Highly Efficient CuPd0.1/γ-Al2O3 Catalyst with Isolated Pd Species for CO2 Hydrogenation to Methanol

CO2 hydrogenation is one of the most effective solutions for mitigating excessive CO2 emissions. In this work, CuPdx/γ-Al2O3 (x = 0.05–5.7 wt %) catalysts were prepared and applied in CO2 hydrogenation to methanol. The results showed CuPd0.1/γ-Al2O3 achieved excellent CO2 hydrogenation activity. It is demonstrated that the Pd species of CuPd0.1/γ-Al2O3 is highly dispersed on the γ-Al2O3 support at the atomic level and separated from Cu nanoparticles by AC-HAADF-STEM, rather than forming CuPd alloy. Part of the hydrogen species activated by isolated Pd atoms overflows onto γ-Al2O3 and influences the reduction of CuO, thus effectively increasing the Cu+/(Cu++Cu0) ratio which is correlated with the prominent CO2 hydrogenation performance. On the other hand, we found that CH3OH retained on catalyst surface can be further reformed into CO, which significantly reduces the selectivity of CH3OH. To limit CH3OH reforming, the activity test of CuPd0.1/γ-Al2O3 in a fixed bed at different weight hourly space velocity was performed, where the remarkable methanol yields of 5.9 mmol/gcat./h were obtained.