Metallic single crystals, application

The title Spectroscopy in Catalysis is attractively compact but not quite precise. The book also introduces microscopy, diffraction and temperature programmed reaction methods, as these are important tools in the characterization of catalysts. As to applications, I have limited myself to supported metals, oxides, sulfides and metal single crystals. Zeolites, as well as techniques such as nuclear magnetic resonance and electron spin resonance have been left out, mainly because the author has little personal experience with these subjects. Catalysis in the year 2000 would not be what it is without surface science. Hence, techniques that are applicable to study the surfaces of single crystals or metal foils used to model catalytic surfaces, have been included. 

In comparison to most other methods in surface science, STM offers two important advantages STM gives local information on the atomic scale and it can do so in situ [51]. As STM works best on flat surfaces, applications of the technique in catalysis concern models for catalysts, with the emphasis on metal single crystals. A review by Besenbacher gives an excellent overview of the possibilities [52], Nevertheless, a few investigations on real catalysts have been reported also, for example on the iron ammonia synthesis catalyst, on which... 

The back-reflection XSW technique has been used mostly on metal and oxide crystals, whose rocking curves often have angular mosaicity up to -0.1°. In application to mineral surfaces, the technique has also been used by Kendelewicz et al. (1998b) to study the exchange between Na and Pb in a Na overlayer on the PbS(100) surface. A review of the BRXSW technique was given by Woodruff (1998). Since the BRXSW method is employed at soft X-ray energies (typically from Er= 1 keV to 4 keV), it is not useful for in situ studies of the mineral-fluid interface. However, the BRXSW is a very useful probe for UHV surface science measurements of adsorbed molecules on metal single crystal surfaces (Jones et al. 2002) and for site-specific valence-band photoemission studies developed by Woicik and coworkers (Woicik et al. 2001 Kim et al. 2002). 

Finally, it should be mentioned that Zintl ions have found a (still) limited application in the production of surface-modified materials. Certain organic polymers can be metallated efficiently in a non-electrochemical route employing Zintl ions of tin in en solution.Similarly, many anisotropic inorganic materials, for instance metal single-crystals and graphite, can be surface-metallated by use of Zintl ions. The surface reaction between Sng " and gold crystals has been studied by electron microscopy. 

Hukin, D.A., 1971, A new design of cold crucible and its application to the growth of rare earth metal single crystals. Clarendon Laboratory rept. no. 24/71, Parks Road, Oxford, England. 

While experiment and theory have made tremendous advances over the past few decades in elucidating the molecular processes and transformations that occur over ideal single-crystal surfaces, the application to aqueous phase catalytic systems has been quite limited owing to the challenges associated with following the stmcture and dynamics of the solution phase over metal substrates. Even in the case of a submersed ideal single-crystal surface, there are a number of important issues that have obscured our ability to elucidate the important surface intermediates and follow the elementary physicochemical surface processes. The ability to spectroscopically isolate and resolve reaction intermediates at the aqueous/metal interface has made it difficult to experimentally estabhsh the surface chemistry. In addition, theoretical advances and CPU limitations have restricted ab initio efforts to very small and idealized model systems. 

In this chapter, we present a brief background account of recent progress in the application of ab initio methods to elucidating the fundamental physicochemical processes that take place at the electrified aqueous metal interface. Our focus is predominantly on model single-crystal surfaces at lower surface coverages. 

The elucidation of the structure of the phthalocyanines followed some pioneering research into the chemistry of the system by Linstead of Imperial College, University of London. The structure that we now recognise was first proposed from the results of analysis of a number of metal phthalocyanines, which provided the molecular formulae, and from an investigation of the products from degradation studies. Finally, Robertson confirmed the structure as a result of one of the classical applications of single crystal X-ray crystallography. 

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