Palladium and Ruthenium Dual-Single-Atom Sites on Porous Ionic Polymers for Acetylene Dialkoxycarbonylation: Synergetic Effects Stabilize the Active Site and Increase CO Adsorption.

Abstract

Heterogeneous single-metal-site catalysts usually suffer from the poor stability, limiting its industrial applications. Herein, the dual-sites Pd1-Ru1 supported on porous ionic polymers (Pd1-Ru1/PIPs) was constructed using wetnessimpregnation method. The two isolated metal species in the form of binuclear complex was immobilized on the cationic framework of PIPs through ionic bonds. Compared to the single-Pd or Ru-site catalyst, it exhibits higher activity with 98% acetylene conversion and near 100% selectivity of dialkoxycarbonylation products as well as better cycling stability for ten times cycles without obvious decay. Based on DFT calculations, it was found that the single-Ru-site exhibited a strong CO adsorption energy of -1.6 eV, leading to an increase in the local CO concentration of the catalyst. Notably, the Pd1-Ru1/PIPs catalyst had a much lower energy barrier of 2.49 eV compared to 3.87 eV of Pd1/PIPs for the rate-determining step. The synergetic effect between neighbouring single-sites Pd1 and Ru1 not only enhanced the overall activity, but also stabilized Pd(II) active sites. The discovery of synergetic effect between single-sites can deepen our understanding of single-site catalysts at the molecular level.