Light-induced Binding and Reduction of CO₂over 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 centres that template dynamic substrate activation within a functionalised cavity or pocket. We report the light-induced reversible binding of CO2 in a cerium-based MOF, Ce-UiO-66-NH2, incorporating an amino functionalised 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 photo-reduction to CO. This work will promote the design of photocatalysts capable of synthesising fuels from CO2.