Role of the nonstoichiometric Zn-Cr spinel in ZnCrOx/ZSM-5 catalysts for syngas aromatization

Bifunctional catalysts composed of ZnCrO x oxide and ZSM-5 were widely used in syngas-to-aromatics (STA). The CO conversion on bifunctional catalysts was generally higher than that on oxide catalysts attributed to the pulling effect of zeolite, but the key factor for the improvement of CO conversion was still short of systematical explanation. In this work, the degree of nonstoichiometric spinel of ZnCrO x (ZxC) oxides was finely tuned through modulating the ratio of Zn/Cr, which could significantly influence the catalytic behaviors of ZnCrO x /ZSM-5 catalysts for the CO hydrogenation to aromatics. The increase of nonstoichiometric spinel corresponded to the increase of oxygen vacancies and the enhancement of Zn-Cr synergistic effect, which promoted the activation of H 2 and CO, leading to a dramatic increase of CO conversion. The work revealed that the action of ZnO and oxygen vacancies was the key factor for CO pulling in ZnCrO x oxide and ZSM-5 catalyzed STA reaction.