Photocatalytic oxidation of dibenzothiophenes in acetonitrile using TiO 2: effect of hydrogen peroxide and ultrasound irradiation

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Photocatalytic oxidation of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6DMDBT) in acetonitrile using titanium dioxide (TiO 2) was studied. Results obtained here can be used as the reference for evaluating reactions in hydrocarbons, which aims at the development of an oxidative desulfurization process for oils. A 200 W Hg–Xe lamp (>290 nm, 19 mW/cm 2) was used as a light source, and the catalytic performances of four commercially available TiO 2 photocatalysts (PC-1, PC-2, PC-3 and P25) were compared. DBT was more stable than 4,6DMDBT under light and in the presence of photocatalyst in acetonitrile. Of the photocatalysts used, P25 showed the highest rate of photooxidation. However with P25, the decrease in initial concentration of DBT or 4,6DMDBT was less than 40% after 10 h of irradiation. To accelerate the reaction, the effect of addition of hydrogen peroxide (H 2O 2) and/or ultrasound irradiation on the TiO 2-containing system was studied. Although the addition of hydrogen peroxide (3%) and/or ultrasound irradiation more than doubled the rate of photooxidation, this efficiency was obtainable with H 2O 2 alone. Tentatively identified reaction products from DBT and 4,6DMDBT included the 5-oxide (sulfoxide) and the 5,5-dioxide (sulfone) of each substrate. Oxidation of the methyl group mainly occurred when 4,6DMDBT was reacted using only TiO 2. This result led to a finding that the acceleration of oxidation for the methyl group occurs in non-polar hydrocarbons.