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.