Solid state, surface and catalytic properties of oxides. Progress report, October 1, 1979-October 31, 1980

Abstract

Fundamental studies on oxide catalysts have been conducted with emphasis on the investigation of the properties of anion and cation vacancies on an oxide surface, on the characterization of an adsorbed oxygen species on an oxide, and on the determination of surface cation densities in solid oxide solutions. An automically well ordered surface of ZnO has been successfully prepared on which a high density of sites resembling those of the anion vacancy is present. Such a surface adsorbs oxygen and methanol more strongly, yet carbon dioxide more weakly than a stoichiometric nonpolar surface. From the kinetics of adsorption and desorption, evidence of an atomic adsorption of oxygen on iron oxide has been observed. The adsorption of this species is activated, and its desorption follows a bimolecular rate law. Attempts are being made to obtain the activation energies of adsorption and desorption, and the saturation coverage of the species. Its reaction with hydrocarbons will be studied later. The surface cation densities of Fe and Cr on a series of solid solutions of Fe/sub 2/O/sub 3/-Cr/sub 2/O/sub 3/ were determined. It was found that Fe was enriched on the surface at low Fe contents, but depleted from the surface at high Femore » contents. The surface Cr on air treated samples is Cr(VI). Calculation on the surface cation densities of oxide solid solutions of cubic structure was performed using a pairwise potential, and a statistical model for the surface layer. For dilute bulk solutions, the larger cation is found to be enriched on the surface.« less