Highly selective oxidation of styrene to benzaldehyde over a tailor-made cobalt oxide encapsulated zeolite catalyst

A tailor-made catalyst with cobalt oxide particles encapsulated into ZSM-5 zeolites (Co₃O₄@HZSM-5) was prepared via a hydrothermal method with the conventional impregnated Co₃O₄/SiO₂ catalyst as the precursor and Si source. Various characterization results show that the Co₃O₄@HZSM-5 catalyst has well-organized structure with Co₃O₄ particles compatibly encapsulated in the zeolite crystals. The Co₃O₄@HZSM-5 catalyst was employed as an efficient catalyst for the selective oxidation of styrene to benzaldehyde with hydrogen peroxide as a green and economic oxidant. The effect of various reaction conditions including reaction time, reaction temperature, different kinds of solvents, styrene/H₂O₂ molar ratio and catalyst dosage on the catalytic performance were systematically investigated. Under the optimized reaction condition, the yield of benzaldehyde can achieve 78.9% with 96.8% styrene conversion and 81.5% benzaldehyde selectivity. Such an excellent catalytic performance can be attributed to the synergistic effect between the confined reaction environment and the proper acidic property. In addition, the reaction mechanism with Co₃O₄@HZSM-5 as the catalyst for the selective oxidation of styrene to benzaldehyde was reasonably proposed.