Electronic properties of the active sites present at the (011)MoO2 surface. Periodic and cluster DFT quantum chemical studies

DFT method is applied to describe electronic structure of catalytically important (011) surface of molybdenum dioxide. MoO2 exists in literature mainly as a product of MoO3 reduction; however the problem of its role in catalytic process is still unsolved. In present paper attention is focused on the properties of surface active sites, both Mo and O, which are present at the selected (011) surface. In addition, comparison of (011)MoO2 and (100)MoO3 surfaces is carried out due to a fact that both surfaces contain not only the differently coordinated O sites but also the bare Mo centers. The electronic structure of studied systems is calculated using both periodic (VASP code) and cluster (StoBe code) approaches with gradient corrected functional. Local properties of different surface sites that are exposed at both surfaces are examined by means of charge densities, bond orders indices and molecular orbital diagrams whereas the global properties of both surfaces are discussed by density of states. The differences (existence of pairs of metallic sites on (011)MoO2 surface) and similarities (electronic states of bare Mo ions in both surfaces) in electronic properties of active sites are investigated taking adsorption of hydrogen and oxygen as examples