Relevance to oxidation catalysis

Extensive research on crystallographic shear (CS) planes has been reported in the literature as described earlier. Based on this research, including beam-heating studies in electron microscopy, it has been concluded that slight reduction of certain transition-metal oxides (e.g. simple model oxides, WO3, M0O3, V2O5, 

VO2 and Ti02) leads to the formation of extended defects, i.e. CS planes, rather than to point defects. In the early literature reports, the definition of CS involved the removal of a complete sheet of anion sites to form an extended CS plane defect (Wadsley 1964, Anderson and Hyde 1967). Consequently, the role played by true point defects in non-stoichiometric oxides was not obvious from these earlier reports and answer to this was sought by Anderson (1970, 1971), Anderson et al (1973) (1.13.2). However, although this definition of CS is a convenient one, the situation is not so straightforward as we now demonstrate. 

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In this section, we extend our treatment on ionic bonding to include covalent contributions and their relevance to oxidation catalysis. We provide a more detailed molecular orbital analysis of the properties of these oxides by relating the electronic structure of cations at the surface of the oxide with that found in corresponding organometallic cluster complexes. As such, we can use more classical hybridization schemes to understand their reactivity. Accurate calculations are available for the Ru02 system that have been used as input to dynamic Monte Carlo simulations of the CO oxidation reaction to be discussed in the next subsection. 

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