The investigation into the dehydroaromatization of ethane over cobalt-modified ZSM-5 catalyst

Abstract

Ethane nonoxidative dehydroaromatization (EDA) to aromatics has been an effective way of upgrading shale gas. In this work, cobalt-modified zeolite catalysts are synthesized and applied to catalyze ethane to aromatics. Reaction conditions, zeolite topology, Co content, Al content and catalyst synthesis strategies are optimized and investigated systemically, in which the catalyst with 2.0 wt%Co over ZSM-5, SiO2/Al2O3 ratio of 60 presents the highest aromatization performance (0.0169 mmol aromatics·s−1· gCo−1) and the lowest catalyst deactivation rate (0.052 h−1). According to systematic characterizations, it is found that the tetrahedral Co2+ species is not only the active center of ethane dehydrogenation to ethylene, but also is beneficial to promote the subsequent ethylene aromatization simultaneously. And the generation rate of ethylene is the rate-limiting step of EDA. The existence of high proportion of Co2+ species and the appropriate Brønsted acid sites of Si–O(H)–Al species over 2.0Co/ZSM-5-60 catalyst are responsible for the high-performance of EDA. Finally, it is demonstrated that Co/ZSM-5-IE via ion exchange synthesis presents superior EDA catalytic performance (0.0395 mmol aromatics·s−1· gCo−1) compared with incipient wetness impregnation method, which comes from more highly dispersed and anti-reduction Co2+ species over Co/ZSM-5-IE.