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.