Mechanistic study of methanol oxidation on Pt(111) single crystal

The oxidation of methanol on a Pt(1 1 1) single crystal was studied using X-ray photoelectron spectroscopy and polarization-modulation infrared reflection absorption spectroscopy in a temperature range between 300 and 600 K. It was shown that the oxidation starts at approximately 350 K, and methanol is oxidized mainly to CO2 and methyl formate. CO was not found among gas-phase products in the whole temperature range. A small amount of formaldehyde was detected in the gas phase only at 350-450 K. On the platinum surface, methyl formate, CO, formates, carbonates, and carbon atoms were detected under reaction conditions. Their concentrations depended on the reaction temperature and the methanol/oxygen molar ratio. Formates were detected only at 300 K, indicating their low thermal stability. Both CO and formate are the key intermediates in the total oxidation of methanol, which can proceed via two different pathways: a CO-based route and a non-CO-included route. Carbonates are formed from formates and demonstrate extremely high thermal stability. This leads us to propose that not only CO but also carbonates can poison the platinum surface and prevent the oxidation of methanol. The overall mechanism of the oxidation of methanol on platinum is discussed.