Promotional role of Ag1 on Pd1 in dual-site configurations from atomic dispersion of alloy nanoparticles for alkyne dialkoxycarbonylation
Heterogeneous single-metal-site catalysts frequently encounter issues related to the poor stability of their coordination structures,hindering their industrial applications.Synthesizing bimetallic single-metal-site catalysts with two closely connected single sites may realize the full potential of single-site catalysts.Herein,we present a"top-down"dispersion process to prepare bimetallic sin-gle-metal-site catalysts from Pd-Ag alloy nanoparticles induced by CO and CH3I mixture,with the unique binuclear complex structure of Pd1-Ag1 established as Pdl2(CO)-12-Agl by combined charac-terization.The Pd1-Ag1/activated carbon(AC)catalyst showed a three times increase in conversion for acetylene dialkoxycarbonylation compared to Pd1/AC,owing to the promotive effect of the sin-gle-Ag-site via the binuclear complex configuration.Moreover,Pd1-Ag1/AC showed 98％selectivity for 1,4-unsaturated dicarboxylic acid esters over ten cycles without apparent decay,with the acti-vated adsorption amount of acetylene doubled and the reduction of active Pd1δ+species partially inhibited.According to density functional theory calculations,the Pd1-Ag1/AC catalyst exhibited a substantially lower reaction energy barrier of 0.45 eV for the rate-determining step compared with that of the Pd1/AC catalyst(1.06 eV).This study provides insight into the preparation and synerget-ic catalysis of bimetallic single-metal-site catalysts.
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