MOLECULAR SIEVES. Principles of Synthesis and Identification

Transcription

1 MOLECULAR SIEVES Principles of Synthesis and Identification

2 MOLECULAR SIEVES Principles of Synthesis and Identification R. Szostak VAN NOSTRAND REINHOLD CATALYSIS SERIES ~ Springer Science+Business Media, LLC

3 ISBN DOI / ISBN (ebook) Copyright 1989 by Springer Science+Business Media New York Originally published by Van Nostrand Reinhold in Library of Congress Catalog Card Number All rights reserved. No part of this work covered by the copyright hereon may be reproduced or used in any form or by any means-graphic, electronic, or mechanical, inciuding photocopying, recording, taping, or information storage and retrieval systems-without written permission of the publisher Library of Congress Cata1oging-in-Publication Data Szostak, Rosemarie, Molecular sieves. lncludes bibliographies and index. 1. Molecular sieves. 1. TItle. TP159.M6S '

4 To Dr. Tudor L. Thomas and the late Professor L. B. Sand, two people who have had a positive influence on the lives of many of us in the jield of zeolites and molecular sieves There is a peculiar affinity between the oxides of aluminum and silicon. -Iler, The Chemistry of Silica, 1976

5 Platel: Natural molecular sieve mineral, cacoxenite, from Polk County, Arkansas. Sampie from Dr. Carl Francis, Harvard Mineralogical Museum, Cambridge, Massaschusetts. (Photo by Mr. lohn Hall, University of Connecticut, Storrs, CL, Reproduced with permission.)

6 Plate 2: Transmission Electron Microscope image of the ultra-iarge pore (I4.2Ä) structure of the natural ferrialuminophosphate mineral cacoxenite. (Image taken by J. L. Brown, Materials Characterization Branch, Georgia Tech Research Institute, Reproduced with permission.)

7 VAN NOSTRAND REIN HOLD CATALYSIS SERIES Burtron Davis, Series Editor Metal-Support Interactions in Catalysis, Sintering, and Redispersion, edited by Scott A. Stevenson, R. T.K. Baker, J.A. Dumesic, and Eli Ruckenstein Molecular Sieves: Principles of Synthesis and Identification, R. Szostak

8 Series I ntroduction Catalysis was defined by Berzelius more than 150 years ago when he correctly recognized that a number of seemingly unrelated phenomena could be due to a single effect. Even at that early date (1834), Berzelius was able to use examples from homogeneous and heterogeneous catalysis, the two broad divisions of the subject. The basis for this division is the number of phases present: one in the case of homogeneous catalysis, and two or three phases for heterogeneous catalysis. In both instances the catalyst!(erves one purpose, to increase the overall reaction rate or to increase the product selectivity by a 'preferential increase of the reaction rate which produces a desired product. The motivation to understand the functionalities of the catalyst exhibits the broad interdisciplinary nature of catalysis science, ranging from the physics of surfaces and the solid state, to the organic chemistry of reaction mechanisms. Studies of catalysis are designed to provide a sound basis for the application of the science to a variety of processes and to add to our understanding of the world. The materials covered in this book provide vivid examples of all areas of catalysis. Under a number of names-zeolite, molecular sieve, etc.-there has been a remarkable growth in the production of these synthetic materials and in the expansion of their applications during the past 40 years. Zeolitic alu minosilicates are probably the best characterized heterogeneous catalysts. It is Iikely that the catalytic site is a Bronstead acid and that hydrocarbon conversion is affected by a carbonium ion mechanism. Some zeolites are thought to.have one acid site per framework aluminum ion and that ail of these acid sites have the same strength and, hence, the same catalytic activity. Adopting this attitude, zeolitic catalysts may be viewed as the ideal model for the interface between homogeneous and heterogeneous catalysts, since they have a homogeneous set of active sites distributed throughout a weil characterized crystailine solid phase. But zeolites did not always occupy this preeminent position. They were discovered when Cronstedt recognized stilbite in 1756 (A. F. Cronstedt, Adak. Handl. Stockholm, 17, 120 (1756»). These pioneering investigators were able to identify and classify zeolite crystals without the aid of X-rays or sophisticated instruments. Zeolite means "boiling stone" and refers to the frothy mass that can result when a zeolite is fused in a blowpipe. The lack of research on zeolites during the last century can be inferred ix

9 x SERIES INTRODUCTION from areport by a Lieutenant Colonel W. A. Ross (Chern. News, Nov.15, 1878, p. 236). Progress did not accelerate during the next 50 years. McBain, in his classic 1932 book, The Sorption oi Gases by So lids, devoted a chapter to sorption by chabasite, other zeolites, and permeable crystals. McBain remarked that "great interest attaches to the finding of Weigel and Steinhoff [0. Weigel and E. Steinhoff, Z. Kris!., 61, 125 (1925») that chabasite rapidly sorbs the vapors of water, methyl and ethyl alcohol and formie acid, whereas acetone, ether and benzene are largely excluded. The significance of their results was pointed out by McBain [J. W. McBain, Colloid. Syrnp. Mon., 20, 1 (1926») and recognized by alliater writers. It is evident that the partially dehydrated chabasite forms a nearly perfect molecular sieve or a semipermeable membrane of extremely regular structure... ". While the significance of the above observation may have been recognized, it had little impact. Thus, an eminent pioneer in the synthesis and characterization af zeolites, Professor R. M. Barrer, spent nearly two decades (following his Ph.D. studies in the 1930s) developing a firm foundation for the rapid growth in scientific understanding and industrial applications of zeolites which has taken place during the last 30 years. In the late 1940s Professor Barrer reported that nitrogen and oxygen could be separated using a zeolite that had been treated to provide the necessary shape selectivity to discriminate between the molecular dimensions of oxygen and nitrogen. The importance of this observation in a commercial application for producing reasonably pure oxygen from air provided the impetus for commercial production of synthetic zeolites. With commercialization the activity in zeolite research rapidly increased. The improvement in gasoline yield for lanthanium or rare earth stabilized zeolites (C. J. Plank, E. J. Rozinski and W. P. Hawthorne, 1& E Chern., Prod. Res. & Dev., 3, 165 (1964» in the early 1960s led almost all U.S. refineries to replace amorphous siliea-alumina catalysts with improved zeolitie catalysts. This success, following so closely commercial applications in adsorption and separations processes, saw a dramatic increase in research in all areas of zeolite science. Aseries of discoveries in catalysis-shape selectivity, alkyl aromatic isomerizations, methanol-to-gasoline, AlPO., etc.-in the following years ensured continued expansion of research ac ti vities. The success of the International Zeolite Conferences, held every three years under the auspices of the International Zeolite Association, is solid evidence of this growth. The 7th conference, held in Tokyo in 1986, witnessed 122 oral and more than 180 poster presentations. The extent and variety of the published work (a volume of 1059 pages for the oral presentations) demonstrates that the time when a single volume can cover all aspects

10 SERIES INTRODUCTION xi of zeolite science is past, and the same is true of the numerous branches of zeolite science. Professor Barrer wrote an outstanding monograph, Hydrothermal Chemistry oi Zeolites, published in That volume provided elegant and authoritative coverage of many aspects of zeolite synthesis. This volume will, in some respects, augment Professor Barrer's book; it compiles and systemizes much of the practical synthetic work and the characterization data. One may view Professor Barrer's book as taking an academic approach, while Dr. Szostak's monograph pro vi des more of an applications approach. Both viewpoints are needed at this stage of the development of zeolite science. The first volume of the series dealt with a topic that was rarely considered 20 years ago-the impact of metal-support interactions in catalysis, sintering and redispersion. The topics covered in this volume differ significantly from those included in the first volume. This volume emphasizes the inorganic chemistry of the synthesis of crystalline molecular sieves. Both volumes provide"ample attention to catalyst characterization. And this is good. During the first 100 years of catalysis research, the inability to characterize catalysts led to a diversity of experimental data and philosophical viewpoints. The volumes in this series will continue to cover a diversity of topics. However, it is anticipated that all will sharethecommonthreadofapproaching catalysis as a science that derives much of its foundation from catalyst characteriza tion. BURTRON H. DAVIS

11 Preface "Abracadabra"-a word that has been in use for nearly 2000 years. The early Romans believed that the god Abraxax could help shield a person from evil if the god's name were inscribed in stone and worn on the person. Individuals new to the zeolite field who have been assigned by their manager or research advisor to prepare a zeolite, and who have experienced the frustrations of attempting to crystaliize these materials for the first time, certainly may have thought of using this incantation, followed by the sprinkling of zeolite powder on the laboratory. Unfortunately, despite great strides being made in understanding the fundamentals of zeolite formation, an incantation and the shaking of my old industrial lab apron over all new autoclaves sometimes still appears to be the only way to encourage the crystaliization of certain zeolite materials in my laboratory. Although zeolite synthesis may still seem an art to many, it nonetheless can be understood, appreciated, and successfully performed. This book focuses on the student or scientist who has IittIe experience in the realm of zeolite crystaliization. The intent is to provide insight into the fundamentals of zeolite synthesis and the techniques employed to encourage crystal formation. Making a white powder is by no means the end of the road in preparing zeolite materials; it is equally important to be able to identify the materials that have been prepared. Thus one cannot compile a text discussing methods of synthesis without considering the methods employed to characterize the materials prepared. In addition to being a basic text for the synthesis and characterization of zeolite and molecular sieve materials, it is hoped that the compilation of information presented in this book will also serve as a quick reference for those actively working in this field. R. Szostak Zeolite Research Program Georgia Institute of Technology xiii

12 ACknowledgments Special thanks go to the Georgia Tech Research Institute, Georgia Institute oftechnology, and the Energy and Material Science Laboratory for a1lowing me to write this book. Much gratitude must go to the staff of the Georgia Tech library for their assistance in rapidly locating the innumerable patents and papers used in writing this text. I especially thank Ms. Ruth McClatchey of the Zeolite Research Program for her diligence in compiling the X-ray powder diffraction patents used in the Appendix; Professor Aaron Bertrand of the School of Chemistry for providing his computer program Plot 3D, as weil 'lis "guidance in generating the structures and subsequent ORTEP drawings used in many of the chapters; and Judy Wiesman and John McKibben for their assistance in reproducing the figures used in this book. I express special appreciation to Dr. Vinayan Nair (Ph.D. '87) and Mr. Donald Simmons (M.S. '86) from the School of Chemical Engineering for their assistance in preparing Chapters I and 4, and to Dr. D. C. Shieh for his help in preparing Chapter 3. The moral support of my sisters, Car Jene, Maryann, Charlotte, and MadeIine, kept me sane through the development of this book. xiv

13 Contents Series Introduction / ix Preface / xiii 1 Molecular Sieves for Use in Catalysis / 1 Structural Overview / 1 Molecular Sieve vs. Zeolite: Adefinition / 2 When is an Aluminosilicate not a Zeolite? / 4 Loewenst.ein's Rule / 6 Pores and Channels: From Simple to Complex / 7 First Level: Pore Size / 8 Second Level: Dimensionality and Shape / 12 Visualize a Hollow Tube / 12 Shape of the Pore Opening / 15 The Secondary Building Unit / 18 Extended Chain Building Unit / 21 Sheet Building Units / 23 Putting It All Together / 25 Producing Zeolite Acidity / 26 Hydrothermal, Thermal and Chemical Modifications / 28 Nature of the Active Sites / 30 Synergistic Effects / 33 Characterization of Acid Sites / 35 Shape Selectivity / 40 Conclusions / 45 References / 45 2 Hydrothermal Zeolite Synthesis / 51 Engineering Zeolite Structures / 51 Factors Influencing Zeolite Formation / 51 Ostwald's Rule of Successive Transformations / 53 Following the Course of a Crystallization / 54 Identifying Crystallization Fields / 56 Reaction Mixture Components / 58 Gel Silica/ Alumina Ratio / 61 xv

14 xvi CONTENTS Increasing Silica Conte nt / 66 Hydroxide Concentration / 68 Monitoring ph in Zeolite Crystallization / 71 Role of Inorganic Cations / 73 The Cation as Crystal-Directing Agent: Template Theory / 79 Template: Void Filler or Buffer? / 84 Evidence for the Role of the Organic Additive as a "Template" for Structure Direction / 95 Extending the Range of Si0 2/ AI 20 J in Zeolite Structures Through Addition of Organic Additives / 101 Crystallizing Zeolite ZSM-5 from an Organic-Free System / 104 Modification of Gel Chemistry / 106 Water Content / 107 Synthesis in Nonaqueous Solvents / 108 Influence of Temperature / 109 Time as a Parameter / 113 Importance of Source Materials / 113 Synthesis of Zeolite Omega, an Example / 118 Comments on Mordenite Synthesis / 122 ZSM-5 Synthesis / 123 Synthesizing New Materials / 126 References / Process of Zeolite Formation on a Molecular Level /133 Background / 133 Methodology for Studying Gels / 135 Q-Units / 136 Silicate Ions in Nature / 137 Synthetic Polysiloxanes: Dimers and Cyclic Structures / 141 Silicates in Water Solutions / 142 Secondary Building Units and Their Role in Zeolite Synthesis / 144 Distribution of Silica and Alumina in the Synthesis Mixture / 145 Infrared and Raman Spectroscopic Techniques Applied to Silicates / 148 Raman Spectra of Aluminosilicate Species in Zeolite Synthesis / 160 Trapping Silicate Fragments through Trimethylsilylation / 162 NMR Techniques to Identify Silicate Species in Solution /165 Alkali Silicate Solutions / 175 Silicate Anions in the Presence of Organic Amine Cations / 177 Role of Hydroxide in Formation of Soluble (Alumino) Silicate Species / 179 Redistribution of Silicate Species with Temperature / 181

15 CONTENTS xvii Aluminum Species in Solution / 185 Aluminum in Silicate-Containing Solutions / 186 Further Analysis of the Solid Precrystalline Phase / 187 Mechanisms of Crystallization: Two Theories / 190 Solid-Solid Transformation / 190 Solution Phase Mechanism / 191 Zeolite Crystallization from Systems Containing Only Solution Phase /192 Compositional Inhomogeneity / 194 Zeolite Framework Stability: Thermodynamic Considerations / 195 Mechanistically Speaking / 197 References / Non-aluminosilicate Molecular Sieves / 205 Molecular Sieves and the Periodic Table / 205 Incorporation into Molecular Sieve Oxide Frameworks / 211 Substitution of Gallium for Framework Aluminum / 212 Boron-Containing Molecular Sieves / 223 Incorporation of Iron / 228 Methods of Synthesis: Ferrisilicate Molecular Sieves / 230 Ferrisilicates with the ZSM-5 Structure / 232 Other Known Metallosilicate Structures Containing Metal Cations in Tetrahedral Framework Locations / 238 Comparing Acidity and Catalytic Activity in Metallosilicate Molecular Sieves / 239 Germanium Aluminate Molecular Sieves / 242 Beryllium Incorporation into the Silicate Lattice / 247 Titanosilicate and Titanoaluminosilicate Molecular Sieves / 250 AIP04 Molecular Sieves: First Examples of Pentavalent Framework Ions / 253 Natural Aluminophosphates / 253 Synthetic Aluminoph05phate Molecular Sieves / 254 Synthesis of AIP04 Molecular Sieves / 257 Role of the Organic Additive / 261 Changing Aluminum Coordination Number in the AIP04 Materials / 264 Adsorption Properties of the Aluminophosphate Molecular Sieves / 265 Structural Information from 21Al and IIp NMR Studies / 267 Addition of Phosphorous to Aluminosilicates: Early SAPO Molecular Sieves / 268 Silica Incorporation into AlP04 / 269 Metalloaluminophosphates (MeAPO) and Related Materials / 272

16 xviii CONTENTS New Molecular Sieve Materials: What Next? / 276 References / Identification of Molecular Sieve Structures / 282 The Bare Necessities / 282 X-Ray Powder Diffraction: Identification of Crystalline Material / 283 Measuring X-Ray Crystallinity / 289 Aluminum Content Through Unit Cell Volume Expansion / 291 Identifying New Materials / 294 X-Ray Powder Diffraction for Zeolite Structure Refinement / 299 Adsorption Properties: Pore Volume / 300 Adsorption Crystallinity / 303 Pore Gauging / 306 Hydrophobicity and Hydrophilicity / 312 Acidity Meas_ur\!ments from Ammonia Desorption / 316 Structural Features from Infrared Spectroscopy / 316 Identification of 5-Membered Rings / 323 Identifying Substitution of Other Elements from IR / 326 Acid Characteristics Determined from IR / 327 Structural Identification by NMR / 327 The Question About Type A / 329 Silicon And Aluminum Ordering / 331 NMR Studies of Silica-Rich Molecular Sieves / 332 Prediction of 29Si NMR Chemical Shifts / 334 Structural Information from Aluminum NMR / 338 High Resolution Electron Microscopy / 340 Identification of Structural Features Through Catalytic Test Reactions / 341 Identification Of New Materials / 343 References / 343 Appendix X-Ray Powder Data for Zeolite and Molecular Sieve Structures and Compositions / 349 Introduction / 349 Summary of Natural, Patented, and Reported Molecular Sieves / 350 Natural Zeolites / 358 Synthetic Zeolites Patented by Mobil Oil Corporation /374 Zeolites Structures Patented by Union Carbide Corporation / 389 Zeolite Structures Patented by Imperial Chemical Industries Limited / 401 Zeolite Structures Patented by Bayer AG / 408

17 CONTENTS xix Zeolite Structures Patented by British Petroleum Company / 410 Zeolites Patented by Chevron / 410 Zeolite Structures Patented by Exxon / 412 Zeolites Patented by Other Agencies / 413 Zeolites Reported in Open Literature / 422 Molecular Sieve Materials with Zeolite or Novel Microporous Structures Patented with Composition Claims other than Aluminosilicate by Standard Oil Company (AMOCO) / 425 Molecular Sieve Materials with Zeolite or Novel Microporous Structures Patented with Composition Claims other than Aluminosilicates by BASF / 426 Molecular Sieve Material with Zeolite or Novel Microporous Structures Patented with Composition Claims other than Aluminosilicates by Shell Internationale Research Maatschappij B. V. / 429 Molecular Sieve Materials with Zeolite or Novel Microporous Structures Patented with Composition Claims other than Aluminosilicates by Mobil Oil Corporation / 430 Molecular Sieve Materials with Zeolite or Novel Microporous Structures Patented with Composition Claims other than Aluminosilicates by Hoechst Aktiengesellschaft / 431 Molecular Sieve Materials with Zeolite or Novel Microporous Structures Patented with Composition Claims other than Aluminosilicates by Union Carbide Corporation / 423 Molecular Sieve Materials with Zeolite or Novel Microporous Structures Patented with Composition Claims other than Aluminosilicates by Other Agencies / 434 Phosphorous Substituted Zeolites Prepared by Union Carbide / 439 AIP04 Molecular Sieves / 441 SAPO Molecular Sieves Patented by Union Carbide / 450 Silicoaluminophosphates Patented by Mobil Oil / 456 MeAPO and MeAPSO Molecular Sieves Patented by Union Carbide / 457 ElAPO Molecular Sieves Patented by Union Carbide / 478 The Inventors of New Zeolite and Molecular Sieve Materials / 481 Compilation of Generally Accepted Topologically Related Material / 489 Full Names of Type Codes / 490 Index / 491