CO2-to-methanol conversion over promoted Cu/ZnO/Al2O3 catalysts by Ga, Zr, and Co: A comprehensive DFT and experimental study

Abstract

Methanol synthesis via CO2 hydrogenation over Cu/ZnO/Al2O3 catalysts is limited by low activity, deactivation, and the reverse water–gas shift reaction. In this study, the influence of Zr, Ga, and Co promoters was evaluated using both co-precipitation and impregnation methods. The catalysts were characterized by XRD, N2O chemisorption, H2-TPR, TGA, H2/CO2-TPD, and FE-SEM, while density functional theory (DFT) calculations provided qualitative insights into promoter effects on methoxy stabilization. Co-precipitated catalysts, particularly those containing Zr and Ga, showed improved copper dispersion, smaller crystallite sizes, and enhanced H2/CO2 adsorption. Under reaction conditions (235 °C, 50 bar, H2/CO2 = 3:1), Zr- and Ga-promoted catalysts achieved CO2 conversions of 42 % and 38 % with methanol selectivities of 98 % and 89 %, respectively. In contrast, Co-promoted catalysts exhibited higher CO and CH4 selectivities, indicating reduced suitability for methanol synthesis. These findings demonstrate that promoter type and synthesis route strongly influence the structural and catalytic properties of Cu-based catalysts for CO2 hydrogenation to methanol.