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

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.