Unraveling the regulation of Mn in Cu-ZnOx formation during methanol synthesis from syngas over Cu/ZnO/Al2O3-Mn catalysts

This study unravels the regulation of Mn promoter in catalytic activity and surface identities of Cu/ZnO/Al2O3 catalysts by reaction kinetics, TPR/TPD, N2O titration experiments and in situ spectra techniques. The methanol formation EA of Cu/ZnO/Al2O3 catalyst almost remained unchanged with the addition of Mn, confirming the methanol synthesis pathways were not affected. With an increase in the content of Mn, the sizes of Cu and ZnO decreased whereas the reduction degree of ZnO to Zn0 on the catalyst surface increased, forming more Cu-ZnOx active sites in CAZ-2%Mn. TPSR confirmed that the amount of the surface CO and H species were highest in CAZ-2%Mn. Therefore, more Cu-ZnOx active site and surface species in CAZ-2%Mn accounts for the higher methanol formation activity. A detailed understanding of the regulation of Mn in the Cu-ZnOx sites formation is expected for the precise design of the CuZnAl catalysts for methanol synthesis.

Automated summary

By using reaction kinetics, TPR/TPD, N2O titration experiments, and in situ spectra techniques, this study reveals the mechanism of Mn promoter in regulating the catalytic activity and surface properties of Cu/ZnO/Al2O3 catalysts. The addition of Mn does not affect the methanol synthesis pathways, as confirmed by the unchanged methanol formation EA of Cu/ZnO/Al2O3 catalyst. However, an increase in Mn content leads to smaller sizes of Cu and ZnO, higher reduction degree of ZnO to Zn0, and more Cu-ZnOx active sites and surface species, resulting in higher methanol formation activity in CAZ-2%Mn.