Collaborative Effect of Zinc and Phosphorus on the Modified HZSM-5 Zeolites in the Conversion of Methanol to Aromatics

Abstract

In this work, the cooperative effect of Zn and P modification on the pore structure and acid properties of HZSM-5 and its catalytic performance in methanol catalytic dehydration to aromatic process were investigated. NH3-TPD and Py-IR tests reveal that introducing P and Zn can significantly decrease the acidic strength and increase the Lewis/Brönsted acid ratio of HZSM-5, which is beneficial for the aromatization of methanol rather than the hydrogen transfer reaction. Meanwhile, P doping also enlarges the pore size of HZSM-5, enhancing the coke resistance and the formation of xylene and C9+ aromatics. Compared to the ones modified by ZnSO4 and Zn(NO3)2, HZSM-5 modified by Zn3(PO4)2 exhibits higher aromatics selectivity and lower paraffin generation, with better durability in long term operation. Furthermore, excessive Zn and P loading will result in negative impact on aromatics selectivity, and the optimal loading of ZnO and P2O5 are about 1% and 2%, respectively; higher reaction temperature and lower Si/Al lead to higher aromatics selectivity. Graphic Abstract: [Figure not available: see fulltext.]