Effects of CuO/ZnO/Al2O3 catalyst modification using Zr, Mn and Si for methanol synthesis via CO2 hydrogenation

Abstract

Currently, the estimated CO2 amount has tended to increase interesting of population. One of the most effective utilization ways of CO2 is to convert CO2 to higher valued chemicals. Thus, methanol was chosen to produce via CO2 hydrogenation by using CuO/ZnO/Al2O3 (CZA) catalyst. In the first part, CZA was prepared by co-impregnation method under different pH (7, 8 and 9) during co-precipitation. It was found that the suitable pH was 8 (CZA-PH8) due to high surface area, high basicity, and reducibility. The CO2 conversion and methanol selectivity were 2.6% and 10%, respectively at 250oC under atmospheric pressure. However, it should be noted that CO was the main product of this study. In the second part, different promoters such as Zr, Mn and Si were employed to improve the catalytic activity of CZA-PH8. It was found that Mn promoter apparently increased the CO2 conversion up to 4.7% (giving the highest methanol yield of ca. 0.46% under the same condition. However, the methanol selectivity of ca. 10% was found over Mn-promoted CZA-PH8 catalyst. On the other hand, the Mn promoter can enhance the CO2 conversion without a change in methanol selectivity. It can be concluded that Mn promoter is chemical promoters since it facilitates the dispersion of CuO and basicity of CZA catalyst. In the final part, the stability of CZA-PH8 and CZA-PH8-Mn catalysts was investigated. It was found that the differences between the fresh and spent catalysts were a decrease of agglomeration of CuO leading to higher activity of the CZA-PH8 with Mn promotion.