Deactivation mechanism and regeneration study of Zn/HZSM-5 catalyst in ethylene transformation

Abstract : The purpose of this study is to identify the deactivation mechanism(s) that occurs during the aromatization of dilute ethylene at 500 °C on Zn/H-MFI catalyst. More than 15 catalysts, with a Zn/H+ molar ratio ranging from 0 (H-ZSM5) to 1.8 (Zn/H-ZSM5), were prepared by wet impregnation. Deactivation does not result from Zn sublimation, but from coking. The deactivation function and coke deposition can be modelled by simple exponential laws. Moreover, the balance between Lewis (Zn) and Brønsted (H+) acid sites is a good descriptor for predicting the catalyst stability. The coke poisoning has a similar impact on the diminution of micropore volume as well as on the reduction of the number of Lewis and Brønsted acid sites. The best suited descriptor for describing deactivation is the reduction of the micropore volume.