The electronic structure of VSbO4 exhibits similarities with that of other metal transition oxides with rutile-type structure, showing O 2s, O 2p, Sb and V bands well differentiated. At lower energy (at -34 eV), there is a band formed by O 2s orbitals with some Sb 5s (bottom) and Sb 5p (top). The Sb 5s orbitals appear in the -20 eV energy region, while around -14 eV there are 0 2p states (metal-oxygen bonding) and also some Sb 5p orbitals contributions. At the Fermi level it can be observed the contribution of V 3d orbitals, which is in agreement with the metal character that vanadium gives to VO2 in the rutile phase. The V 4s and V 4p orbitals can be found higher in energy. On the other hand, the analyses of the electronic populations of the VSbO4 catalyst doped with titanium show that partial substitution of Sb by Ti provokes V-cations oxidation. This occurs mainly by depopulating V 3d antibonding states located around the Fermi level and results in V-O bonds reinforcement. Those vanadium cations in a higher oxidation state improve the catalyst surface reoxidation step, suggesting that Sb partial substitution by Ti gives a more active catalyst. The effect of the Ti-doping on the reaction rate limiting step is also discussed. (c) 2005 Elsevier B.V. All rights reserved.