Molecular Uranium Dioxide-Mediated CO₂ Photoreduction.

Area of Science:

• Inorganic Chemistry
• Photochemistry
• Materials Science

Background:

• Transition metal-mediated CO2 reduction is well-studied, but f-element compound applications remain largely unexplored.
• Investigating CO2 reduction using uranium compounds offers a new avenue for catalytic development.

Purpose of the Study:

• To investigate the photoreduction of carbon dioxide (CO2) to carbon monoxide (CO) using a tetravalent uranium (UIV) compound, UO2.
• To elucidate the reaction mechanism, intermediates, and oxidation state evolution during the process.

Main Methods:

• Matrix isolation infrared spectroscopy was employed to identify reaction intermediates.
• Quantum chemical calculations were utilized to study the electronic states and reaction pathways.
• Photolytic reactions under visible and UV-visible light irradiation were performed.

Main Results:

• A stable carbonate intermediate, OUIVCO3 (A), was formed at low temperatures (4–12 K).
• Visible-light irradiation of (A) produced a charge-separated pentavalent U-isomer (B) via electron transfer.
• UV-visible irradiation led to CO2 bond cleavage, generating CO and a hexavalent uranium compound (UVI O3) through intermediates (C) and (D).

Conclusions:

• A detailed mechanism for the photoreduction of CO2 by UO2 was unveiled, involving sequential electron transfer and bond cleavage.
• The study demonstrates the evolution of uranium oxidation states from UIV to UVI during the catalytic cycle.
• This strategy offers potential for designing molecular and solid-state catalysts based on depleted uranium for CO2 reduction.