Core-shell type SAPO-34-coated ZSM-5 molecular sieve catalyst and preparation method thereof

Abstract

The invention provides a core-shell type SAPO-34-coated ZSM-5 zeolite catalyst and a preparation method thereof, an SAPO-34 microsphere (about 2 microns) formed by stacking nano polycrystalline aggregates is used as a core, a layer of MCM-41 material is deposited on the outer surface of the SAPO-34 microsphere, and then a shell layer MCM-41 in-situ zeolitization is induced by adding a ZSM-5 seed crystal precursor solution to form ZSM-5 zeolite particles (about 150 nm) by using a traditional hydrothermal synthesis method. According to the core-shell type SAPO-34-coated ZSM-5 zeolite catalyst prepared by the preparation method disclosed by the invention, the surface of the SAPO-34 is modified by utilizing the deposited MCM-41, so that the problem that the SAPO-34 crystal is damaged in an alkaline environment system for synthesizing the SAPO-34-coated ZSM-5 is effectively solved. The preparation method provided by the invention has the advantages of easily available raw materials, simple process, relatively mild conditions and the like, can realize industrial application, and has wide application prospects in solving the problem of energy shortage.

Description

technical field [0001] The invention belongs to the field of inorganic materials, in particular to a core-shell type SAPO-34@ZSM-5 molecular sieve catalyst and a preparation method thereof. Background technique [0002] Zeolite molecular sieve is a kind of crystalline material with framework structure, which has been widely used in catalysis, adsorption separation, biotechnology due to its unique microporous structure, adjustable acidity, good thermal / hydrothermal stability and chemical stability. and other fields. Among them, SAPO-34 molecular sieve is one of the important members of the SAPO series. SAPO-34 has a CHA topology, which is composed of SiO 4 , AlO 4 and PO 4 A three-dimensional cross-channel structure formed by interconnecting tetrahedra through oxygen bridges. It has high selectivity to ethylene and propylene in MTO-catalyzed reaction. However, the traditional SAPO-34 zeolite severely limits the mass transfer and diffusion of product molecules in the mic...

AI Technical Summary

Problems solved by technology

The post-treatment method (acid or alkali treatment) is used to extract aluminum or silicon atoms in the zeolite framework to cause lattice defects, so that intracrystalline mesopores are generated in the zeolite crystal, but this method is easy to cause crystal damage and reduce the zeolite. Crystallinity, the released amorphous silicon and aluminum species are easy to block the micropore channels

The use of mesoporous templates and small-molecule organic amines (structure-directing agents) tends to cause incompatibility between templates during the growth of zeolite, which can easily lead to two-phase separation or miscellaneous crystals

In addition, a large amount of waste gas is generated in the process of removing the template agent, which is likely to cause environmental pollution

No matter which method is used, the acid center of the catalyst skeleton will be weakened, so that the catalytic active sites of the catalyst will be greatly reduced during the reaction, which will further affect the reaction performance of the catalyst.

Moreover, complex synthetic procedures, expensive mesoporous templates, and a large amount of time consumption severely limit industrial applications.

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