Synthesis and deep oxidative desulfurization of vanadium-substituted polyoxotungstate phase transfer catalyst

A series of phase transfer catalysts, composed of vanadium-substituted phosphotungstic acid(H₄[PW₁₁VO₄₀]) and different quaternary cationics were synthesized through ion exchange method. The characterization of FT-IR spectroscopy and X-ray diffraction confirmed that the integrity of polyoxometalate anions and quaternary ammonium cations immobilized in the phase transfer catalyst. The as-prepared catalysts were applied to the catalytic oxidative desulfurization of model diesel oil using H₂O₂ as oxidant. The influencing factors such as quaternary cationics species, catalyst composition, catalyst amount, oxygen-sulfur ratio and reaction temperature were investigated.[(C₁₆H₃₃(CH₃)₃)N]₃H[PW₁₁VO₄₀] is found to be efficient and reusable catalyst for oxidative desulfurization reaction. Under the optimized reaction conditions of n(catalyst)/n(model diesel)=1:80, n(H₂O₂)/n(model diesel)=8:1, 50℃, 3 h, the catalyst exhibits the dibenzothiophene conversion of 100% and excellent reusability with 99.7% conversion after five times reaction. The catalyst and reactants form a microemulsion system and behave like homogeneous mixture during reaction, but precipitates with biphase separation when the reaction ends. The catalyst could be quickly separated and recycled by centrifugation.