Alkaline earth metal adsorbent having core-shell structure, and preparation method therefor and use thereof

Abstract

The present application relates to the technical field of the preparation of a catalyst. Disclosed are an alkaline earth metal adsorbent having a core-shell structure, and a preparation method therefor and the use thereof. The alkaline earth metal adsorbent has a core-shell structure, wherein an alkaline earth metal molecular sieve adsorbent acts as a core, and yMxSiO2 acts as a shell. The alkaline-earth metal molecular sieve adsorbent comprises a molecular sieve and an alkaline-earth metal element loaded on the molecular sieve. yMxSiO2 is a silicon dioxide material doped with and modified by a metal assistant M, and the metal assistant M comprises at least one of La, Sm, Nd and Pr. The ratio of y to x in yMxSiO2 represents the mass ratio of the metal assistant M to SiO2, where y:x = 0.01-0.1:1. The thickness of the shell layer of the alkaline earth metal adsorbent is 20-100 nm.

Description

An alkaline earth metal adsorbent with a core-shell structure and its preparation method and application

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on March 1, 2024, with application number 202410234504.3, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the technical field of catalyst preparation, and in particular to an alkaline earth metal adsorbent with a core-shell structure, a preparation method thereof, and an application thereof. Background Art

[0003] In recent years, with the rapid development of the economy, the number of motor vehicles has continued to increase. However, the environmental pollution caused by fuel combustion has also attracted people's attention. Motor vehicle exhaust has caused serious damage to the atmospheric environment, among which NO x Most notably, denitrification has become a very important research topic worldwide, promoting the NO x Emission reduction has become a top priority. The decomposition temperature of urea in the NH3-SCR system is above 180°C; on the other hand, the high efficiency temperature window of the SCR catalyst used is often above 200°C. Therefore, under low exhaust temperature conditions, NO x The treatment of NO has become a difficult problem. In order to solve the problem of low temperature cold start stage x To solve the emission problem, PNA technology (passive NOx adsorption) was born. This technology can efficiently adsorb NO at a lower temperature. x , and at high temperatures NO x PNAs are considered to be the most promising solution to the low-temperature cold start NO x Technology to address emissions issues.

[0004] Research into treating nitrogen oxides during the cold start phase of vehicles is still in the R&D stage. Research is primarily focused on selective nitrogen oxide reduction (PNAs), a class of materials that efficiently adsorb and reduce nitrogen oxides. These materials adsorb nitrogen oxides at low temperatures and then release them at appropriate temperatures. These released nitrogen oxides are then reduced to harmless nitrogen and water by a subsequent SCR adsorbent, achieving a purification effect.

[0005] The use of PNAs to treat nitrogen oxides during the low-temperature cold start phase of motor vehicles has the following main problems:

[0006] 1. Currently, PNAs are mainly composed of precious metal oxide molecular sieve systems. This technology uses precious metal palladium as the active component, and the production cost is relatively high;

[0007] 2. The adsorption capacity of nitrogen oxides by noble metal oxide molecular sieves is low and cannot meet actual needs;

[0008] 3. When alkaline earth metals are used as adsorption materials, there is the effect of competitive adsorption of water vapor, which greatly reduces the adsorption capacity of nitrogen oxides by alkaline earth metal adsorbents.

[0009] Therefore, there is an urgent need for a low-cost, high-absorption rate nitrogen oxide selective adsorption reduction material for absorbing nitrogen oxides emitted during the low-temperature cold start phase of motor vehicles.

[0010] Summary of the Invention

[0011] In order to solve the above technical problems, the present application provides an alkaline earth metal adsorbent with a core-shell structure, which has low cost and high absorption rate for nitrogen oxides.

[0012] The alkaline earth metal adsorbent has a core-shell structure, with the alkaline earth metal molecular sieve adsorbent as the core and yMxSiO2 as the shell;

[0013] The alkaline earth metal molecular sieve adsorbent comprises a molecular sieve and an alkaline earth metal element loaded on the molecular sieve;

[0014] The yMxSiO2 is a silicon dioxide material doped and modified by a metal additive M, wherein the metal additive M includes at least one of La, Sm, Nd, and Pr;

[0015] The ratio of y to x in the yMxSiO2 represents the mass ratio of the metal additive M to SiO2, wherein y:x=0.01 to 0.1:1;

[0016] The shell thickness of the alkaline earth metal adsorbent is 20nm to 100nm.

[0017] Optionally, the alkaline earth metal element includes at least one of Mg, Ca, Sr, and Ba.

[0018] Optionally, the structure of the molecular sieve is at least one of MFI, CHA, BEA, AEI, LTA and FAU.

[0019] Optionally, the molecular sieve comprises silicon and aluminum, and the molar ratio of silicon to aluminum is 6 to 15.

[0020] Optionally, the shell thickness of the alkaline earth metal adsorbent may be 50 nm.

[0021] The present application also provides a method for preparing an alkaline earth metal adsorbent with a core-shell structure, which is used for preparing any of the alkaline earth metal adsorbents with a core-shell structure described above, comprising the following steps:

[0022] Preparation of alkaline earth metal molecular sieve adsorbents;

[0023] Preparation of an alkaline earth metal adsorbent having a core-shell structure: grinding the alkaline earth metal molecular sieve adsorbent and adding it to a solution of a surfactant and a dispersing solvent, and ultrasonically dispersing the solution to obtain a mixed solution A;

[0024] Adding a shell oxide precursor and an auxiliary agent precursor into deionized water at a mass ratio of 0.01 to 0.08:1, stirring to dissolve and ultrasonically dispersing to obtain a mixed solution B;

[0025] The mixed solution B is mixed with the mixed solution A, wherein the mass ratio of silicon in the shell oxide precursor to the molecular sieve in the alkaline earth metal molecular sieve adsorbent is 0.032 to 0.207:1, and the mixture is continuously stirred to obtain a mixed solution C;

[0026] The pH of the mixed solution C is adjusted to 8-10 while stirring to obtain a mixed solution D;

[0027] The mixed solution D is continuously stirred in a water bath at 40-90° C. for 3-10 hours, filtered, washed, dried, and calcined at 300-600° C. for 3-6 hours to obtain the alkaline earth metal adsorbent with a core-shell structure.

[0028] Optionally, the steps of preparing the alkaline earth metal molecular sieve adsorbent are as follows:

[0029] After the soluble alkaline earth metal active component precursor is completely dissolved, molecular sieves are added, ultrasonic treatment is performed, and stirring is carried out at a temperature of 60°C to 120°C for 3h to 8h to carry out ion exchange reaction;

[0030] After the ion exchange reaction is completed, the mixture is filtered, washed, and dried. After drying, the mixture is calcined at 300° C. to 600° C. for 3 h to 6 h to obtain the alkaline earth metal molecular sieve adsorbent.

[0031] Optionally, when preparing the alkaline earth metal molecular sieve adsorbent, the mass ratio of the alkaline earth metal element in the alkaline earth metal active component precursor to the molecular sieve is 0.01 to 0.1:1.

[0032] Optionally, after the soluble alkaline earth metal active component precursor is completely dissolved, the molecular sieve carrier is added and ultrasonic treatment is performed, and stirring is optionally performed at 95°C.

[0033] The present application also provides the use of any of the above alkaline earth metal adsorbents with a core-shell structure or the core-shell alkaline earth metal adsorbent prepared by any of the above alkaline earth metal adsorbent preparation methods with a core-shell structure in the adsorption of nitrogen oxides.

[0034] The embodiments of the present application have the following technical effects:

[0035] 1. The alkaline earth metal adsorbent with a core-shell structure provided in this application uses an alkaline earth metal molecular sieve adsorbent as the core and loads the alkaline earth metal on the molecular sieve. It has excellent adsorption performance for nitrogen oxides, greatly improving the adsorption rate of nitrogen oxides generated during the low-temperature cold start phase of motor vehicles, and better meeting actual needs.

[0036] 2. The alkaline earth metal adsorbent with a core-shell structure in this application is based on an alkaline earth metal molecular sieve adsorbent as the core and yMxSiO2 as the shell, which can effectively block water vapor from entering the core, overcome the disadvantage of alkaline earth metal adsorbent being deactivated in the presence of water, has excellent resistance to competitive adsorption of water vapor, effectively improves the performance of the adsorption material in adsorbing nitrogen oxides, and the metal additive M effectively improves the hydrothermal stability of the shell.

[0037] 3. The core part of the core-shell structure is alkaline earth metal molecular sieve adsorbent. Compared with traditional nitrogen oxide adsorption materials (Pd / SSZ-13), alkaline earth metal molecular sieve adsorbent uses cheap alkaline earth metals as active components and does not require the addition of precious metals, which greatly reduces the cost of adsorption materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the specific implementation methods of the present application or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the specific implementation methods or the description of the prior art. Obviously, the drawings described below are some implementation methods of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0039] FIG1 is a transmission electron microscope (TEM) image of the alkaline earth metal adsorbent having a core-shell structure prepared in Example 1 of the present application;

[0040] FIG2 is a diagram of the NO adsorbent of the alkaline earth metal with a core-shell structure prepared in Example 1 of the present application. x Adsorption performance diagram;

[0041] FIG3 is a scanning electron microscope (SEM) image of the alkaline earth metal adsorbent having a core-shell structure prepared in Example 2 of the present application;

[0042] FIG4 is a comparison diagram of high-angle annular dark field scanning transmission (HAADF-STEM) of the adsorbents prepared in Example 2 and Comparative Example 1 of the present application;

[0043] FIG5 is a scanning electron microscope (SEM) image of the Ba / SSZ-13 molecular sieve adsorbent prepared in Comparative Example 1 of the present application;

[0044] FIG6 is a diagram of the NO adsorbent of the alkaline earth metal core-shell structure prepared in Example 3 of the present application. x Adsorption performance diagram;

[0045] FIG7 is a scanning electron microscope (SEM) image of the alkaline earth metal adsorbent having a core-shell structure prepared in Example 3 of the present application;

[0046] FIG8 is a graph showing the NO adsorbent prepared in Comparative Example 1 of the present application with and without water. x Adsorption performance comparison chart. DETAILED DESCRIPTION

[0047] To make the objectives, technical solutions, and advantages of this application more clear, the technical solutions of this application are described clearly and completely below. Obviously, the embodiments described are only some of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by persons of ordinary skill in the art without inventive effort are within the scope of protection of this application.

[0048] Currently, PNAs for treating nitrogen oxides during the low-temperature cold start phase of vehicles are primarily composed of precious metal oxide molecular sieve systems with palladium as the active component. These systems are expensive to produce and exhibit low nitrogen oxide adsorption capacity, failing to meet practical needs. Furthermore, when alkaline earth metal adsorbents are used as adsorption materials, they compete with water vapor for adsorption, reducing their nitrogen oxide adsorption performance.

[0049] Therefore, the present application provides an alkaline earth metal adsorbent with a core-shell structure, with an alkaline earth metal molecular sieve adsorbent as the core and yMxSiO2 as the shell. Alkaline earth metals are used as active components and are loaded on the molecular sieve to form an alkaline earth metal molecular sieve adsorbent with a core: the molecular sieve has a unique pore structure and a large specific surface area, providing more sites for the alkaline earth metal, increasing the contact area between the alkaline earth metal and nitrogen oxides, and improving the performance of adsorbing nitrogen oxides. At the same time, the yMxSiO2 of the shell effectively blocks water vapor from entering the core, giving it excellent resistance to competitive adsorption of water vapor, further improving the absorption rate of adsorbed nitrogen oxides.

[0050] Specifically, the alkaline earth metal adsorbent has a core-shell structure, with the alkaline earth metal molecular sieve adsorbent as the core and yMxSiO2 as the shell.

[0051] The alkaline earth metal molecular sieve adsorbent comprises a molecular sieve and an alkaline earth metal element supported on the molecular sieve.

[0052] Alkaline earth metal molecular sieve adsorbents have excellent adsorption performance. This is because pure alkaline earth metals have a small specific surface area and a limited contact area with NOx, while the molecular sieve itself has a unique pore structure and a large specific surface area, which provides more sites for alkaline earth metals, is conducive to the dispersion of alkaline earth metals, and can greatly improve the catalytic performance of alkaline earth metals.

[0053] Alkaline earth metals have a low electronegativity in their electronic structure and tend to lose outer-shell electrons, forming positive ions. This positive charge facilitates interaction with the negatively charged nitrogen or oxygen atoms in nitrogen oxides. Secondly, alkaline earth metals have a large ionic radius and a low electron affinity. The large ionic radius means that the positive ions of alkaline earth metals have a larger surface area, which facilitates contact with nitrogen oxide molecules. Their low electron affinity enables them to accept electrons from nitrogen oxides, thereby reacting chemically with them. Finally, alkaline earth metals have high electrical conductivity and catalytic activity. High electrical conductivity means that alkaline earth metals can facilitate electron transfer across their surfaces, thereby strengthening their interaction with nitrogen oxides. Furthermore, alkaline earth metals can act as catalysts, promoting the adsorption and reduction of nitrogen oxides, thereby converting them into more stable substances.

[0054] yMxSiO2 is a silicon dioxide material doped and modified by a metal additive M, and the metal additive M includes at least one of La, Sm, Nd, and Pr.

[0055] The alkaline earth metal adsorbent, with its yMxSiO2 shell, effectively blocks water vapor from entering the core, overcoming the drawback of alkaline earth metal adsorbent deactivation in the presence of water. It exhibits excellent resistance to competitive adsorption by water vapor, effectively improving the adsorption performance of the adsorbent material for nitrogen oxides. The metal additive M forms a bridging effect with the silica matrix, effectively preventing catalyst loosening and desorption, thereby improving the catalyst's hydrothermal stability. Furthermore, the addition of the M element can slow or inhibit the growth and aggregation of alkaline earth metal particles, further enhancing the catalytic performance of the alkaline earth metal.

[0056] The ratio of y to x in yMxSiO2 represents the mass ratio of the metal additive M and SiO2, where y:x = 0.01~0.1:1, to ensure that the generated shell effectively blocks water vapor from entering the core and enhances the anti-water vapor competition ability of the alkaline earth metal adsorbent in the core.

[0057] The shell thickness of the alkaline earth metal adsorbent is 20nm to 100nm.

[0058] Optionally, the alkaline earth metal element includes at least one of Mg, Ca, Sr, and Ba. Alkaline earth metal ions have a high charge density and a small ionic radius, which enables them to generate a strong attraction with other substances. During the adsorption process, they can adsorb a large number of molecules or ions, thereby increasing the reactivity of the adsorption surface.

[0059] Optionally, the molecular sieve has a structure of at least one of MFI, CHA, BEA, AEI, LTA, and FAU. The molecular sieve of this structure is surface treated, and cations are added to its outer layer. The cations in the outer layer react and combine with the silica precursor, so that the alkaline earth metal molecular sieve adsorbent in the inner core is encapsulated to form a stable core-shell structure.

[0060] Optionally, the molecular sieve includes silicon and aluminum, and the molar ratio of silicon to aluminum is 6-15, and optionally 6-10.

[0061] Optionally, the shell thickness of the alkaline earth metal adsorbent may be 50 nm.

[0062] The present application also provides a method for preparing an alkaline earth metal adsorbent having a core-shell structure, which is used for preparing any of the above alkaline earth metal adsorbents having a core-shell structure, comprising the following steps:

[0063] The steps for preparing alkaline earth metal molecular sieve adsorbent are as follows:

[0064] After the soluble alkaline earth metal active component precursor is completely dissolved, molecular sieves are added, ultrasonic treatment is performed, and the mixture is stirred at a temperature of 60° C. to 120° C. for 3 h to 8 h to carry out ion exchange reaction.

[0065] Optionally, when preparing the alkaline earth metal molecular sieve adsorbent, the mass ratio of the alkaline earth metal element in the alkaline earth metal active component precursor to the molecular sieve is 0.01 to 0.1:1.

[0066] Optionally, after the soluble alkaline earth metal active component precursor is completely dissolved, it is added to the molecular sieve carrier and ultrasonically treated, and optionally stirred at 95° C. The stirring temperature can be controlled at 95° C. to maximize the yield of the alkaline earth metal molecular sieve adsorbent and achieve excellent preparation efficiency.

[0067] Furthermore, the stirring time is set to 5 h, which can increase the yield of the alkaline earth metal molecular sieve adsorbent and optimize the yield-time ratio.

[0068] After the ion exchange reaction is completed, the product is filtered, washed, and dried at a temperature below 50°C. After drying, it is calcined at 300°C to 600°C for 3 to 6 hours to obtain an alkaline earth metal molecular sieve adsorbent. The calcination heating rate needs to be controlled to prevent excessive evaporation of water, which would cause alkaline earth metal migration, aggregation, and damage to the molecular sieve structure. The heating rate can be controlled to no more than 5°C / minute.

[0069] Preparation of an alkaline earth metal adsorbent with a core-shell structure: grinding an alkaline earth metal molecular sieve adsorbent and adding it to a solution of a surfactant and a dispersing solvent, and ultrasonically dispersing the solution to obtain a mixed solution A.

[0070] The addition of a surfactant during the preparation process can form an electron layer on the surface of the alkaline earth metal molecular sieve adsorbent, thereby improving the encapsulation of the shell structure. One or more of polyethylene glycol, cetyltrimethylammonium bromide, octadecyltrimethylammonium chloride, glycerol, dodecyldimethylamine oxide, or cetylpyridinium chloride can be used as the surfactant. The surfactant does not participate in the synthesis of the substance but only serves to promote the encapsulation of the shell layer during the preparation process. Therefore, its amount is not specifically limited.

[0071] The addition of a dispersing solvent ensures a more uniform dispersion of the alkaline earth metal molecular sieve adsorbent, facilitating the formation of a single core-shell structure. The dispersing solvent can be one or more of methanol, ethanol, acetone, trichloroethylene, ethylene glycol ether, and triethanolamine. The dispersing solvent does not participate in the synthesis of the substance but serves to disperse the substance during the preparation process. Therefore, its amount is not specifically limited.

[0072] The shell oxide precursor and the auxiliary agent precursor are added into deionized water with a mass ratio of the shell oxide precursor to the auxiliary agent precursor being 0.01 to 0.08:1, stirred to dissolve and ultrasonically dispersed to obtain a mixed solution B.

[0073] The mixed solution B is mixed with the mixed solution A, with the mass ratio of silicon in the shell oxide precursor to the molecular sieve in the alkaline earth metal molecular sieve adsorbent being 0.032-0.207:1, and the mixture is continuously stirred to obtain a mixed solution C.

[0074] The pH of the mixed solution C is adjusted to 8-10 while stirring to obtain a mixed solution D.

[0075] Mixed solution D is stirred continuously in a water bath at 40-90°C for 3-10 hours, filtered, washed, and dried at a drying temperature below 50°C. It is then calcined at 300-600°C for 3-6 hours to obtain an alkaline earth metal adsorbent having a core-shell structure. The calcination heating rate is not to exceed 5°C / minute to prevent rapid evaporation of water and destruction of the shell structure.

[0076] The present application also provides the use of any of the above alkaline earth metal adsorbents with a core-shell structure or the core-shell alkaline earth metal adsorbent prepared by any of the above alkaline earth metal adsorbent preparation methods with a core-shell structure in the adsorption of nitrogen oxides.

[0077] This application also provides the following specific examples to illustrate the preparation process in detail:

[0078] Example 1

[0079] (1) Preparation of alkaline earth metal molecular sieve adsorbent:

[0080] Step 1. After calcium chloride is completely dissolved, add it to the AEI molecular sieve carrier. The mass ratio of alkaline earth metal element calcium to molecular sieve in the alkaline earth metal active component precursor is 0.01:1, and the molar ratio of silicon element to aluminum element is 10. Ultrasonic treatment is performed and stirred at 95°C for 5 hours to carry out ion exchange reaction.

[0081] Step 2. After the ion exchange reaction is completed, the reaction solution after ion exchange is filtered, washed with deionized water, vacuum dried at 40°C overnight, and calcined at 550°C for 5h with a heating rate of 2°C / min to obtain a Ca / SSZ-13 molecular sieve adsorbent.

[0082] (2) Preparation of alkaline earth metal adsorbent with core-shell structure:

[0083] Step 3. Grind the Ca / SSZ-13 molecular sieve adsorbent obtained in step 2, take 1 g of the ground Ca / SSZ-13 molecular sieve adsorbent and add it to a solution prepared by mixing 1 g of surfactant octadecyltrimethylammonium chloride and 200 ml of ethanol, and ultrasonically disperse it for 30 minutes to obtain a mixed solution A.

[0084] Step 4. Add ethyl silicate and lanthanum nitrate to deionized water in a mass ratio of 0.01:1, stir to dissolve, and ultrasonically disperse for 30 minutes to obtain a mixed solution B.

[0085] Step 5. Mix the mixed solution B with the mixed solution A, wherein the mass ratio of silicon in the shell oxide precursor ethyl silicate to the molecular sieve in the alkaline earth metal molecular sieve adsorbent is 0.032:1, and continue stirring to obtain a mixed solution C.

[0086] Step 6. Slowly add aqueous ammonia to the mixed solution C while stirring to adjust the pH of the mixed solution to 8-10 to obtain a mixed solution D.

[0087] Step 7. After the mixed solution D was continuously stirred in a 60°C water bath for 6 hours, it was filtered, washed, and vacuum-dried at 40°C overnight. It was calcined at 550°C for 5 hours at a heating rate of 2°C / min to obtain 0.0015La0.15SiO2@Ca / SSZ-13 alkaline earth metal adsorbent with a core-shell structure.

[0088] Example 2

[0089] (1) Preparation of alkaline earth metal molecular sieve adsorbent:

[0090] Step 1. After the barium acetate is completely dissolved, a BEA molecular sieve carrier is added. The mass ratio of the alkaline earth metal element barium to the molecular sieve in the alkaline earth metal active component precursor is 0.1:1, and the molar ratio of the silicon element to the aluminum element is 15. Ultrasonic treatment is performed and stirred at a temperature of 95°C for 5 hours to carry out an ion exchange reaction.

[0091] Step 2. After the ion exchange reaction is completed, the reaction solution after ion exchange is filtered, washed with deionized water, vacuum dried at 40°C overnight, and calcined at 550°C for 5h with a heating rate of 2°C / min to obtain a Ba / SSZ-13 molecular sieve adsorbent.

[0092] (2) Preparation of alkaline earth metal adsorbent with core-shell structure:

[0093] Step 3. Grind the Ba / SSZ-13 molecular sieve adsorbent obtained in step 2, take 1 g of the ground Ca / SSZ-13 molecular sieve adsorbent and add it to a solution prepared by mixing 1 g of surfactant polyethylene glycol and 200 ml of methanol, and ultrasonically disperse it for 30 minutes to obtain a mixed solution A.

[0094] Step 4. Add ethyl silicate and praseodymium nitrate into deionized water at a mass ratio of 0.08:1, stir to dissolve, and ultrasonically disperse for 30 minutes to obtain a mixed solution B.

[0095] Step 5. Mix the mixed solution B with the mixed solution A, wherein the mass ratio of silicon in the shell oxide precursor ethyl silicate to the molecular sieve in the alkaline earth metal molecular sieve adsorbent is 0.207:1, and continue stirring to obtain a mixed solution C.

[0096] Step 6. Slowly add aqueous ammonia to the mixed solution C while stirring to adjust the pH of the mixed solution to 8-10 to obtain a mixed solution D.

[0097] Step 7. After the mixed solution D was continuously stirred in a 60°C water bath for 6 hours, it was filtered, washed, and vacuum-dried at 40°C overnight. It was calcined at 550°C for 5 hours at a heating rate of 2°C / min to obtain 0.0075Pr0.15SiO2@Ba / SSZ-13 alkaline earth metal adsorbent with a core-shell structure.

[0098] Example 3

[0099] (1) Preparation of alkaline earth metal molecular sieve adsorbent:

[0100] Step 1. After magnesium chloride is completely dissolved, an SSZ-13 molecular sieve carrier is added. The mass ratio of alkaline earth metal element magnesium to molecular sieve in the alkaline earth metal active component precursor is 0.05:1. The structure of the SSZ-13 molecular sieve is CHA, and the molar ratio of silicon element to aluminum element is 6. Ultrasonic treatment is performed and the mixture is stirred at a temperature of 95°C for 5 hours to carry out an ion exchange reaction.

[0101] Step 2. After the ion exchange reaction is completed, the reaction solution after ion exchange is filtered, washed with deionized water, vacuum dried at 40°C overnight, and calcined at 550°C for 5h with a heating rate of 2°C / min to obtain a Mg / SSZ-13 molecular sieve adsorbent.

[0102] (2) Preparation of alkaline earth metal adsorbent with core-shell structure:

[0103] Step 3. Grind the Mg / SSZ-13 molecular sieve adsorbent obtained in step 2, take 1 g of the ground Mg / SSZ-13 molecular sieve adsorbent and add it to a solution prepared by mixing 1 g of surfactant cetylpyridinium chloride and 200 ml of ethylene glycol ether, and ultrasonically disperse it for 30 minutes to obtain a mixed solution A.

[0104] Step 4. Add ethyl silicate and neodymium nitrate into deionized water at a mass ratio of ethyl silicate to neodymium nitrate of 0.01:1, stir to dissolve, and ultrasonically disperse for 30 minutes to obtain a mixed solution B.

[0105] Step 5. Mix the mixed solution B with the mixed solution A, wherein the mass ratio of silicon in the shell oxide precursor ethyl silicate to the molecular sieve in the alkaline earth metal molecular sieve adsorbent is 0.207:1, and continue stirring to obtain a mixed solution C.

[0106] Step 6. Slowly add aqueous ammonia to the mixed solution C while stirring to adjust the pH of the mixed solution to 8-10 to obtain a mixed solution D.

[0107] Step 7. After the mixed solution D was continuously stirred in a 60°C water bath for 6 hours, it was filtered, washed, and vacuum-dried at 40°C overnight. It was calcined at 550°C for 5 hours at a heating rate of 2°C / min to obtain 0.0075Nd0.15SiO2@Mg / SSZ-13 alkaline earth metal adsorbent with a core-shell structure.

[0108] NO x Adsorption performance test method:

[0109] The alkaline earth metal molecular sieve adsorbent prepared in the embodiment (1.0 g, 40-60 mesh) was first pretreated, which included a constant temperature treatment at 550° C. for 30 min in a nitrogen atmosphere containing 10% oxygen, then lowering the temperature to 100° C., and then conducting an adsorption experiment at a temperature of 100° C.; first, the atmosphere was switched to a bypass, and the atmosphere was adjusted to: nitrogen as the balance gas, 10% oxygen, 500 ppm nitric oxide, 500 ppm carbon monoxide, and 5% water vapor; after the atmosphere was adjusted, the gas was switched to a reaction tube for a nitrogen oxide adsorption experiment until adsorption was saturated.

[0110] Example 4

[0111] The experimental conditions were the same as those in Example 1, except that the amounts of ethyl silicate and lanthanum nitrate were adjusted in step 4 so that the shell thickness of 0.0015La0.15SiO2@Ca / SSZ-13 reached 20 nm.

[0112] Comparative Example 1

[0113] The experimental conditions were the same as those in Example 3, except that only the Ba / SSZ-13 molecular sieve adsorbent was prepared, and the alkaline earth metal adsorbent with a core-shell structure was not prepared.

[0114] Comparative Example 2

[0115] The experimental conditions were the same as those in Example 1, except that the amounts of ethyl silicate and lanthanum nitrate were adjusted in step 4 so that the shell thickness of 0.0015La0.15SiO2@Ca / SSZ-13 reached 50 nm.

[0116] Comparative Example 3

[0117] The experimental conditions were the same as those in Example 1, except that the amounts of ethyl silicate and lanthanum nitrate were adjusted in step 4 so that the shell thickness of 0.0015La0.15SiO2@Ca / SSZ-13 reached 100 nm.

[0118] Comparative Example 4

[0119] The experimental conditions were the same as those in Example 3, except that the molar ratio of silicon to aluminum was 15.

[0120] Comparative Example 5

[0121] The experimental conditions were the same as those in Example 3, except that the molar ratio of silicon to aluminum was 50.

[0122] Comparative Example 6

[0123] The experimental conditions were the same as those in Example 3, except that the molar ratio of silicon to aluminum was 10.

[0124] Comparative Example 7

[0125] The experimental conditions were the same as those in Example 2, except that in step 1, the mixture was stirred at 60° C. for 5 h.

[0126] Comparative Example 8

[0127] The experimental conditions were the same as those in Example 2, except that in step 1, the mixture was stirred at 120° C. for 5 h.

[0128] Comparative Example 9

[0129] The experimental conditions were the same as those in Example 3, except that the mass ratio of alkaline earth metal element magnesium to molecular sieve in the alkaline earth metal active component precursor was 0.01:1 when preparing the alkaline earth metal molecular sieve adsorbent.

[0130] Comparative Example 10

[0131] The experimental conditions were the same as those in Example 3, except that the mass ratio of alkaline earth metal element magnesium to molecular sieve in the alkaline earth metal active component precursor was 0.1:1 when preparing the alkaline earth metal molecular sieve adsorbent.

[0132] Comparative Example 11

[0133] The experimental conditions are the same as those in Example 3, except that the masses of ethyl silicate and lanthanum nitrate in step 4 are adjusted so that the mass ratio of yMxSiO2 in the generated shell layer, which is the metal additive lanthanum and SiO2, is 0.01:1.

[0134] Comparative Example 12

[0135] The experimental conditions are the same as those in Example 3, except that the masses of ethyl silicate and lanthanum nitrate in step 4 are adjusted so that the mass ratio of yMxSiO2 in the generated shell layer, which is the metal additive lanthanum and SiO2, is 0.1:1.

[0136] Comparative Example 13

[0137] The experimental conditions are the same as those in Example 3, except that the masses of ethyl silicate and lanthanum nitrate in step 4 are adjusted so that the mass ratio of yMxSiO2 in the generated shell layer, which is the metal additive lanthanum and SiO2, is 0.05:1.

[0138] Comparative Example 14

[0139] The experimental conditions were the same as those in Example 1, except that calcium chloride was replaced with palladium nitrate when preparing the alkaline earth metal molecular sieve adsorbent.

[0140] Figure 1 is a transmission electron microscope (TEM) image of the alkaline earth metal adsorbent with a core-shell structure prepared in Example 1 of the present application. It can be clearly seen from the figure that the prepared alkaline earth metal adsorbent has a clear core-shell structure, wherein the core part is an alkaline earth metal molecular sieve adsorbent composed of a molecular sieve and an alkaline earth metal element loaded on the molecular sieve, and the shell part is a silica material doped and modified by a metal additive M.

[0141] Use NO x Adsorption performance test method: the alkaline earth metal adsorbent with core-shell structure prepared in Example 1 was tested, and the test results are shown in Figure 2. The alkaline earth metal adsorbent with core-shell structure began to adsorb NO from the 6th minute. x , NO x The concentration of NO decreased rapidly, approaching 0 ppm, and was saturated at the 20th minute. x Has good adsorption properties.

[0142] Pure alkaline earth metals have a small specific surface area and are x The contact area is limited, but the molecular sieve itself has a unique pore structure and a large specific surface area, which provides more sites for alkaline earth metals, is conducive to the dispersion of alkaline earth metals, and can greatly improve the catalytic performance of alkaline earth metals.

[0143] Two portions of Ba / SSZ-13 molecular sieve adsorbent were prepared using the method in Comparative Example 1. x Adsorption performance test method: test the adsorption of NO by two Ba / SSZ-13 molecular sieve adsorbents. x The adsorption performance of Ba / SSZ-13 molecular sieve is divided into water test and anhydrous test. The water test is to adjust the atmosphere to contain 5% water vapor, and the anhydrous test is to adjust the atmosphere to contain no water vapor. As shown in Figure 8, the adsorption performance of Ba / SSZ-13 molecular sieve on NO x The adsorption performance of Ba / SSZ-13 molecular sieve is better than that of water in the absence of water, that is, the presence of water vapor will reduce the adsorption of NO by Ba / SSZ-13 molecular sieve. x To reduce the adsorption capacity of the nanostructured carbon, it needs to be wrapped with a shell to reduce the contact with water vapor.

[0144] The alkaline earth metal adsorbent, with its yMxSiO2 shell, effectively blocks water vapor from entering the core, overcoming the drawback of alkaline earth metal adsorbent deactivation in the presence of water. It exhibits excellent resistance to competitive adsorption by water vapor, effectively improving the adsorption performance of the adsorbent material for nitrogen oxides. The metal additive M forms a bridge with the silica matrix, effectively preventing catalyst loosening and desorption, thereby improving the catalyst's hydrothermal stability. Furthermore, the addition of the M element can slow or inhibit the growth and aggregation of alkaline earth metal particles, further enhancing the catalytic performance of the alkaline earth metal.

[0145] FIG3 is a scanning electron microscope (SEM) image of the alkaline earth metal adsorbent with a core-shell structure prepared in Example 2 of the present application, and FIG5 is a scanning electron microscope (SEM) image of the Ba / SSZ-13 molecular sieve adsorbent prepared in Comparative Example 1 of the present application. Comparison of the two images shows that the Ba / SSZ-13 molecular sieve adsorbent without a shell has obvious cracks on its surface. In the presence of water vapor, water molecules can combine with alkaline earth metal ions through the cracks, reducing its adsorption of NO. x The surface of the Ba / SSZ-13 molecular sieve adsorbent is covered with a shell layer, the gaps are filled, and the surface becomes smooth and crack-free, which can effectively block the entry of water vapor and improve the NO x energy absorption capacity.

[0146] Use NO x Adsorption performance test method: the adsorbents prepared in Example 2 and Comparative Example 1 were tested for NO x The energy absorption performance of the test results is shown in Table 1. The alkaline earth metal adsorbent with a core-shell structure prepared in Example 2 can adsorb NO x The adsorption performance is significantly higher than that of the shell-free Ba / SSZ-13 molecular sieve adsorbent in Comparative Example 1, and it has excellent resistance to competitive adsorption of water vapor.

[0147] Table 1 Shell structure of alkaline earth metal adsorbents for NO adsorptionx Performance impact comparison table

[0148] Figure 4 is a comparison diagram of high-angle annular dark field scanning transmission (HAADF-STEM) of the adsorbents prepared in Example 2 and Comparative Example 1 of the present application. It can be seen from the figure that the transmittance is significantly reduced after the shell layer is formed on the surface of the Ba / SSZ-13 molecular sieve adsorbent, which further confirms that the alkaline earth metal adsorbent with a core-shell structure prepared in Example 2 can form a shell layer on the Ba / SSZ-13 molecular sieve adsorbent to fill the cracks on the surface.

[0149] FIG8 is a graph showing the NO adsorbents prepared in Example 2 and Comparative Example 1 of the present application. x Adsorption performance comparison chart,

[0150] Use NO x Adsorption performance test method: the alkaline earth metal adsorbent with a core-shell structure prepared in Example 3 was tested. As shown in Figure 6, the alkaline earth metal adsorbent with a core-shell structure has a good adsorption performance on NO. x Has good adsorption properties.

[0151] Figure 7 is a scanning electron microscope (SEM) image of the alkaline earth metal adsorbent with a core-shell structure prepared in Example 3 of the present application. The alkaline earth metal adsorbent with a core-shell structure prepared in Example 3 has a smooth surface, small cracks, and good resistance to competitive adsorption of water vapor.

[0152] Referring to Table 2, the present application uses different molar ratios of silicon and aluminum when preparing the adsorbent in Example 3, Comparative Example 4, Comparative Example 5 and Comparative Example 6. When the molar ratio of silicon and aluminum is 6, 10 and 15, the adsorption of NO x The adsorption performance is excellent, and the adsorption performance is best when the molar ratio of silicon to aluminum is 10, which can maximize the dispersion of alkaline earth metals. However, when the molar ratio of silicon to aluminum is 50, the adsorption of NO x Lowest adsorption.

[0153] Table 2 Core-shell alkaline earth metal adsorbents with different silicon and aluminum molar ratios for NO x Adsorption performance comparison table

[0154] This application uses Example 2, Comparative Example 7 and Comparative Example 8 to prepare adsorbents. When the stirring temperature is 60°C to 120°C, the alkaline earth metal adsorbents with core-shell structures have good NO x Energy absorption performance. See Table 3. When the stirring temperature is 95℃, the pore structure of the molecular sieve can best disperse the alkaline earth metal, so that it can obtain a larger specific surface area and more reaction sites. x Optimal energy absorption performance.

[0155] Table 3 Core-shell alkaline earth metal adsorbents with different stirring temperatures for NO x Adsorption performance comparison table

[0156] This application uses Example 3, Comparative Example 9 and Comparative Example 10 to prepare adsorbents. The mass ratio of alkaline earth metal element magnesium to molecular sieve in the alkaline earth metal active component precursor is different. The alkaline earth metal adsorbents with core-shell structure have good NO x Energy absorption performance. See Table 4. When the mass ratio in Example 3 is 0.05, the prepared adsorbent has a high absorption capacity for NO. x Optimal energy absorption performance.

[0157] The molecular sieve itself has a unique pore structure and a large specific surface area, which provides more sites for alkaline earth metals, is conducive to the dispersion of alkaline earth metals, and improves the catalytic performance of alkaline earth metals. When the mass ratio of alkaline earth metal elements to molecular sieves is appropriate, the dispersion effect of alkaline earth metals can be maximized, and for NO x Optimal energy absorption performance.

[0158] Table 4 Core-shell alkaline earth metal adsorbents with different mass ratios of alkaline earth metal elements to molecular sieves for NO x Adsorption performance comparison table

[0159] The present application uses comparative example 11, comparative example 12 and comparative example 13 to prepare adsorbents, the mass ratio of ethyl silicate and lanthanum nitrate is different, and the mass ratio of yMxSiO2 in the generated shell is metal additive lanthanum and SiO2 in the range of 0.01 to 0.1:1, all of which have good NO x Energy absorption performance. See Table 5, when the mass ratio of lanthanum to SiO2 in Comparative Example 13 is 0.05:1, the prepared adsorbent has a high absorption capacity for NO x Optimal energy absorption performance.

[0160] The metal additive M forms a bridge with the silica matrix, effectively preventing the catalyst from loosening and desorption, thereby improving the catalyst's hydrothermal stability. Furthermore, the addition of the M element can slow down or inhibit the growth and aggregation of alkaline earth metal particles, thereby helping to enhance the catalytic performance of alkaline earth metals.

[0161] Table 5 Core-shell alkaline earth metal adsorbents with different mass ratios of metal additive M and SiO2 for NO x Adsorption performance comparison table

[0162] In Example 1, alkali metal calcium was used to prepare the adsorbent, and in Comparative Example 14, palladium metal was used to prepare the adsorbent. The two adsorbents were compared for NO x Energy absorption capacity. As shown in Table 6, the adsorbent prepared by alkali metal calcium can absorb NOx 89.63μmol / g, which is higher than that of the adsorbent prepared by palladium metal. The adsorbent prepared by alkali metal has better NO x Suction capacity.

[0163] Alkaline earth metals have a low electronegativity in their electronic structure, tending to lose outer-shell electrons and form positive ions. This positive charge facilitates interaction with the negatively charged nitrogen or oxygen atoms in nitrogen oxides. Secondly, alkaline earth metals have a large ionic radius and low electron affinity. The large ionic radius means that the positive ions of alkaline earth metals have a larger surface area, facilitating contact with nitrogen oxide molecules. Their low electron affinity enables them to accept electrons from nitrogen oxides, thereby reacting with them. Finally, alkaline earth metals have high electrical conductivity and catalytic activity. High electrical conductivity means that alkaline earth metals facilitate electron transfer across their surfaces, thereby strengthening their interaction with nitrogen oxides. Furthermore, alkaline earth metals can act as catalysts, promoting the adsorption and reduction of nitrogen oxides, thereby converting them into more stable substances.

[0164] Alkaline earth metal ions have a high charge density and a small ionic radius, which enables them to have a strong attraction to other substances. They can adsorb a large number of molecules or ions during the adsorption process, thereby increasing the reactivity of the adsorption surface.

[0165] Table 6 Adsorbents prepared from alkali metal calcium and palladium for NO x Adsorption performance comparison table

[0166] It should be noted that the terms used in this application are only for describing specific embodiments and are not intended to limit the scope of this application. As shown in the specification of this application, unless the context clearly indicates an exception, the words "one", "a", "a kind of" and / or "the" do not specifically refer to the singular and may also include the plural. The terms "comprise", "include" or any other variants thereof are intended to cover non-exclusive inclusion, so that the process, method or device including a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such process, method or device. In the absence of further restrictions, the elements defined by the sentence "comprise a..." do not exclude the presence of other identical elements in the process, method or device including the elements.

[0167] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the technical solutions of the embodiments of the present application.

Claims

1. An alkaline earth metal adsorbent having a core-shell structure, wherein: The alkaline earth metal adsorbent has a core-shell structure, with the alkaline earth metal molecular sieve adsorbent as the core and yMxSiO2 as the shell; The alkaline earth metal molecular sieve adsorbent comprises a molecular sieve and an alkaline earth metal element loaded on the molecular sieve; The structure of the molecular sieve is at least one of MFI, CHA, BEA, AEI, LTA and FAU; The yMxSiO2 is a silicon dioxide material doped and modified by a metal additive M, wherein the metal additive M includes at least one of La, Sm, Nd, and Pr; The ratio of y to x in the yMxSiO2 represents the mass ratio of the metal additive M to SiO2, wherein y:x=0.01 to 0.1:1; The shell thickness of the alkaline earth metal adsorbent is 20nm to 100nm; The preparation of the alkaline earth metal adsorbent having a core-shell structure comprises the following steps: Preparation of alkaline earth metal molecular sieve adsorbents; Preparation of an alkaline earth metal adsorbent having a core-shell structure: grinding the alkaline earth metal molecular sieve adsorbent and adding it to a solution of a surfactant and a dispersing solvent, and ultrasonically dispersing the solution to obtain a mixed solution A; Adding a shell oxide precursor and an auxiliary agent precursor into deionized water at a mass ratio of 0.01 to 0.08:1, stirring to dissolve and ultrasonically dispersing to obtain a mixed solution B; The mixed solution B is mixed with the mixed solution A, wherein the mass ratio of silicon in the shell oxide precursor to the molecular sieve in the alkaline earth metal molecular sieve adsorbent is 0.032 to 0.207:1, and the mixture is continuously stirred to obtain a mixed solution C; The pH of the mixed solution C is adjusted to 8-10 while stirring to obtain a mixed solution D; The mixed solution D was stirred continuously for 3 to 10 hours in a water bath at 40 to 90°C, filtered, washed, The mixture is dried and calcined at 300° C. to 600° C. for 3 h to 6 h to obtain the alkaline earth metal adsorbent having a core-shell structure.

2. The alkaline earth metal adsorbent having a core-shell structure according to claim 1, wherein: The alkaline earth metal element includes at least one of Mg, Ca, Sr, and Ba.

3. The alkaline earth metal adsorbent having a core-shell structure according to claim 1, wherein: The molecular sieve comprises silicon and aluminum, and the molar ratio of silicon to aluminum is 6-15.

4. The alkaline earth metal adsorbent having a core-shell structure according to claim 1, wherein: The shell thickness of the alkaline earth metal adsorbent is 50 nm.

5. The alkaline earth metal adsorbent having a core-shell structure according to claim 1, wherein: The steps of preparing the alkaline earth metal molecular sieve adsorbent are as follows: After the soluble alkaline earth metal active component precursor is completely dissolved, molecular sieves are added, ultrasonic treatment is performed, and stirring is carried out at a temperature of 60°C to 120°C for 3h to 8h to carry out ion exchange reaction; After the ion exchange reaction is completed, the mixture is filtered, washed, and dried. After drying, the mixture is calcined at 300° C. to 600° C. for 3 h to 6 h to obtain the alkaline earth metal molecular sieve adsorbent.

6. The alkaline earth metal adsorbent having a core-shell structure according to claim 5, wherein: When preparing the alkaline earth metal molecular sieve adsorbent, the mass ratio of the alkaline earth metal element in the alkaline earth metal active component precursor to the molecular sieve is 0.01-0.1:

1.

7. The alkaline earth metal adsorbent having a core-shell structure according to claim 5, wherein: After the soluble alkaline earth metal active component precursor is completely dissolved, the molecular sieve carrier is added, ultrasonic treatment is performed, and stirring is performed at 95°C.

8. Use of the alkaline earth metal adsorbent with a core-shell structure according to any one of claims 1 to 7 in adsorbing nitrogen oxides.

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