Correlations of the catalyst microstructure with catalytic activity and selectivity

1 Correlations of the catalyst microstructure with catalytic activity and selectivity 

The role of defects in heterogeneous catalysis, including the role of CS planes which form near the catalyst operating temperature in single metal oxides such 

Dynamic ETEM experiments on CS defects have shown mat mey consume anion vacancies and grow (figure 3.7). These correlation studies indicate mat CS planes are secondary or detrimental to catalytic reactivity. They eliminate anion vacancies by accommodating the supersaturation of the vacancies in the reacting oxide catalyst and me catalyst reactivity (selectivity) begins to decrease with the onset of CS formation, i.e. CS planes are the consequence of catalyst reduction reactions rather than the origins of catalytic reactivity (Gai 1981,1992, 1993, Gai etfl/ 1982). 

The results that CS planes (which eliminate anion vacancies in supersaturation by shearing and collapsing the lattice) are detrimental to catalysis are also consistent with me fact mat if the catalyst structure continues to collapse to form CS planes, after a period of time me catalyst is no longer an efficient oxidation catalyst. An efficient catalyst is essential for prolonged catalytic activity. This has led to me discovery of a novel glide shear mechanism (Gai et al 1995, Gai 1997). The role of mis mechanism in mixed-metal practical (commercial) catalysts will be examined when we discuss butane oxidation technology. 

These studies have led to a new understanding of me fundamental defect processes that occur at me oxide catalyst s surface and of the role of extended CS plane defects in oxide catalysts. Furmermore, me studies suggest mat anion point 

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