Study of new Multifunctional Cu-Al-Mg Catalysts for Direct DME Synthesis via CO₂ Hydrogenation

The increasing need to mitigate CO₂ emissions and develop sustainable routes for fuel and chemical production has intensified research on the catalytic hydrogenation of CO₂ to value-added products. This thesis investigates Cu–Al–Mg-based catalysts for the direct (single-step) hydrogenation of CO₂ to dimethyl ether (DME). The catalysts were synthesised by co-precipitation and evaluated with and without the incorporation of HZSM-5 zeolite, aiming to combine hydrogenation and dehydration functionalities within a single catalytic system. The studied formulations include a CuMgAl catalyst with a Cu:Al:Mg molar ratio of 1:1:1, tested both in its sole form and after physical mixing with HZSM-5, and a CuMg/HZSM-5 catalyst (Cu:Mg = 1:1) obtained by co-precipitating the metallic phase onto the zeolite support. The catalysts were characterised by X-ray diffraction (XRD), nitrogen adsorption-desorption (BET/BJH), and temperature-programmed desorption (TPD), in order to investigate their structural, textural, and surface acid-base properties. Catalytic tests were carried out in a fixed-bed reactor at 240 °C and 20 bar, using a CO₂/H₂ feed molar ratio of 1:3 and a gas hourly space velocity (GHSV) of 1560 h⁻¹. Catalyst performance was evaluated in terms of CO₂ conversion, selectivity toward DME, methanol, CO, and CH₄, and the corresponding space-time yields. Although the synthesized catalysts underperformed the commercial benchmark in terms of CO₂ conversion, the integration of HZSM-5 successfully enabled direct DME synthesis and provided valuable insights into the interplay between metallic and acidic functions.