CO₂ VALORIZATION: CATALYSTS FOR CH₄ AND CO₂ RECYCLING AND SYSTEMS FOR THE SUSTAINABLE FORMATION OF C–C BONDS

Rising atmospheric CO2 emission, driven by population growth and continued reliance on fossil carbon, poses several climate, energy, and resource challenges. Beyond capture and storage, CO₂ valorization offers a path to close the carbon circle by converting CO2 (often with CH4 or H2) into fuels and chemicals. This thesis addresses that challenge by developing and exploring different catalytic routes that couple activity and selectivity with robustness, using a consistent synthesis-structure-function framework across multiple processes. The work first targets dry reforming of methane (DRM) to produce syngas with a 1:1 H2/CO ratio advantageous for downstream synthesis. By comparing hydrothermal and microwave-assisted, one-pot pathways for Ni-La catalysts, the study links La-Ni-O network formation to smaller, better-anchored Ni0, reduced coking, and improved 24 h stability at 750 °C, establishing transferable design rules for coke-resistant Ni systems.Next, chemical looping reforming (CLR) is examined as a thermally integrated CO2-capture-ready process. Thermodynamic analysis and materials discussion highlight how oxygen-carrier materials and operating conditions can deliver near-complete CH4 conversion with high syngas yields while enabling autothermal operation and process intensification options.The thesis then addresses CO2 methanation (Sabatier) using Ni-La perovskite-derived catalysts. Partial reduction (notably at 500 °C) preserves defect-rich perovskite structure and generates strong Ni-support interfaces that promote carbonate-mediated pathways, enhancing CH4 selectivity and stability.Finally, CO2-to-light-olefins (CTO) is carried out over Fe/ZrO2 promoted with CeO2. Low-medium ceria (0.5-3 wt%) improves FeOx dispersion/reducibility and favors C2-C4 olefins under 30 bar/40 h TOS tests, whereas excessive ceria lowers conversion and shifts selectivity toward methanation/RWGS.Across four complementary catalytic approaches, dry reforming of methane (DRM), chemical looping reforming (CLR), CO2 methanation (Sabatier), and CO2-to-light-olefins (CTO) the aim of this thesis is to provide a panoramic view of CO2 valorization and show how the catalyst design affects the structure-activity correlation that underlies performance and durability.