Single-crystalline hierarchical ZSM-5 zeolite with intracrystalline mesopore was successfully synthesized by using L-lysine as a mesoporous template,and the Si/Al ratio was changed by adjusting the adding amount of aluminum source(sodium metaaluminate).Then the effect of acidic properties on zeolite's activity and mass transfer in n-heptane catalytic cracking was investigated in detail.The physical structure,acidic properties and micromorphology of single-crystalline hierarchical ZSM-5 zeolite were characterized by using X-ray diffraction(XRD),nitrogen physical adsorption,ammonia temperature-programmed desorption(NH3-TPD),pyridine infrared(Py-IR),scanning electron microscopy(SEM)and transmission electron microscopy(TEM).In addition,the zero-length column(ZLC)device was employed to test the apparent diffusivity of n-heptane in single-crystalline hierarchical ZSM-5 zeolite,which was used to characterize its mass transfer performance.The results showed that the physical structure of single-crystalline hierarchical ZSM-5 zeolite kept almost the same with the increase of Si/Al ratio,while the zeolite's mass transfer performance was improved with the decrease of acid amount,but the catalytic cracking performance was enhanced with the increase of acid amount.When the Si/Al ratio of the single-crystalline hierarchical ZSM-5 zeolite increased from 80 to 140,the apparent diffusivity of n-heptane could be improved by more than 87%.When the Si/Al ratio was 80,the conversion rate of n-heptane could reach up to 97.5%,and the selectivity of ethylene and propylene were 24.3%and 35.1%,respectively.
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