Effect of lanthanum group promoters on Cu/(mixture of ZnO and Zn-Al-spinnel-oxides) catalyst for methanol synthesis by hydrogenation of CO and CO2 mixtures

Abstract

Improvement of copper-based catalyst activity as an industrial catalyst for methanol production from synthesis gas has a great impact on the economy and environmental aspects of this process. CO2 utilization in this research will improve the sustainability of the methanol process using the science of nanocatalysts. For this purpose, a new mixture of ZnO and Zn-Al-Oxides spinel with a Zn/Al ratio of 3 was developed and optimized. This support was synthesized by the co-precipitation method and calcined at temperatures of 110, 300, 500, 700, and 900 °C. The results show that the best calcination temperature is 500 °C (coded as ZA500). Then, Cu-X/ZA500 (X = empty, La, Ce, or Sm) catalysts were synthesized by the co-precipitation-deposition method. Developed supports and catalysts were characterized by N2-physisorption, H2-TPR, XRD, and HRTEM, XPS, TGA, H2-TPD, EXAFS, and XANES techniques. The results show that adding a small amount of CO2 to the syngas (H2 & CO) improves the catalyst activity. When a mixture of CO/CO2 was used, a comparison of catalysts shows that Cu/ZA500 has the highest CO2, CO, and carbon conversions among all samples at 250 °C that prove the role of support and its interaction with copper active sites. Adding La, Ce, or Sm to the Cu-X/ZA500 catalysts enhanced the CO2 conversion in comparison to Cu/ZnO/Al2O3 as a reference catalyst. It was found that the La promoter can enhance the sintering resistivity of the copper catalyst. Cu-La/ZA500 has the highest CO2 conversion of around 25% with methanol selectivity of 54.0% at 250 °C and 40 bar for CO2 hydrogenation (without CO).