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

Heterogeneous single-metal-site catalysts usually suffer from poor stability, thereby limiting industrial applications. Dual Pd -Ru single-atom-sites supported on porous ionic polymers (Pd -Ru /PIPs) were constructed using a wetness impregnation method. The two isolated metal species in the form of a binuclear complex were immobilized on the cationic framework of PIPs through ionic bonds. Compared to the single Pd- or Ru-site catalyst, the dual single-atom system exhibits higher activity with 98 % acetylene conversion and near 100 % selectivity to dialkoxycarbonylation products, as well as better cycling stability for ten 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 Pd -Ru /PIPs catalyst had a much lower energy barrier of 2.49 eV compared to 3.87 eV of Pd /PIPs for the rate-determining step. The synergetic effect between neighboring single sites Pd and Ru not only enhanced the overall activity, but also stabilized Pd active sites. The discovery of synergetic effects between single sites can deepen our understanding of single-site catalysts at the molecular level.