Comparative effects of mesopores and framework defects on the deactivation of HZSM-5 catalyst during alkylphenol dealkylation

Abstract

The dealkylation of alkylphenols over HZSM-5 is regarded as a promising way for the production of phenol from both fossilized and raw lignocellulose-derived oils. However, the pure microporous HZSM-5 deactivates fast due to coking. Although the introduction of mesopores into microporous HZSM-5 can enhance the catalyst stability, the relationship between the catalytic performance and changed properties caused by alkaline treatment remains ambiguous. In this study, the coke analysis reveals that the mesopore introduction primarily promotes the formation of external coke by providing additional diffusion paths for coke precursors. However, the phenolates bound to the Lewis acid sites generated on external surface facilitates the deposition of external coke, the total coke amount is thus not significantly impacted. Furthermore, the reduction of internal silanols (Si-related framework defects) and Lewis acid sites (Al-related framework defects) by ammonium hexafluorosilicate treatment declines the total amount of coke and alleviates catalyst deactivation.