Enhancing thermal CO2 reduction to CO through systematically tailoring oxygen vacancies on Al-doped CeO2 and ZrO2 catalysts

Global warming driven by CO₂ emissions poses a significant environmental challenge, prompting research into catalytic CO₂ conversion technologies. Therefore, developing simplified catalyst structures with well-defined active sites is crucial for advancing this field. Herein, CeO₂ and ZrO₂ were chosen as catalyst due to their excellent oxygen storage capacity and redox properties in thermal CO₂ reduction. Al doping was systematically varied to explore its impact on surface oxygen species and catalytic performance. Characterization techniques including H₂-TPR, H₂-TPD, CO₂-TPD, XRD, EPR, TEM, and in-situ FTIR were employed to analyze the structure and surface properties. For Al-doped CeO₂, XPS and EPR results indicated that Al incorporation increased oxygen vacancy concentration and surface reactivity, H₂-TPR, H₂-TPD and in-situ FTIR confirmed that Al incorporation increased H₂ activation and HCOO⁻ formation, leading to the enhancement of CO₂ conversion. The AlCe20 catalyst exhibited exceptional performance with a CO₂ conversion of 36.66 % at 600 °C and 100 % CO selectivity. Moreover, the AlCe20 catalyst demonstrated remarkable stability over 55 h of continuous operation at 600 °C. In contrast, XRD and XPS results showed that Al doping in ZrO₂ stabilized the tetragonal phase but reduced surface oxygen availability, leading to decreased CO₂ conversion. The undoped ZrO₂ showed the highest conversion at 15.04 % (600 °C) among the tested samples. This work provides valuable insights into the role of surface oxygen species in CO₂ conversion and highlights the importance of doping strategies in catalyst design.