(337d) Activation of CO2 on CeO2 Model Thin Films and Supported Powder Catalysts

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.