Investigation of copper precursors in the synthesis of higher alcohols from syngas over CuZnAl catalysts without promoters

Abstract

The catalytic performances of different CuZnAl catalysts prepared using copper nitrate, copper acetate and copper citrate for CO hydrogenation to higher alcohols (C₂₊OH) were studied in a slurry bed reactor. Among these catalysts, the Cu–N catalyst prepared using copper nitrate showed a relatively higher C₂₊OH selectivity and no obvious deactivation occurred during the lifetime test for 120 h. The influence of copper precursors on the performance of the CuZnAl catalysts was investigated by XRD, ²⁷Al-MAS-NMR, N₂ adsorption–desorption, H₂-TPR, NH₃-TPD, FT-IR and XPS techniques. The results indicated that the size of Cu⁰ particles, textural properties, the chemical state of Cu species, the amount of surface acid and chemical composition varied, which led to diverse catalytic activities toward C₂₊OH synthesis. It was concluded that Cu⁰, Cu⁺ and AlOOH were all necessary in ethanol and C₂₊OH synthesis when using the CuZnAl catalysts without promoters and the synergism of these species was beneficial to the formation of C₂₊OH. This work further demonstrated that alkalis and Fischer–Tropsch elements were not indispensable for C₂₊OH synthesis from syngas.