Cu⁺-Cu⁰ Cluster Pairs in Defective MOFs for Highly Synergistic CO₂ Hydrogenation to Methanol

Precise arrangement of multivalent Cu sites for the synchronized activation of CO₂ and H₂ in selective methanol synthesis remained challenging. Herein, we designed spatially arrayed Cu⁺-Cu⁰ cluster pairs confined within UiO-66 (U66) to achieve spatiotemporally directed CO₂ hydrogenation to methanol. This architecture was constructed by creating missing-linker defects within U66 using L-ascorbic acid (LA), followed by sequential anchoring of high-density, adjacent Cu⁺-Cu⁰ cluster pairs (≈1:1 ratio) to yield a Cu/U66(LA-Cu) catalyst. Under reaction conditions of 220°C and 3 MPa, this catalyst achieved a methanol space-time yield of 688.1 mg·g^-1·h^-1 and an ultra-high methanol selectivity (97.0%). Its unity-methanol selectivity was 1.06-1.77 times that of high-stability oxide materials. Meanwhile, catalyst's stability of 200 h was significantly prolonged compared to high-selectivity MOF-based catalysts that operated stably for 60-175 h. Mechanistic studies revealed that Cu⁺-Cu⁰ cluster pairs within defective U66 not only enabled partitioned synergistic activation of CO₂ and H₂, but established an efficient electron/hydrogen transfer pathway. This facilitated the migration of active hydrogen species to CO₂ adsorption sites, where adsorbed CO₂ was converted into CO intermediates and underwent deep hydrogenation. This structural design synergistically enhanced compatibility between H₂ dissociation and CO₂ hydrogenation steps, enabling reaction to proceed efficiently along the RWGS + CO-hydro pathway.