ZSM-5 composite molecular sieve with a core-shell structure and preparation method and application thereof

Abstract

The invention discloses a ZSM-5 composite molecular sieve with a core-shell structure, a preparation method and an application thereof. The molecular sieve is characterized in that: the core phase is a ZSM-5 molecular sieve, the shell phase is a ZSM-5 molecular sieve with a mesoporous structure, the total molar ratio of silica to alumina is 30-80, the total specific surface area is 460-550 m2 / g, the total pore volume is 0.25-0.38 ml / g, the size of the mesopore in the shell phase is 2-2.5 nm, the specific surface area of the mesopore in the shell phase is 480-650 m2 / g, and the pore volume of the mesopore in the shell phase is 0.2-0.31 ml / g. The preparation method comprises the following steps: firstly performing crystallization of a mixture containing sodium hydroxide, a template, water, a silicon source, an aluminium source, a surfactant and the ZSM-5 molecular sieve, then performing washing, drying, roasting of the crystallized product to obtain the ZSM-5 composite molecular sieve. The composite molecular sieve is applicable to aromatic hydrocarbon conversion reaction, and has the advantages of high conversion rate and selectivity, and long catalyst life.

Description

technical field [0001] The invention belongs to the field of molecular sieve synthesis, and in particular relates to a ZSM-5 composite molecular sieve with a core-shell structure and a preparation method and application thereof. Background technique [0002] At present, composite molecular sieves have attracted more and more researchers' attention, and various composite molecular sieves have been synthesized continuously. In 2006, Younes Bouizi (Chem Mater 2006, 18, 4959~4966) reported a composite molecular sieve Silicalite-1 / MFI with a core-shell structure. In the method, ZSM-5 molecular sieve is wrapped with Silicalite-1 molecular sieve to form a core-shell composite molecular sieve with ZSM-5 as the core and Silicalite-1 as the shell, and the coverage rate is 70% through one synthesis process. The specific synthesis process is as follows: first, nano-scale Silicalite-1 seeds are deposited on the surface of ZSM-5 molecular sieves through tetrapropylammonium hydroxide, tet...

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Problems solved by technology

[0004] Silicalite-1 / ZSM-5 composite molecular sieve is a kind of isomorphic composite molecular sieve with core-shell structure and MFI topology. ZSM-5 molecular sieve is completely wrapped by Silicalite-1 molecular sieve, and Silicalite-1 The type selection effect of ZSM-5 composite molecular sieve is better than that of ZSM-5 molecular sieve, but the conversion rate is reduced due to the lack of acidity on the surface

[0005] In CN101723401A, a ZSM-5 molecular sieve composite molecular sieve with a core-shell structure with different silicon-aluminum ratios was synthesized, and a ZSM-5 zeolite molecular sieve with a relatively low silicon-aluminum ratio was used as a seed crystal and added to a high-silicon-aluminum ratio shell phase rubber Among them, the ZSM-5 molecular sieve composite molecular sieve with core-shell structure was synthesized by hydrothermal method, but the microporous structure mainly exists in this structure, which affects the diffusion process and limits the diffusion of macromolecules, so it cannot be applied to the macromolecular reaction process.

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