Reactivity of V2O3(0001) surfaces: molecular vs dissociative adsorption of water

The adsorption of water on V2O3(0001) surfaces has been investigated by thermal desorption spectroscopy, high-resolution electron energy loss spectroscopy, and X-ray photoelectron spectroscopy with use of synchrotron radiation. The V2O3(0001) surfaces have been generated in epitaxial thin film form on a Rh(111) substrate with three different surface terminations according to the particular preparation conditions. The stable surface in thermodynamic equilibrium with the bulk is formed by a vanadyl (VO) (1 × 1) surface layer, but an oxygen-rich (√3 × √3)R30° reconstruction can be prepared under a higher chemical potential of oxygen (μO), whereas a V-terminated surface consisting of a vanadium surface layer requires a low μO, which can be achieved experimentally by the deposition of V atoms onto the (1 × 1) VO surface. The latter two surfaces have been used to model, in a controlled way, oxygen and vanadium containing defect centres on V2O3. On the (1 × 1) VO and (√3 × √3)R30° surfaces, which expose only oxygen surface sites, the experimental results indicate consistently that the molecular adsorption of water provides the predominant adsorption channel. In contrast, on the V-terminated (1/√3 × 1/√3)R30° surface the dissociation of water and the formation of surface hydroxyl species at 100 K is readily observed. Besides the dissociative adsorption a molecular adsorption channel exists also on the V-terminated V2O3(0001) surface, so that the water monolayer consists of both OH and molecular H2O species. The V surface layer on V2O3 is very reactive and is reoxidised by adsorbed water at 250 K, yielding surface vanadyl species. The results of this study indicate that V surface centres are necessary for the dissociation of water on V2O3 surfaces.