Accessibility and catalysis of acidic sites in hierarchical ZSM-5 prepared by silanization

We have synthesized a series of zeolite ZSM-5 samples with hierarchical porous structure and tunable accessibility using organosilane as silanizing agent. Their structural and textural properties were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and nitrogen adsorption. We derived the acidity property and accessibility of acidic sites in the hierarchical zeolites from the Fourier transform infrared spectroscopy (FTIR) of samples with the adsorption of pyridine and 2,6-dimethylpyridine (DMPy), and found that the accessibility index was linearly correlated with the external surface area of hierarchical zeolite whose hierarchical factor is a constant. Furthermore, the hierarchical ZSM-5 has exhibited a high catalytic activity and long life in both benzylation reaction of benzene by benzyl alcohol and methanol-to-gasoline reaction. The results show that the present synthesis route is highly effective to enhance the accessibility of Brønsted acid sites in zeolite ZSM-5.

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► A new silanizing agent is used in the synthesis of hierarchical ZSM-5 with intercrystal mesopores.
► ACI is a key factor to the hierarchical zeolites whose HF is a constant.
► The ACI is linearly correlated with the external surface area.
► Adsorption of dimethylpyridine by IR is suitable for the hierarchical zeolites.
► The hierarchical ZSM-5 zeolite with high ACI is favor to bulky molecular reaction.