Ethanol oxidation over Au/TiO₂ catalysis

Abstract

The adsorption and reaction of ethanol over Au/TiO₂ catalysts was investigated using pulse flow reactor, DRIFTS, and TPD. The adsorption of ethanol over TiO₂ (P25) indicated a full monolayer adsorption of ethanol, with much of it in a dissociative state, forming ethoxy group on the cationic sites and hydroxyl group at anions. The ethoxy is relatively stable until 300^oC, at which point dehydration to ethene occurs by a bimolecular surface reaction. As the concentration of ethoxy on the surface disappears, so the mechanism reverts to a decomposition pathway, producing methane, CO and hydrogen (~320^oC) in TPD. However, the presence of gold on the catalysts prepared by deposition precipitation method indicates that the reaction is complete oxidation to CO₂ and water similar to Titania. The effect of the presence of low level of gold is marked with complete conversion of ethanol at low temperature (220^oC) lower than Titania (240^oC).Simultaneously, ethanol oxidation on Au/TiO₂ catalyst was followed by dehydration to ethene at 300^oC (characteristic of TiO₂) and dehydrogenation to ethanal at high temperature. The pathway which gives ethene as seen on TiO₂ remains, but a new feature of the reaction is the evolution of CO₂ and H₂ (a peak is seen in TPD above 350^oC) and appears to be due to the production of formate species on the surface of the catalysts. This formate species is mainly involved in the complete oxidation reaction of ethanol on the catalysts.

Keywords: Au catalysis, ethanol oxidation, ethanol catalytic combustion, TPD, DRIFTS