The d-p electron coupling over the unsaturated oxygen coordinated CuCo alloy surface for enhanced N-heteroarenes hydrogenation under mild conditions

Abstract

The development of highly efficient non-noble metal catalysts for the hydrogenation of N-heteroarenes under mild condition is of great importance for both theoretical and industrial applications, which can efficiently reduce energy consumption and environmental pollution. In this work, we found that the prepared CoCu nano-alloy catalyst after exposed in the air over 24 h (named Co₁Cu₁/C) exhibited a dramatically improved catalytic performance (yield from trace to >99%) for quinoline hydrogenation under mild reaction conditions (60 °C, 3 MPa H₂). According to the characterization, the catalyst Co₁Cu₁/C exhibited the strong interaction between Co and Cu. Meanwhile, it was endowed with a stable partial oxidation surface. The unsaturated oxygen coordinated surface of Co₁Cu₁/C presented a moderate binding for quinoline and 1, 2, 3, 4-tetrahydroquinoline, which could efficiently avoid the deactivation of catalyst and favor the hydrogenation kinetics. The density functional theory (DFT) calculations coupled with X ray-based structural analyses suggested that the unsaturated oxygen coordinated surface could lower the diffusion energy of the active hydrogen species and the reaction barrier for quinoline hydrogenation which resulted from the d-p orbital electron coupling. This work revealed that the catalytic performance of nano-alloy catalysts might not only be ascribed to the interaction between metals, while the unsaturated oxygen coordination of metallic surfaces played an important role.