Synthesis and characterization of Cu-Mg-Al catalysts for the hydrogenation of CO₂ to methanol and dimethyl ether

The anthropogenic emission of carbon dioxide (CO₂) is a primary driver of global climate change, prompting the urgent need for efficient Carbon Capture, Utilization, and Storage (CCUS) technologies. The catalytic hydrogenation of CO₂ to methanol and dimethyl ether (DME) represents a promising route to valorize this greenhouse gas into sustainable, carbon-neutral fuels. This thesis investigates the synthesis and performance of Cu/Mg/Al-based catalysts for the hydrogenation of CO₂ to methanol and DME. Specifically, the study evaluates the influence of the co-precipitation method (comparing constant pH 9 and variable pH up to 11) and the Cu/Mg molar ratio (2 vs. 1) on the physicochemical and catalytic properties of the materials. The catalysts were characterized by N₂ physisorption (BET/BJH), XRD, and Temperature-Programmed Desorption (TPD) of NH₃ and CO₂. Catalytic tests were conducted in a fixed-bed reactor (240 °C, 20 bar, H₂/CO₂ = 3) for both bulk catalysts and bifunctional systems, the latter obtained by physically mixing the precursors with HZSM-5 zeolite. Characterization revealed that a higher copper content (Cu/Mg = 2) promotes the dispersion of the active CuO phase and increases the specific surface area, leading to superior catalytic activity. The co-precipitation pH was found to profoundly affect the porous structure and the acid-base surface properties in synergy with the metal composition. The bulk CMA-2-11 catalyst (Cu/Mg=2, pH 11) exhibited the highest CO₂ conversion (8.3%) and methanol space-time yield (3.1 gCH₃OH/gCAT·min). Upon the addition of HZSM-5, the product distribution successfully shifted toward DME, with the CMA-2-11/HZSM-5 bifunctional system reaching a maximum DME productivity of 4.9 gDME/gCAT·min. The results demonstrate that precisely controlling the synthetic parameters is crucial for tuning the structural and acid-base properties of Cu-based catalysts, thereby optimizing their performance in the direct synthesis of DME from CO₂.