Oxidative desulfurization of diesel oil over Ag-modified mesoporous HPW/SiO2 catalyst

Mesoporous HPW/SiO₂ modified with Ag species was used as the catalyst for the oxidative desulfurization of both model and real diesel oils. Three model diesel oils were prepared by using petroleum ether, benzene, and octene, respectively, as solvent and with dibenzothiophene (DBT) as the objective sulfur compound. The catalyst with a molar ratio of Ag to HPW being 2 (Ag₂-HPW/SiO₂) exhibits the highest catalytic activity; however, the catalytic activity decreases with further increase in Ag content. The results of nitrogen adsorption-desorption, X-ray diffraction, UV-vis, and energy dispersive spectroscopy show that isolated Ag⁺ ion is located on the modified catalyst. The modification of HPW/SiO₂ with Ag species may combine the selective absorption capacity of Ag⁺ for sulfur compounds with the catalytic activity of HPW, which is helpful to enhance the selective oxidative desulfurization. During the desulfurization process, the sulfur compounds were first selectively adsorbed on the catalyst surface by π complexation between Ag⁺ and sulfur compounds, which could increase the probability of collision between sulfur compounds and catalytic active sites and then accelerate the oxidation reaction. The sulfur content in the real diesel oil can be reduced to 228×10^-6 from the original 1800×10^-6 over Ag₂-HPW/SiO₂; the desulfurization amount is 4.6% higher than that over the unmodified HPW/SiO₂. In addition, the Ag-modified catalyst shows excellent reusability; after three reaction cycles, the desulfurization ratio of Ag₂-HPW/SiO2 is only slightly lower than that of the fresh catalyst.