Tuning the Cu+ species of Cu-based catalysts for direct synthesis of ethanol from syngas

Abstract

Cu–CuPS catalysts supported on silica were prepared by the ammonia evaporation impregnation (AE-IM) method and employed for CO hydrogenation into ethanol. These catalysts with various ratios of surface Cu⁰ and Cu⁺ were rationally designed by adjusting the relative Cu loading of ammonia evaporation and impregnation processes. Based on mutual corroboration by multiple characterization studies, it was proved that CO could be strongly adsorbed on Cu⁺, which is of vital importance for CO activation. The cooperative effect between surface Cu⁰ and Cu⁺ can effectively promote the efficiency of the catalysts. Herein, we elucidate that adjusting the Cu/CuPS ratio is conducive to generate an appropriate Cu⁺/(Cu⁺ + Cu⁰) ratio during CO hydrogenation, which is responsible for the high ethanol yield of the catalyst. The 0.33Cu/0.67CuPS catalyst exhibited the best catalytic behavior with an ethanol selectivity as high as 36.6 wt% and a space time yield toward alcohols of 38.2 mg mL_cat⁻¹ h⁻¹. These results give insights into the function of Cu⁰ and Cu⁺ species during ethanol production on Cu-based catalysts, and provide a valuable tool for the discovery of high reactivity ethanol industrialization catalysts.