A bimetallic-MOF catalyst for efficient CO2 photoreduction from simulated flue gas to value-added formate

Abstract

Direct CO₂ conversion from flue gas into high-value products is of great significance not only in relieving environmental burden but alleviating the energy crisis by a low-cost and energy-saving avenue, yet few studies in this aspect have been 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. The yield of HCOO⁻ with Ni_0.75Mg_0.25-MOF-74 as a catalyst in pure CO₂ is 0.64 mmol h⁻¹ g_MOF⁻¹ which is higher than that of Ni-MOF-74 (0.29 mmol h⁻¹ g_MOF⁻¹) and Ni_0.87Mg_0.13-MOF-74 (0.54 mmol h⁻¹ g_MOF⁻¹), whereas monometallic Mg-MOF-74 is almost inactive, indicating that reactivity relies on metal nodes. In simulated flue gas without water vapor at 20 °C, ∼80% of the reactivity in pure CO₂ is retained, with HCOO⁻ generation reaching 0.52 mmol h⁻¹ g_MOF⁻¹. This activity is comparable to that of the best MOF catalysts in pure CO₂, demonstrating that Ni/Mg-MOF-74 not only overcomes the limitation from CO₂ concentration, but also has good resistance to other gas components in flue gas at 20 °C. DFT calculations reveal the high output for HCOO⁻ from two crucial factors: strong CO₂ binding affinity of Mg sites, and the synergistic effect of Mg and Ni leading to the stabilization of the key *OCOH intermediate with an appropriate energy barrier. This work paves a new route for double-metal MOFs to enhance the CO₂ photoreduction reactivity in flue gas.