Solid-phase synthesis of titanium-oxo clusters and their unprecedented catalytic performance in oxidative desulfurization of fuel oil

Titanium-oxo clusters (TOCs) have attracted much attention due to their diversity of structure and composition in recent years. Currently, such materials are synthesized by the solvothermal method. In this work, we report that a series of TOCs involving Ti₂₉KO₃₉(OEt)₃₈, Ti₆O₆(4-tbbz)₆(OⁱPr)₆, Ti₆O₆(abz)₆(OⁱPr)₆ and Ti₆O₆(4-tbbz)₁₀(OⁱPr)₂ have successfully been prepared by the solid-phase method. The structure of obtained materials was solved by the single-crystal X-ray diffraction technique. Furthermore, the performance of these TOCs was evaluated by the oxidative desulfurization (ODS) reactions of a model fuel oil. It was found that Ti₆O₆(4-tbbz)₁₀(OⁱPr)₂ exhibited unprecedented catalytic activity with a turnover frequency (TOF) of 729 h⁻¹ and mass activity of 1919 mmol h⁻¹ g⁻¹. The results from the experiments and theoretical calculations reveal that the Ti-hydroperoxo five-membered ring intermediates formed by the combination of binuclear titanium sites in Ti₆O₆(4-tbbz)₁₀(OⁱPr)₂ clusters with H₂O₂ play a key role in the oxidation of sulfur compounds. In addition, it is demonstrated that such TOCs can be utilized as precursors for the synthesis of Ti-MOFs.