Promotional role of Ag1 on Pd1 in dual-site configurations from atomic dispersion of alloy nanoparticles for alkyne dialkoxycarbonylation

ABSTRACT 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 single-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 PdI2(CO)-I2-AgI by combined characterization. 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 single-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 activated 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 synergetic catalysis of bimetallic single-metal-site catalysts.