Water adsorption at low-indices (001) and (100) V2O5 surfaces. Cluster DFT studies

Vanadia-based materials are well known as the catalysts for numerous number of different chemical processes, as a consequence of an existence of non-equivalent active centers, both O and V types, localized on various faces of the catalyst crystal. Dependently on the preparation technique the V2O5 crystals can expose different surfaces, where the low-indices faces like (010), (001) and (100) are the most common. The (010) face is built of fully saturated V and O sites, whereas both (001) and (100) surfaces of unsaturated V and O surface atoms. Thus, the faces built of unsaturated character should behave differently in catalytic reactions compared to the (010) surface and an adsorption of small molecules should be enhanced. In the present study water adsorption at the unsaturated surfaces is examined using cluster DFT approach. In addition a comparison with respect to saturated (010) surface is done. Results of calculations show that water molecule stabilizes at unsaturated surfaces due to the interaction of lone electron pair from O (from water) and unoccupied 3d states of vanadium. Upon adsorption, with low dissociation energy, water can dissociate and two hydroxyl groups are formed V(surface)-OH and O(surface)-H. It is in contrast to the (010) surface where water molecule undergo stabilization but only due to weak hydrogen bonding and its dissociation does not occur