  Supported vanadia catalysts are modeled within the cluster DFT approach to
get an insight into the mechanism in which the support affects the activity of
vanadia in the oxidation processes. The energy of the V=O group dissociation
chosen as a descriptor of the oxidation activity is estimated using two aligned
divanadate V2O3(OH)4 particles at various distances. Separation between
particles allows to imitate (i) the various supporting materials (e.g. TiO2,
SiO2, etc.), and (ii) the coverage of vanadia on a particular support. A
substantial compensation of the energy loss upon the vanadyl oxygen abstraction
via bonding to the vanadyl oxygen of neighboring vanadate particle has been
predicted. On account of such compensation the overall energy of the V=O
dissociation reaches its minimal value of 36 kcal/mol (dropping from maximum of
142 kcal/mol) at small separation of 3 {\AA} between dimers when the nearest
vanadyl oxygen occupies a bridge V-O-V position. For dimers separated by about
4 {\AA}, the dissociation energy achieves its maximal value for isolated dimers
of about 143 kcal/mol. Thus, these findings allows one to conclude that the
oxygen mobility is a result of a compensation effect in a chain-like bonding
between neighboring vanadyl groups on the surface of support.
