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Synthesis of Hierarchical ZSM-5Zeolites Assisted by the Silane Coupling Agents and Mesoporous Template

Author: YaoQiongSi
Tutor: XiaoQiang
School: Zhejiang Normal University
Course: Physical and chemical
Keywords: ZSM-5 hierarchical silane coupling agent mesoporous template Friedel-Crafts alkylation
CLC: O643.36
Type: Master's thesis
Year: 2013
Downloads: 62
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Abstract


Zeolite, a crystalline aluminosilicates with micropores, has been widely used in many fields such as petrochemical industry, adsorption and separation due to its large specific surface area, high hydrothermal stability, and shape-selective properties. However, the narrow pore of zeolite limits the utilization efficiency due to the intracrystalline diffusion limitation in the purely microporous network of zeolite.Hierarchical zeolite refers to zeolite with mesoporous system besides its inherent microporosity. The mesopores in the hierarchical zeolite may greatly improve the performance in catalytic reactions, even in which large molecules are involved, due to the shortened diffusion distance. Silane coupling agent (SCA) is a type of silanes which contain both inorganic and organic functional groups. Aided by the functional groups, SCA could combine with both inorganic materials and organic materials. It has been reported that the addition of silane coupling agents into the zeolites synthesis system could retard zeolite growth and obtain the zeolite nanocrystalline assembly. In this thesis, to construct the hierarchical zeolite with ordered mesopores, mesoporous templates were introduced to the synthesis system besides SCA. Mesoporous templates could enter the zeolite synthesis system and construct ordered mesoporous zeolite with the assistance of the SCA. This thesis mainly consists of two parts as follows:In order to the mesoporous in the hierarchical zeolite becoming ordered, we bring the mesoporous template agents to the zeolite synthesis system. The mesoporous template agents successfully entered the zeolite synthesis system and obtained the ordered mesoporous zeolite, by formation of ionic bonds with Silane coupling agents. The main results are summarized as follows:1) Hierarchical ZSM-5zeolite assemblies with spherical morphology were hydrothermally synthesized in the presence of SCAs in the synthesis system using inexpensive water glass as the silica source and TPABr as the microporous template. The effects of alkalinity, dosage of silane coupling agents (APTES), and type of SCA etc on the synthesis of ZSM-5were investigated. The structure and morphology of the synthesized samples were characterized by means of XRD, SEM, N2sorption, TEM techniques and so on. The results indicated that hierarchical ZSM-5was successfully synthesized aided by silane coupling agents. The crystallinity and crystal size of ZSM-5decreased with increasing the dose of APTES in the synthesis system. Too much dosage of APTES would not produce zeolite. The catalytic cracking of polypropene (PP) over the hierarchical ZSM-5as probe reaction indicated that the synthesized hierarchical ZSM-5displayed much improved catalytic properties compared to the ZSM-5synthesized without silane coupling agents.2) Hierarchical ZSM-5zeolite assemblies were synthesized aided by the synergetic effect of mesoporous templates and SCAs in the synthesis system. The effects of the type and dosage of mesoporous template agents on the synthesis of ZSM-5were investigated. The results indicated that hierarchical ZSM-5with robust mesoporosity was synthesized when an anionic surfactant of Sar-Na was used as mesoporous template. The crystallinity decreased with the increase of the dose of Sar-Na. The F-C alkylation of benzene with benzyl alcohol as probe reaction indicated that the synthesized hierarchical ZSM-5displayed much improved catalytic properties compared to the conventional ZSM-5zeolites. Additionally, hierarchical ZSM-5with high mesoporosity was also synthesized when an anionic polyelectrolyte of PAA and a cationic surfactant of CTAB were used as meosporous template. The F-C alkylation of benzene with benzyl alcohol as probe reaction indicated that the synthesized hierarchical ZSM-5added by PAA and CTAB exhibited an improved catalytic performance due to the robust mesoporosity.

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CLC: > Mathematical sciences and chemical > Chemistry > Physical Chemistry ( theoretical chemistry ),chemical physics > Chemical kinetics,catalysis > Catalytic > Catalyst
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