In Situ Incorporation of Zn into Hierarchical ZSM-5 Zeolites for Olefin Hydroisomerization

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 mu m 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 Bronsted 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 isoalkanes 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.