Methanol oxidation on Au(332): methyl formate selectivity and surface deactivation under isothermal conditions

Methanol oxidation on the stepped Au(332) surface was investigated by pulsed isothermal molecular beam (MB) experiments. The effect of the surface temperature as well as the influence of changes in the methanol and atomic oxygen flux on the partial oxidation to methyl formate was studied. A maximum in methyl formate formation is observed at 250 K under the applied single collision conditions. Increasing the methanol to oxygen ratio was found to increase the selectivity to methyl formate and decrease unwanted overoxidation to surface deactivating formate detected by in situ infrared reflection absorption spectroscopy (IRAS). The results show evidence for the importance of an additional deactivation mechanism for methyl formate formation connected to methanol which is active under oxygen-deficient conditions at low temperatures. Moreover, the measurements suggest a small number of sites to be highly reactive for methyl formate formation which are preferentially blocked under oxygen-deficient conditions.