Light-Induced Binding and Reduction of CO₂ over Transient Open Ce(III) Sites in a Metal-Organic Framework

Metal-organic framework (MOF) materials share some common features with metalloenzymes including site-isolated metal centers that template dynamic substrate activation within a functionalized cavity or pocket. We report the light-induced reversible binding of CO₂ in a cerium-based MOF, Ce-UiO-66-NH₂, incorporating an amino functionalized linker, which enables photoreduction of CO₂ to CO in H₂O without using sacrificial agents. A production rate for CO of 126 μmol·g^-1·h^-1 with 100% selectivity is observed, outperforming its non-amine analogue (Ce-UiO-66) and benchmark catalysts reported to date. In situ infrared, X-ray absorption, electron paramagnetic resonance and transient absorption spectroscopy reveal that photoexcitation induces a ligand-to-metal charge transfer to generate transient open Ce(III) sites that bind CO₂ in a μ-(η¹-O)(η¹-C) binding mode. This binding is reversible and activates CO₂ for subsequent photoreduction to CO. This work will promote the design of photocatalysts capable of synthesizing fuels from CO₂.