Co Single Atoms in ZrO₂ with Inherent Oxygen Vacancies for Selective Hydrogenation of CO₂ to CO

Abstract

Controlling the selectivity of products among CO, methane, and methanol is a challenge in CO2 hydrogenation. Catalysts with oxygen vacancies are helpful for CO2 activation, but they exhibit poor CO selectivity as intermediates stabilized over oxygen vacancies undergo deep hydrogenation to methanol and methane. Here, we report the synthesis of a catalyst with isolated Co atoms in ZrO2 that exhibits oxygen vacant sites near Co atoms owing to charge imbalance between cations. The resulting catalytic site effectively adsorbs CO2 and also achieves more than 95% CO selectivity during hydrogenation. The CO selectivity was independent of other reaction parameters such as reaction pressure, space velocity, and H2/CO2 ratio. Operando DRIFTS analysis showed that CO2 was first hydrogenated to formate, which preferentially decomposed to CO under the reaction condition instead of forming methanol. Furthermore, the adsorption of CO on active sites was less favorable than the adsorption of CO2, limiting its further hydrogenation to methane. The synergy between Co and Zr was crucial for the generation of oxygen vacancy and stabilization of formate species as an intermediate for CO formation. This study shows the importance of strategic design of atomic interface to control the selectivity of a specific product from CO2 hydrogenation.