Contents to Volume 2 ......................................... XIII
Preface ........................................................ XV
List of Contributors ......................................... XVII
1 EPR (Electron Paramagnetic Resonance) Spectroscopy of
Polycrystalline Oxide Systems ................................ 1
Damien M. Murphy
1.1 Introduction ............................................ 1
1.2 Basic Principles of EPR ................................. 2
1.2.1 The Electron Zeeman Interaction .................. 2
1.2.2 Relaxation Processes ............................. 5
1.2.3 The Nuclear Zeeman Interaction ................... 6
1.2.3.1 Isotropic Hyperfme Coupling ............. 9
1.2.3.2 Analysis of Isotropic EPR Spectra ...... 10
1.2.4 The g Tensor: Origin and Significance ........... 14
1.2.5 The A Tensor; Significance and Origin ........... 16
1.2.6 The D Tensor; Significance and Origin ........... 17
1.2.7 Powder EPR Spectra .............................. 19
1.2.8 Analysing EPR Powder Spectra; Experimental
Considerations .................................. 24
1.2.8.1 Quantification of Number of Spins ...... 24
1.2.8.2 Effects of Sample Tumbling and
Rotation ............................... 25
1.2.8.3 Physical State of the Sample ........... 26
1.2.8.4 Multifrequency Measurements ............ 27
1.2.8.5 Variable Power and Temperature ......... 29
1.2.9 A Case Study: Surface Adsorbed NO2 .............. 30
1.3 Example Applications in Oxide Systems .................. 32
1.3.1 Surface Defects ................................. 33
1.3.2 Inorganic Radicals .............................. 38
1.3.3 Transient Radical Intermediates ................. 42
1.3.4 Supported Transition Metal Ions ................. 45
1.4 Conclusions ............................................ 48
References .................................................. 49
2 The Application of UV-Visible-NIR Spectroscopy to Oxides .... 51
Gicmmario Martra, Enrica Cianotti, and Sabatore Coluccia
Dedication .................................................. 51
2.1 Introduction ........................................... 51
2.2 Types of Electronic Transitions Producing UV-Vis-NIR
Bands .................................................. 52
2.2.1 Metal-С entered Transitions ..................... 53
2.2.2 Charge-Transfer (CT) Transitions ................ 55
2.2.3 Transitions between Electron Energy Bands in
Solids .......................................... 56
2.3 UV-Vis-NIR Absorption Spectroscopy ..................... 59
2.3.1 Theory of Diffuse Reflectance (DR)
Spectroscopy .................................... 59
2.3.2 General Remarks on Methodologies for DR
UV-Vis-NIR Measurements ......................... 61
2.3.3 UV Absorption Bands of Insulating Oxides:
Excitonic Surface States ........................ 61
2.3.4 UV Absorption Bands of Semiconductor Oxides ..... 66
2.3.5 Highly Dispersed Supported Oxo-Species and
TMI ............................................. 69
2.3.5.1 LMCT Transition Bands as Source of
Structural Insight ..................... 69
2.3.5.2 d-d Transition Bands as a Source of
Structural Insight ..................... 72
2.4 UV-Vis-NIR Photoluminescence Spectroscopy .............. 76
2.4.1 Franck-Condon Principle ......................... 76
2.4.2 Quantum Efficiency and Lifetime ................. 79
2.4.3 General Remarks on Methodologies Applied for
PL Measurements ................................. 80
2.4.4 Characterization of Oxide Catalysts by PL ....... 81
2.4.4.1 Insulating Oxides: the Case of AEO ..... 81
2.4.4.2 Investigations of Highly Dispersed
Transition Metal Ions in Oxides or
Zeotype-Systems by PL Spectroscopy ..... 85
2.5 Conclusions ............................................ 90
References ............................................. 91
3 The Use of Infrared Spectroscopic Methods in the Field of
Heterogeneous Catalysis by Metal Oxides ..................... 95
Guido Busca
3.1 Introduction ........................................... 95
3.1.1 The Evolution of Vibrational Spectroscopies ..... 95
3.1.2 Application of IR Spectroscopy to the Surface
Chemistry of Oxide-Based Materials:
a Historical Perspective ........................ 96
3.2 Experimental Techniques ................................ 97
3.2.1 The Detection of the Vibrational Spectrum of
a Polyatomic Chemical Species: IR and Raman
Spectroscopies .................................. 97
3.2.2 The Transmission/Absorption IR Technique ....... 100
3.2.3 The Reflection Techniques ...................... 101
3.2.4 The Diffuse Reflectance Technique .............. 104
3.2.5 The Emission Technique ......................... 105
3.2.6 Photoacoustic and Photothermal Techniques ...... 106
3.3 The Vibrational Modes of Molecular Species and of
Inorganic Solids ...................................... 107
3.3.1 "Isolated" Molecular Species ................... 107
3.3.2 Crystalline Solids ............................. 108
3.3.3 Amorphous Solids ............................... 110
3.4 The Skeletal IR Spectra of Metal Oxides ............... 111
3.4.1 Crystalline Simple Anhydrous Oxides ............ 111
3.4.1.1 Oxides of Divalent Elements ........... 112
3.4.1.2 Oxides of Trivalent Elements and
Spinel-Type Structures ................ 115
3.4.1.3 Oxides of Tetravalent Elements ........ 118
3.4.2 Crystalline Complex or "Mixed" Oxides .......... 121
3.4.2.1 Solid Solutions ....................... 121
3.4.2.2 Ternary Phases ........................ 121
3.4.2.3 Oxo-Salts ............................. 122
3.4.3 Amorphous versus Crystalline Oxide Materials ... 129
3.5 Skeletal Spectra of Precursors for Metal Oxide
Catalysts ............................................. 129
3.5.1 Metal Hydroxides ............................... 129
3.5.2 Hydrated Compounds ............................. 132
3.5.3 Layered Double Hydroxides ...................... 132
3.5.4 Impure Metal Oxides ............................ 133
3.6 The IR Spectroscopy of Adsorbed Probe Molecules for
Surface Chemistry Characterization .................... 133
3.6.1 Infrared Characterization of Surface Element-
Oxygen Bonds ................................... 134
3.6.1.1 Surface M-O-M Bridges ................. 134
3.6.1.2 Surface M=0 "Double" Bonds on Binary
Oxides ................................ 135
3.6.1.3 Surface Oxo-Anions .................... 136
3.6.2 Spectroscopic Detection of Surface Br0nsted
Acid Sites ..................................... 139
3.6.2.1 Hydroxyl Groups in Silica ............. 141
3.6.2.2 Hydroxyl Groups in Alumina ............ 141
3.6.2.3 Surface Hydroxyl Groups of Other
Sesquioxides and of Spinel-Type
Mixed Oxides .......................... 142
3.6.2.4 Surface Hydroxyl Groups of Rock-
Salt-Type Metal Oxides ................ 143
3.6.2.5 Surface Hydroxyl Groups of the
Oxides of Tetravalent Metals .......... 143
3.6.2.6 The Surface Hydroxyl Groups of
Sulfated and Tungstated Oxides ........ 143
3.6.2.7 The Surface Hydroxyl Groups of
Protonic Zeolites ..................... 144
3.6.2.8 The Surface Hydroxyl Groups of
Microporous and Mesoporous Silica-
Aluminas (SAs) ........................ 145
3.6.3 Spectroscopic Characterization of the
Strength of the Surface Bransted Acid Sites .... 146
3.6.3.1 Techniques for the Evaluation of the
Strength of Surface Bransted Acid
Sites ................................. 147
3.6.3.2 The Brønsted Acidity of Simple Metal
Oxides ................................ 153
3.6.3.3 The Brønsted Acidity of Protonic
Zeolites .............................. 153
3.6.4 Spectroscopic Detection and Characterization
of the Surface Lewis Acid Sites ................ 157
3.6.4.1 The Lewis Acid Sites of Aluminas and
SAs ................................... 159
3.6.4.2 Lewis Acidity of Other Ionic Oxides ... 160
3.6.4.3 Lewis Acidity of Highly Covalent
Oxides ................................ 161
3.6.4.4 Lewis Acidity of Protonic Zeolites .... 161
3.6.5 Determination of the Oxidation State of
Cationic Centers ............................... 161
3.6.6 External versus Internal Cationic Sites and
Complex Interactions in Cation Exchanged
Zeolites ....................................... 165
3.6.7 Characterization of Surface Basicity ........... 166
3.6.8 Use of Isotopically Labeled Molecules .......... 168
3.7 Infrared Studies of the Mechanisms of
Heterogeneously Catalysed Reactions ................... 169
References ................................................. 170
4 Resonance Raman Spectroscopy - Ө-Al2O3-Supported Vanadium
Oxide Catalysts as an Illustrative Example ................. 177
Zili Wu, Hack-Sung Kim, and Peter C. Stair
4.1 Introduction .......................................... 177
4.2 Structure of Al2O3-Supported Vanadia Catalysts ........ 178
4.2.1 Introduction ................................... 178
4.2.1.1 Dehydrated State ...................... 179
4.2.1.2 Reduced State ......................... 183
4.2.2 Summary ........................................ 185
4.3 Quantification of Surface VOx Species on Supported
Vanadia Catalysts ..................................... 186
4.3.1 Summary ........................................ 189
4.4 Conclusion ............................................ 190
References ............................................ 191
5 Solid-State N MR of Oxidation Catalysts .................... 195
James McGregor
5.1 Introduction .......................................... 195
5.1.1 Oxides in Catalysis ............................ 195
5.1.2 Studying Metal Oxide Catalysts ................. 195
5.2 NMR Techniques ........................................ 196
5.2.1 Bulk Structure of Catalysts .................... 200
5.2.1.1 Magic Angle Spinning .................. 200
5.2.1.2 Multiple Quantum Magic Angle
Spinning .............................. 201
5.2.1.3 Satellite Transition Magic Angle
Spinning .............................. 202
5.2.1.4 Off-Resonance Nutation NMR ............ 203
5.2.1.5 Spin-Echo Mapping ..................... 204
5.2.2 Surface Structure of Catalysts ................. 206
5.2.2.1 Double-Resonance Techniques ........... 206
5.2.2.2 Spin-Echo Techniques .................. 208
5.2.2.3 CRAMPS ................................ 209
5.3 Structure of Bulk Oxides .............................. 209
5.3.1 Vanadium Oxide Catalysts ....................... 210
5.3.1.1 Supported Vanadium Oxide Catalysts .... 210
5.3.1.2 VPO Catalysts ......................... 216
5.3.1.3 Other Vanadates ....................... 216
5.3.2 Other Metal Oxide Catalysts .................... 217
5.3.3 Metal Oxide Supports ........................... 221
5.3.3.1 Aluminum Oxides ....................... 221
5.3.3.2 Other Oxide Supports .................. 225
5.4 Surface Properties of Metal Oxides .................... 227
5.4.1 Surface Structure .............................. 227
5.4.2 Surface Acidity ................................ 229
5.4.2.1 Bronsted Acid Sites ................... 229
5.4.2.2 Lewis Acid Sites ...................... 233
5.5 Outlook ............................................... 235
References ............................................ 236
6 Photoelectron Spectroscopy of Catalytic Oxide Materials .... 243
Detre Teschner, Elaine M. Voss, and Robert Schlögl
6.1 Introduction .......................................... 243
6.2 XPS as a Surface-Sensitive Technique .................. 244
6.2.1 Basic Principles ............................... 244
6.2.2 Instrumentation ................................ 245
6.2.2.1 The Conventional Setup ................ 245
6.2.2.2 In situ (High-Pressure) Setup ......... 245
6.2.3 Quantification of XPS Spectra .................. 247
6.2.4 The XPS Spectrum (a Qualitative Picture) ....... 248
6.2.4.1 X-ray Transitions ..................... 248
6.2.4.2 Binding Energy in Practice; An
Issue? ................................ 249
6.3 Case Studies .......................................... 255
6.3.1 Applications of XPS to Vanadium Oxides ......... 255
6.3.2 Direct and Oxidative Dehydrogenation ........... 260
6.3.2.1 Selective Dehydrogenation of
n-Butane over VxOy/Alumina ............ 260
6.3.2.2 Oxidative Dehydrogenation of
n-Butane .............................. 266
6.3.3 Selective Oxidation ............................ 267
6.3.3.1 n-Butane Selective Oxidation to
Maleic Anhydride Over VPO ............. 267
6.3.3.2 Direct Oxidation of Propane to
Acrylic Acid Over MoV-Based Mixed
Metal Oxides .......................... 281
6.4 Summary ............................................... 291
References ................................................. 292
7 X-ray Absorption Spectroscopy of Oxides and Oxidation
Catalysts .................................................. 299
Michael Stockenhuber
7.1 Principles of EXAFS ................................... 299
7.1.1 Basic Principles of X-ray Absorption
Spectroscopy (XAS) ............................. 300
7.1.2 Experimental Setup ............................. 303
7.1.3 Detection Methods .............................. 304
7.1.4 Data Reduction ................................. 306
7.2 Applications of EXAFS ................................. 309
7.2.1 Acid Zeolites .................................. 310
7.2.2 Transition Metal Exchanged Zeolites ............ 312
7.2.3 Selective Oxidation Catalysts .................. 315
7.3 Conclusion ............................................ 319
References ............................................ 319
8 Theory: Periodic Electronic Structure Calculations ......... 323
Rudy Coquet, Kara L. Howard, and David J. Willock
8.1 Introduction .......................................... 323
8.2 Electronic Structure Methods .......................... 324
8.2.1 Hartree-Fock ................................... 324
8.2.1.1 Exchange Energy ....................... 325
8.2.1.2 Correlation ........................... 327
8.2.2 Density Functional Theory (DFT) ................ 328
8.2.3 Periodic Quantum Chemistry ..................... 332
8.2.3.1 Band Theory ........................... 332
8.2.3.2 Basis Sets ............................ 336
8.2.3.3 Pseudopotentials ...................... 340
8.2.3.4 Density of States ..................... 342
8.3 Bulk Structure: Alumina ............................... 347
8.4 Calculation of Surface Structure ...................... 353
8.4.1 Slab Models .................................... 353
8.4.1.1 Electrostatic Stability of Surfaces ... 355
8.4.1.2 The Effect of Slab Dimensions ......... 357
8.4.2 Surface Calculations on MgO, Al2O3 and TiO2 .... 359
8.4.3 Influence of Environment on Surface
Structure ...................................... 367
8.4.4 Transition Metal Oxides with Partially Filled
d Bands ........................................ 370
8.4.5 Defects on the Surfaces of Transition Metal
Oxides ......................................... 375
8.5 Conclusions ........................................... 384
References ............................................ 385
9 Thermal Analysis and Calorimetric Methods .................. 391
Simona Bennici and Aline Auroux
9.1 Introduction .......................................... 391
9.2 Techniques and Procedures ............................. 393
9.2.1 Experimental Techniques ........................ 393
9.2.1.1 A Static Method: Coupling
Calorimetry and Volumetry ............. 394
9.2.1.2 Gas Flow Methods ...................... 399
9.2.1.3 Calorimetry in Liquid Phase ........... 400
9.2.2 Temperature Dependence of Adsorption-
Desorption Heats ............................... 401
9.2.3 Probe Molecules ................................ 401
9.2.3.1 Probing Surface Basicity .............. 402
9.2.3.2 Probing Surface Acidity ............... 402
9.2.3.3 Probing Redox Properties .............. 403
9.3 Surface Properties of Oxides .......................... 403
9.3.1 Bulk Oxide Catalysts ........................... 404
9.3.2 Doped and Modified Oxides ...................... 408
9.3.3 Supported Metal Oxide or Metal Catalysts ....... 408
9.3.4 Binary Mixed Metal Oxides to Quaternary Metal
Oxides ......................................... 415
9.3.5 Hydrotalcites .................................. 420
9.3.6 Bulk and Supported Heteropolyacids ............. 422
9.3.7 Pillared Clays and Layered Silicates ........... 424
9.3.8 Zeolites ....................................... 425
9.4 A Case Study: Vanadia Catalysts ....................... 429
9.5 Conclusion ............................................ 436
References ................................................. 436
10 Transmission Electron Microscopy ........................... 443
Wuzong Zhou
10.1 Introduction .......................................... 443
10.2 HRTEM and Related Techniques .......................... 444
10.2.1 Ray Diagram of ТЕМ ............................. 444
10.2.2 Electron Wavelength ............................ 445
10.2.3 Interaction between Electrons and Solids ....... 445
10.2.4 Formation of Image Contrast .................... 445
10.2.5 Resolution of ТЕМ .............................. 448
10.2.6 Electron Diffraction ........................... 450
10.2.7 Energy Dispersive X-ray Spectroscopy ........... 452
10.3 Basic Structures of Oxide Crystals .................... 454
10.4 Superstructures ....................................... 455
10.4.1 Superstructures Based on Cation Ordering ....... 455
10.4.2 Superstructures Based on Oxygen Ordering ....... 459
10.4.3 Incommensurate Superstructures ................. 460
10.5 Surface Profile Imaging ............................... 462
10.6 Defects in Oxides ..................................... 465
10.6.1 Layered Defects ................................ 465
10.6.2 Twin Defects ................................... 466
10.6.3 Point Defects .................................. 467
10.7 Porous Materials ...................................... 468
10.7.1 Microporous Zeolites ........................... 468
10.7.2 Mesoporous Silica .............................. 470
10.7.3 Porous Oxides .................................. 472
10.8 Low-Dimensional Oxide Crystals ........................ 476
10.8.1 Nanoparticles .................................. 476
10.8.2 Nanorods, Nanowires and Nanobelts of Oxides .... 477
10.8.3 Oxide Nanotubes ................................ 479
10.9 Summary ............................................... 481
References .................................................... 482
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