Method for seed-assisted synthesis of nanosized high-silica afx zeolite molecular sieves

Abstract

The application provides a method for seed-assisted synthesis of nanometer high-silicon AFX zeolite molecular sieve, and relates to the technical field of molecular sieve.The application mixes a silicon source, an aluminum source, water, an inorganic base, seeds and a template to obtain an initial gel; the initial gel is subjected to hydrothermal crystallization to obtain the nanometer high-silicon AFX zeolite molecular sieve; the seeds are one or more of SAPO-34, SAPO-44, SAPO-47, SAPO-5, SAPO-18, SAPO-56 and SSZ-16 molecular sieve seeds. The application adopts a traditional hydrothermal synthesis method, uses homogenous or heterogeneous seed-assisted structure-directing synthesis to obtain nanometer high-silicon AFX zeolite molecular sieve with a silicon-aluminum ratio of 7.3 and a particle size of 60-300 nm, and has a wide industrial application prospect in the future catalysis field of diesel vehicles and non-road mobile machinery, the field of conversion of non-petroleum resources to prepare low-carbon olefins and the like.

Description

Technical Field

[0001] This invention relates to the field of molecular sieve technology, and in particular to a method for seed-assisted synthesis of nano-high-silica AFX zeolite molecular sieves. Background Technology

[0002] Zeolites are crystalline microporous materials formed by interconnected TO4 tetrahedra (T = Si, Al), possessing uniform pores and voids, and exhibiting specific sizes and shapes within the molecular scale range. By controlling pore size, opening and cavity dimensions, organic and inorganic species can be separated, with geometric differences less than 10%. These remarkable shape selectivity properties, along with their high thermal and chemical stability, make them suitable for applications such as ion exchangers, adsorbents, or catalysts.

[0003] The crystal structure of AFX zeolite molecular sieve belongs to the hexagonal space group P63 / mmc and ABC-6, with a stacking sequence of AABBCCBB and a framework density of 15.1 t atoms / Through the construction of d6r, gme and aft cage are further formed. The AFX structure has a straight 8-ring channel. The three-dimensional pore system it forms belongs to the category of microporous molecular sieves with large pores. It serves as a highly efficient catalyst in the methanol-to-olefins (MTO) process, using ammonia as a reducing agent to reduce NO. x It plays an important role in selective catalytic reduction (SCR) and selective oxidation of methane to methanol.

[0004] However, there are currently few publications on AFX zeolite molecular sieves. This may be because the material is only synthesized under limited conditions, which results in products with a silicon-to-aluminum molar ratio of less than 5 and relatively large crystal sizes (2-3 μm).

[0005] Chinese patent CN202210875382.7 discloses a method for synthesizing high-silicon AFX-type zeolites using small-molecule organic structure-directing agents. This method utilizes a series of simple and inexpensive small-molecule organic template agents to synthesize high-silicon AFX zeolite molecular sieves, yielding a product with a silicon-to-aluminum ratio of 7.1, which is highly suitable for NH3-SCR reactions. This solves the current technical problem that the silicon-to-aluminum ratio of AFX zeolite molecular sieves is not higher than 5 (Si / Al < 5.0). However, this method can only obtain AFX-type zeolites with crystal sizes in the micrometer range.

[0006] Nanoscale molecular sieves possess excellent specific surface area and an abundant number of available active sites, which can effectively lead to improved catalytic reaction efficiency. Therefore, developing a simple and economical method to synthesize AFX zeolite molecular sieves with high silica-to-alumina ratio and nanocrystal size will be of great significance for further exploring their role in industrial catalysis. Summary of the Invention

[0007] In view of this, the purpose of this invention is to provide a method for seed-assisted synthesis of nano-high-silica AFX zeolite molecular sieves. The method of this invention can prepare high-silica, nano-sized AFX zeolite.

[0008] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0009] This invention provides a method for seed-assisted synthesis of nano-high-silica AFX zeolite molecular sieves, comprising the following steps:

[0010] The silicon source, aluminum source, water, inorganic base, seed crystals and template agent are mixed to obtain the initial gel;

[0011] The initial gel was subjected to hydrothermal crystallization to obtain the nano-high silica AFX zeolite molecular sieve;

[0012] The seed crystals are one or more of the following: SAPO-34, SAPO-44, SAPO-47, SAPO-5, SAPO-18, SAPO-56, and SSZ-16 molecular sieve seed crystals;

[0013] The silicon source is SiO2, the aluminum source is Al2O3, the inorganic base is M2O, and the molar ratio of SiO2, Al2O3, M2O, template agent and H2O in the initial gel is (20-60):1:(5-40):(3-20):(600-1500). The mass of the seed crystals in the initial gel is 1-10% of the mass of SiO2, and M in M2O is the metal element of the inorganic base.

[0014] Preferably, the silicon source is one or more of sodium silicate, silica fume, water glass, silica sol, and tetraethyl orthosilicate, and the aluminum source is one or more of sodium aluminate, aluminum isopropoxide, boehmite, aluminum chloride, aluminum sulfate, and aluminum hydroxide.

[0015] Preferably, the Y molecular sieve is used as both the silicon source and the aluminum source.

[0016] Preferably, the inorganic base is one or more of sodium carbonate, potassium carbonate, sodium hydroxide, and potassium hydroxide.

[0017] Preferably, the template agent is N,N′-diethyl-N,N,N′,N′-tetramethyl-1,6-hexanediamine hydroxide or hexamethyldiammonium hydroxide.

[0018] Preferably, the template agent is added in the form of an aqueous template agent solution, wherein the mass fraction of the aqueous template agent solution is 15-40%.

[0019] Preferably, the mixing method is as follows:

[0020] The inorganic base is dissolved in water to obtain an alkaline solution;

[0021] After cooling the alkaline solution to room temperature, a template agent, an aluminum source, a silicon source, and a seed crystal are added to it, and the mixture is stirred until homogeneous.

[0022] Preferably, the hydrothermal crystallization temperature is 120–200°C and the time is 1–7 days.

[0023] Preferably, after hydrothermal crystallization, the resulting crystallization reaction solution is further subjected to filtration, solid-phase washing, and drying in sequence, wherein the drying temperature is 75°C and the time is 24 hours.

[0024] Preferably, the nano-high silica AFX zeolite molecular sieve has a particle size of 60–300 nm and a silica-alumina molar ratio of 5.7–7.3.

[0025] This invention provides a method for seed-assisted synthesis of nano-high-silica AFX zeolite molecular sieves, comprising the following steps: mixing a silicon source, an aluminum source, water, an inorganic alkali, seed crystals, and a template agent to obtain an initial gel; subjecting the initial gel to hydrothermal crystallization to obtain the nano-high-silica AFX zeolite molecular sieves; wherein the seed crystals are one or more of SAPO-34, SAPO-44, SAPO-47, SAPO-5, SAPO-18, SAPO-56, and SSZ-16 molecular sieve seed crystals; wherein the silicon source is SiO2, the aluminum source is Al2O3, the inorganic alkali is M2O, and the molar ratio of SiO2, Al2O3, M2O, template agent, and H2O in the initial gel is (20-60):1:(5-40):(3-20):(600-1500), the mass of the seed crystals in the initial gel is 1-10% of the mass of SiO2, and M in M2O is a metal element of the inorganic alkali. This invention employs a traditional hydrothermal synthesis method, using homogeneous or heterogeneous seed crystals to assist in structure-guided synthesis, to obtain nano-high-silica AFX zeolite molecular sieves with a silicon-to-aluminum ratio of 5.7–7.3 and a particle size of 60–300 nm. These zeolites have broad industrial application prospects in the catalytic field of diesel vehicles and off-road mobile machinery, as well as in the conversion of non-petroleum resources into low-carbon olefins. Attached Figure Description

[0026] Figure 1 The XRD pattern of the high-silica AFX zeolite molecular sieve product synthesized in Example 1 is shown below.

[0027] Figure 2 The image shown is a scanning electron microscope (SEM) image of the high-silica AFX zeolite molecular sieve product synthesized in Example 1.

[0028] Figure 3 The XRD patterns of AFX molecular sieve products obtained by different seed-assisted synthesis in Examples 1-5 and Example 11 are shown.

[0029] Figure 4 The XRD patterns of AFX molecular sieve products synthesized with different organic template agents in Examples 5 and 10 are shown below.

[0030] Figure 5 This is a scanning electron microscope image of the high-silica AFX zeolite molecular sieve product synthesized in Example 11;

[0031] Figure 6 This is a scanning electron microscope image of the high-silica AFX zeolite molecular sieve product synthesized in Example 12;

[0032] Figure 7 The image shows a scanning electron microscope (SEM) image of the AFX zeolite molecular sieve product synthesized in Comparative Example 1.

[0033] Figure 8 The image shows a scanning electron microscope (SEM) image of the AFX zeolite molecular sieve product synthesized in Comparative Example 2. Detailed Implementation

[0034] This invention provides a method for seed-assisted synthesis of nano-high-silica AFX zeolite molecular sieves, comprising the following steps:

[0035] The silicon source, aluminum source, water, inorganic base, seed crystals and template agent are mixed to obtain the initial gel;

[0036] The initial gel was subjected to hydrothermal crystallization to obtain the nano-high silica AFX zeolite molecular sieve;

[0037] The seed crystals are one or more of the following: SAPO-34, SAPO-44, SAPO-47, SAPO-5, SAPO-18, SAPO-56, and SSZ-16 molecular sieve seed crystals;

[0038] The silicon source is SiO2, the aluminum source is Al2O3, the inorganic base is M2O, and the molar ratio of SiO2, Al2O3, M2O, template agent and H2O in the initial gel is (20-60):1:(5-40):(3-20):(600-1500). The mass of the seed crystals in the initial gel is 1-10% of the mass of SiO2, and M in M2O is the metal element of the inorganic base.

[0039] This invention mixes a silicon source, an aluminum source, water, an inorganic base, seed crystals, and a template agent to obtain an initial gel.

[0040] In this invention, the silicon source is preferably one or more of sodium silicate, silica, water glass, silica sol, and tetraethyl orthosilicate, more preferably silica; the aluminum source is preferably one or more of sodium aluminate, aluminum isopropoxide, boehmite, aluminum chloride, aluminum sulfate, and aluminum hydroxide, more preferably boehmite; or, preferably, Y molecular sieve is used as both the silicon source and the aluminum source, and the silicon-to-aluminum ratio of the Y molecular sieve is preferably 30. In this invention, when Y molecular sieve is used as both the silicon source and the aluminum source, the method for synthesizing AFX zeolite molecular sieve is a transcrystalline synthesis method.

[0041] In this invention, the water is preferably deionized water.

[0042] In this invention, the inorganic base is preferably one or more of sodium carbonate, potassium carbonate, sodium hydroxide, and potassium hydroxide, and more preferably sodium hydroxide.

[0043] In this invention, the seed crystals are one or more of SAPO-34, SAPO-44, SAPO-47, SAPO-5, SAPO-18, SAPO-56, and SSZ-16 molecular sieve seed crystals, wherein SAPO-34, SAPO-44, SAPO-47, SAPO-5, SAPO-18, and SAPO-56 are heterogeneous seed crystals, and SSZ-16 is a homogeneous seed crystal. In this invention, SAPO-56 is preferred as the seed crystal. This invention does not have particular requirements regarding the source of the seed crystals; they can be obtained from commercially available products or prepared using methods well-known to those skilled in the art.

[0044] In this invention, the template agent is preferably N,N′-diethyl-N,N,N′,N′-tetramethyl-1,6-hexanediamine hydroxide or hexamethyldiammonium hydroxide; the template agent is preferably added in the form of an aqueous template agent solution, and the mass fraction of the aqueous template agent solution is preferably 15-40%, more preferably 25%. This invention does not have particular requirements regarding the source of the template agent; it can be obtained from commercially available products or prepared using methods well known to those skilled in the art. In this invention, the N,N′-diethyl-N,N,N′,N′-tetramethyl-1,6-hexanediamine hydroxide is provided by Kent Catalytic Materials Co., Ltd., and its structural formula is as follows:

[0045]

[0046] In this invention, the mixing method is preferably:

[0047] The inorganic base is dissolved in water to obtain an alkaline solution;

[0048] After cooling the alkaline solution to room temperature, a template agent, an aluminum source, a silicon source, and a seed crystal are added to it, and the mixture is stirred until homogeneous.

[0049] In this invention, the silicon source is SiO2, the aluminum source is Al2O3 (when Y molecular sieve is used as both the silicon and aluminum source, the Y molecular sieve is SiO2 and Al2O3), the inorganic base is M2O, the molar ratio of SiO2, Al2O3, M2O, template agent and H2O in the initial gel is (20-60):1:(5-40):(3-20):(600-1500), preferably (30-40):1:(5-10):(5-10):(1000-1500), the mass of the seed crystals in the initial gel is 1-10% of the mass of SiO2, preferably 5-10%, and M in M2O is a metal element of the inorganic base.

[0050] After obtaining the initial gel, the present invention performs hydrothermal crystallization on the initial gel to obtain the nano-high silica AFX zeolite molecular sieve.

[0051] In this invention, the hydrothermal crystallization temperature is preferably 120–200°C, more preferably 150–160°C, and the time is preferably 1–7 days, more preferably 4–5 days. Preferably, the initial gel is placed in a stainless steel reactor lined with polytetrafluoroethylene for hydrothermal crystallization.

[0052] In this invention, after hydrothermal crystallization, the process preferably includes filtering, solid-phase washing, and drying the obtained crystallization reaction solution sequentially to obtain the nano-high-silica AFX zeolite molecular sieve; the solid-phase washing is preferably deionized water washing, and the drying temperature is preferably 75°C, and the drying time is preferably 24 hours.

[0053] In this invention, the particle size of the nano-high silica AFX zeolite molecular sieve is 60–300 nm, preferably 120–200 nm, and the silica-alumina molar ratio is 5.7–7.3. In embodiments of this invention, the silica-alumina molar ratio of the nano-high silica AFX zeolite molecular sieve is 5.7, 6.4, 7.1, or 7.3.

[0054] Currently, conventional synthesis readily yields AFX zeolite molecular sieves with crystal particle sizes of 5–10 micrometers. However, this invention synthesizes AFX zeolite molecular sieves with particle sizes of 60–300 nm. These nano-molecular sieves possess excellent specific surface area and a rich number of available active sites, which effectively improves their catalytic reaction efficiency. Furthermore, conventional synthesis often yields AFX zeolite molecular sieves with a Si / Al ratio of no more than 5, exhibiting low hydrothermal stability. In contrast, this invention synthesizes high-silica AFX zeolite molecular sieves with a Si / Al ratio as high as 7.3, demonstrating broad industrial application prospects in the catalytic field of diesel vehicles and off-road mobile machinery, as well as in the conversion of non-petroleum resources into low-carbon olefins.

[0055] Existing improvement techniques are relatively complex, either requiring specially designed template agents or other methods to obtain high silicon properties, or requiring post-processing or the introduction of crystal growth inhibitors to obtain nanoscale properties. This invention, by adding seed crystals, simultaneously yields high-silicon and nanoscale AFX zeolite, with a simple and economical synthesis method. By selecting specific seed crystals, this invention can reduce crystal size and alter the elemental composition of the zeolite, resulting in the simultaneous appearance of dual functionality: a high silicon-to-aluminum ratio and nanoscale size.

[0056] To further illustrate the present invention, the method for seed-assisted synthesis of nano-high-silica AFX zeolite molecular sieves provided by the present invention will be described in detail below with reference to examples, but these should not be construed as limiting the scope of protection of the present invention.

[0057] In each embodiment, OSDA1 is a 25% aqueous solution of N,N′-diethyl-N,N,N′,N′-tetramethyl-1,6-hexanediamine hydroxide, and OSDA2 is a 25% aqueous solution of hexamethyldiammonium hydroxide.

[0058] Example 1

[0059] The method for seed-assisted synthesis of nano-high-silica AFX zeolite molecular sieves is as follows:

[0060] (1) Add 0.18g of sodium hydroxide to 3.6mL of water and stir until dissolved.

[0061] (2) After the above solution has cooled to room temperature, add 2.7g OSDA1, 0.04g boehmite, and 0.05g SAPO-56 seed crystals, and stir for 1h.

[0062] (3) Add 0.5g of silica to the suspension obtained in step (2) and stir evenly at room temperature for 16 hours.

[0063] (4) The mixture obtained in step (3) is transferred to a stainless steel reactor with a polytetrafluoroethylene liner, and the crystallization temperature is 160°C and the crystallization time is 96h.

[0064] (5) The crystallized product was collected by filtration, washing and drying. The drying temperature was 75℃ and the drying time was 24h to obtain the product. The silicon-aluminum ratio (atomic ratio) of the product was determined to be 7.3.

[0065] Figure 1 The XRD pattern of the high-silica AFX zeolite molecular sieve product synthesized in Example 1 is consistent with the standard pattern, indicating high purity and crystallinity.

[0066] Figure 2 The image shown is a scanning electron microscope (SEM) image of the high-silica AFX zeolite molecular sieve product synthesized in Example 1. The product has a crystalline morphology and an average particle size of about 120 nm.

[0067] Example 2

[0068] The method for seed-assisted synthesis of nano-high-silica AFX zeolite molecular sieves is as follows:

[0069] (1) Add 0.25g of sodium hydroxide to 3.4mL of water and stir until dissolved.

[0070] (2) After the above solution is cooled to room temperature, add 4.2g OSDA1, 0.04g boehmite, and 0.06g SAPO-44 seed crystals, and stir for 1h.

[0071] (3) Add 0.6g of silica to the suspension obtained in step (2) and stir evenly at room temperature for 16 hours.

[0072] (4) The mixture obtained in step (3) is transferred to a stainless steel reactor with a polytetrafluoroethylene liner, and the crystallization temperature is 160°C and the crystallization time is 96h.

[0073] (5) The crystallized product was collected by filtration, washing and drying. The drying temperature was 75℃ and the drying time was 24h to obtain the product. The silicon-aluminum ratio of the product was measured to be 7.1.

[0074] Example 3

[0075] The method for seed-assisted synthesis of nano-high-silica AFX zeolite molecular sieves is as follows:

[0076] (1) Add 0.40g of sodium hydroxide to 6.8mL of water and stir until dissolved.

[0077] (2) After the above solution is cooled to room temperature, add 5.4g OSDA1, 0.04g boehmite, and 0.09g SAPO-5 seed crystals, and stir for 1h.

[0078] (3) Add 0.90g of silica to the suspension obtained in step (2) and stir evenly at room temperature for 16 hours.

[0079] (4) The mixture obtained in step (3) is transferred to a stainless steel reactor with a polytetrafluoroethylene liner, and the crystallization temperature is 160°C and the crystallization time is 96h.

[0080] (5) The crystallized product was collected by filtration, washing and drying. The drying temperature was 75℃ and the drying time was 24h to obtain the product. The silicon-aluminum ratio of the product was measured to be 6.4.

[0081] Example 4

[0082] The method for seed-assisted synthesis of nano-high-silica AFX zeolite molecular sieves is as follows:

[0083] (1) Add 0.21g of sodium hydroxide to 3.0mL of water and stir until dissolved.

[0084] (2) After the above solution is cooled to room temperature, add 2.9g OSDA1, 0.04g boehmite and 0.05g SAPO-18 seed crystals and stir for 1h.

[0085] (3) Add 0.5g of silica to the suspension obtained in step (2) and stir evenly at room temperature for 16 hours.

[0086] (4) The mixture obtained in step (3) is transferred to a stainless steel reactor with a polytetrafluoroethylene liner, and the crystallization temperature is 160°C and the crystallization time is 96h.

[0087] (5) The crystallized product was collected by filtration, washing and drying. The drying temperature was 75℃ and the drying time was 24h to obtain the product. The silicon-aluminum ratio of the product was measured to be 7.3.

[0088] Example 5

[0089] The method for seed-assisted synthesis of nano-high-silica AFX zeolite molecular sieves is as follows:

[0090] (1) Add 0.21g of sodium hydroxide to 3.4mL of water and stir until it is evenly dissolved.

[0091] (2) After the above solution is cooled to room temperature, add 2.6g OSDA1, 0.04g boehmite, and 0.06g SAPO-34 seed crystals, and stir for 1h.

[0092] (3) Add 0.6g of silica to the suspension obtained in step (2) and stir evenly at room temperature for 16 hours.

[0093] (4) The mixture obtained in step (3) is transferred to a stainless steel reactor with a polytetrafluoroethylene liner, and the crystallization temperature is 160°C and the crystallization time is 96h.

[0094] (5) The crystallized product was collected by filtration, washing and drying. The drying temperature was 75℃ and the drying time was 24h to obtain the product. The silicon-aluminum ratio of the product was measured to be 7.3.

[0095] Example 6

[0096] The method for seed-assisted synthesis of nano-high-silica AFX zeolite molecular sieves is as follows:

[0097] (1) Add 0.22g of sodium hydroxide to 3.8mL of water and stir until dissolved.

[0098] (2) After the above solution is cooled to room temperature, add 3.2g OSDA2, 0.04g boehmite, and 0.06g SAPO-56 seed crystals, and stir for 1h.

[0099] (3) Add 0.6g of silica to the suspension obtained in step (2) and stir evenly at room temperature for 16 hours.

[0100] (4) The mixture obtained in step (3) is transferred to a stainless steel reactor with a polytetrafluoroethylene liner, and the crystallization temperature is 160°C and the crystallization time is 96h.

[0101] (5) The crystallized product was collected by filtration, washing and drying. The drying temperature was 75℃ and the drying time was 24h to obtain the product. The silicon-aluminum ratio of the product was measured to be 7.3 and the average particle size was about 120nm.

[0102] Example 7

[0103] The method for seed-assisted synthesis of nano-high-silica AFX zeolite molecular sieves is as follows:

[0104] (1) Add 0.33g of sodium hydroxide to 4.2mL of water and stir until dissolved.

[0105] (2) After the above solution is cooled to room temperature, add 5.2g OSDA2, 0.04g boehmite, and 0.12g SAPO-44 seed crystals, and stir for 1h.

[0106] (3) Add 1.0 g of silica to the suspension obtained in step (2) and stir evenly at room temperature for 16 h.

[0107] (4) The mixture obtained in step (3) is transferred to a stainless steel reactor with a polytetrafluoroethylene liner, and the crystallization temperature is 160°C and the crystallization time is 96h.

[0108] (5) The crystallized product was collected by filtration, washing and drying. The drying temperature was 75℃ and the drying time was 24h to obtain the product. The silicon-aluminum ratio of the product was measured to be 5.7.

[0109] Example 8

[0110] The method for seed-assisted synthesis of nano-high-silica AFX zeolite molecular sieves is as follows:

[0111] (1) Add 0.19g of sodium hydroxide to 2.9mL of water and stir until dissolved.

[0112] (2) After the above solution has cooled to room temperature, add 5.1g OSDA2, 0.04g boehmite, and 0.08g SAPO-5 seed crystals, and stir for 1h.

[0113] (3) Add 0.80 g of silica to the suspension obtained in step (2) and stir evenly at room temperature for 16 h.

[0114] (4) The mixture obtained in step (3) is transferred to a stainless steel reactor with a polytetrafluoroethylene liner, and the crystallization temperature is 160°C and the crystallization time is 96h.

[0115] (5) The crystallized product was collected by filtration, washing and drying. The drying temperature was 75℃ and the drying time was 24h to obtain the product. The silicon-aluminum ratio of the product was measured to be 7.3.

[0116] Example 9

[0117] The method for seed-assisted synthesis of nano-high-silica AFX zeolite molecular sieves is as follows:

[0118] (1) Add 0.22g of sodium hydroxide to 1.9mL of water and stir until dissolved.

[0119] (2) After the above solution is cooled to room temperature, add 5.8g OSDA2, 0.04g boehmite, and 0.06g SAPO-18 seed crystals, and stir for 1h.

[0120] (3) Add 0.6g of silica to the suspension obtained in step (2) and stir evenly at room temperature for 16 hours.

[0121] (4) The mixture obtained in step (3) is transferred to a stainless steel reactor with a polytetrafluoroethylene liner, and the crystallization temperature is 160°C and the crystallization time is 96h.

[0122] (5) The crystallized product was collected by filtration, washing and drying. The drying temperature was 75℃ and the drying time was 24h to obtain the product. The silicon-aluminum ratio of the product was measured to be 7.3.

[0123] Example 10

[0124] The method for seed-assisted synthesis of nano-high-silica AFX zeolite molecular sieves is as follows:

[0125] (1) Add 0.22g of sodium hydroxide to 3.5mL of water and stir until dissolved.

[0126] (2) After the above solution has cooled to room temperature, add 4.2g OSDA2, 0.04g boehmite, and 0.06g SAPO-34 seed crystals, and stir for 1h.

[0127] (3) Add 0.6g of silica to the suspension obtained in step (2) and stir evenly at room temperature for 16 hours.

[0128] (4) The mixture obtained in step (3) is transferred to a stainless steel reactor with a polytetrafluoroethylene liner, and the crystallization temperature is 160°C and the crystallization time is 96h.

[0129] (5) The crystallized product was collected by filtration, washing and drying. The drying temperature was 75℃ and the drying time was 24 hours to obtain the product. The silicon-aluminum ratio of the product was determined to be 7.3.

[0130] Example 11

[0131] The method for seed-assisted synthesis of nano-high-silica AFX zeolite molecular sieves is as follows:

[0132] (1) Add 0.15g of sodium hydroxide to 3.6mL of water and stir until dissolved.

[0133] (2) After the above solution is cooled to room temperature, add 2.6g OSDA1, 0.04g boehmite, and 0.06g SSZ-16 seed crystals, and stir for 1h.

[0134] (3) Add 0.6g of silica to the suspension obtained in step (2) and stir evenly at room temperature for 16 hours.

[0135] (4) The mixture obtained in step (3) is transferred to a stainless steel reactor with a polytetrafluoroethylene liner, and the crystallization temperature is 160°C and the crystallization time is 96h.

[0136] (5) The crystallized product was collected by filtration, washing and drying. The drying temperature was 75℃ and the drying time was 24 hours to obtain the product. The silicon-aluminum ratio of the product was determined to be 7.3.

[0137] Tests showed that the particle size of the high-silica AFX zeolite molecular sieve products obtained in Examples 2-5 and Examples 7-10 was in the range of 60-300 nm.

[0138] Example 12

[0139] The method for seed-assisted synthesis of nano-high-silica AFX zeolite molecular sieves (Y-transformation synthesis and addition of SAPO-56 seed crystals) is as follows:

[0140] (1) Add 0.20g of sodium hydroxide to 7.8mL of water and stir until dissolved.

[0141] (2) After the above solution is cooled to room temperature, add 2.6g OSDA1, 1g Y molecular sieve (silicon-aluminum ratio of 30), and 0.06g SAPO-56 seed crystals, and stir for 24h.

[0142] (3) The mixture obtained in step (2) is transferred to a stainless steel reactor with a polytetrafluoroethylene liner, and the crystallization temperature is 160°C and the crystallization time is 96h.

[0143] (4) The crystallized product was collected by filtration, washing and drying. The drying temperature was 75℃ and the drying time was 24h to obtain the product. The silicon-aluminum ratio of the product was measured to be 7.3.

[0144] Figure 3 The XRD patterns of AFX molecular sieve products obtained by different seed-assisted synthesis in Examples 1-5 and Example 11 are consistent with the standard patterns, and have high purity and crystallinity.

[0145] Figure 4 The XRD patterns of the AFX molecular sieve products synthesized with different organic template agents in Examples 5 and 10 are consistent with the standard patterns, showing high purity and crystallinity.

[0146] Figure 5 The image shows a scanning electron microscope (SEM) image of the high-silica AFX zeolite molecular sieve product synthesized in Example 11, with a crystal size of approximately 200 nm.

[0147] Figure 6 The image shows a scanning electron microscope (SEM) image of the high-silica AFX zeolite molecular sieve product synthesized in Example 12, with a crystal size of approximately 160 nm.

[0148] Comparative Example 1

[0149] Similar to Example 1, except that no seed crystals were added, everything else was the same as in Example 1.

[0150] The obtained AFX zeolite molecular sieve had a silica-to-alumina ratio of 3.7 and a crystal size of approximately 10 μm. A scanning electron microscope image of the product is shown below. Figure 7 As shown.

[0151] Comparative Example 2

[0152] Referring to Experimental Example 6, except that seed crystals were not added, the rest was the same as in Example 6.

[0153] The obtained AFX zeolite molecular sieve had a silica-to-alumina ratio of 3.7 and a crystal size of approximately 6 μm. A scanning electron microscope image of the product is shown below. Figure 8 As shown.

[0154] As can be seen from the above embodiments, the present invention achieves a simple and convenient breakthrough by using seed crystals to obtain AFX molecular sieves that have both a high silicon-to-aluminum ratio and nanoscale size.

[0155] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for seed-assisted synthesis of nanosized high-silica AFX zeolite molecular sieves, characterized in that, The method comprises the following steps: mixing a silicon source, an aluminum source, water, an inorganic base, seed crystals and a template agent to obtain an initial gel; hydrothermally crystallizing the initial gel to obtain the nano-high-silicon AFX zeolite molecular sieve; the seed crystals are one or more of SAPO-34, SAPO-44, SAPO-47, SAPO-5, SAPO-18 and SAPO-56 molecular sieve seed crystals; the template agent is N,N'-diethyl-N,N,N',N'-tetramethyl-1,6-hexanediaminium hydroxide or hexamethonium hydroxide; the molar ratio of SiO2, Al2O3, M2O, template agent and H2O in the initial gel is (20-60):1:(5-40):(3-20):(600-1500), the mass of the seed crystals in the initial gel is 1-10% of the mass of SiO2, and M in the M2O is a metal element of the inorganic base; the nano-high-silicon AFX zeolite molecular sieve has a particle size of 60-300 nm and a silicon-aluminum molar ratio of 5.7-7.

3.

2. The method of claim 1, wherein, the silicon source is one or more of white carbon black, water glass, silica sol and tetraethyl orthosilicate, and the aluminum source is one or more of sodium aluminate, aluminum isopropoxide, pseudo-boehmite, aluminum chloride, aluminum sulfate and aluminum hydroxide.

3. The method of claim 1, wherein, Y zeolite is used as both the silicon source and the aluminum source.

4. The method of claim 1, wherein, the inorganic base is one or more of sodium carbonate, potassium carbonate, sodium hydroxide and potassium hydroxide.

5. The method of claim 1, wherein, the template agent is added in the form of a template agent aqueous solution, and the mass fraction of the template agent aqueous solution is 15-40%.

6. The method according to any one of claims 1 to 5, characterized in that, the mixing method is as follows: dissolving the inorganic base in water to obtain a base solution; after cooling the base solution to room temperature, adding the template agent, the aluminum source, the silicon source and the seed crystals thereto and stirring uniformly.

7. The method of claim 1, wherein, the temperature of the hydrothermal crystallization is 120-200°C, and the time is 1-7 days.

8. The method of claim 1, wherein, after the hydrothermal crystallization, the obtained crystallization reaction liquid is sequentially subjected to filtration, solid-phase washing and drying, and the temperature of the drying is 75°C, and the time is 24 h.

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