Hydrogen Formation in the Reactions of Methanol on Supported Au Catalysts

Abstract

The adsorption and reactions of methanol have been investigated on Au metal supported by various oxides and carbon Norit of high surface area. Infrared spectroscopic studies revealed the dissociation of methanol at 300 K, which mainly occurs on the oxide-supports yielding methoxy species. The presence of Au already appeared in the increased amounts of desorbed products in the TPD spectra. The reaction pathway of the decomposition and the activity of the catalyst sensitively depend on the nature of the support. As regards the production of hydrogen the most effective catalyst is Au/CeO₂ followed by Au/MgO, Au/TiO₂ and Au/Norit. In contrast, on Au/Al₂O₃ the main process is the dehydration reaction yielding dimethyl ether. On Au/CeO₂ the decomposition of methanol starts above ~500 K and approaches total conversion at 723–773 K. The products are H₂ (~68%) and CO (~27%) with very small amounts of methane and CO₂. The decomposition of methanol follows the first order kinetics. The activation energy of this process is 87.0 kJ/mol. The selectivity of H₂ formation at 573–773 K was ~90%, this value increased to 97% using CH₃OH:H₂O (1:1) reacting mixture indicating the involvement of water in the reaction. No deactivation of Au catalysts was experienced at 773 K in ~10 h. It is assumed that the interface between Au and partially reduced ceria is responsible for the high activity of Au/CeO₂ catalyst.