ZSM-5 molecular sieve in-situ loaded Fe-based metal catalyst as well as preparation method and application thereof

Abstract

The invention provides a ZSM-5 molecular sieve in-situ loaded Fe-based metal catalyst and a preparation method and application thereof.The preparation method comprises the steps that 1, a molecular sieve template is added into deionized water to be stirred, then a silicon source is added to be stirred, and a reaction precursor solution is obtained; dissolving a complexing agent in deionized water, and then adding Fe metal salt to obtain a metal precursor; 2) dropwise adding a metal precursor into the reaction precursor solution, stirring until the solution is transparent, adding an aluminum source, continuously stirring and reacting, and finally forming a catalyst precursor; and 3) transferring the catalyst precursor to a high-pressure reaction kettle for hydrothermal treatment, sequentially drying and annealing the product, and finally calcining to remove the molecular sieve template, thereby obtaining the ZSM-5 molecular sieve in-situ loaded Fe-based metal catalyst. The method has the advantages of economical efficiency of raw materials and the characteristic of high efficiency, meanwhile, the reaction path meets the clean production standard, and the method is outstanding in the aspects of target product yield and eco-friendliness.

Description

Technical Field

[0001] This invention relates to the field of catalyst technology, and in particular to an in-situ supported Fe-based metal catalyst for ZSM-5 molecular sieve, its preparation method, and its application. Background Technology

[0002] Methane is one of the most important fossil fuels, widely distributed in natural gas, shale gas, coalbed methane, combustible ice, and biogas. It is not only a widely used clean energy source today but also a C1 feedstock for chemical production. Due to its abundant resources and low price, the production of chemicals from methane has attracted great interest from academia and industry. Methane conversion is considered the "holy grail" of catalysis. Formic acid, on the other hand, is an important chemical raw material for the synthesis of many organic products and exists in liquid form at room temperature, making it easy to store and transport.

[0003] The methane molecule has a tetrahedral structure, and its stable nonpolar nature results in low polarization of the CH bond and extremely high dissociation energy (439.3 kJ / mol). -1 The first CH bond is difficult to break due to its low bond energy. Furthermore, the remaining CH bonds have lower bond energies than the first bond, making methane highly susceptible to over-oxidation into CO2, which has a negative environmental impact. Therefore, achieving efficient direct conversion of methane to formic acid under mild conditions has become a research hotspot. Summary of the Invention

[0004] This invention aims to provide an in-situ supported Fe-based metal catalyst for ZSM-5 molecular sieve, its preparation method, and its application. The preparation method of this invention has both the advantages of economical raw materials and high efficiency, while the reaction route complies with clean production standards, and it shows outstanding performance in terms of target product yield and eco-friendliness.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] This invention provides a method for preparing an in-situ supported Fe-based metal catalyst on ZSM-5 molecular sieve, comprising:

[0007] 1) Add the molecular sieve template to deionized water and stir, then add the silicon source and stir to obtain the reaction precursor solution; dissolve the complexing agent in deionized water and then add the Fe metal salt to obtain the metal precursor;

[0008] 2) The metal precursor is dropped into the reaction precursor liquid and stirred until the liquid is transparent. An aluminum source is added and the reaction is continued with stirring to finally form a catalyst precursor.

[0009] 3) The catalyst precursor was transferred to a high-pressure reactor for hydrothermal treatment. The product was then dried and annealed in sequence. Finally, the molecular sieve template was removed by calcination to obtain the ZSM-5 molecular sieve in-situ supported Fe-based metal catalyst.

[0010] Preferably, in step 1), the molecular sieve template is tetrapropylammonium hydroxide (TPAOH), tetramethylammonium hydroxide (TMAOH), or hexadecyltrimethylammonium bromide (CTAB); the silicon source is tetraethyl silicate (TEOS) or tetrapropyl silicate (TPOS); the complexing agent is any one or a combination of two of ethylenediaminetetraacetic acid tetrasodium salt (EDTA-4Na) or ethylenediaminetetraacetic acid disodium salt (EDTA-2Na); and the Fe metal salt is any one or a combination of ferric nitrate nonahydrate (Fe(NO3)3·9H2O), ferric sulfate (Fe2(SO4)3), or ferric chloride (FeCl3).

[0011] Preferably, in step 1), the volume ratio of the molecular sieve template to deionized water is 1:8-3:1, the mass concentration of the molecular sieve template is 20-40 wt%, the mass concentration of the silicon source is 99%, the volume ratio of the silicon source to the molecular sieve template is 1:2-3:1, and the ratio of the Fe metal salt to the complexing agent is 1:1-1:3.

[0012] Preferably, in step 1), the molecular sieve template is added to deionized water and stirred for 3-5 minutes, and then the silicon source is added and stirred for 15-25 minutes.

[0013] Preferably, in step 2), the reaction precursor solution and the metal precursor are stirred uniformly at 20-30°C for about 5-10 minutes, and then the aluminum source is gradually added to generate the catalyst precursor; the mass ratio of the reaction precursor solution to the metal precursor is 1:3-2:1, and the molar ratio of the silicon source to the aluminum source is 0.25:1-5:1; the stirring rate is 300-500 r / min, and the uniform stirring time is 3-5 hours; the aluminum source is any one or a combination of boehmite, γ-alumina, aluminum hydroxide gel, or sodium aluminate.

[0014] Preferably, in step 3), the hydrothermal temperature is 150-180℃ and the hydrothermal treatment time is 2-4 days; the calcination temperature is controlled at 350-800℃ in air, and calcination is carried out by increasing the temperature at 4-8 minutes / ℃ to remove the molecular sieve template.

[0015] The present invention also provides an in-situ supported Fe-based metal catalyst for ZSM-5 molecular sieve, which is obtained by any of the above preparation methods.

[0016] Preferably, the mass percentage of iron in the ZSM-5 molecular sieve-supported Fe-based metal catalyst is 1-5 wt%; and the particle size of the ZSM-5 molecular sieve-supported Fe-based metal catalyst is 200-500 nm.

[0017] The present invention further provides the application of the above-mentioned ZSM-5 molecular sieve in-situ supported Fe-based metal catalyst, comprising: adding the ZSM-5 molecular sieve in-situ supported Fe-based metal catalyst to a reaction solvent, ultrasonically mixing it uniformly to generate a catalytic liquid; adding the catalytic liquid to a high-pressure reactor, and rinsing the reactor multiple times with a methane mixture gas until the gas pressure inside the reactor reaches 0.1-0.5 MPa, so that the methane mixture gas is fully introduced into the reactor; reacting the methane mixture gas with the catalytic liquid to fully increase the reactor temperature from 20-30°C to 40-120°C at a rate of 1-5°C / min, continuing the reaction for 0.1-48 hours, and then cooling the reactor to 30°C, taking the catalytic liquid to obtain formic acid.

[0018] Preferably, the mass ratio of the in-situ supported Fe-based metal catalyst on the ZSM-5 molecular sieve to the reaction solvent is 1:10-2:1; the reaction solvent is a mixed solution of deionized water and hydrogen peroxide, with a volume ratio of 1:10-1:0.

[0019] This invention employs an in-situ method of loading metallic iron within or outside the molecular sieve framework to catalytically oxidize methane, mimicking the structure of biological enzymes. The acidity / alkalinity inside the molecular sieve is altered by controlling the silica-alumina ratio. During preparation, metallic Fe is added to ensure uniform dispersion within the molecular sieve. The Fe-ZSM-5 in this invention undergoes ion exchange and calcination to remove organic template agents and generate acidity. Compared to the previously used impregnation method, the one-step loading method employed in this invention facilitates uniform metal distribution both within and outside the molecular sieve framework. Furthermore, the mixing of metallic Fe with one or more complexing agents, either tetrasodium EDTA or disodium EDTA, results in a layered structure within the molecular sieve. This layering increases the specific surface area of ​​the molecular sieve, thereby increasing the number of catalytically active sites and significantly improving catalytic performance.

[0020] The beneficial effects of this invention are as follows:

[0021] 1. This invention introduces Fe metal in situ into the ZSM-5 molecular sieve. By adjusting the complexing agent and the silicon-aluminum ratio, the metal is anchored inside the molecular sieve. The conventional method for loading metal into ZSM-5 is the impregnation method. However, the impregnation method can cause the metal to easily form clusters and block the molecular sieve, affecting further metal incorporation. This invention uses the in situ method to add metal during the growth of the molecular sieve, so that the metal is uniformly anchored inside the molecular sieve, increasing the number of active sites.

[0022] 2. The complexing agent used in this invention, ethylenediaminetetraacetic acid tetrasodium / disodium, due to its six-coordinate atom (4 oxygen 2 nitrogen) structure, can react with Fe. 2+ / Fe 3+ (especially Fe) 3+ (logK≈25.1) forms a stable octahedral chelate. This not only prevents free Fe... 3+Precipitation under neutral / alkaline conditions as Fe(OH)3 improves the water solubility stability of iron. Furthermore, its efficient dispersion of iron (which readily precipitates) prevents the formation of clusters by the second metal, thus avoiding the loss of active sites. Complexation leads to a layered distribution of the metal, increasing the exposure of active sites and ultimately significantly enhancing the catalyst's practical performance.

[0023] 3. In this invention, an aluminum source is added after stirring the catalyst template with metal and silicon source for approximately 20-30 minutes. The pH ratio is adjusted during the growth of ZSM-5 molecular sieves to regulate the acidity or alkalinity of the sieve pore environment. Under the pH ratio of this invention, framework defect sites (≡Si-O) formed by dehydroxylation are achieved. - It readily adsorbs Fe metal ions, forming Lewis acid centers, which promote oxidation reactions and enhance the catalytic ability of the catalyst.

[0024] 4. This invention innovatively employs a catalyst-aqueous phase composite system construction method. By forming a highly efficient catalytic reaction interface between the catalytically active component and the liquid medium, liquid formic acid is directly generated from a methane mixture during the directed catalytic conversion process. By adding a catalyst during the methane conversion process, the methane conversion rate is increased, the amount of high-value-added products generated is increased, carbon dioxide emissions are lower, energy consumption is reduced, and the adverse impact on the natural environment is significantly minimized.

[0025] 5. The preparation method of the present invention is simple to operate, has relaxed reaction conditions, and the reaction equipment is readily available. The entire preparation process requires less material and has both the advantages of economical raw materials and high efficiency. At the same time, the reaction path complies with clean production standards and shows outstanding performance in terms of target product yield and eco-friendliness. Attached Figure Description

[0026] To more clearly illustrate the embodiments of the present invention and the prior art, the required drawings will be briefly described below. It should be noted that the following drawings are only some embodiments of the present invention, and those skilled in the art can derive the drawings of other embodiments based on the drawings without creative effort.

[0027] Figure 1 This is a schematic diagram of the process for preparing the in-situ supported Fe-based metal catalyst using ZSM-5 molecular sieve according to the present invention.

[0028] Figure 2 This is a transmission electron microscope (TEM) image of the ZSM-5 molecular sieve prepared as a comparative example of the present invention.

[0029] Figure 3 This is a transmission electron microscope (TEM) image of the ZSM-5 molecular sieve-supported Fe-based metal catalyst prepared in situ according to Example 1 of the present invention.

[0030] Figure 4This is a schematic diagram illustrating the application of the ZSM-5 molecular sieve in-situ supported Fe-based metal catalyst of the present invention in the direct conversion of methane to formic acid. Detailed Implementation

[0031] To clarify the core objectives, innovative features, and technical advantages of this technical solution, subsequent content will provide a systematic analysis and explanation of its principles in conjunction with the technical path shown in the accompanying drawings. It should be specifically noted that the embodiments disclosed herein represent only typical implementation scenarios of this technical solution and do not constitute a limitation on the scope of protection. Based on the technical principles disclosed in this document, any equivalent technical solution or derivative implementation variation implemented by a person with conventional skills in the art without inventive effort should be included within the scope of this patent claim.

[0032] Unless otherwise specified, all experimental procedures described in this document follow standardized operating procedures in this field. Unless otherwise stated, all materials and reagents mentioned refer to standard industrial-grade products available through commercial procurement channels.

[0033] The preparation method of the Fe-based metal catalyst supported on ZSM-5 molecular sieve in this embodiment is described in reference to... Figure 1 The main steps include the following:

[0034] Step 101 involves mixing the molecular sieve template and the silicon source at room temperature and continuously stirring to obtain a reaction precursor solution. Specifically, this includes adding the molecular sieve template to deionized water and stirring for approximately 3-5 minutes, then adding the silicon source and stirring for 15-25 minutes. The molecular sieve template is tetrapropylammonium hydroxide (TPAOH), tetramethylammonium hydroxide (TMAOH), or hexadecyltrimethylammonium bromide (CTAB). The silicon source is tetraethyl or tetrapropyl silicate (TEOS) or tetrapropyl or tetraethylammonium hydroxide (TPOS). The volume ratio of the silicon source to the molecular sieve template is 1:2-3:1, and the mass concentration of the molecular sieve template is 20-40 wt%.

[0035] Step 102: After uniformly mixing the reaction solute with an appropriate amount of reaction solvent, a metal precursor is obtained; the reaction solute is an Fe metal salt and a complexing agent; the reaction solvent is deionized water; specifically, this includes: dissolving the complexing agent in deionized water, and then adding a small amount of the mixed solution to the Fe metal salt, so that the mass ratio of Fe metal salt to complexing agent is 1:1-1:3; the Fe metal salt is any one or a combination of ferric nitrate nonahydrate, ferric sulfate, or ferric chloride; the complexing agent is any one or a combination of two of ethylenediaminetetraacetic acid tetrasodium or ethylenediaminetetraacetic acid disodium.

[0036] Step 103 involves uniformly stirring the reaction precursor solution and the metal precursor at room temperature, then adding an aluminum source to generate a catalyst precursor. Specifically, this includes: uniformly stirring the reaction precursor solution and the metal precursor at 20-30°C for approximately 5-10 minutes, then gradually adding an aluminum source to generate the catalyst precursor; the mass ratio of the reaction precursor solution to the metal precursor is 1:3-2:1; the stirring rate is 300-500 r / min, and the uniform stirring time is 3-5 hours; the aluminum source is any one or a combination of boehmite, γ-alumina, aluminum hydroxide gel, or sodium aluminate.

[0037] Step 104: The catalyst precursor is transferred to a high-pressure reactor for hydrothermal treatment. The hydrothermally treated catalyst precursor is washed with water to remove impurities, and then the molecular sieve template is removed by calcination to form a porous structure framework of ZSM-5.

[0038] The preparation method is simple to operate, has mild conditions, low equipment requirements, and saves on materials, making it environmentally friendly.

[0039] Example 1

[0040] 1) Add 3 mL of tetrapropylammonium hydroxide to deionized water and stir for about 3-5 minutes. Then add 3.5 mL of tetraethyl silicate and stir for 15-25 minutes (the mass concentration of tetrapropylammonium hydroxide used is 40 wt%, and the concentration of tetraethyl silicate is 99% or higher) to obtain solution A.

[0041] 2) Dissolve 200 mg of tetrasodium ethylenediaminetetraacetate in 10 mL of deionized water, and add 100 mg of ferric nitrate (Fe(NO3)3·9H2O) to the mixed solution to obtain solution B;

[0042] 3) Slowly add solution B to solution A to obtain a catalyst solution. Stir for 6 hours until the liquid is transparent. Add 54 mg of sodium aluminate, where the silicon-to-aluminum ratio (molar ratio) is 0.25. Transfer the obtained catalyst precursor to a polytetrafluoroethylene reactor and hydrothermally heat it at 160°C for 3 days.

[0043] 4) The hydrothermally heated catalyst solid was washed with deionized water, then dried at 80°C overnight. The product was then annealed by calcination at 500°C for 6 hours to remove the molecular sieve template. Fe was obtained. 0.25 @ZSM-5 molecular sieve-based catalyst, transmission electron microscopy (TEM) image see Figure 3 The catalyst after metal loading is a layered long hexagonal prism. ICP elemental analysis shows the mass percentages of Fe, Si, and Al in the catalyst, which are listed in Table 1.

[0044] Example 2

[0045] The preparation method in this embodiment is basically the same as that in Example 1, except that: 108 mg of sodium aluminate is weighed, and the molar ratio of tetraethyl silicate to sodium aluminate is 0.5, to obtain Fe. 0.5 The ZSM-5 molecular sieve-based catalyst, after ICP elemental analysis, has the following mass percentages of Fe, Si, and Al elements, as shown in Table 1.

[0046] Example 3

[0047] The preparation method of this embodiment is basically the same as that of Example 1, except that: 216 mg of sodium aluminate was weighed, and the molar ratio of tetraethyl silicate to sodium aluminate was 1, to prepare Fe@ZSM-5 molecular sieve-based catalyst. The mass percentages of Fe, Si and Al elements by ICP elemental analysis are shown in Table 1.

[0048] Example 4

[0049] The preparation method of this embodiment is basically the same as that of Example 1, except that: 432 mg of sodium aluminate was weighed, and the molar ratio of tetraethyl silicate to sodium aluminate was 2, to prepare Fe2@ZSM-5 molecular sieve-based catalyst. The mass percentages of Fe, Si and Al elements by ICP elemental analysis are shown in Table 1.

[0050] Comparative Example

[0051] The preparation method of this comparative example differs from that of Example 3 in that ferric nitrate is not added in step 2), while the remaining proportions and steps are the same. In the final step, after calcination in air, 1 g of ZSM-5 and 100 mg of ferric nitrate are dissolved in 50 mL of deionized water. The mixture is heated and stirred in an oil bath at 200 r / min to 80 °C, then cooled to 20-30 °C and washed with deionized water to remove excess impurities. It is then dried at 80 °C and finally calcined at 500 °C under argon gas at a flow rate of 50 mL / min and a rate of 1-5 °C / min for 5 hours. The Fe / ZSM-5 catalyst was obtained. A transmission electron microscope (TEM) image of the metal-unloaded ZSM-5 is shown below. Figure 2 The molecular sieve is a relatively thick regular hexagonal prism. The mapping diagram shows that the molecular sieve is uniformly composed of Si, Al and O. The mass percentages of Fe, Si and Al elements after being loaded with metal are shown in Table 1.

[0052] Table 1

[0053]

[0054] like Figure 4 As shown, the application process of the ZSM-5 molecular sieve-supported Fe-based metal catalyst in the direct conversion of methane to formic acid includes the following steps:

[0055] Step 401: The pre-set ZSM-5 molecular sieve-supported Fe-based metal catalyst is directly added to the reaction solvent placed in a quartz boat, and ultrasonically mixed until the catalyst solution becomes a uniformly dispersed liquid. The mass ratio of the ZSM-5 molecular sieve-supported Fe-based metal catalyst to the reaction solvent is 1:10-2:1, and the catalyst solution is 10 mL. Specifically, the reaction solvent in this application is a mixed solution of deionized water and hydrogen peroxide in a ratio of 1:10-1:0; when the reaction solvent is entirely deionized water, the introduced gas is a mixture of methane, hydrogen, and oxygen in a ratio of 1:1-3:1.

[0056] Step 402: Place the quartz boat containing the catalyst solution directly into the high-pressure reactor, flush the reactor two to three times with the mixed gas used for the reaction to remove the air from the reactor, and then pressurize the reactor to 0.2-0.5 MPa.

[0057] Step 403: Place the reactor on a temperature-controlled heating stirrer, raising the temperature to 40-120°C at a rate of 1-5°C / minute, and continue the reaction for 0.5-6 hours. Then, cool the reactor to room temperature (20-30°C) and remove the liquid to obtain formic acid. In this step, because the catalyst tends to accumulate at the bottom of the reactor, continuous stirring is necessary during heating. This step also ensures sufficient reaction between the methane mixture and the catalyst liquid. The stirring speed is 600-800 rpm. The methane mixture consists of 3.21% hydrogen (H2), 6.77% oxygen (O2), 1.6% methane (CH4), 61.62% argon (Ar), and 26.8% helium (He).

[0058] Application examples

[0059] 1) Take 20 mg of the catalyst prepared in Examples 1-4 and the comparative example and add it to 10 mL of deionized water placed in a quartz boat. Mix it with ultrasound until the catalyst solution becomes a uniformly dispersed liquid. The catalyst solution is 10 mL.

[0060] 2) Place the quartz boat containing the catalyst directly into the high-pressure reactor. Rinse the reactor three times with the mixed gas used for the reaction (3.21% hydrogen (H2), 6.77% oxygen (O2), 1.6% methane (CH4), 61.62% argon (Ar) and 26.8% helium (He)) to remove the air from the reactor. Then pressurize the reactor to 0.3 MPa.

[0061] 3) Place the reactor on a temperature-controlled heating stirrer (600 rpm, continuous stirring) to raise the temperature to 60°C at a rate of 2°C / min, and continue the reaction for 50 minutes. Then, cool the reactor to room temperature (approximately 30°C) and remove the liquid to obtain formic acid. The results are shown in Table 2.

[0062] Table 2

[0063]

[0064] As shown in Table 2, comparing the formic acid yields, it can be seen that the in-situ loaded metal formic acid yield is much higher than that of the impregnation method. Furthermore, as the silicon-to-aluminum ratio decreases, the formic acid yield reaches its highest point of 7.05 mmol / h when the silicon-to-aluminum mass fraction ratio is 163.31. -1 .

[0065] This invention generates a catalytic liquid by uniformly mixing the catalyst with the reaction solution. During the reaction, the catalytic liquid is stirred and heated to ensure full contact with methane, directly generating formic acid under mild conditions. The reaction takes less time and has high formic acid yield and methane conversion rate, greatly reducing the production cost of formic acid and making it highly applicable. The catalyst produces less carbon dioxide during the catalytic process, making it extremely environmentally friendly and a highly efficient and environmentally friendly new material.

[0066] The embodiments described herein are intended to illustrate the basic principles; however, it should be noted that the advantages, benefits, and effects described are merely examples and not mandatory requirements for each embodiment. Furthermore, the specific implementation details listed for ease of understanding are merely illustrative, and the implementation of this application is not limited to the above details.

[0067] The block diagrams of devices, apparatuses, devices, and systems shown in this application are merely examples and do not limit the connections, arrangements, or configurations to be consistent with the figures. Those skilled in the art will understand that these components can be connected, arranged, or configured in any manner. The terms "comprising," "including," and "having," etc., are open-ended expressions meaning "including but not limited to," and are used interchangeably. The words "or" and "and" used herein both mean "and / or," unless the context otherwise requires. Furthermore, "such as" is equivalent to "for example, but not limited to," and the two are interchangeable.

[0068] It should also be noted that the parts or steps in the apparatus, equipment, and methods of this application can be disassembled and / or reassembled. Such operations should be considered as equivalent solutions to this application.

[0069] This disclosure is intended to enable those skilled in the art to implement this application. Modifications to the embodiments will be apparent to those skilled in the art, and the core principles can be extended to other embodiments without exceeding the scope of protection. Therefore, this application is not limited to the specific embodiments shown, but should cover the maximum scope consistent with the principles and innovative features of this disclosure.

[0070] This description is for illustrative purposes only and is not intended to limit the implementation. Although multiple solutions are described, those skilled in the art should understand that adjustments, modifications, or additions are possible.

Claims

1. A method for preparing an in-situ supported Fe-based metal catalyst on ZSM-5 molecular sieve, comprising: 1) Add the molecular sieve template to deionized water and stir, then add the silicon source and stir to obtain the reaction precursor solution; dissolve the complexing agent in deionized water and then add the Fe metal salt to obtain the metal precursor; 2) The metal precursor is dropped into the reaction precursor liquid and stirred until the liquid is transparent. An aluminum source is added and the reaction is continued with stirring to finally form a catalyst precursor. 3) The catalyst precursor was transferred to a high-pressure reactor for hydrothermal treatment. The product was then dried and annealed in sequence. Finally, the molecular sieve template was removed by calcination to obtain the ZSM-5 molecular sieve in-situ supported Fe-based metal catalyst.

2. The preparation method according to claim 1, characterized in that, In step 1), the molecular sieve template is tetrapropylammonium hydroxide, tetramethylammonium hydroxide, or hexadecyltrimethylammonium bromide; the silicon source is tetraethyl silicate or tetrapropyl silicate; the complexing agent is any one or a combination of two of ethylenediaminetetraacetic acid tetrasodium or ethylenediaminetetraacetic acid disodium; and the Fe metal salt is any one or a combination of ferric nitrate nonahydrate, ferric sulfate, or ferric chloride.

3. The preparation method according to claim 1, characterized in that, In step 1), the volume ratio of the molecular sieve template to deionized water is 1:8-3:1, the mass concentration of the molecular sieve template is 20-40 wt%, the mass concentration of the silicon source is 99%, the volume ratio of the silicon source to the molecular sieve template is 1:2-3:1, and the ratio of the Fe metal salt to the complexing agent is 1:1-1:

3.

4. The preparation method according to claim 1, characterized in that, In step 1), the molecular sieve template is added to deionized water and stirred for 3-5 minutes, then the silicon source is added and stirred for 15-25 minutes.

5. The preparation method according to claim 1, characterized in that, In step 2), the reaction precursor solution and the metal precursor are stirred uniformly at 20-30℃ for 5-10 minutes, and then the aluminum source is gradually added to generate the catalyst precursor; the mass ratio of the reaction precursor solution to the metal precursor is 1:3-2:1, and the molar ratio of the silicon source to the aluminum source is 0.25:1-5:1; the stirring rate is 300-500 r / min, and the uniform stirring time is 3-5 hours; the aluminum source is any one or a combination of boehmite, γ-alumina, aluminum hydroxide gel, or sodium aluminate.

6. The preparation method according to claim 1, characterized in that, In step 3), the hydrothermal temperature is 150-180℃ and the hydrothermal treatment time is 2-4 days; the calcination temperature is controlled at 350-800℃ in air, and calcination is carried out by increasing the temperature at 4-8 minutes / ℃ to remove the molecular sieve template.

7. A ZSM-5 molecular sieve in-situ supported Fe-based metal catalyst, obtained by the preparation method according to any one of claims 1-6.

8. The ZSM-5 molecular sieve in-situ supported Fe-based metal catalyst according to claim 7, characterized in that, The mass percentage of iron in the ZSM-5 molecular sieve-supported Fe-based metal catalyst is 1-5 wt%; the particle size of the ZSM-5 molecular sieve-supported Fe-based metal catalyst is 200-500 nm.

9. The application of the ZSM-5 molecular sieve in-situ supported Fe-based metal catalyst according to claim 7, comprising: An in-situ supported Fe-based metal catalyst on ZSM-5 molecular sieve was added to a reaction solvent and ultrasonically mixed to generate a catalytic solution. The catalytic solution was then added to a high-pressure reactor, and the reactor was repeatedly flushed with a methane mixture until the pressure inside the reactor reached 0.1-0.5 MPa, ensuring that the methane mixture fully filled the reactor. The methane mixture was then allowed to react fully with the catalytic solution, raising the reactor temperature from 20-30°C to 40-120°C at a rate of 1-5°C / min, and the reaction was continued for 0.1-48 hours. The reactor was then cooled to 30°C, and the catalytic solution was collected to obtain formic acid.

10. The application according to claim 9, characterized in that, The mass ratio of the in-situ supported Fe-based metal catalyst on the ZSM-5 molecular sieve to the reaction solvent is 1:10-2:1; the reaction solvent is a mixed solution of deionized water and hydrogen peroxide with a volume ratio of 1:10-1:0.

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