Catalytic epoxidation of cyclohexene over different oxide catalysts

Abstract

Cyclohexene oxide is an important intermediate in several chemical industries. It can be produced via partial oxidation of cyclohexene, so-called cyclohexene epoxidation. Many research works have been focused on the development of new active and selective catalysts for cyclohexene epoxidation that can avoid undesired reactions. The purpose of this work is to investigate the cyclohexene epoxidation using different catalysts, i.e. commercial TiO₂ (TiO₂ (P- 25)), sol-gel-synthesized mesoporous-assembled TiO₂ (TiO₂ (SG)), SiO₂, AI₂O₃, and Fe₃C₄. The experimental results showed that TiO₂ (SG) provided the highest cyclohexene conversion and cyclohexene oxide selectivity. The addition of Ru O₂ is investigated on TiO₂ (SG) prepared by two methods: (1) incipient wetness impregnation (IWI) method (RuO₂/TiO₂ (IWI)) and (2) single-step sol-gel (SSSG) method (RuO₂/TiO₂ (SSSG)). Between RuO₂/TiO₂(IWI) and RuO₂/TiO₂ (SSSG), 1 mol% RuO₂/TiO₂(IWI) calcined at 550°C for 4 h was found to possess selectively high catalytic performance based on cyclohexene oxide production. The optimum reaction conditions found are H₂O₂-to-cyclohexene ratio of 1, t-butanol as solvent, catalyst amount of 0.5 g, and reaction temperature of 70°C. The recyclability of the RuO₂/TiO₂ (IWI) and RuO₂/TiO₂ (SSSG) catalysts is also investigated. It was found that after three cycles, RuO₂/TiO₂ (IWI) exhibits slight decrease in cyclohexene conversion with significant decrease in cyclohexene oxide selectivity. On the other hand, RuO₂/TiO₂ (SSSG) exhibits almost unchanged in both conversion and selectivity, indicating its higher stability.