A Gemini quaternary ammonium base type structure directing agent and its preparation method, an AFX molecular sieve and its preparation method and application

Abstract

The present invention provides a gemini quaternary ammonium base type structure directing agent, a preparation method thereof, an AFX molecular sieve, a preparation method thereof and an application thereof, relating to the technical field of molecular sieves. The gemini quaternary ammonium base type structure directing agent provided by the present invention has a molecular formula of X+RX+2OH−, wherein R is an alkylbenzene, and X is an alkylpiperidinyl or an alkylpyrrolidinyl; the alkylpiperidinyl includes 1-methylpiperidinyl, 1-ethylpiperidinyl, 1-propylpiperidinyl, 1-propenylpiperidinyl or 1-butylpiperidinyl, and the alkylpyrrolidinyl includes 1-methylpyrrolidinyl, 1-ethylpyrrolidinyl, 1-propylpyrrolidinyl, 1-propenylpyrrolidinyl or 1-butylpyrrolidinyl. The AFX molecular sieve prepared with the obtained structure directing agent has a high silicon-aluminum molar ratio, good framework stability, high crystallinity and small morphology, is beneficial to the activity of acid sites in catalytic reactions and to improving the diffusion performance, and has high activity when applied to the selective catalytic reduction reaction of ammonia.

Description

Technical Field

[0001] The present invention relates to the technical field of molecular sieves, and in particular to a gemini quaternary ammonium base structure directing agent and a preparation method thereof, an AFX molecular sieve and a preparation method and application thereof. Background Art

[0002] 8-membered ring small pore molecular sieves exhibit excellent performance in treating smaller molecules and ions due to their special pore structure (pore diameter between 0.30 and 0.45 nm) and cage structure, and thus are widely used in the fields of adsorption separation and catalysis. In particular, in recent years, the successful commercial cases of SAPO-34 and SSZ-13 molecular sieves with CHA topological structure in the methane to olefins reaction (MTO) and the selective catalytic reduction of ammonia reaction (NH3-SCR) respectively have attracted wide attention to molecular sieves with the same three-dimensional 8-membered ring pore structure, such as AEI (SSZ-39), AFX (SSZ-16), LEV, and RHO molecular sieves.

[0003] Among them, the AFX molecular sieve, which belongs to the ABC-6 family together with the CHA molecular sieve, has a cage structure and pore characteristics similar to those of CHA, and has been regarded as a potential catalyst for NH3-SCR to replace SSZ-13 in recent years. The AFX framework structure has an elongated aft cage and a smaller gme cage, and the cage structures are connected by d6r structural units. Since 1982, when Zones first used 1,4-bis(1-azabicyclo[2.2.2]octane) dibromobutane as a structure directing agent (OSDAs) to synthesize aluminosilicate AFX (SSZ-16), the OSDAs currently used for synthesizing AFX molecular sieves are mainly N,N,N,N’,N’,N’-hexaethyl-1,5-pentanediammonium dibromide and 1-1’-(1,4-butylene)-bis(1,4-azabicyclo[2.2.2]octane). The obtained products mostly have a silica-alumina ratio of less than 6 and poor framework (hydro)thermal stability, and are prone to framework structure collapse in NH3-SCR, thereby limiting their application in the catalytic field. In recent years, the exploration of structure directing agents for the synthesis of AFX molecular sieves has continued. Jackowski et al. (Journal of the American Chemical Society, 2009, 131(3): 1092-1100; US11148953) found that 1-1’(1,4-butylene)-bis(methylpiperidine) and 1-1’(1,5-pentylene)-bis(methylpiperidine) have high Na +AFX zeolite can be directionally generated in the system. Subsequently, Martinez Franco et al. (US 20210188651) replaced the bridging carbon chain group with 1,6-hexanediyl or 1,7-heptanediyl and also used it for the synthesis of AFX zeolite. Davis et al. (ACS Catalysis, 2012, 2(12): 2490-2495) used 1,3-bis(1-adamantyl)imidazolium salt to obtain the AFX zeolite with the highest silicon-aluminum ratio (Si / Al = 16.8) so far. However, the preparation process of this structure-directing agent is complex and costly, making it difficult to achieve industrial scale-up. Nakazawa et al. (Advanced Porous Materials, 2016, 4: 219-229) used TEBOP as the OSDA to synthesize AFX zeolite with a silicon-aluminum ratio between 4.6 and 8.4, which has high crystallinity and hydrothermal stability. And Chokkalingam et al. used TEBOP as the structure-directing agent to achieve the ultra-fast synthesis of SSZ-16 zeolite in a tubular reactor, and the crystallization time can be shortened from 4 days to 2 hours. Corma et al. (Applied Catalysis B: Environmental, 2017, 217: 125-136) have also been continuously exploring new OSDAs. In 2017, they prepared two large-volume and rigid-structure OSDAs, which can direct the generation of ERI (K + ) and AFX (Na + ) according to different inorganic cations. Elomari et al. (US20170334732) used 1,1'-(1,4-cyclohexylbis(methylene))bis(1-methylpiperidine), 1,1'-(1,4-cyclohexylbis(methylene))bis(1-ethylpiperidine) and 1,1'-(1,4-cyclohexylbis(methylene))bis(1-ethylpyrrole) as structure-directing agents and successfully synthesized AFX zeolite. For these newly developed OSDAs, the rigidity has been improved. Although the silicon-aluminum ratio of the product has been increased to a certain extent, due to their difficult synthesis and high raw material prices, it is difficult to develop, and thus there are few follow-up research reports.

[0004] Generally speaking, as a catalyst, the synthesis and application of AFX zeolite mainly face the following problems: (1) Most of the reported structure-directing agents currently have insufficient rigidity and weak interaction with the framework of AFX zeolite, resulting in a Si / Al < 6 in the synthesized product, poor (hydro)thermal stability, and poor catalyst activity; (2) There are few structure-directing agents that can synthesize AFX zeolite with Si / Al > 6, and they are expensive, making it difficult to achieve industrial applications. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a gemini quaternary ammonium base type structure directing agent, a preparation method thereof, an AFX molecular sieve, a preparation method thereof and an application thereof. The gemini quaternary ammonium base type structure directing agent provided by the present invention has low cost, and the AFX molecular sieve prepared therefrom has a high silicon-aluminum molar ratio (Si / Al>6) and high SCR activity.

[0006] In order to achieve the above-mentioned invention purpose, the present invention provides the following technical solutions:

[0007] The present invention provides a gemini quaternary ammonium base type structure directing agent with the molecular formula X + RX + 2OH - , where R is an alkylbenzene, and X is an alkylpiperidinyl or an alkylpyrrolidinyl; the alkylbenzene includes 1,4-phenylenebis(methylene) or 1,3-phenylenebis(methylene), the alkylpiperidinyl includes 1-methylpiperidinyl, 1-ethylpiperidinyl, 1-propylpiperidinyl, 1-propenylpiperidinyl or 1-butylpiperidinyl, and the alkylpyrrolidinyl includes 1-methylpyrrolidinyl, 1-ethylpyrrolidinyl, 1-propylpyrrolidinyl, 1-propenylpyrrolidinyl or 1-butylpyrrolidinyl.

[0008] The present invention provides a preparation method of the gemini quaternary ammonium base type structure directing agent as described in the above technical solution, including the following steps:

[0009] Mixing a dihaloxylene, a tertiary amine and an organic solvent for a substitution reaction to obtain a gemini quaternary ammonium salt; the dihaloxylene includes dihalo-p-xylene or dihalo-m-xylene; the tertiary amine includes an alkylpiperidine or an alkylpyrrolidine, the alkylpiperidine includes 1-methylpiperidine, 1-ethylpiperidine, 1-propylpiperidine, 1-propenylpiperidine or 1-butylpiperidine, and the alkylpyrrolidine includes 1-methylpyrrolidine, 1-ethylpyrrolidine, 1-propylpyrrolidine, 1-propenylpyrrolidine or 1-butylpyrrolidine;

[0010] Performing anion exchange on the halogen ion in the gemini quaternary ammonium salt with a hydroxide ion to obtain the gemini quaternary ammonium base type structure directing agent.

[0011] Preferably, the molar ratio of the dihaloxylene to the tertiary amine is 1:2 to 6.

[0012] Preferably, the temperature of the substitution reaction is 60 to 100 °C, and the time is 10 to 120 h.

[0013] The present invention provides a preparation method of an AFX molecular sieve, including the following steps:

[0014] Mixing a silicon source, an aluminum source, an alkali source, a structure directing agent, water and an SSZ-16 molecular sieve seed crystal to obtain a molecular sieve mother liquor;

[0015] Hydrothermally crystallize the molecular sieve mother liquor, and calcine the obtained hydrothermally crystallized product to obtain an AFX molecular sieve;

[0016] The structure directing agent is the gemini quaternary ammonium base type structure directing agent described in the above technical solution or the gemini quaternary ammonium base type structure directing agent prepared by the preparation method described in the above technical solution.

[0017] Preferably, the silicon source includes one or more of sodium silicate, silica sol, precipitated silica and FAU molecular sieve; the aluminum source includes one or more of aluminum chloride, aluminum sulfate, aluminum hydroxide, sodium aluminate and FAU molecular sieve; the base source includes one or more of sodium hydroxide, potassium hydroxide and sodium silicate.

[0018] Preferably, the silicon source, aluminum source and base source are calculated as SiO2, Al2O3 and alkali metal respectively. The molar ratio of the silicon source, aluminum source, base source, structure directing agent and water in the molecular sieve mother liquor is 1:(0.02 - 0.05):(0.10 - 0.50):(0.10 - 1.00):(10 - 50), and the mass of the SSZ-16 molecular sieve seed crystal is 3 - 5% of the mass of the silicon source.

[0019] Preferably, the temperature of the hydrothermal crystallization is 130 - 170 °C and the time is 72 - 120 h; the temperature of the calcination is 350 - 700 °C and the time is 6 - 10 h.

[0020] The present invention provides an AFX molecular sieve prepared by the preparation method described in the above technical solution, and the silicon-aluminum molar ratio of the AFX molecular sieve is greater than 6.

[0021] The present invention provides the application of the AFX molecular sieve described in the above technical solution as a catalyst in the selective catalytic reduction reaction of ammonia.

[0022] The present invention provides a gemini quaternary ammonium base type structure directing agent with the molecular formula X + RX + 2OH -, where R is alkylbenzene and X is alkylpiperidinyl or alkylpyrrolidinyl; the alkylbenzene includes 1,4-phenylenebis(methylene) or 1,3-phenylenebis(methylene), the alkylpiperidinyl includes 1-methylpiperidinyl, 1-ethylpiperidinyl, 1-propylpiperidinyl, 1-propenylpiperidinyl or 1-butylpiperidinyl, and the alkylpyrrolidinyl includes 1-methylpyrrolidinyl, 1-ethylpyrrolidinyl, 1-propylpyrrolidinyl, 1-propenylpyrrolidinyl or 1-butylpyrrolidinyl. The present invention provides a structure-directing agent with a new structure. For the first time, it is used in the synthesis of AFX zeolite, and AFX zeolite with an adjustable silicon-aluminum ratio can be directly synthesized by a one-step hydrothermal method. The structure-directing agent provided by the present invention has a low stabilization energy, better matches the internal framework size of AFX zeolite, and the structure-directing agent with a benzene ring is more rigid. Using the structure-directing agent provided by the present invention to prepare AFX zeolite, the obtained AFX zeolite has a high silicon-aluminum molar ratio (Si / Al>6), good framework stability, high crystallinity of the AFX zeolite, and small morphology, which is beneficial to the activity of the acidic sites in the catalytic reaction and improves the diffusion performance, and has high activity in the selective catalytic reduction reaction of ammonia.

[0023] The present invention provides a preparation method of the gemini quaternary ammonium base type structure-directing agent described in the above technical solution. The raw materials are cheap and easy to obtain, the cost is low, the preparation process is simple, and it is easy to realize industrial scale-up. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 XRD pattern of the AFX zeolite hydrothermally synthesized with OSDA1 as the structure-directing agent in Example 3;

[0025] Figure 2 XRD pattern of the AFX zeolite synthesized by FAU conversion with OSDA1 as the structure-directing agent in Example 4;

[0026] Figure 3 XRD pattern of the AFX zeolite hydrothermally synthesized with OSDA2 as the structure-directing agent in Example 5;

[0027] Figure 4 XRD pattern of the AFX zeolite synthesized by FAU conversion with OSDA2 as the structure-directing agent in Example 6;

[0028] Figure 5 SEM image of the AFX zeolite synthesized by FAU conversion with OSDA1 as the structure-directing agent in Example 4;

[0029] Figure 6 SEM image of the AFX zeolite synthesized by FAU conversion with OSDA2 as the structure-directing agent in Example 6;

[0030] Figure 7This is a diagram for the NH3-SCR reaction evaluation of three Cu-type AFX catalysts prepared using the structure-directing agents in the comparative examples and OSDA1 and OSDA2 as structure-directing agents. Detailed implementation mode

[0031] The present invention provides a gemini quaternary ammonium base type structure-directing agent with the molecular formula X + RX + 2OH - , where R is an alkylbenzene and X is an alkylpiperidinyl or alkylpyrrolidinyl; the alkylbenzene includes 1,4-phenylenebis(methylene) or 1,3-phenylenebis(methylene), the alkylpiperidinyl includes 1-methylpiperidinyl, 1-ethylpiperidinyl, 1-propylpiperidinyl, 1-propenylpiperidinyl or 1-butylpiperidinyl, preferably 1-methylpiperidinyl or 1-ethylpiperidinyl, and the alkylpyrrolidinyl includes 1-methylpyrrolidinyl, 1-ethylpyrrolidinyl, 1-propylpyrrolidinyl, 1-propenylpyrrolidinyl or 1-butylpyrrolidinyl, preferably 1-methylpyrrolidinyl or 1-ethylpyrrolidinyl.

[0032] The present invention provides a novel structure-directing agent which has a gemini quaternary ammonium salt structure, that is, it contains quaternary ammonium salt structures at both ends and is connected by an alkylbenzene in the middle.

[0033] The present invention provides a preparation method of the gemini quaternary ammonium base type structure-directing agent as described in the above technical solution, including the following steps:

[0034] Mixing a dihaloxylene, a tertiary amine and an organic solvent to carry out a substitution reaction to obtain a gemini quaternary ammonium salt; the dihaloxylene includes p-dihaloxylene or m-dihaloxylene; the tertiary amine includes an alkylpiperidine or an alkylpyrrolidine, the alkylpiperidine includes 1-methylpiperidine, 1-ethylpiperidine, 1-propylpiperidine, 1-propenylpiperidine or 1-butylpiperidine, and the alkylpyrrolidine includes 1-methylpyrrolidine, 1-ethylpyrrolidine, 1-propylpyrrolidine, 1-propenylpyrrolidine or 1-butylpyrrolidine;

[0035] Performing an anion exchange on the halogen ion in the gemini quaternary ammonium salt with a hydroxide ion to obtain the gemini quaternary ammonium base type structure-directing agent.

[0036] In the present invention, unless otherwise specified, the raw materials involved are commercially available products well-known to those skilled in the art.

[0037] The present invention mixes a dihaloxylene, a tertiary amine and an organic solvent to carry out a substitution reaction to obtain a gemini quaternary ammonium salt.

[0038] In the present invention, the dihaloxylene includes para-dihaloxylene or meta-dihaloxylene. The halogen groups in the para-dihaloxylene and meta-dihaloxylene are preferably bromine, chlorine or iodine. In the embodiments of the present invention, the dihaloxylene is preferably p-dibromoxylene or m-dibromoxylene. In the present invention, the tertiary amine includes alkylpiperidine or alkylpyrrolidine. The alkylpiperidine includes 1-methylpiperidine, 1-ethylpiperidine, 1-propylpiperidine, 1-propenylpiperidine or 1-butylpiperidine, preferably 1-methylpiperidine or 1-ethylpiperidine. The alkylpyrrolidine includes 1-methylpyrrolidine, 1-ethylpyrrolidine, 1-propylpyrrolidine, 1-propenylpyrrolidine or 1-butylpyrrolidine, preferably 1-methylpyrrolidine or 1-ethylpyrrolidine. In the present invention, the molar ratio of the dihaloxylene to the tertiary amine is preferably 1:2 to 6, more preferably 1:2.5 to 3.5.

[0039] In the present invention, the organic solvent is preferably acetonitrile. The present invention has no special requirements for the amount of the organic solvent, as long as it can ensure the smooth progress of the reaction.

[0040] In the present invention, the method for mixing the dihaloxylene, the tertiary amine and the organic solvent is preferably as follows: adding the dihaloxylene to the organic solvent and stirring until completely dissolved to obtain a dihaloxylene solution; dropping the tertiary amine into the dihaloxylene solution.

[0041] In the present invention, the temperature of the substitution reaction is preferably 60 to 100 °C, more preferably 80 °C, the time is preferably 10 to 120 h, more preferably 40 to 60 h, and further preferably 48 h. The substitution reaction is preferably carried out under reflux conditions. After the substitution reaction is completed, the present invention preferably recrystallizes, filters and dries the obtained reaction product in sequence to obtain the gemini quaternary ammonium salt. In the present invention, the reagent used for recrystallization is preferably ether; the drying temperature is preferably 70 °C and the time is preferably 8 h.

[0042] After obtaining the gemini quaternary ammonium salt, the present invention conducts anion exchange between the halogen ions and hydroxide ions in the gemini quaternary ammonium salt to obtain the gemini quaternary ammonium hydroxide structure-directing agent. In the present invention, the anion exchange preferably uses an anion exchange resin, and the anion exchange resin is preferably a 717 anion exchange resin. In the present invention, the method of anion exchange is preferably as follows: dissolve the gemini quaternary ammonium salt in water, then add the anion exchange resin to the solution for anion exchange; filter the mixed solution after anion exchange, and perform rotary evaporation on the obtained filtrate to remove part of the water. The present invention has no special requirements for the amount of water added, as long as the gemini quaternary ammonium salt is fully dissolved; the time for anion exchange is preferably 12 h; in the examples of the present invention, the rotary evaporation is carried out to obtain a solution with a mass fraction of 25%, and the structure-directing agent is used in the form of a solution, which is more stable. Through anion exchange, the present invention exchanges the halogen ions in the gemini quaternary ammonium salt into OH - , that is, exchanges the quaternary ammonium salt into quaternary ammonium hydroxide, thereby obtaining the gemini quaternary ammonium hydroxide structure-directing agent.

[0043] The preparation method of the structure-directing agent provided by the present invention is simple, the raw materials are cheap and easy to obtain, and it is easy to realize industrial scale-up.

[0044] The present invention provides a method for preparing an AFX molecular sieve, comprising the following steps:

[0045] Mix a silicon source, an aluminum source, an alkali source, a structure-directing agent, water, and SSZ-16 molecular sieve seeds to obtain a molecular sieve mother liquor;

[0046] Perform hydrothermal crystallization on the molecular sieve mother liquor, and calcine the obtained hydrothermal crystallization product to obtain an AFX molecular sieve;

[0047] The structure-directing agent is the gemini quaternary ammonium hydroxide structure-directing agent described in the above technical solution or the gemini quaternary ammonium hydroxide structure-directing agent prepared by the preparation method described in the above technical solution.

[0048] In the present invention, a silicon source, an aluminum source, an alkali source, a structure-directing agent, water and SSZ-16 molecular sieve seeds are mixed to obtain a molecular sieve mother liquor. In the present invention, the silicon source preferably includes one or more of sodium silicate, silica sol, fumed silica and FAU molecular sieve, and the Si / Al ratio (molar ratio) of the FAU molecular sieve is preferably 2.73 to 15; the aluminum source preferably includes one or more of aluminum chloride, aluminum sulfate, aluminum hydroxide, sodium metaaluminate and FAU molecular sieve, and the Si / Al ratio of the FAU molecular sieve is preferably 2.73 to 15; the alkali source preferably includes one or more of sodium hydroxide, potassium hydroxide and sodium silicate, that is, the AFX molecular sieve is synthesized in an alkaline system; when the alkali source includes sodium silicate, the sodium silicate serves as the silicon source at the same time. In the present invention, the water is preferably deionized water. In the present invention, the silicon source, the aluminum source and the alkali source are calculated in terms of SiO2, Al2O3 and alkali metal respectively, and the molar ratio of the silicon source, the aluminum source, the alkali source, the structure-directing agent and water in the molecular sieve mother liquor is preferably 1:(0.02 - 0.05):(0.10 - 0.50):(0.10 - 1.00):(10 - 50); the mass of the SSZ-16 molecular sieve seeds is preferably 3 to 5% of the mass of the silicon source. In the present invention, a certain amount of SSZ-16 molecular sieve is added as seeds to induce crystallization.

[0049] In the present invention, the method for mixing the silicon source, the aluminum source, the alkali source, the structure-directing agent, water and SSZ-16 molecular sieve seeds is preferably as follows: the structure-directing agent, the alkali source and water are stirred evenly at room temperature to obtain a first mixed solution; the aluminum source is added to the first mixed solution and stirred evenly to obtain a second mixed solution; the silicon source is added to the second mixed solution and stirred evenly to obtain a third mixed solution; the third mixed solution is transferred to a hydrothermal autoclave, and SSZ-16 molecular sieve seeds are added thereto to obtain a molecular sieve mother liquor.

[0050] After obtaining the molecular sieve mother liquor, in the present invention, the molecular sieve mother liquor is hydrothermally crystallized, and the obtained hydrothermally crystallized product is calcined to obtain an AFX molecular sieve. In the present invention, the temperature of the hydrothermal crystallization is preferably 130 to 170 °C, more preferably 150 to 160 °C, and the time is preferably 72 to 120 h, more preferably 72 to 100 h. In the present invention, the hydrothermal crystallization is preferably carried out under dynamic conditions. Specifically, the reaction kettle for hydrothermal crystallization is placed in an oven, and the reaction kettle is kept rotating. The rotation rate is preferably 50 revolutions per minute. After the hydrothermal reaction is completed, in the present invention, the obtained reaction solution is preferably centrifuged, solid-phase washed and dried in sequence to obtain a hydrothermally crystallized product. In the present invention, the temperature of the calcination is preferably 350 to 700 °C, more preferably 500 °C, the time is preferably 6 to 10 h, and the heating rate from room temperature to the calcination temperature is preferably 1 °C·min -1 ; in the present invention, through calcination, the organic structure-directing agent and water in the molecular sieve are removed.

[0051] For the first time, the above novel structure-directing agent is used and added to inorganic raw materials, and an AFX molecular sieve of aluminosilicate with adjustable silicon-aluminum ratio can be directly synthesized by one-step hydrothermal method, and the synthesis window is relatively wide.

[0052] The present invention provides an AFX molecular sieve prepared by the preparation method described in the above technical solution, and the silicon-aluminum molar ratio of the AFX molecular sieve is greater than 6, preferably greater than 6 and less than or equal to 8.5.

[0053] The present invention provides the application of the AFX molecular sieve described in the above technical solution as a catalyst in the selective catalytic reduction reaction of ammonia (NH3-SCR). The AFX molecular sieve provided by the present invention has a high silicon-aluminum molar ratio (Si / Al>6), good framework stability, and can still maintain its stability after hydrothermal aging at 850 °C; and the AFX molecular sieve has high crystallinity and small morphology, which is beneficial to the activity of catalytic reaction acid sites and improves the diffusion performance, and has high activity when applied to the selective catalytic reduction reaction of ammonia. The present invention has no special requirements for the application method, and the application methods well-known to those skilled in the art can be adopted.

[0054] In order to further illustrate the present invention, the gemini quaternary ammonium base type structure-directing agent provided by the present invention, its preparation method, the AFX molecular sieve, its preparation method and application will be described in detail below with reference to examples, but they cannot be understood as limiting the protection scope of the present invention.

[0055] Example 1

[0056] Synthesis of structure-directing agent (denoted as OSDA1):

[0057] Add raw material p-xylene dibromide (0.05 mol) to 250 mL of acetonitrile solvent. After stirring until completely dissolved, slowly drop 1-methylpiperidine (0.13 mol) into the above solution, and reflux at 80 °C for 48 h. After washing with ether and recrystallization, filter and dry at 70 °C for 8 h to obtain a white solid. Subsequently, Br - is exchanged into OH - , and part of the water is removed by rotary evaporation to obtain a 25 wt% solution denoted as structure-directing agent OSDA1.

[0058] Example 2

[0059] Synthesis of structure-directing agent (denoted as OSDA2):

[0060] Add raw material p - dibromoxylene (0.05 mol) into 250 mL of acetonitrile solvent. After stirring until completely dissolved, slowly add 1 - methylpyrrolidine (0.13 mol) to the above - mentioned solution. React under reflux at 80 °C for 48 h. After washing with ether and recrystallization, filter and dry at 70 °C for 8 h to obtain a white solid. Subsequently, use 717 ion - exchange resin to exchange Br - into OH - , and remove part of the water by rotary evaporation to obtain a 25 wt% solution denoted as structure - directing agent OSDA2.

[0061] Table 1 lists the structural formulas and chemical names of the structure - directing agents obtained in Example 1 and Example 2:

[0062] Table 1 Structural Formulas and Chemical Names of Structure - Directing Agents in Examples 1 - 2

[0063]

[0064] Comparative Example 1

[0065] Add 36.7 mmol of raw material p - dibromoxylene into 500 mL of ethanol. After stirring until completely dissolved, slowly add an excessive amount of triethylamine (73.4 mmol) to the above - mentioned solution. Heat and reflux at 80 °C for 48 h. After washing with ether and recrystallization, filter and dry at 70 °C for 8 h to obtain a white solid. Subsequently, use 717 ion - exchange resin to exchange Br - into OH - , and remove part of the water by rotary evaporation to obtain a 25 wt% solution denoted as structure - directing agent DB.

[0066] Example 3

[0067] Using the OSDA1 obtained in Example 1 as the structure - directing agent and sodium aluminate as the aluminum source to synthesize AFX zeolite, the steps are as follows:

[0068] (1) Weigh 2.3051 g of structure - directing agent OSDA1 and 0.1481 g of deionized water, and stir evenly at room temperature;

[0069] (2) Add 0.1025 g of sodium aluminate to the solution obtained in step (1), and stir evenly again;

[0070] (3) Add 4.5326 g of sodium silicate aqueous solution (SiO₂: 23.1 wt%, Na₂O: 5.96 wt%) and 0.0610 g of silica sol to the solution obtained in step (2), and stir to form a homogeneous solution;

[0071] (4) Transfer the obtained solution to a 100 - mL hydrothermal autoclave, add 0.05 g of SSZ - 16 zeolite as seeds, and carry out hydrothermal crystallization dynamically (rotation speed 50 r / min) at 150 °C for 72 h;

[0072] (5) Centrifuge, wash, and dry the solid obtained in (4), and then calcine it to obtain a pure-phase AFX molecular sieve.

[0073] Figure 1 XRD pattern of the AFX molecular sieve hydrothermally synthesized with OSDA1 as the structure-directing agent in Example 3. It is detected as the crystal phase structure of the AFX molecular sieve by X-ray diffraction (XRD).

[0074] Example 4

[0075] Using the OSDA1 obtained in Example 1 as the structure-directing agent and the Y molecular sieve with FAU structure as the aluminum source, synthesize the AFX molecular sieve. The steps are as follows:

[0076] (1) Weigh 2.7661 g of OSDA1, 0.1786 g of sodium hydroxide, and 0.5923 g of deionized water, and stir evenly at room temperature;

[0077] (2) Add 0.2289 g of FAU (Si / Al = 5.5) as the aluminum source to the solution obtained in step (1), and stir to form a homogeneous solution;

[0078] (3) Add 0.4455 g of silica white to the solution obtained in step (2), transfer the resulting solution to a 100 mL hydrothermal autoclave, and add 0.05 g of SSZ-16 molecular sieve as a seed crystal. Hydrothermally crystallize dynamically (rotation speed 50 r / min) at 150 °C for 72 h;

[0079] (5) Centrifuge, wash, and dry the solid obtained in (4), and then calcine it to obtain a pure-phase AFX molecular sieve.

[0080] Figure 2 XRD pattern of the AFX molecular sieve synthesized by FAU conversion with OSDA1 as the structure-directing agent in Example 4. It is detected as the crystal phase structure of the AFX molecular sieve by X-ray diffraction (XRD).

[0081] Figure 5 SEM image of the AFX molecular sieve synthesized by FAU conversion with OSDA1 as the structure-directing agent in Example 4. It can be seen from Figure 5 that a pure-phase AFX molecular sieve with uniform crystal form has been successfully synthesized, and the grain size is about 100 nm, with a hexagonal prism morphology.

[0082] Example 5

[0083] Using the OSDA2 obtained in Example 2 as the structure-directing agent and sodium aluminate as the aluminum source, synthesize the AFX molecular sieve. The steps are as follows:

[0084] (1) Weigh 2.1712 g of the structure-directing agent OSDA2 and 0.2319 g of deionized water, and stir evenly at room temperature;

[0085] (2) Add 0.1025 g of sodium aluminate to the solution obtained in step (1), and stir evenly again;

[0086] (3) Add 4.5326 g of sodium silicate aqueous solution (SiO2: 23.1 wt%, Na2O: 5.96 wt%) and 0.0610 g of silica sol to the solution obtained in step (2), and stir to form a homogeneous solution;

[0087] (4) Transfer the obtained solution to a 100 mL hydrothermal autoclave, add 0.05 g of SSZ-16 molecular sieve as a seed crystal, and carry out hydrothermal crystallization at 150 °C under dynamic conditions (rotation speed 50 r / min) for 72 h;

[0088] (5) Centrifuge, wash, and dry the solid obtained in (4), and calcine to obtain a pure-phase AFX molecular sieve.

[0089] Figure 3 It is the XRD pattern of the AFX molecular sieve hydrothermally synthesized using OSDA2 as the structure-directing agent in Example 5, and the crystal phase structure of the AFX molecular sieve is detected by X-ray diffraction (XRD).

[0090] Example 6

[0091] Using the OSDA2 obtained in Example 2 as the structure-directing agent and the Y molecular sieve with FAU structure as the aluminum source, synthesize the AFX molecular sieve. The steps are as follows:

[0092] (1) Weigh 0.1786 g of sodium hydroxide, 2.9312 g of the structure-directing agent OSDA2, and 0.5923 g of deionized water, and stir evenly at room temperature;

[0093] (2) Add 0.2289 g of FAU (Si / Al = 5.5) as the aluminum source to the solution obtained in step (1), and stir to form a homogeneous solution;

[0094] (3) Weigh 0.4455 g of fumed silica as the silicon source and add it to step (2). Transfer the obtained solution to a 100 mL hydrothermal autoclave, add 0.05 g of SSZ-16 molecular sieve as a seed crystal, and carry out hydrothermal crystallization at 150 °C under dynamic conditions (rotation speed 50 r / min) for 72 h;

[0095] (4) Centrifuge, wash, and dry the solid obtained in (3), and calcine to obtain a pure-phase AFX molecular sieve.

[0096] Figure 4XRD pattern of Example 6 for the synthesis of AFX zeolite by the conversion of FAU using OSDA2 as the structure-directing agent, which is detected by X-ray diffraction (XRD) as the crystal phase structure of AFX zeolite.

[0097] Figure 6 SEM image of Example 6 for the synthesis of AFX zeolite by the conversion of FAU using OSDA2 as the structure-directing agent. Figure 6 It can be seen that the synthesized AFX zeolite has a uniform morphology, with a particle size of about 200 nm and excellent crystal morphology.

[0098] Comparative Example 2

[0099] Using the DB obtained in Comparative Example 1 as the structure-directing agent and the Y zeolite with FAU structure as the aluminum source, AFX zeolite was synthesized. The steps are as follows:

[0100] (1) Weigh 0.344 g of sodium hydroxide, 0.459 g of the structure-directing agent DB and 5.4 g of deionized water, and stir evenly at room temperature;

[0101] (2) Add 0.215 g of FAU (Si / Al = 2.7) as the aluminum source to the solution obtained in step (1), and stir to form a homogeneous solution;

[0102] (3) Weigh 0.737 g of silica as the silicon source and add it to step (2). Transfer the obtained solution to a 100 mL hydrothermal autoclave, and carry out dynamic (rotation speed 50 r / min) hydrothermal crystallization at 140 °C for 48 h;

[0103] (4) Centrifuge, wash and dry the solid obtained in (3), and calcine to obtain a pure-phase AFX zeolite.

[0104] Application Example

[0105] The AFX zeolites synthesized with the structure-directing agents OSDA1 and OSDA2 in Example 4 and Example 6, and the AFX zeolite synthesized with the structure-directing agent DB in Comparative Example 2 were used for the selective catalytic reduction of ammonia (NH3-SCR). The Cu-type AFX samples (denoted as CuAFX-OSDA1, CuAFX-OSDA2, CuAFX-DB) synthesized with three different structure-directing agents under the same copper ion loading (3 wt%) were compared. The method of copper ion loading is as follows: Prepare a 0.025 M Cu(CH3CO2)2 solution, place the synthesized zeolite in the Cu(CH3CO2)2 solution and stir at room temperature. The dosage of the zeolite and the Cu(CH3CO2)2 solution is 1 g: 100 mL.

[0106] First, the silica-alumina ratios of AFX molecular sieves obtained with different structure-directing agents were investigated. The silica-alumina ratio of the AFX molecular sieve synthesized with the structure-directing agent DB in Comparative Example 2 was 6.5, and the silica-alumina ratios of the pure-phase AFX molecular sieves synthesized with the structure-directing agents OSDA1 and OSDA2 in Examples 4 and 6 were 7.0 and 6.8, respectively, greatly improving the framework stability and (hydro)thermal stability. After testing, the AFX molecular sieves synthesized with the structure-directing agents OSDA1 and OSDA2 in Examples 4 and 6 had stable frameworks at high temperatures and could still maintain their stability after hydrothermal aging at 850 °C for 24 h (the XRD pattern still showed the presence of the crystal structure); while the structure of the AFX molecular sieve synthesized with the structure-directing agent DB in Comparative Example 2 collapsed after hydrothermal aging at 850 °C (XRD showed an amorphous structure).

[0107] Then, the NH3-SCR reaction evaluations were carried out on three Cu-type AFX catalyst samples, CuAFX-DB, CuAFX-OSDA1, and CuAFX-OSDA2 (reaction conditions: 500 ppm NH3, 500 ppm NO, 5% O2, 10% H2O, 30000 h -1 GHSV N2). The test results are as Figure 7 shown. It can be Figure 7 seen that the reaction window of the CuAFX-DB sample was 250 - 400 °C, much smaller than the reaction catalytic activity windows of CuAFX-OSDA1 and CuAFX-OSDA2. Among them, the reaction window of CuAFX-OSDA1 was 250 - 500 °C, and the reaction window of CuAFX-OSDA2 was 250 - 450 °C. Moreover, in the high-temperature section (above 400 °C) of the NH3-SCR reaction, it had excellent reaction activity, and the NO conversion rate could be maintained above 95%, showing good high-temperature catalytic denitrification performance.

[0108] The above are only the preferred embodiments of the present invention and do not impose any formal limitations on the present invention. It should be noted that for those of ordinary skill in the art of this technology, several improvements and refinements can be made without departing from the principle of the present invention, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A preparation method of AFX molecular sieve, characterized in that, It includes the following steps: Mix a silicon source, an aluminum source, an alkali source, a structure-directing agent, water and SSZ-16 molecular sieve seeds to obtain a molecular sieve mother liquor; Perform hydrothermal crystallization on the molecular sieve mother liquor, and calcine the obtained hydrothermal crystallization product to obtain an AFX molecular sieve; The structure-directing agent is a gemini quaternary ammonium base type structure-directing agent, and the molecular formula of the gemini quaternary ammonium base type structure-directing agent is X + RX + 2OH - , where R is alkylbenzene, and X is alkylpiperidinyl or alkylpyrrolidinyl; the alkylbenzene is 1,4-phenylenebis(methylene) or 1,3-phenylenebis(methylene), the alkylpiperidinyl is 1-methylpiperidinyl, 1-ethylpiperidinyl, 1-propylpiperidinyl, 1-propenylpiperidinyl or 1-butylpiperidinyl, and the alkylpyrrolidinyl is 1-methylpyrrolidinyl, 1-ethylpyrrolidinyl, 1-propylpyrrolidinyl, 1-propenylpyrrolidinyl or 1-butylpyrrolidinyl; The silicon source, aluminum source and alkali source are calculated as SiO2, Al2O3 and alkali metal respectively. The molar ratio of the silicon source, aluminum source, alkali source, structure-directing agent and water in the molecular sieve mother liquor is 1:(0.02~0.05):(0.10~0.50):(0.10~1.00):(10~50).

2. The preparation method according to claim 1, characterized in that, The preparation method of the gemini quaternary ammonium base structure-directing agent It includes the following steps: Mix a dihalogenated xylene, a tertiary amine and an organic solvent to carry out a substitution reaction to obtain a gemini quaternary ammonium salt; the dihalogenated xylene includes p-dihalogenated xylene or m-dihalogenated xylene; the tertiary amine includes an alkyl piperidine or an alkyl pyrrolidine, the alkyl piperidine includes 1-methylpiperidine, 1-ethylpiperidine, 1-propylpiperidine, 1-propenylpiperidine or 1-butylpiperidine, and the alkyl pyrrolidine includes 1-methylpyrrolidine, 1-ethylpyrrolidine, 1-propylpyrrolidine, 1-propenylpyrrolidine or 1-butylpyrrolidine; Perform anion exchange on the halogen ion in the gemini quaternary ammonium salt with a hydroxide ion to obtain the gemini quaternary ammonium base structure-directing agent.

3. The preparation method according to claim 2, characterized in that, The molar ratio of the dihalogenated xylene to the tertiary amine is 1:2~6.

4. The preparation method according to claim 2, wherein The temperature of the substitution reaction is 60~100 °C, and the time is 10~120 h.

5. The preparation method according to claim 1, wherein The silicon source includes one or more of sodium silicate, silica sol, fumed silica and FAU molecular sieve; the aluminum source includes one or more of aluminum chloride, aluminum sulfate, aluminum hydroxide, sodium aluminate and FAU molecular sieve; the alkali source includes one or more of sodium hydroxide, potassium hydroxide and sodium silicate.

6. The preparation method according to claim 5, characterized in that, The mass of the SSZ-16 molecular sieve seeds is 3~5% of the mass of the silicon source.

7. The preparation method according to claim 1, 5 or 6, characterized in that, The temperature of the hydrothermal crystallization is 130~170 °C, and the time is 72~120 h; the temperature of the calcination is 350~700 °C, and the time is 6~10 h.

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