Mechanistic insights into the effect of Mg addition on industrial Cu/ZnO/Al2O3 catalysts for methanol synthesis via CO/CO2 hydrogenation

Although promoters are generally introduced to enhance the performance of industrial Cu-based catalysts for CO/CO 2 hydrogenation to methanol, certain additives unexpectedly deteriorate catalytic activity. Understanding the origin of such adverse effects provides a reverse perspective for identifying the key structural features and elementary reaction steps governing methanol synthesis. In this work, two industrial Cu-based catalysts, Cu/ZnO/Al 2 O 3 (CZA) and Mg-modified Cu/ZnO/Al 2 O 3 (CZA-Mg), were systematically investigated to elucidate the role of Mg in regulating catalytic performance. The incorporation of a small amount of Mg (0.3 wt%) markedly decreased the methanol space–time yield at 230 °C from 918.2 to 599.4 g MeOH kgcat −1 h −1 , corresponding to a 34.7 % decrease in activity. Structural characterizations demonstrate that Mg incorporation reduced the dispersion of metallic Cu and the abundance of weak CO adsorption sites. Furthermore, in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) combined with density functional theory (DFT) calculations reveals that Mg incorporation altered the adsorption behavior of reactant molecules and subsequent activation pathways, thereby suppressing methanol formation. These findings provide mechanistic insights into the role of Mg in industrial Cu/ZnO/Al 2 O 3 catalysts and deepen the understanding of the structure–activity relationship governing methanol synthesis, offering valuable guidance for the structural optimization of industrial Cu-based methanol catalysts.