Design of efficient ZnO/ZrO2 modified CuCoAl catalysts for boosting higher alcohol synthesis in syngas conversion

Selective synthesis of higher alcohols from syngas conversion is highly desirable, but still very challenging. Here, focusing on the commonly used CuCoAl (CCA) catalyst, we attempted to reconcile the capability of the non-dissociation of CO species and the activation of H2 through adding ZnO modified ZrO2 composite into the catalyst for the promotion of higher alcohols synthesis. Under the guidance of such concept, a series of CCA|ZnO/ZrO2 (m: n) modified catalysts (m: n, represent the mass ratio of ZnO to ZrO2) were prepared by mortar-mixing CuCoAl and ZnO/ZrO2 components (2/1 wt ratio). It was found that the CCA|ZnO/ZrO2 (4:1) catalyst showed a highest total alcohols (ROH) selectivity of 42.6 wt% with excellent C2+OH/ROH fraction of 83.7% among the investigated catalysts. The surface [H*]/[C*] ratio of CCA|ZnO/ZrO2 catalysts, as revealed by (CO + H2)-TPD-MS results, increased with the rise of ZnO/ZrO2 ratio. Moreover, the CCA|ZnO/ZrO2 (4:1) catalyst with moderate [H*]/[C*] ratio could acquire the highest ROH selectivity and best space time yield of total alcohols (STYROH) due to that the balance of relative amount of CO*, CHx* and H* species provided the more probability of CnHx*-CO* coupling reaction for higher alcohols synthesis, rather than the hydrogenation reaction of CHx* or CnHx* species and water gas shift reaction.