Promoter Effect of Cesium on C–C Bond Formation during Alcohol Synthesis from CO/H2over Cu/ZnO/Cr2O3Catalysts

Abstract

The effect of calcination temperature and Cs-promotion on the ternary Cu–Zn–Cr oxide catalyst has been investigated in connection with both structural and catalytic properties in the high pressure CO hydrogenation. As revealed by TPR and XPS, the reduction of copper is inhibited by incorporation of Cs promoter. Under typical reaction conditions, detectable copper phases are reduced to metallic copper. The crystal size of copper particles tends to increase with increasing reduction temperature and simultaneously Cs is segregated to the catalyst surface. Activity results in CO hydrogenation, with and without cofeeding methanol, ethanol, or 1-propanol, showed that methanol or C2+OH yield increased upon Cs-doping of the catalysts. By feeding a given CnOH alcohol, the Cn+OH yield was enhanced, with the most difficult chain growth being for the reaction CH3OH→CH3CH2OH. While a large surface area of the catalysts, with ill-defined crystalline phases, is the key parameter for an enhancement in the productivity and a low increase in the selectivity to higher alcohols, cesium incorporation leads to substantial improvement in C2+OH selectivity.