Studies in Surface Science and Catalysis 98 ZEOLITE SCIENCE 1994: RECENT PROGRESS AND DISCUSSIONS
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S t u d i e s in S u r f a c e S c i e n c e a n d C a t a l y s i s Advisory Editors: B. Delmon and J.T. Yates Vol. 98
ZEOLITE SCIENCE 1994: RECENT PROGRESS AND DISCUSSIONS S u p p l e m e n t a r y Materials to the 10th International Zeolite Conference, Garmisch-Partenkirchen, Germany, J u l y 17-22, 1994
Editors H.G. Karge
Fritz Haber Institute of the Max Planck Society, Berlin, Germany
J. Weitkamp
University of Stuttgart, Stuttgart, Germany
1995 ELSEVIER
Amsterdam - - Lausanne-- New York-- Oxford ~ Shannon m Tokyo
ELSEVIER SCIENCE B.V. Sara Burgerhartstraat 25 P.O. Box 211, 1000 AE Amsterdam, The Netherlands
ISBN 0-444-82308-5 91995 Elsevier Science B.V. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior written permission of the publisher, Elsevier Science B.V., Copyright & Permissions Department, P.O. Box 521, 1000 AM Amsterdam, The Netherlands. Special regulations for readers in the U.S.A. - This publication has been registered with the Copyright Clearance Center Inc. (CCC), 222 Rosewood Drive, Danvers, MA 01923. Information can be obtained from the CCC about conditions under which photocopies of parts of this publication may be made in the U.S.A. All other copyright questions, including photocopying outside of the U.S.A., should be referred to the copyright owner, Elsevier Science B.V., unless otherwise specified. No responsibility is assumed by the publisher for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions or ideas contained in the material herein. This book is printed on acid-free paper. Printed in The Netherlands
Table of Contents
Preface ................................................................................................................................
vii
List o f Sponsors .................................................................................................................
viii
Welcome Address .................................................................................................................
x ~
Breck Award 1994 .......................................................................................................
xvn
IZA Award 1994 ............................................................................................................
xviii
Election o f Professor R. M. Barrel F. R. S., as Honorary President of the Imemational Zeolite Association ...........................................................................................................
xix
After Dinner Speech given by C. T. O'Connor at the Congress Banquet .............................
xx
List o f Recent Research Reports .........................................................................................
xxv
Recent Research Reports ..................................................................................................... 1 Full-Length Paper "Alkylation of aniline with methanol on Beta and EMT zeolites exchanged with alkaline cations" by P. R. Had Prasad Rao, P. Massiani and D. Barthomeuf ............................................................................................................
287
Index of Authors of Recent Research Reports ..................................................................... 295 Index of Subjects of Recent Research Reports .................................................................... 300 Transcripts o f the Discussions .............................................................................................
304
List o f Participants of the 10th IZC ..................................................................................... 452
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vii
PREFACE
The 10th International Zeolite Conference was held from July 17 to 22, 1994 at Garmisch-Partenkirchen, Germany. The attendance was unexpectedly high and very encouraging with respect to the future perspective of the scientific field to which the conference was devoted. About 950 active and 50 accompanying attendees were welcomed by the Organising Committee. The Proceedings of the Conference were handed out at the beginning of the Conference. As far as one can judge from the immediate response to the presentations as well as from that to the Proceedings, the conference seemed to be a remarkable scientific success. We are now able to issue a supplementary volume which comprises in the first chapter various items, viz. (i) a list of the sponsors to whom the organisers are particularly grateful because of their significant support; (ii) the welcome address; the phrasings of the BRECK AWARD and the IZA AWARD which was first awarded at the 10th International Zeolite Conference; (iii) the address on the occasion of the appointment of the first Honorary President of the International Zeolite Association (IZA), Professor R. M. Barrer, and, finally, the marvellous after dinner speech by Professor Cyril O'Connor from the University of Cape Town. The larger part of the supplementary volume presents the full texts of the Recent Research Reports, which were presented as posters, and the Discussions of all the lectures and posters which were submitted to the editors. One full paper is also included, viz. the paper "Alkylation of aniline with methanol on Beta and EMT zeolites exchanged with alkaline cations" by P. R. Had Prasad Rao, Pascale Massiani and Denise Barthomeuf because, due to a regrettable error, one page was missing in the version published in the Proceedings. Finally, the supplementary volume also contains a complete list of the participants. The editors sincerely hope that not only the attendees of the 10th IZC, but also any colleagues interested in the field will enjoy reading the book and draw some benefit from it.
Berlin and Stuttgart, May 1995
Hellmut G. Karge
Jens Weitkamp
viii
10th International Zeolite Conference July 17- 22, 1994
List of Sponsors The Organizing Committee gratefully acknowledges support by the following institutions and companies: 1
Deutsche Forschungsgemeinschaft, Bonn, Germany
2
Max-Planck-Gesellschaft zur Fiirderung der Wissenschaften e. V.,
Mfmchen, Germany 3
Air Products and Chemicals, Inc., Allentown, PA, USA
4
Altamira Intruments, Incorporated, Pittsburgh, PA, USA
5
BASF Aktiengesellschaft, Ludwigshafen, Germany
6
Bayer AG, Leverkusen, Germany
7
Biosym Technologies GmbH, M~nchen, Germany
8
CEM GmbH, Kamp-Lintfort, Germany
9
Coulter Electronics GmbH, Krefeld, Germany
10
CU Chemie Uetikon AG, Uetikon, Switzerland
11
Degussa AG, Frankfurt am Main, Germany
12
DuPont Company, Wilmington, DE, USA
13
Elsevier Science Publishers B. V., Amsterdam, The Netherlands
14
Engeihard Corporation, lselin, NJ, USA
15
Exxon Chemical International, Brussels, Belgium
16
Fonds der Chemischen Industrie, Frankfurt am Main, Germany
17
Grace GmbH, Worms, Germany
18
Haldor Topme A/S, Lyngby, Denmark
19
Hemmer Repetitorium, Wftrzburg, Germany
20
Henkel KGaA, Di;tsseldorf, Germany
21
Hiden Analytical Limited, Warrington, England
22
Hoechst AG, Frankfurt am Main, Germany
List of Sponsors (continued) 23
Hills AG, Marl, Germany
24
Institut Frangais du P~trole, Rueil-Malmaison, France
25
Merck & Co., Inc., Whitehouse Station, NJ, USA
26
Molecular Simulations, Cambridge, England
27
Perkin-Elmer GmbH, Oberlingen, Germany
28
Quantachrome GmbH, Eurasburg, Germany
29
SKW Trostberg Aktiengeselischaft, Trostberg, Germany
30
Statoil Petrochemicals and Plastics, Stathelle, Norway
31
Siid-Chemie AG, Mfmchen, Germany
32
Texaco Incorporated, Beacon, NY, USA
33
The Dow Chemical Company, Midland, MI, USA
34
The PQ Corporation, Valley Forge, PA, USA
35
UOP Research and Development, Des Plaines, 1L, USA
36
VAW aluminium AG, Schwandorf, Germany
Welcome Address by Jens Weitkamp, Chairman of the Organizing Committee (held on July 18, 1994)
Dear Participants, Distinguished Guests, Friends,
Welcome to the 10th International Zeolite Conference! This is the day we have been looking forward to since the decision of the Council of the International Zeolite Association in early 1991, to have the 10th International Zeolite Conference held in this country, in the beautiful City of Garmisch-Partenkirchen. Our experience with the local authorities and people were so good that we felt a strong temptation to apply again for the 12th International Zeolite Conference, again with Garmisch-Partenkirchen as the venue.
In fact, as many of you will have recognized, this is a truly European rather than a German congress. Not only is our hosting city located fight in the heart of Europe, within walking
distance of Austria and within hiking distance of Italy; but the organization, which extended over years, was done by a team of European experts. Our deeply felt thanks go to a number of colleagues who - upon our request - spontaneously agreed to shoulder large parts of the burden of the organizational work:
Dr. Koos Jansen from Delft University of Technology, The Netherlands, and Dr. Michael StOcker from SINTEF in Oslo, Norway, organized the Summer School on Zeolites held last Thursday, Friday and Saturday in Wildbad Kreuth, some 60 km away from here, and as we understand from the participants, they did an excellent job. Professor Johannes Lercher, who recently moved from Vienna University of Technology in Austria to Twente University at Enschede, The Netherlands, took over the responsibility for the program offered to accompanying persons. And Professor Carmine Colella with his team from the University of Naples, Italy, organized the Post-Conference Field Trip to the Latium and Umbria Regions m Central Italy. Ladies and gentlemen, organizing large international congresses has lately become more difficult, at least in Europe, since both governmental institutions and industrial companies are getting increasingly reluctant to sponsor the flood of scientific conferences. The Organizing Committee appreciates the generous support by
xii -
-
the Max Planck Society, the German Science Foundation (Deutsche Forschungsgemeinschatt) and the State Government of Bavaria.
In addition, an impressive number of industrial companies from many countries were willing to support the 10th IZC, and we express our gratitude to these industrial sponsors whose names are given on posters displayed at various locations in this building and on a list handed out to every participant during registration. This Conference was organized in close contact with the International Zeolite Association, and IZA appointed Jan van Hooff as official IZA observer. We enjoyed very much the cooperation with Jan, and we thank him for his active support of this Conference. Let me now briefly address the scientific program and the procedures of paper selection. The Organizing Committee is grateful to a number of renowned experts from the international zeolite community who agreed to present plenary lectures on key issues of zeolite science and technology: Synthesis and structure analysis are becoming increasingly important and will be dealt with by Peter Jacobs and Lynne McCusker, respectively. The progress in diffusion inside microporous solids will be reviewed by Lovat Rees. And various aspects of the use of zeolites as catalysts ranging from ab-initio calculations to industrial and environmental catalysis will be covered by Werner Haag, Joachim Sauer, .loop Naber and Mazakazu Iwamoto. Ladies and gentlemen, I confess that there was much concern within the Organizing Committee about the repercussions of the IZA's decision to shorten the intervals between successive Conferences from three to two years. We had a number of worst case scenarios in our drawers, but fortunately, when the deadline for submission of papers approached in the 37th week of 1993, we could abandon all these scenarios. Not only was the response to our call for papers overwhelming, but - to our surprise - the authors were willing to meet the deadline.
xiii 100
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27. 28. 29. 30. 31. 32. 33. 34. 35. 36. 37. 38. 39. 40. 41. Calendar week
Still more importantly, the originality and quality of many abstracts were outstanding, and our Sub-Committee for Paper Selection chaired by Dr. Ernst Ingo Leupold and Dr. Lothar Puppe had a very difficult task. The Organizing Committee is deeply indebted to the European experts who spent a huge amount of their precious time on ranking and selecting the submitted abstracts:
E.I. Leupold,
Hoechst AG, Frankfurt, Germany
L. Puppe,
Bayer AG, Leverkusen, Germany
C. Baerlocher,
ETH Zurich, Switzerland
G. Bellussi,
Eniricerche S.p.A., San Donato, Italy
E. Gallei,
BASF AG, Ludwigshafen, Germany
H. Kessler,
E.N.S.C.M., Mulhouse, France
P. Kleinschmit,
Degussa AG, Hanau, Germany
P. Krings,
Henkel KGaA, D0sseldorf, Germany
W. Mortier,
Exxon Chemical Int., Machelen, Belgium
M. StOcker,
SINTEF, Oslo, Norway
K.K. Unger,
University of Mainz, Germany
xiv
6oot
Conference
Papers
Recent Research Reports
- 300
527
243
5OO
- 200
400 139
300 200
- 100
100 0
Subm. Rej. Posters Oral
Subm. Rej.
Acc.
0
Our thanks furthermore go to all those who submitted a contribution. In fact, more than 500 Conference papers were submitted out of which we accepted ca. 100 for oral and ca. 180 for poster presentation. Let me emphasize here again that no quality difference exists between papers presented orally and those displayed as posters, and you will detect no difference at all in the Conference Proceedings you received here in Garmisch-Partenkirchen. In our opinion Elsevier Science Publishers did an excellent job, and we convey our thanks to Elsevier for their efficiency. Another flood of abstracts submitted for presentation as posters in the Recent Research Report Session this afternoon, reached us in March, April and May of this year, and we were able to accept slightly more than 50 % of these. Ladies and gentlemen, one of the very early and most important duties of an Organizing Committee is the selection of a good logo. We were, in fact, extremely lucky in this respect: An exciting new structure was discovered in Europe by our colleagues Lynne McCusker, Christian Baerlocher and Henri Kessler and their coworkers. Our Organizing Committee is grateful to these outstanding scientists not only for having made the discovery, but also for having made it at the fight time for our purposes and for giving us every support, together with Walter Meier, in translating the structure into a suitable logo.
As we believe, it teaches and reminds us of a number of different things, namely (i)
how aesthetic zeolitic structures are,
(ii)
that super- or ultra-large pore zeolites are certainly among the thrust areas of ou science,
Oil)
that, in the heart of our beloved science, considerable darkness continues to exist an, many questions are still obscure.
(iv)
Finally, it wiU accompany us during the whole Conference week with its four-leafe, clover.
xvi The Organizing Committee sincerely hopes that the four-leafed clover will contribute to make this Conference efficient, fi~itful and successful and wishes you a week fifll of luck and happiness. I declare the lOth International Zeolite Conference opened.
Jens Weitkamp
xvii
10th IZC
Garmisch- Partenkirchen, July 17- 22, 1994
Breck Award 1994 In 1992
C.T. Kresge M.E Leonowicz W.J. Roth J.C. Vartuli
and
J.S. Beck of the Mobil Research and Development Corporation reported a significant breakthrough in the synthesis of porous materials. The Mobil group successfully prepared the first ordered mesoporous silicate and aluminosilicate materials containing pores in the range of 16 to 100 A. This startling discovery was accomplished by using liquid crystal "templates". That is surfactant molecules that can self-assemble into ordered structures which interact with the inorganic species to form the final composite material. The Mobil work is the first to use organized organic species as "templates" rather than single molecules as is common in molecular sieve synthesis. The impact of the discovery of the Mobil is large since it: i)
created a new type of material
ii)
developed a new synthetic strategy
iii)
opened new areas of technology for catalysis, separation and guest-host chemistry.
and
The novelty and generality of these concepts provide research directions for years to come.
Thus the efforts of the Mobil group deserve the 1994 Breck Award.
xviii
IZA A W A R D 1994
A decision was made by the IZA Council to create an IZA Award that would be given to an individual who would serve as an ambassador for the IZA to the world zeolite community. This person will be responsible for educating other scientists about zeolite molecular sieves, and a grant will be given to assist them m this task. The mechanism for arranging visits by the Recipient wiLl be handled by a representive of the IZA Council. The individual chosen for this award is being honored by the IZA for long term committments and contributions to Zeolite Science.
At this 10th IZC, the first IZA Award will be presented to an individual, whose name is almost synonymous with zeolites and molecular sieves:
Edith M. Flanigen Edith's Synthesis Group has been called "The Discovery Group". They were adwarded the First Don Breck Award given at the 6th IZC for the discovery of the AIPO4 Molecular Sieve family of material and have gone on beyond that to SAPOs, MeAPOs, MeAPSOs, Sulfide materials and much, much more. She has enthusiastically led her group at Union Carbide and UOP, and we feel that she will be the ideal zeolite ambassador for the IZA to the world.
Hellmut G. Karge IZA President
Roland von Ballmoos IZA Secretary
xix
10th IZC
G a r m i s c h - Partenkirchen, July 17 - 22, 1994
Honorary President The IZA Council honours
Professor Richard Barrer for his outstanding contributions to zeolite science by awarding him the title of Honorary President of the IZA.
With great appreciation.
Hellmut G. Karge
Roland von Ballmoos
IZA President
IZA Secretary
XX
AFTER-DINNER SPEECH PRESENTED AT THE BANQUET OF THE 10TH INTERNATIONAL Z E O L I T E C O N F E R E N C E , G A R M I S C H - P A R T E N K I R C H E N , GERMANY, JULY 1994. by Cyril T. O'Connor Ladies and Gentlemen I hope that you will sympathise with me being requested to deliver an after dinner speech at the end of a long hard-working conference week. When Hellmut asked me to fulfil this duty he suggested that something light hearted would be appropriate. I suppose that after he and the Organising Committee had recovered from the fits of laughter they must have had when they read some of the hilarious contents of the abstracts I submitted they must have immediately concluded that here was an excellent candidate for an equally hilarious after dinner speech. Anyway, I suppose that one of the advantages of this conference slot compared the poor people who landed the early afternoon siesta or graveyard sessions is that my paper hasn't had to be refereed and there is no question time at the end. In preparing a few words for this evening it soon became apparent to me that one difficulty in trying to be humorous in front of such an international audience is that humour does not easily cross geographical boundaries. Each country does have their country bumpkin - in South Africa we call him van der Merwe, in Ireland he's called Paddy and so on. One species of the human race, however, which does lend itself at all times to being laughed at and about are politicians. Before I relate the following story let me remind you that many of you who know me well are very much aware of the fact that I am a great lover of Germany, German life and German hospitality. One distinctive feature of German hospitality is that it is most usually accompanied with excellent wine or beer. A visit to Germany is unfulfilled if one hasn't enjoyed the excellent white wines in particular or the wide variety of beer for which Germany is so famous. One of the most famous of these is, of course, Pils which originates from Czechoslovakia. Any newcomer to the wonders of a Pils soon finds out that it takes a long time to pour a pils. My story revolves around an invitation extended some years ago by a famous Indian Maharajah to President Ronald Reagan, Mrs Margaret Thatcher and Chancellor Helmut Kohl. It was an interesting palace except that the swimming pool was permanently empty. Upon being quizzed on this matter the Maharaja informed his illustrious guests that the distinguishing feature of the pool was that as one stood at the edge ready to dive in one could call out the name of any liquid which one fancied and the pool would immediately be filled with this. Margaret Thatcher, being the lady, was first to take the plunge and just before she jumped in she called out "Guinness Stout". Immediately the pool was filled with marvellous stout even including the froth and upon leaving the pool it promptly drained. President Reagan repeated the trick except that he preferred Jack Daniels. Chancellor Kohl was last in and he fancied a
xxi Pils. Upon leaping into the pool to his dismay no liquid appeared and he bashed his head, rather sorely, on the bottom of the empty pool. Upon protesting to the Indian Prince at this shoddy treatment he was promptly reminded: "Herr Kohl, you of all people should know that it takes 8 minutes to pour a Pils". One of the wonderful privileges we all enjoy as researchers is that we belong to a unique family of friends and I always cherish the opportunity which attending a Conference such as this affords us all to renew old acquaintances as well as to forge new friendships. We are indeed all fortunate to have this opportunity which is one of the great privileges of a research career. Attending conferences can also of course be a source of some considerable humour. How many of you during this week may have stood at a poster wondering what on earth the authors were trying to convey. This experience always reminds me of the story of the famous artist, Pablo Picasso who was visited one day by an old friend. Pablo had been pondering over a new painting of his for hours and when asked by his friend as to the source of his concern, the old artist replied that he was troubled with the look of the nose on the face of the figure in the painting. When his friend simply pointed that he could surely simply touch it up a bit, Picasso replied: "That's exactly what I have been intending to do for the last three hours but the trouble is that I can't find the nose". Writers of scientific papers may be among the greatest perpetrators of the euphemism. Isaac Newton is quoted as having said that "False facts are highly injurious to the progress of science for they often endure long but false views if supported by some evidence do little harm for everyone takes great pleasure in proving their falseness". Of course the history of science is fiddled with wonderful examples of famous men making, with hindsight, incredible statements. Some wonderful examples of these which I enjoy quoting are: 1. "We hope that Professor Langley will not put his substantial greatness as a scientist in further peril by continuing to waste his time and the money involved in further airship experiments. Life is too short, and he is capable of services to humanity incomparably greater than can be expected to result from trying to fly ... For students and investigators of the Langley type there are more useful employments." (New York Times, Dec.10, 1903, editorial page). 2. "My personal desire would be to prohibit entirely the use of alternating currents. They are as unnecessary as they are dangerous ... I can therefore see no justification for the introduction of a system which has no element of permanency and every element of danger to life and property." (Thomas A. Edison 1889). 3. "I would much prefer to have Goddard interested in real scientific development than to have him interested in more spectacular achievements which are of less real value." (Charles A. Lindbergh to the Guggenheim Foundation, 1936). 4. "The biggest fool thing that we have ever done. The bomb will never go off and I speak as an expert in explosives." (Adm William Leahy to President Truman 1945).
xxii Often of course what scientists say in a paper and what they mean can be light years apart. I am indebted to an extract from the same book as that quoted earlier, viz. "A Random Walk in Science" for the examples of this phenomenon peculiar to research scientists often under severe pressure to generate papers to justify next years funding. When scientists say "A surprising finding" they mean "We barely had time to revise the abstract. Of course we fired the technician." When they say "We have a tentative explanation" they mean " I picked this up in a bull session last night". When they say "We didn't carry out the long-term study" they mean " We like to go home at 5pm. What do you think we are, slaves?" When they say " It is hoped that this work will stimulate further work in the field" they mean "This paper isn't very good but neither are any of the others in this miserable subject". When they say " Thanks are due to Joe Glotz for assistance with the experiments and to John Doe for valuable discussions" they mean that Glotz did all the work and Doe explained what it
meant". Anyone who has organised an International Conference will know that one of the more onerous duties which I am sure must have given Jens and his organising committee not a few sleepless nights is the worry over whether the books will balance at the end of the conference. If there's a problem in this regard then I have some good advice to give Jens - hire an accountant. Usually they don't have such delicate consciences and have incredible abilities at being able to show a loss as an incredible profit. They are masters at the an of manipulating the mass - or in their case money - balance. I think maybe I am being unfairly harsh on accountants and to prove that they are not all scoundrels you may have heard the story of the accountant who passed away and arrived at the gates of heaven. Shortly before he died the Pope died and our accountant friend found himself immediately behind the Pope in queue. When the Pope's turn came for his interview with St. Peter the accountant was astonished to see how roughly the Pope was treated and what poor accommodation he was given. When the accountant's turn came he was understandably very concerned about what his fate would be, especially since he hadn't led the most exemplary life. To his amazement St. Peter gave him royal treatment, laying on a chauffeur, giving him one of the plushest houses high on a hill overlooking, among others, all the popes. When at last he had a chance to speak he turned to St. Peter and expressed his amazement at how well he had been treated compared to the shoddy treatment afforded to the great Pope. To which St. Peter replied: "You know that Pope - we've got many more than 200 of his type up here and so we're used to them. We decided to give you special treatment since we were a little concerned as to how to handle you - you see you're the first accountant we've ever had here!!" Ladies and Gentlemen you will all agree with me that the Organising Committee of this years Conference - Jens Weitkamp, Hellmut Karge, Harry Pfeifer and Wolfgang H61derich - as well
xxiii
as the organisers of the pre-conference summer school - Koos Jansen, Michael StOcker, Gianther Engelhardt and J/Srg Karger - have done a marvellous job and we are all greatly indebted to them for the wonderful arrangements, both scientific and social, which have characterised the 1994 IZC. It crossed my mind that we could have some fun dreaming up appropriate Christmas presents for them and this idea was sparked by an article in the New Scientist in December 1993 in which readers were invited to suggest appropriate Christmas presents for various famous scientists past and present. Some of the more interesting ideas of presents were : 1. For Erwin Schr~dinger
a plain-wrapped gitt box marked "Guess?"
2. For Einstein
a visit by his great great grandchildren and a travelling clock without hands
3. For Stephen Hawking
mints with holes in the middle
4. For Isaac Newton
a crash helmet and an Apple computer
5. For Leonardo da Vinci
the address of a good patent lawyer
6. For the Trojans
an airport luggage scanner
7. For Icarus
some superglue and Araldite
8. For Niccolo Machiavelli
Margaret Thatcher's autobiography
9. For the Xerox R&D team
a very large waste paper basket
10.For Werner Heisenberg
a tie - no - maybe socks -um, I'm not sure??
What about our world of zeolites ..... for the proponents of molecular traffic control a motorbike, a canary for the first man to propose the cage structure? Ladies and Gentlemen before I close I would like to remind you all of the wonders which all experience from time to time of paging through the older volumes of the journals and suddenly coming across forgotten pearls of wisdom. I'm sure that so many of you here tonight who have attended many more Internatiol Zeolite Conferences that most of us, could relate many stories reminding us that much of what we heard this week has been done before. So in closing may I remind you of the intellectual wonders of that wonderful old friend of ours, the dinosaur. This poem first appeared in the Chicago Tribune in about 1920 and was later reprinted in the Journal of the Optical Society of America in May 1964. It is called the Triumph of Reason and was written by Bert Liston Taylor: Behold the mighty dinosaur Famous in pre-historic lore, Not only for his weight and length But for his intellectual strength. You will observe by his remains The creature had two sets of brains One in his head (the usual place), The other at his spinal base.
xxiv Thus he could reason a priori As well as a posteriori. No problem bothered him a bit He made both head and tail of it. So wise was he, so wise and solemn, Each thought filled just a spinal column. If one brain found the pressure strong It passed a few ideas along. If something slipped his forward mind 'Twas rescued by the one behind. And if in error he was caught He had a saving afterthought. As he thought twice before he spoke He had no judgement to revoke. Thus he could think without congestion Upon both sides of every question. Oh, gaze upon this model beast Defunct ten million years at least.
XXV
List of Recent Research Reports I. Synthesis RPO01
Synthesis and Characterization of Zeolites LZ-276 and LZ-277 ............................ 3
M. Sears, G. W. Skeels, E. M. Flanigen, C. A. Bateman, N. McGuire and R. All. Kirchner RP002
Zeolite Nu-1 Prepared from Near-Neutral Fluoride Aluminosilicate Gels .............. 5
RP003
Synthesis and Characterization of Transition-Metal-Incorporated Beta-Zeolites .... 7
J. Patarin, P. Caullet, B. Marler, A. C. Faust and 3,. L. Guth S.-H. Chien, Y. K. Tseng, A&. C. Lin and J. C. Her RP004
Synthesis, Characterization and Structure of SAPO-56, a New Member of the ABC Double-Six Ring Family of Materials with Stacking Sequence AABBCCBB ........................................................................................................
9
S. T. Wilson, N. K. McGuire, C. S. Blackwell, C. A. Bateman and R. M. Kirchner RP005
Synthesis and Characterization of CoAPO / CoAPSO-44 and CoAPO-5 ............. 11
RP006
Synthesis and Sorption Properties of the Zirconium Aluminophosphate Molecular Sieves ZrAPO-5 .................................................................................
U. Lohse, E. L6ffler, B. Parlitz and E. Schreier 13
,I. Kornatowski, M. Rozwadowski, W. Lutz, M. Sychev, G. Pieper, G. Finger and W. H. Baur RP007
Molecular or Supramolecular Templating: Defining the Role of Surfactant Chemistry in the Formation of M41S and Zeolitic Molecular Sieves... 15
J. S. Beck, J. C. Vartuli, G. J. Kennedy, C. T. Kresge, W. J. Roth and S. E. Schramm RP008
Synthesis and Characterization of Boron Containing MCM-41 ............................ 17
U. Oberhagemann, 1. Topalovic, B. Marler and H. Gies RP009
Synthesis of V and Ti Modified MCM-41 Mesoporous Molecular Sieves ............ 19
A. Sayari, K. M. Red@ and1. Moudrakowski RP010
Synthesis of Titanium Molecular Sieve ETS- 10 and ETS-4 ................................. 22
A. Nastro, D. T. Hayhurst and S. M. Kuznicki RP011
Preparation by the Sol-Gel Method of Raw Materials for the Synthesis of Ti Containing Zeolites .............................................................................................
M. A. Uguina, G. Ovejero, R. van Grieken, D. P. Serrano and M. Camacho
24
xxvi RP012
The Synthesis and Structure of a New Layered Aluminium Phosphate [AIaP40~6]3" 3(CH3(CH2)3NH3) +. ......................................................................... 26
A. M. Chippindale, Q. Huo, R. H. Jones, .L. M. Thomas, R. Walton and R. Xu RP013
Synthesis and Characterization of (H3N-(CH2)6-NH3)4~ISP2062], a Dawson-Type Anion in a new Environment ..................................................... 28
M. HOlscher, U. Englert, B. Zibrowius and IV. F. HOlderich RP014
Growth of Zeolite A on Rutile, Sapphire and Quartz ........................................... 30
RP015
Preparation and Properties of Primary Leonhardite, (Na, K)-Exchanged Forms of Laumontite .......................................................................................... 32
RP016
Geoautoclave-Type Zeolitization in the Miocene Tufts, Meczek Mrs., SW-Hungary ......................................................................................................
A. Erdem-Senatalar, H. van Bekkum and j C. Jansen
A. Yamazaki, T. Shiraki, H. lshida and R. Otsuka 34
M. P61gari, 1. F6rizs, M. T6th, E. P~csi-Dondtth and Z. Mdtth~ RP017
The Synthesis of Zeolites from Dry Powders ...................................................... 36
R. Althoff, S. Reitmaier, B. Zibrowius, IE. Schmidt, K. K. Unger and F. Schftth RP018
Synthesis and Crystal Structures of the Decasils, A New Family of Porosils ........ 38
B. Marler, A. Grfmewald-Lftke and H. Gies RP019
New Templates for the Synthesis of Clathrasils ................................................... 40
G. van den Goor, C. Braunbarth, C. C. Freyhardt, J. Felsche and P. Behrens RP020
Synthesis of Zeolites in Anhydrous Glycol Systems ............................................. 42
N. B. Milestone, S. M. Hughesy, P. J. Stonestreet RP021
Synthesis of a Novel Microporous Crystal with Organic Group Covalently Bonded to the Skeleton ..................................................................... 44
K. Maeda, Y. Kiyozumiy, F. Mizukami RP022
Synthesis and Properties of Zeolite A with Salt-Containing Beta-Cages .............. 46
C. Gums, D. Reich, d. C. Buhl and W. Hoffmann
II. C h a r a c t e r i z a t i o n
RP023
Structural Characterization of SSZ-26 and SSZ-33 Molecular Sieves by High Resolution Electron Microscopy and Electron Diffraction .......................... 48
M. Pan and P. A. Crozier RP024
Electron Microscopic Study of Cloverite (CLO) ................................................. 50
0. Terasaki, T. Ohsuna, D. Watanabe, H. Kessler and C Schott-Darie RP025
HRM
Study of Pt-clusters on K-LTL Crystal Surfaces ..................................... 52
0. Terasaki, T. Ohsuna and D. Watanabe
~ XXVll
RP026
Location of Tb(III) Ions in Hydrated Y Zeolites by Luminescence Spectroscopy ......................................................................................................
54
J. S. Seo, C.-H. Pyun, C.-H. Kim, Y. S. Uh, W. S. Ahn and S. B. Hong RP027
Localization of Pt 2§ in NaX ................................................................................. 56
t~ Schnell, C Kirschhock and H. Fuess RP028
Characterization of SO2-Contaminated Cu-ZSM-5 Catalysts ............................... 58
C. L. Lengauer, E. Tillmanns and C. Plog RP029
Single Crystal Structure Analysis and Energy Minimizations of a HoZSM-5/p-Dichlorobenzene Complex at Low Sorbate Loading ...................... 61
H. van Koningsveld, J. C Jansen and A. J. M. de Man RP030
Single Crystal Structure Analysis of a High-Loaded Complex of H-ZSM-5 with p-Dichlorobenzene ...................................................................... 63
H. van Koningsveld and J. C. Jansen RP031
Characterization of Bimetallic Zeolite Supported Pt-Pd Catalyst by EXAFS, TEM and TPR ......................................................................................
65
T. Rades, M. Polisset-Thfom, J. Fraissard, R. Ryoo and C. Pak RP032
SIMS Investigation on Vanadium-Zeolite Interactions in Cracking Catalysts ....... 67
RP033
XPS and Adsorption of Dinitrogen Studies on Copper-Ion-Exchanged ZSM-5 and Y Zeolites ........................................................................................
K.-J. Chao, L.-H. Lin and L.-K Hon 69
G. Moretti, G. Minelli, P. Porta, P. Ciamelli and P. Corbo RP034
Model of adsorbed NO Molecules on Lewis Sites in Zeolites .............................. 71
A. Gutsze, M. Plato, F. Witzel and H. G. Karge RP035
A Combined EPR and NMR Study of Oxidation Sites in Dealuminated Mordenites .........................................................................................................
73
G. H. Estermannn, R. Crockett and E. Roduner RP036
Study ofNi-Containing SAPO-5 by ESR Spectroscopy and Hydrogenolysis of Thiophene ............................................................................. 75
A. Spojakina, N. Kostova and K Penchev RP037
Electron Spin Resonance and Electron Spin Echo Modulation in Spectroscopic Study of Pd(I) Location and Adsorbate Interactions in PdH-SAPO-34 Molecular Sieve .......................................................................... 77
RP038
Stability of the Co(II) Valence State in Aluminophosphate-5 Molecular Sieve to Calcination from Low Temperature Electron Spin Resonance ....................................................................................
J.-S. Yu, G.-H. Back, K Kurshev and L. Kevan
79
V. Kurshev, L. Kevan, D. Parillo and R. Gorte RP039
Characterization of Alkali Metal Cluster-Containing Faujasites by Thermal, IR, ESR, Multi-NMR and Test Reaction Studies .................................. 81
1. Hannus, 1. Kiricsi, A. Bdres, J. B. Nagy and H. FOrster
o~176 XXVlll
RP040
A Study of Cu-Y and Cu-Rho Zeolites by ~Z~ N-MR........................................ 83
A. G~d~on, J. Fraissard RP041
Direct Observation of Distributions of Mixed Clusters of Coadsorbed Species in Zeolite NaA ....................................................................................... 85
A. K. Jameson, C. J. Jameson, A. C. de Dios, E. Oldfield and R. E. Gerald H RP042
Studies on the Formation and Structure of the Molecular Cluster of (CdS)4 in Zeolite Y by in-situ IR and ~3Cd MAS NMR ..................................................... 87
RP043
NMR Studies of Hydrofluorocarbon-Zeolite Interactions .................................... 89
M. Qi, Z. Xue, Y. Zhang and Q. Li C. P. Grey and D. R. Corbm RP044
Aluminium-27 Double-Rotation NMR Investigations of SAPO-5 with Variable Silicon Content ................................................................................................... 91
M. Janicke, B. F. Chmelka, D. Demuth and F. Schflth RP045
29Si and 27A1MAS NMR Studies ofFaujasite / Gallium Oxide Catalysts ............. 93
Z. Olejniczak, S. Sagnowski, B. Sulikowski and J. Ptaszynski RP046
A New Assignment of the Signals in ~Na DOR NMR to Sodium Sites in Dehydrated NaY Zeolite .................................................................................... 95
H. A. M. Verhulst, W. J. J. Welters, G. Vorbeck, L. J. M. van de Ven, V. H. J. de Beer, R. A. van Santen and J. W. de Haan RP047
Study of Mordenite Acidity by 1H NMR Techniques: Broad-Line at 4K and High Resolution MAS at 300K. Comparison with HY. Bronsted Acidity Scale and Importance of Structure Defects ............................................. 97
L. Heeribout, V. Semmer, P. Batamack, C. Dor~mieux-Morin and J. Fraissard RP048
Spectroscopic Evaluation of the Relative Acidity of the Bridged Hydroxyl Species in Zeolites and the Isolated Hydroxyl Species in Amorphous Silica ............................................................................................... 99
E. Garrone, B. Onida, G. Spano, G. Spoto, P. Ugliengo and A. Zecchina RP049
One-Point Method for the Determination of Strength of Zeolite Acidity by Temperature Programmed Desorption of Ammonia Based on Trouton's Rule... 101
M. Niwa, N. Katada, M. Sawa and Y. Murakami RP050
Interaction of CO, H20, CH3OI-I, (CHH)20, CH3CN, H2S, (CH3)2CO, NH3 and Py with Brensted Acid Sites of H-ZSM-5" Comparison of the IR Manifestation .................................................................................................... 104
R. Buzzoni, S. Bordiga, G. Spoto, D. Scarano, G. Ricchiardi, C. Lamberti and A. Zecchina RP051
IR Characterization of Hydroxyl Groups in SAPO-40 ....................................... 106
E. Garrone, B. Onida, Z. Gabelica and E. G. Derouane
xxix RP052
FTIR Evidence ofPt Carbonyls Formation from Pt Metal Clusters in KL Zeolite ........................................................................................................
108
A. Yu. Stakheev, E. S. Shpiro, N. 1. Jaeger and G. Schulz-Ekloff RP053
IR Spectra of ~SO Exchanged HZSM-5 ............................................................. 110
F. Bauer, E. Geidel and Ch. Peuker RP054
Structure and Reactivity of Framework and Extraframework Iron in Fe-Silicalite as Investigated By Optical (IR, Ramart, DRS, UV-VIS) and EPR Spectroscopies .........................................................................................
112
F. Geobaldo, S. Bordiga, G. Spoto, D. Scarano, A. Zecchina, G. Petrini, G. Leofanti, G. Tozzola and M. Padovan RP055
Electrochemistry of Transition Metal Complexes Encapsulated into Zeolites ..... 114
C. A. Bessel and D. R. Rolison
I I I . Modification RP056
Structure and Properties of Active Species in Zinc Promoted H-ZSM-5 Catalysts ..........................................................................................
116
H. Berndt, G. Lietz, B. Lftcke and J. VOlter RP057
FT IR and FT Raman Studies of [B, Al]-Beta + Ga203 System ......................... 118
M. Derewinski, J. Krysciak, Z. Olejniczak, ,I. Ptaszynski and B. Sulikowski RP058
Faujasite-Hosted Nickel-Salen ..........................................................................
120
H. Meyer zu Altenschildesche and R. Nesper RP059
Modification of Aluminophosphate Molecular Sieves by Reaction with Organopalladium Complexes ............................................................................
122
K. M. Tearle and J. M. Corker RP060
Zeolite-Stabilized Rhodium Complexes with Molecular Nitrogen as Ligand ...... 124
H. Miessner RP061
Intrazeolitic Redox Chemistry of Manganese Prepared from Chemical Vapor Deposition of Mn2(CO)~0 on NaY .......................................................... 126
C. Dossi, S. Recchia, A. Fusi and R. Psaro RP062
Calcination of Pd(NH3)42§ and Reduction to Pd ~ in NaX and CsX Zeolites ........ 129
A. Sauvage, P. MassianL M. Briend, D. Barthomeuf and F. BozonVerduraz RP063
Ion Exchange in CoAPO-34 and CoAPO-44 ..................................................... 131
C. G. M. Jones, P~ Harjula and A. Dyer RP064
Characterization of ZSM-5 Samples Modified by Ions of Group IIIA ................ 133
L. Frunza, R. Russu, G. Catana, K Parvulescu, G. Gheorghe, F. Constantinescu and K 1. Parvulescu
XXX
RP065
Formation of Small Na and Na-M Alloys (M=Cs, Rb) Panicles in NaY Zeolite ...................................................................................................... 136
L. C. de M~norval, E. Trescos, F. Rachdi, F. Fajula, T. Nunes and G. Feio RP066
Attachment and Reactivity of Tin-Cobalt and Tin-Molybdenum Complexes in Y Zeolites and MCM-41 ............................................................................... 13 8
C. Huber, C. G. Wu, K. Moiler and T. Bein RP067
Simultaneous Exchange and Extrusion of Metal Exchanged Zeolites ................. 140
s N. Armor and T. S. Farris RP068
Modification of Layer Compounds for Molecular Recognition .......................... 142
T. Uematsu, M. lwai, N. lchilcuni and S. Shimazu
IV. Catalysis RP069
H-[B]-ZSM-5 as Catalyst for Methanol Reactions ............................................ 144
RP071
NOx Reduction with Ammonia over Cerium Exchanged Mordenite in the Presence of Oxygen. An IR Mechanistic Study ............................................ 146
E. Unneberg and S. Kolboe
E. Ito, E J. Mergler, B. E. Nieuwenhuys, P. M. Lugt, H. van Bekkum and C. 3/1. van den Bleek RP072
Catalytic Activity and Active Sites in Zeolite Catalysts for N20 Decomposition ................................................................................................. 148
E. B. Uvarova, S. A. Stakheev, L. M. Kustov and V. V. Brei RP073
Role of the Preparation and Nature of Zeolite on the Activity of Cu-Exchanged MFI for NO Conversion by Hydrocarbons and Oxygen ............. 150
G. Centi, S. Perathoner and L. Dall'Olio RP074
Selective Photooxidation of Abundant Hydrocarbons by 02 in Zeolites with Visible Light ..................................................................................................... 153
F. Blatter, H. Sun and H. Frei RP075
Applications of VAPO-5 in Liquid Phase Oxidation Reactions: Indications for the Presence of Different Vanadium Sites .................................................... 155
M. J. Haanepen and J.H. C. van Hooff RP076
Oxidation of Primary Amines over Titanium and Vanadium Silicates: Solvent Effect ................................................................................................... 157
d. S. Red@ and A. Sayari RP077
Room Temperature Oxidation of Methane to Methanol on FeZSM-5 Zeolite Surface ................................................................................................. 159
V. L Sobolev, A. S. Kharitonov, O. V. Parma and G. L Panov
xxxi
RP078
Oxidation and Ammoxidation of Picolines over VSAPO Molecular Sieves ........ 161
S. J. Kulkarni, R. Ramachandra Rao, M. S. Farsinavis, P. Kanta Rao and A. K Rama Rao RP079
Subrahmanyam,
Transition Metal Cations in Zeolites - a Catalyst for HDS Reactions ................. 163
R. Lugstein, O. E1Dusouqui, A. Jentys and H. Vinek RP080
A New Coupling Reaction Between ~-Pinene and Acetone Catalyzed by Beta Zeolites ................................................................................................ 165
J. Vital, J. C. van der Waal and H. van Bekkum RP081
Catalysis of a Liquid-Phase Diels-Alder-Reaction by Zeolites Y, A and Beta ..... 167
K. Bornholdt and H. Lechert RP082
Isomerization of n-Hexane over Platinum Loaded Zeolites ................................ 169
J.-K. Lee and H.-K. Rhee RP083
Benzene Alkylation with Ethanol over Shape Selective Zeolite Catalysts ........... 171
RP084
Effect of Aluminum Content at the External Surface of the ZSM-5 in the Disproportionation of Ethylbenzene .................................................................. 174
RP085
Methanol Conversion to Hydrocarbons over ZSM-5. Use of Isotopes for Mechanism Studies ........................................................................................... 176
RP086
Fischer-Tropsch Synthesis on Ruthenium Supported Titanium Silicate Catalysts .............................................................................................. 178
R. Ganti and S. Bhatia
M. J. B. Cardoso, E. L. Gomes and D. Cardoso
I. M. DaM, S. Kolboe and P. O. Ronning
R. Carli, C. L. Bianchi, R. Bernasconi, G. Frontini and K Ragami RP087
Synthesis and Catalytic Properties of Extra-Large Pore Crystalline Materials for n-Hexadecane Cracking ............................................................... 180
W. Reschetilowski, K. Roos, A. Liepold, M. StOcker, R. Schmidt, A. Karlsson, D. Akporiaye and E. MyhrvoM RP088
Conversion of Ethane into Aromatic Hydrocarbons on Zinc Containing ZSM-5 Zeolites - Role of Active Centers .......................................................... 182
A. Hagen and F. Roessner RP089
Conversion of n-Butane into Aromatic Hydrocarbons over H-ZSM-11 and Ga-ZSM-11 Zeolite Catalysts ................................................... 184
N. Kumar and L.-E. Lindfors RP090
Highly Dispersed Platinum Clusters in Zeolite Beta: Synthesis, Characterization and Catalysis in Liquid-Phase Hydrogenations ........................ 186
E. J. Creyghton, R. A. W. Grotenbreg, R. S. Downing and H. van Bekkum
xxxii RP091
The Effect of the Outer Surface Silylation on the Catalytic Properties ofFeZSM-11 .................................................................................................... 188
L. K Piryutko, 0. 0. Parenago, E. K Lunina, A. S. Kharitonov, L. G. Okkel and G. 1. Panov RP092
Hydrolysis of Disaccharides by Dealuminated Y-Zeolites .................................. 190
RP093
Adsorption and Catalysis Mechanism of CFC- 11 in NaX Zeolite ....................... 192
C. Buttersack and D. Laketic M. Hiraiwa, A. Yamazal#, R. Otsuka and T. Nagoya RP094
Effect of Basicity on the Catalytic Properties of Lead Containing Zeolites ......... 194
P. Kovacheva and N. Davidova RP095
Physico-Chemical and Catalytic Properties of Y Zeolites with High Modulus Obtained by Direct Synthesis. Preparation of Pilot Lot of NaY Zeolite with High Modulus ............................. 196
M. L Levinbuk, M. L. Pavlov, K B. Melnikov, B. K Romanovsky, Y. L Azimova and Y. A. Smorodinska
V. Adsorption and Diffusion RP096
Counter Diffusion of C8 Aromatics in Y Zeolite Pellets ..................................... 198
RP097
Motion of Cyclohexane in Compacted Zeolite NaX .......................................... 200
V. Moya Korchi and A. Methivier R. Stoclameyer
RP098
Mobility of Methane in Zeolite NaY: A Quasi-Elastic Neutron Scattering Study ............................................................................................... 202
H. Jobic and M. Bee RP099
Measurement of Diffusivity of Benzene in a Microporous Membrane by Quasi-Elastic Neutron Scattering and NMR Pulsed-Field Gradient Technique... 204
H. Jobic, M. Bee, J. Kdrger, C. Balzer and A. Julbe RP100
Zeolite MAP: A New Detergent Builder ........................................................... 206
C. J. Adams, A. Araya, S. I~. Carr, A. P. Chapple, P. Graham, A. R. Minihan and T. J. Osinga RP101
Use of Natural Zeolites for Liquid Radioactive Waste Treatment (Russian Experience) ........................................................................................ 208
N. F. Chelishchev RP102
Selectivity for Different Cations of Zeolite-Containing Hydrothermally Treated Fly Ash ................................................................................................ 211
K Berkgaut and A. Singer RP103
Experimental and Theoretical Studies of Water and Sulfur Dioxide Selective Adsorption in 3 A Zeolites .................................................................. 213
K. M. Shaw, M. Eic and R. Desai
xxxiii RP104
Permeation and Separation Behaviour of a Silicalite (MFI) Membrane .............. 215
F. Kapteijn, W. ,1. W. Bakker, G. Zheng, ,I. A. Moulijn and H. van Bekkum RP105
Adsorption and Polarization of Molecular Hydrogen and Light Paraffins on Cationic Forms ofZeolites: IR-Spectroscopic Study .................................... 217
L. A4. Kustov, V. B. Kazansky and A. Y. Khodakov RP106
Promising Air Purifications on Clinoptilolite ..................................................... 219
RP107
Mass Transfer Kinetics Measurements by Thermal Frequency Response Method ............................................................................................. 221
RP108
Study of Fast Diffusion in Zeolites Using Higher Harmonic Frequency Response Method ............................................................................ 223
R. W. Triebe, F. H. Tezel, A. Erdem-Senatalar and A. Sirkecioglu
V. Bourdin and Ph. Grenier
D. Shen and L. V. C. Rees RP109
Purification of Horseradish Peroxidase by the Use of Hydrophobic Zeolite Y .... 225
D. Klint, Z. Blum and H. Eriksson
VI. Theory and Modelling RPll0
Modelling Sorption in Zeolite NaA with Molecular Density Functional Theory ............................................................................................ 227
M. C. Mitchell, P. R. van Tassel, A. V. McCormick and H. T. Davis RPIll
Evaluation of Water Adsorption on Different Kinds of Zeolite through the Monte-Carlo Simulation ................................................................. 229
T. Inui, Y. Tanaka RPll2
Modelling Structural and Dynamical Properties of Silica Sodalites and Comparison to the Experiment ......................................................................... 232
RPll3
Computer Modelling of Iron-Containing Zeolites .............................................. 234
A. M. Schneider, J. Felsche and P. Behrens 17. G. Bell, D. W. Lewis and C. R. A. Catlow RPll4
Theoretical Investigation of the Thermal Decomposition of Neopentane near SIII Centers of Zeolite Y ........................................................................... 236
O. Zakharieva, M. Grodzicki and H. FOrster RPll5
Modelling of High Pressure Propene Oligomerisation Using Skeletal Groups ................................................................................................ 238
S. ,I. Seal),, D. M. Fraser and C. T. O'Connor RPll6
Investigation of the Dynamics of Benzene in Silicalite using Transition-State Theory .................................................................................... 240
R. Q. Snurr, A. T. Bell and D. N. Theodorou
xxxiv
RPII7
Ab Initio Study of the Interaction of Methanol with Bronsted Acid Sites of Zeolites ............................................................................................................ 242
RPll8
Ab Initio Derived Shell Model Potential for Modelling of Zeolites .................... 244
F. Haase and J. Sauer K.-P. Schrrder and J. Sauer RPll9
A Computer Simulation of Shape Selective Catalysis on Zeolites ...................... 246
E. Klemm, H. Seller and G. Emig RP120
Molecular Dynamic and Structural Studies of the Interactions of HFC-134 and CFC-13 with the Faujasite Framework ........................................ 248
J. P. Parise, L. Abrams, J. C. Calabrese, D. R. Corbin, J. M. Newsam, S. Levine and C. Freeman
VII. Structure RP121
The Framework Topology of Zeolite MCM-22 ................................................. 250
,I. A. Lawton, S. L. Lawton, M. E. Leonowicz and M. K. Rubin RP122
Optical Investigations of the Crystal Intergrowth Effects of the Zeolites ZSM-5 and ZSM-8 ........................................................................................... 252
C. Weidenthaler, R. X. Fischer, R. D. Shannon and O. Medenbach RP123
Is the VFI Topology Compatible with Tetrahedral AI? ...................................... 254
J. de Ohate, C. Baerlocher and L. McCusker RP124
Rietveld Refinement of the Tetragonal Variant of AIPO4-16 Prepared in Fluoride Medium ............................................................................ 256
J. Patarin, C. Schott-Darie, P. Y. Le Goff, H. Kessler and E. Benazzi RP125
Structure of the Microporous Titanosilicate ETS- 10 ......................................... 258
M. W. Anderson, O. Terasaki, T. Ohsuna, A. Philippou, S. P. MacKay, A. Ferreira, J. Rocha and S. Lidin RP126
Avoidance of 2 AI Atoms in a 5-Ring. A New Rule Complementing Loewenstein's Rule .............................................. 260
M. Kato, H. Araki and K. Itabashi RP127
The Crystal Structure of the New Boron Containing Zeolite RUB-13 ............... 262
S. Vortmann, B. Marler, P. Daniels, L Dierdorf and H. Gies RP128
Synthesis and Structure of a Novel Microporous Gallophosphate: Na2Gas(PO4)40(OH)3-4H20 ............................................................................. 264
M. P. Attfield, R. E. Morris, E. Gutierrez-Puebla, A. Monge-Bravo and A. K. Cheetham RP129
Structure Determination from Powder Diffraction Data of a New Clathrasil, TMA Silicate ................................................................................... 266
R. W. Broach, N. K. McGuire, C. C. Chao and R. M. Kirchner
XXXV
RP130
The Pore Structure of Alumina Pillared Clays Depending on the Kind of Intercalated Al-Cation ...................................................................................... 268
V. Seefeld, R. Trettin and W.. Gessner RP131
Synthesis and Structure Determination of a New Aluminophosphate from Fluoride Medium .............................................................................................. 270
N. Zabukovec, L. Golic and V. Kaucic RP132
04 Molecule in the Pore of Ca~-A Zeolite ......................................................... 272
T. Takaishi RP133
Structure and proper/ies of Cd4Se6+Nano Clusters Encapsulated in an Aluminate Framework .................................................................................. 274
E. Brenchley and3~1. T. Weller
VIII. New Materials RP134
A New One-Dimensional-Membrane: Aligned A1PO4-5 Molecular Sieve Crystals in a Nickel Foil ........................................................................... 276
M. Noack, P. K61sch, D. Venzke, P. Toussaint and J. Caro RP135
Synthesis of a Zeolite Membrane on the Mercury Surface ................................. 278
Y. KiyozumL K. Maeda and F. Mizukami RP136
Molecular Recognition in Zeolite Thin Film Sensors. Growth of Oriented Zeolite Films ...................................................................................... 281
S. Feng, Y. Yah and T. Bern RP137
Phase Formations in the Sinter Process of Cordierite / Mullite Ceramics from Mg-Exchanged Zeolites A, P and X ......................................................... 283
B. Rfldinger and R.X. Fischer RP138
Silicalite with Polycyanogene ............................................................................ 285
Y. Schumacher and R. Nesper
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Recent Research Reports
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1. Synthesis
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H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
SYNTHESIS
M
9
Sears I !
~UOP,
G
AND
W
9
Tarrytown
2Dow C h e m i c a l 3Manhattan
9
CHARACTERIZATION
OF
ZEOLITES
Skeels I, E M Flanigen I C A and R.M. K i r c h n e r 3 9
Technical
Co.,
College,
1702
9
,
Center,
Building,
Department
9
Tarrytown, Midland,
MI
of Chemistry,
LZ-276
9
NY
AND
LZ-277
B a t e m a n I, N
.
M c G u i r e 2,
10591
48674 Bronx,
NY
ABSTRACT
A new zeolite, p o s s i b l y r e l a t e d to z e o l i t e Phi, has b e e n s y n t h e s i z e d in an o r g a n i c s y s t e m by m o d i f y i n g ~he p r o c e d u r e of J a c o b s and M a r t e n s for the s y n t h e s i s of z e o l i t e Phi. I, A more siliceous zeolite, d e s i g n a t e d LZ-276, can be p r o d u c e d from the same s y n t h e s i s gel by v a r y i n g c r y s t a l l i z a t i o n t e m p e r a t u r e 9 U l t i m a t e l y , a P h i - l i k e z e o l i t e was s y n t h e s i z e d in a t o t a l l y i n o r g a n i c s y s t e m w i t h p r o p e r t i e s ~ i m i l a r to LZ-276. This p r o d u c t was d e s i g n a t e d LZ-277. The c h e m i c a l and p h y s l c a i p r o p e r t i e s ~f LZ-276 ~nd LZ-277 are p r e s e n t e d and c o m p a r e d co the p r o d u c ~ d e s c r i b e d ~s z e o l i t e Phi by G r o s e and F l a n i g e n I and others. 2'3'4'5 INTRODUCTION
The f i r s t s y n t h e s i s of zeolite Phi u s e d a c i d - e x t r a c t e d , calcined c h a b a z i t e as the s i l i c a and a l u m i n a s o u r c e and t e t r a m e t h y l a m m o n i u m h y d r o x i d e as the o r g a n i c base. I The p r o d u c t was c h a r a c t e r i z e d as a l a r g e - p o r e z e o l i t e b a s e d on a d s o r p t i o n data b e c a u s e b o t h n e o p e n t a n e (6.2A radius) and p e r f l u o r o b u t y l a m i n e (10.2A) w e r e a d s o r b e d 9 The SiO2/Al203 r a t i o of the Phi p r o d u c t was 4.6. J a c o b s and M a r t e n s i n a d v e r t e n t l y m a d e Phi in t h e i r a t t e m p t to s y n t h e s i z e ZSM-20. 2 From c a t a l y t i c data, t h e y s u g g e s t e d t h a t t h e i r p r o d u c t was c o n s i s t e n t w i t h a l a r g e - p o r e m a t e r i a l 9 S y n t h e s i s of z e o l i t e Phi was also r e p o r t e d by Li et al. u s i n g t e t r a m e t h y l a m m o n i u m h y d r o x i d e and w a t e r g l a s s . 3 Franc. et al. s y n t h e s i z e d z e o l i t e Phi from a gel t h a t was s i m i l a r to that of J a c o b s and M a r t e n s but it a l s o c o n t a i n e d K§ 4 M. Davis et al. have also r e p r o d u c e d the J a c o b s and M a r t e n s and the F r a n c . et al. s y n t h e s e s of z e o l i t e Phi. 5 EXPERIMENTAL
The
synthesis 16.6SIO2
gel for LZ-276 is as follows: 9 A1203 : 7.8(TEA) 2~ : 1.3Na20
It d i f f e r s f r o m that 2 0 S i O 2 : AI203
: 465H2 O
s u g g e s t e d by J a c o b s and M a r t e n s , 9 9.3(TEA)2 9 : l.iNa20 : 558H20.
which
was:
The
gel
ratio
for LZ-277
is"
8SiO 2
9 AI203
: 1.6Na20
9 256H20
The LZ-276 gels were c r y s t a l l i z e d in T e f l o n - l i n e d s t a i n l e s s steel a u t o c l a v e s at both 100~ and" 125~ for from 1-21 days. The L Z - 2 7 7 gels were c r y s t a l l i z e d in Teflon bottles at 100~ for up to 45 days. A f t e r c r y s t a l l i z a t i o n , the samples were filtered, w a s h e d w i t h d e i o n i z e d water, and dried at room temperature. S y n c h r o t r o n X - r a y p o w d e r d i f f r a c t i o n and e l e c t r o n m i c r o s c o p y were used to c h a r a c t e r i z e the m a t e r i a l s . RESULTS
AND
DISCUSSION
W h e n c r y s t a l l i z e d at 100~ LZ-276 had a SIO2/A1203 r a t i o of 5.0. At 125~ the SIO2/A1203 ratio i n c r e a s e d to 7.7. W h e n c r y s t a l l i z e d at 100~ LZ-277 had a SiO2/AI203 ratio of 6.9. Adsorption measurements on both p r o d u c t s showed them to be small to m e d i u m p o r e m a t e r i a l s thal a d m i t t e d n - h y d r o c a r b o n s and r e j e c t e d the b r a n c h e d - c h a i n h y d r o c a r b o n s . The X - r a y p o w d e r d i f f r a c t i o n p a t t e r n s showed both b r o a d and sharp r e f l e c t i o n s for each synthesis product. R e l a t i v e i n t e n s i t i e s are quite d i f f e r e n t b e t w e e n the samples s y n t h e s i z e d at 100~ and 125~ and they are also d i f f e r e n t from the r e p o r t e d values of G r o s e and Flanigen, Li et al., and Franco et al. A l t h o u g h the X - r a y p o w d e r p a t t e r n s of all of the r e p o r t e d p r o d u c t s have many s i m i l a r d ( A ) spacings, they are not identical in size or shape. A d d i t i o n a l l y , the Franco et al. X-ray d i f f r a c t i o n p a t t e r n showed the p r e s e n c e of a second i m p u r i t y phase, a p o t a s s i u m a l u m i n o s i l i c a t e h a v i n g the X - C H A type structure. TEM-esuits 9n "Z-277 show the m a t e r i a l to be a x t r e m e l y faulted along c. A model for a highly faulted c h a b a z i t e ~as used in c o n j u n c t i o n w i t h the DIFFAX program. 6 A s i m u l a t e d p o w d e r d i f f r a c t i o n p a t t e r n u s i n g the DIFFAX program, c l o s e l y m a t c h e s the e x p e r i m e n t a l LZ276 and LZ-277 S y n c h r o t r o n data. CONCLUSIONS
A l t h o u g h a r e l a t i o n s h i p appears to exist b e t w e e n all of the m a t e r i a l s that are reviewed, there are d i s t i n c t i v e p r o p e r t y differences. Among these d i f f e r e n c e s are the t h e r m a l and h y d r o t h e r m a J stability, and the a d s o r p t i o n p r o p e r t i e s i n c l u d i n g pore size. However, it a p p e a r s that all of these m a t e r i a l s are v a r i a t i o n s of h i g h l y f a u l t e d chabazite. REFERENCES
I. Grose, R.W., and Flanigen, E . M . U . S . Pat. 4 124 686 (1978). 2. Jacobs, P.A., and Martens, J.A. Stud. Surf. Sci. Catal., 1987, 33, 15. 3. Li, H.Y., L i a n g J., Liu G.Y., and Ying M.L., Shiyou H u a q o n g ( P e t r o l e u m C h e m i c a l Engineering) 1990, 19, 148. 4. Franco, M.J., and P e r e z - P a r i e n t e , J. Zeolites 1991, ii, 349. 5. Davis, M.E., Lobo, R.F., and Annen, M . J . J . Chem. Soc. F a r a d a y Trans., 1992, 88(18), 2791. 6. Treacy, M.M.J., Deem, M.W., and Newsam, J.M., D I F F a X vi.76, (1991).
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
Zeolite Nu-1 prepared from near-neutral fluoride aluminosilicate gels J. Patarin, P. Caullet, B. Marler*, A.C. Faust and J.L. Guth Laboratoire de Mat6daux Min~raux URA-CNRS428 ENSCMU - UHA, 3, rue Alfred Werner, 68093 MULHOUSE Cedex, France * institut fQr Mineralogie, Ruhr Universit&t Bochum D-44780 Bochum, Germany SUMMARY The preparation of zeolite Nu-1 from near-neutral (pH ~8-10) fluoride-containing media was found to be only possible in a very narrow range of experimental conditions. The crystals display a pseudo-cubic morphology, with in some cases a size up to 40 I~m. The materials were characterized by conventional techniques. Three 19F nmr signals may be attributed to more or less mobile F- anions incorporated into the structure of Nu-1. INTRODUCTION This work deals with the synthesis and characterization of zeolite Nu-11 from nearneutral synthesis media containing F- ions. The organic templating agent is the usual Me4N + ion. The F- ions replace here the usual OH- ions as the mineralizing agents, according to the method developped in our laboratory 2. EXPERIMENTAL The starting mixture was prepared by first dissolving TMACI and NH4F in water. The combined or separated sources of alumina and silica were then added under stirring.After mixing, the reaction mixture (pH ~ 8-10) was transferred into a Teflon-lined stainless-steel autoclave and heated under static conditions at the desired temperature. After reaction (pH ~ 8-10), the products were filtered and washed with water and sometimes sonicated in order to separate the two main populations, i.e., MTN-type and Nu-1 crystals. After drying, the materials were checked by optical microscopy and powder X-ray diffraction before additional characterizations. RESULTS AND DISCUSSION
Influence of starting composition, temperature and heating time The preparation of pure zeolite Nu-l(experiment 1,Table 1) is only possible in a very narrow range of experimental conditions. Co-crystallisation of MTN-type clathrasil is most often observed.As previously seen for other phases synthesized from fluoride-containing media, the crystals(twinned) of zeolite Nu-l(Sample no.2) obtained here(Figure 1) are very large (20-501~m) in comparison to those prepared from alkaline fluoride-free gels (1-51~m).
Characterization of zeolite Nu- 1 A typical molar composition determined by chemical analysis is (Me4N+)1.25 (Me3NH+)o.29 (AIO2-) (SiO2)13.3.(F')o.41 .The organic species content was
determined from 1H liquid nmr spectroscopy after dissolution of the solid in HF. The presence of Me3NH + ions beside the Me4N + cations is clue to the hydrothermal decomposition of the latter. It appears that only part of the organic cations compensate the negative charges of the tetrahedrally coordinated aluminium atoms, the excess of cations being probably associated with the F- anions in ion-pairs. Table 1 : Description of the most representative syntheses (Starting molar ratio Me4NCI/SiO2=0.5 and NH4F/SiO2=I ) Exp. Mixture(molar ratios) T Time' Produ~s .... Crystal size (~ (d) (minor phases )* of Nu-1 (l~m) No. SIO2/AI203 H20/SiO2 1 16.7 9 170 5 Nu-1 20 2 16.7 9 170 42 MTN + (Nu-1)* 40 3 16.7 30 170 9 MTN + (Nu-1)* 20 4 16.7 9 200 1 MTN + / (NH4)3AIF6) ~ 5 16.7 9 200 3 FER + MTN / 6 _>25 9 170 6 MTN / The typical 19F nmr spectrum shown in Figure 2 (Sample no.2) displays several peaks. The broad signal located at about -140 ppm is attributed to the (NH4)3AIF6 impurity. not observed by XRD.The presence of such an impurity is confirmed by the corresponding 27AI MAS nmr spectrum ;indeed a very small signal at 0 ppm (hexacoordinated AI) is detected besides the main peak at 51 ppm (tetracoordinated AI). The other 19 F nmr signals at -116 (narrow), -73 (broad) and -58 (broad) ppm may be attributed to more or less mobile F- anions incorporated into the structure of Nu-l.Complete removal of the occluded organics is difficult to achieve by calcination. A partial collapse of the structure occurs after heating at 700~
-/,0
Figure 1. Micrograph of Nu-1
- 80
- 120
-
ppm / C FC 13
160
Figure 2. 19F nmr spectrum of Nu-1. 9side bands
REFERENCES
1 - Whittam, T.V. and Youll, B., US Pat. 4060590 (1977) assigned to ICI 2 - Guth, J.L. et al., in New Developments in Zeolite Science and Technology (Eds. Y. Murakami, A. lijima and J.W. Ward), Elsevier, Amsterdam, 1986, p. 121
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
SYNTHESIS AND C H A R A C T E R I Z A T I O N OF TRANSITION-METALI N C O R P O R A T E D BETA-ZEOLITES Shu-Hua ChiCn*, Yung-Kuan Tseng, Maw-Chen Lin and Jen-Cheng Ho Institute of Chemistry, Academia Sinica, Taipei 11529, Taiwan, ROC. SUMMARY. The incorporation of transition-metal ions in Beta-zeolite was carried out by direct hydrothermal synthesis. The synthesized zeolites (H-, Ti- and V-Beta) were characterized by powder X-ray diffraction (XRD), scanning electron microscopy with x-ray energy dispersive analyzer (SEM/EDS), infrared (IR), UV-visible and electron paramagnetic resonance (EPR) spectroscopies. Both XRD and IR spectroscopic studies confirmed that the synthesized Ti-Beta carried out isomorphous substitution of Si by Ti in the Beta-zeolite framework. In case of V-Beta, the EPR studies evidenced the formation of VO 2+ species that seem to be located at the cation sites of the zeolites. INTRODUCTION.
The composite metal oxide-zeolite materials have attracted
attention because of their application as bifunctional catalysts. Due to their reducibility and notable catalytic properties, the zeolites with incorporated titanium and vanadium are of particular interest. The aims of the present study are to synthesize large pore titanium- and vanadium- containing Beta-zeolites by direct hydrothermal method, and to well characterize the synthesized materials for the promising catalytic selective oxidation reactions. EXPERIMENTAL. The transition-metal containing Beta-zeolites (V-Beta and TiBeta) were synthesized by direct hydrothermal method, using tetraethyl ammonium hydroxide (TEA-OH),
amorphous Aerosil silica, aluminum nitrate, and
tetrabutylorthotitanate or vanadium oxide. The procedures were as follows: an aqueous solution of tetrabutylorthotitanate (or vanadium oxide) was oxidized by hydrogen peroxide first, then added with the aqueous solution of TEA-OH, Aerosil silica and finally aluminum nitrate. The mixture was stirred in a water-bath at 80oc for 30 minutes before transferring to an autoclave, which was then heated in an oven at 140oc for 20 days. After cooling the autoclave, the sample was centrifuged at 10000 rpm, the solid was calcined at 550oc. The synthesized zeolites were well characterized by XRD, SEM/EDS, IR, Uv-vis and EPR spectroscopies. The atomic ratios in the three samples are as follows: A1/Si = 1/30 in H-Beta zeolites, Ti/AI/Si = 1/1/30 in Ti-Beta and V/AI/Si = 2/1/30 in V-Beta. RESULTS AND DISCUSSION.
We have successfully synthesized the H-form
(H-Beta), Ti- and V- containing Beta (Ti-Beta and V-Beta) zeolites
by direct
hydrothermal method with A1/Si atomic ratio = 1/30. The powder x-ray diffraction
patterns of the three samples show good crystalline structures in Beta-form zeolites. The SEM micrographs of the three samples exhibit almost the same morphologies of cubic shapes. The average particle sizes are about 0.6 lam, no visible differences among the three. For the synthesized Ti-Beta zeolite, there appears isomorphous substitution of Si by Ti in the zeolite Beta framework, which is confirmed by the increase in the interplanar d-spacing in Ti-Beta as compared to bare H-Beta zeolite. Estimation was taken from the most intense peak at 20 -- 22.60 of the powder x-ray diffraction pattern following the method given in Ref. [1]. The intense IR band at 960 cm "l also gives the evidence of the successful substitution. Besides, an X-ray microprobe examination demonstrated that the titanium is uniformly distributed within the crystal. The EPR spectrum (taken at 77 K) of the evacuated sample exhibits an intense symmetric signal at g = 2.0030 due to the F-center and the signals at gl = 2.025, gz = 2.010 and g3 = 2.0024 due to the presence of 02- in the orthohombic geometry. The typical EPR signals of 02 - were remarkably enhanced when contacting with low pressure oxygen. We have tried to reduce the sample in hydrogen at high temperature, but no visible Ti 3+ EPR signals were observed, while traces of 02- still appeared. The 02- is known to be responsible for the selective oxidation reaction. In the case of the synthesized V-Beta zeolite, it is surprising that no vanadium signal was detected by EDS. The vanadium ions might hide inside the zeolites. The powder XRD pattern of V-Beta is very similar to the H-Beta zeolite and the interplanar d-spacing shows only a subtle increase. The infrared spectrum is similar to that of H-Beta, gives no evidence on the formation of V=O bond or Si-O-V species. However, evacuation of the V-Beta sample at 500oc, it appeared a distinguished EPR spectrum at g~= 1.930 and gi = 1.989 with A~ = 201.1 G and A• = 84.4 G rising from 51V (I = 7/2), which is most likely to be due to VO 2§ in the cation sites [2]. The high temperature interaction between V205 and the zeolite must have taken place during calcination. Apparently, the incorporation of titanium ions into the framework of Beta zeolite is successful in the present hydrothermal synthesis, while vanadium ions seem to prefer to occupy the cation sites.
The consequential
performance may be due to the different electronic properties of both ions. We believe that the results are important and helpful in the catalytic processes occurring in these systems. References: 1. M. Taramasso, G. Perego and B. Notari, US pat. 4 410 501, 1983. 2. M. Petras and B. Wichterlova, J. Phys. Chem. 1992, 96, 1805.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
SYNTHESIS, CHARACTERIZATION, AND STRUCTURE OF SAPO-56, A NEW MEMBER OF THE ABC DOUBLE-SIX RING FAMILY OF MATERIALS WITH STACKING SEQUENCE AABBCCBB. Stephen T. Wilson UOP Research and Development, 50 E. Algonquin Rd., Des Plaines, IL 60017 Nancy K. McGuire 1 Union Carbide Chemicals and Plastics Co., Inc., 777 Old Saw Mill River Rd., Tarrytown, NY 10591 C. Scott Blackwell and Charles A. Bateman UOP Research and Development, 777 Old Saw Mill River Rd., Tarrytown, NY 10591 Richard M. Kirchner Chemistry Department, Manhattan College, Bronx, NY 10471 SUMMARY
Three small pore (8-ring) structures have been synthesized using N,N,N',N'-tetramethyl-l,6-hexanediamine (TMHD) as the structure-directing agent, AIPO-17 or SAPO-17 (ERI), MAPSO-34 (CHA) and a new structure, designated SAPO-56. Synthesis conditions and gel composition influence the structure-type formed. SAPO-56 adsorbs oxygen, nitrogen, and normal paraffins but not isoparaffins, and has a pore volume comparable to SAPO-34 (CHA). Synchrotron x-ray powder diffraction, electron diffraction, and MAS-NMR were used in conjunction with model building to solve the structure. The SAPO-56 structure, a member of the ABC six-ring family, contains only D6R units (like CHA and AFT), arranged to give gmelinite cages (GME) and large cages (AFT) previously observed in AIPO-52. INTRODUCTION The use of novel amine templating agents in the synthesis of AIPO-based molecular sieves continues to produce novel structures. One class of such structures is characterized by parallel stacking of 6-rings, the ABC 6-dng family. The AIPO members of this family include structure-types ERI, SOD, CHA, LEV, AFT, and now SAPO-56. EXPERIMENTAL
SAPO-56 was prepared by heating a reaction mixture with the composition: 1.0 TMHD :0.6 SiO2 : AI203 : P20~ : 40 H20 at 200C for 96 hours. At low Si concentrations (< 0.2 SiO2) SAPO-17 or AIPO-17 is more commonly observed. The best synthesis conditions for the SAPO-56 appear to be: 1) higher Si concentrations, 2) a fumed silica source, and 3) higher TMHD concentrations. Mixtures of SAPO-17 and SAPO-56 are sometimes observed, particularly at intermediate Si synthesis levels. From a gel containing Mg and Si, a pure MAPSO-34 (chabazite framework) was prepared with TMHD. Synchrotron x-ray powder diffraction was used in conjunction with model building to solve the structure of the calcined, never-rehydrated form of SAPO-56. Solid state MAS 27AIand 31p NMR were measured on a similarly prepared sample. Adsorption capacities were measured gravimetrically. currently at Dow Chemical Co., Midland, MI
10
RESULTS AND DISCUSSION Adsorption characterization indicated that SAPO-56 was a small pore structure, most probably with an 8ring controlling sorption. Oxygen and n-butane were readily adsorbed and isobutane was excluded, and the sorption capacity was comparable to that of SAPO-34 (CHA). MAS-NMR was consistent with the presence of D6R units and the absence of S6R units. Electron diffraction produced a 13.8 x 13.8 x 19.9 ~, cell, consistent with one of the unit cells found by the indexing programs. Discussions with J.V. Smith led to a trial model drawn from the hypothetical enumeration of ABC 6-dng structures. 2 This model contains only double 6-rings, arranged to give gmelinite (GME) cages and another type of cage which has only been observed before in AIPO-52, and is referred to as the AFT cage. The stacking sequence of the 6-rings in the structure is AABBCCBB. The trigonal space group is P3barlc. Cell dimensions from a Rietveld refinement using GSAS are a = b = 13.7617(2) ~,, c = 19.9490(5) ~,, "= $ = 90 ~ , ( = 120 ~ . The synchrotron x-ray data and selected area diffraction patterns indicate faulting in the stacking sequence along the c-axis.
2J.V. Smith and J.M. Bennett, Amer. Mineral., 66, 777-788 (1981)
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
11
SYNTHESIS AND CHARACTERIZATION OF CoAPOICoAPSO-44 and CoAPO-5 U. Lohse 1, E. L6ffler 2, B. Parlitz 1 and E. Schreier a t Institute of Applied Chemistry Berlin-Adlershof, Berlin 12484, Germany 2 AUF GmbH, Rudower Chaussee 5, Berlin 12484, Germany 3 Humboldt University, Hessische Str.1, Berlin 10115 Summary It is shown that Co atoms occupy framework positions and create Br6nsted and Lewis acid sites. Introduction The incorporation of Co into the framework positions is studied for two structures (44 and 5). Special interest is devoted to the created acid sites. Experimental Section The composition of the reaction mixtures was the following: CoAPOICoAPSO-44: (0.8-1.0)AI203x (0.6-0.1) P2Osx (0-0.4) SiO2x (0.1-0.4) CoO x 1 CHA x 1HF x 60 H20 CoAPO-5:0.9 AI203 x 1P205 x 0.1 CoO x 1CHA x 190 H20 [CHA: cyclohexylamin]. The crystallization was performed in the common way (stainless steel vessel in an oven at 200~ 4-24h) or in microwave power system ( CEM corporation, 200 ~ 25-30 min). The samples were characterized by XRD, adsorption of N2, TPDA, IR spectroscopy, calorimetric measurement of NH3 sorption. Results and Discussion Characteristic changes of the color were observed after elimination of the template and after adsorption of H20, NH3, N2 (green, greybluelanthracite, blue). The results of the chemical analysis give evidence for the isomorphous substitution of AI atoms by Co (Co+AI=P). The Co content in the crystals is in the range of 2.0-8.7 wt% CoO. From our experience about synthesis it follows that the crystallization of pure CoAPO-44 needs a definite amount of Co in the gel. This confirms the conclusions already drawn for SAPO-44 that the building of the chabazite-like structure requires one negative charge per double-6-ring which may be realized by substitution of P by Si or of AI by Co. [cm3/g STP] 160-
Co
CoAPSO-44(0.2)
(O.Z)
;!
%
120-
.3677
1"3580
80
40
/
4-000
[P/Po] 10-5 10-3 i0-1 Adsorption isotherms of nitrogen at 77 K i
='
1
3500 3000 w o v e n u m b e r s / c m -1 9J
,
4
-
1
[R spectrtu~ of CoAPO--44
12 The X-ray difractograms and the adsorption isotherms demonstrate the full crystallinity of the samples. The pore volumes amount to 0.2 cm3/g for CoSAPO-44 and 0.13 cm3/g for CoAPO-5 and agree with those of the corresponding AIPO4/SAPO samples. The destabilization of the framework in dependence on the cobalt content is significant. The collapse of CoAPO-44 takes place at 600 ~ whereas SAPO-44 is stable up to 1000 ~ Furthermore, CoAPO-44 is attacked by water at low temperature. The loss of adsorption capacity (see isotherms) is due to a hydrolysis process. The heating of the water saturated sample (30 wt%) in air leeds to the total destruction of the lattice at about 250 ~ A higher stability is found for the CoAPSOs. 0.1
- SA~:)-44
21~
"J
-CoA.PO-44
~
15TorrCO
"~ P'~ " v ~ 73 9
$73
G73
z73
- - - - - - - 1" (K)
10~ Tort 5' 10~ ToK
" " - - - - - 1~ 10~ Tort
TPDA cun, es ~
of CO on CoAPO44
From the results of TPDA and calorimetric measurements it follows unambiguously that the total number of acid sites corresponds well with those of SAPO-44 (one acid site per double-6-ring), but the intensity of the low and high temperature peaks are reversed. In contrast to SAPO-44 the IR spectrum for CoAPO-44 shows no bands of isolated bridging hydroxyls. The character of the spectra (a broad band at 30003600 cm -1 with a maximum at 3580 cm-1 and POH groups at 3670 cm -1) is independent of the structure type and confirms the spectra of CoAPO-11 and CoAPO-5 known from the literature. The presence of adsorbed molecular water can be ruled out (no band at 5200 cm-1). It seems that the POH groups are connected with the Co atoms and have a higher acidity than those found in most aluminophosphate molecular sieves. We assign the broad band to interacting hydroxyls which are present beside isolated centers. In dependence on the probe molecule the Co atoms appear as Br5nsted (B) or Lewis (L) sites. 0 H 0 0 Co-- 0 ............... P 0 0 0
~
0 0 Co 0
0 HO P 0 0
B and L sites were detected by IR spectroscopy after adsorption of NH 3. The ratio of B and L sites (about 11) remains unchanged even after evacuation and heating of the sample. After CO adsorption a new band at 2196 cm -1 appear in the IR spectrum which can assign to a CO complex on the Co2+.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
13
SYNTHESIS AND SORPTION PROPERTIES OF THE ZIRCONIUM ALUMINOPHOSPHATE MOLECULAR SIEVES ZrAP0-5
J. Kornatowski 1,2 , M. Rozwadowski 2, W. Lutz 3, M. Sychev 4 , G. Pieper 1 G. Finger i, W. H. Baur 1 1 1 n s t i t u t fGr Kristallographie, Johann Wolfgang Goethe-Universit~t, 60054 Frankfurt/Main, Germany 2 Instytut Chemii, Uniwersytet Miko~aja Kopernika, 87-100 Torun, Poland 3 Institut fGrAngewandte Chemie, 12489 Berlin, Germany 4 Institute of Colloid and Water Chemistry, Ukrainian Academy of Sciences, 252680 Kiev, Ukraine
The sorption isotherms of the synthesized ZrAPO-5 samples indicate that their sorption capacities for water are higher while for benzene and nitrogene are lower than those of ALP04-5. The sorption studies might indicate a framework incorporation of the Zr ions.
INTRODUCTION
The first efforts to incorporate Zr ions into zeolitic materials applied to silicates of the MFI type 1,2. However characterization
of Zr-silicalite-1
the first studies on synthesis
and
have been published much later3.
The
materials have been found to be catalytically active in the synthesis
of
olefins from methanol 2 and in the hydroxylation of benzene 5. This indicates that the Zr materials have properties similar to their Ti analogues. While Ti containing aluminophosphates
have been known
already
since 19864 , the Zr
aluminophosphate derivatives have been first reported by us 5,6 in 1991. This paper presents the results of our syntheses of [Zr]AFI molecular sieves and some of their properties. EXPERIMENTAL The ZrAP0-5 materials were synthesized hydrothermally according to our well established procedure 7,8 for AFI type materials. As the source of zirconium, seven
different
Zr(0H)2C03,
Zr(IV)
compounds
Zr(ethoxide) 4,
were
used:
Zr(propoxide) 4
and
Zr02,
Zr0C12,
Zr(S04)2,
Zr(acetylacetonate) 4.
The
formal molar composition of the reaction gel (triethylamine=TEA as template) was: A1203
90,915P205 " 0,17Zr02
91,37TEA " 270H20.
The materials were characterized using XRD, sorption of H20, C6H 6 and N 2.
SEM,
EPM,
TGA techniques
and
14 RESULTS AND CONCLUSIONS
All batches except those using the last Zr compound yielded large crystalline phases of AFI type. The dimensions of the crystals in particular preparations reached 150 x 60 to 750 x 85 ,m and their colour was white to yellowish. The crystals had the typical shape of hexagonal prisms cavities
spread over
(EPM) with a number of
the surface 6. The content of Zr
(EPM) was
for all
prepartions within a range of 1,0 to 1,5 wt% except for the sample prepared from Zr(0H)2C03 where crystals.
the Zr ions were not found on the surface of the
The XRD patterns were
typical
for the AFI
type structure
and
indicated a good crystallinity of the materials. All samples showed a good sorption
capacity
for water within
a range
of 0,235
to 0,255
cmS/g
at
p/ps=0,95, i.e. higher than the reference AIP04-5 sample (-0,195 cmS/g). The sorption capacity for benzene was nearly independent on the source and amount of Zr and it reached -0,6 to 0,7 mmol/g at p/ps=0,85 except for the sample prepared from Zr0C12 (-0,27 mmol/g). The sorption of N 2 (77K) was different. At p/ps=0,8 the sorption amounted only to -0,35 (Zr0C12) to 2,4 [Zr(OH)2C03] N 2 molecules/unit cell . The sorption rose strongly when approaching p/ps=l,0 but it did not exceed 3 molecules/UC, i.e. it reached only about 1/3 to 1/2 of the experimental value typical for ALP04-5 preparations (about 6). As the sorption of water proves that the pore system is open, the significant discrepancies in sorption of N 2 can be explained by differences in the mutual interaction between the sorbate molecules and the heterocentres located on the Zr atoms. A possible mechanism could be the condensation of N 2 around the Zr
centres
which
could hinder
and
stop
a further
diffusion/sorption
of
nitrogen. Thus, it might indicate a framework incorporation of the Zr ions in all the investigated samples. Acknowledgments. The work was partially supported by the Bundesministerium ffir Forschung und Technik and the Polish Committee for Scientific Research (KBN). REFERENCES
I. B.A. Young, USPats. 3 329 480 and 3 329 481 (1967). 2. H. Baltes, H. Litterer, E.I. Leupold, F.Wunder, Eur.Pat. 77 523 (1983) and Ger.Offen.De 341 285 (1983). 3. M.K. Dongare, P. Singh, P.P. Moghe, P. Ratnasamy, Zeolites ii (1991), 690. 4. E.M. Flanigen, B.M. Lok, R.L. Patton, S.T. Wilson, Stud. Surf. Sci. Catal. 2_88 (1986), 103. 5. J. Kornatowski, M. Rozwadowski, G. Finger, Pol.Pat.Appl. 291.460 (1991). 6. J. Kornatowski, M. Sychev, G. Finger, W.H. Baur, M. Rozwadowski, B. Zibrowius, Proc. Polish-German Zeolite Colloquium, Torun, Apr. 23-24, 1992, ed. M. Rozwadowski, N. Copernicus University Press, Torun. i~J92, p.20. 7. J. Kornatowski, G. Finger, Bull. Soc. Chim. Belg. 99 (1990). 857 and refs. therein. 8. G. Finger, J. Kornatowski, Zeolites i_O0 (1990), 615.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
Molecular Or Supramolecular Templating: Defining The Role of Surfactant Chemistry In the Formation of M41S and Zeolitic Molecular Sieves J. S. Beck 1~ J. C. Vartuli 1, G. J. Kennedy 2, C. T. Kresge 2, W. J. Roth 2, and S. E. Schramm 1 Contribution from Mobil Research and Development Corporation Central Research Laboratory, Princeton, New Jersey 08543 and Paulsboro Research Laboratory, Pauisboro, New Jersey 08066 We have explored the ability of alkyltrimethylammonium surfactants of the type CnH2n+I(CH3)3NBr to serve as structure directing agents, or templates, for the formation of microporous or mesoporous molecular sieves frameworks. At equivalent gel compositions and reaction conditions, it was observed that the alkyl chain length of the surfactant molecule dictated the nature of the silicate product obtained as indicated by the X-ray diffraction patterns shown in Figure 1. Over the entire range of synthesis temperatures examined (100-200~ the shortest alkyl chain length surfactant (n=6), produced amorphous or microporous zeolitic materials, such as ZSM-5. The zeolite contained the intact surfactant cation consistent with a commonly observed molecular templating effect. At 100~ as the surfactant chain length was increased (n=8,10,12,14, and 16), the formation of mesoporous molecular sieves (MCM-41) was observed. In these cases, a combination of surfactant chain length and reaction conditions favor surfactant aggregation (micelles), and hence, the formation and utilization of supramolecular templates. At synthesis temperatures of 200~ zeolitic and dense phase products were obtained for even the higher alkyl chain lengths, suggesting that these supramolecular aggregates were disrupted and molecular structural direction dominated. 13C CP/MAS data of MCM-41 and zeolitic materials prepared with identical surfactants indicates that the role of the organic directing agent is different in the formation of these two classes of materials. MCM-41 materials have NMR spectra that suggest a micellar array of surfactant and the zeolite materials exhibit spectra that are indicative of a more rigid, isolated environment. The data are consistent with a hypothesis that single surfactant molecules serve to direct the formation of microporous materials whereas mesoporous molecular sieves, such as MCM-41, are formed by surfactant aggregates. These results reinforce the LCT (Liquid Crystal Templating) mechanism proposed for the formation of the mesoporous MCM-41 materials and further add to our understanding of the formation of inorganic porous materials. 1 Mobil Research and Development Corporation Central Research Laboratory 2 Mobil Research and Development Corporation Paulsboro Research Laboratory
15
16
rO
~0 0
04
oo ,1--=
(~ o
rO
0
oj rO
rO
0
o
rO
0
~
fq!sumul
rO
rO
~
rO
rO
o
0
00
r
'--
(P
0
_oi--
_0
--
o~I
c~
a
0
oi--
-
0 ',-
0
--
--
0
H.G. Karge and J. Weitkamp (Eds.)
17
Zeolite Science 1994: Recent Progress and Discussions
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
SYNTHESIS AND CHARACTERIZATION OF BORON CONTAINING MCM-41.
U. Oberhagemann, I. Topalovic, B. Marler, H. Gies Institut ih" Mineralogie, Ruhr-Universit/it Boehum, D-44780 Bochum, Germany Introduction MCM-41 is a novel mesoporous material first described by Kresge et al. in 1992 (1). MCM-41 has channel like pores of uniform size which are arranged in a regular hexagonal pattern. The pore diameters are in the range of 25 to 100 ./k depending on the type of detergent cation used as templates during the synthesis. So far, only the aluminosilicate and the pure silica forms of MCM-41 are largely characterized (e.g. 2,3). We report here on the synthesis and general characterization of the boron containing MCM-41 (B-MCM-41). Experimental B-MCM-41 was synthesized from aqueous silicate solutions in the system SiO2/B203//H20/Template. The reaction mixtures were sealed in silica glass tubes and heated at 95~176 for eight weeks. As templates five different n-alkyl-trimethylammonium cations, N(CH3)3-(CH2),-CH3 with n = 5, 9, 11, 13, 15 were used. The boron content of B-MCM-41 samples was determined using a PU7000 ICP spectrometer. X-ray powder data of various samples were collected on a Philips PW1050 diffractometer. 29Si, 13C and I*B MAS NMR spectra were recorded with Bruker MSL-400 or MSL-300 spectrometers using standard Broker MAS probes. Thermal properties of boron containing MCM-41 were investigated by TGA and DTA. Isotherme sorption and TPD experiments were made with n-Hexan and NH3 respectively. Results and Discussion The d-value of the fast X-ray reflexion of the different B-MCM-41 materials depends on the chain lenght of template molecule (see Tab. 1). This reflects the fact that the molecule lenght determines the pore diameter of the channels which is in the range of 27.0A (with hexyltrimethylammonium, n=5) to 42.3A, (with hexadecyltrimethylammonium, n=15). All X-ray powder diagrams can be indexed in the hexagonal symmetry (Fig. 1). 15000-
Template
molecule lenght
d,oo-values
n= n= n= n= n=
11.2A 16.2A, 18.7A, 21.2]k 23.7A
27.0]k 32.0A, 35.5A, 41.0/~ 42.3A
5 9 11 13 15
~oo
oo
0-~
2 ' ,i ' g ' ~ ' lb' 1'2' 1'4' 1%' 1'8 ' ~o 2-THETA
Tab. 1: dloo-values of various B-MCM-41 samples and chain lenghts of the N(CH3)3-(CH2)n-CH3template.
Fig. 1. X-ray powder diagram of B-MCM-41 synthesized with N(CI-I3)3-(CH2)16-CH3
Sorption experiments on various B-MCM-41 samples revealed an uptake of 24.5 to 37.6 weight percent n-hexane proving the high porosity of this material. The results mentioned in the following are obtained from a sample synthesized with tetradecyltrimethylammonium: The chemical analysis of the as synthesized sample revealed a ratio Si/B = 47. In the calcined material the boron content is slightly reduced to Si/B = 55. TGA measurements up to 1200~ revealed a total weight loss of 36 percent which occurs in three main steps. The first step (25-150~ -- 3 %) originates from molecular water, the second (150-500~ -- 25 %) is caused by the decomposition and expulsion of the guest molecule, the
18 third step (500-680"C, - 8 %) is a loss of water which originates from OH groups of the framework. DTA shows that the remaining material (= 64 %) transforms to cristobalite. The 295i M.AS NMR spectrum shows three broad signals (Fig. 2a). Neglecting the very low boron content, we assign these signals to SiO4 groups (with a chemical shift o f - 1 0 8 ppm), SiChOH groups (-101 ppm) and SiCh(OH)2 groups (-89 ppm). The broadness of the signals indicate a framework structure of very low order. The ~IB MAS NMR spectrum of the as synthesized material presents one sharp signal. The chemical shift of about -2 ppm, is typical for tetrahedraJly coordinated boron in the silicate framework (Fig. 2b).
-6o '~o -~o''~o '"'~bo -f~o - ~ " - i ' ~ " - ~ ppm |
|
'
!
!
Fig. 2. a) 29Si MAS NMR spectrum and
~ ' 6 '-h'-lo'-is'-~o pont b) nB MAS NMR spectrum of the as synth, sample. ~b'
The t~B spectrum of the calcined sample shows one strong, shar ~signal at ca. 19 ppm and a weak signal at ca. -2 ppm (Fig 3). The latter value reflects boron atoms which are still tetrahedrally coordinated within the silicate framework. In contrast, a chemical shift of about 19 ppm is typical for boron atoms trigonally coordinated by oxygen atoms in natural and synthetic borates (4). To our knowledge however, the very narrow linewidth of the ] signal is unique among calcined porous borosilicates. As a possible explanation, we assume that boron is removed from the sili4b ' 3b ' 2b ' l b ' 6 '-io'-~o care framework during the calcination process ppn by forming a separate borate phase. Fig. 3. nB MAS NMR spectrum of the calc. sample.
__9
The ~3C NMR spectrum shows a significant pattern of at least 8 signals which proves that the template tetradecylyltrimethylammortium in fact occupies the channels of B-MCM-41. Conclusion The properties of B-MCM-41 are very similar to those of their aluminosilicate and silica analogues. NMR spectroscopy proves that boron is part of the silicate framework in the as synthesized material introducing acid sites into the framework. Preliminary investigatins of the acidity of B-MCM-41 revealed that the material has only a very weak acidity, even lower than the aluminium containing MCM-41. References 1. C.T. Kresge et al, US Patent No. 5.098684 (1992); US Patent No 5.102643 (1992). 2. C. T. Kresge et al, Nature, Vol. 359, 710-712 (1992). 3. Cong-Yan Chen et al., Microporous Materials, 2 (1993), 17-26. 4. G. L. Turner et al, J. M ag;.Resonance 67,ff44Z5_50, (...__1.98_6)= We thank Dr. A.Ryfinska and Dr. C.A.Fyfe for providing the NMR facilities and for helpful advice.
I-I.G. l~arge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions
19
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved. SYNTHESIS OF V A N D Ti MODIFIED MCM-41 MESOPOROUS
MOLECULAR SIEVES Abdelhamid Sayari, Kondam Madhusudan Reddy and Igor Moudrakovski Universit~ Laval, Department of Chemical Engineering and CERPIC, Ste-Foy, Qc, CANADA GIK 7P4
SUMMARY V a n a d i u m and titanium modified MCM-41 mesoporous molecular sieves have been synthesized. Their physico-chemical and catalytic properties indicate a probable incorporation of the Ti(IV) and V(V) cations in the f r a m e w o r k of the molecular sieve.
INTRODUCTION Modification of zeolite frameworks by transition metal cations often leads, to new materials with remarkable catalytic properties. Several well documented Ti and V modified silicates were found to be excellent catalysts for partial oxidation of organic substrates under very mild conditions. Recently, a new family of mesoporous molecular sieves designated as MCM-41 has been discovered (1). These zeolite-like materials have uniform channels with adjustable dimensions from 15 to more than 100 ,~. Modification of MCM-41 by transition metal cations such as Ti and V may lead to new catalysts for redox reactions involving molecules too large to be accommodated in microporous structures. The objective of this communication was to report on the synthesis and characterization of both V and Ti modified MCM-41 molecular sieves. EXPERIMENTAL V-MCM-41 and Ti-MCM-41 were synthesized hydrothermally at 373 K for 6 to 7
days in Teflon lined autoclaves tumbled at 25 rpm. Fumed silica, NaOH, VOSO4, 2H20, dodecyltrimethyl ammonium bromide and water were used for the synthesis of V-MCM-41. Because the presence of Na ions in the synthesis gel is detrimental to the incorporation of Ti in zeolitic frameworks (2), dodecyltrimethyl a m m o n i u m hydroxide was used instead of the corresponding bromide, thus avoiding the use of NaOH. The other ingredients were tetraethylorthosilicate, Ti tetrabutoxide and deionized water. The resulting solids were filtered, washed and calcined at 823 K for 6 h. All samples were characterized by AAS, XRD, IR, UV-Vis., XPS, 51V N M R and nitrogen adsorption. The oxidation of phenol, naphthol and cyclododecane as
20 well as the epoxidafion of 1-hexene by diluted H202 were used to evaluate the catalytic properties of these new materials. Samples of the reaction mixtures were analyzed by GC using a 50 m capillary column (HP-1). RESULTS AND DISCUSSION XRD patterns of V and Ti modified MCM-41 matched well that of pure silica MCM-41. Chemical analysis showed that Ti and V contents in the final products were lower than in the synthesis gel. Nitrogen adsorption isotherms exhibited a step at P / P ~ of ca. 0.20 characteristic of the presence of a mesoporous system with a unique pore size (3). The BET areas were about 950 m2/g. 51V MAS NMR provided definite proof that all vanadium in calcined V-MCM-41 was in tetrahedral symmetry. Two isotropic peaks were observed: a major signal at-527 p p m (relative to VOCI3) with a shoulder at-506 p p m (4). Such features are characteristic of tetrahedral vanadium. No NMR peak with a chemical shift around-300 p p m was detected indicating, in agreement with Raman spectroscopy data, that no free V205 was present. UV-Vis. reflectance spectroscopy showed that Ti-MCM-41 exhibits a strong absorption band at 210 nm attributable to isolated Ti species in tetrahedral environment. Moreover, XPS analysis of Ti-MCM-41 showed that the Ti(2p) signal can be deconvoluted into two doublets the relative intensities of which were 85 and 15%. The strongest doublet corresponded to a Ti(2p3/2) binding energy of 459.9 eV and the weakest to a Ti(2p3/2) binding energy of 457.8 eV. Similar photoelectron transitions were assigned to tetrahedral and octahedral Ti, respectively (5). Pure silica MCM-41 had an IR absorption band at about 960 cm -1, probably due to silanol groups. Modification by Ti brought about an increase in the relative intensity of this band. As stated in the literature, this may be regarded as an indication of Si-O-Ti bonding. Our UV-Vis. and FTIR findings are in agreement with data published recently by Corma et al. (6). As far as catalytic properties are concerned, V-MCM-41 was found to be highly active and selective in the hydroxylafion of cyclododecane and naphthol (4) as well as the epoxidation of 1-hexene in the presence of 30 wt% H202. Based on all this information, it is concluded that V is incorporated in the framework of MCM-41 molecular sieve. Unlike V-MCM-41, the Ti-MCM-41 samples were active only in the epoxidafion reaction. No significant activity was found in the hydroxylation of phenol or nhexane. Similar observations were made concerning Ti-AI-~ (7) and Ti-ZSM-48 (8) zeolites. Moreover, the epoxidafion of olefins by diluted H202 is known to take place even in the presence of highly dispersed TiO2 on silica. To date, the
21 only Ti modified molecular sieves with significant activity in selective oxidation of alkanes and phenols are TS-1 and TS-2, with MFI and MEL structure, respectively. This is probably an indication that Ti in silicalite-1 and 2 has a unique local environment. REFERENCES
1. J.S. Beck et al., J. Am. Chem. Soc., 114 (1992) 10834. 2. B. Notari, Stud. Surf. Sci. Catal. 60 (1991) 343. 3. P.J. Branton, P.G. Hall and K.S.W. Sing, J.C.S., Chem. Commun., (1993) 1257. 4. K.M. Reddy, I. Moudrakovski and A. Sayari, J.C.S., Chem. Commun., (1994) in press. 5. A. Sayari et al., (a) J. Mol. Catal. 74 (1992) 233; (b) in Proc. 9th IZC, Butterworth-Heinemann, Stoneham, 1993, Vol. 1, p. 453. 6. A. Corma, M.T. Navarro and J. P(~rez Pariente, J.C.S., Chem. Commun., (1994) 147. 7. C.B. Khouw, C.B. Dartt, H.X. Li and M.E. Davis, Prepr., Div. Petrol. Chem., 1993, p. 769. 8. A. Sayari et al., Catal. Lett. 23 (1994) 175.
22
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
SYNTHESIS OF TITANIUM MOLECULAR SIEVE ETS-10 AND ETS-4 Alfonso Nastro*, David T. Hayhurst** and Steven M. Kuznicki *)Dept of Chemistry, University of Calabria, Arcavacata di Rende, 87030 Rende (CS), Italy; **)College of Engineering, University of South Alabama, EGCB108, Mobile AL, 36688 USA; ***) Engelhard Corporation, 101 Wood Avenue, Iselin NJ, 08830-0770 USA. SUMMARY In this paper the crystallisation kinetics of the large and small pored crystalline titanium molecular sieve ETS-10 and ETS-4 are reported. These ETS materials have an open structure, both with tetrahedral and octahedral primary building units. The effect of varying the single components of the reaction mixture, as reported in the patent literature on the kinetic parameters, on the gel preparation and on the properties of the final products is discussed. INTRODUCTION In 1967 Young reported that the synthesis of charge bearing titanium silicates can be obtained under reaction conditions similar to aluminosilicate zeolite formation (1). In 1972 a naturally occurring alkaline titanosilicate identified as Zorite was discovered in the Siberian Tundra (2). While these materials were called titanium zeolites, no further reports on titanium silicates appeared in the open literature until 1983, when traces of tetrahedral Ti(IV) were reported in a ZSM-5 analogue (3). The object of this research is to report the synthesis of ETS-4 (4) and ETS-10 (5) crystalline titanium silicates molecular sieve, discussing the effect of the individual chemicals reported in the patents in the preparation of these crystalline materials. EXPERIMENTAL The general batch composition is xNa20-yTiO2-1.63HCI-!.49SiO2-39.5H20, where 0.44<x>2.26, 0.25
0.47. This composition was modified additioning potassium salts or replacing part of NaOH with KOH in the initial reaction mixture. The preparation of both ETS materials was carried out mixing an alkaline sodium silicate solution with a dilute Titanium Oxicloride solution without addition of seeds. The potassium salts, 0.69 moles of KF or KCI, were added alternatively to alkaline (procedure a) or to acidic mixture (procedure b). The relative crystallinity was defined from the intensities of the peaks of the XRD pattern. For use as standard samples of ETS-4 and ETS-10, these materials were synthesised following the procedures type b reported in the patents (4,5) without addition of seeds. RESULTS AND DISCUSSION The attached Figure shows the relative crystallinity versus the reaction time of the ETS-10, referred to procedure a and b. The third curve describes the course of
23 the relative crystallinity of the ETS-10 obtained from the batch without K. The addition of K salts to the batch composition for both ETS molecular sieves produces a negative effect on the nucleation and on the crystal growth. In particular, the combined action of the K and F added to the alkaline mixture, as reported in the patents, produces a modification on the prepolimerization of the titanium silicate gel. In addition, the presence of KF in the batch modifies the solubility of these building units. For these reasons the crystal size of the products obtained in presence of KF is smaller. The replacement of KF with KCI produces a reduction of the yield of the reaction, and the substitution of NaOH with KOH gives an amorphous product after 5 days of reaction time. The higher values of x and/or y in the batch composition produce ETS-4 with a kinetic and a crystallinity higher than the crystallinity obtained following the gel preparation procedures reported in the patent (4) 200
~ Z
160
<
120
~:
80
o
w
~_ I-.
5
w ft.
"
Procedure a 9 Procedure b 9 Procedure c
40 0
0
24
48 72 96 REACTION TIME, HOURS
120
Figure. Value of the relative crystallinity versus the reaction time CONCLUSIONS The titanium zeolites ETS-4 and ETS-10 may be considered as Sodium molecular sieves because the potassium play a negative role on their synthesis. The crystallisation of ETS-4 and ETS-10 is not considered an autocatalitic reaction because the relative crystallinity does not follow a sigmoid course, but, a straight line. The crystallisation domain of ETS-4 and ETS-10 is also function of the ratios Na/Si and Si/Ti in the initial batch composition and of the source of the chemicals.. REFERENCES 1) Young, US Patent, 3,329,481, 1967. 2) P.A. Sandomirskil and N.Y. Belov, Sov. Phys. Crystallogr., 24(6), 1979. 3) 3) G. Perego et al. Proc. 7th Int.Zeolite Conf. p.129, 1986 4) S.M. Kuznicki, US Patent, 4,938,939, 1990. 5) S.M. Kuznicki, US Patent, 4,853,202, 1989.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions
24
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved. PREPARATION BY THE SOL-GEL METHOD OF RAW MATERIALS FOR THE SYNTHESIS OF Ti CONTAINING ZEOLITES M.A. Uguina, G. Ovejero, R. Van Grieken, D. P. Serrano and M. Camacho Chemical Engineering Department, Faculty of Chemistry Complutense University of Madrid, 28040 Madrid, Spain.
SUMMARY Sol-gel methods have been applied for the preparation of amorphous SiO2-TiO2 solids having Si-O-Ti bonds, in order to get a suitable raw material to synthesize TS-1. The procedure involves the wetness impregnation of these solids with TPAOH solutions followed by crystallization under autogeneous pressure. This method seems to be also successful in the incorporation of other elements (A1) and the synthesis of other Ti containing zeolites (TS-2, Ti-Al-13). INTRODUCTION The conventional method of synthesis of Ti containing zeolites is based on the preparation of a liquid gel obtained by basic hydrolysis of Si and Ti alkoxides. Since Ti tends to precipitate as TiO2, the hydrolysis has to be performed under extremely careful conditions according to a laborious procedure (1). A completely different approach recently developed (2) is the TS-1 synthesis via wetness impregnation of a commercial SiO2-TiO2 coprecipitate with TPAOH solutions. We have found this way also successful when SiO2-TiO2 solids prepared by sol-gel methods are used as raw materials (3). The composition and physicochemical properties of the starting SiO2-TiO2 cogels can be adjusted and varied in a wide range through the different variables involved in the sol-gel process.
EXPERIMENTAL The starting SiO2-TiO2 solids were prepared by two step sol-gel processes: acid hydrolysis of the Si and Ti alkoxides and subsequent gelation by different procedures (addition of TPAOH or NH3 and heating at 80~
in the acid medium). TS-1 samples were synthesized by wetness
impregnation of dried SiO2-TiO2 cogels (Si/Ti= 30) with a 20% TPAOH solution followed by crystallization at 170~ for 1 day under autogeneous pressure. The samples obtained were characterized by XRF, XRD, IR and SEM. The catalytic properties were checked using the n-hexane oxidation with H202 (100~
1 h) as test reaction.
RESULTS AND DISCUSSION Figure 1 shows the IR and XRD spectra of a SiO2-TiO2 cogel and those of the corresponding TS-1 sample. No crystalline structure is detected in the cogel but the presence of the 960 cm 1 IR band indicates that Si-O-Ti bonds have been formed in the starting material. This band is also present in the TS-1 sample which denotes that Ti-O-Si linkages remain in the zeolite. In addition, its orthorhombic symmetry shows the effective Ti incorporation into the zeolite framework. Then, the sol-gel method allows Ti atoms to be stabilized previously to the synthesis step.
25
IR
XRD
I4100
-'~oo ,,
2O
,o~ Wavenumber
~
~o
,oo
( c m "1)
Figure 1. XtLD and IR spectra of a starting SiO2-TiO2eogel and the corresponding TS-1 sample.
Table 1 summarizes the major physicochemical and catalytic properties of several TS-1 samples synthesized from SiO2-TiOz cogels prepared by different gelation procedures. All TS-1 samples present orthorhombic symmetry, the typical 960 cm ~ IR band and exhibit high catalytic activity for n-hexane oxidation. However, some differences among them are observed in regards to the Ti content, crystal size and catalytic behaviour, showing how the properties of the starting SiO2TiO,. cogels influence those of the TS-1 samples. Table 1. Physicochemicalproperties of TS-I samplesprepared from different SiO,.-TiO2cogels.
Sample ~
Si/Ti (XRF)
Dp(SEM) (/~m)
I96o/Iso0 (IR)
n-hexane conv.( % )
H20 z conv.( % )
H20~ select.( % )b
TS-1 (1)
45.9
1.0
1.84
52.9
79.3
85.9
TS-1 (2)
40.1
3.5
1.87
33.6
84.4
46.2
TS-1 (3)
44.2
0.2-1.5
1.78
46.5
95.1
TS-1 (4)
49.9
4.0
1.88
38.0
81.7
58.6
...
56.9
aSamples I, 2 and 3 were synthesized from cogels prepared by addition of TPAOH (20%), 1.2 % NI-I3 and 21% NI-I3 respectively, duringthe gelation step. Gelation of cogel 4 was performed by heating at 80"C in acid medium. t'I-I.,O,,selectivity towards oxygenated products. We are also applying this method for the preparation of bifunctional catalysts having Ti and AI atoms in the framework. Thus, the wetness impregnation of a SiO2-TiOz-A1203 cogel leads to AI-TS-1, material with both acid and oxidation sites. Likewise, preliminary results show that other Ti containing zeolites, such as TS-2 and Ti-Al-g, can be obtained by wetness impregnation of solids prepared by the sol-gel method. REFERENCES 1. A.J.H.P. van der Pol and J.H.C. van Hoof, Appl. Catal. A, 1992, 92, 93. 2. ~I. Padovan. G. Leofanti and P. Roffia, Eur. Pat. Appl., 0311983, 1989. 3..XI.A. Uguina. G. Ovejero, R. Van Grieken. D. P. Serrano and M. Camacho, J. Ctzem. Soc., Ctzem. Commun., 1994, 1, 27.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions
26
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
THE SYNTHESIS AND STRUCTURE ALUMINIUM PHOSPHATE
OF A NEW LAYERED
[ A L 3 P 4 0 1 6 ] 3- 3 ( C H 3 ( C H 2 ) 3 N H 3 ) +
A.M. Chippindalea,Q. Huo b, R. H. Jones c, J.M. Thomas d, R. Walton a, R. Xu b a b c d
Chemical Crystallography Laboratory, University of Oxford, 9 Parks Road, Oxford, OX1. 3PD, U.K. Department of Chemistry, Jilin University, Changchun, P.R.C. Department of Chemistry, Keele University, Staffordshire ST5 5BG U.K. Davy Faraday Research Laboratory, The Royal Institution of Great Britain, 21 Albemarle Street, London W1X 4BS U.K.
SUMMARY A new layered framework aluminium phosphate has been obtained by the reaction of aluminium isopropoxide and phosphoric acid in a non-aqueous medium using 1-butylamine as a templating agent. The structure was solved using single crystal X-ray diffractometry. The space group is P -3 with R = 0.107, Rw = 0.119. The structure consists of two-dimensional layers stacked in an AAAA manner. The individual layers containing large 12-membered rings The template molecules are located within the channels created by the stacking of these rings. INTRODUCTION The synthesis
of microporous aluminophosphates in 1982 [1] started
a major
research effort in this field. There has been less success in synthesising layered aluminophosphates, which can be thought of as aluminophosphate analogues of clays. We have recently synthesised and characterised several new layered aluminophosphates [2,3,4,5] having AI:P ratios which are not equal to 1:1. Other workers have also recently produced layered materials which also have non-unitary A1/P ratios. [6,7] EXPERIMENTAL PROCEDURE The title compound was synthesised under hydrothermal conditions. Typically, the starting material consisted of a mixture of phosphoric acid (0.63cm3; 85 wt%), aluminium isopropoxide (lg) with butan-1-ol as the solvent. The mixture was stirred until homogeneous followed by the addition of 1-butylamine as the template. The gel was heated under autogeneous pressure for 10 days at 180~
The product consisted of large single crystals
suitable for 4-circle diffractometry. Crystal data for A13P4016C12H36N3, M = 683.27, trigonal, space group P - 3 , a = 13.165 c = 9.774 .~, U = 1467.0 .~3, Z = 2, Dc = 1.547 g cm -3, ~. = 1.5418A, I.t(Cu-Ka) = 39.36 cm -1, 1929 unique reflections (0 < 20 < 144 ~ number observed 667 I > 3(~(I). The structure was solved by direct methods (SHELXS) and refined by full-matrix least-squares (CRYSTALS) to R = 0.107, Rw = 0.119. A total of 94 parameters were used in the refinement. The new material is illustrated in figures 1 and 2.
27
RESULTS AND DISCUSSION The structure consists of macroanionic layers of empirical formula [A13P4016] 3- with NH3(CH2)3CH3 cations situated between the layers. The individual layers contain a central 12-membered ring which is surrounded by 4 and 6 membered rings (figures 1 and 2). The 6membered tings are capped by PO4 groups, which alternate above and below the plain of the layer. The removal of these capping PO4 groups would leave a 4.6.12 net which we have previously observed [5]. The stacking of the layers in these two compounds is different. In the title compound the layers stack in an AAAA sequence whilst in the previously characterised material an ABAB stacking sequence was observed[5]. The control of the stacking is thus governed by hydrogen bonding to the amine templates. The template ions in the title compound are hydrogen bonded to the sides of the channels with the hydrophobic alkyl groups directed towards the centre of and blocking the channels.
i
I
~.
(
Figure 1 View normal to the plane of the sheet template omitted for clarity Legend
AI
P
O
Figure 2 View normal to the plane of the sheet template retained N
C
t
o
REFERENCES 1. S.T. Wilson, B. M. Lok, C. A. Messina, T. R. Cannan and E. M. Flannigen, J. Amer. Chem. Soc., 1982, 104, 1146. 2 R.H. Jones, A. M. Chippindale, S. Natarajan and J. M. Thomas,, J. Chem. Soc., Chem. Commun., 1994, 565. 3, A.M. Chippindale, A. V. Powell, L. M. Bull, R. H. Jones, A. K. Cheetham, J. M. Thomas and R. Xu, J. Solid State Chem., 1992, 96, 199. 4. R.H. Jones, J. M. Thomas, R. Xu, Q. Huo, A. K. Cheetham and A. V. Powell, J. Chem. Soc., Chem. Commun., 1991, 1266. 5. J.M. Thomas, R. H. Jones, R. Xu, J. Chen, A. M. Chippindale, S. Natarajan and A.K. Cheetham, J. Chem. Soc., Chem. Commun., 1992, 929. 6 B Kraushaar-Czarnetzki, W.J.H Stork, R.J. Dogterom, lnorg.Chem, 1993, 92, 5029. 7 A. Kuperman, S. Nadimi, S. Oliver, G. A. Ozin, J. M. Garcesand M. M. Olken, Nature, 1993, 365, 239.
H.G. Karge and J. Weitkamp (Eds.)
Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
S Y N T H E S I S AND C H A R A C T E R I Z A T I O N
OF
( H 3 N - ( C H 2 ) 6 - N H 3 ) 4 [W 18P2 O621, A D A W S O N - T Y P E A N I O N IN A N E W E N V I R O N M E N T
Markus Hflscherl, Ulli Englert2, Bodo Zibrowius 1 and Wolfgang F. Hflderichl lInstitut fiir Brennstoffchemie und physikalisch-chemische Verfahrenstechnik der RW771 Aachen, Worringerweg 1, 52074 Aachen, Germany 2Institut fftr Anorganische Chemie der RIJ~H Aachen, Prof. Pirlet-Str. 1, 52074 Aachen, Germany
INTRODUCTION One aspect of heterogeneous catalysis with microporous materials lies in the defined structure of the micropore volume, which allows a variety of organic reactions to proceed shape selectively l, 2. Heteropolyoxoanions have served as useful oxidation catalysts both in homogeneous and heterogeneous reactions 3, but to our knowledge they are not known as a part of a microporous material. In the course of our attempts to prepare such a catalyst we were successful in obtaining materials which could serve as catalysts of the above mentioned kind. For the first time we report on the synthesis and characterization of (H3N-(CH2)6-NH3)4[W18P2062] (1), an opened heteropolyoxometallate structure having a unidimensional microporous channel system.
EXPERIMENTAL Hydrothermal syntheses were carried out in stainless steel autoclaves fitted with 250 ml teflon beakers that contained a mixture of tungsten metal, ttmgstenoxide, phosphoric acid, 1,6-diammohexane and water. The reaction mixture was heated to 140 - 220~ After removing the mother liquor the remaining solid was air dried. The sample was characterized by means of X-ray powder diffraction, single-crystal X-ray analysis, FTIR, 13C and 31p MASNMR spectroscopy, TG/DSC, nitrogen and water adsorption, SEM and chemical analysis.
29 R E S U L T S AND DISCUSSION The product obtained from the synthesis yielded dark blue crystals of (1) in tetragonal shape with approximate dimensions of 0.5 x 0.5 x 0.5 ram. FTIR as well as 13C and 31p MASNMR spectroscopy showed, that the compound contained the organic molecule and phosphate. The X-ray powder diffraction pattern could be indexed orthorhombic with a = 19.838, b =18.682, c =12.605. The single crystal structure analysis of (1) showed the compound to consist of P2W18062-anions which are linked by the H3N+-groups of the 1,6diammohexane molecules (Fig. 1). The diamme works as a spacer that opens up the dense structure, in contrast to the known corresponding alkali salts 4.
Figure 1 View of the structure of (1) along the crystallographic c-axis The structure shows the compound to have a defined micropore volume, which we are studying at the present moment by means of adsorption. References: 1 W.F. H61derich and H. van Bekkum, Stud. Surf. Sei. Catal. 58 (1991) 631-727 2 S.M. Csicsery, Zeolites, _4(1984) 202-213 3 M. Misono, Catal. Rev.-Sci.-Eng. 29 (1987) 269-321 4 B. Dawson, Acta Cryst. _6(1953) 113-126
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
GROWTH OF ZEOLITE A ON RUTILE, SAPPHIRE AND QUARTZ A.Erdem-~enatalar*, H. van Bekkum* and J.C. Jansen* * Istanbul Technical University, Department of Chemical Engineering 80626 Maslak, Istanbul, Turkey. * Delft University of Technology, Laboratory for Organic Chemistry and Catalysis Julianalaan 136, 2628 BL, Delft, The Netherlands. SUMMARY Single crystals of zeolite A have been grown on essentially fiat single crystal surfaces of 001 futile and sapphire and on single crystals of quartz. Two events of nucleation were observed, one initially on the support surface directly from dilute solution, and the other from a gel layer which formed later on the surface, resulting in a bimodal size distribution. Type of the support was seen to influence both events as was reflected in the orientation of the crystals. Formation of a monolayer of randomly oriented crystals of A was followed by time experiments on quartz surfaces. INTRODUCTION Recently, thin films and coatings of zeolites have been prepared for catalysis, separation and sensor applications. In particular, continuous monolayers of silicalite-1 crystals were grown on silicon wafer as support, the orientation of the crystals being a function of the presence of a continuous gel layer preceeding the crystallization [1]. In the case of low SilAI zeolites, however, nonuniform multilayers of randomly oriented crystals were reported [2]. The purpose of this work is to gain more insight on whether a particular gel phase can be formed or excluded in order to prepare a monolayer of zeolite A crystals either from a precursor phase or directly on the support surface. For this purpose, we followed the growth of single crystals of zeolite A on essentially flat single crystal supports of rutile, sapphire and quartz, which have physical and/or chemical framework matching properties with the zeolite A crystals. EXPERIMENTAL Single crystal essentially flat 001 wafers of futile and sapphire and quartz single crystals were used as supports. Synthesis mixtures of different compositions were prepared using sodium aluminate, sodium hydroxide and sodium silicate solutions. PET bottles containing the supports, precleaned and placed in teflon inserts, were kept in a preheated oven at 65, 80 or 100 ~ for various periods. The surfaces, after being cooled and cleaned, were studied with optical microscopy, SEM and XRD. The 001 single crystal surfaces of the rutile and sapphire wafers were sampled for at least 100 single crystals of zeolite A, with SEM , using equal areas of I00 l~m2, selected randomly from different sections of the wafers.
3]
RESULTS AND DISCUSSION After the preliminary experiments with typical zeolite A synthesis mixture compositions, it was found to be necessary to strongly dilute the synthesis mixture in order to obtain a monolayer of zeolite A crystals. In a particular series of experiments from synthesis mixtures having a molar oxide composition of 10 Na20:0.2 AI203:1.0 SiO2:200 H20, growth of single crystals of zeolite A could be observed on the surfaces, much earlier than any crystal formation was observed in the bulk solution by conventional techniques. Two events of nucleation were indicated by the bimodal crystal size distribution of zeolite A, especially on rutUe and quartz surfaces. After the initial nucleation which started on the support surface in the dilute synthesis mixture resulting in relatively large crystals with enriched morphology, a continuous thin gel layer was formed on the surface initiating an explosion of small crystal formation. Type of the support surface was seen to influence both events. Of the large crystals born at an early stage on the support surface when still no gel phase was present, a substantial part (60 %) was edge oriented on futile whereas a fiat orientation was preferred on sapphire. No absolute orientation relation occurred though, despite the presence of local lattice matching units, for example in the case of 001 futile. The small crystals were mainly face oriented on futile. However, like the large crystals they were not alligned, which excludes epitaxy. It is therefore concluded that as soon as the crystallites growing in the gel layer touch the support surface, they become face oriented by electrical and surface tension forces, in this case. The absence of small crystals on the sapphire surface and the fact that their fiat orientation was not observed on quartz, indicate that the formation
and
physical/chemical nature of the gel layer are determined by the type of the support surface used. The formation of a monolayer, fiat on one side, of zeolite A crystals could be followed by time experiments at 65 ~
on quartz surfaces. The initial rate of nucleation is strongly
dependent on the surface topology and/or orientation of the support surface in the reaction mixture, as was seen from the markedly different larger crystal populations on different faces of the single quartz crystals. The growth rate, on the other hand, estimated to be 0.8 i~m/h for the initial crystals formed on the surface, was much higher than that for the second crop of smaller crystals growing from the gel, which was on the order of 0.3 l~m/h. REFERENCES 1. J.C.Jansen, W.Nugroho and H. van Bekkum, Proc. 9th. IZC, Montreal (1992), R. von Ballmoos, J.B.Higgins and M.M.J.Treacy (Eds.), 247. 2. M.W.Anderson, K.S.Pachis, J.Shi and S.W.Carr, J.Mater.Chem., 2(1992), 255.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions
32
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All fights reserved. PREPARATION AND PROPERTIES OF PRIMARY LEONHARDITE, (Na, K)-EXCHANGED FORMS OF LAUMONTITE Atsushi Yamazaki, Takahiro Shiraki, Hironori Ishida and Ryohei Otsuka Department of Mineral Resources Engineering, Waseda University, 3-4-10hkubo, Shinjuku-ku, Tokyo 169, Japan
SUMMARY (Na, K)-exchanged forms of laumontite, co-called "primary leonhardite", can be prepared under hydrothermal conditions. The products show two steps of dehydration at about 180 and 240~ on TG-DTA curves, the same as previous reports about primary leonhardite. XRD data recorded under controlled relative-humidity suggest that the synthetic "primary leonhardite" maintains a similar framework structure to the fully hydrated phase of laumontite between 0 and 100% RH at 25~ The number of water molecules varied from 13 to 17 per unit cell when replacing Ca by alkaline cations. The alkaline extra-framework cation sites of "primary leonhardite" are determined by Rietveld's method. INTRODUCTION Laumontite is a Ca-rich zeolite mineral, with the ideal chemical formula Ca4A18Si16048-16H20. It is well known that laumontite partially dehydrates to leonhardite under ordinary atmospheric conditions. This dehydration is normally reversible; if submerged in water, leonhardite reverts to laumontite. Fersman (1909) and Pipping (1966) reported an alkaline-rich laumontite "primary leonhardite", the atomic ratio (Na+K)/Ca was higher than 1.0, and suggested that this chemical character should be related to the impossibility of getting from the specimen the fully hydrated phase. However, mineralogical properties of the primary leonhardite have been scarcely defined because of its rare occurrences. In this study, (Na, K)-exchanged forms of laumontite were prepared from natural laumontite crystals under hydrothermal conditions. Crystallo-chemical properLies, and de- and re-hydration behaviour of the synthetic "primary leonhardite" were determined. EXPERIMENTAL The starting material was a high-temperature phase obtained from natural laumontite, from Hotokezaka, Yamagata Pref., Japan, preheated at 600~ for 1 hour. Hydrothermal experiments were performed with 3 mol dm-3 of (Na, K)C1 soluLions at 200~ using a Morey type bomb, containing a Teflon bottle - 10 ml in
33 volume. The products were characterized by thermal analysis (TG-DTA), hightemperature X-ray diffractometry and XRD measurement under the conditions of strictly controlled relative-humidity. The crystal structure of the products were refined by Rietveld's method. RESULTS AND DISCUSSION (Na, K)-exchanged forms of laumontite with higher (Na+K)/Ca ratio up to 6 were obtained under the above hydrothermal conditions. Assuming that the symmetry of the products was monoclinic, the chemical formula and unit-cell parameters obtained were Na6CaA18Si16048.17H20, a=14.794(8) ~, b=13.091(3) ./~, c=7.525(5) A and ]3=110.79(5) ~ for the sodium form; K4Ca2A18Si16048-13H20, a=14.718(8) A, b=13.182(4) A, c=7.570(5) ,/~ and ]J=110.64(5) ~ for the potassium form, respectively. The (Na, K)-forms dehydrate in two steps at about 180 and 240~ and show the same TG-DTA patterns as that of "primary leonhardite" reported by Pipping (1966). The XRD patterns of the products under ordinary atmospheric conditions were similar to that of natural laumontite (Ca-form) at 80 - 100% RH, and a discernible change of XRD pattern was not observed from 0 to 100% RH. These results suggest that the (Na, K)-forms of laumontite maintained a similar framework structure to the fully hydrated phase of laumontite at 25~ between 0 and 100% RH. The number of water molecules varied from 13 to 17 per unit cell when replacing Ca by alkaline ions, indicating a dependence on the composition of the extra-framework cations. The results of the crystal structure refinement by Rietveld's method suggest that the exchangeable alkaline cations were replaced and occupied only on Ca cation sites of laumontite. REFERENCES Gottardi, E. and Galli, E. (1985) "Natural Zeolites", Springer-Verlag, Berlin, p. 100. Pipping, F. (1966) Mineral. Soc. Indea IMA, Vol. 159. Yamazaki, A., et al. (1991) Clay Sci., 8, 79.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
34
G E O A U T ~ V E - ' r Y P E 71=OLmZATION IN THE MIOCENE "RJF::FS,MECSEK MTS., SW-HUNGARY M. Polg~r 1, h Fbrizs 1, M. Tbth 1, r Pdcsi-Don~th 1 and Z. M&the2 1 Laboratory for Geochemical Research, Hungarian Academy of Sciences, H-1502 Budapest, Pf 132 2 Mecsek Ore Mining Co., H-7633 P~cs, Eszt~g~r L. 0t 19, Hungary Summary Two types of zeolitization has been found in the Mecsek Mountains, Hungary. The economically important reserve was formed in closed system by the so called "geoautoclave" zeolitization. In~oduction Miocene rhyolite tufts and dacite tuft were studied in the Mecsek Mountains (SW-Hungary). The tufts and tuffaceous sediments occur in two horizons. The lower rhyolite tuff has two types, flood tuff and ash-fall tuff, the dacite tuff is ash-fall tuff. The lower rhyolite flood tuff appears among terrestrial and lake sediments, with a thickness of 1020 m. The dacite tuff of the upper horizon was accumulated under partly terrestrial, partly marine conditions, its thickness is less than 10 m (H~mor, 1970). The tufts of the two horizons were partly zeolitized, namely, the welded rhyolite tuff is rich in clinoptilolite (Ravasz-Baranyai, 1973), but at the same time the ash-fall type of the rhyolite tuff is not zeolitized, and some occurrences of the dacite tuff which were accumulated under marine conditions were partly zeolitized. The purpose of this paper is to characterize the main mineralogical characteristics in the frame of accumulation of the tufts and the degree of alteration processes, and to give a new model for zeolitization in the welded tuff. Materials and Methods Samples were collected from drill-cores from the W-Mecsek Mts. and from quarry faces of the M~.aTuff-Mine from the E-Mecsek Mts.. The samples consisted of fresh and more or less altered ash-fall, and welded tuft from the different horizons of Miocene tuff occurrences. 100 samples were investigated under microscope, scanning electron microscope for petrological and textural identification, by X-ray diffraction for mineralogical components, wet chemical and X-ray fluorescence methods, and electron microprobe studies for major and trace element association. Mineralogy According to X-ray diffraction data the welded rhyolite tuff contain 0-80% clinoptilolite, cristobalite, smectite (d < 14.5 ~), quartz, volcanic glass. The ash-fall type of rhyolite tuff and the dacite tuff contain mainly volcanic glass, and smectite (d > 14.5 ~). The main phenocrystals of the tufts are: plagioclase, biotite, quartz, and rarely, sanidine and hornblende. The clinoptilolite occurs in the Y shape caves of the dissolved volcanic glass, and in the matrix. Based on electron-microprobe study the clinoptilolite has three different compositional types. One
35
type is rich in alkali cations (Na and K) and the Ca content is low. The second one is Ca-(Ba)-rich, and the alkali cation content (Na and K) is low. The third one is transitional member between the previous two ones. Results and Discusdon Sporadic zeolitization can be found in the ash-fall dacite tuff accumulated in shallow marine conditions, it can be explained by the well known open system zeolitization. High scale zeolitization has been found in the welded rhyolite tuff. At the time of accumulation this type of tuff was characterized by high temperature, which is proved by the coal fragments, the assimilation of the underlying fluvial sediments, and the partial melting of the outer part of the pumice fragments. The local Ca-(Ba)-rich character of clinoptilolite can be explained by local assimilation of limestone fragments. The only zeolite mineral (clinoptilolite)is microcrystalline. The alteration process of the volcanic glass was similar to the general and well known steps of dissolution of the glass, and increasing alkalinity of the system, which finally created optimal conditions for zeolite precipitation. The associating minerals are smectite and K-rich gel-like glass. On the basis of the results the zeolitization in the Miocene welded type of rhyolite tuff can be explained by the "geoautoclave" model of zeolitization, which was described first by Lenzi and Passaglia (1974) and Aleksiev and Djourova (1975), and emphasized by Gottardi (1989). The main reason of zeolitization was the special accumulation of the tuff, namely the preserved high temperature and the impermeable crusts at the bottom and top of the tuff layer, which created similar conditions inside the ash-flow, what is characteristic in autoclaves. The high volatile pressure probably also influenced the process of zeolitization. The zeolitization in this closed system was very intensive and quick compared to the open system one. Conclusions The zeolitization in the Miocene tufts of the Mecsek Mts. has been described as an open system diagenetic process by Ravasz-Baranyai (1973). The authors has found that the ash-fall type rhyolite tuff zeolitized as was described by Ravasz-Baranyai (1973), but the welded rhyolite tuff zeolitized in a special closed system, in the so called geoautoclave. Probably the revision of "open system" diagenetic zeolitization of some welded tufts would lead to the application of the geoautoclave model. Acknowledgements This study was financially supported by the O'I'KA 4067 Project. References Aleksiev, B. and Djourova, E. G. (1975) C. R. Acad. Bu/g. Sci., 28, 517-520 .~a'va-Sbs, E., M~th~, Z. (1992) Acta Geologica Hungarica, 35(2):177-192 Gottardi, G. (1989) Eur. J. Mineral., 1,479-487. H~mor, G. (1970) Annals of theHungarian Geological Institute, 53, 1, 1-371. Lenzi, G. and Passaglia, E. (1974) Boll. Soc. Geol. Ital., 93, 623-645. Ravasz-Baranyai, L. (1973) Annals of the Hungarian Geological Institute, 53, 2, 1-741.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
36
THE SYNTHESIS OF ZEOLITES FROM DRY POWDERS R. Althoff, S. Reitmaier, W. Schmidt, B.Zibrowius', K.K. Unger, F. SchiJth Institut for A n o r g a n i s c h e C h e m i e und Analytische C h e m i e der J o h a n n e s G u t e n b e r g Universit~it Mainz Institut fQr B r e n n s t o f f c h e m i e und p h y s i k a l i s c h - c h e m i s c h e V e r f a h r e n s t e c h n i k der RWTH Aachen
Summary ZSM-5 was synthesized by different methods with a gradually decreasing water content ending in a reaction mixture with absolutely dry reagents in form of a powder in the complete absence of a solution phase. Amorphous precursors obtained by drying SiO=*AI=O3 gels at 650~ were transformed into zeolites in the presence of dried NH,F and TPABr. The reaction products were characterized by XRD, REM, TG/DTA, MAS NMR and Electron Micropobe. Pure ZSM-5 or Silicalite-1 was obtained in all cases. Some water is probably formed as a reaction product, but the maximum water pressure is appreciably below the saturation pressure at the given reaction conditions. To explain the formation of a zeolite, we suggest a vapor phase mass transfer process with SiF, as the mobile species between the solid phase which contains the amorphous Si/AI-precursor and the formed zeolite.
Introduction In the last 10 years some work has been invested in reducing the water content in zeolite syntheses. Some authors replaced the water by organic solvents, others increased the solid/liquid-ratio up to 3. Another way to form ZSM-5 with a small amount of water is the so called water-organic vapor transport, but in all cases the amount of water was high enough to formulate a classical crystallization mechanism, i.e. a mechanism which includes the presence of a solution phase with OH or F as mineralizer. We here introduce a procedure which leads to the formation of a zeolite without the presence of a liquid phase, starting from powdered reagents. This synthesis process strongly suggests that a vapor phase transport mechanism is possible.
Experimental The ZSM-5 was synthesized by the following three methods with gradually decreasing water content using a dried SVAI- precursor prepared from fumed silica and AI2(SO,)3"18H20. Synthesis A: The precursor was mixed with ammoniumfluoride, organic template (TPABr), and different amounts of water to obtain an overall composition of: 80 SiO 2 : 1 AI20 3 : 145 NH4F : 6 TPABr : 750-3000 H20 The reaction mixture was placed in a 50 ml teflon-lined stainless steel autoclave and sealed before heating it to the reaction temperature of 180"C for 60 hours. After quench cooling, the products were filtered, dried and kept for characterization.
37
Synthesis B: The precursor, the NH,F and TPABr were vacuum dried under a vacuum of 10"4 mbar for 6 hours to remove residual water. The dried reagents were transferred to a glove box, and all the following steps until the sealing of the autoclaves were carried out in the glove box in a dry argon atmosphere. The ammonium fluoride was added and all the reaction components were ground in a mortar for 5 minutes. The composition of the reaction mixture was : 80 SiO 2 : 1 AI20 3 : 6 TPABr : 55 NH4F. The synthesis and the post synthesis treatment were carried out as described above. Results and discussion XRD of the materials proved that pure ZSM-5 was formed in all cases from the amorphous precursor. The morphology of the ZSM-5 obtained from the non aqueous syntheses B is not very different from that observed for ZSM-5 synthesized in the aqueous systems. Bulk analysis of the aluminum content was carried out by X-ray fluorescence. In the dry reaction process there is no aluminum found in the samples, zgSi MAS NMR spectra of these samples showed 11 well resolved peaks which is indicative of an essentially aluminum free framework. The aluminum detected by =TAIMAS NMR could be identified as AIF3. The high SVAI -ratio would support the idea of a gas phase transport mechanism with SiF4 as the mobile species, since AIF3 has a very high melting and boiling point. To explain the formation of a zeolite in the absence of a solution phase as shown in synthesis B, we thus suggest a vapor phase mass transfer process with SiF 4 as the mobile species, based on the reaction SiO 2 + 4 NH4F --) SiF4 + 4 NH 3 + 2 H20 It can be seen that water is formed in this reaction. The maximum amount of water formed, however, is not sufficient to reach the saturation pressure under reaction conditions. Conclusions It was shown that by using a large amount of fluoride (in our case ammonium fluoride) as mineralizer ZSM-5 can be synthesized. The possibility of reducing the amount of additional water down to zero lead to a reaction system only based on powdered reactants. In this system the vapor pressure formed by the reaction of SiO 2 + 4NH4F was high enough to reach the saturation pressure under reaction conditions. Decreasing the amount of added ammonium fluoride lead to a system in which probably no liquid water phase is present under reaction conditions. Based on thermodynamic calculations we propose a gas phase transport process with SiF4 as the transport species.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions
38
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
SYNTHESIS AND CRYSTAL STRUCTURES OF THE DECASILS, A NEW FAMILY OF POROSILS.
B. Marler, A. G r i i n e w a l d - L t i k e , H. G i e s Institut ftir Mineralogie, Ruhr Universit~t Bochum, D-44780 Bochum, Germany Introduction The synthesis of porosil structure types having different pore geometries is strongly influenced by the nature of the template. The size and shape of the template molecules determine the size and shape of the pores and the dimensionality of the pore system. We report here on the synthesis and structure of two new porosils, RUB-3 and RUB-4, which belong to the "decasil" family. Experimental The decasils were synthesized under hydrothermal conditions from a reaction mixture of SiO2H20-Template, where aminonorbornane (ANB) and azabicyclononane (ABN) are the templates. The mixtures were heated in silica tubes at 160~ - 180~ for up to 6 months. Single crystal studies of the materials were performed on precession cameras. High resolution X-ray powder data were collected on a Siemens D5000 diffractometer with Cu K(xl-radiation. Results and Discussion Though the crystal structures of RUB-3 and RUB-4 are closely related RUB-4 is stabilized only by ABN, while RUB-3 is obtained only with ANB. The density of the as synthesized materials of RUB-3 and RUB-4 is 1.99g/cm 3. From thermogravimetry a weight loss of ca. 12% was determined leading in both cases to a framework density of 17.6 Tatoms/1000A 3. Comparing the X-ray powder diagrams (Fig. 1) it is evident that some reflections of the RUB-3 diagram appear as sharp maxima, whereas other reflections are considerably broadened in the pattern of RUB-4. This indicates structural disorder of the structure of RUB-4. The powder diagram of RUB-3 can be indexed in the monoclinic system with a=14.039A, b=13.602A, c=7.428]k and B=102.22 ~ in space group C2/m.
R U B - 3
(
a
s
-
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y
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)
2000-
1500-
1000-
500-
i , . A A . ..... 0
-
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-
,
12
-
-
9,
16
9
20
R U B - 4
24 2B 2 The'La
(
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.
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-
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32
.
)
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o
B
9
9.
l
-
12
.
-
, - .
16
9,
20
.
,
-'.'.
24 2 Theta
,
2B
9 ,
32
.
-
-
,
-
36
.-
,
40
Fig. 1. XRD diagrams of RUB-3 and RUB-4. Complicated intergrowth of the crystals prevented a conventional single crystal structure determination. Nevertheless, "single" crystal X-ray photographs of the hk0-1ayer of RUB-3 and RUB-4 crystals show identical diffraction pattems indicating that the (001) projections of both structures are identical. Higher level photographs of RUB-3 only give sharp diffraction maxima
39 on commensurate sites in reciprocal space. RUB-4, however, shows diffuse intensities extending parallel h01 and 01d and additional intensity maxima on incommensurate sites. RUB-3 and RUB4 are, therefore, two members of a new family of porous structures built from the same basic building units: RUB-3 as an ordered structure and RUB-4 as disordered in two dimensions. The structure of RUB-3 was solved from model building and simulation of X-ray powder diagrams. The structure model was subsequently optimised in a distance-least-sqares (DLS) refinement. The resulting atomic coordinates were used as a starting set for a preliminary Rietveld refinement which proves the correctness of the structure (RF---0.101, Rw--0.153, R,xp--0.059).
Description of the Structure of RUB-3 The fundamental unit of the structure is a cage-like decahedron composed of four 4MR, four 5MR and two 6MR, the [445462]-cage. Neighbouring cages are connected via common 4MR to form 1-dimensional infinite chains (the d e e ~ i l chain) (Fig. 2). Connecting the decasil chains as in RUB-3 leads to another polyhedral unit, the [46546682]-cage (V -- 300 A 3) which houses the ANB guest molecule. With the 8MR pore openings of the [4654668~]-cages a 1-dimensional channel system is formed (Fig. 3).
Fig. 2. The decasil chain
Fig. 3. Schematic representation of the framework of RUB-3.
The decasil chain is the basic building unit of a new family of porous structures, the decasils. By connecting the chains in different ways three simplest ordered structure types (A, B, C) are generated. All of these structure types possess a framework with cage-like voids which are interconnected via common 8MR pore openings to give a 1-dimensional channel system. Type A is represented by the structure of RUB-3; type B is monoclinic (P21/m) with a -- 9.7A, b = 19.6A, c = 7.4A, 13= 98.9 ~ type C is tetragonal (P4m2) with a -- 19.4A, c --- 7.4A.
Description of the Structure of RUB-4 RUB-4 is a disordered material belonging to the decasil family of structures. Diffuse X-ray diffraction intensites which extend along the h01 and 01d directions reveal 2-dimensional disorder indicating that the sequence of decasil chains in the a and b direction has no periodic ordering. From the type of disorder and from the structures of the ordered decasils (A, B, C) it can be concluded that even the disordered structure of RUB-4 has a 1-dim. channel system with 8MR pore openings which is not blocked by the stacking disorder. Therefore, all properties of RUB-4 which are dependent of the pore size and geometry are not effected by the stacking disorder.
H.G. Karge and J. Weitkamp (Eds.) 40
NEW
Zeolite Science 1994: Recent Progress and Discussions
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
TEMPLATES
FOR THE
SYNTHESIS
OF CLATHRASII~S
G. van de Goor, C. Braunbarth, C.C. Freyhardt, J. Felsche and P. Behrens Fakult~t for Chemie, UniversiNt Konstanz, D-78434 Konstanz, Germany SUMMARY Three new templates for the synthesis of silica sodalites and three different clathrasil compounds synthesized with the first metal-organic template molecule are presented. INTRODUCTION The template mechanism in the synthesis of microporous solids is still not fully understood. Besides direct investigations of the crystallization process, it is worthwhile to study the action of new template molecules, which either (a) are derived from known templates by arguments of chemical and geometrical similarity, or which (b) open up new classes of (possible) template molecules. In this contribution, we illustrate point (a) by the judicious choice of templates for synthesis of silica sodalites; point (b) is exemplified by the use of a metal-organic complex as a template. In any case the host matrix is built up from pure silica, in order to simplify the synthesis system and to restrict host-template interactions to van der Waals forces. EXPERIMENTAL All syntheses were carried out in teflon-lined steel autoclaves. Typical data for the synthesis of silica sodalites are given in Table 1. As metal-organic template the cobalticinium cation [Co(C5H5)2] + =- Cocp~ was investigated in the system SiO 2 - N H 4 F - Cocp2PF 6 - H20. Three different clathrasil phases were obtained (Table 2). RESULTS AND DISCUSSION The choice of possible new templates for the synthesis of silica sodalites was guided by arguments of geometric and chemical similiarity to the known templates, namely ethylene glycol (EG) [1] and 1,3,5-trioxane (TR) [2]. The new template 1,3-dioxolane (DI) may be regarded as a hybrid structure between TR and one of the conformations of EG, which contains an intramolecular hydrogen bond and exhibits a five-membered ring structure [3]. Two further new templates for silica sodalite synthesis, namely ethanol amine (EA) and ethylene diamine (ED), are derived by step-wise substitution of the OH groups of EG by NH 2 groups. EA and ED are the first amines that direct the synthesis of silica sodalite [4]. With the Cocp~ cation as template, three different clathrasil phases with structure types nonasil (NON), octadecasil (AST) and dodecasil-lH (DOH) were obtained [5]. All exhibit the yellow colour typical of the cobalticinium cation. The formation of [Cocp~F-]-NON was also recently indicated by BALKUS & SHEPELEV [6]. The fact that also other clathrasil
41
compounds can be formed shows that templating with metal-organic molecules is a general approach for the synthesis of microporous solids. Table 1. Molar composition ratio of the synthesis mixture, crystallization conditions and yield for the synthesis of silica socialites M[SiO2]6. sodalite
SiO 2
M
Na20
H20
T (K)
time (d)
yidd
TRS-SOD
1
0.54
0.07 (Na2CO3)
8.9
443
3
95 %
DIS-SOD
1
2.55
0.20
51
423
6
86 %
EGS-SOD
1
1.60
0.05
-
443
35
90 %
EAS-SOD
1
1.25
0.025
-
443
61
90 %
EDS-SOD
1
1.25
0.025
-
443
33
88 %
Table 2: Molar composition ratio of the synthesis mixture and crystallization conditions for Cocp~-containing clathrasils. SiO 2
NH4F
[Cocp2] PF 6
H20
T (~
time (days)
product
formula
1.0
1.0
0.45
55.5
160
14-21
[Cocp~F-l-NON
[Co(C5H5)~F-I [SiO2122
5.5
5.5
0.45
55.5
170
7
ICocp~F-l-AST
[Co(C5H5)~F-I [SiOzll0
5.5
5.5
0.45
55.5
190
10
[Cocp~F-I-AST and =5% [Cocp~F-l-DOH
ICo(C5H5)~F-] [SiO2110 and [Co(C5H5)~F-] [SiO2134
[COCp~F-]-NON was characterized by a single-crystal x-ray diffraction analysis (Fig. 1) [5]. Surprisingly, the Cocp~ cation is entrapped in a well-ordered manner, with no signs of rotational or other disorder. Also of interest is the position of the F- ion compensating the charge of the Cocp~ cation: It occupies a site in one of the smaller cages of
Fig. 1. Structure of Cocp~-NON as determined by the nonasil structure and is loosely coordinated single crystal structural analysis. Note the alignment tO a Si atom of the framework (dsi_F: 1 84 ,/k) of the Cocp~ ions. The framework is indicated only 9 " by Si-Si connections. This work was supported by the DFG (Fe72/17-1, Be1664/1).
REFERENCES [1] D.M. Bibby, M.P. Dale, Nature 317 (1985) 157. J. Keijsper et al., in "Zeolites: Facts, Figures, Future", Elsevier 1989, p. 237. [2] G. van de Goor, P. Behrens, J. Felsche, Microporous Mater., in the press. [3] [4] C. Braunbarth, G. van de Goor, A.M. Schneider, J. Felsche, P. Behrens, in prep. G. van de Goor, C.C. Freyhardt, P. Behrens, subm. to Z. Anorg. Allg. Chemie. [5] [6] K.J. Balkus, S. Shepelev, Microporous Mat. 1 (1993) 383.1
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
42
SYNTHESIS OF ZEOLITES IN ANHYDROUS GLYCOL SYSTEMS N.B. Milestone', S.M. Hughes and P.J. Stonestreet Industrial Research Limited, PO Box 31-310, Lower Hutt, New Zealand Summary- Sodalite and cancrinite have been synthesized in non aqueous diol systems containing silica, aluminium isopropoxide and sodium hydroxide. Pure sodalite is formed only with 1,2-ethane-diol while other 1,3-diols form predominantly cancrinite. Introduction - Silica sodalite was first synthesized by Bibby and Dalela using a non aqueous route based on alkaline 1,2-ethane-dioi. Later worklb defined the region over which synthesis was possible. Attempts to prepare silica sodalite using other alcohols and diols have not proved successful. Laine et a/. 2 prepared a crystalline potassium trisdiolatosilicate salt in which the silicon was penta-coordinate. The structure of the monomeric sodium salt was determined by Gainsford et al. 3 This penta-coordinated silicon species was shown to be an intermediate in the synthesis route to silica sodalite by Carr eta/. 4 Attempts to prepare other trisdiolato salts directly from silica and alkaline diol solutions have not proved possible except for 1,2-ethane-and 1,2-propane-diol although Kemmitt and Milestone s were able to synthesize several of the other species by ligand exchange of tetraethoxysilane and determine their NMR spectra. Our work has shown that continued heating of the sodium trisdiolatosilicate salt in a minimum amount of 1,2-ethane-diol slowly converts to silica sodalite at temperatures over 150~
Addition of only
a trace of aluminium isopropoxide converts all the salt to sodalite with 24 hours.
Experimental - Pure silica (Aerosil) was heated at 170~ in sealed vessels in a range of anhydrous diols containing sodium hydroxide and varying concentrations of aluminium isopropoxide. The products were examined after 2.5 weeks heating.
Results and Discussion - Pure silica sodalite is formed only with both 1,2-ethane-dioi and 1,2-propanediol provided the Na:Si ratio exceeds 0.5 although Na2Si20s is also formed with the latter. Only a range of different forms of sodium silicates are found with the other diols tested. Additions of small amounts of aluminium as the isopropoxide allows the formation of crystalline aluminosilicates. While 1,2-ethanediol always gives sodalite, 1,3-propane-diol and 1,3-butane-diol consistently produce cancrinite for Si/Ai ratios of 2.5 to 15. At Si/AI ratios of 5 or greater, reactions in 1,2-propane-diol and 2,2-dimethyl-1,3propane-diol tend to produce sodalite while at lower ratios, cancrinite is formed. For all diols other than 1,2-ethane-diol, as the Si/AI is increased, various amounts and forms of sodium silicates are produced. The various crystalline products are presented in Table 1. In pure silica sodalite synthesized in 1,2ethane-diol, one glycol unit per sodalite cage is incorporated. The size of the cage is such that the larger
43
TABLE 1 Crystalline products formed with reactions of glycols with silica and aluminium isopropoxide Si/AI DioI
2.5
1,2-ethane 1,2-propane
sodalite sodalite
1,3-propane
cancrinite sodalite cancrinite sodalite sodalite cancrinite sodalite
1,3-butane 2,3-butane 1,4-butane 2,2-dimethyl 1,3-propane
5
sodalite sodalite cancrinite cancrinite sodalite cancrinite sodalite cancrinite sodalite
10
sodalite cancrinite ~ Na2Si205 sodalite cancrinite cancrinite Na2Si03
~ Na2Si20s
oo
sodalite sodalite ~ Na2Si2Os ,13Na2Si205 ~ Na2SiO3 Na2SiO3 Na2SiO3 J3Na2Si20s
Reaction mixture is 1.5g and SiO2 2.6g NaOH (dry pellet) mixed with lOg of diol and the appropriate amount of Al(OiPr)3 sealed in nitrogen and heated to 170~ for 2.5 weeks.
glycols are unable to pack into the space whereas in the cancrinite structure, the large channel can incorporate the glycol units. Thermogravimetry indicates approximately 1.5 diol per unit cell is retained for the cancrinite products. For the sodalite structures formed with the larger diols, thermogravimetry indicates there is only a small amount of diol present, possibly associated with faults.
It is not
incorporated in the sodalite cages. Only 1,2-ethane- and 1,2-propane-diols are able to initially dissolve the silica to form the penta-coordinated silicon precursor explaining sodalite formation with the pure silica mixtures. Addition of aluminium which readily forms diolato complexes6 is required to allow other glycols to form complexes to provide the nucleation needed for formation of aluminosilicate structures. Clearly the mechanism for formation of these species proceeds by a through solution mechanism via silicon and aluminium complexes. Diethylene and triethylene glycols are unable to form these complexes and do not form crystalline products. REFERENCES
la lb 2
D.M. Bibby and M. Dale, Nature (London) (1985), 37, 157. D.M. Bibby, N.I. Baxter, D. Grant-Taylor and L.M. Parker (1989), ACS Symp Series, p209. R.M. Laine, K.Y. Blohawiak, T.R. Robinson, M.L. Hoppe, P. Nardi, J. Kampf and J. Uhm, Nature (1991), 353, 642. G.J. Gainsford, T. Kemmitt and N.B. Milestone, submitted to Acta Cryst C. B. Heireros, S.W. Carr and J. Klinowski, submitted to Science. T. Kemmitt and N.B. Milestone, submitted to Aust J Chem Soc. T. Kemmitt, unpublished results.
H.G. Karge and J. Weitkamp (Eds.)
44
Zeolite Science 1994: Recent Progress and Discussions
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
SYNTHESIS OF A NOVEL MICROPOROUS CRYSTAL WITH ORGANIC GROUPS COVALENTLY BONDED TO THE SKELETON Kazuyuki Maeda, Yoschimichi Kiyozumi, and Fujio Mizukami National Institute of Materials and Chemical Research, Higashi 1-1, Tsukuba, Ibaraki 305, Japan
SUMMARY
A novel microporous aluminium methylphosphonate (A1MePO-J3) with an approximate composition of A12(CH3PO3)3 was synthesized by a hydrothermal procedure. MAS-NMR measurements revealed that the network structure consists of [A104], [A106], and [CH3PO3] units. The microporous structure of A1MePO-13 is supported by the Langmuir-type N2 adsorption isotherm. INTRODUCTION Microporous crystalline materials with various channel systems represented by zeolites and aluminophosphates were extensively studied. In conventional microporous crystals, however, the wall of the channel is generally composed only of oxygen atoms which are larger in size than aluminum and phosphorus atoms. Therefore, the character of the micropore is fundamentally determined by the arrangement of these oxygen atoms apart from the elements incorporated in the network structure. In this work we intended to construct a new aluminophosphonate network system and modify the character of the channel wall by introducing organic groups directly attached to the phosphorus atoms. Generally, the covalent P-C bond of alkylphosphonates is relatively thermostable towards cleavage. In this article we report the synthesis of a novel microporous crystalline a l u m i n u m methylphosphonate entitled AIMePO-~. EXPERIMENTAL SECTION The typical synthesis procedure was as follows: Pseudo-boehmite p o w d e r ( P U R A L | SCF, Condea Chemie; 74.4 wt.% A1203, 25.6 wt.% water) and methylphosphonic acid (Aldrich, 98 wt.%) were dispersed in water (Al : P : H 2 0 = 1 : 1.5 : 40) by stirring at ambient temperature for 1 hour. The mixture was hydrothermally treated in a Teflon| autoclave at 160~ for 48 hours under autogeneous pressure. The air-dried sample was characterized by ICP, SEM, XRD, and MAS-NMR. Nitrogen adsorption isotherms at 77 K on AIMePO-[5 evacuated at elevated temperatures were also measured.
45 RESULTS AND DISCUSSION The compound obtained (AIMePO-~) consists of well-grown needle-like crystals, as observed by SEM. The elemental analyses of as-synthesized AIMePO-~ gave C 10.5%, H 3.2%, A1 15.2%, and P 27.6%, from which the molar ratio P/A1 was calculated as 1.58. These values correspond with the calculated values; C 10.2%, H 3.1%, A1 15.2%, and P 26,3% for A12(CH3PO3)3- H20, the ideal composition of the neutral salt of aluminum methylphosphonate with water. The XRD of as-synthesized A1MePO-~ gave a complicated pattern with a strong diffraction peak at 7.2 ~ (Cu-K0~, d=12.3 ~). A tentative indexing can be made using a hexagonal lattice with a = 24.7 ,/~, c = 25.3 ~ at present. A1MePO-13 degassed at 500~ under vacuum for 6 h also gave a distinct and intrinsically identical diffraction pattern. The 27Al MAS-NMR spectra of as-synthesized A1MePO-13 gave two sharp signals at-17.6 and 41.2 p p m in the integral ratio of I : 3 attributed to 6- and 4-coordinated aluminum, respectively. These values are consistent with the reported 27A1 chemical shifts for aluminophosphates [1,2] whose aluminate units are surrounded only by phosphate units. The 31p MAS-NMR showed five sharp signals between 1 and 15 p p m and the 13C CP-MAS NMR showed overlapped signals in the region 11 - 14 ppm. As a reference, methylphosphonic acid gave a doublet centered at 11.3 ppm in 13C NMR and a 31p NMR signal at 37.6 ppm. Connection of phosphoric acid with four aluminate units generally gives rise to an up-field shift of 31p from -19 to -30 ppm [1]. The above results and comparisons confirmed that the methyl groups were still attached to the phosphorus atoms in the network structure. Furthermore, it is proposed that a [CH3PO3] unit is connected with two [AIO4] and one [AlO6] units and that all aluminate units are connected only with [CH3PO3] units. A detailed structural analysis is in progress. All of the N2 adsorption isotherms for A1MePO-[Ys degassed at 300-500~ for 6 h were of the Langmuir type (type 1 of the IUPAC classification) which is typical of microporous structures. Although the adsorbed amount of nitrogen remarkably increased from 300~ to 400~ there was no significant increase between 400~ and 500~ The micropore volume of the sample degassed at 400~ was calculated to be 0.117 cm3/g from the DR plot. REFERENCES
[1] C.S. BlackweU and R.L. Patton, J. Phys. Chem., 92 (1988) 3965. [2] D. Mfiller, I. Grunze, E. Hallas and G. Ladwig, Z. Anorg. AUg. Chem., 500 (1983) 80.
H.G. Karge and J. Weitkamp (F_,ds.) 46
Zeolite Science 1994: Recent Progress and Discussions
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved. SYNTHESIS AND PROPERTIES OF ZEOLITE A WITH SALT-CONTAINING [~-CAGES
Ch. Gurris, D. Reich, J.-Ch. Buhl and W. Hoffmann Institut f'tir Mineralogie, Universitfit Miinster Corrensstr. 24, D-48149 Mtinster Summary The enclathration of sodium salts (nitrite, borate, rhodanide) into the 13-cages of zeolite A has been studied. The gel-method combined with hydrothermal treatment proved to be the best way to a maximum degree of salt encapsulation. The products were investigated by X-ray powder diffraction, IR-spectroscopy and simultaneous thermal analysis (TG, DTG, DTA). Introduction The enclathration of stable salt molecules into the 13-cages of zeolites A, X or Y is expected to play an important role to modify the thermal stability, the sorption properties and the reactivity of these zeolites as already proposed by Barrer and co-workers many years ago [ 1-2]. More recently also the imbibition of thermally unstable salts into the polyhedral cages of tectosilicates has become of interest for the development of new materials [3]. In order to study the attainable alterations of zeolites we report here on the synthesis and characterization of zeolite A with salt-filled 13-cages. In this respect it seemed to be worthwile to prepare sodium rhodanide (NaSCN), sodium nitrite (NaNO2) and sodium boratehydrate (NaBO 2 9 4H20) containing zeolites A, because the thermochemical properties of sodalites could already be improved by the imbibition of these guest molecules [3-5]. Experimental Barter and ViUiger described the zeolite treatment with molten salts in order to fill their microporous structures with anions [2], but this method is not suitable here because of the limited thermal stability of the guest salts mentioned above. Therefore different other preparation procedures have been used to study the synthesis of salt-filled zeolite A: (1) The hydrothermal treatment of zeolite A (FLUKA 69836) at low temperatures and pressures (473 K and about 0,015 GPa) in a 4-molar salt solution. (2) The hydrothermal treatment at elevated temperatures and pressures (773K, 0.15 GPa). (3) Hydrothermal synthesis at 353 K using tetraethylorthosilicate as described by Kerr [6] but with an addition of the salts. (4) The gel-method: 15.6 g Na2SiO 3 - 9H20 + 19.7 g NaSCN + 125 ml H20 were added to a second mixture of 12.5 g NaA10 2 + 19.7 g NaSCN + 125 ml H20 and crystallized at 348 K in 50 ml teflon liners for two weeks. An equimolar batch composition is used in the case of nitrite- and borate-zeolite formation. All products were washed extensively in order to extract salt molecules from the s-cages of the zeolite A structure. The crystalline phases were characterized by X-ray powder diffraction, IR-spectroscopy, and simultaneous thermal analysis (TG, DTG, DTA).
Results and Discussion The preparation according to (1) led only to the incorporation of the salts into tx-cages of the zeolite and the enclathrated molecules could easily be removed by washing with water. Using route (2) the initial zeolites were transformed into sodalite phases in the form of small single crystals. Zeolite A with salt containing 13-cages could be observed using the procedures (3) and (4). Whereas (3) only yields a low salt content according to the co-crystallization of sodalite,
47 the gel-method (4) has proved to be the best way for the formation of zeolite A with a maximum degree of salt encapsulation. Obviously the salt is enclathrated into the I]-cages of the structure and therefore could not be removed during extensive extraction with water. IRspectroscopy produced evidence for the salt anions being part of the zeolite structure (see fig. la-c: nitrite absorption at 1260 cm "1, borate absorption in the range of 1150-1500 cm -1 and rhodanide absorption at 2060 cm-1). Boron is found in the 3-fold as well as in the 4-fold coordination. u}
b)
Fig. 1: IR-spectra of zeolites A containing salt molecules in the I]-cages: a) nitrite-zeolite A b) borate-zeolite A c) rhodanide-zeolite A
0
W a ~ ~ b e r (eta- l)
Compared with common zeolite A-hydrate X-ray powder diffraction indicates a slight reduction of the lattice constants in each case. Simultaneous thermal analyses of the new zeolite A species reveal differences in the thermal decomposition behaviour at elevated temperatures. The rhodanide containing zeolite decomposes according to exothermic signals at 1123 K and 1163 K. An additional exothermic reaction in air at lower temperatures indicates the decomposition of rhodanide in connection with the formation of thermally stable SO42-anions inside the [3-cages due to the uptake of oxygen from the atmosphere. The nitrite containing product shows endothermic decomposition at 1173 K and 1193 K respectively. High temperature X-ray powder diffraction shows the formation of carnegieite followed by a nepheline phase at elevated temperatures for both types of zeolites. In contrast to a slight enhancement of the thermal stability of rhodanide- and nitrite-zeolite A (the collapse of saltfree zeolite A-hydrate occurs at 1093 K and 1133 K) the borate containing phase exhibits a much lower stability.
References [1] [2] [3] [4] [5] [6]
R.M. Barrer and W. Meier: J. Chem. Soc. 58 (1958) 299. R.M. Barrer and H. Villiger: Z Krist. 128 (1966) 352. F. Hund: Z. allg. anorg. Chem. 511 (1984) 255. J.-Ch. Buhl: J. Solid State Chem. 94 (1991) 19. J.-Ch. Buhl: Mat. Res. Bull. 28 (1993) 1319. G.T. Kerr: J. Phys. Chem. 70 (1966) 1047.
II. Characterization
This Page Intentionally Left Blank
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions
48
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
S T R U C T U R A L C H A R A C T E R I Z A T I O N OF SSZ-26 AND SSZ-33 M O L E C U L A R SIEVES BY H I G H R E S O L U T I O N E L E C T R O N M I C R O S C O P Y AND E L E C T R O N DIFFRACTION M. Pan and P.A. Crozier Center for Solid State Science, Arizona State University, Tempe, AZ 85287-1704, USA SUMMARY: Framework structures of SSZ-26 and SSZ-33 molecular sieves have been characterized in detail by using high resolution electron microscopy (HREM) and electron diffraction techniques. SSZ-26 and SSZ-33 have similar 3-D pore systems. They are the intergrowth of two end members which have intersecting 10- and 12-member rings. Direct evidence for the two polymorphs and stacking faults has been obtained. For the first time, the 2-D, 3-connected structural net for the projected framework structure has been successfully derived from experimental high resolution images. INTRODUCTION: Molecular sieves of SSZ-26 and SSZ-33 have been synthesized under hydrothermal conditions using the organic structure directing agents [ 1]. The sorption experiment indicates that they have a similar multidimensional pore system [ 1]. The synchrotron x-ray diffraction spectra showed sharp and broad lines indicating the presence of stacking disorder in the structures. In determining their framework structures, HREM and electron diffraction have provided a much deeper insight than x-ray diffraction technique due to the faultings in the structures. EXPERIMENTAL: We have demonstrated the possibilities of performing low-dose HREM on zeolites using a commercial slow-scan CCD camera, and the subsequent image processing procedures to extract the periodic structural information [2]. The same techniques have been used to characterize the framework structures of SSZ-26 and SSZ-33. RESULTS AND
DISCUSSION:
Electron diffraction patterns from single crystals of SSZ-33 frequently showed sharp spots and streakings for certain reflections. The sharp spots occurred at columns of k=3n and the streakings at columns of k=3n.+_+l (n=0,+l,+_2 .... ). Such a characteristic intensity distribution was indicative of layer stackings with frequent faults. The pattern was very similar to that of zeolite beta [3]. By analogy to beta, polymorph A (ABAB...stacking) had an orthorhombic unit cell, and polymorph B (ABCABC... stacking) had a monoclinic unit cell. From the systematic absence observed in electron diffraction patterns, the possible space groups can be obtained. HREM was carried out along the projection discussed above. The two polymorphs were easily seen in the corresponding high resolution images. The averaged unit cells for both polymorph A and B were obtained using the real space averaging techniques, and are shown in figs. 1a and 1b. The bright regions in these figures correspond to regions in the framework with less density, i.e. the pores. Under the approximation for thin crystals, which can be justified for
49 these images, the image intensity is linearly related to the number of T-atoms in a given region. Hence, if the image intensity is reversed, one would obtain a 2-D map representing the projected framework structure (fig.2). This map is identical to the well-known 2-D, 3-connected net in zeolite modeling. For example, the large bright dots in figs. 1a and lb actually correspond to the 10-member tings in the framework structure, and the surrounding 10 rings have been unambiguously identified as two 6-member rings and eight 5-member rings. HREM and electron diffraction have provided critical information in the complete determination of SSZ-26 and SSZ-33 molecular sieve framework structures [4]. CONCLUSIONS: Solving zeolite structures containing defects is generally difficult by using the conventional x-ray diffraction technique. HREM and electron diffraction have proved to be very powerful techniques capable of providing framework structural details at atomic scale (-2A). The 2-D map for the projected framework structure is extremely valuable for the determination of unknown zeolite structures, and has been derived successfully for the first time from experimental high resolution images. We believe that this break-through will contribute a great deal to solving many more zeolite structures in the future.
REFERENCES: [1] S.I. Zones, M.M. Olmstead, and D.S. Santilli, J. Am. Chem. Soc. 114 (1992) 4195. [2] M. Pan and P.A. Crozier, Ultramicroscopy 48 (1993) 322. [3] J.M. Newsam, M.M.J. Treacy, et al. Proc. R. Soc. London Ser. A 420 (1988) 375. [4] R.F. Lobo, M. Pan, et al. Science 262 (1993) 1543.
H.G. Karge and J. Weitkamp (Eds.) 50
Zeolite Science 1994: Recent Progress and Discussions
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
Electron Microscopic Study of Cioverite(-CLO ) O. Terasaki 1), T.Ohsuna2), D.Watanabe2), H.Kessler 3) and C.Schott-Darie 3) 1) Department of Physics, Tohoku University, Sendai 990-77, Japan 2) Department of Materials Science, Iwaki Meisei University, Iwaki 970, Japan 3) Laboratoire de Materiaux Mineraux, URA du CNRS 428, Ecole Nationale Superieure de Chimie, F-68093 Mulhouse Cedex, France S ~ Y Single crystals of gallophosphate, cloverite(-CLO), were studied by scanning electron microscopy(SEM) and high resolution transmission electron microscopy(HRTEM). Both images revealed the existence of parallelepiped-shaped voids, surfaces of which are { 100 } planes inside the crystal. No discernible distortion of the framework structure was observed in lattice images by HRTEM. INTRODUCTION We are interested in zeolites not only from their characteristic structures 1) but also as containers for making new quantum confined materials, which will show physical properties different from those of the bulk crystal, in their spaces2). Recently Nozue et al. published an interesting property that alkali metal K-cluster in LTA shows ferromagnetism at low temperature 3) and this encourages us for making new materials in the spaces. From this view point, it has been always expected to have new zeolites with larger and tunable spaces and also to have high quality large single crystals. A new gallophosphate, cloverite(-CLO), has been synthesized4). From single crystalX-ray diffraction data, the crystal structure was solved. The crystal has the space group of Fm3c with a lattice constant a=51.712/~, and has a characteristic shape of pore opening of a four-leafed clover defined by a ring of 20 gallium and phosphorous atoms 5) . Based . on this structure analysis, the supercage of 29-30 A diameter is expected at the intersection of the channels running along the <100>. We are thus interested in the crystal as a new container for making new materials conf'med in the spaces and in having a large single crystal with high quality. EXPERIMENTAL The -CLO samples were synthesized in Mulhouse, France. The crystal morphology and surface fine structures were studied by using SEM with Field Emission Gun(FEG), Hitachi S-4100, in order to obtain high resolution images at low acc. voltage from as synthesized crystals without metal coating. For HRTEM study, JEOL 4000EX with Cs= 1.0 mm was operated at 400 kV and specimens were prepared by crushing the single crystals and dispersed on microgrids. RESULTS The size of single crystals of-CLO is approximately 80 ttm and the dominant external surfaces of the crystals are either the{ 100} or { 111 } surfaces as shown in Fig. 1. For all samples we have observed in the SEM images craters of rectangular parallelepiped shape on the { 100} or of trigonal pyramids on { 111 } as marked by the arrows in the figure. These craters were also observed in HRTEM images with [ 100] incidence as shown in Fig. 2, where low magnification and high resolution images are shown in (a) and (b), respectively. It is easier to observe contrast from the voids inside the crystal at lower magnification and their density is not small as observed in Fig.2a. The lattice image(Fig. 2b) shows regular structure without any distortion although there are voids inside the crystal. From the observed crystal morphology and the shape of craters, the crystal growth mechanism will be discussed. REFERENCES 1) O.Terasaki: Acta Chem. Scand.45(1991), 785. 2) O.Terasaki: J.Solid State Chemistry 106(1993), 190.
51 3) Y.Nozue, T.Kodaira, S.Ohwashi, T.Goto & O.Terasaki: Phys. Rev. B48(1993), 12253. 4) H.Kessler: Proc. MRS Meeting, Anaheim CA., USA, April 29-May 3, 1991. 5) M.Estermann, L.B.McCusker, C.Baerlocher, A.Merrouche & H.Kessler: Nature 352( 1991 ),320.
Fig. 1. SEM images of CLO without metal coating. Low(a) and high(b) magnifications.
Fig. 2. HRTEM images taken with [ 100] incidence by 400 kV EM. Low magnification(a) and high resolution(b).
H.G. Karge and J. Weitkamp (Eds.) 52
Zeolite Science 1994: Recent Progress and Discussions
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved. H R E M S t u d y o f Pt-clusters on K - L T L C r y s t a l S u r f a c e s Osamu Terasakil), Tetsu Ohsuna 2) & Denjiro Watanabe 2) 1) Department of Physics, Tohoku University, Sendai 980-77, JAPAN 2) Department of Materials Science, Iwaki Meisei University, Iwaki 970, JAPAN
Zeolites containing noble-metal particles have attracted attention as catalysts. The accurate characterization of particles is essential for the understanding of their chemical properties. Highresolution electron microscopy (HREM) is a powerful method for this purpose, but it is not easy to confirm that the particles are inside the channels of the zeolite. This is because that zeolites are electron-beam sensitive and that the strong contribution from the framework masks the contrast from the clusters, when electrons are incident with the direction of the channels. There are several ways to overcome this difficulty: image processing 1), HREM observation of serial ultrathin-sectioned specimens 2) and the Z-contrast method3). Normally, if we can not find the particles on the surface by looking at the direction perpendicular to the channel, we are able to say that the particles are inside. A question then arises, how small particles can be observed along this axis. Consider Pt / K-LTL as an example. The LTL sample ( Si/A1 = 2.4) was kindly supplied by Tosoh Coorp., Japan and Pt was evaporated onto the crystals by the sputtering method. The amount of Pt was controlled by changing the distance between the zeolite powder and the Ptplates, and by the duration of sputtering. HREM images were taken by 400 keV TEM along both the [001] and the <100> directions. The cylindrically shaped K-LTL crystals are electron beam sensitive and show characteristic morphology change ( e.g. to form a waist4)) under the electron beam, also at relatively small electron dose. With the electron beam parallel to the channels, we can observe a contrast from Pt-clusters which are on the (001) plane, if the particles are larger than approximately 30 A. It is however rather difficult to verify that this contrast is caused by the particles, unless the framework is destroyed by the beam. Pt-clusters, which are sticking to the side-wall of the crystals, i.e., { 100}, show a strong tendency to align along the channels facing to the surface (this is observed after morphology change in the beam). HREM images (Fig. 1) taken with the electron beam perpendicular to the channels show clearly where the Pt-particles are before (a) and after (b) a serious damage by the electrons. Pt-particles are stationary on the surface during the electron beam irradiation and this is different from the previous observation of metallic particles5). The Pt-particles, with a diameter larger than 10 ~, are situated on the (001) surface and in the projection shown in Fig.la they can be seen situated above the row of channel openings at the surface. It is clear from all observations that there is a spatial correlation between the channels and Pt-particles (three of them are shown by arrows in Fig 1.a). The shape and darkness of the contrast from the different rows of Pt-particles
53 indicates that the occupancy is not the same for each row and a slight off-set can be seen in some cases. In Fig. lb one can see the lattice fringes of Pt-particles, and it is quite clear from the images that the K-LTL crystal changes its morphology and the Pt-particles are migrated by the beam influence. Therefore one must be careful to discuss the particle size after the destruction of the framework, although it is easier to observe contrast from the particles in this way. REFERENCES 1) V.Alfredsson, O.Terasaki & J-O.Bovin: J.Solid State Chem.,105(1993), 223. 2) J-O.Bovin, V.Alfredsson, G.Karlsson, Z.Blum & O.Terasaki: Proc. MSA'94. 3) S.B.Roce, J.Y.Koo, M.M.Disco & M.M.J.Treacy: Ultramicroscopy 34(1990),108. 4) M.M.J.Treacy & J.M.Newsam: Ultramicroscopy 23(1987), 411. 5) R.Wallenberg, J-O.Bovin & D.J.Smith: Naturwiss. 72(1985), S.539.
Fig. 1 HREM images (a)before and (b)after a serious damage by the electrons.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
54
Location of Tb(lll) Ions in Hydrated Y Zeolites by Luminescence Spectroscopy Jeong Suk Seo, Chong-Hong Pyun, Chang-Hong Kim, Young Sun Uh, Wha Seung Ahn* and Suk Bong Hong Division of Chemistry, Korea Institute of Science and Technology, P.O.Box 131, Cheongryang, Seoul 130-650, Korea *Department of Chemical Engineering, Inha University, Inchon 160, Korea
Abstract Luminescence spectroscopy of the Tb 3§ ion is used to monitor the variation of the cation distribution in Tb, Na-Y zeolites which were fully rehydrated under ambient conditions after thermal treatments at different temperatures.
Introduction In view of zeolite catalysis, the detailed information on the distribution of rareearth ions in zeolites is important because both thermal stability and catalytic performance of zeolites are dramatically enhanced by ion-exchange with rare-earthions. 1 Rare-earth-ion exchanged zeolites are widely used as commercial fluid catalytic cracking catalysts. Luminescence methods have been used to study the effects of thermal or chemical treatments on the physicochemical properties of the rare-earth-ions in zeolites such as changes in coordination environment, oxidation states, or hydrolysis effects. However, no investigations into the distribution of rareearth-ions in zeolites only by luminescence spectroscopy have been reported. Here we report the results obtained from the excitation and emission spectra of Tb, Na-Y zeolites rehydrated after thermal treatments at different temperatures.
Experimental Na-Y (Si/A1=2.43) were obtained from Aldrich. Tb, Na-Y was prepared by ionexchange of Na-Y at room temperature in 0.05 M Tb(NO3)3 solutions for 24 h and followed by heating under the flowing N 2 at desired temperatures for 6 h. Finally, the Tb 3§ -exchanged zeolite powder were fully rehydrated over saturated NH4CI solution at room temperature for 2 days, before the luminescence spectra were taken. Thus, all the samples discuss iex;i in the work were studied in the hydrated state. Excitation and emission spectra were obtained at room temperature using a home-built instrument. A 150-W Xe arc lamp with an Oriel 1/8-meter monochrometer was used as an excitation source.
55
Results and Discussion The emission spectrum of the Tb, Na-Y dried at room temperature shows four emission bands at 491,547, 587 and 624 nm. These bands can be attributed to the transition between the SD and ~F levels of the Tb 3§ion. Their band positions are in agreement with the previous emission data on Tb, Na-Y reported by Tanguay and Suib. 2 Re-exchange of this Tb, Na-Y sample with Na shows significant decrease in their emission intensity, indicating that the Tb 3§ ions exchanged into Na-Y are located in the supercages. Two interesting results are obtained from the emission spectra of Tb, Na-Y samples treated at different temperatures. First, the intensities of the SD4 --> 7Fj transition bands remarkably increase with elevating treatment temperature. In particular, the SD4~ 7Fsemission band at 547 nm begins to split into two bands at 544 and 551 nm, respectively, from the temperatures higher than 423 K. Second, the intensity ratio of SD4 ~ ZFs to SD,~ ZF8 transition, which is 1.5 in the emission spectrum of unheated Tb, Na-Y, is changed to 3.0 in that of Tb, Na-Y heated at 423 K. This value does not vary even with heat treatments at higher temperatures up to 823 K. Also, no noticeable changes in the band shape and intensity are caused by re-exchange with Na. These observations indicate that the migration of Tb 3§ ions from supercages into the internal sites such as sodalite cages or hexagonal prisms of Na-Y begins from at least 423 K. Further evidence to support the conclusion drawn from emission spectra is given by the excitation data. Unheated Tb, Na-Y shows a strong broad band at 224 nm and numerous bands between 250-450 nm, which are due to the ~F ~ 7D transition of f-d level and the SD3---)7Fj transition bands of f-f levels, respectively. As observed in the emission spectra, the intensities of all the excitation bands of Tb, Na-Y increase with elevating the treatment temperature. However, the 7F~TD transition band at 224 nm shifts to 232 nm at the temperatures higher than 423 K, whereas the other bands due to the f-f transitions do not show changes in their band positions by heating up to 823 K. It is well-known that the f-d transition bands of rare-earth-ions doped into inorganic glasses or crystals are very sensitive to variations in the local environment, but the f-f transition bands are not. For example, Brixner et aL 3 show that the 7F ~ ~D transition band of Tb 3§ shifts from 250 to 262 nm when the host is changed from LaOCI to LuOCI. Therefore, it can be concluded from the observations presented here that the variation of the rare-earth-ion distribution in zeolites can be successfully monitored by luminescence technique.
References 1. S. Bhatia, Zeofite Catalysis: Principles and Applications, CRC, Boca Ranton (1990). 2. J. F. Tanguay and S. L. Suib, Catal. Rev.-Sci. Eng. 29, 1 (1987). 3. L. H. Brixner, J. F. Ackerman and C. M. Foris, J. Lumin. 26, 1 (1981).
56
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
LOCALIZATION OF PT2+ IN NAX R. Schnell, C Kirschhock, H. Fuess Fachgebiet Strukturforschung, Fachbereich Materialwissenschaft, Petersenstr. 20, D-64287 Darmstadt
SUMMARY The zeolite NaX was cation exchanged with [Pt(NH3)4] 2+ . The platinum cations were localized by powder X-ray diffraction. Temperature dependent measurements revealed the platinum-cluster formation in the partially reduced material. INTRODUCTION The reduction of transition metals in the cavities of zeolites yields highly dispersed metal particles. These systems are potential materials for catalytic applications. The present note reports results on NaX, partially ion exchanged with [Pt(NH3)4] 2+ [1]. Dispersed Pt-particles are obtained by heating this material. The resulting particle-size depends on the degree of exchange [2,3,4]. Although platinum is a classical catalyst the mechanisms of nucleation and growth of platinum clusters are not understood. To enhance knowledge on this system the [Pt(NH3)4]2+-complexes have been localized within the host for different Ioadings. Furthermore temperature dependent studies should reveal the process of cluster formation. E X P E R I M E N T A L SECTION The ion exchanged samples were prepared by the group of Schulz-Ekloff (Bremen)[1]. The metal content was analysed by AAS and energy-dispersive X-ray analysis. Samples with the following compositions were examined: Na72Pt6AI84Si1080384, Na54Pt15AI84Si1080384, Na40Pt22AI84Si1080384 equaling an Na + exchange degree of 13%, 35% and 52%. To remove the water, the zeolites were heated up to 393-403 K (4-10K/h) in vacuo (10 .4 mbar). The X-ray powder measurements were carried out on a Stoe STADIP powderdiffractometer. Experiments were performed at room temperature and several elevated temperatures ( 423 K, 443 K, 463 K, 483 K, 548 K, 623 K, 723 K ). The structural parameters of the frame and the guest molecules were refined with the program 'RIETAN' [5], the difference Fourier syntheses were calculated using the software package 'XTAL '.
57
RESULTS
AND
DISCUSSION degree of ion exchange were examined at roomtemperature. Depending on the pretreatment the Pt 2+ is distributed over one to three different positions within the supercage. A sample where all the platinumcations could be localized at the position V in the 12 ring window was examined under argon atmosphere as a function of temperature. From 298 K to 443 K all the Pt2+ ions remained at their position. From 463 K up to 543 K the occupation factor decreased while broad Pt-reflections characteristic for Pt metal occurred. No additional Pt 2+ positions were detected. At 543 K the reduction is completed and the Pt 2+ occupation factor is close to zero. At higher temperatures the platinum reflections do not change anymore. The behaviour of the occupation factor of Pt 2+ shows that up to the onset of reaction no extended diffusion takes place but the cations are fixed on their adsorption sites. This is an indication of an undisturbed coordination sphere of platinum cations up to 483 K. It clearly explains why no platinum is found in the small cavities as due to the size of [Pt(NH3)4]2+-complexes access through six ring Three samples with different
windows is excluded.
ACKNOWLEDGEMENT We thank the BMFT and the Max Buchner-Stiftung for financial support.
REFERENCES
[1] [2]
[3]
[4] [5]
Busch, F., Jaeger, N.I., Schulz-Ekloff, G.: in preparation Kleine, A., Ryder, P.L., Jaeger, N.I., Schulz-Ekloff, G.: Electron Microscopy of Pt, Pd, and Ni Particles in a NaX Zeolite Matrix. J. Chem. Soc., Faraday Trans. 1, 82, (1986), 205-212. Tonscheidt, A., Ryder, P.L., Jaeger, N.I., Schulz-Ekloff, G.: Orientation and morphology of iridium, rhodium and platinum nanocrystals in zeolite X. Surf. Sci. 281, (1993) 51-61. Gallezot, P., Bergeret, G.: Characterization of Metal Aggregates in Zeolites. Stud. Surf. Sci. Catal. 1982, 167. Izumi, F., Asano, H., Murata, H., Watanabe, N.: Rietveld Analysis of Powder Patterns. J. Appl. Crystallogr. 20 (1987) 411-418.
ft.(3, l~arge and J. Weitkamp (Eds.) 58
Zeolite Science 1994: Recent Progress and Discussions
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
Characterization of SO2-contaminated Cu-ZSM-5 catalysts C. LLengauer l_, E. Tillmanns l C.Plog, 2 1 Inst. f. Mineralogie und Kristallographie, Universit~t Wien. Dr.Karl Lueger-Ring 1, A-10I0 Wien 2 Dornier GmbH, Deutsche Aerospace, D-7990 Friedrichshafen 1
The removal of nitrogen oxides (NOx), which are considered to play an active role in air pollution processes, is an important topic in the field of catalytic applications of ion exchanged molecular sieves. Beside other types of catalysts, like Y-Ba-Cu-oxides or Pt-coated A1203, copper exchanged zeolites show a high catalytic performance in the direct decomposition of NOx from emissions of diesel engines and industrial boilers. Because of their thermal stability up to 1000~ and their high activity in the oxidised state Cu2+/I+-ZSM-5 zeolites (1) are an important alternative to common noble metal or metal oxide catalysts. A SO2-content in the feeding gas, however, which is inevitable in real exhaust gases, 'poisons' the zeolite catalyst. This behaviour is also reported for Cu-MOR (2) and Cu-FAU (3). To depict the SO2 contamination of ZSM-5 three Na-ZSM-5 materials with Si/AI ratios of 27, 30 and 55 were treated with Cu-solutions and contaminated under a SO2 gas flow. 12 samples (3 Na-ZSM-5, 3 Cu-ZSM-5, 3 Na-SO2-ZSM-5, 3 Cu-SO~-ZSM-5) were investigated by X-ray powder diffraction (XRD) and thermal gravimetry (TG). The 6 copper exchanged zeolites were additionally heated in the range from 100-800~ with an increment of 100~ under reducing conditions (30%I-12, 70%N2). The line broadening of the Cu-111 peak was determined by interactive peak fitting and the mean particle size was calculated with the Scherrer formula (4). The XRD investigation of all 12 samples reveals that the incorporation of copper and SO2 affects the intensity of the low angular reflexions, thus confirming the occupation of distinct sites in the channel system. The lattice parameter of the zeolites do not change upon cation exchange. Only the thermal treatment leads to a slight contraction of the zeolite framework. The TG measurements indicate a clear interaction between Cu and SO2 within the zeolite pore system (Fig. 1). The Cu-ZSM-5 as well as the Na-ZSM-5 phases show a two step dehydration in the range of 50-250~ (Fig. I.A,B). The Na-SO2-ZSM-5 samples, however, are characterized by an additional distinct loss of the SO2 contamination at 300~ (Fig. I.C). The Cu-SO2-ZSM-5 zeolites reveal a completely different behaviour with a three step weight loss at 320~ 575~ and 625~ respectively (Fig. 1.D). The amount of absorbed SO2 decreases with increasing Si/AI ratio. The growth of the Cu-clusters under reducing conditions of the Cu-ZSM-5 samples starts at 200~ after the two dehydration steps. The first recognizable clusters have a mean diameter of 4006 0 0 ~ which is doubled at 300~ and continuosly increases to 1600-3000A at 800~ The final size increases with decreasing Si/AI ratio, i.e. with increasing amount of loaded copper. Simultaneously the amount of the metallic Cu-clusters increases linearly with temperature. The SOz poisoned samples, on the other hand, show a beginning of Cu-cluster growth at 300~ again a steep increase within the next 100~ and a continuous growth up to 800~ to a significantly bigger diameter in the range of 2500-6000A. In these samples the growth of Cu-clusters proceeds differently and is correlated to the gravimetric results (Fig.2). The intensity of the Cu-111 peak rises between 300500~ after the first SO 2 decontamination step, stays constant to 600~ and again increases until 700~ after the second and the third decontamination step. The results of the investigations lead to the assumption that SOz competes with NO• for the adsorption sites and prevents the catalytic reaction by blocking the channels, but is contrary to the interpretation that the deactivating agents are deposited on the surface of the catalyst. References: (1)IWAMOTO,M. et ai.; Jour.Chem.Soc. Faraday Trans.( 1981 ); 1,77,1692. (2)KHULBE, K.C.; MANN, KS.; MANOOGIAN, A.; J.Mol.Catal.(1988);48,365. (3)MIZUMOTO,M.; YAMAZOE, N.: SEIYAMA, T.; J.Catal.(1979)~59,319. (4)JENKINS,R.; DE VRIES,J.L.; Philips Technical Library (1970),Mac Millan.
59
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F i g . l Thermogravimetric measurements of ZSM-5 catalyst with Si/AI-27. A: Na-ZSM-5; B Cu-ZSM-5: C Na-ZSM-5+SO2: D: Cu-ZSM-5+SO2. The upper line represents the first derivative of the TG results.
~
60
-
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Cu-ZSM-5+S02 [counts]
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Fig.2: XRD pattern of the Cu(l I 1) peak of a SO2-contaminated Cu-ZSM-5 during thermal treatment under reducing atmosphere.
4~.5
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
61
SINGLE CRYSTAL STRUCTURE ANALYSIS AND ENERGY MINIMIZATIONS OF A H-ZSM-5/p-DICHLOROBENZENE COMPLEX AT LOW SORBATE LOADING H. van Koningsveld, J.C. Jansen and A.J.M. de Man Laboratories of Applied Physics and Organic Chemistry and Catalysis, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, The Netherlands Arbeitsgruppe
Quantenchemie
an
der
Humboldt-Universit&t
Max-Planck-
Gesellschaft, Jaegerstral3e 10/11, D-10117 Berlin, Germany SUMMARY. The crystal structure of a low-loaded complex of H-ZSM-5 with p-dichlorobenzene has been studied by single crystal X-ray diffraction. The controversy in the literature, concerning the location of the p-dichlorobenzene molecule, is explained by different interpretations of the difference electron density map representing the electron density of the adsorbed molecule. There are 2.56(2) p-dichlorobenzene molecules per unit cell. The adsorbed molecules very probably prefer the position at the intersection of channels. Energy calculations, using the BIOSYM Catalysis and Sorption Software, strongly support this interpretation. The unit-cell is orthorhombic Pnma, with a = 20.009(3), b = 19.909(4) and c = 13.366(2) A. The final R(Rw) is 0.044(0.048), w = 1/o2(F), for 5306 observed reflections with I > 2.0 a(I) measured at 293 K.
INTRODUCTION. The structure of the high-loaded complex of H-ZSM-5 with p-dichlorobenzene (8 pdcb mols/u.c.) has been studied by Mentzen (1) using X-ray powder diffraction data. The structure is in all details comparable to those observed in the H-ZSM-5/8 p-xylene complex (2). Conflicting results are reported on the location of pdcb on the low-loaded complex (< 4 mols pdcb/u.c.) with H-ZSM-5. Two possible locations are suggested differing by a shift of 1A b: one is at the intersection of channels (1) and the other is in between the intersections (3, 4). We prepared a low-loaded single crystal of H-ZSM-5 with 2.6 pdcb mois/u.c. This complex was studied by single crystal X-ray diffraction. In addition, preferred adsorption sites were looked for with energy minimizations using the BIOSYM Catalysis Software (5). EXPERIMENTAL. A calcined single crystal of H-ZSM-5 was evacuated at 353 K and
exposed to a vapour of pdcb. After 3 h the temperature was lowered to room temperature. X-ray data were collected on an CAD-4 diffractometer using Mo-K~ radiation. All X-ray calculations were performed using the XTAL-3.2 system of
62 programs (6). The energy calculations were done on a Silicon Graphics Iris Indigo Workstation.
~ E "~
~'
I' 9 ~
0
, ~
~0 /.I-
.....
~f
~a
!
!
Figure 1.
I Figure 2
RESULTS. Figure 1 shows, in two projections, the location of pdcb at the intersection of channels. Figure 2 gives the rotational energy curves for both models suggested in the literature. The benzene ring is rotated ~~ around the molecular CICI axis, using the CI atomic positions obtained from X-ray refinements. SE gives the guest-host and guest-guest interaction energy per unit cell. The XRD position of pdcb given in Figure 1, is indicated. Full minimizations were performed in the minima of the rotation curves. The results of these calculations will be presented. References: Available from the authors at the poster stand.
H.G. Karge and J. Weitkamp (l~ds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
SINGLE
CRYSTAL
H-ZSM-5
WITH
STRUCTURE
ANALYSIS
63
OF
A
HIGH-LOADED
COMPLEX
OF
PARA-DICHLOROBENZENE
H. van Koningsveld and J.C. Jansen Laboratories of Applied Physics and Organic Chemistry and Catalysis, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, The Netherlands. SUMMARY. The structure of the H-ZSM-5/p-dichlorobenzene complex, containing 8 molecules pdcb/u.c, has been solved by single crystal X-ray diffraction. One of the two independent pdcb molecules lies at the intersection of channels with its long molecular axis nearly parallel to the straight channel axis. The second pdcb molecule is in the sinusoidal channel with its long molecular axis nearly parallel to [100]. The unit cell is orthorhombic, P212121, with a = 20.102, b = 19.797 and c = 13.436 A. All structural details in H-ZSM-5/8 pdcb are comparable with those in the H-ZSM-5/8 p-xylene complex. INTRODUCTION. The adsorption of p-xylene in H-ZMS-5, at high Ioadings, induces a symmetry change to P212121. The adsorption in the sinusoidal channels is accompanied by a cooperative deformation of the (100) pentasil layers (1). To see whether pdcb was able to induce the same symmetry change or not, a high-loaded complex of H-ZSM-5 with pdcb was prepared. A single crystals of this complex was used for X-ray analysis. EXPERIMENTAL. H-ZSM-5 single crystals of 30 x 50 x 110 #m were prepared according to a well established method. To obtain a high loaded complex the following procedure was used. H-ZSM-5 as well as pdcb crystals were placed in a 20 ml vessel. Excess of pdcb was stored in a connecting vessel of 40 ml. After evacuation of both vessels the temperature was kept fixed at 523 K for the first five hours. Subsequently, an alternating temperature profile, between 333 and 373 K with a heating and cooling rate of 2K/min was performed seven times. This procedure was adopted to achieve high Ioadings by making optimal use of the framework flexibility during the adsorption. Finally the crystals were cooled to room temperature. One of these crystals was chosen for the structure analysis. X-ray data were collected on a CAD-4 diffractometer using Mo-K~ radiation. All X-ray calculations were done using the XTAL-3.2 system of programs. The 4final R(Rw)=0.044 (0.040), w = 1/o2(F) for 5836 observed reflections with I > 2.0 o (I) at 293 K.
64 RESULTS. Figure 1 shows the structure of the H-ZSM-5/8 pdcb complex. For comparison the H-ZSM-5/8 p-xylene complex (Figure 2) is added. Both structures are en along the b-axis.
Figure 1
O~3
Figure 2
REFERENCE 1 H. van Koningsveld, F. Tuinstra, H. van Bekkum and J.C. Jansen, Acta Cryst. (1989), B45, 423-431.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
CHARACTERIZATION
65
OF BIMETALLIC
ZEOLITE SUPPORTED
Pt-Pd CATALYST BY EXAFS, TEM AND TPR T. Rades, M. Polisset-Thfoin, and J. Fraissard, (Laboratoire de Chimie des Surfaces, Universit~ Paris 6, France) and R. Ryoo, and C. Pak, (Department of Chemistry and Center for Molecular Science, Korea Advanced Institute of Science and Technology, Taeduk Science Town, Taejon, Korea)
SUMMARY Pd-Pt/NaY catalysts have been characterized by TEM, TPR and EXAFS. TEM was used to determine the particle size distribution and the dispersion, the latter decreasing with increasing Pd content. By TPR it was shown that mixed particles were formed. Intraparticulardistribution of the two metals was analysed and alloy-formation confirmed by EXAFS. EXAFS measurements showed that Pd and Pt are randomly mixed in metal particles. A sample with high Pt content, however, had a Pt core structure.
INTRODUCTION Petrochemistry is based on heterogenous catalysis using mainly zeolites and supported
metals as catalysts.
In hydrogenation
and dehydrogenation
of
hydrocarbons platinum- or palladium-based catalysts are the most widely used. The association of two metals may confer many advantages, such as improvement of activity or modification in selectivity for some kinds of reaction, these differences being mainly due to a mechanistic change. In the case of a Pt-Pd catalyst the Pd may increase the resistance of Pt to poisoning by sulphur or nitrogen compounds, larger amounts of which are present in the heavy petrol cuts [1]. A different surface state or a different dispersion of the metal may lead to synergetic effects. Catalyst characterization is very important in catalysis because it elucidates the chemical, structural and electronic properties of the system. The important information in heterogenous catalysis concerns surface properties (structure and composition) at the atomic scale, but, in the case of bimetallic catalysts, also metal distribution inside the clusters.
EXPERIMENTAL
Preparation:
SECTION Samples consist of small metal particles supported on an
industrial faujasite type NaY zeolite (0.6 mmol of metal per gram of raw zeolite) prepared by simultaneous cation exchange [2]. The sample is calcined in oxygen flow at T c = 300~ T c was chosen in order to obtain free M 2+ metal ions [3]. The sample is purged and then reduced at 300~
Sample Characterization:
under H 2 flow for 2h.
For EXAFS measurements, the powder sample is
reduced again in a Pyrex U-tube flow reactor connected to an EXAFS cell then
66 sealed off under H2 atmosphere. The EXAFS measurements are performed in the transmission mode at the Pt LIII and the Pd K edges at RT. 80nm thick sections of zeolite are analysed by Transmission
Electron
Microscopy. The direct picture of the supported metal particles obtained is used to determine the particle size distribution and then the metal dispersion.
Temperatureprogrammed Reduction is performed in a microflow reactor. After the calcination step the sample is reduced in a 7 ml/min Noxal flow (5% H2-95% Ar) with the temperature increasing linearly from RT up to 650~ at the rate of 600~ H 2 consumption is detected with a thermal conductivity detector.
RESULTS
AND
DISCUSSION
Extended X-Ray Absorption Fine Structure (EXAFS): Significantly large values of coordination numbers of Pt around Pd and Pd around Pt indicate the formation of bimetallic Pt-Pd clusters. The very similar values of the Pd and Pt coordination numbers mean that the two metals are randomly mixed. In the case of Pt75 (75% Pt), however, the coordination numbers are significantly different (Npd < Npt). This suggests that the cluster core is rich in Pt [4]. The size of bimetallic clusters seems to be less than 1.8 nm, but may be underestimated.
Transmission Electron Microscopy(TEM): Very small particles (<1 nm) are always blurred and may therefore not always be recognized. The number of very small clusters is therefore underestimated by TEM. The average diameter decreases with the increase of Pt content 5.8 A for 1% Pt and 1.5 A for 75% Pt.
Temperatureprogrammed Reduction (TPR):
Reduction
temperature
is
heavily dependent on the environment of the ion [5], reduction profiles are therefore like fingerprints of the sample. The bimetallic TPR profiles have one more peak than the monometallic ones. Additionally, we can observe a non-proportional decrease of the characteristic high temperature Pd peak with increasing Pt content. This is a very strong indication that mixed particles have been formed [6]. It seems likely that the reduction of Pd 2+ at unusually low temperatures is catalysed by the dissociation, and hence activation, of hydrogen on Pt 0.
REFERENCES M. Briend-Faure, D. Delafosse. J. Jeanjean, G. Rocherolles, and G. Spector, J. Chem. Phys. 83, 431- 439 (1986). P. Gallezot, A. Alarcon-Diaz, J.-A. Dalmon, A. J. Renouprez, and B. Imelik, J. Catal. 39,334-349 (1975). M. S. Tzou, B. K. Teo, W. M. H. Sachtler, J. Catal. 113, 220-235 (1988). G. H. Via, K. F. Drake, Jr, G. Meitzner, F. W. Lytle, and J. H. Sinfelt, Catal. Lett. 5, 25-34 (1990). S. T. Homeyer, and W. M. H. Sachtler, J. Catal. 117, 91-101 (1989). F. B. Noronha, M. Schmal, M. Primet, and R. Fr~ty, Appl. Catal. 78, 125-139 (1991).
H.G. Karge and J. Weitkarnp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
SIMS I n v e s t i g a t i o n o n V a n a d i u m Cracking Catalysts
67
Zeolite Interactions
in
Kuei-Jung Chao, Long-Hui Lin and Liang-Yuan Hon
Department of Chemistry, National Tsinghua University, Hsinchu, Taiwan, Republic of China Summary. In this study, secondary ion mass spectrometry (SIMS) was employed to study the interaction between vanadium and zeolite in multicomponent cracking catalysts. Because of its ability to view elemental distribution with ~ 0.5 tLm spatial resolution at concentration in the p p m range, S I M S images of 51V+, 139La+ and 27A!+/28Si + distributions are quite suited to probe the location of rare earth exchanged Y and the interaction between Y zeolite and V on a cracking catalyst, which is deposited by V of several thousand p p m and contains Y zeolite of ~ 1 ~ m size embedded in amorphous silica-alumina matrix of diameter ~ 60 pm with or wthout Ca as vanadiumpassivator. The strong interaction between V and Ca compared with zeolite was also confn~ned by MAT (microactivity test).
Introduction. Vanadium has been recogonized as one of the major and poisonous m e t a l - c o n t a m i n a n t s found in typical cracking catalysts. The irreversible destruction of cracking activity by the interaction of vanadium with zeolite in cracking process has been well noted in the literature and application [1-3]. Minimization of the deleterious effect of v a n a d i u m deposition is very important, especially for heavy feedstock processing in current refiners. Using the solid phase to trap vanadium has been considered as the most promising way to reduce the reaction of vanadium with zeolite. Since the formation of vanadates by reacting alkali-earth with acidic H3VO4 was found to be favor thermodynamically at 700~ [4], SiO2" A1203 supported Ca was used as vanadium passivator in this study. The interaction between V and zeolite and the V passivation effect of Ca in cracking catalysts were examined by both MAT and SIMS measurements. E x p - ~ r i m e n t a i . V-loaded samples were prepared by i m p r e g n a t i o n of a cyclohexane solution of vanadyl n a p h t h e n a t e onto the commercial cracking catalysts with and without calcium. Equilibrium cracking catalysts and Vloaded samples were embedding in thermosetting epoxy, sliced using microtom and pressed on indium foil with copper grid for SIMS measurements. The SIMS analyses were performed with a CAMECA IMS-4f ion microscope using a 500 hA, 15 kV, mass filtered 0 2 + primary ion. The images were processed and analyzed with an IBM-compatible microcomputer run by using a home-built image analysis software. Catalytic evaluation was performed u s i n g a microactivity test (MAT). The conditions of the test were at 498~ and catalyst to oil ratio of 3.0. Liquid and gaseous products were analyzed with gas chromatography. R e s u l t s a n d D i s c u s s i o n . The equilibrium cracking catalyst contains 2000 ppm La in its active component, rare earth exchanged Y zeolite, which is
58 distributed on catalyst particles and can be identified by 139La+ ion image. The overlapping of 51V+ ion image with 139La+ ion image indicates that V is more concentrated in zeolite than in matrix. The relative concentrations of V on zeolite and matrix phases of equilibrium cracking catalyst can be estimated by analysizing the SIMS data [2], the RC value (the percentage of V on a phase divided by the area fraction of that phase) of 1.5 on zeolite greater than the average value of 1.0 for the whole particle indicates that V prefers to reside on the zeolite phase than on the matrix (RC -- 0.9) in equilibrium cracking catalyst. The effect of Ca on V passivation is shown in SIMS images of 40Ca+, 139La+ and 51V+ distributions on the cracking catalyst with adding Ca. Since the average Si/A1 molar ratio of Ca phase is greater than that on cracking catalyst determined by EDX, the location of Ca phase is expected to be revealed by both 40Ca+ and 28Si+/27A1 + ion images. For 3650 ppm V-loaded catalyst with adding calcium phase, V was found to be trapped in both zeolite and Ca phase with RC factors of 1.8 and 2.7 respectively. That reduces the RC factor on the matrix phase to 0~3. Adding Ca on cracking catalyst decreases the yield of coke and gas (C4") with increasing gasoline selectivity in MAT test as shown in Table 1. This result confirms that the poison of vanadium on cracking catalyst can be reduced by adding calcium. References 1. Shen, Y.F., Suib, S.L. and Occelli, M.L., ACS Sym. Ser., 517, 185(1993). 2. Leta, D.P., Lamberti, W.A., Disko, M.M., Kugler, E.L. and Varady, W.A., ACS Sym. Ser., 452, 269(1991). 3. Biswas, J. and Maxwell, I.E., Applied Catalysis, 63, 197(1990). 4. Wormsbecher, R.F., Peters, A.W. and Masell, J.M., J. Catal., 100, 130(1986).
Table 1 Microactivity cracking results of 2300 ppm Ni and 4500 ppm V deposited catalysts Catalyst
Coke (wt%)
Gas (wt%)
66.3
4.9
13.2
72.7
52.5
Cracking catalyst + 58.8 SiO2 9A1203 with Ca
2.9
10.5
77.2
52.0
Cracking catalyst
Gasoline Selectivity(%)
H2/Gas
Conversion (%)
(vol%)
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
XPS AND ADSORPTION OF DINITROGEN EXCHANGED ZSM-5 AND Y ZEOLITES
69
STUDIES ON COPPER-ION-
Giuliano Moretti (a), Giuliano Minelli (a), Piero Porta (a), Paolo Ciambelli (b) and Pasquale Corbo (c) (a)Centro di Studio del CNR "SACSO", Dipartimento di Chimica, Universit& "La Sapienza", Piazzale A. Moro 5, 00185 Roma, Italy. (b)Dipartimento di Ingegneria Chimica e Alimentare, Universit& di Salerno, 84084 Fisciano, Salerno, Italy. (c) Istituto Motori del CNR, Via G. Marconi 8, 80125 Napoli, Italy. SUMMARY By X-ray photoelectron spectroscopy (XPS) and X-ray induced Auger spectroscopy (XAES) it is shown that Cu (11)ions exchanged in ZSM-5 and Y zeolites are easily reduced, in vacuum and under X-ray irradiation, to Cu (I). This process is faster for Cu (11) ions in ZSM-5. Dinitrogen adsorption measurements at 273 K have been performed after pretreatments of as prepared samples both in vacuum and in 02 at 788 K . Only on Cu-ZSM-5 zeolites with Cu exchange levels close to 100% we have measured a relatively strong and irreversible adsorption of dinitrogen. INTRODUCTION Copper-ion-exchanged Y and ZSM-5 zeolites are active catalysts for decomposition and for removing NOx from oxygen-rich exhaust gas [1].
NO In a
previous contribution we reported on the catalytic activity of Cu-ZSM-5 and Cu-Y zeolites for NO decomposition at 773 K [2]. It was clearly shown that the superior activity of the Cu-ZSM-5 catalysts can be related to a small fraction of Cu(ll) ions which are easily reduced to Cu (I). These special copper ions are introduced in the ZSM-5 zeolite only at the higher exchange levels [2]. In this report we present XPS, diffuse reflectance spectroscopy (DSR) and adsorption of N2 at 273 K data which help to understand the nature of the active sites in Cu-Y and Cu-ZSM-5 catalysts. EXPERIMENTAL The zeolites used as starting materials were NaY (Si/AI = 2.4, Union Carbide) and HZSM5 (Si/AI =17, Enichem Anic). Copper was introduced into the zeolites by the ion-exchange method. The samples and their main features are reported in Table 1. XPS and XAES spectra were obtained using Mg Ko~ radiation (hv = 1253.6 eV) with a Leybold-Heraeus LHS-10 spectrometer. DRS of fresh and thermal treated samples (10-5 torr, 788 K, 1 h) were recorded using a Cary 5 spectrometer. Dinitrogen adsorption measurements were performed in a vacuum line. The samples were degassed at 788 K under vacuum (10-5 torr) for 1 h, or treated in 350 torr of 02 at 788 K, and the adsorption of N2 was measured at 273 K in the range
?0 0- 100 torr. The reversible and irreversible adsorption were calculated. results obtained on samples pretreated in vacuum are reported in Table1.
The
RESULTS AND DISCUSSION DRS spectra of the as prepared samples show that the d-d transitions lie in the range expected for Cu2+ in octahedral environment of O-containing ligands (range 10000-15000 cm-1) [3]. In the case of Cu-Y and Cu-ZSM5 zeolites treated under vacuum at 788 K the intensity of d-d transitions is confused in the background indicating an almost complete reduction of Cu (11)to Cu (I). On the contrary Cu-Y and Cu-ZSM-5 zeolites pretreated first in oxygen and then in vacuum at 788 K presented a very limited reduction of Cu (11) ions. By a study of the Cu(2p) photoemission and Cu(LMM) Auger transition we conclude that Cu (11) ions are easily reduced, in vacuum and under X-ray irradiation, to Cu (I). This process, equivalent to the treatment in vacuum at 778 K of the as prepared samples, is faster for Cu (11) ions in ZSM-5, in agreement with the work reported by Jirka and Bosacek [4]. On Cu-Y zeolite no adsorption of N2 takes place. On the contrary on Cu-ZSM-5 zeolites with high copper Ioadings we have a relatively strong and irreversible adsorption of N2. The irreversible adsorption does not depend whether the samples were pretreated in vacuum or in 02. (The total amounts of adsorbed N2 on the contrary decreases after treatment in 02.) It appears that the last fraction of Cu(ll) ions exchanged in ZSM-5 zeolite has unique properties which are important both in the catalytic decomposition of NO at 773 K [2] and in the irreversible adsorption of N2 at low temperature. Table1. Samples and their main features. N2 adsorption is measured at 273 K on as prepared samples treated in vacuum at 778 K. Sample NaY Cu-NaY Cu-NaY HZSM5 Cu-HZSM5 Cu-HZSM5 Cu-HZSM5
Cu wt%
% of exchange
mol N2 (total) per mol Cu
mol N2 (irreversible) per mol Cu
5.06 9.38
50 94
0.00 0.00
0.00 0.00
0.73 1.85 3.33
25 65 117
0.14 0.27 0.32
0.03 0.04 0.12
REFERENCES [1] M. Iwamoto and H. Hamada, Catalysis Today 10 (1991) 57. [2] M. C. Campa, V. Indovina, G. Minelli, G. Moretti, I. Pettiti, P. Porta and A. Riccio, Catal. Lett. 23 (1994) 141. [3] R. A. Schoonheydt, Catal. Rev.-Sci. Eng. 35 (1993) 129. [4] i. Jirka and V. Bosacek, Zeolites 11 (1991) 77.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
71
Model of adsorbed NO molecules on Lewis sites in zeolites. A. Gutszel, 3, M. Plato 2, F. Witzel 1, H. G. Kargel 1 Fritz - Haber Institute of the Max Planck Society, Berlin, Germany 2 Physics Department, Free University Bedin, Germany
Results and Discussion
It has already been reported [1] that NO molecule which is a radical, is a very good probe to investigate Lewis acid sites in zeolites. This peculadty comes from the fact that the ground state of the NO molecule is degenerated and therefore the magnetic moment is equal to zero. To observe an ESR signal from NO one has to quench
the orbital mmomentum of the free
electron. This can be done by the electric field originating from an ion on which NO molecule is sorbed, for example from the Lewis site in a
Figure
1
zeolite.
10 mT
To adsorb the NO on this site and therefore to get an ESR spectra one has to cool the whole sample with the gas to the low temperature ( 77 K ). At that temperature one can see very nice ESR spectrum, which shows
the
hyperfine
x,
splitting
comming from the I"N nucleus and the superhyperfine 27AI nucleus.
splitting
from
The ESR spectrum of NO molecules adsorbed in the H-ZSM5zeolite at 277 K. A simulated spectrum which is (Takt =1075 K, p(NO)=50 Pa, Tad. =298 K, in very good agreement with the Xad.=l h.Tmeas" =77 K ) a) experimental b)simulated experimental one, was obtained by
the assumption that we have a symmetry close to axial, that means that the g - factors are equivalent gxx=gyy=l.997 and gzz =1.94 and the hyperfine splitting constant for AI: Axx = Ayy = 4.5 MHz ( Fig. 1 ) Cooling the probe to 10 K, the ESR spectra of NO adsorbed on Lewis sites changes. The superhyperfine splitting is two times smaller 3 Permament Adress: Medical Academy Bydgoszcz, Department of Biophysics, Poland
?2 To understand this change one has to go back to the Hamiltonian of the hyperfine interaction. This interaction is a sum of two parts, the contact and the dipole part. At 77 K the NO molecule adsorbed on a Lewis sites may still rotate around the AI-N axis, that means that the dipole part of the hyperfine interaction is averaged out. Therefore the superhyperfine splitting at 77 K is given by the contact interaction alone. At 10 K the NO molecule is rigidly bound to the Lewis site. The dipole part of the superhyperfine interaction is no longer averaged. Because of the smaller superhyperfine splitting at 10 K than at 77 K, the contact and the dipole
interactions
have
opposite
Figure 2
signs. It was possible for this model to simulate a spectrum which is in good agreement one
with
the
experimental
( Fig. 2 ). In this simulation the
distance between AI and N plays an important role. The best results are for the distance 0.1 nm, which is a resonable result. There
is
one
question
remainnig about the Lewis sites; what is the
charge
of AI in this
site,
because there are three posibilities:
AI 3*, AI 2., AI * ?
The ESR spectrum of NO molecules adsorbed in the H-ZSM5 zeolite at 10 K. (Takt =875 K, p(NO)=50 Pa, Tad . =298 K, Tmeas" =10 K ) a) experimental b) simulated
Figure 5
From these three posibilities,
one is impossible, namely AI 2.. This ion
is
paramagnetic
with a
large
o)
coupling constant and would influence the NO spectrum very strongly. AI 3. has
excatly
the
same
electronic
b)
configuration as the sodium ion (Na § ). For NO adsorbed on Na § ion ( Fig. 3 ) one does not see in the ESR spectra
The ESR spectrum of NO molecules adsorbed
in the Na-ZSM5 zeolite at 10 K. ('l'akt =875 K, p(NO)=50 Pa, Tad. =298 K, sodium nucleus ( 1=3/2 ). Therefore Tmeas" =10 K ) a) experimental b) simulated the most probable state of the AI of the superhyperine splitting from the
the Lewis site is AI *.
References:
1.Witzel, F., Karge, H., G., Gutsze, A., H~irtel, U., Chem. Ing. Tech. (1991), 63, 744
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
73
A COMBINED EPR AND NMR STUDY OF OXIDATION SITES IN DEALUMINATED MORDENITES. G. Harvey Estermann, Laboratorium f0r Technische Chemie, ETH-Zentrum, CH-8092 Z0rich. R. Crockett and E. Roduner, Physikalisch-chemisches Institut der Universit&t ZOrich, CH-8057 ZUrich
Summary The radical cation of 2,5-dimethyl-2,4-hexadiene (1) has been observed after adsorption of 2,5-dimethyl-3-hexene (2), and 2,5-dimethyl-l,5-hexadiene (3) onto dealuminated mordenites. The intensity of the EPR signal correlated with the presence of extra-framework aluminium as observed by 27AI MASNMR. When the extra-framework aluminium was removed by mineral acid leaching or chelation by oxalic acid, only a very weak EPR signal was detected. The conversion of alkenes (2) and (3) to diene (1) was also shown by G.C. analysis to be dependant on the type of mordenite. The generation of radical cations in these mordenites is dependant on the presence of Lewis acid sites located on extra-framework aluminium, although cationic reactions due to Bronsted acid sites often remain the major reaction pathway. Introduction EPR has often been used as a technique to identify intermediates in zeolite catalysis 1, although it remains unclear, which species within the zeolite is responsible for the generation of radical cations 2. One possibility is that the extra-framework aluminium, frequently present in dealuminated zeolites, forms Lewis acid sites, which act as electron acceptors 3. Experimental HM/NH, dV03: Na-mordenite (MOR) (PM-1, CU Chemie Uetikon AG) was exchanged
twice with 1M NH4NO3 and calcined at 700~ in air for ca. 15 h. HM/HN03: Na-MOR was treated first with 1M HCI and then with 6N HNO3 under reflux for 3h. The zeolite was calcined at 700~ for 1 h. The HNO3 treatment was repeated and finally the zeolite heated to 700~ for ca. 15 h. HM/OX: Na-MOR was exchanged with 1M NH4NO3 and then with 2M oxalic acid 3 times and calcined at 550~ for 8h. All zeolites were characterised by XRD and elemental analysis. For EPR and G.C. measurements HM/NH4NO3/A, HM/HNO3, and HM/OX were heated in air, and under vacuum, HM/NH4NO3/B, to 700~ for 15 h. EPR measurements were made at room temp. on a Bruker ESP 300 spectrometer. For G.C. the products were distilled off at room temp. and ca. 5x10-6 mbar. The 27AI, 29Si and 1H MASNMR measurements were recorded on a Bruker AMX400.
Results and Discussion HM/NHdNO3 Following adsorption of diene (3) onto HM/NH4NO3/A, the EPR spectrum of the radical cation of diene (1) was observed. The same signal was
?4
measured after adsorption of hexene (2), and the parent diene (1). In all cases the EPR signal was strong. No EPR signal could be detected after adsorption onto HM/NH4NO3/B. It was thus concluded that oxygen was required to generate the necessary oxidation sites. The Si:AI ratio only increased from 5.8 to 6.4 after treatment but the 27AI NMR spectrum showed that a large proportion of the AI was present as extra-framework species. 1H NMR of the dehydrated sample showed the presence of some Bronsted acid sites. G.C. analysis of the diene (1) showed that no reaction had taken place beyond the formation of a radical cation, the alkene (2) and diene (3) were converted to diene (1) to a small extent on both mordenites (table 1).
2
1
3
Table I Percentage of diene (11 formed after 30 min on mordenites.
diene (1) aikene (2) diene (3)
HM/NH4NO3/A
HM/NH4NO3/B
HM/HNO3
HM/OX
no reaction 0.5% 1%
no reaction <0.02% 4%
no reaction 0.2% 31%
43%
HM/HNO3 The intensity of the EPR spectrum obtained after adsorption of diene (1) onto HM/HNO3 was only 1.5% of that measured above. Acid leaching increased the Si:AI ratio to 63 and the 27AI NMR spectrum showed that the remaining aluminium was present both as framework and extra-framework species. 1H NMR showed that, as above, some Br~nsted acid sites were present. The alkene (2) underwent very little reaction (table 1). However, diene (3) reacted to (1) to a much greater extent. This is probably a Br~nsted acid catalysed reaction, and indicates that the acid sites are stronger or more numerous in the mordenite treated with HNO3. HM/OX This mordenite (Si:AI 51) gave similar results as HM/HNO3 indicating that the presence of extra-framework aluminium is important, and not the method of removal. Conclusion
These results indicate that the generation of radical cations is closely correlated with the presence of a large amount of extra-framework aluminium which has been previously treated at high temperature in air, resulting in the formation of Lewis acid sites. 1: R. Crockett and E. Roduner, J. Chem. Soc. Perkin Trans. 2, 1503, 1993. 2: S. Shih, J. Catal., 79, 390, 1983. 3: R.D. Shannon et al, J. Phys. Chem., 89, 4778, 1985.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
STUDY
OF N i - C O N T A I N I N G
75
SAPO-5
HYDROGENOLYSIS
A. Spoj a k i n a ,
I n s t i t u t e of K i n e t i c s * I n s t i t u t e of Organic
OF
BY E S R
SPECTROSCOPY
AND
THIOPHENE
N. K o s t o v a
a n d V. P e n c h e v *
and Catalysis, 1113 Sofia, B u l g a r i a Chemistry, 1113 Sofia, B u l g a r i a
SUMMARY
ESR m e a s u r e m e n t s and the t h i o p h e n e h y d r o g e n o l y s i s have b e e n carried out on the N i - c o n t a i n i n g (7 wt.% Ni) SAPO-5 s y n t h e s i z e d by i n t r o d u c t i o n of Ni0 and Ni a c e t a t e in the r e a c t i o n m i x t u r e and i m p r e g n a t i o n of SAPO with Ni nitrate. It has been s h o w n that the Ni r e d u c i b i l i t y and d i s p e r s i o n and a c t i v i t y of s a m p l e s in the t h i o p h e n e h y d r o g e n o l y s i s are c o n t r o l l e d by the Ni s t a t e introduced in SAPO-5. INTRODUCTION
Preliminary
perties
studies of N i - m o d i f i e d
of samples
rothermal
synthesis
with
connected
with
conversion.
EXPERIMENTAL
SAPO
5 was
were
(NiSAPO)
pared
Ni
or
by
200
after
by
Ni
the
D
All
acetate
to
calcined
were
at
in
the
flow
samples
and its
we
after
The
SAPO
calcined
a
zeolite
[i].
ESR m e a s u r e m e n t s conditions
The
results
Ni-modified
samples
sample 873
in h y d r o g e n
flow
(40 ml/min).
RESULTS
DISCUSSIONS
the
AND
The
catalytic
of
activities
addition
in
NiacSAPO>/ N i + S A P O
the
of
of
the
Ni
Ni+SAPO
aqueous K for
at
room
the
as NiO
was
pre-
6 h and
con-
solution
of
on a B r u k e r
catalytic
temperature test.
The
flow at a t m o s -
of 673 K, W H S V 0.6 h-1 of t h i o p h e n e .
of t h i o p h e n e
performance
role_in
were p e r f o r m e d
reactor
hyd-
the
addition
with
at
pro-
during
report
c o n v e r s i o n was c a r r i e d out in a h y d r o g e n temperature
to
in these
specific
in
paper
procedure
pheric pressure, Prior
this
(NiacSAPO).
spectrometer
pretreatment
thiophene
of
samples
7 wt.% Ni.
In
according
same
impregnation
nitrate.
tain about ESR
the Ni state
synthesized
prepared
indicated
the Ni i n t r o d u c e d
[1,2].
thiophene
SAPO-5
each
of N i - m o d i f i e d total
thiophene
sample
was
samples
gives
conversion
and that in the h y d r o g e n a t i o n
heated
the
1.5
order
NiSAPO
activity
h
NiSAPO
>>
>
76 NiacSAPO
>> Ni+SAPO.
The acid sites are r e s p o n s i b l e
c o n v e r s i o n but the formed b u t e n e s
No
signal
of nickel
was o b s e r v e d
localization
[3]. H e a t i n g
for t h i o p h e n e
are h y d r o g e n a t e d on m e t a l l i c in the
ESR
spectra
of
all
during
1.5
Ni
air-
c a l c i n e d samples 9 This could be the result of its high d i s p e r s i o n
or/and
to
appearance
The
decrease
of
in order NiacSAPO
overlapping
ESR
in hydrogen
signal
of Ni ~ w i t h
< NiSAPO < Ni+SAPO.
of the
parameters
in the
intensity
spectra
h
leads
increased
of N i S A P O
and two
signals in that of Ni+SAPO are revieled after sequen-
tial treatment
mixture 9 It NiSAPO
the
and
of samples
shows
Ni ~
a
at 673 K for 3 h by h y d r o g e n + t h i o p h e n e
formation
and
Ni
sulfide
of
more
fine
phases
particles
in
Ni+SAPO
due
[3]
in
to
a
c o m p e t i t i o n between sulfidation and reduction of Ni species 9 Note
that,
the
nickel
state
in N i S A P O
makes
easier
its
reduction 9 No
change in the ESR spectra of N i a c S A P O is observed 9
No ESR signals
are revealed
are pretreated
by
nickel
sulfides
of
NiSAPO
to
this
treatment appeared
probably
and
The
result,
in
Ni+SAPO
activity
No
samples
singlet
2. 3.
are
changes
revealed
the
nickel
show
the
during
sample
different
state
reducibility
is
hydrothermal
makes
is
easier
Ni-containing
nickel
observed
in
synthesis 9 The
reduced SAPO-5
and
the
these
spectra
sequantial
(g=2.25)
case H2S
and
of
in
after
nickel
In this
state
when
diamagnetic
mixture 9 A c o n t r a r y
ferromagnetic
REFERENCES 9
essential
of samples
of p r o b a b l y
More nickel is reduced and m i g r a t e s
nickel
of
of
i n c o r p o r a t e d during synthesis 9 1
spectra
spectra of NiacSAPO.
changes
results hard
formed.
Ni+SAPO
in the
introduced
in the
at 673 K because
by the reaction t h i o p h e n e + h y d r o g e n
redusibility.
The
are
H2S
the
samples
by
its
samples. with
impregnated
sulfided.
enhances
easier
to surface 9
in
is
adsorbtion
Hydrogenation Ni
species
V Penchev, H Lechert et al in "Zeolites for the Nineties" J Jansen et al. (Eds.), A m s t e r d a m , p . 2 4 7 , 1989 V. M a v r o d i n o v a , Ya. N e i n s k a , Ch. M i n c h e v , H. L e c h e r t , V. M i n k . v , V. P e n c h e v , S t u d . S u r f . Sci. Catal., 69 295 ( 1 9 9 1 ) . S. S u r i n e t a l . , D o k l . A k a d . N a u k SSSR, 2 4 2 , 649 ( 1 9 7 8 ) . 9
9
9
Ni
nickel
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
77
Electron Spin Resonance and Electron Spin Echo Modulation Spectroscopic Study of Pd(1) Location and Adsorbate Interactions in PdH-SAPO-34 Molecular Sieve Jong-Sung Yu, Gern-Ho Back +, Vadim Kurshev and Larry Kevan ++ Department of Chemistry, Han Nam University, Taejon, Chungnam, 300-791, Korea +Department of Chemistry, Changwon University, Changwon, Kyungnam, Korea ++Department of Chemistry, University of Houston, Houston, Texas 77204-5641,USA
ABSTRACT Electron spin resonance (ESR) and electron spin echo modulation (ESEM) spectroscopies have been used to monitor the location of P d ( I ) a n d its interaction with water, methanol, ethanol, ethylene, benzene, carbon monoxide and ammonia in silicoaluminophosphate type 34 (SAPO-34) molecular sieve containing Pd(II) by ion-exchange. After activation at 600 oC, three different Pd(I) species are observed: Al(g_L = 2.177), A2 (gj_ = 2.136) and A3(g_L = 2.070) with a common gll = 2.92. These correspond to three different site locations in the framework. A1 is assigned to the least accessible site HI in the center of a hexagonal prism, A3 to site I displaced from a six-ring into the ellipsoidal cage and A2 to the most accessible site IV near an eight-ring window based on adsorption of oxygen and hydrogen and 31p modulations from the SAPO framework observed by ESEM. Oxygen and water oxidize Pal(I) ions in an activated sample to Pd(II) ions complexed to O2" indicating water decomposition. Adsorption of methanol and ethanol causes a change in the ESR spectrum which indicates some relocation of Pd(I) to better coordinate with one molecule of the alcohol. Exposure to ethylene also changes the ESR spectrum indicating interaction of Pd(I) with ethylene. ESEM shows that the Pd(I) species coordinates to one ethylene. The adsorption of carbon monoxide results in a Pd(I) complex with three molecules of carbon monoxide based on resolved 13C superhyperfine splittings. Upon adsorption of ammonia, one molecule of ammonia coordinates to Pd(I) based on resolved nitrogen hyperfine coupling. Upon adsorption of big molecules such as benzene, however, no change of ESR spectrum is observed, and no deuterium modulation was detedcted on ESEM spectrum, indicating no detectable interaction between Pd(l) and benzene.
?8
INTRODUCTION In the last ten years the synthesis and characterization of the new group of aluminophosphate (AIPO4-n) and silicoaluminophosphate (SAPO-n) molecular sieves have been reported. These new molecular sieves have some frameworks isomorphous with aluminosilicate zeolites and other novel structures not found in zeolites. SAPO molecular sieves are particularly important because ion-exchange
these have
properties and can incorporate catalytically active ions.
Pal-loaded catalysts are widely used for various reactions. for ethylene dimerization
Pd(I) is active
and for the synthesis of methanol from CO and H2.
In this study Pd(II) is incorporated into H-SAPO-34 by solid state ion-exchange to form PdH-SAPO-34. SAPO-34 is a cage-type molecular sieve with a structure similar to the zeolite aluminosilicate called chabazite. ESR and ESEM spectroscopies
are
used to
monitor
adsorbates to determine the coordination structure of Pd(I).
Pd(I)
the ion
interactions locations
of
Pd(I)
and
with the
various
adsorbate
EXPERIMENTAL SECTION SAPO-34 was synthesized by a modification of the methods of Xu et al. as developed in our laboratory. Pd(II) was ion-exchanged into H-SAPO-34 using a solid-state reaction method. SAPO-34 samples after synthesis, Pdexchange and calcination were examined by powder X-ray diffraction (XRD) with a Philips PW 1840 diffractometer. PdH-SAPO-34 was first loaded into 3 mm o.d. by 2 mm i.d. Suprasil quartz tubes and evacuated at room temperature. Evacuation was continued by raising the temperature to 600 ~ over 8 h and then holding at 600 oC for 12 h. These samples were then heated in about 600 tort of dry o~jgeP, at 600 o c for !6 h and evacuated again at 600oc for about 16 h to give "activated" samples. The "activated" samples were exposed to liquid adsorbates (D20, CH3OD, CD3OH, C2H5OD) at their room temperature vapor pressure or to gaseous adsorbates (ND3, 15NH3,12CO, 13OO and 0204).
The sample tubes were sealed after exposure to adsorbates and
were stored in liquid nitrogen. ESR spectra were recorded at 77 K on a modified Varian E-4 spectrometer interfaced to a Tracor Northern TN-1710 signal averager. ESEM spectra were recorded with a Bruker ESP 380 pulsed ESR spectrometer. Three-pulse echoes were measured by employing a 90o-~:-90~ 90 ~ pulse sequence as a function of T.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
79
STABILITY OF THE Co(II) VALENCE STATE IN ALUMINOPHOSPHATE-5 MOLECULAR SIEVE TO CALCINATION FROM LOW TEMPERATURE ELECTRON SPIN RESONANCE
Vadim Kurshev and Larry Kevan Department of Chemistry, University of Houston Houston, TX 77204-5641 David Parillo and Ray Gorte Department of Chemical Engineering, Univ. of Pennsylvania Philadelphia, PN 19104-6393 SUMMARY As-synthesized CoAPO-5 is blue and it becomes yellow-green after calcination in oxygen. This was interpreted by several research groups as indicating a valence state change from Co(II) to Co(III); however, our electron spin resonance and temperature programmed desorption results provide no evidence for Co(HI) and are consistent with all the framework species existing as Co(II) both before and after calcination. INTRODUCTION Transition metal ion incorporation into aluminophosphate molecular sieve frameworks can increase the stability of the metal ion for catalytic reaction, prevents ion removal by reaction products, and controls the acidity of the molecular sieve. Insertion of a metal ion into a synthetic mixture does not guarantee metal ion incorporation into the framework and it is not easy to definitely verify framework incorporation. Electron spin resonance (ESR) and its temperature dependence can be sensitive to the local symmetry of a paramagnetic center. CoAPO-5 presumably has Co(II) incorporated into the framework of aluminophosphate-5. Upon calcination in flowing oxygen the color of CoAPO-5 changes from blue to yellow-green. This was previously interpreted as oxidation of Co(II) to Co(m). However, new ESR data from 7 to 35 K do not support this and indicate that no valence change occurs during calcination. EXPERIMENTAL SECTION CoAPO-5 was synthesized per literature measured with a Bruker ESR spectrometer.
procedures
and
ESR
was
RESULTS AND DISCUSSION Our ESR measurements verify a Co(N) ESR intensity decrease at 4 K, but show no chan0e at 20 K and higher temperatures. The absence of an ESR
80
signal intensity difference before and after calcination above 20 K indicates that all cobalt in calcined samples remained Co([I). The anomalous (non-Curie) ESR temperature dependence is due to changes in the population of the ESR active level. As follows from a group theory analysis, the ground level of high spin Co(II) ion in a crystal field of tetrahedral symmetry is degenerate and consists of two Kramers doublets with total electron spin projections Ms = __.3/2 and Ms =___1/2. The structure of the ground level has a normal temperature dependence of the ESR intensity (Curie behavior). In a crystal field of lower symmetry like dihedral, the degeneracy is lifted, and when the ESR active level lies at higher energy the ESR intensity can have a maximum at the temperature comparable to the zero field splitting between the two Kramers doublets. We can fit the experimental temperature dependence of the Co(II) ESR intensity in calcined CoAPO-5 for a zero field splitting parameter of 2D =-13 cm -1. The dependence of the Co(II) ESR intensity in as-synthesized Co-APO-5 shows Curie behavior. These facts indicate that Co(I]) has nearly tetrahedral symmetry in as-synthesized CoAPO-5 consistent with framework substitution and that the symmetry is distorted dihedral upon calcination. The absolute value of the zero field splitting parameter supports the distortion to dihedral (D'2h)symmetry. Temperature programmed desorption (TPD) experiments also support nonoxidation of framework Co(II) upon calcination. Since a framework Co(II)ion produces uncompensated framework charge, the number of Br/~nsted acid sites in calcined and "reduced" CoAPO-5 must be identical and equal to the number of Co(H) ions. This was confirmed by TPD measurements. The following experiment suggests distortion of the local symmetry of Co(II) by oxygen. As-synthesized blue CoAPO-5 was evacuated at slowly increasing temperature to remove the tetraethylammonium hydroxide synthesis template from the pores. At 500 oC CoAPO-5 remained blue, but it instantly changed to yellow-green after exposure to oxygen gas at 500 oC. CONCLUSIONS
The ESR temperature dependence indicates cobalt(H) incorporation into tetrahedral sites in the CoAPO-5 framework. Co(H) does not oxidize to Co(HI) upon calcination. The E SR intensity decrease at 4 K is due to distortion of the Co(II) local symmetry from near tetrahedral to a lower dihedral symmetry upon calcination.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
8]
CHARACTERIZATION OF ALKALI METAL CLUSTER-CONTAINING FAUJASITES BY THERMAL, IR, ESR, MULTI-NMR AND TEST REACTION STUDIES 11. Hannus, ~1. Kiricsi, 1A. B~res, 2J.B. Nagy and 3H. F6rster 1Applied Chemistry Department, J6zsef Attila University, H-6720 Szeged, Rerrich Bela ter 1, Hungary. 2Laboratoire de Catalyse, Facultes Universitaires Notre-Dame de la Paix. B-5000 Namur, 61 rue de Bruxelles, Belgium. 3Institute of Physical Chemistry, University of Hamburg, D-20146 Hamburg, Bundesstrasse 45, Germany Summary Characterization of alkali metal clusters in MY-FAU (M=Li§ Na § K§ Rb§ Cs§ by a combination of physical-chemical methods revealed the formation of both charged and neutral Na~ and My clusters upon heat treatment of NaN 3-loaded zeolites. They turned out to be efficient basic catalysts. Introduction Alkali metal clusters in the cavities of zeolites can be prepared via exposure to metal vapour [1]. A convenient method for in situ generation of sodium vapour
in the pore system of zeolites is the
decomposition of sodium azide [2]. The aim was the characterization of the so-formed clusters in alkali metal ion-exchanged faujasites by the concomitant application of thermal analysis, IR, ESR and multiNMR spectroscopy as well as 1-butene isomerization as test reaction. Experimental section NaN 3 was introduced into the Li § Na§ K§ Rb§ or Cs" ion-exchanged zeolite either as a solid material [2] or in methanol solution [3]. The thermal behaviour of the NaNVIVlY-FAU system was studied by thermal analysis. The decomposition of sodium azide was monitored by IR spectroscopy as well, using self-supporting wafers in a variable-temperature cell. The metal clusters formed were characterized by both ESR and MAS-multi-NMR (ZLi-, 23Na-, 87Rb- and l~Cs-) spectroscopies. Isomerization of 1butene was investigated in a recirculation reactor with GC analysis. Results and discussion Thermal analysis showed that decomposition of sodium azide took place in two partly overlapping or one unresolved stages at low and fast heating rates respectively. Similar observation was reported by Martens et al., who proved that the state of sodium formed was influenced by the heating rate and affected by the catalytic activity of the zeolites thus modified [3]. Upon evacuation with increasing temperature the broad band centered at 2080 cm ~ in the IR spectrum splits into two bands at 2060 and 2170 cm ~ which are the only bands present prior to NaN 3 decomposition and remain after heat treatment at 673 K for 12 h. Cooling down to room temperature resulted in absorptions at 2037, 2070, 2170, 2187 and 2205 cm1 assigned to azide species in different environment. From these spectral changes follows that in the zeolite cavities azide ions are stabilized even above the decomposition temperature of neat NaN 3 and distributes over different sites in the pores strongly influenced by temperature.
82 The ESR spectra of samples prepared by solid-solid mixture was changing as a function of time. The rather large clusters formed outside the zeolite crystallites were decreasing in favour of the intra zeolite particles, especially in cases of K, Rb and CsY-FAU. Samples prepared by methanol solution impregnation did not show any evolution with time. The 23Na-MAS-NMR spectra of all MY-FAU samples show the presence of neutral sodium clusters in the region characteristic of a Knight shift [4]. This proves unambigously, the formation of Nax clusters in presence of other alkali cations. The 133Cs-NMR spectra of the decomposed NaN3/CsY-FAU zeolites show in addition the presence of Cs containing metal particles. According to the catalytic activity measurements, the tested Li, Na, K, Rb and CsY-FAU zeolites and their modified varieties proved to be strong basic catalysts, as could be established from the product distribution of 1-butene isomerization as well as the appearance of a carbanion intermediate during isomerization of allyl cyanide. Conclusions NaN3 introduced into the zeolites does not decompose completely during heat treatment. A small portion is stabilized in the pore system as it can be concluded from thermal analysis and IR spectroscopic data. Its decomposition leads to generation of Nax and My clusters, the presence of which is proved by ESR and multi-NMR spectroscopies. Alkali metal ion-exchanged faujasites and their metal cluster-containing derivatives are catalytically active in 1-butene isomerization resulting in product distribution characteristic for basic catalysts. Formation of carbanionic intermediate from allyl cyamde proved to be probable in these basic zeolites. Acknowledgement Financial supports from National Research Foundation of Hungary (OTKA No. 1064), Deutsche Forschungsgemeinschaft and Belgian FNRS are gratefully acknowledged. References [1] J.A. Rabo, P.H. Kasai, Progr. Solid State Chem., 9,1 (1975) [2] P. Fejes, I. Hannus, I. Kiricsi, K. Varga, Acta Phys. Chem., Szeged, 24, 119 Kiricsi, I. Hannus, A. Kiss, P. Fejes, Zeolites, 2, 247 (1982) [3] L.R.M. Martens, P.J. Grobet, W.J.M. Vermieren, P.A. Jacobs, Stud. Surf. Sci. [4]
(1986)
(1978); ~
I.
28, g35
P.J. Grobet, G. van Gorp, L.R.M., P.A. Jacobs, Proc. 23rd Congr. Ampere (Rome, 1g86) p.356
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
83
A Study of Cu-Y and Cu-Rho zeolites by 129Xe NMR A. GEDEON and J. FRAISSARD Laboratoire de Chimie des Surfaces, associe au CNRS -URA 1428 Universite P. et M. Curie Casier 196, Tour 55 4, place Jussieu 75252 PARIS Cedex 05 - France
SUMMARY
The adsorption isotherms and 129Xe nuclear magnetic resonance (NMR) chemical shifts of xenon adsorbed on Cu(ll)-exchanged Y and Rho zeolites were measured. The location and the oxidation state of the copper ions as well as the nature of Xe-cation interactions were determined. INTRODUCTION 129Xe NMR spectroscopy is a useful tool for the determination of the void space, the structural and chemical properties of zeolites and the location and electrostatic effects of cations therein (1,2). In previous papers we observed that the chemical shift of xenon in AgY and Ag-X zeolites ( Ag+: [Kr] 4d 10) was less than that of Na-Y or Na-X and even less than that of the quasi-isolated xenon atom (3,4). We attributed this exceptional result to the formation of an unstable Ag+-Xe complex whose lifetime was however long enough for the instantaneous increase in the electron density, due to 4d10-5d0 transfer from Ag+ to xenon, to cause this variation of the chemical shift. Recently, we have shown that in dehydrated Cu-Y and Cu-X (5,6), the chemical shifts of adsorbed xenon are also lower than in Na-Y or Na-X. These results were attributed to the specific interaction with Cu + formed by the autoreduction of Cu2+ during the dehydration of the zeolites. We have also shown that after dehydration at 400~
many Cu2+ ions have
migrated towards sodalite cavities and prisms and that the Cu2+ ions remaining in the supercages have been autoreducted to Cu +. To confirm these hypotheses, we looked for a system where, even after dehydration, the Cu 2+ were still in supercages or cavities in contact with the xenon. We chose Cu(ll)-Rho zeolite.
EXPERIMENTAL SECTION Copper-exchanged Na-Y zeolite, Cu-Y was prepared conventionally by refluxing at 80~ the zeolite with a 0.1M aqueous copper nitrate solution for 12tl at pH 6. Starting from Cs-Rho zeolite, exchanged Cu(li)-Rho zeolite was also prepared with aqueous solutions of copper nitrate. The Cu2+ cations were quantitatively analyzed by atomic absorption spectroscopy. The samples prepared correspond to 95% cation exchange.
84 The zeolites were evacuated 12 h under 10-5 Torr vacuum at 26~ and then slowly heated to 400~
They were held at this temperature for 12 h and then brought back to ambient
temperature. The adsorption isotherms were measured volumetrically at 26~
129Xe NMR
spectra were recorded on a Bruker spectrometer, either a MSL 400 or CXP 100, at 110.642 and 24.905 MHz, respectively. RESULTS AND DISCUSSION Cu(ll)-Rho zeolite: The observed chemical shift ~)is much greater than that of Na-Y. The form
of the ~>versus N (xenon concentration) curve, in particular the presence of a minimum and the line broadening (about 100 kHz) prove that the xenon interacts with strong adsorption sites which can only be Cu2+ . Such variations due to the presence of paramagnetic ions have also been shown in the case of the Ni(II)-Y zeolite (7,8). in Cu(ll)-Rho zeolite, we attribute this large positive shift to the high polarization of xenon and the distortion of the xenon electron cloud by the strong electric fields created by the Cu2+ ions in contact with it. Cu-Y zeolite: The chemical shift ~>decreases monotonically with N and is always lower than that in NaY and Cu(ll)-Rho zeolites. That there is no minimum (low shifts and lines not wider than 200 Hz), indicates that there are no Cu2+ ions (paramagnetic centers) in the supercages. This suggests that during dehydration at 400~
many C u2+ have migrated
outside the supercages and the Cu2+ remaining in the supercages has been transformed by autoreduction to Cu +. In our opinion, xenon in contact with Cu + ions in special locations (Sill) exhibits unusually large displacements of the resonance line to low frequency via the dx -dTr back-donation mechanism. REFERENCES 1. J. Fraissard and T. Ito, Zeolites, 8 (1988) 350. 2. P. J. Barde, J. Kiinowsld, Progr. NMR Spect., 24 (1992) 91. 3. R. Grosse, R. Burmeister, B. Bocldenberg, A. Gedeon and J. FraJssard, J. Phys. Chem., 95 (1991) 2443. 4. A. Gecleon, R. Burmeister, R. Grosse, B. Boddenberg and J. Fraissard, Chem. Phys. Letters, 179 (1991) 191. 5. A. Gedeon, J. L. Bonardet, and J. FraJssard, J. Phys. Chem., 97 (1993) 4254. ~. A. Gedeon and J. FraJssard, Chem. Phys. Letters, 291 (1994) 440. 7. N. Bansal and C. Dybowsky, J. Phys. Chem., 92 (1988) 2333. 8. A. Gedeon, J. L. Bonardet, T. Ito and J. Fraissard, J. Phys. Chem., 93 (1989) 2563.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
DIRECT OBSERVATION OF DISTRIBUTIONS OF MIXED CLUSTERS OF COADSORBED SPECIES IN ZEOLITE NaA A. K. Jameson, % C. J. Jameson,* A. C. de Dios, @E. Oldfield, @and R. E. Gerald II* Departments of Chemistry, *University of IUinois at Chicago, Chicago IL 60607, %Loyola University, Chicago IL, 60626, and @University of Illinois at Urbana, Urbana, IL 61801 Summary We show for the first time that the individual peaks corresponding to Xe~ clusters inside the alpha cages of zeolite NaA can be narrowed under magic angle spinning. Under these high resolution conditions we observe the individual peaks corresponding to mixed dusters Xe,d~m inside the alpha cages, which allows the direct determination of the distribution of coadsorbates in a microporous solid for the first time. INTRODUCTION.
In our studies of molecular interactions and dynamics of sorbates in
microporous solids using NMR observables together with computer simulations, we have focussed on xenon clusters trapped in the regular array of cages in the NaA zeolite. ~-3 We have directly observed the fractions of alpha cages in zeolite NaA that have trapped from one to eight Xe atoms, ~ and measured the rate constants for migration of xenon atoms from one alpha cage to another, 3 as have the Pines group. 4'5 These direct determinations of adsorbate distribution as a function of loading and temperature provide detailed tests of computer simulations. Furthermore, the chemical shifts of the clusters measured as a function of temperature provides a test of the averaging amongst the large numbers of configurations of a particular cluster within an alpha cage. Thus we have elicited information on the structure of the Xe~ clusters through the simulations. 2 The origin of the width of the lines (about 10 ppm) of the Xe~ clusters has been a continual puzzle, 1 ppm-wide lines being rather commonplace for Xe in other zeolites. 6"s We have been able to "bum" a hole as narrow as 2 ppm in one of the lines in a typical spectrum by using a selective DANTE pulse sequence. Furthermore, T2 (CPMG) experiments in several different samples of Xe in zeolite NaA have yielded relaxation times from 15-40 ms, indicating limiting line-widths in the vicinity of 25 Hz. This information suggested that the broad lines might be narrowed under magic-angle spinning conditions. EXPERIMENTAL RESULTS AND DISCUSSION. A Gay-type spinner held the sealed 3-cm sample tube in a specially built MAS probe in a wide-bore 8.5 T magnet. A substantive improvement in signal/noise is obtained by the factor-of-10 narrower lines
85
86 achieved for the first time for Xe in NaA. The next MAS experiments involve determination of distributions of Xe atoms in the presence of coadsorbate molecules. We have observed the distribution of xenon atoms in the presence of coadsorbed molecules such as argon as a function of the average occupancy number (n)xc and (n)Ar, Ar being in fast exchange, moving freely from cage to cage during the observations. 9 There are however, many molecular species that, like Xe, have long mean residence times in the alpha cages. Because the chemical shift of mXe in the presence of another molecule is quite distinct from that in the presence of another Xe, as we have determined from the second virial coefficients of nuclear shielding in the gas phase, ~~ we expect the distinct 129Xe chemical shifts for those clusters corresponding to one Xe atom and various numbers of B molecules in the alpha cage to provide separate signals. If individually resolved, the peaks should be directly assignable on the basis of the known relative magnitudes of the shielding virial coefficients for Xe-Xe versus Xe-B. 1~ In samples of mixtures of xenon with krypton in zeolite NaA the individual lines overlap so badly that virtually no structure can be seen in the conventional static spectrum at 9.4 T. Under MAS conditions the multitude of 1 ppm-wide lines are well-resolved and are readily assigned to specific mixed clusters of Xe,Kr=. From the relative intensities of each line in the spectrum we can determine the fractions of the alpha cages containing specifically n Xe atoms and m Kr atoms. This is the first direct determination of the distribution of coadsorbates in a microporous solid. 1. C.J.Jameson, A.K.Jameson, R.Gerald II, A.C.deDios, J..Chem. Phys. 96,1676 (1992). 2. C.J.Jameson, A.K.Jameson, B.I.BaeUo, H.M.Lim, J. Chem. Phys. 100, xxx (1994). 3. A.K. Jameson, C. J. Jameson, and R. E. Gerald II, J. Chem. Phys. submitted. 4. B.F.Chmelka, D.Raftery, A.V.McCormick, L.C.deMenorval, R.D.Levine, A.Pines, Phys. Rex,. Lett. 66, 580 (1991); R.G.Larsen, J.Shore, K.Schmidt-Rohr, L.Emsley, H. Long, A.Pines, M.Janicke, B.F.Chmelka, Chem. Phys. Lett. 214, 220 (1993). 6. C.J.Jameson, A.K.Jameson, R.Gerald II, A.C.deDios, J. Chem. Phys. 96, 1690 (1992). 7. T.Ito, J.Fraissard, J. Chem. Phys. 76,5225 (1982); J.Fraissard, Zeits. Physik. Chemie 152, 417 (1987). 9. C.J.Jameson, A.K.Jameson, H.M.Lim, to be published. 10. A.K.Jameson, C.J.Jameson, H.S.Gutowsky, J. Chem. Phys. 53, 2310 (1970). 11. C.J.Jameson, A.K.Jameson, S.M.Cohen, J. Chem. Phys. 59, 4224 (1973). We are grateful to Gary Turner for lending us the special purpose probe used in this work. This work has been supported by the National Science Foundation and the Materials Research Laboratory at the University of Illinois Urbana-Champaign.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions
87
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
STUDIES ON THE FORMATION AND STRUCTURE OF MOLECULAR CLUSTERS OF (CdS)4 IN ZEOLITE Y BY in-situ IR AND 113Cd MAS NMR Qi Ming 1, Xue Zhiyuan 1, Zhang Yongchao I and Li Quanzhi 2 1The Center of Analysis and Measurement, Fudan University, Shanghai, 200433, P.R. China 2The Department of Chemistry, Fudan University, Shanghai, 200433, P.R. China
SUMMARY The formation of molecular clusters of (CdS)4 in zeolite Y was studied by the changes of HF-OH and LF-OH bands of Y zeolite measured with in-situ FT-IR at different stages of preparation such as exchange, thermal treatment, sulphuration etc., and the coordination structure was evidenced by the results of 113Cd MAS NMR.
INTRODUCTION As is well known, molecular clusters of the semiconductor (CdS)x formed in zeolite Y can produce a blue shift of absorbed light relative to bulk CdS. The arrangement among atoms in molecular clusters is also different from bulk CdS with the structure of sphalerite, and its rock-salt structure has been suggested by the EXAFS technique [1]. However, the relationship between preparation conditions and formation of molecular clusters (CdS)x have not been studied in detail. In this work, the changes of hydroxyl groups of zeolite Y in each procedure of preparation of CdS were measured by in-situ FT-IR and from these results, the formation of CdS in Y zeolite cages will be discussed. The coordination structure of molecular clusters of (CdS)4 has also been evidenced by 113Cd MAS NMR. EXPERIMENTAL SECTION The (CdS)4 in zeolite Y was prepared by the following sequence NaY(Si/AI=2.3) --~ NH4Y --~ CdOH-HY--~ CdS-HY whose absorption in UV-Visible spectra is at 410nm (bulk CdS is at 520nm). The spectra of hydroxyl groups of various Y zeolites were measured by an in-situ Nicolet 5SXC FT-IR spectrometer and 113Cd MAS NMR spectra were recorded by a Bruker MAS-300 spectrometer. The chemical shifts are reported relative to Cd(NO3)2 solid.
88
RESULTS AND DISCUSSION The 113Cd MAS N M R results show that the chemical shift of hydrated Cd++-HY sample calcined at 400~
under an atmosphere of oxygen is at 115 p p m which
approximates to the chemical shift of 83.5 p p m for bulk CdO with the rock-salt structure in which the coordination n u m b e r of Cd ++ ions is six. Thus it can be inferred that the structure of Cd(OH) + in Cd(OH)-HY is the same as that of bulk CdO. For the CdS-HY sample, the chemical shift of 113Cd at 109 p p m approximates to that of Cd(OH)-HY, but it is quite different from the chemical shift of 583.9 p p m for bulk CdS with sphalerite structure. It means that the CdS in Y zeolite has the rock-salt structure, like Cd(OH)-HY in Y zeolite. The results of in-situ FT-IR show that w h e n the hydrated Cd++-HY zeolite was evacuated at 150~
the ratio of the strength I(LF)/I(HF) is greater than one. This
is related to the decomposition process of Cd(H20)x ++, i.e. Cd(H20)x ++ --~ Cd(OH) + + H +. Both Cd(H20)x ++ and Cd(OH) + ions located in the supercage bring about the decrease of strength of HF-OH. On evacuating at 200~ I(LF)/I(HF) < 1, it shows that Cd(OH) + ions located at site II near 0(2) in supercage move to site r near 0(3) in the sodalite cage [2], i.e. Cd[O(2)]H) + + O(3)H ~ Cd[O(3)]H) + + O(2)H. In this case, the Cd ++ ions are in site r and the OH-ions located at site Ir in the sodalite cage. Thus the ratio of I(LF)/(HF) decreases with the increase of exchange degree. W h e n the evacuation temperature was elevated to 250~ this ratio did not o b v i o u s l y change. It shows that the Cd(OH) + ions completely m o v e to the sodalite cage at 250~ Maybe there are four Cd ++ ions occupying site r arranged with tetrahedra in one sodalite cage in which the coordination n u m b e r is six and the other three 0(3) are in the six-membered ring of the hexagonal prism cage. Thus the structure of the cluster is Cd4(OH)40(3)12. After s u l p h u r a t i o n , the reaction Cd(OH) + + H2S ---) CdS + H 2 0 + H + occurs. When CdS-HY was evacuated above 150~
one found I(LF)/I(HF)>I, this result is opposite to that f o u n d before
sulphuration. It means that the H + released by s u l p h u r a t i o n r e m a i n s in the sodalite cage and increases the strength of LF-OH, and S2- ions replacing the OH" ions combined with Cd ++ ions to form the guest cluster of (CdS)4 whose structure is that of rock-salt. REFERENCES
[1] N. Herron et al., J. Am. Chem. Soc., 111 (1989) 503. [2]. M. CaUigaris et al., Zeolites 6 (1986) 439.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
NMR STUDIES
OF HYDROFLUOROCARBON-ZEOLITE C. P. Grey* and D. R. Corbin #
89
INTERACTIONS
#DuPont Cr&D, Wilmington, DE 19880-0262, USA (contribution number 6952) and *SUNY Stony Brook, Chemistry Department, NYl1794-3400, USA ABSTRACT A 19F and 27AI NMR study of the reaction of hydrofluorocarbon-134 with the zeolites NaX and NaY is reported. 134 decomposes on NaX at 250oc, and tetrahedral aluminum fluoride species are observed. On hydration, the tetrahedral aluminum fluoride species disappear and octahedral AI species become visible. At these temperatures, 134 does not react with the NaY framework. INTRODUCTION
W e are studying the interactions of HFCs 134 (CF2HCF2H) and 134a (CF3CFH2) with basic zeolites such as NaX and CsY. 134a is one of the new generation replacements for the refrigerant CFC-12. The syntheses of the new CFC alternatives are more complex than the syntheses of the old CFCs, involving many more steps I and unwanted HFC and HCFC isomers are often produced during the reactions. Consequently, the purification of the products remains a concern. We are investigating the differential binding of 134 and 134s to basic zeolites, in order to design methods to separate these two molecules. A correlation has been established between the separation factor of 134 and 134a and the Sanderson electronegativity of the zeolite: the greater the electronegativity, the poorer the separations 2. The NaX zeolite is sufficiently basic that decomposition of the 134 at 275oc was observed to occur in gas chromatography studies3. Only HFC-1123 (CF2CFH) elutes at this temperature. An NMR study was commenced, to investigate this decomposition reaction more fully. This study is reported below. EXPERIMENTAL
The zeolites were dehydrated by heating the samples under vacuum at 400oc. Quantitative amounts of 134 were then adsorbed, and the samples were heated at 250oc or 275oc. Rehydration was achieved by exposing the zeolite sample to a saline solution for 1 hour. The NMR samples were packed in a glove-bag. NMR spectra were acquired on CMX-120 and MSL-360 spectrometers. The HartmannHahn condition for 19F-27AI cross polarization (CP) was determined using AIF3.
90
RESULTS AND DISCUSSION 19F MAS NMR spectra of the 134/NaX system show that partial decomposition of the 134 occurs after heat treatment at 250oc. New peaks, in addition to the resonance from the 134, are observed in spectrum of a sample that has been heated for only 5 minutes. Resonances from the HFCs 134 & 1123 can be observed. In addition, resonances that result from rigid fluorine species are seen. These are assigned to fluorine coordinated to tetrahedral AI species (-203ppm), F- ions (189ppm) and F - N a + species (-255ppm). The intensities of these resonances increase, after heating for longer periods. On hydrating the samples, a resonance at -180ppm, from octahedral aluminum fluoride species, dominates the spectra. 27AI MAS NMR of the 134/NaX samples gave spectra that are similar to those of NaX. On hydration of these samples, however, a resonance at 1.3ppm and a much smaller peak at -36.4 ppm are observed. These resonances can be assigned to octahedral AI. 19F-27AI CP was also performed. A resonance was observed in the spectrum of the dehydrated sample at 47ppm. Since this resonance must arise from AI in close proximity to a fluorine atom, we assign this resonance to a tetrahedral aluminum fluoride species. This is consistent with the 19F spectra assignments. The 27AI CP spectrum of the hydrated sample shows two resonances in the octahedral region of the AI spectra, from AI(H20)6-xFx species. X-ray diffraction show that the crystallinity of NaX decreases considerably on treatment with 134 at 275oc, indicating that the zeolite framework is being destroyed. In contrast to NaX, the sample of 134 adsorbed on NaY shows very little 134 decomposition. Some 1123 is visible, but the only other observable resonance (at -254ppm) is from an F- Na + species. CONCLUSIONS 134 decomposes on NaX to liberate 1123, and tetrahedral aluminum species are observed in the 19F and 27AI NMR. A possible mechanism for the formation of such species involves protonation of a basic oxygen site in the zeolite, followed by an attack of the F- on the adjacent aluminum atom. Attack of the zeolite framework does not occur in the case of the less basic zeolite NaY, and only NaF-type species are formed. We have been able to observe selectively AI species that are in close proximity to fluoride ions, by using 19F-27AI CP. This has important implications for the study of other catalytic AI/F systems. 1. L.E.Manzer, Science, 249, 31 (1990). 2. D.R. Corbin, patent pending. 3. D.R.Corbin, unpublished results.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
91
ALUMINUM-27 DOUBLE-ROTATION NMR INVESTIGATIONS OF SAPO-5 WITH VARIABLE SILICON CONTENT Michael Janicke and Bradley F. Chmelka Department of Chemical and Nuclear Engineering, University of California, Santa Barbara, CA, 93106, USA Dirk Demuth and Ferdi Sch0th Institut fdr Anorganische und Analytische Chemie, Johannes Gutenberg-Universita't 55099 Mainz, Germany
Mainz,
SUMMARY Double-rotation NMR (DOR) studies of 27AI species in SAPO-5, a silicon aluminophosphate molecular sieve with a one dimensional channel system, have revealed a minimum of three aluminum sites resulting from the synthesis. The DOR technique was used specifically to increase the spectral resolution by removing the broadening influences from second-order quadrupolar interactions associated with the spin 5/2 27AI nuclei. The DOR investigations of SAPO-5 crystals with variable Si/AI ratios resulted in the identification of three aluminum species, two consistent with the reported isotropic shift values for ALP04-5; however, these t w o resonances are only observable when small quantities of silicon are added to the synthesis. Increased substitution of silicon into the AFI framework caused the two peaks in the NMR spectra to coalesce into one resolvable resonance. The third aluminum species, observable in syntheses with only small amounts of silicon, corresponds to a condensed aluminophosphate phase similar to cristobalite. INTRODUCTION Recent research into SAPO-5 molecular sieves has been focused on the synthesis of high quality, single crystals for use as optoelectronic materials 1. This requires that the resulting SAPO-5 crystals be sufficiently large such that they can be studied as single crystals, while being nearly defect free. Synthesis of material such as this has been optimized, resulting in optically perfect, single crystals of SAPO-5 2
Examination of the long-range order of these materials using
powder X-ray diffraction, scanning electron microscopy, and optical microscopy establish morphological differences among the samples, with a condensed phase appearing in the materials as the amount of silicon in the synthesis was decreased. To correlate these measurements with the local structure of the materials, 27AI DOR NMR was used to probe changes in aluminum sites associated with the addition of silicon into the AFI structure. EXPERIMENTAL The Silicoaluminophosphate molecular sieves SAPO-5 were synthesized from gels with a molar ratio of 1AI203, 1.03P205, xSi02, 1.55TEA, 750H20 and x = 0.0375 to 0.5 at 210~
for 70h
and an AIPO4-5 reference sample with a gel composition of 1 AI203, 1.03 P2Os, 1.55 TEA, 375 H20 at 195~
for 10h. Powder X-ray diffraction, scanning electron microscopy and optical
microscopy were used to characterize these materials prior to further investigations. Solid-state 27AI DOR NMR investigations of the aluminum species in the SAPO-5 samples were conducted on a Chemagnetics CMX-500 spectrometer at a magnetic field strength of 1 1.7 T. DOR removes the anisotropic broadening influences caused by the quadrupolar nature of the spin-5/2 27AI nuclei 3 and has provided high-resolution spectra for 27AI in other aluminophosphates, not containing silicon 4 .s.
92
RESULTS AND DISCUSSION Determination of the lattice constants and the unit cell volume with P6cc symmetry showed that the silicon incorporation up to a molar ratio of AI203/SIO2 = 0.25 followed the one phosphorus by one silicon replacement mechanism e. Higher silicon amounts showed deviations from the expected unit cell volume and probably followed a mechanism, where two silicons substituted an aluminium-phosphorus pair.
10
20 2 theta
30
75
50
25
0
-25
pprn
Figure la: XRD powder pattern for calcined SAPO-5 sample, molar ratio of AI203/Si02 in
synthesis 0.0375. Reflections 20 = 20.5 ~ 21.5 ~ and 21.8 ~ correspond to the condensed aluminophosphate phase. Figure Ib: 2~AI DOR NMR spectrum for the same SAPO-5 sample acquired at 1 1.7 T. The peak at 42 ppm (referenced to AIN03) corresponds to the condensed aluminophosphate phase, while the two peaks 38 and 36 ppm are similar to reported isotropic shift values for AIPO4-5 s. Based on the 27AI DOR NMR and XRD results, it is apparent that two phases result from the current syntheses for SAPO-5. One phase is the AFI structure and the second is an undesirable aluminophosphate byproduct similar to cristobalite which is formed for synthesis conditions with low amounts of silicon, Figure 1. As the amount of silicon in the synthesis was increased, substantially less of the condensed phase is formed; moreover, the t w o peaks in the 27AI DOR NMR spectra merge to one isotropic shift. Previous studies of the aluminophosphate analog AIPO4-5 suggest three aluminum sites are present in the structure, but not observable at this magnetic field strength 6. The DOR results for SAPO-5 suggest that silicon is substituting randomly into the AFI framework as it replaces the phosphorus. Had the silicon selected specific phosphorus sites, one would have expected a decrease in one peak with respect to the other. Thus, 27AI DOR NMR has provided a new means of observing silicon substitution into the SAPO5 molecular sieve structure and discovered indiscriminate replacement of phosphorus T-sites with silicon.
REFERENCES S.D. Co>~T.E. Gier, and G.D. Stucky, Chem. Mater., 2 (1990) 609. 2 F. ~ , D. Demur, B. Zibmvv~, J. Komatowski,and G. F~ger,J. Am. Chem. Soc., 116 (1994) 1090. 3 A. Samoson, E. Lippm~,andA. F n e s , ~ ~ , 6 5 ( 1 9 8 8 ) 1013;Y. Wu, B.Q. Sun, A. Frnes,A. Samoson, and E. ~ , J. Magn. Reson.,89 (1990) 297. 4 Y. Wu, B.F. ~ , A . Pines,M.E. Davis, PJ. Grobet, P.A.Jacobs, Nature, 346 (1990) 550; R. ~ B.F. Ctwel
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions
93
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
29Si and 27A1 MAS NMR STUDIES OF FAUJASITE/GALLIUM
OXIDE CATALYSTS Z. Olejniczak, S. Sagnowski, B. Sulikowski*, J. Ptaszynski* Institute of Nuclear Physics, ul. Radzikowskiego 152, 31-342 Krak6w, Poland *Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, ul. Niezapominajek 1, 30-239 Krak6w, Poland
SUMMARY 29Si and 27A1 NMR spectroscopy was used to study the changes in the faujasite matrix upon loading with gallium oxide followed by reduction with hydrogen. The gallium-containing faujasites were active catalysts in the oxidative dehydrogenation of propane to propene.
INTRODUCTION Gallium-containing zeolites are, due to their combined redox and acid properties, of considerable interest and are used in a Cyclar process, where low alkanes are dehydrocyclized to benzene and xylenes. Most research has been focused on GaMFI and Ga-MEL systems. Interaction of gallium oxide with other, especially wide pore zeolites, is less known. We studied zeolite Y, loaded with Ga203 and monitored the changes in the zeolite matrix by using solid-state NMR. EXPERIMENTAL
Ultrastable acid-washed zeolite Y was prepared by ion exchange with a m m o n i u m nitrate, followed by hydrothermal and acid treatment. The zeolite matrix had Si/A1=8.91 and Na/AI=0.003 by chemical analysis. Zeolite US-Y-ex was homogenized with spectroscopically pure gallium oxide (III), and the precursors containing 4.76 to 44.4 wt% of Ga203 were reduced in hydrogen at 473 to 873 K. Solid-state magic-angle-spinning (MAS) NMR spectra were recorded at 6.3 T (53.7 MHz for silicon and 70.4 for A1). 29Si MAS spectra were acquired with 7r/2 pulses and repetition time of 10 s. 27A1 MAS spectra were obtained using very short I ~ts with 25 kHz B1 amplitude pulses to ensure that they are quantitatively reliable. The recycle delays were 0.5 s. Typcially 2000 and 1000 transients were accumulated per silicon and aluminium spectra, respectively. The rotors were spun in air at 4kHz.
94 RESULTS AND DISCUSSION The Si/A1 ratio in the aluminosilicate framework can be calculated directly from the 29Si MAS NMR since all the framework sites in zeolite Y are crystallographically and magnetically equivalent. Additionally the siting of aluminium can be monitored by using 27A1 MAS NMR. By comparing (Si/A1)NMR with the results of chemical analysis (which gives bulk composition), the amount of extraframework aluminium can be calculated. Our starting material had well resolved signals with chemical shifts at-106.5, -101, -95.2 and -90.1 p p m from TMS, corresponding to Si (nAl) sites, where n = 0 to 3, respectively. The Si (4AI) signal was missing, as the sample was already quite siliceous. From this material with 55.6 Al/u.c., an ultrastable form with 33.2 A1/u.c. was obtained, which upon acid leaching gave US-Y-ex with 19.9 A1/u.c. The signals of the matrix were very well resolved, with chemical shifts at-95.1,-101.4,-108.1 and-114.7 ppm. The samples loaded with gallium oxide and reduced with hydrogen had a significantly changed spectrum, corresponding to a more siliceous framework. The amount of A1 was in the range 4.5 to 7 Al/u.c. We observed a strong signal corresponding to Si (0A1) groupings and a weak one from Si(1AI) sites. Also weak Si (1Ga) sites were found in the spectra. This confirms directly that gallium oxide, reduced in the presence of the zeolite and transported to faujasite cages as Ga20, is inserted into the defects of the matrix, in agreement with XRD, Laser Raman Spectroscopy and FT IR measurements. Moreover, catalytic studies revealed that propane was oxydehydrogenated to propene, without forming aromatic hydrocarbons [1]. This points to the fact that the siliceous matrix contained the Br~nsted acid sites of intermediate strengths, and hence aromatization of propene did not take place. To conclude, NMR spectroscopy is an indispensable tool and can give direct insights into the behaviour of gallium-containing faujasite catalysts subjected to various treatments. ACKNOWLEDGEMENT We are grateful to the Committee of Scientific Research (Warsaw) for support (project 2P.303.149.04 ). REFERENCES [1] B. Sulikowski, J. Krysciak, R.X. Valenzuela and V. Cortes Corber~n, Stud. Surf. Sci. Catal. (1994) - in press
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All fights reserved.
95
A NEW ASSIGNMENT OF THE SIGNALS IN 23NA DOR NMR TO SODIUM SITES IN DEHYDRATED NaY Z E O L I T E Harry A.M. Verhulst ", Wim J.J. Welters, Gert Vorbeck, Leo J.M. van de Ven", Vincent H.J. de Beer, Rutger A. van Santen and Jan W. de Haan ~ Schuit Institute of Catalysis and Laboratory of Instrumental Analysis ~, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands SUMMARY A new assignment of the signals in the 23Na DOR NMR spectra to the different sodium sites in dehydrated NaY zeolite is presented. 23Na DOR- and MAS NMR measurements of dehydrated NaY, Ca 2§ exchanged NaY samples and NaY samples in which Mo(CO)6 is adsorbed are used for this purpose. INTRODUCTION Several 23Na NMR techniques have been used to probe the distribution of the sodium cations in zeolites. However, NMR spectra of quadrupolar nuclei, like 23Na, are limited in resolution, because of the second-order quadrupolar line broadening of the readily observable central +1/2 ~
-1/2
transition in these spectra. The double rotation NMR (DOR) technique is able to reduce this line broadening and thus gives a much better spectral resolution. Recently, Jelinek et al. 1"2 measured the 23Na DOR NMR spectrum of dehydrated NaY at 11.7 T. They found three different 23Na DOR NMR signals (centrebands). Subsequently, Hunger et al. 3 published a reassignment of the 23Na DOR and MAS spectra with only two distinguishable signals (7.0 and 9.4 T): one is assigned to sodium cations at site SI and the second signal to sodium cations at site SII and site SI'. Here, we present evidence that in fact four out of the possible five different sodium sites can be distinguished with 23Na DOR and MAS NMR, in combination with simulation procedures. The simulations were carried out with the program QNMR 4.
E X P E R I M E N T A L SECTION Dehydrated samples of zeolite NaY, zeolite NaY partly ion-exchanged with CaCI 2 solution and zeolite NaY fully saturated with Mo(CO)6 (gas phase deposition), were used for the measurements. 23Na DOR and MAS NMR measurements were carried out on a Bruker MSL 400 NMR spectrometer at 105.8 M H (9.4 T). DOR spinning speeds were approximately 5 kHz and 850 Hz for the inner and outer rotor respectively. Odd-numbered DOR sidebands were suppressed by synchronized pulsing. Chemical shifts were referred to a saturated NaCl solution as an external standard. The DOR and MAS simulations were performed using the program QNMR 4.
96
Far-IR spectra were recorded using a Bruker IFS 113v FT-IR spectrometer equipped with a heatable in situ cell connected to a vacuum system at 300 K.
RESULTS AND DISCUSSION Four distinct signals are needed to simulate satisfactory the 23Na DOR NMR spectra of dehydrated NaY zeolite at 9.4 T : the first signal, positioned at -6 ppm and a quadrupolar coupling constant PQ of 0.4 MHz, which is - in agreement with literature - assigned to sodium cations in hexagonal prisms (site SI). The second one, at -24 ppm and with a PQ value of 2.3 MHz, is assigned to Na § located in the sodalite cages (sites SI' and SII'). The third and the fourth signal, with chemical shifts of-43 and -46 ppm and PQ values of 4.2 and 4.7 MHz, respectively, are assigned to sodium cations in the supercages (sites SII and SIII) 5. Additional support for the changed and extended assignment of the signals found for the 23Na DOR NMR spectra of dehydrated NaY comes from measurements and simulations of the 23Na DOR NMR spectra (9.4 T) of a CalgNaI6Y zeolite sample. At this level of sodium exchange (70 %) most of the SI sites will be occupied by Ca 2§ after drying at 673 K in a He flow whereas the residual sodium will be mainly located in the supercages. This could be confirmed by additional Far-IR measurements of this sample. It easily explains the markedly lower intensity for the signal caused by Na § in SI positions in the corresponding 23Na DOR NMR spectra compared to that for NaY. For the complete simulation of the spectra again four different signals with PQ values of 0.4; 2-.3; 4.6 and 5.0 MHz are required. Interestingly, the latter two are enlarged compared to those for the dehydrated NaY, implying enhanced electric field gradients at sites SII and Sill. Most likely this is due to the influence of the calcium cations as well as to local changes in the framework geometry caused by these cations. Further evidence for our assignment was taken from the 23Na DOR NMR spectra of NaY, in which Mo(CO)6 has been adsorbed. Mo(CO)6 can interact only with Na § in the supercages (sites SII and Sill). Our results show that the quadrupolar interactions of the sodium cations have decreased considerably, due to a more symmetric surrounding of these cations upon Mo(CO)6 adsorption. On the other hand, the sodalite cage Na § (sites SI' and SII') are not affected, because neither the signal position nor the quadrupolar interaction did change significantly (PQ = 2.3).
REFERENCES 1. 2. 3. 4.
R. Jelinek, S. t3zkar, G.A. Ozin; J. Am. Chem. Soc. 114 (1992) 4907. R. Jelinek, S. t3zkar, H.O. Pastore, A. Malek, G.A. Ozin; J. Am. Chem. Soc. 115 (1993) 563. M. Hunger, G. Engelhardt, H. Koller, J. Weitkamp; Solid State Nucl. Magn. Res. 2 (1993) 111. Program for simulation of solid state NMR lineshapes QNMR, developed and supplied by the Institute of Chemical Physics and Biophysics, Tallinn, Estonia. 5. H.A.M. Verhulst, W.J.J. Welters, G. Vorbeck, L.J.M. van de Ven, V.H.J. de Beer, R.A. van Santen, J.W. de Haan; J. Phys. Chem. accepted for publication.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
97
STUDY OF MORDENITE ACIDITY BY 1H NMR TECHNIQUES: BROAD-LINE AT 4 K AND HIGH RESOLUTION MAS AT 300 K. COMPARISON WITH HY. BRONSTED ACIDITY SCALE AND IMPORTANCE OF STRUCTURE DEFECTS.
L. HEERIBOUT, V. SEMMER, P. BATAMACK, FRAISSARD
C. DOREMIEUX-MORIN
and J.
Laboratoire de Chimie des Surfaces, associ(~ au CNRS -URA 1428 Universite P. et M. Curie, Casier 196, Tour 55, 4, place Jussieu F 75252 PARIS Cedex 05 SUMMARY The interaction of water molecules with the acidic OH groups of decationized zeolites, giving H20...HO- and H30 +, is quantitatively studied using 1H NMR, broad-line at 4 K and MAS at 300 K. Results for industrial Y and mordenite samples are compared. The influence of Lewis acid sites is emphasized. INTRODUCTION
1H broad-line NMR at 4 K allows a quantitative measure of the concentration of hydroxonium ions formed by interaction of water molecules with bridging OH groups in zeolites, denoted Z O H. 1 A Br0~sted acidity scale for solids has been based on this measure. 2 Results previously obtained on a partially dealuminated HY zeolite (D HY) have shown the great influence of Lewis acid sites 1,3 (expressed, using 1H MAS NMR, by the number of water molecules that they bond)4 on the hydroxonium concentration for high loading of adsorbed water, in view of the great industrial interest of zeolite acid strength we propose to compare the concentrations of hydroxonium ions formed in H-mordenites containing different numbers of Lewis sites and to compare them to those known for D HY. 1 EXPERIMENTAL SECTION
Two industial mordenite samples, denoted A and B, were chosen for comparison. Only one of them, A, is a good catalyst for the conversion of toluene to xylenes. The Si/AI ratio measured by 29Si MAS NMR is 9.4 for A and 10.3 for B. All samples are "shallow bed" pretreated. Water adsorption, sample sealing and homogenization have been described previously. 1 The methods and especially the spin 112 magnetic configurations used to simulate the broad-line experimental spectra have also been described. 1 RESULTS AND DISCUSSION
Quantitative analyses of the samples obtained from MAS NMR experiments are summarized in Table 1. The main differences between mordenites A and B are the following: (i) the number of Lewis acid sites per Br0nsted site (sa), denoted m, is much larger for A (0.3) than for B (0.01); (ii) only A contains ZOH of two types (not distinguishable in Table 1), one being ZOH hydrogen-bonded to framework O atoms. 5 The number of hydroxonium ions per
98
Table 1 (1), (2) and (3) obtained using 1H MAS NMR on pretreated samples; (4) after adsorption of small amounts of water; (5) using 27AI MAS NMR on fully hydrated samples. Number of m: Number of Number of Number of Number of Sample extraLewis acid ZOH per uc AIOH per uc SiOH per uc framework AI (1) (2) (3) sites per Br0nsted site (5) 0 0.3L-H3.2 0.5:L-0.2
35~8&2 4.3L--H3.4 3.8_+0.3 , ,
DHY ],3 Mordenite A Mordenite B
1.5L+0.5 2.4_+0.2 3.3L+0.2
(4)
0.04 0.3 0.01
0
0.8_+0.2 0.8_+0.2
BrOnsted acid site (H30 +/sa), obtained from broad-line NMR spectrum simulations, versus the number of adsorbed water molecules per BrOnsted acid site (H20/sa) is shown in Fig. 1. For both mordenites, H30 +/sa is 0.33 when H20/sa is 1. The corresponding value for D HY is 0.2. When H20/sa increases H30 +/sa does not increase very greatly for B though it does for A, to 0.8 when H20/sa is 3.7, m being 0.3 (Table 1). For the same H20/sa value, H30 +/sa is about 0.4 for D HY, m being 0.04 (Table 1). Results obtained on D HY have been interpreted on the basis of a synergy between Lewis and Br0nsted sites which, for enhancing H30 + concentration, necessitates the formation of a network of hydrogen-bonded water molecules also bonded to the acid sites.-3 Lewis acid sites appear responsible for a marked enhancement of the hydroxonium concentration for high adsorbed water molecule concentrations. .o-~
-
mordenl[e
i
[
4{ .
o.s-~
06"i,
9
I
as
=
CONCLUSION
A
morctenite B
In the present state of our results, we
0
conclude that the order of H30 +/sa values
HY Br6nsted
acid
site
for H20/sa equal to 3.7 is to be related to the order of m, the number of Lewis acid
0 "l-
0,4i
9 I
i
sites per BrOnsted acid sites. This common order is: mordenite B < D HY < mordenite A.
I
!o
REFERENCES
1. P. Batamack, C. Doremieux-Morin and J. FraJssard, Catalysis Letters., 11 (1991) 119 and references therein. Fig. 1 H20/as 2. P. Batamack, C. Dor~'nieux-Modn, R. Vincent and J. Fraissard, J. Phys. Chem., 97 (1993) 9779 and references therein. 3. P. Batamack, C. Doremieux-Modn, R. Vincent and J. Fralssard, Microporous Materials, 2 (1994). 4. M. Hunger, D. Freude and H. Pfeifer, J. Chem. Soc., Faraday Trans., 87 (1991) 657. 5. E. Brunner, K. Beck, L. Heedbout, V. Semrner, H.G. Karge and M. Koch, Zeolites, submitted. 0
.
,
i
3
,
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
99
SPECTROSCOPIC EVALUATION OF THE RELATIVE ACIDITY OF THE BRIDGED HYDROXYL SPECIES IN ZEOLITES AND THE ISOLATED HYDROXYL SPECIES IN AMORPHOUS SILICA by E. Garrone, B. Onida, G. SpanS, G. Spoto, P. Ugliengo and A. Zecchina Dipartimento di Chimica Inorganica, Chimica Fisica e Chimica dei Materiali, Universit~ di Torino, via P. Giuria 7 10125 Torino Italy ABSTRACT The classical Bellamy-Hallam-William plot of the shifts in the OH stretching mode suffered by the two types of hydroxyls when H-bonded to a set of base molecules allows a measure of their relative acidity. INTRODUCTION One way to define the acid strength of a surface hydroxyl species is to measure the shift in the OH stretching mode Av(OH), brought about by the formation of H-bonded complexes with mildly basic compounds, like carbon monoxide (1, 2). For instance, the relative acidity of the Si(OH)AI species in various zeolites can be measured in this way (2). The Av(OH) values are usually relatedto either Proton Affinity of the base molecule B (3) or to the Pka value of the conjugated acid BH + (4): eventually, values for the proton donor ability or pka of the acidic hydroxyl are obtained. A different approach is assumed in the present work. The relative acidity of the Si(OH)AI species in zeolites and the Si(OH) hydroxyl groups in amorphous silica is determined via a procedure well known for species in solution (Bellamy-Hallam-William plot BHVV), consisting in the comparison of Av(OH) values in the two cases for the same set of basic molecules. EXPERIMENTAL Molecules considered were: nitrogen, carbon dioxide, nitrous oxide, carbon monoxide, acetylene, methylacetylene, benzene, ethylene, propene. The interaction spans from the very weak N2/SiOH case to the relatively strong cases of Si(OH)AI species interacting with methylacetylene, etc., when H-bonded species show up as short-lived intermediates in the process of PT. As a consequence, three versions of FTIR spectroscopy have been used: i) plain, room temperature; ii) plain, low-temperature; iii) room temperature, time-resolved. The silica sample was Areosil outgassed at 800~
the zeolite was HZSM-5 outgassed at 500~
RESULTS AND DISCUSSION Most Av(OH) data concerning SiOH have already been published (N2, CO2, N20, CO, C6H6, C2H2), as are those concerning CO, N2, N20, C6H6, C2H2 and CH3CCH with Si(OH)AI. All available data, including those measured for the present work, have been plotted one set against the other in a BHW
100
MeCCH 9
1,50 -
/ /
A VSiOH /cm-1
f
/
/
f
/
/
f
J
/
/
9 Me_CH=CH 2
/
HCCHe 100
J
/
/
/
f
/
/
/
/
t
/
2-- Ct.4 2
~/&CO
/
CC~/ //
50 /
t
/
/
AN20
.A'N2 -AVzeOH/cm-~ I
!
plot (4). Triangles refer to stable H-bonded complexes, and dots to short-lived intermediates. A very good linearity is observed: points nearly line up with the origin, though this is not stdctly required. Whithin this set of molecules, an upper limit value at = 350 cm-1 is observed for the Av(OH) in zeolites for H-bonded adducts not evolving to protonated species. The slope is = 3. Such a value may be related, on the one hand, to calorimetrically determined enthalpy of interaction of strong bases (5), with excellent agreement. On the other hand, it may be related to the pka of silica, also experimentally determined to be ~ 7: the indication is that Si(OH)AI is as strong as perchloric acid.
REFERENCES
(1) L. M. Kustov, V. B. Kazansky, S. Beran, L. Kubelkov~, and P. Jiru, J. Phys. Chem., (1987), 91, 5247. (2) E. Garrone, R. Chiappetta, G. Spoto, P. Ugliengo, A. Zecchina and F. Fajula, Proc. 9th International Zeolite Conference, Montreal...1.992, R. von Ballmoos et al., (1993), 267. (3) E. A. Paukshtis and E. N. Yurchenko, React. Kinet. Catal. Lett., (1981), 16, 131. (4) P. G. Rouxhet and R. E. Sempels, J. C. S. Faraday I, (1974), 70, 2021. (5) N. Cardona and J. A. Dumesic, J_..Catal., (1990), 125, 427.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions
101
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
ONE-POINT METHOD FOR THE DETERMINATION OF STRENGTH OF ZEOLITE ACIDITY BY TEMPERATURE PROGRAMMED DESORPTION OF A M M O N I A BASED O N TROUTON'S RULE
Miki Niwa 1, Naonobu Katada 1, Masahiko Sawa 2 and Yuichi Murakami 2 1Department of Materials Science, Faculty of Engineering, Tottori University, Koyama-cho, Tottori 680, Japan 2Department of Applied Chemistry, School of Engineering, Furo-cho, Chiku-saku, Nagoya 464-01, Japan
SUMMARY
We propose a one-point method to measure the strength of zeolie acidity from temperature programmed deorption (TPD) of ammonia. Based on the assumption of constancy of AS, one can determine the AH from the theoretical equation describing the TPD of ammonia which was derived by the authors. The constancey of AS upon desorption of ammonia is in agreement with the Trouton's rule about the vaporization of liquids. INRODUCTION Temperature-programmed desorption (TPD) of ammonia has been used often to characterize zeolite acidity. However, the principle of the method is not simple. Previous investigations by the authors reported the identification of peaks and the freely occurring readsorption of ammonia1, and then derived the theoretical equation as shown below 2. l n T m _ In(AFW) = AH + In fl(1- Ore)2(AH- RTm) p0 exp(AS / R) RTm This equation shows that the temperature of the peak maximum (Tm) is influenced by not only the contact time of carrier gas (W/F), but also by the number of acid sites (Ao); therefore, the s~ength of zeolite acidity is not estimated from the Tm at all. The strength of zeolite acidity (AH) can be derived from this equation, since the second term of the right hand side is invariant under the experimental conditions, and a plot of the left hand side 1/Tm gives a straight line from which AH may be determined. The thus determined AH was in close agreement with the value measured by calorimetry, and the theoretical equation was thereby confirmed experimentally. The above method needs three to four experiments at least. Thus, a more simple method to measure the AH has been proposed. The parameters except for AS and
102 AH are measured from one experiment. However, AS calculated from the measured AH was almost constant on various zeolites, as shown in Table 1. Therefore, we will assume the constancy of AS (averaged value, 150 JK-lmol-1), and by using the AS, AH can be measured by only one experiment. This proposal is supported by following physical chemistry. (1) Trouton's rule claims that a wide range of liquids give approximately the same ASvap, although the AHvap and boiling points are different. Our hypothesis is exactly the same as this rule. (2) A value of AS of 150 JK-lmo1-1 is approximately equal to the change of entropy from solid ammonia to gaseous ammonia at 673 K. In other words, the entropy of adsorbed ammonia is similar to that of solid ammonia. It is natural that there is a similarity between the states of adsorbed ammonia and solid ammonia. Table 2 shows the values of AH thus measured for different weights of various zeolites. AH has only a small exprimental error within 1 kJmo1-1. Thus, a simple and easy method to determine the acid strength of a zeolite has been established. Nomenclature acid amount [mol kg-1] A0 flow rate of carrier gas [m3 s -1] F AH enthalpy change of desorption [Jmol-1] po pressure at standard conditions [1.013 x 105 Pa] gas constant [8.31 JK-lmol-1] R AS entropy change of desorption [JK-lmo1-1] T m temperature at peak maximum [K] zeolite weight [kg] W heating rate [Ks-1] Om surface coverage at peak maximum [-] Table I
AH and AS of measured zeolites
Zeolite
JRC-Z-HM15 JRC-Z-HM20 JRC-Z5-25H JRC-Z5-75H HF15
AH (kJmo1-1) 150 160 130 132 143
AS (JK-lmo1-1) 146 160 149 148 145
JRC-Z, reference catalyst supplied by the Catalysis Society of Japan. HM, mordenite; Z5, ZSM-5; HF, ferrierite
103 Table 2
AH measured by one-point method by using different amounts of zeolite
Zeolite
JRC-Z-HM10
JRC-Z-HM15
JRC-Z-HM20
JRC-Z5-25H
JRC-Z5-70H
HF15
W (g)
AH (kJmo1-1)
0.202 0.302 0.402 0.110 0.141 0.201 0.202 0.300 0.402 0.077 0.141 0.205 0.301 0.400 0.052 0.101 0.500 1.00 0.202 0.412 0.637 1.00 0.061 0.100 0.149 0.200 0.302
147 146 148 152 153 153 152 152 152 153 154 154 154 153 131 132 131 131 133 133 133 133 146 147 147 147 147
REFERENCES
(1) (2)
M. Niwa, M. Iwamoto and K. Segawa, Bull. Chem. Soc. Jpn., 59 (1986) 3735. M. Sawa, M. Niwa and Y. Murakami, Zeolites 10 (1990) 307.
H.G. Karge and J. Weitkamp (Eds.) 104
Zeolite Science 1994: Recent Progress and Discussions
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
INTERACTION OF CO2, H20, CH3OH, (CH3)20, CH3N, H2S, (CH3)2CO, NH3 AND Py WITH BRONSTED ACID SITES OF H-ZSM-5: COMPARISON OF THE IR MANIFESTATION R. Buzzoni, S. Bordiga, G. Spoto, D. Scarano, G. Ricchiardi, C. Lamberti and A. Zecchina* Dipartimento di Chimica Inorganica, Chimica Fisica e Chimica dei Materiali, Universith di Torino, Via Pietro Giuria 7, 10125 Torino, Italy
Summary The object of this study is the interaction of HZSM-5 with probe molcules, characterized by different basicity by using IR spectroscopy. The formation of H-bonded species and the proton transfer are considered. Experimental results are compared with literature data (experimental and theoretical)
,Introduction The acidic properties of H-ZSM-5 zeolite arise mainly from bridged structural hdroxyls inside the channels. During the reaction pathway where protonation is involved these groups often give primarily H-bonded species. As FTIR is a rapid method for demonstrating the existence of H-bonding and for characterizing it, in this work we consider the interaction of Bronsted acid sites with probe molecules characterized by different basicity in order to obtain a complete set of results to be compared with literature data (experimental and theoretical).
Experimental H-ZSM-5 samples with Si/AI=14 were suplied by Enichem Laboratories (Bollate, Milano). Thin self-supporting wafers were activated in vacuum at 673 K for lhr, inside the IR cell. Infrared spectra were taken using a Bruker IFS 66 spectrometer operated at 2 cm ~ resolution and following an "in-situ" procedure.
Results and Discussion The interaction of Bronsted sites with basic molecules (X) such as NH3 and Py leads to a proton transfer reaction following the reaction scheme
H I
~si-O-A(- X-
H X+
Si /0-~ AI/
With molecules like CO at 77K, H2S, (CH3)2CO, CH3CN, proton transfer reactions are less probable. In this case the most plausible structure will be
X H Si
I /O~
/
AI
As far as }-120, CH3OH and CH3OCH3 are concerned, the situation is more controversial and the interpretation of experimental data is still debated. In particular, the problem of the formation of H30 § and of the associate vibrational manifestation have been object of several studies in the recent years by many researchers using spectroscopic [1 ] as well as theoretical
105 methods [2]. The presence of two bands at 2885 and 2465 cm"~ in the IR spectraa of H20 on H-ZSM-5 can be associated with the asymmetric and symmetric stretching modes of the hydroxonium ions formed inside the zeolite channels or can be due to pseudo-bands generated by Evans-holes in hydrogen bonded H20 (this transmission window is typical of medium or strong H-bonds and it is due to the Fermi resonance between overtone bending modes and the components of the broad band characteristic of H-bond absorbing at similar wavenumbers) [3,4]. The presence of two absorptions or a transmission window, very similar to those obtained for water, also in the cases of molecules which can give only one OH...X bond (CH3CN, (CH3)2CO, Py) is in favour of the second hypothesis. An example of the spectra obtained in this investigation is given in Figure 1 where IR spectra of dimethylether at increasing coverages are reported ( the arrow indicate the transmission window) 1.5
I
-.5
.3500
.3000
2500
cm-I
2000
1500
Figure 1: Difference spectra of (CH3)20 on HZSM-5 outgassed at 673 K (increasing coverage) The IR spectra of NH4+ and PyIT species formed by protoin transfer are also discussed in detail, because they represent prototype species when the proton is totally transferred. References
[1] [2] [3] [4]
A. Jentys, G. Earacka, M. Derewinski, J. A. Lercher; J. Phys. Chem. 1989, 93, 4837 J. Sauer, H. Horn, M. Haser, R. Ahlrichs; Chem. Phys. Lett. 1990, 173, 26 D. Hadzi, S. Bratos, in: The Hydrogen Bond. Eds. P. Schuster et al., North-Holland Publ. 1976, 576 S. Bratos, H. J. Ratajczak; J. Chem. Phys. 1982, 76, 77
106
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
IR CHARACTERIZATION OF HYDROXYL GROUPS IN SAPO-40 E. Garronel, B. Onidal,2, Z. Gabelica2 and E. G. Derouane2 Dipartimento di Chimica Inorganica, Chimica Fisica e Chimica dei Materiali, Universita di Torino, via P. Giuria 7, 10125 Torino Italy 2 Facult6s Universitaires N.-D. de la Paix, Laboratoire de Catalyse, rue de Bruxelles 61, B-5000 Namur, Belgium ABSTRACT Adsorption of NH3 and CO allow a thorough IR characterization of four types of Si(OH)AI hydroxyls, the only species present in SAPO-40. INTRODUCTION SAPO-40 is a silicoaluminophosphate recently synthesized in a pure form [1], showing two types of intersecting channels involving respectively 12-membered and 8-membered rings. So far, available data only concem the structure. The first IR investigation of such novel solid is reported in this work, wich deals with the type, number and acidity of hydroxyl species. This latter has been characterized by two methods, i.e. the propensity to transfer the proton to NH3 and to form week H-bonds with CO, N2, benzene and methyl-substituted benzenes. EXPERIMENTAL SECTION
The SAPO-40 samples were prepared according to ref. [1], slowly calcined up to 500~
during 5
hours, then oxidized in 02 at the same temperature for one additional hour. IR spectra were taken on a Perkin-Elmer 1720 and a Bruker IFS 66 FTIR instruments. RESULTS AND DISCUSSION
The figure shows the variation of the absorption pattem in the 3200-3700 cm-1 region of the IR spectrum during the desorption of adsorbed NH 3. The most intense spectrum at high frequencies is that of the naked sample, showing four peaks at 3637 cm-1 (A), 3625 cm-1 (B: shoulder) and 3550 cm-1 (C), 3528 cm-~ (D). Adsorption of NH3 results in the most intense spectrum in the low frequency region, which shows the depletion of the four hydroxyl species and the consequent formation of NH4+ species (bands at 3385 and 3320 cm-~). Both the extremely small population of POH species (tiny band at 3676 cm-~) and the absence of any SiOH species indicate negligible presence of inner structural defects as well as a limited external surface, in agreement with SEM pictures of the samples. The four main bands are all ascribed to bridged Si(OH)AI groups. As in the case of faujasite [2], the high frequency bands (A and B) are assumed to be due to hydroxyl species located in large cavities (here the 12-ring channels), whereas peaks C and D occuring at lower frequencies are most probably
107
.4
=o
..Q
.2
. . . . .
36'o0
. . . . . . . . .
34'oo'
Wavenumbers ( ' c m - 1 )
. . . . . . .
322o
related to hydroxyl species in smaller cavities (here 8-rings channels and "side pockets" in the 12-ring channels). Heat treatments lead to the decomposition of NH4+ species and the recovery of OH species (isosbestic point at 3440 cm-1). Bands A, C and D basically reappear together, thus suggesting a similar acidity in all cases, whereas the band B is the last to be recovered. Upon CO adsorption, species A and B readily form H-bonded complexes, the corresponding shift Z~v(OH) being 290 and 350 cm-1, respectively. Species C requires moderately high CO pressures to be involved in a H-type bond, the corresponding Z~v(OH) being however only of about 100 cm-l. Species D does not react with CO at all. As Av(OH) is directly related to acidity, the following inferences may be drawn: (i) species B appears to be the most acidic species; (ii) species C, which according to the NH 3 experiment has an acidity comparable to that of species A, is probably stedcally hindered in H-bonding with CO; (iii) species D is even more hindered, so that no interaction is seen. Interactions with other molecules (N2, benzene, etc. ) confirm this picture, on the basis of which attempts are being made to locate precisely species C and D in the 8-ring channels and/or "side pockets" by means of molecular graphics. REFERENCES
[1] N. Dumont, Z. Gabelica, E. G. Derouane and L. B. McCusker, Microporus Mat..e.rials, 1 (1993) 149. [2] P. A. Jacobs and J. B. Uytterhoeven, J. Chem. Soc. Faraday Trans. I, 69 (1973) 359.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
108
F T I R E V I D E N C E O F Pt C A R B O N Y L S F O R M A T I O N F R O M Pt M E T A L C L U S T E R S IN K L Z E O L I T E A.Yu. Stakheevl), E.S. Shpirol), N.I. Jaeger2), G. Schulz-Ekloff2) 1) N.D. Zelinskii Institute of Organic Chemistry, Russian Academy of Sciences, Leninskii prospect 47, 117913 Moscow, Russia. 2) Institut far Angewandte und Physikalische Chemic, Universit~t Bremen, 2800 Bremen 33. SUMMARY FTIR spectroscopy revealed the reversible formation o f P t carbonyls upon adsorption at high CO pressure (~ 500 mbar). It is suggested that small Pt clusters located inside zeolite channels are transformed into (Zeol-O:) mPtx(CO)v spezies stabilized by the basic oxygen atoms of KL framework. The transformation is found to be readily reversible upon CO adsorption-desorption at room temperature (RT). INTRODUCTION Pt/KL zeolite exhibit unusual high catalytic activity and selectivity in n-hexane aromatization. These characteristics were ascribed to the effect of zeolite support on the properties of the Pt metal particles [1 ]. The aim of this paper is to study the reactivity of the small Pt clusters entrapped inside the zeolite channels toward CO. EXPERIMENTAL 1 % Pt/KL sample was prepared by incipient wetness impregnation o f KL zeolite with water solution of Pt(NH3)CI 2. The sample was calcined and reduced at 400 ~
FTIR spectra of
adsorbed CO were recorded on a BIO-RAD FT1R spectrometer with a resolution of 2 cm -l . R E S U L T S AND D I S C U S S I O N The CO adsorption on Pt/KL at RT and 1 mbar CO pressure results in the appearance of the very broad band (FWHH ~ 150 cm -l) in the region 2060 - 1910 cm -1, which can be ascribed to the linearly bonded CO molecules. The comparison of the IR spectra obtained upon CO adsorption at RT and desorption at elevated temperature reveal that the broad band consists of at least two distinctive bands. The first is found at 2050 - 2060 cm -1, and we tentatively ascribed it to the Pt particles which are located in the near surface region of the zeolite microcrystals or in voids of the lattice. CO adsorption on this particles is not strongly perturbed by the zeolite matrix. The second band has a frequency o f ~ 1980 - 1930 cm -1 and the extrapolation o f its frequency to the zero coverage gives the value o f 1920 cm -1. We suggest that such low value is related to the strong effect o f the zeolite matrix on the small Pt metal clusters encaged in the zeolite channels. After 30 min o f CO adsorption at 1 mbar the integral band intensity reaches its maximum and does not changed later on. We assume that the surface saturation with CO is achieved under these conditions. However, additional treatment in CO at elevated pressure ( ~. 500 mbar) results in the 5-fold increase of the intensity of the linearly bonded CO band, its narrowing and shift toward higher wavenumbers. Moreover, several sharp, well-defined bands appear at 2130, 2069, 2030 and 2008 cm -1 (Fig.). CO desorption at RT leads to the decrease o f their intensity
109
0.20-
e fl. I 5 o ,r b e'O.I 0 r~
___J ,,,
2256
_
2260
--
~
2150
2100
i
2~50
1
I
2~00 1950 Wav, nu~b,r
I
I
I
i
1
1900 s
1850
1800
1258
12~0
without change of their frequencies. The readsorption of CO at 500 mbar gives reversible spectrum. The observed behavior is similar to those reported by Sachtler et al. [2] for Pd/NaY system and Kubelkova et al. for Ni/NaY [3]. In these systems the formation of Pd and Ni carbonyl clusters was established. The comparison of the data allows us to suggest that the formation of the unknown Pt carbonyl species takes place in Pt/KL upon CO adsorption at high pressure. We presume that highly reactive Pt clusters located inside zeolite channels are converted into the Pt carbonyls of the possible structure: (Zeol-O:)mPtx(CO)y These carbonyls are stabilized by the oxygen atoms of KL framework, which exhibit strong basic properties and can act as 6"-donor ligands [4]. REFERENCES 1. C. Besoukhanova, J. Guidot, D. Barthomeuf, M. Breysse and J.R. Bernard, J. Chem. Soc., Faraday Trans. I, 77 (1981) 1595. 2. L.L. Sheu, H. Knoezinger and W.M.H. Sachtler, J. Am. Chem. Soc., 111 (1989) 8125. 3. L. Kubelkova, J. Novakova, N.I. Jaeger and G. Schulz-Ekloff, Appl. Catal. A., 95 (1993) 87. 4. F.R. Hartley, in: Comprehensive Organometallic Chemistry, Vol. 5, ed. G. Wilkinson (Pergamon Press, Oxford, 1978) 471.
110
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
IR SPECTRA OF 180 EXCHANGED HZSM-5
F.BAUER 1, E.GEIDEL 2, CH.PEUKER 3 1WIP Isotopenchemie, Permoserstr. 15, 04303 Leipzig, Germany 2 Universitat Hamburg, Institut ~ r Physikalische Chemie, Bundesstr. 45, 20146 Hamburg, Germany 3 Humboldt Universitat, FB Chemie, WIP, Rudower Chaussee 6, Geb. 19.5, 12489 Berlin, Germany
INTRODUCTION IR spectroscopy is widely used in zeolite research. Its successful application is depending on a well-founded assignment of the IR bands. Beside empirical assignments some theoretical investigations are published about vibrational spectra of zeolite frameworks. The aim of this study is to obtain more detailed information on the spectrum of HZSM-5 comparing the IR spectra of 180 exchanged HZSM-5 and of HZSM-5 in the framework vibration region and the OH vibration region as well as the combination tones of the framework and the hydroxyl groups of the two samples. The experimental framework spectra have been compared with frequencies calculated for various ditetrahedra (O3Si-O-SiO3) as one of the most simple framework model. EXPERIMENT The commercial, template-free synthesized NaZSM-5 zeolite (Chemiewerke Bad KOstritz GmbI-I, Germany) with a Si/AI ratio of 15 was threefold ion exchanged with aqueous solution ofNH4NO 3 and calcined 12 hours on air at a temperature up to 820 K for yielding the H-form. Hydrothermal route/1/or exchange with 1802 gas at elevated temperatures/2/can be used for the post- synthesis 180-labeUing of zeolites. The zeolite sample was exchanged with H 2180 (95.2% 180, Chemotrade, Germany) in a water/nitrogen stream at 700 K for 1 hour. This way of exchange was chosen because some dealumination of the sample was required for further kinetic studies. The IR measurements were performed on a spectrometer IFS 66 (Bruker). The Praying Mantis DRIFT attachment (Harrick) was connected with a heated vacuum cell (Harfick) to record diffuse reflectance spectra. The samples were measured at temperatures up to 873 K under a dynamical vacuum better than 10-5 mbar. The calculation of vibrations was carried out for various ditetrahedra (O3Si-O-SiO3) by using the method of normal coordinate analysis based on Wilson's GF matrix method/3/. Structural parameters were taken from a single crystal X-ray diffraction study of Olson et al./4/of an assynthesized ZSM-5 (Si/Al=86). According to Blackwell /5/ the so-called bond length scaled force field (BLSF-BR), without adjustment of force constants, was used as model force field.
111
RESULTS AND DISCUSSION The bands in the framework spectrum of the 180 exchanged HZSM-5 sample are shifted to lower wavenumbers (1062, 794, 537, 443 cm-1) compared with the HZSM-5 spectrum (1094, 797, 546, 450 cm-1). The calculation of the v~orational spectra of the ditetrahedra O3Sil-O16-Si403
and
O3Si2-O13-Si803 (Olson's indication) with 180 or with 160 atoms gave the following results. The vibration forms and the sequence of the vibrations remain with 180 exchange. All bands shif~ to lower wavenumbers due to 180 substitution. The highest difference of about 40 cm -1 was calculated between wavenumbers of the anti-symmetrical stretching vibrations of the Si-OSi bridge, which seems to be caused by the low coupling of this vibration with others. This value is in good agreement with the experimental one of 32 cm-1. Similar results concerning the band shifts due to 180 exchange were published for tridymite /6/ and quartz/7/. The DRIFT spectra of undiluted samples show shifts of the f~amework combination tone bands from 1988 cm-i to 1943 cmd and from 1874 cm-1 to 1833 cmd due to the 180 exchange, i.e. the combination tone bands shift 45 and 41 cm-1 to lower wavenumbers compared with 32 cm"1 for the band of the fundamental vibrations. The acid OH band shit, s from 3608 cm-1 to 3586 cm-1 due to the 180 exchange, the combination tone band from 4657 to 4625 cm-1. The appearance of a new band at 3657 cm -1 shows that dealumination takes place during 18O exchange. CONCLUSION Shifts of IR bands were proved due to 180 exchange for framework vibrations and for OH vibrations as well as for the combination tones. The calculated value for the shift of the antisymmetrical Si-O-Si stretching vibration is in good agreement with the experimental finding. The analysis of more extended models for the ZSM-5 fi'ameworlc, including periodic boundary conditions, will allow to compare the calculated band shifts due to 180 exchange with the experimental data for all of the framework bands. ACKNOWLEDGEMENT The authors want to thank the DFG for the support of this work. REFERENCES 1. R.von Ballmoos: The 1SO-exchange method in zeolite chemistry; Otto Salle Verlag, Frankfurt, 1981 2. S.Yang, K.D.Park, E.Oldfield; J.Am.Chem.Soc. 111 (1989) 7278 3. E.B.Wilson, Jr., J.C.Decius, P.C.Cross: Molecular Vibrations; McGraw-Hill Book Company, Inc., New York, 1955 4. D.H.Olson, G.T.Kokotailo, S.L.Lawton, W.M.Meier; J.Phys.Chem 85 (1981) 2238 5. C.S.Blackwell; J.Phys.Chem. 83 (1979) 3251; 83 (1979) 3257 6. A.M.Hofmeister et al.; J.Phys.Chem. 96 (1992) 10213 7. R.K.Sato, P.F.McMillan; J.Phys.Chem 91 (1987) 3494
H.G. Karge and J. Weitkamp (Eds.) 112
Zeolite Science 1994: Recent Progress and Discussions
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
STRUCTURE AND REACTIVITY OF F R A M E W O R K AND E X T R A F R A M E W O R K IRON IN Fe-SILICALITE AS INVESTIGATED BY OPTICAL (IlL RAMAN, DRS UV-Vis) AND EPR SPECTROSCOPIF~S.
Geobaldo FI., BordigaSl., SpotoGl., Scarano DI., ZecchinaAla., PetriniG2., Leofanti G2., Tozzola G2., Padovan M 2. 1) Dipartimento di Chimica Inorganica, Chimica Fisica e Chimica dei Materiali, Universit/~ di Torino, Via P. Giuria 7 10125 TORINO ITALY 2) ENICHEM Centro Ricerche di BoRate, via S. Pietro 50 20021 BoUate (Mi) ITALY
Introduction Silicalites and Al-substituted Silicalites are characterised by substantially identical optical UVVis and EPR spectra. Substitution of Si with a variety of heteroatoms can cause dramatic changes in the spectroscopic properties of the zeolite. Fe-Silicalite has been studied by means of optical (DRS UV-Vis, IlL Raman) and EPR spectroscopies in order to characterise the coordination state of framework species and to identify the presence of extrafi'amework species (isolated and clustered). It is found that the ratio between framework and extraframework Fe species is strictly related to the sample calcination procedure. Probe molecules like CO, NO, NH 3, etc. prove their utility to characterise the properties of this material, through interaction with Brensted and Fe sites and formation of adducts having simple vibrational properties.
Experimental Fe-Silicalite was produced in the ENICHEM laboratory following a procedure described elsewhere (1 and references therein). Samples were calcined in air at 393 K, 823 K and 973 K; thermal treatments was done in suitable in situ cells at increasing temperature under dynamic vacuum.
Results and Discussion The IR and Raman spectra of Fe-Silicalite show the same general features of other substituted silicalites (1 and reference therein). The lattice modes and the Si.OH stetching band at 976 cm "1 (shoulder) associated with internal defective nests, can be easily detected. Beside this, a very prominent peak at 1020 cm" 1 in the Raman spectra is also observed. In the IR spectra an analogous adsorption at 1015 cm" 1 appears as a shoulder. These two peaks can be considered as finger print of framework iron in Fe-Silicalites. Immersion of Fe-Silicalite in a dilute NH 3 solution does not perturbs the iron sensitive Raman mode. This indicates a small propensity of framework iron to increase its coordination sphere. This conclusion is confirmed by CO and NO adsorption experiments from the gas phase, which are specially sensitive to extraframework Fe. The IR spectra of adsorbed CO and NO on FeSilicalite show dramatic changes when calcination and pretreatments conditions are changed, showing feature: ~:e to the presence of va,'i able amount of extraframework ye3+/Fe 2+ pairs,
113 T~-,e presence of extraframework iron can be easily monitored with DRS UV-Vis and EPR spectroscopies. In figure 1 the UV-Vis spectra of a Fe-Silicalite sample in air, after three different calcinations are reported. o
c
1
i
~
c
b
a ~ : o o . ~ o 7. . . .
~o
#,
o
~oooo ,
,,
40600 ,
,
~o6oo
Wavenumbers
zo6oo
(ore-- I)
10600 ,,1
Fig.1 DRS UV-Vis spectra of Fe-Silicalites calcined at a) 393 K, b) 823 K, c) 973 K for 24 h.
As clearly visible, calcination at high temperature, causes an enhancemem of the absorption at lower frequencies and a dramatic absorption decrease of the bands, in 30000-20000 cml range, which are due to forbidden d-d transition of Fe 3+ in tetrahedral coordination. On these samples, an indirect evidence of the formation of extraframework Fe upon calcination at high temperature, is given by IR spectra in the OH stetching region where a decrease of the absorption due to the Brensted acidic species is observed. Moreover EPR spectra show an intense band at g --- 2.00, due to the presence Fe 3+ in octahedral coordination. The intensity of this absorption increases when Fe-Silicalite is calcined at higher temperature (as expected). Conclusion
In as synthesised Fe-Silicalite, only a part of iron of reaction mixture is present in framework positions; DRS UV-Vis, IR and EPR results indicated that calcination at increasing temperature causes a partial iron extraction from the lattice and formation of very small clusters of iron oxides entrapped into the silicalite channels. Finally, when Fe-Silicalite is calcined at high temperature (973 K) no more evidence of structural iron is obtained by means of physical methods. References
1) Scarano D., Zecchina A., Bordiga S., Geobaldo F., Spoto G., Petrini G., Leofanti G., Vzdova 9M., and Tozzola G. Faraday Trans. in press.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
114
ELECTROCHEMISTRY OF TRANSITION METAL COMPLEXES ENCAPSULATED INTO ZEOLITES Carol A. Bessel and Debra R. Rolison* Surface Chemistry Branch (Code 6170), Naval Research Laboratory 4555 Overlook Avenue, SW, Washington, DC, 20375-5342, USA SUMMARY. The electrochemistry of transition metal complexes (Co(salen) and [Fe(bpy)3]2+ ) encapsulated into zeolites was studied using zeolite-modified electrodes (ZME). Grinding time, binding material, carbon source, electrolyte, solvent, scan rate, and the charge of the encapsulated complex all affect the cyclic and differential pulse voltammetry of these ZMEs. INTRODUCTION. Modification of electrode surfaces with zeolites is of current interest to both electrochemical and solid-state disciplines as the suggested applications include chemical sensing and electrocatalysis. 1-5
In order to demonstrate the utility of transition metal
complexes encapsulated into zeolites for electrosynthesgs, the reactivity of these materials [Z(ML)] at modified electrodes was investigated.
The use of Z(ML) for electrocatalysis
requires insight into the mechanism by which redox activity occurs in the zeolite lattice. Optimization of the variables associated with the synthesis of the modified zeolite and their preparation and use as zeolite-modified electrodes must first be investigated before such issues as changes in the redox reactivity due to interior versus exterior lattice sites, the steric strain to the encapsulated complex imposed by the zeolite and/or bonding of the complex to the zeolite, and electronic communication within the zeolite lattice itself can be addressed. Several fundamental studies to optimize the voltammetry of ZME were conducted using monograin films of Z(ML) applied to the working electrode surface to provide a uniform method for systematically studying the variables that arise in the production and use of 7MEs. EXPERIMENTAL SECTION. NaY (Strem Chemical) was equilibrated in an aq. 0.1 M NaCI for 24 h, dnsed free of CI', and then brought to constant weight over a saturated NH4CI solution. Co(salen)-Y was synthesized following published procedures.3, 6 [Fe(bpy)3]2+-Y was similarly synthesized.
The transition metal encapsulated zeolites were characterized by FT-IR and
diffuse reflectance UV-Vis spectroscopies and by cyclic and differential pulse voltammetry. Electrochemical measurements were conducted in a three-compartment cell containing a coiled Pt auxiliary electrode, a saturated sodium chlodde calomel reference (SSCE) and a zeolite-modified glassy carbon working electrode. The ZME was prepared using a variant of Li and Calzaferri's layered-monograin approach: 7 a MeOH suspension of ground Ultra Pure Carbon and modified zeolite was floated onto the electrode surface, dried, and then covered with a thin layer of polyacrylic acid (PAA, MWavg 450,000) from a methanolic solution.
115 RESULTS AND DISCUSSION. Figure 1 demonstrates one of the variables affecting the cyclic voltammetry of Z(ML)-modified electrodes.
This figure shows that as grinding time of the
zeolite plus carbon powder is increased, the resolution of the redox couple(s) improves and the concentration of the redox species increases.
Grinding the zeolite crystallites appears to
fracture the crystallites and with increased grinding time allows a greater extracrystalline surface area of the zeolite to be exposed to the electrolyte thereby enhancing electrochemical response.
the
This implies that the electrochemical response of the ZME is
caused by electron transfer to transition metal complex located on the exterior of the zeolite. Changes in scan rate, electrolyte, binding material, carbon source, solvent, and charge of the encapsulated complex will be discussed in terms of the cyclic and differential pulse voltammetry of zeolite-modified electrodes.
C
-210
,
;
Volts vs. SSCE
,
....
+2.0
Figure 1. Grinding Study. Cyclic voltammetry of [Fe(bpy)3]2+-encapsulated zeolite Y in 0.1 M LiCIO4/ CH3CN at 10 mV/s. 60 mg of carbon + 60 mg of modified zeolite were ground in a sapphire mortar and pestle for the specified period of time with 10 mg removed to prepare the ZME. A: unmodified glassy carbon electrode; B: ZME with 10 min grinding; C: ZME with 30 min grinding; and D: ZME with 60 rain grinding. The wave negative of-1.2 V is consistent with ligand-centered reduction and the couple positive of 0 V is consistent with Fell/Ill-centered redox for [Fe(bpy)3] 2+.
REFERENCES 1. Rolison, D. R.; Chem. Rev. 1990, 90, 867. 2. Li, Z.; Mallouk, T. E. J. Phys. Chem. 1987, 91,643. 3. Bedioui, F.; De Boysson, E.; Devynck, J. Balkus, K. J. Jr. J. Chem. Soc., Faraday Trans. 1991, 87(24), 3831. 4. Shaw, B. R.; Creasy, K. E.; Lanczycki, C. J.; Sargeant, J. A.; Tirhado, M. J. Electrochem. Soc. 1988, 135, 869. 5. Baker, M. D.; Senaratne, C.; Zhang, J. J. Phys. Chem. 1994, 98, 1668. 6. Herron, N. Inorg. Chem. 1986, 25, 4714. 7. Li, J.; Calzaferri, G. J. Chem. Soc., Chem. Commun. 1993, 1430.
III. Modification
This Page Intentionally Left Blank
H.G. Karge and J. Weitkamp (Eds.)
116
Zeolite Science 1994: Recent Progress and Discussions
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
STRUCTURE
AND PROPERTIES
IN ZINC PROMOTED
OF ACTIVE SPECIES
H-ZSM-5 CATALYSTS
H. Berndt, G. Lietz, B. Lticke, and J. V61ter Institute for Applied Chemistry Berlin-Adlershofe.V., Rudower Chaussee 5, 12484 Berlin, Germany SUMMARY Different zinc promoted H-ZSM-5 samples were prepared using ion exchange and impregnation techniques. The samples were characterized by TPSK, TPDA and FTIR and catalytically tested in the conversion of propane to aromatics. Ion exchange generates catalysts with highest activity. TPSR-CO enables to determine the concentration of Lewis acidic [Zn(OH)] + ions and their concentration could be correlated with the catalytic activity. INTRODUCTION Zinc promoted H-ZSM-5 is a very active catalyst for the transformation of low alkanes into more valuable products. However, the best method of preparation, the nature of the active species and their location inside or outside the channels are still questionable [ 1-3]. Samples with different nature of zinc species were prepared. Their concentration should be determined using the TPSR with CO as probe molecule and correlations could be studied between the content of the different zinc species and their catalytic activity in the conversion of propane. EXPERIMENTAL H-ZSM-5 was promoted with zinc either by impregnation (Zni) or by ion exchange (Zne). Propane was converted in a flow reactor between 480 and 510 ~
TPSR-CO studies were
carried out using the equipment AMI-1 coupled with a QMS. The IR spectra in the OHstretching vibration region and the absorption bands of adsorbed pyridine and ammonia were recorded with a Bruker IFS 66 FTIR spectrometer. RESULTS AND DISCUSSION The catalytic experiments showed that Zn e was (z
much more active than Zni, whereas the selectivity for aromatics was nearly the same. Unpromoted H-ZSM-5 was very inselective. The activity of Zn i was increased by a factor of two after a H 2 treatment at 450 ~ C (sample Zni/a). TPSR-CO curves of different samples are shown in Figure 1. Only CO 2 is displayed, but H 2 is obtained in equivalent amounts, too. The peaks o~ and 13 indicate two types of zinc
Zne/l.l --
a
, 200
,.
, 400
0
t 600
.ti 650
T/*C
species.
The
portions
depend
on
the
Figure 1: TPSR-CO plots, zinc content
preparation method and the zinc content.
of the catalysts 1. I- 1.6 wt.-%
Moreover, there is a third type of species (7).
117 This one does not react with CO. Remarkably, the hydrogen activation causes a considerable increase of the a peak of the curve ofZni, a compared to Zn i. The acidity of the samples was studied by TPD of ammonia. On the one hand, the promotion with zinc decreased the high temperature peak (h.t.p.) caused by desorption from the Br/Snsted sites. On the other hand, the h.t.p, was shifted towards higher temperatures indicating the generation of strong acidic sites. The amount of these new sites increases in the sequence Zni, Zni, a and Zn e. FTIR spectroscopy confirmed the decrease of the concentration of Br6nsted sites and the generation of new acidic sites of the Lewis type. Fig. 2 shows the conversion of propane in dependence on the concentration
o~ 80 -~
of zinc
species in Zni, Zni/a, and two Zn e samples determined as i) the total amount of formed
/t/l.e f
CO 2 (a+13), ii) the partial amount (a) and iii)
60
o
9 ~
u~/,.s the total zinc content representing the sum of
40
(a+13+T).
20
a
ell.l
~.~
..... Zn species / pmol g--I
0 "r
I : c:+ 13
curve
based
on
(a+13)
activity. However, using only the a-peak area a 200
I00
The
demonstrates a nearly linear relation to the
A:
Figure 2: Correlation between activity and concentration of zinc species
linear
curve
is
established
crossing
approximately the origin. This finding enables the conclusion that i) the TPSR-CO data can be used for correlations with the activity and ii) only the a species are active. Because of the formation of CO 2 and H 2 by the reaction with CO, the a species contain O and H.
Therefore, we suggest that these are [Zn(OH)] + ions located in the zeolite channels. TPDA and FTIR data showed that Zn species generate strong acidic Lewis sites. These sites should promote the propane conversion by hydride abstraction according to the mechanism proposed by Ono [1]. We suggest that the high activity of the Zn e sample is due to these species in the channels, whereas the Zn i sample contains predominantly less active 13 species and inactive ~/ species (zinc oxide) located on the outer surface of the zeolite crystals. Consequently, the observed activation by hydrogen can be explained by transportation of zinc from outside into the channels enhancing the concentration of strong acidic Lewis sites. CONCLUSION Zinc species of different reactivity could be detected by TPSR-CO. Only the [Zn(OH)] + ions located on Bronsted sites in the channels activate the propane conversion. REFERENCES [1] Y.Ono, Catal. Rev.Sci. Eng., 34 (1992) 179 [2] Le van Mao, L. Dufresne and J. Yao, Appl. Catal., 65 (1990) 143 [3] M. S. Scurrel, Appl. Catal., 32 (1987) 1
118
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
FT IR AND FT RAMAN STUDIES OF [B,AI]-BETA + Ga=Os SYSTEM M. Derewifiski, J. Kn/~ciak, Z. Olejniczak *, J. Ptaszyflski, B. Sulikowski Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, ul. Niezapominajek 1, 30-239 Krak6w, Poland. * Institute of Nuclear Physics, ul. Radzikowskiego 152, 31-342 KrakSw, Poland. Key words: [B,AI]-Beta zeolite, G~O3, H2 treatment, FT IR and FT Raman
INTRODUCTION Gallium can be readily incorporated into numerous zeolitic structures both directly during hydrothermal synthesis [1] and by post-synthesis modifications [2,3]. Such a substitution results in a new chemical properties which make Ga-containing materials useful for certain catalytic applications. Highly siliceous, large pore beta zeolite containing boron and aluminium was chosen for modification with Ga203. Boron is partially removed from tetrahedral framework sites during thermal treatment thus giving defect sites (sUanol nests) in the lattice [4]. The objective of this work is to study the interaction of Ga203 with defects-rich beta zeolite and to examine if Ga can reoccupy sites in the framework previously containing boron atoms. The effect of H2 / thermal treatment on the state of Ga in the [B,AI]-beta/Ga203 system was investigated by means of FT IR and FT Raman spectroscopies.
EXPERIMENTAL [B,AI]-Beta zeolite (Si/AI = 71, Si/B = 14) has been synthesized using tetraethylammonium (TEA) as a template. Calcined and ion-exchanged zeolite was mechanically mixed with 13-Ga203 (5 wt%) and subsequently calcined at 600 ~ under flow of H 2. FT IR and FT Raman measurements were carded out on a Nicolet 800 spectrometer.
RESULTS AND DISCUSSION For as-synthesized [B ,AI]- beta zeolite, boron incorporation into the framework is evidenced by a band at 899 cm-1 (Si-O-B asymmetric stretching vibrations) (Fig.lA). Calcination of zeolite at 500 ~ to remove organic template and subsequent ion-exchange procedure result in a deep deboronation and formation of the lattice defects, i.e. silanol nests, as indicated by formation of a new band at 948 cm ~ (Fig.1B). The decreased in intensity band of tetrahedral framework boron is seen as a shoulder on a band attributed to silanol nests. On the other hand, such a post-synthesis treatment does not result in aluminium extraction from the framework. The decrease of intensities of the structure sensitive bands at 1218, 626, 578, 532 and 428 cm 1 suggests the structural changes in the zeolite framework, no amorphisation could be however detected by XRD. Mechanical mixing of activated
119
[B,AI]-beta sample with
p-Ga~O~do
not modify IR spectra of zeolite (Fig.lC). Subsequent
calcination at 600 ~ under flow of H2 leads to significant changes in the IR spectra (Fig.1D). The band attributed to silanol nests is significantly reduced in intensity and the strongest stretching band is shifted to lower wavenumbers (1095 - 1093 cm 1) thus indicating healing of the framework by gallium. Simultaneously restored structure sensitive bands give rise to the spectrum characteristic for a highly ordered, defects-free beta zeolite as observed for as-synthesized material. Such a behaviour indicates insertion of Ga atoms into the sites previously occupied by boron. The parallel FT Raman studies confirm that bulk gallium oxide is absent in the spectrum of the reduced material. The appearance of bands in the reduced samples recall those found in faujasite/Ga203 system [3]. It can be therefore concluded that interaction of gallium oxide with various zeolitic structures proceeds similarly.
Fig.1. IR spectra of the samples: A - parent [B, AI] - beta zeolite , B - sample A calcined at 500 ~ and ion exchanged, C - sample B mechanically mixed with u
P- Ga203,
Z (12
D - sample C calcined at 600 ~ in the presence of H2.
5"z <12 P--
~
1~
.,
~oo
1500 ~6oo ~oo HAVENUMBER
,
4oo
ACKNOWLEDGEMENT We are grateful to the Committee of Scientific Research (Warsaw) for support (project no. 2P.303.149.04).
REFERENCES [1] J.M. Newsam, D.E.W. Vaughan, Stud.Surf.Sci.Catal., 28 (1986) 457 - and references therein. [2] J.M. Thomas, L. Xinsheng, J.Phys.Chem., 90 (1986) 4843. [3] B. Sulikowski, J. Kry~ciak, R.X. Valenzuela, V. Cortes Corber&n, Stud.Surf.Sci.Catal., (1994) -in the press. [4] M. Derewir~ski, F. Fajula, Appl.Catal., A 108 (1994) 53.
120
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
F A U J A S I T E - H O S T E D NICKEL-SALEN. H. Meyer zu Altenschildesche and R. Nesper, Laboratorium for Anorganische Chemie, ETH Zentrum, CH-8092 ZOrich, Switzerland
SUMMARY. [Ni(salen)] was prepared inside the supercages of NaY by the reaction of Ni-exchanged zeolite witli salen. The 2SNa NMR spectra of dehydrated NaY and (Ni,Na)Y (up to 33% Na+ exchanged) reveal that there is no preferential loss of Na+ from the double six-rings. Thus, the known preference of Ni2+ for this site does not lead to complete substitution of sodium. During reaction with salen, Ni2+-cations are able to migrate back to the supercage. Complex formation was proven by means of IR, diffuse reflectance UVNIS, and solid state 1H NMR spectroscopy. Rietveld refinement of powder X-ray diffraction data indicate a preference of [Ni(salen)] for positions where interaction between Na+ and the oxygen atoms of the guest molecule is favourable. INTRODUCTION. Neutral transition metal complexes of Schiff base ligands, e.g., salen (N,N'bis(salicylaldehyde)ethylenediimine), synthesized in the nanometer-sized voids of porous hosts have attracted much attention recently [1,2]. These materials possess promising properties like shape-selective catalytic reactivity and reversible oxygen binding behavior. In previous investigations the zeolite was assumed to stay essentially unchanged and no specific interactions between the host and guest molecules were discussed. However, transition metal complexes of salen are known to act as ligands towards alkali, alkaline earth and other cations [3]. This implies that interactions between Na+-cations and guest complexes are to be expected and may change structure, properties and accessibility of the guest species.
Structure of Ni[[(salen). EXPERIMENTAL. Zeolite NaY (Chemie Uetikon, Si/A! = 2.94) was partially ion-exchanged with dilute nickel-acetate solution. After washing with deionized water, the exchanged zeolite was calcined in air and dehydrated in vacuo at 723 K. The zeolite was mixed with an excess of salen in an inert-atmosphere glovebox and heated to 413 K for 4-5 hrs.
121
Unreacted ligand was extracted with dichloromethane. The solvent was then removed by evacuation at 473 K. Powder X-ray diffraction of [Ni(salen)]/NaY showed no loss of crystallinity. The dark-red products were investigated by IR, diffuse reflectance UVNIS, and 1H, 23Na, and 13C MAS NMR spectroscopy. Rietveld refinement was performed with the XRS-82 program package. RESULTS AND DISCUSSION. The 23Na MAS NMR spectra of dehydrated NaY and its partially nickel-exchanged derivative are very similar, showing no preferential loss of Na+ from the double sixrings. Therefore, the known preference of Ni2+ for this site does not lead to complete substitution, at least for exchange levels up to 33%. Previously published results indicating that not all double six-rings were occupied by Ni2+ can now be understood in terms of a mixed occupation by Na+ and Ni2+ [4]. Under the synthesis conditions applied, Ni2+-cations are able to migrate back to the supercage. The formation of [Ni(salen)] was proven by means of IR, diffuse reflectance UVNIS, and solid state 1H NMR spectroscopy. Elemental analysis reveals that complex formation is quantitative and adjacent supercages can be occupied, although the phenyl rings of [Ni(salen)] protrude through the 12-ring pore openings. The 2SNa MAS NMR spectrum of [Ni(salen)]/NaY is very different from that of the zeolite precursors. This results from the change in the environment of supercagehosted Na+-cations. A Rietveld refinement of powder X-ray diffraction data indicates a preference of the guest molecules for positions where interaction between Na§ and the oxygen atoms of the complex is favourable. Thus, the properties of uncharged transition metal complexes included in zeolites may depend on the number and type of charge-compensating cations or other coadsorbed molecules. This opens a way to materials which are tailor-made for specific applications.
REFERENCES. [1] N. Herron, Inorg. Chem. 25 (1986) 4714. [2] D. E. de Vos, F. Thibault-Starzyk, P. A. Jacobs, Angew. Chem. 106 (1994) 447. [3] N. Bresciani-Pahor, M. Calligaris, P. Delise, G. Nardin, L. Randaccio, E. Zotti, G. Fachinetti, C. Floriani, J. Chem. Soc., Dalton Trans. (1976) 2310. [4] P. Gallezot, B. Imelik, J. Phys. Chem. 77 (1973) 652.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All fights reserved.
122
MODIFICATION OF ALUMINOPHOSPHATE MOLECULAR SIEVES BY REACTION WITH ORGANOPALLADlUM COMPLEXES. KATHRYN M. TEARLE AND JUDITH M. CORKER DEPARTMENT OF CHEMISTRY, UNIVERSITY OF SOUTHAMPTON, HIGHFIELD, SOUTHAMPTON, SO9 5NH, ENGLAND. SUMMARY Aluminophosphates, VPI-5 and AIPO4-5 were synthesisecl and characterised by powder x-ray diffraction. The AIPO4 materials were treated with Pd(TI3 -C3Hs)(TI~-CsHs). Direct structural evidence of the species formed was obtained using extended x-ray absorption fine structure (EXAFS). On reaction of VPI-5 with Pd(q 3 -C3H5)(~1~ -CsHs), the allyl ligand is lost but the cyciopentadienyl group remains attached to the palladium centre. INTRODUCTION Over the past few years there has been much interest in the development of new types of catalyst materials. The small uniform pores and large internal volumes characteristic of porous, microcrystalline aluminophosphate materials, 1 potentially make them ideally suited as shape-selective catalysts or supports. Most catalytic applications however require quite specific pore geometries or cut off diameters and these can not necessarily be achieved via direct synthesis of the microporous material itself. Efficient processes for structural modification post-synthesis are thus highly desirable. The incorporation of organometallic complexes in such materials is one post-synthesis modification route which has not been extensively investigated. 2 We
are developing
methods
of anchoring organopalladium
complexes within the
large-pore
aluminophosphates, VPI-5 and AIPO4-5. The interest in supporting organopalladium complexes stems oxidation catalysis: it is well known that Pd complexes in solution are capable of catalysing various alkene oxidation reactions, but examples of well-defined organopallaclium complexes on inorganic supports are few in number. One reaction which has been reported is that of Pd(TI3-C3Hs)2 with silica 3 which leads to the apparent formation of [Si]-O-Pd(~l 3-C3H5), but firm spectroscopic evidence is lacking. EXPERIMENTAL AIPO4-5 was synthesised following the method of Wilson et af =. VPI-5 was synthesisecl from an aluminophosphate gel of composition 0.2TMAOH:DPTA:AI203:P2Os:40H20, at 150"C for 20 hours. Pd(TI3 -C3Hs)(TIs-CsHs) was synthesised following the method of Tatsuno et af'. Treatment of VPI-5 and AIPO4-5 with Pd(TI3 -C3Hs)(~I~-CsHs) was carried out using metallo organic chemical vapour deposition (MOCVD) techniques.
123
RESULTS AND DISCUSSION Two carbon shells can be readily identified in the Pd K-edge EXAFS spectrum of Pd(TI3-C3Hs)(TIs-CsHs) at room temperature; the first shell at 2.11A due to 3 carbons of the allyl group and the second at 2.31A caused by the 5 cyclopentadienyl carbons. Physisorption of Pd013-C3Hs)(~-CsHs) onto VPI-5 is apparent initially on room temperature deposition of the organometallic complex in vacuo.
Reaction with the
support then occurs, and a pale yellow colouration is observed. The Pd K-edge EXAFS, recorded at room temperature under vacuum (2xl0Storr), shows a marked change in coordination; the EXAFS is best fitted by 1 shell of 5 carbons at 2.13A and by a more distant shell of cal-2 oxygens at 2.95A, suggesting that the allyl group is last in the reaction.
The distant shell at 2.95A could be attributed to a weak
interaction with the framework oxygens.
Decomposition of the AIPO4-supported organopalladium
complexes species to metallic Pd is observed above 250" C; EXAFS analysis indicates a first coordination sphere of ca6 Pd atoms at 2.75A, indicative of small metal particles.
P'WmlI[:II' N w W l u l l
k
~
POIIIIII ~
f~=~pom~tl
e,p,
Q,,, Lo,
,~,
L,
u
i,o
~
~.J
n,e
l_~
Q,I
a,a
~
L,
u
u
M
I.i
a,o
Figure 1 Pd K-edge EXAFS of VPI-5/Pd(TI3-C3Hs)(TIs-CsHs), at a) 25"C 2xl0~torr and b) after heating to 300" C under 2xl0Storr. REFERENCES 1. D.M.Poojary, J.O.Perez and A.Clearfield, J.Phys.Chem.,1992, 96, 7709. 2. G.Ozin and G.Gil, Chem.Rev., 1989, 89, 1749 3. "Catalysis by supported Complexes", Yu.I.Yermakov, B.N.Kaznetsov and V.A.Zakharov,Eds., Studies in Surface Science and Catalysis, Elsievier, Amsterdam, 1981, Chapter 2. 4. S.T.Wilson, B.M.Lok and E.M.Flanigen, US Patent,4,310,440, 1982. 5 Y.Tatsuno, T.Yoshida and Seiotsuka, Inorganic Synthesis, 1979, 19, 220.
H.G. Karge and J. ~eitkamp (l:xls.) 124
Zeolite Science 1994: Recent Progress and Discussions
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
ZEOLITE-STABILISED RHODIUM MOLECULAR NITROGEN
COMPLEXES
WITH
AS L I G A N D
Hans Miessner* Zentrum ~ r Heterogene Katalyse, KAI e.V., Rudower Chaussee 5, 12484 Berlin, Germany
S ~ Y The surface complexes RhI(CO)fN2) + with v(CO)=2062 cm-1 and v(N2)=2252 cm-1 and RhI(N2)2 +, v(N2)=2242+2218 cm"1 , which are stable in flowing nitrogen up to 250~ have been synthesised from RhI(CO)2 + on highly dealuminated zeolite Y (DAY, US-Ex). INTRODUCTION Several transition metal complexes containing dinitrogen as ligands are known and attempts have been made to utilise these complexes as models to the nitrogen fixation 1 However, the interaction of molecular nitrogen with transition metals has been found to be weak and the adsorption of N 2 on supported metal catalysts has been observed, therefore, generally at low temperature and/or at high pressures.
The adsorption of N 2 on supported Rh at low
temperature 2,3 or at high pressures 4,5 have been studied ]R-spectroscopically. In previous work we could show that dealuminated Y zeolite (US-Ex, DAY) is a unique material to stabilise well-defined surface complexes of transition metals. Subcarbonyls of Rh 6-8, Ru and Ir 9 and mixed carbonyl-nitrosyls of Rh 8,10 could be identified and, due to the unusual sharpness of the infrared bands, structurally characterised. In the present work we will show that these well-defined surface species can be used as the starting material to surface chemistry, to the synthesis of other well-defined surface complexes. EXPERIMENTAL SECTION Rh/DAY and Rh/US-Ex (lwt% Rh) was prepared by impregnating the supports DAY (Si:Al > 100, kindly supplied by DEGUSSA, obtained by exchange of the Al atoms for Si by treating the NaY with SiC14 ) or US-Ex (Si:A1 -- 100, obtained by hydrotherrnal treatment of NH4Y ) with an appropriate amount of RhCl 3 in ethanolic solution and drying the sample at 120~ in air. The transmission ]R studies were performed with self-supported wafers using a special infrared cell made from stainless steel for in-situ measurements up to 400~
and 50 bar,
connected to a gas flowing system, which allows a fast variation of the feed gas. The spectra were recorded with an FT]R spectrometer (BIORAD FTS 60A) at 2 cm-1 resolution.
*Present Address:
ENIRICERCHE S.p.A., CATA, Via Maritano, 26 1-20097 SAN DONATO MILANESE, ITALY
125 RESULTS AND DISCUSSION In a first step, Rh dicarbonyl RhI(CO)2 + was formed on the cation positions of DAY by treating the sample in a flow of CO(5%)/Ar at 150~ In the IR spectra, strong bands at 2118 and 2053 cm -1 appear and, simultaneously, the intensity of the OH-bands at 3630 (HF) and 3567 cm -1 (LF) of the acid hydroxyls decreases 12 A subsequent treatment of the dicarbonyl in a flow of H2/N 2 at 200~ results in a partial decarbonylation as indicated by decreasing of the corresponding IR bands at 2118 and 2053 cm- 1 At the same time, a new carbonyl species is formed with a carbonyl stretching vibration at ca. 2090 cm-1 After switching the gas feed at 200~ fi,om H2/N 2 to pure nitrogen, the band at ca. 2090 cm-1 of the monocarbonyl decreases and new bands in the dinitrogen and carbonyl stretching region appear. The wavenumbers of these bands at r.t. are collected in Tab. 1. A correlation analysis of the integrated absorbances of the corresponding bands in a series of experiments suggests that there are at least two well-defined surface complexes with dinitrogen as ligands: a mixed dinitrogen-carbonyl complex with i.r. bands at 2252 and 2062 cm -1 and a complex with two nitrogen stretching bands at 2244 and 2218 cm -1, most probably a surface complex with two dinitrogen ligands.
The nitrogen complexes are stable in flowing nitrogen, but react
immediately with CO to give the Rh dicarbonyl. The assignment of the IR bands was verified by experiments using isotopic mixtures containing C 180 or 15N2. The two supports used have the same crystal structure and a similar Si:AI ratio, but differ significantly in the mesopore structure. Due to the different dealumination procedure, U S-Ex has a high amount of mesopores and, consequently, a higher amount of terminal silanol groups as compared with DAY 11
The formation and the properties of the well-defined surface
species described in the present work are, nevertheless, similar for both supports. This is an argument in favour of the formation of these species at the cation positions rather than on the outer surface or in the mesopores of the zeolite. REFERENCES 1 G.J. Leigh, Acc.Chem.Res., 1992, 25, 177. 2 Yu. G. Borod'ko and V. S. Lyutov, Kinet.Katal., 1971, 12, 238. 3 H.P. Wang and J. T. Yates, Jr., J.Phys.Chem., 1984, 88, 852. 4 J.P. Wey, H. D. Burkett, W. C. Neely and S. D. Worley, J.Am.Chem.Soc., 1991, 113, 2919. 5 J.P. Wey, W. C. Neely and S. D. Worley, J.Phys.Chem., 1991, 95, 8879. 6 I. Burkhardt, D. Gutschick, U. Lohse and H. Miessner, J.Chem.Soc., Chem.Commun., 1987, 291. 7 H. Miessner, I. Burkhardt, D. Gutschick, A. Zecchina, C. Morterra and G. Spoto, J.Chem.Soc., Faraday Trans., 1, 1989, 85, 2113. 8 H. Miessner, I. Burkhardt, D. Gutschick, A. Zecchina, C. Morterra and G. Spoto, J.Chem.Soc., Faraday Trans., 1990, 86, 2321. 9 H. Landmesser and H. Miessner, J.Phys.Chem., 1991, 95, 10544. 10 H. Miessner, I. Burkhardt and D. Gutschick, J.Chem.Soc., Faraday Trans., 1990, 86, 2329. 11 H. Stach, U. Lohse, H. Thamm and W. Schirmer, Zeolites 1986, 6, 74.
126
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
INTRAZEOLITIC REDOX CHEMISTRY OF MANGANESE PREPARED FROM CHEMICAL VAPOR DESPOSITION OF Mn2(CO)10 ON NaY Carlo Dossi, Sandro Recchia, AchiUe Fusi and *Rinaldo Psaro Dipartimento di Chimica Inorganica, Metallorganica e Analitica and *Centro C.N.R., Via Venezian, 21, 20133 Milano, Italy
ABSTRACT Intrazeolite redox chemistry of manganese has been exploited by the use of vapor-deposited Mn2(CO)10 complex onto NaY. INTRODUCTION Ion exchanged Mn 2+ ions inside Y-type zeolite have a very high stability, being virtually inert under both oxidizing and reducing conditions [1]. The use of neutral organometaUic molecules as metal precursors instead of the exchanged metal ion is supposed to possibly overcome the non-reducibility of several exchanged ions under gas-phase reduction conditions, or, if the reduction is succesful, the stoichiometric creation of protonic acidity [2]. In fact, the original distribution of positive charges inside the zeolite structure is left unaltered upon deposition of the neutral organometaUic precursor, and zerovalent metal atoms are simply obtained by thermal removal of ligands [3]. EXPERIMENTAL Mn2(CO)10 was sublimed inside dehydrated NaY zeolite (Linde LZY-52) at 105~ in flowing argon. Full details of sample preparation and thermoanalytical characterization are reported elsewhere [3]. Diffuse Reflectance Infrared (DRIFT) studies of CO chemisorption have been carried out in a specially designed, hightemperature flow cell. RESULTS AND DISCUSSION Mn2(CO)10 is easily deposited from the vapor phase inside the supercages of NaY zeolite without decomposition, as demonstrated by the similarity of the IR spectrum with that of the pure compound. Removal of CO ligands is then observed in flowing He to start at 120-130~ being complete below 250~ Analysis of the gas evolution during the thermal decomposition showed evolution of H2 paralleling that of CO. This unusual behavior can be rationalized on the basis of a twostep reaction:
127 (i) first, naked zerovalent Mn atoms are formed by removal of CO ligands Mn2(CO)10/NaY B >
2 Mn0/NaY
+
10 CO
(reaction 1)
(ii) these highly reactive monoatomic Mn sites are immediately re-oxidized by reacting with residual traces of water left in zeolite, with formation of small aggregates of MnO inside the supercages of NaY zeolite. Mn~
+
H20
m > MnO/NaY +
H2
(reaction 2)
Accordingly, the color of the sample changes from light yellow to white at the end of the TPRD experiment. Reaction 2 is extremely favored, and is completely shifted to the right even in H2-rich atmospheres, as demonstrated by theoretical predictions based on standard electrode potentials [4]. Reduction of NaY-entrapped manganese(II) oxide is instead feasible by using carbon monoxide as the reducing agent. CO has no action on Mn 2+ exchanged in NaY. On the contrary, a full set of carbonyl IR bands develops in the 22001800 cm -1 region by contacting CO with NaY-entrapped MnO. From the location of such bands, and by comparison with the infrared spectra of pure reference compounds, the presence of entrapped Mn(0) and Mn(I) carbonyls, much likely Mn2(CO)10 and [Mn(CO)3(O-Z)] (O-Z represents a framework oxygen ion) can be inferred. Carbon monoxide has the dual function to reduce MnO and, at the same time, to act as a ligand for the zerovalent Mn atoms forming intrazeolitic Mn carbonyls: (3O MnO/NaY + CO m > CO2 + Mn0/NaY m > [Mnx(CO)y]/NaY + [Mn(CO)3(O-Z)] The coordination of water molecules on metal centers, the first step in the redox chemistry leading to oxidized manganese, is thus prevented by the strong affinity of carbon monoxide for zerovalent transition metals. In further contrast with ion-exchanged Mn2+/NaY, entrapped MnO can be further oxidized in oxygen or air, giving a dark brown material. A Temperature Programmed Reduction (TPR) analysis shows a monoelectronic reduction step occurring around 300~ A reversible oxidation/reduction cycle between MnO and Mn203 is thus suggested, in contrast to the high stability of ion-exchanged Mn 2+ toward 02 oxidation at 500~ CONCLUSIONS The redox chemistry of intrazeolite manganese can only be exploited when it is prepared from neutral organomanganese complexes, such as Mn2(CO)10. In this
128 way, no stable Mn 2+ ions are formed, and the whole range of oxidation states from 0 to 3 can be observed. REFERENCES [1] A Jones and B. McNicol, "Temperature Programmed reduction for solid material characterization", Marcel Dekker, New York (1986). [2] T.T. Wong and W.M.H. Sachtler, ]. Catal., 141 (1993) 407. [3] C. Dossi, R. Psaro, A. Bartsch, E. Brivio, A. Galasco and P. Losi, Catal. Today, 17 (1993) 527. [4] T.P. Wilson, P.H. Kasai and P.C. EUgen, J. Catal., 69 (1981) 193.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
129
CALCINATION OF Pd(NH3)42+ AND REDUCTION TO Pd ~ IN NaX AND CsX ZEOLITES A. Sauvage, P. Massiani, M. Briend, D. Barthomeuf Laboratoire de R6activit6 de Surface, Universit6 Paris 6 (France) F. Bozon-Verduraz Laboratoire de Chimie des Mat6riaux Divis6s et Catalyse, Universit6 Paris 7 (France)
Summary The decomposition in 02 of Pd(NH3)42+ in NaX and CsX followed by TPO, UV-Visible and near IR occurs at lower temperature for PdCsX than for PdNaX. This is connected to different decomposition steps of Pd(NH3)x 2+. The reduction of Pd2+ to Pd ~ is easier in PdCsX than in PdNaX. Introduction The interaction of palladium tetrammine complexes with NaY has been extensively studied 1. It was observed in the case of Pt supported zeolites that the decomposition temperature of the ammine complex is different on PtNaX or PtCsX suggesting an influence of the framework chemical properties on the strength of interaction 2. The aim of the present work is to compare the decomposition of the Pd tetrammine complex and the reduction of Pd2+ on NaX and CsX to check the possible influence of the zeolite properties.
Experimental Pd7,4NaX and Pd8,oCs3oNaX (referred to as PdNaX and PdCsX) are prepared by exchange of the zeolite with a Pd(NH3)4CI2 solution at pH 10. The ion contents are expressed per unit cell. The decomposition, upon heating, of the complex is followed by TPO (thermoprogrammed oxidation) using thermal conductivity (TCD) or mass spectrometry (MS) and by UV-Visible and near infrared (NIR) spectroscopies. The reduction with H2 is studied by TPR (thermoprogrammed reduction) using TCD and by UV-Visible spectroscopy. The materials are heated at a rate of 7,5 K/rain in a flow of O2/He (oxidation) or H2/Ar (reduction). Results and Discussion Common features Figure 1 gives the TPO results (TCD analysis). For both samples a main peak is seen (585 K-PdCsX and 620 K-PdNaX). In addition smaller peaks are present at lower temperature, embedded in the big peak, or at higher temperature (around 610 K-PdCsX and 665 K-PdNaX). The detection of three peaks, comparable to the case of PdNaY, reveals the step-wise removal of NH3 from the supported complex 3. The decomposition of the desorbed phase followed by mass spectroscopy shows for both samples the removal at different temperatures of NH3 (505 K-PdCsX, 545 K-PdNaX) and of N2 (605 and 630 K-PdCsX, 630 and 680 K-PdNaX). As already observed for
130
PdNau 3, oxygen consumption mirrors N2 production. In addition our results show that NH3 is removed at temperature below the main TPO peaks of figure 1. A study using UV-Visible and near infrared spectroscopies shows that the ammine ligands are removed between 470 K and 700 K and replaced by framework oxygen as was reported for PdNaY 4. Simultaneously the NH3 peaks near 1525-1545 nm (NIR) decrease and disappear at about 650-680 K.
Comparison of PdNaX and PdCsX Figure 1, mass spectrometry, UV-Visible and NIR results show that the decomposition of the complex occurs a lower temperature in PdCsX than in PdNaX. The profile of temperature of decomposition steps are then not identical for the two zeolites. This probably arises from at least two parameters. At first the space available in the cavities is less in PdCsX than in PdNaX due to the cation size. This may modify the possibility of formation of specific Pd complexes like those proposed in PdNaY 4. Secondly the higher basic strength of framework oxygen in CsX compared to NaXS very likely influences
A
the energy of Pd2+-Ozeo bonds. The reduction to Pd ~ is followed by TPR and UV-Visible spectroscopy. The
J
maxima of the TPR peaks are near 395 K (PdCsX) and 435 K (PdNaX). The easier reduction of PdCsX is confirmed by UVVisible showing, for this sample,
an
Ta 450
550
650
Temperature(10
750
important disappearance of Pd 2+ ions Figure 1: TPO of PdNaX (a) and PdCsX (b) under an H2 flow at room temperature .. while PdNaX retains a large part of them. This behavior suggests the preferential location of Pd 2+ in the supercage for PdCsX and in the sodalite for PdNaX. In conclusion the zeolite characteristics influence both the decomposition of Pd(NH3)4 2+ and the further reduction of Pd 2+ to Pd metal. 1 W.M.H.Sachtler, Z. Zhang, Adv. Catal., 1993, 39, 129 2 A. de Mallmann, Thesis Paris 1989 A. de Mallmann, D. Barthomeuf,to be published 3 S.T. Homeyer, W.M.H. Sachtler, J. Catal., 1989, 117, 91 4 Z. Zhang, W.M.H. Sachtler, H. Chen, Zeolites, 1990, 10, 784 5 D. Barthomeuf, J. Phys. Chem., 1984, 88, 42
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
131
ION EXCHANGE IN CoAPO-34 AND CoAPO-44 C.G.M. Jones, Dr. R. Harjula*, Dr. A. Dyer University of S.alford, Salford, M5 4WT. U.K. *Department of Radiochemistrv. University of Helsinki, Finland SUMMARY A number of SAPOs, MeAPOs and MeAPSOs with the chabazite structure were synthesised. The uptake of uranium and thorium by these samples was measured by L.S.C. Many of the samples had high K D values. The ion exchange properties of CoAPO-34 and CoAPO-44 were studied further. It was found that these CoAPOs will remove actinides more efficiently when in the Na forms, or in alkaline solutions, than in the H forms, or in acid solutions. INTRODUCTION Zeolites are currently being used in the nuclear power industry in Britain to remove Cs-137 and Sr-90 from spent fuel pond water. When considering storage and final disposal of a waste ion exchanger, zeolites have significant advantages over organic exchangers - namely their low cost, resistance to radiation and compatibility with cements and glass materials. Several actinides, e.g. uranium, thorium, plutonium and americium appear as waste products of the fuel enrichment process and in spent fuel reprocessing. It is with the uptake of these elements by zeolites and zeotypes that this study is concerned. EXPERIMENTAL SECTION Several zeotypes were synthesised according to the patented[ 1-3] methods. Thermogravimetric analysis was used to look at the removal of the template from the structure. The samples were characterised by X-ray powder diffraction. Maintenance of the structure after calcination was also confirmed by X-ray powder diffraction. The distribution coefficients for the uptake of uranium and thorium were measured by liquid scintillation counting after equilibration of samples for 3 days. Many of the zeotypes had high K D values for uranium in these tests. CoAPO-34 and CoAPO-44 were selected for further study. The H-CoAPO forms were converted progressively to their Na forms by equilibration (3 days) with sodium nitrate/hydroxide mixtures (total normality 0.05 or 0.1N). The conversion to the Na form was calculated from the change in activity of Na-22 tracer added to the solutions.
132
RESULTS AND DISCUSSION
In the case of CoAPO-34 the sodium loading increased linearly with pH up to pH 9.5. Above this pH the loading decreased due to dissolution of cobalt from the framework, which was observed by the characteristic cobalt colour change.
The maximum loading was similar to the theoretical ion
exchange capacity which was calculated from electron probe analysis data. For CoAPO-44 the maximum loading was much lower than the theoretical capacity showing that the material was very selective for (H30+). Conversion will need to be repeated using higher sodium concentrations. From the data, the selectivity coefficient, KG, was calculated for CoAPO-34 (using the equation in reference [4]). Log K G increased linearly as a function of the equivalent fraction of H ions in the zeolite. Selectivity coefficients were high showing that the material is selective for H ions. The KD values were measured for the exchange of uranium, plutonium and americium into the H-CoAPOs in solutions of pH 2 to 5. The KDS for U and Am increased linearly with increasing pH. The KD values for U were also measured for the partially converted Na forms ([Na] 0.01 to 1M). The values were higher than in the pure H forms even at high concentrations of sodium. These results confirm that Na ions are less strongly bound than H ions. CONCLUSION
In conclusion, the results show that the CoAPO materials studied will remove actinides more efficiently when in the Na forms (alkaline solution) than in the H forms (acid solutions). REFERENCES [1] B.M. Lok, C.A. Messina, R.L. Patton, R.T. Gajek, T.R. Cannan, E.M. Flanigen, US 4440871 [2] S.T. Wilson, E.M. Flanigen, US 4567029 [3] B.M. Lok, L.D.Vail, E.M. Flanigen, H. Eggert, EP0158348A2, EP0158975A2 B.M. Lok, B.K. Marcus, E.M. Flanigen, EP0161489A1 [4] R. Harjula, A. Dyer, S.D. Pearson, R.P. Townsend, J. Chem. Soc. Faraday Trans. 1992 88 (11 ) 1591 - 1597
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions
133
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved. CHARACTERIZATION OF ZSM-5 SAMPLES MODIFIED BY IONS OF GROUP IIl A L. Frunza 1, R. Russu 2, G. Catana 1, V. Parvulescu 3, G. Gheorghe 2, F. Constantinescu 2 and V.I. Parvulescu 4 1Institute of Physics and Technology of Materials, Bucharest-Magurele, 2Research Institute of Petroleum Processing and Petrochernistry S.A., Ploiesti, 3Institute of Physical Chemistry, Bucharest, 4Faculty of Chemistry, University of Bucharest, Romania
SUMMARY Modification of ZSM-5 zeolites (Si/Al=25) by impregnation with Ga, In or TI salts is obtained. The interaction of Py molecules with the modified samples was spectroscopically studied: the components of IR peaks were ascribed to different adsorption sites, a m o n g which there are the modifier ions. On this basis, the location of modifier ions inside the zeolitic framework is discussed. A m m o n i a adsorption and textural measurements as well as recent electrochemical titration data [1] also s u p p o r t the differences regarding the deposition of the three modifiers.
INTRODUCrION Gallium containing zeolites have received considerable interest in recent years due to the remarkable improvement they brought to the alkane conversion to aromatics, as reviewed e.g. in [2]. There are many papers focuesed on Ga catalysts, but few regard the influence of In or T1 on the catalytic reactions. As a first step of such studies, this work deals with the sites appearing on the surface of some MFI zeolites modified by impregnation not only with Ga salts, but with In or T1 ones. The sites containing ionic T1 species were clearly identified; the other sites were indirectly evidenced. EXPERIMENTAL MFI laboratory samples with Si/Al=25 were synthesized using common patent literature. The H form was obtained either by calcination of the a m m o n i u m exchanged form or by HNO3 treatment of the Na form. The impregnation with a salt of the group IIIA modifier was carried out as it was elsewhere described [1], on the H or Na form of the parent zeolite, so to assure a final content of modifier oxide u p to 7 wt%. The sample structure was characterized by X-ray diffraction, IR spectroscopy in the lattice vibration range, BET surface area and pore size distribution. Acidic pro-
134 perties were investigated before any catalytic pretreatment by ammonia desorption and IR spectroscopy of adsorbed pyridine (Py). The IR peaks were deconvoluted in order to facilitate their attribution. Quantitative comparison of the samples was achieved commonly using the integrated absorbance per unit mass. RESULTS AND DISCUSSION studies showed highly crystalline materials with the ZSM-5 structure. The lines characteristic for Ga and Tl oxides were not observed in the corresponding samples, in contrast, In oxide appears, its lines growing in intensity as the concentration increases. Therefore we supposed Ga and Tl have high dispersion onto o u r samples. The surface area decreases with impregnation showing that the modifier deposition takes place mainly on the zeolite external surface. The pore volume decreases too; this behaviour as well as the observed changes of pore size distribution could be due to the narrowing of access windows by depositions at pore mouths. Ammonia adsorption decreases with impregnation, e.g. by ca. 15% for a temperature of 200~ following the sequence, but show a lower acidity for T1 samples than for Ga or In containing ones. Brensted sites are still present in modified samples, although in a smaller amount than in the parent zeolite: this indicates that neutralization was not complete, some modifier ions have to be present at exchange sites within the zeolite channels. However, there is no straightforward dependence between the concentrations of Brensted sites and of the modifier. Taking into account the Ga content compared to the framework Al, it was found that, under our impregnation conditions, Ga species enter the zeolite to a higher extent than that described in the literature for related samples. The Lewis acidity of Tl samples increases since Py which is coordinated to T1 species contributes to 19b peak. In addition, the 8a peak, appearing as for alkaline ion containing zeolites, can be used to identify TI in cationic positions. Some activation of Py adsorption could be due to TI migration, but it rather shows the presence of steric hindrance by modifier deposition. The contribution of Indium to the sample acidity is reduced because it is deposited as a distinct phase, onto the external surface. The assumption [1] that some new Brensted sites are generated by the modifier species cannot be entirely neglected; these new protons could then appear in connection with the hydroxyl groups coordinated to isolated trivalent ions of the modifier.
135
REFERENCES
[1] L. Frunza et al., Int. Symp. Zeol. Microporous Crystals, Nagoya, 1993, P120 [1] Y. Ono, Catal. Rev. Sci. Engn. 34, 179 (1992)
136
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
FORMATION OF SMALL Na AND Na-M ALLOY (M=Cs, Rb) PARTICLES IN NaY ZEOLITE; by L. C. de M6norval 1, E. Trescos 2, F. Rachdi 2, F. Fajula 1, T. Nunes 3, and G. Feio 3 1Laboratoire de Chimie Organique Physique et Cin6tique Chimique Appliqu6es, URA-418 CNRS, ENSCM, 8 rue de rEcole Normale, 34053 Montpellier C6dex 1, France. 2Groupe de D y n a m i q u e des Phases Condens6es URA-233 CNRS, USTL Place E. Bataillon, 34095 Montpellier C6dex 5, France. 3Instituto de Ciencia e Tecnologia de polimeros, av. Prof. Gama Pinto, 2, 1699 Lisboa, Portugal. Summary A dehydrated NaY zeolite has been reacted with sodium, rubidium or cesium metal vapor. Using 129Xe, 23Na, 87Rb and 133Cs Solid State NMR and ESR techniques, we have characterized the behavior of metal particles and Na-M bimetallic alloys (M=Rb, Cs) in the a NaY zeolite. Introduction Previous experiments(1-2) were focussed on studying the and some properties of alkali metal clusters in zeolite NaY. are still many different aspects to be understood. In this have used Solid State NMR (129Xe, 23Na, 87Rb, 133Cs) together
small Na cavities of
formation But there work we with ESR
techniques to elucidate some physical properties of these m o n o m e t a l l i c or bimetallic clusters, like q u a n t u m size effects, bimetallic alloy formation or physical state of the clusters (solid or liquid). Experimental Section NaY zeolite was evacuated at 750 K under vacuum (10 -2 Torr) overnight. The temperature was then lowered to 520 K and the zeolite was exposed to the alkali vapor. After a suitable reaction time, the sample was transferred to ESR or NMR tubes without exposing it to the atmosphere. ESR measurements were carried out on a Bruker ER 200D spectrometer, operating at 9 GHz (X-band). NMR measurements were performed on a Bruker CXP 200 MHz, using a home build probe head which allows magic angle spinning of the sample in a sealed tube, or with a Bruker AC 250L spectrometer for 129Xe NMR experiments.
137 Results and Discussion F i g . l a shows the temperature independence of the linewidth and a Curie type paramagnetic behavior of the inverse intensity of the ESR signal of the Na loaded metallic particles in the NaY sample. These results suggest the formation of small Na particles having quantum size effect. In Fig.2, the 129Xe-NMR spectra of adsorbed Xe is presented. This technique proves that the Na particles are small and are homogeneously distributed in the supercages. Fig.3 shows the 23Na-NMR spectrum. The fact that the observed line is not positioned at the expected Knight shift position, but near zero position, is a probe of the existence of even Na particles in the zeolite. The Na-Rb metallic alloy formation in the supercages for the NaY samples exposed to Rb. and the corresponding NMR spectra (23Na and 87Rb) as a function of the temperature, were also studied in this presentation. 17
~
16
-
15 -r m
~14
I
0
I
0
0
0
i
!
'"i
0
o
o
1
CO
o
0
o
tZVXc RMN l~: s~ T o f f s
0
oO
'
-
_i f ' , 'o~176
_
-1
Figure 2
,.,13
-r
11 -
o
oo
101-
I
I,,
0
50
100
i
!
so
I 150
I
1
i
1
Iso 2so TEMPEI~AT~JRE ( K ) 1 200
TEMPERATURE
1 250
250 I
300
200
150 I00 (ppttt)
50
20
35C
( K )
Figure 1 Figure 3 I 1000
L 0
~
-I000
Conclusions -~ The unique electronic properties of small alkali and bimetallic alkali alloy clusters encaged in NaY zeolites are well measured using ESR and Solid State (129Xe, 23Na, 87Rb and 133Cs) NMR. References 1) Harrison, M. R.; Edwards, P. P.; Klinowski, J.; Thomas, J. M.; Johnson, D. C. Page, C. J. J. Solid State Chem. 1984, 54, 330. 2) E. Trescos,; L. C. de M6norval,; and F. Rachdi. J. Phys. Chem. 1993, 97, 6943-6944.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
138
ATTACHMENT AND REACTIVITY OF TIN-COBALT AND TINMOLYBDENUM COMPLEXES IN Y ZEOLITES and MCM-41
Christian Huber, Chun-Guey Wu, Karin Moiler and Thomas Bein* Department of Chemistry, Purdue University, West Lafayette, IN 47907, U.S.A. FAX: 317-494-0239 SUMMARY Novel attachment techniques for bimetallic organometallic species in large-pore zeolites are described. The intrazeolite surface chemistry and thermal stability of M e 3 S n C o ( C O ) 4 in NaY and H6Y zeolite (H45NaloAI55Si1370384) were studied with X-ray absorption spectroscopy (Sn, Co edge EXAFS) and in-situ FTIRKPD-MS techniques. In the NaY host, the complex decomposes at about 160oc by loss of CO ligands and cleavage of the Sn-Co bond. Sn-Co bimetallic cluster species containing only a few atoms appear to form above that temperature. The acidic H6Y host can interact with the Me3Sn moiety of the bimetallic complex. IR and EXAFS data indicate attachment of the complex to the zeolite framework already at room temperature, while the Sn-Co bond seems to remain stable up to at least 90oc. These results are compared and contrasted with the reactions of Me3SnMo(CO)3Cp in the new mesoporous host MCM-41. Attachment of the latter complex to the MCM walls is observed, but due to the striking stability of this complex, cluster formation occurs after removal of the CO ligands only at very high temperature. INTRODUCTION The development of catalysts combining organometallic molecular species with a solid support structure (hybrid catalysts) continues to be of great interest. We have recently developed a novel concept for stabilizing Iow-valent
transition metal moieties in large-pore zeolites, by using bimetallic complexes such as CI2(THF)GeMo(CO)51 or Me3SnMn(CO)52 where the oxophilic maingroup element serves to attach the complex to the internal zeolite cage surface. In this contribution we discuss the surface chemistry and stability of M e 3 S n C o ( C O ) 4 in different forms of zeolite Y and compare it with Me3SnMo(CO)3Cp in MCM-41. EXPERIMENTAL
The precursor Me3SnCo(CO)4 was immobilized into zeolite Y containing different proton concentrations. MCM-413 was loaded with Me3SnMo(CO)3Cp. EXAFS samples were prepared by heating to between 90 and 300oc under vacuum. The temperature was ramped up at a heating rate of l oC/min to the desired temperature and kept constant for 6 h. EXAFS measurements were
139
carried out at NSLS (Brookhaven National Laboratories) at beamline X-11A with a stored energy of 2.5 GeV and ring currents between 100-200 mA.
RESULTS AND DISCUSSION Intrazeolite Chemistry of (Trimethylstannyl)tetracarbonylcobalt. EXAFS data analysis shows that the bimetallic complex remains intact when adsorbed into the dry sodium form NaY (Co-CO: 4.1 ligands at 1.79A; CoCO, 3.6 at 2.93A. On heating in vacuum, the complex is stable up to about 90oc, starts to release CO above 120oc, and fragments at about 160oc under evolution of methane. Beyond this temperature, EXAFS data show formation of extremely small cobalt/tin clusters. The reactivity of the SnCo complex in proton-containing zeolite H6Y is very different from that of NaY. Sleight CO evolution begins already at about 60oc, and IR studies indicate that the complex fragments completely above 120oc. No indication for metal clusters but attachment of cobalt to the zeolite framework is observed. Organometallics in Mesoporous Channel Hosts: Reactivity of Tricarb~176176 The bimetallic complex Me3SnMo(CO)3Cp was adsorbed into MCM host (3 nm channels) from hexane solution. The in situ infrared spectra show a weakly distorted CO coordination environment at room temperature, consistent with the absence of Na-ions in the channels of the host. This complex exhibits a striking thermal stability in MCM: the CO ligands are only removed on heating above 250oc. The stability of the Sn-Mo bond in this system, and the nature of the decomposition products determined from EXAFS data will be discussed. ACKNOWLEDGMENTS Funding from the U. S. Department of Energy (DE-FG04-90ER14158 and DE-FG02-92ER14281) for this work is gratefully acknowledged. REFERENCES 1 2 3
Borvornwattananont, A.; Moiler, K.; Bein, T., J. Phys. Chem., 1992, 96, 6713. Borvornwattananont, A.; Bein, T. J. Phys. Chem., 1992, 96, 9447. Beck, J. S., U. S. Patent 5,057,296, Oct. 15, 1991.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
140
SIMULTANEOUS EXCHANGE AND EXTRUSION OF METAL EXCHANGED ZEOLITES John N. Armor and Thomas S. Farris Air Products & Chemicals, Inc., 7201 Hamilton Blvd., Allentown, PA 18195 USA Summary: We wish to report that simple combination of an aqueous transition metal salt, alumina, and the ammonium form of the zeolite can be readily extruded, and upon calcination to 650~ the resulting extrudate as a catalyst behaves similarly to catalysts derived from more complex preparations of multiple, aqueous ion exchange followed by extrusion. Introduction In the course of our recent work to prepare cobalt exchanged zeolites for the removal of NOx by methane/oxygen or N20 by decomposition, we needed to prepare large batches of extruded material for scale up studies. This can be done by extending the traditional ion exchange preparation and then performing an extrusion of the resulting product. Traditionally, for cobalt ions multiple exchange is carded out in dilute, aqueous solutions of cobalt salts under reflux for 24 hours [1]. There are numerous reports of solid state exchange of cations into a variety of zeolites [2-4]. Similarly, there are several reports describing different recipes for extrusion of various zeolites [5,6]. Generally, this requires the addition of an alumina or clay binder and some dilute, aqueous acid to the zeolite to produce an extrudate in a commercial extruder. The binder is often set with some high temperature calcination. It occurred to us that one might be able to simplify the preparative procedure by carrying out both solid state exchange and calcination of the extrudates in one step. This brief report describes our success at producing a tough extrudate of cobalt-ZSM-5 with this simplified procedure. Experimental We attempted to use a slight excess of cobalt salt to achieve near 100% exchange. Ammonium exchange ZSM-5 [template-free synthesis mute] [40.0g] was purchased from VAW Aluminum AG [SM27] [Schwandorf, Germany] and dry mixed with 4.44 g of Vista Dispal alumina [Houston, TX] in a Naigene bottle for 15 minutes using a ball mill. Separately, 0.57 g of 70% HNO3 and 3.90 g of COCI2 were added to 21.5 g of deionized water. This latter solution was kneaded with the dry mixed ZSM-5/alumina powder while adding about 6 cc of water until an extrudable paste was obtained. This
141
paste was extruded in a bench top, 1 inch Bonnot extruder [Kent, OH]. The 1/8 inch extrudates were dried overnight in a purged oven at 110~ The binder was then set while simultaneously carrying out the cobalt ion exchange by slowly heating the extrudates at l~ to 650~ in flowing air and holding at this temperature for 6 hours. Results & Discussion
The resulting pale blue extrudates obtained above were quite hard, and upon breaking the extrudates in half, the blue color was uniform throughout the extrudate. [The above procedure may need to be modified as a function of the extruder, zeolite, and metal ion, but we believe this approach will work with a wide variety of cations and zeolites. It will depend on the thermal stability of the zeolite as well.] Analysis of the extrudate indicated we achieved 110% of the theoretical exchange level. We tested this catalyst for Ng.O decomposition at 450~ under conditions previously established for this reaction [7]. Compared to a catalyst prepared with three aqueous ion exchanges, followed by stepwise extrusion and calcination there was only a slight difference in activity between these two extrudates. We also established that using Na-ZSM-5 in place of NH4-ZSM-5 in the procedure describe above was ineffective for this same reaction. Conclusions
We have demonstrated that one can achieve solid state exchange of cobalt ions into ZSM-5 by first mixing the binder, cobalt salt, and the ammonium form of the zeolite, and then setting the binder and accomplishing ion exchange by calcination at 650~ The resulting catalyst performs similarly for Ng.O decomposition compared to one prepared using a more traditional, complex approach for preparing the catalyst. This new procedure greatly simplifies the preparation of larger quantities of extrudates. References
1. Y. Li and J. N. Armor, Appl. Catal. B, 1993, 3, L1. 2. J. A. Rabo, in Zeolite Chemistry and Catalysis; J. A. Rabo, Ed., ACS Monograph 171, Am. Chem. Soc., Washington, DC, 1976, p. 332. 3. H. K. Beyer, H. G. Karge, and G. Borbely, Zeolites 1988, 8, 79. 4. H. G. Karge, Y. Zhang, and H. K. Beyer, Catal. Lett., 1992, 12, 147. 5. W. H. Flank, W. P. Fethke, Jr., J Marte, US Patent 4818508 (1989). 6. S. Schwarz, M. Kojirna, and C. T. O'Connor, Appl. Catal., 1991,68, 81. 7. Y. Li and J. N. Armor, Appl. Catal. B, 1992, 1, L21.
H.G. Karge and J. Weitkamp (Eds.)
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Zeolite Science 1994: Recent Progress and Discussions
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
MODIFICATION OF LAYER COMPOUNDS FOR MOLECULAR RECOGNITION Takayoshi Uematsu, Makoto Iwai, Nobuyuki Ichikuni and Shogo Shimazu Department of Applied Chemistry, Faculty of Engineering, Chiba University, Yayoi-cho, Inage-ku, Chiba, 263, Japan
ABSTRACT Interlayers of Na-hectorite (HT) and zirconium phosphate (ZrP) were modified with "chirality tuning guests" to enhance enantio-selective adsorption. The modified interlayers were characterized by means of spectroscopic techniques. The enantio-selective entrapments of alkylamines were studied, and their mechanisms will be discussed in terms of chiral pair formation. Regio-selective hydrogenation of geraniol was also found over multiply modified HT. INTRODUCTION Clay minerals and zirconium phosphate are typical swellable ion-exchangers with layer structures, which provide very suitable layers to prepare a new class of inorganic host for molecular recognition. Using "tuning guests" we have been studying various modification methods to control shape-selective and stereo selective entrapment and catalysis [1,2]. The present report gives some results for molecular recognition by multiply modified inter-layer spaces, such as enantio selective adsorption and regio-selective catalysis over asymmetrically modified layers. EXPERIMENTAL Synthetic HT and ZrP were chirally modified by cation exchange with R- or Salkyl-ammonium ions (RA +) in aqueous solution at room temperature. Multiply modified HT's were prepared by the successive intercalation of tuning guests; firstly introducing organic cations (pyridinium ion, Py, or alkylammonium ions, (CnN)), followed by the interlayer polymerization of 3-aminopropyl-tri-methoxysilane (APMS). The catalytically active species of Pd(II) complexes were chemically anchored to the amino groups of polymerized APMS (PAPMS). The modified layer structures were characterized by means of spectroscopic measurements. Catalytic tests and adsorption measurements were carried out in static systems. RESULTS AND DISCUSSION The d001 spacings of these multiply modified HT's expanded according to the molecular size and amount of tuning guest intercalated. They were effective also
143 to control the hydrophobic and/or hydrophilic properties of interlayers, as well. Asymmetry recognition by chirally modified layers was exemplified by Fig. 1. The layer host modified with R-PEA + (R-PEA/HT) entrapped S-PEA predominantly from a racemic mixture of (R+S) PEA. The reverse was also true clearly for SPEA/HT. The recognition ability increased up to 75% enantio excess as a function of the extent of modification. The interlayer distances were larger for the heterochiral coupling structures (R-S; S-R) than those for the homo-coupling structures (R-R; S-S). The peak areas of the XRD intensities were much larger for the hetero pairs. Plausible host-guest complexation models (Fig. 2) were interpreted in terms of the orientation and interaction of CH3 groups between the modifiers and the guest molecules. The enantio-selectivity depended on the structures of the asymmetry modifiers of 1-arylethylammonium ions (aryl=phenyl, p-tolyl, p-nitrophenyl, phenylethyltrimethyl and 1-naphthyl) and decreased in the following order: PEA>TEA>NPEA>PETM>NEA. Similarly, S-PEA + modified ZrP (SPEA+/ZrP) showed effective enantio-selective adsorption of R-PEA. Regio-selective hydrogenation of geraniol over multiply modified HT is shown in Fig. 3. The selectivity is defined by the ratio of the reaction rates R1/R2 as a measure to recognize the inner C=C bond close to the OH group against the other C=C bond adjacent to the terminal CH3 group. The regio-selectivity was controlled by tuning guest of amines in the following order: 0.91 = [Pd(OAc)2]3(Homg) <
)i;)
. (R
I nln
b (,.) j
s)
| ~r~n
F i g . I E ~ _ n t i o selective a d s o r p t i o n a: S-PF_.A/I-1T b: R - I ~ A / H T
4
4O
~3 '-i 2 1
Fig. 2 Plausible m o d e l for ch/ral pair o f h o s t - g u e s t complex. S-PHNH 2 on R-PF-.A+/HT
05 10 doo~ b~m]
Fig. 3 Regio selective h y d r o g e n a t i o n o f geraniol. Selectivity R 1 / R 2 -citroneUol/3.7-d~nethyl-2-octen-l-ol T u n i n g G u e s t 1: CSN. 2: Py(1). 3: Py(5). 4: (C12)2N. 5: (C18)2N
REFERENCES
[1] M. Iwai, H. Shoji, S. Shimazu and T. Uematsu, Chem. Lett. (1993) 403. [2] M. Iwai, H. Shoji, S. Shimazu and T. Uematsu, Chem. Lett. (1993) 989.
IV. Catalysis
This Page Intentionally Left Blank
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All fights reserved.
144
H-[B]-ZSM-5 AS CATALYST FOR METHANOL REACTIONS Erik UNNEBERG and Stein KOLBOE Department of Chemistry, University of Oslo, P.O. Box 1033 Blindern, N-0315 Oslo, Norway SUMMARY
Several characterization techniques confirmed that boron is located in the framework of hydrothermally synthesized [B]-ZSM-5. In protonated form it catalyzes the alkylation of toluene with methanol and also the dehydration of methanol to hydrocarbons, though it was much less active than H-[AI]-ZSM-5 and showed markedly different selectivities. INTRODUCTION
The catalytic properties of borosilicates with the MFI structure ("[B]-ZSM-5") have been discussed by several authors. In order to give rise to Bronsted acidity in the [B]-ZSM-5 when protonated, the boron has to be in the catalyst framework. It has been stated that H-[B]-ZSM5, due to the weaker acid strength of the Si-OH-B sites compared to the Si-OH-AI sites, is neither active in the alkylation of toluene with methanol nor in the dehydration of methanol to hydrocarbons (1). Conflictingly, it has been claimed that the catalyst is active in both reactions (2). Derewi~ski et al., who used a pulse reactor, found a very small activity for transforming methanol to hydrocarbons, and a sizeable alkylation activity with high para selectivity from a methanol/toluene mixture (3). On this background we found it of interest to carry out a reinvestigation of the H-[B]-ZSM-5 system. EXPERIMENTAL
Silicalite-I, [AI]-, [AI,B]- and [B]-ZSM-5 were synthesized hydrothermally by various methods. In order to minimize Ai-contamination in the [B]-ZSM-5's, tetraetoxysilane was used as the silicon source, and the syntheses were carried out in teflon-lined stainless steel autoclaves. The synthesis products were characterized by SEM, IR, BET, XRD, NMR, ion exchange and elemental
(ICP) analyses. Catalytic reactions were performed in a continuous flow
microreactor using methanol and toluene + methanol as reactants. RESULTS AND DISCUSSION
The XRD patterns showed the "as synthesized" products to be pure and highly crystalline MFI's with orthorhombic symmetry, though some of the products became monoclinic upon calcination. Nitrogen adsorption (BET) and SEM confirmed the high crystallinity. XRD also showed the unit cell volumes of the [B]-ZSM-5's to be significantly lower than those of their
145
boron-free analogs, which indicated that boron is located at lattice positions. In addition, the H-[B]-ZSM-5's exhibited ion exchange properties, and the amount of acid sites found by those experiments correlated well with the ICP-determined boron content in the samples. It was found, however, that repeated ion exchange of the H-[B]-ZSM-5 led to loss of boron from the lattice. In the IR spectra O-H stretch frequencies appeared at 3700 cm 1 for H-[B]-ZSM-5 and at 3600 cm 1 for H-[AI]-ZSM-5, indicating weak and strong Bronsted acidity respectively (4). The IR and 11B-NMR spectra of H-[B]-ZSM-5 also showed boron to be located in tetrahedral positions. The reversible transition to trigonal boron (1) could be followed by NMR by heating the sample to 150~
in dry atmosphere. By cooling to 20~
in air tetrahedral boron
reappeared. H-[B|-ZSM-5 was able to convert methanol to hydrocarbons at temperatures above 250~ but the conversions were much smaller than those over H-[AI]- and H-[AI,B]-ZSM-5. Blank test runs gave no hydrocarbons. The hydrocarbon selectivities were markedly different. While mainly ethene and propene were formed over the AI-containing zeolites, methane was the dominating hydrocarbon over H-[B]-ZSM-5. The conversion of toluene in the alkylation reaction (435~
over H-[B]-ZSM-5 was also very
low compared to the conversion over H-[AI]-ZSM-5. Over the [B] catalyst no other alkylation products than xylenes, 1,2,4-trimethylbenzene and durene could be detected (a typical molar distribution was 85/12/3), while p-ethyltoluene was the predominant C9 component in the [AI] case, possibly due to alkylation of toluene with ethene (formed from methanol). While our H-[AI]-ZSM-5 catalyst was fairly para-selective, the typical o-/m-/p-xylene product distribution in the alkylation reaction over H-[B]-ZSM-5 was 38/25/37. This selectivity is in contrast to most literature results on catalysts with the MFI structure where o-xylene usually is much lower. However, in an other study on the H-[B]-ZSM-5 system, using a micro pulse reactor a m-xylene/o-xylene ratio less than unity is reported, but at the same time a high paraselectivity was observed (3). The relatively high o-xylene concentration in our product mixtures indicates that the ortho-para directing effect of the toluene methyl group is not canceled by steric restrictions in H-[B]-ZSM-5. Further discussion is given in the full report. REFERENCES 1. G. Coudurier, A. Auroux, J.C. V~drine, R.D. Farlee, L. Abrams and R.D. Shannon, J. Catal. 108, 1-14 (1987). 2. P. Ratnasamy, S.G. Hegde and A.J. Chandwadkar, J. Catal. 102, 467-470 (1986). 3. M. Derewiflski, S. D~,wigaj, J. Haber, R. Mostowicz and B. Sulikowski, Zeitschrift fQr Physikalische Chemie 171, 53-73 (1991). 4. M.B. Sayed, A. Auroux and J.C. V(~drine, J. Catal. 116, 1-10 (1989).
H.G. Karge and J. Weitkamp (Eds.)
146
Zeolite Science 1994: Recent Progress and Discussions
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved. NO x REDUCTION WITH AMMONIA OVER CERIUM EXCHANGED MORDENITE IN THE PRESENCE OF OXYGEN. AN IR MECHANISTIC STUDY. E. Ito a, Y.J. Mergler b, B.E. Nieuwenhuys b, P.M. Lugt a, H. van Bekkum a and C.M. van den Bleek a Delft University of Technology, Department of Chemical Technology and Material Sciences, lulianalaan 136, 2628 BL Delft (The Netherlands) University of Leiden, Gorlaeus Laboratoria, P.O. Box 9502, 2300 RA Leiden (The Netherlands)
SUMMARY An IR mechanistic study of NO reduction with ammonia in the presence of oxygen was performed over cerium-exchanged mordenite (CeNa-MOR) and compared with lanthanum-exchanged mordenite (LaNa-MOR), which does not possess redox properties. The formation of NO x (x - 2 or 3) species was observed upon NO adsorption, which was obviously enhanced in the presence of oxygen over both mordenites. These NO x species were found to be reactive towards ammonia over cerium already at 300 ~ while the same species remained unreacted over lanthanum. The importance of redox properties in this reaction is indicated. INTRODUCTION The removal of nitrogen oxides in oxygen rich atmosphere is an urgent environmental issue with respect to diesel exhaust cleaning and lean-burn operation of gasoline automobiles. We have found that cerium-exchanged zeolites are very promising catalysts for NO reduction with ammonia in the presence of oxygen providing high activity and selectivity towards nitrogen [1,2]. A reaction mechanism was examined using in-situ infrared spectroscopy and reported here.
EXPERIMENTAL The preparation of cerium and lanthanum exchanged mordenite has been described elsewhere [1]. A sample in the form of a self-supporting wafer was evacuated (10 .5 - 10.6 Tort) for 2.5 h at 330 - 350 ~
(FT-IR apparatus: Mattson galaxy 2020).
Background spectra of mordenite were taken at different temperatures and used for subtraction from the spectra taken in the presence of reactant gases (NO, 0 2 and NH3). RESULTS AND DISCUSSION N O / 0 2 adsorption and the subsequent N H 3 admission
NO was first admitted at room temperature at 1 - 5 Tort, and it turned out that CeNa-MOR and LaNa-MOR gave similar spectra exhibiting two sharp peaks (2248 c m l : N20 and 2163 cm-l: NO + or NO2 + [3]) and slowly growing broad peaks at 1300 - 1500 m
cm -1 (NO 2 or NO 3 ). This indicates disproportionation of NO to N20 and NO 2. The peaks observed at 1635 cm -1 and 3200 - 3700 cm -t are ascribed to water or nitrous acid.
147
At 100 ~
peaks at 1487 and 1337 cm 1 with a shoulder at 1510 cm 1 became evident.
These can be assigned to nitrato (1510, 1487 and 1337 crnq), or to the following three species; nitrato (1510 cmq), nitrito -ONO- (1487 cm 1) and free NO 2- ion (1337 c m l ) . Upon the subsequent admission of 0 2 (5 Torr) at 100 ~
the peak at 2163 cm -1 (NO +
or NO2 +), and the NO x (x = 2 or/and 3) peaks at 1487 and 1337 cm "1 were observed to be greatly enhanced over both rnordenites. NH 3 was then admitted (Figs. 1 and 2). The observed broad peaks at 2200 - 3500 cm "1 and the large peak at 1435 cm -1 were assigned to NH4 + / N H 3. It should be noted that the strong NO x- (x = 2 or/and 3) peak at 1487 cm -1 remained unchanged up to 200 ~ over both cerium and lanthanum. At 300 ~
the peaks assigned to NH3/NH4 + (2500 - 3500 cm "1 and 1435 cm "1) and NO x- (1350 -
1530 cm -1) disappeared simultaneously over cerium, indicating a reaction between these species. In contrast, these species remained unchanged over lanthanum even after 10 min at 300 ~
This demonstrated the important role of the redox property of CeNa-MOR
in high reactivity of these surface species: NH3/NH4 + and NO x (x - 2 or/and 3). 1.4
1.4
-..S t~
t~
0.8-
0.8-
0.6-
0 0.6-
_.j" 02_ . f / 0.4-
0,
4000
J
3500
3000
2500
2000
1500
Wavenumber / cm.1 Fig. 1 N O / O 2 / N H 3 adsorption over CeNa-MOR.
After N O / O 2 adsorption, NH 3 (5 Torr) was admitted and the temperature was subsequently raised. Spectra taken at (a) 100~ (b) 200~ (c) 300 ~ and (c) 300 *C after 10 rain.
4ooo' s~oo' s~oo' 2~oo' 2~oo' ,~oo Wavenumber/ cm-1 Fig. 2 NO/O2/NH 3 adsorption over LaNa-MOR. After N O / O 2 adsorption, NH 3 (5 Torr) was admitted and the temperature was subsequently raised. Spectra taken at (a) 100*C (b) 200 *C (c) 300 *C and (c) 300 *C after 10 rain.
REFERENCES 1. E. Ito, R.J. Hultermans, P.M. Lugt, M.H.W. Burgers, M.S. Rigutto, H. van Bekkum and C.M. van den Bleek, Appl. Catal. B, 4 (1994) 95. 2. E. Ito, R.J. Hultermans, P.M. Lugt, M.H.W. Burgers, H. van Bekkum and C.M. van den Bleek, Proc. of the Third International Congress on Catalysis and Automotive Pollution Control, Brussels (1994). A. Frennet and J-M. Bastin (Editors) Stud. Surf. Sci. Catal. (1995), in press. 3. C-C Chao and J. Ltmsford, J. Am. Chem. Soc., 93 (1971) 71.
H.G. Karge and J. Weitkamp (Eds.) 148
Zeolite Science 1994: Recent Progress and Discussions
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
CATALYTIC ACTIVITY AND ACTIVE SITES IN ZEOLITE CATALYSTS F O R N20 DECOMPOSITION E.B. Uvarova, S.A. Stakheev, L.M. Kustov and V.V. Brei N.D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, Moscow, Russia
SUMMARY Catalytic activity of various modified zeolites and related materials in the reaction of nitrous oxide decomposition is studied. Active sites and mechanisms of this reaction are discussed. INTRODUCTION Modified zeolites are widely used as catalysts for reactions involving NOx oxides. Among them attention should be paid to selective reduction of NO with hydrocarbons, selective oxidation of aromatics with N20 and N20 decomposition as commercially attractive processes. Catalytic properties of zeolites in N20 decomposition have been studied in much detail, but the nature of active sites is not yet revealed. The goal of this work is to find some new zeolite and related catalysts for N20 decomposition and to study the nature of active sites using physicochemical methods, in particular diffuse-reflectance IR spectroscopy and XPS. RESULTS AND DISCUSSION The HZSM-5 pentasil type zeolite (Si/Al = 20) modified with copper and zinc oxides (1-5 wt %) were prepared by impregnation of the starting H-form with 1 M solutions of nitrates followed by calcination in air. Ti-silicalites of the TS-1 type were synthesized according to the known patent procedure. Amorphous Co-Cr-Cu/AI203, Fe-Cr-Cu/AI203, and TiO2/SiO 2 catalysts were prepared by impregnation of AI203 (S-~150 m2/g) and used as reference samples. Catalytic testing in N20 decomposition was carded out at 350 - 600 ~ and a N20 : He (1 : 1) flow rate of 40-50 ml/min, catalyst loading was 0.2 g. The results of testing show that Zn-containing catalysts are somewhat more active in N20 decomposition as compared with Cu/HZSM-5 systems and far more active than amorphous catalysts studied in this work. This effect was explained by a decisive role of strong Lewis sites connected with ZnO microparticles incapsulated in zeolite channels. These centers were revealed IR-spectroscopically by the low-temperature adsorption of molecular hydrogen (VH_H = 3970, 4010 cm-l). Surprisingly, Ti-silicalites revealed high activity in N20 decomposition, which at low temperatures (350 - 375 ~ exceeds the activity of the known Cu/HZSM-5 catalyst. The lower activity of Ti-silicalites passes a maximum at SFTi - 30 - 35. The lower activity of Ti-silicalites with a higher Ti content was explained by the formation of a separate TiO~ phase or coupled Ti-O-Ti fragments in the framework, which seem to be inactive in N20 decomposition. Isolated TiO 4 tetrahedra or titanyl groups (=Ti=O) were assumed to play the
149 role of active sites in this reaction. The state of titanium in Ti-containing systems is studied by XPS and the data obtained agree with the proposed nature of active sites. Adsorption and decomposition of N20 was also studied by diffuse-reflectance IRspectroscopy and an activated form of N20 was observed in ZnS-IZSM-5 zeolites (v3= 2275 cm-1), which is decomposed atter heating the sample at 250 - 300 ~ The mechanisms of N20 decomposition on strong Lewis acid sites and Ti-centers are discussed in detail.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
150
ROLE OF THE PREPARATION AND NATURE OF ZEOLITE ON THE ACTIVITY OF Cu-EXCHANGED MFI FOR NO CONVERSION BY HYDROCARBONS AND OXYGEN Gabriele Centi, Siglinda Perathoner, and Laura DalrOlio Department of Industrial Chemistry and Materials, V. le Risorgimento 4, 40136 Bologna, Italy
SUMMARY The effect of the Cu/A1 ratio for ZSM-5 zeolites with SIO2/A1203 ratios of 50 and 16, the influence of the procedure of copper addition and the role of the acidity of the zeolite are discussed. In particular, the higher activity that it is possible to obtain using a new preparation procedure by hot ion-exchange and the high activity shown by a Cu-Boralite sample with the MH structure are reported.
INTRODUCTION Lean-burn and diesel-engines have several advantages in terms of higher efficiency and lower CO2 emissions, but due to the presence of around 2 - 3% 02 in the exhaust gas, commercial three-way catalysts are not effective in the conv_ersion of NO. Metal-exchanged zeolites and Cu-ZSM-5, in particular, however, show a high activity in the reduction of NO in the presence of 02 and of hydrocarbons (propane, in particular). The further development of these catalysts requires, however, a better understanding of the dependence of their catalytic behavior on the preparation procedure and the nature of the zeolite, in order to obtain samples active at lower temperatures and stable for longer times. In this communication we will discuss the dependence of the activity on the Cu/A1 ratio for ZSM-5 samples with different SIO2/A1203 ratios and the influence of the method of introduction of the copper component into the zeolitic catalyst. The dependence of the activity upon the acidity of the zeolite will be investigated by comparing the activity of samples in the H- and Na-forms with the activity of a Cu-Boralite sample with the same structure of ZSM-5, but lower strength of acid sites due to the substitution of AI with B. EXPERIMENTAL Cu-ZSM-5 was prepared from the sodium of the parent zeolite by conventional ion-exchange at room temperature or under reflux (hot ion-exchange) using an aqueous solution of copper-acetate. The SIO2/A1203 ratio of the zeolites were 49, 52 or 16 and the Cu/A1 ratio was changed in the range 0-1.25 using repeated ion-
151 52 or 16 and the Cu/A1 ratio was changed in the range 0-1.25 using repeated ionexchanges. Cu-Boralite was prepared in the same way using a sample with the MFI structure and a SIO2/B203 ratio of 24. Catalytic tests were performed in a plug-flow-type reactor equipped with an online mass-quadrupole system for real-time analysis of all products. Tests were made using the following feed: [NO]---800 ppm, [C3H8]=2300 ppm, [02]=3.9 %, W/F-0.3 g . sec/cc. The reaction temperature was varied in the range 250-550~
g so ~
40
O
//;/ 7
20 0 200
.
I'.NO(Bora,. )
//
I V C3 (Borml.)
9" " 9 "" '
I I
300
i 400
9NO (ZSM5)
I I = C3 (ZSMS)
500
600
Temperature, "C
Figure I
Catalytic behavior in the selective reduction of NO by propane/O2 of Cu-ZSM-5 (dotted line) and Cu-Boralite (solid line) samples with the same MFI structure and copper content.
RESULTS AND DISCUSSION
Role of the Cu/Al ratio and Si02/A1203 ratio. The introduction of copper by ionexchange promotes the conversion of both NO to N2 and propane to CO2. The activity does not depend on the absolute amount of copper, but on the Cu/A1 ratio in the sample. For the same Cu/A1 exchange level, the zeolite with the higher SIO2/A1203 ratio shows better activity in both reactions with respect to the zeolite with SIO2/A1203 of 16. No significant differences were found, on the contrary, for the two ZSM-5 samples with similar SIO2/A1203 (49 and 52), but from different sources, suggesting that the activity depends weakly on the specific preparation of the parent zeolite, but mainly on the SIO2/A1203 ratio.
152
Role of the method of copper addition. The comparison of the catalytic behavior of three Cu-ZSM-5 samples with the same C u / A I and SIO2/A1203 ratio, but prepared using the conventional ion-exchange procedure, a wet impregnation or a new hot-ion-exchange method is reported. At 350~ the conversion of NO and propane over the sample prepared by conventional ion-exchange are 67.3% and 59 %, respectively. These values decrease to 24.5 % and 32.7 % for the sample prepared by wet impregnation, but increase to 95.5 % and 54.5 % for the hot-ionexchange method. These results show that the method of preparation greatly influences the reactivity, and also that the rates of propane and NO depletions are differently influenced by this factor.
Role of the acidity. At 350~
H-ZSM-5 (SIO2/A1203=16) is around 2-3 times more active both in propane and NO depletion when compared to the sodium form of the same sample, indicating the role of acid sites in both mechanisms. However, the comparison of the activity of Cu-ZSM-5 (SIO2/A1203=16) with that of a CuBoralite sample with similar structure (MFI), total number of active sites (SIO2/B203=24) and copper content (4% wt. as CuO), but lower acid strength due to substitution of A13+ by B3+, shows that a slightly better catalyst can be prepared (Fig. 1) indicating that the role of the acid sites on the mechanism of reaction or formation of active sites should be analyzed in more detail.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions
153
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
SELECTIVE PHOTOOXIDATION OF ABUNDANT HYDROCARBONS BY 0 2 IN ZEOLITES WITH VISIBLE LIGHT Fritz Blatter, Hai Sun, and Heinz Frei Lawrence Berkeley Laboratory, University of California Berkeley, CA 94720 SUMMARY Selective oxidation of small alkenes and of toluene by 02 has been accomplished by irradiation of the reactants in zeolite Y with visible light. Products are industrially important compounds like benzaldehyde (from toluene) and acrolein (from propylene). The key to these tightly controlled reactions is an unprecedented stabilization of hydrocarbonoO2 excited charge-transfer states by the ionic environment of the zeolite matrix cage. INTRODUCTION Selective oxidation of small abundant hydrocarbons is the mostimportant type of reaction in organic chemicals production. For example, essentially all building blocks for the manufacture of plastics and synthetic fibers are produced by oxidation of hydrocarbons. Among these, oxidations by molecular oxygen play a particularly important role. A key problem is the product specificity in hydrocarbon + 02 reactions, and here photoassisted processes hold special promise. They can typically be conducted at or around ambient temperature, thus minimizing the chance for loss of product control due to secondary thermal chemistry of the initial products. Inexpensive artificial light can be used if the reaction can be driven by visible or near-infrared light. All these are attractive ingredients for environmentally benign chemical synthesis. EXPERIMENTAL Hydrocarbon and 02 were loaded from the gas phase into self-supporting zeolite pellets mounted inside a miniature infrared cell. Reaction was induced with light from a cw dye laser (for wavelength dependence studies) or a filtered tungsten source. The chemistry was monitored in situ by FT-infrared spectroscopy. Visible spectra were recorded by diffuse reflectance spectroscopy. RESULTS AND DISCUSSION We have accomplished selective photooxygenation of small alkenes and aromatics by irradiating hydrocarbon.O2 collisional complexes in alkali and earth alkali exchanged zeolite Y with visible and near-infrared light. 1,2 Propylene, cis and trans-2-butene, and 2,3-dimethyl-2-butene (DMB) were oxidized to the corresponding alkene hydroperoxide with very high selectivity. These rearrange thermally at room temperature to a single carbonyl compound in each case, namely acrolein in the case of propylene + 02, methyl vinyl ketone in the case of 2-butene, and acetone when DMB + 0 2 was photolyzed. This is the first selective synthesis of these organic
154 compounds by direct alkeneoO2 photolysis in any phase. Reactions are rather efficient, with quantum yields ranging from 0.1 to 0.3. Diffuse reflectance spectra revealed a continuous visible absorption of alkene + 0 2 loaded zeolites 3 which coincided with the measured laser reaction excitation spectra. The onset of the band increased monotonically with the ionization potential of the alkene, indicating that the absorption originates from an alkeneoO2 charge-transfer transition. Red-shifts relative to corresponding alkeneoO2 charge-transfer bands in the 02 gas phase, O2-saturated solution, or solid oxygen are between 12,000 and 15,000 cm -1 (1.5 to 1.9 eV) depending on the hydrocarbon and the metal cation in the zeolite. This unprecedented stabilization of the excited chargetransfer state is attributed to the very high electrostatic fields (on the order of V/A) inside the charged cages of zeolite Y. The rather high reaction quantum yields imply that the primary elementary step of the excited alkene +02- charge-transfer state competes effectively with back electron transfer. The proposed initial step is deprotonation of the highly acidic alkene radical cation to generate an allyl radical and HO2". Re-combination of the radical cage pair yields the observed alkene hydroperoxide, which then rearranges thermally to the corresponding carbonyl compound. An exciting case is the selective photooxidation of toluene to benzaldehyde by 0 2 in earth alkali exchanged zeolite Y. Diffuse reflectance spectroscopy of toluene and 02 loaded zeolite CaY showed a continuous charge-transfer absorption in the visible region extending to 600 nm. This corresponds to a 10,000 cm" 1 red shift compared to the tolueneoO2 charge-transfer absorption in O2-saturated toluene solution. Irradiation at wavelengths as long as 590 nm led to reaction. In zeolite CaY, an intermediate was formed that reacted upon continued photolysis to yield benzaldehyde as the exclusive final oxidation product. In BaY, yields were lower, but the reaction gave benzaldehyde with complete selectivity as well. This work is supported by the Chemical Sciences Division of the U.S. Department of Energy. REFERENCES [1] [2] [3]
Blatter, F.; Frei, H. J. Am. Chem. Soc. 1993, 115, 7501. Blatter, F.; Frei, H. J. Am. Chem. Soc. 1994, 116, 1812-1820. Blatter, F.; Moreau, F.; Frei, H. Chem. Phys. Lett., submitted.
155
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
APPLICATION OF VAPO-5 IN LIQUID PHASE OXIDATION REACTIONS: INDICATIONS FOR THE PRESENCE OF DIFFERENT VANADIUMSITES
M.J. HAANEPEN and J.H.C. van HOOFF Schuit Institute of Catalysis, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands SUMMARY
VAPO-5's with different vanadium content (0.18 - 2.0 at%) have been used as catalyst for the liquid phase epoxidation of cinnamylalcohol (3-phenyl-2-propan-l-ol) by t-butylhydroperoxide ('I'BHP). It has been found that the activity, expressed as turnover frequency (TOF), increases with increasing vanadium content. Diffuse Reflectance UV VIS (DRUWIS) shows that in samples with a high vanadium content a second type of vanadium species is present that probably is responsible for the observed higher catalytic activity. INTRODUCTION
VAPO-5 has been reported as a potential catalyst for liquid phase oxidation reactions [1-3]. Until now very little is known about the influence of the vanadium content on the catalytic activity and the stability of these materials during the reactions. In this report the results of our investigations on the oxidation of cinnamylalcohol by TBHP catalyzed by VAPO-5 are reported.
~
0H
VAP0-5 .....
CH3CN, 50 oC TBHP
~
0H
EXPERIMENTAL
VAPO-5 samples with different vanadium content have been prepared hydrothermally (boehmite (Condea); phosphoric-acid, vanadylsulfate (Merck); Et3N or Pr3N (Janssen); 1.0-x AI20 3 : 1.0 P2Os : x V20 s : 44 H20 : 1.3 T (x = 0-0.05); cryst: 160~
48h).
Samples have been characterized by XRD, SEM, hAS, DRUWIS and butane sorption. Reactions have been performed in a thermostatted batch reactor at 50~ using 15 ml of a cinnamylalcohol (0.3 M) / TBHP (0.3 M) solution in dry acetonitrile. For a reaction 0.3-0.6 g VAPO has been used. Samples have been analyzed by gaschromatography.
156
RESULTS AND DISCUSSION XRD spectra and sorption data of all VAPO-5's studied indicate a highly crystalline AFI structure. The morphology of the samples is comparable (agglomerates of about 12 pm). In table 1 the performance of the samples in the liquid phase oxidation of cinnamylalcohol is described. A blanc reaction with AIPO4-5 did not show any significant conversion of the substrate. Table 1: Performance of VAPO-5 in the oxidation of cinnamylalcohol by TBHP" Catalyst a b c VO(acac)2
V (at%)
Amount (g)
Activity (mol.hl.I 1) at 30% conversion
TOF (mol.mol V'l.h ~) at 30% conversion
0.18 1.1 2.0
0.60 0.30 0.30
0.018 0.132 0.287
16 37 44
-
0.025
1.67
~ 250
" For reaction conditions see experimental section. The activity of VAPO-5 at 30% substrate conversion increases upon increasing vanadium content, although the activity always remains lower than the homogeneous catalyst VO(acac)2. The activity of different VAPO-5 samples increases more than can be expected from the increasing vanadium content alone. Leaching of vanadium from the lattice, thereby creating a highly active homogeneous vanadium species, seems not to be a likely reason for this increased activity. After three reaction cycles, the calcined VAPO-5's still had the same activity and the same vanadium content. From DRUWIS there is evidence that there are different vanadium species present. Samples with a low vanadium content show absorption between 200-300 nm. Upon increasing of the vanadium content an additional absorption appears between 350 450 nm. The latter species can be related to the more active species. REFERENCES [1] M.S. Rigutto and H. van Bekkum, J. Mol. Cat., 81 (1993) 77-98 [2] C. Marchal, A. Tuel and Y. Ben Taarit, Stud. Surf. Sci. and Cat., 78 (1993) 447-454 [3] M.J. Haanepen and J.H.C. van Hooff, Proceedings of the DGMK-conference 'Selective Oxidations in Petrochemistry', Goslar, (1992) 227-236
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions
157
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved. OXIDATION OF PRIMARY AMINES OVER TITANIUM A N D VANADIUM SILICALITES: SOLVENT EFFECT J. Sudhakar Reddy and A. Sayari Universit6 Laval, Department of Chemical Engineering and CERPIC, Ste-Foy, Qc, CANADA GIK 7P4
SUMMARY In the oxidation of primary amines over titanium (TS-1) and v a n a d i u m (VS-1) silicalites, the solvent plays a significant role in determining the conversion of amine as well as p r o d u c t selectivity. When v a n a d i u m silicalite was u s e d as a catalyst, the selectivity for oxime was low (20-40%) and one of the major p r o d u c t s was imine (30-55%). However, over titanium silicalite, imines were formed only in the presence of chloroform. Chloroform also favors the formation of nitroalkanes over both titanium and v a n a d i u m silicalites. INTRODUCrION Oxidation of various nitrogen containing c o m p o u n d s to the c o r r e s p o n d i n g oxygenated derivatives in the presence of peroxides is known to take place over_ a variety of catalysts. However, attempts to use zeolites as catalysts were not m a d e until recently / . This development is part of an emerging research area, the purpose of which is to use zeolites modified with transition metal cations such as Ti and V to catalyze organic synthesis reactions 2. In this respect, Ti silicalite (TS-1) was f o u n d to catalyze the oxidation of primary amines by diluted H 2 0 2 to the corresponding oximes lb. However, no detailed studies on this reaction are available. In addition, the use of vanadium silicalites as catalysts for the oxidation of primary amines has not been reported. The scope of this work was to investigate the influence of various solvents on the activity and selectivity of titanium a n d v a n a d i u m silicalites in the oxidation of aliphatic primary amines containing (z-hydrogen. EXPERIMENTAL Catalysts were prepared according to the procedures available in the literature3, 4. As-synthesized samples were calcined at 823 K before use. Reactions were carried out in a 100 ml r o u n d bottom flask placed in a heating mantle connected to a t e m p e r a t u r e controller. In a typical reaction, 70 mmol of substrate, 200 m g of catalyst, 15 ml of solvent and 35 mmol of H202 (35 wt.%) were mixed and stirred at 333 K. The products were analyzed using a GC equipped with a 50 m methylsilicon g u m column. Product identification was carried out with GCMS.
158
RESULTS AND DISCUSSION Oxidation of primary amines over TS-1 in the presence of ethanol as solvent led mainly to the corresponding oximes with about 85% selectivity. Similar results were reported by Reddy and Jacobs lb who used methanol and t-butanol as solvents. The present study shows however, that in the presence of chloroform, the major p r o d u c t is an imine (6), instead of oxime (4). In this case, significant amounts of nitroalkanes were also obtained. In the presence of alcohols, no nitroalkanes were formed. Conversely to TS-1, VS-1 favored the formation of imine in all the solvents tested. R-CH2-NO2 [0]/'~ 3 [o] R-CH2-NH2 -'~ R - C H 2 = N O 1 I " - ~ R-CH = NOH 4 R-CH = NOH 4
[0] IV
,'~
R-CH = O 5
R-CH2-NH2 ,'~ R - C H = N - C H 2 - R V 6
To investigate the various reaction pathways, we have carried out additional experiments using cyclohexanone oxime as substrate. Our experimental results are summarized in Table 1 based on the proposed reaction scheme.
Table I
Summary of experimental data
Solvent
Alcohol Alcohol Alcohol Chloroform Chloroform Chloroform
Catalyst TS-1 VS-1 None TS-1 VS-1 None
Reaction
I, HI I, III, IV, V V I, II, HI, IV, V I, II, HI, IV, V IV, V
REFERENCES
1.
2. 3. 4.
(a) S. Tonti, P. Roffia, A. Cesana, M.A. Mantagazza and M. Padovan, EP 0 314 147 5 1988; (b) J.S. Reddy and P.A. Jacobs, Perk. Trans. I, (1993) 2665; (c) J.S. Reddy and A. Sayari, Catal. Lett., (1994) submitted. W.F. H61derich and H. van Bekkum, Stud. Surf. Sci. Catal., 58 (1991) 631. G. Perego et al., Stud. Surf. Sci. Catal., 28 (1986) 129. M.S. Rigutto and H. van Bekkum, Appl. Catal., 68 (1991) L1.
H.G. Karge and J. Weitkamp (Eds.) Zeol#e Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
159
ROOM TEMPERATURE OXIDATION OF METHANE TO METHANOL ON FeZSM-5 ZEOLITE SURFACE V.I.
Sobolev, A . S . Kharitonov,
O.V. Panna and G.I. Panov
Boreskov Institute of Catalysis, Novosibirsk 6 3 0 0 9 0 ,
Russia
Summary A spel;ific surface oxygen form produced upon N20 decomposition on FeZSM5 zeolite was shown to oxidize selectively methane to methanol at room temperature.
Introduction Nitrous oxide decomposition on Fe-containing ZSM-5 zeolites is known to produce a specific surface oxygen form ((z-form) which cannot be produced by 02 adsorption
[1].
(z-Form exhibited remarkable reactivity. The most conspicuous
example is its 1:1 interaction with methane which readily proceeded at room temperature. But product of this reaction were not identified yet since sensitivities of spectroscopic
techniques
( I R , NMR)
proved
to
be
not
sufficient
while
thermodesorption procedure was followed by secondary processes resulting in CO and CO2 desorption into the gas phase. We have shown recently for the case of benzene [2] that surface products of (zoxygen reactions can be reliably identified chromatographically after their extraction from the zeolite. This procedure is applied now for (z-oxygen interaction with methane.
Experimental ZSM-5 zeolite containing 1.54 wt.% AI203 and 0.30 wt.% Fe203 was used as a catalyst. (z-Oxygen form was loaded by N20 decomposition at 240oc according to the following reaction: N20+(
)0c=(O)(z+N2
(1)
This reaction was carried out in vacuum static setup equipped with an on-line massspectrometer. Concentration of (z-oxygen was determined from N2 amount evolved in reaction (1) as well as using its isotope exchange with 02. Interaction with methane at starting pressure P(CH4) = 0.4 Torr was carried out after cooling the sample to room temperature. Then, the sample was taken from the reactor and subjected to extraction procedure. GH "ZWET-500" provided with FID was used for the product analysis.
Results and discussions The amount of methane reacted with (z-oxygen was equal to 6.5 #mol/g zeolite. Extraction wi'th water revealed methanol as the only reaction product, but its amount
160 did not exceed 10-15% of the methane consumption. A mixture of acetonitril with water proved to be more efficient extragent. The figure shows how methanol amount increases with increasing number of acetonitril extractions. One can see that after 4fold extraction the methanol amount _
~6 o
~5 o
~3 .
o ~2
anol e x t r a c t e d Methane reacted
1
0
~,
,,
i
Number
g
of e x t r a c t i o n s
4
is equal to 5 llmol/g which responsible for nearly 80% of methane consumption. In conclusion we discuss a similarity between (~-oxygen oxidation on FeZSM-5 and that by monooxygenases whose unique activity is also relates to iron. References 1. Panov G.I" Sobolev V.I. and Kharitonov A.S., J. Mol. Catal., 61 (1990) 85. 2. Sobolev V.I., Kharitonov A.S., Paukshtis E.A., Panov G.i., J. Mol. Catal., 84 (1993) 117.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
161
OXIDATION A N D AMMOXIDATION OF PICOLINES OVER VANADIUM-SILICOALUMINO-PHOSPHATE MOLECULAR SIEVES
S ] Kulkarni,
R Ramachandra
Rao,
M Subrahmanyam, S Farsinavis, P Kanta
Rao and A V R a m a Rao
Indian Institute of Chemical Technology, Hyderabad 500 007, India SUMMARY :
The oxidation and ammoxidation of 3- and 4-picolines over vanadium s i l i c o - a l u m ino-phosphate and vanadium-alumino-phosphate molecular sieves lead to corresponding 60-85% yields of aldehydes and nitriles. We report crystalline and microporous modified (V-) silico-alumino-phosphates as a new class of oxidation and ammoxidation c a t a l y t i c materials. INTRODUCTION :
The resulting nitriles in the ammoxidation of 3- and 4-picolines are important i n t e r m e d i a t e s in the p h a r m a c e u t i c a l s . We have c a r r i e d out various oxidation and ammoxidation heterocyclic (VSAPO),
reactions
compounds
of aliphatic
like picolines,
vanadium-alumino-phosphates
alcohols,
aromatics
over vanadium (VAPO)
and
like toluene
and
silico-alumino-phosphates silico-alumino-phosphates
(SAPO) molecular sieves. In this paper, we report the oxidation and a m m o x i d a tion of picolines over vanadium silico-alumino-phosphate (VSAPO) and vanadium alumino-phosphate (VAPO) particularly. EXPERIMENTAL :
The 41
type
sulphate,
crystalline, catalytic
microporous
materials
phosphoric
acid,
are
sodium
VSAPO,
VAPO
hydrothermally silicate,
vanadium
like t e t r a p r o p y l a m m o n i u m bromide at 200~
and
SAPO-5,
synthesized
11,
using
pentoxide
37,
40,
aluminium
and
templates
for 24-80 hrs at 20 a t m pressure.
The e x p e r i m e n t a l details are given e l s e w h e r e 1. RESULTS AND DISCUSSION :
The materials tion
was
carried
out
are highly crystalline. The physico-chemical using X-ray diffraction,
infra-red
characteriza-
spectroscopy,
electron
spin resonance spectroscopy, t h e r m a l analysis, e t c . techniques. In case of VSAPO and VAPO catalysts, ESR has shown well resolved hyperfine splitting corresponding to V 4§ cation bonded strongly to oxygen ions in the matrix. The gtt a r e 2.0221 and 2.0046 and ~
values
2.0440 and 2.0380 for VSAPO and VAPO c a t a l y s t s
r e s p e c t i v e l y . Compare to the l i t e r a t u r e , these values correspond to V~'+ bonded -! with oxygen atoms. The IR band at 1400-1460 cm represents V-N-(template) bonding in the catalysts. The e f f e c t of calcination t e m p e r a t u r e has been studied. The i n c r e a s e of vanadium amount varies the crystallographic s t r u c t u r e .
162 The ammoxidation of 4-picoline with ammonia, air and water at 420~ -I and 0.5 hr W.H.S.V. over VSAPO and VAPO leads to 79.3 and 60 wt % yield of
~-cyanopyridine respectively. The ammoxidation of 3-picoline at 420~ and -I W.H.S.V. over VSAPO and VAPO leads to 37.2 and 58.8 wt % yield
0.5 hr of
3-cyanopyridine.
various
reaction
velocity,
the
time
stream
on
The selectivities
parameters
picoline
like
to ammonia
were
studied
were
above
reaction ratio,
over
90% for
temperature,
picoline
various
to
best
catalyst.
weight
water
crystalline,
hourly
ratio
The space
in the feed,
microporous
VSAPO,
VAPO and SAPO catalysts. The oxidation
of 4-picoline
using air and water
at 420~
with
0.5 hr - I
W.H.S.V. over VSAPO and VAPO leads to 51.8 and 57.9 wt % of p y r i d i n e - 4 - c a r boxaldehyde 420~ to
respectively. The oxidation of 3-picoline using water and air at -I 0.5 hr W.H.S.V. over VSAPO, VAPO and Sb203-VSAPO leads
with
45.6,
15.0 and 83.3 wt
% of
pyridine-3-carboxaldehyde,
respectively.
The
reaction mechanism of ammoxidation over these catalysts has been investigated.
The
reaction
of
3-or
4-picoline
with
ammonia
and
of air has been carried out over VSAPO and VAPO at 420~
water
in absence
and 0.5 hr - I W.H.S.V.
But 3- or 4-picolylamine was not observed in the products. So scheme I, reactionroute through aldehyde formation
is recommended. The corresponding carboxylic
acid or amide was also not observed in the products. In case of VSAPO, t e t r a hedraI the
vanadium
substitution
-VO4- , V-O-P of
linkages
and
Bronsted
silicon in place of phosphorus
acidic
centres
are the active
due
centres
to and
the catalyst is bifunctional. It is worth to note here that SAPO-5, I I , 377 40 and 4I, w i t h o u t vanadium or titanium lysts
is a class of mild and selective oxidation and ammoxidation
showing
in one step
~98% via
formation
of
acetonitrile
from
ammoxidation I . Thus we report
ethanol
(SAPO-#0
and emphasize
novel class of oxidation and ammoxidation c a t a l y t i c
catatype)
the new and
materials namely vanadium
of titanium-silico-alumino-phosphate molecular sieves. REFERENCES
1.
:
S 3 Kulkarni, R Ramachandra
Rao,
M Subrahmanyam
Rao, 3 C h e m Soc Chem Commun, (1994) 273.
and
A V Rama
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
163
TRANSITION METAL CATIONS IN ZEOLITES - A CATALYST FOR HDS REACTIONS A. Lugstein, O. El Dusouqui, A. Jentys and H. Vinek lnstitut for Physikalische Chemie, TU Wien, Getreidemarkt 9, A-1060 Wien, Austria SUMMARY We describe the incorporation of Co 2§ cations into ZSM5 zeolites by direct synthesis and by ion exchange methods, carded out in liquid phase and as a solid state reaction. The influence of the preparation method on the density of the sites and the stoichiometry of the ion exchange reactions was investigated.
INTRODUCTION Hydrotreating catalysts usually consist of two components: one which catalyses hydrogenation and the other which catalyses carbon-heteroatom bond cleavage
(hydrogenolysis sites) (1). In
conventional hydrodesulfurization (HDS) catalysts, the active sites for hydrogenation are related to Co(Ni)/Mo(W) sulfide phases and those for hydrogenolysis to the alumina support (2). Zeolites containing transition metal sulfides were commercially introduced and offer interesting alternatives where
enhanced
hydrocracking
activity
is
combined
with
hydrodesulfurization
and
hydrodenitrogenation (1). In these materials, hydrogenation takes place on the metal sulfide sites, hydrogenolysis on the strong Bmnsted acid sites (3). EXPERIMENTAL
Cobalt containing ZSM5 zeoUtes were directly synthesised according to ref. (4). HZSM5 (Si/AI = 42) samples were ion exchanged by conventional liquid phase method with a 0.2 molar COCI2 solution at 353 K for 48 hours (5). Solid state ion exchange was carded out by grinding HZSM5 with CoCl2.6H20 and heating the mixture in He atmosphere at 773 K for 6 - 10 hours (6, 7). Following the ion exchange, the samples were washed with destilled water until no CI~ ions were detected. Ir and XAS spectra of the samples were measured after activating the samples at 673 K in an inert gas atmosphere. The number of acid sites was determined by temperature programmed desorption (t.p.d.) of NH3. the number of sites affiliated with the presence of Co 2§ ions by NO t.p.d. The degree of ion exchange was calculated from the difference in the number of strong Bmnsted acid sites present before and after ion exchange. The structure of the zeolites was vedfied by XRD experiments. RESULTS AND DISCUSSION
The solid state ion exchange was carried out at various C02*/AI 3* ratios. Considering the formal charges of the Co 2§ cations, two protons (from the SiOHAI group) can be exchanged with one Co 2* cation. Therefore, 100% exchange should be achieved at a molar ratio of C02*/AI 3. = 0.5 (stoichiometdc ratio). For samples prepared with an C02*/A! 3+ ratio higher than 1, the ir spectra revealed the complete removal of the strong Br~nsted acid sites. The XANES of the samples indicated that the Co 2§ is surrounded by CI~ ions rather than by 02. The t.pod, of NH3 carded out on these samples showed a new desorption maximum of NH3 at a temperature higher than that of NH3 desorbing from the strong Bmnsted acid sites. The formation of these new sites was also shown in
164 the t.p.d, of NO, where an additional desorption maximum was observed on samples containing Co 2§ cations. We assign these sites to (CoCl)* species with Lewis acid character, which remain within the lattice even after carefully washing the zeolite. The number of strong Br~nsted acid sites present after the ion exchange decreased with increasing Co2*/AI3. ratio and reached a value of zero at a Co2*/AI3. ratio of 1.2. This clearly shows that under our solid state ion exchange conditions only one proton from the SiOHAI group was exchanged for one Co cation. We propose that these cations are associated with c r ligands probably as (CoCI)§ groups. The presence of similar groups was already reported for solid state ion exchange of four and five valent cations into ZSM5 (8) and for Cu into ZSM5 (9). The ion exchange carried out in liquid phase did not lead to a complete removal of the strong Br~nsted acid sites. Moreover, by repeating the ion exchange procedure up to five times, an increase over the initial degree of ion exchange of about 30 % was not observed. The ir spectra and the t.p.d. experiments showed that dudng the ion exchange the number of acid sites decreased without causing the formation of new sites in the zeolite. In the CoZSM5 samples prepared by a direct synthesis, the Co was partially substituted into the lattice (substitution of S='), but was also found to be present in Co-oxide clusters. The XANES indicated that the Co atoms are surrounded by O atoms. Co neighbours at short distances were not observed in the EXAFS. The t.p.d, of NH3 and NO showed an additional desorption maximum, which in the case of NH3 was lower in temperature compared to that on the solid state exchanged samples. CONCLUSIONS
Co ions can be incorporated into ZSM5 zeolites by ion exchange methods and by direct synthesis. In the case of liquid phase ion exchange only a partial cation exchange (30%) is achieved even after multiple ion exchange treatments. When the ion exchange is carried out by a solid state reaction a complete exchange (200%) can be achieved at a Co2*/AI3. ratio above 1. The Co cations are associated with c r ligands, formig new sites with Lewis acid character with a stoichiometry of 1:1 between Co 2. and AI3.. The direct synthesis of CoZSM5 results in a lattice substitution of Si with Co and in the formation of small Co-oxide clusters. ACKNOWLEDGEMENTS The work was supported by the "Fonds zur F0rderung der Wissenschaftlichen Forschung" under project FWF P9167. Partial support of this work by the Christian Doppler Society is gratefully acknowledged. We are grateful to P. Ngan for the synthesis of the CoZSM5 samples. REFERENCES B. Delmon, Catal. Lett. 22, 1 (1993). C. T. Douwes and M. Hart, Erd61 und Kohle 21,202 (1968). C. W. Ward, Stud. Surf. Sci. Catal. 16, 587 (1983). J. A. Rossin, C. Saldarriaga and M. E. Davis, Zeolites 7, 295 (1987). H. S Sherry, Ion Exchange (ed. J. Marinsky), Chap. 3 (1969). H. G. Karge, H. K. Beyer and G. Bart~ly, Catalysis Today 3, 41 (1988). A. V. Kucherov and A. A. Slinldn, Zeolites 7, 43 (1987). A. V. Kucherov and A. A. Slinkin, Zeolites 7, 38 (1987). Z. Schay and L. Guczi, Catalysis Today 17, 175 (1993).
I-I.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved. A
NEW
COUPLING
REACTION
BETWEEN
BY
CATALYSED
BETA
165
c~-PINENE
AND
ACETONE
ZEOLITES
J. V'ffal*, J. C. van der Waal and H. van Bekkum Laboratory of Organic Chemistry and Catalysis, Delft University of Technology, Julianalaan 136, 2628 BL, Delft, The Netherlands. Fax (31-15)-782655 Abstract
When pure ketones, like acetone, 2-butanone or cyclohexanone are used as solvents in the isomerization of a-pinene over zeolite beta, products of a coupling reaction between terpenes and the solvent, are formed.
They were identified by GCMS analysis, as a-terpinyi acetone, 1 - ( a -
terpinyl)-butan-2-one and 2-(a-terpinyl)-cyclohexanone, respectively. Introduction
The hydration and isomerization of a-pinene catalysed by diluted mineral acids yields complex mixtures of monoterpenes, alcohols and hydrocarbons. In the presence of some solvents, e. g. acetone, the medium is homogeneous and the main products are a-terpineol, limonene, and terpinolene. Minor amounts of camphene, a -
3
and -~-terpinene, a - and I~-fenchol, isobomeol, bomeol, 1,4- and 1,8-cineol, 13- and y-terpineol, p-cimene and tricyclene are also formed. In absence of water a new product is formed. 5
2
I 1
10 7
Experimental
11
The catalyst (0.50 g) was suspended into
8
9
=l
__
a).__=
_
b) I
110 i
I
I
I
I
20
I
i
I
I
Time (rain)
~'
30
I
I
i
I
the solvent and the mixture heated up to the reaction temperature u 56oc _ under N2. After
i
40
I
Figure 1 m Isomerization of a-pinene over zeolite beta (Si/AI - 40) at 56 ~ C, in the presence of: a) acetone; b) ethyl methyl ketone; c) cyclohexanone. Chromatograms of the reaction mixtures at high conversions of a pinene. 1 - a-pinene; 2 - camphene; 3 ~a-terpinene; 4 limonene; 5 - y-terpinene; 6 - terpinolene; 7 - 13-fenchol;
a delay of 30 minutes to allow temperature stabilization, the reaction was started by adding the terpene used as starting reagent (1.65 mmoles) to the reaction mixture. Samples were taken at regular intervals and analysed by GC using a 50 m X 0.53 mm CP Sil-5 CB capillary
8 - borneol; 9 - a-terpineol; 10 - a-terpinyl acetone; 11 - column. Peak identification was performed by 1-(a-terpinyl)-butan-2-one; 12 - 2-(a-terpinyl)cyclohexanone. GCMS analysis and co--injection of known compounds.
* Universidade Nova de Lisboa, 2825 Monte de Caparica, Portugal
166
179
100
Results and discussion
80
~
60 40
7911 ~s -
ss
20
s9
When (z-pinene isomerization is carried
121
out over zeolite beta, using acetone as solvent, a
I
new product is formed (peak n o 10 in figure 1).
107
The correspondent mass spectrum (figure 2)
161
._IL14g [
] "
194
allows us to identify this substance as a-terpinyl
acetone. .... 40 80 120 160 200 However, the new product is not formed Figure 2 - Mass spectrum corresponding to the peak ng if limonene, a-terpineol or bomeol are used as 10 in the gas chromatogram shown in figure 1. o
starting materials instead of cr
So, the
a-terpinyl acetone must be formed directly from a-pinene.
100 80
This result suggest that an intermediate carbocation is not involved in the formation of the
60
new product. The new product is assumed to be
40
formed
20
by
a concerted
mechanism
9This
hypothesis is supported by the behaviour of the value of the initial rate of formation of the new
~
179 121
L
165
79
/
107 ~ ~L, L. . . . . . . . .
~2
,
.~[19320e
0 "- . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
80
120
160
200
240
product: it goes through a maximum when the Figure 3 - Mass spectrum corresponding to the peak n9 11 in figure 1, obtained by GCMS analysis of the product initial value of the mole fraction of a - p i n e n e of a-pinene isomerization over beta zeolites in the varies from 0 to 1. presence of ethyl methyl ketone, at 56~ C. When the a-pinene isomerization is carried out catalysed by sulfuric acid instead of beta zeolites, in the same conditions, 100
complete
conversion is achieved in about 1 h. However,
$0
products from reaction between terpenes and
80
the solvent are not found. When zeolite HX was
60
17s 191
used as catalyst no formation of new product was observed. These observations suggest that a terpinyl acetone is formed, if not only with beta
40
80
120
160
__| _2 .t 200
l 240
zeolites, at least only with high silica zeolites.
The reaction above described, can also Figure 4 - Mass spectrum corresponding to the peak ng 11 in figure 1, obtained by GCMS analysis of the product take place with other ketones besides acetone. of a-pinene isomerization over beta zeolites in the Experiments of a - p i n e n e isomerization were presence of cyclohexanone, at 56~ carried out using 2-butanone and cyclohexanone, respectively. In both cases the reaction product presents
new chromatographic
peaks (peaks 11 and 12 in figure 1). The respective mass spectra allow to identify these components as 1-(a-terpinyl)-butan-2-one and 2-(a-terpinyl)-cyclohexanone, respectively (figures 3 and 4).
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
167
CATALYSIS OF A UQUID-PHASE DIELS-ALDER-REACTIONBY ZEOUTES Y,EMT AND BETA K. Bomholdt and H.Lechert Institute of Physical Chemistry, University of Hamburg Bundesslr.45, 20146 Hamburg, Germany SUMMARY The liquid phase catalysis of a Diels-Alder-reaction by zeolites Y, EMT and Beta has been studied. The use of a silica binder has an effect on catalyst activity and selectivity, depending on catalyst pretreatment. EMT has similar performance as zeolite Y, Zeolite Beta exhibits a lower activity than zeolite Y. INTRODUCTION The Diels-Alder-reaction is one of the main routes to six-membered rings in organic chemistry. Though it is highly favourabie for e l ~ reasons, the reacSonoften needs high temperature or pressure to take place [1]. Since the conventionally used catalysts, e.g. Lewis-acids like tin tetrachloride have serious drawbacks (work-up of the reaction mixture, environmental problems) it is advantageous to utilize zeontes as catalysts. With zeolites the necessary temperature is lower and very often an increased selectivity for the endoisomer or the =para"-isomeris observed when cyclic dienes or acyclic dienes rest:mcSvelyare used [2,3]. In this paper we investigated the performance of the zeolites Y, EMT and Beta for the reaction of isoprene (1) with methylvinylketone (2) to 4Ac ety I-1 -methy I-1 -cy do hexen -F-
o (1)
(2)
(3)
(4)
(3) and 4-Acetyl-2-methyl-1cyclohexen (4). Furthermore it was attempted to use a silica sol as a binder in order to make particles easier to handle and with well defined sizes.
EXPERIMENTAL The Y-zeolites were commercial products whereas the samples of EMT and Beta were synthesized in our laboratory and calcined in flowing air at 823K. The ammonium forms of the catalysts were prepared by twofold ion-exchange with 2m NH4NO3 at 353K for 1hour. Afterwards the catalysts were washed with water and dried. When a binder was used the catalysts comptsed 40wt% of silica binder. All catalysts were activated at 673K for 5 hours under reduced pressure. For the reaction the catalysts were suspended in 5ml dry methylene chloride and 10mMole of each reactant in 2ml methylene chloride were added via two dropping funnels over 30 minutes. The reaction was carried out for further 2 hours at 273K under nitrogen atmosphere and rapid stirring. Afterwards the solvent and the reactants were evaporated and the product separated from the catalyst by extraction with pentane. Identification was carried out by 1H- and 13C-NMRand the purity and isomer ratio were checked by capillary column GC.
168
RESULTS AND DISCUSSION
Figure 1 shows the conversion for H-Y with binder. The activity of Y (Si/AI = 2.5) is high and the conversion can be further increased by longer reaction times. Zeolite Y with Si/AI = 100 is rather inactive indicating that the number of active, i.e. 100 acid, sites is crucial for catalytic activity. Experiments with non-exchanged zeolite Y with binder did not reveal any activity at all so it is evident that the amorphous silica i--.i rl D 8]binder is completely inactive without pre.C>
treatment. Experiments with Sodalite confirmed that the outer surface of a zeolite only 40plays a minor role. BET surface measure 9 HY, Si/A1100 merits gave neady the same specif'r surface area of 600m2/g for pure zeolite Y and zeolite Y with 40wt% of binder. or I I Obviously, the catalytic mechanism works o 05 1 via adsorption of the ketone at the active amount of catalyst [g] sites, decreasing of the frontier orbital Fig. 1" Activity of zeolite Y with Si/AI = 2.5 and 100 energy gap of the reactants. The activity of H-EMT is slightly lower than that of H-Y (Si/AI = 2.5) and halves for H-EMT with binder. But H-EMT with binder is submitted to an additional ion-exchange, the activity is even higher than that of H-EMT without binder. The selectivity (= (3)/(4)) was enhanced from 17 for H-Y and H-EMT to 20 for HE~
Si/AI 2.5
EMT with binder and up to 30 for H-{zeolite + binder}. This means that active sites are generated on the binder surface upon ion-exchange. The results of experiments with zeolite Beta are presented in the following table: ....
catalyst pretreatment none binder, ion exchancje binder, ion exchange
amount of catalyst 0.9279 0.67g 1.17
conversion 13% 410 650
Zeolite Beta is less active than Zeolite Y (Si/AI = 2.5) but more active than a zeolite Y with Si/AI = 5 although the number of active sites is lower. This implies that either the sites in Beta are more active or the framework structure of spacious intersecting channels offers advantages such as easier diffusion of reactants and products. REFERENCES
[1] [2]
Sauer,J., Sustmann, R., Angew. Chem., 92, 773, (1980) Ipaktschi,J., Z. Naturforsch., 41b, 496, (1986)
[3]
Hochgr~ber-Paetow, D., Lechert, H., Proc. of the 9th IZC, (von Ballmoos, R. et al.,eds), Butterworth-Heinemann, Stoneham (1993)
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All fights reserved. ISOMERIZATION OVER
PLATINUM
OF
169
n-HEXANE
LOADED
ZEOLITES
J e o n g - K y u Lee and H y u n - K u Rhee Department of Chemical Engineering, Seoul National University K w a n a k - k u , Seoul 151-742, Korea SUMMARY The isomerization of n - h e x a n e w a s studied over bifunctional catalysts, P t - H M , P t - H Z S M - 5 , and P t - H Y , in a f i x e d - b e d flow reactor. In particular, the effects of the pretreatment conditions and the platinum content on the catalytic activity for the isomerization were investigated. T h e catalyst calcined and reduced at 300-350"C and 500~2, respectively, showed the g r e a t e s t activity. Appropriate metal/acid balance w a s achieved by adding as small amount of platinum as 0.2 wt%. With equivalent metal sites the activities and stabilities of the catalysts as well as the product distributions were governed by the acidity of zeolites and the pore size. In case of P t - H M c a t a l y s t the acidity increased with the Si/A1 ratio and there existed an optimum value of the Si/A1 ratio with respect to the stability of the c a t a l y s t and the selectivity of isomers. Based on the experimental results the isomerization of n - h e x a n e was found to proceed by a sequence of reversible reactions. INTRODUCTION Isomerization of n - p a r a f f i n s is an industrially important o c t a n e - u p g r a d i n g process. Thermodynamic consideration of isomerization reactions reveals that the lower the reaction temperature the greater the increase in the octane number[I] and t h u s chlorinated alumina base catalysts, which can be operated at low temperatures(383-453K), are regarded as the best bifunctional catalysts. However, t h e s e catalysts present corrosion problems and are sensitive to impurities, and hence their usage requires severe pretreatment of feedstocks. T h e noble metal loaded zeolite catalysts axe free from these d r a w b a c k s and can be operated at a relatively low temperature. In this study the catalytic activities of various platinum loaded zeolites for the isomerization of n - h e x a n e were examined, compared with one another, and then analyzed in connection with the results from characterization of the catalysts. We also investigated the effects of the p r e t r e a t m e n t conditions, the platinum content and the Si/A1 ratio on the catalytic activity. T h e reaction p a t h w a y s for the isomerization of n - h e x a n e w a s deduced by analyzing the experimental data. EXPERIMENTAL Platinum loaded zeolite catalysts, P t - H Z S M - 5 ( S i / A I = 2 6 . 0 ) , Pt-HM(Si/AI=5.0, 12.5, 22.5) and Pt-HY(Si/AI=2.8), were prepared by i o n - e x c h a n g e method [2] with Pt(NHa)4C12 in competition with NH4NO3. The calcination and reduction of the samples were carried out under various conditions. The acidic properties of the samples w e r e examined by T P D of ammonia and F T - I R spectroscopy of p y r i d i n e - a d s o r b e d c a t a l y s t s whereas T E M , H2 chemisorption and H2-O2 titration in a pulse s y s t e m were employed to characterize the metal site. T h e reaction experiments were conducted in a f i x e d - b e d flow reactor with H2/n-Ce molar ratio of 6.0. RESULTS AND DISCUSSION The pretreatment conditions appeared to have a significant influence upon the metal cluster distribution on the zeolites as well as the dispersion level and thereby upon the activities of bifunctional catalysts for the isomerization of n - h e x a n e . The catalyst
170
calcined and reduced at 3 0 0 - 3 5 0 ~ and 500~ respectively, showed the greatest activity. T h i s is consistent with the previous reports[3,4] which were concerned with the maximum hydrogenation activity and the dispersion value of platinum on P t - X , P t - Y and P t - H Z S M - 5 . The isomerizing activity over bifunctional catalyst was m a r k e d l y enhanced in comparison to that over pure zeolite catalyst. It is to be noted that appropriate metal/acid balance was achieved by addition of as small amount of platinum as 0.2 wt%. The temperature giving m a x i m u m yield of isomers was decreased HY > HM > HZSM-5. T h i s sequence turned out to be the same as acid site strength of zeolites obtained by T P D of ammonia and F T - I R p y r i d i n e - a d s o r b e d catalysts. Among the three different platinum Pt-HM
gave
rise
to
the
largest
yield
of isomers
and
the
in the order of the order of the spectroscopy of loaded zeolites,
highest
selectivity
to
dimethylbutanes(DMB's). Over P t - H Z S M - 5 catalyst, the formation of D M B ' s w a s considerably hindered by the medium sized pore although the conversion of n - h e x a n e w a s the largest. Due to the low acidity, the conversion of n - h e x a n e to isomers over P t - H Y c a t a l y s t s was limited by the thermodynamic equilibria. Both the P t - H Z S M - 5 and the P t - H M catalysts were found stable within the range of experimental conditions of this study whereas rapid deactivation by coking was observed at high reaction temperatures over P t - H Y catalsyt. In case of P t - H M catalyst, the acidity increased with the Si/A1 ratio and there existed an optimum value of the Si/A1 ratio with respect to the stability and activity of the catalyst as well as the product selectivities. Based on the experimental results, it was found that while m e t h y l p e n t a n e s ( M P ' s ) were the primary products formed directly from n - h e x a n e , 2,3-DMB was the s e c o n d a r y product formed from M P ' s and 2,2-DMB was the tertiary product formed f r o m 2,3-DMB. Therefore, it may be concluded that the reaction p a t h w a y s for the isomerization of n - h e x a n e would be represented as follows : n-C6 ~- MP's ~ 2,3-DMB 2,2-DMB. CONCLUSIONS P r e t r e a t m e n t conditions of platinum loaded bifunctional catalysts appeared to a s s u m e an important role for the isomerization of n - h e x a n e and should be carefully selected. Metal/acid balance was achieved by loading 0.2 wt% of platinum. Consideration of both the catalytic activities and the yield of D M B ' s revealed that zeolites with 12 or more membered oxygen ring would be favored and that the stability and the s t r e n g t h of the acid sites should be taken into account. It was found that M P ' s were the primary products, 2,3-DMB the secondary product and 2,2-DMB the tertiary product formed from 2,3-DMB. T h e isomerization of n - h e x a n e may be regarded to proceed by a sequence of reversible reactions.
REFFERENCES 1. A. P. Bolton, in Zeolite Chemistry and Catalysis edited by J. A. Rabo, ACS Monograph 171, Washington, D. C., 714(1976). 2. G. E. Giannettoe, G. R. Perot and M. R. Guisnet, Ind. Eng. Chem. Prod. Res. Dev., 25, 481(1986). 3. D. Exner, N. Jaeger, K. M~ller & G. Schulz-Ekloff, J. Chem. Soc., Farady Trans., 78(1), 3537 (1982). 4. G. Giannetto, G. Perot & M. Guisnet, in Catalysis by Acids and Bases edited by B. Imelik, C. Naccache, G. Coudurier, Y. Ben Taarit & J. C. Vedrine, Elsevier, Amsterdam, 265(1985).
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
171
BENZENE ALKYLATION WITH ETHANOL OVER SHAPE SELECTIVE ZEOLITE CATALYSTS Radhakrishna Ganti and Subash Bhatia Department of Chemical Engineering, Indian Institute of Technology, Kanpur-208016, India
SUMMARY Selective formation of ethylbenzene using benzene and ethanol over HZSM-5 has been studied in the temperature range of 548-648 K at atmospheric pressure. The activity and selectivity of the catalyst showed m a x i m u m conversion at a particular Si/AI ratio of the HZSM-5 catalyst. The experimental data were analyzed based on the p r o d u c t pattern using the L a n g m u i r - H i n s h e l w o o d Hougen-Watson approach. INTRODUCTION Synthesis of ethylbenzene, a raw material for styrene manufacture, in the one step alkylation of benzene with ethanol over shape selective high silica zeolite catalysts is of great commercial importance. Most of the studies reported on the alkylation of benzene have been to improve the selectivity of ethylbenzene ~-3, little is known to be reported on the kinetics of the reaction. This selectivity study was carried out with the following specific objectivities: 1. Kinetics of benzene alkylation with pure ethanol over HZSM-5 catalyst 2. To derive a kinetic model based on the reaction mechanism 3. To estimate the kinetic parameters of the model 4. Effects of important variables such as b e n z e n e / e t h a n o l molar ratio, silica/ alumina ratio of ZSM-5 and reaction t e m p e r a t u r e over selectivity and conversion. Alkylation was carried out in a fixed bed flow reactor at atmospheric pressure. The catalyst (about 2-3 gram) was placed in an electrically h ea t ed stainless steel reactor (1.8 cm i.d. x 7.5 cm length) and reduced in an atmosphere of hydrogen. The reactant mixture of benzene and ethanol was p u m p e d to the reactor through a preheater by a metering pump. Liquid samples were separated through a 1.6mm x 4 m long stainless steel column packed with 5% B e n t o n e - 3 4 and 5% diisodecylphthalate on 60 - 80 mesh chromosorb W using a CIC chromatograph. Experimental data were taken at t e m p e r a t u r e s in the range 5 4 8 - 648 K over HZSM-5 zeolite at W / F values between 30 and 80 g c a t / g m o l / h r at b e n z e n e / ethanol molar ratios of 3/1 to 6 / I . Conversion of benzene, selectivities of
172 ethylbenzene, diethylbenzene and the activity of the catalyst were calculated for each experimental run. The silica/alumina ratio of the HZSM-5 zeolites was varied from 30 - 280. The activity and selectivity of the catalyst showed maximum conversion at a particular silica/alumina ratio of the HZSM-5 catalyst. Both ethylbenzene and diethylbenzene selectivities were found to decrease with increasing temperature. At higher benzene/ethanol molar ratios, the selectivity towards ethylbenzene decreased. Benzene(A) and ethanol(B) react to form ethyl benzene(C) as the primary product and a mixture of diethylbenzenes (ortho, meta and para), considered as a single c o m p o u n d in the present study due to low yields. The overall reaction is represented as: Benzene
+
Ethanol
---> Ethylbenzene
+
Diethylbenzene (DEB) (1)
The surface reaction model which fitted the experimental data is given by equation (2) as: r=
ksKaKaPaPa (1 + KApa + Kap B + KcPc + Kop o)2
(2)
Table 1 gives the kinetic adsorption constants thus estimated by non-linear regression 4 using the Marquardt algorithm.
Table 1
Reaction parameters obtained using non-linear regression
Temperature
KA
K
KB
KC
KD
(arm -1)
ks
(gmol/hr/gca0
548
0.400
1.660
6.50
38.57
0.200
573
0.332
1.580
4.47
40.00
0.382
598
0.363
0.526
5.05
16.20
1.215
623
0.288
0.585
4.50
14.99
1.350
648
0.150
1.468
3.50
21.36
2.500
The above kinetic model (equation (2)) predicted the conversions and rates comparable with the experimental values. The deactivation of the catalyst was completely absent during 20 hours time on stream test.
173 REFERENCES
[1] F. Fajula, M. Lambert and F. Figueras, "Respective Influence of the geometric and chemical factors in the conversion of aromatics over acidic zeolites". In: International Symposium on Zeolites as Catalysts, Sorbents and Detergent Builders: applications and innovations, Wfirzburg, Elsevier Science Publications, Amsterdam, September 1988. [2] Z. Hwang, S. Yu and Y. Qui, Huagong Shiyou 17(8) (1988) 477-482 (Chinese). [3] P. Levesque and L.H. Dao, "Alkylafion of Benzene using an aqueous solution of ethanol", Appl. Catal. 53 (1989) 157-167. [4] J.I. Kuester and J.H. Mize, "Optimization Techniques with Fortran", McGraw Hill Book Co., New York, 1973, 240-250.
H.G. Karge and J. Weitkamp (Eds.) 174
Zeolite Science 1994: Recent Progress and Discussions
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
E F F E C T O F T H E A L U M I N U M C O N T E N T AT T H E E X T E R N A L S U R F A C E O F T H E ZSM-5 IN THE D I S P R O P O R T I O N A T I O N O F E T H Y L B E N Z E N E M. J. B. Cardoso 2 , E. L. Gomes 1. D. Cardoso ~ 1 Chemical Engineering Department, Federal University S. Carlos, 13565 - S. Carlos - SP - Brazil 2 Petrobr~is/CENPES / Dicat - 21910 - R. Janeiro - RJ - Brazil INTRODUCTION One of the main properties of the ZSM-5 is the possibility to form preferentially paraalkylated compounds. These compounds, e.g., p-xylene, p-styrene, are industrially very important but their formations are thermodynamically unfavorable: about 20 to 25% among the other two less important meta and ortho-isomers. The para-selectivity of the ZSM-5 is due to the fact that the diameters of its pores are very close to the kinetic diameter of the benzene ring (about 5,5 A). In consequence, the difusivity of the less bulky para-isomer in this zeolite is about 1000 times faster [1]. Several authors have found that the para-selectivity increases using larger crystals of the ZSM-5. Two main explanations have been done for this behavior: i) the diffusion path increases with the crystal size, favoring the diffusion of the less bulky compound [1,2], ii) the larger crystals have less external surface area and therefore less acid sites at the external surface, which are not para-selective [3,4]. EXPERIMENTAL The aim of this work is to verify the influence of the external acid sites in the paraselectivity of the disproportionation of the ethylbenzene. The synthesis of the zeolite was carried out using a Si/Al = 50 or 75, n-butylamine as template agent and sodium trisilicate as silicium source. To obtain crystals with the same global composition and different sizes, the same gels were aged from l to 7 days at 40 o C and then, for the crystal formation, maintained 21 hours at 170 ~ C. The crystal were characterized by X-Ray diffraction, Scanning Electron Microscopy and X-Ray Photoelectron Spectroscopy. The catalytic disproportionation of ethylbenzene was carded out in a flow micro-reactor at 325 ~ C at conversions of ethylbenzene between 10 and 20%. RESULTS In all preparations, the crystals of the ZSM-5 presented well-formed hexagonal prisms with crystallinity higher than 90%. As found with other zeolites, the crystal sizes (c axis) diminished with the aging time (Fig. 1) due to the greater number of crystal germs. The aging time had no influence in the global composition of the crystals. The XPS analysis reveals, however, an enrichment of aluminum at the outer surface with the aging time, indicating that it is incorporated to the crystals at the latter steps of the synthesis. With respect of the catalytic properties, the formation of para-diethylbenzene increases with the crystal size, but for the same size, depends on its Si/A1 ratio. However, the formation of the para-diethylbenzene decreases with the number of aluminum at the external surface of the crystal, regardless of the global Si/A] ratio (Fig 2). This indicates that in this reaction the para-selectivity depends only on the number of acid sites at the external surface. These sites are responsible for non para-selective reactions, specially the isomerization of the para to metadiethylbenzene. The dependence of the para-selectivity on the crystal size is obviously considered in this proposition, as the larger crystals have a lower specific external surface, and thus, less external acid sites.
175
L e n g t h ( ~t m ) 20 ,\\ 15"
Si/AI = 75 " \\ e,
10" ~ ' , , , ,
I ' I ' I ' I ' T i m e (Days) 0 2 4 6 8 Fig. 1 Influence of the aging time in the size of the crystals of ZSM-5 % p-Diethylbenzene 80 0 Si/AI = 50 e Si/AI = 75 ....... Equilibrium
70 60 t
50
ft.----
40 0 ...................................................................................................................... I
0
'
I
1
'
I
'
2
I
'
3
I
4
External Sites/u. c.
Fig. 2: Influence of the number of aluminum external sites in the p-selectivity of ZSM-5 REFERENCES (1) (2)
N.Y. Chen, W. W. Kaeding, F. G. Dwyer, J. Am. Chem. Soc., 101, 6783, (1979) D.H. Olson, W. O. Haag, in "Relationship Between Structure and Reactivity", ACS, 248, (1984)
(3)
J. Kim, S. Namba, T. Yashima, Zeolites, I1, 59, (1991)
(4)
G. Paparatto, et alli, J. Catal., 105,227, (1987)
ACKNOWLEDGMENTS This work received financial support from "Fundagao de Amparo h Pesquisa do Estado de S. Paulo".
H.G. Karge and J. Weitkarnp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
176
METHANOL CONVERSION TO HYDROCARBONS OVER ZSM-5. USE O F I S O T O P E S FOR M E C H A N I S M S T U D I E S . Ivar M. Dahl 1, Stein Kolboe 2 and Per Ola Ronning 2 1) Department ~ H y ~ b o n Process Chemistry, SINTEF-OSLO P. O. Box 124, N-0314 Oslo, Norway. 2) Department of Chemistry, University of Oslo, P. O. Box 1033, N-0315 Oslo, Norway. SUMMARY Methanol conversion over H-ZSM-5 has been studied in a micro reactor using a mixture of 13C-methanol and propene (isopropanol). The products were analyzed with a GC-MS instrument allowing an isotopic analysis of the emerging reaction products. INTRODUCTION H-ZSM-5 is an efficient catalyst for converting methanol into hydrocarbons [1,2]. The reaction may also be carried out over a large number of other protonated zeolites or other zeo-type materials [3]. The reaction mechanism is still not clarified [2,4]. As a means of obtaining additional information on the methanol to hydrocarbons reaction over zeolites we have investigated the reaction between 13C labeled methanol and (12C) propene (made in situ from isopropanol) over H-ZSM-5. The isotopic composition of the reaction products was measured by GC-MS. From a simplistic view, there are two main mechanism types for olefine formation in the MTH reaction:
A: A consecutive build up type mechanism with one carbon from methanol adding in each step: CH3OH --> C2H4 --> C3H6 --> C4H8 --> 05H10--> ...... B: A "hydrocarbon pool" type mechanism which in a somewhat oversimplified form may be represented by scheme 1. We have tried to discriminate between the two mechanism types, A and B, by reacting isopropanoi (as a propene source) with 130 labeled MeOH. We have chosen to use the C2H4 molar ratio MeOH:iPrOH=3:4. 12C: 13C=4:1. If we then look at the isotopic composition of the butenes formed, we should expect from the type CH3OH-->(CH2) n ~ C3H6 A mechanism above to find only singly and quadruply labeled butene (primary product, scrambling leads to a more complex C4H8 pattern). Type B mechanisms might lead to a random distribution. Scheme 1
1L
1L
EXPERIMENTAL The reactions have been run at 400 ~ and 1 bar total pressure with 30 mg catalyst and a methanol equivalent WHSV of 27 h-1. Helium (99.99+ %), partial pressure 0.6 bar, was used as diluent. Methanol: 99 % 13C1-13OH (Cambridge Isotope Laboratories) or
177
ordinary reagent grade methanol (Merck). lsopropanol: water-free reagent grade. The ZSM-5 was prepared according to the literature. Elemental composition was determined by ICP; authenticity and crystalline purity was verified by X-ray powder diffraction. The experiments were performed using a high precision syringe pump (homemade) for feeding the liquid reactant mixture to an evaporator, and a Brooks Mass Flow Controller for the helium diluent. The water formed was condensed out (4 ~ and the products were analyzed with a Hewlett Packard GC/MS system, model 5890/5970 (equipped with a J&W Scientific DB1, 60m, 0.2mm column). RESULTS Gross product formation and the isotopic composition of selected products (ethene, propene, t-2-butene, 2-methyl-2-pentene, t-2-methyl-3-pentene, an unidentified branched hexene, and p-xylene) have been measured for several TOS. Reported here is TOS=2h. Important findings are: Propene emerges virtually un-reacted. Methanol may possibly methylate propene to a limited extent to form butenes, but this reaction is not a major reaction path for methanol. For propene the major reaction path appears to be dimerization to hexene isomers. (C6 contains little 13C.) The atomic ratio 120:130 in the feed is 4:1. In spite of this the ratio 12C:130 in xylene is only 1:2, showing that the aromatic compounds are not formed rapidly from alkenes by hydrocarbon interconversion reactions. Methanol conversion is much faster. Ethene is essentially a primary product from methanol. The isotopic composition (120=12C, 120=130, 130=130) iS at variance with a possible formation by cracking of higher aikenes. Like in previous works on methanol conversion over SAPO-34 [5] a consecutive mechanism where each alkene is formed by methylation of the next lower homologue is not tenable. A carbon pool mechanism is in agreement with the results. This carbon pool can, however, hardly consist simply of C 1 entities (methoxy groups) since all products also exhibit a very sizeable 120 content. TABLE 1 EFFLUENT COMPOSITION* mbar Carbon %
TABLE 2 ISOTOPE CONTENT OF PRODUCTS % C2 C3 C4 C5 C6 xylene
Ethene Propene DME MeOH+iC 4 rest C4 C5 C6 C7 Xylene
12C 13C
13.4 126.6 6.6 17.9 30.6 10.7 9.3 2.0 3.0
3.8 53.7 1.8 2.5 17.3 7.6 7.9 2.0 3.4
32 68
93 7
77 23
73 27
*Main components REFERENCES 1. C.D. Chang and A. J. Silvestri, J. Catalysis 47 (1977) 249. 2. C.D. Chang, Cata!. Rev.-Sci. Enq. 25 (1983) 1 and 26 (1984) 323. 3. S.W. Kaiser, Arab; J. Sci. En.q. 10 (1985) 361. 4. G.J. Hutchings and R. Hunter, Catalys!s Today 6 (1990) 279. 5. I.M. Dahl and S. Kolboe, Catalysis Letters 20 (1993) 329.
80 20
34 66
178
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All fights reserved.
Fisher-Tropsch Synthesis on Ruthenium Supported Titanium Silicate Catalysts. R.Carli, C.L.Bianchi, R.Bernasconi, G.Frontini and V.Ragaini Department of Physical Chemistry and Electrochemistry, University of Milan, Via Golgi 19, 20133 Milan, Italy. Introduction
CO hydrogenation on classical Fisher-Tropsch ( F T ) catalysts leads to the formation of a wide distribution of products, according to Anderson-Schultz-Flory (ASF) chain-growth probability. Attempts in order to control the product selectivity have been made, involving molecular sieves as catalyst support for metals which are known to be active catalysts in FT synthesis [1-3]. Geometric or diffusional constrains on the product molecules coupled with strong acid functions greatly influenced the normal chain-growth process in FT synthesis. Among the many studies, a large variety of molecular sieves has been used, such as zeolites of FAU, MFI, MOR, LTL and ERI structure types in their acidic or alkaline forms [4 and ref. therein]. There have been a significant number of recent promising developments in FT catalyst technology based on zeolites, leading to a new class of zeolite-based multifunctional metal catalysts. In this work it has been proposed to combine the shape selectivity with the electronic properties of the well-known FT-catalyst support TiO 2, exploiting the unique characteristics of the titanium silicate, ETS-10, recently developed by Engelhard [5].
Materials [] Titanium Containing Molecular Sieves
Molecular sieves, containing titanium in framework position, have been synthesized with MFI [6-7] and MEL [8-9] structure types. These titanium-silicalites, named TS(1) and TS(2), show interesting catalytic activities in oxidation reactions probably due to titanium centers in tetrahedral coordination [10-11]. It is important to note that these materials have no acid sites, because of framework-titanium is present as Ti(IV). Consistently with these characteristics, no significant effects due to metalsupport electronic interactions have been pointed out on TS(1)-supported ruthenium FT-catalyst [12]. In order to allow a suitable interaction between Ti and Ru centers in the final catalyst, a new class of titanium-containing molecular sieves composed of tetrahedral and octahedral oxide polyhedra have been used as catalyst supports. Titanium silicates such as ETS-4 and ETS-10, recently synthesized by Engelhard [13,5] have all the properties of classical molecular sieves with small (ETS-4) or large (ETS-10) pore channel systems. In spite of a lack of strong acidic functions, ETS-10 has a pore diameter of about 8 A and a BET surface area of 300 m2/g. These important characteristics make ETS-10 molecular sieve a suitable catalyst support.
[] Catalyst Preparation
The final form of the catalyst were prepared by impregnation of NaY (LYZ-82, from UOP) and ETS-10 (from Engelhard) samples with a solution of Ru(AcAc)3 in ethanol (both from Fluka). The recovered powders, calcined at 4 5 0 ~ for 12 hr, were reduced in flowing hydrogen at 3 5 0 ~ for 4 hr. All the samples were characterized by means of ESCA measurements, H2-chemisorption, ICP-AES analyses. The content of Ruthenium for all the samples were 1% wt.
179
Results and Discussion The samples were tested in a bench scale reactor designed for FT-synthesis. The testing procedure was as follow: 1 g of fresh catalyst were packed in copper coated stainless steel reactor; the sample was activated in flowing H 2 (12 I/hr) at 3 5 0 ~ and 8 bar for 12 hr; the FT-reaction were carried out with a mixture of CO/H 2 (1:2, W H S V = 1 hr -1) at 235+300~ and 5 bar for 3 hr. The activity of the catalyst samples are summarized in Table 1.
Table 1: Catalytic Activities sample
Temp.~
Ru-NaY
275
7.1
72.6
3.2
24.1
0.5
Ru- ETS- 10 (Na form)
235 275 300
2.9 8.5 25.6
42.3 53.7 60.6
11.4 7.0 3.3
46.3 39.3 36.1
2.0 1.1 0.7
Ru-ETS-IO (K form)
235 275
3.7 11.3
33.5 43.4
36.0 33.5
30.5 23.1
1.8 3.3
CO Cony. % CH 4 % CO 2 % C2+ % C3=/C 3
As one can infer from the data reported in Table 1, it is very interesting to note the higher activity of ETS-catalysts toward olefins production, compared to the reported one for Ru-NaY. While the selectivity to C 1 products (CH4+CO 2) decreases, the selectivity to hydrocarbons C 2+ increases from Ru-NaY to Ru-ETS samples. These results are due to the particular interactions between ETS support and Ru centers.
References [1] R.Oukaci, A.Sayari and J.G.Goodwin, J.Catal., 102(1986)126 [2] R.Oukaci, A.Sayari and J.G.Goodwin, J.Catal., 107(1987)471 [3] R.Oukaci, A.Sayari and J.G.Goodwin, J.Catal., 110(1988)45 [4] C.H.Bartholornew, in "New Trends in CO activation", L.Guczi (ed.), Studies Surf.Sci. and Catal., Vo1.64, Elsevier, Amsterdam, 1991 [5] S.M.Kuznicki, US Pat.4,853,202, (1989) [6] M.Taramasso, G.Perego and B.Nortari, US Pat. 4,410,501, (1983) [7] A.Thangaraj, R.Kumar, S.P.Mirajkar and P.Ratnasamy, J.Catal., 1 31 (1991 ) 1 29 [8] G.Belussi, A.Carati, M.G.Clerici, A.Esposito, R.Millini and F.Buonomo, Belg.Pat. 1,001,038, (1989) [9] J.S.Reddy, R.Kumar and P.Ratnasamy, Appl.Catal., 58(1990)L1 [10] A.Thangaraj, R.Kumar, S.P.Mirajkar and P.Ratnasamy, J.Catal., 1 31 (1 991)294 [11] J.S.Reddy, R.Kumar and P.Ratnasamy, J.Catal., 130(1991)440 [12] R.Carli, unpublished results. [13] S.M.Kuznicki, US Pat.4,938,939, (1990)
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
180
Synthesis and Catalytic Properties of Extra-Large Pore Crystalline Materials for n-Hexadecane Cracking W. Reschetilowski, K. Roos, A. Liepold, Karl-Winnacker-lnstitut der DECHEMA e.V., Theodor-Heuss-Allee25, D-60486 Frankfurt, Germany M. StScker, R. Schmidt, A. Karlsson, D. Akporiaye, E.Myhrvoid, SlNTEF Oslo, Box 124 Blindem, N-0314 Oslo, Non~ay Introduction
9
The Fluid Catalytic Cracking process (FCC) is of paramount importance in petroleum refining [1]. At present, besides an active matrix, the active component of the cracking catalyst is zeolite Y and/or ZSM-5, both of which are limited in the processing of heavier oil fractions due to the restriction caused by their pore dimensions. The new zeotype/mesoporous materials VPI-5 [2], Cloverite [3] and MCM-41 [4] open up interesting perspectives for the conversion of heavier feedstocks because of the accessibility of long-chain and/or bulky molecules to the active centres. This paper presents the synthesis of and discusses the results obtained by using Si-VPI-5 and MCM-41 as catalysts in n-hexadecane cracking in comparison with a commercial FCC catalyst. Experimental " The commercial equilibrium standard catalyst based on zeolite Y was supplied by GRACE GmbH (A1203 42.2 wt.%; 56.2 wt. % SiO2) and the samples of Si-VPI-5 (Si/AIg~ = 0.4) and MCM-41 (Si/AI = 17.3) were prepared by hydrothermal crystallization. The samples were activated beforehand by heating a shallow bed of the catalyst in a crucible ( RT to 120"C, 5 ~ flowing nitrogen ; 120"C for 3 h, flowing nitrogen ; 120 to 590"C, 5 ~C/min, flowing nitrogen ; 590"C for 16 h, flowing synthetic air). MAT (Microactivity Test) equipment according to ASTM D 3907-92 was used to test several types of catalysts with n-hexadecane as feed. Conversion and selectivity investigations were carried out using GC-FID ( VEGA 6300-01, Carlo Erba ) with two different columns for the analysis of crack gas (PLOT, GS-AL 30 m x 0.53 i.d., Megabore) and syncrude (DB-1, 30 m x 0.53 i.d., Megabore). To ascertain the amount of coke on the catalyst an elemental analyser (1106, Carlo Erba) was used. For additional characterisation adsorption/desorption investigations were carried out. Results and Discussion
9
To standardize the MAT testing and to compare conversion and selectivity, a commercial equilibrium standard catalyst was used. The optimal performance of a cracking catalyst will predominantly be the production of syncrude (liquid phase) with a high octane number to get an optimum yield of transport fuels with less gas and coke. If a comparison is made between MCM-41 and Si-VPI-5, the conversion is found to be identical and the syncrude/gas yield almost identical (Fig. 1).
181 Furthermore, compared to the standard catalyst, it is evident that these initial results with the pure materials nearly attain the catalytic properties of the standard catalyst without any further modification. In addition, no activation decay was observed by cyclic regeneration and MAT testing of these extra-large pore materials. Comparison of the pore volume distribution of the zeotype/mesoporous materials used with that of the standard catalyst indicates (Fig. 2) a marked increase in the dimension of the pores inside these new materials. Proceeding from this insight into porosity properties, the cracking of longer or even bulkier molecules than n-hexadecane as the model feed is proposed.
0"0251 Si-VPI-5 .,..-.. .., .~
0.020-~ 0.015 .~ 0.010
!
i.""'.'" /Standab
/,
o oo i ...~.,/:;'
'.
"
","
.
o . o o o J ~ 0
Fig. 1:
Comparison of syncrude / gas and coke yields and conversion of the investigated materials
Fig. 2:
1
2 3 Pore Diameter X (nm)
4
Dubtnin-Stoeckll pore size dtstrtbuUon for standard catalyst. SI-VPI-5 and MCM-41
Conclusion " By optimizing their catalytic properties there is a great possibility of developing the new zeotype/mesoporous MCM-41 and Si-VPI-5 as cracking catalysts for more effective conversion of heavy gas oil. Acknow.ledgem enl;s 9 The authors gratefully acknowledge financial support from the Commission of the EC under the JOULE II Programme and the kind assistance of EURON S.p.A. and GRACE GmbH. References
[1] [2] [3]
[4]
Wojciechowski, B.W. and Corma, A., (1986), Catalytic Cracking : Catalysts, Chemistry and Kinetics, Marcel Dekker, New York. Davis, M.E., Saldarriaga, C., Montes, C., Games, J., Crowder, C., Nature, (1988), 331,698-699. Estermann, M., McCuster, L.B., Baelocher, C., Merrouche, A., Kessler, H., Nature, (1991 ), 352, 320-323. Kresge, C.T., Leonowicz, M.E., Roth, W.J., Vartuli, J.C., Beck, J.S., Nature, (1992), 359, 710-12.
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H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
CONVERSION OF ETHANE INTO AROMATIC HYDROCARBONS ON ZINC CONTAINING Z S M - 5
ZEOLITES - ROLE OF ACTIVE CENTERS A. Hagen, F. Roessner
University of Leipzig, Faculty of Chemistry and Mineralogy, Institute of Technical Chemistry, Linnestr. 3, D-04103 Leipzig, F.R.G. SUMMARY
Zinc ions located at cationic positions of ZSM-5 are effective centers for the activation of ethane and catalyze further reactions to aromatic compounds. However, the rate of aromatization of ethene is enhanced in the presence of Brmnsted acid sites. INTRODUCTION
Investigations concerning the conversion of lower paraffins into aromatic hydrocarbons have been forced during the last years. ZSM-5 zeolites modified with zinc are known to enhance the conversion on one hand and the selectivity for the formation of aromatics on the other. However, the mechanism of the complex aromatization process as well as the roles of active sites involved are still in discussion. In this work we investigate the aromatization of ethane on zinc containing ZSM-5. Results on mechanical mixtures of various components possessing different acid properties should contribute to the discussion about the role of active centers. EXPERIMENTS
H-ZSM-5 was synthesized without template (Si/AI=15, crystallinity nearly 100 %). Starting from this parent material a HNa-ZSM-5 was prepared by 3-fold ion exchange with NaNO 3 solution at 353 K. Zinc was incorporated by mechanical admixing of ZnO to zeolite or ion exchange with Zn(NO3)2 solution at 353 K, denoted as ZnO+Zeolite and Zn-Zeolite, respectively. Samples were in situ pretreated at 723 K in air flow for 2 h. Reactions were carried out in a plug flow microreactor at 773 K, atmospheric pressure and GHSV=600 v/vh (pure ethane). Products were analysed by on line GC. RESULTS AND DISCUSSION
Fig. 1 shows the results of ethane conversion on various mechanical mixtures of the following components: ZnO supported on SiO2 (ZnO/SiO=), Na-ZSM-5, H-ZSM-5
183
and ZnNa-ZSM-5. For comparison, theoretical product distribution determined by addition of yields on single components was added. A synergetic effect with respect to the yields on the single components can be observed on mechanical mixtures of ZnO and Na-ZSM-5 (ZnO+Na-ZSM-5)
and ZnO
Fig. 1 Product distribution on mechanical mixtures after 2 h time on stream at 773 K
supported on SiO 2 and H-ZSM-5 (ZnOISiOz+H-ZSM-5). However, experimental yields correspond to theoretical ones on ZnNa-ZSM-5+H-ZSM-5. Ethene is main product on ZnO+Na-ZSM-5 whereas aromatic hydrocarbons are formed to a large extend on ZnO/SiO2+H-ZSM-5. I.r. investigations reveal traces of Bronsted acid sites in Na-ZSM5 which are completely exchanged by zinc ions at 773 K via solid state ion exchange (SSIE) in ZnO+Na-ZSM-5 111. Furthermore, SSIE takes place in ZnO+H-ZSM-5 121. Consequently, zinc species at cationic positions of ZSM-5 are effective centers for the activation of ethane to form ethene. In the absence of Bronsted acid sites formation of aromatic hydrocarbons is possible on zinc species. However, the rate of further reaction of ethene to aromatics is enhanced by Bronsted acid sites. On the other hand, formation of methane increases. Due to the acid conditions during the introduction of zinc via ion exchange of Na-ZSM-5 in aqueous solution as well as to the PlankHirschler-mechanism also Bronsted acid sites were created in the so formed ZnNaZSM-5. An increase of concentration of these sites by addition of H-ZSM-5, however, does not enhance aromatization activity. Therefore, back spillover of hydrogen discussed in the literature for aromatization of lower paraffins 13/should be excluded in the studied system. REFERENCES 1 A. Hagen, F. Roessner, Proc. Int. Symp. on Zeolites and Microporous Crystals, Nagoya (1993)in press 2 F. Roessner, A. Hagen, U. Mroczek, H.G. Karge, K.-H. Steinberg, Stud. Surf. Sci. Catal., 75 (1993) 1707 3 R. Le Van Mao, L. Dufresne, J. Yao, Appl. Catal. 65 (1990) 143
H.G. Karge and J. Weitkamp (Eds.)
Zeolite Science 1994: Recent Progress and Discussions
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Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All fights reserved.
CONVERSION OF n-BUTANE INTO AROMATIC HYDROCARBONS OVER H-ZSM11 AND G a - Z S M - I I Z E O L I T E CATALYSTS
Kumar, N., Lindfors, L..E., Abo Akademi University, Laboratory of Industrial Chemistry, Biskopsgatan 8, FIN-20500 ~BO, FINLAND. Telefax 358-21-654 479 SUMMARY Conversion of n-butane into aromatic hydrocarbons, mainly benzene, toluene and xylenes, over H-ZSM-11 and Ga-ZSM-11 zeolite catalysts was studied at 713 K,743 K, 773 K and 803 K at a constant WHSV. The effect of gallium was studied by preparing Ga-ZSM-11 zeolite catalysts with Ga contents between 0.5 to 2.5 wt%. The acidic properties of H-ZSM-11 and Ga-ZSM-11 having different Ga contents were studied by using TPD spectra of ammonia.
INTRODUCTION
Light alkanes can be converted into hydrogen and valuable aromatic hydrocarbons, using high silica zeolites of the pentasil family (1). Modification of the proton form of these zeolites by metals such as Ga, Zn and Pt increases the selectivity towards aromatic hydrocarbons. GaZSM-5, Zn-ZSM-5 and Pt-ZSM-5 zeolite catalysts have been studied extensively for the conversion of light alkanes into aromatic hydrocarbons (2,3). The aim of the present work was to study the conversion of n-butane over H-ZSM-11 and Ga-ZSM-11 zeolite catalysts.
EXPERIMENTAL
The zeolite Na-ZSM-11 was synthesized in the laboratory by using the method given in ref (4) with some modification. The XRD analysis of the prepared Na-ZSM-11 indicated that the zeolite was highly crystalline. Na-ZSM-11 was then ion-exchanged with 5 M NH4C1 solution for 24 hours at 300 K. The ion exchanged zeolite was washed free of C1- ions and dried at 353 K over night. The NH4-ZSM-11 was then calcined at 813 K for 8 hours to obtain HZSM-11. Gallium was introduced into H-ZSM-11 by ion exchange with an aqueous solution 0.1 M Ga(NO3)3.9H20 (Fluka; 99.999%) for 30 hours. The zeolite was then filtered and washed with distilled water. This process was repeated three times to complete the exchange of protons by a fixed amount of gallium. The gallium content in J-I-ZSM-11 was varied between 0.5 to 2.5 wt% and determined by X-ray fluorescence analysis (X-Met 800 Outokumpu). The acidity of the H-ZSM-11 and Ga-ZSM-11 zeolite was estimated by TPD
185 of ammonia. The catalytic reaction was carried out at atmospheric pressure in a micro fixedbed reactor consisting of a quartz tube with an inner diameter of 10 mm. The amount of catalyst used in the testing was 0.5 g and the temperature of the catalyst bed was monitored and controlled by a thermocouple. WHSV of n-butane was kept constant during the test reaction and the reaction temperatures selected were 713 K , 743 K, 773 K and 803 K. The reactant feed consisted of 20% butane and 80% nitrogen (99.999 vol% purity).The reaction product analysis was performed by using a Varian 3700 gas chromatograph equipped with a FID detector. Reaction product from the reactor was fed into the gas chromatograph via a short tubing and a control valve, both of which were heated so that all products remained in the gas phase.
RESULTS AND DISCUSSION
The conversion of n-butane over H-ZSM-11 and Ga-ZSM-11 increases with increasing temperature and the maximum conversion was obtained at 803 K. The selectivity towards aromatic hydrocarbons also depends upon the reaction temperature and it increases with increasing temperature. The main aromatic hydrocarbon products obtained were benzene, toluene and xylenes. Yields of the cracking products methane and ethane also increased with increasing temperature. H-ZSM-11 zeolite catalyst shows very low selectivity for aromatic hydrocarbon. Addition of gallium increases selectivity towards aromatic hydrocarbons and the yields of paraffins and olefins decreased with increasing gallium content. The role of gallium is dehydrogenation of alkanes to alkenes which are chemisorbed on the acid sites of the zeolite and undergoes oligomerization reaction to give unsaturated oligomers. The unsaturated oligomers are then quickly converted to aromatic hydrocarbons. There is a rapid deactivation of both H-ZSM-11 and Ga-ZSM-11 zeolite catalyst. The probable reason for deactivation could be the result of poisoning of the acid sites, coke deposition or from sintering of gallium particles.
REFERENCES 1.Oscar A.Anunziata and Liliana B.Pierella, Catalysis Letters 16(1992)437-441. 2.H.Kitagawa, Y.Sendoda and Y.Ono J.Catal. 101(1986)12. 3.T.Mole, J.R. Anderson and G.Creer, Appl.Catal.17(1985)141. 4.Pochen Chu, N.J.Woodbury, US 3,709,979 (1972).
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions
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Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
HIGHLY DISPERSED PLATINUM CLUSTERS IN ZEOLITE BETA: SYNTHESIS, CHARACTERIZATION AND CATALYSIS IN LIQUID-PHASE HYDROGENATIONS
E.J. Creyghton, R.A.W. Grotenbreg, R.S. Downing and H. van Bekkum Laboratory of Organic Chemistry and Catalysis, Delft University of Technology, Julianalaan 136, 2628 BL Delft, The Netherlands
SUMMARY Platinum loaded zeolite Beta was synthesized and characterized by TEM. Homogeneously distributed clusters with an average size smaller than 15/~ were observed; reactivity experiments indicated that these clusters are located in the zeolite. Furthermore, its potential as catalyst in regioselective hydrogenations is indicated. INTRODUCTION Platinum loaded zeolites are important catalysts in various reactions [1] and of particular importance in hydroisomerization [2]. We have selected zeolite Beta for the preparation of a platinum containing catalyst as this material has a three-D structure and can be prepared in a wide range of Si/A1 ratios [3].
EXPERIMENTAL The zeolite catalysts were prepared as described elsewhere [4]. Pt-AI20 3 (5 wt%) was obtained from Janssen Chimica, Pt black from Drijfhout. Platinum dispersions were determined by CO adsorption or TEM. Hydrogenation of allyl 3,5-di-t-butylphenyl ether (2 mmol) was performed in 25 ml EtOAc at 295K and atmospheric pressure; 25 mg catalyst was used. Hydrogenations of 1-decene and trans-5-decene were performed in 25 ml EtOAc at 275K and atmospheric pressure; between 2 and 25 mg catalyst was used.
RESULTS AND DISCUSSION T E M measurements show that all platinum clusters have approximately the same size, less than 15~,, and are homogeneously distributed over the zeolite. To discriminate between platinum clusters on the outer surface and clusters occluded in the zeolite matrix the hydrogenation of the allylic function of allyl 3,5-di-t-butylphenyl ether was used as a probe reaction. The size of allyl 3,5-di-t-butylphenyl ether is approximately 11.0x10.8x5.8 ,~ which means that it cannot enter the pores of zeolite Beta. The hydrogenation results are shown in Table 1. From the large differences in initial rates
187 it is clear that the platinum clusters are almost exclusively located inside the zeolite. Table 1. Conversion of allyl 3,5-di-t-butylphenyl ether over Pt catalysts
a
Catalyst
Si/A1
Pt (wt%)
Dispersion
rinitiala
Pt-A120 3
-
5.0
0.3
25.2
Pt-Beta
11
1.6
0.85
0.02
Pt-Beta
39
2.0
0.85
0.43
initial rate (mol- h"l.g surface Pt-t) Hydrogenation of 1-decene and of trans-5-decene were also carried out over
different platinum catalysts. From the results shown in Table 2. it can be seen that the r l / r 2 ratios (rl: initial rate 1-decene, r2: initial rate trans-5-decene) are higher w h e n the reactions were carried out over platinum contained in the matrix of zeolite Beta. Reaction rates can be expressed using Langmuir-Hinshelwood kinetics, showing zero order behaviour in both alkenes up to conversions over 70%; this indicates a full coverage of available sites. Therefore an end-on approach of the 1-decene to the active site cannot be used here to explain the observed selectivity for hydrogenation of the terminal double bond [5]. We assume that the limited number of sites available for adsorption of trans-5-decene in the zeolite channels is the key factor to determine the observed increase in selectivity. Table 2. Hydrogenation of 1-decene and trans-5-decene over Pt catalysts
a
Catalyst
Pt(wt%)
1-decene (rl) a
trans-5-decene (rE) a
rl/r 2
Pt black
100
1.44
0.64
2.3
E U R O P T - 1 [6]
6.3
5.56
1.71
3.3
Pt-A120 3
5
1.54
0.30
5.1
Pt-Beta (Si/A1 = 11)
1.6
1.06
0.19
5.6
Pt-Beta (Si/A1 =39)
2.0
3.1
0.47
6.6
initial rate (mol-h'l-g Pt-1)
REFERENCES
[1] [2] [3] [4]
W.M.H. Sachtler, Acc. Chem. Res., 26, 1993, 383. R. de Ruiter, K. Pamin, A.M.P. Kentgens, J.C. Jansen and H. van Bekkum, Zeolites, 13, 1993, 611. I.E. Maxwell and W.H.J. Stork, Stud. Surf. Sci. Catal., 58, 1991, 571. E.J. Creyghton, M.H.W. Burgers and H. van Bekkum in Proc. DGMK Conf. "Selective Hydrogenations and Dehydrogenations", M. Baerns and J. Weitkamp, Eds.; Kassel, 1993, pp 247-254. [5] H. Kuno, M. Shibagaki, K. Takahashi I. Honda and H. Matsushita, Bull. Chem. Soc. Jpn., 65, 1992,1240. [6] G.C. Bond and Z. Pa~l, Appl. Catal., 86, 1992, 1.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
188
THE
EFFECT
OF
OUTER
SURFACE
SlLYLATION
ON
THE
CATALYTIC
PROPERTIES OF FeZSM-11 L. V. Piryutko, O.O. Parenago*, E . V . Lunina*, A.S. Kharitonov, L. G. Okkel and G.I. Panov. Boreskov Institute of Catalysis, Novosibirsk 6 3 0 0 9 0 , * M o s c o w State University, Moscow 117234, Russia
Russia
SUMMARY Silylation with polymethylsiloxane suppresses both the acidity of FeZSM-11 outer surface and its activity in mesitylene isomerization reaction, though it does not affect the reaction of benzene oxidation to phenol with dinitrogen monoxide.
INTRODUCTION Benzene oxidation to phenol with N20 belongs to new catalytic reactions arousing a remarkable interest among researchers. Fe-containing zeolites of pentasil type are the most efficient catalysts for this reaction which are much superior to other systems [1]. Their unique properties are related to specific Fe-containing active sites ((z-sites). To elucidate the location of (z-sites in a zeolite matrix (inside the channels or on the outer crystal surface),the silylation effect on FeZSM-11 catalytic activity was studied in this paper.
EXPERIMENTAL SECTION FeZSM-11
chemical
composition
corresponds to SiO2/AI203 = 59;
Fe203 -
0.12 wt.%; Na20 - 0.03 wt.%. Polymethylsiloxane (PMS) was used as a silylation agent for selective deactivation of the outer surface. 3, 10 and 15 wt.% SiO 2 samples were prepared. Texture characteristics were determined from nitrogen adsorption isotherms at 7"7 K. The outer-surface acidity was measured by the paramagnetic probe method upon recording ESR spectra of tanan nitroxyl radicals [2]. A flow reactor was used for catalytic measurements.
RESULTS AND DISCUSSION SiO 2 deposition does not affect the zeolite channel system, the micropore volume remains unchanged upon silylation within the experimental error (5-'7 %). But silylation deactivates the outer surface due to covering it with the inert SiO 2 layer. Thus, deposition
189
of 15 wt.% SiO 2 (this equals to 2.5 monolayer coverage with account of FeZSM-11 outer surface area) suppresses the outer acidity by 75-80 %. This brings about a remarkable deceleration of mesitylene isomerization reaction proceeding over the outer surface of the zeolite, mesitylene conversion drops from 12 % to 2 %.
A
loo
.,_,
90
o~ =
-
20
-
>0 15
-
0
O
o
,.,
,,
10
wt. % 8iO 2
0 - 0.0 (parent) 11-3 e-lO [3-15
m
O N9
m
Fig.
5
I 30
I I I 60 90 120 Time on stream,
I 150 rain
I 180
1. Silylation effect on the oxidation of benzene to phenol over FeZSM-11 at 350~
Fig. 1 shows a silylation effect on FeZSM-11 catalytic activity in benzene oxidation to phenol with N20. Deposited SiO 2 affects practicaly neither benzene conversion nor selectivity, thus indicating that at least the main portion of (z-sites (if not all of them) is located inside the microporous system of the zeolite. Coke deposition usually provides zeolite deactivation. This phenomenon occurs upon the oxidation of benzene. The activity of all FeZSM-11 samples decreases with time on stream (Fig.l), without showing a distinct dependence on the extent of silylation. It means that coke formation also proceeds mainly inside the zeolite channels. REFERENCES
[1]. [2].
G.l.Panov, A.S.Kharitonov and V.i.Sobolev, Appl.Catal.A, 98 (1993) 1. E.V.Lunina, O.E.Lebedeva and I.L.Aleksandrova, Zh. Fiz. Khim., 60 (1986) 183.
190
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All fights reserved.
HYDROLYSIS OF DISACCHARIDES BY DEALUMINATED Y-ZEOLITES Christoph Buttersack and Daniela Laketic Sugar Institute, Technical University, P.O. Box 4636, D-38036 Braunschweig, Germany Hydrolysis of X-O-a-D-glucopyranosyI-D-fructoses w i t h X = 2 (sucrose), X = 5 (leucrose) and X = 6 (isomaltulose) by protonated Y-zeolites w a s s h o w n to be strongly accelerated by dealumination. T w o or less protons per unit cell provide a maximal proton related rate constant of the sucrose hydrolysis. The rate c o n s t a n t is the same compared to diluted homogeneous acid solution. Hydrophobic interactions essentially contribute to the adsorption of the sucrose molecule but not to the energy of the activated transition state. It w a s proven that the zeolite pores are able to include a sucrose molecule plus at least one w a t e r molecule interacting w i t h the glycosidic bond. Because of the limited space inside the zeolite pore a change of c o n f o r m a t i o n compared w i t h the state in solution is required. Introduction The acid catalyzed hydrolysis of sucrose is generally considered to follow an A1 mechanism in which a fast pre-equilibrium protonation is followed by a unimolecular, rate-determining heterolysis of the fructosyl-oxygen bond [1]. The reaction is established on industrial scale using acid ion-exchange resins [2]. In contrast to the polymeric acid system, which bears some problems concerning the microenvironment and swelling [3], acid zeolites are characterized by a fixed geometry. The precisely uniform pore size enables specific interactions, which are the basis for chromatographic separation of carbohydrates on zeolites [4]. To our knowledge nothing has been reported on the utilization of zeolites for the hydrolysis of saccharides. One is tempted to expect that the dimensions of disaccharide molecules are too big to enter even the relative large pores of Y-zeolites [4]. However, it was shown recently that the interaction of sucrose, leucrose and isomaltulose can be significantly enhanced by dealumination of the zeolites [5]. Therefore, we were encouraged to start investigations concerning their corresponding catalytic activities. Experimental section Dealuminated NaY-zeolites (Si/AI ratio: 26, 55, 110) produced by the SiCI4 method [6] and the original Y-zeolite (Si/AI = 2.4) were treated with NH, CI [7] and heated (110 ~ / 16 h plus slowly up to 450 ~ / 16 h). An EDX and AAS analysis revealed a reduction of Na § by more than 60%. Hydrolysis of the disaccharides was carried out in a thermostatted stirred solution of 100 g/L saccharide with 10 g/L zeolite. Results and Discussion A considerable hydrolysis of all three disaccharides was obtained with the highest dealuminated zeolite (Si/AI= 110). As expected, the reaction was found to obey a first order kinetics, and up to a conversion of 50% at 70 ~ no considerable amounts of side products were formed. The rate constant per mass of catalyst observed with a usual Y-zeolite (Si/AI = 2.4) was very low. For sucrose the factor of reduction was about 800. Assuming the ideal case that the process of dealumination by SiCI4 [6] replaces the AI of the original framework in a pure statistical manner, the unit cell of the highest dealuminated zeolite contains only 1.7 Ai-atoms. With reference to the generally accepted assumption that 58% of the quickly exchangeable cation positions are located inside the supercage [7] one can postulate that only one proton per unit cell (8 supercages) exists as an acid site for the catalysis. Table 1 shows the results obtained with Y-zeolites of varying degree of acid sites and different temperature. The rate of hydrolysis was related to the number of acid sites in the supercage nil§ (in mole/g). Thus, the kinetics should obey
. d c s = knH+ Ccat cs dt where cr and c= are the zeolite respective sucrose concentration in g/L. k represents an effective
191
rate constant composed of the actual value and the concentration of sucrose inside the pores n=. On deactivated zeolites (Na*-form) the adsorption was completed within some minutes, and the analysis of the corresponsing isotherm suggests that n, corresponds to the saturation value (about 170 mg/g) when no influence of pore diffusion occurs. The activation energies are 29.7 and 30.1 kcal mole 1 K~ for Si/AI = 110 and 26 resp. These values are very close to that for the homogeneous solution. For the hydrolysis with HCI a value of 2 5 . 9 + 0 . 7 kcal mole "1 K"~ [8] is published. Therefore, the activated transition complex of the sucrose inside the zeolite is very similar to that in the liquid phase with respect to the activation enthalpy. The concentration of the zeolite particles was always 10 g/L. In case of the zeolite with the ratio Si/AI = 110 the amount of protons (58% of the AI-content) is 0.867 mole/I of the reaction volume. Surprisingly, a corresponding diluted solution of HCI causes about the same rate constants (Table 1). Thus one is tempted to postulate that despite the high concentration of protons and sucrose molecules inside the zeolite volume the separation of the reaction centres by the zeolite lattice has the same effect as a dilution of a concentrated solution. In other words: no difference exists when the sucrose molecules are separated by many water molecules or by thin "walls" mainly consisting of SiO2. Literature 1 2 3 4 5 6 7 8
T.L. Mega and R. van Etten, J. Am. Chem. Soc. 110 (1988) 6372 G. Siegers and F. Martinola, Int. SugarJ. 87 (1985) 23 C. Buttersack, React. Polymers 10 (1989) 143 C. Buttersack, W. Wach and K. Buchholz, Stud. Surf. ScL Catal. (1994), this congress C. Buttersack, W. Wach and K. Buchholz, J. Phys. Chem. 97 (1993) 11861 H.K. Beyer and I. M. Belenykaja, Stud. Surf. Sci. CataL 5 (1980) 203 T.L.M. Maesen, H. van Bekkum, T. G. Verbourg, Z. I. Kolar and H. W. Kouwenhoven, J. Chem. Soc., Faraday Trans. 87 (1991) 787 K. Vukov, Int. Sugar J. 67 (1967) 172
Table 1 Rate constants k of the sucrose hydrolysis in Y-zeolites with different degrees of dealumination (The concentration of protons available for the sucrose molecule was assumed to be 58 % of the bulk aluminum content. Data for hydrolysis in acid solution was taken from literature [8]. The k-value for Si/AI=2.4 at 40"C was extrapolated assuming the same activation energy found for Si/AI=27). charge
A
C
Si/AI
2.43
per unit cell
[mmole /g]
32.5
0.171
27 55 110
4.1 2.0 1.0
0.340 0.171 0.0867
110
1.0
0.0867
0.57 M HCI
k [10"1 L mole-1 min"1]
H +
50 "C
60 "C
0.0072 0.536 0.566
0.024
0.096
0.128
0.625
2.46
10.5
0.157
0.622
2.22
7.59
30"C
40 "C [0.00042]
70 "C 0.029 0.505 52.12
23.7
,..
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
192
ADSORPTION AND CATALYSIS MECHANISM OF CFC-11 IN N a X ZEOLITE M.Hiraiwa, A.Yamazaki, R.Otsuka and T.Nagoya Department of Mineral Resources Engineering, Waseda University, 3-4-10hkubo, Shinjyuku-ku, Tokyo 169, Japan
SUMMARY Apply NaX zeolite to catch and decompose the molecules of Chlorofluorocarbons(CFCs) and determine the behaviour of CFC-11 molecules in zeolitic pores by using various methods; powder X-ray diffractometory, Rietveld analysis, Gas Chromatography, Ion Chromatography and Nuclear Magnetic Resonance measurement. Each step of the decomposition process of the CFC-11 molecules in the zeolitic pores were characterized.
INTRODUCTION The supply of Chlorofluorocarbons(CFCs) is decreasing because of its destruction of the stratospheric ozone layer. Using substitutes for CFCs, however, would have many problems of cost and ability, and would take a long time to be applied for practical use. In this situation, the best way not to release CFCs is to catch the gas at source and then to recycle or decompose it. In this study, the adsorption behavior and the catalytic ability of CFC-11 in the zeolitic pores of NaX zeolite were tested. To examine in detail the behaviour of CFC-11 in the zeolitic pores, crystal structures before and after adsorption were refined by using powder X-ray diffraction Magnetic Resonance (NMR) data.
and Nuclear
193 EXPERIMENTAL The catalyst used was NaX zeolite(ZEOSTAR NX-112S) provided by Nippon Chemical Industrial Co.,Ltd. The adsorption procedures were as follows: (1) sampling the adsorbent; (2) drying at 400~
for 1 hour; (3) after cooling in a desiccator, filling in a
flask; (4) exposing the sample to 100% CFC-11 gas in the flask. The catalytic procedure was as follows: (1) CFC-11 gas was prepared in order to obtain the required concentration; (2) heating the catalyst at 400 ~C; (3) the gas is in contact with the catalyst; (4) sampling and analizing the decomposed CFC-11 gas. The structure refinement procedures were as follows: the crystal structures of NaX zeolite before and after adsorption were refined by the Rietveld method (RIETAN, Izumi, 1990) using high-brightness powder X-ray diffraction data. RESULTS AND DISCUSSION The positions of the water and CFC-11 molecules in NaX zeolite were determined. Although water molecules occupied almost all the supercages, the CFC-11 molecules were located only in the 12-ring of the framework structure. Calculated from the results in the adsorption procedure, it was found that about 29.2 CFC-11 molecules were adsorbed per unit cell. On decompositon CFC-11 using the zeolite catalyst, the activity near ordinary temperature is recognized. This fact shows that the deomposition of CFCs at low temperature is possible. Adsorpton of CFC-11 on a zeolite surface is dependent upon not only physisorption but also chemisorption. On investigation of these phenomena, the steps of a decomposition process in zeolitic pores were determined. REFERENCES David H.Olson, The Journal of Physical Chemistry, 72, 2758 (1970). Fujio Izumi, Journal of The Crystallographic Society of Japan, 34, 76 (1992). Koichi Mizuno et al., Ind.eng.Chem.Res., 30, 2340 (1991).
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
194
EFFECT
OF B A S I C I T Y ON THE C A T A L Y T I C
CONTAINING
ZEOLITES
P. K o v a c h e v a Institute
Sciences,
PROPERTIES
OF LEAD
Bulgarian
Academy
and N. Davidova
of K i n e t i c s
Sofia
and Catalysis,
1113,
Bulgaria
of
SUMMARY The b a s i c i t y of lead c o n t a i n i n g X z e o l i t e s was s t u d i e d by m e a n s of t h e r m o p r o g r a m m e d d e s o r p t i o n (TPD) of CO 2. A good r e l a t i o n s h i p b e t w e e n the basicity, the c a t a l y t i c - a c t i v i t y and C 2 s e l e c t i v i t y in the r e a c t i o n of o x i d a t i v e c o n v e r s i o n of m e t h a n e was o b s e r v e d in the p r e s e n c e of the zeolite, c o n t a i n i n g about 3.3 wt.% lead. INTRODUCTION Less a t t e n t i o n
compared former
is paid to the b a s i c p r o p e r t i e s
to t h e i r acidic p r o p e r t i e s .
study,
w h e r e the role of the z e o l i t i c
the reaction of oxidative [i],
conversion
in the p r e s e n t work the b a s i c i t y
zeolites
is e x p e r i m e n t a l l y
EXPERIMENTAL
The catalysts loading.
TPD of CO 2 was c a r r i e d out in a quartz 50~
for 30 min.
heating
conductivity
Chemically
rate of 10~
The c a t a l y t i c
at a t m o s p h e r i c
RESULTS
AND D I S C U S S I O N
were
by m e a n s
of T P D of CO 2.
to give
3-12 wt.%
reactor
detector.
on z e o l i t e lead
of flow type,
CO 2 was
fed at
at a
conducted
in a f i x e d - b e d
temperature
of 750~
flow rate of 60 ml/min.
The TPD plots of CO 2 a d s o r b e d in Fig.l.
supposed
of lead c o n t a i n i n g
s o r b e d CO 2 was d e s o r b e d
pressure,
r a t i o of 4.5/1 and total
shown
in
and a r g o n rate of 20 ml/min.
experiments
reactor
was
as
of our
sites
study w e r e p r e p a r e d
N a X by i m p r e g n a t i o n with lead n i t r a t e
c o u p l e d to a thermal
basic
of m e t h a n e
determined
for the s c r e e n i n g
of zeolites,
As a c o n t i n u a t i o n
on the c a t a l y s t s
examined
flow CH4/O 2
are
195
~
6
~
Fig.l.
TPD profiles
of the samples: 1 - NaX; ~
2 - 3 3%Pb/NaX; 3 - 6.4%Pb/NaX
C
4 - 12.2%Pb/NaX
0
200
zOO
T, o c
------.
600
BOO
The starting NaX zeolite is c h a r a c t e r i z e d by two TPD signals I00-350~
and 600-800~
for the p r e s e n c e
with different After
(curve i). The signals give indication
of high amount of h e t e r o g e n e o u s
strength.
i m p r e g n a t i o n of NaX with 3.3 wt.%
heterogeneous
basic sites with d i f f e r e n t
middle temperature
range are observed,
(curve 2). The origin of these sites
lead-zeolite
interaction.
basic sites
lead a number of strength in the
w h i c h are absent in NaX
is u n d o u b t e d l y due to
This sample,
shows the best activity and s e l e c t i v i t y
oxidative
-
conversion of methane.
c o m p a r e d to the others, in the reaction of
The i m p r e g n a t i o n of NaX with more than 3.3 wt.% lead has as a result gradual
loss of TPD signals
(curves
3 and 4).
In the
m e a n t i m e the same samples show a c t i v i t y and selectivity close to that of 3.3%Pb/NaX, an important,
properties. REFERENCES
i. P. Kovacheva,
N. Davidova,
E x t e n d e d Abstracts 1992,
which fact implies that the b a s i c i t y
is
but not the only factor a f f e c t i n g the catalytic
RP 29.
A.H. Weiss.
of 9th Int.
Zeol.
In: Book of
Conf.,
Montreal,
H.G. Karge and J. Weitkamp (Eds.)
196
Zeolite Science 1994: Recent Progress and Discussions
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved. PHYSICO-CHEMICAL AND CATALYTIC PROPERTIES OF Y ZEOLITES WITH HIGH MODULUS OBTAINED BY DIRECT SYNTHESIS. PREPARATION OF PILOT LOT OF NaY ZEOLITE WITH HIGH MODULUS M.I. Levinbuk 1, M.L. Pavlov 2, V.B. Melnikov, 1 B.V. Romanovsky3, Y.I. Azimova3 and Y.A. Smorodinska 3 1Moscow Oil Academy, 2GrozNII, 3Moscow State University, Russia
SUMMARY
The catalytic cracking of gas oil, adsorptive and acidic properties have been investigated over catalysts containing Y, ultrastable zeolites Y (USY and LZ-210) and high modulus zeolite Y (HMY) obtained by direct synthesis. The catalyst with HMY give higher gasoline and coke selectivities compared with catalysts containing Y and ultrastable zeolites Y. INTRODUCI'ION Industrial preparation of Y zeolites is widely spread throughout the world. However, unlike the zeolites of the pentasil (ZSM) series, their catalytic activity and selectivity are controlled by the molar ratio (modulus) SIO2/A1203, which is often varied by methods of post synthesis modification and not by direct synthesis. Zeolites obtained in such a way (hydrothermal - USY or chemical treatments LZ-210) with the modulus above 5.5 are called ultrastable ones. The disadvantages of ultrastable zeolites are the partial distortion of the crystalline framework, the appearance of extra-framework aluminium and the higher cost of the zeolite product due to construction and operating charges. These additional expenses are due to the necessity of special blocks for modification of NaY zeolite with modulus 4.5 - 5.0 synthesized by the traditional method. Scientists at GrozNII, Moscow Oil and Gas Academy and Moscow State University have modified the method of direct synthesis of NaY zeolites with modulus 5,8 - 6,0 by the silicate method without reconstruction of the existing equipment of zeolite production on the basis of chemical composition of crystallisation. EXPERIMENTAL SECTION Physico-chemical properties of Y zeolite with modulus 4.5, of ultrastable zeolite (LZ-210) with modulus 9.0 and HMY with modulus 5.95 were compared by adsorption of nitrogen, water and n-hexane and X-ray analysis. The acidity was studied by thermal desorption of ammonia chemisorbed at room temperature. The catalytic properties of the moving-bed catalysts (TCC-catalyst) prepared on the basis of the above said Y zeolites (sample-I, sample-2) and commercial catalysts
197 Emcat-Extra (Engelhard, containing USY) Zeokar-2 (GrozNII, containing Y) were examined in a laboratory unit in the cracking of vacuum gas oil at 460~ catalyst/feed ratio 2.2, space velocity 1.5 r -1. Properties of the vacuum gas oil: density- 0.915 g/cc, sulfur - 1.52 wt%, conradson carbon- 0.52 wt%, IBP 321~ FBP 518~ Catalyst pretreatment 750~ 6h, 100% steam. RESULTS AND DISCUSSION Table
Products produced upon testing of vacuum gas oil cracking over spherical catalysts Emcat-Extra Engelhard (USA)
Y type zeolites in catalysts (modulus in brackets) Zeolite content, wt% Product yield, wt% gasoline LC~ gas HC~ coke Conversion, wt% Gasoline / conversion ratio
Re USY (12.0) 10-12
Zeokar-2 GrozNII (Russia) Re Y (4.,5) 10
Sample-1
Sample-2
Re LZ-210 (9.0) 10
Re HMY (6.0) 10
30.1 28.,3 10.7 27.2 3.7 44.5
29.0 27.7 7.7 31.4 4.2 40.9
33.5 32.6 7.9 21,7 4,3 45.7
37.5 28.9 9.8 20.0 3.5 50.8
0.68
0.70
0.73
0.74
It is obvious from the table, that the catalyst containing HMY differed from the other samples by higher selectivity to gasoline and by the lower coke yield. Physico-chemical characterization of the Y zeolites showed that the high gasoline selectivity on HMY is due to the absence of non-framework alumina and defects of zeolite crystalline structure. CONCLUSIONS On the basis of the obtained results, the pilot lot (1 ton zeolite = 2,1 ton bead cracking catalyst) of Y zeolite with a high modulus (M 5.85) was prepared at the catalyst factory of the Anisimov refinery in Grozny and Ufa refinery (Russia). Laboratory tests of the pilot lot confirmed its catalytic properties of high efficiency.
V. Adsorption and Diffusion
This Page Intentionally Left Blank
198
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
COUNTER DIFFUSION OF C8 AROMATICS IN Y ZEOLITE PELLETS V.MOYA KORCHI, A.METHIVIER Institut Francais du Petrole, Applied Physico-Chemistry and Analysis Department, 1 & 4 avenue du Bois Prdau, 92506 Rueii-Malmaison FRANCE SUMMARY: A kinetic study of the counter diffusion of paraxylene and orthoxylene in Y zeolite pellets has been performed at low temperature. This study has shown a change in the rate limiting step for adsorption from micropore diffusion at 293 K to macropore diffusion at 323 K. INTRODUCTION:
The separation process of xylene isomers by adsorption on X or Y exchanged zeolites is well known in chemical engineering [1]. The process which usually operates in liquid phase involves a simulated moving bed adsorption unit whose design requires a deep understanding of mass transfer inside the adsorbent. The adsorbent which consists of small microporous crystals of Y zeolite formed into a macroporous pellet offers two distinct diffusionnal resistances to mass transfer: the micropore resistance of the crystals and the macropore resistance of the pellets [2]. The rate limiting step for the adsorption may be due either to the micropore or the macropore resistance depending on experimental conditions. EXPERIMENTALS:
In order to determine which step is rate limiting for liquid adsorption and to derive corresponding diffusivities, an experimental study of the counter diffusion of paraxylene, orthoxylene and isooctane is performed in a temperature range of 293 to 323 K and for different pellet sizes (0.3 to 0.9 mm). The experiments are conducted in a perfectly stirred thermostated cell. Prior to the experiment, the zeolite is dehydrated at 673 K for 10h in a nitrogen flow and then introduced in the vessel with a known quantity of isooctane or a solution of orthoxylene and isooctane. The experiments consist in injecting a small amount of xylene in the liquid phase and following the subsequent concentration change as a function of time. The uptake can be derived from these measurements. Depending on initial conditions, two kinds of experiments are carried out in order to study either the counter diffusion of isooctane and one xylene or the counter diffusion of the two xylenes. MODELLING AND DISCUSSION:
Figure 1 and 2 show typical examples of results obtained for the counter diffusion of paraxylene and orthoxylene at 293 and 323 K for different pellet sizes.
199
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10000
12000
tlme (s) Figure 1 : Uptake of paraxylene as a function of time at 293 K and for various pellet sizes
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50
100
150
200
250 time ( s )
l
0.71 m m 9 0.56 m m 9 025 m . . .m .
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300
350
400
Figure 2 : Uptake of paraxylene as a function of time at 323 K and for various pellet sizes
It appears that the 