Influence of Al, Cr, Ga, or Zr as promoters on the performance of Cu/ZnO catalyst for CO2 hydrogenation to methanol

Different promoters can be applied to increase the activity, selectivity, and stability of the Cu/ZnO for the CO2 hydrogenation to methanol. Herein, we investigated the effect of the promoters' addition on the physicochemical properties of the Cu/ZnO-based catalysts and their performance in the CO2 hydrogenation to methanol. A series of Cu/ZnO catalysts, Cu/ZnO/X (X = Al2O3, Cr2O3, Ga2O3, ZrO2), were prepared by a co-precipitation method and characterized by XRF, XRD, SEM, TEM, TEM-EDS, H-2-TPR, N2O passivation, and CO2-TPD. Under the explored conditions, the promoters enhanced the catalyst activity and selectivity to methanol in the CO2 hydrogenation reaction. The superior performance of the promoted materials was associated with the increase of specific surface area, metallic copper surface area, basicity, and the decrease of the size of copper oxide crystallites and particles. Among the investigated materials, Cu/ZnO/Ga2O3 (CZG) catalyst showed the best performance in terms of activity (XCO2, 200 degrees C = 5.2%) and methanol selectivity (SMeOH, 200 degrees C = 50%).