Efficient Selective Oxidation of Benzyl Alcohol Over Ordered Mesoporous Metal Oxides-Supported Gold Nanoparticles

Mesoporous metal oxides (CeO₂, Co₃O₄, and Fe₂O₃) were synthesized using a soft template method. Gold nanoparticles (Au NPs) were immobilized by deposition-precipitation method. The as-synthesized catalysts were characterized by powder x-ray diffraction (p-XRD), N₂-sorption (BET), high-resolution transmission electron microscope (HRTEM), and hydrogen temperature programmed reduction (H₂-TPR). The metal oxides have mesostructured pores and surface areas, of 167.45, 35.71, and 42.91 m²/g for CeO₂, Co₃O₄, and Fe₂O₃, respectively. These mesoporous oxides showed reducible characteristics at reduction temperatures above 300°C. The immobilization of the gold nanoparticles caused a shift of the reduction peaks of CeO₂, and Fe₂O₃ to lower temperatures. The catalytic activity of supported gold nanoparticles was evaluated on the liquid phase oxidation of benzyl alcohol with tert-butyl hydroperoxide (TBHP) as an oxidant. The results showed that Au/Co₃O₄ produced higher conversions as compared to their counterparts, whereas the selectivity toward benzaldehyde was 100% when using Au/CeO₂ and Au/Fe₂O₃ catalysts, but when Au/Co₃O₄ was used the selectivity was 82.47%. At higher temperatures low conversions were observed, as a result of decomposition of the oxidant, TBHP. Thus, this reaction gave optimum conversions at 80°C for all supported catalysts.