Midtemperature CO Deoxygenation to CO over Oxygen Vacancies of Doped CeO.

CO 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 CO to CO over the vacancies of CeO. This study examines the influence of the dopant to CeO on the deoxygenation of CO to CO, wherein the examined dopants include Zr, Gd, Sm, and In. Only In-doped CeO exhibits significant reactivity for CO deoxygenation in our sequential temperature-programmed reduction (TPR) and CO-TPRx (temperature-programmed reaction) tests up to 700 °C. InCeO after H-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 In become oxidized in the subsequent CO deoxygenation reaction. XPS indicates that the redox of Ce also occurs during TPR-CO-TPRx with InCeO. InO by itself demonstrates a higher deoxygenation onset temperature, a lower per gram deoxygenation capacity, and a poorer stability than InCeO under the same test conditions, while CeO is inactive. The results suggest a synergy between exsoluted In and the fluorite substrate, leading to the observed deoxygenation activity of In-doped CeO.