Aerobic oxidative esterification of benzyl alcohol and acetaldehyde over gold supported on nanostructured ceria-alumina mixed oxides

Au nanoparticles supported on nanostructured ceria-alumina mixed oxides (10 and 30 wt% ceria) were prepared by a deposition-precipitation method. Their properties were studied by N₂ adsorption, XRD, TEM, X-ray photoelectron spectroscopy, and UV/Vis spectroscopy under temperature-programmed reduction or oxidation. The materials catalyzed the liquid-phase aerobic oxidative esterification of benzyl alcohol and benzaldehyde effectively and showed a much better performance than Au supported on the individual oxides. The reactions occurred with high turnover numbers (up to 19000) in methanol solutions in the absence of any auxiliary base and gave mainly methyl benzoate. The strong synergetic effect of ceria and alumina can be explained by the enhanced oxygen storage capacity of the materials prepared from mixed oxides compared to that of pure alumina and ceria. The order of the catalytic activity (Au/Al₂O₃<Au/CeO₂<Au/Ce(10)-Al<Au/Ce(30)-Al) correlated well with the oxygen activation capacity of the materials.