Self-assembled HPW/silica–alumina mesoporous nanocomposite as catalysts for oxidative desulfurization of fuel oil

Abstract

Mesoporous silica–alumina–polyoxometalate (HPW/SiO2–Al2O3) nanocomposite materials with silica–aluminum molar ratios of 10–80 have been successfully synthesized by evaporation induced self-assembly method with non-ionic surfactant P123 as template agent. The surface areas and pore sizes of the obtained HPW/SiO2–Al2O3 materials are in the range of 509–623 m2 g−1 and 3.6–3.8 nm, respectively, with different silica–aluminum molar ratios. The incorporated polyoxometalate clusters preserve their intact Keggin structure into the mesoporous frameworks. The Py–FTIR investigations indicate that the surface acidity of catalysts gradually increases with an increase in the percentage of aluminium, and the Lewis acidity sites are predominant. The nanocomposites were used as catalysts, and H2O2 as oxidant for oxidative desulfurization (ODS) of model fuel, which was composed of benzothiophene (BT), petroleum ether and benzene. The results show that the adsorption capacity and ODS performance of catalysts have close relationship with their surface acidity. An appropriate amount of Lewis acidity sites can contribute to the selective oxidation of the BT due to the preferential adsorption of BT on the catalyst surface, while the Bronsted acidity sites have a negative impact on the selective oxidation of the BT. As a result, the mesoporous HPW/SiO2–Al2O3 with silica–aluminum molar ratio of 50 shows the highest selectivity for BT oxidation in the presence of benzene and has achieved the goal of desulfurization. In addition, the catalyst shows excellent reusing ability, which makes it a promising catalyst in ODS process.