Cu2O-Supported Atomically Dispersed Pd Catalysts for Semihydrogenation of Terminal Alkynes: Critical Role of Oxide Supports

Abstract

Atomically dispersed catalysts have demonstrated superior catalytic performance in many chemical transformations. However, limited success has been achieved in applying oxide-supported atomically dispersed catalysts to semihydrogenation of alkynes under mild conditions. By utilizing various metal oxides (e.g., Cu2O, Al2O3, ZnO, and TiO2) as supports for atomically dispersed Pd catalysts, we demonstrate herein the critical role of the oxidation state and coordinate environment of Pd centers in their catalytic performance, thus leading to the discovery of an “oxide-support effect” on atomically dispersed metal catalysts. Pd atomically dispersed on Cu2O exhibits far better catalytic activity in the hydrogenation of alkynes, with an extremely high selectivity toward alkenes, compared to catalysts on other oxides. Pd species galvanically displace surface Cu(I) sites on Cu2O to create two-coordinated Pd(I), which is a critical step for the activation and heterolytic splitting of H2 into Pd-H− and O-H+ species for the selective hydrogenation of alkynes. Moreover, the adsorption of alkenes on H2-preadsorbed Pd(I) is relatively weak, preventing deeper hydrogenation and increased selectivity during semihydrogenation. We demonstrate that the local coordinate environment of active metal centers plays a crucial role in determining the catalytic performance of an oxide-supported atomically dispersed catalyst.