 (20 = 1.08°) and 220 (20 = 1.69°) reflections according to the Im3m symmetry group (Fig. 1). Also, quite intense reflections were observed at the low angle range of 2G = 0.5-1.5° for NbSBA-1, which Nb-SBA-ie" could be indexed as 110, 200, and 210 according to the Pm3n symmetry. According to these assignments, 0.8 1.6 1.2 0 the unit cell parameters for the NbSBA-1, NbSBA-16, 20, and FDU-1 mesostructures are equal to 14.5, 16.0, Fig. 1. XRD data for cubic and 23.5 nm, respectively. materials. The BET surface area for all niobium-containing materials studied was similar, over 900 m2g"1. The total pore volume of Nb-containing materials was between 0.6 and 1.0 cm3 g"1 with the highest value for NbFDU-1. The existence of micropores is obvious from Table 1 and it was also the biggest for FDU-1 structure. Fig. 2 shows a comparison of nitrogen adsorption isotherms for a series of cubic samples. The nitrogen adsorption-desorption isotherms obtained for calcined mesoporous niobio-silicates are type IV (Fig. 2) with visible capillary condensation step. As can be seen from Table 1 the mesopore widths are -6.9, 11.4, and 15.3 nm for NbSBA-1, NbSBA-16, and NbFDU-1, respectively. The minimal wall thickness for all samples studied, calculated according to relations provided in [4], was between 1 and 3 nm. The shape and closure of 200

O

Int ensity, a.u.

>110<^

-,nn

J

•

-

'200

\l\

0 tN CV]

71

hysteresis loops for those samples indicate a significant non-uniformity of cage entrance sizes and the possibility of existence of narrow constrictions. Table 1. The structural/textural data for cage-like niobiosilicate materials Pore Min. wall width, thickness, nm Total Meso Micro nm NbSBA-1 14.5 6.9 1.2 143 Pm3n 0.73 0.47 0.12 NbSBA-16 120 Im3m 16.0 11.4 2.5 0.67 0.41 0.21 148 Fm3m NbFDU-1 23.5 15.3 1.3 1.01 0.83 0.14 * Pore width and minimal wall thickness estimated using proper formulas from ref [4]. Catalysts

Si/Nb

Symmetry

ao, nm

Surface area, m2g"' 970 970 920

Pore volume, <

A high structural ordering of NbFDU-1 was further confirmed by transmission electron microscopy (Fig. 3). The TEM image of the Nb FDU-1 recorded along the [111] direction clearly shows well ordered 3D cubic mesostructure. Thus, the assignment of the cubic space group in XRD study is supported by the TEM image. Because of small unit cell 0.2 0.4 0.6 0.8 1.0 5 10 15 20 dimensions, the resoluRelative pressure, p/p Pore diameter, nm tion of the TEM appFig. 2. Nitrogen adsorption-desorption isotherms at 77 K on aratus appeared not to be cubic materials (left) and the pore size distributions (PSD; right). 3 1 enough good to confirm The isotherm for NbFDU-1 was shifted by 100 cm STP g' . The pore widths obtained from PSDs by the KJS method [5] are the space groups of other underestimated [2]. two materials. The structure of NbSBA-1 appeared to be heterogeneous and resembled an aggregation of small porous particles, which explains the origin of textural porosity observed on the nitrogen adsorption isotherm. The NbSBA-16 framework seemed to be partially inhomogeneous. 800

100 nm Fig. 3. Transmission electron micrographs NbSBA-1 (A), NbSBA-16 (B), NbFDU-1 (C).

72

Scanning electron microscopy revealed a number of different morphological structures, going from very small (colloidal) particles, complete and unfinished spheres to rope-like (Fig. 4). The morphology of NbSBA-16 was from spherical shape to cubic rhombdodecahedral shape.

IBM

10|Jn

lBiim

Fig. 4. SEM images forNbSBA-1 (A), NbSBA-16 (B), NbFDU-1 (C).

Niobium incorporation. The EDX analyses performed for all samples show that the synthesis conditions used (low pH, the presence of Cl" anions, etc.) led to twice lower Nb contents (Si/Nb = 120-140 instead of 64). Additionally, Xray diffraction data at high angles (29 = 10-60°) do not show any peaks of niobium(V) oxide phase. The UV-Vis-DR spectra of the Nb-containing samples showed an intense band centered at ca. 225 nm together with a weak shoulder at 260-270 nm. The first band can be assigned to isolated framework niobium in tetrahedral coordination, while the shoulder at 270 nm probably corresponds to partially polymerized Nb species (five and six-coordinated) in small niobia nanodomains. Absence of peak > 300 nm for the prepared samples indicates that no bulk niobia is formed. On the basis of UV-Vis measurements it is believed that niobium was incorporated into the framework of all samples studied. 4. Summary Cage-like cubic mesoporous niobosilicates with large pores, NbSBA-1, NbSBA-16 and NbFDU-1, have been synthesized by using polymeric templates. Their ordered mesostructures were characterized by X-ray diffraction (XRD), transmission and scanning electron microscopy (TEM and SEM), and nitrogen adsorption. 5. References [1] S.A. Bagshaw, E. Prouzet and T.J. Pinnavaia, Science, 269 (1995) 1242. [2] I. Nowak and M. Jaroniec, Langmuir, 21 (2005) 755. [3] T.-W. Kim, R. Ryoo, M. Kruk, K.P. Gierszal, M. Jaroniec, S. Kamiya and O. Terasaki, J. Phys. Chem. B, 108(2004)11480. [4] P.I. Ravikovitch and A.V. Neimark, Langmuir, 18 (2002) 1550. [5] M. Kruk, M. Jaroniec and A. Sayari, Langmuir, 13 (1997) 6267.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

73 73

Synthesis under different conditions of NbMCM-48 with an epoxidation activity Izabela Nowak* and Maria Ziolek Faculty of Chemistry, Adam Mickiewicz University, Grunwaldzka 6, PL-60-780 Poznan, Poland

1. Introduction The discovery in 1992 of ordered mesoporous materials synthesized with supramolecular aggregates of amphiphiles acting as structure-directing agents resulted in an intense scientific research activity and opened up exciting prospects in the fields as diverse as catalysis. MCM-48, one member of the mesoporous materials family, contains two independent three-dimensional pore systems, which are interwoven and situated in a mirror-plane position to each other [1]. Particularly interesting materials could be solids with the threedimensional cubic mesostructure, which provides favorable mass transfer kinetics in catalytic and separation applications. However, the MCM-48 mesoporous silicas remain largely undeveloped due to the difficulties encountered for their synthesis in terms of reproducibility and synthesis yield. One of the fastest-developing areas in molecular sieve science is the synthesis of transition-metal-containing molecular sieves, which can be used as new catalysts for the selective oxidation of a wide range of hydrocarbons. NbMCM48 materials have been exploited to some extent [2]. Therefore, in this work we have synthesized the NbMCM-48 samples using different synthesis conditions. The new catalysts were tested in the liquid phase oxidation of cyclohexene. 2. Experimental Section Materials. MCM-48 materials containing Nb were prepared via three different synthesis methods. In the first one, tetraethyl orthosilicate (TEOS) as a Si source, n-hexadecyltrimethylammonium bromide (CTAB) as a surfactant, NaOH as a base, and niobium(V) oxalate (denoted later in the text as Ox) or ammonium tris(oxalate) complex of niobium(V) (Co) as a Nb precursor were utilized for the sample preparation under static hydrothermal conditions (373 K,

74

96 h) that will be later denoted as Nb(M)MCM-48(ST), where M is a kind of Nb source. A synthesis at room temperature under vigorous stirring for 2 h (denoted later as Nb(M)MCM-48(RT)) was done using CTAB dissolved in the mixture of water with ethanol and aqueous ammonia, followed by addition of Nb and Si sources. A conventional hydrothermal synthesis in autoclave, denoted as Nb(M)MCM-48(A), was completed in the following way: tetramethylammonium hydroxide was diluted with water before adding CTAB under vigorous stirring. After 15 min, Cab-O-Sil silica and a source of Nb were added and the formed gel was heated statically for 40 h at 403 K. The Si/Nb = 32 in the gel was applied in all cases. Characterization. The prepared materials were characterized to find: Si/Nb ratio by XRF, mesoporous phase identification and phase purity by XRD; morphology and textural properties by TEM and SEM; surface area, pore size distribution by nitrogen sorption, and niobium localization by H2-TPR. Cyclohexene oxidation. Reaction conditions: catalyst weight = 40 mg; reaction temperature = 318 K, reaction time = 40 h, cyclohexene/H2O2 (molar ratio) = 1, solvent: acetonitrile. Products were analyzed by GC (CarloErba, FID). 3. Results and Discussion The possibility of isomorphous substitution of silicon with niobium in MCM48 mesoporous molecular sieves is dependent on the metal source and synthesis conditions. With the conventional hydrothermal synthesis route in autoclave 76 and 80 % of the metal precursor is incorporated into the material, with static synthesis 70 and 76 %, while the amount of metal precursor introduced at room temperature is 48 and 65 % for Ox and Co niobium sources, respectively (Table 1). Commensurate to these results, the value of the unit cell constant (ao) was found to change after Nb introduction. The structural/textural properties of the prepared materials are summarized in Table 1. ro.5 The XRD patterns of most of the resultant Nbcontaining materials corresponded well to those reported for purely siliceous MCM-48. However, the (420) and (332) diffraction lines were visible only in the case of Nb(Ox)MCM-48 (ST) and Nb(Co)MCM48 (ST) samples (Fig. 1). For materials obtained with autoclave, we have found that the predominant product was the hexagonal phase besides the cubic one and thus the materials can be considered as Nb(Ox)MCM-48-ST NbMCM-48/-41 composites. The lower regularity of 2 4 2(=) ° 8 1 ° * n e c u ^ ' c structure in these cases was accompanied Fig. 1. XRD patterns of MCM- b y t h e appearance of the additional diffraction lines 48 (ST) samples (110 a "d 200), characteristic of the hexagonal structure. This finding was further confirmed by TEM microscopy. Framework shrinkage during calcination is the lowest in the

75

case of A-type synthesis suggesting the higher condensation and/or sintering during the calcination (Table 1). The TEM images of the calcined samples synthesized with (ST) and (RT) methods showed a uniform cubic structure. Table 1. The structural/textural data for MCM-48 type materials ao shrinkage, % MCM-48(A) 11.27(10.82) 4.0 Nb(Ox)MCM-48(A) 42 10.82(10.40) 3.8 Nb(Co)MCM-48(A) 40 10.82(10.30) . MCM-48(ST) 10.21 (8.73) 14.5 Nb(Ox)MCM-48(ST) 46 11.04(9.33) 15.5 Nb(Co)MCM-48(ST) 42 10.82(9.17) 15.3 MCM-48(RT) 9.02 (8.07) 10.4 Nb(Ox)MCM-48(RT) 67 8.73 (8.01) 8.1 Nb(Co)MCM-48(RT) 49 8.59 (7.78) 9.4 * - after calcination in brackets; ** t = (ao/3.092)-(D/2) Catalysts

Si/Nb

a0, nm

Surface Pore Wall area, volume, width thickness m2 g"' cm3 g'1 (D), nm (t)**, nm 1020 0.95 4.05 1.47 320 0.40 3.96 1.38 690 0.70 3.94 1.36 1070 0.79 3.50 1.07 590 0.48 3.07 1.48 810 0.72 3.35 1.29 1340 0.86 3.43 0.90 1200 0.85 3.35 0.92 1240 0.82 3.07 0.98

All of the N2 isotherms were of type IV indicating the presence of mesoporosity. Some of the isotherms (NbMCM-48 (A)) exhibited a substantial hysteresis loop between the relative pressure p/p0 = 0.4 and 1.0 which may be due to the interparticle capillary condensation. NbMCM-48 materials with mesopore width between 3.0 and 4.0 are obtained (Table 1), while additional macropores for the NbMCM-48 (A) samples were also present. The incorporation of Nb causes a reduction in BET surface area (Table 1). The prepared materials have specific surface areas from 300 ((A) samples) to 1200 m2g"' ((RT) samples). The wall thickness decreases after the Nb introduction in the case of NbMCM-48 (A) samples (NbMCM-48/-41 composite), while increases for other synthesis methods (Table 1). Scanning electron microscopy images in Fig. 2 show nonagglomerated particles for all materials prepared from ammonium tris(oxalate) complex of Nb. Cubic-to-spherical-shaped particles were observed for Nb(Co)MCM-48 (A) (i.e. Nb(Co)MCM-48/-41 composite). The particle sizes of these materials are quite small (<60 nm). Such feature has been in great demand as this is an essential criterion for an efficient catalyst. The particle size was maintained for samples prepared with niobium(V) oxalate as a niobium source; however, the surface of the particles was not uniform.

3pm

3pm

3pm

Fig. 2. SEM micrographs for Nb(Co)MCM-48 prepared via method: A - (A), B - (ST), C - (RT)

Mesoporous molecular sieves containing Nb exhibit both kinds of Nb species: extra framework Nb revealed by a LT-very broad signal in H2-TPR profile and

76

a framework Nb reduced at HT. The shape of the TPR profile depends on the synthesis conditions. For NbMCM-48/-41 composites (A-type samples), the contribution of extra framework Nb species was smaller with the favor for the framework one. The domination of the framework over extra framework was also apparent for samples synthesized with Co as the Nb source. The influence of synthesis conditions Table 2. The cyclohexene oxidation data on cyclohexene conversion and Selectivity, % 6 Catalysts '„ 1 conv.,"/ <> epoxide diol selectivity to the affluent oxidation products are shown in Table 2. The MCM-48(A) 12 4 77 conversion and the epoxide selectivity Nb(Ox)MCM-48(A) 89 86 10 reach maximum levels for Ox and Co Nb(Co)MCM-48(A) 81 52 11 MCM-48(ST) niobium sources, when conventional Nb(Ox)MCM-48(ST) 76 45 23 synthesis method (A) was applied. It Nb(Co)MCM-48(ST) 77 33 22 seems that the special structure MCM-48(RT) . hybrid of hexagonal and cubic ones Nb(Ox)MCM-48(RT) 22 7 70 provided the optimum geometry for Nb(Co)MCM-48(RT) 60 6 37 transport and reaction. It is worthy to add, that NbMCM-41 and NbMCM-48 alone are less active ([3] and this work]). The static conditions applied for the synthesis of MCM-48 materials give better conversion than the room temperature synthesis (Table 2). It seems that the presence of a tetrahedral framework Nb in a special coordination and a small particle size are prerequisites for efficient liquid phase oxidation catalysts. 4. Summary NbMCM-48 materials were prepared by using three different synthesis methods. The excellent performance of the NbMCM-48/-41 composite catalysts in the epoxidation of cyclohexene resulted from its structural properties, i.e., hybrid of hexagonal and cubic structures. 5. Acknowledgement The Polish Ministry of Science and Higher Education (grants no. 3T09A 100 26 and 2006-2009) and CBMM (Brazil) are acknowledged for the financial support and for supplying Nb sources, respectively. 6. References [1] H. Kosslick, G. Lischke, H. Landmesser, B. Parlitz, W. Storek and R. Fricke, J. Catal., 176 (1998)102. [2] K. Schumacher, M. Grun and K.K. Unger, Micropor. Mesopor. Mater., 27 (1999), 201. [3] Nowak and M. Ziolek, Micropor. Mesopor. Mater., 78 (2005) 281.

Progress in in Mesostructured Materials Recent Progress S. Qiu, Y. Tang and C. Yu (Editors) (Editors) D. Zhao, S. © 2007 2007 Elsevier Elsevier B.V. B.V. All All rights rights reserved. reserved.

77 77

Composite hydroxyapatite -Na/MCM-41 for the fluoride retention in contaminated water Oscar A. Anunziata*, Andrea R. Beltramone and Jorgelina Cussa "Grupo de Fisicoquimica de Nuevos Materiales, CITeQ - UTN-FRC, Maestro Lopez esq. Cruz Roja Argentina, Ciudad Universitaria, Cordoba, Argentina. Introduction

A. Laghzizily et al. [1] correlated the fluorination of hydroxyapatite (HaP) results with its physicochemical properties. We introduce the idea of composite, in order to anchor nanocrystals of HaP (guest) in host of the MCM-41 materials developed by us [2]. The pore size of the materials used as support is 1-30 nm. We expect the formation of smaller nanocrystals of HaP than the cavities in the host. We also consider the possibility of growth of the clusters of HaP in the external surface. The composite was characterized by XRD, FTIR, BET and TEM. Fluoride retention capacity increased in one order of magnitude respect to pure HaP, due the formation of HaP nanocrystals in MCM-41 (M41). 1. Experimental Section 1.1. Synthesis of the mesosporous M41 (host) and the composite HaP/Host Na-MCM-41 (M41) was prepared by hydrothermal synthesis under atmospheric pressure, with special attention in the final pH of the gel. The molar gel composition treated for 36-56 hours at 100-120°C was: Si/Al= 33, TEAOH/Si=0.4, HDTMABr/Si= 0.24 and H2O/Si= 75. The obtained M41 shows higher quality than the M41 informed in a previous work [3]. For the HaP/Host, the reactants employed were: CaCl2«2H2O (a), K2HPO4 (b), and bidistilled water. Solutions of variable concentrations were used: 1-0.5M of CaCl2 and 1.8-2.29M of K2HPO4 at pH 8-9. Solution (b) is added to solution (a) in order to have the stoichiometric ratio of HaP in presence of M41. The solution was vigorously stirred for 2 h at 60°C, was filtered and dried at 100°C for 4 h. The composite was activated by heating at 500°C in N2 flow for 10 h; then was calcinated from 100 up to 500°C with a heating rate of 2°C/min for 2 h. The

78

ratio of HaP, synthesized in situ respect to the host was 50 wt%. The ratio was calculated by the difference of the HaP/M41 and M41 weight employed as host. 1.2. The Fluorine retention essay HaP (Biogel HTTP, Ca/P = 1.63; carbonates 0.23-0.25 wt%) with 45 m2/g and 2x4 um and NaF (Fluka pro-analysis) were used. Demineralized and bidistilled water was used. F" ion solutions were prepared at 25°C, using a Teflon device with magnetic stirring, specially designed to burble N2 in order to avoid CO2 contamination. The pH of the solutions was measured with a Mettler pH meter with combined glass electrodes, calibrated with buffers of pH 4 and 7.5. The F" concentration was determined using a specific electrode for F", dynamic range between 1 to 300 ppm. In addition, F" traces were followed by FTIR. 2 g of HaP (4 gr of Hap/M41) in 100 ml of NaF solution with initial concentration of 5x10": M was used in order to determine the F" retention as a function of HaP weight. 2. Characterization ASAP 2010 was employed to determinate superficial area and pore volume. The XRD diffraction patrons were performed with a Rigaku diffractometer equipped with CuKa radiation of 0.15418 nm of wavelength. FTIR studies were performed with JASCO 5300 spectrometer. For the zone of absorption of the host lattice, 0.05 wt% in KBr wafers were prepared. For the HaP/M41 absorptions, self-supporting wafers were introduced into a thermostatized cell with CaF2 windows and warmed up to 400°C and 10"4 Torr. TEM images were recorded using a JEOL 200 CX instrument operated at 110 kV. 3. Results and Discussion Figures 1-3 show the XRD spectra of HaP, Na-M41 and HaP/M41, respectively. We identified each phase and the degree of regularity of the hexagonal structure for Na-M41, indicating a signal (hkl: 100) corresponding to 100: 2.06

Intensity, a.u.

Intensity, a.u.

Hap(Bio Rad)

110: 4.66

200: 5.3

0 0

0

10 10

20 20

30 30

40 40

50 50

60 60

70

2 Theta

Figure 1: XRD of pure HaP Bio Rad

0 11

2

33

44

55 6 6 7 7 8

2 TThheta eta

Figure 2: XRD ofNa-M41

89

9

110 0

79

Intensity, a.u.

hexagonal structure of mesoporous materials, at 29=1.99-2.08° and ao= 4.9-5.1 nm. The less intense signsand long-range order, 110 and 200, at 20 =4.66° and 5.30°, respectively, are characteristics of highly ordered hexagonal structure in pureM41. The intensity of the characteristic peaks of the mesopore structure decreased and shifted to higher angles in the composite inComposite Composite dicating that HaP crystals were loHaP/M41 HaP/M41 cated within the mesopore channels. The physico-chemical properties of these samples are listed in Table 1. M41 HaP The decrease in the pore diameter, total surface area and pore volume suggest that the HaP was essential20 60 0 10 20 30 40 50 60 10 30 so lly located inside the mesopore ch22 Theta Theta annels of M41 material. Figure 1 XRD of HaP/Na-M41 0

Table 1: Textural and structural properties of the calcined samples Sample

SBET m2/g

ao*

M-41 HaP/M41

(nm)

Total

External***

4.90 5.35

1256 710

110 ....

Pore Vol. (ml/g)

Diameter pore** (nm)

0.98 0.38

2 .79 1.53

* ao=2 d1Oo/V 3; ** D = 4V/A (according to ref. 4); ***Calculated before surfactant elimination

Figure 4 shows the FTIR data of the pure HaP and HaP/M41. HaP/M41 with HaP crystals (in the nm range), generates difficulty for the identification of the bands. In spite of this effect, the stretching bands, after 3600 cm"1 in composite, appear free due to the OH" of the HaP, which must remain intact in order that the capacity of F" retention of composite stay unaltered. HaP/MCM

Absorbance, a.u.

Absorbance, a.u.

HaP(Bio Rab) Rab) HaP(Bio

OH-

4000

3500

3000 3000

2500 2500

2000 2000

1500 1500

Wavenumber, cm-1

1000 1000

500 500

HaP MCM OH-

1600 1200 4000 3600 3600 3200 3200 2800 2800 2400 2400 2000 2000 1600 1200 800 800

4000

Wavenumber, cm-1

Figure 4: FTIR of HaP and HaP/M41

400

80 80

Fig. 5 shows TEM images of the M41 and the composite HaP/M41. The TEM study indicates that most of HaP particles were loaded inside the pore channels but that their distribution is not very homogeneous. Some HaP particles were also observed on the outer surface of the host. However, the highly ordered pore structure was still preserved during the preparation, in agree with the XRD data.

20nm

20nm Figure 5: Transmission electron micrograph of the calcined M41 and HaP/M41. Table 2: Capacity of Fluorine retention in water Conc.ofF"(xl03M) Initial 8h 16h

HaP/M41 5.0 1.8 0.15

HaP (Biorad, >2um) 5.0 3.0 1.8

HaP(20-45nm)* 5.0 2.5 1.3

* prepared ex-situ

The F" retention was one order of magnitude greater for HaP/M41 than pure HaP (Bio-Rad) and greater than for nanometric HaP, see table 2. 4. Conclusion The method used for the host inclusion (not reported in literature) seems to be adequate, since the OH- groups of HaP were not blocked. The HaP was essentially located inside the mesopore channels. Furthermore, only HaP was formed and no K oxide and/or PO4" phases were detected by XRD. In the case of HaP (ex-situ), its lower crystal size favored the F" retention compared with the commercial one. M41 acts as a support to anchor the HaP nanocrystals, without exclude the possibility of the growth of few crystals of HaP in the external surface according to TEM images. 5. References [1] [2] [3] [4]

A. Laghzizil, N.Elhrech, O. Britel and O. Bouhaouss, J. Fluorine Chem. 101 (2000) 69. O. Anunziata,A. Beltramone and J. Cussa,Applied Catalysis A.General,270 (1-2) (2004) 77. O. Anunziata, L. Pierella, E. Lede and F. Requejo, Stud. Surf. Scie. Catal. 135 (2001). F. Chen, A.Shen, X-Jun Xu, R.Xu, F. Kooli, Micropor. Mesopor. Mater., 79 (2005) 85.

Progress in in Mesostructured Materials Recent Progress S. Qiu, Y. Tang and C. Yu (Editors) (Editors) D. Zhao, S. © 2007 2007 Elsevier Elsevier B.V. B.V. All All rights rights reserved. reserved.

81 81

Direct synthesis of cerium-incorporated SBA-15 mesoporous molecular sieves Qiguang Dai, Guoping Chen, Xingyi Wang* and Guanzhong Lu Laboratory for Advanced Materials, Research Institute of Industrial Catalysis, East China University of Science and Technology, Shanghai 200237, P.FLChina

Ce-SBA-15 mesoporous molecular sieves were synthesized by the two-step synthetic method in acid media. The obtained materials were characterized by small angle X-ray diffraction (SAXRD), transmission electron microscopy (TEM), N2 adsorption-desorption full isotherm and elemental analysis. Cerium has been incorporated into the framework position and walls of silica network of SBA-15. Additionally, the high catalytic activity of Ce-SBA-15 for trichloroethylene (TCE) combustion was observed. Keywords: Direct synthesis, SBA-15, Cerium incorporated 1. Introduction In the family of mesoporous molecular sieves, SBA-15 synthesized with triblock copolymer as a surfactant under strong acidic conditions exhibits larger pore sizes and thicker pore walls, compared with M41S. As it has been known, the pure-silica molecular sieves show almost no activity for catalytic reactions, and the active sites in the molecular sieves are always from heteroatoms. The hexagonal mesoporous SBA-15 has been synthesized at pH<2, and high quality SBA-15 can be obtained only at pH
82

2. Experimental Section The cerium-incorporated SBA-15 was prepared as follows: 9.4 mL of tetraethylorthosilicate (TEOS) and a calculated amount of cerium (III) nitrate, to obtain a given Si/Ce molar ratio (10, 20 or 30), were added to 30 mL of aqueous HC1 solution (pH~0.7). This solution produced was stirred for 3-5 h at 313 K and then added to 63 mL of aqueous HC1 solution (pH=0.7) containing 4 g of P123 (Aldrich). After stirred for 24 h, this mixture gel was transferred to the Teflon container and kept at 373 K for 24 h. Then it was cooled to room temperature, adjusted to the appointed pH value, and kept in the Teflon container at 373 K for 24 h. The solid obtained was filtered off, washed by anhydrous ethanol, dried at 353 K overnight, heated finally to 823 K at a heating rate of 5 K-min"1 and then maintained for 6 h. 3. Results and Discussion 3.1. Ce-SBA-15 characterization The XRD patterns of samples with Si/Ce=10 prepared at different pH values of the matrix gel are shown in Fig.l and the results are summarized in Table 1. For the samples prepared at pH<7.5, a well resolved XRD pattern with a prominent peak (100) and two weak peaks 110 and 200 are observed at 20 = 0.8 ~ 2°, which matches well with the XRD pattern of pure-silica SBA-15 reported in the literatures [1, 4]. Their three diffraction peaks shift to lower angles with the increase of pH value of the matrix gel. The presence of cerium in the framework of SBA-15 makes the unit-cell parameters increase, probably due to that most of larger size of cerium cations, compared with Si4+, have incur-

2 3 2-Theta (Degree)

Fig. 1. XRD patterns of purely silica SBA-15 (a) and Ce-SBA-15 samples synthesized at different pH value: (b) 0.7; (c) 5.5; (d) 6.0; (e) 7.5; (f) 10.0.

1

2

3 2-Theta (Degree)

4

5

Fig. 2. XRD patterns of purely silica SiSB A-15 (a) and Ce-SBA-15 with different Si / Ce ratio : (b) 30; (c) 20; (d) 10.

83

porated into the framework position and walls of silica network of SBA-15. When the sample is prepared at pH>7.5, the intensity of its diffraction peak 100 decreases drastically and two weak peaks 110 and 200 disappear with further increasing pH value. For the sample synthesized at pH=10.0, 20 of its diffraction peak 100 is similar to that of pure-silica SBA-15, indicating that the cerium species deposit on the surface of SBA-15 and are not introduced into the framework. Table 1 Structural parameters of the XRD spectra of Si-SB A-15 and Ce-SBA-15 samples pH value of 2e(d100)/°

dloo/A

a0VA

Relative Crystajiinity"/

0.7

0.950

93

107

100

0.7

0.970

91

105

73.8

5.5

0.876

101

116

80.4

Ce-SBA-15

6.0

0.812

103

119

96.4

Ce-SBA-15

7.5

0.858

103

119

25.7

10.0

0.926

95

110

Sample

matrixgel

Si-SBA-15 Ce-SBA-15 Ce-SBA-15

c

Ce-SBA-15 1/2

2.7 c

" a o =2d I0 o/3 ; * Relative crystallinity of purely silica SBA-15 as 100%; Si/Ce (mol) =10 in matrix gel for Ce-SBA-15 samples. Table 2 Compositions and structural parameters of Ce-SBA-15 and Si-SBA-15 samples Si/Ce

Si/Ce a

SBETb

dpc

Vp

aod

in the gel

in the solid

/m 2 g"'

/A

/cm3g1

/A

Ce-SBA-15

10

35

632

74

1.34

119

Ce-SBA-15

20

63

615

77

1.37

122

Ce-SBA-15

30

75

642

76

1.36

121

Si-SBA-15

-

-

633

55

0.89

107

Sample

a

b

c

Si/Ce (mol) obtained by ICP. S B E T calculated from the adsorption b r a n c h . B J H pore diameter calculated from the desorption branch. d ao=2d l o o /3 1 / 2 .

The pH value of the matrix gel was controlled at 6.0 for preparing following Ce-SBA-15 samples with different Si/Ce ratio, of which XRD patterns are shown in Fig. 2. From Fig. 2, it can see that all samples possess purely siliceous SBA-15-like mesoporous structure. Their structural parameters obtained from the nitrogen isotherm tests were listed in Table 1. Interestedly, after cerium species were incorporated into the SBA-15 sample, no any blockage of the pore or reduction in pore diameter is observed for Ce-SBA-15 samples. On the contrary, the incorporation of cerium increases the pore diameter and pore

84

volume of SBA-15 drastically, but the surface area of SBA-15 samples has not been influenced by the incorporation of cerium. The TEM images of Ce-SBA-15 (Si/Ce=20) in Fig. 3 show well-ordered hexagonal arrays of mesopore with one-dimensional channels.

Fig. 3. TEM images of Ce-SBA-15 ( Si/Ce=20 ) in the directions of the pore axis (a) and perpendicular to the pore axis (b).

3.2. Activity tests Catalytic combustion of trichloroethylene (TCE) over Si-SBA-15 and CeSBA-15 (Si/Ce=20) samples was evaluated under condition of TCE 1000 ppm, O2 8 %, N2 balance, and GHSV 15000 h"1. It was observed that the Ce-SBA-15 sample required lower reaction temperatures than Si-SBA-15 sample to oxidize TCE. At 500 °C, the conversion of TCE reached 90 % over Ce-SBA-15 sample and 25 % over Si-SBA-15 sample, respectively. The homogeneous reaction occurred only at above 400°C. In addition, the analysis of product showed that the major oxidation products were CO2 and HC1, although Cl2 existed as a product, because there is not enough hydrogen to combine with. Neither C2CI4 nor COCI2 was detected. So, Ce-SBA-15 exhibited the highly catalytic activity and selectivity for catalytic combustion of trichloroethylene. 4. References [1] D. Zhao, Q. Huo, J. Feng, B. F. Chmelka and G. D. Stucky, J. Am. Chem. Soc, 120 (1998) 6024. [2] W. H. Zhang, J. Lu, B. Han, M. Li, J. Xiu, P. Ying and C. Li, Chem. Mater., 14 (2002) 3413. [3] S. Wu, Y. Han, Y. C. Zou, J. W. Song, L. Zhao, Y. Di, S. Z. Liu and F. S. Xiao, Chem. Mater., 16(2004)486. [4] D. Zhao, J. Feng, Huo, G. H. Fredrickson, B. F. Chmelka and G. D. Stucky, Science, 279 (1998)548.

Progress in in Mesostructured Materials Recent Progress S. Qiu, Y. Tang and C. Yu (Editors) (Editors) D. Zhao, S. © 2007 2007 Elsevier Elsevier B.V. B.V. All All rights reserved. reserved.

85 85

Direct synthesis of MgO modified HMS solid basic materials ZhengYing Wu, Xin Dong and JianHua Zhu* Key Laboratory of Mesoscopic Chemistry, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, China

1. Introduction Different from MCM-41 materials prepared by electrostatic assembly, HMS is synthesized through a neutral (SI 0 ) templating route that is based on hydrogen bonding and self-assembly between neutral primary amine surfactants (S°) and neutral inorganic precursors (1°) [l].The neutral and extensively crosslinked frameworks of HMS allows for the efficient and environmentally benign recovery of the template by solvent extraction. And also, HMS mesostructures generally possess thicker framework walls, superior thermal stability upon calcination in air, and a smaller crystallite size, which affords complementary textural mesoporosity for improved access to the framework-confined mesopores [2]. Like other mesoporous silica such as MCM-41 and SBA-15, siliceous HMS lacks active sites due to its inherent chemical composition hence it needs to be modified by other species. On the other hand, solid bases are widely used as catalysts and adsorbents especially for fine chemistry and MgO is a typical solid base but its low surface area limits its application. So, supporting basic guests in mesoporous silica could obtain functional materials with both basic catalytic sites and high surface area. MgO modified SBA-15 has already been synthesized directly from the strong acidic solution [3], however, whether this one-pot synthesis can also be used in neutral templating route to get MgO modified HMS composites is still unknown. Here, we tried this synthesis to HMS and successfully obtained MgO modified HMS basic materials.

86

2. Experimental Section Siliceous HMS was synthesized according to literature except different molar composition of ethanol and water [2]. The MgO coated HMS composites were prepared as follows: 1.02 g of dodecylamine (DDA) and a calculated amount of magnesium acetate were dissolved in 55.2 g of water and 6.11 g of ethanol, then 4.25 g of TEOS was introduced under stirring at 298 K. The molar composition of the mixture was l:0.27:X:6.5:500 TEOS:DDA:Mg(CH3COO)2:HCl:H2O, where X varied from 0.17 to 1.47 corresponding to the mass percentages of MgO varied from 10 to 50 wt%, respectively. The mixture was stirred for 18 h at 298 K and evaporated at 353 K, dried and calcined. The samples are denoted as MgO/HMS(y) where y represents MgO mass percentages in the final sample. The nitrogen adsorption and desorption isotherms at 77 K were measured in a Micromeritics ASAP 2020 system. IR spectra were recorded on Bruker 22 FTIR spectrometers. Thermo-gravimetric and differential scanning calorimetric analysis (TG-DSC) of the as-prepared samples was performed in air using a NETZSCH STA 449C apparatus. The sample was also tested by XRD, SEM and CO2-TPD methods [3]. 3. Results and Discussion Figure 1 indicates that 10, 20 and 30 wt% MgO coated HMS materials, prepared by S°I° templating route, exhibit single
87 Table 1 Textural Properties and Basicities of MgO/HMS Samples

HMS

1000

Relative Intensity (a.u.)

d

3

c b 15

30

45

60

f e d c b a

1

3

Quantity adsorbed (cm /g STP)

MgO/HMS(20) MgO/HMS(30)

22 33 4 5 22 Theta (degrees) (degrees)

6

cm3 -g 1 1.51 1.12 0.72 0.49

nm 2.6 3.3 3.4 2.8

111 591 418

MgO/HMS(10)

'V

-Dp/

800 600

5 4 3 2 1 0

a b c d

100 1000 Pore Width (Å )

400

Adsorption Desorption

a b c d

200 0 0.0

Bacisity/ meqg"1 3.49 8.02 12.19

dvxJ nm 4.11 5.02 5.39 5.59

0.2

0.4 0.6 0.8 Relative ) Relative pressure pressure (p/p (p/p) 0

Fig. 1 (left) XRD patterns and (right) N2 adsorptiondesorption isotherms (Insert: pore-size distribution) of (a) HMS, (b) MgO/HMS(10), (c) MgO/HMS(20), (d) MgO/HMS(30), (e) MgO/HMS(40) and (f) MgO/HMS(50) samples

Basic strength/ H. 22.5 22.5 22.5

Transmittance (%)

S BET / m 2 -g"' 1331

Pore volume (cm /g)

Sample

1.0 1.0

f e d c b a

1500 1500 1000 1000 500 -1 W avenum ber (cm Wavenumber (cm-1)

Fig. 2 FTIR spectra of (a) HMS, (b) MgO/HMS(10), (c) MgO/HMS(20) (d) MgO/HMS(30) (e) MgCO3 and (f) MgO samples

fill some secondary pores of HMS. Insets in Figure 1 shows that the HMS gives a primary pore of 2.6 nm and an accumulated pore of about 27 nm. However, the secondary pore was inconspicuous on the sample of MgO/HMS(10) and almost vanished when 20 and 30 wt%MgO was decorated into HMS. As mentioned above, addition of proper magnesium salts into the synthetic system will lead to better mesostructrure order. Moreover, introduction of magnesium species in HMS gives more effect apart from improving textural properties. TG-DSC analysis of the as-prepared samples was performed to detect the decomposition of DDA template for MgO/HMS samples. The exothermal peak of DDA decomposition in the as-prepared HMS shifted from 618 K to 636 K on the sample of MgO/HMS(10) and to about 705 K in the case of MgO/HMS(20) and MgO/HMS(30) samples (Figure is not shown). It is very likely that introduction of magnesium species in HMS indeed blocks the decomposition of template, like that of MgO/SBA-15 samples [5]. Nevertheless, the more MgO exceeded 20 wt % seemed have no distinctive influence in TGDSC experiments, neither pore size nor pore volume of MgO/HMS(30) was improved in comparison with MgO/HMS(20) sample, which may due to somewhat stuffing of the pore by redundant MgO. Figure 2 illustrates the IR

88

spectrum of HMS and MgO/HMS samples. Two peaks around 1460 and 1530 cm'1 emerge in MgO/HMS samples and their intensities are gradually enhanced along with the increasing of MgO content. These two peaks may be the bands of magnesium carbonate due to the contamination of basic sites by the CO2 in atmosphere. On the other hand, the Si-OH bending bands around 960 cm'1 in the spectrum of MgO/HMS was vanished, which may attribute to.

The remained basicity (%)

100

1 0 0 110% 0 % MgO/HMS MgO/HMS - A - 20% 20% MgO/HMS MgO/HMS - 30% 30% MgO/HMS MgO/HMS

90 80 70 60 50 40 30 20 0

Fig. 3 SEM images of (left) HMS and (right) MgO/HMS(20) samples

3000 6000 9000 12000 12000 15000 15000 passed (ml/g) (ml/g) Total amount of water passed

Fig.4 The remained basicity of MgO/HMS vs the amount of water passed samples

These two peaks may be the bands of magnesium carbonate due to the contamination of basic sites by the CO2 in atmosphere. On the other hand, the Si-OH bending bands around 960 cm'1 in the spectrum of MgO/HMS was vanished, which may attribute to the interaction between the highly dispersed MgO and silanol groups in the surface of HMS. The band at 802 cm"1 assigned to v s (Si-O-Si) were also decreased with the MgO content increasing, which is probably due to some Si-O-Mg bond formed instead of Si-O-Si bond. Morphology of HMS was also changed by introducing magnesium into the synthetic system. SEM images of HMS and MgO/HMS(20) showed that more fine particles were gained after addition of magnesium. It have been reported that different salts would lead to different particle size of silica [6] and adding Mg2+ in PEO could improve the surface morphology of PEO crystallinity from rough to smooth [7]. Hence, it is reasonable that the added magnesium resulted in more subtle HMS grains. The basicity of MgO/HMS composites increases when the MgO content is raised. All MgO/HMS samples possess the high strength (H.) of 22.5 as pure MgO, as measured by use of Hammett indicators, and the basicity of MgO/HMS(10), MgO/HMS(20) and MgO/HMS(30) samples is determined as 3.49, 8.02 and 12.19 mmol OH7g respectively by titration while that detected by CO2-TPD were 0.64, 0.79 and 1.11 mmol OHVg respectively. Appearance of strong basicity on the samples of MgO/HMS is the important evidence that the magnesium species coated on the mesoporous materials form basic compounds like MgO. Moreover, when about 10000 ml/g water passed over the MgO/HMS samples, some 60% of the basicity remained (Figure 4). The high water

89

resistance of MgO/HMS results from the especially low solubility of MgO in water, which will be useful for expanding the application of solid base catalysts in those catalytic processes involving water in the reactants or products [3]. 4. Conclusion MgO modified basic mesoporous HMS material has been directly synthesized from the alkyl amine template system. Textural properties and morphology could be improved when magnesium salt was added in the origin solution. Strong basic sites with high water resistance are obtained when MgO were coated on HMS by one-pot method. 5. Acknowledgement NSF of China (20273031 and 20373024) and Analysis Center of Nanjing University financially support this investigation. 6. References [1] [2] [3] [4]

P. T. Tanev and T. J. Pinnavaia, Science, 267 (1995) 865. P. T. Tanev and T. J. Pinnavaia, Chem. Mater., 8 (1996) 2068. Y. L. Wei, Y. M. Wang, J. H. Zhu and Z. Y. Wu. Adv. Mater., 15 (2003) 1943. S. Damyanova, L. Dimitrov, R. Mariscal, J. L. G. Fierro, L. Petrov and I. Sobrados, Appl. Catal. A-Gen., 256 (2003) 183. [5] Y. M. Wang, Z. Y. Wu, Y. L. Wei and J. H. Zhu, Microporous Mesoporous Mater., 84 (2005) 127. [6] J. Zurawska, A. Krysztafkiewicz and T. Jesionowski, Colloid and Surface A, 223 (2003) 201. [7] M. J. Reddy and P. P. Chu, Solid State Ionics, 149 (2002) 115.

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Recent Progress Progress in in Mesostructured Mesostructured Materials Materials Recent D. Zhao, S. S. Qiu, Qiu, Y. Y. Tang and and C. C. Yu Yu (Editors) (Editors) D. © 2007 2007 Published Published by by Elsevier Elsevier B.V. B.V. ©

91 91

Nitrided BaO-MCM-41 as a new mesoporous basic material Shaoliang Jiang, Fuxiang Zhang, Qingfeng Li and Naijia Guan* Institute of New Catalytic Materials Science, College of Chemistry, Nankai University, Tianjin 300071, China

1. Introduction Alkaline-earth metal oxides have been well known to be strong solid base catalysts. It was demonstrated that the loading of such oxides into zeolites can efficiently enhance the dispersion of active sites and obtain shape-selective catalysis, but unfortunately the basic strength became decreased for the dilution of zeolites and lead to decreased catalytic activity. So far it is still a challenge for the preparation of zeolite supported alkaline-earth metal oxide catalysts with high catalytic activity. Meerwein-Ponndorf-Verley (MPV) reaction is a typical base catalysis with highly selective to the reduction of Aldehydes or ketones leaving C=C double bonds untouched [1]. Alkaline-earth metal oxides, especially for magnesium oxide [2,3], were effective catalysts for the MPV reaction under mild conditions. In this study, one nitridation process was for the first time introduced to adjust the basic strength of BaO-MCM-41. The as-nitrided samples were systemically characterized and testified for the MPV reaction. It was demonstrated that nitridation treatment may be a promising method of adjusting basic strength. 2. Experimental Section MCM-41 was synthesized referring to the procedure reported in the literature [4]. The BaO-MCM-41 sample with Ba/Si stoichiometry of 1:8 was synthesized as follows: 1.2 g MCM-41 was impregnated into 10 ml 0.25 mol/L barium acetic solution. After 2 h stirration under reduced pressure (achieved via water aspiration) and room temperatures, the slurry was evaporated at 50°C under reduced pressure. The solid was dried at 120°C for night, then calcined at 500°C

92

for 5 h (heating rate of 2°C/min). Finally, the nitridation of as-synthesized BaOMCM-41 was carried out at 700°C with NH3 flow rate of 400 ml/min for 10 h. The detailed nitridation process can be referred to our previous work [5]. The as-obtained sample was denoted as BaO-MCM-41-N700. X-ray photoelectron spectroscopy(XPS) was analysed on a PHI 5300 ESCA (PHI inc.) using an unmonochromated Mg Ka(1253.6 eV) X-ray source and C Is peak as reference. Powder X-ray diffraction (XRD) analysis was performed using a BRUKER D8 ADVANCE diffractometer with CuKa radiation (40 KV, 30 mA) in 0.02u step size and 1 s step time. Nitrogen sorption and textural properties of the materials were determined using nitrogen in a conventional volumetric technique by a AUTO SORB-1 sorptometer. TEM images were recorded on a Philip Tecnai G2 20 S-TWIN electron microscope operated at 200 kV. Catalytic hydrogen transfer runs were conducted under refluxing conditions in a two- necked flask containing 0.015 mol of benzaldehyde, 0.3 mol of alcohol and 0.4 g freshly catalyst. A reflux condenser was used for the condensation. After 10 h reaction, a certain amount of samples were withdrawn and the supernatant after centrifugation was analyzed by GC to determine the activity. 3. Results and Discussion The N content (wt %) of BaO-MCM-41-N700 was determined by element analysis and XPS spectra as 2.86% and 3.1% respectively. Compared with pure BaO-MCM-41 sample, the decrease of binding energy of Ols from 532.97 to 532.58 eV on BaO-MCM-41-N700 shown in Fig. 1 indicates that the Lewis basicity of the surface increased after nitridation. This demonstrates that N atoms with lower electronegativity have partly substituted O atoms. Fig. 1 show the low-angle and high-angle XRD patterns, in which the mesoporous framework of MCM-41 was well preserved (Fig. la), and the formation of new crystalline phase of Ba 2 Si0 4 [6] can be demonstrated (Fig. lb). As shown in Fig. lb, the peaks at 26=26.1, 29.7, 30.6 and 30.9° represent the 121, 112, 130 and 200 plane of Ba 2 Si0 4 respectively. Different from the result of literature [6], the highest reflection peak of Ba 2 Si0 4 formed on MCM-41 in this study was observed at 112 plane instead of 121 plane, which also different from the pure Ba2Si04 sample with the strongest diffraction at 130 plane. This demonstrates that the maxtrix of MCM-41 produced a great influence on the growth orientation of Ba 2 Si0 4 . It is also found that the intensity of the characteristic XRD reflections of MCM-41 is slightly reduced after the loading of BaO (BaO-MCM-41) and more strongly for the BaO-MCM-41-N700 sample. This illustrates that the pore wall of MCM-41 was generally modified by the formed Ba 2 Si0 4 [7] and high temperature calcination. The preserved mesoporous frame- work on the BaO-MCM-41 -N700 sample

93

BaO-MCM-41-N700

BaO-MCM -41-N700 BaO-MCM-41-N700

BaO-MCM-41 BaO-MCM -41

BaO-MCM-41 MCM-41 MCM -41 1

2

3

4

5

10

20

30

40

50

2 Theta

2Theta

Fig. 1. X-ray diffraction patterns of the catalysts

can be further testified by the TEM image shown in Fig. 2, in which the hexagonally ordered mesostructure can be clearly observed. Few crystalline particles were found on the external surface of the MCM-41 framework, indicating that most barium sources were dispersed inside the mesostructure homogeneously. 0.30

Dv(d)[cc/10-10/g]

0.25 0.20

MCM-41 0.15 0.10 0.05

BaO-MCM-41-N700 BaO-MCM-41

0.00 2 8 30 3 0 32 3 2 34 3 4 3366 3388 440 0 22 24 262 628 10 PoreWidth[10Pore Width [10 m] -10

Fig. 2 TEM image of BaO-MCM-41-N700

Figure 3. BJH pore size distribution of the catalvsts

As seen in Table 1, due to the modification of Ba2Si04 and subsequent nitridation at high temperatures, the special surface area of BaO-MCM-41 and BaO-MCM-41-N700 decreased greatly, but the BJH pore size distributions shown in Fig. 4 indicates that the mesoporous framework of catalysts are well preserved. It should be mentioned that the average pore-size as well as pore volume was smaller than that of pure MCM-41 support (Table 1). This reveals that to some extent the loading of BaO into MCM-41 lead to the narrowing of

94

zeolite pore diameter, and subsequent nidridation at high temperatures caused the shrinking of pore wall. Table 1: N2 adsorption results of MCM-41 and Ba-MCM-41 catalysts SBET (mz/g)

Pore size (nm)

Pore volume (ml/g)

MCM-41

1032

3J2

L49

BaO-MCM-41

400

2.90

0.326

BaO-MCM-41-N700

232

2.77

0.233

The basic catalytic performance of BaO-MCM-41 and BaO-MCM-41-N700 was valuated and compared by MPV reaction. The experimental results show that the yield of benzyl alcohol is greatly improved from 9.6% over BaO-MCM41 to 36.8% over BaO-MCM-41-N700. This indicates that the nitridation is useful to improve the catalytic activity of BaO-MCM-41 in this reaction. 4. Conclusion To the best of our knowledge, it is the first time that nitridation at high temperatures was employed for treating and adjusting the strength of loaded basic zeolites. The mesoporous framework of zeolite on the sample of BaOMCM-41-700N was found to be well preserved but with pore size shrinked. The result of MPV probe test demonstrates that nitridation may be a promising method of obtaining potential material with both high base catalytic activity and shape- selectivity. 5. Acknowledgement We gratefully acknowledge National Natural Science Foundation of China (20233030, 20020055007) and National Basic Research Program of China (grant no. 2003 CB615 801) for the financial support in carrying out this work. 6. References [1] [2] [3] [4] [5] [6] [7]

M. A. Aramendia, V. Borau, C. Jimenez et al., J. Coll. Inter. Sci. 238(2001) 385. M. A. Aramendia, V. Borau, C. Jimenez et al., J. Mol. Catal. A: Chemical 171(2001)153. M. A. Aramendia, V. Borau, C. Jimenez et al., Appl. Catal. A: General (2003) 249:1. B.H. Wouters, T. Chen, M. Dewilde et al., Micropor. Mesopor. Mater., 44-45(2001) 453. S. Jiang, Y. Song, F. Zhang et al., Chin. J. Catal. 27(2006) 495. Q. Li, S. E. Brown, L. J. Broadbelt et al. Micropor. Mesopor. Mater. (2003) 59:105. B. Marler, U. Oberhagemann, S. Vortmann, et al. Micropor. Mesopor. Mater, 6(1996) 375.

Recent Progress Progress in in Mesostructured Mesostructured Materials Materials Recent D. Zhao, S. S. Qiu, Qiu, Y. Y. Tang and and C. C. Yu Yu (Editors) (Editors) D. © 2007 2007 Elsevier Elsevier B.V. B.V. All All rights rights reserved. reserved. ©

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Synthesis and characterization of SBA-15 type mesoporous silicate containing niobium and tin Izabela Nowak,a* Iveta Nekoksovab and Jifi Cejkab "Faculty of Chemistry, A. Mickiewicz University, Grunwaldzka 6, PL-60-780 Poznan, Poland b J. Heyrovsky Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, Dolejskova 3, CZ-182 23 Prague 8, Czech Republic

1. Introduction Pure SBA-15 showed very limited catalytic activity due to the absence of lattice defects, redox and basic properties. Hence, it has become a remarkable material introducing metals into mesoporous silicates to form the active sites and thus to improve the catalytic activity. Some of the transition metals and main group elements were incorporated into mesoporous silicate of SBA-15 type, e.g. tin, being tetrahedrally coordinated in those materials, acts as Lewis acid sites, while pentacoordinated Nb introduces the oxidative properties. Multi-component incorporation can modify the surface of mesoporous silicate more effective than mono-heteroatom incorporation and could be widely used in catalytic field. In this contribution we report on the incorporation of Nb and Sn, alone or together, into the mesoporous SBA-15 material and on the investigation of their catalytic properties in oxidation of cyclohexene with hydrogen peroxide. 2. Experimental Section Materials. Nb-SBA-15, Sn-SBA-15, Nb, Sn-SBA-15 have been synthesized using the pH adjusting method reported earlier [1]. BASF's P123 copolymer (EO20PO70EO20) was used as a structure-directing agent and tetraethyl orthosilicate as a source of silicon. In Sn-containing materials syntheses, SnCl4 was applied as a tin precoursor, while two different Nb sources were used: ammonium tris(oxalate) complex of niobium(V) or NbCl5 denoted later as Co or Cl, respectively. First, the mixture of surfactant and silica was stirred at 313 K for 4 h, and then a requisite amount of Nb and/or Sn source was added to the

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mixture, followed by additional stirring at 313 K for 20 h. The mixture was then transferred into a plastic bottle for further condensation at 373 K for 2 days. The pH value of the synthesis system was adjusted up to 7.5 by adding ammonia dropwise and the obtained mixture was hydrothermally treated again at 373 K for 2 days. The final solid was collected by filtration, washed with water, and dried at RT. The surfactant was removed by calcination at 823 K for 8 h. The obtained products are denoted as following: T(X)-SBA-15, where T stands for the kind of heteroatom used and X represents the niobium source. Characterization. The structure was confirmed by X-ray diffraction (XRD), transmission electron microscopy (TEM) and nitrogen adsorption/desorption at 77 K. The samples were further characterized by DR-UV-Vis spectroscopy for the incorporation of Nb and/or Sn in the framework and FTIR combined with pyridine adsorption for the acicity measurements. Cyclohexene oxidation. Conditions: catalyst weight = 40 mg; reaction temperature = 313 K, reaction time = 40 h, cyclohexene/H2O2 (molar ratio) = 1, solvent: acetonitrile. Reaction products were analyzed by capillary GC (CarloErba, FID). 3. Results and Discussion 3.1. The quality ofT-SBA-15 molecular sieves All synthesized T-SBA-15 samples maintained the structure and good textural properties typical for SBA-15 material. The XRD results revealed that all the materials exhibited a typical hexagonal arrangement of mesoporous structure and thus that the mesostructure remains intact after the heteroatom introduction. Also adsorption/desorption isotherms (Fig. 1), showing typical IV type shape, confirms the preservation of mesoporous structure after incorporation of Telements. All the samples showed sharp primary mesopore size distributions. The pore widths are higher by applying the pH adjustment method in comparison with the standard method [2]. The samples obtained with a pH-adjusting method do not show a characteristic of a microporous material with pores ranging between 1.5 and 2.0 nm that 0 0 were usually classified as supermicropores Relative pressure, p/p0 and were observed for the SBA-15 materials Fig. 1. N 2 ads./des. isotherms for Tprepared at pH « 1. For all T-SBA-15, the SBA-15 materials: a - Sn; b large mesopores are surrounded by a micrNb(Cl); c - Nb(Cl)Sn; d - Nb(Co); e oporous corona, however, the contribu-tion of - Nb(Co)Sn. micropore volumes, calculated by alfa plot

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analysis was very low (Table 1). The T-SBA-15 materials are found to have high BET surface area (~ 400 m2g"1), large mesopores and pore volume (Table 1). The increase in the primary mesopore size might be caused by the fact that Sn and/or Nb species are incorporated into the silicate framework and substituted with Si, resulting in the expansion of the unit cell. 3.2. The effect ofNb sources on the hexagonal arrangement Low-pressure adsorption curves are very similar for all T-SBA-15 materials (Fig. 1). The main difference in the adsorption/desorption isotherms appeared in the high p/p0 range. The highest loop was found for samples prepared from ammonium tris(oxalate) complex of niobium that is associated with the highest surface area, pore volume and pore diameter (Table 1). The pH ~ 7.5 avoids the formation of interparticle porosity. The assignment of the hexagonal space group in XRD study was supported by the TEM technique (not shown here). Table 1. The structural/textural and catalytic data for T-SBA-15 materials Si/Nb Surface Pore vol. cm3 g"1 Pore Acid site cone, C 6 H, 0 Epoxide and/or area, width, mmo g 1 conv,. sel., b Si/Sna mV Total Meso Micro nm LAS" BAS % % Sn-SBA-15 34 (32) 390 1.13 1.10 0.03 13.2 0.11 0.00 5 31 74 Nb(Co)-SBA-15 35 (32) 0.11 380 1.16 1.12 0.03 14.1 0.01 43 Nb(Co)-SBA-15 c 34 (32) 820 d 1.13 0.59 0.13 8.8 49 48 Nb(Cl)-SBA-15 33 (32) 70 340 1.02 0.96 0.03 13.3 0.98 2.65 36 Nb(Cl)-SBA-15 c 18(32) 67 71 770 e 0.89 0.21 0.11 10.4 Nb(Co)Sn-SBA-15 64,65 0.12 0.01 32 420 1.26 1.15 0.04 15.2 18 (64, 64) Nb(Cl)Sn-SBA-15 58,60 280 0.95 0.83 0.04 13.3 0.08 0.02 23 33 (64, 64) a in the synthesis gel in brackets; MVom FTIR after pyridine ads data: LAS - Lewis acid site (1446 cm"1), BAS - Broensted acid site (1550 cm"') 'without pH adjustment [3]; dconsiderable macroporosity;d considerable macroporosity; external surface area -550 m2 g"1

Catalysts

3.3. The location of heteroatom After the identification of mesophase, the next step was to determine the environment {i.e.coordination) of Sn and/or Nb in the silica matrix. The introduced heteroatoms were incorporated into the framework of SBA-15. An adsorption band was observed at 214 nm in UV-Vis spectra (not shown here) of Sn-containing materials that may be assigned to Sn4+ in tetrahedral coordination, while a band at 221 nm to isolated framework niobium species. The lack of a broad absorption in the region above 300 nm indicates the absence of oxide phases.

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3.4. Catalytic activity ofT-SBA-15 molecular sieves The results are shown in Table 1, which Nb(Co)-SBA-15 Nb(CI)-SBA-15 40gives, for each catalyst, the conversion of Nb(Co)Sn-SBA-15 Nb(CI)Sn-SBA-15 cyclohexene and the selectivity to the desired Sn-SBA-15 product - cyclohexene epoxide. Mesoporous tin and/or niobosilicate samples were used for the liquid phase oxidation of cyclohexene using dilute H2O2 (35% aqueous) oxidant under mild conditions. The prepared materials exhibited a high catalytic activity in this reaction (Table 1 and Fig. 2). The Nb-based samples are the best catalysts for the epoxidation reaction. Cyclohexene conversion reached almost 45% in 40 h. 600 1200 1800 2400 Nb-SBA-15 catalysts are much more selective Time, min to epoxide than Sn-SBA-15. The large amounts of allylic oxidation products were detected in Fig. 2. Catalytic performances of the reaction mixture, when SnCl4 was used as a the modified SBA-15 for cyclohexene oxidation at 318 K. source of a heteroatom. The addition of niobium into the Sn-containing mesoporous molecular sieves improved both the conversion and selectivity to epoxide. Based on the FTIR spectra of adsorbed pyridine (not shown here) it can be concluded that the acid strength of Sn and Nb Lewis acid sites is rather different and thus could significantly influence the activation of cyclohexene and probably is responsible for the consequtive oxidation of epoxide to diols. There is no straightforward relationship between the number of acid sites (Table 1) and catalytic activity. 4. Conclusion A series of tin and/or niobium containing mesoporous silica, Nb-SBA-15, SnSBA-15, Nb, Sn-SBA-15, has been successfully synthesized by pH adjusting method. The tin,niobosilicate SBA-15 materials were found to have high BET surface area (~ 400 m2 g"1), large mesopores (>12 nm) and pore volume (>1 cm3 g'1). The presented results point at the important role of a niobium source used in the synthesis of mesoporous T-SBA-15 and its influence on the structure of the prepared materal. The catalyst with the uniform pore size distribution was obtained from ammonium tris(oxalate)complex of niobium. 5. Acknowledgement BASF and CBMM are acknowledged for donating PI23 surfactant and source of Nb used in this study, respectively. Izabela Nowak thanks the The Polish Ministry of Science and Higher Education (grant 2006-09), while Jiff

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Cejka - the Grant Agency of the Academy of Sciences of the Czech Republic (1ET400400413). 6. References [1] S. Wu, Y. Han, Y.-C. Zou, J.-W. Song, L. Zhao, Y. Di, S.-Z. Liu and F.-S. Xiao, Chem. Mater., 16 (2004) 486. [2] D. Zhao, J. Feng, Q. Huo, N. Melosh, G.H. Fredrickson, B.F. Chmelka and G.D. Stucky, Science, 279(1998)548. [3] 1. Nowak, Stud. Surf. Sci. Catal., 154 (2005) 2936.

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Progress in in Mesostructured Materials Recent Progress S. Qiu, Y. Tang and C. Yu (Editors) (Editors) D. Zhao, S. © 2007 2007 Elsevier Elsevier B.V. B.V. All All rights rights reserved. reserved.

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Effect of concentration of nitric acid on transition of mesoporous silica structure Shuhua Hana*, Wanguo Houa, Xirong Huanga, Liqiang Zhenga and Youshao Wangb "Key Lab of Colloid and Interface Chemistry (Shandong University) Ministry of Education, Shandong University, Jinan, 250100, P. R. China. South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, P. R. China

1. Introduction In the mesoporous materials of M41S [1], there exist hexagonal, cubic, and lamellar mesostructure. Huo et al. [2] applied an effective surfactant packing parameter (g value) to predict mesoporous structure. Several measures, such as, changes of hydrothermal conditions [3], addition of auxiliary organic molecules [4] and inorganic salts [5], etc., were taken to regulate phase transition of mesoporous silica during the synthesis. Although mesoporous silica has been synthesized in the wormlike micelles [6], few reports focused on the phase transition of mesoporous silica accompanied by the change of pore shape under mild conditions, especially, induced just by adjustment of the concentration of counterions in the wormlike micelles. 2. Experimental Section Preparation of mesoporous silica was based on the following two steps: 1) Mesoporous silica was synthesized at a constant NO3" concentration (CN03") of 0.025 mol dm"3 but varied concentrations of H+ (CH+). A mixture of CTAB (1.012 g) and different amounts of HNO3, sodium nitrate and sulfuric acid were dissolved in water, resulting in a lOOmL mixed solution. 2) Mesoporous silica was synthesized at a constant CH+ of 0.025 mol dm"3 but different CN03". A mixture of CTAB (1.012 g) and different amounts of HNO3 and sodium nitrate were dissolved in water, resulting in a 100 mL mixed solution.

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After sonication of the above mentioned mixed solution, a clear solution was obtained. To this solution was added 3.48 mL of tetraethyl silicate. The mixture was sonicated for 45 s, and then stirred at 600 rpm for 24 h at constant temperature of 25°C. The resulting solid was recovered by filtration, then washed with distilled water and ethanol, and finally dried at room temperature. The surfactant was removed by calcinations at 540°C for 6 h. Powder small angle x-ray diffraction data were obtained on a D/max-rB model with a Cu target at 40 kV and 100 mA, and scanning speed 0.2 deg min"1. Transmission electron microscope (TEM) image was recorded using a JEOL JEM-200CX electron microscope, operating at 200 kV. Nitrogen adsorptiondesorption measurement was carried out on a Omnisorp 100 CX gas adsorption analyzer from Coulter Co. Every sample was degassed at 350°C for 4 h under a pressure of 10"5 Pa or below. 3. Results and Discussion With the increase of CH+, three diffraction peaks, indexed as 100, 110 and 200, appeared in the calcinated samples (Figure 1). These peaks were attributed to two dimensional hexagonal lattice symmetry (space group 2D-p6mm). The change of CH+ didn't have any influence on the dm values, suggesting only a ' single hexagonal structure in resulting samples. Transmission electron microscopy (b)-' (TEM) image (Figure 1 inset) show2 3 50 nm ed that there existed many wormhole 29/deg. channels in mesostructure silica. These results indicated that mesostrucFigure 1. Effect of CH+ on XRD patterns of ture silica templated by worm-like mesoporous silica, from top to down: 0.005; micelles was different from that of 0.015; 0.040 mol dm"3. Inset: TEM of the MCM-41, but very similar to that of calcinated mesoporous silica. (a).The CH+ and MSU-1 [7]. CN03" were 0.020 and 0.025 mol dm"3, respectively, (b). The CH+ and CNo3~ were With the increase of CNo3', only 0.040 and 0.025 mol dm"3, respectively. one diffraction peak occurred in these XRD patterns of as-synthesis and calcinated samples at CH+ of 0.025 mol dm"3 (see Figure 2). Compared with the result in Figure 1, the position of the diffraction peak (26) in Figure 2 (a) shifted to larger angles (from 2.200 to 2.810) and the d value became smaller (from 4.01 to 3.14 nm), indicating that the transition of pore structure took place, i.e. from two-dimensional hexagonal to lamellar mesostructure. After calcina-

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tions (see Figure 2(b)), the intensity of diffraction peak (I) decreased with the increase of CNO3". At CNO3" of 0.05 mol dm"3, I was minimum. CTA+ molecules existed in the interlayers of lamellar mesostructure and they stabilized the lamellar mesostructure; at the calcinations temperature of 550°C, however, CTA+ molecules were decomposed completely, and the lamellar mesostructure destroyed, resulting in a decrease in I. Figure 3 (a) showed a lamellar mesotructure in the as-synthesis sample. At a higher level of CNo3 (0.05 mol dm"3), the slit-like pore was observed, and the silica walls were found to be parallel to each other (Figure 3 (b)). These results further indicated that there existed a lamellar structure in the resulting samples. Type IV adsorption isotherm and an H2 hysteresis loop [8] at a CN03" of 0.025 mol dm"3 are shown in Figure 4(a). H2 hysteresis loop was in the range of P/PQ ~ 0.4-0.7 Pa. This result indicated that the pore channels were not uniform, that is, wormhole channels existed in the resulting samples. Compared with Figure 4 (a), a clear and broad triangular hysteresis loop (H4) [8] occurred in Figure 4 (b), no step appeared on the adsorption branch and the amount of N2 adsorbed reduced. These results indicated that there were narrow slit-like pores in resulting silica. According to the IUPAC recommendations [8], H4 hysteresis loop was related to aggregates of plate-like particles giving rise to slit-shape pores. Based on the N2 adsorption-desorption curves we deduced that there existed lamellar mesostructure in the resulting silica. This inference was consistent with the results of XRD.

(a)

(b)

1

2 3 26/deg.

Figure 2. Effect of CN03" patterns of as-synthesis (a) and calcinations (b) samples, from top to down 0.0275; 0.0325; 0.0375; 0.050

Figure 3. TEM of the as-synthesis mesoporous silica, (a) CH+ and CN03" being 0.025 and 0.0275 mol dm"3; (b) CH+ and CN03" being 0.025 and 0.050 mol dm"3, respectively.

0

0.2 0.4 0.6 0.8 Relative pressure

Figure 4. N2 adsorption-desorption curves of mesoporous silica, (a) at CH + and CN03" being 0.020 mol dm 3,0.025 mol dm"3; (b) at CH+ and CN03" 0.025 mol dm"3,0.0275 mol dm"3, respectively.

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4. Conclusion In summary, using the wormlike micellar system formed by CTAB and nitric acid as template, mesoporous silica was synthesized. The wormhole channels to slit-like pores, and the two-dimension hexagonal-to-lamellar mesostructure transition appeared in mesoporous silica. The concentration of nitrate anions (> 0.0275 mol dm'3) dominated the shape of pores and the transition of mesostructure; while hydrogen ions had no effect on the transition. Due to the existence of lamellar mesostructure in resulting samples, H4 hysteresis loop occurred, no step appeared on the adsorption branch and the amount of N2 adsorbed reduced in N2 adsorption-desorption curves. 5. Acknowledgement This research is financially supported by the Key Project Foundation of the Ministry of Education of China (No: 105104), the Natural Science Foundation of China (No: 50572057, 50472069) and the Middle-aged and Youthful Excellent Scientist Encouragement Foundation of Shandong (No: 2005BS 11003). 6. References [1] C. T. Kresge, M. E. Leonowicz, W. J. Roth, J. C. Vartuli and J. S. Beck, Nature, 359(1992) 710. [2] Q. Huo, D. I.. Margolese and G. D. Stucky, Chem. Mater.8(1996) 1147. [3] S. Tolbert, H. Landry, C. C. Stucky, G. D. Chmelka, B. Norby, F. P. Hanson and J. C. A. Monnier, Chem. Mater. 13(2001) 2247. [4] K. W. Gallis, and C. C. Landry, Chem. Mater. 9 (1997) 2035. [5] S. Che, S. Lim, M. Kaneda, H. Yoshitake, O. Terasaki and T. J. Tatsumi, Am. Chem. Soc. 124(2002) 13962. [6] a) W.-J. Kim and S.-M. Yang, Langmuir, 16(2000) 4761. b) H.-P. Lin, S.-B. Liu, C.-Y. Mou and C.-Y. Tang, Chem. Commun. (1999) 583. [7] S. Bagshaw, A. E. Prouzet and T. J. Pinnavaia, Science 269 (1995) 1242. [8] K. S .W. Sing, D. H. R. Everett, A. Haul, W. L. Moscou, R. A. Pierotti, J. Rouquerol and T. Siemieniewska, Pure & Appl. Chem. 57(1985) 603.

Recent Progress Progress in in Mesostructured Mesostructured Materials Materials Recent D. Zhao, S. S. Qiu, Qiu, Y. Y. Tang and and C. C. Yu Yu (Editors) (Editors) D. © 2007 2007 Elsevier Elsevier B.V. B.V. All All rights rights reserved. reserved. ©

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Structure characterization of mesostructured Silica nanowires formed in Porous Alumina membranes Baodian Yaoa'* and Ning Wangb " Department of Chemistry, Fudan University, Handan Road 220, Shanghai, 200433, China Department of Physics, the Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China

1. Introduction Mesoporous silica [1] and anodic aluminum oxide (AAO) [2] porous membranes are two materials which have been widely employed as hosts in synthesizing ordered arrays of nanomaterials [3]. AAO membranes, characterized by one-dimensional regularly arranged, unidirectional parallel pores with uniform pore depth, are relatively easily prepared with pores of welldefined orientation over large areas. Mesoporous silica has smaller pore sizes than AAO and so may offer advantages in terms of quantum size effects and property control. Thus, the filling of mesoporous silica into AAO pores to form new hierarchical structures will make advantages of both materials as hosts in synthesizing other ordered arrays of nanomaterials. Of particular interest is the formation of silica-AAO composites in which the mesopores of the silica (such as MCM-41, SBA-15) are aligned parallel to the channels of the alumina framework. It is well-known that 2D hexagonal mesoporous silica films, say MCM-41, SBA-15 thin films, almost always contain pore channels oriented preferably along the substrates. In this regard, two possibilities of hexagonal pore alignment of mesoporous silica wires formed in a AAO membrane channel exist: one is alignment of the pores in longitudinal direction (columnar orientaion); the other is alignment of the pores in latitudinal direction (circular orientation). To date, studies on the confined assembly of silica-surfactant mesostructures within AAO membranes showed that pure columnar orientation is easily realized when ionic surfactants were used as the structure-directing agent [4-5]; in contrast, mesopores with the columnar and circular orientation usually

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coexist in a membrane when nonionic surfactants were used as templates[5-9]. And it seemed that circular orientation was favored over the columnar ones in most cases [6-8], though single columnar orientation was once reported in the literature [9]. Apart from the mesopore orientations, the confined assembly of silica-surfactant often resulted in some unique mesostructures, such as concentric lamellar structured silica wires [6b]. And such unique silica mesostuctures are easily mistaken as 2D hexagonal silica wires with circular or columnar orientation, for concentric lamellar mesostructured silica wires will exhibit parallel stripes (side view) same to that of 2D hexagonal silica wires with columnar orientation, and exhibit concentric circles (plan view) same to that of 2D hexagonal silica wires with circular orientation. In this regard, conclusions in ref. [9-10] based on just side view TEM observations remain sceptical. Here we report on the structure characterization of mesostructured Silica nanowires formed within the pores of AAO by a sol-gel method from a SBA-15 precursor based on detailed TEM side view and plan view observation. 2. Experimental Section The mesoporous silica nanowires were prepared via a simple sol-gel and rotary evaporation method by using tetraethoxysilane (TEOS) as a silica source and triblock copolymer surfactants (BASF, Pluronic PI23) as the structuredirecting agent. Commercially available porous anodic alumina membranes (Whatman, Anodisc 25, pore diameter 200 nm, thickness 60 urn) were used as the substrate. A viscous silica sol and alumina membranes in a 50 ml beaker were sealed in a container and aged at 60°C for 12 h with (sample A) and without (sample B) the presence of 20 ml water, respectively. All the gelated samples were subsequently calcined at 500°C for 6 h (see ref. [7 ] for Detailed procedures). The mesostructures of the samples were investigated by Transmission Electron Microscopy (TEM) (a JEOL 2011 microscope operating at 200 kV). Plan view TEM samples were prepared by mechanical polishing followed by Argon ion milling. For the preparation of side view TEM samples, the AAO templates were first dissolved using the 5M HCl and silica NWs were collected by filtration. 3. Results and Discussion Figure 1 shows the typical TEM images of Sample A with clear structural characteristics. As can be seen from the plan view images (Figure la and b), most of the silica NWs consist of concentric circular features with a distorted core part and some of them are nearly completely composed of concentric circles (Figure lc). At the same time, hexagonal pore arrangements can be found in every silica wires in side view mode and Figure Id is the represent-

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a

b

a

b

c

c d

d

e e

Figure 1 (Left). TEM images of sample A: (a) Low magnification, (b) and (c) High-resolution plan-view; (d) and (e) High-resolution side view. Scale bar: 1 OOnm.

Figure 2 (Right). TEM images of sample B: (a) Low magnification, (b) and (c) High-resolution planview; (d) and (e) High-resolution side view. Scale bar: 1 OOnm.

tative side view image. By combining the side view with plan view, we can conclude that silica NWs in sample A are of 2D hexagonal and exhibit a circular orientation. Figure le further confirms the circular orientation of mesopores, helix feature to some extent can also be observed. In sample B, for TEM plan view, most silica NWs have well hexagonally arranged pore cores surrounded by layered silica shells (see Figure 2a and b); for side view, parallel strips can be seen in Figure 2d and 2e. It should be noted here that images like Figure Id could not be found in sample B, which indicates that layers of Silica NWs in sample B, not like in sample A, have no further structure features, i.e. no pore exists. Thus, we can conclude that most silica NWs in sample B are composed of 2D hexagonally arranged pore cores with columnar orientation, which are wrapped by lamellar structured silica shells. In extreme cases, some silica NWs probably possess nearly 100% concentric lamellar mesostructure(part suggested by Figure 2c). The structural features of silica wires in sample B, in fact, should be regarded as the co-existence of a 2D hexagonal phase and a lamellar phase of mesoporous silica. Such two phase coexistence is often observed in the synthesis of mesoporous silica and can be easily controlled by process parameters, such as pH value, temperature [11], drying [12], and solvent evaporation [13]. The degree of polymerization of the Si precursor is believed to be one important factor in the phase evolution of mesoporous silica, which determines whether the rearrangement of surfactant can be happened during the synthesis processes [11]. In this regard, sample A may be regarded as the evolution product of sample B, whose polymerization of the Si precursor is not sufficient (for water is insufficient) and thus the rearrangement of surfactant is possible when additional water is provided in the case of sample A.

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4. Conclusion Mesoporous silica NWs formed within the pores of porous alumina membranes have been detailedly charaterized by TEM. The mesostructures of as-prepared NWs can be readily controlled by varying the aging treatment. Two kinds of Silica NWs with nearly completely different structural features were thus obtained. When aged without water, silica NWs consisted of a 2D hexagonal pore core wrapped by a lamellar shell; when aged in the presence of water, 2D hexagonal mesoporous silica NWs with circular orientation were formed. The possible evolution suggested from Sample B to A would provide insight on the rational design and synthesis of mesoporous silica with special structural features. The work here also suggests strongly that both side view and plan view are indispensable in the characterization of mesoporous silica wires using TEM. 5. Acknowledgement This work was supported by the National Natural Science Foundation of China (20503006), Dr.Yao thanks the start-up funding from Fudan University. 6. References [1] B. Z. Tian, X. Y. Liu, H. F.Yang, S. H.Xie, C. Z. Yu, B. Tu, and D. Y. Zhao, Adv. Mater., 15(2003) 1370. [2] H. Masuda, H. Yamada, M. Satoh, H. Asoh, M. Nakao and T. Tamamura, Appl. Phys. Lett.,71(1997) 2770. [3] B. D. Yao and N. Wang, J. Phys. Chem. B, 105(2001)11395. [4] Yamaguchi, F. Uejo, T. Yoda, T. Uchida, Y. Tanamura, T. Yamashita and N. Teramae, Nature Materials. 3(2004) 337. [5] Platschek, N. Petkov and T. Bein, Angew. Chem. Int. Ed., 45(2006) 1134. [6] Z. L. Yang, Z. W. Niu,; X. Y. Cao, Z. Z. Yang, Y. F. Lu, Z. B. Hu and C. C. Han, Angew. Chem. Int. Ed., 42(2003) 4201; (b) D. H. Wang, R. Wang, Z. L. Yang, J. B. He, Z. Z. Yang and Y. F. Lu, Chem. Commun., ( 2005) 166. [7] Yao, D. Fleming, M. A. Morris and S. E. Lawrence, Chem. Mater., 16(2004) 4851. [8] Y. Y. Wu, G. S. Cheng, K. Katsov, S. W. Sides, J. F. Wang, J. Tang, G. H. Fredrickson, M. Moskovits and G. D. Stucky, Nature Mater., 3(2004) 816; (b) Y. Y. Wu, T. Livneh, Y. X. Zhang, G. S. Cheng, J. F. Wang, J. Tang, M. Moskovits and G. D. Stucky, Nano Lett., 4(2004) 2337. [9] Q. Y. Lu, F. Gao, S. Komarneni and T. E. Mallouk, J. Am. Chem. Soc, 126(2004) 8650. [10] W. P. Zhu, Y. C. Han and L. J. An, Microporous. Mesoporous Mater. 84(2005) 69. [11] C. Landry, S. H. Tolbert, K. W. Gallis, A. Monnier, G. D. Stucky, F. Norby and J. C. Hanson, Chem. Mater. 13(2001) 1600. [12] M. C. Liu, H. S. Shen and S. Cheng, Chem. Commun. (2002) 2854. [13] Grosso, F. Babonneau, G. A. A. Soler-Illia, P. A. Albouy and H. Amenitsch, Chem. Commun. (2002) 748.

Progress in in Mesostructured Materials Recent Progress S. Qiu, Y. Tang and C. Yu (Editors) (Editors) D. Zhao, S. © 2007 2007 Elsevier Elsevier B.V. B.V. All All rights rights reserved. reserved.

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CRISP and eMap: software for determining 3D pore structures of ordered mesoporous materials by electron crystallography H. Zhang3, T. Yub, P. Oleynikov0, D.Y. Zhaob, S. Hovmollerc and X. D. Zouc "Materials Science and Engineering, Central South University, 410083, Changsha, P. R. China Department of Chemistry, Fudan University, Shanghai 200433, P. R. China 'Structural Chemistry, Stockholm University, SE-106 91 Stockholm, Sweden

The software CRISP and eMap are developed for determining 3D pore structures of ordered mesoporous materials by electron crystallography. Here

they are demonstrated on the mesoporous material FDU-5 with the space group Ia3d. 1. Introduction Mesoporous materials with ordered pores are of great interests due to their applications in many areas. The structure of these highly ordered mesoporous materials can hardly be determined only from X-ray powder diffraction. Electron crystallography is the most powerful tool for determining the 3D pore structures of such materials [1]. We have developed software CRISP [2,3] and eMap [4] for determining 3D atomic structures of crystalline materials from HREM images [5]. The software is now extended and can be applied to 3D reconstruction of ordered mesoporous materials^An example is given for the mesoporous material FDU-5 with space group la 3d. 2. Experimental Section Synthesis of the cubic la 3d mesoporous silica FDU-5: in a typical synthesis, 1.00 g of P123 and 0.115 g of sodium dodecyl sulfate were dissolved in a mixture of 26.0 g water and 12.0 g of 2.0 M HC1 at 30°C. 2.08 g of tetraethyl orthosilicate (TEOS) was added to this solution under vigorous stirring. The solution was kept at 30°C for 24 h, and then transferred into a Teflon autoclave

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and heated at 100°C for another 24 h. The precipitated solid was collected by filtration, washed with water, and dried in air at room temperature. The assynthesized powders were calcined in air at 550°C for 5 h to remove the template. N2 adsorption/desorption measurements were carried out at -196°C using a Micromeritics ASAP Tristar 3000 system. The samples were degassed at 180°C overnight on a vacuum line. The total pore volume of mesoporous silica was calculated to be 1.18 cm3g"', given by the single point amount adsorbed at a relative pressure of 0.99. Assuming a density of the silica wall of 2.20 gem"3, the fraction of pore volume corresponds to 72.2 %. Transmission electron microscopy was performed on a JEOL JEM-2000FX microscope operating at 200kV. Images were recorded either on films or with a KeenView CCD camera (Soft Imaging System, 1376 x 1032 pixels). The HREM image processing and 3D potential map calculation were performed using the software CRISP [2,3] and eMap [4]. 3. Results and Discussion HREM images of FDU-5 from three different zone axes of the same crystal were collected and the thinnest area were used for further image processing (Fig.l).

a

50 nm

b

50 nm

c

50 nm

Fig. 1 HREM images of FDU-5 taken along the (a) [111], (b) [001] and (c) [110] zone axes.

The images were processed using CRISP. The crystallographic image processing of the HREM image of FDU-5 taken along the [111] direction is shown in Fig. 2. First a Fourier transform was calculated from the thinnest area (512x512 pixels) of the crystal. The defocus value was determined either experimentally and/or from the Fourier transform of the image (-31000 A). The effects of the lens contrast transfer function were compensated for by CRISP (Fig. 2). Then the structure factor amplitude and phase of each reflection were extracted. Finally the symmetry of each projection was determined using CRISP (herep6m) and imposed onto the amplitudes and phases.

111 111

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DOO A Detocus (v]

p3nl p31n

i.l 26.2 2B.2 26.1

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1-31000 A

C Elliptic aproKimali ** Mathematical CTF

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Fig. 2 Crystallographic image processing of the HREM image taken along the [111] zone axis using CRISP. The effects of defocus and crystal tilt were compensated for. Table 1 Structure factors obtained by electron crystallography

hkl

112

022

004

123

024

233

224

044

134

Amplitudes

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180

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180

Reflections from different zone axes were merged into a single set of reflections. Amplitudes of common reflections were used for scaling and the phases were changed according to the common origin. The merged structure factors are listed in Table 1. The data set was expanded according to the symmetry Ia3d and a 3D electrostatic potential map was calculated using eMap. The 3D pore structures were visualized using eMap (Fig. 3). The corresponding surface area and pore volume fraction were calculated simultaneously while the threshold value was changed.

112 112

a

b

c

Fig. 3 Reconstructed 3D electrostatic potential map by electron crystallography (a) FDU-5, (b) reconstructed from the data given by Sakamoto et al. (2004) and (c) FDU-5 using only 2 strongest reflections (211) and (220). The red side is towards the pores and green towards the walls. The mesopore structures are very similar in all 3 cases. However, the micropores are shown differently.

The 3D structure of FDU-5 reconstructed from the three zone axes (Fig. 3a) is similar to that reported by Sakamoto et al. [4] (Fig. 3b). The overall pore structure is accurately determined from only the two (!) strongest reflections (Fig. 3c). For detailed pore structures such as pore shapes and wall thickness, all reflections with significant amplitudes (>1.5% of the strongest reflection (112) are included, all with accurate relative amplitudes and phases. Correct determination of the contrast transfer function is essential for calculating correct amplitudes. The slight differences related to the micropores and wall thickness shown in Figs. 3a and b give an indication of the possible errors that may be generated. In order to detemine the exact sizes and shapes of the micropores, many and very accurate structure factors (amplitudes and phases) are needed. 4. References [1] Y. Sakamoto, T. W. Kim, R. Ryoo and O. Terasaki, Angew. Chem. Int. Ed. 43 (2004) 5231. [2] S. Hovmoller, Ultramicroscopy 41 (1992) 121. [3] Calidris, Image processing of electron micrographs (2005) http://www.calidris-em.com. [4] AnaliTEX, Computational crystallography with eMap (2005) http://www.analitex.com/Index.html. [5] X. D. Zou, Z. M. Mo, S. Hovmoller, X. Z. Li and K. H. Kuo, Acta. Cryst. A59 (2003) 526.

Recent Progress in Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

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A mechanistic study on the degradation of highly ordered, non-ionic surfactant templated aluminosilicate mesoporous materials Al-CMI-1 in boiling water Alexandre Leonard and Bao-Lian Su* Laboratoire de Chimie des Materiaux Inorganiques (CMI), I.S.I.S, The University of Namur (FUNDP), 61, rue de Bruxelles, B-5000 Namur, Belgium

A detailed account of the evolution of aluminosilicate mesoporous materials in boiling water is described. After erosion of the surface silicate layer covering the inner side of the channel walls by hydrolysis, Al atoms become exposed and confer a remarkable resistance to these materials. 1. Introduction Aluminosilicate mesoporous molecular sieves have been conceived as complements to zeolites for cracking heavy gas-oil molecules. [1-3] Due to the number of potential applications in heterogeneous acid catalysis, many studies have been devoted to the synthesis, characterization and application in catalytic processes of aluminosilicate mesoporous materials. As a result, many different structures have been synthesized over recent years via several pathways such as post-synthesis grafting of Al-species, ion-exchange or direct co-condensation of both silica and alumina sources. [4-5] Different Al sources, Si/Al ratios, thermal treatment conditions, pH and surfactants have been used, which has in fine, led to a huge number of materials with similar or different properties. [6-9] Nonionic surfactants are ideal candidates for large-scale preparations because of their easy removal, their non-toxicity and biodegradability. [10] Al-CMI-1 materials, prepared via a non-ionic templating pathway, are characterized by hexagonal channel structures, pores of 3-4 nm and intra-framework Al atoms. Owing to the innumerous application possibilities, it is of crucial importance to have in hand the knowledge of the behaviour of such materials in aqueous media. Pure silica materials are commonly known to be rapidly hydrolyzed in

114 114

boiling water and we demonstrated a degradation-recovery phenomenon of textural properties with immersion time. [11] Aluminosilicate mesoporous sieves could however present a higher resistance. [12-14] The aim of this work was to investigate how Al-doped silica structures, obtained via non-ionic templating methods, behave in boiling water. The originality relies in the fact that the continuous evolution with time has been investigated, as thus far previous studies have only reported the changes after a certain period of time, e.g. 24 h. This could provide important information for the design of new highly efficient mesoporous aluminosilicate catalysts. 2. Experimental Section The aluminosilicate Al-CMI-1 materials have a hexagonal stacking of channels, specific surface areas exceeding 1100 m2/g, homogeneous pore sizes between 3 and 4 nm and the majority of Al atoms located in a tetrahedral environment, i.e. in framework positions. After complete removal of surfactant by solvent extraction, the materials were immersed in boiling water and samples were withdrawn after fixed periods of time ranging from 5 minutes to 97 h, dried and fully characterized. The techniques used for characterization included XRD (Siemens D5000), transmission electron microscopy (TEM, Philips Tecnai T10), scanning electron microscopy (SEM, Philips XL20), 27A1 NMR (Bruker 500) and nitrogen adsorption-desorption (Micromeritics Tristar 3000). 3. Results and Discussion The XRD patterns show that the structure seems to be globally destroyed immediately after immersion as all diffraction peaks disappear, suggesting a far more widespread degradation than in pure silica materials. Intact ordered zones can however still be seen by TEM, indicating that part of the framework resists the extreme conditions (Fig. 1A). The 27A1 NMR spectra show 2 peaks, one at 50 ppm for tetrahedral species, and one less intense signal at 0 ppm for octahedral Al species (extra-framework Al, EFAL) (Fig. IB).

A

J> B

1

52 ppm

-6 ppm

'-

97h 0h 0h

-200 -100 -200-10

0 100 100 200 8 27Al (ppm) (ppm) δ

Fig. 1 : TEM pictures and Al NMR spectra of Al-CMI-1 after different immersion times.

As the time immersed in boiling water is extended, the EFAL species seem to be washed out of the structure and no supplementary EFAL is created upon immersion. The morphology of the particles remains unchanged, thus the

115 115

f

>•

500

1200

A

400

0h 97h

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P o r e d i a m e t e r (n m )

600

S p e c i f i c s u r f a c e a r e a (m ² / g )

V o l u m e a d s o r b e d ( c m ³/g - S T P )

alterations occur on the interior walls of the channels, leaving the global structure unmodified. Same transformations occur in pure silica structures. [11] More striking changes occur from the textural point of view. The starting sample has a type IV isotherm with a steep adsorption branch and a homogeneous pore size distribution centred between 3 and 4 nm (Fig. 2A). Immediately after immersion, the shape of the isotherm tends towards type I, (microporous structure) with a sharp drop in specific surface area (Fig. 2B). This can also be observed for pure silica materials and could result from a partial hydrolysis at the inner surface of the channels, with hydrolyzed species obstructing the apertures. After 13-20 h, the shape of the isotherms tends towards that of mesoporous structures, the pore size increases again and the specific surface area reaches 90% of its initial value. No further changes occur for longer immersion times, except for a slight decrease in surface area, but its value still exceeds 800 m2/g after 97 h. The homogeneous mesopores reformed after 13-20 hours also remain unchanged even after 97 h (Fig. 2C). As reported for pure silica structures, the recovery of the starting textural characteristics could result from dissolution of the pore-blocking species, liberating the mesochannels. [11] The main difference of these structures compared to pure silica relies in the long-term transformation. In the present case, homogeneous pore sizes and high specific surface areas are maintained even for very long immersions, suggesting no further alteration of the framework, whereas the silica analogues completely collapse. Such higher resistance cannot be attributed to a protective AI2O3 layer as already suggested because octahedral Al species are absent in our samples (evidenced by 7A1 NMR measurements, Fig. IB). [15] Instead, we suggest that the Al atoms are not located at the surface of the channels but hidden in the thick walls separating adjacent mesopores. This is supported by the fact that we observed only weak interactions when adsorbing basic probe molecules. [16] The surface of the channels is thus constituted only of SiO2. 3.2

C

2.8 2.4 2.0

0 20 0 20 20 40 40 60 60 80 80 100 100 20 40 40 60 80 100 Immersion duration (hours)

Fig.2 : Nitrogen adsorption isotherms (A) and evolution of specific surface area (B) and pore diameter (C) as a function of immersion time in boiling water.

According to our previous study, the siloxane bonds are rapidly and irreversibly hydrolyzed by the attack of water molecules, thus explaining the rapid degradation upon immersion in boiling water. Then, when the pore-

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blocking silica species are dissolved, the Al atoms become exposed on the surface of the channels. These freshly exposed Si-O-Al groups have a protective action by repelling the hydroxide anions that catalyze the hydrolysis of the framework. [17] For that reason, further collapse of the structure, observed for pure silica mesoporous materials, is prevented and the framework remains unaffected, even for very long immersion times in boiling water. These results show that the introduction of a trivalent heteroatom can considerably improve the resistance of a mesoporous framework. 4. Conclusion The characteristic amorphous wall composition of non-ionic surfactant templated Al-CMI-1 mesoporous materials confers a remarkable stability to boiling water, even after hydrolysis and dissolution of the silica interior coating of the channels. This synthetic pathway could be an interesting alternative approach compared to the steam-stable materials made of crystalline walls separating adjacent mesopores that are obtained via quite tedious syntheses. 5. References [1] C. T. Kresge, M. E. Leonowicz, W. J. Roth, J. C. Vartuli and J. S. Beck, Nature 359 (1992)710. [2] Corma, Chem. Rev., 97(1997)2373. [3] D. T. On, D. Desplantier-Giscard, C. Danumah and S. Kaliaguine, Appl. Catal. A : Gen., 253 (2003) 545. [4] E. M. Serwicka, R. Mokaya, J. Poltowicz and W. Jones, Chem. Phys. Chem., 10 (2002) 892. [5] S. K. Jana, H. Takahashi, M. Nakamura, M. Kaneko, R. Nishida, H. Shimizu, T. Kugita and S. Namba, Appl. Catal. A : Gen., 245 (2003) 33. [6] K. M. Reddy and C. Song, Catal. Today, 31 (1996) 137. [7] Z. Luan, C. F. Cheng, W. Zhou and J. Klinowski, J. Phys. Chem. B, 99 (1995) 1018. [8] S. K. Badamali, A. Sakthivel and P. Selvam, Catal. Today, 63 (2000) 291. [9] S. Biz and M. G. White, J. Phys. Chem. B, 103 (1999) 8432. [10] J. L. Blin, A. Leonard and B. L. Su, Chem. Mater., 13 (2001) 3542. [11] Leonard, J. L. Blin and B. L. Su, Coll. Surf. A : Physicochem. Eng. Aspects, 241 (2004)87. [12] S. Kawi and S. C. Shen, Mater. Lett. 42 (2000) 108. [13] Z. H. Luan, C. F. Cheng, H. He and J. Klinowsky, J. Phys. Chem. B, 99 (1995) 10590. [14] L.Y. Chen, S. Jaenicke and G. K. Chuah, Micropor. Mater., 12 (1997) 323. [15] R. Mokaya, Chem. Phys. Chem., 3 (2002) 360. [16] Leonard, N. Moniotte and B. L. Su, (2006) submitted for publication. [17] R. Mokaya, J. Phys. Chem. B, 104 (2000) 231.

Recent Progress Progress in in Mesostructured Mesostructured Materials Materials Recent D. Zhao, S. S. Qiu, Qiu, Y. Y. Tang and and C. C. Yu Yu (Editors) (Editors) D. © 2007 2007 Elsevier Elsevier B.V. B.V. All All rights rights reserved. reserved. ©

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Tailoring the phase and texture of mesoporous silica by using tetraethylenepentamine and ethanol MingBo Yue, Xin Dong and JianHua Zhu* Key Laboratory of Mesoscopic Chemistry, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, China,-

1. Introduction Mesoporous systems with more effective interchannel accessibility are interesting candidates for many applications [1]. To improve interchannel transportation, a large amount of molecular sieves with bimodal pore system or bicontinuous network structure were synthesized [2,3]. To favor transition of a hexagonal phase to a cubic phase like MCM-48, many parameters are changed in the synthesis of MCM-41. For example, cosolvent additives such as alcohol have been reported in many variants [4,5]. However a few reports involve amine. Amine has not only the same function as aqueous ammonia to promote the hydrolysis and condensation of silica, but also more complex interaction with surfactants to modify the micelles [6]. Here we use tetraethylenepentamine (TEPA) and ethanol (EtOH) and adjust their molar ratios to transform MCM-41 into MCM-48, tailoring not only the phase but also the textural properties of obtained mesoporous material. 2. Experimental Section Mesostructure silica materials were prepared using a mixture of TEPA, EtOH and CTAB (cetyltrimethylammonium bromide) as a structure-directing mixture. The molar composition of the starting reaction mixture was varied in the range of 0.4CTAB/TEOS/xEtOH/yTEPA/314H2O, with x = 0-50, y = 0.3-4.5. In a typical preparation, 1.3 g CTAB was dissolved in 50 g distilled water and 20 g EtOH. After complete dissolution, 3.8 g TEPA was added at once. The solution was stirred at 298 K for 10 min and 1.84 g TEOS was added. This mixture was left under vigorous and constant stirring at 298 K for 24 h and then at 323 K for another 20 h. Subsequently, the mixture was aged at 373 K for 24 h under static

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conditions. The resulting solid was recovered by filtration, washed with distilled water and dried in air. The template was removed by calcination at 823 K for 6 h in airflow and the sample denoted as MS-x-y, where x and y denote the molar ratio of EtOH and TEPA respectively. X-ray powder diffraction (XRD) patterns and N2 adsorption isotherms were taken to character the phase and textural properties of obtained mesoporous silica materials [7]. 3. Results and Discussion Figure 1A depicts the XRD patterns of surfactantQ_ H 03 free mesoporous silicas (MS-x-2.3 materials with varying EtOH moral ratio from 0 to 60), demonstrateing the crucial role of the EtOH concentration played in the formation of the 0.0 0.2 0.4 0.6 0.8 2Theta (degrees) Relative Pressure (P/P ) mesophase structure. Table 1 lists the textural properties Fig. 1. Powder XRD patterns (A), N2 adsorption-desorption of obtained mesoporous isotherm and pore size distribution (B) for the mesoporous silica materials. Figure IB silica MS-x-2.3. The molar ratio of EtOH (x) was varied at: illustrates nitrogen adsorp- a, (0), b (20), c (40), d (50), e (60). The isotherms of the were offset vertically b y l b , (200 cmVg); c, (400 tion isotherms and pore size samples 3 cm /g); d, (600 cm3/g); e, (800 cm3/g) respectively. distributions (PSDs) of these silica materials. From the evolution of the diffraction patterns, mesoporous phase varied from hexagonal P6mm to cubic laid as EtOH molar ratio increasing from 0 to 50; and with EtOH molar ratio further enhanced to 60, less ordered mesophase material formed. Without EtOH, the product of MCM-41 with ordered hexagonal pattern was obtained. When EtOH was added, it caused a phase transformation from MCM-41 to MCM-48. The surfactant packing parameter g = (V)/(ao)(l) modulates the self-assembly of the organic-inorganic structure and directs the phase of acquired mesoporous material [8]. The added EtOH penetrates into the surfactant micelles and increases the effective surfactant volume, raising the value of g and causing transformation from hexagonal phase to a cubic phase (Fig. 1A). However with the EtOH further increased, the value of g increased correspondingly and the cubic phase of the micelles transformed into lamellar phase [8]. So the material obtained at 60 molar ratio of EtOH has a less ordered structure than that obtained at 50 molar ratio of EtOH as shown in Fig. 1A. At first sight, the N2 adsorption isotherms (Fig. IB) is common with a sharp inflection to all these samples existing at P/Po = 0.28. This inflection is typical of a capillary condensation process and the P/Po value corresponds to a pore o

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size of about 2.7 nm. However, sample MS-0-2.3 has an additional uncommon type-H4 hysteresis loop at P/Po between 0.5 and 1. Two kinds of hysteresis loop means bimodal pore in sample MS-0-2.3. There were two kinds of pore with narrow pore size distribution in sample Table 1. Textural properties of samples MS-x-y. sample MS-0-2.3 MS-20-2.3 MS-40-2.3 MS-50-2.3 MS-60-2.3 MS-20-0.3 MS-20-1.2 MS-20-4.5 MS-0-2.3

X

0 20 40 50 60 20 20 20 40

S B ET/(m 2 /g)

y 2.3 2.3 2.3 2.3 2.3 0.3 1.2 4.5 0.3

1133 1060

964 903 558 854 1009 1225

798

Vpore/CcmVg) 1.07

0.9 0.77

0.6 0.42 0.74 0.85 1.08 0.68

d/(nm) 2.83 3.68 2.67 3.75 2.43 2.84 2.96 2.73 2.67 2.65 3.71 2.74

Intensity (a.u.)

3

Volume Adsorbed (cm /g STP)

MS-0-2.3 (2.8 and 3.7 nm), and the pore around 3.7 nm disappeared with the further addition of EtOH. This variety of pore size and distribution is the result of surfactant micelles modified by TEPA and EtOH. As a polar molecule, EtOH or TEPA can change the micelle size and shape [6,9]. The first impact is to decrease the dielectric constant of water upon solubilization of EtOH. It is expected to result in a decrease of micelle aggregation number since the water becomes less water-like [9]. Other effects of EtOH and TEPA associate to their penetration in the micelles. This should increase the micelle size although not necessarily the aggregation number of the surfactant. So bimodal pore in sample MS-0-2.3 obtained with no addition of EtOH may be ascribed to two kinds of micelles coexistence in solution with different size. One directed the small pore (2.83 nm); another was enlarged micelle penetrated by TEPA that directed large pore (3.68 nm). Addition of EtOH promotes the solubilization of TEPA in solution so the larger pore B disappeared at EtOH molar A 1200 ratio 40 in sample MS-40d aa V _ 800 c 2.3. Besides, the addition b b of EtOH reduced micelle 400 a aggregation number and c 0 the micelle size decreased. As shown in Fig. IB and d d -400 V Table 1, the pore diameter 0.0 0.2 0.4 0.6 0.8 1.0 1.0 1 2 3 4 5 6 7 8 Relative Relative Pressure (P/P ) 2Theta (degrees) (degrees) of obtained samples decreased from 2.83 nm Fig.2. Powder XRD patterns (A), N2 adsorption(MS-0-2.3) consecutively, desorption isotherm and pore size distribution (B) for the mesoporous silica MS-20-y. The molar ratio of TEPA (y) achieving 2.67 nm (MS20-2.3) and 2.43 nm (MS- was varied at: a (0.3), b (1.2), c (2.3), d (4.5). The isotherms of the samples were offset vertically: b 40-2.3) at EtOH molar 3 3 ratio 20 and 40 respective- (200cm /g), c (400cm /g) and d (600cmVg). a b c d

5

10

Pore size / nm

0 0

120 120

3

Volume Adsorbed (cm /g STP)

Intensity (a.u.)

ly. However the further increased EtOH penetrated the micelle to enlarge the micelle size, the pore diameter increased to 2.84 nm at EtOH molar ratio 50 (MS-50-2.3). When the EtOH molar ratio increased to 60, the phase of micelles transformed from cubic into lamellar and the pore size distribution of obtained mesoporous material (MS-60-2.3) was broad. Figure 2 illustrate XRD patterns, N2 adsorption isotherm and pore size distribution for the silica materials (MS-20-y with varying TEPA moral ratio from 0.3 to 4.5). With constant molar ratio of EtOH (20), the role of TEPA on the structure of the mesoporous material was studied. Mesoporous phase varied from less ordered to well order hexagonal P6mm (Fig. 2A). At low molar ratio of TEPA, the rate of hydrolysis and condensation of TEOS was slow and less ordered mesoporus material was obtained. With the molar ratio of TEPA increased to 4.5, the sample MS-20-4.5 has not only well ordered hexagonal phase but also bimodal pore (as shown in Fig. 2B). The further increased TEPA penetrated into micelle of CTAB and formed larger size micelle which directed large size pore. Although both samples MS-0-2.3 and MS-20-4.5 have bimodal pore, but the TEPA molar ratio of in the prepare mixture is different. The TEPA molar ratio in the mixture to prepare MS-20-4.5 is 4.5, twice over MS-0-2.3. This can be ascribed to the solubilization of EtOH. When the concentration of TEPA is low in EtOH solution, 600 TEPA can be well dispersed B A a in the solution and there is 500 b only one kinds of micelle in 400 the solution. So there are a 300 one kinds of pore in the sample. However as the 200 molar ratio of EtOH b 100 increased to 40, the pore 1 2 3 4 5 6 7 8 0.0 0.2 0.4 0.6 0.8 1.0 1.0 size was controlled by Relative Pressure (P/P (P/P ) 2Theta (degrees) (degrees) TEPA concentration. Figure 3 indicts XRD Fig. 3. Powder XRD patterns (A), N adsorption-desorption patterns, N2 adsorption iso- isotherm and pore size distribution, 2for the mesostructured therm and pore size distri- silica materials MS-40-y. The molar ratio of TEPA (y) was butions of the silica mater- varied at: a (2.3) and b (0.3). ials (MS-40-y with varying TEPA moral ratio from 0.3 to 2.3). The evolution of diffraction patterns indicates that the sample has deviated the hexagonal P6mm phase (Fig. 3A). With the TEPA concentration increased from 0.3 to 2.3, the 29 values varied from 1.85 to 2.28. Both of them have IV type isotherms with the pore filling restricted to a narrow range of P/Po, which means a sharp pore distribution. However, hysteresis loop of sample MS-40-0.3 at a higher relative pressure than sample MS-40-2.3 indicates a different pore diameter. Sample MS-40-0.3 prepared with a lower concentration of TEPA has a larger pore diameter (2.74 nm) than sample MS-40-2.3 (2.43 nm). With constant EtOH concentration a b

5

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Pore size / nm

0 0

121 121

(molar ratio 40), TEPA can be well dispersed in the solution. Following the increase of TEPA concentration, the dielectric constant of water and critical micelle concentration (CMC) of surfactants (CTAB) were reduced [6], so the micelle aggregation number decreased which results in the decrease of micelle and pore size. 4. Conclusion MCM-41 like material with bimodal pore and MCM-48 were prepared from this TEOS-CTAB-TEPA-water-ethanol system, and the textural properties such as pore diameter could be tailored by modifying the TEPA and EtOH molar ratio. 5. Acknowledgement NSF of China (20273031 and 20373024) and Analysis Center of Nanjing University financially support this investigation. 6. References [1] [2] [3] [4] [5] [6] [7] [8] [9]

C. F. Cheng, Z. Luan and J. Klinowski, Langmuir, 11 (1999) 2815. H. P. Lin, S. T. Wong and C. Y. Mou, J. Phys. Chem. B., 104 (2000) 8967. R. Ryoo, S. H. Joo and J. M. Kim, J. Phys. Chem. B, 103 (1999) 7435. A. Sayari, M. Kruk and M. Jaroniec, Adv. Mater., 10 (1998) 1376. S. Q. Liu, P. Cool and O. Collart, J. Phys. Chem. B, 107 (2003) 10405. B. Y. Jiang, J. Du and S. Q. Cheng, J. Disper. Sci. Technol, 24 (2003) 755. Y. M. Wang, Z. Y. Wu, L. Y. Shi and J. H. Zhu, Adv. Mater., 17 (2005) 323. Q. Huo, D. I. Margolese and G. D. Stucky, Chem. Mater., 8 (1996) 1147. R. Zana, Advances in Colloid and Interface Science, 57 (1995) 1.

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Recent Progress Progress in in Mesostructured Mesostructured Materials Materials Recent D. Zhao, S. S. Qiu, Qiu, Y. Y. Tang and and C. C. Yu Yu (Editors) (Editors) D. © 2007 2007 Elsevier Elsevier B.V. B.V. All All rights rights reserved. reserved. ©

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Synthesis of mesoporous aluminosilicates via recrystallisation of pure silica MCM-41: A stepwise post-synthesis alumination route Robert Mokaya

School of Chemistry, University of Nottingham, University Park, Nottingham NG7 2RD, UK

Mesoporous aluminosilicates are prepared via post-synthesis alumination involving the recrystallisation of pure silica MCM-41 in which increasing proportions of the MCM-41 are aluminated depending on the amount of Al available in the recrystallisation gel. Varying the amount of Al enables a stepwise alumination of the Si-MCM-41 via the formation of an aluminosilicate layer on the inner surface of aluminated pore walls. The aluminosilicates have high surface area (800 - 100 m2/g) and pore volume (0.5 - 0.9 cm3/g), and the Al is incorporated into tetrahedral positions and generates significant acidity. 1. Introduction The synthesis of mesoporous aluminosilicates via direct mixed-gel synthesis results in materials with a uniform spatial distribution of Al [1, 2]. Increasing the amount of Al in the synthesis gel generally results in a uniform increase in the content of Al throughout the entire sample [1, 2]. Here, we describe the post-synthesis alumination of pure silica MCM-41 in which increasing proportions of the MCM-41 are aluminated depending on the amount of Al available in the synthesis gel [3]. The step-wise alumination occurs during a recrystallisation process in which calcined pure silica MCM-41 is used as 'silica source' in the presence of surfactant molecules and an Al source. During the recrystallisation process calcined pure silica MCM-41 particles act as seeds for further silica or aluminosilica deposition [4]. This allows the preparation of acidic mesoporous aluminosilica from a recrystallisation gel comprising of calcined pure silica MCM-41, templating surfactant and Al source.

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2. Experimental, Results and Discussion The recrystallisation of Si-MCM-41 was as follows; tetramethylammonium hydroxide (TMAOH) and cetyltrimethylammonium bromide (CTAB) were dissolved in distilled water by stirring at 35°C. Calcined pure silica Si-MCM-41 and the required amount of Al (as aluminium isopropoxide) were then added to the template solution under stirring for 1 h. After further stirring for 1 h the resulting gel was aged for 20 h at room temperature and then transferred to a teflon-lined autoclave and heated at 150°C for 48 h. The solid product was obtained by filtration, washed with distilled water, dried in air at room temperature and calcined in air at 550°C for 8 h. The samples were designated A1-MCM41-X, where x is the recrystallisation gel Si/Al ratio. As shown in Fig. 1, the parent Si-MCM-41 exhibits an XRD pattern typical of well ordered MCM-41 [5]. The XRD patterns of recrystallised samples prepared at gel Si/Al ratios of 80, 40 and 20 exhibit two low angle peaks; the original 100 peak (i.e., retained from Si-MCM-41) and a new peak at slightly higher 26 values (i.e., lower basal spacing). The intensity of the new peak gradually increases, and at a gel Si/Al ratio < 10, the original basal peak is absent and only the new peak is observed. We propose that the new peak is due nits)

Pure silica Si-MCM-41 f

h Pure silica Si-MCM-41

Si/Al = 80

W1000

_j

rbitr;

Si/Al = 80

A

-5-

~800

Si/Al = 40 Si/Al = 20

(0

-A

c

Si/Al = 10 Si/Al = 5

0

2

f•o

20tdegfees?

10

I OG00 to ^400

>

200 0.0

0.2

0.4

0.6

0.8

1.0

Partial pressure (P/Po)

to aluminated Al-MCM-41, which increases in proportion at higher recrystallisation gel Al contents. At a gel Si/Al ratio < 10, there is enough Al to aluminate all the Si-MCM-41 and therefore only the new peak is observed. The presence of the original peak for samples recrystallised at a Si/Al gel ratio of 80, 40 and 20 implies that a portion of these samples remains essentially nonaluminated and retains the characteristics of the parent Si-MCM-41 material. Fig. 1. Powder XRD patterns and nitrogen sorption isotherms of pure silica Si-MCM-41 and recrystallised Al-MCM-41 samples prepared from gels with varying amounts of Al. The amount of Al is indicated by the Si/Al ratio.

The nitrogen sorption isotherms in Fig. 1 clearly show two capillary condensation (pore filling) steps for the 'partially' aluminated samples (prepared at Si/Al = 80, 40 and 20). We attribute the first step (at lower partial pressure) to the filling of 'aluminated pores' and the second step to the filling of

125 125

pure silica, i.e. 'non-aluminated pores'. The second pore filling step in the partially aluminated samples occurs at the same partial pressure as the filling of pores in the parent Si-MCM-41. This indicates that the pore size of the nonaluminated pores in 'partially' aluminated samples remains unchanged. The textural properties of the samples are summarised in Table 1. The basal spacing of the non-aluminated portion remains unchanged at ca. 43 A, which is similar to that of the pure silica Si-MCM-41. The basal spacing of the aluminated portion gradually decreases at higher Al content from 40.1 to 33.5 A. The surface area and pore volume generally decrease with the extent of alumination.The apparent Al content (Table 1) is higher than expected for samples prepared at gel Si/Al ratio = 80, 40 and 20. This is consistent with the proposal that only part of the Si-MCM-41 is aluminated. The Al content approaches the expected value as the extent of alumination increases, i.e. as the proportion of aluminated material increases, the measured Si/Al ratio becomes more representative of the gel ratio. At gel Si/Al = 10 or 5, the Al content is very close to the expected values; the samples are fully aluminated and essentially homogeneous with respect to spatial distribution of Al. Incorporation of Al onto the silica framework of the aluminated samples was confirmed by 27 Al MAS NMR analysis in Fig. 2. The spectra, of calcined samples, exhibit resonances at 55 and 0 ppm arising from tetrahedral (framework) and octahedrally coordinated (non-framework) Al respectively. From the spectra we estimate that ca. 80% of the Al in the samples (except for A1-MCM41-5 with ca. 65%) is in tetrahedral framework positions. This is consistent with the acidity data in Table 1. The acid content of medium to strong acid sites (obtained via temperature programmed desorption of cyclohexylamine-containing samples after thermally treated at 250°C [6]) increases at higher Al content. Table 1. Elemental composition and textural properties of pure silica Si-MCM-41 and recrystallised Al-MCM-41 samples prepared from gels with varying amounts of Al Sample

Si/Al ratio

basal ((sf1Oo) spacing

(A) Si-MCM-41 A1-MCM41-80 A1-MCM41-40 A1-MCM41-20 A1-MCM41-10 A1-MCM41-5

40.1 28.1 16.9 8.8 5.8

42.8 43.2; 40.1 43.0; 39.7 42.8; 38.2 37.6 33.5

surface area (m2/e) 1017 995 922 840 785 878

pore volume (cnrVg) 0.91 0.87 0.78 0.62 0.53 0.51

acidity (mmol/e) 0.15 0.25 0.39 0.64 0.81

This study shows that well ordered mesoporous aluminosilcates may be prepared via stepwise alumination during recrystallisation pure silica MCM-41 in the presence of discrete amounts of Al. The proportion of aluminated MCM41 increases with the amount of Al in the recrystallisation gel and beyond a

126 126

100

i 50

-50

-100

5AI

Fig. 2. 2IA\ MAS NMR of calcined Al-MCM-41 samples

certain gel Si/Al ratio the whole MCM-41 sample is aluminated. Varying the amount of Al therefore controls the extent of alumination and enables a stepwise alumination of the Si-MCM-41. Alumination of the pure silica MCM41 is thought to occur via the formation of an aluminosilicate layer on the inner surface of the pore walls. Our findings suggest that it is possible to fully aluminate a portion of the pores of a pure silica MCM-41 before alumination of other pores has started. The ability to vary the spatial distribution of Al (or other heteroatoms) in such a manner may find use in the preparation of composite materials and may open new opportunities for selective molecular engineering within the internal surface of mesoporous silicas and aluminosilicas. 3. References [1] S. Biz and M. L. Occelli, Catal. Rev.-Sci. Eng., 40 (1998) 329. [2] (a) A. Sayari, Chem. Mater., 8 (1996) 1840. (b) M. T. Janicke, C. C. Landry, S. C. Christiansen, S. Birtalan, G. D. Stucky and B. F. Chmelka, Chem. Mater., 11 (1999) 1342. [3] R. Mokaya, Chem. Commun., (2000) 1541. [4] (a) R. Mokaya, W. Zhou and W. Jones, J. Mater. Chem., 10 (2000) 1139. (b) R. Mokaya, J. Mater. Chem., 12 (2002) 3027. (c) Y. Xia and R. Mokaya, J. Mater. Chem., 13 (2003) 3112. (d) R. Mokaya, Adv. Mater., 12 (2000) 1681. (e) R. Mokaya, W. Zhou and W. Jones, Chem. Commun., (1999) 51. [5] J. Y. Ying, C. P. Mehnert and M. S. Wong, Angew. Chem. Int. Ed., 38 (1999) 56. [6] R. Mokaya, W. Jones, S. Moreno and G. Poncelet, Catal. Lett., 49 (1997) 87.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

127 127

One-pot synthesis of ionic liquid functionalized SBA-15 mesoporous silicas Yong Liua, Jiajian Peng a , Shangru Zhaib, Ningya Yuc, Meijiang Lia, Jianjiang Mao a , Huayu Qiu^*, Jianxiong Jianga and Guoqiao Laf'*

"Key Laboratory of Organosilicon Chemistry and Material Technology of Ministry of Education, Hangzhou Teachers College, Hangzhou 310012, China Department of Chemical Engineering and Materials, Dalian Institute of Light Industry, Dalian 116034, China 'Institute of Catalysis and Synthesis, and Key Laboratory of Chemical Biology and Traditional Chinese Medicine Research of Ministry of Education, Hunan Normal University, Changsha 410081, China

l-Methyl-3-w-propyl-imidazolium chloride (MPImCl) and ./V-propylpyridinium chloride (PPyCl) ionic liquid functionalized SBA-15 mesoporous materials were sucessfully synthesized through the co-condensation of tetraethoxysilane (TEOS) with l-methyl-3-(triethoxysilyl propyl)-imidazolium chloride (MTESPImCl) and 3-(triethoxysilyl propyl)- pyridinium chloride (TESPPyCl) using EO20PO70EO20 (Pluronic PI23) as surfactant. These organicinorganic hybrid materials may have potential applications in heterogeneous catalysis reactions. 1. Introduction Since the discovery of mesoporous materials in the early 1990s [1], surfacefunctionalized mesoporous materials have attracted great interests due to the combination of unique physico-chemical properties of the parent counterparts (high surface area, uniform pore structure, high adsorption capacity and relative stable framework, etc.) [2-5] with the introduced functional groups, that is, surface-functionalized ones provide distinct properties such as better compatibility and abilities to further graft other reactive complexes. Of the two functionalizing strategies, post-grafting and co-condensation, the latter is often preferred because it offers more uniform surface coverage, higher loading and simpler synthesis steps [6].

128 128

Ionic liquids (ILs), known as novel environmental benign media, have attracted great interests in the last two decades since they can serve not only as favorable media for catalysis [7] but also as green catalyst themselves in many reactions such as Knoevenagel condensation [8], cycloaddition [9] and Biginelli reaction'101. However, in some cases separation of product is still a problem since the miscibility of ionic liquids with some products and reactants. Thus, immobilization of ionic liquids on solid based materials is of particular interest. Recently, several groups have reported the synthesis of ionic liquids immobilized solid hetergenous catalyst [11-13]. It's noteworthy that Mehnert et al. found that ionic liquid functionalized solid could act as support for rhodium which was used as catalyst in hydroformylation reactions [14,15]. However, silica gel were used in most reports and stduies on ordered ionic liquids functionalized mesoporous materials are still quite rare [16,17]. Herein, we report the one-pot synthesis of MPImCl and PPyCl ionic liquid functionalized SBA-15 mesoporous materials which may be used as catalyst or support for heterogeneous catalysts. 2. Experimental Section All reagents were of analytical grade and used as received. MTESPImCl and TESPPyCl were synthesized through the reaction between 1methylimidazole or pyridine and y-chloropropyl triethoxysilane at 120°C for 24 h. The synthesis procedures of ionic liquid functionalized SBA-15 mesoporous materials were similar to those of other functionalized mesoporous silica[18]. Under the direction of PI23, TEOS was allowed to pre-hydrolyzed for specific times and then MTESPImCl was added, followed by hydrothermal treatment in favor of the formation of mesoporous structure. Template was removed from the as-synthesized material by washing with ethanol under reflux for 24 h. X-ray powder diffraction (XRD) data were acquired on a Rigaku D/max 2500V/PC X-ray diffractometer with Cu Ka radiation. IR spectra were taken with a Nicolet 700 FT-IR spectrometer. Nitrogen adsorption and desorption isotherms were measured using a Quantacrome Autosorb-1 system at 77 K. Elemental analysis were performed on an Elementar Vario EC III C/H/N/O/S element analyzer. 3. Results and Discussion Fig 1 gives XRD patterns of MPImCl functionalized SBA-15 with different MPlmCl/(MPImCl + TEOS) ratios with different TEOS prehydrolysis times. With a TEOS prehydrolysis time of 40 min, the produts differed from highlyordered SBA-15 to nearly amorphous materials as MPImCl content increased from 0 to 15%. When TEOS prehydrolysis time was prolonged to 4 h, the regularity of pore structure (MPImCl content 15%) was greatly improved. This could be explained by that MPImCl might perturbe the self-assembly of

129 129

Fig 1 XRD patterns of MPImCl functionalized SBA-15 with different prehydrolysis times and MPImCl ratios: (a) 0.10, 4 h, (b) 0, 0 , (c) 0.05, 0.1540 min, (d) 0.10, 40 min, (e) 0.15, 40 min.

Fig 2 XRD patterns of PPyCl functionalized SBA-15 with different PPyCl ratios prehydrolyzed for 4 h: (a) 0.05, (b) 0.10, (c)

surfactant micelles and longer TEOS prehydrolysis time could faver the formation of highly ordered mesoporous structures, as also observed in the synthesis of other organic functionalized mesoporous materials [18]. As PPyCl functionalized SBA-15 materials were concerned, however, mesopores were less ordered at high PPyCl loading amounts even if the prehydrolysis time was as long as 4 h (Fig 2 ) . N2 adsorption - desorption was carried out to supply further infor- IL ratio SBET Dp Loading vn mation about the physical properties , 0/ . 2 (m-.2/g) (cm7g) (nm) (mmol/g) of the ionic liquid functionalized 0 688 0.937 6.21 0 SBA-15 materials. As shown in Table 1, surface areas, pore volIm5" 482 0.849 0.512 6.18 umes and pore diameters of the ImlO" 400 0.564 5.13 0.943 products all decreased as ionic 0.221 1.322 143 3.62 liquid content increased from 0 to I m l 5 " 15%, which could be attributed to ImlO* 529 0.996 0.653 6.15 the increasing distribution of ionic 0.569 Py5* 558 0.997 8.04 liquid moieties in the interior meso504 0.986 0.901 8.03 pore surfaces. With longer pre- Py 10* hydrolysis time, products, especial- P y l 5 * 5.74 1.409 368 0.755 ly PPyCl functionalized ones displayed much higher surface areas Table 1 N2 adsorption-desorption and elemental and larger pore diameters, which is analysis results of IL-SBA materialsa: TEOS prein consistent with XRD results. hydrolysis time 40 min; b: TEOS pre-hydrolysis Elemental analysis results indicated time 4 h that the loading amounts of MPImCl and PPyCl functionalized SBA-15 were comparable and increased with the raise of IL contents in the initial mixture. IR spectra in Figure 3 convinced

130 130

\

\

smi tabce

the vibrations of imidazolium cation ring (1575 cm 1 ) and pyridium cation ring (1490 cm"1), confirming the successful incorporation of IL moieties in the mesopores. In summary, ionic liquid functionalized SBA-15 mesoporous materials were synthesized through a one-pot cocondensation route, resulting in novel organic-inorganic hybrid materials with forth-coming applications in heterogeneous catalysis.

i

\

/

/^"

b

1/ y

)

— \ \

/

ro I—

\ 4000

3000

2000

1000

Wavenumber (cm1)

Fig 3 IR spectra of (a) MPImCl and (b) PpyCl functionalized SBA-15

4. References [1] C. T. Kresge, M. E. Vartuli, W. J. Roth, J. C. Vartuli and J. S. Beck, Nature, 359 (1992) 710. [2] A. Sayari and S. Hamoudi, Chem. Mater., 13 (2001) 3151-3168. [3] A. Corma, Chem. Rev., 97 (1997) 2373. [4] S. R. Zhai, J. L. Zheng, X. E. Shi, Y. Zhang, L. Y. Dai, Y. K. Shan, M. Y. He, D. Wu and Y. H. Sun, Catal. Today, 93/95 (2004) 675. [5] N. Y. Yu, Y. J. Gong, D. Wu, Y. H. Sun, Q. Luo, W. Y. Liu and F. Deng, Micropor. Mesopor. Mater., 72 (2004) 25. [6] M. Kruk, T. Asefa, M. Jaroniec and G. A. Ozin, J. Am. Chem. Soc., 124 (2002) 6383. [7] J. Dupont, R. F. Souza and P. A. Z. Suarez, Chem. Rev., 102 (2002) 3667. [8] D. C. Forbe, A. M. Law and D. W. Morrison, Tetrahedron. Lett., 47 (2006) 1669. [9] J. J. Peng and Y. Q. Deng, New J. Chem., 25 (2001) 639. [10] J. J. Peng and Y. Q. Deng, Tetrahedron. Lett., 42 (2001) 403. [11] K. Qiao, H. Hagiwara and C. Yokoyama, J. Mol. Catal. A: Chem., 246 (2006) 65. [12] P. Kumar, W. Vermeiren, J. P. Dath and W. F. Hoelderch, Appl. Cataly. A: General, in press. [13] M. Gruttadauria, S. Riela, P. L. Meo, F. D'Anna and R. Noto, Tetrahedron. Lett., 45 (2004) 6113. [14] C. P. Mehnert, R. A. Cook, N. C. Dispenziere and M. Afeworki, J. Am. Chem. Soc, 124 (2002) 12932. [15] C. P. Mehnert, E. J. Mozeleski and R. A. Cook, Chem. Commun., (2002) 3010. [16] M. H. Valkenberg, C. Castro and W. F. Hoelderch, Green Chem., 4 (2002) 88. [17] B. Gadenne, P. Hesemann and J. J. E. Moreau, Chem. Commun., (2004) 1768. [18] D. Margolese, J. A. Melero, S. C. Christiansen, B. F., Chmelka and G. D. Stucky, Chem. Mater., 12(2000)2448.

Recent Progress in Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Published by Elsevier B.V.

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Preparation of novel mesostructured Titaniumpillared hydrotalcite Myung Hun Kima, Seok-Heung Jangb, Youngho Leec, II Mo Kangd, Yungoo Song6, Myongsoo Leea, Jin-Won Parkb and William Jonesf "Department of Chemistry, Yonsei University, Seoul 120-749, Korea Department of Chemical Engineering, Yonsei University, Seoul 120-749, Korea 'Technology Support Division, KICET, Seoul 153-801, Korea Institute of Earth Atmosphere Astronmy, Yonsei University, Seoul 120-749, Korea "Department of Earth System Sciences, Yonsei University, Seoul 120-749, Korea •^Department of Chemistry, University of Cambridge, Cambridge, CB2 1EW, UK

Novel mesostructured titanium-pillared materials with 300-550 m2/g surface area and 11.0-14.0 nm pore were successfully prepared from hydrotalcite(HTlc). 1. Introduction The considerable efforts have been invested in the design of new pores from materials with lamellar structure for the applications of shape-selective adsorption and support in catalyst and material chemistry by various intercalation procedures [1]. Layered materials consisting of stacked sheets can be easily functionalized by the host-guest interaction in the interlayer region. Among layered solids, hydrotalcite-type anionic clays (HTlcs) have been interested in as host materials. Generally, the hydrotalcite-like solids are described the empirical formula [M2+1.xM3+x(OH)2][(Am")x/m-nH2O], abbreviated hereafter as [M2+-M3+-A] where x may vary from 0.17 to 0.33. A represents the m-valent anion necessary to compensate for the net positive charge [2]. Based on these properties, the intercalation of specific elements into such HTlcs is also particular importance in the architecture of novel materials with various pore sizes. The aim of this study is fabricated the mesostructured titanium-pillared HTlc (Ti-HTlc) with different pore size, pore volume, and BET surface area by the intercalation of titanium chain anions, -(Ti-O-Ti)n-, into the gallery space of

132 132

HTlc through host-guest interaction, where TiO6 octahedra run along perpendicular direction with two layers. 2. Experimental Section Titanium chain anions were prepared by reaction of TBOT with basic solution of pH= 12 in stainless steel bomb at 393 K for 24 h. Also HTlc host powder was calcinated to get carbonated free solid at 823 K for 12 h. Ti-HTlcs were constructed by intercalation method starting with the addition of titanum chain anions into host powder, HTlc, under pH = 10.0, 11.0 and 12.0 conditions at 393 K for 24 h. The chemical composition of reactants is consited of host powder, titanium chain anions, and water in 1:0.7:5600 mole ratio. The obtained samples after being filtered off and washed with water were refluxed in acetone at 373 K for 24 h in order to decompose organic species in the interlayer. The resulting materials after reflux in acetone are designated as Ti-HTlc(l), TiHTlc(2) and Ti-HTlc(3), respectively. 3. Results and Discussion Fig. 1 shows the XRD patterns of the mesostructured Ti-HTlcs prepared from pH values of 10.0, 11.0, ,0.45 and 12.0, respectively. All products in the range of about 0.4-1.6 nm"1 ,0.49 exhibit common features of mesoA.0.52 structured material with pores between 11.0 and 14.0 nm consisting \ of pillars. Assuming a thickness of 0.48 nm for the HTlc layer, the newly formed spaces were approxi(c) mately 10.5-13.5 nm, compared with a carbonate HTlc gallery 10.58 \ (b) height of 0.28 nm. Among the products, Ti-HTlc(3) obtained at pH (a) =12 appeared in the largest mesostructured titanium-pillared HTlc. 0.4 0.8 1.2 1.6 The TEM image of Ti-HTlc [3] in q (nm"') Fig. 2 reveals that the pores newly constructed by pillars are about 13 F i g , P o w d e r X R D p a t t e m s o f (a) T i . H T l c ( 1 ) ; nm. Therefore, this result agreed (b ) Ti-HTlc(2) and (c) Ti-HTlc(3). with that of the XRD indicating the mesostructured presence forming new frameworks by intercalating titanium anion chains into HTlc. To the best of our knowledge, this is the first time to i

133 133

obtain the uniform mesoporous HTlc using the intercalation of inorganic anion chains under the basic condition (i.e. pH = 12).

50n

m 50 nm *•

'

-

-

•

•

.

"**!

Fig. 2. TEM micrograph of Ti-HTlc(3).

Furthermore, table 1 provides the basic physical properties of all samples analyzed using N2 adsorption-desorption isotherms. The values for Ti-HTlc series correspond the typical mesostructured solids with mesopore volume saturation capacity between 0.26 and 0.46 mL/g. All samples also have high BET surface areas of 300-550 m2/g and pore sizes of 10.0-13.0 nm. But the reason with the smaller values than those of the typical mesoporous silicas is assumed partial disordering due to the intercalation of the titanium anion chains Table 1. Pore size and specific surface area of HTlc and Ti-HTlc series.

Materials

Pore size (nm)

0.3

HTlc Ti-HTlc(l)

10.6

Ti-HTlc(2)

11.7

Ti-HTlc(3)

13.6

SBET" 2

(m /g)

90 300 360 550

Total amount N2 adsb (mL/g) 0.08 0.26 0.31 0.46

"From the linear ?-plot at low P/Po. *From the isotherm at low P/Pf=0.5

Also the presence and nature of specific vibration bands in HTlc and Ti-HTlcs were investigated with FTIR spectroscopy. The band at 1108 cm"1 is caused by the Ti-O-Ti units, and the decrease of band intensity at 1377 cm'1 assigning vibration mode of CO32" from Fig. 3b to 3d indicates the different pillaring degrees of the titanium anion chains into HTlc. Such bands suggest that TiC>6

134 134

octahedra are linked together with formation of liner .. -O-Ti-O-Ti-Ochains in the perpendicular plane within HTlc structure.

(d)

4000

3000

2000

1000

W avenum b e r (nm " ' ) Fig. 3 FTIR spectra of (a) HTlc, (b) TiHTlc(l), (c) Ti-HTlc(2) and (d) Ti-HTlc (3).

4. Conclusion This paper provides the new approach for the architecture of mesostructured materials from hydrotalcite by the intercalation reaction at specific pH. 5. Acknowledgement We are grateful to the Ministry of Science and Technology of Korea (Grant No. R01-2005-000-11039-0) and 21c Eco-Mat Technology Company for financial support. 6. References [1] G A. Graham, K. H. Robin and R. F. Kevin. A structural consideration of kanemite, octosilicate, magadiite and kenyaite. J. Mater. Chem. 7 (1997) 681-687. [2] V. Rives and M. A. Ulibarri. Layered double hydroxides (LDH) intercalated with metal coordination compounds and oxometalates. Coord. Chem. Rev. 181 (1999) 61-120.

Recent Progress in Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

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Synthesis, characterization and catalytic activity of Titania and Vanadium grafted and substituted on mesoporous silicas T. Williams3, J. N. Beltramini*" and G. Q. Lub "ARC Centre for Functional Nanomaterials,The University of Queensland, Brisbane, Queensland, AUSTRALIA. ''Department of Chemical Engineering, University of Delaware, USA

The catalytic properties of mesoporous silica catalysts with titanium (Ti) and vanadium (V) loadings between 0.5 and 6 wt %, surface areas around 1300m2/g and synthesized using the isomorphous substitution (IS) and molecular designed dispersion (MDD) techniques were tested using toluene as a model VOC in a fixed bed reactor at temperatures between 300 to 550°C. The different behaviour of the Ti and V-HMS catalysts were explained in terms of the location and the total number of Ti and V actives species located on the surface of the HMS. Activation energies calculations support this view. 1. Introduction MCMs and HMSs mesoporous materials are very promising catalyst supports since they are capable of transforming much larger or bulky molecules than their microporous counterparts [1]. This novel class of silica-based materials are characterized by a regular arrangement of uniform mesopores [2]. Several pathways have been reported in recent years for the assembly of mesoporous molecular sieves [3]. The molecular designed dispersion technique (MDD), a very promising technique for creating metal oxide catalysts consists of the irreversible adsorption of metal acetylacetonate complexes onto a silica support followed by decomposition to yield the supported metal oxide catalyst. This study focuses on the adsorption and thermolysis of titanium acetylacetonate and vanadium acetylacetonate respectively onto hexagonal mesoporous silica using MDD technique. The physical, chemical and oxidative

136 136

catalytic properties obtained by the MDD method are then compared to those obtained by the simpler isomorphous substitution (IS) pathway. 2. Experimental Section For the MDD method TiO(acac)2 and VO(acac)2 crystals were used as the Ti and V sources respectively. Once totally dissolved, dry HMS was added to the reaction vessel. After the reaction the silica was filtered and then dried under vacuum. The dry solid was then calcined at 450°C. The HMS catalyst support was synthesized via the neutral templating mechanism [4]. The IS of TiHMS and VHMS were similar to that of HMS except that titanium or vanadium solutions were respectively added drop wise after the addition of TEOS. BET surface area, pore volume, pore size and PSD were calculated. Powder X-ray diffraction (XRD), UV-vis diffuse reflectance spectroscopic, pyridine TPD and TEM were performed on all samples. Ti and V content were determined by chemical analysis. The catalytic activity tests were carried out at atmospheric pressure in a continuous flow, fixed-bed quartz tube micro-reactor loaded with 0.05 g of calcined catalyst using toluene as reactant with a concentration of 1000 ppm and operating between 300 and 550°C. The reaction products were analysed using two Shimadzu GC-17A gas chromatographs equipped with a 30 m DB-5 capillary column connected to a FID and a 30 ft Porapak Q packed column connected to a TCD. 3. Results and Discussion The MDD and IS techniques both result in mesoporous silicas with pore volumes between 0.6 and 1.0 cc/g and high surface areas around 1000 m2/g. For comparison the physical properties of all synthesized Ti and V-HMS samples are listed elsewhere [4-5]. The IS technique is limited in the amount of titanium or vanadium which can be incorporated, (~4 wt %). In contrast, the MDD exceeds 14 wt%. The MDD method however allows much greater control of the physical properties of the final product than the IS. This is because any parent silica support material with the desired physical properties can first be chosen. The subsequent addition of the metal oxide acid sites via the molecular designed dispersion method has very little effect on the parent silica's physical structure. A linear relationship between the amount of metal acetylacetonate complex used during synthesis and the amount of metal incorporated onto the silica surface was also observed. This is a very desirable property and will allow for the design of the Ti- and V-HMS catalysts with the desired metal content. Energy dispersive spectra and UV-vis spectra of TiHMS and V-HMS show that the metal sites are not evenly dispersed over the surface of the material. However using the IS technique the addition of Ti and V sources to the synthesis gel can significantly change the properties of Ti- and V-HMS materials. Results on Table 1 using samples with similar textural

137 137

porosity and close mesoporous volume showed that meanwhile MDD method give rise to a great proportion of 5 and 6 coordinated Ti sites with greater energy of desorption, the IS method gives rise mainly to 4 coordinated Ti sites. V-HMS catalysts prepared by IS results showed a great proportion of isolated tetrahedra at Si/V molar ratio greater than 50. As bulk V content increases the pro-portion of polymeric vanadium species grows as more V is incur-porated into the HMS framework. Table 1: Identification and Quantification of Titanium sites by UV-vis Isomorphous Substitution

Ti Wt %

4 coordinated peaks (% area of spectra)

5 and 6 coordinated peaks (% area of spectra)

Molecular Designed Dispersion

Ti Wt%

4 coordinated peaks (% area of spectra)

5 and 6 coordinated peaks (% area of spectra)

Ti-HMS4[50] 1.20 44 10 90 56 Ti-HMS4[100] 2.29 64 13 87 36 Ti-HMS4[200] 75Ti-HMS3 2.10 3.25 24 76 29 71 75Ti-HMS4 Ti-HMS6[50] 1.155 1.89 70 30 70 30 Ti-HMS6[100] 2.112 75Ti-HMS5 1.35 24 76 43 57 Ti-HMS6[200] 2.998 75Ti-HMS6 1.11 24 76 70 30 35Ti-HMS2 5.06 Ti-HMS7[50] 0.64 17 30 70 83 Ti-HMS7[100] 2.109 35Ti-HMS3 4.61 82 28 72 18 3.199 35Ti-HMS4 5.11 Ti-HMS7[200] 22 79 30 70 35Ti-HMS5 4.22 35 65 35Ti-HMS6 4.49 32 68 Pyridine-TPD results demonstrated that the bulk V content has very little effect on the energy of desorption of the hydrogen-bonded SiOH groups while increasing V content has more pronounced effect on the free SiOH energy of desorption. Activation energies for toluene conversion were calculated assuming first order kinetics [5]. Ti -HMS catalysts synthesized via MDD have lower activation enery that their counterparts synthesiz-ed by IS as can be seen in Table 2. On MDD catalysts Ti atoms are exclusively located on the surface of the silica and therefore are more accessible to the toluene feed lowering the activation energy. Conversion of toluene over Ti-HMS results in total oxidation with detectable products such as: CO, CO2 and H2O. Figure 1 compares effect of Ti loading on toluene conversion samples synthesized using IS and MDD. 75Ti-HMSl

2.10

75Ti-HMS2

2.09

Table 2: Activation Energies for Toluene Oxidation over MDD/IS Ti-HMS Catalysts Synthesized via MDD 3.25TiHMS-0.13 3.20TiHMS-0.60 3.00TiHMS-1.30 1.16TiHMS-1.32 2.11TiHMS-1.37 3.00TiHMS-1.30

E Toluene (kJ/mol) 4.1 1.5 5.9 6.7 5.1 5.9

Catalysts Synthesized via IS 4.61TiHMS-0.75 2.10TiHMS-0.84 4.49TiHMS-0.10 2.09TiHMS-0.35

E Toluene (kJ/mol) 29.1 80.2 35.5 52.1

138 138 — • — i_irnHMS-i_33 -O 2.11T1HMS-1.37 —T— 3.DCmHM&1.30

*

f

I

4.49TiHM50.10

O

4.61TIHMSD.75

v—

2.10TiHM50.84

-J^J/ (a)

—V

-* '

(b) TsmpsraturaCC)

Figure 1: Toluene conversion on Ti-HMS synthesized by (a) IS (b) MDD

In contrast, it can be seen from Figure 2 that the conversion of toluene over VHMS catalysts synthesized by IS results in only partial oxidation with carbon oxides, benzene, benzaldehyde and water as the main reaction products. However V-HMS synthesized by MDD favours only total oxidation to CO and CO2 as no benzaldehide was found. This can be explained in terms of the location and the number of vanadium active species on the surface of the HMS.

S so-

25D

••"O 111 Benzaldshvde Yield

Yield (%)

60 -

3DD

350

4CO

453

SOD

Temperature t°C)

55D

6DD

Temperature (°C)

(a)

(b) (b) Figure 2: Toluene conversion on V-HMS synthesized by (a) MDD, (b) IS

4. Acknowledgment The authors wishes to acknowledge the financial assistance of the ARC Centre for Functional Nanomaterials during the preparation of this work. 5. References [1] J. S. Reddy, R. Kumar and P. Ratnasamy, Appl. Catal, 58 (1990) LI. [2] C. T. Krege, M. E. Leonowicz, W. J. Roth, J. C. Vartuli and J. S. Bech, Nature, 359 (1992) 710. [3] C. Y. Chen, H.X. Li and ME. Davis, Micropor Mater, 2 (1993) 17. [4] T. Williams, J. Beltramini and G. Q. Lu, Microp. Mesop Mat., 88 (2006) 91. [5] T. Williams, J. Beltramini and G. Q. Lu, J. Env. Eng., 130 (2004) 356.

Recent Progress in Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Published by Elsevier B.V.

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Synthesis and characterization of B- and Ti-MCM36 Se-Young Kima, Gon Seob and Wha-Seung Ahna* "Department of Chemical Engineering, Inha University, Inchon, 402-751, Korea b School of Applied Chemical Engineering, Chonnam National University, Gwangju, 500-757, Korea

B- and Ti-containing MCM-36 materials were prepared from MCM-22 type precursors by surfactant swelling followed by silica pillaring. Their structural evolution was investigated by XRD, BET surface area measurements, and UVvis spectroscopy. Catalytic performance data on 1-hexene epoxidation probe reaction demonstrated superior performance of Ti-MCM-36 over TS-1 and TiMCM-22. 1. Introduction MCM-36 is a pillared molecular sieve, which contains micropores inside its crystalline layers and mesopores in the interlayer space. Mesoporous region is created by expansion of MCM-22 lamellar structure and insertion of polymeric silica pillars. MCM-36 has high specific surface area and good accessibility for relatively large molecules and its catalytic application in refinery processes are well documented [1]. Ti-containing MCM-36 is a titanosilicate with isolated tetrahedral Ti sites in the framework, and is expected to function as a partial oxidation catalyst using H2O2 as an oxidant. Ti-MCM-36 with zeolytic layers may demonstrate better catalytic performance over Ti-MCM-41 with amorphous wall structure. Ti-MCM-36 is typically prepared from B-containing MCM-22. In this study, structural evolution of these B- and Ti-MCM-36 structures from MCM-22 precursors was investigated in a systematic manner. 2. Experimental Section B-MCM-22 precursor was initially prepared following the synthesis method reported by Millini et al. [2], and Ti-MCM-22 was synthesized both by direct

140 140

hydrothermal synthesis [3] and post synthesis method [4] reported using Bcontaining MCM-22 as a starting material. Preliminary work indicated that the post-synthesis scheme is a better synthesis approach. To be specific, B-MCM22 precursor was treated with 6 M HNO3 and this treatment was repeated three times to remove boron completely. Afterwards, it was mixed with H2O, piperidine(PI), tetrabutyl orthotitanate(TBOT) with molar composition of 1.0 SiO2 : 0.03 TiO2 : 1.0 PI : 19 H2O. The mixture was heated in a Teflon stainless-steel autoclave at 448 K for 7 days. Ti-MCM-22 precursor prepared was treated with 2M HNO3 to remove octahedral Ti species detrimental to catalytic epoxidation reaction. B- and Ti- MCM-36 were prepared based on the synthesis protocol for AlMCM-36 reported by He et al. [1]. Swelling process was carried out by refluxing a mixture of B- or Ti-MCM-22(P) : 4 CTMAC1 : 1.2 TPAOH, followed by mixing the product obtained with TEOS at a weight ratio of 1:5 for pillaring, and the mixture was heated at 353 K for 25 h in nitrogen atmosphere. After filtration and drying, hydrolysis was carried out in water at 413 K for 6 h. Finally, B- and Ti-MCM-36 were obtained by calcination at 723 K for 3 h in nitrogen and at 812 K for 6 h in air (heating rate of 2 K/min). The crystallinity of the samples prepared was measured by X-ray diffraction using Ni-filtered CuKa radiation (Philips, PW-1700) and the specific surface area and average pore diameters were determined by N2 adsorption-desorption using a Micromeretics ASAP 2000 automatic analyzer. UV-visible spectra were measured on a Varian cary-3E double beam spectrometer using SiO2 as a reference. Catalytic performance of Ti-MCM-36 was investigated by 1-hexene epoxidation with H2O2 oxidant. 3. Results and Discussion Structural evolution of MCM-36 from MCM-22 precursor was shown in Fig. 1. MCM-22 has MWW lamellar structure and swelling step using surfactant expands interlayer distance of MCM-22 precursor. Finally, mesoporous region was formed after pillaring step using polymeric silica.

Mesopore Mesopore

Pillaring

MCM-22 MCM-22 precursor

Swollen material MCM-36Swollen material

Fig.l. Schematic representation of MCM-36 structure.

MCM-36

141 141

The XRD patterns of the various MCM-22 and MCM-36 materials are compared in Fig. 2. The pattern of B-MCM-22 precursor was characterized by 001 and 002 peaks at 20 = 3-7° due to its c-axis. Deboronated MCM-22 with 6 M HNO3 created linkages of lamellar structures, which is reflected by the disappearance of 001 and 002 peaks in XRD. Ti-MCM-22 precursor showed the same XRD pattern as B-MCM-22 precursor due to restored MWW lamellar phase. Ti-MCM-36 showed a characteristic new peak at 26 = 1-2° indicating expansion of distance between sheets and subsequent formation of mesopores. The XRD pattern of B-MCM-36 is virtually identical to that of Ti-MCM-36. 400 400-r 300 200 100

10

20

30

Fig.2. XRD pattern of materials; (a) as-syn B-MCM-22, (b) acid treated B-MCM-22, (c) as- synTi-MCM-22, (d) Ti-MCM-22, (e) Ti-MCM-36.

40

0 0.0

0.2

0.4

0.6

0.8

1.0 1.0

Fig.3. N2 adsorption isotherms of • Ti-MCM-22,0 B-MCM-22 • Ti-MCM-36, D B-MCM-36.

ABS

The N2 adsorption isotherm of B- and Ti-MCM-22 in Fig. 3 is of type I due to the microporous nature of the materials, whereas the isotherms of B- and TiMCM-36 are of type IV with hysteresis loop at p/po= 0.4 for capillary condensation due to the presence of mesopores. While (a) BET surface areas of B-MCM-22 and TiMCM-22 were 234 and 471 m2/g, B- and Ti-MCM-36 showed substantially increase(b) ed surface area of 520 and 674 m2/g, respectively. Ti-substituted materials show large pore volume and surface area than Bcontaining counterparts due to acid 200 300 400 500 600 washing treatment. 300 500 200 UV-visible spectra of Ti-MCM-36 samWavelength/nm Wavelength/nm ples are shown in Fig. 4. Absorption band Fig 4. UV-vis spectra of (a) calcined Ti- of Ti-MCM-36 prepared with Ti-MCM-22 MCM-36 and (b) Ti-MCM-36 using precursor without acid washing produced acid treated MCM-22 precursor. both 220 nm peak corresponding to the

142 142

catalytically active tetrahedral sites as well as 260 nm peak corresponding to detrimental octahedral Ti species. On the other hand, Ti-MCM-36 prepared with acid treated Ti-MCM-22 precursor showed enhanced 220 nm band and most of the octahedral Ti species was found successfully removed. Table 1 compares the catalytic activity and selectivity of Ti-MCM-36 with other Ti containing catalysts. Ti-MCM-36 exhibited higher conversion than either that of Ti-MCM-22 or TS-1, which is believed to be a consequence of reactant molecules having easier access to Ti sites in the framework due to swelling/pillaring. It is known that 1-hexene epoxidation is strongly influenced by diffusion [5]. To evaluate the potential adverse effect of boron remained in Ti-MCM-36, B-MCM-36 is also tested for n-octane cracking reaction and virtually no conversion was observed, demonstrating negligible side reaction due to very weak acidity. 4. Acknowledgement This work was supported by Korea Research Foundation Grant (KRF-2003 041-D00181). 5. References [1] Y. J. He, G. S. Nivarthy, F. Eder, K. Seshan and J. A. Lercher, Micropor. Mesopor. Mater., 25 (1998) 207. [2] R. Millini, G. Perego, W. O. Parker, Jr., G. Bellussi and L. Carluccio, Microporous Materials, 4 (1995) 221. [3] P. Wu, T. Tatsumi, T. Komatsu and T. Yashima, J. Phys. Chem. B, 105 (2001) 2897. [4] P. Wu and T. Tatsumi, Chem. Commun., 10 (2002) 1026. [5] W. J. Kim, T. J. Kim, W. S. Ahn, Y. J. Lee and K. B.Yoon, Catalysis Letters, 91 (2003) 123.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

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Delamination and intercalation of layered aluminophosphate with [AI2P3O12]3" stoichiometry by a controlled two-step method Chen Wang, Ying Li, Weiming Hua,* Yinghong Yue* and Zi Gao Department of Chemistry and Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, Fudan University, Shanghai 200433, China.

1. Introduction Numerous microporous aluminophosphates with non-unity Al/P ratios have been synthesized using solvothermal method [1]. Among them 2-D layered aluminophosphates are of particular interest because of their potential application in separation, catalysis or as functional materials. Delamination and intercalation of these layered compounds are critical for the above application. However, they are more difficult to bring about than those of ordinary layered metal phosphates due to the instability of the microporous sheets and their strong interaction with the protonized organic ammonium cations [2]. We have succeeded in delaminating and intercalation of the layered aluminophosphates with [A13P4O]6]3 stoichiometry by aromatic amine using a novel controlled twostep method [3], in which delamination and intercalation processes proceed separately and sequentially under different controlled conditions, so that the dielectric constant and the pH value of the medium in these two steps can be varied to suit a wider variety of intercalating agents and to guarantee the success of exfoliation and reassembly of the aluminophosphate. [Al2P3Oi0(OH)2] [C6NH8] (A1P) is another kind of aluminophosphate which is prepared from a butanol system using 4-methylpyridine as a template [4]. Its 2-D network is constructed of alternating aluminum units (A1O4 and A1O5) and phosphorous units (PO4, PO3(OH) and PO2(=O)(OH)) and featured by a series of edgesharing bridged-6MRs and zigzag 4MRs arranged in alternative rows. The inorganic sheets are held together through the H-bondings between the two layers as well as the H-bondings between the organic template and the layer. Here, the delamination and intercalation of A1P by C4-Ci6 alkylamines using the two-step method are studied.

144 144

2. Experimental Section A1P was synthesized following the procedure described in the literature [4]. For delamination, A1P (200 mg) was placed in 20 ml of the buffer solution, stirred at ambient temperature continuously. The delaminated A1P was separated by centrifugation and then added into 20 ml of ethanol/water mixture with a calculated amount of alkylamine, stirred for 1 d, and the final product was obtained by centrifugation. XRD patterns were recorded on a Rigaku D/MAX-FLA diffractometer, and SEM images were attained with a Philips XL-30 scanning electron microscope. 3. Results and Discussion The delamination of A1P was carried out in solutions at different pH and different Na+ concentration, and the observations of the systems by XRD were summarized Table 1. The results show that the delamination process would be facilitated in the solution with high pH value and high Na+ concentration but would be slowed down by adding phosphate or phosphonates to the solution. This is consistent with the previous observations in delamination of similar materials [3, 5]. Table 1. Time for complete delamination of A1P in the different solutions . . Solution o

1 2 3 4 5 6 7 8

„ er. . Buffer pair _ H3BO3/NaH2BO3 NaHCO3/Na2CO3 NaHCO3/Na2CO3 Na2HPO4/Na3PO4 Na2HPO4/Na3PO4 Na2HPO4/Na3PO4 Na2HPO4/Na3PO4 Na2HPO4/Na3PO4

,, , pH value 9 10 11 11 12 12 12 12

Concentration of + .. , ..,,. Na cation (mol/1) 0.30 0.30 0.30 0.30 0.30 0.45 0.60 0.75

x.

Time for complete , . . .. ,,, delamination (h) — 14 5 16 10 5 5 5

The intercalation of the delaminated A1P with C4-Ci6 alkylamine in the different water/ethanol solution at pH of 6 was studied. The results are given in Table 2. It can be seen that in the solution of alkylamine with short chain such as butylamine and pentylamine, the intercalation only takes place in pure ethanol, namely in solution with low dielectric constants. A pure phase of butylamine intercalate with d-spacing of 1.22 nm and pentylamine intercalate with d-spacing of 1.33 nm are formed, respectively. As the water/ethanol ratio of the solution is increased, no trace of intercalate was observed. This is quite similar with our previous result in preparing the benzylatnine and aniline intercalates, which shows that low dielectric constant is necessary for ressembly of the intercalates . But in the solution of alkylamine with carbon atoms bigger

145 145

than 6, the results are quite different. Pure phase of intercalation can be obtained in the both solutions with high or low dielectric constants. For example, in the solution of hexadecylamine, which has been proved very difficult to be intercalated into the layer of A1P by one-port method because of its large size and low solubility, an intercalate with a d-spacing of 3.14 nm can be obtained in the pure ethanol. The amount of this new phase decreases with an increase of water/ethanol ratio of the solution while another phase with a d-spacing of 3.75 nm appears. This new intercalate finally becomes a pure phase with d-spacing of 4.07 nm in pure water solution and the solution with water/ethanol ratio of 3:1, namely in solution with high dielectric constants. The different phenomena observed in the intercalation process of low chain alkylamine and high chain alkylamine may come from the different interaction between the intercalated alkylamine and the solvent, which deserves further studies. Table 2 Intercalation of A1P with various alkylamines in different solutions

\ .

W/E

Amin&\^ ^ \ Butylamine pentylamine Hexylamine Octylminae Dodyclyamine Hexadyclmine

Interlayer spacing (nm) Pure water — — 2.01 2.50 3.05 4.07

3:1

1:1

1:3

— — 2.01 2.50 3.05 4.07

— — — 2.41 3.05 3.75+3.14

— — — — 3.05+2.38 3.75+3.14

Pure ethanol 1.22 1.33 1.46

1.70

2.38 3.14

The phase transition associated with the dielectric constants of the solution is probably caused by a different arrangement of alkylamine molecules in the interlayer region. At lower dielectric constants, the stronger interaction between the protonized amine and the oxygen atom of the layer forces the amine to tilt a smaller angle with respect to the layer plane and reduces the interlayer distance. Similar results are obtained in the solution of hexylamine, octylamine and dodecylamine. The packing of the alkyl chains in the interlayer region of the saturated intercalates can be obtained by plotting the interlayer spacing against the number of carbon atoms in the alkyl group. The interlayer spacing of saturated intercalates obtained in pure water and pure ethanol increases linearly with a slope of 0.198 nm/CH2 and 0.160 nm/CH2, respectively, which are both larger than 0.127 nm/CH2 for an all-trans fully extended alkyl chain but smaller than two. This means that the alkyl chains in both saturated intercalates should be arranged as bilayers in the interlayer region, tilted with angles of Sin'1 (0.198/2 x 0.127) = 51.2° and Sin^O.^O^ x 0.127) = 39.0° with respect to the layer plane, respectively. The calculated result is closed to the value of the similar intercalates obtained by one-port method [6].

146 146

The SEM images of and the octylamine intercalate, which is selected as the representation, are shown in Fig. 1. The original A1P is composed of large regular thin plate-like crystals with the size about 6 x 15 x 0.1 um [6]. The platelike crystals break into small thin flakes through hydrolysis of the Al-O-P bonds, and these small thin flakes reassembly new crystals with more irregular morphology compared with original one. There is a bit difference in morphology between the intercalates obtained in pure water and in pure ethanol. The morphology of the saturated intercalate obtained in pure ethanol shows more evident characteristic of rosette-like crystal aggregates.

Fig. 1 SEM images of octylamine intercalates obtained in pure water (left) and pure ethanol (right)

4. References [1] [2] [3] [4]

J. H. Yu and R. R. Xu, Ace. Chem. Res., 36 (2003) 481. L. Peng, J. Yu, J. Li, Y. Li and R. Xu, Chem. Mater., 17 (2005) 2101. C. Wang, W. M. Hua, Y. H. Yue and Z. Gao, Micro. Meso. Mater., 84 (2005) 297. J. Yu, K. Sugiyama, K. Hiraga, N. Togashi, O. Terasaki, Y. Tanaka, S. Nakata, S. Qiu and R. Xu, Chem. Mater., 10 (1998) 3636. [5] D. M. Kaschak, S. A. Johnson, D. E. Hooks, H. N. Kim, M. D. Ward and T. E. Mallouk, J. Am. Chem. Soc, 120 (1998) 10887. [6] Q. Huang, W. Wang, Y. H. Yue, W. M. Hua and Z. Gao, Chem. J. Chin. Univ., 25 (2004) 2065.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

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Novel synthesis method of mesoporous MoSiOx Yanying Zheng,a'b Tao Dou,a* Aijun Duan,a Zhen Zhaoa and Shanjiao Kanga "The Key Laboratory of Catalysis, China University of Petroleum, Beijing, 102249; Basal Science Department, Beijing University of Agriculture, Beijing, 102206;

1. Introduction Mesoporous materials possess advantages as very high specific surface areas and large pore size which qualify them talent material as catalysts especially for bulky molecules treatment. Mo species are important active components and insertion of Mo in silica-based mesostructure have attracted extensive attention. Conventional post-synthesis methods have limitation of low Mo loading which implies possible low activity of catalyst. Recently, In-situ preparation strategies are adopted and mainly focus on preparation in acidic media [1,2] among which Bregeault and coworkers [3,4] have established an effective modification mode and reached an ultra high loading of Mo and W with Si/Mo mole ratio of 25, which is equivalent to Mo loading of 4.6 wt%. Whereas assembling in alkaline medium favors further incorporation of secondary metal ion as Ni2+ through reaction of precipitation, Viswanathan's group [5] had reached Mo loading of 0.1 wt% in weak alkaline medium and Ziolet's group [6] had reached Mo loading of 0.00045 wt% at pH level of 11 respectively. To overcome disadvantages of low Mo loading and low Mo usage, efficient processes for incorporation of Mo in basic media are worth of further investigation. This paper presents a novel in-situ method for synthesis of mesoporous MoSiOx composite in strong caustic medium with acetylacetone (HAcac) introduced, through approaches established, Mo loading of 6.7 wt% have been reached, which is a bit higher than that reported by Bregeault [3,4] in acidic media and much higher than that reported in basic medium [5,6]. The work dedicates to the effects explanations of HAcac on MoSiOx preparation and the characteristics of MoSiOx discussion also.

148 148

2. Experimental Section 2.1. Synthesis MCM-48 was prepared according to procedures described by D. Kumar and coworkers [7]. Mesoporous HAcac-silica was prepared according to the same method but with introduction of HAcac before aqueous ammonia adding. Mesoporous MoSiOx and SiO2 were prepared according to formula as follow: 1.00 TEOS (tetraethyl orthosilicate): x Mo: 2.16 NaOH: 0.13 CTMAB (cetyltrimethyl-ammonium bromide): 107 H2O: 3.56 HAcac with adding sequence of NaOH, (NH4)6Mo7O24.4H2O, HAcac, CTMAB, and TEOS. The mixture was agitated for 3 h and aged for 3-7 days; the resulting solid was filtered and washed, then dried at 373 K for 6 h and calcined at 823 K for 6 hr. 2.2. Characterization techniques XRD (Rigaku D/max 2000), N2 adsorption/desorption (ASAP 2020), TEM (Hitachi-9000) and SEM (Oxford S-36) were used for materials detection. 3. Results and Discussion 3.1. Effects of HAcac The effects of HAcac on mesostructure were studied through com-parison of MCM-48 and HAcac-silica firstly. XRD patterns (Figure 1) of calcined samples show that the 100 diffraction strength of HAcac-silica are higher than or equivalent to that of MCM-48 with dramatic shift toward the lower 2 theta degree with proper amount of HAcac, which indicate 2 3 4 5 2theta /deg. that HAcac contribute to enlargement of pore size without unwanted reduction of Figure 1. XRD patterns of MCM-48 and HAcac-silicas with different mesostructure order. amount of HAcac (xlO~2mol): a. 0; The morphologies of mesoporous MCM-48 and HAcac-silica were investigated by HRTEM shown in Figure 2. The results prove that the pore size of HAcac-silica were much larger than those of MCM-48, which are consistent with analysis of XRD results of Figure 1. Besides pore size enlarging impaction confirmed above, HAcac displays even greater significance in preparation procedures because condensation or precipitation of hydrolysate of TEOS is inhibited when pH level is higher than 14. Synthesis of SiOx show that with no HAcac adding the mixture keeps homogenous when stirred for more than 3 h; while deposition emerging within

149 149

20 min with 0.0195 mol of HAcac and increased amount of HAcac result in decreased condensation time. Synthesis of MoSiOx verifies the promotion effect also. (b)

(a)

(c)

Figure 2. TEM images of MCM-48 (a). HAcac-silica (b) and MoSiOx (c) with scale bars 20nm

3.2. Characteristics ofMoSiOx

-1

(b)

(a )

1.6

(b)

3

Intensity /cps

11800 800

Pore Volume /(cm .g )

Figure 3 shows the XRD patterns of MoSiOx with Mo loading of 3.3 wt%. Lower angle XRD spectrum reveals the characteristics of mesoporous material; and wider angle spectrum inserted reveals no peak of ordered crystal, which indicates that there have no MoOx in the material, or MoOx is highly dispersed with particle size within 30A beyond the detection limitation of XRD even when Mo loading is as high as 6.7 wt%. 9.4 wt% Mo loading result in color change from milk-white to light-blue, despite the mesostructure feature maintained crystal MoO3 is detectable with XRD. SEM results of MoSiOx reveal that the average particle size of spheral MoSiOx is about 200nm, much smaller than that of MCM-48 of 0.5 ~ 2u.m prepared by D. Kumar [11], the results explains the dispersion feature of XRD 100 patterns also. 1200 5

600

20

40

60

80

0 1

2

33

2 th e ta /d e g. 2theta /deg.

44

Figure 3. XRD patterns of MoSiOx (with wider 2theta range 5-75 ° inserted)

5

1.2 0.8

(a)

0.4 0.0 -5

20 00 55 10 Pore Diameter /nm

15

20

Figure 4. Pore size distribution of (a) MCM-48 and (b) MoSiOx (3.3

The HRTEM morphology of MoSiOx shown in Figure 2 is similar to that of HAcac-silica, which suggest that proper amount of Mo insertion brings no dramatic effects on physical features. But excessive Mo loading will reduce order of pore arrangement or even destroy the mesostructure. The maximum Mo loading is 9.4 wt% and the limitation of Mo raw material added is 3 g. Results of Nitrogen adsorption-desorption were summed up in Table 1. The variables claim that the physical features will be affected by HAcac adding and Mo loading, increased amount of Mo loading result in shrinking of surface area,

150 150

diminishing of the pore size and the pore volume. The pore size distributions in Figure 4 show that MoSiOx possesses uniform pore size, which imply that proper amount of Mo loading and HAcac adding have no effect on pore order. Table 1.

Results of N 2 adsorption-desorption

Sample

BET surface area / m2.g"'

BJH pore size / nm

Pore volume / cm'.g"1

MCM-48

1589

2.5

1.02

MoSiOx (3.3 wt%)

966

4.8

1.50

MoSiOx (5.4 wt%)

868

3.7

0.95

The nice features qualify MoSiOx talent catalyst for bulky chemicals processing as hydrodesulfurization (HDS). HDS conversion of diesel on MoSiOx with 3.3 wt% Mo content is 80%, which is a bit higher than that of Y-AI2O3 with the same Mo loading, the remained sulfides are mainly multi-alkyl substituted especially of 4, 6-alkyl substituted naphthalene components. 4. Conclusion The paper presents an original method for MoSiOx synthesis in strong caustic medium with HAcac introduced. Through method established, Mo loading of MoSiOx is higher than or equivalent to the reported best and much higher than those prepared in basic media. Promoting precipitation and enlarging pore size qualify HAcac significant additive in the present method, and its effects on insertion of other transitional metal species are under investigation. 5. Acknowledgment Acknowledge for supporting of NSFC project (No. 20406012), National Basic Research Program of China(2004 CB 217806) and CNPC project (05E7019). 6. References [1] Z. Zhang, J. Suo, X. Zhang and S. Li, Chem. Commun, 2 (1998) 241. [2] F. Somma and G. Strukul, J. Catal., 227 (2004) 344. [3] J. Y. Piquemal, J. M. Manoli, P. Beaunier, A. Ensuque, P. Tougne, A. P. Legrand and J. M. Bregeault, Micropor. Mesopor. Mater., 29 (1999) 291. [4] J. Y. Piquemal, E. Briot, G. Chottard, P. Tougne, J. M. Manoli and J. M. Bregeault, Micropor. Mesopor. Mater., 58 (2003) 279 [5] R. K. Rana and B. Viswanathan, Catal. Lett. 52 (1998) 25. [6] M. Zioleka, I. Nowaka, B. Kilos, I. Sobczak, P. Decyk, M. Trejda and J. C. Voltab, J. Phys. Chem. Solids. 65 (2004) 571. [7] D. Kumar, and K. Schumacher, et al. Colloid. Surf. A: Physicochem. Eng. Aspects 187-188(2001) 109.

Recent Progress in Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Published by Elsevier B.V.

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Birch templated synthesis of macro-mesoporous silica material for sustained drug delivery Huiming Lin a , Fengyu Qu a>b, Shiying Huang a , Guangshan Z h u a and Shilun Qiu a '

State Key Laboratory for Inorganic Synthesis and Preparative Chemistry, Jilin University, Changchun 130023, China Chemistry Department of Harbin Normal University, Harbin, 150025, China.

The hierarchical porous silica material with the structure of macropore and ordered hexagonal mesopore was prepared using birch as hard template and PI23 as soft template, respectively. The products remain the morphology and the macropore structure of birch and the wall was replaced by ordered mesoporous silica. The hierarchical porous silica was characterized by scanning electron microscope, powder x-ray diffraction, transmission electron microscope and nitrogen adsorption/desorption. The drug store and controlledrelease using the products as drug carrier have been investigated. Ibuprofen (IBU) was employed as a model drug and the release profiles showed that the hierarchical porous material can be served as a sustained drug delivery system. 1. Introduction Recently, several groups have tried to use biological templates to synthesize hierarchical porous materials with two or more level and complex morphologies [1]. This kind of materials may improve diffusion and transport of large molecular through the macro- pores and channels; meanwhile high surface areas and large pore volumes provided by meso-pore may be beneficial to larger loading amount of guest molecules [2, 3]. Compared to the artificial templates, biological templates have the characteristics of low-cost, abundant, renewable, environmental friendly and inherent complex structure, which make it possible to synthesize materials with unique multilevel structures and complex morphologies [4-6]. Liu and co-workers reported the mineralization of wood tissue which can form a silica replica with the cellular structures of poplar and pine [7]. 3D

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microscale metallic materials exhibited elaborately detailed and nanometerscale features have been synthesized using diatom as template by direct fabrication method [8]. Synthesized porous micron-sized particles of silica, calcium carbonate, and calcium phosphate with complex morphologies employed pollen grains as direct template have been reported by Mann and coworks [9]. Ogasawara et al. proposed that cuttlebone P-chitin with macroscopic porosity can be used as a highly organized organic template to prepare analogous silica-polysaccharide with 3-D interconnected box structures [10]In this paper, Bio-template (birch) and surfactant PI23 were employed as dual template to synthesize hierarchical porous material. The morphology of the birch has been remained perfectly and the macro-mesopore structure has been obtained. Additionaly, Ibuprofen delivery profiles had been studied by using this hierarchical porous material as drug carrier. 2. Experimental Section The hierarchical porous silica material with the structure of macropore and ordered hexagonal mesopore was prepared using birch as hard template and PI23 as soft template respectively under acidic system. In a typical procedure, 0.9 g P123 was dissolved in the mixed solution of 10 g EtOH, 0.1 g hydrochloric acidic (2 M HC1) solution and 0.8 g deionized water. To above mixture, 2.08 g TEOS was added under stirring. After stirring 2 h at room temperature, several pieces of birch were soaked in the solution and kept at 60°C for 3 days in unsealed polythene container. Finally, the samples were taken out from the solution, air dried and calcined at 550°C for 6 h in room air. The loading of the drug was carried out by immersing the sample (217 mg) in a hexane solution of IBU (10 mL, 0.1 M) and stirred for 2 h at room temperature. The IBU-loaded sample was separated from the solution by vacuum filtration, and dried at room temperature. The loading amount was determined by UV/VIS spectrophotometry. The drug-loaded sample was compressed into a tablet with a diameter of 10 mm and a thick of 0.5 mm. The release rate was obtained by soaking the drug tablets in a solution of simulated intestinal fluid (pH = 6.8 aqueous) maintained at 37°C. At predetermined time intervals, samples (3 mL) were withdrew and immediately replaced with an equal volume of solvent to keep the volume constant. These samples were filtered (0.45 um), diluted, and analyzed for BIU content at 221nm using a GBC-10/20 UV/VIS spectrophotometer. Powder XRD data was collected on a SIEMENSD5005 diffractometer with CuK a radiation at 40 kV and 30 mA. The nitrogen adsorption/desorption, surface areas, and median pore diameters were measured using a Micromeritics ASAP 2010M sorptometer. Before measurement at 77 K, the samples were degassed at 373 K. for 12 h. Specific surface areas and pore size distributions were calculated using the Brunauer-Emmett-Teller (BET) and Barrett-JoynerHalenda (BJH) model from the adsorption branch, respectively. UV-VIS spectra

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were taken on a Lambda 20 spectrophotometer. SEM Micrographs were performed using JEOL-JSM-6300 operating at an accelerating voltage of 2030 kV. TEM image was recorded on JEOL 2010 F and Philips CM200 FEG with an acceleration voltage of 20 kV. 3. Results and Discussion Fig.l shows low angle X-ray diffraction (XRD) pattern for hierarchical porous material using PI23 and birch as templates, which exhibits a strong diffraction peak at 29 = 0.9, indicating that the ordered mesopore structure have been obtained. The morphologies of the bio-template (birch) and the sample the sample 0 11 2 2 3 4 5 6 calcined are revealed by SEM. Fig. 2a, 2 Theta 2b shows that the birch has tubular cross structure, and the di-ameter of the tube is ca. lum. The hierarchical pore material Fig. 1 Low-angle of XRD of birch with surfactant after calcination has re-mained the birch morphologies completely. It can be observed clear-ly that the size of the macro-pore is ca. 1 um from the SEM image (Fig. 2c). The nitrogen adsorption/desorption isotherms and corresponding pore size distribution of the sample are shown in Fig. 3. It yields a type IV isotherm with HI-type hysteresis, which is a typical c characteristic of mesoporous material with hexagonal cylindrical channel. Compared with common mesoporous material (SBA-15) synthesized at similar condition, the BET surface areas (293.85 m2g"'), and pore volumes (0.4835 cm3g"1) decreased somewhat, which may be due to the existing of macropore. The pore Fig. 2 SEM image of birch (a, b), surfactantdiameter is about 5.2 nm, calculating templated birch sample after calcination (c) from the BJH method of mesopore size analysis to the adsorption branch of the nitrogen isotherm. TEM image shows that the sample still possesses ordered hexagonal mesoporous structure (Fig. 4). The pore size observes from image is about 5.5 nm, which is consistent with the results of XRD and nitrogen adsorption/desorption.

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The cumulative release rate is shown in Fig. 5. The diagram clearly proves the system exhibits sustained-release profile. Only 10 wt% of IBU released within 1 h, and it took 8 and 28 h to reach 40 wt% and 60 wt% drug releasing. Compared to the releasing rate of IBU from SBA-15 (Fig. 6), the release rate of IBU from the hierarchical porous material has more sustained releasing behavior. 60 60

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This may be due to the delivery of the drug from hierarchical porous carrier may take two steps: (i) drug released from mesopore to the macropore; (ii) drug released from macropore to the outside. As the drug releasing from mesopore to macropore, the macroporous structure played a role of alleviator, which slowed the release rate of the drug. The concentration of the drug may have a homeostasis between the macropore and releasing media. Consequently, the drug could not release completely, and the final release amount could only reach 60 wt %.

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4. Conclusion We have demonstrated a feasibility method to synthesize hierarchical porous silica material with the structure of ordered hexagonal mesopore and macropore, using PI23 and birch as templates. The structure and morphology of birch have been replicated perfectly. And the material has sustained drug delivery profile. 5. Acknowledgement This work was supported by the National Natural Science Foundation of China (Grant Nos. 20571030, 20531030, 29873017 and 20101004), and the State Basic Research Project (G2000077507 and 2003CB615802). 6. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10]

Z. Y. Yuan, B. L. Su and J. Mater. Chem., 16(2006)663. N. Stachoqiak, A. Bershteyn, E. Tzatzalo and D. J. Trvine, Adv. Mater., 17 (2005) 399. P. Sepulveda, J. R. Jones and L. L. Hecfh, J. Bio. Mater. Research, 59 (2002) 340. J. Zhang, S. A. Davis and S. Mann, chem. commun., (2000) 781. V. Valtchev, M. Smaihi and L. Vidal, Argew. Chem. Int. Ed., 42 (2003) 2782. F. C. Meldrum and R. Seshadri, Chem. Commun., 29 (2000). Y. S. Shin, J. Liu and G. J. Exarchos, Adv. Mater., 137 (2001) 29. E. K. Payne, N. L. Rosi and C. A. Mirkin, Angrew. Chem. Int. Ed., 44 (2005) 5064. S. R. Hall, H. Boleger and S. Mann, Chem. Commun., (2003)2784. W. Ogasawara, W. Shenton and S. Mann, Chem. Mater., 12 (2000) 2835.

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Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

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Synthesis of metal-doped mesoporous silica by spray drying and their adsorption properties of water vapor Akira Endo *, Yuki Inagi, Satoko Fujisaki, Takuji Yamamoto, Takao Ohmori and Masaru Nakaiwa National Institute of Advanced Industrial Science and Technology (A 1ST), Research Institute for Innovation in Sustainable Chemistry Tsukuba Central 5, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8565, Japan.

1. Introduction Ordered mesoporous silicate(MPS) templated by surfactant molecular assemblies have been attracted much attention because of their potential applications as catalysts, adsorbents, molecular sieves, sensors, etc. [1] The Evaporation Induced Self Assembly (EISA) technique is one of the most promising process for the large scale synthesis of ordered mesoporous materials, because of some advantages over the hydrothermal synthesis such as short synthesis time, easiness of controlling silica/metal ratio, possibility of continuous synthesis etc. Some reports on the synthesis of ordered mesoporous materials using spray-drying process, which is a kind of EISA process, have been published, reporting the synthesis conditions and their influence on the porous structure and morphology [2-5]. However, there is no paper describing the metal incorporation into silica network, which is important for the practical application of MPS materials. For example, Bruinsma reported the possibility of Al into silica network by spray-drying [2]. However, the Al was not retained after calcination to remove the templates. In the present study, metal-doped MPS with hexagonal array of cylindrical pores were synthesized by spraydrying using ethanol as a solvent and their water adsorption were investigated. 2. Experimental Section TEOS and C,,TAC (« = 10 - 18) were dissolved into ethanol, where n represents the number of carbon atoms composing the alkyl chain of

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alkyltrimethylammonium chloride (C«TAC). After HC1 aqueous solution (10"3 M) and metal source(ZrO(NO3)2 • 2H2O and A1(NO3)3' 9H2O) was added to the mixture, obtained solution was stirred at room temperature for 1 hour to hydrolyze the TEOS. The typical molar ratio of the starting solution was 1 0.95 TEOS : 0 - 0.05 metal : 0.2 CnTAC : 10 EtOH : 1.8 X 10'4 HC1 : 10 H 2 O. The solution was then transferred to a round-bottom flask and evaporated using a vacuum rotary evaporator at 70 hPa for 0.7-1 h. Then, the solution was spray dried using the spray dryer GS310 (Yamato Kagaku Co. Ltd.). The inlet temperature was 433 K and the gas pressure was 0.075 MPa. The resulting solid, a silica-surfactant composite, was calcined at 873 K for 5 h to remove the surfactant. XRD and nitrogen adsorption/desorption measurements were carried out for the characterization of the metal-doped mesoporous silicas. XRD measurements were performed using a Rigaku Miniflex diffractometer (Cu/Ka radiation, operated at 40 kV and 30 mA). The nitrogen adsorption/desorption isotherm was measured using Belsorp-mini, fully automatic adsorption isotherm measuring equipment (manufactured by BEL Japan, Inc.). The pre-treatment was carried out at 573 K for 5 h under a nitrogen atmosphere. The state of metal incorporated into silica network was investigated by XPS measuremt using Shimadzu ESCA-1000). The acid sites of metal-doped samples was measured by temperature programmed NH 3 desorption (NH3-TPD) using BELCAT(manufactured by BEL Japan, Inc.). 3. Results and Discussion

Intensity / a.u.

All the samples except the 5% Aldoped sample were obtained in the 5% Zr shape of dried powder after the spray-drying. The 5% Al-doped 5% Al sample was not sufficiently dried in our experimental condition described 1% Zr above and resulted in relative large particle size. The XRD patterns of pure silica and Al and Zr-doped 1% Al mesoporous silica tem-plated by pure silica Ci6TAC are shown in Fig. 1. The diffraction peaks indicate that the 2θ /degree 2θ/degree samples have periodic mesostructure with hexagonal array, although the Fig. 1 The XRD patterns of metal-doped peaks of metal-doped samples MPS powder synthesized by spray-drying. broaden-ed with increasing the Al and Zr amount. The same results were obtain-ed for the other samples templated by the different surfactants, although it is not described here. We confirmed the metal incorporation into the silica network by SEM/EDX and XPS measurements. The state of metal species for all samples was not metallic 2

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but oxidized. For example, the O Is XPS of 1%-Zr-doped sample can be attributed to two types of oxygen, Si-O-Si(533.0eV) and Si-O-Zr(531.1eV) [6]. From the N2 adsorption measuremts at 77K, the BET surface area(SBET) of all samples are over 1150 m2/g. The most common pore size(dp) for the metaldoped mesoporous silicas decreased with increasing the metal amount. The pore structural parameters are summarized in Table 1. Table 1 Porous properties of synthesized mesoporous silica

Metal

Sample (mol%)

Zr Zr Al Al

dioo

dp

(nm) 3.85 3.38 3.27 3.34 3.07

(nm) 3.40 2.92 2.66 2.91 2.37

vP (ml/g) 0.90 0.75 0.64 0.75 0.58

dw (nm) 1.05 0.99 1.12 0.95 1.17

SBET

(m2/g) 1154 1155 1176 1178 1286

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Fig. 2 Adsorption/desorption isotherms of water vapor : (a) pure silica, (b)l% Al-doped silica, (c) 1% Zr-doped silica; before ( • )and after(#) the water vapor treatment at 373 K for 24 h.

The water adsorption isotherms at 298K were measured using a Belsorp 18-3, fully automatic adsorption isotherm measurement instruments (manufactured by BEL Japan, Inc.). The pre-treatment was carried out at 573 K for the first measurement and 413 K for the second measurement for 8 h under a pressure of 2 Pa. For evaluating the durability of the samples, the synthesized silicas were not exposed to water directly, but rather were exposed to water vapor in an autoclave at 373 K for 24 h. After this water vapor treatment, the adsorption characteristics of the samples were examined. Fig. 2 shows the water adsorption isotherms before and after the steam treatment for 1%-metal-deoped samples. The shape of adsorption/desorption isotherms for 5%-metal-doped samples (not shown here) were almost identical.

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The shapes of all the water adsorption isotherms were Type V of IUPAC classification with a hysteresis loop. The metal-doped samples adsorbed more water at the lower relative humidity region and the relative pressure where the steep increase in the amount of adsorbed water due to the capillary condensation occurred at lower relative humidity region, compared to the pure silica sample. The existence of acid sites, which influence the surface hydrophilic/hydrophobic properties, on the pore surface for the metal-doped samples was confirmed by the NH3-TPD measurement. This indicates the metal-doped samples posses a stronger hydrophilic nature than the pure silica sample. The pore structure of pure silica (Figure 2(a)) collapsed during the steam treatment, decreasing the BET surface area andthe capillary condensation observed before the steam treatment disappeared. On the other hand, no significant change was observed in the shape of adsorption isotherms of the metal-doped mesoporous silicas(Figure 2(b) and (c)) after the steam treatment, indicating an increase in the stability of these materials in the presence of water vapor. These results clearly show the successful incorporation of metal atoms into silica network, although the incorporation mechanism should be investigated. 4. Conclusion Highly ordered, metal-doped MPSs were successfully synthesized by spraydrying. This synthesis method can easily introduce metals into silica materials in comparison with a hydrothermal synthesis, and can be easily scaled-up as required. The metal-doped samples showed more hydrophilic properties at a lower relative humidity and higher durability towered water vapor. The water adsorption/desorption isotherms, XPS and NH3-TPD measuemts indicated, ithe successful incorporation of Al and Zr atoms into silicate network. This method also can be applied for the synthesis of other kinds of metal-doped MPSs, if an appropriate metal source is used. 5. References [1] C. T. Kresge, M. E. Leonowicz, W. J. Roth, J. C. Vartuli and J. S. Beck, Nature, 359 (1992) 710.

[2] P. J. Bruinsma, A. Y. Kim, J. Liu and S. Baskaran, Chem. Mater., 10 (1997) 2507. [3] N. Baccile, D. Grosso, C. Sanchez and J. Mater. Chem., 13 (2003) 3011. [4] N. Andersson, P. C. A. Alberius, J. S. Pedersen and L. Bergstrom, Micropor. Mesopor. Mater., 72 (2004) 175. [5] B. Alonso, C. Clinard, D. Durand, E. Veron and D. Massiot, Chem.Commun., (2005) 1746. [6] D. J. Jones, J. Jimenez-Jimenez, A. Jimenez-Lopez, P. Marireles-Torres, P. Oliverra-Pastor, E. Rodriguez-Castellon and J. Roziere, Chem.Commun., (1997) 431.

Recent Progress in Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Published by Elsevier B.V.

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Structural characterization and systematic gas adsorption studies on a series of novel ordered mesoporous silica materials with 3D cubic Ia-3d structure (KIT-6) Freddy Kleitz*a, Chia-Min Yangb and Matthias Thommes*0 "Universite Laval, Department of Chemistry, Quebec G1K 7P4, Canada, Department of Chemistry, National Tsing-Hua University, Hsinchu, Taiwan. ''Quantachrome Instruments, 1900 Corporate Drive, Boynton Beach, FL 33426

We present the results of systematic gas adsorption experiments and an advanced structural characterization of novel ordered mesoporous silica materials with 3-D cubic Ia-3d structure (KIT-6). The pore condensation and hysteresis behavior of nitrogen (at 77.4 K) and argon (at 77.4 and 87.3 K) was studied in KIT-6 materials of different porosities and various mean pore diameters (ranging from ~ 5 nm up to 12 nm). We compare further the sorption and phase behavior of nitrogen and argon confined to this 3D cubic porous system with their behaviour in pseudo-ID pore systems (e.g. SBA-15 silica). Our results also shed light on the extent to which the so-called single pore model can be used for the pore size analysis of materials consisting of ordered pore networks. 1. Introduction Recently, a novel type of large-pore mesoporous silica with a cubic Ia-3d structure was synthesized by using a blend of triblock copolymer Pluronic PI23 and H-butanol as a structure-directing mixture [1,2]. This mesoporous silica material is composed of two interwoven mesoporous networks similar to MCM48, but can be synthesized with much larger mean pore diameters. In addition to potential applications in catalysis, adsorption, separation etc, these novel silica materials have the potential to serve as model substances for evaluating the details of the adsorption and phase behaviour of fluids in highly ordered pore

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networks. Even though a lot of progress was achieved in the understanding of the sorption and phase behaviour of fluids in materials consisting of single pores (e.g. MCM-41) [ref. 3 and references therein], the investigation of pore condensation and hysteresis in pore networks is still under investigation [3,4]. To address this problem we performed, in addition to a structural characterization (by various techniques including XRD and gas adsorption), systematic gas adsorption experiments of pure fluids in a series of highly ordered mesoporous 3D silica materials of different porosities and mean pore size. 2. Materials and Experimental The mesostructured silica materials were prepared according to refs. [1,2] using Pluronic PI23 (EO20PO70EO20) and «-butanol as a structure-directing mixture, with TEOS as the silica source. This method has the advantage of being simple and highly reproducible in large quantities. The molar composition of the starting reaction mixture is TEOS/P123/HCl/H2O/BuOH = 1/0.017/1.83/195/1.31 in mole ratio. The reaction temperature is fixed at 35°C for 24 hours and the hydrothermal aging temperature varied from 50 to 130°C for 24 hours more. For comparison, different 2-D hexagonal SBA-15 samples were synthesized following the method proposed by Choi et al. [5]. Powder Xray diffractograms of the calcined samples were recorded on a Stoe STADI P 99 X-ray diffractometer in reflection geometry (MPI fur Kohlenforschung, Miilheim, Germany). High resolution nitrogen (77.4 K) and argon (77.4 K, and 87.3 K) adsorption/desorption isotherm measurements were performed with an Autosorb-I-MP adsorption instrument (Quantachrome Instruments, Boynton Beach, FL) in the relative pressure range from 1 x 10"6 to 1. 3. Results and Discussion In this study, we report (i) results of the structural characterization and (ii) a systematic study of pore condensation and hysteresis phenomena in a series of highly ordered mesoporous 3-D silica materials of different porosities and various mean pore diameters (ranging from ca. 5 nm up to 12 nm). In this short paper we can only present some characteristic results; extensive data are presented in [6]. The XRD patterns of the cubic mesoporous materials indicate excellent structural order with the symmetry being commensurate with the body-centred cubic Ia-3d space group. Fig. la illustrates the XRD pattern measured for a sample synthesized with the hydrothermal step performed at 130°C for 24 hours. The exact assignment to the Ia-3d symmetry for the materials was confirmed by transmission electron microscopy and is reported elsewhere [1,7]. Importantly, highly resolved XRD patterns as well as electron microscopy studies suggest no structural distortion. The unit cell size, calculateed from the 211 reflexion of the cubic Ia-3d phase, is measured to be 24.1 nm

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for the calcined material prepared with aging at 130°C. This is a value substantially larger than the unit cell parameter of other cubic analogues (e.g. MCM-48 [8]). The high degree of structural order of this material is also demonstrated in the gas adsorption data. Some characteristic adsorption results for a Ia-3d material with a (mode) pore diameter of ~ 10 nm (aged at temperatures above 100°C) are shown in Figures 1-2. Figure l(b) reveals argon and nitrogen adsorption data at 77.4 K for Ia-3d silica obtained at 130°C. The high degree of order for this sample is clearly evident from the almost vertical adsorption/desorption branches of the HI hysteresis loop. Figure 2(a) shows an argon sorption isotherm obtained over a wide range of rel. pressures, i.e. 10"6 to 1, sensing the micro-, meso- and macropore ranges of this sample. The argon (87 K) and nitrogen (77 K) isoherms were used to calculate the pore size distribution with proper NLDFT methods, and in both cases, the NLDFT equilibrium transition kernel was applied to the desorption data. 1200

130°C Inte nsi ty ( a.u.)

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Fig. l(a) Powder XRD pattern of the Ia3d KIT-6 silica sample prepared with aging at 130°C. (b) Nitrogen and argon adsorption at 77.35 K on this Ia-3d silica.

The argon and nitrogen pore size distribution curves agree very well as clearly revealed in Fig. 2(b). Moreover, the NLDFT mode pore diameter of 10.13 nm (calculated from the nitrogen desorption branch) is in very good agreement with the pore diameter (10.05 nm) obtained by using a geometrical model based on unit cell (unit cell: 24.1 nm), and wall thickness (2 nm) parameters as derived from the XRD data [9].

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Fig. 2 (a) Semilogarithmic plot of an argon adsorption/desorption at 87.3 K on Ia-3d silica (aged at 130°C) measured over a wide rel. pressure range from 10"6 to 1 (b) NLDFT pore size distributions from argon (87 K) and nitrogen (77 K).

The good agreement between the pore size data obtained with the NLDFT method and the geometrical approach indicates that the independent pore model (which has been confirmed for pseudo 1 -D pore systems such as MCM-41 and SBA-15) appears also to be applicable to this KIT-6 sample. However, a detailed study on a series of KIT-6 and SBA-15 silica's (pore diameter range from ca. 5 to 12 nm) suggests that there are differences in the hysteresis behavior of SBA-15 and KIT-6 materials in the pore diameter range < 9 nm. The hysteresis loop for KIT-6 is slightly (but clearly detectable) narrower as compared to appropriate SBA-15 samples. These differences in the width of hysteresis between SBA-15 and KIT-6 vanish for pore diameters > 9 nm. Details of these results and their interpretation are described elsewhere [6]. 4. References [1] F. Kleitz, S. H. Choi and R. Ryoo, Chem. Commun. (2003) 2136. [2] T.-W. Kim, F. Kleitz, B. Paul and R. Ryoo, J. Am. Chem. Soc. 127 (2005) 7601. [3] M.Thommes, in Nanoporous Materials; Science and Engineering; G. Q. Lu, X. S. Zhao, Eds.; Imperial College Press: London, U.K., (2004) 317. [4] M. Thommes, B.Smarsly, M.Groenewolt, P. I. Ravikovitch and A. V. Neimark, Langmuir 22(2006) 756. [5] M. Choi, W. Heo, F. Kleitz and R. Ryoo, Chem. Commun. (2003) 1340. [6] F. Kleitz, C. M. Yang and M. Thommes, manuscript in preparation, (2006). [7] Y. Sakamoto, T. W. Kim, R. Ryoo and O. Terasaki, Angew. Chem. Int. Ed. 2004,43, 5231. [8] M. S.Morey, A. Davidson and G. D. Stucky, J. Porous Mater. 5 (1998) 195. [9] XRD modeling was performed according to L. A. Solovyov, et al. J. Phys. Chem. B, 109(2005)3233.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

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Synthesis and characterization of mesoporous MCM-41 silica with thick wall and high hydrothermal stability under mild base solution Chi-Feng Cheng,* Po-Wen Cheng , Shu-Hsien Chou, Hsu-Hsuan Cheng and Hwa Kwang Yak Department of Chemistry, Center ofNanotechnology and R&D Center for Membrance and Technology, Chung Yuan Christian University, 200, Chung Pei Rd., Chung Li, Taiwan 32023, China

Abstract Siliceous MCM-41 mesoporous materials with wall thickness up to 36 A could be prepared at 165°C for 7 days under mild basic solution. More than 85% of surface area for these materials was retained even after hydrothermal treatment in boiling water inside autoclave for 14 days. A reasonable model explaining formation of thicker MCM-41 wall, not enlarging pore channel, is proposed. Thermal restructuring process under mild basic condition favors the silica redeposition on silica wall and building up thicker wall. 1. Introduction Low hydrothermal stability restricts practical applications of mesoporous molecular sieve MCM-41. The introduction of Al on the surface or into the framework of MCM-41 results in the remarkable improvement of hydrothermal stability of MCM-41 [1]. The most promising method for improving the hydrothermal stability of aluminosilicate mesoporous materials was using the aluminosilicate zeolitic nanoclusters as a raw material to build up mesostructure [2-5]» However, the improvement of mesoporous silica hydrothermal stability is still developing. Thermal and hydrothermal stabilities of a wide range of mesoporous silica have been studied by Cassiers et al. [6] They concluded that the thermal and hydrothermal stability were strongly related to the wall thickness. Ryoo et al. [7] considered that the wall-thickening approach appears to be the simplest one among these techniques, but no completely synthetic strategies have yet been found for systematic control of the wall thickness. Here, we report that the wall

166 166

thickness can be controlled systematically up to 36.1 A simply by increasing crystallization time to 1 ~ 7 days at 150 ~ 180°C at mild basic condition. 2. Experimental Section The siliceous MCM-41 was prepared as follows. Tetramethylammonium hydroxide (TMAOH) and cetyltrimethylammonium bromide (CTABr) were added to deionized water with stirring at room temperature. Fumed silica was added to the solution with stirring and then aged for 24 h at room temperature. The final gel of composition 1 SiO2: 0.19 TMAOH : 0.27 CTABr : 40 H2O was transferred to a Telflon-lined stainless steel autoclaves at 150 ~ 180°C for 1 ~ 7 days. The reaction product was filtered, washed with distilled water, dried in air at 110°C and calcined at 550°C for 8 h. Hydrothermal stability of the MCM-41 was studied by mixing 0.5 g of calcined samples with 50 g of deionized water, sealing in the closed glass bottles and heating at 100°C for 1 ~ 28 days. The parent samples without hydrothermal treatment are designated MCM-x-yd where x, y respectively are the crystallization temperatures at °C unit and time in days. Samples after hydrothermal treatment for z days are designated MCMx-yd-zd. These materials were characterized by XRD, N2 adsorption/desorption measurement, TEM, solid state NMR and TGA. 3. Results and Discussion Previous studies [8] have shown that the di0o spacing increased sharply when crystallization time increased from 1 to 48 h at 165°C. XRD patterns of sample crystallized for 2 days show a very intense (100) diffraction peak and four additional 110, 200, 210, 300 peaks. This suggests that MCM-165-2d sample has a long ordering of hexagonal pore arrays. However, the d\Oo spacing increases slightly from 58.1 to 61.4 A when crystallization time increases from 2 to 7 days. When the crystallization time increases gradually from 2 to 7 days, 110, 200 diffraction peaks of samples are gradually weakening and 210, 300 peaks progressively disappear (not shown). N2 sorption isotherms of above all samples without hydrothermal treatment exhibit a sharp adsorption/desorption hysteresis (not shown) and indicate that all samples possess good structural ordering and a narrow pore size distribution. Corresponding results are summarized in Table 1. It is shown that the increase of wall thickness results from a slight increase of unit cell and gradual decrease of pore size. Wall thickness increases systematically from 23.3 to 36.1 A as a result of increasing crystallization time from 1 to 7 days at 165°C at the expense of decrease of surface area and pore volume. It is probably that more silica source is used to build thick wall instead of high surface area and pore volume. To our best knowledge, the 36.1 A wall thickness of siliceous MCM-41 reported herein has not been described before. It is also noticed that surface MCM-41 with the wall thickness of 36.1 A prepared at 165°C for 7 days shows outstanding hydrothermal stability as compared to those prepared at 180 and 150°C for one or two days from the X-ray data in Fig. 1. Relative XRD

167 167

intensity of MCM-41 synthesized for different time at 165°C after hydrothermal treatment for 1 to 28 days and relative surface area of those samples are shown in Fig. 2. MCM-165-7d after 7 days of hydrothermal treatment at 100°C reserves 62% of 100 X-ray peak intensity and 90% of surface area as compared to original MCM-165-7d in Fig. 2. After further hydrothermal treatment for two weeks, MCM-165-7d-14d still has 52% of 100 X-ray peak intensity and 90%of surface area. The sharp hysteresis loop of adsorption/desorption and narrow pore size distribution for MCM-165-7d-14d illustrate that most mesostructure of calcined MCM-41 with ultra-thick wall is retained even after hydrothermal treatment at 100°C for 14 days (not shown). However, mesostructure of MCM165-7d after 3 or 4 weeks of hydrothermal treatment is disintegrated gradually. It is interesting that 26 % of 100 X-ray peak intensity is retained but the surface area is only 6.6 m2/g for MCM-165-7d-28d .

MCM-165-7d-7d

1.0 1.0

1.0 01.0

0.8

0.8

0.6

0.6 rO.eg

0.4

0.4 0.4 0

(0

(0

MCM-165-7d-14d
3

4

5

DC

6

Fig. 1 XRD patterns of calcined MCM-41 prepared at 165°C for 7 days and after hydrothermal treatment at boiling water for 1 to 28 days.

Relative Surface area (A/A0)

MCM-165-7d-4d MCM-165-7d-4d

Relative X-ray Intensity (I/Io)

MCM-150-2d-1d MCM-150-2d-1d

0.2

0.0

0.2

- .2 Relative Relative X-ray \ Intensity -•— Relative Surface area area 0

4

8 12 12 16 16 20 24 Treatment time (days) (days)

0.0 e0.0 28

Fig. 2 Relative XRD intensity and relative surface area of MCM-41 synthesized for MCM-41 prepared for 7 days at 165°C after hydrothermal treatment for 1 to 28 days compared to samples without hydrothermal treatment.

The excellent hydrothermal stability of MCM-41 obviously is related to its ultra-thick wall thickness as a result of greater silica condensation after prolonged crystallization time from 2 to 7 days at 165°C. This is evidenced by the Si MAS NMR spectra (not shown), which show the Q /Q ratios are gradually enhanced from 2.2 to 4.6. A reasonable model explaining formation of thicker MCM-41 wall, not enlarging pore channel is proposed on the basis of TGA and C MAS NMR data of samples. The increase in wall thickness is most likely because thermal restructuring process involves silica dissolution, transport, redeposition in inner pore wall and facilitates pore wall thickening under mild basic condition. Ozin et al. and Corma et al. [11,12] showed that

168 168

crystallization of MCM-41 silica at high temperature of 150°C for longer reaction time could increase pore size up to 66 A but the wall thickness is less than 10 A at high basic concentration of 1.7 m [9] and 0.6 m [10]. It is probable that the crystallization in higher basic condition favors dissolution of silica wall, enlargement of pore channels, and disfavors condensation of silica on inner pore wall. Tablel Structural parameters of MCM-41 crystallized at 150, 165, 180°C for 1 to 7 days and after hydrothermal treatment at 100°C for 1 to 28 days. Code of Samples

dioo

Da/A

(A)

Wb

Vtc

ABETd

Q 4 /Q 3

1

/A

/cmy

/my

MCM-165-2d

58.1

43.6

24.1

0.7

617

2.5

MCM-165-3d

59.3

40.6

27.7

0.67

570

3.1

MCM-165-5d

60.9

37.4

32.9

0.52

460

3.7

MCM-165-7d

61.4

34.8

36.1

0.42

392

4.6

MCM-165-7d-4d

61.4

34.3

36.6

0.37

353

MCM-165-7d-7d

63.1

33.3

36.5

0.36

348

MCM-165-7d-14d

62.2

32.5

39.6

0.35

345

MCM-150-2d

43.7

30.2

20.3

1.01

1023

0.54

267

MCM-150-2d-ld MCM-180-ld

57.0

40.5

25.3

0.65

486

MCM-180-ld-4d

69.6

36.3

30.8

0.61

356

1.5

" BJH pore diameter calculated from the adsorption branches. * wall thickness (W = a0- D). c total pore volume. d BETsurface area.

4. References [1] S. C. Shen and S. Kawi, Langmuir, 18 (2002) 4720. [2] Y. Li, J. Shi, Z. Hua, H. Chen, M. Ruan and D. Yan, Nano. Letters, 3(2003) 609. [3] Z. Zhang, Y. Han, F.-S. Xiao, S. Qiu, L. Zhu, R. Wang, Y. Yu, Z. Zhang, B. Zou, Y. Wang, H. Sun, D. Zhao and Y. Wei, J. Am. Chem. Soc, 123(2001) 5014. [4] Y. Liu and T. J. Pinnavaia, Chem. Mater., 14 (2002) 3. [5] D. Li, D. S. Su, J. Song, X. Guan, K. Hofmann and F. S. Xiao, J. Mater. Chem. 15 (2005) 5063. [6] K. Cassiers, T. Linssen, M. Mathieu, M. Benjelloun, K. Schrijnemakers, P. Van Der Voort, P. Cool and E. F. Vansant, Chem. Mater., 14 (2002) 2317. [7] J. M. Kim, S. Jun and R. Ryoo, J. Phys. Chem. B., 103 (1999) 6200. [8] C.-F. Cheng, W. Zhou and J. Klinowski, 1996, Chem. Phys. Lett. 263, 247. [9] D. Khushalani, A. Kuperman, G. A. Ozin, K. Tanaka, J. Graces, M.M. Olken and N. Coombs, Adv. Mater., 7 (1995) 842. [10] A. Corma, Q. Kan, M. T. Navarro, J. Perez-Pariente and F. Rey, Chem. Mater. 9 (1997) 2123.

Mesostructured Materials Recent Progress in Mesostructured D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

169 169

A facile synthesis of MCM-41 by ultrasound irradiation Alina-Mihaela Hanuab, Eveline Popovici3*, Pegie Coolb and Etienne F. Vansantb "Department of Physical and Theoretical Chemistry and Materials Chemistry, "Al. I. Cuza" University oflasi, Bvd. Carol I, no 11, 700506, Romania Laboratory of Adsorption and Catalysis, University of Antwerpen, Universiteitsplein 1, B-2610 Wilrijk, Belgium

1. Introduction Ultrasonic irradiation has been introduced in the preparation of a variety of material synthesis, due to its special acoustic cavitation effect. This effect creates special stirring conditions, high-temperature and high-pressure in solution [1]. Generally, the sonochemical method is faster than the corresponding sol-gel preparation technique [2]. Recently, great efforts have been dedicated to improve the synthesis of mesoporous MCM-41 in view of lowering the temperature, shortening the crystallization time as well as controlling the particle size and morphology [3]. Our work was focused on the study of the ultrasonic irradiation influence on the MCM-41 synthesis in acidic and basic conditions. We evaluated the ultrasound effect on particle size, porosity, specific surface area and adsorption properties. 2. Experimental Section The raw materials: tetraethoxysilane-as silica source, cethyltrimethylammonium bromide (99%) as template, NaOH (2M) and HC1 (37%) were purchased from Acros. For ultrasound-assisted synthesis a Branson 3510EMTH ultrasound bath with (42 ± 6%) kHz frequency and 350 W power was used. The initial mixtures having the compositions:5SiO2:lCTAB:10HCl:500H2O (A) and 8.33SiO2:lCTAB:2.08Na2O:l 133.33H2O(B) with pH = 1 and pH = 12, respectively, were used. After vigorous stirring at room temperature for lh, half part of each composition was crystallized at 40°C, as reference samples (SA and

170 170

SB) and the other half was subjected to ultrasonic irradiation at 40°C (SAU and SBU). The obtained samples were filtered, washed with deionized water, dried and calcined in a programmable oven at 550°C, for 6 h, in air, with a heating rate of 1°C /min. The ultrasounded samples (SAU and SBU) and reference samples (SA and SB) were characterized using XRD, N2 isotherms and SEM. The X-ray diffractions were recorded on a Philips PW 1830 powder diffractometer (45 KV, 25 mA), using Ni filtered Cua (0.154 nm) radiation. N2 sorption measurements were performed on a QUANTACHROME Autosorb 1MP automated gas adsorption system using nitrogen as the absorbate at liquid nitrogen temperature (-196°C). The pore diameter was obtained from the adsorption branch using the BJH method. The specific surface area was calculated by the BET method in the range of relative pressure 0.05-0.35. The total pore volume was chosed at the relative pressure of 0.95. The pore wall thickness was calculated using QUANTACHROME Autosorb 1-MP statistical thickness program. The SEM images were obtained using a JSEM 5510 microscope, operating at an accelerating voltage of 15kV. The samples were sputtered with a thin film of gold to minimize the charging effects. 3. Results and Discussion From XRD analysis it was established the synthesis time for complete crystallization. The experimental results point out that the crystallization process of initial oxide mixture drastically decreases, from 72 to 2 h, under the ultrasound influence. The XRD diffraction results show that all obtained materials have an ordered mesoporous structure type MCM-41, characterized by the appearance of low-angle XRD peak, for both, reference and ultrasounded samples. 2.7

Intensity (A.U.)

Intensity (A.U.)

2.91

2.76

4.6 4.9

SA SAU

SB2.1 2.1 SB

4.6 4.9

\

3.8

4.7 4.3 1 4.3

5.3

v L

SBU 1.5 1.5

2.5

3.5 4.5 3.5 4.5 2 2 theta theta degree degree

5.5

1.5 1.5

3.5 5.5

5.5 7.5

7.5

2 theta theta degree degree

Fig. 1 XRD patterns of the samples without and with ultrasound irradiation.

The sharp peak 100 appear at 20 < 3, corresponding to interplanar spacing d100 = 3.0325; 3.1972; 3.1857 and 4.0293 for SA, SAU, SB and SBU,

171 171

respectively. Another two extremely weak intensity peaks 110 and 200, indexed to hexagonal unit cell, are present between 2 0 = 3-6 (Fig.l). Under ultrasounds influence, the shifting of all peaks at the lower 20 values was observed, suggesting an enlargement of pore diameter. This is further confirmed with the data shown in Table I. Table I Characteristics of synthesized materials.

Samples

29 degree

SA SAU SB SBU

2.91 2.76 2.77 2.19

a0 (nm)

3.501 3.691 3.678 4.652

Total pore Volume (cc/g) 0.887 0.718 0.686 0.603

SBET

(m 2 /g)

1340 1320 950 731

Pore diameter

Wall thickness

(A)

(A)

19.36 20.94 23.58 33.24

3.31 4.44 10.09 3.72

Particles size (urn)

-20 -15 -1 -5

For all samples the nitrogen adsorption/desorption isotherms (Fig. 2) are of type IV in the IUPAC classification, having the pattern corresponding to capillary condensation at a relative pressure, P/Po = 0.2 - 0.4. In all cases there is no hysteresis, indicating a negligible obstruction of the channels, which allows reversible adsorption and desorption of nitrogen [4]. 600

700 -

500 500

SAU

400 400

SB

500

SA Pore volume (cc/g)

Pore volume (cc/g)

600 -

300 300 200

SBU

400 300 200 100

100 100 -

0

0 0

0.2

0.4 0.6 0.8 Relative Relative Pressure Pressure (P/Po)

11

1.2 1.2

0

0.2

0.4 0.4

0.6 0.6

0.8 0.8

1

1.2

Relative Pressure Pressure (P/Po) Relative

Fig. 2 The nitrogen adsorption/desorption isotherms Isotherms obtained for SB and SBU exhibit a different segment at relative pressure 0.9-1.0, which was attributed to the filling of interparticle macropores [5]. as plots show the absence of microporosity in all studied samples. There are obvious differences in the isotherm shape depending of pH reaction medium. Important differences in isotherms shapes could be observed for samples obtained in basic medium. The ultrasounded sample has smaller specific surface area and pore volume. As shown in Table I, SBU sample has larger pore diameter and thicker pore wall then SB sample. The particles obtained by

172 172

ultrasound-assisted synthesis (Fig. 3) have specific shape and size, which is larger in basic medium and smaller in acid medium. SA

SAU

SB

SBU

Fig.3 SEM images of synthesized samples.

4. Conclusion It is possible to quickly synthesize MCM-41 with small particle size, enhanced pore wall thickness and high stability by a sonochemical process. Our results indicate that this method is more satisfactory for time saving than the classic synthesis way. 5. Acknowledgment The authors are grateful for the partial support of the MATNANTECH, Project CEEX No.l/Sl-2005, NOE project 'Inside Pores' and a research project funded by the Special Fund of Research GOA-BOF by the University of Antwerp 6. References [1] [2] [3] [4] [5]

A. Gedanken, Current Science, 85 (2003) 12, 1720. C. Yang, G. Wang, Z. Lu and L. Sun, J. Mater.Chem., 15 (2005) 4252. M. Run, S. Wu and G. Wu, Micropor. Mesopor. Mater., 74 (2004) 37. H. Yang, G. Vovk, N. Coombs, I. Sokolov and G. A. Ozin, J. Mater. Chem., 8 (1998) 743. Y. Yang, S. Lim, C. Wang, D. Harding and G. Haller, Micropor. Mesopor. Mater. 67 (2004) 245.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

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Crystalline micro- and meso-porous materials from inorganic molecular clusters Xiaodong Zoua, Tony Conradssona, Kirsten E. Christensena, Tiezhen Rena and Michael O'Keeffeb "Structural Chemistry, Arrhenius Laboratory, Stockholm University, SE-106 91 Stockholm, Sweden b Chemistry and Biochemistry, Arizona State University, Tempe AZ 85287, USA

1. Introduction Mesoporous materials with ordered pores are of great interests due to their wide range of applications. Most of the mesoporous materials are synthesized using organic surfactants and they have well-ordered pores but the pore walls are often amorphous [1]. On the other hand, microporous materials are synthesized using small organic amines and the structures are often crystalline. Synthesizing materials with both ordered mesopores and crystalline walls remains a great challenge. Here we present two crystalline germanium oxides SU-M and SU-MB with pores into the region of mesopores, using molecular clusters as building units [2]. A new approach of designing mesoporous crystalline structures from molecular building units and scale chemistry is discussed. 2. Experimental Section Both SU-M and SU-MB were synthesized under mild hydrothermal condition from a homogenous solution of germanium dioxide, 2-methylpentamethylenediammine (MPMD) and water with the molar ratios of 1 : 4 - 10 : 17 - 40. In addition hydrofluoric acid with a molar ratio of GeC>2 : HF = 1 : 1.5 was added for the synthesis of SU-MB. The solutions were heated at 160 - 165°C in Teflon-lined Parr autoclaves under autogenous pressure and the synthesis time was 7 days for SU-M and 11 days for SU-MB. The structures were solved and refined by single crystal X-ray diffraction [2].

174 174

3. Results and Discussion SU-M is cubic with a = 51.335(3) A and space group laid. It is built from a single type of cluster Geio02o(OH)3 (Gei0) (Fig. la). Each cluster is connected in such a way that they lie on the gyroidal (G) minimal surface, with pore structures similar to those of MCM-48, but fully ordered crystalline walls (Fig. lb and Fig. 2a). Each Gei0 cluster is connected to five other Ge,0 clusters (Fig. lc). The crystalline wall of SU-M can be described as a 5-coordinated net with vertices at the centers of the Gei0O24(OH)3 clusters.

(a)

Fig. 1 Linkage of Ge10 clusters in SU-M. (a) The Ge10 cluster, (b) Packing of Ge10 clusters within a unit cell (fez net). Each black ball corresponds to a Ge]0 cluster. The clusters lie about the G minimal surface as in MCM-48. (c) Each Ge10 cluster is linked to five neighbouring clusters, (d) A 30-ring window formed by ten Ge10 clusters.

SU-M contains two gyroidal channels with different handedness. The smallest windows limiting the gyroidal channels are 30-rings (Fig. Id). The channels are separated by crystalline walls and the largest openings between the two channels are 12-ring micropores (Fig. 2a). SU-MB is also cubic, with a = 50.873(3) A and space group /4]32. Compared to SU-M, SU-MB has the same framework structure as SU-M, but with one of the two gyroidal channels filled with Ge7 clusters, resulting in a chiral mesoporous crystal with chiral channels (Fig. 2b). The Ge7 clusters are directly connected to the 12-ring micropores, limiting the connection between the two channels (Fig. 2b). The chemical composition is |(H2MPMD)2(H20)x|[Geio020 5(OH)3] for SU-M and |(H2MPMD)5.5(H20)J{[Ge1o02i(pH)2]2[Ge7014F3]} for SU-MB. The framework density is 7.1 T atoms/nm for SU-M and 9.8 T atoms/nm3 for SUM. There is 70% volume available for SU-M, calculated by the volume that is not occupied by spheres with van der Waals radius centred on the framework atoms. It is worth mentioning that each of the gyroidal channels in SU-M can accommodate as many as 336 Ge(O, F)n (n = 4 - 6) polyhedra per unit cell.

175 175

(a)

Fig. 2 (a) The structure of SU-M. The yellow ball represents a cavity of an equatorial diameter of 26.2 A and a polar diameter of 18.6 A. (b) The structure of SU-MB. One of the two channels are filled by Ge7 clusters (in yellow), leaving the other gyroidal channel empty.

Fig. 3 The electron density maps of (a) SU-M and (b) SU-MB showing the pore structures. The density maps were calculated from (a) four strongest unique reflections of SU-M and (b) seven strongest unique reflections of SU-MB with d-values > 12 A.

SU-M can be built from a simple fez net (Fig. lb) [3] by replacing the vertices with Geio clusters (Fig. la). This is an example of "scale chemistry"[4]. Different structures can be built according to a similar topology, but with different building units (BUs). The building units can be of different sizes, from

176 176

atom, polyhedra formed by a group of atoms, molecules or clusters formed by assembling of polyhedra. The BUs act as "bricks" for building the final framework structures. A large number of examples have shown that crystalline framework structures with large pores are often built according to simple topologies from large building units [5, 6, 7]. SU-M is the first metal oxide that has pore-openings larger than 24-rings. Using a similar approach, new structures, probably with even larger pores, may be generated by combining the same or different topologies with even larger building units. 4. Summary Two germanium oxides, SU-M and SU-MB, containing micro- and mesopores and crystalline walls are presented. A new approach of designing mesoporous crystalline structures from molecular building units and scale chemistry is discussed. 5. Acknowledgement This project is supported by the Swedish Research Council. 6. References [1] C. T. Kresge, M. E. Leonowicz, W. J. Roth, J. C. Vartuli and J. S. Beck, Nature 359 (1992) 710. [2] X. D. Zou, T. Conradsson, M. Klingstedt, M. S. Dadachov and M. O'Keeffe, Nature 437 (2005)716. [3] M. O'Keeffe, O. M. Yaghi, D. Moler, G. Joshi, N. Ockwig and O. Delgado-Friedrichs, Reticular Chem. Structure Resource (2004) http://okeeffewsl.la.asu.edu/RCSR/home.htm. [4] G. Fe>ey, J. Solid State Chem. 152 (2000) 37-48. [5] J. Pleivert, T.M. Gentz, A. Laine, H. Li, V.G. Young, O.M. Yaghi and M. O'Keeffe, J. Am. Chem. Soc. 123 (2001) 12706. [6] Y. M. Zhou, H. G. Zhu, Z. X. Chen, M. Q. Chen, Y. Xu, H. Y. Zhang and D. Y. Zhao, Angew Chem. Int. Ed. 40 (2001) 2166. [7] L. Q. Tang, M. S. Dadachov and X. D. Zou, Chem. Mater. 17 (2005) 2530.

Recent Progress Progress in in Mesostructured Mesostructured Materials Materials Recent D. Zhao, S. S. Qiu, Qiu, Y. Y. Tang Tang and and C. C. Yu Yu (Editors) (Editors) D. © 2007 2007 Elsevier Elsevier B.V. B.V. All All rights rights reserved. reserved. ©

177 177

Aluminum incorporation into plate-like ordered mesoporous materials obtained from layered zeolite precursors Raquel Garcia*, Isabel Diaz, Carlos Marquez-Alvarez and Joaquin PerezPariente Instituto de Catdlisis y Petroleoquimica. C/ Marie Curie 2. 28049 Cantoblanco. Madrid. Spain.

1. Introduction The family of ordered mesoporous materials prepared from silicate/aluminosilicate gels containing surfactant molecules have attracted much attention in recent years due to their potential applications in several fields as catalysts, adsorbents and catalysts carriers [1]. However, for certain catalytic applications, the typically amorphous nature of the walls (framework) in these mesoporous materials is a drawback. Different synthesis strategies have been developed in order to improve framework ordering in mesoporous materials. Among these attempts, we have reported recently, the synthesis of an ordered silicate mesophase through the reaction of the complex layer silicate precursor RUB-18 with the cationic surfactant cetyltrimethylammonium chloride followed by a hydrothermal treatment [2]. The as-prepared mesostructured material shows crystal morphology and local atomic arrangement similar to those of the crystalline precursor silicate. However, this is a purely siliceous material with an electrically neutral framework and, consequently, with no acid sites. Incorporation of aluminum into mesoporous materials is of a tremendous interest as it gives rise to materials with Bransted acidity and therefore much effort have been devoted to the introduction of aluminum into mesoporous silicas, via direct synthesis and post-synthesis methods [3]. The purpose of this contribution was to obtain and compare the incorporation of aluminum into the mesostructured material derived from RUB18 via three different postsynthesis procedures.

178 178

2. Experimental Section Preparation and characterisation of the starting materials was performed as reported previously [2]. In order to produce aluminium-containing materials three different routes were employed, an in situ method during the preparation of the mesostructured material and two post-synthesis treatments of the as prepared mesostructured silicates. In route I, aluminum isopropoxide (Fluka 97%) was added during the initial refluxing of Na-RUB-18 with the surfactant solution and then, the mixture was treated hydrothermally at 150°C for 5 days in order to produce the mesostructured silicoaluminate phase. In route II, the as made sample was dispersed in dry ethanol containing A1C13 (anhydrous, Panreac) with magnetic stirring at room temperature for 24 h. In route III, the as made material was dispersed in dry hexane containing aluminum isopropoxide and the resulting mixture was stirred at room temperature for 24 h. The Si/Al ratio of the initial mixture was adjusted to 15 in the three procedures. The samples were heated in N2 (70 ml/min) at 260°C for 1 hour followed by treatment with a flow of ozone/oxygen (60 ml/min, ca. 2 vol% O3) at 200°C for 72 h to remove the surfactant. Ozone in oxygen stream was produced using an ECO-5 ozone generator manufactured by SALVECO Proyectos, S.L. (Spain). Powder X-ray diffraction (XRD) patterns were obtained with a Seifert XRD 3000P diffractometer using monochromatic Cu Ka radiation. Thermogravimetric analysis (TGA) was carried out using a Perkin-Elmer TGA7 instrument at a heating rate of 20°C/min under air flow. 27A1 MAS-NMR spectra were recorded on a Bruker AV400 spectrometer. N2 adsorption-desorption isotherms were measured at 77 K using a Micromeritics TRISTAR3000 volumetric apparatus. 3. Results and Discussion Aluminum incorporation into the mesostructured material derived from RUB-18 was followed by EDX/SEM analysis. SEM micrographs show that in all three samples the crystal morphology of the parent silicate was mostly maintained after the treatments. Incorporation of aluminum was confirmed by EDX made up to 15 crystals of the samples observed by SEM and the mean analysis was taken (Table 1). Remarkably, the Si/Al ratio of sample MSI is very close but lower than that corresponding to the initial aluminum isopropoxide/RUB-18 mixture. This lower value is probably due to the dissolution of silica species during the alkaline hydrothermal treatment that results in the formation of the mesostructured phase, as observed for its pure silica analogous [2]. However, route II and III do not lead to the incorporation of all the initial aluminum, yielding materials with slightly higher Si/Al ratios. The X-ray diffraction patterns of the aluminium modified samples are depicted in Figure 1. The XRD pattern of samples MSI and MSIII after alumination and after surfactant removal in ozone treatment, closely resemble

179 179

that of the pure silica mesostructured material obtained from RUB-18, with the appearance of a characteristic low angle reflection at 20 -1.5° together with diffractions of the residual CTA-RUB-18 phase at 29 -3.2 and 6.4° [2]. TGA analysis of these samples confirmed the organic content of the materials is on the range 35-40% characteristic of the pure silica mesostructured phase. However, the diffraction pattern of sample MSII after alumination is similar to that of the samples after calcination, suggesting the removal of the surfactant by cation exchange during the alumination treatment. TGA analysis confirms a decrease in the surfactant content of this sample, giving a total weight loss of 10.5% in the temperature range 130-600°C. Table 1. Elemental composition and textural properties of the mesostructured silicoaluminates. o b SBET

Pdc

(m2/g)

(ran)

11.1

284

2.5

MSII

22.1

179

2.6

MSIII

26.3

172

2.6

Sample

Si/Ala

MSI

a

By EDX (JEOL JSM 6400 Phillips XL30 microscope operating at 20 kV; );b Specific surface area calculated following the BET procedure.c Pore diameter determined following the BJH method on the N2 isotherm adsorption branch.

10

20 20(°)

30

40

Figure 1. XRD patterns of (a) freshly prepared MSI; (b) sample MSI treated with ozone in oxygen stream; (c) freshly prepared MSII; (d) sample MSII treated with ozone in oxygen stream; (e) freshly prepared MSIII and (f) sample MSIII treated with ozone in oxygen stream.

The 27A1 MAS NMR spectra of the aluminium MS samples, as made and after calcination (Figure 2) indicate the presence of both tetrahedrally coordinated (framework) and octahedrally coordinated (non-framework) Al with resonances at ~ 50 and 0 ppm, respectively. The as made MSI sample shows a higher Altd/Aloh ratio than those of MSII and MSII, thus indicating a

180 180

higher degree of incorporation of aluminium within the framework. Calcination of the samples slightly increases the ratio of octahedral to tetrahedral aluminium, especially for sample MSI, and the final calcined materials show similar Altd/Aloh ratios. Interestingly, the calcined MSII and MSIII, show the presence of a small resonance at 27 ppm which has been assigned to five coordinated aluminium [4]. a)

150

b)

100

50

0

(ppm) chemical shift (ppm)

-50

-100

150

c)

100

50

0

chemical shift (ppm) (ppm) chemical

-50

-100

150

100

50

0

-50

-100

chemical shift (ppm)

Figure 2. 27A1 MAS NMR spectra of a) sample MSI before (top) and after ozone calcination (bottom); b) sample MSII before (top) and after ozone calcination (bottom) and c) sample MSIII before (top) and after calcination (bottom).

Preliminary results on catalytic activity of the calcined samples MSII and MSIII in m-xylene conversion (Ro, reaction rate of 1.3xl0"2 and 2.5><10"3mol g" 1 h'\ respectively) indicate that the materials possess an activity similar to that of conventional aluminium-containing MCM-41 materials but lower than those prepared from zeolite colloidal precursors [5]. 4. Conclusion Alumination of the mesostructured material obtained from RUB-18 have been achieved by three different procedures. Independently of the method employed, the final materials show incorporation of aluminum within the framework but with a significant amount of extra framework aluminum. Preliminary catalytic results indicate the aluminum containing materials are active in the conversion of m-xylene although they show a low activity characteristic of weak acid sites, comparable to that of conventional Al-MCM41 catalysts. 5. References [1] A. Corma, Chem. Rev., 97 (1997) 2373. [2] R. Garcia, I. Diaz, C. Marquez-Alvarez and J. Perez-Pariente, Chem. Mater., 18 (2006) 2283. [3] Y. Xia and R. Mokaya, Micropor. Mesopor. Mater., 74 (2004) 179. [4] S. Biz and M. G. White, J. Phys. Chem. B, 103 (1999) 8432. [5] J. Agundez, I. Diaz, C. Marquez-Alvarez, J. Perez-Pariente and E. Sastre, Chem. Commun., (2003) 150.

Recent Progress in Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

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Shaping of mesoporous molecular sieves Martin Hartmann a *, Sebastian Kunz a , G. Chandrasekara>b and V. Murugesan b

"Advanced Materials Science, University of Augsburg, 86135 Augsburg, Germany Department of Chemistry, Anna University, Chennai 600025, India

1. Intoduction Mesoporous materials such as SB A-15 are synthesized as amorphous powders (particle size 0.1 to 10 urn) and invariably need to be shaped into bodies such as granules, spheres and extrudates prior to their use in fixed-bed adsorbers or reactors. Particle shaping is a complex procedure involving several steps viz. compounding / mixing, shaping, drying and calcination. In the present contribution, SBA-15 powders are shaped into extrudates and the influence of additives such as binder, macropore builder and cross-linking agent on the mechanical strength of the extrudates is tested. Mechanical strength is one of the key parameters for the reliable industrial application of a solid catalyst. Failure of catalyst strength in a fixed-bed reactor causes maldistribution of fluid flow and a large pressure drop through the bed, which results in a low efficiency and (in serious cases) plant failure. Solids catalysts formulations containing zeolites and mesoporous materials are porous and full of defects, dislocations and discontinuations in their bulk phase. The flaws are in the same range of size and nature as the micro-cracks defined by fracture mechanics [1], which states that expanding of microcracks under tensile stress concentrated around the edges of the flaws is the primary reason for fracture [2]. Variations in size shape and orientation of flaws results in a large scattering range of strength data of catalysts. Therefore, the mechanical strength data have to be treated based on statistical analysis. 2. Experimental Section The synthesis SBA-15 was performed employing optimized procedures as described elsewhere [3]. All mesoporous materials were characterized by XRD (Siemens D5005), nitrogen adsorption (Quantachrome Autosorb 1 sorption analyzer), mercury porosimetry (Micormeritics) and thermogravimetric analysis

182 182

(Setaram) before and after shaping into extrudates. The mesoporous material SBA-15 was mixed with bentonite or kaolin as a binder and methyl cellulose in order to controle the macropore structure of the extrudate after calcination. TEOS was added as a cross-linking agent. A typical paste composition is as follows: 7.5 g SBA-15 : 2.0 - 6.0 g bentonite : 1.2 - 6.0 g methyl cellulose : 2.0 - 12.0 g TEOS : 35 - 40 g H 2 O. The components were mixed in ThermoHaake Polylab Rheomix instrument, extruded into cylinders with a diameter of 3 mm, dried at 100°C and subsequently calcined for 24 h at 550°C in air.The vertical crushing strength of the cylinders was measured by Mecmesin strength tester. Prior to the test, the extrudates were cut into discs with a thickness of 2 mm. 3. Results and Discussion

nits ) Intensity / ((arb. arb. u units)

Figure 1 exemplary shows the X-ray diffraction patterns of the SBA-15 extrudates before and after calcination in comparison to the parent powder. The SBA-15 extrudates exhibit at least three well defined reflections, which are somewhat broader than those of the powder sample. The nitrogen adsorption isotherms (not shown) of the powder sample and the extrudates both exhibit type IV isotherms characteristic of well-ordered mesoporous materials. The influences of the different paste components such as bentonite and methyl cellulose on the mechanical strength were evaluated and the results are depicted in Figure 2. The vertical crushing of a disc can be used as a diagnostic test for the mechanical strength of a shaped particle [4]. The method is based on the relationship between the tensile stress and the loading based on elastic theory.

ii

c

00

2 2

4

6

8

1 10

Angle 22 θ/°

Figure 1: XRD patterns of SBA-15 powder, SBA-15 extrudates (mbentonite/mSBA-i5 = 0.5) and calcined extrudates (top to bottom).

The tensile stress cr/i/for a plane-faced disc-like specimen with limited height can be calculated using equation (1) OM = 2-P I (n-d-l), where P denotes the crushing force, d and 1 the diameter and the length of the extrudate, respectively. The tensile stress is increasing with rising amount of binder bentonite (Figure 2a) and the macropore builder methyl cellulose (Figure 2b). However,

183 183

simultaneously the specific pore volume and the specific surface area are decreasing due to the increasing amount of (nonporous) binder. Therefore, for industrial use, a compromise between mechanical strength and specific surface area has to be found depending on the targeted application.

2

4 6 8 10 Amount of bentonite / %

3

4

5

6

7

8

Amount of methyl cellulose / %

Figure 2: Effect of the amount of bentonite (left) and methyl cellulose (right) addition on the crushing strength of the SB A-15 extrudates.

It has been shown that the failure distribution of the crushing strength measurements does not fit a Gaussian-distribution, but rather a so-called Weibull distribution [5]. The two-parameter Weibull equation (2)

was used for the correlation of our data. In Eq. (2), F(crM) is the probability of failure, uM is the maximum tensile stress within the specimen, fi0 a size parameter and m the Weibull modulus. Combining Eqs. (1) and (2), we obtain (3) with P = (3o (2/n-d-[)m. Rearranging and taking the natural logarithm of both sides of equation (3) results in

In In

1 \-F(P)

(4)

In order to prove that the stress follows a Weibull distribution, 110 extrudates of one sample (mbentonjte/mSBA-i5 = 0.5) were measured. In Figure 3, the exponential fit as well as linear fit of the Weibull distribution are shown. The Weibull para-meters m = 4.2 and b = 0.15 (from linear regression analysis) confirm a sufficient mechanical strength but indicate a rather broad strength distribution. The failure probability is already ca. 10 % at a crushing stress of 0.9 MPa and increases to 50% at a = 1.44 MPa. In contrast, conventional analysis gave a crushing stress of 1.7 MPa with standard deviation of 0.2 MPa (20 extrudates).

184 184

1.0

1.5

2.0

2.5

3.0

crushing stress a I MPa

Figure 3: Weibull distribution curve (left) and Weibull plot (right) of the VCS data.

4. Conclusion The influence of bentonite and methyl cellulose content on the mechanical stability of SBA-15 extrudates is studied. The statistical treatment reveals that the VCS data of SBA-15 extrudates scatter in rather large ranges, which is an intrinsic property inherited from the brittleness of the solid porous material and the fracture nature of the strength failure. 5. Acknowledgement Financial support of this work by Deutsche (Ha2527/4-2) is gratefully acknowledged.

Forschungsgemeinschaft

6. References [1] Y. D. Li, X. M. Li, L. Chang, D. H. Wu, Z. P. Fang and Y. H. Shi, Catal. Today 51 (1999) 73. [2] A. Griffith, Philos. Trans. R. Soc. London, Ser. A 221 (1920) 163. [3] M. Hartmann, A. Vinu, Langmuir 18 (2002) 8010. [4] Y. D. Li, D. Wu, J. Zhang, L. Chang, D. Wu, Z. Fang and Y. Shi, Powder Technology 113 (2000)176. [5] W. Weibull, J. Appl. Mech. 18 (1951) 293.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

185 185

A new temperature-programmed calcination route to remove the organic templates from mesoporous aluminophosphate materials Jing Yua, Juan Tanb, An J. Wang,ab* Xiang Li, ab and Yong K. Hu ab " State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian, 116012, P. R. China Liaoning Key Laboratory of Petrochemical Technology and Equipments, Dalian University of Technology, Dalian 116012, P. R. China.

1. Introduction Mesoporous aluminophosphates materials show great promise as catalysts [1], catalyst supports [2] and adsorbents [3]. Though well-developed mesostructured aluminophosphates can be obtained in the synthesis process, most of calcined samples indicated significant collapse of the mesostructures after the removal of organic templates by conventional calcination method [4]. The negative effect of the calcination process may be attributed to the uncompleted condensation in the pore walls of the mesostructure [5, 6]. Therefore, the removal of templates is critical to obtain highly ordered structure in meso-AlPO. Here, we report a novel calcination approach to control the decomposition of the cationic templates in the pores of meso-AlPO materials for obtaining high quality mesoporous aluminophosphates. 2. Experimental Section Mesoporous A1PO materials were synthesized by using cetyltrimethylammonium bromide (CTAB) as a surfactant at room temperature and the gel composition: 1.0 Al 2O3: 2 .0 P 2O5: 0.6 C TAB: 4.4 TMAOH: 330H 2O. In a typical synthesis, 3 g aluminium triisopropoxide (99.8%) was mixed with 18 mL water under stirring. Then, phosphoric acid (85 wt%) was added with stirring. After 1 h, a solution of 1.68 g CTAB was added and stirred for another 1 h. After that, 11.78 g of tetramethylamtnonium hydroxide (TMAOH) (25 wt

186 186

%) was added dropwise in the above mixture and stirred. After 48 h, the solid product was filtered, washed and then dried at 70°C for 12 h. In order to remove of the organic templates, conventional calcination route and a three-stage TP calcination route were adopted. By conventional route, the as-synthesized meso-AlPO sample was directly heated to 500°C at a rate of 1°C min"1 in N2 and maintained for 1 h, then for 8 h in air. The TP calcination process as follows: firstly, the as-synthesized samples were quickly heated to 140°C and kept at this temperature for 3 h. Secondly, the samples were heated linearly to 200°C at 1°C min"1, from 200 to 360°C at 5°C min"1 and from 360 to 500°C at 1°C min"1, and then maintained at 500°C for 1 h in N2. Finally, the samples were heated at 500°C in air for 8 h. The as-synthesized and calcined meso-AlPO samples were characterized by XRD, TEM, TG-DTG and TP-MS. XRD patterns recorded on a Rigaku D/max2400 instrument using Cu-Ka radiation (X = 1.54 A). TEM image was measured by using a JEM-100CXII microscope at an accelerating voltage of 300 kV. The thermogravimetric analysis (TGA) was carried out on a Mettler Toledo TGA/SDTA 85 l e in a flow of nitrogen. The evolved gas analysis of assynthsized meso-AlPO was detected by MS (Balzers, QMS200) at a heating rate of 5 °C/min under a flow of helium at a rate of 20 mL/min. 3. Results and Discussion (b)

200

400 600 Temperature (°C)

800

0

200

400

600

800

Temperature (°C) ,CH, m/z=15

(C)

200

400 Temperature (°C)

600

800

0

200

400 Temperature (°C)

600

Fig. 1. Plots of various molecular species recorded with MS of as-synthsized meso-AlPO in temperature programmed heating (5°C/min) under helium flowing.

187 187

The evolved gas analysis of as-synthesized meso-AlPO is detected by temperature programmed MS (Figure la-d). The initial signal from 25 to 200 °C is characterized by the loss of water (m/z=18, 17, 16) (Fig.la). In Fig.lb and d, they show that a series of the hydrocarbon chains (m/z=97, 83, 69, 55, 41, 28, 26) via Hoffman degradation of CTAB are detected above 150°C and a few losses of CH3OH (m/z=32, 31) due to the decomposition of TMAOH appear about 150 °C. From 200 to 400°C, the masses of CxHy (m/z=15,29,41,43,55), trimethylamine (m/z=58, 59,43,29), CH3OH (m/z=32, 31) and C2H5OH (m/z=46,45) (Fig. lb, lc, Id) are observed, while the water (m/z=16, 17, 18) (Fig. la) is also detected in this period, which is attributed to the condensation of inorganic wall and the cracking of small partial organic species. So the temperature range of 150 to 400°C is the main process of the pyrolysis and decomposition of TMA+ and CTA+ cations, and also the condensation of the inorganic framework of meso-AlPO [2]. Thermogravimetric analysis of the as-synthesized sample shows a total weight loss of ca. 63% on heating to 800°C in N2. The first step occurs between 25 and 200°C, and corresponds to a mass loss of 14%. Further steps can be observed at higher temperature periods: 200-400°C (mass loss of 46%) and 400-800°C (mass loss of 3%). According to the above results, a holding stage on 140°C is chosen to eliminate the partial organic species in the TP calcination route. XRD pattern of the sample heated at 140°C for 3 h and the d]Oo reflection was increased (from 8553 to 9570 cps), which indicates that the condensation of pore walls was strengthened. So the subsequent removal of the template at higher temperature may have little negative effects on the mesostructure. In the second stage of TP route, a higher rate of

8 10 4 6 2e (degrees) Fig. 2. XRD patterns of the smples: (a) assynthesized, (b) calcined by conventional route and (c) calcined by three-stage TP

Fig. 3. TEM image of the msso-AlPO calcined by three stage TP route.

5°C/min from 200 to 360°C will accelerate the condensation of the hydroxyl groups within the inorganic framework. This condensation decreases the collapses of pore structure and framework in the removal process of the templates. In the third stage, the residue organic species was

188 188

eliminated in air, and induces a significant improvement in the thermal stability of the obtained meso-AlPO materials. The XRD pattern of the as-synthesized meso-AlPO shows an ordered hexagonal mesostructured feature in Fig. 2a. For the sample that was calcined by conventional route, the dramatically decreased structure order of the meso-AlPO and intensity of dioo reflection are observed (Fig. 2b). Otherwise, the solid product calcined by TP calcination route gives a single narrow and strong diffraction peak corresponding to dioo (Fig- 2c). Compared with the as-synthesized sample, the intensity of djOo reflection of the sample calcined by TP route is greatly increased while the FWHM is hardly changed, indicating that a highly ordered mesostructure of the aluminophosphate framework is obtained after the TP calcination. The TEM images of the calcined meso-AlPO (Fig. 3) show long-range ordered hexagonal arrays of mesopores which is much better than the wormlike structure [7] and can compare with siliceous hexagonal MCM-41 materials [8]. The pore diameter is estimated to be 28A, which is larger than those reported in literatures [9, 10]. It indicates that the new calcination route can reduce the shrinkage of the mesoporous structure. 4. Conclusion The three-stage temperature-programmed calcination route effectively controlled the evolution of organic templates in mesostructured AlPO materials and the condensation of the inorganic framework of the material, by which can obtain a thermally stable and long-range ordered hexagonal mesoporous AlPO structure. This approach is an easy and effective way to obtain high quality mesoporous AlPO materials, and may be extended to the preparation of other kinds of mesoporous materials. 5. References [1] T. Kimura, Micropor. Mesopor. Mater., 77 (2005) 97. [2] K. U. Nandhini, B. Arabindoo, M. Palanichamy and V. Murugesan, J. Mol. Catal. AChem., 223(2004)201. [3] T. Kimura, Y. Sugahara and K. Kuroda, Micropor. Mesopor. Mater. 22 (1998) 115. [4] P. Y. Feng, Y. Xia, J. L. Feng, X. H. Bu and G. D. Stucky, Chem. Commun., (1997) 949. [5] J. He, X. B. Yang, D. G. Evans and X. Duan, Mater. Chem. Phys., 77 (2002) 270. [6] Z. H. Luan, D. Y. Zhao, H. He, J. Klinowski and L. Kevan, J. Phys. Chem. B., 102 (1998) 1250. [7] M. Tiemann, M. Schulz, C. Jager and M. Froba, Chem. Mater., 13 (2001) 2885. [8] C. T. Kresge, M. E. leonowicz, W. J. Roth, J. C. Vartuli and J. S. Beck, Nature 359 (1992) 710.

[9] Y. Z. Khimyak and J. Klinowski, Phys. Chem. Chem. Phys., 2 (2000) 5275. [10] T. Kimura, Y. Sugahara and K. Kuroda, Chem. Mater., 11 (1999) 508.

Mesostructured Materials Recent Progress in Mesostructured D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

189 189

Calcination mechanism of block-copolymer template in SBA-15 materials Francois Berube and Serge Kaliaguine Chemical Engineering Department, Universite Laval, Ste-Foy, Que, Canada. G1K 7P4 1. Introduction

Since poly(alkeneoxide) triblock copolymers have been used as templates for the synthesis of ordered mesoporous silica [1, 2], several methods have been developed to remove the template such as oxidative ozone treatment [3, 4], supercritical fluid extraction [5, 6], microwave digestion [7] and ether cleavage by an acid [8, 9], but the most common ones are calcination under air and extraction with an organic solvent [5, 10-14]. Several studies have been carried out to understand the influence of calcination on the physico-chemical properties of SBA-15 materials showing that a significant lattice shrinkage occurs upon high-temperature treatment [5, 7, 8, 10, 15]. In spite of the fact that calcination is very often used to remove the organic phase from SBA-15 materials, relatively little works was done to understand the influence of this process on the MMS properties and to quantify and locate the residual template. The present work is aiming at understanding the template degradation reaction mechanism during calcination under oxygen. 2. Experimental Section SBA-15 material was obtained following the procedure reported by Zhao et al. [1]. Tri-block copolymer (P-123) was used as the template and tetraethyl orthosilicate as the silica source. In a typical synthesis, 7.659 g of P123 was dissolved in 290 mL of a 1.6 M aqueous HC1 solution. 16 g of TEOS was then added dropwise. The synthesis was carried out for 20h at 35°C followed by 24h of hydrothermal treatment at 80°C. All the samples were dried at 80°C under vacuum prior to calcination.

190 190

Temperature programmed calcination (TPC) monitored by mass spectrometry (TPC-MS) was performed using a RXM-100 multi catalyst testing and caracterization system (Advanced Scientific Design Inc.). 70 mg of support was placed in a U-shaped reactor coupled with a quadrupole mass spectrometer. All the experiments were carried out under a flow (50 mL/min) of 10% O2 in He from 25°C to the various temperatures of interest with a 2 K/min ramp and then cooled down to room temperature under the same flow. The temperature was maintained for 120 minutes after the end of the ramp to complete the combustion except for the MMS calcined at 160°C which was immediately cooled down after the end of the ramp and the one calcined at 575°C which was maintained at this temperature for 15 min. Water and high molecular weight carbonaceous species were trapped at -80°C (dry ice in ethanol solution) before reaching the mass spectrometer leak in order to increase the monitoring resolution. As-synthesized and calcined samples were characterized using N2 adsorption, carbon elemental analysis, thermogravimetry analysis and 13C NMR. 3. Results and Discussion Table 1 and Fig. 1 respectively show the structural properties and evolution of the various pore volumes of SB A-15 calcined at different temperatures. After calcination at 160°C, the alpha-s plot shows that no micropore volume is accessible to N2. Almost all micropores and mesopores are free for the sample Table 1. Structural properties of SBA-15 after different treatments.

Samples

%C

SBET 2

Water washed C160 C175 C270 C335 C575

29.67 24.23 4.26 1.36 0.82 0.30

(m /g) 40 170 1020 1120 1080 900

DPa (nm) 7.7 8.3 8.8 9.0 8.5 8.3

vtb

(cc/g) 0.09 0.31 1.12 1.19 1.16 1.03

V v

• c-d mes

(cc/g) 0.05 0.26 0.79 0.84 0.81 0.75

V •° v mic (cc/g) 0 0 0.14 0.17 0.17 0.16

a

Pore diameter determined by the modified BJH method from the adsorption branch; b Adsorbed volume at P/Po = 0.995; c Micropore and mesopore volumes determined from alphas plot [16]; d VmeS+mi(. (sum of mesopore and micropore volumes, 1.6 < as < 2.0) — Vmjc (micropore volume, 0.9 < as < 1.2).

calcined at 175°C. After a 2 h. isotherm at 175°C, 84% of the micropore volume and 94% of the mesopore volume are free compared to their maximal values, obtained at 270°C. These results showed that larger mesopores are first emptied followed by intrawall porosity. For higher temperature treatments, mesopore volume decreased suggesting that lattice shrinkage occurred in agreement with the XRD results of F. Kleitz et al. [15]. Surprisingly, the micropore volume

191 191

d%/d °C

W eight loss (%)

V (cc/g)

remained approximately unchanged for treatment temperatures higher than 270°C even if lattice shrinkage occurred indicating that for these temperature, template oxidation was located all within micropores. TGA and DTG of PI23 and SB A-15 material both under air 1,0 and nitrogen are presented in Fig.2. Under air, TGA of the 0,8 organic template inside the MMS showed a major weight loss of 100 nm 0,6 37% between 130 and 190°C as previously reported [10, 15]. 0,4 TGA of PI23 copolymer under air also shows that oxidation of the polyalkoxide begins at the 0,2 same temperature, but at a lower rate than the copolymer inside 0,0 0 100 200 300 400 500 600 700 SBA-15 materials. Both Temperature (°C) experiments showed a subsequent weight loss above 190°C Fig 1. Comparative plots of micropore volumes indicating that the template (solid circles) and mesopore volumes (open oxidation takes place in two steps. circles) of SB A-15 calcined at different Under flowing nitrogen, temperatures. decomposition of the P123/SBA15 composite occurs at a lower 200 6 rate in comparison to PI23, that SBA-15 5 + 100 takes place in a single step 150 between 300 and 375°C. 4 Temperature programmed + 50 calcination (TPC) monitored with 100 3 MS under 10% O2 of the SBA-15 P123 2 material washed with water is 50 presented in Fig. 3. As reported 1 before, the MS signals recorded 0 0 between 140 and 190°C show a 0 100 200 300 400 500 rich spectrum including masses °C} Temper3ture{(°C) Temperature 14, 26, 27, 29, 30, 43 and 58 in Fig 2. TGA and DTG curves under air (solid addition to masses 44, 28 and 12 ijnes) and under N2 (dotted lines) of P123 and that suggests VOC production [15]. Mass 29 is the most important VOC fragment indicating that carbonaceous species formed during that step have carbonyl group terminations. Several molecules such as alchools and aldehydes have been identified among the products of combustion of diethyleneglycol [17]. As demonstrated with the TGA experiments, TPC followed with m/z = 44 also showed a small shoulder between 190 and 300°C due to oxidation of the polyalkoxide fragmentation

192 192

products formed at lower temperature. Above 300°C, mass spectra showed a broad CO2 m/z = 12 peak that continued until 500°C. m/z = 28 m/z = 44 Interestingly, degradation of the copolymer inside the SB A-15 in absence of oxygen occurs within this temperature range (see Fig.l) and also continued at m/z = 14 m/z = 26 higher temperature. Thus, one m/z = 29 m/z = 30 may suggest that this step is 11 jj associated with the template located inside the ultramicroporosity (<10 A) that limits the accessibility of oxygen. Tem perature (°C) (°C) Temperature Fig.4 shows 13C NMR spectra Fig 3. MS monitored temperature programmed of the same sample. As reported oxidation of SB A-15 washed with water. The before, chemical shifts of 19.3, bottom graph scale reduced by a factor of two 73 and 75 ppm are associated compared to the upper one. with polyoxopropylene (PPO) and the shoulder at 72 ppm is attributed to the PEO chains of \ the template [8, 9]. The sample calcined at 160°C clearly shows a decrease of PPO signal in L J comparison to PEO lines proving that an ether cleavage of the PI23 occurs during the first calcination step and first empties |< «j"°<W , the large mesopores. NMR spectra of samples calcined at ppm ppm 175 and 270°C also showed that Fig 4.13C MAS NMR spectra of SBA-15 washed essentially no more PPO with water a), Cl 60 b), C 175 c), C270d) and fragments remain in the material. C335 e). P123 reference spectra was taken from ref 8 Important lines at 70, 66 and 62 - ppm were also obtained for this sample corresponding to the presence of small fragments of PEO chains (as indicated in Fig. 4) instead of the initial copolymer hydrophilic part, proving the previous hypothesis. Finally, no signal was observed for the sample calcined at 335°C.

k

3000 •

2000 •

1000 1000 •

0

:>

SUf

Intensity (A.U.)

T-

m /z = 12 m /z = 28 m /z = 44

i

1600

1200 1200

m /z m /z m /z m /z

= = = =

14 26 29 30

400 •

0

0

100

200

300

400

500

74.3 ppm

(a)

"I

1 163 ppm

600

19.3 ppm

72.0 ppm 69.1 ppm 9.1 p p m 66.2 66.2 p pppm m

62.3 ppm

49 ppm pm

Signal (U.A.)

(b) (b)

(c) (c)

(d)

(e) (e)

J|| '

[CH22CHCH CHCH33O]m O]m

[

CH22CH CH22 O]nn CH22 CH2 [CH 2 OH

HOCH HOCH2CH2OH 2CH2OH

O=CHOCH2CH2O

200

150

OCH3

[CH22CHCH33O]m O]m

100

50

0

4. Conclusion The above results lead to a better understanding of the combustion mechanism of the template in the MMS. N2 sorption and 13C NMR experiments

193 193

of these materials calcined at different temperatures showed that larger mesopores are first emptied followed by intrawall porosity. Further on going studies will investigate the relation between the SBA-15 porosity and the template combustion pattern. 5. References [1] D. Zhao, J. Feng, Q. Huo, N. Melosh, G. H. Fredrickson, B. F. Chmelka and G. D. Stucky, Science 279 (1998) 548. [2] D. Zhao, Q. Huo, J. Feng, B.F. Chmelka and G.D. Stucky, J. Am. Chem. Soc. 120 (1998) 6024. [3] G. Buchel, R. Denoyel, P. L. Llewellyn and J. Rouquerol, J. Mater. Chem. 11 (2001) 589. [4] M.TJ. Keene, R. Denoyel and P.L. Llewellyn Chem. Commun. (1998) 2203. [5] R. van Grieken, G. Calleja, G. D. Stucky, J. A. Melero, R. A. Garcia and J. Iglesias, Langmuir 19 (2003) 3966. [6] S. Kawi and M. W. Lai, Chem. Commun. (1998) 1407. [7] B. Tian, X. Liu, C. Yu, F. Gao, Q. Luo, S. Xie, B. Tu and D. Zhao Chem. Commun. (2002) 1186. [8] C.-M. Yang, B. Zibrowius, W. Schmidt and F. Schuth, Chem. Mater. 16 (2004) 2918. [9] C.-M. Yang, B. Zibrowius, W. Schmidt and F. Schuth, Chem. Mater. 15 (2003) 3739. [10] M. Kruk, M. Jaroniec, C. H. Ko and R. Ryoo, Chem. Mater. 12 (2000) 1961. [11] C.-Y. Chen, H.-X. Li and M.E. Davis Microporous Mater. 2 (1993) 17. [12] A.G.S. Prado and C. Airoldi J. Mater. Chem. 12 (2002) 3823. [13] R. Mokaya and W. Jones, J. Mater. Chem. 8 (1998) 2819. [14] S. Hitz and R. Prins, J. Catal. 168 (1997) 194. [15] F. Kleitz, W. Schmidt and F. Schuth, Micropor. Mesopor. Mater. 65 (2003) 1. [16] M. Jaroniec, M. Kruk and J. P. Oliver, Langmuir 15 (1999) 5410. [17] C. Decker and J. Marchal, Die Makromolekulare Chemie 166 (1973)117.

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Progress in in Mesostructured Materials Recent Progress S. Qiu, Y. Tang and C. Yu (Editors) (Editors) D. Zhao, S. © 2007 2007 Elsevier Elsevier B.V. B.V. All All rights rights reserved. reserved.

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Evolution of mesoporosity and microporosity of SBA-15 during a treatment with sulfuric acid Anja Rumpleckera, Bodo Zibrowiusa, Wolfgang Schmidt3 Chia-Min Yangb and Ferdi Schiith3 "Max-Planck-Institut fur Kohlenforschung, 45470, Mulheim an der Ruhr, Germany, Deptartment of Chemistry, National Tsing Hua University, Hsinchu, 30013 Taiwan

1. Introduction SBA-15 type materials are prepared by cooperative self-assembly of silica and micelles of a triblock copolymer as structure directing agent, which is afterwards removed either by calcination, microwave digestion, solvent extraction, or supercritical fluid extraction. The synthesis of SBA-15 type materials offers great potential for fine-tuning pore dimensions, pore structures and particle morphology which can be achieved by adjusting solution composition, pH, reaction time and temperature. However, selective access to only one of the pore systems remains a challenging task. Such a bimodal, microporous and mesoporous structure is of special interest for applications in various fields, such as in catalysis, in delivery and release techniques, in adsorption and separation processes. Hence, a better understanding of stepwise vacation of mesopores and micropores in SBA-15 type materials prepared at different conditions is of high importance. 2. Experimental Section The SBA-15 silica materials used were synthesized according to the methods described in literature [1,2]. A hydrochloric acid (HC1) solution of the triblock copolymer was prepared and tetraethoxysilane (TEOS) was added after complete dissolution. The molar composition was 1 TEOS : 191 H2O : 0.017 P123 : x HC1, varying systematically the concentration of HC1 (0.3 mol L"1 < x < 1.7 mol L"'). The mixture was stirred at 35 °C and hydrothermally treated at 90 °C. After filtration of the solid was dried at 90 °C. Samples were designated as Sx-48-y, where x stands for the sample number and y stands for drying

196 196

duration in hours. Samples designated as Sx-48-yA were washed with acetone prior to the drying. The influence of HC1 concentration, of acetone washing, and of the drying time on the properties of the material obtained after treating the as-synthesized SB A-15 with H2SO4 (48 %) at 95 °C for 24 h were examined. The materials were characterized by nitrogen physisorption, thermogravimetrydifferential thermal analysis coupled with mass spectrometry, powder X-ray diffraction, 13C CP/MAS NMR and 29Si MAS NMR spectroscopy. 3. Results and Discussion Due to the strong influence on surface properties, mesopore size distribution and the ordered structure itself, the template removal is generally one of the most important steps during the preparation of mesoporous ordered materials. Recently, a procedure for the stepwise removal of the triblock copolymer template Pluronic PI23 has been developed for mesoporous SBA-15 type materials, which is based on the use of concentrated aqueous solutions of sulfuric acid [3]. The method is based on ether cleavage, which happens selectively in the easily accessible mesopores. Afterwards the micropores blocked by poly(ethylene oxide) fractions of the block copolymer template can be made accessible by a calcination at 250 °C. The nitrogen physisorption isotherms and t-plots of two SBA-15 batches prepared at different HC1 concentrations are reported in Figure 1. The structure directing agent was removed by a treatment with H2SO4 and, in comparison to that, by a calcination at 540°C. Sample SI was prepared at low concentration (0.3 mol L"1) of HC1 during the synthesis as described previously by Choi et al [2]. Sample S2 was prepared at high concentration of HC1 (1.7 mol L"1), which corresponds to the conditions described in the original literature of Zhao et al [1]. In all cases, the isotherms are of type-IV with a clear HI-type hysteresis loop, typical of materials with a constant cross section. As described in literature, the isotherms and t-plots of the calcined samples indicate comparable textural properties of both SBA-15 materials using different synthetic approaches [2]. Nevertheless, the isotherms and the t-plots of the SBA-15 samples treated with H2SO4 strongly differ from each other. This clearly suggests different distributions of mesopore volumes and micropore volumes for SBA-15 materials which were prepared with low concentration (0.3 mol L"') and high concentration (1.7 mol L"1) of HC1 during the synthesis. The t-plot in Figure 1 illustrate that only for the latter a post-synthesis treatment with H2SO4 leads to a stepwise vacation of mesopores and micropores. For SBA-15 materials prepared at substantially reduced acid concentrations (SI) a selective removal of only the poly(propylene oxide) fraction of the triblock copolymer template was not possible under any of the conditions applied. The results indicate that the synthesis procedure of SBA-15 has a strong influence on mesopore sizes and micropore sizes after a template removal using acid extraction methods. Therefore, we systematically studied the influence of

197 197

0.2

0.4 0.6 0.8 relative pressures p/p

1.0

0.2

0.4 0.6 0.8 relative pressure p/p

1.0

Figure 1: N2 isotherms and t-plots (inserts) of calcined SBA-15 (filled symbols) and of SBA-15 treated with 48wt % H2SO4 (open symbols); SBA-15 prepared with 0.3 mol I/ 1 HC1 (SI, I) and SBA-15 prepared with 1.7 mol L 1 HC1 (S2,11).

the HC1 concentration (0.3 mol L"1 < x < 1.7 mol L"1) at otherwise fixed molar composition of the synthesis. Furthermore, we analyzed the influence of the drying procedure of SBA-15, prepared at different HC1 concentrations, on the results of a post-synthesis treatment with H2SO4. Figure 2 shows the nitrogen isotherms and the t-plots of acid treated samples of one batch of SBA-15 prepared at low concentration of HC1 (0.3 mol L"1) after the as-made material was dried for 10, 20 or 40 h, respectively. One part of the as-made material was washed with acetone after filtering and lateron dried as described above.

0.0

0.2

0.4

0.6

0.

rel. pressures p/p 0

1.0

0.2

0.4

0.6 0.1

rel. pressures p/p 0

1.0

- • - S 3 48 40 -O-S34840A 0.2 0.4 0.6 0.8 1.0 rel. pressures p/p 0

Figure 2: N2 isotherms and t-plots (inserts) of SBA-15 treated with 48 wt % H2SO4 after different drying times. Open symbols indicate the experimental results for samples washed with acetone prior to drying.

The isotherms of the sample S3-48-10 and the acetone washed S3-48-10A differ strongly in the shape of the hysteresis loop. Therefore, it can be assumed that acetone washing of a freshly prepared as-made material can influence

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mesopore shapes in case of SB A-15 prepared at low concentrations of HCl. For both materials, a treatment with the H2SO4 solution also vacates the micropores. After a longer drying (40 h) of the as-made material, the difference of the textural properties for acid treated samples becomes significantly smaller. Here, washing the as-made material with acetone does not lead to different pore size distributions. The inserts in Figure 2 show that acetone washing and extended drying times facilitate a selective vacation of only the mesopores. 4. Conclusion This study concerns in particular the stepwise vacation of mesopores and micropores using a treatment with H2SO4. Comparing SBA-15 materials prepared at different concentrations of HCl, we conclude that the mesopore and micropore size distribution after a treatment with H2SO4 depends strongly on the HCl concentration during the synthesis of the as-made SBA-15. An acid treatment of as-made SB A-15 prepared at substantially lower concentrations of HCl (0.3 mol L'1) does not necessarily lead to a selective vacation of the mesopores. For such samples the post-synthesis steps are the key factors influencing the mesopore and micropore size distribution. An extended drying period in combination with acetone washing leads to selective vacation of the mesopores. We suggest, that the evolution of mesopores and micropores during acid extraction depends on the degree of condensation of the silica which is influenced both by acid concentration during synthesis and by the drying procedure. 5. References [1] D. Zhao, Q. Huo, J. Feng, B. F. Chmelka and G.D.Stucky, J. Am. Chem. Soc, 120 (1998) 6024. [2] M. Choi, W. Heo, F. Kleitz and R. Ryoo, Chem. Commun. (2003) 1340. [3] C. M.Yang, B. Zibrowius, W. Schmidt and F. Schlith, Chem. Mater. 16 (2004) 2918.

Materials Recent Progress in Mesostructured Materials (Editors) D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 2007 Published Published by Elsevier Elsevier B.V. B.V.

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Framework modification and acidity enhancement of zirconium-containing mesoporous materials Lifang Chena, Xiaolong Zhoub'\ Luis E. Norena3, Guoxian Yub, Chenglie Lib and Jin-An Wang0* "Departamento de Ciencias Bdsicas, Universidad Autonoma Metropolitana-A, Av. San Pablo 180, Col. Reynosa-Tamaulipas, 02200 Mexico D.F., Mexico. Petroleum Processing Research Center, East China University of Science and Technology, 200237Shanghai, P. R. China c Labor atorio de Catdlisis y Materiales, SEPI-ESIQIE, Instituto Politecnico Nacional, Col. Zacatenco, 07738 Mexico D.F., Mexico

Zirconium-modified mesoporous molecular sieves with different Si/Zr molar ratios were synthesized through a surfactant templating route. In situ FTIR characterization shows that surfactant strongly interacts with the solid matrix, and its complete removal could be achieved at 400 °C. The structural ordering, textural properties and surface acidity of the resultant materials vary with the Si/Zr molar ratio. The incorporation of zirconium greatly increases not only the number of both Lewis and Bronsted acid sites but also the acid strength. 1. Introduction Zirconium based materials with large surface areas synthesized by sol-gel and non-ions surfactant synthesis routes show interesting catalytic properties in Fischer-Tropsch synthesis and alcohol dehydration [1-4]. Aiming to developing new acid catalytic materials with enhanced acidity and improved accessibility, this work reports synthesis of Zr-containing mesoporous molecular sieves through a cationic surfactant templated pathway. The removal of the clogged surfactant from the solids, textural properties, crystalline structure, zirconium incorporation and surface acidity of the resultant solids were studied by in situ Fourier transform infrared spectroscopy (FTIR), N2-physisorption isotherms, Xray diffraction (XRD), 29Si MAS-NMR, atomic absorption spectroscopic analysis (AAS) and W-visible spectroscopy and in situ FTIR spectroscopy of pyridine adsorption techniques.

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2. Materials Synthesis The mesoporous materials were prepared by adding 0.6 g of fumed silica into 5.4 g of 45% tetrabutylammonium hydroxide aqueous solution with vigorous stirring for 5 min to form a transparent gel. And then 12 g of cetyltrimethylammonium chloride (25 wt% solution in water) were added into the above gel with agitation. Afterwards, 1 g of fumed silica was immediately added into the above mixture followed by vigorous agitation for approximately 15 min. The final step consisted of adding a given amount of zirconium-npropoxide (70% in propanol). The amount of zirconium-n-propoxide depends on the required Si/Zr mole ratio (Si/Zr = 25, 15, 8 and 4). For example, for a typical synthesis leading to a Si/Zr =15 solid, 0.77 ml of zirconium-n-propoxide were added. The mixture was sealed in a Teflon bottle and heated at 100 °C for 48 h. The resultant white solid was filtered and washed, and then dried at 80 °C for 24 hrs. The dried solid was calcined at 600 °C for 6 hrs in air with a flow rate of 60 ml/min. The actual Si/Zr molar ratio in the obtained materials determined by AAS technique was reported in Table 1. 3. Results and Discussion The features of the in situ FTIR spectra of the samples with various Si/Zr ratios are very similar. As an example, a set of FTIR spectra of the as-made sample with a Si/Zr = 4 are shown in Figure 1. At 25 °C, the IR spectrum consists of a broad band between 3700 and 3000 cm"1, which is due to water adsorbed on the sample surface, and two peaks at 2950 and 2850 cm"1, which are assigned to the stretching vibrations of C-H bonds in hydrocarbons (vCH3as and vCH2as), i.e., herein the surfactant [5]. In the C-H deformation vibrations region, several bands at approximately 1480 and 1371 cm"1, arise from vibrations of the bending modes (scissoring and rocking vibrations) of the C-H bonds. Below 1250 cm", the bands are mainly produced by the fundamental vibrations of the Si-O-Si (1231, 791, 575 cm"1) and Si-O-Zr (960 cm"1) bonds within the framework. Increasing temperature results in water desorption and surfactant removal. It is noted that a peak appears around 3710 cm"1 at 200 °C and it gradually shifts towards a higher energy position with temperature increasing, which is assigned to silanol groups linked to the framework. At 400 °C, the disappearance of the group bands at 2800-3000 cm"1 and at 1485 cm'1 strongly indicates complete removal of the clogged surfactant from the solid. The XRD patterns of the as-made samples show four peaks indexed to the (100), (110) (200) and (210) planes of a typical MCM-41 structure with hexagonal arrangement (not shown). After calcination at 600 °C, the (100) peak loses its sharpness and some peaks disappear, indicating that the ordered structure, in some degree, becomes into wormhole-like arrangements, particularly in the solid with high zirconium content. The mean pore diameter, increases from 2.16 nm to 2.53, 2.93 and 3.69 nm and the surface area decreases

201

from 1113.9 m2/g to 680.6, 654.8 and 668.1 m2/g when the Si/Zr molar ratio varies from 25 to 15, 8 and 4, respectively. 4

3

Q

Q 2

Q

300 °C

200 °C

Si/Zr =25

Intensity (a.u.)

Absorbance (a.u.)

400 °C

Si/Zr=15

100 °C

Si/Zr=8 Si/Zr=4

25 °C

4000 3500 3000 2500 2000 1500 1000 1000 500 500 -1 Wavenumbers (cm-1 ) )

Figure 1. A set of in situ FTIR spectra of the samples with different Si/Zr molar ratios.

-80

-90

-100 -110 -120 -130 -140 -150 δ5 (ppm) (ppm)

Figure 2.29Si MAS-NMR spectra of the samples with different Si/Zr molar ratios.

The 29rSi MAS-NMR spectra of the samples calcined at 600 °C are shown in Figure 2. Each spectrum consists of three main components with chemical shifts at ca. -92 ppm (Q2), -103 ppm (Q3) and -115 ppm (Q4) silicon nuclei. All the samples show (Q +Q2)/Q4 value bigger than 0.49 that corresponds to pure SiMCM-41 solid. The UV-vis profiles exhibit a single band around 201 nm attributable to a charge-transfer from oxygen to an isolated Zr (IV) ion in a tetrahedral environment [6]. The peak intensity of the zirconium-containing sample significantly increases with the zirconium content which significantly differs from the pure Si-MCM-41 sample where no clear band is observed in the given range. Both, 29Si NMR and UV-vis characterization results, confirm that zirconium ions are, indeed, homogeneously incorporated within the framework of the mesoporous materials and they occupy the isolated tetrahedral sites. Both Lewis (L) and BrQnsted (B) acid sites are formed on all the samples as characterized by the formation of the pyridine adsorption bands around 1450 cm'1 (L), 1590 cm"1 (L) and 1540 cm"1 (B). As the Si/Zr molar ratio decreases from 25 to 15, 8 and 4, the B acid sites remarkably increase from 11 to 14, 70 and 142 \imo\lg (Table 1). The total acid sites (T) in all the Zr-modified materials are almost two times greater than that of the pure Si-MCM-41 on which no B acid sites but only 658 umol/g Lewis acid sites are formed. The creation of B acid sites in the zirconium modified mesoporous materials is assumed to be related to the strong polarization of Si4+—O--Zr4+ linkages [7]. When the small Si4+ ions are replaced by large Zr4+ ions in the framework of the solid, the electron density around Si is changed due to a charge unbalance or a local structural deformation resulting from the introduction of Zr4+ ions into the

202

vicinity of the hydroxyls carrying silicon, which may activate the SiO-H bond, favoring the release of the proton. Table 1. Acid properties of the Zr-modified samples

Si/Zr (nominal) Si/Zr (AAS) B (|4.mol/g) L (umol/g) oo(Si-MCM-41) 25 15 8 4

25.4 14.8 8.1 4.3

0 11 14 70 142

658 1045 1165 1217 1134

T (fimol/g) 658 1056 1179 1287 1276

4. Conclusion (1) Zirconium incorporation within the framework increases the pore diameter but diminishes the surface area and the pore volume; (2) The structural regularity of the resultant solids can be improved or reduced, depending on the Si/Zr molar ratio; (3) Zirconium incorporation greatly promotes the formation of Bronsted acid sites, and significantly enhances the acid strength and doubly increases the population of the total acid sites compared to the pure Si-MCM-41. 5. Acknowledgment L. F. Chen thanks the scholarship granted by CONACyT-Mexico for her doctoral study. The financial support from the projects CONACyT (Mexico)NSF (China) (No. J 110.426/2005), CGPI-IPN-2006067 and China 973-Project (No. 2004CB720603) are appreciated. The authors thank to Dr. P. Salas and Dr. J. Navarrete for their technical assistances. 6. References [1] [2] [3] [4] [5] [6] [7]

K. Tanabe and T. Yamaguchi, Catal. Today, 20 (1994) 185. J. Walendziewski, B. Pniak and B. Malinowska, Chem. Eng. J., 95 (2003) 113. M. Wei, K. Okabe, H. Arakawa and Y. Teraoka, Catal. Commun., 5 (2004) 597. Q. Zhuang and J. M. Miller, Appl. Catal. A, 209 (2001) L1-L6. V. Ivanov, E. Zausa, Y. Ben Taarit and N. Essayem, Appl. Catal. A, 256 (2003) 225. M. S. Morey, G. D. Stucky, S. Schwarz and M. Froba, J. Phys. Chem. B., 103 (1999) 2037. J. A. Anderson, C. Fergusson, I. Rodriguez-Ramos and A. Guerrero-Ruiz, J. Catal., 192 (2000) 344.

Materials Recent Progress in Mesostructured Materials (Editors) D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 2007 Elsevier Elsevier B.V. All All rights rights reserved. reserved.

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Pulsed field gradient NMR studies of n-hexane diffusion in MCM-41 materials Ziad Adem,a Flavien Guenneau,a Marie-Anne Springuel-Huet,a Juliette Blanchardb and Antoine Gedeona "Laboratoire Systemes Interfaciaux a I 'Echelle Nanometrique, Laboratoire de Reactivite des Surfaces, Universite Pierre et Marie Curie, 4 place Jussieu, 75252 Paris Cedex 05 (France)

1. Introduction The knowledge of transport properties in heterogeneous catalysis is of important interest since the selectivity and the activity depend significantly on diffusion. Pulsed Field Gradient (PFG) NMR has proved to be a valuable tool to probe the intracrystalline diffusion of molecules adsorbed in microporous solids [1]. This technique can also be used to study the diffusion in mesoporous materials, such as MCM-41 [2]. In this case, the root mean square displacement of the diffusing molecules during the observation time A is usually larger than the particle diameter and the purely intracrystalline diffusivity Dintra can only be attained using a "two region" model involving the intra- and interparticle spaces [13]In this work we use PFG NMR to study the influence of the pore diameter, the hydrophobicity of the pore surface and the adsorbate concentration on the intraparticle diffusion of n-hexane in MCM-41 solids. 2. Experimental Section The MCM-41 materials were prepared according to the procedure proposed by Ryoo et al [4] using various alkyltrimethylammonium (from C12 to C18) as surfactants to obtain materials referred as MCM-Cxx, with different pore diameters. The calcinations were performed under air flow at 823 K or 1273 K for 6 h. The characteristics of the samples are given in Table 1. The adsorption isotherms at 295 K of n-hexane were measured and a known amount (expressed in percentage of the saturation loading) was subsequently adsorbed at

204

equilibrium. The NMR experiments were run on a Bruker DSX spectrometer operating at a proton frequency of 300 MHz. The Bruker DiffiO probe delivers a maximum gradient value of 12 T.m"1 along the Bo direction. We used the stimulated echo variant of the spin echo pulse sequence to take advantage of the long relaxation time Ti. 3. Results and Discussion 0

20

40

60

80

0 -0.5

ln ( Ψ )

-1 -1.5 -2 -2.5 -3 -3.5

gradient strength (Gauss.cm-1)

Fig.l. Echo attenuation ( f ) versus the gradient strength (g) for MCM41-C14 at various observation times. (•, 3.5ms); (A, 4ms); (*, 4.5ms); (+, 5ms); (-, 5.5ms); ( • , 6ms); ( • , 6.5ms); ( • , 7ms). Experimental parameters are indicated by symbols and solid curves represent model fits.

Examples of the signal attenuation Q¥) versus the gradient strength are depicted on Fig. 1 for different observation times A. Those curves were fitted using the "two-region" equation introduced by Karger et al. [1, 3] in order to extract the effective diffusion coefficient of n-hexane inside the mesopores. In this approximation the guest molecule can diffuse in the void space between MCM-41 particles (i.e. interparticle space), region 1, or within the MCM-41 channels (i.e. intraparticle space), region 2. Therefore, the echo attenuation is given by: P\D\

<J 1

3

0)

205

where pi denotes the relative number of molecules in the interparticle space. Dl and D2 are the diffusion coefficients for the two regions, 1 and 2, respectively. T2 is the mean lifetime of the diffusing molecule inside the MCM-41 particles, y the gyromagnetic ratio (yH = 2.67x108 T s-1), g the gradient strength, 8 is the gradient pulse duration. The effective observation time A was chosen in the range of 2.5 ms to 8 ms. The variation of D2 with the square-root of A follows a linear trend (Fig. 2). 2 −1 D2 (m (m2.s 1)

2 D2 (m (m2.s−11)

1.6E-09

1.E-09 1.E-09

1.4E-09 1.2E-09 9.E-10

1.0E-09 8.0E-10

8.E-10

6.0E-10 0

0.02 0.04 0.06 0.08 Δ

1/2

0.1

1/2

(s )

Fig.2. Effective diffusion coefficient versus observation time for MCM41-C14 at two relative concentrations. (O, 40%; D, 90%)

0 50 100 100 concentration (% of max. loading) loading)

Fig.3. Effective diffusion coefficient versus relative concentration of n-hexane in MCM41C14

This is a clear sign of the existence of some restricted diffusion and can be rationalized following the theoretical treatment of Mitra et al [5] for a totally reflecting interface: 3

D2(A) - DinSm - 4

^

The extrapolation of the straight line to A=0 gives us the genuine intracrystalline diffusion coefficient Djntra (Table 1). Figure 3 shows the intracristalline diffusion coefficient versus different pore fillings of n-hexane in MCM-C14. The intracrystalline diffusivity decreases when the amount of nhexane is increased, as previously observed [6], approaching a constant value in the vicinity of the condensation region of the adsorption isotherm. Three different diffusivities exist within the pores corresponding to three regions of diffusion: D s , surface diffusion, Dinter, diffusion between the adsorbed layer and the internal void space and D)jq, liquid-phase diffusion [6]. The measured diffusion coefficient (Table 1) may then be considered as the sum of three components. In spite of a pore diameter similar to that of MCM-C12 and MCMC14 the diffusivity measured for MCM-C16 calcined at 1273 K, which presents

206

a more hydrophobic surface, is much higher. The surface diffusion seems to be an important contribution to the overall diffusion. Table 1: Textural characteristics of the MCM-41 materials determined fromN2 adsorption and the intracrystalline diffusion coefficients of n-hexane (at 40 and 90 % of the saturation loading) measured by PFG NMR

0a(A)

Materials

eb(A)

V^cmV)

Diffusion coefficient (m2.s ') 40%

90%

MCM-C18(823K)

44

6.2

1.04

4.41 xlO 9

1.14xlO"9

MCM-C16 (823 K)

40

6.5

0.94

2.89xlO"9

1.17xlO"9

MCM-C14 (823 K)

36

6.5

0.85

9.95x10"'°

8.50xl0"10

MCM-C12 (823 K)

32

7.2

0.70

5.07x10"'°

3.69x10"'°

MCM-C16 (1273 K)

34

8.2

0.66

1.23x10""

8.92x10"'°

a

b

c

pore diameter, wall thickness, mesoporous volume.

4. Conclusion Intracrystalline diffusion measurements of n-hexane in MCM-41 materials with different pore sizes have been carried out by PFG NMR. The results show that the diffusivities are found to be increasing with pore diameter. However, it seems that the pore diameter is not the only factor affecting the diffusion coefficient. Calcination at high temperature (1273 K) clearly shows that the surface state induces an increase in the intraparticle diffusion coefficient. 5. References [1] J. Karger and D. M. Ruthven Diffusion in zeolites and other microporous solids; Wiley Interscience, 1992. [2] E. W. Hansen et al, Micropor. Mesopor. Mater. 22 (1998) 309-320 ; F. Courivaud et al, Micropor. Mesopor. Mater. 35-36 (2000) 327-339 ; F. Stallmach et al, Micropor. Mesopor. Mater. 44-45 (2001) 745-753; F. Stallmach et al, J. Am. Chem. Soc. 122 (2000) 9237-9242. [3] J. Karger, Ad. Colloid Interface Sci. 23 (1985) 129. [4] R. Ryoo et al, Stud. Surf. Sci. Catal. 117 (1998) 151-158; J. M. Kim et al, J. Phys. Chem. B 103 (1999) 6200-6205;S. Jun et al, Micropor. Mesopor. Mater. 41 (2000), 119-127. [5] P. Mitra et al, Phys. Rev. B 47 (1993) 8565-8574; L. Latour et al, J. Magn. Reson. A 101 (1993), 342-346. [6] F. Courivaud et al., Micropor. Mesopor. Mater. 37 (2000), 223-232.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

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TEM Studies of Bicontinuous Cubic Mesoporous Crystals Yasuhiro Sakamotoa, Chuanbo Gaob, Shunai Cheb and Osamu Terasakia "Structural Chemistry, Arrhenius Laboratory, Stockholm University, 10691 Stockholm, Sweden School of Chemistry and Chemical Technology, State Key Laboratory of Composite Materials, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, China

1. Introduction There are several bicontinuous cubic structures observed in water-surfactant system. The three most well known bicontinuous cubic structures are mathematically described by gyroid minimal surface (G-surface), double diamond minimal surface (D-surface) and primitive minimal surface (P-surface), which have zero mean curvature and belong to Ia-3d (called Q230 in watersurfactant system), Pn-3m (Q224) and lm-3m (Q229) space group, respectively (Figure 1). All the structures are uniquely composed of two interpenetrating, but non-intersecting, domains separated by these surfaces, which are located in the middle of the surfactant bilayer in surfactant rich system. Structural transformation between these bicontinuous cubic structures has been attributed to small temperature or composition changes. Their transition enthalpy is much smaller than that of bicontinuous-hexagonal transition and lamellarbicontinuous transition [1, 2]. Topologically, the three minimal surfaces are related to each other through Bonnet transformation. In 1992, scientists in Mobil corporation discovered one of the bicontinuous cubic structures, MCM-48, with Ia-3d symmetry in surfactant templated silica mesophase [3]. MCM-48 has two independent mesopores, which are divided by silica wall formed on G-surface [4]. The surface of silica wall and mesopore is well described by a constant mean curvature surface. Since its bicontinuous mesoporous crystal was found as a chemically and thermally stable solid inorganic material, it has attracted a lot of attentions from various fields. Especially, this cubic bicontinuous silica mesoporous crystal has been recently expected to be useful medium for the rational design of biocompatible materials

208

for encapsulation, controlled release and uptake, and delivery of drugs and bioactive components [5, 6]. Recently we have succeeded in synthesizing a new bicontinuous cubic Pn-3m mesoporous crystal, AMS-10, and solving its structure [7]. The silica wall structure is formed on a D-surface. Whilst many new mesoporous structures have been prepared, AMS-10 is the first newly discovered bicontinuous structure since MCM-48 was found more than ten years ago.

Figure 1. Typical minimal surfaces, (a) G, (b) D, and (c) P-surfaces.

2. Experimental Section This new mesoporous crystal, AMS-10, was synthesized using anionic surfactant 7V-myristoyl-L-glutamic acid (Ci4GluA) as a template and iVtrimethoxylsilylpropyl-Af,Af,AMximehylammonium chloride (TMAPS) as a costructure-directing agent (CSDA) under the condition which NaOH was added in to control the neutralization degree of the surfactant [7]. The structure was characterized by transmission electron microscopy (TEM) and its threedimensional (3D) structure was reconstructed based on electron crystallography method [8]. High resolution TEM (HRTEM) was performed with a JEOL JEM3010 microscope operating at 300 kV (Cs = 0.6 mm, Point resolution 1.7 A). Images were recorded with a CCD camera (MultiScan model 794, Gatan, 1024 x 1024 pixels, pixel size 24 x 24 |im) at 50,000 - 80,000 magnification under low-dose conditions. 3. Results and Discussion The space group of AMS-10 was determined to be Pn-3m based on reflection conditions obtained from Fourier diffractograms of HRTEM images and electron diffraction patterns (Figure 2), although Pn-3 is another candidate from the conditions. The unit cell parameter as derived from XRD pattern is a = 9.6 nm. The 3D electrostatic potential distribution was unquestionably constructed

209

by an inverse Fourier transform of the structure factors, which were extracted from HRTEM images after a correction of contrast transfer function. Based on this 3D electrostatic potential distribution, direct information on the detailed structures of mesoporous crystal AMS-10 was obtained. The main conclusion is that AMS-10 has a bicontinuous cubic structure where the silica wall follows the minimal D-surface. The crystal has two interpenetrating pore systems without intersections. This is the same situation as MCM-48 with Ia-3d symmetry. However, each pore network has four connected nodes (Figure 3b) at the special position with the -43m site symmetry, while in MCM-48, G-surface, three connected nodes (Figure 3a) are at the positions with 32 site symmetry. For reference, P-surface, which has not yet been discovered in silica mesoporous crystals, has six connected nodes (Figure 3c).

mm:.

Figure 2. TEM images of AMS-10 with their Fourier diffractograms. Taken along (a) [100], (b) [110], and (c) [111] directions.

Figure 3. Network connectivity of the (a) G, (b) D, and (c) P-surface. For silica mesoporous crystals these are pore networks.

210

4. References [1] S. T. Hyde, S. Andersson, B. Ericsson and K. Larsson, Z Kristtallogr., 168 (1984) 213. [2] S. T. Hyde, in Handbook of Applied Surface and Colloid Chemistry. Edited by Krister Holmberg, John Wiley & Sons, Ltd 2001, Chapter 16 . [3] J. S. Beck, J. C. Vartuli, W. J. Roth, M. E. Leonowicz, C. T. Kresge, K. D. Schmitt, C. TW. Chu, D. H. Olson, E. W. Sheppard, S. B. McCullen, J. B. Higgins and J. L. Schlenkert, J. Am. Chem. Soc, 114 (1992) 10834. [4] A. Carlsson, M. Kaneda, Y. Sakamoto, O. Terasaki, R. Ryoo and S. H. Joo, J. Electron Microsc, 48 (1999) 795. [5] M. Vallet-Regi, A. Ramila, R. P. Del Real and J. Perez-Pariente, Chem. Mater., 13 (2001) 308. [6] I. Izquierdo-Barba, A. Martines, A. L. Doadrio, J. Perez-Pariente and M. Vallet-Regi, Eur. J. Pharm. Sci., 26 (2005) 365. [7] C. Gao, Y. Sakamoto, K. Sakamoto, O. Terasaki and S. Che, Angew. Chem. Int. Ed., 45 (2006) 4295. [8] Y. Sakamoto, M. Kaneda, O. Terasaki, D. Zhao, J. M. Kim, G. D. Stucky, H. J. Shin and R. Ryoo, Nature, 408 (2000) 449.

Recent Progress in Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Published by Elsevier B.V.

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Characterization of vesicular mesostructured silica synthesized under alkaline conditions Cheng Chi, Bo Wang, Wei Shan, Yahong Zhang and Yi Tang* Department of Chemistry and Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, Fudan University, Shanghai 200433 (P. R. China)

1. Introduction Ordered mesostructured silica has attracted considerable attention in many different areas, such as catalysis, adsorption and separation. Among the various structural types, MCM-41 is one of the most extensively studied mesostructured silica especially in its application in catalysis [1-10]. Many different micronscale morphologies of MCM-41 have been reported by Ozin's group [6-8]. These products were typically prepared by controlling the hydrolysis of tetraethyl orthosilicate (TEOS) under an acidic synthesis condition. A liquid crystal defect mechanism was proposed by Ozin's group to explain these enigmatic curved morphologies [8]. Recently, we reported a series of MCM-41 type vesicular mesostructured silica (VMS) with a rich diversity of micron-scale topologies [10], which was prepared by using the hydrolysis of ester to drive the assembly of silicate and surfactant in an alkaline system [9]. A comparison between VMS and the traditional vesicles suggests that the formation of vesicular structure is a micron-scale self-assembly behavior of MCM-41 mesostructured silica. In this work, the VMS prepared at different reactant concentrations were further systematically characterized by means of thermogravimetric analysis, nitrogen sorption and electron microscopy. 2. Experimental Section The VMS was prepared in a sodium silicate (SS)-cetyltrimethylammionium bromide (CTAB)-ethyl acetate (EA)-water system, as shown in reference [10]. To clearly observe the vesicular structure of VMS, an ammonium treatment was carried out using a diluted ammonium solution (1 wt%) at 80°C overnight. For comparison, a silica gel was also synthesized under the same condition but

212

without adding the surfactant. The thermogravimetric-differential thermal analysis (TG-DTA) was performed on a Rigaku Thermoflex instrument. The samples were heated at a rate of 10 K min"1 from 300 K to 900 K in an air flow. Prior to TG-DTG and DTA experiment the sample was dried at 350 K for 24 h until the mass became constant. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images were obtained on Philips XL 30 and JEOL JEM-2010, respectively. Nitrogen sorption isotherms were measured using a Micromeritics TriStar 3000 system. Before the sorption measurement, the samples were degassed at 200 °C for about 3 h. 3. Results and Discussion (a)

In order to get a better understanding of the TG-DTA result of the VMS sample, we made a comparison between VMS and the silica gel. Figure 1 shows that the TG-DTA profiles of VMS ranging from 300 K to 900 K are quite different from those of the silica gel. The broad peak within the temperature range 350-450 K in the TG-DTA of silica gel corresponds to the water desorption and the condensation of silanol, which leads to a weight loss of ca 8 wt%. Similarly, the VMS also has a weight loss step beginning at ca 400K, induced by the silanol condensation. However, a larger weight loss peak could be identified above 450 K. Since no obvious exothermic effect was detected from the DTA result, this peak should be ascribed to the surfactant fragmentation/evaporation within the nano-pores of VMS [11, 12]. Another relatively smaller peak at ca 620 K could be observed in the DTG, which has a strong exothermic effect. It should be Temperature/ K induced by the oxidation of surfactant or its Figure 1. TG-DTG curves for fragments at such a high temperature [11,12]. VMS (a), silica gel (b) and DTA When the VMS sample was heated up to curves for both samples (c). 900 K, only the pure silica remains, therefore, the silica content of the VMS could be estimated from its residue weight after calcination at high temperature. It is found by measuring more than 30 samples that the silica content of VMS is ca 45-55 wt%. We further made a comparison between the amount of silica in the VMS product and the silicate sodium we used during the synthesis process. Interestingly, we found that more than 90% of the silicate source transferred into the VMS product within the experimental 300

400

500

600

213

ranges of CTAB and EA concentrations (see figure 2). This result indicates that the surfactant is over-amounted in the synthesis of VMS, as compared to the silicate source. In other words, the over-amounted "soft template" during the self-assembly of vesicular MCM-41 should be an important factor for the formation of ordered 2D hexagonal mesostructure. Insufficient surfactants would lead to the formation of small amorphous silica particles. Our further study shows that amount of the CTAB also plays a role in controlling the dimension of the product. The detailed result will be reported elsewhere. The pore structures of VMS were characterized by nitrogen sorption isotherms. Figure 3 demonstrate a large hysteresis loop at the relative pressure of 0.8-1.0, 0.4 0.6 0.8 Relative pressure (p/p ) corresponding to a large quantity of nonMCM-41 pores in the VMS product. Because Figure 2. Silica yields of VMS of the existence of large pores, such material prepared at different concen-trations was ever considered to be bimodal of CATB and EA (molar ratio, 4.07 SS: x CTAB; y EA: 1,000 H2O). mesoporous silica in the literature [9]. However, we found in this work that these large pores would decrease after a simple hydrothermal treatment in a diluted ammonium solution at 80°C, while the MCM-41 mesopores were well retained. The TEM images of the ammonium-treated VMS exhibit obviously enlarged cavities (Figure 4), suggesting that the non-MCM-41 pores mainly exist in the amorphous phase inside the vesicular structure. (Figure 4f) Figure 3. Nitrogen sorption isotherms Conversely, the MCM-41 pores mainly exist of VMS (molar ratio, 4.07 SS: 1.82 in the shell part of VMS, which could be CTAB; 13.3 EA: 1,000 H2O) before identified in Figure 4d. The assembly process (I) and after (11,111) ammonium leading to the formation of such hybrid pores treatment. Curves I and II were moved in VMS was further discussed as below. up 800 and 400 cm3/g respectively. During the synthesis process various vesicular structures with MCM-41-type mesostructures are formed in the aqueous solution, which is driven by the self-assembly behavior of the silicatesurfactant complexes [10]. However, owing to the closed vesicular structures, some intermediate species (i.e. silicate anion and cationic surfactant) would possibly be encapsulated in the large cavity of VMS. During the recovery process of VMS from the synthesis solution, a fast precipitation might occur to the encapsulated species inside the vesicular structure. It would result in 0

EA (mol /1.000 H;O)

214

unordered silicate-surfactant aggregates with relatively large pores. However, these encapsulated aggregates could be easy to be removed by diluted alkali solution due to the weak interaction between surfactants and silicates. 4. Conclusion Vesicular MCM-41 was further systematically characterized by means of thermogravimetric analysis, nitrogen sorption and electron microscopy. The TG-DTA result of VMS is similar to that of the conventional MCM-41 product [10,11]. The further analysis of the silica yield revealed that more than 90% of the silicate Figure 4. SEM and TEM images of source transferred into the VMS product during VMS (molar ratio, 4.07 SS: x the self-assembly process, and an over-amount CTAB; y EA: 1,000 H2O) before of surfactant is critical to the formation of (a,c,d) and after (b,e,f) ammonium ordered 2D hexagonal mesostructure. Moreover, treatment the combination of the nitrogen sorption and TEM results showed that the nonMCM-41 pores mainly exist in the center of VMS while the MCM-41 pores exist in the shell part. 5. References [1] C. T. Kresge, M. E. Leonowicz, W. J. Roth, J. C. Vartuli and J. S. Beck, Nature 359(1992) 710. [2] A. Firouzi, D. Kumar, L. M. Bull, T. Besier, P. Sieger, Q. Huo, S. A. Walker, J.A. Zasadzinski, C. Glinka, J. Nicol, D. Margolese, G. D. Stucky and B. F. Chmelka, Science, 267(1995)1138. [3] A. Monnier, F. Schuth, Q. Huo, D. Kumar, D. Margolese, R. S. Maxwell, G. D. Stucky, M. Krishnamurty, P. Petroff, A. Firouzi, M. Janicke and B. F. Chmelka, Science, 261(1993) 1299. [4] H. P. Lin and C. Y. Mou, Science, 273(1996) 765. [5] H. P. Lin, Y. R. Cheng and C. Y. Mou, Chem. Mater., 10(1998) 3772. [6] H. Yang, N. Coombs and G. A. Ozin, Nature, 386(1997) 692. [7] H. Yang, G. A. Ozin and C. T. Kresge, Adv. Mater., 10(1998) 883. [8] S. M. Yang, H. Yang, N. Coombs, I. Sokolov, C. T. Kresge and G. A. Ozin, Adv. Mater., 11(1999)52. [9] G. Schulz-Ekloff, J. Rathousky and A. Zukal, Inter. J. Inorg. Mater., 1(1999) 97. [10] B. Wang, W. Shan, Y. H. Zhang, J. C. Xia, W. L. Yang, Z. Gao and Y. Tang, Adv. Mater., 17(2005) 578. [11] A. S. Araujo and M. Jaroniec, Thermochimi. Acta 363(2000) 175. [12] J. Goworekl, A. Borowka, R. Zaleski and R. Kusak J. Therm. Anal. Cal., 79(2005) 555.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

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Zirconium species created within the mesopores of MCM-41 and NbMCM-41 Joanna Goscianska and Maria Ziolek* Adam Mickiewicz University, Faculty of Chemistry, Grunwaldzka 6, PL-60-780 Poznan, Poland

1. Introduction The synthesis and characterization of nanoscale siiicides with potential application in nanotechnology is of a great interest in the development of new materials used in modern technology. The most often used techniques for their preparation is the sputtering method to deposit metal layers for contacts or in the self-aligned silicidation process. As Mo and Ti systems were widely investigated less work has been done on the Zr/Si materials for contacts [1]. The generation of zirconium siiicides could base on the silicon treating with Zr source because Zr readily removes native oxide layers existing at the Zr-Si interfaces (ZrO2 has a larger negative heat of formation than that of SiO2). The formation of silicide is accounted for by a reaction mechanism involving a reaction of ZrO2 with SiO [2]. This feature led us to an idea of the creation of zirconium siiicides in the mesoporous silicate and niobosilicate MCM-41 type materials. The undertaken study faced two basic challenges. First - finding the possibility for the zirconium silicide formation in MCM-41 materials. Second diagnosing the role of Nb in the creation of Zr species towards the formation of the effective ZrNbMCM-41 support for platinum. Pt/ZrNbMCM-41 would be addressed to NSR (NO storage reduction) process. NbMCM-41 was chosen as a matrix for Zr because Nb is an excellent NO storage species [3] and one could expect that the admission of Zr improves both the thermal stability and spillover effect. These issues play an important role in the creation of catalysts for NOx removal from exhaust gases from lean fuel burn engines. Therefore, the studies reported in this paper give the fundamentals for the further preparation of the threefold system (Pt, Zr, Nb) intended to the NOx reduction.

216 216

2. Experimental Section MCM-41 was synthesized following the procedure reported originally by Kresge at al. [4] i.e. by the hydrothermal method from sodium silicate (27% SiO2in 14% NaOH; Aldrich) and cetyltrimethylammonium chloride (25 wt. % in water; Aldrich) as a template. Ammonium complex of niobium(V) trisoxalate solution (CBMM, Brazil) and zirconium dinitrate oxide- ZrO(NO3)2 (Alfa Aesar) were used when mono or bimetallic silicates were produced. The Si/T atomic ratio (T=Nb and/or Zr) in the gels was 128. NbMCM-41 was also impregnated with zirconium salt. The prepared materials were characterized by XRD (TUR62 diffractometer, CuKot radiation), nitrogen sorption (Micrometrics 2010) SEM, TEM (JEOL 2000 electron microscope), UV-VIS (VARIAN CARY 300 Scan), 29Si NMR (Bruker Avance 300dmx spectrometer operating at 59.62 MHz), TG/DSC (TG Setaram SetSysl2 thermobalance, in air or nitrogen, heating ramp 5 K min"1), and FTIR (Bruker FTIR Vector 22, the samples dispersed in KBr pellets). 3. Results and Discussion Table 1. Texture parameters of the catalysts and UV-VIS results. Mesopore Catalyst

d1Oo

ao, nm

-'D'

Wall thickness,

UV-VIS bands, nm

BJHads. PSD, nm

MCM-41

3.65

4.21

1323

3.11

1.25

-

ZrMCM-41

3.26

3.77

1019

2.56

1.33

230, 250 (overlapped)

NbMCM-41

3.87

4.47

1047

2.88

1.73

218

ZrNbMCM-41

3.87

4.47

1015

2.64

1.96

230, 250 (shoulder)

Zr/NbMCM-41* 3.81

4.40

994

2.83

1.70

218, 230 (overlapped)

* - Zr impregnated sample, **- t = ao - D/l.05

XRD patterns (Fig. 1A) as well as nitrogen adsorption isotherms and TEM images confirmed the hexagonal, well ordered arrangement of mesopores in all studied samples. Nitrogen adsorption isotherms of all the materials studied are of type IV according to the IUPAC classification. The significantly increase of adsorption in p/p0 = 0.9-1 for NbMCM-41 and Zr/NbMCM-41 samples indicates the presence of macroporosity, which is less visible in the case of ZrMCM-41 sample and does not occur in ZrNbMCM-41. Texture parameters of the prepared materials shown in Table 1 indicate the significant influence of niobium content on the unit cell (ao) and dioo parameters, whereas Zr admission during the synthesis does not change these values and the

217

impregnation of NbMCM-41 with zirconium salt slightly decreases both features. Interestingly, Zr introduced together with Nb species leads to the diminishing of the mesopore diameter by the increase of wall thickness. The question arises whether zirconium is located inside the skeleton or in the extra framework position. UV-VIS result (Table 1) for ZrNbMCM41 indicates the A B presence of the 31,76 band at 230 nm with a wide 2rO (211) shoulder at ~ 250 45,46 nm. The first one, ZrSi(321) ZrO (140) which is not 66.19 75,28 a exactly at the a £• same position as b described in the c ; literature [5,6] for <_ absorption edge • l d =10000V, -/^*y energy of 243 nm characteristic of 20, 2®,' the charge transfer O2"-» Zr4+ Figure 1. A) Small-angle X-ray diffraction patterns of a) ZrMCM-41, b) in pure zirconia, ZrNbMCM-41, c) Zr/NbMCM-41, d) NbMCM-41; B) High-angle XRD can be assigned to patterns of a) ZrNbMCM-41, b) Zr/NbMCM-41, c) ZrMCM-41. zirconium cations coordinated to Si(IV) by tetrahedral environments of oxygens. The same sample reveals the highest intensity IR band at ca. 970 cm-1 commonly assigned to SiO vibration perturbed by the substitution of ^ silicon by metal cation. The UV shoulder at ~ 250 nm originates from Zr-oxide extra framework species. The samples containing Nb exhibit the UV-VIS band at ~ 218 nm, which is due to O2" —> Nb5+ (Nb located in MCM-41 structure). The interesting finding from this work was that from high-angle XRD patterns which can be indexed to the ZrSi(lll) and (321) - JCPDF file 72-1271, ZrO2(211) and (140) - JCPDF file 86-1451 diffraction planes (Fig. IB). These crystalline phases were observed in XRD patterns of all -60 -120 the materials containing zirconium. However, ppm the highest intensity of these X-ray diffraction peaks was noted for ZrNbMCM- Figure 2. 29Si MAS solid-state NMR 41 sample prepared via the simultaneously spectra of a) ZrNbMCM-41, b) introduction of both metals sources. This issue Zr/NbMCM-41, c) NbMCM-41, d)

1

•

ensity, a.u.

2

2

•

ZrMCM-41.

218

allows us to suppose that the presence of niobium causes the creation of zirconium silicide (or oxysilicide) and oxide in the extra framework positions much easier. This behavior is confirmed by 29SiNMR spectra (Fig. 2) which indicate one main band at -109,14 ppm typical of silicon in tetrahedral coordination with oxygen like in zeolites and mesoporous silicates [e.g. 7,8], and additionally a weak band at -123,5 (127) ppm not registered for Si surrounded by oxygen. Moreover, TG/DTA analysis show the exothermic effect at ca 1000 K without any change of mass for all materials containing zirconium. One can assign it to the decomposition of Zr-silicide (or oxysilicide). It is worthy of notice a very high thermal stability of bimetallic sample deduced from the TG analysis. 4. Summary The application of zirconium dinitrate oxide as a Zr source in the classical hydrothermal route of MCM-41 synthesis allows one to introduce Zr partially into the skeleton (UV-VIS, IR) and to obtain Zr-silicides (or oxysilicides) and oxides in the extra framework positions (XRD, 29SiNMR). It seems to be probable that the use of ZrO(NO3)2 in the synthesis play an important role in the silicide (or oxysilicide) generation as the presence of nitrogen makes the ZrSi formation easier [9]. Especially interesting is the formation of the bifunctional materials containing zirconium and niobium species located in the mesostructured molecular sieves which could be attractive not only for nanotechnology but also for catalysis. 5. Acknowledgement The Polish Ministry of Science and Higher Education (grant No PBZ-KBN116/T09/2004) and CBMM (Brazil) are acknowledged for the financial support and for the supplying Nb source, respectively. 6. References [1] V. Sisodia, W. Boise, D. K. Avasthi, D. Kabiraj and I. P. Jain, Radiation Measurements, 40 (2005) 762. [2] T. S. Jeon, J.M. White and D. L. Kwong, Appl. Phys. Lett.,78 (2001) 368. [3] I. Sobczak, M. Ziolek and M. Nowacka, Microporous Mesoporous Mater., 78 (2005) 103. [4] C. K. Kresge, M. E. Leonowicz, W. J. Roth, J. C. Vartuli and J. S. Beck, Nature, 359 (1992) 710. [5] T. Onfroy, G. Clet and M. Houalla, J. Phys. Chem. B, 109 (2005) 3345. [6] T. Onfroy, G. Clet and M. Houalla, J. Phys. Chem. B, 109 (2005) 14588. [7] Z. Luan, Ch.-F. Cheng, W. Zhou and J. Klinowski, J. Phys. Chem., 99 (1995) 1018. [8] S-Y. Chen, L-Y. Jang and S. Cheng, Chem. Mater., 16 (2004) 4174. [9] M. A. Gribelyuk, A. Callegarii, E. P. Gusev, M. Copel and D. A. Buchanan, J. Appl. Phys., 92(2002)1232.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

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Synthesis and characterization of tetrahedral aluminum-species-containing SBA-15 and its application for selective /-butylation of naphthalene M. Selvaraj and S. Kawi* Department of Chemical & Biomolecular Engineering, National University of Singapore, Singapore - 119260.

Mesoporous Al-SBA-15 molecular sieves with different «si/«Ai ratios have been directly synthesized and characterized. The synthesized mesoporous materials have been used as catalysts for vapor-phase ^-butylation of naphthalene for selective synthesis of 2-mono-/-butylnaphthalene (2-MTBN) and 2,6-di-t-butylnaphthalene (2,6-DTBN) using benzene as the solvent and tbutyl alcohol (£-BuOH) as the alkylating agent under different optimal reaction conditions. A1-SBA-15(5) is found to be more selective to produce 2-MTBN and 2,6-DTBN than other Al-SBA-15 catalysts. 1. Introduction The family of mesoporous SBA-15 materials [l(a)] - synthesized with triblock copolymer as the surfactant under strong acidic conditions - exhibit larger pore sizes and thicker pore walls as compared with M41S materials. However, it is very difficult to introduce the metal ions into SBA-15 directly due to the facile dissociation of metal-O-Si bonds under strong acidic hydrothermal conditions. Therefore, so far only a few papers have reported the direct synthesis of Al-SBA-15 materials [l(b)]. /-butylnaphthalenes - such as 2-mono-/-butylnaphthalene (2-MTBN) and 2,6/2,7-di-^-butylnaphthalene (2,6/2,7-DTBN) - have been used as intermediates in the synthesis of novel polyester resins, such as 2,6-naphthalenedicarboxylic acid and 2-hydroxy-6-carboxynaphthalene. The polymerized products of these molecules are used as thermotropic polyesters and engineering plastics. The dif-butyl naphthalenes can be selectively prepared using shape selective zeolites due to the larger size differences between different butyl naphthalenes [2]. In this work, the vapor phase alkylation of naphthalene over mesoporous Al-SBA-

220

15 catalysts with various nS{/nM ratios under different optimized conditions has been investigated. 2. Experimental Section Mesoporous Al-SBA-15 materials with different nsJnM molar ratios (5, 10, 50 and 100) were directly synthesized by simply adjusting the molar ratio of «H2O/«HCI with NH4F using PI23 Pluronic triblock polymer as the structuring agent. The molar composition of synthesis gel was 1 TEOS/0.01-0.2 A12O3/ 0.06 P123/0.00053 NH4F/0.43-5.2 HC1/ 127-210 H2O. The resulting materials were characterized by ICP-AES, XRD, N2-adsorption, and 27A1-MAS NMR. The vapour phase catalytic reaction was carried out in a fixed bed, tubular, down flow glass reactor. The reaction mixture contained naphthalene and tbutanol, with benzene as the solvent. The reaction products were analyzed using gas chromatograph (Shimadzu) equipped with 2 m long 5%SE-30 column and FID. The products were confirmed by GCMS analysis. 3. Results and Discussion

Intensity (a.u)

Table 1 shows that the HS/HAI atomic ratios of synthesized Al-SBA-15 samples decrease from 49.3 to 2.9 with increasing «H2O/«HCI ratio, clearly showing T -Al that a decrease of acid concentration induces a high loading of Al-ion in the SBA-15 mesoporous structure. The values of «S/«AI atomic ratios for all products were measured by ICP-AES. At high «H2O/«HCI ratio, the «S/WAI atomic ratios in the products are close to the ratios in the corresponding gel. The WS/^AI atomic -50 0 50 100 150 200 ratios of the resulting materials also increase when the -200 -150 -100Chemical (ppm) Shift (ppm) «si/«Ai atomic ratios in the synthesis gel are increased at a fixed «H2O/«HCI ratio of 295. All these results can Fig. 1.27A1MAS-NMR be explained as follows. It is known that Al-SBA-15 spectrum of calcined A1-SBA-15(5). materials can generally be synthesized under strongly acidic hydrothermal conditions that easily induce the dissociation of the Al-O-Si bonds due to high hydrolysis rate of aluminum precursors with silicon precursors. However, lowering the acidity of the solution may decrease the hydrolysis rate of the aluminum precursors, possibly due to the enhanced interaction between the Al-OH and Si-OH species in the synthesis gel and hence resulting in a higher amount of Al-ion incorporation in the silica framework under a high ratio of «H2O/«HCIStructural, textural and acidity properties of the corresponding samples have been analyzed by XRD, N2 adsorption and FTIR-pyridine, and the results are given in Tables 1 and 2. The well-defined XRD patterns of all Al-SBA-15 d

-200 -150 -100 -50

0

50

100 150 200

221 = a40, b70, C166 and d295.

Table 1: Physico-chemical properties of Al-SBA-15 and nm0/nHa n s/«Al

Dp

T

(cm /g)

(A)

(A)

a0

V

P

gel

Product

(A)

(m2/g)

a

5

49.3

119.9

850

1.04

85.6

34.3

Al-SBA-15(5)b

5

27.7

121.7

890

1.06

86.7

35.1

C

A1-SBA-15(5)

5

8.4

122.4

910

1.08

86.7

35.7

Al-SBA-15(5)d

5

2.9

123.1

978

1.10

86.8

36.3

10

5.4

121.2

990

1.11

87.2

34.0

50

26.6

120.4

1015

1.12

87.6

32.8

100

52.5

119.4

1050

1.13

88.2

31.2

Catalysts Al-SBA-15(5)

Al-SBA-15(10)

d

Al-SBA-15(50)

d

Al-SBA-15(100)d

3

100

80

80

Conversion (%)

100

60

60

Conversion of naphthalene selectivity of 2-MTBN selectivity of 2,6-DTBN

40

40

20

0 0.2

20

0.3

0.4

0.5

0.6

0.7 -1

0.8

0.9

1.0

0

Selectivity (%)

samples are similar to those recorded for silica SBA-15 samples [l(a)]. Table 1 shows that increasing «H2O/«HCI ratio (which was adjusted with NH4F) and decreasing KSi/nAi ratio in the gel at a fixed «H2O/«HCI ratio of 295 not only could increase the unit cell parameter (a0), surface area (&4BET)> pore volume (Vp), pore diameter (Dp) and thickness of pore walls (7"w = ao-Dv) but also could produce a high amount of Al-ions incorporated in the framework of silica mesopore walls. Generally, structural and textural properties of Al-SBA-15 samples increase with increasing «si/nAi, except the thickness of pore walls due to a high amount of Al-ion incorporation. The Bronsted acidity in A1-SBA-15(5) is higher than that of other Al-SBA-15 due to an increasing amount of tetrahedral aluminum-ions in the inner surface of mesopores, possibly due to the NH4F treatments (Table 2). The 27A1-NMR spectrum of calcined A1-SBA-15(5) shows a sharp peak with a chemical shift of 50 ppm, indicating the presence of Al3+ in tetrahedral coordination (Fig. 1). Hence all these results suggest that a high «H2O/«HCI ratio (adjusted with NH4F treatment) favours the incorporation of a large amount of Al-ions into the mesoporous framework of SBA-15 without affecting the structural order. Vapor phase /-butylation of naphthalene (N) with f-BuOH (B) over Al-SBA-15 catalysts was carried out under different optimal reaction conditions, such as reaction temperature, WHSV, TOS and different reactant ratios. Table 2 shows that the selectivity of 2-MTBN decreases with increasing temperature (from 200 to 240°C), 0.3 0.4 0.5 0.6 0.7 0.8 0.9 WHSV (h (h ')) TOS (from 3 to 4 h), WHSV (from 0.5 to 1.0 h"1, Figure 2) and molar ratio of N: B (from 1:5 to Fig. 2. Effect of WHSV on 1:8); the decrease was caused by the increase of conversion and selectivity over 2,6-DTBN. When all Al-SBA-15 catalysts were A1-SBA-15(5). tested at 220°C under 1 : 5 molar ratio of N : B, TOS of 3 h, and WHSV of 0.5 h , A1-SBA-15(5) is found to be the best catalyst

222

among Al-SBA-15 catalysts as A1-SBA-15(5) has the best conversion of naphthalene (CN of 75.3%) and the best selectivity of major product 2-MTBN (98.4%), due to the presence of the highest amount of Bronsted acid sites on AlSBA-15(5). Table 2:

/-Butylation of naphthalene over Al-SBA-15 catalysts'1 Selectivity (%)

Catalysts

CN (%)

2-MTBN

Al-SBA-15(5)

75.3

98.4

Al-SBA-15(10)

60.3

80.3

Al-SBA-15(50)

50.2

70.5

Al-SBA-15(100)

40.4

60.7

b

78.5

25.0

Al-SBA- 15(5)c

55.3

48.2

d

40.3

e

55.4

Al-SBA-15(5) Al-SBA-15(5)

Al-SBA-15(5)

2,6-DTBN

Acidity at 250°C Others

B

L

1.5

0.1

32.3

12.4

3.2

16.5

30.4

10.3

4.5

25.0

28.4

6.7

6.7

32.6

24.3

5.3

70.0

5.0

-

-

50.5

1.3

-

-

98.6

1.4

-

-

-

52.4

40.5

7.1

-

-

""Reaction conditions : catalyst = 0.2 g, T = 220°C, TOS (time on stream) = 3 h, molar ratio of N:B = 1:5, WHSV (weight hourly space velocity) = 0.5 h 1 ; bTOS = 4 h; T = c200°C and d240°C; e molar ratio of N: B = 1:8; f|imol.py./g ; L = Lewis acid; B = Bronsted acid; Others include 2,7DTBN and polyalkylated naphthalenes.

4. Conclusion A large amount of Al-ions can be successfully incorporated, for the first time, into the mesoporous framework of SBA-15 by simply adjusting the molar water to hydrochloric acid ratio with NH4F. The resulting Al-SBA-15 materials were found to be active and selective catalysts for vapor phase t-butylation of naphthalene with r-BuOH to produce 2-MTBN and 2,6-DTBN. 5. References [1] (a). D. Zhao, J. Feng, Q. Huo, N. Melosh, G. H. Fredrickson, B. F. Chmelka and G. D. Stucky, Science 279(1998)548; (b).Y. Yue, A. Gedeon, J.-L. Bonardet, N. Melosh, J.-B. D'Espinose and J. Fraissard, Chem. Commun. (1999) 1967. [2] (a). G. Kamalakar, M.R. Prasad, S.J. Kulkarni and K.V. Raghavan, Micropor. Mesopor. Mater. 52 (2002) 151; (b). M. Selvaraj, K. Lee, K. S. Yoo and T. G. Lee, Micropor. Mesopor. Mater. 81 (2005) 343.

Mesostructured Materials Recent Progress in Mesostructured D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

223 223

Adsorption-desorption characteristics of volatile organic compounds over various zeolites and their regeneration by microwave irradiation K.-J. Kima, Y.-H. Kima, W.-J. Jeongb, N.-C. Parkc, S.-W. Jeongd and H.-G. Ahna* "Dept. ofChem. Eng., Sunchon National Univ., 315 Maegok-dong, Suncheon, Jeonnam, 540-742 Korea Opt. Eng. Res. Institute, Mokpo National Univ., Jeonnam, 453-729, Korea c Dept. ofChem. Eng., Chonnam National Univ., 300 Yongbong-dong, Buk-gu, Gwangju, 500-757 Korea Jeonnam Techno Park, 315 Maegok-dong, Suncheon, Jeonnam, 540-742 Korea.

Adsorption of volatile organic compounds (VOCs) over various zeolites was performed to determine the relationship between adsorption capacity and physical properties of zeolites. The desorption characteristics was investigated by means of conventional heating and microwave irradiation. FAU, Z-HY4.8, and MS-13X were better adsorption performance than the others. Desorption efficiency by microwave heating was better than that by conventional heating. 1. Introduction The volatile organic compounds (VOCs) exhaust that is caused by increase of the various organic solvent and the paints has been gradually increased. The VOCs are present in many types of waste gases, and the adsorption by adsorbents is often used to remove them [1, 2]. Desorption to reutilize the adsorbent saturated (or polluted) with VOCs can be carried out by microwave irradiation, so the adsorbent should be repeatedly utilized [3, 4]. The regeneration of the adsorbent using microwave due to dielectric heating is very effective because the microwave irradiates the VOC molecule directly. If the VOC is a nonpolar compound, the supply of the water is required for the microwave heating. Therefore, the microwave heating by dielectric heating can be performed in a relatively short period of time, which implies a lower

224

consumption of energy. And the main advantage of the microwave heating is that treatment utility for removing the VOCs is simpler and tail gas treatment capacity is smaller than that of direct heating method. Activated carbon cannot be used in this study as adsorbent because it is an electric conductor, so the electric current flows in electric field. The spark discharge occurs from the portion, and shows the light emission phenomenon. The zeolites were chosen for removing the VOCs, which were various pore structures and acidities. In this study, the physical properties of various zeolites and its adsorption capacity for VOCs were investigated. Desorption characteristics of the adsorbed VOCs was mainly investigated by means of microwave irradiation, and it was compared to that by the conventional heating. 2. Experimental Section Physical characteristics of various zeolites such as specific surface area, pore volume and pore size distribution was investigated with BET method (ASAP 2010, Micromeritics, USA). Adsorption and desorption of VOCs were performed using a flow system. Model gases were benzene, toluene, o-, m-, pxylenes, methanol, ethanol, i-propanol, and methylethylketone (MEK). All reagents for model gas were GR gr. (Junsei Chem., 99.0% ~ 99.5%). Concentration of VOCs was controlled with vaporizing individual VOCs in the saturator by He stream. He flow rate (mainly 40ml/min) was controlled using mass flow controller. Before adsorption experiment, the adsorbents (O.lg) were pretreated for lhr at 250°C. The adsorbents used as adsorbent were Molecular Sieve 13X [MS-13X], Mordenites [JRC-Z-HM10(2), Na-mordenite], Y-zeolites [JRC-Z-HY4.8, JRC-Z-HY5.6(2), and Faujasite (FAU)]. In the conventional heating, adsorbent column (o.d. 1/4", ss) of U-type was used. It was heated from 25 to 500°C by 5°C /min. In microwave experiment, adsorbent column (o.d. 3/8", quartz) of a U-type was used. All fittings for fixing an adsorbent column in oven were made of Teflon. Microwave source was generated from a microwave producer (2.45GHz). Concentration of VOCs was monitored with TCD of GC (GC-14B, Shimadzu, Japan). 3. Results and Discussion Physical characteristics by N2 adsorption was investigated for various zeolites. The BET surface area and pore volume by t-plot were shown Table 1, containing the amounts of toluene and MEK adsorbed only. The maximum surface area was observed on FAU. FAU and Z-HY4.8 showed the maximum total pore volume, and micropore was well formed in Z-HY4.8. The used zeolites are possessed of different acidities, Si/Al ratios, and average pore sizes, but the properties could not be related to the adsorption capacity. The adsorption capacity of all VOCs adsorbed depended on physical characteristics such as BET surface area and mesopore volume. The FAU with large surface

225

area and pore volume was maximum capacity, so it was considered to be a promising adsorbent for removing the VOCs. Table 1. Physical characteristics and VOCs adsorbed amount of various zeolites Zeolites

Amount of VOCs

Pore volume [m3/g]

BET surface

adsorbed [mmol/g]

area [m2/g] . Total pore

Micropore

Mesopore

Toluene

MEK

Z-HM10(2)

370.0

0.08

0.06

0.02

4.30

2.08

Na-Mor.

332.3

0.16

0.14

0.02

2.46

2.53

Z-HY5.6(2)

650.0

0.22

0.19

0.03

5.79

8.31

Z-HY4.8

663.0

0.28

0.24

0.04

10.38

10.18

MS-13X

581.7

0.21

0.19

0.02

13.20

10.53

FAU

691.0

0.29

0.18

0.11

17.10

10.76

Desorption characteristics of VOCs by the microwave irradiation on the saturated adsorbents was investigated for their regeneration. Also desorption efficiency of microwave heating was examined, compared to conventional heating by electric furnace. Temperature rising curve in conventional heating was linear, and its rising rate was very slow. But temperature rising rate by microwave heating was very fast. Desorption curve of toluene and MEK by microwave irradiation on FAU and MS-13X was investigated, and only desorption curves on MS-13X were shown in Fig. 1. As a whole, desorption by microwave heating was reached to completion faster than that by conventional heating. In microwave heating, desorption concentration of MEK was higher than that of toluene. It is thought because microwave is irradiated to only toluene or MEK in a moment. The desorbed amount from MS-13X was more than that from FAU because of the difference of their dielectric constant. Desorption rate of both MS-13X and FAU were almost same. After initial adsorption, first desorption rate and second desorption rate by heating with electric furnace of 500°C were nearly same. By the way, desorption rate from the saturated adsorbents by microwave irradiation for 5min was low, but desorption rate by microwave irradiation for lOmin was above 95%. The desorbed amounts of toluene and MEK by microwave heating were dependent on irradiation time. Also, desorption performance from MS-13X was more efficient than that from FAU. Besides, MS-13X was pretreated in electric furnace of 250°C for lhr. When the MS-13X saturated with VOCs was irradiated for above lOmin, the desorption rate was higher than 100%. The MS-13X has the undesorbed water and impurities even though it was pretreated at 250°C. They can be removed by microwave irradiation of 10 min. This was therefore considered to be a reason for

226

desorprion rate of over 100%. In other words, undesorbed water and impurities might be desorbed with the adsorbed VOCs. These facts suggest that the microwave heating of the adsorbent for regeneration was very efficient. As a result, the microwave heating was known to be an effective means for desorption of VOCs adsorbed on zeolites. Toluene CH-3O0°C CH-500°C'"

CH-etxfc^1 MW-5min MW-10min

! !

1 1 1 1 1i

ft jj

/

1,

' —

r Time on stream [min]

Time on stream [min]

Fig. 1. Desorption curves of toluene and MEK on MS-13X by conventional heating and microwave heating.

4. Conclusion Adsorption capacity and desorption characteristics of VOC over various zeolites and their regeneration by microwave irradiation were investigated. Among the various zeolites used, FAU and MS-13X showed the greatest adsorption capacity, and took the maximum BET surface area, total pore volume, micropore and mesopore. The microwave heating was very effective for desorption of toluene and MEK on FAU and MS-13X. Desorption rate by microwave heating of MS-13X was very excellent. Microwave heating of toluene and MEK depended on irradiation time. It was known that the microwave heating was very effective for regenerating the polluted zeolites. 5. Acknowledgement This subject is supported by Ministry of Environment as "The Eco-technopia 21 project". 6. References [1] [2] [3] [4]

C. L. Chuang and P. C. Chiang, Chemophere, 53 (2003) 17 . K.-J. Kim, et al., Catal. Today, 111 (2006) 223. P. S. Schmidt and J. R. Fair, Waste Management, 14 (1994) 3. C. O. Ania, J. A. Menendez, J. B. Parra and J.J . Pis, Carbon, 42 (2004) 1383.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

227 227

Reversible and irreversible adsorption of dye on mesoporous materials in aqueous solution Shaobin Wang* and Lili Tian Department of Chemical Engineering, Curtin University of Technology, GPO Box U1987, Perth, WA 6845, Australia

Nanosized mesoporous materials, Si-MCM-41 and Al-MCM-41, were synthesised and characterised. Dye adsorption on the synthesised mesoporous materials in aqueous solution was tested. It is found that Si-MCM-41 exhibits a reversible adsorption while AlSi-MCM-41 presents an irreversible adsorption. Kinetics of adsorption and desorption of dye follows the pseudo first-order kinetics. 1. Introduction Since the discovery of a new family of mesoporous materials, M41S, research efforts have been made extensively in their preparation and applications [1, 2]. Due to the high surface area and pore volume, mesoporous materials have been believed to be the promising materials as adsorbents, catalyst supports and catalysts [3, 4] or carriers for drug delivery [5, 6]. Several investigations have been reported employing mesoporous materials for organic adsorption in aqueous solution [7] and found that these mesoporous materials exhibit low adsorption capacity [8]. In addition, no investigation on dynamic adsorption of organics on mesoporous materials in aqueous solution has been reported. In fact, wastewater treatment involving organic and heavy metal removal is important for environmental protection and adsorption is the cheapest and efficient technology. Understanding the adsorption behaviour of trace components in aqueous solution is important in design of adsorbents. In this paper, we report in-situ dynamic adsorption of a typical dye on silica and aluminosilicate mesoporous materials and found reversible and irreversible adsorption behaviour of mesoporous materials depending on the chemical structure and properties of the adsorbents.

228 228

2. Experimental Section Nanosize mesoporous materials, MCM-41, were synthesised by a sol-gel method [9]. An aqueous solution of analytically pure C16TMABr, nitric acid, tetraethylorthosilicate (TEOS) and aluminium nitrate, were well mixed to obtain a gel and then was poured into 0.25 M ammonia solution at different volume. The Si/Al is 4.4. The precipitate was filtered, dried at 100 °C, and then calcined in air at 540 °C for 4 h. The textural properties of samples were characterised by X-ray powder diffraction and N2 adsorption. The pore size distributions (PSD) of the samples were calculated using the Barrett-Joyner-Halenda (BJH) formula. A basic dye, methylene blue (MB), was selected for adsorption tests in a batch reactor at 30°C. In each run. 20 mg adsorbents were put in a bottle with 200 ml dye solution and set in a shaking bath riming at a rate of 100 rpm. The solution was taken from the bottle at different time interval for dye analysis. The determination of dye concentration was done spectrophotometrically by measuring absorbance at ^max of 665 nm. 3. Results and Discussion The XRD patterns of the calcined samples present an intense diffraction peak between 28 =2° and 3°. These peaks are the characteristics of pure mesoporous materials, MCM-41. XRD patterns also show that Si-MCM-41 and Al-MCM-41 present different pore size. The textural properties of two samples obtained from N2 adsorption are presented in Table 1. As seen that Si-MCM-41 has a larger surface area and pore volume but less pore size than Al-MCM-41. Table 1 Textural properties of mesoporous samples Sample

Surface area

Total pore volume

Average pore size

SBET (m /g)

V (ml/g)

D(nm)

Si-MCM-41

1099

1.09

3.96

Al-MCM-41

484

0.59

4.89

2

Figure 1 presents the dynamic adsorption of methylene blue on Si-MCM-41 mesoporous materials. Si-MCM-41 exhibits a reversible adsorption of dye during the whole process. The adsorption process of methylene blue on SiMCM-41 will finish in around 12 hours achieving equilibrium adsorption at 1.4 x 10"4 mol/g. Then a desorption process will occur in the dye solution, but the desoprtion rate is much slower than adsorption. After 150 h, the dye adsorbed will be completely released into water again. Further investigations indicate that Si-MCM41 samples prepared at different pHs exhibit varying adsorption

229

capacity. Si-MCM-41 prepared at low pH will present higher adsorption capacity. 2.5e-4 0.00014 Experimental Second-order adsorption First-order desorption

2.0e-4

Amount adsorbed (mol/g)

Amount adsorbed (mol/g)

0.00012

0.00010

0.00008

0.00006

0.00004

1.5e-4

1.0e-4

5.0e-5

0.0

0.00002

0.00000 0

50

100

150

200

0

250

50

100 100

150 150

200 200

250 250

300 300

Time Time (h)

Time (h)

Fig.1 Methylene blue adsorption on Si-MCM41 at 30 °C.

Fig.2 Methylene blue adsorption on AI-MCM-41 at 30 °C.

To study the dynamic adsorption/desorption processes, two kinetic models for adsorption and one model for desorption were employed to calculate the kinetic parameters. The first-order and second-order adsorption kinetics are listed in equations (1) and (2) and the results are presented in Table 1. For the desorption, the first-order kinetics was also employed (Eq.3).

qt=qe(\-e-k>') -k2qet) q, =

,-kdt

0) (2) (3)

where is the rate constant of pseudo first-order adsorption (h.-u), k2 ( g m o r ' h ) the rate constant of pseudo second-order adsorption, kd the desorption rate constant. qe and q, are amount of dye adsorbed on adsorbent (mol g ') at equilibrium and at time t, respectively. As shown that the adsorption of dye on Si-MCM-41 mesoporous material follows the second-order kinetics better than the first-order kinetics, evidenced from the regression coefficients. The desorption of dye follows the first-order kinetics. Compared with the rate constant of adsorption, it is seen that desoprion rate constant is much samller than that of adsorption.

230 Table 2 Kinetic parameters of methylene blue adsorption on mesoporous materials Adsorbent

First-order kinetics Desorption

Adsorption 1

Second-order kinetics

2

Adsorption 2

k, (h" )

R

kd (h"')

R

k2 (g/mol h)

R2

Si-MCM-41

1.002

0.973

0.0235

0.966

1.18xlO4

0.987

Al-MCM-41

0.080

0.850

497.6

0.916

Figure 2 shows the dynamic adsorption of methylene blue on Al-MCM-41. One can see that A1-MCM41 presents quite different adsorption behaviour from Si-MCM41. Adsorption of methylene blue on Al-MCM-41 exhibits irreversible trend and can reach equilibrium of 2.4 x 10"4 mol/g after 250 h. The adsorption capacity of Al-MCM-41 is much higher than Si-MCM-41. Kinetic investigation shows that the pseudo second-order kinetics fit adsorption better than the firstorder kinetics, For the effect of preparation pH on adsorption, a similar case was also observed. Al-MCM-41 formed at lower pH will exhibit higher adsorption capacity. Due to the substitution of Si by Al, Al-MCM-41 will produce negative charge on the surface. For a cationic dye like MB, C+ or CH+ will be produced in water, thus resulting in the adsorption of dye on the Al-MCM-41 surface. 4. Conclusion Nanosized Si-MCM-41 and Al substituted Si-MCM-41 were synthesised and tested for dye adsorption. Two materials exhibit different adsorption behaviour. Si-MCM-41 exhibits a reversibale adsorption of dye while Al-MCM-41 presents an irreversible adsorption. Two adsorbents exhibit the second-order adsorption kinetics. 5. References [1] [2] [3] [4]

[5] [6] [7] [8] [9]

N. K. Raman, M. T. Anderson and C. J. Brinker, Chem. Mater., 8 (1996) 1682. Sayari, Chem. Mater., 8(1996) 1840. Taguchi and F. Schuth, Micro. Mesopor. Mater., 77 (2005), 1. T. J. Barton, L. M. Bull, W. G. Klemperer, D. A. Loy, B. McEnaney, M. Misono, P. A. Monson, G. Pez, G. W. Scherer, J. C. Vartuli and O. M. Yaghi, Chem. Mater., 11 (1999) 2633. M. Vallet-Regi, A. Ramila, R. P. del Real and J. Perez-Pariente, Chem. Mater., 13 (2001) 308. G. Cavallaro, P. Pierro, F. S. Palumbo, F. Testa, L. Pasqua and R. Aiello, Drug Delivery, 11 (2004) 41. Cooper and R. Burch, Water Res., 33 (1999) 3689. K. Y. Ho, G. McKay and K. L. Yeung, Langmuir, 19 (2003) 3019. M. C. Chao, H. P. Lin, C. Y. Mou, B. W. Cheng and C. F. Cheng, Catal. Today, 97 (2004) 81.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

231 231

Thermal stability of mesotructured aluminas obtained from different procedures Sebastien Royera, Charles Lerouxa, Alexandra Chaumonnota, Renaud Revela, Stephane Morina and LoTc Rouleaua* " IFP-Lyon, Catalysis and Separation Department, BP 3, 69390 Vernaison, FRANCE 1. Introduction

The synthesis of stable mesostructured alumina is an important challenge for the industry, since it can lead to a high specific surface area, a precise control of the pore size distribution, and then an increase of the catalyst activities in a broad range of temperature. An improvement of the catalytic activities was already reported by some authors when supporting active phases on mesostructured alumina, by comparison with conventional supported y-Al2O3 catalysts, in different reactions [1-3]. Nevertheless, compared to silica based materials, alumina structuration is little studied [4-9]. Yada et al. [10] reported alumina having a hexagonal 2D structure which collapses during calcination while Niesz et al. [11] recently described a 2D hexagonal AI2O3 structure which is stable after thermal treatment under air at 400°C. Although some authors [5-8] studied the effect of the calcination temperature on the textural properties of the mesoporous aluminas, little is known about the thermal stability. In this work, the evolution of specific surface area, porosity, morphology and crystallographic structure with the calcination temperature (up to 1000°C) was studied for three selected mesoporous aluminas using nonionic triblock copolymer with composition EO20PO70EO20 (Pluronic P123). 2. Experimental Section The samples were obtained following procedures described in literature, reported in table 1 and distinguished by composition (inorganic precursor, solvent), and synthesis operation (aging, autoclaving, evaporation), which affect assembly, hydrolysis and condensation processes.

232 Table 1. Synthesis conditions of mesoporous alumina samples Sample Reference synthesis method SI

[5]

Molar composition

aluminum salt 1 A1(NO3)3: 0.011 P123: neutralization 1.75 H O: 3.6 NH,OH 2

Synthesis operation aging 45°C-36 h neutralization pH=8.3 aging 25°C-48 h autoclaving 100°C-24h

S2

S3

[9]

[11]

aluminum alkoxide hydrolysis aluminum alkoxide hydrolysis

1A1 sec but: 0.02 PI 23 :

aging 45°C-40 h

3 H 2 O : 15.5ButOH 1 Alter but: 0.017 P123 :

evaporation under Ar 40°C-5 6 H 2 O : 3 0 E t O H : 1.8 HC1 days

For SI sample, an aqueous solution of surfactant was slowly added to the aqueous solution of aluminum nitrate. The mixture was aged, neutralized with NH4OH solution, aged and then transferred in a teflon-lined autoclave for hydrothermal treatment. The solid was filtered, washed with water, and dried at 100°C. For S2 sample, aluminum-sec-butoxide was slowly added to the surfactant dissolved in butanol. Then, butanol diluted in water was added dropwise and the mixture was aged in a closed vessel. The solid was filtered, washed and dried as for SI sample. For S3 sample, HC1 solution diluted in ethanol was slowly added to the surfactant dissolved in ethanol. Thereafter, aluminum-ter-butoxide was added to the solution. The solvent was slowly evaporated under argon, until a gel was obtained. The gel was dried at 50°C. Each sample was calcined in muffle furnace under air at the desired temperature (ramp=1.5°C min"1, time=8 h). These solids were compared to reference alumina obtained by calcination in the same conditions of a commercial boehmite (Pural SB3, Sasol) which is produced by aluminum alkoxide hydrolysis. 3. Results and Discussion Physical properties of the solids, after calcination at different temperatures are summarized in Table 2. Based on the differences in morphology and crystallographic structure, two classes of materials are distinguished. The first class (samples SI, S2) consists in a packing of elementary crystalline y-Al2O3 particles. The low angle diffraction line observed on these samples (not reported) is indicative of a regular pore to pore correlation length. However, no long range channel packing order is observed on these samples. These materials look like MSU type solids.

233 Table 2. Properties of the mesoporous alumina samples Sample SI

S2

S3

Dp 1 /

m g-'

v p '/1

mlg

500

297

750

dxRD 2 /

Morph.3

nm

Cryst. Phase2 / -

nm

1-

E a "/ kJ mol"1

0.46

4.8

Y

4.3

W

115

211

0.43

5.8

Y

5.1

W

500

415

1.36

5.6/14.8

Y

4.2

106

750

304

1.14

5.7/14.7

Y

4.8

1000

205

0.86

5.6/17.1

Y

5.0

s s s

500

455

0.86

6.1

Amorphous

n.d.

H

120

750

326

0.62

5.9

Amorphous

n.d.

H

1000

188

0.53

11.2

y,e,

n.d.

A

Calcination temp./ °C

^BET 2

'

trace a Reference

500

244

0.52

6.4

Y

2.8

A

750

185

0.49

9.2

Y

4.0

A

1000

121

0.39

10.0

8

5.0

A

121

1

SBET (BET method), Vp, Dp (BJH method on N2 desorption branch) measured by N2 physisorption at 77K on a Micromeritics ASAP2405 sorptometer. 2

Crystalline phase and dxRD, determined by XRD on a Panalytical X'Pert Pro diffractometer: dxRD was the crystal domain size evaluated by mean of the Sherrer equation on [400] peak.

3

Morphology observed by TEM on a Tecnai F20 microscope: W, wormhole-like; S, scaffold-like; H, hexagonal; A, aggregate-like. 4

Ea, sintering energy as defined Ref. [13].

The second class of material (sample S3) presents a completely different morphology. TEM and small angle XRD showed a 2D hexagonal mesostructure. Contrarily to the samples of the first class, walls of the S3 sample are formed by an amorphous alumina phase. This material looks like SBA-15 type solid. For the materials of the first class and reference, an increase in pore size is generally observed with the increase in calcination temperature. Large specific surface areas are however maintained (up to 200 m2g"' at 1000°C) compared to reference. For the materials of the second class, the hexagonal structure is maintained until the wall crystallization. Surprisingly, crystallization occurs at relatively high temperature (above 750°C). Nevertheless, this solid presents a high specific surface area (188 m2g"' at 1000°C). A decrease of the specific surface area is also observed. This increase in pore size is however not observed until the loss of the hexagonal structure. This result was already described by Ji et al. [12] during the calcination of a high surface area amorphous alumina.

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The loss of specific surface area is due to sintering process and can be calculated by the model developed by German and Munir [13]. This model was derived from general kinetics expression for sintering, assuming that the decrease of specific surface area is caused by neck formation between spherical particles. This model involves sintering activation energy which is representative of the thermal stability. High sintering activation energy is indicative of a high thermal stability. Sintering activation energies calculated for the different mesostructured aluminas are very close to the value found for the reference alumina, equal to 121 kJ.mol"1. 4. Conclusion Mesostructured alumina samples of different morphologies were synthesized with triblock copolymer as template. Depending on the synthesis procedure (composition and synthesis operation), controlling the assembly, hydrolysis and condensation processes, MSU like or hexagonal morphology can be obtained. The obtained samples present high specific surface area (from 300 to 450 m2g'') after calcination at moderate temperature (500°C). Increasing the calcination temperature results in the decrease of the specific surface area. The thermal stability of the mesostructured aluminas represented by sintering activation energy and evaluated from the loss of specific surface area is found identical to the value deduced from reference alumina (about 120 kJ.mol"1). Therefore the thermal stability does not depend on the structural and morphological properties. These results are very promising for several applications as catalyst support. The challenge is to better control the assembly, hydrolysis and condensation mechanisms to obtain the highest specific surface area after calcination at low temperature. 5. References [1] L. Kaluza, M. Zdrazil, N. Zilkova and J. Cejka, Catal. Commun. 3 (2002) 151. [2] T. Oikawa, T. Ookoshi, T. Tanaka, T. Yamamoto and M. Onaka, Micro. Meso. Mater. 74 (2004) 93. [3] P. Kim, Y. Kim, H. Kim, 1. Kyu Song and J. Yi, Appl. Catal. A 272 (2004) 157. [4] F. Vaudry, S. Khodabandeh and M. E. Davis, Chem. Mater. 8 (1996) 1451. [5] W. Zhang and T. J. Pinnavaia, Chem. Commun. (1998) 1185. [6] J. Cejka, P. J. Kooyoman, L. Vesela, J. Rathousky and A. Zukal, Phys. Chem. Chem. Phys. 4 (2002) 4823. [7] W. Deng, P. Bodart, M. Pruski and B. D. Shanks, Micro. Meso. Mater. 52 (2002) 169. [8] Z. Shan, J. C. Jansen, W. Zhou and Th. Maschmeyer, Appl. Catal. A 254 (2003) 339. [9] Z. Zhang and T. J. Pinnavaia, J. Am. Chem. Soc. 124 (2002) 12294. [10] M. Yada, M. Machida and T. Kijima, Chem. Commun. (1996) 769. [11] K. Niesz, P. Ying and G. A. Samorjai, Chem. Commun. (2005) 1986. [12] L. Ji, J. Lin, K. L. Tan and H. C. Zeng, Chem. Mater. 12 (2000) 931. [13] R. M. German and Z. A. Munir, J. Am. Ceram. Soc. 59 (1976) 379.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

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Self-formation phenomenon of hierarchically meso(micro-) macroporous zirconium oxide Aurelien Vantomme and Bao-Lian Su Laboratory of Inorganic Materials Chemistry, University ofNamur(FUNDP), 61 Rue de Bruxelles, B-5000 Namur, Belgium.

Spontaneous formation of hierarchical meso-(micro-) macroporous zirconium oxide is achieved by a controlled polymerisation of zirconium propoxide in aqueous solutions. The synthesised structures were characterized by TEM, SEM, nitrogen adsorption-desorption analysis and Hg porosimetry. The selfgeneration of multimodal porosities in different length scales integrated in one body was directly visualized with the help of an in-situ optical microscope. 1. Introduction The continuous pursuit of new porous materials with multi functionalities has in the last few years led to the conception of new hierarchically ordered porous structures with a great variety of pore sizes. These new structures are of great interest as potential catalysts, sorbents, ceramics and membranes. Several groups have reported the preparation of macroporous materials with microporous or mesoporous walls by dual templating, emulsion templating or salt promoted vesicle templating methods [1-3]. All these materials are structurally and texturally very interesting but face drawbacks because of their long and complex synthesis route. Recently a self-formation phenomenon of hierarchically mesoporous metal oxides, with uniform and parallel macrochannels, synthesized via the controlled polymerisation of metal alkoxides without the use of any structural agent has been reported [4-10]. These new materials, with high surface areas, bimodal pore systems, could be the driving force to induce innovations in different fields. In this paper, the mechanistic understanding of the spontaneous formation of these hierarchically meso- (micro-) macroporous metal oxides will be described.

236

2. Experimental Section Meso-(micro)-macroporous particles were obtained by the controlled polymerisation of zirconium propoxide drops in 2ml twice-distilled water. Further polymerisation occurred over the next 15 minutes and each drop forms a millimetre sized particle with a typical shape. The particle was obtained after drying at 60°C in a vacuum vessel. Characterisation was performed by N2 adsorption analysis (Micrometrics Tristar 3000), Hg porosimetry (Carlo-Erba 2000), scanning electron microscopy (Philips XL-20 at 15 KeV), transmission electron microscopy (Philips XL-20 at 15 KeV) and optical microscopy. 3. Results and Discussion

b

0,04

II I 140

•a

X-

dV/dD (cm³/g-A)

120

0,03

0,02

Jj 100 100- 1

0,01

0

5

10

15

20

Pore Diameter (nm)

-4 5,0x10 5,0x10-4inter- inter-

0) 60 60-

5µm

-3

1,0x10

0,00

80 80

j-

particular pores 10-30 nm

40 20 200,0

d

c

-3

1,5x10

dV/dD (cm³/g-nm)

a

V o l u m e a d s o r b e d ( c m³/ g )

The synthesis of hierarchically meso-macroporous materials was carried out via the controlled polymerisation of zirconium propoxide drops, 2mm-sized zirconia particles with a unique "sombrero"-like morphology were obtained. The particles were characterised by a denser shell with smooth surface, below which a regular array of macropores was observed. The macrochannels were parallel to each other, funnel-like shaped and perpendicular to the tangent of the smooth surface. TEM observations confirmed the macroporous structure and highlighted a disordered meso- and microporous framework in the walls separating the macropores and in the denser shell. A type II N2 adsorptiondesorption isotherm was obtained and the pore size distribution ranged from micropores to mesopores. The BET surface area of this material is around 100 m2/g. Hg porosimetry measurements revealed an interparticular porosity in the macropore's walls and confirmed the macroporosity of the final material. The main features are illustrated in figure 1.

0,2

0,4

0,6

0,8

Relative ) Relative pressure pressure (P/P (P/P) 0

1,0

macropores

70-700 nm

0,0 10

100 100

1000 1000

Pore diameter diameter (nm) Pore

Figure 1 : SEM image (a) ,N2 adsorption-desorption isotherm and corresponding pore size distribution (b), larger pore size distribution obtained by Hg porosimetry (c) and TEM picture of ZrO2 final material (d).

Facing such beautiful and sophisticated multimodal porous structures, our attention was focused on the mechanistic understanding of the spontaneous generation of different porosities integrated in one solid. Indeed a better comprehension of the self-formation phenomenon would be an important step forward in inorganic chemistry and could lead to the preparation of a large

237

range of hierarchically meso-macroporous metal oxides with specific features. Hence the formation of a zircon ia meso-(micro-) macroporous particle was studied by "in situ" optical microscopy (O.M). Figure 2 depicts OM and SEM pictures showing the different steps of the process leading to hierarchically meso-macroporous zirconia. The fast polymerisation occured as soon as the zirconium alkoxide came into contact with water (1). After a few seconds the particle began to spin spontaneously around itself generating a strong agitation in the medium (2). The core of the particle then swelled progressively leading to a specific "sombrero"-like morphology (3-4). The self-stirring continued and some parts of the smooth envelope broke away from the particle (5-6). The macroporisty was then observable below this smooth surface (7-8). These observations clearly suggest a mechanism based on the synergy between the polymerisation kinetics of the inorganic precursors and the hydrodynamic flow of the solvent. (1)

(2)

(3)

(4)

(6)

(7)

(8)

1 mm (5)

200 µm

Figure 2: OM and SEM images of the controlled polymerisation of a Zr(OC3H7)4 drop.

Zr(OC3H7)4 drop

Start of polymerisation

Alcohol / water

Macro- and Mesochannels formation

Alcohol and water release

ZrO2

Stirring

%y^

Figure 3 : Schematic representation for the formation of meso-(micro-) macroporous zirconia.

The formation of these new hierarchical meso-macroporous zirconium oxide structures is represented schematically in figure 3. The zirconium propoxide

238

drop added into the aqueous medium polymerise very quickly, leading to a smooth zirconium oxide shell. The alcohol and water molecules released suddenly from within the structure by spontaneous polymerisation gather together leading to the formation of larger water/ethanol macrochannels inside the structure. Meanwhile the polymerisation generates large amounts of Z1O2 nanoparticles giving the interparticular mesoporosity. Inside these nanoparticels another micro- or mesoporosity is formed. The amount of water/ethanol trapped inside the particle creates high pressures, which in turn causes the splitting of the particle resulting in hierarchical meso-(micro-) macroporous zirconium oxide particles with funnel-like shaped macropores oriented perpendicularly to the smooth particle surface observed by SEM. Thus the macrochannels are generated by a sudden release of alcohol molecules and the mesoporosity is due to the assembly of ZrC>2 nanoparticles which quickly formed. A third porosity can be found inside these nanoparticles. New experiments were carried out with several alkoxides (Ti(OR)4, A1(OR)3, Y(OR)3, Nb(OR)5, Ta(OR)5). Similar to the polymerization of Zr(OC3H7)4, hierchically bimodal porous structures were also obtained for the above mentioned alkoxides, but the macropores diameters, meso- and micropores sizes, surface areas and porous volumes were influenced by the type of inorganic precursor. 4. Conclusion In conclusion, the spontaneous pathway for the formation of hierarchical meso- (or micro) macroporous zirconium oxide has been studied. Their formation seems to be based on the synergy between the polymerisation kinetics of the inorganic precursors and the hydrodynamic flow of the solvent. The comprehension of this self-formation strategy should open exciting avenues for the fabrication of new classes of nanostructured porous materials. 5. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10]

Z. Zhong, Y. Yin, B. Gates and Y. Xia, Adv. Mater. 72(2000)206. B. T. Holland, C. F. Blanford and A. Stein, Science 281(1998)538. D. M. Antonelli, Microporous Mesoporous Mater. 33(1999)209. J. L. Blin, A. Leonard, L. Gigot, Z. Y. Yuan, A. Vantomme, A. K. Cheetham and B. L. Su, Angew. Chem. Intl. Ed. 42(2003)2872. Vantomme, Z. Y. Yuan and B. L. Su, New. J. Chem. 28(2004)1083. Z. Y.Yuan, T. Z. Ren, A. Vantomme and B. L. Su, Chem.Mater. 16(2004)5096. T. Z. Ren, Z. Y. Yuan and B. L. Su, Chem.Comm. (2004) 2730. Leonard and B. L. Su, Chem. Comm. (2004)1674. Z. Y.Yuan and B. L. Su, J. Mater. Chem. 16(2006)663. Collins, D. Carriazo, S. A. Davis and S.Mann, Chem.Comm. (2004)568.

Recent Progress in Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

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Synthesis and characteristics of hierarchically porous zirconia-based composite oxides Hangrong Chen, Jianlin Shi* and Dongsheng Yan State Key Lab of High Performance Ceramics and Superfine Microstructures, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050, China

High surface area and thermally stable hierarchically porous zirconia-based composite materials with crystallized framework has been synthesized in a facile process templated from composite surfactants. XRD, nitrogen adsorption analysis, FESEM, FETEM, and EDX were used for the structural characterizations. 1. Introduction Hierarchically porous materials occur widely in nature, and have attracted significant attention owing to their unique properties. The pore sizes of such materials varied from Angstroms to nanometers to microns in one composite material, i.e., several different degrees of porosity incorporated into one body can play important roles in the practical applications, such as catalysis, adsorption, separation, chemical sensors, etc [1-4]. Various synthesitic pathways, including exo-templating and endo-templating strategies have been developed to create porous and high-surface-area inorganic materials. The exo-templates, such as polystyrene latex spheres, emulsions or vesicles can be used to produce a controlled three-dimensionally interconnected macroporosity, and the endotemplates, such as nonionic block copolymer macromolecular can be used to create the mesoscale porosity, and the oligomers, the individual polymers can produce the micropores. In our privious work, a novel hierarchical pure zirconia material with ordered pores-structures and well-crystallized framework has been synthesized by a facile process templated from composite surfactants of an amphiphilic poly block copolymer combined with nonionic alkyl-PEO surfactant [5]. Here, we study the different effects of other elements incorporation, such as titatium and cerium, on the pore structures of hierarchical zirconia.

240

2. Experimental Section In a typical preparation, a 18 wt% micellar solution of Pluronic P-123(BASF) and/or Brij56 [Ci6(EO)i0] (Aldrich) was prepared by dissolving P123 and/or Brij56 with a weight ratio of 1:1.2 in 50mL distilled water at the room temperature under stirring for more than 3 hours. An appropriate amount of zirconium propoxide [Zr(OC3H7)4] and titanium isopropoxide or inorganic cerium source were dropped into the above solution to give the surfactants. After further stirring for lh, the mixture was transferred into a Teflon-lined autoclave and heated at 1 1 0 - 130°C for 24 h. The product was calcined at 500°C for 6 h to remove the surfactant species. 3. Results and Discussion Figure 1A shows the representative FE-SEM image of the as synthesized hierarchically porous titanium doped zirconia, which exhibits macroscopic network structure with a uniformly distributed array of macropores of 200-400 nm in diameter. After calcined at 500°C, the macroporous structure almost remains unchanged (not shown here). Typical TEM image of the calcined sample shown in figure IB reveals that such titanium doped zirconia nanoparticles in the framework of macroporous structure consist of the uniformly distributed nanocrystallites and worm-like mesopores. A clear EDX spectrum shown in figure 2A confirms that about 10 wt% titanium has been incorporated into zirconia framework. Further study indicates that up to 30 wt% titanium can be doped into zironia with maintaining the most of hierarchically macro-mesoporous structures.

A

B

Figure 1 Typical FE-SEM image (A) and TEM image as well as its corresponding electron diffraction patterns (inset) (B) of titanium doped hierarchical porous zirconia after calcined at 723K.

241 350

A

0.12

Pore Volume/cm /g

f

3

Zr

*

0.08

3

V olume A sorbed/(cm /g) Volume Addsor

250 250

y

4.8nm

0.06

0.04

0.02

200

L

_ 0.00 0

10

20

30

40

50

60

70

80

Pore Diameter/nm

8

CPS/a.u.

O

C

B ,

2.2nm 0.10

—. 300 300cn

Zr

150

100 100

Ti Ti 0

5

50

Zr

* 10

15

0.0

20

0.2

Energy/keV

0.4

0.6

0.8

1.0

Relative Pressure(P/P Pressure(P/P) Relative ) 0

Figure 2 (A) EDX spectrum corresponding to the area of figure IB, (B) N2 adsorption-desorption isotherms and the BJH pore size distribution (inset) of the as-prepared sample (* is the Cu element).

The nitrogen adsorption-desorption isotherms of the as-prepared hierarchical titanium doped zirconia sample shown in figure 2B, can be attributed to type IV. For the as-prepared sample, a high BET surface area of 300 m2/g with the total pore volume of 0.44 cm /g is obtained from this material. Two narrow peaks in the BJH pore-size distribution curve are centred on 2.2 nm and 4.8nm. After calcination at 773K for 6h, the BET surface area distinctively decreases to 81m2/g because of the increased material density induced by the crystallization of zirconia framework. However, relative to the lower surface area, the total pore volume still remains as high as 0.19 m2/g, indicative of high thermal stability. B

A

a---CeZr500 b---Zr500 b—--Zr500

Intensity/a.u.

...

'en

I

b

20nm

a 10

20

30

40

50

60

70

80

2 Theta

Figure 3 (A) TEM and FE-SEM (inset, up-left) images of hierarchical porous ceria-zirconia composite after calcined at 773K, (B) XRD patterns of pure porous zirconia and ceria loaded porous zircona after calcination at 773 K.

Figure 3 A shows the typical TEM image and the FE-SEM image of the calcined cerium doped zirconia sample. The macrostructure tends to be

242

destroyed with the increased amount of cerium, which is different from titanium incorporation. In our experiments, less than 10 at% cerium can be incorporated into zirconia lattices, and at the same time, the hierarchically macromesoporous structures can be retained. Nevertheless, higher cerium/zirconium ratio of nanocrystalline ceria-zirconia solid solution with only mesoporous structure can be well obtained. Inorporation of cerium can effectively inhibit the phase transformation of pure zirconia under the high thermal treatments, which can be seen from figure 3B. After calcined at 773K, pure zirconia shows the monoclinic phase, while, cerium doped zirconia maintains the stable cubic phase. Such hierarchical ceria/zirconia nanocomposite can be interestingly used as novel three-way mobile exhausted catalyst. 4. Conclusion In conclusion, high surface area and thermally stable hierarchically porous zirconia-based composite materials has been successfully synthesized. This novel hierarchically porous composite, such as titanium doped porous zirconia, shows a well-defined ordered macroporous structure and a very uniform mesoporous pore size distribution. Both the mesoporous structure and the macroporous structures can be maintained, after calcination at 773K, indicative of high thermal stability. However, there seems to exist different effects of titanium and cerium incorporation on the thermal stability and pore structures of the prepared hierarchically porous zirconium oxide owing to their different atomic diameters. Either Ti or Ce incorporation can effectly inhibit the phase transformation of pure zirconia at 773K. 5. Acknowledgement We gratefully acknowledge the financial support from Shanghai Nanospecial Project with Contract 0552nm030 and Qiming Star Project with Contract 05QMX145 8. 6. References [1] A. Corma, P. Atienzer, H. Garcia and J.-Y. Chane-Ching, Nature, 3 (2004) 394. [2] Y. S. Shin, J. Liu, L.-Q. Wang, Z. Nie, W. D. Samuels, G. E. Fryxell and G. J. Exarhos, Angew. Chem. Int. ed., 39 (2000) 2702. [3] W. Deng, M. W. Toepke and B. H. Shanks, Adv. Func. Mater., 13 (2003) 61. [4] J. -L. Blin, A. Lenoard, Z.-Y. Yuan, L. Gigot, A. Vantomme, A. K. Cheetham and B.-L. Su., Angew. Chem. Int. Ed., 42 (2003) 2872. [5] H. R. Chen, J. L.Gu, J. L.Shi, Z. C. Liu, J. H. Gao M. L. Ruan and D. S. Yan, Adv.Mater., 17(2005)2010.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

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Synthesis of ordered mesoporous zinc oxide obtained by dry gel nanocasting from the mesoporous carbon CMK-3 Helwig H. Thiel,a Pablo Cascales de Paza,a Martin Hartmannb and Stefan Ernst a * " Department of Chemistry, Chemical Technology, Kaiserslautern University of Technology, Erwin-Schrodinger-Str. 54, 67663 Kaiserslautern, Germany b Department of Physics, Advanced Materials Science, University of Augsburg, Universitdtsstr. 1, 86154 Augsburg, Germany

1. Introduction The main application of zinc oxide in industrial processes is as an activator for the vulcanization accelerator in the manufacture of natural and synthetic rubber [1, 2]. ZnO is also used as pigment in colors and surface coatings, in Pharmaceuticals or in the cosmetic industry and, last but not least, as catalyst in, e.g., the synthesis of methanol. In many of its applications, an important property is the specific surface area of ZnO. Two ways have been proposed for the preparation of zinc oxide with high specific surface area. The first possibility is the synthesis of zinc oxide nanoparticles [3, 4]. But there are still problems with the handling of the small particles during the preparation or the use as catalyst. Small particles are difficult to recover from their "mother liquor" and they will cause high pressure drop in a fixed-bed reactor if used as such. The second method of preparing zinc oxide with a large specific surface area is the direct synthesis of mesoporous zinc oxide as prepared by Jiu et al. [5] and Jaramillo et al. [6] with a disordered pore system. Here we report our attempts to synthesize mesoporous zinc oxide with an ordered pore system using a carbon replica method. 2. Experimental Section Mesoporous SBA-15 silica [7] and CMK-3 carbon [8] were obtained as described previously. In a typical synthesis of mesoporous zinc oxide, 0.5 g of

244 244

CMK-3 was mixed with 1 g zinc nitrate hexahydrate (Aldrich) in a mortar and afterwards heated up in air to 75°C for 6 h. Due to its relatively low melting point (46°C), the solid zinc nitrate melts during heating and is sucked by capillary forces into the pores of CMK-3 without the necessity of any further pretreatment. This impregnation sequence has been repeated four times. Finally, the composite was heated to 600°C in air with a constant heating rate of 5°C-min" in order to burn-off the CMK-3 template. 3. Results and Discussion Figure 1 (left) shows the powder XRD patterns of the obtained mesoporous zinc oxide in comparison to those of the templates SBA-15 and CMK-3. In Fig. 1 E and D, the high-angle region of mesoporous ZnO is compared to bulk ZnO. Both ZnO samples show the five signals that are significant for ZnO crystallized in a wurtzite-structure. The low-angle regions of the XRD patterns confirms that CMK-3 is a good replica of SBA-15, since both show the (100), (110) and (200) reflections, while the XRD reflections of mesoporous zinc oxide are somewhat broadened. Nevertheless, the three reflections observed confirm the structural order of the obtained mesoporous ZnO. To characterize the textural properties of mesoporous zinc oxide, nitrogen adsorption at 77 K was measured. The observed isotherms are depicted in Fig. 2. They are of type IV (IUPAC classification) with a hysteresis loop close

,1

CD) 30

11 40 50 29 / degree

60

Figure 1 Left side: low-angle powder XRD patterns of SBA-15 silica (A), CMK-3 carbon (B) and the mesoporous zinc oxide (C). Right side: high-angle powder XRD patterns of bulk zinc oxide (D) and mesoporous zinc oxide (E). The XRD patterns were recorded using a SIEMENS D5005 X-ray diffractometer with CuKa radiation, 30 kV, 20 mA, counting time: 5 s and steps of 0.01 ° (left) or 0.05° (right), respectively.

to type HI. These are typical findings for mesoporous solids. The observed somewhat broad hysteresis loop of type HI (not vertical and almost parallel isotherm sections [9]) indicates that the long-range order of the pore system is disturbed to some extent. The structural properties of SBA-15 and CMK-3 are

245

in good agreement with literature data. The significant difference in specific surface area (1125 m2-g"' vs. 85 m2-g"') and specific pore volume (1.17 cm^g"1 -3 -1 vs. 0.11 cm -g" ) between CMK-3 and mesoporous zinc oxide can be explained 140

2 Relative pressure p N /p N

0

4

6

1

10

Pore diameter / nm

at least in part with the difference in the densities of both materials: the density Figure 2 Nitrogen physisorption on mesoporous zinc oxide recorded using a Quantachrome Autosorb-1 sorption analyzer. Left: nitrogen isotherms at 77 K (o adsorption, D desorption). Right: pore size distribution calculated from the desorption branch employing the BJH method.

of bulk zinc oxide is ca. 2.7 times higher than the density of amorphous carbon. The low specific pore volume of mesoporous zinc oxide is tentatively explained by some sintering of the material during calcination. Fig. 3 shows the results of simultaneous TGA/DTG/DTA/MS (thermogravimetry/differential TG/differential thermal analysis/mass spectrometry) for a sample consisting of 0.5 g CMK-3 which was impregnated with 2 g zinc nitrate hexahydrate. The observed total weight loss amounts to 63 %. At low 7 6 >5 =M

J22 fa , tsi uU

W-l -2 -3

100 200 300 400 500 600 700 T/°C

100 200 300 400 500 600 700 T/°C

Figure 3 TG-DTA analysis (left) coupled with mass spectrometry (right) of CMK-3 impregnated with zinc nitrate. The measurement was performed in an air flow with a heating rate of 2 K per minute on a Setaram-Setsys-16/MS (Balzers Quadstar 422) instrument.

temperatures (20°C to ca. 120°C) an endothermic weight loss of 29% due to the desorption of water is observed. The water comes from both, physically adsorbed and chemically combined H2O. Three further weight losses are

246

detected at ca. 120-150°C (8 wt.-%), ca. 150 to 195°C (12 wt.-%) and ca. 195 to 230°C (2 wt.-%). From the corresponding mass spectra these three weight losses can be attributed to the decomposition of zinc nitrate hexahydrate to nitrogen oxides, water and, of course, zinc oxide. Finally, at temperatures between 230°C and 400°C, the occluded carbon material from the CMK-3 template is burnt-off with the concomitant formation of CO2 (weight loss ca. 11%). An additional TGA/DTA analysis (in air) and FT-IR spectroscopic analysis of the mesoporous zinc oxide obtained in the described manner were used to ascertain that carbon-containing matter was completely removed by the calcination procedure described above. The combustion of neat CMK-3 typically starts at temperatures around 460°C. Hence, the zinc oxide present in the composite material probably acts as an oxidation catalyst leading to reduced combustion temperatures. 4. Conclusion In summary, we have synthesized highly ordered mesoporous zinc oxide with a thermal stability of at least 600°C, using a new "dry" nanocasting route employing CMK-3 as the template. Further investigations on this preparation strategy are currently underway and will be reported in a forthcoming paper. 5. Acknowledgment Financial support by Deutsche Forschungsgemeinschaft and Fonds der Chemischen Industrie is gratefully acknowledged. 6. References [1] G. Pfaff in R. Dittmeyer, W. Keim, G. Kreysa and A. Oberholz (eds.) Winnacker • Kuchler Chemische Technik, Wiley-VCH, Weinheim (2004) 314. [2] G. Heideman, R. N. Datta, J. W. M. Noordermeer and B. van Baarle, Rubber Chemistry and Technology, 77 (2004) 512. [3] Z. L. Wang, J. Phys.: Condens. Matter, 16 (2004) R829. [4] A. M. Khalil and S. Kolboe, Surf. Technol., 18 (1983) 249. [5] J. Jiu, K. Kurumada and M. Tanigaki, Mater. Chem. Phys., 81 (2003) 93. [6] T. F. Jaramillo, S.-H. Baeck, A. Kleiman-Shwarsctein and E. W. McFarland, Macromol. Rapid Commun., 25 (2004) 297. [7] M. Hartmann and A. Vinu, Langmuir, 18 (2002) 8010. [8] M. Hartmann, A. Vinu and G. Chandrasekar, Chem. Mater., 17 (2005) 829. [9] S. J. Gregg and K. S. W. Sing (eds.), Adsorption, Surface Area and Porosity, Academic Press Inc., London, (1982) 287.

Progress in in Mesostructured Materials Recent Progress S. Qiu, Y. Tang and C. Yu (Editors) (Editors) D. Zhao, S. © 2007 2007 Published Published by Elsevier Elsevier B.V. B.V.

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Synthesis of mesostructured TiO2 through selfassembly of nanocrystals of rutile Wenfu YantHc, Zuojiang Li and Sheng Dai*

Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, 37831-6201. Present address: State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of Chemistry, Jilin University, Changchun, 130012, P. R. China

Uniform microspheres of mesoporous titania with a worm-like structure and controlled nanocrystalline framework have been prepared by a simple procedure of the self-assembly of rutile TiO2 nanoparticles based on surfactant (EO) 20 (PPO)70-(EO)2o (PI23) in a nonaqueous system. The crystalline mesoporous TiO2 was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and N2 adsorption/desorption measurements. 1. Introduction Since the first discovery of M41S family of ordered mesoporous silicate and aluminosilicate materials with uniformly sized pores and high surface areas through use of amphilic template-directing methods in 1992 [1], there have been extensive research activities aimed at synthesizing tailored mesoporous silica for catalysis, separation, and nanostructure fabrications [2]. Recently, this approach has been extended to synthesize transition-metal oxides, which have wider applications because of their unique optical, electronic, and magnetic properties [3-6]. Among mesoporous transition-metal oxides, titanium dioxide (titania) is attractive because of its excellent performance in photocatalytic reactions. Titania exists in three naturally occurring polymorphs: anatase, rutile, and brookite. Under ambient conditions, rutile is the most stable phase in bulk forms. However, thermodynamic stability is dependent on particle sizes and at particle diameters below ca. 14 nm, anatase is more stable than rutile [7, 8]. To date, many different synthesis strategies have been developed to synthesize nonsilica mesoporous materials with frameworks composed of transition metal oxides, oxophosphates and oxosulfates, sulfides, and metals [9, 10]. Among the

248

synthesis strategies developed so far, the evaporation-induced self-assembly (EISA) method is one of the most promising methodologies [11] and has already proven to be very efficient for preparing organized thin films of inorganic materials via organic surfactant micelles as templates. By employing this method, mesoporous transition-metal oxide powders (including TiO2, ZrO2, A12O3, SnO2, Nb2O5, WO3, and mixed oxides) with 2D-hexagonal or cubic structures were successfully prepared. Mesoporous anatase thin films and powders were prepared through this technique from TiCl4 or other titanium precursors and surfactants [12]. Crystallization of initial amrorphous TiO2 takes place at high temperature (350-550°C) and is always accompanied by considerable shrinkage of the corresponding mesostructures. Higher temperature treatment can eventually lead to a complete collapsing of the mesopore structures because of extensive growth of anatase nanocrystals [6, 1319]. Accordingly, the studies on the preparation of mesoporous rutile TiO2 are rare [13, 20, 21]. The reported preparation of mesoporous titania with a rutile crystalline structure involves hydrolysis of either TiOCl2 or T1CI4 in the presence of surfactants. The previous study indicates that the mesoporous rutile titania exhibits a good photocatalytic activity for gas-phase photo-oxidation of a mixture of benzene and methanol [21]. In this paper, we present the synthesis and characterization of mesoporous TiO2 with a wormlike structure and controlled crystalline framework through self-assembly of rutile nanocrystals in the presence of triethyl phosphate for formation of a glassy phosphate phase, which acts as a "glue" among the rutile nanocrystals and stabilizes the resultant framework [17]. 2. Experimental Section 2.1. Synthesis The detailed synthesis protocol of the nanosized rutile particles has been given previously [22]. In a typical synthesis, 5 g of PI23 was dissolved in 60 g of anhydrous ethanol (200 proof) in the presence of 35 mL concentrated HC1 at ambient temperature under vigorous stirring. The mixture was continually stirred for 2 h. Meanwhile, 40 mL of deionized water was sonicated by employing a direct immersion titanium horn (Sonics and Materials, VCX-750, 20 kHz, and starting power 100 W) followed by the injection of 5 mL of titanium tetrachloride (Aldrich). The mixture was further sonicated continuously for 40 minutes and sonication was conducted without cooling. The resulted solution containing the nanosized rutile particles (seeds) was mixed with preprepared P123-ethanol-HCl solution followed by the addition of 5 mL triethyl phosphate ((C2H5O)3PO, Aldrich). After further stirring for 20 hours, the mixture was transferred to glass Petri dishes and left to dry

249

under ambient conditions for 7 days. The resultant product was calcined in air at 500°C for 6 h to remove the surfactant molecules (heating rate: 2.2. Characterization Powder XRD data were collected via a Siemens D5005 diffractometer with CuKa radiation (X = 1.5418 A). A Philips XL-30 field emission SEM operated at 15 kV and an HITACH HD-2000 STEM operated at 200 kV were used to carry out SEM analyses. N2 adsorption/desorption measurements for both nanosized rutile and the resulted mesoporous TiC>2 were conducted on a Micromeritics Gemini system. 3. Results and Discussion Powder XRD patterns of separately prepared nanosized titania seeds and the resultant titania microspheres (not shown) revealed the characteristic feature of the rutile structure. The weak and broad diffraction peaks result from the very small size of crystals in nano-scale. The SEM image of nanosized titania seeds in Figure 1 shows that the particle size of the sonicated rutile nanocrystals is approximately 10 nm and these nanoparticles aggregate Figure 1 SEM image of nanosized titania seeds. together to form bigger assemblies. It is believed that the inter-particles mesopores are responsible for the hysteresis loop observed in the N2 adsorption isotherm (Figure 2). Figure 3 shows a representative SEM image of the uniform • microspheres of the resulted mesoporous titania. The resulted spherical TiO2 particles exhibited a characteristic feature of mesoporous materials, which was confirmed by a typical type IV N2 adsorptiondesorption curve, as shown in Figure Figure 2 N2 adsorption isotherm of 4. A hysteresis loop with a sloping sonicated rutile.

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adsorption branch and a relatively sharp steep desorption branch is observed at relative pressure (P/Po) range of 0.40.8. This observation is consistent with the assertion that the mesopores formed by the surfactant-assisted assembly of the rutile TiO2 nanoparticles have similar entrance pore sizes. The BET surface area is about 39.98 m2/g measured by Micromeritics Gemini 2375. The high magnification SEM image of a mesoporous TiO2 microphere in 02 0.4 0.6 Figure 5 reveals the same structural Relative Pressure, P/Pn feature. Compared to the previously Figure 4 N2 adsorption isotherm of the reported mesostructured titania [6, 12resulting micropheres of mesoporous titania. 19], the material described here is

Figure 3 SEM image of the resulting micropheres of mesoporous titania.

Figure 5 High magnification SEM image of a microphere of mesoporous titania.

expected to be more stable because of the formation of the phosphate glassy phase induced by the addition of triethyl phosphate. 4. Conclusion In summary, a simple synthetic approach to generate thermally stable mesostructured titania micropheres with a crystalline framework of rutile was reported. The additive of triethyl phosphate played an important role in stabilizing the resultant mesostructured titania. The material was characterized by XRD, SEM, and N2 adsorption/desorption measurements.

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5. Acknowledgment This work was supported by the Office of Basic Energy Sciences, U.S. Department of Energy (DOE). The Oak Ridge National Laboratory (ORNL) is managed by UT-Battelle, LLC, for the U.S. DOE under Contract DE-AC0500OR22725. This research was supported in part by an appointment for W.Y. to the Oak Ridge National Laboratory Postdoctoral Research Associates Program administered jointly by the Oak Ridge Institute for Science and Education and Oak Ridge National Laboratory. 6. References [1] C. T. Kresge, M. E. Leonowicz, W. J. Roth, J. C. Vartuli and J. S. Beck. Nature 359 (1992) 710. [2] G. J. D. Soler-illia, C. Sanchez, B. Lebeau and J. Patarin. Chem. Rev. 102 (2002) 4093. [3] D. M. Antonelli and J. Y. Ying. Chem. Mater. 8 (1996) 874. [4] P. D. Yang, D. Y. Zhao, D. I. Margolese, B. F. Chmelka and G. D. Stucky. Nature 396 (1998)152. [5] E. L. Crepaldi, G. Soler-Illia, A. Bouchara, D. Grosso, D. Durand and C. Sanchez. Angew. Chem.-Int. Edit. 42 (2003) 347. [6] S. Y. Choi, M. Mamak, N. Coombs, N. Chopra and G. A. Ozin. Adv. Funct. Mater. 14 (2004)335. [7] H. Z. Zhang and J. F. Banfield. J. Mater. Chem. 8 (1998) 2073. [8] H. Z. Zhang and J. F. Banfield. J. Phys. Chem. B 104 (2000) 3481. [9] A. Sayari and P. Liu. Microporous Mater. 12 (1997) 149. [10] F. Schuth. Chem. Mater. 13 (2001) 3184. [11] C. J. Brinker, Y. F. Lu, A. Sellinger and H. Y. Fan. Adv. Mater. 11 (1999) 579. [12] P. C. A. Alberius, K. L. Frindell, R. C. Hayward, E. J. Kramer, G. D. Stucky and B. F. Chmelka. Chem. Mater. 14 (2002) 3284. [13] H. M. Luo, C. Wang and Y. S. Yan. Chem. Mater. 15 (2003) 3841. [14] E. L. Crepaldi, G. Soler-Illia, D. Grosso, F. Cagnol, F. Ribot and C. Sanchez. J. Am. Chem. Soc. 125 (2003) 9770. [15] H. Shibata, T. Ogura, T. Mukai, T. Ohkubo, H. Sakai and M. Abe. J. Am. Chem. Soc. 127 (2005) 16396. [16] Y. Zhou and M. Antonietti. J. Am. Chem. Soc. 125 (2003) 14960. [17] D. L. Li, H. S. Zhou and I. Honma. Nature Mater. 3 (2004) 65. [18] J. M. Du, Z. M. Liu, Z. H. Li, B. X. Han, Y. Huang and Y. N. Gao. Microporous Mesoporous Mater. 83 (2005) 19. [19] T. Sreethawong, Y. Yamada, T. Kobayashi and S. Yoshikawa. J. Mol. Catal. A-Chem. 241(2005) 23. [20] V. Samuel, P. Muthukumar, S. P. Gaikwad, S. R.Dhage and V.Ravi. Mater. Lett. 58 (2004) 2514. [21] Y. Z. Li, N. H. Lee, E. G. Lee, J. S. Song and S. J. Kim. Chem. Phys. Lett. 389 (2004) 124. W. F. Yan, B. Chen, S. M. Mahurin, V. Schwartz, D. R. Mullins, A. R. Lupini, J. Pennycook, S. Dai and S. H. Overbury. J. Phys. Chem. B 109 (2005) 10676.

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Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

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Synthesis of a lamellar mesostructured calcium phosphate using hexadecylamine as a structuredirecting agent in the ethanol/water solvent system Nobuaki Ikawaa, Yasunori Oumia, Tatsuo Kimurab, Takuji Ikeda0 and Tsuneji Sano a* "Department of Applied Chemistry, Graduate School of Engineering, Hiroshima University, Higashi-Hiroshima 739-8527, Japan. b Advanced Manufacturing Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Shimoshidami, Moriyama-ku, Nagoya 463-8560, Japan. 'Research Center for Compact Chemical Process, AIST, Tohoku, Nigatake, Miyaginoku, Sendai 983-8551, Japan.

Control of solubility and crystallization properties of calcium phosphate species in the mixed solvent of ethanol and water led to the successful preparation of a novel lamellar mesostructured calcium phosphate in the presence of w-hexadecylamine. The formation of the lamellar mesostructured calcium phosphate was strongly dependent upon EtOH/H2O and solvent/H3PO4 ratios in the starting gel. 1. Introduction A wide variety of mesostructured and mesoporous metal oxides and phosphates can be prepared by using various surfactants as structure-directing agents (SDAs) [1-4]. Metal species are connected by oxygen atoms in their frameworks through covalent bonds. Although calcium phosphate has attractive much attension as biocompatible materials, there have been few reports on mesostructural control of calcium phosphate by using surfactants as SDAs [5-8]. Calcium and phosphate species are strongly interacted each other through electrostatic interaction, which prevents from interacting between calcium phosphate species and surfactant molecules, and calcium phosphate species are crystallized. Therefore, it is difficult to obtain mesostructured calcium phosphates through surfactant templating. In this study, solubility and

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crystallization properties of calcium phosphate species were controlled according to the synthetic conditions such as EtOH/H2O and solvent/H3PO4 ratios and then a novel lamellar mesostructured calcium phosphate was prepared by using «-hexadecylamine in the ethanol/water system. 2. Experimental Section A lamellar mesostructured calcium phosphate was prepared by using phosphoric acid (85% H3PO4) and calcium acetate monohydrate (Ca(CH3COO)2H2O) in the presence of w-hexadecylamine (C16H33NH2). Ci6H33NH2 (2.41 g) and 85% H3PO4 (1.15 g) were added to a mixed solvent of EtOH (18.4 g) and H2O (6.6 g). After stirring at room temperature for 1 h, Ca(CH3COO)2 • H2O (1.76 g) and aqueous solution of ammonia (25% NH3 aq.) (0.34 g) were introduced into the surfactant solution. The mixture was stirred vigorously for 15 min and then kept at room temperature for 120 h statically. The solid product was filtered, washed with ethanol, and then air-dried. 3. Results and Discussion

001

The XRD pattern of the product showed three well-resolved peaks assignable to (001), (002) and (003) reflections of a lamellar phase with the d]Oo spacing of 4.4 nm (Figure 1).

002

J

hkl 001 002 003

A 4

d /nm 4.4 2.3 1.5

en oo

A 6 28 I

10

12

Figure 1. XRD pattern and TEM image of the lamellar mesostructured calcium phosphate,

the clear striped patterns were observed in the TEM image of the product and the repeat distance of the striped patterns was ca. 4.1 nm. On the basis of the results, mesostructural ordering of the product is considered to be lamellar. 3IP MAS NMR and ICP-AES measurements were carried out to investigate the framework of the product. The 31P MAS NMR spectrum showed two peaks at 0.5 ppm and 3.4 ppm. The Ca/P molar ratio of the product was 1.0. The organic content of the product was measured by CHN analysis. The product contained 36.1 mass % of carbon atoms, 7.9 mass % of hydrogen atoms and 2.6 mass %

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of nitrogen atoms (C: H: N=16.1: 42.1: 1.0). The composition of the product is calculated to be 2.34CaO • 1.17P2O5 • C,6H33NH2 from the results by elemental analyses. Yuan et al. reported the possibility to synthesize the lamellar mesostructured calcium phosphate. However, they cannot show the direct evidence such as TEM image for the formation of a lamellar phase [9]. Thermal analysis (TG/DTA), FT-IR and 13C CP/MAS NMR were conducted to investigate thermal stability of the lamellar mesostructured calcium phosphate and conformation of alkyl chain in the surfactant molecules. The major mass loss in the TG/DTA curve occurred below 150°C and between 150 and 500°C. It seems that the mass loss 4000 3000 2000 1000 below 150°C is due to H2O desorption. Wavenumber / cnT! Burning of the surfactant molecules Figure 2. FT-IR spectrum of the lamellar started at around 220°C and the mass mesostructured calcium phosphate. loss between 150 and 500°C was ca. 48.5 mass %. The peak corresponding to -CN group as well as the peaks corresponding to -CH 3 and -CH 2 - groups were respectively observed at 1070 cm"1 and 2900-3000 cm"1 in the FT-IR spectrum (Figure 2). The 13C CP/MAS NMR spectrum exhibited a large peak at around 33 ppm with a small peak at around 15 ppm. The main peak at around 33 ppm is assigned to all-trans methylene (-CH 2 -) groups of the surfactant molecules. The chemical shift is typical of those observed for alkylammonium type surfactants in lamellar mesostructured materials. Effects of the synthtic conditions such as EtOH/H2O and solvent/H3PO4 (solvent = EtOH + H2O) ratios were investigated when both of the Ca/P and Ci6H33NH2/H3PO4 molar ratios in the starting mixtures were fixed at 1/1. The results are listed in Table 1. Brushite (CaHPO4 • 2H2O) known as one of crystalline calcium phosphates was mainly obtained when EtOH was not used as a solvent. The formation of brushite can be suppressed with an increase in the EtOH/H2O ratio and a lamellar mesostructured calcium phosphate (MCP) was obtained without byproducts at the EtOH/H2O ratio of 50/50 mol %. The EtOH/H2O mixed solvent system is useful for controlling crystallization of calcium phosphate species, leading to the successful formation of the lamellar mesostructured calcium phosphate. When the EtOH/H2O ratio was increased further, unreacted Ca source and lamellar hexadecylammonium phosphate salt ([C16H33NH3+][H2PO4"], HAP) were recovered without the formation of MCP because the solubility of Ca species is low in EtOH. No mesostructured calcium phosphate can be obtained without H2O because Ca species are not solubilized and then hardly reacted with phosphate species. A crystalline calcium phosphate such as monetite (CaHPO4) was formed at higher higher temperatures (50100°C).

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The synthesis of the lamellar mesostructured calcium phosphate were also conducted by changing the solvent/H3PO4 ratio in the starting mixture with the EtOH/H2O ratio of 50/50 mol%. The crystallinity of the lamellar mesostructured calcium phosphate increased with the solvent/H3PO4 ratio. A pure lamellar mesostructured calcium phosphate can be obtained at the ratio of 80. When the ratio was higher than 120, brushite was also formed as byproduct. Table 1. Synthetic conditions and characteristics of lamellar mesostructured calcium phosphates. Starting mixture

Product

EtOH/H2O ratio

Solvent/H3PO4 ratio

Phase

t/ooi /

0/100

40

Brushite, HAP

—

25/75

40

Brushite, MCP

(4.4)

50/50

40

MCP

4.4

75/25

40

MCP (Ca source)

4.4

96/4

40

HAP (Ca source)

—

50/50

80

MCP

4.4

50/50

120

MCP, Brushite

4.4

n m

4. Conclusion A lamellar mesostructured calcium phosphate was successfully prepared by using «-hexadecylamine as a surfactant. Control of the solubility and crystallization of calcium sources and calcium phosphate species was found to be important for synthesizing mesostructured calcium phosphate. This is the first example of surfactant-templated mesostructured calcium phosphates whose frameworks are constructed through ionic bonds, being very important as model systems for biomimetic materials design such as bone and teeth. 5. References [1] F. Schtith, Chem. Mater., 13 (2001) 3184. [2] G. J. de A. A. Soler-Illia, C. Sanchez, B. Lebeau and J. Patarin, Chem. Rev., 102 (2002) 4093. [3] C. Yu, B. Tian and D. Zhao, Curr. Opin. Solid State Mater. Sci., 8 (2003) 191. [4] T. Kimura, Microporous Mesoporous Mater., 77 (2005) 97. [5] M. J. Larsen, A. Thorsen and S. J. Jensen, Calcif Tissue Int., 37 (1985) 189. [6] G. A. Ozin, N. Varaksa, N. Coombs, J. E. Davies, D. D. Perovic and M. Ziliox, J.Mater. Chem., 7(1997)1601. [7] J. Yao, W. Tjandra, Y. Chen, K. Tarn, J. Ma and B. Soh, J. Mater. Chem., 13 (2003) 3053. [8] J. Anderson, S. Areva, B. Spliethoff and M. Linden, Biomaterials, 26 (2005) 6827. [9] Z. Y. Yuan, J. Q. Liu, L. M. Peng and B. L. Su, Lamgmuir, 18 (2002) 2450.

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Recent Progress in Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

Formation of Pt nanowires in mesoporous materials and SiO2 nanotubes Inga Bannat and Michael Wark Institute of Physical Chemistry and Electrochemistry, Leibniz University of Hannover, Callinstr. 3-3A, D-30167 Hannover, Germany

1. Introduction The synthesis of nanowires in different host structures has attracted extensive interest because of their structural, electronic and optical properties which are governed by the anisotropy and differ greatly from the bulk properties of the materials [1]. Furthermore, nanowire core-shell structures are studied as "nanocables" in nanoelectronics [2]. Mesoporous hosts are a perfect matrix for a stabilization of nanowires; the preparation and orientational studies on Pt nanowires in MCM-41 and MCM-48 have been studied for years [3-6]. In our study we compare the formation of Pt nanowires and their orientation in four different host systems. Basing on the approach of Terasaki et al. [3] we synthesized Pt nanowires via an introduction of Pt2+ ions by wetimpregnation in different mesoporous SiO2 hosts (MCM-41, SBA-15) or ionexchange in Al/Si-SBA-15 and subsequent reduction with H2. Scheme 1: Illustration of the formation of In an additional approach Pt Pt-doped SiO2 NTs by the metal salt NF nanowires were in-situ created in thin template method [7]. SiC>2 nanotubes (NTs). Here fibers of the Pt salt [Pt(NH3)4](HCO3)2 are used as templating structures for the sol-gel based synthesis of oxide NTs (Scheme 1) [7]. Continuous Pt nanowires are formed in thin NTs after reduction of the Pt salt template in air. Template nanofiber

sol-gel technique

Tet raethy lortho s i I i cate (TEOS)

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2. Experimental Section 2.1. Pt nanowires in pre-formed mesoporous hosts Si-MCM-41 was synthesized directly in autoclavable polypropylene bottles with CTABr and Na2SiO3 following a procedure reported by Rathousky et al. [8], in which the homo-geneous precipitation of Si-MCM-41 is induced at 307 K by the addition of EtAc and subsequent hydrothermal treatment. Si-SBA15 and Al/Si-SBA-15 were prepared with Pluronic P 123 according to Zhang et al. [9] from tetraethyl orthosilicate (TEOS) and aluminium isopropoxide by aging at 313 K for 16 h and hydrothermal treatment at 373 K for 48 h. The resulting solid products were recovered by filtration, washing with water and calcination at 873 K in air for 6 h. In order to form the Pt nanowires, the mesoporous materials were impregnated repeatedly for 24 h with an aqueous solution of [Pt(NH3)4](NO3)2 (max. 0,1 wt %). After the removal of the solvent, the samples were reduced under H2 atmosphere for 1 h at 873 K. Extracted Pt nanowires were obtained by removing the silica framework with an aqueous HF solution. The study of Pt nanowires is often complicated by SiC>2 gel remaining from the host during the extraction and enhancing agglomeration. The effect is more pronounced the lower the degree of wires. 2.2. In-situformation ofPt nanowires in SiO2 NTs [7] In a first step nanofibers of the templating Pt salt [Pt(NH3)4](HCO3)2 were precipitated with ethanol from an ammonia containing aqueous solution. The system was kept in an ice bath for at least 5 min. Subsequently, 14 uL TEOS were added to the mixture under continuous stirring and finally more ethanol were injected rapidly. After 4 h template-filled SiO2 NTs were achieved and calcined at 773 K for 5 h. High resolution (scanning) transmission electron microscopy (HR(S)TEM) was carried out on a Jeol JEM-21 OOF electron microscope. 3. Results and Discussion Fig. 1 A-C shows high resolution STEM and TEM micrographs of Si-MCM41, Si-SBA-15 and Al/Si-SBA-15 samples after impregnation with the Pt precursor and subsequent reduction. For the different host materials, all possessing a well-ordered channel structure, different degrees of pore filling and formation of nanowires were observed. In Si-MCM-41 Pt nanowires are formed exclusively in the straight channels (Fig. 1 A). The wires are very uniform and their lengths vary from several tens to several hundreds of nanometers (Fig. 1 D). Their maximum diameter of 3.8 nm, deduced from HRTEM micrographs, is almost of the same value as the Si-MCM-41 channel to channel distance of

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4.0 ± 0.2 nm obtained from XRD and TEM. Thicker (8 nm) but shorter (2050 nm) and quite irregular nanowires were received with Al-SBA-15 as host material (Fig. 1 C, F). This seems to be related to diffusion problems in the pores which are more pronounced in SBA-15 systems since in the wider pores (diameter of about 8 nm) more Pt precursors must be transported to form the

50 Fig. 1: HRSTEM and HRTEM micrographs of Pt nanowires and nanoparticles in mesoporous materials (A-C) and extracted Pt nanowires (D-F); host systems: (A,D) Si-MCM-41, (B,E) SiSBA-15, (C,F) Al/Si-SBA-15

Fig. 2 STEM micrographs of Pt nanowires in the inner void of thin SiO,NTs

Fig. 3: HRTEM micrographs of Pt wires extracted from Si-MCM-41 (A-B) and SiO2NTs (C-D)

wires. In the case of Si-SBA15 only Pt nanoparticles were formed (Fig. 1 B, E). They exhibits sizes of about 8 nm in accordance to the channel pores. Compared to Al/SiSBA-15, Si-SBA-15 with its electroneutral structure lacks of ion exchange capacity. Therefore, the [Pt(NH 3 ) 4 r ion incorporation is not attracted by coulomb forces and much less Pt precursor diffuse into the pores of SiSBA-15 so that only some small particles can be formed. Pt nanowires in thin SiO2 NTs, formed during heat treatment in air by an autoreduction of the templating [Pt(NH3)4](HCO3)2 nanofibers in the interior of the tube,

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exhibit diameters of 15-35 nm and wire lengths up to 500 nm. Although the growth of the Pt nanowires in thickness is, in contrast to the situation in the SiMCM-41 or SBA-15 channels, not restricted by the pore geometry, in the about 100 nm wide NTs the Pt particles align to almost continuous but thin nanowires. Fig. 2 shows that the Pt nanowires are either formed by a line-up of individual Pt nanoparticles (A) or consist of one long crystalline segment (B). Forces between the Pt nucleation seeds as well as to the walls seem to support the wire formation. In thicker NTs these forces get weaker and less nanowires but more individual particles are found [7]. The Pt nanowires, observed in Si-MCM-41 and in SiO2 nanotubes, were studied in respect of their orientation in the host systems. High resolution TEM (HRTEM) micrographs of the Pt wires, extracted from Si-MCM-41, show that they consist of single-crystalline Pt segments (Fig. 3). The (111) and (200) planes of Pt, which crystallize in a face-centered cubic structure, were observed to lie parallel to the channels of the MCM-41. This suggests in agreement to findings of Yang et al. and Liu et al. [4, 5], that the nanowires preferentially grow in [110] direction. Although the pore channels are much wider equal results were received with the Pt nanowires extracted from SiC>2 NTs, indicating that this growth orientation is highly preferred for Pt independent of the host structures. 4. Conclusion Uniform Pt nanowires with lenghts up to several hundreds of nanometers were synthesized by two synthesis strategies. One strategy used mesoporous materials as matrix for the formation of the wires. Thus, we received Pt nanowire lenghts up to 200 nm and diameters in accordance to the pore diameters of the mesoporous materials. The other strategy used a metal salt as template to create Pt nanowires of about 500 nm and diameters of 15-35 nm in SiO2 NTs. In both cases the Pt nanowires grow in [110] direction independent of the pore geometries of the host system. 5. References [1] [2] [3] [4] [5] [6] [7] [8] [9]

Y. Wang, K. Takahashi, H. Shang and G. Cao, J. Phys. Chem. B, 109 (2005) 3085. Y. Cui and C. M. Lieber, Science, 291 (2001) 851. O. Terasaki, Z. Liu, T. Ohsuna, H. Shin and R. Ryoo, Microsc. Microanal, 8 (2002) 35. C.-M. Yang, H.-S. Sheu and K.-J. Chao, Adv. Funct. Mater., 12 (2002) 143. Z. Liu, Y. Sakamoto, T. Ohsuna, K. Hiraga, O. Terasaki, C. H. Ko, H. J. Shin and R. Ryoo, Angew. Chem., 112 (2000) 3237. X. Guo, C. Yang, P. Liu, M. Cheng and K. Chao, Cryst. Growth & Design, 5 (2004) 33. L. Ren and M. Wark, Chem. Mater., 17 (2005) 5928. J. Rathousky, M. Zukalova and J. Had, Collect. Czech. Chem. Soc, 120 (1998) 6024. F. Zhang, Y. Yan, H. Yang, C. Yu, B. Tu and D. Zhao, J. Phys. Chem. B 109 (2005) 8723.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

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Synthesis of Pd nanoparticles in La-doped mesoporous titania with polycrystalline framework Shuai Yuana, Qiao R. Shenga, Jin L. Zhanga*, Feng Chen8, Masakazu Anpob and Wei L. Daic a

Lab for Advanced Materials and Institute of Fine Chemicals, East China University of Science and Technology, 130 Meilong Road, Shanghai 200237, P. R. China; b Department of Applied Chemistry, Graduate School of Engineering, Osaka Prefecture University, 1-1 Gakuen-cho, Sakai, Osaka 599-8531, Japan;' Department of Chemistry, Fudan University, 200433, P. R. China

A simple synthetic method to prepare highly dispersed Pd nanoparticles in La-doped mesoporous titania with polycrystalline framework by coassembly and photoreduction is reported. The mesoporous materials were characterized by low angle and wide angle X-ray diffraction (XRD), transmission electron microscope (TEM), high-resolution transmission electron microscopy (HRTEM). 1. Introduction Noble metals, such as Pt, Pd and Au, are widely used in the fields of organic synthesis, petrochemistry, etc. Anchoring noble metal nanoparticles or clusters in zeolites can combine the advantages of nanoparticles and micropores [1]. However, the micropore sizes less than 2 nm restrict applications with the participation of macromolecules. The discovery of mesoporous materials provided a new kind of hosts to load nanoparticles with high dispersity [2]. The combination of noble metal nanoparticles with well ordered mesoporous materials is of interest in the field of catalysis, separation and sensors [3]. The substrates not only provide sites for nanoparticles, but also have great effects on catalytic activities. TiO2 is a kind of transition metal oxide having different

262

crystalline structures. Pd loaded on different crystalline titania have various catalytic activity and selectivity. To introduce Pd nanoparticles into rare earth doped mesoporous titania with highly crystallized walls and long-range ordered mesopores may bring more excellent properties in the redox reactions. However, it is difficult to introduce metal nanoparticles into mesopores by traditional impregnation methods, because they tend to deposit richly on outer surface of mesoporous materials. Moreover it is difficult to control the loading amount by impregnation. In here, a simple method is reported to synthesize highly dispersed Pd nanoparticles in La-doped mesoporous titania with crystallized walls by photoreducing PdO in-situ at room temperature. 2. Experimental Section 2.1. Experimental procedure In the synthesis process, Pluronic P-123 was dissolved in BuOH under vigorous stirring for 30min. Then the required content of La(NO3)3*6H2O and Ti(OBu)4 were added into the P-123 solution, followed by stirring for an additional 60 min. In a test-tube PdCl2 was dissolved in dilute hydrochloric acid (23.8 wt%). Then, the solution was added dropwise to the above mixture under stirring and ultrasonic treatment. The temperature of ultrasonic cell was kept at 298 K. The molar ratio of Pd: La: P-123: HC1: H2O: BuOH: Ti was kept 0.005: 0.01: 0.025: 1: 6.5: 6.5: 1. After 30 min, the transparent sol was transferred from the reactor to an open Petri dish. After aging at 298 K for 4 day, 413 K for 2h and then 473 K for 2h, the cracked-free thin layer was calcined at 673 K for lh in airflow. The brown powder, notated as PdO/MT, was divided into two portions. One portion was dispersed in aqueous solution of ethanol (1: 1, v/v), then illuminated at room temperature by UV light for 0.5 h after saturated by N2 for 20 min. The black product was notated as Pd(P)/MT. The other portion was reduced in H2 (99.99%) flow at 473 K for 4 h. H2 flow was stopped until the sample was cooled down to room temperature. The black product was notated as Pd(H)/MT. 2.2. Characterization X-ray diffraction (XRD) patterns of all samples were collected in 6-26 mode using Rigaku D/MAX-2550 diffractometer. The sample morphology was observed under transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) on a 2100 JEOL microscope using

263

copper grids. The instrument employed for XPS studies was Perkin Elmer PHI 5000C ESCA System with Al Ka radiation operated at 250 W. 3. Results and Discussion In Figure 1, the appearance of low-angle diffraction peaks indicates that mesoporous order was preserved after calcination. Illumination by UV light in aqueous solution of ethanol or calcination in H2 flow did no damage to the mesostructure. From wide-angle XRD patterns, a series of peaks for anatase can be observed. Previous works confirmed that the walls consisted of anatase nanocrystals [4]. No characteristic peaks belonging to PdO appear after calcination. PdO may be amorphous or very small and highly dispersed. Otherwise, the presence of a very small amount of PdO would display characteristic peaks in the wide-angle XRD pattern. Because Pd2+ ion has larger size than Ti4+ ion, it is difficult for Pd2+ to be doped in the lattice of anatase. The PdO may exist on the outer surface, inner surface of mesoporous titania, or in the gaps between anatase nanoparticles. After thermal reduction by hydrogen at 473 K for 4 h, two peaks belonging to Pd (111) planes and (200) planes emerge. However, there is only one weak peak belonging to Pd (111) planes for Pd(P)/MT, which attributes to smaller metal particle size and higher dispersion. The inference is also verified by the following TEM images.

b 2 3 4 5 2-Theta (degree)

I 6 20

30 40 50 2-Theta (degree)

60

Figure 1. Low-angle XRD patterns (left) and wide-angle XRD patterns (right) for Pd(P)/MT (a), Pd(H)/MT (b) and PdO/MT (c).

264

• • :5Onin,

,

•

.

•

Figure 2. TEM and HRTEM images of Pd(P)/MT (a, c) and Pd(H)/MT (b, d)

TEM and HRTEM images are shown in Figure 2. The mesoporous titania matrix has long-range order and polycrystalline framework. There is no obvious agglomerate Pd particles in the mesopores of Pd(P)/MT (Figure 2a). Illuminated by UV light, PdO was reduced in-situ by photo-generated electrons avoiding high temperature in the presence of ethanol as photo-generated holes captor. In contrast, some larger Pd nanoparticles can be observed in the TEM image for Pd(H)/MT (Figure 2b). Pd nanoparticles grew in the mesopores, but the size was restricted by the pore diameter. Before reduction, the sintering of PdO should be slow because of the strong chemical interaction with titania by forming Pd-O-Ti. After reduction, Pd will agglomerate to reduce surface energy. High temperature will accelerate the agglomeration of Pd. From the HRTEM image of Pd(P)/MT(Figure 2c), anatase (101) planes with d= 0.35 nm and Pd (111) planes with d= 0.22 nm can be observed. From the HRTEM image of Pd(H)/MT(Figure 2d), anatase (101) planes with d = 0.35 nm and Pd (200) planes with d= 0.19 nm can be observed. The Pd nanoparticles prepared by photoreduction are smaller than by hydrogen reduction at high temperature, which agree well with XRD analysis. The valence states of palladium were analyzed by XPS spectra. Palladium only has one chemical state in Pd(P)/MT, which indicates the reduction was complete. The dispersion and the particles size of Pd° will affect the Pd 3d5/2 binding energy values greatly. The Pd° 3d5/2 binding energy of Pd(P)/MT is

265 265

335.8 eV, 0.2 eV higher than that of Pd(H)/MT, which may be due to higher dispersion and smaller size of Pd nanoparticles. In contrast, two chemical states of palladium can be distinguished in the XPS spectra for Pd(H)/MT. Pd 3d5/2 binding energies of 335.6 eV and 337.6 eV are attributed to highly dispersed Pd° and Pd2+, respectively [5, 6], By quantitative analysis, there is about 14% residual PdO. 4. Conclusion A simple method is reported to synthesize highly dispersed Pd nanoparticles in La-doped mesoporous titania with crystallized walls by photoreducing PdO in-situ at room temperature. The loading amount of Pd is easy to control, because there is no loss of Pd in such process. Compared with reduction by H2, photoreduction is highly efficient and complete with high dispersion, which profits from the polycrystalline framework of mesoporous titania. 5. Acknowledgment This work has been supported by National Basic Research Program of China (2004CB719500), Shanghai Nanotechnology Promotion Centre (0452nm010, 0552nm019 ), and National Nature Science Foundation of China (20577009). 6. References [1] J. G. Kim; S. K. Ihm, J. Y. Lee and R. Ryoo, J. Phys. Chem. 95 (1991) 8546. [2] C. T. Kresge, M. E. Leonowicz, W. J. Roth, J. C. Vartuli and J. S. Beck, Nature 359 (1992) 710. [3] R. C. Hayward, P. Alberius-Henning, B. F. Chmelka and G. D. Stucky, Microporous Mesoporous Mater. 44 (2001) 619. [4] S. Yuan, Q. Sheng, J. Zhang, F. Chen, M. Anpo and Q. Zhang, Microporous Mesoporous Mater. 79(2005)93. [5] I. Yuranov, L. Kiwi-Minsker, P. Buffat and A. Renken, Chem. Mater. 16 (2004) 760. [6] K. Sun, W. Lu, M. Wang and X. Xu, Appl. Catal. A 268 (2004) 107.

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Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Published by Elsevier B.V.

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Fabrication of metal oxide nanowires templated by SBA-15 with adsorption-precipitation method Renlie Bao, Kun Jiao, Heyong He, Jihua Zhuang and Bin Yue* Department of Chemistry and Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, Fudan University, Shanghai 200433, PR China.

1. Introduction One-dimensional (ID) nanostructured metal oxide materials have aroused current interest due to their exceptional properties and potential applications in many areas, such as electronics, miniaturized devices and catalysis [1-3]. Nanowires have been successfully synthesized by various methods, e.g. laser ablation, electroless deposition, thermal decomposition, cation exchange, selected-control reaction, chemical vapor deposition, arc discharge and conventional template-assisted solution phase growth. Recently, highly ordered silica mesoporous materials, have opened a new pathway for confined growth of nanowires inside the mesopores. SBA-15 is an ideal template for incorporation of precursors and formation of desired nanowires owing to its large surface area, variable pore size, regular pore system, and high thermal and hydrothermal stability [4]. ID nanowire and 3D nanowire array metal oxides have been successfully synthesized [5-7]. In this work a novel method called "adsorption-precipitation" was adopted to prepare Cr2O3, MnOx, NiO, and CO3O4 nanowires using SBA-15 as the template. The formation of these nanowires was monitored by XRD, TG-DTA, TEM and SAED. 2. Experimental Section SBA-15 was synthesized according to literature method [4]. In the adsorption-precipitation route, SBA-15 was refluxed in an aqueous solution containing certain amount of CrCl3-6H2O (MnCl2-4H2O, NiCl2-6H2O and Co(NO3)2-6H2O) overnight, and dried to remove the solvent. The resulting material was put in a flow of ammonia for 12 h at room temperature, then treated at 200°C for 5 h. The Cr2O3/SBA-15 (MnOx/SBA-15, NiO/SBA-15 and

268

CO3O4/SBA-I5) was obtained after calcination for 5 h at 550°C. To get different fillings, repeated adsorption of precursor was performed. The SBA-15 template of all samples was eliminated by 10% (v/v) HF aqueous solution. X-ray diffraction (XRD) was carried out on a Rigaku D/MAX-IIA diffractometer. Thermogravimetric (TG) analysis and differential thermal analysis (DTA) were performed on a Perkin-Elmer TGA7/DTA7 thermal analyzer in air atmosphere. The transmission electron microscopic (TEM) and selected area electron diffraction (SAED) images were taken on a JEOL JEM2010 transmission electron microscope.

ts

30

40

024

104 110 006 113

20

116

Cr O /SBA-15 Cr2O /SBA-15 2 33

012

Intensity

110 2 00

Intensity

100

3. Results and Discussion

50

(b)

60

SBA-15

(a) Cr22O33/SBA-15 (c) 1.0 1.0

2.0

3.0

4.0

5.0

6.0

2 theta (deg.) (deg.)

Fig. 1. The XRD patterns of (a) SBA-15 in the small angle region, (b) Cr2O3/SBA-15 in the large angle region, and (c) Cr2O3/SBA-15 in the small angle region.

The typical XRD patterns (Fig. 1) of Cr2O3/SBA-15 shows the (100) diffraction of hexagonal SBA-15 in the small angle region moved toward high angle in comparison with the parent SBA-15, indicating the shrinkage of silica framework after formation of metal oxide in the channels of SBA-15. In the large angle region the phase of Cr2O3 (JCPDS No. 38-1479) was observed. For the other metal oxide inside SBA-15, they exhibit the similar diffractions in the small angle region. The XRD patterns in the large angle region show that Mn3O4 (JCPDS No. 24-0734) and Mn2O3 (JCPDS No. 41-1442), NiO (JCPDS No. 44-1159) and Co3O4 (JCPDS No. 78-1970) formed in MnOx/SBA-15, NiO/SBA-15 and Co3O4/SBA-15, respectively. Therefore, the nanostructured crystalline metal oxides are formed inside SBA-15 after calcination. The TEM image of Cr2O3 sample (Fig. 2) shows nanowire morphology and SAED reveals their crystalline character. Moreover, it can be found that the diameter of Cr2O3 nanowires is in the region of 7-8 nm, indicating the replication of the mesopores of SBA-15. The improving of order and

269 269

crystallinity of CO3O4 nanowires can be achieved by increasing precursor fillings (Fig. 3). The morphology of MnOx, NiO and Co3O4 nanowires are similar to that of Cr2O3 nanowires (Fig. 2 and Fig. 3) ~|

Fig. 2. TEM image (a), HRTEM image (b), and SAED of Cr2O3 nanowires.

Fig. 3. The TEM images of Co3O4 samples impregnated (a) once, (b) twice and (c) three times; HRTEM images of (d) MnOx and (e) NiO.

The typical TG-DTA curves of Co(NO3)2-6H2O and Co(NO3)2/SBA-15 are shown in Fig. 4. It is noticeable that Co(NC>3)2 in SBA-15 channels decomposed to oxide completely at 200°C, indicating the decomposition of the nitrate in the mesopores occurred at lower temperature in comparison with the bulk sample. To investigate the formation of crystalline CO3O4 nanowires, the impregnated samples were pretreated at 40-150°C prior to calcination at 550°C. It is found that the order of Co3O4 nanowires was improved with increasing pretreatment temperature but not higher than 150°C, preferentially around the nitrate melting point. The similar results are also observed in the other samples. Therefore, we suggest a possible route for the formation of metal oxide nanowires from their nitrates as follow: when the precursor is pretreated below 150°C, the fusible nitrate with high fluidness gathers together in SBA-15 channels through capillary action, then the precursor undergoes the decomposition and crystallization to form metal oxide nanowires at higher temperatures. If the pretreatment temperature is higher than 150°C, the nitrate precursor may decompose to dispersed amorphous oxide particles before aggregation of nitrate in SBA-15 channels. Thus, the difficult mass transfer at higher temperature results in the formation of separated metal oxide nanowires and the decrease of the order of the nanowires.

270 100

(a) (a)

Weight% (%)

80 70 60

Co(NO33)22/SBA-15 /SBA-15

50 40

Co(NO3)2-6H2O

30

(b)

8

Delta T Endo Down (oC)

90

Co(NO3)2-6H2O

6 o

200 C 200°C 4

Co(NO3)2/SBA-15 2

0

o

250 C 250°C

-2

-4

20 100

200

300

400 o

Temperature (°C) ( C) Temperature

500

100 100

200 200

300 300

400 400

500 500

600

o

Temperature Temperature (°C) ( C)

Fig. 4. (a) TG and (b) DTA curves of Co(NO3)2-6H2O and Co(NO3)2/SBA-15.

4. Conclusion Cr2O3, MnOx, NiO, and CO3O4 nanowires have been successfully prepared with the adsorption-precipitation method using SBA-15 as the template. 5. Acknowledgement This work is supported by the National Basic Research Program of China (2003CB615807), the NSF of China (20371013, 20421303) and the Shanghai Science and Technology Committee (05DZ22313). 6. References [1] [2] [3] [4]

Y. Zhang, A. Kolmakov, S. Chretien, H. Metiu and M. Moskovits, Nano Lett. 4 (2004) 403. S. F. Yin, B. Q. Xu, C. F. Ng and C. T. Au, Appl. Catal. B: Environ. 48 (2004) 237. S. C. Laha and R. Ryoo, Chem. Commun. 17 (2003) 2138. D. Y. Zhao, J. L. Feng, Q. S. Huo, N. Melosh, G. H. Fredrickson, B. F. Chmelka and G. D. Stucky, Science 279 (1998) 548. [5] K. K. Zhu, B. Yue, W. Z. Zhou and H. Y. He, Chem. Commun. 1 (2003) 98. [6] F. Jiao, B. Yue, K. K. Zhu, D. Y. Zhao and H.Y. He, Chem. Lett. 32 (2003) 770. [7] K. K. Zhu, H. Y. He, S. H. Xie, X. Zhang, W. Z. Zhou, S. L. Jin and B. Yue, Chem. Phys. Lett., 377(2003)317.

Progress in in Mesostructured Materials Recent Progress S. Qiu, Y. Tang and C. Yu (Editors) (Editors) D. Zhao, S. © 2007 2007 Elsevier Elsevier B.V. B.V. All All rights reserved. reserved.

271 271

Facile synthesis of hierarchically structured titanium phosphate with bimodal wormhole-like mesopores and macropores Hailong Fei, Xiaoquan Zhou, Pingchuan Sun, Zhongyong Yuan and Tiehong Chen* College of Chemistry, Department of Materials Chemistry, Key Laboratory of Functional Polymer Materials ofMOE, Nankai University, Tianjin, 300071, P.R. China

A facile template-free approach has been proposed to synthesize macroporous titanium phosphate with adjustable bimodal worm-like mesopores. Characterizations including SEM, TEM, FT-IR, N2 adsorption and MAS NMR have been performed. The results showed that phosphorus was incorporated into the framework in the form of Ti-O-P bonds. Bimodal worm-like mesoporores within the macropores formed by the crosslink of the blocks were identified in the range of 2.4 to 6.7 nm. 1. Introduction Titanium phosphates can be used not only as ion-exchange regents, but also as catalysts for the liquid partial oxidation [1]. Therefore, great attention has been paid to synthesize novel organically templated titanium phosphates with mixed valences and 2-D layers [2, 3], ordered mesopores [4] , high surface area [5] or crystalline inorganic framework [6]. Uniform titanium phosphate nanotubes [7] and ultrathin Ti (HPO4)2 film [8] were also fabricated. Recently, Yuan et al prepared mesoporous titanium phosphate with adjustable bimodal macropores via changing the concentration of surfactants [9]. Here we synthesized macroporous titanium phosphate with adjustable bimodal mesopores in a simple way without any surfactants. It is possible that the coeffects of n-butanol and phosphoric acid promote the formation of hierarchical titanium phosphate.

272

2. Experimental Section In a typical process, the mixture of titanium n-butoxide (TBT) and n-butanol with certain molar ratio was added dropwise to 30 ml 0.1M phosphoric acid solution under stirring at room temperature. After stirring for another 2 h, the obtained mixture was transferred into a teflonlined autoclave and aged at 80°C for 24 h. The product was filtered, washed with water, dried at 60°C for 12 h and calcined at 500°C for 2 h. All the samples were denoted as R-d or R-c, where R denotes as the molar ratio of n-butanol to TBT, d denotes as-synthesized and dried sample, c denotes calcined sample.. Infrared data were recorded on a Bruker Vector 22 spectrometer. 31P NMR was carried out by a Varian Infinityplus 400 MHz solid NMR spectrometer with H3PO4 at 0 ppm. N2 adsorption and desorption isotherms were determined on a Micromeritics Tristar 3000 system and pore size distribution was calculated by adsorption branch data. Nitrogen pore volumes were determined at P/Po=0.993. Micropore volumes were determined by the t-plot analysis. Scanning electron microscopy (SEM) was performed on a Philips XL-20 at 15 keV. Transmission electron microscopy (TEM) was carried out on a Philips Tecnai F20 electron microscopy instrument. 3. Results and Discussion

Transmittanee [%]

The FT-IR spectrum (Figure 1A ) clarified that phosphorus was mainly incorporated into the as-synthesized and calcined materials in the form of Ti-OP bonds, which is proved by the Ti-O-P framework vibration at 1034 cm"1 and the stretching frequency of P-0 bonds at 1383 cm"1 [10, 11], The deduction A ^

B

1 34 -O-P

/

j

V/

I .

1383 I'-O

J V

\

4000 3500 3000 2500 2000 1500 1000

Wavenumber cm"1

a

500

Figure. 1 FT-IR spectrum (A) and 31P MAS NMR spectra (B) of 2d (a), 2c (b).

above was further verified by 31P MAS NMR spectra (See Figure.lB). A wide peak appeared at -8.6 ppm for 2-d (Figure.lB-a) due to different phosphor environment [5]. The chemical shifts of (H2PO4)\ (HPO4)2', PO4 were reported around -10, -20, -30 ppm respectively [12]. The chemical shift of 2-c

273

Q -o

0.0 0.2 0.4 0.6 0.8 1.0 1.0 •^•__n Relative pressure (P/P00) 0

5

10 10 15 15 20 25 30 35 40 45 50

Pore diameter (nm)

-1

2c 11.5c 27.5c

3

b

3 -1

2d 11.5d 27.5d

dV/dD(cm g nm )

3 -1

-1

dV/dD(cm g nm )

3

Adsorption volume (cm /g)

a

Adsorbed volume (cm /g)

(Figure. lB-b) moved toward to -12.1 ppm caused by the effect of hydrogen bonding or deprotonation (Figure IB) [13].

0.0

0.2

0.4

0.6

0.8

1.0

Relative pressure (P/P0)

0

5 10 10 15 15 20 25 30 35 35 40 45 50 50

Pore diameter (nm)

Figure. 2 N 2 adsorption-desorption isotherms and BJH pore size distribution curves (outside) a) as-synthesized, b) calcined materials. Table 1 The physical sorption properties and pore parameters of as-prepared and calcined titanium phosphate materials of different molar ratio of n-butanol to TBT.

Mesopore Mesopore * micro II (nm) I (nm) (crnVg) 6.3 0.010 2-d 315 0.576 2.6 0.541 0.014 2-c 218 8.3 0.760 2.4 6.2 0.017 11.5-d 391 8.3 0.005 11.5-c 156 0.395 0.984 27.5-d 436 4.5 6.7 0.016 0.584 1.7 9.0 0.006 27.5-c 188 Figure 2 shows N2 adsorption-desorption isotherms and corresponding BJH pore size distributions(inset) of as-synthesized and calcined materials (The results were listed in Table 1). Figure 2a exhibits classical type IV isotherms with type H3 hysteresis loop and bimodal mesopore distributions(denoted as mesopore I and mesopore II). Mesopore I can be enlarged via enhancing the ratio of n-butanol (See Table land Figure. 2a). After calcination mesopore I almost disappeared and the pore size of mesopore II was increased. Therefore, Sample

SBET

(m 2 /g)

'pore

(cm 3 /g)

Figure.3 Morphologies of samples a) SEM image of 2d, b) TEM image of 2d, c) TEM image of 2c.

274

the calcined samples (Figure. 2b) show type IV isotherms with hysteresis loops of type HI (P/Po= 0.5 to 0.8). Uneven macropores on large blocks are shown in the SEM photo (Figure. 3a). Transmission electronic spectroscopy (TEM) was also performed to characterize the as-synthesized and calcined materials (n-butanol/TBT = 2). As displayed in Figure 3 a, the as-synthesized sample consists of cross-linked particles of 200-400 nm. Each particle is mesoporous and the space between the cross-linked particles corresponds to macropores. For the calcined sample (Figure 3 c) the mesopores are more clearly shown, in accord with the larger pore size from the N2 adsorption measurements. 4. Conclusion Macroporous titanium phosphates with adjustable bimodal worm-like mesopores were synthesized in the presence of n-butanol and phosphoric acid. The amount of n-butanol exerted a great influence on the pore size distribution and BET surface area .This kind of titanium phosphates with hierarchical pores is promising materials for catalysis, separation and material science. 5. Acknowledgement This work was supported by National Science Foundation of China (Grants No. 20373029, 20233030), and joint-research fund of Nankai University and Tianjin University on Nano-sciences. 6. References [1] [2] [3] [4] [5]

[6] [7] [8] [9] [10] [11] [12] [13]

A. Bhaumik and S. Inagaki, J. Am. Chem. Soc, 123 (2001) 691. Y. N. Zhao, G. S. Zhu, X. L. Jiao, W. Liu and W. Q Pang, J. Mater. Chem., 10 (2000) 463. C. Serre, S. Ekambaram, G. Ferey and S. C. Sevov, Chem. Mater., 12 (2000) 444. J. Blanchard, F. SchUth, P. Trens and M. Hudson, Micropor. Mesopor. Mater., 39 (2000) 163. D. J. Jones, G. Aptel, M. Brandhorst, M. Jacquin, J. Jimenez-Jimenez, Antonio. JimenezL6pez, Pedro. Maireles-Torres, I. Piwonski, E. Roziere-Castellon, and J. Roziere, J. Mater. Chem., 10(2000) 1957. Z. L. Yin, Y. Sakamoto, J. H. Yu, S. X. Sun, O. Terasaki, and R. R. Xu, J. Am. Chem. Soc.,126 (2004) 8882. Q. F.Wang, L. Zhong, J. Q. Sun, and J. C Shen, Chem. Mater., 17 (2005) 3563. G. S. Li, L. P. Li, B. G. Juliana and B. F.Woodfield, J. Am. Chem. Soc. ,127 (2005) 8659. R. Z. Ren, Z. Y.Yuan, A. Azioune and B. L. Su, Langmuir., 22 (2006) 3886. G. S. Li, L. P. Li, B. G. Juliana and B. F.Woodfield, J. Am. Chem. Soc. ,127 (2005) 8659. S. K. Samantaray and K. Parida, J. Molarcular Catalysis A: Chemical, 176 (2001) 151. H. Nakayama, T. Eguchi, N. Nakamura, S. Yamaguchi, M. Danjyoc and M. Tsuhakoc, J. Mater Chem., 7 (1997) 1063. Y. J. Li and M. S. Whitttingham, Solid State Ionics, 63 (1993) 391.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

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Synthesis of mesoporous alumina using anionic, nonionic and cationic surfactants Jagadish C. Ray,a Kwang-Seok You,b Ji-Whan Ahn,b and Wha-Seung Ahna* "Department of Chemical Engineering, Inha University, Incheon 402-751, Korea. Korea Institute ofGeoscience and Mineral Resource, Daejeon 305-350, Korea.

A series of mesoporous alumina was prepared based on literature recipes using anionic, non-ionic and cationic surfactants with aluminum tri-secbutoxide in organic solvents with controlled amount of water and in aqueous solution using a complexing agent at room temperature to 100°C. The materials obtained demonstrated physicochemical properties in the order of cationic > non-ionic > anionic surfactant system with respect to surface area, thermal stability and porosity. Mesoporous alumina with enhanced textual properties (506 m2/g, 0.83 cnrVg) and thermal stability to 700°C was prepared with cetyltrimethylammonium bromide in substrate composition of Al:surfactant: H2O: sec-butanol = 1.0 : 0.3: 2.0 : 15. 1. Introduction Many attempts have been made to synthesize mesoporous alumina through surfactant templating because of its potential applications in catalysis and adsorption. Thermally unstable lamellar and hexagonal aluminas have been produced using sodium dodecyl phosphate and sulphate, respectively. Carboxylate templating tends to give microporous material and carboxylic acids also give the materials having pore size distribution centered on 2.0 nm [1]. Non-ionics in aqueous [2] and in organic [3] solvent produced wormhole type materials with lower surface area. Cationics in aqueous medium resulted in a soft gel [4] but in non-aqueous hydrothermal synthesis produced a hard gel [5], both leading to wormhole-structured alumina. In this work, we tried to verify the representative recipes for mesoporous alumina to evaluate their reproducibility and their individual merits in physicochemical properties of the product. We optimized the best process selected by making an improvement in

276

substrate choice or in composition to make a mesophase alumina with improved textural properties and enhanced thermal stability. 2. Experimental Section Aluminum tri-sec-butoxide (ASB), lauric acid (LA), Pluronic 64L (PL) [(PEO)i3(PPO)3o(PEO)13], and cetyltrimethylammoniumbromide (CTAB), secbutanol (SB), n-propanol (NP), triethanolamine (TEA) are used in the synthesis. Several synthesis models for synthesis of mesoporous alumina were compared: anionic [1], non-ionic [3] and cationic [4, 5]. The materials are characterized by XRD using DMAX 2500(Rigaku), N2 adsorption analysis using ASAP 2000 and TEM (Philips CM 200). All the samples are prepared in essence according to the protocol given in the references. 3. Results and Discussion The summary of the synthesis conditions and the corresponding results are given in Table 1. Sample 1 is prepared using LA in n-propanol, 2 is prepared using PL in sec-butanol, 3 is prepared using CTAB in aqueous solution using a complexing agent, TEA. Samples 4 and 5 are prepared using CTAB in secbutanol. Table 1. Summary of the experimental conditions and the results obtained Alsource

surfactant

1

ASB

LA

2

ASB

PL

3

ASB

CTAB

4

ASB

5

ASB

No.

Mol ratio

Temp.

Al:surf.:H20:solvent

(°C)

1 0 0 3 -3 0-25 0 (NP)

100

surface

pore

pore

area

diameter

volume

(m 2 /g)

W

Ref.

(cc/g)

412

42

0.44

46 5

49

057

60

437

3. 8

0.42

4

CTAB 1.0:0.5:2.0:10 0 (SB)

100

475

5.9

0.67

5

CTAB 1.0:0.3:2.0:15.0 (SB)

100

506

6.5

0.83

5

1.0:0.1:2.0:25.0

1

Small angle XRD patterns of the calcined samples (sample No. 1, 2 and 5) with wide-angle reflections are displayed in Fig. 1. The single peak in each case indicates the uniformity of the pores without long-range order having y-alumina pore walls. Upon calcinations at higher temperatures, y-phase peaks are amplified. The differences in small angle XRD intensities are also reflected in

277

surface area and pore volume; the higher the peak, the higher were the surface

IIntensity ntensity ((a a. u.)

25000 20000

( c) 0(c) \

ST

\ ( b)

15000

bed aamount mount (cc/g, STP) A dsorrbed Adso

30000

\\ \

% o

V

( c) ( b)

10000

( aa)) 5000 5000( ( a)

20

40

60

80 80

fl0

2

4 6 Two theta (degree)

8

Fig.l Small angle XRD patterns of the samples calcined at 500°C for 4 h (a) sample 1, (b) sample 2, and (c) sample 5. Inset: Wide angle reflections.

10

0.0 0.0

0.2

0.4

0.6

0.8

1.0

Relative Pressure (P/Po)

Fig.2 Nitrogen adsorption-desorption isotherms of the calcined samples 1

area and pore volume of the alumina. Sample 3 showed no small angle peak, but mosopores were confirmed by TEM. Sample 4 using the original recipe [5] gave the lower intensity peak (not shown) but small adjustment in the substrate composition (sample 5) produced significantly improved small angle XRD peak intensity. The N2 adsorption-desorption isotherms of all the materials are portrayed in Fig. 2. The isotherms are all similar and belong to Type IV with a final saturation plateau together with well-defined hysteresis loops indicating capillary condensation in the mesopores. TEM micrographs of the samples are shown in Fig. 3, which are essentially wormhole structures characteristic to mesoporous alumina. Sample 4 is very similar to 5 and omitted. Sample 1 and 3 are inferior to others as they have smaller pore volumes (Table 1) and 3 have no small angle XRD peak indicating lack of uniformity of pores and sample 1 gives smaller intensity peak for calcined material. As-syn sample 1 had a well-defined XRD peak but after calcination, the intensity of the peak decreased and even disappeared in some cases indicating the instability of the mesostructure during removal of surfactant. Recipe of sample 3 appears good because of delaying hydrolysis rate due to complex formation of TEA with ASB prior to hydrolysis but it has two major problems; pore heterogeneity indicated by absence of XRD peak and the possibility of re-formation of the complex of hydrolyzed product resulting in lower yield. Recipe for synthesizing sample 2 could be made at room temperature but the reproducibility and yield are poor probably due to uncontrolled low temperature synthesis.

278

The recipe of sample 4 was found superior to others as it is stable thermally at 500 °C retaining the small angle peak with higher surface area and retaining the surface area ~35O m2/g up to calcination at 700°C. This recipe is further improved by lowering the amount of CTAB and increasing the amount of solvent, which would help to distribute the surfactant molecules evenly and make easy migration of substrate molecules to form the well organized material of uniform porosity (sample 5). It is also improved by changing the solvent from 1-butanol to sec-butanol to facilitate the establishment of the equilibrium during hydrolysis, which is expected to lower the rate of hydrolysis to organize the structure according to the following reaction. A1-[O-CH(CH3)-CH2-CH3]3 + 2H2O •-> A1OOH + 3CH3-CH2-CH(CH3)-OH According to the reaction, formation of boehmite is indicated and XRD of the as-synthesized sample also confirmed it (not shown), but upon calcination it transforms to y-alumina. In short, mesoporous alumina obtained using ASB, CTAB and water in sec-butanol with the mole ratio 1.0:0.3: 2.0: 15.0 is the best among the competing procedures because of its higher BET surface area and pore volume, good reproducibility and thermal stability.

M i

•

20 nm__..

_

1

<•

.

•

20 nm

;.: 1

u

EB - _ ..

Wy.

1

* •

20 nm

-

* '

1 • 1

Fig. 3. TEM micrographs of the samples calcined at 500°C for 4 h (a) sample 1; (b) sample 2; (c) sample 3; and (d) sample 5.

4. Acknowledgement This work was supported by the Korea Energy Management Corporation (KEMCO) through the Energy & Resources Development Program (2005). 5. References [1] [2] [3] [4]

F. Vaudry, S. Khodabandeh, and M. E. Davis, Chem. Mater., 8 (1996) 1451. Z. Zhang and T. J. Pinnavaia, J. Am. Chem. Soc. 124 (2002) 12294. S. A. Bagshaw and T. J. Pinnavaia, Angew. Chem.Int. Ed. Engl., 35 (1996) 1102. S. Cabrera, J. E. Haskouri, J. Alamo, A. Beltran, D. Beltran, S. Mendioroz, M. D. Marcos and P. Amoros, Adv. Mater. 11(1999) 379. [5] H. C. Lee, H. J. Kim, S. H. Rhee, K. H. Lee, J. S. Lee and S. H. Chung, Micro. Meso. Mater., 79(2005)61.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

279 279

Synthesis of 0-SiC nanofiber using PMOs as a single precursor Jeong-Rae Koa, Ju-Won Minb, Byung-Don Youb and Wha-Seung Ahna* " Department of Chemical Engineering, Inha University, Incheon 402-751, Korea. Department of Materials Science, Inha University, Incheon 402-751, Korea.

Highly crystalline p-SiC nanofiber was successfully synthesized using PMOs (Periodic Mesoporous Organosilicas) as a single precursor/structure binder without any additives by pyrolyzing the template-free PMOs for 5 h at 1400 °C under Ar atmosphere. 1. Introduction There have been several attempts to synthesize SiC using mesoporous silica with various carbon species or mesoporous carbon materials with silica additive [1-4]. The motivation behind these attempts is to prepare SiC using reagents having a large surface area to accomplish high degree of homogeneous mixing to improve the physicochemical properties of SiC produced. These works involved SiC synthesis starting from separate sources of silica and carbon well mixed together, but we decided to test a mesoporous hybrid material in which both silicon and carbon species are incorporated together in one substrate as a precursor for SiC. In this work, synthesis of PMOs and their subsequent pyrolysis in Ar to obtain SiC nanofiber are described. 2. Experimental Section Synthesis of PMOs was carried out at the substrate molar ratio of 1 BTME : 0.91 CTMAC1 (cetyltrimethylammonium chloride) : 2.28 NaOH : 336 H2O as suggested by Inagaki et al [5]. BTME represents 1,2-bis(trimethoxysilyl)ethane used as a organic/inorganic hybrid precursor. We have used microwave-assisted heating method to prepare PMO samples instead of conventional hydrothermal method to reduce the particle size of PMOs as we reported earlier [6]. 3.64 gof CTMAC1 and 1.14 g of NaOH was dissolved in 75.6 g of de-ionized water then

280

3.52 g of BTME was added to the surfactant solution. The mixture was stirred for 19 h at 25°C then treated at 95°C for 4 h using microwave heating system. White precipitates obtained were filtered, washed with ethanol and dried at room temperature. 1 g of the dried sample was refluxed in 3.8 g of 35 wt% HC1 in 150 ml ethanol at 50°C for 6 h to remove the surfactant. Synthesized PMOs were introduced to a vertical tubular furnace and pyrolyzed at 1300~1500°C at the heating rate of 10°C /min for 3 ~ 15 h under Ar atmosphere. Subsequently, pyrolyzed product was heated again in air at 600 °C for 2 h to remove the residual carbonaceous species and treated with a 50 % HF solution for 6 h to remove excess silica material. Characterization of PMOs and SiC was done using XRD, N2 adsorption, SEM/TEM. 3. Results and Discussion Fig. 1 shows the morphology of the synthesized PMOs by conventional heating and by microwave heating method, respectively. PMOs prepared by conventional method (Fig. 1 (a)) were composed of ca. 8.0 micron-sized particles with decaoctahedral shape. PMOs prepared by microwave heating, on the other hand, was composed of ca. 2.2 micron-sized particles with spherical morphology as shown in Fig. 1 (b). This reduction in particle size with uniform spherical morphology is expected to be a significant advantage in SiC synthesis in solid-solid reaction.

Fig. 1. SEM images of PMOs prepared by (a) conventional heating method, and (b) microwave heating method.

Fig. 2 (a) shows XRD and TEM analysis of the PMO sample prepared by microwave heating. It exhibited characteristic diffraction peaks at low-angle region assignable to a cubic symmetry similar to the mesoporous silica SBA-1. Fig. 2 (b) corresponds to the N2 isotherm plot and pore size distribution of the material prepared by microwave-assisted system. Corresponding BET surface area of the product was ca. 770 m2/g and PMOs demonstrated a mean pore size of 3.2 nm with narrow pore size distribution. PMOs synthesized by microwaveassisted heating system are selected as a precursor for SiC based upon these differences in textual properties.

281

Fig. 2. (a) TEM image and XRD diffraction pattern, and (b) N2 isotherm and pore size distribution of PMOs prepared by microwave heating method.

sit

intensity

Fig. 3 describes the evolution of XRD patterns of the pyrolyzed PMOs at different (c) synthesis conditions. Highly crystalline P(111) (111) SiC was produced at 1400°C just after 5 h reaction. XRD pattern of the purified sample (220) (311) prepared at 1400°C indicate that high I3 (b) quality p-SiC phase is formed; (111), (220), (311) planes corresponding to cubic SiC (a) phase were clearly detected. Successful transformation of PMOs to SiC could be 40 50 50 60 60 70 70 80 80 10 10 20 20 30 30 40 achieved even at 1300°C but at the expense 22 theta of longer reaction time; over 15 h was Fig. 3. XRD patterns of p-SiC phase obtained at (a) 1300°C 15h, (b) 1400 needed to identify a SiC phase with reasonable peak intensity. Synthesis at °C5h, and(c)1500°C3h. 1500°C for 3 h reaction was also carried out, but crystallinity of the material was not as good as the sample prepared at 1400°C for 5h due to insufficient reaction time. Except for the product synthesized under optimum condition (1400°C, 5 h), XRD patterns showed residual silica species (at 2 9 = ca. 23°) existing even after purification. Fig. 4 (a) shows typical TEM image of an individual SiC nanofiber with diameter of ca. 40 nm. The image also shows stacking faults caused by the irregular deposition of silicon and carbon atom layers. Electron diffraction pattern (inset of Fig. 4 (a)) suggests that the SiC nanofibers are single crystalline and confirms the typical fee structure. According to SEM in Fig. 4 (b), synthesized P-SiC is only made of fiber-like structures. Typical SiC produced has diameters of 40 ~ 90 nm and was up to 30 to 50 micrometer long. Mesoporosity of PMOs is believed to have a role in promoting the linear growth of SiC to a large aspect ratio. Fig. 4 (c) and (d) show SEM and TEM images of the pyrolyzed PMOs at 1500°C after 3 h reaction. It clearly shows the drastic surface state change from smooth spherical to rugged protrusion of small blobs

282

(Fig. 4 (c)). It is believed that SiC nuclei are formed on the PMO surface via sintering of the precursor sub-units and |3-SiC fibers are grown from the surface afterwards (Fig.4 (d)) via typical carbothermal reduction.

Fig. 4. (a) TEM micrograph of the synthesized (3-SiC using PMOs as a precursor at 1400°C for 5 h, (b) SEM micrographs of the sample prepared at 1400°C for 5 h, (c) at 1500°C for 3 h, and (d) TEM micrograph of (c).

4. Conclusion High quality J3-SiC nanofiber was successfully prepared under relatively mild synthesis condition by pyrolysis of PMO powders with spherical micron-sized particles prepared by microwave heating. Further work is in progress to prepare SiC by pyrolyzing a PMO in which a phenyl group instead of ethane group is uniformly incorporated to silica framework. 5. Acknowledgement This work was supported by grant No. R01 -2003-000-10382-0 from the Basic Research Program of the Korea Science & Engineering Foundation. 6. References [1] Z. Yang, Y. Xia and R. Mokaya, Chem. Mater., 16 (2004) 3877. [2] P. Krawiec, C. Weidenthaler and S. Kaskel, Chem. Mater., 16 (2004) 2869. [3] Z. Liu, W. Shen, W. Bu, H. Chen, Z. Hua, L. Zhang, L. Li, J. Shi and S. Tan, Microprous Mesoporous Mater., 82 (2005) 137. [4] J. Paramentier, J. Patarin and J. Dentzer, C. Vix-Guterl, Ceram. Int., 28 (2002) 1. [5] S. Guan., S. Inagaki, T. Ohsuna and O. Terasaki, J. Am. Chem. Soc, 122 (2000) 5660. [6] W. S. Ahn, K. K. Kang and K. Y. K.im, Catal. Lett., 72 (2001) 229.

Recent Progress in Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

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Synthesis of porous TiO2 monolith by organic membrane template Jianxi Yao and Dan Wang* Key Laboratory of Multi-Phase Reaction, Institute of Process Engineering,Chinese Academy of Science, P.O.Box 353, Beijing 100080, China

TiO2 monoliths with a hierarchical macro/mesopores have been successfully fabricated by using cellulose acetate membrane template. The TiO2 particles were deposited as coherent layers on the walls of cellulose acetate framework, which was removed by calcination without significant disruption of TiO2 framework. SEM images of the TiO2 monolith showed three-dimensional TiO2 frameworks with the size of the pores in the range of 30 nm ~ 15 um. By decreasing the concentration of the sols an overall thinning of the walls and increased shrinkage were observed. This revealed that dilution of the dispersions led to insufficient coating. Keywords: TiO2, template, porous materials, cellulose acetate 1. Introduction The unique electronic and optical properties of TiC>2 provide it with utility as chemical sensor, electrochromic display, photocatalysis, and energy conversion devices [1-3]. It is well known that increasing the specific surface area of these devices is a promising way to improve the characteristics. In order to obtain porous TiO2 with a high surface area, several strategies have been used such as powder sintering method and sol-gel methods etc [3]. However, most of the attempts to prepare such materials require expensive surfactant and complicated procedure. Nagaoka et al [4] synthesized carbon/TiO2 microsphere composite from cellulose/TiO2 microsphere composites. However, no porous structure was observed in their samples. Polymer gels with sponge-like internal structure such as selected copolymers and starch sponge have been used to produce hierarchical architectures in the form of macroporous monoliths or thin films with meso-/macroporosity [5, 6]. In the present study, porous TiO2 monoliths

284

with hierarchical structure have been easily produced by using cellulose acetate (CA) membranes as template. CA membrane is stable in aqueous and alcoholic media, and undergoes pyro lysis on heating and easy to be processed, which makes it a possible template used for structural control [7, 8]. 2. Experimental Section In a typical experiment (Fig. 1), Tetrabutylorthotitanate was dissolved in ethanol and stirred vigorously for 30 min at room temperature. A mixed solution of water, nitric acid and ethanol was added dropwise to the above solution under stirring. And then, a prescribed amount of cellulose acetate membrane was dipped into the solution for 2 h. After removal from this solution, the membrane/inorganic composite was dried in air at 60°C and calcined at 500°C with a heating ramp of 8°C min 1 for 6 h.

CA membrane Heat treatment 500 "C (2hr~2days)

Fig.l. Schematic illustration of preparation of porous TiO2 monolith

An X-ray diffraction (XRD) experiment was carried out on a X'Pert PRO MPD with a Cu Ka source. Scanning electron micrographs were recorded on a JSM-35CF instrument operating at an accelerating voltage of 25 kV. Differential thermal and thermogravimetry analysis (TG-DTA) was carried out on a Netzsch STA 449 at a heating rate 10°C /min from room temperature to 1000°Cinair. 3. Results and Discussion The porous structure of the material was observed in the SEM images of the CA membrane to reveal the inner portion of the membrane (Fig. 2). As can be seen, the pore dimensions of the Fig.2. SEM images of the CA membrane a) and the porous membrane lied in the structure in b) at the high magnification

285

micrometer range. Infiltration of these membranes with the TiO2 colloidal dispersion resulted in the formation of a homogeneous TiO2 coating throughout the membrane. After calcina-tion the CA/TiO2 composite, the TiO2 monolith was obtained, which have intact 3-D bicontinuous porous networks. During heat Fig.3. SEM images of the treatment, TiO2 monoliths TiO2 monolith a) and the shrunk by about two-thirds porous structure can be in in comparison with b) at the high magnification CA/TiC>2 composite. The c) prepared at 800 °C shrinkage decreased with increasing TiO2 loading. SEM images of the TiO2 monolith showed three-dimensional TiO2 frameworks with continuous macropores (Fig.3 (a)). High magnification SEM image of the monolith showed that the pores were in the range of 30 nm -15 um although some degree of local collapse and disorganization of the structure was observed. It is proved that hierarchical TiO2 monoliths with macro/mesopores were successfully produced by using CA as the template. The TiO2 monoliths showed structure features indicating the assembly of particles around the organic membrane structure. A direct replica or inverse copy of the membrane is not seen, as complete filling of the membrane pores with particles was not acquired. Instead, coating of the membrane material gives TiO2 monolith having a porous structure with pores of different diameters originating from the pores in the original template and the new pores 100 200 300 400 500 600 700 800 900 1000 Temperature (°C) obtained on removal of the template. The pore size of the structure varies in the range of 30 Fig.4. TG-DTA curve of the TiO2/CA composite nm~15 um. The minimum time required to impregnate the organic template (at room temperature without external shaking or stirring) and obtained the stable inorganic structure is 2 h. XRD confirmed that the TiO2 monoliths consist of crystalline TiO2 (anatase) suggesting that TiC>2 particles didn't transform to rutile during the heat treatment. It could be possible to prepare rutile hierarchical monoliths if the composite is heated over 800°C (Fig.3 (c)). Most of organic fragment was removed from the TiO2 monoliths after heating at 500°C since only broad peaks corresponding to Ti-O, OH and H2O bonds were evident in the IR spectrum of the TiO2 monoliths. TG -DTA curves (Fig. 4) indicated that complete removal of the C A template after 100

90 70 60

Exotherm.

Weight (%)

80

50 40 30 20 10

0

100 200 300 400 500 600 700 800 900 1000 o

Temperature ( C)

286

the calcination at 500°C. The percentage weight losses associated are 4.5 % with a small endothermic peak (< 200°C water) and 90% with large exothermic peaks Fig. 5. SEM images of the TiO2 monolith with high TiO2 loading (200°C -500°C). The a) and b) at the high magnification residual weight (5.5 mass %) corre-sponds to TiO2 loaded onto the CA surface. By decreasing the concentration of the sols an overall thinning of the walls and increased shrinkage were observed. This revealed that dilution of the dispersions led to insufficient coating. If the concentration of the sols was too low, no TiO2 monolith could be obtained. On the other hand, the pores size depended on the TiC>2 loading. Increasing the concentration of the sols could increase the TiC>2 loading, which produced monolith with smaller openings and thicker walls (Fig. 5). 4. Conclusion To summarize, hierarchical TiO2 monoliths with macro/mesopores were successfully produced by using CA as the template. After calcination at 500°C for 6 h, CA template could be complete removed. The final pore size and structure of the as-synthesized monolith were strongly dependent on the TiC>2 loading. 5. Acknowledgement The work is supported by the National Natural Science Foundation of China (20401015, 50574082). 6. References [1] [2] [3] [4] [5] [6] [7] [8]

O'Regan and M. Gratzel, Nature, 353 (1991) 737. A. Fujishima and K. Honda, Nature, 238 (1972) 37. B. Oregan, D. T. Schwartz, S. M. Zakeeruddin, M. Gratzel, Adv. Mater, 12 (2000) 1263. S. Nagaoka, Y. Hamasaki, S. Ishihara, M. Nagata, K. Iio, C. Nagasawa and H. Ihara, J. Mo.lCata.lA, 177(2002)255. B. J. Zhang, S. A. Davis and S. Mann, Chem. Mater, 14 (2002) 1369. R. A. Caruso and M. Antonietti,. Adv. Funct. Mater, 12 (2000), 307. R. A. Caruso and D. G. Shchukin, Chem. Mater, 16 (2004) 2287. H. Zhang, G. C. Hardy, Y. Z. Khimyak, M. J. Rosseinsky and A. I. Cooper, Chem. Mater, 16(2004)4245.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

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Template-free synthesis of hierarchical mesoporous alumina-based materials with uniform channel-like macrostructures Tie-Zhen Rena, Zhong-Yong Yuanb* and Bao-Lian Sua>* "Laboratory of Inorganic Materials Chemistry, The University ofNamur (FUNDP), 61 rue de Brnxelles, B-5000 Namur, Belgium. b Department of Materials Chemistry, Nankai University, Tianjin 300071, P.R. China.

1. Introduction Although several methods of surfactant-templating have been developed to prepare mesoporous alumina materials [1], it is still a challenge to develop one facile and effective method to synthesize mesoporous alumina with controllable crystalline phase, high crystallinity, hierarchical porosity and large surface area. Practical applications require mesoporous materials having hierarchical pore structures at different length scales in order to achieve highly organized functions, since the introduction of secondary larger pores can improve remarkably the activity of mesoporous catalysts due to the enhanced mass transport and reduced diffusion limitation [2]. Bimodal macro-mesoporous aluminum oxide [3, 4] and silica-alumina [5, 6] materials have thus recently been prepared in the presence of one single surfactant without needing colloid crystals or emulsion droplets for the formation of macropores. Their synthesis was based on a self-assembly process by the hydrolysis of the metal alkoxide droplets in a surfactant solution, and the synthesized materials exhibited a parallel-arrayed macrochannel structure. Herein we report the facile preparation of hierarchically mesoporous-macroporous aluminum oxide, alumina-silica, and phosphated aluminum oxide materials without using any templates. 2. Experimental Section In a typical synthesis, aluminum seobutoxide, or a mixture of aluminum secbutoxide and tetraethoxysilane with different Al/Si ratio (denoted as AlnSim for Al/Si ratio of nlm), was added drop-wise into a H2SO4 aqueous solution (pH=2)

288

under slow stirring. For the synthesis of phosphated materials, a mixed solution of Na2HPO4 and H3PO4 solution was used for the hydrolysis of aluminum secbutoxide with phosphate/aluminum molar ratio of 1/2 or 2/2 (denoted as PiAl2 or P2AI2, respectively).The obtained mixture was separated into two parts: one was transferred to a Teflon-lined autoclave and heated statically at 80°C for 24 h, and another was directly filtered, washed and dried at 60°C for comparison. 3. Results and Discussion 3.1. Meso-macroporous alumina and alumina-silica SEM and TEM images reveal that the obtained aluminum oxide samples, either non-autoclaved or autoclaved, presented a dual pore system of mesopores and macropores, indicating that the meso-macroporous aluminum oxide materials can be spontaneously formed by direct hydrolysis of aluminum secbutoxide in the diluted acid solution. The particles are made of tubular macrochannels with openings from 0.5 to 2 urn, separated by wormhole-like disordered mesopores (Fig. 1). The regularity in size of macrochannels is demonstrated by the cross-section observed by TEM. The walls separating the macrochannels of nonautoclaved aluminum oxide sample are amorphous, while the autoclaved sample frameworks are composed of fibrous nanoparticles of crystalline boehmite phase with a scaffold-like array of hierarchical ordering [3]. The similar macroporous structures were also observed in the synthesized AlnSim samples (Fig. 1). However, almost no fibrous nanoparticle assembly of macroporous frameworks was seen in the meso-macroporous AlnSim, but only disordered wormhole-like mesostructures. This is due to the crystalline phase modification of the autoclaved AlnSim from boehmite to amorphous phase with the increase of the silica content in the samples. Very weak and broad XRD peaks in the autoclaved Al7Sij might still be assigned to boehmite, whereas the non-crystalline or amorphous features were presented in the i5 and AljSi7. All the N2 adsorption -desorption isotherms, whatever nonautoclaved or autoclaved, pure alumina or alumina-silica, are of type IV, indicative of Fig. 1. (a) SEM and (b,c) TEM images of autoclaved aluminum oxide; (d) SEM image of autoclaved Al3Si7; (e) TEM image of

mesoporosity ^ with average pore size o f 3 -

autoclaved Al7Si3; (f) SEM image of autoclaved P,A12.

5 n m . The surface areas

289 289

of nonautoclaved and autoclaved aluminas are 320 and 430 m2/g respectively, while the autoclaved alumina-silica samples gave larger BET surface areas and pore volumes than the pure aluminas. The pore sizes of Al«Sim samples decrease with the increase of the content of silica. The textural and structural properties were modified by the introduction of the secondary oxide (silica). 27 A1NMR spectra of the meso-macroporous aluminum oxides contained only one single signal of six-coordinate Al species. Both six- and four-coordinated Al signals were seen in chemical shift ranges of 0 - 5 ppm and 5 5 - 6 0 ppm respectively in the synthesized AlnSim, and the intensity of the six-coordinated Al signal decreased with the increase of the silica content, accompanying with the increase of the intensity of the four-coordinated Al signal. This suggests that Al has partly been incorporated in the tetrahedral network with the formation of Al-O-Si bonds in Al«Sim. The Si MAS NMR spectrum of Al^Siz shows a broad peak that could be deconvoluted into three resonance lines at ~ -109 (shoulder), -102 (main) and -93 ppm (shoulder), assignable to Si(OAl), Si(lAl) and Si(2Al) respectively. The broadness of the signals indicates the random distribution of Si(Al)-0 units with different structures. The resonance lines shift to the range of-85 to -98 ppm for Alj-Sij, and to the range of-82 to -90 ppm for Al7Sij, accompanying with the decrease of the line intensities. This means that a downfield shift of the resonance position occurs with increasing Al/Si ratio, indicating a decreasing number of'pure' SiO2-rich domains (Q4). 3.2. Meso-macroporous phosphated alumina Phosphation has been determined to enhance the surface acidity of alumina remarkably, leading to the improved catalytic activities of the resultant phosphated alumina catalysts in several acid-catalyzed reactions [7]. The hydrolysis/polycondensation of aluminum seobutoxide in the mixed solution of Na2HPO4 and H3PO4 led to the formation of hierarchically phosphated mesomacroporous aluminum oxides. The macroporous structures are uniform with the sizes of 0.5 - 1.8 \xm, and the macropore walls are composed of small interconnected PA1 particles. The macrochannels are mainly of one-dimensional orientation, parallel each other, perforative through almost the whole particle, which are similar with the case of pure aluminas shown in Fig. 1. The XRD patterns revealed that the nonautoclaved PA1 samples are amorphous, while the autoclaved PAls exhibit diffraction lines of crystalline boehmite phase, though the crystallinity is lower than the autoclaved pure alumina. Direct phosphation and autoclaving take significant roles in not only the macroporosity but also the textural properties of the resultant PA1 samples. The N2 adsorption isotherms of PAls, both nonautoclaved and autoclaved, are of classical type IV with a hysteresis loop of type H2. The autoclaved PAls have higher surface areas than nonautoclaved ones (-370 m2/g vs. 270 m2/g), and smaller BJH-pore sizes (4.3 - 5 nm vs. 2.4 - 2.7 nm) with narrower pore size distributions. The surface stoichiometry characterization, performed by XPS,

290 290

indicated that the Al/P ratios of the PA1 samples are in the range of 8 - 13, regardless of whether the P/Al ratio of the initial gel was 1:2 or 2:2, which indicates stable phosphation by a similar quantity of phosphorus. Most of the detected P atoms may be on the surface of aluminum (oxyhydr)oxide particles, but mainly link with Al via O in the form of P-O-Al, which is further confirmed by FT-IR and solid-state 27A1 and 3 1 P NMR spectroscopy (Fig. 2). Most of the Al atoms exist in an octahedral coordination. Moreover, further work has also revealed that the synthesized hierarchical PA1 exhibited remarkably high thermal stability (at least 800°C), possessing large quantity of surface hydroxyl groups and acid sites, which may attract much interest for practical applications including catalysis. 4. Conclusion Hierarchically meso-macroporous aluminabased materials have been prepared by a template-free self-assembly process. The synthesized pure aluminum oxides, aluminasilicas and phosphated aluminum oxides possess a uniform channel-like macroporous structure with disordered mesopores in the walls. Direct phosphation led to the incorporation of phosphorus into the aluminum (oxyhydr)oxide framework by the Al-O-P bonds, which may attract much interest for practical applications including catalysis. 5. Acknowledgement

27

Al

(b) (a) 31

P

(b) (a) 100

50

0 0

(ppm) δδ(ppm)

-50 -50

-100

Fig. 2. 27 A1 and 3 1 P NMR spectra of (a) non-autoclaved and (b) autoclaved PiAl2

This work was supported by the Belgian Government PAI-IUAP-01/5 project, theNSFC (No. 20473041) and the 973 program (No. 2003CB615801) of China. 6. References [1] [2] [3] [4] [5] [6] [7]

J. Cejka, Appl. Cata!. A 254 (2003) 327-338, and the references therein. Z.-Y. Yuan and B.-L. Su, J. Mater. Chem. 16 (2006) 663-677. T. Z. Ren, Z. Y. Yuan and B. L. Su, Langmuir 20 (2004) 1531-1534. W. H. Deng, M. W. Toepke and B. H. Shanks, Adv. Funct. Mater. 13 (2003) 61-65. A. Leonard, J. L. Blin and B. L. Su, Chem. Commun. (2003) 2568-2569. Z. Y. Yuan, T. Z. Ren, A. Vantomme and B. L. Su, Chem. Mater. 16 (2004) 5096-5106. Z. Y. Yuan, T. Z. Ren, A. Azioune, J. J. Pireaux and B. L. Su, Chem. Mater. 18 (2006) 1753-1767.

Recent Progress in Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

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Mesostructured powder of tungsten oxidesurfactant compound: influence of calcination on the material's structure Zhi-mei Qia, Itaru Honmab and Haoshen Zhou,a,b» a

PRESTO, Japan Science and Technology Agency, 4-1-8 Honocho, Kawaguchi, Saitama 332-0012, Japan. Energy Technology Institute, National Institute of Advanced Industrial Science and Technology, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan.

1. Introduction Tungsten oxide with multiple crystal phases has potential applications as an important functional material for catalysis, photoelectrode, electrochromic device, and chemical sensors [1-6]. These applications have been a tremendous driving force in the field of tungsten-oxide-based materials research and engineering. A great number of reports in this field are now available. Recently, much effort has been focused on synthesis of mesostructured and mesoporous tungsten oxides in order to improve the functional properties of the materials [311]. Mesostructured and mesoporous thin films of tungsten oxides are generally fabricated by the sol-gel triblock copolymer templating technique [6, 7]. For preparing mesostructured and mesoporous powder of tungsten-oxide-based compounds, cationic surfactants such as cetyltrimethylammonium chloride (CTAC) and bromide (CTAB) were used, which enable hydrothermal reaction with tungstic acid or salt precursors [9-11]. As-synthesized mesostructured tungsten oxide-based compounds have been well characterized by a lamellar mesostructure and a 3-dimensional periodical array of Keggin clusters [9-11]. Nevertheless, a detailed investigation into the influence of calcination on the structural properties of mesostructured tungsten-oxide-based compounds is absent. As a matter of fact, materials directly synthesized from liquid solution generally have many structural defects and a poor hydrothermal stability. Therefore, as-synthesized materials need to be treated at high temperatures, to remove the structural defects and to improve their hydrothermal stability. In the present study, we first synthesized tungsten-oxide-based compound powder by

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precipitation reaction of peroxopolytungstic acid (PTA) with CTAC in aqueous solution and then carried out calcination of the compound powder under different conditions. The experimental results indicate that the as-synthesized PTA/CTAC compound contains a lamellar mesostructure but lacks a periodical arrangement of PTA polyanions. Calcination of the as-synthesized compound in air at 200°C not only enhanced the order degree of the lamellar mesostructure but also resulted in the formation of crystalline inorganic layers via reaction of tungsten oxides with trimethylamine gas N(CH3)3 that was produced by CTAC decomposition. When the calcination temperature exceeds 250°C, the lamellar mesostructure of the material collapses. Calcination in air at 400°C of the assynthesized compound produces conventional monoclinic-phase WO3 powder without containing the mesoporous mesostructure. The two-step calcination, first in air at 200°C and then in nitrogen at 400°C, resulted in the black powder of carbon-modified, cubic-phase crystalline WO3 particles with a preferred orientation normal to the (100) plane of the cubic structure. 2. Experimental Section PTA, a highly soluble amorphous mineral acid containing 12 tungsten atoms per molecule [12], is often used for fabrication of sol-gel thin film by dip coating or spin coating [7, 13-15]. We prepared the PTA powder by reaction of H2WO4 with H2O2 according to the previous work [7]. After dissolving a given amount of the self-synthesized PTA powder in 100 ml of deionized water, an aqueous solution of ionic surfactant (/. e., 0.2 M CTAC) was slowly added in the PTA solution under vigorous stirring, which resulted in white precipitate. The precipitate was sufficiently rinsed with deionized water until chlorine ions could not be detected in the waste filtrate by titration with aqueous AgNO3 solution. After drying at 70°C for 5 h, the white precipitate turned yellow. The dried sample was grinded into powder and then calcined at different temperatures and in different atmospheres. The as-synthesized and calcined powder samples were characterized by x-ray diffractometry (XRD, MacScience, Cu-Ka irradiation, A, = 1.5406 A), transmission electron microscopy (TEM, JEOS 1200EX, 200kV accelerating voltage), Raman spectroscopy (irradiation wavelength of 532 nm), and TG-DTA technique. 3. Results and Discussion Fig. 1, (a) and (b) show small-angle XRD patterns of the dried powder sample and that calcined in air at 200°C. Pattern (a) for the dried sample exhibits two peaks at 29 = 2.42° and 4.82°, which can be indexed as (100) and (200). It indicates that the as-synthesized PTA/CTAC compound powder has a lamellar mesostructure with a spacing of d = 36.5A that is very close to d = 35A for the mesostructured salt (H^WnC^oXC^IioN^ synthesized by Stein and coworkers [10]. They observed the 3D ordered arrangement of Keggin ions in

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their salt in addition to the inorganic-organic lamellar mesostructure. However, the lack of other peaks in (a) suggests that in the present PTA/CTAC compound PTA polyanions are ordered only in one dimension. The powder sample changed its color from yellow into brown after calcination in air at 200°C for 6.5 h. A gaseous substance with 2theta (dee) an intense ammonia smell was Fig. 1. Small-angle XRD patterns of (a) the asreleased from the furnace synthesized PTA/CTAC compound powder and (b) during the course of calcination. the powder calcined in air at 200 °C for 6.5 h. The gas proved to be trimethylamine (N(CH3)3, responsible for the smell of rotting fish) that arises from dissociation of amine groups from CTAC cations. Beck and coworkers also observed the release of trimethylamine at ~ 200°C when they used a similar cationic surfactant for preparing MCM-41 mesoporous silica [16]. Fig. 1, (b) displays XRD pattern of the calcined sample. The (100) and (200) peaks move to 29 = 3.68° and 7.27°, marking that the lamellar mesostructure of the material is stable at 200°C. Calcination induces a large decrease of the spacing from d = 36.50 A to 24.00 A. An increase of the peak intensity suggests that calcination also results in an enhanced order degree of the material's lamellar mesostructure. The preservation of the lamellar mesostructure at 200°C implies that the organic layers consisting of alky 1 chains (~ 20 A in length) of CTAC molecules are safe at this temperature. With the lamellar mesostructural model shown in Fig. 2 Inorganic layerSurfactant layer — Amine group —-

Fig. 2. Schematic explanation of the calcination induced changes in the lamellar mesostructure of the PTA/CTAC compound (a is the tilt angle between the inorganic layer and the alkyl chains of the CTAC surfactant, d is the spacing of the lamellar mesostructure).

[17], removal of -N(CH3)3 groups (~ 4 A in size) from the surfactant layers would cause a decrease of < 8 A in the spacing of the lamellar mesostructure. It is therefore estimated that shrinkage of the inorganic layers and reduction of the

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tilt angle a between the alkyl chains and the inorganic layer, both induced by calcination, lead to a decrease of > 4.5 A in the spacing of the sample's lamellar mesophase. It is interesting to observe a new peak at 26 ~ 9.22° in Fig. 1, (b). This peak does not belong to the lamellar mesostructure but arises from the lattice diffraction (d ~ 9.57 A), revealing crystallization at 200°C of the inorganic layers of the mesostructured material. According to McMonagle et al, who synthesized the crystalline (NtL^PWnC^o by exposure of H3PW1204o to ammonia gas at 190°C [18], it is most likely that the crystalline inorganic layers of the mesostructured material under investigation is a tungsten oxide-trimethylamine compound that could be formed via reaction of tungsten oxide with trimethylamine gas released from the surfactant layers. By carefully searching the JCPDS cards, the crystalline inorganic layers of the mesostructured sample were determined to be a compound referred to as tungsten oxide tetramethyl ammonium hydrate [(CHs^N^WCvLSF^O (JCPDS card No. 31-1966, its three largest spacings are d = 12.20, 9.62 and 9.09 A, respectively.). There are three reasons to support this determination. The first reason is that the lattice diffraction peak with d = 12.20 A is identical in position with the (200) peak for the lamellar mesostructure of the material. In this case, the peak observed at 20 = 7.27° for the calcined powder sample should include two contributions: the lattice and mesostructure diffractions. The second reason is that d = 9.62 A is very close to d ~ 9.57 A. The last reason is that the right-side broadening of the peak at 26 ~ 9.22° could be ascribed to overlapping of two lattice diffraction peaks with d= 9.62 A and d= 9.09 A. Fig. 3, (a), (b) and (c) are the XRD patterns for the samples calcined at different conditions, (a) for the sample calcined in air at 250°C does not clearly show peaks at smaller angles, giving a sign of collapse of the lamellar mesostructure. The number of peaks at higher angles increases in (a), revealing improvement of crystallization of the sample. The peak at 20 = 10.32° corresponds to d = 8.55 A that is smaller than d ~ 9.57 A for the sample calcined at 200°C. Fig. 3. XRD patterns of the powder samples Moreover, the other high-angle calcined at different conditions (a. in air at 250 peaks in (a) are different in °C; b. in air at 400 °C; c: first in air at 200 °C for 5 position from those given in the h and then in nitrogen at 400 °C for 4 h.) JCPDS card 31-1966. Thus, a crystal-phase change for the sample most likely occurred when the calcination temperature was increased from 200°C to 250°C. Calcination of the sample at 250°C may lead to a new material because we did not find from the JCPDS

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cards a known material whose XRD a pattern matches (a). Increasing the calcination temperature up to 400 °C causes the compound to become a conventional monoclinic-phase WO3 powder, as evidenced by Fig. 3(b). All metastable intermediates disappeared at 400°C. To try to transform the mesostructured PTA/CTAC compound into mesopor-ous tungsten oxide, the b powder sample calcined in air at 200°C underwent the second-step treatment in nitrogen at 400°C. After the second-step calcination, the sample turned its color from brown to black, attributable to the presence of carbon in the sample due to an incomplete combustion of c the CTAC surfactant. Fig. 3 (c) shows the XRD pattern for the sample calcined in two steps. Pattern (c) presents two peaks at 20 = 23.64 and 48.21°C, corresponding to d = 3.760 and 1.886 A. These spacing values are in excellent agreement with those for the (200) and (400) planes of the cubic-phase Fig 4 T E M i m a g e s o f (a) t h e as.synthesized WO3 reported by Sidle et al (JCPDS PTA/CTAC compound powder, (b) the card No. 46-1096: d200 = 3.761 A power calcined in air at 200°C and (c) that and (^400 = 1.878 A) [19]. The XRD calcined first in air at 200°C and then in peaks from the other crystal planes nitrogen at 400°C. Inserts (a) and (b) in (c) of the cubic Structure were not are magnified views of the selected areas. detected for the sample, revealing that the two-step calcination causes the WO3 particles to crystallize along the preferred orientation being normal to the (100) plane of the cubic phase. Note that the XRD peak for the (100) plane of the cubic structure cannot be observed. Growth of crystalline WO3 particles along the other directions in the cubic structure is prohibited, which should be attributed to the dimensional limitation by the lamellar mesostructure contained in the precursor material. The diffraction peaks at smaller angles are absent in (c), indicating that the cubic-phase WO3 particles do not contain the ordered mesoporous structure. However, the TEM investigations indicate that the stepby-step calcined sample contains a wormhole-like mesoporous structure with very small pore diameters (< 1 nm). The above XRD data show that the

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mesostructured PTA/CTAC compound is quite sensitive to the calcination temperature and atmosphere. Fig. 4, (a), (b) and (c) show TEM images of the different powder samples, (a) for the as-synthesized compound powder presents the channel arrays with a spacing of d = 32 A. A reduction in spacing in contrast with d = 36.5 A determined by XRD arises from heating of the sample by electron beam irradiation, (b) for the sample calcined at 200°C indicates that the straight channel array has a spacing of d = 23 A, being very close to d - 24 A measured by XRD. It is clear that the calcined sample is not sensitive to the electron beam irradiation as compared with the as-synthesized one, suggesting a good hydrothermal stability of the calcined sample. Comparison between two images (a) and (b) confirms that after calcination at 200°C the lamellar mesostructure of the sample was indeed improved in its long-range order degree. The selectedarea electron diffraction (SAED) pattern shown in the insert in (b) reveals an amorphous structure despite the fact that the powder sample has become crystalline at 200°C. This is so because the lattice spacing of d ~ 9.57 A determined from the XRD pattern (Fig. 1, b) of the same sample is too large to be clearly observed in the SAED pattern. From the magnified image (another insert in b), the lattice fringes are ambiguously seen in each channel. Fig. 4 (c) displays the TEM image for the sample calcined in two steps (in air at 200°C and then in N2 at 400°C). From this image both a wormhole-like mesoporous structure with a pore diameter of ~ 1 nm and the lattice fringes can be seen. The insert (a) and (b) are the magnified views of the corresponding areas in the image (c). The insert (a) clearly shows the lattice fringes with d = 3.59 A, arising from diffraction of the (200) plane of the cubic-phase WO3. The lack of a wormhole-like mesoporous structure in the insert HDD 1300 (a) implies that crystallization of Wavenumber (cm' ) WO3 is disadvantageous to the „. . _ . , . . ° . ._ . Fig. 5. Raman spectra of seven powder samples mesopore formation. A magnified (a pTA . b P T A / C T A C c o m p o u n d ; c, d , e md f view of the wormhole-like mesop- c o r r e s p o n d i n g t0 t h e p o w d e r s a r n p i e s c a i c i n e d in orous Structure is shown in the air at 200, 250, 300 and 400 °C, respectively; g. insert (b) where the lattice fringes the sample calcined first in air at 200 °C and then were not seen. From this indication in nitrogen at 400 °C.) a conclusion could be derived that during the thermal treatment in nitrogen at 400°C the carbon residue produced by the incomplete decomposition of CTAC is attached to the tiny clusters of tungsten oxide to prevent crystallization of tungsten oxide and consequently 1

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lead to the carbon-modified mesoporous tungsten oxide powder. Our group also prepared the carbon-modified ordered mesoporous silica powder by calcination in nitrogen of the mesostructured silica-surfactant hybrid material [20]. Fig. 5, a - g show Raman spectra for seven powder samples, a for the PTA powder exhibits five bands. The first three bands at 585, 594.3 and 619.2 cm"1 correspond to v(O-W-O) and the other two bands at 917 and 978 cm"1 are ascribed to v(W=0) [21]. b for the as-synthesized PTA/CTAC compound indicates that the v(W=O) bands shift to 968.3 and 999 cm"1 and the v(O-W-O) band locates at 558.3 cm"1. The other bands in b result from the CTAC surfactant (i. e., the broad band centered at 1455 cm'and the other two bands at 1309.5 and 766 cm"1 are due to the deformation, twisting and rock vibrations of CH2 groups, respectively [22].). It is worth noting that no new Raman bands were observed with the PTA/CTAC compound as compared with the Raman spectra of PTA and CTAC (spectrum for CTAC not shown). This is so because the PTA/CTAC compound was formed via the strong electrostatic attraction between PTA polyanions and CTAC cations not via the chemical binding between them. Four Raman spectra, c - f, were obtained with the samples calcined in air at 200, 250, 300 and 400°C, respectively, c for the sample calcined at 200°C does not present the v(W=O) band, implying that the PTA polyanionic structure was destroyed at 200°C. This is in agreement with the XRD results that calcination in air at 200°C caused the reaction of PTA with N(CH3)3 to produce a new compound [(CH3)4N]2WO4-1.5H2O. Comparisons among the Raman spectra c - f suggest that with increasing the calcination temperature the band at 804.5 cm"1 and its shoulder at shorter wave number, both arising from v(O-W-O) [21], gradually become strong. Two broad bands at ~ 1360 and ~ 1590 cm"1, extremely similar to the D and G bands of carbon [23], are present in the spectra c - e but disappear from f, giving an indication that it is difficult to completely remove the CTAC surfactant from the powder samples when the calcination temperature is below 400°C. This is due to the strong interaction between tungsten oxide and CTAC. Pure CTAC was found to be completely decomposed in air at temperatures > 300°C. Spectrum g for the sample calcined in two steps also include the v(O-W-O) bands, evidencing that after the treatment in nitrogen the powder sample still keeps the oxide state of tungsten. Both very weak bands at ~ 1360 and ~ 1590 cm"1 in g indicate that the carbon residue remains in the sample due to the incomplete combustion of CTAC in nitrogen. Combination of the XRD, TEM and Raman spectroscopy analyses makes it clear that calcination of the lamellar mesostructured PTA/CTAC compound first in air at 200°C and then in nitrogen at 400°C can result in the carbon-modified, cubic-phase crystalline WO3 powder with a preferred orientation being normal to the (100) plane of the cubic structure. On the basis of TEM results, the step-by-step calcined powder also contains a wormhole mesoporous structure with a small pore diameter ( < 1 nm). The TGDTA curves recorded during thermal treatments of the as-synthesized PTA/CTAC compound powder in air and in pure nitrogen were shown in Fig.

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6(a). Calcination in air leads to two exothermic peaks, attributable to

20

100

260 340 420 Temperature (C)

CIO

1

1.5

2

2.5

Potenital (V vs Li/Li*)

Fig. 6. (a) TG-DTA curves obtained during thermal treatment of the as-synthesized PTA/CTAC compound powder in air (solid lines) and in nitrogen (dash lines); (b) Cyclic voltammograms of the carbon-modified, cubic-phase WO3 powder immobilized on a nickel mesh with Teflon glue. The scanning rate is 0.1 mV/s.

combustion of carbon chain of the CTAC surfactant. Owing to the lack of oxygen, these peaks were not observed during the thermal treatment in nitrogen. On the other hand, the weight loss induced during thermal treatment in nitrogen is smaller than that induced during calcination in air, giving a support of the presence of carbon in the sample after treatment in nitrogen. As an example of application, the electrochemical lithium-intercalation property of the carbonmodified, cubic-phase WO3 powder was investigated by cyclic voltammetry. The WO3 electrode was prepared by immobilizing the powder sampled mixed with Teflon glue (5 wt%) onto a nickel mesh. Both reference and counter electrodes were lithium metal. The electrolyte is 1M LJCIO4 in a mixed solution of ethylene carbonate (EC) and diethylene carbonate (DC) (V E C/VDC = 1)- Fig. 6(b) shows the first 3 cycles. No characteristic redox peaks were clearly observed. The cathodic charges for the second and third cycles are -286 C/g and -251 C/g, and the corresponding anodic charges are 180 C/g and 173 C/g. 4. Conclusion The present study has demonstrated significant and complicated influence of calcination on both the mesostructure and crystal structure of the tungsten oxide-based compounds. By calcination at 400°C in nitrogen of the PTA/CTAC compound, we successfully obtained the cubic-phase crystalline WO3 powder with a highly preferred orientation being normal to the (100) plane of the cubic structure. Such preferred orientation is attributed to the dimensional limitation by the lamellar mesostructure of the precursor material. Transformation of the amorphous inorganic layers into the crystalline ones through reaction of tungsten oxide with trimethylamine gas released from the CTAC surfactant was observed, for the first time, for the lamellar mesostructured PTA/CTAC

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compound. It was confirmed that the lamellar mesostructure of the PTA/CTAC compound was stable at 200°C and collapsed at > 250°C. Creation of mesoporous WO3 via calcination in air of the mesostructured PTA/CTAC compound is not successful due to a lack of a rigid three-dimensional inorganic network. However, the TEM analyses indicate that the carbon-modified, wormhole-like mesoporous WO3 powder with small pore diameters (< 1 nm) could be prepared from the mesostructured PTA/CTAC compound by the twostep calcination, first in air at 200°C and then in nitrogen at 400°C. 5. References [1] I. Shiyanovskaya and M. Hepel, J. Electrochem. Soc. 146 (1999) 243. [2] M. Misono, Chem. Commun. (2001) 1141. [3] L. G. Teoh, Y. M. Hon, J. Shieh, W. H. Lai and M. H. Hon, Sens. Actuators. B 96 (2003) 219. [4] E. O. Zayim, P. Liu, S. Lee, C. E. Tracy, J. A. Turner, J. R. Pitts and S. K. Deb, Solid State Ioncs 165 (2003) 65. [5] S.-H. Baeck, K.-S. Choi, T. F. Jaramillo, G. D. Stucky and E. W. McFarland, Adv. Mater. 15(2003)269. [6] W. Cheng, E. Baudrin, B. Dunn and J. I. Zink, J. Mater. Chem. 11 (2001) 92. [7] Z. Qi, H. Zhou, T. Watanabe and I. Honma, J. Mater. Chem. 14 (2004) 3540. [8] P. Yang, D. Zhao, D. I. Margolese, B. F. Chmelka and G. D. Stucky, Nature 396 (1998) 152. [9] M. S. Whittingham, J. Guo, R. Chem, T. Chirayil, G. Janauer and P. Zavalij, Solid State Ionics 75 (1995) 257. [10] A. Stein, M. Fendorf, T. P. Jarvie, K. T. Muller, A. J. Benesi and T. E. Mallouk, Chem. Mater. 7 (1995) 304. [11] G. G. Janauer, A. Dobley, J. Guo, P. Zavalij and M. S. Whittingham, Chem. Mater. 8 (1996) 2096. [12] J. OI, A. Kishimoto and T. Kudo, J. Solid State Chem. 96 (1992) 13. [13] B. Orel, N. Groselj, U. O. Krasovec, M. Gabrscek, P. Bukovec and R. Reisfeld, Sens. Actuators. B 50 (1998) 234. [14] K. Itoh, K. Yamagishi, M. Nagasono and M. Murabayashi, Ber. Bunsen-Ges. Phys. Chem. 98 (1994) 1250. [15] H. Okamoto, T. Iwayanagi, K. Mochiji, H. Menace and T. Kudo, Appl. Phys. Lett. 49 (1986)298. [16] J. S. Beck, J. C. Vartuli, W. J. Roth, M. E. Leonowicz, C. T. Kresge, K. D. Schmirt, C. T-W. Chu, D. H. Olson, E. W. Sheppard, S. B. McCullen, J. B. Higgins and J. L. Schlenker, J. Am. Chem. Soc. 114(1992)10834. [17] Z. Chen, B. H. Loo, Y. Ma, Y. Cao, A. Ibrahim and J. Yao, ChemphysChem 5 (2004) 1020. [18] J. B. Mcmonagle and J. B. Moffat, J. Colloid Interface Sci. 101 (1984) 479. [19] A. R. Siedle, T. E. Wood, M. L. Brostrom, D. C. Koskenmaki, B. Montez and E. Oldfield, J. Am. Chem. Soc. 111 (1989) 1665.

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Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

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Hydrothermal synthesis and characterization of mesoporous zirconia templated by triethanolamine Fu Ma a ' b ' c , Jihong Suna*, Hongjian Zhao a b ' c , Yun Lia>b and Shijie Luoa

"Department of Chemistry and Chemical Engineering, College of Environmental & Energy Engineering, Beijing University of Technology, Beijing, 100022, P. R. China b Key Laboratory of Energy and Chemical Engineering, NingXia University, Yinchuan, 750021, P. R. China c Department of Chemical Engineering, Ningxia Normal University, Guyuan, 756000, P. R. China

1. Introduction Since the discovery of M41S in 1992 [1], there has been great interest in the synthesis of mesoporous transition metal oxides with well-ordered and controllable structural features because of their potential applications in the fields of catalysis, optics, electronics, and magnetism [2, 3]. One special characteristic of zirconium oxide is that it contains both weakly acidic and basic surface sites, and promises a high activity in reactions with acid-base bifunctional catalysts. In the past, many great efforts have been performed to extend the surfactant templating strategy to the synthesis of mesoporous zirconia including cationic quaternary ammonium surfactants [4], anionic surfactants [2, 5], primary amines [6] and block copolymers [7] as the structure directing agents. However, relatively expensive surfactants usually cause substantially high cost and make the product poisonous [8]. Additionally, some of them were reported to have poor thermal stability [9]. These facts actually limit many practical applications. Here, by using small, non-surfactant templates to direct the formation of mesosized structural features during the hydrolysis and condensation procedure of zirconium n-propoxide, we report a new templating method to synthesis successfully mesoporous zirconia via the hydrothermal route, which is expected to extend the templating strategy for preparing non-siliceous mesostrutured materials.

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2. Experimental Section Zirconium n-propoxide, triethanolamine (TEA) and water were combined at room temperature in a ratio of 1:0.2-1.0:10-150 to obtain a homogeneous mixture. After heated at 100°C for 24 h in air, a solidified gel was formed, which was then transferred into an autoclave and heated at 80-150°C for 1272h. Finally, the prepared sample was calcined at 600°C for lOh with a ramp rate of 1°C /min in air to obtain the final mesoporous materials. X-ray diffraction (XRD) of the samples was recorded using a Brucker-AXS D8 Advance X-ray diffractometer using Cu K a radiation. Transmission electron microscope (TEM) images were recorded on a JEOL JME-2010. Nitrogen adsorption-desorption isotherms were measured using a Micromeritics ASAP 2010 system, and pore size distributions were obtained from the N2 desorption branch isotherm using BJH method. 3. Results and Discussion XRD patterns for calcined samples are shown in Fig. 1. All of solids show diffraction patterns with only one strong 0 10 20 30 40 50 60 70 80 reflection during the low angle scale, and relative 2 6 value shifted around from 1.0 to 1.5 c CD depending on Zr/TEA/water molar ratio and aging condition during the sol-gel synthesis process. Similar single peak diffraction 10 4 patterns have been previously 26 (° ) observed in mesoporous AI2O3 [10], TUD-1 [11] and TiO2 Fig. 1. XRD patterns of the mesoporous ZrO2 sample, [12], indicating that such a the synthisis condition were as following: prepared sample possesses a (a)1.0Zr:0.6TEA:25H2O, aged at 150°C for 2 h, mesoporous structure. The (b)1.0Zr:0.6TEA:150H2O, aged at 150°C for 48 h, (c)1.0Zr:0.6TEA:25H2O, aged at 150°C for 48 h, shift of the single peak position in the XRD patterns (d)1.0Zr:1.0TEA:25H2O, aged at 150°C for 48 h, Inset: sample (c). All of samples were calcined at 600°C for reflects the change of dlOh. spacing value. After calcinations at 600°C, tetragonal zirconia has been formed (Fig. 1 insert). Meantime, a small amount of monoclinic zirconia may be present as indicated by the small shoulder peaks at 2 0=24.4,28.2,31.5°.

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TEM image (Fig. 2) shows wormhole-like or possibly sponge-like pore channel for the typical mesoporus ZrC>2 sample, which is in good agreement with the only one diffraction peak in the XRD patterns. Similar pore channels have been observed for disordered mesoporous alumia [13] and Ti-TUD-1 [14] when TEA were also used as a template. 100 300

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d V/ d ( l o g D) ( c m3 / g )

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Ads or bed( c m / g)

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Fig.2. TEM image of the typical mesoporus ZrO2 s a m p l e

0

0. 0. 55

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R e l a t i v e ppressure(p/p0) r e s s u r e ( p / p 0) Relative

Fig. 3. The typical N2 adsorption-desorption isotherm and corresponding pore size distribution of mesoporous zirconia (insert)

A typical nitrogen adsorption-desorption isotherm of the sample is shown in Fig. 3. The obvious hysteresis loops can be found at the relative pressure of 0.68-0.97, which is corresponding to the narrow pore size distribution (Fig.3 inset) with the mean pore size at 8.7nm and the surface area of 45 m2/g. On the other hand, it is evident that the mesoporous ZrO2 prepared calcined at 600°C for lOh in this work shows better thermal stability than any other mesoporous ZrC>2 previously synthesized by the surfactant-assisted methods [2, 4, 7], in which mesoporous struture was disappeared after calcined at 600° C. The further studies for the effects of other parameters are in progress. To explain our findings with combination of pioneering work [2, 12, 14-16] the following mechanism is postulated. It is well known that zirconia alkoxides are highly reactive with water to form precipitate. But when the zirconium sources were mixed with TEA firstly, the three OH groups of TEA can easily replace alcohol groups of alkoxides. After chelation with TEA, zirconium transforms into a complex, which oligomerizes by hydrolysis-polycondensation [15, 16]. Upon subjection to the thermal treatment, the oligomers condense further, releasing TEA and aggregating by self-assembly. Moreover, the TEA could template the formation of zirconia, and then, the particles directly condense into well-arranged pore walls. Combined with above results, TEA act not only as a hydrolysis retarding agent but also as a mesopore forming agent.

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4. Conclusion Consequently, with zirconium n-propoxide as Zr source and TEA as template, a new hydrothermal synthesis route has been developed for the preparation of mesoporous zirconia, with a wormhole-like pore channel. The use of TEA as template is believed to be responsible for the improved thermal stability of mesoporus zirconia. 5. Acknowledgement This research was supported by Project Sponsored by the Scientific Research Fundation for the Returned Overseas Chinese Scholars, State Education Ministry, and the Natural Science Fundation of Ningxia Hui Autonomous Region (ZD02). 6. References [1] C. T. Kresge, M. E. Leonowice, W. J. Roth, J. C. Vartuli and J. S. Beck, Nature, 359 (1992) 710. [2] M. S. Wong and J. Y. Ying, Chem. Mater., 10 (1998) 2067. [3] X. Song and A. Sayari, Catal. Rev., 38 (1996) 329. [4] J. A. Knowles and M. J. Hudson, Chem. Commun., (1995) 2083. [5] G. Pacheco, E. Zhao, A. Carcia, A. Sklyarov and J. J. Fripiat, J. Mater. Chem., 8 (1998) 219, T. J. McCarthy and W. M. H. Sachtler, Appl. Catal .A, 148 (1996) 135 [6] P. Yang, D, Y.-Y. Huang, D. Zhao, I. Margolese, B. F.Chmelka and G. D.Stucky, Nature, 396 (1998) 152. [7] S. A. Bagshaw, E. Prouzet and T. J. Pinnavaia, Science, 269 (1995) 1242. [8] X. S. Zhao, G .Q. Lu and G. J. Millar, Ind. Eng. Chem. Res., 35 (1996) 2075 [9] S. A. Bagshaw and T. J. Pinnavaia, Angew. Chem. Int. Ed. Engl, 35 (1996) 1102. [10] J. C. Jansen, Z. S han, L. Marchese, W. Zhou, N.v.d. Puil and Th. Maschmeyer, Chem. Commun., (2001) 713. [11] C . F . M a , J . H. Sun and F. Wang, Chinese Invent Patent, No: CN2005100708798. [12] S. Cabrea, J. E. Haskouri, J. Alamo and P. Amoros, Adv. Mater., 11 (1999) 379. [13] Z. Shan, J. C. Jansen, L. Marchese and Th. Maschmeyer, Micropor. Mesopor. Mater., 48 (2001) 181. [14] S. Cabrea, J. E. Haskouri, M. D. Marcos and P. Amoros, Solid State Sci., 2 (2000) 405. [15] Y.-W. Suh, J.-W. Lee and H.-K. Rhee, Solid State Sci., 5 (2003) 995. [16] Y.-W. Suh, J.-W. Lee and H.-K. Rhee, Catal. Lett., 90 (2003) 103.

Recent Progress in Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

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The role of triethanolamine in the synthesis of mesostructured TiO2 by sol-gel method Feng Wanga, Jihong Sunb* and Chongfang Maa "Key Laboratory of Enhanced Heat Transfer and Energy Conservation, Ministry of Education and Key Laboratory of Heat Transfer and Energy Conversion, Beijing Education Commission, College of Environmental and Energy Engineering, h Department of Chemistry and Chemical Engineering, College of Environmental and Energy Engineering, Beijing University of Technology, Beijing 100022, China.

1. Introduction With its unique characteristics in band position and surface performances, the mesostructured TiO2 material plays a prominent role in fundamental studies and has widely promising applications in many areas, such as solar energy conversion, and photocatalysis [1, 2]. Since the discovery M41S in 1992 [3], Mesoporous titania, with controllable structure and tailoring texture properties simultaneously, has been extensively synthesized for increasing its specific surface area and therefore realizing above high-performance. Among the various synthetic routes developed in the last decades, the most general and versatile hydrothermal synthetic strategy is based on the hydrolysis and condensation of titanium alkoxides via self-assembly mechanism. Meanwhile, progress has been made in using different types of amphiphiles as templates, including small charged surfactant molecules and large block copolymers [4-7]. However, due to the expensive and noxious surfactants, it deeply limits the wide industrialization and practice availability. Therefore, it is exciting useful to explore and design new templates to avoid those problems encountered in fundamental research and industrial demands. Recently, we reported that, by using triethanolamine (TEA) as template which is small, green and inexpensive non-surfactant chemicals, mesoporous TiO2 materials have been successfully synthesized with reproduceable and controllable structure [8, 9]. In this paper, the role of TEA in the synthesis of mesostructured TiO2 was investigated.

306 306

2. Experimental Section The typical synthesis procedure is as following: Tetrabutyltitanate (TBOT), TEA and water were mixed and stirred for 24 h at room temperature in ratio of 1: 0.5-5:20-30. After aging at room temperature for 24 h, this mixture was dried and aged at 373-453 K for 12-72 h in an autoclave. Finally, the sample was obtained as a white mesoporous solid by removal of the template either via Soxhlet extraction using ethanol or via calcinations at 723-873 K for 10 h in air. X-ray diffraction (XRD) data were recorded on a D8-ADVANCE with Cu Ka radiation. Transmission electro microscope (TEM) observations were obtained with JEOL-2010 apparatus. Nitrogen adsorption and desorption isotherms were measured using a Micrometeritics ASAP2020 system. The pore size distributions were calculated by the BJH method. UV-vis absorbance spectra were taken on a Shimadzu UV-2450 spectrophotometer. 3. Results and Discussion The N2 adsorption/desorption isotherms (not shown) of typical mesoporous titania via Soxhlet extraction using weak acid ethanol for 3 days. A clear hysteresis loop at high relative pressure is observed, which is related to the capillary condensation associated with large pores. The BET surface area is 525 m /g and its mean pore size is around 4.5 nm, but decreased to 300 m2/g when calcinated at 573 K. TEM image in Fig. 1 shows a wormhole-like structure with narrow pore distribution [8, 9]. Obviously, The large surface area of mesoporous TiO2 can be related with its special mesostructure. The XRD pattern of typical mesoporous TiO2 is shown in Fig. 2. It displayed that one diffractive peak with strong intensity at low angle of around 1.0 (2 theta), suggesting long-scale order in the arrangement of structure [10]. The analysis of the UV-vis spectrum indicated that absorption intensity of mesostructure TiO2 is higher than that of P25 (Degussa), especially in visible light area (shown in Fig. 3). In the synthesis of mesoporous TiO2, many parameters can be strongly influenced on the final internal structure, such as the sol composition , pH , hydrothermally treated time and Fig. 1 TEM image of the mesoporous TiO2 temperature. Presently, this work is doing under way.

307

v.

5000

60

4000 intensity

intensity

50

3000

40

30

20

10

2000

0 20

30

40

50

2θ/

60

70

80

o

1000

0 0

1

2

3

2θ /

4

5

6

o

Fig. 2 XRD patterns of the mesoporous TiO2 and with wide angle (insert)

2.0

1.5

Absorbtance

It is well known that TEA behaves as a tertiary amine in aqueous solution, and it easily forms weak cationic complexes by acting as a neutral nitrogen-donor ligand [11]. Therefore, it can be used as a inhibitor for the hydrolysis-polycondensation rate of Ti-alkoxide during the sol-gel processing, as can be shown in Fig. 4, leading to forming more stable aminetrialkoxo complexes, which is key to control meso structured TiO2 material by self-assembly route. On the basis of above results, the following mechanism is postulated. Initially, TEA as chelating ligand, the high reactivity of tetratitanium alkoxides Ti(OR)4 can be chemically modified, subsequently, hydrolysis and condensation processes became easily controlled [12]. Secondly, during aging and removal template processing, these complexes were decomposed and organic species were removed, leading to forming mesopore structure.

1.0

b

0.5

a

0.0 300

400

500

600

700

800

Wavelength/ Wavelength/ nm

Fig. 3 UV-DRS absorbtance spectrum for P25 (a) and the mesoporous TiO2 (b)

OBu. HOC2H4 BuOL + . N - C2H4OHBuO/ U Temperature

T

^f

N Ti Fig. 4 Schematic of interaction mechanism between TBOT and TEA

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4. Conclusion This approach provides well defined mesostructured TiO2 with high surface area 525m2/g and wormhole-like pore structure. Meanwhile, the role of TEA is not only as a inhibitor to controll the hydrolyze and condense balance of ingorganic solutes, but also as a mesopore template via the amine-trialoxo ligand by self-assembly mechanism. 5. Acknowledgment This research was supported by the Major State Basic Research Development Program of China (973 Program No.203CB214500), the Natural Science Fundation of Ningxia Province (No. ZD02), and Project Sponsored by the Scientific Research Fundation for the Returned Overseas Chinese Scholars, State Education Ministry. 6. References [1] [2] [3] [4] [5] [6] [7] [8] [9]

P. E. Savage, Chem. Rev., 99(1999) 603. M. R. Hoffman, S. T. Martin and W. Choi, et al., Chem. Rev., 95 (1995) 69. C. T. Kresge, M. E. Leonowicz and W. J. Roth, et al.. Nature, 359 (1992) 710. D. M. Antonelli and J. Y. Ying, Angew. Chem. Int. Ed. Engl., 34 (1995) 2014. Y. D. Wang, C. L. Ma and X. D. Sun, et al., Appl. Catal. A: Gen., 246 (2003) 161. S. Cabrera, J. E. Haskouri and A. Porter, et al., Solid State Sci., 2 (2000) 513. P. D. Yang, D. Y. Zhao and D. Margolese, et al., Nature, 396 (1998) 152. C. F. Ma, J. H. Sun and F. Wang, et al., Chinese Invent Patent, CN2005100708798. F. Wang, L. X. Sang, L. X. Xu and J. H. Sun, et al., Journal of Shanghai Normal University, 11 (2005) 111. [10] T. Abe, A. Taguchi amd M. Jwamoto, Chem. Commum., 11(1994) 1387. [11] A. Naiini, V. Young and J. Verkade, Polyedron 14 (1995) 393. [12] J. C. Zhang and S. L. Marchese, et al., Chem. Commun., (2001) 713.

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Nano-replication to mesoporous metal oxides using mesoporous silica as template Byung Guk So,a Jeong Kuk Shon,a Ji Ae Yu, Oh-Shim Joo b and Ji Man Kima'* " Department of Chemistry and SAINT, Sungkyunkwan University, Suwon, Suwon, 440746, Korea (Tel: 82-31-290-5930; Fax: 82-31-290-7075; E-mail: [email protected]) ' Eco-Nano Research Center, Korea Institute of Science & Technology, Seoul, 136-791, Korea

Mesoporous materials constructed with different framework compositions such as iron oxides and manganese oxides, etc. have been successfully obtained by the impregnation with desired metal precursors into the bicontinuous cubic Ia3d mesoporous silica, crystallization to metal oxides at desired temperature and subsequent silica removal using NaOH aqueous solution. 1. Introduction Since the discovery of mesoporous materials, ordered mesoporous silicas such as MCM-41, SBA-15 and KIT-6 have attracted much attention for various applications due to their tunable mesopore and the subsequent high surface area [1-3]. In addition, it is reported that mesoporous silicas can be used as a sacrificing template for the nano-replication to mesoporous materials constructed with different framework compositions [4]. Recently, preparation of ordered mesoporous materials metal oxides via nano-replication method using mesoporous silicas as a template has been reported [5-6]. These efforts enabled the preparation of mesoporous materials with various framework compositions, which are believed to have inherent properties as catalytic, optical and electronic materials. Moreover, these mesoporous metal oxides prepared by nano-replication method possess regular mesopore and high surface area. This can lead great advantages for applications such as catalysis or sensing due to its extremely high ratio of the number of surface atoms to the number of bulk atom. In this work, we have used large mesoporous silica, KIT-6 as a template for the fabrication of mesoporous materials constructed with various metal oxides such as iron oxide and manganese oxide.

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2. Experimental Section The mesoporous silica KIT-6 has been prepared by the self-assembly method using the Pluronic PI23 triblock copolymer (EO20PO70EO20) and tetraethyl orthosilicate (TEOS). 30 g of P123 was dissolved in the mixture of 1085 g distilled water, 30 g of «-butanol and 59 g of HC1 (35%). After stirring the solution for 1 hr, 64.5 g of TEOS is added to the homogeneous clear solution. This mixture is left under constant stirring at 35°C for 24 hrs. The precipitate was filtered, dried at 80 °C and finally calcined at 550°C. For the synthesis of mesoporous metal oxides, 0.4 g of metal precursors (FeCl3-6H2O, 98%, Mn(NO3)3-xH2O, 98%, Aldrich) was dissolved in 1.0 g of distilled water. These solutions were incorporated into 1.0 g of mesoporous silica template using the impregnation method. The impregnated samples were dried in an oven at 80°C for 1 d and calcined at various temperature ranges, from 300 to 700°C. The silica template was removed from the composites of silica and metal oxide by treating three times using 1 - 2 M NaOH aqueous solution 3. Result and Discussion X-ray diffraction (XRD) patterns in Fig. 1 show typical diffraction patterns of bicontinuous cubic Ia3d mesophases of mesoporous silica KIT-6, and replicated mesoporous metal oxides that were heated at 500°C before the removal of silica template. XRD results of mesoporous metal oxides show relatively weak peaks at low angle, which have similar d-spacing values with the mesoporous silica

1 |L||kfjJ|L^|

Fig. 1. XRD patterns of KIT-6 and mesoporous metal oxides replicated from the KIT-6.

template. The XRD peaks in the 29 ranges of 0.7 - 3° can be indexed to 211, 220, and 332 which are typical characteristics of bicontinuous cubic Ia3d mesophase. Wide-angle XRD patterns on the right side of Fig. 1 clearly show crystalline framework structures for the replicated metal oxides. The line-widths

311 Table 1. Physical property of mesoporous silica and mesoporous metal oxides Materials K.IT-6 Fe2O3 MnO,

(mVg)

Pore Volume (cc/g)

Unit cell Parameter (rim)

700 99 109

0.91 0.22 0.39

22.5 22.5 22.5

Surface Area

Pore Size (nm) 2.5 2.5

of XRD patterns are relatively broad similar with those of nanoparticles. The crystallite size of mesoporous metal oxides that calculated by Scherrer equation is estimated to be around 10 nm. Table 1 show the physical properties such as surface area, pore size, unit cell parameter and pore volume of mesoporous silica, Fe^O^ and MnO2. The mesoporous silica, K.IT-6 with BET surface area of 700 m2/g, total pore volume of 0.91 cc/g and BJH pore size of 8 nm, is replicated to mesoporous Fe2C>3 and MnO2. The replicated mesoporous Fe2C>3 and MnO2 materials (in Fig. 1) exhibit quite high BET surface area of 99 and 109 m2/g, and total pore volume of 0.22 and 0.39 cc/g, respectively. BJH pore sizes of mesoporous Fe2O3 and MnO2 are around 2.5 nm in diameter. One more interesting thing is that the particle morphology of replicated mesoporous metal oxides is quite different with that of sacrificial silica template.

Fig. 2. FESEM images of iron oxide(left) and manganese oxide(right)

Fig. 3. HRTEM images of iron oxide(left) and manganese oxide(right)

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Even though the particles of mesoporous silica template are very irregular and pretty big, the replicated mesoporous metal oxides have spherical morphology with very uniform particle size about 100 nm in diameter as shown in FESEM images in Fig. 2. HRTEM images of mesoporous metal oxides in Fig. 3 clearly reveal that the not only the mesoscopic order but also the atomic crystallinity of the replicated mesoporous metal oxides showing three dimensional network topology of metal oxide nano rods. 4. Conclusion Ordered mesoporous silica is successfully converted to mesoporous materials with various framework composition by means of nano-replication technique. The mesostructural properties are maintained after the template removal and framework crystallinity can be controlled by annealing process before the removal of rigid and thermally stable mesoporous silica template. This nanoreplication route would be able to used as a facile method for the preparation of mesoporous materials constructed with various crystalline frameworks, which would have intense potentials for the practical applications. 5. Acknowledgement The authors thank to the Korea Research Foundation Grant funded by the Korean Government (MOEHRD, KRF-2005-005-J11901). 6. References [1] F. Kleitz, S. H. Choi and R. Ryoo, Chem. Commun. (2003) 2137. [2] C. T. Kresge, M. E. Leonowicz, W. J. Roth, J. C. Vartuli and J. S. Beck, Nature 359 (1992) 710. [3] D. Zhao, J. Feng, Q. Huo, N. Melosh, G. H. Frendrickson,. F. Chmelka and G. D. Stucky, Science 279 (1998) 548. [4] M. Kang, S. H. Yi, H. I. Lee, J. E. Yie and J. M. Kim, Chem. Commun. (2002) 1944. [5] S. C. Laha and R. Ryoo, Chem., Commun. (2003) 2138. [6] B. Tian, X. Liu, H. Yang, S. Xie, C. Yu, B. Tu and D. Zhao, Adv. Mater. 15 (2003) 1370.

Progress in in Mesostructured Materials Recent Progress S. Qiu, Y. Tang and C. Yu (Editors) (Editors) D. Zhao, S. © 2007 2007 Elsevier Elsevier B.V. B.V. All All rights rights reserved. reserved.

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A novel synthesis of manganese oxide nanotubes Li Taoa, Cheng-Gao Suna, Mei-lian Fan3, Cai-Juan Huang3, He-Sheng Zhaib, Hai-Long Wu3 and Zi-Sheng Chao3* "College of Chemistry and Chemical Engineering, Key Laboratory of Chemometrics & Chemical Biological Sensing Technologies, Ministry of Education, Hunan University, Changsha 410082, P. R. China bCollege of Chemistry and Chemical Engineering, Xiamen University, Xiamen, 361005, P. R. China

This paper presents a novel redox-assisted supramolecular assembly of manganese oxide nanotubes, using KMnO4 and MnCl2 as inorganic precursors, polyoxyethylene fatty alcohol (AEO9) a template and acetaldehyde an additive, under hydrothermal condition. The nanotubes were characterized by XRD, TEM, BET, XPS and Raman spectroscopy. The results reveal that the nanotubes have an average inner diameter of ca. 14.7 nm, an average wall thickness of ca. 2 nm, and a length of over several hundreds nanometers, with the walls consisting of monoclinic manganite crystals. 1. Introduction Nanostructured manganese oxides are of considerable scientific interests, because of their versatile applications in the fields of adsorption, catalysis, batteries and functional materials [1-4]. Microporous manganese oxides have been prepared via soft-chemistry routes [5-7] and mesoporous manganese oxides by either a transformation of layered manganese oxides [8] or a supermolecular assembly process [9, 10]. It was also reported recently that nanofiberious Na-birnessite could be synthesized from an oxidation of MnCl2 by K.M11O4 [10] and manganese oxide nanotubes by cyclic voltammetric electrodeposition [2], In this work, we address the synthesis of manganese oxide nanotubes via a novel route of redox-assisted supramolecular assembly.

314

2. Experimental Section Polyoxyethylene fatty alcohol, namely AEO9, acetaldehyde and MnCl24H2O were dissolved into deionized water, forming a clear solution, into which a KMnO4 aqueous solution was then dropwise introduced under strong agitation. The gel obtained had a molar composition of 4.4 KMnO4: 4.4 MnCI2: 1.5 CH3CHO: 1.0 AEO9: 500 H2O. After treating hydrothermally the gel at 373 K for 24 h, precipitate was recovered by filtration and washed with deionized water. To remove the surfactant, the wet filter cake was dispersed into ethanol and refluxed for 6 h. The specimen was dried at 333 K for 10 h and then cooled to room temperature. The characterizations were performed via XRD (Bruker D8 Advance Diffractometer; Cu Kcd), XPS (Phi Quantum 2000 Scanning ESCA Microprobe; Al Ka), TEM and SAED (FEI Tecnai F30 Field Emitting HRTEM; accelerating voltage 300 kV), N2 adsorption-desorption at 77 K (Beckman Coulter SA3100) and Raman spectrcopy (LABRAM-010). 3. Results and Discussion 28=0J604

1.0

1.5 2.0 2.5 3.0

2-Thefci

20

30

40

50

2-Thefci

Fig. 1. XRD spectra of the manganese oxide nanotubes. (a) for low angle; (b) for high angle

The XRD patterns of manganese oxide nanotubes are shown in Fig. 1. An obvious diffraction peak occurs at 29 = 0.604° with a d-spacing of 14.6 nm in the low angle range (Fig. la), indicating the presence of a mesophase that may be constructed via the Fig. 2. SAED pattern and TEM micrographs of the orientated arrangement manganese oxide nanotubes. (a) SAED pattern (b) TEM of the manganese oxide nanotubes in axial direction. A group of diffraction peaks in the high angle range of 20-60° (Fig. lb) coincides with that of

315

monoclinic manganite (MnO(OH); cell parameter: a = 5.300, b = 5.278, c = 5.307, and p = 114.36) [11]. Fig. 2 shows the TEM micrographs and the selected area electron diffraction (SAED) pattern of the nanotubes. It reveals that the nanotubes have an average outer diameter of ca. 16.8 nm, the inner diameter of ca. 14.7 nm, and a length of above several hundred nanometers. The indexing of the SAED pattern suggests a rhombic tetrahedral crystalline structure of the nanotube wall. The N2 adsorption-desorption isotherm is shown in Fig.3, which indicates the presence of the mesostructure. The specific surface area of the specimen was determined to be 69.546 m2/g.

I' an

1 •3

•S

sea

-• sij

IOOO

uso

ism

ITSO

Wavenumber cm-1 Fig. 3. N2 adsorption-desorption isotherm curve of the manganese oxide nanotubes.

Fig. 4. Raman spectrum of the manganese oxide nanotubes

The Raman spectrum of the nanotubes is shown in Fig. 4. The peaks at ca. 660 and 320 cm'1 can be ascribed to the Mn-O vibrations in Mn(III) compounds [12-15]. This result provides further a proof to the conclusion, drawn by the XRD experiment, that the walls of the nanotubes consists of monoclinic manganite crystals. The Mn 2p XPS result indicates that the Mn 2pi/2 and Mn 2p3/2 peak has a binding energy (B.E.) of 652.5 and 641.28 eV, respectively. The B.E. of Mn 2p3/2 is often employed to estimate the oxidation state of manganese [16] It is found that the B.E. of Mn 2p3/2 in the manganese oxide nanotubes we synthesized is ca. 0.3-0.5 eV lower than those of Mn3+ for Mn2O3 [17] and MnO(OH) [17]and ca. 0.68 eV higher than that of Mn2+ for MnO [17], being different from those for the manganese oxides with a nanotubular2 or particulate [4,18] morphology reported in literatures. This results indicates that the nanotubes consist of the Mn(III) species and possess a high tendency to lose electrons. It is deduced that both the nano-tubular morphology and the crystalline phase of the monoclinic manganite in the nanotube walls, presented by our specimen, are responsible for the relatively "free" transportation of

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electron and in turn the comparatively low energy necessitated for exciting electrons off the nanotube surface. 4. Conclusion we have synthesized the manganese oxide nanotubes using a redox-assisted supramolecular assembly route, using Mn7+ and Mn2+ compounds as inorganic procursors, AEO9 a surfactant, and acetaldehyde an additive. The walls of the nanotubes consist of the monoclinic manganite crystals, of which manganese is in a pure +3 valent state, being different from those reported in literatures. The photoelectron performance of the nanotubes, revealed by the XPS and Raman measurements, suggests their promising potential applications as functional materials relating with electron transportation. 5. Acknowledgment This work was supported by the Program for New Century Excellent Talents in University, the Ministry of Education of P.R. China, and the Program for FuRong Scholar in Hunan Province, P.R. China. 6. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18]

F. Caruso, Adv. Mater. 13 ( 2001) 11. M. S. Wu, J. T. Lee, Y. Y. Wang and C. C. Wan, J. Phys. Chem. B, 42 (2004) 16331. J. Chen, J. C. Lin, V. Purohit, M. B. Cutlip and S. L. Suib, Catal. Today, 33 (1997) 205. O. Giraldo, S. Brock, M. Marquez and L. S. Suib, J. Am. Chem. Soc, 122 (2000) 9330. S. L. Brock, N. Duan, Z. R. Tian, O. Giraldo, H. Zhou and S. L. Suib, J. Chem. Mater., 10 (1998)2619. J. K. Yuan, L. Kate, Q. H. Zhang and S. L. Suib, J. Am. Chem. Soc, 125 (2003) 4966. X. L. Hong, G. Y. Zhang, Y. I. Zhu and H. Q. Yang, J. Mater. Res. Bull., 38 (2003) 1695. J. Luo and S. L. Suib, Chem. Commun., (1997) 1031. X. Hong, G. Y. Zhang and H. Y. Zhu, in: Proceedings of the 7th International Conference on Surfactants & Detergents, Shenzhen, China, (2002). S. Ching, J. A. Landrigan, M. L. Jorgensen, N. Duan and S. L. Suib, Chem. Mater. 7 (1995) 1604. T. Rziha, H. Gies and J. Eur. Rius, J. Mineral., 8 (1996) 675. AIST Raman Spectra Database of Minerals and Inorganic Materials, http://www.aist.go.jp/RIODB/rasmin F. Buciuman, F. Patcas, R. Cracium and R. T. D. Zhan, J. Phys. Chem. Chem. Phys., 1 (1999)185. R. Radhakrishnan and S. T. Oyama, .1. Phys. Chem. B, 105 (2001) 4245. B. J. Aronson, C. F. Blanford and A. Stein, J. Phys. Chem. B, 104 (2000) 449. W. Li, G. V. Gibbs and S. T. Oyama, J. Am. Chem. Soc.,120 (1998) 9041. NIST X-ray Photoelectron Spectroscopy Database NIST Standard Reference Database 20, Version 3.4 (Web Version http://srdata.nist.gov/xps/). S. C. Pang and M. A. Anderson, J. Mater.Res., 15 (2000) 2096.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

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Synthesis of well ordered crystalline TiO2 photocatalyst with enhanced stability and photoactivity Zhenfeng Bian,a Jian Zhu b and Hexing Li*a "Department of Chemistry,Shanghai Normal University, Shanghai 200234 b Laboratory of Molecular Catalysis and Innovative Materials, Department of Chemistry, Fudan University, Shanghai 200433, P. R. China

Mesoporous TiO2 was successfully synthesized using a modified evaporation induced self-assembly (EISA) method. We find that doping proper La2O3, mesoporous TiO2 can enhance the thermal stability and also enhance its photocatalytic activity. Key words: Mesoporous TiO2, thermal stability, photocatalytic activity. 1. Introduction Photocatalysis has been widely used to mineralization organic compounds as environmental pollutants. Perhaps, TiO2 is the most frequently used photocatalysts owing to its cheapness, stability, and nontoxicity etc [1]. However, the low quantum efficiency seems a problem for its practical application. It has been proved that the photocatalytic performance of TiO2 is strongly correlated to the anatase/rutile ratio, crystallization degree of anatase, the surface area, the porous structure, lattice defects and oxygen vacancy etc [24], which obviously depend on the preparation methods and conditions as well as the modification of TiO2 [5-6]. One of the promising ways is to design the mesoporous TiO2 with large surface area and well ordered pore structure which might enhance light absorbance and also facilitate the transfer and adsorption of reactant molecules [7-9]. However, the mesoporous TiO2 usually exhibits very poor crystallization degree of anatase phase. Thus, calcination is essential to enhance the crystallization degree of anatase [10-12]. But, such heating treatment may inevitably induce the collapse of pore [13-15]. In this work, Ladoped mesoporous TiO2 was synthesized via a modified evaporation induced self-assembly (EISA) method which could undergo a heating treatment even at

318

550°C to obtain highly crystallized anatase without significant damage of the ordered porous structure and thus, exhibited much high activity than the corresponding undoped TiO2 during photocatalytic degradation of phenol. 2. Experimental Section 2.1. Sample preparation The La-doped TiO2 was prepared according to the following procedures. A mixture containing 1.0 g P123, 12 g ethanol, 1.7 g TiCl4, 3 g Ti(OBu)4, and certain amount of La(OAc)3 was stirred vigorously for at least 5 h at 0°C. The resulted transparent sol was transferred into a Petri dish to form a uniform thin layer. After being aged at 40°C for 24 h, the precursor was heated sequentially at 100, 150, 200, 250, 300°C, each for 12 h. The final sample was obtained by calcination at a desired temperature for 4 h and was denoted as TiO2-n-T, where n refers to La/Ti molar ratio(0~1.8%) in the initial mixture and T refers to the calcination temperature. 2.2. Characterization X-ray diffraction (XRD) patterns of all samples were collected on the Rigaku D/MAX-2550 ( CuKa 1 irradiation). Transmission electron microscopy (TEM) images were recorded on the JEOL JEM2011. Nitrogen adsorption-desorption isotherms were measured at 77 K on the Quantachrome NOVA 4000e from which surface area and porosity were calculated by BJH method. The light absorbance-emission ability were evaluated by using the photoluminescence spectra (PLS, Varian Cary-Eclipse 500). 2.3. Activity test The photodegradation of phenol in aqueous solution was chosen as a probe to evaluate the activity of the as-prepared TiO2-n-T samples. The reactions were carried out at 30°C using 50 ml 0.1 g/1 phenol and 0.05 g TiO2-n-T under vigorous stirring and irradiation with four 8 W UV lamps with characteristic wave length of 254 nm for 3 h. 3. Results and Discussion The low-angle powder XRD patterns revealed that both the undoped and Ladoped TiO2 samples displayed well ordered 2D-hexagonal mesostructure when they were calcinated at relatively low temperature. The N2 adsorptiondesorption measurements further confirmed that these samples show type-IV isotherms indicative of mesoporous structure [16]. The BJH pore-size analyses

319

performed on the desorption branch show that the average pore diameter calculated by BJH model matches well with the result measured from TEM image. The specific surface area of each sample is calculated by the multi-point Brunauer-Emmett-Teller (BET) method. The surface area reaches 120 m2g"! at 550°C. Treatment at 500°C of pure TiC>2 resulted in a complete destroy of the mesostructure. However, the La-doped TiO2(La/Ti = 0.36%) may still retained ordered mesoporous structure even after being treated at 550°C, showing the stabilizing effect of the La-dopant. This could be further confirmed by TEM characterizations.

Fig. 1 TEM images of different TiO2-n-T samples, (left two images) A

R

A R R

R AA

* f l J i ', AR R

AR

A

AA

R

650 A

Relative Intensity / a.u.

Relative Intensity / a.u.

TiO 2 R

A A 650 550

550 450

J

40

2Theta /

50 O

60

R

AA

A

AA

AA A

450 350

. A . . A . A 350 *° A 30

TiO2-0.36

10

20

30

40

50

2Theta/

60

70

80

o

Fig. 2 Wide angel XRD patterns of undoped and La-doped TiO2 treated at elevated temperatures, (right two images)

As shown in Fig. 1, the pure TiC>2 could remain its ordered structure only if the calcination temperature was below 500°C. While, well ordered mesoporous structure could still be observed even after calcination at 550°C. The stabilizing effect of the La-dopants could be attributed to its bigger size(0.1016 nm) than the Ti4+ (0.068 nm) [17]. Thus, the La-dopants could not replace Ti4+ inside the TiC>2 framework and were present mainly on the external surface of the TiC>2. These La2C>3 species could effectively prevent the collapse of mesoporous structure. The wide angle XRD patterns, as shown in Fig. 2, revealed that the crystallization degree of anatase increased with the increase of calcination temperature. The rutile phase appeared when the undoped TiC>2 was calcinated at the temperature above 350°C. While, no significant transformation from anatase to rutile phase appeared in the the La-doped TiC>2 sample (La/Ti = 0.36%) even when the sample was calcinated at 650°C. These results

320

demonstrated that the La-modification of TiO2 could effectively inhibit the formation of rutile phase when treated at high calcination temperature which was essential to obtain high crystallization degree of anatase. Fig. 3 shows the activities of both the undoped TiO2 and La-doped TiO2 samples during liquid phase phenol photocatalytic degradation. The activity of the La-doped TiO2 (La/Ti = 0.36%) first increased and then decreased with the increase of calcination temperature. The optimal calcination temperature was determined as 550°C. On one hand, the increase of calcination temperature could enhance the crystallization degree of anatase which was favorable for photocatalysis. On the other hand, the increase of calcination temperature may result in the decrease of surface area and even the damage of mesoporous structure. Meanwhile, rutile phase may appear at very high calcination temperature. These factors are unfavorable for the photocatalysis and thus, could account for the decrease of activity. Considering the effect of La-dopant, one could see that the photocatalytic activity first increased and then decreased with the increase of the amount of the La-dopant. The TiO2-0.36-550 exhibited the highest photocatalytic activity. The promoting effects of the La-dopant could be understood by considering the following factors. (1) The modification of the La-dopants may increase the crystallization degree of anatase, as shown in Fig. 2, which may facilitate the transfer of photo-generated holes and electrons and inhibit their recombination. (2) According to the PLS spectra, the La-modification may increase the emission peak of TiO2 around 382 nm corresponding to the increase of more oxygen vacancies and/or structural defects which could prevent the recombination between photo-generated holes and electrons. Meanwhile, the La-modification resulted in the decrease in the dual-frequency peak of TiO2 around 558 nm, indicating its absorbance ability for UV light increased after La-modification, which may induce more photogenerated holes acted as photocatalytc centers. (3) The a-modification could stabilize TiO2 from either the damage of mesoporous structure which may remain the surface and well ordered porous channels or the transfer to rutile phase. As well known, the high surface area may facilitate the adsorption of phenol molecules by the catalysts and the ordered pore channels would be favorable for the diffusion of both the reactants and products. Meanwhile, the anatase phase exhibit much higher activity than the rutile and thus, inhibition the transfer from anatase phase to rutile may inhibit the decline of photocatalytic activity. These results clearly demonstrated that modification of suitable amount of the La-dopants may enhance the quantum yield of TiO2 in photocatalysis [18]. However, too much La2O3 was harmful for the activity, possibly due to the coverage of too many active sites. Meanwhile, high amount of La2O3 may serve as the center for the recombination between photo-electrons and photo-holes, resulting in the decrease of quantum efficiency in photocatalysis. Detailed studies are still being underway.

321 100

100

B

90

Phenol degradation ratio %

Phenol degradation ratio %

A

80

70

60 300

400

500 500

600

Calcined Temperature /°C / oC

7700 0

0

90 80 70 60

1.8 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 La/Ti (%)

Fig. 3 Dependence of photocatalytic activity on (A) calcination temperature over the TiO2-0.36 and (B) The amount of the La-dopant after being treated at 550 °C for 3 h.

4. Conclusion The TiO2 sample prepared by EISA exhibited well ordered mesoporous structure and crystallized anatase phase. Doping TiO2 with La2O3 can increase both the structural and anatase phase stabilities against heating treatment at high temperature and in turn, could enhance its photocatalytic activity. The optimum calcination temperature was determined as 550°C and the optimum amount of the La-dopant was determined as 0.36%. The roles of both the calcinations temperature and the La-modification could be explained by considering the crystallization of anatase, the surface area, the porous structure, both the oxygen vacancies and surface defects, and the phase transformation between anatase and rutile, which were related with the quantum efficiency of photocatalysis. 5. Acknowledgment This work was supported by the National Natural Science Foundation of China (No. 20377031), the Shanghai Leading Academic Discipline Project (No. T0402), the Natural Science Foundation of Shanghai Science and Technology Committee (Nos. 02DJ14051, 0452nm070, 05QMX1442, 0552nm036), and the Shanghai Eduction Committee (No. 05DZ20). 6. References [1] J. G. Yu, J. C. Yu, M. K. P. Leung, W. K. Ho, B. Cheng, X. J. Zhao and J. C. Zhao, J. Catal. 69(2003)217. [2] J. C. Yu, J. G. Yu, W. K. Ho and L. Z. Zhang, Chem. Commun. (2001) 1942. [3] J. C. Yu, J. G. Yu, W. K. Ho and J. C. Zhao, J. Photochem. Photobiol. A 148 (2002) 263. [4] J. G. Yu, J. C. Yu, W. K. Ho and Z. T. Jiang, New J. Chem. 26 (2002) 607.

322 [5] H. X. Li, G. S. Li, J. Zhu and Y. Wan, J. Mol. Catal. A: Chemical 226 (2005) 97. [6] H. X. Li, J. Zhu, G. S. Li and Y. Wan, Chem. Letter. 33 (2004) 574. [7] J. C. Yu, X. C. Wang, L. Wu, W. K. Ho, L. Z. Zhang and G. T. Zhou, Adv. Funct. Mater. 14(2004)1178. [8] X. C. Wang, J. C. Yu, H. Y. Yip, L. Wu, P. K. Wong and S. Y. Lai, Chem. Eur. J. 11 (2005) 2997. [9] B. Smarsly, D. Grosso, T. Brezesinski, N. Pinna, C. Boissiere, M. Antonietti and C. Sanchez, Chem. Mater. 16 (2004) 2948. [10] E. Beyers, P. Cool and E. F. Vansant, J. Phys. Chem. B 109 (2005) 10081. [11] K. S. Liu, H. G. Fu, K. Y. Shi, F. S. Xiao, L. Q. Jing and B. F. Xin, J. Phys. Chem. B 109 (2005) 18719. [12] J. C. Yu, X. C. Wang and X. Z. Fu, Chem. Mater. 16 (2004) 1523. [13] P. C. A. Alberius, K. L. Frindell, R. C. Hay ward, E. J. Kramer, G. D. Stucky and B. F. Chemlka, Chem. Mater. 14 (2002) 3284. [14] H. Shibata, T. Ogura, T. Mukai, T. Ohkubo, H. Sakai and M. Abe, J. Am. Chem. Soc. 127 (2005) 16396. [15] E. Beyers, P. Cool and E. F. Vansant, J. Phys. Chem. B 109 (2005) 10081. [16] S. J. Gregg and K. S. W. Sing, Adsorption, Surface Area and Porosity, Academic Press, London, (1997)111. [17] C. P. Sibu, S. K. Kumar, P. Mukundan and K. G. K. Warner, Chem. Mater. 14 (2002) 2876. [18] W. Xu, Y. Gao and H. Q. Liu, J. Cata. 207 (2002) 151.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

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Crystallization of stable mesoporous zirconia and ceria-zirconia Anil K. Sinha and Kenichirou Suzuki Toyota Central R&D Labs Inc., Nagakute-4801192, Aichi, Japan

Crystallization of Mesoporous zirconia and ceria-zirconia structures were realized using a long-chain amine template. By controlled heating of the synthesis gel it was possible to prepare well-crystalline mesoporous strctures for these materials. The surface areas, mesopore ordering and thermal stabilities of the final product is dependent on the composition, ageing and heating condition for the precursor gel. 1. Introduction Ceria and zirconia based materials have received enormous attention due to their applications in various fields such as high temperature ceramics, catalysis and solid oxide fuel cells [1]. CeO2-ZrO2 is a well-known additive in the socalled three-way catalysts for automobile exhaust [2]. Pure ceria is known to be poorly thermostable and undergoes rapid sintering under high temperature conditions, thereby loosing oxygen buffer capacity [3, 4]. It has been more than ten years since our laboratory discovered that the addition of ZrO2 to CeO2 enhances oxygen storage capacity (OSC) as well as thermal stability [5, 6]. Following this discovery, CeO2-ZrO2 has been widely utilized for commercial catalysts. High surface area ceria and ceria-zirconia as well as their mesoporous structure have been prepared by different methods. Such materials by virtue of their large surface area exhibit greater catalytic activity. With the preparation in 1991 of mesoporous silica a new area of chemistry, allowing the exploitation of high surface area materials, was opened up [7]. This silica-based synthesis has been extended to a number of transition metal and main group oxides using various surfactants and inorganic precursors under different reaction conditions [8, 9]. Accordingly, several studies report the fabrication of mesoporous crystalline ceria [10-12]. However, the ceria, zirconia and ceria-zirconia

324

mesostructures often undergoes a severe breakdown throughout the final crystallization step, which leads to rather ill-defined porosity without controlled nanocrystallinity in the pore walls, in terms of the spatial distribution and the size of the oxide nanocrystals. Here in we report a method to prepare mesoporous zirconia and ceria-zirconia using a modified sol-gel route to obtain highly crystalline and stable mesoporous materials. 2. Experimental Section It was possible to prepare stable and crystalline mesoporous zirconia and ceria-zirconia by modified sol-gel method in mixed propanol-water medium, hexadecylamine template, triethanolamine additive and zirconium butoxide/zirconium isopropoxide, cerium acetate precursor. In a typical synthesis of mesoporous zirconia, 2 g of hexadecylamine (Wako) was dissolved in 6 g of propanol (Wako) followed by the addition of 2.1 g of zirconium isopropoxide (75% solution in 1-propanol, Wako). Finally 0.31 g of triethanol amine (Aldrich) was added. The resulting solution was vigorously stirred to obtain a homogeneous gel. The gel was aged at 50-70°C for 7 days followed by heat treatment at 120-200°C (l°C/min.) for 12 h. The sample was finally calcined by heating gradually (l°C/min.) to 400-500°C. Mesoporous ceriazirconia was also prepared in a similar way, adding cerium acetate, (CH3CO2)3Ce.H2O (Wako) prior to the addition of Zr orecursor to the synthesis mixture. The powder X-ray diffraction (XRD) patterns were obtained on a Rigaku Rint - 2400 instrument equipped with a rotating anode and using Cu Ka radiation (wavelength = 0.1542 nm). Nitrogen adsorption/desorption isotherms were obtained at -77 K on a Micromeritics ASAP 2010 apparatus to determine the total specific surface area (SBET), pore volume and pore size distribution of the samples. Transmission electron microscopy (TEM) observations were made using a JEOL JEM200CX instrument. Scanning electron microscopy (SEM) observations were made using a Hitachi S-55OO FE-SEM instrument. 3. Results and Discussion When the mesoporous zirconia precursor-gel was heated, upto 200°C the mesoporous structure was not crystallized completely yet as shown in fig. 1 and wide angle XRD shows that there is no crystalline phase present in the material. But when the sample was gradually heated (at 1°C /min.) to 450°C a well crystalline mesoporous material is obtained as indicated by XRD analysis. In higher 29 range 20-60° broad peaks are observed which could be assigned to the cubic zirconia phases (Fig. la). This implies that in the present synthesis, the evaporation induced self assembly of zirconia into a mesoporous structure assisted by the amine template is enhanced by increasing the crystallization temperature beyond 200°C.

325

In the case of mesoporous Ceria-Zirconia till 1-5 days of crystallization a low intensity broad peak at low angle was observed indicating gradual formation of mesostructure with increasing ageing time (Fig. 1 b). After 15 days 2.9 nm (b) d = 2.9 (b)

.2 nm d=7.2

(a) (a)

OC 450 450OC

/

Template-free

J.

/

V

t&c c

11

,

20 40 50 60 20 30 30 40 50 60

d=3.2 nm

\

15 Days Days v

22

33

44

Intensity (a.u.)

Intensity (a.u.)

10 10

55

20 20 25 25 30 30 35 35 40 40 45 45 50 50 55 55 60 60 65 65 70 70 75 75

22θ θ

10 10

20 60 20 30 30 40 40 50 50 60

Figure 1. XRD patterns of (a) mesoporous zirconia crystallization, (b) mesoporous ceria-zirconia crystallization.

1 5 Days Days

H\

o

Intensity (a.u.)

200 C

2

20

4

25

6

30

8

10

35

40

22θ θ

12

45

2

14

50

V

16

55

4

66

A

88

10

11 Day Day

H 2

44 2Q 66 2θ

88

10 10

3

Volume adsorbed (cm /g)

of crystallization a well crystalline mesoporous material was obtained as indicated by XRD analysis. In higher 20 range 20-60° broad peaks are observed which could be roughly assigned to semicrystalline tetragonal ceria-zirconia phases. After template removal by extraction with ethanol at 70°C followed by drying at 120°C and then calcination to 500°C there is considerable increase in XRD crystallinity along with decrease in d140 spacing (about 0.3 nm) due to appreciable lattice contraction after template removal. 120 Thus, unlike in case of mesoporous zirconia, mesoporous ceria-zirconia could luu -a 100 be formed at lower temperature (70°C) but -o f o "| .Q obtained only after prolonged ageing (about 80 o CA 15 days). CC The 500°C calcined mesoporous zirconia CD 60 E and ceria-zirconia materials showed surface _3 2 o 40 10 15 15 20 0 55 10 areas of 176 and 193 m /g respectively. The Pore size (nm) Pore (nm) materials showed N2 adsorption-desorption 1.0 0.0 0.2 0.4 0.6 0.8 1.0 isotherm of type IV, typical of mesoporous Relative Pressure Pressure P/Po Relative materials with step in the adsorption curve Figure 2. N sorption isotherm of mesoporous ceria-zirconia. between partial pressures P/Po of 0.3 to 0.8, 100

dv/drp

80 60 40 20 0

2

326 326

and a large hysteresis loop, due to capillary condensation in the mesoporous channels and/or cages and mean pore size of 2.0 nm (for mesoporous ceria-zirconia, Figure 2). TEM (fig. 3) and FE-SEM (Fig.4) analyses clearly showed the presence of disordered mesoporosity in these materials. High-resolution TEM (Fig. 3 inset) clearly shows that mesopore walls are made up of well-crystalline ceria-zirconia with less than 10 nm size average particle size.

2 nm 10 nm

Figure 3. TEM of mesoporous ceria-zirconia

4. Conclusion It was possible to prepare stable mesoporous zirconia and ceria-zirconia by a modified sol-gel procedure. Long crystallization time for the ceria-zirconia and higher crystallization temperature for zirconia was necessary to obtain such stable crystalline mesoporous structures.

10 nm

Figure 4. FE-SEM of mesoporous ceria-zirconia

5. Acknowledgement We thank N. Suzuki for TEM analysis, J. Seki for FE-SEM analysis and R. Asahi for helpful suggestions. 6. References [1] [2] [3] [4] [5] [6] [7] [8] [9]

[10] [11] [12]

A. Trovarelli, Catal. ReV. Sci. Eng. 38 (1996) 439 and references therein. J. G. Nunan, H. J. Robota, M. J. Cohn and S. A. Bradley, J. Catal. 133 (1992) 309. A. Laachir et al. J. Chem. Soc., Faraday Trans. 1 87 (1991) 1601. J. E.Kubsh, J. S. Rieck and N. D. Spencer, Stud. Surf. Sci. Catal. 71 (1994) 109. M. Ozawa, et al. : Japanese unexamined patent pub., 116741(1988), (in Japanese) M. Ozawa, et al. J. Alloys Comp., 193 (1993) 73. C. T. Kresge, M. E. Leonowicz, W. J. Roth, J. C. Vartuli and J. S. Beck, Nature, 359 (1992)710. A. Sayari, Microporous Mater., 12 (1997) 149. D. Yang, D. Y. Zhao, D. 1. Margolese, B. F. Chmelka, G. D. Stucky, Nature, 396 (1998) 152; .1. Y. Zheng, J. B. Pang, K. Y. Qiu and Y. Wei, Microporous Mesoporous Mater., 49 (2001) 189. M. Lundberg, B. Skarman, F. Cesar and L. R. Wallenberg, Microporous Mesoporous Mater. 54 (2002) 97. D. Terribile, A. Trovarelli, J. Llorca, C. Leitenburg, G. Dolcetti, J. Catal. 178 (1998) 299. D. M. Lyons, K. M. Ryan and M. A. Morris, J. Mater. Chem., 12 (2002) 1207.

Recent Progress in Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

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Synthesis of mesoporous structures zinc sulfide by assembly of nanoparticles with block-copolymer as template Hongmei Ji,a Jieming Cao,* aJinsong Liu,a Mingbo Zheng,a Yongping Chen,a Yulin Cao a and Nongyue Heb " Nanomaterials Research Institute, College of Material Science and Technology, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, PR China jmcao@nuaa. edu. en b Chien-Shiung Wu Laboratory, Southeast University, Nanjing 210096, China

1. Introduction Since the discovery of M41S family of silicas at Mobil in 1992 [1, 2], much research has been reported on the synthesis of mesoporous materials. The mesoporous materials with different compositions, new pore systems and novel properties have attracted considerable attentions because of their remarkably high surface area, narrow pore size distributions, which make them ideal candidates for catalysts, sorbents and drug delivery system [3]. In recent years, development of the mesoporous materials has been extended from oxide to chalcogenide mesostructured materials. Chalcogenide mesostructured materials were synthesized by using their nanoparticles as the building blocks and employing different surfactants as the structure-directing agents [4, 5]. As a kind of chalcogenide materials, nanosized ZnS materials have received increasing attention due to their unique electronic and optical properities, and their potential applications in light-emitting diode (LED), electrochemical devices, infrared window materials and phosphors for cathoderay tubes. To the best of our knowledge, only Henri Kessler's group synthesized nanosized zinc sulfide in the presence of cationic surfactants at room temperature [6] and a sonochemical technique was used to synthesize ZnS mesoporous network with dodecylamine as templating agent [7]. They both employed low molecular weight surfactants as structure-directing agents in order to obtain the ZnS mesoporous structure. Herein we describe the synthesis the mesoporous ZnS first by using amphiphilic poly (alkylene oxide) block-copolymer EO2Q

328

PO70EO20 as a structure-directing agent through novel alcohothermal method. The obtained products had a high BET (Brunauer-Emmett-Teller) surface area and narrow pore size distribution. And the specific surface area of the ZnS products remained high even after treated at 800°C. 2. Experimental Section In a typical synthesis process, 0.5 g of P123 was dissolved in 10 mL of ethanol and to this a solution of Zn(CH3COO)2-2H2O (0.0046 mol) in 5 mL ethanol was added dropwise. After stirring for 30 min, 8 mL of 0.58 M thioacetamide (TAA) was added into the above solution with further stirring to form a white emulsion. The resulting solution was transferred into a 30ml Telflon-lined stainless steel autoclave. The autoclave was sealed and maintained at 90°C for 10 h, then cooled into the room temperature naturally. The products removed from autoclave were collected by centrifugation and washed with thermal ethanol several times to remove the surfactant, and vacuum-dried at 50°C to obtain the white samples. The products were characterized by means of X-ray diffraction (XRD), Transmission electron microscopy (TEM), and nitrogen physisorption. 3. Results and Discussion

(a)

(111)

I

Jl

10

20

30

40

(220) A

(300)

50

2Theata(Degree)

60

70

80

4 6 2Theata (Degree)

Fig. 1. Powder X-Ray diffraction patterns of the template-extracted mesostructure ZnS sample (a) wide angle and (b) low angle.

Fig. 1 shows the X-ray diffraction (XRD) patterns of the ZnS products after extraction by the thermal ethanol. In the wide-angle of the X-Ray pattern (Fig.la), the observed three diffraction peaks correspond to (111), (220), and (311) planes, respectively, which could be indexed as the cubic sphalerite ZnS according to the JCPDS cards. The XRD pattern of Fig. l(b) shows a highintensity peak at low reflection angle near 20 = 1.1°, which indicates the lattice spacing d = 8.0 nm. However the single intense peak at high d-spacing in the

329

XRD was demonstrated that the products were short-range symmetry, which was in agreement with the results of other two reports about the meso-structure ZnS [6, 7], mesoporous alumina [8], hexagonal mesoporous silica HMS-type materials [9] and some other previous work [10]. We also performed TEM examination (Fig. 2). The as-prepared products are well-dispersed particles, and the TEM images of the sample show that the diameter of the particles produced is basically in the range of 4-10 nm and the particles have a mesoporous structure with a pore size of about 3-5 nm, and the mesophase is less of long-order.

Fig. 2. TEM images of the obtained ZnS products with (a) low and (b) high magnification.

Volume Adsorbed cm3 / g)

160 140

(a)

ZnS ZnS-500 ZnS-800

0.010

ZnS ZnS-500 ZnS-800

dV/dD

180

120

(b)

100 80

0.005

60 40 20 0 0.0

0.2

0.4

0.6

Relative Pressure (P/ P0)

0.8

1.0

2

4

6

Pore Diameter (nm) (nm)

8

10

Fig. 3. N2 adsorption-desorption results of samples treated at different temperature (a) N 2 adsorption desorption isotherms and (b) pore size distribution curves.(ZnS as the templateextracted sample, ZnS-500 as the products calcined at 500°C, ZnS-800 as the products calcined at 800°C)

Typical nitrogen adsorption-desorption isotherms and the corresponding pore size distribution for the products are shown in Fig. 3. The results could be

330

identified as a type IV isotherm. The BET (Braunauer-Emmett-Teller) surface area of the template-extracted ZnS sample was measured as 252 m2/g and this value was bigger than that of the mesostructured zinc sulfide reported previously. After calcined at 500 and 800°C, the BET surface area of the treated products ZnS-500 and ZnS-800 is decreased to 113 and 99 m2/g, respectively. It should be noted that our samples have the potential application at relatively high temperature. With the increasing of heating temperature the pore distribution of the products become broad and the peak of the pore size distribution curve in 3.8 nm decrease. The high temperature treatment lead to the formation of larger pore and reduce the fraction of smaller pore. These changes may be due to the agglomeration of nanoparticles during calcinations. 4. Conclusion In conclusion, we have demonstrated a solvothermal route for the formation of mesostructured ZnS. As a structure-directing agent, the block-copolymer PI23 played an important role in the reaction process. It induced the ZnS nanoparticles to assemble into mesoporous structure and the remaining surfactant after extracting process could prevent the nanoparticles aggregating in the framework. Although in our experiment the obtained products are not long-range symmetry, they still have high specific surface area and narrow pore size distribution, which would provide us with many opportunities for some potential applications as advanced materials. 5. References [1] C. T. Kresge, M. E. Leonowicz, W. J. Roth, J. C. Vartuli and J. S. Beck, Nature, 359 (1992) 710. [2] J. S. Beck, J. C. Vartuli, W. J. Roth, M. E. Leonowicsz, C. T. Kresge, K. D. Schmitt, C. T. W. Chu, D. H. Olson, E. W. Shepard, S. B. McCullen and J. B. Higgin, J. Am. Chem. Soc, 114(1992)10834. [3] X. He and D. Antonelli, Angew. Chem., Int. Ed., 41 (2001) 214. [4] B. J. Scott, G. Wirnsberger and G. D. Stucky, Chem. Mater., 13 (2001) 3140. [5] S. B. Yoon, J. Y. Kim and F. Kooli, Chem. Commun., 14 (2003) 1740. [6] J. Q. Li, H. Kessler, M. Soulard, L. Khouchaf and M. H. Tuilier, Adv. Mater., 10 (1998) 946. [7] R. K. Rana, L. Z. Zhang, J. C. Yu, Y. Mastai and A. Gedanken, Langmuir, 19 (2003) 5904. [8] P. T. Tanev, T. J. Pinnavaia, S. A. Bagshaw and T. J. Pinnavaia, Angew. Chem. Int. Ed., 35(1996)1102. [9] P. T. Tanev and T. J. Pinnavaia, Science, 267 (1995) 865. [10] F. Vaudry, S. Khodabandeh and M. E. Davis, Chem. Mater., 8 (1996) 1451.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

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Surfactant-free synthesis of mesoporous tin oxide with a crystalline wall Jieming Cao*, Haitao Hou, Xianjia Ma, Mingbo Zheng and Jinsong Liu Nanomaterials Research Institute, College of Materials Science and Technology, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, PR China.

1. Introduction Mesoporous materials have gathered considerable attention due to their outstanding application to catalyst and separation technology [1-6]. Since appearance of MCM-41, various surfactants, including anionic surfactants, cationic surfactants, nonionic surfactant, block copolymers, have been used to synthesize mesoporous materials with highly ordered porous structures. However, the wall of these materials is normally amorphous, and crystallization usually results in collapse of the uniform mesoporous structure by means of heat treatment. Some surfactants have been chosen to directly synthesize crystalline ZnS mesoporous network, which also usually results in partial collapse of porous structures after the extraction of surfactants [7]. Recently, some mesoporous materials with crystalline structure have been prepared by initial strengthening of the porous structure through depositing another material on the inside surface of the mesopore and then calcining the sample to cause its crystallization or using a low-temperature crystallization technique in the presence of surfactant [8-13]. It is widely acknowledged that surfactants are necessary to synthesize mesoporous materials. Surfactant-free method to synthesize these materials is a big challenge, and few reports about this have been made until now9. Tin oxide, one of important semiconductors [14], has been widely used in the fileds such as gas sensors [15], electrode materials [16], and solar cell [17]. Two of the most important factors affecting the performance in these fields are its specific surface area and crystallinity. It would be exciting to prepare mesoporous tin oxide with a crystalline porous wall. Here we report a novel surfactant-free synthesis of mesoporous tin oxide with a crystalline wall by an approach of combination of ethanol thermal process and subsequent calcinations.

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2. Experimental Section In a typical synthesis of mesoporous tin oxide with a crystalline pore wall, 7.01 g SnCl4-5H2O and 2.40 g urea were dissolved in 30 mL ethanol, and stirred for lmin, and then transferred into a 50 mL autoclave. The autoclave was sealed and kept at 175°C for 7 h, and then cooled into the room temperature naturally. The solid product was filtrated and dried at 60°C for 12 h, and then the assynthesized sample was calcined at 300°C for 3 h (temperature-rising rate: 2°C/min). The products were characterized by means of x-ray diffraction (XRD), nitrogen physisorption, and Transmission electron microscopy (TEM). 3. Results and Discussion Δ (NH A (NH4)2SnCl6 4)2SnCl6

1

2

33

4

2 θ / degrees 2θ/ degrees

5

6

(b) (b)

(112)

(211)

3

A .A S

0

NH4Cl U NfttQ •• SnO SnO2

(101)

(110)

2

I nt ens i t y ( a. u. )

I nt ens i t y ( a. u. )

(a)

10 10

20

30

40

S

(1) (1)

D

50

60

(2) (2)

70

80

2 θθ//degrees degrees

Figure 1. (a) Low X-ray diffraction pattern of the as-synthesized sample; (b) wide-angle X-ray diffraction patterns of (1) the as-synthesized sample and (2) the sample after calcination.

Figure la shows the low-angle X-ray diffraction patterns of the assynthesized sample. The diffraction pattern has a broad peak at around 26M.45 0 , respectively, which indicats there is meso-structure in the assynthesized sample. But, there's no peak for the calcined sample, which indicates that the meso-structure has been destroyed after calcining. Figure lb shows the wide-angle diffraction patterns of as-synthesized and calcined tin oxide sample. The product before calcining is composed of NH4C1, (NH4)2SnCl6, and SnO2. After calcining, all observed peaks correspond to (110), (101), (211) and (112) planes, respectively, which can be indexed to cassiterite tin oxide. Based on the line width of the diffraction peak corresponding to (110) reflection, the average crystallite size was calculated about 5.5 nm by the Scherrer formula. The mesoporous nature of the calcined sample is confirmed by nitrogen physisorption. Figure 2a shows adsorption-desorption isotherm of the sample after calcinations, which is characteristic of mesoporous materials. The specific surface area of the sample is 205 m2-g"'. The BJH pore diameter distribution

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-1

(a)

3

120 100 80 60 40 20 0.0

(b)

0.006

•g

140

)

160 160

Pore volume / (cm

3 -1 Volume adsorbed / (cm • g ) STP

from adsorption branch was shown in Figure 2b, which is mainly distributed in the range of 3 - 8 nm.

0.004

0.002

0.000

0.2 0.4 0.6 0.8 Relative o) Relative pressure (P/P (P/Po)

1.0 1.0

2

4

66

88 10 10 12 12 14 14 16 16 18 18 20 20 Pore Pore diameter / nm

Figure 2. Nitrogen adsorption-desorption isotherms and BJH pore diameter distribution from adsorption branch (inset) ofmesoporous tin oxide.

The calcined sample was also characterized by TEM (Figure 3). Figure 3a indicates that the calcined product has spongy structure. The ED pattern (inset) shows that the wall of porous structure is made of cassiterite, which is in agreement with XRD result. From its higher magnification image (Figure 3b), the spongy structure is composed of particles with the size in the range of 3 - 5 nm, and some pore structures with the size of about 4 nm. Figure 3c shows the HRTEM image of the particles, which indicates the high crystallinity of the pore wall. The width of 0.34 nm from neighboring fringes corresponds to (110) planes.

Figure 3. (a) Transmission electron microscopy (TEM) and electron diffraction (ED), and (b) its high magnification image, and (c) HRTEM image.

It was reported that urea can react with SnCl4 in methanol to form the compound [SnCl4(urea)2], [18] and urea molecules can construct a coordination sphere around the metal atom and form a stable structure [19]. We think, in our experiment, the same complex was formed through reaction of SnCl4-5H2O, urea and ethanol during the solvothermal process. On one hand, the complex

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prevents the growth of SnO2 particles, and facilitates formation of nanocrystallites, which subsequently act as pore wall; on the other hand, the decomposition of the complex leads to ordered spongy porous structure with the loss of urea molecules, which are absorbed around the metal atom, during subsequent calcinations. 4. Conclusion Mesoporous SnO2 with a crystalline wall was successfully synthesized by a novel surfactant-free method. The complex precursor was synthesized through reaction of SnCl4-5H2O and urea in the ethanol thermal process, and then the precursor was calcined to form mesoporous SnO2. The obtained SnO2 has a high specific surface area and a narrow pore size distribution, and the pore wall is composed of nanocrystallites. This surfactant-free method can be extended to synthesis of other mesoporous metal oxides with a crystalline wall. 5. References [1] C. T. Kresge, M. E. Leonowicz, W. .1. Roth, J. C. Vartuli and J. S. Beck, Nature, 359 (1992)710. [2] G. S. Attard, J. C. Glyde and C. G. Goltner, Nature, 378 (1995) 366. [3] S. A. Davis, S. L. Burkett, N. H. Mendelson and S. Mann, Nature, 385 (1997) 420. [4] Q. Huo, R. Leon, P. M. Petroffand G. D. Stucky, Science, 268 (1995) 1324. [5] D. Li, H. Zhou and I. Honma, Nat. Mater., 3 (2004) 65. [6] H. Miyata, T. Suzuki, A. Fukuoka, T. Sawada, M. Watanabe, T. Noma, K. Takada, T. Mukaide and K. Kuroda, Nat. Mater., 3 (2004) 651. [7] P. K. Rana, L. Z. Zhang, J. C. Yu, Y. Mastai and A. Gedanken, Langmuir, 19 (2003) 5904. [8] H. Shibata, T. Ogura, T. Mukai, T. Ohkubo, H. Sakai and M. Abe, J. Am. Chem. Soc, 127 (2005) 16396. [9] M. Vettraino, M. L. Trudeau, D. M. Antonelli, Adv. Mater., 12 (2000) 337-341. [10] Z. R. Tian, W. Tong and J. Y. Wang, Science, 276 (1997) 926. [11] H. Shibata, H. Mihara, T. Mlikai, T. Ogura, H. Kohno, T. Ohkubo, H. Sakait and M. Abe, Chem. Mater., 18(2006)2256. [12] F. Jiao, A. Harrison, J. C. Jumas, A. V. Chadwick, W. Kochelmann and P. G. Bruce, J. Am. Chem. Soc, 128 (2006) 5468. [13] V. N. Urade and H. W. Hillhouse, J. Phys. Chem. B, 109 (2005) 10538. [14] Y. Liu and M. L. Liu, Adv. Funct. Mater., 15 (2005), 57. [15] G. Xu, Y. W. Zhang, X. Sun, C. L. Xu and C. H. Yan, J. Phys. Chem. B, 109 (2005) 3269. [16] A. C. Bose, D. Kalpana, P. Thangadurai and Ramasamy, J. Power Sources, 107 (2002) 138.

[17] S. Chappel and A. Zaban, Sol. Energ. Mater. Sol. C, 71 (2002)141. [18] P. O. Dunstan, Thermochimica ACTA, 345 (2000) 117-123. [19] L. Qiu and L. Gao, J. Am. Ceram. Soc, 87 (2004) 352-357.

Recent Progress in Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

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Mesoporous crystals of metal oxides and their properties Calum Dickinson,a Andrew Harrison,b Jim A. Anderson0 and Wuzong Zhou8"* "EastChem, School of Chemistry,University of St Andrews, St Andrews, KY169ST, UK b EastChem, School of Chemistry, University of Edinburgh, Edinburgh, EH9 3JJ, UK c Department of Chemistry, Aberdeen University, Aberdeen, AB24 3UE, UK

Porous single crystals of Cr2O3 and Co3O4 were synthesised using mesoporous silica, such as SBA-15 and KIT-6, as a template. Their structures were examined by using XRD and HRTEM. The magnetic properties of Cr2O3 revealed behaviour like nanoparticles and the catalytic properties showed 100% conversion of cyclohexene with 34% selectivity to the epoxide. 1. Introduction Since 1992, advancements in surfactant synthesised mesoporous material have been considerable. One of the biggest achievements has been creating mesoporous silica using the triblock copolymer surfactant. At the end of the century, the reverse framework of mesoporous silica was first replicated using carbon [1] via the so-called hard templating or nanocasting route. Using a similar method, negative replicas of mesoporous silica can be made with metal oxides. These replicas can be porous single crystals (PSC) [2]. With SBA-15 and KIT-6 as templates, several PSCs of metal oxides have been reported [2-4]. There are several ways to synthesise the PSCs by the impregnation of the metal oxide precursor into a mesoporous silica template. We further developed the synthesis method and investigated the physico-chemical properties of these porous crystals. 2. Experimental Section The hard templates, SBA-15 and KIT-6, were synthesised according to the literature and calcined at 500°C for 5 h in air [5, 6]. 0.15 g of the silica was then dispersed in 6.5 ml ethanol containing 0.65 g of Cr(NO3)3-9H2O or Co

336

(NO3)2-6H2O and stirred for 2 h. The ethanol was then evaporated at 40°C and the resulting powder was heated at 500°C. The silica template was dissolved by an aqueous 10% HF solution and centrifuged before decanting and washing with distilled water thrice. The sample was dried and characterised using XRD and high-resolution transmission electron microscopy (HRTEM). For magnetic measurements, -50 mg of the Cr2O3 PSC, templated by KIT-6, was weighed into a gelatine capsule of known, low magnetisation and loaded into a Quantum Design MPMS2 SQUID magnetometer. Magnetisation data were taken from 1.8 - 340 K in an applied field of 0.01 T. For catalytic tests, 0.05 g of Cr2O3 PSC was added to a stainless steel autoclave containing 0.74 mmol cyclohexene, 2.08 mmol dimethylpropanal and 25 ml of toluene as solvent. The reactor was purged with pure oxygen and pressurised to 10 bar. The contents were stirred at 85 °C for 16 h before the solution was analysed using a gas chromatography-mass spectrometer. 3. Results and Discussion 3.1. Characterisation of PSC With HRTEM, it can clearly be seen how the crystallinity of the material within the PSC crosses bridges between nanorods (negative replica of SBA-15) or across a cubic framework (negative replica of KIT-6) (Fig. la, b). It was revealed that the PSC of Cr2O3 filled only one of the bicontinuous channels of KIT-6, whereas the Co3O4 PSC filled both channels. This was believed to have resulted from the collapse of the complimentary pores in the Cr-containing KIT6, disallowing the communication between the two porous frameworks. This is possibly due to the effects of higher temperature for crystal growth and the expansion of the metal oxide crystal destabilising the silica framework. For understanding the formation mechanisms of these materials, XRD studies of the early stages of the decomposition of the nitrate within the silica reveals how it differs from the decomposition of the nitrate without the presence of silica [7]. Not only is the temperature of the decomposition of the material to the final metal oxide vastly reduced, but the intermediate products also differ. Intermediate products can be compounds rarely seen in the decomposition of the bulk, such as cobalt hydroxide nitrate. Fig 1. (c) displays XRD patterns, showing an example of the effect of the mesoporous host in the reduction of the crystallisation temperature of cobalt oxide. 3.2. Magnetic properties of PSC Cr2O3, in the fully dense form, shows antiferromagnetic order below approximately 308 K, whereas the dc susceptibility measurements for the PSC

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show no sign of such a transition at so high a temperature, and indicate behaviour much more like of nanoparticulate Cr2C>3. Fig. Id displays the

Fig. 1. (a) TEM image of the KIT-6 templated PSC Cr2O3 viewed down the [111] zone axis of the mesostructural unit cell, and (b) the corresponding HRTEM image showing the single crystal property, (c) XRD patterns of Co3O4 grown inside the mesopores (bottom) and from bulk specimen (top), (d) Graph of magnetic behaviour against temperature of Cr2O3 PSC measured after cooling in zero magnetic field (zfc), or a field of 0.01 T (fc)

susceptibility taken after first cooling in zero magnetic field (zfc) and then after cooling in 0.0IT (fc): there is a divergence of the fc and zfc data below approximately 100 K, and a cusp in the zfc response at approximately 40 K that is similar to that attributed to the blocking of the magnetisation in 15 nm particles, as reported by Mahklouf [8]. The PSC sample also appears to have a weakly ferromagnetic response at low temperature, like the nanoparticulate sample. For the latter form of the material, the ferromagnetism has been attributed to an uncompensated excess of surface spins. This ferromagnetic effect increases as particles get smaller, as reported for cobalt oxide [9]. Recently, work carried out by Jiao et al, revealed the difference in magnetic properties between near single crystal mesoporous iron oxide and poly crystalline iron oxide [10]. The difference between these materials is rather significant and confirms the importance of the single crystallinity of the porous material.

338

3.3. Catalytic properties ofCr2O3PSC Results in the selective catalytic oxidation of cyclohexene to epoxide (oxabicycloheptane) showed 100% conversion of the cyclohexene along with 98.7% conversion of the sacrificial oxidant, 2,2-dimethylpropanal (pivaldehyde). The reaction was 34% selective to the epoxide with some formation of the non-selective cyclohex-1-one and the majority being the hydrolysis product of the epoxide leading to the diol. Traces of benzaldehyde were detected indicative of oxidation of the solvent. The complete conversion of pivaldehyde indicates that the PSC is capable of activation of molecular oxygen and its insertion into the aldehyde C-H bond. Furthermore, formation of the epoxide product indicates that the catalyst is able to activate the reagent and allow single oxygen atom transfer from the in-situ formed peracid. This is of significant interest given that this process is currently largely restricted to single site metal centered complex catalysts [11, 12]. 4. Conclusion The PSC form of Cr2O3 has been shown to have many different properties compared to the bulk material. The magnetic behaviour bears some similarity to nanoparticulate Cr2O3, with a mean blocking transition in the region of 40 K, and some evidence for weak ferromagnetism at low temperature. The PSC also reveals a possible catalytic application of the oxidation of cyclohexene, with 100% conversion and 34% selectivity to partial oxidation to the epoxide. 5. References [1] R. Ryoo, S. H. Joo and S. Jun, J. Phys. Chem., 103 (1999) 7743. [2] K. K. Zhu, B. Yue, W. Z. Zhou and H. Y. He, Chem. Commun., (2003) 98. [3] B. Yue, H. L. Tang, Z. P. Kong, K. K. Zhu, C. Dickinson, W. Z. Zhou and H. Y. He, Chem. Phys. Lett., 407 (2005) 83. [4] K. Jiao, B. Yue, Y. Ren, S. X. Liu, S.R. Yan, C. Dickinson, W. Z. Zhou and H. Y. He, Chem. Commun., (2005) 5618. [5] D. Y. Zhao, J. L. Feng, Q. S. Huo, N. Melosh, G. H. Fredrickson, B. F. Chmelka and G. D. Stucky, Science, 279 (1998) 546; [6] F. Kleitz, S. H. Choi and R. Ryoo, Chem. Commun., (2003) 2136. [7] C. Dickinson, W. Z. Zhou, R. P. Hodgkins,Y. F. Shi, D. Y. Zhao and H. Y. He, Chem. Mater. 18(2006)3088. [8] S. A. Makhlouf, J. Magn. Magn. Mater., 272 (2004) 1530. [9] Y. Q. Wang, CM. Yang, W. Schmidt, B. Spliethoff, E. Bill and F. Schuth, Adv. Mater., 17 (2005) 53. [10] F. Jiao, A. Harrison, J. C. Jumas, A. V. Chadwick, W. Kockelmann and P. G. Bruce, J. Am. [11] Chem. Soc, 128 (2006) 5468. [12] Y. Yamada, K. Imagawa, T. Nagata and T. Mukaiyama, Chem. Lett., (1992) 2231. [13] S. Bhattacharjee and J. A. Anderson, J. Mol. Catal, A, 249 (2006) 103.

Recent Progress in Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

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Synthesis and characterization of lanthanum oxide nanotubes using dendritic surfactant Li Taoa, Cheng-Gao Suna, Mei-Lian Fan3, Qi Liua, Cai-Juan Huang3, He-Sheng Zhaib, Hai-Long Wua and Zi-Sheng Chaoa* "* College of Chemistry and Chemical Engineering, Hunan University; Key Laboratory of Chemometrics & Chemical Biological Sensing Technologies, Ministry of Education, Hunan University, Changsha 410082, P. R. China. b College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, P. R. China

Lanthanum oxide nanotubes were synthesized via a surpramolecular assembly route, employing a dendritic surfactant, 3,3',3",3'"-(ethane-l,2-diylbis (azanetriyl))tetrakis(N-(2-aminoethyl)propanamide), and a co-surfactant, polyoxyethylene fatty alcohol, namely AEO9. The nanotubes were characterized by means of XRD, TEM, SAED, and N2-physisorption, and the results indicate that the nanotubes possess an average length of above 160 nm and a mesomicroporous hierarchical structure with an average micropore size of ca.1.32 nm and average mesopore sizes of 6-8 nm and 25 nm. The employing of cosurfact AEO9 promoted the formation of dendimer surfactant micells that template the mesophase of the specimen via a cooperation route. The characteristic strip-like shape of the surfactant might contribute the formation of the nanotublar morphology and the hydrothermal treatment result in the crystallization of the lanthanum oxides and in turn the appearance of the micropores within the walls of the nanotubes. 1. Introduction Rare earths have found versatile applications in the areas like functional materials and catalysis and so on [1, 2]. Among the rare earths, lanthanum appeared to be the most extensively studied ones, because of their relatively low price and well physical and chemical performances in applications. In the preparation of La-containing nanomaterials, a few works dealt with the microporous lanthanum oxide with morphologies of thin films, particulates,

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nanowires or nanorods [3-7]. Hexagonal and lamellar mesostructured lanthanum oxide was also synthesized via a cooperative assembly route [8, 9]. To the best of our knowledge, however, no lanthanum oxide nanotubes has been reported in literatures. We shall present here a supramolecular assembly of lanthanum oxide nanotubes, using a novel dendritic surfactant and a cosurfactant AEO9. The novelty we'd like to address here is not only the nanotubular morphology of the lanthanum oxides but also the surfactant employed, the one we synthesized via the reaction between methyl acrylate and ethylenediamine. 2. Experimental section 2.1. Synthesis of dendritic surfactant 3,3',3",3'"-(ethane-l,2-diylbis(azanetriyl) tetrakis(N-(2-aminoethyl)propanamide) At first, excess amount of methyl acrylate was reacted with ethylenediamine at 333-353 K for 6 h under stirring and refluxing, after that the unreacted methylaerylate was removed via vacuum distillation. Then, the product obtained above was reacted with excess amount of ethylenediamine at 353 K for 4 h under stirring and refluxing, with the removal of the by-product methanol and the unreacted ethylenediamine via a rotary evaporator after the reaction. 2.2. Synthesis of lanthanum oxide nanotubes The dendritic surfactant (2.5 g), AEO9 (1.5 g) and La(NO3)3-6H2O (3.0 g) were dissolved into 50 ml deionized water under agitation at room temperature, respectively. The mixture formed was subjected to a hydrothermal treatment at 373 K for 6 d without stirring. Precipitates were finally formed and collected after filtration, washing with distilled water and drying in air at 333 K. 2.3. Characerization TEM and SEAD (JEOL-3100), N2physisorption (Beckman Coulter SA3100) and EDS (Oxford INCA Energy 300) were employed to characterize the specimen. 3. Results and discussion When only the dendimer or AEO9 surfactant was employed, microporous solid and amorphous one was obtained, respectively. The combination of the two surfactants resulted in

Fig. 1. TEM micrograph of lanthanium oxide nanotubes

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the lanthanium oxide nanotubes. Fig. 1 shows the TEM micrograph of the assynthesized nanotubes. It can be seen that the nanotubes have an average inner V(nl) and outer diameter of ca. 0.5 6 to 9 nm and 15 nm and an average length of at least 160 nm, respectively. The SAED pattern (the inset in Fig. 1) manifests, to some extent, a crystalline nature within the walls of the nanotubes. 0.5 Relative Pressure Ps/Po Fig. 2 shows the N2physisorption isotherm of Fig. 2. N2-physisorption isotherm and pore size the specimen. It reveals distribution curves (the insets) of lanthanium the presence of slip-type oxide nanotubes. (a) micropores; (b) mesopores mesopores, as evidenced by a strong hysteresis loop. The specific surface area and the pore volume were determined to be 88.38 m2/g and 0.37 ml/g, respectively. The pore size distribution curves (the insets in Fig. 2) indicate that the specimen contains three groups of pores, i.e., micropores with an average size of ca. 1.32 nm (inset a), two groups of mesopores with an average size of 6-8 and 25 nm (inset b), respectively. These results suggest that the nanotubes may possess a hierarchical pore structure, i.e., the inner diameter of the nanotubes is in the mesopore range and the wall of the nanotubes contains micropores. The mesopores with an average size of 25 nm are probably caused by the interconnected network of the nanotubes. Fig. 3 indicates the EDS Spectrum spectrum of the asO C !•» synthesized specimen which shows the presence of C, O, and La at a surface atomic ratio of 56:35:9. Nitrogen was failed to be detected out, being probably due that N atom has a low content in the surface of the specimen and a small sensitivity in the EDS Fig .3. EDS spectrum of the specimen templated by measurement. the mixture of dendrimers and AEO9 Basing on the above results, a formation mechanism of the lanthanum nanotubes could be proposed. The combination of the dendimers and the AEO9 could reduce largely the repulsive interaction between the polar groups in the former molecules, due to the dispersion interaction .

•

'•

.

.

I

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between these two kinds of surfactants [10, 11], favoring the formation of micelles. Under the regulation of the micelles, the La species polymerized, following possibly a cooperation route, and finally the mesophase was formed. The characteristic strip-like shape of the surfactant is probably responsible to the nanotube morphology of the as-synthesized specimen. The hydrothermal treatment favored the crystallization of the lanthanum oxides within the nanotube walls, and in turn, resulted in the formation of the micropores among the crystals of the lanthanum oxides. 4. Conclusion The dendrimers was synthesized and employed together with the AEO9 to template the nanotubes of lanthanum oxides. The synthesized nanotubes were identified to possess a mesoporous-microporous hierarchical structure. The assembly of the nanotubes is proposed to be controlled by the micelles, consisting of the above mixed surfactants, via a cooperation route. The characteristic strip-like shape of the surfactant is responsible to the nanotube morphology and the hydrothermal treatment to the formation of the micropores within the nanotube walls. 5. Ackonwledgment This work was supported by the Program for New Century Excellent Talents in University, the Ministry of Education of P.R. China, and the Program for FuRong Scholar in Hunan Province, P.R. China. 6. References [1] S. J. Kim, J. R .Ireland and C. Kannewurf, et al., J. Solid State Chem., 155 (2000) 55. [2] D. Andriamasinoro, R. Kieffer, A. Kiennemann and P. Poix, J. Appl. Catal., 106 (1993) 201. [3] M. Nieminen, M. Putkonen and L. Niinisto, J. Appl. Surf. Sci., 174 (2001) 155. [4] X. Y. Ma, H. Zhang, Y. J. Ji, J. Xu and D. R.Yang, J. Materi. Lett., 58 (2004) 1180. [5] A. H. Mekhemer, et al., Colloids Surf. A Physicochem. Eng. Asp., 181 (2001) 19. [6] D. Zhu, H. Zhu and Y. Zhang., J. Phys. Condens. Matter., 14 (2002) 519. [7] Y. J. Zhang and H. M. Guan, J. Mater. Res. Bull., 40 (2005) 1536. [8] .1. M. Cao, H. M. Ji, J. S. Liu, et al. and J. Ma, et al., J. Mater. Lett., 59 (2005) 408. [9] Q. Huo, D. I. Margolese, U. Ciesla, P. Feng, T. E. Gier, P. Sieger, R. Leon, P. M. Petroff, F. Schuth and G. D. Stucky, Nature, 368 (1994) 317. [10] M. J. Rosen, Second Edtion, John Wiley & Sons.Tnc. Surfactants and interfacial Phenomena., (1989). [11] K. M. Prabal, C. Tahir, G. F. Wang and A. G. William, Macromolecules 37 ( 2004) 6236.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

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Nanostructured SiC from preceramic polymer via replication of hard templates Jia Yana, Hao Wangb, In-Kyung Sung0, Kyung-Hoon Park0, Anjie Wanga, Xiaodong Lib and Dong-Pyo Kirn0* " State Key Laboratory of Fine Chemicals, Dalian University of Technology, 158 Zhongshan Road, Dalian, P. R. China, 116012. b Key Lab of Ceramic Fiber and Composites, National University of Defense Technology, Changsha, P. R. China, 410073. c Department of Fine Chemical Engineering and Chemistry, Chungnam National University, Daejeon, Korea 305-764.

1. Introduction Nanocasting process, which is a method for replicating nanoscale structures using hard templates, has been widely used for the preparation of various nanoporous structures such as nanoporous carbon CMK-z, oxides, sulfides and metal [1]. Recently, this approach gradually extended to prepare the ordered nanoporous non-oxide ceramics, including macroporous (> 50 nm) and mesoporous (1.5 ~ 50 nm) materials [2], which possess high chemical and mechanical stabilities. Many nanostructured ceramics can not be fabricated by conventional methods such as powder processing and CVD. Some methods have been used successfully to prepare various nanostructured SiC. According to the Quin et al., a SiC-based disordered macropore structure 'wood ceramic' was prepared from carbonized wood powder and phenol resin via a direct reaction with Si powder [3]. In the field of mesoporous SiC, some disordered SiC structures have been prepared by a solid-gas reaction in active carbon [4] and a chemical vapor infiltration (CVI) into SBA-15 silica [5]. On the other hand, different types of tubular SiC nanostructures have been synthesized since Dai et al. first reported the preparation of SiC nanotubes using a shape memory synthesis method [6]. Most preparation methods are based on a carbothermal reduction and/or chemical vapor deposition, resulting in randomly disordered nanostructures. Liquid preceramic polymers such as polymethylsilane, polycarbonsilane and

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polysilazene provide ideal precursors for the preparation of ordered nanostructured ceramics by nanocasting method, because they can be processed easily at temperatures lower than those required in conventional methods. Therefore, various ordered macroporous [7] and mesoporous [8] SiC ceramics have been prepared by this method. At this paper, we summarize our recent achievements in the field of various SiC porous products prepared by nanocasting of preceramic polymers into different sacrificial hard templates. The main concern is on macroporous SiC with pores larger than 50 nm, mesoporous SiC with pores ranging from 2 to 50 nm, and SiC nanotubes. 2. Experimental Section The various templates (silica or polystyrene spheres ordered assemblies, alumina membrane, macroporous carbon and mesoporous silica) were immersed in the precursor solution for SiC ceramic under nitrogen. After curing at 200°C, the polymer/template composites were pyrolyzed under argon at 1000~1400°C. SiC nanostructures such as macroporous or mesoporous materials, hollow spheres and nanotubes, were obtained upon fully etching the silica hosts with aqueous HF, or upon burning the carbon in air at 650°C. 3. Results and Discussion Fig. 1 summarizingly shows the macroporous and nanotublar SiC products and the used various hard templates. In particular, the macroporous SiC (Fig. IB) with a highly ordered pore array and high surface area (-170 m2/g) was prepared by nanocasting of preceramic polymer into colloidal silica crystalline template (Fig. 1 A). The pore size of 80 ~ 650 nm and the BET surface of 580 ~ 300 m2g"! of the obtained macroporous SiC can be controlled by using different size of the sacrificial templates. It is believed that the high Fig. 1 SEM and TEM images of (A) silica sphere, (B) surface area was due to macroporous SiC, (C) ordered macroporous carbon, (D) hollow the interfacial area beSiC sphere, (E) alumina membrane and (F) SiC nanotube. tween the sphere and the infiltrated polymer as well as to the formation of micropores at the ceramic wall during pyrolysis. In addition, 3-dimensional long range ordered hollow SiC

mm

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sphere assemblies (Fig. ID) were prepared by embedding preceramic polymer into sacrificial 3D ordered macroporous carbon templates (Fig. 1C). After removing of the carbon template, the obtained SiC hollow spheres possessed high thermal stability. The obtained SiC sphere nanostructures with outer diameters ranging from 135 to 890 nm were proportional to the initial pore size of the sacrificial carbon templates. Fig. IF shows SEM and TEM images of well-aligned array of SiC tubes with a uniform wall thickness of 45 nm, which were prepared by nanocasting of polymethylsilane into sacrificial alumina membrane as a template (Fig. IE). After the pyrolysis at 1250°C and the etching off the template, the obtained SiC nanotubes with less crystalline wall displayed an electrical resistance of 6.9 x 10J to 4.85 x 101 Om at temperatures ranging from 20 to 300 °C with a negative temperature dependence, which is similar to a semiconductor-like behavior. In addition, Pt/Ru alloy nanoparticles could be selectively deposited on the inner wall of the nanotube. This material might be useful in the fields of heat-resistant nanodevices, fuel cells and nanofluidic devices. Furthermore, macroporous SiC pattern on Si wafer (Fig. 2B and D) with a high surface area and high thermal stability (>800°C in air) was prepared by a series of processes combined with soft lithography. The preceramic polymer was infiltrated into the polystyrene sphere template (Fig. 2A and C) patterned on a Si wafer, which was prepared from polydimethylsiloxane (PDMS) mold by soft lithography, and transformed to macroporous SiC monoliths after curing and pyrolysis. The pore size could be tailored independently according to the bead size, allowing for the easy integration of porous monoliths into a microreactor. The SiC ceramic monoliths obtained were used in the decomposition of ammonia after depositing a ruthenium catalyst via wet impregnation and calcinations. The efficient conversion of NHU to H2 with Fig. 2 SEM images of polystyrene spheres increasing reaction temperature demonspattern via soft lithgraphy (A, C) and trated its successful performance as a macroporous SiC pattern (B, D). hydrogen reformer for fuel cells [9]. These novel porous materials show great promises for use in high temperature micro-reactors possibly for the on-demand reforming of higher hydrocarbons into hydrogen for portable power sources. Highly ordered mesoporous SiC with a n- ? TCH • r-eo A I« < A^ A sur face area in the range of 495 m2/g and a Fig. 3 TEM images of SB A-15 (A) and

c-r-T/nx mesoporous SiC (B).

•

c

^ ,

.

.?

•

,

pore size or 3.4 nm was also synthesized r

J

346

by nanocasting of allylhydridopolycarbo-silane into trimethylsilyated SBA15 silica as sacrificial hard templates. The void channels of SBA-15 template (Fig. 3A) were converted into the SiC ceramic walls (Fig. 3B), whereas the silica walls of SBA-15 were removed to form hollow channels of mesoporous SiC, which indicated that the structures of the mesoporous SiC samples were exact inverse replicas of their silica templates with highly ordered microstructures. The small-angle XRD patterns of he obtained SiC products also indicated that the ordered mesoporous structures similar to that of their silica templates had been replicated. Alternatively, the similar work was reported by Zhao et al., which formed the ordered mesoporous SiC ceramics via a nanocasting process infiltrating commercial polycarbosilane into mesoporous silica materials, SBA-15 and KIT-6, as hard templates [10]. It is expected that these novel techniques will be suitable for synthesizing many other types of ordered mesoporous non-oxide ceramic materials with interesting pore topologies. 4. Conclusion A variety of SiC nanostructures were prepared by infiltration of preceramic polymer into different types of sacrificial templates. The obtained nanoporous SiC ceramics are promising materials for variety of applications including filters, membranes, sensors, catalyst supports, as well as biomedical and construction materials, due to their unique chemical and physical stabilities. 5. Acknowledgement This work was funded by the 2004 National Research Lab (NRL) Project [M 10400000320-05J0000-32010] administered by the Korean Ministry of Science and Technology (MOST). 6. References [1] H. F. Yang and D. Y. Zhao, J. Mater. Chem., 15 (2005) 1217. [2] P. Dibandjo, L. Bois, F. Chassagneux, D. Comu, J. M. Letoffe, B. Toury, F. Babonneau and P. Miele, Adv. Mater., 17 (2005) 571. [3] J. Quin, J. Wang, J. Zhihao and G. Qiao, Mat. Sci. Eng. A, 358 (2003) 304. [4] M. J. Ledoux and C. Pham-Huu, Cattech, 5 (2001) 226. [5] P. Krawiec, C. Weidenthaler and S. Kaskel, Chem. Mater., 16 (2004) 2869. [6] N. Keller, C. Pham-Huu, G. Ehret, V. Keller and M. J. Ledoux, Carbon, 41 (2003) 2132. [7] I. K. Sung, S. B. Yoon, J. S. Yu and D. P. Kim, Chem. Commun. (2002) 1480. [8] K. H. Park, I. K. Sung and D. P. Kim, J. Mater. Chem., 14 (2004) 3436. [9] I. K. Sung, Christian, M. Mitchell, D. P. Kim and P. J. A. Kenis, Adv. Funct. Mater., 15 (2005) 1336. [10] Y. F. Shi, Y. Meng, D. H. Chen, S. J. Cheng, P. Chen, H. F. Yang, Y. Wan and D. Y. Zhao, Adv. Funct. Mater., 16 (2006) 561.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

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Gas-sensing properties of ordered mesoporous C03O4 synthesized by replication of SBA-15 silica Thorsten Wagner,ab Jan Roggenbuck,a Claus-Dieter Kohl,b Michael Froba a and Michael Tiemann a "Institute of Inorganic and Analytical Chemistry, Justus Liebig University, HeinrichBuff-Ring 58, D-35392 Giessen, Germany b Institute of Applied Physics, Justus Liebig University, Heinrich-Buff-Ring 16, D-35392 Giessen, Germany

1. Introduction The concept of utilizing mesoporous silica or carbon phases as rigid structure matrices has recently become a widely-used procedure for the synthesis of periodically ordered mesoporous metal oxides [1-6]. Contrary to conventional supramolecular structure-directors, such "hard templates" can be applied to the synthesis of a much larger variety of materials. Furthermore, they tolerate high temperatures, allowing for the synthesis of crystalline products. This approach has brought forward the opportunity to prepare new porous metal oxides with interesting properties owing to finite crystal domain sizes, high specific surface areas, and regular mesopore arrangements. For example, mesoporous Co3O4 has been shown to exhibit ferromagnetic behavior scaling with the high surface-tovolume ratio [4]. Various monolithic metal oxides with multimodal porosity are promising candidates for HPLC applications [6]. We have prepared mesoporous MgO with basic surface properties [5]. Another important field for the application of new mesoporous metal oxides is their utilization as gas sensors. We have recently shown that mesoporous SnO2 materials exhibit high sensitivities and fast responses at low and technically relevant concentration ranges of various gas analytes (e.g. CO detection or CH4 explosion prevention according to German/European norms DIN/EN50194); the sensors turned out be largely insensitive towards changes in the relative humidity [7]. Here we report on the gas-sensing properties of mesoporous Co3O4 synthesized by utilization of SBA-15 silica as the structure matrix. As pointed out above, this synthesis concept allows high temperatures,

348

facilitating the preparation of crystalline materials; these will have reduced defect densities at the surfaces, which is essential for sensitivity, selectivity and stability of gas sensors. The suitability of Co3O4 as a gas sensor is based on its non-stoichiometric composition which results in p-type semiconducting properties owing to an excess of oxygen. The interaction of the particle surface with oxidizing/reducing gas molecules will lead to a change in electrical resistance. 2. Experimental Section SBA-15 silica was prepared according to a literature procedure [8]. For the synthesis of mesoporous Co3O4 by the incipient wetness technique 4 g SBA-15 were dispersed in 8 mL of an aqueous solution of Co(NO3)2 (4.5 mol L"1) at room temperature and stirred for ten minutes to impregnate the silica mesopores with Co(NO3)2. After filtration the non-dried sample was immediately transferred to a pre-heated oven (220°C, air atmosphere) to convert Co(NO3)2 to CO3O4. This procedure was repeated twice, with 4 mL Co(NO3)2 solution in the second and third cycle. Finally the sample was heated under air atmosphere to 550°C at a constant rate of 2.5°C min"1. The silica matrix was removed by repeatedly dispersing the sample in an aqueous solution of NaOH (2 mol L") and stirring for three hours at room temperature. For the preparation of the sensors 50 mg of the mesoporous or bulk Co3O4 powders were ground and dispersed in 4 ml water. After ultrasonication the dispersion was deposited onto substrates (Umweltsensortechnik, UST) with integrated heating and interdigitally structured platinum electrodes, dried at room temperature, and tempered for 24 hours at 500°C. The gas sensing properties were measured by means of a gas mixing equipment using standard mass flow controllers to provide a well-defined gas flow and a computer to control the experiment and record the resulting data. 3. Results and Discussion Figure 1 shows the X-ray diffraction diagram, TEM image, and selected area electron diffraction (SAED) pattern of mesoporous Co3O4. The material is the negative replica of the SBA-15 silica structure matrix, consisting of linear rods arranged in a two-dimensional hexagonal symmetry; the low-angle X-ray diffraction peaks are reminiscent to those of the parent SBA-15. The wide-angle X-ray pattern corresponds to the spinel structure of Co3O4; SEAD confirms that the porous material exhibits a relatively high degree of crystallinity. A largepore SBA-15 (9 nm pore diameter) was chosen in order to obtain a Co3O4 product with preferably thick pore walls, since the long-term application of the material as a gas sensor at elevated temperatures requires high stability. This results in a rather moderate specific BET surface area of 40 m2 g"1, lower than that reported for a similar synthesis by Tian et al. (82 m2 g"1) [2]. Nitrogen

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physisorption (not shown) reveals a mean pore diameter of 3.9 nm (BJH method). 500

4 6 291 degrees

Figure 1. Left: Powder X-ray diffraction pattern of mesoporous Co3O4. The low-angle peaks (indexes in parenthesis) correspond to the p6mm hexagonal mesostructure; the wide-angle pattern shows the crystalline Co3O4 spinel structure. Right: TEM image and selected area electron diffraction (SAED) pattern of the same sample.

We have tested the gas-sensing properties of mesoporous CO3O4 for carbon monoxide in technically relevant concentrations between 1 and 5 ppm at a relative moisture of 50%. (In most countries the legal threshold for long-term exposure to CO gas without health damage is specified as ca. 30 ppm.) The performance of the sensor prepared from mesoporous CO3O4 was compared to that of a bulk (non-porous) CO3O4 sensor (specific BET surface area: 12 m2 g"1). The measurements were performed at various temperatures to determine the optimum operation conditions. The bulk sensor reaches its highest sensitivity at a temperature of 300 °C where it is more sensitive than the mesoporous sensor. However, the mesoporous sensor is most sensitive already at 220°C. At this rather low temperature its sensitivity is higher than the maximum sensitivity (i.e. 300°C) of the bulk sensor. In other words, the mesoporous sensor is (i) generally more sensitive and (ii) suitable for lower operating temperatures (lower power consumption for battery backed fail safe applications). Figure 2 (left) shows the sensitivity (which is the measured resistance normalized to the resistance in absence of CO gas) at 220°C. The mesoporous sensor delivers a prompt and steep response to the CO gas, even though saturation is not reached within the measuring interval of 30 min. The bulk sensor shows saturation after 5 min, but the signal is noisy and weak in relation to drift effects. The sensitivities at both temperatures, 220°C and 300°C, are compared in the right-hand plot in Figure 2; as described above, the porous sensor combines the more favorable operating conditions (lower temperature) with a higher sensitivity.

350 1,7

1,5

1,6

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1,1

8

1.0 120

180 240 f/me / minutes

300

360

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1,0 2

3

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CO concentration I ppm

Figure 2. Left: Gas sensor measurement at 220°C showing the CO gas concentration (dotted line) and sensitivities of the mesoporous Co3O4 sensor (black solid line) and of the bulk Co3O4 sensor (grey solid line). Right: Comparison of the sensitivities at the respective optimum operation temperatures, which lie at 220°C for the mesoporous and at 300°C for the bulk sensor. All measurements were performed with 50 % relative humidity.

4. References [1] A.-H. Lu, W. Schmidt, A. Taguchi, B. Spliethoff, B. Tesche and F. Schuth, Angew. Chem. Int. Ed., 41 (2002) 3489. [2] B. Tian, X. Liu, H. Yang, S. Xie, C. Yu, B. Tu and D. Zhao, Adv. Mater., 15 (2003)1370. [3] K. Zhu, B. Yue, W. Zhou, and H. He, Chem. Commun., (2003) 98. [4] Y.Wang, C.-M. Yang, W.Schmidt, B. Spliethoff, E. Bill and F. Schuth, Adv. Mater., 17(2005) 53. [5] J. Roggenbuck, and M.Tiemann, J. Am. Chem. Soc, 127 (2005) 1096. [6] J. -H. Smatt, C. Weidenthaler, J. B. Rosenholm and M. Linden, Chem. Mater., 18 (2006) 1443. [7] T. Wagner, C. -D. Kohl, M. FrOba and M. Tiemann, Sensors, 6 (2006) 318. [8] D. Zhao, Q. Huo, J. Feng, B. F. Chmelka and G. D.Stucky, J. Am. Chem. Soc, 120 (1998) 6024.

Recent Progress in Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

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Direct synthesis of mesoporous spinel-type Zn-Al complex oxide with a crystalline framework Lu Zou, Feng Li *, Xu Xiang, David G. Evans and Xue Duan State Key Laboratory of Chemical Resource Engineering, P. O. Box 98, Beijing University of Chemical Technology, Beijing 100029, P.R. China.

Crystallized mesoporous solid solution of spinel-type Zn-Al complex oxide (Z11AI2O4) with roughly spherical morphology was directly synthesized via a solvothermal route in the presence of urea without using any templates. The assynthesized ZnAl2O4 possesses a disordered mesoporous structure with spineltype framework, and has a high BET surface area of 472 m2 g"1 and narrow pore-size distribution centered at ~3.4 nm. The amount of inversion of the mesoporous ZnAl2O4 is found to be small (4.8 %). 1. Introduction Since the discovery of mesoporous silica materials, increasing attention has been focused on the preparation and applications of non-siliceous mesoporous materials based on transition metal oxides [1-3]. Up to now, a large number of mesoporous metal oxides and complex metal oxides have been reported and they are expected to be useful for various applications particularly as heterogeneous catalysts [1-4]. However, the wall of these materials is normally amorphous, and under heat treatment, crystallization results in collapse of the uniform mesoporous structure [5]. Zinc aluminate (ZnAl2O4), also referred as spinel-type Zn-Al complex oxide, has a wide range of uses. It mainly serves as catalysts and catalyst supports in synthesis, dehydrogenation, dehydrocyclization, hydrogenation, dehydration, isomerization, and combustion processes [6-7]. Besides, it is a wide band-gap semiconductor (3.8ev) that can be used as transparent conductor, dielectric, or optical materials [8]. To prepare ZnAl2O4, high-temperature treatment of precursors such as solid ZnO and a-Al2O3 or Aland Zn-containing complexes are generally employed. In the present study, we report a novel method for preparing crystallized mesoporous ZnAl2O4 via a

352

solvothermal route based on controlled hydrolysis of urea in propanol-water system. 2. Experimental Section In a typical experiment, urea (0.8 mol), and stoichiometric zinc nitrate (0.04 mol) and aluminum nitrate (0.08 mol) were dissolved in 75 ml of deionized water or propanol-water (v/v =1:1) mixed solvent to form a transparent solution. Then the solution was transferred into a teflon-lined autoclave, and heated at 453 K for 12 h. After cooling to room temperature, the product was filtered, washed with deionized water and then ethanol to obtain a white gel. Finally the gel was dried at 363 K for 12 h. Urea is used here as a homogeneous precipitator. The as-synthesized samples in water and propanol-water system are denoted ZA-W and ZA-P, respectively. Powder X-ray diffraction (XRD) patterns were obtained using a Rigaku D/Max2500 with CuKa radiation (A=0.15418 nm). The scanning electron microscopy (SEM) image was obtained on a Hitachi S-3500N scanning electron microscope. Transmission electron microscopy (TEM) image was recorded with a Philips TECNAI-20 highresolution transmission electron microscope. The accelerating voltage was 200 kV. N2 sorption isotherm was measured using a Quantachrome Autosorb-lCVP system. 27A1 solid-state magic-angle spinning (MAS) NMR spectra were measured on a Bruker AV300 spectrometer operating at 78.20 MHz with a pulse width of 0.5 s, spinning rate of 8000 Hz and an acquisition delay of 0.5 s between successive pulses to avoid saturation effects. 3. Results and Discussion Fig. la shows the low-angle power X-ray diffraction (XRD) patterns of samples. Sample ZA-P prepared in propanol-water system shows one broad peak at 10.9 A, meaning that the sample has a disordered mesostructure with no discernible long-range order in the mesopore range. The wide-angle XRD pattern (Fig. lb) of sample ZA-P shows broad characteristic diffraction peaks of cubic ZnAl2O4 spinel phase following JCPDS No.05-0669, signifying that the mesoporous walls of sample ZA-P is composed of nanocrystalline ZnAl2O4. However, if reaction happens in water system, the obtained material is composed of boehmitic AIO(OH) and Zn(OH)2 with a disrupted framework (no low-angle diffraction peak). Therefore it is worth noting that the hydrolysis of urea could be effectively controlled by using propanol/water as the solvent in a closed vessel to obtain a porous ZnAl2O4 network. The morphology of mesoporous ZnAl2O4 (sample ZA-P) was determined by SEM and TEM experiments. As shown in the typical SEM image (Fig. 2a), the ZnAl2O4 product exhibited a roughly spherical morphology. From the TEM image (Fig. 2b), we can see that a disordered mesoporous structure existed in the product, which is consistent with the low-angle XRD result. The selected

353 353

area electron diffraction pattern, shown as inset to Fig. 2b, verifies the presence of crystalline ZnAl2O4 in the mesostructured framework. i x

311

(a)

.-JJ

0 1 2 3 4 5 6 7 8 20 (degrees)

10

20

30

40

50

60

70

80

20 (degrees)

Fig. 1. (a) Low and (b) wide-angle X-ray diffraction patterns of sample (i) ZA-W and (ii) ZA-P. (O) Zn OH)2; ( • ) boehmitic AIO(OH).

Fig. 2. (a) Typical SEM image and (b) TEM image of sample ZA-P. The electron diffraction pattern is shown in the inset of TEM image.

The low temperature nitrogen adsorption-desorption isotherm and the corresponding BJH pore size distribution curve of mesoporous ZnAl2O4 are shown in Fig.3. The nitrogen adsorption isotherm shows an adsorption jump at P/Po of 0.5-0.8, characteristic of capillary condensation in mesopore. The poresize distribution is highly narrow and centered at ~ 3.4 nm. The BET surface area and total pore volume are as high as 472 m2 g"1 and 0.45 cm3 g"1, respectively. The 27A1 MAS NMR spectra of the samples ZA-W and ZA-P are shown in Fig. 4. The presence of both tetrahedral A1O4 sites (chemical shift at ~ 63 ppm) and octahedral A1O6 sites (chemical shift at ~ 6 ppm) is unequivocally demonstrated. The proportion of tetrahedrally coordinated Al for samples ZAW and ZA-P, which is calculated from the octahedral to tetrahedral peak area

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ratio, is approximately 1.7 % and 4.8 %, respectively. It indicates that the amount of inversion is small in mesoporous Z11AI2O4 sample. In addition, investigation of tuning the structural and textural properties of mesoporous ZnAl2O4 through varying reaction parameters is currently underway. 4. Conclusion In summary, we have successfully synthesized mesoporous ZnAl2O4 spineltype oxide via a facile solvothermal route. Such mesoporous ZnAl 2 O 4 spinels should be desirable for various applications, such as for supports in heterogeneous catalysis, as they have very interesting textural and structural properties. Moreover, the one-pot synthesis approach described might open a new route to fabricate many different ceramic, spinel materials concerned with pore systems. ~° 6.30

Pore Volume (cm3g-1nm-1)

0.016

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P/ P0 P/P Fig. 3. N2 sorption isotherms and BJH pore size distribution (inset) of sample ZA-P.

200 150 100 200 15010050 100

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Volume (cm3 g-1, STP)

350

50

0

-50

-100 -100

5 (ppm) (ppm) Fig. 4. Al solid-state MAS NMR spectra of sample (a) ZA-W and (b) ZA-P.

5. References [1] F. Schuth, Chem. Mater., 13 (2001) 3184. [2] M. A. Carreon and V. V. Guliants, Eur. J. Inorg. Chem., (2005) 27. [3] P. Yang, D. Zhao, D. I. Margolese, B. F. Chmelka and G. D. Stucky, Nature, 396 (1998) 152. [4] X. He and D. Antonelli, Angew. Chem. Int. Ed., 41 (2002) 214. [5] H. Shibata, T. Ogura, T. Mukai, T. Ohkubo, H. Sakai and M. Abe, J. Am. Chem. Soc, 127 (2005) 16396. [6] H. Grabowska, M. Zawadzki and L. Syper, Appl. Catal. A: Gen., 265 (2004) 221. [7] L. Chen, X. Sun, Y. Liu, K. Zhou and Y. Li, J. Alloys Compd., 376 (2004) 257. [8] S. Mathur, M. Veith, M. Haas, H. Shen, N. Lecerf, V. Huch, S. Hiifher, R. Haberkorn, H. P. Beck, M. Jilavi, J. Am. Ceram. Soc, 84 (2001) 1921.

Recent Progress in Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

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Visible light activated mesoporous TiO2.xNx nanocrystalline photocatalyst Zheng Jiang, Farhan Al-Shahrani, Tsung-Wu Lin, Yingying Cui and Tiancun Xiao* Inorganic Chemistry Laboratory, University of Oxford, South Parks Road, OX1 3QR, U.K.

Mesoporous TiO2.xNx has been prepared using template-free solvothermal synthesis with post-ammonolysis at 500°C. The characterizations using XRD, Raman, XPS, N2 ad-desorption and TEM showed that the TiO2.xNx is typical mesopores anatase nanocrystaline. The nitrogen dopant causes the absorption edge of TiO2 shift to a lower energy region which enhances its visible light absorption. Under visible light irradiation, the TiO2.xNx exhibits higher activity than commercial P25 but similar activity in decoloration of methylene blue under UV irradiation. 1. Introduction There have been great interests in porous titania for its potential application in photocatalysis, sensor, and photovoltaics [1]. Different synthesis strategies to produce mesoporous titania have been developed using a variety of surfactant templates [1, 2]. However, post-synthetic removal of the template requires additional processes that can be costly, wasteful and of environmental concern, as well as damages the mesoporous texture of titania for thermal nucleation [2]. Despite of its high surface area and accessibility, mesoporous TiO2 absorbs only the UV part (2-3 %) in solar light, which seriously affects its efficient utilization of sunlight [3]. Various methods have also been employed to enhance the adsorption of visible light for TiO2 material through bandgap engineering routes, such as loading or doping with transition metals or noble metals. However, such methods are either inefficient or unstable [4]. The preparation of visible light activated stable titania still remain a challenge. Therefore, visible-light activated titania with mesporous texture has been the aim for development, but not completely available yet.

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Recent investigations showed that N-doped titania, TiO2.xNx is one of the most active and stable candidates among the visible light active titania [3,4]. It possesses the advantages of duration and activity over transition metal doped TiO2. However, no work has been reported so far in preparing mesoporous TiO2.xNx using template-free methods. Herein, we report the mesoporous TiO2 synthesized by solvothermal route, followed by ammonolysis to get TiO2.xNx for the first time. The process is more convenient than template method as it need not directing reagent. 2. Experimental Section Typically, 2 mL distilled water was added dropwise to 20 ml 0.5M Ti(BuO)4 ethanol solution under vigorously stirring. The obtained gel was transferred to autoclave heated at 100°C for 18 h. The resultant gel was dried at 110°C and calcined at 500°C in air for 2 hours, the obtained material was denoted as TiO2ST. The yellowish N-doped TiO2.xNx-ST sample was prepared by ammonolysis of TiO2-ST in NH3/Ar (NH3/Ar=l/4 mol ratio) flow for another 2 h. The asprepared white TiO2-ST and yellowish TiO2.xNx-ST was characterized using various physical techniques. The XRD patterns of the catalysts were obtained with a Philips PW1710 diffractometer using Cu-Ka radiation X-ray at 40 eV and 30 mA. All samples were mounted on a quartz plate with a groove cut into it and measured at room temperature. Nitrogen adsorption-desorption properties were measured at 77 K on a ASAP 2000 sorptionmeter. TEM and HRTEM were conducted on JEOL 2000FX and JEOL 4000 EX respectively. X-ray photoelectron spectroscopy (XPS) measurements were performed with a KROTOS XSAM 800 system, equipped with a dual Mg/Al anode. The spectra were excited with Al Ka. radiation operated at 12 kV and 10 mA. The analysis was carried out in an FRR mode. The Raman spectra of the resultant materials were recorded in a Yion Jobin Labram 300 spectrometer with a resolution of 2 cm"1. It is equipped with a CCD camera enabling microanalysis on a sample point. A 514.5 nm Ar+ laser source was used and the spectra were acquired in a back-scattered confocal arrangement. The visible light photo-catalytic activity on destruction of methylene blue (MB) was compared with commercial P25 (Degussa, SSA ~ 50 m2/g). 3. Results and Discussion Fig.l shows the XRD patterns and Raman spectra of the TiO2-ST and TiO2. N X X-ST photocatalysts calcined at 500°C. It can been seen that the undoped TiO2-ST and the N-doped TiO2.xNx-ST have the similar anatase structure (JCPDS21-1272), but the characteristic diffraction peaks of TiO2.xNx-ST are much sharper and narrower than those of TiO2-ST, suggesting that the particle size of TiO2.xNx-ST anatase is a bit larger than that of TiO2-ST. In addition, the

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two titania are not well-ordered mesoporous oxides because there is no small angle diffraction peaks detected for both of them. Because Raman spectra are much more sensitive than XRD in identifying the coordination and local domain of the surfaces and small crystalline species, it was used to determine the phase

4000

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140.5(E g)

JCPDS 21-1272

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634 (Eg)

514.3 (A1g+B1g)

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(204)

(220)

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2Thela (f)) 2Theta

Fig. 1 XRD patterns and Raman spectra of (a) TiO2-xNx-ST and (b) TiO2-ST calcined at 500°C composition of the two catalysts. As shown in the laser Raman spectra, the observation of Raman shifts at 399, 519 and 638 cm"1 further proves that both Ti(XxNx-ST and TiO2-ST only possesses anatase phase without any rutile phase [5]-" Fig.2 shows the N2 adsorptiondesportion isotherm and BJH pore size distribution (inset) of TiO2-ST and TiO2. 1 / !/1 r XNX-ST. As shown in Fig. 2, the two catalysts are all of obvious IV hysteresis loops, indicating there exists mesopores in the two catalysts. The inset pore size distribution profile shows the mesoporous structures of such materials. In fact, the average pore diameter of TiO2-ST and Fig.2 N2 ad-desportion isotherm and BJH TiO2.xNx-ST are both around 10 nm. pore size distribution (inset) of TiO2-ST Furthermore, the specific surface area of and TiO2.xNx-ST TiO2_xNx-ST is about 85 m2/g which is much smaller than that of TiO2-ST (148 m7g)), but much higher than the SSA of P25 (~ 50 m2/g). This suggests that significant sintering of such mesoporous titania occurred in the ammonolysis process. The isotherm plots also imply there is no ordered mesopores existing in such materials. All the XRD and N2 adsorption-desorption results imply the mesopores of TiO2.xNx-ST resulting from the stacks of TiO2.xNx-ST nano-crystal particles. The images of TEM and 200 180

-m- TiO TiO 2-ST -ST ^.-'-w 2 -m- TiO TiO^N^-ST/" / N -ST 2-x x

I

160 140

Y Axis Title

120 100 80 60

0

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40 20

0 0.0

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HRTEM as shown in Fig. 3 suggested the presence of the irregular mesopores. The TEM image shows that the size of TiO2.xNx-ST particles is about 15 nm. The clear lattice fringe shown in HRTEM image further supports that TiO2_xNxST is crystalline material, which is well consistent with the results of XRD.

Fig. 3 TEM(Left) and HRTEM(Right) images of TiO2.xNx-ST

As shown in Fig. 4, the UV-Vis-DRS indicates the mesoporous TiO2-xNx-ST can adsorb visible light with wavelength up to 550 nm (-2.26 eV), in comparison, TiO2-ST is much similar to the P25(~ 3.20 eV) [3]. This suggests that N-dopant is of visible light activation and the potential activity in visible light photocatalysis reactions. XPS results (inset of Fig.4) indicate that the element N is doped into anatase crystal matrix according to the N bonding energy changing from 395 to 402 eV [3]. As expected, the TiO2.xNx-ST sample shows higher activity under TiO -ST visible light for decolorizing of N1s XPS of TiO N methylene blue, but TiO2-ST and P25 are roughly inactive under the | similar conditions. It is noteworthy f a the absorbance of TiO2.xNx-ST is much lower that that of TiO2-ST in TiO N ultraviolet range. However, the TiO2XNX sample shows the similar UV reactivity in comparison with P25 Wavelength(nm) Wavelength(nm) (results not shown here). The detailed photocatalysis reaction Fig.4 UV-Vis-DRS of TiO2-ST and NIs kinetics and mechanism is under XPS spectra of TiO2.xNx-ST (the inset) study. 2200

1.6

2

1.5

2100

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2-x

CPS

1.1

Absorbence

N1s

Experiment Fitting

1.4

1.0

x

2000

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1900

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1800

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0.3 0.2

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x

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4. Conclusion The combination of the template-free solvothermal synthesis of TiO2-ST and post-ammonolysized TiO2.xNx-ST is an effective method for preparing

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mesoporous N-doped TiO2. The mesopores of TiO2-xNx-ST result from the aggregation of their nano-crystalline particles. The crystal anatase phase of TiO2.xNx-ST is an important feature for photocatalysis. The TiO2.xNx-ST can adsorb the visible light up to 550 nm, therefore exhibits higher visible light activity. 5. References [1] [2] [3] [4] [5]

Y. Yue and Z. Gao, Chem. Commun. (2000) 1755. A. Collins, D. Carriazo, S. A. Davis and S. Mann, Chem. Commun., (2004) 568. S. Sakthivel, M. Janczarek and H. Kisch, J. Phys. Chem. B, 108 (2005) 19384. R. Asahi, T. Morikawa, T. Ohwaki, A. Aoki and Y. Taga, Science, 293 (2001) 269. K. Cassiers, T. Linssen, V. Meynen, P. V. D. Voort, P. Cool and E. F. Vansant, Chem. Commun., (2003) 1178.

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Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

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Mesoporous metal oxides and mixed oxides nanocasted from mesoporous vinylsilica and their applications in catalysis Y. G. Wang, Y. Q. Wang*, Y. Guo, Y. L. Guo, X. H. Liu and G. Z. Lu Lab for Advanced Materials, Research Institute of Industrial Catalysis, East China University of Science and Technology, Shanghai 200237, P. R. China

Mesoporous metal oxides and mixed oxides, such as CeO2, Cr2O3, CoCr 2 0 4 and CexZri.xO2 (x = 0.8 and 0.6) have been synthesized by nanocasting from mesoporous cubic {laid) vinylsilica. Their structural properties were characterized by XRD, TEM and N2 sorption. The redox properties of CexZri_ XO2 were characterized by H2-TPR and the catalytic properties of Cr2O3 and CoCr2O4 were tested in the oxidation of toluene. 1. Introduction: Mesostructured metal oxides/composites with framework compositions other than silica are attractive research targets because of their special properties, such as their magnetic and catalytic properties. Recent research showed that mesoporous Cr2O3 have excellent properties in VOCs removal [1]. There have been several reports concerning the synthesis of mesoporous metal oxides via surfactant-templated, ligand-assisted and triblock copolymer templated pathways. However, the direct synthesis of this kind of mesoporous materials with surfactants is quite difficult compared with that of silica materials. One difficulty may the crystallization induced structural collapse, during the mesostructure formations and the removal of the organic templates. The nanocasting pathway for carbon, pioneered by the group of Ryoo [2], is an attractive alternative to the cooperative assembly routes and has been extended to the nanocasting of metals [3], metal oxides [4-7], and metal sulfides [8]. This is a good method to synthesize mesoporous non-silicious materials, especially metal oxide composites, such as spinal-type ferromagnetic ferrites, cerium-zirconium oxide solid solutions (CexZri_xO2) and perovskites, which are hard to be successfully synthesized with the assembly of surfactant-inorganic

362

precursors [9]. While cerium-zirconium oxide solid solution is the most important three way catalysts [9, 10] due to its high oxygen storage capacity, and CoCr2O4 and perovskites are good catalysts for VOCs removal [11, 12] and methane combustion [13]. So in this work, the nanocasting procedure to transition metal oxides, rare earth oxide (CeO2) and composites were investigated. 2. Experimental Section The synthesis of mesoporous cubic vinyl-funcationalized silica [TEVS/(TEVS+TEOS)* 100=20%] is according to the processor of reference [ 14] and the nanocasting of mesoporous metal oxides and mixed metal oxides is similar to that in reference [7]. The redox properties of mesoporous CexZr].xO2was determined by means of H2-TPR method in a quartz reactor coupled with a thermal conductivity detector. Catalytic activity of Cr2O3 and CoCr2O4 were performed in a continuous-flow fixed-bed microreactor (10 mm i.d.) for toluene combustion (space velocity: 30000 h"'; toluene: 486 ppm; air: 470 ml/min). 3. Results and Discussion Mesoporous metal oxides and mixed oxides were synthesized by nanocasting from mesoporous vinylsilica [14]. Their meso-structures were characterized by small-angle XRD , TEM and N2 sorption, their phase composition were confirmed by wide-angle XRD. The small-angle XRD patterns (Fig. 1) confirm the mesostructure, although it is not well-resolved. The wide-angle XRD patterns of the mesoporous Cr2O3 and CoCr2O4 (Fig. la, inset)

2

3

2e/degree

4

2

3 28/degree

4

Fig. 1. XRD patterns of mesoporous metal oxides and mixed oxides: a) Cr2O3 and CoCr2O4, b) CeO2, Ce0 8Zr0 2O2 and Ce0 8Zr02O2.

clearly show that the materials have well-crystalline rhombohedral phase and spinel phase, respectively. The wide-angle XRD pattern of the CeO2 and CexZri_

363

CeZrO. —<— mesoporous Cr2O3 —*— mesoporous CoCr2O

200

300

400

500

600

700

800

T/°C Fig.2. TPR profiles of mesoporous CeO2 samples.

XO2

100

150

200

250

300

350

400

450

Temperature/°C

Figure 3 Toluene conversion and CexZr]_ in complete oxidation over mesoporous Cr 2 O 3 , CoCr2O4and commercial Cr2O3.

XO2

samples showed peaks corresponding to the cubic fluorite phase (Fig.lb, inset). The observed d-\ines match the reported values for CeC>2 (JCPDS card no.4-0593), whereas for Ceo.8Zro.2O2 and Ceo.6Zro.4O2, the cZ-values are shifted towards higher angle with the increase of zirconium. N2 sorption shows that thus-prepared mesoporous materials possess a high BET surface area (110-190 m2g"'). The H2-TPR of CeO2 and CexZri.xO2 are shown in Figure 2, which is different from that of CeO2 and CexZr].xO2 prepared by reverse emulsion or coprecipitation method[15], it maybe due to the incorporation of silicon in the framework. The catalytic activity of mesoporous Cr2O3 and CoCr2O4 in toluene oxidation is shown in Fig. 3. Mesoporous Cr2O3 shows good activity than commercial Cr2O3, which is in accordance with Sinha's work [1]. In summary, mesoporous metal oxides and mixed oxides were successfully synthesized by nanocasting from mesoporous vinylsilica. Thus-prepared mesoporous materials possess a high BET surface area, pore volume and uniform mesopores. XRD patterns show that some of this materials have a relative ordered structure; H2-TPR shows the mesoporous CeO2 have plentiful of surface oxygen due to it's mesoporous structure and the introduction of zirconium changes the oxygen storage property of the mesostructured CexZri_ XO2 , which is different from previous report. The catalytic activity of mesoporous Cr2O3 and CoCr2O4 in toluene oxidation shows that mesoporous Cr2O3 have good activity than commercial Cr2O3. 4. Acknowledgment

This project was supported financially by the National Basic Research Program of China (No. 2004CB719500) and Commission of Science and Technology of Shanghai Municipality (O552nmO3O), China.

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5. References [1] A. K. Sinha and K. Suzuki, Angew. Chem. Int. Ed. 44 (2005) 271. [2] R. Ryoo, S. H. Joo and S. Jun, J. Phys. Chem. B 103 (1999) 7743. [3] D. H. Wang, H. M. Luo, R. Kou, M. P. Gil, S. G. Xiao, V. O. Golub, Z. Z. Yang, C. J. Brinker and Y. F. Lu, Angew. Chem. Int. Ed. 43 (2004) 6169. [4] K. Jiao, B. Zhang, B. Yue, Y. Ren, S. X. Liu, S. R. Yan, C. Dickinson, W. Z. Zhou and H. Y. He, Chem. Commun. 45 (2005) 5618. [5] B. Z. Tian, X. Y. Liu, H. F. Yang, S. H. Xie, C. Z. Yu, B. Tu and D. Y. Zhao, Adv. Mater. 15(2003) 1370. [6] B. Z. Tian, X. Y. Liu, L. A. Solovyov, Z. Liu, H. F. Yang, Z. D. Zhang, S. H. Xie, F. Q. Zhang, B. Tu, C. Z. Yu, O. Terasaki and D. Y. Zhao, J. Am. Chem. Soc. 126 (2004) 865. [7] Y. Q. Wang, C. M. Yang, W. Schmidt, B. Spliethoff, E. Bill and F. Schuth, Adv. Mater. 17 (2005) 53. [8] X. Y. Liu, B. Z. Tian, C. Z. Yu, B. Tu, Z. Liu, O. Terasaki and D. Y. Zhao, Chem. Lett. 32 (2003) 824. [9] E. L. Crepaldi, Soler-Illia, A. Bouchara, D. Grosso, D. Durand and C. Sanchez, Angew. Chem. Int. Ed. 42 (2003) 347. [10] J. R. Gonzalez-Velasco, M. A. Gutierrez-Ortiz, J. L. Marc, J. A. Botas, M. P. GonzalezMarcos and G. Blanchard, Appl. Catal. B-Environ. 22 (3) (1999) 167. [11] D. C. Kim and S. K. Ihm, Environ. Sci. Technol. 35 (2001) 222. [12] R. Spinicci, M. Faticanti, P. Marini, S. De Rossi and P. Porta, J. Mol. Catal. A-Chem. 197 (2003)147. [13] S. Cimino, L. Lisi, S. De Rossi, M. Fanticanti and P. porta, Appl. Catal. B-Environ. 43 (2003) 397 [14] Y. Q. Wang, C. M. Yang, B. Zibrowius, B. Spliethoff, M. Linden and F. Schuth, Chem. Mater. 15(26) (2003) 5029. [15] M. Daturi, E. Finocchio, C. Binet, J. C. Lavalley, F. Fally, V. Perrichon, H. Vidal and N. Hickey, J. Kaspar, J. Phys. Chem. B 104 (2000) 9186.

Recent Progress in Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

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Surface functionalization of templated porous carbon materials Dan Yu, Zhiyong Wang, Nicholas S. Ergang and Andreas Stein* University of Minnesota, Department of Chemistry, 207 Pleasant St. SE, Minneapolis, MN 55455, U.S.A.

1. Introduction Recently, several important advances have been made to synthesize carbon materials with controlled porosity in both the mesopore and macropore size ranges [1-3]. These include carbonization of porous polymers prepared by block-copolymer templating or colloidal crystal templating, as well as carbonization of precursors infiltrated into hard templates, such as porous silica. Just as surface functionalization of porous silica materials has benefited potential applications, controlled functionalization of porous carbon materials will be useful to modify surface and bulk properties and to adapt the materials to applications as sorbents, catalysts, sensors, electrodes, etc. Here we present methods of attaching molecular surface modifiers and nanoparticles to threedimensionally ordered macroporous (3DOM) carbon materials prepared by colloidal crystal templating. The methods for molecular surface groups should also be adaptable to mesoporous carbons. 2. Experimental Section 3D0M carbon was synthesized by infiltration of resorcinol-formaldehyde precursors into PMMA colloidal crystals and carbonization at elevated temperatures in a nitrogen atmosphere [3]. The surface of 3 DOM C was oxidized by boiling the solid in concentrated HNO3 for 1 h and washing with water by Soxhlet extraction for 1 d. The resulting surface carboxylic acid groups were reduced to hydroxyl groups by refluxing 1 g of dried, oxidized 3D0M C in 50 mLl.OM BH 3 THF solution in THF for 1 d, then washing with water by Soxhlet extraction for 1 d. The 3D0M C-OH surface was then brominated by reacting 1 g material in 10 mL JV,./V-dimethyl formamide (DMF) solution containing 1.65 g CBr4 and 1.31 g PPh3 at 80°C for 1 d. The product

366

was washed by Soxhlet extraction for 1 d using THF as the solvent. For substitution of bromide to thiol groups [4], 1 g 3D0M C-Br was dried under vacuum for 2 h, then 5 mL anhydrous DMF was added, followed by 0.28 g CH3COSK. The mixture was heated at 120 °C for 2 d. The product was washed with DMF and water several times and then stirred in 20 mL of 1 M NaOH solution for 1 d to hydrolyze the thioester group. The final 3D0M C-SH product was washed by Soxhlet extraction in water for 1 d. This procedure is summarized in Figure 1. Heavy metal adsorption on thiol-functionalized carbon was evaluated using 1.5 mM lead nitrate solution at pH 5. Functionalization of 3D0M C with nanoparticles (e.g., titania) by hydrothermal reaction involved prior deposition of polyelectrolyte layers following reported procedures [5]. Materials were characterized by XRD, SEM, TEM, nitrogen sorption analysis, XPS, EDS, FTIR and elemental analysis.

( 3DOM Carbon

Br

Figure 1. Scheme of the surface modification process for 3D0M C.

3. Results and Discussion 3D0M carbon samples with pore diameters between 250-350 nm were used as starting materials for functionalization. The glassy-carbon wall skeleton was mostly microporous with some mesoporosity (140-300 m2/g). Based on analysis by FTIR and titration, oxidation with nitric acid introduced lactone and carboxylic acid groups and enhanced the content of phenol and ketone groups [5]. The IR spectrum showed a carbonyl absorption at 1728 cm"1 after 15 min boiling in HNO3. The absorption intensity increased with time. However, treatments longer than 90 min degraded the mechanical strength of 3DOM C, by oxidizing not only the macropore surface but also bulk components of the carbon skeleton. An appropriate oxidation time was determined to be 60 min. Oxidation increased the surface area of the sample by introducing additional micropores [5]. Two broad (002) and (100) XRD reflections associated with disordered graphene layers became only slightly broader after this treatment [5]. Carboxylic acid groups provided negative charge for electrostatic attachment of

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nanoparticles or could be reduced to hydroxyl groups under mild conditions for subsequent conversion to other molecular surface groups. Modification with molecular surface groups. In porous silicates, thiol groups are known to provide good anchoring sites for toxic heavy metals. Decoration of porous carbon with thiol groups was possible by first brominating hydroxyls and then substituting bromine by a thiolation agent. The transformation of surface carboxylic acid groups to hydroxyl groups was performed using a BH3-THF solution as a mild reducing agent which could readily infiltrate the macropores. Elemental analysis, FTIR and XPS spectra confirmed the transformation of surface functional groups. The CHON mole ratios varied from CH0.072O0.030N0.005 in the original 3 D 0 M C to CH0.i88O0.234N0.010 in the oxidized carbon to CH0.28iO0.140N0.012 in the reduced product ( 3 D 0 M C-OH). The

intensity of the carbonyl peak in the IR decreased significantly after reduction, while the relatively broad hydroxyl absorption around 3430 cm"1 grew in intensity. In the XPS spectra, Figure 2, the major peak at 285.0 eV was present in all three samples and was assigned to skeletal carbon. The original 3D0M carbon showed a weaker shoulder near 287 eV, assigned to carbonyl or quinone groups [6] that had also been identified by titration methods [5]. After oxidation, a distinct peak appeared at 288.8 eV in the spectral region for carboxylic acid groups. Following reduction, a resolved peak was no longer seen in this region, but a broad peak at 287 eV appeared, consistent with a lower oxidation state of carbon. Phenolic peaks may be present in the envelope between 285-287 eV.

B

C

Original 3DOM C

HNO3 treated 3DOM C

BH3 treated 3DOM C-OH

2

71 70 B.E.(eV)

Figure 2. XPS spectra showing (A) the C Is region of the original 3D0M C, HNO3-treated 3D0M C and BH3 treated 3D0M C-OH; (B) the Br 3d region of 3D0M C-Br; (C) the S 2p region of 3DOMC-SH.

A variety of reagents were screened for the bromination reaction, including PBr3, SOBr2 and CBr4/PPh3. Substitution without significant side reactions was only achieved with CBr4/PPh3. In the XPS spectrum of the product, a Br 3d5/2 peak was observed at 71 eV due to Br covalently bonded to C. The transformation of bromine to thiol on the surface of 3D0M C was realized by two steps: the substitution of bromine to thioacetate and the hydrolysis of thioacetate to thiol under basic conditions [4]. The XPS spectrum of the final product showed a major S 2p peak at 164.6 eV, which originated from thiol groups [7]. Elemental analysis of the product revealed 1.6 wt% sulfur,

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corresponding to 0.5 mmol g"1. Based on absorption from 1.5 mM lead nitrate solution the thiol-functionalized 3D0M carbon had a 0.2 mmol/g capacity for lead, compared to 0.06 mmol/g for the unmodified carbon. The periodic macropore structure was maintained throughout the whole conversion process (Fig. 3 left), which is an alternative to functionalization with diazonium compounds [8].

Figure 3. Left: SEM image of 3D0M C functionalized with thiol surface groups. Right: SEM image of 3D0M C coated with polyelectrolytes and titania nanoparticles.

Surface modification with nanoparticles [5]. Macropores in 3D0M C are large enough to accommodate nanoparticles. These can be attached to the carbon surface electrostatically, using layer-by-layer (LbL) growth of positively and negatively charged polyelectrolytes. With multiple layers of poly(diallyldimethylammonium chloride) (PDDA) and poly(4-styrene sulfonate) (PSS), terminating with a PDDA layer, it was possible to synthesize nanocrystalline titania hydrothermally on the surface of 3D0M C, using an aqueous solution of titanium(IV) bis(ammonium lactato) dihydroxide (TAL) at concentrations varying from 0.01 M to 0.2 M and temperatures from 140-200°C (24 h). An example of the uniform titania coating obtained with 0.1 M TAL at 200°C is shown in Figure 3, right. Higher concentrations resulted in thicker walls. At a reaction temperature of 240°C, PDDA decomposed and nanoparticles formed within the macropores, detached from the walls. The LbL coating had the additional effect of blocking micropores and reducing the BET surface area of the porous carbon by an order of magnitude. Thus it can be used to modify the texture (microporosity and mesoporosity) of porous carbon materials. 4. References [1] H. Yang and D. Zhao, J. Mater. Chem., 15 (2005) 1217. [2] R. Ryoo, S. H. Joo and S. Jun, J. Phys. Chem. B, 103 (1999) 7743. [3] K. T. Lee, J. C. Lytle, N. S. Ergang, S. M. Oh and A. Stein, Adv. Funct. Mater., 15 (2005) 547. [4] T. C. Zheng, M. Burkart and D. E. Richardson, Tetrahedron Letters, 40 (1999) 603. [5] Z. Wang, N. S. Ergang, M. A. Al-Daous and A. Stein, Chem. Mater., 17 (2005) 6805. [6] K. Laszlo, E. Tombacz and K. Josepovits, Carbon, 39 (2001) 1217. [7] M. Volmer, M. Sratmann and H. Viefhaus, Surf. Interface Anal, 16 (1990) 278. [8] Z. Li and S. Dai, Chem. Mater., 17 (2005) 1717.

Recent Progress in Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

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Rational control of the micro/mesoporosity of multimodally porous carbon monoliths synthesized by nanocasting Jan-Henrik Smart8, An-Hui Lub, Stefan Backlund3 and Mika Lindena "Dept. Physical Chemistry, Abo Akademi University, Porthansgatan 3-5, FIN-20500 Turku, Finland. b Dept. Heterogeneous Catalysis, Max-Planck-Institutfur Kohlenforschung,D-45470 Miilheim an der Ruhr, Germany

Hierarchically porous carbon monoliths have been synthesized by the nanocasting technique. The macroscopic shape and the macropore structure of the carbon monoliths are direct replicas of the silica mold, while the mesopore size is related to the thickness of the silica mesopore walls. It is shown that the carbon mesopore size decreases with increasing amount of a surfactant, CTAB, used in the synthesis of the monolithic silica mold. Simultaneously, the carbon monoliths become less microporous. 1. Introduction Recently, our group succeeded in preparing hierarchically porous carbon monoliths by using the nanocasting technique [l].The method is similar to the technique for preparing mesoporous carbon material introduced by Ryoo et al. [1]. However, in our case we used macro/mesoporous silica monoliths as molds [1, 2] instead of silica powders with ordered mesopores. A similar approach to prepare carbon monoliths have also been described by Shi et a/.[l]. Later, we investigated the effects of diluting the carbon precursor in order to create carbon monoliths with a bimodal mesopore structure [1, 2]. In this paper, we will demonstrate the possibility to rationally alter the mesopore size and to induce micropores in the nanocast carbon monoliths by variation of amount of surfactant introduced to the sol during the synthesis of the monolithic silica used as the mold for the carbon monoliths.

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2. Experimental Section The monolithic silica molds were prepared according to an earlier described synthesis [4]. TEOS was used as silica precursor, while PEG (Mw ~ 35,000) was used to induce the phase separation and CTAB to form surfactant templated mesopores. In this series of samples the CTAB amount has been set as a variable. The final H2O/HNO3/TEOS/PEG/CTAB molar ratio in the sol was 14.69:0.25:1:0.54:0-0.24. After gelation and further aging in the mother liquid, solvent exchange in 1 M NH4OH is performed and subsequently the monoliths are dried and calcined at 55O°C. Subsequently, the carbon precursor (furfuryl alcohol, FA) was introduced together with a catalyst (oxalic acid, OxA) in the pore system of the different SiO2 monoliths by impregnation (nFA/nOxA = 200-300). Alternatively, the furfuryl alcohol was dissolved in 1,3,5-trimethylbenzene, TMB, in order to dilute the carbon precursor (in this case 60 vol % TMB). The polymerization of FA was carried out at 60 and 80°C for one day each and subsequently the polymer was carbonized at 850°C under an Ar atmosphere. Finally, to obtain the carbon replica, the silica portion of the composite was removed by etching in aqueous hydrofluoric acid solution. The carbon samples are denoted C-x, where x indicates the wt % CTAB in the starting silica molds. The structure of the silica and carbon monoliths was characterized by SEM (S-3500N, Hitachi) and TEM (HF2000, Hitachi). The micropores and the mesopores in the samples were studied by nitrogen sorption (ASAP 2010, Micromeritics). FT-Raman (FRA 106, Bruker) and XRD (X'pert, Phillips) was performed to determine the degree of graphitization of the carbon monoliths. 3. Results and Discussion As can be seen in Figure 1, by using hierarchically porous silica monoliths as molds it has been possible to prepare carbon monoliths with similar hierarchically porous structures by nanocasting techniques [1, 6, 7]. Depending on the studied length scale the carbon replica is either a positive (+) or a negative (-) of the original silica monolith. On the micrometer length scale the carbon monoliths are positive replicas, indicating that the macroscopic shape and the macropores of the carbons can directly be controlled by altering the silica mold. On the nanometer length scale it is possible to alter the carbon structure either by changing the silica mold or by diluting the carbon precursor. The effects of altering the silica mold structure by solvent exchange in different ammonia solutions together with dilution of the carbon precursor in TMB has been described earlier [6, 7]. In this work we have focused on the effects of adding CTAB to the starting sols when preparing the silica molds. When no CTAB is added the silica monoliths only contain textural porosity between the silica particles that build up the monolithic structure. By increasing the CTAB

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concentration the silica particles will obtain an increasing amount of surfactant templated mesopores with pore diameters of ~ 4 nm [4]. Figure 1. Comparison of the starting silica monolith and the carbon replica on different length scales, a) and b) photographs of the macroscopic morphology, c) and d) SEM images of the silica the carbon macropores, e) and f) TEM images of the silica the carbon mesopores.

Table 1. Nitrogen sorption properties for the carbon replica monoliths.

Sample C-0 C-3 C-5 C-7 C-9 C-12

BET area [m2/g]

Micropore area

Mesopore volume

Micropore volume

1493 1015 766 831 1297 1123

460 205 195 122 43 0

2.17 1.41 0.82 0.82 1.19 0.74

0.208 0.088 0.086 0.049 0.007 0.000

rm2/gi

rcm3/gl

rcm3/gl

Pore Size (BJHads) [nml 14.3 7.6 6.0 4.2 2.9 2.4

Based on the results presented Table 1 it is clear that the mesopore size and volume of the carbon monoliths decrease with increasing CTAB amount used in the synthesis of the silica mold. Since the carbon monoliths are negative replicas of the original silica structure on this particular length scale, the silica mesopore walls become carbon mesopores and vice versa. The increase of porosity in the silica particles is reflected as a decrease in both pore size and volume in the replica. Thus, the results imply that the addition of CTAB can be used for a direct control of the pore wall thickness of the silica mesopores.

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Furthermore, by increasing the CTAB amount the micropore portion in the carbon replicas is remarkably reduced, as determined from the nitrogen sorption t-plots (see Table 1). Our hypothesis is that the textural pores are large enough that the carbon structure formed inside these mesopores and also in the macropores is of an amorphous character, which normally is microporous [1]. However, when silica monoliths having a bimodal mesoporosity are used in the nanocasting process, less microporosity can be detected. The carbon structure inside these pores will also have a more dense structure due to the confinement, leading to almost nonexistent internal microporosity. Raman can be used to determine the degree of graphitization by comparing the ratio between the D band (disordered graphene sheets) and the G band (ideal graphene sheets) observed at ~1300 cm"1 and ~1595 cm"1, respectively. The Raman spectra of samples C-0 and C-9 (not shown) were compared and C-0 gave a lower G/D value than C-9 (0.83 vs. 0.89). Moreover, XRD indicated that the carbon was mainly amorphous for both samples. Nonetheless, sample C-9 had a slightly sharper and more intense (101)/(100) reflection at ~44° 29. Both results indicate that the carbon prepared from silica monoliths synthesized with a high CTAB amount have a more organized structure. It has been shown, that by altering the CTAB amount in the starting silica monoliths, the size of the mesopores and the portion of microporosity in the carbon replicas can be varied. 4. Acknowledgement The Academy of Finland, the European Integrated Project: AIMs, and the Alexander von Humbolt foundation (M.L) are gratefully acknowledged for financial support. 5. References [1] [2] [3] [4] [5] [6] [7]

A. Taguchi, J.-H. Smart and M. Linden, Adv. Mater., 15 (2003) 1209. R. Ryoo, S.H. Joo and S. Jun, J. Phys. Chem. B, 103 (1999) 7743. K. Nakanishi, J. Porous Mater. 4 (1997) 67, and references therein. J.-H. Smatt, S. Schunk and M. Linden, Chem. Mater., 15 (2003) 2354. Z. G. Shi, Y. Q. Feng, L. Xu, S. L. Da, M. Zhang, Carbon 41 (2003) 2677. A. H. Lu, J.-H. Smatt and M. Linden, Adv. Funct. Mater., 15 (2005) 865. A. H. Lu, J.-H. Smatt, S. Backlund and M. Linden, Microporous and Mesoporous Mater., 72 (2004) 59. [8] N. R. Khalili, M. Pan, G. Sandi, Carbon, 38 (2000) 573.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Published by Elsevier B.V.

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Synthesis of mesoporous carbon frameworks with graphitic walls by secondary hard template method Renyuan Zhang, Bo Tu, Dongyuan Zhao* Department of Chemistry and Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, Fudan University, Shanghai 200433, P. R. China.

1. Introduction Ordered mesoporous carbons have been intensively studied because of their remarkable properties since reported by Ryoo and co-workers1. The nanocasting strategy is used to prepare the mesoporous carbon replicates from the parent mesoporous silica1'5. The carbon replicates are constructed into nanorod arrays reversed from silica mesostructures. Among them, mesoporous carbon with graphitic walls attracts even more attention for the applications in electrochemistry such as fuel cells and lithium ion batteries4. Recently, selfassembly of surfactant and resol (phenol/formaldehyde) was reported to obtain mesoporous carbon with open framework structures6. However, that carbon frameworks can hardly been graphitized. Here, we report a secondary hard template method to synthesize mesoporous carbon frameworks (MCF) with graphitic walls by using highly ordered mesoporous Co3O4 nanorod replicas as a template mesophase pitch as a carbon source. 2. Experimental Section Mesoporous CO3O4 template was prepared according to the literature method7. MCF-1 preparation: in a typical synthesis, 0.3 g mesophase pitches5 was heated at 140°C in a ceramic crucible with stirring until a highly flexible fluidic black melt was formed. 1.0 g of mesoporous CO3O4 template was added to the melt step by step during stirring, finally yielding powders. The composites were carbonized at 900°C for 6 h under N2. The CO3O4 hard template was dissolved by 2 M HC1 solution. After filtration, washed with water and dried, the solid product was obtained. MCF-2 was obtained by a similar method except that the

374

carbonization was carried out after headed at 400°C and removing the CO3O4 hard template as the first step. Powder XRD patterns were recorded with a Bruker D4 powder X-ray diffractometer, using Cu Ka radiation. Raman spectra were obtained with a Dilor LabRam-lB microscopic Raman spectrum, using the He-Ne laser with the excitation wavelength of 632.8 nm. TEM images were taken with a JEOL JEM2011 electron microscope operating at 200 kV. Nitrogen adsorption/ desorption isotherms were measured at 77 K with a Micromeritcs Tristar 3000 analyzer (USA). 3. Results and discussion Well-ordered hexagonal mesoporous CO3O4 nanorods can be replicated from mesoporous silica SBA-15, which is evinced by its XRD pattern (Fig. 1). The

Intensity

\

>

•

•

\

•

r 002 002

MCF-1 MCF-2 Intensity

— SBA-15 Co3O4 — Co3O4 - MCF-1 — MCF-2

10 004

110

V.

• A — 1.0

1.5 2.5

2.0 3.0

2.5

3.0

20

2 theta theta

30

40

50

60

70

80

2 theta

Figure 1 XRD patterns of mesoporous silica SBA-15, mesoporous CO3O4 replica template and MCF products from the secondary hard template of Co3O4 replica.

Intten ensity

CO3O4 nanorods replicates can be used as the secondary hard template to prepare MCFs. XRD patterns show that MCF-2 has a hexagonal mesostructure in small domain similar to SBA-15 (Fig. 1). The regularity of MCF-1 is much — MCF-1 lower than that of MCF-2, suggesting . —MCF-2 MCF-2 p. ordered hexagonal mesostructure is ~\ lossed, possibly due to the reaction of the C and CO3O4 at high temperature. —"^ A The wide-angle XRD patterns for // \\ / \ MCF products show two intense diffraction peaks which can be A A indexed to 002 and 10 diffractions for typical graphitic structure (Fig. 1). soo 800 1000 1200 1400 1600 1800 -1 It shows that MCF-1 is better Wave number(cm number(cm-1) ) crystallized, probably due to the Figure 2. Raman spectra of MCFs

A / \

375

catalysis of cobalt oxide template at high temperature. And for MCF-1, the 10 diffraction peak splits to two peaks which can be indexed to 100 and 110 reflections of graphitic carbon.

Figure 3 TEM images of MCF-1 (a & b) and MCF-2 (c & d).

Volumn Adsorbed (cm3/g STP)

Raman spectra show a vibration at 1580 cm"1 (G-band) assigned to the interplane sp2 C-C stretching, which is the characteristic feature of graphitic carbon. A strong bond near 1580 cm'1 can be observed for the MCFs (Fig. 2), revealing a well-defined graphitized structure. The bands of MCF-1 are sharper than those of MCF-2, sug-gesting it is better graphitized. TEM image of MCF-1 (Fig. 600 MCF-1 3) shows a piece domain of Q. 500 MCF-2 hexagonal mesostructure, though XRD diffractions is 400 not observed. It is interesting O 300 that in the previous reports of mesoporous carbon with 200 graphitic walls, the orientation 100 of the graphite lattices was all perpendicular to the (001) o 0 0.0 0.2 0.4 0.6 0.8 1.0 direction of hexagonal mesoRelative Pressure(P/P Pressure(P/P0) structures. Here, the graphite 0) lattice orientation of MCF-1 is Figure 4 N2 adsorption-desorption isotherm parallel to the (001) direction plots of MCFs

376

of the mesostructure. Type IV N2 sorption isotherms with Hi hysteresis loop are also obtained for the MCF products. As shown in Fig. 4, MCF-1 has a wide pore size distribution, suggesting a disordered mesostructure. However, MCF-2 shows typical isotherms of ordered mesoporous materials. MCF-1 has a BET surface area of 289 m2/g, a pore volume of 0.55 cm3/g and MCF-2 has a surface area of 612 m2/g, a pore volume of 0.9 cm3/g. The surface areas and pore volumes are much lower than the normal amorphous meso-porous carbons templated by mesoporous silica, such as CMK-3 with the same pore structures (1500 m2/g and 1.3 cm3/g, respectively1). The reason may be attributed to the graphitized crystalline nature of the carbon frameworks. 4. Conclusion We primarily show a secondary hard template method to synthesize mesoporous carbon frameworks with graphitic walls. Small domain of hexagonal mesostructure with graphitized frameworks is observed. Since the growth direction of the graphitic layer of MCF products is parallelized to the (001) direction of the mesostructure, which show a possibility to fabricate highly ordered carbon nanotube arrays. 5. References [1] [2] [3] [4] [5]

R. Ryoo, S.-H. Joo and S. Jun. J. Phys. Chem. B, 103 (1999), 7743. J. -W. Lee, S.-H. Yoon, T. Hyeon, S. M. Oh and K. B. Kim. Chem. Commun., (1999) 2177. R. Ryoo, S. H. Joo, M. Kruk, and M. Jaroniec. Adv. Mater., 13 (2001) 677. T.-W. Kim, I.-S. Park and R. Ryoo, Angew. Chem. Int. Ed., 42 (2003) 4375. H. F. Yang, Y. Yan, Y. Liu, F. Q. Zhang, R. Y. Zhang, Y. Meng, M. Li, S. H. Xie, B. Tu and D. Y. Zhao, J. Phys. Chem. B, 108 (2004) 17320. [6] Y. Meng, D. Gu, F. Q. Zhang, Y. F. Shi, H. F. Yang, Z. Li, C. Z. Yu, B. Tu and D. Y. Zhao, Angew. Chem. Int. Ed. 44 (2005), 7053; F. Q. Zhang, Y. Meng, D. Gu, Y. Yan, C. Z. Yu, B. Tu and D. Zhao. J. Am. Chem. Soc, 127 (2005) 13508. [7] B. Tian, X. Liu, H. Yang, S. Xie, C. Yu, B. Tu and D. Y. Zhao, Adv. Mater., 15 (2003) 1370.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

377 377

Porous carbons cast from meso- or nonporous silica nanoparticles Camila Ramos da Silvaa, Martin Wallauab, Eduardo Prado Baston, Rita Karolinny Chaves de Lima and Ernesto A. Urquieta-Gonzaleza* "Universidade Federal de Sao Carlos, Departamento de Engenharia Qulmica, C. Postal 676, CEP 13565-905, Sao Carlos -SP, Brazil; *e-mail: [email protected] Present adress: Universidade Federal de Pelotas, Instituto de Quimica e Geociencias, C. Postal 354, CEP 96010-900 Pelotas - RS, Brazil

Porous carbons prepared from MCM-41 or MCM-48 silica spheres as nanocast possess uniform pore diameter similar to that of the mesoporous silica wall thickness, while carbons from non-porous silica spheres or from Aerosil show wide pore size distributions. Using MCM-41 or MCM-48 spheres as cast, the parcial preservation of the silica structure in the obtained carbons indicates interconnected mesopores, which is supported by the occurrence of the tensile strength effect. 1. Introduction Mesoporous carbons are of great interest in catalysis and adsorption [1] or as hard template for the synthesis of mesoporous zeolites [2]. Recently, we described carbons cast by silica spheres analogous to MCM-41 and MCM-48 [3]. The results suggested that the MCM-41 spheres possess an interconnected pore system. To support that, we present here the analysis of the pore radius distribution of the carbon replica, obtained from the adsorption and from the desorption branch of the N2 isotherms, which showed the occurrence of the tensile strength effect [[4]], this supporting the pore connection in the used MCM-41 spherical particles, as reported previously by Tan et al. [5]. 2. Experimental Section Mesoporous silica spheres analogous to MCM-41 (S41) and MCM-48 (S48) [3], nonporous silica spheres with diameters of 160 (S16o) and 260 nm (S260) [6]

378

and pyrogenic silica (Aerosil 200 Degussa AG) were used in the form of powders or as agglomerates [3]. The porous carbons were prepared by mixing a sucrose/H2SC>4 solution with the silica powder or soaking it into agglomerates, carbonisation under inert atmosphere and dissolution of the silica cast [3]. The denomination of the carbons is given in Table 1, where Cuncast means sucrose carbonised without a silica cast. The silica casts and the carbons were characterised by physisorption of nitrogen, SEM and SAXRD. 3. Results and Discussion The specific surface area (SBET), the external specific surface area (Sext)> the total specfic pore volume (Vlol) and specific micropore volume (Vmic) of the used silica casts and carbons are given in Table 1 and their pore radius distributions (PRD) calculated by the BJH method are shown in Fig. 1 a - d. Table 1. Used silica cast and textural properties of the obtained carbons.

Aerosil

Powder S48* S41*

Sample

C-Aerosil

C48 n c

C41 n c

SBET[m2/g] S e «[m 2 /g]

369 148

534 429 0.459 0.047

Cast

0.376 V,o, [cm 3 /g] Vmic [crnVg] 0.147

Agglomerate S41+

S48*

S,60?

S 2 60 t

Without

C41 706 652

C48 a c

Cl60

C26O

c

589 262

856 851

0.410 0.135

0.547 0.049

0.714 0.040

1124 852 1.524 0.121

487 387 0.424 0.045

^uncast

61 61 0.056 0.000

*uncalcined; +calcined at 800 °C; Wintered at 700 °C.

5

45 10 (KVt H d l U l [11(11]

1{

S 10 pott f-idlu* [nm]

11

pof* ndiiix |nm

Fig. 1. PRD: a) C41 n c ; C48 n c and C48 a g ; b) S41 and C41; c) C 160 and C 260 ; d) C Aerosi | and C uncast .

Table 1 reveals that sucrose carbonised in the absence of a silica cast yields a carbon with low surface area and pore volume (Cuncast). The formation of such

379 379

carbon explains the lower surface areas of the carbons cast by powders. In the silica powders, the distance between the particles is larger than in the agglomerates and for that reason, the nonporous carbon formed in the large interstices reduces the specific surface area and the pore volume. Another factor influencing the textural properties is the particle size, as it is observed comparing the casts (Fig. 2) for carbons Ci60 and C260- Thus, one expects that CAerosii, which is prepared using primary silica particles with diameters around 12 nm, should show a higher specific surface area. However, in this case, the low Sext and V,n, is probably due to the use of Aerosil powder that favours formation of nonporous carbon or to the small pores between the primary particles, Fig. 2. SEM images of the silica casts: a) S41; b) which do not allow the S48;c)S 160 andd)S 260 . penetration of the sucrose. The PRD obtained from the desorption branch of the nitrogen isotherms of the C41nc, C48nc and C48ag (Fig. la) and of the C41 (Fig. lb) show a peak around 1.8 nm, which is absent in the PRD obtained using the adsorption branch (not shown). This fact indicates the presence of interconnected pores with radii higher than 2.0 nm, which empty through smaller pores, causing a tensile strength effect [4]. Furthermore, the PRD given in Fig. la and lb reveal for C48nc, C48ag and C41 a peak around 1.0 nm, which is also observed as a shoulder for C41nc. This peak is attributed to pores with diameters around 2.0 nm corresponding to the wall thickness of the mesoporous silica S41 (« 1.7 nm) and S48 (« 2.0 nm). On the other hand, for carbons cast with nonporous particles (C]6o, C26o and CAerosji) a wide PRD is observed (Fig. lc and Id). The presence of regular mesopores corresponding to the walls of the silica cast is expected for C48nc (Fig. 3) and C48ag, where the silica S48 possesses a three-dimensional pore system [7] but not for mesoporous materials analogous to MCM-41. Nevertheless, mesoporous spheres prepared by the used method [3] possess in addition to their periodic arrays the pores oriented radially toward the edges of the particles [5]. To explain the formation of radially oriented pores in silica spheres analogous to MCM-41 Tan et al. [5] studied the formation of such silica spheres by different techniques, including transmission electron microscopy, using the same synthesis conditions as applied here. From their results they concluded that mesoporous silica spheres are formed by aggregation of disordered silica/surfactant micelles into spherical aggregates

380

with interconnected pores [5]. During their growing, the micelles are aligned into a hexagonal pore arrangement perpendicular to the sphere surface. The partially preservation of the symmetry of the S41 pore array in its C41 replica (Fig. 4) as well as the presence of uniform mesopores in C41 indicate that the parent mould S41 possesses interconnected pores [7], so that our observations can be taken as an indirect confirmation of the formation mechanism proposed by Tan et. al. [5].

S4M44V 2

Fig. 3. SAXRD of C41nc and C48nc.

4'!l)

S

S

ID

Fig. 4. SAXRD of S41, S41/C41 and C41.

4. Conclusion Mesoporous carbons with uniform pores were obtained using mesoporous silica spheres as cast. This confirms for silica spheres analogous to MCM-41 the presence of interconnected mesopores as it was already proposed by other authors [5]. Carbons with high surface area but a wide pore size distribution are obtained using non-porous silica spheres as cast. 5. Acknowledgement Acknowledgements are given to CNPq, Brazil (grant 477759/2003-3 and 505157/2004-7) and to PVE program/Capes, Brazil (M.W.). 6. References [1] J. S. Lee, S. H. Joo and R. Ryoo, J. Am. Chem. Soc. 124 (2002) 1156. [2] Z. Yang, Y. Xia and R. Mokaya, Adv. Mater. 16 (2004) 727. [3] M. Wallau, L. Dimitrov and E. A. Urquieta-Gonzalez, Stud. Surf. Sci. Catal. 156 (2005) 535. [4] J. C. Groen and J. Perez-Ramirez, Appl. Catal. A 268 (2004) 121. [5] B. Tan and S.E. Rankin, J. Phys. Chem B 108 (2004) 20122. [6] Y. K. Ferreira, M. Wallau and E. A. Urquieta-Gonzalez, Stud. Surf. Sci. Catal. 146 (2003) 197. [7] M. Kruk, M. Jaroniec, R. Ryoo and S. H. Joo, J. Phys. Chem. B 104 (2000) 7960.

Recent Progress in Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

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Carbon fiber-templated growth of hierarchical analcime hollow fibers Xueying Chen, Zhiying Lou, Minghua Qiao*, Kangnian Fan and Heyong He* Department of Chemistry and Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, Fudan University, Shanghai 200433, P. R. China

1. Introduction Zeolites are crystalline materials that have been widely used in catalysis, separation, and adsorption [1, 2]. However, the diffusion of guest species in practical applications is usually limited by the narrow pore size of zeolites (0.32.0 nm), especially in reactions involving large molecules. To overcome such shortcomings, intensive research has been undertaken to construct hierarchical zeolite architectures containing tailored meso- or macro-pores [3-5]. Such hierarchical zeolite architectures are expected to be of great technological importance, since they combine advantages of each pore-size regime [6-8]. Compared with other shapes (such as spherical or corpuscular), fibrous zeolite materials such as zeolite-coated fibers and hollow fibers consisting solely of zeolites have attracted considerable attention, since they can offer faster diffusion and lower pressure drop in practical applications and enhance the efficiency of catalytic and adsorptive reactions [ 9-13]. Here, we report the fabrication of hierarchical ANA hollow fibers with nanozeolite walls by using CF as the template. 2. Experimental Section 2.1. Sample preparation In a typical synthesis, the starting CF template is first treated with a HNO3 aqueous solution (10 wt%) for 2 h at 100°C to facilitate the adhesion of colloidal seed crystals. Then, CF was added into a Na 2 Si0 3 aqueous solution in batches under vigorous stirring at 90°C. After the addition of the Ni5oAl50 alloy

382

in batches, the mixture was stirred under the same condition for 2 h for further dealumination. Then ethylamine was added, followed by sulphuric acid. The nominal molar composition of the mixture was 1 SiO2: 1 Na2O : 0.22 Ni : 0.48 Al : 1.26 C2H5NH2: 0.63 H2SO4: 0.36 CF : 19 H2O. The mixture was stirred to homogeneity and then sealed in a teflon autoclave for crystallization at 180°C for 6 days. The product was washed with distilled water 6 times, ultrasonicated, and separated from the residual Raney Ni by magnetic interaction, then washed with ethanol 6 times, dried at ambient temperature, and finally calcined at 550°C in air for 6 h to remove the CF template. 2.2. Characterization The X-ray diffraction (XRD) patterns were collected on a Bruker AXS D8 Advance X-ray diffractometer using Cu Koc radiation. The morphology and element distribution were measured by scanning electron microscopy (SEM, Philips XL30). The microstructures were characterized by transmission electron microscopy (TEM, JEOL JEM2011). 3. Results and Discussion Fig. 1 shows the SEM and TEM images of the initial CF template. As shown in the figures, the CF template is curving fibers with diameter ranging from 600 nm to 1.2 p.m and aspect ratio (fiber length to fiber diameter) varying in the range of 5-50.

Fig. 1 (a) SEM and (b) TEM images of the initial CF template.

Fig. 2 shows the SEM and TEM images of the as-prepared products. The products are composed of fiber-like materials with uniform diameter of ca. 4 H.m. They are hollow in the interior and the thickness of the walls is relatively homogeneous both along and around the fibers (~ 1 urn). The surface of the hollow fibers is rough, which is composed of aggregates of nanocrystals. From

383 383

Figs. 2c and 2d, we can see that the diameter of the nanocrystals on the surface of the hollow fiber is ranging from 60-150 nm.

Fig. 2 SEM (a, b, c) and TEM (d) images of the as-prepared products.

_WUU IL*_A_J|A~_JWLJA

Fig. 3 XRD patterns of the as-prepared products.

J\~JLJL^yuv_A

384

The XRD patterns of the as-prepared products are shown in Fig. 3. The diffraction peaks are characteristic of ANA which belongs to the laid space group. Neither other crystalline phases nor any indication of amorphous material was found in the XRD patterns. 4. Conclusion Hollow fibers consisting solely of zeolite analcime (ANA) were prepared by in situ deposition of ANA nanoseeds over carbon fiber (CF) template which was removed during a subsequent calcination. Colloidal ANA seeds were produced by reacting Ni5oAl5o alloy with the aqueous solution of Na 2 Si0 3 at 90°C. CF template was surface-modified to facilitate the adsorption and crystallization of the ANA nanoseeds. The ANA hollow fibers produced showed a rough surface constituted of nanocrystals about 60-150 nm and a relatively uniform fiber wall thickness of 1.0 (im both along and around the fibers. This work was supported by Shanghai Science and Technology Committee (03 QB14004, 06JC14009), and the Fok Ying Tong Education Foundation (104022). 5. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13]

M. E. Davis, Ind. Eng. Chem. Res., 30 (1991) 1675. D. W. Breck, Zeolite Molecular Sieves, Wiley, New York, 1974. L. Toshevaand V. Valtchev, Chem. Mater., 17 (2005) 2494. V. Valtchev and S. Mintova, Micropor. Mesopor. Mater., 43 (2001) 41. V. Valtchev, Chem. Mater. 14 (2002) 4371. B. T. Holland, L. Abrams and A. Stein, J. Am. Chem. Soc, 121 (1999) 4308. L. Huang, X. D. Wang, J. Sun, L. Miao, Q. Li, Y. Yan and D. Y. Zhao, J. Am. Chem. Soc, 122 (2000) 3530. Y. J. Wang, Y. Tang, Z. Ni, W. M. Hua, W. L. Yang, X. D. Wang, W. C. Tao and Z. Gao, Chem. Lett., (2000)510. K. Okada, H. Shinkawa, T. Takei, S. Hayashi and A. Yasumori, J. Porous Mater., 5 (1998) 163. K. Okada, K. Kuboyama, T. Takei, Y. Kameshima, A. Yasumori and M. Yoshimura, Micropor. Mesopor. Mater., 37 (2000) 99. S. Mintova and V. Valtchev, Zeolites, 16 (1996) 31. V. Valtchev, B. J. Schoeman, J. Hedlund, L. S. Mintova and J. Sterte, Zeolites, 17 (1996) 408. Y. L. Wang, Y. Tang, X. D. Wang, W. L. Yang and Z. Gao, Chem. Lett., (2000) 1344.

Recent Progress in Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

385 385

Synthesis of mesoporous silica and mesoporous carbon using gelatin as organic template Chun-Han Hsua, Hong-Ping Lina*, Chih-Yuan Tangb and Ching-Yen Linb "Department of Chemistry, National Cheng Kung University, Tainan, Taiwan, 701. b Department of Zoology, National Taiwan University, Taipei, Taiwan 106

Mesoporous silica of high surface area, large pore size were readily prepared by using the bio-degradable gelatin as template and sodium silicate solution as silica source. Pore size of the mesoporous silica is dependent on the pH value of the hydrothermal solution. In addition, the gelatin-phenol formaldehyde polymer blend can also be used as the template to synthesize the mesoporous silica or mesoporous carbon via proper preparation processes. 1. Introduction Since the discovery of the quaternary ammonium surfactant-templated mesoporous silicas by Yanagisawa et al. and Mobile researcher [1], the surfactant-templating method has been extensively performed to prepare various mesoporous silicas with high surface area, tunable pore dimension, and desired morphology for the applications in catalysts, adsorbents, and nanotemplates [2-4]. In the typical synthetic composition, the cationic and neutral block-copolymer surfactants of amphiphilic property have widely used as the mesostructural template [1-4]. The pore size is, thus, mainly determined by the hydrophobic chain length of the surfactants. However, the hydrophobic parts of the surfactants decompose slowly in the environment under ambient condition [5]. With recently increasing concern on the aquatic toxicity from the surfactants, using natural-friendly reagents to prepare the mesoporous silica is much desirable. According to the silica chemistry [6], the gelatin of watersoluble natural protein, which possess lots of amino (-NH2) functional groups can have a high affinity to strongly interact with silanol groups (Si-OH) on the silicate species via multiple hydrogen bonds. Therefore, the gelatin could be regarded as an alternative template to synthesize the porous silicas.

386 386

2. Experimental Section Typical synthetic procedure for the porous silicas using gelatin is as following: 1.0 g of gelatin was dissolved in 25.0 g of water to form a clear solution. To prepare a silicate stock solution, a mixture of 4.0 g of sodium silicate (SiO2: 27 wt.%, NaOH: 14 wt.%, Aldrich) and a 25.0 g of water was added into a 25.0 ml 0.1 M H2SO4, and then the pH value was adjusted to about 5.0 at 40°C. Then, the gelatin solution was poured directly into the silicate stock solution under stirring and light-yellow precipitate was generated within seconds. After stirring for 30 min, the pH value of the gel solution was adjusted to 6.0-3.0. Fin ally, the gel solution was transferred into an autoclave, and hydrothermally treated at 100°C for 1 d. Filtration, washing, drying and calcination at 550°C gave the mesoporous silica. Silica recovery is about 95%. To synthesize the mesoporous carbon, 1.0 g of gelatin and 1.0 g of phenol formaldehyde (denoted as PF) polymer was dissolved in 5.0 g ethanol, then that solution was added into 25.0 g of water. Combining with the silicate stock solution, a PF-gelatin-silica composite was generated. After drying at 100°C, pyrolysis at 1000°C and silica removal by 6.0 wt.% HF, the mesoporous carbon was obtained. To prepare the mesoporous silica, the gelatin-PF-silica composite was hydrothermally treated at 100°C for 1 d and calcined at 550°C [7]. 3. Results and Discussion Figure 1A shows the TGA curves of the gelatin-silica composite before and after hydrothermal reaction. The high gelatin content (~ 40 wt.%) in the composite is due to that the gelatin with lots of amine groups (-NH2) can bind strongly with the silicate species through multiple hydrogen-bonds at pH « 5.0. After hydrothermal treatment, the gelatin content decrease to ~20 wt.%. This decrease indicates that some gelatins leave form the gelatin-silica composite during hydrothermal reaction. Analyzing the N2 adsorption-desorption isotherms of the calcined silicas before and after hydrothermal treatment (Figure IB), one can clearly see that the microporous silica with a type I isotherm was obtained before hydrothermal treatment, and a mesoporous silica with a type IV isotherm was prepared after hydrothermal treatment. The mesoporous silica has an apparent capillary condensation at P/Po around 0.85, and the average pore size calculated by BJH method is about 12.5 nm. It is reasonable to suppose that the pore size expansion results from further silica condensation and gelatin's leaving during hydrothermal reaction. To identify the mesostructure, the TEM image of the mesoporous silica reveals the disordered mesostructure and the pore size is about 10.0 nm (Figure 1C). When pH value of the hydrothermal solution was decreased, the pore size of the mesoporous silica decreases (Figure ID). Combining with a simple hydrothermal treatment, the mesoporous silica of tunable pore size and large

387

105

Weight loss / %

95

After hydrothermal treatment Before hydrothermal treatment

A

3 -1

100

Volume adsorbed/cm g , STP

surface area (>300 m2g"') can be synthesized with the nature-friendly gelatin and cheap sodium silicate.

90 85 80 75 70 65 60 55

700

After hydrotheraml treatment before hydrothermal treatment

hydrotheraml treatment B —— t• —— After before hydrothermal treatment

600 500 400 300 200 100 0

100

200

300

400 0

500

600

0.0

0.2

0.4

Temperature /C Temperature/°C

P/P0

0.6

0.8

D

800

— . — ppH=6.0 H=6.0 —»— pH=5.0 pH=3.0 — • —pH=3.0

700

1.0

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Figure 1. A. The TGA curves of the gelatin-silica before and after hydrothermal treatment at 100°C. B. N2 adsorption-desorption isotherms of the calcined porous silicas. C. TEM image of the calcined mesoporous silica after hydrothermal treatment. D. N2 adsorption-desorption isotherms of the calcined mesoporous silicas hydrothermally treated in solutions of different pH values. The inset is the pore size distributions calculated by BJH method.

Owing to the gelatin is one kind of natural polymers, it thus can blend with other polymers through proper intermolecular interactions. It is well known that the thermal-setting PF polymer, a carbon source widely used in industry, has many -CH2OH and phenol groups. Therefore, the gelatin and PF polymer can form a homogenous blend through multiple hydrogen-bonding interaction. When combinding the gelatin-PF polymer blend with the silicate solution at pH « 5.0, a PF-gelatin-silica composite was readily synthesized. Because the PFgelatin-silica composite contains the carbonizable PF polymer, the mesoporous carbon was obtained from pyrolysis under N2 atmosphere and silica removal. The TEM image of the resulting mesoporous carbon reveals the disordered mesostructure and the meso-voids («few nanometers, Figure 2A). In parallel, the mesoporous carbon exhibits a type-IV N2 adsorption-desorption isotherm (Figure 2B). Analyzing the adsorption isotherm, the BET surface area is about 1200 m2g"] and pore size is around 2.5 nm. The mesoporous carbon shows the apparent vibrational band around 1580 cm"1 (G-band, interplane sp2 C-C stretching) in the Raman spectrum that reflects a high graphitized degree.

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Alternatively, the mesoporous silica can be obtained from hydrothermal treatment and calcination of the PF-gelatin-silica composite (Figure 2C). 800

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Figure 2. (A). N2 adsorption-desorption isotherms of the mesoporous carbon prepared with a template of the PF—gelatin blend. The inset exhibits the pore size distribution analyzed by BJH method. (B). TEM image of the mesoporous carbon. The inset shows the Raman spectrum. (C). TEM image of the mesoporous silica templated by the PF-gelatin blend.

4. Conclusion In conclusion, we performed the environment-friendly gelatin and gelatin-PF polymer blend as new templates to prepare the mesoporous silicas and mesoporous carbons with high surface areas and tunable pore size. With the textural properties of the porous silica and carbons can be feasibly controlled, potential applications in catalyst, absorption for large molecules, solar absorber, hard-template for metal oxides and electrode materials can be further explored. 5. References [1] (a). T. Yanagisawa, T. Shimizu, K. Kuroda and C. Kato, Bull. Chem. Soc. Jpn., 63, (1990) 988. (b). C. T. Kresge, M. E. Leonowicz, W. J. Roth, J. C. Vartuli, and J. S. Beck, Nature, 359,(1992)710. [2] D. Zhao, J. Feng, Q. Huo, N. Melosh, G. H. Fredrickson, B. F. Chmelka and G. D. Stucky, Science, 279(1998)548. [3] J. Y. Ying, C. P. Mehnert and M. S. Wong, Angew. Chem. Int. Ed., 38 (1999) 57. [4] L. Pei, K. Kurumada, M. Tanigaki,; M. Hiro and K. Susa, J. Coll. Int. Sci., 284 (2005) 222. [5] K. Holmberg, B. Jonsson, B. Kronberg and B. Lindman, "Surfactant and Polymers in Aqueous Solution" 2nd ed, England, John Wiley & Sons (2003). [6] R. K. Her, "The Chemistry of Silica: Solubility, Polymerization, Colloid and Surface Properties, and Biochemistry," Wiley, New York (1979). [7] D. W. Chen, C. Y. Chang-Chien, H. P. Lin, and C. Y. Tang, Chem. Lett., 33 (2004) 1574. (b) H. P. Lin, C. Y. Chang-Chien, C. Y. Tang and C. Y. Lin, Microporous and Mesoporous Mater., 93 (2006) 344.

Recent Progress in Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

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A study on the synthesis of mesoporous silica and carbon platelets with perpendicular nanochannels Yi-Qi Yeh a , Gui-Min Teoa, Bi-Chang Chenb, Hong-Ping Lina*, Chih-Yuan Tang0 and Chin-Yen Lin°

"Department of Chemistry, National Cheng Kung University, Tainan 701, Taiwan. b Department of Chemistry, National Taiwan University, Taipei 106, Taiwan. 'Department of Zoology, National Taiwan University, Taipei 106, Taiwan.

Free-standing mesoporous silica platelets in micron-scale consisting of perpendicular nanochannels were prepared with a ternary-surfactant composition of cationic, anionic and neutral block copolymer surfactants. The mesostructure of the mesoporous silica platelet(J_) is templated by Pluronic 123 surfactant, and the platelet morphology is determined by the catanionic surfactant. The mesoporous silica platelet(_L) was utilized as the nano-template to synthesize the mesoporous carbon platelet(-L). 1. Introduction Since the discovery of surfactant-templating technology for the synthesis of mesoporous materials with high surface area, tunable pore size and large pore volume in the early 1990s [1], an increasing interest has been shown in the design of novel porous materials tailored with various pore organizations and dimensions for potential applications in separation, catalysis, chemical sensing, nanotemplate and low-dielectric coating [2, 3]. The macroscopic alignment of nanochannels in the form of thin films is quite important for producing advanced materials with desired functions [3-5]. Although mesoporous silica films can be produced by dip coating or spin coating via evaporation-induce self-assembly on proper substrates [3, 4], the channels direction in the mesoporous silica film is almost parallel to the substrate surface. In order to provide a simple sol-gel synthetic method for aligning the direction of the nanochannels [5,6], we reported a convenient method for the preparation of free-standing mesoporous silica platelets with vertical channels (denoted as platelets(-L)) by using a ternary-surfactant mixture as the template.

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2. Experimental Section The mesoporous silica platelet(-L) in micrometer size was synthesized by a ternary-surfactant mixture with the alkyltrimethylammonium halide (CnTMAX, n > 12, X = Br or Cl, Acros) , dodecyl sulfate sodium salt (SDS, Acros) and triblock copolymer poly(ethylene glycol)-block- poly(propylene glycol)-blockpoly(ethylene glycol) (EO20PO70EO20, PI23, Aldrich). The ternary surfactant system was prepared by dissolving 0.72 g of C]8TMAB, (0.8-1.2) g of SDS, and 0.7 g of P123 in 150 ml water under stirring for 3 hours at 40-45°C to form a solution. After that, a 150 ml sodium silicate (SiO2*NaOH) solution as the silica source with [SiCy** 80.0 mM at pH « 4.0-5.0 was poured into above solution. A white precipitate was formed in minutes and then that gel-solution was hydrothermally treated at 100°C for 1 d. The mesoporous silica platelets(_L) were obtained from filtration, washing, drying, and calcined at 600°C [6]. The synthetic procedures of carbon film were as followed: 1.5 g of phenol formaldehyde (PF) resin was dissolved in 10.0 g of ethanol to form a lowviscosity solution, and then l.Og calcined mesoporous silica platelet(J_) was added. The mixture was opened to allow a slow evaporation of ethanol under stirring and then dried at 100°C. After that, the dried PF resin containing mesoporous silica platelet(J-) was carbonized at 1000°C for 2 h under nitrogen atmosphere. Finally, the silica template was removed by HF (6 wt.%) etching. Filtering, washing, and drying gave the mesoporous carbon platelet(l) [7]. 3. Results and Discussion Figure 1A shows the well-ordered hexagonal mesostructure of the micronsized platelet obtained from silicification of the CigTMACl/SDS/P123 template at SDS/Ci8TMACl molar ratio of 1.66. From the microtome TEM image, we found the mesoporous silica platelet(-L) is consisted of the vertical nanochannels, and the length of nanochannel's were estimated about tens nanometers. In parallel to the TEM observation, the mesoporous silica platelet(l) exhibits four XRD peaks at low angle range of 20«0.7-3.0°, which can be indexed as (100), (110), (200) and (210) reflection of a well-ordered p6mm hexagonal mesostructure with a unit cell ao « 10.0 nm (Figure IB). The N2 adsorptiondesorption isotherms of the calcined mesoporous silica platelet(X) demonstrates a type-IV adsorption-desorption isotherm (Figure 1C). Analyzing the adsorption isotherm, the BET surface area of mesoporous silica platelet(l) is 512 m2g*', and the pore size distribution calculated by BJH method centers around 9.0 nm. According to these analyzing results, the porosity mesoporous silica platelet(-L) is templated with the P123 copolymer rather than the CisTMAB and SDS surfactant. As our previously proposed formation model [6], in the ternary surfactant system, the catanionic (i.e. cationic+anionic) surfactant bilayer acts as the template of the platelet morphology, and the PI23 copolymers intercalated within the negatively-charged platelets of the Ci8TMACl/SDS

391 391 600

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Figure 1. (A). The TEM image of the mesoporous silica platelet(-L) synthesized with C|8TMABSDS-P123 template. The inset exhibit the microtome TEM of the mesoporous silica platelet(J-). (B). XRD pattern of the mesoporous silica platelet(-L). (C). N2 adsorption-desorption isotherms of the calcined mesoporous silica platelet(±). The inset shows the pore size distribution analyzed by BJH method.

catanionic surfactant. After silicification at pH « 4.0-5.0, the vertical silicaPi 23 nanochannels were formed to avoid the energy-unfavorable contact of negatively charged bilayer and negatively charged silica species [6]. In addition to the Ci8TMACl-SDS catanionic surfactant, other CnTMAX-SDS bilayer-template could be used to synthesize the mesoporous silica platelet(-L). Table 1 lists the textural properties of the mesoporous silica platelet(-L) prepared with different CnTMAX-SDS-P123 composites. Obviously, the pore size is not dependent on the CnTMAX, but similar to that of the P123-template SBA-15 mesoporous silica. This result is in agreement with the formation model we proposed [6]. In practice, the mesoporous silica platelet(l) could be used as the solid nanotemplate to synthesize the mesoporous carbon platelet(_L). The TEM micrograph of the resulting mesoporous carbon platelet shows the well-ordered hexagonal-arrayed nanorods vertical to the platelet (Figure 2A). The XRD pattern of the mesoporous carbon platelet(l) shows three peaks indexed as Table 1. The textural properties of the mesoporous silica platelets prepared with different CnTMAX-SDS-Pluronic 123 ternary surfactant composites.

CnTMAX-SDS-Pluronic 123 V, A-'pore dioo '-'BET cmV /nm /nm surfactant template /nm /my C,2TMAB-SDS-P123 693 8.5 0.77 10.6 12.26 C14TMAB-SDS-P123 560 8.5 0.80 10.3 12.13 Ci6TMAB-SDS-P123 520 9.0 0.83 11.0 12.92 (100), (110), and (200) reflections of a well-ordered hexagonal mesostructure with a unit cell (a 0 «10.5 nm). Moreover, the carbon platelet(J_) exhibits two intensive diffraction peaks at high-angle, which are indexed to (002) and (100) diffraction for the graphite carbon [7]. The surface area calculated by BET method is about 865 m g"1. The pore size distribution of the mesoporous carbon platelet(-L), analyzed by BJH method, centers at 3.7 nm.

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Figure 2. (A). TEM image of the mesoporous carbon platelet(X) film prepared by using the mesoporous silica platelet(l) as template. (B). XRD patterns of the mesoporous carbon platelet(_L). The inset show the high-angle XRD. (C) N2 adsorption-desorption isotherms of the mesoporous carbon platelet(_L).The inset exhibits the pore size distribution analyzed by BJH method.

4. Conclusion In this work, we provided the novel ternary-surfactant system as template to synthesize the mesoporous silica platelets(i-) of nanometered channel length. Furthermore, the mesoporous carbon platelets(_L) were also be generated using the mesoporous silica platelets(l) as solid template. Although, the nanochannels direction and length was readily controlled by using terna rysurfactant system, extending the dimension of the mesoporous platelets to millimeter scale is also important for many possible applications in catalysts, absorbents, nanotemplates, sensors, electrode materials and nanotechnology [5].Preparing a well-order 2D mesoporous materials film on substrate will be further studied. 5. References [1] C. T. Kresge, M. E.Leonowicz, W. J.Roth, J. C.Vartuli and J. S. Beck, Nature 359 (1992) 710. [2] D. Zhao, J. Feng, Q. Huo, N. Melosh, G. H. Fredrickson, B. F. Chmelka and G. D. Stucky, Science, 279, 548 (1998). [3] D. Zhao, P. Yang, N. Melosh, J. Feng, B. F. Chmelka and G. D. Stucky, Adv. Mater., 10 (1998) 1380. [4] S. Tanaka, N. Nishiyama, Y. Oku, Y. Egashira and K. Ueyama, J. Am. Chem. Soc, 126 (2004) 4854. [5] Y. Yamauchi, M. Sawada, T. Noma, H. Ito, S. Furumi, Y. Sakka and K. Kuroda, J. Mater. Chem., 15(2005)1137. [6] B. C. Chen, H. P. Lin, M. C. Chao, C. Y. Mou and C. Y. Tang, Adv. Mater., 16 (2004) 1657. [7] D. W. Chen, C. Y. Chang-Chien, H. P. Lin and C. Y. Tang, Chem. Lett., 33 (2004) 1574.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

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Preparation of versatile silica/carbon nanocom positcs via carbonization of ethyl-bridged periodic mesoporous organosilica Zhuxian Yang, Yongde Xia and Robert Mokaya School of Chemistry, University of Nottingham, University Park, Nottingham NG7 2RD, UK

Mesoporous silica/carbon composites may be obtained from periodic mesoporous organosilica (PMO) mesophases via pyrolysis under argon flow at 800 - 950°C. The composite materials are mesostructurally well ordered with surface area of ca. 820 m2/g and pore volume of 0.4 cm3/g. Calcination of the composites, at 550°C for 8 h in air, generates well ordered mesoporous silicas with surface area > 700 m2/g, while nanoporous carbons with surface area > 500 m2/g and which exhibit graphitic characteristics are generated via silica etching of the composites. The silica/carbon composites, mesoporous silicas and nanostructured carbons retained the morphology of the PMO mesophases. 1. Introduction Silica-based composites such as metal/silica, metal oxide/silica, polymer/silica and silica/carbon materials are attractive because of their optical, magnetic, thermal, mechanical, and electric properties. Silica/carbon nanocomposites may be synthesized by carbonization or pyrolysis of various carbon precursors [1-4]. In addition to their interesting properties, nanostructured silica/carbon composites are potentially useful as starting points for the simple and direct preparation of nanoporous silica and carbon materials. This is particularly attractive for mesoporous carbons given that the conventional hard templating process for their formation involves several steps [5]. Recently there have been efforts to prepare mesoporous carbon via more direct routes by carbonization of silica organic-inorganic hybrid composites, [6] or organosilica/surfactant mesophases, [4] followed by removal of silica. Mesoporous carbons have also been fabricated via direct carbonization of

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organic-organic nanocomposites comprising of a thermosetting polymer and thermally decomposable surfactant [7]. Here we report on the formation of versatile silica/carbon composites via carbonization of ethyl-bridged periodic mesoporous organosilica (PMO) mesophases and show that they are suitable precursors for the preparation of mesoporous silica and nanostructured carbon. 2. Experimental, Results and Discussion Ethyl bridged PMO mesophases were prepared using established procedures, [8] from a synthesis gel of molar ratio BTME : 0.8 CTAB : 2.3 NaOH : 340 H2O, (BTME is 1,2-bis(trimethoxysilyl) ethane and CTAB is cetyltrimethylammonium bromide. The gel was stirred for 20 h at room temperature, and then aged at 90°C for 24 h. The product was obtained by filtration and washed with a large amount of distilled water and dried at room temperature to yield the as-synthesised PMO mesophase. To prepare silica/carbon composites, the PMO mesophase was thermally treated under a flow of argon at 800 or 950°C for 20 h and the resulting silica/carbon composites were denoted as COM800 or COM950 respectively. The silica/carbon composites were then calcined, at 550 °C for 8 h in static air, to yield silica products or treated in 25% hydrofluoric (HF) acid to generate carbons. The silica products were denoted as Silica800 and Silica950, while carbon materials were denoted as Carbon800 and Carbon950. As shown in Fig. 1, the silica/carbon composites are well ordered mesoporous materials. The XRD patterns of the composites exhibit a basal diffraction peak consistent with the presence of mesostructural ordering. The basal spacing of the composites (4.1 and 3.97 nm for COM800 and COM950 respectively) is lower than that of the PMO mesophase (4.37 nm) due to thermally induced contraction. The nitrogen sorption isotherms of COM800 and COM950 (Fig. 1) are typical for mesoporous materials. The isotherms exhibit a relatively sharp adsorption step in the PlPo range up to 0.4, indicative of the presence of uniform mesopores. The mesostructural ordering of the composites is confirmed by the TEM images in Fig. 2, which indicate the presence of relatively well-ordered pore channels. The surface area of the silica/carbon composites is relatively high (841 and 818 m2/g for COM800 and COM950 respectively) and they have a pore volume of ca. 0.4 cm3/g. The pore size of composites, estimated using BJH analysis of adsorption data, is ca. 2.3 nm. TGA analysis indicated that the silica/carbon frameworks are made up of 16 wt% carbon and 84 wt% silica. The carbon/silicon molar ratio is therefore 0.95, which is very close to the expected 1/1 ratio based on the C/Si mole ratio in the building units (Oi 5 Si-CH 2 -CH2-Si0i 5) of the BTME organosilica precursor.

395 400

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Fig. 1. XRD patterns (A) and nitrogen sorption isotherms (B) of (a) ethyl-bridged PMO mesophase and silica/carbon composites derived from carbonisation at; (b) 800 °C, (c) 950 °C.

Fig. 2. TEM images of mesoporous (a,b) silica/carbon composite COM800 and (c) Silica800.

The XRD patterns of silicas obtained via calcination of the silica/carbon composites are shown in Fig. 3A. The XRD patterns exhibit a basal peak indicating that the silica materials posses mesostructural ordering retained from the silica/carbon composites. The basal spacing of the silicas (3.91 and 3.8 nm for Silica800 and Silica950 respectively) was lower than that of the PMO mesophase and the composites from which they were derived. The composites underwent a lattice contraction of ca. 4.5% during removal of carbon and conversion to silica. Thermogravimetric analysis confirmed that the silicas were virtually carbon-free. The presence of mesostructural ordering in the silicas was also observed via TEM as shown by the image of sample Silica800 in Fig. 2c. The XRD patterns of carbons derived from the silica/carbon composites after silica etching in HF acid are shown in Fig. 3C; no low angle (basal peak) was observed due to a lower level of mesostructural ordering and therefore only the wide angle region of the patterns is presented. The XRD patterns exhibit peaks at 20= 26° and 43.5°, due to (002) and (101) diffractions from graphitic carbon [9]. These peaks suggest that the carbons possess a significant level of graphitisation. The nitrogen sorption isotherms of the carbons (Fig. 3D) indicate the presence of micropores or small mesopores. The surface area (835 and 536 m2/g) and pore volume (0.3 and 0.43 cnrVg) for Carbon800 and Carbon950

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respectively, are comparable to those of the silica/carbon composites and nanostructured silica described above. The pore size of the nanostructured carbons is in the range 1.8 - 2.2 nm. 300

A

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Fig. 3. XRD patterns (A,C) and nitrogen sorption isotherms (B,D) of mesoporous silica (a) Silica800 and (b) Silica950, and nanostructured carbon (c) Carbon800 and (d) Carbon950.

Fig. 4. SEM images of (a) PMO mesophase, and (b) silica/carbon composite (c) mesoporous silica and (d) porous carbon, derived from the PMO mesophase.

As shown in Fig. 4, the silica/carbon composites, silica and carbon materials retain the particle morphology of the PMO from which they are derived. 3. References [1] J. Aguado-Serrano, M. L. Rojas-Cervantes, A. J. Lopez-Peinado and V. Gomez-Serrano, Microporous and Mesoporous Mater., 74 (2004) 111. [2] P. R. Giunta, L. J. van de Burgt and A. E. Stiegman, Chem. Mater., 17 (2005) 1234. [3] J. Pang, V. T. John, D. A. Loy, Z. Yang and Y. Lu, Adv. Mater., 17 (2005) 704. [4] Z. Yang, Y. Xia and R. Mokaya, J. Mater. Chem., 16 (2006) 3417. [5] S. Jun, S. H. Joo, R. Ryoo, M. Kruk, M. Jaroniec, Z. Liu, T. Ohsuna and O. Terasaki, J. Am. Chem. Soc, 122 (2000) 10712. [6] B.-H. Han, W. Zhou and A. Sayari, J. Am. Chem. Soc, 125 (2003) 3444. [7] S. Tanaka, N. Nishiyama, Y. Egashira and K. Ueyama, Chem. Commun., (2005) 2125. [8] S. Inagaki, S. Guan, Y. Fukushima, T. Ohsuna and O. Terasaki, J. Am. Chem. Soc, 121 (1999)9611. [9] (a) T.-W Kim, I.-S. Park and R. Ryoo, Angew. Chem. Int. Ed., 42 (2003) 4375. (b) Y. Xia and R. Mokaya, Adv. Mater., 16 (2004) 1553. (c) Y. Xia and R. Mokaya, J. Phys. Chem. B, 108 (2004) 19293. (d) Y. Xia and R. Mokaya, Chem. Mater., 17 (2005) 1553. (e) Y. Xia, Z. Yang and R. Mokaya, Chem. Mater., 18 (2006) 140.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

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Ordered mesoporous carbon as new support for direct methanol fuel cell: controlling of microporosity and graphitic character Chanho Paka'*, Sang Hoon Jooa, Dae Jong Youa, Hyung Ik Leeb, Ji Man Kimb*, Hyuk Changa and Doyoung Seunga " Samsung Advanced Institute of Technology, P.O. Box, 111, Suwon, 440-600, Korea Department of Chemistry and SKKU Advanced Institute ofNanoTechnology, Sungkyunkwan University, Suwon, 440-749, Korea ([email protected])

As a new carbon support for the fuel cell, ordered mesoporous carbon (OMC) was prepared by the nano template method using ordered mesoporous silica. The structural properties of OMC such as microporosity and graphitic character were controlled by addition of nano silica powder during synthesis of OMC or the uses of different carbon precursors. The performance of direct methanol fuel cell in the single cell was affected significantly by the graphitic character of OMC support. 1. Introduction Direct methanol fuel cell (DMFC) is considered as a promising power source for the next-generation portable electronics, owing to its characteristics such as a high energy density, green emission, convenient refueling of liquid fuel, and ambient operation conditions [1]. However, there still remain several critical problems to be overcome in order to commercialize the DMFC system as a real power source. Among the technical issues, increasing the catalytic activities of electrode catalysts is one of the most important issues. In this regard, recently, nanostructured carbons, including carbon nanotubes, carbon nanofibers and ordered mesoporous carbons (OMC), were exploited as new carbon supports for DMFC catalysts, to enhance the catalytic activities in electrode reactions. Among a variety of nanostructured carbons, in particular, the OMCs are highly intriguing as support materials for DMFC, due to their high surface area, uniform mesopore, and high thermal and chemical stabilities. Consequently, recent reports demonstrated that the promising catalytic activities were obtained using OMC-supported catalysts [2-6]. In this presentation, as a part of our

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ongoing efforts toward rational design of OMC materials for DMFC application, the effects of structural properties of OMC supports such as microporosity and graphitic character on the performance of OMC supported catalysts were investigated. 2. Experimental Section A hexagonally ordered SBA-15-type mesoporous silica was prepared using sodium silicate solution as a silica source by modifying the methods reported in the literature [7], and used as template for the preparation of OMCs. The synthesis of OMC with controlled microporosity was performed by combination of nano-replication and nano-imprinting techniques using dual silica templates: mesoporous silica and silica nanoparticles (SNP) [7]. Detail synthesis procedure was described in the previous report [7]. Graphitic character of OMC materials was controlled by the uses of different carbon precursors: sucrose and phenanthrene without SNP [8]. Two OMC samples were designated as SuOMC and Ph-OMC, respectively, depending on the carbon precursors. To evaluate the OMCs as supports for the DMFC catalysts, Pt catalysts with nominal loading of 60 wt% were prepared onto OMC supports by impregnation and H2 reduction [6], and used in the cathode of single cell of DMFC. The preparation of membrane electrode assembly and measurement of performance for DMFC single cell was reported in detail elsewhere [8]. 3. Results and Discussion The synthesis of OMC using dual silica templates was resulted bimodal pore system: mesopore from framework of ordered mesoporous silica template and micropore embedded in carbon rods from SNP prepared sol-gel process, respectively [7]. The additional SNP developed a micropore around -1.5 nm within the carbon rods in the OMC. The micropore volume estimated from the Horvath-Kawazoe equation at 0.16 p/p0 was increased from 0.53 to 0.69 cm3/g with the amount of SNP from 0 to 30%. In addition, the surface area of OMC was increased from 1279 to 1635 m2/g with the amount of SNP from 0 % to 30 % SNP-added sample in the synthesis mixture. Preparation of Pt catalysts on the OMC support having increased microporosity and the fabrication of membrane electrode assembly for the DMFC are under investigation. Two OMC samples with different graphitic characters prepared from phenanthrene (Ph-OMC) and sucrose (Su-OMC) exhibited large BET surface area of 884 and 1147 m2/g, respectively, and uniform mesopores around 4 nm in diameter. The XRD (not shown) of two OMC supports showed the good mesoporous structure. The Ph-OMC exhibited lower sheet resistance (54 mQ/cm2 at 75.4 kgf/cm2) than that (202 mQ/cm2) of the Su-OMC sample. The Ph-OMC showed lower surface area and sheet resistance than the Su-OMC

399

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:

Fig.l. TEM images of Pt supported on (a) Su-OMC and (b) Ph-OMC. Scale bars are 20 nm.

because the aromatic precursor is known to be easily graphitized than the nongraphitizing precursor, sucrose [9]. The XRD patterns (not shown) for 60 wt% Pt loaded on Ph-OMC and Su-OMC showed four peaks at 2 6= 39.8°, 46.3°, 67.5° and 81.3°, corresponding to the face-centered cubic structure of Pt crystal. The particle sizes of Pt particles, as shown in Fig. 1, in the catalysts using two OMC supports were controlled to be similar around 2-3 nm. Fig. 1 displays the Pt particles were uniformly dispersed along the carbon nanorods of OMCs without agglomeration of particles. It is worthy to be noted that internal, open mesopore structure of OMS was maintained after the Pt/Ph-OMC loading of Pt particles [6]. Pt/Su-OMC The single cell performances of DMFC were evaluated at 323 K using Pt-supported carbons as cathode catalysts and PtRu black as anode catalysts. The performance curves in Fig. 2 indicate that the Pt/Ph-OMC catalyst the 0.1 higher performance than 0.0 that of Pt/Su-OMC. The 50 100 150 200 250 300 350 400 current densities at 0.4 V 2 Current Density (mA cm' ) and 323 K were found to be Fig. 2 Potentiodynamic polarization curve plots of 119 and 87 m A / W for DMFC single cell at 323 K using Pt/Ph-OMC and, Pt/Ph-OMC and Pt/SuPt/Su-OMC as cathode catalysts. OMC, respectively.

400

Considering that the particle sizes of Pt in two catalysts are very similar, it is suggested that the enhanced performance of Pt/Ph-OMC, compared with Pt/SuOMC, may be originated from the lower sheet resistance (i.e. higher electrical conductivity) of Ph-OMC. Previously, the effect of graphitic character on the DMFC performances was reported using PtRu nanoparticles supported on several types of carbon nanofibers and carbon nanotubes by Steigerwalt et al. [10]. They suggested that activities of DMFC single cells parallel the trend of electrical conductivity of MEA. The results obtained in the present work further support their conclusion, in that the electrical conductivity of carbon support makes a significant effect on the single cell performance. 4. Conclusion The microporosity and graphitic character of OMC were controlled by addition of nano silica powder or the uses of different carbon precursors during the synthesis of OMC. Ph-OMC and Su-OMC were prepared using phenanthrene and sucrose as carbon precursors. Ph-OMC exhibited 4-fold decreased sheet resistance, compared with Su-OMC, indicative of the higher electrical conductivity. Two OMC were used as supports for highly dispersed Pt nanoparticles with less than 3nm in size and 60wt%. It was suggested that the graphitic character of OMC is of significant importance in enhancing the DMFC cell efficiency, as Pt catalyst supported on more graphitic Ph-OMC exhibited better cell performance than Pt catalyst used Su-OMC as a support. 5. References [1] L. Carrette, K. A. Friedrich and U. Stimming, Fuel Cells 1 (2001) 5. [2] S. H. Joo, S. J. Choi, I. Oh, J. Kwak, Z. Liu, O. Terasaki and R. Ryoo, Nature, 412 (2001) 169. [3] J. Ding, K.-Y. Chan, J. Ren and F.-S. Xiao, Electrochim. Acta 50 (2005) 3131. [4] F. Su, J. Zeng, X. Bao, Y. Yu, J. Y. Lee and X. S. Zhao, Chem. Mater. 17 (2005) 3960. [5] J.-H. Nam, Y.-Y. Jang, Y.-U. Kwon and J.-D. Nam, Electrochem. Commun. 6 (2004) 737. [6] C. Pak, D. J. Yoo, S.-A. Lee, J. M. Kim and H. Chang, Samsung J. Innovative Tech. 1 (2005) 239. [7] H. I. Lee, C. Pak, C.-H. Shin, H. Chang, D. Seung, J. E. Yie and J. M. Kim, Chem. Commun., (2005) 6035. [8] S. H. Joo, C. Pak, D. J. You, S.-A. Lee, H. I. Lee, J. M. Kim, H. Chang and D. Seung, Electrochim. Acta, in press (2006). [9] C. H. Kim, D.-K. Lee and T. J. Pinnavaia, Langmuir 20 (2004) 5157. [10] E. S. Steigerwalt, G. A. Deluga and C. M. Lukehart, J. Phys. Chem. B 106 (2002) 760.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

401 401

Direct sulfonation of ordered mesoporous carbon for catalyst support of direct methanol fuel cell Chanho Paka*, Sang Hoon Jooa, Dae Jong You3, Ji Man Kimb, Hyuk Chang3 and Doyoung Seunga " Samsung Advanced Institute of Technology, P.O. Box, 111, Suwon, 440-600, Korea h Department of Chemistry andSKKUAdvanced Institute of NanoTechnology, Sungkyunkwan University, Suwon, 440-749, Korea

Ordered mesoporous carbon (OMC) prepared by nano-replication method was directly functionalized with sulfonic acid group by using the ammonium sulfate salts. PtRu nanoparticles below 3 nm was supported on the sulfonatedOMC support with 70 wt% loading, and the resulting catalysts exhibited promising catalytic activity for methanol oxidation reactions. 1. Introduction Recently, new types of mesostructured carbon materials have been synthesized using mesoporous silica templates [1], and their prospective applications as adsorbent, electrochemical double-layer capacitor and catalyst support for fuel cell have been explored. In particular, the structural characteristics of ordered mesoporous carbon (OMC) including high surface area, uniform mesopore, and high thermal and chemical stabilities are highly intriguing for fuel cell applications. Since Joo et al. [2] reported that the mass activity for oxygen reduction of Pt catalyst supported on CMK-5 increased more than ten times compared to the catalyst using conventional carbon black support, several reports have demonstrated that the promising catalytic activities were obtained using OMC-supported catalysts [3-7]. For example, we reported the enhancement of single cell performance for DMFC by using the 60 wt% Pt supported catalyst on OMC support [6]. To enhance activity of DMFC electrode reactions, the number of triple-phase boundary, where catalyst, ionomer and reactant simultaneously exists, should be increased [8]. In this regard, the sulfonation of carbon support was recently

402

reported to increase proton conductivity and consequently catalyst utilization [9]. In this study, the pore surface of OMC was directly functionalized with sulfonic acid group. The physicochemical properties of OMC and sulfonatedOMC samples were investigated nitrogen adsorption, X-ray diffraction (XRD), thermogravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS). Further, to explore the possibility of sulfonated-OMC samples as support for DMFC catalyst, PtRu nanoparticles were supported onto sulfonated-OMC and their activity toward methanol oxidation reaction was measured 2. Experimental Section

Volume Adsorbed (cm3 g-1, STP)

A template SBA-15-type hexagonally ordered mesoporous silica particle was prepared with sodium silicate solution by modifying the method reported in the literature [10]. The pristine OMC sample was prepared via nano-replication method using new aromatic precursor, phenanthrene [7]. Direct sulfonation of OMC was conducted by using ammonium sulfate salts, (NH^SO^ with different amount as reported earlier [8]. In brief, the ammonium sulfate was dissolved in the mixture solution of acetone and deionized water and mixed with the OMC sample in the plastic bag. After drying the sample at the ambient condition and further in an oven at 60 °C, the mixture was heated to 250 °C and kept for 5 h in static air. Two samples were prepared with different amount of salts for 10 wt% and 20 wt% sulfonic acid group and designated as SulOMCl and SulOMC2. The pore structure and chemical state of OMC and sulfonated OMC samples were characterized 800 by nitrogen adsorption, TGA and XPS. pax D. The 70 wt% PtRu (1:1 atomic to ; ratio) supported catalysts were 600 a) a) prepared using the modified polyol £ process from the reported method [11] with SulOMCl and SulOMC2 i-rT 400 as supports. The methanol r oxidation activity of the catalyst 8 was measured in the 0.5 M H2SO4 b) b < 200 200 JT ' ^h-+ —\ and 2 M CH3OH solution by linear c) c) sweep method from 0.2 to 0.8 vs. o normal hydrogen electrode (NHE).

/ r

f

f *>* Lr

&

0 o.o 0.0

we

0 m 0.2

0.4

0.6

0.8

1.0 1.0

Relative Relative Pressure Pressure (P/P00)

Fig. 1. Nitrogen adsorption-desorption isotherms for (a) pristine OMC ( • ) , (b) SulOMCl ( • ) and (c) SulOMC2 ( • )

3. Results and Discussion

As shown Fig. 1, the typical type IV nitrogen adsorption and desorption isotherms were obtained from

403

Intenity (a.u.)

the pristine OMC, SulOMC 1 and SulOMC2 samples [1,2,6]. The mesopore size of sulfonated-OMCs obtained from the desorption branch of isotherms was 4.3 nm, which is the same as the OMC sample. The surface areas of SulOMC 1 and SulOMC2 decreased from 883 m2/g of pristine OMC to 392 and 319 m2/g, respectively. For the SulOMC 1 and SulOMC2 sample, the pore volume from the micropore (< 2 nm) decreased from the 16.8x10" cm3/g of OMC sample to 6.5xlO'3cm3/g for SulOMCl and 5.1xl0"3cm3/g for SulOMC2, respectively. The XRD patterns for OMC and sulfonated-OMC (not shown) exhibited similar diffraction lines corresponding to the hexagonal mesostructure, indicating that the structural regularity of the pristine OMC was maintained after the functionalization with sulfonic acid groups. The thermal properties and loading amounts of sulfonic acid group in SulOMC samples were analyzed by TGA. The TGA of SulOMC samples showed significant weight loss in temperature range of 250°C and 350°C, which can be attributed to thermal decomposition of sulfonic acid group. The amounts of sulfonic acid group in the SulOMCl and SulOMC2 were determined as 8.6 wt% and 17.5 wt%, respectively, which is similar to the nominal value from the initial amount of salts used in the impregnation step. The chemical nature of attached functional group in SulOMC samples was probed by XPS. The X-ray photoelectron spectra of S 2p core level revealed that the peak position corresponded to the -SO3H, and its intensity linearly increased with the amount of initial sulfate salts. The sulfur to carbon ratios of two samples increased to 0.014 for SulOMCl and 0.027 for SulOMC2 from 0.004 for OMC, respectively. Fig. 2 shows the power XRD patterns for the 70 wt% PtRu supported on SulOMCl and SulOMC2. The peaks corresponding to (111), (200), (220) and (311) of Pt face-centered cubic (fee) crystal structure were observed from all supported catalysts, which suggests that the Ru atoms were homogeneously substituted into the lattice cites of Pt fee crystal [12]. The crystalline size of PtRu particles in the catalysts estimated from the half width of a peak around 68° by Scherrer equation was 2.9 nm for all samples. It is noteworthy that the particle size of PtRu particles was controlled below 3 nm despite the loading of PtRu was as high as 70 wt%. Furthermore, it should be n o t e d tnat 10 20 30 40 50 60 70 80 90 although the 2 θ (degree) 2θ BET surface areas of sulfonated-OMC supports Fig. 2. XRD patterns of 70 wt% PtRu supported on decreased to below the half a) SulOMCl and (b) SulOMC2

404

of that of the pristine OMC, the choice of suitable preparation method (polyol route) could yield the highly dispersed catalysts. The mass activities for the methanol oxidation of PtRu catalysts supported on SulOMCl and SulOMC2 were 14.3 and 16.7 A/gptRU, respectively, which is slightly higher than that (12.2 A/gptRu) of commercial 60% PtRu supported catalyst from Johnson Matthey (HiSpec 10100) and is comparable to that (16.2A/gp(Ru) of PtRu catalyst supported on OMC itself. The preparation of highly dispersed catalyst particles in combination with their promising catalytic activities toward methanol oxidation suggest that the sulfonated OMC support can be applied as catalyst support for the direct methanol fuel cells. The fabrication of membrane electrode assembly employing sulfonated-OMC supported catalysts and optimization of their single cell performances for DMFC are under way. 4. Conclusion The sulfonic acid group was successfully introduced into OMC sample without collapsing the mesostructure and changing the mesopore size. The introduction of sulfonic acid group resulted in the decreasing the surface area of OMC samples. The amount of sulfonic acid group can be controlled by adjusting the amount of ammonium sulfate salts used in the impregnation step PtRu nanoparticle with 2.9 nm in size was supported on the sulfonated OMC supports with 70 wt% loading and showed improved mass activity for the methanol oxidation reaction compared to the commercial PtRu catalysts, which suggest the sulfonated OMC sample can be used as a new catalyst support for DMFC. 5. References [1] R. Ryoo, S. H. Joo, M. Kruk and M. Jaroniec, Adv. Mater. 13 (2001) 677. [2] S. H. Joo, S. J. Choi, I. Oh, J. Kwak, Z. Liu, O. Terasaki and R. Ryoo, Nature 412 (2001) 169. [3] J. Ding, K.-Y. Chan, J. Ren and F.-S. Xiao, Electrochim. Acta 50 (2005) 3131. [4] F. Su, J. Zeng, X. Bao, Y. Yu, J. Y. Lee and X. S. Zhao, Chem. Mater. 17 (2005) 3960. [5] J.-H. Nam, Y.-Y. Jang, Y.-U. Kwon and J.-D. Nam, Electrochem. Commun. 6 (2004) 737. [6] C. Pak, D. J. Yoo, S.-A. Lee, J. M. Kim and H. Chang, Samsung J. Innovative Tech. 1 (2005) 239. [7] Y. S. Choi, S. H. Joo, S.-A. Lee, D. J. You, H. Kim, C. Pak, H. Chang, and D. Seung, Macromolecules 39 (2006) 3275. [8] K. A. Mauritz and R. B. Moore, Chem. Rev. 104 (2004) 4535. [9] Z. Zu, Z. Qi and A. Kaufman, Electrochem. Solid-State Lett. 8 (2005) A313. [10] S.-S. Kim, T. R. Pauly and T. J. Pinnavaia, Chem. Commun. (2000) 1661. [11] Z. Liu, X. Y. Ling, X. Su and J. Y. Lee, J. Phys. Chem. B 108 (2004), 8234. [12] E. Antolini, L. Giorgi, F. Cardellini and E. Passaacqua, J. Solid State Electrochem. 5 (2001) 131.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Published by Elsevier B.V.

405 405

Effect of chemically surface modified MWNTs on the mechanical and electrical properties of epoxy nanocomposites Joohyuk Park* and Abu Bakar Bin Sulong Department of Mechanical Engineering, Sejong University, 98 Kunja-dong, Kwanjin-gu, Seoul 143-747, Korea

1. Introduction The primary benefit of polymer matrix composites is the potential for enhancement in strength-to-weight ratios. Many researches have been conducted on carbon nanotubes (CNT) reinforced nanocomposites due to their exceptional mechanical, electrical and functional properties [1]. Dispersion of CNT in polymer matrix by ultra sonic wave achieved greater nano dispersion than with a mechanical stirrer [2]. Dispersion quality and interfacial bonding strength CNT with polymer matrix can be increased by chemical surface modification of CNT [3]. In this study, epoxy is chosen as a polymer matrix. Recently, many researchers have been interested in the chemical surface modification of CNT (oxidized CNT, amine treated CNT and plasma treated CNT) to achieve a better dispersion and to increase the interfacial bonding strength between CNT and epoxy matrix for enhanced mechanical properties [4, 5]. The effect of Asproduced CNT on both mechanical and electrical properties of CNT reinforced epoxy nanocomposites has been reported [6]. However, few studies reported the effect of different types of the chemically surface modified CNT on both properties of CNT reinforced epoxy nanocomposites. Therefore, the effect of two types of chemically surface modified CNT and surfactant additive CNT on mechanical strength and electrical conductivity are investigated as a function of CNT loading concentrations.

406

2. Experimental Section The epoxy resin is Bisphenol-A-based epoxy resin (KER215), which contains mono-epoxidized alcohol as reactive diluents, is supplied by Kumho P&B Chemicals. Multi-walled carbon nanotubes (MWNT) which synthesized by thermo-chemical vapor decomposition of hydrocarbon gases is supplied by Iljin. Nanocomposites are fabricated by an injection molding process, and their properties in mechanical strength and electrical conductivity are compared to different MWNT functional groups (as-produced MWNT, chemically surface modified MWNT and surfactant additive MWNT-TRITON X-100) and MWNT loading concentrations. Characterization of chemically surface modified MWNT and the optimized dispersion method are reported elsewhere [7]. The characteristics of mechanical strength are measured by the universal test machine based on ASTM D 3039. Change in fracture surfaces have been observed by a scanning electron microscopic to study the effect of chemically surface modified MWNT on the fracture mechanism and interfacial bonding strength. Moreover, the electrical conductivity is measured by an applied controllable DC voltage wherein resistance is obtained from current intensity versus voltage curve.

1.75

(a)

Young's Modulus (GPa)

1.70

(3

Ultimate Tensile Strength (MPa)

3. Results and Discussion

1.65 1.60 1.55 1.50

Pure Epoxy As-produced MWNTs 45As-produced - A - Surfactant Surfactant add. add. MWNTs - » - Carboxylated MWNTs Octadecylated MWNTs -«—Octadecylated

1.45 1.40 1.35 1.30 0.0

0.5

1.0

1.5

2.0

48

( bb ))

46 44 42 40 38 36 34 32

Pure Epoxy Pure As-produced MWNTs - Surfactant Surfactant add. add. MWNTs MWNTs Carboxylated MWNTs MWNTs Carboxylated Octadecylated MWNTs MWNTs Octadecylated

30 28 26 24 22 20 0.0

15

3.0

(( c )

14

2.7 2.6

\

2.5 2.4

J

2.3

I

2.2

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2.1 2.0 1.9 1.8 1.7 1.6

i

. — - " • " " • "

—.0 Pure Pure Epoxy 1.9As-produced As-produced MWNTs - » - Surfactant add. add. MWNTs -T-Carboxylated MWNTs Carboxylated MWNTs 1.6Octadecylated MWNTs Octadecylated MWNTs

1

0.5

1.0

1.5

(wt%) MWNTs concentration (wt%)

2.0

12 11 10

30 25

(d)

20 15 10 5

(e)

0 0.0

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1.0

1.5

2.0

2.5

3.0

Strain (%)

9 8 7

Pure epoxy As-produced MWNTs Surfactant add. MWNTs Carboxylated MWNTs Octadecylated MWNTs

6 5 4 3

1.5 0.0

1.5

Pure epoxy As-produced MWNTs Surfactant add. MWNTs Carboxylated MWNTs Octadecylated MWNTs

35

Stress (MPa)

13

Stress (MPa)

Fracture Strain (%)

2.8

1.0

45 40

2.9

0.5

MWNTs concentration (wt%) (wt%) MWNTs

MWNTs MWNTs concentration (wt% (wt%))

2.0

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Strain (%) (%) Strain

Figure 1. Variation of mechanical properties of epoxy nanocomposites (a) Young's modulus, (b) ultimate tensile strength, (c) fracture strain, (d) representative stress-strain behavior of 2.0 wt% MWNT nanocomposites, and (e) magnification of stress-strain behavior of (d).

407

Figure 1 shows the variation of mechanical properties of epoxy nanocomposites as a function of MWNT functional types and loading concentrations. Incorporating MWNT into epoxy matrix greater enhanced the mechanical properties than pure epoxy. It is clear that the mechanical properties are increased with increase in MWNT loading concentration. Moreover, chemically surface modified MWNT (carboxylated and octadecylated MWNT) gave higher Young's modulus and ultimate strength than non-chemically surface modified MWNT reinforced nanocomposites. It can be assumed that chemically surface modified MWNT gave a higher interfacial bonding strength than epoxy matrix. Figure 2 shows the fracture surfaces of the various MWNT functional types. The fracture surfaces of pure epoxy and as-produced MWNT reinforced nanocomposites show less rough surface area than chemically surface modified MWNT nanocomposites, which indicates more easily fractured during the uniaxial tensile loading.

Figure 2. Initiation of the fracture for (a) Pure epoxy, (b) As-produced MWNTs, (c) Carboxylated MWNTs and (d) Octadecylated MWNTs reinforced epoxy nanocomposites.

In figure 3, non-chemically surface modified MWNTs are pulled out from epoxy matrix, so longer CNTs can be observed. This indicates the lower interfacial bonding strength of MWNTs with epoxy matrix. However, chemically surface modified MWNTs were shown to be firmly embedded in the epoxy matrix, which indicated stronger interfacial bonding strength with epoxy matrix than non-chemically surface modified MWNTs nanocomposites.

Figure 3. Interfacial bonding strength of (a) As-produced MWNTs, (b) Carboxylated MWNTs, and (c) Octadecylated MWNTs with epoxy polymer matrix.

Moreover, non-conductive epoxy polymer becomes conductive by adding MWNTs, as in figure 4(a). The electrical conductivity is increased with increases in MWNTs loading concentrations. By introducing chemical functional groups on the surface of MWNT, the electrical conductivity of nanocomposites is significantly decreases compared to as-produced MWNT and

408

(a)

1E-4

(b)

0.05

1E-5 1E-6 1E-7 1E-8

electrostatic dissipation line

1E-9 1E-10 1E-11

As-produced MWNTs Surfactant add. MWNTs Carboxylated MWNTs Octadecylated MWNTs

1E-12 1E-13 0.0

0.5

1.0

1.5

MWNTs concentration (wt%)

2.0

Current Intensity (A)

Electrical Conductivity (S/cm) - DC Voltage

Surfactant additive MWNT nanocomposites. It can be assumed that chemical functional groups produce repulsive force due to unbalance polarity for separate CNT agglomeration into individual CNT. Thus, it could disturb the electrical conductivity CNT pathway network which was occurred at as-produced CNT in epoxy matrix. Moreover, severe defects on the CNT walls through chemical surface modification also may damage tube chirality of graphite sheet at CNT which react as medium for selectivity either metallic or semi-conducting property of CNT. However, surfactant (TRITON X-100) only increased dispersion of As-produced MWNT agglomeration, instead of allowing electric current flow through it due to its non-ionic property.

0.04

0.03

0.02

2wt% Surfactant add. add. MWNTs-a 2wt% 2wt% Surfactant add. add. MWNTs-b 2wt% 2wt% Surfactant add. add. MWNTs-c 2wt% Linear fit curve (a) Linear fit cutve (b) Linear fit curve (c)

0.01

0.00 0

25

50

75

100

125

150

175

200

225

250

DC Voltage (V)

Figure 4. (a) Variation of electrical conductivity of MWNT reinforced epoxy composites, and (b) representative of variation of current intensity versus voltage results and its linear fit lines.

4. Conclusion This study's results indicate the chemical surface modification increases the interfacial bonding strength of CNTs with polymer matrix. Furthermore, it can be concluded that chemical surface modification is necessary to enhance the mechanical properties for structural application. However, non-chemically surface modified CNTs are more suitable for electrical applications. 5. Acknowledgement This work was supported by grant No. R01-2003-000-10-72-0 from the Basic Research Program of the Korea Science & Engineering Foundation 6. References [1] [2] [3] [4] [5] [6] [7]

E. T. Thostenson, Z. Ren and T. W. Chou, Comp. Sci. & Tech., 61 (2001) 1899. Y. Wang, J. Wu and F. Wei, Carbon, 41 (2003) 2939. A. Hirsh, Angrew Chem. Int. Ed., 41 (2002) 1853. J. A. Kim, D. G. Seong, T. J. Kang and J. Youn, Carbon, 44 (2006) 1898. F. H. Gojny and K. Schulte, Comp. Sci. & Tech., 64 (2004) 2303. A. Allaoui, S. Bai, H. M. Cheng and J. B. Bai, Comp. Sci. & Tech., 62 (2002) 1993. A. B. Sulong, J. H. Park, N. S. Lee and J. H. Goak, J. of Comp. Mat., (2006) to be appeared.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

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Synthesis of uniform carbon nanotubes by chemical vapor infiltration method using SBA-15 mesoporous silica as template An-Ya Loa, Shou-Heng Liub, Shing-Jong Huangb, Huang-Kai Shena, Cheng-Tzu Kuoa and Shang-Bin Liub * "Department of Material Science and Engineering, National Chiao Tung University, Hsingchu 300, Taiwan Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan

1. Introduction Carbon nanotubes (CNTs) have been widely studied for the past decade owing to their practical applications in a variety of different areas [1-5]. Various attempts have been made to manipulate the physical properties of CNTs using different strategies and synthesis conditions [6-10]. For example, by using anodic aluminum oxides (AAOs) as template, Yuan et al. [11] have demonstrated that CNTs with tunable diameters can be synthesized with modest yield using chemical vapor deposition (CVD) method. In view of the recent advances in routine synthesis of mesoporous silica materials that possess welldefined pore structure with uniform and tunable pore size (5-50 nm), this study aims to employ mesoporous silica SBA-15 [12] as support to incorporate metal (Fe) catalyst with controlled particle size to fabricate CNTs with uniform diameter and improved production yield by chemical vapor infiltration (CVI) method [13]. In addition, the morphologies, structural and physical properties, and product yields of CNTs fabricated by two supported Fe/SBA-15 catalysts respectively prepared by using co-precipitation and impregnation methods, were compared and discussed. 2. Experimental Section Mesoporous SBA-15 silica with an averaged pore size of 7.7 nm was prepared following the recipe reported earlier by Mou et al. [14]. Subsequently, two different methods, namely co-precipitation and impregnation, were adopted

410

to incorporate the iron (Fe) catalyst particles into the pore channels of the silica support. The supported Fe/SBA-15 catalyst prepared by co-precipitation method (denotes as Fe(co)/SBA-15) was carried out by stirring ca. 0.4 g of Fe(NO3)3(S) in suspended solution of SBA-15 (ca. 1 g) for 0.5 h, followed by filtering and drying (at 373 K). The resultant product was then subjected to reduction treatment under flowing H2 (50 seem; ca. 2 kPa pressure) from room temperature to 1073 K and kept at the same temperature for ca. 10 min. On the other hand, samples prepared by impregnation method (denotes as Fe(im)/SBA15) was obtained by the following procedures: first, ca. 0.4 g Fe(NO3)3(s) and ca. 1 g of SBA-15 powder were stirred, and dried by a vapor evaporator. Subsequently, the CH2C12(1) was added to facilitate the migration of residual Fe(NO3)3(aq) into the pore channels of SBA-15 [15]. This procedure was repeated once, and then the sample was also subjected to the same reduction treatment mentioned above. Fabrication of CNTs was carried out by introducing either Fe(co)/SBA-15 or Fe(im)/SBA-15 catalyst in a home-made quartz reactor, followed by CVI procedure carried out at 1073 K. This was done by injecting C2H2/H2 gas mixture under a flow rate of 50/50 seem and ca. 2 kPa pressure. The resultant product was then digested with aqueous HF solution (1M) to remove the silica support, followed by filtering and drying. X-ray diffraction (XRD) patterns were obtained with a Philips X'Pert PRO diffractometer using CuKa radiation. Transmission electron microscopy experiments were performed on a JEOL JEM-2100 instrument operated at 200 keV. 3. Results and Discussion The TEM image (Fig. la) and XRD profile (Fig. 2a) of the parent SBA-15 sample reveal the expected well-ordered hexagonal structure with uniform pore diameter. While the XRD pattern of Fe(co)/SBA-15 (Fig. 2b) shows characteristic diffraction peaks analogous to that of the parent SBA-15, its TEM micrograph (not shown) revealed that majority of the Fe catalyst particles are deposited on the external surfaces of the support. On the other hand, while the XRD pattern of the Fe(im)/SBA-15 exhibits only a weak (100) diffraction peak

Fig. 1. TEM images recorded alone the [110] direction of (a) parent SBA-15 and (b) Fe(im)/SBA-15. Insert: along the [100] direction.

411

compared to the parent SBA-15, indicating that incorporation of Fe catalyst does have substantial influence to the hexagonal mesostructure, they are most likely presented in the pore channels of the mesoporous silica support. This is further verified by the TEM image shown in Fig. lb, which reveals welldispersed, nano-sized Fe particles within the pore channels of the SBA-15. Further CVI process using the supported Fe(co)/SBA-15 and Fe(im)/SBA-15 catalysts both lead to formation of CNTs. However, owing to the uncontrollable catalyst particle size in Fe(co)/SBA-15, the CNTs so produced tend to have a wide distribution of diameter (10-30 nm). In contrast, the CNTs produced using Fe(im)/SBA-15 appears to have uniform s diameter of ca. 8 nm, which is comparable to the pore diameter of it parent SBA-15 support, as shown by the TEM image in Fig. 3a. A closer examination of the TEM image observed no Fe catalyst particle in the tips of these close-end type CNTs (Fig. 3b), suggesting that their formation follow the base growth mechanism. The reasons for such preferred mechanism in the powdered substrate system is rather intriguing and deserves further investigation. Finally, it is worth mentioning that the 1 2 3 4 5 6 7 8 methodology and CVI procedure 26 /degree reported herein for fabricating CNTs Fig. 2. Low angle XRD patterns of (a) with controllable sizes were also found parent SBA-15, (b) Fe(co)/SBA-15, and to be unique in promoting the production (c)Fe(im)/SBA-15. yield. More specifically, a maximum

Fig. 3. TEM images of CNTs growth from Fe(im)/SBA-15 revealing that they are CNTs with (a) an averaged diameter of ca. 7.7 nm and (b) closed ends.

412

CNTs yield of ca. 2.5 g/h was achieved for the supported Fe/SBA-15 catalysts in the present system design with a reactor chamber volume of ca. 30 mL. Taking the weight ratio of CNTs/carbon in C2H2 into account, it is estimated that ca. 78% of the C2H2 carbon source were effectively transferred into CNTs. Thus, the methodology reported herein should be useful for industrial applications, particularly in quality control and mass production of CNTs. 4. Conclusion By using mesoporous silica as template and catalyst support, we have demonstrated that high quality CNTs can be fabricated not only with superior yield but also with uniform diameter tailored by the pore size of their template. 5. References [1] Y. Saito and S. Uemura, Carbon, 38 (2000) 169. [2] C. Liu, Y. Y. Fan, M. Liu, H. T. Cong, H. M. Cheng and M. S. Dresselhaus, Science, 286 (1999)1127. [3] E. T. Thostenson, Z. Ren and T. W. Chou, Compos. Sci. Technol., 61 (2001) 1899. [4] R. K. Roy, M. P. Chowdhury and A.K. Pal, Vacuum, 77 (2005) 223. [5] C. T. Kuo, C. H. Lin and A. Y. Lo, Diamond Relat. Mater., 12 (2003) 799. [6] C. J. Lee, S. C. Lyu, Y. R. Cho, J. H. Lee and K. I. Cho, Chem. Phys. Lett., 341 (2001) 245. [7] Y. C. Choi, Y. M. Ghin, Y. H. Lee, B. S. Lee, G. S. Park, W. B. Choi, N. S. Lee and J. M. Kim, Appl. Phys. Lett., 76 (2000) 2367. [8] Z. F. Ren, Z. P. Huang, J. W. Xu, J. H. Wang, P. Bush, M. P. Siegal and P. N. Provencio, Science, 282(1998)1105. [9] W. Z. Li, D. Z. Wang, S. X. Yang, J. G. Wen and Z. F. Ren, Chem. Phys. Lett., 335 (2001) 141. [10] C. H. Kuo, A. Bai, C. H. Huang, Y. Y. Li, C. C. Hu and C. C. Chen, Carbon, 43 (2005) 2760. [11] Z. H. Yuan, H. Huang, L. Liu and S. S. Fan, Chem. Phys. Lett., 345 (2001) 39. [12] D. Zhao, J. Feng, Q. Huo, N. Melosh, G. H. Fredrickson, B. F. Chmelka and G. D. Stucky, Science, 279 (1998) 548. [13] A. Y. Lo , S. J. Huang, W. H. Chen, Y. R. Peng , C. T. Kuo and S. B. Liu, Thin Solid Films, 498(2006)193. [14] C. Y. Mou and H. P. Lin, Pure Appl. Chem., 72 (2000) 137. [15] Y. J. Han, J. M. Kim and G. D. Stucky, Chem. Mater., 12 (2000) 2068.

Recent Progress in Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

413 413

Synthesis of large pore mesoporous carbon using colloidal silica template Huachun Li and Shunai Che* School of Chemistry and Chemical Technology, State Key Laboratory of Composite Materials, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, China.

1. Introduction Recently, Ryoo et al. reported the synthesis of mesoporous carbon by employing mesoporous silicas as templates [1]. The carbons exhibited varieties of pore structures and pore diameters, depending on silica templates that are synthesized with various structures and wall thickness. Usually, these wellordered mesoporous carbons exhibited the pore size smaller than 4 nm arising from the dissolved silica wall. Compared to mesoporous silica, the use of the colloidal silica as template provides another way to fabricate macroporous carbons [2-7]. In this report, we present the synthesis of large pore mesoporous carbon with high surface area and large mesopore volume affected by particle size and pH value of colloidal silica sol. In comparison to small pore mesoporous carbons, these latter carbons should be much more suitable templating media for the "nanocasting" of various materials. 2. Experimental Section The synthesis of large pore meosporous carbon using colloidal silica as template and sucrose as carbon source was performed according the method of Ryoo et al [1]. Snowtex (ST) colloidal silica solutions (Table 1) with different silica particle sizes and pH values were used as sources of porous silica accumulations, provided by Nissan Chemical Ltd. The silica sols with higher pH were stabilized by Na+; Na+ was removed in the silica sol with lower pH; and silica sol ST-AK was stabilized by Al3+. The silica templates and carbon replicas were denoted as S-X and C-X, respectively, where X indicates the colloidal silica sol used.

414

The colloidal sols were evaporated under 373 K for overnight to get the mesoporous silica templates. In a typical synthesis of the mesoporous carbon, the solution of 0.8 g sucrose and 0.08 g H2SO4 dissolved in 6.0 g H2O was added to 2.0 g S-ST-OS silica template. After dried at 373 K for 6 h, raised to 433 K. and kept for 6 h, the silica containing partial carbonizing sucrose was mixed with a clear aqueous solution consisting of 0.48 g sucrose, 0.046 g H2SO4 and 6.0 g H2O. The resultant mixture was dried again at 373 K for 6 h, raised to 433 K and kept for 6 h. The carbon/silica composite sample was then heated to 1173 K for 6 h under N2 flow. The carbon replicas were obtained after the silica removal by using HF solution. 3. Results and Discussion The particle sizes and pH values of colloidal silica sols, pore sizes of the mesoporous silica templates obtained from the corresponding colloidal silica sols, and pore sizes and BET (Brunauer-Emmett-Teller) surface areas of the corresponding large mesoporous carbon replicas are summarized in Table 1. Table 1. Properties of colloidal silica sols, mesoporous silica templates and the corresponding carbon replicas. pH value of silica sol 2.0-4.0

Silica template

Ds (nm)

Carbon replica

Dc (nm)

(m*g-')

ST-OS

Particle size (nm) 8-11

S-ST-OS

1.8

C-ST-OS

6.7

1361.1

ST-S

8-11

9.5-10.5

S-ST-S

2.4

C-ST-S

14.4

1038

ST-O

10-20

2.0-4.0

S-ST-0

3.6

C-ST-O

7.3

1161.7

ST-AK

10-20

4.0-6.0

5.8

C-ST-AK

9.1

1585.8

ST-20

10-20

9.5-10.0

S-STAK S-ST-20

4.3

C-ST-20

14.4

758.7

ST-O40

20-30

2.0-4.0

5.3

13.6

1327.8

ST-50

20-30

8.5-9.5

C-STO40 C-ST-50

20.3

1090.1

Colloid al silica

S-STO40 S-ST-50

6.8

Ds and Dc are the pore size of silica template and carbon replica calculated using BJH method from desorption branch, respectively. S is the BET surface area.

Figure la, b and c show N2 adsorption-desorption isotherms and the corresponding pore size distributions of the different colloidal silica accumulation that obtained from the colloidal silica sols with particle size of 811, 10-20 and 20-30 nm with different pH, respectively. All the samples show type IV isotherms with capillary condensation at relative pressure PlPo = 0.40.8, indicating the presence of mesopores caused by the voids space of silica particles. As expectation, the pore size of silica templates was increased with increasing silica particle size when the silica sols have the same pH value.

415

However, interestingly, the larger pore size of the silica template obtained from higher pH value of silica sol with the same particle size, which caused by the repulsion between the same charged silica particles covered by Na+ in base medium. Among the silica sols with the same particle of 10-20 nm (Fig. lb), SST-AK with middle pH value shows the largest pore size, which would caused by strong repulsion of the silica particles highly charged by Al3+.

80 60 40 1

2 3 4 5 Pore siz e(nm)

6

160

b

3 -1

3 -1

120

100

20

S-ST-O S-ST-AK S-ST-20

Adsorbed amount (cm g , STP)

S-ST-S

120

140

a

S-ST-OS

Adsorbed amount (cm g , STP)

3 -1

Adsorbed amount (cm g , STP)

140

100 80 60 40 20

c

140 120 100 2

80

4 6 8 10 Pore Size(nm)

12

60 40 20

S-ST-O40 S-ST-50

0

0 0

0.2

0.4

0.6

0.8 0.8

Relative pressure pressure P/Po P/Po Relative

1

0

0.4 0.2

0.6 0.4

2

0.81 0.6

4 6 Pore Pore size (nm) (nm) 0.8 size 1

Relative pressure pressure P/Po P/Po Relative

8

0 0

0.2 0.2

0.4 0.4

0.6 0.6

0.8 0.8

11

Relative Relative pressure pressure P/Po P/Po

Fig. 1 N2 adsorption-desorption isotherms and the corresponding pore size distributions of silica templates.

Figure 2 and 3 shows the N2 adsorption-desorption isotherms, the corresponding pore size distributions and scanning electron microscope (SEM) images of the mesoporous carbons synthesized with different colloidal silica templates shown in Figure 1. All the isotherms of the mesoporous carbons show the hysteresis loops at high relative pressures corresponding to type IV behavior, indicating the presence of larger mesopores. The sharpness of the isotherm indicates the narrow pore size distribution. The pore size uniformity was also confirmed by SEM images. Mesoporous carbons with large pore size of 6-20 nm, large surface area of 700-1600 m g"1, and large pore volume of 1.24.4 cm g" have been formed through the carbon replication of mesostructured silicas. As shown in Figure 2 and 3, the pore size of the carbon replicas was increased with increasing silica particle size, when the silica sols with similar pH have been used. On the other hand, interestingly, the larger pore size of carbons has been obtained with higher pH value of silica sol with the same particle size, which is not in agreement with the particle size of the colloidal silicas. The carbon replicas seem quite different based on the nature of the colloidal silica. The pore size larger than particle size of silica has been replicated with colloidal silicas with higher pH value. In the mesoporous carbon synthesized with silica sol having particle size of 10-20 nm in different pH value, C-ST-AK shows the thickest carbon walls than the others, which is consistent with the largest pore size in the silica templates.

416

1000

15 25 35 Pore size(nm)

800 600 400 C-ST-OS

200

1200

3 -1

1200

b

1400

5

1000

15 25 Pore siz e (nm)

35

800 600 400 C-ST-O C-ST-AK C-ST-20

200

C-ST-S

0

0 0

0.2

0.4

0.6

0.8

Relative pressure P/Po P/Po

1

Ad so rb ed amo u n t (cm g , ST P)

3 -1

1400 5

3000

1600

a

1600

Adsorbed amount (cm g , STP)

3 -1

Adsorbed amount (cm g , STP)

1800

0

0.2

0.4

0.6

0.8

Relative pressure P/Po

c

2500 2000 1500 5

1000

15 25 35 Pore size(nm)

500 C-ST-O40 C-ST-50

0

1

0

0.2

0.4

0.6

0.8

1

P/Po Relative pressure P/Po

Fig.2. N 2 adsorption-desorption isotherms and the corresponding pore size distributions of carbon replicas.

Fig.3. SEM images of mesoporous carbons: (a) C-ST-O, (b) C-ST-AK, (c) C-ST-20, (d) C-STO40 and (e) C-ST-50.

4. Conclusion The colloidal silica template presented here was a simple and viable route for the production of large mesoporous carbons with high surface areas and large pore volumes, whose pore sizes can be easily controlled by monitoring the sizes of the silica spheres and the pH value of silica sols. 5. References [1] (a) R. Ryoo, S. H. Joo and S. Jun, J. Phys. Chem. B 103 (1999) 7743. (b) J. S. Lee, S. H. Joo and R. Ryoo, J. Am. Chem. Soc. 124 (2002) 1156. [2] A. A. Zakhidov, R. H. Baughman, Z. Iqbal, C. Cui, I. Khayrullin, S. O. Dantas, J. Marti and V. G. Ralchenko, Science 282(1998) 897. [3] J. Jang and B. Lim, Adv. Mater., 14 (2002) 1390. [4] F. Schuth, Angew.Chem., Int. Ed., 42 (2003) 3604. [5] S. A. Johnson, P. J. Ollivier and T. E. Mallouk, Science, 283 (1999) 963. [6] Z. Li and M. Jaroniec, J. Am. Chem. Soc, 123 (2001) 9208. [7] J. S. Jang, B. K. Lim and M. J. Choi, Chem. Commun. (2005) 4214.

Progress in in Mesostructured Materials Recent Progress S. Qiu, Y. Tang and C. Yu (Editors) (Editors) D. Zhao, S. © 2007 2007 Elsevier Elsevier B.V. B.V. All All rights rights reserved. reserved.

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Study of mercury(II) binding to thiol-modified ordered mesoporous silicas by analytical and electrochemical analyses: influence of the pore structure and the functionalization process Fabrice Gaslain,a Cyril Delacote,b Benedicte Lebeau,a Claire Marichal,a Joel Patarina and Alain Walcarius b " Laboratoire de Materiaux a Porosite Controlee - UMR 7016 - CNRS - ENSCMu Universite de Haute Alsace, 3 rue Alfred Werner, 68093 Mulhouse, France b Laboratoire de Chimie Physique et Microbiologie pour VEnvironnement - UMR 756 CNRS - Universite H. Poincare Nancy I, 405 rue de Vandoeuvre, 54600 Villers-lesNancy, France

1. Introduction During the last decade, an increasing interest has been devoted to the organic pore surface modification of ordered mesoporous siliceous materials [1]. In particular, the high potential of these mesoporous hybrid materials for heavy metal sorption has been demonstrated [2]. Among the ligands available, the widely studied thiol ligand has been chosen as a model Hg(II) sorbent ligand. However, two critical parameters affecting the performance of such hybrid materials in remediation and sensing that are the sorption capacity and the rate of access to the active center have received low attention [2, 3]. MCM-41- and MCM-48-type silicas functionalized with thiol groups by postsynthesis grafting or by direct synthesis have been prepared following a very similar procedure to obtain comparable materials in terms of particle size, morphology and framework. Indeed the aim of this work was to study the influence of the porous network geometry and the functionalization process on the accessibility to the thiol sites and diffusion rates of the Hg(II) species in the mesoporous solids. Their ability to bind Hg(II) species was evaluated from batch experiments and the reaction rate of the uptake process was characterized by applying an electrochemical methodology developed in our group [3].

418

2. Experimental section All the materials were prepared by adapting procedures previously reported [4, 5]. The amount of water was doubled for the preparation of MCM-48 siliceous materials. Direct synthesis was made from a mixture of TEOS and 3mercapto-propyltrimethoxysilane (MPTMS) in the molar ratio 9.1 TEOS: 0.9MPTMS. For post-synthesis grafting, pure siliceous materials [5] were suspended in dry toluene containing MPTMS (1.8 mmol g"1) under reflux for 24 h. Removal of the surfactant was performed by calcination (pure silica materials) or under reflux with a mixture of HC1 and ethanol (direct synthesis of functionalized materials). All hybrid materials were characterized by X-ray diffraction (XRD), nitrogen adsorption-desorption measurements, 29Si and 13C solid state nuclear magnetic resonance (NMR), scanning electron microscopy (SEM), and elemental chemical analysis. The electrochemical method applied to study the rate of access of Hg(II) species to the binding sites was reported earlier [3]. 3. Results and discussions 3.1. Physico-chemical characterization X-ray diffraction patterns (Fig. 1) were characteristic of well ordered hexagonal or cubic pore arrangements (of MCM-41 and MCM-48 types, respectively). Nearly spherical particles with an average diameter of 0.5 um were observed for all samples by SEM (Fig. 2). For all surfactant extracted solids, the nitrogen adsorption-desorption isotherms were of type IV characteristic of mesoporous materials. In all cases a sharp pore size distribution was observed with an average BJH pore size of 2.5-3 nm (Table 1). Whatever the type of material and the functionalization process, distinct resonances characteristic of the silica network [Qn = Si(OSi)n(OH)4.n, n = 2-4] and of the Table 1. Some physico-chemical date for thiol-functionalized materials. Material

Surf, area

Pore vol.

Pore0

SH groups

Hg" binding (mmol g"1)

type

/mV

/mL g 1

/mmol g"1

pH2

pH4

0.9

0.7

0.9

MCM41-SHgr

839

0.60

MCM41-SHM

1550

0.76

/nm 2.8 2.6

1.4

1.3

1.5

MCM48-SHgr

938

0.68

2.9

0.9

0.8

1.0

MCM48-SHC

941

0.58

2.9

1.4

1.2

1.4

m

organosiloxane network [T = RSi(OSi)m(OH)3.m, m=l-3] after functionalization were observed by 29Si MAS NMR. The presence of the T units (ca. 10%) confirms that the functionalization was successful. Post-synthesis grafted sample showed a more condensed silica network but a lower condensed

419

Intensity (a.u.)

organosiloxane network (due to extraction and functionalization processes, respectively). 13C CP-MAS NMR confirms that 3-mercaptopropyl groups are present as intact organic moieties.

40000

(a) (b) (c) (d) 2

3

44

5

2 θθ (degree)

6

7

Fig. 1. XRD patterns of MCM-41 (a,b) and MCM-48 (c,d) materials obtained by direct synthesis: pure silica (a,c) and mercaptopropyl-functionalized solids (b,d).

Fig.2. SEM pictures of MCM-41 (a,b) and MCM-48 (c,d) materials obtained by direct synthesis: pure silica (a,c) and mercaptopropyl-functionalized solids (b,d).

3.2. Mercury(II) accumulation The uptake of mercury(II) by these thiol-functionalized materials was studied at two pH values (i.e., 2 & 4). A complete accessibility was observed at pH 4 where Hg(II) species are in the form of Hg(OH)2. A less complete filling (Table 1) was obtained when performing the uptake experiments at pH 2 where Hg(II) species are in the form of Hg2+. Because Hg2+ binding to thiol groups involves the formation of a positive charge, this results in significant repulsive electrostatic interactions in the mesopore channels [2d], which could contribute to explain the restricted access of Hg2+ to the binding sites. The speed of this binding reaction was not very much affected by the structure of the materials, yet displaying slightly faster processes in materials with a hexagonal mesostructure (Fig. 3). For materials having approximately the same structure (hexagonal or cubic), the hybrids obtained by post-synthesis grafting were characterized by uptake reaction rates higher than their homologues obtained by the one-step co-condensation route, especially at the early beginning (<20% filling) of the binding process and at higher (>50-70%) filling levels. This is probably due to the fact that the grafting would preferentially occur at the mesopore entrance, resulting in a greater density of binding sites at the boundaries of the particles, while a somewhat more homogeneous distribution of the organo-functional groups is thought to occur in mesoporous hybrids obtained by co-condensation. In this last case, a higher amount of Hg2+ species

420

must diffuse deeply in the bulk of the particle and 100% filling occurs in several hours, while this binding capacity was observed in less than 10 min for grafted adsorbents (Fig. 3).

100

Time (s)

200

300

100

500

Time (s)

Fig.3. Evolution of reaction rates for Hg2+ binding to thiol functionalized MCM-41 (A) and MCM-48 (B) materials (Q/Qo represents the extent of uptake which is equal to 1 at 100% binding): (a) post-synthesis grafted solids, (b) in situ functionalized adsorbents. Insets represent the variations of apparent diffusion coefficients (Dapp) with Q/Qo-

4. Conclusion MCM-41 and MCM-48 organized mesoporous silicas were functionalized by mercaptopropyl groups using two routes: post synthesis treatment of pure silica and direct functionalization by a co-condensation procedure. 29Si NMR showed that the functionalization process lead to different T and Q condensed units. The reaction rates of Hg2+ binding are faster for the post-synthesis grafted samples, especially at high uptake levels. Such a result suggests that grafting would preferentially occur at the mesopore entrance, resulting in a greater density of binding sites at the boundaries of the particles. 5. References [1] A. Stein et al. Adv. Mater. 12 (2000) 1403; b) A. Vinu et al. J. Nano. Nanotechnol. 5 (2005) 347. [2] X. Feng et al. Science 276 (1997) 923; b) L. Mercier, T. Pinnavaia, Adv. Mater. 9 (1997) 500; c) J. Brown et al. Microporous Mesoporous Mater. 37 (2000) 41; d) A. Walcarius et al. Anal. Chim. Acta 547 (2005) 3. [3] A. Walcarius et al. Chem. Mater. 14 (2002) 2757; b) A. Walcarius et al. Chem. Mater. 15 (2003) 2161; c) A. Walcarius et al. Chem. Mater. 15 (2003) 4181. [4] M. Etienne et al. New J. Chem. 26 (2002) 384. [5] M. Grun et al. Microporous Mesoporous Mater. 27 (1999) 207.

Mesostructured Materials Recent Progress in Mesostructured D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

421 421

The effect of inorganic salt on the synthesis of large-pore PMO with aromatic moieties in the framework Sung Soo Park, Booyoun An, Yunji Kang, Mina Park, II Kim and Chang-Sik Ha* Department of Polymer Science and Engineering, Pusan National University, Busan 609-735, Korea

We report on the effect of inorganic salt on the synthesis of large-pore PMO materials with aromatic groups inside the channel wall. The triblock copolymer template with the aid of inorganic salt could provide a new method to prepare large-pore mesoporous organosilica material with hollow sphere morphology. By adding inorganic salt in reaction mixture, we have successfully controlled ordered structure, morphology, wall thickness, and pore size of PMO with aromatic moieties in the framework. 1. Introduction Periodic mesoporous organosilica (PMO) materials with organic groups inside the channel walls [1] provide new opportunities for controlling the chemical, physical, mechanical properties of the materials. Inorganic salts have been used to improve the hydrothermal stability, control the morphology, extend the synthesis domain, and tailor the framework porosity during the formation of mesoporous materials, via self-assembly interaction between surfactant head groups and inorganic species. Previous studies have shown that the reaction conditions, inorganic salts and solvent-assistance play important roles in controlling the morphology of mesoporous silicas [2, 3]. Guo et al. [4] and Qiao et al. [5] reported synthesis of PMOs with highly ordered mesostructure, rod- and plate-like morphologies using ethane-bridged organosilica precursor with the assistance of inorganic salts. In this work, we report on the effect of inorganic salt for the synthesis of large-pore PMO with hollow sphere morphology, controllable pore size and wall thickness, ordered structure, and aromatic moiety in the framework.

422

2. Experimental Section The PMO materials were synthesized using the following reactant molar ratios [2]: 0.6 for (EtO)3SiC6H4Si(OEt)3 (BTES-benzene) and (EtO)3Si(C6H4)2(OEt)3 (BTES-biphenyl)} : 0.017 P123 : 0-6.08 NaCl : 5.07 HCl : 178 H2O. The reactant solution was stirred at 40 °C for 24 h and heated at 80 °C for 24 h. Template in PMO material was removed by solvent-extraction with HC1EtOH solution. Small angle X-ray scattering (SAXS) was performed at Pohang Accelerator Laboratory (PAL), Korea with Co-Ka (A, = 1.608 A) radiation. Nitrogen adsorption and desorption isotherms were measured at -196°C using a NOVA 4000e instrument. Scanning electron microscopy (SEM) images were obtained using a Hitachi E-1010 sputter coater prior to imaging. Transmission electron microscopy (TEM) images were obtained using a JEOL JEM-2010 microscope operating at 200 kV. 3. Results and Discussion

0.2 0.4 0.6 0.8 Relative pmssure(P/J'o)

Fig. 1. TEM images of BTES-benzene (a and b) and BTES-biphenyl (c and d) synthesized without (a and c)and with (b and d) NaCl in reaction mixture.

Fig. 2. N2 adsorption-desorption isotherms of (A) BTES-benzene and (B) BTES - biphenyl synthesized using different content of NaCl in the range from 0 to 6.08 in reaction mixture.

Fig. 1 shows TEM images of PMO materials synthesized with bridged organic groups such as benzene and biphenyl in the framework using the nonionic triblock copolymer Pluronic PI23 as template with and without inorganic salt in reaction mixture. PMO materials synthesized with the aid of inorganic salt have huge hollow spherical morphologies with the smaller mesopores in shell, as shown in TEM images of Fig. l(b) and (d). Inorganic

423

salts can reduce the solubility (salting-out effect), critical micellar concentration, critical micellar temperature, and the cloud point of the block copolymers, and can also decrease the thermodynamic radius of the micelles [6]. In this work, formation of huge hollow spherical morphologies can be attributed to the lower solubility of micelles' solution by the addition of inorganic salt in reaction mixture. Table 1. Textural properties ofPMO materials with aromatic moieties in framework synthesized using reactant composition with different content of inorganic salt. Sample BTES -benzene

BTES -biphenyl

NaCl ratios in reaction mixture 0 2.54 4.06 6.08 0 2.54 4.06 6.08

dioo

(A) 113.0 117.4 138.4 139.9 125.7 128.2

Wall thickness* (A)

(m2g')

29.8 49.2 48.9 45.9 46.1

1964 1277 1332 1385 1497 1245 1557 1320

SBET

Primary pore (A)

Secondary pore (A)

30-800 57.8 40.0 42.2

188 169 152 15-800

33.6 33.9 36.0

148 147 142

Total pore volume 1.07 1.85 1.51 0.75 1.10 0.92 1.26 1.05

Wall thickness = ao-primary pore size, ao=2dioo/V3.

Table 1 shows textural properties of PMO materials with aromatic moieties in framework synthesized using reactant composition with different content of inorganic salt. The formation of secondary pores can be attributed to the aggregated particles based on nanosized particles and hollow spheres. The analysis of N2 adsorption-desorption isotherms clearly exhibited the strong adsorption at relative pressure (P/Po) close to 1.0, as shown in Fig. 2. BTESbenzene and BTES-biphenyl samples synthesized without NaC 1 have broad pore size distribution in the range of 30-800 A and 15-800 A, respectively. On the other hand, BTES-benzene and BTES-biphenyl samples synthesized with NaCl containing reactants have hollow sphere morphologies with narrow pore size distribution. The result is explainable based on the fact that inorganic salt plays an important role in the increased interaction between organosilane species and dehydrated PEO end blocks and the decreased solubility of triblock copolymer solution in water [4, 6]. The addition of inorganic salt causes dehydration of ethylene oxide units from the hydrated PEO shell remaining adjacent to the PPO core, leading to an increase in the hydrophobicity of the PPO moieties and a reduction in the hydrophilicity of the PEO moieties [4, 6]. For both the BTES-benzene and BTES-biphenyl samples, the secondary pore size was decreased from 188.0 to 151.5 A and from 148.3 to 142.0 A with increasing NaCl contents. It is due to the decrease in the micelles' size on adding salt, leading to the decrease of aggregated nanoparticle size[7]. In case

424

of the BTES-benzene samples, with the different content of NaCl in reactant, primary pore size changed from 57.8 A to 40.0 A. It is also due to the increase of interaction between hydrophobic benzene-group containing organosilane and dehydrated PEO shell. BTES-benzene sample synthesized with 6.08 NaCl ratio have slightly higher primary pore size than that of 4.06 NaCl ratio. It may be attributed to the increase of micelle diameter by the existence of surplus salt layer around triblock copolymer micelles. Increment of primary pore size for BTES-biphenyl sample synthesized with 6.08 NaCl ratio can be explained with the same reason. With the different NaCl content, surface area and total pore volume of BTES-benzene and BTES-biphenyl samples were 1964.0 m g' 1 1277.0 m2g"\ 1245 - 1557.0 m2g"' and 1.85 - 0.746 cm3g"\ 0.919 - 1.260 cm3g" ', respectively. 4. Conclusion The triblock copolymer template with the aid inorganic salt could provide a new method to prepare bridged aromatic moieties containing PMO hollow spheres. Hollow sphere, permeable shell, large pore size, high adsorption capacity of the samples may be useful as the solid nanocapsules for drug delivery, DNA therapy application, immobilization of hydrophobic enzymes, and bio-catalyst. 5. Acknowledgment This study was supported by the National Reserch Laboratory Program, the SRC/ERC program of MOST/KOSEF (Rl 1-2000-070-080020) and the BK21 Project. Thanks to the Pohang Accelerator Laboratory for SAXS measurements. 6. References [1] [2] [3] [4]

T. Asefa, M. J. MacLachian, N. Coombs and G. A. Ozin, Nature, 402 (1999) 867. C. Z. Yu, J. Fan, B. Z. Tian and D. Y. Zhao, Chem. Mater., 16 (2004) 889. C. Z. Yu, J. Fan, B. Z. Tian, D. Y. Zhao and G. D. Stucky, Adv. Mater., 14 (2002) 1742. (a) W. Guo, I. Kim and C.-S. Ha, Chem. Commun., (2003) 2692. (b) W. Guo, J.-Y. Park, M.-O. Oh, H.-W. Jeong, W.-J. Cho, I. Kim and C.-S. Ha, Chem. Mater., 15 (2003) 2295. [5] S. Z. Qiao, C. Z. Yu, Q. H. Hu, Y. G. Jin, X. F. Zhou, X. S. Zhao and G. Q. Lu, Micropor. Mesopor. Mater., 91 (2006) 59. [6] W.-H. Zhang, L. Zhang, J. Xiu, Z. Shen, Y. Li, P. Ying and C. Li, Micropor. Mesopor. Mater., 89 (2006) 179. [7] C. Booth and D. Attwood, Macromol. Rapid Commun., 21 (2000) 501.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

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Bovine serum albumin adsorption in large pore amine functionalized mesoporous silica S. Z. Qiao,a* Haiying Zhang,a Xufeng Zhou,ab Sandy Budihartonoa and G. Q. Lua* "ARC Centre for Functional Nanomaterials, The University of Queensland, St Lucia, QLD 4072, Australia h Department of Chemistry, Fudan University, Shanghai 200433, P.R.China

1. Introduction Ordered mesoporous materials with functionalized groups are promising for many emerging applications in adsorption separation, enzyme immobilization, bio-catalysis, drug delivery and sensors [1-3]. Some studies reported that the adsorption of proteins on mesoporous solids was size selective and the small entrance sizes of mesoporous materials may limit their applications in the processes involving large protein molecules [4, 5]. Meanwhile the loading amount of proteins was strongly influenced by the functional surface of materials and the adsorption conditions such as pH and ionic strength of solution [2, 3, 6]. Recently, the mesoporous silica FDU-12 with very large pore size (>20 nm) was successfully synthesized by a low temperature strategy using nonionic block copolymer as template [7]. The large entrance size of the material provided great advantages in the adsorption and diffusion of protein [8]. However, to the best of our knowledge, there have been no reports on the synthesis of hybrid mesoporous silica with very large pore by the low temperature strategy and their protein adsorption so far. Here we report a low temperature synthesis of highly ordered amine functionalized mesoporous silica with very large pore size. BSA was selected as model protein to study the effect of functional surface, entrance size and pH on the adsorption capacities. 2. Experimental Section In a typical synthesis, 0.5 g of triblock copolymers EOi06PO70EOi06 (Pluronic F127), 2.5 g of KC1 and 0.6 g of trimethylbenzene (TMB) were dissolved in 30

426

g of 2 M HC1 at 15 oC for 6 hours. The mixture of 1.97 g tetramethyl orthosilicate (TEOS, 99%, Fluka) and 0.14 g of 3-aminopropyl-triethoxysilane (APTES, 99%, Aldrich) was then added to the solution under stirring. The final reactant molar composition Si/F127/TMB/KCl/HCl/H2O was 1.00/0.0037/0.50/ 3.36/6.00/155. After being stirred for 24 hours at 15°C, the solution was transferred into an autoclave and heated at 100°C for 24 h. The as-made sample was collected by filtration. The sample was washed by 100 ml of ethanol and 5 ml of 2M HC1 at 60°C for two times to remove the templates and denoted as N100. For the 140°C hydrothermal treatment, as-made sample was added to a solution of 30 ml 2 M HC1 in an autoclave and heated at 140°C for another 48 h. The resulting product was obtained by filtration and washed by the mixture of ethanol and HC1 as mentioned above. The sample was denoted as N-140. Adsorption isotherm of BSA (Sigma Aldrich) was measured by batch experiments performed in a water bath at 25 °C. 50 mg of solid degassed under vacuum at 120°C was put in 5ml of BSA solution with different concentrations (from 0.5 to 15.0 g/L, acetic buffer of pH 3.4 or 4.7). The mixture was left in a shaker operating at 180 rpm for 24h, which was confirmed to reach equilibrium. The samples were centrifuged and filtered through cellulose nitrate membrane filters, and the equilibrium concentration of protein in the supernatant liquid was diluted and analyzed using UV-Vis spectrophotometer at 280 nm. The amount adsorbed on solids was determined by the mass balance of the protein.

331 3 31

N-140 33 3 44 2

31 1

0.5

(a)

1.0 , -11) q (nm

N-100 1.5

2.0

Amount Adsorbed (cm3 STP g-1)

0.0

31 1

111

111

3. Results and Discussion

|

1200

(b) 800 N-140 400 N-100 0 0.0

0.2 0.4 0.6 0.8 Relative Pressure Pressure (p/p (p/poo) Relative

1.0 1.0

Fig. 1 SAXS traces (a) and nitrogen adsorption isotherms (b) of samples synthesized using different hydrothermal temperatures

Figure la shows the small angle X-ray scattering (SAXS) patterns of surfactantextracted amine functionalized mesoporous silicas. Five well-resolved peaks of sample N-l 00, which can be exactly indexed to the 111,311,331, 333 and 442 reflections, indicate that it is a highly ordered Fm3m fee structure. The SAXS pattern of sample N-140 shows three well-resolved peaks at least. High peak intensity and resolution of peaks can be attributed to the regularity of porous materials. The cell parameters of N-100 and N-140 are 31.2 and 36.4 nm respectively. The transmission electron microscopy (TEM) images of samples N-100 and N-140 are shown in Figure 2, which confirms their highly ordered

427

mesostructure. The nitrogen adsorption and desorption isotherms are shown in Figure lb. The cavity size and entrance size can be determined from the adsorption and desorption branches of the isotherms respectively by BdB model. Our study revealed that the entrance sizes of materials were enlarged from 5.8 nm to 10.4 nm by increasing the hydrothermal treatment temperature from 100 to 140°C. Meanwhile the cavity sizes also increased from 19.0 to 27.9 nm. The cavity size, entrance size, BET surface area (calculated using adsorption data in a relative pressure range p/p°=0.05-0.25) and pore volume (estimated from the adsorbed amount at a relative pressure of about 0.99) are summarized in Table 1. For comparison, the structural parameters of large pore mesoporous pure silica (b)

Fig. 2 TEM images of samples synthesized using different hydrothermal temperature (a) 100 °C (b) 140 °C.

(denoted as S-140), synthesized according to the reference 7 with 140°C hydrothermal treatment, are also listed in Table 1. Table 1. Physicochemical properties of samples Unit cell

Cavity size

Surface area

(nm)

Entrance size (nm)

Pore volume

(nm)

(cmV1)

(mV)

N-100

31.2

19.0

5.8

0.826

441.2

N-140

36.4

27.9

10.4

1.146

482.4

S-140

40.2

36.3

13.0

0.917

239.3

Sample

Figure 3 shows the adsorption isotherm of BSA on different samples. All isotherms show a sharp initial rise and then reach maximum adsorption amounts, suggesting that isotherms are of Langmuir type. It can be seen that the adsorbed amount of BSA on N-140 (entrance size 10.4 nm) reaches to 222.0 mg/g, much higher than the adsorbed amount (60.4 mg/g) on sample N-100 (entrance size 5.8 nm). BSA is a large protein (the size is 4*4*14 nm) and can not enter the pore smaller than 4 nm. However it may undergo orientation adjustment and adapt its long axis to be parallel to the pore axis to enter into the pore larger than 4 nm [5]. Moreover, BSA molecules can be adsorbed on the external

428

Amount Adsorbed (mg/g)

surface of the material. Our study reveals 300 that the entrance size of sample affects "5) N-140,pH 4.7 N-140,pH4.7 the adsorbed amount significantly. 200 Comparing with BSA adsorption on the amine functionalized surface (N-140), the S-140,pH S-140,pH 4.7 adsorbed amount on pure silica FDU-12 < 100 (S-140) is significantly decreased (79.0 N-100,pH 4.7 N-100,pH4.7 N-140,pH3.4 N-140,pH 3.4 mg/g) although it has larger entrance 0 sizes. It indicates that amine functional 0 3 6 9 12 15 12 15 groups improve BSA adsorption. The Equilibrium Concentration (mg/ml) reason is probably the hydrophobic surface of amine functional silica which Fig. 3 Adsorption isotherm curves of BSA. The solid lines are fitting results of is beneficial to the adsorption of BSA. The adsorbed amount of BSA on the the Langmuir equation. sample N-140 at pH 3.4 (15.9 mg/g) is much lower than the adsorbed amount of 222.0 mg/g at pH 4.7 (isoelectric point of BSA, 4.7-4.9). It is believed to be largely due to the strong electrostatic repulsion between positively charged BSA and amine groups as well as among BSA molecules at pH 3.4. 4. Conclusion In this study we investigated the adsorption of BSA on the large pore amine functionalized mesoporous silica synthesized by a low temperature strategy. The BSA adsorption capacity was found to be highly dependent on the entrance size of materials and surface properties. The modification of the inner surface with amine group can enhance its interaction with BSA and improve the protein adsorption. The adsorbed amount of BSA is higher at its isoelectric point and the electrostatic and hydrophobic interactions are dominative forces in the BSA adsorption on amine functionalized silica surface. 5. References [1] [2] [3] [4] [5] [6] [7] [8]

J. Y. Han, G. D. Stucky and A. Butler, J. Am. Chem. Soc, 121 (1999) 9897. H. H. P. Yiu and P.A. Weight, J. Mater. Chem., 15 (2005) 3690. M. Hartmann, Chem. Mater., 17(2005) 4577. H. H. P. Yiu, C. H. Botting, N. P. Botting and P. A. Weight, Phys. Chem. Chem. Phys., 3 (2001)2983. S. W. Song and K. Hidajat, Langmuir, 21 (2005) 9568. S. Z. Qiao, C. Yu, W. Xing, Q. H. Hu, H. Djojoputro and G. Q. Lu, Chem. Mater., 17 (2005)6172. J. Fan, C. Yu, J. Lei, Q. Zhang, T. C. Li, B. To, W. Zhou and D. Y. Zhao, J. Am. Chem. Soc, 127 (2005) 10794. J. Fan, C. Yu, F. Gao, J. Lei, B. Tain, L. Wang, Q. Luo, B. Tu, W. Zhou and D. Y. Zhao, Angew. Chem. Int. Ed., 42 (2003) 3146.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

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Effect of various templates on the formation of mesoporous benzene-silica hybrid material K.-F. Zhou a , Q.-H. Xia a '*, H.-B. Zhu a , D. Hu a and Z.-M. Liu b * a

Ministry-of-Education Key Laboratory for the Synthesis and Application of Organic Functional Molecules, Hubei University, Wuhan 430062, China b Dalian Institute of Chemical Physics, Academia Sinica, Dalian 116023, China.

The chain length of the template seriously affected the formation of mesoporous benzene-silica hybrid material from a basic medium under our experimental conditions. Only Ci6 surfactant could template a PMO solid with XRD peaks at low angles of 26 = 2.0, 3.6, 4.2°, similar to those of ordered MCM-41. PMO materials could not be formed by [CnH2n+i(CH3)3N+, n=8, 12, 22] and [(CnH2n+i)4NOH, n = 2, 4], but the recovered organosilica solids possessed similar infrared framework vibrations and XRD peaks at high angles of ca. 20=11.5, 23.4, 35.4°. In an acidic medium mesoporous benzene-silica hybrid materials could be mediated by [CnH2n+i(CH3)3N+, n=12, 16], in which C ]6 templated a 3D-cage like mesopore structure, similar to SBA-1. Keywords: mesoporous benzene-silica, PMO, MCM-41, SBA-1 1. Introduction Inagaki et al. reported the surfactant-mediated synthesis of a benzene-silica hybrid PMO material in 2002 [1]. Since then, much effort has been focused on the research of various organic-inorganic hybrid periodic mesoporous organosilicas (PMO) using some organic silicate esters as starting materials [2]. Those PMO materials are thought to consist of crystal-like wall structures, as evidenced mainly by XRD patterns, where additional four sharp peaks emerge at d=1.6, 3.8, 2.5 and 1.9 A (29 = 10-70°), different from those of MCM-41. The literature proposed that the self-assembly of organosilane BTEB molecules formed the periodic structure in the walls of the mesoporous benzene-silica, probably because hydrophobic and hydrophilic interactions directed the selfassembly of BTEB molecules [1]. Our present results show that the formation

430

of mesoporous benzene-silica hybrid solid in a basic medium could be similar to that of MCM-41, while in an acidic medium similar to that of SB A-1. 2. Experimental Section The used alkyl ammoniums included [CnH2n+i(CH3)3NBr, n=8,12,16,22] and [(CnH2n+i)4NOH, n=2,4) ], and organosilica source was 1,4-bis(triethoxysilyl) benzene (BTEB, 98 wt%, self-made [3]). The synthesis of PMO in a basic medium was carried out in the following procedure. Appropriate amount of surfactant was first dissolved in the solution consisting of 120 g of distilled water and 7 ml of 3 M aqueous NaOH at 25°C. While stirring vigorously, 3.24 g of BTEB was well dispersed into the basic solution. The molar composition was 0.806BTEB: 0.63surf.: 2.1NaOH : 667H2O. The stirring was continued for another 24 h, then the suspension was statically refluxed at 90°C for a period of 72-240 h. Thereafter, the white solid was recovered by filtration, washed repeatedly with distilled water, and dried at 100°C overnight. The surfactant molecules were removed by extraction through stirring the as-prepared solids in the solution of 200 ml ethanol and 6 ml concentrated HC1 (36%) at60°C for 6 h, followed by filtration and drying at 80 °C for 5 h. This extraction was repeated twice. In an acidic medium mesoporous benzene-silica materials were synthesized in the presence of [CnH2n+i(CH3)3N+, n=12,16]. Under stirring the surfactant was dissolved in the solution consisting of 10 ml concentrated HC1 and 36 ml water at 0, 23, 30 and 60°C, respectively. While stirring vigorously, 2.25 g of BTEB was dispersed into the acidic solution. The molar composition was 5.6BTEB: 3.3surf.: 323.6HC1: 2000H2O. The stirring was continued for another 24 h, and then the suspension was statically aged for 72 h at 0, 23, 30 and 90 °C, respectively. Finally, the recovered solid underwent identical treatments as described above. All the solid samples were well characterized by XRD, IR, BET, TEM and 13C CP MAS NMR techniques. 3. Results and Discussion In a basic medium the addition of Ci6H33(CH3)3N+ achieved benzene-silica PMO material, while the use of both [CnH2n+,(CH3)3N+, n=8,12,22] and [(CnH2n+i)4NOH, n=2,4] did not yield any mesoporous solid. Figure 1 compares XRD patterns and IR spectra of six solids templated by [CnH2n+i(CH3)3N+, n=8,12,16,22] and [(CnH2n+i)4NOH, n=2,4] in the basic medium, in which six samples show similar IR framework vibrations. The sample synthesized with Ci6 exhibits an XRD pattern of highly ordered PMO solid, but others mediated by Cg, C12, C22 and [(CnH2n+04NOH, n=2,4] do not show any mesoporous characteristic. These samples show similar diffraction peaks at high angles of ca 20=11.5, 23.4 and 35.4°, while the PMO induced by Q 6 contains diffraction peaks at low angles of 26= 2.0, 3.6 and 4.2°, similar to ordered MCM-41.

431 C-22 5000 5000 -

C-16

Intensity /cps

SB 4000 -

C-12 C-8

' 3000 3000 -

C-4 C-2

C-16 C-22 C-12 C-8

2000 1000 1000 -

4000 400 4000 3600 3600 3200 3200 2800 2800 2400 2400 2000 2000 1600 1600 1200 1200 800 800 400

0 0

-1 WAVENUMBER / / cm-1

C-4

C-2 5

10

15 15

20 25 20 25 2θ 2θ/°/°

30

35

40

Figure 1. Effect of basic medium on IR spectra and XRD patterns of samples. -Ph-Ph* band * Side band

*

ULU *

*

300 300

250 250

200 200

150 150

100 100 ppm ppm

50

0

-50 -50

Figure 2. 1 3 C CP MAS NMR spectrum. 13/-

Figure 3. TEM image of 3D-cage pore.

C CP MAS NMR spectrum of thus-synthesized PMO solid contains only one signal at 133.2 ppm, with some side bands, due to the phenylene carbon (Fig. 2). The formation of benzene-silica PMO solid from a basic medium was affected by the chain length of the template. The PMO solid induced by C 1 6 had well-defined mesopores averaging 31 A, a pore volume of 0.46 cm3/g, and a surface area of 858 m2/g. Surface area (m2/g) and pore volume (crnVg) of other organosilica solids were (342.8, 0.18)for C 22 , (595.6, 0.62)for C 12 , (233.2, 0.35) for C8, (541.2, 1.17) for (C4H9)4NOH, (504.4, 0.93) for (C 2 H 9 ) 4 NOH without detectable mesopore. This seems to indicate a possible mechanism, i.e. BTEB molecules were first hydrolyzed by aqueous base to form negatively-charged benzene-silica hybrid colloidal particles with a certain degree of polymerization, which then surrounded positively-charged rod-like micelles in the solution to array hexagonally into integrated mesoporous framework.

432 C-16 (60°C, (60°C, 90°C)

^f

5000

Intensity/cps

^T\

C-16 (30°C, 30°C) C-16 (0°C, 30°C)

4000 . 4000

C-16 (0°C, 0°C) C-12 (23°C, 23°C)

3000

°C) C-16 (30°C, 30 C-16(30°C, 30°C) C-16(0°C, C-16 (0°C, 00°C) °C) C-16(0°C, 30°C) C-16 (0°C, 30 °C) C-16 (60 (60°C, 90°C) C-16 °C, 90 °C) C-12 °C, 23 °C) C-12 (23 (23°C, 23°C)

2000 • 1000 1000 •

4000 3600 400 4000 3600 3200 3200 2800 2800 2400 2400 2000 2000 1600 1600 1200 1200 800 800 400 -1 WAVENUMBER/cm WAVENUMBER /cm-1

0 0 0

2

4

6

8

10

2θ /° 2θ/°

Figure 4. Effect of acidic medium on IR spectra and XRD patterns of samples.

In an acidic medium mesoporous benzene-silica hybrid materials could be formed in the presence of d e ^ C F t ^ N * and Ci2H25(CH3)3N+. After the removal of tern plate molecules by extraction, the sample templated by Ci6 exhibits three diffraction peaks at low angles of ca. 20 = 2.02, 2.24, 2.44°, similar to those of a 3D-cage SBA-1, obviously different from that induced by Cn with only a broad XRD peak at ca. 2.92° 20 (Fig. 4). IR spectra in Fig. 4 show the similarity of their infrared framework vibrations, and the difference from those in Fig. 1. The use of C]6 was beneficial to the formation of benzenesilica solid from an acidic medium, which was evidenced by TEM image in Fig. 3. This material possessed a 3D-cage like pore structure [4], with a pore size of ca. 28 A, a pore volume of 0.31 cm /g, and a surface area of 529.3 m /g. 4. Conclusion The formation of mesoporous benzene-silica solid from a basic medium was affected by the chain length of organic templates, in which only Ci 6 effectively templated a PMO solid with XRD peaks at low angles of 20 = 2.0, 3.6, 4.2°, similar to those of ordered MCM-41. Six samples displayed similar diffraction peaks at high angles of ca. 2#=11.5, 23.4, 35.4°, which seems to propose the similarity of formation processes of PMO and ordered MCM-41 in the basic solution. In an acidic medium mesoporous benzene-silica materials could be mediated by [CnH2n+i(CH3)3N+, n=12,16], in which only Ci6 templated a 3Dcage like mesopore structure similar to SBA-1. 5. References [1] [2] [3] [4]

S. Inagaki, S. Guan, T. Ohsuna and O. Terasaki, Nature, 416 (2002) 304. F. Fajula and F. Di Renzo, Microporous Mesoporous Mater., 82 (2005) 227. K. J. Shea, D. A. Loy and O. Webster, J. Am. Chem. Soc, 114 (1992) 6700. Y. Goto and S. Inagaki, Microporous Mesoporous Mater., 89 (2006) 103.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

433 433

Synthesis of layered organosilica binding with selfassembled LB film Takayuki Chujo,a Yu Gonda," Yasunori Oumi,* Tsuneji Sano * and Hideaki Yoshitakea " Division of Materials Science and Chemical Engineering, Graduate School of Engineering, Yokohama National University, 79-5 Tokiwadai,Hodogaya-ku Yokohama 240-8501, Japan b Department of Applied Chemistry, Graduate School of Engineering, Hiroshima University, 1-3-2 Kagamiyama, Higashi-Hiroshima 739-8511, Japan.

We synthesized a layered organosilica whose interlayer is a micelle of alkanoic acid. The bond between carboxylate and 3-aminopropylsiloxane is critical for the formation of the layered structure. The micelles can be exchanged with carboxylic acids with a different chain length to form a lamellar structure with the corresponding basal spacing. 1. Introduction Mesostructured organosilicas have extensively been studied since the discovery of synthetic routes of ordered mesoporous silica with the aid of selfassembly of surfactant molecules [1, 2]. This has been a success due to the utilization rod-like micelles. On the other hand, one of the most widely studied self-assembled structures of amphiphilic molecules is Langmuir or LangmuirBlodgett film, which has been recognized as a versatile and stable layered structure. If a cationic organosilane can be polymerized with the ionic interaction with film-like carboxylate micelles, the resulting "solid" will have an extremely high density of anionic and cationic sites. Such mesostructured silicate will theoretically provide the densest functional groups, all of which could work without mutual interference. In this study, we report how to synthesize a layered organosilica binding with self-assembled LB film and how to control the layer distance by interlayer exchanges.

434

2. Experimental Section The surfactant used in this study were in the form of CnH2n+iCOONa: laurate (LAS, n=l 1), myristate (MAS, n=13), palmitate (PAS, n=15) and stearate (SAS, n=17). The surfactant was dissolved in ethanol-water at 333 K by continuously stirring. 3-aminopropyltriethoxysilane (APTES) was added dropwise into the solution. The molar ratio of the reactants were 1 surfactant: 1 APTES: 180H2O: 20 EtOH (40EtOH for SAS). This mixture was kept in stirring at room temperature (for LAS) or at 333 K (for the other surfactants) for lh before the addition of 0.1 M HC1 to adjust pH (= 10) of the solution where the initial pH = 11. The mixture was then heated at 373 K for 2 d. The product was dried in air at 373 K. This organosilica composite is hereafter denoted as SiOi 5-X (X: carboxylate), because the formula of these products was determined to be CnH2n+iCOOHNH2C3H6SiOi.5. With caprylate and decanoate (n=7 and n=9, respectively), no precipitate was formed. To exchange the surfactant interlayer, the reactant mixture without APTES was added to a SiOi 5-X and was stirred under reflux condition for a certain time. The solid was filtrated, dried at 373 K and the lattice constant was measured by XRD. 3. Results and Discussion Figure 1 shows the time evolutional XRD patterns of SiOi 5-PAS in the course of drying. The pattern with peaks at 2.4, 3.0, 3.5, 4,6, 6.8, 9.1 and 11.2'o for the solid after 6 h-drying suggests the formation of a phase mixture. Although the number of peaks decreased, new peaks emerged until 2 d. Finally, the pattern conversed into a lamellar structure with 29 = 2.5, 5.0 and 6.9°. This complicated change implies that several stable phases exist near the most stable one, which shows a typical lamellar pattern. The degree of condensation in the final product is nearly 100 %, revealed by 29Si-MAS NMR, and it is likely that the formation of siloxane network is closely related to these phase changes. This mode of growing was more or less observed in all SiOi 5-X. With the Bragg's formula, the basal spacings were calculated for the XRD pattern of each product. The result was plotted against (h2+/^+l2)'05 in Figure 1, where h=\, 2, 3, 4 and 5 and &=/=0. (For LAS and MAS, h=\,2 and 3 due to the absence of higher diffractions.) The af-value decreased linearly for all XRD patterns, showing the formation of a series of lamellar structures. In fact, when dm is determined in Figure 1 and plotted against n, all dm is well explained with the equationrfioo(/nm)=1.082 + 0.166«. This linearity demonstrates that the layer distance increases at the same ratio with the number of carbons in alkanoate. If all carbons in the alkyl chain are in the anti- conformation and the chain is normal to the layer plane, the increase ratio par carbon atom would be 0.25 that is clearly larger than the slope observed for a series of SiOi 5-X. This disagreement suggests that, unlike lamellar alkylsiloxanes [3-5], the alkyl chain is inclined to the plane of siloxane layer.

435 3.57 nm nm

4.5

(300) (500)

(100)(200)

4

(g) (g)

×5

3.5

(f)

×5

j O

(e)

×5

(d)

×5

(c) (c)

×5

(b)

×5

(a)

d / nm

Intensity/a.u

3

×5

2.5 2 1.5 1 0.5

3.74 nm 0

5

10 10

15 15 2θ/degree

20 20

25 25

30

0 0

0.2

0.4 0.4

0.6 0.6 2

0.8 0.8 2

11

1.2

2 -0.5

(h +k +l )

Figure 1 (Left) XRD of SiO, 5-PAS dried for (a)6 h (b) 12 h (c)l d (d)2 d (e)3 d (f)4 d and (g)10 d at 373 K. (Right) d-value vs (h2+l^+l2y0$ of SiO, 5-X. X= LAS(»), M A S ( B ) , PAS(^), SAS(A).

The elemental analysis of these SiOi 5-LAS revealed that the contents of carbon and nitrogen were 56.5 and 4.3 wt %, respectively. We propose the chemical formula of SiO,.5-LAS from this result (CnH 23 COOH) (NH2C3H6SiOi 5). The condensation of silane was confirmed by the absence of 2 T and lT peaks in 29Si-NMR spectrum of SiO,.5-LAS. The f3C-NMR of the same solid showed the peaks at 174.5, 30.7, 23.5 and 14.6 ppm. They can be assigned to carboxyl, 2 and 4-9 carbons, 3 and 11 carbons, and methyl carbon, respectively, where the carbons were numbered from carboxyl (1) to methyl (12) in LAS. An additional shoulder peak appeared around 32.0 ppm. The pattern for the alkyl carbons is similar to the spectra of alkane (main peak at 31 ppm) in a liquid phase. In a liquid phase, the configuration is considered to be in the antigauche equilibrium. In contrast, a position of resonance 6.5 ppm higher than the liquid alkane has been observed in high density crystalline polyethylenes. This NMR result implies that the alkyl chains in SiOi 5-LAS include the anti- and gauche- configurations. The lack of lateral "crystallization" in these SiOi5-X layered material suggests an easy accessibility of guest molecule into the interlayer surfactant assembly, which can facilitate intercalation, ion exchange, substitution of surfactant, etc. We show here an example of such reactions. The interlayer alkanoate micelles can be substituted by another carboxylate with a different chain length as shown in Figure 2. When SiOi 5-LAS was treated with ethanol-water solution of PAS, the peaks observed in XRD were

436

gradually shifted and the positions finally became almost identical to those measured for SiOi 5-PAS (see Fig. l(g)). The d2oo and J3Oo peaks were clearly observed, though their relative intensities were not the same as those in the fresh SiOi 5-PAS, suggesting the degradation of the periodic structure. The result implies the possibility of controlling the layer distance by an ionic exchange reaction of interlayer micelle. This exchange has not been carried out successfully in the previous studies on lamellar organosilicates [3-5], simply because the alkyl chain was covalently bound to silicone atom in their materials.

3.59 nm

(c) 3.62

in

I

(b) 2.94 nm

-5

0

5

10

15

20

25

30

26/degree

Figure 2 Exchange of surfactant molecules in SiO, 5-LAS by PAS. (a) SiO, 5-LAS, (b) after the reaction for 3 d and (c) after the reaction for 1 w.

4. References [1] C. T. Kresge, M. E. Leonovicz, W. J. Roth, J. C. Vartuli and J. S. Beck, Nature 710 (1992) 359. [2] T. Yanagisawa, T. Shimizu, K. Kuroda, and C. Kato, Bull. Chem. Soc. Jpn., 63 (1990) 988. [3] N. Parikh, M. A. Schivley, E. Koo, K. Seshadri, D. Aurentz, K. Mueller and D. L. Allara, J. Am. Chem. Soc. 119 (1997) 3135. [4] R. Maoz, S. Matlis, E. DiMasi, B. M. Ocko and J. Sagiv, Nature 384 (1996) 150. [5] Shimojima, Y. Sugaharaand K. Kuroda, Bull. Chem. Soc. Jpn. 70 (1997) 2847.

Progress in in Mesostructured Materials Recent Progress S. Qiu, Y. Tang and C. Yu (Editors) (Editors) D. Zhao, S. © 2007 2007 Elsevier Elsevier B.V. B.V. All All rights reserved. reserved.

437 437

Synthesis of highly ordered mesoporous benzenesilicas using PEO-PLGA-PEO triblock copolymers Eun-Bum Choa*, Hyojung Kimb and Dukjoon Kima " Polymer Technology Institute, Sungkyunkwan University, 300 Chunchun-dong, Jangan-gu, Suwon, Gyeonggi-do 440-746, Korea. b Central R&D Center, Samsung Electro-Mechanics, 314 Maetan-dong, Youngtong-gu, Suwon, Gyeonggi-do 443-803, Korea.

1. Introduction The synthesis of mesoporous materials using organic templates has been investigated using high molecular weight block copolymers as well as low molecular weight surfactants to expand pore size, increasing of stability, modifying of inorganic network, and constructing of extraordinary mesophases and so on [1]. In preparing periodic mesoporous organosilica (PMO) materials using high molecular weight block copolymer, interactive interfaces originated from each block of the block copolymer and the organo-bridged inorganic specie have to be considered in hybridizing them in solution. The independent control of hydrophobicity in one specific block, which leaves other interactive forces intact, has an important meaning in academic concern as well as in property of end products [2]. Herein, we have used poly(ethylene oxide)-poly(DL-lactic acid-coglycolic acid)-poly(ethylene oxide) (PEO-PLGA-PEO) block copolymers with a different hydrophobic interactive force from that of typical PEO-PPO-PEO triblock copolymers in aqueous solution and report more facile synthesis and characterization of highly ordered mesoporous benzene-silica powder and film including the structural property of framework wall. PLGA chain is about quadruple as hydrophobic as PPO chain [3] and the adequate solubility of PEOPLGA-PEO block copolymer in aqueous solution makes it feasible to build the homogeneous co-assembly, which is believed to be a main factor to obtain highly ordered mesoporous functionalized materials with high surface area in water based sol-gel process.

438 438

2. Experimental Section We have synthesized the PEO-PLGA-PEO triblock copolymer in laboratory through ring opening metathesis polymerization. Number averaged molecular weight of EO16(L29G7)EOi6 (LGE538) was obtained to be 5,310 and polydispersity index 1.28 by using a GPC-RI (Waters HPLC) system. The volume fraction of PEO block (O P E O) was calculated to be 0.38 from the group contribution method. l,4-bis(triethoxysilyl)benzene (BTEB) (Aldrich) used as the benzene-silica precursor. The molar composition of the final mixture was LGE538:BTEB:HCl:ethanol:H2O = 1.0:19.0-21.9:23.7-30.1:0-115.4:12,8192,850. Precipitates were obtained after the mixture was stirred for about 1 h at 313 K and the white solids were aged for 24 h at 368 K. Mesoporous benzenesilica films with 0.5-2 mm thickness were obtained through slow solvent evaporation method at the aging step of 368 K. Extraction of the block copolymer template was carried out by successive treatment with distilled water, ethanol, and acetone using a suction flask and then dried at 353 K. In the case of film, residual block copolymer was removed by stirring mesoporous benzenesilica film (0.5 g) in HCl/ethanol (4 g of 37 wt%/120 ml) solution for 10 h. 3. Results and Discussion We have synthesized LGE538 PEO-PLGA-PEO triblock copolymer with an adequate molecular weight soluble in water and reasonable volume ratio of the PEO block to get the hexagonal mesophase. Synchrotron SAXS (A. = 1.246 A) and WAXD results of mesoporous benzene-silica powder and film are shown in Figure 1. We found that block copolymer-free benzene-silica powder has highly ordered 2D-hexagonal (p6mm) mesophase with four well- ( a ) ' resolved peaks indexed as (100), (110), (200), and (210) reflections as shown in Figure l(a). The intense (100) peak represents the large lattice spacing of hkl d(A) d = 8.78 nm corresponding to 110 50.63 the 2D-hexagonal unit cell 200 43.79 210 33.16 parameter a = 10.13 nm. Wideangle diffraction pattern of the inset in Figure l(a) displays two Fig. 1 Synchrotron SAXS and WAXD patterns of reflection peaks at d = 7.7 and 3.8 A indicating molecular scale mesoporous benzene-silicas prepared in this study. Trace (a) is SAXS pattern of the block copolymerperiodicity of bridged-benzene free powder and (b) is of the film with 0.5 mm moiety inside benzene-silica thick-ness. Diffraction patterns in the high-angle framework wall. However, the region (0.88 < qz < 5.78; 10 < 29 < 70) are shown degree of periodicity is not in the insets, respectively.

439

significant and framework wall of benzene-silica is just crystal-like pattern. Benzene-silica films are obtained by slow evaporation induced self-assembly (EISA) at the final condensation step, and their thickness are obtained as 0.5-2 mm, and SAXS patterns represent the p6mm hexagonal mesostructure as shown in Figure l(b). Wide-angle diffraction pattern also displays two weak reflection peaks at d = 7.7 and 3.8 A (the inset of Figure l(b)) indicating molecular scale periodicity. Figure 2 demonstrates TEM images and corresponding Fourier transform images of mesoporous benzene-silicas synthesized with a LGE538 template. Figure 2(a) and (b) images, which are parallel and perpendicular to the channel, also represent uniform 2D hexagonal patterned mesopores. Fig. 2 TEM images and corresponding Fourier Nitrogen sorption isotherms transform images of mesoporous benzene-silicas synthesized with a EO16(L29G7)EOi6 template. of polymer-free mesoporous benzene-silica powder and film show the typical type-IV adsorption isotherms with a steep increase at P/Po = 0.65-0.70 due to capillary condensation of nitrogen in the mesopores. The BET surface area, pore volume, and micropore volume of a benzene-silica powder are determined to be 1,415 m2/g, 1.417 cm3/g, and 0.194 cm3/g, respectively, as shown in Table 1. Uniform pore size distribution with a maximum pore diameter of 6.5 nm is obtained from the BJH method and wall thickness is as 3.6 nm. In the case of the benzene-silica film, BET surface area, pore volume, and micropore volume are obtained to be 1,543 m2/g, 1.824 cm3/g, and 0.082 cm3/g, respectively. Pore size with a maximum pore diameter of 6.4 nm is obtained and wall thickness is as 3.7 nm. High porosity is a characteristic of mesoporous benzene-silica synthesized in this study.

440 Table 1. Physicochemical properties of mesoporous benzene-silica prepared in this study Sample

(m2/g)

V (cm3/g)

(nm)

W (nm)

BSP42

1,415

1.417

6.5

BSF26

1,543

1.824

6.4

SBET

Dp

V v

^micro

(cmVg)

Vv • micro

(cmVg)

(%)

3.6

1.223

0.194

13.7

3.7

1.742

0.082

4.5

meso

BSP42: mesoporous benzene-silica powder, BSF26: mesoporous benzene-silica film, SBET: BET surface area, V: pore volume, Dp: pore diameter, W: wall thickness (= 2afioc/V3 - Dp), Vmeso: mesopore volume, Vmicro: micropore volume, Omicro: fraction of micropore volume to total pore volume.

The 13C CP-MAS NMR spectrum represents a resonance peak at 133 ppm assigned to carbons on the benzene ring and 29Si CP-MAS NMR spectrum shows the characteristic signals assigned to GS7(OSi)3 (T3, 8 -78), CSi(OSi)2(OH) (T2, 8 -69), and GS7(OSi)(OH)2 (T1, 8 -61) confirming the homogeneous distribution of benzene moieties inside the benzene-silica framework. The absence of Q peaks between -90 and -120 ppm confirms that carbon-silicon bond cleavage of BTEB precursors is not occurred through sol-gel synthesis. The T3/T2 peak intensity ratio is lower than that of mesoporous benzene-silica prepared with a surfactant under basic condition [4]. The low T3/T2 peak intensity ratio and low molecular-scale periodicity suggests the interactive forces of BTEB precursors and between PEO chain and BTEB precursors works weakly under acidic condition. However, the framework wall of benzene-silica prepared in this study represents extremely high thermal stability up to 863 K in N2 atmosphere by thermogravimetric analysis. 4. Conclusion We have synthesized highly ordered 2D hexagonal (p6mm) mesoporous benzene-silica hybrid materials using new EOi6(L29G7)EOi6 triblock copolymer templates in wide experimental conditions. Mesoporous benzene-silica materials prepared with PEO-PLGA-PEO triblock copolymer templates display spherical external morphology and molecular scale periodicity different from the benzene-silica prepared with PI23 (PEO-PPO-PEO) template, which is believed to be originated from the end-capping property of a PEOPLGA-PEO template. Moreover, mesoporous benzene-silica can be formed easily as the film pattern of 0.5-2 mm thickness by tuning of solvent evaporation rates at the final condensation step of silanol group and has high thermal stability up to 863 K in N2 atmosphere. From these results, PEOPLGA-PEO triblock copolymers are successfully proved to be the useful structure-directing agent to prepare periodic mesoporous benzene-silica.

441

5. Acknowledgement This work was supported by the Korea Research Foundation Grant (KRF 2004-005-D00064). Small angle X-ray scattering experiment performed at 5C2 beam line of the Pohang Light Source was supported in part by GIST. We special thank Dr. Y. Lim at LG Chem Research Park for TEM evaluation and thank Mr. Y. Kim for assistance in synthesis. 6. References [1] [2] [3] [4]

Y. Goto and S. Inagaki, Chem. Commun., (2002) 2410. E.-B. Cho and K. Char, Chem. Mater., 16 (2004) 270. C. Booth and D. Attwood, Macromol. Rapid. Commun., 21 (2000) 501. S. Inagaki, S. Guan, T. Ohsuna, and O. Terasaki, Nature, 416 (2002) 304.

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Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

443 443

Tailoring cage-like organosilicas with multifunctional bridging and surface groups Rafal M. Grudzien, Bogna E. Grabicka, Donald J. Knoblocha and Mietek Jaroniec* Department of Chemistry, Kent State University, Kent, Ohio 44242, USA

Monofunctional and bifunctional cubic silicas with cage-like structure (FDU1) containing surface and bridging groups were prepared by one-pot synthesis route using various organosilanes such as tetraethyl orthosilicate (TEOS) along with ureidopropyltrimethoxysilane (UP), 3-mercaptopropylsilane (MP) and bis(triethoxysilylpropyl)disulfide (DS). The aforementioned mesostructures were characterized by X-ray diffraction, N2 adsorption and elemental analysis. 1. Introduction Ordered mesoporous organosilicas (OMOs) of FDU-1-type structure [1] feature spherical cages of uniform dimensions connected with twelve identical cages via small apertures creating a three-dimensional arrangement of pores. Cage-like OMOs are very attractive because of great opportunities in tailoring their surface and structural properties as well as their potential applications in many fields such as selective adsorption of toxic compounds from air and water, catalysis, host-guest chemistry, and separations. The aim of the current work is to synthesize cage-like OMOs with multifunctional surface and bridging groups and to monitor the changes in their adsorption, surface and structural properties upon introduction of various concentrations of functional groups. The present study is focused on the FDU-1 materials [1], which are face-centered (Fm3m) cubic mesostructures [2].

Corresponding author: Email. iaroniec(a),kent.edu Tel. 1-330-672 3790, Fax. 1-330-672 3816 " This work was partially supported by NSF Grants CHE-0093707 and CTS-0553014. " NSF-REU 2005 (CHE-0353737) undergraduate student from Saint Vincent College, Latrobe, PA 15650, USA.

444

2. Experimental Section Synthesis of functionalized FDU-1 mesoporous silicas [1] was carried out by co-condensation of TEOS and proper organosilanes (see Scheme 1) in the presence of poly(ethylene oxide)-poly(butylene oxide)-poly(ethylene oxide) triblock copolymer B50-6600 [(EO)39(BO)47(EO)39]. The synthesis recipe was analogous to that reported elsewhere [3]. In a typical synthesis, TEOS was added slowly to the polymer solution at 25°C under vigorous stirring followed by addition of organic silane (see Table 1). After being further stirred for 6 h at room temperature, the slurry was sealed in a polypropylene bottle and kept at 100°C for 6 h. The samples were collected by filtration, washed with deionized water and dried at 70°C. Extracted with 1) ethanol and HC1 solution the resulting Si SH samples are denoted as UPx, UP-MPx and DSx, where UP, UP-MP and DS denote A 2) O ureidopropylsilyl ligand, bifunctional Si NH2 NH ureidopropylsilyl-mercapto-propylsilyl surface ligands and bis(silylpropyl)3) S Si disulfide bridging group, respectively, Si S whereas x refers to the concentration of ligands (see Table 1). Scheme 1. Mesopore cage (A) together with Nitrogen adsorption isotherms were chem i ca i structures of ligands: 3measured at -196°C using 2010 and 2020 mercaptopropylsilyl (1), ureidopropylsilyl volumetric analyzers, Micromeritics, Inc. (2) and bis(silylpropyl) disulfide (3) Powder X-diffraction (XRD) data were incorporated to FDU-1. recorded using a PANanalytical, Inc. X'Pert Pro (MPD) Multi Purpose Diffractometer with Cu Ka radiation. Elemental analysis was conducted using a LECO Model CHNS-932 instrument from St. Joseph, MI. 3. Results and Discussion Quantitative characterization of incorporated organic groups into cage-like mesoporous silicas was performed by CHNS elemental analysis of nitrogen and sulfur (Table 1). As can be seen from this table the percentages of nitrogen and sulfur increase progressively with increasing concentration of functional organosilanes. These data confirm the presence of surface and bridging groups in the resulting materials. The structural ordering of extracted materials was examined by powder X-ray diffraction, which provided the XRD profiles characteristic for a cubic structure of Fm3m symmetry. The calculated unit cell parameters (see Table 1) tended to insignificantly decrease with increasing concentration of surface groups for UP FDU-1 and more meaningfully decrease for UP-MP and DS FDU-1 silicas.

445

Amount Adsorbed (cm3 STP g-1)

Shown in Figures 1A, IB and 1C are nitrogen adsorption isotherms measured at -196°C for template-free cage-like FDU-1 silicas with the following ligands: ureidopropylsilyl, bifunctional ureidopropylsilyl-mercaptopropylsilyl and bis(silylpropyl)disulfide, respectively. The corresponding pore size distributions (PSDs) for these OMOs are presented in Figures ID, IE and IF. The adsorption parameters such as the BET surface area, pore volumes and pore diameters are given in Table 1. These isotherms are of type IV with apparent hysteresis loops A

to

00

600

400

700

500 B

o UP 1 UP • UP 2 <• UP 3 T UP 4

UP-MP 1 UP-MP 2 UP-MP 3 UP-MP 4

400 300

C

c

500

o • a

400

T

DS 1 DS 21 DS DS2 DS 3 DS3 DS 4

DS4

300

200

^ 200

PSD (cm3 g-1 nm-1)

600

200 100

ft

100

0

0 0 0.0 0.2 0.4 0.6 0.8 1.0 1.0 0.0 0.2 0.4 0.6 0.8 1.0 1.0 0.0 0.2 0.4 0.6 0.8 1.0 1.0 Relative Pressure Relative Pressure Relative Pressure 0.3

D

0.2

UP 1 UP 2 UP 3 UP 4

E F,

0.2

T

0.1

0.1

nn 0.0

0.0 2 4 6 8 10 10 12 12 14 14 Pore Diameter (nm) (nm)

•

U P - M P 11 A UP-MP UPP-M-MP 2 P 1 2 UP-MP UP-MP 3 T V \ UP-MP UPP-M-MP P UP-MP 4 3 4

fa

10 12 12 14 14 2 4 6 8 10 Pore Diameter (nm) (nm)

F

0.2

DS 1 DS 2 DS 3 DS 4

0.1 0.0 2 4 6 8 10 10 12 12 14 14 Pore Diameter (nm) (nm)

Fig. 1. Nitrogen adsorption isotherms (A, B, C) measured at - 196 °C and the corresponding pore size distributions (D, E, F) calculated according to the KJS method4 for the FDU-1 samples having various concentrations of ureidopropylsilyl (UP) surface groups (A, D), bifunctional FDU-1 samples with ureidopropylsilyl (UP) and mercaptopropylsilyl (MP) ligands (B, E) and FDU-1 samples with bis(silylpropyl)disulfide bridging groups (C, F), respectively.

typical for mesoporous materials with cage-like structures. As can been seen from Figures 1A and ID, ureidopropyl-functionalized FDU-1 samples exhibit not only narrow PSDs but also uniform pore entrances, even for the sample with highest concentration of the surface ligand. This is not the case for bifunctional silicas (Figures IB and IE), which possess narrow PSDs and uniform pore openings for the first two samples (UP-MP 1 and UP-MP2), whereas OMOs with higher ligand concentrations show non-uniform pore entrance sizes as evidenced by two-step capillary evaporation. A similar behavior as that for UPMP FDU-1 samples is observed for the FDU-1 silicas with disulfide bridging

446

groups. As can be seen from Table 1 the BET surface area and total pore volume gradually decrease with increasing amount of organic groups. Moreover, the pore size calculated according to the KJS method4 shows the same trend Table 1. Adsorption, structural parameters and elemental analysis data for the OMOs studied.8 Sample

UP1 UP2 UP3 UP4 UP-MP1 UP-MP2 UP-MP3 UP-MP4 DS1 DS2 DS3 DS4

V,

vc

WKJS

wd

norgsilane

n-rEOS

S

N

nm

2

m /g

cc/g

cc/g

nm

nm

mmol

mmol

%

%

22.5

890 658 505 437 668 521 658 302 835 907 492 453

1.07 0.82 0.62 0.51 0.80 0.53 0.62 0.27 1.02 0.96 0.60 0.38

0.23 0.16 0.13 0.10 0.17 0.15 0.20 0.09 0.20 0.26 0.14 0.15

11.6 11.2 10.8 9.3 10.9 9.0 8.20 6.5 11.7 9.9 8.6 5.2

14.3 12.9 12.9 12.3 11.5 9.7 9.7 7.9 13.1 11.5 10.4 7.4

0.50

9.46

1.00 1.49 1.99 0.5 - (0.25) 0.5 - (0.5) 0.5-(1.0) 0.5-(1.5) 0.125 0.25 0.50 1.0

8.97 8.47 8.00 9.21 8.96 8.47 7.97 9.71 9.46 8.96 7.97

0 0 0 0 0.74 1.39 3.32 4.81 0.70 2.12 3.94 7.07

0.93 2.77 4.39 5.23 1.46 1.45 1.43 1.14 0 0 0 0

a

20.8 21.8 21.3 18.7 17.3 17.1 16.4 20.6 18.7 17.8 14.9

SBET

" a, unit cell parameter; SBET > BET surface area; Vt, total pore volume; Vc, volume of micropores and interconnecting pores of the diameter below 4 nm; wKJS, pore diameter calculated by the KJS method4; wd, pore diameter calculated on the basis of XRD data and the pore volume for Fm3m symmetry2; norg snane, number of mmoles of the organosilanes used; the number in brackets refers to number of mmoles of MP organosilane; nTEOs, number of mmoles of TEOS; %S and %N, sulfur and nitrogen percentages obtained by elemental analysis.

and decreases slightly from 11.6 to 9.3 nm for the UPx silicas; however in the case of UP-MPx and DSx silica this change is more substantial. It is noteworthy that the KJS method,4 which was developed for cylindrical pores, tends to underestimate the size of spherical pores (see Table 1). 4. Conclusion In conclusion, the introduction of multifunctional surface and bridging groups into cage-like FDU-1 mesostructures was successfully accomplished by direct one-pot synthesis using triblock copolymer B50-660 as template. The resulting materials exhibited high surface area, large pore volume and pore diameters. 5. References [1] C. Yu, Y. Yu and D. Zhao, Chem. Commun., (2000) 575. [2] J. R. Matos, M. Kruk, L. P. Mercuri, M. Jaroniec, L. Zhao, T. Kamiyama, O. Terasaki, T. J. Pinnavaia and Y. Liu, J. Am. Chem. Soc, 125 (2003) 821. [3] R. M. Grudzien and M. Jaroniec, Chem. Commun., (2005) 1076. [4] M. Kruk, M. Jaroniec and A. Sayari, Langmuir, 13 (1997) 6267.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

447 447

Synthesis and morphology of functionalized mesoporous ethanesilica Yaojun Wang, Yanqin Wang *, Xiaohui Liu and Guanzhong Lu Lab for Advanced Materials, Research Institute of Industrial Catalysis, East China University of Science and Technology, Shanghai 200237, P. R. China

1. Introduction With the development of mesoporous materials, the properties of the original mesoporous silicates and aluminosilicates can't satisfy the demands in the practical applications. The surface properties of mesoporous materials require to be modified in order to gain special surface properties. The successful synthesis of periodic mesoporous organosilica (PMO) materials [1-3] has opened prospects for the development of new technologies in catalysis, separation, drug delivery and immobilization of enzymes. Scientists have used many organic groups such as vinyl, aminopropyl and mercaptopropyl groups to functionalize mesoporous silicas for special applications. But most of the reports use cocondensation of tetraethoxysilane (TEOS) and organosilanes to synthesize mesoporous materials. Little work has done to prepare the functionalized materials using -C-C- bond bridged organosilane instead of TEOS [4, 5]. While the C-C bond in the framework can enhance the hydrophobicity and improve the mechanical and hydrothermal stability [6, 7]. 2. Experimental Section Functionalized mesoporous ethanesilica have been synthesized by cocondensation of BTEE and various organosilanes with CTAB as template. The template was removed by stirring the as-synthesized sample under the acidic solution of ethanol. The template of glycidoxypropyl modified mesoporous ethanesilica was extracted twice in the ethanol solution.

448

3. Results and Discussion Organic group and Ce-functionalized mesoporous ethanesilica were successfully synthesized. Thus-synthesized materials have high quality and their physical properties were summarized in Table 1. Table 1. Structural properties of functionalized mesoporous ethanesilica. Sample

VT

DP

W

(m /g)

(cmVg)

(nm)

(nm)

5.44

645

0.57

2.79

1.92

4.37

5.04

660

0.53

2.50

1.87

3 -glycidoxy propy 1trimethoxysilane (GPS) 10%

4.45

5.14

613

0.53

2.63

1.82

3-mercaptopropyltrimethoxysilane (MPTMS )10%

4.30

4.96

682

0.58

2.80

1.50

Ce 3%

4.49

5.18

542

0.56

2.60

1.89

vinyltriethoxysilane (TEVS )10%

4.75

4.48

564

0.36

2.30

2.45

TEVS 20%

4.83

5.57

597

0.43

2.30

2.53

TEVS 30%

4.86

5.61

644

0.33

2.30

2.56

dioo

ao

(nm)

(nm)

Ethanesilica

4.71

3-aminopropyltrimethoxysilane (APTMS) 10%

SBET 2

Notes: ao, unit cell dimension; SBET, BET surface area; VT> total pore volume; Dp, pore diameter from desorption branch; W, wall thickness.

3.1. X-ray diffraction (XRD) Various functionalized mesoporous materials were obtained under the conditions investigated. Figure l(a) shows the XRD patterns of mesoporous ethanesilica and its funtionalized products. It can be seen clearly that the solvent-extracted ethanesilica display three well-resolved reflections, indicating that the material has well-ordered two-dimensional hexagonal structures. When the mixture of organosilane and BTEE was added as the silicon source, most of the materials exhibited hexagonally arranged pore system except for 10%MPTMS. The addition of MPTMS to the starting mixture induced the partial disruption of well-ordered structure, even though other organic groups functionalized mesoporous ethanesilica remained mesostructured ordering. The XRD patterns reveal that the intensity of the dlOO reflection lowered and the position moved slightly to higher 29 values, which corresponds to the lowering of d spacings and the shrinkage of unit cells.

449

a

(100)

(110)

b 30 %TEVS 30%TEVS

(200)

100%BTEE 10%APTMS 10%GPS 10%MPTMS 3%Ce

2

4

2theta/degree

6

8

L 2

4

%TEVS 20 20%TEVS

10 %TEVS 10%TEVS

6

8

2theta/degree

Figure 1. XRD patterns of the solvent-extracted mesoporous ethanesilica :(a) various group (atom) functionalization; (b) vinyl-functionalization.

Figure l(b) compares the XRD patterns of different ratios of TEVS to BTEE. Each sample consisted of a broad peak which indicates the strongly disorder in the mesostructure. It might due to the interaction between the vinyl group and the surfactant which causes the change of the curvature of the micelle. 3.2. SEM Figure 2 shows the SEM images of functionalized mesoporous organosilica. Modifying with different organic groups or atoms can obtain materials with various morphologies. The particle shape of ethanesilica is sphere (Figure 2a). When modifying with aminopropyl and glycidoxypropyl group, the resulted materials present wormlike and rodlike shapes (Figure 2b and c). But, mercaptopropyl functinalized material still maintains the spherical morphology (Figure 2d). It is due to the hydrophobicity and hydrophilicity of organic groups, which affects the curvature of the micelles, and furthermore induces the oriented growth of the particles [4, 8]. Ce-doped ethanesilica displays rough surface which is consistent of small particles (Figure 2e), the big difference may be due to different base used in the starting gels. Besides the type of functional group, the ratio of organosilane also plays an important role in the morphologies control. The low amount of vinyl groups into the framework leads to the formation of coralloid particles (Figure 2f), while aggregated spherical particle and wormlike particle formed with the increase of vinyl groups (Fig. 2g and h).

450

Figure 2. SEM images of a) 100% BTEE, b) 10% APTES, c) 10% GPS, d) 10% MPTMS, e)3%Ce, f)10%TEVS, g) 20% TEVS, h)30%TEVS.

In summary, using different organic groups and different ratios, various organic group or atom-functional ized mesoporous ethanesilica can be obtained with different morphologies. 4. Acknowledgment This work was supported financially by the National Basic Research Program of China (No. 2004CB719500), the Commission of Science and Technology of Shanghai Municipality (No. 04ZR14036). 5. References [1] S. Inagaki, S. Guan, Y. Fukushima, T. Ohsuna and O. Terasaki, J. Am. Chem. Soc. 121 (1999)9611. [2] T. Asefa, M. J. MacLachlan, N. Coombs and G. A. Ozin, Nature 402 (1999) 867. [3] B. J. Melde, B.T. Holland, C.F. Blanford and A. Stein, Chem. Mater. 11 (1999) 3302. [4] M. A. Wahab, I. Imae, Y. Kawakami and C.S. Ha, Chem. Mater. 17 (2005) 2165. [5] Q. Yang, M. P. Kapoor and S. Inagaki, J. Am. Chem. Soc. 124 (2002) 9694. [6] M. C. Burleigh, M. A. Markowitz, S. Jayasundera, M. S. Spector, C. W. Thomas and B. P. Gaber, J. Phys. Chem. B 107 (2003) 12628. [7] E. B. Cho and K. Char, Chem. Mater. 16 (2004) 270. [8] S. Huh, J. W. Wiench, J. C. Yoo, M. Pruski and V. S.-Y. Lin, Chem. Mater. 15 (2003) 4247.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

451 451

Periodic mesoporous organosilicas : thermal stability and etherification of phenol Micha Rat, M. Hassan Zahedi-Niaki, Serge Kaliaguine and Do Trong-On Department of Chemical Engineering, Laval University, Ste-Foy, Quebec, G1K 7P4 Canada

1. Introduction Functionalized periodic mesoporous organosilicas [1,2] have attracted much attention because of their unprecedented catalytic and adsorption properties. Both post-synthesis and co-condensation methods have been reported for the preparation of various kinds of these materials. The presence of organic groups within the framework enhances their hydrophobicity while still allowing introduction of new functionalities. These properties may be very useful for the design of new catalysts. Few studies have however been reported on the thermal stability of these materials under different conditions. In the present work, we describe the synthesis of mesostructured ethane silica (MES) and arene sulfonic groups [3] containing MES (ASMES)4. The thermal degradation of these hybrid materials as well as the catalytic activity for the etherification of phenol will therefore be discussed. 2. Experimental Section Two types of mesoporous organosilicas were prepared [4] under acidic conditions from the mixture with molar composition BTME: 1.22-x; CSPTMS: x; HC1: 12.97; H2O: 360.5; P123: 0.0378. The materials were characterized using various techniques including BET, TEM, TPD monitored by mass spectroscopy, MAS-NMR, and catalytic test. The materials have been ethanol extracted. For thermal treatment, the samples were placed inside a quartz reactor and heated either in helium (3°C/min) or air (5°C/min) at different temperatures. The catalytic test was performed in a Stainless-Steel batch reactor equipped with an ATR-FTIR probe (ASI, Mettler-Toledo, USA). Before each reaction 0.5 g of catalyst was predehydrated for 30 min at 60°C under vacuum.

452 452

600

ASMES ASMES ASMES-490 ASMES-490 ASMES-575 ASMES-575 ASMES-700 ASMES-700

400 • 400

r /I'

300 300 0,14

0,12

200 • 200

dVP / dRP

V adsorbed (ml/g)

500 500 •

0,10

?—

00 100

•

r

0,08

0,06

0,04

11

-

0,02

0,00 20

40

! !l 60

80

100

iameter(A) pore diameter (A)

00 0,0 JJ,JJ

0,2 \t*£

0,4 Wi * 1

_

m

P/P0

0,6 'JIV

0,8 U|O

! 1,0 i iW

Fig. 1 N2 adsorption/desorption isotherms and BJH pore size distributions (inset) of the extracted ASMES after and before treatment under helium.

Fig. 2: TEM image of ASMES after treatment at 700°C in helium

MS signal (mV/g)

40

—•— o —T— —a—

30

M M= = 51 (from (from benzene benzene sulfonic acid) M == 64 64 (SO (SO2) M 2) M= = 78 78 (Benzene) (Benzene) M M= = 92 92 (Toluene) (Toluene) M

20

10

0 0

200

400 400

600 600

Temperature (°C)

Fig. 3 Thermal decomposition of arene sulfonic groups of ASMES in helium

Typically the catalyst was added to a solution of 16.74 g phenol and 28.49 g of methanol (molar ratio : methanol/phenol = 5), and stirred with a magnetic stirrer under autogenous pressure for 24 h. The IR spectra of the reactor content were recorded at specific time intervals and for quantification were later processed using the React IR software. 3. Results and Discussion The N2 adsorption/desorption isotherms and pore size distribution obtained from the extracted ASMES sample before and after treatment at different temperatures are shown in Fig. 1. No essential change in the mesopore structure was observed for this sample after treatment in helium at different temperatures, even at 700°C (Table 1). The pore volume and surface areas varied slightly from 1,80 to 1,45 cnvVg and 780 to 630Dm2/g, respectively. This is also confirmed by the TEM observation (Fig. 2). By contrast, a significant collapse of the mesopore structure for these samples after treatment in air at 600°C was observed (not shown). Similar results also obtained in helium with an extracted ASMES are reported in Fig. 3. The sulfonic acid groups only start decomposin at 460°C. This result means that these materials have a high thermal stability and potential applications as catalysts in the fine chemical industry. The acid exchange capacity of ASMES was measured

453 Table 1. Structural properties of the extracted ASMES samples before and after treatment in helium at different temperatures. ASMES-x where x: temperature of treatment (°C) Sample

SBET (m 2/g)

Pore diameter (A)

Vtotal (mL/g)

ASMES

780

60

1.79

0.170

ASSBA15

728

40

1.78

0.172

MES

1452

60

3. 34

0.330

* micro

(mL/g)

by means of acid-base titration, using sodium chloride as exchange agent. The capacity obtained is about 0.80 mmol If" / g SiC>2. CH3-O-CH3

CHj-OH + C6H5-OH

acid

O-alkylation

H2O

catalyst C-alkylation

CH 3 -C 6 H 4 -OH

Scheme 1 Etherification reactions of phenol and methanol over acid catalyst

Figure 4 shows an illustration of in situ FT-IR 3D spectra recorded for 24 h. The evolution of the peaks in IR spectra during the reaction is clearly visible by decreasing the intensity of the methanol peaks and appearing of new peaks. The trend of methanol and phenol conversion to dimethylether, anisole and cresol is shown in the figure 5. A negligible amount of polyaromatics was also observed. It is evident that the major product is dimethylether and little anisole and cresol were formed. In etherification reaction of phenol on acid catalyst, at least three

Fig. 4:3D in situ FTIR spectra of the etherification reactions of methanol and phenol on ASMES material at 180°C

454 20

3,5

0,25

(b

16

(a)

14

2,5

12

2

10 1,5

8 6

1

4

C o n c e n t r a t i o n ( m o l/ L )

3

C o n c e n t r a t io n ( m o l/L )

C o n c e n t r a t io n ( m o l/L )

18

0,2

0,15

0,1

0,05

0,5

2 0

0

0

2

4

6

8

10

12

14

Reaction Time (hr) F»-Methanol Methanol

Dimethylether

Phenol

Anisole & Cresol

0 0

2

4

6

8

10

12

14

Reaction Time (hr) experimental

Fig. 5 Evolution of concentrations of (a) methanol & phenol (b) anisole & cresol at 180°C on ASMES

parallel reactions are competing. These reactions as shown in scheme 1 are alcohol condensation, O-alkylation and C-alkylation [5,6]. The very preliminary results reported in Figure 5 indicate that the arene sulfonic mesostructured ethane silica synthesized in this work can be used as an etherification catalyst. Obviously the etherification of methanol to dimethylether is much faster than both O- and C-alkylation of phenol in the conditions of the limited experimental tests reported here. Actually we reported recently the high activity of ASMES materials in the formation of dibutylether from 1-butanol [7]. The present results indicate that the etherification of methanol over these catalysts is at least two times faster than the one of butanol. 4. Conclusion Arene sulfonic mesostructured ethane silica with exchange capacity of 0.80 mmol H+/g SiO2 was prepared and its thermal stability was studied. Some limited data indicated that this catalyst having acid sites in hydrophobic surface environment is potentially useful as catalyst for etherification of alcohols and phenolic compounds. 5. References [1] F. Hoffman, M. Cornelius, J. Morell and M. Froba, Angew. Chem. Int. Ed., 45 (2006) 3216. [2] S. Inagaki, S. Guan, T. Ohsuna and O. Terasaki, Nature, 416 (2002) 304. [3] S. Mikhailenko, D. Desplantier-Giscard, C. Danumah and S. Kaliaguine, Micropor. Mespor. Mater., 52 (2002) 29. [4] S. Hamoudi and S. Kaliaguine, Micropor. Mespor. Mater., 59 (2003) 195. [5] K. G. Bhattacharyya, A. K. Talukdar, P. Das and S. Sivasanker, J. Mol.Catal., 195 (2002) 255. [6] M. C. Samolada, E. Grigoriadou, Z. Kiparissides and I. A.Vasalos, J.Catal., 152 (1994) 52 [7] B. Sow, S. Hamoudi, M. H. Zahedi-Niaki and S. Kaliaguine, Micropor. Mespor. Mater., 79 (2005) 129.

455 455

Recent Progress in Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Published by Elsevier B.V.

Highly efficient microwave-assisted asymmetric transfer hydrogenation with SBA-15-supported TsCHDA chiral ligands Myung-Jong Jin*, M. S. Sarkar and Ji-Young Jung School of Chemical Science and Engineering, Inha University, Incheon, 402-751, Korea

A fast and efficient procedure has been developed for microwave-assisted asymmetric transfer hydrogenation of ketones. The reactions were brought to full conversion in short time using SBA-15-supported TsCHDA chiral ligands. 1. Introduction Asymmetric transfer hydrogenation of ketones is an attractive method for the synthesis of optically active secondary alcohols [1]. The heterogeneous transfer reactions facilitated by supported catalysts have received much attention in recent years. Heterogeneous catalysis typically requires long reaction time to reach completion. It is well known that microwave-assisted reactions can occur much faster than reactions using conventional heating [2]. Efficient supported chiral ligands have been developed for the heterogeneous catalysis [3]. This strategy offers practical advantages such as simplified separation and potential reuse of the expensive chiral ligands. SBA-15-supported Ru-TsDPEN 3b has been previously used for asymmetric transfer hydrogenation of ketones [4].

i)

O (MeO) ( M e O3)Si3 S i ^

\ NH2

H2 N 1

/=\ i

II 4 ' , NH SS HN HN N H 22 0 O 22

ii)

O

*-

O

S i - OO- SSii - v Si S Oi O S

/—v II i S HN S H N O O

SBA-15

SBA-15-TsCHDA SBA-15-TsCHDA 33

i) 2-(4-chlorosulfonylphenyl)ethyltriraethoxysilane, Et3N, CH2C12, -10 "C, 2 h ii) toluene, reflux, 18 h

Scheme 1

.

NH

N H 22

456 Recently, we developed new mesoporous silica SBA-15-supported TsCHDA chiral ligand 3. Our interest in the catalysis using microwave irradiation led to investigate microwave (MW) assisted asymmetric transfer hydrogenation in the presence of the SBA-15-supported chiral ligands. In this paper, we describe the results of the microwave-assisted asymmetric transfer hydrogenation using the immobilized TsCHDA chiral ligand 3. 2. Experimental Section 2.1.

Preparation of SBA-15-supported TsCHDA 3

A solution of 2-(4-chlorosulfonylphenyl)ethyltrimethoxysilane (0.198 g, 0.61 mmol) in CH2C12 (5 mL) was slowly added to a stirred solution of (\R,2R)diaminocyclohexane (0.070 g, 0.61 mmol) and triethylamine (0.067 g, 0.67 mmol) in CH2C12 (10 ml) at -10 °C. The reaction mixture was allowed to warm to RT. After stirring for 2 h, the mixture was diluted with CH2C12, and washed with cold water. The organic layer was dried with MgSC>4, and concentrated under reduced pressure. The crude product was purified by flash chromatography to give (liJ^^-A^trimethoxysilylpropyl-Af-sulfonyO-l^-cyclohaxanediamine 2 in 80% yield. SBA-15 silica (0.7 g) was added to a solution of compound 2 (46 mg, 0.11 mmol) in hot toluene (15 ml) and the mixture was refluxed for 18 h. After filtering the reaction mixture, the solid was washed several times with methylene chloride and dried under vacuum at 70 °C to give SBA-15-supported TsCHDA 3. Weight gain showed that 0.15 mmol of TsCHDA was grafted in 1.0 g of the SBA15 silica 3. 2.2.

Asymmetric transfer hydrogenation under microwave-irradiation

SBA-15-supported TsCHDA 3 (0.090 g, 0.013 mmol) was suspended in water (1.5 ml) and heated with [Ru(p-cymene)Cl2]2 (3 mg, 0.005 mmol) for 3 min under MW (60 W). Ketone (0.45 mmol) and HCO2Na (0.153 g, 2.2 mmol) were added to the solution and heated under MW (40-60 W) for short time. The mixture was cooled to RT, and diluted with diethyl ether. After general work-up, crude product was purified by short-column chromatography. Conversion was measured by GC analysis. Chiral HPLC analysis using Daicel OD-H column was used for the determination of enantiomeric excess of the diol. 3. Results and Discussion The immobilization of the TsCHDA chiral ligands onto SBA-15 silica was

2S

Fig I. XRD pattern profiles

457

performed in two steps. Reaction of (li?,2/?)-diaminocyclohexane with 2-(4chlorosulfonylphenyl)ethyltrimethoxysilane afforded trimethoxysilylpropylated 2amino(sulfoamido)cyclohexane 2 in high yield. Subsequent treatment with SBA-15 silica in refluxing toluene gave SBA-15-supported TsCHDA 3 (0.15 mmol/g). Hexagonal mesoporous structure of the SBA-15 could be sustained after the modification steps. The XRD obtained from the supported SBA-15 material is shown in Fig 1. Apparently, no changeoccurred in the lattice upon the immobilizing process and pore arrays are conserved. Table 1. Asymmetric transfer hydrogenation under microwave irradiation3 O

OH Supported ligand 3

^Y^R HCO2Na - H2O, MW

I*

Ketoneb

Ligand

Power (W)

Time (min)

Conv. (%)c

E.e. (%)d

Acp

3b

60

40

60

51

Acpe

3a

0 W, 90 °C

600

72

73

Acp

3a

60

30

100

80

Acp

3a

50

30

99

79

Acp

3a

40

40

96

80

Pp

3a

60

40

90

61

a-tetralone

3a

60

40

90

92

3-Cl-Acp

3a

40

20

100

85

3-Cl-Acp

3a

40

30

95

83

3-CI-ACD

3b

40

40

57

55

"Molar ratio; ketone : Ru : ligand 3 (loading ratio = 0.15 mmol/g) = (100 : 1 : 3), HCO2Na (5 equiv.) and H2O 1 ml. bAcp = acetophenone, Pp = propiophenone. 'Determined by GC analysis. d

Determined by HPLC analysis using Chiralcel OD-H column (3% 2-propanol in hexane, 1 ml/min). 'Conventional themal condition.

With the supported TsCHDA 3, we performed microwave-assisted asymmetric transfer hydrogenation of ketones in aqueous HCO2Na. The SBA-supported chiral Ru(II) complexes were prepared in situ by MW-heating a mixture of [Ru(pcymene)Cl2]2 and the supported TsCHDA 3 in H2O for 3 min. As indicated in

458

Table 1, the MW-assisted reactions could reach completion with 20~40 min. Satisfactory enantioselectivities were obtained with excellent conversions. When the identical reaction was performed under thermal condition, the reaction required considerably longer reaction time of 600 min. 4. Conclusion It is noteworthy that our SBA-15-supported TsCHDA 3 a gave better enantioselectivity and higher reactivity than SBA-15-supported TsDPEN 3b. In conclusion, it has been shown that MW-assisted reaction can be an useful methodology for the heterogeneous transfer hydrogenation of ketones. 5. References [1] [2] [3] [4]

R.Noyori and S. Hashiguchi, Ace. Chem. Res. 30 (1997) 97. C. O. Kappe, Angew. Chem. Int. Ed. 43 (2004) 6250. C. E. Song and S.-g. Lee, Chem. Rev. 102 (2002) 3495. P. N. Liu, J. G. Deng, Y. Q. Tu and S. H. Wang, Chem. Commun. (2004) 2070.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

459 459

Preparation of bimodal MCM-41 encapsulated Co(III)-porphyrin complex and its catalytic properties in cyclohexane oxidation Shijie Luo and Jihong Sun* Department of Chemistry and Chemical Engineering, College of Environmental & Energy Engineering, Beijing University of Technology, Beijing, 100022, P. R. China

1. Introduction Following the discovery of the M41S family of silicas [ 1], considerable research effort has recently been focused on the preparation of hybrid mesoporous materials with controllable hierarchical structure, and its potential application [2]. The heterogenization of metal complexes is an area of growing interest, particularly on zeolite and mesoporous silicate with its large pore, high surface area, and a large number of surface silanol groups. Recently, several metals have been immobilized on ZSM-5 [3] and M41S [4]. Moreira et al. [5] have grafted Iron porphyrins on the surface of MCM-41 through aminosilane linker by adduct formation, and such kind of the catalysts were found to be active for hydrocarbon oxidation. Here, we report that a new hybrid material by using bimodal mesoporous materials (BMMs) as support, whereas, Cobaltporphyrins have been immobilized on the pore surface of BMMs via grafted techniques. We hope this new hybrid material could give more promising catalytic activity for cyclohexane oxidation. 2. Experimental Section BMMs were hydrothermally synthesized according to the literature [6]. The preparation procedure of new hybird material is as followed: BMMs (0.5 g) was mixed with a chloroform solution contained 3-aminopropyltriethoxysilane (APTES) (50 ml, 0.1M) [7], and stirred at room temperature for 12 h, after filtered, washed with chloroform, and dired at room temperature in vacuum overnight. The product was named BMMs (m). Stirring a mixture of BMMs(m)(0.5 g) and Co-porphyrin in dichloromethane (10 ml, 0.2 mM) at

460

room temperature for lh gave the encapsulated product (Co-BMMs). The oxidation of Cyclohexane with oxygen by Co-BMMs were carried out in the reactor. X-ray diffraction (XRD) of the samples was recorded using a BruckerAXS D8 diffractometer using Cu Kal radiation. Scanning electron microscopy (SEM) images were obtained with a JEOL JSM-6500 microscope. Transmission electron microscope (TEM) images were recorded on a JEOL JME-2010. Nitrogen adsorption-desorption isotherms were measured using a Micromeritics ASAP 2010 system. Pore size distributions were obtained from the N2 desorption branch isotherm using BJH method. The content of phenanthrene in filtrate (solution) was analyzed using GC-17A with a capillary column. 3. Results and Discussion 1400

0

Figure 1 XRD patterns of BMMs (a) and CoBMMs (b)

0.2 0.4 0.6 0.8 1 Relative Pressure (p/p )

Figure 2 N2 adsorption-desorption isotherms of (b) and corresponding t 0 t n e p O r e s j z e distribution (inset)

B M M s ( a ) a n d Co -BMMs

The XRD pattern of the calcined BMMs (in Figure l a ) shows two reflections in the 2 theta range 2 - 10 °, indexed for a hexagonal cell as (100) and (110) respectively. However, the peak (110) is not obvious, the most reason is that the peak (100) was very broad with high intensity in the XRD pattern. The d value of the (100) reflection was 35.4 A leading to a lattice constant of a = 40.9 A. Upon functionalization of BMMs and subsequent inclusion of the Cobalt porphyrin complex (Co-BMMs), the two characteristic diffraction peaks in XRD pattern, as can be seen in Figure lb, were still observed at about the same positions as that of BMMs, demonstrating that the long range hexagonal

461

symmetry of the mesoporous host was preserved after modification by APTES and immbization by Cobalt-porphyrin complex. The isotherms of both BMMs and Co-BMMs on the basis of N2 adsorptiondesorption data exhibit two inflections: a first increase occurs at relative pressures 0.4

462

molecules easier access to the pores, reduce diffusion limitations, improve reaction efficiencies and diminish pore channel blocking. Detailed mechanistic examinations of the heterogenous system are currently under way. Table 1 Reaction properties of cyclohexane oxidation by using Co-BMMs as catalyst Mass of catalysts(g)

0.1

0.15

0.20

Cyclohexane conversion(%)

10.38

0.34

4.41

Yields of alcohole (%)

98.08

33.3

64.2

Yields of ketone (%)

0.24

17.8

14.7

Reaction conditions: Temperature =150°C, Pressure =1.5MPa, Time=6h

4. Conclusion A new hybrid material by BMMs as support has been successfully prepared with Cobalt-porphyrins as ligand via grafted routes by using APTES as modified agent. Meantime, its catalytic properties for cyclohexane oxidation has been investigated. The results show that the reactivity about 10.38% conversion of cyclohexan and 98.08% alcohol selectivity with O2, respectively. 5. Acknowledgement This research was supported by the Excellent Oversea Chinese Scholars Fundation of the Personal Ministry of the Chinese Govenment and the Natural Science Fundation of Ningxia Hui Autonomous Region (ZD02). 6. References [1] [2] [3] [4] [5] [6] [7] [8]

C. T. Kresge, M. E. Leonowicz, W. J. Roth and J. S. Beck, Nature, 359 (1992) 710. J. M. Thomas, Angew. Chem., Int. Ed., 38 (1999) 3588. L. Zhao, D. Ji, G. Lv, G. Qian and J. Suo, J. Chem. Soc, Chem. Commun., (2004) 904. M. S. Hamdy, G. Mul,, W. Wei, R. Anand and J. A. Moulijn, Catalysis Today, 110 (2005) 264. M. S. M. Moreira, P. R. Martins and Y. Iamamoto, J. Mol. Catal. A: Chemical, 233 (2005) 73. J. H. Sun, Z. P. Shan, T. Maschmeyer and M. O. Coppens, Langmuir, 19 (2003) 8395. C.J. Liu, S.G. L i , W. Q. Pang and C.M.Che, Chem. Ccommun., 1 (1997) 65. X. S. Zhao and G. Q. Lu, J. Phys. Chem. B, 102 (1998)1556.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

463 463

Synthesis of optically active monoesters via enantioselective reaction catalyzed by heterometallic chiral (salen) Co complex immobilized on acid sites of Al-MCM-41 Geon-Joong Kim*, Chang-Kyo Shin and Rahul B. Kawthekar Department ofChemcal Engineering Inha University, Incheon 402-751, South Korea

The new heterogeneous dinuclear chiral (salen)Co-GaCl3 catalyst immobilized on Al-MCM-41 showed high activity for the enantioselective ring opening of terminal epoxides with carboxylic acids. Various chiral monoester derivatives could be synthesized with relatively high enantioselectivity. 1. Introduction Among the myriad of nucleophiles that have been employed in epoxides ring openings catalyzed by chiral (salen) metal complexes [1], carboxylic acids have been paid very less attention. In contrast to chemo- and regioselective ring openings of terminal epoxides with carboxylic acids [2], only one literature is available for the enantioselective ring openings of meso epoxides using carboxylic acid as nucleophile [3]. We recently reported that that dinuclear complexes bearing Lewis acids of Al and Ga elements are highly efficient catalyst for the enantioselective ring opening of terminal epoxides with H2O and HC1 [4]. Encouraged with these results we have extended the applicability of these catalysts for enantioselective ring opening of terminal epoxides with carboxylic acids. Carboxylic acids are interesting candidates because of their low cost, ease of handling and reaction with epoxides provide a direct route to monoesters [3]. To broaden the application range of dinuclear chiral (salen)Co catalysts [4], herein we report the catalytic enantioselective ring opening of terminal epoxides with carboxylic acids. Indeed, the Jacobsen's chiral (salen) Co complex shows low activity (<10% ee) in that reaction. The coupled routeof asymmetric ring opening(ARO)/cyclization for epichloro-hydrin (ECH)

464

experienced to synthesize highly enantioenriched valuable terminal epoxides, such as glycidyl butyrate(GB). 2. Experimental Section The homogeneous chiral salens having different structures as shown in Scheme 1, and Al-MCM-41 with well hexagonal pore structure were prepared by the procedure as reported in the previous papers [4,5]. Subsequently, the heterogenized Co(salen) MX3 complex was prepared by reacting H+ type AlMCM-41 with Cl-containing salens partners in refluxing CH2CI2 for lh (Scheme 1). The dark red complex was rinsed sequentially with CH2CI2 and dried in vacuo to yields a heterogenized Co(salen) complex. The catalytic activities were evaluated mainly by using (±)ECH. The conversion and ee% values were determined by capillary GC using chiral columns (CHIRALDEX (G-TA) and (A-TA), 20 m x 0.32 mm i.d. (Astech)). 3. Results and Discussion The XRD pattern and TEM image of synthesized Al-MCM-41 with Si/Al=17 are presented in Fig.l. The sample exhibited a very intense (100) diffraction peak and three (110), (200) and (210) peaks after calcination. This mesoporous material was used as a support to combine the chiral salen complexes after hydronium ion exchange. We have investigated the catalytic activity after immobilization of homogeneous salens for asymmetric ring opening of terminal epoxides with carboxylic acid. In a representative example of ARO of ECH with propionic acid, a series of homogeneous chiral (salen)Co complexes (Scheme 1) were screened. Complex II-1 -d was proved to be most active and enantioselective (86 % ee, 4 h) as a homogeneous type [6]. t-Bu t-Bu N N CoO O

t-Bu

N

O

But

t-Bu t-Bu

t-Bu

N OCo Co N

tBu M

X

O Bu

t

X

t-Bu

N

II

Co

t

Bu

O

MX3

t

Bu

X

Mononuclearcomplex Mononuclear complex (I)

H+ HO O

OH tBu

2

8

10

41 MMC

M; 1 = Al 2 = Ga X; a = Cl b = Br c=I d = NO3

N O Co N O

t

tBu

MX3 t

Bu

Fig. 1. XRD pattern and TEM image of A1MCM-41 used as a support.

Bu 2

Dinuclear complex (II) Dinuclearcomplex (II) Heterogeneous chral catalyst immobilixed on H+type/¥-MCM41

Schema 1

465 Table 1. Asymmetric ring opening of terminal epoxides with carboxylic acids catalyzed by II -1a/MCM-41. OH IM-a/MCM-41, 4.0 mol% R' R'COOH

A+

2.22 equiv.

0-4 °C, TBME 1.00 equiv.

o 55-75 ee%, 35-47 yield %

Yield a

eeb

44

58

43

60

Entry

R

1

CH 2 C1

2

CH 2 C1

3

CH 2 C1

^ 1

44

73

CH,C1

_

45

71

R'COOH 0

O

0

1

a

Isolated yield is based on racemic epoxides (theoretical maximum=50%).b ee% was determined by chiral GC or chiral HPLC. TBME was taken as a solvent. Catalyst; II -1 -a/MCM-41, Catalyst loading; 4 mol% (The loading is on the basis of per [Co] unit w.r.t. racemic epoxide), Reaction time; 6 h.

Furthermore, complex II-1-a was identified as one of the effective homogeneous catalysts, and it was chosen for the preparation of heterogenized one in further study. The obtained results by using chiral salens immobilized on Al-MCM-41 are summarized in Table 1. Table 1 shows the optimized reaction conditions for racemic ECH with acetic, propionic, butyric and propynolic acids. It is quite obvious from Table 1 that catalyst II-1-a immobilized on MCM-41 showed relatively morderate enantioselectivity(58-73% ee). In all the cases studied, the conversion of entry 1-4 to the corresponding monoesters underwent in one-pot within 8 h. However, for the catalysts of immobilized type, as compared to the unsupported homogeneous one, the prolonged reaction time was required to reach the high level of ECH conversion. The reactivity of Co(salen)-AlCl3 and Co(salen)-GaCl3 has not shown great differences, however slightly higher ee% of products was obtained by Co(salen)-AlCl3 than Co(salen)-GaCl3. In the catalytic reaction using heterogenized chiral salens, non-polar solvent such as TBME showed dramatical increase in reactivity as compared to other CH2C12, CH3CN, THF and 1,4-dioxane solvent. The reaction using heterogenized Co salen catalyst (II-1-a type) exhibited the same activity and enantioselectivity as homogeneous ones. The enantioselectivity was slightly increased as the chain

466 length of reactant acid increased under the same conditions. The salen complex attached on MCM-41 was not only stable in the acidic media, but also recoverable by simple filtration and solvent rinse. The heterogeneous catalyst was reused repeatedly without any regeneration treatment after filtration. This heterogenized salen catalysts retained unchangeable catalytic activity and enantioselectivity without regeneration for 3 times recycle, indicating the no extraction of salen complex from the support and no deactivation of active site during the repeated use (Scheme 2). Scheme 2. OH

(R,R>n-I-a/NCM41 Cata 01

(R=n-ft)

RaoECH

Cl TBMEsolvent

„ ^

cycle > 73%ee 2CyClC>

3 cycle > 73°/oee

4. Conclusion

In summary, we have synthesized heterogeneous chiral dinuclear complexes and demonstrated their catalytic activity in ARO of terminal epoxides with carboxylic acid as a nucleophile. The resolved ring opened product combined with ring closing in the presence of base and catalyst afforded optically pure terminal epoxides such as (R)-GB in morderate ee% and quantitaive yield by using immobilized chiral salen catalyst on H-MCM-41 and chiral ECH as a reactant. The heterogeneous catalyst can be easily synthesized and the catalytic activity was retained for several times reuse without any regeneration step. Further studies concerning the application in the chiral catalysis are currently under investigation for a broad applicability as a general catalyst. 5. References [1] M. Tokunaga, J.F. Larrow, F. Kakiuchi and E.N. Jacobsen, Science, 277 (1997) 936; M. E. Furrow, S. E. Schaus and E. N. Jacobsen, J. Org. Chem. 63 (1998) 6776. [2] M. Moghadam, S. Tangestaninejad, V. Mirkhani and R. Shaibani, Tetrahedron, 60 (2004) 6105. [3] E. N. Jacobsen, F. Kakiuchi, R. G. Konsler, J. F. Larrow and M. Tokunaga, Tetrahedron Lett., 38(1997)773. [4] S. S. Thakur, W. Li, S. J. Kim and G.-J. Kim, Tetrahedron Lett., 46 (2005) 2263. [5] R. Ryoo, C.H. Ko and R.F. Howe, Chem. Mater., 19 (1997) 1607. [6] W. Li, S. S.Thakur, S.-W. Chen, C.-K.Shin, R. B.Kawthekar and G.-J. Kim, Tetrahedron Lett., 47 (2006) 3453.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

467 467

Chiral (salen) cobalt complexes encapsulated in mesoporous mordenite as an enantioselective catalyst for phenolic ring opening of terminal epoxides Kwang-Yeon Lee, Young-Hee Lee, Chang-Kyo Shin and Geon-Joong Kim* Department of Chemical engineering, Inha University Incheon 402-751, Korea

Phenolic ring opening of epoxides was performed successfully by using chiral (salen) Co(III) caralysts encapsuled in mesoporous mordenite. 1. Introduction The chiral (salen) Co (III) catalysts is the great interest for the synthesis of chiral intermediates [1]. Many types of heterogeneous catalysts have been developed by grafting on the inorganic material [2] or copolymerization on the polymer [3] and by encapsulation in the pores [4] or attachment on the membrane [5] due to simple separation. Microporous crystalline zeolites have unique properties, but their pore sizes are not efficient at processing large molecules. The mesoporous cage structures can be the attractive hosts for the design of hybrid systems. Herein we report the synthesis of chiral (salen) Co (III) complex in the pores of mosoporous mordenite by ship-in-bottle method and enhanced catalytic activity in the phenolic ring opening of terminal epoxides. 2. Experimental Section 2.1. Mesoporosity formation in mordenite by desilication-dealumination Mordenite (JRC-Z-M-15(1), TOSOH Corporation) was treated in 0.3-0.9 N NaOH solution at 338K for 5 hr to form mesoporisity by desilication [6]. After treatement of alkaline solution, dealumination was carried out [7] by refluxing

468

the sample in 3-N HCl solution for 3h. This support was ion-exchanged in hot CoCl2-6H2O aqueous solution for 5 h. The obtained sample was characterized by XRD, SEM and BET analyses. The formation of mesoporosity was confirmed by N2-adsorption by BET method. 2.2. Preparation of the chiral (salen) Co (III) complex encapsulated in mesoporous mordenite ooooooo I ooooooo ooooooo ooooooo 1 .Alkarine ooooooo ooooooo 2-Acld I ooooooo ooooooo ooooooo

i

AOBOOOO

1 .CO(II)O*

c

4H 2 O

THF

A

1. coated by water 2. end-capped by Ti[OCH(CH3)2l4

Scheme 1

Scheme 1 shows the sequence to incorporate the chiral (salen) Co (III) catalysts into the mesopores of mordenite by ship-in-bottle method. First, (lR,2R)-l,2-cyclohexandiamine solution in MC was introduced into the drying mordenite and the sample was dried by evaporation under vacuum. Additionally 3,5-di-tert-butyl-2-hydroxybenzaldehyde was added by the same procedure. This treatment step was adopted repeatedly for 3 times. The mixture of additional components for salen construction, pre-treated mordenite and MeOH soution were stirred together for 12h. The powder was collected after washing with different solvents and incorporation of Co(II) ion and the treatment of MX3 and 4-nitrobenzenesulfonic acid(NBSA) was done to obtain the corresponding Co(III)-NBSA type catalyst. After removal of solvent, the surfaces of mordenite were coated with water and then Ti[OCH(CH3)2]4 in MC/THF was treated to reduce the opened large aperture by hydrolysis. The repeated treatment for three times was performed for encapsulation of salen molecules. 3. Results and Discussion Fig. 1 shows the SEM images of starting mordenite sample and desilicated and dealuminated one. Mordenite was so stable to maintain the crystal structure

469

under the severe condition of 0.9-N NaOH and 3-N HCl treatment as shown in Fig. 1. The strong XRD peak was found after alkaline and acid solution. However, mesopore formation could be confirmed by BET analysis. The mesopores of 15-20 nm was formed inside of mordenite crystals. This mesopore channel was used to Hfti.SEMilI1H8esof<)riginalnK)ntolite(A)aild modified encapsulate

the

Chiral

Salen

by using 0.9NNaOH solution and 3N HCl solution (B).

complexes.

Relative Pressure (pypo>

Fig 2. XRD patterns of mordenites (A) and pore distribution of mordenites (B). Adsorptiondesorption isotherms for original mordenite(C), desilicated powder by 0.3N NaOH (D) and 0.9N NaOH (E) solution, treated by 0.9N NaOH solution and 3N HCl solution (F). Table 1. The Phenolic Kinetic Resolution using Heterogeneous Co(III) Catalysts. OH

Cat. Cl

t-BME

Salen

Conversion

Enantiomeric

(MX,)

(%)

Excess(%)

H

AlCb

44

88

H

InCI3

46

3-CHj

AlCb

40

Ri

Salen

Conversion

Enantiomeric

(MX3)

(%)

Excess(%)

3-CH3

InCl3

38

68

91

3-CI

AlCb

43

86

75

3-C1

GaCl3

45

86

Ri

470 Table 2. Recycle Ability of Co(III)-NBSA type Salen Catalyst Encapsulated in Mesoporous Mordenite.

The enantioselective catalytic activity of encapsulated chiral (salen) catalyst was examined for the phenolic ring opening Salen Conversion Enantiomeric Recycle reaction of epichlorohydrin Excess(%) (MXs) (ECH). The obtained result is 42 91 H summarized in Table 1. The salen catalysts showed 87 Cycle 2 38 remarkable enhanced reactivity Cycle 3 90 43 with substantially low loadings. The reaction using encapsulated 74 Cycle 1 36 3-CH3 AICI3 Co-salen catalysts exhibited 33 Cycle 2 70 slightly lower enantioselectivity than homogeneous ones (conv.; 40 73 Cycle 3 >45%, ee%; >99%). Cobaltexchanged zeolite itself shows no 86 43 3-CI GaCl3 Cycle 1 activity in this reaction, As a 80 42 Cycle 2 result, the formation of large mesopores in mordenite can be 86 44 Cycle 3 supported by the activity of salens encapsulated in pores. The For cycle 1 and cycle 2, heterogeneous salens were used immobilized catalyst was without regeneration by 4-NBSA. Cycle 3 shows the recoverable by simple filtration result of PHK after regeneration of catalyst with 4-NBSA. and solvent rinse. It is so easy to isolate the immobilized salen catalysts from the product solution containing epoxide and diols. This heterogenized salen catalysts retained the catalytic activity and enantioselectivity after repeated use without regeneration. The ship-in-bottle encapsulation of chiral salen showed not only the formation of mesopores in microporous mordenite crystal but also the way to expand the application of salen catalysts as a heterogenized form. 4. References [1] H. J. Federsel and J. Crosby, Chirality in industry II, J.Wiley & Sons, 1997, p. 295. [2] G. J. Kim and J. H. Shin, Tetrahedron Letters, 40 (1999) 6827. [3] K. B. M. Janssen, I. Laquiere, W. Dehaen, R.F. Parton, I. F. J. Vankelecom and P. A. Jacobs, Tetrahedron: Asymmetry, 8 (1997) 3481. [4] L. Drozdova, J. Novakova, G. Schulz-Ekloff and N. I. Jaeger, Microporous and Mesoporous Materials, 28 (1999) 395. [5] S. D. Choi and G. J. Kim, Catalysis Letters, 92 (2004) 35. [6] J. S. Jung, J. W. Park and G. Seo, Appled Catalysis A:General, 288 (2005) 149. [7] C. Schuster and W. F. Holderich, Catalysis Today, 60 (2000) 193. [8] C. K. Shin, S. J. Kim and G. J. Kim, Tetrahedron Letters, 45 (2004) 7429.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

471 471

Effect of surface functional groups on adsorption and release of bovine serum albumin on SBA-15 S.-W. Song, S.-P. Zhong, K. Hidajat and S. Kawi* Department of Chemical and Biomolecular Engineering, National University of Singapore, 4 Engineering Drive 4, Singapore 119260

1. Introduction The rapid progress of peptide and protein synthesis technology has boosted the development of controlled protein or peptide delivery systems. The most widely investigated protein delivery systems are polymer or liposome-based system [1-2]. With an emerging and increasing interest in the application of mesoporous silica as a drug delivery system, we propose to employ SBA-15, a member of mesoporous silica as an alternative candidate for protein drug matrix as it has tunable large pores to host protein molecules [3] and the potential to overcome the limitations associated with polymers or liposomes, such as detrimental protein integrity during processing, small protein loading or low mechanical stability. As surface chemical composition is one of the important factors determining the availability of certain functional species to interact with proteins, we introduce three different functional groups, -NH2, -SH, or -COOH onto SBA-15 to study their effects on the adsorption and release of model protein drug bovine serum albumin (BSA). 2. Experimental Section Functionalized SBA-15 materials were prepared by one-pot synthesis according to the procedure reported by our previous study [4]. The molar composition of the mixture was 1 TEOS: 0.05 X-TES: 0.017 P123: 2.9 HC1: 202.6 H2O. (X-TES refers to 3-aminopropyltriethoxysilane, mercaptopropyltriethoxysilane, or 4-triethoxysilylbutyronitril). The adsorption isotherms of BSA on SBA-15 were obtained at 22°C in citrate-phosphate buffer solution of pH 4.69. The BSA release studies were conducted in phosphate buffered saline solutions (PBS, pH 7.4) at 37±0.1°C. Surface areas, pore size distributions and

472

total pore volumes were determined from N2 adsorption/desorption data using Quantachrome Autosorb-1. FT-IR spectra were collected using Shimadzu FTIR-8700. XPS was performed on Kratos Axis His instrument. The cytotoxicity of SBA-15 materials was evaluated using 3-[4,5-dimethylthiazol-2-yl]2,5-diphenyltetrazolium bromide thiazolyl blue (MTT) assay, and the cell viability was expressed as % of the corresponding control values. Circular Dichroism (CD) spectra were collected on a Jasco-810 spectropolarimeter over 200-250 nm at 22°C. 3. Results and Discussion 3.1. Characterization of SBA-15 materials Table 1 shows that the hydrothermal treatment temperature has a more significant effect on enlarging the pore sizes of NH2-SB A-15 than on other functionalized SBA-15. In addition, it should be noted that the advantage of one-pot synthesis of COOH-SBA-15 is that no further hydrolysis step is required during the synthesis as the intermediate -CN group could be directly converted to -COOH group in the highly acidic hydrothermal treatment condition [5]. Table 1. Physicochemical characteristics of pure and functionalized SBA-15 samples Sample ID

Reaction temperature* (°C)

BET surface area

(A)

Pore volume (cm}/g)

Nitrogen content (wt%)

Sulphur content (wt%)

Pore size

2

(m /g) S-0

40, 100

602.3

86.2

1.12

0

0

NH2-S-1

40, 100

424.7

86.8

1.10

0.56

0

NH2-S-2

40, 140

421.8

106.1

1.03

0.58

0

COOH-S-1

40, 100

475.2

84.2

1.02

0

0

COOH-S-2

40, 130

437.3

86.1

0.99

0

0

SH-S-1

40, 100

559.4

71.5

1.04

0

1.31

SH-S-2

40, 130

512.8

86.7

0.94

0

1.13

* Reaction at 40 °C for 24 hours, then hydrothermal treatment at higher temperature for 48 hours.

The incorporation of functional groups can be confirmed from elemental analysis results, FTIR or XPS spectra. The FTIR spectra (not shown) show that there is a peak appearing at 1602 cm'1 for NH2-S-1 (corresponding to -NH2 bending mode) or 1718 cm"1 for COOH-S-2 (corresponding to -C=O stretching vibration for -COOH group). The XPS spectra of Cls, Nls and S2p (not shown)

473

respectively show that there are peaks at 286 eV for COOH-S-2, 399 and 401 eV for NH2-S-1, and 164 eV for SH-S-2, showing the presence of-COOH [6], NH2 [7] or -SH groups [8] on functionalized SBA-15.

3.3. Cytotoxicity of SBA-15 and conformational change of released BSA

BSA loading amount (mg/g solid)

Figure 1 shows the adsorption isotherms of BSA (in phosphate-citrate buffer solutions having an ionic strength of 0.16 M at pH 4.69) on S-0, COOH-S-2, SH-S-2 and NH 2 -S-1, all of which have similar pore sizes. A higher loading amount of BSA is obtained on SH-S-2 and NH2-S-1 than on S-0 and COOH-S-2. The initial slope of the adsorption isotherm of BSA on NH2-S-I is steeper than that on SH-S-2, suggesting - based on pseudo-Langmuir model - that there is a stronger binding affinity between BSA and NH2-S-1 [9]. Figure 2 shows the release profiles of BSA from SH-S-2 and NH2-S-1. BSA is immediately released from SH-S-2 (within 30 min) but sustainedly released from NH2S-l (within 480 min) due to the stronger interaction between BSA and NH2-S-1.

200

d c

150

b 100

a 50

0 0.0

0.5

1.0

1.5

2.0

2.5

3.0

Solution concentration (mg/ml)

Figure 1. Adsorption isotherms of BSA on: a- COOH-S-2; b- S-0; c- SH-S-2 andd-NH,-S-l. 100

Cumulative released BSA (%)

3.2. Adsorption and release of BSA on SBA-15

90

80

70 SH-S-2 NH2-S-1

60

50

0

100

200

300

400

500

Figure 2. Release profiles of BSA fromNH2-S-l and SH-S-2.

Since a higher BSA loading amount and a slower release rate could be obtained on NH2-S-1, subsequent studies of cytotoxity and conformation of the released BSA were conducted on NH2-SBA-15. Figure 3 shows the cell viability of pure and NH2-SBA-15 at two different concentrations of SBA-15, i.e. 0.1 and 0.5 mg/ml. The results indicate that the cytotoxicity effect of NH2SBA-15 is very low as compared with pure SBA-15; the cell viability is more than 80% even at a high concentration of 0.5 mg/ml, suggesting that introduction of amine groups could attenuate the cytotoxicity induced by pure SBA-15. Figure 4 shows that CD spectrum of the released BSA from NH2-SBA-15 is similar to that of the native BSA. In addition, the calculated percentage of ahelix in the native and released BSA are 66.8% and 64.3%, respectively, indicating that BSA conformation has not been severely or irreversibly altered by its adsorption on hydrophilic NH2-SBA-15 prepared by one-pot synthesis.

474

H Amine-Functionalized Amine-Functionalized SBA-15 SBA-15

• Control Control

Cell Viability (%)

100

.2 >

80

60

3 «40 20 0

0.1

0.5

Concentration (mg/ml)

20

2

• Pure Pure SBA-15 SBA-15

10

-3

120

Molar Ellipticity (10 deg•cm /dmol)

This result is in good agreement with that reported by Norde and Giacomelli [10], who found that BSA adsorption is reversible on hydrophilic surfaces.

0

-10

Released BSA

-20

Native BSA

-30 200

210

220 220

230

240

250

Wavelength (nm) Wavelength

Figure 3. Cytotoxicity of pure and fitnctionalized SBA-15 materials.

Figure 4. CD spectra of native BSA and released BSA.

4. Conclusion Three different functional groups, -NH2, -SH, or -COOH, were directly incorporated into mesoporous silica SBA-15 materials by one-pot synthesis. Adsorption isotherms of BSA on the resulting SBA-15 materials show that higher adsorption capacities were obtained on NH2- and SH-functionalized SBA-15. However the release profiles show that BSA could be sustainedly released only from NH2-functionalized SBA-15. CD spectra show that BSA conformation could be well-maintained even after adsorption and subsequent release from NH2-functionalized SBA-15. Furthermore, the cytotoxicity results indicate that surface NH2 groups can inhibit cytotoxicity of pure mesoporous silica materials. 5. References [1] E. Mathiowitz (ed), Encyclopedia of controlled drug delivery, Vol.2, Wiley-Interscience, New York, 1999. pp. 816 [2] D. Simberg, S. Weisman, Y. Talmon and Y. Barenholz, Crit Rev. Ther. Drug, 21 (2004) 257. [3] D. Zhao, J. Feng, Q. Huo, N. Melosh, G. H. Fredrickson, B. F. Chmelka and G. D. Stucky, Science, 279 (1998) 548. [4] S. W. Song, K. Hidajat and S. Kawi, Langmuir, 21 (2005) 9568. [5] H. H. P. Yiu, P. A. Wright and N. P. Botting, J. Mol. Catal. B, 15 (2001) 81. [6] C. D. Bain, E. B. Troughton, Y.-T. Tao, J. Evall, G. M. Whitesides and R. G. Nuzzo, J. Am. Chem. Soc, 111(1989)321. [7] K. M. R. Kallury, P. M. Macdonald and M. Thompson, Langmuir, 10 (1994) 492. [8] Q. Zhang, H. Z. Huang, H. X. He, H. F. Chen, H. B. Shao and Z. F. Liu, Surf. Sci., 440 (1999) 142. [9] C. A. Haynes and W. Norde, Colloids Surf. B, 2 (1994) 517. [10] W. Norde and C. E. Giacomelli, J. Biotechnol, 79 (2000) 259

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

475 475

Microstructure understanding of organic-inorganic hybrid mesoporous silica by SAXS Yan-jun Gonga*, Zhi-hong Lib and Tao Doua "Catalysis Key Laboratory, CNPC, University of Petroleum, Beijing 102249, China. Lab of Synchrotron Radiation, Institute of High Energy Physics, Beijing 100039, China.

1. Introduction Incorporation of organic moieties into mesoporous silica framework is of considerable interest due to its scientific and industrial applications [1]. For organically modified mesoporous silica (OMMS), their pore structure and composition properties have been examined clearly by HRTEM, N2 adsorption, FT-IR, NMR and SAXS [1,2], but the microstructure concerning its interfacial and skeleton is less reported, mainly due to the higher difficulty in achieving well-established analysis procedures used for OMMS. We previously synthesized the OMMS by one-pot template-directed synthesis strategies and employed SAXS technique to characterize the microscopic structure [3-5]. The results showed that the organically modified groups covalently linked with the matrix of mesoporous silica and formed an interfacial layer, which led to the scattering of the pore distortion and gave a negative deviation from Porod's law. The average wall thickness of the interfacial layer could be obtained by analyzing this deviation [3-5]. The present report focuses on a detailed study of a negative deviation behavior of organically modified MSU-X mesoporous silica by SAXS. In order to evaluate the textural characteristics of organicinorganic MSU-X, the porod's deviation resulted from some different synthesis parameters, such as template, the organic groups and their fractal dimensions were also discussed. 2. Experimental Section As shown in Scheme 1, the organically modified silica (R-MSU-1) were prepared by one-pot synthesis strategy using tetraethoxysilane (TEOS) and organotriethoxysilane (RTES, R=methyl or Phenyl) as precursor and non-ionic

476

surfactant Cn-isI^-^tCI-kCHO^H as template [3]. The bi-functionalized mesoporous silicates were prepared by using TEOS and other two organosiloxanes as silicon sources to form binary organically modified-MSU-1. The template was extracted over ethanol for 48 hrs.

RSi(OEt)3 + Si(OEt)4

Tem late Template p

R R

R R

R R

R R R R

R R

R R

Template Extraction •

R R

R R

R R

R R R R

R R

R R R R R R

Scheme. 1 Synthesis of organically modified MSU-1

SAXS experiments were performed using synchrot ron radiation as X-ray source with a long-slit collimation system at Beijing Synchrotron Radiation Facility. Incident X-ray wavelength A. was 0.154 nm, and the scattering angle 29 was approximately 0-3°, the scattering vector was denoted as q, <7=47tsin9/A,. The scattered X-ray intensities were recorded using imagery plate technology. 3. Results and Discussion 3.1. Porod 's Deviation All the produced samples was characterized by XRD, HRTEM, N2 adsorption, FT-IR, NMR techniques, which showed that the mesoporous structure was formed and the organic groups covalently existed on the pore of the silica framwork [3]. SAXS is a powerful tool that originates from spatial fluctuations of the electronic density within a material, which is especially useful for determination of the microstructure of organically functionalized materials. Porod's law could be used to distinguish the ideal two-phase system from the non-ideal two-phase system. In the ideal two-phase system of a porous material, this implies a solid matter (matrix) with a constant electron density and pores with zero density. Only the scattering by ideal two-phase system with sharp boundary obey Porod's law. For a non-ideal two-phase system with a diffuse interfacial layer between two phases, the SAXS will show negative deviation from Porod's law [6, 7]. A linear relation with a negative slope of ln[gf3JObS(^)]~^2 curve in the high values of scattering vector can be fitted with the Porod's curve [6-8]. ln[Abs(<7)] = \nK-Jq2 where cris a parameter in relation to the thickness of the interfacial layer. Based on SAXS experiments and Porod's theory, the deviation, i.e. the slope of ln[q*J(q)] vs. q2 in high angle range is listed in the Table 1. It was very

477 477

interesting that there appeared three types of Porod scattering, i.e. no deviation, negative deviation and positive deviation from Porod's law [8]. This suggested that there existed structural differences between these materials. Both sample land 2 were pure mesoporous silica (MSU-1) and no incorporated organic groups remained in the pore channels. The slope from Porod's law was zero for the template extracted sample 1, whereas it's positive for sample 2 due to its template still existed after synthesis. The templates remaining in the mesochannels produced the additional scattering background and led to a positive deviation. For the sample 3 to 7 (R-MSU-1), the slope was negative due to organic groups remained covalently to the silica matrices. It was these organic groups that comprised the interfacial layers, and their average thickness E could also be obtained (Table 1) by reported method [3-5]. With the increase of the molar ratio of MTES/TEOS from 5 mol% to 20 mol% (sample 3, 4, 5), the negative slope was increased and the E reasonably increased from 1.09 to 1.61nm. Under the same molar ratio of RTES/TEOS (for sample 4, 6), there were not the same slope and E value. This might be due to that the steric effect of phenyl is strong than that of methyl and other factors influencing the hydrolysis and condensation of precursors. For sample 8 (R-MSU-1), the template was not extracted, its absolute slope was little smaller than that of the template-extracted sample 6, which might be attributed to the both of positive and negative results from remained the templates and covalently linked organic groups, respectively. Take M-MSU-1 for a typical sample (not shown), when both the template and organic group were removed after calcination at 550°C, its slope was zero. These further demonstrated that the organic groups covalently linked to the silica skeletons and existed on the pore surface to form the interfacial layers, which influenced the scattering results of porous system. Table 1 SAXS structural parameters of SiMSU-1 and R-MSU-1 Organic group

Template Extraction

Slope

E/nm

Ro/nm

TEOS

0

YES

0

0

1.65

2

TEOS

0

NO

+0.162

0

0.79

3

TEOS+MTES

Methyl(5)

YES

-0.189

1.09

1.40

4

TEOS+MTES

Methyl(lO)

YES

-0.245

1.24

1.42

5

TEOS+MTES

Methyl(20)

YES

-0.413

1.61

1.38

6

TEOS+PhTES

Phenyl(lO)

YES

-0.392

1.57

2.00

TEOS+MTES+

Methyl(lO) +Phenyl(10)

YES

-0.510

1.79

1.53

PhTES TEOS+PhTES

Phenyl(lO)

NO

-0.169

—

1.41

sample

Precursor

1

7 8

478

3.2. Fractal Characteristics According to SAXS data plotted as ln[J(q)]~lnq for R-MSU-1, both surface fractal (Ds) and pore fractal structure (Dp) were obtained for OMMS (Table 2) [9,10]. The pore dimensions measured by SAXS represent the statistical average of all the individual pore sizes in the mesoporous matrix. Whether the pure SiMSU-1 or R-MSU (M-MSU-1, Ph-MSU-1), the fractal dimension (Ds) of so-produced mesophases indicated the presence of rough surface. The Ds changed from 2.38 to 2.54 due to the presence of different kind of the organic groups. Table 2 SAXS Structural parameters of organically functionalized MSU-1 Samples

Template Removal

Organic Group

Porod Deviation

E/nm

Ds

SiMSU

extraction

NO

NO

0

2.38

M10-MSU

extraction

Methyl

Negative

1.24

2.46

PhlO-MSU

extraction

Phenyl

Negative

0.99

2.54

4. Conclusion For organically modified mesoporous silica, the SAXS slope of Porod's curve in high angel was determined, which indicated the interface layer thickness was different with the organic groups and their amounts in the mesoporous framework. The negative deviation from Porod's theory caused by organic groups existed on the pore surface. These materials possessed different of fractal dimensions varying the material preparation condition. 5. Acknowledgment This work was supported by National Basic Research Program of China (No. 2004CB217806). 6. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10]

B. Hatton, K. Skron, W.Whitnall, D. Perovic and G. A. Ozin, Ace. Res., 38 (2005) 305. X. Ji, Q. Hu, J. E. Hampsey.X. Qiu, L. Gao.J. He and Y. Lu, Chem. Mater.,18 ( 2006) 2265. Y. J. Gong, Z. H.Li, D.Wu and Y. H.Sun, Microporous Mesoporous Mater., 49 (2001) 95. Z. Li, Y. J. Gong, D.Wu and Y. H. Sun, Microporous Mesoporous Mater., 46 (2001) 75. Y. J. Gong, Z. H. Li, D.Wu and Y. H.Sun, Stud. Surf. Sci. Catal., 146 (2003) 461. K. J. Edler and J. W. White, J. Mater. Chem., 9 (1999) 2611. T. R. Pauly,Y. Liu and T. J. Pinnavaia, et.al. J. Am. Chem. Soc, 121(1999) 8835 G. Porod, Kolloid-Z, 124 (1951) 83. Z. Li, Y. J. Gong, D. Wu and Y. H. Sun, Nuclear Tech., 27 (2004) 14. P. J. McMahon and S. D. Moss, J. Appl. Cryst., 32 (1999) 956.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

479 479

Surface aminosilylated mesoporous SBA-15 with rare earth metal sandwiched polyoxometalates as heterogeneous catalyst Yan Zhou, Bin Yue*, Renlie Bao, Min Gu and Heyong He* Department of Chemistry and Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, Fudan University, Shanghai 200433, P. R. China.

1. Introduction Polyoxometalates (POM) have been well-known as active catalysts for the oxidation of organic compounds with hydrogen peroxide in both heterogeneous and homogeneous systems [1-3]. Although high conversion and selectivity have been reported for homogeneous POM catalyzed reactions, they are far from industrial application since the separation of the catalysts from the products is very difficult. Heterogenization of POM is an ideal approach to solve this problem. Previous studies of POM supported on amorphous silica and MCM-41 surfaces focused on the Keggin-type POM acids introduced onto the silica by impregnation method [4]. However, the leaching of supported POMs is inevitable. In this study, three of rare earth metal phosphotungstate anions ([RE(PW,iO39)2]n\ RE = La, Ce, Y) were anchored onto the aminosilylized surface of the silica SBA-15 and their catalytic activity for alkene oxidation with H2O2 as oxidant has been investigated. It is found that the leaching of POM clusters during the reaction is negligible due to the strong interaction between RE-PWn and amino-groups on the silica surface. 2. Experimental Section The rare earth metal sandwiched phosphotungstate were prepared according to the literature procedures [5]. SBA-15 was synthesized using the block copolymer Pluronic PI23 (Aldrich) and tetraethyl orthosilicate (TEOS, 98%, Aldrich) under acidic condition. The aminosilylation procedure was performed according to the literature method [6]. RE-PWn was immobilized within the modified SBA-15 channels through incipient wetness method. Catalytic tests

480

were performed using 8 mL t-butanol, 2.5 ml (25 mmol) hydrogen peroxide, 0.838 g (10 mmol) cyclohexene, 0.150 g catalyst and 2 ml n-hexane as the internal standard. The mixture was stirred in a round-bottom flask fitted with a reflux condenser and reacted at 60°C for 4 h. After the reaction, an aliquot was extracted and filtered. The products were analysed by gas chromatography. Element analysis was determined by ICP. The specific surface area, pore diameter and pore volume were determined from N2 adsorption isotherms. 3. Results and Discussion Elemental analysis was employed to testify whether the RE-PWn ligands were supported onto the SBA-15. The content of RE, P, W and Si are listed in Table 1. The molar ratio of RE, P and W is consistent with that of bulk REPW n . Table 1 ICP elemental analysis and the catalytic performance of RE-PW,, and RE-PW,,/APTSSBA-15 Catalyst KnfLaCPW.Ask] /APTS-SBA-15 K,,[Ce(PW, ,O39)2] /APTS-SBA-15 K,,[Y(PW,,O39)2] /APTS-SBA-15 a b

W

Si

0.619 0.321

23.3

24.1

0.622 0.474

30.2

23.1

0.599 0.386

28.1

23.8

RE

Conversion of Yield of cyclohexene cyclohexene epoxide after 4 h reaction 67 (81)a 44 (67)a 81 (89)a 79b

49 (77)a 30 (51)a 64 (61)a 62b

catalytic performance of bulk RE-PW,, (in parentheses). Y-PW,,/APTS/SBA-15 recycled after the fifth run.

In Figure 1 the typical IR characteristic bands of Y-PWn and Y-PWU/APTS-SBA-15 in the region of 700-1100 cm"1 are attributed to W-O-W and W=O vibrations and P-O in the central PO4 unit of PW H [7]. Among these bands those at 900-1050 cm"1 are partially obscured by the presence of silica [8]. It can be seen that the Y-PW n /APTSSBA-15 has vibration bands similar to the bulk Y-PWH, suggesting the structure of primary PW U polyanion

APTS-SBA-15

8

I\

Y-PW^/APTS/SBA-15

CO 10

c

.

H 1100

1000

900

800

700

600

500

Wavenumbers Fig. 1 IR spectra of APTS/SBA-15, YPWU/APTSSBA-15 and bulk Y-PW,,.

481

dV / dd ml / (g.nm)

2

V o l u m e A d s o r b e d (c m / g )

remained intact after immobilization onto the mesoporous silica surface. The nitrogen adsorption isotherm of Y-PWn/APTS-SBA-15 in Figure 2 is of type IV classification, which has the typical hysteretic loop of mesoporous materials [9]. The surface modified and Y-PWn immobilized samples retain the same shape of the isotherm. The inflection point of the step is shifted to lower P/Po, which is caused by the smaller pore size. The filling and contraction of the channels after aminosilylation of the surface and immobilization of RE-PWn account for the decrease of the pore volume, the pore size and the specific surface area (Table 2). The results confirm that Y-PW n ligands are located inside the channels and the mesoporous channels are preserved. The behavior of La-PWn/APTS-SBA-15 and Ce-PWi,/APTS-SBA-15 on IR and nitrogen adsorption is very similar to that of Y-PWn/APTS-SBA-15. The catalytic activities of RE-PWU/APTS-SBA-15 were tested by studying the reaction of cyclohexene to cyclohexene oxide with hydrogen peroxide. The results in Table 1 indicate that Y-PWn/APTS-SBA-15 and La-PWn/APTSSBA-15 are catalytically active for cyclohexene epoxidation. Ce-PWu/APTSSBA-15 is somehow less effective, this may arise from the oxidation of Ce(III) to Ce (IV) with H2O2, thus decreasing its catalytic activity. The conversions of bulk RE-PWn catalysts are higher than those for the 350-, 350 0.30 supported ones. 0.25 300 0.20 Considering the POM 0.15 content in RE-PW n APTS250 0.10 SBA-15 is much lower 0.05 T3 200 0.00 than in the bulk RE-PWU, CD 0 10 20 Pore diameter (nm) •e the supported catalysts 150 150 o have much higher catalytic CO 100 100 efficiency per POM atoms < CD than the bulk POM. This 50 growth should be E 0 attributed to the increase in O °0.0 0.2 0.4 0.6 0.8 1.0 1.0 surface area and the Relative / p 0) Relative Pressure Pressure (p(p/p) decrease in particle size of POM after immobilized Fig. 2 N2 adsorption-desorption isotherm of Yonto SBA-15. RE-PW,, /APTS-SBA-15 shows high PWn/APTS-SBA-15. Insert: pore size distribution. stability in polar solvent, where the leaching of POM is negligible. For an example, the catalytic activity of the fifth recycled Y-PWU/APTS-SBA-15 catalyst remains unchanged, indicating that the strong interaction between REPW11 and amino-groups on the silica surface prevents leaching of active species of POM.

482 Table 2 Physicochemical properties of SBA-15 and RE-PW ,,/APTS-SBA-15 Samples SBA-15 K,, [La(PW, ,O39)2]/APTS-SBA-15 K,, [Ce(PW, ,O39)2]/APTS-SBA-15 K,, [Y(PW, ,O39)2]/APTS-SBA-15

Specific surface area (m2/g) 674 308 278 302

Pore diameter (nm) 7.78 6.24 7.59 7.32

Pore volume (cm3/g) 1.25 0.496 0.465 0.458

4. Conclusion La, Ce, and Y-containing POM, RE-PWn, are sucessfully immobilized in the channels of aminosilylated ATPS/SBA-15. RE-PW,,/APTS/SBA-15 combines catalytic activity of RE-PWn and high surface area of SBA-15 and shows high catalytic activity. The strong interaction between RE-PWn and amino groups grafted on the silica channel surface leads to negligible leaching of RE-PWn species after catalytic reaction. 5. Acknowledgement This work is supported by the National Basic Research Program of China (2003CB615807), the NSF of China (20371013, 20421303) and the Shanghai Science and Technology Committee (05DZ22313). 6. References [1] [2] [3] [4] [5] [6] [7] [8]

T. Okuhara, N. Mizuno and M. Misono, Appl. Catal. A: Gen. 222 (2001) 63. C. L. Hill and C. M. Prosser-McCartha, Coord. Chem. Rev. 143 (1995) 407. N. Mizuno and M. Misono, Chem. Rev. 98 (1998) 199. T. Blasco, A. Corma, A. Martinez and P. Martinez-Escolano, J. Catal. 177 (1998) 306. W. P. Griffith, R. G. H. Moreea and H. I. S. Nogueira, Polyhedron 15 (1996) 3493. K. K. Zhu, B. Yue, W. Z. Zhou and H. Y. He, Chem. Commun. (2003) 98. S. Choi, Y. Wang, Z. Nie, J. Liu and C. H. F. Peden, Catal. Today 55 (2000) 117. D. F. Li, Y. H. Guo, C. W. Hu, L. Mao and E. B. Wang, Appl. Catal. A: Gen. 235 (2002) 11. [9] D. Y. Zhao, J. L. Feng, Q. S. Hou, N. Melosh, G. H. Fredrickson, B. F. Chmelka and G. D. Stucky, Science 279 (1998) 548.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

483 483

Characterization of nickel metal distribution in Ni/Y -zeolite Dul-Sun Kim, Jung-hee Yoon, Jae-Suk Shin and Dong-keun Lee Dept. of Chemical and Biological Engineering, Environmental Biotechnology National Core Research Center(EBNCRC), Environmental and Regional Development Institute, GyeongsangNational University, Kajwa-dong 900, Jinju, Gyeongnam 660-701, Korea

1. Introduction Zeolites have been known to be promising supports because they can be utilized to prepare catalysts containing highly dispersed metals, to show molecular sieving effect and to induce polyfunctional activity[l-5]. In this research Ni/Y-zeolite catalysts having different nickel metal distribution were prepared, and the nickel metal distribution in the reduced Ni/Y-zeolites was investigated. 2. Experimental Section NaY zeolite with a Si/Al molar ratio of 2.5 was provided from Strem Chemicals. The 10 wt% Ni/Y-zeolite (42.5% Ni cation exchange) sample was prepared by a conventional ion exchange method. The prepared Ni/Y -zeolite was dried in air at 80°C for 12 h, and was then reduced in hydrogen stream to the desired extent of reduction. All the reduced samples used in the present study will be abbreviated by the symbols of (reduction temperature, °C) (reduction time, h) in the rest of the text. Temperature programmed reduction (TPR) and oxidation (TPO) experiments were performed in a closed system with gas circulating unit to determine the amount of nickel metal inside and outside the zeolite by following the procedure of Jacobs et al. [6]. Ferromagnetic resonance (FMR) spectra of nickel metal were recorded at Xband frequencies on a Varian E-4 spectrometer. The quartz sample tube was designed for the in situ operation. X-ray diffraction line broadening was measured on a diffractometer (JEOL, JDX-1193A) using CuKoc radiation. Transmission electron microscopy was done with a JEOL 200 CX microscope

484

using 160 KeV electrons.The adsorption isotherms of H2 were measured at 25°C in a conventional Pyrex glass volumetric adsorption apparatus. The dispersion of nickel particles were calculated from the irreversible uptakes of H2 [7]. 3. Results and Discussion A typical result of TPR/TPO consecutive experiments for a 10 wt% Ni/Y-zeolite catalyst is shown in Figure 1. Curve A denotes the rate of nickel ion reduction to nickel metal which may be formed inside or outside the zeolite. The degree of nickel ion reduction can be calculated from the ratio of the amount of the hydrogen consumed and the total amount of the nickel ion in zeolite by considering the reaction 200 300 400 500 600 of Ni2+ + H2 -» Ni° + 2H+. Upon oxidation TEMPERATURE ("C) each metal phase inside or outside the zeolite Figure 1. Typical curves of may be oxidized at different routes as TPR/TPO experiments. suggested by Jacobs et al. [8]. Curve B represents the oxidation rate, but no discrimination could be achieved. During a second reductive treatment of this oxidized sample (curve C) a new low temperature maximum together with a new high temperature maximum in the reduction rate is observed. At the end of the first and second reduction nearly the same amounts of hydrogen were consumed. From the peaks of the low- and high- temperature maxima the amounts of nickel metal phase inside and outside the zeolite can be deduced, respectively. In Table 1 are listed the degree of reduction and the fraction of the amounts of nickel metal inside and outside the zeolite. Both the degree of reduction and the fraction of nickel metal outside the zeolite are known to increase with increasing reduction temperature and time. Figure 2 shows the four representative photographs obtained by TEM on the 10 wt% Ni/Y-zeolite catalysts reduced at different conditions. Photographs a, b and c are 153 representative for the samples of 500Fl 8, 400-8 and 350-8, respectively. The size of nickel crystallites existing at the exterior surface of the zeolite is • shown to increase with increasing reduction temperature indicating that more and more metal migrates out of _ the zeolite pores and agglomerates as bulky crystallites. When the sample n f N i / v . , m 1 i t , ^ i v ^ ^ - s n o - s , b : 400-8, of Ni/Y-zeolite catalysts c:350-8, d:300-l).

485

was reduced at 300°C for lh (photograph d), no nickel crystallites of detectable size are found. In this case most of the nickel crystallites are believed to exist within the Degree of Nickel metal pores of the zeolite and the size will be Catalyst Reduction distribution(%) (%) Inside Outside less than that of faujasite supercage (=1.3 500-12 60.0 64.0 36.0 nm). 500-4 59.8 60.0 40.0 FMR spectra for the 10 wt% Ni/Y500-1 59.7 58.5 41.5 zeolite catalysts do change significantly 400-12 32.2 44.3 67.8 with reduction conditions as shown in 400-4 40.1 28.4 71.6 Figure 3. When the catalyst was reduced 450-1 37.5 73.9 26.1 at 300°C for 1 h, nearly symmetric and narrow peak (line width=l 100 G) appears at the g-vavle of 2.22. As the reduction temperature increases, the peak becomes asymmetric and its line width broadens to have 2300 gauss for the 600-1 catalyst. Following the suggestions by Jacobs et al. [8], the symmetric and narrow peak is representative of the small nickel metal Figure 3. FMR spectra of Ni/Y- zeolite within the pores of Y-zeolite, while the catalysts (detection temperature = 20 °C). highly asymmetric broad peaks are mainly due to the large nickel metal at the exterior surface of the zeolite. Aforementioned results of TPR/TPO, TEM and FMR show the existence of the bidispersion of nickel metal inside and outside the zeolite. The sizes of nickel crystallites obtained from X-ray line broadening, TEM and H2 chemisorption are listed in Table 2. Table 2. Nickel crystallite size in the Ni/YBetween the sizes from X-ray line zeolite catalysts broadening and those from H2 Nickel crystallite size (nm) chemisorption incompatible results Catalyst H2 H2 are obtained. XRD TEM Chem. Chem.* The size from X-ray line 500-12 20.4 31.0 30.6 19.6 broadening increases with increasing 30.4 500-8 21.8 30.9 18.8 reduction temperature, while the size 500-1 16.3 29.9 17.5 calculated from H2 chemisorption 450-1 15.2 43.0 11.2 does not show a distinct tendency 10.9 400-8 13.6 28.9 36.0 and is always larger than that from 12.4 30.4 7.6 400-1 X-ray line broadening. In particular 12.2 21.7 58.1 7.0 the size of 45.0 nm for the 300-1 350-8 + + 300-1 45.0 catalyst from H2 chemisorption is • Nickel crystallite size was calculated by following the unreasonably too large when assumption that the nickel metals inside the zeolite pores are compared with the TEM photograph inactive to H2 chemisorption. (Figure 2-d) and X-ray line + No nickel crystallites of detectable size were observed. broadening which showed no nickel crystallites of detectable size. Table 1. Degree of reduction and nickel metal distribution in the Ni/Y-zeolite catalysts reduced at different conditions

486

Kubo et al. [9] reported that atomically dispersed platinum was inactive to H2 chemisorption. Therefore, if the zeolite includes a number of nickel species inactive to H2 chemisorption, the size from H2 chemisorption must have been overestimated. The size of nickel crystallites was calculated again from H2 chemisorption by assuming that the nickel metal phase within the zeolite pores is inactive to H2 chemisorption. The sizes from the modified hydrogen chemisorption (listed in the fifth column in Table 2) agree well with those from X-ray line broadening. Therefore H2 chemisorption is believed to be suppressed on the small nickel metal particles within the zeolite pores. 4. Conclusion Ni/Y-zeolites were prepared by a conventional ion exchange method, and the samples were reduced with H2 at different temperature and time. The nickel metal distribution in the reduced Ni/Y-zeolit was then studied by using TPR/TPO, TEM and FMR. TPR/TPO, TEM and FMR investigations on the reduced Ni/Y-zeolite catalysts have shown the existence of a bidispersion of nickel metal particles. Small nickel metal particles were restricted inside the zeolite, while large particles were formed outside the zeolite crystal. With increasing reduction temperature and time both the degree of reduction and the fraction of nickel metal outside the zeolite increased. The primarily formed nickel metal inside the zeolite migrated out of the pores continuously, and then agglomerated at the exterior surface of the zeolite as large particles. 5. Acknowledgement This work was supported by a grant from the KOSEF/MOST to the Environmental Biotechnology National Core Research Center (grant #: R152003-02002-0). Some scholarship was supported by BK21 Program. 6. References [1] K. M. Minachev and Y. I. Isakov (1976), Zeolite Chemistry and Catalysis(J.A. Rabo, Eds.), American Chemical Society, Washington. [2] D.-K. Lee and S.-K. Ihm, Appl. Catal., 32 (1987) 85. [3] D.-K. Lee and S.-K. Ihm, J. Catal., 106 (1987) 386. [4] J. H. Lee, S.-K. Ihm and D.-K. Lee, React. Kinet. Catal. Letts., 57 (1996) 301. [5] J. H. Lee, D.-K. Lee and S.-K. Ihm, Stud. Surf. Sci. Catal., 83 (1994) 355. [6] P. A. Jacobs, J. P. Linart, H. Nijs and J. B. Uytterhoeven, J. Chem. Soc. Faraday I, 73 (1977) 1745. [7] C. H. Bartholomew and R. B. Pannell, J. Catal., 65 (1980) 390. [8] P. A. Jacobs, H. Nijs, J. Verdonck, E. G. Derouane, J. P. Gilson and A. Simoens, J. Chem. Soc. Faraday Trans. I, 75 (1979) 1196. [9] T. Kubo, H. Arai, H. Tominaga and T. Kunugi, Bull. Chem. Soc. Japan, 45 (1972) 607.

Progress in in Mesostructured Materials Recent Progress S. Qiu, Y. Tang and C. Yu (Editors) (Editors) D. Zhao, S. © 2007 2007 Elsevier Elsevier B.V. B.V. All All rights reserved. reserved.

487 487

Synthesis of MCM-22/MCM41 composites with zeolite MCM-22 as a precursor Li Yuping3, Zhang Weib, Wang Xiaolib, Dou Taobc' * and Xie Kechanga "Key Laboratory of Coal Science and Technology, Ministry of Education and Shanxi Province, bInstitute of Special chemicals, Taiyuan University of Technology, No. 79 West Yingze Street, Taiyuan 030024, China. c The CNPC key laboratory of Catalysis, China University of Petroleum, Fuxue road, Changping, Beijing 102249, China

1. Introduction In the last decade, many efforts have been devoted to the synthesis of meso/microporous composites as this could give rise to material with bi-mode pore system, and thus, perhaps with interesting catalytic properties. In this aspect, FAU-, MFI-, MOR- and BEA/MCM-41 composites have been synthesized [1-9]. MCM-22 has a unique structure. It consists of two independent pore systems. One is formed by two-dimensional sinusoidal channels, the other is defined by large supercages (0.71 x 0.71 x 1.82 nm). As we know, the characteristics of zeolites depend on their structure. MCM-22 has been proved to be a good acid catalyst [10]. A further combination with mesostructure would lead to the formation of an interesting material. In this paper, we report for the first time the synthesis and characterization of a MCM22/MCM-41 composite (denoted as MMC) from zeolite MCM-22. 2. Experimental Section The sample was synthesized via two steps, zeolite MCM-22 (Si/Al=15) was first stirred in NaOH aqueous solution for about half hour, and then added into a CTAB aqueous solution. The obtained mixture was autoclaved at 373 K for 24 h. This was followed by adjustment of the pH value to 8.5 with 2M HC1 after cooling to the room temperature. The well-adjusted mixture was then heated for 24 h again in a sealed autoclave. The solid product was filtered, washed and dried at 353 K overnight. For comparison, Al-MCM-41 was synthesized under

488

the same conditions as those for the MMC sample except that zeolite MCM-22 was replaced by a corresponding amount of tetraethyl orthosilicate and aluminum isopropoxide. 3. Results and Discussion Fig. 1 shows the XRD patterns of the calcined MMC samples synthesized with different amounts of NaOH. It is clear that the mesostrcuture could not be formed when a small amount of NaOH was used. An increase in NaOH amount to the NaOH/SiO2 ratio of 0.75 resulted in the formation of highly ordered mesoporous material As expected, the unit cell parameters and mesopore opening increased with increasing NaOH amount as a result of the increase in condensation degree. Despite of this, when the NaOH/SiO2 ratio was increased to more than 1.15, the MCM-22 structure was completely destroyed. This shows that the appropriate NaOH/SiO2 ratio in the MMC synthesis gel should be in the range of 0.75 ~ 0.95. By carefully controlling the NaOH amount, the MCM-22 phase and the mesostructured phase contents could be controlled to meet our demands. 1-0.50 1-0.50

800

7000 70002- 2-0.75 2-0.75

600

.»

Intensity/(a.u.)

Intensity/(a.u.)

8000

3-0.95 3-0.95 « 6000 4-1.15 4-1.15 / 5000 50005- 5-1.42 5-1.42 / !

5

'•' ' '

' ^

_

j

i 400 |

4 3

(MM* 2

200 1

0

4000

5

10

15

20

25

30

35

2Theta/degrees

5

3000

4

2000 2000

3

1000 1000

2 V ^ ^ l ^ ^ ^ •£ 1

0 1

2

3

4

5

6

Theta/degrees 2 Theta/degrees

Fig. 1 XRD patterns of Samples in regions of mesoporous and microporous (inset) with different NaOH/SiO2 molar ratios

Fig.2 SEM image of the MMC (NaOH/SiO 2 = 0.75)

Fig.2 shows that partially destructed zeolite MCM-22 platelets interconnected or inter-grew with spherical mesostrutured particles (100 ~ 200 nm) in the composite sample, as indicated by a close joint of these two phases and a uniform distribution. This is different from the mechanical mixture of MCM-22 and Al-MCM-41, which consists of intact thin hexagonal platelets (0.5 - 1.5 u m in length and 0.05 - 0.15 u m in thickness) of MCM-22 crystals and independent spherical Al-MCM-41 particles of about 2 urn. This indicates that the MCM-41 phase in the composite might be constructed by condensing the zeolite structural units originated from the dissolved MCM-22 crystals around surfactant micelle, leading to the more uniform and closer combination of mesostructured phase and zeolitic phase in the composite sample than in the

489

mechanical mixture. The MCM-41 phase might epitaxially grow around partially dissolved zeolite MCM-22 crystals, as shown by HRTEM (Fig. 3).

1-MCM-22(P) 2- MMC(NaOH/SiO2=0.75) 3- Al-MCM-41

400

Fig.3 HREM image of the MMC (NaOH/SiO2 = 0.75)

600 800 1000 Temperature(K)

1200

Fig.4 DTG curves for the as-synthesized samples

Fig. 4 shows the DTG curves for the as-synthesized MMC (NaOH/SiO2 = 0.75) composite> lamellar precursor of MCM-22 (P) and the conventional AlMCM-41. The peak maxima at 494, 539 and 574 K, assigned to the desorption and decomposition of CTAB, in the DTG curve of the MMC are lower than those of the Al-MCM-41, indicating a weaker interaction between CTAB and the wall of mesophase in the composite. This supports that the wall of the mesophase might contain zeolitic structural units because the condensation degree of zeolitic unit is much higher than that of the conventional Al-MCM-41 with an amorphous wall. In addition, the high rigidity of zeolitic units would also weaken the interaction of CTAB surfactant with the wall. The formation of the MMC composite is further confirmed by the result that the mesostructure in the composites showed much higher hydrothermal stability than the conventional Al-MCM-41 with a similar Si/Al ratio. Table 1 shows that Table 1 Physical properties of the MMC (NaOH/SiO2 = 0.75) sample and its treated analogue in boiling water. Samples

MMC

Al-MCM-41

Treating time (h)

Surface area 2

(m /g)

Total pore volume (mL/g)

Micropore volume (mL/g)

Mesopore diameter (nm)

0

638.8

0.82

0.060

2.90

100

626.4

0.80

0.054

2.88

0

935.5

0.87

-

3.00

100

262.0

0.28

-

-

after treatment in boiling water for 100 h, the MMC sample still had a surface area and a pore volume of 626 m2/g and 0.80 cm3/g respectively.

490

These values are comparable to those of the untreated MMC. In contrast, the same treatment exerted on the conventional Al-MCM-41 led to a reduction in the surface area by more than 70%. This gives another piece of evidence for the assembly around the surfactant micelles of structural units-containing dissolved fragments of zeolite MCM-22 into the wall of the mesophase. 4. Conclusion A new material of MCM-22/MCM-41 composite has been successfully synthesized by using zeolite MCM-22 as initial material and CTAB as a surfactant. It was shown that the secondary zeolitic structural units of MCM-22 might be incorporated into the wall of mesophase in the MMC by simultaneously assembling the nutrients dissolved from the zeolite MCM-22 together with amorphous silcate and aluminosilicate species around the surfactant micelle. This led to a much higher hydrothermal stability than the conventional Al-MCM-41. It is worth noting that the amount of the zeolite phase, and hence the composition and the structure of the composites can be controlled to a certain extent by the adjustment of the alkalinity in the synthesis gel. This paper presents a general synthesis route for preparing the composites of zeolites and mesoprous materials. 5. Acknowledgement This work is supported by the National Science Foundation of China (No. 20476060) and National Basic Research Program of China (No. 2004 CB 217806). 6. References [1] K. R. Kloetstra, H.W. Zandbergen, J. C. Jansen and H. van Bekkum, Microporous Mater., 6(1996)287. [2] A. Karlsson, M. Stacker and R. Schmidt, Microporous Mesoporous Mater., 27 (1999) 181. [3] L. M. Huang, W. P. Guo, P. Deng, Z. Y. Xue and Q. Z. Li. J. Phys. Chem. B , 104 (2000) 2817. [4] W. P. Guo, L. M. Huang, P. Deng, Z. Y. Xue and Q. Z. Li, Micropor Mesopor Mater., 4445(2001)427. [5] R. F. Li, W. B. Fan, B. B. Fan, J. H.Cao and K. C. Xie, Stud. Surf. Sci. Catal., 129 (2000)117. [6] C. M. Zhang, Q. Liu, Z. Xu and K. S.Wan, Micropor. Mesopor. Mater., 62 (2003) 157. [7] D. T.On and S. Kiliagunine, Angew. Chem. Int. Ed, 41 (2002) 1036. [8] S. Wang, T. Dou, Y. P. Li, Y. Zhang, X. F. Li and Z. C.Yan, Catal. Commun., 6 (2005) 87. [9] V. Mavrodinova, M. Popova, V. Valchev and R. Nickolov, Ch. Minchev, J. Colloid Interface. Sci., 286 (2005) 268. [10] A. Corma, U. Diaz, V. Fornes, J. M. Guil, J. Martinez-Triguero and E. J. Creyghtony, J. Catal., 191 (2000)218.

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Recent Progress in Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

Micro-mesoporous composite molecular sieves with wormlike morphology prepared from zeolite Beta Ying Zhang ab , Tao Doua*, Qiang Li a and Shanjiao Kang a " The CNPC Key Laboratory of Catalysis, China University of Petroleum, Fuxue road, Changping, Beijing 102249, China h Department of Materials Science and Engineering, China University of Petroleum, Fuxue road, Changping, Beijing 102249,China 1. Introduction

Because both microporous zeolites with small pore opening (<1.5 nm) [1] and mesoporous molecular sieves such as M41S with weak acidity and poor hydrothermal stability [2] cannot be practically applied to treat the relatively large molecules present in crude oils, great interest has been generated in the synthesis of composite materials which combine the advantages of both mesoporous and microporous molecular sieves. Since the early 1990s, various synthesis routes have been explored [3-7]. Recently, our group reported a general methodology for the synthesis of micro-mesoporous molecular sieves in which preformed zeolites are used as silicaalumina source. We have now prepared MOR/MCM-41, ZSM-5/MCM-41 and Beta/MCM-41 composites [8, 9]. These composites all show improved hydrothermal stability and acidity because of the introduction of zeolite secondary building units into the mesopore walls. Here, we

1 - 1.0 M 4 - 2.5 M 2 - 1.5 M 5-3.0 M 3 - 2.0 M 6 - 3.5 M

Fig. 1 XRD patterns of calcined BMC-1 samples prepared through the dissolution of zeolite Beta in different alkali concentrations: (a) in small angle range, (b) in wide angle range, for clarity, the patterns are offset by 1.0 degree along the x-axis.

492

report synthesis of a Beta/MCM-41 composite with a wormlike morphology from sub-micron sized zeolite Beta (~0.8 u m). 2. Experimental Section 2.1.

synthesis The Beta/MCM-41 composites with wormlike ,

,

/J

. ,

n

.,

n

n

,

_ „„,...

.,

. . .

Fig. 2 TEM image of the calcined

morphology (denoted as BMC-1) were prepared gMC_] s a m ie mp e following the similar procedure we had reported in the papers [8, 9]. Differently, sub-micron sized zeolite Beta (Si/Al=15, -0.8 u m in size) was used as silica-alumina source. For comparison, microsized Beta (Si/Al=15, -1.9 u m in size) was used to obtain a Beta/MCM-41 composite (denoted as BMC-1'). Also, a highly ordered Al-MCM-41 sample was synthesized with a synthesis gel having a Si/Al ratio of 15 by following the procedures established for the synthesis of the Beta/MCM-41 composites except for the replacement of zeolite Beta with a corresponding amount of tetraethyl orthosilicate (TEOS) and aluminum isopropoxide. The content of zeolite Beta in the Beta/MCM-41 composite was deduced from a working curve, which had been obtained by plotting the intensity of the diffraction peak at 29 of 22.40° against the weight percent of zeolite beta of a series of quantitatively mixed Beta and MCM-41. Accordingly, the typically prepared BMC-1 and BMC-1' composites respectively contained about 80.5% and 81.2% of Beta phase. The protonated form samples were prepared by ammonium exchange at 343 K for 2 h followed by calcination at 773 K for 5 h. 2.2.

characterization

X-ray diffraction (XRD) patterns were obtained with a Shimadzu XRD-6000 diffractometer using CuKa radiation. TEM images were recorded on a JEM2000EX electron microscope operating at 100 kV. SEM images were obtained with a LEO 435VP. The nitrogen adsorption-desorption isotherms were measured with a Micromeritics ASAP 2020 system. The mesopore structure was analyzed from the desorption branch of the isotherm by the Barrett-JoynerHalenda (BJH) method. The catalytic performance for the hydrodealkylation of C10+heavy aromatic hydrocarbon was assessed in a continuously flowing fixed-bed microreactorof I.D. 9 mm operated under the following conditions: catalyst loading 0.5 g, temperature 823 K, pressure 5.0 MPa, WHSV 1 h"1 and H2/HC=5.

493

3. Results and Discussion XRD patterns of calcined BMC-1 samples show two types of peaks which are from the Beta crystals (Fig. lb) and from the hexagonally symmetrical mesoporous molecular sieves (Fig. la). With increasing the alkali concentration employed in the dissolution of zeolite Beta, the peak intensities from mesoporous structure are increased and those from zeolite Beta are decreased. This indicates that the amount of zeolite Beta phase in the composite can be controlled simply by varying the alkali concentration. Furthermore, the hydrothermal stability of the samples is investigated. After treatment in boiling water for 100 h, the calcined BMC-1 still maintains almost 50% mesoporous structure. BMC-1' also shows similarly high hydrothermal stability. In contrast, after treatment in boiling water for 24 h, the mesostructure of the calcined MCM-41 sample is almost destroyed completely. According to our previous report [8], the improved hydrothermal stability of two composite samples may arise from the presence of zeolite structure building units in the mesoporous walls. Interestingly, the BMC-1 sample shows a peculiar wormlike morphology (Fig.2), which is absolutely different from the irregular ball shape of BMC-1'. And the Beta crystals are embedded in the loose amorphous MCM-41 matrix with ordered pore structure, which seems also different from the simple mechanical mixture of Beta and MCM-41 (not shown). SEM images of the BMC-1 sample also exhibit this peculiar particle morphology (not shown). Such a wormlike morphology has never been observed for the micro-mesoporous composite materials. Small zeolite beta nanocrystals have been reported to exhibit higher catalytic activity, lower rate of catalyst deactivation and higher product quality compared to conventional type microcrystalline Beta material [10]. Will a micromesoporous composite containing sub-micron sized Beta exhibit higher Table 1 Textural and catalytic properties of the samples" „„„ . Total pore BET surface , , , ,. volume areaCmg) ^ ^

. Mesopore size Beta crystal , . . (ran) s,ze(um)

(%)

BMC-1 (80.5%)

617.9

0.57

3.0

~0.5

49.38

BMC-1'(81.2%)

590.8

0.60

2.8

-1.5

43.62

Beta

576.0

0.38

-

-0.8

38.56

A1MCM-41

935.5

0.87

3.0

-

12.05

Samples

a

Conversion ofreactant

The Si/Al ratio in all samples is about 15.

catalytic activity than the one containing microsized Beta? So the catalytic

494

activity of BMC-1 and BMC-1' was compared by C10+ heavy aromatics hydrodealkylation. The BMC-1 shows much higher conversion (Table 1) than BMC-1' as well as the pure Beta and MCM-41.The BET surface area from the N2 adsorption isotherms of BMC-1 is also higher than that of BMC-1' (Table 1). Thus, the higher catalytic activity of BMC-1 than BMC-1' might be caused by the faster diffusion of reactant in the sub-micron sized zeolites due to the short diffusion path and the higher amount of acid sites accessible to reactant due to the higher zeolite external surface. 4. Conclusion A micro-mesoporous material with a wormlike morphology (denoted as BMC-1) composed of sub-micron sized zeolite Beta crystals embedded in the loose MCM-41 was produced by first dissolving zeolite Beta (-0.8 u m in size) in NaOH solution and then assembling the dissolved species from zeolite Beta using CTAB as template. By varying the NaOH concentration, the content of microporous zeolite phase in the composite can be controlled. Compared with the BMC-1' composite containing microsized Beta crystals, BMC-1 shows higher surface area and higher catalytic activity in the C10+ heavy aromatics hydrodealkylation. 5. Acknowledgement This work was financially supported by National Natural Science Foundation of China (No.20473039) and National Basic Research Program of China (2004CB217806). 6. References [1] M. E. Davis, Nature, 364 (1993) 391. [2] C. T. Kresge, M. E. Leonowicz, W. J. Roth, J. C. Vartuli and J. S. Beck, Nature, 359 (1992) 710. [3] K. R. Kloeststra, H. W. Zandbergen, J. C. Jansen and H. van Bekkum, Micropor. Mater., 6 (1996)287. [4] A. Karlsson, M. Stacker and R. Schmidt, Micropor. Mesopor. Mater., 27 (1999) 181. [5] R. H. P. R. Poladi and C. C. Landry, J.Solid State Chem., 167 (2002) 363. [6] L. Huang, W. Guo, P. Deng, Z. Xue and Q. Li, J. Phys. Chem.B., 104 (2000) 2817. [7] Z. Zhang, Y. Han, F. Xiao, S. Qiu, L. Zhu, R. Wang, Y. Yu, Z. Zhang, B. Zou, Y. Wang, H. Sun, D. Zhao and Y. Wei, J.Am.Chem.Soc, 123 (2001) 5014. [8] S. Wang, T. Dou, Y. Li, Y. Zhang, X. Li and Z. Yan, Catal. Commun., 6 (2005) 87. [9] Y. Li, R. Pan, Q. Huo, W. Zhang, T. Dou and K. Xie, Chin. J. Inorg. Chem., 21 (2005) 1455. [10] M. A. Arribas and A. Martinez, Catal.Today, 65 (2001) 117.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

495 495

Steam stable mesoporous silicalite-1 with semicrystalline framework Xiong Lia, Sun-Jin Kimb and Wha-Seung Ahna* "Department of Chemical Engineering, Inha University, Incheon 402-751, Korea b Nano-materials Research Center, Korea Institute of Science and Technology, Seoul 130-650, Korea

Mesoporous silicalite-1 (MS-1) with semi-zeolytic connectivity in mes-opore walls was synthesized from an assembly of preformed nano-sized silica-lite-1 precursors in a block copolymer solution. MS-1 showed substantially enhanced hydrothermal stability in steaming condition at 700°C compared to MCM-41 or SBA-15. By controlling the amount of the MFI structure directing agent TPAOH in the substrate mixture, we could impart increasingly zeolytic properties to MS-1 even though structural ordering of the materials deteriorated progressively.B eckmann rearrangement probe reaction demonstrated increasing conversion by the MS-1 sample prepared with higher TPAOH concentration, which indicates that MS-1 contains structural elements similar to those in crystalline silicalite-1. 1. Introduction M41S type mesoporous materials discovered by Mobil are highly useful as catalyst support in the chemical transformation of bulky organic substrates. In order to increase the acid strength and to enhance the hydrothermal stability, several researchers have recently attempted to prepare mesoporous materials composed of pore walls with zeolytically ordered structure. In this work, we have applied a direct assembly of colloidal silicalite-1 precursors in the presence of EO20PO70EO20 block copolymer to make a mesoporous silica with improved hydrothermal stability [1]. Physicochemical properties of the material obtained were evaluated employing various instrumental analyses. To study the nature of the mesoporous walls in MS-1, we have performed vapor phase Beckmann rearrangement of cyclohexanone oxime to e -caprolactam as a probe reaction [2].

496

2. Experimental Section A zeolite precursor solution was prepared at 45°C with the substrate molar ratios of SiO2 : TPAOH : H2O = 1 : 0.25 : 50. This mixture was added to Pluronic PI23 solution and heated to 100°C for 1 day. The amount of TPAOH was varied 5 to 15 % excess to the initial composition. Characterization of MS1 was conducted using XRD, N2 adsorption and TEM. Vapor phase Beckmann Rearrangement reaction was performed under atmospheric pressure using cyclohexanone oxime diluted with ethanol (1 : 9), which was injected via a syringe pump. The reaction was conducted at 350°C for 8 h. The catalyst (0.3 g) was loaded into the reactor, activated in helium at 500°C for 2 h, and then cooled to the reaction temperature. The products were analyzed using a gas chromatography (HP 5890A). 3. Results and Discussion 600

(110)

1

2

3

4

5

2 theta

6

500 400 300 0.12 0.10

200

dV/dD (cm3g-1)

Volume Adsorbed (cm3/g STP)

Intensity

(100)

100

0.08 0.06 0.04 0.02 0.00 0

5

10

D (nm)

0 0.0

0.2

0.4

0.6

0.8

1.0

(P/P0)

Fig. 1. X-ray diffraction pattern of MS1 in the low-angle region.

Fig. 1 represents the X-ray diffraction pattern of MS-1 with peaks indexed to (100) and (110) at 29 = 0.9° and 1.6°, which are indicative of reasonably well ordered hexagonal symmetry. The intense peak (100) showed relatively large lattice spacing of d = 100 A corresponding to the hexagonal unit cell parameter of a = 115 A. The unit cell parameter was calculated by using the formula a = 2dm/-j3, where the dm represents the d-spacing of the (100) diffraction peak in the XRD pattern. Typical type IV nitrogen adsorption-desorption isotherm with Hi hysteresis loop and narrow distribution of the pore diameter of MS-1 are shown in Fig. 2. The inflection at P/Po = 0.4 ~ 0.5 is related to the pore diameter in the mesopore range, and a sharp rise in the adsorption isotherm at P/Po < 0.1 region corresponds to the microporosity of the material. Fig. 3 shows TEM images and corresponding electron diffraction patterns of MS-1.

497

Well ordered hexagonal array with uniform mesopores (a) and side channels (b) are observed clearly. These TEM images are in accordance with the results of XRD pattern and nitrogen adsorption-desorption isotherm. Most importantly, high resolution transmission electron microscopy (HR TEM) image of MS-1 in (d) illustrates the presence of microporosity and periodic micropore arrays in the mesopore walls. These structural features are known to enhance the hydrothermal stability of mesoporous materials [3].

Fig. 3. TEM images and electron diffraction patterns (inset) of MS-1. Area A in (c) is enlarged in (d) and areas marked with circles in (d) clearly show ordered micropore arrays.

Table 1 shows the properties of the MS-1 samples obtained after steam treatment at 700°C for 6 h. MS-1 exhibited high physical strength and maintained almost the same BET surface area from 835 to 823 m2/g. On the other hand, conventional mesoporous molecular sieves lost their structural features and the mesostructure was almost completely destroyed after the same hydrothermal treatment. These results are in agreement with previous reports for stability comparison between the mesoporous materials containing zeolytic pore wall and other conventional mesoporous molecular sieves [1]. Table 1. Textual properties of MS-1, MCM-41 and SBA-15 Condition

BET specific surface area (m2g"')

Pore volume (cm3g"')

Average Pore size (A)

MS-1

Raw / Steam

835/823

0.82 / 0.79

39/40

MCM-41

Raw / Steam

1107/280

0.98/0.18

35/34

SBA-15

Raw / Steam

665/158

0.67/0.28

45/53

Materials

In order to study the nature of MFI zeolytic structure in MS-1 frameworks, we had selected vapor phase Beckmann Rearrangement of cyclohexanone oxime to e -caprolactam as a probe reaction [4]. The experimental results are summarized in Table 2, and SBA-15 with amorphous wall demonstrated ca. 9%

498

oxime conversion whereas zeolite silicalite-1 led to ca. 99% conversion. MS-1, on the other hand, resulted in ca. 53% conversion. Table 2. Vapor phase Beckmann Rearrangement of cyclohexanone oxime to e -caprolactam over various catalysts Oxime Conversion (%)

Lactam Selectivity (%)

Lactam Yield (%)

Silicalite-1

99.1

97.4

96.6

MS-1

53.3

68.5

31.7

•MS-1-T5

85.9

85.6

73.6

MS-1-T10

93.1

82.3

76.6

MS-1-T15

96.3

88.8

85.5

SBA-15

9.2

67.0

6.5

Materials

Time (h)

The amount of zeolytic structure directing agent TPAOH was also increased from 5 to 15 % in excess to the initial composition of MS-1 precursor solution to enhance the zeolytic structure of silicalite-1 in mesopore framework of MS-1. These samples are designated as MS-1-T5, MS-1-T10 and MS-1-T15, respectively in Table 2 (T represents TPAOH and the number indicates the increased concentration). The corresponding cyclohexanone oxime conversion was significantly and gradually increased from 85 to 96% from MS-1-T5 to T15. These results can be interpreted as a consequence of improved transformation of amorphous MS-1 pore walls to a semi-crystalline zeolytic structure upon increasing the structure directing agent TPAOH in MS-1 preparation. 4. References [1] X. Meng, D. Li, X. Yang, Y. Yu, S. Wu, Y. Han, Q. Yang, D. Jiang and F. Xiao, J. Phys. Chem. B, 107(2003)8972. [2] S. J. Kim, M. J. Park, K. D. Jung and O. S. Joo, J. Ind. Eng. Chem., 10 (2004) 995. [3] J. Liu, X. Zheng, Y. Han and F. Xiao, Chem. Mater., 14 (2002) 2536. [4] C. Ngamcharussrivichai, P. Wu and T. Tatsumi, J. Catal., 235 (2005) 139.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

499 499

Synthesis of bimodal mesoporous material with the primary/secondary structure of ZSM-5 as building unit Yong Niu and Jihong Sun* Department of Chemistry and Chemical Engineering, College of Environmental & Energy Engineering, Beijing University of Technology, Beijing, 100022, P. R. China

1. Introduction Since the M41S family was developed by Kresge et al. [1], the bimodal porosity materials with hierarchical structure are of considerable interest for indutrial applications because they offer multiple benefits arising from each pore size regime. For example, while micro- and meso-pores may provide sizeor shape-selectivity for guest molecules, the presence of additional macropores can offer easier transport and access to the active sites that should improve reaction efficiencies and minimise channel blocking. Unfortunately, It has been recognized that the stabilities (thermal, hydrothermal and mechanical) of the mesostructured materials strongly influence their practical applications [2]. The most reason is that the mesoporous structure may collapse upon calcination at high temperature or degrade by treating in a hydrothermal condition due to the hydrolysis of the amorphous silicate wall. During the last decade, improvements in hydrothermal stability of mesoporous silicates have been achieved by the addition of salts during the hydrothermal synthesis, or by modification of the pore surface to eliminate reactive surface silanol groups, or by increasing the wall thickness [3, 4], Recently, one of the most attractive examples is the MAS-5 type mesoporous aluminosilicate showing extraordinary thermal and hydrothermal stability due to the crystalline zeolite-structured pore wall [5]. In this study, we report that the bimodal mesoporous silica [6], containing the primary/secondary building units of ZSM-5 (PSBU), has been successfully synthesized using cationic CTAB as co-templates, which is expected to be stable in many catalytic applications.

500

2. Experimental Section

Disolv ed Ma ss (g)

3 2. 5 2 1. 5 1 0. 5 0 0

1

2

2

3

4

5

6

NaOH Concentration (mol/L) Fig. 1 The relationship curve between dissolved mass and alkali concentration

In the first step, 3g high silica ZSM-5 and the 30ml NaOH solution with different concentration range from 1M to 6M were mixed in the polytetrafluoroethylene vessel, with keeping stirred at 60°C for 4 hrs. After that, mixture with clear sol and white precipitate was obtained. This mixture was filtered, resulting in the clear sol product containing PSUB, in the meantime, after washed with distilled water and dried at 120°C for 24 hrs, the filted cake was obtained. After deducted from 3 g of high silica ZSM-5, the dissolved mass can be calculated. The relationship between dissolved mass and alkali concentration was shown in Fig. 1. According to the results in Fig. 1, the best dissolved parameters were as follwing that: dissolved time: 4 hrs, alkaline concentration: 4M of NaOH solution, and dissolved temperature: 330 K. In the second step, the above clear sol product containing PSBU as silica source on the basis of dissolved mass of ZSM-5, cetyltrimethylammonium bromide (CTAB), and water, were mixed in a ratio of 1: 0.2: 160, in which the alkalinity of pH was around 10 adjusted by using the strong hydrochloric acid. Then the mixture was stirred continuously at room temperature, and after filtered and repeatedly washed with distilled water, the white gel was obtained. Finally, the product was dried in air at 393 K, and calcined in air at 823 K for 6 hours, at a ramp rate of 1 K/min. In the third step, the mixture with clear sol and white precipitate obtained in the first step was used as silica source, and the follwing synthesis procedure was the same as that in the second step. X-ray diffraction (XRD) of the samples was recorded using a Brucker-AXS D8 Advance X-ray diffractometer using Cu Ka radiation (A.Ka=0.154nm). FTIR spectrum of the samples were recorded on an FT-IR spectrometer (PE 430), and samples were pressed to tablet with KBr according to the mass ratio of 1:100.

501

3. Results and Discussion

Intensity

The XRD patterns (Fig. 2) of samples obtained by using both sol a product and mixture prepared in the first step as silica source show that two diffraction peaks indexed as (100), and (110) respectively [1], which is b similar to our previous report [6], indicating the bimodal mesostructure, 0. 5 2. 5 4. 5 6. 5 8. 5 2θ/º as can be seen in Fig. 3. The N2 adsorption-desorption isotherm of the Fig. 2 XRD patterns of samples synthsized by typical bimodal mesoporous material, using sol product (a) and mixture (b) prepared synthsized by using sol product, in the first step exhibits two inflections: a first increase occurs at relative pressures 1200 0.4

15

25

35

45 2θ/º

55

65

Vol Adsobed (cm3/g STP)

3

dV/dlogD (cm /g)

7.0 6.0 5.0 4.0 3.0 2.0 1.0 0.0

1

10

100

1000

Pore Diameter (nm)

0

75

502

In contrast, the normal mesoporous material only exhibits a broad band at 455 cm"1. These results indicate that both samples contain PSBU of 5- and -rings of T-O-T, similar to those in aluminosilicate ZSM-5. 4. Conclusion In summary, at first, the best dissolved condtions in the NaOH solution has been found, and then by using both sol and mixture prepared in the dissolved solution of ZSM-5 as silica source and CTAB as template, the bimodal mesoporous silica has been successfully synthesized. By means of XRD, ~N2 adsorption/desorption isotherms and FT-IR instruments, the results show that there are the PSBUs of ZSM-5 in the sample, suggesting a promise material in the industrial application. 5. Acknowledgement This research was supported by the Excellent Oversea Chinese Scholars Fundation of the Personal Ministry of the Chinese Government, the Natural Science Fundation of Beijing (No.2063024 ), and Xing Huo Fundation of BJUT for undergraduate (XH-2005-05-03). 6. References [1] [2] [3] [4] [5] [6]

C. T. Kresge, W. J. Roth and J. C. Vartuli.et al., Nature, 359(1992) 710. Corma. Chem. Rev., 97(1997) 2373. Y. Liu and T. J. Pinnavaia, J. Mater. Chem., 12(2002) 3179. Stein, Adv. Mater., 15(2003) 763. Z. Zhang, Y. Han and F. S. Xiao, et al., J. Am. Chem. Soc, 123(2001) 5014. J. H. Sun, Z. Shan, J. C. Jansen, T. Mashmyer and M. O. Coppens, Chem. Commun., (2000) 2670. [7] J. Schoeman, Stud. Surf. Sci. Catal., 105(1997) 647.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

503 503

Synthesis of meso-structured silicalite-1 by combining solid phase crystallization and carbon templating Jia Wang* and Marc-Olivier Coppens Physical Chemistry & Molecular Thermodynamics, DelftChemTech, Delft University of Technology, Julianalaan 136, 2628 BL Delft, The Netherlands 1. Introduction

Zeolites are important heterogeneous catalysts, in oil refining and petrochemical processes as well as in fine chemical and environmental applications. Major problems arising during catalytic applications of zeolites are transport limitations caused by a slow diffusion rate of reactants and desired products in zeolite micropores (0.3-1.5 nm), as well as catalyst deactivation by pore blocking [1,2]. To address these issues, industry employs various types of post-synthesis treatments of zeolites, such as steaming, which creates mesopores but also affects the intrinsic catalytic activity. It should be noted that the improvement on overall diffusion, however, is recently under debate [3,4]. Structured mesoporous materials, such as MCM-41 [5] and SBA-15 [6], are attractive, but have limited practical applications due to a relatively low acidity and poor hydrothermal stability [7, 8]. Many researchers are therefore trying to combine the unique acidity of zeolites with structured mesoporosity. A reliable method to achieve a truly meso-structured zeolite remains a challenge [9]. This may well relate to the stability and growth mechanism of zeolites. Using mesoporous carbon materials (such as CMKs, carbon black) as templates might provide one approach to reach this goal [10]. On the other hand, some researchers have used solid phase transformation to partially crystallize the walls of mesoporous materials [11]. Here, we examine the possibility to synthesize truly meso-structured silicalite-1 by a combination of carbon templating and solid crystallization methods. 2. Experimental Section Our method involves the formation of a carbon structure in SBA-15, followed by crystallization. SBA-15 was synthesized as described in [12]. The wet SBA-15 samples were then washed and calcined at 550°C. The procedure of carbon precursor impregnation was similar to the one reported by Lu et al.

504 504

[10]. Carbonization was performed under Ar gasflow at 850°C for 3 h to obtain Si-C composites. Then, 0.18 ml 1M TPAOH solution was introduced into 0.15 g composite. After 16 h, 20 u.1 water was added to the samples before crystallization reactions were performed at 130°C for 7, 24 and 48 hours. Finally, organic components were removed by combustion at 550°C for 6 hours. Powder X-ray diffraction measurements were performed on a Bruker-AXS D5005 diffractometer. X-ray scattering results were obtained by a Bruker-D8 Discover set-up. Nitrogen adsorption-desorption isotherms were measured using a Quantachrome Autosorb-6B sorption analyzer. HRTEM images were obtained by a Hitachi-1500 operated at an accelerating voltage of 820 kV. 3. Results and Discussion

2.5

7 hr 24 hr 48 hr

2.0 1.5 1.0 0.5

0.0 10

100

Volume [cc/g]

Adsorption Dv(log d) [cc/g]

The chosen strategy is designed to overcome the problem of meso-structural deterioration during the solid crystallization process. A well-developed carbon structure inside the mesopores of SBA-15 should be rigid 600 550 550 enough to sustain the force of 7 hr 500 500 the zeolite crystals' growth. 450 450 On the other hand, our design 400 400 24 hr requires much less time as j [ 350 350compared to a carbon a> 300 3ootemplating method involving 48 hr 250 ^ 250 preparation of mesoporous o 200 > 150 200 carbon. Note that SBA-15 is 150 100 chosen as an example of a 100 50 50 mesoporous material to 0.8 0.0 0.2 0.4 0.6 0.8 1.0 examine our method. To Relative Pressure, P/Po P/Po Relative retain an ordered mesoFigure 1. N2 adsorption/desorption isotherms structure is not our present 1000

Pore Diameter [Å]

of the final samples. The insert shows the adsorption pore size distributions.

aim.

Table 1. N2 sorption data of selected samples Crystallization time

Surface area (m2/g)

Micropore volume (cc/g)

Pore diameter (adsorption, nm)

Total pore volume (cc/g)

7h

333

-

5.2

0.477

24 h

382

-

5.4

0.456

48 h

327

0.07

2.5; 6.0

0.263

N2 adsorption and desorption isotherms, shown in Fig. 1, indicate that there is a gradual decrease of the mesoporous volume as a function of crystallization time. However, after 48 h crystallization a significant amount of mesopores remains (Table 1). In comparison with experiments without carbon (also carried out in our lab), the mesopores are more stable because of a well-developed carbon structure. Though the force exerted by the growing zeolite crystals is

505

Intensity / au

very strong the carbon in the SBA-15 mesopores is not crushed. The decrease in mesopore size is associated with the growth of zeolite crystals. Bigger crystals may be stripped from the mesopore walls or even move out of the mesostructure because the wall thickness (in between 3.1-6.4 nm) is too small to accommodate larger particles. XRD patterns (Fig. 2) indicate the formation of silicalite-1 (MFI type) crystals in samples after 24 h and 48 h. The steady increase of 4000 the diffraction peaks suggests 3500 the increasing amount of 7h 3000 crystalline material in the samples. N2 sorption data also 2500 \ 24 h reveals the appearance of fc. 2000 2000 micropores (Table 1), which is 1500 1500 in agreement with XRD results. 1000 1000 The small angle X-ray scattering results (Fig. 3) reveal 500 •Si JUJU UUL 48 h that samples 7h and 24 h have 0 0 10 20 30 40 50 the typical SBA-15 (100) peak. Figure 2. XRD patterns of the final samples. However, in sample 48 h the peak is very small, demonstrating the deterioration of the mesoporous order after a longer 7 hh crystallization time. The HRTEM image of sample 24h (Fig 4) shows ordered 'in 24 h mesopores. A longer treatment 48 48hh (48h), however, results in worm-like mesopores. While the mesopores are retained 0.5 1.01.52.0 1.0 1.5 2.0 2.5 3.03.54.0 3.0 3.5 4.0 during the crystallization / 2-Theta degree process, the order deteriorates with time. This is in a good Figure 3. X-ray scattering patterns of the samples. agreement with X-ray scattering results. A similar phenomenon was reported by Trong On and Kaliaguine [11, 13]. To explain why the carbon structure did not preserve the ordered structure,

i

600

I n t e n s i t y / a .u .

500

400

300

200

100

0

Fig. 4 HRTEM images of samples 24h (left) and 48h (right).

506

we suspect that the transformation to a worm-like structure happened during the final combustion of the carbon framework. In both samples zeolitic features can be recognized by EDX. It appears that crystalline material is imbedded in the mesoporous structure in most parts of the sample, while in some areas it is more like a composite of mesoporous and crystalline materials. 4. Conclusion By employing a method combining carbon templating and crystallization we have synthesized zeolite materials (silicalite-1) with a meso-structure. Our method shows promising results. The stability of the mesopores probably improves because of a well-developed carbon structure inside the mesopores of SBA-15. Further testing, including chemical reactions, should provide us with a better understanding of the samples. 5. References [1] M.-O. Coppens, Structured Catalysts and Reactors, 2nd Editon, edited by A.Cybulski and J. A. Moulijn, (2006) 779. [2] Y. S. Tao, H. Kanoh, L. Abrams and K. Kaneko, Chem. Rev., 106 (2006) 896. [3] S. van Donk, A. H. Janssen, J. H. Bitter and K. P. de Jong, Catal. Rev., 45 (2003) 297. [4] P. Kortunov, S. Vasenkov, J. Karger, R.Valiulin, P.Gottschalk, M.Fe" Elia, M.Perez, M. Stacker, B. Drescher, G. McElhiney, C. Berger, R. Glaser and J. Weitkamp, J. Am. Chem.Soc, 127 (2005) 13055. [5] C. T. Kresge, M. E. Leonowicz, W. J. Roth, J. C. Vartuli and J. S. Beck, Nature, 359 (1992)710. [6] D. Y. Zhao, J. L. Feng, Q. S. Huo, N. Melosh, G. H. Fredrickson, B. F. Chmelka and G. D. Stucky, Science, 279 (1998) 548. [7] T. Linssen, K. Cassiers, P. Cool and E. F. Vansant, Adv.Coll.Inter.Sci, 103 (2003) 121. [8] A. Taguchi and F.Schuth, Micro.Meso.Mater., 77(2005)1. [9] J. Wang and M. -O. Coppens, in Preparation, (2006) [10] A. -H. Lu, W. Schmidt, A. Taguchi, B. Spliethoff, B. Tesche and F. Schuth, Angew.Chem., 114(2002)3639. [11] D. Trong On and S. Kaliaguine, Angew.Chem.Int.Ed., 40(2001)3251. [12] A. -H. Lu, W. -C.Li, W. Schmidt, W. Kiefer and F. Schuth, Carbon, 42 (2004) 2939. [13] D. Trong On and S. Kaliaguine, Nanoporous Materials: Science and Engineering, edited by G. Q. Lu and X. S. Zhao, Imperial Colleage Press, (2004) 47.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

507 507

Assembly of mesocellular silica foams from colloidal zeolite nanocrystals through template free process Yuxin Jiaa'b, Wei Han ab , Guoxing Xionga*and Weishen Yang"1* "State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Acedemy Science, 457 Zhongshan Road, Dalian 116023, People's Republic of China h Graduate School of the Chinese Academy of Sciences, Beijing 100049, People's Republic of China

Mesocellular silica foams were successfully prepared by assembly of colloidal silicalite-1 nanocrystals without templates. The products were examined by scanning electron microscopy (SEM), transmission electron microscopy (TEM), N2 adsorption-desorption and FTIR, showing foam-like structure composed of spherical cells with pore size of about 10 nm and zeolitic walls. 1. Introduction The discoveries of MCM-41 [1] and other oxides were met with great excitement in the hope of their potential applications as host structures, adsorbents, and catalysts for reactions involving large molecules [2]. By using dilute Pluronic P123 solutions in the presence of 1,3,5-trimethylbenzene (TMB) as organic cosolvent, the mesocellular foams composed of uniformly sized, large spherical cells were synthesized in aqueous acid, which were promising candidates in separations involving large molecules and low-dielectric applications [3-5]. Unfortunately, limited success had been made in industrial applications of these materials owing to the weak acidity and hydrothermal stability originated from the amorphous nature of the mesoporous materials [6], Recently, efforts have been made to prepare mesoporous materials that exhibit the acidity and stability of zeolitic materials. Starting with the work of Kloetstra et al, in which mesoporous materials with surface-tectosilicate structures were prepared by partial recrystallization of the surface of MCM-41 and HMS [7],

508

the mesoporous materials with zeolitic characters were obtained by fabrication of mesoporous solids [ 8, 9] or template-directed assembly of zeolite nanocrystals [10]. However, the environmental and economic problems were brought by using templates in the methods mentioned above. As far as we know, no one has described the synthesis of mesoporous materials with zeolitic walls and foam-like structure other than by using templates. Here we report a novel and facile template free route to prepare mesocellular silica foams with zeolitic walls and large spherical cells by assembly of zeolite nanocrystals. 2. Experimental Section Mesocellular silica foams (denoted as MSF) were prepared by the following procedure: mixing tetraethyl orthosilicate (TEOS) and tetrapropylammonium hydroxide (TPAOH) under vigorous stirring, a clear silicalite-1 nanocrystal sol was achieved followed by drying in ambient temperature for several days without stirring till a transparent gel formed. Subsequently, the gel was heated in air up to 823 K with a constant heat rate of 5K/min and calcinated for 6 h at 823 K. Characterization was carried out using SEM, TEM, N2 adsorptiondesorption measurements and FTIR. 3. Results and Discussion

10

°

Figure 1 displays the particle size distribution as measured by dynamic light scattering (DLS) of the silicalite-1 nanocrystal sol. The average DLS colloid size was about 3 nm, which contributed to the formation of 2.8-nm-sized primary units known as zeoslabs [11]. Figure 2 is the typical SEM image of 10 100 1000 MSF. The morphologies of the materials Size (nm) show an array of pores with circular Figure 1. Particle size distribution as openings ranging from 0.5 to 3.0 urn (Figure 2a), which generated from the measured by dynamic light scattering (DLS) of colloidal zeolite nanocrystals. phase-separation of gaseous species [12], and an amorphous phase when observed at a high magnification (Figure 2b). TEM was conducted to show the details of the morphologies of MSF (figure 3a). The solid is clearly characterized by a spherical cellular structure. The cells deviated from the spherical shape originate from the interference by the neighboring cells. The HRTEM image (Figure 3a inset) illustrates in more details of the material lattice fringes, which is compatible with silicalite-1. FTIR band at ca. 550 cm"1 (Figure 3b) which is characteristic of five-membered ring units in the pentasils also indicates that silicalite-1 nanocrystals are present within the MSF materials [13].

509

Nitrogen adsorptiondesorption isotherm and pore size distribution of MSF were shown in figure 4. The isotherm (TEM was conducted to show the details of the morphologies of MSF (figure 3 a). The solid is clearly characterized by a spherical cellular structure. The cells deviated from the spherical shape originate from the interference by the neighboring cells. The HRTEM image (Figure 3a inset) illustrates in

1 |im

Figure 2. SEM images of MSF at low (a) and high (b) magnification

700

6.0

5.0

400

material lattice fringes, which is compatible with silicalite-1. FTIR band at ca. 550 cm-1 (Figure 3b) which is characteristic of five-membered ring units in the pentasils also indicates that silicalite-1 nanocrystals are present within the MSF materials [13]. 4a) located between type I and type IV was obtained, which attributes to the coexistence of micporosity and mesoporosity. Micropore size distribution (TEM was conducted to show the details of the morphologies of MSF (figure 3a). The solid is clearly characterized by a spherical cellular structure. The cells deviated from the spherical shape originate from the interference by the neighboring cells. The HRTEM image (Figure 3a inset) illustrates in more details of the material lattice fringes, which is compatible with silicalite-1. FTIR band at ca. 550 cm-1 (Figure 3b) which is characteristic of five-membered ring units in the pentasils also indicates that silicalite-1 nanocrystals are present within the MSF materials [13]. 4b) of MSF determined by HK method centralizes in 0.53 nm corresponding to the channel opening size of silicalite-1. Mesopore size distribution (TEM was conducted to show the details of the morphologies of MSF (figure 3a). The solid is clearly characterized by a spherical cellular structure. The cells deviated from the spherical shape originate from the interference by the neighboring cells. The HRTEM image (Figure 3a inset) illustrates in more details of the material lattice fringes, which is compatible with silicalite-1. FTIR band at ca. 550 cm-1 (Figure 3b) which is characteristic of five-membered ring units in the pentasils also indicates that silicalite-1 nanocrystals are present within the MSF materials [13]. 4c) calculated from BJH method using the adsorption branch of the isotherm shows the average Figure 3. TEM images of MSF (a) and FTIR for MSF (b)

510

pore size of MSF is 7 nm, which was less than the results observed by TEM because the BJH method underestimated the size of the mesopores [14]. 4. Conclusion Without using template, the mesocellular silica foam was successfully prepared by assembly of colloidal zeolite nanocrystals. The as-synthesized products are hierarchical pore structured composite. T he microporosity was introduced by silicalite-1 nanocrystals. Further studies of mesoporous foamed structure are now ongoing in our group to investigate the formation mechanism and various factors in controlling the porosity. 5. Acknowledgment This work was supported by SINOPEC (NO.X503008) and NSFC (NO. 20321303). 6. References [1] C. T. Kresge, M. E. Leonowicz, W. J. Roth, J. C. Vartuli and J. S. Beck. Nature 1992, 359, 710. [2] G. J. D. Soler-illia, C. Sanchez, B. Lebeau and J. Patarin. Chem. Rev 2002, 102, 4093. [3] P. Schmidt-Winkel, W. W. Lukens, D. Y. Zhao, P. D. Yang, B. F. Chmelka and G. D. Stucky. J. Am. Chem. Soc. 1999,121, 254. [4] P. Schmidt-Winkel, W. W. Lukens, P. D. Yang, D. I. Margolese, J. S. Lettow, J. Y. Ying and G. D. Stucky. Chem. Mater. 2000, 12, 686. [5] W. W. Lukens, P. D. Yang and G. D. Stucky. Chem. Mater. 2001, 13, 28. [6] A. Corma. Chem. Rev 1997, 97, 2373. [7] K. R. Kloetstra, H. vanBekkum and J. C. Jansen. Chem. Commun. 1997, 2281. [8] D. T. On and S. Kaliaguine. J. Am. Chem. Soc. 2003, 125, 618. [9] Y. Liu, W. Z. Zhang and T. J. Pinnavaia. J. Am. Chem. Soc. 2000, 122, 8791. [10] Z. T. Zhang, Y. Han, F. S. Xiao, S. L. Qiu, L. Zhu, R. W. Wang, Y. Yu, Z. Zhang, B. S. Zou, Y. Q. Wang, H. P. Sun, D. Y. Zhao and Y. Wei. J. Am. Chem. Soc. 2001, 123, 5014. [11] V. B. C. E. A. Kirschhock, S. Kremer, R. Ravishankar, C. J. Y. Houssin, B. L. Mojet, R. A. van Santen, P. J. Grobet, P. A. Jacobs and J. A. Martens. Angew. Chem. Int. Ed. 2001, 40, 2637. [12] K. Kurumada, N. Kitao, M. Tanigaki, K. Susaand M. Hiro. Langmuir 2004, 20, 4771. [13] E. G. D. a. J. W. P. A. Jacobs. J. Chem. Soc. Chem. Commun. 1981, 591. [14] P. S.-W. W.W. Lukens Jr., J. Feng and G.D. Stucky. Langmuir 1999, 15, 5403.

Recent Progress in Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

511 511

Microwave assisted-direct synthesis of highly ordered large pore functionalized mesoporous SBA Sujandi, Sang-Cheol Han, Dae-Soo Han and Sang-Eon Park* Lab. ofNano-Green Catalysis, Nano Center for Fine Chemicals Fusion Technology, Dep't of Chemistry, Inha University, Incheon 402-751, Korea

Microwave sysnthesis has been successfully applied for the direct synthesis of organo-functionalized SBA-15 and 16 mesoporous materials through the cocondensations of organosilanes with sodium metasilicate in the presence of triblock copolymers as structure directing agents. The obtained materials have large pores, long range order of cubic and hexagonal mesostructures, and the loading of organo groups up to 10% of the silica frameworks. 1. Introduction Recently, microwave sysnthesis has been applied to the rapid and economical synthesis route of various nanoporous materials which normally required several days to prepare under traditional hydrothermal conditions. The microwave synthesis also offers potential advantages over hydrothermal synthesis, such as rapid and homogeneous heating throughout the reaction vessel, homogeneous nucleation and rapid crystallization, phase selectivity, and facile particle size and morphological control, etc. This method has been successfully applied to the synthesis of various kind of nanoporous materials, namely zeolite A, Y, Beta, ZMS-5, MCM-41, SBA-15, and SBA-16 [1-5]. Recently, Kormaneni and co-worker have applied microwave synthesis method in the direct synthesis of transition metal substituted SBA-15 under acidic condition.6"7 It rapid heating and fast supersaturation were believed to facilitate the co-condensation processes during the synthesis [6]. However, to the best of our knowledge, there has been no report on the microwave synthesis of organofunctionalized SBA-15 and 16 through the co-condensation of organosilanes and silica source. The organo-functionalization has been known to play important role in expanding the applications of mesoporous silica in catalysis, separation, and sensor design [8]. Herein, we report the synthesis of large pore

512

organo-functionalized SBA-15 and 16 mesoporous silica through cocondensation reactions between organosilanes and sodium metalicate in the acidic condition under microwave irradiation. 2. Experimental Section The organo-functionalized SBA-15 and 16 mesoporous materials were synthesized according to the same procedure by co-condensations of organosilanes (chloropropyltriethoxysilane/CPTES, cyanopropyltriethoxysilane/ CNPTES, propylanilinetriethoxysilane/PATES, and aminopropyltriethoxysilane/APTES) with a sodium metasilicate in the presence of a triblock copolymer as a structure directing agent under microwave irradiation. Preparation of chloropropyl-functionalized SBA-15 is given as an example. In a typical synthesis, 16 g of 10% (w/w) aqueous solution of PI23 was poured into 26.6 g distilled water and then 0.016-(0.016 x x%) mole of sodium metasilicate was added to the solutions. To the vigorously stirred solutions, 13 g of concentrated hydrochloric acid (37.6%) was quickly added followed by 0.016 x x% mole ofCPTES (x = 5, 7.5, and 10). The final gel mixtures were stirred for 1 hour at 313 K before subjected to the microwave digestion system (CEM Corporation, MARS-5) of which condition was set at 373 K for 2 h at operated power of 300 W (100%). The crystallized products were filtered, washed with warm distilled water and finally dried at 333 K. The surfactant was then selectively removed by Soxhlet extraction over ethano} for 24 h. For the synthesis of the organo-functionalized SBA-16, a triblock copolymer F127 was used as the structure directing agent. 3. Results and Discussion Surfactant-free SBA-15 and SBA-16 functionalized with different organic functional groups prepared by the microwave assisted-direct synthesis showed XRD patterns (not shown) with a very intense diffraction peak in the range of 0.8-1.0° 20 and two or more additional peaks at higher degree within 1.2-2.0° 20. The XRD patterns indicated the long range ordered and excellent textural uniformity of the organo-functionalized SBA-15 and SBA-16 mesoporous materials with hexagonal and cubic mesostructures obtained from triblock copolymers as structure-directing agents [9]. The N2 adsorption and desorption isotherms (not shown) of all the surfactant-free samples showed the defined type IV behavior with hysteresis loops, which are characteristic for mesoporous materials with narrow distribution of pore size that facilitate the condensation of N2 [9]. Table 1. provides the textural properties of the organo-functionalized mesoporous materials synthesized from the microwave assisted-direct synthesis. These results show that well ordered mesoporous materials could be synthesized at organo functionalization levels corresponding to x values of at

513

(f) (f)

Intensity (a.u.)

(e)

(d)

(c) (b)

(a) 1

2

3

2 theta (degree) (degree)

Fig. 1. XRD patterns of Clpr-SBA-16: (a)x=10, (b)*=7.5, (c)*=5 andClprSBA-15: (d)x=10, (e)jt=7.5, (f)*=5

4

least 10% organic group to silica molar ratio regardless the nature of the organosilanes added into the synthesis gel. In all cases the mean pore sizes were large than 5 nm for SBA-15 and 3 nm for SBA-16, respectively. In general, the pore sizes were not affected by the amounts of organosilanes added to the synthesis gels. The successful functionalizations were proven by near infrared and mid infrared spectra which showed the vibration bands for the organic moieties. Addition of different amounts of CPTES into the initial gel mixtures during the synthesis seems to give effect to the mesostructure of the SBA15 materials. At CPTES to silica molar ratio = 5 and 7.5%, the XRD patterns (Fig. le and If) could be indexed as a hexagonal mesostructure of SBA-15 mesoporous materials, respectively.

However, at molar ratio = 10%, the XRD pattern showed the characteristic for mesoporous material with cubic structure of laid symmetry.10 The mesophase transformation due to the presence of CPTES during the synthesis were clearly shown by the TEM image (Fig. 3d). The XRD patterns of Clpr-SBA-16 synthesized from the co-condensation of CPTES and sodium metasilicate in the presence of F127 surfactant were characteristic for the expected SBA-16 mesoporous material with Im3m symmetry, with very intense main diffraction peaks of 110 plane and additional diffraction peaks at higher 20 of 200, 211, and 220 planes. Further evidences were provided scanning electron microscopic (SEM) and transmission electron microscopic (TEM) images (Fig. 3a and 3b). The SEM and TEM images showed the typical dodecahedron morphology and cage-type Im3m cubic structure of SBA-16, respectively.4 (a)

(b)

(c)

(d)

50 nm

Fig. 2. SEM and TEM images of Clpr-SBA-16 and Clpr-SBA-15. (a) and (b) SEM and TEM images of Clpr-SBA-16 (x = 10); (c) and (d) SEM and TEM images of Clpr-SBA-15 (* = 10).

514 Table 1. Textural properties of organo-functionalized SBA-15 and 16 Resulted material P123 5 Clpr-SBA-15 CPTES P123 7.5 Clpr-SBA-15 CPTES P123 10 CPTES Clpr-SBA-15 F127 5 CPTES Clpr-SBA-16 F127 7.5 CPTES Clpr-SBA-16 F127 10 CPTES Clpr-SBA-16 P123 5 CNpr-SBA-15 CNPTES P123 10 CNPTES CNpr-SBA-15 PATES P123 5 ANpr-SBA-15 PATES P123 10 ANpr-SBA-15 APTES P123 5 NH2pr-SBA-15 P123 7.5 APTES NH2pr-SBA-15 P123 10 NH2pr-SBA-15 APTES *Calculated from desorption branch of the full isotherm Organosilane

SDA

X

Framework d/nm structure Hexagonal/P6m/« 8.9 Hexagonal//'(5/n/n 9.7 Cvtb\dla3d 8.7 Cub\c/Im3m 10.4 Cubic/Im3m 10.0 Cubic/Im3m 9.7 HexsLgonai/P6mm 8.8 Hexagona\/P6mm 8.5 Hexagonal/P6mm 10.2 Hexagonal/.P<5/?im 10.2 Hexagonal/P6/nm 9.9 Hexagonal/.P6mm 9.8 Hexagonal/P6mm 11.2 by using a BJH method.

Pore size/nm* 5.1 5.0 4.3 3.3 3.4 3.2 7.7 7.2 7.9 7.1 7.1 7.7 7.8

4. Conclusion Microwave assisted-direct synthesis has been used to synthesize organofunctionalized SBA-15 and 16 with highly ordered mesostructures, large pore size and high loading of organic group. It was proven to be an effective and convenient method for the organic functionalization on mesoporous silica. 5. Acknowledgement This work was supported by Brain Korea 21 (BK21) Program. 6. References [1] S. A. Galema, Chem. Soc. Rev. 26 (1997) 233. [2] C. S. Cundy, Collect. Czech. Chem. Commun. 63 (1998) 1699. [3] S-E. Park, J.-S. Chang, Y. K. Hwang, D. S. Kim, S. H. Jhung and J. S. Hwang, Catal. Surv. Asia 8 (2004) 91. [4] Y. K. Hwang, J.-S. Chang, Y.-U. Kwon and S.-E. Park, Micro. Meso. Mater. 68 (2004) 21. [5] Y. K. Hwang, J.-S Chang, S.-E. Park, D. S. Kim, Y.-U. Kwon, S. H. Jhung, J.-S. Hwang and M. S. Park, Angew. Chem. Int. Ed. 44 (2005) 556. [6] B. L. Newalkar, J. Olanrewaju and S. Komarneni, Chem. Mater. 13 (2001) 552. [7] B. L. Newalkar, J. Olanrewaju and S. Komarneni, J. Phys. Chem. B 105 ( 2001) 8356. [8] R. J. P. Corriu, A. Mehdi and C. Reye", J. Mater. Chem. 15 (2005) 4285. [9] D. Zhao, Q. Huo, J. Feng, B. F. Chmelka and G. D. Stucky, J. Am. Chem. Soc. 120 (1998) 6024. [10] T.-W. Kim, F. Kleitz, B. Paul and R. Ryoo, J. Am. Chem. Soc. 127 (2005) 7601.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

515 515

Template-free sol-gel synthesis of mesoporous materials with ZSM-5 structure walls Wei Hanab, Yuxin Jiaab, Guoxing Xiong3* and Weishen Yanga* "State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, People's Republic of China b Graduate School of the Chinese Academy of Sciences, Beijing 100049, People's Republic of China

A novel template-free sol-gel method is developed to synthesize a series of mesoporous materials with ZSM-5 structure walls. This method involves solvothermal crystallization of the xerogel converted from uniform ZSM-5 sol by a vacuum drying process. The products with different mesopore sizes can be obtained facilely by adjusting solvent and temperature of crystallization. 1. Introduction Mesoporous materials have attracted much attention because of their potential use as catalysts and catalyst supports for conversion of larger molecules. Until now, mesoporous materials have not been applied on a large scale in petrochemical industries because of their low hydrothermal stability and acidity which may be attributed to their amorphous pore walls [1]. It is a possible method to improve stability and acidity of mesoporous materials by introducing zeolite structures into the pore walls, e.g. assembly of zeolite precursor method developed by Pinnavaia [2] et al. and Xiao [3] et al. and zeolite-coated mesopore walls method developed by Kaliaguine [4] et al. Generally, templates including surfactants, small organic molecules and mesoporous silica are necessary for the formation of uniform-sized mesopores. Here we develop a new strategy to fabricate mesoporous materials with zeolitic walls without using any templates on the basis of our previous work [5].

516

2. Experimental Section Mesoporous materials with ZSM-5 structure walls were synthesized by a three-step procedure. The first step consists of the preparation of ZSM-5 precursor sol. Clear ZSM-5 precursor sol containing a little floccule was obtained by stirring the turbid solution with molar composition of 1.0TEOS: 0.02Al(i-OPr)3: 0.25TPAOH: 11.3H2O at 50°C for 48 h. In the second step, the ZSM-5 precursor sol filtrated floccule was dried at 30°C in a vacuum box retaining the vacuum value of 50mmHg until it became xerogel. The silica content in the xerogel was about 7.7><10"3mol/g. The third step involves the crystallization of the xerogel. The mixture of xerogel and polyol (ISi: 150 polyol, molar ratio) was transferred into Teflon lined autoclaves and carried out solvothermal synthesis at a certain temperature for 24h. For comparison, the sample is also synthesized by using water as medium of crystallization. Finally the solid products were filtered, washed, dried at 30°C in a vacuum box and calcined at 550°C in air for 6 h to remove TPA ions. A N 4 plus laser scattering particle meter (Coulter) was used to measure particle size distribution of ZSM-5 sol. N2 adsorption/desorption isotherms of samples were measured on a Coulter Omnisorp-100CX apparatus at 77 K. SEM and TEM images of samples were made using a KYKY-2800B scanning electron microscope and a Philips Tecnai G2 20 transmission electron microscope, respectively. 3. Results and Discussion BOO

Figure 1 shows N2 adsorption/ desorption isotherms and pore size distribution of the calcined samples prepared under different conditions. Their isotherms' shape is ascribed to a composite of types I and IV, corresponding respectively to microporous and mesoporous materials. As the hydroxyl number of solvent molecular decreases, the type of loop has a tendency towards type HI. Type HI is often associated with porous materials which consist of agglomerates or compacts of uniform spheres in fairly regular array according to interpretation of IUPAC. Figure 1(B) shows that samples synthesized in polyol have narrower mesopore size distributions and smaller mesopores than that synthesized in water. Table 1 summarizes the surface area, the pore volume and the pore size of different calcined samples. All samples have similar

rii

-x-Glycol(180°C)

"* 400 F iff 300 0 200

""""'

(A)

-o-GlycerQlj130°C) -±-Glycol(130°C) -x-Glycol(180°C) - £ - Water (130°C)

(B)

Pore Siza(nm)

Figure 1 (A) N2 adsorption/desorption isotherms and (B) pore size distribution of the calcined samples prepared under different conditions of crystallization

517

micropore size distribution centralizing in 0.52 ~ 0.55nm which corresponds to the channel opening o size of ZSM-5. Samples with 2 50 different mesopore sizes can be 40 I) obtained facilely by adjusting solvent f 30 and temperature of crystallization. Generally, it is favored for the I i formation of the sample with higher 0 20 40 60 80 100 120 140 160 180 200 Particle Size(nm) surface area and narrower mesopore Figure 2 Particle size distribution of ZSM-5 size distribution by using the lower temperature or the solvent with more hydroxyl number. Compared with them, the directly-calcined xerogel only has a few macropores. Its surface area and pore volume are 4.4 m2/g and 0.05 cm3/g, respectively. Obviously, the precursor sample has not ZSM-5 structures. Based on our previous study [5], we think uniform pores form in xerogel via packing of uniform-sized sol particles (-12 nm, Figure 2) due to the evaporation of solvents as the dispersion medium of them during vacuum drying. These nanoparticles composing porous structures crystallize to form ZSM-5 structures during solvothermal treatment, which is identified by the appearance of 557cm"1 shoulder peak in IR spectra of the sample after solvothermal treatment. Figure 3 (A) shows TEM image of Sample 2 synthesized in glycol. It presents the existence of mesopores several nanometers in size (areas marked by black arrows), which results from the agglomeration of many ca. 15nm particles with regular shape. Large domains ordered bright stripes of ca. 0.5nm in width could be observed clearly within these nanoparticles composing walls of mesopore structures, which correspond to microchannels of ZSM-5 zeolite. Sample 3 synthesized in glycerol has a similar morphology. It is different from Sample 2 that nanoparticles composing Sample 3 are only 7nm in size. Consequently smaller mesopores form in interparticle spaces. XRD shows there is no existence of bulky ZSM-5 crystals in those samples synthesized in polyol. On the contrary, Sample 1 synthesized in water is made up of over 200nm ZSM-5 crystals which have been identified by the result of XRD. Polyol as medium of crystallization plays important roles of restraining the growth of ZSM-5 crystals 80 70

60

20

10

0

Figure 3 TEM images of (A) Sample 2 and (B) Sample 3; (C) SEM image of Sample 1

518

and retaining better mesoporous structures of samples because of very low solubility of silica and alumina species in it [4]. Table 1 Texture properties of different calcined samples Sample

Solvent

SBET

Mesopore

Micropore

Mesopore

Micropore

No.

(Temperature) of

2

Volume

Volume

Size

Size

(m /g)

crytallization

3

(cm /g)

(cmVg)

(nm)

b

(nm)c

1

Water (130°C)

431. l a

0.53

0.16

14.7

0.54

2

Glycol(130°C)

499.3

0.81

0.22

4.6

0.54

3

Glycerol(130°C)

675.5

0.72

0.29

2.5

0.52

4

Glycerol(150°C)

524.7

0.97

0.23

4.9

0.54

5

Glycerol(180°C)

532.9

0.84

0.23

4.2

0.54

6

Glycol(180°C)

354.6

0.80

0.15

6.2

0.55

a. For Sample 1 we use Langmuir surface area because of its BET C value be negative and unreasonable, b. Mesopore size distribution was determined by BJH method from desorption branch, c. Micropore size distribution was determined by HK method from adsorption branch.

4. Conclusion We develop a convenient template-free sol-gel method to synthesize mesoporous materials with ZSM-5 structure walls. Utilizing this method we keep successfully materials' uniformity in total preparation process from precursor sol, xerogel to products. We can manipulate facilely mesopore size of products by controlling conditions of synthesis. 5. Acknowledgement This work is supported by NSFC (No. 20321303) and SINOPEC (No. X503008). We sincerely thank Miss. Min Zhang for fruitful discussions and Senior Engineer Shishan Sheng and Associate Prof. Wenling Chu from DICP for N2 adsorption/desorption isotherms measurement. 6. References 1. A. Corma, Chem. Rev. 97 (1997) 2373. 2. Y. Liu, W. Z. Zhang and T. J. Pinnavaia, J. Am. Chem. Soc. 122 (2000) 8791. 3. F. S. Xiao, Y. Han, Y. Yu, X. J. Meng, M. Yang and S. Wu, J. Am. Chem. Soc. 124 (2002) 888. 4. D. Trong On and S. Kaliaguine, J. Am. Chem. Soc. 125 (2003) 618. 5. N. Yao, G. X. Xiong, M. Y. He, S. S. Sheng, W. S. Yang and X. H. Bao, Chem. Mater. 14 (2002) 122.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

519 519

Facile low temperature synthesis of primary amine templated super-microporous aluminosilicates Graham Ranee, Yongde Xia and Robert Mokaya School of Chemistry, University of Nottingham, University Park, Nottingham NG7 2RD, UK

Super-microporous silica and aluminosilicate materials that possess pores in the range 14 - 19 A have been prepared at low temperature (ca. 5 °C) using a primary amine (dodecylamine) as template. The structural ordering of the materials is similar to that of primary amine-templated mesoporous analogues prepared at higher temperature. The surface area of the materials varies between 450 and 1230 m2/g and generally decreases at higher Al content. The pore size also decreases with Al content from 19 to 14 A. Al is successfully incorporated into the framework of the materials to generate significant acidity. Our findings show that low synthesis temperature allows the facile formation of supermicroporous silicas and aluminosilicates via primary amine templating. 1. Introduction The synthesis of solid acid materials that have well defined pore structures similar to those of zeolites, but with larger pores, is a desirable research goal [1]. Well ordered mesoporous materials that possess solid acid properties may be prepared via a variety of supramolecular templating methods [2]. Despite the success in preparing mesoporous solid acids with pores larger than 25 A, much less attention has been focused on materials with pores in the supermicroporous (10 - 20 A) range. Solid acid materials in this pore size range are important since they bridge the gap between microporous zeolites and mesoporous materials and would crucially allow shape-selective catalysis involving molecules that are too large to access the pores of microporous zeolites. Silica-based super-microporous materials have so far been prepared using alkylammonium ions [3-6] or amines [7, 8] as soft templates. It is noticeable that the formation of super-microporous materials required room temperature conditions [4-8], which may suggest that temperature is a key

520

synthesis parameter. Super-microporous silica materials have recently been prepared at low synthesis temperature (between 0 and -20°C) using semifluorinated surfactants as template [9]. The effect of synthesis temperature on the formation of primary amine templated silica-based materials therefore deserves further investigation. We have previously employed a primary amine (dodecylamine) as template for the formation of super-microporous aluminosilicates at room temperature [8]. However, the super-microporous materials were only obtained via a modified procedure that enhanced the incorporation of Al in the materials; the high Al content contributed to the formation of super-micropores [8]. Here, in an effort to simplify the procedure, we explore the preparation of supermicroporous aluminosilicates by simply lowering the synthesis temperature to ca. 5°C. Our findings show that low temperature synthesis allows the facile formation of super-microporous silicas and aluminosilicates. 2. Experimental Section The aluminosilicate materials (designated as LTAl-MMSx, where x is the Si/Al ratio in the synthesis gel) were prepared as follows; desired quantities of aluminium isopropoxide (in 35 ml isopropyl alcohol) and 0.2 mol tetraethyl orthosilicate (TEOS, in 80 ml ethanol) at Si/Al molar ratios in the range 50:1 5:1 were stirred vigorously at ca. 5 °C (i.e., in a refrigerator) for 15 minutes before adding 0.05 mol dodecylamine (DDA, in a mixture of 80 ml water and 120 ml ethanol), and ageing (at ca. 5 °C) for 20 h. The pure silica material (LTHMS) was prepared by directly adding TEOS to DDA. The resulting solids were obtained by filtration, washed with water, air-dried overnight at room temperature and calcined at 650°C for 4 h. 3. Results and Discussion The XRD patterns of the pure silica and aluminosilicate materials are shown in Fig. 1. In all cases, the XRD patterns exhibit a single basal peak, which is typical for primary amine-templated mesoporous materials [10]. The structural ordering of the present samples is comparable to that of primary amine templated mesoporous materials [10]. The low synthesis temperature does not therefore compromise the structural ordering of the materials. The basal spacing of the samples, given in Table 1, varies between 29.5 and 26.5 A and decreases with the Al content. These basal spacing values are the lowest we have ever observed for primary amine templated materials of similar Al content [8, 10], and are much lower than for M41S type mesoporous materials [1,2]. The nitrogen sorption isotherms of the materials are shown in Fig. 1. The isotherms exhibit high adsorption at low {PlPo < 0.2) partial pressures which is characteristic of super-microporous materials. The isotherms do not exhibit the mesopore filling step (at PlPo > 0.2) normally observed for mesoporous

521 (100)

500 LTHMS 450

LTAl-MMS50

Volume adsorbed (ml/g STP)

400

Intensity (a.u.)

LTHMS

LTAl-MMS50

LTAl-MMS20

LTAl-MMS20 350 300 250 LTAl-MMS10 200 LTAl-MMS5

150 150

LTAl-MMS10

100 100

LTAl-MMS5

50 50 0

22

44

66

88

(degrees) 22 θθ (degrees)

10 10

0.0

12 12

0.2

0.4

0.6 P/P0

0.8

1.0 1.0

Fig. 1. Powder XRD patterns (left) and nitrogen sorption isotherms (right) of primary amine templated silica (LTHMS) and aluminosilicate (LTAl-MMS) materials prepared at ca. 5 °C.

materials [1, 2]. The pore size of the materials (obtained via BJH analysis of adsorption data), given in Table 1, ranges from 14 - 19 A and confirms the super-microporous nature of the materials. It is interesting that even the pure silica sample, LTHMS, is super-microporous. The surface area (450 and 1230 m2/g) and pore volume (0.24 - 0.57 cm3/g) are similar to those of comparable mesoporous materials [1,2,8,10]. In particular samples prepared at Si/Al of 20 and 50 exhibit high surface area. The proportion of micropore surface area (47 86%) and pore volume (40 - 75%), given in Table 1, is the highest we have ever observed for primary amine-templated materials [8,10]. This further emphasizes the super-microporous nature of the LTHMS/LTAl-MMS materials. Table 1. Textural properties, elemental composition and acidity of primary amine templated materials prepared at ca. 5°C. Values in parenthesis are micropore surface area and pore volume. Sample

LTHMS LTA1-MMS50 LTA1-MMS20 LTAl-MMS 10 LTA1-MMS5

Si/Al ratio

51.7 26.2 13.7 7.3

Pore

(A)

Surface area (m2/g)

Pore volume (cm3/g)

29.4 28.9 28.1 27.3 26.6

1036 1190 1230 482 444

0.50 (0.24) 19.3 0.56 18.8 0.57 (0.23) 18.5 0.28 (0.19) 14.0 0.24 (0.18) 14.0

Basal spacing

(561) (581) (406) (384)

size (A)

Acidity (mmol/g)

0.19 0.45 0.62 0.73

522

LTAl-MMS5

LTAl-MMS10

LTAl-MMS20

LTAl-MMS50 150

100

50

0

-50

-100

-150

ppm

Fig. 2.27A1 MAS NMR of calcined primary amine-templated super-microporous aluminosilicate materials prepared at ca. 5°C.

The Al content of the materials (Table 1) is similar to that of comparable mesoporous analogues [10]. Super-microporosity cannot therefore be ascribed to a high Al content [8], but rather appears to be a consequence of the low synthesis temperature. Al MAS NMR of the super-microporous materials is shown in Fig. 2. The spectra of all samples exhibit resonances at 55 and 0 ppm arising from tetrahedral (framework) and octahedrally coordinated (nonframework) Al respectively. Most of the Al is in tetrahedral framework positions, and the proportion of non-framework Al is greatest at high Al content (sample LTA1-MMS5). As expected, the samples exhibit significant acidity (Table 1), which increases with the Al content. In summary, we have shown that low temperature synthesis offers a facile route for the preparation of primary amine-templated super-microporous silica and aluminosilica materials, with structural ordering, textural parameters, and acidity similar to those of comparable mesoporous materials. 4. References [1] A. Corma, Chem. Rev., 97 (1997) 2373. [2] D. T. On, D. Desplantier-Giscard, C. Danumah, S. Kaliaguine, Appl. Catal. A: Gen., 222 (2001) 299. (b) J. Y. Ying, C. P. Mehnert and M. S. Wong, Angew. Chem. Int. Ed., 38 (1999) 56. [3] S. A. Bagshaw and A. R. Hayman, Chem. Commun., (2000) 533. [4] D. P. Serrano, J. Aguado, J. M. Escola and E. Garagorri, Chem. Commun., (2000) 2041. [5] K. Yano and Y. Fukushima, J. Mater. Chem., 13 (2003) 2577. [6] Y. S. Lin, H. P. Lin and H. Y. Mou, Microporous Mesoporous Mater., 76 (2004) 203. [7] T. Sun, M. S. Wong and J. Y. Ying, Chem. Commun., (2000) 2057. [8] (a) E. Bastardo-Gonzalez, R. Mokaya and W. Jones, Chem. Commun., (2001) 1016. (b) E. Bastardo-Gonzalez, R. Mokaya and W. Jones, Stud. Surf, Sci. Catal., 141 (2002) 141. [9] Y. Di, X. Z. Meng, L. F. Wang, S. G. Li and F. S. Xiao, Langmuir, 22 (2006) 3068. [10] (a) R. Mokaya and W. Jones., J. Catal., 172 (1997) 211. (b) R. Mokaya and W. Jones, J. Mater. Chem., 8 (1998) 2819. (c) R. Mokaya, W. Jones, S. Moreno and G. Poncelet, Catal. Lett., 49 (1997) 87. (d) R. Mokaya, W. Jones, Chem. Commun., (1996) 981.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Published by Elsevier B.V.

523 523

Synthesis of zeolitic mesoporous titanosilicate using mesoporous carbon as a hard template Haijiao Zhang, Yueming Liu, Mingyuan He and Peng Wu * Shanghai Key Laboratory of Green Chemistry and Chemical Processes, Department of Chemistry, East China Normal University, North Zhongshan Rd. 3663, Shanghai 200062, P .R.China

A crystalline MFI type titanosilicate showing mesoporous characteristics has been synthesized by crystallizing the zeolitic synthesis gel with the assistant of mesoporous carbon (CMK-3) using a dry gel conversion (DGC) method. The resulting zeolitic mesoporous titanosilicate (ZMTS) has been applied to the oxidation of alkenes with H2O2, and its catalytic properties have been compared with TS-1 and Ti-MCM-41. ZMTS proves to be superior in activity. 1. Introduction Recently, it is very attractive and desirable to synthesize catalytic materials which combine the advantages of crystalline zeolites and mesoporous materials from the viewpoint of processing large chemicals more effectively. Particular attentions have been focused on the nanocasting of mesopore-containing zeolites using various forms of carbon as templates [1, 2]. In this study, we have been trying to create mesopores within zeolite crystals by crystallizing the titanosilicate zeolite in and out of the pore system of well-ordered mesoporous carbon CMK-3. The mesoporous titanosilicate material with zeolitic characteristics has been synthesized successfully by using CMK-3 as the hard template with a dry gel conversion (DGC) method. The catalytic performance of ZMTS has been studied in the oxidation of alkenes and alkanes with H2O2 by comparing with conventional TS-1 [3] and Ti-MCM-41 [4] catalysts. 2. Experimental Section The synthesis of ZMTS was carried out using a DGC method. Mesoporous carbon CMK-3 was first prepared by nanocasting mesoporous silica SBA-15

524

following the literatures [5, 6]. CMK-3 was impregnated using incipient wetness method with a gel containing tetrapropylammonium hydroxide (TPAOH), tetrabutylorthotitanate (TBOT), water and ethanol. After evaporating ethanol slowly from the mixture at 40°C, tetrathylorthosilicate (TEOS) was added to the mixture to at a C/Si molar ratio of 3:1. The dry gel obtained gives a molar composition of TEOS/TBOT/TPAOH/H2O of 1 : 0.01 : 0.40 : 4. The dry gel was placed into a Teflon cup and was then transferred to a Teflon-lined autoclave. The gel was crystallized statically in the vapor of hydrofluoric acid or water at 180°C for 72 h. The final power was calcined in air at 550°C for 8 h to remove the CMK-3 template and organic additives to obtain ZMTS. The catalytic reactions for the oxidation of alkenes and cycloalkenes with H2O2 (30% wt) were run with CH3OH or CH3CN as a solvent in a 50 mL glass reactor. After stirred at 60°C for 2 h, the reaction mixture and remained H2O2 were analyzed on a gas chromatography (Shimadzu GC-14B) and determined by the titration method with a 0.1 M Ce(SO4)2 solution, respectively. 3. Results and Discussion Fig. 1 shows the XRD patterns of various samples. Similar to SBA-15, CMK3 obtained from SBA-15 template showed the typical pattern of hexagonal structure in the low angle range. The N2 adsorption isotherms of SBA-15 and CMK-3 were also characteristic of mesoporous materials (Fig. 2). In particular, the two samples showed the highly ordered mesostructures, which was also confirmed by means of FE-SEM (Fig. 3). The ZMTS prepared using CMK-3 as a hard template exhibited the typical diffraction peaks at 20 = 7.8, 8.8, 23.2, 23.8, 24.3° etc. due to MFI structure (Fig. lc and d), but no peaks due to hexagonal mesophase in lower angle region (not shown). These results indicate that ZMTS is essentially a crystalline material with zeolitic framework. Seen from the sorption isotherms

d

b

1 ..

c

a 0

11

2

3

22Theta/degree Theta/degree

44

5

5

10 10

15 15

2 0 2 255 3 030 20

35

2 Theta/degree

Fig. 1 XRD patterns of (a) SBA-15, (b) CMK-3, (c) As-syn.-ZMTS, (d) Cal.-ZMTS.

900

b

750

a

600 450 300 150 0 0.0

0.2

(U 0.4

0.6

0.8

1.0 1.0

Relative pressure (P/P0) (P/P0)

Amount adsorbed (cm3 STP g-1)

Amount adsorbed (cm3 STP g-1)

525 250

d 200

c 150

100 0.0

0.2 0.

0.44

0.6

0.8 08

1.0 L0

(P/P0) Relative pressure (P/P0

Fig. 2 Nitrogen adsorption-desorption isotherms of (a) SBA-15, (b) CMK-3, (c) ZMTS, (d) TS-1. a

b

Fig. 3 FE-SEM images of (a) SBA-15, (b) CMK-3. (Fig. 2), the ZMTS showed obvious hysteresis loops at P/Po = 0.05-0.20 and 0.45-0.80, probably due to the presence of mesopores within the zeolite crystals or inter-particle voilds after removing the CMK-3 carbon template. All samples showed the characteristic adasoprtion at 960 cm"1 in IR spectra and and mainly the 210 nm band in UV-visible spectra, which confirmed that the Ti atoms had been incorporated into the framework of zeolites. Table 1 summarizes the catalytic properties of TS-1, Ti-MCM-41 and ZMTS for Si/Ti = 100 (molar ratio) samples in oxidation of alkenes with H2O2. TiMCM-41 hardly showed catalytic activity in the oxidation of 1-Hexene because of its high hydropholicity related to silanol groups and the amorphous nature of its silicate framework wall. On the contrary, ZMTS and TS-1 showed a higher conversion. These results indicate that ZMTS contains the same type of Ti acid site as TS-1. For the oxidation of cycloalkene, an improved catalytic activity of

526 Table 1 Catalytic properties in oxidation of alkenes with H2O2

Cyclohexene /mol".Vo l-Hexene/mol% Oxide sel. H2O2 Conv. Oxide H2O2 conv. sel. conv. 11.0 21.0 6.1 42.6 20.7 ZMTS 96.5 TS-1 11.3 99.9 21.6 3.8 39.5 20.3 Ti-MCM-41 28.8 0.5 5.2 5.7 42.6 20.8 Reaction conditions: cat., 0.05 g; substrate, 10 mol; H2O2, 10 mmol; solvent, 10 mL; temp., 333 K; time, 2 h. Sample

Conv.

ZMTS was observed when compared with TS-1. This may be due to a result of the presence of mesopores in ZMTS which serves as an open reaction space suitable for bulky molecules. 4. Conclusion A novel titanosilicate molecular sieve microporous structures can be synthesized by (CMK-3) as a template with a DGC method. cycloalkenes with H2O2, the material showed MCM-41 andTS-1.

having both mesoporous and nanocasting mesoporous carbon In the oxidation of alkenes and superior catalytic activity to Ti-

5. Acknowledgement Financial supports by Program for New Century Excellent Talents in University (NCET-04-0423), Pujiang project (05PJ14041), 973 project (2006CB202508), STCSM (05DZ22306, 05JC14069) and NSFC (20473027 and 20233030) are appreciated. Z. H. J. thanks PhD Program Scholarship Fund ofECNU2006. 6. References [1] B. T. Holland, L. Abrams and L. A. Stein, J. Am. Chem. Soc, 121 (1999) 4308. [2] C. J. H. Jacobsen, C. Madsen, J. Houzvicka, I. Schmidt and A. Carlsson, J. Am. Chem. Soc, 122(2000)7116. [3] M. Taramasso, G. Perogo and B. Notari, US Pat., 4 410 501 (1983). [4] T. Blasco, A. Corma, M. T. Navarro and J. P. Pariente, J. Catal. 156 (1995) 65. [5] D. Y. Zhao, J. L. Feng, Q. S. Huo, N. Melosh, G. H. Fredrickson, B. F. Chmelka and G. D. Stucky, Science, 279 (1998) 548. [6] S. Jun, S. H. Joo, R. Ryoo, M. Kruk, M. Jaroniec, Z. Liu, T. Ohsuna and O. Terasaki, J. Am. Chem. Soc, 122 (2000) 10712.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

527 527

Synthesis of micro- and mesoporous ZSM-5 composites and their catalytic application in glycerol dehydration to acrolein Chun-Jiao Zhoua, Cai-Juan Huanga, Wen-Gui Zhanga, He-Sheng Zhaib, HaiLong Wua and Zi-Sheng Chaoa* "College of Chemistry and Chemical Engineering, Key Laboratory ofChemometrics & Chemical Biological Sensing Technologies, Ministry of Education, Hunan University, Changsha 410082, P. R. China College of Chemistry and Chemical Engineering, Xiamen University, Xiamen, 361005, P. R. China

The micro- and mesoporous ZSM-5 composites were, for the first time, onestep synthesized, employing dual-templates. Influencing factors such as crystallization temperature, crystallization time, and pH were investigated. The composites were characterized by XRD, HRTEM and N2-adsorption. The studies on dehydration of glycerol to acrolein show that the micro- and mesoporous ZSM-5 composites provided a glycerol conversion of 98.27% with an acrolein yield of 73.64 mol%, the result being better than all those reported in literatures. 1. Introduction Zeolites have found versatile applications in separation and catalytic process due to their unique properties such as shape-selective effect, high thermal stability and intrinsic acidity [1]. On the other hand, transport limitation occurs, however, for the catalytic conversion of large molecules in zeolites, due to their microporosity. While mesoporous materials such as M41S, have emerged as promising catalytic materials in the conversion of large hydrocarbons [2], they are hard to find a practical application due to their low acidities and hydrothermal stabilities. Thus, the exploitation of novel materials with both microporous and mesoporous properties is of great interest. Recently, a few reports have dealt with the synthesis of this kind of materials using dual

528

templating method through a two-step process or zeolite seeding methods [3-7]. In this work, we address, for the first time, an one-step synthesis of micro- and mesoporous ZSM-5 composites, employing dual-templates, and also the catalytic application of the composites in the dehydration of glycerol to acrolein. 2. Experimental Section Synthesis A12(SO4)3 and TPAOH aqueous solutions were mixted at ice-water temperature and then TEOS was dropwise introduced under stirring. After that, the mixture formed was mixed with CTABr solution under strong agitation. To adjust the pH value of the batch, dilute H2SO4 solution was employed. Unless mentioned otherwise, the pH value of batches was adjusted to 9. The final gel had a molar composition of 60.4 SiO2 : A12O3 : 21.1 TPAOH : 9.8 CTABr : 2004.7 H2O and was subjected to a hydrothermal treatment for 1-8 d at given temperatures. The solid products were recovered by filtration, washing and drying. To remove the organic molecules, the specimens were calcined at 813 K in a N2 flow for 1 h and subsequently in air for 5 h. Characterization The specimens were characterized by XRD (Bruker D8 Advance Diffractometer; Cu Karl), HRTEM (JEM-3010; accelerating voltage 300 kV), N2 adsorption-desorption (Quantachrome Autosorb-1 MP) Catalytic reaction The catalysts tested included the micro- and mesoporous ZSM-5 composites, the pure ZSM-5 and MCM-41 as well as a mixture of the later two, all of which were prepared using same sources and Si/Al ratio in batches. Besides, a solid phosphoric acid catalyst, which was reported to possess the largest yield for the dehydration of glycerol to acrolein [8-9], was also prepared, according to the procedure in Ref. 8, and employed in this work. The catalytic experiments were performed in a fix-bed quartz reactor (0.9 x 25 cm), under the conditions of 588 K, 4 g catalyst, and 40 wt% glycerol aqueous solution. The products were analyzed by a Varian GC-Mass, equipped with a FID detector and a VF-5 capillary column (30m x 0.25mm, 0.25um). 3. Results and Discussion Fig. 1 to Fig. 3 show the XRD patterns of the specimens synthesized under S4

10 2

4

6

8

2 Theta

10

10

20

30

40

50

2 Theta

20 30 40 2 Theta

2 Theta

Fig. 1 XRD patterns of specimens synthesized at 8d and different temperatures. SI: 373 K; S2:398K;S3:418K

Fig. 2 XRD patterns of specimens synthesized at 398 K and different time. S4: 2d; S5: 4d; S6: 6d; S7: 8d

529

different conditions. Only a mesoporous phase could be identified for the specimen synthesized at 373 K (see Fig. 1 SI) or in a short period of crystallization time (see Fig. 2, S4 and S5), while both a mesoporous and a microporous phases were present for those at higher temperatures (see Fig. 1, S2 and S3 and Fig. 2, S6 and S7). The microporous phase was indexed to ZSM5 (JCPD 44-0003). With increasing temperature, the crystallinity of ZSM-5 increased and that of the mesoporous phase decreased, (see Fig. 1). The prolonging of crystallization time promoted the formation of the microporous phase ZSM-5 but hindered that of the mesoporous phase (see Fig. 2). With decresing the pH, the formation of the microporous phase ZSM-5 was hampered slightly and that of the mesoporous phase was promoted largely (see Fig. 3). The HRTEM of the specimen S8 synthesized under the condition of 398 K, 8 d and pH = 8 is shown in Fig. 4, which reveals the presence of the disordered mesoporous phase. The mesurement of N2 adsorption- desorption indicats that the scpecimen S8 has a BET specific surface area of 764.2 m2/g. The adsorption-desorption isotherm and BJH pore size distribution curve of the specimen S8 is shown in Fig. 5, which reveals the presence of both micropores and mesopores. Table 1 lists the catalytic reaction results. It indicates that the catalyst S8, among all the catalysts studied in both A S8 this work and literatures, presents the V. largest acrolein yield (73.64 mol%). It ^ S7 is suggested that the presence of both S9 microporous and mesoporous phases is ;=f^ 4 6 8 10 20 30 40 SO responsible for the well catalytic 2 Theta 2 Theta performance of the catalyst, may Fig. 3 XRD patterns of specimens synthesized being due to the high dispersion of at 8 days, 398 K and different pH value. S8: acidic sites and the decrease of the 8;S7:9;S9:10 resistance to diffusion.

3500 400-

|300<200-

I loo's

i:"' 4

6

Pore Diameter tiuii.)

o.o

Fig. 4 HRTEM micrograph of specimen S8

0.2 0.4 0.6 0.8 Relative Pressure (P,'F )

Fig.5 N2 adsorption-desorption isotherm and BJH pore size distribution curve (the inset) for specimen S8

530 Table 1 The result of dehydration of glycerol to acrolein over different catalysts Catalyst

Conversion (mol%)

Selectively (mol%)

Yield (mol%)

S8

98.27

74.94

73.64

ZSM-5

71.27

80.83

57.61

MCM-41

35.52

49.01

17.41

ZSM-5+MCM-41

60.00

71.53

42.92

SPA*,a

96.25

73.24

70.49

SPA*,b

100.0

70.50

70.50

a

b

SPA*: Solid phosphoric acid; in this work; in Ref. 8.

4. Conclusion Micro- and mesoporous ZSM-5 were synthesized using dual templates via a one-step crystallization route and at optimized conditions. Among various influencing factors, crystallization temperature and time appeared to be more important for the formation of the micro- and mesoporous ZSM-5 than pH value. The micro- and mesoporous ZSM-5 composite provided the largest yield of acrolein for the catalytic dehydration of glycerol, among all the catalysts investigated in this work and ever reported in literatures. 5. Acknowledgment This work was supported by the Program for New Century Excellent Talents in University, the Ministry of Education of P.R. China, and the Program for FuRong Scholar in Hunan Province, P.R. China. 6. References [1] A. Corma, Chem. Rev., 97 (1997) 2373. [2] A. Corma, M.S. Grande, V. Gonzalez-Alfaro and A.V. Orchilles, J. Catal. 159 (1996) 375. [3] D. Zhao, J. Feng, Q. Huo, N. Melosh, G. H. Fredrickson, B. F. Chmelka and G. D. Stucky, Science., 279(1998)548. [4] Y. Han, S. Wu, Y. Y. Sun, D. S. Li and F. S. Xiao, Chem. Mater. 14(2002) 1144. [5] D. T. On and S. Kaliaguine, Angew. Chem., Int. Ed. 40 (2001) 3248. [6] Y. Sun, Y. Han, L. Yuan, S. Ma, D. Jiang and F. S. Xiao, J. Phys. Chem. B, 107 (2003) 1853. [7] Y. S. Tao, Y. Hattori, A. Matumoto, H. Kanoh and K. Kaneko, J. Phys. Chem. B, 109 (2005) 194. [8] A. N. Brachttal, T. H. Frankfurt, D. A. Oberursel, H. Klenk and W. Girke, US 5387720 (1995). [9] L. Ott, M. Bicker and H. Vogel, Green Chemistry. 8 (2) (2006) 214.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

531 531

Comparative time-resolved luminescence studies of Tb-ZSM-5 and Tb-MFI mesoporous materials C. Tiseanu", M. U. Kumke\ V. I. Parvulescuc\ B. C. Gagead and J. A. Martens'1 "1NCDFLPR, Bucharest Magurele, MG-36, Romania b Institutfur Chemie, Physikalische Chemie Universitdt, Potsdam, Karl-Liebknecht-Str. 24-25, 14476 Golm b. Potsdam, Germany '"University of Bucharest, Department of Chemical Technology and Catalysis, 4—12 Regina Elisabeta Bvd., Bucharest 030016, Romania. d KU Leuven, Kasteelpark Arenberg 23, 3001 Leuven, Belgium.

The present work presents a comparative time-resolved photoluminescence (PL) study of terbium (Tb)-exchanged ZSM-5 and terbium- exchanged- MFI mesoporous materials prepared from ZSM-5 nanoslabs. Mesoporous hybrid ZSM-5/MCM-41 with Si/Al ratios in the range 33-200, and ZG- Zeogrid (Si/Al ratio 75) were exchanged with terbium using a common procedure. Terbium PL obtained upon laser excitation at 337 nm was analyzed in terms of decays and time-resolved photoluminescence spectra (TRES). The effects of compositional tuning of mesoporous materials (Si/Al ratio) as well as well as of the activation conditions of the exchanged materials (drying, calcinations) on terbium PL properties were correlated with the terbium distribution in these materials. 1. Introduction Synthesis of mesoporous hybrid materials containing crystalline walls is of current interest [1-3]. Among these, the mesoporous materials based on ZSM-5 offer new perspectives in preparing new catalysts for strong acid catalyzed reactions [4]. However, reports concerning the location of the active sites in different mesoporous materials comparatively with the precursor are scarce. The exchange of the sites with a lanthanide ion such as Tb, followed by analysis of the resulted materials by time-resolved photoluminescence spectra may offer valuable information about the location of these sites. To give an answer to this question, Tb-exchanged mesoporous hybrid ZSM-5/MCM-41 (ZT) (Si/Al in the

532

range 30-200), and a Zeogrid (ZG) (Si/Al 75) were compared with Tb-ZSM-5 (Si/Al 75). 2. Experimental Section Nanoslabs with MFI structure were prepared following a reported procedure [2]. The resulted suspension was further used to prepare ZSM-5 zeolite or mesoporous materials (ZT and ZG). The materials were characterized by XRD and N2 physisorption. The XRD patterns confirmed the MFI structure of high crystallinity for ZSM-5 samples, while for the mesoporous materials only low angle peaks were observed. ZT presented a hexagonal symmetry and ZG a laminar structure with the d value of 3nm. The materials were then exchanged with a 0.004M Tb3+ aqueous solution for 30 min at 80°C. Time-resolved luminescence measurements were made with a nitrogen laser (LTB) operated at 10 Hz. The luminescence was detected in the 450 nm- 650 nm spectral range using an intensified CCD camera (Andor DH720-18H-13, Andor) equipped with a spectrograph (MS257, Oriel Instruments). The PL transients were analyzed/? by means of a multiexponential function / ( / ) = 2_. Aj exp(— 11Ti)+ B where Aj is the decay amplitude, B is a constant (the baseEne offset) and ij is the time constant of the decay. 3. Results and Discussion Upon laser excitation at 337 nm, all hydrated terbium-ALL display the terbium 5D4 -related PL. Photoluminescence spectra of Tb-zeolites show no marked differences among the samples, related to the peak positions, relative intensities and transitions widths. However, upon a closer examination differences between the spectral shapes of 545 nm- centered emission line and corresponding widths could easily be noticed for all samples investigated. The PL decays were found non-exponential in all investigated samples and were best fitted with a two-exponential function. However, TRES did not sustained a two- species distribution as PL spectra remained identical at all time delays in range 1-300 us. Therefore, a single average terbium species was considered in all hydrated samples. The compositional tuning of Tb-ZSM-5/MCM-41 obtained by varying the Si/Al ratio from 33 to 200 lead to an increase of terbium lifetime from 474 us in Tb-ZSM-5/MCM-41(33) to 535us in Tb-ZSM5/MCM-41(200). The longest lifetime was measured with Tb-ZSM-5 (570us) while the lifetime measured for Tb-ZG was 480|xs. As the lifetime of Tb aqueous complex measured with the same experimental set-up is 395 ±10(a.s, the values above indicate that terbium is complexed by water molecules as well by framework oxygens with framework contribution increasing with Si/Al ratio in mesoporous ZSM-5/MCM-41 materials, being greatest for Tb-ZSM-5. Upon calcination at 450°C, the terbium PL display stronger intensity as well as longer decays compared to those measured with the hydrated samples (Figure

533

1, Inset) with three exponentials used in the decays fitting. The three groups of decay times were centred on ca. 200 us, 500- 1000 us and 1500-2000 us. The possibility of three emissive species with the lifetimes delivered by discrete exponential fit was further verified by TRES analysis. In contrast with the hydrated samples, they display a continuous variation with time with the variation extent depending on the sample type (Figure 2). The minor changes with TRES were recorded with the Tb- ZSM-5/MCM-41 where the peak(s) positions and spectral shape were slightly modified and a decrease of the intensity of the 548.2 nm centered peak relative to that based on 542 nm could be noticed. The TRES at lus after the laser pulse displaying the various PL lineshapes for terbium in ZSM-5/MCM-41 (200), ZG and ZSM-5 are also illustrated in Figure 2.

10

normalised intensity

1

0.1

0.01

0

10

-1

10

-2

10

-3

10

-4

10

-5

00

4000

8000 8000

12000 12000

16000 16000

time(µs) time( µ s) 1E-3

Tb-ZSM-5 Tb-ZG Tb-ZSM-5/MCM-41 (200) Tb-ZSM-5/MCM-41(200)

1E-4 1E-4

1E-5 1E-5 0

4000 4000

8000 8000

12000 12000

16000 16000

time(µs) time( µ s)

Figure 1. Photoluminescence decays of annealed Tb- ZSM-5/MCM-41(200), Tb-ZG and TbZSM-5. Comparison between photoluminescence decays of hydrated and calcined Tb- ZSM5/MCM-41(200).

Generally, at a given temperature, the spectral profile of an optical transition is determined by the crystal-field splitting and oscillator strengths of the individual crystal- field transitions as well as homogeneous and inhomogeneous broadening [5]. The latter is due to short-range disorder in the host lattice and is expected to be comparable or greater than the overall crystal-field splitting of the 2S+!Lj multiplets of terbium in zeolites. The appearance of the resolved features in the PL spectra of terbium-zeolites is therefore an indicative for a local order at the terbium sites which, according to the comparison of the PL

534 534

normalized intensity

lineshapes illustrated in Figure 2 follows the sequence Tb-ZSM-5/MCM-41> Tb-ZG>Tb-ZSM-5.

1.0

0.8

0.6

0.4

0.2

0.0 530

Tb-ZSM-5/MCM-41(200) 540

550

Tb-ZSM-5

Tb-ZG 560

530 530

540 540

550 550560

530 560 530

540

550

560

wavelength(nm) Figure 2. TRES of calcined Tb- ZSM-5, Tb-ZG and Tb- ZSM-5/MCM-41(200). Directions of arrows indicate delay times after laser pulse in range 1- 4200 us. With bold lines are represented TRES at 1 us delay after laser pulse

4. Conclusion The time-resolved photoluminescence spectra analysis indicated a single average terbium species in all hydrated Tb-zeolites with lifetimes varying between 474 us and 535 \is. For the calcined samples, lineshapes and TRES analysis correlated with terbium distribution that display a two species distribution in mesoporous materials with lifetimes centred on several hundreds of (j.s up to 2 ms while for ZSM-5 zeolite a distinct number of species could not be inferred indicating a more heterogeneous distribution. These data suggest that in mesoporous materials two distinct location of Tb exist, which might be correlated with two types of exchange sites: one on the external surface, the other inside the pores, while for ZSM-5 predominate the sites inside the pores. 5. References [1] Y. Liu, W. Zhang and T. J. Pinnavaia, J. Am. Chem. Soc. 122 (2000) 8791. [2] Z. Zhang, Y. Han, L. Zhu, R. Wang, Y. Yu, S. Qiu, D. Zhao and F.-S. Xiao, Angew. Chem. Int. Ed. 40 (2001) 1258. [3] D. T. On and S. Kaliaguine, Angew. Chem. Int. Ed. 40 (2001) 3248. [4] S. P. B. Kremer, C. E. A. Kirschhock, A. Aerts, K. Villani, J. A. Martens, O. I. Lebedev and G. van Tendeloo, Adv.Mater. 15 (2003) 1705. [5] M. P. Hehlen, N. J. Cockroft, A. J. Bruce and T.R Gosnell, Phys. Rev. B 56 (1997) 9302.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Published by Elsevier B.V.

535 535

Acylation of fatty acids with amino-alcohols on ULMFI type materials M. Musteata3, V. Musteata3, A. Dinua, V.I. Parvulescu3*, V.T. Hoangb, D. Trong-Onb and S. Kaliaguineb "University of Bucharest, Department of Chemical Technology and Catalysis, 4—12 Regina Elisabeta Bvd., Bucharest 030016, Romania b Universite Laval, Ste-Foy, Quebec, G1K 7P4.

Acylation of oleic acid with ethanolamine was carried out using large mesoporous materials of UL-MFI-type. Mesostructured precursors having Si/Al ratios from 100 to 20, designated as Al-Meso-x were synthesized using SiCU and A1C13 as silicon and aluminum sources, and Pluronic PI23 in ethanol as surfactant. UL-ZSM-5 materials were obtained from surfactant containing the above precursors which were impregnated with an aqueous solution of tetrapropylammonium hydroxide followed by drying for several days. Chemoand regioselectivity was controlled via a strong correlation of temperature and solvent effects. 1. Introduction Acylation of fatty acids with amino-alcohols leads to valuable surfactants. In spite of this practical importance the literature is scarce, and the very few contributions in this subject refer to synthesis of pharmaceutical applications [1]. One of the major problems encountering in these syntheses is the regioselectivity, O- or N- acylation leading evidently to compounds with different properties [2]. To control O-acylation, Kihara et al. [3] suggested the use of trifluoromethanesulfonic acid as catalyst in the presence of a crown ether. Another serious problem concerns the conditions in which these reactions are carried out. All the reported acylations occur under very non-green conditions, using fatty acid chlorides and homogeneous acid Lewis catalysts. The aim of this study was to investigate a green route for the acylation of oleic acid with ethanolamine, with a good control of selectivity. Since these

536 536

molecules are very large, heterogeneous catalysis requires mesoporous materials. 2. Experimental Section UL-MFI materials were prepared according to the synthesis method described previously [4]. Mesostructured precursors having Si/Al ratio from 100 to 20, designated as Al-Meso-x (where x is the atomic Si/Al ratio), were synthesized using SiCLt and A1C13 as silicon and aluminum sources, respectively and Pluronic PI23 in ethanol as surfactant. UL-ZSM-5 materials were obtained from surfactant containing the above precursors which were impregnated with 10% aqueous solution of tetrapropylammonium hydroxide followed by drying for several days. The solid-state crystallization was performed at 120°C for different lengths of time in a Teflon-lined autoclave after the addition of a small quantity of water not contacting the sample. Table 1. Textural properties of the investigated catalysts

Sample

Si/Al ratio

SBET

Mesopore diameter

m2/g

Mesopore volume cm3/g

nm

Micropore volume cmVg

gel product

Crystallinity

%

AlMeso100 AlMeso50 AlMeso20 ULZSM5-100

100

100

800

1.6

6.9

-

50

50

745

1.5

6.2

-

20

20

680

1.4

5.4

0.008

-

100

100

440

1.2

30

0.127

58.0

ULZSM-550 ULZSM-520

50

51

470

1.2

32.5

0.133

60.0

20

21

395

1.2

27.0

0.110

40.0

The final partially crystalline products were dried in air at 80°C and calcined at 55O°C for 6 h to remove organics. The effect of crystallization conditions on the mesopore structure as well as the crystalline phase has been obtained from nitrogen adsorption experiments, transmission electron micrograph (TEM)

537

images, and from XRD patterns. Textural characteristics of these catalysts are given in Table 1. Batch catalytic tests were performed by reacting oleic acid (lmmole) with ethanolamine (1 mmole) in the presence of 30mg catalyst in the range of temperatures (rt-180°C) with (octane) and without solvents. The experiments were carried out in 50 mL teflon-lined autoclave, under a vigorous stirring. ZSM-5 have been also tested as reference catalysts. Products were analyzed by GC-MS and FTIR. 3. Results and Discussion Figures 1 and 2 describe the acylation of oleic acid at different temperatures without solvent and in octane. Scheme 1 describes the reactions occurred. The presence of the catalyst enhances the reaction rate, and controls the selectivity. This is a good evidence of the participation of the acid sites in this reaction. CH3(CH2)7CH=CH (CH2)7COOH + H2NCH2CH2OH -> -> CH3(CH2)7CH=CH(CH2)7COHNCH2CH2OH + CH3(CH2)7CH=CH(CH2)7COOCH2CH2NH2 Scheme 1. Reactions occurring in acylation of oleic acid with ethanolamine

• RT/24h • 80 80 °C/24h °C/24h

°C/24h • 120 120°C/24h 180 °C/24h 180°C/24h

y ield , %

100 90 80 70 s? 60 2 50 '?. 40 30 20 10 10 0

n UL-20/ester UL-20/amide Al-20/ester Al-20/amide Blank/ester Blank/amide

catalyst/product Figure 1. Acylation of oleic acid with ethanolamine without solvent

Till 80°C, the predominant reaction is the temperatures higher than 80°C the acylation predominate, and the NH acylated compound product. In octane, the yields are smaller than

esterification of the OH. For of the NH2 group starts to becomes the most important in the absence of the solvents

538

(Figure 2). In the investigated series, UL-ZSM-5-20 was by far the best catalyst, indicating that textural characteristics should be well correlated with the acidity. By using ZSM-5, the yields in the acylated compounds were much smaller, which is in a good agreement with the accessible surface of these catalysts. 100 90 80 70 60 3 s 60 50 3 50 40 40 30 30 20 20 10 10 0

y ield , %

0RT/octane/24h RT/octane/24h • 80 80°C/octane/24h °C/octane/24h 120°C/octane/24h 120 °C/octane/24h • 120 120°C/octane/24h °C/octane/24h

1 UL-20/ester

UL- Al-20/ester Al-20/amide Blank/ester Blank/amide UL20/amide catalyst/product

Figure 2. Acylation of oleic acid with ethanol amine in octane

4. Conclusion Large mesoporous materials are very effective catalysts for acylation of large acids with aminoalcohols. Chemo- and regioselectivity was controlled via a strong correlation of temperature and solvent effects. Depending on the conditions, this study demonstrates that it is possible to produce under very green conditions surfactants in which either OH or NH2 are fully accessible. 5. References [1] J. D. Riedel, DE Pat 181175(1903); S.Yano et al., JP 63216852(1988) for Kao Corp., Japan. [2] M. Bouzouba, G. Leclerc, J. D. Ehrhardt and G. Andermann, Bull. Soc. Chim. Fr. (1985) 1230. [3] N. Kihara, J.-I. Shin, Y. Ohga and T. Takata, Chem. Lett. (2001) 592. [4] D. Trong-On and S. Kaliaguine, Angew. Chem. Int. Ed. 40 (2001) 3248.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

539 539

Creating mesopores in ZSM-5 for improving catalytic cracking of hydrocarbons Yingxu Wei, Fuxiang Chang, Yanli He, Shuanghe Meng, Yue Yang, Yue Qi and Zhongmin Liu* Applied Catalysis Laboratory, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, P. O. Box 110, Dalian, P R China 116023.

Alkaline treatment method was employed in preparing high efficient catalytic cracking catalyst. The crystalline structure, morphology and new porosity formation was evidenced by XRD, SEM and N2 adsorption. The n-hexane catalytic cracking were carried out over the two sample prepared with and without alkaline treatment. The enhanced conversion was attributed to the coexistence of mesoporous and microporous surface. 1. Introduction The light olefins, ethylene and propylene, are the most important base chemicals among the petrochemical products. The main commercial technique for light olefins production is steam cracking of naphtha, which is known as the first energy-consuming process in petrochemical industry. Development of alternative and highly efficient route, such as catalytic cracking, is attracting considerable interest. Usually the cracking feedstock from crude oil is in a large boiling range and the target products are small molecular, so ideal catalyst will combine the mesopores for reactant diffusion and micropores for high selectiviey of light olefins. In recent years, preparing hierarchical material, with meso- and micro-pores attracts the interest from material preparation and catalytic process development [1, 2]. One of the method for preparing this kind of material is post-treatment with alkaline solution. In the present study, mesopores were created in ZSM-5 zeolite catalyst by alkaline treatment. The prepared sample was employed as the catalyst for catalytic cracking of n-hexane.

540

2. Experimental Section 2.1. Catalyst preparation The ZSM-5 (Si/Al = 60) was added to an aqueous NaOH solution of 0.1 M and stirred for 1 h under 80°C. After filtering and drying, the obtained sample was ion-exchanged with NH4NO3 solution and then calcined at 550°C to form H form catalyst. The ZSM-5 catalysts without and with alkaline treatment were denoted as Cat-1 and Cat-2. 2.2. Catalyst characterization The crystallinity was analyzed by powder X-ray diffraction (RIGAKU D/max-rb powder diffractometer) with CuKa radiation. The chemical composition of the samples was determined with Bruker SRS-3400 XRF spectrometer. Scan electron microscope (SEM) images were obtained on a KYKY-1000 instrument operated at 25 kV. N2 adsorption properties were measured with Micrometric2010 physical adsorption instrument. 2.3. Catalytic performance evaluation A pulse reaction system was used for n-hexane catalytic transformation. The catalyst (60-80 mesh) of 23 mg was loaded in the quartz reactor of 3 mm i.d. and heated at 500°C in a flow of N2 for 1 h. The reaction was performed at 400°C. The n-hexane vapor (1.98g/h) was generated in a saturator and injected automatically into the reactor. The products were analyzed by on-line Varian 3800 chromatograph with capillary column of Pona. The data was processed with DHA software. CAT-2 3. Results and discussion The XRD patterns of the two samples are shown in Fig. 1. The position of the diffraction peaks of alkaline treated sample CAT-2 are identical to those of the sample without alkaline treatment, CAT-1. High intensity of XRD lines and no any baseline drift indicate high crystallinity even

6

10

20

30

40

50

60

2 Theta (degree)

Fig. 1 XRD patterns of Cat-1 and Cat-2

70

541

Cat-1

Cat-2 Fig. 2 SEM photos of two samples

after treatment. No evident crystalline changes occur with alkaline treatment. Comparing the SEM photos given in Fig. 2, CAT-1 presents very uniform morphology, while some small particles appear in the photo of CAT-2. Even no change observed for crystalline with MFI structure, the morphology is different. Some of the ZSM-5 particles in a few microns were broken to the submicronsized nanoparticles by the alkaline solution treatment. The N2-adsorption isotherms of the two samples are shown in Fig. 3. The amount increase of N2 adsorption on Cat-2 is observed. The hysteresis loop on its desorption isotherm indicates the existence of mesopores. Textural properties listed in Table 1 show that alkaline treatment leads to a clear increase in BET specific area and pore volume, and especially the increases are from the mesopore of the sample, while the surface area and pore 0.170volumn of micropores decrease r> 160to some extent. ..:*• E 150The effect of the coexistence |140of mesopores and micropores on ;,.»*»•• n-hexane catalytic transfor< 120 - • - Cat-1 mation was investigated. The - • - Cat-2 I nopulse reaction tests were carried 's J out at low temperature and very > 100r 9(1short contact time to show the 1.0 0.0 0.2 0.4 0.6 0.8 catalyst activity difference. The Relative pressure (P/P ) conversion and product yield are compared in Fig. 4. Prodominent Fig. 3 N2-adsorption isotherm of the two samples conversion increase can be 01

f

542

Conversion and yield (%)

12 observed for CAT-2. The BTX* BTX* conversion is 4.05% over C5+ 10 10C5+ CAT-1, while the value is • C4H10 8 11.09% for the sample with C4H8 6 alkaline treat-ment. The yield • C3H8 enhancement of light olefins, 4 C3H6 4C3H6 ethylene, propylene and C2H6 2 butenes is also observed. The C2H4 0 improved catalytic CH4 Cat-1 Cat-2 performance may stem from the increased active sites and Fig. 4 Catalytic performance of the two samples optimized pore structure for *BTX:Benzene+Tolene+Xylene mass transfer caused by mesopores creation. Beside the yield increase in light olefins, more alkanes (methane, ethane, propane and butane) also generate over CAT-2. This indicates that the mesopores creation and enhanced surface activity also favor the second reactions, such as oligomerization and H-transfer.

Table 1 Textural properties of the prepared catalysts Sample

SBET

c . '-'micro

V tota i

mico

(m /g)

(cm /g)

(cm3/g)

Cat-1

394

282

0.23

0.13

Cat-2

414

252

0.28

0.11

2

3

V v

(m /g)

2

4. Conclusion Alkaline treatment can create mesopores in ZSM-5 catalyst with inherent micropores. The catalyst prepared in this way keeps the crystalline structure of ZSM-5 and has higher specific area and pore volume. The coexistence of mesopores could greatly improve the catalytic acitivity in n-hexane cracking compared with the untreated ZSM-5 catalyst. The yield of light olefins and alkane increase at the same time with CAT-2 as catalyst. The newly formed porosity favored the reactant diffusion and conversion. No obvious selectivity improvement for light olefins could be observed. 5. References [1] T. Suzuki and T. Okuhara, Micropor. Mesopor. Mater. 43 (2001) 83. [2] L. Su, L. Liu, J. Zhuang, H. Wang, Y. Li, W. Shen, Y. Xu and X. Bao, Catal. Lett., 91 (2003) 155.

Progress in in Mesostructured Materials Recent Progress S. Qiu, Y. Tang and C. Yu (Editors) (Editors) D. Zhao, S. © 2007 2007 Elsevier Elsevier B.V. B.V. All All rights rights reserved. reserved.

543 543

Effect of surfactant on the morphology of TiMMM-2 mixed-phase materials Sean M. Solberg, Dharmesh Kumar and Christopher C. Landry* The University of Vermont, Department of Chemistry, Burlington, VT 05405

This paper presents a study on the synthesis of Ti-MMM-2 (Ti-MCM-48/TS1) mixed-phase materials prepared by a one-pot method using different gemini surfactants and TPA+ ions. Powder XRD and 29Si MAS-NMR reveal that materials prepared using longer chain gemini surfactants such as 22-12-22 favored the formation of TS-1 more strongly than the shorter 16-12-16 surfactant. N2 physisorption data shows a decrease in surface area and pore volume and an increase in pore diameter as the surfactant chain length is increased. 1. Introduction Significant efforts have been made in the last few years to overcome the drawbacks of mesoporous materials, particularly with respect to improvements in the crystalline nature and catalytic properties of these materials. One approach has been to introduce zeolitic order within the walls of the mesoporous materials, thereby leading to the formation of "mixed-phase" materials, containing both microporous and mesoporous phases [1-3]. Recently, we published a report on Ti-MMM-2 mixed-phase materials, in which the TS-1 microphase was shown to form within the walls of mesoporous Ti-MCM-48 [4]. The research used a one-pot synthesis of Ti-MMM-2 using the gemini surfactant 18-12-18 as the structure-directing agent for theMCM-48mesophase. These mixed-phase materials exhibited better activity for oxidation of cyclohexene than either pure TS-1 or pure Ti-MCM-48. 2. Experimental Section In continuation of this work, we report here on a comparative study of the synthesis of Ti-MMM-2, using gemini surfactants with different alkyl tail chain

544

lengths, which leads to overall changes in the porous properties of the mesophase and in the extent of microphase formed. The Ti-MMM-2 samples with different gemini surfactants were prepared per our earlier reported procedure [4] holding the molar ratios of reaction components constant among the three materials. The samples were crystallized for 30 h at 150°C using the gemini surfactants 16-12-16, 18-12-18 and 22-12-22, which were synthesized according to an earlier report [5] The Ti-MMM-2 samples prepared using these surfactants are hereby referred to as Ti-MMM-2(16), Ti-MMM-2(18) and TiMMM-2(22). 3. Results and Discussion

(x4) \j

c

&

Figure 1: Powder XRD patterns of calcined TiMMM-2 samples that were crystallized for 30 h: (a) Ti-MMM-2(16), (b) Ti-MMM-2-(18), and (c) Ti-MMM-2(22).

(x4)

b <--*—^

(x4)

a 1

10

20

30

26/degrees

Figure 1 shows the powder X-ray diffraction (XRD) patterns of calcined TiMMM-2 using the different gemini surfactants. As seen from the figure, all three samples show the formation of a mixed-phase material. In the lower angle region (1-6°), strong XRD reflections are observed due to the MCM-48 mesophase, while in the higher angle region (6-30°) peaks are seen due to formation of TS-1 microphase. A considerable shift is observed in peak position to lower 20 values with increase in the surfactant chain length from 16-12-16 to 22-12-22, indicating an increase in the unit cell parameter. This is clearly evident from the data given in Table 1.

545 Table 1: XRD parameters and physical properties of Ti-MMM-2 crystallized for 30 h. Sample

U n k Ce,, P a r a m e t e r

Surface Area (m2/g)

Pore Diameter (A)

Pore Volume (cc/g)

Ti-MMM-2(16)

74.6

1451

29.7

1.3

Ti-MMM-2(18)

83.9

1017

34.0

1.4

Ti-MMM-2(22)

96.6

744

40.4

1.1

a

Calculated from (211) peak

Figure 2:29Si MAS-NMR spectra: (a) TiMMM-2(16), (a1) Ti-MCM-48(16), (b) TiMMM-2(18), (b1) Ti-MCM-48(18), (c) TiMCM-48(16), and (c1) Ti-MCM-48(22).

-100

-125

-150

ppm

Similarly, an increase in the pore diameter was also observed with the increase in the surfactant chain length. This is consistent with the previously reported studies, where the value of unit cell and pore diameter depended upon the surfactant chain length [6]. In addition to the changes observed at low angles, it was also observed that the growth of TS-1 is more prominent in the Ti-MMM-2 sample synthesized using longer chain length surfactant. Figures 2a and 2a' show the 29Si MAS-NMR spectra of Ti-MMM-2(16) and Ti-MCM-48(16) samples. Ti-MCM-48 samples were synthesized following the same conditions as Ti-MMM-2(16) but without the zeolite templating agent (tetrapropylammonium, TPA+). Both samples show a single distinct peak at about -108.1 ppm, indicating the predominance of mostly mesoporous Q4 sites, (Si(SiO)4), in these samples. However, the peak width of Ti-MMM-2(16) is larger than Ti-MCM-48(16). This is attributed to the presence of Q4 sites (114.8 ppm) of the TS-1 phase in this sample. The Q sites assigned to TS-1 were found to grow with an increase in the surfactant size along with a

546

simultaneous decrease in mesophase Q4 sites, as seen in Figures 2b and 2c. This is in accordance with the XRD data where the peaks due to the TS-1 phase became stronger with an increase in the chain length of the gemini surfactant. The studies thus clearly indicate that the gemini surfactants with longer chain lengths favor the formation of the microphase for a given crystallization time and temperature. It has previously been shown that micelles of large gemini surfactants such as those employed here may be able to interact at their surfaces with surrounding molecules [5]. With an increase in the alkyl tail chain length, the size of the micelle and thus the hydrophobic region increases; therefore, the interaction of the TPA+ ions with the micelle must be different in each case. We theorize that the folding of the longer chain surfactants produces a more favorable interaction with the TPA+ ions, allowing more of them to be incorporated into the overall composite material. The increased hydrophobicity and size of the micelle created by longer chain surfactants thus allows more of the microporous template to interact with the silica in the vicinity of the mesophase leading to increased microphase formation. Further studies to understand this behavior are in progress. Additionally, other reports have shown a relationship between the pore size and optimal catalytic activity [7]. Therefore, studies are underway to test the catalytic activity of these mixedphase materials under different reactions as a function of pore diameter and extent of microphase. 4. References [1] [2] [3] [4] [5] [6]

A. Karlsson, M. Stocker and R. Schmidt, Microporous Mesoporous Mater., 27 (1999)181. D. Trong On and S. Kaliaguine, Angew. Chem. Int. Ed. 41 (2002) 1036. L. Huang, W. Guo, P. Deng, Z. Xue and Q. Li, J. Phys. Chem. B 104 (2000) 2817. S. M.Solberg, D. Kumar and C. C. Landry, J. Phys. Chem. B 109 (2005) 24331. Q. Huo, D. I. Margolese and G. D. Stucky, Chem. Mater. 8 (1996) 1147. M. Kruk, M. J aroniec, Y. Sakamoto, O. Terasaki, R. Ryoo, and C. H. Ko, J. Phys. Chem. B 104 (2000) 291. [7] M. Iwamoto, Y. Tanaka, N. Sawamura and S. Namba, J. Am. Chem. Soc. 125 (2003) 13032.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

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Chiral mesoporous silica tubules by achiral surfactant template Jingui Wang, Wenqiu Wang, Pingchuan Sun, Zhongyong Yuan and Tiehong Chen* College of Chemistry, Department of Materials Chemistry, Key Laboratory of Functional Polymer Materials ofMOE, Nankai University, Tianjin, 300071, P.R. China

Chiral hollow tubule with chiral mesoporous channels was observed for the first time. The chiral tubule possessing a hexagonal cross section, with outer diameter of about 300 nm, and inter diameter of about 50 nm, was synthesized from a two-phase acidic system using achiral surfactant cetyltrimethylammonium bromide (CTAB). Furthermore, the helical meso-channels in the tubule exhibited zigzag lattice fringes along the tubule axis in TEM micrographs. 1. Introduction In the past decade, new materials possessing well-defined macroscopic forms and microscopic structures, such as mesoporous spheres, mesoporous films, mesoporous fibers and mesoporous tubules [1-5], have attracted great interest. Due to the large physical strengths, well-ordered mesopores and high surface area, most of these materials possess great potential applications for catalysis, chromatographic separation and photodevice [6]. Helical morphology is a fascinating shape observed in nature and arouses great interest. Organic materials with helical shape such as DNA, helical polymer, and helical organogel have been widely reported [7, 8]. However, helical inorganic materials with high surface area and mesopores have rarely been reported. In this paper, we report a novel morphology of twisted mesoporous silica tubules, which possess interior chiral meso-channels winding around the tubular axis. This novel mesoporous silica tubule with outer diameter of 300 nm and inter diameter of 50 nm was synthesized from a two-phase acidic system

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2. Experimental Section Cetyltrimethylammonium bromide (CTAB) was from Amresco Inc. (USA). The mesoporous silica was synthesized by a two-phase route. In a typical synthesis, the lower aqueous phase was a 15.0 g solution of 100H2O/0.025CTAB/2.5HCl (molar ratio) and the upper oil phase was 0.327mmol TEOS dissolved in 0.75 mL hexane. The purpose of dilution of TEOS in hexane is to control the diffusion rate of TEOS from the oil phase to the water phase. The vessels were left at room temperature under quiescent condition. After 5 days, the suspended flocculates were carefully taken out, washed with water, and then dried at 60°C in oven. The surfactant templates were removed by calcinations of the samples in air at 550°C for 6 h. Transmission Electron Microscope (TEM) observations were performed on a Philips Tecnai F20 microscope, working at 200 kV. 3. Results and Discussion The TEM image (Fig. la) shows flexible rope-like tubule with outer diameter about 300 nm and length as long as several micrometers. This tubule possesses hexagonal sections, which can be observed clearly in inserted image. Mesoporous lattice fringes appear periodic in the TEM image (Fig. lb). These periodic lattice fringes indicate a twisted hexagonal rod-like shape with hexagonal pore channel arrangements, based on the precious studies of chiral mesoporous silica fibers [9]. However, our finding of these lattice fringes in the tubule was not absolutely the same to the lattice fringes of chiral rods as reported [9]. The appearance of lattice fringes has a periodic direction, which indicates by white arrows. The direction of lattice fringes exhibits zigzag curve, and these lattice fringes were designed as zigzag lattice fringes. This unique form of zigzag lattice fringes may be a transition morphology, Fig. 1. (a) TEM images of calcined which can give us an inspiration to find the twisted mesoporous silica tubule. formation mechanism of chiral materials Inserted image is the magnified image of rectangle, which indicates synthesized by achiral surfactant. the hexagonal section, (b) Zigzag lattice fringes along the tubule axis indicate by the white arrow.

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4. Conclusion Chiral hollow tubule chiral mesoporous channels and hexagonal cross section, was synthesized for the first time from a two-phase acidic system using achiral surfactant. The chiral tubule possesses outer diameter of about 300 nm and inter diameter of about 50 nm. Furthermore, the helical meso-channels in the tubule exhibited zigzag fringes along the fiber axis in TEM micrographs, which can give us an inspiration to find the formation mechanism of chiral materials synthesized by achiral surfactant. 5. Acknowledgement This work was supported by National Science Foundation of China (Grants No. 20373029, 20233030), and joint-research fund of Nankai University and Tianjin University on Nano-sciences. 6. References [1] Y. F. Lu, H. Y. Fan, A. Stump, T. L. Ward, T. Rieker and C. J. Brinker, Nature 398 (1999) 223. [2] D. Zhao, P. Yang, N. Melosh, J. Feng, B. F. Chmelka and G. D. Stucky, Adv. Mater. 10 (1998) 1380. [3] F. Marlow, I. Leike, C. Weidenthaler, C. W. Lehmann and U. Wilczok, Adv. Mater. 13 (2001) 307. [4] J. Wang, J. Zhang, B. Y. Asoo and G. D. Stucky, J. Am. Chem. Soc. 125 (2003) 13966. [5] F. Marlow and F. Kleitz, Micropor. Mesopor. Mater. 44-45 (2001) 671. [6] C. T. Kresge, M. E. Leonowicz, W. J. Roth, J. C. Vartuli and J. S. Beck, Nature 359 (1992) 710. [7] F. B. T. Simon, A. S. Peter, R. A. Myles, J. I. William and F. B. M. John, Nature 399 (1999) 566. [8] C. Y. Li, D. Yan, S. Z. D. Cheng, F. Bai, T. He, L. Chien, F. M. Harris and B. Lotz, Macromolecules 32 (1999) 523. [9] S. Che, Z. Liu, T. Ohsuna, K. Sakamoto, O. Terasaki and T. Tatsumi, Nature 49 (2004) 281. [10] Q. H. Zhang, F. Lu and C. L. Li, et al, Chem. Lett. 353(2006)190. [11] B. Wang, C. Chi and W. Shan, et al. Angew. Chem. Int. Eng. Ed. 45 (2006)2088.

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Aspects of a novel method for the pore size analysis of thin silica films based on krypton adsorption at liquid argon temperature (87.3 K) Matthias Thommesa*, Norikazu Nishiyamab and Shunsuke Tanakab "Quantachrome Instruments, 1900 Corporate Drive, Boynton Beach, FL 33426, USA B Division of Chemical Engineering, Graduate School of Engineering Science, Osaka University, Osaka 560-8531 Japan

The adsorption and phase behavior of krypton at 87.3 K {i.e. 28.5 K below krypton's triple point temperature) has been systematically studied as a function of pore size by using a series of micro- and mesoporous molecular sieves. Our results indicate that pore condensation of krypton cannot be observed for pore diameters > 10 nm, but occurs in smaller mesopores. An important result is further that the density of the confined krypton phase at 87.3 K corresponds to the density of supercooled liquid krypton, which is important for applying krypton adsorption for pore size analysis. We used the results of our systematic krypton adsorption studies to develop a method for the characterization of thin micro/mesoporous silica films based on krypton adsorption at liquid argon temperature (87.3 K). This method allows determining the pore size distribution of thin films in the pore diameter range from < 1 to ~ 9 nm. 1. Introduction Thin mesoporous (silica) films have important applications in many fields {e.g., sensors and low-k dielectrics). Detailed knowledge of the pore size and pore volume is crucial in order to optimize the application of such thin films for instance as low k-materials in microelectronic applications. However, the pore size analysis of such films is difficult, also because convenient methods such as nitrogen and argon adsorption at 77.4 and 87.3 K [1, 2] cannot be easily applied for the pore size analysis of thin films. Such films are only a couple of hundred nanometers thick (~ 100 - 900 nm), and the application of nitrogen and argon adsorption at 77.4 and 87.3 K, respectively, is (because of the high saturation pressure of 760 Torr) not sensitive enough to detect the small pressure changes

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due to adsorption on thin films (deposited for instance on a Si wafer). Krypton adsorption provides in principle an alternative because krypton has very low saturation pressures at liquid nitrogen (77.4 K) and liquid argon temperature (87.3 K), i.e. 1.6 Torr and 13 Torr, respectively (these saturation pressures refer to solid krypton). Until now however, krypton adsorption has not been routinely used for pore size analysis at these temperatures because the sorption and phase behavior of krypton far below its triple point temperature (115.8 K) is still under investigation. Methods for pore size analysis based on the Kelvin equation (e.g., BJH approach) cannot be applied here, and the study of krypton adsorption by approaches based on statistical mechanics (such as nonlocal density functional theory (NLDFT) and molecular simulation) is still under development [4]. Hence, in order to address these problems we have performed systematic krypton adsorption experiments on selected zeolites and mesoporous silica molecular sieves (e.g., MCM-41, MCM-48 [2], SBA-15). This allowed us to study the effect of confinement on the sorption and phase behavior of krypton below its triple point temperature, and to use the set of krypton adsorption data to develop a procedure applicable for the pore size analysis of thin mesoporous films by krypton adsorption at 87.3 K [3]. 2. Results and Discussion The experimental adsorption studies of krypton at 87.3 K on micro and mesoporous molecular sieves revealed that pore filling (condensation) cannot be observed anymore in those cases the pore diameter exceeds ~ 9 nm, which reflects the upper limit of the application range of krypton for mesopore analysis [3]. However, for pore sizes below this threshold we observe pore condensation and hysteresis. Further, we suggest a novel method for the pore size analysis of thin films which is based on the development of a specific calibration curve at liquid argon temperature, 87.3 K. Liquid argon temperature is used rather than 77 K (liquid N2), because of two main considerations: (i) The available total pressure range for the adsorption experiments (before solidification of krypton occurs) extends up to -13 Torr, instead of only 1.6 Torr at 77.4 K. This increase in available pressure range makes it possible to resolve even microporosity (down to < 1 nm), [3b] with a sorption apparatus suitably equipped with turbomolecular pump and corresponding low-pressure transducers); (ii) There is evidence that within the mesopore diameter range from 2 - 9 nm both capillary condensation and solidification can occur as a function of pore size at 77.4 K, but it appears that at 87.3 K only gas-liquid phase transitions are observed up to a pore diameter of ~ 9 nm. Hence, contrary to the situation at 77.4 where the adsorbate density may depend on the pore size, the state of the adsorbed krypton phase is better defined at 87.3 K. The density of the confined krypton phase at 87.3 K could be calculated from our experimental data (i.e., 2.6 ± 0.1 g/cm3) and corresponds to the density of supercooled liquid krypton [3b]. A supercooled liquid krypton state at 87.3 K

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was also found in very recent molecular simulations of krypton adsorption [4] in MCM-41 like systems, and in experimental studies on freezing and melting of krypton in MCM-41 silica [5]. This is a prerequisite in order to obtain a clearly defined relationship between pore filling pressure and pore size, and to determine the pore volume of a material from krypton adsorption data. The unique krypton calibration curve (i.e. the relation between the pore filling pressure of krypton at 87.3 K and the pore size) for pore size analysis of thin films of mesoporous silica of pore sizes between 2 and 10 nm is based on the following: (a) Krypton reference adsorption isotherms measured at liquid argon temperature (87.3 K) in highly ordered mesoporous molecular sieves of defined pore size and geometry (such as MCM-41, SBA-15, MCM-48, covering the pore diameter range from 2 - 1 0 nm. (b) Pore sizes and pore volumes of these mesoporous molecular sieves were obtained by applying Non-Local Density Functional Theory (NLDFT, which is considered to be the most accurate method currently available for pore size analysis), to nitrogen (at 77.4 K) and argon (at 87.3 K) sorption isotherms, which were measured on the same mesoporous molecular sieves used for obtaining the krypton reference isotherms. 300

0.625

Silica film450 mthick RUN 1 (ads) Silicafilm450mthickRUN1(ads) SilicaFilm, 450nmthick, RUN2(ads/des) Silica Film, 450 nmthick, RUN 2 (ads/des)

180

120

60

0

0

t \

0.502 0.502

Dv(logd) [cm3 g-1]

Volume [cm3 g-1 STP

240

•

0.256 0.256

0.133

0.2

0.4

0.6 P/P0

0.8

1

i

0.379

0.01

\ \

•J\

15

\

\

25

35

45

55 65 75 55 65 75 Pore Diam eter [Å] Diameter

85

95 95

105 105

Fig 1 (a) Plot of two krypton (87.3 K) sorption isotherms measured on a thin mesoporous silica film sample (thickness 400 nm, structure directing agent: Brij30), which was deposited on a Si wafer (b) Pore size distribution curve obtained from the krypton adsorption data shown in Fig l(a) by applying the new method.

Hence, pore sizes obtained for thin mesoporous silica films by applying this unique krypton calibration curve are traceable to NLDFT pore size analysis [3]. The novel krypton adsorption method at 87 K has been applied for the pore size analysis of thin ordered mesoporous silica films deposited on a Si wafer (see Fig. 1), which were synthesized as described in ref. [6]. In order to reveal details of the low pressure range of the krypton isotherm, we display in Fig.2 the isotherm data of Fig. la in form of a semi-logarithmic plot.

554 300

Silica film 450 m thick R U N 11 (A d s) RUN (Ads) Silica film 450 nm thick R U N 2 (A ds/D es) RUN (Ads/Des)

Volume [cm3 g-1 STP

240

180

120 I 120 S

I

60

60 0

-4 10 10-4

5

10 -3

5

10 -2 P/P 0

5

10 -1

5

10 0

Fig. 2 Semi-logarithmic plot of the krypton adsorption isotherm at 87.3 K shown in Figure l(a). (The steep increase in the adsorption isotherm at P/Po = 1 indicates sublimation of the bulk fluid)

Fig. 2 clearly shows that krypton adsorption at 87.3 K can be measured over a wide relative pressure range from below 10'5 up to 1. This demonstrates the potential of krypton adsorption at 87.3 K to assess micro- and mesoporosity in thin silica films. 3. References [1] M. Thommes, In: Nanoporous Materials Science and Engineering (edited by Max Lu and X. S. Zhao), World Scientific, 11 (2004) 317. [2] M. Thommes, R. Kohn and M. Froba, J. Phys. Chem. B 104 (2000) 7932. [3] (a) M. Thommes, E-MRS 2005 spring meeting, Symposium E, Poster PI-45; (b) M. Thommes et al, manuscript in preparation, (2006). [4] F. Hung, B. Coasne, K. Gubbins, F. Siperstein, M. Thommes and M. Sliwinska-Barkowiak, Studies in Surface Science and Catalysis, in press (2006). [5] K. Morishige, K. Kawano and T. Hayashigi, J. Phys. Chem. B 104(2000) 102898. [6] Y Oku, N. Nishiyama, S. Tanaka, K. Ueyama, N. Hata and T. Kikkawa, Mater. Res. Soc Symp. Proc716 (2002)587.

Mesostructured Materials Recent Progress in Mesostructured D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Published by Elsevier B.V.

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Dynamics of xenon adsorbed in organically modified silica thin films using hyperpolarized 129 Xe 2D- exchange NMR M. Nader3, F. Guenneau3, C. Boissiereb, D. Grossob, C. Sanchezb and A.Gedeon3* "Laboratoire Systemes Interfaciaux a I'Echelle Nanometrique, CNRS-UMR 7142, Universite Pierre et Marie Curie, case 196, 4 place Jussieu, 75252 Paris cedex 05, France h LaboratoireChimie de la Matiere Condensee, CNRS-UMR 7574, Universite Pierre et Marie Curie, case 174, 4 place Jussieu, 75252 Paris cedex 05, France

Mesoporous silica thin films having 2D-hexagonal (p6m), 3D-hexagonal (P63/mmc) and 3D-cubic (Pm3n) structures were prepared via the sol-gel chemistry process using CTAB as surfactants. 2D exchange 129Xe spectroscopy (EXSY) of hyperpolarized (HP) xenon has been performed to probe the geometry of pores in organically modified siliceous thin films and to obtain exchange pathways and rates of xenon mobility between different zones. 1. Introduction 129

Xe NMR has been widely used for the characterization of nanometer-scale void spaces in solids, such as zeolites and clathrates [1]. It has been also applied for studies of mesoporous silicas, silica glasses and more recently for purely siliceous thin films [2]. Hyperpolarized (HP) xenon produced by optical pumping methods can attain spin polarizations 104 times larger than thermal ones and greatly facilitate the applications of xenon for the characterization of porous materials. In this study we report the first use of 2D exchange I29Xe spectroscopy (EXSY) of hyperpolarized (HP) xenon to probe the geometry of pores in organically modified siliceous thin films and to obtain exchange pathways and rates of xenon mobility between different zones.

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2. Experimental Section The mesoporous silica thin films having 2D-hexagonal (p6m), 3D-hexagonal (P63/mmc) and 3D-cubic (Pm3n) structures were prepared via the sol-gel chemistry process using CTAB as surfactants. The thin films were deposited on a glass substrate via the dip-coating method. While the substrate was withdrawn, evaporation took place leading to a self assembly-condensation process. Thus, once the pure silica films are formed and consolidated at 130°C for 48 h in air, they were calcined at 450°C in order to eliminate the template and to form free silanols. After the 450°C thermal treatment, the films were transferred to a receptacle containing the organic function: (2-phenylethyl) trimethoxysilane (2 g, commercial product) dissolved in anhydrous toluene (20 g, commercial product), which will be closed and kept at 60°C for 24 h. In order to eliminate anhydrous toluene, a final washing of films by absolute ethanol is performed. 3. Results and Discussion 129

Xe 2D EXSY experiments allow determining whether exchange occurred between these different regions and how fast these exchange processes might be

PL (ppm)

(ppm)

8

8

16 16

16 16

24 (ppm)

160 160 120 120 80 80 40

0

Fig. 1: EXSY spectrum of 129Xe on phenyl SiO2 thin film (0.1) with mixing time at 1 ms.

24 (ppm)

160 120 120 80 40 160

0

Fig. 2: EXSY spectrum of 129Xe on phenyl SiO2 thin film (0.1) with mixing time at 10 ms.

In 2D-EXSY experiments, the exchange between regions with different chemical shifts manifests itself in the appearance of cross-peaks between the signals from the sites in exchange. Figure 1 shows the 2D spectra of phenyl grafted SiO2 thin film with loading at 0.1 using an exchange time tm of 1 ms. As expected, the signals appear only

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on the main diagonal. Off-diagonal intensities, however, appear at 10 ms and become quite pronounced with tm > 10 ms (Fig. 2). The 2D EXSY spectra show that on a time scale of a few milliseconds there is exchange between all the adsorption regions and xenon in the gas phase. Fig. 3 shows the 2D spectra at T = 555 K for high SiO2 film with high phenyl loading (1.5) using an exchange time (/m) of 0.1 ms, respectively. The observed three diagonal peaks at ca. 0, 120, and 160 ppm are assigned to gaseous Xe, mobile Xe adsorbed in the mesopores, and Xe residing in the organic phase, respectively. In addition, the off-diagonal peaks intensified with increasing exchange times set in the experimental pulse sequence. Traces of cross peaks appeared at tm = 0.1 ms indicating that the exchange between the mobile (87 ppm) and gaseous (0 ppm) Xe occurred even on a time scale less than a fraction of 1 ms. As tm is increased to 5 ms, wherein such exchange became more pronounced, the exchange between mobile Xe adsorbed in the mesopores and Xe in the organic phase (98 ppm) began to take place. Eventually, the exchange between the organic phase and the gaseous Xe was also evident with tm = 100 ms, indicating that the exchange between Xe species in different adsorption regions and the gas phase appeared to be completed. Consequently, the observed evolution with 8 clearly indicates a hierarchical set of exchange processes. The exchange of Xe gas follows the sequence (from fastest to slowest): mesopores with free gas, mobile Xe in the mesopores and Xe residing in the organic free gas with -160 micropores, and finally, among (ppm) 120 40 gaseous- mobile Xe and gaseousorganic phase. Experiments carried out Fig. 3: EXSY spectrum of l29Xe on phenyl SiO 2 on SiO2 film with different structures at thin film (1.5) with mixing time at 0.1 ms. different phenyl loadings will be discussed. Exchange pathways and rates of xenon mobility between different zones are obtained. 4. Conclusion 129

Xe NMR has been applied for studies of purely and modified siliceous thin films mesoporous silicas. In this study we have shown for the first time that 2D exchange ' 9Xe spectroscopy (EXSY) of hyperpolarized (HP) xenon can be used to probe the geometry of pores to obtain exchange pathways and rates of xenon mobility between different zones.

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5. References [1] a) T. Ito and J. Fraissard, Chem. Phys. Lett., 136 (1987) 314; b) J. Ripmeester and C. Ratcliffe, J. Phys. Chem. 94 (1990) 7652. [2] A. Nossov, E. Haddad, F. Guenneau, C. Mignon, A. Gede'on, D. Grosso, F. Babonneau, C. Bonhomme and C. Sanchez, Chem. Comm. (2002) 2476. [3] a) I. L. Moudrakovski, C. I. Ratcliffe and J. A. Ripmeester, Appl. Magn. Reson., 8 (1995) 385. b) K. Knagge, J. R. Smith, L. J. Smith, J. Buriak and D. Raftery, Solid State NMR 29 (2006) 85.

Progress in in Mesostructured Materials Recent Progress S. Qiu, Y. Tang and C. Yu (Editors) (Editors) D. Zhao, S. © 2007 2007 Published Published by Elsevier Elsevier B.V. B.V.

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Nanocrystal-micelle: a new building block for facile self-assembly and integration of 2, 3-dimensional functional nanostructures Hongyou Fan1a,b* "Sandia National laboratories, Albuquerque, NM87106, USA Department of Chemical and Nuclearing Engineering, The University of New Mexico, Albuquerque, USA. h

1. Introduction Self-assembly has been testified to be one of the powerful and efficient methods to the synthesis of complex functional nanomaterials with precisely controlled dimension, function, and topology [1, 2]. Its combination with lithography and pattern techniques is an ideal tool kit that allows fabrication and integration of nanomaterial platforms providing functions and forms at multiple scales and locations, which emulates nature complex systems [3, 4]. Here I present our recent series of work on the synthesis of a new building block, NCmicelle and its use for further self-assembly and integration of 2, 3-D functional nanostructures [6-10]. 2. Results and Discussion Our concept is to consider monosized, organically-passivated NCs as large hydrophobic molecules that, if incorporated individually into the hydrophobic interiors of surfactant micelles, would result in the formation of monosized NC micelles composed of a metallic (or other) NC core and a hybrid bilayer shell with precisely defined primary and secondary layer thicknesses (see Fig. 1H). The hydrophilic NC micelle surfaces provide water-solubility and allow further assembly or derivatization as depicted in Fig. 1. The formation and stability of individual gold NC-micelles (as opposed to aggregated dimers, trimers etc.) was confirmed by ultraviolet/visible spectroscopy and TEM (Fig. ID), where we observed no difference between the positions and widths of the plasmon resonance bands (~ 510-nm) of the C12-alkanethiol stabilized gold NCs in

560 Biospecies tagging

Spin-coating

Films and devices fabrications

Fig 1. Schematic diagram for the synthesis of water-soluble gold nanocrystal-micelles and periodically ordered gold NC/silica superlattices.

chloroform and those of the corresponding water soluble NC-micelles. In addition, evaporation of the NC-micelle solutions resulted in self-assembly of hexagonally ordered NC arrays (Fig.lC) as expected for individual, monosized nanocrystals. Judging from UV/visible spectroscopy and TEM and the ability to make ordered arrays, these solutions were stable for over two years at room temperature. Formation of ordered gold NC/silica thin films is analog to that of selfassembly of surfactant and silica. Charge interaction and hydrogen bonding between hydrolyzed silica Fig 2. Representative transmission electron microscope (TEM) images of gold nanocrystal/silica superlattices. (A) [100] orientations of bulk samples prepared according to pathway i-ii-iii (Fig 1). Inset (al): high resolution TEM of sample (A) showing gold NC lattice fringes. Inset (a2): selected area diffraction pattern from the image in (A). (B) well-shaped superlattice solids. (C) Optical image of ordered gold NC/silica thin film spin-coated on glass. (D) TEM image of [21 l]-oriented NC/silica superlattice film. Inset (d) selected area diffraction pattern from image in (D). (E) Hierarchically ordered superlattice crystals on glass. (F) Patterned ordered gold NC/silica films through umolding.

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and surfactant head groups on NC-micelle surface drive the formation of ordered gold NC/silica mesophase. However, the two systems exhibit distinct tendency to form mesostructures. Prior work on self-assembly of pure surfactant and silica indicated that a series of mesostructures can be formed including lamellar, 1-d hexagonal, cubic, and 3-d hexagonal periodic symmetries. In the case of self-assembly of NC-micelles and silica, only fee mesostructure are preferentially formed regardless of basic and acidic catalytic conditions. This is probably due to the fact that the gold NC-micelles are pre-formed in a homogeneous solution and behave rather like a "hard" sphere tending to form fee close packing than "soft" pure surfactant micelles that incline to undergo phase transformation. Vital to the formation of transparent, ordered gold NC/silica superlattice films is the use of stable and homogeneous spinning or casting solution that upon evaporation of water undergoes self-assembly of NCmicelles and soluble silica. For this purpose, we prepared oligomeric silica sols in NC-micelle aqueous solution at a low hydronium ion concentration (pH~2) designed to minimize the siloxane condensation rate, thereby enabling facile silica and NC-micelle self-assembly during spin-coating or casting. The aging experiments (Fig. 3, Cl to C5) unambiguously demonstrate that extensive silica condensation, that results in polymeric silica species, does not favor the selfassembly, leading to a less (111)

Fig. 3. A. Low-resolution scanning electron microscope (SEM) micrograph of ordered gold NC/silica superlattice thin film. B. Highresolution SEM from same specimen in A. C. cs XRD patterns of gold NC/silica superlattice films. Cl. Ordered gold/silica film prepared using a coating solution that was aged at ambient condition for 24 hours, and C2 for 5 hours. C3. Ordered gold/silica film prepared C3 using a coating solution without aging. C4. Ordered gold/silsesquioxane film prepared using a solution that was aged at ambient condition for 24 hours. C5. Ordered C1 gold/silsesquioxane film prepared using a 2 4 6 8 10 Two theta (degrees) solution without aging.

V

ordered film. In addition to silica, we have demonstrated the synthesis of ordered gold NC arrays inside organo-silsesquioxane framework. The ordered gold NC/ silsesquioxane was prepared by using ~3-nm DM-stabilizedgold NCs, CTAB, and BTEE. The corresponding XRD patterns (Fig. 3-C4&5) reveal that films exhibit ordered fee mesostructure. In addition, we observed from XRD results that the self-assembly when using BTEE is not strongly affected by solution aging unlike that when using TEOS. This is due to that organo-bridged

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precursor has relatively slower hydrolysis and condensation rate than TEOS. The ability to form patterned films is essential for device fabrication. We have demonstrated the formation of patterned gold NC/silica superlattice films based on our previous work on patterning surfactant templated silica mesophases. Figure 2f shows the patterned stripes and dots containing ordered gold NC/silica superlattice fabricated using (i-molding techniques. The pattern sizes are determined by the feature sizes of the PDMS stamps 3. Conclusion The uniform The formation of water soluble NC micelles and their selfassembly into ordered 3D mesophases provides a new means to integrate model 3D NC arrays into robust devices. The arrays provide the ideal media for the study of the variety of transport and collective phenomena predicted to occur for such systems). Beyond transport, these robust, highly ordered NC arrays could be useful for catalysts and photonic devices such as lasers, and the watersoluble NC micelle intermediates have shown promise for biological labeling or sensors. 4. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10]

Y. N. Xia and G. M. Whitesides, Ann. Rev. Mater. Sci., 28 (1998) 153. N. B. Bowden, M. Week, I. S. Choi and G. M. Whitesides, Ace. Chem. Res., 34 (2001) 231. P. D. Yang et al., Science, 287 (2000) 465. H. Y. Fan, Y. Lu, A. Stump, S. T. Scott, T. Baer, R. Schunk, V. Perez-luna, G. P. Lopex and C. J. Brinker, Nature, 405 (2000) 56. H. Y. Fan, K. Yang, D. M. Boye, T. Sigmon, K. J. Malloy, H. Xu and C. J. Brinker, Science, 304 (2004) 567. H. Y. Fan, A. Wright, J. Gabaldon, A. Rodriguez, C. J. Brinker and Y. B. Jiang, Adv. Func. Mater. 16(2006)891. H. Y. Fan, E. W. Leve, C. Scullin, J. Gbaldon, D. Tallant, S. Bunge, T. Boyle, M. C. Wilson and C. J. Brinker, Nano Lett. 5 (2005) 645. H. Y. Fan, E. Leve, J. Gabaldon, A. Wright, R. E. Haddad and C. J. Brinker, Adv. Mater. 17(2005)2587. H. Y. Fan, Z. Chen, C. Brinker, J. Clawson and T. Alam, J. Am. Chem. Soc. 127, (2005) 13746. H. Y. Fan, J. Gbaldon, C. J. Brinker and Y. B. Jiang, Chem. Commun. 22 (2006) 2323.

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Direct visualization of mesoporous structures in the framework of SBA-15 mesoporous films Jinlou Gua>b, Hangrong Chen b , Xiongping Dong b , Zhicheng Liu b and Jianlin Shi b

"Department of Chemical System Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8654, Japan. b State Key Lab of High Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, Chinese Academy of Science, Shanghai 200050, China.

Two separated experiment methods including electroless deposition and pulse electrochemical deposition were employed to incorporate high-density gold and platinum nanowire arrays into the pore channels of mesoporous thin films (MTFs). The incorporated metallic nanowires served as the inverse replicas to determine directly the structure properties of the SBA-15 mesoporous films. Both experiments support on the facts that the presence of mesopores structure rather than micropores in the framework of SBA-15 MTFs. 1. Introduction SBA-15 mesoporous silica, in the form of powder or films, has attracted much attention due to its current and potential applications [1,2]. This remarkable interest stems from the many desire features of SBA-15, including appealing textural properties, high surface area and appreciable thermal and hydrothermal stability [3,4]. Despite all this interest in the synthesis, modification and application of SBA-15, the very structure identification of this material was largely uncertain until recently [5-7]. The consensus was come to that the large uniform ordered pores of SBA-15 channels were actually accompanied by the smaller disordered pores that provided connectivity between adjacent large pore channels [8-10]. In the past few years, several attempts have been made to control directly the inter-connecting porosity since such control is particularly desirable for applications involving host-guest interactions and diffusion process [11-13]. High temperature hydrothermal treatment, even introducing TMB into embryo mesostructure, was employed by Zhao et al. [12] to generate three dimensional large-pore mesoporous networks.

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The pore size and microporosity within the pore walls of ordered mesoporous silica SBA-15 could also be tuned by means of salt addition under microwave hydrothermal conditions [13]. Recently, Ryoo et al. [11,14] efficiently controlled the porous network connectivity of SBA-15 through optimizing synthesis conditions, such as synthesis temperature or TEOS/surfactant ratio. However, these investigations were mainly focused on mesoporous powder while few efforts were about, needless to say the control of, the structural properties of SBA-15 MTFs [15, 16]. Herein, we employed gold and platinum replicas, prepared by electroless deposition (ELD) and pulse electrochemical deposition (PED) methods, respectively, to directly visualize the mesoporous structures in the framework of MTFs. 2. Experimental Section 2.1. The procedure for the preparation of MTFs The MTFs were prepared as our recent reports [17]. Specifically, 7.68 mLof tetraethyl orthosilicate (TEOS, 98% Aldrich) were prehydrolyzed in a solution containing 3.71 g of dilute hydrochloric acid (PH~2, isoelectric point of silica) and 10 mL of THF under vigorous stirring at room temperature. Following 120 minutes of stirring, this prehydrolyzed silica solution was mixed with a solution containing 1.78 g of the poly (ethylene-oxide)-poly(propylene oxide)-poly (ethylene-oxide) block copolymer EO20PO70EO20 (Pluronic PI23, BASF) dissolved in 30 mL of THF. The two solutions were further stirred for 15 minutes. From this mixture with a final molar composition of TEOS : PI23 : H2O : HC1 : THF = 1 : 0.0094 : 5 : 0.0090 : 25, thin films were prepared by dip-coating onto cleaned glass slides at 75 mm min'1. The films were stored at room temperature for 24 hours and then extracted using ethanol with a little HC1 being added under refluxed condition to remove the surfactant. 2.2. The procedure of ELD Highly dispersed palladium nanoparticles within the pore channels of the MTFs were prepared as our previous work [18]. These Pd nanoparticles will serve as catalysis centers for the following ELD of gold nanowires. As-prepared Pd loaded MTFs were immersed into gold electroless plating bath [19] for 1-1.5 min. to obtain gold nanowires loaded MTFs. The silica template was removed by dropping 2% HF on the films. The template removal was confirmed by energy dispersive spectroscopy (EDS, not shown). In order to observe the nanobridges directly, sonic dispersion was used to obtain separated nanowires.

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2.3. The procedure ofPED The PED was performed using a conventional three-electrode system in a glass cell with a mesoporous silica coated conductive glass slide as the working electrode, Pt wire as a counterelectrode and Ag/AgCl as a reference electrode [20]. Square wave pulses were applied with a duty cycle of 0.25, i.e.cathodic pulse time ton of 300 ms and time between pulses tOff of 900 ms based on our trial and error experiments. The deposited silica/platinum composite films were annealed at 400°C in a nitrogen atmosphere for at least 2 hours to enhance their structural strength and adhere more strongly to the conductive glass substrates. The silica template was removed by submersing the films in a 2M NaOH at 60 °C followed by rinsing with water. 3. Results and Discussion In the procedure of evaporation induced self-assembly [2, 21] to dip-coat the MTFs, PI23 surfactant enriches by solvent evaporation to exceed critical micelle concentration and therefore develops mesophases only during the last few seconds of film deposition, which suggests that the formation of films is very fast in kinetical conditions [22]. The inherent hydrophilic poly (ethyleneoxide) (PEO) blocks of the template are expected to be deeply occluded within the silica walls during the quick gelation of silica matrix and have limited time

Fig. 1 (a) TEM image of unsupported gold nanowires by removal of silica matrix with 2% HF aqueous solution. The arrows highlight the bridges between the nanowires. (b) The enlarged image of ellipse portion of image a.

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to redistribute from silica framework to the region adjacent to the cores of micelles [23]. Thus, the calcined MTFs are likely to exhibit complementary pores in the parts of the framework where once the EO blocks are located [2]. In addition, the temperature used in the synthesis of MTFs is generally at room temperature [17, 24], which means EO blocks are substantially restrict in the silica framework since the degree of hydration of the EO blocks dramatically increases at low temperature [23]. Both of above mean MTFs may have the different structure from that of the SBA-15 powder. Firstly, high density gold nanowires as replicas were synthesized using our previous electroless deposition route [19] to determine directly the structure properties of MTFs. Fig. 1. shows the structure and morphology of unsupported nanowires after the silica film matrix is removed by 2% HF solution followed with sonic dispersion. The bridges between the two nanowires can be clearly seen as highlighted by arrows in the Fig. lb, which is the reflection of interconnections between pore channels in MTFs. This indicates that the synthesized gold nanowires are the replicas of the pore structure of the MTFs and we are able to detect defects and other structure variables within the channels. However, as enlarged in fig. lb, we find that the width of bridge is about 6 nm almost identical to the diameter of pore channels, which indicates IInt nteensity nsity ((a.u.) a.u.)

100

i

1

c

a

A 200 x10

B 22

3 3

2 θ (degree) 2θ (degree)

4

5

•b

in

/

m _

NUKE

SEI

•ft 2 •*<sa z? Lin

m K 28nT

Fig. 2 (a) XRD patterns of mesoporous silica/ metal composite films before (A) and after (B) removal of the silica template, (b) SEM top-view image of platinum nanowire arrays after the removal the silica, (c) TEM image of a bundle of platinum nanowires and the corresponding selected area diffraction.

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the presence of mesopores rather than micropores in the framework of silica as SBA-15 powder demonstrated [4-10]. Since the deposited nanowires have no adhesion to the glass substrate, we could not characterize the ordered properties of synthesized nano arrays, thus a PED method as our previous reported [20] was also utilized to prepare high-density platinum nanowire arrays to confirm the structure properties. Fig. 2a shows the XRD patterns of a silica/platinum thin film before (A) and after (B) removal of the silica template by 2M NaOH. It should be point out that trace B in fig. 2a could only be obtained after the composite films were annealed at 400 °C for at least two hours to enhance their structural strength and adhere more strongly to the conductive glass substrates. Curve A shows the typical one dimensional hexagonal pattern with an intense (100) diffraction peak at 20=1.57 degree and relatively week (200) peak at 20=3.02 degree. Although the silica matrix is removed by NaOH, the ordered structure could be maintained from XRD patterns in curve B. The peak at ca. 20=1.6 degree, with slight broadened width and decreased strength, not only shows the synthesized nanowires had formed the arrays but also indicates the connectivity between the adjacent nanowires [15,20]. In fact, the top-view SEM image after the removal of silica, as shown in fig. 2b clearly shows the parallel nanowire arrays spread across the whole film plane. It is reasonable to conclude that both XRD and SEM show the presence of the connectivity between the adjacent nanowires, otherwise, these nanowires could not form the nanoarrays as reported for MCM-41 [21], which consisted of separated continuous walls. After the silica template was removed, large quantity of nanowire bundles were observed when we employed TEM to visualize directly the size of connectivity again. Fig 2c shows a bundle of self-standing platinum nanowires. This large bundle of parallel nanowires is of the uniform diameters consistent with the size of the ordered pores of SBA-15, and separated by the repeating distance corresponding to the silica framework in the structure of SBA-15 mesoporous porous films. If there is no connectivity between the adjacent nanowires, it is impossible to obtain so uniform repeating distance. As highlighted by the arrows in fig 2c, the bridges in the size range of 6-7 nm could be clearly seen again. These results further indicated that mesoporous rather than microporous voids were present in the framework of SBA-15 MTFs. 4. Conclusion Through the reverse replications of high density gold and platinum nanowire arrays, mesoporous structures in the framework of SBA-15 MTFs were visualized directly. This new finding of pore-pore communication by randomly distributional mesopores rather than micropors is very important in the fields of microreactors and sensors etc. wherein the diffusion is decisive to its success.

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5. Acknowledgment The work was supported by National Natural Science Foundation of China, Grant No. 50232050 and Shanghai Special Project, Grant No.03DJ 14004. 6. References [1] D. Zhao, J. Feng, Q. Huo, N. Melosh, G. H. Frederickson, B. F. Chmelka and G. D. Stucky, Science, 279 (1998) 548. [2] D. Zhao, P.Yang, N. Melosh, J. Feng, B. F. Chmelka and G. D. Stucky, Adv. Mater., 10 (1998) 1380. [3] S. Andreas, Adv. Mater., 15 (2003) 763. [4] J. L. Gu, L. M. Xiong, J. L. Shi, Z. L. Hua, L. X. Zhang and L. Li, J. Solid State. Chem., 179(2006)1060. [5] W. Lukens, Jr., P. Schmidt-Winkel, D. Zhao, J. Feng and G. D. Stucky, Langmuir, 15 (1999) 5403. [6] R. Ryoo, C. H. Ko, M. Kruk, V. Antochshuk and M. Jaroniec, J. Phys. Chem. B, 104 (2000) 11465. [7] M. Imperor-Clerck, P. Davidson and A. Davidson, J. Am. Chem. Soc, 122 (2000) 11925. [8] K. Miyazawa and S. Inagaki, Chem. Commun., (2000) 2121. [9] P. L. Ravikovitch and A. V. Neimark, J. Phys. Chem. B, 105 (2001) 6817. [10] S. Jun, S. H. Joo, R. Ryoo, M. Kruk, M. Jaroniec, Z. Liu, T. Ohsuna and O. Terasaki, J. Am. Chem. Soc, 122 (2000) 10712. [11] H. J. Shin, R. Ryoo, M. Kruk and M. Jaroniec, Chem. Commun., (2001) 349. [12] J. Fan, C. Yu, L. Wang, B. Tu, D. Zhao, Y. Sakamoto and O. Terasaki, J. Am. Chem. Soc, 123(2001)12113. [13] J. R. Matos, L. P. Mercuri, M. Kruk and M. Jaroniec, Chem. Mater., 13 (2001) 1726. [14] M.Choi, W. Heo, F. Kleitz and R. Ryoo, Chem. Commun., (2003) 1340. [15] D. H. Wang, W. L. Zhou, B. F. McCaughy, J. E. Hampsey, X. L. Ji, Y. B. Jiang, H. F. Xu, J. K. Tang, R. H. Schmehl, C. O'Connor, C. J. Brinker and Y. F. Lu, Adv. Mater., 15(2003) 130. [16] M. P. Tate, B. W. Eggiman, J. D. Kowalski, and H. W. Hillhouse, Langmuir, 21 (2005) 10112. [17] J. L. Gu, G. J. You, J. L. Shi, L. M. Xiong, S. X. Qiang, Z. L. Hua and H. R. Chen, Adv. Mater., 17 (2005) 557. [18] J. L. Gu, J. L. Shi, L. M. Xiong, H. R. Chen and M. L. Ruan, Micro. Meso. Mater., 74 (2004) 199. [19] J. Gu, J. Shi, L. Xiong, W. Shen, M. Ruan, Y. Zhu and J. Liang, Solid State Sci., 7(2004) 747. [20] J. Gu, J. Shi, H. Chen, L. Xiong, W. Shen and M. L. Ruan, Chem. Lett., 33 (2004) 828. [21] Y. Lu, R. Gangull, C. A. Drewlen, M. T. Anderson, C. J. Brinker, W. Gong, Y. Guo, B. Dunn, M. H. Huang and J. I. Zink, Nature, 389 (1997) 364. [22] S. Besson, C. Ricollean, T. Gacion, C. Jacquiod and J. P. Boilot. J. Phys. Chem. B, 104 (2000) 12095. [23] G. S. Christine, Current Opinion in Colloid and Interface Science, 7 (2002) 173. [24] P. C. A Alberius, K. L. Frindell, R. C. Hayward, E. J. Kramer, G. D. Stucky and B. F. Chmelka, Chem. Mater., 14 (2002) 3284.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

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Preparation, texture and electrochemical properties of TiO2 films with highly ordered mesoporosity and controlled crystallinity D. Fattakhova Rohlfing,3 M. Wark,a J. Rathousky,b T. Brezesinski0 and B. Smarsly0 "Institute of Physical Chemistry and Electrochemistry, University Hannover, Callin Str. 3-3a, D-30167 Hanover, Germany h Academy of Sciences of the Czech Republic, J. Heyrovsky Institute of Physical Chemistry, Dolejskova 3, 18223 Prague, Czech Republic c Max Planck Institute of Colloids and Interfaces, 14 424 Potsdam, Germany

1. Introduction Mesoporous layers of TiO2 attract great attention owing to important applications in photocatalysis, solar cells, sensors and displays due to their large surface area, excellent accessibility of the inner surface and suitable morphological form in comparison with powders. A recently developed generalized procedure for the preparation of layers of mesoporous metal oxides is based on a mechanism combining block copolymer self-assembly with complexation of inorganic species [1, 2]. However, obtained materials suffer from important drawbacks, especially the relatively low thermal stability and robustness and only partial crystallinity of the mesoporous framework. Recently, we have demonstrated that a new type of diblock poly(ethylene-cobutylene)-b-poly(ethylene oxide) copolymers (KLE) enables to obtain mesoporous films of TiO2 with high crystallinity whilst maintaining the mesostructure up to 700 °C due to the thicker pore walls and generally much improved robustness [3, 4]. Based on the former work, the present communication aims at the systematic study into the electrochemical Li insertion into these films. This technique is highly sensitivity towards different TiC>2 phases enabling to detect crystalline phases even in trace amounts. The Li insertion process is characterized by the fundamental thermodynamic characteristics such as the specific insertion potential and the maximum insertion capacity, which differ for various TiO2 phases rendering them easily

570

recognizable. The fundamental process of Li insertion into anatase is the phase transition from tetragonal TiC>2 to orthorhombic Lio.5Ti02, taking place at formal potential Ef of 1.85 V. The maximum insertion capacity x of 0.5 mol of Li per 1 mol of anatase is given by the number of the vacant sites for the Li insertion. This enables quantification of the anatase fraction. Rutile has comparable insertion capacity but more negative insertion potential Efof 1.45 V. Layered TiO2(B) exhibits a pair of symmetric insertion/extraction peaks at potentials Ef of 1.5-1.6 V and the maximum insertion capacity x = 0.8. The amorphous forms of TiO2 show activity towards Li insertion in broad potential range without defined insertion/extraction potentials and insertion capacity of up to 1 mol/mol, but low stability towards multiple insertion/extraction cycles. 2. Experimental Section An isotropic solution containing 0.068 g KLE, 3 ml of ethanol and 0.5 ml of water was added to a solution of 0.6 g of TiCL, in 3 ml of ethanol, the resulting sol being stirred for 24h. The thin films were prepared by dip-coating onto FTO-coated glass slides in a controlled atmosphere of 20 % relative humidity at a withdrawal rate of 1 mm/s. The dried films were calcined in air at varying temperatures achieved at a ramp of 5°C/min. 2D-SAXS measurements were carried out on samples prepared on ultrathin silicon wafers with the variation of the angle of incidence p. WAXS measurements were performed in symmetric reflection using a D8 diffractometer from Bruker. Transmission electron microscopy images were taken with a Zeiss EM. The texture properties were determined from adsorption isotherms of Kr at 77 K using ASAP 2010 from Micromeritics. Electrochemical measurements were carried out using Autolab 12 potentiostat (Eco Chemie). The measurements were performed in 1 M LiN(SO2CF3)2 solution in 1 : 1 by weight mixture of ethylenecarbonate (EC) and 1,2-dimethoxyetane (DME). TiO2 films on FTO glass were used as working electrodes, Li foil as both auxiliary and reference electrodes. The efficiency of the Li insertion, actual amount of the material involved in the electrochemical reaction as well as relative fractions of contributing electrochemically active phases were characterized by insertion coefficient x = Q/Qtheor, which is calculated as the amount of charge Q consumed in the relation to the maximum theoretical amount Qtheor calculated according to Faraday's law Qtheor = zF m/M, where z is number of electrons in electrochemical reaction (here 1), F is the Faraday constant, m and M are mass and molar mass of electroactive compound.

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3. Results and Discussion 3.1. Characterization of the structure and texture of the films 2D-SAXS experiments showed that all the films treated at 400-700 °C exhibit an oriented, highly-ordered mesoporous structure with a distorted bcc Im3m symmetry in the [110] orientation with respect to the substrate. The temperature treatment deforms the originally spherical mesopores into ellipsoids. TEM images of the films show a well-defined cubic arrangement of mesopores 14 nm in diameter distributed in a TiO2 matrix with pore walls 9-10 nm in thickness. WAXS analysis proves that the films are amorphous up to 450°C, while the treatment at 650°C leads to practically complete crystallization of the TiO2 framework. The crystallization starts at 500°C after the complete dehydration of the framework and provides practically completely crystalline material of exclusively one phase, namely anatase, without any X-ray detectable traces of rutile or brookite. Treatment at 650-700°C only slightly influences the crystal size and phase composition of the material. The Scherrer equation provides the nanocrystal size of 15 nm for the films treated at 550°C, which does not change with increasing the temperature up to 700°C. The adsorption isotherm of Kr at 77 K on the film calcined at 450°C significantly differs from those for samples calcined at higher temperature. As significant pore blocking during desorption was observed, the pores have access to the external gas phase only via narrow constrictions {e.g., ink-bottle pores). Film calcined at 550°C is characterized by developed mesoporosity, any pore blocking being removed due to the structure changes caused by the higher calcination temperature. In spite of the rather small thickness of the films, they exhibit large specific surface areas, ranging from 57 to 30 m2/g for films calcined at 450 to 650°C. The porosity of samples is similar of about 30 %. 3.2. Electrochemical measurements The film calcined at 450 °C exhibits broad and featureless insertion/extraction curves of amorphous TiO2 phase with some traces of anatase, which can be identified by characteristic insertion/extraction peaks (Fig. 1). Even if the peaks of crystalline anatase are clearly distinguishable, the corresponding charge fraction is practically negligible, which is ingreement with the X-ray amorphous character of the material. Calcination at 550-700°C causes a drastic change in the structure and corresponding electrochemical behavior. Films calcined at 550°C show pronounced anatase insertion and extraction peaks at 1.7 and 2.0 V, respectively (Fig. 1). The contribution from anatase is equal to 4 2 % of the theoretical insertion capacity, which corresponds to 85 % of anatase. The voltammograms of the films calcined at even higher temperature of 600 700°C correspond to pure crystalline anatase phase, sharp and symmetric insertion/extraction peaks characterizing the uniformity of insertion behavior for the whole material and evidencing the very narrow size distribution of the crystallites. Another feature of the Li insertion in the TiO2 films is the absence

572

of any detectable traces of other crystalline phases, which are typically present in varying amounts in almost all sol-gel prepared TiC>2 materials. The percentage of the anatase phase, determined precisely from the galvanostatic experiments, increases from 85 to 100 % for films calcined at 550 and 700°C.

E, Vvs. Li

E, Vvs. Ll

Figure 1. Cyclic voltammograms of TiO2 films calcined at 450-550 °C Scan rate 0.5 mV/s.

4. Conclusion The KLE-templated films have been shown to be practically amorphous if calcined at temperatures lower than 450°C. Above this temperature, complete crystallization occurs within relatively narrow temperature range. The films are distinguished by very high phase purity, consisting of uniform nanocrystals of anatase with easy and complete accessibility from the voids, and high temperature stability of both texture and structure properties. Due to their unique structure and texture properties, these novel films are very promising materials for a number of applications, the first test having confirmed their excellent photocatalytic performance for decomposition of wax layers and easily reachable and stable superhydrophilicity. 5. Acknowledgement The authors are grateful to the DFG (projects WA 1116/10 and 436 TSE/130/46/0-1), DAAD (D/04/25758), the Max Planck Society and the Ministry of Education, Youth and Sport of the Czech Republic (project 1M0577) for the financial support. 6. References [1] P. Yang, D. Zhao, D. I. Margolese, B. F. Chmelkaand G. D. Stucky, Nature 396 (1998) 152. [2] C. J. Brinker, Y. F. Lu, A. Sellinger and H. Y. Fan, Adv. Mater. 11 (1999) 579. [3] A. Thomas, H. Schlaad, B. Smarsly and M. Antonietti, Langmuir 19 (2003) 4455. [4] B. Smarsly, D. Grosso, T. Brezesinski, N. Pinna, C. Boissiere, M. Antonietti and C. Sanchez, Chem. Mater. 16 (2004) 2948.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

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Optimization of the silylation procedure of thin mesoporous SiO2 films with cationic trimethylaminopropylammonium groups Dina Fattakhova-Rohlfing,a Michael Warka and Jiri Rathouskyb "Institute of Physical Chemistry and Electrochemistry, Gottfried Wilhelm Leibniz Universitdt Hannover, D-30167 Hannover, Germany b J. Heyrovsky Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, CZ-18223 Prague 8, Czech Republic

1. Introduction Mesoporous silicas are excellent hosts for incorporation of various guest molecules. The properties of the relatively inert silica surface can be drastically changed by the covalent grafting of functional groups, such as thiol-, amino- or alkylammonium ones, by silylation with chloro- or alkoxysilanes [1]. While the silylation procedure has been optimized for powdered mesoporous silica materials with differing porosity, it has not been developed for mesoporous silica thin films yet, even if the obvious differences in diffusion properties and pore accessibility of powders and films would imply the different conditions needed for their silylation. Recently we have faced a serious problem of poor reproducibility of silylation procedure of silica films when investigating their applicability as a matrix for anchoring electrochemically active species and dye molecules [2]. Therefore, the optimization of their silylation procedure has been aimed at in this communication. The procedure for the silylation of mesoporous silica films with trimethoxysilylpropyltrimethylamonium chloride (MAPTMS) bearing cationic trimethylammonium groups has been optimized. The introduced functional groups enable the ionic immobilization of anionic species, such as anionsubstituted dye molecules. The optimization criteria are (i) the reproducibility of the silylation reaction and (ii) the degree of surface modification providing the maximum incorporation of the guest species. The adsorption of Kr at 77 K was used as the checking method, combined with the UV/VIS analysis of the amount of incorporated dye molecules. Silica films used were prepared by

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template-assisted procedure using commercial block copolymer Pluronic F127, yielding crack-free mesoporous films with 3D - worm hole like texture [3]. 2. Results and Discussion Kr adsorption data obtained for parent films reveal the highly pronounced mesoporosity with a narrow pore size distribution, the typical pore diameter, porosity and specific surface area being 6-7 nm, 60 % and 130-140 cm2/cm2 (corresponding to 435 m2/g) for films 340 nm in thickness. Fig. la clearly proves the excellent reproducibility of the texture properties of the parent films. 0.020 0.010 0.010b)

0.015

C/3

0.010

. • ^"

/ /

0.005

0.005

0.000 0.00

b)

VA / cm3/cm2 STP

VA / cm3/cm2 STP

a)

0.25

0.50

P/Po

0.75

1.00

0.000 0.00

0.25

0.50 0.250

0.75

1.00

P/Po

Figure 1. Adsorption isotherms of Kr at 77 K on five parent silica films (a) and on the same films silylated with MAPTMS in dichloromethane according to the non-optimized procedure (b)

The silylation with MAPTMS has been first attempted according to the recipe developed for mesoporous SiO2 powders, where long reaction times (12-16 hours) and aprotic solvent with relatively high dielectric constant (dichloromethane) were shown to give the best results [4]. This procedure, however, resulted in considerable scatter of the texture properties (Fig. lb). One of the reasons for different reactivity of powders and films is the difference in the accessibility of the silica surface for the silylation agent. For powders, even if some of the pores got stuck, there would be always enough free pathways at disposal for the sylilation agent to access virtually all the inner surface. Due the openness of a mesoporous particle to the diffusion from all the directions from the whole environment of the particle (Scheme la), the diffusion is fast and easy, enabling to use high concentrations of the sylilation agent. With a mesoporous film on a non-porous support, however, the inner surface is accessible only from one direction (Scheme lb), which makes it prone to blocking. In order to minimize this undesirable effect, the concentration of the sylilation agent should be substantially decreased.

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Further, the total surface area of the sample to be sylilated vastly differs. For a film with mass of only few milligrams, it does not exceed one square meter, while for powders with almost arbitrary mass many hundreds of square meters are always at disposal. Of course, such large surface areas need much larger amount of the agent and much longer times to achieve complete modification than mesoporous films.

Scheme 1. Availability of surface for the silylation agents in mesoporous silica with cubic pore orientation (mesoporosity is not shown) in the form of particle (a) and thin film on a substrate (b)

The procedure was optimized with respect to the MAPTMS concentration, reaction time and reaction temperature as well as the polarity of the aprotic solvents used, namely toluene and dichloromethane. A low MAPTMS concentration in dichloromethane of 8 mmol/L and short reaction time of 4 hours provided the best results, while an increase in the temperature did not have practically any effect. Adsorption isotherms of Kr on the films silylated at given conditions are highly reproducible, showing the expected decrease in the pore size and film porosity (Fig. 2a). The use of toluene as a solvent leads just to a very slight change in the texture properties due to the low degree of the surface modification (Fig. 2a, B), which is not sufficient for the efficient immobilization of the guest species (Fig. 2b, B). Carrying out silylation in dichloromethane having higher dielectric constant somewhat increases the efficiency of silylation reflected in a slightly larger decrease in the pore volume (Fig. 2a, C) and the higher amount of the incorporated NiPc molecules (Fig. 2b, C). The higher efficiency of silylation reaction in dichloromethane can be due to the better solubility and reactivity of the MAPTMS bearing polar ammonium groups. Besides the choice of appropriate solvent, the efficiency of the coverage of the surface by alkoxysilanes requires also a sufficient concentration of free silanol groups on the silica surface, acting as the anchoring centers for the silylation. The lower efficiency of the silylation reaction can be caused by the partial deactivation of those groups due to the bonding of the products of the

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template destruction or condensation leading to the formation of bridge -Si-OSi- groups due to the thermal treatment.

Q_ CO

0.00

0.4

0.8

500

600

700

P/Po Wavelength, nm Figure 2. (a) Typical Kr adsorption isotherms on the parent mesoporous silica films (A), after the optimized silylation procedure in toluene (B), dichloromethane (C) and dichloromethane including the pretreatment of the silica surface in mild alkaline solution (D). (b) Corresponding UV/VIS spectra of NiPc anchored on the surface of silylated silica films (the scattering patterns arise from the FTO substrate).

Thus, a short pretreatment of the surface of silica films in mild alkaline solution, which ensures the cleavage of the bridge siloxane groups and the activation of silica surface, allows reaching the optimum silylation efficiency. The pretreated films silylated in dichloromethane according to the optimized procedure exhibit the decrease in the pore size from 6.8 (for the parent film) to 6.3 nm, porosity from 56 to 37 % and specific surface area from 122 to 82 cm2/cm2. At the same time, the narrow pore size distribution without any pore blocking has been maintained, resulting in the maximum incorporated amount of guest NiPc molecules (Fig. 2, D). The anchoring of NiPc did not cause practically any change in the texture properties, the pore size decreasing and porosity decreasing by only 0.1 nm and 1 % abs., respectively. 3. Experimental Section Preparation of silica films according to a modified template-assisted procedure using Pluronic F127 is described elsewhere. Silylation with MAPTMS was carried out in a Schlenk flask equipped with a Teflon holder with magnetic stirrer. Prior to the silylation, the SiO2-coated glass slides were dried at 100 °C in air and activated in 0.3 % ethanolic solution of Et4NOH for 30 min. The optimum concentration of MAPTMS in dichloromethane or toluene and the duration of the silylation at room temperature were 8 mmol/L and 4 h. The samples were washed by repeated stirring in dichloromethane and ethanol. Tetrasodium salt of Ni(II) phthalocyanine tetrasulfonic acid (NiPc) was anchored from its 5 mmol/L solution in dimethylsulfoxide for 12 hours. After

577

the dye adsorption, the films were repeatedly washed in ethanol and dried in air. The intensity of the NiPc adsorption was determined from their UV/VIS spectra in the transmission mode using Varian 5000 spectrometer. Texture characteristics of the films were determined from the adsorption isotherms of Kr at the boiling point of liquid nitrogen (approx. 77 K) using an ASAP 2010 apparatus (Micromeritics). Minimum of 5 films was used for the statistical analysis of silylation reproducibility. 4. Conclusion The development of post-synthetic silylation procedure of mesoporous silica films with cationic trimethylaminopropylammonium groups, aimed at efficient reproducible incorporation of the anionic guest molecules, has clearly demonstrated different silylation reactivity of film and powder mesoporous materials. The major difference in case of the films is caused by the restricted accessibility of the silica surface to silylation agent, resulting in the proneness to the pore blocking after prolonged reaction times. A low concentration of silylation agent and a short reaction time are therefore needed for reproducible silylation of thin mesoporous films. Additionally, an activation of the silica surface by short pretreatment in mild alkaline allows achieving the optimum silylation efficiency. 5. Acknowledgement The authors are grateful to the DFG (projects WA 1116/10 and 436 TSE/130/46/0-1), DAAD (D/04/25758) and the Ministry of Education, Youth and Sport of the Czech Republic (project 1M0577) for the financial support. 6. References [1] E. F. Vansant, P. Van Der Voort and K. C. Vrancken, Characterization and chemical modification of the silica surface, Elsevier, Amsterdam (1995) [2] D. Fattakhova Rohlfing, J. Rathousky, Y. Rohlfing, O. Bartels and M. Wark, Langmuir, 21 (2005)11320. [3] D. Zhao, P. Yang, N. Melosh, J. Feng, B. Chmelka and G. Stucky, Adv. Mater., 10 (1998) 1380. [4] Y. Rohlfing, D. Woehrle, Y. Rathousky, A. Zukal and M. Wark, Stud. Surf. Sci. Catal. 142 (2002) 1067.

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Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

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Synthesis of transparent mesoporous aluminum organophosphonate films through triblock copolymer templating Tatsuo Kimura and Kazumi Kato Advanced Manufacturing Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Shimoshidami, Moriyama-ku, Nagoya 463-8560, Japan

1. Introduction Morphological design of ordered mesoporous materials is one of the most important researches for their industrial uses in sensors, membranes, electronic, photonic, and optical devices. Although silica does not show photochemical and electrochemical properties, those properties can be given to ordered mesoporous silica by embedding organic groups in the framework. For example, hydrolysis and condensation of bridged silsesquioxanes in the presence of surfactants lead to the formation of periodic mesoporous organosilicas. Non-silica-based hybrid materials have attracted much attention because of the combination of properties due to the inorganic units and organic groups. Although a variety of non-silica-based mesoporous oxides and phosphates have been synthesized so far [1,2], there have been few reports on the preparation of non-silica-based hybrid mesoporous material [3-5]. Recently, a synthetic strategy of non-silica-based hybrid mesoporous materials by using organically bridged diphosphonic acids has been proposed [6]. Indeed, a successful preparation of mesoporous aluminum organophosphonates (AOPs) with 2-D hexagonal structures was reported by using alkylenediphosphonic acids [6-10]. Here, the synthesis of transparent mesoporous films composed of aluminophosphate-like units and alkylene groups was carried out in the presence of poly(ethylene glycol)-Z>/ocA:-poly(propylene glycol)-i/ocA:-poly(ethylene glycol) triblock copolymers (EOnPOmEOn).

580

2. Experimental Section In a typical synthesis, a triblock copolymer (EOgoPOsoEOgo, 1.2-1.6 g) was dissolved in a mixed solvent of water (30 mL) and ethanol (5 mL). Ethylenediphosphonic acid ((HO)2OPC2H4PO(OH)2, 0.96 g) was dissolved in the solution. The solution became cloudy at first during the gradual addition of aluminum chloride (A1C13, 0.67 g) to the solution under stirring (A1/2P = 1.00). After all of A1C13 was added to the solution and the stirring was continued, a clear solution can be obtained within several minutes. The clear solution was spin-coated on a glass substrate at a spinning rate of 4000 rpm. The transparent film was air-dried, dried at 100 °C, and calcined at 250°C for 3 h. 3. Results and Discussion The XRD pattern of a calcined mesoporous AOP film containing ethylene groups prepared in the presence of EOgoPC^oEOgo is shown in Figure 1. A peak with the ^-spacing of 5.7 nm was maintained after calcination. Porosity of the film was checked by N2 adsorption of the corresponding bulk sample calcined at 250°C. The N2 adsorption isotherm was type IV. The BET surface area and the pore volume were 348 m2 g"1 and 0.84 cm3 g"1, respectively. The BJH pore diameter calculated using desorption branch was 7.5 nm. Although periodic structure of the transparent mesoporous AOP film cannot be defined from the XRD pattern, the TEM image (Figure 1) which was obtained by using a sample scrapped off from the grass substrate would reveal the presence of periodic mesostructure.

4 6 8 29 /°(FeKo)

12

Fig. 1. XRD pattern and TEM image of a calcined mesoporous AOP film containing ethylene groups prepared in the presence of EOgoPC^oEOgo

On the basis of the high-resolution SEM image showing a direct observation of the mesopores (Figure 2), we have considered possible formation of cage-

581

type mesopores though distinct images due to the corresponding mesostructures such as 3-D hexagonal could not be taken by TEM. If the mesostructure is 3-D hexagonal, the XRD peak with the ^-spacing of 5.7 nm is assigned to the (002) plane due to a 3-D hexagonal structure (a = 11.4 nm) and the wall thickness is calculated to be 3.9 nm. However, the high-resolution SEM observation concluded that mesopores are present whole the transparent films but do not stack regularly. __^_^^

Fig. 2. High-resolution SEM image of a calcined mesoporous AOP film containing ethylene groups prepared in the presence of E080P03oE08o.

Solid-state NMR spectra of the calcined bulk sample showed the retaining of the hybrid framework structure (Figure 3). The P MAS NMR spectrum showed that broad peaks were observed at around 12.5 ppm, being assignable to P atoms in diphosphonate groups [6-8]. Only one peak due to carbon atoms in the ethylenediphophonate groups was observed at 21.5 ppm in the 13C CP/MAS NMR spectrum [9,10]. The NMR results indicate that ethylene groups within the hybrid framework are maintained after calcination at 250 °C. The results also revealed that P—C bonds in the diphosphonate groups are not decomposed during calcination. The 27A1 MAS NMR spectrum of the as-synthesized sample showed that all of the Al species are present as six-coordinated species. After calcination, a small amount of four-coordinated Al species were formed through condensation of the hybrid framework. Thus, it is considered that the hybrid framework is also maintained in the calcined film. The FT-IR spectra of the as-synthesized and calcined films also exhibited the successful removal of only triblock copolymers. Strong peaks assignable to CH stretching bands observed in the range of 2800-3000 c m 1 disappeared after calcination at 250°C and then small peaks due to C2H4 groups were observed in the same region. Ethylene groups in the diphosphonate groups are stable up to 400°C [7]. But complete removal of triblock copolymers was not confirmed by XPS. Although any peaks due to EOgoPOaoEOgo were not observed through the I3 C CP/MAS NMR measurement of the calcined bulk sample, the calcined film

582 (31P)

I

I I I I I I 100 0 -100 Chemical shift/ppm

ft

I I I I I 80 40 0 -40 -80 Chemical shift /ppm

(«CCP)

I I I I 150 100 50 0 Chemical shift /ppm

Fig. 3. Solid-state 27Al MAS, 31P MAS and 13C CP/MAS NMR spectra of a corresponding calcined bulk sample containing ethylene groups prepared in the presence of E08oP03oE08o.

contained ca. 22 mass % of carbon atoms (XPS). The value is somewhat larger than the calculated value (ca. 11 mass %, A1(O3PC2H4PO3) though the presence of OH groups and hydrated water molecules is not considered. A large number of water molecules were liganded to Al atoms in the hybrid frameworks (27A1 MAS NMR). The Al/P molar ratio of the film was 4.7 (XPS), being consistent with that in the precursor solution (0.5, A1/2P = 1.0). 4. Conclusion Mesoporous films whose frameworks are mainly composed of AOP can be synthesized by the reaction of aluminum chloride and ethylenediphosphonic acid in the presence of triblock copolymers. Triblock copolymers can be eliminated by calcination at low temperature (250 °C) without decomposition of the hybrid framework and mesopores formed whole the films with high surface areas. The insight contributes to further development of non-silica-based hybrid mesoporous films though further study is needed for developing methods to control mesostructural orderings of mesoporous AOP films. 5. References [1] C. Yu, B. Tian and D. Zhao, Curr. Opin. Solid State Mater. Sci., 7 (2003) 191. [2] B. Tian, X. Liu, B. Tu, C. Yu, J. Fan, L. Wang, S. Xie, G. D. Stucky and D. Zhao, Nature Mater., 2 (2003) 159. [3] T. Kimura, Chem. Lett., 31 (2002) 770. [4] T. Kimura and J. Mater. Chem., 13 (2003) 3072. [5] P. C. Angelome, S. Aldabe-Bilmes, M. E. Calvo, E. L. Crepaldi, D. Grosso, C. Sanchez and G. J. A. A. Soler-Illia, New J. Chem., 29 (2005) 59. [6] T. Kimura, Chem. Mater., 15 (2003) 3742. [7] T. Kimura, Chem. Mater., 17 (2005) 337. [8] T. Kimura, Chem. Mater., 17 (2005) 5521. [9] J. E. Haskouri, C. Guillem, J. Latorre, A. Beltran, D. Beltran and P. Amoros, Eur. J. Inorg. Chem., (2004) 1804. [10] J. E. Haskouri, C. Guillem, J. Latorre, A. Beltran, D. Beltran and P. Amoros, Chem. Mater., 16(2004)4359.

Progress in in Mesostructured Materials Recent Progress S. Qiu, Y. Tang and C. Yu (Editors) (Editors) D. Zhao, S. © 2007 2007 Elsevier Elsevier B.V. B.V. All All rights rights reserved. reserved.

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Electrical/Mechanical properties of nanoporous thin films by using various sized cyclodextrins Jin-Heong Yima Jong-Ki Jeonb and Young-Kwon Park "Division of Advanced Materials Engineering, Kongju National University, 182, Gongju, Chungnam, 314-701, Korea h Dept. of Chemical Engineering, Kongju National University, 182, Gongju, Chungnam, 314-701, Korea 'Faculty of Environmental Engineering, University of Seoul, 90, Jeonnong-dong, Seoul 130-743, Korea

1. Introduction As the dimension of integrated circuit decreases, it has been required a replacement of conventional Al/SiO2 interconnects to Cu/low-k (dielectric constant) to decrease RC (resistance and capacitance) delay. The predictions from the semiconductor industry indicate that inter level dielectric with a bulk dielectric constant (k) below 2.4 will be realized for 2007 [1]. This requirement would only be obtained by incorporation of nano voids into the matrix film. Many porous thin films have been demonstrated as low-k (low dielectric) materials in large scale integrated circuits (LSI) to reduce RC (resistance and capacitance) delay [2, 3]. One approach to generate nanoporous structures in thin films is to formulate a thermally stable low-k precursor with a pore generator (porogen) that can be decomposed and volatilized at the high temperature to leave pores in the film. It has been introduced the potentials to use cyclodextrin (CD) derivatives as a porogen. CD-based porogens have the attractive properties [3, 4]. Even though, several studies of nanoporous film, which templated by various types of CD based porogen have been performed [3-6], there has not been studied on the effect of core size of CD molecules. In this study, the electrical/mechanical properties of various sized CD (i.e. a-CD, P-CD and Y-CD) templated nanoporous films have been investigated to know the potential of low-k applications.

584

2. Experimental Section (a)

(b)

(c)

4-methyl-2-pentanone (Aldrich Chemical Co.) as solvent was used as-received without further purification. Hexakis (2,3,6-tri-Omethyl)-P-cyclodextrin (CYCLO LAB. Co.), heptakis (2,3,6-tri-O- Figure 1. PM3-optimized structures of various sized CD molecules; shows the front view of methyl)-P-cyclodextrin (CYCLO (a) a -tCD, (b) 3 -tCD, (c) y -tCD, Red LAB. Co.), and octakis (2,3,6-tri- sphere stands for a oxygen atom and gray O-methyl)-P-cyclodextrin sphere denotes a carbon atom.. (CYCLO LAB. Co.) were used as-received. In this study, MTMS(methyl trimethoxy silane) and TCS (2,4,6,8tetramethyl-2,4,6,8-tetrakis (trimethoxysilylethyl) cyclotetra siloxane) were used as monomers to synthesize the matrix precursor (mCSSQ) [7]. The spin-on coating solutions were prepared by properly mixing the SSQ precursor as a matrix with CD compounds as a porogen and propylene glycol methyl ether acetate (PGMEA) as a solvent. The porous films were prepared in accordance with our previous paper [4]. Depth-profiled PALS was used to determine the pore size and pore interconnectivity in these thin films [8]. The dielectric constant of each film with MIM (metal-insulator-metal) structure was measured by LCR meter (HP 4284) instrument at a frequency of 100 kHz. The hardness (H) and elastic modulus (E) of the thin films were measured by using the continuous stiffness measurement (CSM) of nano-indentation method. 15.7 Å

17.0 Å

19.1 Å

3. Results and Discussion

Weight loss (wt %)

The CDs are cyclic oligosac120 charides consisting of at least six Alpha_tCD Alpha t C D glucopyranose units that are joined 100 CD Beta_tCD Gamma_tCD Gamrr a_tCD together by a(l->4) linkages. The six 80 glucose unit containing CD is 1 specified as a-CD, while the CDs with 60 seven and eight glucose unit are I 40 designated as |3-CD and y-CD, 20 respectively. According to the molecular modeling based on the 0 250 300 350 400 450 500 semi-empirical quantum mechanic oC) Temperature ( (°C) theory (PM3), the methyl group substituted CD (tCD) compounds Figure 2. Thermogravimatric analysis (TGA) have three-dimensional structure with of various cyclodextrin compounds maximum diameter varying from 15.7 to 19.1 A as shown in Figure 1. The thermal decom-position of tCDs is observed around 350 ~ 400°C (Figure 2.). Considering that vitrification of the

I

A

V

585

Dielectric constant (k)

mCSSQ polymer almost complete up to 300°C, the tCDs could be 2.8 effectively used as porogen. The alpha-tCD • alpha-tCD range of thermal decomposition of alpha-tCD 2.6 • beta-tCD beta-tCD y-tCD is higher than that of 0-tCD beta-tCD and a-tCD as shown in Fig 2. Gamma-tCD • Gamma-tCD •£ 2.4 2.4 Gamma-tCD Refractive index decreased as expected and the porosity increased ' i 2.2 as a function of content of tCD in J_ the mixture as shown in Table 1. 2.0 I 2.0 . 5 Dielectric constant of the porous -J--J-iv-I1.8 thin film made from tCD varied from 2.4 to 1.9 as tCD content 1.6 increases from 10 to 50 wt% as can 0 10 20 30 40 50 60 be seen in Figure 3. Among the tCD (%) Porogen Concentration (%) based porogens, y -tCD templated porous film shows the lowest kvalue at the high content of porogen Figure 3. The variations of dielectric constant. (50 wt%). It is speculated that the most thermal stable porogen (y-tCD) may be favorable in the terms of dielectric constant of the film. Mechanical properties of the films decrease with increasing porosity in the evaluated range. Table 1. The mechanical properties of various CD templated porous thin films. Porogen content

Thickness (nm)

Refractive Index

a -tCD 10% a -tCD 30% a -tCD 50% B-tCD10% B -tCD 30% B -tCD 50% y -tCD 10% y -tCD 30% y -tCD 50%

1088 1187 937 673 1133 922 803 1136 959 710

1.4144 1.3715 1.3313 1.3169 1.3709 .3316 .3025 .3728 .3335 .3069

Porosities

9.2 18.1 21.4 9.4 18.1 24.7 8.9 17.6 23.7

0)

Elastic Modulus (GPa) (2)

Hardness (GPa)<2)

5.85 4.00 3.07 2.86 4.21 3.12 2.50 4.26 3.72 2.68

1.11 0.79 0.51 0.47 0.80 0.52 0.40 0.81 0.62 0.42

^porosity calculated by Lorentz-Lorentz equation (2) value was collected at 50nm displacement in the nanoindentation Positronium annihilation lifetime spectroscopy (PALS) has been used to measure the pore size and to elucidate the nature of the pore structure, i.e., interconnection length as shown in Table 2. The pore size are around 1.7—1.9

586

nm, which is similar to the molecule size of CD. However, the pore size would not be exactly correlated with CD molecule size. All have interconnected pores to some degree and the length of pore ranges from less than 30 nm. This length might be thought of as the axial length of a long cylindrical pore. In conclusion, among the tCD porogens, y~tCD snowed fairly good performance for the low-k application. The dielectric constant of the film by using 50 wt% of y-tCD reached below 1.8, and the elastic modulus of the porous film was 2.68 Gpa. The pore size is almost similar to the CD molecular size (1.7-1.9 nm), which calculated from PM3 modeling. Table 2. Summary of PALS results for the mesopores of the mCSSQ thin films prepared with 30 % of various CD compound loading.

„o m C

... P°Sltlon

o-Ps Lifetime ^(D

mCSSQ/a-tCD30% mCSSQ/P-tCD30% mCSSQ/Y-tCD 30 % UJ Ortho positronium lifetime Cylinder Model

„ , \Q) Dcyl,nder(nm)()

Interconection Length (nm)

27.9 1.85 25 23.5 1.69 15 26J) L78 15 measure by PALS. w Pore diameter deduced by

4. References [1] International Technology Roadmap for Semiconductors; Semiconductor Industry Association: Gaithersburg, MD, (2003). [2] J. L Hedrick, R. D. Miller, C. J. Hawker, K. R. Carter, W. Volksen, D. Y. Yoon and M. Trollsas, Adv. Mater. 10(1998) 1049. [3] I.-H Yim, Y.-Y. Lyu, H.-D. Jeong, S. A. Song, I.-S. Hwang, J. Hyeon-Lee,; S. K. Man, S. Chang, J.-G. Park, Y. F. Hu, J. N. Sun and D. W. Gidley, Adv. Funct. Mater. 13 (2003) 382. [4] J.-H. Yim, J.-B. Seon, H.-D. Jeong, Y. S. Pu, M. R. Baklanov and D.W. Gidley, Adv. Funct. Mater. 14(2004)277. [5] Y. Y. Lyu, J. H. Yim, Y. Byun, J. M. Kim and J. K. Jeon, Thin Solid Film 496 (2006) 526. [6] H.G. Peng, R.S. Vallery, M. Liu, W.E. Frieze, D.W. Gidley, J. H. Yim, H.D. Jeong and J. Kim, Appl. Phys. Lett., 87 (2005) 161903. [7] J.-H. Yim, Y.-Y. Lyu, H.-D. Jeong, S. K. Mah, J. Hyeon-Lee, J.-H. Hahn, G. S. Kim, S. Chang, and J.-G. Park, J. Appl. Polym. Sci. 90 (2003) 626. [8] D. W. Gidley, W. E. Frieze, T. L. Dull, J. Sun, A. F. Yee, C. V. Nguyen and D. Y. Yoon, Appl. Phys. Lett. 76/10 (2000) 1282.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

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Synthesis of MSU-1 silica particles with spherical morphology Kalidas Biswasa, Soo-Hyun Janga, Wha-Seung Ahna*, Yoon-Suk Baikb and Won-Jo Cheongb "Department of Chemical Engineering, Inha University, Incheon, Korea 402-751 b Department of Chemistry, Inha University, Incheon, Korea 402-751

Mesoporous silica particles MSU-1 with spherical morphology were prepared using either TEOS (tetraethylorthosilicate) or BTME (1, 2 bis (trimethoxysilyl) ethane) as silica source and Tergitol 15-S-12 surfactant. The hydrolysis step of TEOS / BTME was conducted in acidic condition at room temperature and the condensation step was promoted by fluoride at 308 K. Static condensation period was essential for the formation of spherical morphology and a full particle growth occurred within 2 h. Increases of NaF amount decreased the particle size but enhanced the mesoporosity, whereas increases in the silica / surfactant molar ratio increased the particle sizes. Higher amount of NaF was required for BTME to produce spherical particles. Reversed phase chromatographic separation was conducted to test the properties of MSU-1 samples prepared under different synthesis conditions. 1. Introduction Mesoporous silica materials, which can be prepared with a variety of surfactant template molecules, have been studied exhaustively since the discovery of MCM-41 in 1992 [1]. Among these, MSU-1 mesoporous silica was initially reported by Bagshaw et al. [2] using alkyl polyethylene oxides as template and TEOS as a silica source. Subsequently, Prouzet and Pinnavaia [3] introduced F' catalyst for the condensation of silicate species, and finally Boissiere et al. [4] modified the synthesis protocol by introducing separate hydrolysis and condensation steps. We have been testing different synthesis routes to produce spherical mesoporous silica particles and found that MSU-1 is very reproducible and produces narrow particle size distribution. In this work, we report the details on the effect of synthesis parameters such as the amount of

588

NaF, TEOS/surfactant mole ratio, and synthesis temperature on particle shape and size. Furthermore, it will be demonstrated that the same synthesis route is equally applicable to a preparation of organic-inorganic hybrid particles. 2. Expenrimental Section 3.33 g TEOS was added to a solution of 1.476 g Tergitol and 98.0 g water at room temperature. The resulting milky mixture was vigorously stirred for 3 h and HC1 was added to make pH = 2. After stirring for 10 h, 1.28 ml 0.25 M NaF was added. The solution was aged for 72 h at 308 K at static condition. A white precipitate formed was filtered, washed with water and dried at 318 K for 24 h. This is calcined at 893 K for 6 h. Synthesis protocol using BTME is basically identical, and 1 g of the dried sample was refluxed in 3.8 g of 35 wt% HC1 in 150 ml ethanol at 50 °C for 6 h to remove the surfactant. The particles produced were characterized by XRD, SEM, and N2 adsorption. Details of the HPLC separation experiment using a micro-column can be found in our earlier work [5]. 3. Results and Discussion Either stirring or static condition in the hydrolysis step did not affect the final morphology of the silica particles obtained but stirring during the condensation step always resulted in irregular shapes as shown in Fig. 1; for isotropic particle Fig. 1. Scanning electron micrographs of the as-made MSU-1 samples (a) with stirring and (b) without stirring in the condensation steps : NaF/TEOS = 0.02, condensation temperature = 308 K, Si/surfactant = 8, aging time = 72 h.

Fig. 2. Scanning electron micrographs of the samples prepared with varying NaF amount over BTME (a) 4 mol % and (b) 11 mol %: condensation temperature = 308 K, Si/surfactant = 8, aging time = 72 h.

growth, condensation step had to be mechanically undisturbed to obtain spherical particles with narrow size distribution. It is found that particles grow

589

to 2-3 um after 30 min and reaches to the maximum of 5-7 urn after 120 min condensation period but 72 h was desirable for structure cementation [6]. Decrease in particle size was observed with increasing NaF up to 6 mol % due to enhanced nucleation; beyond 6 mol %, saturation in nucleation occurred so that no further decrease in size was found. But the size increased (ca. 3 to ca. 7 um) with the increase of the silica to surfactant ratio from 4 to 10. The effect of condensation temperature indicates that the optimum temperature is 308-318 K to get uniform-sized particles. Further increase in temperature resulted in non-uniform size distribution. Table 1. Textural properties of MSU-1 samples prepared with different NaF/TEOS mole ratios and at different temperatures (Si/surfactant = 8, aging time = 72 h) Samples

1 mol%(NaF/TEOS) 2 mol%(NaF/TEOS) 2 mol%(NaF/TEOS) 2 mol%(NaF/TEOS) 4 mol%(NaF/TEOS) 6 mol%(NaF/TEOS) 8 mol%(NaF/TEOS) 10 mol%(NaF/TEOS) 1

Synthesis Temp (K) 308 308 318 328 308 308 308 308

Surface area (m2/g) 594 654 661 681 816 837 867 860

Pore volume (cc/g) 0.28 0.31 0.31 0.32 0.46 0.48 0.58 0.59

Diameter

(A) a

<20 <20 <20 20 20 21 27 30

pore diameter was calculated by BJH method using desorption branch of the isotherm

Ca

-JLLA)

40

AJU_

80

120

rb

140

Fig. 3. Chromatograms obtained with MSU-1 prepared with different NaF amount (a) 2 mol %, (b) 6 mol %, and (c) 10 mol % at 308 K(C18 + Endcapping, 70/30 v/v % MeOH/H2O at the flow rate of 10 ml/min). 1: 4-Methoxyphenol, 2: Acetophenone, 3: Ethylbenzoate, 4: Ethylbenzene, 5: Acenaphthylene, 6: Acenaphthene, 7: Phenanthrene, 8: Anthracene.

The effects of NaF and temperature on textual properties of MSU-1 are summarized in Table 1. There is a gradual increase in pore size, pore diameter,

590

pore volume, and surface area with increases in the amount of F" ions, illustrating increases in mesoporosity. A substantially higher amount of NaF (11 mol %) was required to get a spherical hybrid silica material using BTME as a silica source as shown in Fig.2 (a) and (b). Apparently, due to its larger monomeric precursor size, BTME seems to need additional impetus for enhancing hydrolysis and condensation. Finally, MSU-1 samples prepared were surface functionalized using a C18 compound and applied as a stationary phase in reversed phase HPLC. According to the performance results shown in Fig. 3, pore volume or surface area of the MSU-1 could be correlated to the separation behavior of the organic molecules; the larger the pore volume and surface area of the MSU-1 the longer it took for complete separation but with improved resolution. 4. Conclusion To have the desired spherical morphology in a reproducible manner in MSU1 synthesis, static condensation period was found essential as well as the separation of hydrolysis and condensation steps. Fully-grown particles were obtained within 2 h condensation period. The optimum condensation temperature was 308-318 K. By changing the moles of NaF/ TEOS and TEOS/ surfactant, the particle size can be controlled. The mesoporosity of the material increased with increasing amount of NaF. Pore size up to 3.0 nm with pore volume 0.59 cc/g and BET surface area up to 860 m2/g can be achieved using 10 mol % of NaF. 5. Acknowledgement This work was supported by Inha University Research Found (2006). 6. References [1] C. T. Kresge, M. E. Leonowicz, W. J. Roth, J. C. Vartuli and J. S.Beck, Nature, 359 (1992)710. [2] S. A. Bagshaw, E. Prouzet and T. J. Pinnavaia, Science, 269 (1995) 1242. [3] E. Prouzet and T. J. Pinnavaia, Angew. Chem. Int. Ed. Engl., 36 (1997) 516. [4] C. Boissie're, A. Larbot, A. Vander Lee, P. J. Kooyman and E. Prouzet, Chem. Mater. 12 (2000) 2902. [5] D. J. Kim, J. S. Chung, W. S.Ahn, G. W. Kang and W. J. Cheong, Chem. Lett. 33 (2004) 422. [6] M. Ocana, R. Rodringues-Clemente and C. Serna, Adv. Mater., 7 (1995) 212.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

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Proton conductivity of cubic silica-based mesostructured monolithic membranes Liangming Xiong,° Yong Yang," Hangrong Chen,* Jianlin Shi* and Masayuki Nogami"* "Department of Materials Science and Engineering, Nagoya Institute of Technology, Showa, Nagoya, 466-8555, Japan. b State-Key Laboratory of High Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, Chinese Academy, Shanghai 200050, China.

1. Introduction Proton exchange membrane fuel cells (PEMFCs) are an exciting clean energy technology for power delivery for a range of devices from automotive applications to portable digital equipment [1]. Proton-conducting membrane is the key component of PEMFC. Nafion and sulfonated aromatic polymers are two main types of electrolytes for the current PEMFC technologies, but they are limited to the temperature below about 100°C, owing to decreased mechanical strength at higher temperature and the need to keep the membrane hydrated. Therefore, many efforts have been focused on how to resolve these problems and the development of new proton conducting membranes with the capabilities of high conductivity and operating at higher temperature to replace the above organic membranes. Porous inorganic solid acid membranes such as phosphates may be the promising candidate [2]. As for these membranes, an effort on synthesis routes and surface area maximization combined with surface functionalization may lead to further surface transfer property improvements. In this regard, ordered mesoporous materials may be an avenue. Ordered mesoporous materials have favorable structural properties, chemical and mechanical variabilities, and capabilities of surface functionalization, which allow for significant optimization of electrochemical performance and may be beneficial for their use as possible solid-state electrolyte alternatives. Therefore, very recently ordered mesoporous materials as proton-conducting electrolyte for fuel cells have attracted an increasing research interest [3-6]. Most of the efforts have been focused on the uses of mesoporous powders and thin films as

592

possible electrolyte alternatives for PEMFCs, but little was carried out on mesostructured monoliths. Mesoporous monoliths with bulk size can be prepared with many methods [7] and may be an ideal candidate for a proton conducting electrolyte, besides a good host for optical devices. Herein, we present a preparation of silica-based monoliths with ordered 3D cubic mesostructures and investigate into their proton conductivity for fuel cell application. 2. Experimental Selection The silica-based mesostructued F127 + EtOH. TEOS,EtOH,H 2 O monoliths (SBMMs) were prepared by a (65°C> (30 °C> sol-gel technique, as shown as Fig. 1. In Stirring.' the preparation, the polymeric silica sol had final molar compostion of about {pQ(OCH3)3ornot>) 1TEOS: 0.007F127: 0.21HC1: 9.2H2O: 40EtOH. The drying was processed at Aging* below 50°C under decresed pressure T conditions. UV radiation was by the use Dryings of a deep-UV lamp whose wavelength is ~r UV Radiation. from 187 to 254 nm. For the phosphorous oxide-doped samples trimethyl , F ] o w cha[1 o f (he , js o f phosphate with the amount of 5-10 % silica . based monoliths. P/Si ratio was added. The samples were characterized using XRD (Philips, X Pert-MPD), N2sorption ( Quantachrome, Autosorb-1), AFM (Seiko II, SPA-300HV), and AC impedance spectroscopy (AC IS, Solartron, SI-1260). The proton conductivity was determined from the resistence, obtained from the AC impedance spectra, the thickness of the samples and the area of the Au electrodes. 3. Results and Discussion Fig. 2 shows the macro-morphology photographs of SBMMs. They are transparent and exhibit a considerable ductibility. The small-angle XRD (SAXRD) patterns of both the P-doped and undoped samples (Fig. 3) give the characteristic of ordered cubic mesostructures. The diffraction peaks can be indexed to (110), (220) and (222) reflections of this 3D cubic mesostructure [8]. For the doped sample (pattern b), its peaks were localized at larger 29 values than those of the undoped sample (pattern a), which indicates that Fig. 2 Macromorphology photographs of SBMM the doped sample had a smaller

Fig. 5 AFM image of SBMM.

a:

dd (nm) 10.64 10.64 7.52 4.34

222

220

b: h kk ll 11 11 00 2 22 0 2 22

dd (nm) (nm) 11.32 11.32 8.00 8.00 4.62

110

a

220

X5

1

222

Intensity /a.u.

h k ll 1 11 00 2 2 00 2 22 2

b

2

3

4

5

6

22θ/° θ /o CuK

α

Fig. 3 SAXRD patterns of SBMMs: (a) the undoped and (b) the P-doped samples. 350 350

—•—Undoped, Undoped, Abs —•—Undoped, Undoped, Des —•— P-doped, P-doped, Abs —o—P-doped, P-doped, Des

300 300 250 250

V (cc/g, STP)

200 ? 200 r> ri>150 150-

! 38.12 38.I2MM!

! -B-Uruopea Undoped

! !

P-doped

I

•

100 J" 10050 50

s j i l l j iiiii 10

0 0.0

!

38.23 o

8

A Dv(d) [cc/A/g]

unit cell parameter than the undoped sample. The unit cell parameters of both the doped and undoped samples were calculated to be about 150.4 A and 160.0 A, respectively, following Bragg Equation. This fact shows that the doping of phosphorous oxides affected the mesostructure of the monoliths. The N2-sorption isotherms for the (circles) doped and (squares) undoped monoliths (Fig. 4) are both of type IV character and exhibited distinct capillary condensation steps at a relative pressure P/Po of 0.4-0.8 and a H2 hysteresis loop, which is typical of sorption for mesoporous solids. Both samples exhibited almost the same narrow pore size distributions between 2-4 nm. Both the SAXRD and N2-sorption results indicated the meostructure of SBMMs is similar to that ot SBA16 with a space group Im3m. An accessible porous structure open to surface sides is very important for proton-condcuting membrane, which is beneficial for its proton transfer. A tipycal AFM image of SBMM (Fig. 5) illustrated the rough surface nature, where mesopore structure was accessible, open to the surface.

110

593

0.2

0.4

M M iiiii

100

-,

•

0.6

i ii

1000 o

MIUH^IIUU.HPI Pore Diameter [A]

0.8

,

1.0

Relative Pressure, Pressure, P/P P/P00 Relative

Fig. 4 N2-sorption isotherms and pore size distribution curves (inset) of the (circles) doped and (squares) undoped monoliths.

These SBMMs were support-free and facile to be coated with Au electrodes on both surface sides for the collection of AC impedance spectrum. Fig. 6 illustrates the typical complex impedance responses (Nyquist plots) of the (•) doped and (o) undoped monoliths at 98 °C under 82% RH conditions. The different shapes of the plots suggest different equivalent circuses for proton conduction in the doped and undoped monoliths. The proton conductivity (o) of the

594 594 -2000

sample is obtained following Doped -1800 Undoped the formula: a = L/(AR), -1600 where A is the area of Au -1400 electrode, L is the distance -1200 between the electrodes, and -1000 R can be detemined from the -800 diameter of the semi-circles -600 Z' (real) / in Fig. 6. The calculated -400 3 conductivities are up to 10" -200 and 10"4 S cm'1 for the doped 0 0 200 200 400 400 600 600 800 800 1000 1000 1200 1200 1400 1400 1600 1600 1800 1800 2000 2000 and undoped monoliths at 98 Z' (real) /Ω (real)/Ω °C under 82% RH conditions, respectively. This indicates that the doping of phosphorous oxides led to a Fig. 6 A.C. impedance responses of the (•) doped and (o) undoped monoliths at 98 °C under 82% RH higher conductivity for the conditions. mesostructured monolith. Moreover, both temperature and RH increase the conductivity of both samples. -200

Z'' (imaginary) / Ω

Z'' (imaginary) / Ω

-150

-100

1 MHz

1 Hz

-50

0

0

50

100

150

200

250

300

Ω

4. Conclusion In summary, we proposed a preparation of 3D cubic SBMMs and investigated into their proton conductivity. The conductivity of the P-doped samples was higher and up to 10"3 S cm"1 under 82% RH, compared to that of the undoped. 5. Acknowledgement This work was supported by the 21st Century COE Program in Nagoya Institute of Technology, Japan and National Fundmental Research Programm of China (Grant No. 2002CB613305). 6. References [1] [2] [3] [4] [5] [6] [7] [8]

K. D. Kreuer, Solid State Ionics, 97 (1997) 1. M. Nogami, R. Nagao and C. Wong, J. Phys. Chem. B, 102 (1998) 5772. M. Yamada, D. Li, I. Honmaand H. Zhou, J. Am. Chem. Soc, 127 (2005) 13092. W. H. J. Hogarth, J. C. D. da Costa, J. Drennan and G. D. Max Lu, J. Mater. Chem., 15 (2005) 754. H. Li and M. Nogami, Adv. Mater., 14 (2002) 912. L. Xiong and M. Nogami, Chem. Lett., 35 (2006) 972. H. Yang, Q. Shi, B. Tian, S. Xie, F. Zhang, Y. Yan, B. Tu and D. Zhao, Chem. Mater., 15 (2003) 536. D. Zhao, P. Yang, N. Melosh, J. Feng, B. F. Chmelka and G. D. Stuky, Adv. Mater., 10 (1998), 1380.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

595 595

Vapor phase preparations of mesoporous silica thin films for ultra-low-A: dielectrics Shunsuke Tanaka,ac* Takanori Maruo,a Norikazu Nishiyama,a Korekazu Ueyarna3 and Hugh W. Hillhouseb "Division of Chemical Engineering, Graduate School of Engineering Science, Osaka University, 1-3 Machikaneyama, Toyonaka, Osaka 560-8531 Japan h School of Chemical Engineering, Purdue University, 480 Stadium Mall Drive, West Lafayette, Indiana 47907 USA 'Current Address; Department of Chemical Engineering, Faculty of Engineering, Kansai University, 3-3-35 Yamate-cho, Suita-shi, Osaka 564-8680

1. Introduction Low dielectric constant (low-&) materials are a central development target in the electronics industry. For example, microchip device densities continue to increase, generating much demand for insulators with a lower dielectric constant. In 45 nm technology node for ultralarge-scale integrated circuits, it is essentially inevitable to attain the film with the dielectric constant of less than 2.0. Introduction of nanoscale pores in the dielectric film is an efficient way to reduce the dielectric constant. Surfacatant-templated ordered mesoporous silicas may be a promising material for low-& films because the film has extremely high porosity, uniform pores, and ordered structure [1-3]. Thin films made of mesoporous silica have conventionally been fabricated using dip or spin coating via evaporation-induced self-assembly (EISA) [2-5]. On the contrary, we have previously synthesized mesoporous silica thin films by the vapor phase preparations [6-8]. In this study, we have characterized the detailed structure (space group, lattice constants, and orientation) and dielectric constant of the films prepared by the vapor phase method using PEO106-PPO70-PEO106 (Pluronic F127). The films were characterized using grazing-angle of incidence small-angle X-ray scattering (GISAXS), high-resolution field emission scanning electron microscope (FESEM), Fourier transform infrared spectroscopy (FTIR), and N2 adsorption/desorption measurements.

596

2. Experimental Section First, the polymer films were prepared on the silicon wafer by spin-coating using a starting solution with a molar ratio of 0.02 Pluronic F127: 100 EtOH: 100 H 2 O. The polymer films were placed in a closed vessel along with a separate, small amount of TEOS and HC1 (5 N). The vessel was then placed in an oven at 90°C for 60 min. Thus, the polymer films were exposed to a saturated TEOS vapor under autogenous pressure. The film was calcined at 400°C in air for 5 h. End-capping of residual silanols was conducted by silylation using trimethylchlorosilane at 150°C for 1 h after calcination. The GISAXS experiments were performed at the Advanced Photon Source at Argonne National Laboratory on the 1-BM-C beamline using synchrotron source. The spot patterns at various angles of incidence were simulated using NANOCELL, a Mathematica-based program [5,9]. FESEM images were recorded on a Hitachi S-5000L microscope. The N 2 adsorption/desorption isotherms of products were measured using a Quantachrome AUTOSORB-1 instrument. The dielectric constant of the films was measured at room temperature with a Solatron SI 1260 impedance analyzer. Platinum electrodes were deposited on the films with the ULVAC QUICK COATER VPS-20. 3. Results and Discussion Complete removal of copolymer by calcination at 400°C was confirmed by the FTIR spectrum of the calcined films. The FTIR spectra for the films prepared by vapor phase method show that the concentration of residual silanol group is lower than that of conventional sol-gel films (data not shown). 3.0

αf (deg.)

2.0 0) "D

^ -

„:

o o0 O o o o o o o o 1.0 1.0 o o o o o 1 oo 1 Q o o QD O O OO j 0 –2.0 -2.0

–1.0 -1.0

:

o

o

O

0 0

o

O

o

l°l II 11 o

{

° O

O O

0 (deg.) 2θf (deg.)

0 0

o

0 0

o o

0

oo o

o

o o o |

1.0 1.0

2.0 2.0

0 0 0 OO oo ao |

Figure 1 GISAXS pattern collected from synchrotron source (<Xi= 0.21°) for the mesoporous silica film with overlays showing simulated spot pattern by NANOCELL.

GISAXS pattern shown in Figure 1 has the large number of well resolved peaks, indicating that the film is highly ordered. Note that the spots not overlaid

597

1000 800 600 400 200 0

0

0.2

0.4 0.6 P/P P/P0

0.8

1

Pore volume (cc/nm/g)

Volume adsorbed (cc/g)

by the white circles can be simulated by NANOCELL. Several spots not overlaid arise from diffraction of the transmitted then reflected incident beam. The GISAXS pattern was described by the rhombohedral space group R-3m oriented with the (111) axis perpendicular to the substrate. The lattice constants for the film were determined to be a = 16.8 nm and a = 70°. The d\u spacing, the periodic distance perpendicular to the substrate, is 12.6 nm. At a relative N2 pressure of 0.7-0.8, a steep increase in the amount of adsorbed N2 with a hysteresis loop corresponds to the filling of ordered mesopores (Figure 2). The pore size distribution was obtained using the BJH model for the desorption isotherm. The BET surface area and pore diameter were 720 m2/g and 7.2 nm, respectively. 1.0 0.8 0.6 0.4 0.2 0 0

10 5 10 Pore diameter (nm) (nm) Pore

15 15

Figure 2 N 2 adsorption/desorption isotherms and a pore size distribution for a calcined film. The measurements were performed with the powdery sample which was peeled from the substrate. (b) (b)

10 9 8 7 6 5 4 3 2 1• i 1 0 1.00E+04 1.00E+04

Dielectric constant

(a) (a)

1

1.00E+05 1.00E+05 Frequency (Hz) (Hz) Frequency

1.00E+06 1.00E+06

Figure 3 FESEM image of the cross-section of mesoporous silica film (Scale bar; 60 nm). The portion of the enclosed with dotted lines is platinum electrode, (a) Dielectric constant (at 10 kHz1 MHz) of MIS (Pt/film/Si) structure fabricated using the mesoporous silica film.

No shrinkage was observed in the pore size after heating at 650°C and immersing in water at 180°C in a closed vessel for 3 h. These results show high thermal and hydrothermal stability. Mechanical strength was investigated by pressurizing the films for 5 min using a pressing apparatus. The ordered structure of the films was maintained even after compression at 3500 kg/cm2. It was found from FESEM observations that the mesoporous silica films have silicate layers with ordered pillars. The dielectric constant was measured using

598

the 150 nm thick film, which has thirteen layers. After the silylation, new bands appeared at 760 and 1260 cm"1 in the FTIR spectra, indicating that the residual silanol groups were replaced with the methylsilyl groups. The upper platinum film was prepared by sputter deposition as electrode (Figure 3a). The electric constant of 1.8 was obtained (Figure 3b). The result suggests that the porosity of the film was approximately 60%. 4. Conclusion The mesoporous silica thin films have two-dimensionally connected cagelike mesopores and are indexed with (111) oriented R-3m structure. The silica layers play a role as passivating films, capping of the mesopores on the film surface. The structure, high thermal and hydrothermal stability, and low dielectric constnat of the films are of advantage for next-generation \ow-k films. 5. Acknowledgement The authors wish to acknowledge use of the NSF funded facility for In-situ X-ray Scattering from Nanomaterials and Catalysts (MRI program award 0321118-CTS) and the use of the Advanced Photon Source supported by the U. 5. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. W-31-109-ENG-38. The authors gratefully acknowledge the assistance of the GHAS laboratory and Mr. M. Kawashimaat Osaka University with the FE-SEM measurements. S. Tanaka acknowledges the Japan Society for the Promotion of Science (JSPS) Research Fellowships. 6. References [1] C. T. Kresge, M. E. Leonowicz, W. J. Roth, J. C. Vartuli and J. S. Beck, Nature, 359 (1992)710. [2] F. Schuth and W. Schmidt, Adv. Mater., 14 (2002) 629. [3] R. C. Hayward, P. C. A. Alberius, E. J. Kramer and B. F. Chmelka, Langmuir, 20 (2004) 5998. [4] C. J. Brinker, Y. F. Lu, A. Sellinger and H. Y. Fan, Adv. Mater., 11 (1999) 579. [5] M. P. Tate, B. W. Eggiman, J. D. Kowalski and H. W. Hillhouse, Langmuir, 21 (2005) 10112. [6] N. Nishiyama, S. Tanaka, Y. Egashira, Y. Oku and K. Ueyama, Chem. Mater., 15 (2003) 1006. [7] S. Tanaka, N. Nishiyama, Y. Egashira, Y. Oku and K. Ueyama, J. Am. Chem. Soc, 126 (2004) 4854. [8] S. Tanaka, N. Nishiyama, Y. Hayashi, Y. Egashira and K. Ueyama, Chem. Lett., 33 (2004) 1408. [9] M. P. Tate, V. N. Urade, J. D. Kowalski, T. -C. Wei, B. D. Hamilton, B. W. Eggiman and H. W. Hillhouse, J. Phys. Chem. B, 110 (2006) 9882.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

599 599

Synthesis of silica nanospheres with well-ordered mesopores assisted by amino acids Toshiyuki Yokoia*, Marie Iwamab, Tatsuya Okubob, Yasuhiro Sakamoto0, Osamu Terasaki0, Yoshihiro Kubotad and Takashi Tatsumf " Chemical Resources Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503 Japan Department of Chemical System Engineering, The University of Tokyo, 7-3-1 Hongo,Bunkyo-ku, Tokyo 113-8656, Japan. c Structural Chemistry, Arrhenius Laboratory, Stockholm University, 10691 Stockholm, Sweden d Division of Materials Science and Chemical Engineering, Graduate School of Engineering, Yokohama National University 79-5 Tokiwadai, Hodogaya-ku, Yokohama 240-8501, Japan.

1. Introduction The realm of nanoparticles has been extended by the emergence of innovative synthetic method, the Stober method, which was reported in 1968 [1]. The need for monodispersed colloidal silica spheres with two or three-dimensionally well-ordered arrangement is thus constantly increasing because high-tech industries provide a tremendous demand for such well-ordered and nano-sized silica spheres [2]. Bio-inspired and biomimetic chemistries have demonstrated the marvelous power for assembling and structure-directing small species into unique materials [3-5]. Recently, unique anionic surfactants derived from diverse amino acids have been applied to the synthesis of mesoporous materials [6]. In particular, the development of an anionic surfactant Af-myristoyl-L-alanine sodium salt enabled us to obtain a chiral mesoporous silica with a twisted hexagonal-rod-like morphology [7]. The use of polypeptide as a template for assembling inorganic materials with a unique structure has also been reported [8, 9]. Here we report a novel and simple liquid-phase method for crystallizing uniform-sized SNS (Silica NanoSpheres) by using tetraethyl orthosilicate (TEOS) and a basic amino acid, L-lysine.

600

2. Experimental Section SNS was synthesized by using tetraethyl orthosilicate (TEOS) as a silica source in the presence of a basic amino acid, L-lysine. In a typical synthesis, Llysine was dissolved in the solution containing deionized water and octane with stirring. After the mixture was stirred for 1 h, TEOS was added to the mixture with stirring (the final molar composition; 1 TEOS: x L-lysine: 1.3 C8H!8: 154.4 H2O; x = 0 - 0.5). The resulting mixture was stirred for 20 h followed by being kept statically at 373 K for 20 h. Finally, the solution was directly evaporated in an oven at 373 K, resulting in the formation of the silica nanospheres. Thus obtained silica was calcined in an oven at 873 K to remove organic components. The silica materials prepared by using L-lysine were designated as n-L-Lys.-SNS. SEM images were taken on a Hitachi S-5200 microscope. The samples were observed without any metal coating. TEM images were taken on a JEM-3010 microscope operating at an accelerating voltage of 300 kV. The XRD were recorded on a M03X-HF22 powder diffractometer equipped with Cu-Ka radiation (40 kV, 40 mA). Nitrogen adsorption-desorption measurements were conducted at 77 K on a Bell Japan Belsorp 28SA sorptionmeter. The pore size distributions were calculated by the DH (Dollimore-Heal) method using the adsorption branch. 3. Results and Discussion High-resolution scanning electron microscopic (HRSEM) images of the 0.02L-Lys.-SNS sample revealed that the micro-sized silica block consisted of uniform-sized nanospheres, and that silica nanospheres with a uniform size of around 12 nm were well ordered (Fig. 1). This HRSEM image also revealed that there was a uniform nanospace between the nanospheres and that its size was estimated to be around 3 nm. Although silica spheres with sizes of 100 - 200 nm have been easily obtained by the Stober method, to the best of our

500 nm

vrf

100 IB nm

Fig. 1 Representative high-resolution scanning electron microscopic (HRSEM) images of the calcined 0.02-L-Lys.-SNS sample.

knowledge, silica nanospheres with a size of the level of 10 nm arranged in a highly regular order is unprecedented. High-resolution transmission electron

601

dVp / dRp

3

V ol ume a ds or be d / cm g

-1

Int e ns i ty / a .u.

microscopic (HRTEM) images of the 0.02-L-Lys.-SNS sample also demonstrated that the spheres of this sample were well ordered. The XRD pattern of the calcined 0.02-L-Lys.-SNS sample is shown in Fig. 2, which shows marked three diffraction peaks in the region of 26 = 0.5 - 2.0 °. These peaks can be indexed as the 111, 220 and 331 reflections based on the cubic closed pack (ccp) structure. When x was 0 or 0.01, no precipitate was formed even after aging at 373 K for 10 h, likely due to the lack of catalysis for the hydrolysis of TEOS followed by condensation of the resultant products. On the other hand, when x was increased up to 0.5, the diffraction peaks became | unresolved, and the position of the first main peak was broadened, and was shifted to higher angle with an increase in x; the dm spacing values at x = 0.02 and 0.5 were found to be 11.9 and 7.7 nm, respectively. The HRSEM image revealed that the 0.5-L-Lys.-SNS s ample 0 1 2 3 4 5 6 was merely aggregates of silica particles without regularity. It is 22theta/deg. theta / deg. concluded that the optimum x to Fig. 2 XRD pattern of the calcined 0.02-Lobtain the mesos tructured Lys.-SNS sample. product is 0.02. The nitrogen adsorptiondesorption isotherms of the 0.02200 L-Lys.-SNS sample after the removal of the organic moieties by calcination exhibit the type IV pattern, indicating the 100 presence of uniform mesopores (Fig. 3); the BET (BrunauerEmmett-Teller) surface area and the average pore size were found 0 5 10 15 20 Pore size / nm to be 228 m 2 g 4 and 3.2 nm, 0 0 0.5 1 respectively. The presence of Relative pressure Relative pressure uniform mesopores is attributed to the crystallization of the wellFig. 3 Nitrogen adsorption-desorption isotherms ordered silica nanospheres. with corresponding pore size distributions of the Combining the data from the calcined 0.02-L-Lys.-SNS sample. CHN elemental analysis and the TG-DTA measurement of the 0.02-L-Lys.-SNS sample before the calcination, the contents of silica and L-lysine were estimated to be 15.02 and 0.33 mmolg"1,

602

respectively; the molar ratio of L-lysine / SiO2 was found to be 0.022, which is consistent with the starting molar gel composition. Since the pKa of a -COOH, a-NH 3 + and a -(CH2)4NH3+ in L-lysine molecule is estimated to be 2.18, 8.90 and 10.28, respectively and the isoelectric point of L-lysine is 9.74, about 92 % of a -(CH2)4NH2 and 33 % of a -NH2 in L-lysine molecule would be protonated under the synthesis conditions (pH 9.2). Therefore, two kinds of interaction comprising the electrostatic one between anionic silicates ( = SiO") and protonated amino groups in L-lysine, and hydrogen-bonding between L-lysine molecules could be operative. They might result in the formation of the wellordered SNS. L-lysine, L-histidine and L-arginine are categorized as basic amino acids. We found that the use of L-arginine led to the formation of similar well-ordered SNS under the same conditions. On the other hand, the use of L-histidine was unsuccessful probably due to the low basicity. Even when the pH of the solution containing L-histidine was increased by means of addition of aqueous NH3 solution, well-ordered SNS was not formed. 4. Conclusion The uniform and nano-sized SNS (silica nanospheres) assisted by basic amino acids, which can work as an inducement to three-dimensional arrangement as well as a catalyst for the formation of silica were successfully synthesized. Thus simple basic amino acids show a talent for assembling silica nanospheres, leading to their crystallization. Our approach for preparing mesostructured materials by means of assembling nanospheres with regularity is not a general liquid-crystal templating method and will stimulate the development of a new family of ordered mesoporous materials. 5. References [1] W. Stober and A. Fink, J. Colloid Interface Sci., 26 (1968) 62. [2] S.-M. Yang, S. G. Jang, D.-G. Choi, S. Kim and H. K.Yu, Small, 2 (2006) 458. [3] Y. Lu, Y.Yang, A.Sellinger, M. Lu, J. Huang, H. Fan, R. Haddad, G. P. Lopez, A. R. Bums, D. Y.Sasaki, J. Shelnutt and C. J. Brinker, Nature, 410 (2001) 913. [4] K. J. C. van Bommel, A. Friggeri and S. Shinkai, Angew. Chem. Int. Ed., 42 (2003) 980. [5] E. Dujardin and S. Mann, Adv. Mater., 14 (2002) 775. [6] S. Che, A. E. Garcia-Bennett, T. Yokoi, K. Sakamoto, H. Kunieda, O. Terasaki and T. Tatsumi, Nature Materials, 2 (2003) 801. [7] S. Che, Z. Liu, T. Ohsuna, K. Sakamoto, O. Terasaki and T. Tatsumi, Nature, 429 (2004) 281. [8] J. N. Cha, G. D.Stucky, D. E. Morse and T. J. Deming, Nature 403 (2000) 289. [9] K. M. Hawkins, S. S.-S. Wang, D. M. Ford and D. F. Shantz, J. Am. Chem. Soc, 126 (2004)9112.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

603 603

Size and morphology control in the synthesis of SBA-15 Huanling Xie ac , Ranbo Yub, Dan Wang0*, Jianxi Yaoc, Xianran Xingb and Wenguo Xua "The Institute for chemical physics, Beijing institute of Technology, Beijing 100081, China Department of physical Chemistry, University of Science & Technology Beijing, Beijing 100083, China c Key Laboratory of Multi-phase Reaction, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100080, P. R. China

1. Introduction It has been about two decades since the discovery of large-pore periodic mesoporous silica [1]. Recent developments have been reported on their versatile applications in catalysis, separation, adsorption and host materials [2]. For the purpose of these applications to industry, the synthesis of mesoporous molecular sieves with controllable morphologies and size is one of the main areas of interest in materials chemistry. And, extensive work was devoted to the morphology and size control mesoporous silicas [3-9]. In this work, we report a size and morphology control technique by using different mixing method and tuning the molar ratios of tetraethyl orthosilicate (TEOS) to the surfactants to form crystal-like sphere- and gyroid- particles of mesoporous silica SBA-15. 2. Experimental Section In a typical experiment, a certain amount of triblock copolymer Pluronic P123 (P123) and potassium chloride (KCl) were dissolved in 2 M hydrochloric acid (HC1) aqueous solution, and then TEOS was added to this solution under ultrasonic irradiation or magnetic stirring. The final molar raio of TEOS: PI23: KCl: HC1: H2O was 1: 0.0052-0.0172: 1.48: 6.6: 170. Eight minutes later, this mixture was sealed in Teflon-lined stainless steel autoclaves, and kept under

604

static conditions at 30°C for 24 h, followed by heating at 100°C for 24 h. The synthetic conditions for the typical samples are shown in Table 1. The solid products were collected by filtration, washed with water and dried. The assynthesized SBA-15 samples were calcined in air at 550°C for 6 h to remove the surfactant. SEM images were achieved by JEOL JSM-35CF. HRTEM images were recorded on a JEOL JEM-2010. Small-angle X-ray powder diffraction were taken on an X' Pert PRO diffractometer (PANalytical, Netherlands). N2 adsorption-desorption isotherms were measured with a QUANTACHROM analyzer (Autosorb-1, USA) Table 1 . Different synthetic conditions and physical properties for materials c i

nno

Spl v

PI23

1 2 3 4 5 6 7

0.0052 0.0086 0.0121 0.0172 0.0086 0.0121 0.0172

Mixing

iU j method ultrasonic ultrasonic ultrasonic ultrasonic stirring stirring stirring

TEOS

mi_.

/PI 23 192 116 83 58 116 83 58

dioo

, \ (nm) 8.81 9.32 9.39 9.68 8.79 8.93 9.16

»,,

. i

Morphology v bJ Irregular particles Sphere (d = 5um) Sphere (d = 7 urn) Larger gyroid Sphere (d = 4um) Smaller gyroid Gyroid-like

3. Results and Discussion The reactant molar ratio of TEOS/P123 plays an important role in the morphology and size of the as-synthesized samples. In the SEM image of sample 1 (not shown here), a lot of particles with a kind of irregular shape and few spherical particles could be observed. Decreasing the molar ratio to 116 and 83 (sample 2, 3), large and uniform spheres with the mean size about 5 urn and 7um, respectively, could be clearly observed in the SEM images of (Fig. 1.(1) and (2)). SEM images of the sample 4 prepared with the TEOS/P123 molar ratio of 58 is shown in Fig. 1. (3). As can be seen, Gyroid particles with about lOum were obtained. To investigate the effect of mixing method on the morphology of the samples, the magnetic stirring was used to mix precursor solution. The SEM images of sample 5 prepared at the same TEOS/P123 molar ratio as sample 2 showed that the magnetic stirring resulted in the formation of sphere with the samller mean size of 4 um (Fig. 1. (4)). With the decrease of the TEOS/P123 molar ratio to 83 and 58, the gyroid particles with much smaller mean size and wider size distribution, respectively, could be obtained (Fig. 1 (5) and (6)). The SEM results indicated that the morphology and the size of the assynthesized sample could be easily controlled by means of the synergetic effects of the reactant molar ratio of TEOS/P123 and the mixing method for the

605

precursor solution. The HRTEM image of the typical samples displays a wellordered 2D mesostructure (not shown here).

Figure 1. SEM images of (1) sample 2, (2) sample 3, (3) sample 4 synthesized by ultrasonic irradiation; (4) sample 5, (5) sample 6, (6) sample 7 prepared under magnetic stirring.

sample 5 and 6, which display

200000

150000

Relatively Intensity (a.u.)

Fig. 2 shows the small-angle XRD patterns of the samples calcined at 55O°C for 6h. The three obvious peaks in the XRD patterns could be indexed as (100), (110), and (200) reflection. The values of d spacing between the (100) planes of the arrays were summarized in table 1. It could be seen that the dioo value slightly increases with the decrease of the TEOS/P123 molar ratios. On the condition of using the same TEOS/P123 molar ratio, the samples prepared under ultrasonic irradiation showed larger d1Oo value compared with that of the samples prepared under magnetic stirring. Apart from

J

\

X

^,

100000 100 110

0

(6)

×5 x5

(5) (5)

×5

(4)

300 ×4 ×4

(3) (3)

×5

(2) (2)

×5

(1) (1)

\

T

~2-

×5

A

200

-

V__

2210 10

50000

0

rr

0

1

2

2

2 2 θθ (( °°) )

3

4

Figure 2. Small-angle X-ray diffraction of (1) sample 2, (2) sample 3, (3) sample 4, (4) sample 5, (5) sample 6, (6) sample 7.

5

606

broad and weak (110) and (200) peaks, sample 2 and 3 exhibit higher (110) and (200) peaks. XRD pattern of sample 4 showed well-resolved (210) and (300) peaks, whereas, such reflections were not seen on the sample 7. It indicated that materials prepared by ultrasonic irradiation have relatively good mesostructure ordering. The nitrogen adsorption-desorption isotherms of the materials basically show type IV in IUPAC nomenclature. From BJH pore size distribution, it can be seen that the pore size increased with the decrease of TEOS/P123, in accord with XRD patterns results. 4. Conclusion Sphere and gyroid of SBA-15 mesoporous silicas with different size were successfully synthesized under hydrothermal condition. The result showed that the mixing method for the precursor solution and the reactant molar ratios of TEOS/P123 have great effects on the morphology and size of the mesoporous silicas SBA-15. The morphology and size control in the synthesis of SBA-15 introduces more flexibility and diversity into the designed synthesis of shaped mesoporous silicas. Such morphological SBA-15 mesoprous silicas are promising for applications in industry. 5. Acknowledgment This work was partially supported by National Natural Science Foundation of China (NSFC) (No. 20401015, 50574082), Foundation of University of Science & Technology Beijing (Grant No.: 2004214890 and 20050214890) and CNPC Innovation Foundation (No. 04E7018). 6. References [1] D. Zhao, J. Feng, Q. Huo, N. Melosh, G. H. Fredrickson, B. F. Chmelka and G. D. Stucky, Science, 279 (1998) 548. [2] H. Song, R. M. Rioux, J. D. Hoefelmeyer, R. Komor, K. Niesz, M. Grass, P. Yang and G.A. Somorjai, J. Am. Chem. Soc, 128 (2006) 3027. [3] J. Fan, J. Lei, L. Wang, C. Yu, B. Tu and D. Zhao, Chem. Commun., (2003) 2140. [4] D. Zhao, J. Sun, Q. Li and G. D. Stucky, Chem. Mater., 12 (2000) 275. [5] K. Kosuge, T. Sato, N. Kikukawa and M. Takemori, Chem. Mater., 16 (2004) 899. [6] Sayari, B. Han, Y. Yang and J. Am. Chem. Soc, 126 (2004) 14348. [7] Z. Yu, J. Fan, B. Z. Tian and D. Y. Zhao, Chem. Mater., 16 (2004) 889. [8] S. K. Lee, J. Lee, J. Joo, T. Hyeon, W. S. Ahn, H. I. Lee, C. H. Lee and W. Choi, J. Ind. Eng. Chem., 9 (2003) 83. [9] X. Y. Bao and X. S. Zhao, J. Phys. Chem. B, 109 (2005) 10727.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

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Synthesis and characterization of mesostructured silica sphere particles with core space Jung-Sik Choi3, Kyung-Ku Kangb and Wha-Seung Ann3* "Department of Chemical Engineering, Inha University, Incheon, 402-751, Korea Research Institute of Chemicals and Electronic Materials, Cheil Industries, INC. Gyeonggi-do, 437-711, Korea

Spherical mesostructured silica particles with inner core space were prepared under acidic condition using TEOS and a block copolymer template in an aqueous/butanol emulsion system. Mesoporous silica particles obtained were highly uniform in 125 um - 1 mm size range with core space in 100 - 170 um depending on the synthesis condition. The sphere diameter was directly proportional to the concentrations of TEOS and butanol. Butanol plays an important role of making the silica particles hollow and spherical as well as being involved in mesopore formation; an increase in butanol concentration produced mesoporous silica with larger pore diameter. 1. Introduction The preparation of mesoporous silica materials has evolved to a new stage in which the hierarchical structures having at least two length scales of micro- and nanometer can be achieved [1]. The controlling of structures in both length scales has important impacts on design of nanomaterials and their potential applications such as catalyst/supports, drug release, micro reactor, separation, and chromatography packing materials. Making spherical silica particles with mesopore structure by chemical and hydrodynamic approach has advantages on cost and performance. In this work, spherical mesoporous silica particles with core space were prepared by promoting condensation of silica/surfactant assembly around an organic phase in an aqueous/butanol emulsion system. Synthesis process is very simple and uses cheaper reagents than the previous report by Stucky's group on a similar material [2].

608

2. Expermental Section TEOS was used as silica source and 1-butanol with Pluronic 123 dissolved in water was used to form an O/W emulsion. In a typical synthesis, surfactant solution was prepared by adding P123 to 2 M HCl solution and stirred at room temperature. Independently, TEOS was added in 1-butanol with stirring and this solution was added to the surfactant solution. The substrate mixture was then stirred for 24 h at 35°C. Particles obtained were recovered by filtration, washed, and dried. Finally, the product was carefully calcined in air at 550°C. The morphology of the samples was examined by SEM (Hitachi S-4300) and TEM (Philips, CM 200). The specific surface area and average pore diameters were determined by N2 physisorption using a Micromeretics ASAP 2000 automatic analyzer. 3. Results and Dicussion In this work, spherical mesoporous silica particles were synthesized by solgel method under acidic condition with controlled morphology, using butanol as the organic phase in O/W emulsion. Scheme 1 represents the formation process of the sphere particles as suggested by Schacht et al. [1]. In our synthesis, TEOS mixed with butanol was added to acidic surfactant solution with stirring.

Direction of silica growth

r c?s> v

Surfactant as emulsion

stabilizer

Organic phase (Emulsion)

>{

Surfactant as rjoi^ej) template with random orientation

Aqueous phase Scheme 1. Proposed growth mechanism of spherical mesoporous silica [1].

Surfactant plays an important role both as emulsion stabilizer and as micelle template. TEOS also contributes to the stabilization of this emulsion phase after partial hydrolysis. TEOS is eventually fully hydrolyzed under acidic conditions at the organic/water interface and forms the mesostructure under the influence of the surfactant.

609

1^ (a)

y^

Macro pore

(b)

V

100 µm 100

1 mm

µmy

Core Core space space Fig. 1. SEM micrographs of the spherical mesoporous silica and the particle cross section.

Amount of adsorption (cc/g, STP)

SEM image (Fig. la) shows uniform spherical particles with ca. 500 urn in diameter. It was also possible to prepare particles up to 1 mm by controlling the synthesis condition. Fig. lb is a cross section image of a spherical mesoporous silica particle with ca. 200 um in diameter, which are made of 3 different types of pores: core space with 100-170 urn, macro pores with 1-5 um and mesopores as measured by nitrogen adsorption-desorption isotherm. Spherical particle size and core space could be controlled by changes in stirring rate and concentrations of TEOS and butanol. Increasingly large particles were obtained as the stirring speed decreased from 1200 to 300 rpm. At a fixed amount of butanol, increases of TEOS amount led to increases in particle size and also increased the particle thickness. TEOS concentration did not sensitively govern the particle size as butanol concentration. At a fixed amount of TEOS, increases of butanol/TEOS molar ratio led to particle size increase from 125 urn to 1 mm. Increase of butanol concentration was 800 related not to only particle size but also to mesostructure formation. Pore 600 diameter was increased from 3.2 to 4.9 nm with increasing concentration of butanol. 400 Pore diameter As shown in Fig. 2, nitrogen adsorption-desorption isotherm of 200 type IV for mesopore structure and hysteresis loop of type H2 was 0 0.0 0.2 0.4 0.6 0.8 1.0 observed, which is known due to the Relative Pressure (P/Po) presence of pores with narrow mouths (cage-like pores). The isotherm Fig. 2. Nitrogen adsorption-desorption isotherm inflection point for the spherical plot and BJH desorption pore size distribution mesoporous silica particles was (inset) of spherical mesopore silica. 10

100

1000

610

located at relatively high P/Po between 0.6 and 0.7, which indicates larger pore diameter than other mesoporous materials such as MCM-41 and HMS. BET surface area was ca. 890 m /g, single point total pore volume at relative pressure of 0.98 was 0.96 cm3/g, and the BJH desorption pore diameter was 4.9 nm. Fig. 3 shows the TEM micrograph of the spherical silica material prepared. Disordered pore structure but with uniform diameters similar to the disordered mesoporous silica materials obtained using nonionic surfactant or in the presence of organic salt [3,4] was observed. Ordered pore structures are seldom found in the case of spherical particles for which an oil phase is employed to control the morphology. It seems that its mesostructure was disordered because of the presence of butanol in the synthesis mixture. Increasing amount of butanol added to the synthesis batch for SBA-15 in acidic condition led to transition from 20 nm 2D hexagonal to the cubic Ia3d mesophase and finally to the disordered phase through the smaller Fig. 3. TEM micrograph of the spherical domains of intermediate mixed phase mesoporous silica. [5]. 4. Conclusion Spherical mesostructured silica particles with core space were synthesized under acidic condition in an aqueous/butanol emulsion system. Concentration of TEOS or butanol was directly proportional to the sphere diameter in such a manner that high concentration of both TEOS and butanol resulted in particle size increases. Butanol, however, was the more critical variable controlling the particle size and also found to affect the pore diameter of the silica obtained. 5. References [1] S. Schacht, Q. Huo, I. G. Voigt-Martin, G. D. Stucky and F. Schuth, Science, 273 (1996) 768. [2] Q. Huo, J. Feng, F. Schuth and G. D. Stucky, Chem. Mater., 9 (1997) 14. [3] P. Tanev and T. Pinnavia, Science, 269 (1995) 1242. [4] R. Ryoo, J. Kim, C. Ko and C. Shin, J. Phys. Chem., 100 (1996) 17718. [5] T. Kim, F. Kleitz, B. Paul and R. Ryoo, J. Am. Chem. Soc, 127 (2005) 7601.

Recent Progress in Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Published by Elsevier B.V.

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Synthesis of highly ordered large pore mesoporous silica SBA-16 spheres Hongxiao Jina, Qingyin Wua*, Chao Chenb, Daliang Zhang1 and Wenqin Pangab* "Department of Chemistry, Zhejiang University, Hangzhou 310027, P. R. China h State Key Lab of Inorganic Synthesis and Preparative Chemistry, Jilin University, Changchun 130023, P. R. China

1. Introduction It is well-known that the morphology of mesoporous materials plays one of the key roles for their advanced applications [1]. This is because that the applications of these materials depend on not only the intra-particle structures but also the inter-particles mass transport process. Mesoporous materials with spherical morphology have attracted considerable attention due to the potential applications in macromolecular separation, drug deliveries, catalysis supports and template agents for photonic crystals [2]. Sine e the first report of the synthesis of mesoporous silica spheres through a modification of Stober's procedure [3], several synthetic methods, including solution self-assemble aero sol spraying [4, 5], hard template and evaporation-induced self-assemble process were developed [6, 7]. Compared with other process, the solution selfassemble route was relatively technologically simple. The diameter of these products is less than Ca. 10 um excluding a few examples. Recently, Kosuge K. and co-workers reported the forming of porous silica spheres over 100 um in diameter using triblock copolymer as template. But the quality of the intraparticle mesostructure is still limited. Herein, we present a facile synthesis of highly ordered SBA-16 spheres with diameter of 2~6 um in a ternary F127H2O-HC1-TEOS system.

612

2. Experimental Section 2.1. Synthesis of Materials The preparation procedure was as follow: triblock copolymer Pluronic F127 was added to HC1 aqueous solution and allowed to stir at a certain temperature overnight. Then, TEOS was added to this solution under vigorous stirring. After 10 min stirring, the mixture was kept under static conditions at aforementioned temperature for 3 ~ 72 h. The solid products were collected by filtration, washed with ethanol, dried, and calcined at 550°C in air for 5 h. The preparation of SBA-16 single crystals relies on the control of the reaction temperature and the reactants ratio. 2.2. Characterization of Materials XRD patterns were recorded on a SIEMENS D8 ADVANCE powder diffraction system using Cu Ka (1=1.5418 A) radiation (40 kV and 40 mA). The Scanning electron micrographs (SEM) were taken on FEI SIRJON electron microscope with an acceleration voltage of 5 KV. The samples were deposited on a sample holder with an adhesive carbon foil and sputtered with gold prior to imaging. Transmission electron microscopy (TEM) measurements were taken on a JEM-3010 electron microscope (JEOL Japan) with an acceleration voltage of 300 KV. The nitrogen sorption experiments were performed at -196 °C on Micromeritics ASAP 2010M systems. The samples were outgassed at 300 °C for 10 h before the measurement. The pore diameter was calculated from the analysis of desorption branch of the isotherm by the BJH (Barrett-JoynerHalenda) method. 3. Results and Discussion As revealed by field emission scanning electron microscopy (FE-SEM), mesoporous silica SBA-16 of decaoctaheron shape consists of a large quantity of cubic structure with typical diameter of 2~6 micrometers (part a and b in Figure 1). The evidences for the mesostructure are provided by a combination of TEM, XRD and N2 adsorption/desorption measurement. Part c in figure 1 show TEM image taken along 100 incidence, which reveals a lattice constant of ao = 10 nra. Low-angle X-ray diffraction (XRD) measurements (part d in Figure 1) show that the calcined powder exhibits 3 diffraction peaks in the region of 20 = 0.9 -1.8 degree, which are indexed to the 110, 200 and 211 diffractions of cubic symetery with a lattice constant of ao = 11 nm [8]. The lattice value is in accordance with the TEM result. The corresponding nitrogen adsorption/ desorption measurement give type-IV isotherms with a H2 hysteresis loop (part e in figure 1), which suggests that the mesopores are cage like. The average

613

pore diameter was calculated to be 7.2 nm from the adsorption branch of the isotherm by using the Barrett-Joyner-Halenda (BJH) method. The results give a pore volume of 0.5 crnVg, a BET surface area of 700 m2/g. Recently, a time-resolved in-situ study of the formation of SBA-16 suggests that globular micelles in a silica matrix involves in early stage, which directly transforms into cubic structure in final. Moreover, to visualize the selforganization of spherical micelles, a "colloidal phase separation" mechanism was proposed [9]. Thus, the formation of mesoporous spheres could be considered as meso-scaled self-organization of spherical micelles and inorganic species into micrometer structured domains. To maintain the high curvature spherical building block, various parameters which can greatly influence the final mesostructure and morphology of the products, such as reaction temperature the surfactant/silica ratio, and anions present in the reaction, should be carefully controlled.

Fig. 1 Calcined SBA-16 spheres: (a), (b) FE-SEM image; (c) TEM image taken along 100 incidence; (d) XRD pattern; (e) N2 adsorption/ desorption isotherm.

Various synthesis conditions were investigated as shown in Figure 2. Part a, b and c show the effect of HCl concentration under the synthetic condition: 1.00

614

TEOS: 0.049 F127: X HC1: 182.4 H2O at 30°C, where X=1.6, 4.8 and 8.0. Part d, e and f show the effect of the surfactant ratio under the synthetic condition: 1.00 TEOS: Y F127: 4.8 HC1: 182.4 H2O at 30°C, where Y=0.016, 0.033 and 0.057. Part g, h and i in show the effect of the reaction temperature under the synthetic condition: 1.00 TEOS: 0.049 F127: 4.8 HC1: 182.4 H2O at 24, 28 and 34 °C, respectively. The results showed that a middle surfactant concentration (TEOS/F 127=0.016-0.057), strong acidic conditions (1.0-2.5M HC1) and a moderate reaction temperature (24~32°C) were necessary for the syntheses. Moreover, lower surfactant concentration leads to amorphous porous powder with poor structure order; higher concentration would not promote the surfactant/silicates condensation. Stronger acidity or higher temperature would promote a rapid, uncontrolled hydrolysis/condensation of silica species which would not lead to the formation of spheres. Weaker acidity with an HC1 concentration less than 1.2 M would lead to the formation of other mesoporous structure, and lower reaction temperature would result in materials with amor-

Fig. 2 SEM micrographs of samples synthesized under various conditions of which more details are presented in text: HC1 = a) 0.5 M, b) 1.5 M and c) 2.5 M; TEOS/F127 molecular ratio = d) 0.016, e) 0.033, f) 0.057; reaction temperature = g) 24 °C, h) 28 °C, i) 34 °C. Scale bar: 5 j i m .

phous morphology and poorly ordered mesostructures. It should also be noted that mesoporous SBA-16 single crystals (part h) could be obtained by a more carefully control of the synthetic condition. It was reported that the addition of co-surfactant, cosolvents and inorganic salts are beneficial to the synthesis of mesoporous silica spheres. In that case PI23 was used as template; however, F127 was used in our case. The difference

615

of the solution behavior between PI23 and F127 cause the result spheres different in both morphology and intrinsic mesostructure: ~luxn VS 2~6 urn in size, hexagonal VS cubic in structure. Moreover, Kosuge K. and co-workers reported the forming of porous silica spheres which over 100 um in diameters and less order in structure using various triblock copolymers as template and sodium silicate solution as silica source. In this study, TEOS was used as silica source under similar other synthetic conditions. 4. Conclusion Highly ordered large pore mesoporous silica SBA-16 spheres with 2-6 \im in diameter were synthesized in a ternary F127-H2O-HC1-TEOS system. The effect of various synthetic conditions such as HC1 concentration, TEOS/surfactant ratio, silica and template source, and reaction temperature were investigated. The results show that the TEOS which results in more dispersed silicate under hydrolysis in acid solution favors the formation of highly ordered small mesoporous spheres, while sodium silicate which possesses poly condensed silicate drives larger spheres with less structural order. 5. Acknowledgement The financial support of the State Basic Research Project of China (G200077507), the National Natural Science Foundation of China (Grant No. 20233030, 20271045), and the State Key Laboratory of Inorganic Synthesis and Preparative Chemistry of Jilin University for this work is greatly appreciated. 6. References [1] [2] [3] [4] [5] [6]

L. Li, Q. Y. Wu, Y. H. Guo and C. W. Hu, Microporous Mesoporous Mater., 87 (2005) 1. A. Stein, Adv. Mater., 15 (2003) 763. M. Grttn, I. Lauer and K. K. Unger, Adv. Mater., 9 (1997)254. K. Kosuge, N. Kikukawaand M. Takemori, Chem. Mater., 6 (2004) 4181. Y. Lu, H. Fan, A. Stump, T. L.Ward, T. Rieker and C. J. Brinker, Nature, 398 (1999) 223. M. L. Breen, A. D. Dinsmore, R. H. Pink and S. B. Qadri, B. R. Ranta, Langmuir, 17 (2001) 90. [7] C. J. Brinker, Y. Lu, A. Sellinger and H. Fan, Adv. Mater., 11 (1999) 579. [8] D. Zhao, Q. Huo, J. Feng, B. F. Chmelka and G. D. Stucky, J. Am. Chem. Soc.,120 (1998) 6024. [9] C. Yu, B. Tian, J. Fan and D. Zhao, Chem. Mater., 16 (2004) 880.

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Progress in in Mesostructured Materials Recent Progress S. Qiu, Y. Tang and C. Yu (Editors) (Editors) D. Zhao, S. © 2007 2007 Elsevier Elsevier B.V. B.V. All All rights rights reserved. reserved.

617 617

Effects of the different amount of phosphoric acid on the resulting morphology of SBA-15 Yun Li ab , Jihong Sun a \ Fu Ma ab and Shijie Luoa "Department of Chemistry and Chemical Engineering, College of Environmental & Energy Engineering, Beijing University of Technology, Beijing, 100022, P. R. China Key Laboratory of Energy and Chemical Engineering, NingXia University, Yinchuan, 750021, P. R. China

1. Introduction For the synthesis of the SBA-15 with controllable morphology, most approaches were based on changes in synthesis conditions including the silica source [2], the nature of surfactants, co-surfactants and co-solvent [3], additive of organic substances, inorganic salts [4], acids and bases as well as the overall composition of the synthesis mixture. While, SBA-15 film can be grown at solid-liquid and liquid-vapor interfaces through an interface silica-surfactant self-assembly process [5]. All of these films were formed by using acidic condition, and low molecular weight surfactants. Up to now, only few contributions have been published on the synthesis of large mesoporous silica free standing film by using non-ionic triblock copolymer as template at the interface of air/water [1]. A simple method is reported to synthesize SBA-15 with controlled distinct morphologies. Well ordered transparent mesoporous silica freestanding film and cake-like structure were produced by using nonionic surfactant (PI23) in the presence of phosphoric acid under static conditions. In this experiment, in order to further our understanding of the fundamental mechanism by using the mild phosphoric acid replacing the commonly strong hydrochloric acid, we also investigated in detail the influence of adding different amount of phosphoric acid on the resulting morphology of SBA-15.

618

2. Experimental Section SBA-15 samples were prepared by using triblock copolymer P]23 (EO20PO70EO20, MW 5800, Aldrich) as template, tetraethyl orthosilicate (TEOS) as silica source and phosphoric acid (H3PO4, 85%) as acid source through hydrothermal synthesis. The synthesis approach is based on the hydrothermal route reported by Coppens and co-workers [1]. X-ray diffraction (XRD) of the samples was recorded using a Brucker-AXS D8 Advance X-ray diffractometer using Cu K a radiation (X Ka : =0.154056nm). Scanning electron microscopy (SEM) images were obtained with a JEOL JSM6500 microscope. Transmission electron microscope (TEM) images were recorded on a JEOL JME-2010. Nitrogen adsorption-desorption isotherms were measured using a Micromeritics ASAP 2010 system, and pore size distributions were obtained from the N2 desorption branch isotherm using BJH method. 3. Results and Discussion (100)

(100) (100)

(110)

a

b

(110) (200)

0

2

4

6

2θ/°

8

10

0

2

4

6

2θ/°

8

10

Fig. 1 The typical XRD patterns of calcined solid product (a) and film (b) of SBA-15

It can be seen that the pattern of the solid product in Figure la shows a series of well-defined reflections, which could be assigned to the (100), (110), and (200) planes of SBA-15, demonstrating a long-range ordered 2-D hexagonal space group (P6mm), similar to traditional hexagonal phase SBA-15 [1, 11]. While the pattern of film in Figure lb, shows only two low-angle peaks assigned to (100) and (110) reflections of the hexagonal symmetry. Very interestingly, we also found that, for the SBA-15 film, the intensity of (100) peak of XRD pattern in Figure lb is less than that of (110) peak. The SBA-15 particles are randomly oriented, while the pores in the film run parallel to the surface [1]. It should also be mentioned that these findings are in agreement with [1]. Compared with that of the random hexagonal SBA-15 particle, both the weak intensity of the (100) reflection and strong intensity of

619

(110) peak for the film imply that the effects of phosphoric acid on the processing of between inorganic species and surfactant in the solution play an important rule in limiting the growth of film along with (100) dimensional arrays. TEM for film SBA-15 (Figure 2a) shows the parallel one-dimensional nanochannels of uniform diameter around 6nm running along the long axis (110) of the bundles, in good agreement with that as observed with XRD patterns in Figure lb.

a

b

20nm Fig. 2 TEM (a) and SEM (b) images of SBA-15 film

SEM image of the calcined SBA-15 film shows that the film is continuous and composed of the randomly aggregated uniform particles. Whereas, enlarged image for film SBA-15 (Figure 2b) reveals that each individual is composed of a well-defined nanopatricle with a uniform diameter around lOOnm. 14

1000

f e

800

d

600

12 12

dv / dlog (D) (cm3 / g)

Volume Adsorbed (cm3 / g STP)

1200

-»

c b a

400

o

8

f\

6fi

il

1 jk *^ Ax

A

>

0 0. 4 0.4

d c

4

| \

2

b

^ ^ ^ * ^ v^

0 0. 2 0.2

ee

^y\^v

O>

200 0 0

^f

M—

10 10

0. 6 0.6

0. 8 0.8

Relative 0) Relative Pressure Pressure (P/P (P/P0)

1

1

aa

10

B 100

Pore Diameter Diameter (nm) (nm) Pore

Fig. 3 Nitrogen adsorption-desorption isotherms (A) and corresponding to the pore size distribution plots (B) for solid SBA-15 prepared using different amount of phosphoric acid. The molar composition of H3PO4/TEOS in the starting reactant solution was (a) 0.5, (b) 1, (c) 2, (d) 4, (e) 6, (f) 8

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Meantime, we investigated in detail the influence of adding different amount of phosphoric acid on the resulting texture properties of solid product. Figure 3 shows the nitrogen adsorption/desorption isotherms and corresponding to the pore size distribution plots for series of SB A-15 solid prepared with increasing the amount of phosphoric acid in the starting reactant solution. All of the isotherms for the different calcined SBA-15 solid (Figure 3a) show the typical type IV isotherm with HI type hysteresis loop, indicative of an ordered, welldefined mesoporosity. The position of the inflection point is relative to pore size, and the sharpness of these steps indicates the uniformity of the pore size distribution. The shift of the capillary condensation step to lower relative pressures with increasing the amount of phosphoric acid (n (H3PO4) /n (TEOS> =0.5-8.0 suggests a decrease in the pore size, which was changed from around 3.5nm to 6.5nm in Figure 3b. The other factors such as reaction temperature, aging time and inorganic salt are under way recently. 4. Conclusion In the XRD pattern of SBA-15 film, the intensity of (100) peak is lower than that of (110) peak indicates that the effect of phosphoric acid on limiting the growth of film along with (100) dimensional arrays during the period processing of between silicate species and surfactant PI23. SEM image of the SBA-15 film shows that the film is continuous and composed of a well-defined nanopatricle with a uniform diameter (100 nm). The mean pore size of SBA-15 solid was decreased from around 3.5 ~ 6.5nm with increasing the molar ration of n (H3PO4) /n (TEOS) from 0.5 to 8.0. 5. Acknowledgement This work was supported by the Doctoral Science Fundation of BJUT and the Natural Science Fundation of Ningxia Hui Autonomous Region (ZD02). 6. References [1] [2] [3] [4] [5]

R. Pitchumani, W. J. Li and M. O. Coppens, Catalysis Today, 105 (2005) 618. K. Kosuge, T. Sato, N. Kikukawa and M. Takemori, Chem. Mater., 16 (2004) 899. D. Y. Zhao, J. Y. Sun, Q. Z. Li and G. D. Stucky, Chem. Mater., 12 (2000) 275. D. Y. Zhao, P. D. Yang, B. F. Chmelka and G. D. Stucky, Chem. Mater., 11 (1999) 1174. I. A. Aksay, M. Trau, I. Honma, N. Yao, L. Zhou, P. Fenter, P.M. Eisenberger and S. M. Gruner, Science, 273 (1996) 892.

Mesostructured Materials Recent Progress in Mesostructured D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

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Morphology control of SBA-15 in chiral organic acid media Shengrong Ye, Yueming Liu, Mingyuan He and Peng Wu* Shanghai Key Laboratory of Green Chemistry and Chemical Processes, Department of Chemistry, East China Normal University, North Zhongshan Rd. 3663, Shanghai 200062, P. R. China

SBA-15 siliceous materials have been synthesized in chiral organic acid media, and their physicochemical properties have been characterized by various techniques. The resultant materials exhibited distinctive macroscopic morphologies and textural properties different to conventional SBA-15. By changing the aging temperature, a range of mesoporous silica with independently tailored mesopores were obtained. 1. Introduction SBA-15 is a mesoporous SiO2 with a hexagonal arrangement of channels with diameters in the range of 6-30 nm, templated by nonionic triblock copolymers EOnPOmEOn via a hydrogen bonding [S H+][X"I+] assembly pathway [1, 2]. Because of its promising applications to catalyst supports, hostguest assembling materials and adsorbents etc., it is important to control its morphologies. Mesoporous materials in the form of sphere, fibber, doughnut, rope, egg-sausage, and gyroid have been obtained by controlling the synthesis conditions and varying the nature of surfactants [3]. In the present work, we report a simple approach to selectively synthesize unique morphologies of SBA-15 with highly ordered large mesopore hexagonal structures in the media of chiral organic acids of tartaric acids, D-(-)-TA and L-(+)-TA. 2. Experimental Section The SBA-15* materials have been synthesized by modifying the methods described in the literature [1] from typical synthesis batches with the gel composition of Pluronic PI 23 or Pluronic F68, aqueous solution of tartaric acid,

622

and tetraethyl orthosilicate (TEOS) (Table 1). XRD, SEM, TEM, and N2 adsorption were used to characterize these materials. 3. Results and Discussion SBA-15* materials are very well-defined and characteristic of ordered hexagonal materials (Fig. 1). After calcination, a 2 % contraction is observed for samples synthesized at 120 °C, giving cell parameters around 12.0 nm (Table 1, No. 1-4). For samples synthesized at temperatures between 35 and 90 °C, the cell parameter of calcined samples are in ranges from 10.1 to 12.2 nm, revealing a much heavier contraction (10-12 %) (Table 1, No. 9-20). In the case of the samples synthesized at 0 °C, the calcination caused a less contraction (4 %) and the solids retained their cell-unit sizes (ca. 12.0nm) (Table 1, No. 22-24). Table 1 Preparation Conditions and Physicochemical Properties of Calcined SBA-15* b V e Template/Acid/Aging Unit Cell3 n td SBET vtc mi 2 Temperature (nm) (nm) (m /g) (crnVg) (nm) 1 P123/D-(-)-TA/120°C 0.9 0.06 12.2(12.4) 11.3 673 1.6 2 P123/L-(+)-TA/120°C 12.2(12.3) 11.3 2.0 0.9 0.06 731 3 F68/D-(-)-TA/120°C 12.1(12.4) 11.3 614 1.6 0.8 0.05 4 F68/L-(+)-TA/120°C 754 1.8 0.5 0.04 11.8(12.0) 11.3 P123/D-(-)-TA/100°C 5 11.7(12.7) 10.2 892 1.6 1.5 0.09 P123/L-(+)-TA/100°C 11.6(12.6) 10.0 1.6 0.07 706 1.3 6 F68/D-(-)-TA/100°C 11.6(12.6) 9.9 818 1.6 1.7 0.07 7 F68/L-(+)-TA/100°C 9.9 869 .6 1.5 0.07 11.4(12.6) 8 9 P123/D-(-)-TA/90°C 1125 .8 2.1 0.13 12.1(12.7) 10.0 10 P123/L-(+)-TA/90°C 0.14 12.2(12.9) 9.9 1089 .8 2.3 11 F68/D-(-)-TA/90°C .6 1.9 0.11 11.9(12.6) 10.0 1007 12 F68/L-(+)-TA/90°C 0.12 11.9(12.5) 9.9 929 .6 2.0 13 P123/D-(-)-TA/60°C 0.14 10.1(11.7) 6.1 711 0.8 4.0 14 P123/L-(+)-TA/60°C 4.2 10.2(11.6) 6.0 796 0.9 0.15 F68/D-(-)-TA/60°C 0.22 15 10.6(11.2) 6.1 1210 1.5 4.5 16 F68/L-(+)-TA/60°C 780 1.1 3.8 0.16 10.5(11.6) 6.7 17 P123/D-(-)-TA/35°C 1.2 3.9 0.14 10.6(12.0) 6.7 895 18 P123/L-(+)-TA/35°C 4.0 0.13 10.7(12.1) 6.7 789 1.1 19 F68/D-(-)-TA/35°C 10.2(12.0) 6.2 601 0.8 4.0 0.15 20 F68/L-(+)-TA/35°C 10.8(12.2) 696 1.0 3.5 0.13 7.3 21 P123/D-(-)-TA/0°C 10.2(12.2) 0.8 3.5 0.11 6.7 690 22 P123/L-(+)-TA/0°C 0.16 12.0(12.3) 8.1 920 1.1 3.9 0.14 23 F68/D-(-)-TA/0°C 783 1.0 4.0 12.0(12.5) 8.0 24 F68/L-(+)-TA/0°C 5.4 0.25 12.2(12.7) 6.8 111 0.7 a The numbers in parentheses indicate the unit cell dimension of as-synthesized samples. b Pore size obtained from adsorption isotherm.c Total pore volume. d Wall thickness. e Micropore volume.

No.

v

623 (100) (100)

A(100) (100)

A

(110) (200)

110)(200) 1 A

a b

h-

a b c

c d

A j\

f 2

3 2Theta/°o 2Theta/

d

•A

e

1

B

(110)(200)

4

5

1

e f 2

3 o 2Theta/ 2Theta/°

4

Fig. 1 Powder XRD patterns of as-synthesized (A) and calcined (B) SBA-15* synthesized at 120°C (a), 100°C (b), 90°C (c), 60°C (d), 35°C (e) and 0°C (f). The difference between the cell parameter and the pore size, namely the pore wall thickness (/), became thicker at lower temperatures but it did not increase at temperatures below 60°C; in contrast, the samples prepared at 60°C, 35°C, 0°C possessed nearly the same pore wall thickness (Table l,No. 13-24). Fig. 2 shows several representative SEM and TEM images for SBA-15*. The mesoporous channels running parallel to the long axis were ca. 10 nm in diameter and had a uniform 2D hexagonal array (P6mm) (Fig. 2a-c). The presence of the roughness in the pore windows was observed. Here, the use of the chiral tartaric acids resulted in the well-defined rodlike aggregates (Fig. 2d-g). It seems that the different counterions of acids have a large effect on the macroscopic morphology. The main reason is that the tartaric acid is not a strong acid (pKal = 3.2; pKa2 = 4.8); which led to the pH value of about 1.1. Increasing the pH value decreases the .. , .. r^, .... .. aggregation velocity of the silicic acid. SBA-15 tends to form more curved

Fi

8- 2 T E M ( a ' c ) a n d S E M i m a 8 e s (d-§> " * PrePared in the media of D( } TA at 9 C -°° < c ) , ™ d ^ ^ l f i e d images off (b) and (d). SBA-15 prepared in typica , m e t h o d (HC1) is for c o m p a r i s o n (h) . o f SBA 15

5

624

morphology such as the ropelike ones according to the literature [3]. However, the morphology of SBA-15* is unexpectedly close to rodlike one with a low curvature. The nitrogen sorption isotherms of SBA-15* materials with different pore size distribution are shown in Fig. 3. All the N2 adsorption-desorption isotherms are of type IV. A shift to higher relative pressure of the pore-filling step was observed in the isotherms with increasing synthesis temperature, indicating that hydrothermal synthesis at higher temperatures leads to an increase of pore diameter. It is also in agreement with the pore size distribution calculated by BJH method (Fig. 4 and Table 1, No. 1-16). 0.09 0.09

e

0.08

a

2000

b

1500

c

1000

d e

500 0 0.0

0.07

a

6 0.06

3

2500

dV/dD (cm /(nm g))

3

Vol Adsorbed (cm /g STP)

3000

I

-o

f 0.2

0.4

0.6

0.8

1.0 1.0

Relative Pressure (P/P (P/P00)

Fig. 3 The isotherms of SBA-15* prepared at different synthesis temperatures. For a-f, same in Fig. 1.

•

fi c lf\

f

0.05

d

0.04 0.03 0.02 0.01 -

1b

11/^ ^

1 ft

0.00 00

55

10 10

15 15

20 20

25 25

30

Pore Diameter (nm)

Fig. 4 BJH pore size distribution of SBA-15* prepared at different synthesis temperatures. For a-f, same in Fig. 1.

4. Conclusion SBA-15 materials with unique morphology and pore properties have been synthesized in chiral acid media. The weak acidity of acetic acids tends to lead to rodlike shape with larger crystal sizes. 5. Acknowledgement Financial supports by NCET-04-0423, Pujiang project (05PJ14041), 973 project (2003CB615801), STCSM (05DZ22306, 05JC14069) and NSFC (20473027 and 20233030) are appreciated. 6. References [1] D. Y. Zhao, J. L. Feng, Q. S. Huo, N. Melosh, G. H. Fredrickson, B. F. Chmelka and G. D. Stucky, Science, 279 (1998) 548. [2] D. Y. Zhao, Q. S. Huo, J. L. Feng, B. F. Chmelka and G. D. Stucky, J. Am. Chem. Soc, 120 (1998) 6024. [3] D. Y. Zhao, J. Y. Sun, Q. Z. Li and G. D. Stucky, Chem. Mater. 12 (2000) 275.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Published by Elsevier B.V.

625 625

Synthesis of the mesoporous TiO2 films and their application to dye-sensitized solar cells Dong-Hyun Cha, Young-Suk Kim, Jia Hong Pan, Yoon Hee Lee, Wan In Lee* Nano Materials and Devices Lab., Department of Chemistry, Inha University, lncheon 402-751, Korea.

Mesoporous titania films with worm-like structure have been fabricated on the FTO substrates by evaporation-induced self-assembly (EISA) process using triblock copolymer as a structure-directing agent. The prepared mesoporous films were applied to the electrode material in the dye-sensitized solar cells (DSSCs). SAXRD patterns and TEM images show that the mesoporous structure was thermally stable at least up to 450 °C. The DSSC fabricated from these mesoporous films showed 1.7 times of photovoltaic current (Jsc) than those from the nanocrystalline films in the same thickness. It is deduced that the high Jsc is caused by the efficient transport of electrons due to far less grain boundaries in the mesoporous TiO2 structure, and by the fast diffusion of electrolytes with the high uniformity in the mesopore size. 1. Introduction Recently, DSSC draws great attention with low production cost of electricity and high energy conversion efficiency. One of the highest photoconversion efficiency of DSSCs derived from the nanocrystalline titania is 10.4%, as reported by GratzeFs group [1]. Typically for the construction of DSSC, the TiO2 nanoparticles are deposited as a thick film layer on the transparent conductive oxide (TCO). Then, the dye molecules are anchored on its surface, and the redox couples and electrolytes are filled between two electrodes. The photo-excited electrons from the dye molecules are injected to the conduction band of TiO2 and transferred to the TCO. Recently, the tailoring of TiO2 nanostructures in the DSSC has been studied for the purpose of efficient transfer of the injected electrons [2,3]. The mesoporous TiO2 films would be a promising candidate with high surface area and uniform pore diameter. In this work, the 1.2 fxm-thick the mesoporous titania films were deposited on the TCO,

626

and they were applied to the DSSC. The advantage of the mesoporous titania films on the photoconversion efficiency of DSSCs was also discussed. 2. Experimental section The mesoporous TiO2 films were prepared by spin-coating the Ti-sol on a pre-cleaned FTO glass [4]. The molar composition TTIP: F127: HC1: H2O: EtOH was 1: 0.005: 1.7: 10: 24. The deposited films were aged for 3 days in the closed chamber, whose relative humidity was maintained to 60% by a saturated Mg(NO3)2 aqueous solution. The nanocrystalline TiO2 films were prepared by screen-printing method. Both films were calcined at 450 °C for 30 min, and immersed into the dye solution (N3, Solarnonix Inc.) for 24 hr. The dye/TiO2 layer/FTO and Pt/FTO were used as working and counter electrodes, respectively, and the electrolyte was filled into the interval between these two electrodes. The photovoltaic properties of the DSSCs were measured by a Keithley 2400 source meter under the AM 1.5 direct illumination provided by a Thermo Oriel Xenon 300 W lamp fitted with AM 1.5D filters. 3. Results and discussion It was found that the periodic texture of the prepared mesoporous titania films was greatly dependent on the nature of substrates. With the given EISA condition, the highly organized cubic mesoporous structures in the thickness of 300 nm could be grown on the Pyrex glass, but the worm-like mesostructure was obtained by on the (a) (b) ITO or FTO glass, as indicated in the Planview TEM images of Fig. 1. The structure of the Meso-Ti02 films was stable up to 450 °C, which is a typical heattreatment temperature 50nm for the fabrication of DSSCs. Fig. 1. TEM images of the Meso-TiO2 films in about 300 nm For the application thickness, (a) A cubic mesoporous structure grown on Pyrex of mesoporous TiO2 glass, (b) A worm-like structure grown on FTO substrate. films to DSSC, the 1.2 (im-thick films (Meso-TiO2) were fabricated on FTO glass, by applying the four times of EISA process, since the thickness of the mesoporous titania films obtained by the single EISA process is only 300 nm. For the comparison, 1.8 u.m-thick nanocrystalline TiO2 films (NC-TiO2) were formed by screen-printing method. 1.00 g of 7 nm-sized TiO2 nanoparticles was suspended in 8 ml of ethanol/H2O solution (50: 50 in volume), and then 0.30 g of polyethylene glycol

627

20,000 (Fluka Co.) and 0.10 g of polyethylene glycol 500,000 (Wako Pure Chemical Co.) were added to obtain highly viscous paste for the screen printing. Fig. 2 shows the cross-sectional SEM images for the 1.2 |wn-thick Meso-TiO2 and the 1.8 (am-thick NC-TiO2 films annealed at 450 °C. Both films do not have cracks, and seem to have good contact with the FTO substrate.

(b)

(a)

1

1

Fig. 2. Cross-sectional SEM images for the Meso-TiO2 (a) and NC-TiO2 (b) films.

Fig. 3 shows the photocurrent versus voltage curves for the DSSCs derived from Meso-TiO2 and NC-TiO2 films. The Jsc of the DSSC derived from the Meso-TiO2 film was 15% higher than that of the DSSC from NC-TiO2 films, even though the thickness of the Meso-TiO2 film is only 2/3 of that of the NCTiO2 film. This indicates that the Jsc of DSSC from the Meso-TiO2 film is 1.7 times, when it is compared at the same thickness. Furthermore, the Voc was increased from 0.615 V to 0.645 V. It was observed that the Meso-TiO2 film was very tightly bound to the FTO substrate. This may induce the appreciable increase of Voc due to the low contact resistance between the TiO2 layer and the FTO substrate. From the BET measurements, the surface area of the Meso-TiO2 was determined to 142 m2/g, while that of the NC-TiO2 was 108 m2/g. Considering the thickness difference in these two films, the surface area of the Meso-TiO2 film was only 0.51 times of that of NC-TiO2 film. The amount of the adsorbed N3 dye in the both films was analyzed in this work. That is, the adsorbed dye in the TiO2 films was retrieved by the addition of 0.1 M NaOH ethanol solution, 5

voc

F.F

n [%]

Jsc (mA/cm2)

4

3

NC-TiO2

3.07

615

0.69

1.92

Meso-TiO2

3.52

645

0.69

2.32

2

NC-TiO NC-TKX,2 Meso-TiO2

1

0 0

200

400

Applied Voltage (mV)

600

Fig 3.1-V curves for the DSSCs derived from the Meso-TiO2 and NC-TiO2 films. The thicknesses of films were controlled to 1.2 and 1.8 |im, respectively. The measured results are summarized in the table.

628

Absorbance (a.u.)

and the concentration of the eluted dye was estimated by UV-Visible absorption spectra, as shown in Fig. 4. The absorption maxima at around 500 nm indicate the characteristic absorption peak of N3 dye. The peak height for the MesoTiO2 sample was 0.54 times that for the NC-TiC>2 film. This suggests that the adsorption amount of N3 dye is simply proportional to the surface area of TiO2 regardless of the film structure. Herein we found the Meso-TiO2 film containing 54% of N3 dye NC-TiO2 showed 115% of photovoltaic current Meso-TiO2 0.2 than the NC-TiO2 film. Then why does the mesoporous film show 8 higher photovoltaic current? First, the mesoporous TiO2 structure have 0.1 much less grain boundary. Thus the injected electrons to the conduction band of TiO2 from the photo-excited 0.0 N3 dye can be efficiently transported 400 500 600 700 800 500 600 700 to the TCO without the back Wavelength (nm) transport to the HOMO of the dye. Fig. 4. The absorption peaks of N3 dye eluted Second, the mesopore of Meso-TiO2 from the Meso-TiO2 and the NC-TiO2 films, respectively. film is highly uniform in size and have good connectivity without blind ally. Thus the diffusion of the electrolyte is expected to be greatly efficient. The optimum thickness of nanoporous TiO2 films providing the highest photovoltaic efficiency in the DSSC is higher than 10 m in general. Therefore, the preparation of very thick mesoporous TiO2 film is prerequisite for the realization of high efficiency solar cell. More attention is necessary in this issue. 4. Acknowledgement The authors gratefully acknowledge the financial support of the Korean Science and Engineering Foundation (KOSEF R01-2003-000-10667-0). 5. References [1] M. Gratzel, (2001). Photoelectrochemical Cells. Nature 414 (2001) 338. [2] L. I.. Halaoui, N. M. Abrams and T. E. Mallouk,. Increasing the Conversion Efficiency of Dye-Sensitized TiO2 Photoelectrochemical Cells by Coupling to Photonic Crystals. J. Phys. Chem. B 109 (2005) 6334. [3] M. Zukalova, A. Zukal, L. Kavan, M. K. Nazeeruddin, P. Liska and M. Gratzel, Organized Mesoporous TiO2 Films Exhibiting Greatly Enhanced Performance in Dye-Sensitized Solar Cells. Nano Lett. 5, (2005) 1789. [4] J. H. Pan and W. I. Lee, Selective Control of Cubic and Hexagonal Mesophases for Titania and Silica Thin Films with Spin-Coating. New J. Chem. 29(2005) 841.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

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Formation mechanism of monodispersed mesoporous silica spheres and its application to the synthesis of core/shell particles Hiroshi Nozaki, Noritomo Suzuki, Tadashi Nakamura, Yuusuke Akimoto and Kazuhisa Yano Toyota Central Research & Development Labs. Inc., Nagakute, Aichi, 480-1192, Japan. 1. Introduction

After the discovery of the M41S family [1], considerable amounts of research have been made on the synthesis of mesoporous silicas possessing uniform mesopores and high specific surface areas [2-4]. Many researchers have investigated the formation mechanism of mesoporous silicas so far [5-8], no simple mechanism exists because it greatly depends on the synthesis conditions. Recently, we have successfully synthesized monodispersed mesoporous silica spheres (MMSS) possessing highly ordered hexagonal regularity from tetramethoxysilane and alkyltrimethylammonium halide in very diluting conditions [9-13]. During the reaction, a clear solution turned opaque suddenly, a white precipitate appearing. It is very important to study the formation mechanism of MMSS to control particles size and monodispersity precisely. In order to address the mechanism, in situ particle size development was measured by means of TEM. A newly developed method for MMSS with core/shell structure based on the proposed mechanism will be also described. 2. Experimental Section Synthesis was conducted according to the literature [11]. Core/shell particles were obtained by adding TMOS/mercaptopropyltrimethoxysilane (MPTMS) mixture 30 min after the commencement of the experiment. Transmission electron microscopy (TEM) was performed on a Jeol-200CX TEM using an acceleration voltage of 100 kV. A small amount of a reaction solution was dropped on a carbon-coated copper grid at every half minute for ten minutes during the synthesis. Liquid portion immediately passed through the membrane,

630

and only solid particles remained on the grid, quenching particle growth. Scanning electron micrographs (SEMs) were obtained using a SIGMA-V (Akashi Seisakusho). The average particle diameter was calculated from the diameters of 50 particles observed in a SEM picture. 3. Results and Discussion In order to investigate the formation mechanism of MMSS, particles size development was captured on TEM images at every 30 sec during the synthesis. Fig. 1 shows some of the images. After 150 sec experimental started, small particles (ca. 200 nm) emerged suddenly, and grew to the final size (ca. 500 nm) in 600 sec. It was confirmed by TEM observation that primary generated small particles grew homogeneously into larger particles, leading to the formation of monodispersed spherical particles.

Fig. 1 Transmission electron micrographs of samples obtained at different time, (a) 130, (b) 150, (c) 200, and (d) 360 sec after the synthesis had started. Scale bar represents 500 nm.

From the above results, it is assumed that residual silica precursors in solution preferentially reacted with existing particle surface silanols, preventing generation of new particles. This leads to the formation of MMSS. To confirm this assumption, TMOS was added different number of times after the completion of the initial reaction. Fig. 2 shows SEM images of particles obtained upon two and four additions of TMOS to the initial reaction mixture.

0.61 jim (5.1%) 1.1 lum

0.80 urn (3.1%) 1.Hum

1.21 |im (2.8%) 1.09um

Fig. 2 SEM images of particles obtained by the different TMOS addition times: (a) 0, (b) 2 and (c) 4.

631

The diameter of the particles was clearly increased upon the addition of TMOS, while retaining the monodispersion characteristic (standard deviation in parenthesis). This result indicates that additional TMOS prefers to react with the surface silanol of existing particles rather than generates new particles. It was confirmed by nitrogen adsorption measurement that pore volume (ca. 0.7 ml/g) and specific surface area (ca. 1100 m2/g) were unchanged upon the further addition of TMOS. On the basis of the above results, it MPTMS-TMOS is assumed that MMSS with TMOS TMOS core/shell structure can be obtained by adding different type of silica i MPTMS MPTMS -TMOS precursor from the original one to the addition pre-existing particles, as illustrated in Fig. 3. Synthesis was conducted in which double the molar amount of Fig. 3 Schematic illustration of the formation mercaptopropyltrimethoxysilane of core/shell MMSS. (MPTMS)/TMOS (=20/80 mol/mol) mixture was added to the solution including pre-existing particles obtained with TMOS. Fig 4 (a) shows a SEM image of the particles obtained. The average diameter was 0.73 um, and the standard deviation was 4.3 %, indicating that the particles were highly monodispersed. In addition, specific surface area and pore volume determined by nitrogen adsorption measurement were 998 m2/g and 0.49 ml/g, respectively. It was confirmed that mesoporous structure was retained in core/shell particles. It is anticipated that the particles possess a silica core/mercaptopropyl-modified silica shell structure, more specifically, a hydrophilic core /hydrophobic shell structure. To confirm this, platinum was incorporated into the particles. An egg type structure is clearly seen in Fig. 4 (b).

T

(b)

(a)

1.11 µm

nm 200 nm

Fig. 4 (a) SEM image of the silica/mercaptopropyl-modified silica core/shell MMSS. (b) TEM image of the platinum incorporated silica/mercaptopropyl-modified silica core/shell MMSS.

Platinum (dark portion) is concentrated in the hydrophilic core part. Because

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platinum was incorporated into mesopores by using an aqueous solution of tetra ammine complex as a precursor, platinum particles (black part) existed in only hydrophilic core portions. From these results it is obvious that MMSS with core/shell structure was successfully synthesized by changing the type of additive silica precursor. 4. Conclusion In conclusion, it was found that small particles emerged suddenly during the synthesis of monodispersed mesoporous silica spheres (MMSS). The primary generated small particles grew homogeneously into larger particles, leading to the formation of MMSS. Furthermore, MMSS with core/shell structure have been successfully obtained for the first time by adding different type of silica precursor to pre-existing particles. Work is underway to explore new potential applications for these unique materials, which possess both monodispersed shape and mesoporous core/shell structure. 5. Acknowledgement This research was partially supported by Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (B), 17310079, 2005. 6. References [1] C. T. Kresge, M. E. Leonowicz, W. J. Roth, J. C. Vartuli and J. S. Beck, Nature 359 (1992) 710. [2] J. S. Beck, J. C. Vartuli, W. J. Roth, M. E. Leonowicz, C. T. Kresge, K. D. Schmitt, C. TW. Chu, D. H. Olson, E. W. Sheppard, S. B. McCullen, J. B. Higgins and J. L. Schlenker, J. Am. Chem. Soc. 114 (1992) 10834. [3] P. Yang, D. Zhao, B. F. Chmelka and G. D. Stucky, Chem. Mater. 10 (1998) 2033. [4] P. J. Bruinsma, A.Y. Kim, J. Liu and S. Baskaran, Chem. Mater. 9 (1997) 2507. [5] J. C. Vartuli, K. D. Schmitt, C. T. Kresge, W. J. Roth, M. E. Leonowicz, S. B. McCullen, S. D. Hellring, J. S. Beck, J. L. Schlenker, D. H. Olson and E. W. Sheppard, Chem. Mater. 6 (1994)2317. [6] A. Firouzi, F. Atef, A. G. Oertli, G. D. Stucky and G. G. Chmelka, J. Am. Chem. Soc. 119 (1997)3596. [7] J. Frasch, B. Lebeau, M. Soulard, J. Patarin and R. Zana, Langmuir 16 (2000) 9049. [8] J. Morell, C. V. Teixeira, M. Cornelius, V. Rebbin, M. Tiemann, H. Amenitsch, M. Froba and M. Linden, Chem. Mater. 16 (2004) 5564. [9] K. Yano, N. Suzuki, Y. Akimoto and Y. Fukushima, Bull. Chem. Soc. Jpn. 75 (2002) 1977. [10] K. Yano and Y. Fukushima, J. Mater. Chem. 13 (2003) 2577. [11] K. Yano and Y. Fukushima, J. Mater. Chem. 14 (2004) 1579. [12] Y. Yamada, T. Nakamura, M. Ishii and K. Yano, Langmuir, 22 (2006) 2444. [13] Y. Yamada and K. Yano, Microporous Mesoporous Mater. 93 (2006) 190.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

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Controllable synthesis of cubic MCM-48 with different morphologies by using ternary surfactant templating route Lingdong Konga, Su Liub, Yi Wanga, Xuewu Yana, Heyong Hea and Quanzhi Lia " Department of Chemistry and Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, Fudan University, Shanghai 200433, P. R. China. Department of Environmental Science and Engineering, Fudan University.

Cubic MCM-48 with different morphologies, such as cube shape, vesicle-like, microtubule-like and spherical particles was synthesized in the same ternary mixed surfactants system. This system not only make high-quality cubic phase MCM-48 prepared at extremely low surfactant concentration (1.76 ~ 2.4 wt%) but also facilitate the formation of various morphologies, which is closely correlated to the strong synergistic effects of the ternary mixed surfactants system and the amount of ethanol coming from the hydrolysis of TEOS. Keywords: synergistic effect, MCM-48, surface tension, morphology 1. Introduction Cubic MCM-48, a member of M41S mesoporous family [1], has attracted much attention for its interwoven bicontinuous pore structure. In the past over ten years, many methods for the synthesis of MCM-48 were developed by using the single cationic surfactant systems [1, 2] and binary mixed surfactants systems [3-5]. Recently, we developed a ternary mixture of cationic surfactant, anionic surfactant and non-ionic surfactant as template for the synthesis of MCM-48 with various morphologies under alkaline conditions. This is the first observation for the existence of so many morphologies in the same synthesis system of cubic MCM-48.

634

2. Experimental Section The typical ternary mixed surfactants were composed of cationic surfactant, cetyltrimethylammonium bromide (CTAB), anionic surfactant, sodium laurate (SL) and nonionic surfactant, poly (ethylenglycol) monooctylphenyl ether (OP10). The detail synthetic procedures have been reported elsewhere [6, 7]. In a typical synthesis, 1.458 g of CTAB, 0.095 g of SL, 0.173 g of OP-10 and 1.504 g of NaOH were dissolved in 70 g of distilled water in an open beaker by stirring at 311 K to give a clear solution, and then 15.2 mL of TEOS was added dropwise to the solution. The molar composition of the resulting synthesis gel was 1.0SiO2: 0.06CTAB: 0.004OP-10: 0.0064SL: 0.282Na2O: 58H2O. The different morphologies of MCM-48 were obtained through controlling the hydrolysis rate of TEOS and ethanol amounts produced by TEOS' hydrolysis with changing the stirred time before the synthesis gels were transferred into the Teflon-lined stainless steel autoclave for the hydrothermal treatment. The assynthesized samples are designated as sample A, B, C and D, corresponding to the stirred time of 1, 1.5, 3.5 and 6h, respectively. Different amount of water was added for compensating for the loss of water which evaporated from the synthetic system corresponding to the different stirred time. 3. Results and Discussion The first observation of our experimental results demonstrated that the "cmc" and surface tension of the ternary surfactants system can be dropped more greatly than that of binary surfactants system. From Table 1 one can see that the strong synergism effects in the mixture of the ternary surfactants can make high-quality cubic phase MCM-48 be prepared at extremely low surfactant concentration, which is only 1/10 that of in single cationic surfactant synthesis system and 1/3-1/2 that of in binary mixed surfactants synthesis system. Table 1. "cmc" and corresponding surface tension of the different surfactants mixtures (298K), and the molar ratios of total surfactant to silicon (Sur/Si) of the different systems for the synthesis of MCM-48 Surfactant systems CTAB a CTAB+OP-10 b CTAB+SL C CTAB+OP-10+SL

cmc (mol/L)

1.09X10" 3 4.35 X10" 4 3.89X10" 4 2.45 XI0" 4 a. see ref. [2]. b. see ref. [3]. c. ref. [4].

Surface tension (mN/m) 39.6 41.0 37.4 29.5

Total Sur/Si 0.55 0.144 0.168 0.07

The small-angle X-ray diffraction patterns for as-synthesized samples are shown in Figure 1. As can be seen from Figure 1, besides intense 211 and 220

635 635

diffraction peaks, several well-resolved Bragg diffraction peaks that can be indexed as 321, 400, 420, 332 and 422 reflections associated with cubic symmetry can be observed, which is typical for MCM-48. Figure 2a shows that the particles of sample A have various hollow morphologies, such as spherical and cocoon-like shapes with micron size covered by MCM-48 particles of nano or submicron size. The ternary surfactants' strong synergistic effects create an extremely dilute surfactants concentration offering an environment for meeting the co-existence of vesicles and MCM-48. Thus, the hollow morphologies come from the result that vesicles act as soft template.

29 /degree

Figure 1. XRD patterns of as-synthesized samples: (a) sample A, (b) sample B, (c) sample C; (d) sample D.

Figure 2. SEM images of the as-synthesized MCM-48: (a) sample A; (b) sample B; (c) sample C; (d) sample D.

636

The as-synthesized sample B possesses cube shapes, consisting of 6 welldefined crystal faces (see Figure 2b). This is the first synthesis of MCM-48 with such less crystal faces. The synergism effects, the low "cmc" of forming micelles, and the residual ethanol produced by the hydrolysis of TEOS delaying the condensation of silicate-surfactant aggregates, all may benefit the formation of cube morphology in the ternary mixed surfactant synthesis system. With the decrease of the amount of ethanol, the particles of sample C exhibit another unique morphology shown in Figure 2c, which consists of well-defined irregularly flat spherical particles with concave, and seem to be growing in pairs or growing up on each other. While sample D has more round and smaller spherical particles (Figure 2d) than that of sample C when the ethanol amount further decreases with the increase of stirred time of synthesis gel before crystallization. These diverse morphologies of MCM-48 would have potential applications for various fields. 4. Conclusion We have synthesized mesoporous MCM-48 with various morphologies by employing the ternary mixed surfactants templating method. This synthesis method provides a better control over particle morphologies compared with the other methods, which will further deepen the understanding of the morphology control during the synthesis of mesoporous materials. 5. Acknowledgement Financial support from National Science Foundation of China (Project 20303005) is greatly acknowledged. 6. References [1] C. T. Kresge, M. E . Leonowicz, W. J. Roth, J. C. Vartuli and J. S. Beck, Nature, 359 (1992)710. [2] J. Xu, Z. Luan, H. He, W. Zhou and L. Kevan, Chem. Mater., 10 (1998) 3690. [3] W. Zhao, J. D. Yao, X. D. Huang and Q. Z. Li, Chinese Science Bulletin, 46 (2001) 1436. [4] F. X. Chen, L. M. Huang and Q. Z. Li, Chem. Mater., 9 (1997) 2685. [5] R. Ryoo, J. M. Kim and S. H. Joo, J. Phys. Chem., 103 (1999) 7435. [6] L. D. Kong, S. Liu, X. W. Yan, H. He and Q. Z. Li, Stud. Surf. Sci. Catal., 154 (2004) 468. [7] L. D. Kong, S. Liu, X. W. Yan, Q. Z. Li and H. He, Microporous Mesoporous Mater., 81 (2005)251.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

637 637

Mesoporous silica hosts for polyenzymatic catalysis Anne Galarneau, Lai Truong Phuoc, Aude Falcimaigne, Gilbert Renard and Francois Fajula Laboratoire de Materiaux Catalytiques et Catalyse en Chimie Organique, UMR 5618 CNRS/ENSCM/UM1, Institut Gerhardt FR 1878, ENSCM, 8 rue del'Ecole Normale, 34296 Montpellier Cedex 5, France. E-mail: [email protected]

Lipases, oxidase and peroxidase have been immobilized or coimmobilized in mesoporous silica hosts by using a novel sol-gel procedure based on the use of lecithin as surfactant and lactose as enzyme protector. The resulting biocatalysts demonstrate high activities in various model reactions. Furthermore, the preparation procedure allows to generate in-situ hydrogen peroxide from glucose and oxygen, opening new perspectives for soft oxidation reactions. 1. Introduction The immobilization of enzymes in/on solid supports is expected to provide breakthroughs in the area of heterogeneous catalysis. Biological molecules such as enzymes are outstanding catalysts combining very high activity with very high specificity. However they are only barely used to date because of their fragility. Appropiate immobilization should preserve their quaternary structure -to protect them against the external environment- while permitting easy recovery of the products and, ultimately, develop continous flow processes. According to Whitesides and Wong [1] enzymes can be classified in five types: very stable enzymes, enzymes with self-regenerated co-factor, enzymes with sacrificial co-factor, very fragile enzymes and polyenzymatic systems. Generally, their immobilization in/on a solid support either by adsorption, covalent tethering or encapsulation leads to denaturation, with a severe loss of activity, and necessitates specific preparation procedures. We present here a simple and versatile enzyme encapsulation method giving access to very efficient biocatalysts.

638

2. Materials and Reactions 2.1. Monoenzymatic biocatalysts Several solid biocatalysts have been prepared by immobilization of a lipase (from Mucor miehei, obtained from Gist-Brocades) via encapsulation in porous silicas. Materials loaded with 3 to 9 mg of enzyme per gram of silica were prepared by using either conventional methods, such as adsorption on mesostructured silicas of varying pore sizes and surface polarities (MCM-41type, 3.7-10 nm, as-made, calcined, dimethylbutyl-grafted) [2] and sol-gel encapsulation [3], or via a new direct encapsulation procedure enabling control of both the textural and surface characteristics of the porous host [4]. Two different new types of nanostructures were thus prepared by the latter method: a three dimensional isotropic structure with cavities of 6 nm in diameter, named Sponge Mesoporous Silicas (SMS, 622 m2/g, 1 mL/g), and 20 nm Silica Porous Nanocapsules (SPN, 400 m7g, 0.62 mL/g). The preparation of SMS and SPN biocatalysts is based on an improved sol-gel synthesis involving: i) a natural phospholipid surfactant (egg lecithin) to avoid direct interaction between silanol groups and the enzyme which may denaturate its activity by changing its conformation, ii) amines, to generate a porous structure thanks to their curvature effect on the phospholipid bilayer and iii) lactose to preserve the enzyme activity by replacing the conformational water of the protein. The activity of the immobilized lipases was evaluated in aqueous medium at RT and pH = 8 for the hydrolysis of ethyl thiodecanoate and of the esters of p-nitrophenol bearing acyl chains with 2 to 16 carbon atoms, hereafter C2-C16. 2.2. Poly enzymatic biocatalysts The system chosen to investigate the possibility to design polyenzymatic solid biocatalysts from SMS and SPN combines a Glucose Oxidase (GOD, from Aspergillus niger, Sigma) and a Horse Radish Peroxidase (HRP, from Horseradish, Sigma). The reaction is performed at RT, pH= 7, under conditions chosen so that the overall activity (measured by the generation of quinoneimine, a red dye, which is titrated by UV-Vis at 508 nm [5]) is controlled by the production of hydrogen peroxide from glucose and oxygen. 3. Results and Discussion 3.1. Monoenzymatic biocatalysts Figure 1 summarizes typical activity data expressed as the % of specific activity of the biocatalysts (IU per mg of protein) compared to the specific

639

SMS

activity of the enzyme in solution for the hydrolysis of ethyl thiodecanoate. Materials prepared by adsorption on MCM-41 developped a moderate activity, regardless of the polarity of the surface (hydrophilic in calcined solids, hydrophobic in grafted ones, intermediate in as-made solids) and pore size. The sol-gel procedure, which provides a balanced hydrophobic/ hydrophilic environment to the enzyme [3] generates a better catalyst but the most active system was the one prepared via the SMS route. The efficiency of SMS-type biocatalysts was also demonstrated in the reaction of hydrolysis of esters of p-nitrophenols susbituted with C2-C16 chains. In this reaction the native enzymes in solution shows a very high specificity for long alkyl chain esters [2]. As shown in Figure 2, upon encapsulation a dramatic change in typoselectivity is observed, probably on account of the unfolding of the entrapped enzyme. As a consequence the SMS biocatalyst demonstrates a specific activity for the C2 and C3 esters of

< CM

tr

I i

. 5

~

ci ~n3

QJ *•=

o

2

i—i,-^-,

/I-41

ICM

ss.

CD

cn "o

en

o

c to CO 03

-syn.

J3 CD

1-41

•41

T—'

CO CO

2 Biocatalysts

Fig.l: Percentage of relative specific activity (IU lipasesoHd/IU lipaseSO|ulion x 100) in ethyl thiodecanoate hydrolysis

3 8 12 Ester chain length, Cn

Fig. 2: Relative specific activity for the hydrolysis of esters of p-nitrophenol as a function of acyl chain length

the p-nitrophenol six and nine times higher, respectively, than the activity of the native enzyme. Here again, direct SMS encapsulation generates a much active catalyst than adsoprtion in a pre-formed solid (MCM-41, 10 nm). These results clearly illustrate the synergistic influence of surface polarity and porosity in enzyme silicate hosts. 3.2. Poly enzymatic systems The SMS and SPN synthesis procedure has been applied to the coimmobilization of Horse Raddish Peroxidase (HRP) with Glucose Oxidase

640

(GOD). In this system hydrogen peroxide is generated in situ and immediately consumed quantitatively preventing the peroxidase denaturation [5, 6]. Glucose + H2O + O2 H2O2 +PhOH + 4-AAP

GOD

HRP

Gluconic acid + H2O2

(1)

Quinoneimine + H2O

(2)

(with PhOH: phenol, 4-AAP: 4-aminoantipyrine) The HRP and GOD enzymes catalyse two independent but consecutive reactions and the activity of HRP is regulated by the rate of formation of hydrogen peroxide (deliberately limited in all experiments by the amount of glucose and GOD engaged in the system). Figure 3 shows the relationship between the ratio of activities of HRP to GOD determined separately (UHRP/UGOD) and the relative activity (respective to the maximum GOD activity) of the catalytic systems consisting of the native enzymes (Fig. 3a), of the two enzymes encasulpated individually in different SPN hosts (Fig. 3b, • ) and of the two enzymes coimmobilized is SPNs (Fig. 3b, o). In the case of the native enzymes in solution, the maximum GOD activity (68 umol.min'.mg'1) is reached for a ratio UHRP/UGOD close to 2. The immobilized and coimmobilized enzymes produce a catalytic system which is less effective (the activity of the encapsulated GOD is decreased to 15 umol.mhf'.mg"1). The overall activity increases to ca 80% of the nominal value for UHRP/UGOD ratios higher than 10. Such a behaviour could be well related to the loss of activity of the fragile HRP upon encapsulation (from 165 in solution to 12 umol.mhv'.mg"1 in the solid)and to a restricted diffusion of the substrates and oxidant in the confined space of the silica hosts. Further optimization of this biosystem is in progress. However, the most remarkable conclusion drawn from these preliminary experiments is the high level of activity that can be reached with these easy-to-prepare bienzymatic biocatalysts.

Fig. 3: Relative activity of the HRP /GOD systems versus the maximum activity that could be reached if all H2O2 produced by GOD be consumed by HRD, ie for well balanced reactions (1) and (2). (a: free enzymes in solution, b: enzymes immobilized separately, • or coimmobilized,o)

641

4. Conclusion Lipases as well as HRP and GOD have been immobilized individually or in association in porous silicate hosts prepared by using a combination of natural phospholipid and lactose in order to control both the textural and surface properties of the rigid matrix. The resulting biocatalysts exhibit relatively high enzymatic activity with, in some cases, unique typoselectivities. The synthesis procedure we introduce is attractive by its simplicity and versatility. 5. References [1] G. M. Whitesides and C-H, Wong, Angew. Chem., Intern. Ed. Eng., 24 (1985) 617. [2] A. Galarneau, M. Mureseanu, S. Atger, G. Renard and F. Fajula, New J. Chem, 30 (2006) 532. [3] M. T. Reetz, A. Zonta and J. Simpelkamp, J. Biotechnol. Bioeng., 49 (1996) 527. [4] M. Mureseanu, A. Galarneau, G. Renard and F. Fajula, Langmuir, 21 (2005)4648. [5] Y. Wei, H. Dong, J. Xu and Q. Feng, Chem. Phys. Chem., 9 (2002) 802, US 2004/0014189 Al (2004). [6] F. van de Velde, N. D. Lourenco, M. Bakker, F. van Rantwijk and R. A. Sheldon, Biotechnol. Bioeng., 69 (2000) 286.

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Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

Mesoporous silica-supported chiral norephedrine ligands for asymmetric transfer hydrogenation Myung-Jong Jina*, M. S. Sarkara and Sang-Eon Parkb " School of Chemical Science and Engineering, Inha University, Incheon, 402-751, Korea h Department of Chemistry, Inha University, Incheon, 402-751, Korea

Optically active norephedrine was anchored on three different mesoporous silica materials. The immobilized norephedrines could be served as enantioselective ligands in the asymmetric transfer hydrogenation of ketones. The heterogeneous catalysts gave satisfactory enantioselectivity as well as high levels of catalytic activity in the transfer hydrogenation. 1. Introduction Asymmetric transfer hydrogenation of ketones is known to be one of the most attractive methods for the synthesis of optically active secondary alcohols [1]. Efficient chiral ligands have been developed for the homogeneous catalysis. Successful development of homogeneous ligands has been sometimes followed by attempts to attach the ligands on an insoluble polymeric support. This strategy offers practical advantages such as simplified separation, easy recovery of catalyst, and potential reuse [2]. Recently, mesoporous silica materials with OH Si OH OH

1a. SBA-15 1a.SBA-15 1b. SBA-16 SBA-16 1c. MCM-48

Scheme 1

i)

O Si O O

ii) Si

Cl

O Si O

Si

O

2a-c

2 a - c

H3C

Ph

N

OH

H

3a-c

i)i) (C22H C, 10 C, 48 H55O) O)33Si(CH Si(CH22))33Cl Cl,, toluene, 105 105 o°C, 10 h. h. ii) ii) (-)-norephedrine, DIPEA, toluene, 105 105 o°C, 48 h

644

uniform pore diameters and high specific surface areas have become of high interest as inorganic supports [3]. Our interest in the field led to prepare mesoporous silica-supported norephedrine ligands. Herein, we describe the application of the immobilized ligands 3 for the asymmetric transfer hydrogenation of ketones. 2. Experimental Section 2.1. Preparation of mesoporous silicas la-c All the supporting silica la-c were prepared according to the reported methods [4]. 2.2. Preparation of 3-chloropropylated mesoporous silicas 2a-c To a solution of 3-(chloropropyl)triethoxysilane (0.11 g, 0.45 mmol) in toluene (8 mL) was added mesoporous silica la (1.0 g). The mixture was stirred at 105 °C for 10 h. The modified silica was collected by filtration and washed with CH2CI2. After drying in vacuo at 80°C, 3-chloropropylated silica 2a was obtained. The modified silicas 2b and 2c were prepared by the same procedure. Weight gain showed that 0.40 mmol, 0.37 mmol, and 0.40 mmol of 3-(chloropropyl)triethoxysilane were immobilized on 1.0 g of mesoporous silicas 2a-c respectively. 2.3. Preparation of mesoporous silicas-supported norephedrine 3a-c To a solution of (-)-norephedrine (0.151 g, 1.0 mmol) and diisopropylethyl amine (0.142 g, 1.1 mmol) in toluene (10 mL) was added 3-chloropropylated silica 2a (1.0 g). The mixture was gradually heated at 105°C and allowed to react for 48 h. The silica powder 3a was collected by filtration and successively washed with H2O, methanol and CH2CI2. Mesoporous silica-supported norephedrine 3a was obtained after drying in vacuo at 70°C. The supported ligands 3b and 3c were prepared by the same procedure. Elemental analysis and weight gain showed that 0.35 mmol, 0.31 mmol and 0.36 mmol of norephedrine were anchored on 1.0 g of 3-chloropropyl silicas 3a-c respectively. 2.4. General procedure for the Ru-catalyzed asymmetric transfer hydrogenation with immobilized ligands 3a-c A suspension was formed by the mixture of [RuCl2(p-cymene)]2 (5 mg 0.008 mmol) and mesoporous silica-supported norephedrine 3 (0.016 mmol) in 2propanol (5 mL). The mixture was heated at 80°C for 30 min under nitrogen atmosphere. To this resulting solution, a degassed solution of ketone (0.83 mmol)

645

with KOH (2.3 mg, 0.04 mmol) in 2-propanol (10 mL) was added and the mixture was stirred at RT for 3~6 h. The reaction was monitored by TLC and neutralized with aqueous NH4CI. The immobilized ligand 3 was separated by centrifugation from the reaction mixture. Excess 2-propanol was removed under reduced pressure and the residue was extracted with ethyl acetate. Organic layer was washed with brine and dried over MgSO4. The crude product was purified by short-column chromatography (hexane-ethyl acetate, 95:5, as eluent). Enantiomeric excess of the product was determined by HPLC analysis using Chiralcel OD-H column (3% 2-propanol in hexane, 1 ml/min). 3. Results and Discussion The immobilization of norephedrine onto three mesoporous silicas SBA-15 la, SBA-16 lb and MCM-48 lc were performed in two steps (Scheme 1). Reaction of mesoporous silicas la-c with (3-chloropropyl)triethoxysilane in refluxing toluene gave chloropropylsilanized silicas 2a-c with loading ratio of 0.37-0.4 mmol/g. Subsequent treatment of 2a-c with an excess of (-)-norephedrine in refluxing toluene in the presence of diisopropylethylamine afforded the heterogenized norephedrine Iigands 3a-c. The mesoporous silica-supported chiral Ru(II) complexes were prepared in situ by heating a mixture of the Iigands 3 and [RuCl2(p-cymene)]2 in 2-propanol. Asymmetric transfer hydrogenation of ketones with isopropanol as a hydrogen source was examined in the presence of the supported Ru(II) complexes as chiral catalysts. As indicated in Table 1, the ketones were reduced to (7?)-secondary alcohols with satisfactory enantioselectivities in high conversions. It is noteworthy that the mesoporous silica-supported norephedrines 3 are comparable to the homogeneous counterpart (-)-ephedrine in terms of enantioselectivity [5]. 4. Conclusion In conclusion, the immobilized norephedrines 3 could be served as efficient enantioselective Iigands in the asymmetric transfer hydrogenation of ketones. We have proven that mesoporous silicas SBA-15, SBA-16 and MCM-48 can be served as suitable supports for the immobilization of chiral Iigands. Further synthesis of mesoporous silica-supported chiral Iigands and their use to asymmetric catalysis are underway in our laboratory.

646 646 Table 1 Asymmetric transfer hydrogenation of ketones using immobilized ligands 3 a

R

O

OH

)|n

o II

[Ru(arene)Cl2]2 chiral ligand 3, j-PrOK OH

A

0

A

Entry

Ketoneb

Ligand

Time (h)

Conv. (%)c

E.e. (%) d

1

Acp

3a

6

85

80

2

Acp

3b

4

86

81

3

Acp

3c

3

96

77

4

Pp

3a

6

80

72

5

Pp

3b

5

87

70

6

Pp

3c

3

94

70

7

3'-OMe-Acp

3a

6

90

77

8

3'-OMe-Acp

3b

3

95

80

9

3 '-OMe-Acp

3c

3

98

75

10

4'-Cl-Acp

3b

4

99

85

11

4'-Cl-Acp

3c

3

99

71

e

82 12 4'-Cl-Acp 4 92 3c "The reactions were carried out at RT in 2-propanol; ketone : Ru : ligand : KOH = 100 : 1 : 2 : 5. b Acp = acetophenone, Pp = propiophenone. cDetermined by GC analysis. dDetermined by HPLC analysis using Chiralcel OD-H column (3% 2-propanol in hexane, 1 ml/min). e [RuCl2(hexamethylbenzene)]2 was used instead of [RuCl2(p-cymene)]2

5. References [1] [2] [3] [4] [5]

R. Noyori and S. Hashiguchi, Ace. Chem. Res. 30 (1997) 97. N. E. Leadbeater and M. Marco, Chem. Rev. 102 (2002) 3217. A. P. Wright and M. E. Davies, Chem. Rev. 102 (2002) 3589. J. Y. Ying, C. P. Mehnert and M. S. Wong, Angew. Chem. Int. Ed. 38 (1999) 56. J. Takehara, S. Hashiguchi, A. Fujii, S.-I. Inoue, T. Ikariyaand R. Noyori, Chem. Commun. (1996)233.

Progress in in Mesostructured Materials Recent Progress S. Qiu, Y. Tang and C. Yu (Editors) (Editors) D. Zhao, S. © 2007 2007 Elsevier Elsevier B.V. B.V. All All rights rights reserved. reserved.

647 647

Facile heterogenization of homogeneous ferrocene catalyst on SBA-16 David Raju Burri, Isak Rajjak Shaikh, Sang-Cheol Han and Sang-Eon Park* Laboratory ofNano-Green Catalysis andNano Center for Fine Chemicals Fusion Technology, Department of Chemistry, Inha University, Incheon, 402-751, Korea

1. Introduction Heterogenization of homogeneous catalysts has been an indispensable requirement for the green and sustainable chemistry. Ferrocene is one of the important homogeneous catalysts for the oxidation and hydroxylation of aromatic compounds due to its redox centre, ^-conjugation system and exclusive electron transfer ability [1]. Recently, ferrocene has been heterogenized on SBA-15 support via multi-step post-synthetic grafting method [2]. A versatile synthetic methodology has recently been reported for the condensation of primary amine that attached to the SiC>2 support with one of the aldehyde groups of terepthaldicarboxaldehyde. Based on this methodology ferrocene has been heterogenized on SBA-16 support in a simple and an environmentally benign technique with Schiff s base attachment (C = N). Of late, it has been reported that the Schiff s base attached cobalt (III) immobilized SiO2 catalysts are highly stable and active for the oxidation reactions than that of cobalt (III) immobilized SiC>2 catalysts without Schiff s base attachment [3]. Recently, there has been increasing interest for the direct hydroxylation of benzene to phenol [4] aiming at the replacement of complex conventional threestep cumene process [5], To the best of our knowledge, the reports on ferrocene functionalized mesoporous oxidation / hydroxylation catalysts are very rare [2] and in particular, ferrocene functionalized SBA-16 catalysts are nil. Hence, in the present work, a simplified technique of Schiff s base containing ferrocene heterogenized SBA-16 synthesis and its catalytic application for the direct hydroxylation of benzene to phenol have been delineated.

648

2. Experimental Section 2.1. Synthesis of ferrocene heterogenized SBA-16 Propylamine functionalized SBA-16 was synthesized by direct cocondensation technique under strong acidic conditions (2 M HC1) similar to pure SBA-16 synthesis [6]. In a typical synthesis, 10 g of pluronic F127 (E0106P07oEOio6, Mav=12600) was dispersed in 256 g of H2O and added 29.4 g of sodium metasilicate nonahydrate (Na2SiO3.9H2O). Prehydrolysis was conducted for 1 h at 40°C under vigorous stirring prior to the addition of 1.86 g of 3- aminopropyltrimethoxysilane. The hydrolysis was continued for further 3 h and then, the reaction mixture was subjected to hydrothermal treatment at 100 °C for 12 h under static conditions. The solid product was separated by filtration under reduced pressures and dried at room temperature for 12 h. The template was extracted from this as-synthesized material by using acidified boiling ethanol for 24 h. Ferrocenecarboxaldehyde (Aldrich) was dissolved in absolute ethanol / toluene and added to aminopropyl functionalized SBA-16 under stirring at room temperature for 4 h. The solid product was recovered by filtration and washed with diethyl ether and dried at 60°C for 12 h. 2.2. Characterization of ferrocene heterogenized SBA-16 Nitrogen adsorption-desorption isotherms were generated at liquid nitrogen temperature with an ASAP 2020 adsorption analyzer supplied by Micromeritics. The pore size distribution curves were calculated using BJH equation from the analysis of adsorption branch of isotherm. X-ray diffraction patterns were recorded using a Rigaku, Multiflex, diffractometer with a nickel filtered CuKa radiation in the 29 ranges from 0.5 to 3° for the estimation of SBA-16 textural parameters. The FT-IR spectra for propylamine and ferrocene functionalized SBA-16 samples were obtained over a range of 400-4000 cm "' on a Shimadzu FT-IR spectrophotometer. 2.3. Catalytic activity studies Benzene hydroxylation reactions were performed in a sealed glass reactor at room temperature, as described by Li et al [2]. In a typical experiment, 0.5 g of catalyst, 12.84 mmol of benzene, 4.28 mmol of 30% aq. H2O2 (H2O2/Benzene = 3) and 25 ml of 0.025 M H2SO4 were loaded prior to seal the reactor. The product samples were collected every 1 h and analyzed by gas chromatography equipped with a capillary column (DB-1). The product identification was made by GC-MS.

649

3. Results and Discussion The designed Schiff s base containing ferrocene heterogenized SBA-16 was synthesized as shown in Scheme 1, wherein the propylamine functionalized SBA-16 was directly synthesized by using F127 as structure directing agent, sodium metasilicate nonahydrate as silica source and 3-aminopropyltrimethoxy silane as the source of propylamine anchoring group.

NH2

N O

F127 H2O HCl SMS APTMS

Fe

Fe Toluene *Room Room Temp. Temp.

+ Si

Si O

O

C H

O

O

O O

SBA-16 Silica Wall

SBA-16 Silica Wall

Scheme 1: Schematic representation of ferrocene heterogenization, SMS: Sodium metasilicate, APTMS: Aminopropyltrimethoxysilane

(a)

(B) (B)

Inntens tensity (a. u)

(A)

l'

CD

(b)

Ail

1 ——-——'(b)b)

dV / dD

V o l u m e o f N2 a d s o r b e d ( c m 3/ g , S T P )

Ferrocene heterogenized SBA16 was obtained by tethering of amine and aldehyde groups of propylamine functionalized SBA-16 and ferrocenecarboxaldehyde respectively (Scheme 1). The nitrogen adsorptiondesorption isotherms of type IV with HI hysteresis loops and the highly intense low angle XRD patterns revealed the high quality of propylamine functionalized and ferrocene heterogenized SBA-16 materials.

(a)

(a)

(b) 0

50

100

150

200

Pore diameter (Angstrom)

0.0

0.2

0.4

0.6

0.8

Relative Relative Pressure Pressure (p/Po) (p/Po)

1.0 1.0

0.5

1.0

1.5

2.0

2.5 2.5

3.0

ao

22theta(degree) theta (degree)

Fig. 1 (A) N2 sorption isotherms (B) low angle XRD patterns (a) propylamine (b) Ferrocene functionalized SBA-16

650 (b) -CH2-

Intensity (a. u.)

The propyl chain attachment in propylamine functionalized SBA-16 and ferrocene heterogenized SBA-16 was confirmed by IR spectroscopy. The well resolved C-H stretching band at 2927 and 2857 cm "" represent the aminopropyl functional group attachment, which are shown in Fig. 2. Similarly, the presence of aminopropyl groups have been identified by several authors by the appearance of these absorption bands[7, 8].

(a) -CH2-

0

1000 1000

2000 2000

3000 3000

4000 4000

Wavenumber cm cm-1 -1

Fig. 2: FT-IR Spectra of (a) propyl amine and (b) ferrocene functionalized SBA-16

4. Conclusion Ferrocene heterogenized SBA-16 catalyst has successfully been synthesized in a single step using aminopropyl functionalized SBA-16 and ferrocenecarboxaldehyde and it was found that this novel heterogeneous catalyst is highly active towards the direct hydroxylation of benzene to phenol. 5. Acknowledgement The authors gratefully acknowledge the Asia 3 (A3: Korea, Japan and China) foresight program of Korea Science and Engineering Federation (KOSEF) 6. References [1] H. Yang, X. Chen, W. Jiang and Y. Lu, Inorg. Chem. Commun., 8 (2005) 853. [2] L. Li, J. Shi, J. Yan, X. Zhao and H. Chen, Appl. Catal. A, 263 (2004) 213. [3] I. C. Chisem, J. Chisen, J. S. Rafelt, D. J. Macquarrie, J. H. Clark and K. A. Utting, J. Chem. Technol. Biotechnol 74 (1999) 923. [4] J. He, H. Ma, Z. Guo, D. G. Evans and X. Duan, Topics in Catal. 22 (2003) 41. [5] A. K. Uriarte, M. A. Rodkin, M. J. Gross, A. S. Kharithonov, G. I. Panov, Stud. Surf. Sci. Catal. 110(1997)857. [6] Y. K. Hwang, J. S. Chang, Y. U. Kwon and S. E. Park Micropor. Mesopor. Mater. 68(2004) 21. [7] T. Ishikawa, M. Matsuda, A. Yasukawa, K. Kandori, S. Inagaki,T. Fukushima and S. Kondo, J. Chem. Soc, Faraday Trans. 92 (1996) 1985. [8] Z. Luan, J. A. Fournier, J. B. Wooten and D. E. Miser, Micropor. Mesopor. Mater. 83 (2005) 150.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

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Naphthalene alkylation with i-PrOH over bimodal mesoporous catalysts containing alumina Fang Liua'b, Jihong Suna* ,Quansheng Liub and Haibo Jinc "Department of Chemistry and Chemical Engineering, College of Environmental & Energy Engineering, Beijing University of Technology, Beijing, 100022, P. R. China 1 'Applied Chemistry,college of Chemical Engineering, Inner Mongolia University of Technology, Huhhot,Inner Mongolia, 010062, P. R. China 1 Beijing Institute of Petrochemical Technology

1. Introduction 2, 6-naphthalene dicarboxylic acid (2, 6-NDCA) can be obtained by oxidizing 2, 6-diisopropylnaphthalene (2, 6-DIPN), which can be used to make high quality polyester and thermo-tropic liquid polymer (LCP) [1, 2]. 2, 6-DIPN can be synthesized by naphthalene and i-PrOH over zeolites. But products of the isopropylation of naphthalene are very complicated, and the selectivity of 2, 6-DIPN is usually lower than other products. Therefore, it is very important to research the increasing of the selectivity of 2,6-DIPN and search for a new chemical material as the catalyst of appropriate operation conditions in order to improve the quality of naphthalene alkylation which have a better activity and stability. The usually used zeolites are easily to lose its activity for coking. So people are looking for a new catalyst to overcome the limitations. Wellconnected pores and a combination of independently controlled smaller and larger pore sizes would be very beneficial in, for example, reducing or eliminating transport limitations in catalysis, while simultaneously taking full advantage of the high intrinsic reaction rates per unit catalyst mass [3]. In this paper, the novel bimodal mesoporous molecular sieves (BMMs) incorporated of aluminum into the framework has been synthesized, and naphthalene alkylation with z-PrOH over Al-BMMs has been investigated.

652

2. Experimental Section First, the BMMs were synthesized according to the literature [3]. For postsynthesis modification, BMMs were reacted with different Al salt, namely AICI3, A12(SO4)3, A1(NO3)3, A1(OC3H7)3. we carried out as follows: 2 g BMMs were dried by air at 120°C for 2 h, then transferred into a 500 ml roundbottomed flask about 100 ml of a solution which contained the necessary amount of the Al ion. The mixture was stirred for 24 h. After filtered off, washed with distilled water, and dried at 150°C for 2h, the final materials containing Al ion were prepared. Nitrogen adsorption-desorption isotherms were measured using a Micromeritics ASAP 2010 system. Pore size distributions were obtained from the N2 desorption branch isotherm using BJH method. The Temperatureprogrammed desorption of ammonia (TPD) of samples was carried out in a CHEM BET-3000 instrument. The catalytic activities of the prepared samples with different Al loadings were tested for naphthalene alkylation with /-PrOH. 3. Results and Discussion cb

a

A

B d

b

e f

c a

d 1

3

5

θ /° 2 26/°

7

9

1

3

5 5

7

9

2 θ /° 26/°

Fig. 1. XRD patterns of BMMs. (A) different Al source: a: A1C13, b: A12(SO4)3, c: A1(NO3)3, d: AI(PiO)3; (B) different Si/Al molar ratio: a: pure SiO2, b: 20, c: 40, d: 60, e: 80, f: 100.

As shown in Figure 1, all samples appeared two diffraction peaks at two theta of around 2° and 4 ~ 6°, indicating the typical hexagonal mesoporous structure. For all samples, the decreasing in intensity of lower angle peaks with different Al salt in Fig.lA was as following order: A1C13> A12(SO4)3> A1(NO3)3> AIP, showing that the degree of long-scale order was decreased. On the other hand,

653 653

b

A

B

b

a

a

c

c d

d e

0

100 100 200 200 300 300 400 400 500 500600 600 T(°C) T(°C)

00

200 100

300 200

400 300

500 400

600 500

100 600

T(°C)

Fig. 2. TPD patterns of BMMs. (A) different Al source: a: AlCl3, b: AI(PiO)3, c: Al(NO3)3, d: A12(SO4)3; (B) different Si/Al molar ratio: a: pure SiO2, b: 20, c: 40, d: 60, e: 80, f: 100.

intensity of the diffracting peaks of two theta of around 2° in Figure IB decreased gradually with increasing Al content, implying the decrease of the long-distance order. On the basis analysis of nitrogen adsorption/desorption isotherms of BMMs and corresponding pore size distributions (not shown), it clearly indicates that there are two pores of Al-BMMs: around 3nm and 20nm respectively. Because the type of acid site could affect the catalytic Table 1 Catalysis data of all samples for reactions, it is preferable to naphthalene alkylation with i-PrOH measure these acid sites Yield(%) of individually. The measured TPD Sample was shown in Figure 2 2, 6-DIPN quantitatively. The BMMs AIP/BMMs-20 6.95 containing different Al source (in Figure 2A) and different Al A1(NO3)3/ BMMs -20 5.01 content (in Figure 2B) showed a A1 (SO ) / BMMs -20 5.07 2 4 3 broad peak at below 500 °C, 7.30 which was characteristic of AlCy BMMs -20 ammonia desorption from acidic A1C13/ BMMs -40 5.12 centers, however, desorption peak 4.49 at any high temperature was not AICI3/ BMMs -60 shown. Further, the two peaks A1C13/ BMMs -80 4.11 were centered at about 250°C and AICI3/ BMMs -100 3.48 440°C, respectively, which

654

indicated that acid sites of two different strengths were present on the catalyst surface with different Al amounts. As shown in Table 1, the BMMs of different aluminum source synthesized have greatly difference on Naphthalene alkylation with i-PrOH. The sequence of activity of samples was as following that: A1C1 3 /BMMS>A1P/BMMS> Al2(SO4)3/BMMs ~ Al(NO3)3/BMMs, on the other hand, obviously, the yields of 2,6-DIPN product were increasing with the increasing aluminum content of BMMs. It indicated that the activity of catalyst not only depend on its acid amount but also its porous structure and acid distribution. The influence of various reaction parameters such as reaction temperature, reactant feed ratio and catalyst amount, and the affecting activity of Al-BMMs, are being investigated 4. Conclusion The Al-BMMs with different nSi/nAl ratios and different salts as alumina source have been synthesized. The Al-BMMs catalyst by using A1C13 salt as Al source and, Si/Al of 20 shows the best activity for naphthalene alkylation. The influence of various reaction parameters and related mechanism are under way. 5. Acknowledgement We thank the Natural Science Fundation of Beijing (No.2063024), the Excellent Oversea Chinese Scholars Fundation of the Personal Ministry of the Chinese Government and the Natural Science Fundation of Ningxia Hui Autonomous Region (ZD02) for the financial support. 6. References [1] A. D. Schmitz and C. Song, Prepr. pap.-Am. Chem. Div. Fuel. Chem., 39 (1994) 985. [2] S. F. Newman, Pantent No. US5000312 (1991). [3] J. H. Sun, Z. Shan, J. A. Moujin and M. O. Coppens, Langmuir, 19 (2003) 8395.

Recent Progress in Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

655 655

Synthesis and application of MCM-41 molecular sieves modified by lanthanum in oxidation of cyclohexane Wangcheng Zhan, Yanglong Guo*, Yanqin Wang, Yun Guo and Guanzhong Lu* Lab for Advanced Materials, Research Institute of Industrial Catalysis, East China University of Science and Technology, Shanghai 200237, P.R. China

1. Introduction Since the scientists in Mobile Corporation synthesized the M41S molecular sieves in 1992 [1], the mesoporous MCM-41 materials has attracted much attention on their interesting structures and potential applications in various fields. However, the purely siliceous molecular sieve is hardly effective for the catalytic reactions, so it is essential to functionalize the purely siliceous molecular sieves by the introduction of heteroatoms, such as B, Ga, Ti, V, Cr and Co [2-4]. However, the structural and catalytic properties of mesoporous molecular sieves modified by La are unclear. In this paper, MCM-41 molecular sieves modified by La were synthesized and characterized by XRD, UV-Vis, N2 adsorption, and 2 Si MAS NMR. Their catalytic behaviors for the cyclohexane oxidation by molecular oxygen as oxidant were firstly investigated in detail. 2. Experimental Section The synthesis procedures of MCM-41 molecular sieves modified by La were similar to those described in the literature [5], and ethamine was used as alkaline source. The molar composition of the synthesis solution was SiO2: 0.2CTAB: xLa: 0.6EA: 120H2O (where JC=0.02, 0.04 or 0.06). The samples prepared were denoted as La-MCM-41-x, where x is the La/Si molar ratio in the synthesis solution. In the oxidation of cyclohexane, 9 g cyclohexane and 0.3 mmol H2O2 (used as initiator) were mixed with La-MCM-41 catalyst, and heated to 140°C at 0.5 MPa O2. The reaction products were analyzed by Perkin-Elmer Clarus 500 gas

656

chromatograph (PE-2, 25m><0.32mmxl.0nm). After the first run, the catalyst was separated and regenerated at 823 K for 6 h, and used for the subsequent recycling runs. 3. Results and Discussion

tensity ((CPS) Intensity

The XRD patterns of La-MCM-41 samples are shown in Fig. 1. All the samples exhibit the typical diffraction peaks of MCM-41 [1]. It shows that the structure of MCM-41 retains and ordered degree of pore channel array decreases after the direct introduction of La into pure silica MCM-41. The unit cell parameters (a 0 ) are listed in Table 1. The a 0 value of La-MCM-41 is larger than that of pure silica MCM-41, and increases with increasing La/Si molar ratios in the matrix gels. As the radii of La3+ cation (103.2 pm) is larger than that of Si4+ cation (26 pm), and when La cations are incorporated into the framework of MCM-41, its unit cell parameter will increase. In addition, no diffraction peaks of La 2 O 3 crystal appears in the high-angle XRD patterns of La-MCM-41 samples (data not shown). The results above indicate that La3+ cations may be incorporated into the framework of MCM-41. The N 2 adsorption-desorption isotherms of all samples show the IV type isotherms, which is characteristic of the mesoporous materials. The textural properties of all samples are shown in Table 1. With an increase in La content, the pore size of La-MCM-41 increases, which is attributed to the larger radii of La 3 + thanthatofSi 4 + [6]. The FT-IR spectra of La-MCM-41 are similar to those described in the literature [5]. The absorption peak at -1080 cm'1 is assigned to vas(Si-O-Si). The absorption peak around 960 cm"1 can be observed for pure silica MCM-41 and La-MCM-41, and assigned to the stretching vibration of Si-O in the Si-O"-R+ groups, that is, v^Si-OH) vibration present in the framework of MCM-41. With an increase in La content in the samples, the absorbance intensity of peak at 960 cm"1 decreases, which implys that part of Si-O"-R+ or Si-OH groups were

1

K J

//h 1 \ A ^. —-— 22

4

1 /\

\ 2 3

\ 2 292 > 252 292

4 \5 ^

11 2 3 4

6

8i

2θ 2θ (degree)

Fig.l XRD patterns of Si-MCM-41(1), LaMCM-41-0.02 (2), La-MCM-41-0.04 (3) and La-MCM-41-0.06 (4).

200

250

300

350

400

450

500

Wavelength (nm)

Fig.2 UV-Vis spectra of SiO 2 -La 2 O 3 (l), SiMCM-41(2), La-MCM-41-0.02(3), LaMCM-41-0.04(4) and La-MCM-41-0.06 (5)

657 Table 1 Textural properties of Si-MCM-41 and La-MCM-41 samples Sample Si-MCM-41 La-MCM-41-0.02 La-MCM-41-0.04 La-MCM-41-0.06

flo(A)

ratio 0 0.021 0.031 0.048

45.5 46.4 47.0 48.6

Surface area (m2/g) 838 782 542 563

Pore volume (cmVg) 0.70 0.68 0.50 0.59

Wall thickness

Pore diameter

(A)

(A)

33.3 34.8 36.7 38.1

12.2 11.6 9.7 10.5

transformed to Si-O-La bonds. The above results indicate that La + species may be incorporated into or attached to the framework of MCM-41. The UV-Vis spectra of the powder mixture of La2O3 and SiO2 (SiO2-La2O3), Si-MCM-41 and La-MCM-41 are shown in Fig. 2. There are a strong absorption peak at 210 nm and a shoulder peak at 230 nm for SiO2-La2O3, and no peak for pure silica MCM-41. There are two distinct adsorption peaks for La-MCM-41, a large peak at 252 nm is due to the tetra-coordinated La + species in the framework and a small peak at 292 nm is assigned to hexa-coordinated La3+ species in the extraframework oxide clusters. Moreover, the intensity of the absorption peak at 252 nm increases with an increase of La content in the synthesis gel, which indicates that most of La cations may be incorporated into the framework of MCM-41 and a few La cations may be attached to the framework of MCM-41. 80 70 60 50

2

40

Selectivity (%)

Conversion (%)

4

30

0

20 0

2

4

6 8 Time (h)

10

12

Chemical shift (ppm) Fig.3 29Si MAS NMR spectra of MCM-41(1), La-MCM-41-0.02(2), La-MCM-41-0.04 (3) and La-MCM-41-0.06 (4)

Fig.4 Effect of reaction time on the conversion and selectivity of cyclohexane oxidation over La-MCM-48-0.02. Conversion (D); selectivity of cyclohexanone (•) and cyclohexanol ( • ) .

The 29Si MAS NMR spectra of Si-MCM-41 and La-MCM-41 samples are shown in Fig. 3. The peaks around -110 ppm are assigned to (-O-^Si groups (Q4). The peaks around -99 and -90 ppm are usually assigned to (-O-)3SiOH groups (Q3) and (-O-)2Si(OH)2 groups (Q2), respectively. The intensities of Q3 and Q2 for La-MCM-41 are lower than that for Si-MCM-41. The Q4 around 113 is also present for pure silica MCM-41. However, an additional peak at 120 ppm can be observed in the spectra of La-MCM-41 and its intensity increases with an increase in La content in the synthesis gel, which seems to be

658

attributed to the incorporation f La into the MCM-41 matrix, resulting in the dramatic changes in the Si coordination sphere [7]. Table 2 shows the performance of La-MCM-41 catalyst for the oxidation of cyclohexane. In all cases, the products are only cyclohexanol and cyclohexanone. It is interesting that the catalytic activity of catalyst increases at the second run compared with the first run, and its activity is nearly unchanged even after several runs. Those may be attributed to two reasons, firstly, the catalyst structure rearranged to more ordered mesostructure after the first run (confirmed by the XRD test); secondly, the leaching of La species in the extraframework position leads to more accessible for the reactants to the active sites. Thus, it is concluded that the La3+ species in the framework of MCM-41 may play an important role in the oxidation of cyclohexane. Fig. 4 shows effect of reaction time on cyclohexane oxidation over La-MCM41-0.02 catalyst. The conversion of cyclohexane increases with increasing reaction time until 9 h, and reaction temperature up to 428K (data not shown). Table 2 The performance of La-MCM-41 catalyst for the oxidation of cyclohexane Catalyst Si-MCM-41 La-MCM-41-0.02 2drun 3th run La-MCM-41-0.04 La-MCM-41-0.06

La content (wt. %) 5.17 4.23 4.02 7.87 11.7

Conversion (%) — 1.3 3.4 3.4 2.2 3.8

Selectivity (%) Cyclohexanone Cyclohexanol — — 38.7 61.3 41.5 58.5 40.5 59.5 40.2 59.8 38.7 61.3

4. Conclusion La-MCM-41 was successfully prepared by the direct hydrothermal method. The characterization results show that La species may be incorporated into or attached to the framework of MCM-41. La-MCM-41 is an efficient catalyst for the oxidation of cyclohexane by molecular oxygen. This project was supported financially by National Basic Research Program of China (2004CB719500), Shanghai Rising-Star Program (04QMX1431) and Program for Outstanding Young Teacher of Shanghai Universities (04YQHB050). 5. References [1] [2] [3] [4] [5] [6] [7]

C.T. Kresge,M.E. Leonowicz,WJ. RothJ.C. Vartuli and J.S. Beck, Nature, 359 (1992) 710. U. Oberhagemann,I.Kinski,I.Dierdorf,B. Marler,H. Gies,J.Noncryst. Solids., 197 (1996) 145. Y. X. Zhi, A. Tuel, Y. Ben Taarit and C. Naccache, Zeolites, 12 (1992) 138. P. T. Tanev, M. Chibwe and T. J. Pinnavaia, Nature, 368 (1994) 321. L. Chen, T. Horiuchi, T. Mori and Kazuyuki Maeda, J. Phys. Chem. B, 103 (1999) 1216. S. C. Laha, P. Mukherjee, S. R. Sainkar and R. Kumer, J. Catal., 207 (2002) 213. W. Z. Zhang and T. J. Pinnavaia, Catal. Lett., 38 (1996) 261.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

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Microwave synthesis of Fe-SBA-16 mesoporous silica and Friedel-Crafts type reaction Dae-Soo Han, Sujandi, Jeong-Boon Koo and Sang-Eon Park Lab.ofNano-Green Catalysis, Nano Center for Fine Chemicals Fusion Technology Dep't of Chemistry, Inha University, Incheon 402-751, Korea

Iron-substituted SBA-16 materials have been synthesized by using direct microwave synthesis method under weak acidic conditions. Different iron species including isolated framework iron species, iron cluster and iron oxides were formed by adjusting the pH value and Si/Fe molar ratios. All the materials has been characterized by XRD, N2 sorption and SEM. Lewis acid catalyzed Friedel-Crafts type alkylation reaction of benzene with benzylchloride has been investigated over Fe catalysts prepared with different pH values and iron contents. 1. Introduction Mesoporous silica materials have opened many new possibilities for the applications in catalysis, separation and adsorption [1]. Due to the inert surface of silica, mesoporous materials have been suffered from lack of active sites, which are inevitable for adsorption or catalysis application. Hence, the incorporation of transition metals into the framework of silica has been considered as an indispensable requirement. Incorporation of trivalent metals atom into mesoporous framework could create Lewis acidity, which could play a key role in catalytic activities and adsorption properties [2]. Iron(III)substitution could generate the redox as well as acidic properties which gave catalytic activities in the Friedel-Crafts alkylation, acylation and oxidation reactions [3]. SBA-16 silica materials with three-dimensional pore systems could be more resistant to pore blocking and allow a faster diffusion of reactants than one-dimensional mesoporous materials. Many groups including our groups have used microwave synthesis method for the nanoporous materials, for example zeolite-A and-Y, ZSM-5, MCM-41, and SBA-16. Microwave synthesis has many advantages, such as rapid synthesis, the possibility of

660

selective heating of desired materials, homogeneous nucleation, and short crystallization time [4]. In this work, iron-substituted SBA-16 materials have been synthesized by using microwave irradiation under weak acidic conditions, wherein, different amounts of framework iron could be introduced. The catalytic activities of obtained Fe-SBA-16 catalysts were tested for the Friedelcrafts type alkylation benzene with benzylchloride. Indeed this Friedel-Crafts reaction is very important reaction both in laboratory and in industry for the synthesis of pharmaceutical intermediates. It was found that the catalytic activities seemed to be ascribed to the Lewis acid sites generated by the framework-substituted iron registered a quantitative conversion and a very high selectivity with small amounts of catalyst and relatively short reaction times. 2. Experimental Section Fe-SBA-16 mesoporous materials were prepared according to following procedure. The triblock copolymer Pluronic F127 was dissolved in deionized water and then certain amount of sodium metasilicate was added till getting the clear solution. To this solution, concentrated hydrochloric acid was quickly added with vigorous stirring to obtain a gel. To this gel solution, Fe(acac)3 was added under constant stirring for 1 hour and then adjusted required pH and continued the stirring for further 1 h at 313 K to get the reactive gel before moving to microwave digestion system at 373 K. All the materials have been characterized by XRD, N2 sorption, ESR spectra and SEM. 3. Results and Discussion Fig.l shows the XRD patterns of the calcined Fe-SBA-16 samples which were prepared by microwave synthesis at different pH values (Si/Fe molar ratio = 128 in the gel). -pH2 -pH3 PH4

Magnetic Field

2 Thcta(e)

Fig. 1 Powder XRD patterns of calcined Fe-SBA-16 samples (Fe/Si=128 in the initial gel) with different pH values.

Fig. 2 ESR spectra of calcined Fe-SBA-16 with different pH values

All the XRD patterns show well-ordered mesoporous structures, in which, sharp (110) reflection and other weak peaks collectively interpreted the

661

formation of cubic SBA-16 phase. The coordination environment of Fe in the calcined samples was studied by ESR spectroscopy. The ESR spectra of FeSBA-16 sample prepared by microwave method with different pH values are shown in Fig. 2, wherein, two signals, at g = 2.0 and 4.3, were clearly seen. The ESR signal at g = 2.0 is usually attributed to Fe3+ ions in octahedral coordination as iron oxide clusters. The line at g = 4.3 is typically assigned to tetrahedrally coordinated Fe3+ ions. The tetrahedral coordinated Fe3+ species were supported by the UV-Vis spectra in which showed strong adsorption peak at 210-250 nm. The porosities of Fe-SBA-16 samples were measured by N2 sorption. The N2 sorption isotherms of all the calcined samples show the type IV full isotherm with hysteresis loops (Fig. 3a) characteristic for the cage type pore structure of SBA-16. Analyses of the data in pressure (P/Po) of 0.04-0.25 a BET surface area of 761 m2.g"'. The pore size distributions calculated by BJH equation from desorption branches represented the cagelike pore structures of SBA-16 with the cavity diameter of the spherical cage of 3.6 nm. SEM analysis revealed that the Fe-SBA-16 catalysts prepared with different pH values have the basic cubic structure with slight variations. Among them, synthesized Fe-SBA-16 at pH2 had the clear cubic morphology (Fig. 3b).

sj Relative Pressure (

I

pH2 pH3 pH4

Pore Diameter A

Fig. 3 (a) Nitrogen adsorption-desorption isotherm and (b) Pore size distributions for calcined Fe- SBA-16 samples with Si/Fe molar ratio = 128 in the initial gel; (c) SEM image of Fe-SBA16 samples with Si/Fe molar ratio =128 prepared at pH = 2.

The liquid-phase benzylation of benzene catalytic activity over Fe-SBA-16 catalyst with molar ratio (Si/Fe = 128) prepared from different pH values. The products obtained were diphenylmethane and other isomers with high selectivites on diphenylmethanes. Fig.4 shows the conversion of benzylchloride with reaction time on Fe-SBA-16 samples at 343 K. All the catalysts showed around 100% conversion and selectivity 95 ~ 100% for diphenylmethane at reaction times of 180 min. From the catalytic activities have been studied, among which, Fe-SBA-16 prepared at pH value of 2 showed the highest activity. These results clearly indicated that framework-substituted the cubic structure of SBA-16 played a vital role in the reaction of benzylation of benzene both in

662

conversion and selectivity. The well-formed cubic structure appeared in the SEM of Fe-SBA-16 prepared at pH 2 gave higher catalytic activity. The used catalyst was regenerated by washing three times with absolute acetone followed by drying overnight in an oven at 373K and activated at 773K for 4h under air flow. The activity of the regenerated catalyst was determined in two repeated cycles and gave slightly a marginal decreases in conversion.

^~, 80 80-

Conversion(% )

a

— 0 0 ppH2 H2 — • — ppH3 H3 pH4 — 0 p H 4

l~

100

/'

\^ Conversion(% )

100

Ia

60

•

40

b

- First Run Run - Second Run Run

80

60

40

20

20 20

0

0

10min

30min

60min

90m in

120min

Time(min)

150min

180min

10min

30min

60min

90min

120min

150min

Time(min)

Fig. 4 a) Effect on pH values (•) Fe-SBA-16 (pH2), (•)Fe-SBA-16(pH3), (A)Fe-SBA-6(pH) b) Repeatability of catalyst f«)First run and (•) Second run.

However, these catalysts seemed to be eco-friendly heterogeneous conditions for the benzylation of benzene.

and reusable in

4. Conclusion Fe-substituted mesoporous silica SBA-16 catalysts with highly ordered structures of cubic phase were successfully synthesized under mild acidic conditions using microwave. And particularly, Fe-SBA-16 prepared at pH2 showed more well ordered morphological and remarkable catalytic activity for the liquid-phase benzylation of benzene. These activities of Fe-SBA-16 were described to the framework substituted of iron and could be eco-friendly and recyclable. 5. Acknowledgment The authors gratefully acknowledge BK21 (Brain Korea 21). 6. References [1] Y. K. Hwang, J.-S. Chang, Y.-U. Kwon and S.-E. Park, Micro. Meso. Mater., 21 (2004) 68. [2] Y. Li, Z. Feng, Y. Lian, K. Sun, L. Zhang, G. Jia, Q. Yang and C. Li. Micro. Meso. Mater., 41 (2005) 84. [3] V.. A. Krithiga, T. Murugesanand V. Hartmann, M. Adv, Mater, 16 (2004) 1817. [4] D. S. Kim, S.-E. Park, Sayari, M. Jaroniec and T J. Pinnavaia. Nanoporous Materials II, Stud. Surf. Sci. Catal.,. 129 (2000) 107.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Published by Elsevier B.V.

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Photocatalytic oxidation of phenylsulfonephthalein by hydrogen peroxide over Ti containing SBA-15 mesoporous materials Phuong T. Dang *a, Tuan A. Vu a, Thang C. Dinh a, Yen Hoang a, Thang G. Vuong b, Thang V. Hoang a, Hoa K.T. Tran a, Lan K. Lea and Phu H. Nguyen a "Laboratory of Surface Science and Catalysis(LSSC), Institute of Chemistry, Vietnamese Academy of Science and Technology, 18 Hoang Quoc Viet, Cau Giay, Hanoi, Vietnam Department of Chemical Engineering, Laval University, Quebec G1K 7P4 Canada.

Titanium containing SBA-15 mesoporous materials were synthesized by two methods-direct synthesis (denoted as Ti-SBA-15) and post-synthesis (Ti/SBA15). All the synthesized samples were characterized by XRD, BET and UV-Vis techniques. Interestingly, by direct synthesis, titanium was almost incorporated into SBA-15 framework in the form of tetrahedral coordination while by postsynthesis, titanium was well dispersed onto the surface of SBA-15, existed as extra - framework sites. Ti-SBA-15 and Ti/SBA-15 materials were used as photo - catalysts in oxidation of a bulky molecule phenylsulfonephthalein (red phenol) by using hydrogen peroxide as oxidant. Both samples exhibited high catalytic activity. However, framework Ti sites were more active than extraframework Ti ones. 1. Introduction SBA-15 material is a novel mesoporous siliceous one that is prepared using tri-block copolymer as template [1]. This material has attracted much attention of many researchers and engineers working in the field of adsorption and catalysis because it has the large pore, thick walls, and consequently, a high hydrothermal stability. Due to its electrically neutral framework, the purely siliceous SBA-15 cannot of course become acidic or redox catalysts. Hence, the incorporation of some chemical elements such as Al, V, Fe, Ti,... into the framework of siliceous SBA-15 enables to create active sites onto SBA-15 surface has been widely studied. [1-5]. In present work, titanium was introduced into siliceous SBA-15 by two methods - direct synthesis and post-synthesis.

664

Catalytic properties of obtained catalysts in photocatalytic oxidation of phenylsulfonephthalein were illustrated and discussed. 2. Experimental Section

I n t e n s i ty

The procedure of synthesis Ti-SBA-15 materials (atomic Si/Ti ratio of 100) was as follows: 15 g P123 was dissolved in the solution of 112.5 ml H2O and 450 ml HC1 (2 M). The solution containing Ti in isopropanol (/C3H7OH) was added to 31.87 g of TEOS to form homogeneous mixture and then this mixture was added dropwise to the solution containing PI23. The obtained mixture was vigorously stirred for 2 h at 313 K and then 100 moderately stirred for 24 h and hydrothermally 100 treated at 353 K for 24 h. The solid product was 110 200 200 filtered, washed, dried in air and then calcined at Ti/SBA-15 773 K for 10 h. Ti/SBA-15 samples were prepared by post-synthesis: Purely siliceous SBA-15 was J Ti-SBA-15 impregnated with the equivalent amount of the above titanium solution (as used for preparation of 2-Theta (degree) Ti-SBA-15). The product was dried under N2 flow at the room temperature and then calcined at 773K Figure 1. XRD patterns of for 5h. Ti containing SBA-15 were characterized Ti/SBA-15 and Ti-SBA-15 by XRD, BET, UV-Vis techniques. Ti-content in Ti-SBA-15 and Ti/SBA-15 determined AAS was the same (0.8 wt%). Red phenol photocatalytic oxidation process Ti/SBA-15 was carried out under conditions: ambient temperature, 0.05 g catalyst, 500 ml aqueous red phenol solution of 50 mg/1 and 0.6 ml H2O2 30 wt. Ti-SBA-15 % as oxidant, irradiation with flow rate of 2 1/h. 0 0.2 0.4 0.6 0.8 1 Irradiation source is a 400W medium pressure P/Po mercury lamp. Concentration of red phenol was Figure 2. N2 isotherm of determined by colorimetric method on Ti/SBA-15 and Ti-SBA-15 spectrophotometer 722 with A, = 430 nm. 1

2

3

4

5

V o l u m e a d s o rb e d (c c / g )

0

3. Results and Discussion The XRD patterns of Ti-SBA-15 and Ti/SBA-15 \ \ samples (Figure 1) presented the three peaks corresponding to the (100), (110), and (200) reflections associated with p6mm hexagonal symmetry and highly ordered mesostructure. Figure 2 presented the N2 adsorption - desorption isotherms of Ti-SBA-15 and Ti/SBA-15 samples. Figure 3. UV-Vis spectra of From N2 isotherms and pore size distribution (not Ti/SBA-15 and Ti-SBA-15 400 QOO "Wavelength (nm)

665

Conversion (%)

showed here) of these samples, the hysteresis loops that typically featured the kind of mesoporous materials were observed Ti-containing SBA-15 samples have the large pore size (68A for Ti-SBA-15 and 52A for Ti/SBA-15). In the UV-Vis spectra of Ti-SBA-15 and Ti/SBA-15 (figure 3), a relatively intense absorption band at ~270nm appeared in the spectrum of Ti/SBA-15 sample is assigned to the highly dispersed titanium 100 species. In the spectrum of Ti- SBA-15 an 80 absorption band at 214 nm is attributed to tetrahedrally coordinated titanium species in 60 Ti/SBA-15-in presence of UV the framework [2, 5]. Figure 4 plotted Ti-SBA-15 in presence of UV 40 conversion a as a function of reaction time. For Ti/SBA-15 in absence of UV Ti-SBA-15-in absence of UV both Ti-SBA-15 and Ti/SBA-15 catalysts 20 conversions of reaction were very high (95% and 99%, respectively). However, the Ti-SBA0 0 4 6 8 10 2 15 sample was more active than Ti/Sba-15 in Reaction time (h) both cases: in presence of UV and in absence of UV (in dark). This tentatively indicated that the Figure 4. Conversion of reaction on Ti/SBA-15, Ti-SBA-15 framework Ti was more active than the welldispersed. Figure 5 showed UV-Vis spectra of initial red phenol solution and reacted solution. In the UV-Vis spectrum of initial red phenol solution appeared two peaks: one at 264 nm and the other at 431 nm were characteristic of red phenol molecule [6], With increasing reaction time, the intensities of these peaks deceased. After 5 hours, those peaks were practically disappeared; it was shown that the molecular structure of red phenol was completely decomposed. However, UV-Vis spectra red phenol solution did not show the mineralization of organic compound when reaction time prolonged more 1h 431 than 5 hours. To analyze more profoundly the 0h 2h 264 evolution of reaction after 5 hours, the first 3h 5h order derivative spectrum method of UV-Vis spectrum was applied [7]. Figure 6 showed the significant difference in the first order Wave length (nm) derivative spectra of UV-Vis spectra after 5 and 9 hours of reaction. In the derivative spectra of Figure 5. UV-Vis spectra of initial Ti-SBA-15, the peak appeared at 200-210 nm red phenol and reaction products on which was characteristic of C=C and C=O Ti-SBA-15 bonds in the linear-chain organic acids formed by breaking of aromatic rings in red phenol molecule shifted to shorter wavelength compared to that observed on Ti/SBA-15. Moreover, the peak intensities for Ti-SBA-15 were always lower than those for Ti/SBA-15. From these results, it could be concluded that reaction products over Ti-SBA-15 catalyst contained organic compounds with smaller carbon number and smaller amount. This indicated that Ti sites existed in Ti-SBA-15 were more active than Ti/SBA-15-in presence of UV Ti-SBA-15 in presence of UV Ti/SBA-15in absence of UV

Ti-SBA-15-in absence of W

4.50 4.00 3.50 3.00 2.50 2.00 1.50 1.00 0.50 0.00

200

250

300

350

400

450

500

550

666

those in Ti/SBA-15. Thus, over Ti-SBA-15 most red phenol molecules were mineralized. 0.05 0.025 0 -0.025

Abs -0.05

Abs

-0.075

Ti-SBA-15

-0.1

Ti/SBA-15

-0.125 -0.15 200

225 225

250 250

275 275

300 325 300 325

nm

350

375

400

0.01 0 -0.01 -0.02 -0.03 -0.04 -0.05 -0.06 -0.07 -0.08 -0.09 -0.1 -0.11 -0.12 -0.13 -0.14 200

Ti-SBA-15

Ti/SBA-15

225 250 225 250

275 275

300 325 300 325

350 375 400 400 350 375

nm

Figure 6. First order derivative spectra of UV-Vis spectra of reaction product on Ti/SBA-15 and Ti-SBA-15 and Ti/SBA-15 samples

4. Conclusion Ti-SBA-15 and Ti/SBA-15 were successfully synthesized by direct synthesis and post-synthesis. Based on results obtained from XRD, BET, UV-Vis, it could be concluded that those samples have p6mm hexagonal symmetry and highly ordered mesostructure. By direct synthesis, titanium was almost incorporated into SBA-15 framework while by post-synthesis, titanium was well dispersed onto the surface of SBA-15, existed as extra - framework sites. Both Ti-containing SBA-15 samples were active in photocatalytic oxidation of red phenol. However, framework Ti sites were more active than extraframework Ti ones. 5. References [1] W. Stober and A. Fink, J. Colloid Interface Sci, 26 (1968) 62. [2] S.-M. Yang, S. G. Jang, D.-G. Choi, S. Kim and H. K. Yu, Small, 2 (2006) 458. [3] Y. Lu, Y.Yang, A.Sellinger, M. Lu, J. Huang, H. Fan, R. Haddad, G. P. Lopez, A. R. Burns, D. Y. Sasaki, J. Shelnutt and C. J. Brinker, Nature, 410 (2001) 913. [4] K. J. C. van Bommel, A. Friggeri and S. Shinkai, Angew. Chem. Int. Ed., 42 (2003) 980. [5] E. Dujardin and S. Mann, Adv. Mater., 14 (2002) 775. [6] S. Che, A. E. Garcia-Bennett, T. Yokoi, K. Sakamoto, H. Kunieda, O. Terasaki and T. Tatsumi, Nature Mater., 2 (2003) 801. [7] A. E. Garcia-Bennett, O. Terasaki, S. Che and T. Tatsumi, Chem. Mater., 16 (2004) 813. [8] S. Che, Z. Liu, T. Ohsuna, K. Sakamoto, O. Terasaki and T. Tatsumi, Nature, 429 (2004) 281. [9] J. N. Cha, G. D. Stucky, D. E. Morse and T. J. Deming, Nature 403 (2000) 289. [10] K. M. Hawkins, S. S.-S. Wang, D. M. Ford and D. F. Shantz, J. Am. Chem. Soc, 126 (2004)9112.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

667 667

Influence of the catalyst on the formation and structure of bimodal mesopore silica Xiaozhong Wanga*, Wenhuai Lib, Bing Zhongb andKechang Xiea " Key Laboratory of Coal Science and Technology, Ministry of Education and Shanxi Province, Institute of Special Chemicals, Taiyuan University of Technology, Taiyuan, 030024 China. State Key Laboratory of Coal Conversion, Institute of Coal Chemistry, the Chinese Academy of Sciences, Taiyuan, 030001 China.

1. Introduction In earlier investigations [1], we found that through controlling gelation other than precipitation of a reaction system which was used usually to prepare MCM-41 materials [2], a hierarchically structured porous silica gel monolith with well-defined bimodal mesopore size distribution (i.e. BMS) can be formed at ambient conditions. The unique bimodal mesostructure and fair thermal stability of BMS silica may find broad potential application in catalyst, catalyst supports, electronic, optical or sensing devices. Since the key to BMS silica synthesis is the gelation control of the reaction system, thus, any variation of the synthesis parameters all may influence the reaction kinetics of sol-gel alkoxides and then influences the mesostructure of the resultant BMS silica. In various synthesis parameters, the catalysts used undoubtedly are of the very importance, as that has been seen not only in the synthesis of conventional silica gels [3, 4], but also in the preparation of MCM-41 materials [5, 6]. For the reason, a study was conducted in our BMS silica synthesis employing various organic amines as catalyst to investigate their direct influence on the gelation and the bimodal mesostructure of the BMS silica produced. At the same time a full account of the trend of pore size adjustment of BMS silica was also given. 2. Experimental Section The synthesis of BMS silica followed the same procedures as previously reported [l(a), l(b)], except that the initially used mineralization agent

668

ammonia was replaced with some small molecule organic amines such as ethylamine (EA), n-butylamine (BA), n-hexylamine (HA), 1,2-ethanediamine (EDA), 1,4-butanediamine (BDA), 1,6-hexanediamine (HAD) for the hydrolysis and condensation of tetraethoxysilane (TEOS). The molar composition of the starting solutions was: 1.0 TEOS: 0.18 Ci6TAB (cetyltrimethylammonium bromide): (0.016-0.64) amine: 75 H2O. Gelation was determined visually by the fact that the solution no longer exhibited bulk fluid behavior. The resultant silica samples were characterized using XRD, N2 adsorption isotherms, SEM and TEM. 3. Results and Discussion Our preliminary tests under various sol-gel conditions show that the amount of the catalysts used in the starting compositions plays a key role in determining the morphology and the textural properties of the resultant silica materials. Fig. 1 shows the physical appearance of the sol-gel products prepared by various amounts of different amines addition with a constant other composition concentration. It is clear that three different typed of behavior can be classified, although these regions were significantly different for different amines used. Following the increase of the amount of amines used, the resultant silica products all change gradually from an initial opaque gel monolith via a viscous liquids between gel and precipitation (i.e. intermediate) to a rapid formed precipitation, as that has been seen in previous work [l(b)]. By way of convenient for comparing, the amount of different catalysts used is selected in such a region, typical as 0.064mol, to ensure the formation of a silica gel rather than precipitation. The relationship between the catalysts used and the gelling rate was investigated by measuring the time necessary for the solution to lose fluidity. This time, which we call gelation time, expressed in minutes after the addition of catalysts, is listed in Table 1. It is clear that the gelation times are influenced by the catalysts used in the synthesis, steeply decreasing with a increase of the carbon atom number in organic amine molecules, indicating a 0.064

0.064 Gel Intermediate

I ' ' I ' ' I 0. 192 0 . 3 3 4 0 . 5 7 6

I ' ' I ' ' I 0. 192 0. 384 0. 5 7 6

Precipitation

Molalkali/molTEOS Fig. 1 Appearance of sol-gel products prepared with various amount of different alkali catalysts

669 Table 1. Structure parameters of BMS silica prepared with different amines as catalyst

Catalysts

Gel

(2M)

Time (min)

Framework Mesopore A/BET 2

NH3

90

(m /g) 624.7

Textural Mesopore V,

(cmVg)

(nm)

(m /g)

(cm /g)

D, (nm)

0.64

2.90

337.3

0.85

12.60

vf

A,BET 2

3

EA

45

487.1

0.32

2.63

303.2

1.22

18.42

BA

40

500.6

0.33

2.74

344.4

1.28

18.52

HA

30

559.1

0.36

2.66

274.9

1.35

20.94

EDA

35

633.9

0.43

2.74

307.24

1.15

16.35

BDA

10

774.3

0.56

3.01

290.2

1.32

21.03

HDA

6

893.9

0.64

2.95

284.9

1.36

22.30

rapid increasing of condensation rate, which would accelerate the aggregates of micelle-encapsulated silica colloidal particles in the sol. The gelation times also imply a relative strength of each amine in acting as a catalyst for the condensation of the hydrolyzed alkoxide. Generally, the weaker the alkalinity strength of the catalysts used is, the wider the concentration range suitable to the formation of a homogeneous gelis. The characteristic results show that the qualitative form of the XRD patterns, N2 adsorption isotherms, SEM and TEM images of the calcined silica samples obtained with various mineralization agents all are similar to the previous reported BMS silica phase [1]. However, the positions of the XRD intense reflection, the adsorption steps at lower and higher p/p0 on N2 adsorption curves and thus the pore size distribution of the framework and textural mesopores along with the size and the packing geometry of primary silica particles vary with the catalysts used. The related structure parameters are listed in Table 1. It is found that the diamine catalysts are more favorable for the formation of a well-ordered framework mesopore than that of monoamine catalysts, especially in increasing the carbon atom numbers in amine molecules used. The reason causing this difference may be related not only to the alkalinity strength resulting from the intrinsic difference in structure and properties of these amine molecules, but also to their locus dissolved in the micelles. For the monoamine molecules, the increase of carbon atom numbers makes them easier to be solubilized in the palisade layer of micelles, which would make the surface charge density of micelles decease and thus weaken the interaction force between micelles and silicate species. On the contrary, the diamine molecules are better solubilized close to the surface in the palisade layer or by adsorption at the micelle-water interface, which would improve the surface charge density of micelles and thus strengthen the interaction between surfactant micelles and silicate species and finally result in a more well-defined ordered framework

670

mesopore to be formed. Compared with the previous synthesized BMS silicas [1], the decrease in the specific surface areas and the pore volumes of framework mesopores may be related to the lower alkalinity provided by the catalysts used. The present results also show that the textural mesopore size of resulting silicas is more sensitive to the variation of catalysts used than its framework mesopore size. Moreover, the textural mesopore volume can be up to 2.0 or more times as large as the framework mesopore volume, which is of great interest to catalysis because they greatly facilitate mass transport to the framework mesopore. The TEM images show that all samples consist of agglomerations or packing of approximately equal sized like-spherical nanometer silica particles with an average diameter of c.a.20-40nm, depending on the catalysts used, that are joined together to form agglomerates a few tens of microns in diameter. The textural mesoporosity originating from the cavities between close-packed particles increases gradually in the order of NH3-EDABDA-HDA and NH3-EA-BA-HA, which is consistance with the changes of the gelation times and the XRD and N2 adsorption results. The framework mesopores consist of randomly distributed hexagonal and wormhole-like mesoporous channels and there is no apparent long-range order to the pore arrangement. 4. Conclusion It is found that BMS silica can be synthesized using a series of organic amine as catalysts. However, due to the difference in the structure and properties of these catalysts used, not only is their concentration scope suitable to the BMS silica synthesis clearly different, but the gelation time, thus the surface area, pore volume and bimodal mesoporosity of the resultant BMS silica can be tuned by this variable over a suitable range. (NSFC Grant No.20371034) 5. References [1] (a) X. Z. Wang, T. Dou and Y. Z. Xiao, Chem. Commun., (1998) 1035. (b) X. Z. Wang, W. H. Li, G. S. Zhu, S. L. Qiu, D. Y. Zhao and B. Zhong, Micropor. Mesopor. Mater., 71 (2004) 87. (c) X. Z. Wang, T. Dou, Y. Z. Xaio and B. Zhong, Stud. Surf. Sci. Catal., 135 (2001) 199. (d) X. Z. Wang, T. Dou, D. Wu and B. Zhong, Stud. Surf. Sci. Catal., 141 (2002) 77. (e) X. Z. Wang, T. Dou and B. Zhong, Frontiers of Solid State Chemistry, World Sci Publ, (2002) 227. (f) X. Z. Wang, W. H. Li, T. Dou and B. Zhong, Stud. Surf. Sci. Catal., 146 (2003) 255. (g) X. Z. Wang, W. H. Li, B. Zhong and D. Y. Zhao, Stud. Surf. Sci. Catal., 154 (2004) 555. (h) X. Z. Wang, W. H. Li, J. Y. Lin, H. L. Fan, C. S. Tian, B. Zhong and K. C. Xie, Stud. Surf. Sci. Catal., 158 (2005) 257. [2] C.T. Kresge, M.E. Leonowicz, W.J. Roth, J.C. Vartuli and J.S. Beck, Nature 359(1992)710. [3] S. M. Jones, J. Non-Cryst Solid., 291 (2001) 206. [4] E. Framery and P. H. Mutin, J. Sol-Gel. Sci. Tech., 24 (2002) 191. [5] X. Z. Wang, T. Dou, Y. Z. Xiao and B. Zhong, J. Natural Gas Chemistry., 8 (1999) 216. [6] W. Lin, Q. Cai, W. Pang, Y. Yue and B. Zou, Micropor. Mesopor. Mater., 33 (1999) 187.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

671 671

Mesoporous zirconia with different pore size for Fischer-Tropsch synthesis Yachun Liuab, Jiangang Chena, Kegong Fangaand Yuhan Suna* "State Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan, 030001, China "Graduate School of the Chinese Academy of Sciences, Beijing 100039, China

1. Introduction Mesoporous silica have attracted widespread attention in cobalt-based F-T synthesis because of their high surface area, large pore size and narrow pore size distribution [1-5]. However, these materials possess surface silanol (Si-OH) groups that can interact with cobalt oxides, and consequently, are inclined to form the irreducible cobalt silicates species [3]. Therefore, seeking other mesoporous support is necessary to improve the reducibility and the F-T reaction performance of cobalt catalyst. In the present work, mesoporous zirconia with different pore size have been prepared according to our work reported previously [6] and have been investigated in F-T synthesis. It was found that the reducibility and the F-T reaction performances of the catalysts strongly depended on the pore sizes of mesoporous zirconia. Furthermore, the cobalt catalyst supported on such a mesoporous zirconia with the pore-size of 12.6 nm showed good catalytic performance in F-T synthesis. 2. Experimental Section The synthesis of mesoporus zirconia was carried out according to our work reported previously [6]. The overall molar composition of the final mixture was 1 Zr: (0 or 2) diglycol: 0.017 P123: 30 H2O: 90 ethanol. The as-synthesized samples were then calcined at 873 K for 4 h to remove the template. The resulting mesoporous zirconia were designated as PMZ-3, PMZ-5, PMZ-7 and PMZ-12 according to the pore size, respectively (shown in table 1). The cobalt catalysts (Co 10 wt %), denoted as Co/PMZ-3, Co/PMZ-5, Co/PMZ-7 and Co/PMZ-12, respectively, were prepared by incipient wetness impregnation. N2

672

adsorption/desorption isotherms of the samples were measured at 77 K on a Micromeritics Tristar 3000 sorptometer. X-ray diffraction (XRD) patterns of the samples were recorded on a Bruker B5OO5 diffractometer using Cu Ka radiation. TPR was carried out in a self-made U-tube quartz reactor at the ramp rate of 10/K min"1 in the 5 % H2/Ar (vol.) flow of 30/ml min"1. Catalysts were evaluated in a pressured fixed-bed reactor at 2MPa, lOOOh"1, 503 K and with the H2/CO ratio of 2 after reduction at 673 K for 6 h. The catalytic data were obtained after the reaction reached the steady state in a 24 hour. The gas effluents were analyzed by using Carbosieve-packed column with TCD. The gas hydrocarbons were analyzed using Porapack-Q column with FID. Oil and wax were analyzed in OV-101 capillary columns. 5 % N2 was added to syngas as an internal standard. The carbon balance and mass balance were 100±5%. 3. Results and Discussion The type IV isotherms with Hi hysteresis loops for these samples were observed, indicating the existence of the mesopore structure (see Fig. 1). The XRD patterns of these samples (see Fig. 2) showed a single broad diffraction peak in the low-angle range. This implies that the materials possess disordered wormlike mesostructures without long-range symmetry [7].

0.2

0.4 0.6 0.8 Relative Presure !P/Pn

Fig. 1 N2 isotherms of the samples.

1.0

2

3 4 5 2 Thetra (degrees)

Fig. 2 XRD patterns of the samples

The variation of pore size with the synthesis parameters of the samples is listed in Table 1. Obviously, the pore properties depended on the synthesis parameters, including the pH of the synthesis system and the molar ratio of diglycol/Zr added. Under the same pH of 3, the addition of diglycol at the molar ratio of diglycol/Zr from 0 to 2 led to the enhancement of the pore sizes from 2.9 to 7.4 nm. On the other hand, at the constant molar ratio of diglycol/Zr of 2, the pore sizes of the resultant materials decreased from 12.6 to 4.8 nm

673 Table 1 Synthesis parameters of mesoporous zirconia with different pore size

Sample

pH Diglycol Pore size HNO3 (ml) (nm) (ml) PMZ-3 2.9 6 3.0 0 4 PMZ-5 4.8 4.5 30 7.4 6 3.0 PMZ-7 30 PMZ-12 12.6 8 2.5 30 3.0 2.4 with the increase of pH from 2.5 to 4.5. 1.8 1.2 The observation was in good agreement 0.6 3.0 with the result in our previous report [6]. •CM.8 The peaks appeared at 600°C corresponded to the reduction of cobalt species S2.4 1.8 derived from a Co-ZrO2 interaction to 0.61.2 30 metallic Co. Fig. 3 indicated that the Co- 2.4 i.s ZrO2 interaction decreased, and the 0.61.2 reducibility was enhanced with the 200 400 600 800 Temperature(°C) increase of the pore size. The F-T reaction performances of the Fig. 3 TPR profiles of the catalysts. catalysts are listed in Table 2. Under the same reaction temperature of 230°C, the FTS catalytic activity (CO conversion %), C5+ selectivity, Ct8+ selectivity, and the selectivity to Ci2-Ci8 paraffin were enhanced, whereas C\ selectivity (methane selectivity) decreased with increasing the pore size of mesoporous zirconia supports. It was especially worth to note that the cobalt catalyst (Co/PMZ-12) supported on the mesoporous zirconia with the pore size of 12.6 nm snowed the high FTS catalytic activity and selectivity to Ci 2 -Q 8 fraction, as high as 32 %. It has been accepted that the support with a smaller pore size results in a higher dispersion of cobalt catalyst, but a lower reducibility, thus yielding light hydrocarbons; in contrast, the support with a larger pore size improves the reducibility, favors the diffusion of syngas and products, and thus produces heavy hydrocarbons [2, 5]. In combination with TPR result, it was well understood that F-T reaction performances of the catalysts varied as a function of the pore sizes. Furthermore, the large pore size and narrow pore size distribution of the mesoporous molecular sieve support permit better control of the cobalt particle size and the distribution of hydrocarbon products from the F-T synthesis compared with the conventional supports [2, 5] due to the control of the re-adsorption of a-alkene and chain growth [8]. And also, the cobalt-based catalyst supported on zirconia is characterized by a mild Co-ZrO2 interaction, thus leading to the high reducibility of cobalt oxide species and further the high activity and Cs+ selectivity for F-T reaction [9-11]. The complex interplay among these factors might result in the high FTS catalytic activity and selectivity to Cn-Cig paraffin as the main component of diesel oil fraction for the Co/PMZ-12 with a large pore-size mesoporous zirconia as support. In short, the result may be attributed

Is!

674 Table 2 F-T reaction performance of the catalysts

Sample CO Conv.(%) Ci(%) C5+(%) C,8+(%) Ciri8(%) 13.58 44.91 36.36 9.56 Co/PMZ-3 1.03 42.41 Co/PMZ-5 24.40 46.46 14.01 1.95 81.03 12.15 69.86 20.31 Co/PMZ-7 12.87 86.12 Co/PMZ-12 10.61 86.69 32.32 19.23 Reaction conditions: T = 230°C , P= 2 MPa, GHSV = 1000 rf\ H2/CO = 2/1 to the combination of the improvement of the reducibility and the control of readsorption of a-alkene and chain growth derived from the large pore size and narrow pore size distribution of the mesoporous support with the high FTS activity and C5+ selectivity from zirconia as the support of the cobalt catalyst. 4. Conclusion It was found that the reducibility and the F-T reaction performances of cobalt catalysts were closely related to the pore sizes of mesoporous zirconia supports. Furthermore, the cobalt catalyst supported on such a mesoporous zirconia with the pore-size of 12.6 nm showed good catalytic performance in F-T synthesis. The result was attributed to the combination of the improvement of the reducibility of cobalt catalyst and the control of re-adsorption of a-alkene and chain growth derived from the large pore size and narrow pore size distribution of the mesoporous support with the high FTS catalytic activity and C$+ selectivity from zirconia as the support of the cobalt catalyst. 5. References [1] D. Yin, W. Li, H. Xiang, Y. Sun, B. Zhong and S. Peng, Micropor. Mesopor. Mater., 47 (2001)15. [2] Y. Ohtsuka, Y. Takahashi, M. Noguchi, T. Arai, S. Takasaki, N. Tsubouchi and Y. Wang, Catal. Today, 89 (2004) 419. [3] D. J. Kim, B. C. Dunn, P. Cole, G. Turpin, R. D. Ernst, R. J. Pugmire, M. Kang, J. M. Kim and E. M. Eyring, Chem. Commun., (2005) 1462. [4] J. Panpranot, J. G. Goodwin, Jr. and A. Sayari, J. Catal., 211 (2002) 530. [5] A. Y. Khodakov, A. Griboval-Constant, R. Bechara and F. Vilain, J. Phys. Chem. B, 105 (2001) 9805. [6] Y. C. Liu, J. G. Chen and Y. H. Sun, Stud. Surf. Sci. Catal., 156 (2005) 249. [7] N. Yu, Y. Gong, D. Wu, Y. Sun, Q. Luo, W. Liu and F. Deng, Micropor. Mesopor. Mater., 72 (2004) 25. [8] E. Iglesia, Appl. Catal. A, 161( 1997) 59. [9] Y. Zhang, M. Shinoda and N. Tsubaki, Catal. Today, 93-95 (2004) 55. [10] D. I. Enache, M. Roy-Auberger and R. Revel, Appl. Catal. A, 268 (2004) 51. [11] J. G. Chen and Y. H. Sun, Stud. Surf. Sci. Catal., 147 (2004) 277.

Recent Progress in Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

675 675

Catalytic phenol hydroxylation over Cuincorporated mesoporous materials Huili Tang, Yu Ren, Bin Yue, Shirun Yan and Heyong He* Department of Chemistry and Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, Fudan University, Shanghai 200433, P.R. China

1. Introduction The production of diphenols from the hydroxylation of phenol under homogeneous and heterogeneous conditions has attracted much attention since 1970s [1]. Among many catalysts studied TS-1 is a promising environmentalfriendly one with aqueous H2O2 as the oxidant [2]. However, the small pore size of microporous molecular sieves restricts the substrates to access the active sites. The advent of mesoporous silica paved a new way for designing the catalysts with larger pore size where many active species can be immobilized or supported on the surface or incorporated into the matrix of mesoporous silicas [3]. In the previous work, we prepared Ti-containing mesoporous silicas through "one-pot" method using short chain carboxylic acids as the templates, exhibiting high catalytic activity in the cyclohexene epoxidation reaction [4]. Here we report the synthesis of Cu-incorporated mesoporous materials CMM-x (x stands for the Cu/Si molar ratio in starting materials) using glutaric acid as the template and their catalytic activity in phenol hydroxylation. 2. Experimental Section CMM-x (x = 0, 1/20, 1/50, 1/200) were synthesized by the sol-gel method. Copper(II) acetate, glutaric acid, HC1 (2 mol/1) and H2O were stirred together followed with TEOS to form a clear solution with a molar ratio of 1.00 Si : x metal: 0.50 glutaric acid : 2 HC1 : 45 H2O. After hydrolysis of TEOS for 1 h, the mixture was dried at 423 K for 2 h and the gel obtained was calcined in air at 773 K for 5 h. Phenol hydroxylation was carried out at 343 K in a three-necked flask (50 ml) equipped with a magnetic stirrer and a reflux condenser. 1.0 g phenol, 15.0 g distilled water and 50 mg catalyst were added successively into

676

the flask and heated to 343 K. 30 wt.% H2O2 was then added dropwisely and the reaction was carried out for 4 h. The analysis of products was carried out on an Agilent 1100 HPLC equipped with a 150 mm reversed phase C18 column at ambient temperature. The conversion of phenol, the selectivity of diphenol and the product distribution are all based on molar percentages. 3. Results and Discussion The XRD patterns of all CMM-x samples in the small angle region are similar to that of HMS mesoporous molecular sieve (Fig. 1) [5]. In the large angle region a hump at 15-30° from the amorphous silica is observed. Besides the hump, CMM-1/200 has no other diffreaction peak, whereas the samples with higher Cu content exhibit two weak peaks at 20 = 35.3 and 38.5° assigning to ( i l l ) and (111) diffractions of copper oxide, tenorite. The XRD results, along with the similar UV-visible diffuse reflectance spectra (not shown), indicate that the copper in the CMMs with low content mainly forms the highly dispersed Cu(II) oxide aggregates within mesoporous siliceous matrices [6].

CMM-0

a. u.)

CMM-0

CMM-1/200

CMM-1/200 c/>

CO

Ic

(D

CMM-1/50

CMM-1/50 _ifr-VjLi__

^JL^^^^IH^^^N^

111

111

CMM-1/20

CMM-1/20 4

5

6

7

8

9

10

10 15 20 25 30 35 40 45 50 55 60

2 Theta (°)

2Theta(°)

Fig. 1 X-ray diffraction patterns of Cu-incorporated mesoporous materials with different Cu/Si ratios in small angle region (a) and large angle region (b). Table 1 Physicochemical properties of the CMMs Sample CMM-1/20 CMM-1/50 CMM-1/200 CMM-0 "Analyzed by EDX

Molar ratio of Cu/Sia 1/19.6 1/49.8 1/196.4 0

Average pore size (nm) 5.67 3.84 3.36 3.30

Pore volume (cm3/g) 0.87 0.69 0.66 0.70

BET surface area (m2/g) 624 726 780 786

677

The typical N2 adsorption isotherm of the catalysts is of type IV classification with a H2 hysteresis loop (Fig. 2). CMM-x have BET surface areas of 620-780 m2g~' and pore volume of 0.66-0.87 cm3g~'. BET surface area of CMMs increases but pore size and pore volume roughly decrease with decreasing the molar ratio of Cu/Si (see Table 1). 400

0.0

Fig. 2 Typical N2 adsorption/desorption isotherm andpore size distribution for CMM-1/50.

The TEM images of all CMM-x catalysts show worm-like mesoporous structures (see Fig. 3), which is similar to HMS [4]. In order to confirm whether the pore structure of CMMs is three dimensional, an inverse carbonaceous mesoporous material was prepared using CMM-1/50 as the hard template [7]. The TEM image of carbonaceous structure reflects similar interconnected mesopore network, which is inferred that CMM-x catalysts have a threedimensional interconnected mesopore system. The catalytic performance of the CMM-x catalyst in phenol hydroxylation, as well as TS-1 and CuO are listed in Table 2. The non-porous bulk oxide CuO shows relatively low conversion of 9.8%. Although the catalytic activity of CMM-x does not change significantly with varying the copper content, the best phenol conversion of 25.1% is observed over CMM-1/50, which is comparable to that of TS-1 [8]. The catalyst also shows remarkable stability. In the third run reaction, CMM-1/50 still exhibits phenol conversion of 24.0%. Fig. 3 Typical TEM images of CMM-1/50

678 Table 2 The catalytic activities in the phenol hydroxylation reaction using H2O2 as oxidant Catalyst CMM-0 CMM-1/20 CMM-1/50 CMM-1/200 TS-1C CuO (tenorite)

Phenol Conversion

H2O2 efficiency3

0 22.5 25.1 18.4 20.8 9.8

67.6 75.4 55.3 62.5 29.4

Product distribution11 (%) HQ CAT BQ 53.9 2.3 43.8 59.5 39.3 1.2 54.0 0.6 45.4 44.4 55.5 0.1 40.9 11.8 7.3

a

H 2 O 2 efficiency = 100 * (H2O2 consumed in the formation of diphenol and benzoquinone, mole) •*• (total H2O2 added, mole) b HQ = hydroquinone, BQ = para-benzoquinone, CAT = catechol. The product of tar is not included. c Ti/(Ti+Si) = 0.022.

4. Conclusion Novel Cu-incorporated mesoporous materials CMMs were synthesized by a sol-gel method using glutaric acid as template. It was demonstrated that the CMMs had a 3D worm-like mesoporous structure with a large surface area of 600 to 800 m 2 g'', exhibiting high catalytic activity in the phenol hydroxylation with H2O2 comparable to TS-1. 5. Acknowledgement This work is supported by the National Basic Research Program of China (2003CB615807), the NSF of China (20421303, 20371013) and the Shanghai Science and Technology Committee (05DZ22313). 6. References [1] J. O. Edwards and R. Curci, in: Catalytic Oxidations with Hydrogen Peroxide As Oxidant, eds. G. Strukul (Kluwer Academic Publishers, Dordrecht, 1992) pp. 97. [2] M. Taramasso, G. Perego and B. Notari, US Patent 4410501 (1983). [3] L. Norena-Franco, I. Hernandez-Perez, P. Aguilar and A. Maubert-Franco, Catal. Today 75 (2002) 189. [4] Y. Ren, L.P. Qian, B. Yue and H. Y. He, Chinese J. Catal. 24 (2003) 947. [5] P. T. Tanev and T. J. Pinnavaia, Science 267 (1995) 865. [6] Tkachenko, K.V. Klementiev, E. Loffler, I. Ritzkopf, F. Schuth, M. Bandyopadhyay, S. Grabowski, H. Gies, V. Hagen, M. Muhler, L. H. Lu, R.A. Fischer and W. Griinert, Phys. Chem. Chem. Phys. 5 (2003) 4325. [7] R. Ryoo, S. H. Joo and S. Jun, J. Phys. Chem. B 103 (1999) 7743. [8] P. S. E. Dai, R. H. Petty, C. W. Ingram and R. Szostak, Appl. Catal. A: Gen. 143 (1996) 101.

Progress in in Mesostructured Materials Recent Progress S. Qiu, Y. Tang and C. Yu (Editors) (Editors) D. Zhao, S. © 2007 2007 Published Published by Elsevier Elsevier B.V. B.V.

Alumina-promoted sulfated mesoporous zirconia and catalytic application in butane isomerization Chi-Chau Hwang,a Jung-Hui Wang,a She-Tin Wonga and Chung-Yuan Moua "Department of Chemistry and Center of Condensed Matter Science, National Taiwan University, Taipei, Taiwan 106

Mesoporous zirconia (m-ZrC>2), possessing high surface area, would be an interesting catalytic material to investigate. Instead of using the conventional strategy to dope S and Al onto m-ZrO2 separately, our group used aluminium sulfate (abbreviated as AS) as the source of Al and S directly to prepare alumina-promoted sulfated mesoporous zirconia catalysts. The best catalyst in «-butane isomerization reaction was one prepared by the addition of 2 mole% of AS onto m-ZrO2 with a 630°C calcination temperature. Various characterization techniques were used to locate the surface sites active for the isomerization reaction. The X-ray photoelectron spectra were employed for the identification of acid sites on the catalysts. And the amount of Al loaded onto the catalyst also has a direct influence on the balance of surface acid sites on the catalysts. The best performance of catalysts is optimized at a WT value of- 4.4 wt% and S/Al value of ~ 1.7. 1. Introduction Sulfated mesoporous zirconia (labelled as SZm) has been successfully synthesized and incorporated with the alumina to enhance its catalytic performance in «-alkane isomerization reactions [1-4]. Our group has also reported that the addition of small amounts of Al onto the sulfated zirconia catalyst supported on high surface area MCM-41 and sulfated mesoporous zirconia gives rise to a catalyst which is much more active than the corresponding unpromoted one [5, 6]. It is of great interest to understand the chemistry of the different active sites in alumina-promoted SZ catalyst and correlates them to the reaction mechanism, and hence catalytic performance, in «-alkane isomerization reactions. In this paper, we focused on alumina-promoted SZm catalysts with different amount of sulfur and aluminium. Our primary goal is to know the origin of the catalytic active sites and the role of these sites in the various stages of reaction.

679 679

680

These results will in turn help us in optimizing the composition of aluminium and sulfur for a best performing catalyst. 2. Experimental Section The mesoporous ZrO2 was synthesized by the surfactant assisted route and loaded with aluminium sulfate (AS) via incipient wetness impregnation. Besides, the excess sulfur ions were provided form ammonium sulfate (S) which added in the synthetic process. The catalysts are hereafter labelled as xAS and xAS+S with x corresponding to the nominal aluminium sulfate concentration in mole% based on the mesoporous zirconia and S corresponding to the extra fixed concentration of nominal sulfate based on the total sample amount. Pyridine-adsorbed sample was first degassed ex-situ under vacuum at about 120°C for 0.5 h. Then the pretreated sample was transferred into the XPS instrument and spectra were collected in the Nls region. Catalytic reaction was carried out by introducing a mixture of w-butane and H2 («-C 4 : H2 = 1 : 10 v/v) with a total inlet flow rate of 15.5 ml/min at 250°C. 3. Results and Discussion Sulfated zirconia catalysts are commonly used for the study of «-alkane isomerization reaction. We chose to study a small molecule, «-butane, in order to minimize the diffusion limitation of reactant and product in the pore structures. Besides, the reaction trend can be better correlated to the acidity effect without over concerning the morphology aspect of the catalysts.

XRD Intensity (a.u.)

50 3

1 2

0

1

2

Surface Area: 114.7 m /g 3 Pore Volume: 0.085 cm /g Pore Size: 3.2 nm

3

2 theta (degree)

40

-1

Differential Pore Volume (ml g nm )

0.10

2AS o Calcined @ 630 C 30

40

50

2 theta (degree)

(i -1

1

20

2AS

2AS 1AS 1AS+S

W.B.

60

70

0.0

0.2

0.4

0.08

30

0.06

0.04

0.02

20

N1s Photoelectron Intensity (a.u.)

XRD Intensity (a.u.)

(a) 60

Adsorption Desorption

S.B.

80

L

(b)

60

1AS W.B.

L

S.B.

40 (c)

1AS+S

n-Butane Conversion (%)

(b)

1A 1 •\

Volume Adsorbed (cm /g)

(a)

0.00

0

0.6

2

4

L

6

Pore Size (nm)

S.B.

10 0.8

20

W.B.

1.0

Relative Pressure (P/P0)

404

402

400

Binding Energy (eV)

Fig.l The XRD and BET curves of 2AS catalyst calcined at 630°C.

398

0

60

120

180

240

300

360

Time on Stream (min)

Fig.2 The Nls photoelectron profiles with pyridine adsorbed and catalytic performances of catalysts.

The XRD profiles of 2AS catalyst which is calcined at 630°C are shown in Fig. l(a). The feature of mesostructure displays the peak at 0.9° and peaks in the high angle region are characteristic of tetragonal phase of ZrO2. Comparing the

681

XRD results with those of Al-free sample, it is concluded that addition of alumina not only retards the phase transformation from tetragonal to monoclinic, but also stabilizes the mesostructure of catalysts. The nature of surface acid sites can been investigated and classified by XPS using pyridine as probe molecules. The acidity of different sites provides unlike chemical environment resulted in the shift of binding energy and broad peak. In the left of Fig. 2, all acid sites can be divided into three species: strong Bransted (SB), weak Bransted (WB) and Lewis sites (L). Obviously these catalysts exhibit different balance of surface acids (summarized in Table 1). And there is a good agreement between XPS and GC results. The right of Fig. 2 illustrates the typical conversion versus reaction time profiles in w-butane isomerization reaction over catalysts of IAS and 2AS series. The sequence of catalytic performance has the correlation between the ratios of acid sites: the catalyst exhibited more Bransted sites owns better catalytic ability. It is reasonable to assume these Bransted sites, weak acids especially, play an important role in the catalytic process. Table 1 Relative ratios of various acid sites over catalysts with different Al and S loadings. Relative Ratio of N Is core level Catalyst Strong Bransted

Weak Bransted

Lewis

0.33

0.50

0.17

IAS

0.21

0.37

0.42

1AS+S

0.10

0.28

0.62

2AS

Comparing the small-angle XRD spectra of these three catalysts, we found that 2AS catalyst which contains more alumina not only displays better mesostructure but also exhibits higher conversion. More active sites can be formed on the larger surface and resulted in raising the catalytic activity directly. Table 2 listed more details about catalytic data in the steady state and elemental analysis of samples. The 2AS catalyst displays best TON value and lower selectivity which is caused by high acidity. On the other hand, the sample, 1AS+S, contains similar total promoter amount with 2AS, display a lower catalytic ability and decay substantially. This phenomenon may be caused by the high content of sulfur. Although the addition of sulfur ions can induced more Bransted acid sites, the high acidity of these sites cause coke on the catalyst too. The selectivity of main product, /'-butane, for these catalysts was higher than 85 % while small amounts of methane, propane, and pentane were also observed. Here, the best performing catalyst is 2AS and its steady state H-butane conversions reach about 64 % after 6 h at 250°C.

682 Table 2 Elemental analysis and catalytic results of catalysts. Catalyst

Contents (wt%)

Total

TON

Selectivity

(umol/g-s)

of (-Butane (%)

Al

S

Amount (wt%)

2AS

1.45

2.89

4.34

1.09

85.0

IAS

0.84

1.77

2.61

6.70x10"'

92.4

1AS+S

1.24

3.40

4.64

2.78x10"'

94.4

Finally, we try to propose the reaction process in our experiments by analysis of product distribution. Table 3 summarized the conversion, selectivity and individual product yield of catalysts. The optimal catalyst, 2AS, its conversion decayed from 88 % to 64 % after 360 minutes while corresponding selectivity varied from 72% to 85%. Variation in the selectivity could be interpreted with different reaction mechanisms: high selectivity implies the isomerization through a unimolecular pathway; and low selectivity became dominated that infers a bimolecular one. Table 3 The catalytic conversion, selectivity, and yield after 5min and at steady state regime over 2AS, IAS, and 1AS+S catalysts. Catalyst

Conversion

Selectivity

Yield (

c2

c3

i-C 4

«-C4

c5

After 5 min 2AS

87.9

72.0

2.01

15.57

58.59

18.63

5.2

IAS

41.2

91.2

0.58

1.40

34.76

61.87

1.39

1AS+S

66.2

85.0

0.65

4.64

53.33

37.25

4.13

2AS

63.9

85.0

1.54

4.18

52.81

37.86

3.61

IAS

39.3

92.4

0.46

1.08

33.74

63.47

1.25

1AS+S

16.3

94.4

0.18

0.32

12.95

86.28

0.27

After 360 min

Therefore, it's proposed that the bimolecular reaction is preferred in the initial period, especially in 2AS and 1AS+S catalysts, which correlates with the formation of side products and leads to coke and subsequently decreases the conversion. After 360 minutes, the activity decayed gradually and selectivity maintained a stable value above 0.9. The high selectivity and retarded decay suggested that the unimolecular mechanism is dominant in the later reaction. But in the overall reaction, even in the steady state, the bimolecular reaction plays an important role on 2AS catalyst.

683

4. Conclusion Alumina was successfully incorporated into SZ and enhanced substantially the catalytic activity and stability of w-butane isomerization reaction. Such promotional effect comes mostly from the stabilization of tetragonal crystalline phase of zirconia and from the enhancement of Bransted acidity. 5. References [1] Z. Gao, Y. D. Xia, W. M. Hua and C. X. Miao, Top. Catal. 6 (1998) 101. [2] J. A. Moreno and G. Poncelet, J. Catal. 203 (2001) 453. [3] F. C. Jentoft, A. Hahn> J. Krohnert, G. Lorenz, R. E. Jentoft, T. Ressler, U. Wild, R. Schlogl, C. Ha|3ner and K. Kohler, J. Catal. 224 (2004) 124. [4] Y. Sun, L. Yuan, S. Ma, Y. Hua, L. Zhao, W. Wang, C. L. Chen and F. S. Xiao, Appl. Catal. A: 268 (2004) 17. [5] W. Wang, J. H. Wang, C. L. Chen, N. P. Xu and C. Y. Mou, Catalysis Today 97 (2004) 307. [6] J. H. Wang and C. Y. Mou, Appl. Catal. A, 286 (2005) 128.

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Recent Progress in Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

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Reducibility of Cobalt Oxides over SBA-15 supported Cobalt Catalysts for Fischer-Tropsch Synthesis Dae Jung Kima*, Brian C. Dunnb, Min Kangc, Jae Eui Yied, Seong-Hyun Kime, Jenifer Gasserb, Eric Fillerupb, Louisa Hope-Weeks1 and Edward M. Eyringb "Department of Chemistry & Biochemistry, Texas Tech Universiy, TX 79409, USA. h Department of Chemistry, University of Utah, Salt Lake City, UT'84112, USA c Department of Chemistry and Sungkyunkwan Advanced Institute ofNano technology, Sungkyunkwan University, Suwon, 440-746, Republic of Korea Department of Applied Chemistry, Division of Biotechnology & Nanotechnology, Ajou University, Suwon, 443-749, Republic of Korea e Department of Environmental Engineering and Biotechnology, Myongji Unversity, Yongin 449-728, Republic of Korea

1. Introduction Fischer-Tropsch (FT) synthesis is a promising pathway to clean alternative fuels derived from coal syngas. The development of active catalysts with high selectivity for the production of long chain hydrocarbons is critical for the further advancement of this technology. Since the catalytic activity depends primarily on the overall amount of exposed metal atoms, an active catalyst requires a high reducibility of metal oxides. Mesoporous silica materials such as SBA-15 have been recently used as supports for cobalt [1-3]. The high surface area (500 - 1500 m2/g) of the mesoporous materials results in increased metal dispersions at higher cobalt loadings compared with conventional amorphous silicas. The objective of this present study is to elucidate the impact of cobalt impregnation method on the reducibility of cobalt oxides and the catalytic activity in Fischer-Tropsch synthesis. The SBA-15 supported cobalt catalysts were prepared by three different cobalt impregnation methods: incipient wetness, post-synthesis, and supercritical solvent. The physical and chemical properties of the catalysts were obtained from N2 adsorption/desorption, XRD

686

and TPR experiments. The catalytic performance in FT synthesis was evaluated with a fixed-bed reactor. 2. Experimental Section The cobalt precursors used in the incipient wetness (IW) and post-synthesis (PS) impregnations were Co(NO3)2-6H2O and (CH3CO2)2Co-4H2O. The impregnation of SBA-15 with cobalt using a supercritical solvent (SS) proceeded as follows: The SBA-15 was added to a 250 ml ethanol solution of Co(NO3)2-6H2O, and stirred at ambient temperature for 1 h. The suspension was transferred to an autoclave placed inside a furnace. The autoclave was purged ten times with 200 psi N2 to remove any oxygen trapped in the system. The autoclave was heated to 350°C at 5°C/min, then held at 350°C for 3 h. The pressure inside the autoclave was maintained at 2000 psi by controlled venting through a high-pressure valve. The system was cooled to 200°C, and the gas inside the autoclave was vented for 1 h. The system was then cooled to ambient temperature. The cobalt impregnated samples were calcined in air at 550°C overnight. For all cobalt catalysts, the cobalt loading was 6 wt. %. The FT synthesis was carried out in a fixed-bed stainless steel reactor (5 mm I.D. and 168 mm length) at 100 psi and 265°C. A H2/CO molar ratio of 2 was used, and the tests for the cobalt catalysts followed the experimental procedures described earlier [4]. 3. Results and Discussion XRD patterns shown in Fig. 1 and nitrogen adsorption isotherms obtained indicated that all the cobalt catalysts had a typical 2-D hexagonal structure of the pure SBA-15. This suggests that the mesopore structure is still retained after cobalt impregnation. Pore structural parameters calculated from nitrogen adsorption/desorption isotherms for the SBA-15 supported catalysts are listed in Table 1. The pore structural parameters of the pure SBA-15 such as surface area, pore volume and average pore size were decreased by the cobalt loading. The three cobalt catalysts having the same loading of cobalt showed similar values in the parameters. The mean CO3O4 crystallite diameters of the three cobalt catalysts deduced from the XRD data using the Scherrer equation are presented in Table 1. The XRD peak of Co3O4 for the PS sample was not detectable. This suggests that most of cobalt oxides are present as cobalt silicates in the framework of the SBA-15, and the crystallite size of CO3O4 on the surface of the SBA-15 is very small. The mean Co3O4 crystallite size on the SS sample is larger than on the IW sample. This result indicates that the crystallite size of CO3O4 is clearly dependent on the cobalt impregnation method. Figure 2 shows TPR profiles of the SBA-15 supported cobalt catalysts. The IW and SS samples exhibited similar TPR profiles with three typical peaks.

687

However, the TPR profile for the PS sample with two peaks was significantly different. The maximum intensities of the three TPR peaks for the SS sample were located at lower temperatures than for the IW sample. For the PS sample, the peak at temperatures above 760°C can be assigned to the reduction of cobalt oxides in the framework of SB A-15. The reduction degrees of the cobalt oxides on the three cobalt catalysts at temperatures less than 500°C are presented in Table 1. The SS sample showed the highest reducibility of cobalt oxides among the three catalysts prepared by different cobalt impregnation methods. According to the TPR results, undesireable cobalt oxides such as cobalt silicates (those not easily converted to active cobalt metal at lower temperature) were abundantly produced in the PS sample. Table 1. Physical and chemical properties of the SBA-15 supported cobalt catalysts Co3O4 d Re Catalyst Diameter (nm) . 724 1.243 8.09 Pure SBA-15 IW 465 0.811 8.08 11.1 49 472 PS 0.858 8.08 18 SS 461 0.815 8.08 11.6 63 a BET Surface area, b Total pore volume,c average pore diameter,d Co3O4 crystallite diameter calculated from the widths of XRD peaks using the Scherrer equation (2 theta = 36.68°), e reduction degree of cobalt oxides during TPR at 30 - 500°C,f IW: incipient wetness, PS: post-synthesis, SS: supercritical solvent Table 2 . . CO conversion, hydrocarbon selectivity and chain growth probability of the SBA-15 supported cobalt catalysts Sa (m2/g)

Catalyst

CO conversion

Vt b (cc/g)

Dc (nm)

Product selectivity (C mol%) Cl

C2-C5

C5-C10

C10+

IW 15.7 8.6 38.6 39.0 13.8 4.6 15.8 56.8 24.2 3.2 PS 21.1 32.4 45.3 15.0 7.3 SS a chain growth probability obtained from Anderson-Schulz-Flory equation

a a 0.86 0.82 0.88

Catalytic activities of the SBA-15 supported cobalt catalysts in FT synthesis are summarized in Table 2. CO conversion and higher hydrocarbon selectivity can be related to the reducibility of the cobalt oxides and pore structure of a cobalt catalyst. The three samples (IW, PS, SS) having the same loading of cobalt showed similar values in BET surface area, pore volume and average pore size. However, the three samples showed differences in the reducibility of cobalt oxides. The SS sample exhibited the highest CO conversion, C5+ selectivity and chain growth probability among the three catalysts obtained by three different cobalt impregnation methods. This result is quite consistent with the TPR result.

688

j LJLi

ss

^_3JL

ps

/

100

isity

8

IB

J

i

I

- §

iw

'."

Pure SBA-1S

a u

0

20 / degree

Fig.l XRD patterns of the SBA-15 supported cobalt catalysts

100 200 300 400 500 600 700 BOO 900

Temperature (°C)

Fig.2 TPR profiles of the SBA-15 supported cobalt catalysts

4. Conclusion The supercritical solvent method for cobalt impregnation on the SBA-15 gave the largest crystallite size of Co3O4 and highest reducibility of cobalt oxides on a cobalt catalyst. The cobalt catalyst with cobalt impregnation by the supercritical solvent method showed the highest CO conversion, C5+ selectivity and chain growth probability among the three cobalt catalysts obtained by three different cobalt impregnation methods: incipient wetness, post-synthesis, and supercritical solvent. This result indicates that CO conversion and higher hydrocarbon selectivity can be related to the reducibility of the cobalt oxides. 5. Acknowledgement The U.S. Department of Energy provided financial support to the Consortium for Fossil Fuel Science for this study (contract # DE-FC2602NT41954). 6. References [1] [2] [3] [4]

K. Okabe, M. Wei and H. Arakawa, Energy & Fuels, 17 (2003) 822. A. Martinez, C. Lopez, F. Marquez and I. Diaz, J. Catal., 220 (2003) 486. J. Panpranot, J. G. Goodwin Jr. and A. Sayari, Catal. Today, 77 (2002) 269. D. J. Kim, B. C. Dunn, P. Cole, G. Turpin, R. D. Ernst, R. J. Pugmire, M. Kang, J. M. Kim, and E. M. Eyring, Chem. Commun., (2002) 1462.

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Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Published by Elsevier B.V.

Microencapsulation of heterocyclic carbene-Pd complex in SBA-15 silica for Heck reactions M. S. Sarkar, Ji-Young Jung and Myung-Jong Jin* School of Chemical Science and Engineering, lnha University, lncheon, 402-751, Korea

./V-Heterocyclic carbene-Pd complex was microencapsulated with the aid of ionic liquid onto mesoporous silica SBA-15 material. The immobilized Pd complex was used as an effective catalyst in Heck reactions. The Pd catalyst exhibited high reactivity and outstanding stability. 1. Introduction The palladium-catalyzed Heck coupling reaction is one of the most powerful methods for carbon-carbon bond formation and has found wide applications in organic synthesis [1]. Pd complexes with various ligands have proven to be excellent homogeneous catalysts for Heck reactions [2, 3]. Ionic liquids have received much attention as a medium to reuse such catalysts [4, 5]. However, the use of ionic liquids frequently suffers from high cost and high viscosity of ionic liquids. The immobilization of ionic liquids on a solid support would be highly • :: NHC-Pd complex complex Ionic liquid confined onto onto SBA-15 SBA-15

Bu =

N PF6-

+

i)

N Me

SBA-15 Supported NHC-Pd complex

ii)

SBA-15

1 o o i) toluene, 105 C, 12 C, 2.5 h; 110 C, 0.5 h. 105 o°C, 12 h. ii) Pd(OAc)2, DMF, 65 °C, 110°C,

Scheme 1

desirable from such viewpoints. Recently, N-heterocyclic carbene (NHC)-Pd complex has been successfully used in coupling reaction [6]. The immobilization of the useful homogeneous catalysts offers several potential advantages over traditional solution-phase chemistry. The supported catalysts can be recovered

690

from reaction mixture by simple filtration and they can be reused. For this purpose, we confined ionic liquid phase containing NHC-Pd(II) complex 3 in the surface of mesoporous SBA-15 silica material. Herein, we wish to describe the microencapsulated NHC-Pd complex 3 and its application for palladium catalyzed Heck reaction. 2. Experimental Section 2.1. Immobilization of ionic liquid 1 onto SBA-15 silica To a solution of l-butyl-3-methylimmidazolium hexafluorophosphate 1 (0.154 g, 0.54 mmol) in toluene, SBA-15 silica (1.0 g) was added. The mixture was stirred at 105°C for 12 h and washed with methylene chloride. After drying under vacuo at 60°C, SBA-15-supported ionic liquid 2 was obtained. Elemental analysis and weight gain showed that 0.36 mmol of ionic liquid was anchored on 1.0 g of SBA-15-supported ionic liquid 2. 2.2. Preparation of SB A-15-supported NHC-Pd(II) complex 3 To a stirred solution of SBA-15-supported ionic liquid 2 (0.700 g, 0.25 mmol) in DMF (10 ml), Pd(OAc)2 (0.07 g, 0.31 mmol) was added. The mixture was stirred for 2.5 h at 65°C and then heated to 110°C. After stirring for an additional 30 min, the SBA-15 supported NHC-Pd(II) complex 3 was separated by filtration. The powder was washed by methylene chloride and dried under vacuum at 60°C. Elemental analysis and weight gain showed that 0.18 mmol of Pd was anchored on 1.0 g of the SBA-15 silica complex 3. 2.3. General procedure for the Heck reaction Reactions were carried out in a 2 mL glass vial equipped with a Teflon screw cap. A mixture of aryl halide (0.5 mmol), alkene (0.6 mmol), Et3N (1.0 mmol), and the Pd catalyst 3 (corresponding to 3 mol% Pd with respect to the aryl halide) in dodecane (0.8 ml) was stirred at 130°C for an appropriate time, monitoring periodically by GC analysis. The immobilized Pd complex 3 was separated by filtration. The reaction mixture was diluted with H2O and ether. The organic layer was dried over MgSO4 and then evaporated under reduced pressure. The residue was purified by short column chromatography on silica gel. Conversion was determined by GC analysis. 3. Results and Discussion l-butyl-3-methylimmidazolium hexafluorophosphate 1 was easily confined into mesoporous silica SBA-15 in toluene at 105°C (Scheme 1). The ionic liquid

691

confined SBA-15 silica 2 was obtained after washing by methylene chloride. NHeterocyclic carbine (NHC)-Pd complex 3 was prepared by the reaction of 1butyl-3-methylimmidazolium hexafluorophosphate confined SBA-15 silica 2 and palladium acetate in DMF at 110°C. The reaction mixture was subsequently washed with methylene chloride to give microencapsulated NHC-Pd complex 3. Through this convenient process ionic liquid-supported supported NHC-Pd complex could be encapsulated onto SBA-15 material. The Pd complex 3 was used as a catalyst for the Heck coupling reaction. As shown in Table 1, the catalyst gave high reactivity (conversions: 96-99%) and nearly 100% selectivity Table 1 Heck reaction of aryl iodides with acrylates using NHC-Pd complex 3 a

COjR

Entry

1 2

Acrylate b

Time (h)

iodobenzene iodobenzene

MA

4.5

EA

4.5

99 96

iodobenzene

5

96

6 4

90 96

4

94

1

100

1.5

100

2

100

1

100

1.2

100

Aryl iodide

Conv.(%

3 4 5

2-iodoanisole 4-iodoanisole

6

4-iodoanisole

7

4-iodophenol

8

4-iodophenol

9 10 11

4-iodophenol 1 -iodo-3 -nitrobenzene l-iodo-3-nitrobenzene

BA MA MA EA MA EA BA MA EA

12

1 -iodo-3-nitrobenzene

BA

1.5

100

13

1 -iodo-3-nitrobenzene

styrene

2

100

14 15 16 17

1 -iodo-4-nitrobenzene

1

100

1.2

100

1 -iodo-4-nitrobenzene

MA EA BA

1.5

100

1 -iodo-4-nitrobenzene

styrene

2

100

1 -iodo-4-nitrobenzene

"Reactions were carried out with aryl iodide (0.5 mmol), Pd complex 3 (0.03 equiv., loading ratio = 0.18 mmol/g), acrylate (1.2 equiv.) and Et3N (2.0 equiv.). bMA = methyl acrylate, EA = ethyl acrylate, BA = butyl acrylate. determined by GC analysis.

692

in the coupling of iodobenzene and acrylates (entries 1-3). Reactions of nitro-, methoxy- and hydroxy-substituted iodobenzenes with acrylates were also excellent (entries 4-17). Moreover, the catalyst could be recycled without a significant loss of activity. The HRTEM image obtained after the modification of the parent SBA-15 silica is shown in Fig 1. The hexagonal symmetry of the pore

Fig 1. TEM image of SBA-15-supported NHC-Pd complex 3.

Fig 2. XRD patterns of SBA-15-supported NHC-Pd complex 3.

Table 2. Recycling of the immobilized catalyst 3

cycle

yield (% 100 100 100

cycle 4 5

yield(098 96

93 Reaction was carried out under the optimized conditions as described in Table 1, entry 7.

arrays is conserved after the immobilization of NHC-Pd(II) complex 3 onto SBA-15 silica, which is also confirmed by XRD of Fig 2. Apparently, there is no change of the lattice parameters upon the immobilizing process. 4. Conclusion In conclusion, we have achieved excellent results for the heterogeneous catalytic Heck reaction using a new heterocyclic carbene-Pd complex 3 onto SBA-15. 5. References [1] [2] [3] [4] [5] [6]

I. P. Beletskaya and A. V. Cheprakov, Chem. Rev. 100 (2000) 3009. V. Farina, Adv. Syn. Catal. 346 (2004) 1553. C. M. Crudden, M. Sateesh and R. Lewis, J. Am. Chem. Soc. 127 (2005) 10045 T. Welton, Chem. Rev. 99 (1999) 2071. A. Closson, M. Johansson and J. Backvall, Chem. Commun. (2004) 1494. W. A. Herrmann, Angew. Chem. Int. Ed. 41 (2002) 1290.

693

Recent Progress in Mesostructured Mesostructured Materials D. D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Published by Elsevier B.V.

Heterogeneous asymmetric transfer hydrogenation with mesoporous silica SBA-15-supported RuTsCHDA catalyst Ji-Young Jung, M. S. Sarkar and Myung-Jong Jin* School of Chemical Science and Engineering, Inha University, lncheon, 402-751, Korea

Chiral TsCHDA was successfully anchored on SBA-15 silica material. The mesoporous system was used as an efficient heterogeneous chiral ligand in the asymmetric transfer hydrogenation of ketones. 1. Introduction Solid catalysts offer beneficial opportunities for simplified separation and potential reuse of the catalysts from reactions [1]. Attachment of organic moiety with the active site onto solids creates a heterogeneous catalyst bearing the advantages. Such supported catalysts have been employed in various transition metal catalyzed reactions. Recently, mesoporous SBA materials with uniform pore diameters and high specific surface areas have become of high interest as

+ N H2N

MeO MeO Si MeO

NH2

i)

MeO MeO

SO2Cl

O Si NH

NH2

SS—NH NH

NH2 NH

S

MeO

O

2

1

ii) i) Et3N,CH2Cl2, -10 C, 22 h -10 o°C, ii) SBA-15, toluene, reflux, 18 18 hh

Si

O O O

SBA-15

Si

O

O TsCHDA 3 loading ratio == 0.15 mmol/g mmol/g

Scheme 1

694

inorganic supports [2]. Tu and coworkers have exploited asymmetric transfer hydrogenation of ketones with immobilized Ru-TsDPEN catalysts [3]. Our interest in the field led to prepare new SBA-15 silica-supported TsCHDA chiral ligand 3. Herein, we describe the application of the immobilized chiral ligand for the asymmetric transfer hydrogenation of ketones. 2. Experimental Section 2.1. Preparation of SB A-15-supported TsCHDA 3 A solution of 2-(4-chlorosulfonylphenyl)ethyltrimethoxysilane 1 (0.198 g, 0.61 mmol) in CH2C12 (5 mL) was slowly added to a stirred solution of (1R,2R)diaminocyclohexane (0.070 g, 0.61 mmol) and triethylamine (0.067 g, 0.67 mmol) in CH2CI2 (10 ml) at -10°C. The reaction mixture was allowed to warm to RT. After stirring for 2 h, the mixture was diluted with CH2C12, and washed with cold water. The organic layer was dried with MgSO^ and concentrated under reduced pressure. The crude product was purified by flash chromatography to give (li?,2i?)-iV-(trimethoxysilylpropyl-A/-sulfonyl)-l,2-cyclohaxanediamine 2 in 80% yield. SBA-15 silica (0.7 g) was added to a solution of compound 2 (46 mg, 0.11 mmol) in hot toluene (15 ml) and the mixture was refluxed for 18 h. After filtering the reaction mixture, the solid was washed several times with methylene chloride and dried under vacuum at 70°C to give SBA-15-supported TsCHDA 3. Weight gain showed that 0.15 mmol of TsCHDA was grafted in 1.0 g of the SBA-15 silica 3. 2.2. General procedure for asymmetric transfer hydrogenation A mixture of SBA-15-supported of TsCHDA ligand 3 (51 mg, 0.007 mmol) was suspended in water (1 ml) and heated with [Ru(p-cymene)Cl2]2 (2.75 mg, 0.004 mmol) at 80°C for 1 h. The solution was cooled to RT, and then ketone (0.45 mmol) and HCC^Na (153 mg, 2.25 mmol) were added. The mixture was stirred at 40°C for 17 h. After general work-up, crude product was purified by short-column chromatography. Conversion was measured by GC analysis. Chiral HPLC analysis using Daicel OD-H column was used for the determination of enantiomeric excess of the diol. 3. Results and Discussion The immobilization of ./V-(/>-toluenesulfonyl)-l,2-diaminocyclohexane (TsCHDA) onto SBA-15 silica material was easily performed through two steps (Scheme 1). Reaction of optically pure (l/?,27?)-diaminocyclohexane with 2-(4-chlorosulfonyl phenyl)ethyltrimethoxysilane afforded (IR,2R)-N(trimethoxysilylpropyl-Af-sulfonyl)-l,2-cyclohaxanediamine 2 in high yield.

695

Subsequent treatment of SBA-15 silica with 2 in refluxing toluene gave SBA-15supported TsCHDA 3 (0.15 mmol/g). Some physical properties of the immobilized TsCHDA 3 are summarized in Table 1. Table 1.Structural characteristics of SBA-15-supported TsCHDA 3 Sample SBA-15 3

Pore

Surface area 2

8.33 nm

0.83 cm

2

7.43 nm

0.43 cm3

750 m /g 476 m /g

Loading

Pore volume

diameter

amount

3

The data show that the TsCHDAfunctionalized SBA-15 3 possesses characteristic pore structure of mesoporous material containing high specific surface area and high mesoporous volumn. Pore size distribution of 3 was similar to parent SBA-15. Surface area and pore diameter of 3 decreased due to the grafting of organic functional group. The XRD pattern of the used SBA-15 3 was similar to that of the parent SBA-15 support (Fig. 1).

0.15 mmol/g

Fig I. XRD pattern profiles

Table 2. Asymmetric transfer hydrogenation of ketones with supported ligand 3 a OH supported ligand 3 [Ru(p-cymene)Cl2]2 HCO2Na, H 2 O,40°C, 17 h

Entry

Ketoneb

Conv. (%)c

E.e.

1

Pp

72

70

2

Acp

72

73

3

Tetralone

91

95

4

3'-Cl-Acp

99

83

5

4'-Cl-Acp

96

74

6

2'-OMe-Acp

96

71

7

3'-OMe-Acp

91

76

"All reactions were carried out at 40 °C; ketone : Ru : ligand : HCO2Na = 100 : 1 : 1.7 : 500. bPp = propiophenone. Acp = acetophenone. ^Determined by GC analysis. dDetermined by HPLC analysis using Daicel OD-H column (3% 2-propanol in hexane, lml/min.

696

The SBA-supported chiral Ru(II) complex was prepared in situ by heating a mixture of [Ru(p-cymene)Cl2]2 and the supported TsCHDA 3 in H2O. With the heterogeneous Ru complex, we attempted the asymmetric transfer hydrogenation of ketones. As indicated in Table 2, the catalyst gave satisfactory enantioselectivities in reasonable conversions. The enantioselctivity seems to depend on the structure of the ketone. The decreased steric hinderance around the carbonyl group resulted to improve the enantioselctivity (entries 1-3). The highest enantioselectivity of 95% was observed for the transfer of a-tetralone (entry 3). Reactions of chloro- and methoxy-substituted acetophenone exhibited high hydrogen transfer rates and comparable enantioselectivities to acetophenone (entries 4-7). 4. Conclusion In conclusion, we have developed new heterogeneous chiral ligand 3, derived from relatively cheap optically pure (li?,2i?)-diaminocyclohexane, for the asymmetric transfer hydrogenation. Further synthesis of mesoporous silicasupported chiral ligands and their use to asymmetric catalysis are underway. 5. References [1] G. Bhalay, A.Dunstan and A. Glen, Synlett. 12 (2000) 1846. [2] D. Zhao, Q. Huo, J. Feng, B. F. Chemlka and G. D. Stucky, J. Am. Chem. Soc. 120 (1998) 6024. [3] P. N. Liu, J. G. Deng, Y. Q. Tu and S. H. Wang, Chem. Commun. (2004) 2070.

697 697

Recent Progress in Mesostructured Materials D. D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Published by Elsevier B.V.

Mesoporous silica-SBA-15 supported TV-heterocyclic carbene-Pd complex for Suzuki coupling reaction Myung-Jong Jin* and M. S. Sarkar School of Chemical Science and Engineering, Inha University, Incheon, 402-751, Korea

N-Heterocyclic carbene-Pd complex was anchored on mesoporous silica SBA15 material. The heterogenized Pd complex was employed as a highly effective catalyst for Suzuki cross-coupling reaction under aqueous conditions. The catalyst was reusable without a significant loss of catalytic activity as well as airstable and thermally stable to allow easy use. 1. Introduction

S B A -15

Suzuki cross-coupling reaction is one of the most fundamental methods for carbon-carbon bond formation in organic synthesis [1]. Homogeneous Pd complexes possess high activity for the cross-coupling reaction [2-4]. One practical limit to performing homogeneously catalyzed reactions is the difficulty of separating the product from the catalyst and reusing the catalyst. In particular, homogeneous Pd catalyst tends to lose catalytic activity due to forming Pd clusters. To overcome this difficulty, homogeneous Pd catalysts have been OH OH OH OH Sii-oH OH OH OH OH

i) _j)^

O N O Si O S i N ++ CCllO N

Si OO Si

+N

O O Si O SBA-15

Me N+ N Cl

Cii)l

M Mee 1 loading ratio = 0.40 0.40 mmol/g

O O Si O

-Si

S— O i O O S Si O SBA-15

Cl

N Me Pd

N

Cl Me N NNMe

22 loading ratio = = 0.2 mmol/g

105 o°C, 12 hh i) triethoxysilylpropylimidazolium chloride, toluene, 105 C, 12 oC; 110 oC, 0.5 ii) Pd(OAc)2, DMSO, 2.5 2.5 h, 65 65 °C; 110°C, h

Scheme

N

698

attached to various supports including amorphous silica and mesoporous silicas [5]. Recently, N-heterocyclic carbene (NHC)-Pd complex has been successfully used in Suzuki cross-coupling reaction [6]. In this paper, we present our recent finding in the development of highly effective mesoporous silica SBA-15supported NHC-Pd complex 2 for Suzuki cross-coupling reaction. 2. Experimental Section 2.1. Immobilization of ionic liquid 1 onto SBA-15 silica To a stirred solution of triethoxysilylpropylimidazolium chloride (150 mg, 0.46 mmol) in toluene was added SBA-15 silica (1.0 g). The mixture was stirred at 105°C for 12 h and washed with methylene chloride. After drying under vacuo at 60 °C, SBA-15-supported ionic liquid 1 (1.08 g) was obtained. Elemental analysis and weight gain showed that 0.40 mmol of ionic liquid was anchored on 1.0 g of SBA-15-supported ionic liquid 1. 2.2. Preparation of SBA-15-supported NHC-Pd(II) complex 2 To a solution of SBA-15-supported ionic liquid 1 (0.34 g, 0.13 mmol) in DMSO (8 ml), was added Pd(OAc)2 (0.1 g, 0.44 mmol). The mixture was stirred for 2.5 h at 65°C and then heated to 110 °C. After stirring for an additional 30 min, the supported NHC-Pd(II) complex 2 was separated by filtration. The powder was washed by methylene chloride and dried under vacuum at 60 °C. Elemental analysis and weight gain showed that 0.2 mmol of Pd was anchored on 1.0 g of the SBA-15 silica complex 2. 2.3. General procedure for the Suzuki reaction A mixture of aryl halide (0.3 mmol), phenylboronic acid (0.040 g, 0.33 mmol), Na2CO3 (0.063 g, 0.6 mmol), and NHC-Pd complex 2 (1 ~ 0.05 mmol%, corresponding to iodobenzene) in the solvent (Table 1, 0.8 ml) was stirred at 5075 °C for an appropriate time. The reaction was monitored by GC until complete consumption of aryl halide. The immobilized Pd complex 2 was separated by filtration and the reaction mixture was diluted with H2O and ether. The organic layer was dried over MgSO4 and then evaporated under reduced pressure. The residue was purified by short column chromatography on silica gel. Conversion was determined by GC analysis. 3. Results and Discussion The immobilization of ./V-heterocyclic carbene-Pd complex (NHC) onto SBA15 silica was performed in two steps (Scheme 1). Reaction of SBA-15 silica with

699 of triethoxysilylpropylimidazolium chloride in refluxing toluene gave SBA-15supported ionic liquid 1. The desired SBA-supported NHC-Pd(II) complex 2 was prepared by treatment of the supported ionic liquid 2 with palladium acetate in Table 1. Suzuki coupling of iodobenzene with phenylboronic acida Ligand2, Na 2 CO 3 -I

-B(OH) 2

+

Solvent

Solvent (1:1)

2 (mol %)

Temp. (°C)

Time (min)

Conv. (%)"

DMF:H 2 O

1

50

30

93

DMF:H 2 O

1

65

20

100

DMF:H 2 O

0.5

65

25

100

DMF:H 2 O

0.1

65

30

100

DMF:H 2 O

0.05

75

30

95

DMA:H 2 O

0.1

65

20

100

EtOH:H 2 O

0.1

65

25

99

a

Molar ratio: aryl iodide 1.0 equiv., Pd complex 2 1-0.05 mol% (loading ratio = 0.2 mmol/g), phenylboronic acid 1.1 equiv. andNa2CO3 2 equiv. bDetermined by GC analysis. Table 2. Suzuki coupling of aryl halides with phenylboronic acida Ligand2, Na2CO3 B(OH) 2

DMF:H 2 O(1:1),65°C R = I, Br

Time (min)

Conv. (%)b

Entry

Substrate

1 2

2-iodoanisole 4-iodoanisole

35 30

92

3

2-iodotoluene

35

86

4

1 -iodo-3-nitrobenzene

20

100

5

1 -iodo-4-nitrobenzene

20

100

6 7 8

1 -iodo-4-nitrobenzene 4-iodophenol bromobenzene

20

99

25 30

100

9

2-bromoanisole

30

90

10

4-bromoanisole

30

95

95

95

100 11 1 -bromo-3 -nitorobenzene 25 a Molar ratio: aryl iodide 1.0 equiv., Pd complex 2 0.1 mol% (loading ratio = 0.2 mmol/g), phenylboronic acid 1.1 equiv. andNa2CO3 2 equiv. bDetermined by GC analysis.

700 Table 3. Recycling of the SBA-supported NHC-Pd(II) complex 2 recycle 2, Na2CO3 B(

°H)2

DMF:H2O(1:1),65°C

R aryl halide /=\

R cycle

yield (%)

cycle

yield (%)

1

100

4

98

2

100

5

96

3

100

6

93

100

100

100

99

100

98

Reactions were carried out under the optimized reaction conditions as described in Table.

DMSO at 110°C. The immobilized Pd(II) complex with palladium loading of 0.2 mmol/g was characterized by physical methods. With the heterogeneous Pd complex 2 in hand, the initial investigation started with the cross-coupling reaction of iodobenzene with phenylboronic acid. The results are summarized in the Table 1. The catalyst showed high activity in the coupling of iodobenzene and acrylates. Surprisingly, using a Pd concentration of 0.05 mol% gave us a 95% conversion of the desired product within 30 min. It is worthy to note that the reaction in aqueous ethanol gave excellent results. On the basis of the high activity of the Pd complex 2, we also performed the Suzuki reaction of substituted iodobenzene with phenylboronic acid (Table 2). High catalytic activity was found in the couplings of iodoanisole, 1-iodo-4-nitrobenzene and 4iodophenol with phenylboronic acid (entries 1-7). Moreover, catalytic activity in the coupling of substituted bromobenzene was also excellent (entries 8-11). The catalyst could be recycled without a significant loss of activity. 4. Conclusion In conclusion, we have found that SBA-supported NHC-Pd(II) complex 2 can be used as an outstanding heterogeneous catalyst for Suzuki-coupling reactions. 5. References [1] [2] [3] [4] [5]

N. Miyaura and A. Suzuki, Chem. Rev. 95 (1995) 2457. S. Liu, M. J. Choi and G. C. Fu, Chem. Commun. (2000) 2475. F. Bellina, A. Carpita and R. Rossi, Synthesis. 2419 (2004) 2440. N. Jiang and A. Ragauskas, Tetrahedron Lett. 47 (2006) 197. O. Vassylyev, J. Chen, A. P. Panarello and J. G. Khinast, Tetrahedron Letters. 46 (2005) 6865. [6] J.-H. Kim, B.-H. Jun, J.-W. Byun and Y.-S. Lee, Tetrahedron Lett. 45 (2004) 5827.

Recent Progress in Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

701 701

Selective oc-alkylation of ketones with alcohols catalyzed by highly active mesoporous Pd/MgOA12O3 type basic solid derived from Pd-supported MgAl-hydrotalcite Suman K. Janaa, Yoshihiro Kubotab and Takashi Tatsumia aChemical Resources Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Yokohama 226-0583, Japan Division of Materials Science & Chemical Engineering, Graduate School of Engineering, Yokohama National University, 79-5 Tokiwadai, Hodogaya-ku, Yokohama 240-8501, Japan

Mesoporous Pd/MgO-Al2O3 type basic solid obtained by calcining Pdsupported MgAl-hydrotalcite showed very high catalytic activity, product selectivity and reusability in the liquid-phase a-alkylation of ketones with alcohols under solvent-free and mild conditions. 1. Introduction Hydrotalcite has attracted interest because of alternate cationic layers and anionic interstitial species, surface tunable basicity and adsorption capacity. These unique properties of hydrotalcites offered the design of multifunctional heterogeneous catalysts aiming at environmentally friendly organic synthesis. a-Alkylated ketones are important intermediates in fine chemicals industry and are traditionally synthesized by the reaction of ketones with alkyl halides using stoichiometic amounts of inorganic bases. However, during this reaction a large volume of undesirable waste is formed. Hence, heterogeneously catalyzed aalkylation, particularly by using alcohol as an alkylating agent, is preferred on both economical and environmental grounds. A few transition metal based catalysts: RuCl2(PPh3)3, [Ir(cod)Cl2/PPh3, Pd/A1O(OH) and Pd/C are reported so far to accomplish a-alkylation processes; however, all those catalysts additionally require inorganic base and/or hydrogen acceptor as additive for exhibiting their high alkylation performances [1 - 4]. We report here for the first

702

time the high activity of mesoporous Pd/MgO-Al2O3 type basic solid, possessing both active palladium species and surface basic sites as a bifunctional catalyst, derived from Pd-supported MgAl-hydrotalcite for direct aalkylation of ketones with alcohols in the absence of any solvents and additives under mild reaction conditions (Scheme 1). The catalytic performance of Pd/MgO-Al2O3 was found to be much higher when compared with various other Pd based solids in the a-alkylation under identical reaction conditions. o Mesoporous Pd/MgO-AI 2 O 3 120°C,N 2 atmosphere

Scheme 1

[R = H or CH3O and X = C6H5, C6H5(OCH3) or C ln H 21 ]

2. Experimental Section Mesoporous Pd/MgO-Al2O3 type basic solid used in the present investigation was obtained by calcining Pd-supported MgAl-hydrotalcite at 450°C. The Pdsupported hydrotalcite was synthesized by adsorbing/absorbing Pd species (0.5 mmol per g of MgAl-hydrotalcite having a Mg/Al molar ratio of 3.0) onto the surfaces of MgAl-hydrotalcite by allowing it to have contact with aqueous Pd (II) sodium chloride solution. Other Pd based solids with a similar Pd loading were prepared by the conventional incipient wetness impregnation technique. All the solid samples were characterized for their phase identification by XRD, surface area by BET, chemical analysis by ICP, surface composition by XPS and basicity by measuring the pH of their suspension in water. Liquid-phase aalkylation of ketones with alcohols over different Pd-containing catalysts was carried out in a batch reactor under N2 atmosphere. The reaction products and unconverted reactants were analyzed and quantified by GC and the conversion [C] and selectivity [S] were calculated based on alcohol. 3. Results and Discussion A number of Pd based solids including hydrotalcite, hydrotalcite-derived mixed metal oxides and supported catalysts were prepared and screened in order to identify and develop highly efficient heterogeneous catalysts for the synthesis of a-alkylated ketones. The physico-chemical properties and catalytic performances of various Pd-containing catalysts in the a-alkylation of acetophenone with benzyl alcohol under solvent-free conditions are summarized in Table 1. The phase(s) present in the different solid samples as indicated in Table 1 was confirmed by X-ray diffraction measurements. It was observed that a-alkylation proceeded over Pd-containing solids only when the catalyst additionally having the basic properties was used and the reaction was performed under strictly N2 atmosphere (entries 1, 3 - 6, 8). Over Pd based basic

703 Table 1: a-Alkylation of acetophenone with benzyl alcohol over various Pd-containing solid catalysts." Entry

Catalyst

1

Pd/MgO-Al2O3

(mV1)

Surface area

pHof suspension in water*

C[%]

S[%]

324

10.6

53.2

93.7

2

Pd/MgO-Al2O3

c

324

10.6

55.3*

3.1

3

Pd/MgO-Al 2 O/

324

10.6

99.7

99.1

4

Pd-supported on MgAl-HT

149

9.7

29.3

95.3

5

Pd/MgO

32

10.2

4.1

86.5

6

Pd/Mg(OH)2

29

10.0

3.9

87.1 g

7

Pd/Al2O3

94

6.8

10.8

0.0

8

Pd/MgO-Al 2 O/

310

10.6

52.9

94.5

9

PdCl2

-

-

11.3*

0.0

10

MgO-Al 2 O/

337

10.7

1.5

96.8

11

no

-

-

1.2*

0.0

"reaction mixture = 20 mmol acetophenone + 20 mmol benzyl alcohol + 0.25 mmol Pd, temperature = 120°C and reaction time = 4 h; 'suspension of 0.3 g solid in 20 ml of water; 'under O2 atmosphere; ^reaction time = 10 h ; "third reuse of the catalyst; ^amount of catalyst = 0.4 g; ^benzyl alcohol was selectively transformed to benzaldehyde.

solids 1,3-diphenylpropan-l-one was found to be the major product along with small amounts of benzaldehyde, benzalacetophenone, 2,3-diphenylpropan-l-ol and/or 1-phenylethyl alcohol. Among the various Pd-containing basic solids used in the present study, the hydrotalcite and hydrotalcite-derived mixed metal oxides were found to be the most efficient. Pd/MgO-Al2O3 obtained by calcining Pd-supported MgAl-hydrotalcite at 450°C was found to be the best one, showing benzyl alcohol conversion 53.2 % and 1,3-diphenylpropan-l-one selectivity over 93 % in the a-alkylation after the reaction period of 4 h (entry 1). Importantly, the catalyst preserved its high activity even after the third successive use in the reaction (entry 8). By ICP analysis, only a trace amount of Pd was detected in the liquid reaction mixture after its separation from the solid catalyst by hot filtration, indicating the extent of Pd leaching was negligibly small. The very high activity of Pd/MgO-Al2O3 as compared to the other Pdcontaining basic catalysts seems to be due to the highly dispersed Pd on high surface area mesoporous magnesium and aluminum mixed oxides type solid (having BET surface area of 324 m2g"' and pore diameter of about 10 nm). The presence of surface enriched Pd in Pd/MgO-Al2O3 type solid was confirmed by the remarkably higher surface Pd/(Pd+Mg+Al) molar ratio of 0.115 (obtained from XPS analysis result) as compared to the bulk Pd/(Pd+Mg+Al) molar ratio

704 Table 2: a-Alkylation of various ketones with alcohols over Pd/MgO-A^C^." Ketone

Alcohol

C[%]

S[%]

Acetophenone

Benzyl alcohol

53.2

93.7

p-Methoxy acetophenone

Benzyl alcohol

54.7

95.8

Acetophenone

p-Methoxy benzyl alcohol

60.1

95.1

Acetophenone

1-Undecanol

17.1

89.3

"reaction mixture = 20 mmol ketone + 20 mmol alcohol + 0.25 mmol Pd, temperature = 120°C and reaction time = 4 h.

of 0.036 (measured by ICP). It is interesting to note that Pd/MgO-Al2O3 gave benzaldehyde as a major product under O2 atmosphere. Additionally it is observed that in the absence of basic sites in the catalyst the a-alkylation hardly occurred; however, over these non-basic Pd catalysts benzyl alcohol was selectively transformed into benzaldehyde (entries 7 and 9). Mesoporous Pd/MgO-Al2O3 type solid, the best catalyst in the present study, was also found to be active for a-alkylation of a variety of ketones with alcohols, including less active aliphatic alcohols, forming a-alkylated phenones in good yields (Table 2). By several control experiments it is confirmed that a-alkylation over Pd based basic solids proceeds through the following three sequential reaction steps: (i) dehydrogenation of alcohol to aldehyde, (ii) base catalyzed aldol condensation between the resulting aldehyde and the ketone forming a,P-unsaturated ketone, and (iii) selective hydrogenation of a,P-unsaturated ketone leading to aalkylated ketone. The detailed reaction mechanism including the specific role of each catalytically active species will be described elsewhere [5]. 4. Conclusion We have demonstrated, for the first time, the high catalytic performance of Pd/MgO-Al2O3 promoted liquid-phase a-alkylation of ketones with alcohols under solvent-free and mild reaction conditions. The bi-functional Pd based mesoporous solid was also reusable in the reaction. 5. References [1] C. S. Cho, B. T. Kim, T. J. Kim and S. C. Shim, Tetrahedron Lett. 43 (2002) 7987. [2] K. Taguchi, H. Nakagawa, T. Hirabayashi, S. Sakaguchi and Y. Ishii, J. Am. Chem. Soc. 126 (2004) 72. [3] M. S. Kwon, N. Kim, S. H. Seo, I. S. Park, R. K. Chedrala and J. Park, Angew. Chem. Int. Ed. 44 (2005) 6913. [4] C. S. Cho, J. Mol. Catal. A: Chem. 240 (2005) 55. [5] S. K. Jana, Y. Kubota and T. Tatsumi (to be published).

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Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Published by Elsevier B.V.

Asymmetric dihydroxylation catalyzed by SBA-15 silica-supported bis-cinchona alkaloid M. S. Sarkar, Ji-Young Jung and Myung-Jong Jin* School of Chemical Science and Engineering, Inha University, lncheon, 402-751, Korea

SBA-15-supported bis-cinchona alkaloid was examined as a heterogeneous chiral ligand for asymmetric dihydroxylation of olefins. The desired diols were obtained in high yield with excellent enantiomeric excess. High ordered mesoporous silica SBA-15 was found to be a valuable support for the catalytic system. 1. Introduction

O O Si O

S

Si

S N

N

N N O

O OMe

MeO N

N

1

O O O

SBA-15

SBA-15

Osmium-catalyzed asymmetric dihydroxylation (AD) of olefins has emerged as an attractive method for the synthesis of optically active diols [1]. Cinchona alkaloid-based osmium complexes are known to be the most effective chiral catalysts for AD reactions in terms of both reactivity and enantioselectivity [2]. However, for large scale synthesis the high cost of chiral ligands and toxicity of the osmium must be taken into consideration. The development of chiral heterogeneous catalysts is a field of great interest in order to overcome the problems. Besides these economical and environmental reasons, heterogeneous catalysts offers practical advantages over homogeneous catalytic system which include simplified separation, easy recovery of catalyst and potential reuse.

706

Heterogenizing homogeneous catalysts by immobilization onto supports is a major trend toward the development of heterogeneous catalysts. Silica gel and mesoporous silica SBA-15 were successfully used as inorganic supports for the immobilization of homogeneous catalysts [3-5]. Our interest in the field led to prepare SBA-15 silica-supported bis-cinchona alkaloid. Herein, we describe our preliminary results on the AD reaction of olefins using the SBA-15-supported chiral ligand 1. 2. Experimental Section 2.1. Preparation of 1,4-bis(9-O-quininyl)phthalazine 2 To a solution of quinine (5.0 mmol), 1,4-dichlorophthalazine (2.5 mmol) in THF (15 ml) was slowly added 5-fold excess of NaH (25 mmol) at 0 °C. The mixture was stirred at 60 °C for 2 h, and then quenched at 0 °C by careful addition of water. The mixture was diluted with ether. The product was extracted with EtOAc and the solvent was removed under reduced pressure. Column chromatography of the residue gave of white powder 2 in 82 % yield. 2.2. Preparation of trimethoxysilanized 1,4-bis(9-O-quininyl)phthalazine 3 l,4-bis(9-O-quininyl)phthalazine 2 (1.0 mmol) was added to a solution of (3mercaptopropyl)trimethoxysilane (2.4 mmol) and AIBN (0.2 mmol) in 12 ml of degassed chloroform. The reaction mixture was refluxed for 24 h and then concentrated under reduced pressure. The residue was purified by flash short column on silica gel to give 3 of a glass in 75 % yield. 2.3. Immobilization of bis-cinchona alkaloid 3 onto SBA-15 silica 1 SBA-15 silica (1.0 g) was suspended in toluene and refluxed with compound 3 (120 mg, 0.1 mmol). After 18 h, the powder was collected by filtration and washed with methanol and methylene chloride. After drying in vacuo at 70 °C, SBA-15-supported alkaloid 1 (1.08 g) was obtained. Elemental analysis and weight gain showed that 0.08 mmol of l,4-bis(9-O-quininyl)phthalazine 3 was anchored on 1.0 g of the SBA-15-supported chiral ligand 1. 2.4. Asymmetric dihydroxylation ofolefm catalyzed immobilized ligand 3 To a mixture of SBA-15-supported bis-cinchona alkaloid 1 (0.02 mmol), potassium ferricyanide (3 mmol), potassium carbonate (3 mmol), and OsO4 (1 mol %, 0.5 M in water) in 5 mL of tert-butyl alcohol-water mixture (1:1, v/v) at room temperature, the olefin (1 mmol) was added at once and stirred for 8~12 h. The reaction mixture was diluted with water and CH2C12, and then immobilized

707

ligand 1 was separated by filtration. After general work-up, the crude product was purified by flash column chromatography. Enantiomeric excess of the diol was determined by chiral HPLC analysis. 3. Results and Discussion The immobilization of cinchona alkaloid ligand 3 was accomplished following the route shown in Scheme 1. Treatment of quinine with 1,4-dichlorophthalazine in the presence of NaH gave chiral 4-bis(9-O-quininyl)phthalazine 2. Dimeric quinine 2 was converted to 3 having pendant trimethoxysilane functional group by radical reaction with (3-mercaptopropyl)trimethoxysilane. The chiral ligand 3 was easily grafted in pores of SB A-15 silica by reacting with SBA-15. Scheme 1

OMe

MeO

toluene, reflux, 18 h

We performed the AD reactions of stilbene using the heterogeneous chiral ligand 1. Surprisingly, the desired diol was obtained in excellent yield with perfect 100 % enantioselectivity (entries 1-3). A catalyst loading of 1 mol % was sufficient to obtain the same result. The heterogeneous ligand 1 was also highly effective to different olefins (entries 4 and 5). The results are summarized in the Table 1. The SBA-supported ligand 1 gave higher asymmetric induction than amorphous silica-supported bis-cinchona alkaloid [4]. The improved outcome of the reaction seems to be attributed to crystalline structure of SBA-15 support. The SBA framework allows an ordered array of chiral catalytic sites on the pore surface. The ordered array leads to elegant site-isolation, which may result in enhanced enantioselectivity. It is noteworthy that these results are superior to

708

those of its homogeneous counterpart. The SBA-15-supported alkaloid-OsO4 complex could be reused without a significant loss of reactivity (entry 3). Table 1. Heterogeneous AD of olefins using SBA-15-supported ligand l a 'R

SBA-15-supported ligand 1 cat. OsO4 K3Fe(CN)6-K2CO3, /-BuOH-H2O

Entry

Olefin

Time (h)

Yield (%)

(%) Eeb

Configb

1

stilbene

8

95

100

S,S

2°

stilbene

8

92

100

S,S

3d

stilbene

12

90

100

s,s

4

methylcinnamate

8

94

100

2R,3S

5

1-pheny-lcyclohexene

10

91

96

25,35

a

The reaction was carried out at RT; Molar ratio of olefin/OsO4/supported ligand = 1/0.01/0.02.

b

Ee and absolute configuration were determined by chiral HPLC analysis. cMolar ratio of olefin/OsO4/supported ligand = 1/0.005/0.01. dReaction was carried out with regenerated 1 without further addition of OsO4.

4. Conclusion In conclusion, we achieved remarkable results in the heterogeneous catalytic AD using SBA-15-supported bis-cinchona alkaloid 1. Moreover, the SBA-15 was proven to be an excellent support for the heterogeneous chiral ligand. Efforts for the synthesis of further mesoporous silica-based chiral ligands are currently underway in our laboratory. 5. References [1] E. N. Jacobsen, A. Pfaltz and H. Yamamoto, In Comprehensive Asymmetric Catalysis II, Springer-Verlag, Berlin, (1999). [2] H. C. Kolb, M. S. VanNieuwenhze and K. B. Sharpless, Chem. Rev. 50 (1994) 2483. [3] C. E. Song, J. W. Yang and H. J. Ha, Tetrahedron: Asymmetry. 8 (1997) 841. [4] H. M. Lee, S. W. Kim, T. H. Hyeon and B. M. Kim, Tetrahedron: Asymmetry. 12 (2001) 1537. [5] Y.-M. Song, J. S. Cho, J. W. Yang and H. Han, Tetrahedron Lett. 45 (2004) 3301.

709

Recent Progress in Mesostructured Mesostructured Materials D. D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Published by Elsevier B.V.

Mesoporous silica SBA-15-supported palladium catalyst for green Sonogashira coupling reactions Myung-Jong Jina*, M. S. Sarkara, Dong-Hwan Leeb and Ik-Mo Leeb "School of Chemical Science and Engineering, Inha University, Incheon, 402-751, Korea b Department of Chemistry, Inha University, Incheon, 402-751, Korea

We have immobilized diphosphane palladium onto mesoporous SBA-15 silica. The immobilized Pd complex was used as a highly effective catalyst for Sonogashira coupling reaction. Excellent conversions as well as high reactivities have been observed in 1 h for the Sonogashira couplings of aryl halides. 1. Introduction The immobilization of catalysts to solid supports opens the possibility for extending the benefits of heterogeneous system to homogeneous catalysts. The benefits may include the ease of work-up procedures and the potential for reuse of the supported catalysts [1]. These features can offer environmental-friendly OH OH OH

i)

O O

Si

ii) NH2

O

O O

PPh2 PPh2

O 1

SBA-15

N

Si

loading ratio 0.46 0.46 mmol/g mmol/g

2

loading ratio 0.40 mmol/g

iii) i) (CH3O)33Si(CH Si(CH22))33NH NH22,, toluene, 105 C, 12 105o°C, 12 h 12 h ii) 2Ph22PCH2OH, toluene, reflux, 12 iii) (CH33CN)2PdCl2, CHCl3, C, 10 65 o°C, 10 hh 3, 65

O O

PPh2 N

Si

O

PdCl2 PPh2

3

Scheme 1

loading ratio 0.36 0.36 mmol/g mmol/g

catalytic systems as well as improved processing steps. Indeed, a considerable amount of research has been performed in the area. Immobilized catalysts suffer from the inherent nature of their low activity. However, catalytic properties of the heterogenized catalysts can be improved compared to the homogeneous counterpart due to the site-isolation and constraint effects. Inorganic supports have been extended into ordered mesoporous silicas from amorphous silica gel [2]. In

710

particular, SBA-15 silica having large surface areas, lots of surface silanol groups and good chemical stability has been extensively used as a promising support [3]. Herein, we report the synthesis of SBA-15-supported Pd complex 3 and its catalytic activity in heterogeneous Sonogashira coupling reactions. The Sonogashira cross-coupling of aryl halide and terminal alkyne is a useful tool for the synthesis of aryl-substituted acetylene [4]. 2. Experimental Section 2.1. Preparation of 3-aminopropylated SBA-15 silica 1 SBA-15 silica (1.0 g) was added to a solution of 3-(aminopropyl) trimethoxysilane (87 mg, 0.48 mmol) in toluene (15 mL). The mixture was stirred at 105°C for 12 h. The 3-(aminopropyl)trimethoxysilanized SBA-15 silica was collected by filtration, washed repeatedly with CH2C12, and dried under vacuo at 70°C. Weight gain showed that 0.46 mmol of 3-(aminopropyl)trimethoxysilane was immobilized on 1.0 g of SBA-15 silica 1. 2.2. Preparation of (diphenylphosphinomethyl)aminopropylatedSBA-15 silica 2 To a solution of diphenylphosphinomethanol (0.65 mmol) in toluene (10 mL) was added SBA-15 silica 1 ( 1.0 g). The mixture was refluxed for 12 h. The immobilized complex 2 was separated by filtration, and washed by methylene chloride and dried under vacuum at 60°C. Elemental analysis showed that 0.40 mmol of phosphino complex was anchored on 1.0 g of the SBA-15 silica 2. 2.3. Preparation of SBA-15-supported Pd (II) complex 3 To a solution of bis(acetonitrile)dicholoropalladium (0.35 mmol) in CH3C1 was added SBA-15 silica 2 (0.85 g). The mixture was stirred for 10 h at 65°C. The immobilized complex 3 was separated by filtration, and washed by methylene chloride and dried under vacuum at 65°C. Elemental analysis showed that 0.36 mmol of Pd complex was anchored on 1.0 g of the SBA-15 silica 3. 2.4. General procedure for the Sonogashira reaction A mixture of aryl halide (1.0 mmol), phenylacetylene (1.1 mmol), piperidine (2.0 mmol) and 1 mol % of SBA-15 Pd complex 3 was stirred at 50-70°C, and the reaction was monitored by GC. The immobilized ligand 3 was separated by filtration and the reaction mixture was diluted with H2O and ether. The organic layer was dried over MgSO4 and evaporated under reduced pressure. The crude product was purified by short column chromatography on silica gel. Conversion was determined by GC analysis.

711

3. Results and Discussion Treatment of SBA-15 silica with (3-aminopropyl)trimethoxysilane in refluxing toluene gave aminoropropylated SBA-15 1 (0.46 mmol (CH2)3Cl/g).Reaction of 1 with 1.2 equiv. excess of diphenylphosphinomethanol in refluxing toluene afforded SBA-15-supported diphosphine 2 (0.4 mmol/g). SBA-15-supported Pd catalyst 3 (0.36 mmol/g) was prepared by treatment of the modified SBA-15 silica 2 with (CH3CN)2PdCl2.The degrees of functionalization were determined by weight gain or elemental analysis for the modified SBA-15.TEM images show that SBA-15 silica 3 retains the original ordered meso structure of SBA-15 (Figure 1).

Table 1 Structural characteristics of SBA-15-supported Pd complex 3 Sample

Pore Surface area 2

diameter

Loading

Pore volume

amount 3

SBA-15

720 m /g

8.33 nm

0.83 cm

3

385 m2/g

7.21 nm

0.35 cm3

0.36 mmol/g

However, the surface area, pore volume and pore size decreased due to the grafting of organic moieties (Table 1). With the heterogeneous Pd complex 3 in hand, we then investigated its catalytic activity in heterogeneous Sonogashira coupling reactions of aryl halides with phenylacetylene in the presence of piperidine as a base. The results are summarized in the Table 2. The catalyst showed high activity in the Sonogashira coupling reactions under solvent-free condition. Moreover, activity in the coupling of bromobenzene was also excellent. These results came as a bit of a surprise since most of the reactions were completed within very short time in nearly 100% yield and 100% selectivity. The catalyst could be recycled with a little loss of activity. Table 2. Catalytic activity of SBA-15-supported Pd complex 3 for Sonogashira Coupling11

712 Entry

Aryl iodide

Temp. (°C)

Time (h)

Conv. (%)"

1

iodobenzene

50

1

90

2

iodobenzene

70

0.5

100

3

2-iodoanisole

70

1

95

4

4-iodoanisole

70

1

99

5

4-iodophenol

70

1

100

6

2-iodotoluene

70

1

100

7

1 -iodo-3 -nitrobenzene

70

1

100

8

1 -iodo-4-nitrobenzene

70

1

100

9

bromobenzene

70

2

90

10

1 -bromo-3-nitrobenzene

70

1.5

93

11

1 -bromo-4-nitrobenzene

70

1.5

92

12

4-bromoanisole

70

2

88

13

2-bromoanisole

70

2

85

a

Molar ratio: aryl halide (1.0 equiv.), Pd complex 3 (0.01 equiv., loading ratio = 0.36 mmol/g), phenylacetylene (1.1 equiv.) and piperidine (2.0 equiv.). 'Determined by GC analysis. Table 3. Recycling of the supported Pd complex 3 cycle

yield (%)

cycle

yield (%)

1

100

4

96

2

100

5

93

3

98

6

88

Reaction was carried out under the optimized reaction conditions as described in Table 2, entry 7.

4. Conclusion In conclusion, mesoporous silica SBA-15-supported Pd complex 3 can be efficiently served as a highly effective catalyst for Sonogashira coupling reaction under solvent-free condition. 5. References [1] [2] [3] [4]

N. E. Leadbeater and M. Marco, Chem. Rev. 102 (2002) 3217. A. P. Wright and M. E. Davis, Chem. Rev. 102 (2002) 3589. D. Zhao, J. Sun, Q. Li and G. D. Stucky, Chem. Mater. 12 (2000) 275. K. Sonogashira, J. Organomet. Chem. 653 (2002) 46.

713 713

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Published by Elsevier B.V.

VO(acac)2 incorporated in mesoporous silica SBA15-confined ionic liquid as a catalyst for epoxidation M. S. Sarkar, Ji-Young Jung and Myung-Jong Jin* School of Chemical Science and Engineering, Inha University, Incheon, 402-751, Korea

VO(acac)2 was incorporated with the aid of ionic liquid onto mesoporous silica SBA-15 material. The immobilized VO(acac)2 was used as an effective catalyst for epoxidation of allylic alcohols. 1. Intorduction The metal-catalyzed epoxidation of allylic alcohols has attracted much attention since the epoxides constitute important building blocks in organic synthesis [1]. A fast and efficient epoxidation of allylic alcohols is still on continuous demands. Vanadyl acetylacetonate (VO(acac)2) is among the most effective catalysts for the epoxidation [2]. However, most of the epoxidations Bu

=

N PF6-

•

*

;

*

.

*

*

+

N

n Me |

-

1 Me 1 toluene reflux, 12 h SBA-15

2

• = VO(acac) VO(acac)22 THF C, 1 h 60 o°C,

3

Scheme 1 have operated under homogeneous conditions. The simplified separation, easy recovery of catalyst and reuse of the catalysts should be desirable in scale-up

714

processes. For this reasons the development of heterogeneous catalysts is a field of great interest [3]. Ionic liquids have recently received much attention as novel reaction media for numerous catalytic reactions due to the ease of separation [4]. However, the use of ionic liquids frequently suffers from high cost of the ionic liquids and high viscosity in using as solvents. Because reduced use of ionic liquids is required from such viewpoints, the immobilization of ionic liquids on a solid support would be highly desirable. Recently, Hagiwara has reported new immobilization method of Pd catalyst in ionic liquid-confined silica gel [5]. Our interest in the field led to prepare highly ordered mesoporous SBA-15 silicaconfined ionic liquid containing VO(acac)2. The SBA-15 silica area has often used as inorganic supports for the immobilization of homogeneous catalysts. Herein, we present preparation of the immobilized VO(acac)2 into pores of SBA15 silica and its application for epoxidation of allylic alcohols. 2. Experimental Section 2.1. Immobilization of ionic liquid 1 onto SBA-15 silica 2 SBA-15 silica (1.0 g) was added in to a solution of l-butyl-3methylimmidazolium hexafluorophosphate 1 (0.154 g, 0.54 mmol) in toluene. The mixture was stirred at 105°C for 12 h and washed with methylene chloride. After drying under vacuo at 60°C, SBA-15-supported ionic liquid 2 was obtained. Elemental analysis and weight gain showed that 0.36 mmol of ionic liquid was anchored on 1.0 g of SBA-15-supported ionic liquid 2. 2.2. Preparation of SBA-15 supported VO(acac)2 3 To a stirred solution of SBA-15-supported ionic liquid 2 (0.500 g, 0.18 mmol) in THF (10 ml), VO(acac)2 (0.05 g, 0.188 mmol) was added. The mixture was stirred at 60°C for 1 h. The SBA-15 supported VO(acac)2 complex 3 was separated by filtration. The powder was washed by ether and dried under vacuum at 60 °C. Elemental analysis and weight gain showed that 0.2 mmol of VO(acac)2 was anchored on 1.0 g of the immobilized 3. 2.3. General procedure for epoxidation of allylic alcohols To a stirred solution of SBA-15 supported VO(acac)2 (75 mg, 0.015 mmol) 3 in hexane (1 ml) was added allylic alcohol (0.5 mmol). After 10 min, TBHP (1.5 equiv. in hexane solution) was added and stirring was continued at RT for the time indicated in Table 2. The immobilized 3 was separated by filtration. The reaction mixture was diluted with ether and water. The orgnaic layer was washed with brine and dried over MgSO4. The solvent was evaporated under reduced pressure and the crude product was purified by flash chromatography.

715

3. Results and Discussion We have easily immobilized VO(acac)2 on the surface of mesoporous silica SBA-15 material as shown in Scheme 1. SBA-15 was mixed with l-butyl-3methylimmidazolium hexafluorophosphate 1 and allowed to react for 12 h at 105 °C. The ionic liquid confined SBA-15 2 was collected by simple filtration and washed with methylene chloride. The SBA-15 supported VO(acac)2 was prepared by the reaction of ionic liquid confined SBA-15 2 and VO(acac)2 in THF at 65°C. THF was removed under reduced pressure and the residue was completely washed with a large amount of Et2O to afford a microencapsulated VO(acac)2 (loading ratio: 0.2 mmol/g). It is interesting that VO(acac)2 can be immobilized onto the mesoporous silica by this very simple process.

allot anchoring of VO(acac],oriSBM5

Fig 1. TEM of parent SBA-15

Table 1

Fig. 2. TEM of immobilized SBA-15 3 with VO(acac),

Fig

3. XRO pattern pro

Epoxidation of allylic alcohols with microencapsulated VO(acac) 2 3 a

allyl alcohol (substrate)

epoxy alcohol (product)

\}~

OH

Klaso Time (h)

Conv. (%)c

3-penten-2-ol

1.5

98

2

3-decen-5-ol

2

96

3

2-cyclohexen-1 -ol

2

98

4b

2-cyclohexen-l-ol

2

96

5

1,3-diphenyl-2-propen-l -ol

2.5

97

Entry

Allylic alcohol

1

"Reactions were carried out with allylic alcohol (0.5 mmol), VO(acac)2 3 (0.03 equiv., loading ratio = 0.2 mmol/g), f-BuOOH (1.5 equiv.) in hexane (1.0 ml). bRegenerated VO(acac)2 catalyst 3 was used. c Determined by GC analysis.

716

The loading ratio was measured by weight gain. The immobilized VO(acac)2 3 was characterized by physical methods. The HRTEM images obtained from the parent SBA-15 and the modified SBA-15 are shown in Fig 1 and Fig 2, respectively. The hexagonal symmetry of the pore arrays is maintained after immobilizing VO(acac)2. The SBA-15 structure 3 is well evidenced from XRD pattern of Fig 3 which is similar to that of the parent SBA-15 support. Apparently, there is no change of the lattice parameters upon the immobilizing process. The immobilized VO(acac)2 3 was used as a catalyst for for epoxidation of allylic alcohols. As shown in Table 1, the catalyst gave high activity in the epoxidation of cyclic 2-cyclohexen-l-ol as well as aliphatic 3-penten-2-ol and 3decen-5-ol at RT. (entries 1-3). Epoxidation of l,3-diphenyl-2-propen-l-ol containing aromatic ring was also highly effective under the same conditions (entry 5). The immobilized VO(acac)2 3 proved to be an excellent catalyst for the epoxidation. The SBA-15 silica confined VO(acac)2 is easily separated by simple filtration after reaction. It is noteworthy that the VO(acac)2 catalyst could be recycled without a significant loss of activity (entry 4). In most cases, recovery and reuse of the immobilized catalysts have so far been unsatisfactory due to their significant metal leaching and low catalytic activity. Our results show that it is possible to use homogeneous catalysts without additional modifications of the catalysts as well as to minimize the disadvantages of the immobilized catalysts. This strategy may open up a path to the development of new immobilization process. 4. Conclusion In conclusion, we have achieved excellent results for the heterogeneous catalytic epoxidation using VO(acac)2 incorporated with SBA-15-confined ionic liquid. 5. References [1] R. A. Sheldon and J. K. Kochi, Metal-Catalyzed Oxidation of Organic Compounds; Academic Press, (1991). [2] K. A. Jorgensen, Chem. Rev. 89 (1989) 435. [3] A. Closson, M. Johansson and J. Backvall, Chem. Commun. (2004) 494. [4] T. Welton, Chem. Rev. 99 (1999) 2071. [5] H. Hagiwara, Y. Sugawara, K. Isobe, T. Hoshi and T. Suzuki, Org. Lett. 6 (2004) 325.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

717 717

Selective photocatalytic oxidation of methane into methanol on V-MCM-41 mesoporous molecular sieves Yun Hu, Yasuhito Nagai, Masaya Matsuoka and Masakazu Anpo* Department of Applied Chemistry, Graduate School of Engineering Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku, Sakai, Osaka 599-8531, Japan

The partial photocatalytic oxidation of methane with NO led to the selective methanol formation over the V-MCM-41 catalysts under UV irradiation at 295 K, while only a complete oxidation of methane proceeded in the presence of O2. The yield of methanol well corresponded to the yield of the photoluminescence due to the isolated tetrahedral V +-oxides species, indicating that the charge transfer excited triplet state of these species plays an importat role in the reaction. 1. Introduction The selective conversion of methane into higher hydrocarbons and/or more valuable oxygen-containing compounds such as methanol and formaldehyde has attracted much attention in the last decade since there are still difficulties in activating C-H bonds of CH4 and C2H6 [1, 2]. In most of these studies, high temperatures are required even for the low conversion levels. It has been reported that a silica supported vanadium oxide catalysts exhibit relatively high reactivity for the oxidation of methane into methanol and formaldehyde [3]. However, few studies on the selective photooxidation of methane have been successful [4, 5]. In this study, we report on the preparation of V-MCM-41 mesoporous molecular sieves which can accommodate the high concentrations of the isolated V5+-oxide species as active sites and their photocatalytic activities for the partial oxidation of methane with various oxidative gasses. This work was supported by the Japan Society for the Promotion of Science, Grant-inAid for JSPS Fellows.

718

2. Experimental Section

3. Results and Discussion

Yields of products / µmol •g-cat-1

V-MCM-41 gels were synthesized under acidic or basic conditions. Under both pathways, cetyltrimethylammonium bromide served as the template. For the acidic pathway, tetraethyl orthosilicate (TEOS) and NH4VO3 were used as the Si source and the V ion precursor, respectively. For the basic condition pathway, sodium silicate solution and SiO2 (Aerosil) or TEOS were used as Si source, while VOSO4-3H2O or NH4VO3 were used as the V ion precursor. After the as-synthesized products were recovered by filtration, washed with water and dried at 373 K for 12 h, calcination of the samples was carried out in air at 773 K for 8 h. Prior to the photocatalytic reactions and spectroscopic measurements, the catalysts were degassed at 773 K for 1 h, heated in O2 at 773 K for 2 h, and finally degassed at 473 K for 2 h. Photoluminescence spectra were measured at 295 K with a Spex Fluorog-3 spectrophotometer. The photocatalytic partial oxidations of methane with O2 and NO were carried out with the catalysts in a quartz cell under UV irradiation (A, > 270 nm) by a 100 W high pressure mercury lamp at 295 K. Reaction products were analyzed by gas chromatography. 15

CO CO22

The XRD patterns showed that all 10 10 CH 3 OH CHOH of the prepared V-MCM-41 catalysts have a siliceous MCM-41 meso5 porous structure. Figure 1 shows the results of the photocatalytic oxidation of methane with O2 and NO over the 0 V-MCM-41 (0.6 wt%) catalyst at 295 CH O 2= CH NO = CH 4//O =11 CH4//NO = 11 K. No products could be detected without the catalysts or UV light Fig. 1. Yields of CO2 and CH3OH in the irradiation. In the presence of O2, photocatalytic oxidation of CH4 with O2 or only the complete oxidation of NO on V-MCM-41(0.6 wt%) prepared by methane into CO2 and H2O proceeded acidic pathway. Amount of reactant: 4 under UV light irradiation. However, Torr. Reaction time: 3 h. the photocatalytic oxidation of methane with NO on V-MCM-41 resulted in the selective formation of methanol, accompanying the formation of the trace amounts of CO2 and acetaldehyde. The methane conversion and the methanol selectivity reached 6% and 88%, respectively, after the UV irradiation for 3 h. Figure 2 shows the effect of the V content of the V-MCM-41 catalysts on the reactivity for the photocatalytic oxidation of methane with NO. The yield of methanol was found to increase with the increase in the V content up to 0.6 wt%, and then decrease with a further increase in the V content. It was also found that V-MCM-41 exhibits photoluminescence at around 500 nm under excitation at 300 nm, as shown in Fig. 3, due to the radiative decay process 4

2

4

719

Yields of CH3OH / µmol• g- cat-1

10 8

6 4 2 0

0.15

0.6

3.6

V content //wt% wt%

Fig. 2. Relationship between the yields of CH3OH in the photocatalytic partial oxidation of CH4 with NO on V-MCM-41 prepared by acidic pathway and the intensities of the photoluminescence spectra.

0 Torr (a)

Intensity / a.u.

Intensity of photoluminescence / a.u.

from the charge transfer excited triplet state of the isolated tetrahedral V4+-oxide species [5]. The addition of CH4 or NO molecules onto the catalyst leads to an efficient quenching of the photoluminescence, their extents depending on the amount of added gas, indicating that the CH4 or NO molecules interact with the photoexcited V5+-oxide species. The good correspondence between the yield of methanol and the intensity of the photoluminescence indicates that the isolated tetrahedral V5+-oxide species act as active sites for the photocatalytic oxidation of methane with NO into methanol.

0.007 Torr

0.04 Torr 0.1 Torr excess

400

500 600 Wavelength / nm

700

Fig. 3. Effect of the addition of CH, on the photoluminescence spectrum of VMCM-41 (0.6 wt%) prepared by acidic pathway. (a): after degassing at R.T. for 30 min.

The effects of the preparation method of the catalyst, such as pH value of the starting solution and kinds of V and Si source, on the reactivity for the photocatalytic oxidation of methane with NO were investigated. As shown in Table 1, the high conversion of methane and high selectivity for the formation of methanol were obtained for V-MCM-41 prepared in acidic solution using TEOS as the Si source. In the case of the V-MCM-41 prepared in basic solution using TEOS as the Si source, selective formation of methanol was also observed. On the contrary, quite low methanol selectivity was observed for VMCM-41 prepared in basic solution using sodium silicate as the Si source. It has been reported that pre-impregnation of the silica support with sodium strongly diminishes V=O concentration due to the formation of tetrahedral monomers with a high degree of symmetry, leading to the strong inhibition of the partial oxidation of methane on V/SiO2 [6]. The low methanol selectivity of V-MCM-41 prepared from sodium silicate can be attributed to the presence of sodium ion in the mesoporous framework structure. The low methane conversion on V-MCM-41 prepared in basic condition can be also ascribed to the efficient incorporation of V +-oxide species within the framework of MCM41 due to the high ordered framework of MCM-41 [7], which inhibits the efficient interaction of V5+-oxide species with gaseous reactants. Furthermore,

720

no significant difference in the methanol selectivity was observed between the catalysts prepared using NH4VO3 and VOSO4 as the V source. The activity on V-MCM-41 (acidic method) was found to be higher than that on V/SiO2, suggesting that the higher surface area and mesopore structure of MCM-41 could favor the dispersion of the V-oxide species, leading to a higher photocatalytic activity for methane oxidation. The reactivity on the V-MCM-41 catalysts remained at least after three circles. Table 1. The CH4 conversion and the selectivity of products in the photocatalytic oxidation of CH4 on V-MCM-41 (0.6 wt%) prepared by different methods. CH,

PH

V source

Si source

1

NH4VO3

11

VOSO,

11

sodium silicate, N H4V O 3 SiO2

0.7

11

sodium silicate, SiO2

3.7 3.6

VOSO,

Selectivity (% )

(%)

C H 3 OH

CO2

C2HX

TEOS

6.0

87 .6

4.2

TEOS

2.6

85 .5

7.6

i m p - V / S i O 2 (V : N H , V O , |

CjH,

CH3CHO

other

0.6

2.6

5.0

1.1

5.8

-

1 0.2

23.3

66.5

5. 6

10.1

14.6

87 .8

5.8

1.0

39.4

22.9

7.4

5.4

-

4. Conclusion The photocatalytic partial oxidation of methane proceeds efficiently on the V-MCM-41 catalyst prepared in acidic condition, the reaction selectivity strongly depending on the kind of oxidative gasses. Selective formation of methanol was observed when NO was used as oxidative gas, while complete oxidation reaction proceeds in the presence of O2. The yield of methanol corresponded to the yield of the photoluminescence of the isolated tetrahedral V5+-oxide species, indicating that the photoexcited V5+-oxide species plays an important role in the photocatalytic oxidation of methane into methanol. The activity as well as the selectivity of V-MCM-41 greatly depends on the preparation methods of the catalysts. It has been elucidated that the methanol selectivity of V-MCM-41 can be enhanced dramatically by using TEOS as starting reagent for the Si source. 5. References [1] Z. Sojka, R. G. Herman and K. Klier, J. Chem. Soc. Chem. Commun. (1991) 185. [2] A. Parmaliana, F. Frusteri, A. Mezzapica, D. Miceli, M.S. Scurrell and N. Giordano, J. Catal. 143(1993)262. [3] M. M. Koranne, J. G. Goodwin Jr. and G. Marcelin, J. Phys. Chem. 97 (1993) 673. [4] K. Wada,K. Yoshida,Y.Watanabe and T. Suzuki,! Chem. Soc.,Chem. Commun.(1991)726. [5] Y. Hu, S. Higashimoto, S. Takahashi, Y. Nagai and M. Anpo, Catal. Lett. 100 (2005) 35. [6] S. Irusta, A.J. Marchi, E.A. Lombardo and E.E. Miro, Catal. Lett. 40 (1996) 9. [7] Y. Hu, N. Wada, M. Matsoka and M. Anpo, Catal. Lett. 97 (2004) 49.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

721 721

Hydrodesulfurization of dibenzothiophene and 4,6dimethyldibenzothiophene over Ni-Mo catalysts supported by siliceous SBA-15 Jing Rena, Anjie Wang*a, Juan Tana, Guangwei Caoab, Chang Liub, Yongtai Lib, Mohong Lua and Yongkan Hu ab aState Key Laboratory of Fine Chemicals, Dalian University of Technology, 158 Zhongshan Road, Dalian, 116012, P. R. China. b.Fushun Research Institute of Petroleum and Petrochemicals, Fushun, 113001, China.

A deep hydrodesulfurization (HDS) catalyst, which was considerably active to desulfurize dibenzothiophene (DBT) and 4, 6-dimethyldibenzothiophene (4,6-DMDBT), was prepared by depositing Ni-Mo species over SBA-15. The extremely high surface area of SBA-15 favors the dispersion of the active species, which result in very high HDS activity. The optimal Ni/Mo atomic ratio for this series of catalysts is 0.25. Ni-Mo(0.25)/SBA-15 exhibited excellent performance in HDS of DBT and 4,6-DMDBT. 1. Introduction The production of clean transportation fuels in a modern refinery occurs mainly via the hydrotreating process to remove sulfur and nitrogen and to improve their specifications. Since sulfur is the major heteroatom in petroleum, and its content is related to the particle emissions from internal combustion engines, the sulfur content in transportation fuels has been increasingly reduced by regulation worldwide. An economically affordable approach to meeting the increasingly stringent regulations is to develop high-performance hydrodesulfurization (HDS) catalysts. Recently, a novel family of mesoporous silicas (SBA) was synthesized [1]. This new materials have larger pores, thicker pore walls and higher hydrothermal stability with respect to MCM-41. Shortly after the discovery of SBA-15, it has been developed for a variety of reaction, including of hydrodesulfurization [2]. Vradman et al. [2] used SBA-15 to support Ni-W species to prepare catalysts. They found that Ni-W-S/SBA-15 catalysts

722

displayed 1.4 times higher HDS activity (DBT) and 7.3 times higher activity in toluene HYD compared with sulfided commercial CO-MO/AI2O3. Klimova et al. [3] supported Ni-Mo on Al-containing SBA-16 to investigate the HDS of 4,6DMDBT. They reported that Ni-Mo catalysts supported on Al-SBA-16 show high activity in 4,6-DMDBT HDS; this can be attributed to good dispersion of Ni and Mo active phases and to the bifunctional character of those catalysts. In the present study, the HDS of DBT and 4,6-DMDBT over Ni-Mo catalysts supported by siliceous SBA-15 was investigated. 2. Experimental Section All the reagents in synthesizing SBA-15 and in preparing the catalysts were of chemical grade. SBA-15 was synthesized according to the literature [1]. The catalysts were prepared by the wet impregnation method [3]. SBA-15 was impregnated with an aqueous solution of (NH^MovC^^HzO and Ni(NO3)2.6H2O for 2 h at room temperature, followed by the evaporation of solvent, with an oven drying at 120°C for 12 h and calcination in air at 450°C for 5 h. A 20 wt% MoO3 loading level in proportion to the supports was chosen to prepare this series of catalysts. The content of nickel was determined by varying the atomic ratio of Ni/Mo in the range of 0-1.0. The catalysts were denoted as Ni-Mo(x)/SBA-15. The value in parentheses represents the atomic ratio of Ni to Mo. The catalysts were presulfided prior to HDS reaction of DBT and 4,6-DMDBT. A model fuel containing 1 wt% DBT or 0.5 wt% 4,6DMDBT in decalin was used to investigate the HDS activities of the prepared catalysts. 700

—•—Adsorption —o— Desorption

" v 10

26 .degree

Fig. 1 XRD pattern of the synthesized SBA-15

0.2

0.4

0.6

0.8

1.0

Relative Pressure

Fig. 2 N2 adsorption-desorption isotherm of the siliceous SBA-15

The X-ray diffraction pattern of the synthesized SBA-15 is shown (Fig. 1) that sharp peak in low angel region around 98.07 A d spacing is the characteristic of SBA-15. There were also small peaks around 56.58, 49.59 A d

723

spacing, indicating that the synthesized SB A-15 has a high degree of hexagonal mesoscopic organization. The N2 adsorption-desorption isotherm of the prepared siliceous SBA-15 is shown in Fig. 2. In contrast to N2 adsorption result for MCM-41 mesoporous silica with pore sizes ~ 40 A, a clear typeHl hysteresis loop is observed, and the capillary condensation occurs at a higher relative pressure (P/Po ~ 0.7). This sharp increase in uptake results from the capillary condensation of N2, which suggests that uniform mesopores are present in the siliceous SBA-15. The BET surface area of the support was found to be 587.9 m2/g. Fig. 3 TEM image of the synthesized SBA-15 The mesopore distribution is sharp around 62.4 A. The XRD and pore size distribution data agreed with those reported in literature [1]. Transmission electron microscopy (TEM) image (Fig.3) of calcined SBA-15 show well-ordered hexagonal arrays of mesopores. 3. Results and Discussion Fig.4 shows the conversion of DBT during HDS catalyzed by Ni-Mo/SBA-15 as a function of temperature, compared with Ni/SBA-15 (NiO 20 wt%) and KF848 (a commercial ultra deep hydrodesulfurization catalyst, made by Akzo Nobel/Nippon Ketjen, which has been applied over the world for produce ultra deep desulfurization diesel oil). All the Ni-Mo/SBA-15 catalysts showed substantially high activity for HDS of DBT. The HDS activities of the catalysts substantially heighten by the introduction of Ni. The maximum activity was observed for the Ni-Mo/SBA-15 catalysts at a Ni/Mo atomic ratio of 0.25. When the Ni/Mo atomic ratio at 0.25 and 0.5, the catalysts display rather higher hydrodesulfurization activity, which exhibit comparable HDS activity with KF848. It is believed that alkyl-dibenzothiophenes substituted by alkyl groups at the 4 and/or 6 position are the most refractory sulfur-containing molecular due to the increased steric hindrance [4, 5]. To evaluate the performance of the prepared Ni-Mo/SBA-15 HDS catalysts, Ni-Mo(0.25)/SBA-15 was chosen to investigate the HDS of 4,6-DMDBT. The variation of HDS conversion with temperature is illustrated in Fig.5. It is shown that the Ni-Mo(0.25)/SBA-15 catalyst exhibited excellent performance in desulfurizing the more refractory DBT derivatives, which superior to the KF-848. So I thinks the result may be attributed to Ni-Mo(0.25)/SBA-15 with higher hydrogenation activity than KF848.

724

280

300

320

340

Temperature,°C

Fig. 4 Variation of DBT conversion with temperature during HDS catalyzed by siliceous SBA-15-supported Ni-Mo catalysts: (•)Mo/SBA-15;(«)Ni-Mo(0.25)/SBA-15; (A)Ni-Mo(0.5)/SBA-15;(Y)Ni-Mo(0.75)/SBA-15 (•)Ni-Mo(1.0)/SBA-15;(-*)Ni/SBA-15; (•)KF-848.

280

300

320

340

Temperature, °C

Fig. 5 Variation of 4,6-DMDBT conversion with temperature during HDS catalyzed by: (•)Ni-Mo(0.25)/SBA-15, (•)KF-848.

4. Conclusion In summary, SBA-15 is a promising support for preparing deep hydrodesulfurization catalysts. The optimal atomic ratio for Ni-Mo/SBA-15 is 0.25. It is assumed that Ni-Mo pairs have been created on the extremely high surface area, yielding considerably high activity for HDS of DBT and 4,6DMDBT. 5. References [1] [2] [3] [4] [5]

D. Zhao, J. Feng, Q. Huo, et al., Science, 279 (1998) 548. L. Vradman, M. V. Landan, M. Herskowitz, et al., J. Catal., 213 (2003) 163. T. Klimova, L. Lizama, J. C. Amezcua, et al., Catal Today., 98 (2004) 141. T. Kabe, A. Ishihara and H. Tajima, Ind. Eng. Chem. Res., 31 (1992) 1577. X. Ma, K. Sakanishi and I. Mochida, Ind. Eng. Chem. Res., 33 (1994) 218.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

725 725

Photocatalytic preferential oxidation of CO with O2 in the presence of H2 (photo-PROX) on Mo-MCM41 at 293 K Masaya Matsuoka*, Takashi Kamegawa and Masakazu Anpo* Department of Applied Chemistry, Graduate School of Engineering Osaka Prefecture University, 1-1 Gakuen-cho, Nakaku, Sakai, Osaka 599-8531, Japan

The photocatalytic preferential oxidation of CO with O2 in the presence of H2 (photo-PROX) proceeded on Mo-MCM-41 with a high CO conversion (98%) and high CO selectivity (98%) under UV light irradiation for 3 h at 293 K. Various spectroscopic investigations have revealed that the reaction is closely associated with the high reactivity of the charge transfer excited triplet state of the isolated tetrahedral Mo6+-oxide species to oxidize the CO in H2 into CO2 as well as with the high reactivity of the photo-reduced Mo4+-oxide species with O 2 to produce the original Mo6+-oxide species. 1. Introduction Recently, the development of the catalytic systems which preferentially oxidize CO with O2 in the presence of H2 at ambient temperature is strongly desired to realize the small scale on-site supply of pure H2 to fuel cells. On the other hand, zeolites incorporated with Mo-oxide species in a highly dispersed state exhibit high photocatalytic activity for the oxidation reaction of hydrocarbons and CO with O2 or NO at ambient temperature [1-3]. The present study deals with spectroscopic characterizations of the Mo-oxide species on Mo-MCM-41 and their photocatalytic activity for the preferential oxidation of CO with O2 in the presence of excess amount of H2 (photo-PROX). 2. Experimental Section Mo-MCM-41 (1.0 Mo wt%) was synthesized in accordance with previous literature [1]. Prior to spectroscopic measurements and photocatalytic reactions, the catalyst was calcined in O2 at 773 K, then degassed at 473 K.

726 726

Photoluminescence was measured at 298 K with a Spex Fluorog-3 spectrophotometer. The XAFS spectrum was recorded at the Mo K-edge absorption in the transmittance mode at 298 K at the BL-10B facility of the High Energy Acceleration Research Organization (KEK) in Tsukuba. The photocatalytic reactions were carried out at 293 K in a closed system (101 cm3) with a 100 W high pressure mercury lamp through water filter. Reaction products were analyzed by gas chromatography. 3. Results and Discussion The XRD investigation showed that the Mo-MCM-41 has a siliceous MCM-41 mesoporous structure. UV-vis spectrum of Mo-MCM-41 exhibited broad absorption bands at around 240 and 280 nm due to the charge transfer absorption bands of the tetrahedrally coordinated dioxomolybdenum species (Mo(VI)O42") [3-5]. The local structure of the Mo-oxide species on Mo-MCM41 was investigated by Mo K-edge XAFS measurements. Fourier transform of EXAFS of Mo-MCM-41 showed well-resolved peaks due to the presence of the neighboring oxygen atoms (Mo-O) at ca. 0.8-2.0 A (without phase-shift correction), while peaks that would normally be observed at ca. 3.0-4.0 A if a Mo-O-Mo bond was present were not observed, showing that the Mo-oxide species were highly dispersed on MCM-41 [1,3]. The curve-fitting analyses of the Mo-0 peaks show that the Mo-oxide species exists in tetrahedral coordination with two Mo=O double bonds (bond length (R) = 1.68 A, a coordination number of CN = 2.1, a Debye-Waller factor of a 2 = 0.005 A2) and two Mo-O single bonds (R = 1.88 A, CN = 1.9, a 2 = 0.005 A2) [1, 3]. As shown in Fig. 1, Mo-MCM-41 exhibited a photoluminescence (PL) spectrum at around 450 nm upon excitation with UV light of wavelengths shorter than 350 nm. The absorption and PL spectrum are attributed to the following charge transfer processes on the Mo=O moieties of the isolated /6o\ ^ lifetime: 62 Ms tetrahedral Mo6+-oxide species, involving / (0 \ an electron transfer from the O2" to Mo \ ions and a reverse radiative decay from the charge transfer excited triplet state [3s \ 5]r

//A

[Mo6+ = O2"]

hv hv'

[Mo 5 - 0 1 * 400 6+

[Mo =( The PL is easily quenched by the addition of CO, O2 and H2, indicating that the Mo6+-oxide species, in its charge transfer excited triplet state, easily interacts with CO, O2 and H2. The

500

600

700

Wavelength / nm

Fig. 1. Effect of the addition of CO on the photoluminescence spectrum of the Mo-MCM-41 (kex = 300 nm). Added CO (Pa): (a) 0.0, (b) 1.6, (c) 5.2, (d) 14.4, (e) excess, (f) degassed for 1 h after (e).

727

evacuation of the added gasses after the quenching of the PL led to almost a complete recovery of the original PL yield for H2 and O2, while only a partial recovery of the PL yield was observed for CO, showing that irreversible reaction between CO and the photo-excited Mo6+-oxide species can proceed under UV irradiation. The following Stern-Volmer equation can be obtained for the quenching of the PL with the quencher molecules by applying steady-state treatment [3] (O0/O = 1 + x okq[Q]), where O0 and
29

Amounts of gasses / µmol

The photocatalytic preferential oxidation of CO with O2 in the presence of H2 (photo-PROX) was investigated. UV irradiation of Mo-MCM-41 in the presence of CO, O2 and H2 led to the efficient oxidation of CO into CO2 accompanying the stoichiometric consumption of O2, while the amount of H2 remained almost constant. The amount of CO2 produced (CO2 (t=3 h)) and the amount of H2 consumed (AH2 (t=3 h)) during the reaction were 3.74 and 0.08 |^mol, respectively. Based on these results, the CO

H2

CO

CO2

2

O2

27 25

(24.6)(24.52)

23 (7.61)

8

(5.69)

6 4

(3.81)

(3.74)

2 0

(0.06) (0.0)

Kind of gasses Kind

Fig. 3. The amounts of gasses in the gas phase before (left bars) and after (right bars) the photo-PROX on Mo-MCM-41 for 3 h at 293 K. Amount of catalyst: 20 mg.

728

conversion and CO selectivity after UV irradiation for 3 h were determined to be 98% and 98%, respectively. Here, the CO selectivity is calculated from the following equation : CO selectivity (%) = 100 x [CO2 (_3 h) / (CO2 (_3 h) + AH2 (t_3 h))] The photo-PROX was, thus, seen to proceed on Mo-MCM-41 at 293 K. Furthermore, the turnover number reached 1.8 after 3 h UV irradiation for the reaction, showing firmly that the reaction proceeds photocatalytically. The photo-PROX was also performed on 50 mg of TiO2 (P-25). The photocatalytic activity of TiO2 was less efficient when compared to the Mo-MCM-41, i.e., the CO conversion and selectivity reached 81 % and 89 %, respectively, after 6 h UV irradiation. Moreover, FT-IR investigations show that UV irradiation of Mo-MCM-41 in the presence of CO led to the appearance of the bands at 2077 and 2126 cm "' due to the dicarbonyl species (Mo4+(CO)2)[6], while the addition of O2 onto the photo-reduced Mo-MCM-41 led to the complete disappearance of these bands. The redox cycle of the Mo-oxide species was, thus, seen to be involved in the photocatalytic oxidation of CO. [Mo6+ = CT] • [Mo5+ - O"]* 5+ [Mo - O]* + CO (+ H2) • [Mo4+(CO)2] + CO2 (+ H2) 4+ [Mo (CO)2] + O2 • [Mo6+ = o h + 2CO The high CO selectivity observed for the Mo-MCM-41 can be attributed to the high and selective reactivity of the photo-excited Mo6+-oxide species with CO, as indicated by the high quenching efficiency of CO as compared to H2 and O2. 4. Conclusion Mo-MCM-41 was found to act as an efficient photocatalyst for the photoPROX at 293 K (CO conversion: 98%, CO selectivity: 98%), showing higher photocatalytic performance than TiO2. Various spectroscopic investigations have revealed that the high CO selectivity can be attributed to the high reactivity of photo-excited Mo6+ species with CO as compared to H2. 5. References [1] S. Higashimoto, Y. Hu, R. Tsumura, K. lino, M. Matsuoka, H. Yamashita, Y. G. Shul, M. Che and M. Anpo, J. Catal. 235 (2005) 272. [2] S. Takenaka, T. Tanaka, T. Funabiki and S. Yoshida, J. Chem. Soc. Faraday Trans. 94 (1998) 695. [3] T. Kamegawa, R. Takeuchi, M. Matsuoka and M. Anpo, Catal. Today 111 (2006) 248. [4] M. F. Hazenkamp and G. Blasse, Ber. Bunsenges. Phys. Chem. Chem. Phys. 96 (1992) 1471. [5] I. R. Subbotina, B. N. Shelimov, V. B. Kazansky, A. A. Lisachenko, M. Che and S. Coluccia, J. Catal. 184 (1999) 390. [6] C. C. Williams and J. G. Ekerdt, J. Phys. Chem. 97 (1993) 6843.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

729 729

Influence of the location of Rh(0) particles within MCM-41 materials on the selectivity of hydrogenation reactions Maya Boutrosa, Franck Launaya, Audrey Nowickib, Thomas Onfroya, Virginie Semmer-Herledana, Alain Roucouxb and Antoine Gedeona "Laboratoire Systemes Interfaciaux a I'EchelleNanometrique, CNRS-UMR 7142, Universite Pierre et Marie Curie, case 196, 4 place Jussieu, 75252 Paris cedex 05, France ([email protected]) b Equipe Synthese Organique et Systemes Organises, CNRS-UMR 6226 "Sciences chimiques de Rennes ", Ecole Nationale Supe'rieure de Chimie de Rennes, Avenue du General Leclerc, 35700 Rennes, France

Rh°-MCM-41 solids have been prepared by the alkaline hydrolysis of silicon precursors in the presence of cetyltrimethylammonium bromide (CTABr) and Rh(III) salts or 2-3 nm Rh° colloids. All the resulting solids were used in the catalytic hydrogenation of xylenes and lead to lower selectivities in cis dimethylcyclohexanes than Rh colloids tested either under biphasic conditions or deposited onto silica gel. Such variations have been attributed to the insertion of the Rh precursors into the MCM-41 synthesis gel. 1. Introduction Hydrogenation of aromatic rings under low H2 pressure is a very attractive methodology to remove pollutants and reduce the content of benzenic derivatives in fuels [1]. Some of us showed that such process can be performed efficiently under biphasic conditions in the presence of aqueous rhodium(O) colloids (Rh° coll) [2-4]. The aim of the present work is to compare the reactivity of such Rh° colloidal suspensions with that of Rh° particles incorporated onto mesoporous solids. The latter were prepared either by the addition and reduction of RhCl3 (Rh°-M solids) [5] or by the insertion of preformed nanoparticles (Rh°coll-M samples) [6] in the synthesis gel of pure silica MCM-41. Besides the characterization of the new solids and of their active

730

phase, particular attention is paid to the effect of the support and of the Rh precursors on the selectivity of xylenes hydrogenation reactions. 2. Experimental section Rh-MCM-41 solids were prepared according to a "one-pot" procedure adapted from that described by Briihwiler et al. in the case of pure silica MCM41 [7]. Rh precursors (RhCl3.xH2O or a suspension of 2-3 nm Rh(0) colloids [8]) were introduced into the solution of CTABr and ammonia prior to the introduction of tetraethoxysilane affording Rh(III)-M and Rh°coll-M solids (see details in ref. [5] and [6], respectively). The surfactant of as-synthesized Rh°coll-M solids was extracted by ethanol. On the other hand, dry Rh(III)-M solids were calcined at 823 K and the Rh°-M materials obtained by a reduction step under hydrogen flow (8.3 mL min"1) at 493 K. Rhodium compositions of the various materials were determined by ICPAES. Nitrogen adsorption and desorption isotherms were measured at 77 K using a Micromeritics ASAP 2010 instrument. Powder X-ray diffraction patterns were collected on a Bruker D8 Advance X-ray diffractometer at CuKa radiation. Transmission electron microscopy images were recorded using a JEOL TEM 100CXY electron microscope. The samples were used as catalysts in the hydrogenation of o- and m-xylene. Reactions were monitored by gas chromatography using a Carlo Erba GC 6000 with a FID detector and equipped with a Factor Four capillary column (30 m, 0.25 mm i.d). 3. Results and Discussion The incorporation of both Rh precursors (Rh(III) or Rh°coll) has been tested with increasing amounts of metal (Table 1). The Rh content could be varied Table 1: Physicochemical properties of Si-MCM-41, Rh°coll-M and Rh°-M samples. Si/Rh (gel)

Rh wt. %

SBETVITIV

V B J H b /cmV

Ddesb/ nm

oo

-

800

0.70

2.6

Rh°coll-M/0.01

5920

0.01

740

0.56

2.6

Rh°coll-M/0.1

2960

0.10

650

0.55

2.4

Rh°coll-M/0.11

1480

0.11

535

0.43

2.3

Rh°-M/0.1

1400

0.1

840

0.74

2.8

Rh°-M/0.5

330

0.5

800

0.74

2.9

Rh°-M/1.3

80

1.3

720

0.63

2.8

Sample Si-MCM-41

a

b

Specific surface area obtained by the BET procedure; Specific pore volume and pore diameter determined from the BJH method.

731

Intensity (a.u.)

from 0.1 to 1.3 wt % in the case of Rh°-M materials whereas the insertion of the pre-formed particles turned out to be limited to small amounts (< 0.11 wt %) in Rh°coll-M samples. Whatever the solids considered, hexagonal arrays of mesopores were obtained (Fig. 1). The intensities of the diffraction peaks of the Rh°-M materials (Fig. 1 e-g) decrease with the metal content. However the mesopores of all these solids are still more structured than those of the corresponding Rh°coll-M samples (Fig. 1 b-d). The insertion of Rh(III) leads to much less decrease of the textural parameters than the corresponding amounts of Rh(0) colloids (see Rh°coll-M/0.1 and Rh°-M/0.1, Table 1). IR monitored carbon monoxide adsorption studies (not shown here) indicate that the reduction of rhodium (III) is complete in Rh°-M samples. This has been checked by the absence of CO containing species characterized by wavenumber values higher than 2092 cm"1 [5]. TEM micrographs of all the solids are consistent with the presence of ordered channels. In the case of Rh°-M solids, 2-3 nm particles embedded in the pores could be easily observed (Fig. 2, see Rh -M/0.5)

(a) (b) (c) (d) (e) (f) (g)

1

2

3

4

5

6

7

2 θ (degree)

Fig. 1 Small angle X-ray diffraction patterns of (a) MCM41, (b) Rh°coll-M/0.01, (c) Rh°coll-M/0.1, (d) Rh°collM/0.11, (e) Rh°-M/0.1, (f) Rh°-M/0.5 and (g) Rh°-M/1.3.

Fig. 2 TEM picture of Rh°-M/0.5.

The activity of the different solids was studied at 0.1 MPa H2 in the room temperature hydrogenation of o- and m-xylene into 1,2 and 1,3 dimethylcyclohexanes (DMC), respectively. Whatever the Rh content, all the Rh°-MCM-41 solids are globally less active than Rh(0) colloids under biphasic conditions. Reaction completion in less than 24 h was only obtained in the case of Rh°-M solids with % Rh > 0.5 [5]. That is why the heterogeneous catalysis tests reported in table 2 were carried out under 1 MPa H2 pressure. Cis DMC compounds are the major products and o-xylene leads to a higher selectivity in CM compounds than m-xylene. Despite the use of a higher H2 pressure, RhMCM-41 materials afford more trans products than the colloidal suspension {cisltrans ratio are 75-81/25-19 and 87-92/13-8 for m- and o-xylenes, respectively). It is interesting to note that the selectivity of the reactions performed with the same colloids deposited onto silica gel is closer to that

732

obtained under biphasic conditions [8]. Then, it appears that the more significant changes of the cis I trans selectivity obtained in the presence of Rh°-MCM-41 are caused by the insertion of the Rh precursors (RhCls.xft^O or Rh(0) colloids) in the synthesis gel of MCM-41. However, the very weak activity of Rh°collM/0.1 compared to that of Rh°-M/0.1 suggests that the environment of Rh° particles may be different in both solids. Table 2: Catalytic performances of the catalysts in the hydrogenation of o- and m-xylenes. Catalyst

m-xylene —> 1,3 DMC

o-xylene-> 1,2 DMC

t(h)

cis/trans

Yield (%)

t(h)

cis/trans

Yield (%)

24

78/22

15

24

92/8

19

-

-

-

24

88/12

7

Rh°-M/O.la

24

75/25

100

24

87/13

100

Rh°-M/0.5

0.7

81/19

100(100)b

0.75

89/11

100 (100)b

Rh°-M/1.3

0.5

80/20

100 (100)b

0.9

91/9

100(90)b

Rh(O) colloidal [4]c

7.3

87/13

100

7.5

95/5

100

Rh°coll-M/O.la Rh°coll-M/O.ll

a

Heterogeneous conditions: catalyst (100 mg), H2 pressure (1 MPa), temperature (293 K), solvent (hexane, 10 mL), molar substrate/Rh (100), stirring (1500 min"1).3 molar substrate/Rh (130); b yield in the second run;cBiphasic conditions: Rh catalyst (3.8 x 10*5 mol), surfactant (7.6 x 10"5 mol), molar substrate/Rh = 100, water (10 mL), hydrogen pressure (0.1 MPa).

4. Conclusion The insertion of Rh(III) salts or pre-formed nanoparticles in the synthesis gel of MCM-41 affords hydrogenation catalysts which are less active than aqueous Rh° colloidal suspensions. We have shown that the slight decrease of the selectivity in cis dimethylcyclohexanes observed in the presence of Rh°-MCM41 solids is mainly governed by the use of a "one-pot" synthesis procedure. 5. References [1] [2] [3] [4] [5]

A. Stanislaus and H. B. Cooper, Catal. Rev. 36 (1994) 75. J. Schulz, A. Roucoux and H. Patin, Chem. Commun. (1999) 535. A. Roucoux, J. Schulz and H. Patin, Adv. Synth. Catal. 345 (2003) 222. J. Schulz, A. Roucoux and A. Patin, Chem. Eur. J. 6 (2000) 618. M. Boutros, F. Launay, A. Nowicki, T. Onfroy, V. Semmer-Herl6dan, A. Roucoux and A. Gedeon, J. Mol. Catal. A: Chem. 259 (2006) 91. [6] R. Mouawia, M. Boutros, F. Launay, V. Semmer-Herledan, A. Gedeon, V. Mevellec and A. Roucoux, Stud. Surface Sci. Catal. 157B (2005) 1573. [7] D. Bruhwiler and H. Frei, J. Phys. Chem. B 107 (2003) 8547. [8] V. Mdvellec, A. Nowicki, A. Roucoux, C. Dujardin, P. Granger, E. Payen and K. Philippot, New J. Chem. 30 (2006) 1214.

Recent Progress in Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

733 733

Platinum catalysts supported on SBA-15 for the selective catalytic reduction of lean NOX with propylene Kwang-Eun Jeonga, Joo-Il Parka and Son-Ki Ihma "Deapartment of Chemical and Biomolecular Engineering, Korea Advanced Institute of Science and Technology, 373-1, Guseong-dong, Yuseong-gu, Daejeon 305-701, Korea

1. Introduction Selective catalytic reduction (SCR) of NOX in oxygen rich exhaust streams of lean burn and diesel engines is one of the major challenges in environmental catalysis. M41S family has drawn much attention in catalysis due to its large surface area and unique pore structures. Even if they have been applied as catalyst supports for various reaction [1-4], their application to NOX reduction has been mostly devoted to HC-SCR [5-7]. In this work, platinum containing catalysts were prepared using the mesoporous silica SBA-15 as support material and tested for the SCR of NO with hydrocarbon. SBA-15 with an ordered hexagonal structure has very interesting properties to act as a catalytic support especially due to its high thermal and hydrothermal stability. 2. Experimental Section The SBA-15 support was prepared according to a procedure described by Stucky et al. [8]. Al-SBA-15 was prepared by incorporating aluminum to siliceous SBA-15 by the post synthetic metal implantation method [9]. All samples were calcined in air at 55O°C for 5 h. Supported Pt catalysts were prepared by incipient wetness impregnation method. Pt(NH3)4Cl2-H2O (98%, Aldrich) was used as platinum precursor and 1 wt.% of Pt was loaded on the silica supports, which were dried at 100°C and calcined at 550°C for 5 h. The activity of the catalysts in the selective catalytic reduction of NO was measured in a fixed bed apparatus at a temperature range of 150 to 500°C. The reaction feed mixture contained 2000 ppmv of NO, 2000 ppmv of QiH6, and 5 vol.% of O2 with balance He, respectvely. The space time (W/F) was 0.012 g-cat-h/L.

734 734

3. Results and Discussion The physical properties of prepared catalysts are summarized in Table 1. The Pt/SBA-15 catalysts were found to have narrow pore size distribution with pore sizes near 50 nm, high BET surface areas (> 800 m2/g) and large pore volumes (> 1.0cm3/g). Table 1. Physical properties of Pt/SBA-15 and Pt/Al-SBA-15 catalysts Pt Pore Pore dPt' (nm) dispersion volume diameter (cm3/g) (nm) (%) n 32 916 1.18 5.21 8.5 Ptl /SBA-15 21 901 1.15 4.96 10.8 Pt3/SBA-15 8 810 1.01 4.87 12.8 Pt5/SBA-15 39.1 Ptl/SBA-15'" 608 0.81 4.92 0.77 Ptl/Al(10lv)-SBA-15 605 4.85 22.4 Ptl/Al(10)-SBA-15"' 545 0.73 4.81 ' : average Pt particle size estimated from HR-TEM," : Pt loading (wt.%),'" : Calcined at 800°C for 5 hours, lv : Si/Al mole ratio Catalysts

Surface area (m2/g)

Al incorporation leads to decrease in surface area and pore volume. The catalytic performance of Pt/SBA15 with different Pt loading for the reduction of NO with C3H6 is shown in Figure l(a). N2 yield of 1 wt.% Pt/SBA-15 showed a monotonous increase and decrease pattern with temperature. On the other hand, the curve of N2 yield versus temperature of 3 and 5 wt.% Pt/SBA-15 had two peaks, indicating more than one reaction route was involved in N2 formation. The turnover frequencies (TOF) for the conversion of NO into N2, defined as the number of NO molecules converted per surface Pt atom per second, are also given in Figure l(b). TOFN2 of 3 and 5 wt.% Pt catalysts were found to be 300 higher rather in the higher Temp.(°C) temperature region than that of 1 wt.% Pt catalyst, which indicates Figure 1. N2 yield and TOF into N2 of Pt/SBA-15 for selective catalytic reduction of NO.

735

that simple increase in total amount of Pt is not the only reason for the increase in N2 yield in the higher temperature region. From the H2-TPR profiles shown in Figure 2, two main peaks are observed: one around 50-150°C and another

c o

I §

Temp. (°C)

Figure 2. H2-TPR patterns of Pt/SBA-15 catalysts with different Pt loading.

around 300-500°C. The results indicate that there are two types of Pt species on SBA-15. An increase of Pt loading leads to the formation of Pt species having higher reduction temperature while little influence on the formation of Pt species having lower reduction temperature. The difference between these two types of Pt species may be attributed to their agglomeration state. The first one at a lower temperature seems to correspond to the highly dispersed Pt species and the second peak at higher temperature is assigned to bulk Pt species [7, 10]. Also, the formation of some large Pt particles on the catalyst having higher Pt loading is confirmed by XRD and HR-TEM results (Table 1). Combined with the results of H2TPR and Pt particle size, the P11/S15 (55 0"C) pii/sis (sore) highly dispersed Pt species seems P11/AI11-S15 (S50"C) P11JAI10 515 (800"C) to be more active for NO reduction in the lower temperature region while bulk Pt species contributes to N2 formation in higher temperature region. Figure 3 shows that the catalytic activity for the selective catalytic reduction of NO over Pt/SBA-15 was improved by the Al incorporation. Improvement of the Figure 3. N2 yield of Pt/SBA-15 and Pt/Al-SBA-15 activity is suggested to be due to calcined at 55O°C and 800°C.

736

the enhancement of surface acidity which is evidenced by NH3-TPD. Figure 3 also shows the catalytic activity for SCR of NO over Pt/SBA-15 and Pt/AlSBA-15 catalysts which were calcined at different temperatures. Calcination at higher temperature (800°C) led to a drastic decrease in N2 yield at low temperatures and also to a shift of maximum yield toward higher temperature. Higher thermal stability of Pt/Al-SBA-15 catalyst than that of Pt/SBA-15 catalyst could be expected since the surface Al species prevents the active Pt species from sintering at high temperature. 4. Conclusion The highly dispersed Pt species are more active for NO reduction in the lower temperature region while bulk Pt species contributes to N2 formation in higher temperature region. The activity of NO reduction is found to be increased by the incorporation of Al species due to the enhancement of surface acidity. 5. Acknowledgement This work was partially supported by Daedeok Innopolis R&D Project from the Ministry of Science & Technology (MOST), by the National Research Laboratory (NRL) program from the Korea Institute of Science & Technology Evaluation and Planning (KISTEP) and also by the Brain Korea 21 (BK21) Project from the Ministry of Education. 6. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10]

K. S. Lee, C. G. Oh, J. H. Yim and S. K. Ihm, J. Mol. Catal. A., 159 (2000) 301. K. C. Park, D. J. Yim and S. K. Ihm, Catal. Today, 74 (2002) 281. S. K. Song, J. H. Lee and S. K. Ihm, Stu. Surf. Sci. Catal., 154 (2004) 2923 S. K. Song, Y. Wang and S. K. Ihm, Catal. Today, 111 (2006) 194. R. Long and R. T. Yang, Catal. Lett., 52 (1998) 91. W. SchiePer, H. Vinek and A. Jentys, Appl. Catal. B, 33 (2001) 263. S. C. Shen and S. Kawi, Appl. Catal. B, 45 (2003) 63. Y. J. Han, J. M. Kim and G. D. Stucky, Chem. Mater., 12 (2000) 2068. S. Jun and R. Ryoo, J. Catal., 195 (2000) 237. I. Sobczak, M. Ziolek and M. Nowacka, Micropor. Mesopor. Mater., 78 (2005) 103

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

737 737

Catalytic activity of dinuclear chiral salen complexes immobilized on modified SBA-15 Chang-Kyo Shin, Chul-Heng Ahn, Wenji Li and Geon-Joong Kim* Department of Chemical Engineering, Inha University, Incheon 402-751, South Korea,

The new heterogeneous dinuclear chiral (salen) Co-GaCl3 catalyst immobilized on modified SBA-15 showed high activity for the enantioselective kinetic resolution of terminal epoxides with H2O. The heterogeneous catalysts can offer practical advantages of the facile separation from reactants and products, as well as recovery and reuse. 1. Introduction Design of simple and efficient chiral catalyst for asymmetric reactions is one of the most important tasks in organic synthesis [1]. The stereoselective synthesis of chiral terminal epoxides is of immense academic and industrial interest due to their utility as versatile starting materials as well as chiral intermediates for the preparation of bioactive molecules. Hydrolytic kinetic resolution (HKR) technology [2] is the very prominent way to prepare optically pure terminal epoxides among available methods. The recently developed chiral salen catalysts are appealing candidates for covalent attachment to the polymer or inorganic supports. Microporous crystalline zeolites have very interest and unique properties, but they have one limitation as catalysts in processing large molecules of nanometer-scale sizes. The mesoporous materials have expanded the application areas, e.g. selective catalysts for large molecules and cooperative complexes for enantioselective catalytic reactions. Recently, Okamoto group has developed the method to synthesize SBA-15(B) having very large 3dimensional pore system by dimethylcarbonate (DMC) treatment [3]. Herein we report the application of that SBA-15(B) with 3-dimensionally connected mesopores as a support on anchoring the chiral salen compexes onto the surfaces. This heterogeneous salen showed higher activity than that immobilized on conventional SBA-15 (having only regular hexagonal pores) in asymmetric HKR reaction of terminal epoxides with water.

738

2. Experimental Section 2.1. Preparation ofSBA-15 treated with DMC SBA-15(A) with well hexagonal pore structure was prepared using poly(ethyleneoxide)-block-poly(propyleneoxide)-block-(ethyleneoxide) by the procedure as reported in the previous paper [4]. In addition, SBA-15(B) having very large 3-dimensional pore system was synthesized by the method reported in the paper by treatment of dimethylcarbonate after impregnation of KCl as a catalyst for partial removal of SiO2 as tetramethoxysilane [3]. The synthesized SBA-15(A) and the treated SBA-15(B) were showed in Scheme 1. and were characterized by X-ray diffraction(XRD) analysis(Rigaku DMAX 2500) in Fig.l.

O

O

O

(CH2O)n

OH

OH

HCl, R.T. 48h Cl

t-Bu

1. Ph3P

OH

2.HCHO aq, NaOH

t-Bu O

O

OH H2N

(b) O O Si

(a)

SH

5 A-1 H3CO SB Hexagonally Hexagonally ordered SBA-15(A)

t-Bu

t-Bu

EtOH, BOH, Reflux

CHCI33 AIBN, CHCl ,Reflux

O O Si 5 1 H3CO BA

J"x N

tBu

S

EtOH, Reflux

(c)

N

2

3

O O Si 5 H CO 1 3 BA

04

N O

S

t Bu t

10 11

2 Theta(Deg.)

Fig.l The XRD patterns of SBA-15(A) and SBA-15(B).

t-Bu

Co

(1d,2d)

N O

t

Bu

t

MX3But Bu O O Co N N

Bu

S

2 3 4 5 6 7 8 9

N

Precatalyst Chiral Co (salen) CH2Cl2, 1h

20000 1

Co

O O t-BuMX3 t-Bu

S

S

30000-

(c)

(1m,2m) O O Si 5 H CO 1 3 BA

40000

tBu

tBu

1. Co(II)OAc.4H Co(II)OAc.4H2O, 2O, EtOH, Reflux 2. 2. Anhydrous Anhydrous MX MX3,3, CH CH2CL2, 2h 2Cl2, 2h

-SBA-15(B) - SBA-16 (A)

50000

N

OH HO

S

60000

0 1

NH2

t-Bu

HO

DMC SBA-15(B) treated with DMC

Scheme 1. The structure of SBA-15 treated with DMC

10000

(a)

t-Bu

But

t

Bu

X M X 1 1 Al AL Cl a 2 Ga Cl

2Ga A

Scheme 2. The structure of salen catalysts immobilized on SBA-15.

739

2.2. Preparation ofchiral Co(salen) MX3 complexes immobilized on SBA-15 The step of synthesizing heterogenised chiral salen was shown in Scheme 2. Heterogenized chiral(salen) MX3 complex(c) from the 3-tert-butyl-2-hydroxy-5vinylbenzaldehyde(a) and mercaptopropylsilyl-functionalized SBA-15(b) were prepared by the procedure as reported [5]. The catalytic activities were evaluated in the HKR of (±)epichlorohydrine (ECH). The general procedures for the HKR of epoxides follow the method as reported in the previous paper [6]. The conversion and ee% values were determined by capillary GC using chiral columns (CHIRALDEX (G-TA) and (A-TA), 20 m x 0.32 mm i.d. (Astech)). 3. Results and Discussion Fig.l shows the X-ray diffraction patterns of the synthesized SBA-15(A) and the treated SBA-15(B). Although the X-ray diffraction patterns of SBA-15(B) has slightly lower intensity than the original SBA-15 (A), all of the specific SBA-15 patterns are same. From the X-ray diffraction patterns, we can know that SBA-15(B) treated with DMC is kept both hexagonal structure. And the FT-IR Spectra ofchiral Co(salen) MX3 complexes immobilized on SBA-15(A) and (B) in this work are shown in Fig.2. The salen immobilized samples showed similar spectra. As pursuant to our own efforts directed towards the designing of the di-and multimeric chiral (salen)Co catalysts, dinuclear catalysts ld,2d show remarkable enhanced reactivity and may be employed substantially lower loadings than its monomeric analogues lm,2m without suffering solubility problem and their deactivation. Table 1. HKR of terminal epoxides on chiral Co salen complexes immobilized on the SBA-15 Substrate

Catalyst

Time(h)

Yield of epoxide(%)

ee%ofdiol

ECH

lm/SBA-15(A)

10

10

>98

ECH

lm/SBA-15(B)

10

19

>98

ECH

ld/SBA-15(A)

10

22

>98

ECH

ld/SBA-15(B)

10

37

>98

ECH

2m/SBA-15(A)

10

16

>98

ECH

2m/SBA-15(B)

10

37

>98

ECH

2d/SBA-15(A)

10

30

>98

ECH

2d/SBA-15(B)

10

42

>98

*HKR : Epoxide;1.0mmol, water; 0.5mmol, room temperature

740 740

The trends in the activity and enantioselectivity of the heterogeneous salens were examined for the HKR of epoxides and it is shown in Table 1 and Fig. 3. The reaction using heterogenized Co-salen catalysts exhibited the almost same enantioselectivity as homogeneous ones. It is so easy to isolate the immobilized salen catalysts from the product solution containing epoxide and diols. The immobilized catalyst was recoverable by simple filtration and solvent rinse. The same catalytic activity was obtained through the repeated use for three times in HKR of ECH. The salen catalysts immobilized on SBA-15(B) with 3dimensionally connected mesopores showed higher activity than that anchored on SBA-15(A) having regular hexagonal pores in asymmetric HKR reaction of terminal epoxides with water. It may be due to the easy diffusion and access of reactants to the active sites in the mesopores.

5? 40I O LU

•s » S E O 20 c o

o

1000

2000

—

2d-SBA-15(B) 2m-SBA-15(B) —-2d-SBA-15(A) 2m-SBA-15(A)

3000

Wave number(cm'1)

Fig .2. FT-IR Spectra of SBA-15(A), Co-AlCl3(lm)/ SBA-15(A) and Co-AlCl3 (lm)/SBA-15(B).

Time(hr)

Fig .3. The conversion of ECH for the various catalysts (* The theorectical ECH conversion is max 45% in this work.).

4. References [1] (a) I. Ojima (Ed.), Catalytic Asymmetric Synthesis, 2nd ed., Wiley, New York, 2000. (b) E. N. Jacobsen, A. Pfaltz and H. Yamamoto (Eds.), Comprehensive Asymmetric Catalysis, vols. I-III, Springer, Heidelberg, 1999. [2] (a) M. Tokunaga, J. F. Larrow, F. Kakiuchi and E. N. Jacobsen, Science, 277 (1997) 936: (b) M. E. Furrow, S. E. Schaus and E. N. Jacobsen, J. Org. Chem., 63 (1998) 6776. [3] M. Okamoto et al., SHOKUBAI(Catalysts & Catalysis), 47 (2005) 2A10. [4] Y. K. Kwon, D. H. Kim, G.-J. Kim and Y. S. Han, Stud, in Surf. Sci. Catal., 146 (2003) 355. [5] D. W.Park, S. D. Choi, S. J. Choi, C. Y. Lee and G. J. Kim, Catal. Lett, 78 (2002) 145. [6] S. S. Thakur, W. Li, S. J. Kim and G.-J. Kim, Tetrahedron Lett., 46 (2005) 2263.

Recent Progress in Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

741 741

Simultaneous separation and enantioselective hydrolysis reaction of epoxides in membrane system containing chiral polymer salen catalyst immobilized on MCM-41 Young-Hee Lee, Kwang-Yeon Lee, Chang-Kyo Shin, Sang-Han Kim and Geon-Joong Kim Department of Chemical Engineering, Inha University, Inchon 402-751, Korea

Very high yield of optically pure epichlorohydrin (ECH) was obtained enantioselectively in the catalytic membrane system having chiral polymer salen complexes, due to simultaneous separation of the product during the reaction. The hydrophobic epoxide product diffuses across the membrane into the organic solvent phase. 1. Introduction The need to use optically pure isomers in pharmaceuticals, food additives, flavours, agrochemicals etc, is becoming increasingly important [1]. The homogeneous reaction has a very high selectivity and rate. The heterogeneous chiral catalyst offer practical advantages of the facile separation, as well as recovery and reuse [2]. The catalytic membrane system represents one of the most promising areas for the development of membrane catalysis [3]. It allows to separate the reagents with markedly different polarities without the need for a mutual solvent and to increase the conversion of reactant. In order to obtain a high productivity, thin mesoporous membrane with a high catalyst volume fraction has been applied. The catalytic reactors installed with inorganic membranes can increase the reaction conversion beyond the chemical equilibrium [4]. Biphasic membrane reactor is maintained to separate the product as optically pure isomer.

742

2. Experimental Section The synthesis of MCM-41 coated membrane composites was performed using a silica sol containing surfactant in ethanol solvent. To prepare the prehydrolyzed inorganic precursor solution, tetraethoxyorthosilane (TEOS) in EtOH was hydrolyzed in aqueous HCl solution. The molar ratio was 1.0 TEOS : 0.2 CTABr : 0.14 HCl : 36.5 Ethanol : 8.0 H2O. The surface of porous disk (D 40, Por 1, DURAN Co. LTD) was coated with MCM-41 sol and dried sample was calcined in air at 823K for 4 h [5]. 3-Aminopropyl trimethoxysilane (3ATPS) was linked to the surfaces of MCM41 by the reaction with silanol in the boiling toluene. The polymeric salen ligand immobilized on MCM41 membrane was obtained by the condensation reaction between dimeric dialdehyde derivative and (1R, 2R)-(-)-l,2-diamino cyclohexane in boiling ethanol solution as shown in Fig. 2 [6, 7].

(a)

(b)

(c)

Fig. 1. (a) Porous disk, (b) MCM-41 coated pororous membrane, (c) 3-APTS linking on the surface of MCM41 by the reaction with silanols. OHC,

CHQ

H6-(j-CH-n-0H

A

VA J

Co-OAc 411-0 -»

•

EtOH+Tiff. Relk E(OH f THF. Reflux

n

-HN-,

8. •0

-+

r

»

-s

i

# «-(")-%

A t

VfU y I

Hi.

Fig. 2. The procedure to immobilize the polymeric salen on the surface of membrane composite coated with mesoporous MCM-41. For the synthesis of chiral Aquaous Co(III) polymer salen membrane phase catalyst, chiral salen-containing MCM-41 was treated with ferrocenium hexafluoro phosphate in boiling acetonitrile after cobalt insertion in the center position of Catalyst Immobilized MCM-41 membrane salen structure. The sample was Suppated H I Porous disk washed with hexane to remove the Fig. 3. Membrane Reactor

743

side product, ferrocene. Fig. 3 shows the membrane reactor configuration which was used for asymmetric hydrolysis of racemic epoxides. The mixture of water (15 ml) and THF (5 ml) was charged in one side of reactor and the other side was filled with racemic epoxide (5 ml) dissolved in MC(15 ml). The reaction was preformed at room temperature for 10-120 hr. The characterization of the chiral salen immobilized MCM-41 was carried out by using TG, XRD, and UV-vis reflectance spectroscopy. The ee% value of product was determined by capillary GC using a chiral column (CHORALD EXTM, Gammacyclodextrin trifluo roacetyl, 20mx0.25mm I.d. (Astec)). 3. Results and Discussion

3000

2500

Intensity

2000

1500

1000

500

0 0

5

10

15

20

25

30

35

2 Theta

Fig.4. TEM image of synthesized MCM-41 used for coating.

Fig. 5. X-Ray diffractogram of MCM-41 sample.

The XRD pattern and TEM image of synthesized MCM-41 are presented in Fig.4 and 5. The sample exhibited only a very intense (100) diffraction peak, showing the disordered pore structure. The wormhole like pore can be found by TEM image. This mesoporous material was used as a coating sol to synthesize the chiral salen containing membrane. The enantioenriched ECH could be obtained in the MCM-41 membrane reactor containing chiral salen complexes as can be seen in Figure 3. Relatively hydrohpilic chloropropanediol was dissolved easily in aqueous phase. The simultaneous reaction and separation happened in the same system through membrane reactor. Immobilized salen catalyst was located between two phases of reactants. This Membrane reactor system could be successfully applied to the HKR reaction of epoxides. The result of the asymmetric HKR is summarized in Fig. 6. The ee % of ECH increased linearly with the increasing of the reactant conversion in the membrane reactor system. The leaching of polymer salen complexes was not detected both in the aqueous and organic solution. This means polymer salen complexes immobilized on the membrane could be recycled repeatedly only by filling the reactants in the separated reactor. The polymer salen complexes could be reused for more than three times refill of reactants without loss of the

744

catalytic activity and enantioselectivity as shown in Figure 7. The chiral salen complexes in the membrane layer exhibited a high optical purity of product during the reuse in the HKR reaction.

•<,'•

CJ

100 90

80 7n 1 w

- * - 1 " use - * - 2™* racyele - * - 3 r f recycle

B0

50 40 30 20 10 0 0

10 20 30 «) 50 60 70 80 90 100 110 120

Hous

Fig. 6. Catlytic activity of chiral salen membrane for HKR.

HOLTS

Fig.7. Recyclabilities of salens in the immobilized in membrane reactor for repeated use.

4. Conclusion In summary, the asymmetric hydrolysis of the terminal and meso epoxides to afford diols using the heterogenized catalysts can be applied successfuly by using the mesopours membrane reactor. High enantioselectivity was attainable on the polymeric salen catalysts. The polymeric salen complexes immobilized on mesoporous material by the present procedure can be applied as an effective heterogenized catalyst for the asymmetric reactions. 5. References [1] [2] [3] [4] [5] [6]

H.-J.Federsel and J. Crosby (Eds). Chirality in industry II., J.Wiley & Sons, 1997,p. 295. S. D. Choi, and G. J. Kim, Catal. Lett., 92 (2004) 35. E. Drioli and L. Giomo, Chemistry & Industry., 1996, N. 1. L. P. Szabo, E. H. Lipai and J. Bodnar, J. Ind. Chem., 26 (1998) 147. S. Yuming and C. Huilin, Tetrahedron Lett., 44 (2003)7081. Y. M. Song, H. L. Chen, X. Q. Hu, C. M. Bai and Z. Zheng, Tetrahedron Lett., 44 (2003) 7081. [7] Y. Song, X. Yao, H. Chen, C. Bai, X. Hu and Z. Zheng, Tetrahedron Lett., 43 (2002) 6625.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

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Mesoporous silica MCM-41-supported norephedrine and ephedrine as heterogeneous chiral ligands in asymmetric catalysis Sang Han Kima*, Chang kyo Shina, Jong Hyuk Seokb, Choong Young Leeb and Geon Joong Kima "Department of Chemical Engineering, Inha University, Incheon 402-751, Korea Department of Chemical and Environmental Technology, Inha Technical College, Incheon 402-752, Korea

Mesoporous silica MCM-41-supported norephedrine (3a) and ephedrine (3b) were prepared from available amino alcohol and utilized as ligand for the ruthenium-catalyzed asymmetric transfer hydrogenation of ketones and for the asymmetric addition of diethylzinc to aromatic aldehydes respectively. The mesoporous silica MCM-41 was found to be potential inorganic support in the asymmetric catalysis. 1. Introduction Asymmetric catalysis is recognized as the most promising area in the synthesis of optically active compound. The ruthenium-catalyzed asymmetric transfer hydrogenation of ketones and the asymmetric addition of diethylzinc to aromatic aldehydes are attractive methods that lead to the formation of optically active secondary alcohol which play an important role as intermediate in organic chemistry. Covalent immobilization of chiral catalysts to insoluble supports has created fast-growing interest, as it provides an easy separation of the product and enables the recovery of expensive catalyst [1]. Recently, mesoporous silica MCM-41 with large uniform pore diameter has become of high interest as an inorganic support. Our interest in the field led to prepare mesoporous silica MCM-41-supported norephedrine (3 a) and ephedrine (3 b) as heterogeneous chiral ligand (Figure 1). Herein, we report our experimental results on the asymmetric transfer hydrogenation of ketones [2] and the asymmetric addition of diethylzinc to aldehydes [3] catalyzed by the MCM-41 supported heterogeneous chiral ligands. Figure 2 shows the TEM image of the

746

organo-functionalized MCM-41 material. The MCM-41 prepared by an evaporation method exhibited a fully ordered hexagonal structure. Me

41 MMC

O O Si O O O SiPh O

N H

Ph

Me

OH

41 MMC

3a

Fig. 1. Structure of the ligands.

O O Si O O O SiPh O

N Me

Ph OH

3b

Fig. 2. TEM image of mesoporous functionalized MCM-41 material.

2. Experimental Section Preparation of the heterogeneous chiral ligands immobilized onto the mosoporous silica MCM-41. ;The immobilization of ephedrine and norephedrine onto MCM-41 was performed in three steps. Reaction of MCM41(1) with an excess of (3-chloropropyl)trimethoxysilane in refluxing toluene gave the chloropropylsilanized MCM-41 (2a) (2.8 mequiv (CH3)2Cl/g), which was reacted with phenyltrimethoxysilane to give the resulting MCM-41 (2b). Subsequent treatment of the 2b with 1.5 equiv of (IS, 2R)-(+)-norephedrine and (1R, 2S)-(-)-ephedrine in refluxing toluene in the presence of 1.1 equiv of triethylamine afforded the MCM-41-supported norephedrine (3a) (0.5 mmol/g) and ephedrine (3b) (0.35 mmol/g) respectively. (Scheme 1) The degrees of functionalization were determined by nitrogen element analysis. 3. Results and Discussion First, with the mesoporous silica MCM-41-supported norephedrine (3a), we examined its catalytic activity in ruthenium-catalyzed asymmetric transfer hydrogenation of ketones. The chiral ruthenium complex was prepared in situ by heating a mixture of [Ru(p-cymene)Cl2]2 and the MCM-41-supported norephedrine (3a) in 2-propanol at 80°C lh. The reaction conditions and results are summarized in Table 1.

747

MCM-41

2a

1

1 Me

Ph „ iii

V

C1

iv

—O

—a —O^SiPh

-oN —O;SiPh —O

—o 3a

2b

i) excess (MeO)3Si(CH2)3Cl, toluene, reflux, 24h. ii) excess (MeO)3SiPh, toluene, reflux, 36h. iii) 1.5 eq. (15, 27?)-(+)-norephedrine, 1.2 eq. triethylamine, toluene, reflux, 24h. iv) 1.5 eq. (\R, 2S)-(-)-ephedrine, 1.2 eq. triethylamine, toluene, reflux, 36h. Scheme 1. Synthesis of the heterogeneous ehiral ligands immobilized onto the mosoporous silica MCM-41. Table 1. Asymmetric transfer hydrogenation of ketonesa o R

OH

[Ru(/7-cymenc)Cl2]2 ligand 3a

[

/-PrOH/KOH

Conversion

E.e.

100/1/1

Time (h) 16

61

84

R=Me

200 /I /I

16

48

82

3 4

R=Me R=Et

200 /I /2 100/1/1

16 30

52 62

82 74

5 6

R=Et a-tetralone

200 /111 100/1/1

30 16

65 30

73 96

Entry

Ketone

Ketone/Ru/ligand

1

R=Me

2

"The reaction was carried out at room temperature using 0.1M solution of ketone in 2-propanol. b c

Determined by GC analysis. Determined by HPLC on Chiralcel OB-H column (5% 2-propanol in n-hexane, 0.5 ml/min).

As can be seen from Table 1, mesoporous silica MCM-41-supported norephedrine (3a) afforded (-K)-secondary alcohols and the asymmetric induction seems to be affected by the structure of substrate. As the bulkiness of the alkyl substitutent increased, the enantioselectivity was somewhat lowered. Next, the efficiency of mesoporous silica MCM-41-supported ephedrine (3b)

748 748

was tested in the heterogeneous asymmetric addition of diethylzinc to aromatic aldehydes. The reaction conditions and results are summarized in Table 2. Table 2. Asymmetric Addition of Diethylzinc to Aromatic Aldehydesa OH ArCHO +

Entry d

l 2 3 4 5

Et2Zn

Ar C6H5 C6H5 /?-ClC 6 H 4 o-MeOC 6 H 4 p-MeOC 6 H 4

-

10 mol% chiral ligand 3b hexane, 0°C

Time (h) 48 16 16 16 16

Ar W \ H

Conversion (%)b 75 85 89 89 78

E.e. (%)c 25 66 68 83 80

a

The reaction was performed in hexane atO'C —» 20 'C using 2.2 equiv. Et2Zn. Determined by gas chromatography analysis. ' Determined by HPLC on Chiralcel OD-H column (2.5% 2-propnol in rc-hexane, 1.0 ml/min). d The reaction was carried out using silica gel-supported ephedrine as ligand. b

Aldehydes were converted to (/?)-secondary alcohol with high ee's in reasonable conversion. The MCM-41 supported ephedrine (3b) gave much higher reaction rate and better enantioselectivity than silica gel-supported ephedrine [4]. In the case of benzaldehyde, enantioselectivity was greatly increased from 25 to 66%. These results are comparable to those of the homogeneous system using ./V-alkyl ephedrine [5]. We have shown that the mesoporous silica MCM-41 could be utilized as a potential support for heterogeneous chiral ligand in asymmetric transfer hydrogenation of ketones and asymmetric addition of diethylzinc to aldehydes. Efforts for the synthesis of further MCM-based chiral ligands are currently underway in our laboratory. 4. References [1] N. E. Leadbeater, M. Macro etal., Chem. Rev., 102 (2002) 3217. [2] H. Karl-Josef, H. Shohei, F. Akio , I. Takao and R. Noyori, Angew. Chem. Int. Ed. Engl, 36 (1997) 285. [3] X. Ariza, J. Bach, R. Berenguer, J. Farras, M. Fontes, J. Garcia, M. Lopez and J. Ortiz, J. Org. Chem, 69 (2004) 5352. [4] K. Soai, M. Watanabe and A. Yamamoto, J. Org. Chem, 55 (1990) 4832. [5] P. A. Chaloner and S. A. Renuka Perera, Tetrahedron Lett, 28 (1987) 3013.

Recent Progress in Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

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Catalytic performance of Cu-MCM41 with high copper content for NO reduction by CO Yan Kong3*, Yanhua Zhangb, Xiaoshu Wab, Jun Wang", Haiqin Wanb, Lin Dongb and Qijie Yana* "College of Chemistry and Chemical Engineering, Key Laboratory of Material-oriented Chemical Engineering ofJiangsu Province and MOE, Nanjing University of Technology, No5Xinmofan Road, Nanjing 210009, P.R.China b Key Laboratory ofMesocopic Chemistry, Department of Chemistry, Nanjing University, Nanjing 210093, P. R. China.

1. Introduction NO is a major atmospheric pollutant, for it has the ability to generate secondary contaminants through its interaction with other primary pollutants [1]. It is no doubt that the catalytic removal of NO, especially the selective catalytic reduction (SCR) of NO with reducing agents, such as NH3, CO, H2 and hydrocarbons is the most effective way [2]. Current used catalysts are based on various noble metals, such as Pt, Pd and Rh as the active ingredients [3]. However, it is limited due to their scarce and high cost, and the substitution by the cheap metals for the noble metals has attracted much interest. Copper is an efficient ingredient in many catalysts. Copper oxides dispersed on oxidic supports such as Cu/Si-Nb3O8 [4], Cu/CeO2 [5], CuO/Ce0.8Zro.202 [6], CuO-MnOx [7] etc., and copper ion exchange molecular sieves such as CuZSM5 [8], Cu-FAU [9], Cu-MFI [10], Cu-MCM41 [11,12] etc. show favorable activity in the catalytic removal of NO. However, they are not sufficient yet used instead of the catalysts containing noble metal [13] because of the lower activity, partially due to the low content of copper and small amount of active sites, which generally limit their catalytic activity. Our group has successfully synthesized Cu-MCM41 containing high content of copper up to 26.1 wt% [14, 15]. Detail characterization results indicate that most of the atoms of copper are in the framework of MCM41 [16] and the thermal stabilities are higher than pure MCM41 [14]. In the present paper, the

750

catalytic activities of this series samples in NO+CO reaction are reported. The active species in the catalysts are also discussed briefly. 2. Experimental Section All the catalysts are synthesized under the best experimental procedure as our previous study [15]. The catalysts with the copper content of 4.7, 10.6, 16.9 and 26.1 wt% (determined by ICP) are designated as 5Cu, lOCu, 20Cu, 30Cu, respectively, and some structure parameters of them are listed in reference [16]. For comparison, Cu/MCM41 is prepared by impregnated method according to reference [17]. Powder XRD patterns are recorded on a Shimadzu XD-3A diffractometer. XPS analyses are conducted on an ESCALAB MK-II spectrometer. CO-TPR is carried out in the fixed-bed reactor. After reaction, the catalysts are cooled down to room temperature under the protection of N2, then 10% CO/He mixed gas is brought in and the temperature rise from 298 K to 1073K. NO and CO adsorbed FT-IR spectra are collected on a Nexus 870 FTIR spectrometer. The wafers of the catalysts are outgassed to a residual pressure of 0.2Pa then NO and/or CO gas is introduced to a pressure of l.OxlO4 Pa and maintains at different temperature for lh before analyzed at room temperature. A 4 mm internal diameter quartz tube is used as a fixed bed, atmospheric pressure reactor for catalyst testing. The reactant gas mixture consist of 3.33 vol.% NO and 6.67 vol.% CO in a helium balance. Reactor output is analyzed by on-line gas chromatography (FULI GC 9790). 3. Results and Discussion Table 1 Comparative of the activity for our catalysts with some others Catalysts La2.xSr,Th(x)Cu04±^ Cu, Mn/Active carbon Cu-Ce synergism CuO/CeogZrojOz CuO/CeO2 CuO/TiO2-CeO2 Pd/Ceo.6Zro.402/Al2C>3 Pt-Rb/r-Al 2 O 3 Pd-Cu/(Ce,Zr)Ox/Al2O3 10CU-MCM41 20Cu-MCM41 30Cu-MCM41 10Cu/MCM41c

TOFa(molg"1h-1) 0.48 4.73 3.86 42.8" 13.4 8.92 54.7 8.30 1.34 12.6 22.7 44.6 0.7

Ref. 18 19 20 6 21 22 23 24 25 Present work Present work Present work Present work

a Best results of MolNO converted to N2 gcataiyst ' h ' * 103; b NO mainly converted to N2O; c Prepared by impregnated method

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Catalytic tests indicate that the conversion of NO and the selectivity to N2 for the catalyst containing 26.1 wt% copper (30Cu) are all 100% with the space velocity in the range of 3000 to 30,000mlg"-h at 723K. Other materials with relative lower copper content exhibit the same activities at certain space velocity and the activities increase with the copper content in the catalysts. The rate of NO converted to N2 over per gram 30Cu per hour is about 44.6><10"3 molg'h" 1 , not only much higher than over other copper-containing catalysts in the literatures (table 1), but also close to the catalysts containing noble metals, implies our catalysts exhibit excellent activity in relative high concentration of NO and high space velocity. It might be due to the much higher copper content in our catalysts than the reported copper-containing catalysts. It can be seen from figure 1 that the catalytic activity of the lOCu is twovolcano type curve, i.e., there are two maximum peaks at 573 K and 723-773 K, respectively. Same phenomena are obtained for other catalysts. In order to search for the reason, the catalysts reacted in the reactant gas at 723 K and a S.V. of 30,000 mlg'h" 1 for 1 h are cooled down to room temperature and test the changes of their activities over temperature. It is surprising that the activities increased straight before the temperature of 623 K (Fig. 1) and NO can be fully converted to N2 from 623 to ca. Ill K. This phenomenon might be due to the different active species and/or different catalytic mechanisms of the catalysts at lower and higher temperature. Several techniques are carried out to probe the active species of the catalysts. 933.0 935.2

1.0

723K

0.8

673K

Intensity/a.u.

C onversi o n o f NO

10000

0.6

0.4

623K

9000

573K

8000 523K

0.2

7000 0.0 450

500

550

600

650

700

750

800

850

Temperature/K

Fig. 1 Conversion of NO over origin lOCu catalyst (o) and lOCu treated in reactant gas at 723K for lh (A) (S.V.:

930

935

940

945

950

955

960

965

Energy/e.V. Binding Energy/e.V.

Fig. 2 XPS spectra of copper species in 20Cu catalysts reacted at different

The catalytic activities increase with the copper content in the catalysts at the same reaction conditions proves a necessity of high copper content for the catalysts. Pure MCM41 has less activity and the sample prepared by impregnated method has a very low activity (the conversion of NO is only 8.1% at 723 K and a S.V. of 6000 mlg' ! -h' 1 ), which suggest that it is necessary that

752 752

the atoms of copper in the framework of MCM41 for our catalysts exhibit high catalytic activities and the copper species incorporated into the framework of MCM41 are the active species. In fact, XRD spectra indicate that the hexagonal pore structures of the catalysts are still maintained after reaction and the catalytic activity doesn't decrease until the hexagonal pore structure collapse, also indicate that the atoms of copper in the framework of MCM41 are the active species. In the XPS spectra of 20Cu catalyst reacted at different temperature (Fig. 2), a peak centered at 935.2 eV, correspondence to Cu(II)2p3/2 incorporated into the framework of MCM41 are observed for the catalyst reacted below 523K, similar with original Cu-MCM41, and it can be concluded that Cu(II) is the active sites at lower temperature. Another peak centered at 933.2eV, correspondence to Cu(I)2p3/2 are observed for 20Cu reacted at higher temperature, thus probably Cu(II) and Cu(I) are the active sites at higher temperature. CO-TPR profiles of 20Cu (figures not given) reacted at different temperature show two peaks centered at about 730 and 990 K, corresponded to the reduction of Cu(II) to Cu(I) and Cu(I) to Cu, and the profiles of 20Cu reacted below 523 K are also the same as original Cu-MCM41. The areas of the peaks centered at 730 K does not vanished despite the catalyst reacted at any temperature, which suggest Cu(II) species are one of the active sites. On the other hand, a strong peak centered at 2124 cm"1 is observed in CO absorbed FT-IR spectra. It must be ascribed to the vibration of C=O absorbed on Cu(II) species, for our previous study indicate that there are only Cu( II) species in the materials. The peak appears at lower temperature and vanishes at higher temperature in CO adsorbed FT-IR spectra due to the reduction of Cu( II) to Cu( I ), but it is always visible in the NO/CO mixed adsorbed FT-IR spectra (Fig. 3), suggest that the oxidation of Cu( I ) to Cu( II) by NO is one of reaction steps. In fact, catalytic tests 2300 2200 2100 2000 1900 of the samples show that the original Wavenumber/cm" 20Cu have less activity for NO direct decomposition, but after treated in Fig.3 CO and CO+NO absorbed FT-IR the reactant gas for 1 h it gives a spectra of 20Cu catalyst at different teirroerature: a CO and b NO+CO 40.2% conversion of NO and a 85.5% selectivity to N2 at 723 K and 1 a S.V. of 6000 mlg'h" , confirm that Cu(I) are the active components for NO direct decomposition. Combined with CO-TPR and XPS results, one can easily conclude that Cu( II) are the active species at lower temperature, otherwise Cu( II )/Cu( I ) are the active species at higher temperature.

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4. Conclusion Cu-MCM41 with high content of copper in the framework is an efficient catalyst for NO reduction by CO. The active sites were different at low and high temperature, it might be Cu( II) and Cu( II )/Cu( I ) species respectively. This project was supported by Natural Science Foundation of Jiangsu Province (BK2005120) and National Natural Science Foundation of China (20476046 and 20173026). 5. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25]

V. I. Parvulescu, P. Grange and B. Delmon, Catal. Today, 46 (1998) 233. F. Mathis, Catal. Lett., 28(1994)33. R. Burch, J. P. Breen and F. C. Meunier, Appl. Catal. B., 39 (2002) 283. X. Wang, W. Hou, X. Wang and Q. Yan, Appl. Catal. B, 35 (2002) 185. Y. Hu, L. Dong, M. Shen, D. Liu, J. Wang, W. Ding, Y. Chen. Appl. Catal. B, 31 (2001) 61. L. Ma, M. Luo and S. Chen, Appl. Catal. A, 242 (2003) 151. I. Spassova, M. Khristova, D. Panayotov and D. Mehandjiev, J. Catal.,185 (1999) 43. S. Matsumoto, K. Yokota, H. Doi, M. Kimura, K. Sekizawa and Kasahara, Catal. Today, 22(1994)127. M. Iwamoto, H. Furukawa, Y. Mine, F. Uemura, S. Mikuriya and S. Kagawa, J. Chem. Soc. Chem. Commun., (1986) 1272. A. V. Salket and W. Weisweiler, Appl. Catal. A, 203 (2000) 221 M. Ziolek, I. Sobczak, I. Nowak, M. Daturi and J. C. Lavalley, Appl. Catal. B, 28 (2000) 197. G. Moretti, C. Dossi, A. Fusi, S. Recchia and R. Psaro, Appl. Catal. B, 20 (1999) 67. H. Yahiro and M. Iwamoto, Appl. Catal. A, 222(2001)163. X. Guo, M. Lai, Y. Kong, W. Ding, Q. Yan and P. C. T. Au., Langmuir, 20 (2004) 2879. Y. Kong, J. Chen, X. Guo, H. Ma, W. Hou and Q. Yan, Chem. J. Chin. U, 25 (2004) 320. Y. Kong, H. Zhu, G. Yang, X. Guo, W. Hou, Q. Yan, M. Gu and C. Hu., Adv. Funct. Mater., 14 (2004)816. C. L. Tsai, B. Chou, S. Cheng and J. F. Lee, Appl. Catal. A, 208 (2001) 279. Y. Wu, Z. Zhao, Y. Liu and X. Yang, J. Mol. Catal. A, 155 (2000) 89. N. B. Stankova, M. S. Khristova and D. R. Mehandjiev, J. Colloid. Interf. Sci., 241 (2001) 439. B. Wen and M. He, Appl. Catal. B, 37 (2002) 75. X. Jiang, L. Lou, Y. Chen and X. Zheng, J. Mol. Catal. A, 197 (2003) 193. H. Zhu, M. Shen, Y. Kong, J. Hong, Y. Hu, T. Liu, L. Dong, Y. Chen, C. Jian and Z. Liu, J. Mol. Catal., 219(2004) 155. R. D. Monte, P. Fornasiero, J. KaSpar, P. Rumori, G. Gubitosa and M. Graziani, Appl. Catal. B, 24(2000)157. M. Konsolakis, I.V. Yentekakis, A. Palermo and R.M. Lambert, Appl. Catal. B, 33 (2001) 293. A. B. Hungria, A. Iglesias-Juez, A. Martinez-Arias, M. Fernandez-Garcia, J. A. Anderson, J. C. Conesa, J. Soria, J. Catal., 206 (2002) 281.

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Recent Progress in Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

755 755

Influence of iron content on the structure and catalytic activity for the hydroxylation phenol of Fe-MCM41 Cheng Wu a , Yan Kong 3 *, Xingjie Xu a , Jun Wang a *, Fei Gao b , Lin Dong b and Qijie Yan b

"College of Chemistry and Chemical Engineering, Key Laboratory of Material-oriented Chemical Engineering of Jiangsu Province and MOE, Nanjing University of Technology, Nanjing 210009; Key Laboratory of Mesocopic Chemistry, Department of Chemistry, Nanjing University, Nanjing 210093, P. R. China

1. Introduction Diphenols are important chemical materials. Hydroquinone has been widely used as photographic developer, polymerisation inhibitor and catechol is a starting material for a series of important fine chemicals used for pest control, flavours and aromas [1-3]. Direct catalytic hydroxylation of aromatic compounds is current interest both from fundamental and industrial standpoints [4]. A series of microporous and mesoporous materials such as TS-1, TAPO-5, VS-2 were investigated as the catalysts'51. The metal modified MCM-41s have attracted considerable attention in recent years [6, 7]. There are lots of reports that concern the doping of MCM-41 with metallic cations such as Cu, Ni, Al, Mo, Zn, Ti via direct synthesis, cation exchange and impregnation methods [8-11]. Fe-containing molecular sieves show high activity for alkylation and oxidation reactions [12]. The activity of Fe-MCM41 in the hydroxylation of phenol has been described before [11, 13, 14]. However, the iron content in the literature was lower and there is no description about the regularity with the iron content in the framework of MCM41 for the phenol hydroxylation under mild condition. In the present study, the iron modified-MCM41 s with different content were synthesized by sol-gel method and the relationship of structure and catalytic activity was studied.

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2. Experimental Section The Fe-containing mesoporous materials were synthesized similar to reference [11]. In this work, iron nitrate was used as iron source instead of ferric sulfate and iron trichloride, and the Fe/Si molar ratios (0.00-0.14) was much higher than that in the literature (0.00-0.04). A typical synthesis procedure was as follows: 1.9 g sodium silicate and 1.4g CTMAB were dissolved in 15ml water with heating. After cooled to the room temperature, 5ml solutions containing desired amounts of the Fe(NO3)3-9H2O were added and the mixture was stirred for 2 h. Then 10.85 g TMAOH solution was added and the pH was adjusted to 11 by diluted sulfuric acid (1 mol-L"1). The resulting gel was transferred into a polypropylene bottle and kept at 373 K for 5 days. The products, with molar ratio of xFe: 700Si(x=2-14), were washed with distilled water and ethanol for three times, respectively. The surfactant was removed by calcination at 823 K for 5 h in air. The calcined samples were designated as xFe. Fe-impregnated MCM41 was prepared [6] (denoted as Fe/MCM41) for comparison. The XRD patterns were identified by Philips PW 170 diffractometer. The surface areas and pore properties were obtained on Micromeritics ASAP-2020 analyzer and determined by conventional BET and BJH equations using adsorption data. FT-IR spectra were recorded with Bruker VECTOR22 FT-IR spectrometer. The iron contents were analyzed using ICP-AES. The hydroxylation of phenol was performed on self-made equipment. The reaction in which the reactants consisted of 1 g of phenol, 8.4 g of water, 0.05 g of catalyst and 30% aqueous solution of H2O2 (phenol: H2O2 ratio of 3:1) was carried out at 40°C for 2 h. The product distributions were determined by an Agilent 1100 HPLC equipped with a reversed phase C18 column. 3. Results and Discussion Fig. 1 shows the low angle XRD patterns of some samples. An intense (100) peak at about 26 = 2° together with weak (110), (200) and (210) peaks in the small angle range indicated that the hexagonal regularity of MCM-41 was still maintained as Fe was introduced. The shift of (100) peak and the reduction of peak intensities are the indication of the slight reduction of hexagonal symmetry of MCM41 due to Fe incorporation [15]. In high angle XRD patterns (figures not given), no characteristic peaks of Fe2O3 were found, suggested that Fe species might be in the framework of MCM41 or highly dispersed on the surface. Fig. 2 shows the nitrogen adsorption isotherm of some samples an d the corresponding pore size distributions (inner). The slow increase in nitrogen uptake at P/Po<0.2 was corresponding to monolayer-multilayer adsorption on the pore walls. The sharp step at P/Po between 0.2 and 0.4 indicated the mesoporous nature of the materials and a plateau with a slight inclination at

757

high P/Po was associated with multilayer adsorption on the external surface of crystals [16, 17]. The narrow pore size distribution also revealed a uniform mesoporosity. Po re V olum e/a.u .

(100) (1 00) \

(a)

(b)

/

•5

\

(110) (200)

c

(210)

\

/

Quantity Adsobed/a.u.

Inttensity ensity/a.u.

(c)

"

~~

(a)

~^~

—-

"

(b) SL

l^—•——

(c)

1

10

100

Pore Diameter(nm)

(c)

(b)

(a)

Ads Des

(d) 1

2

3

4

5

6

7

8

9

0.0

0.2

22θ/Deg θ / Deg

0.4

0.6

0.8

1.0

Relative pressure(P/P pressure(P/P0) Relative 0)

Fig. 1 XRD patterns of (a) 6Fe (b)8Fe(c)12Fe(d)14Fe

Fig.2 Nitrogen adsorption/desorption isotherms and pore size distributions (inner) of (a) 6Fe (b) 8Fe (c) 12Fe

The FT-IR spectra of some samples are given in Fig. 3. The disappearance of C-H vibration band at about 2921 and 2852 cm'1 confirmed the complete removal of the template after calcinations [18].The absorption bands at about 1080 and 800 cm"1 corresponded to the anti-symmetric and symmetric stretching modes of Si-0 stretching vibrations, respectively [19]. The bands at ca.970 and 460 cm"' were due to the stretching and bending vibrations of surface Si-O" groups, respectively. It could been seen that a slight red shift at about 1080 cm"1, which might be another evidence that iron was incorporated into the framework of MCM41 and M-O-Si bonds were formed [8, 9].

y Transmittance/a.u.

r (d)

(1072)

3.0

• average average pore porediameter(nm) diameter(nm) • thickness thicknessof ofpore porewall(nm) wall(nm) o Yield Yield of ofDiphenol Diphenol

A

f

16 2.5

(c)

(1074)

(b)

(1078)

(a) (1082)

4000 TOO

3000

2000

/ /

A

1000 1000 -1 -1

Wavenumber/cm

Fig.3 FT-IR spectra of some samples (a) 4Fe; (b) 6Fe; (c) lOFe; (d) 12Fe

2.0

14

0.02

0.04 0.04

0.06 0.06

0.08 0.08

0.10 0.10

0.12 0.12

0.14 0.14

0.16 0.16

the molar ratio ratio of of Fe/Si Fe/Si the Fig.4 Variations of some structure parameters and the catalytic activity on the Fe content

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The results of ICP and some structure parameters of the samples are summarized in table 1. It is interesting that the unit cell parameters (a0), the average pore diameters and the thickness of pore wall were all increasing slightly as the Fe/Si molar ratios was smaller than 0.08 and increased rapidly as Fe/Si molar ratio higher than 0.08. The decrease of the specific surface areas and the average pore diameters with the iron content exhibited the same tendencies. It may be that some of the iron in the gel was migrated from framework to the outer in the phase of Fe2O3 after calcinations, which was confirmed by the rapidly increase of thickness of pore wall during the increasing of Fe content. Table 1 Some Structure Parameters of the Samples sample

2Fe 4Fe 6Fe 8Fe lOFe 12Fe 14Fe

n F e /n s i Gel Product 0.02 0.04 0.06 0.08 0.10 0.12 0.14

0.024 0.045 0.075 0.091 0.118 0.146 0.155

BET surface area (m2/g) 666.4 668.2 688.3 655.5 582.6 534.9 499.5

Pore volume (cmVg) 0.5122 0.6512 0.6944 0.5767 0.6795 0.6675 0.6261

do

ao

D

6

/nm

/nm

/nm

/nm

3.91 3.94 3.98 4.05 4.21 4.29 4.42

4.52 4.56 4.60 4.68 4.86 4.95 5.10

2.59 2.55 2.53 2.51 2.34 2.26 2.06

1.93 2.01 2.07 2.17 2.52 2.69 3.04

All the prepared materials exhibit excellent catalytic activity for the direct hydroxylation of phenol at 40°C. The phenol conversion could reach to 30.9% (phenol: H2O2 ratio of 3:1) over 8Fe catalyst. The selectivity of diphenols was 47.1 to 68.2% over different catalysts might be because some of the products were oxidized to tar or polymerized to oligomer. However, the Fe/MCM41 prepared by impregnation method and FeCl3 with the same Fe content as catalysts gave a 25.6% and 11.7% conversion of phenol and 57.8% and 36.2% selectivity of diphenols, respectively. The fact that Fe incorporated into the framework of MCM41 has higher activity than the two others suggested the Fe ion in the framework of MCM41 was the active sites for the reaction. Fig.4 shows the variations of some structure parameters and the catalytic activity for phenol hydroxylation over catalysts with different Fe/Si ratios. It could be seen that the yield of diphenols increased as the Fe/Si molar ratio smaller than 0.08, and decreased after the iron content increased further. The conversion of phenol and the efficiency of H2O2 exhibited the same variations. The regularly varying of catalytic activities was associated with the status of iron species in the catalysts and the structure parameters of samples. The activity of the reaction increased as the iron content in the framework increased. However, as the Fe content in the gel exceeded the limitation, the redundant

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iron was accumulation in the surface of the catalyst. The falling of catalytic activities could be due to the decreasing of surface areas and pore volumes because of accumulated of Fe2C>3 in the surface. 4. Conclusion Fe-MCM41 with different iron contents has been synthesized. Catalytic test indicated that the samples had excellent activity for the hydroxylation of" phenol with H2O2 under mild conditions. The catalytic activity increased with iron contents and decreased as Fe/Si molar ratio more than 0.08. The regularity was accord to the structure parameters of the catalysts. This project was supported by Natural Science Foundation of Jiangsu Province (BK2005120) and National Natural Science Foundation of China (20476046 and 20173026). 5. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19]

G. Rocha, R. Johnstone and M. Neves. J. Mol. Catal. A : Chem. 187 (2002) 95. L. A'ida, A. Cesar and M. Consuelo. J. Mol. Catal. A: Chem. 228 (2005) 233. G. Bellusti and V. Fattore. Stud . Surf. Sci. Catal. 69 (1991) 79. E Karakhanov, T. Filippova, S. Martynova,, A Maximov, V. Predeina and I. Topchieva. Catal. Today 44 (1998) 189. J. Sun, X. Meng and Y. Shi. J. Catal. 193 (2000) 199. L. Norena-Franco, I. Hernandez-Ptrez, J. Aguilar-Pliego and A. Maubert-Franco. Catal. Today 75 (2002) 189. M. Trejda and M. Ziolek. Catal. Today 101 (2005) 109. Y. Kong, H. Zhu, G. Yang, X. Guo, W. Hou, Q. Yan, M. Gu and C. Hu. Adv. Func. Mater. 14 (2004) 816. Y. Kong, S. Jiang, J. Wang, S. Wang, Q. Yan and Y. Lu. Micro. Meso. Mater. 86 (2005) 191. D. Bruhwiler and G. Calzaferri. Micro. Meso. Mater. 72 (2004) 1. V. Parvulescu V and B. Su. Catal. Today 69 (2001) 315. N. S. Nesterenko, O.A. Ponomoreva and V. V. Yuschenko etc. Appl. Catal. A: Gen. 254 (2003)261. S. Agnes, K. Zoltan, M. Dora and S. Edit. Appl. Catal. A: Gen. 272 (2004) 257. J.-S. Choi, S.-S. Yoon, S.-H. Jang and W.-S. Ahn. Catal. Today 111 (2006) 280. R. Savidha, A. Pandurangan, M. Palanichamy and V. Murugesan. J. Mol. Catal. A: Chem. 211(2004)165. M. Selcaraj, P.K. Sinha, K. Lee, I. Ahn, A. Pandurangan and T.G. Lee. Micro. Meso. Mater. 78(2005)139. B. Chakraborty and B. Viswanathan. Catal. Today 49 (1999) 253. W. Zhao, Y. Luo, P. Deng and Q. Li. Catal. Letters 73 (2001) 2. J. Chomaa, M. Jaroniecb, W. Burakiewicz-Mortkaa and M. Kloskea. Appl. Surf. Sci. 196 (2002)216.

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Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

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Basic catalysis by surfactant containing MCM-41 Leandro Martins and Dilson Cardoso Federal University of Sao Carlos, Chemical Engineering Department, PO Box 676, 13565-905, Sao Carlos - SP, Brazi

1. Introduction Usually, the basicity in Si-MCM-41 is achieved by functionalizing its surface with compounds containing terminal amines in their composition [1]. Before functionalizing, the cationic surfactant present in the pores is removed by calcination, generating silanol groups, which are anchoring points. Another way to obtain basic MCM-41 is dispersing alkali metal oxides in the channels [2], but due to the high pH of the solution used in the impregnation the MCM-41 structure is somewhat damaged. Both procedures are hard to handle and not always lead to basic sites stable enough for catalysis application. Recently, Kubota et al [3]. achieved excellent results during Knoevenagel condensation by using as-synthesized SiMCM-41 molecular sieve while keeping the surfactant inside the pores. In this catalyst, called [CTA] Si-MCM-41, the active sites are highly basic =SiO" sites, which are occluded in the mesopore channels. This work is designed to explore the chemical behavior of catalyst [CTA] Si-MCM-41 by using it in the Knoevenagel condensation. 2. Experimental Section [CTA]Si-MCM-41 catalyst was synthesized through Cheng et al. method'4'. Small angle X-ray diffraction patterns were achieved with a diffractometer D5000 (Siemens), using powder method, at 1.4° < 29 < 10° interval. Nitrogen adsorption/desorption isotherms were achieved with an equipment supplied by Quantachrome (Nova-1200). Before analysis, 50 mg of the sample, assynthesized or calcined, was vacuum treated at 110°C for 2 h. MAS NMR analyses were performed at a VARIAN unit INOVA spectrometer operating at 79.5 MHz and 400 MHz for 29Si and *H, respectively. 29Si direct polarization experiments (DP/MAS) were performed using a 5-ms % /2 excitation pulse and 30

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s of recycle delay. In order to obtain more enhanced spectra, a cross-polarization radiofrequency ramp (ramp CP/MAS) was used [5]. Knoevenagel condensation was performed by using 10 mmol equimolar amounts of ethyl cyanoacetate and benzaldehyde in 18 mL of toluene, to which 1 g of the catalyst was added. Reaction temperature was varied from 10 to 50°C. 3. Results and Discussion Si-MCM-41 samples, calcined or not, showed a typical diffratogram (Figure la). As-synthesized sample showed a specific area of 1.0 m2.g"! while calcined sample snowed a specific area of 990 m2.g'' (Figure lb). Elemental C, H and N analysis of as-synthesized Si-MCM-41 sample showed a C/N ratio close to 19, which corresponds to the CTA chemical composition, indicating that no other organic compound is not included in the solid phase. i 600EEl"

t *>°"

m

-S

/• D /

n 400o {ft*

T3 3 0 0
S

/

S EE =l,Om 2 /g

JZ 100o / >

29/'

0n OJO

0^

0,+

E e l i t i v e

OjS Pressure

OyS

1J0

/ P.P

Figure 1. (a) X-ray diffraction pattern of as-synthesized MCM-41 sample and (b) Nitrogen sorption isotherms of calcined and as-synthesized MCM-41 samples - filled points corresponds to adsorption and empty points to desorption.

Yield results from Knoevenagel condensation between benzaldehyde and ethyl cyanoacetate to form ethyl 2-cyano-3phenylacrylate are shown in Figure 2a. [CTA]Si-MCM-41 catalyst had a high activity: conversion and yield reaches 100% even at temperatures very below the ones reported using other catalysts'61. The presence of a single product indicates that subsequent Michael addition reaction does not take place at the temperatures here used. When only calcined Si-MCM-41 was added to the reaction medium, only a very low conversion was seen (less than 2%). Figure 2b, curve 1, shows the benzaldehyde conversion after 6 h of reaction for the catalyst reused in up to 4 successive batches. Its activity is slightly reduced after every new use as a result from the leaching of small part of the CTA to the reaction medium.

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Results from thermogravimetry indicated that CTA leaching to the reaction medium, in the first use of a catalyst, is only ca, 0.3% m/m. These CTA cations are probably the ones most weakly connected to the micelles and their leaching, therefore, could be one of the responsible for the slight reduction of the catalyst activity.

— _— — •

80604020-

\J

[CTA]-Si-MCM-41

i

50°C A 30 °c T 10

100 ; 80-

[CTA]3i-MCM-41

5 60! 40H

n2

3 4 Time / li

200-1—r 2 Times

3 Used

Figure 2. (a) Knoevenagel product yield as a function of time for different reaction temperatures and (b) after 6h of reaction for reused [CTA+]Si-MCM-41 catalyst.

To verify if the reaction also occurred in homogeneous phase, the liquid phase resulting from a catalytic test was isolated from the as-synthesized solid catalyst and new reactants were added to the filtrated. The new mixture was submitted to the same reaction conditions as in the presence of the solid catalyst. The results are in curve 2 of Figure 2b and show that, despite low quantity of leached CTA, by utilizing the filtrated from the catalyst used for the first time, a significant catalytic activity, but smaller than curve 1, can be seen. When the filtrated from the second reaction is used, a much smaller activity is seen, thus confirming that smaller CTA+ quantity is leached to the reaction medium. Finally, the third filtrate has practically no activity. These results differ from that of Kubota et al. [3], which found no activity in the homogeneous phase, because they washed the catalyst exhaustively with hot water, before using it. Despite the fact that in the third use of the catalyst, no activity was found in the homogeneous phase, the activity of the solid remains practically the same (Figure 2b, curves 2 and 1, respectively). The explanation for CTA stability can be achieved taking into account the hypothesis of Kubota et a/.[3], which proposed that active sites leaching occur mainly at poremouth. The remaining CTA, at the interior of the pore, are not so easily leached because they are more stable, as a consequence of a higher interaction of the non-polar tails, as stated byPoolandBolhuis[7]. Table 1 shows 29Si DP and CP/NMR spectra of as-synthesized and calcined MCM-41 samples. For as-synthesized, [CTA]Si-MCM-41 sample, almost no difference between DP/ and CP/MAS NMR spectra is observed (not shown), as

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well in Q3/(Q2+Q4) ratio (51.9 to 50.4 %, in Table 1). This is a strong indication that the as-synthesized MCM-41 has almost no silanol group, and, consequently, the Q3 signal is due to SiO'CTA+ ionic pairs, generating SiO' basic sites. Because there is a longer distance between 29Si in the lattice and 'H nuclei belonging to CTA+ chain, the CP transfer between these nuclei is not very effective. This makes the contribution of the SiO"CTA+ ionic pair to the Q3 signal similar in both CP/MAS and DP/MAS spectra [8]. In contrast, there is a very large difference between DP/ and CP/MAS spectra in the calcined sample, especially in the Q3 species and as well in Q3/(Q2+Q4) ratio (36.3 to 65.5 %, in Table 1). Because silanol groups are expected to exhibit a very effective 'H-29Si CP transfer, the higher intensity of the peak at -100 ppm in the CP/MAS as compared with the DP/MAS spectra suggests the presence of a very high concentration of silanol groups in the calcined sample, not observed in the noncalcined one. Table 1. Peak areas (%) in the 29Si CP and DP / MAS NMR spectra of MCM-41.

Sample

Signal

%Q2

%C?

%Q*

Q3/(Q2+Q4)

[CTA]SiMCM-41

CP DP CP DP

11.6 17.7 18.0 15.7

50 .4 51 .9 65 .5 36 .3

38.0 30.4 16.5 48.0

1.02 1.07 1.90 0 .57

SiMCM-41 calcined 4. Conclusion

As-synthesized mesoporous silica Si-MCM-41, with its pores still filled with the surfactant cation, provided strong =SiO" basic sites and showed to be a very promising catalyst for fine chemistry synthesis. The high catalyst activity in toluene and at low temperatures was evidenced by the conversion of 99 % of the reactants in a short reaction period. 5. References [1] C.-M. Yang and K.-J. Chao, J. Chin. Chem. Soc. 49 (2002) 883. [2] K. R. Kloetstra, M. van Laren and H. van Bekkum, J. Chem. Soc, Faraday Trans. 93 (1997) 1211. [3] Y. Kubota, Y. Nishizaki, H. Ikeya, M. Saeki, T. Hida, S. Kawazu, M. Yoshida, H. Fujii and Y. Sugi, Microp. Mes. Mat. 70 (2004) 135. [4] C. F. Cheng, D. H. Park and J. Klinowski, J. Chem. Soc, Faraday Trans. 93 (1997) 193. [5] O. B. Peersen, X. L. Wu, I. Kustanovich and S. O. Smith, J. Magn. Res. Ser. A 104 (1993) 334. [6] U. D. Joshi, P. N. Joshi, S. S. Tamhankar, V. V. Joshi, C. V. Rode and V. P. Shiralkar, Appl. Catal. A: Gen. 239 (2003) 209. [7] R. Pool and P. G. Bolhuis, J. Phys. Chem. B. 109 (2005) 6650. [8] X. S. Zhao and G. Q. Lu, J. Phys. Chem. B 102 (1998) 1556.

Progress in in Mesostructured Materials Recent Progress S. Qiu, Y. Tang and C. Yu (Editors) (Editors) D. Zhao, S. © 2007 2007 Elsevier Elsevier B.V. B.V. All All rights rights reserved. reserved.

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Growth of carbon nanotubes with different inner diameter on mesoporous silica Lingxia Zhang, Ji-na Yan, Jian-lin Shi*, Lei Li, Zi-le Hua and Hang-rong Chen State Key Lab of High Performance and Superfine Microstructure, Shanghailnsitute of Ceramics, Chinese Academy of Science, 1295 Ding-xi Road, Shanghai, 200050, China.

1. Introduction Since the discovery of carbon nanotubes (CNTs) in 1991, these nanomaterials are attracting increasing intense research efforts for their excellent properties (high mechanical strength, thermal conductivity and unique electronic properties). In the past decade, catalysis chemical vapor deposition (CCVD) has been extensively used to synthesize CNTs. Mesoporous materials, which have uniform and ordered pore structure, are proved to be good template to confine the growth of guest nanoclusters and nanowires [1]. Their pore size can be tuned at a range of 2-50nm, so control synthesis of nanomaterials with different size can be realized. Recently, mesoporous silica loaded with Fe, Co et al nanoclusters has been reported as catalyst to produce CNTs [2-4]. However, diameter control of CNTs in mesoporous silica has been less demonstrated in their works. In fact, the catalysts nanoparticles can be restrict in size by pore wall, so catalysts with controllable particle size can be obtained. The diameter of CNTs is usually dominated by the catalyst particle size; the diameter of the CNTs thus can be controlled. In the present work, the inner diameter of CNTs was tuned by different grafting methods (wet impregnation and grafting with silane coupling agents) of catalyst nanoclusters. 2. Experimental Section The synthesis of mesoporous silica SBA-15 is described in reference [5].The introduction of catalyst was realized by two routes: (1) Wet Impregnation. 1.0 g of SBA-15 was impregnated with 0.05 g of Ni(NO3)3- 9H2O and 0.05 g of CoCl2- 6H2O in 30ml dried ethanol under stirring

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for 12 h. Then the ethanol was evaporated at 60°C. The powder was calcined at and denoted as CoNiSBA(WI). (2) Grafting with Silane Agent. 1.0 g of SBA-15 was refluxed with 5ml of (CH3CH2O)3SiCH(NH2)CH2(NH2) in 100ml dried toluene for 10 h under N2 flow [6]. Subsequently, the powder was filtered and washed with toluene to remove the residue silane agent. After drying at 50°C, the powder was impregnated with 0.5 g of Ni(NO3)3- 9H2O and 0.5 g of CoCl2- 6H2O in 100ml dried ethanol under stirring for 20 hours. Completely washed with ethanol, the powder denoted as CoNiSBA(SA) was obtained after being dried and calcined at 500°C for 6 h. CNTs was produced under a 30ml/min C2H4flow in a quartz tube fixed with a tubular furnace at 700 or 800°C for 1 h. HRTEM images are recorded on a JEM-2010 electron microscope operated at 200 kV. 3. Results and Discussion Fig.lA and B reveal that numerous multi-walled CNTs grow from the catalyst nanoclusters in CoNiSBA(WI). The inner diameter of the CNTs synthesized at 700°C are about 15nm (Fig. 1C), corresponding to the size of catalyst particle. High resolusion TEM shows that the tube walls of CNTs are quasi-crystallined. Moreover, tube ends are all opened. The inner diameter of

Fig. 1 HRTEM images of CNTs synthesized at (A) 700°C and (B) 800°C on CoNiSBA(WI) by using 30 ml/min C2H4 flow for 1 hour, (C) and (D) corresponding to much higher resolution image of the selected area as the arrow directed.

CNTs is much larger than the pore size of SBA-15, because of the catalyst immigration out of the pore channels. The out-growth of the catalyst

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nanoparticles at higher synthesis temperature lead to a few large nanotubes with inner diameter up to about 50 nm (Fig.IB). However, amorphous CNTs will formed at lower temperature (e.g. 600°C). Fig. 2A shows that the CNTs all grow from the pore opening of CoNiSBA(SA). The inner diameter of the CNTs is about 4 nm, which is smaller than the pore size of mesoporous matrix (about 6.3 nm). Highly dispersed catalyst nanoclusters with uniform size can be clearly seen confined in the pore channels. Therefore, the size of the catalysts has been well controlled. No nanotubes with ultra large inner diameter were found for the CoNiSBA(SA) even at higher synthesis temperature. However, the highly dispersion of catalysts also brings less exposed particles, so the amount of CNTs is much smaller than that in CoNiSBA(WI) sample. Figure 2B shows CoNi nanoparticles covered by graphite layers at the pore openning of SBA-15 channels. The adjacent two nanotube incline to join together with each other (Fig. 2C). No catalyst nanoparticles are found in CNTs. This indicated the catalyst particles are still confined in the mesopore channels.

Fig. 2 HRTEM images of carbon nanotubes synthesized at 700°C on CoNiSBA(SA) by using 30 ml/min C2H4 flow for 1 hour, (B) carbon layer covering catalyst particle and (C) the joint of carbon nanotubes corresponding to the arrow directed and the circle selected area in (A).

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4. Conclusion CoNi nanoparticles were introduced into mesoporous silica SBA-15 by wet impregnation and grafting with silane coupling agents. These CoNiSBA-15 nanocomposites have been used as catalysts to grow CNTs by CVD method. We found the inner diameter of CNTs can be tuned by different grafting methods of catalyst nanoclusters. Wet impregnation lead to out-growth of catalysts, so the size of the nanoparticles are usually larger than SBA-15 mesopore channels and also has a wide distribution. Thus the inner diameter of CNTs growing on CoNiSBA-15(WI) is much (1 ~ 6 times) larger than the pore diameter of SBA-15. Catalysts introduced by silane coupling agent are wellconfined in the mesopore channels and CNTs synthesized on the CoNiSBA15(SA) samples have uniform inner diameter smaller than the pore size of SBA15. However, much less CNTs were obtained because the highly dispersion of catalysts in the pore channels also brings less exposed particles. Mesoporous materials have great advantages over other matrix because they have uniform and tunable pore size. Thus preparation of uniform CNTs with controllable inner diameters can be realized using the latter process. The authors gratefully acknowledge the financial supports from the Ceter of Shanghai Nanotechnology (Grant No. 0452nm056) 5. References [1] J. L. Shi, Z. L. Hua and L. X. Zhang, J. Mater. Chem., 5 (2004) 795. [2] D. Ciuparu, Y. Chen, S. Lim, G. L. Haller and L. Pfefferle, J. Phys. Chem. B, 108 (2004) 503. [3] S. Lim, D. Ciuparu, C. Pak, F. Dobek, Y. Chen, D. Harding, L. Pfefferle and G. Haller, J. Phys. Chem. B, 107 (2003), 11048. [4] Y. Yang, Z. Hu, Y. N. Ltl and Y. Chen, Mater. Chem. Phys., 82 (2003) 440. [5] D. Y. Zhao, Q. S. Huo, J. Feng, B. F.Chemlka and G. D. Stucky, J. Am. Chem. Soc, 120(1998)6024. [6] W. H. Zhang, J. L. Shi and H. R. Chen, Chem. Mater., 13 (2001) 648.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

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Selective hydrogenation of benzene over Ru/SBA 15 catalyst prepared by the "double solvents" impregnation method Juan Bu, Yan Pei, Pingjun Guo, Minghua Qiao*, Shirun Yan and Kangnian Fan* Department of Chemistry and Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials Fudan University, Shanghai 200433, P. R. China

1. Introduction Cyclohexene and its derivatives are important intermediates in chemical industry. Since the first report that cyclohexene can be prepared by catalytic hydrogenation of benzene [1], various catalysts have been developed to improve the selectivity. It is generally accepted that Ru is the most selective metal for this reaction. Silicas [2, 3], aluminas [4], other oxides [5], and insoluble salts [6] have been used to support Ru, however, no mesoporous molecular sievesupported Ru catalyst has been used in this reaction so far. Regular mesoporous molecular sieves have great potential in catalysis, which is closely related to their special characteristics such as high surface area and narrow pore-size distribution. In this paper, we chose SBA-15 as the support and used the "double solvents" method to prepare the Ru catalyst (Ru/SBA-15-ds). The conventional wetness impregnation method was also used for comparison (Ru/SBA-15-wi). The effects of preparation method on the physical properties of the catalysts were investigated. Their catalytic performances in the title reaction were compared and discussed.

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2. Experimental Section 2.1. Catalyst preparation Ru/SBA-15-ds was prepared as follows. Pure siliceous SBA-15 mesoporous molecular sieves were synthesized according to the procedure by Zhao et al. [7]. Pre-calcined SBA-15 powders were suspended in dry cyclohexane, used as the first solvent, under stirring. Then a desired amount of RuCl3 aqueous solution was added dropwisely. After being dried at 120°C, the precursor was reduced by hydrogen at 400°C for 4 h. Ru/SBA-15-wi was prepared by wetness impregnation of RuCl3 aqueous solution, with other treatments similar to those of Ru/SBA-15-ds. The nominal Ru contents in both catalysts are 4 wt%. 2.2. Characterization The textural properties were measured on a Micromeritics TriStar3000 adsorption apparatus by N2 physisorption at 77 K. The morphology and particle size were observed by TEM (JEOL JEM2011). XRD patterns were collected on a Bruker AXS D8 Advance X-ray diffractometer using Cu-Ka radiation. 2.3. Activity test and product analysis About 1 g catalyst, 50 ml benzene, 100 ml water, and 4.0 g ZnSO4-7H2O as additive were loaded into a 500 ml autoclave. The reaction was carried out at 423 K, hydrogen pressure of 4 MPa, and a stirring rate of 1000 rpm. The reaction mixture was sampled at intervals and analyzed chromatographically. 3. Results and Discussion 3.1. Catalyst texture and structure Table 1 shows that after the loading of Ru on SBA-15, the surface area and pore volume decreased noticeably. The decrement in pore volume is more drastic for Ru/SBA-15-ds, suggesting that more pores were occupied by Ru, which is confirmed by TEM. Fig. 1 directly discloses that the "double solvents" method can lead to Ru particles preferentially locating in the channels of SBA15, while the wetness impregnation method results in Ru particles mainly situating on the exterior of SBA-15. The Ru particles in Ru/SBA-15-ds (~7 nm) are more uniform and much smaller than those on Ru/SBA-15-wi (~16 nm).

771 Table 1. Some physical properties of the SBA-15, Ru/SBA-15-wi, and Ru/SBA-15-ds samples Sample

SBET

SBA-15

2

Pore volume (cmVg)

Pore diameter (nm)

401

1.14

9.1

Ru/SBA-15-wi

360

1.03

9.6

Ru/SBA-15-ds

359

1.01

9.4

(m /g)

Fig. 1 TEM images of (a) SBA-15, (b) Ru/SBA-15-wi, and (c) Ru/SBA-15-ds.

100

Fig. 2a shows the small-angle XRD patterns of SBA-15 and the Ru/SBA-15 catalysts. The well-resolved (100), (110), and (200) diffractions suggest the preservation of the regular mesoporous structure of SBA-15 during catalyst preparation, corroborating well with the TEM results. Fig. 2b shows that there are no distinct peaks of metallic Ru for Ru/SBA-15-ds, which can be explained by the high dispersion and small particle size of Ru in the sample, which is also confirmed by the TEM images in Fig. 1. b

Intensity / a.u.

110

200

Intensity / a.u.

a

SBA-15

Ru/SBA-15-wi

Ru/SBA-15-wi

Ru/SBA-15-ds

Ru/SBA-15-ds 1

2

3

4

degree 22 θ / degree

20 20

30 30

40 40

50 50

60

70

80

degree 22 θθ//degree

Fig. 2 (a) Small- and (b) wide-angle XRD patterns of the SBA-15 and Ru/SBA-15 catalysts.

3.2. Benzene selective hydrogenation Fig. 3 shows the yield and selectivity of cyclohexene versus benzene conversion over the Ru/SBA-15 catalysts. On both catalysts the concentration of cyclohexene increased first, reached a maximum, and then declined gradually following the known behavior of a consecutive reaction. However, over Ru/SBA-15-ds, the yield of cyclohexene reaches 21.5% at benzene conversion

772

Cyclohexene Selectivity / mol%

Cyclohexene Yield / mol%

80 40 of 64.9%, and the initial Ru/SBA-15-ds 70 35 selectivity is as high as 65.0%, Ru/SBA-15-wi while over Ru/SBA-15-wi, the 60 30 maximum yield of cyclo50 25 hexene is only 10.8% at 40 20 33.3% conversion. It clearly 30 15 demonstrates that the 20 s 10 preparation method imposes J! 10 o 5 drastic influence on the u > selectivity and yield of 0 0 0 20 60 80 100 40 o cyclohexene for the Ru/SBABenzene Conversion / % 15 catalyst. The superiority of Fig. 3 Selectivity and yield to cyclohexene Ru/SBA-15-ds to Ru/SBA-15as a function of benzene conversion over the wi can be attributed to the Ru/SBA-15 catalysts. confined formation of Ru particles in the channels of SBA-15, leading to Ru particle size of ca. 7 nm. It has been proposed that benzene selective hydrogenation to cyclohexene is a structural sensitive reaction, and a crystallite size less than 10 nm is essential to achieve both high activity and selectivity [8]. Thus the "double solvents" method can be a facile and promising way to prepare Ru catalyst suitable for the title reaction.

4. Conclusion The Ru/SBA-15 catalyst prepared by the "double solvents" method is more selective than the catalyst prepared by the wetness impregnation method in benzene hydrogenation to cyclohexene. The superiority of the former method is attributed to the confined formation of Ru nanoparticles in the channels of SBA-15, leading to particle size suitable for the title reaction. 5. References [1] J. R. Anderson, Aust. J. Chem., 10 (1957) 409. [2] S. Niwa, F. Mizukami, S. Isoyama, T. Tsuchiya, K. Shimizu, S. Imai and J. Imamura, J. Chem. Technol. Biotechnol., 36 (1986) 236. [3] S. H. Xie, M. H. Qiao, H. X. Li, W. J. Wang and J. F. Deng, Appl. Catal. A, 176 (1999) 129 [4] M. M. Johnson and G. P. Nowack, J. Catal., 38(1975) 518. [5] J. Q. Wang, Y. Z. Wang, S. H. Xie, M. H. Qiao, H. X. Li and K. N. Fan, Appl. Catal. A, 272 (2004) 29. [6] H. Ichihashi and H. Yoshioka, Eur Patent No. 170 915 (1985). [7] D. Y. Zhao, J. L. Feng, Q. S. Huo, N. Melosh, G. H. Fredrickson, B. F. Chmelka and G. D. Stucky, Science, 279 (1998) 548. [8] G. Luo, MSc. Thesis, Zhengzhou University, (2002).

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

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Mesoporous calcined Mg-Al hydrotalcites as catalysts for synthesis of propylene glycol Gongde Wuab, Xiaoli Wangab, Junping Lia, Ning Zhao3, Wei Weia and Yuhan Suna* "State Key Laboratory of Coal Coversion, Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan, 030001, China; b Graduate School of the Chinese Academy of Sciences, Beijing, 100039, China.

The Mg-Al hydrotalcites (HTs) precursors containing different anions (CO32", F , Cl", Br") were prepared by hydrothermal method and characterized by XRD patterns. The results showed that the precursors had the hydrotalcites-like structure. The mesoporous Mg-Al mixed oxides modified by different anions were calcined from the resulting HTs and theirs catalytic performances were tested in the reaction of propylene oxides (PO) with methanol. Among them, the fluorine-modified mixed oxides exhibited much high catalytic performance, which was ascribed to the fluorine nucleophilicity and the high basicity. 1. Introduction Propylene glycol is an important solvent in the field of printing inks, dyes and agricultural chemicals and widely used as antifreeze in oil fuel [1]. The propylene oxide method is mostly convenient and industrial feasible to synthesize propylene glycol [2]. Catalyzed by base, the mildly toxic 1-methoxy2-propanol (PPM) is the predominant product. Although basic homogenous reactions showed high selectivity to PPM, they had the shortcomings of catalyst recovery and product separation. So the solid basic catalyst, such as basic zolites [3], MgO [4], mixed oxides calcined from HTs [5] has attracted much attention in recent years. The mixed oxides have been used extensively in many reactions because they were grafted by many cations to form a range of different nature of the active sites [6, 7]. However, there were few reports on anions-grafted mixed oxides. Here we first prepared anions-grafted mesoporous Mg-Al mixed oxides from HTs precursors synthesized by alkali-free route. And CO2 TPD and the reaction

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of propylene oxides with methanol were used to investigate the relation between basic sites and catalytic performance of the fluorine-modified mesoporous MgAl mixed oxides. 2. Experimental Section 2.1. Samples preparation The precursors were prepared as in the reference [8], a solution of Mg(NO3)2-6H2O (0.09 mol) and A1(NO3)3-9H2O (0.03 mol) in deioned decarbonated (DD) water (120 mL) was added dropwised under nitrogen to a solution of NH4OH (0.36 mol) and NH4X (X = CO3 , F Cl", BO (0.06 mol) in DD water (120 mL) at room temperature under vigorous stirring. The resulting gellike slurry was hydrothermal at 373 K for 24 h before filtered and washed with DD water until pH=7. The product was dried at 373 K for 12 h. To obtain the mixed oxide, the precursors were calcined at 723 K for 5 h under a flowing stream of N2. By changing the concentration of the two metal salts and the kinds of anions, the other hydrotalcites and mixed oxides were also obtained. 2.2. Characterization techniques The powder X-ray diffraction (XRD) of HTs were carried out using a Rigaku Miniflex diffractometer using Cu target with Ni filter in a 28 range of 5-70°.The N2 adsorption isotherms were measured on a Micromeritics ASAP-2000 instrument (Norcross, GA). Thermogravimetric analysis (TGA) was performed on a Setaram TGA-92 thermal analyzer connected to a PC via a TAC7/DX thermal controller, and the samples were heated from 303 K to 1073 K at 10 K/min under nitrogen. The FTIR spectra of the samples were recorded on a Shimadzu (model 8201 PC) spectrophotometer after being pressed into 13 mm discs with KBr. The effluents of CO2 TPD were detected by a Balzers-mass spectrometer. The samples were pretreated for 2 h in Ar flow at 723 K, and then cooled to 303K. Once the physically adsorbed CO2 was purged off, TPD experiment was started from 303 K to 773 K with heating rate of 10 K/min under Ar flow (50 mL/min). 2.3. Catalytic test The reaction was studied in a 100 mL stainless steel autoclave equipped with a magnetic stirrer. Typically, 16 g methanol, 5.8 g propylene oxide and 0.5 g catalyst were introduced. The autoclave was heated to 393 K and run for 10 h. The product was then analyzed by a gas chromatograph with a flame ionization detector after centrifugal separation from the catalyst.

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3. Results and Discussion 3.1. Characterization The XRD patterns of HTs precursors containing different anions showed a series of reflections at 10.6, 22.7, 34.1, 38.3, 45.6, 60.0 and 61.7°, which suggested the formation of hydrotalcite-like structure (see Fig. 1). The similar reflections were observed for the fluorine-containing HTs with different Mg/Al molar ratio. The TGA programs of the HTs showed two main gradual weight losses at about 393 K and 689 K implying completely decomposed mixed oxides were obtained at 723 K. The N2 adsorption isotherms of the mixed oxides displays type IV isotherms with clear hysteresis loops associated with capillary condensation, which suggests the formation of mesoporous structure. In the FTIR spectra of anion-modified mixed oxides, the presence of bands at about 620, 450-500 cm"1 spectra indicated the Cl" and Br" were loaded on the mixed oxides, respectively. Especially, the fluorine-modified mixed oxides with different Mg/Al molar ratio showed typical features at 793 cm"1 without any peak shift (see Fig. 2), which was due to stretching vibrations of the DAI-F double molecules [9] and strongly illustrated that the fluorine was successfully loaded on the mesoporous Mg-Al mixed oxides (except the F/Mg(Al)O). For the fluorine-modified Mg-Al mixed oxides, three peaks were appeared at about 376, 490, 566 K in CO2 TPD, which were assigned to OH groups, Mg-O and O2" ions basic sites, respectively [4]. And their basicity was listed in Table 1.

30 20 40

Fig. 1. XRD of hydrotalcites: 1, Mg3Al-Br; 2, M&Al-Cl; 3, Mg3AlF; 4, Mg3Al-CO3.

3500

3000

2500 2000 1500 1000 wavenumbers (cm )

500

Fig. 2. FTIR spectra: 1, F/Mg(Al)O; 2, F/Mg2(Al)O; 3, F/Mg3(Al)O; 4, F/Mg4(Al)O; 5, F/Mg5(Al)O

3.2. Catalytic Performances The catalytic performances of the as-prepared catalysts were listed in Table 1. Among them, the F/Mg3(Al)O exhibited the highest catalytic performance. This might be due to the fluorine nucleophilicity and the support base. On the

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one hand, the fluorine nucleophilicity led to the formation of H-bonds between fluorine and methanol. Therefore, the excessive active methoxide ions were easily generated over the fluorine-modified Mg-Al mixed oxides, and then the propylene-like species [4] were attracted by the methoxide ions to form the PPM. On the other hand, basic site in the support, especially the Mg-O pairs and O2" ions could also attract proton from methanol to generate methoxide ion. The more basic sites, the more methoxide ions would be generated. As a result, the F/Mg3(Al)O with the most basicity exhibited the highest PO conversion of 94% with PPM selectivity of 86.6%. Table 1. The effect of modified anions and supports basicity on the catalytic performance Cat. Blank Mg3(Al)Oa F/Mg3(Al)O Cl/Mg3(Al)O Br/Mg3(Al)O a

PO Con. (%) 32.4 61.7 94.0 52.4 50.4

PPM Sel. (%) 64.9 79.1 86.6 79.9 79.8

Cat.

PO Con.

PPM Sel.

F/Mg(Al)O F/Mg2(Al)O F/Mg3(Al)O F/Mg4(Al)O F/Mg5(Al)O

(%) 64.9 76.3 94.0 91.8 90.1

(%) 82.3 85.7 86.6 87.7 87.5

CO2 uptake (mmol/g) 1.464E-2 1.627E-2 1.733E-2 1.220E-2 1.183E-2

Calcined from the Mg3Al-HTs precursors containing CO32".

4. Conclusion The anion-modified Mg-Al mixed oxides with mesoporous structure were successfully prepared from the HTs. In terms of the nucleophilicity of fluorine and the basic support of Mg-Al mixed oxides, the F/Mg3(Al)O showed high activity and selectivity towards the reaction of propylene oxides with methanol. 5. References [1] [2] [3] [4] [5] [6] [7] [8] [9]

European Chemical Industry Ecology and Toxicological Center Report, No. 4, 1982. H. C. Chitwood, J. Am. Chem. Soc, 68 (1946) 680. Z. S. Jin, X. M. Jiang and L. Zhang, CN Patent No. 1087651C, 1998. W. Zhang, H. Wang, W. Wei and Y. Sun, J. Mol. Catal. A, 231 (2005) 83. W. J. Smith and F.C. Malherbe, US Patent 6291720B1 2001. R. J. Davis and E. G. Derouane, Nature, 349 (1991) 313. M. J. Climent, A. Corma, S. Iborra and A. Velty, J. Catal., 221 (2004) 474. Z. P. Xu and H. C. Zeng, J. Phys. Phem. B, 105 (2001) 1743. Snelson, J. Phys. Chem., 71 (1967) 3202.

Recent Progress in Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

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Application of Ti-containing mesoporous silica (single-site photocatalyst) and photo-assisted deposition (PAD) method for preparation of nanosized Pt metal catalyst Hiromi Yamashitaa*, Toshiaki Shimizua, Naoki Mimuraa, Makoto Shimadaa, Shuai Yuana, Kohsuke Mori3, Tetsutaro Ohmichia, Iwao Katayama3, Takao Sakatab and Hirotaro Morib "Division of Materials and Manufacturing Science, Graduate School of Engineering, Osaka University, 2-1 Yamada-oka, Suita, Osaka 565-0871, Japan b Research Center for Ultra-High Voltage Electron Microscopy, Osaka University, 7-1, Mihogaoka, Ibaraki, Osaka 567-0047, Japan

1. Introduction The development of convenience and useful method to prepare nano-sized Pt metal loaded on support with controlled particle size is essential to design of the active metal catalyst [1, 2]. On the other hand, the unique and fascinating properties of zeolite and mesoporous silica involving transition metals within their cavities and framework have opened new possibilities for many application areas not only in catalysis but also for various photochemical processes. Especially, Ti-containing mesoporous silica (Ti-HMS) was used as unique photocatalyst and called as "single-size photocatalyst" [3-6]. Furthermore, as the support of nano-size Pt metal, Ti-containing mesoporous silica is very attractive. Its unique photocatalysis under UV-light irradiation should be applied as the method for a preparation of nano-size metal catalyst. In this study the photoexcitation state of Ti-HMS under UV-light irradiation was used to disperse Pt metal highly. Using a photo-assisted deposition (PAD) method [7, 8], quite uniform nano-sized Pt metal can be highly deposited on the photo-excited Ti-HMS.

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2. Experimental Section The synthesis of the Ti containing mesoporous silica (Ti-HMS, Si/Ti ratio : 100, pore size: about 5 nm) was carried out using tetraethylorthosilicate and titaniumisopropoxide as the starting materials and dodecylamine as template3"6. The Pt loaded on Ti-HMS (PAD-Pt/Ti-HMS, 1 wt% as Pt metal) was prepared using the PAD method: Pt metal was deposited on Ti-HMS from aqueous solution of H2PtCl6 under UV-light irradiation. The samples were dried at 378 K and reduced by H2 (20 ml min"1) at 473 K for 1 h. XAFS spectra for Pt L m edge absorption were recorded in the fluorescent mode at BLOIBI of Spring-8. The normalized spectra were obtained by a procedure described in previous literature [9, 10] and Fourier transformation was performed on k3-weighted EXAFS oscillations in the range of 3-14"1. TEM micrograph was recorded with Hitachi H-9500 operated at 300 kV. 3. Results and Discussion From the characterization of Ti-HMS, it has been found that Ti species exists as the tetrahedrally coordinated Ti-oxide moieties within the framework of mesoporous silica (HMS) [3-6]. Under UV-light irradiation of the Ti-HMS in aqueous H2PtCl6 solution, the Pt metal can be deposited on the Ti-HMS. On the other hand, Pt metal particles could not be deposited on HMS support in the PAD method. Therefore, Pt metal was deposited directly on the photo-excited tetrahedrally coordinated Ti-oxide moieties of Ti-HMS

Distance/A Figure 1. Fourier transforms of the Pt Lm-edge EXAFS spectra for (a) imp-Pt/HMS, (b) impPt/Ti-HMS, and (c) PAD-Pt/Ti-HMS (1 wt% as Pt metal, Ti/Si=100).

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The Fourier transforms of Pt Lm.edge EXAFS spectra of the Pt-loaded catalysts are shown in Figure 1. The presence of the peak assigned to the Pt-Pt bond of Pt metal indicates the formation of nano-size Pt metal. The intensity of the Pt-Pt peak decreases with the catalysts as imp-Pt/HMS, imp-Pt/Ti-HMS and PAD-Pt/Ti-HMS, indicating that the size of Pt metal depends on the preparation method and the presence of tetrahedrally coordinated Ti-oxide and that the smaller nano-sized Pt metal was formed on the photo-deposited catalyst (PADPt/Ti-HMS). The TEM images show that the photodeposited catalyst (PAD-Pt/Ti-HMS) has nano-sized Pt metal with well-controlled size of about 4-5 nm as shown in Fig. 2-a), while the impregnated catalyst (imp-Pt/Ti-HMS) has Pt metal particles with various size in 2-30 nm as shown in Fig. 2-b). The results of CO adsorption measurements show that the particle size of Pt metal are 4.7 nm with PAD-Pt/Ti-HMS and 30.7 nm with IMP-Pt/Ti-HMS, respectively, supporting the results obtained from XAFS and TEM measurements.

Figure 2. TEM images of PAD-Pt/Ti-HMS (a) and IMP-Pt/Ti-HMS (b) (1 wt% as Pt metal, Ti/Si=100).

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The PAD-Pt/Ti-HMS exhibited the higher reactivity than the imp-Pt/HMS for various catalytic reactions such as degradation of organic compound diluted in air and CO oxidation. 4. Conclusion Using the PAD method and Ti-HMS, nano-sized Pt metal particles with the well-controlled size and well dispersion state can be deposited on tetrahedrally coordinated Ti-oxide of the support. The direct interaction between nano-sized Pt metal and the photo-excited tetrahedrally coordinated Ti-oxide realized by the PAD method under UV-light irradiation has possibility to design the unique and active nano-sized metal catalyst. 5. Acknowledgement The present work is supported by the Grant-in-Aid for Scientific Research (KAKENHI) in Priority Area "Molecular Nano Dynamics" from Ministry of Education, Culture, Sports, Science and Technology (No. 17360388 and No. 18656238). This work is partly performed under the project of collaborative research at the Joining and Welding Research Institute (JWRI) of Osaka University. The X-ray adsorption experiments were performed at the Spring-8 (2006A1278-NXa-np). 6. References [1] Z. Liu, Y. Sakamoto, T. Ohsuna, K. Hiraga, O. Terasaki, C.H. Ko, H. J. Shin and R. Ryoo, Angew. Chem., 39 (2000) 3107. [2] A. Fukuoka, Y. Sakamoto, S. Guan, S. Inagaki, N. Sugimoto, Y. Fukushima, K. Hirahara, S. Iijima and M. Ichikawa, J. Am. Chem. Soc, 123 (2001) 3373. [3] H.Yamashita and M. Anpo, Curr. Opin. Solid State Mater. Sci., 7 (2004) 471. [4] H. Yamashita, S. Nishio, I. Katayama, N. Nishiyama and H. Fujii, Catal. Today, 111 (2006) 254. [5] H. Yamashita, K. Ikeue, T. Takewaki and M. Anpo, Top. Catal., 18 (2002) 95. [6] H. Yamashita, K. Maekawa, H. Nakao and M. Anpo, Appl. Surf. Sci., 237 (2004) 393. [7] H. Yamashita, O. Chiyoda, Y. Masui, S. Ohshiro, K. Kida and M. Anpo, Stud. Surf. Sci. Catal., 158(2005)43. [8] Y. Masui, S. Ohshiro, M. Anpo, T.Ohmichi, I. Katayama and H.Yamashita, e-J. Surf. Sci. Nanotech., 3 (2005) 448. [9] H. Yamashita, M. Matsuoka, K. Tsuji, Y. Shioya and M. Anpo, J. Phys. Chem. B., 100 (1996) 397. [10] F. Montilla, E. Morallon, A. De Battisti, A. Benedetti, H. Yamashita and J. L. Vazquez, J. Phys. Chem. B., 108 (2004) 5044.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Published by Elsevier B.V.

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Hydroisomerization and hydrocracking of long chain /t-alkane and Fischer-Tropsch wax over bifunctional Pt-promoted Al-HMS catalysts Yanyong Liu, Toshiaki Hanaoka, Kazuhisa Murata and Kinya Sakanishi Biomass Technology Research Center, National Institute of Advanced Industrial Science and Technology (AIST), Hirosuehiro 2-2-2, Kure, Hiroshima 737, Japan

In this manuscript, the hydroconversion of long chain ra-alkanes («-Ci6, H-C28, M-C36) and Fischer-Tropsch waxes (including hydroisomerization and hydrocracking) over bifunctional Pt-promoted and Al-containing hexagonal mesoporous silica (HMS) were investigated. Al/HMS prepared by a post-modified method showed stronger acidity than that of Al-HMS prepared by a sol-gel method. Because the w-alkane hydroconversion undergoes via a bifunctional mechanism, the balance of Pt sites and acid sites in Al-containing HMS is crucial for the catalyst performance and final product distribution. 1. Introduction Fischer-Tropsch (FT) synthesis produces clean n-alkanes (> 90%) from syngas, while the latter is easily obtained from biomass, coal and natural gas. As consequence of the chain growth mechanism, a large fraction of FT products has a boiling point higher than 370°C (C22+, i.e. FT waxes). Thus hydroisomerization and hydrocracking of FT waxes are necessary for improving the yield and the quality of middle distillates. Mesoporous silica possesses high thermal stability (up to 850°C), large surface area (above 1000 m2g"') and uniform-sized pores (about 40 A). Moreover, hexagonal mesoporous silica (HMS) has thicker framework walls, small crystallite size of primary particles and complementary textural porosity [1, 2]. These advantages render HMS-based materials very interesting in the catalysis filed as catalysts and supports [3-7].

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2. Experimental Section Al-HMS was prepared by a sol-gel method [3]. The mixture of Al(iso-OC3H7)3 in isopropyl alcohol and Si(OC2H5)4 in ethanol (Al : Si = 1/100 (molar ratio)) heated with vigorous stirring at 70°C for 4 h, and then the solution was added to a dodecylamine water/ethanol solution. The resultant gel mixture reacted at room temperature for 20 h. Then the solid products were filtrated, air dried and calcined in air at 650°C for 4 h to remove the template. Al/HMS was prepared by a post-modified method. The HMS support after calcination at 650°C for 4 h was impregnated with Al(iso-OC3H7)3 in isopropyl alcohol (Al : Si = 1/100 (molar ratio)), following by adding 25 ml H2O to precipitate aluminum oxide. Then the solid products were filtrated, air dried and calcined at 650°C K for 4 h. The 0.5 wt% of Pt was loaded on Al-HMS and Al/HMS using Pt(NH3)4Cl2 solution. After impregnation, the product was dried at 110°C for 5 h, calcined at 400°C for 2 h, and reduced by flowing H2 at 350°C for 1 h. The hydroconversion reaction was carried out using a 50 ml stainless steel autoclave reactor. The catalyst and long chain w-alkanes or F-T waxes were added into the reactor. The reaction started at the range from 250 to 350°C (mainly at 300°C) with stirred speed at about 300 rpm. After reacted, the products were analyzed by gas chromatographys. 3. Results and Discussion In XRD pattern (Fig. 1), each HMS-based sample exhibits an intense reflection corresponding to the (100) plane at 2-3 degrees. The dioo spacing calculated from the degree of (100) plane was 35.3 A for HMS, and the value of

8 4 6 2 4 6 8 0 10 Pore diameter/A 26>/degree Fig. 1. XRD pattern and pore-size distribution of various samples after calcination.

2

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d^o spacing decreased by incorporating Al in the HMS framework (Al-HMS). On the other hand, Al/HMS showed a dioo spacing similar to that of HMS. The BET surface areas were over 1000 m2 g~ for all HMS-based simples. The average pore sizes were about 26 A for HMS and about 24 A for Al-HMS. Introducing Al3+ into the framework of HMS caused the reduction of pore size. In the FT-IR spectra, HMS exhibits no band at around 960 cm"1 [1], while Al-HMS exhibits a band at 960 cm"1. Because this band has been widely used to characterize the incorporation of metal ions in the silica framework as the stretching Si-0 vibration mode perturbed by the neighboring metal ions, Al3+ ions entered into the HMS framework in Al-HMS prepared by sol-gel method. Al/HMS did not show a band Al/HMS 960 cm"1 indicating Al3+ ions Al/HMS prepared by modified method exist Al-HMS outside of the HMS framework. In the NH 3 -TPD profiles (Fig. HMS 2), HMS did not show any peaks. Both the desorption amount and the maximum temperatute of 100 200 300 400 500 600 Al/HMS were much higher than Desorption temperature/°C those of Al-HMS, suggesting that Al/HMS contains much more and Fig. 2. NH3-TPD profiles of various stronger acid sites comparing to samples after calcination. Al-HMS. Al3+ located uniformly in the HMS fremework in L: Lewis acid site Al-HMS since Al3+ was B: Bronsted acid site introduced in the preparing step of 3+ 3 hydrogel. On the other hand, Al introduced in Al/HMS by posto modified mainly existed at the B extra-framework. The extra3+ framework Al ions are strong acid sites while the intra3+ framework Al ions are weak acid sites. FT-IR spectra of chemisorbed 1650 1600 1550 1500 1450 1400 pyridine (Fig. 3) indicate that both Wave number/cm"1 Al-HMS and Al/HMS possess two types of acid sites: Lewis acid Fig. 3. FT-IR spectra of chemisorbed sites and Bronsted acid sites. The pyridine over (a) Al/HMS and (b) intensities of bands for chemi- Al-HMS after treated at 473 K for 1 h.

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sorbed pyridine over Al/HMS were much stronger than those over Al-HMS, indicating that the acidic strength of Al/HMS is stronger than that of Al-HMS with the same Al amount, coinciding with the results obtained from the NH 3 -TPD. While using Pt/Al-HMS and Pt/Al/HMS as catalysts for the hydroconversion of long chain H-alkanes (w-Ci6, n-C2g, n-Cie), at the same conversion level, higher reaction temperatures lead to the cracking products with a lower ratio of /so-alkane/«-alkane. The rate constants showed a considerable increase between n-C\6 and n-C2&, whereas a slight decrease between n-C2& and n-Cx, was observed. The increase in reaction temperature leads to a small decrease in isomerization selectivity. Furthermore, an increase in hydroisomerization selectivity at higher hydrogen pressure for n-C2& conversion was observed. Pt/Al/HMS is effective for hydroisomerization of n-C\6- As for the hydrocracking of FT wax over Pt/Al-HMS, although the selectivity to naphtha distillate increased with increasing the conversion of C22+, the maximum yield achieved to middle-distillate was obtained over 70% over 0.5wt% Pt/Al-HMS (Al/Si = 1/100 (molar ratio)). The hydroconversion (including hydrocracking and hydroisomerization) of w-alkanes over Pt/Al-HMS and Pt/Al/HMS undergoes a bifunctional mechanism [8]. Pt site achieves the function of dehydrogenates and hydrogenates and acid site achieves the function of isomerization or cracking. The balance of the acid catalyst and dehydrogenation/hydrogenation catalyst is very important for preparing a bifunctional catalyst for the hydroconversion of «-alkanes [9]. Moreover, hydrocracking and hydroisomerization of «-alkane are competitive reactions which occur in parallel sharing a common intermediate (carbenium cation). Pt sites decide the amounts of carbenium cation in the system. Whether the carbenium cations ab sorbed on the acid sites undergo an isomerization process or undergo a p-scission process, determined the occurrence of hydrocracking or hydroisomerization of rc-alkane. The carbenium intermediate is not stable and cannot exist in the system for a long time. If strong acid sites exist in the system, the «-carbenium can be isomerized to wo-carbenium quickly Thus it is reasonable to assume that strong acid sites would promote n-alkane isomerization and weak acid sites would promote «-alkane cracking. As shown in NH3-TPD profiles (Fig. 2), Al-HMS possesses weak acid sites because Al3+ ions entered the framework of HMS and Al/HMS possesses strong acid sites because Al3+ ions existed at the outside of HMS framework, which causes that Pt/Al-HMS is a good catalyst for hydrocracking of w-alkanes while Pt/Al/HMS is a good catalyst for hydroisomerization of w-alkanes. 4. References [1] P. T. Tanev, M. Chibwe and T.J. Pinnavaia, Nature, 368 (1994) 321. [2] T. R. Pauly, Y. Liu, T. J. Pinnavaia, S. J. L. Billinge and T. P. Rieker, J. Am. Chem. Soc, 121(1999)8835.

785 [3] R. Mokaya and W. Jones, J. Catal. 172 (1997) 211. [4] Y. Liu, K. Suzuki, S. Hamakawa, T. Hayakawa, K. Murata, T. Ishii and M. Kumagai, Catal. Lett., 66 (2000) 205. [5] Y. Liu, T. Hayakawa, K. Suzuki, S. Hamakawa, T. Tsunoda, T. Ishii and M. Kumagai, Applied Catalysis A: General, 223 (2002) 137. [6] Y. Liu, K. Murata and M. Inaba, N. Mimura, Catal. Lett., 89 (2003) 49. [7] Y. Liu, K. Murata and M. Inaba, Green Chem., 6 (2004) 510. [8] Y. Liu, K. Na and M. Misono, J. Mol. Catal. A: Chem., 141 (1999) 145. [9] Y. Liu, G. Koyano and M. Misono, Topic in Catal., 11 (2000) 239.

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Materials Recent Progress in Mesostructured Materials (Editors) D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 2007 Elsevier Elsevier B.V. All All rights rights reserved. reserved.

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Preparation and characterization of SBA-15 supported molybdenum nitride for NH3 decomposition Hongchao Liuab,Hua Wanga, Zhongmin Liua*, Jianghan Shen ab and Ying Sunab a

Applied Catalysis Laboratory, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, Liaoning, PR China; b Graduate School of the Chinese Academy of Sciences, Beijing 100039, PR China

1. Introduction The generation of COjc-free hydrogen from NH3 for proton-exchange membrane fuel cells has attracted great attention due to the remarkable advantages comparing with the conventional routes based on the carbonaceous materials [1,2]. Ru catalysts exhibit the highest performance for the decomposition of NH3 among the transition metals catalysts especially group VIII metals [3]. However, the wide use of Ru could be a limitation due to its high prices and restricted availability. Transition metal nitrides, normally with similar character as noble metals, are proved to be effective for NH3 decomposition reaction [4], providing an alternative to Ru catalysts. Catalyst supports play crucial role for a high active catalyst [2]. Mesoporous materials are therefore being interesting supports for their large pores, thicker walls and higher thermal stability [5]. In this paper, SBA-15 supported molybdenum nitrides were prepared and tested for NH3 decomposition. 2. Experimental Section MoO3/SBA-15 (0.2g ,40~60mesh) with theoretical loading of 12% Mo, prepared by the wetness impregnate method, was nitrided in the flow of nitrogen and hydrogen mixture by first increased from room temperature to 623K with a heating rate of 8 K/min, then at 0.5 K/min to 773 K and 2 K/min to 923 K, respectively, finally maintained at 923 K for 150 min. The oxide precursor and the nitrided samples were designated as MOS and MNS-X

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respectively, in which the X represented the ratio of H2 to N2 in the nitridation step. Powder XRD measurements were carried out on a D/max-rb type X-ray diffractometer using monochromatic Cu Ka radiation (A, = 1.5418 ). BET surface area and pore size distribution of samples were measured on NOVA4000 physical adsorption equipment using liquid nitrogen as adsorbent at 77K. Transmission electron microscopy (TEM) images were performed using a JEOL JEM2000EX electron microscope with an accelerating voltage of 100 kV. The NH3 decomposition tests were performed on a fixed-bed continuous flow reaction system (quartz reactor) at atmospheric pressure with on-line gas chromatograph (Varian 3800, Poropak N column, thermal conductivity detector) to analyze the effluent. 3. Results and Discussion Fig. 1 shows powder XRD patterns of MOS and MNS-X samples. All samples exhibit broad diffraction perks of siliceous material. The diffraction patterns of MOS shows peaks at 12.75, 23.33, 25.77, 27.45, and 38.98(Fig. 1 a), which are assigned to the {020}, {110}, {040}, {021} and {060} reflection of MOO3. Comparison with that of the MOS sample, the XRD patterns of MNS-X samples illustrate the diffraction peaks of M063 is absent and very weak peaks of molybdenum nitride is present. If we observed carefully, peaks at 37, 43.2, 63.1, 75°, which are assigned to the {111}, {200}, {220}, {311} reflection of yMo2N (JCPDS, 25-1366), respectively, could be found only over the MNS-5.2 among all MNS-X samples. The results indicates that the MoO3 in the MOS sample has been completely nitrided and the small size molybdenum nitride crystals are well dispersed on the surface of the supports. In view of the difference of XRD patterns between the MNS-5.2 and the other samples, the

g f e d c a 110 0

220 0

330 0

440 0 550 0 Theta 2 T h e ta

660 0

770 0

b 880 0

10 10

20 20

30 30

40 40

50 50

^ 60 60

70 70

80

2 Theta Theta

Fig. 1 XRD patterns of (a) MOS, (b) MNS-2.1, (c) MNS-3.5, (d) MNS-4.4, (e) MNS-4.5, (f) MNS-5.2 and (g) MNS-6.3.

effect of H2-N2 ratio on the formation of crystalline phase for molybdenum should not be neglected.

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Table 1 Physical properties of support, MOS and MON-X

SBA-15 MOS MNS-2.1 MNS-3.5 MNS -4.4 MNS -4.5 MNS -5.2 MNS -6.3

SBET

VP

Dp

(m /g) 601 277 372 306 304 295 279 290

(crnVg) 0.903 0.728 0.823 0.717 0.701 0.667 0.682 0.688

(nm) 6.59 6.61 6.58 6.58 6.55 6.58 6.57 6.57

2

From table 1 it is apparently that the

500

Pore volume(cc/g STP)

Sample

600

•5*

400 300

s

£

200 100 0 0.0

0.2

0.4

0.6

0.8

1.0

P/PO

Fig. 2. Nitrogen adsorption and desorption isotherms of SBA-15(A), MOS (D) andMNS-5.2 (•).

loaded MoO3 and molybdenum nitride has a great impact on the surface area and pore volume of SBA-15. After the MOS samples were nitrided, the surface area of the samples were enlarged and the pore diameters were faintly lessened. This might attribute to the migration of Mo species due to the significant reduction in crystallite size in the process of nitridation [6]. Fig. 2 shows the nitrogen adsorption-desorption isotherms of MOS and MNS-5.2. The illustration indicates that the silica mesostructure has been largely maintained during the operation of impregnation and the subsequently nitriding process. It is noteworthy that the surface area changes when the MOS samples were nitrided via different H2-N2 ratios. The surface area of the samples is above the 300 m2/g when the H2-N2 is below 4.5, which is higher that above 4.5 of H2-N2. The results indicate that the H2-N2 ratio has a impact on the physical properties of samples nitrided. The micrograph (Fig. 3) shows well-defined mesoporous structure, suggesting in further that the MNS-5.2 sample keep the pore structure of SBA15. The image reveals regular periodicity over very large areas and clearly indicates highly dispersed y-Mo2N particles clustered within the pores of SBA15. The effect of H2-N2 ratio is not only on the physical properties of samples but also on the catalytic activity on NH3 decomposition. When the H2-N2 ratio is 5.2 the catalytic activity is highest. Fig. 4 shows the influence of GHSV on the catalytic activity of MNS-5.2. At 873 K, the conversion of NH3 can arrive at 79.2% even when the GHSV is 15800 ml/h-g.cat and 93.1% at 3400 ml/h-g.cat. Furthermore, NH3 could be completely decomposed with GHSV from 2300 to 15800 ml/hg.cat at 923K, which shows higher performance than that of MoNx/a-Al2O3 or NiMoNy/a-Al2O3 catalysts [4 ]. S uch results indicate that ammonia decomposition over the MNS-5.2 catalyst is an effective route to produce COx-free hydrogen.

790

4. Conclusion Though that on the formation of molybdenum nitride is fine, the effect of H2N2 ratio on the physical properties of MNS-X and even catalytic activity is obvious. The mesoporous structure when the SBA-15 was supported on the MoO3 and subsequently nitriding procedure was largely kept. At 923 K the NH3 could be completely decomposed on MON-5.2 in the GHSV range of 2300 to 15800 ml/hg.cat. 100 100

—o—

—o

90

Ammonia conversion (% )

lOOnm

80 70

•

-»-773K-»823K 773 K 823 K

60

- A - 8873 7 3K K - O - 923 923K K

50 40 30 20 10

. I

3400

.

6400

_

" i

I

.

9400

i

12400

'— • I

15400 15400

gcat GHSV (ml/h g cat)

Fig.3 TEM image of MNS-5.2

Fig. 4 Influence of GHSV on catalytic activity of MNS-5.2

5. References [1] [2] [3] [4] [5]

A. S. Chellappa, C. M. Fisher and W. J. Thomson, Appl. Catal. A 227 (2002) 231. T. V. Choudhary, C. Sivadinarayana and D. W. Goodman, Catal. Lett.72 (3-4) (2001) 197. H. C. Liu, H. Wang, J. Shen, Y. Sun and Z. Liu, Petrochem. Tech. 34(2005) 495. C. Liang, W. Li, Z. Wei, Q. Xin and C. Li, Ind. Eng. Chem. Res. 39 (2000) 3694. D. Y. Zhao, J. L. Feng, Q. S. Huo, N. Melosh, G. H. Fredrickson, B. F. Chmelka and G. D. Stucky, Science 279 (1998) 548. [6] Z. L. Liu, M. Meng, Y. L. Fu, M. Jiang, T. D. Hu,. Y. N. Xie and T Liu, Mater. Lett. 54 (2002) 364.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

791 791

Comparative study of the catalytic activity of AlSBA-15 and Ga-SBA-15 materials in a-pinene isomerisation and oxidative cleavage of epoxides B. Jarry, F. Launay, J. P. Nogier and J. L. Bonardet Laboratoire des Systemes Interfaciaux a I'Echelle Nanome'trique (SIEN) UPMC - CNRS UMR 7142, Tour 54 case cowrier 196, 4 Place Jussieu, Paris 75252 Cedex 05, France.

Materials of the SBA-15 type with well dispersed Ga or Al atoms were prepared successfully by using different procedures (direct synthesis or grafting). Depending on the heteroelement sources, gallium-based samples displayed different catalytic activities in the isomerisation of a-pinene but led to better selectivities than Alsolids did. However, these last ones turned out to be more adapted to the formation of adipic acid (AA) by the oxidative cleavage of cyclohexene oxide (CHO) in the presence of tert-burylhydroperoxide (TBHP). 1. Introduction Incorporation of gallium in porous materials has been mainly studied in the case of zeolites or mesostructured silicas like MCM-41 or MCM-48 [1] but anchoring of gallium on SBA-15 has not been extensively investigated [2, 3]. However GaSBA-15 materials could be interesting catalysts for the transformation of large molecules. In this paper, we report on their performances in a-pinene isomerisation and in the oxidative cleavage of cyclohexene oxide (CHO). The catalytic activity of four Ga-SBA-15 materials prepared by different procedures (direct synthesis or grafting) and gallium sources is compared with that of Al-SBA-15 solids obtained in a similar way. The structure and texture of all materials were characterised by classical methods (XRD, TEM, 27A1 and 71Ga NMR, porosimetry measurements and XPS). The acidity of the solids was evaluated by ammonia adsorption. 2. Experimental Section 2.1. Preparation and characterisation In the case of gallium, two different direct synthesis procedures were tested. The first one (DS1) is derived from the pH adjusting method described by Wu et al. [4]

792 792

for Al incorporation. The gallium and silicon precursors are hydrated gallium sulphate and tetraethoxysilane (TEOS); the sample is denoted Ga-Sulph. The second method (DS2) is derived from that reported by Li et al. [5]. The Ga and Si sources are gallium acetylacetonate and tetramethoxysilane (TMOS); the sample is denoted Ga-Acac. Grafted Ga-SBA-15 samples were obtained from pure SBA-15 silica [6] and two different combinations of gallium sources and solvents: Ga(NO3)3 in ethanol (Ga-Nit.) or GaCl3 in chloroform (Ga-Cl). In the case of AlSBA-15 materials, aluminium was incorporated in the synthesis gel using A12(SO4)3. 18 H2O [4] or grafted from Al(O-/Pr)3 in dry hexane [7]. Detailed preparation procedures and textural properties of Ga-SBA-15 and Al-SBA-15 have been described in two previous papers [1,8]. 2.2. Catalysis tests The isomerisation of a-pinene (1.47 g, 10.6 mmol) was carried out in the presence of 0.1 g of Ga (or A1)-SBA-15 for 1 (or 3) h at 353 K. Oxidative ring opening of CHO (7 mmol) was performed in refluxing acetonitrile (10 mL) in the presence of an aqueous (70 wt.%) or a decane (5.5 M) TBHP solution; molar TBHP/substrate ratio was 3 and the catalyst weight was 0.2 g. The starting materials and the reaction products of both tests were identified by GC-MS. The compounds were quantified using either tetradecane or mesitylene as internal standards. 3. Results and Discussion 3.1. Characterisation The textural properties of Ga-Acac. samples (prepared following DS2) and of the grafted solids Ga-Nit. and Ga-Cl are comparable (Table 1). A slight decrease of the SBET value and of the pore volume is observed compared to pure silica. Furthermore the lattice parameter, ao, and the mean pore diameter, D, are roughly the same. Then, it turns out that the DS2 method is more an "in situ-grafting" than a true "one pot" procedure. The hydrolysis rates of Ga(acac)3 and TMOS would be less well-adjusted than those of TMOS and Al(O-/Pr)3, the precursors used in the original work [5]. On the other hand, Ga-Sulph. samples are characterised by a more significant decrease of the SBET and a shift of D towards higher values. The variation of D is even more important in Ga than in Al samples certainly because of the bigger size of Ga atoms compared to that of Al ones. 27 A1 and 71Ga NMR spectra of "as synthesised" samples (not shown here) show that Al and Ga atoms are located in a tetrahedral environment thus proving their incorporation in the silica framework. Thermal treatments generate hexacoordinated species in both cases. Nevertheless a large part of Ga and Al atoms remains in a tetrahedral environment. Moreover, XPS measurements indicate that the Ga 3d5/2 binding energies of the four Ga samples are quasi-

793

constant (21.7 + 0.2 eV) and clearly different from 20.5 eV, the value for Ga2O3 oxide. Hence, there is no cluster of this later at the nanometric scale. At last, the amount of ammonia irreversibly chemisorbed at 373 K is roughly proportional to the metal content in Al- and Ga-SBA-15 solids. A more detailed analysis of the results obtained by the different characterization methods (including NH3 TPD and FTIR spectroscopy of adsorbed probes (2,6-dimethylpyridine and deuterated acetonitrile)) is presented in reference [1]. Table 1. Structural and textural properties of Ga- and Al-SBA-15 solids Sample

Si/M

S B E T ( m V ) V p (cm 3 g-

ao(nm)

D pore (nm)

n

NH3 (tnmol g )

SBA-15

-

940

1.10

11.6

6.7

-

Ga-Sulph.

17

575

1.21

13.8

8.9

0.82

Ga-Acac.

23

901

1.15

11.6

6.6

0.56

Ga-Nit.

35

756

0.91

12.4

6.7

0.40

Ga-Cl

140

798

0.95

11.6

6.8

0.10

Al-Sulph.

16

427

0.84

11.6

8.3

0.94

Al-OiPr

15

737

0.89

11.6

6.4

0.99

3.2. Catalysis tests The four Ga-SBA-15 solids have been tested comparatively as catalysts in the isomerisation of a-pinene at 353 K (Table 2). Pure SBA-15 silica is shown to be unreactive even under harder conditions (373 K for 3 h) and thus, emphasizes the need for acidity. The conversion of a-pinene is not complete within 1 h (3 h for GaCl) and the material having the lowest Ga content is the less efficient. Strong differences observed in the conversion of a-pinene in the presence of materials with similar Ga loading (Ga-Sulph.: 56%; Ga-Acac: 87%) mean that the nature of their gallium precursors has also to be considered. Catalysts with the highest Ga contents are leading to significant amounts of heavy by-products as a result of parallel polymerisation pathways. The two main compounds i.e. camphene and limonene are produced roughly to the same extent. Both of them can represent 70% of all the products formed at 353 K. Al-OiPr. catalyst is very active. More than 90% of a-pinene is converted after 1 h at 353 K but the mass balance of carbon in light products is only 60% showing a degree of polymerisation widely higher than that observed with Ga catalysts. In the oxidative ring opening of CHO (Table 3), attention is focused on GaSulph. and its comparison with Al-Sulph. prepared following the same way. All Sulph. materials are active: CHO is first consumed, leading to 1,2cyclohexanediol(Diol) which is further converted into adipic acid (AA) and other by-products. Whatever the catalyst, reactions carried out with aqueous TBHP are slower than those performed with the anhydrous oxidant. Aqueous TBHP favours the diol accumulation in the reaction mixture (up to 80-85%). Higher adipic acid

794

yields are obtained with Al-Sulph. This leads us to emphasize the role of acid strength in the oxidative ring opening of CHO. Table 2. a-pinene isomerisation: main compounds distribution at 353 K Material

Ga-Cl

Si/M

140

Reaction time (h)

3

Ga-Nit.

Ga-Acac.

Ga-Sulph.

Al-OiPr

35

23

17

15

1

1

1

1

43.6 21.4

24.1

a-pinene

56.2

41.2

12.6

Camphene

17.2

19.6

25.5

a-terpinene

6.7 14.9

5.8

12.1

3.7

17.4

Limonene

19.2

20.0

18.3

4.9

terpinolene

5.1

4.6

8.6

4.1

3.1

8.7

Table 3. Kinetic parameters and yields (after 96 h) in the oxidative ring opening of CHO by TBHP / Ga(or A1)SBA-15 catalysts Material

Oxidant

Ga-Sulph. (17)b

aq. TBHP

b

Ga-Sulph. (17)

org. TBHP

Al-Sulph. (16)"

aq. TBHP

Al-Sulph. (16)b

org. TBHP

Time (h)

Yield (%)

M.B.a (%)

100%conv.

Diol max. yield

Diol

AA

72

72 [84 % ] c

72

13

85

53

26

79

35.5

44.5

80

20

34

54

48

65 [65 % ]

48

48 [83%]

c

60 [40%]

c

36

c

"Mass Balance: total amount of cyclohexene oxide and its derivatives detected by GCMS. Si/Al molar ratio c Maximum yield of 1,2-cyclohexanediol (diol).

Si/Ga or

4. References [1] B. Jarry, F. Launay, J. P. Nogier, V. Montouillout, L. Gengembre and J. L. Bonardet, Appl. Catal. A: Gen., 309 (2006) and references therein. [2] Z. El Berrichi, L. Cherif, O. Orsen, J. Fraissard, J.-P. Tessonnier, E. Vanhaecke, B. Louis, M.-J. Ledoux and C. Pham-Huu, Appl. Catal. A: Gen., 298 (2006) 194. [3] C. F. Cheng andH. H. Cheng, Stud. Surf. Sci. Catal., 156 (2005) 133. [4] S. Wu, Y. Han, Y.-C. Zou, J.-W. Song, L. Zhao, Y. Di, S.-Z. Liu and F.-S. Xiao, Chem. Mater., 16(2004)486. [5] Y. Li, W. Zhang, L. Zhang, Q. Yang, Z. Wei, Z. Fen, C. Li, J. Phys. Chem. B,108 (2004) 9739. [6] D. Zhao, J. Feng, Q. Huo, N. Melosh, G. H. Frederickson, B. F. Chmelka and G. D. Stucky, Science, 279 (1998) 548. [7] Z. Luan, M. Hartmann, D. Zhao, W. Zhou and L. Kevan, Chem. Mater., 11 (1999) 1621. [8] B. Jarry, F. Launay, J. P. Nogier and J. L. Bonardet, Stud. Surf. Sci. Catal., 158B (2005).

Recent Progress in Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

795 795

Mesoporous silica supported Ni catalysts for CO2 reforming of methane Shaobin Wang Department of Chemical Engineering, Curtin University of Technology, GPO Box U1987, Perth, WA 6845, Australia

Mesoporous silica (MCM-41) supported Ni catalysts were prepared, characterised and tested for catalytic reforming of methane with CO2 to syngas. It is found that Ni/MCM41 and Ni/La-MCM41 exhibit high catalytic activity while they show different deactivation behaviour in this reaction. Ni/MCM41 can maintain the stability after an initial deactivation while Ni/La-MCM41 shows a continuing deactivation due to higher carbon deposition and lower reaction activity. 1. Introduction In recent years, many researches have been devoted to the chemical transformation of methane and carbon dioxide into more valuable feedstock. CO2 reforming of methane can produce CO-riched synthesis gas, which is good for many synthetic processes. It has been found that group VIII metals are effective but Ni as a cheaper material shows advantage than noble metals in the viewpoint of industrial application [1]. In the last two decades, a lot of researches have been done to this reaction but a few papers have been reported on mesoporous materials as supports for this reaction [2-5]. Mesoporous materials can provide large surface area favouring the dispersion of Ni particles on the surface. In this work, we report an investigation on Ni catalysts supported on mesoporous silica (MCM-41) for this reaction. 2. Experimental Section Si-MCM41 was prepared by sol-gel method. La-substituted MCM41 samples were prepared by grafting method. For reference, a commercially available silica is also employed as a support. SiC>2, MCM41 and La-MCM41 supported

796 796

catalysts were prepared by impregnation with an aqueous solution of Ni(NO3)2. The catalysts were dried in air at 103-105°C for 14 h after evaporation of water and calcinated at 500°C for 4 h in air. The textural structure of supports, SiO2 and MCM41 and their supported Ni catalysts was determined by N2 adsorption. Chemical phases were determined by XRD. The mean crystallite diameters of nickel were estimated from application of the Scherrer equation. CO2 adsorption was used for acid/base measurement. The carbon deposition was investigated by a temperature programmed oxidation (TPO) using TGA. Catalytic reactions were carried out on a fixed-bed quartz reactor at atmospheric pressure with 0.2 g catalysts. The reactant stream consisting of CH4:CO2=1:1 is fed in at 60 ml/min. Before reaction, the catalysts were reduced in H2 at 500°C for 3 h and then the temperature was increased to the desired reaction temperature (800°C). 3. Results and Discussion The physicochemical properties of silica, prepared mesoporous silica (MCM41) and the supported Ni catalysts are presented in Table 1. As shown that mesoporous silica has much higher surface area than comericial silica mainly contributed by mesopores. Impregnation of Ni reduces the total surface area and mesoporous surface area while resulting in the increase in micropore. La substitution further decreases the surface area and pore volume. For three supports, mesoporous silica can produce high Ni dispersion and La substituted Si-MCM41 induces the highest dispersion of Ni particles on the support. Table 1 Characteristics of MCM-41 and its supported Ni catalysts Catalyst

SBET(m2/g)

SiO2

90

Ni/SiO2

64

Smicro ( m 2 / g )

S meS o(m 2 /!g)

V (cmVg)

DNi(nm) 15.5

MCM-41

737

0.706

-

806

69

Ni/MCM41

642

164

478

0.685

9.8

Ni/La-MCM41

410

87

323

0.545

8.7

Fig.l shows CO2 adsorption on Ni/MCM-41 and Ni/La-MCM-41 catalysts. It is seen that Ni/La-MCM-41 exhibits higher CO2 adsorption than Ni/MCM-41, suggesting strong basicity of Ni/La-MCM-41. Catalyst testing shows that Ni/SiO2 exhibits low catalytic activity than mesoporous silica supported catalysts. At 800°C, initial CH4 conversion on Ni/SiO2 is only 7% while other two catalysts can produce about 90% methane conversion and Ni/La-MCM41 gives a higher methane conversion than Ni/MCM41. This can be ascribed to the

797

higher dispersion of Ni and stronger basicity of Ni/La-MCM41. The catalytic stability of two mesoporous Ni catalysts is displayed in Fig. 2. As seen that they exhibit different patterns of deactivation. Methane conversion on Ni/MCM41 shows a decreasing trend during the initial 20 h performance and can maintain the catalytic activity at 80 % methane conversion without further deactivation for 100 h. On the contrary, Ni/La-MCM41 shows a behaviour of continuing deactivation within 100 h. The methane conversion decreases from 94 % to 75 % after 100 h.

• O

Ni/MCM-41 Ni/La-MCM-41

O O

0 D

0.000

0.005

0.010

0.015

0.020

0.025

0.030

Ni/La-MCM41 Ni/MCM41

0.035

Relative pressure (p/pQ)

Fig.l CO2 adsorption isotherm on Ni catalysts at 0 °C.

Time(h) 2

J ^ Catalytic performance of Ni/MCM41 and Ni/La-MCM41 in CO2 reforming of methane at 800 °C.

XRD analyses (Fig. 3) show that a small carbon peak occurring on Ni/MCM41 but a higher intensity of Ni peaks, suggesting the less carbon deposition and higher sintering of Ni particles on this catalyst. For Ni/LaMCM41, the carbon peak is much stronger than that on the Ni/Si-MCM41, indicative of higher amount of carbon deposition on this catalyst, which is confirmed by the experimental results of TPO. Temperature programmed oxidation shows that two peaks occurring at 600 and 680°C on Ni/MCM41, attributed to carbon whisker and graphite [6], while a strong oxidation peak occurs on Ni/La-MCM41 centred at 700°C. Thus, it is believed that the lower oxidation activity of the graphite carbon contributes to the deactivation of Ni/La-MCM41. Previous investigations have shown that two or three carbon species can form on catalyst surface in CO2 reforming of methane and that the reactivity of carbon determines the catalyst stability [1].

798

Ni/MCM-41 Ni/La-MCM-41

e

0.15

E

gijr

^™H0

I

500

A/ /\A

600

700

Temperature (°C)

Fig. 3 XRD patterns of reacted catalysts M/MCM41 and Ni/La-MCM41 in C0 2 reforming of methane at 800°C.

Fig. 4 Temperature programmed oxidation of carbon deposited on Ni catalysts after reaction.

4. Conclusion Ni supported on MCM41 and La exchanged MCM41 mesoporous materials have been employed as catalysts for CO2 reforming of methane. Both catalysts present high catalytic activity but the catalytic stability are quite different. Due to high coking problem, Ni/La-MCM41 exhibit faster deactivation while Ni/MCM41 will maintain the catalytic activity after initial deactivation. Two types of carbon species will form on the catalysts during the reaction. 5. References [1] S. B. Wang, G. Q. M. Lu and G. J. Millar, Energ. Fuel 10 (1996) 896. [2] H. V. Fajardo, A. O. Martins, R. M. de Almeida, L. K. Noda, L. F. D. Probst, N. L. V. Carreno and A. Valentini, Mater. Lett. 59 (2005) 3963. [3] Z. P. Hao, H. Y. Zhu and G. Q. Lu, Appl. Catal. A. 242 (2003) 275. [4] Z. P. Hao, C. Hu, Z. Jiang and G. Q. Lu, J. Environ. Sci.-China 16 (2004) 316. [5] S. B. Wang, H. Y. Zhu and G. Q. Lu, J. Colloid. Interf. Sci. 204 (1998) 128. [6] S. B. Wang and G. Q. Lu, Ind. Eng. Chem. Res. 38 (1999) 2615.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

799 799

SBA-15 mesoporous molecular sieve as an appropriate support for highly active HDS catalysts prepared using Mo and W heteropolyacids Lilia Lizamaa, Juan C. Amezcuaa, Ramon Resendiza, Sergio Guzmana, Gustavo A. Fuentesb and Tatiana Klimovaa* a

Facultad de Quimica, Universidad National Autonoma de Mexico (UNAM), Cd. Universitaria, Coyoacan, Mexico D.F. (04510) Mexico h Area de Ingenieria Quimica, Universidad Autonoma Metropolitana - Iztapalapa, Av. Michoacdny Purisima, Iztapalapa, Mexico D.F. (09340) Mexico

A series of Mo/W HDS catalysts promoted by Ni/Co, supported on SBA-15 were prepared using Keggin-type heteropolyacids as active phase precursors to study the activity of different catalytic formulations in the 4, 6dimethyldibenzothiophene (4, 6-DMDBT) hydrodesulfurization (HDS). Catalysts' characterization showed that SBA-15-supported heteropolyacids were well-dispersed and maintained their characteristic Keggin structure after calcination at 623 K for 2 h. NiPW and NiPMo catalysts supported on SBA-15 resulted to be highly active in HDS of hindered dibenzothiophenes. 1. Introduction A growing interest in the removal of sulfur from gasoline and diesel oil by means of deep hydrodesulfurization is due to the implementation of more stringent fuel specifications in many countries. Many efforts are aimed to improve HDS catalysts by using new materials as catalytic supports, changing the promoter and the precursor of the active phase. To date, there have been very few reports on the application of heteropolyacids (HPAs) in the preparation of HDS catalysts [1,2]. Different carriers have been used to support HPAs. It was found that, when HPAs are deposited on alumina, very strong interaction with the support leads to the destruction of the characteristic heteropolyanion precursor structure [3], and, consequently, catalytic behavior of the catalysts prepared from HPAs and other traditional Mo/W precursors resulted to be similar. New mesoporous molecular sieves such as SBA-15 [4],

800

highly stable and with better textural properties compared to the traditional yalumina support, seem to be especially suitable for depositing large HPA precursors. The aim of the present work is to demonstrate that SBA-15supported heteropolyacids are good oxidic precursors for the preparation of highly active HDS catalysts and to analyze the effect of different promoters (Co, Ni) on catalysts' behavior in HDS of hindered dibenzothiophenes. 2. Experimental Section The pure siliceous hexagonal p6mm SBA-15 was prepared according to literature [4] using Pluronic PI23 as structure-directing agent and TEOS as the silica source. Mo/W, as well as P, were incorporated to the SBA-15 support by incipient wetness impregnation of methanol solutions of Keggin-type heteropolyacids (H3PM012O40 or H3PW12O40). After the impregnation, the catalysts were dried (373 K, 12 h) and calcined (623 K, 2 h) in air. Ni or Co were incorporated to calcined Mo/W catalysts by the same impregnation technique using corresponding nitrates as promoter sources. After promoter impregnation, catalysts were dried and calcined again as described above. The nominal composition of the catalysts was 12 wt % of MoO3 or WO3 and 3 wt % of NiO or CoO. The samples were designated as HPW(HPMo)/SBA-15 for unpromoted catalysts and MPW(MPMo)/SBA-15, where M is Ni, Co, for promoted catalysts. The support and catalysts were characterized by N2 physisorption, small- and wide-angle XRD, UV-Vis DRS, 31P MAS-NMR, and TPR, and tested in the 4, 6-DMDBT HDS reaction. Catalysts' activation was carried out ex situ in a tubular reactor at 673 K for 4 h in a stream of H2S (15 vol. %) in H2 under atmospheric pressure. The HDS activity tests were performed in a batch reactor at 573 K and 7.3 MPa total pressure for 8 h. 3. Results and Discussion The nitrogen adsorption-desorption isotherms, as well as the small-angle XRD patterns (Fig. 1) show that W and Mo heteropolycompounds can be supported on SBA-15 without substantial loss of the support's characteristics (texture and structural order). Results from textural characterization of the catalysts (Table 1) 1.0 indicate that the incorporation of HPW or HPMo on the SBA-15 surface produces a decrease in Fig. 1. Small-angle XRD patterns the textural properties (Sg, S^, Vp), which of SBA-15 (a); NiPMo/SBA-15 (b); becomes stronger for the Ni- or Co-promoted NiPW/SBA-15 (c); C0PM0/SBAsamples. This decrease can be explained taking 15 (d); and CoPW/SBA-15 (e). into account the weight of the deposited metal species. Wide-angle XRD of the catalysts (not shown) demonstrated that

801

deposited metal oxidic species were well-dispersed in all catalysts. The formation of any crystalline phase was not detected. Table 1. Textural and structural characteristics of SB A-15 support and catalysts Dp

ao

8

(m /g)

vP (cmVg)

(A)

(A)

(A)

881

121

1.22

66

106

40

HPW/SBA-15

733

104

1.04

67

106

39

NiPW/SBA-15

690

88

0.96

66

106

40

HPMo/SBA-15

780

112

1.10

66

106

40

NiPMo/SBA-15

734

88

1.05

67

105

38

Sample

Sg 2

(m /g) SBA-15

2

The solid state 31P MAS-NMR spectra of Mo catalysts are shown in Fig. 2. In all these spectra a peak at -3.5 ppm, characteristic of the Keggin structure of the parent HPMo, can be observed. Similar results were obtained for the catalysts of the W series, where the signal of HPW structure was observed at -15 ppm. These results, as well as the absence of a signal at 0 ppm (a phosphate formed from HPA decomposition), indicate that the characteristic Keggin structure was preserved in the oxidic precursors supported on SBA-15. An increase in the dispersion of octahedral Mo and W species supported on SBA-15 in comparison with bulk HPMo and HPW precursors was observed by UV-Vis DRS (Fig. 3). Addition of promoters (Ni, Co) results in a further increase of catalysts' dispersion. Unpromoted and Co-promoted catalysts showed high reduction temperatures (Fig. 4) and low catalytic activities (Table 2).

a 2 0 - 2 - 4 -6 -8 5, ppm Fig. 2. 31 P NMR spectra of dried (a) and calcined (b) HPMo/SBA-15 catalysts and calcined NiPMo/SBA-15 s a m p l e d .

Table 2. 4,6-DMDBT conversions obtained over different catalysts at 8 h reaction time Catalyst Conv. (%)

HPW/ SBA-15 29

CoPW/ SBA-15 30

NiPW/ SBA-15 91

HPMo/ SBA-15 46

CoPMo/ SBA-15 55

NiPMo/ SBA-15 79

NiMo/ A12O3 61

However, Ni-promoted catalysts showed a significant decrease in the temperature of reduction of metal oxide species. Both, Mo and W, Ni-promoted

802

catalysts showed high activity in 4,6-DMDBT HDS, which was substantially higher than that of the NiMo/Al2O3 analog. The 4,6-DMDBT reaction products were methylcyclohexyltoluene (the principal product), dimethylbiphenyl and dimethylbicyclohexyl. Catalysts' deactivation after HDS catalytic tests was not detected.

400 600 Wavelength (ran)

800

Fig. 3. UV-Vis DRS spectra of parent bulk HPMo (a); HPMo/SBA-15 (b); NiPMo/SBA15 (c) and CoPMo/SBA-15 (d).

200

400

600 800 Temperature (°C)

1000

Fig. 4. TPR profiles of mechanical mixture of HPMo and SBA-15 (a); HPMo/SBA-15 (b); CoPMo/SBA-15 (c); and NiPMo/SBA-15 (d).

4. Conclusion The use of SBA-15 materials as supports together with Keggin-type Mo or W heteropolyacids as HDS active phase precursors show promising features for the preparation of Mo and W-based Ni-promoted catalysts, active for HDS of hindered dibenzothiophenes. 5. Acknowledgement Financial support for this work by DGAPA-UNAM (Mexico, grant IN104106) is gratefully acknowledged. The authors wish to thank M. Aguilar and C. Salcedo for technical assistance with XRD characterizations. 6. References [1] B. Pawelec, S. Damyanova, R. Mariscal, J. L. G. Fierro, I. Sobrados, J. Sanz and L. Petrov, J. Catal., 223 (2004) 86. [2] R. Shafi, M. R. H. Siddiqui, G. J. Hutchings, E. G. Derouane and I. V. Kozhevnikov, Appl. Catal. A: General, 204 (2000) 251. [3] A. Griboval, P. Blanchard, E. Payen, M. Fournier and J. L. Dubois, Catal. Today, 45 (1998) 277. [4] D. Zhao, Q. Huo, J. Feng, B. Chmelka and G. Stucky, J. Am. Chem. Soc, 120 (1998) 6024.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

803 803

SBA-15 mesoporous molecular sieves doped with ZrO2 or TiO2 as supports for Mo HDS catalysts Oliver Y. Gutierrez3, Fernando Pereza, Cecilia Salcedoa, Gustavo A. Fuentesb, Manuel Aguilarc, Xim Bokhimic and Tatiana Klimovaa* "Facultad de Quimica and3Institute) de Fisica, UniversidadNational Autonoma de Mexico (UNAM), Cd. Universitaria, Coyoacdn, Mexico D.F. (04510) Mexico b Area de Ingenieria Quimica, Universidad Autonoma Metropolitana - Iztapalapa, Av. Michoacdny Purisima, Iztapalapa, Mexico D.F. (09340) Mexico

SBA-15 materials with different TiO2 or ZrO2 loadings were prepared by chemical grafting procedure and used as supports for Mo hydrodesulfurization (HDS) catalysts. Ti and Zr oxide species were found to be well-dispersed on SBA-15 surface (DRS, XRD). In the catalysts supported on the TiO2 or ZrO2 modified materials, the dispersion of Mo oxide species increased with TiO2 or ZrO2 loading in the SBA-15 support. Catalytic activity tests in hydrodesulfurization of 4,6-dimethyldibenzothiophene (4,6-DMDBT) showed that the modification of SBA-15 supports with Ti and Zr species significantly improves the performance of unpromoted Mo catalysts in HDS of refractory dibenzothiophenes. 1. Introduction Hydrodesulfurization is a key process for producing clean engine fuels. Nowadays, many efforts are aimed to improve the HDS catalysts by using new materials as catalytic supports. Among them, mesoporous molecular sieve SBA15 has attracted much interest. However, up to now only purely siliceous SBA15 materials were tested in HDS and published information is limited to a few papers [1-3]. The incorporation of heteroatoms (Al, Ti, Zr, etc.) on the SBA-15 surface should modify dispersion and coordination of the deposited active metal species (Mo, W) and therefore their efficiency and selectivity in HDS reaction. In the present work, a series of Mo catalysts supported on TiO2 or ZrO2modified SBA-15 was prepared, characterized and tested in 4,6-DMDBT HDS.

804

2. Experimental Section Purely siliceous SBA-15 was synthesized according to the well-known procedure [4]. T1O2 and ZrC>2 incorporation was made by grafting of titanium or zirconium alkoxides on SBA-15 surface according to the previously reported procedure [5]. Supports with 11 and 19 wt % of TiO2 (Ti-SBA-15(ll) and TiSBA-15(19), respectively) and with 16 and 22 wt % of ZrO2 (Zr-SBA-15(16) and Zr-SBA-15(22)) were prepared. Mo/M-SBA-15 catalysts (where M is Ti or Zr) were prepared by impregnation of (NH4)6Mo7O24 aqueous solutions. The nominal composition of the catalysts was 12 wt % MoO3. The 4,6-DMDBT HDS activity tests were performed in a batch reactor at 300°C and 7.3 MPa total pressure for 8 h. 3. Results and Discussion Results from textural characterization of the supports indicate that the incorporation of Zr or Ti oxides in the SBA-15 surface produces a decrease in the SBA-15 textural properties (Table 1). This decrease is larger for the Zr-containing material because of higher zirconia weight loading. However, the characteristic shape of N2 adsorption isotherms (type IV in Brunauer classification) and small-angle XRD patterns (Fig. 1) are still maintained after titania or zirconia incorporation. TiC>2 and ZrC>2 surface species were found to be well-dispersed. In the DRS spectra of Ti- and Zr-containing SBA-15 samples (Fig. 2), absorption bands at 225 and 200 nm, respectively, are observed, which correspond to the presence of isolated Ti(IV) or Zr(IV) species in tetrahedral coordination. This result is in line with powder XRD observations, where the formation of any kind of TiO2 or ZrO2 bulk crystalline phases was not detected. A significant decrease in the textural properties was observed after Mo incorporation to the supports (Table 1). This decrease indicates the possibility of some obstruction of the support pores by deposited Mo oxidic species.

5

•v/

1

20 (°) Fig. 1. XRD patterns of SBA-15 (a); TiSBA-15(19) (b); and Zr-SBA-15(22) (c) supports.

200

300

400

500

A. (nm) Fig. 2. UV-Vis DRS spectra of supports: SBA-15 (a); Ti-SBA-15(ll) (b); Ti-SBA-15(19) (c); Zr-SBA-15(16) (d): and Zr-SBA-15(22) (e).

805 Table 1. Textural characteristics of supports and catalysts Sample 2

2

(m /g)

(m /g)

VP

Dp

a0

5

(cmVg)

(A)

(A)

(A)

SBA-15

863

139

1.16

56

100

44

Ti-SBA-15(19)

649

121

0.85

57

102

45

Zr-SBA-15(22)

583

105

0.77

57

100

43

Mo/SBA-15

601

82

0.85

55

102

47

Mo/Ti-SBA-15(19)

466

69

0.66

52

102

50

Mo/Zr-SBA-15(22)

394

49

0.60

50

102

52

The formation of crystalline MOO3 phase was detected by XRD for Mo catalysts supported on pure siliceous SBA-15 and Ti-containing supports (Fig. 3). The dispersion of Mo oxide species increases with TiO2 or ZrO2 loading in the SBA-15 support. Thus, the size of MOO3 crystallites decreases from 825 A (Mo/SBA-15) to 500 A for Mo/Ti-SBA-15(19) catalyst, and it becomes smaller than 50 A for the catalysts supported on Zr-SBA-15. This may be due to the stronger interaction of Mo species with Ti- or Zr-containing supports. The size of MoO3 crystallites detected by XRD compared to the pore diameter of the used SBA-15 materials makes evident that they should be located on the external surface of the support particles being responsible for pore entrance blocking and textural properties decrease after Mo deposition. The TPR results for Mo catalysts are shown in Fig. 4. The TPR profile of Mo/SBA-15 catalyst exhibits two main reduction peaks at 560°C (the first step of reduction of polymeric octahedral Mo species (Mo(Oh)) weakly bound to the silica surface) and 730°C (the second step of reduction of Mo(Oh) species and the first step of reduction of

10

15

20

25

30

35

40

45

50

Fig. 3. Powder XRD patterns of Mo catalysts supported on SBA-15 (a); Ti-SBA-15(l 1) (b); Ti-SBA-15(19) (c); Zr-SBA-15(16) (d); and Zr-SBA-15(22) (e). * MoO3 400

200

400 600 800 1000 Tern peratu re (°C )

Fig. 4. TPR of Mo catalysts supported on SBA-15 (a); Zr-SBA-15(22) (b) and TiSBA-15(19)(c).

806

tetrahedral Mo species). The shoulder at 6OO0C can be assigned to the reduction of crystalline MoO 3 detected by XRD. TiO 2 or ZrO 2 grafting on SBA-15 surface leads to a decrease in both: the proportion of tetrahedral Mo species, difficult to reduce, and the temperature of reduction of Mo(Oh) species evidencing their better dispersion. T ui 1 A a T-.n^r.-r Table 2. 4,6-DMDBT conver' ., , , . . , . sion over Mo catalysts (at 8 h)

Table 2 vpresents the 4,6-DMDBT . * o u t ! i conversions over A/r Mo catalysts at 8 h .g ^ ^ ^ reactk)n tjme ft

Catalyst

incorporation of Ti or Zr atoms on the SBA-15 surface significantly increases (almost twice) the activity of unpromoted Mo catalysts in the HDS reaction of 4,6DMDBT. Observed activities of the sulfided catalysts were closely related with coordination and dispersion of Mo species in the oxide-state materials.

Conv (%)

Mo/SBA-15 Mo/Ti-SBA-15(ll)

28 45

Mo/Ti-SBA-15(19) Mo/Zr-SBA-15(16) Mo/Zr-SBA-15(22)

52 47 57

4. Conclusion It can be concluded that the interaction of Mo species with the SBA-15 support becomes stronger with TiO 2 or ZrO 2 loading which increases the dispersion of oxidic Mo species especially for Zr-containing SBA-15 supports. Mo catalysts supported on Ti- and Zr-containing SBA-15 molecular sieves are active for the elimination of hindered dibenzothiophenes. Catalyst activity increases with an increase in the proportion of octahedral Mo species and their dispersion. 5. Acknowledgement Financial support by CONACyT-Mexico (grant 46354-Y) is acknowledged. 6. References [1] L. Vradman, M.V. Landau, M. Herskowitz, V. Ezersky, M. Talianker, S. Nikitenko, Y. Koltypin and A. Gedanken, J. Catal., 213 (2003) 163. [2] G. M. Dhar, G. M. Kumaran, M. Kumar, K. S. Rawat, L. D. Sharma, B. D. Raju and K. S. R. Rao, Catal. Today, 99 (2005) 309. [3] A. Sampieri, S. Pronier, J. Blanchard, M. Breysse, S. Brunet, K. Fajerwerg, C. Louis and G. Perot, Catal. Today, 107-108 (2005) 537. [4] D. Zhao, Q. Huo, J. Feng, B. Chmelka and G. Stucky, J. Am. Chem. Soc, 120 (1998) 6024. [5] Z. Yongzhong, S. Jaenicke and G. Chuah, J. Catal., 218 (2003) 396.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

807 807

Isopropylation of naphthalene over mesostructured aluminosilicate nanoparticles with wormhole framework structures Shang-Ru Zhaia*, Chang-Sik Hab, Yong Liuc, Hua-Yu Qiuc, Dong Wud, Yu-Han Sund, Shao-Jun Wanga and Bin Zhaia "Department of Chemical Engineering and Materials, Dalian Institute of Light Industry, Dalian 116034, China b National Research Laboratory ofNano-lnformation Materials, Department of Polymer Science and Engineering, Pusan National University, Busan 609-735, South Korea "Key Laboratory of Organosilicon Chemistry and Material Technology of Education Ministry, Hangzhou Teachers College, Hangzhou 310012, China d State Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan 030001, China

The preparation and catalytic properties in isopropylation of naphthalene of nanosized mesostructured alumiosilicate with worm-like framework structures were presented in this work. Catalytic results showed that, under optmium conditions, the present nanocatalyst exhibited high activity making ca. 90 mol% of naphthalene conversion into mono-, di- and triisopropyl substituted derivatives. It should be mentioned that, however, the present nanocatalyst showed no considerable selectivity to objective products, and this may be attributed to its somewhat large mesopores in comparsion with microporous alkylating catalysts. 1. Introduction The fabrication of nanoscale devices and the preparation of structures with ordered mesoporosity are two hotspot of current research in materials chemistry. As is known, materials with length scales between 1 and 100 nm possessing uncommon catalytic, magnetic, optical and semi-conducting properties. Similarly, mesostructured materials, such as the M41S, SBA-n, MSU-n and AMS-n family of silicas, are important new classes of inorganic oxides with enormous potentials in molecular sieving, catalysis (e.g. for large molecule

808

transformations) and adsorption processes [1-4]. Thus, it is scientifically interesting to combine the methods for nanomaterials synthesis with those leading to the templating of open framework mesoporous materials to produce nanosized objects with both external (surface) and internal (bulk) functionalization. In the present work, we present a route to the production of highly catalytic mesoporous alumiosilicate nano-particles with particle size in 40-60 nm range, and experimental results show that the material with wormlike but uniform mesostructured interiors exihibted much high reaction activity in isopropylation naphthalene. 2. Experimental Section The present nanocatalyst was prepared from TEOS and A1(NO3)3«9H2O as inorganic source and CTAB as template, respectively, and all chemicas were industral grade as received without further treatment. The comphrensive preparation procedures have been introduced in our previous work [5], and thus will not be repeated here. Utilizing this method, about 2 kg nanocatalyst was prepared and used as alkylating catalyst. Isopropylation of naphthalene was carried out in a 100 mL stainless steel autogneous reactor with a stirrer. Reaction conditions are: reaction time = 4 h, naphthalene/isopropanol = 1/2, catalyst = 0.5 g, solvent (decahydronaphthalene) = 15 mL. Prior to the reaction, N2 was introduced into the reaction mixture to eliminate air. At the required reaction temperature and the reaction time, the reaction mixture was sampled and then centrifuged to remove catalyst particles, followed by GC analysis using a SE30 capillary column (50mx0.2mm) fitted with FID. The calculation of naphthalene conversion and products selectivity can be referenced to the previous literature [6]. Besides, IPN, DIPN and PIPN stand for mono-, di- and polyisopropylnaphthalene, respectively, and the selectivity to p and P'(Sp.p) substitued derivatives was used as an indicator for selective performance of catalyst. 4 00

1 .2

-1

dV/dlog(D) (cmg nm )

3. Results and Discussion

3 -1

0 .4

3

(cm /g)

0 .8

2200 00

0 .0

1

10

100

ads

D(nm)

V

The sorption isotherms and pore size distribution for the catalyst are shown in Fig. 1. Clearly, the isotherm exhibits a complicated form not only with a definite step in the low relative pressure 0.15 to 0.3, typical of capillary condensation of N2 into framework mesopores, but also with another clearer hystersis above 0.8, which may be related to the presence of larger mesopores

3300 00

11 0 00

0 00.0 .0

0 .2

0 .4 0 .6 P /P0

0 .8

Fig. 1 N2 sorption isotherms and pore size distribution (inset) for nanocatalyst.

11.0 .0

809

formed by aggregation of nanosized particles [5, 7]. Indeed, this speculation is instantly proved by the pore size distribution that there exist two distinct mesopores at 2.4 and 30 nm, respectively, and this may be repsonsible for the complicated sorption isotherms. The 27A1 MAS NMR of as-synthesized nanocatalyst indicates that all aluminum was -5.6 1 i A* incorporated into the framework skeleton, even 53 — \ /'\ with a much low Si/Al (gel) ratio as 7.5. In 27 contrast, the A1-NMR spectrum for calcined V \ nanoparticles shows three distinct signals center \ Cal. at-5.6, 21 and 53 ppm, respectively. Of interest is the presence of the line at 21 ppm, which can be assigned to five-coordinated aluminum. It is reported that, although five-coordinated As-syn. J aluminum has been identified under certain 150 100 50 0 -50 -100 synthesis conditions, it can not generally be ppm observed in calcined aluminum-rich A1MCM-41 27 materials even for very low Si/Al ratios. This Fig. 2 A1 MAS NMR for the fact indicates that the quick addition of ammonia nanocatalyst. water for inorganic precursors condensation might play an unfavorable role, owing to the fast increase of pH from mild acidic to much basic [8]. Meanwhile, the presence of large amount of five- and six-coordinate aluminum centers is especially noteworthy, though uncommon for directly prepared aluminosilicate mesostructures, as they may be used as Lewis solid acids in many organic reactions. Commercially, alkyl naphthalenes are produced by alkylation of naphthalene with an alcohol or alkene over solid acid catalysts, and many zeolites as Hmordenite, H-beta, HY, HZSM-5 and HMCM-22 have been extensively investigated. Relative to instenive studies on zeolitic catalysts, however, there are only a few papers reported on naphthalene isopropylation over mesocatalysts [6, 9]. Following structural charactrization on the nanocatalyst, its alkylating performance in naphthalene isopropylation was investigated in detail. Firstly, the dependence of naphthalene conversion and product selectivities on the reaction temperature over nanocatalyst and comparative results of Y and USY were shown in Figs.3 and 4, respectively. With increasing reaction temperature, the naphthalene conversion increased dependently and amounted to the maximum value at around 270°C. Similarly, other reacton parameters also significantly changed with the reaction temperature. It is revealed that, based on comphrensive calculation, the optmium reaction temperature is about 280°C, when naphthalene conversion and Sp.p- are about 92.0% and 74.1%, respectively. Besides, the present mesostructured nanocatalyst showed comparable reactivity in comparison with microporous zeolites Y and USY as evidenced by results in Fig. 4, once again indicating its superior reactivity, and this may be issociated • .

J

V

810

with its integrated effects of high density of active sites and facilitated transport of guest molecules in the bimodal pore arrays [5]. 100 80H o 6040 -Niph.conv. -Sel.lPN -5al.DIPN -Snl.PIPN -5el.B-B -2.&V2.7-DIPN

20200

220

240 260 280 Temperature (°C)

300

320

Fig.3 Reaction results over nanocatalyst as a function of reaction temperature.

Nano

USY Catalyst

Fig.4 Catalytic results over different catalysts.

4. Conclusion Catalytic results in the alkylation reaction showed that, although naphthalene conversion over the present nanoparticles was high amounting up to 90%, indicating the nanocatalyst possessing excellent reaction activity, the selectivity to the objective products was not unexpectedly high as its relatively large mesopores. 5. References [1] C. T. Kresge, M. E. Leonowiez, W. J. Roth, J. C. Vartuli and J. S. Beck, Nature, 359 (1992) 710. [2] S. A. Bagshaw, E. Prouzet and T. J. Pinnavaia, Science, 269 (1995) 1242. [3] D. Y. Zhao, J. Feng, Q. Huo, N. Melsoh, G. H. Fredrickso, B. F. Chemelka and G. D. Stucky, Science, 279 (1998) 548. [4] S. Che, Z. Liu, T. Ohsuna, K. Sakamoto, O. Terasaki and T. Tatsumi, Nature, 429 (2004) 281. [5] S. R. Zhai, Y. Zhang, X. Shi, D. Wu, Y. Sun, Y. Shan and M. He, Catal. Lett., 93 (2004) 225. [6] Q. Y. Liu, W. L. Wu, J. Wang, X. Q. Ren and Y. R. Wang, Micropor. Mesopor. Mater., 76(2004)51. [7] K. Suzuki, K. Ikari and H. Imai, J. Am. Chem. Soc, 126 (2004) 462. [8] C. Boissiere, M. A. U. Martine, M. Tokumoto, A. Larbot and E. Pouzet, Chem. Mater., 15(2003)509. [9] X. S. Zhao, G. Q. Lu and C. Song, J. Mol. Catal. A: Chem, 191 (2003) 67.

Recent Progress in Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

811 811

Adsorption desulfurization from gasoline by silver loaded on mesoporous aluminum oxide Wenzhong Shenab*, Xiangping Yanga, Qingjie Guoa, Yihong Liua and Yanru Songa a

State Key Laboratory of Heavy Oil, China University of Petroleum, Dongying, 257061, P. R. China b Key Laboratory of Carbon Material, Chinese Academy Sciences, Institute of Coal Chemistry, Taiyuan, Shanxi, 030001, P. R. China

1. Introduction Deep desurization has become more difficult because the lower and lower limit of sulfur content in fuel products is required by regulatory specifications, and the higher and higher sulfur contents is in the crude oils. The hydrodesulfurization (HDS) process is an efficient method of removing thiols, sulfides, and disulfides but it is not adequate for the removal of aromatic thiophenes and their derivatives. The remained sulfur compounds after the HDS process are thiophene, benzothiophene, and so on. The sulfide content could be higher than several hundred ppm even after hydrodesulfurization. The adsorption is a promising method to reach deep desulfurization due to the adjustable pore structure and alterable surface function groups of adsorbents. The adsorption mechanism is based on the property of sulfur compounds in fuel. Adsorption desulfurization could be improved to remove the thiophene compounds if chemical force is taken place between the molecules containing thiophene rings and adsorbents and the force is also easy to rupture[l-4]. The porous materials are always selected as the adsorbents, and some metals compounds or ions were impregnated to improve its adsorption properties [4, 5]. Thiophenic sulfur compounds could be separed from aromatic compounds based on n -complexation using Cu- and Ag-exchanged Y zeolites [6]. In this work, the HDS and FCC gasoline were selected as the objects; the adsorption desulfurization of mesoporous aluminum oxide loaded with silver/oxide was investigated. The adsorption property was compared and discussed.

812

2. Experimental Section The mesoporous aluminum oxide was sythesized at lab and nominated as A-0; it was impregnated with the aqueous solution of silver nitrate by equal volume for 4 h. The loaded molar amount of silver nitrates was 0.006 and 0.030 on a gram aluminum oxide and were denoted as A-1 and A-5, respectively. The samples were then dried at 353 K for overnight and heated at 473 K for 60 min under nitrogen flow. The structures of samples were characterized by nitrogen adsorption, XRD patterns, FTIR spectra and SEM images. 0.25 g A-0, A-1 and A-5 were filled in a glass column to investigate its adsorption capacity for sulfides from HDS and FCC gasoline, respectively. The gasoline flew from top at 1 milliliter per minute; the total treated amount was 10 milliliter. The sulfur contents and kinds in HDS and FCC gasoline were determined using a microcoulomb sulfur analyzer and Hewlett-Packard 5890 series II gas chromatograph. 3. Results and Discussion 1 .8 1 .6

400

A -1 A -5 A -0

1 .4 1 .2

3

dV/dlog(D) (cm /g)

3

Volume adsorbed (cm /g)

The primary structure parameters of samples were listed in Table 1. The micropore volume markedly decreased with the sliver nitrate loaded amount. The nitrogen adsorption-desorption isotherms and pore size distributions were drawn in Fig. 1; the mesopore size of samples mainly ranged from 5 nm to 20 nm. The silver ion could enter the micropore and blocked it after heating treatment, so the micropore volume decreased with silver nitrate loading amount; the micropore could be total blocked for A-5.

300

200

1 .0 0 .8 0 .6 0 .4 0 .2 0 .0 1

10

100

100

P o re s iz e ( n m )

0 0 .0

0 .2

0 .4

0 .6

0 .8

1 .0

P /P 0

Fig. 1 the nitrogen adsorption-desorption isotherms and pore size distributions of samoles (inset)

Table 1: the structure parameters of adsorbents and its adsorption of organosulfur Sample

SBET

Pore volume (cm3/g)

2

(m /g)

'total

v v

V • v meso

micro

HDS (35Oppm S)

FCC (843ppm S)

(ppm)

Adsored amount(mg/g)

(ppm)

Adsored amount(mg/g)

S Residue

" Residue

A-0

161

0.672

0.668

0.003

336

0.56

778

2.7

A-1

138

0.569

0.567

0.001

234

4.64

675

6.72

A-5

120

0.509

0.509

—

141

8.36

441

16.08

The XRD patterns of samples, which were heated at 473 K for 60 min, were shown in Fig. 2. The characteristic peaks of aluminum oxide were at 66.73, 45.9,

d -

>•

'•

CD

s-

1.

A-5

V>

.A

A-1 A-0 A-0

00

<**<***i~*ir

10 10

20 20

30 30

V \~~?J*J 40 40

50 50

60 60

r""""*" 70 70

80 80

22 Theta Theta (degree) (degree)

Fig. 2 the XRD patterns of samples

Absorptivity (%)

39.38, 37.53, 32.59 and 19.58° relating to the (440), (400), (222), (311), (220) and (111) surfaces. Thermal decomposition of silver nitrate impregnated on mesopore aluminum oxide leads to the formation of silver oxides (Ag2O or Ag2O2). Both the metal oxides are decomposed at fairly low temperatures (300°C for Ag2O, and >100°C for Ag2O2). The character peaks of silver were appeared at 38.02°, 44.31°, 64.38° and 77.43°, which were relating with the (111), (200), (220) and (311) surface. The higher silver was loaded, the higher peak was. This indicated that the silver particles aggregated and grew during the heat treatment, and these silver/oxide particle would be responsible for the adsorption behavior. The FTIR spectra of A-5 were shown in Fig. 3. The A-5 before and after adsorption were no difference except at 1392 cm"1, this suggested that the interaction between adsorbed sulfides and silver was weak and the sulfides would be desorbed during the analysis processing; this implys that the adsorbent is easy to be regenerated. The SEM images of samples were shown in Fig. 4. The surface of A-0 was smoother than the others. The surface of A-5 was crude and with some holes; the aggregated silver particles appeared on the surfaces. The surface of A-5 was smoother after adsorption, this showed that the silver/oxide particles were interacted with the adsorbed sulfides and the silver/oxide particles immigrated and dispersed well. After regeneration by treated at 473 K, the adsorption capacity of A-5 didn't decrease.

R elatively iml ntenISI sity ((a. a.u.) Relati

813

e-

o

(0

<

u u

After adsorption \

/

Before Before adsorption \

/

500 1000 1500 2000 2500 3000 3500 4000 10001500 -1 Wave number number (cm (cm-1)

Fig. 3 the FT-IR spectra of A-5 before and after adsorotion of surfide

Fig. 4. The SEM images of samples, (a) A0; (b) A-5 before adsorption and (c) A-5 after adsorption

814 814

250

S 350ppm

S 141 ppm

,1

i 50.1

Hr

4700-

5

»

#

ji

raintues

S 843ppm

S 441ppm

300

100-

11

1 11

LJ

ikk.

i, i

1,

Fig. 5. The gas gas chromatograph of FCC and HDS gasoline before and after adsorption by A-5

The adsorption capacities of sulfides from HDS and FCC gasoline by samples were also listed in Table 1. The adsorption capacity of sulfides could be significantly improved when the silver was loaded on the aluminum oxide; this indicated that the silver/oxide could form interaction with sulfide in gasoline. The A-5 displayed better adsorption capacity; its adsorption capacities were 8.36 mg/g and 16.08 mg/g for HDS and FCC gasoline, respectively. The gas chromatograph of HDS and FCC gasoline before and after adsorption by A5 were drawn in Fig. 5, which indicated that the adsorption capacity and desulfurization degree were not equal for the same adsorbent due to the difference of sulfide type and its content; at same time, the adsorption selectivity was poor. Adsorption desulfurization could occur due to a n complexation between the silver atom (Is22s22p63s23p63dio4s24p64dio5s1) and the thiophenic aromatic rings. Through ;r-complexation mechanism, the silver atom can form the usual a bonds with its empty s orbitals and its d orbitals can back-donate electron density to the antibonding {n*) orbitals of the thiophene rings [5, 6]. 4. Conclusion The mesopore aluminum oxide could be used as support to impregnate with silver nitrate; after heating at 473 K, it could efficiently remove the sulfides from gasoline by adsorption and the removal percent was near 60%. The adsorption capacities of A-5 for HDS and FCC gasoline were 8.36 mg/g and 16.08 mg/g, respectively. The silver could former and ;rbond with thiophene ring but the adsoprtion selectivity was relatively poor. The higher silver contained was, the higher adsorption capacity was.

815

5. References [1] A. J. Hemandez-Maldonado and R. T. Yang, Ind. Eng. Chem. Res., 43 (2004) 1081. [2] S. Velu, X. L. Ma and C. S. Song, Ind. Eng. Chem. Res., 42 (2003) 5293. [3] A. J. Hemandez-Maldonado, S. D. Stamatis, R. T. Yang, A. Z. He and W. Cannella, Ind. Eng. Chem. Res., 43 (2004) 769. [4] X. L. Ma, S. Velu, J. H. Kim and C. S. Song, Appl. Catal. B Environ., 56 (2005) 137. [5] P. Jeevanandam, K. J. Klabunde and S. H. Tetzler, Micropor. Mesopor. Mater., 79 (2005) 101. [6] R. T. Yang, A. J. Hemandez-Maldonado and F. H. Yang, Science, 301 (2003) 79.

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Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

817 817

Proton conduction of ordered mesoporous silicamethanesulfonic acid hybrids Yonggang Jin, Zhi Ping Xu, Shizhang Qiao, Joao C. Diniz da Costa and G. Q. Max Lu* ARC Centre for Functional Nanomaterials, School of Engineering and Australia Institute of Bioengineering and Nanotechnology, The University of Queensland, Brisbane, QLD 4072, Australia.

In this paper we report the thermal stability and the proton conduction of mesoporous silica-methanesulfonic acid hybrids. Two mesoporous silicas, i.e. SBA-15 and MCM-41, were pore-filled with methanesulfonic acid, resulting in hybrids with the proton conductivity comparable with that of Nafion in a wide range of relative humidity (RH) and at temperatures of 25-100°C. 1. Introduction Proton exchange membrane (PEM) fuel cells have attracted considerable attention due to their potential application in clean and efficient energy systems [1]. PEM, the core component of fuel cells, is generally composed of perfluorosulfonic acid polymers, such as Nafion. However, perflurosulfonic acid polymers are expensive even though their cost has been reduced lately. Further, these polymers have operational limitations for temperatures above 100°C. Therefore, search for cheap proton conductors with suitable proton conductivity and thermal stability is much desirable in fuel cell technology. In this connection, ordered mesoporous silicas (MCM-41 and SBA-15), with cylindrical mesopores and a large pore volume, were chosen as the matrix of proton conductors and made into hybrid proton-conducting materials via pore-filling with a protonic acid in this study. Simultaneously, the uniform and nano-sized pores are deemed to effectively anchor the acid and water at a low relative humidity via the capillary effect, in particular at high operating temperatures.

818

2. Experimental Section Two ordered mesoporous silica samples with SBA-15-type and MCM-41-type structures were prepared with the methods described elsewhere [2,3]. The surfactant in SBA-15 was removed by refluxing in ethanol for 8 hours in order to attain a large pore size while the surfactant in MCM-41 was burnt out at 550°C for 4 hours. Methanesulfonic acid (MSA, 99.5%) was filled into surfactant-removed SBA-15 and MCM-41 pores by adding 1.0 mL of MSA into 1.0 g of each material and homogenously mixing with a vortex mixer for 30 minutes. The powder X-ray diffraction (XRD) tests were carried out on a Bruker D8 Advacned diffractometer with Cu-Ka radiation. Nitrogen sorption isotherms were measured with a Quardrasorb RI adsorption apparatus. Thermogravimetric analysis (TGA) was performed using a Shimadzu TGA 50H at a heating-rate of 5°C/min under nitrogen atmosphere. Proton conductivity of the hybrids was tested using an impedance analyzer (Solartron SI 1260) in a frequency range of 1MHz to lOHz. Prior to each test, the powder sample was pressed into a pellet and then sandwiched between gold electrodes enclosed by a chamber, in which both temperature and humidity were well controlled to equilibrate the pellet at various testing conditions. 3. Results and Discussion The ordered framework structure of surfactant-removed SBA-15 and MCM41 is confirmed by XRD patterns as shown in Fig. 1. Three diffraction peaks 7 are observed for both samples, which J can be indexed as 100, 110 and 200 § reflections of a 2-D hexagonal structure (p6mm). The N2 sorption isotherm of calcined SBA-15 shows a type IV curve with an H] hysteresis loop, characteristic of mesoporous materials with 1-D 26 0 cylindrical channels (Fig. 2a). In comFig. 1. XRD patterns of surfactantpareson, the isotherm of MCM-41 moves removed SBA-15 and MCM-41. the sudden increase in adsorption to a lower relative pressure of 0.25-0.35 (Fig. 2b), implying the existence of smaller pores. The relevant structural and pore parameters are summarized in Table 1. Therefore, two highly ordered mesoporous silicas with uniform pore size were successfully obtained.

819 Table 1. Structural and pore parameters of surfactant-removed SBA-15 and MCM-41

Unit cell a (nm) 11.9 4.4

^100

Samples

(nm) 10.3 3.8

SBA-15 MCM-41

BET (m2/g) 712 983

BJH pore diameter (nm) 8.57 2.61

Pore volume (cm3/g) 1.04 0.76

600

1000

3

0.6 0.4 0.2 0.0

400

5

10

15

20

25

30

35

40

Pore diameter (nm)

200

0 0.0

0.2

0.4

0.6

0.8 0.8

1.0

(b) 400 1.8 1.6

200

3

0.8

Pore volume (cm STP/g/nm)

600

(a)

1.0

Volume adsorbed (cm STP/g)

3

Pore volume (cm STP/g/nm)

800

3

Volume adsorbed (cm STP/g)

1.2

1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 5

10

15

20

25

30

35

40

Pore diameter (nm)

0 0.0

0.2

0.4

0.6

0.8

1.0

Relative pressure pressure P/P P/P0 Relative

Relative pressure pressure P/P P/P 0 Relative

Fig. 2. N2 sorption isotherms of surfactant-removed SBA-15 (a) and MCM-41 (b). The inset shows the corresponding pore size distribution calculated using BJH model from the adsorption branch.

DrTG

As shown in Fig. 3 for differential TGA (DrTG), dehydration occurs at ~100°C while the major weight loss occurs at 200-250°C that is predominantly due to the evaporation of MSA. Very interestingly, SBA-15 hybrid t SBA-15 undergoes a single evapo-ration event at 217°C while MCM-41 hybrid involves two MCM-41 228 steps of the evaporation at 208 and 228°C, 217 respectively. It is our suggestion that the first 208 evaporation is responsible for MSA outside 0 100 200 300 400 the pores and the second one for that within Temperature ((°C) C) the pores in the case of MCM-41 hybrid since its pore volume is only 0.76 cm3/g. The Fig. 3. First derivative of the TGA of capillary force in this case increases the temperature of MSA evaporation by 20°C. However, the larger pores (8.57 vs. 2.61 nm) in SBA-15 produce a weaker capillary force, and make the evaporation of MSA from SBA-15 pores easier (by 10°C lower) than from MCM-41 pores. Fig. 4a depicts proton conductivity of these two hybrids changing with RH at 25°C. Proton conductivity increased with humidity, from 0.002 (SBA-15) and 0.003 S/cm (MCM-41) at 15% RH to 0.084 (SBA-15) and 0.077 S/cm (MCM-41) at 100% RH. It is noted that their conductivity changes by less than two orders of magnitude in 15-100% RH, revealing that the proton conduction of these hybrids is much less dependent on hydration than that of Nafion, especially for RH above 45%. At 100% RH the conductivity of Nafion is generally between 0.01-0.1 S/cm o

820

0.1

(a)

S B A -15, E a =38.3 kJ/m ol

(b)

M C M -41, E a = 29.7 kJ/m ol

-1

log10σ (S/cm)

Proton conductivity, σ (S/cm)

and drops by 3-4 orders of magnitude in this humidity range [4]. The difference may be attributed to the peculiar structure of the hybrids, in which the cylindrical nanopores could retain more water molecules at low RH due to the capillary effect. In addition, SBA-15 hybrid exhibits a lower conductivity at RH below 45% while a higher conductivity at RH above 45% in comparison with MCM-41 hybrid. This may result from the capillary effect and protonic transport in differently sized pores. MCM-41 has smaller pores so that it can adsorb more water at a lower RH and thus shows a higher conductivity than SBA-15. However, at a higher RH, the strong diffusion restriction of proton ions (e.g. H5O2+ and H9O4+) in smaller pores of MCM-41 could induce a smaller conductivity than SBA-15 [5]. Arrhenius plots of the proton conductivity vs. temperature at 30% RH are presented in Fig. 4b. There is a linear relationship in 25-100°C, giving the activation energy of 38.3 (SBA-15) and 29.7 kJ/mol (MCM-41), respectively. The smaller activation energy in MCM-41 hybrid means a lower energy hurdle for the proton conduction in the low RH range due to more capillary-condensed water in the pores. Moreover, the hybrids show high proton conductivity of at high temperature and low humidity, at values of 0.066 and 0.083 S/cm at 100°C and 30% RH, respectively for SBA-15 and MCM-41 hybrid.

0.01 S B A -15 SBA-15 MCM-41 M C M -41

1E -3

-2

-3 15

30

45

60

75

R e lative hu m idity (% Relative humidity (%))

90

105

2.6

2.8

3.0

3.2

3.4

(1/K) 11000/T 00 0/T (1 /K )

Fig. 4. Proton conductivity dependence of pore-filled SBA-15 and MCM-41 on RH at 25°C (a), and on temperature at 30% RH (b).

4. Conclusion In conclusion, the hybrids exhibit high proton conductivity at temperatures of 25-100°C in a wide range of humidity. The conductivity is dependent upon not only the RH & temperature, but also the pore size of the silica matrix. 5. References [1] [2] [3] [4] [5]

G. Alberti and M. Casciola, Solid State Ionics, 145 (2001) 3. C. Z. Yu, J. Fan, B.Z. Tian, D.Y. Zhao and G.D. Stuky, Adv. Mater., 14 (2002) 1742. X. S. Zhao, G. Q. Lu, G. J. Millar and X. Li, Catal. Lett., 38 (1996) 33. K. A. Mauritz and R. B. Moore, Chem. Rev., 104 (2004) 4535. Y. Daiko, T. Kasuga and M. Nogami, Micropor. Mesopor. Mater., 69 (2004) 149.

Mesostructured Materials Recent Progress in Mesostructured D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Published by Elsevier B.V.

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Oligodeoxynucleotide molecule delivery by organically modified SBA-15 mesoporous materials Xi-chuan Cao abc Zhuo-qi Zhangb, Jian R. Lu,b Michael W. Anderson0 "School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou 221009, China Biological Physics Group, School of Physics and Astronomy, The University of Manchester, Sackville Street Building, Manchester M60 1QD, UK c Centre for Microporous Materials, School of Chemistry, The University of Manchester, Oxford Road Manchester Ml 3 9LP, UK

SBA-15 modified with 3-aminopropyltrimethoxylsilane (APTS) and dimethyl- octadecyl[3-(trimethoxyl) propyl]ammonium chloride (DOTPA) are candidate vehicles for loading and controlled release of oligodeoxynucleotide (ODN) molecules. Crude ODN from herring sperm was selected as a model drug and loaded onto the modified SBA-15. It is shown that the loading capacity and release behavior of these ODN drugs are strongly dependent on the surface properties of the mesoporous materials and the pH of the loading buffer. 1. Introduction Highly ordered large pore mesoporous silica such as SBA-15[1, 2] is an ideal candidate as a host for bio-molecules. Variation of the synthesis and postmodification conditions enables tailoring of their pore diameters and their internal surface functionalization for encapsulation of a variety of amino acids, proteins, enzymes, and other important biological molecules such as some oligodeoxynucleotide molecules. Wright and coworkers [3] have shown, for instance, that trypsin immobilized on SBA-15 is superior compared to MCM41 [4, 5] for the hydrolysis of N-a-benzoyl-DL-arginin-4-nitroaniline. It was shown that the larger pore diameter of SBA-15 is advantageous in terms of substrate diffusion and pore blocking. The immobilization on SBA-15 of different proteins and enzymes, for instance, albumin, cytochrome, trypsin, amylase, papain and chloroperoxidase[6-12], for drug delivery and medical applications have also been recently investigated. In our work crude ODN from

822

herring sperm was selected as a model drug and loaded onto SBA-15 modified with APTS and DOTPA. We describe the controlled release via surface functionalization, concentration and pH stimulation. 2. Experimental section The synthesis of SBA-15 was according to the literature. In a typical synthesis 4 g of PI23 (polyethylene oxide/polypropylene oxide block copolymer) was dispersed in 30 g of pure water and 120 ml 2 M HCl solution and stirred for 5 hrs, thereafter 9.5 g of tetraethylorthosilicate was added to the homogeneous solution with stirring. The resulting gel was aged at 40 °C for 24 hrs and finally heated to 100°C for 24 hrs. The resulting material was collected by filtration then air dried at room temperature overnight. The powder was calcined in the oven to 55O°C at one degree per minute temperature ramp then kept at 550"C for 5 hrs. The functionalization of nanoporous silicate SBA-15 was carried out by treating 2g of SBA-15 with 2% (v/v) APTS or TPODA solution in dry toluene (40ml) and the resulting solution was heated at reflux under an inert nitrogen atmosphere for 20h. The material was collected by filtration, washed with a large quantity of acetone, dichloromethane and ether, and then put into a 250ml round bottom flask with additional 150ml toluene Solex extraction for 18hr. 29Si MASNMR measurements were recorded on a solid-state Bruker DSX-400 spectrometer. For loading and release, ODN was diluted in ether distilled water or 0.1 mol/L HAc/NaA or PBS buffer solution with variable pH value. The concentration of the ODN was determined using a GENESYS 6 spectrophotometer. 3. Results and discussion The spectrum from the bare SBA-15 sample shows a very wide a peak centered around -105 ppm. This broad peak arises from three b types of silica atoms: Q4 at <S = -114 ppm, Q3 at 8 = -101 ppm, and Q2 at c 8 = -93 ppm, where Qn stands for Si(OSi)n(OH)4.n (where n = 2-4, as -30 -70 -110 -150 n equals the number of bridging ppm oxygen (-OSi) bonded to the central Si, 4-n equals the number of Fig.l 29Si NMR spectra of a: pure SBA-15; b: OH groups bonded to the central Si). SBA-15 modified by APTS and c: SBA-15 In comparison with the bare SBAmodified by DOTPA 15 spectrum the coating of APTS onto the porous SBA-15 reduces the intensity of the broad peak centered around -105 ppm, but a new peak occurs around -70 ppm, indicating the formation of

823

Cu mu lative release (mg /g )

Loading capacity (mg/g)

new Si-O-C bonds and hence successful chemical grafting. If we similarly use Tm to denote the new bonds, where Tm stands for RSi(OSi)m(OH)3.m (m = 1-3), T3 at S =-70 ppm, T2 at 8 = -60 ppm and T! at 5 = -50 ppm. Coating of DPOTA causes a further decrease in the intensity of the broad peak around -110 ppm, but the rise of the new peak around -70 ppm is substantially lower. This apparent inconsistency would indicate that whilst chemical grafting has indeed occurred, there was not straightforward stoichiometric chemistry between different coating agents used, although, if it is assumed that for a given coating species, the relative decrease in the integrated intensity of Qn leads to equivalent increase in Tm, then Tm/(Tm + Qn) would be indicative of the extent of surface coverage. This value was found to 200 about 0.25 for APTS and 0.1 for TPODA. Whilst the difference 160 indicates that the APTS coats better 120 than TPODA as expected, the absolute values of the actual surface 80 coverage for the two coating agents 40 should be much greater. Figure 2 shows the ODN 0 0 24 48 72 96 120 adsorption onto the APTS modified Time (h) SBA-15 to demonstrate the effect of solution pH. The pH range studied Fig.2 ODN Adsorption of APTS modified varied from pH = 3.5 to 9.5. The main SBA-15 atpH: • : 3.5, H :4.5, A:8.5, * 9.5 observation from this diagram is that as pH becomes acidic the adsorbed 150 amount increases. At the highest pH 120 of 9.5 the equilibrated amount of 90 adsorption was only 16 mg/g whereas 60 as the pH was lowered to 4.5 the adsorbed amount increased to 145 30 mg/g. However, as the pH was at the 0 lowest value of 3.5, the adsorbed 0 24 48 72 96 120 Time (hrs) amount did not show any further increase but a slight decrease to Fig.3 ODN release from APTS modified about 120 mg/g. Similar studies have SBA-15 • : 175 mg/g loading amount with been undertaken using TPODA PBS (pH=7.5) buffer eluting. A: 145 mg/g loading amount with PBS (pH=7.5) buffer modified SB A-15 under the same pH wash. *: 116 mg/g loading amount with values. PBS buffer wash, • : 175 mg/g loading It can be seen from Figure 3 that amount ddH2O wash, x: 145 mg/g loading upon increasing the loading capacity amount with PBS (pH=7.5) buffer eluting, the release rate also increases under •:145 mg/g loading amount ddH2O wash. the same solution conditions. This is also reasonable because as the surface adsorbed amount increases the direct interaction incorporating the binding sites between the surface and ODNs is

824

reduced although direct contact between neighboring ODNs also increase. The latter does not seem to be significant in this case. In all cases the absorption reaches near equilibrium after 24h. Neither strong acid nor strong base is preferable for ODN loading. The adsorption behaviour is, however, very sensitive to pH control with optimum loading near to pH 3.5. At this value the silica surface is close to neutral and the functional group positively charged resulting in a favorable interaction with the negatively charged ODN. Release is also pH sensitive in the opposite sense to the loading. However, we further demonstrate that components in the eluting media can also facilitate the process. In the PBS solution anions such as H2PO4 , HPO42" are able to replace ODN from the surface with the consequence of enhanced elution compared to ddH2O. In this later system, although some hydroxyl anions come from the equilibrium Si_(CH2)3NH2 + H2O <->• Si(CH2)3NH2 + OH this does not generate sufficient OH to replace the ODN from the amino groups. TPODA showed much less pronounced adsorption compared with APTS. 4. Conclusion Nanoporous SBA-15 silicates have been successfully synthesized and modified with APTS and DPOTA characterized and confirmed subsequently by XRD, 29Si MAS NMR and N2 adsorption-desorption works. Loading and release was examined and comparison made between the bare SBA-15 and the two surface modified versions. There was little loading of ODN into the bare SBA-15 as expected. The APTS modified system produced a high level of ODN loading owing to the electrostatic attraction between the positively charged amine groups and negatively charged ODN. However, the exact amount of loading showed a strong response to pH owing to the variation of surface charge density of the ATPS surface with pH. The same interaction is also responsible for the pH sensitive change in the release profile observed. In contrast, the pH response effect did not occur on the DPOTA modified surface. 5. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12]

D. Y. Zhao, J. L. Feng and Q. Huo et al., Science 279 (1998) 548. D. Zhao, Q. Huo and J. Feng et al, J. Am. Chem. Soc. 120 (1998) 6024. H. H. P.Yiu and T. Botting et al, Phys. Chem. Chem. Phys. 3(2001)2983. C. T. Kresge and M. E. Leonowicz et al. Nature 359(1992)710. J. S. Beck, J. C. Vartuli and W. J. Roth et al, J. Am. Chem. Soc. 114 (1992) 10834. H. Takahashi, B. Li and T. Sasaki et al, Chem. Mater. 12 (2000) 3301. H. Takahashi, B. Li and T. Sasaki et al. Micro. Meso. Mater. 44-45 (2001) 755. J. Fan, W.Shui and P. Yang et al, Chem.--A Euro. J. 11 (2005) 5391. J. Yang and A. Daehler et al, J. Stud. Surf. Sci. and Catal. 146 (2003) 775. P. H. Pandya and R. Vet Jasra et al. Micro. Meso. Mater. 77 (2005) 67. Yong-Jin Han and Jordan T. Watson et al, J. Mol. Catal. B: En. 17 (2002) 1. Amit, K.; Lei, J.; Panagiotis, S.; Neville, P. J. Chromato, A 119 (2005) 1069.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

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Release of guest molecules from modified mesoporous silica Magdalena Stempniewicz,ab Michael Rohwerderb and Frank Marlowa* "Max-Planck Institutfur Kohlenforschung, Kaiser-Wilhelm-Pl. 1, 45470 Miilheim/Ruhr, Germany, * h Max-Planck Institut fur Eisenforschung, Max-Planck-Str. 1, 40237 Diisseldorf Germany

The mechanisms and kinetics of release of guest molecules from mesoporus silica were studied on SBA-3-like fibers. Rhodamine 6G was used as guest molecule. Transport through silica walls (cross-wall transport) has been identified as the release rate determining process. The analysis of experimental release curves delivered the value of the effective diffusion coefficient and indicated a barrier at the external fiber surface. Two different types of surface modification were applied to the fibers and their effect on the release kinetics was studied. 1. Introduction Release kinetics of guest molecules from matrices and capsules is a topic of considerable interest for many applications. Since also mesoporous silica has been proposed as a matrix for drug delivery we study the mechanisms of transport of the guest molecules through the mesoporous system and the factors determining the rate of their release. It is recognized that interactions between the guest molecules and the host matrix as well as the geometry of the releasing device influence the kinetics of release. This kinetics can also be substantially affected by the structural parameters of the matrix. Usually, guest molecules are transported within the mesopores. This pore transport makes the main contribution to the observed release [1, 2]. However, in many systems transport across the silica walls is possible due to the presence of microporosity [3,4 ]. In a system of loosely interconnected mesopores the pore tortuosity is the determinant factor and cross-wall transport is not influencing the release behavior. But it is different in systems with oriented

826

pores especially if the concentration gradient is perpendicular to the direction of the pores. This is the case for some SBA-3-like systems with circular symmetry of mesopores [5]. Such a symmetry combined with the presence of microporosity should lead to slow release, limited by the cross-wall transport. For this reason SBA-3-like fibers are in the focus of our study. In this study we measure the average release from separated particles dispersed in a solvent. Analysis of the release curves delivers information on both the intraparticle diffusion coefficient and the transport through the external particle surface. Additionally, we attempt to tune the kinetics of release by modification of the external surface of the um-size fibers without changing the diffusion within the fiber. The applied treatments account for deposition of a thin layer and a moderate destruction of the native fiber surface. 2. Experimental Section Mesoporous silica fibers of an SBA-3-type synthesis were made through the acidic route using CTAB (cetyltrimethylammonium bromide) as a structure directing agent and TBOS (tetrabutoxysilane) as a silica source [3,4]. Our release probe, rhodamine 6G, was incorporated into the particles during their synthesis so that no calcinations or further loading were required. Modification of the external fiber surface was achieved by a short-time treatment (10 sec) by either H2O, NaOH (pH = 10.7) or a solution of waterglass (WG, pH = 10.7). Detailed description of the treatments will be discussed in a forthcoming work [8]. The morphology of the sample was examined under light microscopy and scanning electron microscopy (SEM). The internal structure was characterized by X-Ray diffraction (XRD) and transmission electron microscopy (TEM) showing only slight observable changes. Release curves were measured using conventional UV-Vis spectroscopy. A small portion of particles (0.1 mg) was brought into a spectroscopic cuvette and filled up with water. To assure homogeneity of the sample the experiment is conducted under continuous stirring. For a chosen time interval, an extinction curve is collected in the spectral range specific to rhodamine (450-570 nm). The information about the absorption due to the released dye is extracted numerically from each distinct extinction curve. A release curve is constructed using the corrected absorption data. 3. Results and Discussion The microscopic observation of release shows that individual fibers loose the dye homogenously without dye depletion at the fiber ends. This homogeneity indicates that the molecules are transported in a radial direction rather than along the axis of symmetry. Considering the known circular arrangement of the

827

pores such a radically symmetric diffusion of guest molecules is only possible when mediated by the pore walls (cross-wall transport). Therefore, we have to consider a release model based on the solution of diffusion equation in cylinder geometry [7]. We extend the model to include the inhomogeneity of the sample. There can be a certain percentage of fibers with a defect external surface leading to faster release. They should be characterized by the same intraparticle diffusion coefficient so that the model is represented as a sum of releases from the two types of fibers: 4a 2

where D^ , R, A and a are the effective intraparticle diffusion coefficient, the representative fiber diameter, the fraction of fibers having surface barrier and the barrier parameter, respectively. The qn and sn are the roots of the characteristic equations: = Q> respectively, where m is a Bessel 3\(
0.8 Parent Parent H22O-modified H

E/E

0.6 * n

0.4

NaOH-modified NaOH-modified WG-modified WG-modified

0.2

0 0

0.5

1.5 1.5

1.5 1.5

2

tt /hours Figure 1. Experimental release curves for the parent, H 2 O-, NaOH- and WG-treated fibers fitted with the release model (1).

The time needed to release l/e of the total releasable amount, 4, is considerably prolongated by our modifications. Surprisingly, already the apparently immune H2O-treatment results in a modified release. The fitted

828

parameters reveal that the effective diffusion coefficients are similar for all the samples and that the modified release behavior results from the variation of the parameter a and the fraction A . The dimensionless parameter a originates from mass transfer resistance at the external particle surface, with lower values indicating a stronger barrier. The barrier is ascribed to blocking of micropores related to surface degradation or to the formation of a coating layer. It should be noted that already the parent sample shows a significant fraction of blocked micropores, which arise either in the synthesis or during drying. Table 1. Parameters fitted to the model (1) for R = 4 nm.

Sample Parent H2O-treated NaOH-treated WG-treated

te

De{f [cm /s]

a [-]

A [-]

7 min 24 min 39 min 6h

6.7- 10"" 1.8- 10"" 1.7- 10"" 2.3- 10"11

0L43 0.67 0.49 (H3

0Tl6 0.17 0.27 0.95

This result shows that the kinetics of release can be tuned in either a fine or a coarse manner. The aqueous treatments (H2O and NaOH) result in release time variations below an order of magnitude. On the other hand the WG-treatment effectively slows down the release by at least one order of magnitude. TEM examination confirms that the fine tuning of the release kinetics in the case of H2O- and NaOH-treatments is achieved without visible destruction of the internal silica structure but possibly with slight modifications of the external fiber surface. In the case of WG-treatment the significant slowdown of release results from deposition of few-nm thin layer of silica. 4. Acknowledgement The International Max-Planck Research School for Surface and Interface Engineering in Advanced Materials (SurMat) is kindly acknowledged for financial support. 5. References [1] R. Bujalski and F. F. Cantwell, Langmuir, 17 (2001) 7710, [2] T. Sekine and K. Nakatani, Chem. Lett., 33 (2004) 600, [3] F. Chen, X.-J. Xu, S. Shen, S. Kawi and K. Hidajat, Microporous Mesoporous Mater., 75(2004)231, [4] F. Kleitz, W. Schmidt and F. Schuth, Microporous Mesoporous Mater., 65 (2003) 1, [5] F. Marlow, B. Spliethoff, B. Tesche and D. Zhao, Adv. Mater., 12 (2000) 961, [6] Q. Huo, D. Zhao, J. Feng, K. Weston, S. Buratto, G. D. Stucky, S. Schacht and F. Schuth, Adv. Mater., 9 (1997) 974, [7] J. Crank, The Mathematics of Diffusion, Second Ed., Oxford Press (1975).8O, [8] M. Stempniewicz, M. Rohwerder and F. Marlow, Chem Phys Chem, (2006) (in press).

Recent Progress in Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

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Spherical siliceous mesocellular foam particles for high-speed size exclusion chromatography Yu Han, Su Seong Lee and Jackie Y. Ying* Institute of Bioengineering and Nanotechnology, 31 Biopolis Way, TheNanos, Singapore 138669

1. Introduction Size exclusion chromatography (SEC) is commonly used for the separation and molecular weight (MW) determination of polymers, peptides and proteins [1]. The separation mechanism in SEC is based strictly on the molecular size of the analytes with respect to the pore size of the stationary phase. SEC requires the column packing material to have narrow pore size distribution and large pore volume to achieve high selectivity and resolution in separations. This is different from interactive HPLC, whereby the separation performance is mainly dependent on the surface area and the surface property of the packing material. For high column efficiency, packing materials in SEC should be fine, uniform and spherical particles (3-20 \xm), as in the common interactive HPLC. SEC is conventionally conducted using 2—4 columns of large dimensions (7.8 mm I.D. x 300 mm) connected in series. The use of these large column banks provides sufficient pore volume to achieve high resolution and accurate MW measurement [2]. However, it requires long analysis time and significant solvent consumption. In recent years, there is increasing interest to develop high-speed SEC using a single column of small dimensions [2]. High-speed SEC would not only improve sample throughput substantially, but also greatly reduce solvent usage. Thus, it would be very useful for combinatorial polymerization studies. Moreover, small SEC columns would allow for rapid analysis even under a low flow rate, which is very important for on-line SECmass spectrometry applications [2]. Herein, we describe a simple method that enables the synthesis of micron-sized, uniform and spherical siliceous mesocellular foam (MCF) particles with tuneable pore sizes. These MCF beads were demonstrated as an excellent packing material for high-speed SEC applications.

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2. Experimental Section Three spherical MCF samples were synthesized by modifying the conventional MCF synthesis. MCF-10, MCF-17 and MCF-26 were prepared with the window sizes denoted in nm. In a typical preparation of MCF-17, 4 g of triblock copolymer Pluronic PI23 (BASF) were dissolved in an acidic solution (10 ml of HC1 and 65 ml of H2O). 4 g of 1,3,5-trimethylbenzene (TMB) were then added, and the resulting solution was heated to 37-40°C with vigorous stirring for 2 h. 9.2 ml of tetraethoxysilane (TEOS) were then added and stirred for 5 min. The solution was aged at 40°C for 20 h under a quiescent condition. 46 mg of NFI4F were added, and the mixture was aged at 100°C for 24 h. The precipitate was filtered, dried and calcined in air at 900°C for 6 h. 3. Results and Discussion Conventional MCF consists of large, irregular particles (of tens of microns), and therefore, cannot be used for packing HPLC columns [3]. In contrast, our method results in spherical MCF particles with a uniform size of 3-5 [a m (Figure 1). Particle size analysis indicates a narrow size distribution centered at 5 |J.m (Figure 1), which is consistent with the SEM observation. The window size and pore volume of spherical MCF particles could be easily controlled, without affecting the particle morphology and particle size distribution (see Table 1). 7000

Particle Number / ml

6000 6000 5000 5000

4000

13

Z o

.a

I

3000 3000

1

I

2000 1000 0 11 2 2

55 10 202 0 3 300 4400 5500 660 10 0 Particle µm ) Particle diameter ((µm

Figure 1. SEM micrograph and particle size distribution of spherical MCF-17.

Three MCF samples with different window sizes were slurry-packed separately into standard HPLC columns (4.6 mm I.D. x 250 mm). Calibration curves were obtained for the three MCF columns using a series of polystyrene samples with MWs of 104 (monomer) to 7.7x105 as calibration standards and THF as the mobile phase. In the size exclusion region, all three columns showed good linearity, which was desirable for high accuracy of MW determination. This could be attributed to the narrow window size distribution

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of the MCF materials. Columns packed with MCF materials of different window sizes were applicable for the separation of different MW ranges (Table 1). High column efficiency was required to minimize the MW error due to peak broadening [2]. The relationship between the plate height (H) and linear velocity (w) for a MCF-17 column of 25 cm was studied using polystyrene standard of MW = 2980 as the solute. A minimum plate height of 50 u.m was observed at a linear velocity of 0.13 cm/s, which corresponded to a flow rate of 0.6 ml/min. The MCF-26 and MCF-10 columns also achieved their best efficiencies at a flow rate of 0.6 ml/min. Table 1. Characteristics of the spherical MCF particles.

MCF-26 MCF-17 MCF-10 MCF-26 MCF-17 MCF-10

Window Size (nm) 26.5 17.0 10.2 Vo (cmJ) b

Pore Volume (cmVg) 2.4 2.1 1.6 Vj ( c m 3 ) b

Mass of Silica per Column (g) a 0.81 0.86 1.04 V g (cm J ) b

Effective MW Range 5.8xl0 3 -1.8xl0 5 2.2x10 3 -6.9xl0 4 5.1xl0 2 -1.9xl0 4 Vi/V,(%)b

1.84 1.94 1.99

1.95 1.82 1.69

0.36 0.39 0.47

47 44 41

a

The mass of spherical MCF packed in each column (4.6 mm I.D. x 250 mm). The pore volume of the packing material (V,) in the 4.6 mm I.D. x 250 mm column was determined by multiplying the mass of the packing material in the column by its specific pore volume. The volume of the solid part of the packing material (Vg) was determined by dividing the mass of the packing material by the density of amorphous silica (2.2 g/cm3). The void volume between the particles of the stationary phase (Vo) was calculated by subtracting V; and Vg from the total column volume (Vt).

b

To determine the performance of MCF columns, a mixture of four polystyrene standards with MWs of 510, 2980, 17500 and 188000 was used as analytes. The polystyrene mixture was dissolved in THF, which was also used as the mobile phase with a flow rate of 0.5 ml/min. Figures 2(a) and 2(b) shows that the polystyrene mixture was separated effectively by MCF-26 and MCF-17 columns as four sharp, symmetric peaks, although some overlap was noted for the peaks associated with polystyrenes of 510 and 2980 MWs. In contrast, MCF-10 column could not separate the polystyrenes of 17500 and 188000 MWs well due to its small window size (Figure 2(c)). The elution profiles of the MCF columns illustrated that better resolution, especially for larger molecules, was achieved with the increase in porosity and window size. It was also notable that the MCF columns attained rapid separation with total analysis times of < 8 min. For comparison, a conventional SEC system consisting of two 7.8 mm I.D. x 300 mm columns (Styragel HR5E, Waters) connected in series was employed to separate the mixture of polystyrenes. Styragel HR5E column was selected since its packing material had similar particle size (5 |um)

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and effective molecular weight range (low-to-medium) as the spherical MCF particles. Figure 2(d) shows that it took over 20 min to elute all the analytes from the two commercial columns even at the relatively higher flow rate of 1.0 ml/min. In comparison, the single, compact MCF column set increased sample throughput by 2.5 times, while reducing solvent consumption by 80%. Notably, the reduced analysis time and solvent usage were obtained without compromising the separation resolution.

18 K 17K 5K 2.9K

I W IS A

(d) 2 Retention Time (min)

4

6

8

1Q

12

14

16

1 Solvent peak

v-= 20

22

24

Retention Time (min)

Figure 2. Separation of polystyrene samples with MWs of 510,2980, 17500 and 188000 by a single column of (a) MCF-26, (b) MCF-17 and (c) MCF-10, and (d) by two Waters HR5E columns connected in series.

4. Conclusion Spherical siliceous mesocellular foam (MCF) particles with tuneable window sizes were successfully synthesized and used as packing material for size exclusion chromatography applications. Compared to a conventional twocolumn SEC system, a single, smaller MCF column could achieve similarly high resolution with significantly reduced analysis time and solvent consumption. 5. References [1] W. W. Yau, J. J. Kirkland and D. D. Bly, Modern Size Exclusion Chromatography; Wiley, New York, (1979). [2] H. G. Barth, LC-GC Europe 16 (2003) 46. [3] P. Schmidt-Winkel, W. W. Lukens, Jr., P. Yang, D. I. Margolese, J. S. Lettow, J. Y. Ying and G. D. Stucky, Chem. Mater., 12 (2000) 68 Figure 2. Separation of polystyrene samples with MWs of 510,2980, 17500 and 188000 by a single column of (a) MCF-26, (b) MCF-17 and (c) MCF-10, and (d) by two Waters HR5E columns connected in series. 6.

Materials Recent Progress in Mesostructured Materials (Editors) D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 2007 Elsevier Elsevier B.V. All All rights rights reserved. reserved.

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Synthesis of meso/macroporous SBA-15 and its application to VOCs' adsorption Jisun Yuna, Joo-Il Parka, Kwang-Eun Jeonga and Son-Ki Ihma " Department of Chemical and Biomolecular Engineering, Korea Advanced Institute of Science and Technology, 373-1, Guseong-dong, Yuseong-gu, Daejeon 305-701, Korea.

1. Introduction The porous materials with well ordered and uniform pores could be applied in various fields such as catalysis, adsorption, and separation. Recently, biporous materials make interest to many researchers because of multiple benefits induced from each pore-size regime. In the case of micro/macroporous composite, Holland et al. [1] prepared structures of macroporous zeolites by filling void in polymer sphere arrays with synthesis gel. In the case of mesoporous silica with macroporous architecture, Kaliaguine and coworkers [2] synthesized mesoporous MCM-48 with macropore structure using sedimenttation-aggregation method. Ihm et al. [3] showed that well ordered macroporous skeletal MCM-41 was synthesized by a new and simpler dual-templating method. 2. Experimental Section Biporous SBA-15 was prepared by colloidal crystal templating method, where the precursor of SBA-15 was chosen as the one reported by Stucky et al. [4]. Well ordered polystyrene (PS) beads were directly added to the mixture of Pluronic 123 and 1.6 M HC1 solution. After 1 hour, the silica source, tetraethylorthosilicate (TEOS), was added in the mixture. The mixture was kept at 308 K for 24 h and subsequently at 373 K for 12 h. The precipitates were filtered, dried in an oven at 373 K, and then calcined in air at 823 K for 5 h. The adsorption isotherms of toluene and p-xylene on biporous silicate were measured with 0.2 g of adsorbent at 35°C under a flow rate of 50 cm3/min with 1000 ppm concentration. Temperature programmed desorption of the adsorbates

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was conducted from 35 to 300°C at a heating rate of 10°C /min to obtain the adsorption breakthrough curve. 3. Results and Discussion 3.1. Synthesis of meso/macroporous SBA-15 The synthesized silicate was designated as SBA15(1:2)PS, where the 1:2 is the weight ratio of Si:PS. The bead size of PSl is about 250 nm, and that of PS2 is about 500 nm. The macropore size is almost the same as the bead size. In the case of both SBA-15 and biporous SBA-15, the surface area was above 800 m2g"', the pore volume was about 1.0 cm3g"', and the diameter of mesopores was about 5nm. The characteristic XRD peaks of biporous SBA-15 were identified at the same angle as each of pure SBA-15, and the N2 adsorption isotherms curve was also similar. Not only disordering of the SBA-15 hexagonal array but also shrinking of the mesopores during the silicate formation in the interstitial space between the PS beads does not seem to be significant. The unique mesophases of SBA-15 were maintained regardless of the existence of macropores. Figure 1 (a) shows the morphology of biporous SBA-15 which is similar to that of pure SBA-15.

Fig. 1 (a) SEM images of macrostructured SBA-15 (b) TEM images of macrostructured SBA15.

In the case of macrostructured SBA-15, with the increasing the PS bead size, mesopores were introduced in a better ordering and the macroporous region became dominant (as observed with SEM). Furthermore, the interconnectedness of macropores was improved with the PS bead size. The coexistence of mesopores and macropores in biporous silicates was confirmed by TEM images as shown Figure 1 (b). It is believed that meso/macroporous silicate can be successfully synthesized without losing unique properties of each pore size regime.

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3.2. Adsorption/desorption ofVOCsfor meso/macroporous SBA-15 The adsorption and TPD (temperature programmed desorption) of toluene for macrostructured SBA-15 having the different macropore size were carried out, and the results are shown in Figure 2. In this case, not only the breakthrough curves but also TPD curves of toluene on macrostructured SBA-15 samples with different macropore size were almost the same. The existence of macropores did not influence the dynamics of adsorption and desorption. It is because the mesopore size of SBA-15 is large enough for the movement of toluene molecules, and mass transfer problems of toluene was not important any more.

/f

1

(a)

(b)

SBA-15 — SBA-15(1:2)PS1 — SBA-15(1:2)PS2

f— ^

0 0

2000

A /\ /\ \

Intensityy(A.U (A.U.)

Concentration (C/C0)

f //_-

'% s

_____^:

/ 4000

6000

8000

10000

12000

*

50

14000

100

150

,, SBA-15 SB A -15 SBA-15(1:2)PS1 SBA-15(1:2)PS2 SBA-15(1:2)PS2

200

250

300

(oC) Temp. (°C)

Time (sec)

Figure 2. (a) Adsorption isotherms of toluene at 50 STPcmVmin at 35 °C (b) TPD curve of toluene for macrostructured SBA-15 with different PS bead sizes.

With bulkier adsorbate such as p-xylene, however, the shorter breakthrough times and the steeper slope of the breakthrough curve were observed as shown in Figure 3(a). Furthermore, TPD curve like Figure 3(b) was shifted to a lower temperature region since the existence of macropores may contribute to a faster desorption of p-xylene molecules. This effect was more pronounced with the

1

(b)

Concentration (C/C0)

SBA-15 SBA-15(1:2)PS1 SBA-15(1:2)PS2

Intensity(A.U.)

(a)

SBA-15 SBA-15(1:2)PS1 SBA-15(1:2)PS2

0 0

5000

10000

Time (sec)

15000

20000

50

100

150

200

250

300

T(0C)

Figure 3. (a) Adsorption isotherms of p-xylene at 50 STPcmVmin at 35°C (b) TPD curve of p-xylene for macrostructured SBA-15 with different PS bead sizes.

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size and interconnectedness of macropores. The present work demonstrates that the adsorption characterestics were determined not only by the feature of mesoporous region, but also by the macropore characteristics such as easy accessibility of an adsorbate to mesoporous region and short diffusion paths through the thin sample walls. 4. Conclusion Meso/macroporous SBA-15 was synthesized by the new and simple dualtemplating method combined by colloidal crystal templating for macroporous structures and liquid crystal templating for mesoporous structures. The morphology of mesostructure of biporous SBA-15 was maintained regardless of the existence of macropores. Furthermore, macropores were introduced in a better ordering with the PS bead size. Meso/macroporous SBA-15 should be attractive as adsorbents for adsorption and desorption of VOCs due to high surface area induced from mesopores and also due to the accessibility derived from macropores. The adsorption breakthrough curves with macrostructured SBA-15 showed that the adsorption dynamics were improved (i.e., the slope was steeper). The temperature programmed desorption of VOCs (toluene and p-xylene) showed that the maximum desorption peaks were shifted to a lower temperature. When bulky materials like p-xylene were used as adsorbate, the differences of adsorption/desorption behavior between meso/macroporous SBA-15 and mesoporous SBA-15 were found more significant. 5. Acknowledgement This work was partially supported by Daedeok Innopolis R&D Project from the Ministry of Science & Technology (MOST), by the National Research Laboratory (NRL) program from the Korea Institute of Science & Technology Evaluation and Planning (KISTEP) and also by the Brain Korea 21 (BK21) Project from the Ministry of Education. 6. References [1] B. T. Holland, L. Abrams and A. Stein, J. Am. Chem. Soc. 121 (1999) 4308. [2] Ch. Danumah, S. Vaudreuil, L. Bonneviot, M. Bousmina, S. Giasson and S. Kaliaguine, Microporous Mesoporous Mater. 44 (2001) 241. [3] C. G. Oh, Y. k. Baek and S. K. Ihm, Adv. Mater. 17 (2005) 270. [4] Y. J. Han, J. M. Kim and G. D. Stucky, Chem. Mater. 12 (2000) 2068.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Published by Elsevier B.V.

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Novel hydrophobic mesostructured materials: synthesis and application for VOCs removal Thang C. Dinh, Yen Hoang, Thanh V. Ho, Phuong T. Dang, Nam H.T. Le, Hoa K. T. Tran, Hoa V. Nguyen, Tuan A. Vu and Phu H. Nguyen Institute of Chemistry, Vietnamese Academy of Science and Technology 18 Hoang Quoc Viet Street, Cau Giay district, Hanoi city, Vietnam

Novel hydrophobic MCM-41 and SB A-15 analogue samples were successfully synthesized by hydrothermal treatment using silicalite-1 nanoseeds as precursors. The mesostructure of the samples was characterized by XRD and N2 adsorption/desorption isotherms. High hydrophobicity of the samples was revealed by high adsorption capacity of ethanol and very low adsorption capacity of water. The samples exhibited high adsorption capacity of m-xylene and high hydrothermal stability after steaming. This indicated potential as selective adsorbents of these materials for VOCs removal from high concentration and high humidity stream. 1. Introduction Recently, hydrophobic mesoporous Si-MCM-41 and Si-SBA-15 have been shown as potential adsorbents for VOCs removal [1-3]. However, due to the amorphous nature of the walls, these materials exhibited low hydrothermal stability under steaming condition. To improve the hydrothermal stability, Liu et al. [4] developed new mesostructured material (denoted Al-MSU) using zeolite nano-seeds as precursors. In this paper, we report the synthesis, characterization and application of hydrophobic Si-MCM-41 and Si-SBA-15 analogues prepared by hydrothermal treatment using silicalite-1 nano-seeds as precursors. 2. Experimental Section The preparations of Si-MCM-41 and Si-SBA-15 analogue samples were performed by a two-step procedure: in the first step Silicalite-1 nano-seeds were

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synthesized by hydrotherraal treatment from following gel composition: 7TPAOH: 25SiO2: 900H2O: 200EtOH at 100°C for 3h. In the second step, mesostructured Si-MCM-41 and Si-SBA-15 analogues were hydrothermally synthesized using silicalite nano-seeds as precursors and CTMABr and PI23 as surfactants, the gel compositions were of SiO2: 0.08CTMABr: I36H2O for SiMCM-41 analogue and SiO2: 0.02P123: 5.91HC1: 163H2O for Si-SBA-15 analogue. Both achieved gels were heated at 100°C for 48 h. For comparison, the two samples Si-MCM-41 and Si-SBA-15 were also prepared [4, 5]. The samples were characterized using Infrared spectroscopy (IR), powder X-ray diffraction (XRD), nitrogen adsorption/desorption isotherm (BET) and transmission electron microscopy (TEM). The adsorption equilibrium measurements were carried out by gravimetric method at 40°C. 3. Results and Discussion The Si-MCM-41 and Si-SBA-15 analogue samples were first characterized by XRD. In the XRD patterns (Fig.l), the intense peak at 29 of 1-2 attributed to the Si-MCM-41 analogue 100 reflection which is characteristic of mesostructure as observed on Si-MCM41 and Si-SBA-15. The mesostructure of the samples was also revealed by N2 adsorption/desorption isotherms as shown 2-Theta (degree) in Fig.2. The N2 adsorption/desorption Figure 1. XRD patterns of Si-SBA-15 isotherms of the two samples Si-SBA-15 and Si-MCM-41 analogues and Si-SBA-15 analogue are 600 characteristic of the two-dimensional 500 hexagonal structure with the hysteresis in Si-SBA-15 analogue the relative pressure range of 0.4 to 0.7 400 due to the capillary condensation in 300 mesopores. The textural characteristics of 200 the samples were given in table 1. In 100 Si-SBA-15 comparison to Si-MCM-41 and Si-SBA0 15, Si-MCM-41 and Si-SBA-15 0 .0 0 .2 0 .4 0 .6 0 .8 1 .0 analogues had smaller pore diameter. P /P o P/Po This can be rationalized by the fact that Figure 2. Nitrogen adsorption/desorption the wall of Si-MCM-41 and Si-SBA-15 isotherms of the samples analogues was built by relatively big nano-seeds (size of 5 - 10 nm) as "bricks" so the wall of these materials should be thicker than that of corresponding Si-MCM-41 and Si-SBA-15. Consequently, the pore size of Si-MCM-41 and Si-SBA-15 analogues is expected to be reduced. Thus, the thicker wall and narrower pore of Si-SBA-15 analogue is illustrated in Fig. 3. The high portion of micropores observed on SiIntensity (a.u)

Si-SBA-15 analogue I

Volume adsorbed (cc/g)

0

1

2

3

4

5

839

MCM-41 and Si-SBA-15 analogues as compared to the corresponding SiMCM-41 and Si-SBA-15 could be explained by the existence of microporous materials (silicalite-1 nano-seeds - pure silica form of MFI structure). The IR result supported this confirmation. Table 1. Textural characteristics of the samples Sample

Specific surface area SBET(m2/g)

Mesopore volume (cmVg)

Micropore volume (cnrVg)

Pore diameter (nm)

d-spacing

Si-MCM-41 Si-MCM-41 analogue

1020 815

0.925 0.851

0.011 0.087

3.0 2.5

3.9 4.2

Si-SBA-15

620

0.734

0.059

6.1

9.6

Si-SBA-15 analogue

740

0.539

0.112

4.2

10.5

(nm)

Amount adsorbed (w%)

Transmittance(%)

The IR spectra of Si-MCM-41, Si-MCM-41 and SiSBA-15 analogues in the lattice vibration region were shown in Fig. 4. The appearance of the shoulder at about 550 cm"1 in the IR spectra of Si-MCM-41 and SiSBA-15 analogue samples (which was A not observed on SiB MCM-41 or SiFigure 3. TEM image SBA-15) indicated C 1 of Si-SBA-15 . .» the presence ot iivemembered rings units in the samples. The hydrophobicity of the samples was 100 " 800 800 ' 600 600 ' 400 400 120 ' 100 120 (cm--11) Wave number (cm characterized by water and ethanol Figure 4. IR spectra of Si-MCM-41 adsorption isotherms at 40°C (Fig.5). It was (A), Si-MCM-41 analogue (B) and noted that Si-MCM-41 analogue sample was Si-SBA-15 analogue (C) highly hydrophobic as indicated by high 80 ethanol adsorption capacity (70 %) and low water adsorption capacity (~7 %) (at P/Po of 60 0.8) as shown in Fig. 5. Interestingly, the 40 higher ethanol adsorption capacity of SiA MCM-41 analogue compared to that of SiB 20 C MCM-41 sample at low relative pressure proved the contribution of micropores 0 0.0 0.2 0.4 0.6 0.8 1.0 existed in Si-MCM-41 analogue. Moreover, Si-MCM-41 analogue sample indicated high Relative pressure pressure (P/Po) (P/Po) Relative hydro-thermal stability under steaming Figure 5. Adsorption of ethanol on condition. Indeed, this sample exhibited high MCM-41 analogue (A) and MCM-41 adsorption capacity of m-xylene (60 w% at (B), water on MCM-41 analogue (C) 40°C) and still maintained its high adsorption

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Amount adsorbed (w%)

70 60 50 40 30

B efo re steam in g A fter steam in g

20 10 0 0 .0

0 .2

0 .4

0 .6

0 .8

1 .0

R elativ e pressure p ressu re (P /P o ) Relative (P/Po)

Figure 6. Adsorption of m-xylene on MCM-41 analogue before and after steaming at 600°C for 3 h 70

Amount adsorbed (w%)

capacity after steaming at 600°C for 3h (Fig. 6). The same trend was observed on SBA-15 analogue. The m-xylene adsorption iso-herms of Si-MCM-41 analogue and Si-SBA-15 analogue were presented in Fig.7. Comparing to SiMCM-41 analogue, Si-SBA-15 analogue showed lower m-xylene adsorption capacity. At partial pressure of 0.8, the amount of m-xylene adsorbed on Si-SBA15 analogue and Si-MCM-41 analogue were 50 and 60% respectively. It was expected that Si-SBA-15 analogue should exhibit higher m-xylene adsorption capacity due to its larger pore size (4.2 nm) compared to that of Si-MCM-41 analogue (2.5 nm). However, due to the thicker wall of Si-SBA-15 analogue, its pore volume and specific surface areas reduced as compared to those of Si-MCM-41 analogue. This caused the reduction of mxylene adsorption capacity of Si-SBA-15 analogue.

60 50 40 30 20 S i-M C M -4 1 an alo gu e Si-MCM-41 analogue S i-S B A -1 5 an alogue Si-SBA-15 analogue

10 0 0 .0

0 .2

0 .4

0 .6

0 .8

1 .0

R elative pressure (P /P o) Relative (P/Po)

Figure 7. m-xylene adsorption isotherms of Si-SBA-15 and Si-SBA-15 analogue

4. Conclusion Novel hydrophobic mesostructured Si-MCM-41 and Si-SBA-15 analogues were successfully synthesized by hydrothermal treatment using silicalite-1 nano-seeds as precursors. The characterization results revealed that the two samples had mesostructure with the wall of crystalline nature. Very low adsorption capacity of water and high adsorption capacity of ethanol observer on Si-MCM-41 and Si-SBA-15 analogues indicated the high hydrophobicity of the samples. High m-xylene adsorption capacity of both samples exhibited their high potential for removal of VOCs in air treatment. 5. References [1] X. S. Zhao, Q. Ma, and G. Q. (Max) Lu. Energy & Fuels, 12 (1998) 1051. [2] C. Nguyen, C. G. Sonwane, S. K. Bhatia and D. D Do. Langmuir 14 (1998) 1950. [3] D. P. Serrano, G. Calleja, J. A. Botas and F. J. Gutierrez. Ind. Eng. Chem. Res. 43 (2004) 7010. [4] Y. Liu and T. J. Pinnavaia. J. Mater. Chem. 12 (2002) 1. [5] D. Zhao, J. Feng, Q. S. Huo, N. Melosh, G. H. Fredrickson, B. F. Chmelka and G. D. Stucky, Science, 278 (1998) 548.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

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Synthesis of silver nanowire/mesoporous silica composite as a highly active antiseptic Dieqing Zhang, Ying Wan*, Guisheng Li, Jing Zhang and Hexing Li* Department of Chemistry, Shanghai Normal University, Shanghai 200234

Silver nanowire/mesoporous silicate nanocomposites have been synthesized by simple impregnation of silver salts in SBA-15 mesochannels. The characterization using XRD, TEM, FT-IR and N2 sorption techniques indicate that the highly ordered mesostructure of SBA-15 is retained after immobilization of Ag nanowires. Silver nanowires are entrapped and uniformly distributed in the pore channels of SBA-15 without obvious aggregation to large particles. The BET surface areas of silver nanowires/SBA-15 nanocomposites are about 650 m2/g. Ag/SBA-15 samples exhibit a highly inhibitory effect on the growth of Escherichia coli ( ATCC 25922). Key words: silver nanowires, mesoporous silica, antiseptic, Escherichia coli. 1. Introduction Antibacterial materials have attracted more and more interests owing to rapid increase of problems caused by microbial pollution and contamination from microorganisms in living conditions, public health and industrial fields [1]. Silver-based antiseptics, especially supported silver-based antiseptics, are most frequently used owing to their strong inhibitory and bactericidal effects as well as a broad spectrum of antimicrobial properties [2]. The support hosts can be organic and inorganic materials, however, organic hosts are seldom used due to their poor stability. Because of the small pore size, silver particles supported on inorganic materials, such as zeolites [3], silicates [4] and active carbon fibers (ACFs) [5-7] etc., are usually present on the outer surface rather than in the pore channels of these supports. Thus, these silver active sites are not well distributed on the support and easily leached off from the support. As well known, mesoporous materials possess large pore sizes, narrow pore distributions, high surface areas and rich mesostructures. By using mesoporous

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materials as supports, metal nanowires or nanopaticle clusters with diverse mesostructures could be successfully embedded in pore channels. Silver nanowires in mesoporous silica template have been reported by using MCM-41 and SBA-15 as supports [8, 9], but their application as the antiseptic has never been reported so far. Silver nanowires which are fixed in the uniformed pores of mesoporous silicates are expected to facilitate antisepticise. Two reasons can be inferred. The reactions take place in the confined spaces which can magnify the collision frequency between the bacteria and the active metals. Besides that, the fixation of silver wires inside the mesoporous silicates channels may reduce the leaching. However, the main problems are the poor distribution of Ag particles especially on the external surface and the use of CH2CI2 solvent which might cause environmental pollution. We report, here, a simple method to fabricate silver nanowires embedded in the mesoporous channels of SBA-15 support. The antibacterial activities against Gram-negative Escherichia coli (E. coli, ATCC 25922) of these nanocomposites were examined and their correlation to the structural characteristics is briefly discussed. 2. Experimental Section SBA-15 was synthesized according to the methods reported in the literatures [9]. The silver nanowires were prepared by impregnation of SBA-15 with AgNC>3 aqueous solution, followed by H2 reduction. In a typical synthesis, a mixture containing 0.25 g AgNO3, 20 ml water, 20 ml ethanol and 2 g SBA-15 was stirred for 24 h at room temperature. Then, the solid was dried at 353 K and reduced at 573 K or 773 K under a nitrogen flow containing 10% hydrogen gas for 3h. All the as-prepared samples are denoted as Ag(x)/SBA-15-y, where x and y is Ag loading (wt.%) and reduction temperature, respectively. For example, Ag(6.4)/SBA-15-573 refers to a Ag/SBA-15 sample with 6.4 wt.% Ag obtained by reduction at 573 K. E. coli (ATCC 25922) was selected as indicators for antibacterial test to confirm the minimal inhibiting concentration (MIC). X-ray diffraction (XRD) measurements were performed on a Rigaku D/max.B diffractometer with CuKa. Transmission electron microscopy (TEM) images were obtained on a JEOL JEM2011 electron microscope. Nitrogen sorption isotherms were measured on a Quantachrome NOVA 4000e analyzer. FT-IR transmission spectra were determined in transmission mode using a Nicolet Omnic 405 Model spectrometer. 3. Results and Discussion Figure 1 shows the low-angle and wide-angle XRD patterns of pristine SBA15 and Ag/SBA-15 materials^ Three well-resolved diffraction peaks with 28 value of 0.83, 1.45 and 1.69° are observed in the pristine SBA-15 material,

843

which can be indexed as 10, 11 and 20 Bragg reflections of a 2-D hexagonal (p6m) structure [10] . The cell parameter is calculated to be 11.1 nm. The Ag(6.4)/SBA-15-573 exhibits a similar low-angle XRD pattern to the pristine SBA-15 with a minor decrease in cell parameter. The Ag(6.4)/SBA-15-573 exhibits A more resolved diffraction peaks and a further smaller cell parameter to 10.7 nm. From the wide-angle XRD patterns, one could see that, besides a broad peak around 26 = 23 °, the Figure 1 Small-angle(A) and wide angle(B) XRD patterns of (a) SBAAg(6.4)/SBA-15-573 exhibits four new 15, (b) Ag(6.4)/SBA-15-573 and (c) diffraction peaks with 26 values around 37.9°, 44.2 , 64.3 and 77.3°, respectively, corres- Ag(6.4)/SBA-15-773 samples ponding 111, 200, 220, and 311 reflections of Ag metal [4]. No significant peaks indicative of oxidized Ag species were observed. The TEM images (Figure 2) of the Ag(6.4)/SBA-15-573 sample display a typical hexagonally stripe-like morphology recorded along 01 and 10 incidences, suggesting a highly ordered 2-D hexagonal p6m mesostructure. Almost no wires or particles are Figure 2 TEM images of Ag(6.4)/SBA-15-573 observed on the external surface of recorded along [01] and [10] directions SBA-15, implying that the silver nanowires are totally immobilized inside the channels and the distribution of these nanowires is very uniform. The estimated cell parameter is 10.9 nm, in good agreement with the XRD result. Table 1 lists the textural parameters of different Ag(x)/SBA-15-y samples. It is reasonable to conclude the successful immobilization of silver nanowires inside the SBA-15 channels. According to FT-IR spectra, the Ag(6.4)/SBA-15 exhibits a strong and relatively broad peak around 3458 cm" which is assigned to the hydroxyl stretching of surface silanols. Several bands observed at 1094, 798 and 460 cm"1 are associated with the Si-O-Si asymmetric stretching, symmetric stretching and bending vibrations, respectively. The bands at 970 and 571 cm"1 are attributed to the stretching and bending vibrations of Si-OH [4]. These results demonstrate the formation of Si-O-Si framework with abundant hydroxyl groups. The other two bands at 1390 and 1450 cm"1 are attributed to NO3" ions [11], indicating the presence of trace nitrate salt in the channels. These two bands disappear after annealing the material at a temperature above 573 K under a nitrogen atmosphere containing hydrogen owing to the complete decomposition. A

844

continuous decrease of the bands at 970 and 571 cm'1 is observed in the Ag(6.4)/SBA-15 materials with the increase of reduction temperature, possibly due to the polycondensation between silanols. Based on above experimental results, a possible mechanism for the formation of Ag nanowires in the mesochannels of SBA-15 is discussed Firstly, the aqueous solutio-n of silver nitrate diffused into the mesopores of SBA-15. Because of the interaction of silver ions with - Si Table 1 Textural parameters of Ag(x)/SBA-15-y samples Sample

SBET(m2/g)

D(nm)

SBA-15

111

7.5

1.56

Ag(1.6)/SBA-15-573

671

5.5

1.04

Ag(3.2)/SBA-15-573

682

5.4

1.06

Ag(6.4)/SBA-15-573

640

5.5

0.78

Ag(6.4)/SBA-15-773

602

5.5

0.67

V(cmVg)

-OH groups on the internal surfaces of silica framework, a equilibrium is established between the free silver ions in solution and those adsorbed in the mesochannels. During the H2 reduction at high temperature, the nitrate salt is decomposed and the silver ions are reduced to silver metal within the pore channels. Improvement of AgNO3 solution immigration process into the mesochannels is extraordinarily important to obtain uniform Ag nanowires. Otherwise, partial silver particles are probably formed on the external surface if silver ions are not completely trapped in the silica matrix [4]. One important factor is the solvent since only Ag nanoparticles were obtained by using AgNO3 solution in pure water or a mixture of ethanol and water with the volume ratios of 3:7 and 8:2, while a blend of nanoparticles and nanowires was formed when AgNO3 precursor was dissolved in an equivalent ethanol and water solution. This effect can be assigned to the quite different surface tension of H2O and ethanol at room temperature, namely 71.99 and 21.97 mN m"1, respectively. Selection of a mixture of ethanol of water with the volume of Scheme 1. Possible mechanism for 1:1 as the solvent may lead to a rapid transfer the formation of Ag nanowires in of silver ions into the SBA-15 mesochannels the mesochannels of SBA-15. since a suitable surface tension influences the immigration rate [12]. Besides, the ultrasonic treatment is favorable to enhance the immigration of silver ions into the mesopores in SBA-15 and interaction

845

MIC (p p m)

with the surface Si-OH groups. During the thermal treatment under 10% H2/N2, the adjacent Ag+-SiO species are in situ reduced to silver nanowires. Figure 3 gives the activities of Ag/SBA-15 samples in killing E. coli, estimated by MIC values. The Ag can kill E. coli via its reaction 350 with protein molecules through 300 the combination with the -SH 250 groups, which leads to the 200 inactivation of bacterial proteins 150 [13]. The enrichment of E. coli 100 species in mesopores also 50 facilitates the contact of silver 0 metals with E. coli and thus, Ag(1.6)/SBA-15- Ag(3.2)/SBA-15- Ag(6.4)/SBA-15- Ag(3.2)/SBA-15- Ag(6.4)/SBA-15573 573 573 773 773 enhances the combination Ag/SBA-15 Ag(SB 5ssamples *' ~pb reaction. The MIC value reduces from 300 to 90 ppm with the increase of silver loading on Figure 3. Antibacterial activity over Ag/SBA-15 SBA-15 support from 1.6 % to sam les P 6.4 %, indicating that silver is the active center. In addition, the increase of reduction temperature also shows an great improvement on the antibacterial activity, especially for the Ag(3.2)/SBA15. On one hand, the increasing reduction temperature may enhance the reduction degree of Ag/SBA-15 samples, which may supply more active sites. On the other hand, the increase of reduction temperature may also enhance combination strength between the silver nanowires and the SBA-15 support, which may inhibit the leaching of Ag particles from the SBA-15 support during reaction with E. coli in aqueous solution. It is expected that the as-prepared Ag/SBA-15 samples can be used in killing other kinds of microorganisms besides E. coli. Detailed studies are being underway. Ag(1.6)/SBA-15-

Ag(3.2)/SBA-15-

Ag(6.4)/SBA-15-

Ag(3.2)/SBA-1 5-

Ag(6.4)/SBA-15-

573

573

573

773

773

4. Conclusion A new Ag/SBA-15 sample with uniform distribution of Ag nanowires in the pore channels of SBA-15 support is prepared by simple method including the impregnation of silver nitrate dissolved in a solution comprised of equivalent ethanol and water, ultrasonic dispersion, solvent evaporation and reduction in 10% H2/N2 atmosphere. Such Ag/SBA-15 exhibits high activity in killing Escherichia coli (ATCC 25922). The MIC value could be reduces from 300 to 90 ppm with the silver loading increasing from 1.6 % to 6.4 %, possibly owing to the ordered mesostructure and large surface area of of SBA-15 which may ensure the high and homogeneous distribution of Ag particles in the pore channels. The reduction temperature also plays important role in enhancing the bacterial activity owing to the improvement of reduction degree of the Ag/SBA15 and interaction strength between Ag particles and SBA-15 support.

846

5. Acknowledgment This work was supported by the National Natural Science Foundation of China (20377031, 20407014 and 20521140450), Shanghai Municipal Scientific Commission (03DJ14005 and 03QF14037) and Shanghai Municipal Educational Commission (04DB05). 6. References [1] J. H. He, W. S. Ma, S. Z. Tan and J. Q. Zhao, Appl. Surf. Sci. 241 (2005) 279. [2] H. Y. Kang and Y. K. Jeong , J. Biotechnol. Bioeng. 15 (2000) 521. [3] M. Rivera-Garza, M. T. Olguin, I. Garcia-Sosa, D. Alcantara and G. Rodriguez-Fuentes, Micropor. Mesopor. Mater. 39 (2000) 431. [4] H. J. Jeon, S. C. Yi and S. G. Oh, Biomaterial 24 (2003) 4921. [5] A. Oya, S. Yoshida, Y. Abe, T. Iizuka and N. Makiyama, Carbon 31 (1993) 71. [6] Y. L. Wang, Y.Z. Wan, X. H. Dong, G. X. Cheng, H. M. Tao and T. Y. Wen, Carbon 36 (1998) 1567. [7] S. J. Park and Y. S. Jang, J. Coll. Inter. Sci. 261 (2003) 238. [8] P. V. Adhyapak, P. Karandikar, K. Vijayamohanan, A. A. Athawale and A. Chandwadkar, J. Mater. Lett. 58(2004)1168. [9] Y. J. Han, J. M. Kim and G. D. Stucky, Chem. Mater. 12 (2000) 2068. [10] D. Zhao, J. Feng, Q. Huo, N. Melosh, G. H. Fredrickson, B. F. Chmelka and G. D. Stucky, Science 279 (1998) 548. [11] N. B. Colthup, L. H. Daly and S. E. Wiberiey, Introduction to infrared and Raman spectroscopy, 2nd ed. New York: Academic Press; 1975. [12] M. H. Huang, A. Choudrey and P. D. Yang, Chem. Commun. (2000) 1063. [13] Q. L. Feng, J. Wu, G. Q. Chen, F.Z. Cui, T. N. Kim and J.O. Kim, J Biomed. Mater. Res. 52 (2000) 662.

Recent Progress Progress in in Mesostructured Mesostructured Materials Materials Recent D. Zhao, S. S. Qiu, Qiu, Y. Y. Tang and and C. C. Yu Yu (Editors) (Editors) D. © 2007 2007 Elsevier Elsevier B.V. B.V. All All rights rights reserved. reserved. ©

847 847

Preparation and conductivity of decatungstomolybdovanado-germanic heteropoly acid supported on mesoporous silica SBA-15, SBA16, MCM-41 and MCM-48 Qingyin Wua*, Hongxiao Jina, Wenqi Fenga and Wenqin Pang a,b* "Department of Chemistry, Zhejiang University, Hangzhou 310027, P. R. China 1 State Key Lab of Inorganic Synthesis and Preparative Chemistry, Jilin University, Changchun 130023, P. R. China

1. Introduction Heteropoly acids (HPA) with Keggin structure have been attracted a lot of attention because of their high proton conductivity [1] and their potential application as solid electrolyte in hydrogen-oxygen fuel cells, electrochromic displays, desiccators, ¥t sensors at low temperature, solid modified electrodes, etc. [2, 3]. Mesoporous silica (MPS) materials are known as excellent supporter for HPAs, and have been extensively studied for their use of catalysts [4]. Because of the existence of large, uniform mesopore and the abundance of silanol (SiOH) groups, HPAs supported on mesoporous materials are also of solid highproton conductor, however, limited research papers were published in this field. Therefore, research on the conductivity of HPAs supported on MPS was significant. As a further study of our previous works which were mainly on decatungstomolybdovanadogermanic heteropoly acid and polyvinyl alcohol (PVA) doped decatungstomolybdovanadogermanic heteropoly acid [5, 6], we report here the preparation and conductivity of decatungstomolybdovanadogermanic heteropoly acid supported on mesoporous silica SBA-15, SBA-16, MCM-41 and MCM-48.

848

2. Experimental Section 2.1 Synthesis Decatungstomolybdovanadogermanic acid, H5GeWioMoV04o'21H20 was prepared according to the literature method [5]. SBA-15, SBA-16, MCM-41 and MCM-48 were synthesized according to the literature methods [7-9]. Preparation of MPS (MPS= SBA-15, SBA-16, MCM-41 and MCM-48) containing 75 wt% of H5GeW10MoVO40 (HPA/MPS): HPA (1.125 g) was dissolved in 20 ml of boiling water, then 0.375 g MPS were added to the solution with stirring. The stirring was continued for 2h and then kept static at 40°C over night, drying in vacuum oven. 2.1. Characterization IR spectra were recorded on a Nicolet Nexus 470 FT-IR spectrometer using KBr pellets and X-ray diffraction patterns were obtained with a Siemens D5005 diffractometer using Cu Ka radiation (A, = 0.15418 nm). The conductivity was determined by complex impedance spectroscopy using an M273 electrochemical impedance analyzer over the frequency range from 99.9 kHz to 12Hz at room temperature. The compound was pressed at 20 MPa into a compact pellet with 10.00 mm in diameter. The conductivity was calculated as o = (1/R) • (L/S), where L is the pellet thickness, and S is the area of the pellet. 3. Results and Discussion 3.1. Infrared Spectra Fig. 1 compares the infrared (IR) spectra of the H5GeWioMoV04o (HPA) and HPA/MPS. The Keggin structure of GeM1204o5" (M=W, Mo, or V) consists of one GeO4 tetrahedron surrounded by four M3O13 sets formed by three edgesharing octahedra. There are six characteristic bands in the IR spectrum of H5GeW10MoV04o: 978 cm"1, vas (M-Od); 877 cm"1, vas (M-Ob-M); 767 cm"1, vfl, (M-Oc-M); 816 cm"1, vas (Ge-Oa); 458 cm"1, 6(O-Ge-O), all of which correspond to the spectrum of the heteropoly complex of Keggin structure previously reported. In 3800-1200 cm"1 region the absorptions associated with OH modes (stretching v and bending S) are also present: 3434.7 cm"1, v(OHXieiS.Ocm"1, <5(H-O-H). In the spectra of HPA/MPS the characteristic bands associated with Keggin structure were also observed at 974±2, 886±3, 813±3, 774±3 and 462±1 cm" .

849 849

CO

2

4000 3500 3000 2500 2000 1500 1000 500

Wavenumber(cm"1) Fig. 1 IR spectra of the HPA and HPA/MPS.

Generally, the M-Od stretching can be considered as pure vibration and is an increase function of the anion-anion interaction. The M-Od asymmetrical stretching frequency of HPA decreases from 978 to 974±2 cm"1 when doped with MPS. This is attributed to the weakening of anion-anion interactions of the electrostatic type. We assume that due to the influences of silica such as the lengthening of the anion-anion distances, the anion-anion interactions are weakened. The stretching involved Ob or Oc are different from M-Od stretching and they present some bending characteristics. This can be assumed from geometrical considerations. Because M-Ob-M and M-Oc-M are not pure and can not be free from bending characteristics, there is competition of the opposite effects. The electrostatic anion-anion interactions lead to an increase in the stretching frequencies, but they lead to a decrease in the bending vibrations. Moreover, perturbations due to water molecules and anion-cation interactions lead to a decrease in the frequencies of vibrations and can strengthen the decreasing effect of anion-anion interactions. As a result, we can see another five peaks of HPA had a little shift from higher wave number to lower wave number (i.e. v^ (M-Ob-M) from 885.2 to 886±3 cm'1) or otherwise lower wave number to higher wave number(/.e. vas (M-O c -M) from 771.4 to 774±3 cm"1). 3.2. X-ray Powder Diffraction XRD patterns of MPS show three well-resolved peaks at small angle rang (20=0.6-6°,) are indexed as mesoporous silicate. In each of the four ranges of 26 that are 7-10°, 16-22°, 25-30° and 33-38°, although the intensities are changed due to the influence of MPS, the characteristic diffraction peaks of HPA crystal

850

are still observed in pattern of HPA/MPS. Combined with IR spectra, we are sure that the Keggin anions exist in the HPA/MPS.

MCM-41

jl

/]

MCM-41

\

( l

,;,,

' MCM-48

Interisity

MCM-48

i \

SBA-15

SBA-15 SBA-16

SBA-16

/ i | i

1 2

3

4

26 / °

5

6

5

10

15

20

25

30

35 40

26 /

Fig.2 Low-angle (left) and wide-angle (right) XRD patterns of various GeMoWnV/MPS: MPS=MCM-41, MCM-48, SBA-15, SBA-16. The labels in the figure show the MPS type.

Comparing the four wide-angel XRD patterns in Fig. 2, we can find that HPA was dispersed better in SBA-15 than in the other three MPS, which might be important for conductivity of HPA/MPS. 3.3. Conductivity Conductivity is an important parameter. The conductivity of HPA/MPS at 20"C was as follows: 1.29xl(T3 S-cm"1, HPA/SBA-15; 5.14xl(r4 S-cm"1, HPA/SBA-16; 2.67xlO 4 S-cm'1, HPA/MCM-48; 2.25xl(r 4 Sxm- 1 , HPA/MCM41. The conductivity of HPA/SBA-15 and HPA/SBA-16 is bigger than pure H5GeWioMoV04o which is 3.58xl0' 4 Scm"1 at room temperature. Considering HPA supported on the mesoporous SBA-15/SBA-16, the protons could be come from: i) HPA itself; ii) hydrolysis of the water molecules attached to the HPA crystal and the surface of mesoporous SBA-15; iii) ionization of the surface silanol (Si-OH) groups. The high-proton conductivity of SBA-15/HPA and HPA/SBA-16 is because of that: firstly, the SBA-15/SBA-16 contains a large number of micropores and mesopores that well dispersed of 'liquid HPA' which can be utilized for fast proton transport could be expected; secondly, an abundance of mesopores and micropores in SBA-15/SBA-16 facilitates the adsorption of much water than pure HPA, thus the number of protons improved;

851

thirdly, a lot of silanol groups present in the surface of SBA-15/SBA-16 strongly interact with HPA anions (confirmed by IR) that ionization of the surface silanol groups are much easier than pure mesoporous silica itself. Proton conduction in solids is suggested to take place according to the Grotthuss mechanism or vehicle mechanism [10], all those facts contribute the slightly improvement of the conductivity, however further work should be done to prove how proton conduction in HPA/SBA-15 and HPA/SBA-16 is going on. 4. Conclusion Decatungstomolybdovanadogermanic heteropoly acid H5GeWioMoV040 with Keggin structure was introduced onto mesoporous silica SBA-15, SBA-16, MCM-41 and MCM-48 by incipient wetness method, respectively. The composite materials were characterized by IR and XRD to confirm the existence of Keggin structure. The protonic conductivity of the composite materials is also reported with the 75 wt.% heteropoly acids at 20 °C. HPA/SBA-15 showed highest proton conductivity among the four composite materials. The results indicated that GeW]0MoV/SBA-15 is a new excellent high-proton conductor. 5. Ackonwledgement The financial support from the National Natural Science Foundation of China under Grant No. 20271045, the Foundation of NSFC-RFBR under Grant No. 20511120009 and the Foundation of State Key Laboratory of Inorganic Synthesis and Preparative Chemistry of Jilin University for this work is greatly appreciated. 6. References [1] [2] [3] [4] [5] [6] [7] [8]

X. G. Sang and Wu, Chem. Lett., 33 (2004) 1518. M. T. Pope and A. Muller, Angew. Chem. Int. Ed. Engl., 30 (1991) 34. X. G. Sang, Q. Y. Wu and W. Q. Pang, Mater. Chem. Phys., 82 (2003) 405. T. Okuhara, N. Mizuno and M. Misono, Appl. Catal. A, 222 (2001) 63. Q. Y. Wu and X. G. Sang, Mater. Res. Bull., 40 (2005) 405. W. Q. Feng, J. Q. Wang and Q. Y. Wu, Mater. Chem. Phys., 93 (2005) 31. H. X. Jin, Q.Y. Wu, P. Zhang and W. Q. Pang, Solid State Sci., 7 (2005) 333. D. Y. Zhao, Q. Huo, J. Feng, B. F. Chmelka and G. D. Stucky, J. Am. Chem. Soc, 120 0998)6024. [9] H. X. Jin, Q.Y. Wu and W. Q. Pang, Mater. Lett., 58 (2004) 3657. [10] S. L. Zhao and Q. Y. Wu, Mater. Lett., 60 (2006) 2650.

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Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

853 853

Fabrication of highly dispersed Pt nanoparticles in tubular carbon mesoporous materials for hydrogen energy applications Shou-Heng Liua, Rong-Feng Lub, Shing-Jong Huanga, An-Ya Loa, Wen-Hua Chena, Wen-Yueh Yub, Shu-Hua Chienb and Shang-Bin Liua* a h

Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan Institute of Chemistry, Academia Sinica, Taipei 11529, Taiwan

1. Introduction The R&D of safe and effective hydrogen storage systems is one of the key issues in future realization of hydrogen energy applications, particularly in commercialization of fuel cell vehicles [1]. Among various adsorbents, nanostructured carbon materials are promising candidates for hydrogen storage due to their high surface area and light-weight characteristics, however, no available storage materials are capable of meeting the US-DOE target (6.5 wt%) for commercial exploitation at present [2]; a further 40-50% increase in storage capacity is needed for currently available carbon-based materials, such as carbon nanotubes, activated carbon and carbon nanofibers [3]. Recent developments in carbon mesoporous materials (CMMs) have drawn some attention in R&D [4] owing to their potential applications as catalytic supports [5], hydrogen fuel storage [3], and fuel cells [6]. In particular, fabrications of metal-incorporated CMMs, which normally invoke methods such as adsorption [5], impregnation [6], and ion-exchange [7], also received much attention. Nonetheless, these conventional synthesis routes normally lead to uncontrollable growth of metal-particles particularly in terms of their sizes and shapes. We report herein a novel synthesis route to fabricate tubular CMMs with well-dispersed Pt nano-particles studded on the pore walls. Their performances on hydrogen adsorption, carbon monoxide tolerance, and cyclic voltammetry test were also investigated.

854

2. Experimental Section Platinum-incorporated CMMs (Pt-CMMs) were prepared according to the method reported elsewhere [8]. All Pt-CMMs samples were further characterized by powdered XRD, N2 adsorption/desorption measurements, and TEM. Hydrogen (99.9999% purity) adsorptions were done at 77 K over a pressure range of 0-4,000 torr on a home-built volumetric apparatus. Electrocatalytic activity measurements were performed on a \i Autolab potentiostat at a scan rate of 10 mV/s. Electrooxidation of MeOH was carried out with an electrolyte of 0.5 M H2SO4 and 1 M MeOH between -0.2 and 1.0 V at room temperature. 3. Results and Discussion As illustrated by the TEM images in Fig. la, Pt-CMMs exhibit uniform array of mesopores with long-range order and bimodal mesopore distribution with average diameters of ca. 2.5 and 4.5 nm, similar to that of CMM. This is in excellent agreement with the BJH pore sizes and physical properties derived from N2 adsorption /desorption isotherms summarized in Table 1. Similar to CMK-3 [9], the CMM sample was replicated from SBA-15 but in the absence of Pt source (platinum acetylacetonate). The smaller pore with constant pore size of 2.3 nm may be unambiguously ascribed due to the voids generated after the removal of silica template, whereas the larger pore, which appears to decrease with increasing Pt loading, is attributed to the formation of hollow, tubular mesoporous carbon similar to that of CMK-5 [6a]. Intere- Fig. 1. TEM images of (a) Ptstingly, most of the Pt particles were studded and CMM-0.6 and (b) Pt-CMMdispersed uniformly on the inner carbon walls 0.61. with a narrow particle-size distribution of ca. 2-3 nm. Notable decreases in both BET surface area (S) and total pore volume (V) upon increasing Pt loading (Table 1) were observed. Moreover, compared to the Pt-CMM-0.6 sample, Pt-CMM-11.5 reveals the existence of only one type of pore with a pore size of 2.3 nm indicating that the formation of hollow tubular carbon is greatly hindered. This is in accordance with the findings obtained from XRD measurements (not shown), which revealed that the concentration of the Pt precursor and hence the density of the Pt particles greatly affect the structure of the carbon support formed, as suggested earlier by Xiao and coworkers [6b].

855 Table 1: Physical and adsorptive properties of CMM and Pt-CMMs with varied Pt loading. Sample

Pt (wt%)

S(mV)a

D (nm)b

V (cm3 g ' ) c

CMM

—

2,195

2.3; 4.4

1.67

1.89

Pt-CMM-0.6

0.6

1,818

2.3; 4.0

1.30

2.04

Pt-CMM-0.6Ie

0.6

1,508

2.5; 4.3

1.16

1.54

Pt-CMM-11.5

11.5

997

2.3

0.65

-

a

C (wt %) d

c

BET surface areas. Pore diameters. Total pore volumes. Hydrogen adsorption capacities obtained at 850 mmHg and 77 K. eSample prepared by wet impregnation method.

In addition, by comparing the results obtained from Pt-CMM-0.6 to the PtCMM-0.6I sample prepared by conventional impregnation method [6], it is obvious that much larger and non-uniformly distributed Pt particles (typically ca. 10-20 nm in size; see Fig. lb) were formed. Hydrogen adsorption isotherms observed for CMM and Pt-CMMs at 77 K all show typical Langmuir-type curves (not shown). A hydrogen capacity of 2.04 wt% was obtained (at 77 K and 850 mmHg) for the Pt-CMM-0.6 sample (S = 1818 m2 g"1 and V = 1.30 cm3 g"1). By comparison, the H2 adsorption capacities for the CMM and Pt-CMM0.61 samples were lower by ca. 8% and 25%, respectively. This implies that, our Pt-CMMs samples exhibit improved H2 adsorption capacity compared to bare CMM and metal-CMM samples prepared using conventional post-synthesis treatments. It is clear that, in this case, our Pt-CMM samples facilitate H2 storage through not only physisorption but also chemisorption. Figure 2 displays the cyclic voltammograms for methanol oxidation activities of a commercial Johnson-Matthey Pt/C catalyst (that is, 20 wt% Pt on Vulcan XC-72 activated carbon) and the Pt-CMM-11.5 sample. It is indicative that the our sample, which possesses well-dispersed, highly stable Pt nano-sized 2.0 1.5 1.0

0.0

-0.5 -1.0

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

Potential (V) Fig. 2. Cyclic voltammograms of methanol oxidation on (a) commercial Johnson-Matthey Pt/C and (b) Pt-CMM-11.5 catalysts in 0.5 M H2SO4 and 1 M MeOH at 10 mV/s.

856

particles on porous carbon supports, exhibits catalytic activities surpassing that of the commercial Johnson-Matthey catalyst. In particular, a lower oxidation peak potential was observed. In terms of the ratio of the forward anodic peak current density (If) to the reverse anodic peak current density (It,), the If/Ib ratio obtained for the Pt-CMM-11.5 and the commercial Johnson-Matthey Pt/C were found to be 4.23 and 1.03, respectively, indicating that the latter is more vulnerable to coking by carbonaceous deposits [10] and less tolerance towards CO poisoning. This is in accordance with our CO tolerant test results (not shown) performed by H2 chemisorption measurements with/without the presence of 500 ppm CO. 4. Conclusion A novel route for synthesizing CMMs with well-dispersed, highly stable platinum nanoparticles (2-3 nm) has been developed. By incorporating carbonrich metal precursor, such as Pt(CH(COCH3)2)2, as co-feeding carbon source during replicated synthesis using mesoporous silicas with well-defined pore sizes as templates, tubular carbon mesoporous materials (CMMs) with welldispersed metal nanoparticles and tailored sizes can be obtained. These metalCMMs, which can be easily fabricated with controllable loading even with multifunctional metal characteristics were found to possess high surface areas, highly accessible and stable active sites, improved hydrogen adsorption capacities, and superior electrocatalytic properties, rendering for future practical and cost-effective commercial applications in hydrogen-energy related areas. 5. References [1] Report of National Research Council, US National Academy of Engineering, in: The hydrogen Economy: Opportunities, Costs, Barriers, and R&D Needs, The National Academy Press, Washington D. C. (2004); URL: http://www.nap.edu/catalog/10922.html. [2] S. Hynek, W. Fuller and J. Bentley, Inter. J. Hydrogen Energy, 22 (1997) 602. [3] J. Pang, J. E. Hampsey, Z. Wu, Q. Hu and Y. Lu, Appl. Phys. Lett., 85 (2004) 4887. [4] B. Sakintuna and T. Yiirum, Ind. Eng. Chem. Res., 44 (2005) 2893, and references therein. [5] R. Ubago-Perez, F. Carrasco-Man'n and C. Moreno-Castilla, Appl. Catal. A, 275 (2004) 119. [6] (a) S. H. Joo, S. J. Choi, I. Oh, J. Kwak, Z. Liu, O. Terasaki and R. Ryoo, Nature, 412 (2001) 169; (b) J. Ding, K. Y. Chan, J. Ren and F. S. Xiao, Electrochimica Acta, 50 (2005) 3131. [7] V. Lordi, N. Yao and J. Wei, Chem. Mater., 13 (2001) 733. [8] S.-H. Liu, R. F. Lu, S. J. Huang, A. Y. Lo, S. H. Chien and S. B. Liu, Chem. Commun., 3435 (2006). [9] S. H. Joo, R. Ryoo, M. Kruk and M. Jaroniec, Chem. Commun., 349 (2001). [10] J. Huang, Z. Liu, C. He and L. M. Gan, J. Phys. Chem. B, 109 (2005) 16644.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Published by Elsevier B.V.

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Membranes with Ni, Mn-MCM-41 mesoporous molecular sieves and their applications for waste water purification Viorica Parvulescu *a, Gabriela Romanb, Simona Somacescu", Isabella Dascalua, Bujor Albub and Bao-Lian Suc a

Institute of Physical Chemistry, Spl. Independentei 202, R-060021 Bucharest, Romania Research Center for Molecular Materials and Membranes, Spl. Independentei 206, Bucharest. Romania c Laboratoire de Chimie des Materiaux Inorganiques, ISIS, The University ofNamur (FUNDP), 61 rue de Bruxelles, B-5000 Namur, Belgium

1. Introduction In recent years, increasing attention has been paid to zeolite membranes because of new applications in gas and liquid separation and heterogeneous catalysis [1]. New metal-containing molecular sieves with new adsorptive and catalytic properties are very attractive potential membranes for use in water purification. A variety of materials have been used to produce both unsupported and supported membranes. Composite membranes have been extensively explored due to the necessity to obtain a material with specific properties. The addition of a fourth organic component to a plymer/solvent/nonsolvent system is a well-known technique to enhance the properties of wet cast ultrafiltration membranes [2, 3]. When this fourth component is an inorganic particle, a unique ceramic-polymer membrane material is developed. We present the results on synthesis, characterization and evaluation in separation and catalytic oxidation of Ni-MCM-41 mesoporous membranes supported on y-Al2O3 or inorganic/ polymeric hybrid membranes based on Ni, Mn-MCM-41 molecular sieves. The inorganic/polymeric hybride that will be discussed here are composed of polysulfone polymer network and Ni, Mn-MCM-41 molecular sieves as inorganic filler and catalytic materials. The composite membranes were tested as absorbent and catalysts in purification of the waste water with varied impurity as hydrocarbons, sulfides and phenols.

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2. Experimental Section All the MCM-41 membranes materials are obtained by hydrothermal transformation of the Me-MCM-41 mesostructured gel [4]. The gels with the molar composition of 1.00 SiO2: 0.04 Me2+: 0.48 CTMABr: 0.28 Na2O: 2.70 TMAOH: 196.00 H2O were obtained from sodium silicate (25.5-28.5% silica) cethyltrimethylammonium bromide (CTMABr), tetramethylammonium hydroxide (25 wt% TMAOH in water), Ni or Mn acetate and aged in air under ambient conditions for 2 days. Ni-MCM-41 membranes (NM) were obtained by hydrothermal treatment of the pretreated support into the gel and Ni, Mn-MCM41 powders were obtained by hydrothermal treatment of the gels, y -AI2O3 support disk (0=28.5 mm and 3 mm in thickness, 0.5 jxm in diameter of the pores and 186 m2/g in surface area) were cleaned in an ultrasonic bath containing a HC1 acidified solution mixture of 2-propanol, ethanol and water (volume ratio of 1:2:2). The support was pretreated with an aqueous solution of TMAOH+H2O2. The obtained membranes and precipitates were extensively washed with deionized water, dried in air at 373 K and calcined at 823 K. The composite membranes with Ni-MCM-41 (NP), Mn-MCM-41 (MP) and polysulfone we re obtained by phase inversion method. A polysulfone solution (10%) and PVP (polyvinyl-pyrrolidona-2%) in N-methylpyrrolidona (NMP) with 2% Ni, Mn-MCM-41 was prepared and characterized. When this fourth component is an inorganic particle, a unique ceramic-polymer membrane material is developed. The inorganic powders and membranes were characterized by XRD, SEM, TEM, N2 adsorption-desorption. The pore sizes of NP and MP composite membranes were investigated by liquid porometry by using Coulter porometer and a fluorinated hydrocarbon as wetting fluid. The measurement of the liquid permeability was carried out by the use of a CELFA membrane system, P28 laboratory module, with a cross-flow regime at pressures ranging between 0.4 and 6 bars. The active membrane surface was of 16-25 cm2, and the cell volume was of 500 mL. Permeation measurements and catalytic properties of NM membranes supported on y -A12O3 were tested, in oxidative conditions5, for purification of the waste water with hydrocarbons and phenols. 3. Results and Discussion Nickelsilicate membranes, obtained on y-alumina treated with an aqueous solution of TMAOH+H2O2 present an ordered mesoporous structure (Fig. 1 A). X-ray diffraction diagrams of the materials formed on the surface of y-alumina support show typical MCM-41 materials. TEM images and X-ray diffraction diagrams of both the membrane synthesis on y-alumina support pretreated with the mixture of TMAOH+H2O2 and the nickelsilicate powder obtained in the same autoclave exhibit a mesoporous structure with a hexagonal channel array of pore system. Composite membranes obtained by dispersion of Ni, Mn-

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MCM-41 molecular sieves in an organic polymer solution have the advantage of the enhanced properties of materials utilized. Permeability, homogeneity and activity of these composite membranes are influenced by the inorganic powders properties. The porous structure of such membranes can be greatly varied according to changes in the preparation characteristics and composition. Distribution of mesoporous solid powders is very homogeneous in all the composite membranes. SEM images of the obtained composite membranes (Fig. lb) show an intimate mixture of the polymer and the inorganic powder with a spherical ordered morphology. ••

b

z

A

i A

h.

h4C

_

H

r %

50 ^m

Fig. 1 SEM images of NM (A) and MP composite membrane (B)

These experiments show that the addition of even relatively small amounts of inorganic powder to a 10% PSF/NMP solution influences the membrane formation process. The inorganic particles are promoters for the formation of polymer-lean nuclei and a highly porous and interconnected polymer-rich phase results. Water was firstly filtered by a tubular polypropylene pre-filter type FRN AQUA System (flow water obtained was between 100-150 L/m2h) and then, was included within the structure of an experimental module made of stainless steel circular panels, in order to be tested. The waste water flow obtained, in this case, was between 70-100 L/m2h. The performances obtained as a result of the waste water processing, by using the composite membranes and two waste waters with different composition are included in Table 1. All the membranes are active in separation of the impurities by physic and catalytic processes from the wasted water. Composition of the waste water after permeation through membranes (P) and catalytic reaction (R), in oxidative conditions, show a very good separation and activity for the hydrocarbons,

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sulfides and phenols. A very low concentration of hydrocarbons and phenols were obtained after permeation with catalytic reaction (PR) Table 1. Performances of composite membranes in purification of waste water Composition of the permeated water 2 P/hydr

CCO-Cr, mgO2/l

NH, + , mg/1

P

PR

P

PR

P

P

PR

69.2-63.4/

8.5-8.5/

0.41-0.39/

0.4/

0.64-0.62/

40.039.4/

38.9/

MP

32.3

8.0

0.21/

-

0.50

32.6/

-

NP

29.4

6.2

0.26/

-

0.36

31.2/

-

/300.0-298.5

/15.014.5

/14.7

Mem.

W-B

W-B

213.8-212.9

s -,

mg/1

/146.0145.2

mg/1

/145.0

Cl"/Phenols mg/1

MP

128.4

-

/5.0

/0.6

/6.1

/8.0

/2.1

NP

98.7

-

/3.2

/0.8

/5.2

/5.4

/0.4

NM

89.6

-

/0.6

/l.l

/0.5.

/2.8

(w- waste water, B-blank experiment). 4. Conclusion

Ni-MCM-41 membranes are obtained by hydrothermal treatment of the support into the gel. The obtained hybrid membranes were utilized, as absorbent and catalyst, to purify the water resulted from industry. 5. References [1] R. Lai, Y. Yan and G. R. Gavalas, Microporous Mesoporous Mater., 37 (2000) 9. [2] P. Aerts, E. Van Hoof, R. Leysen, I. F. J. Vankelecom and P. A. Jacobs, J. Membr. Sci., 176(2000)63. [3] H. L. Frisch, S. Maaref and H. Deng-Nemer, J. Membrane Sci., 154 (1999) 33. [4] C. Constantin, V. Parvulescu, A. Bujor, G. Popescu and B. L. Su, J. Mol. Catal. A, 208 (2004) 245. [5] V. V. Parvulescu, C. Constantin,G. Popescu and B. L. Su, J. Mol. Catal. A 208 (2004) 253.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Published by Elsevier B.V.

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Hybrid mesoporous SC/SBA as a chemosensor for recognizing Cu2+ Ling Gao,a Jian-qiang Wang,a Li-ying Shi,a Li Huang,a Ying Wang,a*Xiaoxing Fan,b Tao Yu,b Mei Zhub and Zhi-gang Zoub* "School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, h Ecoenergy and Ecomaterials Center (EEMC), Nanjing University, Nanjing 210093, China.

A novel organic/inorganic hybrid material was synthesized involving the selfassembly of fluorescent molecules (4-chloroaniline-N-salicylidene, SC) within the channel of modified SBA-15. The fluorescent active hybrid mesoporous material exhibits high selectivity for sensing Cu2+ in polar solution. 1. Introduction Grafting chromophore moieties to the inner surface of mesoporous silica leads to a series of fantastic hybrid materials with novel properties which extend its promising applications as chemosensor [1-3], adsorbent [4] and catalyst [5]. The most attractive focus is that the introducing of organic chromophore guest induces some new optical properties of the resulted composites. In this paper, we reported our new kind of hybrid mesoporous composite that was synthesized by the self-assembling of Schiff base 4-chloroaniline-N-salicylidene (SC) within the channel of aminopropyl-functionalized SBA-15. A good linearity in the fluorescent intensity for the concentration change of added Cu2+ was constructed, which enables this hybrid mesoporous material to be a fluorescent chemosensor for detecting Cu2+ cations. 2. Experimental Section The preparation and silylation of SBA-15 with aminopropyl-terethoxysilane (APTES) was performed following the reference [6, 7]. 4-chloroaniline-Nsalicylidene (designated SC) as a fluorescent ligand is easily prepared by the reaction of salicylaldehyde with parachloroaniline in ethanol. The fluorescence

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chemosensor material SC/SBA-15 was prepared by stirring a mixture of 500 mg APTES modified SBA-15 in 38 ml SC solution (derived from 25 mg SC dissolved in 38 ml ethanol) for at least 24 h at room temperature. Followed that a yellowish powder was filtered and washed 3 times with ethanol to remove SC monomers from the external surface and then dried in air. The X-ray powder diffraction (XRD) patterns were recorded on Brucker AXS D8 ADVANCE diffractometer. The pore diameter and the pore size distribution were determined on a Micrometrics ASAP2000 system by the BJH (Barrett, Joyner, Halenda) method. Fourier transform infrared (FTIR) was carried on a Brucker Vector 22 spectrometer with a resolution of 2 cm"1. Fluorescence spectra were obtained on the Cary Eclipse spectrometer. 3. Results and Discussion 3.1. Characterization of Samples

(100)

A

Intensity/a.u.

S B A -1 5 0 .0 6

0 .0 4

0 .0 2

OH

3500

-NH2

3000

C=N -NH2

NH

(110)

2

4

500

Figure 1. FTIR spectra of (A) calcained SBA-15 SBA-15 (B) modified SBA-15 and (C) SC/SBA-15

8

10

= 8 A B C

Si-OH

2500 2500 2000 2000 1500 1500 1000 1000 Wavelength(nm)

6

P o re d ia m e te r(n m )

(200)

1560

m o d ifie d S B A -1 5

0 .0 0

CO

1085

Transmittance/a.u.

B C

4000

P o re v o l u m e ( c c / g )

Figure 1 illustrates the FTIR spectra of calcained SBA-15, APTES modified SBA-15 and the SC/SBA-15 composites. A broad band at 2700-3400 cm"1 is attributed to the -NH2 stretching vibration accompanied with the N-H bending vibration around 696 cm'1 and the symmetric -NH 2 bending vibration at 1560 cm"1, which corroborates the presence of aminopropyl groups in the APTES modified SBA-15 (Fig.IB). In addition, the intensity of Si-OH band of silica network at 960 cm"1 [8] declines after the functionalization, which imply the decrease of Si-OH is resulted from the reaction between APTES and SBA-15 by covalent cross-linking to three oxygen atoms on the interface surface of SBA-15. Fig. 1(C) shows the characteristic stretching band of-C=N- at 1636 cm"1, mirroring the successfully grafting of organic guest to the silica [9].

1

2

3

4

22 Theta/degree

Figure 2. XRD patterns of (A) calcained (B) modified SBA-15 and (C) SC-SBA-15

XRD patterns of calcined SBA-15, APTES modified SBA-15 and SC/SBA15 samples are shown in Figure 2. The XRD pattern of the parent SBA-15 shows three low-angle reflections (dioo, duo and d2oo) characteristic of a well-

863

ordered hexagonal pore arrangement with dioo spacing value of 6.0nm [10]. The (100) peak in the patterns of APTES modified SBA-15 and SC/SBA-15 indicates the hexagonal pore arrangement of SBA-15 is well remained after post grafting. However, the duo and J200 reflections are no longer observed, and an overall decrease in the intensity of dm is observed. These results could be attributed to the local orderless, such as variations in the wall thickness or as it was previously mentioned by Lim et al. [11], due to the interaction between the amorphous silicate framework and APTES-Schiff base complex located inside the channels of SBA-15. Judged on the BJH pore size distribution plots of samples, the pore size of SBA-15 is estimated to be 6.0 nm whereas that of APTES modified SBA-15 is narrowed to 3.4 nm (see the insert), mirroring the anchoring of APTES. And the channel size of 3.4 nm is still sufficiently large to accommodate SC whose approximate dimension is ca.1.2 nmx0.5 nm. 3.2. As a chemosensor for sensing Cu2* The emission spectra of SC/SBA-15 and its fluorescence titration with Cu2+ are displayed in Figure 3. The spectrum of SC/SBA-15 shows typical emission bands at 310 nm (excitation 248 nm). However, when Cu2+ cation is added to the solution of SC/SBA-15, the fluorescence of SC/SBA-15 was dramatically quenched, enabling the free Cu2+ concentration to be determined. 70

Cu Cu

4.0

0

intensity(a.u.))

50 50

40 40

5 ,3030

1

I/(I0-I)

60 60

^

3.2 2.4 1.6 1B 0.8 0.8

\\®^|/S^®Vv

4000

0.4m M 0.4mM

8000

12000

16000

2+

1/[Cu ]

20 20 10 10 0

P 300

350 350

400 400

450 450

500

550

(nm) Wavelength (nm)

Figure 3. The effect of Cu2+concentration on the fluorescence of SC/SBA-15 (0.1 g/L) in ethanol water (9:l,v/v) solution. The insert shows the plot of I/(I-I0) vs [Cu2+]"'. Excitation was 248nm

The corresponding fluorescence spectra (Fig. 3) de picts the fact that the interaction between the organic molecular SC and the Cu2+ ions in the quenching by forming a kind of metal-to-ligand charge transfer transition in energy. It is necessary and important that the -OH or/and -N=CH- groups of compound SC serves as a part of the metal ion receptor. Evidence for 1:1 complex formation is provided by linear relationship obtained in the BenesiHiledbrand plot [12]. A good linear relationship (R = 0.9952) was obtained from the variation in the fluorescent intensity at the appropriate wavelength by plotting the ratio of I/(Io-I) against [Cu ]" in the concentration range of Cu 10 ~ 300 |^mol/L. As a result, the presence of Cu2+ ion will induce an evident

864

change in the complex and means that the chemosensor SC/SBA-15 has an outstandingly high detect sensitive for Cu2+. The fluorescence titration of SC/SBA-15 with various metal ions is conducted to examine its detection selectivity. The competition experiments are performed in the solution of Cu2+ with a concentration of 1.0xl0~5M mixed with another cation, such as K+, Na+, Ag+, Ca2+, Mg2+, Ba2+, Al3+, Cr3+, Fe3+, Co2+, Ni2+, Pb2+; and Mn2+ at 5.0xl0"5M, respectively. Addition one of these metal cations does not cause significant variation in the fluorescence intensity of copper cation (l.OxlO'5 M). Also, no obvious interference is observed in its fluorescence in the case of adding the mixtures of three kinds of among above metal ions. All of these results reveal the excellent selectivity of SC/SBA-15 for detection of Cu2+ cation. 4. Conclusion In summary, we have successfully developed a new fluorescent chemosensor material by grafting a small chromophore within the channel of mesoporous SBA-15. The sufficient sensitivity and selectivity upon the ionic concentration change allow the resulted hybrid material SC/SBA-15 as a promising chemosensor for recognising Cu + ion in polar solution. 5. Acknowledgement Financial support from the NSF of China (20273031 and 20373024), and Analysis Center of Nanjing University is gratefully acknowledged. 6. References [1] V. S. Y. Lin, C. Y. Lai, J. Huang, S. A. Song and S. Xu, J. Am .Chem. Soc, 123 (2001) 11510. [2] G. Wimsberger, B. J. Scott and G. D. Stucky, Chem.Commun., (2001) 119. [3] A. B. Descalzo, D. Jimenez, M. D. Marcos, R. Martinez-Manex, J. Soto, J. El Haskouri, C. Guillem, D. Beltran, P. Amoros and M.V. Borrachero, Adv. Mater., 14 (2002) 966. [4] H. Yoshitake, T. Yokoi and T. Tatsumi, Chem. Mater., 15 (2003) 1713. [5] X . He and D. Antonelli, Angew. Chem. Int. Ed., 41 (2002) 214. [6] D. Zhao, J. Feng, Q. Huo, N.Melosh, G. H. Fredrickson, B. F. Chmelka, and G. D. Stucky, Science 279 (1998) 548. [7] W. Xu, H. Q. Guo, and D. L. Akins, J. Phys. Chem B. 106 (2002) 1191. [8] Y. Luo and J. Lin, Microporous Mesoporous Mater., 86 (2005) 23. [9] C. Lesaint, B. Lebeau, C. Marichal and J. Patarin, Microporous Mesoporous Mater., 83(2005) 76. [10] M. H. Lim and A. Stein, Chem. Mater., 11(1999) 3285. [11] P. Sutra and D. Brunei, Chem. Commu., (1996) 2485. [12] V. K. Indirapriyadharshini, P. Karunanithi and P. Ramamurthy, Langmuir, 17 (2001) 4056.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Published by Elsevier B.V.

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Aluminosilicate mesoporous MCM-41 for drug famotidine delivery Qunli Tang a b , Yao Xu a , Dong Wu a and Yuhan Suna*

" State Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan, 030001, China Graduate School of the Chinese Academy of Sciences, Beijing 100039, China.

Aluminosilicate mesoporous MCM-41 material was prepared and investigated as drug delivery system for famotidine. It was found that the adsorption of famotidine strongly depended on the introduction of aluminum into the mesoporous framework. Furthermore, a delayed drug release rate was obtained in this drug carrier system. 1. Introduction Inorganic materials, such as silica, alumina, titania, etc., are well known for their compatibilities in biological systems. Some types of these materials have been investigated as drug delivery carries for biology, agriculture and pharmacy in relating work [1]. Recently, considerable investigations have been performed for the applications of mesoporous silicas in potential drug carrier systems for high drug loading capacity and sustained or controlled drug release [2-5]. In our recent work, carboxylic-modified mesoporous materials were used as effective adsorption carriers and controlled release carriers for drug famotidine, which contains several terminal amino groups [6]. Herein, aluminosilicate mesoporous MCM-41 material was prepared and investigated as drug famotidine carrier. Significant adsorption of famotidine and a delayed famotidine release was observed in the simulated body fluid. 2. Experimental Section Aluminosilicate MCM-41 was prepared according to the documented procedure for the preparation of low-silica MCM-41 in Ref. 7, and the template was removed using alcoholic solutions of ammonium nitrate. In this work, the

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molar gel compositions were 1.0 Al(OiPr)3:1255 H2O:4.32 NaOH:2.13 CTAB:9.0 SiO2. The obtained sample was denoted as A1-M41. Famotidine was adsorbed from a co-solution of deionized water and methanol (V/V = 1:1) as already reported [6], but with the famotidine concentration of 1.5 mg/mL. In vitro release of famotidine was studied in simulated body fluid (SBF). In a typical case, 0.1 g of this famotidine-charged composite was soaked in 300 mL of SBF. The measurement was carried out at 37 °C. The resultant release medium (2 mL) was removed for analysis at given time intervals, and replaced with 2 mL of fresh SBF. Famotidine content in the clear fluid was measured by UV spectrophotometer. Powder X-ray diffraction (XRD) patterns of the samples were measured on a Bruker Axs (Germany) diffractometer using CuKa radiation. Nitrogen adsorption/desorption isotherms at 77 K were measured using a Micromeritics Tristar 3000 sorptometer. The 27A1NMR experiment was performed at 9.4 T on a Varian Infinityplus-400 spectrometer using 5 mm probehead. The resonance frequency is 104.3 MHz. The 90° pulse width was measured to be 0.4 us. The content of famotidine in the clear solution was determined on a Shimadzu UV2501 PC UV spectrometer. 3. Results and Discussion A strong reflection peak in (100) and two very weak reflection peaks in (110) and (200), characteristic of a hexagonally ordered MCM-41 structure, was observed in the XRD pattern of as-prepared sample (see Fig. 1). N2 adsorption showed a type IV N2 adsorption isotherm (see Fig. 2), being indicative of a well-ordered mesoporous structure. Such anAl-M41 material had the BET surface area, pore volume and pore diameter of 786 m2/g, 0.72 cm3/g and 2.7 nm, respectively.

2

3 4 5 2 Theta/degrees

6

Fig. 1 XRD pattern of the sample.

o.o

0.2

0.4 0.6 0.8 Relative pressure (P/P^)

1.0

Fig. 2 N2 isotherm of the sample.

Fig. 3 shows the 27A1 MAS NMR spectrum of the sample A1-M41. The 27A1 MAS spectrum only exhibited a single peak centered at about 53 ppm, which could be assigned to tetrahedrally-coordinated 27A1 atoms (in which aluminum

867

was covalently bound to four Si atoms via oxygen bridges) [8, 9]. This indicated that the Al contained in the A1-M41 has been completely incorporated into the silicate framework. The adsorption of famotidine by the A1-M41 indicated that 0.38 g of famotidine could be impregnated into the 1 g of the matrix. In addition, it has been found that the pure silica mesoporous material can't adsorb any amount of famotidine under the same adsorption conditions. These suggested tha t the introduction of aluminum into the A1-M41 played an important role in the impregnation of famotidine. As displayed in Fig. 3, the Al species in the sample A1-M41 were tetrahedrally-coordinated Al atoms, in which aluminum was covalently bound to four Si atoms via oxygen bridges. In addition, in combination with the reported analysis about the surface property of the assynthesized sample (before removing the template) prepared under the similar conditions [8], the tetrahedrally-coordinated Al species in aluminosilicate frameworks of the as-synthesized materials led to the accompanying anionic charges on the surface, and then gave rise to strong interactions between these aluminum sites and the long-chain ammonium cations. During the process of removing the template using alcoholic solutions of ammonium nitrate, the surface long-chain ammonium cations were exchanged by ammonium ions (NH/) [7] and with washing the obtained sample by excessively deioned water, the ammonium ions could be replaced by the compensating proton. As a result, it was reasonable that those cationic species, which compensated the negative

150

100

50 0 -50 ppm Fig. 3 27A1 MAS NMR spectrum.

12

14

Fig. 4 Famotidine release profile.

framework charges associated with tetrahedral Al sites in the aluminosilicate framework of the A1-M41, imparted desirable famotidine adsorption by ionexchange process. The famotidine release from the famotidine-impregnated A1-M41 revealed that a delayed drug delivery rate could be obtained in this drug carrier system (see Fig. 4), and the release of 80% of the impregnated famotidine needed about 3 h. The release of the impregnated drug from the mesostructures occurred as follows: the release fluid penetrated into the drug-matrix phase through pores and then followed by the drug dissolution into the release fluid and diffusion

868

from the system along the solvent-filled pore channels, i.e. the drug release process from the mesoporous matrix was mainly controlled by the diffusion of famotidine molecules through the nanochannels. Consequently, the famotidine release should be mainly influenced by the effective pore size of the drugmatrix complex. Besides, the strong interactions between these tetrahedral aluminum sites and the famotidine might be responsible for the delayed drug delivery rate. 4. Conclusion It was found that aluminosilicate mesoporous MCM-41 material had the high loading capacity for famotidine, which could be attributed to the negative framework charges associated with tetrahedral Al sites in the aluminosilicate framework. The drug release was mainly controlled by the strong interactions between these tetrahedral aluminum sites and the famotidine. 5. References [1] T. K. Jain, I. Roy, T. K. De and A. N. Maitra, J. Am. Chem. Soc, 120 (1998) 11092.; M. Shimada, N. Shoji and A. Takahashi, Anticancer Res., 15 (1995) 109.; D. Gong, V. Yadavalli, M. Paulose, M. Pishko and C. Grimes, Biomedical Microdevices., 5 (2003) 575.; M. Lai, L. Levy, K. S. Kim, G. S. He, X. Wang, Y. H. Min, S. Pakatchi and P. N. Prasad, Chem. Mater., 12 (2000) 2632. [2] M. Vallet-Regi, A. Ramila, R. P. del Real and J. P6rez Pariente, Chem. Mater., 13 (2001) 308. [3] J. Andersson, J. Rosenholm, S. Arevaand M. Lind6n, Chem. Mater., 16 (2004) 4160. [4] Y. Zhu, J. Shi, Y. Li, H. Chen, W. Shen and X. Dong, Micropor. Mesopor. Mater., 85 (2005) 75. [5] W. Zhao, J. Gu, L. Zhang, H. Chen and J. Shi, J. Am. Chem. Soc. 127 (2005) 8916. [6] Q. Tang, N. Yu, Z. Li, D. Wu and Y. Sun, Stud. Surf. Sci. Catal., 125 (2005) 649.; Q. Tang, Y. Xu, D. Wu, Y. Sun, Journal of Solid State Chemistry., 179 (2006) 1512. [7] N. Lang and A. Tuel, Chem. Mater., 16 (2004) 1961. [8] M. T. Janicke, C. C. Landry, S. C. Christiansen, S. Birtalan, G. D. Stucky and B. F. Chmelka, Chem. Mater., 11 (1999) 1342. [9] M. T. Janicke, Landry, S. C. Christiansen, D. Kumar, G. D. Stucky and B. F. Chmelka, J. Am. Chem. Soc, 120 (1998) 6940.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

869 869

DNA delivery using polyethyleneimine (PEI) coated iron oxide-silica mesostructured particles. Stuart C. McBain, Humphrey H. P. Yiu, Alicia J. El Haj and Jon Dobson* Institute of Science and Technology in Medicine, Keele University, Thomburrow Drive, Hartshill, Stoke-on-Trent, Staffordshire, ST4 7QB, United Kingdom;

1. Introduction Magnetic nanoparticles have attracted significant interest in recent years through their ability to act as vehicles for targeted delivery of DNA and pharmaceutical agents [1, 2]. In order to act as efficient carriers, these particles must be able to effectively bind, and then release their target molecules. As such, much work has focused on surface functionalisation of these particles. One of the most effective approaches for binding DNA is to exploit electrostatic interactions between positively charged molecules or surfaces and the negatively charged phosphate groups present within DNA. Polyethylenimine (PEI) has been one of the popular choices in this application [3, 4] and PEI functionalised magnetic particles for DNA delivery are now commercially available. The use of magnetic particles as support for PEI combines the ability of PEI to bind and condense DNA [5], with the potential for targeted delivered offered by such particles [6]. In this work we demonstrate the use of mesoporous silica as a template for synthesising magnetic iron oxide-silica composite particles. These particles were prepared using SBA-15 as a support for both the iron oxide core and the PEI coating. The iron oxide core is embedded inside the mesochannels of SBA15 and the dimension of the channels restricted the growth of iron oxide particles. With the positively charged PEI coating, negatively charged DNA will bind on the surface of the composite particles. Here, we describe a new approach for producing composite magnetic nanoparticles for DNA binding and gene delivery.

870

2. Experimental Section 2.1. Preparation ofFOSC-1 PEI particles Mesoporous silica SBA-15 was used as a template for preparing iron oxidesilica composite (FOSC-1). Iron(III) nitrate nonahydrate (99%, Aldrich) was used as the iron precursor. A 33% w/w iron oxide solution was prepared by dissolving 1.23 g Fe(NO3)3-9H2O in 5 cm3 ethanol and 1 g of calcined SBA-15 particles added to the solution. The mixture was heated at 40°C overnight. When all of the solvent had evaporated, the composite particles were heated to 300°C at 10°C min 1 in a furnace. The resultant solid showed a deep brown colour. Short chain polyethylenimine (PEI, m.w. = 1800, Aldrich) were coated onto the surface of FOSC-1 particles by suspending the particles in a 50% PEI aqueous solution for 24 hours. The particles were then recovered and washed with deionised water three times. 2.2. DNA binding capacity In order to determine the DNA binding capacity of the particles, the particles were suspended at 5 - 300 (ig cm"3 in sterile dd H2O together with pCI plasmid DNA at a final DNA concentration of 50 ug cm"3. The suspensions were kept at room temperature for 2h with constant rotation. After centrifugation at 13,000 rpm for 10 mins, the DNA concentration of the supernatant was determined using an Eppendorf Biophotometer. 2.3. Transfection of HEK293T cells with FOSC-1 PEI 1800 HEK293T cells were were cultured in DMEM medium supplemented with 10% foetal calf serum, lOOU/ml penicillin, O.lmg/ml streptomycin, 0.25 ng/ml amphortericin B and 2mM L-glutamine. For transfection studies, cells were seeded at 2.5 x 104 cells/well in 24 well tissue culture plates and incubated overnight at 37°C 5% CO2. In order to attach DNA to the surface of FOSC-1 particles, the particles were resuspended at 300 ug cm'3 in sterile dd H2O together with pCIKLux plasmid DNA at a final DNA concentration of 100 \ig cm"3. The suspension was incubated for 2h at room temperarture with constant rotation. Prior to transfection, the medium was removed from the cells and replaced with 500 uL of serum free (SF) RPMI containing 20 u,g FOSC-1 PEI 1800 particles coated with pCIKLux plasmid DNA, supernatent from FOSC-1 PEI- DNA binding procedure (50 ul) or naked DNA (5 |ig). Untransfected (serum free medium only) cells were included as control. At 18 hours post transfection, the medium was supplemented with 500uL of DMEM medium supplemented with 20% foetal calf serum, 100 U/ml penicillin, 0.1 mg/ml streptomycin, 0.25 ug/ml amphortericin B and 2 mM L-glutamine. At 48 hour

871

post transfection the media was removed from each well and the cells lysed in 50 uL of reporter lysis buffer (Roche). Each sample was assayed for luciferase activity and total protein concentration. 3. Results and Discussion The design of PEI coated FOSC-1 particles is shown in Figure 1. Mesoporous silica SBA-15 was used as a template for preparing iron oxide-silica composite (FOSC-1) and the procedure has been described elsewhere [7]. The positively charged PEI molecules are bound on the negatively charged surface of FOSC-1 via electrostatic interactions. DNA molecule

PEI coating Silica walls of SBA-15 " - . Iron oxide nanoparticles

Mesochannels

Figure 1: Schematic representation of PEI coated FOSC-1 PEI particles. 2.00E+07 1.80E+07 • 1.80E+07 1.60E+07 • 1.60E+07

/ y = 0.318 x RLU/mg protein

1.40E+07 • 1.40E+07 j 1.20E+07 1.20E+07 • n 1.00E+07 1.00E+07 • ! 8.00E+06 8.00E+06 •

6.00E+06 • 4.00E+06 • 2.00E+06 • 0.00E+00 10

20

30

40

50

Amount of particles (ug)

Figure 2: DNA binding curve for FOSC-1 particles. • = FOSC-1 PEI • = FOSC-1.

Control

Naked DNA

SN SN

FOSC-1 1800 1800 FOSC-1 PEI PEI

Bound DNA (ug)

Figure 3. Luciferase activity in HEK293T cells transfected with FOSC-1 PEI nanoparticles coated with pCIKLux DNA. Cells were transfected with either 5jxg of naked DNA, 20\ig FOSC-1 PEI 1800 particles coated with pCIKLux plasmid DNA, or supernatent from FOSC-1 PEI DNA binding procedure (50ul). Data shown as mean ± SEM n=5.

872

Due to the large number of postive charges carried by secondary amine groups present within the bound PEI, FOSC-1 PEI particles possess a high binding capacity for DNA (Figure 2). In contrast, uncoated FOSC-1 particles are unable to bind DNA since the negatively charged FOSC-1 surface will repel negatively charged DNA molecules. The binding capacity of FOSC-1 PEI particles was calculated to be 0.32ug DNA per ug FOSC-1 PEI. In order to examine the ability of FOSC-1 PEI particles to act as gene delivery agents, particles coated with a luciferase reporter construct (pCIKlux) were used to transfect HEK2923T cells (Figure 3). Cells transfected with FOSC-1 PEI particles showed a high level of luciferase expression in comparison to cells transfected with naked DNA alone. In order to confirm that this expression was associated with FOSC-1 PEI particles and not simply free PEI-DNA complexes released from the surface of the particles, cells were also exposed to supernatant from FOSC-1 PEI DNA binding reactions. Although luciferase activity was detectable under these conditons, the level of expression was significantly lower than that observed using FOSC-1 PEI particles. 4. Conclusion PEI coated FOSC-1 particles showed a high binding capacity of DNA, and are an effective transfection reagent. The novel use of mesoporous silica significantly increases the surface area available for functionalisation increasing the DNA binding capacity of these particles. Studies to investigate the ability of these particles to transfect cells in the presence of magnetic fields are currently in progress and will be reported elsewhere. 5. Acknowledgement The authors thank BBSRC and the UK Cystic Fibrosis Gene Therapy Consortium for funding. JD acknowledges support from a Wolfson Foundation / Royal Society Research Merit Award. 6. References [1] [2] [3] [4]

Q. A. Pankhurst, J. Connoly, S. K. Jones and J. Dobson, J. Phys. D, 36 (2003) R167. J. Dobson, J. Gene Ther. 13 (2006) 283. M. Neu, D. Fischer and T. Kissel, J. Gene Med. 7 (2005) 992. C. Plank, U. Schillinger, F. Scherer, C. Bergemann, J. S. Remy, F. Krotz, M. Anton, J. Lausier and J. Rosenecker, Biol. Chem. 384 (2003) 737. [5] O. Boussif, F. Lezoualc'h, M. A. Zanta, M. D. Mergny, D. Scherman and B. Demeneix, J. P. Behr. Proceeedings of the National Academy of Sciences USA. 92 (1995) 7297. [6] C. Mah, T. J. Fraites Jr, I. Zolotukhin, S. Song, T. R. Flotte, J. Dobson and C. Batich, B. J. Byrne Mol. Ther. 6 (2002) 106. [7] T. Tsoncheva, J. Rosenholm, C. V. Teixeira, M. Dimitrov, M. Linden and C. Minchev, Microporous Mesoporous Mater. 89 (2006) 209.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

873 873

A new highly sensitive and selective nanosensor for Mercury (II) ions Noan Nivarlet, Samuel Martinquet and Bao-Lian Su Laboratoire de Chimie Materiaux Inorganiques, The University of Namur (FUNDP), 61 Rue de Bruxelles, B-5000 Namur, Belgium

A new selective nanosensor for Hg (II) ions based on the immobilization of a fluorescence probe on the surface of CMI-1 mesoporous materials is described. 1. Introduction Mercury contamination is widespread, resulting from a variety of natural sources including oceanic and volcanic emissions [1], gold mining [2], solid waste incineration, and the combustion of fossil fuels [3]. Moreover, mercury's unique properties facilitate many industrial applications such as the preparation of chlorine and caustic sauda [4], electrical equipments, paints, fungicides, dental amalgam fillings and antiseptics. Once mercury is introduced in the marine environment, bacteria convert it into methylmercury, which enters the food chain and can cause severe brain diseases to humans. Therefore, the development of new or improved methods of detection is highly desirable.The use of chromo- or fluoroionophore molecules is particularly attractive. Therefore, we report a highly sensitive bifunctional molecule combining a specific mercury (II) ion receptor such as benzoylthiourea and a fluorescent sensitive site like anthracene. Both functions are separated by a methylene spacer who minimizes the distance between the receptor and the fluorophore and facilitates thus efficient photoinduced electron transfer (PET) [5]. This type of molecule, also called fluoroionophore, responds with a fluorescence enhancement proportional to the mercuric ions concentration. In order to conceive portable fluoroionosensors, the immobilization of the N-methyl-N-9(methylanthracene)-N'-benzoylthiourea (AnthBT) in a CMI-1 and in hydrophobic functionalized CMI-1 silica mesoporous materials is carried out.

874

2. Experimental Section N-methyl-N-9-(methylanthracene)-N'-benzoylthiourea (AnthBT) was synthesized with a 95 % yield accordingly with the literature [6] and was fully characterized by FT-IR, ! H NMR, UV-visible and fluorometry. The CMI-1 and iodopropane-modified CMI-1 mesoporous materials were synthesized as reported [7, 8]. Hydrophobic mesoporous materials with different grafted iodopropane amounts were obtained by using different (3iodopropyl)trimethoxysilane quantities. The immobilization of AnthBT was realized by immersing the CMI-1 material in an acetone solution of AnthBT during 3 hours. The solid sensors were recovered by filtration, washed two times with acetone and dried during 2 hours at 60°C. These materials were characterized by BET, XRD, TEM, SEM, TG, 29Si NMR, FT-IR and fluorometry. Nanosensor leaching tests were performed in a solution of MeOH/H2O (10:1 v/v). The calibration curves of nanosensors were established by adding, successively to 1.0 x 10"1 g of hybrid, 50.0 ul of mercuric ion solutions and after a contact time of 6 minutes. 3. Results and Discussion The UV-visible and fluorescence spectra of AnthBT depicted in figure la, registered in MeOH/H2O (10:1 v/v), show four characteristic bands of the vibrational structure of anthracene. The sensitivity of AnthBT towards different ions i.e. Ag+, Cd2+, Co2+, Cu2+, Hg2+, Pb2+ and Zn2+ (2.0 equivalents) was studied. The fluorescence intensity of AnthBT increased upon addition of Cd2+, Hg2+, Pb2+ and Zn2+ reaching a maximum for the Hg (II) ions. No significant wavelength shifts were observed upon ion complexation. For the other ions studied, the same or a decrease in fluorescence intensity was observed. To explore further the effectiveness of AnthBt as an ion-selective fluorescence chemosensor for Hg2+ ions, competition experiments were conducted in the presence of Hg2+ at 10"5 M and also Hg2+ mixed with either Cd2+, Pb2+ or Zn2+ at 10"5 M in 5xlO'6 M probe molecules solutions. No significant variation in the fluorescence intensity was found compared to the sample containing Hg2+ only (all were less than 7 %). The intensity of the fluorescence emission of AnthBT was sensitive to Hg (II) ions and increased with the concentration of Hg (II) (Figure lb). The analysis of this curve, obtained by adding succesively 5.0 |nl of a 2.5xlO'4M mercuric ion solution to 2.5 ml of a 5.0xl0"6M AnthBT alcoholic solution, revealed that the Hg (II) ion complexation is a two step process. These binding steps with the fluoroionophore were attributable to different binding modes present in the ligand i.e. the 1:1 and 2:1 stoichiometry, transition ensured by the loss of protons to form finally a 2:1 neutral complex (Figure lc). The detection limit, fixed by the 1:1 stoichiometry was estimated at 2.0x10"8 M.

875

The fluorescence enhancement of AnthBT in the presence of Hg2+ can also be observed by fluorescence quantum yield measurements. The AnthBT quantum yield was evaluated at 5.7xl0'3 (calculated on the basis of the one of anthracene O F = 0.27) without mercuric ions and at 1.73xlO"2 in the presence of 10.0 equivalents of Hg2+. 170

Emmission Absorption

a)

b)

Intens ity (a.u.)

In te n s ity (a .u .)

160 150

stoichiometry 1:1

140

y == 93.21 93.21 ++3.27E8x 3.27E8 x 2 r* == 0.996 0.996

130

stoichiometry 2:1 y = 102.91 + 1.68E7 x 2 r = 0.992

120 110 100

300

350

400

450

0,0

500

-7

-6

-6

-6

-6

-6

O

+

-H

c)

-6

N

N

S

-6

2+

[Hg ] (Molar)

Step 1

H N

N

-6

5,0x10 1,0x10 1,5x10 2,0x10 2,5x10 3,0x10 3,5x10 4,0x10 4,5x10

Wavelength (nm)

Step 2

N

N S

O

Hg

+

O

-H

Hg

+

O

S

S N

N

Figure 1: a) UV-visible and fluorescence (^ xc = 365 nm) specta of AnthBT in MeOH/H2O (10:1 v/v) b) Calibration curve of AnthBT in the presence of Hg2* increasing concentrations in aqueous alcoholic medium c) Reaction scheme showing the stepwise binding of Hg (II) ions by AnthBT

The structural and chemical characterization of CMI-1 and Iodo-modified CMI-1 materials which will be used as supports for the AnthBT immobilization is depicted in figure 2. The amount of grafted iodopropyle on the mesoporous material surfaces was determined due to thermogravimetric measurements (weight loss between 250 and 350°C). These results have emphasized that a grafted functional group maximum of 0.67 mmol/g was obtained for the use of 7.0 mmol of silylating agent. Q4

50000

d100

Iodo-modified CMI-1

SiO Si

I

OSi

40000

Intensity (a.u.)

Q3

OSi

CMI-1

T3 30000

Q2

20000

d110 d200

10000

0 2

4

2θ (°)

0

-100

-200

δ (ppm)

Figure 2: a) Small angle XRD pattern which is typical of hexagonal structures, b) 29Si NMR of a CMI-1 and an Iodo-modified CMI-1 material

AnthBT was physisorbed in CMI-1 and in hydrophobic group modified CMI1 materials. These hybrid materials were characterized by the UV-visible and fluorescence spectroscopies where the AnthBT typical signal was found again (with no wavelength shift) and by 29Si NMR and FT-IR where no signal attribuable to AnthBT was detected, probably due to the small incorporated probe molecule quantities. The study of immobilized probe molecule quantities

876

revealed that highest AnthBT loadings were obtained for the functionalized mesoporous materials reaching 1.22xlO"4 mole/g for the most hydrophobic material. The leaching tests of AnthBT/CMI-l(CMI-l-IPr-xmmol of grafted Iodopropyle) hybrid materials (Figure 3a) revealed that the leaching rate decreases with the increase of grafted iodopropyle amount since its value did not exceed 4 % for the most hydrophobic material. The nanosensor test was performed in alcoholic medium (MeOH/H2O 10:1 v/v) with increasing mercuric ion concentrations (figure 3b). 20

CMI-1 18 16

650

CMI1-IPr0.17mmol —CMI-1-IPr0.34mmol CMI-1-IPr0.34mmol — CMI-1-IPr0.67mmol CMI-1 -IPr0.67mmol

A

550

Intensity (u.a.)

Leaching rate (%)

14 12 10 8 6

" 1

Stoichiometry 1:1 y = 421.61 + 1.46E10 x

600

500

Stoichiometry2:1y= Stoichiometry 2:1 y = 491.37 + 2.21E8 x 2 r = 0.993

450 400

4

a)

2 0 0

20

40

60

Time (minutes)

80

100

120

350

.. b)

300 0.0

-7

2.0x10

4.0x10

-7

6.0x10

-7

-5

2.0x10

2+

[Hg ] (M)

Figure 3: a) Leaching profile of AnthBT/CMI-1 and CMI-1-IPr hybrids in MeOH/H2O (10:1 v/v) b) Calibration curve of nanosensor (X^xc = 365 nm) in the presence of different concentrations of Hg2+ ions (solvent: MeOH/H2O 10:1 v/v)

The calibration curve also shows the two binding modes as observed in solution. The nanosensor allows the Hg (II) ion detection for concentrations ranging from l.OxlO"8 to 3.9xlO"7 M with a response time of 4 minutes before any increase in fluorescence. 4. Conclusion We have demonstrated a novel and practical system for the fluorometric sensing of Hg2+ in aqueous solution based on the immobilization of a mercuric ion selective molecule in hydrophobic functionalized CMI-1 mesoporous materials. We have proved that once immobilized in functionalized mesoporous materials, AnthBT kept its sensor properties. 5. References [1] A. Renzoni, F. Zino and E. Franchi, Environ. Res. 77 (1998) 68. [2] O. Malm, Environ. Res. 77 (1998) 73. [3] Mercury Update : Impact on Fish Advisories (2001). EPA Fact sheet EPA-823-F-01-011 ; EPA, Office of Water : Washington, DC. [4] C. A. McAuliffe, (1977). The Chemistry of Mercury, Macmillan Press Ltd, London. [5] R. A. Bissel, A. P. de Silva, H. Q. N. Gunaratne, P. L. M. Lynch,G. E. M. Maguire, C. P. McCoy and K. R. A. S. Sandanayake, Top. Curr. Chem. 168 (1993) 223. [6] E. Unterreitmaier and M. Schuster, Anal. Chim. Acta. 309 (1995) 339. [7] J. L. Blin, A. Leonard and B. L. Su, Chem. Mater. 13 (2001) 3542. [8] D. Brunei, Microporous Mesoporous Mater. 27 (1999) 329.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

877 877

SBA-15 functionalized by epoxy groups for immobilization of penicillin G acylase Yongjun Lti, Qiaoling Zhao, Yanglong Guo*, Yanqin Wang, Yun Guo and Guanzhong Lu Lab for Advanced Materials, Research Institute of Industrial Catalysis, East China University of Science and Technology, Shanghai 20023 7, P. R. China

1. Introduction The discovery of the large pore mesoporous materials, such as SBA-15 [1], broadens their application in the biotechnological fields, and more molecular sieves of biological interest have really attracted much attention [2]. The studies show that the surface functionalization of mesoporous silica by organic groups can enhance the interaction between the enzyme and the support and increases its operation stability [3]. The organic groups functionalized SBA15 have been used to immobilized penicillin G acylase (PGA) [4,5]. Epoxy groups can react with amino groups (NH2) of the enzyme under mild conditions without pretreatment and cross linkage. The organic copolymer supports with epoxy groups have been developed to immobilize PGA successfully, and appreciative apparent activity and operation stability were achieved [6,7]. However, mesoporous silica functionalized by epoxy groups has not yet been reported. In this paper, SBA-15 functionalized by epoxy groups was prepared, characterized and used as the support for the immobilization of PGA. Effect of the amount of epoxy groups on the apparent activity and operation stability of immobilized PGA (IMP) were also investigated. 2. Experimental Section SBA-15 was synthesized according to Zhao et al. [1]. y-glycidoxypropyltrimethoxylsilane (GPTMS) was used as the functionalization agent. The functionalization of SBA-15 was carried out by a post-synthesis route [3]. Changing the amount of GPTMS in the synthesis solution from 0.5 g, 1 g and 1.5 g, the functionalized samples of SBA-15(0.5), SBA-15(1) and SBA-15(1.5)

878

were prepared. The immobilization of PGA (804 IU/ml for the free enzyme) and assay of IMP apparent activity were the same as Reference [8]. After testing the apparent activity of IMP, IMP was separated by centrifugation, and used repeatedly to assay its apparent activity. 3. Results and Discussion The powder XRD pattern of SBA-15 (Figure 1) agrees well with that reported by Zhao et al. [1], which confirms the successful synthesis of SBA-15. The XRD pattern of SBA-15(0.5) functionalized by GPTMS is similar to that of SBA-15, which indicates that the framework of SBA-15 is not destroyed after the functionalization. Compared with the FT-IR spectrum of GPTMS, the absorption peaks at 2927, 2854, 1461 and 1398 cm"1 in the IR spectrum of SBA-15(0.5) (Figure 2) are attributed to the presence of glycidoxypropyl groups on the functionalized SBA-15. The characteristic absorption peak of epoxy groups should be located at ~910 cm"1, but it is too weak to be seen clearly. The nitrogen adsorption-desorption isotherms of SBA-15 and functionalized SBA-15(0.5) are shown in Figure 3, which belong to the isotherms of type IV. The isotherm of SBA-15(0.5) still retains the characteristic step of the isotherm of SBA-15, in which the capillary condensation step shifts slightly to lower relative pressures. This indicates that the pore size decreases after being functionalized, which can be also confirmed by the pore size distribution curve shown in Figure 4. For the functionalization SBA-15, a significant reduction in the amount of nitrogen adsorbed implies decreasing of its pore volume. 100 100

Absorbance

Intensity

GPTMS

110 110 200

•

V

SBA-15 SBA-15(0.5)

V

x/~^

/

^

ft

910

SBA-15

__

SBA-15(0.5) 1

22

33

4 o

Theta ( 2 Theta ()

Fig. 1 XRD patterns of SBA-15 and the functionalized SBA-15(0.5)

5

4000 4000 3500 3500 3000 3000 2500 2500 2000 2000 1500 15001000 1000 500 500 -1 ) Wavenumber (cm )

Fig. 2 FT-IR spectra of GPTMS, SBA-15 and the functionalized SBA-15(0.5)

The pore size distribution curves of the samples are shown in Figure 4. No obvious difference is observed between two pore size distribution curves, that is, SBA-15(0.5) is structurally similar to SBA-15. However, the pore diameter of SBA-15 is about 1.2 nm larger than that of SBA-15(0.5), which indicates that

879

GPTMS has been grafted on the pore surface of SBA-15 and the surface functionalization results in a decrease in the pore size. SBA-15 12 3

25 20 15

SBA-15 10 5

Pore Volume (cm /g)

Quantity Adsorbed (mmol/g)

14 30

SBA-15(0.5)

10

SBA-15(0.5) 8 6 4 2 0

0 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.0

0

5

100 100 Relative activity(%)

Weight (%)

Fig. 5 TGA profiles of SBA-15 and the functionalized SBA-15 samples

15 15

20

25

30 30

35

Fig. 4 Pore size distribution curves of SBA-15 and SBA-15(0.5)

Fig. 3 Nitrogen adsorption-desorption isotherms of SBA-15 and SBA-15(0.5) 100 98 A 96 94 92 90 B 88 C 86 84 D 82 100 100 200 300 400 500 600 700 800 o Tempreture ((°C) C)

10 10

Pore Diameter (nm)

Relative Pressure (P/Po)

PGA/SB A-15(0.5) PGA/SBA-15(0.5)

90 80 70

PGA/SB A- 1 5 PGA/SBA-15

60 50 40 30

0

11 22 33 4 4 5 5 6 6 7 7 8 8 Recycle time time

10 11 11 9 10

Fig. 6 Operation stability of PGA immobilized on SBA-15 and SBA-15(0.5)

The TGA profiles of SBA-15(A) and SBA-15(0.5)(B), SBA-15(1.5)(C), SBA-15(1)(D) are shown in Figure 5. The results show that SBA-15 has a slight weight loss, mainly due to surface dehydration or dehydroxylation. However, the functionalized SBA-15 samples have a remarkable weight loss at 300-500 °C, which can be attributed to the decomposition of the incorporated glycidoxypropyl groups. With an increase in the GPTMS concentration in the synthesis solution, the weight loss of the functionalized SBA-15 increases slightly. SBA-15(1) has the largest weight loss. It is possible that too much GPTMS molecules blocked their entrance into the inner channel. The results above show that glycidoxypropyl groups are chemically grafted on the surface of SBA-15. The results in Table 1 show that, the apparent activity of PGA immobilized on SBA-15(0.5) is higher than that on SBA-15. When the amount of glycidoxypropyl groups grafted on SBA-15 is higher, its pore size diminishes obviously to block more enzymes and reactants entering into the channel,

880

therefore the apparent activity of PGA immobilized on SBA-15(1) and SBA15( 1.5) are lower than that of PGA/SBA-15. The operation stability (Figure 6) of PGA immobilized on SBA-15(0.5) is better than that on SBA-15. After being recycled for 10 times, PGA immobilized on SBA-15(0.5) preserved 88% of the initial apparent activity, and that on SBA-15 only preserved 65%. It indicates that PGA has been immobilized on the functionalized SBA-15 by covalent bond and the combination between PGA and the functionalized SBA-15 is more stable than that between PGA and SBA-15 by hydrogen bond only. Table 1 Apparent activity of IMP and BJH adsorption pore diameter of functionalized SBA-15 Supports Apparent activity (IU/g dry support) BJH adsorption pore diameter(nm)

SBA-15 1343 8.2

SBA-15(0.5) 1408 7.3

SBA-15(1) 1316 6.9

SBA-15(1.5) 1191 6.7

4. Conclusion SBA-15 was successfully functionalized by glycidoxypropyl groups without destroy its framework, and the presence of glycidoxypropyl groups on the surface of SBA-15 leads to a decrease in the pore size. PGA immobilized on the functionalized SBA-15 by covalent bond is more stable than that on SBA-15, which improves obviously the apparent activity and operation stability of PGA/functionalized SBA-15. This project was supported financially by National Basic Research Program of China (No. 2004CB719500), Shanghai Rising-Star Program (No. 04QMX1431) and Program for Outstanding Young Teacher of Shanghai Universities (No. 04YQHB050). 5. References [1] D. Y. Zhao, J. L. Feng, Q. S. Huo, N. Melosh, G. H. Fredrickson, B. F. Chmelka and G. D. Stucky, Science, 279 (1998) 548. [2] H. H. P. Yiu and P. A. Wright, J. Mater. Chem., 15 (2005) 3690. [3] J. F. Kennedy and A. Wiseman (Ed.). Handbook of Enzyme Biotechnology, Ellis Horwood, London, (1995), 235. [4] A. S. M. Chong and X. S. Zhao, Catal. Today, 93-95 (2004) 293. [5] A. S. M. Chong and X. S. Zhao, Appl. Surf. Sci., 237 (2004) 398. [6] P. Xue, G. Z. Lu, Y. L. Guo, Y Guo and Y. S. Wang, Chem. J. Chinese U., 25 (2004) 361. [7] J. Torres-Bacete, M. Arroyo, R. Torres-Guzman, I. de la Mata, M. P. Castillon and C. Acebal, Biotechnol. Lett., 22 (2000) 1011. [8] P. Xue, G. Z. Lu, Y. L. Guo, Y. S. Wang and Y Guo, J. Mol. Catal. B, 30 (2004) 75.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

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Adsorptive desulfurization of diesel using metallic Nickel supported on SBA-15 as adsorbent Chang Hyun Ko, Jung Geun Park, Sang-Sup Han, Jong-Ho Park, Soon-Haeng Cho and Jong-Nam Kim Separation Process Research Center, Korea Institute of Energy Research, 71-2, Jangdong, Yuseung-gu, Daejeon, 35-343, Korea

1. Introduction Government world-wide are trying to reduce air pollution by decreasing sulfur concentration in transportation fuel from current 300 parts per million weight (ppmw) to 10 ppmw until 2010 [1]. However, the decrease of sulfur concentration in transportation fuel down to 10 ppmw by current hydrodesulfurization (HDS) process is extremely difficult due to the low reactivity of HDS catalysts for refractory sulfur compounds, such as 4,6dimethyldibenzo thiophene (4,6-DMDBT). In order to meet this regulation, the reactor size of HDS process based on current technology is expected to be 3 times larger [2]. To overcome these problems, many researchers have tried to develop alternative methods. Yang and co-workers reported that metal ions, such as Ni2+ and Cu+ which were exchanged on Y zeolites, showed remarkable adsorption capacity for sulfur compounds in diesel at ambient conditions [3-5]. They proposed that the main driving for selective adsorption was ncomplexation. Their capacity, however, strongly depended upon compositions of diesel fuels [6]. Song and co-workers reported that metallic nickel particles supported on high surface area silica and zeolite Y were effective for sulfur removal in transportation fuels regardless of their composition [7,8]. Based on these previous results, we prepared metallic nickel particles supported on SBA15 (Ni/SBA-15) and used as an adsorbent for selective remolval of sulfur compounds in diesel. Nickel loading, and solvent used in impregnation method were optimized to maximize sulfur adsorption capacity of Ni/SBA-15.

882

2. Experimental Section Mesoporous silica SBA-15 was synthesized by adopting the procedure reported elsewhere [9]. As-synthesized SBA-15 was calcined at 823 K for 2 h in oxygen environment. Nickel nitrate (Ni(NO3)2- 6H2O, Junsei) was dissolved in tetrahydrofuran (THF, Aldrich) or doubly distilled water. This solution was ill,,.. II...I.. . , impregnated on calcined SBA-15 by incipient wetness method. After impregnation, excess solvent was dried in an Fig. 1 GC-FPD chromatogram of oven at 373 K for 4 h. Then, the nickel commercial diesel nitrate impregnated SBA-15 was reduced in hydrogen atmosphere at 873 K for 2 h. Feed liquid for breakthrough test was commercial diesel purchased at a gas station near Daejeon. The sulfur concentration in the feed liquid was 240 ppmw. As shown in Figure 1, major sulfur compound in the feed was identified as 4,6-DMDBT. The sulfur concentration of diesel, which passed through adsorbent was measured by Antek 9000LLS total sulfur analyzer. Sulfur adsorption temperature was 473 K.

s

3. Results and Discussion X-ray diffraction pattern and pore size distribution curve, calculated by BJH method for calcined SBA-15, are shown in Figure 2. Well-resolved 3 A l\ peaks in XRD pattern implied that /\ SBA-15 has one dimensional pore structure. Lattice spacing and previous results reported elsewhere [9] showed that pore size of SBA-15 was around 7 nm. The pore size distribution by BJH method also confirmed this pore size. BET surface area and single point pore Fig. 2 X-ray diffraction pattern and N2 volume, calculated from N2 adsorption adsorption isotherm of calcined SBA-15 isotherm, were 671 m7g and 1.08 ml/g respectively. These results indicated that SBA-15 seems to be useful support for metal particles because it has high surface area, well-ordered mesopores with uniform size. On this support, metallic nickel particles were formed by converting nickel nitrate into metallic nickel via thermal reduction in H2 environment. 1dOQO

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In the breakthrough curves, as shown in Figure 3, sulfur concentrations in commercial diesel were varied according to the volume passed through adsorbent. There were negligible changes of sulfur concentrations in the initial stage of the tests. However, it increased drastically at a certain point. We defined breakthrough volume as diesel volume passed through adsorbent bed before outlet sulfur concentration goes over 10 ppmw, and calculated sulfur capacity based on this volume. Figure 3 also shows the change of sulfur adsorption capacity depending on the solvent used for nickel nitrate impregnation. All the samples were prepared with the same treatment procedure except solvent for impregnation. At the same nickel loading of 10 wt%, solvents for nickel impregnation, water and tetrahydrofuran (THF), did not affect the sulfur adsorption capacity of adsorbents. As the Ni loading increased to 20 wt%, sulfur adsorption capacity of Ni/SBA-15 decreased when THF was used as solvent in impregnation step. However, 20 wt% Ni/SBA-15 adsorbent with THF increased. Because THF is much more volatile than water, rapid drying during the preparation of adsorbent by THF might have positively affected the nickel nitrate distribution in pores of SBA-15. Therefore, as an attempt to increase the sulfur adsorption Volume of Diesel/ Weight of Adsorbent (ml/g) capacity, THF was fixed as a Fig. 3 Breakthrough curves of Ni/SBA-15 solvent for impregnation. In addition to solvent, nickel prepared by different methods: Parenthesis indicated which solvent was used for impregnation loading amount on adsorbent was optimized to maximize sulfur adsorption capacity. As shown in Figure 4, sulfur adsorption capacity increased until the nickel ? 1 .4 ? 1 .2 loading increased to 30 wt%. ? 1.0 Maximum capacity was 1.7 mg f 0.8 S/g. However, adsorption ji 0.6 capacity decreased to 0.6 mg S/g : 0.4 at 40 wt%. This might be caused ° 0.2 2 by agglomeration of nickel Ni loading (wt.%) accompanied with high nickel Fig. 4 The change of sulphur adsorption loading amount. This assumption capacity depending on the nickel concentration of was supported by molar ratio Ni/SBA-15 analysis as shown in Figure 5. Molar ratio of adsorbed sulfur molecules to nickel atom (S/Ni) was displayed according to the nickel concentration in SBA-15. As the nickel concentration 240 220 200 180 160 140 120 100

80

10 wt.% SBA-15 (Water) 20 wt.% SBA-15 (Water) 10 wt.% SBA-15 (THF) 20 wt.% SBA-15 (THF) Initial Sulfur Concentration

60 40 20 0

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12

15

18

21

24

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260

1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0

0

10

20 Ni lo a ding ( wt. %)

30

40

884

increased, S/Ni decreased. Until 30 wt%, less than 100 nickel atoms were able to adsorb one sulfur molecule. However, at 40 wt%, more than 350 nickel atoms were required to fixate one sulfur compound. It indicated that large nickel particles were formed at 40 wt% Ni loading (wt.%) and the particle size was at least Fig. 5 The change of molar ratio of adsorbed 3 times larger than that formed sulfur-molecules to nickel atom according to the at 30 wt%. In addition to the nickel concentration in adsorbent increase of particle size, pore blockage induced by particle size increase might also be considered. As the nickel particle size increased, one-dimensional pores of SBA-15 might be blocked. In this case, nickel particles located deep inside the one dimensional pores, which were blocked by particles near the entrance, were not accessible to sulfur compounds in diesel. The increase of nickel particle size and possible pore blockage might decrease the number of sulfur adsorption sites in Ni/SBA15. From these results and consideration, we reached the conclusion that optimum nickel loading was 30 wt% and particle size of nickel must be maintained as small as possible to maximize sulfur adsorption capacity. 0.02

S /Ni (mol)

0.015

0.01

0.005

0

0

10

20

30

40

50

4. Conclusion Nickel particles incorporated SBA-15 were prepared and used as adsorbents for the desulfurization of commercial diesel. Impregnation method, and nickel loading were the important factor to control the sulfur adsorption capacity of adsorbent. 5. References [1] [2] [3] [4] [5] [6]

A. Avidan, B. Klein, R. Ragsdale and H. Topsoe, Appl. Catal. A-Gen., 205 (1999) 189.. C. Song and X. Ma, Appl.Catal. B-Env, 41 (2003) 207. R. T. Yang, A. J. Hernandez-Maldonado and F. H. Yang, Science, 301 (2003) 79. A. J. Hernandez-Maldonado and R. T. Yang, Ind. Eng. Chem. Res., 42 (2003) 123. A. J. Hernandez-Maldonado and R. T. Yang, AIChE, 50 (2004) 791. V. M. Bhandari, C. H. Ko, J. G. Park, S. S. Han, S. H. Cho and J. N. Kim, Chem. Eng. Sci., 61 (2006) 2599. [7] J. H. Kim, X. Ma, A. Zhou and C. Song, Catalysis. Today, 111 (2006) 74.. [8] X. Ma, S. Velu, J. H. Kim and C. Song, Appl. Catal. B-Env., 56 (2005) 137 [9] R. Ryoo, C. H. Ko, M. Kruk, V. Antochshuk and M. Jaroniec, J. Phys. Chem. B, 104 (2000) 11465

Progress in in Mesostructured Materials Recent Progress S. Qiu, Y. Tang and C. Yu (Editors) (Editors) D. Zhao, S. © 2007 2007 Elsevier Elsevier B.V. B.V. All All rights rights reserved. reserved.

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Highly hydrophobic mesoporous materials as matrix for gas chromatography separation of water-alcohols mixtures Lianxiu Guan^, Junping Lia, Dongjiang Yangab, Xiuzhi Wanga, Ning Zhaoa, Wei Weia and Yuhan Suna* " State Key Laboratory of Coal Coversion, Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan, 030001, P. R. China; Graduate School of the Chinese Academy of Sciences, Beijing, 100039, China

1. Introduction Since the first mesoporous silica material with regular pore channels was reported in 1992 [1], the application of porous materials with tailored properties is one of the most attractive areas of materials science [2, 3]. Their extremely high surface areas, accessible pores and selective adsorption, which may enhance superior chromatographic performance to class silica-based columns by providing higher and more homogeneous molecular diffusivity, make these mesoporous materials potentially useful for chromatography separation. And it was found that the mesoporous materials were also proposed as possible stationary phases for size-exclusion chromatography [4], normal-phase HPLC [5], reversed-phase HPLC [6], capillary gas chromatography [7], and enantioselective HPLC [8]. However, the purely inorganic mesoporous materials are limited in applications by their lack of organic functional groups. The organic/inorganic hybrid mesoporous organic silicas obtained using a structure-directing template pathway were also limited in their chromatographic separation application because of their low thermal stability. Hence there is still a need to develop the tailored stationary phases with better extraction, enrichment, and separation behavior. Recently, the chloropropyl-modified MCM-41 was found to be the gas chromatography matrix for the separation of the water-alcohols [9], but the separation of the propanol isomers was still the problem, although there were some papers for the separation of alcohols [10,11]. Thus, a silica-based super hydrophobic materials were prepared using

886

nonsurfactant route [12,13] and firstly investigated as the gas chromatography matrix for the separation of complicated water-alcohols systems. 2. Experimental Section 2.1. Materials The materials were synthesized as in the reference [13]. In a typical synthesis, 1.5 g polymethylhydrosiloxane (PMHS) were dripped into a flasks containing 60 ml ethanol. The formed liquids were further stirred for 48 h at room temperature to allow PMHS to react with a part of ethanol and release hydrogen in the presence of NaOH as catalyst. Then 4.6 g of tetraethyl orthosilicate (TEOS) and determined deionized water were introduced to the systems with vigorous stirring for 3 h. The resultant sols were statically aged for 2 d to turn into gels. The obtained gels were heated in a 60°C vacuum oven to remove the ethanol. 2.2. Characterization Transmission Electron Microscope (TEM) images were recorded using a JEOL 100CX microscope with a CeB6 filament and an accelerating voltage of 200 kV. Nitrogen adsorption /desorption isotherms were obtained at -196°C on a Tristar 3000 Soptometer, using static adsorption procedures. Samples were degassed at 150°C for a minimum of 12 h under vacuum (10-6 Torr) prior to measurement. Surface areas were measured using the BET method and pore size distributions were calculated using the modified BJH method. 2.3. Chromatographic Tests In a typical column preparation, a stainless steel pump ( l m long, 3 mm id) was filled with 0.9 g materials (particle diameter of 0.15 ~ 0.18 mm). And then the packed column was aged for 24 h at 250°C. The separation performances of the samples were investigated on the GC 950 gas chromatograph equipped with a thermal conductivity detector. Hydrogen was used as the carrier gas and was driven at the inlet pressure of 0.2 Mpa.The separation experiments were carried out under the conditions: carried gas: H2; flow rate: 15 ml/min; temperature: 3. Results and Discussion Fig.la shows the representative TEM image of the sample. Obviously, it depicted a direct image of the 3D wormhole-like pore frameworks. The obtained hybrids were grinded and tabletted to measure the hydrophobicity. As

887

shown in Fig. lb, the water droplet with ~3 mm diameter on the tablets looked like a round ball, and the contact angle exceeded 150°, indicating the super hydrophobic nature of the materials.

Fig. 1 (a) HRTEM image and (b) Photographs of a water droplet on the tablets of the samples.

methanol

b

watel ll 1 lethanol

III niso propanol

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0 ICPJ

50

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"7 100

150

200

250

300

350

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Fig. 2 (a) N 2 adsorption/desorption isotherm of the samples; (b)The hydrophobic mesoporous materials as matrix for the gas chromatographic separation of water-alcohols mixtures.

The N2 adsorption/desorption isotherms clearly illustrated that the sample exhibited type IV isotherm with type H2 hysteresis loop (see Fig. 2a), which further confirmed the mesoporous sturcture of the samples. The results were consistent with Yang's reports [13]. The BET surface area was 758.76 m2g"' with the pore volume of 0.62 cm3g'' and the pore diameter of 3.27 nm, respectively. The hydrophobic materials exhibited the high resolution and efficiency for the wa ter-alcohols mixtures (see Fig. 2a). The separation order was highly consistent with the polarity of alcohols and water. With the decrease of the polarity, the attraction between the stationary phase and these alcohols increased gradually, extending the retention time. Interestingly, the hydrophobic mesoporous material column could achieve the baseline separation of the propanol isomers, which was hardly achieved by the chloropropyl-modfied MCM-41 [9]. The selective separation of the propanol isomers on the hydrophobic column was the result of their different van der Waals interaction with the mesoporous walls. Futhermore, the nanochannels of mesoporous

888

materials were accessible to the linear chains, but not to the branched parts of the iso-propanol. As a result, the retention property of the linear n-propanol was stronger than the branched iso-propanol. At trie same time, the large amount of the hydrophobic methyl groups enlarged the difference of the polarity of the isomers, which also directly enhanced the different retention property. 4. Conclusion The hydrophobic mesoporous materials was synthesized and investigated as GC stationary phase for the separation of complicated water-alcohols systems. The hydrophobic mesoporous materials showed high resolution and efficiency for the tested systems. Importantly, the matrix achieved base-line separation of the propanol isomers via their different Van Der Waals interactions with functionalised surfaces in nanochannel. 5. References [1] C. T. Kresge, M. E. Leonowicz, W. J. Roth, J. C. Vartuli and J. C. Beck, Nature, 359 (1992) 710. [2] A. Corma, L. Nemeth, M. Renz and S. Valencia, Nature, 412 (2001) 423. [3] A. Corma, M. J. Diaz-Cabanas, J. Martinez-Triguero, F. Rey and J. Rius, Nature, 418 (2002)514 [4] A. Kurganov, K. Ungerand T. Issaeva, J. Chromatogr. A., 753 (1996) 177. [5] M. Grun, A. A. Kunganow, S. Schacht, F. Schuth and K. K. Knger, J. Chromatogr. A., 740 (1996) 1. [6] T. Martin, A. Galarneau, F. D. Renzo, D. Brunei and F. Fajula, Chem. Mater., 16 (2004) 1725. [7] M. Raimondo, G. Perez, M. Sinibaldi, A. D. Stefanis and A. A. Tomlinson, Chem. Commun., (1997) 1343. [8] C. Thoelen, K. V. D. Walle, I. F. J. Vankelecom and P. A. Jacobs, Chem.Commun., (1999) 1841. [9] L. X. Guan, J. P. Li, H. Cao, N. Zhao, X. Z. Wang, W. Wei and Y. H. Sun, Chem. Letter., 35(2006)516. [10] D. Guillarme, S. Heinisch, J. Y. Gauvrit, P. Lanteri and J. L. Rocca, J. Chromatogr. A., 1078(2005)22. [11] C. L. Hsueh, J. F. Kuo, Y. H. Huang, C. C. Wang and C. Y. Chen, Sep. Purif. Technol, 41 (2005) 39. [12] D. J. Yang, S. R. Zhai, Y. Xu, J. L. Zheng, D. Wu, Y. H. Sun and F. Deng, Stud. Surf. Sci. Catal. 156(2005)473. [13] D. J. Yang, Y. Xu, S. R. Zhai, J. L. Zheng, J. P. Li, D. Wu and Y. H. Sun, Chem. Letter. 34 (2005)1138.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

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Photoluminescence study of [Eu(bpy)2]3+ supported on mesoporous materials of different pore sizes Shuxun Ge a b , Nongyue Heb*, Song Li a b , Jiqing Wanga, Libo Niea and Hong Chena "Key Laboratory of Green-Packaging and Application of Biological Nanotechnology of Hunan Province, Hunan University of Technology, Zhuzhou 412008, China. h State Key Laboratory of'Bioelectronics, Southeast University, Nanjing 210096, China.

[Eu(bpy)2]3+(bpy: 2, 2'-bipyridine) was encapsulated in HMS, MCM-41 and SBA-15, respectively. Effect of dispersion degree of Eu3+ species and mesoporous structure on the photoluminescence efficiency was investigated. 1. Introduction It has been well-known that mesoporous materials possess well-defined mesopores with pore diameter of 2-10 nm [1-2], which can hold bulk ions or molecules with specifically chemical and optical properties, providing a challenging approach to novel chemical and optical applications [3]. After the development of mesoporous materials, Eu3+ complexes have been studied on the photoluminescence (PL) properties of europium complexes immobilized in mesoporous materials [4-9]. The properties of the guests in the mesoporous channels greatly depend on the structure and the microenvironment of the mesopores [6]. In the present paper, [Eu(bpy)2]3+ was encapsulated in the mesopores of HMS, MCM-41 and SBA-15, respectively. The PL properties and the structural effect on the PL efficiency per Eu mass unit of the samples were investigated. 2. Experimental Section SBA-15, MCM-41 and HMS was respectively synthesized and calcined as given in References [2, 10-12]. A controlled amount of [Eu(bpy)2]3+ was dissolved in 10 cm"3 of N, N-dimethylformamide (DMF) and the calcined SBA15 was suspended in this solution, then stirred vigorously at room temperature

890

for 24 h. After the impregnation, the solid product is recovered by filtration, washed with DMF, dried at 373 K for 10 h and finally kept in a vacuum desiccator. 5%, 10% and 20% by weight of [Eu(bpy)2]3+ were separately employed for the impregnation, and the obtained samples were designated as 5%-, 10%- and 20%-Eu-SBA-15, respectively. Furthermore, 5%-, 10%-, 20%Eu-HMS, 5%-, 10%- and 20%-Eu-MCM-41 were prepared in the same method. Powder X-ray diffraction (XRD) patterns were recorded on a Rigaku D/maxrB diffractometer using Cu Ka radiation and scanning in the 20 range of 1° to 10°. PL spectra were recorded on a Perkin Elmer LS50B spectrofluorometer using an excitation wavelength of 300 nm with a xenon lamp, and a 350 nm filter to block out the excitation signal. Both the excitation and emission slit widths were kept as 5.0 nm. N2 sorption for surface areas, total pore volumes and pore size distributions was per formed on a Micromeritics ASAP 2010 instrument. Eu3+ contents were analyzed on a Leeman PS-1 ICP instrument. 3. Results and Discussion The XRD patterns of samples are displayed in Fig. 1. SBA-15 exhibits a narrow and strong peak attributed to (100) in low-angle range, indicating that SBA-15 possesses the typical SBA-15 structure [2]. MCM-41 exhibits the peaks of (100), (110), (200) and (210), meaning that MCM-41 possesses a higher ordered structure [1]. However, HMS shows only a broad peak of (100), indicating its worst order structure among the three mesoporous hosts. Fig. 2. shows that 20%-Eu-SBA-15 exhibits 100, 110 and 200 peaks, indicating that the impregnation seems not to destroy the mesoporous structure of 20%-Eu-SBA-15 but improves the mesoporous structure. Actually, all the three impregnated SBA-15 samples (not shown here) showed the obviously improvement in the mesoporous structure. The reason for this kind of improvement needs further investigation in depth. Compared to the HMS host, 20%-Eu-HMS shows a similar 100 peak, indicating the impregnation did not 100

100

100 ty 3

d

1

3

d

100

c b

110 200 210

c b a

-TiooV. 2

4 6 2 theta / deg.

Inte

c

8

10

Fig. 1 Powder XRD patterns of mesoporous hosts: (a) SBA-15, (b) HMS, and (c) MCM-41.

110 VV.200

0

2

a 4 6 2 theta / deg.

10

Fig. 2 XRD patterns of (a) 20%-Eu-SBA-15, (b) 20%-Eu-HMS, and (c) 20%-Eu-MCM-41.

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influence the structure order of the 20%-Eu-HMS. Furthermore, the 20%-EuMCM-41 exhibits only a 100 peak, indicating the impregnation significantly damaged the order structures of 20%-Eu-MCM-41. Above results are consistent with the hydrothermal stability order: SBA-15>HMS>MCM-41, attributed tothe wall thickness and the polymerization degree [13]. Table 1 lists the structure properties of samples before and after impregnation. The pore size and pore volume of SB A-15 samples is the largest among the three samples before and after impregnation. For the partial collapse of structure, surface area of the impregnated samples decrease with the impregnation of [Eu(bpy)2]3+, while the tendency of 20%-EuTable 1 Structural properties of samples SBA-15 is less drastic, BET Va Db Ld Sample 3 1 2 1 due to the much better (m g ) (cm g ) (nm) (nm) (nm) stability of SBA-15. HMS 644.7 0.74 4.59 5.53 0.94 450.4 0.50 4.44 5.73 20%-Eu-HMS 1.29 All samples exhibit MCM-41 961.9 0.75 3.13 4.43 1.30 two main PL peaks at 20%-Eu-MCM-41 472.1 0.60 3.05 4.11 1.06 the red light region that 5 SBA-15 548.6 1.04 7.60 8.76 1.16 originated from 7 7.72 20%-Eu-SBA-15 502.6 0.97 8.93 1.21 nm) and Do "Pore volume; bPore diameter; cao=2d100/3'/2; dThichness of pore F2 (k=6\2 nm) of wall, L=ao-D. .3+ Eu [5], respectively (not shown). This indicated that the electron transition energy of Eu was not affected after the impregnation of the [Eu(bpy)2]3+. The contents of Eu3+ in 5%-, 10%- and 20%-Eu-SBA-15 by ICP are 0.44%, 0.56% and 0.78%, respectively. Based on the PL intensity per Eu atom equation, i.e., PL intensity per Eu atom = (the intensity of PL peak at X = 612 nm)/(the content of Eu3+), the PL intensity per Eu atom of the impregnated SBA-15 are found to be 20.52, 11.63 and 10.91, respectively (as shown in Table 2). However, the PL intensity per Eu atom of the unassembled [Eu(bpy)2]3+ molecule is 3.27. It meant that mesoporous structure prevents PL quenching of Eu3+ ion [4]. Furthermore, the impregnated MCM-41 and HMS Table 2 The effect of [Eu(bpy)2]3+ content on the PL intensity samples also exhibit the mesoporous materials stronger PL intensity per The content of Intensity PL intensity Eu atom than the Sample 3+ Europium (%) (a.u.) per Eu atom unassembled [Eu(bpy)2] [Eu(bpy)2]3+ 136.00 41.58 3.27 (as shown in Table 2). 0.20 1.17 5%-Eu-HMS 5.85 For the impregnated 4.74 0.99 10%-Eu-HMS 4.79 samples, the PL intensity 7.85 20%-Eu-HMS 1.80 4.36 per Eu atom decreases 5%-Eu-MCM-41 0.14 4.98 36.57 according to following 4.41 10%-Eu-MCM-41 0.20 22.05 trend: MCM-41>SBA18.35 20%-Eu-MCM-41 1.14 16.10 15>HMS (shown in Table 0.44 5%-Eu- SBA-15 8.51 19.34 10%-Eu-SBA-15 0.56 6.50 11.63 2). The PL of Eu3+ in 9.03 20%-Eu-SBA-15 0.78 11.58 MCM-41 was quenched

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by the silanol groups [5, 7]. The silanol group number of MCM-41 was more than that of HMS but less than that of SBA-15 [14-15], i.e., one has an order from the smallest HMS to the largest SBA-15 in term of the silanol content. The PL intensity per Eu atom of MCM-41 is greater than that of SBA-15, which could be attributed to the less silanol group number in MCM-41 than in SBA-15. HMS exhibits less silanol group number than that of MCM-41 and that of SBA15, but the PL intensity per europium of the impregnated HMS samples are the weakest. This may be due to the narrow pore size distribution of the latter has effect on the microenvironment of the Eu3+ [6, 16] and needs study in depth. 20%-Eu-MCM-41 and 20%-Eu-SBA-15 samples show high PL intensity per europium. As MCM-41 shows poor stability, SBA-15 should be a better support for the encapsulation of the europium complexes. 4. Conclusion [Eu(bpy)2]3+was incorporated into mesopores of HMS, MCM-41 and SBA15, respectively. The silanol group and pore size distribution of samples provide effect on the Eu atom microenvironment which influence PL intensity. Although the impregnated SBA-15 exhibited a little weak PL intensity per europium than MCM-41 sample, SBA-15 is stable and may become an interesting medium to encapsulate the europium complex. 5. References [1] C. T. Kresge, M. E. Leonowicz, W. J. Roth, J. C. Vartuli and J. S. Beck, Nature, 359 (1992) 710. [2] P. Yang, D. Zhao, D. I. Margolese, B. F. Chmelka and G. D. Stucky, Nature, 396 (1998) 152. [3] H. Maas, A. Currao and G. Calzaferri, Angew. Chem. Int. Edit., 41 (2002) 2495. [4] G. Vicentini, L. B. Zinner, J. Zukerman-Schpector and K. Zinner. Coord. Chem. Rev., 196 (2000) 353. [5] L. Bian, H. Xi, X. Qian, J. Yin, Z. Zhu and Q. Lu, Mater. Res. Bull., 37 (2002) 2293. [6] Q. Xu, L. Li, B. Li, J. Yu and R. Xu, Micropor. Mesopor. Mat., 38 (2000) 351. [7] S. Ge, N. He, C. Yang, J. Cao, H. Chen and M. Gu, Stud. Surf. Sci. Catal., 156 (2005) 711. [8] Q. Xu, L. Li, X. Liu and R. Xu, Chem. Mater., 14 (2) (2002) 549. [9] S. Ge, N. He, C. Yang and M. Gu and J. Cao, J. Nanosci. Nanotechnol., 5 (2005) 1305. [10] C. Yang, S. X. Ge and N. Y. He, Stud. Surf. Sci. Catal., 146 (2002) 129. [11] C. Yang, X. P. Jia, Y. D. Cao and N. Y. He, Stud. Surf. Sci. Catal., 146 (2002) 485. [12] N. He, C. Yuan, Z. Lu, C. Yang, S. Bao and Q. Xu, Supramol. Sci., 5 (1998) 523. [13] K. Cassiers, T. Linssen, M. Mathieu, M. Benjelloun, K. Schrijnemakers, P. Van Der Voort, P. Cool and E. F. Vansant, Chem. Mater., 14 (2002) 2317. [14] W. Z. Zhang, Design, synthesis and catalytic applications of mesoporous silica molecular sieves (dissertation). East Lansing (MI): Michigan State University, Chapter 2 27(1999)56. [15] I. G. Shenderovich, G. Buntkowsky, A. Schreiber, E. Gedat, S. Sharif, J. Albrecht, N.S. Golubev, G.H. Findenegg and H.H. Limbach, J. Phys. Chem. B, 107 (2003) 11924. [16] A. F. Kirby, D. Foster and F. S. Richardson, Chem. Phys. Lett., 95 (1983) 507.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Published by Elsevier B.V.

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Benzene sensors based on surface photo voltage of mesoporous organo-silica hybrid thin films Brian Yuliarto,a Yoko Kumai,b Itaru Honma,a Shinji Inagakib and Haoshen Zhoua "Energy Technology Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba 305-8568, Japan h Toyota Central R&D Laboratories, Inc., Nagakute, Aichi, 480-1192, Japan

1. Introduction Detection of VOCs such as benzene, toluene and methanol is a very important aim in sensor technology. In the last few years many research groups have been focusing their attention in this type of sensors towards environmental applications, electronic noses, food or chemical industry. Benzene has been classified by the Environmental Protection Agency as a Group A, known human carcinogen of medium carcinogenic hazard. [1] Benzene, together with toluene, and xylenes can be found in motor gasoline as light high-octane aromatic hydrocarbons. As the variety using of benzene in many chemical processes, the measurement of benzene concentration is of significance important to control the benzene affect for human and environmental dangerous. The use of mesoporous silica material for separation and sensor devices is interesting because the large surface area of mesoporous material, which can be as high as 1100 m2g"', allows especially good gas access. The large surface area created by mesoporous materials enables an improvement in the gas adsorption properties of SPV devices. In this work, an ordered organo-silica hybrid thin film [2] is used as a sensitive layer in the MIS sensor structure. An ordered mesoporous organo-silica hybrid thin film is used as a sensitive layer in the MIS sensor structure [3]. The sensing performance is measured using surface photovoltage (SPV) technique for VOC detection at room temperature.

894

2. Experimental Section The ordered organo-silica hybrid material was prepared from alternating hydrophilic and hydrophobic, composed of silica and phenol, respectively. The sensor device is constructed following the previous method on our publications. [2] The n-type silicon (n-Si), with SiO2 and Si3N4 layers was used as the substrate. The mesoporous organo-silica hybrid thin film was prepared on the Si3N4 layer of the substrate, as a VOC adsorption insulator layer. The film preparation method has been detailed explained in the previous publications [3]. After deposition of mesoporous organo-silica hybrid, the Au electrode was deposited on the mesoporous film by sputtering while an Al electrode was fabricated on the backside of the n-Si surface by vacuum vapor deposition. The complete structure of the SPV sensor device based on MIS structure is Au/ mesoporous phenol-silica/ Si3N4/ SiCV n-Si/ Al as shown in Figure 1. 1.E+05

1.E+04

Au Mesoporous Int e ns it y

Si3 SiO A

n-Si

n-Si V VB

LED

1.E+03

1.E+02

1.E+01

1.E+00 1.0

2.0

3.8nm 4.0

3.0

2θ / θ

5.0

6.0 .0

7.0 7.0

8.0

Fig. 1 A mesoporous organo-silica hybrid SPV sensor with MIS structure, and the XRD of mesoporous organo-silica hybrid.

The gas sensing properties were characterized using automatic gas sensor characterization based on SPV system. The structure of the sensor consisted of four layers that formed a MIS structure. The sensor system consisted of a computer that controlled a lock in amplifier. An alternating modulated LED (930 nm, 1 kHz) beam was irradiated on the reverse side of the semiconductor to induce an ac photocurrent. A volume flow controller and multi-port valve controlled the VOC compounds during measurement. A two channels volume flow controller has been used to vary VOC compound concentration from 100 to 800 ppm. 3. Results and Discussion The XRD pattern of mesoporous organo-silica hybrid (Fig. 1) shows the peaks at low angle, indicating that the mesostructure is exist in the thin films.

895

The typical transient response of 195 mesoporous organo-silica hybrid is 190 shown in Figure 2. The figures show the photocurrents output variation of 185 the SPV sensor versus time for 180 increasing VOC concentrations. Measurements performed upon certain 175 bias voltage application showed clear 170 photocurrent variations related to 0 20 40 60 80 100 100 120 120 140 140 160 160 180 180 exposure in environments containing Time (minutes) N2 and VOC compounds. The Fig. 2 The response dynamic of benzene on photocurrent signals response increases mesoporous organo-silica SPV sensor. upon a given concentration of benzene due to any chemical and physical interaction of VOC molecules adsorbed into mesoporous silica layer. Moreover, after switching to recovery ambient of nitrogen, the sensors signal turn to decrease to the baseline and then returns to a stable reference level. The change in both the dielectric constant and the charge of the gas sensitive layer, due to physical adsorption and interaction between benzene compound and mesoporous silica layer with phenol chain produce a clear photocurrent shift. The sensitivity (Sen) of each concentration of VOC compound can be calculated from the Figure 1 using the definition of sensitivity as follow: Photo currents (nA)

f: r.

J

en VOC

i \

x 100%

N2

Vol adsorpt ion (ml STP/ gr)

Where Ivoc is the photocurrent after exposure of VOC and IN2 is the photocurrent under N2 condition. 300 250 200 150

Benzene

100 50 0 0

0.1

0.2 0.3 Relative pressure Relative pressure (P/ (P/ Po) Po)

0.4 0.4

0.5

Fig. 3 The benzene absorption-desorption on the SPV sensor

The increasing of photo-capacitive current indicates that the positive surface potential has changed due to reaction between benzene compound and the

896

mesoporous layer. The sensitivity for 100, 200, 400 and 800 ppm of benzene are 1.7, 3.3, 6.3 and 11.7% respectively. The response time for all concentrations of VOC compounds is less than 1 minutes providing clear evidence that both type of sensors can absorb and react easily with benzene compounds. This response time is much faster than the time response of NO2 SPV gas sensors based on a MCM-41 structure. Figures 2 also show that the photocurrent returns to its starting value after the gas is switched to N2. This proves that the absorption process is reversible. The recovery time is also much better than that of NO2 SPV gas sensor. The accessibility of benzene to the organo-silica hybrid mesoporous film is confirmed by the benzene adsorption-desorption measurement as show in Figure 3. It is clear that the benzene compound can be adsorbed and desorbed on the organo-silica mesoporous layer. In the organo-silica hybrid mesoporous, which consist of the phenol chain, the densities of Si-O- and silanol (-Si-OH) bonds would be replaced by the phenol-silica in a crystalline super lattice structure. The inner surface of the phenol-silica hybrid mesoporous transfers from hydrophilic into hydrophobic, which makes the mesoporous structure could be easy to be accessed by the organic molecules comparing to the inorganic compound. As a result, the benzene which is organic molecules would be easily absorbed 4. Conclusion The mesoporous organo-silica hybrid thin film was successfully prepared as benzene sensors. Good response properties have shown that the device can be used, at room temperature, as a detector of benzene compound in the range of 100-800 ppm. 5. References [1] Y. H. Lanyon, G. Marrazza, I. E. Tothill and M. Mascini, Biosensors and Bioelectronics 20 (2005) 2089.

[2] S. Inagaki, S. Guan, T. Ohsuna and O. Terasaki, Nature 416 (2002) 304. [3] B. Yuliarto, I. Honma, Y. Katsumura and H. S. Zhou, Sens. Actuators. B 114 (2006) 109.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

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Lipase immobilization in ordered mesoporous materials Elias Serraa, Alvaro Mayoralb, Yasuhiro Sakamotob, Rosa M. Blancoa and Isabel Diaz3* "Institute de Catdlisis y Petroleoquimica, CSIC. C/ Marie Curie 2, Cantoblanco (Madrid) 28049. Spain. Arrenhius Laboratory, University of Stockholm. Stockholm S-10691. Sweden

1. Introduction Enzyme immobilization in solid supports is an increasing technology. Lipase immobilization in amorphous mesoporous silicas has been achieved with high loadings and good retention of activity [1]. However sol-gel materials lack of precise mesopore size control and display small surface areas, limiting their application as suitable hosts. Ordered Mesoporous Materials (OMM) possess high surface areas, narrow pore size distribution and well defined connectivity that may solve problems related to diffusion and accessibility to the bulk material. Hexagonal two-dimensional (p6mm) OMM such as SBA-15 and MCM-41 have been tested as lipase carriers in recent years [2]. Although valuable loadings have been achieved, leaching problems have not been solved yet [2d, 2e], and the total solid surface is used only in a small percentage. The influence of the porous structure in the immobilization process has not been assessed yet. Here we present a systematic study in which a variety of OMM with different structures and pore sizes have been tested as lipase (CALB) carriers. The candidates include materials with cylindrical pores as well as cagelike systems. Due to lipase dimensions (9.92 x 5.05 x 8.67 nm), too close to the range of conventional OMMs, recent developments to enhance and control pore diameters have been applied [3-5]. 2. Experimental Section A variety of surfactants, synthesis conditions and additives were used to obtain p6mm (MCM-41 [6]), la-Id (KIT-6 [3]), Im-3m (SBA-16 [4]) and Fm-

898

3m (FDU-12 [5]) structures. Powder X-ray diffraction (XRD) patterns of the solids were obtained with a Seifert XRD 3000P diffractometer using monochromatic Cu Ka radiation. Thermogravimetric analysis (TGA) was performed using a Perkin-Elmer TGA7 instrument, from 20 to 900°C at a heating rate of 20°C/min. N2 adsorption isotherms were obtained on a Micromeritics ASAP apparatus. Surface areas were calculated through the BET procedure. Pore sizes were estimated applying the BJH analysis to the adsorption branch of the isotherm. SEM images were obtained with a JEOL JSM 6400 Phillips XL30 microscope operating at 20 kV. TEM images were obtained in JEOL 2000FX (200 kV) and JEOL JEM 3010 (300 kV) microscopes. Immobilization of CALB was performed by suspending 100 mg of solid in 20 mL of a solution of enzyme in phosphate buffer with different enzyme concentrations at pH = 5. The immobilization yield was monitored by measuring the amount of enzyme in the supernatant using UV-Vis absorption at 348 nm, with p-nitrophenyl acetate (p-NPA) as substrate. As-made materials were also tested in order to quantify enzyme adsorption on the external surface. 3. Results and Discussion The structure of all the OMM was initially evaluated by XRD, and further confirmed to be in good agreement with the literature by TEM/SAED. As an example, Figure 1 shows the XRD patterns of KJT-6 and FDU-12-a. The main peaks can be indexed to the corresponding reflexions of the expected space groups (la-Id and Fm-3m, respectively). Besides, TEM tilting series allowed doubtlessly assessment of the expected space groups. SEM micrographs supplies information about the morphology of the particles and are also in good agreement with the literature. Figure 1 shows an example of TEM and SEM images of SBA-15 and SBA-16. As it can be observed, Figure le reveals the 100 direction of SBA-15 and Figure lg the perpendicular orientation, demonstrating a hexagonal and well ordered p6mm structure. SEM image shows the typical morphology of SBA-15, consisting of rod-like particles associated into wheat-like macrostructures [7]. Cage-like structures (SBA-16 and FDU-12) show globular type of particles with different faceted termination depending on the space group. Table 1 collects the textural properties of the solids. All of them present surface areas above 500 m2/g, excepting the sample FDU-12-a, probably due to a major presence of intergrowths. The materials cover a pore range of 4.7 - 27.9 nm, including amorphous silica with large mesopores that was used as reference. The immobilization results (Table 1) indicate that cage-like solids require extremely longer times to achieve maximum loading than cylindrical-pore systems. This can be explained because the enzyme (9.92 x 5.05 x 8.67 nm) has to diffuse in an adequate orientation to be able to pass through the pore entrances and access the cages. To evaluate this effect, different synthetic attempts led to samples with at least two different pore windows. However,

899 899

there are no straightforward techniques to estimate accurately the entrance/cage size and it is only possible to assure that systems with larger cages lead to higher loadings (FDU-12-a > FDU-12-b > SBA-16). In the case of the SBA-16 sample, the loading was identical for the as-made and calcined materials, clearly 2U

Intensity (a.u.)

1 211 '

a

) \ 220 22C

b

A 111 111

'\

311 311 1

22θ θ 2

3

SOnm

50nm

Figure 1. XRD patterns of a) KIT-6, and b) FDU-12-a. SEM images of c) SBA-15 and d) SBA16. TEM images of SBA-15 along e) [100] and g) perpendicular orientations. TEM images of SBA-16 along f) [100] and h) [111] zone axes.

indicating that the enzyme is not able to pass through the window and hence the immobilization takes place only on the external surface. Enzyme immobilization can therefore provide an indirect evidence of the size of the pore entrances. In any case, further 3D reconstruction based on Electron Crystallography has to be applied in order to have an accurate cage systemlipase sketch. When CALB is immobilized in OMM with hexagonal arrangement of cylindrical pores (MCM-41 and SBA-15), a clear increase of enzyme loading with pore diameter is observed. MCM-41, with 4.7 nm pore size, exhibits lower enzyme content and at longer contact time than SBA-15 with a 8.8 nm pore size (see Table 1). By comparing as-made and calcined MCM-41 samples it can be concluded that 50% of the immobilization is on the external surface, and only 5 mgE/g penetrates inside the channels. Amorphous silica exhibits the highest values (45.3 mg/g in 120min), however it is remarkable that such a big pore size difference (27.9 in SiO2 and 8.8 nm in SBA-15) showed almost the same loading in very similar times (see Table 1). This seems to indicate that, above a minimum value, pore size might not be the only limiting step for a larger enzyme loading to be reached, not even when increasing the enzyme concentration. On the other hand, it was expected that KIT-6 material (MCM-48 type of structure) would show better performance than SBA-15 in terms of diffusion properties. However it exhibits an intermediate behaviour, with lower loading and higher contact time than SBA15, probably due to a slightly smaller pore diameter (8.4 nm). This seems to

900

indicate that pore diameter, window size in cage-type mesostructures, is a crucial factor for the immobilization process. However, it has to be highlighted that crystal morphology and textural properties of the mesophase affect the immobilization properties so the results should be view with some caution. Table 1. OMM textural properties and immobilization results Mesoporous support

Enzyme-Mesoporous support

Name

Structure

Pore size (nm)

SBET (m2/g)

V mesop (m3/g)

Contact time (h)

Enzymatic loading* (mgE/g support)

Organic content (nig/g support)**

S1O2

Amorphous p6mm

27.9 4.7

305 595

2.70 0.82

2 24

45.3 10

50.9 14.9

SBA-15 KIT-6

poTwn

la-Zd

8.8 8.4

890 917

1.31 1.20

~2 ~4

44 37

57 45.2

SBA-16 asmade-SBA-16 FDU-12-a as-made FDU-12-a FDU-12-b

Im-3m Im-3m Fm-3m Fm-im Fm-3m

10.2 10.4 9.2

658 . 261 501.2

. 0.38 _ 0.62

24 24 48 48 48

5 5 28 5 21

8.6 10.7 36.3 10.1 30

as-made FDU-12-b

Fm-3m

-

-

48

5

8.8

MCM-41

'Determined by the activity assay. **Determined by Thermogravimetric Analysis of the solid once filtered and dried.

4. Acknowledgement The authors acknowledge Comunidad Autonoma de Madrid (CAM) for financial support within the Project GR/MAT/0694/2004. E. Serra acknowledges the support of a CAM PhD fellowship. 5. References [1] R. M. Blanco, P. Terreros, M. Fernandez-Perez, C. Otero and G. Diaz-Gonzalez, J. Mol. Catal. B: Enzimatic 30 (2004) 83. [2] a) A. Macario, V. Calabro, S. Curcio, M. De Paola, G. Giordano, G. Iorio and A. Katovic, Stud. Surf. Sci. Catal. 142 (2002) 1561; b) E. L. Pires, E. A. Miranda and G. P. Valenca, Appl. Biochem. Biotechnol. 98 (2002) 963; c) Z. Z. Chen, Y. M. Li, X. Peng, F. R. Huang and Y. F. Zhao, J. Mol. Catal. B: Enzym. 18 (2002) 243; d) H. Ma, J. He, D. G. Evans and X. Duan, J. Mol. Catal. B: Enzim. 30 (2004) 209; e) A. Salis, D. Meloni, S. Ligas, M. F. Casula, M. Monduzzi, V. Solinas and E. Dumitriu, Langmuir 21 (2005) 5511. [3] K. Tae-Wan, F. Kleitz, B. Paul, and R. Ryoo, J. Am. Chem. Soc. 127 (2005) 7601. [4] T. W. Kim, R. Ryoo, M. Kruk, K. P. Gierszal, M. Jaroniec, S. Kamiya and O. Terasaki J. Phys. Chem. B 108 (2004) 11480. [5] J. Fan, C. Z. Yu, T. Gao, J. Lei, B. Z. Tian, L. M. Wang, Q. Luo, B. Tu, W. Z. Zhou and D.Y. Zhao, Angew. Chem. Int. Ed. 42 (2005) 3146. [6] M. Boveri, J. Agundez, I. Diaz, J. P6rez-Pariente, E. Sastre and Collect. Czech. Chem. Commun. 68 (2003) 1914. [7] D. Y. Zhao, J. Sun, Q. Li and G. D. Stucky, Chem. Mater. 12 (2000) 275.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

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Microwave synthesis of Zr incorporated SBA-16 mesoporous silica as a catalyst for MeerweinPonndorf-Verley (MPV) reduction Nanzhe Jiang, Kwang-Min Choi, Sang-Cheol Han, Jeong-Boon Koo and Sang-Eon Park* Lab. ofNano-Green Catalysis andNano Center for Fine Chemicals Fusion Technology, Dept. of Chemistry, Inha University, Incheon, 402-751, Korea

Zr incorporated and pure SBA-16 were prepared by microwave synthesis method. These microwave synthesized Zr-SBA-16 played a role as Lewis acid sites for the Meerwein-Ponndorf-Verly reduction of ketones giving almost 100 % selectivities with high activities. 1. Introduction Metal incorporation into nanoporous materials could give birth to Lewis acid sites through the framework substitution onto silica matrix. The supported Lewis acid sites can offer several advantages in various heterogeneous catalytic systems such as Baeyer-Villiger reactions [1], and Meerwein-Ponndorf-Verley (MPV) reduction reactions [2]. The MPV reductions of carbonyl compounds using secondary alcohols as hydrogen donor are one of the highly selective transfer hydrogenation reactions [3]. Zr is an important element which it is being increasingly used in catalysis, because the addition of Zr in catalysts led to the improvements in activity and selectivity. The incorporated Zr could played a role as the active Lewis acid sites through the activation of C=O groups of the ketone [2]. For the incorporation of Zr into the silica framework, microwave-assisted synthesis method could offer many distinct advantages over conventional hydrothermal method. Besides the rapid and homogeneous nucleation, direct intrusion of metallic components forced by microwave was expected. It is caused by the difference in the electronegativities of Zr-0 bonding and Si-0 bonding which could absorb microwave energy selectively [4].

902

Herein, we report a successful synthesis of Zr substituted SBA-16 materials by microwave method. Those incorporated Zr species have tetragonal structure which were confirmed by the UV-vis spectroscopy. The generated Lewis acidic sites by the framework Zr were investigated by the pyridine adsorption in FT-IR measurements. These active sites played a role as Lewis acid sites in the MPV reduction of cyclohexanone giving almost 100% selectivities with high activities as well. 2. Experimental Section 2.1. Synthesis In a typical synthesis, 16 g of a 10 % aqueous solution of F127, 26 g of distilled water and 4.71 g of Na2SiO3»9H2O was mixed at 313 K. To this solution, 13.6 g of HC1 (35 %) with ZrOCl2»8H2O were added quickly under vigorous stirring to obtain a gel. The gel solution was stirred for 120 min before loaded into a microwave digestion system (CEM Corporation, MAR-5), and microwave was irradiated for 120 min at 100°C. The solid product was calcined at 500°C. Pure siliceous SBA-16 was synthesized with the same procedure except that no Zr was added. 2.2. Characterization XRD patterns were recorded on a Rigaku Multiflex diffractometer with a monochromated high-intensity Cu Ka radiation (X = 0.15418 nm). Nitrogen adsorption/desorption isotherms were measured at 77 K on a ASAP 2020 apparatus.The UV diffuse reflectance spectra were measured with a Solidspec 3700 UV-Vis-NIR spectrometer of Shimazu. A BaSO4 was used as a standard. FT-IR spectroscopy was carried out on a Nicolet Magna-AEM FT-IR spectrometer using KBr windows. The samples were preheated at 450°C for 15h, and pyridine was adsorbed at 150 °C for 30 min followed, desorbing at 150°C for 20 min before measurement. The samples were measured at 25°C. SEM images were obtained from a SEM (JEOL 630-F) instrument. 2.3. Catalytic reaction 0.127 g (1.3 mmol) of the cyclohexanone and 5 g (83 mmol) of 2-propanol were placed in the tube and heated to 82°C. A quantity of 100 mg of catalyst was added to the reaction mixture. The products were analyzed by gas chromatography. The o-xylene was used as internal standard.

903

3. Results and Discussion

5 X

0 5 X

X

a 1

0.005 5

5 2 2 Theta

0.008 0.01 0 .0.02 02 3

750

1.6

6.1 nm

4.7 nm

1.2 0.8

"T" i0

g

1 b)

3 Pore Volume ( cm /g)

Zr/Si X

AdsorbbedV ed Volume ( cm3/g)

Fig. la illustrates the XRD patterns of calcined pure and Zr containing SBA16. It showed that the Im3m structures were obtained when the Zr/Si atomic

500

i

250

0.4 0.0

0

50

100

150

Pore Diameter

C^^ 0.0

0.2

0.4

" 0.6

0.8

1.0 1.0

P/P P0 0

Fig. 1 a) Small-angle X-ray diffraction patterns of calcined Zr-SBA-16 with varid Zr/Si atomic ratios (in gel), b) N2 sorption isotherms and the pore size distributions of 0.01 ZrSBA-16 and pure SB A-16

ratios lower than 0.01. They were identified with sharp ( 1 1 0 ) and small (2 0 0) reflections [5]. The lattice parameters were calculated as about 88A which was smaller to those reported in the literature [6, 7]. It might be due to the incorporation of zirconium which caused the more closed condensation. The textural ordering of the Zr- SBA-16 decreased as the Zr/Si was 0.02. It indicated that maximum Zr content was lower than 2 % under such synthesis condition. The physical properties of the 0.01 Zr-SBA-16 and pure SBA-16 samples were characterized by N2 sorption studies (Fig. lb). The pore volume and BET decreased apparently from 6.1 to 4.7 nm and 948 to 537 m2/g, respectively. It indicates the incorporation of Zr leeds to the more closed condensation of silica framework. Fig 2a presents the UV-visible spectra of the calcined Zr-SBA-16 samples. Zr containing samples exhibited a band around 210 nm which was ascribed to an oxygen to Zr(IV) charge-transfer transition. Sharp band at 210 nm showed the presence of isolated Zr4+ ions in the framework of silica. Increases in Zr contents resulted in the increases in intensities. But Zr/Si ratios of higher than 0.01, the ZrC>2 phase might be formed which gave band at about 230 nm [7]. Fig 2b shows infrared spectra of pyridine adsorbed on the varied content of ZrSBA-16. The peak at 1447 cm'1 indicated the presence of Lewis acid sites and the absence of a peak at 1540 cm'1 showed the absence of any strong Bransted acid sites. The weak peaks at 1480 and 1580 cm"1 could be ascribed to Hbonded pyridine [8]. It means, in the framework of directly synthesized ZrSBA-16, most of incorporated Zr shows Lewis acid sites, because of these Zr species have tetragonal structure in the silica framework. MPV reduction of cyclohexanone on Zr-SBA-16 with different contents of Zr are presented in Figure 2c. The selectivities on cyclohexanol were higher than

904

98 % for all samples. It was due to the moderate acidity of Zr active sites in the SBA-16 framework. And reaction results showed the 0.01 (Zr/Si) is the best ratio for MPV reduction. 4. Conclusion From above results, we could conclude that direct synthesis of zirconium substituted SBA-16 mesoporous silica (with the best molar ratio Zr/Si = 0.01) have been achieved using zirconyl chloride octahydrate as a zirconium source under microwave irradiation without any loss in textural properties. Such obtained Zr-SBA-16 had Lewis acidity which had played highly selective catalysts for the MPV reduction of cyclohexanone. a

b Zr/Si

1580 1580

J

1480 1480

1448 1448

1__A.

Zr/Si 0.005 0.005

cc

100 100 90

0.02

%

0.008 0.008

0.01 0.008 0.005

200

250

300

350 400450500 400 450

Wavelength nm Wavelength / nm

——^^— ^\

A 0.01 0.02

500 1700 1700 1650 1650 1600 1600 1550 1550 1500 1500 1450 1450 1400 1400 -1 Wavenumber/Cm Wavenumber / Cm- 1

80 70 008Conversion Conversion of cyclohexanone - • - Selectivity Selectivity of cyclohexanol cyclohexanol

60 0.005

0.010

0.015

0.020

Zr/Si (mol / mol) (mol/mol)

Figure 2. a) UV spectra of Zr-SBA-16 with various Zr/Si atomic ratios (in gel), b) FT-IR spectra of chemisorbed pyridine on Zr-SBA-16 at 150 °C, and c) Effect of Zirconium content on MPV reduction of cyclohexanone.

5. Acknowledgement This work was supported by KOSEF A3 Foresight Program (33426-1) 6. References [1] [2] [3] [4] [5]

A. Corma, L. T. Nemeth, M. Renz and S. Valencia, Nature, 412 (2001), 425. Y. Z. Zhu, G. Chuah and S. Jaenicke, J. Cat., 227 (2004) 1. C. F. de Graauw, J. A. Peters, H. van Bekkum and J. Huskens. Synthesis, 10 (1994) 1007. Young Kyu Hwang, J. S. Chang and S. E. Park, Angew. Chem. Int. Ed., 44 (2005) 556. Y. K. Hwang, J. S. Chang, Y. U. Kwon and S. E. Park, Microporous and Mesoporous Materials, 68(2004)21. [6] D. Zhao, Q. Huo, J. Feng, B. F. Chemlka and G. D. Stucky, J. Am.Chem. Soc, 120 (1998) 6024. [7] M. S. Morey, S. Schwarz, M. Froba and G. D. Stucky, J. Phys. Chem. B, 103 (1999) 2037. [8] G. G. Juttu and R. F. Lobo, Catalysis Letters, 62 (1999) 99.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Published by Elsevier B.V.

905 905

One and three dimensional mesoporous carbon nitride molecular sieves with tunable pore diameters Ajayan Vinua*, Toshiyuki Moria, Sunichi Hishitaa, Srinivasan Anandana, Veerappan Vaithilingam Balasubramanianb and Katsuhiko Arigac "Fuel Cell Materials Center, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Ibaraki, Japan; Email: [email protected] b Department of Marine Biotechnology, Asan-City 336-745, Chungnam, Soonchunhyang University, South Korea c Supermolecules Group, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Ibaraki, Japan One- and three-dimensional mesoporous carbon nitride materials have been synthesized using SBA-15 and SBA-16 mesoporous silica hard templates, respectively. The obtained materials have been unambiguously characterized by sophisticated techniques such as XRD, HRTEM, EELS, XPS, FT-IR and nitrogen adsorption. The pore diameter of the above materials can easily be tuned by changing the pore diameter of mesoporous silica template with keeping the weight ratio of carbon and nitrogen source constant. 1. Introduction Mesoporous carbon materials [1-2] with nanoscale pore sizes prepared from periodic inorganic silica templates have been receiving much attention because of their versatile uses in size and shape selective adsorption media, chromatographic separation, catalysts, nanoreactors, battery electrodes, capacitors, energy storage and biomedical engineering. Mesoporous carbon nitride materials (MCN) with one and three dimensional pore systems promise access to an even-wider range of application possibilities because of their unique properties such as semi-conductivity, intercalation ability, hardness, etc. Until now no such materials have been reported. However, there are lots of report on the synthesis and characterization of nonporous carbon nitride materials [3]. These materials can be prepared either from molecular or chemical precursors at very high temperatures. Very recently, Gao and Giu have reported the chemical synthesis of nonporous turbostratic carbon nitride crystallites from polymerized ethylenediamine and carbon tetrachloride [4]. Here, we used the similar chemical method for the preparation of the highly ordered one and three dimensional mesoporous carbon nitride material, designated as MCN, having pores with various diameters, high specific surface area and specific pore volume [5].

906

2. Experimental Section In a typical synthesis, the calcined mesoporous silica SBA-15 or SBA-16 was added to a mixture of ethylenediamine (EDA) and carbon tetrachloride (CTC). The resultant mixture was refluxed and stirred at 90°C for 6 h. The materials prepared using SBA-15 and SBA-16 as templates were named as MCN-1 and MCN-2, respectively. Another set of samples was prepared using SBA-15 materials synthesized at different temperature and the samples were labeled as MCN-1-T where T indicates the synthesis temperature of mesoporous silica. The template-carbon nitride polymer composites were then heat treated in a nitrogen flow to carbonize the polymer. The MCN was recovered after dissolution of the silica framework in 5 wt% hydrofluoric acid. The powder X-ray diffraction (XRD) patterns of mesoporous carbon nitride materials were collected on a Rigaku diffractometer using CuKoc (A, = 0.154 nm) radiation. The specific surface area was calculated using the Brunauer-Emmett-Teller (BET) method. HRTEM images were obtained with TEM JEOL JEM-2000EX2. The preparation of samples for HRTEM analysis involved sonication in ethanol for 2 to 5 min and deposition on a copper grid. The accelerating voltage of the electron beam was 200 kV. 3. Results and Discussion The ordered one-dimensional (1-D) mesoporous carbon nitride MCN-1 structure was investigated by powder XRD and nitrogen gas adsorption measurements. The XRD pattern of MCN-1 material shows three, clear peaks, which can be assigned to 100, 110, and 200 diffractions of 2-D hexagonal lattice (space group p6mm) with a lattice constant a1Oo = 9.52 nm, similar to the XRD pattern of parent template SBA-15 which consists of the hexagonal arrangement of cylindrical pores and the pores are interlinked by the micropores present in the walls, as shown in Fig. la. Such materials with 1-D mesopores are arranged in a hexagonal net are defined as 2-D mesostructure because the XRD pattern shows 2-D p6mm symmetry. The powder XRD pattern of MCN-1 before carbonization also exhibits the pattern similar to SBA-15, consisting of a week 100 reflection at low angle and two small peaks at a higher angle (not shown). However, the intensity of the low angle (100) and high angle peaks (110 and 200) decreases as compared to the parent SBA-15 material upon loading the CN matrix inside the mesopores. This can not be interpreted as a severe loss of structural order, but it is likely that larger contrast in density between the silica walls and the open pores relative to that between the silica walls and the CN matrix inside the pores is responsible for the observed decrease in intensity. Moreover, the unit cell constant of the MCN-1 material before carbonization (10.7 nm) is higher than the respective carbonized sample.

907

This can be ascribed to the condensation reaction between the free carbon and nitrogen in the walls resulting in a lattice contraction. The powder XRD pattern and HRTEM of 2-D mesoporous carbon nitride materials synthesized using SBA-15 with different pore diameters prepared at different synthesis temperature are also shown in Fig. la and lb, respectively. All the materials possess a sharp 100 reflection at very low angle which is typical for hexagonally ordered mesoporous materials. It is interesting to note that the d-spacing and the unit cell size of the MCN-1 materials synthesized using different pore diameters of SBA-15 materials as templates increase in the following order : MCN-1-150 > MCN-1-130 > MCN-1-100. This is a direct evidence of pore size enlargement in the MCN-1 materials. The overall carbon to nitrogen ratio of all the materials obtained from the CHN and EELS is almost same and is found to be 4.35. EEL spectra exhibit C and N K-edges located at 284 and 401 eV. The fine structure of the edges, in particular, their left-hand 2 shoulders revealing ls-Jt* electron transitions, is a fingerprint of a sp hybridization. The FT-IR and XPS data also confirm that the materials are mainly composed of C and N with a small amount of hydrogen. The trace of H comes either from the moisture or ethanol adsorbed on the surface or NH group on the MCN-1 matrix. Higher angle XRD pattern shows that the materials are partially amorphous and possess turbostratic ordering of carbon and nitrogen atoms in the CN graphene layers. 100 100

aa -

Intensity (a.u)

10.7 10.7 nm nm

b

MCN-1-150 MCN-1-150

(0

I

110

MCN-1-130 MCN-1-130 9.51 9.51 nm nm

200

00

22

MCN-1-100 MCN-1-100

44

66

Angle θ (theta) Angle 22θ (theta)

88

10 10

Fig. 1 (a) Powder XRD patterns of mesoporous carbon nitride materials with different pore diameters and (b) HRTEM of MCN-1-130. The powder XRD pattern of MCN-2 shows a sharp 110 reflection with a broad 200 reflection and is almost similar to that for SBA-16 template (Fig. 2a), demonstrating that 3-D mesoporous cage structure is successfully replicated to the MCN-2 sample. The intensity of the 110 peak of MCN-2 is much higher than that of the silica template, indicating that the enhancement in the structural order is occurred during the replication process. The unit cell

908

3e+4

600 500

MCN-2

b

3

Intensity (cps)

-1

a

3e+4

Amount Adsorbed (cm .g STP)

parameter of the MCN-2 is calculated using the formula 2 2 dnoand is found to be 13.4 nm. The nitrogen adsorption isotherm of MCN-2 in comparison to that of the parent silica template is shown in Figure 2b. Both the materials exhibit type IV isotherm with a broad hysteresis loop which is typical for the well ordered cage type mesoporous material. It should be also noted that the specific surface area and the specific pore volume of MCN-2 are much higher than those of the template and the 2-D mesoporous carbon nitride, MCN-1, prepared from the SBA-15 template. It is also important to note that the preparation of MCN-2 failed when our previous synthesis procedure for MCN-1 was used in this study. This could mainly be attributed to difference in the pore structure and the diameter of SBA-16 as compared to SBA-15 template.

2e+4 2e+4

MCN-2

1e+4 5e+3 SBA-16

0 2

4 4

2 θ (degrees) 2θ

6 6

8

400

SBA-16

300 200 100 0 0.0

0.2

0.4

0.6

0.8

1.0

1.2

Relative Pressure P/P0

Fig. 2 (a) powder XRD pattern and (b) nitrogen adsorption isotherms of MCN-2 in comparison with SBA-16

4. Conclusions Novel mesoporous carbon nitride materials with different structures have been synthesized using SBA-15 and SBA-16 hard templates, respectively. The obtained materials have been unambiguously characterized by various sophisticated techniques. Moreover, the pore diameter of the above materials can easily be tuned by changing the pore diameter of mesoporous silica template with keeping the weight ratio of carbon and nitrogen source constant. 5. References 1. R. Ryoo, S. H. Joo, S. Jun, J. Phys. Chem. B, 103 (1999), 7743. 2. A. Vinu, C. Streb, V. Murugesan, M. Hartmann, J. Phys. Chem. B, 107 (2003), 8297. 3. A. Vinu, M. Miyahara, K. Ariga, J. Phys. Chem. B, 109 (2005), 6436. 4. Y. Qiu, L. Gao, Chem. Commun., (2003), 2378; E. Kroke, M. Schwarz, Coordin. Chem. Rev., 248 (2004), 493. 5. A. Vinu, K. Ariga, T. Mori, T. Nakanishi, S. Hishita, D. Golberg, Y. Bando, Adv. Mater., 17(2005), 1648.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Published by Elsevier B.V.

909 909

Synthesis of well-ordered carboxyl group functionalized mesoporous carbon using non-toxic oxidant, Ajayan Vinua*, Kazi Zahir Hossainb, Sunichi Hishitaa, Toshiyuki Moria, Narasimhan Gokulakrishnan0, Veerappan Vaithilingam Balasubramanianc and Katsuhiko Arigab "Fuel Cell Materials Center, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Ibaraki, Japan; Email: [email protected] b Supermolecules Group, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Ibaraki, Japan 'Department of Marine Biotechnology, Asan-City 336-745, Chungnam, Soonchunhyang University, South Korea Carboxyl group substituted mesoporous carbons were synthesized by oxidation of well-ordered mesoporous carbon materials with a solution of (NH4)2S2Og for a different periods of time and temperature. The effect of the oxidation treatment on the textural parameters of the mesoporous carbons was studied. The amount of carboxyl groups on the pore surface of the mesoporous carbon with very high structural order can be easily tuned by changing the oxidation conditions such as oxidation time, oxidant concentration and the oxidation temperature. 1. Introduction Mesoporous carbon materials with very high surface area, pore volume and uniform pore size distribution synthesized from periodic mesoporous silica templates are quite useful in many applications such as gas separation, catalysis, water and air purification and energy storage. However, the hydrophobic and inert nature of mesoporous carbons can be unfavourable for several applications. Surface modification or functionalization of porous carbon surface is crucial for the development and application of hybrid nanoporous materials and to make new adsorbent or catalyst for the selective removal of organic contaminants and biomaterials adsorption [1]. However, there have been only a limited number of studies on the functionalization of mesoporous carbon. Variety of functionalities can be introduced upon oxidising the surface of mesoporous carbons by various oxidation agents. This would also help to enhance the wettability for polar solvents and making the surface more reactive. Very recently, Ryoo and his coworkers have reported that COOH groups can easily be introduced on the surface of the mesoporous carbon by simple HNO3 oxidation [2]. It is expected that the COOH functionalized mesoporous carbon could have a great potential for high enzyme immobilization or low leaching because the size of the pore is much larger than the molecular size of the protein and can easily be tuned to the size of proteins for selective adsorption, and the

910

anchoring ability of COOH groups on the pore entrances. Unfortunately, to our knowledge, the preparation of -COOH functionalized mesoporous carbons by (NH4)2S2Og (APDS) as an oxidant and its great potential advantage in the enzyme immobilization have not been yet realized. 2. Experimental Section Mesoporous carbon material (CMK-3) was synthesized using a reported procedure elsewhere [3,4] and was oxidized using a solution of APDS with different concentration (0 to 1.75 M) in 2 M H2SO4, different periods of time up to a maximum of 48 h, and different temperatures starting from 0 to 60°C. All the oxidized samples were washed with several times with distilled water until there was an absence of sulphates in the washing water. However, a trace amount of sulphur was detected in the oxidized samples when they were analyzed using CHNS and EDS analysis. The nature and the amount of surface functional groups on the surface of mesoporous carbon were determined using FT-IR spectroscopy. The powder XRD patterns of mesoporous carbon materials after the APDS treatment were collected on a Rigaku diffractometer. The textural parameters of the mesoporous carbon after oxidation were calculated from the nitrogen adsorption and desorption isotherm using a Quantachrome Autosorb-lC instrument.

3. Results and Discussion Fig. la shows the FT-IR spectra of mesoporous carbon samples (CMK-3) treated with APDS at different reaction times. The efficiency of the oxidation treatment to create the carboxyl groups on the surface of the CMK-3 material using APDS is clearly reflected on the FT-IR spectra. All the samples after the oxidation treatment show four bands centered around 1723, 1587, 1400 and 1250 cm"1. Such peaks are not observed for the sample without the oxidation treatment. The band at 1723 c m 1 can be attributed to C=O stretching vibration of non-aromatic carboxyl groups while the band at 1587 c m 1 may be assigned to aromatic ring stretching coupled to highly conjugated keto groups. The band at 1400 cm"1 could be assigned either to carboxyl-carbonate structures or to aromatic C=C bond. It is interesting to note that the intensity ratio of the bands corresponding to the carboxyl and keto groups increases with increasing the oxidation time. The above results reveal that the prolonged treatment of mesoporous carbon with APDS could help the easy conversion of a large number of surface carbon atoms into keto groups and then to carboxyl groups on the surface of CMK-3. In order to study the changes on the textural parameters and structural order of the CMK-3 after APDS treatment, the materials were thoroughly characterized

911

by powder XRD, nitrogen adsorption and HRSEM measurements. Fig. lb shows the powder XRD patterns of CMK-3 treated with APDS solution at different reaction times. It can be clearly seen from Fig. lb that the structural order of the CMK-3 materials is almost maintained upto the reaction time of 24 h, while the structure is completely collapsed with a further increase from 24 to 48 h. The unit cell parameter of CMK-3 increases with increasing the oxidation time, suggesting that the oxidation can remove several layers of carbon from the pore walls and makes the walls thinner, resulting in an increase of pore size. The powder XRD results reveal that the structure of the CMK-3 materials is quite stable after the APDS treatment for 24 h. Though the mesoporous structure of the functionalized CMK-3 remained intact, the specific surface area, and pore volume of the material decrease with the severity of oxidation treatment. At one stage, i.e., above 24 h of reaction time, the pore walls are completely destroyed by the oxidation treatment which is clearly seen on the Figure lb.

1.4

b

a

1.42

48H

1.04

Intensity [a.u]

Absorbance (a.u)

1.6

24H

1.2

0.53

6H

0.48

0.8 0.6 0.6

12H

0.75

1.0

2H

24H 48H

0H

•

2000

2H 6H 12H

1800 1800

1600

1400 1400

1 -1 wavenumber /cm/cm 1

1200 1200

1000

0

2

4

6

Angle [2θ]

8

10

Fig. 1 (a) FT-IR spectra (inset numbers: Left-intensity ratio between the carboxyl and keto groups; Right-oxidation time) and (b) Powder XRD patterns of CMK-3 materials treated with APDS at different oxidation time. The surface morphology mainly the particle size, shape and structure of the CMK-3 materials after the APDS treatment was thoroughly studied by HRSEM technique. It is very interesting to note that the surface morphology of the materials except CMK-3-48H was completely retained after the APDS treatment. The observation of morphological disorder in the CMK-3-48H is consistent with the results obtained from the XRD and nitrogen adsorption measurements. All the above results clearly indicate that the oxidation time of 24 h is the best condition to functionalize mesoporous carbon without affecting its structural order and has been followed in the rest of our investigation. The effect of the concentration of the APDS on the degree of functionalization, structural order and the textural parameters of CMK-3 was also investigated. The degree of COOH functionalization increases with increasing the concentration of APDS as shown in Fig. 2a. It should be noted that the amount of COO groups calculated from the IR and HRSEM-EDX data increases from

912

0.5M

0.26M None

'.

1

2000 2000

.

1800 1800

1600 1600

1400 1400

1200 1200 -1

Wavenumber [cm ]

'

1000

0.8

800 0.6 600 0.4

400

0.2

200 0 0.0

0.5

1.0

1.5 1.5

0.0 2.0

-1 3

1.0

1000

5 4 3 2 1

Pore Diameter [nm]

0.52 '"X_/\^

1200

Mesopore Volume [cm .g ]

ioiir^ ^ " 0.5M

1.0M

*^^ ^

1.2

-1

1.75M 0.89

1400

Surface Area [m .g ]

Absorbance [a.u]

1.05

2

1.463 to 5.307 mmol.g"1 with increasing the oxidation time from 0 to 48 h. It can be also seen from the Fig. 2b that the pore diameter of the carbon materials after the APDS treatment is slightly larger than that of the sample before the treatment. The large reduction in the surface area and specific pore volume of the CMK-3 after APDS treatment could not be attributed as a severe loss of structural order as powder XRD pattern of all the materials exhibit strong 100 reflection after the treatment (not shown), but, however, could be mainly due to the formation of COOH groups inside the micropores of the mesoporous carbon as these micropores are mainly responsible for its very high specific surface area and specific pore volume. The effect of the temperature on the degree of functionalization has also been studied. It has been found that the structure of the CMK-3 was completely collapsed after the APDS treatment at 60°C for 24 h though the degree of functionalization is higher at 60°C.

0

Concentration of Oxidant [M]

Fig. 2 (a) FT-IR spectra and (b) textural parameters of mesoporous carbons treated with different concentration of APDS for 24 h. 4. Conclusions COOH functionalization on mesoporous carbon materials has been successfully achieved using a novel non-toxic oxidant, APDS. The effect of the oxidation treatment on the textural parameters of the mesoporous carbons was reported. The amount of carboxyl groups on the pore surface of the mesoporous carbon with very high structural order can be easily tuned by changing the oxidation conditions such as oxidation time, oxidant concentration and the oxidation temperature. 5. References 1. A. Vinu, C. Streb, V. Murugesan, M. Hartmann, J. Phys. Chem. B, 107 (2003), 8297. 2. S. Jun, M. Choi, S. Ryu, H-Y. Lee, R. Ryoo, Stud. Surf. Sci. Catal, 146 (2003), 37. 3. A. Vinu, M. Miyahara, K. Ariga, J. Phys. Chem. B, 109 (2005), 6436. 4. S. Jun, S. H. Joo, R. Ryoo, M. Kruk, M. Jaroniec, Z. Liu, T. Ohsuna, O. Terasaki, J. Am. Chem. Soc, 122 (2000), 10712.

913 STUDIES IN SURFACE SCIENCE AND CATALYSIS Advisory Editors: B. Delmon, Universite Catholique de Louvain, Louvain-la-Neuve, Belgium J.T. Yates, University of Pittsburgh, Pittsburgh, PA, U.S.A.

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Preparation of Catalysts I. Scientific Bases for the Preparation of Heterogeneous Catalysts. Proceedings of the First International Symposium, Brussels, October 1 4 - 1 7 , 1 9 7 5 edited by B. Delmon, P.A. Jacobs and G. Poncelet The Control of the Reactivity of Solids. A Critical Survey of the Factors that Influence the Reactivity of Solids, w i t h Special Emphasis on the Control of the Chemical Processes in Relation to Practical Applications by V.V. Boldyrev, M. Bulens and B. Delmon Preparation of Catalysts ll.Scientific Bases for the Preparation of Heterogeneous Catalysts. Proceedings of the Second International Symposium, Louvain-laNeuve, September 4 - 7 , 1978 edited by B. Delmon, P. Grange, P. Jacobs and G. Poncelet Growth and Properties of Metal Clusters. Applications to Catalysis and the Photographic Process. Proceedings of the 32 n d International Meeting of the Societe de Chimie Physique, Villeurbanne, September 2 4 - 2 8 , 1979 edited by J. Bourdon Catalysis by Zeolites.Proceedings of an International Symposium, Ecully {Lyon), September 9 - 1 1, 1980 edited by B. Imelik, C. Naccache,Y. BenTaarit, J.C.Vedrine, G. Coudurier and H. Praliaud Catalyst Deactivation. Proceedings of an International Symposium, A n t w e r p , October 1 3 - 1 5 , 1 9 8 0 edited by B. Delmon and G.F. Froment New Horizons in Catalysis. Proceedings of the 7 th International Congress on Catalysis, Tokyo, June 3 0 - J u l y 4 , 1980. Parts A and B edited by T. Seiyama and KJanabe Catalysis by Supported Complexes by Yu.l.Yermakov, B.N. Kuinetsov and V.A. Zakharov Physics of Solid Surfaces. Proceedings of a Symposium, Bechyne, September 2 9 - O c t o b e r 3 , 1 9 8 0 edited by M. Laznicka Adsorption at the Gas-Solid and Liquid-Solid Interface. Proceedings of an International Symposium, Aix-en-Provence, September 2 1 - 2 3 , 1981 edited by J. Rouquerol and K.S.W. Sing Metal-Support and Metal-Additive Effects in Catalysis. Proceedings of an International Symposium, Ecully (Lyon), September 1 4 - 1 6 , 1982 edited by B. Imelik, C. Naccache, G. Coudurier, H. Praliaud, P. Meriaudeau, P. Gallezot, G.A.Martin and J.C.Vedrine Metal Microstructures in Zeolites. Preparation - Properties - Applications. Proceedings of a Workshop, Bremen, September 2 2 - 2 4 , 1982 edited by P.A. Jacobs, N.I. Jaeger, P. Jiru and G. Schulz-Ekloff Adsorption on Metal Surfaces. An Integrated Approach edited by J. Benard Vibrations at Surfaces. Proceedings of the Third International Conference, Asilomar, CA, September 1 - 4 , 1982 edited by C.R. Brundle and H.Morawitz Heterogeneous Catalytic Reactions Involving Molecular Oxygen by G.I. Golodets

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Preparation of Catalysts III. Scientific Bases for the Preparation of Heterogeneous Catalysts. Proceedings of the Third International Symposium, Louvain-la-Neuve, September 6 - 9 , 1982 edited by G. Poncelet, P. Grange and PA. Jacobs Spillover of Adsorbed Species. Proceedings of an International Symposium, Lyon-Villeurbanne, September 12-16, 1983 edited by G.M. Pajonk.S.J.Teichner and J.E. Germain Structure and Reactivity of Modified Zeolites. Proceedings of an International Conference, Prague, July 9 - 1 3 , 1984 edited b y PA. Jacobs, N.I. Jaeger, P. Jiru, V.B. Kazansky and G. Schulz-Ekloff Catalysis on the Energy Scene. Proceedings of the 9'h Canadian Symposium on Catalysis, Quebec, P.Q., September 30-October 3, 1984 edited by S. Kaliaguine and A.Mahay Catalysis by Acids and Bases. Proceedings of an International Symposium, Villeurbanne (Lyon), September 2 5 - 2 7 , 1984 edited by B. Imelik, C. Naccache, G. Coudurier.Y. Ben Taarit and J.C.Vedrine Adsorption and Catalysis on Oxide Surfaces. Proceedings of a S y m p o s i u m , Uxbridge, June 2 8 - 2 9 , 1984 edited b y M. Che and G.C.Bond Unsteady Processes in Catalytic Reactors by Yu.Sh. Matros Physics of Solid Surfaces 1984 edited by J.Koukal Zeolites:Synthesis, Structurejechnology and Application. Proceedings of an International Symposium, Portoroz -Portorose, September 3 - 8 , 1984 edited by B.Driaj.S. Hocevar and S. Pejovnik Catalytic Polymerization of Olefins. Proceedings of the International Symposium on Future Aspects of Olefin Polymerization, Tokyo, July 4 - 6 , 1985 edited by T.Keii and K.Soga Vibrations at Surfaces I98S. Proceedings of the Fourth International Conference, Bowness-on-Windermere, September 15-19, 1985 edited by DA. King, N.V. Richardson and S. Holloway Catalytic Hydrogenation edited b y L. Cerveny New Developments in Zeolite Science and Technology. Proceedings o f t h e 7 th International Zeolite Conference, Tokyo, August 1 7-22, 1 986 edited by Y.Murakami.A. lijima and J.W.Ward Metal Clusters in Catalysis edited by B.C. Gates, L. Guczi and H. Knozinger Catalysis and Automotive Pollution Control. Proceedings of t h e First International Symposium, Brussels, September 8 - 1 1 , 1986 edited by A. Crucq and A. Frennet Preparation of Catalysts IV. Scientific Bases for the Preparation of Heterogeneous Catalysts. Proceedings of the Fourth International Symposium, Louvain-laNeuve, September 1-4, 1986 edited by B. Delmon, P. Grange, PA. Jacobs and G. Poncelet Thin Metal Films and Gas Chemisorption edited by P.Wissmann Synthesis of High-silica Aluminosilicate Zeolites edited b y P A Jacobs and J.A.Martens Catalyst Deactivation 1987. Proceedings of the 4"1 International Symposium, Antwerp, September 29-October 1, 1987 edited by B. Delmon and G.F. Froment Keynotes in Energy-Related Catalysis edited by S. Kaliaguine

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Methane Conversion. Proceedings of a Symposium on the Production of Fuels and Chemicals from Natural Gas, Auckland, April 2 7 - 3 0 , 1987 edited by DM. Bibby, C.D.Chang, R.F.Howe and S.Yurchak Innovation in Zeolite Materials Science. Proceedings of an International Symposium, Nieuwpoort, September 13-17, 1987 edited by P.). Grobet, W.J.Mortier, E.F.Vansant and G. Schulz-Ekloff Catalysis l987.Proceedings of the 1 0 * North American Meeting of the Catalysis Society, San Diego, CA, May 17-22, 1987 edited by J.W.Ward Characterization of Porous Solids. Proceedings of t h e IUPAC S y m p o s i u m (COPS I), Bad Soden a, Ts., April 26-29,1987 edited by K.K.Unger, J. Rouquerol, K.S.W.Sing and H. Krai Physics of Solid Surfaces 1987. Proceedings of the Fourth Symposium on Surface Physics, Bechyne Castle, September 7 - 1 1 , 1987 edited by J.Koukal Heterogeneous Catalysis and Fine Chemicals. Proceedings of an International Symposium, Poitiers, March 15-17, 1988 edited by M. Guisnet, J. Barrault, C. Bouchoule.D. Duprez, C. Montassier and G. Perot Laboratory Studies of Heterogeneous Catalytic Processes by E.G. Christoffel, revised and edited by Z. Paal Catalytic Processes under Unsteady-State Conditions by Yu. Sh. Matros Successful Design of Catalysts. Future Requirements and Development. Proceedings of the Worldwide Catalysis Seminars, July, 1988, on the Occasion of the 30 th Anniversary of the Catalysis Society of Japan edited by T. Inui Transition Metal Oxides. Surface Chemistry and Catalysis by H.H.Kung Zeolites as Catalysts, Sorbents and Detergent Builders. Applications and Innovations. Proceedings of an International Symposium, Wiirzburg, September 4-8,1988 edited by H.G. Karge and ].Weitkamp Photochemistry on Solid Surfaces e d i t e d by M.Anpo and T. Matsuura Structure and Reactivity of Surfaces. Proceedings of a European Conference, Trieste, September 13-16, 1988 edited by C.Morterra.A. Zecchina and G. Costa Zeolites: Facts, Figures, Future. Proceedings of the 8Ih International Zeolite Conference, Amsterdam, July 10-14, 1989. Parts A and B edited by P.A. Jacobs and R.A. van Santen Hydrotreating Catalysts. Preparation, Characterization and Performance. Proceedings of the Annual International AlChE Meeting, Washington, DC, November 27-December 2, 1988 edited by ML. Occelli and R.G.Anthony New Solid Acids and Bases.Their Catalytic Properties by K.Tanabe, M. Misono.Y. Ono and H. Hattori Recent Advances in Zeolite Science. Proceedings of the 1989 Meeting of the British Zeolite Association, Cambridge, April 17-19, 1989 edited by ]. Klinowsky and P.J. Barrie Catalyst in Petroleum Refining 1989. Proceedings of the First International Conference on Catalysts in Petroleum Refining, Kuwait, March 5 - 8 , 1989 edited by D.L.Trimm,S.Akashah, M.Absi-Halabi and A. Bishara Future Opportunities in Catalytic and Separation Technology edited b y M. Misono,Y.Moro-oka and S. Kimura

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Hew Developments in Selective Oxidation. Proceedings o f an International Symposium, Rimini, Italy, September 18-22, 1989 edited by G. Centi and F.Trifiro Olefin Polymerization Catalysts. Proceedings of the International Symposium on Recent Developments in Olefin Polymerization Catalysts, Tokyo, October 2 3 - 2 5 , 1989 edited by T.Keii and K.Soga Spectroscopic Analysis of Heterogeneous Catalysts. Part A: Methods of Surface Analysis edited by J.L.G. Fierro Spectroscopic Analysis of Heterogeneous Catalysts. Part B: Chemisorption of Probe Molecules edited by J.L.G. Fierro Introduction to Zeolite Science and Practice edited by H. van Bekkum, E.M. Flanigen and J.C. Jansen Heterogeneous Catalysis and Fine Chemicals II. Proceedings o f t h e 2 n d International Symposium, Poitiers, October 2 - 6 , 1990 edited by M. Guisnet, J. Barrault, C. Bouchouie.D. Duprez, G. Perot, R.Maurel and C. Montassier Chemistry of Microporous Crystals. Proceedings of the International Symposium on Chemistry of Microporous Crystals, Tokyo, June 26-29, 1990 edited by T. Inui.S. Namba and T.Tatsumi Natural Gas Conversion. Proceedings of the Symposium on Natural Gas Conversion, Oslo, August 12-17, 1990 edited by A. Holmen, K.-J, Jens and S.Kolboe Characterization of Porous Solids II. Proceedings of t h e IUPAC S y m p o s i u m (COPS II), Alicante, May 6 - 9 , 1990 edited by F. Rodriguez-Reinoso, J. Rouquerol, K.S.W. Sing and K.K.Unger Preparation of Catalysts V. Scientific Bases for the Preparation of Heterogeneous Catalysts. Proceedings of the Fifth International Symposium, Louvain-la-Neuve, September 3 - 6 , 1990 edited by G. Poncelet, PA. Jacobs, P. Grange and B. Delmon New Trends in CO Activation edited by L. Guczi Catalysis and Adsorption by Zeolites. Proceedings o f ZEOCAT 9 0 , Leipzig, August 20-23, 1990 edited by G . Ohlmann, H. Pfeifer and R. Fricke Dioxygen Activation and Homogeneous Catalytic Oxidation. Proceedings of t h e Fourth International Symposium on Dioxygen Activation and Homogeneous Catalytic Oxidation, Balatonf ured, September 10-14, 1990 edited by L.I. Simandi Structure-Activity and Selectivity Relationships in Heterogeneous Catalysis. Proceedings of the ACS Symposium on Structure-Activity Relationships in Heterogeneous Catalysis, Boston, MA, April 22-27', 1990 edited by R.K. Grasselli and A.W.SIeight Catalyst Deactivation 1991. Proceedings of the Fifth International Symposium, Evanston, IL, June 2 4 - 2 6 , 1991 edited by C.H. Bartholomew and J.B. Butt Zeolite Chemistry and Catalysis. Proceedings of an International Symposium, Prague, Czechoslovakia, September 8-13, 1991 edited by PA.Jacobs, N.I.Jaeger, LKubelkovaand B.Wichterlova Poisoning and Promotion in Catalysis based on Surface Science Concepts and Experiments by M. Kiskinova

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Catalysis and Automotive Pollution Control II. Proceedings of t h e 2 n d International Symposium (CAPoC 2), Brussels, Belgium, September 10-13, 1990 edited by A. Crucq New Developments in Selective Oxidation by Heterogeneous Catalysis. Proceedings of the 3rd European Workshop Meeting on New Developments in Selective Oxidation by Heterogeneous Catalysis, Louvain-la-Neuve, Belgium, April 8 - 1 0 , 1991 edited by P. Ruiz and B. Delmon Progress in Catalysis. Proceedings of the 12 th Canadian Symposium on Catalysis, Banff, Alberta, Canada, May 25-28, 1992 edited by K.J. Smith and EX. Sanford Angle-Resolved Photoemission.Theory and Current Applications edited by S.D. Kevan New Frontiers in Catalysis, Parts A-C. Proceedings of the 10th International Congress on Catalysis, Budapest, Hungary, 19-24 July, 1992 edited by L. Guczi, F. Solymosi and P.Tetenyi Fluid Catalytic Cracking: Science and Technology edited b y J.S.Mageeand M M . Mitchell,jr. New Aspects of Spillover Effect in Catalysis. For Development of Highly Active Catalysts. Proceedings of the Third International Conference on Spillover, Kyoto, Japan, August 17-20, 1993 edited by T. Inui, K. Fujimoto.T.Uchijima and M. Masai Heterogeneous Catalysis and Fine Chemicals III. Proceedings of the 3rd International Symposium, Poitiers, April 5 - 8, 1 993 edited b y M. Guisnet, J. Barbier, J. Barrault, C. Bouchoule.D. Duprez, G. Perot and C. Montassier Catalysis: An Integrated Approach to Homogeneous, Heterogeneous and Industrial Catalysis edited by J.A. Moulijn, P.W.N.M. van Leeuwen and R.A. van Santen Fundamentals of Adsorption. Proceedings of the Fourth International Conference on Fundamentals of Adsorption, Kyoto, Japan, May 17-22, 1992 edited by M. Suzuki Natural Gas Conversion II. Proceedings of the Third Natural Gas Conversion Symposium, Sydney, July 4 - 9 , 1993 edited by H.E. Curry-Hyde and R.F.Howe New Developments in Selective Oxidation II. Proceedings of t h e Second W o r l d Congress and Fourth European Workshop Meeting, Benalmadena, Spain, September 2 0 - 2 4 , 1993 edited by V. Cortes Corberan and S.Vic Bellon Zeolites and Microporous Crystals. Proceedings of the International Symposium on Zeolites and Microporous Crystals, Nagoya, Japan, August 2 2 - 2 5 , 1993 edited byT. Hattori and T.Yashima Zeolites and Related Microporous Materials: State of the Art I994. Proceedings of the 10th International Zeolite Conference, Garmisch-Partenkirchen, Germany, July 17-22, 1994 edited b y J.Weitkamp, H.G. Karge.H. Pfeifer and W. Holderich Advanced Zeolite Science and Applications edited b y J.C. Jansen, M. Stocker, H.G. Karge and J.Weitkamp Oscillating Heterogeneous Catalytic Systems by M M . Slinko and N.I. Jaeger Characterization of Porous Solids III. Proceedings of t h e IUPAC S y m p o s i u m (COPS III), Marseille, France, May 9 - 1 2 , 1993 edited by J.Rouquerol, F. Rodriguez-Rdnoso, K.S.W. Sing and K.K.Unger

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Volume 102 Volume 1 03 Volume 104 Volume 1 05

Catalyst Deactivation 1994. Proceedings of the 6 * International Symposium, Ostend, Belgium, October 3 - 5 , 1994 edited by B. Delmon and G.F. Froment Catalyst Design for Tailor-made Polyolefins. Proceedings o f t h e International Symposium on Catalyst Design for Tailor-made Polyolefins, Kanazawa, Japan, March 10-12, 1994 edited by K.Soga and M.Terano Acid-Base Catalysis II. Proceedings of the International Symposium on Acid-Base Catalysis II, Sapporo, Japan, December 2 - 4 , 1 993 edited b y H. Hattori.M. Misono and Y.Ono Preparation of Catalysts VI. Scientific Bases for the Preparation of Heterogeneous Catalysts. Proceedings of the Sixth International Symposium, Louvain-La-Neuve, September 5-8, 1994 edited by G. Poncelet, J.Martens.B. Delmon, P.A. Jacobs and P. Grange Science and Technology in Catalysis I994. Proceedings o f t h e Second T o k y o Conference on Advanced Catalytic Science and Technology, Tokyo, August 21-26, 1994 edited by Y. Izumi, H.Arai and M. Iwamoto Characterization and Chemical Modification of the Silica Surface by E.F.Vansant, P.Van Der Voort and K.C.Vrancken Catalysis by Microporous Materials. Proceedings of ZEOCAT'95, Szombathely, Hungary, July 9-13, 1995 e d i t e d by H.K. Beyer, H.G.Karge, I. Kiricsi and J.B.Nagy Catalysis by Metals and Alloys by V. Ponec and G.C.Bond Catalysis and Automotive Pollution Control III. Proceedings o f the Third International Symposium (CAPoC3), Brussels, Belgium, April 2 0 - 2 2 , 1994 edited by A. Frennet and J.-M. Bastin Zeolites:A Refined Tool for Designing Catalytic Sites. Proceedings of the International Symposium, Quebec, Canada, October 15-20, 1995 edited by L. Bonneviot and S. Kaliaguine Zeolite Science I994: Recent Progress and Discussions. Supplementary Materials t o t h e 10th International Zeolite Conference, Garmisch-Partenkirchen, Germany, July 17-22, 1994 edited b y H.G. Karge and J.Weitkamp Adsorption on New and Modified Inorganic Sorbents edited by A.Dabrowski and V.A.Tertykh Catalysts in Petroleum Refining and Petrochemical Industries 1995. Proceedings of the 2nd International Conference on Catalysts in Petroleum Refining and Petrochemical Industries, Kuwait, April 22-26, 1995 edited by M.Absi-Halabi, J. Beshara, H. Qabazard and A. Stanislaus II th International Congress on Catalysis - 4 0 * Anniversary. Proceedings of the 11 t h ICC, Baltimore, MD, USA, June 30-July 5, 1996 edited by J.W. Hightower.W.N. Delgass, E. Iglesiaand A.T. Bell Recent Advances and New Horizons in Zeolite Science and Technology edited by H. Chon.S.I.Woo and S. -E. Park Semiconductor Nanodusters - Physical, Chemical, and Catalytic Aspects edited by P.V. Kamat and D. Meisel Equilibria and Dynamics of Gas Adsorption on Heterogeneous Solid Surfaces edited by W. Rudziriski.W.A. Steele and G. Zgrablich Progress in Zeolite and Microporous Materials Proceedings of the 11 t h International Zeolite Conference, Seoul, Korea, August 12-17, 1996 edited by H. Chon,S.-K. Ihm and Y.S.Uh

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Volume 1 2 0 A

Hydrotreatment and Hydrocracking of Oil Fractions Proceedings of the 1 s t International Symposium / 6' h European Workshop, Oostende, Belgium, February 17-19, 1997 edited by G.F. Froment.B. Deimon and P. Grange Natural Gas Conversion IV Proceedings of the 4 t h International Natural Gas Conversion Symposium, Kruger Park, South Africa, November 19-23, 1995 edited by M. de Pontes, R.L. Espinoia, C.P. Nicolaides, J.H. Scholtz and M.S. Scurrell Heterogeneous Catalysis and Fine Chemicals IV Proceedings of the 4 t h International Symposium on Heterogeneous Catalysis and Fine Chemicals, Basel, Switzerland, September 8-12, 1996 edited by H.U. Blaser, A. Baiker and R. Prins Dynamics of Surfaces and Reaction Kinetics in Heterogeneous Catalysis. Proceedings of the International Symposium, Antwerp, Belgium, September 15-17, 1997 edited by G.F. Froment and K.C.Waugh Third World Congress on Oxidation Catalysis. Proceedings of the Third World Congress on Oxidation Catalysis, San Diego, CA, U.S.A., 21-26 September 1997 edited by R.K. Grasselli.S.T.Oyama, A.M. Gaffney and J.E. Lyons Catalyst Deactivation 1997. Proceedings of the 7 th International Symposium, Cancun, Mexico, October 5-8, 1997 edited by C.H. Bartholomew and G.A. Fuentes Spillover and Migration of Surface Species on Catalysts. Proceedings of the 4 t h International Conference on Spillover, Dalian, China, September 15-18, 1997 edited by Can Li and Qin Xin Recent Advances in Basic and Applied Aspects of Industrial Catalysis. Proceedings of the 1 3 th National Symposium and Silver Jubilee Symposium of Catalysis of India, Dehradun, India, April 2-4, 1997 edited by T.S.R. Prasada Rao and G.Murali Dhar Advances in Chemical Conversions for Mitigating Carbon Dioxide. Proceedings of the 4 t h International Conference on Carbon Dioxide Utilization, Kyoto, Japan, September 7 - 1 1 , 1997 edited by T. Inui, M.Anpo.K. lzui,S.Yanagida and T.Yamaguchi Methods for Monitoring and Diagnosing the Efficiency of Catalytic Converters. A patent-oriented survey by M. Sideris Catalysis and Automotive Pollution Control IV. Proceedings of the 4 t h International Symposium (CAPoC4), Brussels, Belgium, April 9 - 1 1 , 1997 edited by N. Kruse, A. Frennet and J.-M. Bastin Mesoporous Molecular Sieves 1998 Proceedings of the 1 s ' International Symposium, Baltimore, MD, U.S.A., July 10-12, 1998 edited by L.Bonneviot, F. Beland, C.Danumah, S. Giasson and S. Kaliaguine Preparation of Catalysts VII Proceedings of the 7 l h International Symposium on Scientific Bases for the Preparation of Heterogeneous Catalysts, Louvain-la-Neuve, Belgium, September 1-4, 1998 edited by B. Deimon, PA. Jacobs, R. Maggi, J.A.Martens, P. Grange and G. Poncelet Natural Gas Conversion V Proceedings of the 5 t h International Gas Conversion Symposium, Giardini-Naxos, Taormina, Italy, September 20-25, 1998 edited by A. Parmaliana, D. Sanfilippo, F. Frusteri, A.Vaccari and F.Arena Adsorption and its Applications in Industry and Environmental Protection. Vol I: Applications in Industry edited by A. Dqbrowski

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Adsorption and its Applications in Industry and Environmental Protection.

Vol II: Applications in Environmental Protection Volume 121

edited by A. D;|browski Science and Technology in Catalysis I998

Proceedings of the Third Tokyo Conference in Advanced Catalytic Science and Technology, Tokyo, July 19-24, 1998 Volume 122

edited by H. Hattori and K. Otsuka Reaction Kinetics and the Development of Catalytic Processes

Proceedings of the International Symposium, Brugge, Belgium, April 19-21, 1999 Volume 123

edited by G.F. Froment and K.C.Waugh Catalysis:An Integrated Approach

Second, Revised and Enlarged Edition Volume 124 Volume 125

edited by R.A. van Santen, P.W.N.M. van Leeuwen, J.A. Moulijn and B.A.Averill Experiments in Catalytic Reaction Engineering by J.M. Berty Porous Materials in Environmentally Friendly Processes

Proceedings of the 1S1 International FEZA Conference, Eger, Hungary, September 1-4, 1999 Volume 126

edited by I. Kiricsi, G. Pal-Borbely, J.B.Nagy and H.G. Karge Catalyst Deactivation 1999

Proceedings of the 8th International Symposium, Brugge, Belgium, October 10-13, 1999 Volume 127

edited by B. Delmon and G.F. Froment Hydrotreatment and Hydrocracking of Oil Fractions

Proceedings of the 2nd International Symposium/7th European Workshop, Antwerpen, Belgium, November 14-17, 1999 Volume 128

edited by B. Delmon, G.F. Froment and P. Grange Characterisation of Porous Solids V

Proceedings of the 5th International Symposium on the Characterisation of Porous Solids (COPS-V), Heidelberg, Germany, May 30- June 2, 1999 Volume 129

edited by K.K.Unger.G.Kreysa and ).P. Baselt Nanoporous Materials II

Proceedings of the 2nd Conference on Access in Nanoporous Materials, Banff, Alberta, Canada, May 25-30, 2000 Volume 130

edited byA. Sayari.M. Jaroniec and T.J. Pinnavaia 12th International Congress on Catalysis

Volume 131

edited byA. Corma, F.V. Melo.S. Mendioroz and J.L.G. Fierro Catalytic Polymerization of Cycloolefins

Proceedings of the 12 th ICC, Granada, Spain, July 9-14, 2000

Ionic, Ziegler-Natta and Ring-Opening Metathesis Polymerization Volume 132

By V. Dragutan and R. Streck Proceedings of the International Conference on Colloid and Surface Science, Tokyo, Japan, November 5-8,2000

25 'h Anniversary of the Division of Colloid and Surface Chemistry, The Chemical Society of Japan Volume 1 33

edited by Y. Iwasawa, N.Oyama and H.Kunieda Reaction Kinetics and the Development and Operation of Catalytic Processes

Proceedings of the 3 rd International Symposium, Oostende, Belgium, April 2225, 2001 Volume 134

edited by G.F. Froment and K.C.Waugh Fluid Catalytic Cracking V

Materials and Technological Innovations edited by M L Occelli and P. O'Connor

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Zeolites and Mesoporous Materials at the Dawn of the 21st Century. Proceedings of the 13lh International Zeolite Conference, Montpellier, France, 8-13 July 2001 edited by A. Galameau, F. di Renso, F. Fajula ans J. Vedrine Natural Gas Conversion VI Proceedings of the 6m Natural Gas Conversion Symposium, June 17-22, 2001, Alaska, USA. edited by J.J. Spivey, E. Iglesia and T.H. Fleisch Introduction to Zeolite Science and Practice. 2nd completely revised and expanded edition edited by H. van Bekkum, E.M. Flanigen, P.A. Jacobs and J.C. Jansen Spillover and Mobility of Species on Solid Surfaces edited by A. Guerrero-Ruiz and I. Rodriquez-Ramos Catalyst Deactivation 2001 Proceedings of the 9lh International Symposium, Lexington, KY, USA, October 2001 edited by J.J. Spivey, G.W. Roberts and B.H. Davis Oxide-based Systems at the Crossroads of Chemistry. Second International Workshop, October 8-11, 2000, Como, Italy. Edited by A. Gamba, C. Colella and S. Coluccia Nanoporous Materials III Proceedings of the 3"1 International Symposium on Nanoporous Materials, Ottawa, Ontario, Canada, June 12-15, 2002 edited by A. Sayari and M. Jaroniec Impact of Zeolites and Other Porous Materials on the New Technologies at the Beginning of the New Millennium Proceedings of the 2nd International FEZA (Federation of the European Zeolite Associations) Conference, Taormina, Italy, September 1-5, 2002 edited by R. Aiello, G. Giordano and F.Testa Scientific Bases for the Preparation of Heterogeneous Catalysts Proceedings of the 8th International Symposium, Louvain-la-Neuve, Leuven, Belgium, September 9-12, 2002 edited by E. Gaigneaux, D.E. De Vos, P. Grange, P.A. Jacobs, J.A. Martens, P. Ruiz and G. Poncelet Characterization of Porous Solids VI Proceedings of the 6lh International Symposium on the Characterization of Porous Solids (COPS-VI), Alicante, Spain, May 8-11, 2002 edited by F. Rodriguez-Reinoso, B. McEnaney, J. Rouquerol and K. Unger Science and Technology in Catalysis 2002 Proceedings of the Fourth Tokyo Conference on Advanced Catalytic Science and Technology, Tokyo, July 14-19, 2002 edited by M. Anpo, M. Onaka and H. Yamashita Nanotechnology in Mesostructured Materials Proceedings of the 3rd International Mesostructured Materials Symposium, Jeju, Korea, July 8-11, 2002 edited by Sang-Eon Park, Ryong Ryoo, Wha-Seung Ahn, Chul Wee Lee and Jong-San Chang Natural Gas Conversion VII Proceedings of the 7th Natural Gas Conversion Symposium, Dalian, China, June 6-10, 2004 edited by X. Bao and Y. Xu Mesoporous Crystals and Related Nano-Structured Materials Proceedings of the Meeting on Mesoporous Crystals and Related Nano-Structured Materials, Stockholm, Sweden, 1-5 June, 2004 edited by O. Terasaki Fluid Catalytic Cracking VI: Preparation and Characterization of Catalysts Proceedings of the 6th International Symposium on Advances in Fluid Cracking Catalysts (FCCs), New York, September 7 - 1 1 , 2003 edited by M. Occelli

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Volume 151

Coal and Coal-Related Compounds Structures, Reactivity and Catalytic Reactions Reactions edited by T. Kabe, A. Ishihara, E.W. Qian, Kabe I.P. Sutrisna and Y. Kabe Petroleum Biotechnology Biotechnology Developments and Perspectives Perspectives edited by R. Vazquez-Duhalt and R. Quintero-Ramirez Quintero-Ramirez

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Fisher-Tropsch technology edited by A.P. Steynberg and M.E. Dry

Volume 153

Carbon Dioxide Utilization for Global Sustainability Sustainability Proceedings Proceedings of the 7th International Conference on Carbon Dioxide 12-16, 2003 Seoul, Korea Utilization (ICCDU VII), October 12–16, K.-W. Lee edited by S.-E. Park, J.-S. Chang and K.-W.

Volume 154

Recent Advances in the Science and Technology of Zeolites and Related Materials Proceedings Proceedings of the 14th International Zeolite Conference, 25-30th April 2004 Cape Town, South Africa, 25–30th edited by E. van Steen, L.H. Callanan and M. Claeys

Volume 155

Oxide Based Materials Materials New Sources, Novel Phases, New Applications edited by A. Gamba, C. Colella and S. Coluccia

Volume 156

Nanoporous Materials IV edited by A. Sayari and M. Jaroniec

Volume 157

Zeolites and Ordered Mesoporous Materials Materials Progress and and Prospects Prospects Progress edited by J. Cejka and H. van Bekkum

Volume 158

Molecular Sieves: From Basic Research to Industrial Applications rd rd International Zeolite Symposium (3rd FEZA), Proceedings Proceedings of the 3rd Prague, Czech Republic, August 23-26, 2005 Prague, Nachtigall edited by J. Cejka, N. Zilková and P. Nachtigall

Volume 159

Engineering New Developments and Application in Chemical Reaction Engineering Proceedings Proceedings of the 4th Asia-Pacific Chemical Reaction Engineering Engineering (APCRE'05), Syeongju, Korea, June 12-15, 12-15, 2005 Symposium (APCRE’05), edited by H.-K. Rhee, I.-S. Nam and J.M. Park

Volume 160

Characterization of Porous Solids VII Proceedings Proceedings of the 7th International Symposium on the Characterization Characterization Porous Solids (COPS-VII), Aix-en-Provence, France, France, May 26-28, 2005 of Porous Rouqerol edited by Ph.L. Llewellyn, F. Rodríquez-Reinoso, J. Rouqerol and N. Seaton

Volume 161

Progress in Olefin Polymerization Catalysts and Polyolefin Materials Proceedings Proceedings of the First Asian Polyolefin Polyolefin Workshop, Nara, Japan, December 7-9, 2005 edited by T. Shiono, K. K. Nomura and M. Terano

Volume 162

Scientific Bases for the Preparation of Heterogeneous Catalysts Proceedings of the 9th International Symposium, Louvain-la-Neuve, Belgium, Proceedings September 10-14, 2006 edited by E.M. Gaigneaux, M. Devillers, D.E. De Vos, S. Hermans, P.A. Jacobs, J.A. Martens and P. Ruiz

Volume 163

Fischer-Tropsch Synthesis, Catalysts and Catalysis edited by B.H. Davis and M.L. Occelli

Volume 164

Biocatalysis in Oil Refining edited by M.M. Ramirez-Corredores Ramirez-Corredores and A.P. Borole