Deep oxidative desulfurization of dibenzothiophene using a flower-like WO3·H2O catalyst in an organic biphasic system

Novel flower-like WO3·H2O micro/nano-architectures are conveniently synthesized via a low-temperature oil bath route, and its catalytic oxidative desulfurization (ODS) activity for dibenzothiophene (DBT) in a model oil is systematically evaluated within an n-octane/acetonitrile (MeCN) biphasic system in the presence of H2O2 as an oxidizing reagent. The results indicate that DBT can be effectively removed using the as-synthesized WO3·H2O catalyst in the presence of H2O2 and that the catalytic process follows pseudo-first-order kinetics. Under optimal conditions, i.e., n(S/catalyst) = 5 and n(H2O2/S) = 8 at 70 °C, the sulfur content is diminished from 4000 to approximately 220 μg g−1 after 60 min of reaction. The mechanistic study reveals that the desulfurization route is dominated by direct catalytic oxidation rather than indirect oxidation by radicals. The oxidation product is dibenzothiophene sulfone (DBTO2) with almost 100% selectivity, and it can quickly migrate into the MeCN phase due to its highly polar nature, resulting in the removal of DBT from the oil phase. By combining the experimental results with the theoretical DFT calculations, the crystal structure of WO3·H2O and the electronic structures of DBT vs. DBTO2 are considered to be the key roles in this synchronized adsorption-catalytic oxidation-extraction process. In addition, the as-synthesized WO3·H2O is structural stable during the reaction and can be also used to remove 4,6-dimethyldibenzo-thiophene (DMDBT), benzothiophene (BT), and thiophene (Th) in fuel oils, suggesting its potential for practical applications.