Midtemperature CO₂ Deoxygenation to CO over Oxygen Vacancies of Doped CeO₂

CO₂ capture and utilization are a must for easing the global warming caused by the use of fossil fuels. Previous studies demonstrate the possibility of thermal deoxygenation of CO₂ to CO over the vacancies of CeO₂. This study examines the influence of the dopant to CeO₂ on the deoxygenation of CO₂ to CO, wherein the examined dopants include Zr, Gd, Sm, and In. Only In-doped CeO₂ exhibits significant reactivity for CO₂ deoxygenation in our sequential temperature-programmed reduction (TPR) and CO₂-TPRx (temperature-programmed reaction) tests up to 700 °C. In_0.5Ce_0.5O after H₂-TPR demonstrates a deoxygenation onset temperature as low as 400 °C and it can maintain a stable performance in cycle tests. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses indicate that In exsolutes from the fluorite framework during TPR and the exsoluted In⁰ become oxidized in the subsequent CO₂ deoxygenation reaction. XPS indicates that the redox of Ce also occurs during TPR-CO₂-TPRx with In_0.5Ce_0.5O. In₂O₃ by itself demonstrates a higher deoxygenation onset temperature, a lower per gram deoxygenation capacity, and a poorer stability than In_0.5Ce_0.5O under the same test conditions, while CeO₂ is inactive. The results suggest a synergy between exsoluted In and the fluorite substrate, leading to the observed deoxygenation activity of In-doped CeO₂.