Aerobic oxidation of alcohols catalyzed by gold nanoparticles supported on gallia polymorphs

Gold nanoparticles supported on polymorphs of gallia (α-, β-, and γ-Ga₂O₃) were evaluated for the solvent-free liquid phase oxidation of benzyl alcohol by molecular oxygen. High selectivity to benzaldehyde was obtained under the reaction conditions of 130 °C, 5 atm and 5 h in an autoclave. The Au/γ-Ga₂O₃ catalyst was also evaluated for oxidation of a range of alcohols using mesitylene as solvent under flowing oxygen at atmospheric pressure and 90 °C. Under these conditions the conversion of benzyl alcohol reached 100% after 2 h and it was demonstrated that the catalyst can be recycled four times without significant loss of activity. The structural data (TEM, XPS and TPSR of 2-propanol adsorption) along with the catalytic results indicate that the unique dehydrogenation capabilities of the Au/γ-gallia system are responsible for the enhanced activity achieved in the liquid phase oxidation of benzyl alcohol.