Mixed alcohols synthesis from syngas over Cs- and Ni-modified Cu/CeO2 catalysts

Cu/CeO2 (cop) was prepared by a coprecipitation method using NH3·H2O as a precipitant (in order to avoid the residues of alkali metals), followed by a boiling process to eliminate NH3 and decompose [Cu(NH3)4]2+ complex. Because the Cu particles in Cu/CeO2 (cop) were much smaller than those in Cu/CeO2 (imp) (prepared by an impregnation method), Cu/CeO2 (cop) showed a higher activity than that over Cu/CeO2 (imp) for the synthesis of mixed alcohols. Moreover, Cu/CeO2 (cop) showed a higher CO conversion than that over the industrial catalyst Cu/ZnO due to the reducibility of CeO2-based compounds. Although either Cu/ZnO or Cu/CeO2 (cop) produced methanol as a dominant product, the STY of higher alcohols (C2+OH) formed over Cu/CeO2 (cop) was much larger than that over Cu/ZnO because CeO2-based compounds could catalyze the synthesis of isobutane from syngas (isosynthesis). When Cs was introduced into the Cu/CeO2 (cop) catalyst, the mass ratio of C2+OH to MeOH in the products greatly increased from 0.13 to 0.71 but the CO conversion decreased slightly. Both the CO conversion and the selectivity for higher alcohols over CsCu/CeO2 (cop) were higher than those over CsCu/ZnO. By introducing Ni (an F-T element) into CsCu/CeO2 (cop), the CO conversion increased from 22.2% to 37.6% and the mass ratio of C2+OH to MeOH in the products increased from 0.71 to 0.85. Therefore, CsNiCu/CeO2 (cop) is an excellent catalyst for the synthesis of mixed alcohols. A slow deactivation was observed over CsNiCu/CeO2 (cop) in the reaction at 573 K for 18 h. The deactivated catalyst could be regenerated by calcination in air at 723 K and followed by reduction in H2 at 573 K.