Metal–Oxo Cluster Composition in Metal–Organic Frameworks Controls Solar-Driven CO2 Methanation Pathways

Abstract Although metal–organic frameworks have emerged as versatile and tunable heterogeneous photocatalysts for the hydrogenation of gaseous CO2 to CH4, the role of metal–oxo cluster composition in governing this photocatalytic process remains largely unexplored. Herein, we employ an isostructural series of monometallic MIL-100(M) frameworks (M = Cr3+, Fe3+, Sc3+, Al3+, and In3+) to systematically investigate how metal–oxo cluster composition governs solar-driven CO2 methanation within a common structural platform. MIL-100(Cr)-based solids markedly outperform their analogues, achieving highly selective CO2 conversion to CH4 as confirmed by isotopic 13CO2 labeling experiments and high integral stability, with sustained catalytic operation for 132 h over six consecutive cycles under simulated sunlight irradiation. This superior photocatalytic performance arises from the synergistic combination of chemical robustness, favorable CO2/CO chemisorption within the framework, efficient photothermal energy conversion, and enhanced photoinduced charge-carrier dynamics. Operando Fourier Transform infrared measurements reveal a CO2 methanation mechanism involving formate, mono-, and bi-dentate methoxy species as key intermediates. These findings identify metal–oxo cluster composition as a key descriptor controlling adsorption behavior, charge-carrier dynamics, photothermal response, and dominant light-driven reaction pathways in MOF photocatalysts for solar-driven CO2 methanation.