Ionic Liquid-Modified Co/ZSM-5 Catalyzed the Aerobic Oxidation of Cyclohexane: Toward Improving the Activity and Selectivity

Ionic liquid (IL)-modified metal/ZSM-5 composites served as heterogeneous catalysts toward cyclohexane aerobic oxidation, demonstrating excellent KA oil (cyclohexanol and cyclohexanone) selectivity with improved activity. The effects of the different functional groups of the IL on the oxidation were further systematically investigated. The catalytic activity of the catalyst was closely related to the anionic group of the IL, whereas the cationic group had no obvious effects. The cyclohexane conversion and selectivity of KA oil reached 9.7 and 92.2%, respectively, using the optimized catalyst C6mimHSO4-Co/ZSM-5. This favorable catalytic performance was mainly attributed to the activation of the cyclohexane by the anionic group of the IL, whereas the excellent selectivity was ascribed to the superior solubility of KA oil in the IL while avoiding overoxidation. Based on the results of in situ electron paramagnetic resonance spectra, a catalytic mechanism involving a free-radical process was also proposed.