A kind of nano all silicon beta molecular sieve and preparation method thereof

Abstract

The invention discloses a nanometer all-silicon beta molecular sieve and a preparation method thereof. The preparation method comprises the following steps: (1) uniformly mixing a silicon source, a mineralizer containing fluorine and / or sodium, a templating agent and water to obtain an alkali and The molar ratio of silicon source is OH-:SiO2=0.21-4 reaction mixture; (2) the reaction mixture that step (1) obtains is transferred in the airtight container of pressure resistance, and at the temperature of 60-115 ℃ and autogenous pressure (3) heating the aging product obtained in step (2) to 130-230° C. and crystallizing under autogenous pressure for 0.5-30 days to obtain a crystallized product; wherein the crystallized The temperature of curing is at least 15° C. higher than the aging temperature; (4) recovering the crystallized product obtained in step (3). The nano all-silicon beta molecular sieve obtained by this technical scheme has a sheet shape, its length and width are not more than 490 nanometers, and its thickness is not more than 150 nanometers. In the characterization results of 29Si NMR, Q4 / Q3 is not less than 25, and the specific surface area SBET is greater than 430m2 / g.

Description

Technical field [0001] The invention relates to a nano all-silicon beta molecular sieve and a preparation method thereof. Background technique [0002] β molecular sieve is a molecular sieve with BEA structure developed by R. Wadlinger et al. in 1967. Its appearance is a sign of high-silicon molecular sieve research. β molecular sieve is a stacking fault symbiosis composed of several different but closely related polymorphs, and has a three-dimensional twelve-membered ring pore structure. Among them, the channels in the [100] and [010] directions are straight channels, and their pore diameters are both about 0.66×0.67 nanometers; the channels in the [001] direction are formed by the intersection of the straight channels in the [100] and [010] directions The sine-shaped structure of the pore size is about 0.55×0.55 nanometers. [0003] Because β molecular sieve has a high framework silicon to aluminum ratio and a special three-dimensional twelve-membered ring pore structure, it ha...

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Problems solved by technology

However, when a new template is used, the synthesis of the template is complicated and the cost is high. Therefore, the new template method is difficult to promote industrially; the method of preparing all-silicon β molecular sieve in a neutral fluorine-containing system has a high mold-to-silicon ratio and a long synthesis period. , large particle size of the crystallized product, etc.; the method of preparing all-silicon β molecular sieve under acidic conditions has the advantages of wide range of materials and fast crystallization speed, but under acidic conditions, HF will seriously corrode the equipment, and considering HF The toxicity of this method is not suitable for popularization and use; and the all-silicon β molecular sieve prepared by the alkaline fluorine-containing system has the disadvantage of large particles, and the particle size distribution of the crystallization product of this method is not very uniform

[0010] The smaller the particle size of the all-silicon β molecular sieve, the more superior its catalytic performance; but as far as the inventors know, no all-silicon β molecular sieve product with an average particle size of less than 500 nanometers has been developed in the prior art, so it is necessary to develop a cost-effective Method for synthesizing all-silicon beta molecular sieves with small particle size and uniform distribution, low cost, environment-friendly

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