A method of constructing hierarchical pores in a molecular sieve

Abstract

The application discloses a method for constructing multistage pores in a molecular sieve, and comprises the following steps: providing an NH4F organic solution, wherein the NH4F organic solution is composed of NH4F and an organic solvent; adding the molecular sieve into the NH4F organic solution, stirring at a low temperature for a first preset time, then increasing the temperature and stirring for a second preset time; and cleaning and drying the stirred molecular sieve to obtain a molecular sieve with multistage pores. Different from an existing NH4F water solution etching method, the application adopts the NH4F organic solution to etch the molecular sieve, realizes the construction of mesopores in the molecular sieve, and the mesopore size distribution is uniform and the mesopore size is adjustable.

Description

Technical Field

[0001] This invention relates to the field of inorganic material catalysis technology, and in particular to a method for constructing hierarchical pores in molecular sieves. Background Technology

[0002] Molecular sieves are highly efficient catalysts and adsorbents, widely used in petrochemicals, biomass conversion, fine chemicals, food, and pharmaceuticals. Molecular sieves typically contain pores and cages of molecular size (less than 2 nm). These nano / subnanopore spaces provide a confined environment for active sites (such as Brønsted acid sites), influencing the stability of reaction intermediates and the shape selectivity of reactants or products, thereby modulating the activity and selectivity of the molecular sieve. However, in reactions such as cracking, oxidation, alkylation, esterification, and isomerization, the microporous structure of molecular sieves often restricts the diffusion of reactant and product molecules. Furthermore, the microporous structure makes it difficult for larger reactant molecules to access acid sites, thus reducing the utilization rate of active sites. The problems of molecular diffusion and active site accessibility are particularly pronounced in small-pore molecular sieves, which are generally defined as molecular sieves with a maximum pore size of an eight-membered ring. Of 255 different molecular sieve topologies, 51 are classified as small-pore molecular sieves, with the most representative structural codes being CHA, AEI, AFX, ERI, and RHO. These molecular sieves are effective in the selective catalytic reduction of NO. x With its commercial applications in catalytic reactions such as NH3-SCR and methanol-to-olefins (MTO), it has attracted increasing attention.

[0003] However, the narrow eight-eight ... This not only restricts the contact of reactants or intermediate molecules with active sites, but also greatly hinders the diffusion ability of molecules in the channels, leading to rapid deactivation of the molecular sieve. To solve this problem, it is often necessary to introduce mesoporous structures to prepare hierarchical porous molecular sieves, that is, to have both microporous (0.5-2 nm) and mesoporous (2-50 nm) structures.

[0004] Over the past few decades, various strategies have been developed to synthesize hierarchical porous molecular sieves. These strategies can be broadly categorized into post-modification and in-situ synthesis routes. Post-modification methods include high-temperature steam treatment, acid or alkali rinsing, and NH4F etching. Compared to in-situ synthesis, post-modification methods do not require expensive organic templates and are easier to scale up industrially, making them one of the best choices for synthesizing hierarchical porous molecular sieves. However, using conventional high-temperature steam to create mesopores often results in the deposition of a large number of non-framework aluminum species on the outer surface of the molecular sieve grains, leading to blockage of the molecular sieve channels. Moreover, alkali etching for mesopore creation is generally only suitable for molecular sieves with a silicon-to-aluminum ratio between 20 and 50, which often leads to severe damage to the crystal structure. For example, alkali etching of the small-pore molecular sieve CHA with an octagonal window introduces a small amount of mesoporous structure (mesoporous specific surface area is less than <20 m²). 2 g -1 However, its crystal structure was severely damaged (Catalysis Science & Technology, 2017, 7, 3851–3862).

[0005] In recent years, the pore-forming method based on NH4F aqueous solution has attracted widespread attention (Chemistry of Materials, 2013, 25, 2759-2766). The difluoride ions (HF2+) generated by the double hydrolysis of NH4F... - This method can non-selectively remove framework silicon and aluminum atoms, making it suitable for constructing mesoporous structures in various types of molecular sieves. Patent (US10647585B2) discloses a method for introducing mesoporous structures into molecular sieves (such as MFI-type molecular sieves with ten-membered ring channels and FAU-type molecular sieves with twelve-membered rings) based on NH4F aqueous solution. However, the etching pore-forming process based on NH4F aqueous solution is severely limited by the active etchant species (HF2). - The diffusion of HF2 species from the outside to the inside of the molecular sieve grains leads to uneven etching and extremely poor controllability, resulting in an uncontrollable mesopore size distribution with a very wide range, typically from 10 nm to 100 nm. Furthermore, due to the diffusion of HF2 species from the outside to the inside of the molecular sieve grains... - Large clusters formed with water have difficulty diffusing into the interior of small-pore molecular sieves with eight-membered ring channels. This means that the NH4F aqueous solution method can only etch the surface and cannot effectively introduce mesoporous structures into these molecular sieves (Chemistry A European Journal 2022, 28, e202104339). Currently, there is no effective post-modification method to introduce mesoporous structures into small-pore molecular sieves and uniformly control their pore size.

[0006] Therefore, existing technologies still need to be improved and developed. Summary of the Invention

[0007] In view of the shortcomings of the prior art, the purpose of this invention is to provide a method for constructing multi-level pores in molecular sieves, which aims to solve the problem that existing post-modification methods have failed to effectively introduce mesoporous structures into small-pore molecular sieves and uniformly control their pore size.

[0008] The technical solution of the present invention is as follows:

[0009] A method for constructing hierarchical pores in a molecular sieve, comprising the following steps:

[0010] An NH4F organic solution is provided, wherein the NH4F organic solution is composed of NH4F and an organic solvent;

[0011] Molecular sieves are added to the NH4F organic solution, and the mixture is stirred at a low temperature for a first preset time, and then the temperature is increased and stirred for a second preset time.

[0012] The molecular sieve after stirring is washed and dried to obtain a molecular sieve with multi-level pores.

[0013] Optionally, the concentration of NH4F in the NH4F organic solution is 0.5–30 wt%.

[0014] Optionally, the organic solvent includes one or more of methanol, ethanol, ethylene glycol, acetone, ethyl acetate, and dimethyl sulfoxide.

[0015] Optionally, the water content in the pores of the molecular sieve is 0–40 mmol / g.

[0016] Optionally, the low temperature range is -50 to 25°C, and the temperature rise is 25 to 200°C.

[0017] Optionally, the first preset time is 1 to 12 hours, and the second preset time is 1 to 48 hours.

[0018] Optionally, the drying temperature is 60–120°C.

[0019] Optionally, the hierarchical pores include micropores and mesopores, wherein the size of the mesopores is from 2±1 nm to 50±5 nm.

[0020] Optionally, the hierarchical pores include micropores and mesopores, wherein the specific surface area of ​​the mesopores is 200–690 m². 2 / g.

[0021] Optionally, the molecular sieve is a small-pore molecular sieve, a medium-pore molecular sieve, or a macroporous molecular sieve.

[0022] Beneficial Effects: Unlike existing NH4F aqueous etching methods, this invention uses an organic NH4F solution to etch molecular sieves, achieving the construction of mesopores within the molecular sieve. These mesopores have a uniform pore size distribution and adjustable size. The construction of the mesoporous structure significantly improves the stability and lifetime of the small-pore molecular sieve in the methanol-to-olefins reaction. This construction method is of great significance for improving the diffusion of organic macromolecules within the molecular sieve channels and for enhancing catalytic performance through the directional design of the mesoporous structure. Furthermore, this construction method is low-cost, simple, and universally applicable, facilitating the large-scale industrial preparation of hierarchical porous molecular sieves. Attached Figure Description

[0023] Figure 1 This is a process flow diagram of constructing a hierarchical pore structure in a small-pore molecular sieve according to Example 1;

[0024] Figure 2 The images show the XRD patterns of SSZ-13 molecular sieves before and after etching in Examples 1 and 2.

[0025] Figure 3 These are scanning electron microscope images of SSZ-13 molecular sieves before and after etching in Examples 1 and 2.

[0026] Figure 4 Argon adsorption-desorption curves and pore size distribution curves of SSZ-13 molecular sieve before and after etching in Examples 1 and 2;

[0027] Figure 5 This is a performance evaluation diagram of SSZ-13 molecular sieve before and after etching in the methanol-to-olefins reaction in Example 1;

[0028] Figure 6 The nitrogen adsorption-desorption curves and mesopore size distribution curves at different etching temperatures in Examples 1, 3 and 4 are shown.

[0029] Figure 7 The argon adsorption-desorption curves and pore size distribution curves at different etching concentrations are shown in Examples 5 and 6.

[0030] Figure 8 The image shows the mesopore size distribution curves of the ZSM-5 molecular sieve before and after etching in Example 7.

[0031] Figure 9 The mesopore size distribution curves of the Y molecular sieve before and after etching in Example 8;

[0032] Figure 10 The image shows the mesopore size distribution curves of the Beta molecular sieve before and after etching in Example 9. Detailed Implementation

[0033] This invention provides a method for constructing hierarchical pores in small-pore molecular sieves. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0034] In recent years, the pore-forming method based on NH4F aqueous solution has attracted widespread attention. The difluoride ions (HF2) generated by the double hydrolysis of NH4F... - This method can non-selectively remove framework silicon and aluminum atoms, making it suitable for constructing mesoporous structures in various types of molecular sieves. However, the etching process based on NH4F aqueous solution is severely limited by the active etchant species (HF2). - The diffusion of HF2- etched species from the outside to the inside of the molecular sieve grains leads to uneven etching and extremely poor controllability, resulting in an uncontrollable mesopore size distribution with a very wide range, typically from 10 nm to 100 nm. Furthermore, due to the diffusion of HF2- etched species from the outside to the inside of the molecular sieve grains, the etching process becomes uneven and extremely difficult to control, leading to an uncontrollable mesopore size distribution. - Large clusters formed with water have difficulty diffusing into the interior of small-pore molecular sieves with eight-membered ring channels. This means that the NH4F aqueous solution method can only etch the surface and cannot effectively introduce mesoporous structures into these molecular sieves. Therefore, there is currently no effective post-modification method that can introduce mesoporous structures into small-pore molecular sieves and uniformly control their pore size.

[0035] Based on this, embodiments of the present invention provide a method for constructing hierarchical pores in a small-pore molecular sieve, comprising the following steps:

[0036] S1: Provide an NH4F organic solution, wherein the NH4F organic solution is composed of NH4F and an organic solvent;

[0037] S2: Add the molecular sieve to the NH4F organic solution, stir at a low temperature for a first preset time, and then raise the temperature and stir for a second preset time.

[0038] S3: The molecular sieve after stirring is washed and dried to obtain a molecular sieve with multi-level pores (also referred to as a multi-level porous molecular sieve in this article).

[0039] This embodiment provides a method for constructing uniform and controllable hierarchical pores in molecular sieves. Specifically, it is a method for preparing hierarchical porous molecular sieves applicable to catalytic cracking, hydrocracking, pollution control, and fine chemical industries. Unlike existing NH4F aqueous etching methods, this embodiment uses an organic NH4F solution to etch the molecular sieve, achieving the construction of mesopores within the molecular sieve. The mesopore size distribution is uniform, and the mesopore size is adjustable. The construction of the mesoporous structure significantly improves the stability and lifetime of the small-pore molecular sieve in the methanol-to-olefins reaction. This construction method is significant for improving the diffusion of organic macromolecules within the molecular sieve channels and for enhancing catalytic performance through the directional design of the mesoporous structure. Furthermore, this construction method is low-cost, simple, and universally applicable, facilitating large-scale industrial preparation of hierarchical porous molecular sieves.

[0040] This embodiment can construct mesopores with uniform size distribution and adjustable pore size in molecular sieves with different topologies while retaining the intrinsic microporous structure. The adjustable pore size range is from 2±1nm to 50±5nm.

[0041] This embodiment can control the content and pore size distribution of mesopores by adjusting the water content, NH4F concentration, and etching temperature in the molecular sieve.

[0042] Compared to small-pore molecular sieves without hierarchical pores, the construction of hierarchical pores significantly extends the service life of molecular sieves by 1 to 20 times.

[0043] In step S1, in some embodiments, the concentration of NH4F in the NH4F organic solution is 0.5–30 wt%.

[0044] In some embodiments, the organic solvent includes one or more of methanol, ethanol, ethylene glycol, acetone, ethyl acetate, and dimethyl sulfoxide.

[0045] In step S2, in some embodiments, the water content in the pores of the molecular sieve is 0–40 mmol / g. To control the water content in the molecular sieve pores, it needs to be dehydrated under high temperature and vacuum, and then exposed to a certain amount of water vapor for adsorption. By controlling the adsorption time and the amount of water vapor, the molecular weight of water in the molecular sieve pores is controlled to be 0–40 mmol / g.

[0046] In some embodiments, the low-temperature range is -50 to 25°C, and the temperature is raised to 25 to 200°C. That is, etching is performed at 25 to 200°C. Preferably, the temperature is raised to 30 to 70°C.

[0047] First, stir the mixture evenly at a low temperature (-50 to 25°C), then heat it to 25 to 200°C and stir and etch for several hours. In some embodiments, the first preset time is 1 to 12 hours, such as 1 hour, 2 hours, or 4 hours, and the second preset time is 1 to 48 hours, such as 6 hours, 12 hours, or 24 hours.

[0048] In some embodiments, step S3 specifically involves: using deionized water as a cleaning agent to clean the molecular sieve after stirring, and then drying the cleaned molecular sieve to obtain a molecular sieve with multi-level pores.

[0049] In some embodiments, the drying temperature is 60–120°C.

[0050] In some embodiments, the molecular sieve is a small-pore molecular sieve (with pores smaller than eight-membered rings), a mesopore molecular sieve, or a macropore molecular sieve. That is, the method of this embodiment is not only applicable to molecular sieves with small pore sizes (including eight-membered rings), such as CHA, AEI, AFX, ERI, and RHO, but also to molecular sieves with medium pore sizes (including ten-membered rings), such as MFI type molecular sieves, and is also suitable for molecular sieves with large pore sizes (including twelve-membered rings), such as FAU type molecular sieves.

[0051] Compared with the prior art, this embodiment has the following advantages:

[0052] It can maintain the integrity of the molecular sieve crystal structure after etching, keep the grain size distribution unchanged, and prevent the grain surface from being severely etched.

[0053] It can construct mesopores while retaining the intrinsic micropores of molecular sieves;

[0054] It can construct mesoporous structures in small-pore molecular sieves (with eight-membered ring channels) and can control the mesoporous content and mesoporous size distribution, with mesoporous size ranging from 2±1 nm to 50±5 nm;

[0055] The specific surface area and pore volume of the adjustable mesoporous material range from 18 to 420 m². 2 / g and 0.02~0.31cm 3 / g;

[0056] Suitable for small-pore molecular sieves with various topologies, such as CHA, AEI, AFX, ERI and RHO, as well as medium-pore molecular sieves (containing ten-membered rings) (such as MFI molecular sieves) and large-pore molecular sieves (containing twelve-membered rings) (such as FAU and BEA molecular sieves).

[0057] The construction of mesopores in small-pore molecular sieves significantly extends the service life of molecular sieves in catalytic reactions such as methanol-to-olefins reaction by 1 to 20 times.

[0058] The raw materials used are inexpensive and the synthesis process is simple.

[0059] The present invention will be further described below through specific embodiments.

[0060] Example 1

[0061] A method for constructing hierarchical pores in molecular sieves, such as Figure 1 As shown, it includes the following steps:

[0062] In a 20 ml polytetrafluoroethylene (PTFE) reactor, a 3.5 wt% NH4F organic solution (methanol as the organic solvent) was added, followed by 0.5 g of SSZ-13 molecular sieve. The mixture was stirred at room temperature (25°C) for 1 hour. The PTFE reactor was then transferred to a 50°C oil bath and stirred for 12 hours (i.e., etching). The molecular sieve, after 12 hours of stirring, was washed three times with deionized water and dried at 90°C to obtain a multi-level porous molecular sieve (i.e., the product).

[0063] XRD tests were performed on the molecular sieve before and after etching. The results showed that the crystal structure of the molecular sieve remained unchanged, still exhibiting the CHA topology. Figure 2 As shown in the figure; SEM analysis of the molecular sieve before and after etching showed that the grain size and morphology remained unchanged before and after etching. Figure 3 As shown; the argon (Ar) adsorption-desorption curve and pore size distribution curve are as follows. Figure 4 As shown, the presence of hysteresis loops in the argon adsorption-desorption curves indicates the formation of mesoporous structures after etching, with uniform mesopore size distribution, concentrated in the range of 7±2 nm; the mesopore specific surface area and mesopore volume are as high as 107 m². 2 / g and 0.12cm 3 / g, see Table 1 below. This embodiment successfully introduced a large number of mesoporous structures with uniform size distribution into the small-pore SSZ-13 molecular sieve.

[0064] This example demonstrates the performance evaluation of SSZ-13 molecular sieves before and after etching in the methanol-to-olefins reaction:

[0065] Experimental procedure: Before and after etching, the SSZ-13 molecular sieve sample was activated by heating to 500°C at a rate of 2°C per minute and maintaining the temperature for 2 hours, then cooled to the reaction temperature of 350°C, and subjected to a WHSV of 0.8h. -1 Under the test conditions, the methanol conversion rate and olefin (ethylene and propylene) selectivity of SSZ-13 molecular sieve before and after etching were compared.

[0066] Test results: such as Figure 5 It can be seen that, compared with the SSZ-13 molecular sieve before etching, the multi-level porous SSZ-13 molecular sieve obtained in Example 1 can double its service life (conversion rate of more than 50%) while maintaining the olefin selectivity of up to 70%.

[0067] Table 1

[0068]

[0069]

[0070] Example 2

[0071] A method for constructing hierarchical pores in a molecular sieve is described in this embodiment. The method is basically the same as that in Example 1, except that the organic solvent methanol is replaced with water.

[0072] XRD tests were performed on the molecular sieve before and after etching. The results showed that the crystal structure of the molecular sieve was not destroyed before and after etching. Figure 2 As shown in the figure; SEM tests were performed on the molecular sieve before and after etching. After etching with NH4F aqueous solution, the surface of the molecular sieve crystals became rough, indicating that the grain surface was severely etched. The results are as follows. Figure 3 As shown; the argon (Ar) adsorption-desorption curve and pore size distribution curve are as follows. Figure 4 As shown, the presence of a hysteresis loop in the argon adsorption-desorption curve indicates the existence of mesopores. However, the pore size distribution curve reveals an extremely wide pore size distribution, ranging from 10 nm to 125 nm, including large mesopores and macropores (over 50 nm). Moreover, the specific surface area of ​​the introduced mesopores is only 69 m². 2 / g, see Table 1.

[0073] Example 3

[0074] A method for constructing hierarchical pores in molecular sieves is described in this embodiment. The method is basically the same as that in embodiment 1, except that the oil bath temperature (i.e., etching temperature) is changed from 50°C to 25°C.

[0075] As shown in Table 1, the mesopore specific surface area and mesopore volume of this embodiment are only 35m³. 2 / g and 0.04cm 3 / g indicates that a small number of mesoporous structures can be constructed under these conditions.

[0076] Example 4

[0077] A method for constructing hierarchical pores in molecular sieves is described in this embodiment. The method is basically the same as that in embodiment 1, except that the oil bath temperature (i.e., etching temperature) is changed from 50°C to 80°C.

[0078] like Figure 6 As shown, the appearance of a hysteresis loop in the nitrogen (N2) adsorption-desorption curve indicates the introduction of mesoporous structures. Figure 6The pore size distribution diagram shows that the mesopore size distribution range is relatively wide (10-50 nm). Table 1 shows that the microporous structure of the samples etched at this temperature is severely damaged, decreasing from 0.22 cm... 3 / g reduced to 0.02cm 3 / g. The above phenomena indicate that although this etching temperature is conducive to the introduction of mesopores, the intrinsic microporous structure is greatly damaged.

[0079] Example 5

[0080] A method for constructing hierarchical pores in molecular sieves is described in this embodiment. The method is basically the same as that in Example 1, except that the concentration of NH4F is changed from 3.5 wt% to 0.5 wt%.

[0081] As shown in Table 1, the specific surface area and mesopore volume of the etched molecular sieve samples were 54 m². 2 / g and 0.06cm 3 / g indicates that a small number of mesoporous structures can be constructed under the conditions of this embodiment.

[0082] Example 6

[0083] A method for constructing hierarchical pores in molecular sieves is described in this embodiment. The method is basically the same as that in Example 1, except that the concentration of NH4F is changed from 3.5 wt% to 1.7 wt%.

[0084] like Figure 7 As shown, the appearance of a hysteresis loop in the argon (Ar) adsorption-desorption curve indicates the introduction of mesoporous structures. Figure 7 The pore size distribution curve shows that the pore size is concentrated at 6±2 nm. Table 1 shows that after etching, the specific surface area and volume of the mesopores significantly increased, reaching 86 μm². 2 / g and 0.11cm 3 / g indicates that a large number of mesoporous structures with uniform pore size distribution can be obtained at the concentration of this embodiment.

[0085] Example 7

[0086] A method for constructing hierarchical pores in a molecular sieve. The method in this embodiment is basically the same as that in Embodiment 1, except that the SSZ-13 molecular sieve is replaced with the ZSM-5 molecular sieve.

[0087] like Figure 8 As shown in the figure, the mesopore size distribution curve indicates that the mesopores after etching are mainly concentrated in the range of 2±1 nm; as shown in Table 1, the mesopore volume was effectively increased to 0.17 cm³. 3 / g.

[0088] Example 8

[0089] A method for constructing hierarchical pores in a molecular sieve. The method in this embodiment is basically the same as that in Embodiment 1, except that the SSZ-13 molecular sieve is replaced with a Y molecular sieve.

[0090] like Figure 9 As shown in the figure, the mesopore size distribution curve indicates that the mesopores after etching are mainly concentrated in the range of 2±1 nm; as shown in Table 1, the specific surface area and volume of the mesopores increase significantly, reaching 320 nm. 2 / g and 0.22cm 3 / g.

[0091] Example 9

[0092] A method for constructing hierarchical pores in a molecular sieve. The method in this embodiment is basically the same as that in Embodiment 1, except that the SSZ-13 molecular sieve is replaced with a Beta molecular sieve.

[0093] like Figure 10 As shown in the figure, the mesopore size distribution curve indicates that the mesopores after etching are mainly concentrated in the range of 8±3 nm; as shown in Table 1, the specific surface area and volume of the mesopores were effectively increased to 118 m². 2 / g and 0.31m 3 / g.

[0094] As can be seen from the above, Examples 1 and 2 illustrate that the solvent is a key factor affecting the formation of mesoporous structures by NH4F in molecular sieves. Compared with conventional NH4F aqueous solution etching methods, the NH4F organic solution etching method based on the present invention can introduce mesoporous structures with uniform size distribution into small-pore molecular sieves while retaining the intrinsic microporous structure.

[0095] Examples 1, 3, and 4 illustrate that, based on the pore-forming method of the present invention, temperature is one of the important influencing factors affecting the content of introduced mesopores and their pore size distribution.

[0096] Examples 1, 5, and 6 illustrate that, at the same etching temperature, the content and size distribution of mesopores can be adjusted by changing the NH4F concentration.

[0097] Examples 7-9 illustrate that the method of the present invention is applicable not only to small-pore molecular sieves, but also to mesopore (ten-membered ring) ZSM-5 and macropore (twelve-membered ring) Y and Beta molecular sieves.

[0098] In summary, this invention provides a method for constructing hierarchical pores in molecular sieves. Compared with other methods, this invention can prepare mesopores with uniform size distribution and tunable pore size in molecular sieves with different topologies while retaining the intrinsic microporous structure. The pore size can range from 2±1 nm to 50±5 nm. The construction of the mesoporous structure significantly improves the stability and lifetime of the molecular sieve in the methanol-to-olefins reaction. This method is of great significance for improving the diffusion of organic macromolecules in the molecular sieve channels and for improving catalytic performance through the directional design of the mesoporous structure. In addition, this method has low preparation cost, simple process, and universality, which is conducive to the large-scale industrial preparation of hierarchical porous molecular sieves.

[0099] It should be understood that the application of the present invention is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A method for constructing hierarchical pores in a molecular sieve, characterized in that, Includes the following steps: An NH4F organic solution is provided, wherein the NH4F organic solution is composed of NH4F and an organic solvent; Molecular sieves are added to the NH4F organic solution, and the mixture is stirred at a low temperature for a first preset time, and then the temperature is increased and stirred for a second preset time. The molecular sieve after stirring is washed and dried to obtain a molecular sieve with multi-level pores. The organic solvent includes one or more of methanol, ethanol, ethylene glycol, acetone, ethyl acetate, and dimethyl sulfoxide; The low temperature is 25°C, and the temperature is raised to 30-70°C; The molecular sieve is a small-pore molecular sieve, a medium-pore molecular sieve, or a macroporous molecular sieve. The concentration of NH4F in the NH4F organic solution is 1.7–3.5 wt%.

2. The method for constructing hierarchical pores in a molecular sieve according to claim 1, characterized in that, The water content in the pores of the molecular sieve is 0–40 mmol / g.

3. The method for constructing hierarchical pores in a molecular sieve according to claim 1, characterized in that, The first preset time is 1 to 12 hours, and the second preset time is 1 to 48 hours.

4. The method for constructing hierarchical pores in a molecular sieve according to claim 1, characterized in that, The drying temperature is 60–120°C.

5. The method for constructing hierarchical pores in a molecular sieve according to claim 1, characterized in that, The hierarchical pores include micropores and mesopores, and the size of the mesopores ranges from 2±1 nm to 50±5 nm.

6. The method for constructing hierarchical pores in a molecular sieve according to claim 1, characterized in that, The hierarchical pores include micropores and mesopores, and the specific surface area of ​​the mesopores is 200–690 m². 2 / g.

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