Structural regulation of CuAl binary catalyst through heat-treatment pressure adjustment for enhanced synthesis of higher alcohols

The valence state and size of copper species play a critical role in the conversion of syngas to higher alcohols. In this study, CuAl binary catalysts with tunable Cu + -Cu 0 ratios and broad size distributions were successfully synthesized by adjusting the heat-treatment pressure of complete liquid-phase method, and their performance in CO hydrogenation was evaluated. The characterization results demonstrated that increasing heat-treatment pressure led to a general increase in both the Cu species size and the Cu⁺/(Cu⁺+Cu 0 ) ratio. Additionally, heat-treated under high pressure significantly enhanced the interaction between the Cu and Al components, promoted the formation of oxygen vacancies on AlOOH, and facilitated electron transfer. Notably, the oxygen vacancy content exhibited a linear correlation with the Cu + /(Cu + +Cu 0 ) ratio. The catalytic performance revealed a synergistic effect between the valence state and size of copper species in promoting higher alcohol synthesis. The percentage of C 2+ OH increased with the rise in Cu + /(Cu + +Cu 0 ) ratio and the size of Cu 0 and Cu 2 O. Among the catalysts, C-4 exhibited the largest Cu 0 and Cu 2 O sizes and the highest Cu⁺/(Cu⁺+Cu 0 ) ratio, achieving the highest proportion of higher alcohols (53.52 %). In-situ DRIFTS experiments also confirmed the synergistic effect of both factors. Larger Cu particles facilitated the dissociative adsorption of CO, while Cu⁺ sites favored the non-dissociative adsorption of CO. This work significantly expands the understanding of the role of Cu + -Cu 0 ratios and larger copper species in syngas conversion, offering valuable insights for the design of Cu-based catalysts with a high selectivity toward C 2+ OH.