Liquid-Phase Cyclohexene Epoxidation with H₂O₂ over RuO₂-Loaded Mesoporous-Assembled TiO₂ Nanocrystals: Catalyst Preparation and Recyclability

摘要

Abstract The purpose of this work was to investigate the liquid-phase cyclohexene epoxidation with H₂O₂ using RuO₂-loaded mesoporous-assembled TiO₂ nanocrystals. The loading of RuO₂ on the mesoporous-assembled TiO₂ was performed by two methods: (1) incipient wetness impregnation (IWI) (RuO₂/TiO₂ (IWI)) and (2) single-step sol–gel (SSSG) (RuO₂/TiO₂ (SSSG)). Among the investigated RuO₂/TiO₂ (IWI) and RuO₂/TiO₂ (SSSG) catalysts, 1 mol.% RuO₂/TiO₂ (SSSG) calcined at 450 °C was found to possess relatively high catalytic performance based on the cyclohexene conversion and cyclohexene oxide selectivity. The recyclability of the RuO₂/TiO₂ (IWI) and RuO₂/TiO₂ (SSSG) catalysts was also investigated. It was found that after three consecutive catalytic reaction cycles, the RuO₂/TiO₂ (IWI) exhibited a slight decrease in cyclohexene conversion, but a significant decrease in cyclohexene oxide selectivity. On the other hand, the RuO₂/TiO₂ (SSSG) exhibited almost unchanged conversion and cyclohexene oxide selectivity, indicating its much higher stability. XRF and TPR results indicate that the high stability of the RuO₂/TiO₂ (SSSG) is due to the strong metal oxide-support interaction.