Ethylene Hydrogenation on Ni(111) by Bulk Hydrogen

We report that bulk H atoms, upon moving out from the bulk metal to the surface, readily hydrogenate C[sub 2]H[sub 4] adsorbed on Ni(111) to form C[sub 2]H[sub 6], while surface-bound H atoms have no hydrogenation activity under the conditions of these experiments. This result is the first observation of the role of bulk H specifically as a reactant in the hydrogenation of an unsaturated hydrocarbon on a transition metal and calls into question the generality of the Horiuti-Polanyi mechanism for catalytic hydrogenation reactions. This results is also a plausible molecular level basis for the correlation between the hydrogenation activity of a Raney Ni catalyst and the H content in the catalyst. 17 refs., 2 figs.