Mechanism of extractive/oxidative desulfurization using the ionic liquid inimidazole acetate: a computational study

A DFT study on catalytic oxidative desulfurization with H2O2 over Ti-MWW zeolite

The catalytic mechanism of Ti-MWW in oxidative desulfurization with H₂O₂ was investigated by quantum chemical calculations. A defect model (Ti-d) and a perfect model (Ti-p) were proposed for Ti-MWW, and two possible reaction pathways starting from Ti-d and Ti-p were considered. On Ti-d, the hydroperoxy bidentate intermediate TiOOH (η²) was formed by activating H₂O₂ at the Ti center. Afterwards, aromatic sulfides were oxidized to sulfoxides and to ultimate sulfones by TiOOH (η²). The order of oxidation reactivity was benzothiophene > dibenzothiophene > thiophene, conforming to experimental observations. The Ti-p pathway proposed for oxidation of sulfides with H₂O₂ resulted in higher energy barriers compared to the Ti-d pathway. Natural bond orbital charge analysis was carried out to understand the charge distribution. This work showed that the defective Ti-MWW model for oxidative desulfurization was more active than the perfect model. Graphical abstract Catalytic oxidative desulfurizationwith H₂O₂ over Ti-MWW zeolite.