Ethane conversion in the presence of CO2 over Co-based ZSM-5 zeolite: Co species controlling the reaction pathway

Abstract

Two cobalt-based ZSM-5 catalysts CoZ-IE and CoZ-IM were prepared by ion-exchange and incipient wetness impregnation method, respectively, and characterized by XRD, N2 adsorption, TEM, XPS, UV–vis, H2-TPR and Py-IR. The catalytic performance towards ethane conversion over the two catalysts in the presence of CO2 was compared. Despite of their similar textual properties and Co contents, the product distributions over the two catalysts were quite different. Ethylene with high selectivity of 95% formed over CoZ-IE while syngas was produced as the main product on CoZ-IM, indicating dry reforming becomes the dominant reaction pathway instead of dehydrogenation. The difference pathway can be ascribed to the different nature of Co species in two catalysts. The isolated Co2+ anchored at zeolitic framework in CoZ-IE is quite stable and can only act as Lewis acid sites for ethane dehydrogenation. In contrast, the cobalt oxides on the zeolitic surface in CoZ-IM can proceed oxidation-reduction cycles in the CO2-C2H6 system, facilitating the activation of CO2 and the scission of C−C bonds, leading to the dry reforming of ethane.