A preparation method and application of Fe / ZSM-5 catalyst

Abstract

The present invention relates to a high-efficiency Fe / ZSM-5 catalyst and a preparation method and application thereof. The catalyst comprises an active component and a carrier, wherein the carrier is a ZSM-5 molecular sieve, and the active component is a Fe 3+ The species is located on the five-membered ring in the ZSM-5 molecular sieve and replaces the proton of the acid. The catalyst provided by the present invention can convert methane into acetic acid more efficiently and selectively; it can catalyze the reaction quickly at a lower temperature; and the catalyst has a certain stability.

Description

Technical Field

[0001] The invention belongs to the technical field of catalytic oxidation, and specifically relates to a method for preparing a high-efficiency Fe / ZSM-5 catalyst and application of the catalyst in preparing acetic acid by low-temperature catalytic oxidative carbonylation of methane. Background Art

[0002] Methane is the smallest saturated hydrocarbon and the main component of natural gas. It is expected to become a potential carbon resource to replace oil, so direct conversion of methane is of great significance. The production area of ​​methane is often far away from the use area, and it will be costly to transport it through pipelines. Therefore, converting methane into liquid products such as methanol, formic acid and acetic acid at the production area will greatly improve the difficult situation of methane transportation.

[0003] The methane molecule consists of four equivalent C–H bonds and has a highly symmetrical tetrahedral structure. Its thermodynamic properties are extremely stable. Due to the problems of weak methane reactivity, the current industrial application of methanol production from methane is mostly carried out indirectly: first, under high temperature (>800℃) conditions, methane is reformed with water, oxygen or carbon dioxide to form synthesis gas (CO / H2), and then the synthesis gas is further converted into important basic chemical raw materials or synthetic liquid fuels such as methanol, dimethyl ether, low-carbon mixed alcohols, and low-carbon olefins under pressurized conditions. Since the conversion of methane to synthesis gas is a thermodynamically favorable process, the carbon yield of indirect conversion of methane to methanol in industry is very high (about 70%), but the process has the disadvantages of high energy consumption and cumbersome steps, which greatly limits the efficient utilization of methane. Compared with the traditional process of indirect conversion of methane to methanol, direct conversion of methane to produce oxygen-containing compounds such as methanol, formic acid and acetic acid does not require the synthesis gas step, and has potential advantages in theory, such as mild reaction conditions and simple process.

[0004] Acetic acid is an important chemical raw material, mainly used to synthesize vinyl acetate, acetic anhydride, acetate, terephthalic acid and ethanol. In 2019, the global market share of acetic acid was US$8.92 billion, and the annual growth rate is expected to be 5.2% between 2020 and 2027. In 2019, China's apparent consumption of acetic acid was 6.26 million tons.

[0005] At present, my country's acetic acid synthesis mainly adopts the methanol carbonylation method, and most of the domestic production equipment adopts the rhodium / iodine catalyst system developed by Monsanto. Due to the use of homogeneous rhodium-based catalysts, corrosive hydroiodic acid, and toxic methyl iodide in the reaction, the reaction has many unfavorable factors, such as expensive catalysts, difficult catalyst recovery, the need to use special corrosion-resistant materials, and potential environmental risks. Summary of the invention

[0006] The invention provides a preparation method and application of a Fe / ZSM-5 catalyst. The catalyst is used for low-temperature and high-efficiency catalytic oxidative carbonylation of methane to prepare acetic acid, and has the advantages of high acetic acid yield, good stability, low price, easy recovery, etc.

[0007] First, the present invention provides a high-efficiency Fe / ZSM-5 catalyst, which includes an active component and a carrier, wherein the carrier is a ZSM-5 molecular sieve, and the active component is a mononuclear Fe 3+ Species, and it is located in the five-membered ring in the ZSM-5 molecular sieve and replaces Acid proton.

[0008] According to some embodiments of the catalyst of the present invention, Fe 3+ The species accounted for more than 50% of the total Fe.

[0009] According to some embodiments of the catalyst of the present invention, the mass loading of Fe is 0.01wt%≤Fe / (molecular sieve+Fe2O3)≤10wt%. Preferably, the mass loading of Fe is 0.1wt%≤Fe / (molecular sieve+Fe2O3)≤1wt%. Preferably, the mass loading of Fe is 0.2wt%≤Fe / (molecular sieve+Fe2O3)≤0.75wt%. Preferably, the mass loading of Fe is 0.25wt%≤Fe / (molecular sieve+Fe2O3)≤0.5wt%, for example, 0.2wt%≤Fe / (molecular sieve+Fe2O3)≤0.3wt%.

[0010] According to some embodiments of the catalyst of the present invention, the molar silicon-to-aluminum ratio of the ZSM molecular sieve n(SiO2) / n(Al2O3) is ≥30.

[0011] According to some embodiments of the catalyst of the present invention, the molar silicon-to-aluminum ratio of the ZSM molecular sieve is n(SiO2) / n(Al2O3)≤100.

[0012] Preferably, the molar silicon-aluminum ratio n(SiO2) / n(Al2O3) of the ZSM molecular sieve is 30.

[0013] In addition, the present invention provides a method for preparing a high-efficiency Fe / ZSM-5 catalyst, the method comprising the following steps:

[0014] (1) subjecting the ZSM-5 molecular sieve after removing the template to ion exchange in an ammonium salt solution to obtain NH4–ZSM-5;

[0015] (2) vacuum pretreatment of NH4–ZSM-5 molecular sieve;

[0016] (3) impregnating the NH4-ZSM-5 molecular sieve treated in step (2) with an Fe salt solution,

[0017] (4) Drying and calcining the molecular sieve treated in step (3).

[0018] According to some embodiments of the preparation method of the present invention, in step (1), the ammonium salt is ammonium nitrate with a concentration of 0.1-1.5 mol·L -1 The ion exchange time is 12-48 hours; the temperature is 50–90°C.

[0019] According to some embodiments of the preparation method of the present invention, in step (2), the treatment time is ≥ 0.5 h, and the treatment temperature is 20-40° C.

[0020] According to some embodiments of the preparation method of the present invention, in step (3), the Fe salt is selected from ferric acetylacetonate, FeCl3, Fe(NO3)3 and Fe2(SO4)3; the solvent in the Fe salt solution is a C1-C6 alcohol solvent (preferably ethanol) or a mixture of a C1-C6 alcohol solvent (preferably ethanol) and water.

[0021] According to some embodiments of the preparation method of the present invention, in step (3), the immersion temperature is 20-40° C., and the immersion time is 12-48 h.

[0022] According to some embodiments of the preparation method of the present invention, in step (4), the drying method is rotary evaporation drying, and the rotary evaporation drying temperature is 20-70°C.

[0023] According to some embodiments of the preparation method of the present invention, the ZSM-5 molecular sieve after removing the template is obtained by calcination. Preferably, the calcination temperature is 300-800°C, the calcination time is 1-10h, and the heating rate is 0.1-5°C·min -1 The calcination atmosphere was air, and the air flow rate was 0–50 mL min -1 .

[0024] In addition, the present invention also provides the use of the Fe / ZSM-5 catalyst or the Fe / ZSM-5 catalyst obtained by the above preparation method in the synthesis of acetic acid by methane carbonylation.

[0025] According to some embodiments of the present invention, the raw gas used includes methane and CO, and the oxidant used is a hydrogen peroxide solution.

[0026] According to some embodiments of the present invention, the concentration of the hydrogen peroxide solution is 0.1-10 mol·L -1 , preferably 0.5–2 mol·L -1 .

[0027] According to some embodiments of the present invention, the feed gas pressure is 1-20 MPa, and the higher the pressure, the better. Due to experimental conditions, 8 MPa is best.

[0028] According to some embodiments of the present application, the reaction temperature is 0-100°C, preferably 50-80°C.

[0029] According to some embodiments of the present application, the reaction time is 0.5-10 h, preferably 0.5-2 h.

[0030] According to some embodiments of the present application, the rotation speed is 500-1500 rpm.

[0031] According to some embodiments of the present invention, P CH4 / P CO =0.1–10, preferably 3 / 2.

[0032] According to some embodiments of the present invention, the mass volume ratio of the catalyst to the hydrogen peroxide solution is (10-100) mg / (1-20) mL.

[0033] The beneficial effects of the present invention are as follows:

[0034] The catalyst provided by the present invention can convert methane into acetic acid more efficiently and with high selectivity; can catalyze the reaction quickly at a relatively low temperature; and has a certain stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is the powder X-ray diffraction pattern of ZSM-5, Fe / ZSM-5(0.05) of Example 2, Fe / ZSM-5(0.1) of Example 3, Fe / ZSM-5(0.25) of Example 1, used-Fe / ZSM-5(0.25) after the reaction of Example 1, and Fe / ZSM-5(0.5) catalyst of Example 4.

[0036] Figure 2 It is the UV-visible spectra of Fe / ZSM-5(0.05) of Example 2, Fe / ZSM-5(0.1) of Example 3, Fe / ZSM-5(0.25) of Example 1, and Fe / ZSM-5(0.5) of Example 4 catalysts.

[0037] Figure 3 The relationship between the catalytic performance of Fe / ZSM-5 (molar Si-Al ratio 30) with different loading amounts and the mononuclear Fe species is shown.

[0038] Figure 4It is the UV Raman spectra of NH4–ZSM-5 and Fe / ZSM-5 (0.25) catalyst of Example 1.

[0039] Figure 5 Shown are ion fragments of the Fe / ZSM-5 catalyst of Example 1 measured by time-of-flight secondary ion mass spectrometry (ToF-SIMS).

[0040] Figure 6 It is the UV-visible spectrum of the used-Fe / ZSM-5 (0.25) catalyst (molar silicon-aluminum ratio 30) after the reaction in Example 1. DETAILED DESCRIPTION

[0041] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only a part of the present invention, not all embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. It should be noted that the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

[0042] The catalyst system is composed of a heterogeneous catalyst of NH4-ZSM-5 molecular sieve loaded with Fe, wherein NH4-ZSM-5 is prepared by calcining purchased ZSM-5 molecules to remove the template and reacting with NH4NO3 solution (1 mol L -1 ) by ion exchange (stirring time 12h; exchange four times; exchange temperature 80°C) to remove sodium ions, wherein the molar silicon-aluminum ratio of the ZSM molecular sieve SiO2 / Al2O3 is ≥30.

[0043] The method of introducing Fe into the catalyst is vacuum impregnation: NH4-ZSM-5 is subjected to vacuum treatment for a treatment time of ≥0.5h; ethanol solutions of Fe salts such as ferric acetylacetonate, Fe(NO3)3 and Fe2(SO4)3 and water are added, and the volume ratio of water to ethanol is 0-10; the impregnation temperature is 20-40°C, the impregnation time is 12-48h, and the stirring is 500-1500rpm; after impregnation, it is dried by rotary evaporation and then calcined, wherein the Fe source is an ethanol solution of ferric acetylacetonate, and the mass loading of Fe is 0.01wt%≤Fe / (molecular sieve+Fe2O3)≤10wt%.

[0044] The above calcination operations were all carried out in a muffle furnace, with a calcination temperature of 300–800°C, a calcination time of 1–10 h, and a heating rate of 0.1–5°C min -1 The calcination atmosphere was air, and the air flow rate was 0–50 mL min -1 .

[0045] At the same time, the present invention also provides an application of the Fe / ZSM-5 catalyst obtained by the above preparation method. The Fe / ZSM-5 catalyst can be used for the synthesis of a series of oxygen-containing compounds such as methanol, formic acid and acetic acid by oxidative carbonylation of methane. The specific steps are as follows: the reaction activity evaluation of the catalyst for preparing acetic acid by oxidative carbonylation of methane is carried out in a 100mL high-pressure reactor. The reaction conditions are: 10-100mg catalyst, 1-20mL of 0.1-10mol L -1 Hydrogen peroxide solution, raw gas pressure is 1-20MPa, reaction temperature is 0-100℃.

[0046] Example 1

[0047] First, weigh 20g of ZSM-5 molecular sieve powder (molar silicon-aluminum ratio n(SiO2) / n(Al2O3)=30) and place it in a muffle furnace. Then, air is introduced into the muffle furnace. -1 The original molecular sieve powder was calcined at 500℃ for 5h, and then cooled naturally to obtain the Na-ZSM-5 molecular sieve with the template removed. The Na-ZSM-5 molecular sieve with the template removed was added with 250mL of 1mol L -1 NH4NO3 solution, and then stirred at 80℃ and 500rpm for 12h for ion exchange. Then, centrifuged at 4500rpm for 5min. After centrifugation, wash with ultrapure water, centrifuge and wash four times. After centrifugation four times, add 250mL1mol L -1 The NH4NO3 solution was used to carry out the next ion exchange, and a total of 4 ion exchanges were carried out. After the last centrifugation, the molecular sieve sludge was transferred to a petri dish and dried in an oven at 80°C for 10 hours. The dried block was taken out and ground to obtain NH4–ZSM-5 molecular sieve powder. At room temperature, 0.016g of ferric acetylacetonate was dissolved in a beaker containing 5mL of ethanol. Then, the ferric acetylacetonate solution was transferred to a flask containing 1g of NH4–ZSM-5 molecular sieve and pre-vacuumed for 30 minutes. The residual ferric acetylacetonate solution in the beaker was washed twice with ultrapure water, using 5mL each time, and the washed solution was also transferred to the above flask. The mixture in the flask was stirred continuously at room temperature for 24 hours. The impregnated catalyst was dried in a rotary evaporator at 70°C and calcined in a muffle furnace at 500°C for 3 h to obtain a Fe / ZSM-5 (0.25) catalyst (Fe mass loading of 0.25 wt%, molar silicon to aluminum ratio of 30).

[0048] Weigh 30 mg of the prepared catalyst and 10 mL of 0.5 mol L -1The hydrogen peroxide solution and the magnet are loaded into a 100mL glass liner, which is then loaded into a sealed high-pressure reactor. The air inside the reactor is replaced twice with 2MPa methane and 2MPa carbon monoxide in turn. The exhaust gas is discharged to the outside through the exhaust pipe. 2.5MPa methane and 2.5MPa carbon monoxide are filled into the reactor, stirring is started at 1500rpm, and the timing is started when the reactor is heated to 50°C. After 0.5h, the high-pressure reactor is placed in an ice water bath and cooled for 30 minutes to reduce the loss of volatile products. The gaseous products are collected by air bags and TCD tests are performed on a GC 9790plus chromatograph. The residue in the reactor is collected and centrifuged to remove the catalyst in the liquid product. By 1 H NMR is used to quantify the liquid product. NMR measurement should be performed immediately after the liquid product is collected to prevent residual hydrogen peroxide from oxidizing the product to carbon dioxide. Typically, 0.4 mL of filtered liquid reaction product and 0.1 mL of D2O (containing 0.02 wt% DSS) are placed in a liquid NMR tube for measurement. In addition, the NMR tube is covered with aluminum foil during the transfer process to prevent hydrogen peroxide from decomposing in the presence of light to generate free radicals, thereby oxidizing carbon-containing products. The catalyst evaluation results are shown in Table 1.

[0049] Example 2

[0050] The mass of ferric acetylacetonate used in catalyst preparation was 0.0032 g, and the other catalyst preparation steps were the same as those in Example 1. The obtained catalyst was recorded as: Fe / ZSM-5 (0.05) (the mass loading of Fe was 0.05 wt %, and the molar silicon-aluminum ratio was 30). The catalyst evaluation steps and reaction conditions were the same as those in Example 1. The catalyst evaluation results are shown in Table 1.

[0051] Example 3

[0052] The mass of ferric acetylacetonate used in catalyst preparation was 0.0064 g, and the other catalyst preparation steps were the same as those in Example 1. The obtained catalyst was recorded as: Fe / ZSM-5 (0.10) (the mass loading of Fe was 0.10 wt %, and the molar silicon-aluminum ratio was 30). The catalyst evaluation steps and reaction conditions were the same as those in Example 1. The catalyst evaluation results are shown in Table 1.

[0053] Example 4

[0054] The mass of ferric acetylacetonate used in catalyst preparation was 0.0320 g, and the other catalyst preparation steps were the same as those in Example 1. The obtained catalyst was recorded as: Fe / ZSM-5 (0.50) (the mass loading of Fe was 0.50 wt %, and the molar silicon-aluminum ratio was 30). The catalyst evaluation steps and reaction conditions were the same as those in Example 1. The catalyst evaluation results are shown in Table 1.

[0055] Example 5

[0056] The molar silicon-to-aluminum ratio of ZSM-5 used in the catalyst preparation was n(SiO2) / n(Al2O3)=60, and the other catalyst preparation steps were the same as those in Example 1. The obtained catalyst was recorded as: Fe / ZSM-5 (0.25; 60) (the mass loading of Fe was 0.25wt%, and the molar silicon-to-aluminum ratio was 60). The catalyst evaluation steps and reaction conditions were the same as those in Example 1, and the catalyst evaluation results are shown in Table 1.

[0057] Example 6

[0058] The molar silicon-to-aluminum ratio of ZSM-5 used in the catalyst preparation was n(SiO2) / n(Al2O3)=130, and the other catalyst preparation steps were the same as those in Example 1. The obtained catalyst was recorded as: Fe / ZSM-5 (0.25; 130) (the mass loading of Fe was 0.25wt%, and the molar silicon-to-aluminum ratio was 130). The catalyst evaluation steps and reaction conditions were the same as those in Example 1. The catalyst evaluation results are shown in Table 1.

[0059] Example 7

[0060] The molar silicon-to-aluminum ratio of ZSM-5 used in the catalyst preparation was n(SiO2) / n(Al2O3)=300, and the other catalyst preparation steps were the same as those in Example 1. The obtained catalyst was recorded as: Fe / ZSM-5 (0.25; 300) (the mass loading of Fe was 0.25wt%, and the molar silicon-to-aluminum ratio was 300). The catalyst evaluation steps and reaction conditions were the same as those in Example 1. The catalyst evaluation results are shown in Table 1.

[0061] Comparative Example 1

[0062] The ZSM-5 used in the catalyst preparation is composed entirely of silicon dioxide, and the other catalyst preparation steps are the same as those in Example 1. The obtained catalyst is recorded as: Fe / ZSM-5 (0.25; ∞). The catalyst evaluation steps and reaction conditions are the same as those in Example 1. The catalyst evaluation results are shown in Table 1.

[0063] Example 8

[0064] The catalyst preparation steps and conditions are the same as those in Example 1, except that the reaction conditions in the catalyst evaluation step are changed to: 4 MPa methane and 4 MPa carbon monoxide.

[0065] Table 1: Catalytic evaluation results of Fe / ZSM-5 catalysts with different Fe loadings and different Si-Al ratios.

[0066]

[0067] Example 9

[0068] The solid-liquid mixture after the reaction in Example 1 was collected in a 100 mL glass liner, dried at 120° C. for 12 h to remove the liquid product, and then the catalytic reaction was repeated. No fresh catalyst was added, and the other steps and reaction conditions were the same as in Example 1. After the above steps were repeated 4 times, the catalyst evaluation results are shown in Table 2.

[0069] Table 2: Fe / ZSM-5 (0.25; 30) catalyst stability test.

[0070]

[0071] pass Figure 1 The powder X-ray diffraction characterization found that no diffraction peak of Fe2O3 was observed, indicating that Fe was highly dispersed on the molecular sieve carrier and the particle size was below the detection limit (about 4nm). Figure 2 The characterization of the UV-visible spectrum found that Fe has four forms: mononuclear four-coordinated Fe 3+ Species (220–237nm), mononuclear hexacoordinated Fe 3+ (267–289nm), Fe x O y Clusters (353-368 nm) and Fe2O3 nanoparticles (>500 nm). By analyzing the catalytic data obtained in Examples 1, 2, 3, and 4, it was found that the yields of the oxidation products (acetic acid, formic acid, methanol, and methyl hydroperoxide) were similar to those of the mononuclear hexacoordinated Fe 3+ The content of the species has a linear relationship, and the selectivity of acetic acid is related to the mononuclear tetracoordinated Fe 3+ The proportion of the species also has a linear relationship, indicating that the high activity of the catalyst in the present invention comes from the uniformly dispersed mononuclear Fe 3+ Species, see Figure 3 .Depend on Figure 4 The ultraviolet Raman spectroscopy in the results showed that the Fe species was located in the five-membered ring of the ZSM-5 molecular sieve and replaced By analyzing the catalytic data obtained in Examples 1, 5, 6, and 7, and Figure 5 Time-of-flight secondary ion mass spectrometry (ToF-SIMS) characterization found that the activity of the mononuclear Fe site is also closely related to the Al element in the ZSM-5 zeolite framework.

[0072] The catalyst obtained by the preparation method of the present invention can effectively convert methane into acetic acid, and its optimal reaction temperature is 50°C. The catalyst has the advantages of low cost and high activity. In Example 8, at 8MPa, 50°C, 10mL 0.5molL -1Hydrogen peroxide, 30 mg Fe / ZSM-5 (Fe mass loading is 0.25 wt%, molar silicon-aluminum ratio is 30), the iron salt reagent is iron acetylacetonate, the calcination temperature of the catalyst is 500 ° C, P CH4 / P CO =1, 1500 rpm, 0.5 h, the maximum space-time yield of acetic acid reached 12.01 mmol g cat -1 h -1 , the selectivity for acetic acid is 63.24%. Comparative Document 1 (Fe binuclear sites convert methane to acetic acid with ultrahigh selectivity, Bo Wu et al., Chem, Vol. 8, pp. 1658–1672, March 2, 2022, for details of the preparation process, see page 10, Synthesis of catalysts section) as the closest prior art discloses a Fe-BN / ZSM-5 (BN is the abbreviation of binuclear, representing the active site is binuclear Fe) catalyst prepared by vacuum impregnation method, the iron salt reagent used for the synthesis of the catalyst is FeCl3·6H2O, the calcination temperature of the catalyst is 400°C, and the space-time yield of acetic acid is 0.20 mmol g cat -1 ·h -1 , acetic acid selectivity 57%. Different from the above documents, the present invention uses ferric acetylacetonate as the iron source, wherein three acetylacetone molecules are wrapped around each iron atom, which helps to form a physical barrier between iron atoms and achieve the purpose of high dispersion; in addition, the calcination temperature used in the present invention is 500°C, which helps the iron species to repeat the experimental method in the comparative document 1 at high temperature, and the results are shown in Comparative Example 2.

[0073] Comparative Example 2

[0074] At room temperature, 0.072 g of FeCl3·6H2O was dissolved in a beaker containing 15 mL of ultrapure water. Then, the ferric chloride solution was transferred to a flask containing 1 g of NH4–ZSM-5 molecular sieve and pre-vacuumed for 30 minutes. The mixture in the flask was stirred continuously overnight at room temperature. The impregnated catalyst was dried in an oven at 100°C and calcined in a muffle furnace at 400°C for 4 h to obtain a Fe-BN / ZSM-5 catalyst. The catalyst evaluation steps and reaction conditions were the same as those in Example 1. The catalyst evaluation results are shown in Table 1.

[0075] By comparing the Fe / ZSM-5 (0.25) catalyst before and after the reaction ( Figure 1 and Figure 6) were characterized and found that the ZSM-5 molecular sieve carrier and the mononuclear Fe 3+ The number of species was well maintained, with the main loss being inactive Fe x O y Clusters, therefore, the stability of the Fe / ZSM-5 (0.25) catalyst in the present invention is well maintained, and is also verified in Example 9.

[0076] The above embodiments are only used to illustrate the present invention, but not to limit the present invention. Although the present invention is described in detail with reference to the embodiments, it should be understood by those skilled in the art that various combinations, modifications or equivalent substitutions of the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention, and should be included in the scope of the claims of the present invention.

Claims

1. A Fe / ZSM-5 catalyst comprising an active component and a carrier, wherein: The carrier is ZSM-5 molecular sieve, and the active component is Fe in mononuclear form. 3+ species, and it falls on the five-membered ring in the ZSM-5 molecular sieve and replaces Acid protons, mononuclear Fe 3+ The species accounts for more than 50% of the total Fe; the mass loading of Fe is 0.25%≤Fe / (molecular sieve+Fe2O3)≤0.5%; the molar silicon-aluminum ratio of the ZSM molecular sieve n(SiO2) / n(Al2O3)≥30 and ≤100. The preparation method of the Fe / ZSM-5 catalyst comprises the following steps: (1) subjecting the ZSM-5 molecular sieve after removing the template to ion exchange in an ammonium salt solution to obtain NH4–ZSM-5; (2) vacuum pretreatment of NH4–ZSM-5 molecular sieve; (3) impregnating the NH4-ZSM-5 molecular sieve treated in step (2) with an Fe salt solution, wherein the Fe salt is ferric acetylacetonate; (4) drying and calcining the molecular sieve treated in step (3), wherein the calcination temperature is 500-800°C.

2. The Fe / ZSM-5 catalyst according to claim 1, characterized in that In step (4), the drying method is rotary evaporation drying.

3. The Fe / ZSM-5 catalyst according to claim 1, characterized in that The ammonium salt in step (1) is ammonium nitrate with a concentration of 0.1–1.5 mol·L -1 The ion exchange time is 12–48 hours; the temperature is 50–90°C.

4. The Fe / ZSM-5 catalyst according to claim 1, characterized in that In step (2), the treatment time is ≥0.5h and the treatment temperature is 20–40°C.

5. The Fe / ZSM-5 catalyst according to claim 1, characterized in that In step (3), the solvent in the Fe salt solution is a C1-C6 alcohol solvent or a mixture of a C1-C6 alcohol solvent and water; the immersion temperature is 20-40°C, and the immersion time is 12-48h.

6. The Fe / ZSM-5 catalyst according to claim 5, characterized in that In step (3), the solvent in the Fe salt solution is ethanol or a mixture of ethanol and water.

7. The Fe / ZSM-5 catalyst according to claim 2, characterized in that In step (4), the rotary evaporation drying temperature is 20-70°C.

8. The Fe / ZSM-5 catalyst according to claim 2, characterized in that The ZSM-5 molecular sieve after removing the template is obtained by calcination.

9. The Fe / ZSM-5 catalyst according to claim 8, characterized in that The calcination temperature for removing the template in the ZSM-5 molecular sieve by calcination is 300-800°C, the calcination time is 1-10h, and the heating rate is 0.1-5°C·min -1 The calcination atmosphere was air, and the air flow rate was 0–50 mL min -1 .

10. Use of the Fe / ZSM-5 catalyst according to any one of claims 1 to 9 in the synthesis of acetic acid by oxidative carbonylation of methane.

11. The use according to claim 10, characterized in that: The raw gases used include methane and CO, and the oxidant used is hydrogen peroxide solution; the concentration of hydrogen peroxide solution is 0.1–10 mol·L -1 ; The feed gas pressure is 1–20 MPa; the reaction temperature is 0–100°C; the reaction time is 0.5–10 h; the rotation speed is 500–2000 rpm, P CH4 / P CO =0.1–10; the mass volume ratio of catalyst to hydrogen peroxide solution is (10–100) mg / (1–20) mL.

12. The use according to claim 11, characterized in that: The concentration of hydrogen peroxide solution is 0.5–2 mol L -1 ; Feed gas pressure is 2–8 MPa; Reaction temperature is 25–75°C; Reaction time is 0.5–2 h; P CH4 / P CO =3 / 2.

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