MOFs (Metal-Organic Frameworks)-based solid acid for adsorbing and separating trace ammonia gas in ammonia fuel cell system as well as preparation method and application of MOFs-based solid acid

Abstract

The invention belongs to the technical field of porous organic-inorganic nano composite materials, and particularly relates to MOFs (Metal-Organic Frameworks)-based solid acid for adsorbing and separating trace ammonia gas in an ammonia fuel cell system as well as a preparation method and application of the MOFs-based solid acid. A solvent-free mechanochemical synthesis process is adopted, and the method comprises the following steps: firstly, enabling an inorganic zirconium source to be fully mixed and coordinated with terephthalic acid, sulfonic group modified terephthalic acid and a template agent under a solid-state condition through mechanical grinding; then carrying out high-temperature curing treatment to obtain a sulfonic acid group modified initial product; and finally, through the steps of template agent removal and acidification, the sulfonic group functionalized MOFs-based solid acid adsorption material with excellent crystallinity is prepared. According to the prepared MOFs-based solid acid material, a strong chemical bond stable system is constructed through in-situ introduction of sulfonic acid groups, the excellent ammonia gas adsorption performance is shown under the low-pressure condition, the synthesis method of the material is simple in condition and environmentally friendly, and good large-scale production potential and wide industrial application prospects are shown.

Description

Technical Field:

[0001] The present invention belongs to the technical field of porous organic-inorganic nanocomposites, and particularly relates to a MOF-based solid acid for trace ammonia adsorption and separation in an ammonia fuel cell system, a preparation method thereof, and an application thereof. Background Art: The removal of trace ammonia (NH 3 ) is crucial in various environmental and industrial processes, especially in ammonia-hydrogen energy conversion systems. Ammonia, with its high hydrogen content and energy density, has become an efficient hydrogen carrier, effectively reducing the storage and transportation costs of hydrogen, and thus is widely used in fuel cells and other energy fields. In an ammonia-hydrogen fuel cell system, the generation of trace ammonia stems from the incomplete reaction in the ammonia decomposition process for hydrogen production: when ammonia is catalytically decomposed at high temperature (2NH 3 → 3H 2 + 1N 2 ), due to reaction kinetics limitations and catalyst efficiency, usually 0.5 - 2% of undecomposed NH 3 remains. And these trace amounts of ammonia can cause triple hazards: First, NH 3 combines with the sulfonic acid groups in the proton exchange membrane (NH 3 + H + → NH 4 + ), reducing the proton conductivity and causing the membrane structure to swell and rupture; Second, ammonia molecules are strongly adsorbed on the surface of the platinum catalyst, hindering the hydrogen oxidation reaction, resulting in a battery output power attenuation of more than 40%; In addition, residual ammonia reacts with oxygen at high temperature to form nitrogen oxides (4NH 3 + 5O 2 → 4NO + 6H 2 O), corroding the metal bipolar plate and deteriorating the carbon-based diffusion layer. At the same time, the leakage of untreated NH 3 will also form an explosive mixture, threatening the safety of the system. Trace amounts of ammonia residue not only directly lead to a cliff-like decline in battery performance, but also seriously hinder the industrialization process of ammonia-hydrogen energy technology. Therefore, achieving the efficient removal of trace NH 3 has become the key to breaking through the bottleneck in this field. Among the current NH 3 removal technologies, adsorption and desorption technologies based on pressure swing adsorption (PSA) and temperature swing adsorption (TSA) show unique advantages: PSA regulates the capture and release of NH 3 by periodic pressure changes (0.1 - 3.0 MPa), featuring low energy consumption and fast cycle speed; TSA uses temperature gradients to drive the adsorption-desorption process and is suitable for the deep purification of low-concentration ammonia. However, traditional adsorbents, such as zeolites, porous organic polymers, and porous carbon materials, often struggle to meet the requirements for efficient separation of NH 3The required high selectivity and high stability requirements.

[0003] Metal-organic framework (MOF) materials, with their significant advantages such as high specific surface area, abundant metal active sites, chemical and structural diversity, and designable pore structures, show broad application prospects in the fields of adsorption separation, catalytic conversion, molecular sensing and detection, gas storage, and membrane materials. Among them, the zirconium-based MOF material UiO-66 has become a research hotspot in the field of ammonia adsorption due to its strong chemical stability (resistant to hydrothermal and acid-base environments), high structural designability (flexible regulation of ligands and metal clusters), and pore function modification. By introducing functional sites such as sulfonic acid groups (-SO 3 H), UiO-66 can achieve high NH 3 adsorption capacity and selectivity under mild conditions. Its stable zirconium-oxygen cluster framework provides a rigid support for the adsorption sites, while the adjustable micro-mesoporous hierarchical pore structure further optimizes the ammonia diffusion kinetics and mass transfer efficiency, thus showing outstanding performance in trace ammonia capture and separation applications. Currently, the preparation methods of MOFs mainly include solvothermal method, electrochemical method, and microwave synthesis method, etc. Among them, although the solvothermal method is the most common synthesis method, it requires the use of dangerous and non-renewable solvents (such as toxic N,N-dimethylformamide, etc.), and the obtained MOF crystals have large randomness and poor result reproducibility. The electrochemical method utilizes the charge induction mechanism. By applying an external voltage, ligand ions migrate to the anode and coordinate with the dissociated metal ions to form MOF materials on the electrode surface. The electrochemical method has the advantages of being green, environmentally friendly, fast, and continuous synthesis, but this method has problems such as high production cost, high requirements for electrode materials, and low yield. The microwave synthesis method is only applicable to the cases where small-sized crystals need to be synthesized quickly and specific crystals need to be synthesized within a short time due to its disadvantages such as cumbersome preparation process, large energy consumption, harsh reaction conditions, and poor reproducibility, and has not been widely used.

[0004] Aiming at the problems existing in the preparation process of the above-mentioned MOFs, such as cumbersome steps, use of harmful solvents, and environmental pollution, this patent proposes a green, simple, and solvent-free preparation method of MOF-based solid acid and its efficient selective adsorption application for ammonia. By mechanical grinding, inorganic zirconium source, terephthalic acid, sulfonic acid group-modified terephthalic acid, template agent and other reactants are fully mixed under solid-state conditions. After crystallization, a primary product with sulfonic acid groups is obtained, and then through steps such as removing the template agent and activation, a MOF-based solid acid ammonia adsorption and separation material with good crystallinity is obtained. The MOF-based solid acid material prepared by this method constructs a strong chemical bond stable system by in-situ controllable introduction of sulfonic acid groups, shows excellent ammonia adsorption performance under low-pressure conditions, and the synthesis method of this material has simple conditions and is environmentally friendly, showing good potential for large-scale production and broad industrial application prospects. Summary of the Invention: The present invention overcomes the above deficiencies and provides a MOF-based solid acid for trace ammonia adsorption and separation in an ammonia fuel cell system, a preparation method thereof, and an application thereof. Using an inorganic zirconium salt, terephthalic acid, sodium sulfoterephthalate, and a template agent as raw materials, through steps such as mechanical mixing, crystallization, template removal, and activation, a MOF product is prepared. This preparation method has simple operation steps and uses environmentally friendly raw materials, embodying the concept of green chemistry.

[0006] To achieve the above object, the present invention adopts the following technical solutions: A preparation method of a MOF-based solid acid for trace ammonia adsorption and separation in an ammonia fuel cell system, comprising the following steps: a. Mix an inorganic zirconium salt, terephthalic acid, sodium 2-sulfoterephthalate monohydrate, and a template agent in a certain molar ratio and grind evenly; b. After grinding, transfer to a polytetrafluoroethylene-lined reaction kettle, and subject the mixture to high-temperature curing to obtain a primary product modified with sulfonic acid groups; c. After the curing reaction is completed, reflux the primary product in ethanol to remove the template agent; d. Stir the product after removing the template agent in an acidic solution for activation treatment; e. After activation, dry the product to obtain a sulfonic acid group-functionalized MOF-based solid acid adsorption material.

[0007] In the above step a, the molar ratio of the inorganic zirconium source to terephthalic acid is 0.5:1.0 to 2.0:0.5, the molar ratio of sodium 2-sulfoterephthalate monohydrate to terephthalic acid is 0.1 - 1.0, the mass ratio of the template agent to the inorganic zirconium source is 0.5:3.0 to 3.0:0.5, and the grinding time is 5 - 30 min.

[0008] In the above step a, the inorganic zirconium salt is any one of zirconium chloride, zirconium oxychloride octahydrate, or zirconium nitrate; the template agent is any one of the triblock polyether copolymer F108, F127, or P123.

[0009] In the above step b, the high-temperature curing reaction temperature is 80 - 140 °C, and the time is 10 - 30 h.

[0010] In the above step c, the template agent removal solution includes ethanol, methanol, or an ethanol aqueous solution.

[0011] In the above step d, the acidic solution is an aqueous solution of hydrochloric acid, sulfuric acid, or nitric acid, with a concentration of 0.02 - 1.00 M.

[0012] In the above step d, the activation temperature is 25 - 60 °C, and the activation time is 4 - 12 h.

[0013] In step e above, the drying temperature is 60 - 120 °C and the drying time is 12 - 24 h.

[0014] A MOFs-based solid acid prepared by the above method.

[0015] Application of the above-mentioned MOFs-based solid acid in the adsorption and separation of low-concentration ammonia, and the specific conditions are as follows: the flow rate of the raw material gas is 25.0 mL / min, where the concentration of NH 3 is 3000 ppm, the balance gas is a mixture of hydrogen and nitrogen in a ratio of 3:1, the dosage of the adsorbent is 0.1 g, the adsorption temperature is 25 °C, and it is required that the ammonia concentration is reduced to 0 - 0.1 ppm after passing through the adsorbent.

[0016] Technical principle of the present invention: The technical solution of the present invention mechanically mixes an inorganic zirconium salt, terephthalic acid (BDC), sodium 2-sulfonate terephthalate (BDC-NaSO 3 ) with a template agent in proportion; then transfers the mixture to a reaction kettle lined with polytetrafluoroethylene; subsequently places the reaction kettle in an oven and conducts a crystallization reaction at a certain temperature and time. During the crystallization process, the "quasi-molten" phase formed by the template agent at high temperature provides a dynamic contact interface for the solid-solid reaction between the inorganic zirconium salt and the organic ligand, significantly promotes the migration of reactants and the efficient coordination of Zr-O clusters with ligands by reducing the molecular diffusion resistance and guiding the formation of coordination bonds in a directional manner, thereby accelerating the formation of the primary product; subsequently, selectively removes the template agent in the primary product using an ethanol solution, and the space originally occupied by the template agent in the MOFs crystal forms a through-packed pore structure to construct a hierarchical pore system; finally, further activates the primary product in an acidic solution with a certain concentration to obtain the final product, and the sulfonic acid groups introduced in situ in the product are connected to the MOFs skeleton in the form of covalent bonds, showing strong stability compared with the post-modification introduction method.

[0017] Advantages of the present invention: (1) The preparation method of the present invention can achieve one-step in-situ introduction of sulfonic acid groups to modify MOFs materials, with the advantages of simple, fast, and efficient synthesis steps; (2) The present invention realizes the construction of highly stable sulfonic acid groups in MOFs-based solid acid materials and shows excellent ammonia adsorption performance under low-pressure conditions; (3) The present invention realizes the construction of a hierarchical pore structure and the controllability of B acid strength in MOFs-based solid acid materials, balances the structural integrity and functional performance of MOFs materials, and endows them with good ammonia adsorption performance; (4) The material synthesis conditions of the present invention are simple and the reaction is rapid. No organic solvents need to be added during the preparation process, with high atomic utilization rate and no wastewater generation, meeting the requirements of green environmental protection. Description of the drawings: Figure 1XRD patterns of the MOF-based solid acids prepared in Examples 1-3 and Comparative Examples 1-2; a. Solid acid A; b. Solid acid B; c. Solid acid C; h. Solid acid H; i. Solid acid I.

[0019] Figure 2 N₂ adsorption-desorption isotherm curves of the MOF-based solid acids prepared in Examples 1-3; a. Solid acid A; b. Solid acid B; c. Solid acid C.

[0020] Figure 3 Pore size distribution curves of the MOF-based solid acids prepared in Examples 1-3; a. Solid acid A; b. Solid acid B; c. Solid acid C.

[0021] Figure 4 XPS spectra of S element of the MOF-based solid acids prepared in Examples 1-3.

[0022] Figure 5 Static ammonia adsorption curves of the MOF-based solid acids prepared in Examples 1-3 and Comparative Examples 1-2; a. Solid acid A; b. Solid acid B; c. Solid acid C; h. Solid acid H; i. Solid acid I.

[0023] Figure 6 Breakthrough curves of the low-concentration ammonia adsorption and separation performance of the MOF-based solid acids prepared in Examples 1-3; a. Solid acid A; b. Solid acid B; c. Solid acid C. Specific implementation method: The following details the specific implementation method of the present invention. The specific implementation method described herein is only for illustrating and explaining the present invention and is not used to limit the present invention.

[0025] Example 1: Weigh 0.4834 g of zirconium oxychloride octahydrate, 0.2243 g of terephthalic acid, 0.0249 g of sodium 2-sulfoterephthalate monohydrate, and 0.5 g of F127 respectively. Transfer the above raw materials to an agate mortar and manually grind for 5 min. After mechanical mixing is completed, place the mixture in the polytetrafluoroethylene liner of a hydrothermal autoclave and react at 120 °C for 24 h. After the reaction is completed, cool to room temperature to obtain the crude product. Then reflux the crude product in an ethanol solution at 60 °C for 8 h. After natural cooling, stir and activate in a sulfuric acid solution (0.1 M) at 25 °C for 7 h. Vacuum dry the product at 150 °C for 12 h to obtain the MOF-based solid acid for ammonia adsorption and separation, denoted as solid acid A.

[0026] Example 2: Weigh 0.4834 g of zirconium nitrate, 0.1744 g of terephthalic acid, 0.0748 g of sodium 2-sulfoterephthalate monohydrate and 2 g of F108 respectively, transfer them to an agate mortar, and manually grind for 15 min. After the mechanical mixing is completed, place the mixture in the polytetrafluoroethylene inner liner of a hydrothermal autoclave and react at 80 °C for 16 h. After the reaction is completed, cool to room temperature to obtain the primary product. Then reflux the primary product in an ethanol solution at 80 °C for 12 h. After natural cooling, stir and activate it in a nitric acid solution (0.5 M) at 30 °C for 3 h. Vacuum dry the product at 150 °C for 12 h to obtain the MOF-based solid acid for ammonia adsorption separation, denoted as solid acid B.

[0027] Example 3: Weigh 0.9668 g of zirconium chloride, 0.1246 g of terephthalic acid, 0.1246 g of sodium 2-sulfoterephthalate monohydrate and 1.5 g of P123 respectively, transfer them to an agate mortar, and manually grind for 20 min. After the mechanical mixing is completed, place the mixture in the polytetrafluoroethylene inner liner of a hydrothermal autoclave and react at 120 °C for 10 h. After the reaction is completed, cool to room temperature to obtain the primary product. Then reflux the primary product in an ethanol solution at 100 °C for 8 h. After natural cooling, stir and activate it in a hydrochloric acid solution (0.2 M) at 30 °C for 8 h. Vacuum dry the product at 150 °C for 12 h to obtain the MOF-based solid acid for ammonia adsorption separation, denoted as solid acid C.

[0028] Example 4: Weigh 0.4834 g of zirconium oxychloride octahydrate, 0.1744 g of terephthalic acid, 0.0748 g of sodium 2-sulfoterephthalate monohydrate and 3 g of P123 respectively, transfer them to an agate mortar, and manually grind for 10 min. After the mechanical mixing is completed, place the mixture in the polytetrafluoroethylene inner liner of a hydrothermal autoclave and react at 140 °C for 30 h. After the reaction is completed, cool to room temperature to obtain the primary product. Then reflux the primary product in an ethanol solution at 90 °C for 24 h. After natural cooling, stir and activate it in a sulfuric acid solution (1 M) at 40 °C for 4 h. Vacuum dry the product at 150 °C for 12 h to obtain the MOF-based solid acid for ammonia adsorption separation, denoted as solid acid D.

[0029] Example 5: Weigh 0.4834 g of zirconium chloride, 0.1744 g of terephthalic acid, 0.0748 g of sodium 2-sulfoterephthalate, and 3 g of F127 respectively, transfer them to an agate mortar, and manually grind for 15 min. After mechanical mixing is completed, place the mixture in the polytetrafluoroethylene liner of a hydrothermal autoclave and react at 100 °C for 12 h. After the reaction is completed, cool to room temperature to obtain the crude product. Then reflux the crude product in an ethanol solution at 120 °C for 16 h. After natural cooling, stir and activate in a sulfuric acid solution (0.05 M) at 50 °C for 5 h, and vacuum dry the product at 150 °C for 12 h to obtain the MOF-based solid acid for ammonia adsorption separation, denoted as solid acid E.

[0030] Example 6: Weigh 0.4834 g of zirconium nitrate, 0.1744 g of terephthalic acid, 0.0748 g of sodium 2-sulfoterephthalate, and 3 g of F127 respectively, transfer them to an agate mortar, and manually grind for 20 min. After mechanical mixing is completed, place the mixture in the polytetrafluoroethylene liner of a hydrothermal autoclave and react at 100 °C for 12 h. After the reaction is completed, cool to room temperature to obtain the crude product. Then reflux the crude product in an ethanol solution at 120 °C for 16 h. After natural cooling, stir and activate in a hydrochloric acid solution (1 M) at 60 °C for 6 h, and vacuum dry the product at 150 °C for 12 h to obtain the MOF-based solid acid for ammonia adsorption separation, denoted as solid acid F.

[0031] Example 7: Weigh 0.4834 g of zirconium nitrate, 0.1744 g of terephthalic acid, 0.01253 g of sodium 2-sulfoterephthalate, and 3 g of F108 respectively, transfer them to an agate mortar, and manually grind for 15 min. After mechanical mixing is completed, place the mixture in the polytetrafluoroethylene liner of a hydrothermal autoclave and react at 120 °C for 12 h. After the reaction is completed, cool to room temperature to obtain the crude product. Then reflux the crude product in an ethanol solution at 80 °C for 16 h. After natural cooling, stir and activate in a hydrochloric acid solution (0.02 M) at 25 °C for 12 h, and vacuum dry the product at 150 °C for 12 h to obtain the MOF-based solid acid for ammonia adsorption separation, denoted as solid acid G.

[0032] Comparative Example 1: Weigh 0.5423 g of zirconium oxychloride octahydrate, 0.18 g of terephthalic acid, and 0.02 g of sodium 2-sulfoterephthalate monohydrate, and dissolve them in a mixed solvent of 10 mL of acetic acid and 10 mL of N,N-dimethylformamide (DMF). Place the mixture in the polytetrafluoroethylene inner liner of a hydrothermal reactor and react at 120 °C for 24 h. After the reaction is completed, the sample is naturally cooled to room temperature, and then the product is collected by centrifugation and washed three times with DMF and ethanol respectively. Subsequently, it is stirred and activated in a sulfuric acid aqueous solution (0.02 M) at 35 °C for 8 h. Finally, the product is vacuum dried at 150 °C for 12 h to obtain the solid acid H.

[0033] Comparative Example 2: Weigh 0.3256 g of zirconium oxychloride octahydrate and 0.144 g of 2-aminoterephthalic acid and dissolve them in a mixed solvent of 9 mL of acetic acid and 6 mL of N,N-dimethylacetamide (DMF). Place the mixture in the polytetrafluoroethylene inner liner of a hydrothermal reactor and react at 120 °C for 24 h. After the reaction is completed, the sample is naturally cooled to room temperature, and then the product is collected by centrifugation and washed three times with DMF and methanol respectively, and then dried to obtain the preliminary product. Subsequently, weigh 0.5 g of the preliminary product and place it in 30 ml of toluene solution, and add 150.9 μL of 1,3-propane sultone dropwise to the solution and reflux at 150 °C for 12 h. After the reaction is completed, it is cooled to room temperature, and the obtained solid is filtered and washed three times with DMF. Subsequently, it is stirred and activated in a sulfuric acid ethanol solution (0.8 M) at 40 °C for 4 h. Finally, the product is vacuum dried at 150 °C for 12 h to obtain the solid acid I.

[0034] Comparative Example 3: Weigh 2 g of P123 and 2 g of hydrochloric acid solution with pH = 2 in a beaker and stir for 30 min. Then add 6.04 mL of tetraethyl orthosilicate and stir for 45 min. Transfer the above solution to a polytetrafluoroethylene inner liner reaction kettle and hydrothermally cure it at 100 °C for 24 h to obtain. Then, under the condition of oil bath reflux at 100 °C, the above sub-product is dispersed in an ethanol hydrochloric acid solution and stirred for 48 h to remove the template. Then, 1 g of the preliminary product is dispersed in 20 mL of H2O2 and stirred for 24 h, washed with water and ethanol, and then dispersed in a 1 M H2SO4 solution and stirred for 24 h to obtain ordered mesoporous silica, denoted as solid acid G.

[0035] Perform corresponding analysis and testing on the obtained MOFs-based solid acids: Figure 1 XRD patterns of the MOFs-based solid acids prepared in Examples 1-3 and Comparative Examples 1-2 are shown by Figure 1It can be seen that the five samples all showed significant diffraction peaks at 2θ = 7.3°, 8.5°, 12.0°, 17.7°, 22.3°, 25.7° and 33.1°. These peaks corresponded to the (111), (002), (022), (113), (115), (335) and (137) crystal planes respectively, which were highly consistent with the characteristic peaks of UiO-66, indicating that the prepared MOFs-based solid acid had a crystal structure similar to that of typical UiO-66. In addition, as the content of ligand 2-sulfoterephthalic acid monosodium replacing terephthalic acid increased, the crystallinity of the material decreased significantly, indicating that the presence of -SO 3 H groups might significantly affect the coordination reaction between metal ions and organic ligands, thus leading to the formation of linker defects or irregular connections.

[0036] Table 2 shows the structural parameters of the MOFs-based solid acids prepared in Examples 1-3. As can be seen from Table 2, as ligand BDC-SO 3 Na continuously replaced BDC, the specific surface area of the prepared MOFs-based solid acids decreased from 700 m 2 / g (Example 1) to 343 m 2 / g (Example 3), while the pore volume showed the opposite trend and increased significantly. This phenomenon might be related to the deterioration of the material's crystal structure and the packing of nanoparticles.

[0037] Table 2 shows the structural parameters of the MOFs-based solid acids prepared in Examples 1-3

[0038] Figure 2 And Figure 3 are the low-temperature nitrogen adsorption-desorption isotherm curves and pore size distribution diagrams of the MOFs-based solid acids prepared in Examples 1-3 respectively. It can be seen from the figure that all three MOFs-based solid acid materials showed a hierarchical pore structure, which was mainly attributed to the microporous structure of the nanoparticles themselves and the mesoporous-macroporous structure caused by the packing of nanoparticles. The formation of this pore structure was attributed to the template agent forming a viscoelastic "quasi-molten" phase at a certain temperature, providing a dynamic contact interface for the solid-solid reaction between inorganic zirconium salts and organic ligands, promoting the migration and coordination of reactant molecules. At the same time, the template agent encapsulated in the MOF crystal left a mesoporous structure after being removed by an ethanol solution.

[0039] Figure 4 is the XPS spectrum of the S element of the MOFs-based solid acids prepared in Examples 1-4. It can be seen from the figure that all four MOFs-based solid acid materials showed a single S 2p peak near 169.12 eV, which not only proved the introduction of stable sulfonic acid groups but also indicated that all S elements existed in the form of -SO 3It exists in the form of H groups, and as the degree of sulfonic acid group modification increases, the S signal also gradually strengthens.

[0040] Figure 5 It is the static ammonia adsorption curve graph of the MOFs-based solid acids prepared in Examples 1-3 and Comparative Examples 1-2. As can be seen from the figure, the adsorption capacity of solid acid B for NH 3 is as high as 10 mmol / g at 25 °C and 1 bar pressure. Although solid acid C has a higher content of sulfonic acid groups, due to its smallest specific surface area, the adsorption capacity of the material decreases, indicating that the high NH 3 adsorption capacity of this material is mainly attributed to the synergistic effect of abundant acidic active sites and large specific surface area. In addition, the NH 3 adsorption isotherm of this material shows an obvious upward convex shape, indicating a strong interaction between ammonia molecules and acidic adsorption sites on the solid acid material. This characteristic convex isotherm is related to the existence of heterogeneous adsorption sites on the adsorbent surface. In addition, the hierarchical pore structure of this material not only provides a channel for the mass transfer of NH 3 but also exposes more chemisorption sites.

[0041] Figure 6 It is the breakthrough curve graph of the low-concentration ammonia adsorption and separation performance of different MOFs-based solid acids. The specific experimental conditions are: the flow rate of the raw material gas is 25 mL / min, in which the concentration of NH 3 is 3000 ppm, and the balance gas is a mixture of hydrogen and nitrogen in a ratio of 3:1. As can be seen from the figure, solid acid B has the highest ammonia adsorption performance, with an adsorption time reaching about 300 minutes and an ammonia saturated breakthrough capacity of about 10.42 mmol / g.

[0042] 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 covered by the present invention.

Claims

1. A method for preparing a MOFs-based solid acid for adsorption and separation of trace ammonia in an ammonia fuel cell system, characterized in that: The following steps are involved: a. Inorganic zirconium salt, terephthalic acid, monosodium 2-sulfonate terephthalate and template are mixed in a certain molar ratio and ground evenly in an agate mortar; b. After the grinding is completed, the mixture is transferred to a polytetrafluoroethylene-lined reactor and cured at high temperature; c. After the curing reaction is completed, the initial product is placed in a template removal solution for reflux to remove the template; d. placing the product after template removal in an acidic solution and stirring it for activation treatment; e. After activation, the product is dried to obtain the MOFs-based solid acid.

2. The preparation method according to claim 1, characterized in that: In step a, the molar ratio of the inorganic zirconium salt to terephthalic acid is 0.5:1.0~2.0:0.5, the molar ratio of 2-sulfonato monosodium terephthalate to terephthalic acid is 0.1~1.0, and the mass ratio of the template to the inorganic zirconium salt is 0.5:3.0~3.0:0.5 g.

3. The preparation method according to claim 1, characterized in that: The inorganic zirconium salt in step a is any one of zirconium chloride, zirconium oxychloride octahydrate or zirconium nitrate; the template is any one of triblock polyether copolymers F108, F127 or P123.

4. The preparation method according to claim 1, characterized in that: The curing reaction temperature in step b is 80-140° C. and the time is 10-30 h.

5. The preparation method according to claim 1, characterized in that: The template removal solution in step c comprises ethanol, methanol or ethanol aqueous solution.

6. The preparation method according to claim 1, characterized in that: The acidic solution in step d is any one of hydrochloric acid, sulfuric acid or nitric acid aqueous solution, and its concentration is 0.02-1.00 M.

7. The preparation method according to claim 1, characterized in that: The activation temperature in step d is 25-60°C and the activation time is 4-12 h.

8. The preparation method according to claim 1, characterized in that: In the above step e, the drying temperature is 60-120° C. and the drying time is 12-24 h.

9. The MOFs-based solid acid prepared by the method according to any one of claims 1 to 8.

10. Use of the MOFs-based solid acid as claimed in claim 9 in the adsorption and separation of low-concentration ammonia.

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