Vacancy-Driven Pathways in CO 2 Hydrogenation over Ni/CeZrO 2

Oxygen vacancies in CeO2-containing catalysts are critical for enhancing CO2 hydrogenation activity, but there is a lack of understanding of the roles of these species in CO2 activation. Herein, we report how variation in the compositions of the support in Ni/CeZrO2 catalysts leads to samples with identifiable surface oxygen vacancies, showing how to control their densities, coordination environments, and adsorption properties. Characterization of the samples with a family of spectroscopic methods and density functional theory provided evidence of surface reaction intermediates, reaction pathways, and catalyst deactivation mechanisms. Among the catalysts investigated, Ni/Ce0.5Zr0.5O2 is the most active, exhibiting the highest concentrations of surface oxygen vacancies─favoring CO2 adsorption and its subsequent hydrogenation. Raman and infrared data point to monodentate and bridging bidentate formate as key intermediates in the catalytic methanation reaction. The results open unrecognized perspectives regarding the roles of oxygen vacancy sites on the redox-active supports and distinguish the active and inactive vacancies in CO2 methanation, which is helpful for understanding the mechanism of CO2 methanation and the complex roles of oxygen vacancies in catalysis more broadly, pointing to insights into the design of redox-active catalysts involving vacancy-driven catalytic cycles.