CN111977663A - Hierarchical pore structure zeolite molecular sieve and preparation method and application thereof - Google Patents

Abstract

The invention discloses a zeolite molecular sieve with a hierarchical pore structure and a preparation method and application thereof.A zeolite molecular sieve with the hierarchical pore structure is prepared by a one-step method by adding a trace amount of cationic polymer structure directing agent, and compared with the conventional molecular sieve, the zeolite molecular sieve has higher specific surface area and pore volume and rich pore structure, and solves the problems of complicated post-treatment operation or expensive organic template agent in the conventional preparation of the molecular sieve with the hierarchical pore structure; meanwhile, after the active metal component is loaded, the carbon capacity of the catalyst is enhanced, the reaction stability of the molecular sieve is effectively improved, and the catalyst shows good reaction performance when being applied to methane oxygen-free aromatization reaction.

Description

A kind of multi-stage pore structure zeolite molecular sieve and its preparation method and application

technical field

The invention belongs to the technical field of energy chemical catalysts, and particularly relates to a multi-level pore structure zeolite molecular sieve and a preparation method and application thereof.

Background technique

Since the discovery of zeolite molecular sieve, it has been widely used in petrochemical industry due to its rich specific surface area and pore structure. The characteristics of zeolite have also been explored more and more thoroughly. Although some zeolite molecular sieves have been industrialized, there are more stringent requirements for molecular sieves with various experimental reaction conditions. For example, different methods are used to improve catalytic activity. To modify the molecular sieve itself to improve the catalytic stability, researchers have also been exploring new technologies and methods for the synthesis of zeolite molecular sieves, and have prepared various forms of molecular sieves to meet the requirements of reaction conditions.

Hierarchical pore zeolite molecular sieves generally refer to materials with two or more pore sizes, such as micropore-mesoporous, micropore-macropore, micropore-mesoporous-macropore materials, and the like. Microporous molecular sieves (such as HZSM5) have regular pore structure, good hydrothermal stability, suitable acidity and ideal shape-selective catalytic selectivity, but due to their small pore size, it is difficult for macromolecules to enter the pores and the diffusion resistance is large. Therefore, mesopores are introduced into molecular sieves to obtain hierarchically porous molecular sieves. This material has the characteristics of large pore volume and external specific surface area of mesopores and the characteristics of acidic sites of micropores, which can enhance the mass transfer during the reaction process. It can reduce the carbon deposition in the catalytic process, improve the activity and service life of the catalyst, and can be used in the fields of heavy oil cracking, macromolecular catalysis and fine chemicals. With the deepening of the research on the synthesis of multi-stage porous molecular sieves, more and more methods have been gradually confirmed to be able to effectively synthesize multi-stage porous molecular sieves, mainly including hard template method, soft template method, post-processing method, indirect guidance method and combination method. Wait.

In order to prepare molecular sieves with mesoporous and macroporous structures, the existing technical methods are often acid-base treatment, recrystallization and other modifications and secondary synthesis to increase the specific surface area and pore volume of zeolite molecular sieves, but the above processes are often complicated and require repeated steps. The treatment and modification of the molecular sieve destroys the crystallinity and strength of the molecular sieve to a certain extent, which is time-consuming and labor-intensive; and the synthesis of hollow HZSM-5, nano-HZSM-5, and core-shell MCM-22 also requires the addition of expensive soft and hard templates. Pore formation is not only harsh, but also reduces the wear resistance of the catalyst in the fluidized bed.

SUMMARY OF THE INVENTION

The main purpose of the present invention is to provide a zeolite molecular sieve with a multi-level pore structure and a preparation method and application thereof, so as to overcome the existing problems, the zeolite molecular sieve with a multi-level pore structure is prepared by a one-step method of the invention, and active metal is loaded at the same time. After the composition, the carbon-accommodating ability of the catalyst is enhanced, the anti-carbon deposition ability of the molecular sieve is effectively improved, and it exhibits a good reaction performance in the oxygen-free aromatization reaction of methane.

To achieve the above object, the present invention adopts the following technical solutions:

A preparation method of a multi-stage pore structure zeolite molecular sieve, comprising the following steps:

Step 1: Mix deionized water and cationic polymer structure directing agent PDDA and stir at constant temperature;

Step 2: in the mixture obtained in step 1, sodium aluminate and sodium hydroxide are mixed and stirred until the solution is clear;

Step 3: add hexamethyleneimine to the mixture obtained in step 2, then mix and stir;

Step 4: add silica sol to the mixture obtained in step 3, and then stir vigorously;

Step 5: Dynamically crystallize the mixture obtained in Step 4, firstly crystallize at 50°C for 2-6h, and then heat up to 140°C for 5-7d;

Step 6: After the crystallization is completed, the product is washed, centrifuged and dried, and then placed in roasting to obtain Na-MCM-22;

Step 7: Mix Na-MCM-22 with 1 mol/L ammonium nitrate solution in a volume ratio of 1:30, exchange ammonium for several times in a water bath at 80°C, and then calcine to obtain HMCM-22, a zeolite molecular sieve with a hierarchical pore structure;

Among them, the molar ratio between silica sol, sodium aluminate, sodium hydroxide, hexamethyleneimine, deionized water and cationic polymer structure directing agent PDDA is 1:0.033:0.18:0.5:45:(0.0004～0.001 ).

Further, in step 1, constant temperature stirring was performed in a water bath, the stirring temperature was 30° C., and the time was 3 h.

Further, in step 3, hexamethyleneimine was added at a rate of 1 drop per second, followed by mixing and stirring for 30 min.

Further, in step 4, the silica sol was added at a rate of 2 drops per second, and then vigorously stirred for 30 min.

Further, in step 5, the mixture obtained in step 4 is poured into a hydrothermal kettle with a polytetrafluoroethylene substrate, and placed in a rotary oven for dynamic crystallization at a rotation rate of 60 r/min.

Further, in step 6, the calcination temperature is 550° C., and the time is 10h.

Further, in the seventh step, the calcination temperature is 550° C., and the time is 4 h.

A zeolite molecular sieve with a multi-level pore channel structure is prepared by adopting the above-mentioned preparation method of a zeolite molecular sieve with a multi-level pore channel structure.

An application of a zeolite molecular sieve with a hierarchical pore structure on a catalyst for oxygen-free aromatization of methane. Ammonium molybdate tetrahydrate is dissolved in deionized water, and the volume of the deionized water is the saturated water absorption of the zeolite molecular sieve with a hierarchical pore structure. , ultrasonically dispersed for 20 min, and then impregnated with this solution to zeolite molecular sieve with hierarchical pore structure, stirred and mixed evenly, soaked at room temperature for 24 h, dried, and then calcined at 550 ° C for 6 h to obtain methane-free aromatization catalyst Mo-HMCM-22 .

Further, every 1 g of zeolite molecular sieve corresponds to 0.13 g of ammonium molybdate tetrahydrate.

Compared with the prior art, the present invention has the following beneficial technical effects:

The present invention prepares a zeolite molecular sieve with a multi-level pore channel structure by adding a trace amount of cationic polymer structure directing agent in one step. Compared with conventional molecular sieves, the zeolite molecular sieve prepared by the present invention has higher specific surface area and pore channel volume. , the pore structure is rich, which solves the problem of tedious post-processing or expensive organic template when conventionally preparing molecular sieves with hierarchical pore structure; at the same time, after the active metal component is loaded, the carbon-accommodating capacity of the catalyst is enhanced, effectively It improves the anti-carbon deposition ability of molecular sieve and shows good reaction performance in the anaerobic aromatization of methane.

In addition, the preparation process of the present invention is simple, in-situ synthesis is required, no post-processing is required, and it is suitable for mass production. Only a small amount of structure-directing agent is added. The specific surface area and pore volume of the zeolite molecular sieve with multi-level pore channel structure are formed, and the structure-directing agent is added to shorten the synthesis cycle of the catalyst, save time and reduce the production cost. This molecular sieve is used for methane anaerobic aromatization In the reaction, it has strong anti-carbon deposition performance and improves the methane conversion rate at the same time.

Description of drawings

Fig. 1 is the XRD pattern comparison of the multi-stage pore structure molecular sieve obtained in Example 2 and conventional molecular sieve;

Fig. 2 is the SEM image of the zeolite molecular sieve with hierarchical pore structure obtained in Example 2, wherein (a) is a magnification of 7850 times, and (b) is a magnification of 20,000 times;

Fig. 3 is the multistage pore structure molecular sieve that embodiment 2 obtains and conventional molecular sieve N Adsorption-desorption isotherm;

Fig. 4 is the multi-stage pore structure molecular sieve that embodiment 2 obtains and conventional molecular sieve pore size distribution;

Figure 5 is a comparison diagram of the catalytic effect of the oxygen-free aromatization reaction of methane.

Detailed ways

Embodiments of the present invention are described in further detail below:

The invention adopts a hydrothermal synthesis method to prepare a zeolite molecular sieve with a multi-level pore structure, and its composition is mainly silicon and aluminum. Using this molecular sieve as a carrier, a certain amount of metal active components can be loaded by the incipient wetness impregnation method to obtain a finished catalyst for the oxygen-free aromatization of methane.

The preparation method of the hierarchical pore structure zeolite molecular sieve HMCM-22 is as follows:

The molar ratio of the synthesis formula of zeolite molecular sieve is silicon source: aluminum source: alkali source: template agent: water: structure-directing agent: 1: 0.033: 0.18: 0.5: 45: x (x=0.0004-0.001).

Take a clean 100ml beaker, add 47.96ml of deionized water and 1-2.5g of cationic polymer structure directing agent PDDA, and place it in a water bath at 30°C for constant temperature stirring for 3h.

1. Accurately weigh 0.4896g sodium aluminate and 0.2025g sodium hydroxide, pour them into a beaker, mix and stir until the solution is clear.

2. Add 4.5 ml of hexamethyleneimine at a rate of 1 drop per second, mix and stir for 30 min.

3. Add 24.848 g of silica sol at a rate of 2 drops per second and stir vigorously for 30 min.

4. Pour the mixture obtained in the above 3 into a hydrothermal kettle with a polytetrafluoroethylene substrate, and place it in a rotary oven for dynamic crystallization at a rotation rate of 60 r/min.

5. The crystallization is divided into two steps, firstly, 50℃ for 2-6h, and then the temperature is raised to 140℃ for 5-7d.

6. After crystallization, washing, centrifuging and drying, and then calcining at 550°C for 10h in a muffle furnace to obtain Na-MCM-22.

7. Exchange Na-MCM-22 and 1 mol/L ammonium nitrate solution with ammonium in a water bath at 80°C for 3 times at a volume ratio of 1:30, and then calcinate at 550°C for 4 hours to obtain HMCM-22 with multi-level pores.

Active metal component loading:

The active component Mo is loaded by incipient wetness impregnation. The specific method is as follows: take a certain amount of ammonium molybdate tetrahydrate and dissolve it in an appropriate amount of deionized water. The solution was impregnated with the carrier molecular sieve, stirred and mixed evenly, impregnated at room temperature for 24 hours, dried, and calcined in a muffle furnace at 550°C for 6 hours to obtain the finished catalyst Mo-HMCM-22.

Catalyst reaction effect evaluation:

A continuous-flow fixed-bed reactor was used to evaluate the effect of methane-free aromatization catalyst. The reactor was a U-shaped quartz tube with an inner diameter of 8 mm; the catalyst loading was 0.5 g, and the feed gas was the feed space velocity of 4800 ml/g· h, the reaction temperature is 1073K, normal pressure; before the reaction at 1073K temperature, the catalyst is pre-activated at 923K for a certain period of time.

Below in conjunction with embodiment, the present invention is described in further detail:

Comparative ratio

Take a clean 100ml beaker. Accurately weigh 0.4896g of sodium aluminate and 0.2025g of sodium hydroxide, dissolve in 47.96ml of deionized water, add 4.5ml of hexamethyleneimine at a rate of 1 drop per second, mix and stir for 30min. Add 24.848g of silica sol at a rate of 2 drops per second, stir vigorously for 30min. Pour the above mixture into a hydrothermal kettle with a polytetrafluoroethylene substrate, place it in a rotary oven, and dynamically crystallize at 150°C at a rotation rate of 60r/min. After crystallization, washing, centrifuging, drying, and then calcining at 550 ° C for 10 h in a muffle furnace to obtain Na-MCM-22. Na-MCM-22 and 1 mol/L ammonium nitrate solution were 1:30 The ratio of ammonium was exchanged three times with ammonium in a water bath at 80 °C, and then calcined at 550 °C for 4 h to obtain HMCM-22.

Example 1

Take a clean 100ml beaker, add 47.96ml of deionized water and 1g PDDA, and place it in a water bath at 30°C for constant temperature stirring for 3h. Accurately weigh 0.4896g of sodium aluminate and 0.2025g of sodium hydroxide, pour them into a beaker, mix and stir until the solution is clear. Add 4.5 ml of hexamethyleneimine at a rate of 1 drop per second, and mix and stir for 30 min. 24.848 g of silica sol was added at a rate of 2 drops per second, and vigorously stirred for 30 min. The above mixture was poured into a hydrothermal kettle with a polytetrafluoroethylene substrate, and placed in a rotary oven for dynamic crystallization at a rotational speed of 60 r/min. First, it was crystallized at 50°C for 2h, and then heated to 140°C for 5d. After the crystallization, washing, centrifuging and drying, and then calcining at 550 ° C for 10 h in a muffle furnace to obtain Na-MCM-22. Na-MCM-22 and 1 mol/L ammonium nitrate solution were mixed with 80 in a ratio of 1:30. The ammonium was exchanged 3 times in a water bath at ℃, and then calcined at 550 ℃ for 4 h to obtain HMCM-22 with multi-level pores.

Example 2

Take a clean 100ml beaker, add 47.96ml deionized water and 1.5g PDDA, and place it in a water bath at 30°C for constant temperature stirring for 3h. Accurately weigh 0.4896g of sodium aluminate and 0.2025g of sodium hydroxide, pour them into a beaker, mix and stir until the solution is clear. Add 4.5 ml of hexamethyleneimine at a rate of 1 drop per second, and mix and stir for 30 min. 24.848 g of silica sol was added at a rate of 2 drops per second, and vigorously stirred for 30 min. The above mixture was poured into a hydrothermal kettle with a polytetrafluoroethylene substrate, and placed in a rotary oven for dynamic crystallization at a rotational speed of 60 r/min. The crystallization was carried out step by step. First, 50 °C was crystallized for 4 hours, and then the temperature was raised to 140 °C for 5 d. After the crystallization, washing, centrifugal drying, and then calcining at 550 °C for 10 hours in a muffle furnace were performed to obtain Na-MCM-22. Na-MCM-22 and 1 mol/L ammonium nitrate solution were exchanged three times with ammonium in a water bath at 80 °C in a ratio of 1:30, and then calcined at 550 °C for 4 h to obtain multi-level pore HMCM-22.

Example 3

Take a clean 100ml beaker, add 47.96ml of deionized water and 2.5g of PDDA, and place it in a water bath at 30°C for constant temperature stirring for 3h. Accurately weigh 0.4896g of sodium aluminate and 0.2025g of sodium hydroxide, pour them into a beaker, mix and stir until the solution is clear. Add 4.5 ml of hexamethyleneimine at a rate of 1 drop per second, and mix and stir for 30 min. 24.848 g of silica sol was added at a rate of 2 drops per second, and vigorously stirred for 30 min. The above mixture was poured into a hydrothermal kettle with a polytetrafluoroethylene substrate, and placed in a rotary oven for dynamic crystallization at a rotational speed of 60 r/min. The crystallization was carried out step by step. First, 50 °C was crystallized for 6 h, and then the temperature was raised to 140 °C for 5 d. After the crystallization, washing, centrifugal drying, and then calcining at 550 °C for 10 h in a muffle furnace were performed to obtain Na-MCM-22. Na-MCM-22 and 1 mol/L ammonium nitrate solution were exchanged three times with ammonium in a water bath at 80 °C in a ratio of 1:30, and then calcined at 550 °C for 4 h to obtain multi-level pore HMCM-22.

Example 4

Take a clean 100ml beaker, add 47.96ml of deionized water and 1g PDDA, and place it in a water bath at 30°C for constant temperature stirring for 3h. Accurately weigh 0.4896g of sodium aluminate and 0.2025g of sodium hydroxide, pour them into a beaker, mix and stir until the solution is clear. Add 4.5 ml of hexamethyleneimine at a rate of 1 drop per second, and mix and stir for 30 min. 24.848 g of silica sol was added at a rate of 2 drops per second, and vigorously stirred for 30 min. The above mixture was poured into a hydrothermal kettle with a polytetrafluoroethylene substrate, and placed in a rotary oven for dynamic crystallization at a rotational speed of 60 r/min. The crystallization was carried out step by step, firstly, 50°C for 4h, then the temperature was raised to 140°C for 6d crystallization, after the crystallization, washing, centrifugation, drying, and then calcining at 550°C for 10h in a muffle furnace to obtain Na-MCM-22. Na-MCM-22 and 1 mol/L ammonium nitrate solution were exchanged three times with ammonium in a water bath at 80 °C in a ratio of 1:30, and then calcined at 550 °C for 4 h to obtain multi-level pore HMCM-22.

Example 5

Take a clean 100ml beaker, add 47.96ml deionized water and 1.5g PDDA, and place it in a water bath at 30°C for constant temperature stirring for 3h. Accurately weigh 0.4896g of sodium aluminate and 0.2025g of sodium hydroxide, pour them into a beaker, mix and stir until the solution is clear. Add 4.5 ml of hexamethyleneimine at a rate of 1 drop per second, and mix and stir for 30 min. 24.848 g of silica sol was added at a rate of 2 drops per second, and vigorously stirred for 30 min. The above mixture was poured into a hydrothermal kettle with a polytetrafluoroethylene substrate, and placed in a rotary oven for dynamic crystallization at a rotational speed of 60 r/min. The crystallization was carried out step by step, firstly, 50°C for 6h, and then the temperature was raised to 140°C for 6d. After the crystallization, washing, centrifugation, drying, and then calcining at 550°C for 10h in a muffle furnace were performed to obtain Na-MCM-22. Na-MCM-22 and 1 mol/L ammonium nitrate solution were exchanged three times with ammonium in a water bath at 80 °C in a ratio of 1:30, and then calcined at 550 °C for 4 h to obtain multi-level pore HMCM-22.

Example 6

Take a clean 100ml beaker, add 47.96ml of deionized water and 2.5g of PDDA, and place it in a water bath at 30°C for constant temperature stirring for 3h. Accurately weigh 0.4896g of sodium aluminate and 0.2025g of sodium hydroxide, pour them into a beaker, mix and stir until the solution is clear. Add 4.5 ml of hexamethyleneimine at a rate of 1 drop per second, and mix and stir for 30 min. 24.848 g of silica sol was added at a rate of 2 drops per second, and vigorously stirred for 30 min. The above mixture was poured into a hydrothermal kettle with a polytetrafluoroethylene substrate, and placed in a rotary oven for dynamic crystallization at a rotational speed of 60 r/min. The crystallization was carried out step by step. First, 50 °C was crystallized for 2 hours, and then the temperature was raised to 140 °C for 6 d. After the crystallization, washed, centrifuged and dried, and then placed in a muffle furnace at 550 °C for 10 hours to obtain Na-MCM-22. Na-MCM-22 and 1 mol/L ammonium nitrate solution were exchanged three times with ammonium in a water bath at 80 °C in a ratio of 1:30, and then calcined at 550 °C for 4 h to obtain multi-level pore HMCM-22.

Example 7

Take a clean 100ml beaker, add 47.96ml of deionized water and 1g PDDA, and place it in a water bath at 30°C for constant temperature stirring for 3h. Accurately weigh 0.4896g of sodium aluminate and 0.2025g of sodium hydroxide, pour them into a beaker, mix and stir until the solution is clear. Add 4.5 ml of hexamethyleneimine at a rate of 1 drop per second, and mix and stir for 30 min. 24.848 g of silica sol was added at a rate of 2 drops per second, and vigorously stirred for 30 min. The above mixture was poured into a hydrothermal kettle with a polytetrafluoroethylene substrate, and placed in a rotary oven for dynamic crystallization at a rotational speed of 60 r/min. The crystallization was carried out step by step, firstly, 50°C for 6h, then the temperature was raised to 140°C for 7d. After the crystallization, washing, centrifugation, drying, and then calcining at 550°C for 10h in a muffle furnace were performed to obtain Na-MCM-22. Na-MCM-22 and 1 mol/L ammonium nitrate solution were exchanged three times with ammonium in a water bath at 80 °C in a ratio of 1:30, and then calcined at 550 °C for 4 h to obtain multi-level pore HMCM-22.

Example 8

Take a clean 100ml beaker, add 47.96ml deionized water and 1.5g PDDA, and place it in a water bath at 30°C for constant temperature stirring for 3h. Accurately weigh 0.4896g of sodium aluminate and 0.2025g of sodium hydroxide, pour them into a beaker, mix and stir until the solution is clear. Add 4.5 ml of hexamethyleneimine at a rate of 1 drop per second, and mix and stir for 30 min. 24.848 g of silica sol was added at a rate of 2 drops per second, and vigorously stirred for 30 min. The above mixture was poured into a hydrothermal kettle with a polytetrafluoroethylene substrate, and placed in a rotary oven for dynamic crystallization at a rotational speed of 60 r/min. The crystallization was carried out step by step, firstly, 50℃ for 2h, then the temperature was raised to 140℃ for 7d, after the crystallization, washing, centrifugal drying, and then calcining at 550℃ for 10h in a muffle furnace to obtain Na-MCM-22. Na-MCM-22 and 1 mol/L ammonium nitrate solution were exchanged three times with ammonium in a water bath at 80 °C in a ratio of 1:30, and then calcined at 550 °C for 4 h to obtain multi-level pore HMCM-22.

Active metal Mo component loading

The molecular sieves synthesized above are all impregnated with the initial wetness to load the active component Mo. The specific method is as follows: 0.26g of ammonium molybdate tetrahydrate is dissolved in 2.8ml of deionized water, and ultrasonically dispersed for 20min, and then the above-mentioned carrier molecular sieve is impregnated with this solution and stirred. Mixed uniformly, soaked at room temperature for 24 hours, dried, and calcined in a muffle furnace at 550 °C for 6 hours to obtain the finished catalyst Mo-HMCM-22.

Referring to Figure 1, it can be seen from the XRD pattern of the zeolite molecular sieve prepared in Example 2 that, compared with the standard pattern of HMCM-22 (JCPDS: 48-0075), the synthesized HMCM-22-P is at 2θ=7.09°, 14.32°, Characteristic diffraction peaks appear at 22.67° and 25.96°, and no impurity peaks appear. It indicated that a relatively pure phase of HMCM-22 was obtained. However, comparing the conventional HMCM-22 and the multi-stage hole HMCM-22-P of the present invention, it is not difficult to find that the characteristic diffraction peaks corresponding to HMCM-22-P at 2θ=5°-30° are more complex and stronger, which means that The molecular sieve synthesized by the invention has abundant pore structure and multi-level pore structure; stronger peak intensity indicates better crystallinity.

Referring to Figure 2, the zeolite molecular sieve obtained in Example 2 can be seen from the scanning electron microscope image that the molecular sieve with multi-level pore structure is spherical in appearance, with a typical sheet-like structure on the surface, and has a large specific surface area.

Table 1 shows the specific surface area and pore structure distribution results of the molecular sieves with multi-stage pore structure and conventional molecular sieves.

Table 1 Specific surface area and pore structure distribution of molecular sieves with hierarchical pore structure and conventional molecular sieves

From the N isothermal adsorption and desorption results (Fig. ₃ , Fig. 4, Table 1), it can be seen that the molecular sieve prepared in Example 2 of the present invention has abundant pore volume, and the total pore volume is 0.692 cc/g compared to the conventional molecular sieve. The pore volume increased to 1.204cc/g, and the pore volume increased by 74%. With reference to Figure 4, the macromolecular sieve prepared by the present invention produced a large number of mesopores and mesopores with a diameter greater than 2nm, indicating that a micro-meso-mesopore was successfully prepared. Molecular sieves with intersecting multi-stage pore structure. Due to its unique pore structure, it is more suitable for applications in the fields of heavy oil cracking and macromolecular catalysis.

Fig. 5 is the comparison diagram of the catalytic effect of the multi-stage porous molecular sieve HMCM-22-P of the present invention and the conventional molecular sieve HMCM-22 in the oxygen-free aromatization reaction of methane. Aromatic yield plot. It can be seen intuitively that the HMCM-22-P of the present invention can effectively increase the catalytic performance in the reaction, especially in the selectivity of aromatic hydrocarbons. 30%-40% increase. This is because the hierarchical porous molecular sieve contains more mesopores, which is more conducive to the diffusion of aromatic products in the catalyst pores. When the reaction is carried out for 60 minutes, the yield of HMCM-22-P aromatics of the present invention is 4869 nmol/(g·s), which is 122% higher than that of HMCM-22, which is 2195 nmol/(g·s).

Claims (10)

1. A preparation method of a zeolite molecular sieve with a hierarchical pore structure is characterized by comprising the following steps:

the method comprises the following steps: mixing deionized water and a cationic polymer structure directing agent PDDA, and stirring at constant temperature;

step two: mixing and stirring sodium aluminate and sodium hydroxide in the mixture obtained in the step one until the solution is clear;

step three: adding hexamethyleneimine into the mixture obtained in the step two, and then mixing and stirring;

step four: adding silica sol into the mixture obtained in the third step, and then stirring vigorously;

step five: performing dynamic crystallization on the mixture obtained in the step four, firstly crystallizing at 50 ℃ for 2-6h, and then heating to 140 ℃ for crystallization for 5-7 d;

step six: after crystallization is finished, washing, centrifuging and drying the product, and then roasting to obtain Na-MCM-22;

step seven: Na-MCM-22 and 1mol/L ammonium nitrate solution are mixed according to the proportion of 1: 30, ammonium exchange for a plurality of times in water bath at 80 ℃, and then roasting to obtain the zeolite molecular sieve HMCM-22 with the hierarchical pore structure;

wherein, the mol ratio of the silica sol, the sodium aluminate, the sodium hydroxide, the hexamethyleneimine, the deionized water and the cationic polymer structure directing agent PDDA is 1: 0.033: 0.18: 0.5: 45: (0.0004 to 0.001).

2. The method for preparing the zeolite molecular sieve with the hierarchical pore structure according to claim 1, wherein in the first step, the mixture is stirred in a water bath at a constant temperature, wherein the stirring temperature is 30 ℃ and the stirring time is 3 hours.

3. The method of claim 1, wherein hexamethyleneimine is added in step three at a rate of 1 drop per second, and the mixture is stirred for 30min.

4. The method of claim 1, wherein the silica sol is added at a rate of 2 drops per second in step four, and the mixture is vigorously stirred for 30min.

5. The method for preparing the zeolite molecular sieve with hierarchical pore structure as claimed in claim 1, wherein the mixture obtained in step five is poured into a hydrothermal kettle with a polytetrafluoroethylene substrate, and is placed in a rotary oven for dynamic crystallization at a rotation speed of 60 r/min.

6. The method for preparing the zeolite molecular sieve with the hierarchical pore structure as recited in claim 1, wherein the calcination temperature in the sixth step is 550 ℃ and the calcination time is 10 hours.

7. The method for preparing the zeolite molecular sieve with hierarchical pore structure according to claim 1, wherein the calcination temperature in step seven is 550 ℃ and the calcination time is 4 hours.

8. A hierarchical zeolite molecular sieve, characterized in that it is prepared by the method of any one of claims 1 to 7.

9. The application of the zeolite molecular sieve with the hierarchical pore structure in the methane oxygen-free aromatization catalyst is characterized in that ammonium molybdate tetrahydrate is dissolved in deionized water, the volume of the deionized water is the saturated water absorption capacity of the zeolite molecular sieve with the hierarchical pore structure, the deionized water is subjected to ultrasonic dispersion for 20min, then the zeolite molecular sieve with the hierarchical pore structure is soaked in the solution, the mixture is stirred and mixed uniformly, the soaked mixture is dried after being soaked for 24h at room temperature, and then the mixture is roasted for 6h at 550 ℃, so that the methane oxygen-free aromatization catalyst Mo-HMCM-22 is obtained.

10. The use of a hierarchical pore structure zeolite molecular sieve in an oxygen-free methane aromatization catalyst as claimed in claim 9 wherein every 1g of zeolite molecular sieve corresponds to 0.13g of ammonium molybdate tetrahydrate.

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