Synthesis and Characterization of Hierarchical ZSM-5 Zeolites with Outstanding Mesoporosity and Excellent Catalytic Properties

Abstract

Abstract A novel soft-template (ST) is fabricated and successfully employed as mesoporogen to synthesis hierarchical ZSM-5 zeolites with outstanding mesoporosity and high hierarchy factors. The as-produced soft-template can connect steadily with the MFI frameworks by covalent bonds of –Si–O–Si– during the high-temperature hydrothermal crystallization process. This type of connection mode can effectively avoid the formation of amorphous materials, and the specific structure of this soft-template can efficiently introduce plentiful of mesopores with few micropores being consumed. The particles of as-synthesized hierarchical ZSM-5 zeolites are in size of about 1 μm, which are made up of nanocrystals of 60–150 nm. The structure parameters of these samples are characterized with the techniques of X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, nitrogen sorption, scanning electron microscope (SEM), transmission electron microscope (TEM), NH3 temperature-programmed desorption (NH3-TPD) and thermogravimetric (TG). Due to the nature of zeolites and great microporosity, these hierarchical samples present great tolerance of hydrothermal treatment. And because of the intracrystalline mesopores, large external surface areas, and abundant accessible acid sites, whether in conversion rate of reactants or selectivity of products, the hierarchical samples exhibit excellent catalytic performance in the reactions of alkylation between benzene and benzyl alcohol, cracking of 1,3,5-tri-isopropylbenzene, and thermal cracking of low-density polyethylene (LDPE), respectively.

Keywords

• Hierarchical
• ZSM-5 zeolites
• Soft-template
• Benzylation
• LDPE cracking