A kinetic study of vapor-phase cyclohexene epoxidation by H2O2 over mesoporous TS-1

• Vapor-phase cyclohexene epoxidation was performed over mesoporous TS-1 using H2O2.
• The gas-phase production of cyclohexene epoxide was very stable with high selectivity.
• Detailed kinetic studies were performed on gas-phase alkene epoxidation.
• A compensation effect was observed with varied partial pressure of water or H2O2.
• We report a kinetic model to understand the mechanism and the compensation effect.

A kinetic analysis of gas-phase cyclohexene epoxidation by H2O2 over mesoporous TS-1 was performed. The production of cyclohexene oxide was very stable with high selectivity. Based on the kinetic analysis, the gas-phase mechanism is proposed to be similar to that of the liquid-phase reaction: an Eley–Rideal type mechanism, in which the reaction between a Ti–OOH intermediate and the physisorbed alkene is the rate-determining step. When the partial pressure of water or H2O2 was varied, a compensation effect was observed. Based on the kinetic model, the compensation effect is attributed to variations in the surface coverage of intermediates, specifically the competitive adsorption of water and H2O2 at the Ti active sites. A meaningful activation energy can only be obtained at high surface coverages of H2O2 and was determined to be 40 ± 2 kJ/mol.

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