Rising atmospheric concentration of CO2 could cause severe climate change and ocean acidification. To mitigate this potential problem, significant reduction in emissions and active removal of CO2 from the atmosphere are necessary. A catalytic process that utilizes CO2 as a feedstock to produce valuable chemicals and fuels is more desirable than sequestration. However, the inert nature of CO2 makes the activation of CO2 a critical step in improving the overall reaction kinetics during its chemical conversion. It is generally believed that activation of CO2 occurs at the supporting materials or the interfacial sites between the active metal and the oxide support. Metal oxides form the major category of active support materials and the capability to activate CO2 largely depends on the reducibility of the metal oxides.
In this study, activation of CO2 on CeO2 model thin films and supported powder catalysts has been explored by both experiments and density functional theory (DFT) calculations. Multiple in-situ spectroscopic techniques including Ambient Pressure X-ray Photoemission Spectroscopy (AP-XPS), X-Ray Diffraction (XRD) and Diffuse Reflectance Infrared Fourier transform (DRIFTs) are utilized to probe the catalyst structures and the surface species under reaction conditions. This study has revealed that the reducing state of Ce3+ is critically important in stabilizing the active nanoparticles. Meanwhile, the reduced oxide has strong tendency to react with CO2, even causing direct C-O bond dissociation. By creating appropriate combination between active metals and CeO2 supports and controlling the particle sizes and structures, highly active catalysts have been synthesized for catalyzing both methanol synthesis from CO2 hydrogenation and dry reforming light alkanes (CH4 and C2H6). Overall, this study has not only provided important understanding of the nature of CeO2 supported catalysts, but also led to designing effective catalysts for converting CO2 into other useful chemicals.