Mesoporous Copper-Cerium Mixed Oxide Catalysts for Aerobic Oxidation of Vanillyl Alcohol

The production of vanillin from lignin-derived vanillyl alcohol poses a great deal of research interest because of the availability of renewable lignin in abundant quantities. In the present study, a series of copper-doped ceria (CeO2) catalysts were prepared by a modified template-assisted method, characterized by various techniques, and explored for the oxidation of vanillyl alcohol to vanillin with molecular oxygen as the oxidant at normal atmospheric pressure. Interestingly, a 10% Cu-doped ceria (Cu0.1Ce0.9O2−δ) catalyst exhibited superior catalytic activity for the oxidation of vanillyl alcohol with 95% and 100% conversions at atmospheric and moderate pressures, respectively, with 100% vanillin selectivity in both cases. A thorough characterization (XRD, BET surface area, Raman spectroscopy, SEM, TEM, XPS, and H2-TPR) of the synthesized mesoporous oxides (CuO, CeO2, Cu0.05Ce0.95O2−δ, Cu0.1Ce0.9O2−δ, and Cu0.15Ce0.85O2−δ) revealed that mixed oxide catalysts exhibit more oxygen vacancies and better redox behavior in comparison to the single oxides, which lead to improved catalytic activity and selectivity. Reaction parameters, such as reaction temperature, reaction time, catalyst amount, and the solvent, were also optimized for the reaction.