Experimental Studies of the Highly Active Cu–Ni/In₂O₃ Catalyst for CO₂ Hydrogenation to Methanol

The copper-based catalysts have been extensively exploited for the hydrogenation of CO₂ to methanol. The In₂O₃-supported copper catalyst has also been investigated. However, its activity is not satisfactory, compared to that of other metal-promoted In₂O₃ catalysts. Herein, the In₂O₃-supported Cu–Ni bimetallic catalyst with a high dispersion of Ni and Cu species was prepared by chemical reduction. The addition of nickel leads to significantly higher activity at each temperature tested compared to Cu/In₂O₃. The activity of the bimetallic catalyst is also slightly higher than that of Ni/In₂O₃. For example, over Cu–Ni/In₂O₃ with a ca. 5/5 Cu/Ni weight percentage ratio, the CO₂ conversion reaches 12.7% at 275 °C with a methanol selectivity of 66.6% and a methanol STY of 0.46 g_MeOH g_cat^–1 h^–1. However, the CO₂ conversion and methanol selectivity are only 5.9 and 68.7% for Cu/In₂O₃ and 12.1 and 62.7% for Ni/In₂O₃ under the same condition. The use of Ni promotes the dispersion and activity of Cu/In₂O₃ and improves the stability of oxygen vacancies on the surface of In₂O₃, inhibiting the formation of the CuIn alloy. With the assistance of nickel, the Cu species also causes the formation of strongly CO adsorbed sites, resulting in improved methanol selectivity. Moreover, the Cu–Ni bimetallic catalyst has a strong hydrogen spillover effect, leading to more oxygen vacancies and improved CO₂ adsorption.