XPS and TPD investigation of CO adsorption on mixed Rh-V layers supported by gamma-alumina

Alumina-supported mixed bimetallic Rh-V thin films, with the overall thickness of 0.8 ML, were prepared under the ultrahigh vacuum (UHV) conditions and characterized with respect to their electronic and CO adsorption properties. X-ray photoelectron spectroscopy (XPS) was utilized to characterize electronic changes accompanying bimetallic Rh-V interaction and interaction between metal and polycrystalline γ-Al₂O₃ substrate. The chemisorption properties were probed by temperature-programmed desorption spectroscopy (TPD) of CO molecules. The electronic and chemisorption properties of the mixed layers were compared with pure Rh and V layers grown on the same γ-Al₂O₃ substrate and with a model bimetallic Rh-V system prepared by V deposition on a polycrystalline Rh foil. By varying the preparation conditions, we observed a strong dependence of the studied properties on the position of the V atoms. The presence of V atoms on the surface led to a fast deactivation, while vanadium presented under the surface resulted in a weakening of CO-metal surface bond, a change in the proportion of the adsorption side species, and an increase of CO dissociation.