In Situ Incorporation of Zn into Hierarchical ZSM-5 Zeolites for Olefin Hydroisomerization
Tao Pan, Wu Zhi, Kuanyu Zhou
Abstract
Zn species were incorporated into hierarchical ZSM-5 zeolite (Zn-ZSM-5) via in situ hydrothermal crystallization of aluminosilicate gel containing zinc metal salts. Compared to bulk ZSM-5 zeolite, incorporating 2.3 wt % Zn increased the zeolite particle size from 1–2 to 3–5 μm and changed the morphology of the zeolite crystal from cube to cuboid. The acid density of zeolite also decreased from 1.12 to 0.37 mmol/g, as well as the ratio of the Brønsted acid site to the Lewis acid site (B/L) decreased from 1.2 to 0.3. However, the proportion of medium-strong acid sites was increased from 5.4 to 35.1%. Compared with Zn-modified ZSM-5 zeolite (Zn/ZSM-5) prepared by impregnation, Zn-ZSM-5 is characteristic of homogeneous dispersed ZnOH+ species with a higher proportion of medium-strong acid sites (35.1 versus 15.5%) and a lower ratio of B/L (0.3 versus 0.6). For 1-hexene hydroisomerization, Zn-ZSM-5 zeolite possessed a higher selectivity of iso-alkanes than that of Zn/ZSM-5 zeolite (51.4 versus 42.4%), as well as the selectivity of aromatics (2.3 versus 1.4%), suggesting potential application in the reduction of the olefin content in FCC gasoline.