Tuneable oxidation of styrene to benzaldehyde and benzoic acid over Co/ZSM-5

Abstract

Co/ZSM-5 prepared via the simple impregnation method was used as a catalyst for the solvent-free oxidation of styrene with molecular oxygen as the oxidant. Co/ZSM-5-500 catalyst prepared at a calcination temperature of 500 °C demonstrated high catalytic activity (TON 566.6 mol mol_Co⁻¹) and selectivity toward benzaldehyde (96%) at 80 °C. Meanwhile, the Co/ZSM-5-450 catalyst showed ca. 100% conversion and 94.7% selectivity to benzoic acid for styrene oxidation at 90 °C. The tuneable synthesis of benzaldehyde and benzoic acid by styrene oxidation over Co/ZSM-5-500 and Co/ZSM-5-450 catalysts, respectively, was realized. This reason that the two catalytic systems exhibited two different target products was explored by analyzing the surface properties of the catalysts by XRD, ²⁹Si and ²⁷Al MAS NMR, NH₃-TPD, pyridine-adsorption IR, and H₂-TPR techniques, and the related reaction mechanism was authenticated by in situ DRIFTS. Besides, the recovery and reuse of the catalyst was tested and the activity was effectively maintained even in the fourth run.