Al2O3 Effect on the Catalytic Activity of Cu-ZnO-Al2O3-SiO2 Catalysts for Dimethyl Ether Synthesis from CO2 Hydrogenation

The effect of Al2O3 on the Cu-ZnO-Al2O3-SiO2 catalysts prepared by a pseudo sol-gel method has been investigated and these catalysts were characterized by XRD, H2-TPR, XPS, NH3-TPD and CO2- TPD techniques. As revealed by XRD and H2-TPR, the added alumina produces high dispersion of CuO and makes the reduction of CuO difficult. XPS analysis detects a remarkably high Al^3＋ enrichment at the surface of calcined samples, along with a decrease of Eb of Cu 2p3/2, which confirms the Cu-Al interaction. Another important role of Al203 would be to incorporate into the SiO2 structure to form the acid-base sites for ether formation. The reaction results shows that the addition of Al2O3 exhibits a promoting effect on the CO2 conversion only when its content is below 1.4%, and an optimal DME selectivity is obtained when 4.0%Al2O3 is added, indicating a better ＇synergistic effect＇ is present between the methanol forming component and the acidic component in bifunctional catalysts. Possible relationship between the catalytic activity and the Cu-Al interaction as well as the surface acidity is discussed.

Al2O3 Effect on the Catalytic Activity of Cu-ZnO-Al2O3-SiO2 Catalysts for Dimethyl Ether Synthesis from CO2 Hydrogenation

by a pseudo sol-gel method has been investigated and these catalysts were characterized by XRD,H2-TPR,XPS,NH3-TPD and CO2-TPD techniques. As revealed by XRD and H2-TPR,the added alumina produces high dispersion of CuO and makes the reduction of CuO difficult. XPS analysis detects a remarkably high Al3+ enrichment at the surface of calcined samples,along with a decrease of Eb of Cu 2p3/2,which confirms the Cu-Al interaction.Another important role of Al2O3 would be to incorporate into the SiO2 structure to form the acid-base sites for ether formation. The reaction results shows that the addition of Al2O3 exhibits a promoting effect on the CO2 conversion only when its content is below 1.4％,and an optimal DME selectivity is obtained when 4.0％Al2O3 is added,indicating a better 'synergistic effect' is present between the methanol forming component and the acidic component in bifunctional catalysts. Possible relationship between the catalytic activity and the Cu-Al interaction as well as the surface acidity is discussed.