Influence of oxygen vacancies of CeO2 on reverse water gas shift reaction

• Volcano-like relationship between activity and surface defect level of CeO 2 for CO 2 hydrogenation. • Redox mechanism demonstrated by in-situ DRIFTS and isotope switch experiments. • Surface oxygen vacancy as a key factor for tuning competitive adsorption and activation of H 2 and CO 2 on CeO 2 . Catalytic CO 2 hydrogenation on metal oxides is attractive to realize carbon neutrality initiatives. Understanding roles of oxygen vacancies of oxide-based catalysts is critical for the catalytic mechanism of CO 2 hydrogenation. Herein, we used CO 2 hydrogenation as model reaction on CeO 2 to investigate the effects of oxygen vacancies and provided direct spectroscopic evidence for redox mechanism via in-situ DRIFTS and isotope switch experiments. A volcano-type activity curve was found for CO 2 hydrogenation to CO on CeO 2 upon the continuous variation of the surface defect concentration of oxygen vacancy. Kinetic analysis and ex-situ techniques indicate that surface oxygen contributes to H 2 activation and oxygen vacancy accelerates the dissociation of CO 2 , emphasizing the unique roles of surface oxygen and oxygen vacancies, respectively. These results enrich the understanding of surface defect chemistry of CeO 2 and lay an important theory foundation for design of oxide-based catalysts for hydrogenation.