CLUSTER MODEL STUDIES ON OXYGEN SITES AT THE (010) SURFACES OF V2O5 AND MOO3

Cluster model studies have been performed to examine the electronic st ructure and adsorption properties near structurally different oxygen s ites at the (010) surfaces of vanadium pentoxide, V2O5, and molybdenum trioxide, MoO3. In addition, adsorption of hydrogen at the oxygen sit es and desorption of OH groups has been studied in order to find site specific differences. The electronic properties and total energies of the clusters have been obtained from ab initio density functional theo ry (DFT) calculations. The surface oxygen sites are found to be ionic where bridging oxygens become more negative than terminal ones. Furthe r, hydrogen adsorbs at all oxygen sites where binding is strongest at the bridge sites on the V2O5(010) surface whereas on MoO3(010) the ter minal sites are preferred. The latter difference can be understood by simple geometric arguments, Surface OH groups formed by H adsorption a nd involving terminal oxygens are strongly bound to the surface wherea s those involving bridging oxygens are mobile and become available for subsequent reactions.