Molecular sieve adsorbent for adsorbing and separating trace ammonia gas and application of molecular sieve adsorbent

Abstract

The invention discloses preparation of a molecular sieve adsorbent and application of the molecular sieve adsorbent in high-precision and high-selectivity adsorption separation of trace ammonia gas. Transition metal ions are exchanged to a molecular sieve structure which is high in specific surface area and proper in pore channel structure in an ion exchange mode, and the molecular sieve adsorbent with high adsorption precision and high adsorption capacity is obtained. According to the invention, the molecular sieve carrier with abundant pore structures and high specific surface area is screened, cations in the molecular sieve structure are exchanged into transition metal ions, and the reversible coordination effect between the transition metal ions and ammonia gas is combined with the mass transfer characteristic of the pore channels of the molecular sieve to synergistically realize efficient capture of trace ammonia. The obtained molecular sieve adsorbent shows high adsorption capacity, selectivity and separation precision for low-concentration ammonia gas, has excellent thermal stability and cyclic reversibility, and can effectively solve the problems of efficient utilization of ammonia energy and poisoning of a catalyst by trace ammonia in a conversion system.

Description

Technical Field

[0001] The present invention belongs to the field of inorganic material preparation and application, and particularly relates to the preparation of a molecular sieve adsorbent and its application in the high-precision and high-selectivity adsorption and separation of trace ammonia gas. Background Art

[0002] As an efficient green hydrogen carrier (hydrogen content 17.6 wt%), NH3 does not produce carbon emissions and is a clean energy source. Compared with H2 which requires a low temperature of -253°C to liquefy, NH3 can be liquefied at room temperature with a pressure of only 8 atmospheres, and its energy density is as high as 2916.7 Wh / L. NH3 is also safer than H2 and does not pose a high risk of highly flammable and explosive. Moreover, NH3 has a history of being used as a fertilizer raw material for a hundred years, and related storage and transportation technologies are very mature. Therefore, using NH3 as a H2 energy carrier can significantly reduce the use cost of H2.

[0003] NH3 can provide energy in two ways: direct combustion and decomposition into H2. The direct combustion of NH3 is restricted due to problems such as high operating temperature, carbonate formation, and NO emissions. In contrast, converting NH3 into H2 is considered more practical. This method produces a mixture of N2 and H2 through the dehydrogenation reaction of NH3, which is then used to drive existing fuel cell systems. Currently, on-site hydrogen production technology for ammonia cracking fuel cells has attracted extensive attention, and its practical applications in aspects such as portable and vehicle-mounted NH3-driven fuel cell vehicle systems are steadily advancing.

[0004] An ammonia-hydrogen fuel cell consists of two parts: an NH3 decomposition system and a proton exchange membrane fuel cell. The residual NH3 after NH3 decomposition will combine with protons on the proton exchange membrane to form NH4 + , thus hindering the transmission of protons and reducing the performance of the fuel cell. Therefore, it is crucial to develop efficient NH3 decomposition and removal technologies. So far, various catalysts based on Ru, Fe, Ni, and Co have been studied to decompose NH3. Among them, the ruthenium-based catalyst has a decomposition conversion rate of NH3 reaching 99.8% (773 - 823 K, 0.1 MPa), approaching the chemical equilibrium value, but the resulting H2 still contains approximately 3000 ppm of NH3. This is fatal for proton exchange membrane fuel cells because even trace amounts (about 1 ppm) of NH3 can cause fuel cell poisoning. In addition, according to the ISO 14687-2 standard, the NH3 concentration in the H2 used in hydrogen fuel cell vehicles should be less than 0.1 ppm. Therefore, removing the residual trace ammonia gas in ammonia decomposition gas is a very challenging task, and when using NH3 as a hydrogen carrier, a technology capable of efficiently removing NH3 from H2 is needed.

[0005] In existing ammonia separation technologies, the liquid absorption method is limited by the solvent characteristics and difficult to achieve industrial application. For example, water is the most commonly used liquid solvent for NH3 absorption. However, due to the high volatility and large heat capacity of water, a large amount of energy is required to desorb NH3 from water; inorganic acids such as H2SO4 and H3PO4 are highly corrosive, and the reaction with NH3 is almost irreversible, making NH3 desorption difficult; ionic liquids (ILs) have a wide liquid range, extremely low volatility, and adjustable structures. However, most ILs are expensive, and due to the strong electrostatic attraction between cations and anions, most ionic liquids have high viscosities, making it difficult to transport them in pipelines.

[0006] In contrast, solid adsorption, as another important technology for separating ammonia in the chemical industry, exhibits unique advantages due to its lack of volatility, viscosity, or corrosion problems. Solid adsorbents are usually filled in two parallel adsorption towers to form a switchable dual-channel system for adsorption and desorption in sequence. Desorption is achieved by changing the temperature, changing the pressure, or a combination of both. Currently, solid adsorbents suitable for mild conditions, such as polymer resins, silica gels, aluminas, zeolites, and carbonaceous materials (including activated carbon, charcoal, and activated carbon fibers), have been widely studied and applied. For the adsorption of NH3, under the same conditions, zeolites have shown higher adsorption capacities and accuracies than polymer resins, silica gels, and aluminas. Zeolite molecular sieves are hydrated aluminosilicate minerals with a porous structure and functional properties such as cation exchange, molecular sieving, catalysis, and adsorption. Among them, the specific surface area and pore size distribution of the molecular sieve are the key factors affecting its adsorption performance. A higher specific surface area can provide more active sites, and an optimized pore structure (including micropores and mesopores) can promote the diffusion and adsorption of gas molecules. At the same time, in the pore channels and frameworks of zeolites, metal cations are coordinated with a certain number of surrounding water molecules and combined with oxygen atoms on the zeolite framework, and can be exchanged with other transition metal ions. A strong reversible coordination interaction can form between the transition metal ions and ammonia molecules to form a stable multi-coordination structure, thereby efficiently and accurately capturing ammonia. Summary of the Invention

[0007] The purpose of the present invention is to provide a preparation method of a molecular sieve adsorbent and its application in the high-precision and high-selectivity adsorption separation of trace ammonia. By screening molecular sieves with micro-mesoporous structures for ion exchange and exchanging transition metal ions into the molecular sieve structure, a molecular sieve adsorbent rich in transition metal ions is prepared. Among them, the microporous structure of the molecular sieve can accommodate transition metal ions to form dense adsorption sites, and the mesoporous structure can serve as a mass transfer channel to accelerate the diffusion of ammonia molecules, thereby significantly improving the adsorption capacity and separation accuracy. Therefore, the adsorbent prepared by this method can reduce the ammonia concentration to below 0.1 ppm, achieving high-precision adsorption in a trace ammonia atmosphere and being easy to regenerate and use.

[0008] To achieve the above object, the present invention adopts the following technical solutions: A molecular sieve adsorbent for trace ammonia adsorption and separation, and its preparation includes the following steps: 1) High-temperature activation of the molecular sieve in air; 2) Preparation of a transition metal ion solution with a certain concentration; 3) Adding the activated molecular sieve to the transition metal ion solution for ion exchange; 4) Washing and drying the obtained molecular sieve to obtain a molecular sieve adsorbent for efficient adsorption and separation of trace ammonia.

[0009] Further, the specific surface area of the molecular sieve in step 1) is 400 - 800 m 2 / g, the micropore diameter is 0.60 - 1.50 nm, the mesopore diameter is 2 - 10 nm, the micropore volume is 0.005 - 0.300 cm 3 / g, the mesopore volume is 0.020 - 0.200 cm 3 / g, and it can be selected from Beta, 13X, ZSM-5 or Y, etc., preferably Y molecular sieve (its specific surface area is 500 - 650 m 2 / g, the micropore diameter is 0.8 - 1.2 nm, the mesopore diameter is 8.0 - 10.0 nm, the micropore volume is 0.150 - 0.300 cm 3 / g, the mesopore volume is 0.100 - 0.150 cm 3 / g).

[0010] The exchanged Y-type molecular sieve, due to its supercage structure (pore diameter about 1.18 nm) and specific surface area as high as 500 m 2 / g, can effectively load transition metal ions and achieve rapid mass transfer of ammonia molecules. In contrast, too small pore diameter (such as 3A molecular sieve, pore diameter 0.3 nm) will limit the diffusion of ammonia molecules, while too low specific surface area (such as ordinary silica gel, specific surface area <400 m² / g) will result in insufficient adsorption sites, both of which cannot meet the high-precision separation requirements of trace ammonia.

[0011] Further, the temperature of the high-temperature activation in step 1) is 300 - 500 °C, and the time is 2 - 6 h.

[0012] Further, the concentration of the transition metal ion solution in step 2) is 0.1 - 2.0 mol / L.

[0013] Further, the metal source for preparing the transition metal ion solution in step 2) is one of copper nitrate, nickel nitrate, cobalt chloride, copper chloride, nickel chloride, iron chloride, copper sulfate, nickel sulfate, iron sulfate, and preferably metal sources containing copper ions such as copper nitrate, copper chloride, and copper sulfate.

[0014] Further, the temperature of the ion exchange in step 3) is 25 - 80 °C, and the time is 6 - 24 h.

[0015] Further, during the ion exchange in step 3), 10 - 30 mL of the transition metal ion solution is used per gram of the molecular sieve.

[0016] Further, the temperature of the drying in step 4) is 60 - 120 °C, and the time is 12 - 24 h.

[0017] The molecular sieve adsorbent prepared by the above method can be applied to efficiently adsorb and separate trace ammonia in an ammonia fuel cell system.

[0018] The advantages of the present invention are as follows: (1) The preparation process of the molecular sieve adsorbent of the present invention is simple and easy to operate; (2) The molecular sieve adsorbent of the present invention has excellent adsorption performance for ammonia and excellent cyclic regeneration performance. Description of the Drawings

[0019] Figure 1 XRD spectra of the molecular sieve adsorbents prepared before and after ion exchange in Examples 1, 4, and 6.

[0020] Figure 2 Low-temperature nitrogen adsorption-desorption curves and pore size distribution diagrams of the molecular sieve adsorbents prepared by ion exchange in Examples 1, 4, and 6 and Comparative Examples 1 - 3.

[0021] Figure 3 Static ammonia adsorption curves of the molecular sieve adsorbents prepared in Examples 1 - 4, 6 and Comparative Examples 1 - 4.

[0022] Figure 4 Ammonia breakthrough curves of the molecular sieve adsorbents prepared in Examples 1, 4, 6 and Comparative Examples 1 - 4. Detailed Embodiments

[0023] A molecular sieve adsorbent for adsorbing and separating trace ammonia, the preparation of which comprises the following steps: 1) Activate the molecular sieve in an air atmosphere at a high temperature of 300 - 500 °C for 2 - 6 h; 2) Prepare a transition metal ion solution with a concentration of 0.1 - 2.0 mol / L; 3) Add the activated molecular sieve to the transition metal ion solution at a rate of 10 - 30 mL / g, and perform ion exchange at 25 - 80 °C for 6 - 24 h; 4) Wash the obtained molecular sieve, dry it at 60 - 120 °C for 12 - 24 h, to obtain a molecular sieve adsorbent for efficiently adsorbing and separating low-concentration ammonia.

[0024] Among them, the specific surface area of the molecular sieve in step 1) is 400-800 m 2 / g, the micropore aperture is 0.60-1.50 nm, the mesopore aperture is 2-10 nm, the micropore volume is 0.005-0.300 cm 3 / g, and the mesopore volume is 0.020-0.200 cm 3 / g.

[0025] In step 2), the metal source used for preparing the transition metal ion solution is one of copper nitrate, nickel nitrate, cobalt chloride, copper chloride, nickel chloride, iron chloride, copper sulfate, nickel sulfate, and iron sulfate.

[0026] To make the content of the present invention easier to understand, the technical solutions of the present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited thereto.

[0027] Example 1: The Y-type molecular sieve (BET specific surface area is 620 m 2 / g, micropore aperture 0.85 nm (calculated by DFT model), mesopore aperture 8.2 nm (analyzed by BJH method), micropore volume 0.28 cm 3 / g, mesopore volume 0.17 cm 3 / g) was activated in an air atmosphere at 400 °C for 4 h, then added to a 1 mol / L copper chloride solution at a rate of 10 mL / g, and ion-exchanged at 60 °C for 24 h. After that, it was washed and dried at 100 °C for 18 h to obtain a molecular sieve adsorbent.

[0028] Example 2: The Y-type molecular sieve (BET specific surface area is 620 m 2 / g, micropore aperture 0.85 nm (calculated by DFT model), mesopore aperture 8.2 nm (analyzed by BJH method), micropore volume 0.28 cm 3 / g, mesopore volume 0.17 cm 3 / g) was activated in an air atmosphere at 400 °C for 4 h, then added to a 0.1 mol / L iron sulfate solution at a rate of 15 mL / g, and ion-exchanged at 60 °C for 24 h. After that, it was washed and dried at 100 °C for 18 h to obtain a molecular sieve adsorbent.

[0029] Example 3: The Y-type molecular sieve (BET specific surface area is 620 m 2 / g, micropore aperture 0.85 nm (calculated by DFT model), mesopore aperture 8.2 nm (analyzed by BJH method), micropore volume 0.28 cm3 / g, the mesopore volume is 0.17 cm 3 / g) was activated in air atmosphere at 400 °C for 4 h, then added to a cobalt nitrate solution with a concentration of 0.5 mol / L at a rate of 15 mL / g, and ion-exchanged at 60 °C for 24 h. After washing, it was dried at 100 °C for 18 h to obtain a molecular sieve adsorbent.

[0030] Example 4: The Beta-type molecular sieve (BET specific surface area is 537 m 2 / g, the micropore diameter is 0.66 nm (calculated by DFT model), the mesopore diameter is 2.5 nm (analyzed by BJH method), the micropore volume is 0.11 cm 3 / g, the mesopore volume is 0.13 cm 3 / g) was activated in air atmosphere at 400 °C for 4 h, then added to a copper chloride solution with a concentration of 1 mol / L at a rate of 10 mL / g, and ion-exchanged at 60 °C for 24 h. After washing, it was dried at 100 °C for 18 h to obtain a molecular sieve adsorbent.

[0031] Example 5: The Beta-type molecular sieve (BET specific surface area is 537 m 2 / g, the micropore diameter is 0.66 nm (calculated by DFT model), the mesopore diameter is 2.5 nm (analyzed by BJH method), the micropore volume is 0.11 cm 3 / g, the mesopore volume is 0.13 cm 3 / g) was activated in air atmosphere at 400 °C for 4 h, then added to a nickel chloride solution with a concentration of 0.5 mol / L at a rate of 30 mL / g, and ion-exchanged at 40 °C for 24 h. After washing, it was dried at 80 °C for 16 h to obtain a molecular sieve adsorbent.

[0032] Example 6: The 13X-type molecular sieve (BET specific surface area is 593 m 2 / g, the micropore diameter is 0.72 nm (calculated by DFT model), the mesopore diameter is 3.2 nm (analyzed by BJH method), the micropore volume is 0.15 cm 3 / g, the mesopore volume is 0.18 cm 3 / g) was activated in air atmosphere at 400 °C for 4 h, then added to a copper chloride solution with a concentration of 1 mol / L at a rate of 10 mL / g, and ion-exchanged at 60 °C for 24 h. After washing, it was dried at 100 °C for 18 h to obtain a molecular sieve adsorbent.

[0033] Example 7: The 13X molecular sieve (BET specific surface area is 593 m 2 / g, micropore diameter is 0.72 nm (calculated by DFT model), mesopore diameter is 3.2 nm (analyzed by BJH method), micropore volume is 0.15 cm 3 / g, mesopore volume is 0.18 cm 3 / g) was activated in air atmosphere at 400 °C for 2 h, then added to a cobalt chloride solution with a concentration of 1.5 mol / L at a rate of 20 mL / g, and ion-exchanged at 60 °C for 24 h. After that, it was washed and dried at 100 °C for 20 h to obtain the molecular sieve adsorbent.

[0034] Example 8: The 13X molecular sieve (BET specific surface area is 593 m 2 / g, micropore diameter is 0.72 nm (calculated by DFT model), mesopore diameter is 3.2 nm (analyzed by BJH method), micropore volume is 0.15 cm 3 / g, mesopore volume is 0.18 cm 3 / g) was activated in air atmosphere at 400 °C for 4 h, then added to a copper sulfate solution with a concentration of 2 mol / L at a rate of 30 mL / g, and ion-exchanged at 40 °C for 12 h. After that, it was washed and dried at 60 °C for 24 h to obtain the molecular sieve adsorbent.

[0035] Example 9: The 13X molecular sieve (BET specific surface area is 593 m 2 / g, micropore diameter is 0.72 nm (calculated by DFT model), mesopore diameter is 3.2 nm (analyzed by BJH method), micropore volume is 0.15 cm 3 / g, mesopore volume is 0.18 cm 3 / g) was activated in air atmosphere at 400 °C for 6 h, then added to a nickel sulfate solution with a concentration of 1.5 mol / L at a rate of 10 mL / g, and ion-exchanged at 40 °C for 16 h. After that, it was washed and dried at 80 °C for 24 h to obtain the molecular sieve adsorbent.

[0036] Comparative Example 1: The 3A molecular sieve (specific surface area is 343 m 2 / g, micropore diameter is 0.3 nm, micropore volume is 0.18 cm 3 / g, no mesopores) was activated in air atmosphere at 400 °C for 4 h, then added to a copper chloride solution with a concentration of 1 mol / L at a rate of 10 mL / g, and ion-exchanged at 60 °C for 24 h. After that, it was washed and dried at 100 °C for 18 h to obtain the molecular sieve adsorbent.

[0037] Comparative Example 2: 4A molecular sieve (specific surface area of 311 m 2 / g, micropore diameter of 0.4 nm, micropore volume of 0.25 cm 3 / g, without mesopores) was activated in an air atmosphere at 400 °C for 4 h, then added to a copper chloride solution with a concentration of 1 mol / L at a rate of 10 mL / g, and ion-exchanged at 60 °C for 24 h. After that, it was washed and dried at 100 °C for 18 h to obtain a molecular sieve adsorbent.

[0038] Comparative Example 3: 5A molecular sieve (specific surface area of 267 m 2 / g, micropore diameter of 0.5 nm, micropore volume of 0.28 cm 3 / g, without mesopores) was activated in an air atmosphere at 400 °C for 4 h, then added to a copper chloride solution with a concentration of 1 mol / L at a rate of 10 mL / g, and ion-exchanged at 60 °C for 24 h. After that, it was washed and dried at 100 °C for 18 h to obtain a molecular sieve adsorbent.

[0039] Comparative Example 4: Y-type molecular sieve (BET specific surface area of 620 m 2 / g, micropore diameter of 0.85 nm (calculated by DFT model), mesopore diameter of 8.2 nm (analyzed by BJH method), micropore volume of 0.28 cm 3 / g, mesopore volume of 0.17 cm 3 / g) was activated in an air atmosphere at 400 °C for 4 h, and then washed and dried at 100 °C for 18 h to obtain a molecular sieve adsorbent.

[0040] The obtained molecular sieve adsorbents were analyzed and tested, and the results are as follows: Figure 1 XRD patterns of the molecular sieve adsorbents prepared before and after ion exchange in Examples 1, 4, and 6. As can be seen from the figure, compared with before the exchange, there is no obvious change in the crystal structure after the exchange, indicating that this method does not damage the crystal structure of the molecular sieve; at the same time, no diffraction peak of copper ions is detected in the XRD pattern, indicating that copper ions are highly uniformly dispersed on the molecular sieve framework and do not form large stacked particles.

[0041] Figure 2 Low-temperature nitrogen adsorption-desorption curves and pore size distribution maps of the molecular sieve adsorbents prepared by ion exchange in Examples 1, 4, and 6 and Comparative Examples 1-3. It can be seen from the figure that the molecular sieve adsorbents prepared in the examples all have a certain amount of micropores, mesopores, and some stacked macropores, while the molecular sieve adsorbents prepared in the comparative examples have fewer micropores.

[0042] Table 1 Textural parameters of low-temperature nitrogen adsorption-desorption curves of molecular sieve adsorbents prepared in Examples 1, 4, 6 and Comparative Examples 1-3

[0043] As can be seen from Table 1, after ion exchange of the molecular sieve, certain changes have occurred in its textural parameters, such as a decrease in specific surface area and an increase in pore size. Among them, the Y molecular sieve has the least reduction in specific surface area after exchange, the largest mesopore size, and the highest micropore volume and mesopore volume, which makes it more conducive to the passage and storage of gases.

[0044] Figure 3 Figure 1 shows the static ammonia adsorption curves of the molecular sieve adsorbents prepared in Examples 1-4, 6 and Comparative Examples 1-4. It can be seen from the figure that using the Y molecular sieve as a carrier, the molecular sieve adsorbents obtained after ion exchange with different transition metal ions (Examples 1-4) have a rapid increase in the adsorption isotherm in the low-pressure region below 0.05 bar. Among them, the ammonia adsorption capacity of Example 1 at a pressure of 1 bar is as high as 12.3 mmol / g, which is significantly higher than other samples. This is not only due to the unique supercage structure, large pore channels and high specific surface area of the Y molecular sieve, which can provide sufficient entry and diffusion space for basic ammonia molecules; but also due to the high sodium ion content of the Y molecular sieve, which can exchange a high density of transition metal ions and form uniformly distributed active sites, and the abundant acidic sites of unexchanged transition metals can also cooperate with basic ammonia molecules. Among the exchanged transition metal ions, Cu 2+ ions, due to their strong Lewis acidity and the ability to form coordination bonds with the lone pair electrons of ammonia molecules, become excellent active centers. In contrast, other transition metal ions (such as Fe 3+ , Ni 2+ , Co 2+ , etc.) have a weak coordination ability with ammonia, and the smaller pore sizes of some molecular sieves (such as 3A, 4A, 5A, etc.) limit the diffusion and adsorption of ammonia. Therefore, the synergistic effect of the pore channels of the Y molecular sieve and copper ions significantly enhances its ammonia adsorption ability, so that its adsorption performance is far superior to that of other materials composed of molecular sieves and transition metal ions.

[0045] The obtained molecular sieve adsorbent was applied to the adsorption and separation of ammonia in a low-concentration ammonia atmosphere. The gas used was ammonia at 3000 ppm, the balance gas was nitrogen, the flow rate was 25 mL / min, the mass of the molecular sieve adsorbent was 0.1 g, and the temperature was 25°C.

[0046] Figure 4Ammonia breakthrough curves of the molecular sieve adsorbents prepared in Examples 1, 4, 6 and Comparative Examples 1-4. It can be seen from the figure that the molecular sieve adsorbents prepared in Examples 4, 6 and Comparative Examples 1-4 cannot completely adsorb the gas during the adsorption process and can only reduce the ammonia concentration to about 3 ppm, while the molecular sieve adsorbent of Example 1 reduces the ammonia concentration to below 0.1 ppm, achieving high-precision adsorption of trace ammonia. At the same time, the molecular sieve adsorbent of Example 1 has the highest ammonia adsorption capacity. At about 300 minutes, the ammonia saturation breakthrough capacity can be as high as 10.24 mmol / g. It can be seen that within a certain specific surface area range, appropriate pore size and uniform copper ion distribution are more conducive to high-precision gas adsorption., In summary, through the scalable ion exchange process, the present invention can achieve the preparation of molecular sieves at the kilogram level and the precise regulation of the performance of adsorbents. In practical applications, by selecting the combination of specific transition metals (such as Cu 2+ and Co 2+ etc.) and molecular sieve carriers (such as Y-type, Beta-type, etc.), different scenario requirements can be adapted, with high flexibility. This characteristic makes the technology suitable for large-scale industrial applications, bringing great convenience and benefits to industrial production.

[0047] The above are only the preferred embodiments of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention shall fall within the scope of the present invention.

Claims

1. A preparation method of a molecular sieve adsorbent for trace ammonia adsorption and separation, characterized in that: After the molecular sieve is activated at high temperature in air, it is subjected to ion exchange in a transition metal ion solution, and then washed and dried to obtain a molecular sieve adsorbent for efficient adsorption and separation of trace ammonia.

2. The preparation method according to claim 1, characterized in that: The specific surface area of the molecular sieve is 400~800 m 2 / g, the micropore aperture is 0.60~1.50 nm, the mesopore aperture is 2~10 nm, the micropore volume is 0.005~0.300 cm 3 / g, and the mesopore volume is 0.020~0.200 cm 3 / g.

3. The preparation method according to claim 1, characterized in that: The temperature of the high-temperature activation is 300-500 °C, and the time is 2-6 h.

4. The preparation method according to claim 1, wherein: The concentration of the transition metal ion solution is 0.1-2.0 mol / L.

5. The preparation method according to claim 1 or 2, characterized in that: The metal source used to prepare the transition metal ion solution is one of copper nitrate, nickel nitrate, cobalt chloride, copper chloride, nickel chloride, iron chloride, copper sulfate, nickel sulfate, and iron sulfate.

6. The preparation method according to claim 1, characterized in that: The temperature of the ion exchange is 25-80 °C, and the time is 6-24 h.

7. The preparation method according to claim 1, characterized in that: During ion exchange, 10-30 mL of the transition metal ion solution is used per gram of the molecular sieve.

8. The preparation method according to claim 1, wherein: The temperature of the drying is 60-120 °C, and the time is 12-24 h.

9. Application of a molecular sieve adsorbent prepared by the method according to claim 1 in efficiently adsorbing and separating trace ammonia in an ammonia fuel cell system.

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