Heterogeneous Isomerization for Stereoselective Alkyne Hydrogenation to -Alkene Mediated by Frustrated Hydrogen Atoms.

Stereoselective production of alkenes from the alkyne hydrogenation plays a crucial role in the chemical industry. However, for heterogeneous metal catalysts, the olefins in -configuration are usually dominant in the products due to the most important and common Horiuti-Polanyi mechanism involved over the metal surface. In this work, through combined theoretical and experimental investigations, we demonstrate a novel isomerization mechanism mediated by the frustrated hydrogen atoms via the H dissociation at the defect on solid surface, which can lead to the switch in selectivity from the -configuration to -configuration without overhydrogenation. The defective RhS with exposing facet of (110) exhibits outstanding performance as a heterogeneous metal catalyst for stereoselective production of -olefins. With the frustrated hydrogen atoms at spatially separated high-valence Rh sites, the isolated hydrogen mediated -to- isomerization of olefins can be effectively conducted and the overhydrogenation can be completely inhibited. Furthermore, the bifunctional Rh-S/Pd nanosheets have been synthesized through the surface modification of Pd nanosheets with rhodium and sulfide. With the selective semihydrogenation of alkynes into -olefins catalyzed by the small surface PdS ensembles, the bifunctional Rh-S/Pd nanosheets exhibit excellent activity and stereoselectivity in the one-pot alkyne hydrogenation into -olefin, which surpasses the most reported homogeneous and heterogeneous catalysts.