Probing the metal sites of a vanadium oxide–Pd(111) ‘inverse catalyst’: adsorption of CO

Abstract

The adsorption of CO on V-oxide covered Pd(111) multicomponent surfaces, so-called ‘inverse catalyst’ surfaces, has been studied by high-resolution X-ray photoelectron spectroscopy using synchrotron radiation. Since CO does not chemisorb on V oxide surfaces at room temperature, the adsorption of CO reflects the reactivity of the free Pd sites of this inverse catalyst surface. The C1s and Pd3d core level spectra have been monitored to follow the CO surface coverage as a function of CO exposure and V oxide coverage and to investigate the CO adsorption sites. The results indicate that the adsorption of CO on V-oxide/Pd(111) surfaces is kinetically influenced by the V oxide phase via spill-over of CO molecules from a mobile physisorbed precursor state on the oxide surface on to Pd sites. As a result of this spill-over effect the initial sticking probability of CO per free Pd site increases beyond unity with increasing oxide coverage. The analysis of C1s binding energies as a function of CO and oxide coverage suggests that the distribution of CO adsorption sites is altered by the V-oxide/Pd phase boundary.