Effect of ZrO2, Al2O3 and La2O3 on cobalt–copper catalysts for higher alcohols synthesis

• ZrO2, Al2O3 and La2O3 promoted catalysts showed no major differences in reduction behavior and surface composition.
• A higher dispersion was achieved on La2O3 promoted catalyst.
• La2O3 promoted catalyst had highest ethanol selectivity(10.5%) at 250 °C and 30 bar.
• CO conversion of La2O3 promoted catalyst decreased during 9 h of time-on-stream. The selectivity distribution shifts to favor methanol and ethanol during the transition state.

Three cobalt–copper catalysts singly promoted with La, Zr, or Al were studied for catalytic conversion of syngas to higher alcohols. The properties of the promoted catalysts have been characterized by TPR, XRD, XPS and BET. CO hydrogenation was carried out in a plug-flow reactor under 30 bar, GHSV = 36000 scc/gcat/h, H2/CO = 2, and 250 °C at differential conversions. The catalyst activity and selectivity to higher alcohols are greatest on CuCoLa2O​3: ethanol selectivity 10.5% at a conversion of 0.76%. During 9 h of time-on-stream, CO conversion decreased on CuCoLa2O3​ while methanol and higher alcohol selectivity increased. The behaviors on CuCoZrO2 and CuCoAl2O3 were different. On these two catalysts, CO conversion and selectivity reached a near-steady state much more quickly than CuCoLa2O3. These results suggest changes on CuCoLa2O3 that increase the selectivity for oxygenates continue with time, at least over the time scale investigated here.

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