Enhanced oxidative desulfurization of dibenzothiophene in the presence of cyclohexene, indole, quinoline, and p-xylene using surface-silylated titania-silica catalyst

Heterogeneously catalyzed oxidative desulfurization (ODS) offers a mild pathway to remove refractory sulfur compounds from liquid hydrocarbon fuels. However, adsorption of polar oxidation byproducts on the catalyst surface decreases desulfurization efficiency at the low ODS reaction temperature. Here, we report that high-performance surface-silylated titania-silica catalysts can be prepared by a silylation method using hexamethyldisilazane (HMDS) and trimethylchlorosilane (TMCS) as the silane reagents. The bulk structure and surface properties of the catalysts before and after surface silylation were characterized by N2 adsorption–desorption, XRD, FTIR, TGA, UV–vis DRS, FESEM, EDS, and water contact angle measurement to establish the structure–function relationship. The effects of silyl groups loading, reaction temperature, type of oxidant, and inhibiting compounds on the ODS performance of the catalysts were systematically evaluated. The results revealed that TS-H-2 catalyst with the optimum loading of silyl groups was an excellent catalyst capable of ultra-fast oxidizing ∼100 % of DBT, after only 5 min, which was due to increased surface hydrophobicity and decreased accumulation of poisoning polar byproducts on the active sites. The ODS performance of TS-H-2 was better preserved compared to unmodified TS-nonsil catalyst in the presence of inhibiting compounds such as cyclohexene (CH), indole (IND), and quinoline (QU), while it increased in the presence of p-xylene (PX). The negative effects of the three former inhibiting compounds were resulted from their competition with the sulfur compound for the oxidant and poisoning of the active sites. The positive effect of PX on the ODS rate was due to solubilization of the strongly adsorbed molecules on the surface of catalyst.