Role of Na in promoting n-butanol production via CO2 hydrogenation over a Cu-Co catalyst

Alkali-metal-promoted Cu catalysts have significant potential for the direct conversion of CO2 to alcohols. However, the effect of alkali metals on alcohol selectivity during CO2 hydrogenation is poorly understood. Therefore, we aimed to understand the impact of Na on selective hydrogenation over a Cu-Co catalyst. We found that the catalyst without the Na promoter (UCuCo-9P) converted only 14.8% of CO2 with a 7.3% alcohol selectivity at 330 degrees C, 4 MPa, and an H2/CO2 ratio of 1. In contrast, the addition of Na by coprecipitation (Na-CuCo-9P) increased the CO2 conversion to 20.6%, coinciding with a dramatic increase in alcohol selectivity up to 27.9%. Further, over 70% of alcohols produced by Na-CuCo-9P were C3+ alcohols, with n-butanol having the highest composition of 51.5%. In contrast, the Na-promoted catalyst prepared by wet impregnation (Na-CuCo-9W) achieved only half the alcohol selectivity of Na-CuCo-9P, at a low CO2 conversion of 12.8%. Crucially, Na-CuCo-9P was more stable than UCuCo-9P during a 200 h on-stream stability test. Further, we found that Na promotion lowers the activation energy barrier for the C2+ oxygenate intermediate, which favors n-butanol synthesis during tandem reactions. This work elucidates the role of Na in Cu-Co catalysts on direct CO2-to-higher-alcohol synthesis and offers insights into the rational design of catalysts using alkali promoters.