INTERACTION OF HYDROGEN WITH CARBIDIC CARBON ON NI(100)

The interaction of hydrogen with carbidic carbon deposited on Ni(100) by decomposing methane has been studied by isothermal hydrogenation experiments and by temperature-programmed hydrogen desorption (H-2-TPD). The hydrogenation experiments were made in the hydrogen-pressure range 0.5-10 Torr and the temperature range 450-550 K The hydrogenation curves indicate the presence of carbon states with different reactivities. A kinetic model with carbon-state reactivities, which depend on the local carbon concentration, is compatible with the hydrogenation results. H-2-TPD spectra were recorded for carbon coverages in the range 0-0.34 ML. Application of a simple kinetic expression shows that the ''effective'' hydrogen binding energy of the model depends on both the carbon and the hydrogen coverage.