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 C₂ hydrocarbons with atomic H and clarify the site-specific selective hydrogenation of C₂H₂ on Au(997) at low temperatures. On atomic H­(a) covered Au(997), hydrogenation of C₂H₂ goes with 100% selectivity to C₂H₄ at steps, yet no hydrogenation occurs at terraces; adsorbed C₂H₄ on neither steps nor terraces reacts with H­(a). DFT calculations suggest that the increased adsorption free energies and appropriate reaction barriers of C₂ species at steps lead to the step-site specific semihydrogenation of C₂H₂. These results elucidate the elementary surface reactions between C₂ hydrocarbons and atomic H on Au surfaces at the molecular level and significantly deepen the fundamental understanding of the unique selectivity of Au catalysts.