Bimetallic-MOF Catalyst for Efficient CO2 Photoreduction from Simulated Flue Gas to Value-added Formate

Direct CO2 conversion from flue gas into high-value products is of great significance not only in relieving environmental burden but alleviating energy crisis by a low-cost and saving-energy avenue, yet few works in this aspect is reported. Herein, we report metal-node-dependent catalytic performance for solar-energy-powered CO2 reduction to formate in simulated flue gas by bimetallic Ni/Mg-MOF-74. Yield of HCOO- with Ni0.75Mg0.25-MOF-74 as a catalyst in pure CO2 is 0.64 mmol.h-1gMOF-1 which is higher than that of Ni-MOF-74 (0.29 mmol.h-1gMOF-1) and Ni0.87Mg0.13-MOF-74 (0.54 mmol.h-1gMOF-1), whereas monometallic Mg-MOF-74 is almost inactive, indicating reactivity relies on metal nodes. In simulated flue gas without water vapor at 20 OC, ~80% of the reactivity in pure CO2 is retained, with HCOO- generation reaching 0.52 mmol.h-1gMOF-1. This activity is comparable to that of the best MOF catalysts in pure CO2, demonstrating Ni/Mg-MOF-74 not only overcomes the limitation from CO2 concentration, but has good resistance to other gas components in flue gas at 20 OC. DFT calculations reveal the high output for HCOO- from two crucial factors: strong CO2 binding affinity of Mg sites, and synergistic effect of Mg and Ni leading to stabilization of key *OCOH intermediate with appropriated energy barrier. This work paves a new route for double-metal MOFs to enhance the CO2 photoreduction reactivity in the flue gas.