Liquid-phase cyclohexene epoxidation over mesoporous-assembled TiO₂-CeO₂ mixed oxide catalysts

Abstract

Epoxides are valuable and versatile commercial intermediates used as key raw materials for producing several useful chemical products. The epoxidation of olefins is indispensable for the petrochemical industry. It is an oxygen transfer reaction, resulting in oxygenated molecules, so-called epoxides. The aim of this work was to investigate the cyclohexene epoxidation over mesoporous-assembled TiO2- CeO2 mixed oxide catalysts using H2O2 as an oxidant. The catalysts were synthesized by a sol-gel process with the aid of a structure-directing surfactant and characterized by several techniques, i.e. surface area analysis, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and thermogravimetric differential thermal analysis (TG-DTA). The experimental results showed that among various studied TiO2 -CeO2 mixed oxide catalysts, the 0.98TiO2- 0.02CeO2 mixed oxide (with 2 mol% CeO2) calcined at 500 ℃ gave the highest cyclohexene oxide selectivity and comparatively low undesired product selectivities. The optimum reaction conditions—H2O2-to-cyclohexene molar ratio of 0.25:1 and catalyst-to-reaction volume ratio of 3.33 mg/ml—gave a maximum cyclohexene oxide selectivity of 70.1% after the reaction time of 5 h.