Investigation of Al precursor for ethanol synthesis from syngas on Cu-based multifunctional catalyst

The use of cheap Cu-based catalyst to directly synthesize ethanol and higher alcohols from syngas has been favored by researchers. However, the role of Al-based components and carbon chain growth are still unclear. Herein, a series of Cu-based multifunctional catalysts prepared by various Al precursors using complete liquid phase method are investigated for ethanol and higher alcohols synthesis. It is found that the catalysts using aluminium isopropoxide and Al2O3 as the Al precursor exhibit comparable activity with about 20% of CO conversion, 27% of ROH selectivity and >50% of C2+OH selectivity. Results show that different Al precursors can simultaneously adjust the ratios of Cu+/(Cu++Cu0) and the amount of weak acid on catalyst surface, thus leading to various concentration of CHn*/CHxO* on catalyst surface. In-situ DRIFT experiment indicates that a strong intensity of bridge-adsorbed of CO occurs over slurry ternary CuZnAl catalysts, which facilitates the cleavage of C???O bond and consequently favors the formation of CHn* key intermediates. Moreover, we have found that the carbon chain growth can be proceeded by the C-C coupling of CHn* and CHxO*, or via CO* insert into CHn* to form CHnCHxO*/CHnCO* which is further hydrogenated to form ethanol and higher alcohols.