Selective oxidative esterification of alcohols on Au/ZrO2 catalyst under ambient conditions

Nano-gold catalysts were prepared by the liquid reduction method and employed in the oxidative esterification of alcohols under ambient conditions. The effects of the supports and gold loading on the catalytic behavior were investigated. The catalysts were characterized by transmission electron microspectroscopy, X-ray diffraction, X-ray photoelectron microspectroscopy and atomic absorption spectrometry. The results indicated that nano-scale metallic state gold was highly dispersed on the support. 95 % methyl benzoate yield was obtained over 3 wt% Au/ZrO2 catalyst at 30 °C under air atmosphere. Under optimized reaction conditions, benzyl alcohols with electron-withdrawing groups could give high selectivity to the corresponding methyl ester at moderate conversion of alcohols. However, when a benzyl alcohol with electron-donating group was used, high conversion of alcohol but low selectivity of the corresponding methyl ester was obtained. Low yields were obtained with aliphatic alcohols as substrates even at high temperature. The kinetic analysis of the oxidation from benzyl alcohol to benzaldehyde and from benzaldehyde to methyl benzoate was also described. The facile and simple procedure was a great option for direct synthesis of methyl esters from alcohols.