OXIDATION OF CARBIDIC CARBON ON A RHODIUM SURFACE

Different mechanisms of atomic carbon and oxygen recombination on a rh odium surface are studied with Auger electron spectroscopy (AES) and X -ray photoelectron spectroscopy (XPS). The kinetics of adsorbed carbid ic carbon oxidation (carbon coverage theta(C) almost-equal-to 0.1-0.3 ML) by gas-phase oxygen that proceeds by a Langmuir-Hinshelwood reacti on mechanism, provides the value of the activation energy for recombin ation (E(rec)act almost-equal-to 170 +/- 20 kJ/mol). E(rec)act) depend s slightly on the carbon coverage. An Eley-Rideal type of reaction was observed for adsorbed oxygen and atomic gas-phase carbon recombinatio n which occurs in a dynamic regime. The low value found for the activa tion energy (near zero) is consistent with the mechanism that this exo thermic reaction is too fast for energy dissipation into the substrate ; the energy is mainly transferred into translational, vibrational and rotational energy of CO.