CO₂ Hydrogenation to Formate Catalyzed by Ru Coordinated with a N,P-Containing Polymer

Abstract

Development of high-performance catalysts for carbon dioxide (CO2) hydrogenation is crucial for CO2 utilization. Herein, a heterogeneous catalyst for CO2 hydrogenation to formate was developed by coordinating the mononuclear Ru3+ center (Ru hereafter) with a N,P-containing polymer, which was synthesized from phosphonitrilic chloride trimer and 2,6-diaminopyridine. Multiple nitrogen functionalities in the polymer (N content: 25.9 wt %) containing pyridine nitrogen and phosphazene nitrogen not only provided an electron-rich coordination environment for stabilizing mononuclear Ru center but also facilitated CO2 conversion by interacting with CO2 molecules. The polymer-coordinated mononuclear Ru catalysts (Ru/p-dop-POMs) could promote the hydrogenation of CO2 to formate with a turnover number (TON) up to 25.4 × 103 in aqueous solutions, and the concentration of formate in the solution could reach 3.4 mol/L. DFT calculations revealed that the electron-rich mononuclear Ru site could promote H2 dissociation, which is the rate-determining step in the reaction, thereby enhancing the catalytic activity. Systemic studies demonstrated that the synergistic effect between individually electron-rich Ru centers and nitrogen-rich polymer enhanced catalytic efficiency.