Synthesis method and application of ssz-39 molecular sieve with low silicon to aluminum ratio

Abstract

The application discloses a synthesis method and application of SSZ-39 molecular sieve with a low silicon-aluminum ratio, and comprises the following steps: S10, adding a template agent, a silicon source, natural clay and molecular sieve seeds into an alkaline aqueous solution in sequence, and forming an initial mixed gel after fully stirring; S20, transferring the obtained initial gel solution into a reaction kettle to perform hydrothermal crystallization treatment; S30, performing calcination after separating, washing, drying and treating the obtained crystallization liquid after complete crystallization, so that pure-phase SSZ-39 molecular sieve is obtained. The molecular sieve seeds have a double six-membered ring and an eight-membered ring secondary structure unit configuration, and the molecular sieve structure is AEI or CHA or FAU type. The synthesis method of the molecular sieve improves the yield of the molecular sieve, effectively reduces the production cost, and simplifies the technological process. The SSZ-39 molecular sieve has a large specific surface area and pore volume, and exhibits high catalytic activity and excellent high-temperature hydrothermal stability in an NH3-SCR catalytic reaction.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of molecular sieve, and particularly relates to a synthesis method and application of SSZ-39 molecular sieve with low silicon-aluminum ratio. BACKGROUND

[0002] Currently, the NH3 selective catalytic reduction (NH3-SCR) is mainly used for the purification treatment of NOx in automobile exhaust emissions, and the key of the technology is to select a catalyst with excellent performance; the eight-membered ring silicon-aluminum SSZ-39 molecular sieve is a good SCR reaction catalyst in addition to the SSZ-13 molecular sieve; according to the literature reports, the catalytic performance of the SSZ-39 molecular sieve can even surpass the SSZ-13 molecular sieve catalyst which has been industrialized.

[0003] The SSZ-39 molecular sieve is a silicon-aluminum series molecular sieve with AEI topology structure and a three-dimensional pore structure of eight-membered rings; it was synthesized by Zones S I et al. in 1997 by using N-di(cyclo)alkyl-dimethylpiperidinium cations as a structure directing agent by a hydrothermal synthesis method; the SSZ-39 molecular sieve has ordered pore structure, high specific surface area and good hydrothermal stability, and can be used as a catalyst for the methanol-to-olefin reaction; meanwhile, the SSZ-39 molecular sieve loaded with metal exhibits unique selective reduction reaction (SCR) activity and has very good reduction treatment performance for nitrogen oxides (NOx), which has attracted extensive attention and become a research hotspot in recent years; in addition, the SSZ-39 molecular sieve catalyst does not contain phosphorus and is a silicon-aluminum molecular sieve, which overcomes the shortcomings such as the easy collapse of the framework of the SAPO series molecular sieve, and has good industrial application prospects.

[0004] China has abundant reserves of natural clay resources and low prices, which shows great potential in the aspect of synthesizing zeolite molecular sieves as raw materials. Using natural silicon-aluminum clay instead of conventional inorganic chemicals as raw materials to prepare zeolite molecular sieves not only shortens the production route of molecular sieves, but also realizes the green synthesis of molecular sieves from the source, so it has gradually attracted widespread attention. In addition, developing a green synthesis route of molecular sieves using natural silicon-aluminum clay as raw materials has important scientific significance and application value for the green industrial synthesis of zeolites and the high-value utilization of natural clay resources. At present, researchers have synthesized Y, ZSM-5, A, β and other molecular sieves using natural silicon-aluminum clay (such as kaolin, rectorite, diatomite, etc.) as all or part of the silicon-aluminum source, but there are few research reports on the synthesis of SSZ-39 molecular sieves using natural clay as the main raw material.

[0005] The synthesis method of the prior art for the SSZ-39 molecular sieve is basically to convert and synthesize the SSZ-39 molecular sieve by using expensive USY molecular sieve as a raw material, and these synthesis methods generally have the disadvantages of low molecular sieve yield, relatively small specific surface area, high production cost, and are not conducive to large-scale industrial production, and the silicon-aluminum ratio range of the SSZ-39 molecular sieve reported in the prior art is relatively high, and the present application overcomes the shortcomings of the prior art. SUMMARY

[0006] In view of the above problems, the present application provides a synthesis method for preparing a low-silicon-aluminum ratio SSZ-39 molecular sieve by using natural clay as an aluminum source and part of a silicon source and adding molecular sieve seeds;

[0007] To achieve the above technical purposes and effects, the present application is implemented by the following technical solutions:

[0008] A synthesis method of a low-silicon-aluminum ratio SSZ-39 molecular sieve, comprising the following steps:

[0009] A template agent, a silicon source, natural clay, and molecular sieve seeds are sequentially added to an alkaline aqueous solution, and an initial mixed gel is formed after sufficient stirring, and the initial mixed gel solution is transferred to a reaction kettle for hydrothermal crystallization treatment; after complete crystallization, the obtained crystallization liquid is separated, washed, dried, and then calcined to obtain a low-silicon-aluminum ratio SSZ-39 molecular sieve.

[0010] Further, the following steps are included:

[0011] S10: A template agent, a silicon source, and natural clay, AEI or CHA or FAU type molecular sieve with double six-membered ring and eight-membered ring secondary structural unit configuration as seeds are sequentially added to an alkaline aqueous solution, and an initial mixed gel is formed after sufficient stirring;

[0012] S20: The obtained initial gel solution is transferred to a reaction kettle for hydrothermal crystallization treatment;

[0013] S30: After complete crystallization, the obtained crystallization liquid is separated, washed, dried, and then calcined to obtain the target SSZ-39 molecular sieve.

[0014] Further, the molar ratio of Al2O3, SiO2, alkali source, template agent, and water in the initial mixed gel is (0.02-0.05):1:(0.5-1):(0.05-0.3):(10-45).

[0015] Further, the natural clay is kaolin or montmorillonite; the molar ratio of silicon-aluminum oxide of the kaolin is 1-5:1, and the molar ratio of silicon-aluminum oxide of the montmorillonite is 5-15:1.

[0016] Further, the molecular sieve seed crystal has a double six-membered ring and eight-membered ring secondary structural unit configuration, and the molecular sieve structure is AEI or CHA or FAU type; the molecular sieve seed crystal comprises one or more of SSZ-39 molecular sieve, SAPO-18 molecular sieve, AlPO-18 molecular sieve, SIZ-8 molecular sieve, SSZ-13 molecular sieve, HY molecular sieve, and USY molecular sieve; the molar ratio of silicon aluminum oxide of the molecular sieve seed crystal is 0.1-15:1; and the addition amount of the molecular sieve seed crystal is 1%-30% of the mass of SiO2 contained in the initial mixed gel.

[0017] Further, the molar ratio of silicon aluminum oxide of the synthesized SSZ-39 molecular sieve is 5-18:1.

[0018] Further, the silicon source is one or more of silica sol, tetraethyl orthosilicate, sodium silicate, and water glass; and the content of SiO2 in the silicon source is 10-40wt%.

[0019] Further, the alkaline aqueous solution is one or more of sodium hydroxide solution or potassium hydroxide solution; and the concentration of the alkaline aqueous solution is 0.5-40wt%.

[0020] Further, the template agent is selected from one or more of N,N-dimethyl-2,6-dimethylpiperidinium hydroxide, N,N-dimethyl-3,5-dimethylpiperidinium hydroxide, N,N-diethyl-2-ethylpiperidinium hydroxide, N-ethyl-N-methyl-2,6-dimethylpiperidinium hydroxide, tetraethylphosphonium hydroxide, tetrapropylphosphonium hydroxide, and tetrabutylphosphonium hydroxide; and the template agent is an aqueous solution with a concentration of 20-40wt%.

[0021] Further, in the step S20, the hydrothermal crystallization treatment comprises crystallization reaction at 25-40℃ for 1-24h, and then crystallization reaction at a temperature of 140-180℃ for 48h-72h; and the hydrothermal crystallization treatment is in a dynamic crystallization mode.

[0022] Further, in the step S30, the temperature of the calcination is 550-600℃, and the calcination time is 6-12h.

[0023] The SSZ-39 molecular sieve synthesized by the above-mentioned synthesis method of the SSZ-39 molecular sieve is used as an NH3-SCR catalytic reaction catalyst.

[0024] This invention provides a method for synthesizing SSZ-39 molecular sieves with a low silicon-to-alumina ratio. It utilizes inexpensive natural clay as an aluminum source and partially as a silicon source, while adding molecular sieves with dual six-membered and eight-membered ring secondary structural units, such as AEI, CHA, or FAU, as seed crystals to guide the structure. By promoting the formation of crystal nuclei in the gel and shortening the intermediate crystallization stage, this method assists in the crystallization of SSZ-39 molecular sieves and effectively inhibits the formation of impurity crystals. Furthermore, by introducing an additional silicon source during gel preparation, the silicon-to-alumina ratio of the product molecular sieve can be effectively adjusted, achieving controllable silicon-to-alumina ratio in the synthesized molecular sieve.

[0025] The SSZ-39 molecular sieve synthesized by the preparation method provided by the present invention is a low silica-alumina ratio molecular sieve, and the synthesized SSZ-39 molecular sieve has high relative crystallinity, good crystal morphology, and large specific surface area and pore volume.

[0026] Beneficial effects

[0027] (1) The molecular sieve prepared according to the molecular sieve synthesis method and corresponding synthesis steps proposed in this invention is SSZ-39 molecular sieve with a single crystal phase and a high relative crystallinity, with a relative crystallinity of more than 80%.

[0028] (2) On the one hand, the present invention introduces molecular sieves with AEI structure as seed crystals, which is beneficial to promote the synthesis of pure phase SSZ-39 molecular sieve; on the other hand, it uses inexpensive natural clay as aluminum source and part of silicon source, reducing the use of artificially synthesized silicon-aluminum source, which can greatly reduce carbon emissions, and the silicon-aluminum ratio of the product molecular sieve can be effectively adjusted by introducing additional silicon source.

[0029] (3) The preparation method provided by the present invention greatly shortens the crystallization time in the molecular sieve synthesis process, effectively improves the crystallinity of the molecular sieve, and the added seed crystals can play a structural guiding role, thereby reducing the amount of expensive template agent used. Compared with the existing synthesis method, the yield of molecular sieve is increased to 55-85%, effectively reducing production costs and simplifying the process.

[0030] (4) The SSZ-39 molecular sieve synthesized by this invention is a low silica-alumina ratio molecular sieve with a silica-alumina oxide molar ratio of 5-18. Moreover, the synthesized SSZ-39 molecular sieve has good crystal morphology and a large specific surface area and pore volume.

[0031] (5) This invention uses inexpensive natural clay as a silicon-aluminum source and adds molecular sieves with AEI structure as seed crystals. This can effectively adjust the composition and concentration of the gel. By promoting the formation of crystal nuclei in the gel and shortening the intermediate crystallization stage, it can play an auxiliary crystallization role in the synthesis of SSZ-39 molecular sieve, effectively inhibit the formation of impurity crystals and improve the relative crystallinity of the product. At the same time, it reduces the silicon-aluminum ratio of the product and appropriately adjusts the pore volume and specific surface area of ​​the molecular sieve.

[0032] (6) The low silicon-to-aluminum ratio SSZ-39 molecular sieve synthesized in this invention not only has high efficiency NH3-SCR catalytic activity, but also excellent high temperature hydrothermal stability. Therefore, it has certain economic and environmental benefits and is conducive to industrial scale-up applications. Attached Figure Description

[0033] Figure 1 The XRD patterns of SSZ-39 molecular sieves prepared in Examples 1, 2, 3, 4 and Comparative Examples 1, 2, 3, 4, 5 are shown.

[0034] Figure 2 This is a SEM image of the SSZ-39 molecular sieve prepared in Example 1;

[0035] Figure 3 This is a SEM image of the SSZ-39 molecular sieve prepared in Example 2;

[0036] Figure 4 The image shows a SEM image of the SSZ-39 molecular sieve prepared in Example 3.

[0037] Figure 5 This is a SEM image of the SSZ-39 molecular sieve prepared in Example 4;

[0038] Figure 6 This is a SEM image of the SSZ-39 molecular sieve prepared in Example 5;

[0039] Figure 7 The image shows a SEM image of the SSZ-39 molecular sieve prepared in Example 6.

[0040] Figure 8 This is a comparison chart showing the SCR reactivity test results of Cu-SSZ-39 molecular sieves with the same copper content, prepared by ion exchange treatment of SSZ-39 molecular sieves synthesized in Example 1, Comparative Example 1, and Comparative Example 2.

[0041] Figure 9 This is a comparison chart of the SCR reactivity test results of Cu-SSZ-39 molecular sieve and Cu-SSZ-13 molecular sieve with the same copper content, prepared by ion exchange treatment of SSZ-39 molecular sieve and SSZ-13 molecular sieve standard samples synthesized in Example 1.

[0042] Figure 10 This is a comparison chart showing the SCR reactivity test results of Cu-SSZ-39 molecular sieve and Cu-SSZ-13 molecular sieve with the same copper content, prepared by ion exchange treatment of SSZ-39 molecular sieve and SSZ-13 molecular sieve standard samples synthesized in Example 1, after hydrothermal aging treatment. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments; it should be understood that the specific embodiments described herein are merely for explaining the invention and are not intended to limit the invention.

[0044] The application principle of the present invention will be described in detail below with reference to the accompanying drawings;

[0045] Example 1:

[0046] First, weigh 9.0888g of sodium hydroxide and 41.4999g of deionized water and mix them evenly. Stir at room temperature for 0.5h. Then, while stirring, slowly add 42.9270g of a 22wt% aqueous solution of N,N-dimethyl-3,5-dimethylpiperidinium hydroxide and stir for 1h. Next, while stirring, slowly add 63.7939g of silica sol (29wt% concentration, calculated as SiO2) and stir for 1h. Then, while stirring, add 3.6048g of kaolin (silicon-aluminum oxide molar ratio of 2) and react for 2h. Finally, while stirring, add 2.8968g of SAPO-18 molecular sieve (silicon-aluminum oxide molar ratio of 0.5) seed crystals and continue stirring for 2h to obtain the initial gel mixture. The gel mixture was transferred to a high-pressure reactor, heated to 30°C for 12 hours, then heated to 170°C for 48 hours to crystallize. After cooling to room temperature, the mixture was centrifuged and washed until neutral. The resulting solid was dried in an oven at 110°C for 6 hours. The product was then calcined in a muffle furnace at 550°C for 10 hours to obtain white powdered SSZ-39 molecular sieve Y1.

[0047] The yield of molecular sieve Y1 was calculated to be 83.67%. The molecular sieve yield was calculated as follows: Yield % = (mass of the dry molecular sieve powder obtained after calcination) * 100 / (total mass of dry basis in the initial mixed gel). (The following yield calculation methods are the same.)

[0048] Example 2:

[0049] First, weigh 8.3450g of sodium hydroxide and 54.5220g of deionized water and mix them evenly. Stir at room temperature for 0.5h. Then, while stirring, slowly add 42.9341g of a 22wt% aqueous solution of N,N-dimethyl-2,6-dimethylpiperidinium hydroxide and stir for 1h. Next, while stirring, slowly add 43.3814g of silica sol (29wt% concentration, calculated as SiO2) and stir for 1h. Then, while stirring, add 11.7657g of montmorillonite (silicon-aluminum oxide molar ratio of 9) and react for 2h. Finally, while stirring, add 1.3519g of SSZ-39 molecular sieve (silicon-aluminum oxide molar ratio of 12) seed crystals and continue stirring for 2h to obtain the initial gel mixture. The gel mixture was transferred to a high-pressure reactor, heated to 30°C for 12 hours, then heated to 170°C for 48 hours to crystallize. After cooling to room temperature, the mixture was centrifuged and washed until neutral. The resulting solid was dried in an oven at 110°C for 6 hours. The product was then calcined in a muffle furnace at 550°C for 10 hours to obtain white powdered SSZ-39 molecular sieve Y2.

[0050] The yield of molecular sieve Y2 was calculated to be 82.25%.

[0051] Example 3:

[0052] First, weigh 7.3186 g of sodium hydroxide and 45.3098 g of deionized water and mix them evenly. Stir at room temperature for 0.5 h. Then, slowly add 38.3621 g of a 20 wt% tetraethylphosphonium hydroxide aqueous solution while stirring for 1 h. Next, slowly add 67.9930 g of water glass (26 wt% concentration, calculated as SiO2) while stirring for 1 h. Then, add 1.8929 g of kaolin (silicon-aluminum oxide molar ratio of 2) while stirring and react for 2 h. Finally, add 3.5134 g of HY molecular sieve (silicon-aluminum oxide molar ratio of 5) seed crystals while stirring and continue stirring for 2 h to obtain the initial gel mixture. The gel mixture was transferred to a high-pressure reactor, heated to 35°C for 8 hours, then heated to 160°C for 72 hours to crystallize. After cooling to room temperature, the mixture was centrifuged and washed until neutral. The resulting solid was dried in an oven at 110°C for 6 hours. The product was then calcined in a muffle furnace at 550°C for 10 hours to obtain white powdered SSZ-39 molecular sieve Y3.

[0053] The yield of molecular sieve Y3 was calculated to be 80.68%.

[0054] Example 4:

[0055] First, weigh 12.2579 g of potassium hydroxide and 49.5400 g of deionized water and mix them evenly. Stir at room temperature for 0.5 h. Then, while stirring, slowly add 37.2847 g of an aqueous solution of 22 wt% N,N-dimethyl-3,5-dimethylpiperidinium hydroxide and stir for 1 h. Next, while stirring, slowly add 59.2899 g of silica sol (concentration 29 wt%, based on SiO2) and stir for 1 h. Then, while stirring, add 2.5048 g of kaolin (silicon-aluminum oxide molar ratio of 2) and react for 2 h. Finally, while stirring, add 4.3248 g of SSZ-13 molecular sieve (silicon-aluminum oxide molar ratio of 10) seed crystals and continue stirring for 2 h to obtain the initial gel mixture. The gel mixture was transferred to a high-pressure reactor, heated to 35°C for 8 hours, then heated to 160°C for 72 hours to crystallize. After cooling to room temperature, the mixture was centrifuged and washed until neutral. The resulting solid was dried in an oven at 110°C for 6 hours. The product was then calcined in a muffle furnace at 550°C for 10 hours to obtain white powdered SSZ-39 molecular sieve Y4.

[0056] The yield of molecular sieve Y4 was calculated to be 84.06%.

[0057] Example 5:

[0058] First, weigh 8.0577 g of sodium hydroxide and 58.8294 g of deionized water and mix them evenly. Stir at room temperature for 0.5 h. Then, slowly add 34.8849 g of a 30 wt% tetrabutylphosphonium hydroxide aqueous solution while stirring for 1 h. Next, slowly add 50.7096 g of silica sol (concentration 29 wt%, based on SiO2) while stirring for 1 h. Then, continue to add 8.4353 g of montmorillonite (silicon-aluminum oxide molar ratio of 9) while stirring and react for 2 h. Finally, add 1.9902 g of SSZ-39 molecular sieve (silicon-aluminum oxide molar ratio of 12) seed crystals with a silicon-aluminum ratio of 8 while stirring and continue stirring for 2 h to obtain the initial gel mixture. The gel mixture was transferred to a high-pressure reactor, heated to 30°C for 12 hours, then heated to 170°C for 48 hours to crystallize. After cooling to room temperature, the mixture was centrifuged and washed until neutral. The resulting solid was dried in an oven at 110°C for 6 hours. The product was then calcined in a muffle furnace at 550°C for 10 hours to obtain white powdered SSZ-39 molecular sieve Y5.

[0059] The yield of molecular sieve Y5 was calculated to be 85.18%.

[0060] Example 6:

[0061] First, weigh 6.8769 g of sodium hydroxide and 52.4538 g of deionized water and mix them evenly. Stir at room temperature for 0.5 h. Then, while stirring, slowly add 36.1151 g of a 22 wt% aqueous solution of N,N-dimethyl-3,5-dimethylpiperidinium hydroxide and stir for 1 h. Next, while stirring, slowly add 56.6279 g of an aqueous solution of sodium silicate (20 wt% concentration, calculated as SiO2) and stir for 1 h. Continue to add 8.9073 g of montmorillonite (silicon-aluminum oxide molar ratio of 9) while stirring and react for 2 h. Finally, while stirring, add 4.2031 g of USY molecular sieve (silicon-aluminum oxide molar ratio of 6) seed crystals and continue stirring for 2 h to obtain the initial gel mixture. The gel mixture was transferred to a high-pressure reactor, heated to 35°C for 8 hours, then heated to 160°C for 72 hours to crystallize. After cooling to room temperature, the mixture was centrifuged and washed until neutral. The resulting solid was dried in an oven at 110°C for 6 hours. The product was then calcined in a muffle furnace at 550°C for 10 hours to obtain white powdered SSZ-39 molecular sieve Y6.

[0062] The yield of molecular sieve Y6 was calculated to be 82.78%.

[0063] Comparative Example 1: SSZ-39 molecular sieve was synthesized using USY molecular sieve as an aluminum source and part of a silicon source according to the existing patented method. The specific steps are as follows:

[0064] First, 4.6217 g of sodium hydroxide and 77.6194 g of deionized water were weighed and mixed evenly, and stirred at room temperature for 0.5 h. Then, 24.0051 g of a 22 wt% aqueous solution of N,N-dimethyl-3,5-dimethylpiperidinium hydroxide was slowly added while stirring and stirred for 1 h. Next, 9.7687 g of USY molecular sieve (silicon-aluminum oxide molar ratio of 6) was added while stirring and reacted for 2 h. Finally, 44.9519 g of silica sol (concentration of 29 wt%, based on SiO2) was slowly added while stirring and stirred for another 2 h to obtain an initial gel mixture. The gel mixture was transferred to a stainless steel reactor with a polytetrafluoroethylene liner and crystallized at 180 °C for 48 h under hydrothermal conditions. After cooling to room temperature, the mixture was centrifuged and washed until neutral. The resulting solid was dried in an oven at 110 °C for 6 h. The resulting product was calcined in a muffle furnace at 550 °C for 10 h to obtain a white powdery SSZ-39 molecular sieve C1.

[0065] The yield of molecular sieve C1 was calculated to be 36.01%.

[0066] Comparative Example 2: SSZ-39 molecular sieve was synthesized using USY molecular sieve as an aluminum source and part of a silicon source, according to an existing patented method, with the addition of molecular sieve seed crystals. The specific steps are as follows:

[0067] First, weigh 4.1382 g of sodium hydroxide and mix thoroughly with 90.6921 g of deionized water. Stir at room temperature for 0.5 h. Then, while stirring, slowly add 20.5012 g of a 22 wt% aqueous solution of N,N-dimethyl-3,5-dimethylpiperidinium hydroxide and stir for 1 h. Next, while stirring, add 10.8385 g of USY molecular sieve (silicon-aluminum oxide molar ratio of 6) and react for 2 h. Finally, while stirring, slowly add 34.8062 g of silica sol (concentration of 29 wt%, calculated as SiO2). Stir for 1 hour, and finally add 3.5150g of SAPO-18 molecular sieve (silicon-aluminum oxide molar ratio of 0.5) seed crystals while stirring. Continue stirring for 2 hours to obtain the initial gel mixture. Transfer the gel mixture to a stainless steel reactor with a polytetrafluoroethylene liner, and crystallize at 180℃ for 48 hours under hydrothermal conditions. Cool to room temperature, centrifuge and wash until neutral, and dry the obtained solid in an oven at 110℃ for 6 hours. Calcine the obtained product in a muffle furnace at 550℃ for 10 hours to obtain white powdered SSZ-39 molecular sieve C2.

[0068] The yield of molecular sieve C2 was calculated to be 33.36%.

[0069] Comparative Example 3: SSZ-39 molecular sieve was synthesized using natural clay as the aluminum source and part of the silicon source, with MOR-type molecular sieves added as seed crystals. The specific steps are as follows:

[0070] First, weigh 3.2199 g of sodium hydroxide and 66.2994 g of deionized water and mix them evenly. Stir at room temperature for 0.5 h. Then, slowly add 25.7821 g of a 22 wt% aqueous solution of N,N-dimethyl-3,5-dimethylpiperidinium hydroxide and stir for 1 h. Next, add 2.5929 g of kaolin (silicon-aluminum oxide molar ratio of 2) and react for 2 h. Continue to slowly add 63.0127 g of silica sol (concentration of 29 wt%, based on SiO2) and stir for 1 h. Finally, add 2.4657 g of mordenite molecular sieve (silicon-aluminum oxide molar ratio of 11) seed crystals and stir for 2 h to obtain the initial gel mixture. The gel mixture was transferred to a high-pressure reactor, heated to 30°C for 12 hours for aging, then heated to 180°C for 48 hours for crystallization, cooled to room temperature, centrifuged and washed until neutral, and the resulting solid was dried in an oven at 110°C for 6 hours. The resulting product was then calcined in a muffle furnace at 550°C for 10 hours to obtain white powdered SSZ-39 molecular sieve C3.

[0071] The yield of molecular sieve C3 was calculated to be 15.43%.

[0072] Comparative Example 4: SSZ-39 molecular sieve was synthesized using natural clay as the aluminum source and part of the silicon source, but without the addition of seed crystals. The specific steps are as follows:

[0073] First, 5.5311 g of sodium hydroxide and 55.4580 g of deionized water were weighed and mixed evenly, and stirred at room temperature for 0.5 h. Then, while stirring, 27.6255 g of a 22 wt% aqueous solution of N,N-dimethyl-3,5-dimethylpiperidinium hydroxide was slowly added and stirred for 1 h. Next, while stirring, 70.2073 g of silica sol (29 wt% concentration, calculated as SiO2) was slowly added and stirred for 1 h. Then, while stirring, 2.1381 g of kaolin (silicon-aluminum oxide molar ratio of 2) was added and stirred for 2 h to obtain the initial gel mixture. The gel mixture was transferred to a high-pressure reactor, heated to 30 °C for 12 h, then heated to 170 °C for 48 h for crystallization. After cooling to room temperature, the mixture was centrifuged and washed until neutral. The resulting solid was dried in an oven at 110 °C for 6 h. The product was then calcined in a muffle furnace at 550 °C for 10 h to obtain white powdered SSZ-39 molecular sieve C4.

[0074] The yield of molecular sieve C4 was calculated to be 33.83%.

[0075] Comparative Example 5: The raw material composition and ratio, as well as the reaction conditions, of Example 1 were used, but the order of addition of the raw materials was changed. The specific steps are as follows:

[0076] First, weigh 9.0888g of sodium hydroxide and 41.4999g of deionized water and mix them evenly. Stir at room temperature for 0.5h. Then, slowly add 63.7939g of silica sol (concentration of 29wt%, based on SiO2) while stirring and stir for 1h. Next, add 3.6048g of kaolin (silicon-aluminum oxide molar ratio of 2) while stirring and react for 2h. Continue to slowly add 42.9270g of 22wt% aqueous solution of N,N-dimethyl-3,5-dimethylpiperidinium hydroxide while stirring for 1h. Finally, add 2.8968g of SAPO-18 molecular sieve (silicon-aluminum oxide molar ratio of 0.5) seed crystals while stirring and continue stirring for 2h to obtain the initial gel mixture. The gel mixture was transferred to a high-pressure reactor, heated to 30°C for 12 hours, then heated to 170°C for 48 hours to crystallize. After cooling to room temperature, the mixture was centrifuged and washed until neutral. The resulting solid was dried in an oven at 110°C for 6 hours. The product was then calcined in a muffle furnace at 550°C for 10 hours to obtain white powdered SSZ-39 molecular sieve C5.

[0077] The yield of molecular sieve C5 was calculated to be 41.58%.

[0078] Specifically, analyses and tests were conducted on Examples 1-6 and Comparative Examples 1-5:

[0079] (1) XRD test

[0080] Figure 1 The XRD patterns of the SSZ-39 molecular sieves prepared in Examples 1, 2, 3, 4, Comparative Examples 1, 2, 3, 4, and 5 of this invention are shown in the figures. It can be seen from the figures that the samples all exhibit characteristic diffraction peaks near 2θ = 9.5°, 10.6°, 13°, 16.9°, and 20.8°. Meanwhile, the molecular sieve prepared in Comparative Example 5 also shows obvious characteristic diffraction peaks near 2θ = 15.8°, 18.3°, and 26°. Therefore, it can be concluded that the molecular sieves synthesized in Examples 1-4 and Comparative Examples 1-4 are all SSZ-39 molecular sieves with an AEI topology, while the molecular sieve synthesized in Comparative Example 5 has both AEI and ANA crystalline phases. Furthermore, the relative crystallinity of the samples obtained in Examples 1, 2, 3, 4, and Comparative Examples 1, 2, 3, 4, and 5 can be calculated, and the specific results are shown in Table 1 below. The relative crystallinity of the sample is calculated as follows: Relative crystallinity % = (Sum of the characteristic XRD diffraction peak heights of the experimental sample near 2θ = 9.5°, 16.9°, and 20.8°) * 100 / (Sum of the characteristic XRD diffraction peak heights of commercially available standard SSZ-39 molecular sieve samples near 2θ = 9.5°, 16.9°, and 20.8°)

[0081] Table 1. Statistical Table of XRD Test Results

[0082] Sample Name Relative Crystallinity (%) Y1 85.35 Y2 93.28 Y3 96.89 Y4 90.22 C1 73.52 C2 69.30 C3 61.67 C4 75.69 C5 42.85

[0083] As can be seen from the data in Table 1 above, the relative crystallinity of the samples prepared by Examples 1, 2, 3, and 4 is significantly higher than that of the samples prepared by Comparative Examples 1, 2, 3, 4, and 5. This indicates that the SSZ-39 molecular sieve prepared by the present invention has a single crystalline phase and a high relative crystallinity.

[0084] (2) SEM testing

[0085] Figures 2-7 The scanning electron microscope images corresponding to the SSZ-39 molecular sieves prepared in Examples 1-6 of the present invention show that the prepared SSZ-39 molecular sieves have clear morphology, distinct particles, and crystals with a cubic or cuboid structure.

[0086] (3) BET test

[0087] The SSZ-39 molecular sieves synthesized in Examples 1-6 and Comparative Examples 1-4 of this invention were subjected to BET analysis, and the results are shown in Table 2.

[0088] Table 2. BET Test Result Statistics

[0089] Sample Name Total specific surface area (m 2 / g) Total pore volume (cm 3 / g) Y1 772.34 0.30 Y2 771.82 0.29 Y3 775.67 0.31 Y4 772.77 0.29 Y5 781.83 0.30 Y6 769.58 0.29 C1 630.72 0.26 C2 571.09 0.24 C3 502.11 0.23 C4 587.89. 0.24

[0090] As can be seen from the data in Table 2, the specific surface area and pore volume of the SSZ-39 molecular sieves prepared in Examples 1-6 are significantly higher than those prepared in Comparative Examples 1-4. This indicates that the SSZ-39 molecular sieves prepared by the present invention using natural clay as an aluminum source and part of the silicon source, and adding molecular sieve seed crystals, have a larger specific surface area and pore volume, which helps to improve its catalytic reaction performance.

[0091] (4) XRF testing

[0092] XRF analysis was performed on the SSZ-39 molecular sieves synthesized in Examples 1-6 and Comparative Examples 1-4 of this invention, and the results are shown in Table 3.

[0093] Table 3. Statistical Table of XRF Test Results

[0094]

[0095]

[0096] As can be seen from the data in Table 3, the silicon-to-aluminum ratio of the SSZ-39 molecular sieves prepared in Examples 1-6 is lower than that of the SSZ-39 molecular sieves prepared in Comparative Examples 1-4. This indicates that the SSZ-39 molecular sieve prepared in this invention is a low silicon-to-aluminum ratio molecular sieve.

[0097] (5) SCR catalytic activity test

[0098] Figure 8 The figure shows a comparison of the SCR activity test results of Cu-SSZ-39 molecular sieves with the same copper content, prepared by ion exchange treatment of SSZ-39 molecular sieve Y1 synthesized in Example 1 of the present invention and SSZ-39 molecular sieves C1 and C2 synthesized in Comparative Examples 1 and 2. As can be seen from the figure, the Cu-SSZ-39 molecular sieve prepared in Example 1 has superior SCR catalytic activity.

[0099] Figure 9 The figure shows a comparison of the SCR activity test results of Cu-SSZ-39 molecular sieve and Cu-SSZ-13 molecular sieve with the same copper content, prepared by ion exchange treatment of SSZ-39 molecular sieve Y1 synthesized in Example 1 of this invention and SSZ-13 molecular sieve standard sample C0. As can be seen from the figure, the SCR catalytic activity of Cu-SSZ-39 molecular sieve prepared in Example 1 is significantly better than that of Cu-SSZ-13 molecular sieve.

[0100] Figure 10 The figure shows a comparison of the SCR catalytic activity of Cu-SSZ-39 molecular sieve and Cu-SSZ-13 molecular sieve with the same copper content, prepared by ion exchange treatment of SSZ-39 molecular sieve Y1 synthesized in Example 1 of this invention and SSZ-13 molecular sieve standard sample C0, after hydrothermal aging treatment. As can be seen from the figure, the SCR catalytic activity of Cu-SSZ-39 molecular sieve prepared in Example 1 after hydrothermal aging treatment is still higher than that of Cu-SSZ-13 molecular sieve after hydrothermal aging treatment.

[0101] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the present invention. Various changes and modifications can be made to the present invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for synthesizing SSZ-39 molecular sieve with a low silica-to-alumina ratio, characterized in that, Includes the following steps: Template agent, silicon source, natural clay and molecular sieve seed crystals are added sequentially to an alkaline aqueous solution. After thorough stirring, an initial mixed gel is formed. The initial mixed gel solution is then transferred to a reaction vessel for hydrothermal crystallization treatment. After complete crystallization, the obtained crystallization solution is separated, washed, dried, and then calcined to obtain SSZ-39 molecular sieve with a low silicon-to-aluminum ratio; the natural clay is kaolin or montmorillonite; the silicon-to-aluminum oxide molar ratio of the kaolin is 1-5:1, and the silicon-to-aluminum oxide molar ratio of the montmorillonite is 5-15:1; the hydrothermal crystallization treatment includes first crystallizing at 25-40℃ for 1-24 hours, and then crystallizing at 140-180℃ for 48-72 hours; the hydrothermal crystallization treatment is dynamic crystallization; the calcination temperature is 550-600℃, and the calcination time is 6-12 hours.

2. The synthesis method according to claim 1, characterized in that, The molar ratio of Al2O3, SiO2, alkali source, template agent and water in the initial mixed gel is (0.02-0.05):1:(0.5-1):(0.05-0.3):(10-45).

3. The synthesis method according to claim 1, characterized in that: The molecular sieve seed crystals have a dual six-membered ring and eight-membered ring secondary structural unit configuration, and the molecular sieve structure is AEI, CHA, or FAU type; the molecular sieve seed crystals include one or more of SSZ-39 molecular sieve, SAPO-18 molecular sieve, AlPO-18 molecular sieve, SIZ-8 molecular sieve, SSZ-13 molecular sieve, HY molecular sieve, and USY molecular sieve; the molar ratio of silicon and aluminum oxide in the molecular sieve seed crystals is 0.1-15:1; the amount of molecular sieve seed crystals added is 1%-30% of the mass of SiO2 contained in the initial mixed gel.

4. The synthesis method according to claim 1, characterized in that, The molar ratio of silicon to aluminum oxide in the synthesized SSZ-39 molecular sieve is 5-18:

1.

5. The synthesis method according to claim 1, characterized in that, The silicon source is one or more of silica sol, tetraethyl orthosilicate, sodium silicate, and water glass; the SiO2 content in the silicon source is 10-40 wt%.

6. The synthesis method according to claim 1, characterized in that, The alkaline aqueous solution is one or more of sodium hydroxide or potassium hydroxide aqueous solution; the concentration of the alkaline aqueous solution is 0.5-40 wt%.

7. The synthesis method according to claim 1, characterized in that, The template agent is one or more of N,N-dimethyl-2,6-dimethylpiperidinium hydroxide, N,N-dimethyl-3,5-dimethylpiperidinium hydroxide, N,N-diethyl-2-ethylpiperidinium hydroxide, N-ethyl-N-methyl-2,6-dimethylpiperidinium hydroxide, tetraethylphosphonium hydroxide, tetrapropylphosphonium hydroxide, and tetrabutylphosphonium hydroxide; the template agent is an aqueous solution with a concentration of 20-40 wt%.

8. A catalyst for NH3-SCR catalytic reaction, characterized in that, Prepared by the method described in any one of claims 1 to 7.

Images