Molecular Spectroscopy of Oxide Catalyst Surfaces

684 Pages·2003·5.04 MB·English

by  A. A., Davydov

MOLECULAR
SPECTROSCOPY
OF OXIDE CATALYST
SURFACES
MOLECULAR
SPECTROSCOPY
OF OXIDE CATALYST
SURFACES
Anatoli Davydov
University of Alberta, Edmonton, Canada
Syntroleum Corporation, Tulsa, Oklahoma, USA
Edited by N. T. Sheppard
Copyright  2003 John Wiley & Sons Ltd, The Atrium, Southern Gate, Chichester,
West Sussex PO19 8SQ, England
Telephone [phone]
Email (for orders and customer service enquiries):
Dedicated to my wife Marina
CONTENTS
Preface xi
Symbols and Abbreviations xiii
Introduction xv
1 Theoretical fundamentals and experimental considerations of the
spectroscopic methods used in surface chemistry 1
1.1 Electronic spectroscopy 1
1.1.1 Transmission spectra 4
1.1.2 Diffuse reflection spectra 5
1.2 Vibrational spectroscopy 5
1.2.1 Infrared spectroscopy 11
1.2.2 Photoacoustic spectroscopy 18
1.2.3 Raman spectroscopy 19
1.3 Electron energy loss spectroscopy 21
1.4 Inelastic electron tunneling spectroscopy 22
1.5 Inelastic neutron scattering spectroscopy 23
1.6 Other vibrational spectroscopies 23
1.6.1 Infrared ellipsometric spectroscopy 23
1.6.2 Surface electromagnetic wave spectroscopy 23
1.7 In situ measurements 24
1.8 Quantitative measurements 25
2 The nature of oxide surface centers 27
2.1 Systems investigated 27
2.1.1 Solid structures 27
2.1.2 Surfaces 28
2.1.3 Active sites 29
2.2 Spectra of oxide surfaces 31
2.2.1 Vibrations of metal–oxygen bonds on oxide surfaces 32
2.2.2 Molecular forms of adsorbed oxygen 44
2.2.3 Surface hydroxyl groups 56
2.3 Determination of the nature of surface sites and their chemical properties
using the adsorption of simple molecules 77
2.3.1 Adsorption of ammonia and pyridine 78
2.3.2 Adsorption of carbon monoxide 95
2.3.3 Adsorption of hydrogen and nitrogen 114
viii CONTENTS
2.3.4 Adsorption of water 120
2.3.5 Adsorption of nitrogen oxide and nitrogen dioxide 123
2.3.6 Adsorption of carbon dioxide 133
2.3.7 Adsorption of hydrogen sulfide 139
2.3.8 Adsorption of sulfur dioxide 146
2.3.9 Surface isocyanate complexes 157
2.4 Determination of acidic surface properties 161
2.4.1 Protic acid sites 162
2.4.2 Lewis acid sites 166
2.5 Determination of basic surface properties 171
2.6 Surface defects 177
3 Study of cation states by DRES and FTIR spectroscopies of the probe
molecules 181
3.1 Copper-containing systems 182
3.1.1 Zeolites 182
3.1.2 Oxides 200
3.2 Nickel-containing systems 207
3.2.1 Zeolites 207
3.2.2 Oxides 215
3.3 Co-containing systems 217
3.3.1 Zeolites 217
3.3.2 Oxides 218
3.4 Iron-containing systems 220
3.4.1 Zeolites 220
3.4.2 Oxides 222
3.5 Silver-containing systems 223
3.6 Palladium-containing systems 228
3.6.1 Zeolites 228
3.6.2 Oxides 235
3.7 Rhenium-, ruthenium-, and rhodium-containing systems 237
3.8 Platinum-containing systems 238
3.8.1 IR-Spectra of CO adsorbed on supported metals 238
3.8.2 Cationic states of platinum 248
3.9 Molybdenum-containing systems 252
3.9.1 Molybdenum–aluminum oxide compounds 252
3.9.2 Molybdenum–silicon oxide compounds 253
3.9.3 Molybdenum–titanium oxide compounds 255
3.10 Vanadium-containing systems 257
3.10.1 Vanadium–titanium oxide compounds 259
3.10.2 Vanadium–silicon oxide compounds 263
3.10.3 Vanadium–aluminum oxide compounds 266
3.11 Chromium-containing systems 269
3.12 Effects of the states of adsorption sites on the stretching frequencies of
adsorbed carbon monoxide and nitrous oxide and the problem of detecting
the states of cations in oxide catalyst surfaces 271
2+ n+
3.12.1 M –CO, M –CO (n > 2) 272
+ 0
3.12.2 M –CO and M –CO 274
CONTENTS ix
4 Interactions of inorganic compounds with oxide surface
active sites 277
4.1 Organometallic complexes 281
4.2 Metal carbonyls and nitrosyls 282
4.3 Interactions with simple acids and bases 284
− −
4.3.1 F - and Cl -modified oxide systems 285
2−
4.3.2 SO4 -modified oxide systems 286
2−
4.3.3 BO3 -modified oxide systems 291
4.4 Heteropoly compound systems 294
4.4.1 Effects of the supports 295
4.4.2 Acidic properties of molybdenum heteropoly compounds 300
4.5 Thermal stabilities of molybdenum compounds, decomposition mechanisms
and the role of modifiers 303
4.5.1 Bulk and supported heteropoly acids 303
4.5.2 Modified molybdates 305
4.6 Cationic modification 308
5 Formation of surface complexes of organic molecules 309
5.1 Complexation of alkenes 310
5.1.1 Complexation with OH groups 310
5.1.2 Carbenium ions and alkoxy compounds 313
5.1.3 Interaction with cations 327
5.1.4 Interaction with cation–anion pairs 342
5.1.5 The complexation of alkenes with surface oxygen 351
5.2 Complexation of aryls and aryl halides 355
5.2.1 Hydrogen-bonding 355
5.2.2 Alkylaromatic carbenium ions 358
5.2.3 π-complexes 366
5.2.4 Interaction with ionic pairs 373
5.2.5 Complexation with surface oxygen 376
5.2.6 Formation of aryl halide complexes 378
5.3 Complexation of alkynes 381
5.3.1 Silicon dioxide zeolites 381
5.3.2 Aluminum oxide 385
5.3.3 Zinc oxide 386
5.3.4 Titanium oxide 387
5.4 Complexation of alkanes 389
5.4.1 Interactions with OH groups, carbenium-like ions 389
5.4.2 Interaction with cations 392
5.4.3 The activation of C–H bonds in alkane molecules 395
5.5 Complexation of chlorofluorocarbons 407
5.6 Complexation of nitriles 411
5.6.1 Acetonitrile 411
5.6.2 Benzonitrile 415
5.7 Complexation of alcohols 416
5.7.1 Saturated alcohols 416
5.7.2 Phenol 427
5.8 Complexation of aldehydes and ketones 430
5.8.1 Formaldehyde and acetaldehyde 430
x CONTENTS
5.8.2 Acrolein 435
5.8.3 Benzaldehyde 439
5.8.4 Maleic anhydride 440
5.8.5 Acetone 442
5.9 Complexation of acids 445
5.9.1 Formic acid 445
5.9.2 Acetic acid 453
5.9.3 Acrylic acid 453
5.9.4 Benzoic acid 455
5.10 Deactivation catalysts due to carbonaceous depositions as a result of
catalyst interactions with hydrocarbons and their derivatives 456
6 The mechanisms of heterogeneous catalytic reactions 459
6.1 Reactions involving carbon monoxide 461
6.1.1 The oxidation of carbon monoxide 461
6.1.2 The water-gas shift reaction 466
6.1.3 Carbonization and hydroformylation 473
6.1.4 The synthesis and decomposition of alcohols 475
6.2 Reactions with the participation of hydrocarbons 479
6.2.1 Complete oxidation of hydrocarbons and their derivatives 479
6.2.2 Selective transformations of alkenes 483
6.2.3 Partial oxidation 499
6.2.4 Ammoxidation of hydrocarbons and their derivatives 518
6.3 Transformations of aldehydes and ketones 526
6.3.1 Oxidation of acrolein 526
6.3.2 Oxidation of formaldehyde 531
6.3.3 Transformation of acetone 531
6.3.4 Hydrogenation of aldehydes and ketones 532
6.4 Transformations of alcohols 532
6.4.1 Dehydration of alcohols 532
6.4.2 Dehydrogenation of alcohols 536
6.4.3 Methanol oxidation to formaldehyde 538
6.5 Transformations of nitrogen-containing compounds 545
6.5.1 Decomposition of nitric oxide 545
6.5.2 The reduction of nitrogen oxides 552
6.5.3 Reactions of NOx and NH3 Mixtures 556
References 559
Index 643
PREFACE
Molecular spectroscopic methods, together with X-ray diffraction, have played key roles in estab-
lishing the concepts of coordination chemistry, as originally developed in the study of individual
transition-metal complexes in aqueous solutions or the solid state. This present book is concerned
with the even greater importance of molecular spectroscopic methods in developing similar under-
standings of the coordination chemistry of oxide surfaces where application of diffraction methods
is much more difficult. The adsorption of molecules on the surfaces gives rise to ligands attached
to free sites on the surface cations.
The book commences with an account of the basic theoretical principles and experimental
techniques of the various molecular spectroscopic methods as applied to surfaces, namely the
electronic (UV–Vis), vibrational (transmission IR, diffuse reflection, reflection–absorption IR
and Raman), electron energy loss, inelastic electron tunneling, and inelastic neutron scattering
spectroscopies. Special attention is devoted to in situ measurements where the oxide or catalyst
sample is in contact with the adsorbate or reactant. The local approach has been chosen as the
basis of the spectroscopic analysis of adsorption on the active sites of the oxide surfaces, while
the collective properties of the solid adsorbents, based on analysis of their crystal structures, is
used to describe the sites themselves. This approach is applied to pure oxides and also to oxide
systems such as cation-substituted zeolites, heteropoly compounds of molybdenum, or supported
catalysts prepared by ionic exchange or the interaction of the support with various complexes.
In some cases, the crystallographic positions of both cations and anions can be unambiguously
determined by means of molecular spectroscopic (ESR, UV–Vis, Mo¨ssbauer, etc.) or diffraction
(for zeolites, etc.) methods.
An attempt has been made to cover all of the spectroscopic literature on oxide adsorption
studies, covering many different oxide–adsorbate systems in a comparative manner. Because
the number of such publications is now very large (numbered in thousands), it is impossible to
analyze all of them individually in one single book. A particular goal is to provide a critical
analysis of the literature on the interpretation of the spectra of surface compounds on oxides
going back to the earliest days of the 1950s. A comparative analysis of the changes in the IR
spectra of adsorbed molecules, based on an improved knowledge of the bonding between the
adsorbed molecule and the surface site, has allowed this present author to improve the reliability
of interpretation of many of the spectra. Special emphasis is placed on the spectral characteristics
of active sites on oxide surfaces–hydroxyl groups, or coordinatively unsaturated surface cations
and oxygen anions. The concept of the decisive role played by surface sites in surface–molecule
adsorption is used to systematize and classify the spectral data relating to the interaction of
numerous organic and inorganic molecules, and their transformation products, with the types of
surfaces referred to above. The structures of many surface species have been identified from the
spectroscopic data.
A detailed account is presented of methods for spectroscopically characterizing the oxida-
tion state and degree of coordination of surface cations and oxygen anions by the adsorption of
probe molecules such as NH3, pyridine (Py), CO, CO2, H2, N2, H2O, NO, NO2, H2S and SO2
(Chapter 2). Special attention is paid to the critical investigation of protic and aprotic acidic and
xii PREFACE
basic surface centers, including specific correlations for comparing the strengths and concentra-
tions of surface centers on different oxides, zeolites, supported oxides, etc. by using the UV–Vis,
ESR and IR spectral characteristics of the adsorbed probe molecules, particularly CO and NO.
This includes the testing of cation states during the process of stationary-state heterogeneous
catalytic reactions. Systems containing Cu, Ni, Co, Fe, Ag, Pd, Re, Ru, Rh, Pt, Mo, V and Cr
are examined in detail. The vibrational frequency ranges of the CO and NO probes characteristic
of different surface states are presented.
Attention is also paid to the interactions of organometallic (allylic and other types) and inorganic
compounds (such as metal carbonyls), simple acids and heteropoly compounds with various
supports (Al2O3, SiO2, TiO2 and MgO), i.e. to the problems that occur during the preparation or
modification of supported catalysts. The dependence of the structure and properties of the surface
complexes formed and the properties of the catalytic systems are also shown.
The complexation of many organic molecules – alkenes, alkene halides, alkynes, aryls, aryl
halides, alkanes, nitriles, alcohols, aldehydes, ketones and acids (saturated and unsaturated, aro-
matic and non-aromatic) – with different oxide systems are critically examined. The surface
compounds formed are classified in relation to the nature and properties of the available surface
+ − 2− n+ n+ 2−
centers (H , OH , O , M , M O , etc.).
The final chapter is devoted to discussions of possible mechanisms of catalytic reactions as
deduced from spectroscopic identification of the reaction intermediates. The latter identifica-
tions are based on the comparison of the rates of reaction with those of the transformations
of surface compounds. The catalytic reactions discussed include carbon oxide oxidation, the
water–gas shift (WGS) reaction, the synthesis and decomposition of alcohols, carbonization,
hydroformylation, full and partial transformations of alkenes (including isomerization, hydro-
genation, oligomerization, polymerization, cracking and metathesis), partial oxidation of alkanes,
alkenes and aryls, ammoxidation of hydrocarbons, alcohols and aldehydes, conversion of alco-
hols, transformations of aldehydes and ketones, NO decomposition, NO + CO, NO/hydrocarbons,
and reactions between NO and NH3.
Taking into account common understandings and the results of the analysis of detailed schemes,
the mechanisms of heterogeneous catalytic reactions can be classified as stepwise (when sequen-
tial interactions of the reaction components occur) or associative (where the stages of product
separation and interaction of the reaction mixture components with the catalyst occur in parallel)
with the help of spectroscopic analyses.
This book is intended for specialists working in the fields of surface physical chemistry, surface
science, adsorption phenomena and heterogeneous catalysts.
Special thanks are due to Professor N.T. Sheppard for his attention, interest, valuable correc-
tions and useful advice, to Professor J.T. Yates Jr for important comments, and also to my wife,
Dr M. Shepot’ko, and son, Davydov, A.A. Jr, for their help in the preparation and design of
this book.
Anatoli Davydov
Tulsa, OK, USA