ZSM-5 molecular sieve and preparation method thereof

Abstract

The invention relates to a ZSM-5 molecular sieve and a preparation method thereof. According to the molecular sieve, the molar ratio of silicon oxide to aluminium oxide is 45-80, the molecular sieve possesses weak acids, strong acids and superacids at the same time, the total acid content is 0.25-0.65 mmol / g, the molar ratio of Bronsted acids to Lewis acids is 1.2-2.1, and the molar ratio of the acid content sum of strong acids and superacids to the acid content of weak acids is 1.2-2. The preparation method comprises: first step, performing crystallization on a mixture containing sodium hydroxide, water, an aluminium source and a silicon source; and second step, adding a proper amount of an aluminium source into the crystallization product of the first step, performing crystallization at a certain temperature, then washing ,drying and roasting to obtain ZSM-5 molecular sieve. The molecular sieve provides an excellent catalytic material for catalytic processes needing relatively more superacid amount or needing different acidity, also the method does not employ any templates, so that the synthetic cost is substantially reduced and the method is green and environment-friendly.

Description

technical field [0001] The invention belongs to the field of molecular sieve synthesis, and in particular relates to a ZSM-5 molecular sieve and a preparation method thereof. Background technique [0002] In 1984, after Haag et al first proposed that framework aluminum is the active center of silica-alumina zeolite molecular sieves, according to the properties of donating protons and accepting electrons, the concepts of Bronsted (ie B acid) and Lewis acid (ie L acid) were introduced to distinguish zeolite molecular sieves type of acid. by NH 3 -High-temperature peaks and low-temperature peaks in the TPD spectrum to represent strong acid sites and weak acid sites, thereby characterizing the acid strength distribution of silica-alumina molecular sieves. ZSM-5 molecular sieve has a unique three-dimensional channel structure and shape selection of acid strength distribution. It also has the characteristics of high silicon-aluminum ratio, lipophilic and hydrophobic characterist...

AI Technical Summary

Problems solved by technology

For some reaction processes that require superacids or reaction processes in which superacids are combined with strong acids and weak acids, the acid properties of ZSM-5 molecular sieves prepared by existing methods are difficult to meet their needs, which limits the application of their good shape-selective properties.

[0004] At present, the use of organic templates is still the most important method for synthesizing ZSM-5 molecular sieves. The price of organic templates is relatively expensive, the cost of preparation is high, and most of the organic templates are toxic and will pollute during the production and post-treatment of zeolite. surroundings

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