Nanostructured Cerium Oxide-based Catalysts for the Chemical Conversion of CO2 to Dimethyl Carbonate and Methane.

The focus of this thesis lies within the context of Carbon Capture and Utilization (CCU) technologies, aiming to transform carbon dioxide into high value-added compounds such as dimethyl carbonate (DMC) and methane. Specifically, the research activity was centered on the design and characterization of ceria-based catalysts to improve the efficiency of the direct synthesis of DMC from CO₂ and methanol. Additionally, ceria-based materials were employed as supports for nickel-based catalysts in the methanation reaction. Various synthetic strategies were developed (hydrothermal synthesis, solution combustion, soft-template method, two-solvent impregnation, and combination with self-combustion), and their influence on the morphology, surface area, and chemical-physical properties of the catalysts was investigated. Particular attention was devoted to iron doping and to the presence of oxygen vacancies, acidic and basic sites, key elements for CO₂ reactivity. The most promising systems, obtained through hydrothermal synthesis, showed a significant improvement in DMC yield, especially when using dehydrating agents such as methyl trichloroacetate compared to 2-cyanopyridine, which is widely reported in the literature. In parallel, mesoporous ceria was used as a support for the synthesis of Ni@CeO₂ catalysts, evaluated for the hydrogenation of CO₂ to methane. The catalysts obtained exhibited high dispersion of the active metal, good catalytic performance, and high selectivity towards methane, thanks to the adopted synthetic strategy. Overall, the results highlight the crucial role of catalyst material design in the valorization of CO₂, confirming the potential of CCU technologies for a more sustainable chemical industry.