Step Site-Specific Semihydrogenation of Acetylene on the Au Surface.

Supported Au catalysts are highly selective and size-sensitive in catalytic hydrogenation of alkynes under mild conditions. Using thermal-programmed desorption and density functional theory calculations, we study the hydrogenation reactions of C hydrocarbons with atomic H and clarify the site-specific selective hydrogenation of CH on Au(997) at low temperatures. On atomic H(a) covered Au(997), hydrogenation of CH goes with 100% selectivity to CH at steps, yet no hydrogenation occurs at terraces; adsorbed CH on neither steps nor terraces reacts with H(a). DFT calculations suggest that the increased adsorption free energies and appropriate reaction barriers of C species at steps lead to the step-site specific semihydrogenation of CH. These results elucidate the elementary surface reactions between C hydrocarbons and atomic H on Au surfaces at the molecular level and significantly deepen the fundamental understanding of the unique selectivity of Au catalysts.