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 crystal size of SZ-3 molecular sieve is large and its catalytic activity in denitration reaction is low. A gel is prepared by using a silicon source, an aluminum source, an alkali source, an organic template and a saccharide compound as raw materials, and the molar ratio of the saccharide compound to the silicon source satisfies: (0.001-0.1): 1, and the saccharide compound is a soluble saccharide compound; the gel is crystallized into an SSZ-39 molecular sieve. The molecular sieve and application are used to reduce the crystal size of the SSZ-39 molecular sieve and improve its catalytic activity 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] Generally speaking, the main active component of SSZ-39 zeolite used as a denitrification catalyst is copper ion. There are certain problems with single copper ion. For example, when the engine is running at high temperature for a long time, the molecular sieve catalyst will often become blocked and deactivated due to its large grain size, resulting in a significant reduction in its denitrification performance, and even structural collapse and deactivation, leading to a reduction in catalytic activity. Summary of the invention

[0004] The object of the present invention is to provide a method for preparing a molecular sieve, so as to reduce the grain size of the SSZ-39 molecular sieve and improve its catalytic activity in the denitration reaction.

[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 sugar compound as raw materials, wherein the molar ratio of the sugar compound to the silicon source satisfies: (0.001-0.1):1; preferably (0.001-0.05):1, for example: 0.0015:1, 0.001:1, 0.003:1, 0.002:1, 0.01:1, 0.1:1, etc.;

[0007] The gel was crystallized into SSZ-39 molecular sieve.

[0008] Compared with the prior art, the SSZ-39 molecular sieve provided by the present invention adds sugar compounds to the synthesis system of the SSZ-39 molecular sieve. The hydroxyl groups in these sugar compounds interact with the silicon-aluminum compounds and form a three-dimensional distribution under the action of the intermolecular forces of the sugar compounds, thereby forming a confined area similar to a grid structure, so that the SSZ-39 molecular sieve crystals are restricted or affected during the crystallization process, thereby reducing the grain size of the SSZ-39 molecular sieve during the molecular sieve crystallization process, and at the same time, a higher relative crystallinity (>90%) and specific surface area (>>740m 2 / g). And because the prepared SSZ-39 molecular sieve has a small grain size, it avoids the phenomenon of molecular sieve grains blocking the pores and causing catalyst deactivation when the engine is running at high temperature for a long time, thereby improving the catalytic activity of SSZ-39 molecular sieve in the denitration reaction. According to experiments, the conversion rate of nitrogen oxides produced in the denitration reaction is as high as 97% at 150℃~350℃.

[0009] Furthermore, the sugar compounds selected in the present invention are not arbitrarily selected, because the hydroxyl groups contained in the sugars usually can only take effect in solution or under fully mixed conditions, especially the effect on the microstructure also needs to occur under conditions of microscopic full contact. Therefore, the hydroxyl groups of the sugars and the silicon-aluminum substances need to interact with each other in a solution or a colloid-like homogeneous system. Therefore, the solubility of the sugars will affect the control of their crystals, and soluble sugars need to be selected to achieve the purpose of effectively controlling the crystal size of the molecular sieve.

[0010] Furthermore, the more sugar added, the better. Too much sugar will cause the hydroxyl group to act too strongly, which will have too great an impact and limit the crystallization process of the molecular sieve, resulting in the inability to obtain a molecular sieve with a SSZ-39 structure or a pure crystalline SSZ-39 molecular sieve. Therefore, under normal circumstances, the molar ratio of sugar added to silica should be controlled to not exceed 0.1.

[0011] In addition, due to the small content of added sugar compounds, the catalytic activity of SSZ-39 molecular sieve is significantly improved at a lower cost, making it better adapted to the denitration catalyst coating structure and suitable for denitration reaction under airflow conditions. Therefore, when this 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.

[0012] 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 particle size of the molecular sieve is 0.1 μm to 10 μm.

[0013] In a third aspect, the present invention further provides an application of a molecular sieve in a denitration reaction, comprising:

[0014] At 150°C to 350°C, the conversion rate of nitrogen oxides produced in the denitration reaction is 61% to 97%.

[0015] Compared with the prior art, the beneficial effects of a molecular sieve and its application provided by the present invention are the same as the beneficial effects of the method for preparing a molecular sieve in the first aspect, and are not described in detail here. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] 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:

[0017] Figure 1 The preparation flow chart of the molecular sieve provided in this embodiment is shown;

[0018] Figure 2 The preparation flow chart of the gel prepared in this embodiment is shown;

[0019] Figure 3 The X-ray diffraction diagrams of Examples 1 to 4 of the present invention and Comparative Example 1 are shown;

[0020] Figure 4 The X-ray diffraction diagram of Comparative Example 2 of the present invention is shown;

[0021] Figure 5 The scanning electron microscope image of the molecular sieve in the first embodiment is shown;

[0022] Figure 6 The scanning electron microscope image of the molecular sieve in the second embodiment is shown;

[0023] Figure 7 The scanning electron microscope image of the molecular sieve in the third embodiment is shown;

[0024] Figure 8 The scanning electron microscope image of the molecular sieve in the fourth embodiment is shown;

[0025] Fig. 9 The scanning electron microscope image of the molecular sieve in Comparative Example 1 is shown;

[0026] Fig.10 The scanning electron microscope image of the molecular sieve in Comparative Example 2 is shown. DETAILED DESCRIPTION

[0027] 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.

[0028] 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.

[0029] Generally speaking, the main active component of SSZ-39 zeolite used as a denitrification catalyst is copper ion. There are certain problems with single copper ion. For example, when the engine is running at high temperature for a long time, the molecular sieve catalyst will often become blocked and deactivated due to its large grain size, resulting in a significant reduction in its denitrification performance, and even structural collapse and deactivation, leading to a reduction in catalytic activity.

[0030] In view of the above problems, the present invention provides a method for preparing a molecular sieve, which can reduce the grain size of the SSZ-39 molecular sieve and improve its catalytic activity in the denitration reaction. 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:

[0031] Step 101: Prepare gel using silicon source, aluminum source, alkali source, organic template and sugar compound as raw materials.

[0032] Exemplarily, the carbohydrate compound used in the embodiment of the present invention is a soluble natural carbohydrate compound, including at least one of monosaccharides, oligosaccharides and polysaccharides. When the carbohydrate compound is a monosaccharide, the monosaccharide includes at least one of glucose, fructose, galactose, ribose and deoxyribose. When the carbohydrate compound is an oligosaccharide, the oligosaccharide includes at least one of maltose, sucrose and lactose. When the carbohydrate compound is a polysaccharide, the polysaccharide includes at least one of glycogen and xylose. Glucose or sucrose is preferred. The hydroxyl groups in these carbohydrate compounds will interact with silicon and aluminum, and at the same time, form a three-dimensional distribution under the action of the intermolecular force of the carbohydrate molecules, and then form a confined domain similar to a grid structure, so that the SSZ-39 molecular sieve crystals are restricted or affected during the crystallization process, thereby being able to reduce the grain size of the SSZ-39 molecular sieve during the molecular sieve crystallization process, and at the same time, a higher relative crystallinity (> 90%) and specific surface area (>> 740m 2 / g). The more sugars are added, the better. Too much sugar will lead to too strong a hydroxyl effect, which will have too much influence and restriction on the crystallization process of the molecular sieve, resulting in the inability to obtain a molecular sieve with a SSZ-39 structure or a pure crystalline SSZ-39 molecular sieve. Therefore, in general, the molar ratio of sugar compounds to silicon sources should be controlled to meet the following conditions: (0.001-0.05):1, for example: 0.0015:1, 0.001:1, 0.003:1, 0.002:1, 0.01:1, 0.1:1, etc.

[0033] For example, the sugar compounds selected in the present invention are not arbitrarily selected, because the hydroxyl groups contained in the sugars usually can only take effect in solution or under fully mixed conditions, especially the effect on the microstructure also needs to occur under conditions of microscopic full contact. Therefore, the hydroxyl groups of the sugars and the silicon-aluminum substances need to interact in solution or a colloid-like homogeneous system. Therefore, the solubility of the sugars will affect the control of their crystals, and soluble sugars need to be selected to achieve the purpose of effectively controlling the crystal size of the molecular sieve.

[0034] Step 102: crystallizing the gel into SSZ-39 molecular sieve.

[0035] Exemplarily, by introducing the above-mentioned specific types and proportions of sugar compounds into the synthesis system of SSZ-39 molecular sieve, the prepared SSZ-39 molecular sieve has smaller grains, which avoids the phenomenon of molecular sieve grains blocking the pores and causing catalyst deactivation during long-term high-temperature engine operation, thereby improving the catalytic activity of SSZ-39 molecular sieve in the denitration reaction. According to experiments, at 150°C to 350°C, the conversion rate of nitrogen oxides produced in the denitration reaction is as high as 97%.

[0036] In addition, due to the small content of added sugar compounds, the catalytic activity of SSZ-39 molecular sieve is significantly improved at a lower cost, making it better adapted to the denitration catalyst coating structure and suitable for denitration reaction under airflow conditions. Therefore, when this 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.

[0037] 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 sugar compound as raw materials, including:

[0038] 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.

[0039] 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 NaY molecular sieve, USY molecular sieve, ZSM-5 molecular sieve, Beta molecular sieve, sodium aluminate, aluminum hydroxide, pseudo-boehmite, aluminum isopropoxide, aluminum sol, and boehmite. When USY molecular sieve is selected as the aluminum source, the effect is better. The alkali source used in the embodiment of the present invention is at least one of sodium hydroxide and potassium 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 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- One or more combinations of ethyl-N, N-dimethyl piperidine ion, 2,2,6,6-tetramethyl-N-methyl-N-ethyl piperidine ion, 2,2,6,6-tetramethyl-N, N-dimethyl piperidine ion salt and / or alkali, preferably N, N-diethyl-2,6-dimethyl piperidine hydroxide and / or 3,5-dimethyl-N, N-dimethyl piperidine hydroxide and N, N-dimethyl-N, N-bicyclononane etc. One or more combinations, more preferably 3,5-dimethyl-N, N-dimethyl piperidine ion. Such templates can play a structural guidance and filling role in the synthesis process of SSZ-39 molecular sieves. In addition, such templates are all 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, so that unexpected ionic impurities can be avoided in the mixing process, ensuring the good molecular sieve crystal form in the subsequent crystallization process and the smooth progress of the subsequent steps.

[0040] 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.

[0041] Step 202: The sugar compound and the semi-finished gel product are mixed and aged for a second time to form a gel.

[0042] Exemplarily, the molar ratio of the aluminum source, alkali source, organic template, sugar compound and silicon source in the embodiment of the present invention satisfies: n(Al2O3):n(OH-):n(R):n(sugar compound):n(SiO2)=(0.005-0.2):(0~2):(0~0.50):(0.001~0.1):1; the gel contains water, and the molar ratio of water to silicon source satisfies: n(H2O):n(SiO2)=(2~80):1. It is worth noting that OH- represents the alkali source and R represents the organic template. Within this range, the silicon source and the aluminum source can make the silicon in the silicon source and the aluminum in the aluminum source connected together by oxygen bonds 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 the denitration reaction, the conversion rate of nitrogen oxides is high. Especially when n(Al2O3):n(OH-):n(R):n(sugar compound):n(H2O):n(SiO2)=(0.033~0.2):(0~0.5):(0~0.2):(0.001-0.05):(5~40):1, the catalytic activity of the molecular sieve prepared in the embodiment of the present invention is better.

[0043] For example, sugar compounds are added to the synthesis system of SSZ-39 molecular sieve. The hydroxyl groups in these sugar compounds interact with the silicon-aluminum compounds. At the same time, a grid-like structure is formed between the sugar molecules, so that the SSZ-39 molecular sieve crystals are restricted or affected during the crystallization process, thereby reducing the grain size of the SSZ-39 molecular sieve during the molecular sieve crystallization process.

[0044] Exemplarily, the second aging time is 1 h to 2 h, and the second aging temperature is 50° C. to 70° C. The saccharide compound and the semi-finished gel product are mixed and aged for the second time, so that the saccharide compound and the semi-finished gel product react fully, thereby ensuring that the prepared SSZ-39 molecular sieve has small grains, thereby ensuring that the quality of the obtained product is stable when the SSZ-39 molecular sieve is prepared on a large scale.

[0045] In an optional manner, the gel is crystallized into SSZ-39 molecular sieve, comprising:

[0046] After the gel is stirred, crystallization is performed by heating.

[0047] 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.

[0048] Exemplarily, the gel in the embodiment of the present invention is crystallized at 120°C to 210°C for 38h to 150h. In this process, the hydroxyl groups in the carbohydrate compound interact with the silicon and aluminum to form a confinement domain similar to a grid structure, so that the SSZ-39 molecular sieve crystals are restricted or affected during the crystallization process, and the grain size of the SSZ-39 molecular sieve can be reduced during the molecular sieve crystallization process. And according to experiments, it can obtain a higher relative crystallinity (>90%) and specific surface area (>>740m 2 / g). If the crystallization time exceeds this time length, the production efficiency will be relatively low, and the unexpected effect cannot be achieved. Secondly, if the crystallization time in the reactor is less than 38h, it will lead to incomplete change of grain size, reduced relative crystallinity and other problems, so that small-grained 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°C, filtered, washed, the solid sample is dried, and calcined to obtain small-grained SSZ-39 molecular sieve. According to experiments, the molecular sieve provided in an embodiment of the present invention has a smaller grain size, and it has a higher DeNOx activity than the SSZ-39 molecular sieve synthesized with a conventional template.

[0049] A molecular sieve provided by an embodiment of the present invention is prepared by the method for preparing a molecular sieve provided by an embodiment of the present invention. Compared with zeolites of conventional sizes, the molecular sieve has smaller crystals and better catalytic activity.

[0050] According to an application of a molecular sieve in a denitration reaction provided by an embodiment of the present invention, at a temperature of 150° C. to 350° C., the conversion rate of nitrogen oxides produced in the denitration reaction is 61% to 97%.

[0051] 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.

[0052] In the following examples and comparative examples, the specific surface area is measured by the BET method; the relative crystallinity refers to the XRD crystallinity, which is measured as follows: the standard SSZ-39 molecular sieve (particle size 1.5 μm-3 μm) of Tosoh Corporation of Japan is used as the standard sample, and its crystallinity is calculated as 100%. The relative crystallinity of the synthetic sample is calculated as follows: relative crystallinity (%) = XRD diffraction peak area of ​​synthetic sample / XRD diffraction peak area of ​​standard sample × 100%; the 2θ range of the XRD diffraction peak is 5-35°.

[0053] Embodiment 1

[0054] The first step is to fully mix USY molecular sieve, sodium hydroxide, 25wt% aqueous solution of 3,5-dimethyl-N,N-dimethylpiperidine hydroxide (organic template R), pure water, and silica sol with a SiO2 content of 40wt% according to the following molar ratio, and perform the first aging at 35°C for 1h to make a gel semi-finished product; then, sucrose and the gel semi-finished product are mixed and aged for a second time at 35°C for 2h according to the proportion to make a gel. Among them, the molar ratio of USY molecular sieve, sodium hydroxide, 3,5-dimethyl-N,N-dimethylpiperidine hydroxide, sucrose, pure water and silica sol contained in the gel satisfies:

[0055] n(Al2O3):n(OH-):n(R):n(sucrose):n(H2O):n(SiO2)=0.017:0.7:0.2:0.01:20:1

[0056] The second step is to prepare SSZ-39 molecular sieve: the gel is placed in an autoclave, stirred at 35°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 SSZ-39 molecular sieve.

[0057] Figure 3 The X-ray diffraction diagrams of Examples 1 to 4 and Comparative Example 1 of the present invention are shown. From top to bottom, they are Comparative Example 1, Example 4, Example 3, Example 2 and Example 1. Figure 3 As shown, the molecular sieve prepared in Example 1 of the present invention is SSZ-39 molecular sieve. Figure 5 FIG. 2 shows a scanning electron microscope image of the molecular sieve in Example 1. Figure 5 As shown, the length of the SSZ-39 molecular sieve prepared in Example 1 of the present invention is about 1.2 μm-1.8 μm, the thickness is about 500 nm-700 nm, and the relative crystallinity is 92% and the specific surface area is 746 m 2 / g.

[0058] Embodiment 2

[0059] The first step is to prepare the gel: USY molecular sieve, sodium hydroxide, 25wt% aqueous solution of 3,5-dimethyl-N,N-dimethylpiperidine hydroxide (organic template R), pure water, and silica sol with a SiO2 content of 40wt% are fully mixed according to the following molar ratio, and the first aging is carried out at 35°C for 0.5h to prepare a gel semi-finished product; then ribose and the gel semi-finished product are mixed in proportion to prepare a gel. Among them, the molar ratio of USY molecular sieve, sodium hydroxide, 3,5-dimethyl-N,N-dimethylpiperidine hydroxide, ribose, pure water and silica sol contained in the gel satisfies:

[0060] n(Al2O3):n(OH-):n(R):n(ribose):n(H2O):n(SiO2)=0.017:0.5:0.2:0.015:20:1

[0061] The second step is to prepare SSZ-39 molecular sieve: the gel is placed in an autoclave, stirred at 35°C for 0.5h, and then heated to 180°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 SSZ-39 molecular sieve.

[0062] Figure 3 The X-ray diffraction diagrams of Examples 1 to 4 and Comparative Example 1 of the present invention are shown. From top to bottom, they are Comparative Example 1, Example 4, Example 3, Example 2 and Example 1. Figure 3 As shown, the molecular sieve prepared in Example 2 of the present invention is SSZ-39 molecular sieve. Figure 6 FIG. 2 shows a scanning electron microscope image of the molecular sieve in Example 2. Figure 6 As shown, the length of the SSZ-39 molecular sieve prepared in Example 2 of the present invention is about 1.2 μm-1.9 μm, the thickness is about 500 nm-700 nm, the relative crystallinity is 91%, and the specific surface area is 741 m 2 / g.

[0063] Embodiment 3

[0064] The first step is to prepare the gel: USY molecular sieve, sodium hydroxide, 25wt% aqueous solution of 3,5-dimethyl-N,N-dimethylpiperidine hydroxide (organic template R), pure water, and silica sol with a SiO2 content of 40wt% are fully mixed according to the following molar ratio, and the first aging is carried out at 25°C for 2h to prepare a semi-finished gel; then glycogen and the semi-finished gel are mixed in proportion to prepare a gel. Among them, the molar ratio of USY molecular sieve, sodium hydroxide, 3,5-dimethyl-N,N-dimethylpiperidine hydroxide, glycogen, pure water and silica sol contained in the gel satisfies:

[0065] n(Al2O3):n(OH-):n(R):n(glycogen):n(H2O):n(SiO2)=0.022:0.5:0.2:0.005:20:1

[0066] The second step is to prepare SSZ-39 molecular sieve: the gel is placed in an autoclave, stirred at 25°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 SSZ-39 molecular sieve.

[0067] Figure 3 The X-ray diffraction diagrams of Examples 1 to 4 and Comparative Example 1 of the present invention are shown. From top to bottom, they are Comparative Example 1, Example 4, Example 3, Example 2 and Example 1. Figure 3 As shown, the molecular sieve prepared in Example 3 of the present invention is SSZ-39 molecular sieve. Figure 7 The scanning electron microscope image of the molecular sieve in this embodiment 3 is shown. Figure 7 As shown, the length of the SSZ-39 molecular sieve prepared in Example 3 of the present invention is about 1.2 μm-1.6 μm, the thickness is about 500 nm-700 nm, the relative crystallinity is 95%, and the specific surface area is 751 m 2 / g.

[0068] Embodiment 4

[0069] The first step is to prepare the gel: USY molecular sieve, sodium hydroxide, 25wt% aqueous solution of 3,5-dimethyl-N,N-dimethylpiperidine hydroxide (organic template R), pure water, and silica sol with a SiO2 content of 40wt% are fully mixed according to the following molar ratio, and the first aging is carried out at 25°C for 1h to prepare a semi-finished gel; then glucose and maltose are mixed with the semi-finished gel in proportion, and the second aging is carried out at 25°C for 3h to prepare a gel. Among them, the molar ratio of USY molecular sieve, sodium hydroxide, 3,5-dimethyl-N,N-dimethylpiperidine hydroxide, glucose, maltose, pure water and silica sol contained in the gel satisfies:

[0070] n(Al2O3):n(OH-):n(R):n(glucose):n(maltose):n(H2O):n(SiO2)=0.022:0.5:0.2:0.003:0.002:20:1.

[0071] The second step is to prepare SSZ-39 molecular sieve: the gel is placed in an autoclave, stirred at 25°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 SSZ-39 molecular sieve.

[0072] Figure 3 The X-ray diffraction diagrams of Examples 1 to 4 and Comparative Example 1 of the present invention are shown. From top to bottom, they are Comparative Example 1, Example 4, Example 3, Example 2 and Example 1. Figure 3 As shown, the molecular sieve prepared in Example 4 of the present invention is SSZ-39 molecular sieve. Figure 8 FIG. 4 shows a scanning electron microscope image of the molecular sieve in Example 4. Figure 8As shown, the length of the SSZ-39 molecular sieve prepared in Example 4 of the present invention is about 1.1 μm-1.8 μm, the thickness is about 500 nm-700 nm, the relative crystallinity is 95%, and the specific surface area is 749 m 2 / g.

[0073] Comparative Example 1

[0074] The first step is to prepare the gel: USY molecular sieve, sodium hydroxide, 25wt% aqueous solution of 3,5-dimethyl-N,N-dimethylpiperidine hydroxide (organic template R), pure water, and silica sol with a SiO2 content of 40wt% are fully mixed according to the following molar ratio, and aged at 25°C for 1h to prepare the gel. The molar ratio of USY molecular sieve, sodium hydroxide, 3,5-dimethyl-N,N-dimethylpiperidine hydroxide, pure water, and silica sol in the gel satisfies:

[0075] n(Al2O3):n(OH-):n(R):n(H2O):n(SiO2)=0.022:0.5:0.2:20:1

[0076] 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.

[0077] Figure 3 The X-ray diffraction diagrams of the embodiments 1 to 4 and the comparative example 1 of the present invention are shown. From top to bottom, they are the comparative example 1, the embodiment 4, the embodiment 3, the embodiment 2 and the embodiment 1. Figure 3 As shown, the molecular sieve prepared in Comparative Example 1 of the present invention is SSZ-39 molecular sieve. Fig. 9 The scanning electron microscope image of the molecular sieve in Comparative Example 1 is shown. Fig. 9 As shown, the SSZ-39 molecular sieve prepared in Comparative Example 1 of the present invention has a length of about 3.0 μm-4.5 μm and a thickness of about 1 μm-2 μm.

[0078] Comparative Example 2

[0079] The specific preparation method is the same as in Example 1, except that the molar ratio n(sucrose):n(SiO2)=0.3:1, Figure 4 The X-ray diffraction diagram of the comparative example of the present invention is shown. Figure 4 As shown, the molecular sieve powder prepared by comparative example 2 is not SSZ-39 molecular sieve after testing, indicating that excessive addition of sucrose will affect the crystallization process of the molecular sieve, resulting in failure to obtain a pure phase SSZ-39 molecular sieve. Fig.10The scanning electron microscope image of the molecular sieve in Comparative Example 1 is shown. Fig.10 As shown, the crystal morphology of the molecular sieve prepared in Comparative Example 1 of the present invention is also very different from the crystal morphology of the SSZ-39 molecular sieve prepared in Examples 1 to 4 and Comparative Example 1.

[0080] 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 embodiments one to four and comparative example one.

[0081] Specific testing methods include:

[0082] The first step is molecular sieve ammonium exchange: the SSZ-39 molecular sieves prepared in Examples 1 to 4 and the SSZ-39 molecular sieve prepared in Comparative Example 1 are mixed in a ratio of ammonium nitrate: molecular sieve: water (mass ratio) = 1:1:10, the pH is adjusted to 8-8.5 with ammonia water, exchanged at 90°C for 1h under stirring, filtered, washed, dried, and calcined at 550°C for 4h. The above process is repeated 3 times until the Na2O content in the molecular sieve is less than 0.1%.

[0083] 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.

[0084] The third step is performance testing: the Cu-SSZ-39 composite molecular sieve prepared in Examples 1 to 4 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.

[0085] NO x The conversion rate is defined as:

[0086] The conversion rate of nitrogen oxides in the reaction mixture at 150°C-350°C is shown in Table 1.

[0087]

[0088]

[0089] 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 4 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 small-grain SSZ-39 synthesized by the molecular sieve preparation method provided by the present invention has better catalytic activity in the denitration reaction.

[0090] 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 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 sugar compound and the semi-finished gel product are mixed and aged for a second time to prepare a gel, wherein the molar ratio of the sugar compound to the silicon source satisfies: (0.001-0.015): 1; crystallizing the gel into SSZ-39 molecular sieve; The carbohydrate compound is a soluble carbohydrate compound; Wherein, the crystallization of the gel into SSZ-39 molecular sieve comprises: After the gel is stirred, crystallization is performed by heating; the stirring time is 0.5h-20h.

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, sugar compound and silicon source satisfies: n(Al2O3):n(OH-):n(R):n(sugar compound):n(SiO2)=(0.005-0.2):(0~2):(0~0.50):(0.001~0.1):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 first aging time is 0.1h~100h, and the first aging temperature is 25℃~100℃; the second aging time is 0h~3h, and the second aging temperature is 30℃~50℃.

4. The method for preparing a molecular sieve according to claim 1, characterized in that: The carbohydrate compound is a soluble natural carbohydrate compound, including at least one of monosaccharide, oligosaccharide and polysaccharide.

5. The method for preparing a molecular sieve according to claim 4, characterized in that: When the carbohydrate compound is a monosaccharide, the monosaccharide includes at least one of glucose, fructose, galactose, ribose and deoxyribose; and / or, When the carbohydrate compound is an oligosaccharide, the oligosaccharide includes at least one of maltose, sucrose and lactose; and / or, When the carbohydrate compound is a polysaccharide, the polysaccharide includes at least one of glycogen and xylose.

6. The method for preparing a molecular sieve according to claim 1, characterized in that: The temperature of the crystallization operation is 120° C. to 210° C., and the time of the crystallization operation is 38 h to 150 h.

7. A molecular sieve prepared by the method for preparing a molecular sieve according to any one of claims 1 to 6, characterized in that: The particle size of the molecular sieve is 0.1 μm to 10 μm.

8. 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.

9. The use according to claim 8, characterized in that: At 150°C to 350°C, the conversion rate of nitrogen oxides produced in the denitration reaction is 61% to 97%.

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