Hydrogenation of CO2 to methanol over Pd-Cu/CeO2 catalysts

Abstract

CO2 hydrogenation to methanol receives great attention recently not only in conventional CO hydrogenation process but also in CO2 and H-2 storage technologies. CO2 can be converted to methanol by catalytic hydrogenation, and it is supposed that CO2 is hydrogenated to methanol via hydrocarboxyl (COOH) intermediate (rWGSR route) rather than formate (HCOO) intermediate. It was reported that CeOx/Cu(111) surface stabilizes COOH intermediate, which consecutively results in lower activation energy for methanol formation than on Cu(111) and Cu/ZnO(0001) surfaces. The activity of Cu/CeO2 catalysts can be further enhanced by Pd addition, because it can enhance reducibility of Cu site. In this study, therefore, Cu/CeO2 and Pd-CuiCeO(2) catalysts were applied to CO2 hydrogenation to methanol. Pd-promoted Cu/CeO2 catalysts achieved higher methanol productivity than Cu/CeO2 catalyst due to the increase in CO2 conversion, Because methanol productivity over Pd weight (mmolmeou/gm"h) simply decreased as the amount of Pd increased, it is considered that the enhanced activity of Pd-Cu/CeO2 catalysts mainly resulted from the increase in the reactivity of active Cu sites. The dispersion and surface concentration of Cu increased due to the interaction with highly-dispersed Pd, and Cu sites were more reduced by Pd promotion due to electron donation from Pd. Pd promotion also generated more reduced CeO2 surface. These promoting effects of Pd was the highest in the catalyst containing 1 wt.% Pd (1Pd-10Cu/CeO2 ), because further increase in the amount of loaded Pd lowered the textural properties of catalyst. As a result, methanol productivity was enhanced in Pd-promoted Cu/CeO2 catalysts and the highest in 1Pd-10Cu/CeO2 catalyst. (C) 2017 Elsevier B.V. All rights reserved.