Synthesis Of Hierarchical Zsm-5Zeolites In The Presence Of3-glycidoxypropyl-Trimethoxysilane

Zeolites, a class of crystalline aluminosilicates with uniform micropores, have been widely used in many fields such as petrochemical industry, petroleum processing, adsorption and separation due to their large specific surface areas, high hydrothermal stability, and their shape-selective properties endowed by the intricate channel structures. However, the pore sizes of most zeolites are in a molecular dimension scale (0.3～1.0nm). The purely microporous network of zeolites frequently results in intracrystalline diffusion limitations, leading to the reduction of effectiveness.Hierarchical zeolites, with additional mesopore system besides their inherent microporosity, show a greatly improved performance in catalytic reactions even large molecules involved due to the available mesopores enhancing the mass transport in zeolites. Silane coupling agents (SCAs), a type of silanes with organic functional groups, are widely used in the modification of polymer materials. In an SCA molecule, the groups ready to combine with inorganic materials and those preferring to interact with organic materials are both involved. It has been reported that the addition of SCA into the zeolite synthesis system could retard the zeolite crystal growth, leading to the zeolite nanocrystalline assembly. In this thesis, hierarchical ZSM-5zeolites were hydrothermally synthesized in the presence of3-Glycidoxypropyl-trimethoxysilane (GPTMS) in the synthesis system with TPABr as the template and inexpensive water glass as the silica source. The main results are summarized as follows:1) The effects of some factors, such as GPTMS content, alkalinity, and crystallization conditions etc., on the synthesis of ZSM-5were investigated. The structure and morphology of the synthesized samples were characterized by XRD, SEM, N2sorption, TEM techniques and so on. The results indicated that hierarchical ZSM-5assemblies with spherical morphology were synthesized in the presence of GPTMS. In contrast, in the absence of GPTMS, ZSM-5assemblies composed of rod-like crystals were obtained under the same crystallization conditions. When increasing the content of GPTMS, the sizes of the ZSM-5crystalline and of the spherical assemblies decreased. Furthermore, an excess of GPTMS used resulted in the production of amorphous materials, indicating the retarding effect of GPTMS on the growth of ZSM-5crystals. Additionally, the prolonging of the crystallization time led to growing the ZSM-5crystallines up and an enlargement of the spherical assemblies as well. The probe reactions involving of alkylation of benzene with benzyl alcohol and the catalytic cracking of polypropene (PP) indicated that the synthesized hierarchical ZSM-5displayed much improved catalytic properties compared with the ZSM-5zeolites synthesized without GPTMS.2) Hierarchical ZSM-5zeolites with different Si/Al ratios were synthesized. SEM images revealed that the morphology of zeolites transformed from spherical assemblies to single-crystal ones, when the Si/Al ratio in the starting synthesis was increased from20to200. Additionally, the external surface area and the mesopore volume increased correspondingly, confirmed by the N2sorption measurement. The Pt/ZSM-5catalyst prepared by the impregnation method of Pt species onto the hierarchical ZSM-5exhibited an excellent performance in the hydroisomerization of n-hexane.