DFT calculations were performed for models of the (0 0 1) surfaces of non-reduced and reduced vanadia, represented by V12O30 and V12O29 clusters, as well as for models of (0 0 1) V2O5 surfaces with Mo defects, represented by V11MoO30 and V11MoO29 clusters. The clusters were embedded in a set of point charges in order to consider electrostatic bulk influence. Surface reduction was modeled by the removal of vanadyl/molybdenyl oxygen. Analysis of the electronic structure in all the clusters was conducted in terms of the Mulliken population analysis, Mayer bond-orders, atomic Fukui function values, and molecular electrostatic potential (MEP) distribution. The results show that substituting a V atom with Mo leads to a reduction of the adjacent metal atom, practically without changing the electronic properties of the oxygen atoms. Furthermore, the NO adsorption on the reduced surfaces Of V2O5 and V2O5 with Mo defects has been studied. In all cases, adsorption is exothermic; the energetic stabilization is the largest for the V11MoO29 from which the molybdenyl atom was removed. However, the calculated adsorption energies are similar, within ca. 3 kcal/mol (12 kJ/mol). Thus, the effect of the molybdenum presence for energetic stabilization of adsorbed NO is not very distinct. (c) 2005 Elsevier B.V. All rights reserved.