Oxidation of adsorbed CH3 and C2H5 species on Rh(111)

The reaction pathways of adsorbed CH3 and C2H5 in the presence of coadsorbed oxygen atoms on the Rh(111) surface were investigated by means of temperature-programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS), and high-resolution electron energy loss spectroscopy (HREELS). CHx fragments were produced by the dissociation of the corresponding iodo compounds. Oxygen adatoms significantly stabilized carbon-iodide bonds and induced the desorption of strongly adsorbed methyl and ethyl iodides. A weak signal of methoxy species has been detected by HREELS in the low temperature interaction of CH3 and O. Oxidation of hydrocarbon fragments led to the production of H2O, CO, and CO2 above 350 K. In the case of the adsorbed ethyl species, the formation of gaseous acetaldehyde was also established. It is assumed that the oxidation of CHx fragments proceeds through the transient formation and reactions of adsorbed methoxy and ethoxy species, preceded by the interaction of methyl and ethyl groups of adsorbed iodo compounds with the adsorbed oxygen atoms. (C) 1996 Academic Press, Inc.