A method for static in-situ synthesis of highly dispersed ZSM-5 nanosheets

Abstract

The present invention discloses a method for static in-situ synthesis of highly dispersed ZSM-5 nanosheets. This method has a simple synthesis process, low cost, and avoids the synthesis process of special templates and the harsh rotational crystallization process. The present invention discloses a method for static in-situ synthesis of highly dispersed ZSM-5 nanosheets. Specifically, tetraethyl silicate, hydrated aluminum sulfate, N,N,N,N-tetramethyl-1,6-hexanediamine, 1-bromohexane, 1-bromodocosane, sulfuric acid, sodium hydroxide and water are used as raw materials. ZSM-5 nanosheet molecular sieves are synthesized by a static in-situ assembly method. It has the advantages of simple synthesis method, low cost and high template utilization efficiency. The synthesized ZSM-5 nanosheet has a thickness of a multi-cell stacking structure and has higher self-support and stability.

Description

Technical Field

[0001] The present invention relates to a method for static in-situ synthesis of highly dispersed ZSM-5 nanosheets. Specifically, the method uses tetraethyl silicate, hydrated aluminum sulfate, N,N,N,N-tetramethyl-1,6-hexanediamine, 1-bromohexane, 1-bromodocosane, sulfuric acid, sodium hydroxide, and water as raw materials to synthesize ZSM-5 nanosheet molecular sieves through a static in-situ assembly method. Background Art

[0002] ZSM-5 molecular sieves, due to their unique pore structure, suitable acidity, and excellent thermal stability, are widely used in adsorption, separation, and catalysis, with industrial catalysis being the most widely used. ZSM-5 nanosheet molecular sieves, due to their large specific surface area, numerous active sites, and short diffusion paths, have great potential for development in catalytic reactions.

[0003] At present, the commonly used methods for synthesizing nanosheet molecular sieves include post-processing exfoliation method, additive-assisted method, seed-directed assisted method and special template method. The post-processing exfoliation method is only applicable to some layered molecular sieves with special structures. The nanosheets synthesized by additive-assisted method and seed-directed assisted method have made great progress. However, there are still some limitations in reducing the thickness of nanosheets. It is difficult to achieve the thickness of the unit cell level. The special template method realizes the synthesis of nanosheets with unit cell thickness. The special template method refers to the design of special organic structure directing agents to guide the generation of molecular sieves with specific structures. Che et al. designed a monoquaternary ammonium salt surfactant C6H5-C6H4-OC 10 H 20 N + (CH3)2-C6H 13 (Br - ) and named C Ph-Ph-10-6 , synthesized MFI nanosheets with a b-axis thickness of about 3 nm. Wu et al. reported that nanosheet MOR molecular sieves can be used in the presence of amphiphilic bifunctional long-chain surfactants C 16 H 33 -N + (CH3)2-C4H8N + The appropriate spatial distance between the two quaternary ammonium cations in the template is designed to guide the formation of nanosheet MOR, while the hydrophobic tail hinders the growth of the zeolite crystals along the b-axis.

[0004] The specialized template method, which allows the synthesis of nanosheets with unit cell-level thicknesses through the design of templates, presents a major limitation: the cumbersome and costly synthesis process. Currently, dynamic crystallization, with its advantages of short crystallization times, high synthetic stability, and excellent reproducibility, is often used in laboratory research to synthesize nanosheet molecular sieves using rotational crystallization. However, industrial production of rotational crystallization presents challenges such as high equipment investment, complex process control, and practical operational difficulties. Therefore, the use of inexpensive templates or template precursors and the development of a simple and feasible synthesis process are key to achieving large-scale industrial production of nanosheet molecular sieves.

[0005] In view of the above research background, this study used cheap and readily available raw materials to prepare nanosheet ZSM-5 molecular sieves through an in situ static assembly method, avoiding the synthesis process of special templates and the harsh rotational crystallization process. The template raw materials were statically assembled in situ during the formation of the molecular sieve, guiding the formation of nanosheet ZSM-5 molecular sieves. Summary of the Invention

[0006] The invention discloses a method for static in-situ synthesis of highly dispersed ZSM-5 nanosheets. The ZSM-5 nanosheets synthesized by this method have a thickness of 3-5 unit cells. The synthesis method is simple and low in cost, and avoids the synthesis process of special templates and the harsh rotational crystallization process.

[0007] The present invention discloses a method for static in-situ synthesis of highly dispersed ZSM-5 nanosheets. Specifically, the method uses tetraethyl silicate, hydrated aluminum sulfate, N,N,N,N-tetramethyl-1,6-hexanediamine, 1-bromohexane, 1-bromodocosane, sulfuric acid, sodium hydroxide, and water as raw materials. The ZSM-5 nanosheet molecular sieve is synthesized via a static in-situ assembly method. This method has the advantages of being simple, low-cost, and highly efficient in utilizing the template. The synthesized ZSM-5 nanosheets have a multi-cell stacked structure, exhibiting enhanced stability.

[0008] The typical synthesis process is (taking Si / Al=150 as an example):

[0009] Accurately weigh sodium hydroxide, N,N,N,N-tetramethyl-1,6-hexanediamine, 1-bromohexane, and 1-bromodocosane, dissolve them in deionized water, and stir at 70°C for 1-2 hours (Solution a). Accurately weigh aluminum sulfate 18hydrate and sulfuric acid, dissolve them in an appropriate amount of deionized water, and stir at room temperature until a homogeneous solution is obtained (Solution b). Solutions a and b are mixed uniformly, and tetraethyl silicate is added dropwise. Stir at a constant temperature for 3 hours to obtain an initial gel. This initial gel undergoes a special aging treatment and is transferred to a polytetrafluoroethylene-lined reactor for crystallization at a constant temperature for a period of time. After crystallization, the reactor is cooled, opened, filtered, washed, and dried in an oven at 100°C overnight to obtain a white powder sample. The resulting product is then placed in a muffle furnace and calcined at a constant temperature to remove the template, thereby obtaining the nanosheet ZSM-5 molecular sieve.

[0010] Compared with the previous preparation method, the present invention has the following advantages:

[0011] 1) The present invention adopts a one-pot synthesis method, which is simple and low-cost;

[0012] 2) The present invention avoids the use of organic solvents in organic synthesis and improves the utilization efficiency of templates;

[0013] 3) The present invention is synthesized under static conditions, avoiding the harsh rotational crystallization process; BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 is the X-ray powder diffraction pattern of the catalyst obtained in Example 1;

[0015] Figure 2 is a scanning electron microscope image of the catalyst obtained in Example 1;

[0016] Figure 3 This is the X-ray powder diffraction pattern of the catalyst obtained in Example 2 with Si / Al = 100, crystallization temperature 150°C, and crystallization time 120h;

[0017] Figure 4 This is a scanning electron microscope image of the catalyst obtained in Example 2 with Si / Al=100, crystallization temperature of 150°C, and crystallization time of 120h;

[0018] Figure 5 This is a transmission electron microscope image of the catalyst obtained in Example 2 with Si / Al = 100, crystallization temperature 150°C, and crystallization time 120h;

[0019] Figure 6 is the X-ray powder diffraction pattern of the catalyst obtained in Example 3;

[0020] Figure 7 is a scanning electron microscope image of the catalyst obtained in Example 3; DETAILED DESCRIPTION

[0021] Example 1: 1.72g of sodium hydroxide, 2.10g of bromodocosane, 1.22g of n-hexane bromide, and 1.53g of tetramethylhexanediamine were accurately weighed and dissolved in 30g of deionized water. Stirring was complete, denoted as solution a. 0.26g of aluminum sulfate 18hydrate was accurately weighed and dissolved in 30g of deionized water, followed by the dropwise addition of 1.26g of concentrated sulfuric acid, denoted as solution b. Solutions a and b were uniformly mixed, and then 12.5g of tetraethyl orthosilicate was slowly added dropwise. The mixture was stirred at a constant temperature for 3 hours to obtain an initial gel. The resulting initial gel was aged at 40°C for 48 hours, then transferred to a polytetrafluoroethylene-lined reactor with a silicon-to-aluminum ratio of 150 and crystallized at 150°C for 120 hours. After the crystallization is completed, the kettle is cooled and opened, filtered and washed, and dried in an oven at 100°C overnight to obtain a white powder sample; the above-obtained product is placed in a muffle furnace, first heated to 300°C at 2°C / min, maintained for 2h, then heated to 500°C at 5°C / min, and calcined for 8h to obtain nanosheet ZSM-5 molecular sieve.

[0022] Example 2: 1.44g of sodium hydroxide, 1.95g of bromodocosane, 0.99g of n-hexane bromide, and 1.03g of tetramethylhexanediamine were accurately weighed and dissolved in 30g of deionized water. Stirring was complete, denoted as solution a. 0.40g of aluminum sulfate 18hydrate was accurately weighed and dissolved in 30g of deionized water, followed by the dropwise addition of 1.06g of concentrated sulfuric acid, denoted as solution b. Solutions a and b were mixed uniformly, and then 12.5g of tetraethyl orthosilicate was slowly added dropwise. The mixture was stirred at a constant temperature for 3 hours to obtain an initial gel. The resulting initial gel was aged at 20°C for 120 hours, then transferred to a polytetrafluoroethylene-lined reactor with a silicon-to-aluminum ratio of 100 and crystallized at 150°C for 120 hours. After the crystallization is completed, the kettle is cooled and opened, filtered and washed, and dried in an oven at 100°C overnight to obtain a white powder sample; the above-obtained product is placed in a muffle furnace, first heated to 350°C at 2°C / min, maintained for 2h, and then heated to 600°C at 5°C / min, and calcined for 6h to obtain nanosheet ZSM-5 molecular sieve.

[0023] Example 3: 2.04g of sodium hydroxide, 2.50g of bromodocosane, 1.54g of n-hexane bromide, and 1.03g of tetramethylhexanediamine were accurately weighed and dissolved in 30g of deionized water. Stirring was complete, marking this as solution a. 0.20g of aluminum sulfate 18hydrate was accurately weighed and dissolved in 30g of deionized water, followed by the dropwise addition of 1.36g of concentrated sulfuric acid, marking this as solution b. Solutions a and b were mixed uniformly, and then 12.5g of tetraethyl orthosilicate was slowly added dropwise. The mixture was stirred at a constant temperature for 3 hours to obtain an initial gel. The resulting initial gel was aged at 60°C for 24 hours, then transferred to a polytetrafluoroethylene-lined reactor with a silicon-to-aluminum ratio of 200 and crystallized at 200°C for 48 hours. After the crystallization is completed, the kettle is cooled and opened, filtered and washed, and dried in an oven at 100°C overnight to obtain a white powder sample; the above-obtained product is placed in a muffle furnace, first heated to 250°C at 2°C / min, maintained for 2h, and then heated to 700°C at 5°C / min, and calcined for 4h to obtain nanosheet ZSM-5 molecular sieve.

Claims

1. A method for static in-situ synthesis of highly dispersed ZSM-5 nanosheets, characterized by: Nanosheet ZSM-5 was synthesized using tetraethyl silicate, aluminum sulfate 18-hydrate, N,N,N,N-tetramethyl-1,6-hexanediamine, 1-bromohexane, 1-bromodocosane, sulfuric acid, sodium hydroxide, and deionized water as raw materials. The specific steps are as follows: (1) Accurately weigh sodium hydroxide, N,N,N,N-tetramethyl-1,6-hexanediamine, 1-bromohexane, and 1-bromodocosane, dissolve them in deionized water, and stir at 70°C for 1-2 hours; (2) Accurately weigh aluminum sulfate 18hydrate and sulfuric acid, dissolve in an appropriate amount of deionized water, and stir at room temperature until a homogeneous solution is obtained; (3) The solutions obtained in steps (1) and (2) above were mixed evenly, tetraethyl silicate was added dropwise, and stirred at a certain temperature for 3 h to obtain an initial gel; (4) The initial gel obtained above is subjected to a special aging treatment, transferred to a polytetrafluoroethylene-lined reactor, and crystallized for a period of time at a certain temperature, wherein the crystallization is static crystallization, and the special aging treatment is static aging at 20-60° C. for 24-120 hours; (5) After the crystallization is completed, the kettle is cooled and opened, filtered and washed, and dried in an oven at 100°C overnight to obtain a white powder sample; (6) The white powder sample obtained in step (5) is placed in a muffle furnace and calcined at a certain temperature to remove the template, thereby obtaining a nanosheet ZSM-5 molecular sieve.

2. The method for static in-situ synthesis of highly dispersed ZSM-5 nanosheets according to claim 1, characterized in that: The concentration of sodium hydroxide in step (1) is 0.8-2.0 mol / L.

3. The method for static in-situ synthesis of highly dispersed ZSM-5 nanosheets according to claim 1, characterized in that: In step (2), the concentration of aluminum sulfate 18hydrate is 0.004-0.02 mol / L, and the ratio of sulfuric acid to aluminum sulfate 18hydrate is 10-90.

4. The method for static in-situ synthesis of highly dispersed ZSM-5 nanosheets according to claim 1, characterized in that: In steps (2) and (3), the silicon-aluminum ratio is adjusted by adjusting the amount of aluminum sulfate and tetraethyl silicate, and the silicon-aluminum ratio range is 50-250.

5. The method for static in-situ synthesis of highly dispersed ZSM-5 nanosheets according to claim 1, characterized in that: The crystallization temperature in step (4) is 120-200° C., and the crystallization time is 48-120 h.

6. The method for static in-situ synthesis of highly dispersed ZSM-5 nanosheets according to claim 1, characterized in that: The calcination step in step (6) is a step-by-step calcination, first heating to 250-400°C at 2°C / min, maintaining for 2h, then heating to 500-700°C at 5°C / min, and calcining for 4-8h.

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