Cu2O hydrides promote the selective semihydrogenation of alkynes on Pd–Cu2O/TiO2 under mild conditions

Abstract

The selective semihydrogenation of alkynes is of importance in many industrial applications, but great challenges still remain in the full utilization of noble metals for the catalysis of hydrogen spillover on mixed supports. As Pd⁰ is chemically loaded on Cu₂O/TiO₂, this work reports that Pd⁰ is imparted with a high electron density to dissociate H₂ efficiently and the active Cu₂O hydride is responsible for the high catalytic activity in spillover semihydrogenations. As compared with inert Pd–Cu₂O/SiO₂ interfaces, the studies demonstrate that the high chemoselectivity and stereoselectivity originate from the well-defined p–n junctions of Cu₂O/TiO₂, therein alkynes are adsorbed in their trans configurations and the product is desorbed from them. As catalyzed by 1.3Pd–3.6Cu₂O/TiO₂ in 1 atm H₂ at 30 °C, the semihydrogenations can be completed in 90 min with 97.6% chemoselectivity for phenylacetylene, and in 45 min with 92.4% stereoselectivity for methyl non-2-ynoate. These studies provide new ideas to design and synthesize noble metal-based catalysts through manipulating the interface properties of the mixed supports.