Model catalyst studies on vanadia particles deposited onto a thin-film alumina support. 1. Structural characterization

A model system of alumina-supported vanadia particles, representing catalysts of the type oxide(1)/oxide(2), was prepared under ultrahigh vacuum (UHV) conditions and characterized regarding its structural and electronic properties. As supporting oxide we used a thin, well-ordered alumina film grown on NiAl(110), which allows the application of scanning tunneling microscopy (STM), infrared reflection-absorption spectroscopy (IRAS), and X-ray photoelectron spectroscopy (XPS) without charging effects. Vanadium oxide particles were prepared via metal evaporation in an oxygen ambient, leading to the growth of small, roundish oxide particles with vanadium in the +3 oxidation state. The particles are shown to interact strongly with the alumina support, resulting in an increased alumina film thickness and a distortion of the alumina film structure. IR absorption signals of the deposits could be successfully assigned to specific V-containing species, thus providing insight into the inner structure of the particles. The species identified are surface-localized vanadyl groups (V=O), interface-localized vibrations involving V, O, and Al ions, and lattice structures typical of bulk V2O3