Synthesis of High-Silica Aluminosilicate Zeolites (Studies in Surface Science and Catalysis)

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Studies in Surface Science and Catalysis 33 SYNTHESIS OF HIGH-SILICA ALUMINOSILICATE ZEOLITES

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Studies in Surface Science and Catalysis Advisory Editors: B. Delman and J.T. Yates

Vol. 33

SYNTHESIS OF HIGH-SILICA ALUMINOSILICATE ZEOLITES Peter A. Jacobs and Johan A. Martens Leboretorium voor Oppervlektecnemie, Katholieke Universiteit Leuven, B-3030 Leuven, Belgium

with technical assistance from M. Geelen, L. l.eplat. J. Pierre, M.J. Struyven and M. Tielen

ELSEVIER

Amsterdam - Oxford - New York - Tokyo 1987

ELSEVIER SCIENCE PUBLISHERS B.V. Sara Burgerhartstraat 25 P.O. Box 211, 1000 AE Amsterdam, The Netherlands Distributors for the United States and Canada:

ELSEVIER SCIENCE PUBLISHING COMPANY INC. 52, Vanderbilt Avenue New York, NY 10017, U.S.A.

ISBN 0-444-42814-3 (Vol. 33) ISBN 0-444-41801-6 (Series)

© Elsevier Science Publishers B.V., 1987 All rights reserved. No part of this publication rnav 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, Elsevier Science Publishers B.V.j Science & Technology Division, P.O. Box 330, 1000 AH Amsterdam, The Netherlands. Special regulations for readers in the USA - This publication has been registered with the Copyright Clearance Center Inc. (Ccq, Salem, Massachusetts. Information can be obtained from the CCC about conditions under which photocopies of parts of this publication may be made in the USA. All other copyright questions, including photocopying outside of the USA, should be referred to the copyright owner, Elsevier Science Publishers B.V., unless otherwise specified. Printed in The Netherlands

v CONTENTS

Studies in Surface Science and Catalysis (other volumes in the series)

x

Scope of the work

xv

Acknowledgements

XVI

PART I : SELECTED RECIPES FOR THE SYNTHESIS OF HIGH-SILICA ZEOLITES

* Introduction * General procedure used for the synthesis of high-silica zeolites * Specific recipes 1. Synthesis 2. Synthesis 3. Synthesis 4. Synthesis 5. Synthesis 6. Synthesis 7. Synthesis 8. Synthesis 9. Synthesis 10. Synthesis 11. Synthesis 12. Synthesis 13. Synthesis 14. Synthesis * General comments * References

PART II CHAPTER I

of of of of of of of of of of of of of of

ZSM-34 ferrieritejZSM-35-type materials ZSM-39 high-silica ZSM-6 with TMA high-silica mordenite ZSM-12 zeolite PHI zeolite BETA zeolite ZSM-25 ZSM-5 with TPA ZSM-ll ZSM-8 ZSM-48 ZSM-22

HIGH-SILICA ZEOLITES WITH SOLVED STRUCTURE-TYPE SYNTHESIS OF ZSM-5 ZEOLITES IN THE PRESENCE OF TETRAPROPYLAMMONIUM IONS

* Introduction

3 3 6 6 8 10 11 12 13 15 16 17 17 20 21 22 24 25 44

45

47 47

VI

* The chemistry of aqueous tetrapropylammonium silicate solutions

* The Argauer-Landolt invention * The isothermal metastable phase transformation * The dominant factors influencing the crystallization of the MFI

*

* * * * *

* *

structure 1. The Si0 2A1 203 ratio of the gel 2. The TPA/Si0 2 ratio of the gel 3. The degree of dilution or the H20/Si0 2 ratio 4. The M/Si0 2 ratio 5. The OH/Si0 2 ratio 6. The nature of the silica source Morphology of ZSM-5 zeolites Mechanism of ZSM-5 synthesis The repartition of aluminium throughout the ZSM-5 crystal Synthesis of ZSM-5 from reactive mixtures prepared with unusual reactants Forming of ZSM-5 crystals Use of seeds The ZSM-5-silicalite dispute References

CHAPTER II

SYNTHESIS OF THE MFI TYPE OF STRUCTURE IN THE ABSENCE OF TPA

* Introduction

48 53 55 58 58 61 64 65 70 71 72 80 91 96 97 100 103 107

113 113

* Synthesis of ZSM-5 in the presence of quaternary ammonium cations different from TPA

* Synthesis of ZSM-5 in the presence of amines * Synthesis of ZSM-5 in the presence of alcohols * The use of various templates in ZSM-5 synthesis

* Synthesis of ZSM-5 in the absence of any organic compound * References

CHAPTER III

SYNTHESIS OF HIGH-SILICA ZEOLITES WITH THE MEL TYPE OF STRUCTURE

* Introduction * Quaternary salts used as templates in the synthesis of ZSM-ll

113 119 125 132 134 144

147 147 147

VII

* Parameters influencing the crystallization rate of ZSM-11 * Synthesis of the MEL structure type using diamines * X-ray invisible ZSM-11 zeolites * References

CHAPTER IV

POTENTIAL MEMBERS OF THE SILICA ZEOLITES

153 157 162 166

PENTASIL FAMILY OF HIGH-

* * * *

167

Introduction Crystallographic structure of ZSM-5 and ZSM-11 Intergrowths in the pentasil family of zeolites Experimental discrimination between pure ZSM-5, ZSM-11 zeolites and their intergrowths * Symmetry changes of ZSM-5 zeolites * Overview of some pentasil-type zeolites claimed in the literature 1. ZSM-8 2. ZETA-l 3. ZETA-3 4. NU-4 5. NU-5 6. Other pentasils * References

180 185 188 191 193 195 195 197 198 212

CHAPTER V : HIGH-SILICA ZEOLITES OF THE FERRIERITE FAMILY

217

* * * *

Structure Synthesis of FER-type materials using inorganic gels Synthesis of FER-type zeolites in the presence of organics Differences between various proprietary FER-type materials * References

217 217 220 226 231

CHAPTER VI : ZEOLITES WITH TON STRUCTURE TYPE

233

* * * *

233 243 248 249

Structure Synthesis of TON structure types Differences between the TON-type proprietary zeolites References

167 167 177

VIII

CHAPTER VII: HIGH-SILICA ZEOLITES WITH MTT FRAMEWORK TOPOLOGY

251

* MTT structure types * Synthesis of MTT and related zeolites * References

251 260 274

CHAPTER VIII

A FAMILY OF ZEOLITES WITH DISORDERED FERRIERITE-TYPE STRUCTURE

* Members of the family * Structure of zeolite ZSM-48

275

1. General conditions 2. Influences of silica: alumina ratio 3. Nature of templates * Morphology and sorption capacity * References

275 275 281 281 283 284 289 295

CHAPTER IX : HIGH-SILICA ZEOLITES WITH MTW FRAMEWORK TOPOLOGY

297

* Potential family members of MTW zeolites * Structure of ZSM-12 * Synthesis of MTW zeolites * Retention of organics in MTW zeolites * References

297 297 303 312 319

* Synthesis of ZSM-48 and related materials

CHAPTER X

* * * * * *

SYNTHESIS OF ZEOLITES THAT DO NOT BELONG TO THE HIGH-SILICA AND/OR SHAPE-SELECTIVE CLASS OF ZEOLITES

Synthesis of siliceous mordenite Materials with MTN structure type Siliceous Levynite zeolites Offretite-erionite zeolites and their intergrowths Faujasite-type siliceous zeolites References

321 321 330 333 342 343 346

IX

CHAPTER XI

PART III

* * * * *

* * * * *

*

* * *

* *

GENERAL CONSIDERATIONS

BRIEF DESCRIPTION OF POTENTIAL HIGH-SILICA ZEOLITES WITH UNKNOWN STRUCTURE

Introduction ZSM-43 CSZ-l ZSM-18 Zeolite PHI Zeolites BETA and NU-2 ZSM-25 EU-7 and EU-12 NU-23 NU-6(l) TMA-zeolites FU-l and NU-l ZSM-6 and ZSM-47 ZSM-50 ISI-6 PSH-3 References

Subject index

349

355

357 357 357 358 358 359 359 359 360 360 361 361 361 362 362 382 385

x STUDIES IN SURFACE SCIENCE AND CATALYSIS Advisory Editors: B. Delmon, Universite Catholique de Louvain, Louvain-Ia-Neuve, Belgium J.T. Yates, University of Pittsburgh, Pittsburgh, PA, U.S.A.

Volume

Volume

Volume

Volume

Volume

Volume

Volume

Volume Volume

Volume

Volume

Volume

Volume Volume

1 Preparation of Catalysts I. Scientific Bases for the Preparation of Heterogeneous Catalysts. Proceedings of the First International Symposium, Brussels, October 14-17,1975 edited by B. Delmon, P.A. Jacobs and G. Poncelet 2 The Control of the Reactivity of Solids. A Critical Survey of the Factors that Influence the Reactivity of Solids, with Special Emphasis on the Control of the Chemical Processes in Relation to Practical Applications by V.V. Boldyrev, M. Bulens and B. Delmon 3 Preparation of Catalysts II. Scientific Bases for the Preparation of Heterogeneous Catalysts. Proceedings of the Second International Symposium, Louvain-Ia-Neuve, September 4-7, 1978 edited by B. Delmon, P. Grange, P. Jacobs and G. Poncelet 4 Growth and Properties of Metal Clusters. Applications to Catalysis and the Photographic Process. Proceedings of the 32nd International Meeting of the Societe de Chimie Physique, Villeurbanne, September 24-28, 1979 edited by J. Bourdon 5 Catalysis by Zeolites. Proceedings of an International Symposium, Ecully (Lyon), September 9-11, 1980 edited by B. Imelik, C. Naccache, Y. Ben Taarit, J.C. Vedrine, G. Coudurier and H. Praliaud 6 Catalyst Deactivation. Proceedings of an International Symposium, Antwerp, October 13-15, 1980 edited by B. Delmon and G.F. Froment 7 New Horizons in Catalysis. Proceedings of the 7th International Congress on Catalysis, Tokyo, June 30-July 4, 1980. Parts A and B edited by T. Seiyama and K. Tanabe 8 Catalysis by Supported Complexes by Yu.1. Yermakov, B.N. Kuznetsov and V.A. Zakharov 9 Physics of Solid Surfaces. Proceedings of a Symposium, Bechyi'ie, September 29-0ctober 3, 1980 edited by M. Laznieka 10 Adsorption at the Gas-Solid and Liquid-Solid Interface. Proceedings of an International Symposium, Aix-en-Provence, September 21-23, 1981 edited by J. Rouquerol and K.S.W. Sing 11 Metal-Support and Metal-Additive Effects in Catalysis. Proceedings of an International Symposium, Ecully (Lyon), September 14-16, 1982 edited by B. Imelik, C. Naccache, G. Coudurier, H. Praliaud, P. Meriaudeau, P. Gallezot, G.A. Martin and J.C. Vedrine 12 Metal Microstructures in Zeolites. Preparation - Properties - Applications. Proceedings of a Workshop, Bremen, September 22-24, 1982 edited by P.A. Jacobs, N.1. Jaeger, P. Jiru and G. Schulz-Ekloff 13 Adsorption on Metal Surfaces. An Integrated Approach edited by J. Benard 14 Vibrations at Surfaces. Proceedings of the Third International Conference, Asilomar, CA, September 1-4, 1982 edited by C.R. Brundle and H. Morawitz

XI Volume 15 Heterogeneous Catalytic Reactions Involving Molecular Oxygen by G.!. Golodets Volume 16 Preparation of Catalysts III. Scientific Bases for the Preparation of Heterogeneous Catalysts. Proceedings of the Third International Symposium, Louvain-Ia-Neuve, September 6-9, 1982 edited by G. Poncelet, P. Grange and P.A. Jacobs Volume 17 Spillover of Adsorbed Species. Proceedings of an International Symposium, LyonVilleurbanne, September 12-16,1983 edited by G.M. Pajonk, S.J. Teichner and J.E. Germain Volume 18 Structure and Reactivity of Modified Zeolites. Proceedings of an Intenational Conference, Prague, July 9-13, 1984 edited by P.A. Jacobs. N.!. Jaeger, P. Jiru. V.B. Kazansky and G. Schulz-Ekloff Volume 19 Catalysis on the Energy Scene. Proceedings of the 9th Canadian Symposium on Catalysis, Quebec, P.Q., September 30-0ctober 3. 1984 edited by S. Kaliaguine and A. Mahay Volume 20 Catalysis by Acids and Bases. Proceedings of an International Symposium, Villeurbanne (Lyon), September 25-27, 1984 edited by B. lmelik, C. Naccache, G. Coudurier, Y. Ben Taarit and J.C. Vedrine Volume 21 Adsorption and Catalysis on Oxide Surfaces. Proceedings of a Symposium, Uxbridge, June 28-29. 1984 edited by M. Che and G.C. Bond Volume 22 Unsteady Processes in Catalytic Reactors by Yu.Sh. Matros Volume 23 Physics of Solid Surfaces 1 984 edited by J. Koukal Volume 24 Zeolites: Synthesis. Structure. Technology and Application. Proceedings of an International Symposium, Portoroz-Portorose. September 3-8, 1984 edited by B. Drza], S. Hocevar and S. Pejovnik Volume 25 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 Volume 26 Vibrations at Surfaces 1985. Proceedings of the Fourth International Conference, Bowness-on-Windermere, September 15-19, 1985 edited by D.A. King. N.V. Richardson and S. Holloway Volume 27 Catalytic Hydrogenation edited by L. Cerveny Volume 28 New Developments in Zeolite Science and Technology. Proceedings of the 7th International Zeolite Conference, Tokyo, August 17-22. 1986 edited by Y. Murakami. A. lijima and J.W. Ward Volume 29 Metal Clusters in Catalysis edited by B.C. Gates. L. Guczi and H. Knozinqer Volume 30 Catalysis and Automotive Pollution Control. Proceedings of the First International Symposium, Brussels, September 8-11, 1986 edited by A. Crucq and A. Frennet Volume 31 Preparation of Catalysts IV. Scientific Bases for the Preparation of Heterogeneous Catalysts. Proceedings of the Fourth International Symposium, Louvain-Ia-Neuve, September 1-4,1986 edited by B. Delmon. P. Grange. P.A. Jacobs and G. Poncelet Volume 32 Thin Metal Films and Gas Chemisorption edited by P. Wissmann Volume 33 Synthesis of High-silica Aluminosilicate Zeolites by P.A. Jacobs and J.A. Martens

XII

XIII

TO

JAN B. UYTTERHOEVEN Who we consider to be the founder of all this

It should be stressed that some of the data in this book, mainly the zeolite synthesis recipes, might be the subject of patent claims. It is not our intention to violate any patent rights and the recipes should not be used for any other than strictly scientific purposes without checking that this is not so. In every case proper reference is made to what we consider to be pertinent patents.

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xv SCOPE OF THE WORK This work certainly does not have the pretension to be a complement to the famous books by Breck (ref l ) and Barrer (reL2) and also it was not the authors' aim to write an exhaustive review of high-silica zeolites. First of all, the zeolites denoted as high-silica are not well defined, from either a scientific or a compositional point of view. Those using this term tacitly assume that high-silica zeolites with shape-selective properties are the subject of the discussion. The term shape-selectivity has to be understood in the context used by those working on catalysis in the petroleum or petrochemical area. Consequently, as in these areas one deals with relatively simple and small hydrocarbons, the zeolites concerned should contain ten-membered rings of T-atoms, belonging to tetrahedra sharing corner oxygen atoms. Zeolites with highly distorted twelve-membered rings, exerting the same sieve effects, are also considered to belong to this class of zeolites. High-silica zeolites, in the authors' opinion, should be susceptible to synthesis over a wide compositional range. Those included generally can be synthesized with an Si02/A1 203 ratio varying over at least one order of magnitude and consequently producing materials for which the composition varies over the same range. The subject has been narrowed still further, as only aluminosilicate zeolites are described. The potential substitution of half of Mendeleev's table for aluminium in these structures is still a matter of debate and it is considered that an attempt to rationalize the knowledge in this area would be premature. As a consequence of this narrowed scope, materials have occasionally been included that strictly are not zeolites, namely the so-called silica polymorphs with structures identical with those of many high-silica zeolites. The preparation methods covered are also confined to direct synthesis methods. The preparation of high-silica zeol ites by dealumination methods is not considered. Faced with the problem of keeping track of many new zeolites, or claimed as such in the patent literature, with the help of many students and technicians a number of standard recipes have been established in the "Laboratorium voor Oppervlaktechemie", under guidance of the authors. We considered it useful to offer this knowledge to the scientific comnunt ty. Therefore, part of this book contains proven recipes for the synthesis of certain high-silica zeol~tes (and sometimes others) and data on their identification and characterization. i

XVI

Another objective was to review critically many of the claimed materials and, based on the available data, to classify them into groups or families of materials of the already

or

same structural

remains

to

be

type,

established.

whether this It

will

be

structure

is

known

evident

that

this

classification is based on the information available to the best knowledge of the authors

at the time of writing and may be subject to changes in some

ins tances when pertinent i nforma t i on on the mostl y propri eta ry materi a1sis released. Many data, mainly published in patents, have been discussed but as none of the authors is familiar with the Japanese, Chinese or Russian languages, it might well be that essential information has been overlooked. In

principle,

the

literature has

been

covered

up to

the end

of

1985.

Particularly relevant work which appeared in the first half of 1986 was added afterwards. As mostly newly claimed crystalline materials in this area of science are identified based on their X-ray diffraction patterns, the authors have defined a specific layout of these patterns, containing all necessary data for collecting them in a personal 1 ibrary useful for the identification of potentially new products synthesized by readers. 1. D.W. Breck, Zeolite Molecular Sieves, Wiley, 1974. 2. R.M. Barrer, Hydrothermal Chemistry of Zeolites, Academic Press, 1982. ACKNOWLEDGEMENTS The authors particularly appreciate the stimulating influence of Jan B. Uytterhoeven duri ng the past 20 years, and consequently they deci ded to dedicate this book to him. The senior author also acknowledges continuous sponsoring of his research activities by the National Fund for Scientific Research (Belgium) and more recently to K.U. Leuven to allow him to teach in this area of science. The junior author is also grateful to the National Fund for Scientific Research (Belgium) for several research fellowships.

PART I: SELECTED RECIPES FOR THE SYNTHESIS OF HIGH-SILICA ZEOLITES

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3

INTRODUCT ION Zeol ites in general and high-sil ica zeol ites more in particular are often crystall ized by nucleation from inhomogeneous supersaturated mother liquids. Therefore, the origin, purity and exact chemical composition of the reactants used for their synthesis may sometimes be critical. The commercial origins and grades of the reagents used in this chapter in the recipes for the synthesis of high-silica zeolites are given in Table 1.1. They are not necessarily the most advantageous reactants for the synthesis of bulk amounts of zeolites but their prices are such that the average budget of a university laboratory will permit the synthesis of kilogram amounts of these materials. The recipes advanced here are highly reproducible. They were checked independently by two laboratory technicians. Each synthesis was carried out in home-made stainless-steel autoclaves, which could be equipped with a PTFE coating or a glass 1iner. A drawing representing the PTFE-l ined version of these autoclaves is shown in Fig. 1.1. Twenty of such autocl aves coul d be mounted together ina furnace and heated while they are being rotated at 50 rpm (rotations per minute). In each autoclave from 10 to 15 g of zeolite on a dry calcined basis can generally be recovered.

GENERAL PROCEDURE USED FOR THE SYNTHESIS OF HIGH-SILICA ZEOLITES For the synthesis of high-silica zeolites, in most instances two solutions are prepared. Solution A contains the organosilicate and solution B is prepared by dissolving successively in water the inorganic base(s) and the aluminium salt. Solution A is prepared by adding the organic molecule (or its solution) to the silicate solution for all silica sources except Aerosil. In the latter instance, the silica powder is added with continuous stirring to an aqueous solution of the organic material. Solution B is added slowly to A with vigorous st i rri ng, and the pH iss ubsequent ly adj usted by dropwi se addition of a mineral acid. The gel thus obtained is then autoclaved; the autoclaves are mounted in the heated furnace and are continuously rotated at 50 rpm during synthesis. The synthesis efficiency is defined as the weight

4

65

~I

oCO) ,...

~-:050rpm

I"

40

~I

FIGURE 1.1. Technical drawing of the PTFE-lined version of autoclaves used for the synthesis of laboratory-scale amounts of high-silica zeolites. Dimensions in millimetres.

5

TABLE 1.1 Origin of reactants used in the recipes for the synthesis of high-sil ica zeolites

REACTANT

ORIGIN

GRADE

Aeros il-200 Silicic acid Water glass Ludox AS30 Ludox AS40 TEO-sil icate a

Degussa Riedel-De Haen Merck Du Pont de Nemours Du Pont de Nemours Merck

Sodium aluminate Al(N0 3)3· 9H20 A12(S04)3·18H20

Hopkin and Williams Merck Merck

Technical Pro analysi Purum

NaOH KOH

Merck Merck

Pro analysi Pro analysi

TMA-OH b TEA-OH c TMA-Br b TEA-Br c TPA-Br d Choline chloride Piperidine Pyrrol idine Ethylamine Propylami ne Octylamine Ethylenediamine 1,8-Diaminooctane 1,6-Diaminohexane

Fluka Fluka Fluka Fluka Fluka Aldrich Aldrich Merck Fluka Aldrich Fluka Merck Aldrich Fluka

25 %aqueous; technical 40 %aqueous; technical Purum Purum Purum 99 % 98 % Technical 70 %aqueous 98 % Purum Technical 98 % Purum

Technical Technical Technical

a, tetraethyl orthosilicate; b, tetramethylammonium; c, tetraethylammonium; d, tetrapropylammonium.

6

percentage of Si0 2 + A1 203 that is recovered after the whole operation compared with the Si0 2 + A1 203 in the gel. This operation includes synthesis, several washings (to neutral pH), air drying at 325 K and air calcination at 823 K. In every instance, the recipes are optimized synthesis methods which to our knowledge give maximum efficiency. The zeolites thus obtained are phase pure and also are free from significant amounts of residual amorphous material. The phase purity was checked by comparing the peaks in the X-ray diffractograms (XRD) with those given in the 1iterature. Using scanning electron microphotographs, it was decided whether residual amorphous material was present.

SPECIFIC RECIPES 1. Synthesis of lSM-34

1.a. ~t~!~~~!~_9f_~~~:~~_~!!~_I~~:Q~_~~_9~9~~!~_~~~~ Solution A 42 ml TMA-OH (2.5 M) + 27.2 g silicic acid Solution B 118 g water + 5.5 g sodium hydroxide + 5.2 g sodium aluminate Mixing was carried out in an ice-bath and afterwards concentrated sulphuric acid was added dropwise until a pH of 11 was reached. Synthesis occurred at 353 K for 7 days with stirring. The gel had the following molar composition:

The efficiency of the synthesis method was about 80 %. The Si/A1Z ratio of the zeolite was 15. This method is original and has not been derived, as far as we are aware, from eXisting information. Individual elongated crystals about 1 ~m long dominate (Photograph 1.1), and the presence of a small number of 0.2-0.4 ~m crystals is indicative of secondary nucleation.

PHOTOGRAPH 1.1. Scanning electron micrograph (SEM) of ZSM-34 synthesized with T~IA

1.b. ?~~!~~~1~_~!_~?~:~~_~1!~_I~~_~~9_1~_e~~~~~~~_~!_~_~1:~9_~l~~l1:~~~~~~ Solution A 33.3 9 Ludox AS30 + 3.2 g TMA-OH (25 %, aqueous) Solution 8: 2.5 9 KOH + 7.4 9 NaOH + 3.9 NaA10 2 + 10 9 water

Bo tf solutions, pre-cooled in ice, were mixed together at the same temperature and autoclaved at 463 K for 2 h with continuous agitation. The gel had the following molar composition:

The efficiency of the method was 70 %. The Si/A12 ratio of the zeolite was 12.

8

I.e. ~~~!~~~~~_~!_~~~:~~_~~!~_~~~l~~~_~~_~~~~~~~_~~l~~~l~ {~~~~~~_!~~~_~~!~_!!_~~~~~l~_!Q2

Solution A: 45 g Aerosil in 155 g water Solution B : 17 g NaA10 2 + 6 g NaOH + 5.6 g KOH + 110 g H20 This solution was stirred until it became transparent and then 50 g of choline chloride were added. Solution A was mixed with B; the final gel was then autoclaved at 423 K for 8 days with continuous agitation. The gel had the following molar composition:

in which R represents the choline molecule. The efficiency was 80 % and the ZSM-34 showed an Si/A1 2 ratio of 10. The XRD of ZSM-34 looks like the one of offretite materials and possibly the material belongs to the offretite-erionite family. 2. Synthesis of ferrierite/ZSM-35-type materials Based on their X-ray diffractograms, ZSM-35, -38 and -21 and ferrierite are not easily distinguishable and therefore belong possibly to the same family of zeolites. The distinction made in this paragraph between ferrierite and ZSM-35 is therefore only formal. The crystalline solid is denoted according to the notation used in the initial publication from which the present materials are derived. 2.a. ~~~!~~~~~_~!_~~~:~~_~~_!~~_~~~~~~~~_~!_~!~~l~~~~~~~~~~ {~~~~~~~_!~~~_~~!~_~l_~~~~pl~_§2

Solution A 46.47 g Ludox AS30 + 18.3 g ethylenediamine (C 2DN) Solution B : 129 g H20 + 0.7 g NaOH + 3.3 g NaA10 2 Solution A was mixed with B. Crystallization: 10 days at 450 K with agitation. In this way, a gel with the following molar composition

was transformed into crystalline ZSM-35, with an efficiency of 60 % and giving an Si/A1 2 ratio of 13. The crystals were elongated with a length of about 1 urn (Photograph 1.2).

9

PHOTOGRAPH 1.2. SEM of lSM-35.

2.b. ~~~!~~~!~_~!_~~~:~~_!~_!~~_~~~~~~~~_~!_~~~~~!!~!~~ i~~~!~~~_!~~~_~~!:_~1_~~~~~!~_!~2

Solution A 48.39 9 Ludox AS30 + 8.25 9 pyrrolidine Solution B : 0.5 9 NaOH + 3.3 9 NaA10 2 + 136 9 H20 Solution A was mixed with B. Crystallization occurred at 450 K during a period of 15 days. The molar composition of the gel was

in which R represents pyrrolidine. The efficiency of this synthesis was 65 %, and the zeolite had an Si/A12 ratio of 15.

10

Z.c. ?t~!b~~1~_2!_!~~~1~~1!~_~1!b_!2~_~!_~2~!~~!_~~2~9_E2E~~192~~ i~9~E!~9_!~2~_~~!~_~1_~~~~E!~_~2

Solution A Zl.l g water glass + 3.1 g piperidine Solution B : ZZ.l g HZO + 1.3 g A1Z(S04)3.18HZO Synthesis conditions : 473 K for 1 day with agitation. The molar composition of the gel was

in which R represents piperidine. The efficiency of the synthesis was 60 % and the Si/A1 Z ratio of the zeol ite was 40. In contrast to the statement in the original patent, it was found that using our raw materials, a more crystalline material was obtained at a crystallization temperature that was 50 K higher. Z.d. ~t~!b~~!~_2!_!~~~!~~!!~_~!!b_~!~~9~~9_~b~~!~~!_~2~e2~!!!2~_~~!~9 e!E~~!9!~~_i~9~e!~9_!~2~_~~!~_~1_~~~~E!~_~2

Solution A 18.6 g Ludox AS30 + 3.1 g piperidine Solution B : ZZ g HZO + Z.Z g NaOH + Z.7 g A1Z(S04)3.18HZO Synthesis conditions : 473 K for 1 day with agitation. The molar composition of the gel was

in which R represents piperidine. The efficiency was 65 % and the Si/A1 Z ratio of the zeol ite was ZO. The modification consisted in the use of Ludox as the silica source and in an increase of the synthesis temperature by 50 K.

3. Synthesis of lSM-39 3.a. ~t~!b~~!~_2!_~~~:~~_~2!b_e!e~~!92~~_~~_!b~_2~9~~!~_~~!~~!~! This recipe was derived from a method which in the original patent (ref. 3) produced ferrierite. The synthesis temperature was increased by 50 K and the pH of the gel was lower, as sulphuric acid was added. Based on example 8, the following recipe is then obtained:

11

Solution A Solution B

21.1 g water glass + 3.1 g piperidine 1.3 g A12(S04)3.18H20 in 20 g water

Solution B was added to A with stirring and sulphuric acid was added dropwise until the pH reached a value of approximately 10.5. Synthesis was carried out at 473 K for 3 days. The molar composition of the gel was

in which R represents piperidine. The efficiency of the synthesis was 100 % and the Si/A1 2 ratio of the zeolite was 50. 3.b. ?~~!~~~~~_~!_~!:!~~~_~?~:~~_~~!~_~!~~!~~~~~_~~9_I~~ In contrast to the procedure followed in the original patent (ref. 4), TMA-Cl was replaced with TMA-Br and propyl amine with ethylamine. When this was done, very pure ZSM-39 was obtained instead of ZSM-48, as claimed in the patent. Solution A 18.7 g water glass + 39.3 g water + 1.7 g concentrated sulphuric acid Solution A* 4.2 g TMA-Br in 8.7 g ethyl amine (C 2N) (70 % aqueous) + 36.7 g water Solution A* was slowly and under stirring added to A. The gel with the following molar composition: ((TMA)2 0)13.7 (C 2N)135.4 (Na 20)38.3 (Si0 2)82.4 (H 20)5,091 was transformed into Al-free ZSM-39 after a synthesis period of 2 days at 433 K. The efficiency of this synthesis was 100 %, which indicates that all the sil ica present in the gel was transformed completely into crystalline silica.

4. Synthesis of high-silica ZSM-6 with TMA Example 1 of ref. 5 has been modified by replacing TMA-Cl with TMA-Br, increasing the synthesis temperature by 30 K and decreasing the synthesis time from 6 to 3 days. In this way ZSM-6 with a variable Si/A1 2 ratio could be obtained. It has been checked that the method works within the range 200 < Si/A1 2 < 1000.

12

Solution A Solution B

40.9 g Ludox AS40 + 8.6 g TMA-Br in 14.6 g water 0.3 g NaA10 2 in 15.5 g water + 3.1 g NaOH

After addition of solution A to B in the usual way, the following gel was obtained

The final zeol ite lSM-6 had an crystallization efficiency was 75 %.

Si/A1

2

ratio

of

250

and the

5. Synthesis of high-silica mordenite Natural or synthetic mordenite, synthesized in the absence of organics, always has a very typical Si/A1 2 ratio, between 9 and 10 (ref. 6). When organics are added during the synthesis an enhanced Si/A1 2 ratio can be obtained. 5.a. ~!9b:~!!!~~_~9~~~~!!~_~!!b_E!E~~!~!~~ When in example 9 of ref. 3, Ludox is used as the silica source and the synthesis temperature is increased by 50 K, mordenite instead of ferrierite is crystallized. When the same amounts were used as in Section 2.d., the crystalline mordenite had an Si/A1 2 ratio of 30.

In this recipe TEA-Br was used instead of a TEA-OH solution and water glass was the silica source. In the original work (ref. 7, example 4) lSM-12 was obtained. Solution A Solution B

22.6 g water glass + 5.1 g TEA-Br 0.4 g NaA10 2 in 4 g water

The resulting gel with a pH of 12 was transferred into a glass-l ined autoclave and kept at 453 K for 7 days. The autoclave was not agitated in this synthesis. In this way the following gel :

13

was converted into a crystalline high-silica mordenite. The efficiency of the operation was only 60 %.

6. Synthesis of ZSM-12 6.a. ~?~:!~_~~!~s_I~~ Example 4 of ref. 7 was the basis of this recipe. Only the nature of the product used as the silica source was modified. Solution A Solution B

22.6 g water glass + 7 g TEA-OH (40 %) 0.3 g NaA10 2 in 5 g water

The composition of the gel was :

ZSM-12 was obtained after heating the gel at 453 K for 7 days without agitation in a glass lined autoclave. 6.b. ~?~:!~_~~!~S_I~~_~~9_~~!~!~~!~~ Solution A

18.67 g of water glass + 30 g water + 1.7 concentrated sulphuric acid Solution A* 7.48 g of TMA-OH (25 %) + 33.5 g water + 18.10 g octylamine (C 8N) Solution B : 1.24 g Al(N03)3.9H20 in 10 g water

g of

Solutions A* and B were added to A under stirring. The final gel

was autoclaved during 5 days at 433 K. The morphology of this sample is very peculiar, as shown in Photograph 1.3. Large cylindrical crystals (5 x 1 IJm) were present in addition to very small ones (0.1-0.4 IJm). This is definitely an example of secondary nucleation. Microprobe analysis in a region where these small crystallites were highly agglomerated allowed the calculation of an Si/A1 2 ratio of about 400, while the large crystals covered with smaller ones had Si/A1 2 ratios of approximately 25. The overall Si/A12 ratio of the sample was 50.

14

PHOTOGRAPH 1.3. SEM of ZSM-12. Hence it seems that first large Al-richer ZSM-12 crystals are formed (5 x 1 ~m) and at a given moment when the mother liquid has become rich in silica the same structure starts to nucleate again and grows to smaller crystals with a higher Si content. In this example a procedure for the synthesis of ISM-48 was modified (ref. 4, example 1) as follows: (i) aluminium was added to the gel, (ii) TMA-Cl was replaced with TMA-OH, (iii) octylamine was used instead of propylamine and (iv) the synthesis time was extended from 2 to 5 days.

15

7. Synthesis of zeolite PHI In an attempt to synthesize zeolite ZSM-ZO, which is of the faujasite family (ref. 8), zeolite PHI (ref. 9) was systematically obtained. Solution A:

Solution B

obtained when Z5.6 g of TEO-silicate was slowly hydrolysed in 4Z.4 g TEA-OH (40 %) and the ethanol formed was distilled off contained 1.3 g NaA10 Z' which was added to 36 g water with 0.13 g NaOH

Solution B was then added to A with stirring. This mixture was first aged at 277 K for Z days and finally autoclaved at 373 K for 14 days without agitation. The following gel:

was transformed in this way into a highly crystalline zeolite PHI with very particular morphology, as shown in Photograph 1.4. It should be noted that the notation "PHI" here does not represent phill ipsite zeol ite, as might be assumed when abbreviations that have been suggested for the notation of zeol ite structure types are used (ref. 10).

PHOTOGRAPH 1.4. SEM picture of zeolite PHI

16

8. Synthesis of zeolite BETA Another zeolite that is often crys ta 11 i zed when TEA is present as an organic material (ref. 11) is BETA. It also often crystallizes when the procedures for ZSM-20 synthesis (ref. 8) are only slightly modified. A first recipe is derived from original patent (ref. 11) without any major modification Solution A Solution B

72.7 g Ludox AS40 3.9 g NaA10 2 in 30 g water + 37 ml TEA-OH (40 %)

The gel obtained after addition of solution A to B

was aged in an autoclave for 10 days at 423 K. After this period zeolite BETA with an Si/A1 2 ratio of 31 was obtained, with the morphology shown in Photograph 1.5.

PHOTOGRAPH 1.5. SEM of zeolite BETA

17

The recipe for ZSM-ZO (example 1 of ref. 8) was modified

in the

fo11 owi ng way : (i) tetraethyl orthos il i cate was used instead of the methyl form, (ii) the synthesis time was limited to Z instead of 4 weeks and (iii) the synthesis temperature was increased by ZO K. To a solution of 1.3 9 NaA10 Z + 4Z.6 9 TEA-OH (40 %) + 0.36 9 NaOH + 8 9 water, TEO-silicate (38.5 g) was added dropwise. The ethanol formed during the TEA-silicate hydrolysis was distilled off and the gel with following composition

was then autoclaved at 393 K for Z weeks, without stirring. Crystalline zeolite BETA was obtained with an Si/A1 Z ratio of 31.

9. Synthesis of zeolite ZSM-Z5 A zeolite ZSM-Z5 with a morphology s imil ar to that of zeol i te BETA (Photograph 1.5) was obtained using a procedure described earlier in the patent literature (ref. 1Z). However, Aerosil was used instead of colloidal silica. In this way a solution A was prepared by dissolving 33 9 of TEA-Br in 39 9 of water; 6.84 9 of Aerosil mixed with ZO,3 9 HZO were then stirred into this solution. Solution B contained 3 9 of NaA10 Z' 0.9 9 of NaOH and 15 9 of water. The gel obtained after mixing both solutions :

was agitated for 5 days in an autoclave at 408 K.

10. Synthesis of ZSM-5 with TPA Photograph 1.6 shows three crystal morphologies of ZSM-5, which were obtained with recipes that will be described in detail.

18

PHOTOGRAPH 1.6. SEM respective recipes.

crystals

of

ZSM-5

prepared

according

to

the

19

10.a In this method a relatively diluted gel is used.

The method is derived

from the work of von Ballmoos (ref. 13). It gives large elongated hexagonal prisms as crystal "habitus" and, as Photograph 1.6 shows, they are single and not twinned. To obtain this material the following solutions were mixed: Solution A Solution B

15 g Aerosil in 624 g water with 166 g TPA-Br and 458 g glycerol 3.5 g of 25 % ammonia solution (25 %) + 3.99 g NaOH + 2.6 g Al(N03)3.9H20 in 30 g water

From the resulting gel with the following molar composition

ZSM-5 was crystallized after 3 days at 423 K. This zeolite had an Si/A1 2 ratio of 70.

10.b Using a more concentrated gel, slightly smaller single crystals of ZSM-5 with distinct morphology were obtained under the same synthesis conditions. to 11.1 g Aerosil in 1.6 g NaOH and 32 g water, 2.5 g TPA-Br in 78 g water were added Solution B : 0.6 g NaA10 2 in 10'g water

Solution A

The pH of the final gel was adjusted to 11 with sulphuric acid. The final gel

was then crystallized in the same way as in the previous method.

10.c When water glass is used as the silica source, ZSM-5 with a totally different morphology is obtained (agglomerates of smaller elementary crysta11 ites) .

20

In addition to a distinct morphology, the three preparations after calcination at 823 K, NH; ion exchange and subsequent heat treatment at 673 K also show a distinct infrared absorption spectrum in the hydroxyl stretching zone (Fig. 1.2).

w z

(J

« m

a:::

0

['

(/)

m

IL 1

«

3750

FIGURE 1.2. Hydroxyl stretching spectrum of ISM-5 samples prepared according to methods lOa, lOb and 10c after removal of residual organics and Na+ ions.

11. Synthesis of ISM-II Pure ISM-II samples, which means that all the XRO lines of these samples could be indexed ina tetragonal symmetry, caul d only be synthes i zed using either tetrabutylphosphonium ions (TBP) or in the presence of 1,8-diaminooctane. As TBP became difficult to obtain commercially, only the recipe using 1,S-diaminooctane (CSON) will be presented. Solution A Solution B

40 ml water glass + 1.3 9 CSON in 3S g water 0.7 g NaA10 2 in 40 9 water

21

The pH of the final gel was adjusted to 11 with sulphuric acid. The gel obtained

was autoclaved at 423 K for 3 days. A pure ZSM-ll with the morphology shown in Photograph 1.7 was then obtained.

PHOTOGRAPH 1.7. SEM picture of pure ZSM-11

12. Synthesis of ZSM-8 12.a. ~t~!~~~!~_~!_~~~:§_!~_!~~_E~~~~~~~_~!_!~~_l~!!~~_~~!:_

!~2

Solution A : 50 g Ludox AS30 + 10 g TEA-OH (40 %) Solution B : 1.~ g NaA10 2 + 0.1 g NaOH + 30 g water Solution A was added to B. The synthesis of the resulting gel was carried out in a glass-lined autoclave for 7 days at 453 K. The gel composition was

22

12.b. ~t~!~~~~~_2f_~~~:~_~~_P~~~~~~~_2f_Pt~~2l~9~~~ When the procedure of ref. 15, exampl e 9, is followed and the crystallization time is extended from 5 to 10 days, lSM-8 is obtained instead of lSM-23. Solution A : 98.3 9 Ludox AS40 + 14.6 9 pyrrolidine Solution B : 0.6 9 NaA10 2 in 56.8 9 water and 0.2 9 NaOH Solution A was mixed with B. The following gel

in which R represents pyrrol idine, was autoclaved at 453 K and gave lSM-8 with an Si/A1 2 ratio of 300.

13. Synthesis of lSM-48 When example 1 of a patent (ref. 4) in which the synthesis of lSM-48 is described, is modified as follows: (i) TMA-Cl is replaced with TMA-Br, (ii) propylamine is replaced with octy1amine and (iii) the synthesis time is reduced from 2 days to 1 day, then a recipe is obtained that allows the synthesis of lSM-48 in the following compositional range: 100 < Si/A1 2 < 00.

Solution A:

to 18.7 9 water glass and 29.3 9 water was first added 1.7 g sulphuric acid. After vigorous stirring were added 4.2 9 TMA-Br + 41 9 water + 18.1 g octylamine (C 8N) Solution B: 0.6 9 Al(N03)3.9H20 in 10 9 water The gel composition was :

The gel was agitated in an autoclave for 1 day at 433 K. The crystals had the shape of bundles of needles, their size being dependent on the amount of Al present in the gel. Photograph 1.8 clearly illustrates this morphology. It also shows that from a gel that contains only aluminium as impurity in the other reactants, needles are obtained that are up to five times longer than those crystall ized from the silica-alumina gel described in the present recipe.

23

PHOTOGRAPH 1.8. SEM pictures of lSM-48 crystals: (a) with no Al added to the gel and (b) with an Si/A1 2 ratio of the gel of 100.

24

14. Synthesis of ZSM-22 Zeolite ZSM-22 was obtained according to a recipe described in the patent 1iterature (method A of ref. 16). In this procedure the organic molecule is not added to the silicate solution but to solution B. Solution A Solution B

72 g Ludox AS40

124 g H 20 3.5 g A12(S04)3.18 H20 + 1,6-diaminohexane (C + 177 6DN) +

g

+

16.7

g

Solution B was added to A under vigorous stirring. The gel had the following molar composition

The gel was filled in autoclaves and rotated at 433 K. Pure zeol ite ZSM-22 crystallized in the shape of agglomerates of 10-20 ~m in diameter, consisting of very small needle-like crystallites of about 1-2 ~m in length and 0.1-0.5 ~m in diameter (Photograph 1.9).

PHOTOGRAPH 1.9. SEM picture of pure ZSM-22.

25

GENERAL COMMENTS In all attempts to synthesize high-sil ica zeol ites, it turned out that stirring during synthesis was an important parameter insofar that the overall yield of crystalline material in most instances was much higher (up to 50 %) than when the agitation of the autoclaves was omitted. The recipes were optimized in such a way that the yield of crystalline material from the gel was always higher than 75 % (based on Si0 2 + A1 203), except for the ferri erite family of zeolites, for wh i ch such a hi gh yi e1d could never be obtained. The different zeolites were identified using their XRD patterns. For several of these materials no other means of identification is described in the literature. The XRD lines (relative intensity Ill o against the 28 obtained with Cu Ka) are shown graphically in addition to a table giving the relative intensities and their corresponding d-values (Fig. 1.3, 1 to 14). The infrared spectra of the lattice vibrations are shown in Fig. 1.4 as a supplementary means of identification. As was shown recently, mid-infrared spectra of zeol ites indeed permit the rapid differentiation of lSM-type zeol ites (ref. 17). The detailed frequencies of these bands together with a qualitative indication of their relative intensities and a tentative assignment are given in Table 1.2. The spectra were recorded on a PE-580 B dispersive instrument using the KBr pellet technique. The recipes described here can be reproduced easily, provided that the recommended amounts of materials are used. It is our experience that when the amounts are scaled up, no major problems are encountered and the claimed crystalline materials are obtained. When the recipe is used for much smaller amounts of gel than indicated above, the chances of effecting a successful synthesis decrease rapidly and the reproducibility under those conditions is poorer.

"" m

TABLE 1.2 Frequencies (em-I) and tentative band assignment a of the zeolite frameworks Zeo1i te type

Asym. stretching External Internal

ZSM-34

(1175 sh)

ZSM-35

1225 s

Ferrierite ZSM-39 ZSM-6/ZSM-47 b

1220 sh

Morden~te

ZSM PHI 612 BETA b

1200 1225 1220 1220

sh sh s sh

1220 s

1075 vs 930 sh 1085 vs

Sym. stretching External Internal 800 m 810 750 780 780 775 800 795 850

m m m w

1060 1090 1090 1050 1080 1125

vs vs vs vs vs vs vs sh vs sh vs

850 sh 800 m 780 s

ZSM-5

1220 s

ZSM-11

1220 s

1085 vs

795 m 755 sh

ZSM-8 b ZSM-48 bb ZSM-22

1200 sh 1220 sh 1220 sh

1100 1110 1120 1090

790 m 790 m 810 m 785 m

a, Using the information in refs. 17-20. b, Published for the first time.

vs vs sh vs

690 w

5

m m m

1080 930 1075 900 1085

ZSM-25 b

650 m

795 m 755 sh

now 730 s

730 s

-

640 m

Double ring 580 w 580 m 545 w 565 w 530 sh,w 580,560 w 575 s 620 m 560 sh 575 m 525 m 630 s 545 570 620 545 570 620 540 555 555

s sh sh s sh sh m s m

T-O bending 460 450 460 445 455 460 450 450 460 525

s sh vs sh vs s vs 5 5 5

475 5 430 sh 430 5 450

5

450 s 450 5 475 s 460 5

FIGURE 1.3.1. ZSM-34 (U.S.P. 4.086.186. Table 2)

5L

II-

2

e

... I-

... I-

... I-

... II-

III-

d [0. 1nml

I1Io

11.55 7.59 6.62 6.32 5.73 5.33 4.97 4.57 4.33 4.16 3.81 3.76 3.59 3.30 3.16 2.92 2.85 2.68 2.51 2.49

100.00 25.00 52.00 10.00 31.00 4.00 10.00 64.00 4.00 7.00 55.00 86.00 86.00 34.00 40.00 9.00 84.00 16.00 4.00 21.00

l-

II-

5.0

•

, 9.0

•

.I. I , 1,1 I.

13.0

17.0

21.0

,

I,

25.0

, 29.0

I.

, 33.0

, I

I

37.0

I

41.0

I

I

45.0

I

49.0

53.0

"" --J

FIGURE I.3.2. ZSM-35 (U.S.P.4.016.245)

d [0 • 1nm]

9.52 7.06 6.92 6.60 5.76 4.95 3.9B 3.93 3.B4 3.77 3.73 3.66 3.53 3.46 3.39 3.31 3.13 3.04 1.99 1.92

s~ I-

~ ~

f-

III

5.0

9.0

13.0

,I I , I

17.0

I

21.0

,I

II 25.0

29.0

I

I

I

33.0

37.0

41.0

I

,I ,I 45.0

IlIa 100.00 19.69 19.69 21.26 9.45 7.B7 49.61 30.71 15.75 40.16 9.45 25.98 7B.74 62.99 22.05 1B.90 14.17 6.30 6.30 7.09

I

49.0

53.0

tv

(y:)

FIGURE I.3.3. ZSM-5CU.S.P. 3.702.886. Table 1)

r.

.. .. .. >.. >..

2

e

f-

>-

. .

d [0 . 1nml I1Io 11.10 60.00 10.00 60.00 7.40 10.00 7.10 10.00 6.30 10.00 6.04 5.00 5.97 5.00 5.56 10.00 5.01 10.00 4.60 10.00 4.25 10.00 3.85 100.00 3.71 60.00 3.04 10.00 2.99 10.00 2.94 10.00

>flIlI-

5.0

9.0

I"I

/11, /

13.0

/ 17.0

.I l 21.0

, 25.0

I

,II / 29.0

I

33.0

37.0

41.0

45.0

49.0

53.0

"" ~

FIGURE 1.3.4. ZSM-11 (as-synthes1zed) (U.s.p.a 709. 979. eX.1)

SL.e

d [0. 1nm]

I1Io

11.19 10.07 6.73 6.03 5.61 4.62 4.37 4.00 3.86 3.73 3.68 3.49 3.35 3.07 3.00 2.50 2.01 1.97 1.93 1.88

27.00 23.00 3.00 5.00 5.00 4.00 9.00 4.00 100.00 39.00 5.00 6.00 5.00 6.00 10.00 4.00 21.00 4.00 5.00 7.00

~

I~

IIII~

I~ ~ I

5.0

I

9.0

• I. I

13.0

I

17.0

,I

I.

I

21.0

II

.1 25.0

I

I,

J 29.0

I

33.0

I

I

I

37.0

I

I

41.0

I

I

45.0

I

I, 49.0

53.0

w

o

FIGURE 1.3.5. FERRIERITE (ref.B)

s~

"" I-

II-

I-

I-

il-

d [0. 1nm)

IlIa

13.80 10.70 9.57 7.12 6.70 5.68 4.54 4.00 3.76 3.66 3.57 3.49 3.40 3.33 3.22 3.15 3.06 2.91 2.69 2.57

10.00 10.00 100.00 20.00 20.00 40.00 10.00 80.00 60.00 40.00 50.00 70.00 60.00 10.00 40.00 40.00 20.00 50.00 10.00 10.00

I-

"I I

5.0

9.0

, 13.0

I

17.0

I,

I 21.0

25.0

.I 29.0

33.0

l

I

37.0

I

I

41.0

45.0

49.0

I

53.0

cc ......

FIGURE 1. 3.6. ZSM-39 (as- synthesized) (U. S. P. 4. 287. 166. ex. 4)

i. 2

e

-

-

I

5.0

I

I

9.0

I

I

13.0

17.0

I

, 21.0

I

I

25.0

II

I, 29.0

33.0

I I. 37.0

I

41.0

II

•

45.0

d [0. 1nm) 11.15 6.84 5.83 5.58 4.83 4.43 3.95 3.72 3.42 3.27 3.23 3.06 2.95 2.52 2.37 2.28 1.95 1.86 1.81 1. 77

l I,

49.0

I/Io 5.00 23.00 93.00 69.00 47.00 36.00 48.00 100.00 42.00 84.00 10.00 12.00 8.00 9.00 10.00 17.00 4.00 10.00 6.00 5.00

I 53.0

W tv

FIGURE 1.3.7. ZSM-6 CU.S.P.4. 187.283. Table 1)

t.

.

2 9

i-

-

-

d [0. 1nml

I1Io

11.60 9.00 8.33 6.64 6.55 6.27 5.77 5.41 4.65 4.48 4.33 4.24 4.17 4.11 4.05 4.01 3.97 3.91 3.85 3.56

20.00 20.00 70.00 40.00 20.00 70.00 20.00 20.00 20.00 70.00 70.00 20.00 20.00 40.00 100.00 40.00 70.00 100.00 40.00 40.00

. I

5.0

I

9.0

I

13.0

I

I

17.0

I

21.0

25.0

I

29.0

I

I

33.0

I

I

37.0

I

I

41.0

I

45.0

I

49.0

53.0

cc cc

FIGURE 1. 3.8. ZSM-12 (as- synthes 1zed) (U. S. P. 3, 832, 449, ex. 5)

d [0 . 1nm]

IlIa

11.90 11.60 11.15 10.02 9.72 6.02 5.57 4.96 4.75 4.70 4.45 4.28 4.10 3.98 3.85 3.75 3.71 3.65 3.49 3.39

27.00 10.00 10.00 35.00 5.00 5.00 5.00 5.00 14.00 11.00 6.00 100.00 8.00 14.00 67.00 5.00 9.00 7.00 16.00 20.00

t.

-

2 8

-

,.. ~

f~

I

5.0

IIIJ 9.0

I

I I'

13.0

1.11

I 17.0

I

II

I III

21.0

25.0

I

29.0

33.0

I

37.0

I

41.0

I

, 45.0

,

I

49.0

I

I

53.0

"" >l'>-

FIGURE 1.3.9. Zeolite Phi (as-made) (U.S.P.4. 124.686. Table A)

t. 2 8

-

rf-

...

d [0. 1nml

r/re

11.62 9.50 7.69 6.96 5.60 5.03 4.31 3.97 3.42 2.92 2.69 2.60 2.51 2.09 1.90 1.81 1. 74 1. 72

50.00 75.00 10.00 75.00 75.00 75.00 75.00 10.00 100.00 100.00 10.00 25.00 10.00 25.00 25.00 25.00 10.00 25.00

f-

fff-

f-

.1

5.0

9.0

l.

i3.0

I

I

i7.0

I

I

I.

21.0

•

25.0

I

I

29.0

I

.I 33.0

I

I

I

37.0

I

I

41.0

I

45.0

I

49.0

I 53.0

W

01

FIGURE T.3. ro - Zeolite Beta (sodium ._ form) (U.S.P.3. 308. 069. Table II. B) •

r

SL.e

l

~

l

d [O.1nm]

11.50 I 7.56 6.97 6.61 6.10 5.36 4.91 4.16 3.97 3.53 3.32 3.21 3.10 3.03 2.93 2.69 2.48 2.40 2.31 2.25

i

IIIo 93.75 12.50 6.25 6.25 6.25 6.25 6.25 62.50 100.00 12.50 37.50 6.25 12.50 37.50 12.50 6.25 6.25 6.25 6.25 6.25

~

1

5.0

I'-L

9.0

1.1 I. I. I. 13.0

17.0

. 21.0

I

•

25.0

II

29.0

I

.1 ~ I I I I ' 33.0

37.0

41.0

45.0

49.0

53.0

cc

en

FIGURE I.3.1i. Z5M-25 (as-synthesized) (E.P. 15.702. Table II)

d [0 • 1nm]

1/10

8.08 7.04 6.44 6.08 5.28 5.01 4.62 4.54 4.10 3.70 3.36 3.32 3.25 3.15 3.11 3.04 2.81 2.73 2.64 1. 77

67.00 86.00 56.00 22.00 30.00 34.00 72.00 26.00 29.00 44.00 22.00 67.00 100.00 34.00 80.00 50.00 22.00 28.00 40.00 35.00

t.

-

2 9

.. rfff-

rfffffff-

rff-

• 5.0

9.0

•

I

13.0

17.0

21.0

I

25.0

I.

29.0

,

I,

33.0

I

I

37.0

I

I

41.0

I

, 45.0

I

I

49.0

I

I

53.0

W

_1

FIGURE I.3.12. ZSM-8 (Brit.P.Specification 1.334.243. Table 1)

sL

f-

,.. ,..

2 8

,.. ,..

,.. ,.. ,.. ,.. ,.. ,..

,.. ,.. f-

,..

,.. 11

5.0

9.0

I 13.0

I

I

17.0

I

II 21.0

.III

25.0

.1 29.0

I

I

33.0

I

I

37.0

I

I

41.0

d [0. 1nm]

IlIa

11.10 10.00 9.70 7.42 6.35 5.97 5.69 5.56 4.25 4.07 4.00 3.85 3.82 3.75 3.71 3.64 3.43 3.34 3.31 3.04

46.00 42.00 10.00 10.00 12.00 12.00 9.00 13.00 18.00 20.00 10.00 100.00 57.00 25.00 30.00 26.00 9.00 18.00 8.00 10.00

I

45.0

I

49.0

53.0

cc 00

FIGURE I. 3.13. ZSM-48 (ca Ic 1ned) (E. P. 23. 089. ex. 1)

t.

.

2 8

f-

,..

f-

,..

.. ,..

f-

,.. f-

d [0. 1nm)

IlIa

11.81 10.19 7.19 6.89 6.10 5.B6 5.61 4.21 4.08 3.99 3.89 3.74 3.62 3.59 3.37 3.27 3.07 2.85 2.46 2.37

74.00 29.00 7.00 3.00 7.00 20.00 4.00 82.00 9.00 8.00 100.00 3.00 3.00 4.00 4.00 4.00 4.00 14.00 4.00 4.00

,.. f-

..

I

5.0

I

9.0

I

I.. I 13.0

I

I

17.0

I

II

21.0

1.1.

25.0

I

II

I 29.0

I

I

33.0

I

I. I 37.0

I

I

I

41.0

45.0

49.0

53.0

W

<0

FIGURE 1. 3.14 ZSM-22 (as -synthes rzed) (U. S. P. 4, 481, 177, ex. 7)

t.

I~

2 9

I~

I~

I~

I-

d [0 . 1nm]

I1Io

10.90 8.70 6.94 5.40 4.58 4.36 3.68 3.62 3.47 3.30 2.74 2.52

40.00 10.00 13.00 8.00 10.00 100.00 97.00 65.00 46.00 5.00 3.00 19.00

~

I~

ilI~

ii-

l-

5.0

,

I, 9.0

I

13.0

I17.0 ,I

I.

21.0

25.0

,

I 29.0

33.0

• 37.0

I

I

41.0

I

45.0

I

• 49.0

53.0

01>-

o

41

cm-1

1100

900

700

500

300

z o (f) (f)

:!: (f)

Z

PHI

0::

BETA

« I-

't.

FIGURE 1.4. Mid-infrared spectra of the framework vibrations of the zeolites synthesized according to the procedures described.

42

Z

o en en :::E Z

en

a::

*

cm-1

FER

MOR

1300 1100

900

700

500

Z 0

en

:E

en Z

en ex a:::

I-

*

MFI

ZSM-12

ZSM-47 ZSM-6

ZSM-35

ZSM-34

43

44

REFERENCES

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

M.K. Rubin, LJ. Rosinski and C.J. Plank, U.S.P. 4,116,813 (1978), assigned to Mobil Oil. C.J. Plank, E.J. Rosinski and M.K. Rubin, U.S.P. 4,016,245 (1977), assigned to Mobil Oil. J.M. Nanne, M.F.M. Post and W.H.J. Stork, E.P. 12,473 (1980), assigned to Shell Int. Res. P. Chu, E.P. 23,089 (1981), assigned to Mobil Oil. G.T. Kokotailo and S. Sawruk, U.S.P. 4,187,283 (1980), assigned to Mobil Oi 1. D.W. Breck, Zeolite Molecular Sieves, Wiley, New York, 1974, pp. 162-163. E.J. Rosinski and M.K. Rubin, U.S.P. 3,832,449 (1974), assigned to Mobil Oi 1. J. Ciric, U.S.P. 3,972,983 (1976), assigned to Mobil Oil. R.W. Grose and E.M. Flanigen, U.S.P. 4,124,686 (1978), assigned to Union Carbide. W.M. Meier and D.H. Olson, Atlas of Zeolite Structure Types, Polycrystal Books, Pittsburgh, 1978, p. 77. R.L. Wadlinger, G.T. Kerr, LJ. Rosinski, U.S.P. 3,308,069 (1975), assigned to Mobil Oil. H.G. Doherty, LJ. Rosinski and C.J. Plank, E.P. 15,702 (1980), assigned to Mobil Oi 1. R. Von Ballmoos, Diss. ETH ZUrich, no. 6765 (1981) p. 71. J. Plank, E.J. Rosinski and M.K. Rubin, Brit. P. 1,334,243 (1973), assigned to Mobil Oil. M.K. Rubin, C.J. Plank and E.J. Rosinski, U.S.P. 4,104,151 (1978) assigned to Mobil Oil. D.H. Olson, R.B. Calvert and E.W. Valyocsik, E.P. 102,716 (1984), assigned to Mobil Oil. J.C. Jansen, F.J. van der Gaag and H. van Bekkum, Zeolites i, 369 (1984). P.A. Jacobs, H.K. Beyer and J. Valyon, Zeolites 1, 161 (1981). G. Coudurier, C. Naccache and J.C. Vedrine, J.C.S Chern. Comm. 1413 (1982). E.M. Flanigen, Zeolite Chemistry and Catalysis, J.A. Rabo, ed., Adv. Chem. Ser. No 1Zl (1976), Chapt. 2.

45

PART II: HIGH·SILICA ZEOLITES WITH SOLVED STRUCTURE-TYPE

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47

CHAPTER I

SYNTHESIS OF ZSM-5 ZEOLITES IN THE PRESENCE OF TETRAPROPYLAMMONIUM IONS

INTRODUCTI ON The formation of natural zeolites with volcanic glass and saline water as reactants occurred in the temperature range from 300 to 328 K at pH values between 9 and 10 but required crystallization times as long as 50,000 years. Sarrer's gel method was proposed as early as 1940 as a means of duplicating these natural conditions at higher pH and temperatures and consequently with much shorter reaction times. The primary variables of this method are synthesis temperature, pH, reactivity of the silica source, silica to alumina ratio in the synthesis mixture and nature of the al kal i. In any case at pH values above 12, and generally above 14, a silica-alumina hydrogel was prepared. Such a system is always supersaturated with respect to the concentration of its chemical constituents. Under hydrothermal conditions (373 - 473 K) this supersaturation is then removed through nucleation of metastable zeolite phases. After nucleation of such a phase, the nuclei grow further to glve larger crystals. These crystals can subsequently be dissolved in their mother liquor and eventually other zeolite phases may nucleate from it. As a consequence synthesis time is also a primary variable. Later, the gel method was sl ightly modified insofar that to the usual silica, alumina and alkali sources an organic quaternary cation was added. These quaternary organic ammonium (or phosphonium salts) have a dual function : they act as strong bases and add more OH ions to the system; hence they increase the pH, the solubility of silica and the degree of supersaturation of the system; - such quaternary ions are able to form water clathrates and possibly can "clathrate" sil ica.

48

The addition of these organics to a gel used for zeolite synthesis also has two effects - zeolite structures with an increased silicon content are always obtained, or with a lower degree of substitution of aluminium for sil icon; - sometimes totally new structures are obtained, possibly as a direct consequence of the templating effect of the organic bases. This is a short and personal summary of the state of the art of zeolite synthesis. This matter is extremely complicated and not easily accessible to experimental approach. The area has received a fair degree of attention as far as regular reviews of the state of the art are concerned (refs. 1-10). It should be emphasized that what is summarized here in one page represents the knowledge of almost 30 years of experimental work. It is the aim of this chapter to review in more detail the degree of understanding of the synthesis of zeolite ZSM-5 in the presence of tetrapropyl ammon i um (TPA) ions more specifically. Zeolite ZSM-5 will also be denoted by MFI, its structure type as proposed by the International Zeolite Association (ref. 11).

THE CHEMISTRY OF AQUEOUS TETRAPROPYLAMMONIUM SILICATE SOLUTIONS The structure of silicate species in solution has long been a matter of speculation. Only during the last decade has considerable progress been made, using mainly trimethylsilylation techniques and 295i nuclear magnetic resonance (NMR). Although each method may have its own drawbacks, the picture is now relatively clear (refs. 12,13). Alkali metal silicates dissolve in water at high pH and form solutions containing monomeric species and polymeric anions, depending on pH and concentration (ref. 12). All species are in dynamic equilibrium and, again depending on pH and concentration, this equilibrium is stable or metastable (ref. 15). Current species detected in alkali metal silicate aqueous solutions (at 3.0 mol dm- 3 of silicon) are shown in Fig. 11.1, together with their respective concentrations. To represent these species, the generally accepted notation for silicate anions in solution (ref. 16) has been used. The symbol Qi is used to indicate the number, i. of siloxane bridges surrounding a tetrahedrally coordinated silicon atom; QO, Q1, Q2 and Q3 therefore refer to monomer, end groups, middle groups and branching positions, respectively.

49

1.5

c:' E "tl

1.0

..---

-

o

E

"c

-. .2 C1l

C Ql

0.5 '-

(J

c

o

(J

~

n

n

n o

2

o

!

~

02

~

FIGURE ILL Nature and concentration of silicate species in an aqueous alkali metal silicate solution at 3.0 mol dm- 3 of silicon. Data from ref. 14 were used to construct this figure.

50

It is clear from Fig. 11.1 that under such conditions monomeric silicate anions largely dominate in concentration, whereas all other relatively simple oligomers present can hardly be considered as direct precursors of zeolite building blocks in general, or of MFI in particular. Using two-dimensional 295i NMR of potassium silicate enriched in 295i, however, at a concentration of 1.4 mol dm- 3 of silicon, other silicate oligomers have been detected (ref. 17). In addition to the dimer (Q~), the cyclic (Q~) and linear (Q~Q2) trimer, a cyclic tetramer (Q~) was also found; a prismatic hexamer (Q~) and other complex oligomers have been reported to be present. However, for none of these silicate structures is a direct precursor role in the synthesis of MFI obvious. When otherwise identical sodium and TPA silicate solutions are investigated, the monomer, QO, remains the most abundant ion but decreases significantly in concentration when the organic cation is present (ref. 18). As a general rule, the TPA silicate solution contains a much smaller number of discrete silicate species compared with the corresponding sodium silicate system. This can be derived from the much simpler 295i NMR spectrum for the former solution (ref. 18). The Q1 silicons, more particularly, are much less abundant, suggesting that "linear oligomers and chains exocyclic to ring or cage polysilicates are uncommon in such tetrapropylammonium silicate solutions" (ref. 18). These effects persist for more concentrated solutions and there is even evidence for the existence of a cubane cage Q~ ion (ref. 18). In a real synthesis mixture for MFI with the molar composition

295i NMR shows that many silicate species, from monomers to highly branched polysilicates, are present (ref. 19). On addition of organic solvents such as methanol, ethanol or dimethyl sulphoxide to this mixture, a dominant silicate species appears in the reaction mixture (ref. 19), with the following characteristics (ref. 19) : i. a 295i chemical shift of -98 ppm, indicative of a highly symmetric species; ii. attenuated total reflection Fourier transform infrared bands at 1126 and 1011 cm- 1, which precludes a double four-ring sil icate being present with typical bands at 1081 and 1026 cm- 1; iii. a molecular ion in the mass spectrum of the methylsilylated species of lTl/e =' 1395.

51 All

th is represents conv i nc i ng ev i dence for the presence of a doub 1e

five-ring silicate (Qfo) in real synthesis mixtures of l5M-5 to which organic solvents are added. As it was also demonstrated that such a mixture could be transformed

at

403

K into

MFI

zeol ite while

the

Qfo species

gradually

decreased in intensity, this Qfo silicate seems to be the real and direct precursor of the l5M-5 structure. Indeed, Fig. 11.2 shows that during a minor transformation of the Qfo precursor (addition of Q1 and

Q~Q2

species and

breaking and formation of a relatively small number of 5i-O bonds), the real precursor of lSM-5 is obtained (ref. 20).

3 FIGURE 11.2. Transformation of a Q silicate species into a l5M-5 building 10 block

The effect of aluminium on the nature of precursor species of l5M-5 has also been reported (ref.

21).

It is common

knowledge that only Al (OH)4

monomers occur in an aqueous sodium aluminate solution when the aluminium 3 concentration is higher than 1.5 mol dm- and when the Na to Al ratio is lower

than

2.5

(ref.

22).

Under

such

alkaline conditions,

concentration varies as follows (ref. 23) :

the Al(OH)4

52

pH

AI (OH)4 concentration

5.87 10.00 -l3.00

13+, At pH values below 7, 27Al NMR indicates also that !Al(H 20)6 IAl (OH)2(H 20)n 1+ and Al (OH)3.nH20 are important species (ref. 21) . Above pH 10.5, Al(OH)4 is exclusively present (ref. 21). Na+ and TPA+ cations compete for charge neutralization in these aluminate solutions but the Na+ ion is most preferred. An explanation for this preference may be the more localized charge on Na+ which, compared with the more diffuse charge on TPA+, should be more efficient for charge neutralization (ref. 21). It was also shown by the same workers that the replacement of Na+ cations by larger alkali metal cations such as Cs+ has a structure-breaking effect on the hydrogen bonding of water, hence distorting the environment of the Al nucleus. l cr silicon-rich aluminosilicate (with SijAl > 5) it has been suggested that there exists a relatively stable species that intermediate, i.e., Al(OSi03)~3(ref. 22). In order

is to

a potential explain its

formation, the following condensation reaction has been assumed (ref. 24)

-

01

O-Si-O-

4

o HO-~i-OH+40H-:+AI(OH): 1 0-

I

_

1 0

1 0-

0 0 1 1_ I -+ 6-Si-0-AI-0-Si-0-+ 8H20

-

0-

<+

I 0-

O-:"~i-OI 0-

(IT.1)

53

As there is infrared evidence for the occurrence of a Q~ species that is partially protonated (ref. 22), the subsequent condensation of Q~ with Al(OSi03)~3would explain the formation of five-ring systems under conditions relatively rich in silica (ref. 24) :

r H-O-I H-O--

'O=Si

=-\1\r _ \ ,,0, =-0"• \ I0",C, 0-0 - '- '- ,-/

-=0

(n.z:

It can then easily be visualized that such species condense and give rise to aluminium substituted analogues of the Gio silicate species described earl ier. In summary, it can be stated that with the present state of knowledge, the solution chemistry under conditions in which MFI zeolites can be synthesized is to a certain extent understood, at least as far as the nature of the potentially important precursor species is considered.

THE ARGAUER-LANDOLT INVENTION In the first patent in which the preparation of a new high-silica zeolite was claimed, a synthesis gel containing sodium and tetrapropylammonium hydroxide, alumina, silica and water was used (ref. 25). This historical discovery, filed on November 14, 1972, and possibly made a few years earlier, is now of extreme industrial and scientific importance. Indeed, this new zeolite, denoted by ZSM-5 (Zeolite Socony Mobil Number 5), is very superior to many other materials for use as a sorbent and catalyst. As a special tribute to honour the authors of this historical invention, we report here in extenso the five first original crystallization reactions (Table 11.1).

54

TABLE 11.1 Synthesis of lSM-5 according to the original Argauer and Landolt patent (ref. 25)

Example 1

2

3

4

5

Molar composition of the gel (A1 203=1) (TPA)20 * Na 20 A1 203 Si0 2

H2O

9.0 1.2 1.0 29.1 481

17.1 1.0 1.0 27.7 453

17.1 17.1 1.0 1.0 1.0 1.0 27.7 27.7 453 453

423 5.0

423 8.0

17.1 1.0 1.0 27.7 453

Crystallization conditions Temperature (K) Time (days)

423 6.0

398 448 5.5 5.0

Molar composition of the crystalline product (A1 203 = 1) on an inorganic basis 0.50 1.0 32.5

0.89 1.0 31.1

0.86 1.0 35.5

1.31 0.83 1.0 1.0 45.0 37.0

Nature of product, based on its X-ray diffractogram lSM-5

* TPA

tetrapropylammonium

lSM-5

lSM-5

lSM-5

lSM-5

55

Basic knowledge of the mechanism of the synthesis of this material has been gathered using recipes derived from the basic patent. It should be noted that the materials prepared according to this method are extremely costly, as a large amount of concentrated aqueous tetrapropylammonium hydroxide solution is used. Such a pure solution is prepared as follows (ref. 26) : (I!. 3)

(I1.4) where R represents CH 3(CH2)2- and X represents Br-. Reaction (11.4) explains why a pure aqueous solution of TPA-OH containing no other cations is so expensive.

THE ISOTHERMAL METASTABLE PHASE TRANSFORMATION The chemistry involved in the conversion of the relatively simple oxide system, consisting of water-silica-alumina-alkali metal-organic, at an autogeneous pressure below 473 K, is extremely complex as the following factors may intervene (ref.7) : -

the formation of an intermediate gel phase; the occurrence of transformations of metastable phases; nucleation phenomena provoked by supersaturation; differences in rates of dissolution of the reactants, depending on their origin and content of oligomers and polymers.

Such a series of successive transformations is shown in a general way in Fig. 11.3. This metallurgistic approach in the case of ZSM-5 synthesis has been pursued by Sand and co-workers (refs. 7,27,28) at 448 K for the following reaction system : ((TPA, alkali metal)20)lO (A1 203)l (Si0 2)28 (H 20)750 (alkali metal chloride)4 More specifically, for the ((TPA,Na)20)lO (A1 203)l (Si0 2)28 (H 20)750 reaction system, the following phases are success ive ly obtained depending on the Na/(TPA + Na) ratio (F) (ref. 27) :

56

oxide system(sol)

crystals of equilibrium phases

1

TGROWTH

PRECIPITATION

gel phase I

nuclei of equilibrium phaset s )

T

1

DISSOLUTION NUCLEATION

NUCLEATION

metastable nuclei of phase I

crystals of metastable phase II

T

lGROWTH

GROWTH

crystals of metastable phase I

metastable nuclei of the more stable phase II

DISSOLUTION NUCLEATION

FIGURE 11.3. General representation of the isothermal metastable phase approach (schematic representation of ideas advanced in ref. 7) for 0.7 < F < 1.0 AMO ~ MOR for 0.4 < F < 0.7 AMO ~ MOR ~ MOR + MFI + ANA

~

MFI + ANA

~

MFI

where AMO, MOR and ANA represent amorphous, mordenite and analcime phases respectively. It follows that the initial gel, after an induction period, is transformed into a mordenite phase, which then dissolves and recrystallizes in two other phases, analcime and l5M-5. The latter phase is the more stable as it does not disappear while analcime is dissolving. At low values of the Na cation fraction (F < 0.3), pure l5M-5 is formed right away. When 4NaCl is added to this gel, gismondine is formed at the early stages of the crystallization (ref. 28), whereas in the potassium system. harmotone, phillipsite and offretite are found as zeolitic metastable intermediate phases as well as feldspar (ref. 28). In Fig. 11.4 are summarized the sections of isothermal phase diagrams in which pure l5M-5 is formed as a unique crystalline phase from the initial gel after an induction period.

0.6

«0-

t-

+

..J

«

0.5

t-

III

::E

::J

0.4

« ~ ..J

« 0.3

<, ..J

«t-

III

0.2

::E

::J

_ - - - - - - '0 -750H20-2 a I1O(TPA,Na,KhO-AI203-28SI 2

« 0.1 ~

/

..J

«

/

0.0 0

40 SYNTHESIS TIME /

60

80

100

HOURS

FIGURE 11.4. Sections of isothermal phase diagrams at 448 K in which pure lSM-5 occurs as the only crystalline phase (derived from ref. 27, Fig. 13, and ref. 28, Figs. 1, 2 and 3).

It is striking that pure ZSM-5 in any case is crystallized when F is rather low. When as source of alkali metal only sodium is present, pure ZSM-5 is crystallized over a wide range of F values. Addition of K+ or Cl- anions to this system compresses this area to a different extent. The high TPA concentrations needed in the gel and the absence of K+ to avoid nucleation of other phases could indicate that there exists a TPA selectivity (compared with hydrated Na+), for the synthesis of building blocks of the ZSM-5 phase. The hydrated K+ ions in this context seem to exhibit specificity for other zeolitic phases. This potassium specificity has indeed been established for the synthesis of offretite (ref. 5). Not only the TPA fraction but also the Si/Al ratio of the synthesis gel helps to determine the phase purity of the MFI zeolite structure type (ref. 29). Indeed, in the following diluted reaction system ((TPA)2 0)34.7 (K 20 + Na 20)10.6 (A1 203)1 (Si0 2)x (NH 3)24.4 (HN0 3)6 (glycerol)10 (H 20)6,600

58

sanidine, a potassium feldspar, is the main impurity phase when x > ZO; for lower values of x, only zeolites G and Ware the main crystalline phases and MFI fails to crystallize. From gel with a low aluminium content, extensive secondary nucleation of a form of quartz (e.g. cristobalite - ref. 30) often occurs. It is our own experience that for silica-rich gels secondary nucleation of magadiite and kenyaite-type phases is also possible. It should also be stressed that after prolonged ageing of ZSM-5 crystals in their basic mother liquor, the metastable but open MFI structure may be transformed gradually into a dense silica-rich and aluminium-rich structure, as for instance in cristobalite and analcime, respectively.

THE DOMINANT FACTORS INFLUENCING THE CRYSTALLIZATION OF THE MFI STRUCTURE The influence of the concentration of the different components in a typical gel for the synthesis of ZSM-5 zeol ites will now be examined. A priori the following factors may influence the rates of nucleation and crystal growth : - the aluminium content of the gel, or its SiO Z/A1 Z03 ratio; - the degree of dilution (HzO/SiO Z ratio); - the alkalinity of the medium (Na/SiO Z' TPA/SiO Z and/or OH/SiO Z ratios); - the nature of the silica source or its degree of polymerization. It will now be considered how, under conditions in which a pure phase is obtained, these parameters influence the rate of crystallization. The basicity of the gel in the classical sense consists of a combination of the second and third parameters.

1. The SiO Z/Al z0 3 ratio of the gel It may be expected that the concentration of alumina in the gel will

influence the rate of crystallization of ZSM-5 from this gel. Therefore, the Al/(Al+Si) rather than the Si/Al z molar ratio will be handled as a physically meaningful parameter. Several workers have investigated the influence of the aluminium content on the rate of ZSM-5 crystal 1ization, all other factors remaining unchanged (refs.31-37). Representative data were taken from some of these studies and are plotted in Fig. 11.5.

fi9

All data tend to show that the rate of crystallization of lSM-5 becomes faster when, all other factors remaining equal, the aluminium content of the gel is lower. This is opposite to the normal hydrothermal behaviour of such systems : higher Si/Al ratios give a system with higher viscosity of the solution and a lower reaction rate (ref. 31). Fig. 11.5 shows that the incorporation of aluminium into an MF1 type of structure is of a disruptive nature and becomes increasingly difficult when the system contains more aluminium. This has also been confirmed from a kinetic point of view. Such data are given in Table 11.2, which shows the apparent activation energies for nucleation and crystal growth and the respective crystallization induction periods, determined in the presence and absence of alumina (refs. 27,31).

o~

co

(/)

...o>.

Ol--

o

---J~-----~

25 3xAI/(AI+Si) 10

50

FIGURE 11.5. Influence of the Al/(Al+5i) composition of the synthesis gel on the crystallinity of lSM-5 : (a) rearrangement of data from ref. 31, Fig. 3, in the system ((TPA)zO)1 (NazO)1 (5iOZ)18 (H ZO)Z70 at 448 K after Z4 h; (b) rearrangement of data from ref. 33, Fig. I, in the system ((TPA)zO)1 (Na zO)3 (5iOZ)5 (HZO)ZOO at 4Z8 K after 7 h; (c) from ref. 35, Fig. 4, in the system ((TPA)zO)1 (NazO)O.Z (5iOZ)7 (H zO)Z50 at 448 K after 48 h.

60

TABLE 11.2 Kinetic data for synthesis of Z5M-5 in the absence (A) or presence (B) of alumina at 448 K

Ea cn (kJ/mol) Ea cd (kJ/mol)

Aa

Bb

20.2

107.4

42.0

91.5

Induction period (h)

Ref.

9

31

27

a, in the system ((TPA)2 0)1 (Na 20)1 (5i0 2)18 (H 20)270. b, with ((Na,TPA)2 0)10 (A1 203)1 (5i0 2)28 (H 20)750. c, apparent activation energy for nucleation. d, apparent activation energy for crystal growth.

The apparent activation energies for MFI nucleation and for crystal growth are much lower in the absence of alumina and the induction period before crystals appear that are detectable by X-ray diffraction techniques is also much shorter for the alumina-free system. Unfortunately, no other data are available to show whether these properties vary continuously with the aluminium content or not. 5everal explanations have been advanced for such behaviour : - for a given amount of OH in a system, the amount of OH left to act as depolymerization agent on silica will decrease with increasing amount of Al, as Al(OH)4 species are formed in the synthesis solution (refs. 36,37); consequently, the rate of silica depolymerization and the rate of zeolite formation will decrease with increasing aluminium content in the gel; - there is an equilibrium reaction between Al and TPA (ref. 35) : (Al ... TPA) ~ Al + TPA The complexed aluminium is present in tetrahedral coordination, whereas

61

the presence of octahedral aluminium is associated with the existence of free undissociated TPA-OH. These changes in concentration of Al(IV) and Al(VI) are confirmed by NMR measurements and the existence of free TPA-OH is shown by therma 1 ana lys i s (ref. 35). When ina gi ven sys tem the A1 concentration

is

increased,

the

amount

of

dissociated

TPA-OH

will

decrease and the effect is reduced to one of decreased a 1ka 1in ity or basicity (see below). - in the early moments of the crystal 1ization a s i l i ca framework with the MFI structure is formed, occluding most of the aluminium; this structure gradually dissolves then and incorporates aluminium in its lattice when it

crystallizes

a

second

time

38-40);

(refs.

aluminium then plays again on the residual

the

presence

of

more

basicity of the synthesis

mixture. In this respect the mineralizing role of free OH detail

by Sarrer (ref.

8).

An increasing OH

bring about an accelerated crystal before

viable

amphoteric

nuclei

hydroxides,

are OH

has been discussed in

concentration will

generally

growth and a shortened induction period

formed.

As

will

cause

it

is

a

greater

good

complexing

supersaturation

agent and

of

will

provoke an increased number of encounters of suitable precursors in solution. An

immediate

application of

the

effect of

the

Si/Al

ratio

on

the

crystallization rate is the following (ref. 102) : when instead of adding the aluminium at once to the synthesis mixture it is added gradually, a much faster crystallization is expected. is

gradually added

is

reduced

In practice, the synthesis time when Al

to one

tenth of

the

time

required for a

synthesis in which aluminium is added at once (ref. 102).

2. The TPA/Si0 2 ratio of the gel TPA cations have been recognized to be able to form complexes with either silicate (ref. 41) or aluminosilicate (ref. 21) species and to compete with Na+

ions

species

for (ref.

charge

21).

compensation

These

of

these

silicate

cations may stabilize

the

or

aluminosilicate

formation

of

certain

subunits (ref. 5) and then further cause replication of these primarily formed building units via a stereospecific hydrogen bond between the TPA ion and oxygen ani ons (ref. 5). Hence the presence of TPA may be necessa ry for the formation of a particular structure or may be structure-directing. This effect is now generally known as the TEMPLATING EFFECT in zeolite synthesis (refs.

21,41-43). The following facts are in favour of such an effect during the

62

synthesis of zeolite ZSM-5 : 1.This structure is easily synthesized in the presence of TPA, using a very broad range of experimental conditions (refs. 25-40); 2.The rate of crystallization increases with increasing TPA/Si0 2 ratio, at least up to certain values (refs. 32-37). Pertinent literature data to illustrate this are given in Fig. 11.6.

o

10

100r-------T-~---,.r----~

,

0~

->.

TPA

t:

CU 11l

Si02

50

...o>.

100 crystallization I h

FIGURE II .6. Dependence of the ZSM-5 crystall ization rate on the TPA/Si0 2 ratios in the gel : full 1ines, derived from data shown in ref. 35, Fig. 2; OH/Si0 2 = 0.35, Si/A12 = 56 and 448 K; dashed lines, from ref. 35, Fig. 3; OH/Si0 2 = 0.1, Si/A12 = 90 and 433 K.

63

3.

This rate inc rease is seen to become sa turated when a gi ven TPA/Si O 2 value is reached. Rollmann and Valyocsik (ref.33) reported a saturation value of about 0.05, which corresponds (in the case when all organics are retained by the structure and all sil ica is transformed into zeol itic silica)

to

approximately

3 -

4 TPA molecules

per

unit

cell.

This

corresponds then to a situation in which every intersection of the lSM-5 pores is filled by a TPA molecule and represents a situation of perfect pore filling.

From the work of Romannikov et al.

(ref. 35)

it also

follows that a saturation value is reached but this value seems to be reached only at considerably higher TPA/Si0 ratios. This does not 2 necessarily contradict the previous explanation, as the synthesis in this instance

is

effected

at

higher

temperatures

and

basicity.

It

may

therefore simply be that the Hoffmann elimination reaction (ref. 44) (11.5)

occurs to a larger extent. From this moment on, the crystallization rate is no longer influenced by the TPA content and the reaction mechanism should switch from solution phase to surface nucleation. Indeed, at high TPA

concentration,

this

second

nucleation

is

faster

than

further

arrangement of aluminosilicate units around TPA ions. This is confirmed by changes in crystal morphology that occur at this stage (ref. 33). 4.

TPA molecules are found intact in the pores of crystals of MFI; the expected C/N ratio of TPA is 12.0, while experimentally values of 13.3 have been reported (refs. 34,45). The specificity of an MFI type of structure can also be derived from

synthesis experiments carried out in the presence of minor amounts of TPA (ref. 68). Under the specific conditions reported, only poorly crystalline lSM-5 is obtained with a TPA/Si0

ratio of 0.005. On addition of amines to 2 amine/Si0 ratio of 0.045), the rate of 2 crystallization is considerably increased, irrespective of the exact chemical such

a

system

(with

an

nature of the amine (ethyl-, propyl- and butylamines were added as primary, secondary or tertiary amines). Crystallization does not occur, however, in the absence of TPA. This indicates that templation is important only for zeolite nucleation and much less for its subsequent crystal growth.

64

3.

The degree of dilution or the HZO/SiO Z ratio

Rollmann and Valyocsik (refs. 3Z,33) stated that the HZO/SiO Z ratio of an ZS~1-5 synthesis mixture had little effect on its rate of crystallization. In Table 11.3 are shown typical HZO/SiO Z ratios used by various workers. It is clear that MFI can crystall ize out of gel s with an extremely wide range of HZO/SiO Z ratios (from 7 to lZZ). This at least qualitatively indicates that the water concentration is of minor importance. Von Ballmoos (ref. Z6) intentionally used very dilute conditions in order to ensure that the aluminium distribution was homogeneous throughout the gel. Whether this goal was reached is unknown, but it is obvious now that the homogeneous distribution of aluminium throughout the zeolite crystal is not determined by the degree of dilution of the gel (in the diluted system (ref. Z6) the existence of Al gradients throughout the crystals was reported), but rather by the mechanism of nucleation and by the nature of the silica source (refs. 46,47). It should be noted that values of the HZO/SiO Z ratio as low as 7 physically correspond to complete pore filling of a high surface area silica (refs. 38-40) and represents a special way of synthesizing ZSM-5.

TABLE 11.3 Water and sodium concentrations (expressed as molar ratios) used by various workers for the synthesis of ZSM-5 Na/SiO Z ratio lZ2 45 45 40 27 25 22.2 17 17 11

7.4

0.20 0.72

0.50 0.59-1.18 0.07 1.08 0.26 0.07-0.08 0.09 0.43 0.2

Ref.

26 46 45 33 27 47 49 25 46 48 38

6,5

4.

The 1,1/Si0 2 ratio

As stated by Rollmann and Valyocsik (ref. 33), the M/Si0 ratio also has 2 no rate-determining function in the synthesis of ZSM-5. Table 11.3 shows that the MFI type of structure is obtained over a wide range of values of this ratio (from 0.07 to 1.18). However, there is evidence that the addition of a second alkali or alkaline earth metal cation and the use of another alkali metal source definitely influences the crystallization and nucleation rates. In contrast, it should not be forgotten that addition of alkali increases the basicity of the system and consequently the effects of the different parameters are not always easily separable. For the present discussion it should. be added that the overall nucleation rate, R, is defined as the n inverse of the nucleation period. In the early work of Erdem and Sand (ref. 27) at constant basicity and TPA content of the system, the replacement of Na by K and also its influence on the crystall ization kinetics have been reported. How an increase in the K/(K+Na) ratio in the gel influences the rate of nucleation is derived from their data and is illustrated in Fig. 11.7. Initially, the substitution of K for Na in the gel does not seem to influence Rn very much, whereas afterwards. it exerts a positive effect. The authors (ref. 27) interpreted this as a potassium effect on the formation of building units. They also suggested that from their data it can be concl uded that initially the addition of K has a negative effect. However, on reconsidering and replotting their experimental data, we found no evidence for such an effect. On the other hand, it has been reported by several workers that Na rather than K has such a favourable effect on the formation of primary building units in lSM-5 (refs. 46,51,56), which indicates that the role of the Na/K ratio is not clear. Other roles for alkali metal cations in a TPA-containing aluminosilicate gel have been proposed: 1.

In small amounts, alkali metal cations may catalyse (in a not further disclosed way) the crystallization of lSM-5 (refs. 53,57);

2.

At constant OH concentration, the first consequence of the addition of bare alkali metal cations, which will become hydrated in a firm sphere, is that the degree of supersaturation will increase and nucleation will become faster (ref. 54);

66

/

/

f

/

20-

/

/

/

/ /

......

/

/

o

/

o .....

x e

c::

/

/

10~

OL....

o

Na

A'

.",

"

~

"

I ~------~

0.5 K

1

K

Na+K

FIGURE 11.7. Influence of the K fraction of alkali metal cations on the rate of nucleation (R n) at 448 K of the gel ((TPA + K, Na)20)10 (A1 203)1 (5i0 2)28 (H 20)750' Reorganized data are derived from ref. 27, Figs. 5 and 6.

67

3.

The hydrated alkali metal cations will interact with the hydrophobic aluminosilicate sol particles; consequently, their stability will decrease and they will agglomerate and precipitate as a gel (ref. 54). This is the so-called salting-out effect. Its efficiency will be dependent on the charge density and therefore on the nature of the alkali metal.

4.

Depending on their size, alkal i metal cations have either a templating or a structure-forming abil ity (Li ,Na) or a structure-breaking effect (K, Rb, Cs, and also NH 4) (refs. 46,54). Indeed, large cations are less strongly hydrated and will eventually disrupt the water structure through breaking of the hydrogen bonds.

5.

Depending on their electrostatic potential (proportional to I/r), alkali metal cations will be able to interact more or less efficiently with point charges and compete among each other and with TPA for charge compensation of aluminosil icate anions. Indeed, TPA cations are structure-ordering, as they will form stable water clathrates (ref. 54).

In view of all this, it may well be that the data in Fig. 11.7 and the increase in nucleation rate on addition of K to the system is explainable by a less efficient competition of the potassium ions for TPA ions compared with sodium and in fact simply reflects a more efficient use of TPA ions. In synthesis mixtures containing as a source of inorganic basicity a single al kal i metal cation, the activation energies for nucleation decrease with increasing electrostatic potential (I/r) of the cation, while at the same moment the overall rate of nucl eat i on also increases. Representat i ve data taken from two literature sources illustrate this in Fig. 11.8. In contrast to this behaviour, the rate of lSM-5 crystallization is not dependent on the nature of the alkali metal cations (ref. 49). The 1inear dependence of Ea n and Rn on the electrostatic potential of the alkali metal is considered to be of general validity, irrespective of the deviation noted for Li in one of the studies (ref. 52). As these data relate rather to the inverse of the bare ionic than to the hydrated ionic radius, it is concluded that these effects represent efficient charge neutralization or increased salting out effects. It seems straightforward that such effects will influence only nucleation and not crystal growth kinetics.

68

60

•

~

0

E

, ~

~

c ~

40

w

•

30

25

t

Li

•

c 0

~ ~

>

20

~

~ ~ ~

15

FIGURE 11.8. Variation of the apparent activation energy for lSM-5 nucleation (Ean) and the relative rates of nucleation (R n) with the electrostatic potential of the alkali metal cation present. Open points represent data from ref. 52 (Fig. 1) obtained after appropriate recalculation; full points are derived in the same way from ref. 49 (Fig. 4 and Table 2).

69

Ammonium ions exert a pronounced structure-breaking effect on a synthesis gel (ref. 54) and therefore should decrease the rate of nucleation. This effect cannot be associated with its ionic size, hydrated or not. As the interaction of NH; with surrounding water molecules is weak, it seems to be questionable whether a hydrated NH; species is formed (ref. 54). However, as the basic dissocation constant of NH; is about two orders of magnitude lower than a tetraalkylammonium ion (ref. 38), the apparent structure-breaking role of NH; may also be simply a basicity effect. Anyway, the presence of an i ncreas i ng fraction of NH +4 as chargecompensating ion in addition to TPA has a drastic effect on the nucleation rate (Fig. 11.9). When to such ammonium rich gels ((TPA)20)4 (NH4)20)38 (A1 203)1 (5i0 2)59 (H 20)750 small amounts of Na 20 or K20 are added, the nucleation rate drastically increases again, the effect being much more pronounced for Na than for K (Fig. 11.9). This clearly illustrates the superior role of Na as a structure-directing agent compared with K.

20

a

+ Na --

15

b

....

:c

<, 0

~

10

x

c cr

b

5

NH4/ NH4 + (Na,K)+ TPA

FIGURE 11.9. Change of the nucleation rate of l5M-5 (a) with an increasing fraction of NH; ions (recalculated data from ref. 50, Fig. 2) and (b) on addition of supplementary amounts of KZO and Na 20 (recalculated data from ref. 55, Figs. 11 and 12).

70

The influence of K/Na on the nucleation rate of lSM-5 seems to be dependent on the exact nature and concentration of the other ions present (compare Figs. 11.7 and 11.9). In the presence of an excess of NH; ions (structure-breaking environment), both Na+ and K+ exhibit structure-directing propert i es . As expected, these are more pronounced for Na + than for K+. In the presence of excess of TPA, K+ is competing less efficiently than Na+ with TPA ions and consequently K+ shows "apparent" structure-directing properties. The nucleation of lSM-5 also can occur in the complete absence of any alkal i metal cation (refs. 36,37,57,59). Its nucleation rate under such conditions increases with increasing TPA/SiO Z ratio or with increasing basicity of the gel. This has important consequences for the use of this lSM-5 zeolite for catalytic applications. If sodium-free catalysts are requi red, it is des i rab1e to use such a synthes is method, as it is common knowledge that it is not always easy to remove the last traces of sodium from a zeolite by ion exchange techniques.

The influence of the alkalinity on the rate of nucleation of lSM-5 has been discussed several times. Barrer (ref. 60) in general emphasized that an increasing OH- concentration increases the degree of supersaturation and accelerates crystal growth. An increased OH- concentration will also increase the solubility of zeolites in their mother liquor. From these general ideas, it follows that for a given zeolite to nucleate as a single phase in a short period of time, an optimum OH- concentration or optimum OH/SiO Z ratio will exist. This optimum OH/SiO Z ratio for lSM-5 synthesis has been recognized by several workers (refs. 3Z,35,36,37,64). For an SiO Z/A1 Z0 3 ratio of 90, an HZO/SiO Z ratio of 40, an Na/SiO Z ratio of 0.59 and an TPA/SiO Z ratio of 0.10, the optimum OH/SiO Z ratio is 0.05. The al kal inity has to be high enough to maintain sufficient dissolved hydroxysilicate and aluminate species and not too high in order to avoid inhibition on the nucleation and growth of these species (ref. 37).

71

6.

The nature of the silica source Data now exist that clearly show (Table 11.4) that the crystallization

of lSM-5 from the usua 1 gel

is also dependent on, among other factors, the

nature of the silica source. Silica sources initially containing high amounts of the silicate monomer crystallize faster than gels in which

silica is

present in a higher polymeric form. It can therefore be concluded that the rate of dissolution or of depolymerization of silica, which is known to be slow (ref. 46), intervenes in the rate-determining step for nucleation of lSM-5. As the crystal growth is influenced in the same way (Table 11.4), this indicates that its rate is also determined by the concentration of monomeric s il i cate. TABLE 11.4 I nfl uence of the nature of the s il i ca source on the crysta 11izat ion rate of lSM-5

Sil i ca source

Nature

Induction

Time to reach 50%

period (h)

crystallinity (h)

Ref.

Water glass

Monomeric

25

40

46

Gel

Polymeric

60

140

46

Quso

Precipitated

Cabosil

Fumed s il i ca

8

12.5

49

10.0

49

Ludox

Colloidal sol

4.7

5.5

49

Sil icate

Monomeric

3.5

4.0

49

It should be noted,

however, that changing the nature of the sil ica

source (e.g., going from sodium sil icate to a sil ica sol (ref. 90)) might alter the viscosity of the gel. With sodium silicate very stiff gels are usually obtained, which require a high degree of dilution in order to obtain relatively rapid crystallization. Therefore at comparable viscosities, the gel from the silica sol contains more solids and higher yields are obtained in the same crystall ization time. At equal H ratios (20 in ref. 90), 20/Si02 the crystallization rate of the gel using the sol as silica source was twice as fast as when the gel was made with sodium silicate.

72

MORPHOLOGY OF Z5M-5 ZEOLITES From the conclusions reached in the previous section on the nature of the parameters that determine the rate of crystallization, some statements can be made that are important as morphology-directing parameters : i. the basicity of the synthesis mixture will be an important morphology-

determining factor: high basicity will create high crystal dissolution rates compared with rates of crystal growth and consequently the zeolite crystals will be small; i i. as incorporation of aluminium into ZSM-5 was found to be a disruptive process, it is clear that larger crystals will be more easily prepared in aluminium-poor environments; iii. in principle, all parameters that cause an increased rate of nucleation, i.e., with nuclei formed in a very short period of time, will produce smaller crystals; therefore, increased TPA concentrations in the synthesis mixture are expected to give smaller crystals. lSM-5 crystal morphologies that have been reported several times are small crystals below the 1 ~m size range, single or twinned crystals with a euhedral morphology, spherulitic agglomerates of various sizes, agglomerates of crystals or crystals in the form of intergrown disks and large monocrystals, lath-shaped, which represent an elongated euhedral morphology. These typical morphologies are illustrated in Photograph 11.1. Data selected from pertinent publications on this subject are collected in Tables 11.5, 11.6 and 11.7. These data, together with information from other papers, illustrate the influence of various parameters on the morphology of the zeolite crystals: 1.

When ions with structure-breaking properties are added to the gel, larger crystal sizes are obtained, the morphology of which changes from spherulite aggregates to euhedral single or twinned crystals. The effect increases with the nature of the cation in the following order (refs. 27,28,49,50, 52,53,55) : Li < Na < K < Rb < Cs < Ba < Sr.

PHOTOGRAPH ILL Typical crystal morphologies encountered for ZSM-5 : A, spherulitic agglomerates; B, twinned slightly elongated euhedral crystals; C, intergrown disks; D, lath-shaped single crystal

74

2.

High TPA concentrations normally give small crystals, whereas in the presence of low TPA contents large single crystals are easily obtained (refs. 27,28,32,33,49,50,61).

3.

From more silica-rich gels larger crystals are obtained (refs. 35,50). When in a given mixture aluminium is complexed (with, e.g. tetraureacobalt, ref. 63), the same increase in crystal size is observed. When in the synthesis gel 10.c (Part I) the amount of aluminium is decreased, the morphology of the crystalline product changes from spherul i t i c aggregates (Si/A1 2 = 46) to intergrown disks (Si/A1 2 = 1,500) (Photograph 11.2). These changes are not due to a pH effect since in this recipe aluminium is added as sodium aluminate. The aluminate ion requires only two molecules of water to form Al(OH)4 which is the predominant species above a pH value of 10 (ref. 8) : (I1.6)

4.

The addition of salts (anions or cations) to the synthesis mixture directs the synthesis to the formation of mostly larger crystals, the morpho logy of whi ch is determi ned by the nature of the forei gn ion (refs. 28,62). At present these data are difficult to rationalize and it is not possible to relate the presence of a specific morphology to a particular property of the ion.

5.

The nature and the degree of polymerization of the silica source determine the morphology (refs. 46,62,118); as expected monomeric silica SOurces give smaller crystals Or their agglomerates whereas from a polymeric silica source large crystals can be obtained.

6.

The OH/Si0 2 ratio (or system alkalinity) influences the size and degree of agglomeration (refs. 32,33,65) : at high basicity small but dispersed crystals are obtained, whereas at low OH/Si0 2 ratios (0.01) well defined large crystals are obtained.

Apart from point 4, the effects of all other parameters were predictible from the knowledge developed in the previous section. It is evident, however, that the combined change of two parameters may cause unexpected changes that are difficult to predict. Rollmann and Valyocsik (ref. 33) have shown that when two effects (high TPA/Si0 2 and low OH/Si0 2 ratio) are combined, large

75

PHOTOGRAPH 11.2. SEM of lSM-5 obtained from gels with Si/A12 = 46 (A), Si/A1 2 = 350 (8), Si/A1 2 = 1,500 (C) prepared following recipe 10.c (Part I).

76

well dispersed single crystals were obtained instead of an agglomeration of intergrown smaller crystals. Sand and co-workers (refs. 50,62) (Tables 11.5 and 11.7) were able to grow extremely large single crystals in an ammonium-rich medium. This, of course, confirms the structure-breaking role of ammonium. However, when small amounts of an alkali extremely

large

metal

lath-shaped

and

particularly Li

single

crystals

20, could

were added be

(ref.

obtained.

It

62) is

d i f f t cu l t to conceive how the addition of a structure-directing cation that favours nucleation could have such an effect. The influence of several parameters on the morphology of lSM-5 crystals has

been reconsidered in a classical

NaHC0

gel synthesis with TPA and Na 2C03, and NaOH in variable proportions present as cation sources (ref.11B).

3 The alkalinity is again found to be a habitus and size determining parameter.

The crystal size steadily decreases from 50 to 10 um when the OH/SiO ratio Z 6 1 is increased from 10- to 10This is consistent with an increased rate of dissolution at higher basicity as explained earlier. However, at very high

> 0.5), it appears that the crystal size increases Z again. This is very surprising, and cannot be attributed to an alkalinity

alkalinities

(OH/SiO

effect. The authors (ref. liB) mention that the degree of crystallinity is far from being perfect at these high pH values (pH is only 56

= 14.2 and % crystallinity

%). Although no photographs are included, it is probable that the

increased size is due to agglomerations of smaller crystals "glued" together via

amorphous

residues.

At

lower OH/SiO ratios the degree of dilution Z increases al so and consequently the water content of the synthesis gel has

also an "apparent" effect on crystal size.

TABLE 11.5 Survey of parameters influencing lSM-5 morphology Malar composTtion -of-gel M20 A1 203 Si0 2 H20.

{TPA)20

1

90 90 90

2000 2000 2000

1 1 1

28 28 28

750 750 750

4.5 4.5 4.5

12Na 20 12K20 12Li 20

1 1

8 8 8

2Na 2O 2Na 2O 2K2O

Synthesis temperature

Morphology

( K)

413-443 413-443 413-443

+ 8NaCl + 4KCl

448 448 448

Crysta 1 Size

Ref.

(~m)

<1

spherul itie spherul itic spherul itic

4-7 2

49,Fig. 7 49,Table 4 49,Table 4

single aggregates intergrown disks

0.5 50-20 5-10

27,Fig.3 28,Fig. 5c 28,Fig. 5a

---------------------------------------------------------------------------------------------------------------------4 4 4 4

5(NH 4)20 5(NH 4)20 50(NH 4)20 50(NH 4)20

1 1 1 1

28 59 59 59

750 750 750 750

4.5 4.5

5BaO 5SrO

1 1

90 90

2000 2000

4.5 4.5 4.5

-

1 1 1

90 90 90

2000 2000 2000

+10 NH

4Cl

453 453 453 453 413-443 413-443

spherul itic spherul i ti c euhedral euhedra 1

1-2 2-3 35 40

50 50,Fig. 1 50,Fig. 13 50

euhedra 1 euhedral

15 30

49,Table 4 49

+91CH 3COONa 443 spherul ites 52,Table 2.2 5-12 +12Na 2C03 (TPA-OH) 443 intergrown dlSks 52,Fig. 5 14 +12Na (TPA-Br) 443 spherulites 5-10 52,Fig. 7 2C03 ---------------------------------------------------------------------------------------------------------------------1 90 2000 +24NaHC0 (Ludox) 443 euhedral 4.5 12-20 52,Table 3,14 443 1 90 2000 +24NaHC0 33 (Cabosil) 4.5 s pherul i tes 2-10 62,Table 3,16

-

-l -1

-J 00

TABLE 11.6 Synthesis of ISM-5 in the presence of different alkali metal cations

Gel composition : ((TPA)ZO)4.5 (Na ZOJ Z8. 8 (MC1)47.1 (A1 Z0 3)1 (SiOZ)96.5 (H ZOJ Z,440 Synthesis temperature (K) :

M

Li Na K

Rb Cs

Average crystal size (from ref. 55, Fig.Z)

1.7 4.5 18 ZZ Z5

((TPA)ZO)3.3 (MZO)Z (A1 Z0 3)1 (SiOZ)50 (H ZO)583

403

(~m)

438

Morphology (from ref. 55,

~igs.

1 and 3)

agglomerates of single crystals spherul ites euhedral, twinned euhedral, twinned euhedral, twinned

Average dimensions (~m) (from ref. 5Z, Table Z) length x width x thickness

7.7 15.9 ZI.4 19.0 ZO.1

x x x x x

4.7 11.3 lZ.7 13.7 14.7

x x x x x

3.9 4.4

5.5 6.6 7.4

79

TABLE II. 7 Parameters influencing the growth and morphology of large crystals in the system ((TPA)20)4 ((NH4)20)38 (M 20)x (A1 203)1 (Si0 2)59 (H 20)750 at 450 K (after ref. 62)

Morphology

x

0.0 0.3 1.0 0.85 0.5 1.5

KLO K20 Na 20 Li20 Li 20

euhedral, twinned euhedral, twinned euhedral, twinned euhedral, twinned lath-shaped, single lath-shaped, single

Size

(~m)

3 5

17 20 40 x 75 30 x 140

The effect ot the crystallization temperature on the crystallization rate and the subsequently obtained morphology has not yet been considered. However, this effect should be obvious: at low temperatures where nucleation and growth are well separated phenomena all the above-mentioned parameters will exert their specific effects well. At high temperatures this is expected to be much less the case; indeed, under such conditions the absence of distinct nucleation and 9rowth causes large misshapen crystals and also new smaller crystals to be formed (ret. 33). This secondary or surface nucleation (which was also found to be dependent on the basicity of the system (refs. 33,36) produces mixtures of crystal sizes with less desirable properties. It has been reported that the additlon of TMA (tetramethylammonium ions) to the gel inhibits this surface nucleation, mainly when high OH/Si0 2 ratios are used (refs. 33,66). This addition of TMA to a typical synthesis mixture at high OH/Si0 2 ratio causes mainly a progressive decrease in the crystallization rate, with the expected consequences for the crystal morphology. Hence, it appears also that TMA has a lower templating power than TPA in the crystallization of ZSM-5, and will therefore act as a structure breaking cation. A method for determining the amount of smaller crystals or the degree of surface nucleation is worth mentioning here (ref. 66). It is based on the following principle : when o-xylene is adsorbed (here at 393 K) on large

80

organics), its uptake is slow and diffusion controlled. When small crystals are present, an initial fast uptake occurs on them, followed by a gradual increase of the sorption. The determination of this initial fast uptake then allows the proportion of smaller crystals to be determined. The addition of triethanolamine to gels of the type (ref. 62) ((TPA)20)4.5 (A1 203)1 (Si0 2)90 (H 20)400 (NaHC0 3)24 results in a decrease in the size of 80 ~m crystals to 25-35 ~m (when 100 parts of triethanolamine are added) or to 10-12 ~m (when 400 parts of triethanolamine are added). The only effect of triethanolamine therefore is to decrease the viscosity or increase the degree of dilution of the initial gel. The same effects are observed when ethanol or acetone is used (ref. 62). The previously mentioned influence of basicity, OH/Si0 2 ratio or pH of the starting gel on the final morphology can be very carefully controlled when the mixture is buffered with phosphate, tartrate, citrate, oxalate, gluconate, salicylate, acetate or carbonate (ref. 89). In this way, pH changes remain constant during crystallization and the secondary effects of all others are excluded. The following morphology can thus be obtained: at pH 10 - 10.5, rod-type large crystals, and at pH 12 - 12.5, spherulitic morphology. At intermediate pH an intermediate morphology can then be obtained (ref. 89). When the amount of gel used is scaled up from 100 g to 3 kg quantities it is our experience that the morphology of the lSM-5 product does not change. A gel was prepared according to recipe 10.c (Part I) and filled either in a small autoclave with a volume of 0.1 dm 3 (Part I, Fig. 1.1) mounted in a furnace and rotating at 50 rpm or in a large autoclave with a volume of 5 dm 3, equipped with a stirrer that rotates at 430 rpm. Crystallization at 423 K in both equipments yielded aggregates of comparable morpho logy (Photograph 11. 3) . A method for deagglomeration of lSM-5 crystallites is worth mentioning here (ref. 122). When after crystallization a basic solution is added it is possible to obtain separated crystals out of the aggregates.

MECHANISM OF lSM-5 SYNTHESIS When the amount of zeolite crystals formed during a crys te l l iz at i on reaction is plotted against the time of crystallization, generally a sigmoid-type curve is obtained (ref. 8) : after an induction period, a phase of accelerated formation of crystals occurs, followed by a decline in deposition of these crystals as the amount of essential nutrients present is

81

PHOTOGRAPH 11.3. SEM of ZSM-5, crystallized in a 5 dm 3 (A) and a 0.1 dm 3 (8) autoclave. gradually exhausted. This type of crystallization may occur following two essentially different mechanisms, in which nucleation occurs either in the gel phase or from solution (refs. 1-10). The succession of events in both mechanisms is shown schematically in Fig. 11.10. Flanigen (ref. 6) suggested that in the synthesis of low-silica zeolites, the crystallization mechanism is controlled by the solution chemistry of aluminate and aluminosilicate species and four- and six-membered rings of aluminosi 1icate tetrahedra, stabi Iized in the presence of mineral alkali metal, appear in the synthesis solution. This nucleation-from-solution mechanism is switched to a nucleation-via-gel mechanism when the amount of alumina is less abundant and when organic base is added to the system. When the concentration of Al is below one per six-ring, five-membered rings are

82

TRANSPORT OF MONOOLIGOMERS IN SOLUTION

GEL REARRANGEMENT

GROWTH crystals

FIGURE 11.10. Schematic representation of zeolite synthesis according to (I) nucleation from solution or (II) in the gel. stabil ized and, depending on the templating effect of the organic base, a particular structure with a high concentration of 5-MRs should crystall ize (ref. 6). An overview of the recent literature that has appeared in this area will show how far this hypothesis predicts reality. In previous sections it was shown that ZSM-5 crystall ization always occurs after an induction period. During this period, it was shown, however, that already small LSM-5 nuclei were formed that showed, because of their small size, an amorphous appearance to X-ray diffraction (ref. 69). These "X-ray amorphous nuclei" were shown to exhibit typical properties of X-ray crystall ine ZSM-5 (ref. 69). Using 29Si and 27Al MAS-NMR, IR, thermal and texture analysis Scholle and co-workers (ref. 120) confirmed the presence of increasing

amounts

of lPA-ZSM-5

comparable to an unit cell

entities

with

dimensions

less

than

at early stages of the crystall ization.

or The

concentration of these nuclei can be followed using the intensity of the lattice vibration at 550 em-I, specific for ZSM-5 zeolite (refs. 69,70). The change in concentration of nuclei and crystals formed during the synthesis procedure described in Part I, paraqrephTn.c , (which gives agglomerates) is shown in Fig. 11.11.

83

100,....---------------~

0~

<,

>-

.1:

50

III

l /)

...>-

I)

0

0 synthesis time / days

FIGURE II.ll. (c) nucleation and (a) growth curves for lSM-5 synthesis (for method, see Part I, lOc). Curve (a) represents X-ray crystallinity and curve (b) the IR crystallinity; the nucleation curve (c) is the difference between (b) and (a). It is clear that just as for any other zeolite crystallization, lSM-5 also

crystallizes according to successive nucleation and growth processes. lhe sudden growth of the zeolite crystals in the presence of tetraalkylammonium ions and alkali metal ions is associated with an increase in pH of the synthesis liquld (ref. 71). This change in pH can be explained as follows (ref. 71) poorly crystalline material formed during the initial crystallization may redissolve, leaving behind a more crystalllne phase. The change in pH of the synthesis mixture with time is therefore a practical method for following the course of the crystallization reaction. The "pH value will also give an indication of the quality of the crystals: higher values are expected to be typical of material with better crystallinity (less or no included gel) and will also be higher for the more stable phases, if zeolites other than lSM-5 appear (ref. 72). These pH changes and the parallel changes in crystal yield have been accounted for in terms of a simple equilibrium model for crystallization of high-silica zeolites (ref. 72). This model uses as dominant parameters the

84

relative solubility of the gel and zeolite phases (denoted by Ksi and Ksf' respectively, ref. 72), the content of quaternary ions (x ) and the sil i ca content (z). The pH change is then (ref. 7Z) (I 1. 7)

where the factor F varies from 1 to 0.05 on going from low to high pH mixtures. The approximate yield of zeolite based on silica (V) is (ref. 7Z) V ;;; 100 11-(fx/z) I

(11.8)

where f is a pH-dependent factor varying between and Z. According to this model, the yield of a synthesis depends mainly on the stoichiometry of the reaction mixture and is a maximum when fx = z

(I1.9)

From the model it also can be derived (ref. 72, Fig. Z) that the yield 9radually decreases when the maximum cation molality increases. Using modified versions of the recipes for l5M-5 synthesis in Part I, we performed a few syntheses to test the effectiveness of such a model. The gel composition was (NaZO)x «TPA)ZO)18 (A1 Z0 3)1 (5iOZ)90 (H ZO)700 and crystallization was effected at 400 K. Fig. I LIZ shows that there is surpri si ngly good agreement between the theoretical values predicted by this simple model and the experimental values. Therefore, the conclusion can be drawn that this model can be used to predict changes in maximum crystallization yield with the basicity of the system. Fegan and Lowe (ref. 73) used the following gel (NaZO)x (TPA-Br)Z (5iOZ)ZO (H ZO)l,OOO to test the validity of their model. Fig. 11.13 shows that there is only good agreement between bpH and the Na fraction in a narrow range. The very strong deviations from the theoretically predicted values at low sodium contents were ascribed to occlusion of Na ions in the bulk of the crystals. At higher contents of Na, a less significant deviation may be the result of Na occlusion in the rim of the crystals (ref. 73).

85

i.o r - - - - - - - - - - - - - - - - - - - - - , 100

o

::c0<1

<, ...,::...

.....

0.75

....

.....

'< ............

........

•

--- --

90

0

~

0-

-, 0~

0.5

0

0.1

0.2

0.3

80

Q /mol kg- 1

FIGURE 11.12. ~pH and changes in yield for a lSM-5 synthesis with the cation (Na + TPA) molality. Q. of the synthesis mixture: The lines correspond to the values predicted by the Lowe theoretical model (ref. 72. Table 1) with K2 = 2 10- 2 mo~ kg-I. (K is the equilibrium constant of (HO)3 Si O- t H+ + 2 (HO)2 Si 02-)'

86

I

I o

Na

~

occlusion in bulk

J:

a.

I I

~Na

\ -, \

occlusion in crystal rim

-1

~

-2

1.0

0.25

Na / (Na +TPA)

FIGURE II.13. "pH changes of zeolite crystallization in an aluminium free Na _ TPA - 5i0 - H system: (a) range predicted by the Lowe model (ref. 72); 20 2 (b) experimental curve (data calculated from ref. 73, Fig. 1).

87

Studies on the mechanism of ZSM-5 synthesis have also been reported by Oerouane and co-workers (refs. 46,47) and by Moretti and co-workers (refs. 38,40). Oerouane et al. (ret. 46) proved that the predictions made by Flanigen(ref.6) were not entirely true, as they were able to synthesize ZSM-5 according to either the solution method (their method A) or the gel nucleation method (their method B), 'depending mainly on the relative concentrat icns of the reactants and the nature of the sil ica source. The arguments developed by these workers (refs. 46,47) can be summarized as follows: 1.

The compositions of the synthesis gels used differ in - the silica source (A, highly polymeric and B, highly monomeric); the amounts of water, silica and TPA relative to alumina (A) ((TPA)2 0)7.2 (Na 20)1 (A1 203)1 (Si0 2)24.2 (H 20)410 (B) ((TPA)2 0)4.6 (Na zO)32.3 (A1 203)1 (Si0 2)gO.2 (H 20)4,020 (see Experimental and Table I in ref. 47); - sulphate ions are present in the system in method B, so that its overall basicity is lowest (OH/Si0 2 = 0.20 compared with 0.68 for method A). Several of these differences cause opposite effects so that it is difficult to predict, a priori, crystallization rate and crystal size - from the nature of the silica source, fastest crystallization and smaller crystals are expected with method B; - from the differences in alkalinity and TPA content of the system (highest for A), fastest crystallization and smaller crystals are expected for A; - from the Si/Al content, the crystalllzation of B is expected to be faster; - the effect of foreign anions (SO~in B) is not known.

2.

X-ray diffraction indicates fastest crystallization for method B and the concomitant formation of smaller crystals. This fact shows that from the parameters enumerateq in paragraph I, the nature ot the silica source or its depolymerization rate and the Si/Al ratio are of major importance. In method A, depolymerization is slow, which would point to the occurrence of a solution transport mechanism; in method B, much less depolymerization of silica has to occur and the formation of a homogeneous hydrogel should be rapid as well as extensive nucleation in the gel.

88 3.

The

chemical

analysis

of

the

Si/Al

ratio

of

the

solids

during

crystallization is clarifying: this ratio remains constant for method B but gradually decreases in the method A. As incorporation of Al is known to be disruptive, crystall ization A cannot occur in the gel; crystal growth occurs using a small number of nuclei, the Si/A'I ratio of which continuously decreases as their size increases and has necessarily to occur via transport in solution. 4.

The variation of the TPA content of the sol ids during crystall ization followed

by thermal

analysis varies

i

n parallel

with the aluminium

content. 5.

Surveying the crystall ization process by scanning electron microscopy shows that for method A the disappearance of the gel and the appearance of the crystalline phase occur gradually, whereas with method B crystals appear only when the gel

phase has disappeared comoletely. This again

points to solution or gel nucleation in methods A and B, respectively. 6.

The measurements of changes in the Si/Al ratio of the crys t al s using various penetration depths of the me asur i no technique or using bulk analysis constitute the final arguments: bulk analysis was made by PIGE (proton-induced gamma ray emission),

surface analysis by XPS

(X-ray

photoelectron spectroscopy) (1-2 um depth) and outer rim analysis by EDX (energy-dispersive X-ray analysis with a penetration depth of 8-10 ~m). In method B, the Al content at various penetration depths hardly changes with the degree of crystallinity, whereas during an A-type synthesis they all grow in a parallel way. As a result, method B produces crystals and

nuclei

that

retain

the

same

composition

throughout

the

whole

process. This is once more consistent with direct nucleation in

the

hydrogel. Summarizing, methods A and B constitute distinct ways of synthesizing ZSM-5 via a solution or gel nucleation mechanism, respectively. It seems that a high basicity and/or the presence of foreign ions in the synthesis mixture and also the polymerlc nature of the silica source and the Si/Al ratio of the gel

direct the reaction to solution nucleation, and that TPA content and

degree of dil ut i on are 1ess

important as

determi ni ng pa rameters for the

nucleation mechanism. lhe effect of high alkalinity is consistent with the commonly encountered solution nucleation mechanism for the synthesis of lowsil ica zeol t tes . Indeed, low-sil ica zeol ites are generally synthesized at

89 higher al kal inity (OH/Si0

of the synthesis mixture and their crystal 1iza2) tion occurs predominantly via solution nucleation (refs. 1,2,5,6, 74). A special type of ZSM-5 synthesis, using a reduced amount of water, was reported by Moretti and co-workers (refs. 38-40). It consists of impregnating all reactants into the pores of a high surface area sil ica gel

in the molar

ratios ((TPA)20)3.3 (Na 20)3.6 (A1 203)1 (Si0 2)24 (H20)180 with an OH/Si0 2 ra t i 0 of 0.22 (ref. 38). When these data are compared with the work of Derouane and co-workers (refs. 46,47) a gel expected as far as the OH/Si0

nucleation mechanism would be

ratio is concerned (this ratio is equal to

2 that used in method B). When the nature of the silica, which

is highly

polymeric, and the Si/Al ratio, which is the same as that in method A, are considered

a

solution-phase

nucleation

would

crystallite morphology was reported (refs.

be

expected.

38-40), which

solution nucleation. At the low alkalinity used,

A euhedral

is expected for

the depolymerization of

silica will still be lower than that in method A. Indeed, at decreasing pH in the

range

pH

exponentially

12-10, with

the

the

solubil ity

pH

(ref.

75).

of

amorphous

We

agree,

sil ica

decreases

therefore,

conclusion (refs. 38-40) that the synthesis mechanism is most

with

the

probably a

solution nucleation, even in such a concentrated system. However, a new aspect to zeol ite synthesis is provided by other data advanced by the same workers. Indeed, based on Fi g. II. 14, whi ch represents data from Padovan et al. concluded

that

structure

is

initially formed,

(ref. and

which

40)

very then

plotted quickly

in a different way, an

gradually

it

is

type

of

starts

to

alumina-free MFI redissolves

and

incorporate aluminium in its framework. The cation balance (both Na/Al crystalline

materials

decreases

(TPA + Na)/Al

and

linearly

with

the

ratios)

square

for 100%

root

of

the

reorganization time. The (TPA + Na)/Al ratio more particularly comes close to its

theoretical

value

of

unity

at

long

equilibration

times.

This

is

indicative of diffusional processes, causing rearrangements of the crystals. At short equilibration times, such a material (after the proper activation) shows no activity for acid catalysis, whereas after prolonged equllibration these materials become very active. This

definitely

indicates

incorporation of aluminium in

that

a

diffusion

the framework.

process

involves

the

It confirms the previously

developed ideas about the disruptive nature of aluminium incorporation. This hypothesis

was

further

confirmed

using

a

two-stage

synthesis

an

aluminium-free MFI type of structure was flrst prepared in the absence of any

90

t5.....~---------------

......

«

'to CU

z

0.5 2.0 CO

o

to

10

15

20

Vt/h FIGURE 11.14. A square root-time diffusion plot of the change in the cation balance (CB) and the NatAl ratio of 100% crystalline materials. The graphs were obtained by replotting some data from ref. 40, Table 1. aluminium. To these crystals were then added NaOH + TPAOH + NaA10 2 + H20 and, according to the increase in catalytic activity of the so treated and properly activated samples, incorporation of aluminium seemed to have occurred. Following these data, we want to modify the solution-phase nucleation mechanism as depicted in Fig. 11.15.

I

solution nucleation

silica alumina gel

--l.

I

partial redissolution and AI incorporation

AI-free nuclei

..l...

AI-containing crystals

FIGURE 11.15. Solution-phase nucleation mechanism of ZSM-5.

91

THE REPARTITION OF ALUMINIUM THROUGHOUT THE Z5M-5 CRYSTAL von Ballmoos and Meier (ref. 76) were the first to report that in large crystals of Z5M-5 "zoning" of aluminium existed : electron microprobe analysis showed that a significant decrease in aluminium concentration occurred on moving from the crystal rim to the inner core. Ihe presence of these gradients has been related to the nature of the synthesis mechanism. It was assumed (refs. 76,77) that in their synthesis method nucleation from solution occurred : all aluminium present in the mixture is contained in the aluminosilicate gel; fault-free and silicon-rich MFI is then nucleated in solution; the gel dissolves gradually when the solution becomes depleted in silica and more and more aluminium is incorporated, which is found back rn the rim of the zeolite crystallites. Irregularities in the Al gradients have been reported for Al-rich syntheses and were associated with the existence of crystal domain boundaries. Possibly, at the boundaries of intergrowing crystals either amorphous Al-rich gel is included or crystal boundaries just occur when the Al concentration in the zeol ite lattice shows a strong variation. In terms of the previously developed concepts, it is logical to assume that the Von Ballmoos method of zeolite synthesis (ref. 26) is a method of solution nucleation. Indeed, a typical composition of a gel is (ref. 76) (TPA)20)72 (Na 20)2 (A1 203)1 (5i0 2)22 (H 20)6,600 using TPAOH, NaOH, Al(N0 3)3 and silicic acid (ref. 26) as reactants. Although the OH/5i0 2 ratio is very high, the overall basicity is very low, because of the high degree of dilution, and the silica source is of a highly polymeric nature. In more recent work, surface and bulk chemical compositions determined by various physical techniques have been reported (refs. 46,47,78-88). From this work, there is at least one general conclusion that is obvious : the decl i ne inA1 concentrati on from the rim to the core of a Z5M-5 crysta 1 is not of a general occurrence. Indeed, not only constant Al concentrations throughout the Z5M-5 crystals seem to exist, but even increases in Al content from the rim to the core of the zeol ites have been reported. Four typical types of Al profiles encountered in the literature are shown schematically in Fig. 11.16. In reality, these protiles may exist in a much more pronounced form inso far that depletion (type I) and surface enrichment (type II) with aluminium is very striking (ref. 119). A survey of most literature data is given in Table 11.8. It follows that the type I gradient occurs only when highly polymeric sil ica is used as the major reactant, when the crystal size is relatively large and when a solution nucleation has either been proved (refs. 46,47) or suggested (refs. 76,77).

92

FIGURE 11.16. Typical Al profiles in ZSM-5 zeolites.

93

It should be noted that in order to assign a solution nucleation mechanism to a particular synthesis, the existence of a type I gradient is the major argument. The occurrence of a type IV gradient has been associated with a crystallization process via gel nucleation. It occurs when monomeric silica sources are used and/or relatively high bulk Si/A1 The type

II

gradient,

which

represents

ratios exist in the gel. 2 surface depletion in aluminium,

possibly corresponds to a gel nucleation mechanism in which amorphous AI-rich species

are occluded

initially

(refs.

82,84).

The type

III

gradient is

interpreted as being the result of a third growing mechanism (ref. 84) : silicon rich moieties start to nucleate (probably via a solution nucleation mechanism),

rejecting

the

incorporation

of aluminium.

When

the

silicate

concentration in solution becomes depleted, a phase richer in aluminium may grow epitaxically on the surface of the silica-rich crystals. This effect may be amplified when alumina-rich amorphous gel is incorporated in the growing crystal. These data further show that : i. The kind of gradient may switch from one type to another using a single synthesis method, just by increasing the Al content (Nos.

3

and 4, Table 11.8). i i. As the nuc l eati on mechani sm determi nes also

the

average

crystals and gel

crystal

Slze

the a1umini um gradi ent and

(solution

nucleation

gives

large

nucleation smaller crystals (refs. 46,47), large

crystals without an aluminium gradient will

be very difficult to

obtain. Apparently, one exception to this general rule can be found in Table 11.8 (No.8). However, as

in this particular instance a

surface technique with lower resol uti on (Auger spectroscopy)

has

been used (ref. 82) to probe the gradient, it may be worthwhile to check whether (and why) thi s method can produce 1arge homogeneous crystals. iii. The factors determining the nucleation mechanism are the nature of the silica source, the basicity and the aluminium content of the synthesis mixture. They constitute as many parameters as can be used for the design of a given Al profile in a given lSM-5 morphology. When it is assumed that in a synthesis with TPA the maximum Al content of an MFI type of structure is five Al atoms per unit cell (ref. 26) (Si0

2/A1203

~

38), the relative changes in

94

the Al concentration across certain crystals may be as high as 30 or 50% for type III (ref. 84) and type I profiles (ref. 76), respectively. For type II profiles, relative changes as high as 200% seem to exist (ref. 83), which indicates that a substantial part of amorphous alumina is indeed incorporated in such crystals. Another approach to the manipulation of Al gradients consists in a mUlti-step synthesis method (ref. 96), which produces layered crystals as far as composition is concerned but single crystals with regard to structure and morphology of the crystalline phase. This can be achieved in the following ways 1.

Classical crystallization in a first step, which produces small crystals (0.2-0.6 ~m) with a given silica/alumina ratio. Growing of these crystals to 1 um then occurs in a second step in the absence of aluminium, avoiding secondary nucleation. This is realized when ln the second step (ref. 96, ex. 1). the TPA/Si0 2 ratio is kept very low (O.O~)

2.

A classical crystallization (with an Si/A1 2 ratio of 90) is stopped half way and only after addition of an aluminium complexant is it allowed to go to completion. The overall Si/A1 2 ratio of this material is 131 (ref. 96, ex. 3).

3.

Seeds of ISM-5 (Si/A12 ratio = 72) are added to an aluminium-free gel containing low TPA/Si0 2 ratios and a tartrate complexant. The overall Si/A1 2 ratio of the product is 148 (ref. 96, ex. 6).

The preparation of such layered ISM-5 single crystals with an Al-rich core and an Al-free outer rim should be extremely useful in catalytic reactions where the selectivity is determined by differences in the diffusional rates of the products.

TABLE 11.8 Survey of literature data relating to Al profiles in ZSM-5 zeolites

No.

Nature of silica source

OH/Si0 2 ratio

Crystal morphology

Size (IJm)

Sil icic aci
High but large dilution

Euhedral twinned

60-200

22

I

76,77

2

Polymeric (method A)

High

Intergrown disks

5-8

24

I

46,47

3

Ludox (01 igomeric)

0.13 (low)

Single

2.2

80

III

83,84

4

Ludox (01igomeric)

0.13

Aggregates

0.3

18

5

Water glass (monomeric)

Low (pH 10-11)

Aggregates

5

6

Water glass (method B)

Low

Aggregates

7

Water glass

Low

Small

8

Ludox

Low

Large rods

9

Ludox

High

Small

a. see Fig. 11.16

Bulk Si/A12 ratio

Type of Al gradien't a

II and IV

Ref.

83,84

20-200

II

82

0.1-1

90

IV

46,47

0.1-0.3

36

IV

85-87

8-20

-

IV

78

-

-

IV

88 t{)

on

96

SYNTHESIS OF lSM-5 FROM REACTIVE MIXTURES PREPARED WITH UNUSUAL REACTANTS A lSM-5 type aluminosilicate crystallized from a mixture of two different colloids and containing fluorine has the following pecul iarities (ref. 91) : when the final synthesis mixture is prepared by laminar-flow mixing of a classical gel (containing TPA, alkali metal, silica and alumina) and a sil ica sol, so that the overall TPA/Si0 ratio is relatively small, the 2 as if the TPA/Si0 ratio of the gel were rate 2 determining. Possibly the special mixing technique of the two colloids avoids intense interpenetration and consequently zeol ite nucleation occurs in the initial gel. On addition of a neutral fluoride source (NaF, NH to this 4F) mixture, larger crystal s grow out of this gel. In the 1ight of previous crystallization occurs

considerations, the effect of F- 1S not unexpected, but as mentioned earlier is not understood at present. As was found earlier for low-silica zeolites (ref. 9L), lSM-5 can also be

synthes i zed

from

reactive

substrates

other

than

TPA-conta i ni ng

aluminos1 licate gels. Clays, and more particularly acid-leached and thermally activated kaolinite (which thus treated becomes metakaolin) and other zeolites, can be used for this purpose. Two approaches have been reported 1.

2.

Raw kaolin was added to a classical gel conta irri nq TPA, Na, SiO and L water. When the ratio of the silica sources from the clay and the gel was close to 1, a 70% crystalline ZSM-5 was obtained after 72 h at 422 K (ref. 93, ex. 10). Kaolin was tirst transformed into metakaolin by heating at 1143 K. The metakaol in, on refluxing in concentrated HC1, was then transformed. into a silica-alumina with an Si0 molar ratio of 29. This material was 2/A1 203 then transformed into highly crystall ine ZSM-5 in the usual way after addition of H TPA-OH and NaOH (ref. 94). In a similar way to that 20, described for raw kaolin, zeolites NaX, NaY, mordenite and ferrierite can also be transformed i nto ZS~1-5 (ref. 95) . Morden i te and clinoptilolite, which are resistant against treatment with mineral acid, can first be dealuminated until an appropriate Si/Al ratio is reached and then transformed into ZSM-5 without further add i ti on of any other source of silica (ref. 15).

97

FORMING OF lSM-5 CRYSTALS Before

a

zeolite

sample

can

be

used

in

a

chemical

reactor or

adsorption column, the powder must be given a suitable physical

an

form with

sufficient resistance against abrasion with the reactor wall, attrition of the particles with one another and erosion by the reactants. For fluidized bed appl ications particle sizes of 50 - 500 IJm are convenient, so that the large crystals prepared as described earlier (refs. 50,61) can be used as such in a fluid-bed reactor, provided they have sufficient physical strength. For liquid phase and slurry applications, zeolite powder may also be used as such; there is only a lower limit as to the minimum crystal size, which is determined by filtrability considerations, and usually this limit is below 1 IJm. For

appl ications

in

fixed-bed

reactors

and

in

order

to

avo id

intraparticular diffusion becoming slow, laminar flows should exist in such a reactor. In order to achieve this, the ratio of reactor to catalyst particle diameter should be in the range 6-10 (ref. 97), so that, depending on the exact reactor diameter, which

is determined by the exotherrnicity of the

chemical reaction, catalyst particles in the range 1-5 mrn are requlred, with sufficient physical stability. In the particular case of lSM-5 based catalysts, these particles can be made in the following ways:

1.

By

classical

extrudation

on

addition

of

hydroxymethylcellulose and 5% of tetraorthomethyl

water,

2.5%

of

silicate to a lSM-5

zeolite, a high-viscosity paste is obtained that can be extruded as 4 x 10 mm cylinders. After drying and calcination at 773 K, these extrudates have a high resistance to crushing (they resist pressures of 340 N) and a high macroporosity (50%) (ref. 98). 2.

Using a special type of extrusion die, it has also been reported that lSM-5

can

be

extruded

as

hol low-shaped

extrudates

(ref.

99).

Such

particles in a chemical reactor present a much lower physical resistance to the reactants

and

a 11ow longer col umns to

be fill ed

before the

pressure drop along the catalyst bed becomes too high. The following components were added subsequently to Na-lSM-5

(i n wei ght-%) and the

final mixture was extruded (ref. 99) : Na-lSM-5, 36.3%

containing 87.6%

of solids; a-alumina (monohydrate), 23.1% cont.a i n i nq 74.4% of solids; cellulose extrusion aid, 1.0%; and water, 39.6%. With a hydraulic press and

a

die

plate with

a

certain orifice,

extrudates with

different

98 physical

forms

and

after

drying

and

calcination

with

sufflcient

resistance against crushing forces, and with sufficient porosity could be obtained. Pertinent data are given in Table 11.9. 3.

Contacti ng a preformed precursor with the essenti a1 components for a ZSM-5 synthesis. This preformed precursor was the following: - An extrudate of 2.3 mm diameter of metakaolin and sodium silicate (ref. ~3,

ex. 9); to this was added TPA, Na and water so as to obtain a

suitable

composition

tor

ZSM-5

synthesis;

this

mixture

converted into a 60 weight % crystalline product with

could

the

be

initial

physical shape, which after drying and calcination showed sufficient crushing strength. - A silica

carrier (3 x 5 mm cylinders) {ref. 100, ex. 1); this precursor

was impregnated first with the Al- and Na-containing reactants, dried and impregnated agai n with TPA and tri sodi umphosphate. Thi s material could also

be

converted

into ZSM-5

containing cylinders with

good

crysta 11i nity. - An amorphous silica-alumina formed catalyst of !J mm diameter with an Si/A1

ratio of 100 (ref. 101, ex. 1); to this was added a solution of 2 (Na + TPA)OH; this material could also be converted into a crystalline

ZSM-5 type material

without loss of its

strength; the final material had an Si/A1 the composition of the initial catalyst.

2

initial

physical

form

and

ratio of 134, very close to

99

TABLE 11.9 Comparative crushing strengths of extrudates (force in kg/cm 3 at which the extrudates break) for various forms of ZSM-5 based extrudates (derived from ref. 99)

QU ~ d (mm)

o (mm) length (mm) crushing strength (kg/cm 3) particle density in extrudate (g/ml) source

A~

0.99 3.2 7.05 50.4

0.7-1.0 3.2 6.6 268

0.12-0.72 3.2

0.72-1.02 3.2

223

141

0.84 Table 3

0.85 Table

0.86 Table 2

0.86 Table 2

1.02 3.2 3.34 6.78 642 III

0.86 0.85 Table 4

It should be stressed that the methods are difterent from those reported earl ier in which the impregnation is carried out on a non-preformed sil ica carrier. This carrier immediately loses its porous structure and crystallization via solution nucleation seems to occur. When preformed carriers are used, however, they keep their physical form, provided that the crystallization progresses slowly enough and is interrupted in time. Indeed, the crystallization is slow and requires at least 10 days. At present one can only speculate about the nature of such a product. All characteristics of the reaction mixture (ref.101, ex. 1) : i. ii. iii. iiii.

TPA/Si0 2 = 0.06, very low and thus slow nucleation; OH/SiO z = 0.06, also very low and thus slow silica depolymerization; polymeric silica source and low crystalllzation temperature; Si/A1 2 is high (= 101)

point to a solution-phase nucleation, the subsequent formation of large crystals and the presence of type I Al gradients. Possibly these crystals are glued together chemically by an unaltered residue of catalyst carrier, the

100 presence of which causes the retention of the original physical form. It is obvious that more work is required in order to obtain a clear picture of this interesting material.

USE OF SEEDS When a crystallization is directed using seed crystals, several effects may be

depending on the amount of crystals added and their Si/A1

obtai~ed,

2

ratio: i. When relatively large amounts of seeds are used, multi-step synthesis of lSM-5 may be performed (strictly, and in crystallographic terms, this is not a case of true seeding).

In this way,

zeolite crystals with an

Al-ri ch core may be obta i ned when the seeds are ri ch ina1uminum and when an overlayer of silica with the same structure is crystalllzed on top of it (ref. 96). Conversely, lSM-5 crystals may be formed with an aluminium-free core and aluminium-rich rim (refs. 103-106). It is clear that

both

groups

applications.

The

of

materials

first

group

may will

find

interesting

increase

the

catalytic

shape-selective

properties of reactions in which diffusion of the products out of the crystals is rate determining. The second group of materials will have just the opposite effect. The synthesis of such materials

requt res , of course,

that secondary

nucleatlon is absent. This can be realized when the synthesis is carried out at low TPA/Si0

ratios. The sumnary of data given in Table 11.10 2 shows that this is true in most instances (Nos. 1-4); the No.2 set of

data seems to be an exception in this respect; considering our previous discussions,

it

is

secondary nucleation

doubtful

whether

at

a

TPA/Si0

is absent and whether the

ratio of 0.75 2 claimed material is

present in excess. i i. True seeding occurs when only small amounts of seeds are added to a synthesis mixture: silica ratios in seed to gel are below 0.04 (Table 11.10). These data further show that when seeds are used, ZSM-5 crystal growth is easily effected in the absence of TPA+ cations. As under such conditions

ZSM-5

nucleation

will

be

very

difficult,

it

seems

less

probable that surface nucleation occurs. Possibly only crystal growth occurs,

indicating

that

the

discussed

effect

of

templation

or

101

clathration with TPA further crystal

is

important

only

for

nucleation

and

not

for

growth. Such ZSM-5 material s do not contain any TPA,

which tightly fits in the zeolite pores and requires high calcination temperatures for its removal.

When the synthesis is carried out at high

basicity (relatively high OH/SiOZ and low HZO/SiO Z ratios, e.g., No.6 in Table I I .10), the crystal growth and dissolution rates should be comparable and consequently relatively small crystals are found. Given, however, the small amount of seeds, the small increase in size and the high crystallization yields obtained, it has to be concluded that under such

conditions

TPA should

occur

separate on

top

surface of

the

nucleation crystal

of

seeds.

ZSM-5 fhis

free

allows

from us

to

anticipate and to conclude that possibly under very specific conditions the MFI structure can also be synthesized in the absence of TPA and of any organic material. The addition of other organic molecules such as acetone and methyl ethyl ketone seems to inhibit extensive gelation of the reactlon mixture (ref. 109) and to suppress the nucleation of other phases, e.g., quartz (ref.l09). It is also worth mentioning here that a TPA-free mixture in which no

aluminium is present, on true seeding always fails to crystallize as ZSM-5

(ret . 109). With Si/A1 Z ratios in the range 50-ZOO, a ZSM-5 zeolite is obtained, the aluminium content of which is governed by that of the gel. Apparently, in absence of any aluminium the synthesis of ZSM-5 seems to obey other laws.

(5

TABLE 11.10 Overview of data available on seeding for lSM-5 crystallization

No. Ref.

1 106, ex.1

2 105

""

3 96, ex.1

4 107, ex.2

5 108, ex.1

6 ex.5

7 110, ex.5

108,

8 109 b

Si0 2 in seed/ 1.5 Si0 2 in gel ratio

5.0 a

0.50

0.33

0.04

U.U5

0.05

0.005

TPA/Si0 2 ratio

U.04

0.75

0.05

0

0

0

0

OH/Si0 2 ratio

0.77

?

0.27

O./tl

0.18

°0.21

0.22

0.30

H20/Si0 2 ratio Silica source

7

34

44

42

17.tl

8.98

41.2

46

-

Ludox

Sodium sil icate

Sil i ca sol

Colloidal Precipitated Precipitated Sodium silica silicate s il i ca s il i ca

0.5

?

0.2-0.6

't

0.02-0.05

0.02-0.05

?

U.19

Size of crystals 10

?

1

?

0.1-0.2

0.02-0.1

?

2.5

No organic in zeolite

No organic in zeolite

Size of seeds (lAm) (um)

Specificity of product

Al-rich rim, Si-rich core

Al-rich rim

AI-rich core

Al-rich rim

?

a, zeollte/Si0 2 in gel(g/g); b, ln the presence of acetone tacetone/Si02 molar ratio

= 1.3)

No organic in zeolite

Na organic in zeal ite

103

THE ZSM-5-SILICALITE DISPUTE From preceding materials that have unique material materials differing aspects :

discussions, it follows that there are a whole variety of the MFI structure and consequently ZSM-5 zeolite is not a whole family of crystalline but contains a from each other by one or several of the following

i. the Si/Al and/or AliNa ratio of the framework; ii. the nature of the Al gradient and consequently of the accompanying . Na + or H+ gradlents across the crystal; iii. the crystal morphology; iiii. the existence ot multi-layered materials the presence of overlayers of AI-rich ZSM-5 on top of ZSM-5 devoid of Al or vice versa. It is obvious that an MFI structure obtained in the ((TPA)20)x (Na 20)y (Si0 2)z (H 20)n system will belong to the same family of materials. However, looking chronologically how knowledge in this area came to the scientific and industrial community, the following remarks seem pertinent to us : 1.

The discovery of the M~I type of researchers at the Mobil Oil Company;

structure

is

an invention of

2.

In the first patent on this material (ret. 25), it was thought that ZSM-5 can be prepared with various Si/Al ratios in its matrix, but it was not explicitly stated that the material obtained when no additional a1umi ni urn is added to the synthes i s mi xture belongs to th i s family of materials;

3.

A patent was then granted to researchers at Union Carbide Corporation for a material denoted as "sillcalite" (ref. Ill) and synthesized without addition of aluminium in a mixture of an aforementioned composition. Such a material is free of aluminium if the reactants are pure.

In 1982, Mobil Oil considered silicalite to be an infringement of its ZSM-5 patent (ref. 112). Scientifically speaking, and llmiting ourselves for the moment to the synthesis aspects of this debate, the following points are striking and important as far as the difference between ZSM-5 and silicalite

104

is concerned i . Incorporation of aluminium into the MFI structure is a difficult and disruptive process; there lS even evidence now that at least for a solution nucleation mechanism silicalite is first nucleated, then dissolves partially and recrystallizes as ZSM-5 (ref. 40); ii. The dominant feature of silicalite crystallization in an (Na, TPA)20 Si0 2-H 20 system is base occlusion (ref.13). The charge neutralized by these cations can be occluded OH- or broken siloxane groups in the silicalite structure. Although this has not been investigated in detail, general chemistry tells us that both should be in equilibrium and consequently that "true" sil ical ite might have cation-exchange properties despite the complete absence of aluminium. (In our terminology, silicalite is a material with the MFI structure that is synthesized from extremely pure reactants and that is therefore devoid of any contamination with aluminium.) These two points possibly suggest that true silicalite has to be considered as a phase different from the ZSM-5 phase. The silicalite phase is then zeolitic and not merely a crystalline silica polymorph as it may have ion-exchange properties of a totally different nature from that found in zeolites in general, associated with lattice aluminium. It was demonstrated, however, that ZSM-5 has also ion exchange capacity that is in excess of the framework Al content (ref. 121). This aluminium-independent exchange phenomenon was attributed to framework SiO- groups formed during the synthes i s as counterions for the quaternary cations. The contribution of Al-independent cation exchange increases with increasing Si0 2/A1 203 ratio of the framework what could be understood if Al occupies the same sites as the SiO- groups that give rise to AI-independent exchange. It should be stressed, however, that an early patent assigned to Mobil Oil described the preparation of crystalline metal organosi licates (ref. 113) with an X-ray diffractogram identical with that of ZSM-5. Afterwards, several others obtained patents for analogous materials. Pertinent data on the manner of the synthesis of these materials are collected in Table II.ll. They are either crystallized at low temperatures or for short times at higher temperatures, which seems to be a general feature of aluminium-free synthesis mixtures. Table 11.11 also shows that synthesis may occur in the absence of sodium, which also was found for Al-containing mixtures (see above). As these materials are defined by their X-ray diffractograms (XRDs), the respective XRDs for these silica polymorphs are compared in Fig. 11.11.

105

TABLE II.11 Synthesis of silicalite-type materials Sample

Molar composition of gel (TPA)20 Na 20 Si0 2 H20 OH/Si0 2

A

1. 61

B

6.20 0.22

C 0

3.2 38.4 6.5 46.0

213 413 96 760

0.50 0.27 0.24 0.04

Synthesis tempera- time ture (K) (days)

373 373 423 433

Ref.

113,ex. 3 1I4,ex. 3 115,ex. 16 116,ex. 1

6 3 2 0.17

D

c

B

A

vs 5

2

4

6

10

8 d / nm x10

FIGURE 11.17. Comparison of the most intense silicalite-type materials (see Table 11.11).

XKD

peaks

in

different

106

In every instance, the d-values of typical peaks are the same within experimental error. For some materials, splitting of some bands occurs, which indicates that the structure is monocl inic rather than orthorhombic. This feature has also been reported for ZSM-~ (ref. 117) and will be discussed in Chapter IV. Also, the relative intensities of some peaks are different. As shown also for ZSM-5 (ref. 55), orientation effects of crystals (mainly when they are relatively large) may cause these apparent discrepancies.

107

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.

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108

26. R. Von Ballmoos, "The 180-Exchange method in Zeol ite Chemistry" Salle and Sauerlander, Frankfurt am Main, 1981, p. 83. 27. A. Erdem and L.B. Sand, J. Catalysis QQ (1979) 241. 28. A. Erdem and L.B. Sand, Proceed. 5th Int. Conf. Zeolites, L.V. Rees, ed., Heyden, London, 1980, p. 64. 29. Ref. 26 p. 75 30. Ref. 26 p. 95 31. V. l.ec l uze and L.B. Sand, Rec. Progr. Rep. Vth Int. Conf. Zeolites, Giannini, Napoli (1980) p. 41. 32. L.D. Rollmann and E.W. Valyocsik, E.P. 21,674 (1981), assigned to Mobil

Oil. 33. L.D. Rollmann and E.W. Valyocsik, E.P. 21,675 (1981), assigned to Mobil Oi l. 34. L.D. Rollmann, "Zeolites: Science and Technology", F.R. Ribeiro, A.E. Rodrigues, L.D. Ro 11 mann and C. Naccache, eds., M. Ni j hoff, Den Haag, (1984) p. 109. 35. V.N. Romannikov, V.M. Mastikhin, S. Hocevar and B. Drzaj, Zeolites 3 (1983) 311. 36. K.J. Chao, T.S. Tasi, M.S. Chen, I. Wang, J.C.S. Faraday I 3 (1981) 547 .. 37. K.J. Chao, Proceed. Nat. Sci. Counc. ROC, l (1979) 233. 38. E. Moretti, G. Leofanti, M. Padovan, M. Solari, G. De Alberti and F. Gatti, Proceed. 8th Int. Congr. Catalysis, Dechema, Frankfurt, (1984), IV p. 713. 39. E. Moretti, G. Leofanti, M. Padovan, M. Solari, G. De Alberti and F. Gatti, Stud. in Surf. Sci. and Catalysis ~ (1984) 159. 40. M. Padovan, O. Leofanti, M. Solari and E. Moretti, Zeolites ~ (1984) 295. 41. E.M. Flanigen, J.M. Bennett, R.W. Grose, J.P. Cohen, R.L. Patton, R.M. Kirchner and J.V. Smith, Nature ~ (1978) 512. 42. L.D. Rollmann, "Inorganic Compounds with Unusual Properties", R.B. King, ed., A.C.S., Washington, 1979, II p. 387. 43. L.D. Rollmann, Adv. Chern. Ser. lLl (1979) 387. 44. Ref. 26 p. 80. 45. L.D. Rollmann and E.W. Valyocsik, Inorg. Synthesis ~ (1982) 61. 46. E.G. Derouane, S. Detremmerie, Z. Gabelica and N. Blom, Appl. Catalysis 1. (1981) 201. 47. Z. Gabelica and E.G. Derouane, A.C.S. Symp. Ser. 248 (1984) 219. 48. S. Ueda, T. Sera, Y. Suzuki, M. Koizumi and S. Takahashi, Nendo Kagaku 1l (1983) 45. 49. R. Mostowicz and L.B. Sand, Zeolites £ (1982) 143. 50. M. Ghamami and L.B. Sand, Zeolites l (1983) 155.

109

51. R. Aiello, A. Nastro and C. Colella, Proceed. l e Convegno A.S.M.!. Milano, 1983. 52. A. Nastro, Z. Gabelica, P. Bodart and J.B. Nagy, Catalysis on the Energy Scene, S. Kaliaguine and A. Mahay, eds., Elsevier, Amsterdam, New York, 1984, p. 131. 53. A. Nastro, R. Aiello and C. Colel la, Ann. Chim. Zi (1984) 579. 54. Z. Gabelica, N. Blom and E.G. Derouane, Appl. Catalysis 2 (1983) 227. 55. A. Nastro and L.B. Sand, Zeolites l (1983) 57. 56. E.M. Flanigen, Pure Appl. Chem. ~ (1980) 2191. 57. D.M. Bibby, N.B. Milestone and L.P. Aldridge, Nature 285 (1980) 30. ~8. R.M. Barrer and R.J. Denny, J. C. S. (1961) 971. 59. H. Nakamoto and H. Takahashi, Chem. Lett. (1981) 1739. 60. Ref. 4 p. 155. 61. L. Fiilth and U. Hakansson, Rec. Progr. Rep. Vth Int. Conf. Zeolites, Giannini, Napol i (1980) p. 37. 62. R. Mostowicz and L.B. Sand, Zeolites l (1983) 221. 63. B.P. Pelrine, U.S.P. 4,100,262 (1978), assigned to Mobil Oil. 64. S.B. Kulkarni, V.P. Shiralkar, A.N. Kotasthane, R.B. Borade and P. Ratnasamy, Zeolites ~ (1982) 313. 65. L.D. Rollmann, U.S.P. 4,296,083 (1981), assigned to Mobil Oil. 66. D.H. Olson, L.D. Rollmann and E.W. Valyocsik, E.P. 26,962 (1981), assigned to Mobil Oil. 67. D.H. Olson and E.W. Valyocsik, E.P. 26,963 (1981), assigned to Mobil Oil. 68. R.B. Calvert and L.D. Rollmann, E.P. 101,183 (1981), assigned to Mobil Oi 1. 69. P.A. Jacobs, E.G. Derouane and J. Weitkamp, J.C.S. Chem. Cornm. (1981) 591. 70. G. Coudurier, C. Naccache and J.C. Vedrine, J.C.S. Chem. Comm. (1982) 1413. 71. J.L. Casci and B.M. Lowe, Zeolites l (1983) 186. 72. B.M. Lowe, Zeolites l (1983) 200. 73. S.G. Fegan and B.M. Lowe, J.C.S. Chem. Comm. (1984) 437. 74. B.D. Menicol, G.T. Pott, R.K. Loos and N. Mulder, Adv. Chem, Ser. 121 (1973) 152. 75. K.B. Krauskogh, Geochim. Cosmochim. Acta 1Q (1956) 1. 76. R. Von Ballmoos and W.M. Meier, Nature 289 (1981) 782. 77. R. Von Ballmoos, R. Gubser and W.M. Meier, Proceed. VIth Int. Conf. Zeolites, D. Olson and A. Bisio, eds., Butterworths, Guildford, 1984, 803. 78. S.L. Suib, G.D. stucky and R.J. Blattner, J. Catalysis 65 (1980) 174.

110

79. H.J. Doelle, J. Heering, L. Riekert and L. Marosi, J. Catalysis 71 (1981) 27. 80. E.G. Derouane, J.P. Gilson, Z. Gabelica, Ch. Mousty-Desbuquoit and J. Verbist, J. Catalysis 21 (1981) 447. 81. J.C. Vedrine, A. Auroux, P. Dejaive, V. Ducarme, H. Hoser and S. Zhou, J. Catalysis Zl (1982) 147. 82. A.E. Hughes, K.G. Wilshier, B.A. Sexton and P. Smart, J. Catalysis 80 (1983) 227. 83. C.E. Lyman, A.C.S. Symp. Ser. 248 (1984) 1984. 84. C.E. Lyman, P.W. Betteridge and E.F. Moran, A.C.S. Symp. Ser. 218 (1983) 199. 85. J. Dwyer, F.R. Fitch, F. Machado, G. Qin, S.M. Smyth and J.C. Vickerman, J.C.S. Chern. Comm. (1981) 422. 86. J. Dwyer, F.R. Fitch, G. Qin and J.C. Vickerman, J. Phys. Chern. 86 (1982) 4574. 87. A.G. Ashton, J. Dwyer, I.S. Elliott, F.R. Fitch, G. Qin, M. Greenwood and J. Speakman, Proceed. Vlth Int. Conf. on Zeolites, D. Olson and A. Bisio, Eds., Butterworths, Guildford, 1984, 704. 88. S.L. Suib and D.F. Coughlin, J. Catalysis 84 (1983) 410. 89. G.H. Kuehl, E.P. 93,519 (1983), assigned to Mobil Oil. 90. R.B. Calvert and L.D. Rollmann, E.P. 59,540 (1982), assigned to Mobil Oil. 91. T. Suzuki, S. Hashimoto and R. Nakano, LP. 53,499 (1981), assigned to Mitsubishi gas chemical compo 92. Ref. 3 p. 313. 93. F.G. Dwyer and A.B. Schwartz, U.S.P. 4,091,007 (1978), assigned to Mobil Oi l. 94. I.P. Reid, E.P. 68,817 (1982), assigned to English Clays Lovering Pochin & Compo 95. M. Bourgogne, J.L. Guth and R. Wey, LP. 74,900 (1982), assigned to Compagnie Fran~aise de Raffinage. 96. L.D. Rollmann, U.S.P. 4,148,713 (1979), assigned to Mobil Oil. 97. J.F. Le Page, J. Cosijns, P. Courty, E. Freund, J.P. Franck, Y. Jacquin, B. Juquin, C. Marcilly, G. Martino, J. Miquel, R. Montarnal, A. Sugier, H. Van Landeghem, "Catalyse de contact", Technip, Paris, 1978, 172. 98. W. Hoelderich, L. Riekert, M. Kotter and U. Hammon, G. Offenl. 3,231,498 (1984), assigned to BASF AG. 99. Y.Y. Huang, E.P. 95,851 (1983), assigned to Mobil Oil. 100. J. Weisser, J. Grolig and G. Scharfe, G. Offenl. 3,014,636 (1981), assigned to Bayer AG.

..

111

101. J. Weisser, J. Grolig and G. Scharfe, G. Offenl. 3,014,637 (1981), assigned to 8ayer AG. 102. N.Y. Chen, J.N. Miale and W.J. Reagan, U.S.P. 4,112,056 (1978), assigned to Mobil Oil. 103. S.J. Miller, U.K.P. 2,097,374A (1981), assigned to Chevron Res. Compo 104. S.J. Miller, U.S.P. 4,394,362 (1983), assigned to Chevron Res. Compo 105. S.J. Miller, U.S.P. 4,394,251 (1983), assigned to Chevron Res. Compo 106. W. Koetsier, E.P. 55,044 (1981), assigned to Exxon Res. Eng. Compo 107. T. Onodera, 1. Sakai, Y. Yamasaki, K. Sumitani, E.P. 94,693 (1983), assigned to Teijin Petrochem. Ind. 108. P. Chu and E.J. Rosinoki, E.P.A. 110,650 (1983), assigned to Mobil Oil. 109. E. Narita, K. Sato and T. Okabe, Chern. Lett. (1984) 1055. 110. C.J. Plank, E.J. Rosinski and M.K. Rubin, U.S.P. 4,341,748 (1982), assigned to Mobil Oil. 111. R.W. Grose and E.M. Flanigen, U.S.P. 4,061,724 (1977), assigned to Union Carbide Corp. 112. S. Budiansky, Nature 300 (1982) 309. 113. F.G. Dwyer and E.E. Jenkins, U.S.P. 3,941,871 (1976), assigned to Mobil Oil. 114. Be1g. P. 860,979 (19/8) and French P.A. 7,734,776 (1979), assigned to Union Carbide Corp. 110. H.W. Kouwenhoven, W.H.J. Stork and L. Schaper, D. Offenl. 2,755,770 (1978), assigned to Shell Int. Res; Maatsch. 11b. P. Vo1gnandt and K.H. Worms, D. Offen1. 2,940,103 (1981), assigned to Henkel K.GaA. 117. E.L. Wu, S.L. Lawton, D.H. Olson, A.C. Rohrman and G.T. Kokotailo, J. Phys. Chern. 83 (1979) 2777. 118. R. Mostowicz and J.M. Berak, Stud. Surf. Sci. Catal. 24 (1985) 65. 119. G. Debras, A. Gourge, J.B. Nagy and G. De C1ippe1eir, Zeolites ~ (1985) 369. 120. K.F.M.G.J. Scholle, W.S. Veeman, P. Frenken and G.P.M. Van der Velden, Appl. Catalysis 1l (1985) 233. 121. A.W. Chester, Y.F. Chu, R.M. Dessau, G.T. Kerr and C.T. Kresge, J. C. S., Chern. Commun. (1985) 289. 122. P. Chu, A. Huss Jr. and J.C. Vartu1 i, U.S.P. 4,497,786 (1985) assigned to Mobil Oil.

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113

CHAPTER II

SYNTHESIS OF THE MFI TYPE OF STRUCTURE IN THE ABSENCE OF TPA

INTRODUCTION In the early period of the synthesis of ZSM-5, it was the general belief that tetrapropylammonium cations were necessary ingredients in the synthesis mixture in order to obtain this structure. In the previous chapter it was clearly demonstrated, however, that this is not generally true: once nuclei of ZSM-5 are present, further crystal growth occurs readily in the presence of other organic bases or even in the total absence of any organic compound. It is also the authors' belief that the total removal of residual nuclei from a synthesis autoclave is a very difficult and critical operation. vJe observed several times that it is much more difficult to prepare ZSM-5 in high yields in a new than in a used autoclave. Even extended HF treatment to remove any residual nuclei did not remove this effect completely. Moreover, we also found that once a vessel had been used for the synthesis of ZSM-5, it was then impossible to synthesize pure ZSM-II. These remarks do not prove anything but reflect only our critical attitude to statements in which it is claimed that ZSM-5 zeal ites can be synthesized in the presence of any basic molecule, organic or not. This chapter aims to consider critically selected data that prove or disprove this. SYNTHESIS OF ZSM-5 IN THE PRESENCE OF QUATERNARY AMMONIUM CATIONS DIFFERENT FROM TPA Kulkarni et al.(ref.I) and Borade et al.(ref.Z) have systematically studied the crystallization of ZSM-5 in the presence of triethylpropylammonium cations (TEPA). From a typical gel (ref. I), ((TEPA)zO)4.38(NazO)Z7.6(Alz03)I(SiOZ)87.7(HzO)3,Z6Z' pure ZSM-5 could be obtained in the temperature range 433 - 473 K. The crystals detectable by XRD appeared via the expected sigmoid process and the data could be linearized

114

via the so-called Avrami-Erofeev equation (ref.1,2) ln (1/1 - x) = (kt)m

(II1.1)

where x and t are the degree of crystallization and the time, respectively; k is an apparent crystallization rate and m is a constant. Using k values obtained at different temperatures, reliable values for Ea n and Ea c' the apparent activation energies for nucleation and crystal growth, respectively, could be obtained. Pertinent data derived from the original results (ref.1) are given in Table 111.1 and a comparison of kinetic parameters for the crystallization of lSM-5 in the presence of TEPA and TPA under otherwise identical conditions. TABLE II1.1 Comparison of kinetic parameters for the crystallization of lSM-5 in the presence of TEPA or TPA

R a (h- 1)

t~. Ean~

b (h) (kJ mol-I)

TEPA

TPA

0.03 4.0 270.4

3.0 0.8 199.5

a, rate of nucleation at 433 K derived from ref. 1, Fig. 5 ; b, time to reach 50% crystallization at 433 K, derived from ref. 1, Fig. 5; c, apparent activation energy for nucleation taken from ref. 1, Table 5.

All kinetic parameters indicate that lSM-5 crystall ization is considerably faster in the presence of TPA cations than with TEPA ions. Kulkarni et al.(ref.1) therefore clearly proved that if templation is important in lSM-5 synthesis, TPA is a much better templating agent than TEPA. If, after the templation, the most ideal pore fill ing by the template is important, as suggested by Gabelica and Derouane (ref.3), TPA should fill the pores of the lSM-5 nuclei to a greater extent than TEPA and 1ead to an energetically more favourable pore filling. All parameters that influence further the crystall ization of lSM-5 in the presence of TPA (see Chapter I) were also found to be of importance in the presence of TEPA (refs.l,2) :

115

101'--------------,10

., CD Ql

o

r+

0::

<

4l

CD

....

:0 :::s

>

III

...

4l

°o~----_7-----+---.JO 1

2

% (AI/AI+Si) FIGURE 111.1 Relative crystall ization (R c) and nucleation rates (R n) of ZSM-5 in the presence of TEPA and of i ncrea sing amounts of Ali n the synthesis mixture. Data are derived from ref. 2, Table 1 and Fig. 2.

1. The Si/AI 2 molar ratio of the gel (ref.2). Fig. 111.1 shows that crystallization of ZSM-5 is faster when less aluminium is present in the gel. Moreover, these data confirm that a more than linear increase in the crystallization rate occurs when the gel becomes more devoid of AI. This could not be derived directly from the data available in the TPA system. 2. The alkalinity of the reaction mixture (ref.l). An optimum value for the alkalinity was found to exist for both the induction period and the rate of crystallization, just as reported in the TPA system. This is illustrated in Fig. II1.2 for the variation of the time to reach 50% crystallization. 3. The TEPA/Si0 2 ratio. As found for TPA, the crystallization rate also increases (the time to reach 50% crystallization decreases, Fig. 111.2) when this ratio increases. At the same time, the average diameter of the polycrys ta 11 i ne aggregates thus formed was also found to decrease when this ratio increased (ref.2). A simil~r behaviour was reported for the TPA system (Chapter I).

116

(TEPAh O/ S i02 o

0.1

0.05

I

,

/"

/"

/'

1"1-

40 I

I

I

I 'II \ s:

30

"ci 10

\

\

\

I 1

¥

I I I

/

....

20

100':---------'------~

10

FIGURE 111.2. Influence of the (TEPA)20/Si02 and OH/H 20 ratios on the time to reach SO% crystallization (t • o S). Data are derived from ref. 1, Fig. 7 and from ref. 2, Fig. 1.

117

There is some evidence of the mechanistic pathway that is followed in such a synthesis. Monomeric silica is used as the silica source. As this is a dominating parameter (ref.3), a hydrogel nucleation mechanism is to be expected. The composition of the intermediate solid phases during crystall ization gives supplementary evidence for the occurrence of such a mechanism. Indeed, both the SiO Z/A1 203 and the A1 203/Na 20 ratios of the solids remain constant during the whole crystallization process. The formation of a polycrystalline morphology and the absence of any large crystal in SEM observations before 100% crystallinity is achieved confirm the existence of such a synthesis mechanism. Instead of TEPA ions, TPMA (tripropylmethylammonium) ions can also be used to synthesize ZSM-5 (ref.4). The latter ions are a less expensive source of templating molecules. The data, however, also clearly demonstrate that the crystallization of ZSM-5 is also slower with TPMA than with TPA, which confirms the ideal geometry of the TPA ion for directing the synthesis to a fast crystallization of ZSM-5. ZS~1-5 can also crystallize in the presence of tributylmethyl-, tributylethyl-, tributylhexyl-, tributyloctyl-, trimethylbenzyland diethylpropylethylammonium cations or N,N,N,N' ,N' ,N'hexamethyl 1,6-hexanediammonium cations (ref.52). No data are available, however, which allow to make a comparison with TPA. Fast crystallization of ZSM-5 also occurs when the template TPA cations are formed in situ in the synthesis mixture (ref.3). This occurs using tripropylamine and propyl bromide as the organic source +

( III.2)

With the amine alone a pure ZSM-5 phase is not obtained (ref.3). So it seems that under the synthesis conditions at least a small number of TPA cations are present that direct the synthesis. As the final material contains only the amine in its pores, as evidenced by 13C NMR spectroscopy, it was concluded that TPA ions act only as a structure-directing agent during the initial nucleation (ref.3). This conclusion is in general accord with what was derived in this and the previous chapter from other data : nucleation of ZSM-5 is very sensitive to the nature of the template and crystal growth of ZSM-5 is much less sensitive in this respect. This is also illustrated by data of ref. 51. The use of a mixture of TPA and an amine, e.g. n-butylamine (C 4N) in the gel with composition (Na 20)27 (TPA-Br)x (C 4N)y (A1 203)1 (Si0 2)90 (H 20)1,800 after 6h crystallization

118

at 433K resulted in the following degrees of crystall i ni ty of the product :

No.

1 2 3 4 5 6 7 8

x

y

0.11 0.09 0.22 0.27 0.45 0.45 0.72 9.00

2.02 4.05 4.05 4.05 4.05 0.00 4.05 0.00

degree of crystallinity (%) 50 55 95 80 85 40 95 90

ZS~1-5

ref.

51,ex.14 51,ex.l0 51,ex.9 51,ex.8 51,ex.7 51,ex.4 51,ex.6 51,ex.5

These results demonstrate that: i.

a minimum amount of TPA is neccessary to obtain more than 80% crystallinity (Nos. 1-4); below this minimum amount of TPA, C4N is not efficient to improve the degree of crystallinity (Nos. 1 and 2); ii. when sufficient TPA is present, C4N enhances the crystallization of ZSM-5 (Nos. 5 and 6); iii. TPA and C4N are both good pore fillers (Nos.7 and 8). In a further attempt to decrease the cost of the raw materials for ZSM-5 synthesis, Dwyer and Chu (ref.5) used n-propylamine and n-propylbromide. An excellent solvent for ooth molecules seems to be essential for success in such a synthesis. Methyl ethyl ketone has such properties. Possibly, in presence of this solvent and under the conditions of the synthesis (temperature, basic conditions), small amounts of TPA cations are also formed : (IIL3) 2 CH 3CH2CH2NH 2 ~ (CH3CH2CH2)2NH + NH 3 N (CH3CH2CH2)2NH + CH 3CH 2CH2NH 2 ~ (CH 3CH2CH2)3 + NH 3 (I1I.4) (IIL5) (CH 3CH2CH2)3 N + CH 3CH 2CH2Br ~ (CH3CH2CH2)4N+ Br-

119

The relatively high amine to halide ratio that is advantageously used in this procedure (ratios from 2 to 10) points to such a chemistry. The same method also produces materials with a very low residual Nat content (from 0.01 or less to about 0.2% (ref.5)). There is no clear explanation for this, but may be that this time crystallization occurs in the organic phase containing the amine, the ketone and the reaction products of amine and halide. Transfer of silicate and aluminate species from the aqueous to the organic phase would have to occur. As a result of differences in the solubility of, e.g., NaBr in the two phases, the crystallization of an lSM-5 phase devoid of Nat is then obvious.

SYNTHESIS OF lSM-5 IN THE PRESENCE OF AMINES In contrast to quaternary ammonium ions, amines added to a basic synthesis mixture may have the following effects: 1. They buffer the

reaction mixture so that the pH increase during the synthesis is reduced (ref.6) : if a substant i al amount of amine is occluded in a crystallizing zeolite phase, the organic material in the remaining gel or solution will cause a smaller increase in pH during crystall ization. In an aqueous synthesis mixture, amine will be partially protonated : (111.6) (111.7)

The total amine (A) concentration in the reaction mixture will be (ref.6) JA[

IAI

I

RNH21

(l + KaIH+I-1 )

(II1.8) (II1.9)

and, consequently, the pH will be considerably lower than in the corresponding amine-free system. According to the Lowe model (ref.6) (see Chapter I), this will result in an increased yield of the crystallization. 2. They exclude Na from the final products(ref.7). A possible explanation for this effect has already been advanced in the case when a separate solvent

120

for the amine is added to the mixture. In the present instance, the exclusion of Na is of another nature, as no such solvent is present and as the effect occurs only with primary and not with secondary amines (ref.?). Such an observation points rather to an effect of charge density for the smaller amines; competition in their protonated form with sodium seems to be efficient. If competition of the hydrated ions is considered, the charge density _(e2/r) will be higher for the protonated amine (with its hydrophobic tail) and the observations are at least qualitatively understood. Typical conditions for the synthesis of ZSM-5 in the presence of different amine molecules are given in Table 111.2. It follows that several structurally different molecules can function as templates in the synthesis of ZSM-5. Crystallization is also relatively fast at mild reaction temperatures. All this casts some doubt about the existence of a "unique" template for the crystallization of ZSM-5 and it therefore seems more probab1e that the funct i on of the organi c compound is to fill the pores, rather than to act as a template. It cannot be concluded from the present or other data in the literature whether the use of all these molecules slows the crystall ization of ZSM-5 down compared with the case were TPA is used. It would be interestlng to know this and also to have an idea of the morphology of these particular samples. In a single instance the superiority of TPA with respect to an amine (isopropyl amine) has been demonstrated. Data from ref. 51 allow to compare the crystallization rates of ZSM-5 at 433K in the presence of TPA or isopropylamine in the gel (Na 20)27 (TPABr or amine)x(A1 203)1 (Si0 2)90 (H 20)1,800

degree of crystallinity after 6h (%)

Organic

x

isopropyl ami ne

4.05

°

51,ex.2

TPABr

0.45

40

51,ex.1

ref.

121

Crystalline phases have been identified using XRD only, and it is often stated that the material has an XRD pattern like that of ZSM-5. Possibly, these crystalline

phases

obtained

using

the different

organic molecules

differ slightly. Indeed, it is difficult to distinguish by XRD the different members of the pentasil family of zeolites to which ZSM-5 belongs, but at least one other type of structure and their intergrown phases (see Chapter III

and IV) exist. This kind of information cannot be derived from the

available data. The use of amines (reL7) or alkanolamines (reLIZ) during synthesis seems to confirm at least one particular property of the ZSM-5 materials crystall ized this way: they all contain only 1ittle residual Na after synthesis. This is an advantage when they are to be used as catalysts in

acid-catalysed reactions as

it simpl ifies considerably the activation

procedure of such catalysts. It should be stressed that conflicting data have been published in this respect: for amines the Na exclusion seems to occur only for primary amines (ref.7), whereas with alkanolamines this effect has also been reported for secondary alkanolamines (ref.lZ).

.... tv

TABLE 111.2 Synthesis of ZSM-5 like structures in the presence of amines Amine (R)a

tv

R2

TPA

R3

R4

R5

R6

R7

R8

R9

36.7 8.3 93.5 3877

36.8 8.4 94.4 3894

34.2 1.0 27.7 453

56.0 7.7 59.5 1786

53.1 53.1 90 3600

26.1 53.1 90 3600

12.0 36.0 60 2400

50.9 3.5 27.6 41.9

13.7

25.6

28.9 546

31.3 677

450

450

423

443

433

433

433

423

443

443

2 7,ex.1

3 7,ex.8

5 8,ex.2

2.7 9,ex.3

3 10,ex.3

3 10,ex.4

3 1l,ex.1

2.5 12,ex.1

2.75 13,ex.1

2 13,ex.2

R1

~9!~~_~9~P9~~!~9~_9!_9~!_~~!2Q3_:_!2

R Na 20 SiO L HLO

?

?

~~~~!~!!~~~!~9~_~9~9~!!9~~

Temperature (K)

Time (days) Ref.

a,R1 = propylamine ICH3CHLCH2NH21; R2 = isopropylamine I (CH3)2CHNH21; R3 = 3-dimethylamino-2,2-dimethyl-1-propanol IHOCH2C(CH3)2CH2N(CH3)21; R4 = 1,5-diaminopentane INH2(CH2)5NH21; R5 = 1,6-diaminohexane !NH2(CH2)6NHZ!; CH - CH R6 = 1-methyl-4-aza-1-azoniabicycloI2,2,2Ioctane 4-oxide-iodide 10 • N ~ CH~ - CH~ ~ N+- CH 3 I-I; R7 = CH 2 - CH 2 diethanolamine!(HOCH2CH2)2NHI; R8 = dimethanolamine !(HOCH2)2NH1; R9 = ethanolamine I HOCH 2CH 2NH 2 I·

123

A possibly non-exhaustive overview of basic molecules not of the quaternary ionic type is listed in Table II1.3. Alkanolamines are generally prepared NH

3

~

or

situ in the following way (ref.13) :

~

+ CHXCH , I

o

(111.10)

Z

or NHZCHZCHXOH

+

C~XfHZ

(111.11)

NH(CHZCHXOH)Z

~

o NH(CHZCHXOH)Z

+

C~X(HZ

~

o

(111.1Z)

N(CH ZCHXOH)3

In the reactions (111.10-111.1Z), X is either an H atom or a methyl group. Zeo1i tes synthes i zed in the presence of a1kano1ami nes seem to be very susceptible to ion exchange. In other words, only a small amount of residual sodium remains

ln

the material

after

ion

exchange

without

calcination

(ref.13). Table 111.3 shows that a variety of nitrogen containing basic molecules can function as an efficient template for the synthesis of the MFl type of structure. Unfortunately, the data identify the materials by XRD, which for legal purposes is sufficient, and sometimes by sorption data. The exact conditions for the synthesis of these materials have not been related to specific changes in the values of the main parameters. The questions that have been more or less solved, or at least have been rationalized for the TPA-ZSM-5 synthesis, at this stage are totally ~nknown for each of the basic molecules. Qualitatively, it can be derived from the result of Gabelica and Derouane (ref.3) and in fact from every result in Tables II1.Z and 111.3, that rather than a strict templating effect a pore size filling model may determine the nature of the nuclei formed. It would be very illuminating in this respect if for some of the important and cheap basic molecules (R), the effect of changes in the most OH/SiO A1 important parameters !R/SiO (R + alkali)/alkali Z; Z; Z03/SiO Z; ratios I were known in systems free of contaminants. The changes in the kinetics of nucleation and growth, the chemical composition of well selected samples during a crystallization run and the effect of all this on crystal morphology and Si/Al gradients across individual crystals are, according to our viewpoint, basic knowledge for understanding the crystallization of zeolites in basic media that do not consist of organic tetraalkylammonium cations. A few remarks can be made when the mo s t ly patent data illustrating the subject are considered in detail :

124

i. From 3-dimethylamino-Z,Z-dimethyl-l-propanol, either a ZSM-5 or a mordenite zeolite is crystallized; mordenite crystallizes when higher alumina contents are present in the gel and when the reaction occurs at lower temperatures; in other instances (less alumina, higher temperature and longer synthesis) ZSM-5 is formed (ref. 13,ex.l and Z). Such behaviour is indicative of no templating effect at all. ii. As far as the effect of alkanolamines is concerned, it was stated (ref.lZ), but no data were given to illustrate the statements, that sma 11 amounts of a1kano 1ami nes compete for Na+ in the gel and deli ver Na+-free gels (less than 0.05 weight % of Na+). Moreover, this effect is more pronounced for longer chain alkanolamines (ref.lZ). A discontinuity of a zeolite property with the chain length of the alkanolamine was reported for the crystallization rate (ret.lZ). The rate of crystall ization of ZSM-5 from which any inorganic alkal i or organic compounds can be easily washed away increases in the order (HOCHZCHZ)ZNH < (HOCHZ)ZNH « (HOCHZCHZ)3N. Unfortunately, no such order has been derived for propanolamines. It could well be that the most rapid crystallization rate could occur for triethanolamine (compared with tripropanolamine). It is our belief, and for certain molecules this is based on facts, that templation in zeolite synthesis is a pore filling effect. Many molecules are able to function as templates, but before the template theory is rejected, based on the observation that almost all organics at a suitable pH seem to be able to catalyse the formation of ZSM-5, one should consider the following: templation should be expressed as its effect on the rate of nucleation, and comparison between templates should be carried out under comparable conditions. The most important parameters in this respect were discussed in Chapter I. iii. The use of the polyamines dipropylenetetramine, diethylenetriamine, dihexamethylenetetramine and triethylenetetramine has been reported for the synthesis of ZSM-5. It is remarkable that in any case Aerosil and freshly precipitated Al(OH)3 are used as SiO Z and A1 Z03 sources and a polyamine solution as base. No mineral alkali metal such as NaZO is added nor has to be removed afterwards from the crystals. From the gel composition it is estimated that not more than one amino function is protonated. Anyway, for these polyamines hydrogen bonding would be preferable, just as has been reported for silica, in which templating is most pronounced on molecules with a high charge density (ref.Z4).

125

The polyamines seem to be a group of templating agents the detailed study of which could give particular information on the way ZSt'l-5 synthesis works. i v,

The effect of the hydrocarbon chain length, however, should not be overlooked entirely. Indeed, data are given in Table 111.3 that show that diaminoalkane molecules of discrete hydrocarbon chain length are able to catalyse the synthesis of ZSM-5. Pure MFI can be obtained with diaminopentane, -hexane and -dodecane(ref.16). This again is definitely an example of templation by pore filling, although all experiments were not carried out under the same conditions. The subject will be treated in detail in Chapters III and IV when the synthesis of different pentasil zeolites is considered.

It can be concluded that in this chapter a strict templation effect as explained in Chapter I possibly does not exist. However, it is not known how the nucleation rate is influenced by the nature and the intensity of this effect.

SYNTHESIS OF ZSM-5 IN THE PRESENCE OF ALCOHOLS If alcohols can be used as templates for ZSM-5 synthesis and if the basicity of the supersaturated solution is then provided by a source of mineral alkali metal, this would have to be interpreted in terms of the pore filling model. Several alcohols have been found to be able to induce ZSM-5 synthesis. Most of them are given in Table 111.4 together with the reaction conditions (gel composition, reaction temperature and time required for the synthesis).

...... rc

m

TABLE 111.3 Overview of organic non-quaternary bases used to synthesize ZSM-5 like zeolites

Orqarnc base (R)

Ref. Formula

Molar composltion of gel (A120~ R Na 20 Na 2So4 Si0 2 H2O

Propylamine

CH 3CH 2CH2NH 2

7,ex.1

36.7

8.3

93.5

3877

Isopropylamine

(CH3)2CHNH2

7,ex.8

36.8

8.4

94.4

3894

5.5

8.2

42.5

936

18.5

83.8

30.8

2020

Oxyethyllactamide

14

Ethylenediaminetetraacetic acid (EDTA)

Na 2H2EDTA

15,ex.1

Nitrilotriacetic acid

Trisodium salt

15,ex.3

0.46

10.7

30.8

2020

15,ex.5

3.1

20.9

30.8

3U8

C5DN C6DN

16,ex.2

0.87

0.3

30.0

1200

16,ex.4

26.1

0.9

90.0

3600

C12DN HOCH 2CH 2NH2

16,ex.24

26.1

0.9

90.0

3600

13,ex.1

25.6

0.12

31.3

423

12,ex.1

50.9

3.5

27.6

1150

Na 4EDTA Diaminopentane Diaminohexane Diaminododecane Monoethanolamine

19.6

11

Monoisopropanolamine

NH 2CH 2CHOHCH 3

13

2~.6

0.19

31. 3

423

Monopropanolamine

HOCH 2CH 2CH2NH 2

13,ex.4

16.2

0.19

26.6

394

Triethanolamine

(HOCH 2CH2)3 N

12,ex.10

52.8

3.5

27.6

950

20,ex.14

difficult to derive

Methylanoxide cation 3-Dimethylamino-2,2-dimethyl-1-propanol

O"'N~N+-CH

17,ex.1 3 HOCH2C(CH3)2CH2N(CH3)2 18,ex.3 "-~

1.2

60

2400

very susceptible to mordenite synthesis

19,ex.3

55.9

difficult to derive

Morpholine

O~NH

20,ex.13

Tripropylamine N-oxide

(CH3CHZCHZ)3N+0

21,ex.1

4.3

N-ethylpiperidine

C5HlQNC 2H 5

52

?

'--/

1.7

7.7

90.2 ?

59.5

134Z

94.1

3395

35

.....

"" -l

,...

""

00

TABLE 111.4 Synthesis of ZSM-5 materials in the presence of alcohols Nature of alcohol (R)

Molar composition of gel _ _-,-,-(A.:. .:. l;2Q~ R Na 20

Ethano1 Ethanol Ethanol Ethanol 1,6-Hexanediol

37.8 9.5 146 114 20

Si0 2

28.9 55.8 9.5 18.6 8.6 94 b 8.6 94 10 60

Synthesis Temperature Time

H20

(K)

(h)

48444 16418 3870a 3870a 3000

448 450 449 449 473

24 48 24 21 17

Pinacol f 1,12-Dodecanediol

10 20

6.7 d 10

40 60

2000 3000

653 473

68e

2,2-Dimethyl-1,3-propanediol

30

10

60

3000

523

68

b, a, addition of 19 mol of Na 2S04; e, after 176 h : kenyaite; f, 2,3-butanediol.

NH 4OH;

c,

compos it ion

17

Molar composition of crystals Ref. ~203 = 1) or remarks Si0 2 Na 20

48 1 0.01 22 1.14 68.4 0.78 c 67.8 c Pure ZSM-5; prismatic 8 x 3 x 5 urn Low temp. to minimize tridymite Large amounts of diol avoid kenyaite formation

unchanged

during

calcination;

25,ex.1 25,ex.4 26,ex.1 27,ex.1 27,ex.5 27,ex.6 27,ex.8 27,ex.7

d,

K2O;

129

A few remarks should be made concerning Table 111.4 1. The necessary basicity to reach supersaturation is caused by mineral bases.

2. When NH 40H is used as a mineral base together with an alcohol (the function of which is not clear at this stage), a zeolite is finally obtained that can be freed of any organic compound or base without heating of the sample; for low-temperature acidic applications, this is of extreme importance. 3. With some alcohols (e.g., pinacol), ZSM-5 is a metastable phase that turns

into kenyaite (a layer silicate) on longer exposure; large amounts of a diol seem to suppress this kenyaite formation effectively. 4. Low synthesis temperatures help to prevent the formation

dense quartz

structures such as tridymite. From Tables 111.3 and 111.4 a comparison can made for the synthesis of good ZSM-5 material using 1,6-hexanediol and 1,6-diaminohexane :

gel compositions Synthesis Temperature Time

R

Diamine Dialcohol

26.1 20.0

0.9 10.0

90.0 60.0

1

1

3600 3000

(K)

(h)

433 473

72

17

It is clear, although the data are not entirely comparable, that both samples crystallize relatively fast. The alcohol system contains much more mineral alkali metal so that strictly the effect of the alcohol itself is obscured. In Table 111.5 synthesis data are collected referring to ZSM-5 prepared in the TPA, butylamine and butanol systems.

130

TABLE IIL5

Comparative synthesis of lSM-5 in the butanol at 423 K for 24 h (ref.28).

Template (R)

TPAOH C4Nb C4OH c C40H C40H

Molar composition of gel (A1 2Q3 = 1) NH 3 Si0 2 H2O R Na 20

3.0 27.0 25.9 25.9 25.9

13.5 36.7 34.8 15 55

a, addition of H2SO4 c, n-butanol

a 55 15

75 93.5 88.4 88.4 88.4

1350 970 1820 1820 1820

presence of TPA,

Ref.

Synthesis effi ci ency

(%)

28,ex.l 28,ex.2 28,ex.3 28,ex.4 28,ex.5

H2S04/Si02 molar rati 0

100 100 80 90 100

butylamine and

Crystal size (um)

<1 >3

>2

0.2; b, n-butylamine;

Table IIL5 shows that a 100% crystalline lSM-5 is obtained in a predetermined time and at a given temperature for the samples synthesized in the presence of ami ne. The tetrapropyl ammoni um system reaches thi s degree of crystallization with a minimum of alkali metal. With the weaker base, butylamine, more organic base and mineral alkali metal are needed to achieve the same efficiency. If butylamine is replaced with butanol, the conversion is not complete in the time applied (24 h). This is achieved again by adding ammonia to the system. When lines 3, 4 and 5 of Table 111.5 are compared, it is also clear that a reasonable amount of alcohol is needed to achieve the synthesis of lSM-5 at rates comparable to that with amines. Table IlL5 suggests that only a few parameters are important in the synthesis of lSM-5 with alcohols, although the extent to which they intervene is not known: alcohols probably serve as pore filling agents and hence have a templating function as do the primary amines (theory of pore filling); to adjust the pH of the gel (OH/Si0 2), ammonia or alkali is useful, but the latter is more difficult to remove; the synthesis mechanism is not known: from the practical point of view, it is crucial to know whether the degree of polymerization of the silica source involved here determines the synthesis

131

mechanism

and

consequently

the

nature

of

the

Al

gradient

through

the

individual crystals. As crystals prepared with alcohols are easily activated, they can obviously become extremely important catalytic materials. An unusual preparation of lSM-5 in alcoholic medium is worth mentioning here (ref.29). Tetraethyl orthosilicate is used as the silica source, but is first hydrolysed after addition of alumina.

The silica alumina to which

glycerol and Na are then added is transformed into lSM-5 (ref. 29,ex.1). 20 here a low-sodium zeolite is obtained. 1,2-Propanediol,

Also

triethyleneglycol,

hydroquinone and

1,4-cyclohexanedimethanol

also exhibit

the same effect. Not only alcohols but also their ethers have a "templating" effect in the synthesis of lSM-5 (ref.30). This preparation method is classical. The ethers

commonest diethylene

tetraethylene methylal.

mentioned

glycol glycol

(ref.30)

dimethyl

ether,

dimethyl

ether,

The necessary basicity

in

are

ethylene

triethylene

glycol glycol

tetrahydrofuran, this

dimethyl

ether,

dimethyl

ether,

diethyl

ether

and

instance was brought about by

addition of NaOH. TABLE II1.6 Template dependence of the maximum Al content (Al atoms per unit cell) at which lSM-5 can still be crystallized with at least 90% selectivitya

5 il i ca source Template

aeros il

I-propanol

5.1 7.1 5.1

1,6-hexanediol pentaerythrytol

water glass

5.9 7.3 5.4 6.1

1-propaneamine

9.8

7.1 7.1

1,6-hexanediamine TPA-Br

6.1

a, derived from ref.46, Fig.2. An homogeneous distribution of AI atoms over the lSM-5

framework is

possible in several ways (ref.46), but in any case a limiting number of 8 Al atoms

per unit cell

maximum

seems

to exist.

In Table 111.6 the variation of the

number of Al atoms which can be incorporated in a

lSM-5 matrix with

132

high crystallinity is shown. Three features are important: i. there is indeed a maximum in the amount of incorporated aluminium, which does not exceed significantly a value of 8 Al per unit cell; ii. the amount incorporated is template dependent and is always higher for the amine compared to the corresponding alcohol; iii. the amount incorporated is dependent on the nature of the silica source. These observations are far from being clearly understood at the moment. In connection with i, it is indeed possible that 4-MRs in ZSM-5 constitute more stable configurations than 5-MRs (ref.46). A distibution of Al in the former sites according to Lowenstein's rule would explain a maximum Al content of 8 atoms per unit cell. The neutral template molecules are expected to act as ligands for Na+ (ref.46) as Na+ (template)x' in which form they ressemble to TPA. The better templat i ng effect of ami nes with respect to a1coho1sis then explained by their stronger H-bond interactions with silicate-terminating silanol groups (ref.46).

THE USE OF VARIOUS TEMPLATES IN ZSM-5 SYNTHESIS ZSM-5 samples can also be synthesized in the presence of a mineral base and molecules of the groups carboxymethylcellulose, the condensation product of a fatty acid and an alkanolamine or cellulose hydroxyethyl ether (ref.3I). Several transition metal complexes that are stable at a pH suitable for ZSM-5 synthesis have also been used as templates for the crystallization of this zeolite (ref.32). The origin of the basicity is inorganic. In the same way, a transition element or its complex seems to be tightly held in the zeolite pores and can be used as such in further catalytic applications. Such experi ments generally gi ve low crysta11 i nity and often mordenite instead of ZSM-5 is obtained. Some results that are worth mentioning are given in Table IlL7.

All the samples obtained in this way are of very low crystallinity and the procedure should be further optimized for industrial use. However, even the 25% crystalline materials seem to contain 3.5% of V or Fe (Table 111.7, ref. 32), which should be enough for some shape-selective metal-catalysed reactions. Surfactants have also been used to synthesize ZSM-5 zeol ites (refs.47 ,48). This zeol ite was easily synthesized with SDBS (Sodium n-dodecyl benzene sulfonate) (ref .47) SAOES (sodium and with

TABLE II!.7 Synthesis of lSM-5 with transition metal complexes as templates (ref.32).

Template (R)

Molar composition of gel (A1 2Q :?U5i0 2 OH R

Phthalocyanine Co phthalocyanine a VO phthalocyanine Cu phthalocyanine b RUC1 2(o-Phenanthroline)3 c FeC10 4(bipY)3 !(C5H5)Fe(C5H4)N(CH3)3!Br

90 90 180 90 180 90 90

9 9 18 9 18 9 9

36 36 72

36 72

36 36

Time

Ref.

(days)

3 4 3 2 2 2 2

lSM-5 (%)

32,ex. 1 32,ex. 5 32,ex. 9 32,ex.l0 32,ex.14 32,ex.20 32,ex.23

35 50 15 25 15 10 25

a,b,c : see Fig. 111.3

a

_

0=

NUN

II

I (C ~

N

I I

N-CO-N

I

GO"'.::: -I

N-8=N II

N

h

b[6b]:

UCI2

c

[Q01FeC~4

FIGURE.III.3 Chemical structure of some transition metal complexes used for the synthesis of MFI (ref.32).

n-alkyl-polyoxyethylene sulfates with a degree of ethoxylation varying between 3.5 and 10% (ref.48). Irrespective of the degree of ethoxylation the synthesized materials all contain close to 105; by weight of organic material, which is in favour of a pore filling mechanism of only one set of pores.

SYNTHESIS OF ZSM-5 IN THE ABSENCE OF ANY ORGANIC COMPOUND In the above discussions the following was derived : in presence of tetrapropylammonium ions, ZSM-5 crystals could be obtained very rapidly; in the presence of mixed quaternary cations this was also possible, but not necessarily at the same rate; in later work amines were used as source of basicity and still later it was proved that the addition of alcohols, ethers and other molecules induced the formation of ZS~'-5, provided an inorganic base was present. This changed the theory of synthesis from one of strict templation to one of complete filling of one or both sets of pores. In the following paragraphs a summary of published data on ZSM-5 synthesis in the absence of any organic molecule will be given. All these results should be handled with caution, as one can never be entirely sure that no residual nuclei are present in the autoclaves used for the synthesis or that no absorbed organic material is still present in the PTFE lines of these autoclaves. It follows qualitatively from the above that the synthesis process should be slower and occur with continuously narrowing ranges of successful synthesis conditions when the specific template is replaced by a certain organic molecule. Therefore, in principle it should be possible to synthesize ZSM-5 in the absence of any organic compound, but in a narrow set of well defined conditions. As far as the crystallization rate is considered, the reaction rate is expected to be much slower. Chao (ref. 33), ina very early stage of research on ZSM-5 synthesis, reported the synthesis of partially crystalline ZSM-5 in the absence of any organic compound. The remarks in previous paragraphs should be borne in mind here. Some of Chao's data are given in Fig. 111.4 to illustrate the point. Fig. 111.4, although not containing enough experimental data, shows clearly that the crystallization in the absence of TPA is extremely slow.

135

10.....-----------".

c

b,..../

,.... ,.... ,/

*' 8

4 synthesis time I days FIGURE 111.4

Synthesis of lSM-5 in (a) the presence and (b) the absence of

TPA (from ref. 33, Table 1); 0.1 M in (OH-), 440 K; Na

20/Si02

ratio = 0.4.

The precise set of working conditions for the synthesis of lSM-5 in absence of an organic compound are summarized in Fig.III.5. This stability field is velY narrow and easy co-crystall ization of mordenite is observed. Si0

molar ratios above 100 have not been investigated. The figure also 2/A1203 shows that for strongly differing values of z (=water molar ratio), the

stable field shifts significantly. It should be stressed at this stage that the experimental stable window does not gi ve perfect materi a1s but products the

crystallinity

of which

most

of

the

time

is

not

better

than

60%

(refs.40,50). It should be noted that the highest quality lSM-5 is obtained at relatively high reaction temperatures when the mixture is not stirred (refs. 40,49). Stirring decreases the time of lSM-5 formation by a factor three (ref.50), but the other phases (as e.g. quartz) show also an increased rate of formation, and consequently it is hard to improve the quality of the lSM-5 material this way.

136

Several patents report the synthesis of lSM-5 in the absence of organic compounds. In order to define the important parameters in this synthesis, all available data are collected in Table 111.8. The only parameter that does not vary over a wide range is the OH/Si0 2 ratio. When this value is close to 0.200, pure lSM-5 is always obtained. For the extreme values (higher than 0.200) the system readily produces mordenite. This behaviour is less sensitive to lower. values of the OH/Si0 2 ratio.

100

• • MOR

+

MFI MOR

+

50

• MFI

• 10

20

30

FIGURE 111.5. Field for formation of MFI in the system with the following molar composition: (Na20)x(A1203)(Si02)y(H20)z; a, z = 3,000, synthesis temperature 463K and time 7 days (ref.40); b, z = 46 and the synthesis time 24 h at 463K (ref.49); for the full points (ref.50)z = 2,000.

TABLE 111.8 Synthesis of lSM-5 in the absence of any organic compound

Ref.

Si0 2/A1 203

Na 2O/Si02

H2O/Si02

X/Si0 2

OH/Si0 2

ratio

ratio

ratio

ratio

ratio

34,ex.16 35 34,ex.18 40 34,ex.17 40 35,ex. 2 31.8 35,ex. 4 31.8 34,ex. 9 30 36,ex. 2 33.3 37,ex. 1 50 37,ex. 4 100 37,ex. 6 50

0.33 0.34 0.34 0.33 0.17 0.40 0.30 0.50 0.10

90 69 39 13.3 11.1 50 41 20 13.6 20

0.223 a 0.390 b a .160

0.100 0.104 0.200 0.171 0.167 0.260 0.248 0.200 0.200 0.200

a,X = SO~;

o.ic''

b,X = Cl-; c,X = SO~;

°

-

0.182 a 0.060 c

-

Crystallization Time Temperature (K) (days)

14 21 11

2.7 2.7 6 0.75 1.4 3.8 1.5

423 423 423 443 443 423 453 448 423 448

Product

lSM-5 + trace of mordenite lS~1-5

lSM-5 High silica zeolite High silica zeolite Mordenite lSM-5 lSM-5 lSM-5 lSM-5

addition of aluminiumphosphate : P20S/Si0 2 = 0.029; d,0.005 CaO + 0.095 Na 2O. ......

cc

-1

138

The decrease in the degree of crystall inity with increasing OH/SiO Z ratio of the gel is illustrated in Fig. 111.6, using data from two different sources. Fig. 111.6 clearly shows that the crystallization rate of lSM-5 in the absence of an organic compound decreases when the basicity of the system increases beyond the critical value of the OH/SiO ratio of O.Z. Possibly the Z rate of synthesis in the absence of an organic compound and in a strongly basic medium is so slow that its redissolution rate may even become faster than its formation.

100 I

*<,

--

/a

X

a

>-

c

CU

50

l /l

...0>.

o ~ -

o

~,--

0.5

---;",=-

1.0

~:--

~

2.0

OH /Si0 2

FIGURE 111.6. Change in the degree of crystallinity of lSM-5 with increasing OH/SiO ratio (a, from ref. 37; b, from ref. 38) Z

139

17

•

C'I

0 CIl 0.10

d-

C'I

ell

Z

50

50

•

0.05 250

500

750

1000

H2O/Na 2O

FIGURE 111.7. Relationship between NaZO/SiO Z and HZO/NaZO ratios for the synthesis of ISM-5 in an inorganic medium. Values on the curve are SiO ratios of the gel. The data are taken from the different examples Z/A1 Z0 3 given in ref. 39.

When synthesis is carried out at OH/SiO Z ratios far away from the value of O.ZOO, this basicity parameter has to be compensated for by the HZO/NaZO ratio. The smooth relationship between NaZO/SiO Z ratios and HZO/NaZO ratios derived from ref. 39 is shown in Fig. 111.7. When the basicity decreases far below the critical value, it seems that the synthesis mixture must be much less concentrated (ref .39) in order to obtain ISM-5. It is possible that crystallization then no longer occurs via a gel phase but directly in solution.

140 It

is

striking

that

in

all

the

synthesis

methods

mentioned

the

SiO

z/A1 Z03 ratio of the materials is restricted. Preferred ranges seem to be located between 15 and 100 (ref.34,50). No synthesis of a very high-silica

lSM-5 in the absence of any organic compound has been reported. This casts some doubt on the generality of the laws that govern the synthesis of ZSM-5 in

the presence of organic compounds.

It was found that incorporation of

aluminium in such a matrix is of a disruptive nature. Berak and Mostowicz (ref.50)

In contrast to this

have shown that in an organic-free synthesis

mixture after a given period of time, ZSM-5 of a higher crystall inity is obtained when the starting gel is richer in alumina. If the same synthesis mechanism would hold in the absence of organic compounds, it is surprising that as far as we are aware nobody has high-sil ica

reported the synthesis of an ultra

ratio of 100 corresponds to the Z/A1Z03 upper compositional limit above which the MFI lattice, becoming more and more

hydrophobic, molecules.

Perhaps an SiO

ZS~1-5.

is

thermodynamically

On the other hand,

zeolites can

be

synthesized,

unstable

although

in

in

absence

of

any

organic

inorganic medium high-alumina

the highest amount of alumina which can

be

incorporated in a lSM-5 matrix doesnot seem to be affected by the presence or absence of organics (refs. 40, 49, 50). earlier (not more than

Z Al atoms

In view of the hypothesis advance

per 4-MR

(ref.46),

this

is

perfectly

understandable. Nastro et al.

(ref.40)

recently started a systematic study of lSM-5

synthesis in the (Na,K)ZO (A1 (SiOz)y (HzO)z system. They confirmed Z03)x the ready co-crystallization of lSM-5 with mordenite. The desired product was obtained only at high reaction times (7 - 14 days compared with 1 - 3 days in a standard procedure). According to Nastro et al., hydrated Na+ ions are able to function

as

a

template for

the fonnation

of the following secondary

building units (SBU), which are common to lSM-5 and also to the mordenite structure. It was proposed that in a suitable chemical environment N/ ions allow the very slow assembly of these units to give the precursor structures of lSM-5 nuclei.

141

Natro et al. (ref.40) demonstrated that in an Na 20 - Al 203 - Si0 2 - H20 mixture from which mordenite is otherwise crystallized, lSM-5 appeared after the addition of small amounts of TPA. The particular aptitude of TPA for lSM-5 nucleation is further demonstrated in Fig.III.S.

90 80 a c

70

*'~

I-

Z

60 b

50

:J

...J

40

l-

ll) ~

0:: U

30 20 10 0 0

2

4

6

8

10

12

14

16

18

20

CRYSTALLIZATION TIME/DAYS

FIGURE 111.8. Crystallization of lSM-5 in absence and presence of organics a, from (TPA)4 (Na 20)4.5 (A1 203)1 (Si0 2)90 (H 20)3,000 and b, from the same gel without TPA (ref.40); c , from (Na ZO)6 (Al203)1 (Si0 2)90 (H 20)2,000 (ref.50) . Fig.III.8. shows that the data of Fig. 111.4. obtained for low crystallinity materials are of a general nature. The removal of the organics from a gel from which a lSM-5 zeolite rapidly crystallizes has a dramatic retarding effect on the crystallization rate. Thus, hydrated sodium ions constitute a poor replacement as template or pore filling agent for TPA. The same figure confirms again (compare curves b -and c) that in the inorganic system, the alkal inity (OH/SiO Z and NaZO/HZO ratios) are the key parameters in determining the crystallization rate.

142

KUhl (ref.41,42) reported more than a decade ago that the utilization of silica in an inorganic system increased considerably in the presence o-F phosphate and that in this way zeolites with enhanced Si/Ill ratios could be obtained. Breck (ref.43) reviewed this issue in 1974 and explained this chemistry as follows: the concentration of Al(OH)4 ions is lowered as a result of a complex formation reaction with the phosphate, and in fact depends on phosphate and hydroxyl ion concentration Al(OH)4

+

( ) 32 P0 34 t Al P0 4 2 + 40H

(III.13)

Although the detailed chemistry is not clear, the phosphate might have a buffering action, which control s the pH and the depolymerization rate of polymeric silica (ref.43). It is therefore not surprising that on addition of phosphate to an inorganic mixture, from which mordenite would otherwise be formed, ZSM-5 type materials can also be obtained (ref.44). Typical data on this important issue are given in Table III.9. TABLE III.9 Molar compositions free of organic compounds from which ZSM-5 synthesized: effect of phosphate (ref.44)

Molar composition (A1 2Q3=1) Na 20 Si0 2 P205 H2O

11. 4 10.1 7.4

33.3 33.3 24.4

a 0.98 b 1.50

1367 1367 1000

Structure type

Synthesis Time Temperature (K) (h)

Mordenite ZSM-5 ZSM-5 c

18 18 18

453 453 463

can be

Ref.

44,ex.1 44,ex.2 44,ex.3

a, 2.5 mol and b, 2.0 mol of S03 are added; c , the Si0 2/A1 203 ratio of the product is 41.6 . Table 11I.9 shows definitely that on addition of phosphate to an otherwise identical mixture no longer mordenite but ZSM-5 type materials are obtained. It also indicates that the system is in no way different from those

143

described in earlier literature (e.g., A and Y zeolites (ref.43)) the silica is more efficiently used when phosphate is added. The question of whether phosphate is occluded (ref.41,4Z) or is incorporated in the lattice, as demonstrated for zeolite Y (ref.45), is irrelevant for the moment, as the data given do not allow any conclusion to be drawn in this respect. Unfortunately, also nothing is known about the maximum synthesis efficiency on a silica basis that can be attained in the absence of organic compounds or in the presence of phosphate, or on the morphology of the crystals. Table 111.9 further shows that in the presence of phosphate short synthesis times are required compared with earlier data. A patent (ref.44) also claims materials in a restricted range: 15 < SiO Z/A1 < ZOO. Z03 Similar ranges are covered in most of the other patents treating this subject. In conclusion, it can be stated that under very specific operating conditions it is possible to synthesize ZSM-5 in the absence of any organic compound. There are a few indications, however, that such a synthesis is very slow and that mechanistically the system obeys changes in the operating parameters as is known for other mineral gels or supersaturated solutions. Apparently, one has not yet succeeded in synthesizing ultra-high-silica ZSM-5 in the absence of organic compounds and nothing is known about the crystal morphology, the chemical homogeneity of these crystals or their chemical and physico-chemical properties.

144

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.

S.B. Kulkarni, V.P. Shiralkar, A.N. Kotasthane, R.B. Borade and P. Ratnasamy, Zeolites, ~ (1982) 313. R.B. Borade, A.J. Chandvadkar, S.B. Kulkarni and P. Ratnasamy, Indian J. Technol. ~ (19B3) 358. Z. Gabelica and E.G. Derouane, A.C.S. Symp. Ser. 248 (1985) 219. P. Chu, F.G. Dwyer and H.A. McVeigh, E.P. 28,516 (1980), assigned to Mobil Oi 1. F.G. Dwyer and P. Chu, E.P. 11,362 (1979), assigned to Mobil Oil. B.M. Lowe, Zeal ites, l (1983) 300. M.K. Rubin, E.J. Rosinski and C.J. Plank, U.S.P. 4,151,189 (1979), assigned to Mobil Oil. R.J. Argauer and G.R. Landolt, U.S.P. 3,702,886 (1972), assigned to Mobil Oi 1. W.J. Ball and D.G. Stewart, U.S.P. 4,376,104 (1983), assigned to BP Camp. L.D. Rollmann, U.S.P. 4,108,881 (1978), assigned to Mobil Oil. C.A. Audeh and E.W. Valyocsik, U.S.P. 4,285,922 (1981), assigned to Mobil Oi l. E. Moretti, M. Padovan, M. Solari, G. Marano and R. Covini, Belg. P. 895, 663 (1983), assigned to Montedison S.P.A. W.J. Ball, K.W. Palmer and D.G. Stewart, U.S.P. 4,346,021 (1982), assigned to BP Compo H. Nakamoto and H. Takahashi, Chern. Lett. (1981) 169. E. Bohres and K. Peterlein, G. Offenl. 3,239,054 (1984), assigned to Chemische Werke Hills. L.D. Rollmann, U.S.P. 4,108,881 (1978), assigned to Mobil Oil. C.A. Audeh and E.W. Valyocsik, U.S.P. 4,285,922 (1981), assigned to Mobil Oi 1. D.G. Stewart and W.J. Ball, E.P.A. 14,023 (1980), assigned to BP Camp. D.G. Stewart and W.J. Ball, U.S.P. 4,376,104 (1983), assigned to BP Compo M.R. Klotz, U.S.P. 4,377,502 (1983), assigned to Standard Oil of Indiana. C.A. Audeh and W.J. Reagan, U.S.P. 4,430,319 (1984), assigned to Mobil Oil. L. Marosi, J. Stalenow and M. Schwarzmann, G. Offenl. 2,909,429 (1980), assigned to BASF AG. L. Marosi, H.U. Schlimper, M. Schwarzmann and J. Stabenow, E.P.A. 41,621 (1981), assigned to BASF. R. Snel, Appl. Catal. 1£ (1984) 347.

145

25.

26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 36. 37.

38.

39. 40. 41. 42. 43. 44. 45. 46. 47. 48.

J.R. Anderson, R.A. Rajadhayaksha, D.E. Weiss, Th. Mole, K.G. Wilshier and J.A. Whiteside, E.P.A. 22,640 (1981), assigned to Commonwealth Scientific and Industrial Research Organization, Australia. C.J. Plank, E.J. Rosinski and M.K. Rubin, U.S.P. 4,341,748 (1982), assigned to Mobil Oil. J.L. Casei , B.M. Lowe and T.V. Whittam, E.P.A. 42,225 (1981), assigned to ICI . M.F.M. Post and J.M. Nanne, Can. Pat. 1,135,679 (1982). Nederl. Octrooiaanvraag, 8,101,216 (1981), assigned to Snam Progetti. W. Hoelderich, L. Marosi, W.D. Mross and ~L Schwarzmann, E.P.A. 51,741 (1982), assigned to BASF. J.G. Robinson and D.l. Barnes, Brit. Pat. 2,132,993 (1984), assigned to Coal Industries Patents Ltd. L.A. Rankel and E.W. Valyocsik, U.S.P. 4,388,285 (1983), assigned to Mobil Oil. K.J. Chao, Proc. Nat. Sci. Counc. ROC, 3(1979) 233. B. Notari, G. Manara, G. Bellussi and M. Tamarano, E.P.A. 98,641 (1984), assigned to Snam Progetti. W.J. Ball and D.G. Stewart, E.P.A. 71,328 (1980), assigned to BP Compo H.P. Rieck, G. Offenl. 3,242,352 (1984), assigned to Hoechst AG. W. Roscher, K.H. Bergk, W. Schwieger, F. Wolf, U. Haedicke, W. Krueger and K.H. Chojnacki, DDR P. 207,186 (1984), assigned to VEB Chemiecombinaat, Bitterfeld. W. Roscher, K.H. Bergk, K. Pilchowski, W. Schwieger, F. Wolf, H. Fuertig, U. Haedicke, W. Hoese, W. Krueger and K.H. Chojnacki, DDR P. 207,185 (1984), assigned to VEB Chemiecombinaat, Bitterfeld. B. Latourrette and L. Seigneurin, E.P.A. 94,288 (1983), assigned to Rhone-Poulenc. A. Nastro, R. Aiello and C. Colella, Stud. Surf. Sci. Catal. 24 (1985)39. G.H. KUhl, J. Inorg. Nucl. Chem. 33 (1971) 3,261. G.H. KUhl, Inorg. Chem. 1Q (1971) 2,488. D.W. Breck, "Zeolite Molecular Sieves", Wiley, New York, 1974, p. 328. H.P. Rieck, G. Offenl. 3,242,352 (1984), assigned to Hoechst AG. E.M. Flanigen, Adv. Chem. Ser. ~ (1973), 119. F.J. Van der Gaag, J.C. Jansen and H. Van Bekkum, Stud. Surf. Sci. Catal. 24 (1985) 8l. H. Hagiwara, Y. Kiyozumi, M. Kurita, T. Sato, H. Shimada, K. Suzuki, S. Shin, A. Nishijima, N. Todo , Chem. Lett. (1981) 1653. J. Batista, B. Drzaj and A. Zaje, Stud. Surf. Sci. Catal. 24 (1985) 97.

146

49. E. Narita, K. Sato, N. Yatabe, T. Okabe, Ind. Eng. Chem. Prod. Res. Dev. 24 (1985) 507. 50. J.M. Berak and R. Mostowicz, Stud. Surf. SCi. Cata1. ~ (1985) 47. 51. R.B. Calvert, L.D. Ro11mann, U.S.P. 4,495,166 (1985), assigned to Mobil Oil. 52. E. Moretti, S. Contessa, M. Padovan, Chem. Ind. ~ (1985) 21.

147

CHAPTER III

SYNTHESIS OF HIGH-SILICA ZEOLITES WITH THE MEL TYPE OF STRUCTURE

INTRODUCTION As has been established in previous chapters, zeolite ISM-5 with the MFI structure type denotes not a single material but encompasses a whole family of materials differing from each other in their chemical composition, their crystal size and morphology and even in the nature of the composition gradients across the crystal. As will be illustrated later, ZSM-II has a structure type related to ZSM-5 (ref. I). In the ZSM-II case, this structure type is denoted MEL (ref. 2). According to Kokotailo and Meier (ref. 3), the framework structure types MEL and MFI are members of the same family of molecular sieves and/or zeolites, so that a single generic name "PENTASIL" can be used to denote all members. In this notation, ZSM-5 and ZSM-II-type zeolites or molecular sieves then represent the END-MEMBERS of this family of materials. In this chapter, some data selected from the literature available on MEL materials will be discussed, in addition to some new unpublished data.

QUATERNARY SALTS USED AS TEMPLATES IN THE SYNTHESIS OF ZSM-II Previous chapters indicated that ZSM-5 was originally synthesized using tetrapropylammonium (TPA) ions. The original literature on ZSM-II (ref. 4) indicates that quaternary salts with one carbon atom more per hydrocarbon cha in such as tetrabutyl ammoni um (TBA) and tetrabutyl phosphoni um (TBP) ions are necessary as templates for the synthesis of this particular zeolite. Tetraalkylammonium cations with alkylgroups bulkier than butyl, for instance with pentyl, hexyl and heptyl groups in the same synthesis conditions yield exclusively ZSM-5 (ref. 22). Moretti and co-workers (ref. 23) stressed also on the specificity of TBA for the crystallization of ISM-II. The presence of TEA or TPA in addition to TBA results in. the formation of ZS~1-5 (ref. 23). Typical compositions of the gel used for the synthesis of ZSM-II and

148

synthesis conditions taken from the literature are given in Table IV.1. It follows that only a restricted number of organic bases were used for this synthesis according to the classical gel method: in addition to TBA and TBP, benzyltriphenylphosphonium (BeTPhP) also causes the crystallization of this zeolite from a wide range of gel compositions using a broad range of crystall ization temperatures and times. It seems that the presence of a strong inorganic base with a cation of the Group Ia elements is not a prerequisite for crystallization of lSM-11, as successful synthesis only in presence of NH 4 ions and TBA has been reported (ref. 5). The main characteristics of the material synthesized this way are given in Table IV.2.

TABLE IV.l Molar gel composition per 100 Si0 2 and synthesis conditions for lSM-ll

No.

Organic base

1 2 3 4 5 6

TBp a TBP TBA a TBA TBA BeTPhp a

8.5 36.4 11.8 19.5 9.4 8.0

Na 20

A1 203

H2O

15.4 30.0 17.6 b 10.8 10.9 d 47.3

1.12 0.09 c

3,960 6,500 1,180 2,740 2,030 4,150

1. 00 1. 56 1.71

a, TBP = tetrabutylphosphonium; TBA phenyl phosphonium.

H2SO4 Temp/K Timelh Ref.

20.0

10.7

533 403 443 373 450 422

67 4,ex.5 40 7 72 5 552 4,ex.8 72 6 96 4,ex.4

tetrabutylammonium; BeTPhP

b, (NH4)20. c, A1 203 < 30 ppm. d, Assuming the sodium silicate composition of ref. 8.

benzyltri-

149

TABLE IV.2 Characteristics of ISM-ll zeolites, synthesized under the conditions given in Table IV.l No.

Morphology

Size/~m

2 3

Ovate Ovate Ovate (twinned)a Ovate (twinned)

1-1.5 x 2-3 1-1.5 x 2-3 3 x 6a 4 x 6

4

5

Si0 2/A1 203 compos it i on

s il i ca polymorph 78 62

a, According to ref. 1 The ovate-shaped crystals are typical of high quality ISM-II synthesized in the presence of quaternary compounds. In most instances twinning of these crystals is observed. Photograph IV.l shows ovate twinned crystals of ISM-II crystallized in the presence of tetrabutylammonium ions.

PHOTOGRAPH IV.I. Ovate-shaped and twinned crystals of lSM-ll (synthesized according to the method of ref. 6).

150

In some instances the co-crystallization of a blade-shaped MAGADllTE phase on top of ZSM-ll crystals occurs. The typical crystal morphology of ZSM-II and the co-crystall ization of magadi ite on top of it and therefore probably

through

secondary

nucleation

is

shown in

ZSM-II is crystallized using I,8-diaminooctane, morphology is obtained (Part I, Photograph 1.7).

Photograph IV.2. a

totally

When

different

PHOTOGRAPH IV.Z. Crystals of ZSM-ll with a blade-shaped magadiite phase on top of some of them (synthesis method of ref. 6 with an Si/A1Z ratio in the

gel of ZOO).

151

Table IV.2

further shows that ZSt",-II crystals can have a composition

differing over a wide SiO the Al-free

Z/A1 203 analogue of ZSM-II,

SILICALITE-2

by

composition for

analogy the

with

synthesis

range. It even seems possible to synthesize which

the

is

ZSM-5

of ZSM-II

a

silica

case

polymorph denoted

(ref. 5).

claimed

in

the

Hence

the

original

broad patent

(ref. 4) : Na

0.05 - 0.7

20/Si0 2

R 0.02 - 0.20 20/Si0 2 50 - 800 H ZO/Na 20 20 - 300 Si0 2/A1 Z03 a posteriori was proved to be correct (ref. 5) as far as the first three pa rameters a re concerned, but too 1imited when the chemi ca 1 compos it i on of the

gel

is

ratio of the 2/A1 Z03 crystals which was originally thought to be in the range 20 - 90 (ref. 4). Just

as

considered.

for

ZSM-5,

The same holds

numerous

for

the Si0

procedures

and

methods

have

also

been

claimed for the synthesis of ZSM-II with specific composition and properties. Low sodium ZSM-II is obtained when benzyltrimethylammonium (BeTMA) ions are introduced into the gel and partly replace the TBA ions (ref. 9). Although this set of data

is not complete enough to establish true relationships

between some parameters, some trends seem to emerge from

thi s work with

regard to the nature of the parameters that determine the Na/Al content of the freshly prepared

ZS~l-II

crystals. A selection of data from

this work

(ref. 9) is presented in Fig. IV.!. For the high-alumina ZSM-II materials in Fig. less

sodium

is

incorporated

in

the

crystals

IV.IA, it is seen that

when more

BeTMA

ions

are

substituted for TBA ions in the synthesis gel. For the high-sil ica ZSM-II crystals,

however,

the method seems

to work less satisfactorily:

for a

TBA/BeTMA ratio of 0.48 an Na/Al ratio of 0.43 is found (ref. 9,ex.Z) in a sample with an SiO

ratio of 503, which is much higher than predicted Z/A1Z03 by the data in Fig. IV.IA. At a fixed TBA/BeTMA ratio (Fig. IV.IB), even for

high-alumina zeolites, the efficiency of the method to avoid Na incorporation is dependent on the SiO final

zeol ite becomes

ratio of the zeolites and decreases when the 3 richer in sil ica. According to the present authors

z/Al z0

these data can be rationalized as follows. Nucleation of ZSM-II in the gels mentioned occurs via a strict template mechanism with TBA as the templating agent.

These nuclei are silica rich and have a high Na/Al ratio,

indicating

152

TBA/BeTMA (molar) 0.3

0.4

0.5

0.6

A

0.2

OL..-------L.----:7'=------='':-=-----:-=-=-' 50

75

100

125

150

FIGURE IV.l. Variation of Na/Al ratio of ZSM-ll zeolites synthesized with TBA and BeTMA as quaternary ammonium ions. The numbers on the curves refer to the respective examples in ref. 9. (A) Data for 68 < Si0 2/A1 203 < 125; (B) TBA/BeTMA between 0.32 and 0.36.

that charge neutralization of the few aluminium ions incorporated in the structure occurs preferentially with sodium. In this interpretation TBA is the perfect templating agent for nucleation but BeTMA seems to be a more efficient pore filling and charge neutralizing agent. When the Al content in the gel is high, the latter ion is preferred over Na and also over TBA for executing at the same time a pore filling and charge neutralizing function. This interpretation is perfectly in line with the general principles derived for ZSM-5 synthesis in earlier chapters, viz., nucleation is faster in a silica-rich environment and the function of an organic compound may be one of templating or pore filling.

153

PARAMETERS INFLUENCING THE CRYSTALLIZATION RATE OF ZSM-II In previous chapters, the rate of crystallization of ZSM-5 zeolites was shown to be influenced mainly by the basicity and the Si0 2/A1 203 ratio of the gel. These factors in the case of ZSM-II have not been investigated in such detail. Hou and Sand (ref. 7) studied the behaviour of the gel (TBPCl )40 (Na 20)33 (A1 203)0.I (Si0 2 )110 (H 20)7,I50 (H 2S04 )22 at different reaction temperatures (from 373 to 493 K) and changed the K/(K + Na) ratio at 430 K. The crystal 1ization kinetics at every temperature showed the usual induction period and at different temperatures followed an Arrhenius behaviour. In the Na field, ZSM-ll crystallized below 408 K and ZSM-5 above this critical temperature. In the critical temperature zone a two-phase mixture of both zeolites was found. The temperature dependence of the nucleation rate (inverse of the induction period) and the crystal growth rate (tangents of the crystallization-time curve at 50% crystallization) expressed as apparent activation energies Ea n and Ea c' respectively in both temperature domains shows the following values (ref. 7) :

Ea (kJ mol-I) n Ea (kJ mo 1-1) c

ZSM-ll

ZSM-5

78.7 82.8

59.8 54.4

.

Although the physical meaning of the kinetic data expressed in this way is not directly obvious (refs. 10,11) and the experimental accuracy of the data is unknown (temperature control is within :2 K and the crystallinity is determined by XRD, for which an error of :5% is not uncommon), the decreased energi es for ZSM-5 obta i ned at hi gher temperatures seem to be real and possibly reflect that diffusion phenomena intervene more in the rate determining events at higher temperatures. Under diffusion controlled conditions, it is logical that the structure is formed with the lowest symmetry (ZSM-ll is tetragonal and ZSM-5 is orthorombic or monoclinic (refs. 1,2 and 12)).

154

It should be stressed that ZSM-5 is crystallized out of a TBA containing gel at high alkalinity (high ratios of (RZO + NaZO)/SiO Z) and high silica/alumina ratios (no aluminium was added intentionally). All other attempts to use TBA in this high temperature region (> 408 K) gave ZSM-ll crystals but lower alkalinities were used (Table IV.I) (refs. 4-6). Other results using the same synthesis mixture refer to the low-temperature crystallization region (ref. 7). The addition of more than 5% of K in the Group Ia cation fraction to such a high al kal ine gel containing TBP is detrimental to the formation of ZSM-II (ref. 7). At the expense of ZSM-II, a pure ZSM-5 phase is then formed even at low synthesis temperatures. Although the authors did not advance any explanation and in view of the present work this behaviour is difficult to rationalize, all this points into the same direction, indicating that nucleation of the tetragonal ZSM-II framework is very difficult indeed. More examples of such behaviour will be given later in this section. Some of the parameters that affect the crystall ization rate of ZSM-ll are now discussed in more detail. Fig. IV.Z shows the influence of the Al content of the gel on the degree of crystallization of a gel with a relatively low (RzO + NaZO)/SiO Z ratio containing TBA ions. 100

s:

'
~

QJ

...-

ell

>...-

e

...-ell IJl

>-

~

u 0~

0

0

1

2

3

100 AI / AI+5i

FIGURE IV.Z. Change of the degree of crystallization with the Al content of the synthesis gel. Gel composition : (TBA)g.4(Na zO)10.g(Alz03)x(SiOZ)100 (HZO)ZOOO at 413 K with TBA-OH, aerosil, aluminium sulphate and NaOH as reactants.

155

Mainly

for

the

very

high-sil ica

gels

(Al

<

1%),

the

overall

crystall ization rate increases significantly when the Al content of the gel is further decreased. Similar behaviour was reported for ZSM-5 (Chapter I). For a given zeol ite to nucleate as a single phase, an optimum OH/Si0 2 ratio seems to exist as was clearly evidenced for ZSM-5. When increasing amounts of sulphuric acid are added to the gel used synthesis of ZSM-ll,

the overall

in Fig.

IV.2 for the

crystall ization rate gradually increases

(Fig. IV.3) and at a given pH decreases again. This behaviour suggests that an optimum OH/Si0

2

ratio also exists for the rate of ZSM-II crystallization.

Further evidence that the rate of formation of ZSM-ll is very sensitive towards the nature of the organic template used is given in Table IV.3.

100

s: '
...

...... ...>4l

III

50

C

... III l/l

...>o 0::oS?

0

8

10

9

11

12

pH

FIGURE IV.3 Change of the overall H to the gel (x 2S04

= 3.3)

rate of crystallization on addition of

in Fig.IV.2 under the conditions indicated there.

156

TABLE IV.3 Influence of the nature of the template (R) on the degree of crystallization (a) of the gel (R)9.4(Na20)1O.9(A1203)3.3(Si02)100(H20)2,OOO crystallized at 433 K for 24 h.

R

Benzyltriphenylphosphonium (BeTPhP) chloride Tetrabutylphosphonium (TBP) chloride Tetrabutylammonium (TBA) iodide 1,8-Diaminooctane

a

0.1 0.7 0.4 0.75

Although the three quaternary salts mentioned in Table IV.3 are known to act as effective templates in the synthesis of ISM-II (ref. 4), their templating efficiency seems to be largely dependent on the size of the organic base. As the corresponding hydroxides of the quaternary ions are very strong bases and will be completely dissociated under the reaction conditions used, this effect will not have its origin in different OH/Si0 2 ratios. Under the present conditions of relatively low alkalinity (compared with the conditions in which ISM-5 is obtained with TBA (ref. 7)), the size of the template is seen to determine to a large extent the overall crystallization rate, indicating that a true effect of templation directs the gel crystallization to the formation of a pure ISM-II phase. Table IV.3 further shows that 1,8-diaminooctane is even more effective than TBP for ISM-II synthesis. Rollmann and Valyocsik have reported extensively on the use of diamines in the synthesis of high-silica zeolites (refs. 13-16). However, in order to obtain significant protonation of this diamine relatively low OH/Si0 2 ratios will be needed in order to make the amine soluble and effective as a template or pore filling agent (ref. 14). Compared with the TBP-containing gel, the gel with 1,8-diaminooctane will have a substantially lower OH/Si0 2 ratio and consequently this diamine is not necessarily a more efficient templating agent than TBP.

157

SYNTHESIS OF THE MEL STRUCTURE TYPE USING OIAMINES Oiamines (CnON) are weaker bases than the previously mentioned hydroxides of quaternary ions. For diaminobutane for example, the first (pK a1) and second (pK aZ) dissociation constants are I1.Z and 9.7, respectively (ref. 16). Therefore, in order to have significant protonation of the diamines, the OH/SiO Z ratio will have to be low. Given the way the OH concentration is calculated as proposed in the Mobil patents and in pertinent patents on this subject (see, e.g., ref. 16), the OH/SiO Z ratios used may have negative values and will be very much dependent on the CnON/SiO Z ratio. The OH/SiO Z ratio is calculated using the OH- content obtained as follows : any moles of hydroxide - moles of acid or aluminium taking into account that any mole of zeolite-incorporated A10 consumes Z moles of OH

Z

and that no assumptions are made regarding amine protonation. In other words amine is not included in the calculations. Some reactants are considered to be composed of several molecules, e.g., Sodium silicate Aluminium sulphate

NaOH + SiO Z A1 Z03 + HZS04.

Negative OH/SiO Z values then indicate that more moles of acid were added compared with the hydroxide. The higher the CnON/SiO Z ratio, the more alkaline the synthesis mixture will be at a given OH/SiO Z ratio. In other words, in order to reach a certain pH value needed for complete protonation of a diamine, a lower OH/SiO Z ratio will be required when higher CnON/SiO Z ratios are used. The influence of the chain length of the diamine used as a template or pore filling agent on the nature of the zeolite obtained has been studied by Rollmann and Valyocsik (refs. 14,16). It was found that with C30N (diaminopropane) and C40N, pure ferrierite-type zeolites were crystallized. From a gel containing C50N and C60N, pure ZSM-5 was obtained, whereas with CSON and CgON pure ZSM-ll crystallized. Other diamines gave mixed phases of ZSM-5 and ZSM-ll. Pertinent results are shown in Fig. IV.4.

158

100

I

A

50

50 4

,--

FER+ ZSM-5

10

l/l

N

0 100

~

~

,.,

I

:E

O

.--

100

"

.--

sO

,-r-r-r-

,--

50

s: I

~

r-r-r-

.--

N l/l

50

j

~

.-0

3

4

5

6

7

8

9

10

11

12

100

en DN

FIGURE IV.4 Influence of diamines with different chain lengths (CnON) on the nature of the zeal ite crystal 1ized after 3 days at 433 K. (A) From refs. 14 and 16; (B) our unpublished results. The gel composition from which the materials are crystallized is as follows:

CnON/Si02 OH/Si0 2 Si02/A1 203 Na/Si02

A

B

0.29 < 0.01 90 0.59

0.09 0.02 120 0.23

The main difference between the two sets of data is the CnON and Na. The phase purity was determined by XRO. More specifically, the crystallinity data in Fig. IV.4B were obtained using the following equation:

159

lSM-5

100 D:6

( 111.1)

where 19. 06 and IS. S refer to peak heights at 28 reflections of the Cu Kc radiation of 9.06 and S.S, respectively. The former peak is absent in lSM-11. The maximum ratio of the heights of these peaks that we ever obtained on a lSM-5 sample was 0.6; this ratio therefore corresponds arbitrarily to 100% ZSM-5. Both sets of data (Fig. IV.4) clearly show that in order to synthesize pure lSM-11 in diaminoalkane-containing gels, the diaminoalkane should have a very specific chain length. Apparently 1,S-diaminooctane is a preferred "template". In an attempt to specify the action of 1,S-diaminooctane, based on the organi c content of the synthes i zed materi a1s , the degree of pore filling was estimated assuming an all end-to-end arrangement of the organics at Van der Waals distances (ref. 17). The results are represented graphically in Fig. IV.5. The data show that there is a direct relationship between the amount of organic used in the gel and the amount of it incorporated during the crystall ization. In the work of Rollmann and Valyocsik (Fig. IV.5A) almost no sodium was retained (ref. 16) and the lSM-11 pores were well filled with the organic component. In our work (Fig. IV .5B), using less organic compound, only one set of pores was filled with diaminooctane. With diaminopentane, a similar degree of pore filling can be achieved in each instance. However, ZSM-ll is not crystall ized with C5DN but ZSM-5 (Fig. IV.4). In addition to pore filling, it therefore seems that another factor is important as a structure-di rect i ng agent. Such a factor may be the charge density of the molecule. For all other diaminoalkanes either a higher degree of pore filling is encountered (Fig. IV.5A) or a smaller degree (Fig. IV.5B). It follows from the former instance that several organic molecules have to be accommodated at the intersections of the pores of the zeolite, whereas in the latter instance pore filling is incomplete.

160

,'--"'-

\

A ,' I

'\

,

\ " ~,.

100---==- - - - - - - - - MFI

Ol

c::

.= ... ... o

MEL

MFI

-----'!

MEL

MEL

b - ,,

Q)

\

B \

a.

/

\

50~

,-,'

'

,--, r \

,-'

',----

~

I

I

I

I

I

I

I

I

I

I

C5DN C6DN C7DN CaDN CgDN FIGURE IV.5. Degree of pore filling with diaminoalkanes of the ZSM-5 (MFI) and ZSM-ll

(MEL)

zeolites obtained in

Fig.

IV.4. Level

a corresponds to

complete pore fill i ng of ZSM-ll and 1eve 1 b corresponds to fi 11 i ng of the pores in one crystallographic direction. (A) Derived from ref. 16;

(B) our

unpublished results.

Comparing the theoretical CIN ratios of monoamines and diamines with the organic composition

IC/N (observed)

I

of the zeolite gives an idea of the

average chemical nature of the occluded organics (Fig. IV.6). Although all the data are not decisive, a majority fit very well the line for monoamines, which

indicates that diamines are relatively easily

deaminated under the synthesis conditions. The picture emerging from all

these data stresses the importance of

diamines as pore filling agents which direct the synthesis of MEL, MFI and mixed

phases

or

intergrowths

of

those

two

zeolites.

In

the

case

of

tetraalkylammonium ions and tertiary amines, Derouane and co-workers (refs. 18,19) advanced a well-founded hypothesis that this function of the organic component is dominant as a structure-directing parameter.

161 10,-----------

---,.-,

•

/-

/ ~amines

./

- /"

8

/

/

6

/ /

•

/

z

/

\

/

•

/-

u

•

/

4~

/'

/'

/'

./

/ ' "'diamines

•

./

/'

»:

»:

./

./

./

22:--------I.-----'-------LJ 4 3 5 C/N theoretical

FIGURE IV.6. Comparison of theoretical CIN ratios of diamines with the observed CIN ratios of the zeolite-occluded material. The lower dashed line gives the expected relationship for diamines and the upper line for monoamines and assumes deamination. The round and square points correspond to the data in Fig. IV.4A and B, respectively. In this way, tetrapropylammonium ions and tributylamine are ZSM-5 directing organics, whereas tetrabutylammonium and tripropylamine give crystals rich in ZSM-ll (ref. 19). However, a mixture of propyl bromide and tri propyl ami ne does not behave in the expected way, as it produces ZSM-5 (ref. 19). As only tripropylamine is found as an occluded organic, this necessarily means that trace amounts of tetrapropylammonium formed on reaction of the tertiary amine and the bromide are templating during nucleation, whereas during crystal growth the amine is progressively incorporated (ref. 19). This again shows that the tetraalkylammonium ions are superior templating agents but also that once nuclei of a given structure (here ZSM-5) are formed, it is difficult to change the crystall ization towards another structure type even with the help of an otherwise effective directing agent. The data in Figs. IVA - IV.6 further suggest that, in addition, the charge density or distribution is also important as a structure-determining parameter. The understanding of this behaviour at the molecular level is not clear.

.

162

X-RAY-INVISIBLE ZSM-11 ZEOLITES It has been shown experimentally that an ordinary ZSM-5 synthesis can be interrupted at the stage of nucleation and that a solid which is amorphous to X-rays but with IR framework vibrations and shape selective behaviour, typical of crystalline ZS~1-5, can be obtained. Jacobs et al. (ref. 20) denoted these solids , which probably were ZSM-5 nuclei dispersed in an amorphous matrix, as X-ray amorphous ZSM-5 zeolites. As no systematic study has been devoted to the mechanism of ZSM-11 synthesis, and everyone assumes a behaviour identical with that of ZSM-5, we decided to interrupt a classical ZSM-11 synthesis in the presence of tetrabutylphosphonium ions at different synthesis times. For this purpose a gel of composition (Na 20)43 (TBPCl )4.7 (Al 203)1.0 (Si0 2)93 (H 20)3,150 was prepared using water glass and sodium aluminate. The pH was adjusted to pH 10 by adding H2S04. The final gel was distributed over a set of autoclaves and heated at 423 K with continuous agitation. At selected crystallization times, one autoclave was opened and the solids were recovered by filtration. As techniques to follow the events during the X-ray amorphous period we used the IR bands specific for the pentasil framework (ref. 20) and a shape-selective catalytic reaction, the bifunctional conversion of n-decane (ref. 21). Fig. IV.7 shows the catalytic activity of the solids recovered after different crystallization times, the X-ray crystallinity and the crystallinity on an IR basis. Similarly to the behaviour of ZSM-5, ZSM-ll crystallites that do not show X-ray diffraction were shown to exist by the IR technique. The catalytic activity of the materials after a very short crystallization period increases significantly but returns to its basic level. At the point where the XRD or IR crystall inity is still zero, the activity has already significantly increased. Hence small nuclei invisible by both XRD and IR spectroscopy exist, as shown by their catalytic activity. When the catalytic activity of the materials is considered in terms of product distribution (Fig. IV.8; Clo is the ratio of 2- to 5-methJlnonane and EC8 the amount of ethyl octanes in the branched isomers (ref. 21)), it is seen that during the first slight increase in activity dramatic changes in the product distribution occur. The cr? value, which is a sensitive measure of steric constraints in 10-MR zeolites, shows a first maximum after 2-3 h of crystallization. During the same period the formation of bulky ethyloctane isomers is suppressed. This behaviour is typical of 10-MR zeolites in general and of ZSM-5 and ZSM-11 in particular

163

*- , ~

0 0

It)

....I1l

100

G)

(II

c

G)

~

.-

0

c:

0

en ~

G)

> c: 0 u

100

><

:::0

o o

~

~

'<

<,

....>-

en

50

50 Dr

=

.S

....en

I1l

>-

~

o IX

00 crystallization time/ h

FIGURE IV.7. Changes in IR and XRD crystall inity and catalytic activity in the hydroconversion of decane during the synthesis of ISM-II in the presence of tetrabutylphosphon;um.

164

10 Z5M-11

9 15

'2R

8

m o OJ

:i"

3 10

0

;:,

0

...0-01

a

-

;:,

o

U

~

C'D Q. (fl

5

0

3

...C'D (fl

crystallization time/h

FIGURE IV.8. Variation of the shape-selective properties of solids recovered during an l5M-ll synthesis, measured by the amended constraint index Clo and the ethyl octane (EC8) content of the monobranched isomers (see text). The hatched area corresponds to the thermodynamically expected val ue of ct? in the temperature range of interest.

165

(ref. 21). In parallel to the crystal growth period (after 12 h crystallization), a similar but more pronounced change in shape selectivity of the solids is again encountered. This behaviour clearly demonstrates that in the early stages of the crystall ization when no crystal 1ine material is yet detectable by physical methods, l5M-ll nuclei are formed with low catalytic activity or acidity. During further crystallization, these nuclei are dissolved at least partially and recrystallize with incorporation of aluminium. This mechanism fits exactly the ultimate picture derived for l5M-5. In conclusion, compared with the l5M-5 case a much smaller number of organics can be used as structure-directing agent in the synthesis of l5M-11. The function of the organic is one of true templation (TBA, TBP, BeTPheP and 1,8-diaminooctane) or of pore filling (BeTMA). The nature of the organic is important as fa r as charge density and dis tri but ion is concerned. 50 fa r , no-one has apparently succeeded in making the material in the absence of any organic. Mechanistically, l5M-11 nucleation and crystal growth seem to occur along similar lines to those found for l5M-5.

166

REFERENCES 1.

G.T. Kokotailo, P. Chu, S.L. Lawton and W.M. Meier, Nature ill (1978), 119.

2. 3. 4. 5. 6.

7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21.

22. 23.

W.M. Meier and D.H. Olson, "Atlas of zeolite structure types", IZA, Polycrystal Book Service, Pittsburgh, PA, 1978, p. 63. G.T. Kokotailo and W.M. Meier, Chem. Soc. Special Publ. 1l (1980) 133. P. Chu, U.S.P. 3,709,979 (1973), assigned to Mobil Oil. D.M. Bibby, N.B. Milestone and L.P. Aldridge, Nature 280 (1979) 664. P.A. Jacobs, J.A. Martens, J. Weitkamp and H.K. Beyer, Disc. Faraday Soc. E (1981) 353. L.Y. Hou and L.B. Sand, Proceed. VIth Int. Conf. Zeal ites, D. Olson and A. Bisio, eds., Butterworths, Guildford, 1984, p. 887. M.K. Rubin, C.J. Plank, E.J. Rosinski and F.G. Dwyer, E.P.A. 14,059 (1980), assigned to Mobil Oil. P. Chu, E.P.A. 112,006 (1983), assigned to Mobil Oil. S.P. Zdanov, Adv. Chem. Ser. 1Ql (1971) 20. H. Lechert, Stud. Surf. Sci. Catal. ~ (1984) 107. LL. Wu, S.L. Lawton, D.H. Olson, A.C. Rohrman and G.T. Kokotailo, J. Phys. Chem. 83 (1972) 2777. L.D. Rollmann, U.S.P. 4,107,195 (1978), assigned to ~10bil Oil. L.D. Rollmann and E.W. Valyocsik, U.S.P. 4,108,881 (1978), assigned to Mobil Oil. L.D. Rollmann and E.W. Valyocsik, U.S.P. 4,139,600 (1979), assigned to Mobil Oil. E.W. Valyocsik and L.D. Rollmann, Zeolites 2 (1985) 123. P.A. Jacobs, H.K. Beyer and J. Valyon, Zeolites 1 (1981) 161. Z. Gabelica, E.G. Derouane and N. Blom, Appl. Catal. 2 (1983) 109. Z. Gabelica and E.G. Derouane, A.C.S. Symp. Ser. 248 (1984) 219. P.A. Jacobs, E.G. Derouane and J. Weitkamp, J.C.S. Chem. Conm. (1981) 591. J.A. Martens, M. Tielen, P.A. Jacobs and J. Weitkamp, Zeolites i (1984) 98. Z. Gabelica, M. Cavez-Bierman, P. Bodart, A. Gourgue and J.B. Nagy, Stud. Surf. Sci. Catalysis 24 (1985) 55. E. Moretti, S. Contessa, M. Padovan, Chim. Ind. ~ (1985) 21.

167

CHAPTER IV

POTENTIAL MEMBERS OF THE PENTASIL FAMILY OF HIGH-SILICA ZEOLITES

INTRODUCTION The advent of zeol ites ZSM-5 and ZSM-ll, propri eta ry zeol ites from Mobil Oil Company, has triggered extremely large research efforts by other companies and also by academics and research institutes. Apparently numerous ZSM-5- and ZSM-ll-like materials seem to exist that differ only in minor detail from the originally described materials. In this respect the ZSM-5silicalite dispute has already been mentioned in Chapter 1. Materials have been described, mainly in the patent literature, that differ from ZSM-5 mainly in their chemical composition, their X-ray diffraction pattern, their sorption capacity or their detailed catalytic behaviour. Although the differences may be sufficient in some instances for a patent to be granted in certain countries, it does not necessarily mean that they belong to different structure types. In this present chapter, data on some of these ZSM-5- and ZSM-ll-l ike materials will be examined and their differences from or similarities to the originally described materials will be stressed. In order to be able to do so, it is necessary to elaborate on the crystallographic structure of ZSM-5 and ZSM-11.

CRYSTALLOGRAPHIC STRUCTURE OF ZSM-5 and ZSM-11 The framework structures of ZSM-5 and ZSM-11 have been solved by Kokotailo and co-workers (refs. 1,2) and Flanigen et al. (ref. 3) derived the framework topology of silicalite. A stereo plot of a ZSM-5 ( denoted as an MFI structure type) and ZSM-11 (MEL structure type) was given by Meier and Olson (ref.4). Experimental and calculated powder diffraction data on ZSM-5 have been published by von Ballmoos (ref. 5) and the structure refinement of TPA-ZSM-5 was published by Baerlocher (ref.6). The secondary building units in both MEL and MFI are 5-1 units, containing a five-membered ring of T-atoms (Al or Si) (refs. 1-4,6,7).

168

The structures can also be viewed as being based on pentasil units (Photograph v.r.a) , which are joined to form chains or columns (Photograph Volob)o When adjacent columns are related by reflection, the basic layer, the so-called pentasil layer, is formed, which is common to both ZSM-5 and ZS~1-11

(refs. 7,8). A model of such a pentasil layer is shown in Photograph

V.2.

PHOTOGRAPH V.l. A model representing (a), the pentasil unit and (b), the pentasil chain, common to ISM-5 and ISM-II zeolites. The tetrahedra represent Si(Al) T-atoms and the sticks indicate the diameter of the T-atom connecting oxygen atoms.

169

PHOTOGRAPH V.2.

A model representing a pentasil layer, common to ZSM-5 and

ZSM-ll zeolites.

All structures containing these specific configurations (pentasil unit, chain or layer) have been described by the generic name PENTASIL (ref.l). This designation refers to "a remarkable and apparently continuous series (ref. 3) of porotecto silicates, exhibiting common X-ray diffraction patterns with

respect

characteristics"

to

significant

(ref.

10).

lines

indicating

common

Only the two end-members

structural

(ZSM-5 and ZSM-lI)

correspond to discrete structure types (MFI and MEL, respectively) and will therefore be found in an atlas of zeolite structure types (ref.4). The most symmetrical (ref.2).

pentasil

The unit

zeolite is ZSM-lI, which cell

dimensions

are

2.01

has

a tetragonal

and 1.34 nm for

symmetry a and c ,

respectively (refs. 2,4). The structure type consists of pentasil joined in related

such a way that neighbouring by a

reflection

layers,

layers are enantiomeric and are

(a) (ref.7). A model of ZSM-ll in the three

crystallographic directions of the crystal is shown in Photograph V.3. The framework atoms circumscribe a two-dimensional

network of straight pores,

which intersect perpendicularly. These pores are identical in the 11001 and

170

jOlOl

crystallographic directions and consists of ten-membered rings of

(T-O) atoms. If neighbouring pentasil layers are related by an inversion and thus are also enantiomeric, the framework of ZSM-5 is generated (ref.7). The unit cell of such a crystal is orthorhombic (reL1) with the dimensions a = 2.01, b = 1.99 and c = 1.34 nm (refs. 2,4). In this way the 10-MR pores along the [010[ direction remain unaltered whereas along the 11001 direction the straight set of pores of ZSM-11 disappear and are replaced with a sinusoidal set of pores, intersecting the straight set perpendicularly. A framework model of ZSM-5 is shown in Photograph V.4 along these two crystallographic directions. In Photograph V.5 framework models show how the two sets of pores intersect in the two pentasil end-members and also illustrate the nature and shape of the pore intersections. In ZSM-ll, two types are present with different sizes: type (large) and type II intersections (small). In the 11001 crystallographic direction type I and type II intersections alternate. Along a pore in the 10101 direction, either type I or type II intersections are present. In ZSM-5 intersections type III of a size intermediate between type I and II are present. The framework topology of silicalite, or of fluoridesilicalite (ref.11), "a silica polymorph with properties similar to those of silicalite", is identical with that of zeolite ZSM-5 (reL12). Further discussions on this issue, relevant for crystallographers but less so in the present context, can be found in the discussions of the 5th International Zeo1ite Conference (reL13). The unit cell of both pentas il end-members consists of 96 tetrahedra (refs. 1-4). The straight channels along 10101 or b show an elliptical shape and have a free cross-section of 0.57-0.58 x 0.51-0.52 nm (ref.3). The zig-zag or sinusoidal channels along 11001 or a are nearby circular and have a free cross-section of 0.54 ± 0.02 nm (ref.3). With the crystallographic data a theoretical channel length per unit cell (ref.14) can be calculated. For ZSM-5 and ZSM-ll, its value is 8.8 and 8.0 nm, respectively (refs. 14,15) if the diameters of the pore intersections are counted twice. Another important structural difference between MFI and MEL is the presence of four 4-MRs per unit cell in the former structure and eight 4-MRs per unit cell in the latter.

171

PHOTOGRAPH V.3. Framework models of zeolite ZSM-ll !0101,110ol and [0011 crystallographic directions.

viewed along

the

172

173

PHOTOGRAPH V.4.

Framework model of zeolite lSM-5 viewed along the

11001 crystallographic directions.

10101 and

174

175

PHOTOGRAPH V.5. Illustration of the two types of pore intersections present in

ZS~l-lI

(A) and of sinusoidal

(B) and straight pores (C) in the

direction in ZSM-5 and ZSM-ll, respectively.

11001

176

177

INTERGROWTHS IN THE PENTASIL FAMILY OF ZEOLITES As pentasil layers can be assembled via at least two symmetry operations (a reflection or an inversion), it seems a priori possible that in the same crystal this may occur to different extents. In these instances neither pure nor

ZS~'-5

pentasil

pure

ZSM-ll

is

obtained

but

intergrowths

(ref.?)

of

the

two

end-members. The generation of such an intergrowth starting from

individual pentasil layers is shown in Fig. V.l.A.

It is evident that this

phenomenon influences the pore shape (Fig. V.2) in the ilOOI direction and also the concentration of type I, II and III pore intersections. In fact, the sequence of the different types of intersections of the pores in the 11001 direction with those in the [0101 direction can be varied without limit (Fig. V.3). Crystallographically, the presence of intergrowths will mainly influence the dimension

of the

unit cell

in

situation for the pure end-members (a

the a direction.

=

In

contrast to the

2.0 nm), the minimum value

of a is

4.0 nm and can be expressed in the following more general way (refs. 22,23) :

= 4.0

a(nm)

where n is an Fig. V.l (0

2.0n

+

integral i 0)

(IV.l) number.

The sequence of pentasil

layers shown in

corresponds to a repeat distance of 4.0 nm. A regular

repetition of pentasil layers connected via a sequence of symmetry operations such as

(0 0

0

i

0

0

0

i ) would create a unit cell dimension of 8.0 nm in

the a direction (ref.23). The existence of local

intergrowths in ZSM-ll and ZSM-5 crystals

has

..

been demonstrated experimentally by Thomas and co-workers using mainly highresolution electron microscopy and optical diffractometry (refs. 16-20). As this kind of "defect" is generally encountered in so-called "pure" ZSM-5 or ZSM-ll,

it does not mean that

phase

pure ZSM-5 or ZSM-ll crystals are

impossible to synthesize. Indeed, a report exists in which these intermediate structural

variants

could not be

detected

(ref.

21).

Unfortunately,

authors did not elaborate on the origin of the pentasil intergrowhts are easily detectable (refs. (ref. 21).

the

samples in which

16-20) or are completely absent

A

cr

6' o

o

o

o

o

o

~

-.]

00

'-

ZSM-11

ZSM-5

ZSM-5

[oo~

ZSM-11

[100J FIGURE V.I. Generation of an intergrowth of the pentasil family of zeolites. (A) stacking of a (0 pentasil layers; (B) a pentasil layer.

0) sequence of

179

FIGURE V.2. Section of a pore in the 11001 crystallographic direction of the structure shown in Fig.V.1. Intersections of this pore with the channels in the 10101 crystallographic direction are of type I, II or III.

6

6

I

I

FIGURE V.3. Section through two parallel pores in the 11001 direction illustrating the relationship between the stacking sequence of the pentasil layers and the sequence of type I,ll and III cavities.

180

EXPERH1ENTAL DISCRIMINATION BETWEEN PURE ZSM-5, ZSM-II ZEOLITES AND THEIR INTERGROWTHS X-ray diffraction (XRD) patterns constitute a generally used way of discriminating between discrete zeol ite phases. As a result of its highest symmetry in the pentasil class of materials, ZSM-II shows the lowest number of diffraction peaks. As indicated earlier, the absence of a diffraction line at 9.06 °28 using Cu Ka radiation (third line in ZSM-5) (Chapter III) is a first rough indication of a pure MEL phase. This is not, of course, a sufficient criterion to identify unambiguously a pure ZSM-II phase, as small crystal

samples

of

ZSM-5

or

its

intergrowths

with

ZSM-ll will

cause

considerable peak broadening and an eventual disappearance of this peak in the more intense peak close to 8.80 °28. The only satisfactory way to identify pure ZSM-II is to index ~ peaks, even those with weak intensities, using the tetragonal symmetry class. Only when this is possible does strong evidence exist that a given pentasil sample is pure ZSM-II. The discrimination between a pure ZSM-5 phase and an intergrowth by XRD alone is therefore hardly possible. A semi-quantitative measure for doing so was given earl ier, based on the relative intensity of the XRD peaks around 8.80 and 9.06 °28. The highest intensity ratio of the 9.06 to 8.80 °28 peaks, in the authors' experience, never exceeded 0.60 for hydrated and uncalcined samples. A literature survey of these peak intensities is given in Table V.1 for the sake of comparison. Several remarks can be made in this respect: i.

Only in one case is this ratio higher than 0.60, but the data refer to a dehydrated sample (refs. 5,6) ; futher, no deta il s of the ori gi n of the sample were given, but considering the identity of the author (ref. 6) it might well be that it is similar to the sample which has a ratio of 0.61 (ref.32). The latter sample was synthesized under highly dilute cond it ions.

ii.

Unfortunately, we have been unable to

determine this ratio using a

sample considered to be pure ZSM-5 by Mobil researchers; only for ZSM-5 that is not phase pure can peak intensities for the XPD spectrum be found in the literature; the ratio in this instance is 0.48.

181

TABLE V.l. Literature values of XRD intensity ratios of the 9.06 (III) to 8.80 (II) 028 peaks a

Sample

ZSM-5 type ZSM-5 ZSM-5 + unidentified phase High-silica ZSM-5 P-containing ZSM-5 type

ZSM-5 type ZSM-5 ZSM-5

a,

peak height of

Ref.

IrrI/I rr

hydrated

0.32 0.40 0.48 b 0.35 0.58 0.55 0.44 0.41 0.21 0.68 c 0.61

uncalcined

24 25 26 27 28 29(Table 1) 29(Table 2) 29(Table 3) 30 31 32

samples;

b,

measured from the

diffraction pattern shown; c, 19.08/18.87'

As al ready mentioned, local intergrowths can be directly viewed using high-resolution electron microscopy (HREM). Unfortunatly, it is not possible to quantify the degree to which intergrowths are present in a particular crystal, or in a whole sample. Ul tra-high-resolution microscopy allows crystal regions of approximately 30 by 35 nm to examined for the existence of regular, trrequt ar and random isolated intergrowths (ref.46). In such images the eye readily discerns intergrowths of less than a unit cell.

182

Extended strips of semi-regular intergrowths of ISM-ll seem to occur very often in samples considered to be ISM-S (ref.46). As the theoretical channel lengths of the pores in a ISM-S or a ISM-II unit cell are different (refs.I4,IS), careful adsorption work might allow one to estimate to a certain extent the phase purity of a pentasil sample. Gabelica et al. (ref.I4) determined the amount of organic material retained after a particular synthesis and calculated the degree of pore volume filling. It was concluded that in agreement with a maximum pore filling model, the synthesis of pentasils in the presence of tripropylamine gives a phase rich in ISM-II, whereas with tributylamine an intergrowth rich in ISM-S could be obtained. With triethylamine and tripentylamine only amorphous phases are obtained. The authors (ref.7S) speculated that the maximum space filled by four such entities does not correspond to a unit cell space length of 8.0 or 8.8 nm. Sorption of hydrocarbons on pure ISM-S and ISM-II (ref.IS) showed that the degree of pore filling was also dependent on the size of the sorbate : for small n-alkanes (C I - CS)' complete pore fill ing occurs on ISM-S via an end-to-end type of adsorption of the sorbate molecules and at the pore intersections two molecules are accommodated; with the same sorbate molecules the pores of ISM-II are filled via the same type of sorption but only in one crystallographic direction. Intermediate behaviour is therefore expected to reflect the presence of an intergrowth. The so-called Mobil Contraint Index (CI) characterizes medium-pore zeolites in catalytic conditions. The sample has to be in the acid form (the residual organics have to be burned off and the residual Na+ ions exchanged by H+) and the cracking of hexane and 3-methylpentane has to be investigated under specific conditions (ref.33). It is defined as follows (ref.33) : CI

109IO Ifraction of hexane unconverted I 10910 Ifraction of 3-methylpentane unconverted I

For H-ISM-S and H-ISM-ll, CI values of 8.3 and 8.7, respectively, were reported (ref. 38). As the pore sizes of ZSM-S and ZSM-ll are similar, differences in the CI values are the result of differences in transition states for hydride transfer of both feed molecules in the pores (ref.74). Apparently, this catalytic test reaction is insensitive to the differences in size and shape between type I and II pore intersections (in ZSM-II) and type III pore intersections (in ZSM-S). Moreover, it seems that at least for ISM-S, the exact values of CI are also dependent on several non-structural parameters, including the silica-alumina ratio of the zeolite, the reaction temperature and the presence of impurities (ref.34).

18:3

To distinguish between MFI and MEL structure types and hence characterize their intergrowths, a catalytic reaction can only be useful if it allows one to estimate the rel ative amounts of

type I,

II or I I I intersections in a

given amount of pentasil material. Therefore, a reaction is needed for which contraints on the formation of the transition state influence the reaction selectivity. In principle many reactions behave in this way (refs.35,36) but only the hydroisomerization of n-decane has been studied in sufficient detail (ref.37). isomers,

For

the

branching

reaction

of

n-decane

it was found that certain product

into

its

methylnonane

ratios were mainly structure

dependent and did not vary substantially with reaction conditions and sample acidity or crystal morphology. Therefore, a refined constraint index (CIO) was defined at 5% conversion of n-decane (see also Chapter III) : amount 2-methylnonane formed amount 5-methylnonane formed It turned out that in sterically restricted environments, branching occurred preferentially near the end of the hydrocarbon chain. Clo values of 6.8 and 2.7 have been reported (ref.37) for ZSM-5 and ZSM-ll, respectively, samples with comparable chemical therefore

be

useful

composition and morphology. This criterion should

in

determining

pentasil

intergrowths

in

a

more

quantitative way. In search of a confident criterion for estimating the overall nature of a pentasil

sample,

the catalytic Cl " criterion was plotted against the XRD

criterion, IIII/III

in Fig. V.4. There is a surprisingly good correlation

between these criteria. As, for reasons explained already, Clo is sensitive to the concentration of type 1,11 and

III

intersections in a sample and

therefore measures directly the phase purity of a pentasil sample, the XRD criterion, although less accurate, seems also to be sensitive to the phase purity of a pentasil sample. More recently, the 29Si MAS NMR (magic angle spinning nuclear magnetic resonance) spectra of highly siliceous ZSM-5 and ZSM-11 zeolites were shown to

be

different

with

respect

to

chemical

intensities of these signals (ref.8).

shift

values

and

relative

They should therefore constitute a

fingerprint of the zeolite structure (ref.8).

In early low-resolution work

(ref. 76,77) the intensity ratio of the - 115 ppm peak in ZSM-11 to ZSM-5 was found to be 2,

irrespective of the Al content of the samples.

This was

correlated with the different numbers of 4-MRs present in the two structures, viz., 8 and 4 spectra,

in ZSM-11 and ZSM-5, respectively. Later high-resolution 29Si

however,

showed

a

peak-height

ratio equal

to one

for the same

184

spectral line (ref.B). For dealuminated ZSM-5 and ZSM-11, the spectral intensities of the different lines agree with the number of non-equivalent Si atoms that can be derived from the proposed structures for the two materials. In ZSM-5, the intensities of the outermost resolved peaks at - 109 or -116 ppm to the total resonance envelope is 1: 24 (refs.7,76,77) as required by the space group proposed for this zeolite (ref.47). For similar reasons, the ratio of the most intense resonance line of zeol ite ZSM-ll to the total resonance envelope should be 16 : 96 (a maximum of 16 crystallographically

8

pure MEL

pure

MFI~

6

o

o

2l.-

....L-

o

0.2

----L

0.4

..L...-J

0.6

FIGURE V.4. Plot of the refined contraint index (CIO) against the peak height ratio of specific X-ray peaks (1111/111) for pentasil samples synthesized in the presence of: 1, diaminooctane; 2, diaminoheptane; 3, benzyltriphenylphosphonium chloride; 4, diaminohexane; 5, an equimolar mixture of octylamine and tetraethylammonium hydroxide; 6, tetrapropylammonium bromide; 7, dodecyltrimethylammonium chloride and 8,diaminopentane. The syntheses followed are those described earlier for the diaminoalkanes(Part. r., p. 20) and, for the quanternary ions, that described with TBP (Chapter III, p. 157).

unique Si atoms exist per unit cell), which corresponds to the experimental ratio of 1: 6.4 (ref.l). The 29Si spectra of the pentasil end-members seem to be sufficiently different to be able to distinguish qualitatively between intergrowths. To put this on a more quantitative basis, however, will require a substantial amount of further work.

SYMMETRY CHANGES OF ZSM-5 ZEOLITES Wu et al.

(ref.39) were

the first

to

observe a "reversible, displacive

transformation" of the orthorhombic symmetry of ZSM-5 into a monocl inic form on certain treatments. Subsequently this observation has been confirmed by several other workers (refs. 39-45) using both XRD and 29Si MAS NMR. The most striking observations are summarized in Table V.2. Changes

in

the

XRD

lines

and

in

systematically on certain treatments.

the

29Si

MAS

NMR

spectrum

occur

In the former instance they can be

attributed to a symmetry change from orthorhombic to monoclinic and vice versa; in the latter instance, changes occur in a parallel way but are not understood in detail.

NMR shows that a similar effect also occurs in ZSM-II

(ref.7), which, however, has not yet been attributed to particular symmetry changes. In the XRD lines of ZSM-5, the following reversible changes occur, "resul ting from crystal

symmetry changes between

topologically equivalent

forms", which do not imply a difference in framework structure (ref.39) : i.

the intensities of the lines at about 7.9 and 8.8 °2e increase when extra-framework inorganic or

organic material

fill ing the pores

is

removed. It should be stressed that the IIII/III ratio changes only from ..0.42 to 0.38, implying that this criterion for estimating the degree

of

intergrowths

can

probably

be

used

irrespective

of

the

sequence of treatments to which a particular ZSM-5 sample has been subjected; ii. lines at about 11.9 and 12.5

°2e decrease in intensity;

iii. singlets are replaced by doublets (at 23.2, 24.4, 29.2 and 48.6 °2e) and vice versa (at 14.7 and 23.9 Crystallographic

computations

on the

°2e). line

positions

confirm

that

these

changes are consistent with the symmetry changes mentioned (ref.39). Typical changes in the XRD lines from orthorhombic to monoclinic symmetry are shown schematically

in Fig V.5.

TABLE V.2. Treatments for which the orthorhombic (0) - monoclinic (m) symmetry transition and vice versa is observed in the MFI structure type.

Starting sample

Si0 2/A1 203

TPA/Na-ZSM-5 H/Na-ZSM-5 H-ZSM-5 Sil i ca1i te Sil i ca1ite Sil ical ite Sil ical ite

70-3,000 70-3,000 70-3,000 450 450 130 130 40 <160 >160 >3,000 high high

ZS~1-5

ZSM-5 ZSM-5 Silicalite TPA-ZSM-5 H-ZSf'iI-5

Treatment

Calcination + NH 4 exchange Moisture adsorption NH 3 adsorption Calcination Calcination Calcination Calcination Calcination Calcination Calcination Calcination p-xylene adsorption p-xylene adsorption

Temp./K

811

<383 873 748 873 773 873 823 823 <798

-

Symmetry from to

0 0 m

-

0 0

m m 0 m 0 m 0 0 0 0 0 0 m

Technique

XRD XRD XRD XRD XRD XRD XRD XRD XRD XRD XRD XRD + NMR XRD + NMR

Ref.

39 39 39 45 45 45 45 45 41 41 42 44 44

.....

gs

I"'"

I I

I

I

.... ~

I I I I

ll-

U)

c

....c:

l-

I I I

I

I

I

I

I

Q,)

i

I I

l-

I

III

ll-

I I

r-

I

....

L 5

I

...L

9

l 13 ...1.

.V

II

II

"

!r I

17

I

I

21

1111 25

I I I I

i

29

33

i

1

37

I

I

...1.

41

45

I

1 11.

49

degrees 28 FIGURE V.5. Changes in the XRD lines of Z5M-5 samples with orthorhombic symmetry on changing to a monoclinic symmetry after calcination and exchange with ammonium (after ref.3g). >-'

00

-J

188 It is now unequivocally established that the orthorhombic-monoclinic symmetry change in the MFI structure type: i. is a reversible transformation (Table V.2); ii. is dependent on its aluminium content (the higher the Si0 2/A1 203 ratio, the easier the transformation occurs on certain treatments (ref.39), including calcination and sorption). iii. is temperature dependent (refs. 42,43). Calcined ZSM-5 at room temperature is orthorhombic for Si0 2/A1 203 < 160 (ref.41). The transformation temperature (Tt) changes as follows with the chemical composition (ref.42) :

> 460

317 - 325 295 <272 < 110 iv. occurs on adsorption over a small concentration range, suggesting that a phase transition mechanism occurs (ref.44). 198

OVERVIEW OF SOME PENTASIL-TYPE ZEOLITES CLAIMED IN THE LITERATURE In previous paragraphs in this chapter, several possible reasons have been discussed as to why XRD 1ines can change in position and intensity in pentasil zeolites. In addition to the already mentioned changes in symmetry c1ass dependi ng on the sample his tory, the presence of i ntergrowth s , the crystallite size and the chemical composition will also influence the dimensions of the unit cell and therefore the 1ine positions. Moreover, in addition to intergrowths the formation of mechanical ZSM-5/ZSM-11 mixtures is another possibility, e.g. using C2 - C5 n-alkylamines (ref.75). With ZSM-5, the unit cell increases when the number of heteroatoms (in casu, Al) increases (refs.48,49). Patent attorneys may consider such variations sufficient for granting a patent but scientifically this does not necessarily mean that a new zeol ite structure type has been synthesized. The material s that are described below have often been the subjects of granted patents or patent applications and, according to their XRD lines, belong to the pentasil family of zeolites. For all these particular pentasil materials, several examples are given in the respective patents and consequently they can be synthesized in a reproducible manner, at least by the authors of the patents. Their peculiarities will also be summarized below.

TABLE V.3. Conditions for the synthesis of various zeolites belonging to the pentasil group of materials with sodium as inorganic alkali ion

Zeol ite

Ref.

ZS~1-8a

50 54,ex.1 56 58 59 59 65 71

ZETA-3 a NU-4 a NU-5 a rSM-5 b ZSM-ll b CASb,c,d TZ-01 AZ-01 b

72

73

Si0 2/H20

0.05 - 0.23 0.02 0.025 - 0.05 0.022 - 0.050 0.003 - 0.125 0.003 - 0.125 0.014 - 0.033 0.05 0.05 0.1 - 0.02

Si0 2/ A12°3

64 - 150 59 - 88 60 - 300 89 40 - 20,000 30 - 3,000 200 - 2,000 30 30 20 - 300

R/Si0 2

0.3 0.51 0.9 0.22 - 1. 0 - 1. 0 - 0.8 0.08 0.08 0.5 - 3.0

0.05 0.39 0.05 0.12 0.1 0.1 0.2

-

OH/Si0 2

0.1 0.17 0.02 0.09 0.01 0.01

-

0.3 0.43 0.3 0.18 0.2 0.2

?

0.09 0.9 ?

R

TEA alcohols polyamines pentaerythritol TPA TBA TPA carboxylic acids tartaric acid 1,8 diamino-4ami nomethyloctane

a, actual spread of experimental data shown in the examples; b, preferred conditions claimed in the patent; crystalline aluminosilicates; d, F- is necessary so that F-/Si0 2 = 0.2 - 0.8.

c, CAS

( 1)

w

190

TABLE V.4. Templates used for the synthesis of some proprietary pentasil zeolites

Zeol ite

Templates

Ref.

ZSM-8 ZETA-l ZETA-3 NU-4 NU-5

TEA TPA; cetyltrimethylammonium isopropanol; glycerol; alcohol mixture TEPA a; TETA b; N,N-diethylethylenediamine Pentaerythritol or its oligomers

51 53 54 56 58

a, TEPA

tetraethylenepentamine; b, TETA = triethylenetetramine.

TABLE V.5. Characterization of some proprietary pentasil materials based on some XRD lines in terms of the intergrowth percentage of ZSM-ll in ZSM-5

Zeol ite

ZSM-8 a ZETA-l a ZETA-3 a H-NU-5 a NU-5 a H-NU-5 b

Ref.

50 53 54 56 58 58

Proprietary holder

IIII/Ill

Mobil

0.24 0.13 0.09 0.28 0.49 0.44

leI leI leI leI leI

% intergrowth

(ZSM-ll in ZSM-5)

60 78 85 53 18 27

a, as synthesized forms; b, hydrogen form, after removal of organic material and acid treatment.

191

1.

ZSM-8 (refs. 50-52)

This member of the pentasil family of zeolites is a Mobil proprietary material, with an X-ray diffractogram very similar to that of ZSM-5 (Fig.V.9.1), synthesized under the conditions used for ZSM-5 (Table V.3) but with TEA (tetraethy"lammonium) as a specific template (Table V.4). According to the XRD criterion handled for intergrowth characterization, the Mobil material seems to be a 40:60 ZSM-5-ZSM-11 intergrowth. Moretti et al. (ref.60) classified the material as ZSM-5, whereas Gabel ica et al. (ref.52), using a laboratory made sample (8-14 ~m aggregates of 1-2 ~m tubular crystals) consider it to be a ZSM-5-rich intergrowth, based on its 90% pore filling (compared with TPA-ZSM-5) with TEA after synthesis. Using the n-decane hydroisomerization reaction, a CI o value of 5.6 was also obtained for a laboratory made sample. This value is slightly below that of ZSM-5 (CI O 6.5), categorizing this sample as a ZSM-5-rich intergrowth. The efficiencies of the synthesis of ZSM-8 and other pentasils are compared with that of ZSM-5 in Fig.V.6. It is our experience that in the presence of TPA zeolite ZSM-5 can be easily synthesized with 100% efficiency based on the sil ica involved. In Fig. V.6, literature data either confirm this (with the experimental points on the diagonal 1ine of a graph of chemical composition of the gel plotted against that of the zeol ite) or indicate an equal preference of the ZSM-5 matrix for Si and Al. The latter has now been sufficiently proved not to be true (see Chapter I), which allows us to conclude that Fig.V.6 is a measure of the synthesis efficiency. The data for ZSM-8 in Fig.V.6 indicate a significantly decreased efficiency of synthesis, which can possibly be related to the different nature of the template used for ZSM-5 (TPA) and for ZSM-8 (TEA). According to Moretti et al., "ZSM-8" can be obtained using tributylheptylammonium, trioctylmethylammonium, diethylmorpholinium, ethylpentylpiperidinium or ethylquinolinium cations or with tributyl- and tripropylamine (ref.60). The assignment as ZSM-8 is, however, not disputed (ref. 60). The sorption capacities of several pentasil zeolites are compared in Fig. V.7. ZSM-5 and ZSM-8 show comparable sorption data for m-xylene but are distinctly different for cyclohexane. In view of the proposed structural assignment of this zeolite such a difference should not exist, so that more detailed work is needed to clarify this issue.

192

e

150

ZSM-5 I I

I

oQ)

NU-4 i;;./ T.

N

..-

C

C")

oC\I

100

-ZETA-3

-, C\I

o

--

a

(f)

0-

50

~-8

o

a

O~~

o

L-

50

L-

100

~

150

FIGURE V.6. Preference of pentasil zeolites for aluminium incorporation from the synthes i s gel to the zeol ite with s i 1i ca as reference, obta i ned by comparing the SiO Z : A1 203 ratio in the synthesis gel with the composition of the crystallites. a, ZSM-8 (ref.48); b, ZETA-3 (ref.50); c, NU-4 (ref.52); d, NU-5 (ref.54); e, ZSM-5 (Part I, recipe IO.a); f, ZSM-5 (ref.52).

19:1

2. ZETA-l (ref.53) According to the inventor of this material ZSM-5, and

can

only

be

synthesized with

(ref.53), it is related to

solid silicic

acid

as

a silica

source. Surprisingly, in a recent review of the synthesis and properties of certain l CI proprietary zeolites (ref.5?), this material According

to

its

X-ray

diffractogram

(Fig.

is not mentioned.

V.9.2)(ref.60),

it definitely

belongs to the pentasil family, is very rich in ZSM-ll (Table V.5), but is synthesized

with

similar

templates

to

ZSM-5 (Table

capacities for n-hexane, cyclohexane and

V.4).

The

sorption

p-xylene are comparable to those

of ZSM-5 (Fig.V.7), but it is not accessible to m-xylene, indicating that the pores are only accessible to molecules with a kinetic diameter of 0.6 nm or less

(ref.53)

Ethylbenzene,

which

has

the

same

kinetic

diameter

as

cyclohexane, also hardly enters the ZETA-l pores. The discrepancy between the sorption data of ZETA-l and ZSM-5 for these sorbates is only apparent as their kinetic flexibility.

diameters

do not account for

the differences

Indeed, cyclohexane can undergo configurational

in

molecular

changes (from

boat to chair form), which can explain the lower sorption capacity of ZETA-l for ethyl benzene compared with ZSM-5. The XRD 1 ines can be indexed in the tetragonal system, such as ZSM-ll, but with a unit cell size of a c

=

=

2.23 and

4.24 nm (ref.53), as required for a pentasil intergrowth. All these data

indicate that ZETA-l is a ZSM-ll-rich pentasil intergrowth, containing pore occlusions. The presence of pore occlusions can also be derived from the low intensity of the XRD lines in the 7-9 °20 region, compared with those between 22 and 25 °20 (Fig.V.9.2.) and compared with those of ZSM-8 (Fig.V.9.l) and ZSM-5 (Fig.I.3.3).

194

0000000

10

-

•••••••• >-0-0 "C

-----_.

(1)

X

x

--- ZSM-5

0000000

-0-ZSM-11

•••••••

oooZETA-1

X )(

x x x

~

o (/)

ZSM-8

------ ------ ------ ------

x x x x

.c

-

0000000 1-0-0-

~Q:=.9:-

xxZETA-3

>-

... NU-5

5

x x x x

~o

.... ~

o

x x x x x x \~~

~i~~~ water

0.28

n-

cyclohexane 0.42 0.60

0000000

ggggggg

p-

methylxylene benzene 0.60 0.62 0.60

sorbate and kinetic diameter/nm

FIGURE V.l. Room temperature adsorption of various sorbates on different pentasil zeolites: Z5M-8 (ref.51), Z5M-5 (ref.51), Z5M-ll (ref.53), ZETA-1 (ref.53), ZETA-3 (ref.55) and NU-5 (ref.58).

195

3. ZETA-3(refs.54,55) ZETA-3

is

another pentasil

zeolite that can

be synthesized in

the

absence of N-containing organics, but with alcohols (Table V.4). For ZSM-5 similar synthesis procedures have been discussed (Chapter II). It should be stressed that at that time of the discussion no distinction was made between individual materials of the pentasil group; they were all considered as pure ZSM-5. Moreover, no data are available in the literature cited at that time, that

would

allow

one

to

categorize

these

ZSM-5

materials

as

potential

intergrowths. ZETA-3 is a ZSM-5-type material (refs.54,55,60) (Fig.V.9.3) synthesized under similar conditions of basicity and chemical composition (Table V.3), can

be categorized as

ZSM-ll-rich (Table V.5), and has

capacity than ZETA-l for cyclohexane and p-xylene

a lower sorption

(Fig.V.?). Its synthesis

efficiency is only slightly lower than that of ZSM-5 (Fig.V.6). Continuing the interpretation of the data in this figure as "template efficiency", it follows that alcohols are very efficient agents for ZETA-3 synthesis, either as "true" templ ates or as pore fill i ng agents. 4. NU-4 (refs.56,57) NU-4 zeolite is an ICI proprietary material that permanently exhibits monoclinic symmetry (ref.56,57) (Fig.V.9.4), in contrast to ZSM-5, for which the

monoclinic-orthorhombic

conversion

is

reversible

and

for

which

the

as-synthesized form is orthorhombic. It seems to be a random intergrowth (50% ZSM-ll) (Table V.5), synthesized in the presence of polyamines (Table V.4) under conditions of basicity, content of organics and chemical composition comparable to those for other pentasil zeolites (Table V.3). It is therefore a pentasil zeolite with the lowest possible symmetry (refs. 56,57). The synthesi s efficiency of NU-4 (and in

the context of the present

interpretation of the polyamine template molecules) is only slightly lower than that for ZSM-5 (and TPA). The crystals of NU-4 are large (3 - 100 ~m), prismatic and twinned (ref.56). It has a sorption capacity comparable to that of

ZSM-5

for

sorbates with

kinetic

diameters

smaller

than

0.6

nm

but

permanent pore occlusions impede the fast adsorption of m-xylene (Fig.V.S). The permanent presence of pore occlusions of H-NU-4 compared with H-ZSM-5 is also evident when the intensity of the XRD lines at small °28 are compared. For NU-4

they are very low in intensity (Fig.V.9.4). In order to synthesize

this zeolite as a pure phase free of any NU-lO (another high-silica zeolite, described in Chapter VI), very low H and high OH/Si0 ratios, or both 2 20/Si02

196

are needed. In other words, the synthesis gel has to be very concentrated and basic, as both parameters are interdependent. Typical effects of changes in these parameters on the crystallization time and on the nature of the phases synthesized are given in Table V.6. The data clearly show that a higher basicity (compare I with II and III) substantially decreases the crystallization time for NU-4 or that a lower concentration at equal basicity (compare IVa with IVb) gives ultimately a different zeolite.

10.--------------="1 p-xylene

5

o

o ~-......I---L.-----'---l.-..-.....J o

1

4

5

FIGURE V.8. Diffusion plot of p- and m-xylene sorption on the H-forms of ZSM-5 and NU-4 zeolites (after data in ref.56).

197

TABLE V.6 Synthesis of NU-4 zeolites (calculated from the data in ref.56)

I (ex.3 a)

SiOZ/HZO SiO Z/A1 Z0 3 R/SiO Z Na/SiO Z OH/SiO Z Crystal 1ization Time/days Temp./K Zeolite phase

II (ex.9)

I II (ex.10)

IVa (ex.7)

IVb (ex.7)

0.OZ5 60 0.33 0.60 0.06

0.OZ5 61.8 0.33 0.56 O.OZ

0.OZ5 61.8 0.33 0.56 0.15

0.OZ5 96.3 0.Z8 0.6Z 0.05

(0.05)b 96.3 0.Z8 0.6Z 0.05

Z 453 NU-4

5 453 NU-4

1 453 NU-4

40 378 NU-10

4 378 NU-4

a, ex. = example (described in ref.56). b, more concentrated gel obtained by refluxing before autoclaving. With N,N'-diethylethylenediamine as template it seems difficult to obtain pure NU-4 (ref.56). When K replaces Na in an otherwise identical gel (ref.56), NU-10 is obtained instead of NU-4. Supplementary addition of salts to the gel (e.g., NaCl) accelerates the crystallization but is difficult to remove after crystallization. and therefore influences the sorption characteristics of NU-4 (ref.56). At the same time either a quartz or a cristobalite co-crystallizes (ref.56). 5. NU-5 (refs. 57,58) This ICI proprietary material also has an XRD pattern similar to that of ZSM-5 (Fig. V.9.5), but with additional lines and intensity changes. It also seems to be very close to a ZSM-5-rich intergrowth (Table V.5) synthesized under conditions comparable to those for ZSM-5 (Table V.3) but with pentaerythritol as the basic template molecule. The hexane sorption capacity is comparable to that of ZSM-5 (Fig.V.5), but in contrast to this material it does not allow cyclohexane or m-xylene into its intracrystall ine void

198

volume. The p-xylene sorption capacity for both materials remains unaltered, however. This pentasil material therefore seems to be very suitable for the isolation of p-xylene from a mixture of its configurational isomers (ref.58). 6. OTHER PENTASILS Zeolite ZBM-IO (ref.6I) is possibly another ZSM-ll-rich member of the pentasil family, synthesized in the presence of polyamines. Depending on the nature of the amine, the lowest Si0 material

is

obtained

varies

ratio for which a crystalline 2/A1203 from 38 (dihexamethylenetriamine) to 19

(triethylenetetramine). Assuming that all aluminium is in the framework, the latter value corresponds to nine Al atoms in a pentasil unit cell containing 96 T-atoms. This is close to the theoretical maximum of eight Al atoms per unit cell of ZSM-5, or to half of the theoretical Al-capacity of ZSM-II. Another pentasil-like zeolite with catalytic properties differing from those of ZSM-5 was prepared in absence of organics using regular ZSM-5 seeds (ref.62). Its X-ray diffractogram in shown in Fig.V.9.6. TRS has

an XRD pattern (Fig.V.9.?)

that is unique (ref.63). Careful

examination shows the presence of pentasil lines (p) and of cristobalite (c), but also of lines at specific positions or with unusual intensities (x). The available data (ref.63) do not allow one to decide whether this is a new zeolite or a mixture of several phases. Zeolite MB-28

is

synthesized

in

the presence of diethylpiperidinium

(ref.64) and is classified by one of the inventors in another publication (ref.60) as ZSM-5-like. Some of the pentasil lines (indicated by (x) in Fig. V.9.8), however, show very unusual intensities.

Based on this XRD

pattern

the MB-28 materi a1 coul d also belong to the mordenite family (see Chapter X). Also, a ZSM-ll-like pentasil has been claimed (ref. 65) using fluoride ions in the synthesis gel, under conditions otherwise comparable to those for pentasils (Table V.3). Some peaks (indicated by (x) in Fig.V.9.9) have very unusual

intensities. In this way, a unique crystal morphology is obtained.

The crystals are "pillar-like octahedra whose vertices and edges have been worn" (ref.65), with a length of at least 10 um. "Ultrasil" zeolites are denoted as properties are

similar to

those

"one of those new zeolites whose

of ZSM"

vibration bands around 550, 595 and 625 cm(refs.I5,67,68).

Therefore,

it

is

(ref.66). I

The specific

lattice

are typical of pentasil zeolites

evident

(ref. 66) ZSM-5 is meant by ZSM and ultrasil

that

in

the

original

article

is yet another member of the

pentasil family. In the same way, a high-silica Ultrazet zeolite is said to be a "Polish counterpart of the ZSM-5" (ref.69) ,while TsVKs are its "Soviet analogues"(ref.70).

TABLE V.7. Characteristics of some pentasil-like proprietary zeolites

Zeolite

Ref.

Patent holder

Template

ZBM-IO CAS a TRS

61 62 63

BASF Teijin Petrochem. Snam Progetti

Polyamines

MB-28

64

Montedison

CAS a

65

Mitsubi shi

Ultrasil Ul trazet TsVK TZ-Ol AZ-l

66 69 70

-

72

73

Toray Asai K.K

a, CAS: crystalline aluminosilicates.

Characteristics

ZSM-ll-like according to XRD ZSM-5 seeds, pentasil-like Pentasil-lines + cristobalite lines + TPA unknown lines diethylpiperidinium Pentasil lines with very unusual intensities ZSM-ll-like, with very unusual peak TPA intensities, synthesized with F Pentas il TPA ? ZSM-5 ? ZSt1- 5 Pentasil intergrowth (55% ZSM-5) Tartaric acid Pentasil-like, with constrained pore 1,8-diamino4-aminoethyloctane access

-

'"-' so «o

200

Pentasil-like materials have also been synthesized in the presence of carboxylic acids such as succinic, o-toluic, citric and salicylic acid (ref.71), under conditions comparable to those for other pentasils (Table V.3). In an attempt to replace the expensive and corrosive quaternary ammonium ions with their "offensive odour" (ref.72) in the synthesis of high-silica zeolites, zeolite TZ-Ol was claimed, using tartaric acid under otherwise comparable conditions to obtain pentasil zeol ites (Table V.3). TZ-Ol, according to the XRD lines, is pentasil-like (Fig. V.9.l0) and, depending on the criterion considered, could be a random intergrowth. A zeolite denoted as TZ-02, synthesized under similar conditions but with salycilic acid, belongs to the mordenite family according to its XRD lines. Zeolite AZ-l (ref.73) is a high-silica zeolite synthesized in the presence of 1,8-diamino-4-aminomethyloctane, which shows a pentasil-like XRD spectrum with unusual line intensities (Fig. V.9.11). According to its sorption data it has a significantly lower pore accessibility than ZSM-5. Indeed, pyridine is sorbed in comparable amounts on both materials, whereas the adsorption ratios of pyridine to 4-methylquinoline are 250 and 20 on AZ-l and ZSM-5, respectively (ref.73). Some useful characteristics of the zeolites discussed here are summarized in Table V.7. This overview is meant to be as complete as possible, but only U.S. and European patents have been systematically consulted. Even then, new pentasil materials might have escaped us. The aim of this section has been two-fold: i. to give the reader who does not follow the patent literature in detail an impression of the complexity of the situation with regard to new zeolites and the family to which they belong; and ii. to give to the same reader a collection of useful data that will be of much help in his own synthetic efforts in this area.

FIGURE V.9.1. ZSM-8(Nederl.Octrooiaanvrage 7.014.807. Table A)

sL

f-

-

2

a

fff-

d [0. 1nm]

1/10

11.10 10.00 9.70 7.42 6.35 5.97 5.69 5.56 4.25 4.07 4.00 3.85 3.82 3.75 3.71 3.64 3.43 3.34 3.31 3.13

46.00 42.00 10.00 10.00 12.00 12.00 9.00 13.00 18.00 20.00 10.00 100.00 57.00 25.00 30.00 26.00 9.00 18.00 8.00 10.00

- ,

IJ

5.0

9.0

I 11.1 I

13.0

I ,II

17.0

.I I

I

21.0

III IL 25.0

I h, 29.0

I 33.0

I 37.0

II 41.0

45.0

,

GO

49.0

53.0

o

FIGURE V.9.2. ZETA-1 (G.Offenl. 2,548,695, Table 1)

d [0. inm]

t.

-

2

II

5.0

9.0

I

I . III, I ,I 13.0

17.0

.1

II, I 21.0

•

25.0

,

.II. 29.0

• 33.0

,

• 37.0

•

, 41.0

,

11.12 9.97 9.72 7.44 6.35 6.04 :.98 5.56 5.00 4.60 4.34 4.26 4.00 3.84 3.82 3.75 3.72 3.65 3.05 2.98

e

, 45.0

,

, 49.0

•

I1Io 30.00 23.00 3.00 7.00 8.00 7.00 7.00 8.00 4.00 6.00 7.00 8.00 7.00 100.00 77.00 38.00 44.00 31.00 7.00 10.00

• 53.0

"" o

""

FIGURE V.9.3. ZETA-3(G.Offenl. 2.548.695. Table 2)

sL 2

d [0. 1nm]

r/re

10.97 9.85 7.36 6.30 5.94 5.S7 5.52 5.33 4.58 4.33 3.98 3.82 3.73 3.70 3.63 3.04 2.97 2.93 2.00 1.99

35.00 23.00 8.00 10.00 6.00 7.00 9.00 15.00 7.00 9.00 7.00 100.00 14.00 34.00 28.00 10.00 11.00 11.00 8.00 8.00

e

I

(... I

~

t-

~ 5.0

9.0

13.0

III

,I 17.0

I

I

21.0

I

25.0

.L

,I

,

29.0

33.0

,

I

37.0

I

I

41.0

I

,II , 45.0

I

49.0

I

I

53.0

ec w

o

FIGURE V. 9.4. NU-4 (aa-mede) (E.P. A. 65. 401. ex. 3)

t.

ff-

2 9

ffffff-

ff-

ffff-

ff-

d [0 . 1nm]

IlIa

11.30 11.10 10.0B 9.90 9.77 5.75 5.65 4.63 4.39 4.29 4.12 4.04 3.BB 3.B5 3.74 3.73 3.6B 3.65 3.47 3.33

16.00 20.00 15.00 B.OO 6.00 B.OO 6.00 9.00 13.00 10.00 13.00 6.00 100.00 69.00 51.00 50.00 27.00 22.00 12.00 9.00

fff-

5.0

I I 9.0

,

, I 1.11 13.0

I

I

17.0

J

I,

I

21.0

I

25.0

III.

I

29.0

I

I

33.0

I

I

37.0

I

, 41.0

I

I

45.0

I

I

49.0

I

I

53.0

"" o

""

FIGURE V. 9.5. NU-5 (as- made) (E. P. A. 54. 386. ex. 1)

sL

ff-

2

f-

e

ffffffff-

f~

f~

d [0 . 1nm]

IlIa

11.11 10.02 9.96 9.74 6.36 5.99 5.70 5.59 4.37 4.27 4.10 3.86 3.82 3.75 3.72 3.64 3.32 3.05 2.99 2.98

70.00 41.00 37.00 18.00 14.00 15.00 12.00 13.00 15.00 15.00 14.00 100.00 70.00 39.00 54.00 31.00 12.00 12.00 13.00 13.00

f-

lf-

• 5.0

I

9.0

•

1,,1 13.0

.111 17.0

.I

II 21.0

II

25.0

I

29.0

33.0

I

I

37.0

41.0

I

II

45.0

I

• 49.0

I

53.0

o '" en

FIGURE V.9.6. crystalline aluminosilicate(E.P.A. 94,693, Table A)

i.

f-

2

'-

e

~

f-

~

f~

f~

f-

d [0. 1nm]

I1Io

11.26 10.11 6.05 5.74 5.61 4.39 4.28 4.04 3.86 3.83 3.75 3.74 3.66 3.46 3.36 3.33 3.06 3.00 2.98 2.96

37.00 24.00 9.00 7.00 8.00 8.00 14.00 7.00 100.00 75.00 45.00 53.00 33.00 10.00 19.00 10.00 16.00 18.00 18.00 8.00

~

ffI

5.0

II 9.0

I

I

13.0

III

I 17.0

I

I II

II

21.0

25.0

II

1.1

I

I

29.0

33.0

37.0

41.0

45.0

I

49.0

53.0

"" o en

FIGURE V.9.7. TRZeG.Offen.2.924.870.Fig.1)

t. 2 9

l-

d [0 . 1nm]

IlIa

11.47 10.04 9.11 7.25 5.60 5.06 4.07 3.90 3.86 3.78 3.74 3.70 3.46 3.42 3.18 3.07 2.99 2.90 2.70 2.49

35.30 25.50 17.70 35.00 70.95 25.50 27.30 100.00 78.40 47.00 54.60 35.30 25.50 100.00 50.90 15.70 19.60 50.90 35.00 15.70

f-

lfI

I

I

5.0

9.0

13.0

I

I .I Il

17.0

21.0

.I 25.0

29.0

33.0

37.0

I

I

41.0

I

I

45.0

I

I

49.0

I

I

53.0

co o

-1

FIGURE V.9.8. MB-28 (calcined) (E.P.A.2i. 445. ex.i)

t. 2

I

5.0

I.

I

9.0

I

I

I II

13.0

JI

I

I

17.0

I. I

I 21.0

III. I

I

25.0

29.0

I 33.0

37.0

I 41.0

e

.I 45.0

d [0 . 1nml

I1Io

11.16 10.01 9.05 5.57 4.26 3.97 3.84 3.83 3.75 3.72 3.65 3.46 3.35 2.98 2.46 2.13 1.82 1.54 1.38 1.38

13.00 7.00 4.00 4.00 22.00 5.00 30.00 5.00 4.00 8.00 6.00 6.00 100.00 4.00 7.00 5.00 11.00 7.00 5.00 6.00

49.0

53.0

tV

~

FIGURE V.9.9. crystalline aluminosilicate (as-made) (E.P.A.31. 255. ex.i)

t. 2

I

5.0

I

9.0

13.0

17.0

I

21.0

25.0

29.0

I

11.30 10.00 5.01 3.84 3.75 3.72 3.65

I

I

33.0

e

d[0.1nm]

37.0

41.0

IlIa 13.00 94.00 22.00 100.00 24.00 25.00 15.00

I

45.0

49.0

53.0

t:2 Cl5

FIGURE V.9.10. TZ-01(as-made) (E.P.A. 57.016.ex.1)

sL 2

d [0. 1nm]

I1Io

11.30 10.09 9.82 6.75 6.40 6.04 5.75 5.61 4.39 3.86 3.83 3.76 3.74 3.66 3.47 3.38 3.06 2.99 2.02 2.00

49.00 33.00 11.00 8.00 9.00 12.00 10.00 13.00 10.00 100.00 82.00 50.00 55.00 27.00 15.00 9.00 10.00 16.00 9.00 11.00

e

...

... I

5.0

I 9.0

I

I JII 13.0

J .1 II" I dI

17.0

21.0

1.1 25.0

II..

J 29.0

•

I. '.1 33.0

I •. 37.0

•

I

41.0

I

.1.

III.

45.0

• I

49.0

53.0

,.... "" o

FIGURE V. 9 .11. AZ-1 (as-made) (E. P. A.113, 116, ex .1)

t.

rr-

2

r-

e

f-

r-

d [0. 1nm]

I1Io

11.32 10.16 9.93 5.06 5.01 3.85 3.77

18.42 100.00 100.00 18.42 15.79 57.89 36.84

f-

rf-

rf-

rf-

rf-

rff-

rfI

I

5.0

9.0

I

13.0

I

I

17.0

I

I

21.0

I

25.0

I

I

29.0

I

I

33.0

I

I

37.0

I

41.0

45.0

49.0

53.0

""

>-' >-'

212

REFERENCES 1. G.T. Kokotailo, S.L. Lawton, D.H. Olson and W.M. Meier, Nature ~ (1978) 437 and D.H. Olson, G.T. Kokotailo, S.L. Lawton and W.M. Meier, J. Phys. Chern. ~ (1981) 2238. 2. G.T. Kokotailo, P. Chu, S.L. Lawton and W. H. Meier, Nature 275 (1978)119. 3. E.M. Flanigen, J.M. Bennett, R.W. Grose, J.P. Cohen, R.L. Patton, R.M. Kirchner and J.V. Smith, Nature ~ (1978) 512. 4. W.M. Meier and D.H. Olson, Atlas of Zeolite structure types, Structure Commission IZA, 1978, Polycrystal book service, Pittsburgh. 5. R. von Ballmoos, Collection of simulated XRD powder patterns for zeolites, Butterworth, Guildford, 1984, p.74. 6. C. Baerlocher, Proceed. 6th Int. Zeolite Conference, D. Olson and A. Bisio, eds., Butterworths, Guildford, 1984, p.823. 7. G.T. Kokotailo and W.M. Meier, Chern. Soc. Spec. Publ. ~ (1980) 133. 8. C.A. Fyfe, G.T. Kokotailo, G.J. Kennedy and C. De Schutter, J.C.S. Chern. Commun. (1985) 306. 9. W.M. Meier, ref. 7, p.274. 10. G.T. Kokotailo, ref. 7, p.214. 11. E.M. Flanigen and R.L. Patton, U.S.P. 4,073,865 (1978), assigned to Union Carbide Corp .. 12. G.D. Price, J.J. Pluth, J.V. Smith, T. Araki and J.M. Bennett, Nature ~ (1981) 818. 13. Recent Progress Reports and Discussion, 5th Int. Conf. Zeolites, R.Sersale, C. Colella and R. Aiello, eds., Giannini, Naples, 1980, p.210-225. 14. Z. Gabelica, E.G. Derouane and N. Blom, A.C.S. symp. Ser. 248 (1984) 219. 15. P.A. Jacobs, H.K. Beyer and J. Valyon, Zeolites 1 (1981) 161. 16. J. Thomas, G.R. Millward and S. Ramdas, A.C.S. Symp. Ser. ~ (1983) 181. 17. J.M. Thomas, S. Ramdas, G.R. Millward, J. Klinowski, M. Audier, J. Gonzalez-Calbet and C.A. Fyfe, J. Sol. St. Chern. ~ (1982) 368. 18. J.M. Thomas, A.C.S. Symp. Ser. III (1983) 445. 19. S. Ramdas, J.M. Thomas, P.W. Betteridge, A.K. Cheetham and E.K. Davies, Angew. Chern. ~ (1984) 629. 20. J.M. Thomas and C. Williams, Chemical Reactions in Organic and Inorganic Constrained Systems, R. Setton, ed., Nato ASI Ser., Reidel, Dordrecht, C165 (1985)49. 21. J.M. Thomas, G.R. Millward, S. Ramdas, L.A. Bursill and M. Audier, J.C.S. Faraday Disc. ~(1981)345.

213

22. G.T. Kokotailo, U.S.P. 4,289,607 (1981), assigned to Mobil Oil Corp.. 23. G.T. Kokotailo, E.P.A. 18,090 (1980), assigned to Mobil Oil Corp.. 24. M.A.M. Boersma and M.F.M. Post, E.P.A. 40,444 (1981), assigned to Shell Int. Res .. 25. M. Bourgogne, J.L. Guth and R. Wey, E.P.A. 74,900 (1982), assigned to CFR. 26. C.A. Audeh and W.J. Reagan, U.S.P. 4,430,314 (1984), assigned to Mobil Oi I Corp.. 27. W. Roscher, K.H. Bergk, W. Schwieger, F. Wolf, V. Haedicke, W. Krueger, K.H. Chojnacki, DDR P. 207,186 (1984) assigned to VEB chemiecombinat Bitterfel d. 28. id., DDR P. 207,185(1984). 29. H.P. Rieck, G. offenl. 3,242,352 (1184), assigned to Hoechst AG. 30. W.J. Ball, K.W. Palmer and D.G. Stewart, USP 4,346,021(1982), assigned to BP. 31. C. Barlocher, Proceed. 6th Int. Conf. Zeolites, D. Olson and A. Bisio, eds., Butterworths, Guildford 1984, p. 823. 32. R. von Ballmoos, Diss. ETH 6765, Verlag Sauerlander, Aarau, 1981, p.91. 33. W.J. Frilette, W.O. Haag and R.M. Lago, J. Catal. §2 (1981) 218. 34. for a review: F.R. Ribeiro, F. Lemos, G. Perot and M. Guisnet, in Chemical Reactions in Organic an Inorganic Constrained Systems, R. Setton, ed., NATO ASI Series, Reidel, Dordrecht, C165 (1985) 141. 35. P.A. Jacobs and J.A. Martens, Pure Appl. Chem. Vol. 58 No. 10 (1986) 1329. 36. A. Auroux, H. Dexpert, C. Leclercq and J. Vedrine, Appl. Catal. ~ (1983)95. 37. J.A. Martens, M. Tielen, P.A. Jacobs and J. Weitkamp, Zeolites i (1984) 98. 38. Y.Y. Huang, E.P.A. 95,851(1983), assigned to Mobil Oil Corp. 39. E.L. Wu, S.L. Lawton, D.H. Olson, A.C. Rohrman and G.T. Kokotailo, J. Phys. Chem. 83 (1979) 2777. 40. C.A. Fyfe, S.J. Kennedy, C.T. De Schutter and G.T. Kokotailo, J.C.S. Chem. Commun. (1984) 541. 41. H. Nakamoto and H. Takahashi, Chem. Lett. (1981)1013. 42. D.G. Hay and H. Jaeger, J.C.S. Chem. Commun. (1984) 1433. 43. D.G. Hay, H. Jaeger and G.W. West, J. Phys. Chem. 89 (1985) 1070. 44. C.A. Fyfe, G.J. Kennedy, G.T. Kokotailo, J.R. Lyerla and W.W. Fleming, J.C.S. Chem. Commun.(1985) 740.

214

45. G.E.M. De Clippeleir, R. Cohen, G.L. Debras and H. Van Thillo, E.P.A. 146,525 (1984) assigned to Co,den Technol .. 46. J.M. Thomas and G.R. Millward, J.C.S. Chem. Commun. (1982) 1382. 47. C.A. Fyfe, G.C. Gobbi, J. Klinowski, J.M. Thomas and S. Ramdas, Nature ~ (1982) 530. 48. B.L. Meyers, S.R. Ely, N.A. Kutz, J.A. Kaduk and E. Van den Bossche, J. Catal. 21. (1985) 352. 49. P.A. Jacobs, M. Geelen and M. Tielen, Proceed. Siofok Meeting on Zeolite Catalysis, Acta Phys. Chem. Szegedensis (1985) p.1. 50. Nederl. Octrooiaanvrage 7,014,807(1971), assigned to Mobil Oil Corp .. 51. C.J. Plank, E.J. Rosinski and M.K. Rubin, G. Offenl. 2,049,755 (1971), assigned to Mobil Oil Corp. 52. Z. Gabelica, E.G. Derouane and N. Blom, Appl. Catal. 2 (1983)109. 53. T.V. Whittam, G. Offenl. 2,548,697 (1976), assigned to lCI. 54. T.V. Whittam, G. Offenl. 2,643,929 (1977), assigned to ICI. 55. T.V. Whittam, G. Offenl. 2,548,695 (1976), assigned to lCI. 56. T.V. Whittam, E.P.A. 65,401 (1982) assigned to lCI. 57. J. Dewing, M.S. Spencer and T.V. Whittam, Catal. Rev. Sci. Eng. ~ (1985) 461. 58. T.V. Whittam, E.P.A. 54,386 (1981), assigned to ICl. 59. P. Chu, J.C. Vartuli and J.A. Herbst, E.P.A. 127,399 (1984). 60. E. Moretti, S. Contessa and M. Padovan, Chim. Ind. §l(1985) 21. 61. L. Marosi, J. Stabenow and M. Scharzmann, E.P.A. 34,727 (1981) assigned to BASF. 62. T. Onodera, T. Sakai, Y. Yamasaki, K. Sumitani, E.P.A. 94,693 (1983) assigned to Teijin Petrochem. Ind: 63. M. Taramasso, O. Foriani, G. Manara and B. Notari, G. Offenl. 2,924,870 (1978), assigned to Snam Progetti. 64. R. Le van Mao, O. pilato, D. Moretti, R. Covini and F. Genoni, E.P.A. 21,445 (1980), assigned to Montedison. 65. T. Suzuki, S. Hashimoto and R. Nakano, E.P.A. 31,255(1980) and E.P.A. 53,499 (1982) assigned to Mitsubishi Gas. Chem. Compo 66. A.A. Kubasov, L.B. Gorelik, N.F. Meged', Ya. B. MirskU and T.V. Limova, Russ. J. Phys. Chem. ~ (1981) 1175. 67. G. Coudurier, C. Naccache and J.C. Vedrine, J.C.S. Chem. Commun. (1982) 1413. 68. J.C. Jansen, F. Van der Gaag and H. van Bekkum, Zeolites i (1984) 369. 69. J.M. Berak, B. Kanik, J. Mejsner and B. Kontnik-Matecka, React. Kin. Catal. Lett. 20 (1982) 431.

215

70. S.S. Shepelev and K.G. lone, React. Kin. Catal. Lett.

12.

(1981) 233.

71. K. Iwayama, T. Inoue, K. Sato, N. Hayakawa and M. Fujii, E.P.A. 119,709 (1984), assigned to Toray Ind .. 72. K. Iwayama, T. Kamano, K. Tada and T. Inoue, E.P.A. 57,016 (1982) assigned

to Toray Ind ..

73. M. Chono and H. Ishida, EPA 113,116 (1983) assigned to Asahi Kasei K.K. 74. W.O. Haag and R.M. Dessau, Proceed. 8th Int. Congress Catalysis, Vol.II, Verlag Chemie, Weinheim, 1984, p.302. 75. Z. Gabelica, M. Cavez-Bierman, P. Bodart, A. Gourgue and J.B. Nagy, Stud. Surf. Sci. Catalysis

~

(1985) 55.

76. J.B. Nagy, Z. Gabelica, E.G. Derouane and P.A. Jacobs, Chem. Lett. (1982) 2003. 77. Z. Gabelica, J.B. Nagy, P. Bodart, J. Debras, E.G. Derouane and P.A. Jacobs, Zeolites Science and

Technology, F.R. Ribeiro, A.E. Rodrigues,

L.D. Rollmann and C. Naccache, eds., Nato ASI Ser., M. Nijhoff Publ., E80 (1984) 193.

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217

CHAPTER V

HIGH-SILICA ZEOLITES OF THE FERRIERITE FAMILY

STRUCTURE The mineral ferrierite occurs abundantly in nature (ref. 1), with a typical chemical composition, since its Si0 2/A1 203 ratio always varies around an average value of 12. Samples of this mineral have been distributed by Norton Chemical Co. as Zeolon-700. Its crystal structure has been determined by Vaughan (ref. 2) and Kerr (ref. 3). Breck (ref. 1) classifies this zeolite in GROUP 6, together with mordenite, dachiardite, epistilbite and bikitaite. Its structure consists of so-called ferrierite columns (Photograph VI.IA) (ref. 4), the association of which can be seen in the same figure. In the ab plane (Photograph VI.IB) it is seen that the structure consists of chains of 5-MRs, which are interconnected successively through 10- and 6-MR elements. In this way, a two-dimensional network of IO-MR and 8-MR pores is formed, which intersect perpendicularly (Fig. VI.I). The free channel dimensions are 0.43 x 0.55 and 0.34 x 0.48 nm for the IO-MR and 8-MR pores, respectively (ref. 5). As both sets of pores intersect perpendicularly, intersections are formed, which according to Kibby et al. (ref. 6) have a free diameter from 0.6 to 0.7 nm. Careful inspection of a scale ball-and-stick model (as in Photograph VI.I) indicates, however, that this is exagerated, as the dimension of the IO-MR pore hardly changes when it intersects with an 8-MR. This is logical as the 8-MR perforates the IO-MR right in the middle, which is not the case with the IO-MR pores intersecting in a ZSM-ll or ZSM-5 structure, in which this perforation is acentric and consequently specific intersections are formed. The ferrierite structure type is abbreviated to FER and the crystal has an orthorombic symmetry with a ': 1.92, b = 1.41 and c = 0.75 nm (refs. 2 and 5) as unit cell dimensions. The unit cell contains 36 T-atoms (ref. 5).

SYNTHESIS OF FER-TYPE MATERIALS USING INORGANIC GELS Barrer and Marshall (ref. 7) reported the synthesis of an FER-type material, which they denoted Sr-D. A typical reactant composition was

218

PHOTOGRAPH VI.l. Structural elements of zeolite ferrierite. A, The ferrierite columns, and a view along the 8-MR pores in the along the 10 MR channels in the iOOl[ direction.

10101

direction; B,. a view

219

FERRIERITE

FIGURE VI.I. Schematic representation of the pore system of ferrierite.

220

(SrO)1(A1 Z0 3)1(SiOZ)g(H ZO)485. Autoclaving at an unusually high temperature (613 K) gave a ferrierite-type zeolite after 10 days. Lower synthesis temperatures and/or different SiO Z/A1 Z03 ratios produced other structure types (such as chabasite, gmelinite, analcime, yugawaralite, mordenite and heulandite types). Other reports (refs. 8 and g) on the synthesis of this zeolite indicate the same high temperature requirements and narrow SiO Z/A1 Z03 ranges in the Ca and mixed Ca/Na systems. Also in the Na system, the crystallization of pure ferrierite requires a temperature of at least 573 K and an SiO Z/A1 Z03 ratio in the synthesis mixture of 1Z. Seeding and the simultaneous use of different alkaline earth metal hydroxides as a source of basicity reduces the synthesis time from 7 days to 1 day (ref. 10). The same authors showed that in such instances the SiO Z/A1 Z03 ratio of the starting gel (SiOZ/A1 Z03 = 10) corresponds to the composition of the sol id, which is indicative of efficient synthesis conditions. Winquist (ref. 11) succeeded in synthesizing ferrierite from gels containing Na 3P04 and KF, with an SiO Z/A1 Z03 ratio of 11 and temperatures between 448 and 483 K, which are significantly lower than those in all other previous syntheses. The critical parameter, however, in obtaining pure ferrierite under these conditions is the SiOZ/HZO ratio, which should be between 0.037 and 0.046. At lower ratios mixed phases, containing mordenite, are obtained, and at higher ratios ferrierite of lower crystallinity is found. This holds provided the K fraction of the alkali metal cations is between 0.15 and 0.40 (ref. 11). On the acid-activated form of ferrierite (H-ferrierite) less than 1% by weight of aromatics or iso-alkanes is adsorbed, whereas for n-alkanes the amount sorbed depends on the chain length of the sorbate (ref. 6), indicating an end-to-end adsorption of n-alkanes in the pore system, as observed for ZSM-5 (see Chapter IV).

SYNTHESIS OF FER-TYPE ZEOLITES IN THE PRESENCE OF ORGANICS More than a decade ago the first report appeared (ref. 6) mentioning the use of quaternary cat i ons (TMA) for the synthes is of ferri erite. Unfortunately, it did not allow one to decide whether this resulted in the synthesis of a zeolite with an enhanced silica to alumina ratio. Since then, many N-containing molecules and also oxygenated hydrocarbons have been used in this synthesis. Relevant data are summarized in Table VI.l. Different proprietary zeolitic materials belong to this structure type. Many of them are just denoted as ferrierite, whereas some have specific names, such as

TABLE VIol.A Synthesis of FER structure types in the presence of organics No.

Notation

Ref. Si0 2/H2O

TMAferrierite Ferrierite Ferrierite Ferrierite Ferrierite Ferrieri te Ferri erite FER-type FER-type

6

0.036

12 13 14 15 16 17f 18 18g

0.040-0.067 a

11

FER-typel FER-type

18'

12

ZSM-35

13

ZS~1-35

Synthesis Mixture Si0 2/A1 203 OH/Si0 2 12

M/Si02

0.49

12

30 30 30

0.42 b ? . e 0.2 -0.77 e 0.09-0.51 0.01 0.33 0.0 0.0

0.025 0.025

30 30

0.3 0.3

0.60 0.15

0.60 0.60

14 15

ZSM-35 m ZSM-38 m

19jk 19 21 21

0.05 0.031 0.014-0.143 0.020-0.167

30 50 12-60 12-60

0.09 0.19 0.07-0.49 0.07-0.49

0.6-1.5 0.06-0.5

0.07-0.49 0.07-0.49

16

FU-9 n

22

0.028

25

0.36

0.08

0.36

2 3 4 5 6 7 8 9 10

18~

?

0.0006-0.003t 0.031-0.048 0.11 0.02 0.025 0.025

12-22 ad 12-25 39-95 e e 46-187

0.66

R/Si0 2

?

0.34 b ? . e 0.18-0.54 e 0.39-0.61 1 0.33 0.14 0.14

0.58 b ?

0.20~0.77e 0.29-0.90 ?

0.33 0.60 0.60

a, most preferred conditions; b, ex. 3; c , after 3 days ageing at room temperature; d, claimed range; the actual Si0 2/A1 203 ratio in the example = 20; e, spread of actual data; f, run 2; g, run 3; h, run 19; i, run 21; j, ex. 1; k, ex. 8;1, in ref. 20 denoted as ZSM-35; m, preferred limits claimed; n, ex. 1. 'tv -.:J

"" "" ""

TABLE VI.1.B Synthesis of FER structure types in the presence of organics No.

Notation

Ref.

Synthesis temp./K t ime/days

R

M

TMA

Na

573

2,4-pentanedione 1,4-diaminobutane N-methylpyridinium piperidine glycerol 1,6-diaminohexane

Na

K

438 443 423 373-473 463 453

1,3-diaminopropane

Na

373

125

2 3 4 5 6 7

TMAferri erite Ferrierite Ferrierite Ferrierite Ferrierite Ferrierite Ferrierite

8

FER-type

14 15 16 17 18f

9

FER-type

18g

1,4-diaminobutane

Na

373

32

10

FER-type l FER-type

18'

18~

1,4-diaminobutane 1,4-diaminobutane

Na Na

373 373

98 50

ZSM-35 ZSM-35 m ZSM-35

19k 19

17 41 2-21

21

Na Na Na Na

408 372 403-448

ZS~1-38m

FU_9 n

22

pyrrol idine diaminoethane C20N or pyrrolidine 2-hydroxyethyltrimethylammonium 90% TMA + 10% trimethylammonium chloride

Na

453

1

11

12 13

14 15 16

6

12 13

j

21

-

Na Na Na

1.7 3c 7 6 ?

6 2.7

Remarks high temp., reduced time reduced temp. alkali free new template new template

-

ZSM-5 in presence of K low pH through add. of acid C40N better than C ON faster c;ystal1ization with less amine new temp1ate new template

a, most preferred conditions; b, ex. 3; c , after 3 days ageing at room temperature; d, claimed range; the actual Si0 2/A1 203 ratio in the example = 20; e, spread of actual data; f, run 2; g, run 3; h, run 19; i, run 21; j, ex. 1; k, ex. 8; T, in ref. 20 denoted as ZSM-35; m, preferred limits claimed; n, ex. 1.

223

ZSM-35 (refs. 19,20), ZSM-38 (ref. 24) and FU-9 (ref. 22). A family of materials, encompassing both ZSM-35 and ZSM-38, is sometimes termed the ZSM-21 group of zeolites (refs. 23,25). Generally the data in Table VI.1 suggest that as far as the composition of the synthesis mixture is concerned (Si0 2/H20, OH/Si0 2, R/Si0 2 and M/Si0 2 ratios), the synthesis conditions for all the proprietary materials do not differ very much. They are distinguishable mainly by the different nature of the organic used in the synthesis. Compared with the conditions used to obtain ferrierite in the absence of organics, there is a clear effect of these organics: they reduce the synthesis time and/or temperature and allow the crystallization of FER-type structures from mixtures with an Si0 2/A1 203 ratio far above 12. The highest value reported is approximately 190 (ref. 15), which suggests that the zeolites thus obtained should also have a Si0 2/A1 203 framework ratio far above 12. From consideration of Table VI.1, a few important remarks can be made : i. It seems possible to synthesize ferrierite free from residual inorganic alkali (ref. 13); although the methods of synthesis and characterization have been reported with only few details, this material can be converted into its hydrogen form merely by calcination, thus avoiding ion-exchange or acid treatments in order to remove the last traces of alkali, which are harmful in many adsorptive and catalytic applications. ii. Although Rollmann and co-workers (refs. 18,20) claimed that with diamines as template only diaminobutane and the smaller homologues can be used in the synthesis of FER type structures, there is a recent report (ref. 17) in which ferrierite was synthesized in the presence of diaminohexane and potassium. The argument by Rollmann and Valyocsik (ref. 18) that larger diamines are unsuitable as pore filling agents in FER structures, but are very suitable for filling the pores of pentasil materials should therefore be reconsidered; the main difference between the two synthesis methods (ref. 17 against ref. 18) is the use of K as a source of inorganic alkali; it is not clear how this difference can be translated at the molecular level, but there is also no fundamental reason why diaminobutane should fit tightly in the pores of FER types while diaminohexane should not; this does not preclude, however, the hydrocarbon chain length of the diaminoalkane having an influence on the rate of crystallization; indeed, Table VI.1 also indicates that when, under otherwise identical synthesis conditions, C3DN replaces C4DN, the synthesis time increases from 32 to l25 days.

224 iii. The

add i t i on of a mi nera 1 ac i d to

a

synthes i s mixture

reduces

the

crystallization time considerably, provided the mixture remains basic (ref.

18);

this

is

in

line

with

observations

made on

ZSM-5

in

a

restricted pH range (ref. 18). Although wide SiO ranges in the synthesis mixtures for FER-type Z/A1Z03 zeol ites have been claimed (Table VIol), it remains to be proved that the crystals

indeed

contain increased SiO ratios. Therefore, the Z/A1Z03 ratios in the mixtures were plotted against the same ratios in the

SiO

Z/A1Z03 FER-type structures

VI.Z).

(Fig.

Depending

on

the

exact

value

compositional ratios. Fig. VIoZ indicates that up to an Si0 ca.

35, a zeolite with the same chemical

of

some

ratio of

2/A1 203 composition can be obtained.

In

other words, it is also possible for this zeolite to synthesize the material

75

~---------------.,.--------------,

//

.:a

* / //

o:b x:c

.:d c::

A:e

LlJ

u,

.S

/

501-

/

*: f

/

/

/

/

o

/

N

/

*

*

*

/

0"

-, o

/

/

M

N

/

*

x

* •x

*

/

251-

/,(, /

(j)

0/

~

0

x

// .i /

0

/

*

•

/

1/

o

FIGURE VIo2.

25

50

75

100

200

Si0

ratios in a synthesis mixture and in the final 2/A1 203 FER-type zeol ite obtained : a, ref. 18 (FER-type); b, ref. 23 (ZSM-21, pyrrolidine); c, ref. 23 (ZSM-21, C d, ref. 19 (ZSM-35, pyrrolidine); e, 2DN); ref. 24 (ZSM-38); f, ref. 15 (ferrierite).

225

with high efficiency in the Si0

range 15-35. A further increase in the 2/A1203 silica content of the gel has only a minor effect on the ultimate composition

of

the zeolite.

For

ZSM-5, the

proportionality between gel

and

zeol ite

composition was found to hold over a much wider range (Chapter IV, Fig. V.6). In

pentasil

zeolites,

the

incorporation of aluminium in

matrix is a disruptive process (Chapters I and III).

the silica

In other words, the

incorporation of aluminium occurs through partial redissolution of Al-free nuclei. Based on the 1iterature available (Table VI.l and Fig. VI.2), the mechani sm of the synthes is of FER-type zeolites, although ri ch in

5-MRs,

should be totally different as a highly siliceous framework is very difficult to synthesize (Fig. VI.2). Probably aluminium is required in some building units

and

precursors.

The major

structural

differences

between

pentasil

frameworks and FER is the absence of 4-MRs, but the presence of two 6-MRs per unit cell in the latter structure. Isomorphic substitution of Al for Si in a framework

gives

a

net

destabilization

(ref.

27).

For

a

6-MR

this

destabilization on introduction of Al is, however, more than compensated for by the presence of a cation in the centre of the ring (ref. 27). The lower limit of the Si0 (Si0

2/A1 203

ratio of FER, which is observed in natural ferrierite

= 12), might then correspond to the presence of three Al per

2/A1203 6-MR. Assuming all Al is present exclusively in the 6-MRs, the upper limit of one Al per 6-MR corresponds then to an Si0

ratio of 34. In Fig. VI.2 2/A1 203 it is indeed observed that the exclusion of more aluminium from the FER

framework

is

hardly achieved.

The effect the

mixture has on the ratio, R, of the Si0

2/A1203

gel I is also informative in 2/A1203) this respect. This ratio, R, is plotted against the OH/Si0 ratio for a set 2 of synthesis mixtures in Fig. VI.3, which shows that, irrespective of the in the gel

I (Si0 2/A1203)

basicity of the synthesis ratio in the zeolite to that

zeolite: (Si0

synthesis conditions and

sil ica/alumina molar ratio of the gel,

in

the

present case more aluminium is incorporated in the FER framework at higher basicity. A decrease in the Si/A1 ratio of the zeol itic product from more 2 alkaline gels is a general observation with low-silica zeolites (ref. 28), but has not been observed for pentasil zeol ites. This is a strong argument for

the

formation

of

Al-containing

6-MRs

as

elementary

steps

in

the

crystallization of zeolites with the FER type of structure. It should also be stressed that this holds for

2ll

ferrierite-type structures, irrespective of

the method of synthesis and the specific nature of the individual members.

family

226

a-50

1.0

b x

x

•

0.5

a-94

b

•

a -94

0.25

0.50

OH /Si02 FIGURE VI.3. Effect of the OH/SiO FER-type structures

(a,

ref.

ratio of a gel for the synthesis of Z 15 and b, ref. ZO, ex. 5 and ZO) on R

(SiOZ/A1 Z0 3 ratio in the zeol ite to SiO ratio in the starting gel). Z/A1 Z03 The values on the curve refer to the Si0 ratio in the synthesis 2/A1 Z03 mixture.

DIFFERENCES BETWEEN VARIOUS PROPRIETARY FER-TYPE MATERIALS The FER structures synthes i zed in the presence of C (ref. IS) and 4DN denoted elsewhere (ref. 20) as ZSM-35, retain approximately 3.6 molecules per unit cell of C4DN (ref. IS), whereas in an MEL-type structure 5.3 molecules of CSDN (ref. IS) are retained per unit cell. Taking into account the differences in their chain lengths, the ratio of pore lengths fil led with the diamines retained in MEL to that in FER is approximately Z.S. For MEL structures, it has been shown that preferentially one set of 10-MR pores retain adsorbate (ref. Z6). In the direction of the 10-MR in MEL and FER, the ratio of the unit cell dimensions is

a MEL c FER

= 3.0

227

while aMEL _ (length 10-MR)MEL ~-..,..,--------,,~~;:-:=-= 1. 4 bFER - (length of 8-MR)FER This suggests that the C4DN templates fill only the 10-MR in the case of FER. For the synthesis of lSM-35 at 373 K without agitation, the C/N ratio of the retained C4DN is approximately 2 (refs. 18 and 20), irrespective of the composition of the mixture used for the synthesis. The number of retained C4DN molecules is twice the Al content of the unit cell of the sample, suggesting that after synthesis C4DN remains intact and is present in its monoprotonated form. TABLE VI.2. Composition of the template and amount retained after synthesis of zeolite lSM-35 in the presence of C4DN

Synthesis tempe ra tu rei K 373 373 433

Stirring

A1/UC

N/UC

C/N

Ref.

no yes

2.3 2.5 2.0

8.2 7.5 2.6

2.4 4.2 4.1

18 20,ex.14 20,ex.19

When'"the same mixture is stirred, or its crystallization occurs at 433 K, the C/N ratio of the retained diamine doubles, which suggests that the aforementioned treatments deaminate the template into a monoamine, which is used to neutral ize most of the aluminium. The data illustrating this are given in Table VI.2. The family of lSM-21 zeolites can be distinguished from natural ferrierite based on their XRD lines. A significant line at 1.133 nm present in natural ferrierite has, when present, only a weak intensity in these propri etary ferri erites (refs. 19, 23 and 24). This has been attributed by Kokotailo et al. (ref. 4) to differences in cation content. A further means of discrimination is to consider the sorption capacity for hexane and 2-methylpentane (refs. 19, 23 and 24). At 636 K, the hexane/2-methylpentane

228

sorption ratio is high for natural ferrierite (34 or higher), whereas for lSM-21 materials it is in the range 1.9 - 2.7 (refs. 19 and 23). It would be very instructive as to the nature of the other proprietary ferrierites if the same data were available for these materials. The only difference between lSM-35 and lSM-38 seems to be in the nature of the template used. For the synthesis of lSM-38, 2-hydroxytrimethylammonium has been used exclusively (Table VI.1). The sorption data for water, hexane and cyclohexane differ over such a wide range, depending on the individual sample used (ref. 19 and 23), that discrimination between lSM-35 and lSM-38 on this basis is impossible. lSM-35 is isostructural with ferrierite but has a significantly shorter a-axis (1.916 nm for ferrierite compared with 1.892 nm for lSM-35) (ref. 4). FU-9, an leI proprietary material (ref. 22), also belongs to the FER-type structures, as all the XRD 1i nes requi red by the framework are present as deri ved by Vaughan (ref. 2). Some of the arguments used by the inventors (ref. 22) to distinguish this material from other members of the family are summarized in Table VI.3. The differences in their sorptive behaviour are illustrated in Fig. VI.4. The total pore volume and the volume of the 10- and 8-MR pores were calculated using the unit cell dimensions and pore size apertures reported by Vaughan (ref. 2). For a11 members wa ter apparently fills only the 10-MR pores, whereas with n-hexane almost complete pore filling is achieved, except for FU-9, in which only the 10-MR pores are filled. In lSM-35, both p- and m-xylene fill the 10-MR pores, whereas the other members show incomplete filling. For cyclohexane, access is very 1imited. It is clear that lSM-21 and FU-9 are unique members of the FER family

and possibly differ in the degree of faulting. Seddon and Whittam (ref. 22) consider lSM-35 as an FER structure with fault lines perpendicular to the b axis, whereas FU-9 is closer to the theoretical structure. We have difficulty in visualizing this based on the model in Photograph VI.1 and do not see how this would decrease the sorption capacity of FU-9. It seems logical to us that stacking faults will occur preferentially along the cleavage plane (be), which means that neighbouring ferrierite columns are displaced. This has no effect on the porosity in the b direction (8-MR pores), but changes the 10-MR pores into 8-MR pores at the level of such a stacking fault. This then explains that the porosity decreases as the number of stacking faults increases. With such an interpretation, lSM-35 would be an FER structure with a fewer stacking faul ts than FU-9. A photograph along the c-axis of such a faulted model of FER is shown in Photograph VI.2.

229

8MR +10MR 15

•••••••

1------

"0

10MR

Q)

.0

10

~

o

I!-•••.!..•••..!

...... -.- 1---- . -

----

(Jl

-----

0')

o o .,...

-, c o

8MR

5

----1- 0

-

1-----

0 -

•••••• •••••••

o

----- FU-9 ZSM-35 ••••••• SrD

- 0 - 0-

Ii••-•••• !water

cyclonhexane

p-

mxylene

sorbate

FIGURE VI.4. Difference in sorptive behaviour at 298 K of FER-type zeolites. (Data selected from ref. 22).

230

TABLE VI.3. Proposed differences between different members of the FER family (ref. 22) Technique

Ferrierite natural

lSM-35

FU-9

XRD lines Line at 1.13 nm Crystal morphology

FER- type strong i rregul ar

FER-type absent or very weak thin rods

Electron diffraction

faul ts

FER-type weak small regular crystals no faults

1b

faults .1 b

PHOTOGRAPH VI.2. FER structure viewed along the c-axis, with stacking faults in the bc plane, replacing 10-MR by 8-MR pores.

231

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. 26.

D.W. Breck, Molecular Sieve Zeolites, J. Wiley, 1974 p. 219. P.A. Vaughan, Acta Crystallogr. ~ (1966) 983. 1.S. Kerr, Nature n:.Q (1966) 294. G.T. Kokotailo, J.L. Schlenker, F.G. Dwyer and E.W. Valyocsik, Zeolites 2. (1985) 349. W.M. Meier and D.H. Olson, Atlas of zeolite structure types, IZA, 1978, Polycrystal Books, p. 39. C.L. Kibby, A.J. Perrotta and F.E. Massoth, J. Catalysis 35 (1974) 256. R.M. Barrer and D.J. Marshall, J. Chem. Soc. (1964) 2296. D.S. Coombs, A.J. Ellis, W.S. Fyfe and A.M. Taylor, Geochim. Cosmochim. Acta 11 (1959) 53. D.B. Hawkins, Mater. Res. Bull. ! (1967) 951. D.E.W. Vaughan and G.C. Edwards, USP 3,966,883 (1976), assigned to W.R. Grace. B.H.C. Winquist, USP 3,933,974 (1976), assigned to Shell Oil Compo J.A. Kaduk, USP 4,323,481 (1982), assigned to Standard Oil Compo (I ndiana) L. Marosi, M. Schwarzmann and J. Stabenow, EPA 49,386 (1981), assigned to BASF. D.E. Martin, G. Offenl. 2,507,426 (1975), assigned to BP. J.M. Nanne, M.F.M. Post and W.H.J. Stork, EPA 12,473 (1979), assigned to Shell Int. Res. M. Taramasso, G. Perego and B. Notari, Fr. P. 2,478,063 (1981), assigned to Snamprogetti. A. Araya and B.M. Lowe, J. Chem. Res. (S)(1985) 192. E.W. Valyocsik and L.D. Rollmann, Zeolites 2. (1985) 123. C.J. Plank, E.J. Rosinski and M.K. Rubin, USP 4,016,245 (1977), assigned to Mobil Oil Corp. L.D. Rollmann, G. Offenl. 2,817,575 (1978), assigned to Mobil Oil Corp. P. Chu, J.C. Vartuli and J.A. Herbst, EPA 127,399 (1984), assigned to Mobil Oil Corp. D. Seddon and T.V. Whittam, EPA 55,529 (1981), assigned to ICI. C.J. Plank, E.J. Rosinski and M.K. Rubin, USP 4,046,859 (1977), assigned to Mobil Oil Corp. C.J. Plank, M.K. Rubin and E.J. Rosinski, USP 4,105,541 (1978), assigned to Mobil Oil Corp. Nederl. Terinzagelegging 7,605,229 (1977), assigned to Mobil Oil Corp. P.A. Jacobs, H.K. Beyer and J. Valyon, Zeolites 1 (1981) 161.

232

27.

W.J. Mortier, P. Geerlings, C. Van Alsenoy and H.P. Figeys, J. Phys. Chern. 83,7 (1979) 855.

28.

S.P. Zhdanov, in "Molecular Sieves", Soc. Chern. Ind., London, 1968, p. 10.

233

CHAPTER VI

ZEOLITES WITH TON STRUCTURE TYPE

STRUCTURE Recently, several comparable XRD

novel

lines

proprietary zeol ites have been

: THETA-1

(refs.1-5),

ISI-1

cl aimed, with

(ref. 7) ,

KZ-2

(ref.6),

ZSM-22 (refs. 8,9) and NU-10 (refs. 1,2,8), which, according to IUPAC rules (ref.15), should be denoted as TON.

An X-ray diffractogram typical of this

new family of zeolites was given in Part I (Fig. 1.3.14). Barri et al.

(ref.1) were the first to report the resolution of the

structure of THETA-I, one of the members of the family with the TON structure type. Almost

1 year later (ref.8), the structure of ZSM-22, resolved by

greatly differing methods, was reported. The

proposed

structure

of

THETA-I,

studied

by

X-ray

and

electron

diffraction (ref.1) using small zeolite crystals, can be constructed from the 5-1 secondary building units, which are also used with pentasil (Chapter IV). The new structure type

zeolites

therefore belongs to the mordenite

group of zeol ites (ref .16). The structure of ZSM-22 was deri ved from the ferrierite structure using model building and comparison of calculated XRD lines

with

columns

experimental

reduced

the

lines

c-axis

(ref.8).

from

0'.75

Sigma to 0.5

contraction

of

nm. Association

ferrierite of

these

contracted columns gave a related structure, with the unit cell dimensions of ZSM-22 but without a C-centre in the lattice. A rearrangement from Cmmm to Cmcm

symmetry

after

the

orthorhombic and centric ZS~1-22 (refs.1,8),

apparently

introduction

of

the

C-centre

produced

the

framework (ref.8). Both groups of workers

independently

and

using

different

approaches

and

different proprietary materials, deduced the same structure. The building blocks and their linkage

in

TON zeolite are shown in

Photographs VII.1 and VII.2, respectively. As will be shown later, another structure (MTT)

is generated when these building blocks are linked in a

different way. The model of a TON zeolite is shown in Photograph VII.3. A view down the c-axis

(Photograph

VII.3.A)

shows

clearly

the

existence

of

parallel

one-dimensional 10-MR channels. Zig-zag chains of double 5-MRs, edge-Sharing, run in the a-direction and are linked by 6-MRs of T atoms in the b-direction,

234

PHOTOGRAPH (ref. I?).

VII.I.

Building

block

of

zeolites

with

the

TON

structure

235

PHOTOGRAPH VII.2. Linkage of four building blocks in the TON structure (refs. 1,8).

236

thus forming the elliptical IO-MR. The only IO-MR zeolite structure type with one-dimensional non-interpenetrating parallel channels which had been known previously and that is catalogued by IZA (reLIS), is LAU, to which the natural but low-silica zeolite laumontite belongs. In the mean time other zeolites with structures containing one-dimensional non-interpenetrating parallel IO-MR channels have been obtained (Chapters VII and VIII). A view along the a-axis (Photograph VII.3.B) shows interlinked 6-MRs, which produce the repeat distance (0.5 nm) along the c-axis (reL2). This projection is common with the (ac) projection in the zeol ite bikitaite (reL2). A view down the b-axis again shows

an interlinked network of 6-MRs of

T atoms. The structure has no 4-MRs, but consists of 5-, 6- and 10-MRs. The 6-MRs are not flat as in the FER framework but are in either "boat" or "chair" form (Photograph VI I.3.C). The crystal characteristics of zeol ites THETA-I, lSM-22 and NU-IO are compared in Table VII.I. They agree closely in all

respects,

which confirms

that

their structure frameworks

should be

related. For NU-IO it in stated that" the fibre direction is the c-axis" (reLI3) or, in other words, the IO-MR pores run through the needle-like crystals parallel to the length of the needles.

FIGURE VII.I. Section through the centre of a structure, parallel to the (be) plane.

IO-MR pore of the TON

237

The IO-MR pores are not entirely straight but undulated or slightly sinusoidal. A schematic representation of a cross-section through the centre of such a pore and parallel to the (be) direction is shown in Fig. VII.I.

PHOTOGRAPH VII.3. Model of a TON zeolite structure with orthorhombic symmetry (refs.I,8) A, viewed along the c-axis and the IO-MR one-dimensional channels; B, viewed down the a-axis, showing interlinking 6-MRs; C, viewed down the b-axis, again shOWing interlinking 6-MRs.

238

:2:J9

... t-o

o

TABLE VII.1.

Characteristics of zeolites THETA-1 (refs.1,Z), ZSM-22 (ref.22) and NU-10 (ref.13)

Zeolite

Symmetry

Unit cell size/nm abc

T atoms per UC

Crystal density/ g/cm3

Channel dimensions/ nm

Morph.

Crys ta 1 s i ze/ IJm

THETA-1

c-centred 1,3836(3) orthorhombic

1. 7415(4)

0.5042(1)

24.9

2.05

ZSM-22

c-centred 1.386(3) orthorhombic

1.741(4)

0.504(2)

24

1. 97

0.55 x 0.45

acicular

NU-10

c-centred 1. 3853 orthorhombic

1. 7434

0.504

-

-

-

fibrous

rods

2 x 0.1

{' x 0.1

1-3 x 0.05-0.15

TABLE VII.2. Preferred synthesis conditions of TON type zeolites

Zeolite

ref.

THETA-1 a THETA-1 a

4

KZ-2 g

6

ISI-1

7,ex.1

3

organic component(R) Si0 2/A1 203

Synthesis mixture (molar ratios) Si0 2/H 2O OH/Si0 2

diethanolamine h

60 - 500

0.067 - 0.2

U.03 - 0.11

(ammonia) c

60 - 500

0.02

0.14 - 0.05

138

110

- 0.5

- 0.27 0.29 i

0.022

R/SiO"L

0.5 _ 4b 0.45

-

0.009

80-500

0.OO7 e

0.020 - 0.033

0.2 - 0.5

diaminoalkanes f

50 - 60

-

0.017 - 0.067

0.1 - 1.0

N-ethylpyridinium

30 - 1,000

0.1 - 0.4

0.017 - 0.05

0.05 - 1.0

NU-10 a

10

methanol PAPAd

NU-lO a

11

ZSM-22 a

9

a, most preferred range; b, ammonia to silica; c, diethylamine, 1-aminobutane, 1,4-diaminohexane or 2,2' - diaminodiethylamine; d, PAPA = polyalkylene polyamines such as triethylenetetramine and tetraethylenepentamine; e, ref. 10, ex. 18; f; C ON with n = 4,6,8,10,12; g, also made as Al-free form; h, or related compounds such as N-(2-aminoethyl) ethanolam~ne, 2-(2-aminoethoxylethanol or digol; i; addition of acid to pH 8.5.

..."".....

"'"""""

TABLE VII.3. Examples of hydrogel compositions used for TON zeolite synthesis

No.

1 2 3 4 5 6 7 8 9

Si0 2/ OH/Si0 2 Si0 2/ H2O A1 203 ratio ratio ratio 54 55

0.09 0.09

77

-

75 171 171 171 85 85

R/Si0 2

M/Si02

ratio

ratio

0.09 0.16 0.16 0.16 0.10

0.075 0.074 0.079 0.076 0.020 0.020 0.020 0.046

0.56 0.55 0.53 0.33 0.33 0.33 0.42

0.09 0.04 + 0.05 0.04 + 2.60 0.09 0.17 0.17(10%Rb) 0.17(2%Rb) 0.12

0.10

0.046

0.42

0.12

-

R

M

diethanolamine diethanolamine

Na Na + K Na + NH 4 Na Rb K + Rb K + Rb Na

448 443 443 443 423 423 423 443

40 24 48 24 41 25 42

Na

448

C12DN C12DN C12DN N-(2-aminoethyl) ethanolamine 2-(2-aminoethoxy) ethanol

Synthesis TON temp./K time/h material

Ref.

72

THETA-1 THETA-1 THETA-1 THETA-1 NU-10 NU-10 NU-10 THETA-1

2 4 2 ll,ex .14 ll,ex.15 ll,ex.19 2

96

THETA-1

2

L

243

SYNTHESIS OF TON STRUCTURE TYPES The most preferred compositional ranges claimed for the synthesis of different proprietary materials, which based on their XRD lines belonging to the TON structure type, are given in Table VII.Z. All materials can be made with comparable SiOZ/HZO ratios, over a wide range of SiO Z/A1 Z0 3 ratios and with very weak to strong basicity. The major difference between the different methods of synthesis is in the nature of the organic component used. They all have one characteristic in common they all are linear oxygen- or nitrogen-containing molecules with no branchings in the side-chain. In contrast to the templates used for ZSM-5, there lS a strict relationship between the nature of the templates that can be used and the structure of the pore system of the ultimate zeol ite. In view of their templating or pore filling function, this is of course a prerequisite for the formation of one-dimensional 10-MR pores. Only the THETA-l materia I can apparently be crystallized from a hydrogel free from organic alkali (ref.4). Such a material even seems to have superior crystall inity to those synthesized in the presence of diethanolamine, as the baseline of the X-ray diffractogram at small °26 values is lower for the former material (ref.4) and hence it contains less amorphous material. KZ-Z (ref.5) and 151-1 (ref.7) are prepared at very low pH and, for the latter material to crystallize from the hydrogel, free acid has to be added so as to arrive at a pH of 8.5, which is unusually low for the crystallization of a zeolite. This was also possible for FER materials synthesized in the presence of diaminoalkanes(Chapter V). The ISI-1 material is the only TON material that is prepared in the absence of N-containing basic molecules. The addition of alkali metal salts, which are generally known as mineralizing agents in zeolite synthesis (ref.15), also accelerates the growth of NU-10 materi a 1 s l refs. 10,11), but also tends to initiate the co-crystallization of different quartz forms (ref. 10). KZ-2 is the only TON material that apparently can be synthesized in its aluminium-free form (ref.5). It should be recalled that FER-type materials (Chapter V) with few or no aluminium atoms have not yet been claimed, whereas it seems that Al-free pentasil zeolites are easier to synthesize than their Al-rich counterparts (Chapters I and III). The silica-alumina ratios of the hydrogels and the composition of the TON materials crystall ized from it are plotted against each other in Fig. VII.2. Although generally wide compositional ranges are claimed for these materials, the actual data illustrating the syntheses show that only for

244

/ / 450 f-

/

/

~Yg

/

/ /

/ /

z

of0r.:

/

3001-

/

/

(¥)

/

oC"I

/

~

/

C"I

o

V;

150-

/

/

/

•

3

.: THETA-1, ref.4

./15

12/

o

151-1 , ref. 7

X :

NU -10 , ref .10

.: ZSM-22, ref.9

~t5

18/ '5.8•• /'.1 6 / ·2 3 0 .... / __

0:

a

1

a 2 -'I 150

-'-..,...I 300

.1.-_----' I

450

FIGURE VII.Z. SiO Z/A1 Z0 3 ratios of the hydrogel versus that of the final TON zeolite obtained according to different procedures (the figures next to the experimental points indicate the example numbers in the original patents). NU-I0 is a super-high-silica TON material prepared with 100% efficiency. The composition of the high-silica ZSM-ZZ is considerably lower than the gel composition, indicating that this material crystallizes less efficiently than NU-I0 and than ZSM-ZZ, with a higher Al content. 151-1 crystallizes in an inefficient way, whereas for THETA-l only experimental compositions covering a relatively sma II Si/A1 Z range are available. The influence of several parameters on the crystallization of these zeolites has been the subject of only one publication (ref.12). The data

245

scattered through the 1iterature, however, are indicative of some trends (Table VII.3.), as follows. 1. Addition of potassium to a sOdium-containing hydrogel (lines 1 and Z) reduces the crystall ization time of THETA-I, al though conditions seem to exist for lower R/SiO Z ratios where the crystallization time decreases in the series (ref.3) K(140h) > Na(93h) > Li (48h between 443 and 448K). For monocationic hydrogels from which NU-10 crystallizes (ref.1Z), it was shown that the induction period decreased in the series Cs (ZOh) > Rb (9h) > K (7h) > Na (6h). This indicates that the nature of the alkali metal cation plays a role in the nucleation of the TON structures, the smaller cations being the preferred template. For NU-10, the addition of traces of Rb to a K-containing hydrogel prevents the formation of lSM-5 (ref.11) (Table VII.3, No.7). The addition of 10% Rb to a K-containing gel results in a shorter synthesis time (Table VII.3 Nos.5,6 and 7). The preference of a certain structure for mixed cations has not yet been encoutered. As a pure Rb hydrogel crystallizes more slowly than those containing mixtures of Rb and K, the explanation (ref.1Z) that Rb is a more effective nucleation agent cannot be valid. An explanation that rationalizes all these data is that hydrated alkali metal cations intervene directly in the nucleation, some as true templates and others as mineralizing agents with more or 1ess pronounced structure-formi ng or -breaking properties. This could explain the preference of alkali metal cation mixtures and the influence of the nature of the alkali metal ions in pure systems. The organics are only pore fill ing agents that act on the growth rate of the nuclei. 2. The replacement of an organic pore filling agent with a linear structure by ammonium is possible for THETA-1 but prolongs the crystallization time (Table VII:3, Nos. 1 and 3). As suggested above, this can be the result of a decreased crystal growth rate. 3. THETA-1 grows faster from a gel with an SiO Z/A1 Z03 ratio of 75 than one of 54 (Table VII.3, Nos. 1 and 4). This is in line with the behaviour of pentasil zeolites (Chapters I and III), but it is not certain that this behaviour can be generalized over a wide SiO Z/A1 Z03 ratio. The crystall ization of NU-10 is al so very dependent on the al uminium content of the gel (reL1Z). For Si-rich gels, only traces of NU-10 are formed and lSM-48 is the major product, whereas for Al-rich gels, ferrierite becomes a major phase. In the composition range in which pure and highly crystalline NU-10 is formed, 30 < SiO Z/A1 Z0 3 < 600 (refs. 11,lZ), the crystallization is faster for the more siliceous gels (reL1Z). When Na is the only alkali metal ion and polyalkylene polyamines are the organics used,

246

this critical SiO

ratio narrows to 56-170 (ref.13). In terms of the Z/A1 Z03 general principles outlined for pentasil materials, this critical aluminium content is not easily understood. Possibly it is related to the formation of a less soluble solid gel

phase outside this critical composition, which is

not an unexpected phenomenon in thi s kind of system (ref .IZ).

Indeed,

in

general the mono-cationic hydrogels behave as expected, as a sharp rise in pH occurs

only

when

a

considerable

amount

of

hydrogel

has

already

been

transformed into zeolite (ref.IZ). This is illustrated in Fig. VII.3 for the crystallization

of

NU-lO in

the

Rb-C system. Strictly, this general 60N picture is true only for sodium. With K and Rb, the initial pH increases

slightly without any crystallization occurring. According to Araya and Lowe (reLIZ), such behaviour indicates either the presence of a less soluble hydrogel phase or recrystall ization of one zeol ite phase (at the stage of nuclei) into a less soluble zeolite. 4.

The nature of the organic component, which according to previous

remarks influences the crystal growth process, is seen to influence also the crystallization time (Table VII.3, Nos. 8 and 9) for THETA-I zeolites. For the synthesis of NU-IO with diamines, a change in

the length of the

alkane part of these molecules mainly influences the purity of the product and much less the crystallization time. For CnON with n=6-10 (ref.IZ), pure NU-IO is formed. For longer or shorter chains, the product under the same conditions is always contaminated with dense siliceous phases. With symmetric N,N'-diethylethylenediamine

pure

NU-IO

is

also

obtained,

whereas

with

asymmetric N,N-diethylethylenediamine only NU-4 is formed (ref.IO). 5. As already shown (Table VII.Z1, some TON materials can be synthesized over a wide range of OH/SiO values, even at very low pH values (KZ-Z). Z NU-IO can also be prepared at low alkalinity (OH/SiO = 0.01) (reLlO). In Z the total absence of alkali metal cations, however, only quartz is formed (ref.IO). In the K-system, NU-IO is formed over a very wide range of OH/SiO Z values (up to 0.Z3), whereas for Na alone, at high alkal inity NU-4 is also formed (ref .10). Although these observati ons can at present be interpreted only in general terms, the critical effect of the nature of the alkali metal cations on the synthesis of TON materials is confirmed again.

247

100

~

.....

C

0

CO N

-...

50

CO

III ;>.

o

~pH/%

FIGURE VII.3. Effect of relative pH change (bpH) of synthesis medium on the crystallization of NU-10 zeolite from Rb-C 6DN-containing hydrogels. Data selected from ref.12. The initial pH is 12 (bpH = 0) and the final pH is 12.5 (bpH = 100%).

248

DIFFERENCES BETWEEN THE TON-TYPE PROPRIETARY ZEOLITES Hogan et al. (reLlO) compared the XRD patterns of NU-lO, KZ-2 and THETA-I in detail and concluded that they are the same in all respects for NU-lO and KZ-2. It should be stressed, however, that KZ-2 can be synthesized easily in an aluminium-free form whereas NU-lO apparently cannot (see above). According to Hogan et al. (reLlO) for THETA-l the intensities of the lines are different and about ten lines are even absent. They concluded, therefore, that "THETA-l is an impure form of NU-lO or that it has a related but not identical framework structure". Crystallographically, THETA-I, NU-lO and ZSM-22 have already been shown to be closely related (Table VII.l). The pronounced preference for p-xyl ene sorpti on is also common to both THETA-l and NU-lO (refs. 2,10), whereas n-hexane sorbs on both ZSM-22 and NU-lO (refs. 9,10). In order to obtain reproducible sorption results, it seems critical to remove the last traces of organic (ref.lO). The constraint index (el) for ZSM-22 is reported to be 2.6 (ref.9). Given the TON-type structure of this material, this is an unusually low value, as for pentasil zeol ites values ranging from 8.3 to 8.7 are reported. In addition to the high-silica zeolites reported in previous chapters, the TON materials· are also reported to be thermally stable up to at least 1273 K. In conclusion, it is clear that al I these proprietary zeolites belong to the same, unique structure type. Whether the differences reported in these different materials can be attributed to the occurrence of stacking faults is not clear. In a structure type such as TON with one-dimensional pores and a dense network of 6-MRs in two crystallographic directions, no clear cleavage plane is present and stacking faults that would block these pores partially or completely are not easy to visualize. A1so, it cannot be unambiguously concl uded whether these materi a1s are all different or are just the same zeolite synthesized by different methods.

249

REFERENCES 1. S.A.l. Barri, G.W. Smith, D. White and D. Young, Nature ~ (1984) 533. 2. A.G. Ashton, S.A.l. Barri, J. Dwyer, Proceed. Siofok Meeting on Zeolite Catalysis, Acta Phys. Chem. Szegedensis (1985) p.25. 3. S.A.l. Barri, P. Howard and C.D. Telford, E.P.A. 57,049 (1982), assigned to BP. 4. W.J. Ball, S.A.I. Barri and D. Young, U.S.P. 4,533,649 (1985), assigned to BP. 5. W.J. Ball, S.A.l. Barri and D. Young, E.P.A. 104,800 (1983), assigned to BP. 6. L.M. Parker and D.M. Bibby, Zeolites l (1983) 8. 7. K. Takatsu and N. Kawata, E.P.A. 87, 017 (1983), assigned to Research Association for Petroleum Alternatives Development. 8. G.T. Kokotailo, J.L. Schlenker, F.G. Dwyer and E.W. Valyocsik, Zeolites 2 (1985) 349. 9. E.M. Valyocsik, U.S.P. 4,481,177 (1984), assigned to Mobil Oil Corp. 10. P.J. Hogan, A. Stewart and T.V. Whittam, E.P.A. 65,400 (1982), assigned to lCI. 11. B.M. Lowe and A. Araya, E.P.A. 77,624 (1982), assigned to lCI. 12. A. Araya and B.M. Lowe, Zeolites i (1984) 280. 13. P.J. Hogan, T.V. Whittam, J.J. Birtill and A. Stewart, Zeolites 4 (1984) 275. 14. A. Araya and B.M. Lowe, J. Chem. Res. (S) (1985) 192. 15. lUPAC Commission, Pure Appl. Chem. 21 (1979) 1093. 16. R.M. Barrer, Hydrothermal Chemistry of Zeolites, Academic Press (London) (1982), 17. A.C. Rohrman,jr, R.B. Lapierre, J.L. Schlenker, J.D. Wood, E.W. Valyocsik, M.K. Rubin, J.B. Higgins and W.J. Rohrbaugh, Zeolites 2 (1985) 352. 18. W.M. Meier and D.H. Olson, Atlas of Zeolite Structure Types, IZA (1978), Polycrystal Books, Pittsburgh, p.49.

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251

CHAPTER VII

HIGH-SILICA ZEOLITES WITH MTT FRAMEWORK TOPOLOGY

MTT STRUCTURE TYPES Another group of proprietary zeolites with related XRD patterns that apparently have related framework topologies exists in the literature ZSM-23 (refs. 1-3), ISI-4 (ref.4), KZ-l (reL10), EU-l (refs. 5,7,12), EU-4 (reL6)

and

EU-13

(ref.lg).

Rohrman

et

al.

(reLB)

state

that

after

comparison of the XRD patterns of ZSM-23, ISI-4 and KZ-l the latter two materials "possess the framework topology of ZSM-23". In the original patents (refs.5,6) the following statements are made concerning the nature of EU-l and EU-4 : "We believe that zeolite EU-l is similar to the ZSM-23 family of zeolites" (reL5) and "we believe that zeolite EU-4 is, like zeolite EU-l, yet another member of the ZSM-23 family of zeolites" (reL6). In later publ ications EU-l is referred as to " a novel zeolite of unknown structure, characterized by its unique X-ray powder diffraction data and unit cell" (reLIl) and as the first high-sil ica zeol ite to be synthesized with a bis quaternary ammonium compound (ref.12). From the good agreement between

experimental

XRD

patterns

and

theoretical patterns obtained using hypothetical frameworks consistent with the symmetry of ZSM-23 and its unit cell size, the structure of this zeolite was determined (ref.B). The structure type proposed for this material is MTT (ref.B). The nature of the building blocks and their connection are shown in Photograph VIII.l

and the MTT

structure

in

the

three crystallographic

directions is shown in Photograph VIII.2 .. The elementary building blocks are identical with those proposed for the TON type structure (Chapter VI). The way in which they are 1inked is different, however, and determines the ultimate structure type. The crystal structure is orthorhombic and the framework model shows lO-MR pores parallel to the a-axis. In the (be) plane the lO-MR pores are separated by sinusoidal chains of 5-MRs, which are interconnected by 6-MRs. In the other two crystallographic directions only a dense network of 6-MRs is observed. Thus, the MTT structure contains only one-dimensional parallel pores del imited by lO-MRs. Just as for FER and TON structure types, and in

252

PHOTOGRAPH VIII.i. Model representing the building blocks for the structure according to ref.8 and their association to form lO-MR pores.

MTT

PHOTOGRAPH VIII.2. Model of MTT (constructed using the data in ref.8) : (A), along the crystallographic a-axis, (B), along the b-axis and (e) along the c-axis.

254

255

256

contrast to, e.g., pentasil zeolites, no 4-MRs are present and the framework is generated by interconnected 5-, 6- and 10-rings of T-atoms. Just as for ZSM-22 and THETA-I (Chapter VI), the structure of ZSM-23 was also resolved independently by two groups of workers. Wright et al. (ref.g), using different methods, considered zeolite ZSM-23 to be a "recurrently twinned variant of zeol ite THETA-I" but arrived at the same framework topology as proposed by Rohrman et al. (ref.B). The exact framework topology of zeolites EU-I and EU-4 is not available, but some crystallographic properties of EU-I have been released (ref. II). These data are given in Table VIlLI. The symmetry and unit cell size of zeolite ZSM-23 according to the two mentioned groups of workers are identical. Zeolite EU-I, on the other hand, seems to belong to the same symmetry class, but has a totally different unit cell size. Irrespective of the resemblance of the XRD patterns (which are shown for sake of comparison in Fig.VIII.6.1-6), it seems that at least zeolites ZSM-23 and EU-I have different structure topologies. The shape of the pores in MTT structures is distinctly different from that in TON structure types, although this is not easily seen on inspection of the photographs of the models. Both pore types are undulated but in MTT on cross-section of the bc plane at a value of a = 0.25 nm a "teardrop" (ref.B) or "egg"-shaped 10-MR is observed with dimensions of 0.40 x 0.56 nm. A schematic representation of the shape of the pore wall in both TON and MTT structure types is shown in Fig. VIlLI.

TABLE VIlLI.

Comparison of some crystallographic properties of zeolites ZSM-23 and EU-l

unit cella dimensions/nm b a c

Zeol He

Symmetry

Proposed space group

Morphology of crystals

lSM-23

orthorhombic

Pmmn

0.501(2)

2.152(4)

1.113(3)

?

8

lSM-23

orthorhombic

Pmmn

0.52

2.17

1.12

thin fibres

9

EU-l

orthorhombic

?

2.01

1.33

2.22

ell ipsoidal aggregates of plates

11,12

Ref.

a, containing 24 T atoms in lSM-23.

""

en -..]

258

TON

MTT

FIGURE VIlLI. Schematic representation of the 10-MR pore walls of TON and MTT structures. Fig.VIII.2 shows schematically sections perpendicular through the 10-MR pores for MTT and TON zeolites. In the former types the sinusoidal chains of 5-MRs run across the structure in the direction of the b-axis and consecutive chains are parallel, whereas in the latter zeolites, the same phenomenon occurs via the a-axis and consecutive chains are in "opposite phase". The planes ot the six-membered rings that connect consecutive chains are parallel in TON and perpendicular in MTT: As ZSM-23 is generated by "twinning across successive equivalent 11101 planes of the THETA-l structure" (ref.g), it is logical that zeol ites THETA-l and ZSM-23, or in general terms TON and MTT structure types, easily form intergrowths (ref.g). The generation of such a possible TON/MTT intergrowth is also shown schematically in Fig.VIII.2. Such intergrowths will have an enlarged unit cell size in the plane perpendicular to the 10-MR pores, but should in principle retain the short repeat distance of approximately 0.5 nm, characteristic of both TON and MTT zeolites. Therefore, an infinite number of zeol ites can be generated consisting of regular intergrowths of TON/MTT structures. Even then, it seems difficult to accommodate EU-l in this family, as its shortest unit cell size is 1.33 nm (ref.Il). By linking the building blocks ,of Photograph VIlLI in a similar way, so that a l2-MR egg-shaped pore is formed instead of a 10-MR as in MTT,

~

A

------

~

~

B

~ c

./'

"-

TON

c

FIGURE VIII.2. Schematic representation of sections perpendicular to the direction of the lO-MR pores in (A), TON; (B), MTT and (C), TON/MTT intergrowths.

""en ~

260

a hypothetical structure with 12- and S-MRs parallel to each other is formed (ref.S). The structure is tetragonal, however, and again has one very short unit cell dimension (a=2.22 and c = 0.55 nm) (ref.S). Although it is doubtful that zeolite EU-1 is an MTT-type structure or a TON/MTT intergrowth, its synthesis conditions and certain properties will be discussed in this chapter, The situation encoutered for TON/MTT intergrowths is identical with that encountered with MEL/MFI intergrowths and confirms that a family of structurally related zeol ites can contain an infinite number of crystallographically different zeolites.

SYNTHESIS OF MTT AND RELATED ZEOLITES The most preferred conditions under which ZSM-Z3, KZ-1, 151-4, EU-1 and tU-4 zeolites can be synthesized are given in Table VIII.2. For ZSM-23 and KZ-1, which can be synthesized from pyrrolidinecontaining gels, crystallization occurs at lower alkalinity (OH/Si0 2) than for the quaternary and bis-quaternary alkylammonium ion containing hydrogels (for ZSM-23 according to an improved method, EU-1 and EU-4 synthesis). When amine~ other than pyrrolidine are used (for KZ-1 or 151-4 synthesis), the zeolites crystallize at extremely low crystallinities. 151-4 under similar conditions is prepared in the absence of N-containing molecules. With this variety of organic materials, it is striking that no bulky molecules have been reported. The alkyldiammonium compounds are again chain-type molecules, as was the case for the organics used for TON zeol ite synthesis. It is therefore not unexpected that given the pore filling function of these organics, a one-dimensional structure with 10-MR pores crystallizes out of it. An improved method of ZSM-23 synthesis uses diquat-7 (ref.3), whereas for EU-I diquat-6 (ref.5) or diquat-3 (ref.18), other N,N,N,N',N',N'-hexamethylalkyldiammonium molecules with an al kyl chain with six and three instead of seven carbon atoms, are used (ref.5). When the synthesis conditions of typical ZSM-Z3 and EU-I samples are compared (Table VIII.3), only the amount of the respective "diquat" used differs significantly. In general, this difference would provoke a faster crystal 1ization of EU-I as R/SiO Z is higher. The lower al kal inity used for lSM-Z3 together with the s1i ghtly enhanced synthes is temperature might compensate for its faster crystallization, assuming, of course, that the general rules derived for pentasil synthesis also hold here. Faced with these conditions and with the facts that the XRD lines of both materials have

TABLE VIII.Z Preferred synthesis conditions for MTT and possibly related zeolites

ZEOLITE

MOLAR RATIOS OF HYDROGEL SiOZ/A1 Z03

HZO/SiO Z

OH/SiO"

R/SiO"

M/SiO Z

R

Ref.

55-70 50-2.000 110

ZOO-600 5-200 46

0.01-0.049 0.10-0.40 -0.27

0.05-1.0 0.45

0.10-0.10 0.41

1,2 3 10

ISI-4

>10

-

0.01-0.5

2-100

-

EU-1 EU-4

10-150 > 40

1-100 1-100

0.1-1.0 0.1-1.0

-

-

-

EU-1 EU-1

60-120 60

50 50

0.33 0.25

O.OS O.OS

0.33 O.OSe

pyrrol idine diquat-7 b pyrrolidine, dimethylamine, 2-aminopropane ethylene glycol or monoethanolamine diquat-6 C propyltrimethylammonium diquat-3 diquat-3

ZSM-Z3 ZSM-23 a KZ-1 d

a, improved method; b, 1:7 N,N,N,N' ,N' ,N'-hexamethylheptamethylenediammonium; hexamethylenediammonium; d, standard conditions; e,M = NH 4.

c,

1:6

4 5 6

18 IS

N,N,N,N' ,N' ,N'-hexamethylt>:l

""'

262

TABLE VII!.3. Comparison of typjcal synthesis conditions for ZSM-23 and EU-1

ZEOLITE ZSM-23

EU-1

diquat-7

diquat-6

ref.

3,ex.2

!:J,ex.4.

SiO Z/A1 203 OH/Si0 2 Si0 2/H 2O R/Si02 R/Na+R

90 0.30 0.025 0.07 0.18

86 0.44 0.OZ9 0.12 0.33

433 3

423 7

R

crystall ization temp./K time/days

certain simjlarities and that a whole family of TON/MTT intergrowths possibly exist, the exclusion of EU-1 from this family of materials on the basis of the reported unit cell dimensions is difficult. From the data available on this group of zeolites, only a few systematic trends can be derived, as follows. i. Materials with a chemical composition reflecting that of the hydrogel used for their synthesis are found only in a restricted Si0 2/A1 Z0 3 ratio range (Fig.VIII.3) (50 < Si0 2/A1 203 < 250). For silica-richer hydrogels, inefficient crystallization based on silica is found. A similar situation is also encountered for FER and TON zeolites. Although silica frameworks with the TON structure are reported for KZ-2 (ref. 10), nothing is known about the efficiency of this kind of synthesis. For EU-1, an even narrower Si0 2/A1 Z03 range is reported (Fig. VIII.3 and ref.12). Above an Si0 2/A1 203 ratio of 120, EU-Z is indeed formed

,/

/

4001-

3001-

/

N

/

M

/.

2001-

/

('\J

'-"

/

/ o 7

9

• : ref.1,lSM-23

/0

« <, ('\J o l/)

/

/

/

o

QI

--o

9

/

/

....QI

o

/

/

/

4

/

/.8

100 I-

0:

ref.3,lSM-23

X:

ref.4,ISI-4

• : ref.5, EU-1

2/_4

1 1.602 /'':'3

o lL o

/- X

7 1

I

100

---l

200

..L300

.1. 400

...L. 500

I

I

600

700

( Si02 / AI203 )gel

FIGURE VIII.3. 5iOZ/A1 Z03 ratios of Z5M-Z3, EU-l and 151-4 zeolites compared with the ratios in the starting hydrogel. The figures next to the experimental points indicate the example numbers in the original patents. GO

0>

GO

264 (refs.

12,18).

pattern

EU-2 (ref.13)

similar to

is

a

high-silica

that of ZSM-48(ref.14),

zeolite with

and

will

be

an

treated

XRD in

Chapter VII I. For ZSM-23 synthesized with diquat-7, an unusual relationship also seems to exist between crystallization time and the Si/A1 of

the

hydrogel

(Fig.VIII.4).

A

minimum

is

molar ratio 2 observed in this

relationship, indicating for the more aluminium-rich compositions that crystallization is faster when less aluminium is present and for the sil iceous

compositions

that

crystallization

becomes

increasingly

difficult. For pentasils the rate of crystall ization increases all the way down to the sil ica polymorphs. The minimum

therefore reflects the

difficult synthesis of ultra-high-silica MTT structures. The FER, TON and MTT materials and None of

these

their intergrowths show this common behaviour.

structures

contain

4-MRs as

pentasils

do.

From the

energetic point of view, Al atoms in zeolites containing 4- and 5-MRs of T atoms (MFI, see above; MOR, ref.15.) seem to prefer these 4-MRs. In FER structures with two 6-MRs per unit cell, the natural zeolites always

200 J:

<,

\

Q)

E

\

:;:;

c: .2

...

C'C .~

9

,, \

,,

,

5

100

7

...

(ij (/)

...0>. 0

0

200

400

600

Si02/A1203 ratio of gel

FIGURE VIII.4. Si0

2/A1 Z03 with OH/Si0

Variation of the crystallization time of ZSM-23 with

the

ratio of the synthesis gel at 433K in the presence of diquat-7 (R)

Na/SiO SiO and R/Si0 ratios of O.ZO, 0.21, 0.OZ5 and 2 Z' Z/H20 2, 0.1, respectively. The figures on the curve indicate the example numbers in the original patent (ref.3).

265

ii.

have SiO Z/A1 Z0 3 ratios between 11 and 13 (Chapter V), which correspond to an occupation of 3 Al atoms per 6-MR. This is the maximum occupation when Al-O-Al bonds have to be avoided. Isomorphic substitution of Al for Si gives a net destabi lization of this ring, which is more than compensated for, however, through the introduction of an exchangeable cation (ref.16). Hence occupancies of Z or 1 Al atoms per unit cell (SiO Z/A1 Z03 between 34 and 70) will be limiting compositions in FER. For TON and MTT, similar reasoning can be used to explain why these structures are not easily crystallized in siliceous-rich fonns. It should be mentioned that in TON, the 6-MRs are less planar than in FER, and are typically present in the form of the "boat" of "chair" configuration, known from organic chemistry. Previous considerations in this chapter indicated that EU-l and ZSM-Z3 are structura 11 y related to some extent. EU-4 crysta 11 i zes much more rapidly from siliceous compositions. Indeed, when under otherwise identical conditions the SiO Z/A1 Z0 3 ratio of this zeolite increases from 60 to 6000, the crystall ization time changes from 90 to 19 h (ref.6). Therefore, according to these data, EU-l seems to behave as an MTT zeolite, in contrast to EU-4, which behaves as a 4-MR containing high-silica zeolite. EU-l crystallization further depends on the temperature (an activation energy of 95.4 kJ mole- I predicts that at 368 K crystallization of EU-l would take I year (ref.IZ)), the presence ot seeds and even the stirring speed, an increase in which was found to have a positive influence on the crystall ization rate of EU-I (reLIZ). The activation energy of nucleation and crystal growth of EU-I from the gel (diquat-3

BrZ)5(NazO)lOiAlz03)1 (SiOZ)60(HZO)3,000 were detennined to be 79.4 and 45.8 kJ mole- , respectively. iii. For ZSM-Z3, data are available (ref.l?) that suggest that this zeolite also crystallizes faster at lower alkalinities. iv. The diquat-7 dications remain intact during the synthesis conditions of ZSM-Z3, as the experimental C/N atomic ratio, irrespective of the Al content of this zeolite, is identical with or close to the theoretical value of 6.5 (ref.3). The number of diquat-7 molecules retained per unit cell is constant between 0.6 and 0.7 (ref.3), irrespective of the SiO Z/A1 Z03 ratio of the zeolite which varies from 56 to Z74. The number of Al atoms per unit cell for an SiO Z/A1 Z03 ratio of 60 is apprOXimately 0.8, indicating that in the most favourable case one diquat molecule is associated with one Al atom, indicating that at least one charge is

266

15

C)

_:EU-1 ref.5

10 -

0 0

••••••

'I'-

M'\.

E u

C'O Co

_._._.: EU-4 ref.6

Ie ••••••

u ~

•••••.. :ZSM-23 ref.1

5-

••••••• 10MR

(J)

_,.1-

:Q 0

>

..... 0

•..... •••••••

water hexane cyclophexane xylene

0.27

0.43

0.60

0.58

adsorbate kinetic diameter/ nm

FIGURE VIII.5.

Void space of Z5M-23, EU-1 and EU-4 zeolites available to

sorbates with

different kinetic diameters.

10-MR was

calculated

using

the

The theoretical

crystallographic data

space of the

presented

in

this

chapter.

neutralized by occluded OH

anions. This becomes more pronounced for

more siliceous materials. V.

The

replacement

of

Na

with

NH

in the gel (diquat-3 Br 4 2)5 (Na20)x((NH4)zO)y(Al 203)1 (5i0 2)60 (H20)3,000 with x+y = 10 results in a decrease of the rate of nucleation and an increase of the crystal size (from 1-31Jm for x = 10 to 30 IJm for.x=2.5) (reL18). An alkali

267

metal-free EU-l was obtained from the gel (diquat-3(OH)2)5 ((NH 4)2 0) 2.5 (AI 203)1 (Si0 2)60 (H 20)3,000' A superior role of Na as a structure-directing agent compared with NH 4 was also observed for MFI zeolites (Chapter II). The available sorption data which can further characterize the different proprietary zeol ites of this group are represented schematically in Fig. VIII.5. Sorption data for water and hexane on ZSM-23 agree fairly well with the theoretical amount expected for pure ZSM-23. The actual data for EU-l are at least twice as high as the theoretically expected values. The lack of cyclohexane adsorption with a kinetic diameter of 0.60 nm agrees with the crystallographic determination of the diameter of the 10-MR pores in ZSM-23 (0.45 x 0.56 nm). EU-l sorbs more p-xylene than expected for an MTT framework. The adsorption of m-xylene is more restricted (ref.5).

FIGURE VIII. 6 .1. ZSM-23 (as-made) (U. S. P. 4. 076. 842. ex .1)

t.

,.. I-

,..

2

.. ..

e

,...

-

-,.. ,..

... ,.. I-

,.. l-

d [0. 1nm]

IIIo

11.19 10.07 7.86 4.54 4.45 4.37 4.27 4.17 4.12 4.07 3.90 3.83 3.73 3.63 3.54 3.45 2.85 2.54 2.50 2.47

47.00 24.00 15.00 54.00 15.00 15.00 73.00 21.00 23.00 50.00 100.00 31.00 79.00 58.00 33.00 40.00 12.00 29.00 13.00 12.00

i-

,.. ,.. I

5.0

I

9.0

13.0

I

I

17.0

--L_J

I

21.0

25.0

29.0

'33.0

37.0

41.0

I

I

45.0

49.0

53.0

1'0

m

00

FIGURE VIII.6.2. EU-1 (as-made) (E.P.A. 42. 226. Table 1) --_._--------

d [0. 1nm]

11.03 100.00 10.10 80.00 9.72 10.00 6.84 10.00 2 e 5.86 5.00 4.66 100.00 4.31 100.00 4.00 100.00 3.82 80.00 3.71 80.00 3.44 50.00 3.38 50.00 3.26 80.00 5.00 13":16 r 3.11 5.00 2.96 11.00 2.71 ' 5.00 2.55 10.00 2.48 5.00 2.42 5.00

t.

lililililililililiII

5.0

IlIa

IJ 9.0

I

l

13.0

l

I

17 .0

I

21.0

I

I

25.0

I

II.

w

29.0

33.0

-

37.0

I

41.0

I

I

45.0

I

I

49.0

I

I

53.0

tv

en

'"

FIGURE VIII.6.3. KZ-1(ref.10. Table 2) 0 H <, H

~

r~

d [O.1nm]

IIIo

iO.n1 9.q3 7.132 6.06 5.57 5./0 4.90 4.50 4.24 4.13 3.88 3.70 3.60 3.52 3.42 3.15 2.82 2.52 2.45 2.32

100.00 25.00 48.00 6.00 7.00 16.00 7.00 90.00 76.00 19.00 94.00 74.00 86.00 36.00 48.00 10.00 9.00 27.00 13.00 8.00

L-.e

'--.-

r~

r-

I

I

I

5.0

9.0

I

13.0

I.

I I J

17.0

II -

I

21.0

25.0

J

I. I I I

29.0

I

I

33.0

I

Lll-L

37.0

----1__-1-

41.0

45.0

I

I

49.0

I

I

53.0

"" 0 -]

I

FIGURE VIII.6.4. I8I-4 (calcined) (E.P.A. 102.497. ex. 1)

t.

II-

2

I-

e

II-

-

I

5.0

I

9.0

•

13.0

I.

I. I 17.0

21.0

I. 25.0

I, 29.0

.I . 33.0

I

•

37.0

41.0

45.0

d [0. 1nm]

I1Io

11.31 10.92 10.03 7.83 6.08 5.61 5.24 4.90 4.51 4.42 4.24 3.89 3.73 3.69 3.61 3.53 3.43 3.16 2.97 2.52

84.00 100.00 33.00 47.00 8.00 14.00 16.00 7.00 77 .00 20.00 61.00 68.00 50.00 73.00 66.00 34.00 47.00 10.00 13.00 34.00

49.0

53.0

""...... ...;]

FIGURE VIII.6.5. EU-4 (as-made) (E.P.A. 63.436. Table 2) I

d [0. 1nm]

Sl_

11.10 9.20 7.62 6.87 2 e 6.29 5.98 4.63 4.47 4.29 3.98 I 3.80 3.75 3.68 3.58 3.42 3.32 3.27 3.23 3.11 3.00

Il-

~.

t-

~

L_LL-LL-1

5.0

9.0

_11.--._

13.0

L__

17.0

11

21.0

,I

.IL..

_

25.0

l-L. ~o

-1 __ ----1--..

33.0

L~

____1-----L____L _ L ___1

37.0

41.0

45.0

,

1

49.0

I1Io 100.00 50.00 50.00 50.00 50.00 40.00 100.00 45.00 100.00 100.00 10.00 50.00 80.00 45.00 50.00 80.00 90.00 50.00 10.00 .~~

I

I

53.0

"" -J ""

FIGURE VIII.6.6. EU-13 (as-made) ((E.P.A. 108,486)

sL

II-

2 8

III-

,.. I-

,.. I-

,.. I-

fI-

fI-

f-

d [O.1nm)

I1Io

11.20 10.80 10.00 7.79 5.60 5.41 4.85 4.51 4.44 4.25 4.15 3.89 3.72 3.61 3.55 3.43 3.35 3.16 2.83 2.53

42.00 46.00 22.00 27.00 9.00 8.00 12.00 63.00 20.00 73.00 19.00 100.00 77.00 63.00 39.00 51.00 9.00 10.00 13.00 30.00

lIlI

5.0

I

9.0

I

13.0

IJ

II.

17.0

1.1

I

21.0

25.0

I II J

29.0

I

I

I

I

33.0

I

I

37.0

I

I

41.0

I

I

45.0

I

I

49.0

I

I

53.0

"" ---J W

274

REFERENCES 1. C.J. Planck, E.J. Rosinski and M.K. Rubin U.S.P. 4,076,842 (1978),

2. 3. 4. 5. 6. 7. 8.

9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19.

assigned to Mobil Oil Corp. M.K. Rubin, C.J. Planck and E.J. Rosinski, U.S.P. 4,104,151 (1978), assigned to Mobil Oil Corp. E.W. Valyocsik, U.S.P. 4,490,342 (1984), assigned to Mobil Oil Corp .. K. Takutsu and N. Kawata, E.P.A. 102,497 (1983), assigned to Research Association for Petroleum Alternatives Development. J.L. Casci, B.M. Lowe and T.V. Whittam, E.P.A. 42,226 (1981), assigned to ICI. J.L. Casci, B.M. Lowe and T.V. Whittam, E.P.A. 63,436 (1982), assigned to ICI. J.L. Casci, and B.M. Lowe, Zeolites l (1983) 186. A.C. Rohrman, Jr., R.B. Lapierre, J.L. Schlenker, J.D. Wood, E.W. Valyocsik, M.K. Rubin, J.B. Higgings and W.J. Rohrbaugh, Zeolites 5 (1985) 352. P.A. Wright, J.M. Thomas, G.R. Millward, S. Ramdas and S.A.I. Barri, J.C.S. Chern. Commun. (1985) 1117. L.M. Parker and D.M. Bibby, Zeolites l (1983) 8. J. Dewing, M.S. Spencer and T.V. Whittam, Catal. Rev. Sci. Eng. ~ (1985) 461. J.L. Casci, T.V. Whittam and B.M. Lowe, Proceed. 6th. Int. Zeolite Conf., Butterworths (1984), p. 894. J.L. Casci, B.M. Lowe and T.V. Whittam, U.K. P.A. 6B 2,077,709 (1981) assigned to ICI. J.L. Schlenker, W.J. Rohrbaugh, P. Chu, E.W. Valyocsik and G.T. Kokotailo, Zeolites 2 (1985) 355. E.G. Derouane and J.G. Fripiat, Proceed. 6th Int. Conf. Zeolites, Butterworths (1984), p.717. W.J. Mortier, P. Geerlings, C. Van Alsenoy and H.P. Figeys, J. Phys. Chem. 83 (1979) 857. see ref.1, examples 1,2 and 8. G.W. Dodwell, R.P. Denkewicz and L.B. Sand, Zeolites 2 (1985) 153. A. Araya and B.M. Lowe, E.P.A. 108,486 (1983), assigned to ICI.

275

CHAPTER VIII

A FAMILY OF ZEOLITES WITH DISORDERED FERRIERITE-TYPE STRUCTURE

MEMBERS OF THE FAMILY The following proprietary zeolites, denoted ZSM-48 (refs. 1,3-5), EU-2 (refs.2,7), EU-ll (reL8) and ZBM-30 (reL6), have comparable XRD patterns. All pertinent XRD data referring to these four zeol ites are collected in Fig.IX.I.I-4 for synthesized materials. Araya and Lowe (ref.2), in comparing XRD patterns of EU-II, ZSM-48 and ZBM-30 zeolites, concluded that "these materials have essentially the same XRD pattern and aluminosilicate structure .... ". Fig.IX.I shows the same to be true for EU-2. Schlenker et al. (reLI) al so state that based on thei r powder XRD patterns, zeol ites EU-2, EU-II and ZBM-30 "possess the framework topology of ZSM-48". The most intense line in synthesized EU-II decreases linearly with increasing A1 203 content of the synthesis mixture (ref.2). This change is attributed to the presence of varying amounts of amorphous occlusions or is related to changes in the organic or moisture content of the materials. STRUCTURE OF ZEOLITE ZSM-48 A possible structure for zeolite ~SM-48 has been proposed by Schlenker et al . (reLI). It seems that ZSM-48 has a structure that is based on ferrierite sheets linked via bridging oxygens located in a mirror plane. In contrast to all other high-silica zeolites reported so far in this work, more than one framework topology can be attributed to the zeolitic material denoted ZSM-48 as a result of the existence of weak broad lines. The X-ray data are consistent with either a pseudo-lor -C-centred orthorhombic lattice with the unit cell dimensions a = 1.424, b = 2.014 and c = 0.840 nm and consisting of 48 T-atoms (ref. I). Two structures and random intergrowths of them, all containing sheets of 6-MRs normal to the 2.014 nm axis, generate the best fit between calculated and experimental XRD lines (Table IX.I) The linkage of ferrierite sheets according to symmetries CmCm and Imma is shown in Photograph IX.1. The view is along the parallel 10-MR channels. At first sight there is no essential difference between the UUDD and UDUD variants of ZSM-48. The walls of the 10-MR channels are composed exclusively

276

TABLE IX.I Possible structures of ZSM-48 (according to ref.l)

Symmetry

Unit cell size/nm

Pore characteristics

a

b

c

UUDD a - CmCm

1.424

2.U14

0.840

equivalent 10-MRs

UDUD

0.840

1. 424

2.014

equivalent 10-MRs

- Imma

a, U, 0 : up and down position, respectively, of neighbouring tetrahedra in the ferrierite sheet.

of distorted 6-MRs. The ideal channel dimensions are 0.53 x 0.56 nm (ref-I). Similar but 12-MR tubular channels exist in

the crystalline microporous

aluminophosphate molecular sieve A1PO-5 (reLIO). Parallel 12-MR tubes also composed exclusively of six-rings are found in cancrinite (ref. II). A view through a ZSM-48 lattice perpendicular to the di rection of the 10-MR

pores

(Photograph

distorted 6-MRs.

IX.2)

clearly

shows

the

dense

arrangement

of

PHOTOGRHAPH IX.I. Possible structure models for lSM-48. (A) View along the c-axis of the UUDD variant; (8) view along the a-axis of the UDUD variant. Identical IO-MR channels are perpendicular to the plane of the photographs.

"" -1

_1

279

PHOTOGRAPH IX.2 View through the lattice of ZSM-48 UDUD variant showing a crossing of a IO-MR channel (dark surface) The UDUD and UUDD arrangement of neighbouring tetrahedra in two structure types for ZSM-48 causes a different distribution of 4-MR elements through these structures. This is shown schematically for both structure types in Fig.IX.I.

280

UUDD

UDUD

FIGURE IX.l. Distribution of 4-MRs through UDUD and UUDD

structure types for

ZSM-48. The bold lines are edges of the 4-MRs, the planes of which are all perpendicular to the plane of the figure.

For both structures, the plane of the 4-MRs intersects the main pores, whereas with the MFI structure type this plane is part to the pore walls (Chapter IV).

For the UDUD structure variant, each 4-MR belongs to two

neighbouring 10-MR pores. For the UUDD variant every 4-MR belongs only to a single lO-MR pore. Only two T-atoms of such a 10-MR pore, while the other

4-MR therefore belong to a

two T-atoms are part of a distorted double

six-ring unit. This difference in arrangement should have consequences for the

incorporation

high-silica

of

zeolites

aluminium

atoms

of

mordenite

the

in

such group

a

lattice.

Indeed,

for

aluminium

atoms

are

preferentially located in the 4-MRs.For ZSM-5 this has been argued in Chapter II. In earlier work (refs.12 and 13) the same was concluded for mordenite. When protonated amines are used as templating agents in the synthesis of ZSM-48, it is expected that the UDUD structure would be able to accommodate

281

more Al, as every 4-MR is accessible from the two sides for charge neutralization by bulky organic cations. This is not the case for the UUDD structure variant. Moreover, in the UUDD structure on both sides of the 10-MR channel, edges of 4-MRs are present at a distance of 0.84 nm . As the locations of the 4-MRs alternate along both sides of the 10-MR channel the distance between two 4-MRs in the 10-MR channel direction is only 0.42 nm. Schlenker et al. (ref. 1), possibly in an attempt to associate the name of a specific zeol itic material with a single structure type, found that .£. random intergrowth of the UDUD-UUDD frameworks gives rise to an XRD pattern that is in best agreement with that of zeolite lSM-48. The zeolite structure types dealt with in this chapter probably belong to a family of materials, consisting of pure structure types, which are end-members, and an infinite number of undergrowths between them. SYNTHESIS OF lSM-48 AND RELATED MATERIALS 1. General conditions The conditions for which it is claimed that these zeol ites can be synthesized are compared in Table IX.2. A series of organics can be added to a s il i ceous synthes i s gel to form these zeol ites. These have also been used to synthesize other high-sil ica zeol ites with monodimensional lO-MR pores, such as those with the FER (Chapter V), TON (Chapter VI) and MTT (Chapter VII) structure types and their intergrowths. The data are remarkable in that the lower Si0 2/A1 203 limit that is claimed by different workers is relatively high (higher than or equal to 50), whereas siliceous materials seem to be easily" obtainable. In Part I also a proven recipe is given for a silica polymorph of lSM-48. The other ratios cover the usual ranges, although EU-ll and EU-2 are prepared in the absence of a mineral alkali source.

"" 00 ""

Table IX.2. Preferred conditions for the synthesis of ZSM-48 and related high-silica zeolites

ZSM-48

Si0 2/A1 203 OH/Si0 2 Si0 2/H 2O R/Si0 2 Na/Si0 2 R

Ref.

ZSM-48

ZS~1-48

EU-2

EU-2

EU-2

EU-lI

50-00

100-00

100-10,000

>150

120-00

00

60-00

0.05-0.2 0.010-0.050 0.1-0.5 0.2-1.0 alkylamine + trialkylamine

0-0.1 0.01-0.1 0.05-1 0.1-1.0

0.1-0.4 0.014-0.050 0.05-1 0.1-1.0 diquaternary al11110nium

0.1-1.0 0.01-1.0

0.33 0.02 0.08 0.08-0.33 a diquat-3

0.25 0.02 0.08 Ob diquat-3

0 0.020 0.33 0 C60N

3

4

14

14

8

CnON

a, addition of NH 40H : NH + Na/Si0 = 0.33 4 2 b, NH 4/Si02 = 0.08.

5

? ?

di quaterna ry ammonium

7

283

2.

Influence of silica: alumina ratio

The formation of ISM-48 from low-alumina gels was also reported by Araya and Lowe (ref.8). From the reaction mixture (K ZO)IO(A1 Z03)x(SiOZ)60 (C 6DN)ZO (H ZO)3,000 at 453K ISM-48 only co-crystallized with zeolite NU-I0 when the SiO Z/Al z0 3 ratio exceeded 300; with a lower content of organics (10 C6DN) ISM-48 is never obta i ned (ref. Z). Also IBM-3D (ref. 6), wh i ch is obta i ned in the presence of alkane polyamines such as dipropylenetriamine, di hexamethyl enetri ami ne, tri ethyl enetetrami ne or hexamethyl enedi ami ne, propylenediamine, is only formed when the SiO Z/A1 Z0 3 ratio of the gel is relatively high (usually> lZ0, depending on the nature of the organic). At lower ratios ISM-5 is crystallized from the same gel. Dodwe11 and co-workers (ref.14) determined that EU-Z crystallized from gels with SiO Z/A1 Z0 3 ratios of 240 and higher. Mixtures of EU-l and EU-2 were formed at SiO Z/A1 Z0 3 ratios between lZ0 and Z40 whereas below an SiO Z/A1 Z0 3 ratio of 120 EU-l was obtained. ISM-48 easily crystallizes from gels containing CnDN diamines with 4 <. n <. lZ, provided that no aluminium is intentionally added (ref.4). When the SiO Z/A1 203 ratio of a gel is ZOO (R/SiOZ = 0.30; Na/SiO Z = 0.59; HZO/SiO Z = 40) with C8DN ISM-II is co-crystallized (ref.4, eX.IZ), whereas with C5DN only pentasi1 zeolites are formed under the same conditions (ref.4,ex.13). In previous chapters, the limits for aluminium incorporation in a high-silica zeolite were found to be dependent on the nature of the building units present in the structure. High-silica zeolites containing no 4-MRs such as the FER, TON and MTT structure types, seem to have narrow limits in which pure zeolites can be synthesized with high efficiency. When the structure contains a relatively high concentration of these 4-MRs a wide range of SiO Z/A1 Z0 3 ratios can usually be obtained. In ISM 5 there exist 4 x 4-MRs per 96 T atoms, which would correspond to a lower limit for the SiO z/A1 z0 3 ratio of ZZ if all A1 is located in 4-MRs and every 4-ring contains two A1 atoms. This represents the lower SiO Z/A1 Z0 3 ratio for highly pure and crystalline ISM-5 zeolites made in the presence or absence of organic templates (Chapter II, p.I3?). ISM-48 and the zeolites with related topology also contain a high concentration of 4-MRs : 4 x 4-MR per 48 T-atoms, which on maximum A1 occupation would correspond to an SiO Z/A1 Z0 3 ratio of 10. Using a limiting value for aluminium incorporation of one A1 per 4-MR, the lower limit for the SiO Z/A1 Z0 3 ratio is ZZ. This is definitely too low compared with the published values. In the UUDD structure, only two T-atoms of every 4-MR are directly accessible through the 10-MR pores. Thus, during synthesis only 0.5

284

Al atoms are expected to be stabilized in a 4-MR by charge neutralization via a bulky organic cation with hydrophobic moieties larger than 0.42 nm. This would lift the lower limit for the Si0

2/A1203

ratio to 46, which is in the

same range as reported in this chapter. 3.

Nature of templates In

order to attain higher structural

alumina

contents,

the

use of

certain diquaternary ammonium ions as structure-directing agents for ZSM-48 seems

to

be

a

preferred

method

(ref.5);

with

diquat-6,

(CH3)3N+(CH2)6+N(CH3)3,the lowest Si0 ratio reported is 85 (ref.5, 2/A1203 ex.14). For a repeat distance of 0.42 nm between Al sites (in UUDD) , diquat-6 allows theoretically the location of one Al per three 4-MRs, corresponding to an Si/A1

ratio in the framework of 70. 2 When the efficiency of a crystallization is considered

with either

diamines or diquats, a different behaviour becomes apparent (Fig.IX.2). With di amines,

there is an a1mast

one to one correspondence between the

chemical composition of the gel and the zeolite product. Using diquats, the Si0

ratio of the zeolite is decreased, except for low Si0 2/A1203 2/A1 203 values, for which the agreement between the chemical composition of the

zeolite and the gel

is also excellent. For the more siliceous gels, this

agreement becomes worse, which is in disagreement with other 4-MR containing high-silica

zeolites,

such

as

MFI

(Chapter

IV,

Fig.V.6.)

A possible

explanation is that diamines are preferred over the diquaternary ions as structure-directing agents. This is understandable, as a tighter fit of the former organics can be expected in the unidirectional 10-MRs of ZSM-48 and related materials. The latter organics provide, however, a higher positive charge density, which might explain the decreased lower Si0

limit of 2/A1203 this zeal ite and the difficulties in crystall izing a sil ica polymorph. Both phenomena

together

can

account

then

for

the

behaviour

illustrated

in

Fig.IX.2. The chain length of the hydrocarbon part of both templates mentioned influences

the chemical composition of the ultimate zeal ite to a certain

extent. Pertinent data to illustrate this were selected and are collected in Fig. IX.3.

285

3001------------~-----------.

/ /

/

-

/

CIl

/ /

o

/

CIl N

c

/

M

o

C'l

«

/

<,

oC'l

0

/

200

/

/

-11 -10

/ //

1001-

/ _ / 14

(/)

0

1-3

-

7

/

_ 12

/ /

/

V/ I 0:r:------==-----:~-----.L-------l..----lJ 200 100 o I

300

400

500

FIGURE IX.Z. Correlation between the SiO Z/A1 Z0 3 content of the zeolite obtained and of the synthesis gel. The open points are for EU-ll synthesized (ref.8) and the full poi nts for lSM-48 synthes i zed from a diquat with C 6DN -containing gel (ref.5). The figures near some of the experimental points correspond to the example number in the reference concerned.

286

o

o

<,

~

:::J

< -, -, ~

:::J

0:

c:

eX

o

0:

2.0 0.10

0.2

18 I

I

0

19

1.5 I I

0

I

22 0

20

I 25

0.05

0.1

10

'~4423:

/ /

/

0

1.0 4

'~,/~

0,

5

6

7

8

n

9 10

4

5

6

7

8

n

9

10

4

5

.: 6

7

8

9

10

n

FIGURE IX.3. Dependence of the Al content (Al/UC) of lSM-48, of the number of organics retained (R/UC) in the zeol ite after crystall ization and of the number of organics molecules retained per aluminium atom in the zeol ite (R/Al) on the chain length (n) of the structure-directing organic. The open points refer to CnDN (ref.4) and the full points to diquat-n (ref.5).

TABLE IX.3. Synthesis conditions for crystalline ZSM-48 with diamines and diquat ions with varying hydrocarbon chain length

Template

Gel composition H20/Si02

CnON

Diquat_na,c

Na/Si0 2

R/Si0 2

Si0 2/A1 203

Synthesis time/ days

Synthesis temperature/ K

Ref.

40

0.59

0.30

2

433

4

4U

0.09

0.10

b 3 - 7

433

5

a, Diquat = (CH3)3N+(CHz)n N+tCH3)3 b, 3 days for n = 6, 5 days for n = 8 and 7 days for n = 10 c, Under these conditions ZSM-48 synthesized with diquat-10 was only 50% crystalline. to 00 _J

288

The detailed synthesis conditions are compared in lable IX.3. Apart from the amount of organic used, which was three times higher for the diamines, these conditions are identical. The longer synthesis time needed to obtain fully crystalline ZSM-48 with the diquaternary ions is probably the result of the smaller amounts used and of the lower synthesis efficiency when using these ions (Fig.IX.2). The number of template molecules retained in ZSM-48 after synthesis decreases for both organics with increasing length of their hydrocarbon chain. Apart from the exceptional behaviour of diaminobutane, both curves representing these changes decrease in a parallel way (Fig. IX.3A). Therefore, this systematic difference has to be attributed to differences in the t r effective chain lengths. Indeed, if the lower curve is shifted two carbon numbers to the right, they coincide. This points strongly to the pore filling role of these organics, irrespective of their detailed chemical structure. The amount of impurity aluminium retained is not influenced by the chain length of the diamines, wheras it decreases with increasing chain length of the diquats (Fig.IX.3B). The figure also clearly illustrates that all diquats considered are more efficient than diamines in complexing 1.1.1 species and incorporating them in a ZSM-48-type lattice. When the high RIAl ratios are considered (Fig. IX.3C), it follows that only a fraction of the organics are effective for aluminium build-in, but that the diquats are again more efficient than the diamines.

289

MORPHOLOGY AND SORPTION CAPACITY All the zeolites belonging to the present family seem to have a typical morphology consisting of needles or agglomerates of them (Table IX.4). There is no direct information available as to the direction of the lO-MR pores through this needle-type morphology. Given the short repeat distance of the unit cell of the UUDD or UDUD structure variants, it would not be unexpected to find that these pores run through the crystal parallel to the direction of the needle. For ZSM-48 crystals grown epitaxially on ZSM-39, the needle axis was found to be normal to the (110) face of the substrate (ref.1). The epitaxy of ZS~1-48 with ZSM-39, a zeolite rich in 5-MRs (ref.9), probably occurs via the plane containing most 5-MRs and which is normal to the shortest axis and the 10-MR channel. TABLE IX.4. Morphology of ZSM-48-like zeolites

Dimensions/lJm Materi a1

Morphology

EU-11

spherical agglomerates of needle shaped crystals

ZSM-48

needles

ZSM-48

aggregate

individual needle

diameter

length

diameter

ref.

3-16

0.4-1.0

0.1.

8

?

?

3

fi brous rods

4-5

1

1

ZSM-48

needles

1-4

EU-2

radial aggregates of needles

EU-2 (alkali metal free)

needles

0.02-0.3

Part 14

30-40 20

0.3

14

290

........

10 -

....... ........

0)

o o,...

-,

M

E

5

-

.:.;.;.:.;.;..........

-

........

'II!I!I!!!I!I!I!I!!!!!!

o

_._.-

o ........

10 MR

........ EU-2

ref.7

\ ~ \ \ \ j; _._--

water hexane cyclomphexane xylene xylene

- - Z5M-48 ref.4 ----- Z5M-48 ref.3

sorbate

FIGURE IX.4. Sorption capacity of lSM-48-like materials for different sorbates. The expected capacity for end-to-end sorption in the IO-MR pores of a lSM-48 UUDD or UDUD structure is indicated by the solid line.

The available sorption capacity data are collected in Fig. IX.4. The hexane sorption capacity of lSM-48 agrees very well with its expected values, assuming end-to-end adsorption in the IO-MRs. For EU-2, this value is twice as high, which is difficult to account for when exclusively pore adsorption occurs. The values for cyclohexane sorption are also significantly higher in EU-2 than lSM-48. It remains to be established, however, whether this is due to changes in the effective pore diameter of both materials or to changes in the crystal size or morphology.

FIGURE IX. 1. 1. ZSM-48

(as - made)

(E. P . A.

15. 132. ex .5)

t.

""

!-

2 8

.."" ""

!-

-

I

5.0

L 9.0

I

I

13.0

I

I

17.0

I

II

21.0

II

II

25.0

I

I

.1

29.0

33.0

37.0

I

41.0

I

I

d [0 . 1nml

IlIa

11.87 10.22 7.22 5.88 4.66 4.20 3.91 3.60 3.47 3.41 3.38 3.10 2.86 2.73 2.63 2.47 2.39 2.34 2.10 2.07

14.00 6.00 2.00 6.00 4.00 76.00 100.00 12.00 2.00 3.00 3.00 2.00 11.00 2.00 2.00 2.00 3.00 2.00 2.00 3.00

I

45.0

49.0

53.0

-

tv to

FIGURE IX.1.2. EU-2

2.077. 709,Table 1 )

(B~1t.P.

t.

~ ~

2 8

~ ~ ~

~ ~ ~

f-

d [0. 1nm]

I1Io

11.74 10.13 6.33 5.85 4.33 4.18 3.89 3.69 3.37 3.08 2.85 2.09

17.00 14.00 7.00 7.00 5.00 86.00 100.00 7.00 7.00 5.00 18.00 5.00

l-

f~

f~

I~

I~

l-

5.0

IJ 9.0

13.0

, 17.0

I

I 21.0

I I,

I

25.0

29.0

I

,

I

33.0

,

I

37.0

I

I

41.0

,I

I

45.0

I

I

49.0

I

I

53.0

"" «o

""

FIGURE IX.1.3. C60M-EU-11 (as-made) (J.Catalysis 85 (1984) 135. Table 1)

t.

-

2

e

foo

-

I

5.0

I.

9.0

,

, 13.0

J

_I

17.0

•

, 21.0

II

I,

25.0

I, 29.0

,

I

33.0

".

II,

37.0

d [0 . 1nml

I1Io

11.67 10.24 7.17 6.15 5.86 5.26 5.12 4.63 4.18 3.90 3.61 3.39 3.10 2.85 2.72 2.62 2.52 2.47 2.38 2.35

24.00 9.00 2.00 2.00 7.00 2.00 2.00 3.00 93.00 100.00 11.00 4.00 5.00 11.00 1.00 2.00 3.00 3.00 4.00 4.00

I

41.0

45.0

49.0

I

I

53.0

tV CD

w

FIGURE IX. 1.4. ZBM-30

(as -made) (E. P . A. 46. 504 ex. 1)

t.

-

2

lI.

5.0

9.0

I. 13.0

I.

,I

I

17.0

21.0

II.

25.0

•

29.0

I

33.0

I

I

37.0

•

e

I

41.0

I ."

I

45.0

d [0. 1nm]

I1Io

11.60 10.20 7.08 6.05 5.80 4.18 3.87 3.60 3.56 3.40 3.35 3.06 2.84 2.09 2.07

36.00 15.00 5.00 6.00 11.00 100.00 79.00 4.00 6.00 5.00 7.00 3.00 16.00 8.00 4.00

I

49.0

I

53.0

tv CD

...

295

REFERENCES 1.

2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14.

J.L. Schlenker, W.J. Rohrbach, P. Chu, E.W. Valyocsik and G.T. Kokotailo, Zeolites ~ (1985) 355. A. Araya and B.M. Lowe, J. Chem. Res. (S) (1985) 192. P. Chu, EPA 23,089 (1980) and USP 4,397,827 (1983), assigned to Mobil Oil Corp .. L.D. Rollman and E.W. Valyocsik, EPA 15,132 (1980), assi9ned to Mobil Oil Corp.. E.W. Valyocsik, EPA 142,317 (1984), assigned to Mobil Oil Corp .. L. Marosi, M. Schwarzmann and J. Stabenow, EPA 46,504 (1981), assigned to BASF. J.L. Casci, B.M. Lowe and T.V. Whittam, U.K. P.A. GB 2,077,709A (1981) assigned to ICI. A. Araya and B.M. Lowe, J. Catal. 85 (1985) 135. J.L. Schlenker, F.G. Dwyer, E.E. Jenkins, W.J. Rohrbaugh, G.T. Kokotailo and W.M. Meier, Nature 294 (1981) 340. J.M. Bennett, J.P. Cohen, E.M. Flanigen, J. J. Pluth and J.V. Smith, ACS Symp. Ser. ~ (1983) 109. W.M. Meier and D.H. Olson, "Atlas of zeolite Structure Types", IZA 1978, Polycrystal Books, Pittsburgh, Pa. W.M. Meier, R. Meier and V. Gramlich, Zeit. fUr Krist. liL (1978) 329. G. Debras, J.B. Nagy, Z. Gabelica, P. Bodart and P.A. Jacobs, Chem. Letters (1983) 199 G.W. Dodwell, R.P. Denkewicz and L.B. Sand, Zeolites ~ (1985) 153

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297

CHAPTER IX

HIGH-SILICA ZEOLITES WITH MTW FRAMEWORK TOPOLOGY.

POTENTIAL FAMILY MEMBERS OF MTW ZEOLITES Based on their XRD patterns, several zeolites seem to be closely related, suggesting that they possess the same framework topology (ref.l). They all are proprietary materials, denoted ZSM-12 (refs. I-g), NU-13 (ref.lD), CZH-5 (ref.ll), TEA-silicate (ref.13) or TPZ-3 (ref.12). To illustrate these statements, typical XRD patterns are given in Figs. X.l.l to 5. For ZSM-12, the framework structure has been proposed and the computed XRD pattern compares very well with the experimental pattern (ref.l). For zeolite NU-13, it is explicitly stated that it is "a member of the ZSM-12 family of zeolites" (ref.lO). TEA-silicate in said to belong to a "new class of crystall ine metal organosil icates which are synthesized from reaction systems essentially free of aluminium-containing reagents ... "(ref.13). This is said to be in contrast to ZSM-12 zeolites, which are synthesized using the same organic structure-directing agent. Zeolite TPZ-3 is said to be related to ZSM-12 but has a much stronger XRD peak at 0.402 nm (ref.12). It differs from ZSM-5 in the presence of a strong peak at 0.433 nm (ref.12). In Fig. X.1.5, it is illustrated that the ultimate XRD pattern might eventually be composed of a ZSM-12-like material, kenyaite (k) and cristobalite (c), which could account for the differences in the number of lines and intensities. Some specific doublets observed in ZSM-12 are present in TPZ-3 as single lines, perhaps indicative of a higher synme try , A monoclinic-orthorhombic symmetry transition for ZSM-5 has been discussed in Chapter IV. STRUCTURE OF ZSM-12 The XRD patterns of ZSM-12 samples, synthesized using different methods, can be indexed using a monoclinic cell (Table X.l). It is clear that in the earlier work (refs.3,6), the a dimension was only half of the value used for structure refinement, wheras the band c dimensions had twice these values. The usual combination of X-ray and electron diffraction data with model building resolved for ZSM-12 a framework with 28 T-atoms per unit cell, enclosing 12-MR pores of 0.57 x 0.61 nm which are 1inear and parallel (ref.l). A photograph of a model of the proposed structure in the three

298

TABLE X.l. Dimensions of the monoclinic cell in which XRD patterns of ZSM-12 samples have been indexed

a

b

c

S

Ref.

(nm) 2.488 + 0.004 2.49 + 0.04 1. 26 + 0.02 1.246

0.502 + 0.002 0.50 + 0.01 1.11 + 0.02 1.099

1.215 + 0.003 1.215 + 0.02 2.44 + 0.02 2.433

107.7 0 + 0.1 0 107.7° + 0.1 0 + 10 1080 0 108.07

1 9 3 6

PHOTOGRAPH X.l.A. Model of ZSM-12 viewed along the b-axis. Sheets of 4- and 5-MRs are linked via 6-MRs.

299

PHOTOGRAPH X.I.B. Model of the structure of ZSM-12 viewed along the c-axis, perpendicular to the direction of the 12-MRs.

300

PHOTOGRAPH X.l.C. Model of the structure of ZSM-12, viewed along the a-axis, perpendicular to the direction at the l2-MRs.

301

PHOTOGRAPH X.2. Model of mordenite, viewed along the parallel 8- and 10-MRs. Sheets of 4- and 5-MRs are seen to be linked through 8-MRs. crystallographic directions is shown in Photograph X.l. In Photograph X.l.A this framework is viewed along the b-axis and the lZ-MR channels. The structure consists of sheets of four interconnected 5-MRs, which are linked via 4-MRs. Such chains are then combined via 6-MRs. Photograph X.Z shows that a similar situation exists for mordenite, in which these sheets of 5- and 4-MRs are interconnected via 8-MRs. Therefore, ZSM-12 belongs structurally to the mordenite group of zeolites (reLl). Viewed along the c-direction, the ZSM-1Z structure shows an arrangement of distorted interconnected 6-MRs (Photograph X.l.B). The wall of the lZ-MR pores in this direction is limited by this kind of arrangement of 6-~1Rs. In the a-direction an arrangement of highly distorted 6-MRs becomes visible (Photograph X.l.C), which limits the pores in this direction, giving them an undulating nature. The shape of the lZ-MR pores is shown schematically in Fig.X.Z. lO-MR pores with an undulating nature were also encountered with the TON (Chapter V1) and MTT structure types (Chapter VI 1). The unit cell contains two 4-MRs. These share edges with the 6-MRs which limit the pores. Every T-atom of these 4-MRs is accessible via these pores. If the same hypothesis is again true that the 4-MRs accommodate preferentially the aluminium atoms, then it is predicted that the lower limit of the SiO Z/A1 Z0 3

302

FIGURE X.l. Schematic diagram of the undulating nature of the 12-MR pores in MTW framework topologies. ratio in this framework, corresponding to two Al-atoms per 4-MR, is 12. As all previously encountered high-silica zeolites with a framework containing 4-MRs can be easily synthesized devoid of any aluminium, when organic molecules ire added to the synthesis gel, it is expected that silica polymorphs with the MTW structure type constitute the upper 1imit for the compositional range. Such material (TEA-silicate) (ref.13) was claimed long before the structure of lSM-12 was known. The morphology of the lSM-12 crystals seems to be euhedra1 with an acicular habit (ref.l). When dabco-Cs-diquat (see later) is used as organic, crystals of O.OL um are obtained (ref.8), whereas with dabco-C 10-diquat, crystals of O.OS x O.L ~m are obtained. Differences between computed and observed XRD line intensities for lSM-12 can be explained by twinning or intergrowing (ref.l). This phenomenon will change the local symmetry and unit cell sizes and might account for the differences in the dimensions of the unit cell of lSM-12, given in Table X.l for different samples. This phenomenon, however, in this instance will hardly affect the porosity of the materials. When the XRD patterns of the materials, considered to be members of this family of zeolites are compared (Fig.X.l),

303

they sometimes show substantial changes in the intensity of some lines (e.g., TPZ-3). It might therefore well be that all the claimed materials mentioned have the MTW structure type but differ in their degree of crystallographic purity. SYNTHESIS OF MTW ZEOLITES The preferred ranges of synthesis conditions in which different variants of ZS~l-lZ are claimed to be susceptible to crystallization are summarized in Table X.Z. The material apparently can be synthesized with a wide range of organics, which have in common that they are all quaternary ions, added as such or made in situ, or their polymers. The nature of these individual molecules is given in Table X.3. CZH-5, TEA-silicate and TPZ-3 are obtained using individually different organics, each belonging to the same class of molecules. Only NU-13 is prepared using an amine as organic. Table X.Z further shows that ZSM-lZ materials crystallize from gels with an SiO Z/A1 203 ratio of 20 as the lower limit. It also crystallizes when no aluminium is intentionally added, depending on the nature of the organic. Low -silica ZSM-12 seems to crystallize only when polymers of quaternary ions are added (ret.4). Mordenite then crystallizes when lower HZO/OH ratios or higher UH/SiO Z ratios are used. The OH/SiO Z ratio is also critical for the synthesis of NU-13. At low ratios NU-13 easily crystallizes. When the ratio increases, however, a very rapid crystallization of a-quartz is observed (ref.lO). With the monomeric quaternary ions, the lower SiO Z/A1 Z03 limit for ZSM-lZ seems to be close to 80 under otherwise very similar conditions. At lower silica contents of the mixture (ref.3), zeolite BETA crystallizes. Zeolite TPZ-3 (ref.lZ) crystallizes from gels with ZO ~ SiO Z/A1 Z0 3 ~ Z50, CZH-5 when this ratio is between lZ and ZOO (ref. 11) and NU-13 for ratios in the range 70-ZOO (ref.lO). It therefore seems that only TPZ-3 and CZH-5 zeolites can be synthesized from Al-rich mixtures. ZSM-lZ only does so when polymers of the type mentioned are in the synthesis gel. From the data reported in the patent literature (Fig.X.Z), it is seen that the lower SiO Z/A1 Z03 ratio for MTW materials is near 30. This is far away from an occupation bf two Al atoms per 4-MR, but agrees better with a single Al atom occupying every 4-MR. Using TPA in the synthesis of ZSM-5 the lower limit of the Al content of the zeolites was also found to be one Al per 4-MR (Chapter I, p.93). The number of positive charges accommodated in the l2-MR pores by the bulky organic cations listed in Table X.3 is not sufficient to allow the incorporation of more than one Al per 4-MR. Edges of

w

TABLE X.Z. Preferred conditions for the synthesis of ZSM-1Z variants Zeol ite R

ZSM-1Z N-containing polymers

SiO z/Al z03 HZO/OH OH/SiO z R/R+M MzO/SiO z Ref.

ZO-40 50-150 0.2-0.8 0.17-0.33 0.Z-0.7 4

Zeol ite R

ZSM-1Z a TEA

SiO/Al z03 HzO/OH OH/SiO z R/R+~i

MzO/SiO z Ref.

.,. 0

MTEA

ZSM-1Z TEA

>80 70-350 0.1-0.3 0.36-0.77

90-100 80-100 0.17-0.Z0 0.3-0.5

80-10 0.17-0.Z0 0.3-0.5

?

?

?

5

3

3

ZS~1-12

BETA TEA

~50

ZSM-5 TEA

ZSM-1Z Cyclic quaternary ammonium

ZSM-IZ

>8U 70-350 0.1-0.3 0.36-0.77

>80 70-350 0.1-0.3 0.36-0.77

85-500 5-100 0.15-0.Z5 0.Z8-0.90

400-00

?

?

5

5

a, when room temperature ageing of the gel is applied

MOR N-containing polymers

~1TEA

ZSM-1Z DABCOCn-diquat

15-40 10-50 0.5-1.Z 0.09-0.33 0.4-1.0 4 ZSM-12 DEDMA

0.Z-1.0 0.4-0.8

90-300 80-150 0.17-0.Z5 0.3-0.5

> 80 70-350 0.1 -0.3 0.36-0.77

?

?

?

?

6

7

8

9

?

TABLE X.3. Chemical nature of the organics used in the synthesis of ZSM-12 and related materials

306

4-MRs are indeed present in pairs at a repeat distance of only 0.5 nm along the pore walls. If the prediction regarding the location of Al is correct, theoretically DAB-4 (Table X.3) should be the only template that would allow two Al atoms to be incorporated per 4-MR. Fig.X.2 also shows that in the Si0 2/A1 203 range from 30 to 100, members of the MTW family of zeolites can be synthesized with a composition identical with that of the gel. For more siliceous compositions this direct correlation is perturbed. These phenomena have been ascribed in previous chapters to a decreased crystallization efficiency.

3001- .:ref.4 ,ZSM-12 o:ref.5,ZSM-12 *:ref.6,ZSM-12 ():ref.9 ,ZSM-12

Q)

(5

8:ref.3 ,ZSM-12 200- .:ref.10,NU-13

Q)

N

'f':ref.11,CZH-5

r::::

x :ref .12, TPZ-3

1 ()

()5

o

3 100~

I

I

I

100

200

300

FIGURE X.2. Si0 2/A1 203 compositions of gels and corresponding ratios for ~ITW-type zeolites crystallized from them. The numbers next to experimental points are the example numbers in the original patent.

the the

The data on the synthesis of zeolites with the MTW structure type and their intergrowths which are scattered through the patent literature are far from systematic but point to the eXist~nce of a certain number of parameters that direct the crystallization reaction. In Fig.X.3 data are plotted that

307

150

III

7

>.

III

'0

-, CI> .E.... c: .2

....III

100

N

....IIIIII

...>. (J

50 0.20

0.30

0.40

0.50

R/R+Na

FIGURE

X.3.

Influence

of

the

fraction

of

TEA

cations

(R)

on

the

crystallization time of lSM-12. The data are from ref.3 and refer to the crystall ization conditions Si0

=

373K, OH/Si0

100 - 125. The figures

~ext

= 0.17-0.20, H20/OH = 78-90 and 2 to the experimental points indicate

2/A1 203 the example numbers in the original patent.

308

illustrate the influence ot the fraction of the organic ions, in this instance TEA, on the crystallization time of ZSM-12. It is clear that an increase in the organic content of such gels results in a faster crystall ization. The increase seems to be more effective for the higher fraction of organics. This effect has also been observed for other high-silica zeolites and is illustrative of a pore filling function of the organic. Unfortunately, the data do not allow it to be established whether at higher TEA contents more siliceous zeolites can be obtained.

i.

tt ,

In Table X.4 a few other effects are illustrated: Dimethylpiperidinium ions are more effective than dimethylpyrrolidinium as the organic in the ZSM-12 synthesis. It is therefore highly probable that there exists also in this instance an organic whose size and shape are best suited for a fast crystallization of MTW zeolites. Tab l e X.3 shows an impressive number of candidates, but the present data do not allow one to select the preferred crystal 1ization agent; an identical situation has been discussed for ZSM-5, for which TPA is the preferred organic. As already pointed out earlier, an increase in basicity and in' the amount of organic, or a combination of both effects, accelerates crystallization.

TABLE X.4. Illustration of the effect of some parameters on the crystallization of lSM-12

Gel composition

Si0 2/A1 203

R/R+M

98.4 98.4

0.48 079

0.22 0.22

0.67 0.70

0.31 0.10

0.43 0.89

0.20 0.25

100 125

Synthesis temp./K time/days

R

Remarks

Ref.

OH/Si0 2 H2O/OH

73.1 73.1

423 423

21 24

212 167

433 433

b.H 13.6

78 9

451 451

12 7

pyrrolidinium is the less effective organic

6,ex.1

MTEA MTEA

higher basicity gives faster crystallization

7,ex.4 7,ex.8

TEA TEA

combined effect of basicity 3,ex.1 and amount organic 3,ex.4

dimethylpiperidinium dimetylpyrrolidinium

co

o

(!)

310

TABLE X.5. Compositlon of MTW-type zeolites

Zeol ite

ZSM-12 Z91-12 ZSM-12 ZSM-12 ZSM-12 NU-13 ZSM-12 ZSM-12 ZSM-12 ZSM-12 ZSM-12 ZSM-12 CZH-5 TPZ-3 TEAs il i cate

Molar composition per A1 203 Si0 2

Na 2

R20

82 44.8 194 214 97 90

0.74 0.11

2.20 0.89

72

0.61 0.45 0.27 0.28

87 80 78 2594 132 64.2 62.7 1342

0.2 0.88

0.69 0.31

R/UC a

Na/UC b

TEA TEA MTEA MTEA MTEA Piperazine Piperidinium Piperidinium Pyrrol idinium Pyrrol idinium MTEA DEDMA Choline Diquat-6

1. 25 0.91 1.12 1. 22 1. 20 0.47 1. 36 1.04 1.07 1. 34 1.06 1.19 1.00 0.24

0.42 0.1 0.33 0.29 0.32 0.10 0.40 0.25 0.16 0.17 0.26 0.29 0.15 0.65

3,ex.8 3,ex.1 5,ex.1 5,ex.7 5,ex.5 10,ex.1 6,ex.3 6,ex.4 6,ex.6 6,ex.9 7,ex.6 9,ex.5 11,ex.3 12,ex.1

TEA

1.1

0.44

13,ex.1

R

Ref. c

a, organics (R) per unit cell, assuming that all zeolites belong to the MTW structure type; b, Na per unit cell under the same assumption; c, referring to the specific examples in the patents.

TABLE X.60 Influence of synthesis conditions on the retention of alkali metal ions and organics in the final ZSM-12 zeolite.

Molar gel composition Si0 2/A1 203

R/R+M

Zeolite composition

OH/Si0 2 H2O/OH

R

Si0 2/A1 203

Na/UC

R/UC

Ref.

Remark

more R in gel resul ts in more R in zeolite

98.4

0.52

o.zz

73.1

pyrro 1i di ni um

79.8

0.16

1.07

6,ex.6

98.4

0.79

0.22

73.1

pyrrol idinium

77.8

0.17

1.34

6,ex.9

0.43

0.15

122

DEDMA

144

0.30

1. 33

9,exol

0.60

0.15

114

DEDMA

2930

0029

0.96

9,ex.4

338

more Si results in less organic in zeol ite although more organic in gel

cc ..... .....

312

As systematic data on synthesis are lacking and because of the potential interest in shape-selective zeolites in catalysis, Ernst et al. (ref.14) undertook a systematic study to investigate the influence of the parameters mentioned on the crystallization of ZSM-12 using MTEA as the organic. These results can be summarized as follows and indicate that many features are in common with the synthesis of ZSM-5 : i. The MTEA fraction directly influences the crystallization kinetics: at higher fractions not only is the nucleation period lengthened, but also the crystal growth rate is decreased and materials of poorer ultimate crystallinity are obtained. In the synthesis of ZSM-12, MTEA certainly does not act like TPA in the synthesis of ZSM-5. These results suggest that MTEA does not play an active role in the nucleation event, but that hydrated alkali metal cations intervene directly in the nucleation. ii. An increase in the basicity of the synthesis gel expressed as OH/H 20 or the OH/Si0 2 in the usual composition range also increases crystallization rate. iii. In the range of Si0 2/A1 203 ratios between 60 and 240 and for the more siliceous gels, the nucleation period decreases, the crystal growth increases and the ultimate crystallinity of the product increases. The crystals obtained are elongated with dimensions of 4-6 x 1 ~m. When Dabco-Cn-diquat was used as the organic, an influence of the length of the molecule on the crystallization time was reported (ref.8). When n was increased from 5 to 10, the crystallization time decreased from 299 to 253 h under otherwise identical conditions. When with Dabco-ClO-diquat as the template, potassium replaced sodium as the source of mineral al kal i, the synthesis time increased to 367 h under the same conditions (ref.8). For TON zeolites smaller alkali metal cations are also the preferred templates (Chapter VI). The effect of chain length of the organic has been encountered for almost every high-silica zeolite discussed so far, and the influence of the nature the mineralizing agent has been treated in detail for ZSM-5 (Chapter I I) . RETENTION OF ORGANICS IN MTW ZEOLITES Table X.5 shows typical compositions of MTW type zeol ites. It is striking that for all members, apart from TPZ-3 and NU-13, irrespective of the organic used and of the ultimate A1 203 content of the zeolite, the number of organlc molecules retained in the zeolites after synthesis is very close to one per unit cell. This indicates that no strict templating effect or strict pore tilling function can be attributed to the organic. For 10-MR

313

high-silica zeolites, there is considerable evidence for a close relationship between the size of the organic and its pore filling potential. When lt is taken into account that 6-8 weight % of cyclohexane on the average is sorbed in ZSM-12 (refs.3-9), this corresponds to sorption figures of 1-1.4 per unit cell for this sorbate, which agrees reasonably well with the number of organic molecules retained after synthesis. A pore fill ing action of the organic therefore exists, but its efficiency seems to be determined by other parameters. The existence of two such parameters for ZSM-12 is illustrated in Table X.6. Under otherwise identical conditions, it is shown that when the fraction of organics in the synthesis gel is higher, more organic is retained in the zeolite. It is also illustrated that this effect can be counteracted by the aluminium contents of the gel: when more siliceous gels are used, less organic is retained in the zeolite even when this gel contains a higher fraction of organics. It isnot clear, however, how such effects would be explained in terms of the presently handled synthesis mechanisms. The lower preference of zeol ites TPZ-3 and NU-13 for organics (Table X.5) cannot be linked with a decreased sorption capacity for organic molecules, as comparable sorption data are lacking.

FIGURE X.i. 1. CZH (Brit.P. 2.079.735)

sL 2

e

f..

f..

d [0. 1nm]

IIIo

11.84 11.58 9.00 4.73 4.68 4.63 4.42 4.16 4.08 4.04 3.95 3.87 3.83 3.53 3.45 3.39 3.32 3.19 2.89 2.80

50.00 30.00 96.00 14.00 5.00 8.00 5.00 100.00 14.00 15.00 6.00 37.00 28.00 6.00 16.00 11.00 13.00 7.00 6.00 1.00

f..

I

5.0

I

9.0

I

I

13.0

I

I

17.0

IIII

I

21.0

I

,I

I, l

25.0

29.0

I

33.0

I

I

37.0

,

I

41.0

I

I

45.0

I

I

49.0

53.0

co

..... ....

FIGURE X.1.2. NU-13 (E.P.A. 59.059)

sL

II-

2

I-

9

I-

III-

-

d [0. 1nm]

IlIa

11.80 10.05 4.79 4.26 4.08 3.83 3.65 3.54 3.40 3.32 3.20 3.14 3.04 2.89 2.52 2.50

19.00 9.00 16.00 100.00 46.00 23.00 3.00 10.00 11.00 12.00 6.00 6.00 5.00 8.00 12.00 13.00

-

l-

5.0

I, 9.0

I

13.0

I

I

17.0

21.0

j

25.0

11,1 29.0

l

I

33.0

I

I

37.0

I

I

41.0

I

I

45.0

I

I

49.0

,

I

53.0

w >-'

""

FIGURE X. 1.3. TEA-SILICATE (U.S.P. 4,104,294)

d [0. 1nm]

11.90 10.20 4.98 4.77 4.29 3.88 3.66 3.49 3.39 3.21 3.06 2.89 2.65

t. 2

-

e

-

1/10 60.00 26.00 5.00 18.00 100.00 84.00 16.00 24.00 32.00 10.00 8.00 5.00 5.00

f-

, 5.0

I,

9.0

,

, 13.0

I

I

I

17.0

I,

I.

21.0

I

25.0

,I

J l 29.0

,I 33.0

I

I

37.0

I

I

41.0

I

I

45.0

I

I

49.0

I

, 53.0

w

>-'

C>

FIGURE X.1.4. ZSM-12 (U.S.P. 3.832.449)

sL

-

2 6

f-

f-

rrf-

d [0. 1nm]

IIIo

11.90 11.60 11.15 10.02 9.72 6.02 5.57 4.96 4.75 4.70 4.45 4.28 4.10 3.98 3.85 3.75 3.71 3.65 3.49 3.39

27.00 10.00 10.00 35.00 5.00 5.00 5.00 5.00 14.00 11.00 6.00 100.00 8.00 14.00 67.00 5.00 9.00 7.00 16.00 20.00

49.0

53.0

rf-

rI

5.0

II

lj 9.0

I

I

13.0

1.11

I 17.0

I

I

I ,II.

21.0

25.0

I

I

29.0

I

I

33.0

I

, 37.0

I

I

41.0

I

45.0

w ...... -J

FIGURE.X.1.5. TPZ-3 (E.P.A.51.318)

SL

-

2

d [0. 1nm]

IIIo

20.10 11.19 9.94 8.64 5.83 4.98 4.67 4.33 4.02 3.83 3.72 3.65 3.44 3.33 3.28 3.21 3.15 3.10 2.96 2.54

81.00 49.00 41.00 4.00 4.00 5.30 39.00 100.00 56.00 28.00 17.00 4.00 32.00 41.00 35.00 13.00 5.30 4.00 6.70 6.70

e

C

Z5M-12

"..

...

Z5M-12

k

I-

k

....

II

I-

k

I-

I-

k

-

k

l-

k

II

5.0

I

9.0

I

• 13.0

.1

I

I

17.0

I

21.0

I,

~~

II.

25.0

29.0

• 33.0

.1

I

37.0

, 41.0

,

I

45.0

, 49.0

53.0

co ~

C/O

319

REFERENCES

1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14.

R.B. La Pierre, A.C. Rohrman,Jr., J.L. Schlenker, J.D. Wood, M.K. Rubin and W.J. Rohrbaugh, Zeolites ~ (1985) 346. J.C. Trewella, J.L. Schlenker, D.E. Woessner and J.B. Higgins, Zeolites ~ (1985) 130, E.J. Rosinski and M.K. RUbin, U.S.P. 3,832,449 (1974), assigned to Mobil Oil Corp. Nederl. Octrooi 7,701,382 (1977), assigned to Mobil Oil Corp. P. Chu and G. Kuehl, EPA 18,089 (1980), assigned to Mobil Oil Corp. E.J. Rosinski and M.K. Rubin, U.S.P. 4,391,785 (1983), assigned to Mobil Oil Corp. G.H. Kuehl, E.P.A. 135,621 (1983), assigned to Mobil 011 Corp. G.H. Kuehl, U.S.P. 4,482,531 (1984), assigned to Mobil Oil Corp. G.H. Kuehl, E.P.A. 147,952 (1984), assigned to Mobil Oil Corp. T.V. Whittam, E.P.A. 59,059 (1982) assigned to ICI. D.A. Hickson, U.K.P.A. 2,079,735A (1982), assigned to Chevron Res. Compo K. Sumitani, T. Sokai, Y. Yamasaki and T. Onodera, E.P.A. 51,318 (1981) assigned to Teijin Petrochem. Ind. R.W. Grose and E.M. Flanigen, U.S.P. 4,104,294 (1978), assigned to Union Carbide Corp. S. Ernst, P.A. Jacobs, J.A. Martens and J. Weitkamp, Zeolites, in press.

This page intentionally left blank

321

CHAPTER X : SYNTHESIS OF ZEOLITES THAT DO NOT BELONG TO THE HIGH-SILICA AND/OR SHAPE-SClECTIVE CLASS OF ZEOLITES

SYNTHESIS OF SILICEOUS MORDENITE It is beyond the scope of th is book to e1abora te on the synthes is of mordenite-type zeolites, as strictly it does not behave as a shape-selective high-silica zeolite. The photograph of the structure given in previous chapter (Photograph X.2) views down the O.67xO.70 nm 12-MR pores and the parallel 0.29xO.57 nm 8-MR pores (ref.l). These main channels are interconnected via small side pockets of free diameter 0.29 nm (ref.2). The pore system of mordenite is depicted in Fig.XI.l. The mordenite unit cell is orthorhombic with cell dimensions of a=I.81, b=2.05 and c=0.75 nm and contains 48 T-atoms (ref.l). The synthesis of mordenite has been reviewed recently by Bajpai (ref.3). It seems that most of the previous methods for the synthesis of large-pore (ref.3) and small-pore mordenites (ref.4) invariably result in zeolites with Si0 2/A1 203 ratios ranging from 9 to 12. This range corresponds to that encountered in the natural mineral. This "magic" ratio has been accounted for in terms of the preferential location of Al atoms in the 4-~lRs of the mordenite structure, requlrlng a double occupancy of these structural elements (ref.5). This concept has also been utilized to rationalize the lower limits for the Si0 2/A1 203 ratio in high-silica zeolites (see previous chapters). Self-consistent field molecular orbital calculations have confirmed that aluminium is indeed energetically favoured in the 4-MRs, and that diagonally paired Al sites across 4-MRs are more stable than isolated ions in the same ring (ref.6). The T-sites in adjacent 5-MRs are estimated to be about 42 kJ mol- 1 less stable (ref.6). From these considerations, it can be anticipated that the energy barrier to make mordenite structures containing two to one Al atoms per 4-MR should be relatlvely easily to overcome. This corresponds to Si0 2/A1 203 ratios varying from 10 to 20. Bodart et al. (ref.7) showed that this was the case when in inorganic media the alkalinity was increased. Hydrogels of (Na 20)z(Si02)x(AI2U3) (HzO)y in Pyrex-lined autoclaves form mordenite at 438K depending on the gel composition and alkalinity. For the product with

322

(OH/H

ratios varying from almost zero to 0.5, a direct ZO).(SiO Z/A1 Z03) negative correlation exists between this value and the Al content of the zeolite. In this range the Al content varies from eight to four atoms per unit cell (ref.7), corresponding to two and one Al atoms per 4-MR, respectively. For higher val ues of this al kal inity times composition ratio, no further decrease in the Al content of mordenite was observed. In Fig. XI.Z data obtained by other workers are plotted according to the relationship of Bodart et al. (ref . 7). The data of Sakurada et al. (ref.9), obtained under inorganic conditions, presence of

and of Ball substituted

and stewart (reL8), obtained in neopentylamines such

3-dimethylamino-Z,Z-dimethylpropan-1-ol,

do

not

fit

this

the as

relationship

exactly, although they show the same trend : at higher values of the alkalinity times composition ratio, the mordenite samples that crystallize become increasingly sil iceous with a lower 1imit for the aluminium content which on average is not significantly below one Al per 4-MR. The discrepancy between the two sets of data can be eas ily accounted for, because in the experimental set-up used by Bodart et al. (reL7) silica wi II be dissolved from the walls of the Pyrex-lined autoclaves and consume OH ions of the synthesis gel, thus shifting the abscissa values to apparently higher values. A mordenite synthesis

carried out the

presence of

DAB-4,

a quaternary

ammonium polymer synthesized by reaction of 1,4-diazabicyclo!Z.Z.Z!octane with 1,4-dibromobutane (ref.10), also fits the relationship of Bodart et al. (reL7), because with an (OH/H ratio as high as 1.7 the ZO).(SiO Z/A1 Z0 3) ultimate product contains not less than four Al atoms per unit cell. Whittemore (ref.11), who reported first the synthesis of a siliceous mordenite,

obtained as

the most siliceous material

a mordenite with

an

SiO ratio of 19.5. Ueda et al. (reL1Z), on addition of Z/A1 Z03 benzyltrimethylammonium to a gel that otherwise gives a mordenite with an SiOZ/A1 Z0 3 ratio of 1Z.8 (reL13), reported an increase of the SiO Z/A1 Z03 ratio up to Z5.8. Itabashi et al. (reL14) showed also that the Si0z/A1 203 ratio of mordenite crystallized from a mineral gel could be varied from 10.Z to 19.1 when the NaZO/S iOZ ratio of the gel was decreased from 0.145 to 0.108. Unfortunately, the data presented do not allow one to calculate the (OH/H ZO).(SiO ratios and verify the general val i d i ty of the Z/A1 Z03) relationship advanced by Bodart et al. (ref. 7). It should be stressed that attempts to relate the Al content of mordenite (refs.7,8,lZ and 14) to either the HZO/OH or OH/SiO Z ratios of the synthesis gels always show low degrees of correlation.

323

MORDENITE

FIGURE XI.I. Schematic representation of the pore system of mordenite. Sil iceous mordenite can be synthesized in the presence of organics, as has already

been indicated (refs.ll,I2) . Klotz (ref.I8) also showed that,

depending on the Si0 crystallized from

ratio of the gel, different zeol ites can be 2/A1 203 otherwise identical gels. The preferred conditions for

mordenite synthes is in

the presence of 2-ami nopyri di ne are withi n

limits for the Si0

ratio of the gel.

However,

2/A1 203 mordenite over much wider ratios has been claimed.

na rrow

crystallization of

Preferred conditions are

summarized in Table XI.I. Unfortunately, it cannot be concluded from the data available whether the combined use of orqan i cs and high SiO does give materials with SiO

Z/A1 Z03

ratios Z/A1 L03 ratios significantly higher than 20-25.

324

7,---..----------------------.....,

6

4

•

1AI/4-MR

3~---..L----_L.---~:__--~_:__--___:!

o

0.2

0.1

....Q!!... x H2 0

0.3

0.4

0.5

Si02 AI203

FIGURE XI.Z. Influence of the (OH/H ZO).(SiOZ/ A1Z03) ratio of the gel for mordenite synthesis on the aluminium content of the zeolites. The broken line represents part of the relationship advanced in reL7; the full points are data from ref.9 and the open point represents data from ref.8.

Z5M-4

o .

MOR

FER

Z5M-5

40

FIGURE XI.3. Typical SiO Z/ A1Z03 ratios for zeolite synthesis from a Z-aminopyridine-containing gel (reL18). (0.01 < OH/SiO Z < 3; 10 < HZO/OH < 500; O.Z < R/R + Me < 0.95).

325

TABLE XLI Conditions for the synthesis of mordenite-type zeolites in the presence of organics

SiOZ/A1 Z03 HZO/SiO Z OH/SiO Z Na/SiO Z R/SiO Z R

Ref. Product SiO Z/A1 Z0 3 of product

60 - 90 10 - 100 0.1 - 1.0 0.1 - Z.O 0.1 - 1.0 phthalocyanines bipyridyl phenanthroline 15 < 40% MOR ?

30 15 - 30 0.3 - 0.5 0.6 - 0.8 0.01 - 0.5 TEA ethylpyridinium aminesa 16 MOR ?

9 10 0.15 -

30 50 0.35

0.01 - 0.4 organic acids b

17 TZ-OZ ?c

a, tributylamine, diisobutylamine, isobutyl amine, diisopropylamine, cycloheptylamine, triethylamine, trioctylamine. b, malic, citric, L-glutaric, benzoic, propionic, salicylic acid. c, only ex. 3 shows the composition of the mordenite (SiOZ/A1 Z03 = 13.3), from a gel with a ratio of 15.

:326

In the presence of organic acids (reLI?), a phase transition between TZ-OZ, a moruen i te-Lype zeolite, and TZ-OI, a pentasil-like material, has been elaborated. Table XI.Z shows that the mordenite-type structure compared with

the pentasil-like material

can

be obtained from gels with a lower

0 ratio, a higher basicity (OH/SiO or a lower yield of organics SiO Z/A1 Z 3 Z) (R/A1 A systematic increase in the SiO ratio in an Z03). Z/A1 Z03 Z-aminopyridine-containing gel resul ts in the crystall ization of subsequent

ZSM-4, MOR,

FER and

ZS~1-5

phases (Fig.X!.3). With TEA added to the gels

(reL19), mordenites with SiO

molar

Z/A1 203

ratios between 15 and 30 are

obtained. TABLE X!.2. General conditions for the synthesis of mordenite (TZ-02) and pentasil-type structures (TZ-Ol) from gels containing organic acids (data are from ref.17)

TZ-U2

TZ-Ol

< 30

In

view

of

the

> 30

0.25 - 0.35

0.15 - 0.17

0.3

2.5

structure

- 2.5

of

mordenite

and

- 7

the

priciple

of

the

preferential location of aluminium in 4-MRs, a limiting range of 10 - 22 for the Si0 2/A1203 ratio of this zeolite can be explained. An enhancement of the Si0 ratio by adding organics can be expected easily up to 22. This 2/A1203 corresponds to an occupation of every 4-MR by a single AI atom. This can be achieved by decreasing the alkalinity or the alkali cation content in mineral gel s or by addi ng organi cs. As the organ i cs used cannot be accommodated in the 8-MRs and as every 4-MR belongs to both a

l2~MR

and an 8-MR pore, it is

logical that aluminium incorporation via l2-MRs can easily be blocked with organics but not via 8-MRs. In this way the ultimate Si0

ratio of 20 2/A1203 (i.e., four Al/UC or one Al/4-MR) can be easily explained. It is also logical

that,

when in

such

gels

the

Na/SiO

z

ratio

is

further

decreased,

the

SiO

ratio will be further enhanced but only to an upper 1imit. An

SiO

3 ratio of 30 then corresponds to an occupation of about one Al per

z/Al z0 3

z/Al z0

327

every second 4-~1R in the 8-~IR pores and a probable upper 1imit for the SiO Z/A1 Z0 3 ratio in mordenite. If all this is true, it should be somehow reflected in the chemical or physico-chemical properties of the mordenites with ZO<SiO Z/A1 Z03<30. Three siliceous mordenite-like materials, TEA-MOR (ref.19), ME-MOR (ref.Zl) and MB-28 (ref.ZO), have been claimed and were synthesized in the presence of tetraethylammonium (TEA) or diethylpiperidinium (DEPiP). The SiO Z/A1 Z03 gel ratios and the corresponding ratios in the zeolites can be found in Fig.XI.4 for all mordenite-like zeolites discussed in this chapter. For mordenites synthesized with SiO Z/A1 Z0 3 ratios in the range 10 - 30, there is a direct proportional ity between these ratios in the gel and the zeol ite phase, which is indicative of a very high synthesis efficiency. ME-mordenites are apparently obtained at a lower efficiency but with approximately two Al atoms per unit cell (SiOZ/A1 Z03 = 40) (ref.Zl). Surprisingly, zeolite MB-Z8 crystallizes with a significantly different efficiency: the SiO Z/A1 Z0 3 ratio in the crystalline solid is higher than that in the gel (ref.ZO). It is doubtful, however, whether this material is a mordenite, as next to the XRD lines characteristic of mordenite some pentasil lines are present (see Chapter IV, p.193). Differences in the molar gel composition for the synthesis of MB-Z8 and TEA- and ME-mordenites are summarized in Table XI.3. MB-Z8 and ME-MOR are obtained from a gel containing DEPiP with very high cation dilution ratio (HZO/RZO or HZO/NaZO) compared with TEA-MOR. In terms of the previously advanced hypothesis on the distribution of Al in the 4-MRs, this behaviour can be understood. Indeed, the organic cannot be accommodated in 8-MR and consequently, the only way left to increase the SiO Z/A1 Z03 ratio far beyond 30 is to reduce the Na/HZO ratio, components which fill the 8-MR pores. The difference in synthesis conditions between MB-Z8 and ME-MOR is mainly found in the higher SiO Z/A1 Z03 gel ratios used to synthesize the former zeolite. The high SiO Z/A1 Z03 ratio in the MB-Z8 zeolite and its higher value compared with the gel composition remain to be explained, however, but could be related to its crystallographic impurity. The catalytic data available indicate that ME-MOR is a large-port mordenite variety whereas MB-Z8 behaves like a 10-MR shape-selective zeolite. Indeed, in the isomerization of m-xylene (ref.Zl) over the acid form of these zeolites, the p-selectivity of MB-Z8 is more like that of lSM-5, whereas ME-MOR behaves like a large-pore zeolite for the low SiO Z/A1 Z0 3 ratios or has an intermediate selectivity for SiO Z/A1 Z03 ratios between 30 and 40 (ref.Zl). The sorption data for MB-Z8 also tend to indicate the same conclusion. Indeed, in sorption capacity for n-hexane is twice as high as for cyclohexane (ref.ZO), whereas for a distorted 12-MR zeol ite such as lSM-12 {previous

.

328

chapter) the sorption capacities for both sorbates are comparable. The old debate as to whether the generation of a small-port mordenite material is the result of a particular localization of Na cations, the presence of amorphous material or of stacking faults now seems to be settled (ref.4) in favour of the last hypothesis.

8 0 . . . . - - - - - - - - - - - - - - - - -........- - _ //

• : ref. 21 , ME - MOR

/

o : ref. 20,MB-28 .:ref. X :

9,MOR

/

ref.14,MOR

60 .... : ref.19, TEA-MOR

8 o

a:

o

/

~

C'?

N

/

/

/

/

e

o

/

/

40

f-

et

<,

../

N

o

3/

. /

/

/

/ .6

•4

5

V

Cf)

20 -

}'

x

/xx

/( V/ o

0lC.-.

; ...L...-

I

20

....L..

I

40

......L. I

60

~

80

FIGURE XI.4. SiO Z/A1 Z03 ratios of the hydrogel versus that of the final MOR zeolite obtained according to different procedures (the figures next to the experimental points indicate the example numbers in the original publications).

TABLE XI.3 Molar gel compositions for the synthesis of siliceous mordenite-type zeolites

Si0 2/A1 203

Na 2O/Si02

R2O/Si02

H2O/Na2O

H2O/R2O

CMF b

Sp f

R

Ref.

TEA-MOR

30.7

0.2!>

0.10

22.7

54.2

0.33

0.70

TEA

19,ex.1O

MB-28 a

40-8!>

0.07-0.25

0.10-0.20

150-400

>190

0.22-0.38

0.25 e

DEPiP

20

ME-MUR

20-50

0.1-0.16

0.10-0.20

L50-375

250-300

?

0.5-0.7 c

DEPiP

21

0.4-0.6 d

a, Preferred conditions; b , cation mineralization factor = (R 20 + Na 20)/(Si02 + 2 A1 20); c , at 453K; d, at 413K; e, ex.1; f = SP = Na 20/R20 + Na 20.

cc

"" <0

MATERIALS WITH MTN STRUCTURE TYPE Porotectosilicate analogues of water clathrasils constitute a new family of high-silica materials (ref.22) or silica polymorphs (ref.23). The first synthetic member of this family of materials has been denoted ZSM-39 (ref.22). Its framework consists of 12- and 16-hedra (ref.22), each 12-hedron containing twelve edge-shared 5-MRs. When these elements are joined by face-sharing, a layer of 12-hedra is generated (Fig.XI.5). When these layers are stacked in an ABC sequence, they form the ZSM-39 structure (ref.22) and give rise to a structure type denoted MTN (ref.24). This ABC stacking sequence of the layers of face-shared 12-hedra creates the 16-hedra which contain twelve 5-MRs and four 6-~lRs. Such a 16-hedron which only can trap molecules that are able to diffuse through 6-MRs is shown in Fig.XI.5. When the layers are linked in an AB sequence, the hypothetical structure shown in Photograph XI.l is formed, which contains two types of cages, of which the larger one is again only accessible throu9h 6-MRs.

PHOTOGRAPH XI.l. Hypothetical structure formed through AB stacking of layers of face-shared dodecahedra.

331

12-hedron

16-hedron

layer of face - shared 12-hedra

FIGURE XI.5 Structural elements of ZSM-39 (after ref.22) : the 12-hedron, the association of 12-hedra into layers of face-shared dodecahedra and the 16-hedron formed via an ABC stacking of these layers. Although these materials, chemically speaking, are high-silica zeolites, they are not expected to exhibit any shape selectivity towards hydrocarbons. ZSt~-39 is obtained from siliceous gels, which should contain organics wi th a smalls i ze so that they can be accommodated in the 16-hedra. Organics tha t can be used are TMA (ref. 26,29), TEA (ref. 25), morpho 1i ne or di oxane (ref.28) or pyrrolidine (ref.27). According to its structure, a maximum cage filling of one organic molecule per 16-hedron, or one R per 28 T-atoms is

332

possible.

Available data for TMA indicate that T/R = 27 (ref.25,ex.4),

which is indicative of a cage-filling function of the organic. In contrast to the claims (refs.26-28) that the Si0 lSM-39 crystals can be from 40 to 00, actual data the upper Al content as

the lowest Si0

2/A1203

2/A1203

(refs.22,23,2~-28)

ratio of the restrict

ratio encountered is 176

(ref. 27). Although no shape-selective catalytic properties are to be expected, one should real ize that the rapid removal of the organics from this structure might open it to a certain extent and consequently create defects, which might attribute to such materials some shape-selective properties. The XRD pattern of lSM-39 is shown in Part I (Fig.I.3.6).

333

SILICEOUS LEVYNITE ZEOLITES To the high-alumina mineral Levyne (Si0 2/A1 203 = 4), the structure type LEV has been attributed. This mineral is a 6-MR zeol ite with this structure element in an AABCCABBC sequence. The unit cell contains 54 T-atoms and is trigonal with an a=1.33 and c=2.3 nm (ref.30). In this structure a two-dimensional set of 8-MRs of 0.33xO.53 nm section is present (ref.30). A photograph of such a structure is shown in Photograph XI.2. The 17-hedra of type I which form the LEV structure type consist of three 8-MRs, five 6-MRs and nine 4-MRs (ref.38). Such a 17-hedron has free inside dimensions of 0.77 x 0.64 nm (ref.38). The pores will therefore be of a lobate nature. Such a structure will only be accessible to linear organic molecules and thus may be of potential use to remove n-alkanes in a selective way by cracking from a mixture with larger molecules. The synthesis of sil iceous members of this family of materials with the LEV structure type has also been reported. They are denoted ZK-20 (ref.31), NU-3 (ref.32), LZ-132 (ref.33), LZ-133 (ref.34) and ZSM-45 (refs.35-37). The Si0 2/A1 203 ratio of the gel in which these materials can be synthesized is claimed to vary from 4 to 80, depending on the typical family member and using organic molecules (Table XI.4). TABLE XI.4. Some preferred synthesis conditions for zeolites with the LEV structure type

Zeolite

Si0 2/A1 203

NU-3 LZ-132 LZ-133 ZK-20 ZSM-45 ZSM-45 ZSM-45

15-70 15-tlO 15-tlD 4-11 20-60 10-30 15-80

R N-methylquinuclidiniuma methylquinuclidine methylquinucludine methyl-dabco b '), DMDEA c cobaIt ini umd choline

a, N-methyl-1-azobicycloI2.2.2!octane; b, 1-methyl-1-azo-4-azobicyclo!2,2,2Ioctane; c, dimethyldiethylammonium; d,ICo(C5H5)2 1+.

Ref. 32 33 34 31 37 36 35

ON ON

"'"

PHOTOGRAPH XI.2.

~1odel

association in space (8)

of a LEV structure type with a linkage of two 17-hedra and hexagonal prisms (A) and their

335

The individual members in Table XI.4 differ in either the way they are synthesized, the nature of the organic used and/or the detailed XRD pattern. A typical XRD pattern of levyne vias given by von Ballmoos (ref.39). All individual members have patterns that resemble it, but differ in minor characteristics. For the sake of completeness and to make comparisons possible, the XRD patterns of the individual synthesized materials taken from the original patents and adapted using our usual format are represented in Figs.XI.6.1-4. When these LEV-type zeol ites are crystall ized in the Si0 2/A1 203 range claimed, almost perfect agreement is obtained between the composition of the gel and the zeol ite, at least as far as their Si0 2/A1 203 ratio is concerned (Fig.XI.7). This points to a highly efficient synthesis. Table XI.5 indicates also that the LEV-zeolites synthesized in the presence of methylquinuclidinium with the lowest silica content have R/Al ratios that are close to unity, indicating a charge neutralization function of the organic compound. This figure in terms of occluded R molecules per unit cell is also close to 4, which corresponds in turn to an occupation of one molecule of organic in every 17-hedron. At higher Si0 2/A1 203 ratios, this degree of occupation seems to decrease.

TABLE XI.5. Typical compositions of synthesized LEV-type zeolites

Zeolite

Si0 2/A1 203

LZ-133 LZ-133 LZ-132 LZ-132 NU-3 NU-3 NU-3 ZSM-45

23.9 45 27.4 47.5 20.8 45 98 27.0

R/Me

1 1.5 1.14 1.85 1.2 1.5 2.0 7.6

* assuming 54T-atoms per unit cell.

R/UC *

4.4 3.4 3.2 4.0 5.7 3.5 2.2 7.1

R

Methylquinuclidine Methylquinuclidine Methylquinuclidine Methylquinuclidine Methylquinuclidine Methylquinuclidine Methylquinuclidine DMDEA

Ref.

34,ex.l 34,ex.3 33,ex.l 33,ex.6 32,ex.6 32,ex.l 32,ex.3 37,ex.l

336

100r---------------------~

o

Q)

N

.S

50

I-

M

•1

oN «

<, N

o (/)

25-

I

I

I

I

25

50

75

100

FIGURE XL7. Si02/A1 203 ratios of the synthesis gel and in the ultimate LEV-type zeolites. The figures next to the experimental points refer to data from the corresponding examples in the original patents.

From the sorption data in Fig.XI.8 it follows that ZSt'1-45, LZ-132 and LZ-133 have comparable sorption capacities for n-hexane, whereas the n-hexane sorption in NU-3 is significantly lower. Slightly larger molecules (isobutane, p-xylene or cyclohexane) apparently do not enter the inner voids of the structure, as a result of their restricted diffusion through 8-MRs.

15

:.:;:::::;:;:::;::::::: ~m~m~ r~ r~

---

::::::::::::::;:::::;

----- cyclo -

.........

n-hexane hexane isobutane

----_. p-xylene

o-

5-

----

o

........ ........ LZ-132 LZ.133 ZSM45 37 33 34

----NU-3

ZEOLITE

32

ref.

FIGURE XI.S. Sorption capacities of LEV-type zeolites.

F1g.XI.6.1 NU-3 CE.P.A. 040.016.ex.1)

sL 2 8

-

d [0 . lnml

I1Io

10.11 8.01 6.56 5.50 5.07 4.94 4.69 4.62 4.39 4.21 4.01 3.78 3.54 3.42 3.27 3.18 3.12 3.03 2.81 2.75

8.00 33.00 19.00 10.00 79.00 14.00 6.00 2.00 3.50 56.00 100.00 35.00 6.00 3.00 18.00 2.00 48.00 9.00 5.00 38.00

rfI

5.0

I 9.0

I

13.0

I

I,

17.0

l.

I

21.0

•

J

I

25.0

.1 29.0

I

I

I

33.0

I

37.0

41.0

I

45.0

49.0

53.0

w

co 00

Fig.XI.6.2 LZ-133 CE.P.A. 91,049,ex.1)

t.

~

...

2

~

... ... ...

e

-

~

I

5.0

I

I

I I, il. II

9.0

I

13.0

17.0

Il 21.0

I,

I.

25.0

29.0

L

I.

I

33.0

J

I

37.0

I

41.0

I

d (0. In.]

I1Io

6.56 6.42 6.24 5.47 5.16 4.80 4.60 4.48 4.15 3.90 3.80 3.66 3.58 3.48 3.28 3.21 3.14 3.12 3.02 2.32

31.00 26.00 24.00 11.00 32.00 18.00 100.00 34.00 20.00 24.00 13.00 62.00 11.00 28.00 23.00 29.00 26.00 27.00 27.00 11.00

49.0

53.0

I

45.0

co co

CD

Fig.XI.6.3 LZ-132 (E.P.A. 91. 048. eX.1l

t.

I-

... ... ... ... ... ...

2 8

I-

... I-

... I-

... ... ... ... ... I

5.0

I.

9.0

• 13.0

I

17.0

21.0

,II , 25.0

J ,I L" I,

29.0

33.0

37.0

, I ,

41.0

.J

.1 I 45.0

I

d [0 . 1nm]

IlIa

10.20 7.97 6.51 5.47 5.07 4.93 4.19 4.00 3.75 3.52 3.40 3.26 3.11 3.02 2.81 2.75 2.58 2.09 1.85 1. 76

12.00 41.00 21.00 11.00 84.00 15.00 58.00 100.00 32.00 7.00 4.00 18.00 50.00 9.00 6.00 39.00 9.00 7.00 5.00 9.00

1,1 49.0

I

I

I

53.0

co

.... o

Fig.XI.6.4 ZSM-45 (U.S.P. 4. 495.303.ex.1)

5~ f-

f-

>>>>>>-

d [O.lnll]

IIID

iO.18 8.04 7.54 6.58 5.52 5.08 4.98 4.20 4.02 3.80 3.29 3.10 3.05 2.79 2.76 2.58 2.56 2.10 1. 76 1.64

12.00 40.00 8.00 38.00 6.00 69.00 21.00 47.00 100.00 28.00 21.00 33.00 12.00 11.00 36.00 8.00 5.00 5.00 8.00 7.00

>>-

I 13.0 I

I

5.0

9.0

I

I

I

17.0

I

I

21.0

II

25.0

I

29.0

I

33.0

II

I

37.0

I I

I

I.

41.0

I

I

I.

45.0

1.1 I . 49.0

I

I

53.0

W

01>.....

342

OFFRETITE-ERIONITE ZEOLITES AND THEIR INTERGROWTHS The end-members of this family of materials correspond to the structure types erionite (ERI) and offretite (OFF), which have been described in detail (refs.38-48). The lZ-MR pores in OFF can be easily blocked randomly by stacking faults. The family member TMA-OFF (refs. 40-43, 45) seems to be such a structure (ref.42). The highest SiO Z/A1 Z03 ratio in TMA-OFF reported so far is approximately 11 (ref.41). ZSM-34 (ref.44) and zeolite T (refs.46,47) seem to be offretite-erionite intergrowths, all of which have a relatively low silicon content. For ZSM-34, the highest SiO Z/A1 Z0 3 ratio reported is less than 15 (ref.44). The latest claimed zeolite apparently belonging to this family is denoted ZKU (ref.48). It is also not clear which SiO Z/A1 Z0 3 range can be covered by direct synthesis for these materials. Based on the available data, we therefore do not wish to classify these materials as high-silica shape-selective materials.

343

FAUJASITE-TYPE SILICEOUS ZEOLITES Several attempts to synthesize siliceous variants of zeolite Y have been published (refs.49-60). Lechert (ref.49) and Kacirek and Lechert (ref. 51) reported that when in a sodium aluminosilicate gel the excess alkalinity, expressed as the Na-Al/SiO Z ratio, where Na-Al represents (NaOH)-(NaA10 2), was increased from 0.69 to 0.79 a zeolite was crystallized with decreasing Al content (from approximately 53 to 45 Al per unit cell). At the same time the crystallization time increased by a factor of more than five. From this work (ref.49), it follows that the upper SiO Z/A1 Z0 3 ratio of the faujasite structure is close to 6.5. In Fig.XI.9 a selection of data taken mostly from the patent literature show that for faujasites synthesized in this way a smooth relationship exists between the SiO Z/A1 Z03 ratio in the gel and the zeolite. To increase this ratio in the zeolite from 4.Z to 6.5 the gel composition has to be enhanced by a factor 5. It therefore follows that it becomes increasingly difficult to synthesize siliceous faujasites. It is far from clear why this is so. ZSM-3 has an XRD pattern that is related to that of zeolite Y (refs. 54,55) but is synthesized using a lithium sodium aluminosilicate gel: Fig.XI.9 shows that for this material the efficiency for crystallization of siliceous materials is still lower. For the synthesis of ZSM-ZO, another zeolite with faujasite-like XRD pattern, which occurs in the presence of TEA, an enhanced efficiency is observed and SiO Z/A1 Z0 3 ratios of approximately 8.5 are obtained. The presence of Rb ions in a sodium aluminosilicate gel was also found to enhance the Si/Al ratio of the faujasite (ref.6Z) or to generate CSZ-1 zeolite (ref.63), another siliceous faujasite-like zeolite. From a topological point of view, with the truncated octahedra of faujasite a large number of structures can be produced from a close packing of hexagonal 1ayers of these soda1ite cages (ref. 55). ZSM-3 is a member of this family (refs.54,54). It has been proposed to denote this structure type MTH (ref.24). ZSM-20 might be another member. Multiple twinning in Y zeolites also seems to be possible (ref.59), thus generating a new hypercage of 0.74 nm, the length of which is dependent on the degree of twinning (refs.59,61). A view through such a structure is shown in Photograph XI.3.

:144

.:ref.49,FAU

8: ref. 54,ZSM-3

10f- 0:ref.60, FAU

. : ref. 57, ZSM- 20

x . ref.50, FAU

() : Zeolite X our results

(;

.:ref.53, FAU

1

•

111 N

...... -

e

1

.

x

3 1 0- 0,./..... 7

5-

o ."

// /

3 • ----- • x _---.-_--

8 1

cJ

I I I O'----------'-------L..--------'---'

o

10

20

30

FIGURE XI.9. Relationship between the SiO Z/A1 Z0 3 ratio in the gel and in the faujasite-type zeolites crystallized from it (the figures next to the experimental points refer to the example numbers in the original patents).

OJ U

O"l <0

0.

OJ

>-

>,

OJ

s:

<=

+-'

s:

0

:;: ""0

OJ

:;:

OJ

""0

OJ

> +-'

::::l <0

ro '" ......, 4-

<= <=

OJ

""0

:;: c-,

+-'

OJ s,

~ <=

::::l

s, r0

40

<0

U OJ s,

><

..... <:(

0-

:c

0::

::E

0

OJ ""0

~

~

0

:c

t0

0-

346

REFERENCES 1. 2. 3. 4.

5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22.

W.M. Meier and D.H. Olson, Atlas of Zeolite Structure Types, Structure commission of IZA, Polycrystal Books, Pittsburg, PA, 1978, p.69. W.f1. Meier, Z. Kristallogr . .1:12 (1961) 439. P.K. Bajpai, Zeolites ~ (1986) 2. a, J. Bandiera, C. Hamon and C. Naccache, Proceed. 6th Int. Zeolite Conf., D. Olson and A. Bisio, eds., Butterworth, Guildford, 1984, p.33/; b, F. Raatz, C. Marcilly and E. Freund, Zeolites 2 (1985) 329. W.M. Meier, R. Meier and V. Gramlich, Z. Krystallog. ~ (1978) 329. E.G. Derouane and J.G. Fripiat, Proceed. 6th Int. Zeolite Cont., D. Olson and A. Bisio, eds., Butterworth, Guildford, 1984, p. 717. P. Bodart, J.B. Nagy, E.G. Derouane and Z. Gabelica, Stud. Surf. Sci. Catal. ~ (1984) 125. W.J. Ball and D.G. Stewart, U.S.P. 4,376,104 (1983), assigned to BP. S. Sakurada, N. lagaya, T. Maeshima, T. Toyoizumi, T. Numura and T. Hasimoto, E.P.A. 40,104 (1981) assigned to Toa Nenryo Kogyo K.K. R.H. Daniels, G.T. Kerr and L.D. Rollmann, J. Am. Chem. Soc. 100 (1978) 3097. O.J. Whittemore, Am. Mineral 2L (1972) 1146. S. Ueda, T. Fukushima and M. Koizumi, J. Clay Sci. Japan 22 (1982)18. S. Ueda, H. Murata and M. Koizumi, Am.Mineral. 65 (1980) 1012. K. Itabashi, T. Fukushima and K. 19awa, Zeolites ~ (1986) 30. L.A. Rankel and E.W. Valyocsik, U.S.P. 4,500,503 (1985), assigned to , Mobil Oil Corp. L.D. Rollmann and E.W. Valyocsik, U.S.P. 4,205,052 (1980), assigned to Mobil Oi. Corp .. K. Iwayama, T. Kamano, K. Tada and T. Inoue, E.P.A. 57,016 (1982), assigned to Toray Ind. M.R. Klotz, U.S.P 4,390,457 (1983) assigned to Standard Oil Compo (I ndiana) . E.N. Givens, C.J. Plank and E.J. Rosinski, U.S.P. 4,052,472 (1977), assigned to Mobil Oil Corp. R. Le Van Mao, O. Pilati, E. Moretti, R. Covini and F. Genoni, U.S.P. 4,366,135 (1982), assigned to Montedison. E. Moretti, V. Zamboni, R. Le Van Mao, M. Padovan and M. Solari, U.S.P. 4,525,466 (1985), assigned to Montedison. J.L. Schlenker, F.G. Dwyer, E.E. Jenkins, W.J. Rohrbaugh, G.T. Kokotailo and W.M. Meier, Nature 294 (1981) 340.

347

23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 36. 37. 38.

39. 40. 41. 42. 43. 44. 45. 46. 47. 48.

D.M. Bibby and L.M. Parker, Zeolites l (1983) 11. R.M. Barrer, Hydrothermal Chemistry of Zeolites, Academic Press, London, 1982. F.G. Dwyer and E.E. Jenkins, U.S.P. 4,357,233 (1982), assigned to Mobil Oil Corp. F.G. Dwyer and E.E. Jenkins, U.S.P. 4,287,166 (1981), assigned to Mobil Oil Corp. B.P. Pelrine, U.S.P. 4,259,306 (1981), assigned to Mobil Oil Corp. S.A.I. Barri, UK PA GB 2,144,727 A (1985), assigned to BP. H. Gerke, H. Giess and F. Liebau, DE offenl. 3, 128,988 (1983). W.M. Meier and D.H. Olson, Atlas of Zeolite Structure Types, IZA, Polycrystal Books, Pittsburgh, PA, 1978, p. 51. G.T. Kerr, U.S.P. 3,459,676 (1969), assigned to Mobil Oil Corp. G.D. Short and T.V. Whittam, E.P.A. 40,016 (1981), assigned to ICI. 1.R. Cannan, M-T. L. Brent and E.M. Flanigen, LP.A. 91,048 (1983), assigned to Union Carbide Corp. ~1-1. L. Brent, T.R. Cannan and LM. Flanigen, E.P.A. 91,049 (1983), assigned to Union Carbide Corp. E.J. Rosinski and M.K. RUbin, LP.A. 107,370 (1983), assigned to Mobil Oi 1 Corp. E.W. Valyocsik, E.P.A. 143, 642 (1984), assigned to Mobil Oil Corp. G.H. Kuechl, U.S.P. 4,495,303 (1985), assigned to Mobil Oil Corp. R.M. Barrer, Zeolites Science and Technology, F.R. Ribeiro, A.E. Rodrigues, L.D. Rollmann and C. Naccache, eds., Martinus Nijhoff Publ., 1984, p. 54. R. von Ballmoos, Collection of Simulated XRD Powder Patterns for Zeolites, Butterworth, Guildford, 1984, p.56. T.E. White, jr., LL. Wu, G.T. Kerr and P.B. Venuto, J. Catalysis .?Q (1971) 88. F. Faj ul a, F. Fi gueras and L. Moudafi, PCT W084/03489 (1984), ass i gned to CNRS. N.Y. Chen, J.L. Schlenker, W.E. Garwood and G.T. Kokotailo, J. Catalysis 86 (1984) 24. M.L. Ocell i and A.J. 'Perrota, ACS Symp. Ser. (1983) 21. M.K. Rubin, E.J. Rosinski and C.J. Plank, U.S.P. 4,086,186 (1978), assigned to Mobil Oil Corp. L.B. Sand, U.S.P. 4,093,699 (1978), assigned to Zeochem. Corp. D.W. Breck, Zeolite Molecular Sieves, John Wiley, New York, 1974. A. Cichocki, JCS Faraday Trans. I ~ (1985) 1297. Y. Takegami, 1. Inui, T. Ishibara, E. Araki and T. Kanie, U.S.P. 4,400,328 (1983).

m

348

49. 50.

H. Lechert, Stud. Surf. Sci. Catal.

~

(1983) 107.

J. Arika, M. Aimoto and H. Miyazaki, E.P.A. 128,766 (1984), assigned to Toya Soda.

51.

H. Kacirek and H. Lechert, DE offenl. 2,324,235 (1973).

52.

G.H. Kuhl, J. Inorg. Nucl. Chem.

53.

L. Puppe and F. Schwochow, DE offenl.

11 (1971)

326l. 2,605,083 (1977), assigned to

Bayer AG. 54.

J. Ciric, U.S.P. 3,415,736 (1968), assigned to Mobil Oil.

55.

G.T. Kokotailo and J. Ciric, Adv. Chem. Ser. No. 102 (1971) 823.

56.

E.W. Valyocsik, E.P.A. 12,572 (1979), assigned to Mobil Oil Corp.

57.

J. Ciric, U.S.P. 3,972,983 (1976) assigned to Mobil Oil Corp.

58.

R.B. La Pierre and V.W. Werkman, Jr., E.P.A. 23,802 (1980) assigned to Mobil Oi1 Corp.

59.

M. Audier, J.M. Thomas, J. Klinowski, D.A. Jefferson and L.A. Bursill,

60.

O. Seiya, K. Sando, K. Matsumura, K. Iwayama, T. Nakac and K. Yokohama,

J. Phys. Chem. 86 (1982) 583. De offenl. 2,425,267 (1974), assigned to Toray Ind. Inc. 61.

M. Audier and J.M. Thomas, E.P.A. 69,594 (1982), assigned to BP.

62.

N. Dewaele, P. Bodart, Z. Gabelica and J.B. Catal.

63.

~

Nagy, Stud. Surf. Sci.

(1985), p.106.

D.E.W. Vaughan and M.G. Barrett, U.S.P. 4,333,859 (1982), assigned to W.R. Grace.

349

CHAPTER XI

1.

GENERAL CONSIDERATIONS

An extraordinary diversity of high-silica aluminosilicate zeolites is

now available. Materials with known structure types are classified in famil ies with related crystallographic structure. The best known family is the pentasil family of zeolites. In addition to the two structural end-members ZSM-5 and ZSM-II with MFI and MEL structures, respectively, this family encompasses intergrowths of domains of the one structure in the other. Next to the pentasil zeolites the existence of other families composed of intergrowths of two structures have been recogni zed. I ntergrowths of ERI/OFF are known to exist, and intergrowths of TON/MTT and of the ZSM-48 variants constitute other potential families. Other crystallographically pure structure types such as FER, MTW, MOR, MTN and LEV seem to contain different individual zeolites.

members and in

this book have been denoted as

a family of

Specific names have been given to individual family members, each of which is usually a proprietary material. A probably non-exhaustive list of names of materials belonging to the high-silica zeolite families with known structure types is given in Table XII.l. Proprietary materials of the same family can differ in several respects, but it shou Id be stressed that the individual members do not always represent single materials. ZSM-5, for instance, does not denote a single zeolite but encompasses a whole range of materials differing from each other in their chemical composition, their crystal symmetry (monoclinic or orthorhombic), their crystal size and morphology or even the nature of compositional gradients across the crystals. Stacking faul ts and pore occlusions are typical reasons for differentiation between family members (e.g., in the MOR and FER families). 2. As the predominant T-atom in high-silica aluminosilicate zeolites is silicon, the location and distribution of the few aluminium atoms in the framework is not obvious and for certain structures (MFI, MOR) has been a ma tter of debate. In th is part of the book a hypothes i s has been developed concerning the location of Al in a zeolite framework. It states that 4-MRs and regular 6-MRs constitute preferential

sites of Al.

While low-silica

zeolite structures (FAU, OFF, LTL, LTA, etc.) are composed mainly of these structural elements, in the frameworks of shape-selective high-silica

350

zeolites (MFI, MEL, FER, MTW and

ZSM-48 variants) and also in MOR these

4-MRs and 6-MRs are diluted by 5-MRs and have no corners or edges in common. All experimentally observed upper limits of the content of framework Al of these zeolites can be rationalized if an occupation of two Al atoms per 4-MR and three Al atoms per 6-MR is assumed. High-silica zeolites with a minimum Si/Al ratio crystallize from inorganic gels or in the presence of carefully selected organic compounds such as certain alcohols and amines (for MFI), but seldom from gels containing quaternary alkylammonium ions. In view of the pore-filling function of the organic mineralizers (see later), this is readily understood as all negative charges of the framework created by substitution of Si by Al have to be compensated for by these organic cations fitting tightly in the pores. For several structures (MFI, MEL, ~nw and the ZSM-48 variants), in the presence of quaternary alkylammonium cations incorporation of Al seems to be restricted to one Al atom per 4-MR owing to the bul ky nature of these organic compounds. This brings us to yet another important aspect, namely the location of the 4-MRs and 6-MRs with respect to the 10- and lZ-MR pores. In MFI all

~-atoms

of the 4-MRs are constituents of

the pore wall s and therefore are readily accessible to organic moieties. In the MTW s t ructu re the 4-MRs bri dge the lZ-MR pores. A s i mil ar s itua t i on exists in the UDUD variant of the structure proposed for ZSM-48, where the 4-MRs are 1inkages between the 10-MR pores. In the UUDD variant, however, only one edge of every 4-MR is accessible through the pore, the other edges being hidden in a dense and therefore probably siliceous wall, reducing the maximum Al content to one Al per 4-MR. Similar reasoning leads to an understanding of the lower 1imit of the Al content of aluminosil icate zeol ites. As highly sil iceous frameworks are hydrophobic and crystallization occurs in aqueous media, perfect pore filling by hydrophobic moieties is essen~ial in order to exclude all water and alkali from the pores. This explains why structures containing 8-MR pores next to the main 10- and lZ-MR channel s (MOR, FER and OFF) fai I to crystall ize as highly sil iceous forms. In order to summarize and for use as a tool in synthesis work, all data on actual, claimed and speculative SiO Z/A1 Z03 compositions of the high-silica zeolites with known crystallographic structure are collected in Fig. XII.I. 3.

In the terminology used for the description of phenomena occurring

during the synthesis of high-silica zeolites, the term "template" has been often used for whatever organi c mol ecul e may be present in the synthes i s mixture. One should make a clear distinction between templates and pore filling agents. A molecule acts as a template if, on addition of increasing amounts of it, the rate of nucleation is enhanced under otherwise identical

351

experimental conditions. A second prerequisite is that in the presence of a given template it should be possible to obtain a particular zeolite structure using a broad range of experimental conditions. Organic molecules that do not act

in

this way but which are present

in

the

pores of the

synthesized

material as such are pore filling agents. Their presence accelerates the rate of crystal growth. Examples of templates are TPA (for MFI), TBA, TBP, BeTPheP and 1,8-diaminooctane (for MEL). For the other structure types the present data do not allow one to identify preferred crystall ization agents or to distinguish between templates and pore fillers. An example of a pore filler for MTW is MTEA, for whi ch it is shown that it fill s up the pores but its presence

in the gel

increases the length of the nucleation period. With

respect to templation the role of alkali metal and ammonium cations should not be overlooked, however. Depending on their electrostatic potential they exert structure-directing or -breaking effects and compete with the template for charge neutralization of aluminosilicate anions. All the synthesis of MFr, MEL, TON and MTT zeolites particular is a structure-ordering ion.

data available on

indicate that sodium in

cc

en

TABLE XII.1 Members of siliceous aluminosilicate zeolite families with known structure-type

FER

TON

Z5M-48-type

Faujasites

LEV

ferrierite FU-9 5R-D Z5M-21 Z5M-38 Z5M-35

151-1 KZ-2 NU-I0 THETA-l Z5M-22

EU-l EU-ll ZBM-30 Z5M-48

C5Z-1 zeolite Xa zeolite ya Z5M-3 a

Levyne a LZ-132 LZ-133 NU-3 ZK-20

MOR

MTT

MTW

ERr/OFF

MTN

MB-28(?) ME-MOR Mordenite TEA-MOR TZ-02

EU-13 151-4 KZ-l ZSM-23

CZH-5 NV-13 TEA-sil icate TPZ-3

erionite a offretite a HIA-OFF zeolite Ta ZKU

ZSM-39

Pentasil (MFI/MEL) AZ-l MB-28(?) NU-4 NU-5 sil icate-l s il i cate-2 TR5-22 Ts VK TZ-Ol Ultrasil Ultrazet ZBM-I0 ZETA-l ZETA-3 ZSM-5 ZSM-8 ZSM-ll

tv

a, low-silica members.

Z5~1-20

Z5~1-45

ZS~1-12

Z5~134

TON/MTT EU-l( ?) EU)-4(?)

-~

FER LEV

t:L

..........•.• ...

MEL MFI/MEL

...................

-------------_.

MFI

N -----_.

MOR

'.1.'.'.'.'.'.

MTN

.•.......

MTT MTW

••• 1 ••••• -.' •

••• 1 ••• ,

...... •..... -----_ .....•.•.... ..•.....-::

TON

_

_

•• 1 ••••• •

•••••••

UDUD ..............•.

ZSM-48type I

I

I

I

I

I

I

I

5

10

25

50

100

250

500

1000

Si02/ AI203

FIGURE XII.I. Actual (full lines), claimed (dot-dashed lines), speculative (dotted lines) and natural (N) Si02/A1 203 ratios of high-silica zeolites with known crystall ographi c structure types. The dashed 1i nes represent actual compositions of zeolites synthesized from inorganic gels. Data collected from Part II.

This page intentionally left blank

355

PART III: BRIEF DESCRIPTION OF POTENTIAL HIGH-SILICA ZEOLITES WITH UNKNOWN STRUCTURE

This page intentionally left blank

357 INTRODUCTION Based

on the

available data,

zeolites with unknown structures

it in

is not always

terms

easy to select all

of high-silica Shape-selective

zeolites. As the identification of these zeolites is always made using their "unique"

XRD

patterns,

the

latter are

given

in

Fig.

XII1.I,

where

not

reported in Part 1. Based on these patterns it seemed impossible to us to classify them within a family of known and previously treated zeol ites, in agreement with other workers

(reLI).

The most essent i a1 data

on these

zeolites will be summarized in the following sections. ZSM-43 (reL 2)

The XRD pattern of this zeolite is shown in Fig. XIII.I.I. The synthesis gel contains Na and Rb as al kal i metal

ions and chol ine as

the organic.

Typical synthesis conditions, gel compositions and composition of the final zeolite are summarized in lable XIII.I. It has a sorption capacity for hexane and cyclohexane comparable to that of ZSM-12, but the available data do not allow one to decide whether it should be classified as a IO-MR or a 12-MR zeolite. It crystallizes only with a narrow range of Si0

2/A1 203

ratios.

CSZ-I (ref.3)

This is a zeolite that requires Cs in the synthesis gel and ageing of the latter. No organic is used and the resulting zeolite is aluminium rich. The water sorption capacity is similar to that of V-zeolites and it is used as a cracking catalyst substitute. Its XRD pattern is given in Fig. XIII.I.2. It is possibly a 12-MR zeolite.

358

ZSM-18 (ref. 4)

This zeolite is synthesized with a very specific and bulky triquat [tr l s (quaternary ammonium) i on] :

It seems that the composition of the reaction mixture is very critical : the preferred range of SiO Z/A1 Z03 ratios is 15-18; from a synthesis gel with an SiO Z/A1 Z0 3 ratio of 9 ZSM-18 crystall izes al so, but with decreased thermal stability. The XRD pattern (Fig.XIII.l.3) can be indexed in a hexagonal cell with a = 1.3Z ! 0.03 and b = 1.58! 0.03 nm (ref.4). The structure of ZSM-18 seems to be very open, as large amounts of organics can be taken up. Considerable amounts of the tris(quaternary) ion are also kept into this structure after synthesis (Table XIII.I) ZEOLITE PHI (ref.5)

Zeolite PHI is a low-silica proprietary material with large-pore characteristics, as perfluorobutylamine with a kinetic diameter of 1.02 nm is sorbed. TMA is used in the synthesis, but at low cationic fractions. Only small amounts of organic are left in the zeolite after synthesis. According to the n-decane method (ref.6), this zeolite contains lZ-MRs with lobes (ref.6), which intersect in at least two dimensions (ref.l). Its XRD pattern is given in Part I (Fig.I.3.9).

359

ZEOLITES BETA AND NU-Z (refs.B,IO)

Based on their related XRD patterns (for BETA see Part I, Fig.I.3.10) zeolite BETA (refs.B,9) and NU-Z (ref.IO, Fig.XIII.1.4) belong to the same family of materials. In every instance the first diffraction line (at the lowest °Ze)} of the pattern is always much broader than the subsequent lines. This might be indicative of a high degree of disorder (stacking faults) in one crystallographic direction. The difference between BETA and NU-Z is mainly due to differences in line intensities (ref.IO). BETA is a true high-silica zeolite as it can be synthesized over a wide SiO Z/A1 Z03 range in the presence of TEA (ref.9). The same is true for NU-Z, but no data on the synthesis of zeolites with SiO Z/A1 Z03 ratios exceeding 50 have been reported, although for BETA values as high as ZOO (ref.9) have been claimed. A proven recipe for synthesizing zeolite BETA is given in Part I. The major difference between BETA and NU-Z is in their cyclohexane sorption capacities (Table XIIl.I) when both zeolites are in their sodium-hydrogen form. When the NU-Z zeolite is converted into its H-form, the cyclohexane sorption capacity is increased to the value found for n-hexane (ref.IO). ZSM-Z5 (refs.II,IZ)

The XRD-pattern of this low-silica proprietary zeolite is shown in Part I, (Fig.I .3.11), together with a proven recipe for its synthesis. After synthesis, relatively small amounts of the organic TEA are retained in this structure. It has a sorption capacity for hexane and water comparable to that of the most open zeol ites, but a reduced capacity for cyclohexane uptake. According to the n-decane method, this is a IZ-MR zeolite with a unidimensional pore system (refs. 6,7), the effective diameter of which is comparable to that of ZSM-IZ (ref.13). EU-7 AND EU-IZ (refs.15,16)

These two zeal ites are proprietary zeol ites, which are not necessarily structurally related but which are treated together as no data are available apart from their synthesis methods. In zeolites EU-7 (ref.15) and EU-IZ (ref.16) no aromatics are formed in the methanol to gasoline reaction

360

(ref.I4), just as on NU-3 zeolite, a material with a LEV structure type which contains 8-MRs. Their XRD patterns are given in Figs.XIII 1.5 and 6. For EU-7 Cs and diaminobutane are the preferred sources of alkali metal and mineralizing agent, respectively. The zeolite formed is fairly siliceous. Zeolite EU-I2 (ref.I6) is synthesized with Rb and TMA. According to Dewing et al. (reLI4) both zeolites are related to EU-I3 and consequently to the MTT family of materials. Indeed, they stated that "recently the syntheses of three related zeolites, EU-7, EU-I2 and EU-I3, have been disclosed". NU-23 (reLI?)

The available data are sunmarized in Table XIII.l. This zeolite is synthesized in the presence of Na and cyclohexylamine and is definitely a high-silica zeolite as Si0 2/A1 203 ratios between 22 and 55 have been reported. The zeolite is also hydrophilic. It shows a reduced sorption capacity for cyclohexane and p-xylene. From this behaviour, it was concluded (ref.I?) that the zeolite (at least in its H-form), has a dual pore system with apertures of 0.63 and 0.59 nm. The characteristic XRD pattern is shown in Fig.XIII.I.7. NU-6(I) (refs.I8,I9)

This again is a true high-silica zeolite with a specific XRD pattern and a typical crystal morphology. The zeolite crystallizes as thin plates (Ix2xO.I urn to IOx3xI urn) from a bipyridyl-containing gel. It can be made with a wide range of Si0 2/A1 203 ratios (Table XIII.I.). This zeolite has a very limited thermal stability, as between 523 and 723K, it is converted into a related structure, denoted NU-6(2). The XRD data for the two materials are shown in Figs. XIII.I.8 and 9, respectively. Around 523K the phase transformation is slow, requiring 3 days, whereas at 723K it is very fast (reLI8). This thermal phenomenon does not reflect a shrinkage of the unit cell of NU-6(I), as the diffraction lines are broadened, indicating that the platelets, which keep their original morphology, now consist of an agglomeration of much finer materials. Around I073K zeolite NU-6(2) is in turn transformed into u-cristobalite (ref.I8). The sorption data reported for zeolite NU-6(2) (Table XIII.I) indicate a restricted access of cyclohexane in th~ pores of this zeolite.

361

TMA-ZEOLITES FU-I AND NU-l

Zeolite FU-l is a novel proprietary zeolite synthesized in the presence of TMA and Na (ref.20). This new species has already received some attention in the open literature (refs. 14,21-2~). The properties of this material have been reviewed by Dewing et al. (ref.14), and as no new data have become available since then, we refer to this work. FU-l and more in particular its H-form appears to be intrinsically a small-pore zeolite with a special plate morphology and consequently high external surface area. It therefore possesses significant non-zeolitic microporosity (ref.14). It also has an unusually broad XRD pattern (refs.14,20,21). The positions of the XRD maxima are indicated in Fig.XIII.I.IO. Zeolite NU-l is also a novel proprietary zeolite, the structure of which has not yet been resolved . . It is also made in the presence of TMA and Na but, in contrast to FU-l, it crystallizes only under quiescent conditions (refs.14,26). It was stated by the inventors that the reproducible manufacture of NU-l catalysts is very difficult (ref.14). The zeolite seems to have a dual pore system with 10- and 8-MRs. The Br~nsted acid sites seem to be subjected to the spatial constraints imposed by the 8-MR pore system (ref.14). The XRD pattern of NU-l is given in Fig.XIII.I.II. ZSM-6 AND ZSM-47 (ref.27)

Both zeolites have very similar XRD-patterns. They are reported in terms of line positions, the actual intensities being given in only a semi-quantitative way. This pattern for ZSM-6 is given in Part I (Fig.I.3.7). For ISM-47, it is shown in Fig.XIII.1.12. They can both be made with TMA. Only for ISM-47 do the data indicate that the zeal ite is a high-sil ica material. The sorption data for cyclohexane and for n-hexane are reduced (Table XIII.I). The n-decane test classifies this material as an 8-MR zeolite (ref.6,13). ISM-50 (ref.28)

The semi-quantitative pattern publ ished for this zeal ite is given in Fig.XIII.l.13. The material is crystallized from diquat-6 containing gels and

362

is classified as a 10-MR zeolite. With this kind of template 10-MR zeolites are always obtained (see Part II). ISI-6 (ref.29)

Zeolite ISI-6 is a high-silica zeolite synthesized in the presence of both ethylene glycol and pyridine. When no pyridine is used ISI-4, a zeolite with an MTT structure type, is crystallized (Part II, Chapter VII). Zeolite ISI-6 has a typical XRD pattern (Fig.XIILl.14), and is shown to have an Si0 2/A1 203 ratio close to 70. In the catalytic decomposition of methanol it forms olefins, a characteristic comparable to that of ZSM-34 (ref.29). PSH-3 (ref.30)

The XRD pattern of this high-silica zeolite (Fig.XIlI.1.15) has some lines in common with that of FU-l. The almost equal amounts of cyclohexane and hexane sorbed (6-7%) suggest its classification as a 10-MR zeolite (Table. XIII.l).

TABLE XIII.1 Summary of characteristics of siliceous zeolites with unknown structure

ZEOLITE

ZSM-43

CSZ-1

ZSM-18

PHI

BETA

NU-Z

ZS~1-Z5

EU-7

Na Tri s (quaternary ammonium) 15-18 33.3 (ex.3)

Na TMA

Na TEA

Na TEA

Na TEA

Cs C4DN

9-15

10-Z00 Z-75

Molar synthesis gel compositions

M R

Na + Cs Choline

Na + Cs none

SiO z/Al z03 HzO/SiO z OH/SiO z R/R+M M1/M1+Mz

10-Z0 9-4Z 0.3-0.6 0.4-0.6 0.Z-0.6 a

6-Z0 15-30

-

0.OZ-0.15 a

temp./K time/days

370-4Z3 20-170

368 1

-

-

-

10-3,000 0.6-30 0.1-Z.0

0.64(ex.3)

0.05-0.Z

-

-

8-10 30-1Z0 Z4-90 15-85 0.4-0.6 0.6-0.8 0.67(ex.7)

423 5

373 2.7

348 42

368(ex.l) 28(ex.l)

394-4;(Z 4

4Z3

a, M1 = Cs co

O"l

W

~

ISM-43

CSI-1

ISM-18

PHI

BETA

NU-2

48(ex.1) 8.5 20(ex.9) 10.9 (ex.!) 44 0.43 (ex.I) 8.3

ZS~1-~5

EU-7

zeolite composition (molar)

Si0 2/A1 203

10-16

5.54(ex.5)

10.5-11.5

4.55(ex.1)

13.9 (ex. I) 98(ex.2)

(Si + Al )/R Al/N

12-15 1.22(ex.l)

-

7-8 1.25(ex.3)

109 (ex.l) 33 (ex.l)

-

22

24.7(ex.4) 18.9(ex.4) 16.0(ex.4)

-

-

8.1

20.l(ex.l) 14.6(ex.l) 13.8(ex.l) -

-

-

8.0

3

4

5

34(ex.7)

Sorption (wt%) Water 10-20 Cyclohexane 5 (ex.1) Hexane 6.2(ex.l) Butane Tri fl uorobutylamine -

-

Ref.

2

-

9

12.8 1.0 12.2 .

-

10

9.2 3.6 10.9

-

11

?

15

""

TABLE XIII.1. Continued

ZEOLITE

EU-12

NU-23

NU-6(1)

ZSM-50

ZSM-6

zsr~-47

PSH-3

Molar synthesis gel compositions

r~

R Si0 2/A1 203 H2O/Si02 OH/Si0 2 R/R+M

Rb TMA

Na Cyclohexylamine

Na 4,4' -bi pyri dyl

Na+(K) Na TMA/(choline)TMA

Na diquat-6

10-120 25-75

20-3,000 15-300 0.01-0.3

10-80

25-300

30-90

-

25-100 15-50 0.05-0.3

Na Hexamethyleneimine 10-200 0.05-1. 0

-

-

0.001-0.25 0.1-0.99

0.1-0.3

0.4(ex.3)

0.1-0.8 0.1-0.99

453

453 4

413 3

422 7

?

?

?

?

423 3

~VM1+M2

temp./K time/days

-

eN

m

CJ1

w

m m

NU-23

NU-6( 1 )

18.5(ex.3) 18 (ex.3) 3.6(ex.3)

22(ex.l) 44(ex.l) 3.7(ex.l)

65(ex.l)-230(ex.7) 32(ex.l) 13.4(ex.l) 174(ex.l) 0.4(ex.l) 1O.4(ex.l)

water Cyclohexane Hexane Butane trifl uorobutylamine

?

12.1(ex.l) 2.6 6.7

11.5 2.7 2.4

?

?

?

?

?

?

-

?

?

?

-

3.9 b 4.8 b 8.0 b -

?

Ref.

16

17

18

27

27

EU-12

ZS!"-47

ZSM-6

ZSM-50

PSH-3

?

?

55(ex.l)

?

?

zeolite composition (molar) Si0 2/A1 203 (Si+Al)/R Al/N

?

Sorption (wt%)

? ? ?

b, these data are for NU-6 (2).

28

7.1 6.1 6.9

30

FIGURE XIII.1.1 ZSM-43 (U.S.P.4. 247. 728. eX.1)

t.

ff-

...

2 8

f-

IIIIIII-

...

d [0. lnll]

IlIa

U.72 9.93 7.56 7.19 6.86 6.54 5.06 4.75 4.44 3.79 3.65 3.52 3.42 3.31 3.21 3.07 2.91 2.84 2.58 2.53

22.00 6.00 65.00 8.00 31.00 7.00 6.00 100.00 5.00 62.00 26.00 30.00 52.00 59.00 92.00 49.00 22.00 28.00 11.00 24.00

f-

l-

5.0

i 9.0

I

I I, 13.0

,I 17.0

I

I 21.0

II

I

25.0

29.0

I

33.0

I

37.0

41.0

45.0

49.0

53.0

w

(J)

-J

FIGURE XIII.1.2 Na-Cs-CSZ-1 (Belg.Pat.888.915)

s~

IIII~

I~

I-

I~

I~

I-

d [0. 1nm]

IlIa

15.14 14.24 13.06 8.66 4.71 4.14 4.08 3.68 3.39 3.35 3.28 2.99 2.97 2.88 2.78 2.68 2.46 2.37 2.03 2.02

30.00 90.00 10.00 15.00 21.00 15.00 31.00 65.00 100.00 20.00 ?o7.00 70.00 15.00 40.00 25.00 23.00 18.00 12.00 15.00 21.00

~

l~

5.0

I

I 9.0

13.0

I

I . I I. 17.0

21.0

.I 25.0

I 29.0

I

I J I II JI I I

33.0

I

37.0

I

41.0

I

45.0

I

49.0

53.0

cc

O"l

00

FIGURE XIII.i.3 ZSM-18 (U.S.P.3. 950. 496)

t.

f-

2

8

f-

f-

f-

.. f-

f-

d [0. 1nm]

IlIa

11.48 9.30 7.94 6.61 6.51 5.08 4.79 4.63 4.33 4.17 4.13 3.95 3.88 3.80 3.34 3.31 3.24 3.12 3.05 2.86

100.00 15.00 25.00 20.00 38.00 25.00 15.00 17.00 25.00 80.00 67.00 38.00 17.00 50.00 15.00 24.00 20.00 15.00 22.00 17.00

ff-

. 5.0

9.0

I

13.0

I.

, 17.0

II 21.0

I

25.0

29.0

I I ,I I I I 33.0

37.0

I 41.0

45.0

I

II. 49.0

53.0

GO

m

CD

FIGURE XIII. 1.4 NU-2 (E.P.A.55.046.ex.1l

5~

~ ~

~

~

~

~

I~

I~

d [0. 1nm]

I1Io

11.33 9.04 7.56 6.61 6.03 5.37 4.51 4.14 3.96 3.51 3.46 3.38 3.31 3.10 3.02 2.93 2.91 2.68 2.59

23.00 3.00 4.00 3.00 3.00 5.00 2.00 23.00 100.00 12.00 3.00 2.00 21.00 7.00 21.00 8.00 5.00 6.00 3.00

I~ ~

... I

5.0

I

I

9.0

I

I. II

I

I

13.0

17.0

21.0

25.0

29.0

,I . 3a.0

37.0

41.0

45.0

49.0

53.0

'" o -J

FIGURE XIII. 1.5 EU-7 (E.P.A.107.908)

sL

~

~

~

~

d [0. 1nm]

I1Io

7.96 6.66 4.23 3.97 3.65 3.44 3.33 3.26 3.12 2.91 2.87 2.77 2.69 2.52 2.50 2.48 2.37 2.34

12.00 15.00 100.00 11.00 9.00 2.00 98.00 51.00 7.00 10.00 1.00 3.00 1.00 20.00 13.00 1.00 10.00 5.00

~

~

I

5.0

I

9.0

I

13.0

17.0

I

I

21.0

I.

25.0

II

I. I. . 29.0

I

33.0

II

37.0

I

41.0

45.0

49.0

I

I

53.0

W

,....

-J

FIGURE XIII. 1.6 EU-12 (E.P.A.105.679)

d [0. 1nm]

IlIa

11.20 8.93 7.58 7.23 6.70 5.62 5.51 4.93 4.60 4.48 4.20 3.81 3.62 3.55 3.35 3.21 3.10 2.95 2.91 2.41

40.00 14.00 19.00 31.00 30.00 21.00 10.00 19.00 46.00 34.00 57.00 52.00 49.00 73.00 100.00 37.00 57.00 22.00 17.00 12.00

t.

f-

2 8

~

~

~

~

~

I~

lIl-

I-

I,

5.0

, 9.0

I II

, 13.0

17.0

21.0

I25.0-I

I.

I 111 I 29.0

I ,I II

33.0

37.0

I

, 41.0

45.0

. 49.0

I

I

53.0

W -1

""

FIGURE XIII.1.7 NU-23 (E.P.A. 103.981)

5L

f-

If-

2

e

~

f-

d [0. In.] 9.40 7.00 6.89 6.58 5.70 3.97 3.94 3.93 3.82 3.77 3.64 3.54 3.48 3.36 3.32 3.13 3.04 2.89 1.99 1.92

IlIa 53.00 21.00 13.00 12.00 14.00 66.00 8.00 39.00 35.00 49.00 24.00 100.00 75.00 21.00 28.00 27.00 18.00 8.00 9.00 11.00

~

~ I

5.0

9.0

I

I

13.0

I

17.0

I

I

21.0

I

25.0

29.0

I I

I.

I

33.0

37.0

41.0

I

45.0

I. 49.0

•

I

53.0

co -J

cc

FIGURE XIII.i.8 NU-6 (1)

(U.S.P.4. 397. 825)

sL 2 8

-

-

~

~

d [0. 1nll]

13.40 11.30 6.89 5.46 4.52 4.48 4.29 4.23 4.00 3.68 3.48 3.38 3.33 3.11 3.11 2.99 2.96 2.48

IlIa 89.00 6.00 3.00 13.00 17.00 15.00 84.00 19.00 100.00 34.00 40.00 91.00 61.00 11.00 13.00 3.00 3.00 17.00

~

~

I . 5.0

9.0

.

II

13.0

I

I

17.0

I

I

21.0

I

25.0

II

I.

II

29.0

I

I

33.0

I

37.0

I

I

41.0

I

I

45.0

49.0

53.0

W

--J ....

FIGURE XIII .1.9 NU-6 (2)

(U. s. P. 4. 397. 825)

SL.e

....

... ..."" f-

d [0 . 1nm]

IlIa

8.41 8.67 6.09 4.61 4.33 3.94 3.76 3.65 3.44 3.33 3.17 3.05

45.00 42.00 15.00 27.50 100.00 2.00 11.00 15.00 27.00 76.00 15.00 9.00

"" f-

f-

f-

I

5.0

I

9.0

I

, I

13.0

I

17.0

I

21.0

I

I

25.0

.I 29.0

I

I

33.0

I

I

37.0

I

I

41.0

I

I

45.0

49.0

I

53.0

W --J

'"

FIGURE XIII. 1. 10. FU-1 (as made) (U. s. P. 4. 209. 498. ex .1)

5L 2 9

~

~ I

5.0

I

9.0

I. ,II 13.0

I 17.0

I

II

21.0

II

I

?5.0

I

I

29.0

33.0

I

1

37.0

I

I

41.0

I

, 45.0

I

d [0 • 1nm]

IlIa

9.51 8.35 6.92 6.61 6.26 5.25 4.61 4.48 4.35 4.07 4.00 3.89 3.73 3.68 3.44

31.00 8.00 28.00 9.00 9.00 16.00 63.00 6.00 13.00 19.00 9.40 13.00 28.00 3.00 100.00

I

49.0

53.0

W

-J

00

FIGURE XIII. 1. 11. NU-1 (H-for-m) (r-ef .14. table 2)

t.

~ ~

2

~

e

efo~

fo~

f~

f-

f0-

d [0. 1nm]

I1Io

8.87 8.28 6.53 6.19 4.43 4.30 4.08 4.03 3.97 3.85 3.81 3.69 3.51 3.26 2.86

18.00 69.00 43.00 75.00 52.00 51.00 37.00 100.00 73.00 74.00 22.00 16.00 29.00 27.00 15.00

ef0-

eeef-

I

5.0

I

9.0

II

I

13.0

I

17.0

I

21.0

25.0

I

I

29.0

I

33.0

I

37.0

1

I

41.0

1

I

45.0

I

I

49.0

I

53.0

W --J -1

FIGURE XIII.1.12. ZSM-47 (U.S.P.4. 187. 283. table 2)

sL

~ ~

2

~

e

f~

If-

If-

If-

If~

f~

d [0. lnm]

IlIa

11.60 9.00 8.41 6.60 6.27 5.71 5.42 4.65 4.48 4.34 4.12 4.06 4.00 3.89 3.73 3.55 3.29 3.15 3.13 3.03

10.00 10.00 75.00 30.00 75.00 10.00 10.00 10.00 75.00 75.00 75.00 100.00 100.00 100.00 10.00 30.00 30.00 10.00 10.00 10.00

f~

f-

5.0

I I 9.0

13.0

II.

17.0

J

I

21.0

I

25.0

1I.IIIlii 29.0

, 33.0

37.0

I

I

41.0

,

I

45.0

49.0

I

53.0

W -J C/O

FIGURE XIII.1.13 ZSM-50 (E.P.A.127.399)

t.

-

-

2 8

~

~

"" ~ ~

~

~

d [0 . 1nm]

IlIa

20.10 11.10 10.10 9.70 5.77 5.61 4.64 4.35 4.30 4.00 3.85 3.70 3.42 3.35 3.27 3.24 2.94 2.53

25.00 75.00 50.00 25.00 25.00 25.00 50.00 50.00 100.00 75.00 75.00 50.00 25.00 25.00 50.00 25.00 25.00 25.00

~

"" ~

I

5.0

9.0

I

13.0

I

17.0

I.

21.0

I

25.0

II

I

29.0

I

I

33.0

I

I

37.0

I

41.0

45.0

49.0

53.0

cc -.]

co

FIGURE XIII. 1. 14. lSI-6 (as made) (E. P . A. 121. 730. ex 1)

t.

...

.. I-

2

e

I-

I-

II-

.. I-

I-

d [0. 1nm]

I1Io

9.44 7.07 6.92 6.59 5.74 5.05 3.97 3.92 3.83 3.77 3.64 3.53 3.46 3.36 3.30 3.12 3.04 2.94 2.84

100.00 7.00 7.00 11.00 9.00 7.00 33.00 26.00 14.00 21.00 25.00 33.00 28.00 12.00 9.00 12.00 8.00 5.00 5.00

l-

I-

-

I-

l-

II.

I

5.0

9.0

13.0

,I

I 17.0

21.0

25.0

I ,I 1.1 29.0

I

33.0

I

37.0

41.0

45.0

49.0

53.0

cc 00

o

FIGURE XIII. 1. 15. PSH-3 (as made) (E. P. A. 64. 205. ex. 1)

t. 2

e

I-

I~

I-

d [0. 1nm]

r/re

12.63 10.92 8.84 6.86 .6.15 5.50 4.39 4.09 3.91 3.75 3.56 3.41 3.30 3.19 3.11 2.84 2.69 1.97 1.87 1.86

100.00 30.00 60.00 5.00 40.00 15.00 15.00 20.00 30.00 5.00 3.00 100.00 2.00 3.00 2.00 2.00 3.00 5.00 3.00 5.00

~ ~

I-

I

L

5.0

9.0

13.0

17.0

21.0

.1

25.0

29.0

,

II

33.0

,

I

37.0

,

, 41.0

I

I 45.0

,l 49.0

53.0

cc

~

382 REFERENCb 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. 26.

E. Moretti, S. Contessa and M. Padovan, Chim. Ind. §l (1985) 21. M.K. Rubin, E.J. Rosinski and C.J. Plank, U.S.P. 4,247,728 (1981), assigred to Mobil Oil Corp. M.G. Barrett and D.E.W. Vau9han, Belg. Pat. 888,915 (1981j, assigned to W.R. Grace. J. Ciric, U.S.P. 3,950,496 (1976), assigned to Mobil Oil Corp. R.W. Grose and E.M. Flanigen, U.S.P. 4,124,686 (1978), assigned to Union Carbide Corp. J.A. Martens, M. Tielen, P.A. Jacobs and J. Weitkamp, Zeolites i (1984) 98. J.A. Martens and P.A. Jacobs, Zeolites ~ (1986) 334. C.J. Plank, E.P.A. 64,328 (1982), assi9ned to Mobil Corp. R.L. Wadlinger, G.T. Kerr and E.J. Rosinski, U.S.P. 3,308,069 (1967), Re.28,341 (1975), assigned to Mobil Oil Corp. T.V. Whittam, E.P.A. 55,046 (1981) assigned to ICI. H.G. Doherty, E.J. Rosinski and C.J. Plank, E.P.A. 15,702 (1980), assigned to Mobil Oil Corp. H.G. Doherty, C.J. Plank and E.J. Rosinski, U.S.P. 4,247,416 (1981), assigned to Mobil Oil Corp. P.A. Jacobs and J.A. Martenss, Pure Appl. Chem. 58, 10 (1986) 1329. J. Dewing, I'I.S. Spencer and T.V. Whittam, Catal. Rev. Sci. Eng. 27 (1985) 461. A. Araya and B.M. Lowe, E.P.A. 107,908 (1983), assigned to ICI. A. Araya and B.M. Lowe, E.P.A. 105,679 (1983), assigned to ICI. T.V. Whittam, E.P.A. 103,981, assigned to ICI. T.V. Whittam, U.S.P. 4,397,825 (1983), assigned to ICI. T.V. Whittam, E.P.A. 54,364 (1981) assigned to ICI. T.V. Whittam, Ger. Offenl. 2,748,278 (1978), assigned to ICI. T.V. Whittam, U.S.P. 4,209,498 (1980), assigned to leI. M.S. Spencer and T.V. Whittam, The properties and applications of zeolites, R.P. Townsend, ed., Chemical Society London, 1980, p. 342. J. Dewing, F. Pierce and A. Stewart, JCS Chern. Commun. (1980) 718. J. Dewing, F. Pierce and A. Stewart, Catalysis by Zeolites, B. Imelik et al., eds., Elsevier, Amsterdam 1980, p.39. B.W. Cook, J. Dewing and A. Stewart, Zeolite 1 (1981) 5. T.V. Whitham, Ger. Offenl. 2,643,928 (1978) assi9ned to ICI.

383

27. 28. 29. 30.

G.T. Kokotailo and S. Sawruk, U.S.P. 4,187,283 (1980), assigned to Mobil Oil Corp. P. Chu, J.C. Vdrtuti and A.J. Herbst, E.P.A. 127,399 (1984), assigned to Mobil Oil Corp. N. Morimoto, K. Takatsu and M. Sugimoto, E.P.A. 121,730 (1984), assigned to Res. Ass. Petro Alternatives Dev. L. Puppe and J. Weisser, E.P.A. 64,205 (1982), assigned to Bayer AG.

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385

SUBJECT INDEX

Epistilbite 217

Alkalinity (OH/Si0 2) 157 ALPO-5 276

ERI structure 342

Aluminium

ERI/OFF intergrowths 342

-,octahedral 61

EU-l 251, 283

-,species in solution 52

EU-2 262, 275

ANA: see analcime

EU-4 251

Analcime 56, 58, 220

EU-7 359

Avrami-Erofeev equation 113

EU-ll 275

AZ-l 200

EU-12 359 EU-13 251, 360

Bikitaite 217, 236 FER Cancrinite 276

-,structure 217

Chabas ite 220

-,column 218

Charge density of templates

-,pores 219

120, 124, 159, 161, 312

-,sheet 275

Clathrates 47, 67

-,stacking faults 228, 230

Clinoptilolite 96

-,unit cell 217

Constraint index 182

Ferrierite 217

Constraint index (refined) 161, 183

-,adsorption 220, 228

Cristobalite co-crystallization

-,co-crystallization 326

58, 197, 198, 297, 361

-,crystallization

CSZ-l 343, 357

-,alkali metal-free gel 223

CZH-5 297, 303, 306, 310, 316

-,aluminium incorporation 224, 246, 264

Dachiardite 217

-,basicity of gel 223, 225

Deamination 160

-,deamination of amines 227 -,organic-free gel 217

386

-,pore filling theory 157, 223, 226 LEV structure 333 -,stirring of gel 227

Levyne 333, 335

-,temperature 217, 227

Lowe model for crystallization 83, 119, 246

-,lattice vibrations 26, 42 -,mineral 96, 217, 225, 227, 264

LZ-132 333, 340

-,structure see FER

LZ-133 333, 339

-,synthesis recipe 8 -,X-ray diffraction 31

Magadiite 58, 150 28 198, 327

FU-1 361

~lB-

FU-9 220, 228, 229

MEL -,structure 167

Gismondine 56

-,secondary building unit 48, 140

Gmelinite 220

-,pore shape 170 ME-MOR 327

Harmotone 56

Metakaolin 96, 98

Heu 1andite 220

MF1

Hoffmann elimination reaction 63

-,structure 167 -,secondary building unit 48, 140

151-1 233

-,pore shape 170

151-4 251, 362

MOR

151-6 362

-,structure 301, 321 -,pores 327

Koalin 96,98

Mordenite

Kenyaite co-crystallization

-,aluminium incorporation 264, 280,

58, 127, 129, 297 KZ-1

251

KZ-2 233, 262

321, 326 -,co-crystallization 56, 124, 126, 132,

13~,

140, 142,

220, 303, 323 LAU structure 236

-,group of zeolites 217, 220, 233

Laumontite 236

-,lattice vibrations 26, 42

387

-,raw material 96

Pentasil

-,structure: see MOR

-,intergrowths 167

-,synthesis 321

-,pore shape 17/

-,synthesis efficiency 327

-,unit cell 177

-,synthesis recipe 12

- ,structure 177

MTH structure 343

Phi11 i ps ite 56

MTN structure 330

PSH-3 362

MTT -,structure 251 -,pores 256

Quartz co-crystallization 136, 197, 243, 246, 303

MTW -,structure 297

Sanidine 58

-,pores 302

Silica polymerization-depolymerization

60, 71, 75, 91, 99, 117, 142

NU-1 361

Silicalite 103

NU-2 359

-,ion-exchange 104

NU-3 333, 338, 360

-,structure 170

NU-4 195, 246

-,synthesis 105

NU-5 197

-,XRD-pattern 105

NU-6(l) 360

Silicalite-2 151

NU-6(2) 360

Solubility of zeolites 70, 83

NU-10 195, 233, 283

SR-D 217, 229

NU-13 297, 303, 306, 310, 312, 315

Supersaturation 55

NU-23 360

Synthesis efficiency 3

Nucleation rate 65 TEA-MOR 327 OFF structure 342

TMA-OFF 342

Offretite 56, 57, 342

TEA-Silicate 297,302,310,317 THETA-1 233, 258

888

TON

ZSM-5

-,structure 233, 258

-,adsorption

-,pores 236, 258

-,xylenes 79, 194

-,stacking faults 248

-,paraffins 182, 194

TON/MTT intergrowths 258

- ,water 194

TPZ-3 297, 302, 306, 310, 312, 318

-,constraint index 182

Tri dymite 127

-,constraint index (refined) 183

TRS 198

-,crystallization

TsVK 198

-,activation energie 60

TZ-01 200, 326

-,alkali-free gels 70, 104,

TZ-02 200, 326

119, 121, 124 -,alkali metal cations 52,

Ultrasil 198 Ultrazet 198

67, 69, 70, 75 -,aluminium complexing 60, 74, 94, 142

Yugawaralite 220

-,aluminium incorporation

59,

61, 89, 140, 280 ZBM-10 198 ZBM-30 275 Zeolite BETA 16, 26, 36, 43, 303, 359 Zeolite PHI 15, 26, 35, 43, 358

-,ammonium ions in gel 69, 72, 75, 129 -,basicity of gel 61, 70, 75, 115, 139

Zeol ite T 342

-,buffering of pH 80, 119, 142

Zeolite X 96, 344

-,curve 83

Zeolite Y 96, 143, 343, 345

-,dilution effect 64, 71, 76, 80,

ZETA-1 193

91, 135

ZETA-3 195

-,efficiency 192

ZK-20 333

-,multi-step 94, 100

ZKU 342

-,organic-free gels 100, 134

ZSM-3 343

-,pore filling theory 63, 114, 118,

ZSM-4 326

120, 123, 125, 130, 134, 141,159

389

-,preformed precursor 98

-,phase diagram 56

-,rate 115, 124, 129, 130

_,29 Si NMR 183

-,salt addition 75, 126, 127

-,silanol groups 132

-,solvents 101, 118

-,structure: see MFI

-,stirring 80, 135

-,synthesis from other zeolites 96

-,temperature 79

-,synthesis recipes 17

-,templation 61, 82, 100, 114, 117,

-,X-ray amorphous nuclei 82, 162

120, 124, 161, 283

-,XRD-diagram 29, 158, 180, 187

-,viscosity 59, 71, 80

ISM-6 11, 26, 33, 42, 361

-,yield 84, 119

ISM-8 21, 26, 38, 42, 191, 201

-,crystals

ISM-II

-,aluminium content 93, 131, 140

-,adsorption 182, 194

-,aluminium zoning 64, 88, 91

-,constraint index 182

-,cation balance 90

-,constraint index (refined) 161,

-,deagglomeration 80 -,morphology 63, 72, 115

183 -,crystallization

-,sodium occlusion 84

-,activation energy 153

-,symmetry changes 106, 185

-,alkali-free gels 148, 151 ,

-,extrudates 97

-,aluminium incorporation 162

-,hydroxyl stretching spectra 20

-,basicity of gel 154, 155, 157

~

-,ion-exchange 104, 123

-,pore filling 152, 159

-,lattice vibrations 334, 41, 82

-,rate 155

-,nucleation

-,templating 151, 156

-,activation energy 60, 114

-,crystals

-,curve 83

-,aluminium content 151

-,mechanism 81, 91, 99, 117

-,morphology 149

-,organic-free gels 101, 117

-,symmetry changes 185

-,rate 65, 114, 115, 124

-,lattice vibrations 26, 41, 162

-,secondary 79

-,nucleation

-,surface 63, 79, 101

-,activation energy 153

390

-,mechanism 162

-,cage filling 331

_,29 Si NMR 183

-,co-crystallization 289

-,structure: see MEL

-,lattice vibrations 26, 42

-,synthesis recipe 20

-,structure: see MTN

-,X-ray amorphous nuclei

-,synthesis 330

162

-,XRD-diagram 30, 158, 180

-,synthesis recipe 10

ZSM-12

-,XRD-diagram 32

-,adsorption 313

ZSM-43 357

-,crystallization

ZSM-45 333, 341

-,aluminium incorporation 301, 303

ZSM-47 26, 41, 361

-,efficiency 306

ZSM-48-type zeolites

-,pore filling theory 306, 312

-,adsorption 289

-,crystals

-,crystallization

-,chemical composition 310

-,aluminium incorporation

-,morphology 302, 312

280, 283, 288

-,lattice vibrations 26, 41

-,efficiency 284

-,synthesis 303

-,pore filling 285, 288

-,synthesis

recipe 13

-,crystal morphology 289

-,XRD-diagram 34, 314

-,lattice vibrations 26, 42

ZSM-18 358

-,structures 275

LSM-20 343

-,synthesis 22, 246, 281

ZSM-21 220, 224, 227

-,XRD-diagram 39

ZSM-22 24, 26, 40, 43, 233

ZSM-50 362

ZSM-23 251 ZSM-25 17, 26, 37, 43, 359 ZSM-34 6, 26, 27, 41, 342 ZSM-35 8, 26, 28, 41, 220, 224, 227, 229 ZSM-38 220, 224, 228 ZSM-39 -,aluminium incorporation 332

Catalysis by Zeolites: International Symposium Proceedings (Studies in surface science and catalysis)

Catalysts for Upgrading Heavy Petroleum Feeds, Volume 169 (Studies in Surface Science and Catalysis) (Studies in Surface Science and Catalysis)

Fluid Catalytic Cracking V (Studies in Surface Science and Catalysis)

Catalysis: An Integrated Approach to Homogenous, Heterogenous and Industrial Catalysis (Studies in Surface Science and Catalysis)

Catalysis and Adsorption by Zeolites

Zeolites and Catalysis: Synthesis, Reactions and Applications (2 Volume set)

Past and Present in DeNOx Catalysis: From Molecular Modelling to Chemical Engineering, Volume 171 (Studies in Surface Science and Catalysis) (Studies in Surface Science and Catalysis)

Zeolites in Industrial Separation and Catalysis

New Developments in Selective Oxidation by Heterogeneous Catalysis: Proceedings (Studies in Surface Science and Catalysis)

Catalysis by Metals and Alloys (Studies in Surface Science and Catalysis)

Catalysis and Automotive Pollution Control III (Studies in Surface Science and Catalysis, Volume 96)

Zeolites As Catalysts, Sorbents, and Detergent Builders: Applications and Innovations : Proceedings (Studies in Surface Science and Catalysis)

Surface and Nanomolecular Catalysis

Zeolites and Microporous Crystals: Proceedings of the International Symposium on Zeolites and Microporous Crystals, Nagoya, August 22-25, 1993 (Studies in Surface Science and Catalysis)

Catalysis by Acids and Bases (Studies in Surface Science and Catalysis)

Fluid Catalytic Cracking VII:, Volume 166: Materials, Methods and Process Innovations (Studies in Surface Science and Catalysis) (Studies in Surface Science and Catalysis)

Synthesis of High-Silica Aluminosilicate Zeolites (Studies in Surface Science and Catalysis)

Catalysis by Zeolites: International Symposium Proceedings (Studies in surface science and catalysis)

Catalytic Polymerization of Olefins (Studies in Surface Science and Catalysis)

Preparation of Catalysts VII (Studies in Surface Science and Catalysis)

Catalysts for Upgrading Heavy Petroleum Feeds, Volume 169 (Studies in Surface Science and Catalysis) (Studies in Surface Science and Catalysis)

Fluid Catalytic Cracking V (Studies in Surface Science and Catalysis)

Photochemistry on Solid Surfaces (Studies in Surface Science and Catalysis)

Fluid Catalytic Cracking V (Studies in Surface Science and Catalysis)

Catalysis: An Integrated Approach to Homogenous, Heterogenous and Industrial Catalysis (Studies in Surface Science and Catalysis)

Catalysis and Adsorption by Zeolites

Zeolites and Catalysis: Synthesis, Reactions and Applications (2 Volume set)

Past and Present in DeNOx Catalysis: From Molecular Modelling to Chemical Engineering, Volume 171 (Studies in Surface Science and Catalysis) (Studies in Surface Science and Catalysis)

Zeolites in Industrial Separation and Catalysis

Zeolites in Industrial Separation and Catalysis

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Zeolites and Microporous Crystals: Proceedings of the International Symposium on Zeolites and Microporous Crystals, Nagoya, August 22-25, 1993 (Studies in Surface Science and Catalysis)

Catalysis by Acids and Bases (Studies in Surface Science and Catalysis)

Zeolites, science and technology

Studies in Surface Science and Catalysis 110. 3rd World Congress on Oxidation Catalysis

12th International Congress on Catalysis (Studies in Surface Science and Catalysis)

Laboratory Studies of Heterogeneous Catalytic Processes (Studies in Surface Science and Catalysis)

Fluid Catalytic Cracking VII:, Volume 166: Materials, Methods and Process Innovations (Studies in Surface Science and Catalysis) (Studies in Surface Science and Catalysis)

Advanced Zeolite Science and Applications, Volume 85 (Studies in Surface Science and Catalysis)

Synthesis of High-Silica Aluminosilicate Zeolites (Studies in Surface Science and Catalysis)

Catalysis by Zeolites: International Symposium Proceedings (Studies in surface science and catalysis)

Catalytic Polymerization of Olefins (Studies in Surface Science and Catalysis)

Preparation of Catalysts VII (Studies in Surface Science and Catalysis)

Catalysts for Upgrading Heavy Petroleum Feeds, Volume 169 (Studies in Surface Science and Catalysis) (Studies in Surface Science and Catalysis)

Fluid Catalytic Cracking V (Studies in Surface Science and Catalysis)

Photochemistry on Solid Surfaces (Studies in Surface Science and Catalysis)

Fluid Catalytic Cracking V (Studies in Surface Science and Catalysis)

Catalysis: An Integrated Approach to Homogenous, Heterogenous and Industrial Catalysis (Studies in Surface Science and Catalysis)

Catalysis and Adsorption by Zeolites

Zeolites and Catalysis: Synthesis, Reactions and Applications (2 Volume set)

Past and Present in DeNOx Catalysis: From Molecular Modelling to Chemical Engineering, Volume 171 (Studies in Surface Science and Catalysis) (Studies in Surface Science and Catalysis)

Zeolites in Industrial Separation and Catalysis

Zeolites in Industrial Separation and Catalysis

Zeolites in Industrial Separation and Catalysis

New Frontiers in Catalysis, Parts A-C (Studies in Surface Science and Catalysis)

Surface and nanomolecular catalysis

Catalysis and Automotive Pollution Control (Studies in Surface Science and Catalysis)

New Developments in Selective Oxidation by Heterogeneous Catalysis: Proceedings (Studies in Surface Science and Catalysis)

Catalysis by Metals and Alloys (Studies in Surface Science and Catalysis)

Catalysis and Automotive Pollution Control III (Studies in Surface Science and Catalysis, Volume 96)

Zeolites As Catalysts, Sorbents, and Detergent Builders: Applications and Innovations : Proceedings (Studies in Surface Science and Catalysis)

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Zeolites and Microporous Crystals: Proceedings of the International Symposium on Zeolites and Microporous Crystals, Nagoya, August 22-25, 1993 (Studies in Surface Science and Catalysis)

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