A molecular sieve and its preparation method and application

Abstract

The present invention discloses a molecular sieve and a preparation method and application thereof, and relates to the technical field of molecular sieve synthesis, in order to solve the problem that the diffusion path of the SSZ-39 molecular sieve with a larger grain size is larger when it reacts as a denitration catalyst in an SCR reactor, it is easy to produce carbon deposition and deactivation, and the catalytic activity is reduced. The molecular sieve is a sheet-like SSZ-39 molecular sieve, including: a gel is made from a silicon source, an aluminum source, an alkali source, an organic template agent and a quaternary ammonium salt inducer as raw materials, and the molar ratio of the quaternary ammonium salt inducer to the silicon source satisfies: (0.0001-1): 1; the gel is crystallized into a sheet-like SSZ-39 molecular sieve, and the quaternary ammonium salt inducer is used to induce the crystal nucleus of the SSZ-39 molecular sieve to grow along a two-dimensional direction. The molecular sieve and application are used to improve the catalytic activity of the molecular sieve in the denitration reaction.

Description

Technical Field

[0001] The present invention relates to the technical field of molecular sieve synthesis, and in particular to a molecular sieve and a preparation method and application thereof. Background Art

[0002] SSZ-39 molecular sieve is a molecular sieve with AEI topological structure, which is specifically characterized by: AlO4 and SiO4 tetrahedrons are connected end to end through oxygen atoms to form a double six-membered ring secondary structure unit (SBU), the two adjacent layers of double six-membered rings are rotated 180° around the z-axis and arranged in a cross distribution, and the double six-membered rings are connected and arranged through four-membered rings to form an aei cage (asymmetric pear-shaped cage) with an eight-membered ring structure and a three-dimensional pore structure, and the pore size is Due to the characteristics of SSZ-39 molecular sieve, such as orderly pore structure, high specific surface area, good hydrothermal stability, more surface proton acidic centers and excellent cation exchangeability, it has shown excellent performance in industrial catalytic processes such as selective catalytic reduction reaction (NH3-SCR) and methanol to olefins reaction (MTO) in recent years.

[0003] At present, SSZ-39 molecular sieves are often synthesized by hydrothermal synthesis, but the SSZ-39 molecular sieves synthesized by this method often have a larger grain size of 1-3 microns. Therefore, when the SSZ-39 molecular sieve is used as a denitrification catalyst in an SCR reactor, a larger diffusion path and easy carbon deposition and deactivation will occur, resulting in a decrease in catalytic activity. Summary of the invention

[0004] The object of the present invention is to provide a method for preparing a molecular sieve to improve the catalytic activity of the SSZ-39 molecular sieve.

[0005] In order to achieve the above object, the present invention provides the following technical solutions:

[0006] The gel is prepared by using silicon source, aluminum source, alkali source, organic template and quaternary ammonium salt inducer as raw materials, wherein the molar ratio of the quaternary ammonium salt inducer to the silicon source satisfies: (0.0001-1):1, preferably (0.001-0.5):1, for example: 0.005:1, 0.01:1, 0.1:1, 0.2:1, etc.;

[0007] The gel is crystallized into a sheet-like SSZ-39 molecular sieve, and the quaternary ammonium salt inducer is used to induce the crystal nucleus of the SSZ-39 molecular sieve to grow along a two-dimensional direction.

[0008] Compared with the prior art, the SSZ-39 molecular sieve provided by the present invention is by introducing a quaternary ammonium salt inducing agent into the synthesis system of the SSZ-39 molecular sieve, the quaternary ammonium salt can form a micellar structure, these micellar structures interact with silicon-aluminum species, affect its nucleation and crystal growth, thereby inducing the crystal morphology in the induction crystallization process, inducing it to form a lamellar crystal nucleus, and making it grow in a two-dimensional direction, thereby reducing its thickness under the premise of not affecting the length of the SSZ-39 molecular sieve, and preparing a lamellar SSZ-39 molecular sieve. Relative to the SSZ-39 molecular sieve with a larger grain size of 1-3 microns in the prior art, the lamellar SSZ-39 molecular sieve is extremely beneficial to the catalytic reaction, if there is a macromolecular reactant to participate in the reaction, the catalytic reaction mainly occurs at the orifice, the lamellar molecular sieve has a larger specific surface area, can expose more acidic sites, and therefore has a good catalytic activity, and can greatly reduce the generation of by-products and the deactivation of the catalyst.

[0009] In addition, due to the small content of the added quaternary ammonium salt inducer, the catalytic activity of the SSZ-39 molecular sieve is significantly improved at a lower cost, so that it can better adapt to the denitration catalyst coating structure and is suitable for denitration reaction under airflow conditions. Therefore, when the SSZ-39 molecular sieve with good catalytic activity is used as a denitration catalyst in the experiment, the progress and direction of the reaction can be better controlled, so that the reaction can achieve the expected effect.

[0010] In a second aspect, the present invention further provides a molecular sieve prepared by the method for preparing a molecular sieve according to the technical solution of the present invention, wherein the thickness of the molecular sieve is 0.1 μm to 3 μm.

[0011] In a third aspect, the present invention further provides an application of a molecular sieve in a denitration reaction, comprising:

[0012] At 150°C to 350°C, the conversion rate of nitrogen oxides produced in the denitration reaction is 65% to 98%.

[0013] Compared with the prior art, the beneficial effects of the preparation method and application of a molecular sieve provided by the present invention are the same as the beneficial effects of the preparation method of a molecular sieve in the first aspect, and are not described in detail here. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0015] Figure 1 The preparation flow chart of the molecular sieve provided in this embodiment is shown;

[0016] Figure 2 The preparation flow chart of the gel prepared in this embodiment is shown;

[0017] Figure 3 The X-ray diffraction diagrams of Examples 1 to 3 of the present invention and Comparative Example 1 are shown;

[0018] Figure 4 The scanning electron microscope image of the molecular sieve in the first embodiment is shown;

[0019] Figure 5 The scanning electron microscope image of the molecular sieve in the second embodiment is shown;

[0020] Figure 6 The scanning electron microscope image of the molecular sieve in the third embodiment is shown;

[0021] Figure 7 The scanning electron microscope image of the molecular sieve in Comparative Example 1 is shown. DETAILED DESCRIPTION

[0022] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0023] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "multiple" is two or more, unless otherwise clearly and specifically defined. The meaning of "several" is one or more, unless otherwise clearly and specifically defined.

[0024] At present, SSZ-39 molecular sieves are often synthesized by hydrothermal synthesis, but the SSZ-39 molecular sieves synthesized by this method often have a larger grain size of 1-3 microns. Therefore, when the SSZ-39 molecular sieve is used as a denitrification catalyst in an SCR reactor, a larger diffusion path and easy carbon deposition and deactivation will occur, resulting in a decrease in catalytic activity.

[0025] In view of the above problems, the present invention provides a method for preparing a molecular sieve, which can improve the catalytic activity of the SSZ-39 molecular sieve. Figure 1 The preparation flow chart of the molecular sieve provided in this embodiment is shown. Figure 1 As shown, the preparation method of the molecular sieve comprises:

[0026] Step 101: Prepare gel using silicon source, aluminum source, alkali source, organic template and quaternary ammonium salt inducer as raw materials.

[0027] Exemplary, the quaternary ammonium salt inducer used in the embodiment of the present invention is at least one of dodecyl dimethyl benzyl ammonium bromide, dodecyl dimethyl ethyl phenoxy ethyl ammonium bromide, bis (dodecyl dimethyl) ethylene diammonium bromide, lignin quaternary ammonium salt, cocamide quaternary ammonium salt, and hexadecyl dimethyl benzyl ammonium bromide. Due to the longer carbon chain of the above-mentioned quaternary ammonium salt inducer, after it forms a micellar structure, these micellar structures will interact better with silicon aluminum species, which is more conducive to affecting its nucleation and crystal growth. The molar ratio of the quaternary ammonium salt inducer to the silicon source satisfies: (0.0001-1): 1, preferably (0.001-0.5): 1, for example: 0.005: 1, 0.01: 1, 0.1: 1, 0.2: 1, etc.

[0028] The above-mentioned specific type and ratio of quaternary ammonium salt inducers are introduced into the synthesis system of SSZ-39 molecular sieve, which can induce the crystal morphology in the induced crystallization process, induce it to form a lamellar crystal nucleus, and make it grow in two dimensions, thereby reducing its thickness without affecting the length of the SSZ-39 molecular sieve, thereby preparing a lamellar SSZ-39 molecular sieve. In addition, since the content of the added quaternary ammonium salt inducer is small, the catalytic activity of the SSZ-39 molecular sieve is significantly improved at a relatively low cost.

[0029] Step 102: crystallizing the gel into a sheet-like SSZ-39 molecular sieve, wherein the quaternary ammonium salt inducer is used to induce the crystal nuclei of the SSZ-39 molecular sieve to grow in two-dimensional directions.

[0030] In an alternative approach, Figure 2 FIG. 2 shows a flow chart of the preparation of gel provided in this embodiment. Figure 2 As shown, the gel is prepared using silicon source, aluminum source, alkali source, organic template and quaternary ammonium salt inducer as raw materials, including:

[0031] Step 201: A silicon source, an aluminum source, an alkali source, an organic template and water are mixed and aged for the first time to prepare a semi-finished gel product.

[0032] Exemplarily, the silicon source used in the embodiment of the present invention is at least one of silicon dioxide, silica sol, silicate, orthosilicate, water glass, silicon powder, kaolin and bentonite. When silica sol and silicate are selected as the silicon source, the effect is better. The aluminum source used in the embodiment of the present invention is at least one of FAU type molecular sieve, USY type molecular sieve, MFI type molecular sieve, Beta type molecular sieve, sodium aluminate, aluminum hydroxide, pseudo-boehmite, aluminum isopropoxide, aluminum sol, and boehmite. The alkali source used in the embodiment of the present invention is at least one of sodium hydroxide, potassium hydroxide, calcium hydroxide, barium hydroxide, and strontium hydroxide. When sodium hydroxide is selected as the alkali source, the effect is better. The organic template used in the embodiment of the present invention is a piperidine derivative template, specifically including: N, N-diethyl-2,6-dimethylpiperidinium ion, 3,5-dimethyl-N, N-dimethylpiperidinium ion, N, N-diethyl-2-ethylpiperidinium ion, N-ethyl-N-propyl-2,6-dimethylpiperidinium ion, N-methyl-N-ethyl-2,6-dimethylpiperidinium ion, N-methyl-N-ethyl-2-ethylpiperidinium ion, 2,5-dimethyl-N, N-diethylpyrrole ion, 2,6-dimethyl-N, N-dimethylpiperidinium ion, 2-ethyl-N, N-dimethylpiperidinium ion, 2,2,6,6-tetramethyl-N-methyl-N-ethylpiperidinium ion, at least one of the salts and / or bases of 2,2,6,6-tetramethyl-N, N-dimethylpiperidinium ion. Such templates have a moderate molecular size and can play a structural guiding and filling role in the synthesis process of SSZ-39 molecular sieves. In addition, such templates are charged in aqueous solution and play a charge filling role in the synthesis process of molecular sieves. In addition, in order to more easily obtain the molecular sieve of the present invention, the water used in the raw material is deionized water, which can avoid unexpected ionic impurities in the mixing process, ensuring the good molecular sieve crystal form in the subsequent crystallization process and the smooth progress of the subsequent steps. When 3,5-dimethyl-N,N-dimethylpiperidinium ion is selected as an organic template, the effect is better.

[0033] Exemplarily, in the embodiment of the present invention, a silicon source, an aluminum source, an alkali source, an organic template and water are added in a certain ratio, stirred evenly, and then the reaction mixture is subjected to a first mixing and aging to prepare a semi-finished gel product. The molar ratio of the aluminum source, the alkali source, the organic template, the quaternary ammonium salt inducer, water and the silicon source satisfies:

[0034] n(Al2O3):n(OH-):n(R):n(quaternary ammonium salt inducer):n(H2O):n(SiO2)=(0.005-0.2):(0~2):(0~0.50):(0.0001~1):(2~80):1. It is worth noting that OH- represents an alkali source and R represents an organic template. Within this range, the silicon source and the aluminum source can be connected together by oxygen bonds in the silicon source and the aluminum source after the crystallization reaction, and there is basically no free aluminum source, which helps to achieve the expected effect of the molecular sieve. It has been proved by experiments that when the molecular sieve prepared by the preparation method provided in the embodiment of the present invention is used as a denitration catalyst in a denitration reaction, the conversion rate of nitrogen oxides is high. Especially when n(Al2O3):n(OH-):n(R):n(quaternary ammonium salt inducer):n(H2O):n(SiO2)=(0.033-0.2):(0~0.5):(0~0.2):(0.0001~1):(5~40):1, the catalytic activity of the flaky SSZ-39 molecular sieve prepared in the embodiment of the present invention is better.

[0035] For example, the first aging time is 0.1 h to 100 h, and the first aging temperature is 25° C. to 100° C. Within this temperature and time range, it can be ensured that the unreacted materials are fully reacted and the skeleton structure of the porous material is further stabilized through slight reconstruction.

[0036] Step 202: The quaternary ammonium salt inducer and the semi-finished gel product are mixed and aged for a second time to prepare a gel.

[0037] Exemplarily, introducing a quaternary ammonium salt inducer into the synthesis system of SSZ-39 molecular sieve can induce the crystal morphology during the induced crystallization process, inducing it to form a lamellar crystal nucleus and causing it to grow in two dimensions, thereby reducing the thickness of the SSZ-39 molecular sieve in subsequent preparation steps and preparing a lamellar SSZ-39 molecular sieve.

[0038] Exemplarily, the second aging time is 1 h to 2 h, and the second aging temperature is 50° C. to 70° C. The quaternary ammonium salt inducer and the semi-finished gel product are mixed and aged for the second time, so that the quaternary ammonium salt inducer and the semi-finished gel product react fully, thereby ensuring that the crystal morphology of the prepared SSZ-39 molecular sieve is flaky, and the thickness of the prepared product is relatively uniform, thereby ensuring that the quality of the obtained product is stable when the flaky SSZ-39 molecular sieve is prepared on a large scale.

[0039] In an optional manner, the gel is crystallized into a sheet-like SSZ-39 molecular sieve, comprising:

[0040] After the gel is stirred, crystallization is performed by heating.

[0041] For example, the gel is placed in an autoclave at room temperature and crushed and mixed, which has a positive effect on the nucleation and crystal growth. The stirring time is 0-20 hours, and when the stirring time is 0.5 hours to 20 hours, the stirring effect is the best and the mixing is more uniform.

[0042] Exemplary, the gel in the embodiment of the present invention is crystallized at 120 ℃ ~ 210 ℃ for 38h ~ 150h. In this process, the quaternary ammonium salt inducing agent induces the formation of flaky nuclei and simultaneously causes the crystal to grow in two dimensions. If the crystallization time exceeds this time length, the production efficiency will be relatively low, and unexpected effects cannot be achieved. Secondly, if the crystallization time in the reactor is less than 38h, the crystal morphology will not be completely changed, so that the flaky SSZ-39 molecular sieve cannot be prepared, thereby affecting the catalytic activity of the molecular sieve. After the crystallization is completed, the temperature is lowered to below 40 ℃, filtered, washed, the solid sample is dried, and the flaky SSZ-39 molecular sieve can be obtained by roasting. Compared with the zeolite of conventional size, the specific surface area of ​​the flaky SSZ-39 zeolite has changed significantly, and its external specific surface area has increased significantly, and the thinner crystal grains can reduce the diffusion restrictions of reactants and products, and its larger specific surface area can provide good dispersibility for the raw materials, thereby avoiding excessive reaction of the raw materials.

[0043] A molecular sieve provided in an embodiment of the present invention is prepared by the method for preparing a molecular sieve provided in an embodiment of the present invention. Compared with zeolites of conventional sizes, the molecular sieve has thinner crystals, larger specific surface area, and better catalytic activity.

[0044] According to an application of a molecular sieve in a denitration reaction provided by an embodiment of the present invention, the conversion rate of nitrogen oxides generated in the denitration reaction is 65% to 98% at 150° C. to 350° C.

[0045] In order to verify the effect of the molecular sieve provided by the embodiment of the present invention, the embodiment of the present invention is demonstrated by comparing the embodiment with the comparative example.

[0046] Embodiment 1

[0047] The first step is to prepare the gel: 20.88g of sodium hydroxide is dissolved in 328g of pure water, 200g of silica sol with a SiO2 content of 40wt%, 220g of an aqueous solution of 3,5-dimethyl-N,N-dimethylpiperidine hydroxide with a concentration of 25wt%, and 35.46g of USY molecular sieves are fully mixed, and the first aging is carried out at 25°C for 1h to make a gel semi-finished product; then 6.8g of octadecyltrimethylammonium bromide and the gel semi-finished product are mixed and aged for a second time at 50°C for 1h to make a gel. Among them, the molar ratio of USY molecular sieve, sodium hydroxide, 3,5-dimethyl-N,N-dimethylpiperidine hydroxide, octadecyltrimethylammonium bromide, pure water and silica sol contained in the gel satisfies:

[0048] n(Al2O3):n(OH-):n(R):n(octadecyltrimethylammonium bromide):n(H2O):n(SiO2)=0.022:0.5:0.2:0.01:20:1.

[0049] The second step is to prepare the SSZ-39 molecular sieve in sheet form: the gel is placed in an autoclave, stirred at 25°C for 5 hours, and then heated to 180°C for crystallization for 50 hours. After the crystallization, the temperature is lowered to below 40°C, the obtained product is filtered, washed, dried, and calcined at 550°C for 4 hours to obtain the SSZ-39 molecular sieve in sheet form.

[0050] Figure 3 The X-ray diffraction diagrams of the first to third embodiments of the present invention and the comparative example 1 are shown. From top to bottom, they are the X-ray diffraction diagram of the comparative example 1, the X-ray diffraction diagram of the third embodiment, the X-ray diffraction diagram of the second embodiment and the X-ray diffraction diagram of the first embodiment. Figure 3 As shown, the molecular sieve prepared in Example 1 of the present invention is SSZ-39 molecular sieve. Figure 4 FIG. 2 shows a scanning electron microscope image of the molecular sieve in Example 1. Figure 4 As shown, the SSZ-39 molecular sieve prepared in Example 1 of the present invention has a length of about 2.5 μm-3.9 μm and a thickness of about 0.5 μm-0.8 μm.

[0051] Embodiment 2

[0052] The first step is to prepare the gel: 29.50g of sodium hydroxide is dissolved in 318g of pure water, 200g of silica sol with a SiO2 content of 40wt%, 215g of an aqueous solution of 3,5-dimethyl-N,N-dimethylpiperidine hydroxide with a concentration of 25wt%, and 31.01g of USY molecular sieves are fully mixed, and the gel semi-finished product is aged for the first time at 25°C for 2h; then 6.7g of hexadecyl dimethyl benzyl ammonium chloride and the gel semi-finished product are mixed and aged for the second time at 50°C for 1.5h to prepare the gel. Among them, the molar ratio of USY molecular sieve, sodium hydroxide, 3,5-dimethyl-N,N-dimethylpiperidine hydroxide, hexadecyl dimethyl benzyl ammonium chloride, pure water and silica sol contained in the gel satisfies:

[0053] n(Al2O3):n(OH-):n(R):n(hexadecyldimethylbenzylammonium chloride):n(H2O):n(SiO2)=0.02:0.63:0.2:0.01:20:1.

[0054] The second step is to prepare the SSZ-39 molecular sieve in sheet form: the gel is placed in an autoclave, stirred at 50°C for 0.5h, and then heated to 160°C for crystallization for 60h. After the crystallization, the temperature is lowered to below 40°C, the obtained product is filtered, washed, dried, and calcined at 550°C for 4h to obtain the SSZ-39 molecular sieve in sheet form.

[0055] Figure 3 The X-ray diffraction diagrams of the embodiments 1 to 3 and the comparative example 1 of the present invention are shown. Figure 3 As shown, the molecular sieve prepared in Example 2 of the present invention is SSZ-39 molecular sieve.

[0056] Figure 5 FIG. 2 shows a scanning electron microscope image of the molecular sieve in Example 2. Figure 5 As shown, the SSZ-39 molecular sieve prepared in Example 2 of the present invention has a length of about 2.5 μm-3.9 μm and a thickness of about 0.5 μm-1.0 μm.

[0057] Embodiment 3

[0058] The first step is to prepare the gel: 20.30g of sodium hydroxide is dissolved in 316g of pure water, 200g of silica sol with a SiO2 content of 40wt%, 215g of 3,5-dimethyl-N,N-dimethylpiperidine hydroxyl and 31.01g of USY molecular sieve, and the mixture is fully mixed, and the mixture is aged for the first time at 25°C for 2h to prepare a semi-finished gel product; then 2.9g of cocamidopropyl betaine and the semi-finished gel product are mixed and aged for the second time at 50°C for 1.5h to prepare a gel. The molar ratio of USY molecular sieve, sodium hydroxide, 3,5-dimethyl-N,N-dimethylpiperidine hydroxyl, cocamidopropyl betaine, pure water and silica sol contained in the gel satisfies:

[0059] n(Al2O3):n(OH-):n(R):n(cocamidopropyl betaine):n(H2O):n(SiO2)=0.02:0.5:0.2:0.005:20:1.

[0060] The second step is to prepare the SSZ-39 molecular sieve in sheet form: the gel is placed in an autoclave, stirred at 50°C for 0.5h, and then heated to 170°C for crystallization for 40h. After the crystallization, the temperature is lowered to below 40°C, the obtained product is filtered, washed, dried, and calcined at 550°C for 4h to obtain the SSZ-39 molecular sieve in sheet form.

[0061] Figure 3 The X-ray diffraction diagrams of the embodiments 1 to 3 of the present invention and the comparative example 1 are shown. Figure 3 As shown, the molecular sieve prepared in Example 3 of the present invention is SSZ-39 molecular sieve.

[0062] Figure 6 The scanning electron microscope image of the molecular sieve in this embodiment 3 is shown. Figure 6 As shown, the SSZ-39 molecular sieve prepared in Example 3 of the present invention has a length of about 2.5 μm-3.5 μm and a thickness of about 0.5 μm-0.9 μm.

[0063] Comparative Example 1

[0064] The first step is to prepare the gel: 20.88g of sodium hydroxide is dissolved in 328g of pure water, 200g of silica sol with a SiO2 content of 40wt%, 220g of 3,5-dimethyl-N,N-dimethylpiperidine with a concentration of 25wt% and 35.46g of USY molecular sieve are mixed thoroughly.

[0065] The gel was aged at 25°C for 1 hour. The molar ratio of USY molecular sieve, sodium hydroxide, 0 3,5-dimethyl-N,N-dimethylpiperidine hydroxide, pure water and silica sol in the gel satisfies:

[0066] n(Al2O3):n(OH-):n(R):n(H2O):n(SiO2)=0.022:0.5:0.2:20:1.

[0067] The second step is to prepare the molecular sieve: the gel is placed in an autoclave, stirred at 25°C for 0.5h, and then heated to 160°C for crystallization for 50h. After the crystallization, the temperature is lowered to below 40°C, the obtained product is filtered, washed, dried, and calcined at 550°C for 4h to obtain the SSZ-39 molecular sieve.

[0068] 5 Figure 3 The X-ray diffraction diagrams of the embodiments 1 to 3 of the present invention and the comparative example 1 are shown. Figure 3 As shown,

[0069] The molecular sieve prepared in Comparative Example 1 of the present invention is SSZ-39 molecular sieve.

[0070] Figure 7 The scanning electron microscope image of the molecular sieve in Comparative Example 1 is shown. Figure 7 As shown, the SSZ-39 molecular sieve prepared in Comparative Example 1 of the present invention has a length of about 3.5 μm-4.5 μm and a thickness of about 1 μm-2 μm.

[0071] In order to test the effects of the molecular sieves provided in the embodiments of the present invention and the comparative examples, the present invention provides an NH3-SCR reaction performance test of the SSZ-39 molecular sieve samples prepared in Examples 1 to 03 and Comparative Example 1.

[0072] Specific testing methods include:

[0073] The first step is molecular sieve ammonium exchange: the SSZ-39 molecular sieves prepared in Examples 1 to 3 and the SSZ-39 molecular sieve prepared in Comparative Example 1 are mixed in a mass ratio of ammonium nitrate: molecular sieve: water = 1:1:10, and the pH is adjusted to 8-8.5 with ammonia water.

[0074] The mixture was exchanged at 90°C for 1 hour under stirring, filtered, washed, dried, and calcined at 550°C for 4 hours. The above process was repeated 3 times until the Na2O content in the 5 molecular sieve was less than 0.1%.

[0075] The second step is molecular sieve copper loading: dissolve copper acetate equivalent to 5% molecular sieve CuO loading in 50 times water, add ammonium-exchanged molecular sieve under stirring, adjust pH to 8-8.5 with ammonia water, filter, wash, dry, and calcine at 550°C for 4 hours.

[0076] The third step is performance testing: the Cu-SSZ-39 composite molecular sieve prepared in Examples 1 to 3 and Comparative Example 1 after ammonium exchange and Cu loading is pressed into tablets, crushed, sieved, and hydrothermally aged at 650°C in a 10% H2O+90% nitrogen atmosphere for 100h. Then, 0.5g of a 40-60 mesh sample is taken for NH3-SCR reaction, wherein the composition of the reaction mixture is: 1000ppmNO, 1100ppmNH3, 10Vol%O2, 10Vol%H2O, N2 is used as the balance gas, and the volumetric space velocity is 120000h. -1 The reaction temperature is 200℃-600℃, and the NO in the tail gas is detected online using an MKS infrared gas analyzer. x concentration.

[0077] NO x The conversion rate is defined as:

[0078] The conversion rate of nitrogen oxides in the reaction mixture at 150°C-350°C is shown in Table 1.

[0079] Case Conversion rate at 150℃ Conversion rate at 350℃ Conversion rate at 550℃ Embodiment 1 65％ 98％ 96％ Embodiment 2 65％ 97％ 95％ Embodiment 3 66％ 96％ 95％ Comparative Example 1 52％ 95％ 93％

[0080] As can be seen from the above table, from the data in Table 1, it can be seen that the Cu-SSZ-39 molecular sieves prepared in Examples 1 to 3 of the present invention have better catalytic activity in the temperature range of 150 to 550°C than conventional SSZ-39 molecular sieves, which further illustrates that the flaky SSZ-39 synthesized by the molecular sieve preparation method provided by the present invention has good catalytic activity in the denitrification reaction.

[0081] The above is only a specific embodiment of the present invention. Obviously, various modifications and combinations can be made without departing from the spirit and scope of the present invention. Accordingly, this specification and the drawings are only exemplary illustrations of the present invention as defined by the attached claims, and are deemed to have covered any and all modifications, changes, combinations or equivalents within the scope of the present invention. Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is intended to include these changes and variations. Any technician familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be based on the scope of protection of the claims.

Claims

1. A method for preparing a molecular sieve, characterized in that: The molecular sieve is a sheet-like SSZ-39 molecular sieve, comprising: The silicon source, the aluminum source, the alkali source, the organic template and water are mixed and aged for the first time to prepare a semi-finished gel product; The quaternary ammonium salt inducer and the semi-finished gel product are mixed and aged for the second time to prepare the gel, wherein the molar ratio of the quaternary ammonium salt inducer to the silicon source satisfies: (0.0001-1):1; the alkali source is at least one of sodium hydroxide, potassium hydroxide, calcium hydroxide, barium hydroxide, and strontium hydroxide; the quaternary ammonium salt inducer is at least one of dodecyl dimethyl benzyl ammonium bromide, dodecyl dimethyl ethyl phenoxy ethyl ammonium bromide, bis (dodecyl dimethyl) ethylene diammonium bromide, lignin quaternary ammonium salt, cocamide quaternary ammonium salt, and hexadecyl dimethyl benzyl ammonium bromide; The gel is crystallized into a sheet-like SSZ-39 molecular sieve, and the quaternary ammonium salt inducer is used to induce the crystal nucleus of the SSZ-39 molecular sieve to grow along a two-dimensional direction.

2. The method for preparing a molecular sieve according to claim 1, characterized in that: The molar ratio of the aluminum source, alkali source, organic template, quaternary ammonium salt inducing agent and silicon source satisfies: n(Al2O3):n(OH - ):n(R):n(quaternary ammonium salt inducer):n(SiO2)=(0.005-0.2):(0~2): (0～0.50):(0.0001～1):1； The gel contains water, and the molar ratio of water to silicon source satisfies: n(H2O):n(SiO2)=(2-80):

1.

3. The method for preparing a molecular sieve according to claim 1, characterized in that: The time of the first mixed aging is 0.1h to 100h, and the temperature of the first mixed aging is 25°C to 100°C; the time of the second mixed aging is 1h to 2h, and the temperature of the second mixed aging is 50°C to 70°C.

4. The method for preparing a molecular sieve according to claim 1, characterized in that: The process of crystallizing the gel into a sheet-like SSZ-39 molecular sieve comprises: After the gel is stirred, a crystallization operation is performed by heating.

5. The method for preparing a molecular sieve according to claim 4, characterized in that: The temperature of the crystallization operation is 120° C. to 210° C., the time of the crystallization operation is 38 h to 150 h, and the stirring time is 0 to 10 h.

6. A molecular sieve prepared by the method for preparing a molecular sieve according to any one of claims 1 to 5, characterized in that: The thickness of the molecular sieve is 0.1 μm to 3 μm.

7. Use of a molecular sieve prepared by the method for preparing a molecular sieve according to any one of claims 1 to 6 in a denitration reaction.

8. The use according to claim 7, characterized in that: At 150°C to 350°C, the conversion rate of nitrogen oxides produced in the denitration reaction is 65% to 98%.

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