Influence of Mg loadings in copper-based catalysts for CO2 hydrogenation to methanol

The conversion of carbon dioxide (CO₂) to methanol offers a sustainable route to mitigate greenhouse gas emissions while producing a key chemical feedstock. In this study, we investigate the effect of magnesium (Mg) loadings on the performance of copper-based catalysts for CO₂ hydrogenation to methanol. Catalysts based on Cu/ZnO/Al₂O₃ (CZA) were synthesized via co-precipitation and modified with varying amounts of Mg to yield Mg-promoted samples (CZAM). Comprehensive characterization using X-ray diffraction, N₂ adsorption–desorption isotherms, H₂ temperature-programmed reduction, and N₂O chemisorption revealed that moderate Mg incorporation decreases Cu crystallite size and enhances the BET surface area, thereby improving copper dispersion. Catalytic tests conducted at 240 °C and 50 bar with varying Gas Hourly Space Velocities (GHSV) showed that an intermediate Mg loading (approximately 0.8 wt.%) yields optimal performance, achieving a CO₂ conversion of 23.3% and methanol selectivity of 55%, comparable to that of a commercial catalyst. Excessive Mg content, however, adversely affects dispersion and selectivity despite higher intrinsic site activity. Stability tests over 120 hours confirm sustained catalytic performance under reaction conditions. These results demonstrate that careful control of Mg loading and GHSV is critical to optimize catalyst structure and activity, offering insights for developing catalysts for sustainable methanol production from CO₂.