Effect of the Oxygen Vacancy-Tunable Ce1–xGdxO2−δ Support on the Ni-Catalyzed CO2 Utilization via the Reverse Water–Gas Shift Reaction

The reverse water–gas shift (RWGS) reaction offers a critical option for CO₂ utilization, yet challenged by the endothermic nature of the reaction and high activation energy required for cleavage of the inert C═O bond. Oxygen vacancy engineering has been increasingly attractive as an effective strategy to activate CO₂ via the electrostatic interaction. Herein, we develop a novel RWGS catalyst by dispersing metallic nickel on the gadolinia-doped ceria (GDC) support, where the oxygen vacancy concentration is tuned by varying the Gd/Ce molar ratio. The electron paramagnetic resonance (EPR), Raman, and X-ray photoelectron spectrometry (XPS) characterization of the Ni-GDC catalysts revealed that the oxygen vacancy concentration of the catalysts was increased with the increasing doping percent of Gd until 50%, and the interaction between metallic Ni and the GDC support kept strengthening as the Gd percent was increased. The developed Ni-GDC catalysts exhibited excellent activity and stability in driving the RWGS reaction, achieving a maximum CO yield of 19.4 mmol g^–1 min^–1 at 700 °C and retaining stable catalytic performance with no loss of activity throughout 20 h of the continuous test. It was found in this study that the CO₂ conversion rate of the catalyst was positively correlated with its oxygen vacancy concentration, despite the observation that the oxygen vacancy concentration was less influential to CO₂ conversion compared to temperature and the H₂/CO₂ feeding ratio.