Facile Preparation of Cu-Al Oxide Catalysts and Their Application in the Direct Synthesis of Ethanol from Syngas

A simplified catalytic system K-Cu/Al₂O₃ (KCA-xCu-T) with Cu-Al oxides was prepared by a facile impregnation method and was successfully applied in the direct synthesis of ethanol from syngas. The results demonstrated that the distribution of CuO, CuAl₂O₄, and CuAlO₂ in KCA-xCu-T catalysts can be effectively tuned by varying the calcination temperature (T/°C) and CuO loading (xCu/wt%). The cooperative effect between Cu⁰ and CuAlO₂(Cu⁺) was proved to be responsible for the enhanced ethanol selectivity. Furthermore, the formation of CuAlO₂ could efficiently fix Cu⁺ species in KCA-10Cu-900 sample, and thus lead to excellent catalytic stability (300 h at 400 °C). CuAl₂O₄ itself has no catalytic effect but can be gradually decomposed into Cu⁺ and/or Cu⁰ species during reaction, which further influenced the ethanol selectivity (38.4 wt%).