Abstract: The adsorption and decomposition of ethanol on the clean Rh (100) surface werestudied using thermal desorption spectroscopy(TDS) and high resolution electron energy lossspectroscopy (HREELS).At 130 K, on Rh (100) surface, the adsorption started from achemisorbed ethanol structure which was bonded to the surface through both Oand Hmoi-eties, with the O-Hbond almost parallel to the surfaces.Additional condensed phase of ad-sorbed ethanol was found to exist through hydrogen bonding.At about 150 K, the multilay-er-adsorbed ethanol desorbed from the surfaces, while the remaining chemisorbed ethanolcompletely converted to an ethoxy species via the first decomposition step in which O-Hbond scission occurred.The small amount of methane formed indicated that the dehydro-genation of the ethoxide intermediates on the clean Rh(100) surface was non-selective.Lossof hydrogen from the methylene group would result in the formation of an aldehyde interme-diate.Decarbonylation of the aldehyde intermediates produced methane and CO.This path-way appeared to be a minor one for ethoxide decomposition on Rh(100).The main ethoxidedehydrogenation proceeded via the cleavage of a C-Hbond on the methyl group, resultingin the formation of an oxametallocyclic intermediate.The loss spectra at 629 cm^-1 is as-signed to this intermediate.The C-Cbond scission occurred at the same time in the oxamet-allocyclic dehydrogenation sequence.Then the COand hydrocarbon moieties were formed onthe surface.

Key words: Adsorption and decomposition of ethanol, Rh (100), High resolution electron en-ergy loss spectroscopy, Thermal desorption spectroscopy, Oxametallocyclic intermediate