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WO x /TiO 2 catalysts were synthesized by impregnating aqueous (NH 4 ) 2 WO 4 on hydrous titania nanotubes. The materials were annealed in air at 500 °C and characterized by X-ray diffraction (XRD), Raman spectroscopy, high-resolution transmission electron microscopy (HRTEM), high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), and X-ray photoelectron spectroscopy (XPS); their catalytic activity was evaluated in the oxidation reaction of dibenzothiophene (DBT). After annealing at 500 °C, the structure of the support transformed from orthorhombic, with nanotubular morphology, to tetragonal, yielding anatase nanoparticles decorated by tungsten nanoparticles on its surface. During this transformation, the nanotubes released residual Na + ions from the interlayer space, which reacted with tungstate species to change the W coordination from octahedral to tetrahedral, yielding e1 nm Na x (WO 4 ) nanoparticles on the surface of anatase TiO 2 . These nanoparticles were highly active for the DBT oxidation, showing a linear dependence on the W surface density at concentrations below 6.9 W/nm 2 . In TiO 2 oversaturated with tungsten nanoparticles, the intrinsic kinetic velocity (r DBT ) of the DBT oxidation reached its maximum value; 6.9 W /nm 2 is then the optimum surface density concentration to attain a high catalytic activity in the DBT oxidation.

In this work a study of dibenzothiophene removal by an oxidation-extraction scheme is presented. Experiments were carried out to observe the role that the solvent plays during the process, as well as the oxidizing agent and catalyst. The oxidation was carried out with hydrogen peroxide in the presence of a catalyst of tungsten supported on zirconia (WO x -ZrO 2 ). A dibenzothiophene + n-hexadecane model mixture was employed to simulate a diesel fuel. Methanol, ethanol, acetonitrile, and γ-butyrolactone were used as extraction solvents. Dibenzothiophene (DBT) was removed more efficiently by γ-butyrolactone with respect to other solvents. The highest reactivity was achieved when γ-butyrolactone was used during DBT oxidation with and without catalyst. When oxidation was carried out without catalyst, the oxidant behavior of the mixture could be explained in terms of the dissociation of hydrogen peroxide to produce strong oxidant species such as perhydroxyl ions (HO 2 -) by the influence of the aprotic solvents. Finally, when a catalyst was used during the oxidation, there was an additional oxidation contribution through the formation of surface peroxo-metal intermediates

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