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

Abstract

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 Cu⁰ 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.