Yttrium oxide modified Cu/ZnO/Al2O3 catalysts via hydrotalcite-like precursors for CO2 hydrogenation to methanol

Y2O3-modified Cu/ZnO/Al2O3 catalysts (Cu2+: Zn2+ : (Al3+ + Y3+) = 2: 1: 1) via hydrotalcite-like precursors were synthesized with Y3+ : (Al3+ + Y3+) atomic ratios between 0 and 0.5. With the introduction of certain amounts of Y2O3, the surface area and dispersion of Cu for the Cu/ZnO/Al2O3 catalysts increased significantly. However, excess Y2O3 content would decrease the dispersion of both Cu and ZnO as a result of the reduced amount of hydrotalcite-like phases in the precursors. It was suggested that Y2O3 and the hydrotalcite-like structure could prevent the aggregation of Cu nanoparticles during reduction and reaction and improve the reducibility of Cu2+ species. As Cu-0 species were the predominant active sites for methanol synthesis from CO2 hydrogenation, addition of suitable amounts of Y2O3 to the Cu/ZnO/Al2O3 catalyst enhanced the catalytic activity for CO2 hydrogenation remarkably. Nevertheless, CO2 conversion decreased significantly when Y3+ : (Al3+ + Y3+) > 0.1 due to the lower surface area of Cu and a relatively weaker interaction between Cu and ZnO. The Cu/ZnO/Al2O3/Y2O3 catalyst with Y3+ : (Al3+ + Y3+) = 0.1 derived from hydrotalcite-like compounds exhibited the best catalytic performance with high stability.