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297 p., The impact of human activity on the Earth and related anthropogenic CO2 emissions have significantly elevated GHG concentration in atmosphere leading to global warming of around 1.5°C since preindustrial period, which is nowadays reflected as notorious climate change. Accordingly, strategic policies for decarbonizing the energetic system are being applied such as Power-to-Gas (Gas: CH4), which is gaining interest to reduce CO2 emissions while generating Synthetic Natural Gas (SNG). This technology requires an active, selective and stable catalyst to carry out CO2 methanation using renewable H2 at mild industrial conditions.In this thesis, alumina- and zeolite-supported Ni and Ru catalysts have been synthesized and optimized for efficient CO2 methanation. Reaction kinetics on Ni/Al2O3 are studied and satisfactorily described by akinetic model with high statistical significance, including the role of formates and carbonyls as reaction intermediates. Substantial insights into the reaction mechanism on Ni/Na-BETA and Ni-La2O3/Na-BETA catalysts are reported, identifying the type of adsorbed species on different surface sites (BETA zeolite, exchanged Na+, impregnated La2O3 and Ni).

The CO2 methanation mechanism over the highly active (TOF=75.1 h−1), selective (>92%) and stable 10% LaNiO3/CeO2-derived catalyst is still unresolved. The surface of the catalyst is monitored under hydrogenation (H2), oxidizing (CO2) and CO2 methanation (H2 +CO2) conditions by near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) using synchrotron radiation. Meanwhile, the main reaction intermediates are identified by in situ FTIR analysis. NAP-XPS experiments confirm that LaNiO3 perovskite reduction leads to the ex-solution of Ni0 nanoparticles and Ni2+single bondCeO2−x and Ni2+single bondLa2O3 interfaces conformation, favouring the CO2 adsorption and the H2 dissociation/transfer. In situ FTIR experiments combined with the C1s spectra (NAP-XPS) suggest that the CO2 activation occurs on CeO2−x (oxygen vacancies and OH–) at low temperatures, in the form of bicarbonates; whereas, mono-/bidentate carbonates are formed on different strength La2O3 sites at increasing temperatures. These species are consecutively reduced to formates, as the main reaction intermediate, and methane by the H spilled from Ni0 nanoparticles near to NiOsingle bondCeO2−x and NiOsingle bondLa2O3 interfaces.

CO2 valorization in form of synthetic natural gas is a convenient way to store large amounts of intermittent energy produced from renewable sources for long periods of time. Here reported research addresses the development of novel dual function materials (DFMs) for the utilization of CO2 from simulated post-combustion effluent by cyclic adsorption and in-situ methanation. These DFMs, obtained after the controlled reduction of 20% La1−xCaxNiO3/CeO2-type precursors (with x = 0–0.5), are widely characterized before and after catalytic tests. XRD diffractograms, H2-TPD experiments and STEM-EDS images denote that Ca-doping shows low influence on materials composition, slight detrimental effect on textural properties and no influence on Ni, La and Ce distribution. Meanwhile, the concentration of Ca-based species increases as long as La3+ substitution by Ca2+ increases, which leads to a progressively promotion of medium and, especially, strong basic sites concentration (CO2-TPD). As a result, the 20% La0.5Ca0.5NiO3/CeO2-derived DFM almost doubles (188.8 µmol g−1) the CH4 production of the 20% LaNiO3/CeO2-derived DFM (96.5 µmol g−1) at high temperatures. Indeed, this novel DFM enhances the methanation capacity of the conventional 15% Ni-15% CaO/Al2O3 DFM (143.0 µmol CH4 g−1), with higher stability during long-term experiments and adaptability under variable feed compositions, which further support the applicability of these novel DFMs. Thus, Ca doping emerges as an effective way of tailoring CO2 adsorption and in-situ hydrogenation to CH4 efficiency of 20% LaNiO3/CeO2-derived DFMs.

The Integrated Carbon Capture and Utilization-Methanation (ICCU-Methanation) requires a Dual Function Material (DFM), which firsts captures CO2 and then converts it into CH4, working in alternating adsorption and hydrogenation periods. The ICCU technology can be applied directly to a flue gas leaving a combustion chamber, which usually contains oxidizing species such as oxygen and nitrogen oxides. In this work, the stability of a DFM with composition 4%Ru-8%Na2CO3-8%CaO/Al2O3 is studied for the CO2 adsorption and hydrogenation in alternate cycles including O2 (0–10%) and NOx (0–2000 ppm) during the adsorption period. The variation of CO2 concentration in the usual range of flue gases (5–15%) has little influence on the global performance of the ICCU technology. However, the incorporation of O2 during the adsorption period decreases the production of CH4, and this decrease is even accentuated with increasing the oxygen concentration. This fact is mainly attributed to the oxidation of metal sites that limits the reduction behavior. On the other hand, the addition of NOx competes with CO2 for the basic adsorption sites, which slightly limits the amount of CO2 stored, and consequently the production of CH4. Helpfully, the proposed DFM presents high stability during the 207 cycles here performed, which corresponds to 34 h of time-on-stream, including different CO2 concentrations, and in the presence or absence of O2 and/or NOx. It is concluded that the proposed DFM formulation is competent for long-term operation in the presence of O2 and NOx during the CO2 adsorption period.