Characterisation of adsorbed intermediates in the CH3OH/O/Cu(100) system by secondary ion mass spectrometry

The coadsorption of methanol and oxygen on Cu(100) has been examined using secondary ion mass spectrometry (SIMS). The study provides a mass-spectrometric observation of the surface intermediates present during adsorption at 130 K, and after heating to 320 K. Isotopically-labelled reagents (18O2, CD3OD, CH3OD) have been used to facilitate the interpretation of spectra. The SIMS data indicate that MeOD dissociates at 130 K in the presence of pre-adsorbed 18O2 to yield a physisorbed D2O layer, in addition to a methoxy (MeO) intermediate and other products. Spectra obtained at 320 K reveal an enhanced concentration of formate species (predominantly as HC18O16O). The principal positive secondary ion associated with the methoxy intermediate was found to be CuCH2O‡, rather than the expected CuCH3O‡, which was not detected. The observed behaviour is consistent with reaction mechanisms proposed by Wachs and Madix to account for methanol oxidation on O/Cu surfaces [J. Catal. 31 (1982) 243]. # 2001 Elsevier Science B.V. All rights reserved.