Catalysts and processes for CO2 utilization for e-methane and chemical productions.

In recent decades, CO2 emissions have risen dramatically, primarily due to population growth and accelerated fossil fuel consumption. Therefore, in order to address climate change, a transition from fossil to renewable resources is needed. This will require considerable effort to develop new technologies that can supply the energy system. For this reason, this thesis focuses on Power-to-Gas (PtG) technology, especially CO2 methanation, and alternative uses of CO2. Using a bottom-up approach, this project investigates a multi-scale system beginning with the laboratory-scale catalyst development, characterization, and testing (including mechanistic and kinetics analysis, and catalytic performance), and progressively moving toward industrial-scale reactor engineering and techno-economic evaluation for CO2 valorization systems. The work focuses primarily on Ni-based catalysts, which were selected for their optimal balance between activity and cost. Different catalyst formulations were proposed and tested. Firstly, the influence of different loadings of phosphorous on a conventional Ni/Al2O3 catalyst was investigated in CO2 hydrogenation and Methane Dry Reforming (MDR) systems. The catalytic activity and the morphology of the samples before and after the experimental tests were evaluated in order to understand how P modified the Ni/Al2O3 catalyst. The kinetics and the catalytic performance were also evaluated on Ni-MgAlOx catalysts derived from hydrotalcite precursors. These mixed oxides generated highly dispersed metallic Ni sites upon activation, demonstrating superior low-temperature activity and selectivity in CO2 methanation compared to conventional Ni/γ-Al2O3 catalysts. Kinetic analysis and IR spectroscopy confirmed that the basic oxides promote CO2 activation through the formation of surface (bi)carbonate intermediates. These results provided further insight into the role of support basicity and Ni dispersion in methanation performance. In addition, the kinetics and the reaction mechanism of a La-promoted Ni/Al2O3 catalyst were investigated by applying both a power law and a Langmuir-Hinshelwood type model to the experimental data. Lanthanum was chosen as the promoter because it provides better resistance at higher temperatures, i.e. improved hotspot tolerance, and enhances performance at low temperatures. Several assumptions were made in order to carry out the mechanistic investigation. Unlike with conventional Ni/Al2O3 catalysts, the formation of intermediate carbonate species was observed. These lumped steps were introduced in the reaction mechanism pathway, resulting in a model that reproduced the experimental data. However, this thesis focused not only on improving the catalyst performance at laboratory scale, but also on designing and evaluating a novel strategy for thermal management in industrial biogas methanation reactors. At an industrial scale, biogas was introduced as CO₂-feedstock to simulate a more complex and realistic case study and to develop a carbon-neutral process. Firstly, a multi-layer dilution strategy was proposed as an effective solution to enhance reactor stability while maintaining high CO2 conversion. The aim was to enhance axial heat dispersion and distribute the heat release more uniformly along the reactor by exploring the possibility of varying the catalyst dilution profile. The integration of biogas methanation with green hydrogen production was assessed through a techno-economic analysis based on 2030 cost projections. A sensitivity analysis on different electrolyzer types and power availability was performed, revealing that hydrogen production dominates the Levelized Cost of Methane (LCOM). SOECs (Solid Oxide Electrolyzer Cells) show the best performance under continuous operation, whereas AEM (Anion Exchange Membrane) electrolyzers are more suitable for intermittent renewable power thanks to their lower CAPEX (capital expenditure) and better flexibility. Consequently, costs remain above current synthetic natural gas prices, requiring either cheaper renewable electricity or stronger carbon policies for future industrial competitiveness. Finally, the thesis broadens the perspective on CO2 utilization by examining its role as a soft oxidant in the oxidative dehydrogenation (ODH) of light alkanes. The design of the catalyst and the type of light alkane feed mixture were analyzed to explore alternative pathways for converting CO2 into value-added products.