Methanol synthesis from CO2 and H2 over gallium promoted copper-based supported catalysts. Effect of hydrocarbon impurities in the CO2/H2 source

Abstract

Gallium-promoted copper-based catalysts supported on ZnO and SiO₂, respectively, Cu-Ga/ZnO and Cu-Zn-Ga/SiO₂, were tested in the hydrogenation of CO₂ to methanol under a range of experimental conditions. Long-term methanol synthesis operation and catalytic tests under high pressure (up to 5 MPa) at 523 K indicated that the catalysts were highly effective. The methanol synthesis was sensitive to the presence of small amounts of methane and ethane in the CO₂/H₂ source, producing significant deactivation of the catalysts, especially of Cu-Zn-Ga/SiO₂, and promoting the formation of by-products. After reaction with hydrocarbon-containing CO₂/H₂ feed, TEM experiments showed copper-based particles covered by an amorphous layer that is probably carbonaceous in nature. XPS allowed determination of differences in surface composition for catalysts tested with clean or hydrocarbon-containing CO₂/H₂. These differences allowed the performance of Cu-Zn-Ga/SiO₂ to be related to the presence of Cu⁺ and the quantity of gallium in the near-surface regions, which was lower for the catalyst tested under hydrocarbon-containing CO₂/H₂ feed.