Effect of Cu/Zn ratios and Zr, Mn promoters on CuO/ZnO-based catalysts for methanol synthesis via hydrogenation of CO and CO2

Abstract

The aim of this research is to investigate CuO/ZnO/Al2O3 (CZA) catalysts with different Cu/Zn weight ratios including CZA-0.5, CZA-1, CZA-2 and CZA-3.5 catalysts having Cu/Zn weight ratios is 0.5, 1, 2 และ 3.5, respectively. Catalysts were prepared by the co-precipitation method. Catalysts were characterized to determine the physical and chemical properties using various techniques such as N2 adsorption, CO-Chemisorption, SEM-EDX, ICP-MS, XRD, XPS, H2-TPR, CO2-TPD and TGA. The catalysts were tested in CO hydrogenation and CO2 hydrogenation at 250 °C under atmospheric pressure. From reaction test, it was found that CZA-3.5 catalyst exhibited the highest catalytic activity due to the highest copper contents resulting in increasing surface area, metallic copper surface and number of strong basic sites. In addition, effect of Zr and Mn promoters was also investigated. The results presented that Mn promoter can increase the surface area, metallic copper surface, copper dispersion, number of strong basic sites, but decrease crystallite size of CuO. The CZ-Mn-2 catalyst had the highest catalytic activity for CO2 hydrogenation. Meanwhile, the CZ-Zr-2 catalyst exhibited the highest catalytic activity for CO hydrogenation. In the final part, the stability of CZA-2, CZ-Zr-2 and CZ-Mn-2 catalysts was investigated to determine the differences between the fresh and spent catalysts for comprehend cause of catalyst deactivation.