A core-shell structure molecular sieve, a preparation method and application thereof

Abstract

The application belongs to the field of adsorption separation, and discloses a core-shell structure molecular sieve, a preparation method and application thereof. A silicon source, an aluminum source, an alkali source and water are mixed to form a uniform gel I; the gel I is subjected to hydrothermal treatment and calcination to obtain 13X molecular sieve core phase powder; the silicon source, the aluminum source, the alkali source and water are mixed and stirred at room temperature to form a gel II; the gel II is subjected to constant temperature aging to obtain a 4A precursor gel; the prepared 13X molecular sieve core phase powder is treated by a dilute alkali solution and then added to the 4A precursor gel, and then subjected to stirring at room temperature to form a core-shell precursor gel; and the core-shell precursor gel is subjected to hydrothermal treatment, washing, drying and calcination to obtain a core-shell structure molecular sieve. The prepared core-shell structure molecular sieve material has excellent adsorption capacity and gas selectivity, and the core-shell structure molecular sieve combines the structural advantages of two kinds of molecular sieves, and has a wide application prospect in the field of adsorption separation.

Description

Technical Field

[0001] This invention belongs to the field of adsorption separation, and particularly relates to a core-shell structured molecular sieve and its preparation method. Background Technology

[0002] The severe problems caused by the continued intensification of global warming have drawn significant attention to CO2 emissions, driving the research and application of various emission reduction technologies. As one of the most promising emission reduction technologies, direct air capture (DAC) can play a crucial role in achieving carbon neutrality (ChemSusChem 2021, 14, 4439−4453). Compared to traditional carbon capture and storage (CCS) technologies (which capture high-concentration CO2 at industrial point sources such as power plants and steel mills, then compress, transport, and store it in underground geological structures such as depleted oil and gas fields and salt caverns), DAC (direct carbon dioxide capture technology) (which captures low-concentration CO2 directly from the atmosphere, without relying on emission sources, and can be stored or utilized as a resource after capture) can effectively address global point-source and non-point-source CO2 emissions, eliminating the need for storage and transportation infrastructure (Int. J. Energy Res. 2022, 46, 10320−10344).

[0003] The core of direct air carbon capture (DOCC) technology lies in the design of adsorbent materials (Chem. Soc. Rev. 2022, 51, 6574). Currently, alkaline aqueous solutions and porous solid adsorbents are the two main media for capturing low concentrations of CO2. However, the solution regeneration process is energy-intensive, the solution is corrosive to equipment, and it is highly volatile, easily causing environmental pollution. To solve these problems, there is an urgent need to develop different types of porous solid adsorbents. These adsorbents mainly include carbon-based materials, molecular sieves (ACSSustainable Chem. Eng. 2022, 10, 1759−1764), and metal-organic frameworks (MOFs). Compared with alkaline aqueous solutions, porous solid adsorbents have significantly lower heat of adsorption, which can greatly reduce regeneration energy consumption. However, MOF materials are unstable in humid air, and their coordination bonds are easily hydrolyzed. Carbon-based materials such as activated carbon and carbon nanotubes are more stable than MOF materials, but they have lower selectivity for CO2 (Appl. Therm. Eng. 2022, 213, 118746).

[0004] Molecular sieves are a class of crystalline materials with regular microporous structures, high specific surface areas, high hydrothermal stability, and tunable structures. Their framework is negatively charged, with balanced cations (such as Na+). + Ca 2+ Li +Molecular sieves can generate strong local electrostatic fields, and CO2, with its large quadrupole moment, undergoes strong ion-quadrupole interactions with the equilibrium cations, resulting in its powerful adsorption. This has led to extensive research on molecular sieves in the field of adsorption separation (Chem. Eng. Sci. 2020, 220, 115636). Among them, 13X molecular sieves have a pore size of approximately 10 Å (1 nm) and a three-dimensional intersecting pore system, far exceeding the kinetic diameter of CO2 (approximately 0.33 nm), ensuring that CO2 can rapidly diffuse to most of the equilibrium cation adsorption sites inside the pores. At the same time, its FAU-type framework forms a supercage cavity with a diameter of approximately 11.8 Å (1.18 nm), providing ample space to accommodate large amounts of CO2. However, the pore size of 13X zeolite (1 nm) is much larger than the kinetic diameter of N2 (0.36 nm), allowing both CO2 and N2 molecules to freely enter the channels, thus preventing the 13X zeolite from efficiently adsorbing and separating CO2 / N2 (Chem. Eng. J. 2021, 420, 129975). 4A zeolite has an effective pore size of approximately 4 Å (0.4 nm) and a three-dimensional interlocking channel system (Cryst. Struct. 133, 1971, 134-149), which is slightly larger than the kinetic diameter of CO2 (0.33 nm) while still allowing N2 (0.36 nm) to enter. Due to the large quadrupole moment of CO2, the Na+ in the 4A zeolite framework... + The strong electrostatic field generated has a significantly stronger interaction force between CO2 and the quadrupole moment than N2. Although both molecules can enter the pores, CO2, due to its slightly smaller size and faster diffusion rate, is more effective at reaching the Na+ inside the cage. + The adsorption sites are limited, and the diffusion of N2 in narrow channels is relatively restricted, making diffusion difficult. Therefore, developing a novel core-shell molecular sieve adsorbent to achieve efficient CO2 / N2 separation has become a key technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention proposes a core-shell structured molecular sieve, its preparation method, and its applications. This method eliminates the need for any organic template agent. Pretreated 13X molecular sieve powder is uniformly dispersed in a 4A molecular sieve precursor gel after treatment with a dilute alkali solution. The silicon-aluminum species on the surface of the 13X molecular sieve particles serve as heterogeneous nucleation sites, lowering the energy barrier for 4A crystal growth. This induces the in-situ growth of the 4A crystal phase on the 13X surface, forming a continuous and dense shell, ultimately constructing a composite structure with a tightly bonded core-shell interface.

[0006] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0007] A method for preparing a core-shell molecular sieve, comprising the following steps:

[0008] (1) Mix silicon source, aluminum source, alkali source and water, and stir at room temperature for a period of time until a uniform gel I is formed; then transfer gel I to a hydrothermal reactor for hydrothermal treatment. After the reaction is completed, wash the product several times, and then dry and calcine it in sequence to obtain 13X molecular sieve core phase powder.

[0009] (2) The silicon source, aluminum source, alkali source and water were mixed and stirred at room temperature to obtain 4A precursor gel;

[0010] (3) The 13X molecular sieve core phase powder obtained in step (1) is treated with dilute alkali solution and then added to the 4A precursor gel in step (2). After stirring at room temperature, a core-shell precursor gel is formed.

[0011] (4) The core-shell precursor gel obtained in step (3) is transferred to a hydrothermal reactor and subjected to hydrothermal crystallization, washing, drying and calcination to obtain a core-shell molecular sieve (named 13X@4A core-shell molecular sieve).

[0012] The silicon source mentioned above includes at least one of sodium silicate, silica, and silica sol; the aluminum source is at least one of sodium aluminate, aluminum hydroxide, and aluminum sol; and the alkali source is sodium hydroxide.

[0013] In step (1) above, the composition of gel I, in terms of the molar ratio of oxides, satisfies the following relationship: SiO2 / Al2O3=2.8-5, Na2O / SiO2=1.8-4, H2O / Na2O=40-160.

[0014] In step (2) above, the composition of the 4A precursor gel, in terms of the molar ratio of oxides, satisfies the following relationship: SiO2 / Al2O3=1.5-2.5, Na2O / SiO2=1.8-3, H2O / Na2O=30-100.

[0015] In steps (1) and (2), the content (amount of substance) of SiO2, Al2O3, H2O and Na2O is calculated as oxides or water based on the total amount of the corresponding elements in the raw materials used. H2O includes added water and crystal water contained in the raw materials. Na2O comes from silicon source, aluminum source and alkali source.

[0016] In step (3) above, the dilute alkali solution is a NaOH solution with a concentration of 0.1-1 mol / L, the temperature of the dilute alkali solution treatment is room temperature, and the time is 1-3 h; the amount of 13X molecular sieve core phase powder added in the dilute alkali solution treatment is 1-10% of the mass of the 4A precursor gel.

[0017] In steps (1) and (4) above, the temperature of hydrothermal treatment is 90-120℃ and the time is 6-18 h; the temperature of calcination treatment is 500-600℃ and the time is 3-6 h.

[0018] Furthermore, the hydrothermal treatment time in step (1) is 6-18 h; the hydrothermal treatment time in step (4) is 6-12 h.

[0019] The core-shell molecular sieve was prepared using the above-described method.

[0020] The above-mentioned core-shell molecular sieves are used in the field of gas adsorption and separation.

[0021] Furthermore, the above-mentioned core-shell molecular sieves are applied in the adsorption and separation of CO2 / N2 gases.

[0022] The beneficial effects of this invention are:

[0023] (1) This invention employs an in-situ coating synthesis strategy. Pretreated 13X molecular sieve core phase powder, treated with dilute NaOH solution, is uniformly dispersed in a 4A molecular sieve precursor gel. The silica-alumina species on the 13X core phase surface serve as natural heterogeneous nucleation sites, inducing the directional growth of the 4A crystal phase on the 13X core phase surface, thus achieving a uniform and dense coating of the 4A shell. This core-shell structure of the 13X core phase provides ample microporous structure and high adsorption capacity, while the 4A shell plays a molecular sieving role. Compared to single 13X or 4A molecular sieves, it exhibits higher selectivity and adsorption capacity.

[0024] (2) The 13X@4A core-shell molecular sieve prepared in this invention has a specific surface area of ​​522 m² compared to 13X molecular sieve. 2 / g increased to 695 m 2 / g, pore volume from 0.31 cm 2 / g increased to 0.43 cm 2 / g. The prepared molecular sieve was subjected to CO2 / N2 gas adsorption tests. The CO2 adsorption capacity of the prepared 13X@4A core-shell molecular sieve was 7.56 mmol / g, which is 24.5% higher than that of 13X molecular sieve. At the same time, the CO2 / N2 separation factor increased from 19 to 54.

[0025] (3) The entire preparation process of the present invention does not require the use of any organic template agent or complex modification steps. The molecular sieve structure and performance can be precisely controlled by adjusting parameters such as the core-shell ratio and crystallization conditions. This not only simplifies the synthesis process and shortens the preparation cycle, but also avoids the cost pressure and environmental burden brought by template agents, and has significant economic benefits and industrial application prospects. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 The images show the XRD patterns of the 13X molecular sieve (adsorbent) prepared in Comparative Example 1, the 4A molecular sieve (adsorbent) prepared in Comparative Example 2, and the 13X@4A core-shell structure molecular sieve (adsorbent) prepared in Example 1.

[0028] Figure 2 The images show SEM images of the 13X molecular sieve (adsorbent) prepared in Comparative Example 1, the 4A molecular sieve (adsorbent) prepared in Comparative Example 2, and the 13X@4A core-shell structure molecular sieve (adsorbent) prepared in Example 1.

[0029] Figure 3 The XRD patterns are of the 13X@4A core-shell molecular sieve adsorbents prepared in Examples 1-6 of this invention.

[0030] Figure 4 This is a SEM image of the 13X@4A core-shell molecular sieve adsorbent prepared in Example 7 of the present invention.

[0031] Figure 5 This is a SEM image of the 13X@4A core-shell molecular sieve adsorbent prepared in Example 8 of the present invention.

[0032] Figure 6 This is a SEM image of the 13X@4A core-shell molecular sieve adsorbent prepared in Example 9 of the present invention.

[0033] Figure 7 This is a SEM image of the 13X@4A core-shell molecular sieve adsorbent prepared in Example 10 of the present invention.

[0034] Figure 8 This is a SEM image of the 13X@4A core-shell molecular sieve adsorbent prepared in Example 11 of this invention.

[0035] Figure 9 This is a SEM image of the 13X@4A core-shell molecular sieve adsorbent prepared in Example 1 of the present invention.

[0036] Figure 10This is a comparison chart of the CO2 adsorption capacity and CO2 / N2 separation factor of the 13X molecular sieve (adsorbent) prepared in Comparative Example 1, the 4A molecular sieve (adsorbent) prepared in Comparative Example 2, and the 13X@4A core-shell structure molecular sieve (adsorbent) prepared in Example 1.

[0037] Figure 11 This is a comparison chart of the CO2 adsorption capacity and CO2 / N2 separation factor of the 13X@4A core-shell structure molecular sieve adsorbents prepared in Examples 1, 5, 7, 12, and 20 of this invention.

[0038] Figure 12 This is a comparison chart of the CO2 adsorption capacity and CO2 / N2 separation factor of the 13X@4A core-shell structured molecular sieve adsorbents prepared in Examples 1, 21-24 and Comparative Example 3 of the present invention. Detailed Implementation

[0039] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0040] In this specification, the range of values ​​referred to as "value A to value B" refers to the range including the endpoint values ​​A and B.

[0041] Unless otherwise stated, in this instruction manual, "more" in "multiple", "multi-variety", "multiple", etc., means a value of 2 or more.

[0042] Unless otherwise specified, "%" in this instruction manual refers to the percentage content by mass.

[0043] The temperature referred to as "room temperature" in this article is generally between 20-30℃.

[0044] First aspect

[0045] The first aspect of the present invention provides a method for preparing a core-shell structured molecular sieve for gas adsorption and separation, comprising the following steps:

[0046] Sodium hydroxide (NaOH) was dissolved in deionized water and stirred at room temperature for a period of time to obtain a sodium hydroxide solution. A certain amount of sodium aluminate (NaAlO2) was weighed and dissolved in the sodium hydroxide solution prepared above, and stirred at room temperature for a period of time to obtain an aluminum source solution.

[0047] Sodium metasilicate nonahydrate (Na₂SiO₃·9H₂O) was dissolved in deionized water and stirred at room temperature for a period of time to prepare a silicon source solution. The silicon source solution was then slowly added dropwise to an aluminum source solution through a constant-pressure separatory funnel at a certain temperature. After stirring for a period of time, the resulting gel was allowed to stand at room temperature for a certain period. The gel solution after standing was transferred to a hydrothermal reactor and subjected to hydrothermal crystallization at a certain temperature and time. The crystals were then washed with deionized water, dried, and calcined to obtain 13X molecular sieve seed crystals.

[0048] The above steps were repeated to prepare the 4A precursor gel. Sodium hydroxide (NaOH) was dissolved in deionized water and stirred at room temperature for a period of time to obtain a sodium hydroxide solution. A certain amount of sodium aluminate (NaAlO2) was weighed and dissolved in the prepared sodium hydroxide solution, and stirred at room temperature for a period of time to obtain an aluminum source solution. Sodium metasilicate nonahydrate (Na2SiO3·9H2O) was dissolved in deionized water and stirred at room temperature for a period of time to obtain a silicon source solution. The obtained silicon source solution was slowly added dropwise to the aluminum source solution through a constant pressure separatory funnel at a certain temperature, and the mixture was stirred for a period of time to obtain the 4A precursor gel.

[0049] Weigh a certain amount of the 13X molecular sieve seed crystals obtained in the above steps, treat them with dilute NaOH solution, and then uniformly disperse them in the 4A precursor gel. Continue stirring at room temperature for a period of time to obtain the synthesized core-shell gel solution.

[0050] The synthesized gel obtained in the above steps was transferred to a hydrothermal reactor for hydrothermal crystallization to obtain a hydrothermal product. The synthesized product was washed with water, dried, and calcined sequentially to obtain a core-shell molecular sieve powder.

[0051] Synthetic liquid gel

[0052] In some specific embodiments of the present invention, the silicon source can be one or more of sodium silicate, silica, or silica sol. The aluminum source is one or more of sodium aluminate, aluminum hydroxide, or aluminum sol. In the present invention, the optional alkaline source can be any feasible alkaline substance in the art; in some specific embodiments, the alkaline source is sodium hydroxide.

[0053] The present invention does not particularly limit the solvent; it can be any solvent that can be used in the art, such as polar solvents like water or alcohol. Water is preferred as the solvent.

[0054] hydrothermal crystallization steps

[0055] The synthesized liquid gel was subjected to hydrothermal crystallization treatment to obtain the hydrothermal crystallization product. Specifically, the 13X precursor gel obtained above was placed in a hydrothermal reactor for hydrothermal crystallization treatment to obtain the product.

[0056] The temperature for hydrothermal treatment can be above 85℃ and below 150℃, preferably 90-120℃; the time for hydrothermal treatment can be 4-48 h, preferably 6-12 h.

[0057] Furthermore, the present invention typically involves post-processing operations such as washing and drying of the hydrothermal crystallization product. Specifically, for washing, deionized water can be used, and the drying can be carried out at a temperature of 80-120°C.

[0058] roasting

[0059] The hydrothermal product is calcined once to obtain the 13X molecular sieve powder of the present invention. There are no particular restrictions on the conditions for the first calcination; it can be carried out at a temperature of 500-600°C for 3-6 hours.

[0060] Similarly, the present invention typically involves post-processing operations such as washing, drying, and calcination of the molecular sieve after the addition of the core phase. Specifically, washing can be performed using deionized water until neutral, and drying can be carried out at a temperature of 80-120°C for 4-12 hours. The product is then calcined to obtain the core-shell structured molecular sieve of the present invention. There are no particular limitations on the calcination conditions; calcination at 500-600°C for 3-6 hours is acceptable. This yields a molecular sieve with a core-shell structure.

[0061] Second aspect

[0062] A second aspect of the present invention provides a molecular sieve with a core-shell structure prepared by the preparation method described in the first aspect of the present invention.

[0063] Third aspect

[0064] The third aspect of the present invention provides the application of the core-shell structured molecular sieve prepared by the preparation method described in the first aspect of the present invention for gas adsorption and separation.

[0065] Example 1

[0066] The preparation method of the core-shell structured molecular sieve in this embodiment includes the following steps:

[0067] (1) Weigh 5.2 g of sodium silicate (Na2SiO3•9H2O) and dissolve it in 30 g of deionized water. Stir at room temperature for 15 min to obtain a silicon source solution. Weigh 2.44 g of sodium hydroxide (NaOH) and dissolve it in 30 g of deionized water. Stir at room temperature for 10 min to obtain a sodium hydroxide solution. Weigh 1 g of sodium aluminate (NaAlO2) and dissolve it in the above sodium hydroxide solution. Stir at room temperature for 15 min to obtain an aluminum source solution. Slowly add the silicon source solution to the aluminum source solution through a constant pressure dropping funnel at 60℃. Stir at room temperature for 1 h to form a 13X precursor gel. After standing and aging for 12 h, transfer the 13X precursor gel to a hydrothermal reactor and hydrothermally crystallize at 100℃ for 12 h. Then, it was washed with deionized water, dried at 120°C for 6 h, and calcined at 550°C for 4 h in an air atmosphere in a muffle furnace to obtain 13X molecular sieve seed crystals, i.e., 13X molecular sieve core phase powder.

[0068] (2) Weigh 7.106 g of sodium silicate (Na2SiO3·9H2O) and dissolve it in 35 g of deionized water. Stir at room temperature for 15 min to obtain a silicon source solution. Weigh 1 g of sodium hydroxide (NaOH) and dissolve it in 35 g of deionized water. Stir at room temperature for 10 min to obtain a sodium hydroxide solution. Weigh 2.049 g of sodium aluminate (NaAlO2) and dissolve it in the above sodium hydroxide solution. Stir at room temperature for 15 min to obtain an aluminum source solution. Slowly add the silicon source solution dropwise to the aluminum source solution through a constant pressure dropping funnel at 60℃. Stir at room temperature for 1 h to form a 4A precursor gel.

[0069] (3) Treat 13X molecular sieve seeds with 0.5 mol / L NaOH solution at room temperature for 2 h, wherein the mass ratio of 13X seeds to NaOH solution is 1:50. Weigh 8.016 g of the 13X molecular sieve seeds treated with the above NaOH solution and add them to 4A precursor gel (80.16 g, the amount of 13X molecular sieve seeds added is 10% of the mass of 4A precursor gel), and continue stirring at room temperature for 1 h to obtain the synthesis solution, namely the core-shell precursor gel.

[0070] (4) The synthesis solution obtained in step (3) above was transferred to a hydrothermal reactor and hydrothermally treated (crystallized) at 100°C for 12 h to obtain the hydrothermal product. The synthesized product was washed with water until neutral, dried at 120°C for 6 h, and calcined at 550°C for 4 h in an air atmosphere in a muffle furnace to obtain 13X@4A molecular sieve powder, namely, core-shell molecular sieve (named 13X@4A core-shell molecular sieve).

[0071] Comparative Example 1

[0072] The preparation method of the 13X molecular sieve in this comparative example is as follows:

[0073] (1) Weigh 5.2 g of sodium silicate (Na2SiO3•9H2O) and dissolve it in 30 g of deionized water. Stir at room temperature for 15 min to obtain a silicon source solution. Weigh 2.44 g of sodium hydroxide (NaOH) and dissolve it in 30 g of deionized water. Stir at room temperature for 10 min to obtain a sodium hydroxide solution. Weigh 1 g of sodium aluminate (NaAlO2) and dissolve it in the above sodium hydroxide solution. Stir at room temperature for 15 min to obtain an aluminum source solution. Slowly add the silicon source solution to the aluminum source solution through a constant pressure dropping funnel at 60 °C. Stir at room temperature for 1 h to form a 13X precursor gel. After standing and aging for 12 h, transfer the 13X precursor gel to a hydrothermal reactor and hydrothermally crystallize it at 100 °C for 12 h. Then wash it with deionized water, dry it at 120 °C for 6 h, and calcine it at 550 °C for 4 h in an air atmosphere in a muffle furnace to obtain 13X molecular sieve.

[0074] Comparative Example 2

[0075] The preparation method of the 4A molecular sieve in this comparative example is as follows:

[0076] 7.106 g of sodium silicate (Na₂SiO₃·9H₂O) was dissolved in 35 g of deionized water and stirred at room temperature for 15 min to prepare a silicon source solution. 1 g of sodium hydroxide (NaOH) was dissolved in 35 g of deionized water and stirred at room temperature for 10 min to prepare a sodium hydroxide solution. 2.049 g of sodium aluminate (NaAlO₂) was dissolved in the above sodium hydroxide solution and stirred at room temperature for 15 min to prepare an aluminum source solution. The silicon source solution was slowly added dropwise to the aluminum source solution through a constant-pressure dropping funnel at 60 °C, and stirred at room temperature for 1 h to form a 4A precursor gel. The gel was transferred to a hydrothermal reactor and hydrothermally crystallized at 100 °C for 12 h. It was then washed with deionized water, dried at 120 °C for 6 h, and calcined in a muffle furnace at 550 °C for 4 h in air atmosphere to obtain 4A molecular sieve.

[0077] Figure 1 The image shows a comparison of the XRD patterns of the 13X molecular sieve adsorbent prepared in Comparative Example 1, the 4A molecular sieve adsorbent prepared in Comparative Example 2, and the 113X@4A core-shell molecular sieve prepared in Example 1. Comparing the PDF cards (JCPDS-00-038-0237) and (JCPDS-00-039-0222) in Jade software, it can be found that Comparative Examples 1 and 2 conform to typical FAU and LTA molecular sieve crystal forms, respectively. This indicates that 13X and 4A molecular sieves were successfully prepared. Example 1 contains characteristic peaks of both molecular sieves, indicating that the prepared composite molecular sieve contains both molecular sieve structures.

[0078] Figure 2The image shows a comparative SEM image of the 13X molecular sieve prepared in Comparative Example 1, the 4A molecular sieve prepared in Comparative Example 2, and the 13X@4A core-shell molecular sieve prepared in Example 1. The 13X molecular sieve has an octahedral morphology, while the 4A molecular sieve is cubic. The SEM image of Example 1 clearly shows a layer of cubic particles uniformly grown on the surface of the octahedral crystal, indicating that this core-shell molecular sieve with 13X molecular sieve as the core and 4A as the shell was successfully prepared.

[0079] Example 2

[0080] The preparation method of the core-shell molecular sieve in this embodiment differs from that in Example 1 in that, in step (4), the hydrothermal crystallization temperature is 80°C and the time is 12 h. The specific steps are as follows:

[0081] The synthesis steps (1)-(3) are the same as in Example 1.

[0082] (4) The synthesis solution obtained in step (3) above was transferred to a hydrothermal reactor and hydrothermally treated (crystallized) at 80°C for 12 h to obtain the hydrothermal product. The synthesized product was washed with water until neutral, dried at 120°C for 6 h, and calcined at 550°C for 4 h in an air atmosphere in a muffle furnace to obtain 13X@4A molecular sieve powder, namely, core-shell molecular sieve (named 13X@4A core-shell molecular sieve).

[0083] Example 3

[0084] The preparation method of the core-shell molecular sieve in this embodiment differs from that in Example 1 in that, in step (4), the hydrothermal crystallization temperature is 100℃ and the time is 8 h. The specific steps are as follows:

[0085] The synthesis steps (1)-(3) are the same as in Example 1.

[0086] (4) The synthesis solution obtained in step (3) above was transferred to a hydrothermal reactor and hydrothermally treated (crystallized) at 100°C for 8 h to obtain the hydrothermal product. The synthesized product was washed with water until neutral, dried at 120°C for 6 h, and calcined at 550°C for 4 h in an air atmosphere in a muffle furnace to obtain 13X@4A molecular sieve powder, namely, core-shell molecular sieve (named 13X@4A core-shell molecular sieve).

[0087] Example 4

[0088] The preparation method of the core-shell molecular sieve in this embodiment differs from that in Example 1 in that, in step (4), the hydrothermal crystallization temperature is 100℃ and the time is 16 h. The specific steps are as follows:

[0089] The synthesis steps (1)-(3) are the same as in Example 1.

[0090] (4) The synthesis solution obtained in step (3) above was transferred to a hydrothermal reactor and hydrothermally treated (crystallized) at 100°C for 16 h to obtain the hydrothermal product. The synthesized product was washed with water until neutral, dried at 120°C for 6 h, and calcined at 550°C for 4 h in an air atmosphere in a muffle furnace to obtain 13X@4A molecular sieve powder, namely, core-shell molecular sieve (named 13X@4A core-shell molecular sieve).

[0091] Example 5

[0092] The preparation method of the core-shell molecular sieve in this embodiment differs from that in Example 1 in that, in step (4), the hydrothermal crystallization temperature is 80°C and the time is 16 h. The specific steps are as follows:

[0093] The synthesis steps (1)-(3) are the same as in Example 1.

[0094] (4) The synthesis solution obtained in step (3) above was transferred to a hydrothermal reactor and hydrothermally treated (crystallized) at 80°C for 16 h to obtain the hydrothermal product. The synthesized product was washed with water until neutral, dried at 120°C for 6 h, and calcined at 550°C for 4 h in an air atmosphere in a muffle furnace to obtain 13X@4A molecular sieve powder, namely, core-shell molecular sieve (named 13X@4A core-shell molecular sieve).

[0095] Example 6

[0096] The preparation method of the core-shell molecular sieve in this embodiment differs from that in Example 1 in that, in step (4), the hydrothermal crystallization temperature is 120°C and the time is 12 h. The specific steps are as follows:

[0097] The synthesis steps (1)-(3) are the same as in Example 1.

[0098] (4) The synthesis solution obtained in step (3) above was transferred to a hydrothermal reactor and hydrothermally treated (crystallized) at 120°C for 12 h to obtain the hydrothermal product. The synthesized product was washed with water until neutral, dried at 120°C for 6 h, and calcined at 550°C for 4 h in an air atmosphere in a muffle furnace to obtain 13X@4A molecular sieve powder, which was named 13X@4A core-shell molecular sieve.

[0099] Figure 3These are XRD comparison charts of a series of 13X@4A core-shell molecular sieves prepared using different crystallization temperatures and times in Examples 1-6. The XRD comparison charts indicate that a crystallization temperature of 100℃ and a crystallization time of 12 h are the optimal crystallization conditions. When the crystallization temperature is too low / too high, or the crystallization time is too short / too long, the quality of the crystal phase reflected by XRD characterization shows a downward trend. Specifically, "low temperature, short time" and "suitable temperature, too short time" both lead to deterioration of the crystal phase quality. When the crystallization temperature is 100℃ and the crystallization time is 12 h, the heterogeneous nucleation rate on the surface of the 13X nucleus phase and the crystal growth kinetics of the 4A shell phase can simultaneously ensure the full and regular development of both FAU-type (13X) and LTA-type (4A) crystal phases, resulting in high crystallinity and no crystal distortion in the product. Low temperatures weaken the driving force for crystal growth, and extending the time can only partially compensate for this defect. High temperatures easily lead to uneven grain size. If the time is too short, crystallization will be insufficient, and if the time is too long, crystal distortion will occur. All of the above-mentioned temperature-time mismatches will reduce the regularity and crystallinity of the crystal phase, ultimately manifesting as deterioration characteristics such as broadened XRD peaks and increased impurity peaks.

[0100] Example 7

[0101] The preparation method of the core-shell molecular sieve in this embodiment differs from that in Example 1 in that the amount of 13X seed crystals added in the core-shell precursor gel is 1%. The steps are as follows:

[0102] The synthesis steps in steps (1)-(2) are the same as in Example 1.

[0103] (3) Treat 13X molecular sieve seeds with 0.5 mol / L NaOH solution at room temperature for 2 h, wherein the mass ratio of 13X seeds to NaOH solution is 1:50. Weigh 0.802 g of the 13X molecular sieve seeds treated with the above NaOH solution and add them to the 4A precursor gel (80.16 g, the amount of 13X molecular sieve seeds added is 1% of the mass of the 4A precursor gel), and continue to stir at room temperature for 1 h to obtain the synthesis solution, namely the core-shell precursor gel.

[0104] The synthesis steps in step (4) are the same as in Example 1.

[0105] Example 8

[0106] The preparation method of the core-shell molecular sieve in this embodiment differs from that in Example 1 in that the amount of 13X seed crystals added in the core-shell precursor gel is 2%, and the steps are as follows:

[0107] The synthesis steps in steps (1)-(2) are the same as in Example 1.

[0108] (3) Treat 13X molecular sieve seeds with 0.5 mol / L NaOH solution at room temperature for 2 h, wherein the mass ratio of 13X seeds to NaOH solution is 1:50. Weigh 1.603 g of the 13X molecular sieve seeds treated with the above NaOH solution and add them to 4A precursor gel (80.16 g, the amount of 13X molecular sieve seeds added is 2% of the mass of 4A precursor gel), and continue to stir at room temperature for 1 h to obtain the synthesis solution, namely the core-shell precursor gel.

[0109] The synthesis steps in step (4) are the same as in Example 1.

[0110] Example 9

[0111] The preparation method of the core-shell molecular sieve in this embodiment differs from that in Example 1 in that the amount of 13X seed crystals added in the core-shell precursor gel is 3%. The steps are as follows:

[0112] The synthesis steps in steps (1)-(2) are the same as in Example 1.

[0113] (3) Treat 13X molecular sieve seeds with 0.5 mol / L NaOH solution at room temperature for 2 h, wherein the mass ratio of 13X seeds to NaOH solution is 1:50. Weigh 2.405 g of the 13X molecular sieve seeds treated with the above NaOH solution and add them to 4A precursor gel (80.16 g, the amount of 13X molecular sieve seeds added is 3% of the mass of 4A precursor gel), and continue to stir at room temperature for 1 h to obtain the synthesis solution, namely the core-shell precursor gel.

[0114] The synthesis steps in step (4) are the same as in Example 1.

[0115] Example 10

[0116] The preparation method of the core-shell molecular sieve in this embodiment differs from that in Example 1 in that the amount of 13X seed crystals added in the core-shell precursor gel is 5%, and the steps are as follows:

[0117] The synthesis steps in steps (1)-(2) are the same as in Example 1.

[0118] (3) Treat 13X molecular sieve seeds with 0.5 mol / L NaOH solution at room temperature for 2 h, wherein the mass ratio of 13X seeds to NaOH solution is 1:50. Weigh 2.405 g of the 13X molecular sieve seeds treated with the above NaOH solution and add them to 4A precursor gel (4.008 g, the amount of 13X molecular sieve seeds added is 5% of the mass of 4A precursor gel), and continue to stir at room temperature for 1 h to obtain the synthesis solution, namely the core-shell precursor gel.

[0119] The synthesis steps in step (4) are the same as in Example 1.

[0120] Example 11

[0121] The preparation method of the core-shell molecular sieve in this embodiment differs from that in Example 1 in that the amount of 13X seed crystals added in the core-shell precursor gel is 8%, and the steps are as follows:

[0122] The synthesis steps in steps (1)-(2) are the same as in Example 1.

[0123] (3) Treat 13X molecular sieve seeds with 0.5 mol / L NaOH solution at room temperature for 2 h, wherein the mass ratio of 13X seeds to NaOH solution is 1:50. Weigh 6.412 g of the 13X molecular sieve seeds treated with the above NaOH solution and add them to 4A precursor gel (80.16 g, the amount of 13X molecular sieve seeds added is 8% of the mass of 4A precursor gel), and continue to stir at room temperature for 1 h to obtain the synthesis solution, namely the core-shell precursor gel.

[0124] The synthesis steps in step (4) are the same as in Example 1.

[0125] Figure 4-9 The 13X@4A core-shell molecular sieves prepared in Examples 7-11 and Example 1 are respectively. With the gradual increase of the amount of 13X core phase seed crystals added to the 4A precursor gel (from 1% to 10%), SEM images clearly show a significant improvement in the uniformity and continuity of the 4A shell coating on the 13X core surface. This phenomenon stems from the optimization of the heterogeneous nucleation mechanism: when the amount of core phase added is low, excessive 4A precursor species easily undergo spontaneous homogeneous nucleation in solution, leading to the coexistence of free 4A crystals and the core-shell structure, resulting in uneven coating; as the proportion of core phase increases, the density of heterogeneous nucleation sites provided by the 13X particle surface increases accordingly, effectively guiding the preferential and uniform growth of the 4A crystal phase on its surface, thereby forming a more complete and dense core-shell structure.

[0126] Example 12

[0127] The preparation method of the core-shell structured molecular sieve in this embodiment differs from that in Example 1 in that, in step (1), the Na2O / SiO2 molar ratio in the precursor gel of the 13X molecular sieve seed crystal is 2, as detailed below:

[0128] (1) Weigh 5.2 g of sodium silicate (Na2SiO3•9H2O) and dissolve it in 30 g of deionized water. Stir at room temperature for 15 min to obtain a silicon source solution. Weigh 0.976 g of sodium hydroxide (NaOH) and dissolve it in 30 g of deionized water. Stir at room temperature for 10 min to obtain a sodium hydroxide solution. Weigh 1 g of sodium aluminate (NaAlO2) and dissolve it in the above sodium hydroxide solution. Stir at room temperature for 15 min to obtain an aluminum source solution. Slowly add the silicon source solution to the aluminum source solution through a constant pressure dropping funnel at 60℃. Stir at room temperature for 1 h to form a 13X precursor gel. After standing and aging for 12 h, transfer the 13X precursor gel to a hydrothermal reactor and hydrothermally crystallize at 100℃ for 12 h. Then, it was washed with deionized water, dried at 120°C for 6 h, and calcined at 550°C for 4 h in an air atmosphere in a muffle furnace to obtain 13X molecular sieve seed crystals, i.e., 13X molecular sieve core phase powder.

[0129] The synthesis steps (2)-(4) are the same as in Example 1.

[0130] Example 13

[0131] The preparation method of the core-shell structured molecular sieve in this embodiment differs from that in Example 1 in that, in step (1), the Na2O / SiO2 molar ratio in the precursor gel of the 13X molecular sieve seed crystal is 2.5, as detailed below:

[0132] (1) Weigh 5.2 g of sodium silicate (Na2SiO3•9H2O) and dissolve it in 30 g of deionized water. Stir at room temperature for 15 min to obtain a silicon source solution. Weigh 1.708 g of sodium hydroxide (NaOH) and dissolve it in 30 g of deionized water. Stir at room temperature for 10 min to obtain a sodium hydroxide solution. Weigh 1 g of sodium aluminate (NaAlO2) and dissolve it in the above sodium hydroxide solution. Stir at room temperature for 15 min to obtain an aluminum source solution. Slowly add the silicon source solution to the aluminum source solution through a constant pressure dropping funnel at 60℃. Stir at room temperature for 1 h to form a 13X precursor gel. After standing and aging for 12 h, transfer the 13X precursor gel to a hydrothermal reactor and hydrothermally crystallize at 100℃ for 12 h. Then, it was washed with deionized water, dried at 120°C for 6 h, and calcined at 550°C for 4 h in an air atmosphere in a muffle furnace to obtain 13X molecular sieve seed crystals, i.e., 13X molecular sieve core phase powder.

[0133] The synthesis steps (2)-(4) are the same as in Example 1.

[0134] Example 14

[0135] The preparation method of the core-shell structured molecular sieve in this embodiment differs from that in Example 1 in that, in step (1), the Na2O / SiO2 molar ratio in the precursor gel of the 13X molecular sieve seed crystal is 3.5, as detailed below:

[0136] (1) Weigh 5.2 g of sodium silicate (Na2SiO3•9H2O) and dissolve it in 30 g of deionized water. Stir at room temperature for 15 min to obtain a silicon source solution. Weigh 3.172 g of sodium hydroxide (NaOH) and dissolve it in 30 g of deionized water. Stir at room temperature for 10 min to obtain a sodium hydroxide solution. Weigh 1 g of sodium aluminate (NaAlO2) and dissolve it in the above sodium hydroxide solution. Stir at room temperature for 15 min to obtain an aluminum source solution. Slowly add the silicon source solution to the aluminum source solution through a constant pressure dropping funnel at 60℃. Stir at room temperature for 1 h to form a 13X precursor gel. After standing and aging for 12 h, transfer the 13X precursor gel to a hydrothermal reactor and hydrothermally crystallize at 100℃ for 12 h. Then, it was washed with deionized water, dried at 120°C for 6 h, and calcined at 550°C for 4 h in an air atmosphere in a muffle furnace to obtain 13X molecular sieve seed crystals, i.e., 13X molecular sieve core phase powder.

[0137] The synthesis steps (2)-(4) are the same as in Example 1.

[0138] Example 15

[0139] The preparation method of the core-shell structured molecular sieve in this embodiment differs from that in Example 1 in that, in step (1), the Na2O / SiO2 molar ratio in the precursor gel of the 13X molecular sieve seed crystal is 4, as detailed below:

[0140] (1) Weigh 5.2 g of sodium silicate (Na2SiO3•9H2O) and dissolve it in 30 g of deionized water. Stir at room temperature for 15 min to obtain a silicon source solution. Weigh 3.903 g of sodium hydroxide (NaOH) and dissolve it in 30 g of deionized water. Stir at room temperature for 10 min to obtain a sodium hydroxide solution. Weigh 1 g of sodium aluminate (NaAlO2) and dissolve it in the above sodium hydroxide solution. Stir at room temperature for 15 min to obtain an aluminum source solution. Slowly add the silicon source solution to the aluminum source solution through a constant pressure dropping funnel at 60℃. Stir at room temperature for 1 h to form a 13X precursor gel. After standing and aging for 12 h, transfer the 13X precursor gel to a hydrothermal reactor and hydrothermally crystallize at 100℃ for 12 h. Then, it was washed with deionized water, dried at 120°C for 6 h, and calcined at 550°C for 4 h in an air atmosphere in a muffle furnace to obtain 13X molecular sieve seed crystals, i.e., 13X molecular sieve core phase powder.

[0141] The synthesis steps (2)-(4) are the same as in Example 1.

[0142] Example 16

[0143] The preparation method of the core-shell molecular sieve in this embodiment differs from that in Example 1 in that, in step (2), the molar ratio of SiO2 / Al2O3 in the 4A precursor gel is 1.8, as detailed below:

[0144] The synthesis steps in step (1) are the same as in Example 1.

[0145] (2) Weigh 7.106 g of sodium silicate (Na2SiO3·9H2O) and dissolve it in 35 g of deionized water. Stir at room temperature for 15 min to obtain a silicon source solution. Weigh 1 g of sodium hydroxide (NaOH) and dissolve it in 35 g of deionized water. Stir at room temperature for 10 min to obtain a sodium hydroxide solution. Weigh 2.227 g of sodium aluminate (NaAlO2) and dissolve it in the above sodium hydroxide solution. Stir at room temperature for 15 min to obtain an aluminum source solution. Slowly add the silicon source solution dropwise to the aluminum source solution through a constant pressure dropping funnel at 60℃. Stir at room temperature for 1 h to form a 4A precursor gel.

[0146] (3) Treat 13X molecular sieve seeds with 0.5 mol / L NaOH solution at room temperature for 2 h, wherein the mass ratio of 13X seeds to NaOH solution is 1:50. Weigh 8.033 g of the 13X molecular sieve seeds treated with the above NaOH solution and add them to the 4A precursor gel (the amount of 13X molecular sieve seeds added is 10% of the mass of the 4A precursor gel). Continue stirring at room temperature for 1 h to obtain the synthesis solution, namely the core-shell precursor gel.

[0147] The synthesis steps in step (4) are the same as in Example 1.

[0148] Example 17

[0149] The preparation method of the core-shell molecular sieve in this embodiment differs from that in Example 1 in that, in step (2), the molar ratio of SiO2 / Al2O3 in the 4A precursor gel is 1.9, as detailed below:

[0150] The synthesis steps in step (1) are the same as in Example 1.

[0151] (2) Weigh 7.106 g of sodium silicate (Na2SiO3·9H2O) and dissolve it in 35 g of deionized water. Stir at room temperature for 15 min to obtain a silicon source solution. Weigh 1 g of sodium hydroxide (NaOH) and dissolve it in 35 g of deionized water. Stir at room temperature for 10 min to obtain a sodium hydroxide solution. Weigh 2.157 g of sodium aluminate (NaAlO2) and dissolve it in the above sodium hydroxide solution. Stir at room temperature for 15 min to obtain an aluminum source solution. Slowly add the silicon source solution dropwise to the aluminum source solution through a constant pressure dropping funnel at 60℃. Stir at room temperature for 1 h to form a 4A precursor gel.

[0152] (3) Treat 13X molecular sieve seeds with 0.5 mol / L NaOH solution at room temperature for 2 h, wherein the mass ratio of 13X seeds to NaOH solution is 1:50. Weigh 8.026 g of the 13X molecular sieve seeds treated with the above NaOH solution and add them to the 4A precursor gel (the amount of 13X molecular sieve seeds added is 10% of the mass of the 4A precursor gel). Continue stirring at room temperature for 1 h to obtain the synthesis solution, namely the core-shell precursor gel.

[0153] The synthesis steps in step (4) are the same as in Example 1.

[0154] Example 18

[0155] The preparation method of the core-shell molecular sieve in this embodiment differs from that in Example 1 in that, in step (2), the molar ratio of SiO2 / Al2O3 in the 4A precursor gel is 2.1, as detailed below:

[0156] The synthesis steps in step (1) are the same as in Example 1.

[0157] (2) Weigh 7.106 g of sodium silicate (Na2SiO3·9H2O) and dissolve it in 35 g of deionized water. Stir at room temperature for 15 min to obtain a silicon source solution. Weigh 1 g of sodium hydroxide (NaOH) and dissolve it in 35 g of deionized water. Stir at room temperature for 10 min to obtain a sodium hydroxide solution. Weigh 1.951 g of sodium aluminate (NaAlO2) and dissolve it in the above sodium hydroxide solution. Stir at room temperature for 15 min to obtain an aluminum source solution. Slowly add the silicon source solution dropwise to the aluminum source solution through a constant pressure dropping funnel at 60℃. Stir at room temperature for 1 h to form a 4A precursor gel.

[0158] (3) Treat 13X molecular sieve seeds with 0.5 mol / L NaOH solution at room temperature for 2 h, wherein the mass ratio of 13X seeds to NaOH solution is 1:50. Weigh 8.006 g of the 13X molecular sieve seeds treated with the above NaOH solution and add them to 4A precursor gel (the amount of 13X molecular sieve seeds added is 10% of the mass of 4A precursor gel). Continue stirring at room temperature for 1 h to obtain the synthesis solution, namely the core-shell precursor gel.

[0159] The synthesis steps in step (4) are the same as in Example 1.

[0160] Example 19

[0161] The preparation method of the core-shell molecular sieve in this embodiment differs from that in Example 1 in that, in step (2), the molar ratio of SiO2 / Al2O3 in the 4A precursor gel is 2.2, as detailed below:

[0162] The synthesis steps in step (1) are the same as in Example 1.

[0163] (2) Weigh 7.106 g of sodium silicate (Na2SiO3·9H2O) and dissolve it in 35 g of deionized water. Stir at room temperature for 15 min to obtain a silicon source solution. Weigh 1 g of sodium hydroxide (NaOH) and dissolve it in 35 g of deionized water. Stir at room temperature for 10 min to obtain a sodium hydroxide solution. Weigh 1.863 g of sodium aluminate (NaAlO2) and dissolve it in the above sodium hydroxide solution. Stir at room temperature for 15 min to obtain an aluminum source solution. Slowly add the silicon source solution dropwise to the aluminum source solution through a constant pressure dropping funnel at 60℃. Stir at room temperature for 1 h to form a 4A precursor gel.

[0164] (3) Treat 13X molecular sieve seeds with 0.5 mol / L NaOH solution at room temperature for 2 h, wherein the mass ratio of 13X seeds to NaOH solution is 1:50. Weigh 7.997 g of the 13X molecular sieve seeds treated with the above NaOH solution and add them to the 4A precursor gel (the amount of 13X molecular sieve seeds added is 10% of the mass of the 4A precursor gel). Continue stirring at room temperature for 1 h to obtain the synthesis solution, namely the core-shell precursor gel.

[0165] The synthesis steps in step (4) are the same as in Example 1.

[0166] Example 20

[0167] The preparation method of the core-shell molecular sieve in this embodiment differs from that in Example 1 in that, in step (2), the molar ratio of SiO2 / Al2O3 in the 4A precursor gel is 2.3, as detailed below:

[0168] The synthesis steps in step (1) are the same as in Example 1.

[0169] (2) Weigh 7.106 g of sodium silicate (Na2SiO3·9H2O) and dissolve it in 35 g of deionized water. Stir at room temperature for 15 min to obtain a silicon source solution. Weigh 1 g of sodium hydroxide (NaOH) and dissolve it in 35 g of deionized water. Stir at room temperature for 10 min to obtain a sodium hydroxide solution. Weigh 1.782 g of sodium aluminate (NaAlO2) and dissolve it in the above sodium hydroxide solution. Stir at room temperature for 15 min to obtain an aluminum source solution. Slowly add the silicon source solution dropwise to the aluminum source solution through a constant pressure dropping funnel at 60℃. Stir at room temperature for 1 h to form a 4A precursor gel.

[0170] (3) Treat 13X molecular sieve seeds with 0.5 mol / L NaOH solution at room temperature for 2 h, wherein the mass ratio of 13X seeds to NaOH solution is 1:50. Weigh 7.989 g of the 13X molecular sieve seeds treated with the above NaOH solution and add them to 4A precursor gel (the amount of 13X molecular sieve seeds added is 10% of the mass of 4A precursor gel). Continue stirring at room temperature for 1 h to obtain the synthesis solution, namely the core-shell precursor gel.

[0171] The synthesis steps in step (4) are the same as in Example 1.

[0172] Example 21

[0173] The preparation method of the core-shell molecular sieve in this embodiment differs from that in Example 1 in that the concentration of the NaOH solution in step (3) is 0.2 mol / L, as detailed below:

[0174] The synthesis steps of steps (1) and (2) are the same as in Example 1.

[0175] (3) Treat 13X molecular sieve seeds with 0.2 mol / L NaOH solution at room temperature for 2 h, wherein the mass ratio of 13X seeds to NaOH solution is 1:50. Weigh 8.016 g of the 13X molecular sieve seeds treated with the above NaOH solution and add them to 4A precursor gel (80.16 g, the amount of 13X molecular sieve seeds added is 10% of the mass of 4A precursor gel), and continue to stir at room temperature for 1 h to obtain the synthesis solution, namely the core-shell precursor gel.

[0176] The synthesis steps in step (4) are the same as in Example 1.

[0177] Example 22

[0178] The preparation method of the core-shell molecular sieve in this embodiment differs from that in Example 1 in that the concentration of the NaOH solution in step (3) is 0.4 mol / L, as detailed below:

[0179] The synthesis steps of steps (1) and (2) are the same as in Example 1.

[0180] (3) Treat 13X molecular sieve seeds with 0.4 mol / L NaOH solution at room temperature for 2 h, wherein the mass ratio of 13X seeds to NaOH solution is 1:50. Weigh 8.016 g of the 13X molecular sieve seeds treated with the above NaOH solution and add them to 4A precursor gel (80.16 g, the amount of 13X molecular sieve seeds added is 10% of the mass of 4A precursor gel), and continue to stir at room temperature for 1 h to obtain the synthesis solution, namely the core-shell precursor gel.

[0181] The synthesis steps in step (4) are the same as in Example 1.

[0182] Example 23

[0183] The preparation method of the core-shell molecular sieve in this embodiment differs from that in Example 1 in that the concentration of the NaOH solution in step (3) is 0.6 mol / L, as detailed below:

[0184] The synthesis steps of steps (1) and (2) are the same as in Example 1.

[0185] (3) Treat 13X molecular sieve seeds with 0.6 mol / L NaOH solution at room temperature for 2 h, wherein the mass ratio of 13X seeds to NaOH solution is 1:50. Weigh 8.016 g of the 13X molecular sieve seeds treated with the above NaOH solution and add them to 4A precursor gel (80.16 g, the amount of 13X molecular sieve seeds added is 10% of the mass of 4A precursor gel), and continue to stir at room temperature for 1 h to obtain the synthesis solution, namely the core-shell precursor gel.

[0186] The synthesis steps in step (4) are the same as in Example 1.

[0187] Example 24

[0188] The preparation method of the core-shell molecular sieve in this embodiment differs from that in Example 1 in that the concentration of the NaOH solution in step (3) is 0.8 mol / L, as detailed below:

[0189] The synthesis steps of steps (1) and (2) are the same as in Example 1.

[0190] (3) Treat 13X molecular sieve seeds with 0.8 mol / L NaOH solution at room temperature for 2 h, wherein the mass ratio of 13X seeds to NaOH solution is 1:50. Weigh 8.016 g of the 13X molecular sieve seeds treated with the above NaOH solution and add them to 4A precursor gel (80.16 g, the amount of 13X molecular sieve seeds added is 10% of the mass of 4A precursor gel), and continue stirring at room temperature for 1 h to obtain the synthesis solution, namely the core-shell precursor gel.

[0191] The synthesis steps in step (4) are the same as in Example 1.

[0192] Comparative Example 3

[0193] The preparation method of the core-shell molecular sieve in this comparative example differs from that in Example 1 in that NaOH solution is not used in step (3), as follows:

[0194] The synthesis steps of steps (1) and (2) are the same as in Example 1.

[0195] (3) Weigh 8.016 g of the 13X molecular sieve seed crystals prepared in step (1) above, add them to the 4A precursor gel (80.16 g, the amount of 13X molecular sieve seed crystals added is 10% of the mass of the 4A precursor gel), and continue to stir at room temperature for 1 h to obtain the synthesis liquid, namely the core-shell precursor gel.

[0196] The synthesis steps in step (4) are the same as in Example 1.

[0197] Example 25

[0198] The preparation method of the core-shell structured molecular sieve in this embodiment includes the following steps:

[0199] (1) Weigh 5.2 g of sodium silicate (Na2SiO3•9H2O) and dissolve it in 75 g of deionized water. Stir at room temperature for 15 min to obtain a silicon source solution. Weigh 3.87 g of sodium hydroxide (NaOH) and dissolve it in 75 g of deionized water. Stir at room temperature for 10 min to obtain a sodium hydroxide solution. Weigh 1.07 g of sodium aluminate (NaAlO2) and dissolve it in the above sodium hydroxide solution. Stir at room temperature for 15 min to obtain an aluminum source solution. Slowly add the silicon source solution to the aluminum source solution through a constant pressure dropping funnel at 60℃. Stir at room temperature for 1 h to form a 13X precursor gel. After standing and aging for 12 h, transfer the 13X precursor gel to a hydrothermal reactor and hydrothermally crystallize at 90℃ for 18 h. Then, it was washed with deionized water, dried at 120°C for 6 h, and calcined at 600°C for 3 h in an air atmosphere in a muffle furnace to obtain 13X molecular sieve seed crystals, i.e., 13X molecular sieve core phase powder.

[0200] (2) Weigh 7.106 g of sodium silicate (Na2SiO3·9H2O) and dissolve it in 65.6 g of deionized water. Stir at room temperature for 15 min to obtain a silicon source solution. Weigh 3.2 g of sodium hydroxide (NaOH) and dissolve it in 65.5 g of deionized water. Stir at room temperature for 10 min to obtain a sodium hydroxide solution. Weigh 1.64 g of sodium aluminate (NaAlO2) and dissolve it in the above sodium hydroxide solution. Stir at room temperature for 15 min to obtain an aluminum source solution. Slowly add the silicon source solution dropwise to the aluminum source solution through a constant pressure dropping funnel at 60℃. Stir at room temperature for 1 h to form a 4A precursor gel.

[0201] (3) Treat 13X molecular sieve seeds with 0.1 mol / L NaOH solution at room temperature for 2 h, wherein the mass ratio of 13X seeds to NaOH solution is 1:50. Weigh 8.016 g of the 13X molecular sieve seeds treated with the above NaOH solution and add them to 4A precursor gel (the amount of 13X molecular sieve seeds added is 10% of the mass of 4A precursor gel), and continue stirring at room temperature for 3 h to obtain the synthesis solution, namely the core-shell precursor gel.

[0202] (4) The synthesis solution obtained in step (3) above was transferred to a hydrothermal reactor and hydrothermally treated (crystallized) at 90°C for 12 h to obtain the hydrothermal product. The synthesized product was washed with water until neutral, dried at 120°C for 6 h, and calcined at 500°C for 6 h in an air atmosphere in a muffle furnace to obtain 13X@4A molecular sieve powder, namely, core-shell molecular sieve (named 13X@4A core-shell molecular sieve).

[0203] Example 26

[0204] The preparation method of the core-shell structured molecular sieve in this embodiment includes the following steps:

[0205] (1) Weigh 5.2 g of sodium silicate (Na2SiO3•9H2O) and dissolve it in 45 g of deionized water. Stir at room temperature for 15 min to obtain a silicon source solution. Weigh 0.850 g of sodium hydroxide (NaOH) and dissolve it in 45 g of deionized water. Stir at room temperature for 10 min to obtain a sodium hydroxide solution. Weigh 0.66 g of sodium aluminate (NaAlO2) and dissolve it in the above sodium hydroxide solution. Stir at room temperature for 15 min to obtain an aluminum source solution. Slowly add the silicon source solution to the aluminum source solution through a constant pressure dropping funnel at 60℃. Stir at room temperature for 1 h to form a 13X precursor gel. After standing and aging for 12 h, transfer the 13X precursor gel to a hydrothermal reactor and hydrothermally crystallize at 100℃ for 12 h. Then, it was washed with deionized water, dried at 120°C for 6 h, and calcined at 500°C for 6 h in an air atmosphere in a muffle furnace to obtain 13X molecular sieve seed crystals, i.e., 13X molecular sieve core phase powder.

[0206] (2) Weigh 10 g of sodium silicate (Na2SiO3·9H2O) and dissolve it in 33 g of deionized water. Stir at room temperature for 15 min to obtain a silicon source solution. Weigh 0.66 g of sodium hydroxide (NaOH) and dissolve it in 33 g of deionized water. Stir at room temperature for 10 min to obtain a sodium hydroxide solution. Weigh 3.84 g of sodium aluminate (NaAlO2) and dissolve it in the above sodium hydroxide solution. Stir at room temperature for 15 min to obtain an aluminum source solution. Slowly add the silicon source solution dropwise to the aluminum source solution through a constant pressure dropping funnel at 60℃. Stir at room temperature for 1 h to form a 4A precursor gel.

[0207] (3) Treat 13X molecular sieve seeds with 1 mol / L NaOH solution at room temperature for 2 h, wherein the mass ratio of 13X seeds to NaOH solution is 1:50. Weigh 6.016 g of the 13X molecular sieve seeds treated with the above NaOH solution and add them to 4A precursor gel (the amount of 13X molecular sieve seeds added is 10% of the mass of 4A precursor gel), and continue stirring at room temperature for 1 h to obtain the synthesis solution, namely the core-shell precursor gel.

[0208] (4) The synthesis solution obtained in step (3) above was transferred to a hydrothermal reactor and hydrothermally treated (crystallized) at 100°C for 6 h to obtain the hydrothermal product. The synthesized product was washed with water until neutral, dried at 120°C for 6 h, and calcined at 600°C for 3 h in an air atmosphere in a muffle furnace to obtain 13X@4A molecular sieve powder, namely, core-shell molecular sieve (named 13X@4A core-shell molecular sieve).

[0209] Example 27

[0210] The preparation method of the core-shell structured molecular sieve in this embodiment includes the following steps:

[0211] (1) Weigh 5.2 g of sodium silicate (Na2SiO3•9H2O) and dissolve it in 18 g of deionized water. Stir at room temperature for 15 min to obtain a silicon source solution. Weigh 2.44 g of sodium hydroxide (NaOH) and dissolve it in 18.6 g of deionized water. Stir at room temperature for 10 min to obtain a sodium hydroxide solution. Weigh 1 g of sodium aluminate (NaAlO2) and dissolve it in the above sodium hydroxide solution. Stir at room temperature for 15 min to obtain an aluminum source solution. Slowly add the silicon source solution to the aluminum source solution through a constant pressure dropping funnel at 60℃. Stir at room temperature for 1 h to form a 13X precursor gel. After standing and aging for 12 h, transfer the 13X precursor gel to a hydrothermal reactor and hydrothermally crystallize at 100℃ for 12 h. Then, it was washed with deionized water, dried at 120°C for 6 h, and calcined at 550°C for 4 h in an air atmosphere in a muffle furnace to obtain 13X molecular sieve seed crystals, i.e., 13X molecular sieve core phase powder.

[0212] (2) Weigh 7.106 g of sodium silicate (Na2SiO3·9H2O) and dissolve it in 35 g of deionized water. Stir at room temperature for 15 min to obtain a silicon source solution. Weigh 1 g of sodium hydroxide (NaOH) and dissolve it in 35 g of deionized water. Stir at room temperature for 10 min to obtain a sodium hydroxide solution. Weigh 2.049 g of sodium aluminate (NaAlO2) and dissolve it in the above sodium hydroxide solution. Stir at room temperature for 15 min to obtain an aluminum source solution. Slowly add the silicon source solution dropwise to the aluminum source solution through a constant pressure dropping funnel at 60℃. Stir at room temperature for 1 h to form a 4A precursor gel.

[0213] (3) Treat 13X molecular sieve seeds with 0.5 mol / L NaOH solution at room temperature for 2 h, wherein the mass ratio of 13X seeds to NaOH solution is 1:50. Weigh 6.016 g of the 13X molecular sieve seeds treated with the above NaOH solution and add them to 4A precursor gel (the amount of 13X molecular sieve seeds added is 10% of the mass of 4A precursor gel), and continue stirring at room temperature for 1 h to obtain the synthesis solution, namely the core-shell precursor gel.

[0214] (4) The synthesis solution obtained in step (3) above was transferred to a hydrothermal reactor and hydrothermally treated (crystallized) at 100°C for 12 h to obtain the hydrothermal product. The synthesized product was washed with water until neutral, dried at 120°C for 6 h, and calcined at 550°C for 4 h in an air atmosphere in a muffle furnace to obtain 13X@4A molecular sieve powder, namely, core-shell molecular sieve (named 13X@4A core-shell molecular sieve).

[0215] Implementation Results Example

[0216] All molecular sieve adsorbents prepared in the examples and comparative examples were subjected to gas adsorption tests. The specific procedures are as follows:

[0217] Weigh 100 mg of the dried sample and place it into a sample tube of known weight. Connect the sample tube to the degassing port of the MICROMERITICS ASAP2020 instrument analyzer. Degas the sample under vacuum by heating (degassing at 300℃ for 8 hours). After degassing, transfer the processed sample to the analysis station at 273 K and 1 bar for CO2 and N2 adsorption tests (separation factor = CO2 adsorption amount / N2 adsorption amount).

[0218] Figure 10 This chart compares the CO2 adsorption capacity and CO2 / N2 separation factor of the 13X molecular sieve (adsorbent) prepared in Comparative Example 1, the 4A molecular sieve (adsorbent) prepared in Comparative Example 2, and the 13X@4A core-shell molecular sieve (adsorbent) prepared in Example 1. Compared to pure 13X and pure 4A molecular sieves, the core-shell molecular sieve prepared in Example 1 has a higher specific surface area of ​​695 m². 2 / g, with a maximum pore volume of 0.43 cm³. 2 / g, CO2 adsorption capacity increased to 7.56 mmol / g, CO2 / N2 separation factor reached 54, combining the high adsorption capacity of 13X with the high molecular screening of 4A, effectively solving the problems of insufficient selectivity of pure 13X and limited adsorption capacity of pure 4A.

[0219] Figure 11 This is a comparison chart of the CO2 adsorption capacity and CO2 / N2 separation factor of the 13X@4A core-shell structure molecular sieve adsorbents prepared in Examples 1, 5, 7, 12, and 20 of this invention.

[0220] Crystallization temperature is the primary factor determining the performance of core-shell molecular sieves, and the inhibitory effect of low temperature on performance far outweighs the slight influence of high temperature. At a crystallization temperature of 80℃, even extending the crystallization time from 12 h (Example 2) to 16 h (Example 5) only increased the CO2 adsorption capacity from 6.26 mmol / g to 6.54 mmol / g and the separation factor from 22 to 28, a very small increase. This indicates that 80℃ is below the optimal temperature for the growth of 4A shell crystals, and the crystallization driving force is severely insufficient; simply extending the time cannot compensate for the structural defects caused by the low temperature. When the temperature is 120℃, the performance is slightly lower than at 100℃, with a decrease of 0.17 mmol / g in CO2 adsorption and a decrease of 5 in the separation factor. This indicates that the temperature has a relatively small impact on the core-shell structure at this point, but it has already caused the performance to deviate from the optimal value. Further heating may significantly damage the core-shell structure.

[0221] The amount of 13X seed crystals added is the core parameter for controlling the core-shell coating state. Its addition ratio directly determines the density of heterogeneous nucleation sites. Low addition amount easily leads to homogeneous 4A nucleation, while high addition amount can achieve directional heterogeneous 4A nucleation, forming a dense core-shell structure. When the amount of 13X seed crystals added is 1% (Example 7), the CO2 adsorption capacity and CO2 / N2 separation factor of the molecular sieve are only 6.31 and 24, respectively (Example 7). 10% is the optimal addition ratio of 13X seed crystals. At this point, the CO2 adsorption capacity (7.56 mmol / g) and CO2 / N2 separation factor (54) of the core-shell molecular sieve both reach their peak values, achieving the optimal synergy between adsorption capacity and molecular sieve performance. 8% is the critical point for cost-effectiveness of the addition amount. At this point, the performance is close to the optimal level of 10% addition amount (CO2 adsorption capacity 7.44 mmol / g, separation factor 51). Considering the raw material cost of industrial production, 8% addition amount can reduce raw material consumption while taking performance into account.

[0222] The molar ratio of NaO2 / SiO2 in the 13X gel precursor regulates the alkalinity of the gel system. A moderate alkalinity (NaO2 / SiO2 = 3) meets the crystallization requirements of the 13X seed crystals. The distribution of silicon and aluminum species on the surface of the 13X seed crystals is suitable, and the density of heterogeneous nucleation sites is moderate. This can accurately induce the directional growth of the 4A shell on its surface, forming a continuous and dense shell, effectively limiting N2 diffusion, and achieving the dual optimization of adsorption capacity and separation selectivity.

[0223] The silicon-to-aluminum ratio of the 4A precursor is the core parameter that determines the quality of the 4A shell. It directly affects the molecular sieving and adsorption capacity of the core-shell molecular sieve by regulating the crystal form, crystallinity, and shell density of 4A. Therefore, the ratio of silicon and aluminum raw materials must be strictly controlled during the preparation process to avoid deviation from the optimal range. A SiO2 / Al2O3 ratio of 2.0 is the optimal parameter for preparing 13X@4A core-shell molecular sieves. At this ratio, the 4A molecular sieve has a regular crystal form and high crystallinity, and can form a dense and defect-free shell on the surface of the 13X core phase. The CO2 adsorption capacity (7.56 mmol / g) and CO2 / N2 separation factor (54) of the core-shell molecular sieve both reach their peak values. A SiO2 / Al2O3 ratio of 1.9-2.0 is the suitable range for the Si / Al ratio of the 4A precursor. Among them, a SiO2 / Al2O3 ratio of 1.9 is the second best choice. At this point, the performance of the core-shell molecular sieve is close to the optimal value, which can be used as a tolerance range for slight process fluctuations in industrial production. If the SiO2 / Al2O3 ratio is further increased, the 4A gel is prone to crystal transformation, which leads to a significant decrease in CO2 adsorption capacity and CO2 / N2 separation factor (Example 20, where the SiO2 / Al2O3 ratio is 2.3, and the CO2 adsorption capacity and CO2 / N2 separation factor are 6.37 and 25, respectively).

[0224] Figure 12 This is a comparison chart of the CO2 adsorption capacity and CO2 / N2 separation factor of the 13X@4A core-shell molecular sieve adsorbents prepared in Examples 1, 21-24 and Comparative Example 3 of this invention. 0.5 mol / L NaOH solution is the optimal concentration for treating 13X seed crystals. Moderate etching at this concentration can achieve sufficient exposure of heterogeneous nucleation sites and complete preservation of the 13X core phase structure, allowing the 4A shell to form a uniform and dense coating structure. The CO2 adsorption capacity (7.56 mmol / g) and CO2 / N2 separation factor (54) of the core-shell molecular sieve both reach their peak values. The essence of concentration control in dilute alkali treatment is to balance the etching effect with the protection of the core phase structure: insufficient etching at low concentrations and excessive etching at high concentrations will both lead to defects in the 4A shell coating. Only when the concentration is appropriate can the synergistic performance of the core-shell structure be achieved. The tolerance range for dilute alkali treatment is 0.4-0.6 mol / L. Although the concentration deviation within this range will cause a slight decrease in performance, it is still far better than the untreated and high-concentration groups. It can be used as a reference range for process fluctuations in industrial production, taking into account both preparation accuracy and production feasibility.

[0225] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a core-shell molecular sieve, characterized in that, The steps are as follows: (1) Mix silicon source, aluminum source, alkali source and water, and stir at room temperature until a uniform gel I is formed; then perform hydrothermal treatment on gel I and calcination to obtain 13X molecular sieve core phase powder; (2) The silicon source, aluminum source, alkali source and water were mixed and stirred at room temperature to obtain 4A precursor gel; (3) The 13X molecular sieve core phase powder obtained in step (1) is treated with dilute alkali solution and then added to the 4A precursor gel in step (2). After stirring at room temperature, a core-shell precursor gel is formed. (4) The core-shell precursor gel obtained in step (3) is subjected to hydrothermal treatment, washing, drying and calcination to obtain a core-shell molecular sieve.

2. The method for preparing core-shell structured molecular sieves according to claim 1, characterized in that, The silicon source includes at least one of sodium silicate, silica, and silica sol; the aluminum source is at least one of sodium aluminate, aluminum hydroxide, and aluminum sol; and the alkali source is sodium hydroxide.

3. The method for preparing core-shell structured molecular sieves according to claim 2, characterized in that, In step (1), the composition of gel I, in terms of the molar ratio of oxides, satisfies the following relationship: SiO2 / Al2O3=2.8-5, Na2O / SiO2=1.8-4, H2O / Na2O=40-160.

4. The method for preparing core-shell structured molecular sieves according to claim 2, characterized in that, In step (2), the composition of the 4A precursor gel, in terms of the molar ratio of oxides, satisfies the following relationship: SiO2 / Al2O3=1.5-2.5, Na2O / SiO2=1.8-3, H2O / Na2O=30-100.

5. The method for preparing core-shell structured molecular sieves according to claim 4, characterized in that, In step (3), the dilute alkali solution is a NaOH solution with a concentration of 0.1-1 mol / L, and the dilute alkali solution treatment is carried out at room temperature for 1-3 hours.

6. The method for preparing a core-shell structured molecular sieve according to claim 5, characterized in that, In step (3), the amount of 13X molecular sieve core phase powder treated with dilute alkali solution added is 1%-10% of the mass of 4A precursor gel.

7. The method for preparing core-shell structured molecular sieves according to claim 6, characterized in that, In steps (1) and (4), the hydrothermal treatment temperature is 90-120℃ and the time is 6-18 h.

8. The method for preparing core-shell structured molecular sieves according to claim 7, characterized in that, In steps (1) and (4), the calcination temperature is 500-600℃ and the time is 3-6 h.

9. A core-shell molecular sieve prepared using the preparation method of the core-shell molecular sieve according to any one of claims 1-8.

10. The application of the core-shell molecular sieve of claim 9 in the field of gas adsorption and separation.

Images