Methanol synthesis from CO2 and H-2 over gallium promoted copper-based supported catalysts. Effect of hydrocarbon impurities in the CO2/H-2 source

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/H-2 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/H-2 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/H-2. 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/H-2 feed.