(623b) Structure Sensitivity of Methanol Synthesis From Carbon Dioxide On Copper-Based Catalysts

Natesakhawat, S., National Energy Technology Laboratory
Abdelsayed, V., National Energy Technology Laboratory
Lekse, J. W., National Energy Technology Laboratory
Ohodnicki, P. R., National Energy Technology Laboratory
Howard, B. H., National Energy Technology Laboratory
Deng, X., Lawrence Berkeley National Laboratories
Matranga, C., National Energy Technology Laboratory

Thermocatalytic conversion of carbon dioxide to methanol has recently gained considerable attention because it is regarded as an optimal solution to mitigate CO2 emissions while generating revenues to offset carbon management costs.  Currently, commercial synthesis of methanol is accomplished by hydrogenation of CO-rich syngas over Cu/ZnO/Al2O3 catalysts.  However, the low activity and stability of existing formulations create major barriers towards using them in realistic CO2-rich conditions.  Despite extensive studies of methanol synthesis over Cu-based catalysts, the nature of active sites and structure sensitivity of methanol synthesis on Cu surfaces are not fully understood.  Thus, a better understanding of active sites and structure-activity relationships is essential for the rational design of new catalysts that would be suitable for CO2 conversion applications.

We have investigated coprecipitated Cu-based catalysts possessing different metal oxide additives, Cu crystallite sizes, and varying degrees of support crystallinity.  Using a variety of ex situ and in situ characterization techniques, we have verified that Cu0 species are active sites for methanol synthesis from a stoichiometric CO2/H2 mixture.  The possibility of Cu+ species acting as active sites is excluded because these species are not observed on the surface of the working catalysts.  The reaction is structure-sensitive with smaller Cu particles demonstrating higher turnover frequency.  An explanation for an activity enhancement upon promotion will be presented.  Possible reaction pathways for CO2 hydrogenation to methanol will also be discussed.