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Oxide-based Systems at the Crossroads of Chemistry -  C. Colella,  S. Coluccia,  Aldo Gamba

Oxide-based Systems at the Crossroads of Chemistry (eBook)

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2001 | 1. Auflage
452 Seiten
Elsevier Science (Verlag)
978-0-08-053830-3 (ISBN)
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This volume includes papers presented at the second International Workshop on Oxide-based Systems at the Crossroads of Chemistry, held at Villa Olmo in Como, Italy, 8-11 October.

The selected papers present the highlights of recent research in the field of oxide structure. A wide range of oxidic materials, including real oxides, zeolites and layer-structured systems, is considered and described in terms of preparation methods, structural characterization and the relation between active sites, structure and catalytic properties. The application of the most powerful simulation and physical-chemical techniques show their usefulness in discovering and explaining structural and dynamic properties of complex materials. Moreover the development of sophisticated spectroscopical and analytical techniques are shown to significantly improve the growth of surface oxide science, generating new tools for the knowledge of catalyst structure and reaction mechanisms. An interesting feature is the inclusion of papers which show the mutual roles of experiment and theoretical models.

This volume includes papers presented at the second International Workshop on Oxide-based Systems at the Crossroads of Chemistry, held at Villa Olmo in Como, Italy, 8-11 October.The selected papers present the highlights of recent research in the field of oxide structure. A wide range of oxidic materials, including real oxides, zeolites and layer-structured systems, is considered and described in terms of preparation methods, structural characterization and the relation between active sites, structure and catalytic properties. The application of the most powerful simulation and physical-chemical techniques show their usefulness in discovering and explaining structural and dynamic properties of complex materials. Moreover the development of sophisticated spectroscopical and analytical techniques are shown to significantly improve the growth of surface oxide science, generating new tools for the knowledge of catalyst structure and reaction mechanisms. An interesting feature is the inclusion of papers which show the mutual roles of experiment and theoretical models.

Cover 1
Contents 8
Preface 6
Chapter 1. High-Resolution Electron Microscopy, Neutron Diffraction with Isotopic Substitution and X-Ray Absorption Fine Structure for the Characterisation of Active Sites in Oxide Catalysts 12
Chapter 2. Location of Brønsted and cation sites in dehydrated zeolites: A comparison 24
Chapter 3. Characteristics in the Photocatalytic Reactivity of the Tetrahedrally Coordinated Ti-Oxide Species Designed within various Types of Zeolites and on Support Surfaces 38
Chapter 4. Polymer-silica composite membranes for Direct Methanol Fuel Cells 48
Chapter 5. Mixed vanadium oxides for application as electrode materials in the Li-ion cells 58
Chapter 6. Search and Optimization of Multi-Metal-Oxide Catalysts for the Oxidative Dehydrogenation of Propane - A Combinatorial and Fundamental Approach- 66
Chapter 7. FT-IR study of Pt, Cu and Pt-Cu phases supported on hydrotalcite-derived mixed oxides 78
Chapter 8. Chemisorption and catalytic properties of gold nanoparticles on different oxides: electronic or structural effects? 88
Chapter 9. Modeling soil ped formation: properties of aggregates formed by montmorillonitic clay, A1 or Fe poorly-ordered oxides and polyphenol in acidic milieu 98
Chapter 10. The vibrational spectra of phosphorous oxynitride at high pressures 114
Chapter 11. Fixed-bed ion-exchange process performance of Pb2+ removal from a simulated ceramic wastewater by Neapolitan yellow tuff 122
Chapter 12. Adsorption features of clinoptilolite-rich tuff from Thrace, NE Greece 132
Chapter 13. Dissociative Adsorption of H2 on Defect Sites of MgO: A Combined IR Spectroscopic and Quantum Chemical Study 142
Chapter 14. Modification of redox and catalytic properties of Keggin-type, Sb-doped P/Mo polyoxometalates in the selective oxidation of isobutane to methacrylic acid: control of preparation conditions 152
Chapter 15. Evaluation of Italian phillipsite and chabazite as cation exchangers for Ba2+ and Co2+ 164
Chapter 16. The role of A1- and Fe-oxy-hydroxides in determining surface properties of soil ped models, with emphasis on phosphorus sorption/desorption phenomena 174
Chapter 17. Doped zirconia catalysts for the dehydration of 4-methylpentan-2-ol 186
Chapter 18. Carbon tetrachloride hydrodechlorination with organometallics based platinum and palladium catalysts on MgO: EXAFS characterization and catalytic studies 196
Chapter 19. Effect of Ti insertion in the silicalite framework on the vibrational modes of the structure: an ab initio, and vibrational study 206
Chapter 20. Surface Properties of Mesoporous Ti-MCM-48 and their Modifications Produced by Silylation 220
Chapter 21. Computer simulations of ethane sorbed in an aluminophosphate molecular sieve 232
Chapter 22. Stabilisation of nanostructured CeO2-ZrO2 solid solutions by addition of Al2O3: a suitable way for production of thermally stable oxygen storage/release promoters for three-way catalysts 240
Chapter 23. Chemistry and Photochemistry of H2 on MgO surfaces 248
Chapter 24. Intracage chemistry: nitrite to nitrate oxidation via molecular oxygen. A Car Parrinello study. 262
Chapter 25. Synthesis, Spectroscopic and Catalytic Properties of Cobalt and Copper Ions in Aluminophosphates with Chabasite-Like Structure. Studies of the NO Reactivity 280
Chapter 26. Highly dispersed CaO in mesoporous silica as efficient trap for stabilizing azo dyes 290
Chapter 27. Preparation and characterisation of WOx/SnO2 nanosized powders for thick films gas sensors 298
Chapter 28. Factors affecting the isomorphous substitution of Al with Fe in the MFI-type zeolite in presence of TPABr and ethylene glycol 308
Chapter 29.Synthesis and adsorption properties of iron containing BEA and MOR type zeolites 318
Chapter 30. Local Structures of Active Sites on Mo-MCM-41 Mesoporous Molecular Sieves and their Photocatalytic Reactivity for the Decomposition of NOx 326
Chapter 31. The factorial experimental design applied to the zeolite synthesis 334
Chapter 32. Spectroscopic characterisation and photocatalytic properties of Mg 2+ -modified MCM- 41 342
Chapter 33. Electroceramics in solid oxide fuel cell technology 352
Chapter 34. Synthesis and characterization of Co-containing zeolites of MFI structure 364
Chapter 35. Synthesis and Characterization of dye-containing MCM-41 materials 372
Chapter 36. Modeling of breakthrough curves in fixed-bed zeolite columns 380
Chapter 37. A kinetic study of NO decomposition on Cu-ZSM5 388
Chapter 38. Characterisation of palladium catalysts supported on hydrotalcite-derived mixed oxides 402
Chapter 39. Silica-aluminas: sol-gel synthesis and characterization 412
Chapter 40. The Reductive Activation of Molecular Nitrogen on "electron-rich" MgO: Details on the Structure of the Adsorption Site via the N2-OH Superhyperfine Interaction 424
Chapter 41. Kinetics of NO Photocatalytic Reduction by CO over MoO3/SiO2 Catalysts 432
Author Index 442

High-Resolution Electron Microscopy, Neutron Diffraction with Isotopic Substitution and X-Ray Absorption Fine Structure for the Characterisation of Active Sites in Oxide Catalysts


John Meurig Thomasjmt@ri.ac.uk    Davy Faraday Research Laboratory, The Royal Institution of Great Britain, 21 Albemarle Street, London W1S 4BS, UK
Department of Materials Science, University of Cambridge, Cambridge CB2 1QY

ABSTRACT


The power of high-resolution electron microscopy (HREM) for both ex situ and in situ studies of complex oxide catalysts is illustrated with specific reference to La2CuO4, zeolite-L and (VO)2P2O7. The surfaces of stoichiometric La2CuO4 are seen by combined HREM and X-ray emission spectroscopy to be essentially La2O3. Unlike the surfaces of simple oxides (e.g. those with corundum structures), those of zeolite-L are unreconstructed, and have essentially the same composition and structure as the bulk zeolite. In situ HREM studies (by Gai) shed considerable light on the catalytic properties of (VO)2P2O7 in its conversion of butane to maleic anhydride. Isotopic substitution of 62Ni for natural nickel in NaNi-exchanged zeolite Y catalysts (for the cyclotrunerisation of acetylene) offer novel insights into the initial act of bonding (via a π-complex) between C2H2 and individual Ni2 + active sites in the zeolite. The great advantages attendant on the use of X-ray absorption fine structure (XAFS) for in situ studies of active site participation Ti-SiO2 and FeAlPO-31 catalysts are also illustrated.

1 HISTORICAL INTRODUCTION


“After a long silence, for which I will not try to excuse myself, I have the pleasure of communicating to you, Sir, and through you to the Royal Society, some striking results which I have obtained in following up my experiments … … the electricity developed by the mere contact of different metals … …

These words were read by Sir Joseph Banks, President of the Royal Society in London in mid-April, 1800. They constitute the opening sentence of Alessandro Volta’s letter, despatched from Como on 20th March, 1800. I chose to open this lecture with these historical comments because, like others here this evening, I rejoice in being in Como, the birthplace of Plinius the Elder and Plinius the Younger, and also the place where Alessandro Volta was born and where he died. In common with millions of scientists world-wide, I have revered the memory of Volta ever since I first heard of his work. That reverence was enhanced when, nearly twenty years ago, my dear friend, the late Massimo Simonetta, with whom I had an exciting collaboration up until he passed away, took me to Pavia, where Volta was Professor. Later, more than a decade ago, my family and I came to this wonderful place, where I purchased (in the Volta Museum) a copy of Bertini’s famous painting of the occasion when Volta demonstrated his pile to the Emperor Napoleon in 1801.

My predecessor but seven as Director of The Royal Institution (RI), Michael Faraday, greatly admired Volta, who gave him a special Voltaic pole that Faraday frequently demonstrated at the RI, and which we still have (and exhibit).

In October 1842, Faraday received a letter from W.R. Grove (a Welsh lawyer-scientist working in London), describing the fuel cell, which Grove had invented. The opening of that letter is rather evocative:

“I have just completed a curious voltaic pile, which I think you would like to see ……”

When Faraday died in 1867, his successor John Tyndall (famed for the Tyndall effect, and also as the first person to describe the greenhouse effect and global warming) wrote a brilliant biography entitled “Faraday as Discoverer”[1]. Tyndall was a fine stylist and wrote with mellifluous charm. I should like to draw to your attention a passage in that book, which has particular resonance for this occasion when this Symposium honours Volta’s name:

“In one of the public areas of the town of Como stands a statue with no inscription on its pedestal, save that of a single nameVolta’ … … ”

Tyndall then proceeds to describe in beautiful English prose what Volta did, and the controversy that raged for some considerable time as to the origin of the electromotive force of a voltaic pile. Tyndall’s words merit repetition here, for they echo the essence of many subsequent scientific disputes.

The objects of scientific thought being the passionless laws and phenomena of external nature, one might suppose that their investigation and discussion would be completely withdrawn from the region of the feelings, and pursued by the cold dry light of the intellect alone. This, however, is not always the case. Man carries his heart with him into all his works. You cannot separate the moral and emotional from the intellectual; and thus it is that the discussion of a point of science may rise to the heat of a battle-field”.

2 BACKGROUND


The only major ex situ technique that I propose to dwell upon is high-resolution (transmission) electron microscopy (HRTEM) which, nowadays (see later) can also be used for in situ studies. Its value as a tool in post mortem (as well as pre natal) studies of many catalysts has been highlighted on numerous previous occasions — see, for example, refs. [25]. I also wish to say a few words about electron crystallography[4].

So far as microporous oxide catalysts are concerned — and here I focus predominantly on zeolitic ones or their aluminophosphate analogues — the great merit of HRTEM[47] is that it can be used to “read off”, in real-space images, the symmetry elements of the structure, and often yield a reasonably accurate value of the number of tetrahedral sites in a pore aperture. (In general, 5-, 6-, 8-, 10- or 12-membered (T sites) can be straightforwardly discerned from the HRTEM images recorded down the appropriate zone axis). This real-space approach also proves invaluable in identifying intergrowth structures. I have given elsewhere[8] an account of how several of the ostensibly different members of the ZSM family of synthetic zeolites turned out to be no more than intergrowth variants of well defined end-members. HRTEM, twenty years ago, was shown[9] to be capable of “seeing” in real space the intergrowth variants of ZSM-5 and ZSM-11.

With CCD detectors and other instrumental advances[4,6] the age of electron crystallography is well and truly with us. Small, ultrathin specimens of zeolites (or mesoporous silicas) can be processed by a combination of electron diffraction and HRTEM imaging, so as to yield a full, hitherto unknown, structure, thanks to the pioneering work of Terasaki and his colleagues in Tohuku University.

Surface structures of complex oxides are also amenable to direct imaging and determination by HRTEM (which has the advantage over scanning tunnelling microscopy in being able, through the observation of parallel X-ray emission spectra, to yield elemental composition)[10]. There are two examples which I wish to cite.

First, La2CuO4, a material that is of great relevance in the field of warm superconductors, has been studied in detail by my former colleague Wuzong Zhou, now of the University of St. Andrews. A strictly stoichiometric powdered sample of La2CuO4 was viewed down the [110] direction by HRTEM. The outline of the [001] surface is seen in Figure 1.

Figure 1 A typical region of the surface of La2CuO4 viewed down the [110] direction. The outer layers of the solid have the structure and composition of La2O3 (after Zhou et al[11])

Significantly, it is found that the surface composition does not correspond to La2CuO4. The images leave no doubt (and microanalysis confirms it) that the exterior surfaces (the last three layers or so) have the so-called C-La2O3 structure and composition[11]. Zhou and I have recently reported[10] that, in the warm superconductor HgBa2CuO4 + δ, the exterior and immediate sub-surface region is stoichiometrically quite different from the bulk. There are well-known reasons, discussed by Freund[12] recently, which lead us to expect polar surfaces (of oxides) to undergo reconstruction on exposure to vacuum (or an ambient gas). What is surprising here, in this powdered specimen of (nominally) La2CuO4, is that there is extensive reconstruction and reconstitution at the surface regions.

Low-energy electron diffraction (LEED) studies conducted by Freund et al[13], show that, in simple oxides belonging to the corundum family (e.g. Al2O3, Cr2O3 and Fe2O3), there is quite extensive reconstruction (in a direction perpendicular to the [0001] surface), amounting to between 50 and 60 percent change, compared with the inter-planar distances inside the bulk of the oxide. With the complex oxides that have zeolitic structure, however, the degree of reconstruction is rather minute. Thus, in zeolites L (idealised formula Na3K6[Al9Si27O72]) Terasaki et al has shown[14]...

Erscheint lt. Verlag 27.11.2001
Sprache englisch
Themenwelt Naturwissenschaften Chemie Anorganische Chemie
Naturwissenschaften Chemie Technische Chemie
Technik Bauwesen
Technik Umwelttechnik / Biotechnologie
ISBN-10 0-08-053830-4 / 0080538304
ISBN-13 978-0-08-053830-3 / 9780080538303
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