Molecular Sieves Principles of Synthesis and Identification Second Edition R. SZOSTAK Clark Atlanta University Atlanta, GA USA V D BLACKIE ACADEMIC & PROFESSIONAL An Imprint of Chapman & Hail London Weinheim New York Tokyo Melbourne Madras
Contents Preface to the second edition Acknowledgments 1 Molecular sieves: history and nomenclature 1.1 Molecular sieves today 1.2 Zeolithos 1.3 Early commercial zeolites 1.4 Green zeolite technology 1.5 Molecular sieve nomenclature 1.5.1 Identifying new zeolite minerals 1.5.2 Synthetic zeolites 1.5.3 Rules for naming synthetic zeolites 1.6 Zeolites, molecular sieves and microporous materials: a series 1.6.1 Zeolite 1.6.2 Molecular sieve 1.6.3 Microporous materials 1.6.4 Clathrasils 1.6.5 Interrupted structures 1.6.6 Mesoporous materials 1.7 Compositional variability in zeolites and material identity 1.7.1 Crystallographic criteria 1.7.2 Synthetic criteria 1.7.3 Nomenclature and mixed elemental compositions 1.8 Other zeolite definitions 2 Structural aspects 2.1 Molecular sieve structures 2.2 Lowenstein's rule 2.3 Dempsey's rule 2.4 Zeolite and molecular sieve frameworks 2.4.1 First level: pore size 2.4.2 Determining pore size 2.4.3 Second level: dimensionality and shape 2.4.4 Visualizing as a hollow tube or a room with Windows 2.4.5 Shape of the pore opening 2.4.6 Void volume 2.5 Drawing zeolite structures 2.6 Sorting out molecular sieve structures: other approaches 2.6.1 Early Classification of zeolites 2.6.2 Secondary building unit 2.6.3 Three-dimensional nets and polyhedra 2.6.4 Sigma transformation 2.6.5 'Pentasü' net
Vlll CONTENTS 2.6.6 Structural representation via cages or tubes 2.6.7 Categories based on synthesis method 2.6.8 Summary 3 Faulted and intergrown phases 3.1 Crystal imperfections 3.1.1 Rotational stacking faults 3.1.2 Twin faults 3.1.3 Inclusion faults 3.1.4 Domain intergrowths 3.1.5 Random phases 3.2 Difficulties in naming faulted or intergrown phases 3.3 Early identification errors 3.4 Characterizing faulted phases 3.5 Dealing with faulted phases in synthesis 3.6 Point defects 4 Fundamentals of synthesis 4.1 Where do we begin? 4.1.1 Reproducing nature 4.2 Ostwald's rule and Goldsmith's 'simplexity principle' 4.3 Crystallization flelds 4.4 Crystallization curves 4.5 Practical considerations in zeolite synthesis 4.5.1 Chemical purity of reagents 4.5.2 Laboratory handling of reagents 4.5.3 Crystallizing vessels 4.5.4 Cleaning crystallizing vessels 4.5.5 Calculation of zeolite batch composition 4.6 Reaction mixture components 4.6.1 Gel silica/alumina ratio 4.6.2 Hydroxide concentration 4.6.3 Monitoring ph in zeolite crystallization 4.6.4 Role of inorganic cations 4.6.5 Anions other than hydroxide 4.6.6 Water for transport and structure direction 4.6.7 Influence of temperature and heating rate 4.6.8 Seeds and aging 4.6.9 Source materials 4.6.10 Stirring or static? 4.7 Summary 5 Process of zeolite formation on a molecular level 5.1 From macro to micro 5.1.1 Methodology for studying gels 5.1.2 Q-units 5.2 Silicate fragments in zeolite synthesis 5.2.1 Orthosilicates 5.2.2 Pyrosilicates 5.2.3 Metasilicates, specifically those containing ring Silicate ions 5.2.4 Synthetic polysiloxanes: dimers and cyclic structures 5.3 Silicates in water Solutions 5.4 Amphoteric oxides in water Solutions
CONTENTS IX 5.5 Secondary building units and their role in zeolite synthesis 130 5.6 Starting very small: probing species in Solution 131 5.6.1 Distribution of silica and alumina; compositional analysis 131 5.6.2 Infrared and Raman spectroscopic techniques applied to Silicates 132 5.6.3 Trapping Silicate fragments through trimethylsilylation 138 5.6.4 NMR techniques to identify Silicate species in Solution 139 5.6.5 Light scattering and nucleation events 142 5.6.6 Electron microscopy methods 143 5.7 Theories of zeolite nucleation and growth 144 5.7.1 Solid-gel transformation 145 5.7.2 Zeolite crystallization from Solution 145 5.7.3 So what's happening in there? 147 5.8 Thermodynamics, telling us something 149 5.9 Can we put it together? 149 150 Organosilicates and organoaluminosilicates 154 6.1 Polymorphs of silica 154 6.2 Organic additives in zeolite synthesis 156 6.3 Template theories 159 6.3.1 Circumstantial evidence for the role of organic additives as 'templates' 160 6.3.2 Non-spherical organic amines: diquats 163 6.3.3 Void filier, buffer or what? 165 6.4 ZSM-5(MFI) synthesis 167 6.4.1 Step 1: synthesis from Na 2 0-Si0 2 -Al 2 03-H 2 0 167 6.4.2 Step 2: addition of organic amines to change the Si/Al ratio 168 6.5 Crown ethers in synthesis 170 6.6 Synthetic routes to clathrasils 172 6.7 Organometallic complexes in organosilicate synthesis 174 6.8 Mesoporous silicas 175 6.9 Organoaluminosilicates versus zeolites 176 6.9.1 Observing differences in acidity 177 6.10 Exploring bulky organic additives 181 6.10.1 C/Nfactor 182 6.10.2 Adamantane derivatives 183 6.10.3 Tricyclodecane derivatives 183 6.11 Slow-release sources of oxide reagents: zeolites and other microporous materials 185 6.12 The next generation 186 186 Specialized methods of synthesis 192 7.1 Tailoring synthesis to applications 192 7.2 Secondary methods of synthesis 193 7.2.1 Dealumination 193 7.2.2 Aluminum insertion into a Silicate or defected silica 198 7.3 Non-aqueous synthesis 198 7.4 Preformed zeolites and Silicates 199 7.5 Large crystal production 201 7.6 Microporous films and coatings 203 205 Metal Silicate molecular sieves 208 8.1 Molecular sieves and the periodic table 208 8.2 Breaking the rules 208
CONTENTS 8.2.1 Substitution of gallium for aluminum 210 8.2.2 Germanium aluminate molecular sieves 214 8.2.3 Boron 219 8.2.4 Iron 226 8.2.5 Comparing acidity and catalytic activity in M 3+ (M = B, AI, Ga, Fe) Silicates 233 8.2.6 Beryllium incorporation into Silicate lattices 235 8.2.7 Zinc Silicates 237 8.2.8 Tin- and lead-containing materials 238 8.2.9 Titanium 239 8.2.10 Synthesis of other microporous metal Silicates 242 8.3 Metal Sulfides: their inorganic chemistry 243 244 The aluminophosphates 251 9.1 Aluminophosphate molecular sieves: first examples of pentavalent framework ions 251 9.2 Natural aluminophosphates 252 9.3 Early synthetic aluminophosphates 254 9.4 Phosphate zeolites 256 9.5 Synthesis of aluminophosphate molecular sieves 259 9.6 Role of the organic additive 262 9.7 Stability and solubility 264 9.8 Adding inorganic cations 264 9.9 Studies of gel chemistry 264 9.10 Changing aluminum coordination number in aluminophosphate materials 265 9.11 Adsorption properties of aluminophosphate molecular sieves 267 9.12 Structural information from 27 AI and M P NMR 268 9.13 Gallophosphates 269 9.14 Silica incorporation into aluminophosphates 270 9.15 Metal aluminophosphates (MeAPO) and related materials 271 9.16 New functional materials or interesting soil science? 274 274 Identification of molecular sieve structures 278 10.1 The bare necessities 278 10.2 X-ray powder diffraction: identification of a crystalline material 279 10.2.1 Typical examples of diffraction patterns from synthesis experiments 280 10.2.2 Characterizing faulted phases 286 10.2.3 Measuring X-ray crystallinity 290 10.2.4 Aluminum content through unit cell volume expansion 291 10.2.5 Identifying new materials 294 10.3 Adsorption properties: pore volume 295 10.3.1 Adsorption crystallinity 298 10.3.2 Pore gaging 300 10.3.3 Hydrophobicity and hydrophilicity 306 10.4 Optical and scanning electron microscopy 307 10.5 Acidity measurements from ammonia desorption 308 10.6 Structural features from infrared spectroscopy 309 10.6.1 Identification of 5-member rings 310 10.6.2 Identifying Substitution of other elements from infrared spectroscopy 312 10.6.3 Acid characteristics determined from infrared spectroscopy 312 10.7 Structural identification by NMR spectroscopy 314 10.7.1 NMR studies of silica-rich molecular sieves 316
CONTENTS XI 10.7.2 Structural Information from alummum NMR 317 10.8 High-resolution electron microscopy 317 10.9 Molecular modeling 318 10.10 Identification of structural features through catalytic test reactions 319 10.11 Identification of new materials 320 321 Appendix Zeolite structures 325 Prepared by DEWI LEWIS Index 339 Microporous materials and their structure codes 355