Deep Oxidative Desulfurization of Model Fuels Catalyzed by Subnanosized Ti Oxoclusters

Oxidative desulfurization is a highly effective approach to decrease the sulfur content in transportation fuel and has become an attractive research topic in recent years. Herewith, we have developed a new kind of carboxylic acid-functionalized imidazolium-based ionic liquid-stabilized Ti oxoclusters via a solvothermal method. The as-synthesized Ti oxoclusters were investigated by elemental analysis, Fourier transform infrared spectroscopy, diffuse reflectance UV-vis, X-ray diffraction, thermogravimetric analysis, high-resolution transmission electron microscopy (HRTEM), and high-angle annular dark field-scanning TEM. Characterization indicated that Ti oxoclusters existed in the form of subnanosized structure and uniformly dispersed with an average particle size of ca. 1 nm due to the protection role of the ionic liquids (ILs). Especially, Ti oxo-HSO4 afforded a superior catalytic activity in the extraction and catalytic oxidative desulfurization process with MeOH as an extractant and H2O2 as an oxidant. The full removal of dibenzothiophene in model fuels was achieved within 30 min at 60 degrees C. Besides, the Ti oxoclusters were robust and exhibited high stability in consecutive catalytic recycles. The parent Ti oxoclusters treated with H2O2 can afford Ti-OOH species, which was catalytically active species. The anion HSO4- in IL played a crucial role in the activation of Ti-hydroperoxo species by forming hydrogen bonds. This may provide a new insight into the construction of metal oxoclusters for oxidative desulfurization.