(183l) Computational Design of Metal–N-Heterocyclic Carbene Complexes Immobilised in a Metal–Organic Framework for CO2 Hydrogenation

By integrating the advantages of homogeneous and heterogeneous catalysis, single-site heterogeneous catalysis represents a highly promising opportunity for many catalytic processes. Particularly, the versatility of metal-organic frameworks (MOFs) promotes them a suitable platform for designing such catalysts. Herein, we employ density functional theory (DFT) to design MOF-supported single-site catalysts for CO₂ hydrogenation, a reaction of great significance in CO₂ utilization. Specifically, N-heterocyclic carbene (NHC) is used to anchor Ir(I) hydride, Ir(III) hydride and Cu(I) hydride to the organic linker of UiO-68. The mechanisms of CO₂ hydrogenation to formic acid (HCOOH) are investigated in detail by computing the optimized structures and the corresponding Gibbs free energies for the elementary processes involved in the hydrogenation. The calculations suggest that CO₂ first inserts into the metal hydride to form a formate (HCOO) intermediate, then H₂ dissociates via a heterolytic manner above the metal site. The resultant proton (H⁺) is added into HCOO, while the hydride (H^−) is transferred to the metal site to recovery the catalytic active site. The proposed mechanism is similar to that in homogeneous catalysis. This study would assist in the rational design of new single-site catalysts for CO₂ hydrogenation.