Selective oxidation of ethanol in the liquid phase over Au/TiO2

The selective oxidation of aqueous ethanol solutions with air over two commercial 1.5 and 1wt% Au/TiO2 catalysts was investigated in six stirred mini-autoclaves operated in parallel. The catalysts were characterised by various techniques including elemental analysis, N2 physisorption, X-ray diffraction and transmission electron microscopy (TEM). Temperature, pressure, ethanol concentration, catalyst concentration and reaction time were varied in the batch experiments to study the reaction kinetics. It was possible to confirm the generally accepted mechanism of primary alcohol oxidation, in which acetaldehyde is a primary product of the oxidation that quickly undergoes further transformation to acetic acid. In presence of both acetic acid and ethanol the formation of ethyl acetate takes place until equilibrium conditions are reached. The high yields of acetic acid can be rationalised by the inhibited total oxidation of acetic acid under the applied reaction conditions. Improper storage of the gold catalysts in air exposed to light was found to lead to an irreversible change of the performance, which cannot be restored by means of recalcination. Sintering and blocking of surface sites by deposits were ruled out as possible causes for the deactivation.