Chemisorption and the electronic structure of transition metal oxides and transition metals bonded to oxide surfaces

Abstract

Some simple transition metal oxides such as NiO have incomplete atomic subshells and yet are highly insulating. This implies a high degree of electronic localization and also indicates that the chemical bonds are saturated. In this respect these oxides are similar to alkaline earth oxides such as MgO. The analogy extends to their surface properties. MgO and NiO, for example, are both good catalysts although a pure, perfect surface of either seems inactive. It is argued that defects or impurities are required to activate the perfect surface and that catalytic properties relate weakly, at best, to the nature of the cation. These oxides are contrasted with the more studied industrial catalyst which consists of a group of transition metal ions bonded to an oxide surface. The electronic structure properties which determine the behaviour of such catalysts are explored in terms of the unrestricted Hartree-Fock model augmented with explicit inclusion of correlation. The results obtained produce a satisfactory band structure and describe surface prupcrties adequately.