The unique chemistry of hydrogen beneath the surface: catalytic hydrogenation of hydrocarbons.

Hydrogen atoms emerging from the bulk of Ni metal to the surface are observed to be the reactive species in the hydrogenation of adsorbed methyl radical, ethylene, and acetylene to gas-phase products. Surface-bound H atoms are unreactive. The distinctive chemistry of a bulk H atom arises largely from its significantly higher energy as compared to that of a surface-bound H atom. These results demonstrate that bulk H is not solely a source of surface-bound H in catalytic hydrogenation as proposed 50 years ago, but rather, a reactant with a chemistry of its own.