CO2 hydrogenation using MOFs encapsulated PdAg nano-catalysts for formate production

Catalytic hydrogenation of CO2 for the production of formic acid/formate, a valuable commodity and renewable hydrogen carrier, is a promising strategy to achieve an economic and sustainable CO2-mediated hydrogen energy cycle. The rational design of highly active and stable heterogeneous catalysts for CO2 hydrogenation in gas–liquid-solid phase still remains challenging. In this work, we report a series of dual-function catalysts namely PdAg@MIL-101-PEI, where PdAg alloy nanoparticles (NPs) for hydrogen activation and dissociation are encapsulated into MIL-101 supports tethered with CO2 adsorption agent polyethyleneimine (PEI). The optimal PdAg@MIL-101-PEI catalyst displays exceptional performance for CO2 hydrogenation, affording a high turnover number (TON) of 4968 at 120 °C under 8 MPa in 2 h. Thermodynamic and kinetic studies illustrate that Ag incorporation and PEI functionalization dramatically reduce the activation energy barrier of PdAg@MIL-101-PEI catalyst for CO2 hydrogenation. Furthermore, the optimal PdAg@MIL-101-PEI catalyst demonstrates outstanding structural stability and reusability over multiple catalytic cycles. We also propose a reaction mechanism for CO2 hydrogenation through in situ DRIFTS study.