Cooperative structure direction of organosilanes and tetrapropylammonium hydroxide to generate hierarchical ZSM-5 zeolite with controlled porous structure

Abstract

Hierarchical ZSM-5 zeolite with short-range ordered mesoporosity and hierarchical ZSM-5 zeolite nanorods were obtained via a direct hydrothermal synthesis by the cooperative structure direction of dimethyloctadecyl[3-(trimethoxysilyl)propyl]- ammonium chloride (TPOAC) and tetrapropylammonium hydroxide (TPAOH). Dimethyloctadecyl[3-(dimethoxymethylsilyl)propyl]ammonium chloride (DPOAC) and octadecyltrimethylammonium chloride (OTAC) were also employed as structure directing agents (SDA) to further explore the role of methoxysilyl groups in organosilanes during the formation of hierarchical structure. The prepared materials were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), N₂ adsorption–desorption, FT-IR, UV-vis and inductively coupled plasma-optical emission spectroscopy (ICP-OES). The characterization results showed that the use of TPOAC and DPOAC would generate short-range ordered mesopores and irregular mesopores, respectively. Hierarchical ZSM-5 zeolite nanorods with worm-like intracrystalline mesopores could be obtained by adjusting the amount of silicon source. The lack of methoxysilyl groups in OTAC however could lead to phase separation problems. Furthermore, the hierarchical Fe-ZSM-5 zeolite with short-range ordered mesoporosity showed enhanced catalytic activity and stability for the hydroxylation of phenol at room temperature.