Enhancement of Cu+ stability under a reducing atmosphere by the long-range electromagnetic effect of Au.

Abstract

In conventional thermocatalytic reactions under a reducing atmosphere, stabilization of the active Cu+ component and inhibition of over-reduction into metallic Cu0 are extremely challenging. In this study, Au@Cu2O core-shell nano-catalysts with different Cu2O shell thicknesses were synthesized, and the effect of the Au nano-core on Cu+ stability under a reducing atmosphere and the catalytic performance of Cu+ in the ethynylation of formaldehyde were investigated. The Au nano-core facilitates Cu2O dispersion and leads to an increase of 0.2-0.5 eV in electron binding energies of Cu2O and Cu2C2 in the range of 27-55 nm, attributed to the long-range electromagnetic effect of Au NPs. Specifically, active Cu+ centers exhibit high stability under a reducing atmosphere due to the long-range electromagnetic effect of the Au nano-core. In the ethynylation of formaldehyde as a probe reaction, Cu+/(Cu0 + Cu+) on Au@Cu2O catalysts remained at 88-91%. The catalytic performance in the ethynylation of formaldehyde revealed that the introduction of an Au nano-core into Cu-based catalysts increased the TOF from 0.37 to 0.7 h-1, and decreased the activation energy from 42.6 to 38.1 kJ mol-1. Additionally, the Cu+/(Cu0 + Cu+) ratios and the catalytic performance in the ethynylation of formaldehyde (BD yield = 65%, BD selectivity = 95%) on Au@Cu2O catalysts remained constant after nine cycles, while pure Cu2O readily deactivated due to the dramatically reduced Cu+/(Cu0 + Cu+) ratios and carbyne deposition. In summary, Cu+ in Cu-based catalysts showed high catalytic activity and stability during the ethynylation of formaldehyde due to the long-range electromagnetic effect of the Au nano-core.