Nanometer total-silicon beta molecular sieve and preparation method thereof

Abstract

The invention discloses a nanometer total-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 template and water so as to obtain a reaction mixture with a mol ratio of alkali and silicon source satisfying the equation OH<->: SiO2 = 0.21-4; (2) transferring the reaction mixture obtained in the step (1) to a pressureproof enclosed container and carrying out ageing at a temperature of 60 to 115 DEG C and a self-generated pressure for 0.05 to 30 d so as to obtain an ageing product; (3) heating the ageing product obtained in the step (2) to 130 to 230 DEG C and then carrying out crystallization self-generated pressure for 0.5 to 30 d so as to obtain a crystallization product, wherein crystallization temperature is at least 15 DEG C higher than ageing temperature; and (4) recovering the crystallization product obtained in the step (3). The nanometer total-silicon beta molecular sieve obtained in the invention has flake-like morphology and has a length and a width of no more than 490 nm and a thickness of no more than 150 nm; and in <29>Si NMR characterization results, a ratio of Q4 / Q3 is no less than 25 and a specific surface area S<BET> is greater than 430 m<2> / g.

Description

technical field [0001] The invention relates to a nanometer 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 in 1967, and its appearance is a symbol of high silicon molecular sieve research. β molecular sieve is a stacking fault symbiosis composed of several polymorphs with different structures but closely related, and has a three-dimensional twelve-membered ring channel structure. Among them, the channels in the [100] and [010] directions are straight channels with a diameter of about 0.66×0.67 nanometers; the channels in the [001] direction are formed by the intersection of straight channels in the [100] and [010] directions. The sinusoidal structure has a pore size of about 0.55×0.55 nm. [0003] Because β molecular sieve has a high skeleton silicon aluminum ratio and a special three-dimensional twelve-membered ring channel 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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