Strong metal–support interactions on rhodium model catalysts

Abstract

Reactive processes on catalyst surfaces are studied in this work for Rh/metal oxide model systems by means of surface science techniques. Published results in the literature deal with titania, alumina, and silica as support materials and are briefly reviewed. For the present studies Rh/Al 2O 3 and Rh/TiO 2 model catalysts with about one monolayer Rh coverage are specially prepared and analyzed by ion scattering spectroscopy, X-ray photoelectron spectroscopy, and thermal desorption measurements as main techniques. In part these measurements are supported by a variety of other analytical and imaging techniques. For thermal treatment in hydrogen atmosphere at low and elevated pressures a complete Rh encapsulation by titania is observed for temperatures above 773 K. The results from ion bombardment depth profiling are corroborated by the concomitant drastic reduction of the CO adsorption capacity of these samples. The model catalysts thus exhibit the typical features of ‘strong metal–support interaction’. The effect was not found for alumina supports, for which thermal treatments mainly resulted in gradual interdiffusion of the various surface species. These results also demonstrate that characteristic catalyst behavior can be successfully studied by applying surface science methods to model catalysts.