Synergy between Active Sites of Ternary CuZnAlOOH Catalysts in CO Hydrogenation to Ethanol and Higher Alcohols

Currently, the Cu-based catalyst has become a promising candidate for ethanol and higher alcohols synthesis (HAs) from synthesis gas (H₂ + CO), but all these catalysts contain F–T elements (e.g., Co and Fe) and alkalis because carbon chain growth reaction occurs on these metal components. Herein, two series of ternary CuZnAlOOH catalysts with various Cu and Al proportions were synthesized using a complete liquid-phase method and studied in the conversion of syngas in a slurry bed reactor. Significantly higher selectivity of ethanol (40 wt %) and HA (65 wt %) with approximately 20% CO conversion was achieved when the n_(Cu)/n_(Al) = 2/0.8, which was ascribed the highest copper surface area (S_Cu) and the surface Cu content. It was found that the Cu component had a significant effect on CO conversion, while the Al component had more influence on the selectivity of HA. Besides, the coke deposition was discovered to be the main reason for catalyst deactivation. The generation of hydrocarbons and alcohols followed A–S–F distributions, which was consistent with a representative mechanism of HA generation by CO insertion into the CH_x intermediate. A synergetic mechanism between Cu⁰–Cu⁺ and AlOOH active sites was proposed based on the characterization analysis and activity results, in which Cu⁰–Cu⁺ synergy acted as sites for H₂ dissociative adsorption and associative adsorption of CO, while the AlOOH facilitated the dissociation of the C–O bond. Bifunctionality of the Cu and AlOOH active sites and their cooperation created their synergy in CO hydrogenation to ethanol and HA. This work provided us a new concept to understand and develop carbon chain growth mechanism, and it also could provide reference for other related carbon chain growth reactions.