The interaction of water molecules with the reduced and fully oxidized surface sites of the supported vanadium oxide catalyst VO x /TiO 2 has been investigated by the Periodic DFT method. It has been found that the molecular structures of the surface VO x species are radically altered when adsorbed water is involved in the redox cycle. Water dissociates spontaneously on the reduced vanadium sites forming the surface hydroxyl groups OH. The following reoxidation by gas-phase oxygen results in the formation of active sites OdVO 2 (OH) including both the Bro ¨nsted acid sites OH and the vanadyl oxygen VdO more reactive than on the dehydrated surface. Gas-phase oxygen, embedded on the surface under oxidation, does not take part in the formation of surface hydroxyl groups. The hydroxylation-hydration reaction path on the fully oxidized VO x /TiO 2 surface has been calculated. It has been found that the recombination reaction of the two surface hydroxyl groups VsOH to form water with the following water desorption prevails over the reverse reaction of hydroxylation. In agreement with the experimental data we conclude that lattice oxygen of surface vanadia species VO x , rather than gas-phase oxygen, undergoes isotope exchange with that of the adsorbed water.

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New very effective results on the liquid-phase oxidation of cyclohexene to cyclohexanone by nitrous oxide are analyzed using the B3LYP/6-31G* approximation to predict a two-step reaction mechanism correlated with the experimental data.