Methanol oxidation over Au/γ-Al2O3 catalysts

Abstract

Methanol adsorption and reaction was investigated over Au/γ-Al₂O₃ catalysts. The catalysts were prepared by deposition precipitation (DP) and incipient wetness impregnation methods. The catalysts were used to catalyze the oxidation of methanol and characterised using X-ray diffraction (XRD), temperature programmed desorption(TPD), temperature programmed pulse flow reaction, scanning electron microscopy(SEM), X-ray photoemission spectroscopy (XPS) and Energy dispersive x-ray analysis (EDAX). The adsorption of methanol over γ-Al₂O₃ indicated a monolayer adsorption of methanol, forming methoxy group on the surface. The methoxy is relatively stable until 120oC, at which point dehydration to dimethyl ether occurs by bimolecular surface reaction. As the concentration of methoxy diminishes, so the mechanism reverts to a decomposition pathway, producing methane, CO and hydrogen (~340oC) in TPD. The gold supported on γ-Al₂O₃ play a role on the performance of the catalyst with respect to methanol oxidation. The oxidation reaction of Au/γ-Al₂O₃ catalysts prepared by deposition precipitation and incipient wetness impregnation both shows the reaction is complete oxidation to CO2 and H2O. However, it involved dehydration of methanol to dimethyl ether (DME) at about 150oC followed by decomposition of DME to CH4, CO, and H2. The main product from TPD is DME due to high surface coverage of methoxy species on the catalysts surface. The XPS, SEM, EDAX, indicated high dispersion of gold with complete methanol conversion attained at lower temperature compared to when γ-Al₂O₃ catalyst was used alone.

Key Words: Au catalysis, methanol oxidation, methanol catalytic combustion, TPD, XPS, SEM, and EDAX