Molecular Uranium Dioxide-Mediated CO 2 Photoreduction

The reduction of CO mediated by transition metals has garnered significant interest, yet little is known about the reduction of CO using f-element compounds. Herein, the reduction of CO to CO by tetravalent uranium (U ) compound UO is investigated via matrix isolation infrared spectroscopy and quantum chemical study. Our results reveal that a stable carbonate intermediate OU CO ( ) can be prepared at low temperatures (4-12 K). Through photolytic reactions of under irradiations (495 nm < λ < 580 nm), the charge-separated pentavalent U isomer [U O ] [(η -O C)] ( ) is produced through electron transfer from the quasi-atomic U-7s orbital to the CO moiety. Sequentially, one C═O bond in CO breaks by successive irradiation (250 nm < λ < 580 nm), and the photolysis generates the products CO and hexavalent U compound U O following two intermediates U O (CO) ( ) and U O (OC) ( ) with a physiosorbed carbonyl group. Moreover, the evolution of oxidation states from electron-rich U to U on multiple potential energy surfaces of different electronic states involving configurations U(f s → f → f → f ) is further demonstrated. Our findings unveil a mechanism for the photoreduction of CO by a UO molecule. This strategy can be used to design molecular and solid-state catalysts for depleted uranium for CO reduction reactions.