Methanol aromatization over Zn-modified HZSM-5 catalysts derived from ZIF-8.

The 1% Zn Z8 (SAC)/Z5 catalyst prepared by steam-assisted crystallization method with ZIF-8 as sacrificial template and Zn source shows high BTX selectivity (69.8%) and excellent stability in MTA reaction. [Display omitted] • The Zn modified HZSM-5 zeolite was prepared by using ZIF-8 as sacrificial template and Zn source. • The steam-assisted crystallization method is the key to the preparation of high crystallinity nano-hierarchical pore structure Zn/Z5 catalyst. • The grain size, physical properties and acidity distribution of Zn/Z5 can be adjusted by controlling the addition amount of ZIF-8. • Appropriate acid distribution, smaller particle size, larger specific surface area and abundant mesoporous structure are the keys to obtaining higher BTX selectivity and excellent stability. Methanol to aromatics (MTA) is an effective way to produce aromatics by non-petroleum route. The acidity and structure of zeolite catalysts are the key to aromatics yield and stability of catalysts in MTA reaction. Here, Zn-modified HZSM-5 catalysts were prepared by physical mixing method (PM), in-situ hydrothermal synthesis method (SH) and steam-assisted crystallization method (SAC) using ZIF-8 as sacrificial template and Zn source. XRD, SEM, TEM, N 2 adsorption-desorption, ICP-OES, NH 3 -TPD, Py-IR, XPS, H 2 -TPR, TG characterization methods were used to investigate the physical and chemical properties of the catalysts. The influence of preparation methods of catalysts, the addition amount of ZIF-8, different Zn sources and reaction conditions on the products distribution in MTA reaction were investigated. The results showed that the crystallinity of Zn Z8 (SAC)/Z5 catalyst was improved and the hierarchical pore structure was obtained successfully after introduced ZIF-8 by steam-assisted crystallization method. Among them, Zn Z8 mainly exists as ZnOH+ species, which improved the utilization rate of Zn atoms and more L acid sites and moderate acid concentration were formed. The addition amount of ZIF-8 can affect the crystalline size, pore structure and the concentration of ZnOH+ species of Zn Z8 (SAC)/Z5. An appropriate ratio of B/L acid concentration was formed when adding an appropriate amount of ZIF-8. Compared with the traditional Z5 catalyst modified with Zn(NO 3) 2 as Zn source (1% Zn ZN (SAC)/Z5), there are smaller particle size, larger specific surface area and mesopore volume as well as suitable acid distribution in 1% Zn Z8 (SAC)/Z5 catalyst. The preparation method of catalyst, the addition amount of ZIF-8, different Zn sources and reaction conditions have a significant effect on the selectivity of BTX. [ABSTRACT FROM AUTHOR]