Synthesis of modified amphiphilic quaternary ammonium silicotungstate and its application in heterogeneous catalytic oxidative desulfurization

Abstract

A series of novel modified amphiphilic quaternary ammonium phosphotungstate catalysts with a Keggin structure were synthesized. Their physical and chemical properties were characterized by FT-IR, XRD, SEM, and TG-DSC. Heterogeneous catalytic oxidation desulfurization was carried out with dibenzothiophene (DBT) as a typical organic sulfide to be removed in n-octane and H₂O₂ as the oxidant. The effects of different quaternary ammonium salt structures on the desulfurization effect were studied. By the optimization of experimental conditions, the desulfurization efficiency of the catalyst hexadecyl trimethyl ammonium silicotungstate (HTA)₄SiW could reach 98.42% under the following optimal reaction conditions: 50 °C, a H₂O₂/DBT molar ratio (O/S) of 10 : 1, 0.2 g (HTA)₄SiW and 75 min. The catalyst (HTA)₄SiW could be recycled 5 times, and the recovered (HTA)₄SiW still exhibited a stable chemical structure and achieved the purpose of deep desulfurization. Finally, the possible desulfurization mechanism was proposed.