Ethylene hydrogenation on fcc Co and Fe thin films grown on Ni(100)

We have investigated the effect of the strength of adsorbed ethylene and H-atom on ethylene hydrogenation by fabrication of fcc Co and Fe thin films on Ni(100). Epitaxial layer-by-layer growth of fcc Co and Fe thin films, at least up to 3 ML, was indicated by a (1×1) low energy electron diffraction (LEED) pattern and the intensity change of overlayer and substrate 2p level photoelectrons which is expressed by linear segments with different slopes in a constant evaporation rate. The increase in the potential energy of adsorbed ethylene on H-preadsorbed surface was estimated from the shift of the desorption peak temperature of ethylene in TPR spectra — it was found to be 5 and 8 kJ/mol for the 1 ML Co and Fe thin films respectively. Since surface ethyl species, derived from an ethyl iodide precursor, are hydrogenated to ethane at 180 K, this stabilization of adsorbed ethylene is interpreted to increase the activation barrier for the formation of surface ethyl species and cause a reduction in ethane production.