Oxidation of methanol by molecularly adsorbed oxygen on Pt(111) under vacuum and ambient pressure conditions studied by infrared reflection absorption spectroscopy: identification of formate intermediate

Abstract

The reaction of methanol with oxygen on Pt(111) has been studied under ultrahigh vacuum and ambient pressure conditions by infrared reflection absorption spectroscopy (IRAS). On the surface pre-adsorbed by molecular oxygen, which was prepared by oxygen adsorption at 100K on Pt(111), adsorbed methanol was oxidized to formate at 160K in vacuum. The formate was decomposed to CO2 and H2 by heating to 270K. When the pre-adsorbate was dissociatively adsorbed oxygen atoms, produced by annealing the molecule covered surface at 300K, methanol did not directly react with the oxygen atoms but was decomposed to CO, H2, and H2O on heating. The molecularly adsorbed oxygen was thus concluded to be the reactive species for the oxidation of methanol to formate. In catalytic oxidation of methanol in the flow of CH3OH, O2, and He with pressures of 1.6×102, 1.3×103, and 1.2×103Pa, respectively, formate was detected on in situ IRA spectra at 330–400K, suggesting that the reaction pathway through formate plays an important role in methanol oxidation under catalytic conditions.