Oxidative removal of dibenzothiophene in a biphasic system using sol–gel Fe[sbnd]TiO2 catalysts and H2O2 promoted with acetic acid

Abstract

FeTiO2 catalysts were synthesized with the sol–gel method and were characterized by X-ray diffraction, N2 adsorption measurement, Mössbauer spectroscopy, UV–vis spectroscopy, Raman spectroscopy, temperature programmed reduction, and temperature programmed desorption of NH3. The FeTiO2 catalysts chiefly consist of crystalline anatase. Fe3+ ions are highly dispersed on the surface and distributed in octahedral-coordinate sites within different environments in TiO2. The FeTiO2 catalysts were then evaluated for oxidation desulfurization of dibenzothiophene in a biphasic reaction mixture consisting of an acidified polar phase and a hexadecane model fuel phase. Compared to control tests, the catalytic activity for dibenzothiophene (DBT) oxidation is markedly improved by addition of acetic acid, typically at least doubling DBT conversion compared to that observed under control conditions. Under optimal conditions (10wt% Fe in the FeTiO2 catalyst and a pH adjusted to 0), 100% of the 300ppm DBT initially present in the reaction mixture could be completely oxidized within 5min. Oxidation of DBT formed sulfoxide/sulfones which were found to be enriched in the polar phase. The sol–gel FeTiO2 catalysts possess several attributes which may contribute to their activity for DBT oxidation: (1) their hydrophilic–hydrophobic character that facilitates DBT oxidation as a phase transfer catalyst; (2) coordination and activation of acetic acid and peroxyacetic acid with Fe3+ and Ti4+ present at the FeTiO2 surface, and (3) formation of superoxides at the FeTiO2 surface.