A (FeIn) / ZSM-5 catalyst, its preparation method and application

Abstract

This invention relates to a (FeIn) / ZSM-5 catalyst, comprising a ZSM-5 molecular sieve support and an active component supported on the ZSM-5 molecular sieve; the active component is a Fe species and an In species, with the Fe loading in the catalyst being 0.1~1.0 wt% and the In loading being 0.25~1.5 wt%. The invention also discloses a method for preparing the catalyst and its applications. This invention employs a "molecular anchoring" strategy, introducing a second metal, indium. Utilizing the stronger electronic interaction between indium and aluminum in the molecular sieve framework, the migration and aggregation of iron during preparation and reaction are effectively suppressed, significantly increasing the proportion of mononuclear iron in the (FeIn) / ZSM-5 catalyst and promoting the yield of the target product, acetic acid, in the methane oxidative carbonylation reaction.

Description

Technical Field

[0001] This invention relates to a (FeIn) / ZSM-5 catalyst, its preparation method, and its application. Background Technology

[0002] Methane, as a carbon resource with abundant reserves, wide availability, and low cost, is widely recognized as a core potential resource for producing high-value-added chemicals, replacing petroleum, in the context of increasingly depleted petroleum resources. Simultaneously, as the world's second-largest greenhouse gas, the efficient conversion of methane can effectively reduce greenhouse gas emission intensity and achieve high-value utilization of carbon resources. Therefore, the efficient conversion and utilization of methane is crucial for optimizing the energy structure.

[0003] However, methane molecules have a highly symmetrical tetrahedral configuration with high CH bond energies (approximately 439 kJ / mol) and strong thermodynamic stability. This means that the activation of the CH bonds in methane requires overcoming a high energy barrier, typically requiring high-temperature reaction conditions. More critically, the target oxygen-containing compounds (such as acetic acid and methanol) generated after methane activation have significantly higher reactivity than methane itself, easily undergoing over-oxidation reactions to produce low-value-added byproducts such as CO2. This severely reduces the selectivity of the target oxygen-containing compounds, thus hindering the industrial application of methane conversion technology. Therefore, achieving efficient activation and targeted conversion of methane into high-value-added oxygen-containing compounds has always been a highly challenging research direction in the field of catalytic chemistry, considered the "holy grail" of the field.

[0004] In existing technologies, the technical pathways for converting methane into oxygen-containing compounds are mainly divided into two categories: indirect conversion pathways and direct conversion pathways. Traditional methane conversion processes generally rely on energy-intensive indirect conversion pathways: methane is first converted into syngas (CO + H2) through a reforming reaction, and then oxygen-containing compounds are prepared through subsequent processes such as Fischer-Tropsch synthesis and methanol synthesis under high temperature and pressure. This pathway is complex, energy-intensive, and has high equipment investment costs. Moreover, the overall conversion efficiency is limited by the coupling of multiple reaction steps, making it difficult to meet the industrial demands for low-carbon and high-efficiency processes.

[0005] Compared to indirect conversion pathways, direct methane conversion pathways using oxidants such as N2O, O2, and H2O2 offer significant advantages, including high energy efficiency, simple processes, and relatively mild reaction conditions. Among these, hydrogen peroxide (H2O2), as a mild oxidant, can efficiently generate reactive oxygen species under low-temperature conditions, exhibiting unique advantages in direct methane conversion systems.

[0006] In the system of direct methane-to-acetic acid conversion at low temperatures in the liquid phase, a combination of hydrogen peroxide and iron-modified molecular sieve catalysts can be used to achieve the direct conversion of methane with carbon monoxide and hydrogen peroxide to obtain the product acetic acid. Mononuclear Fe catalysts are a representative class of highly efficient catalysts, capable of converting methane to acetic acid under mild reaction conditions and achieving a certain acetic acid yield. However, in the traditional catalyst preparation process, iron species readily migrate and aggregate on the support surface, forming low-activity iron clusters or nanoparticles. This results in a low proportion of highly active mononuclear iron in the catalyst, limiting the yield improvement of the target product acetic acid in the methane oxidative carbonylation reaction, thus becoming a core obstacle restricting further increases in acetic acid yield.

[0007] Therefore, how to stabilize and maximize the "mononuclear Fe" site through a simple synthetic strategy to improve the yield of the product acetic acid has become an urgent problem to be solved. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to provide a (FeIn) / ZSM-5 catalyst that significantly improves the yield of direct conversion of methane to acetic acid.

[0009] Another technical problem to be solved by the present invention is to provide a method for preparing the (FeIn) / ZSM-5 catalyst.

[0010] The third technical problem to be solved by the present invention is to provide the application of the (FeIn) / ZSM-5 catalyst.

[0011] To address the aforementioned problems, the present invention provides a (FeIn) / ZSM-5 catalyst, characterized in that: the catalyst comprises a ZSM-5 molecular sieve support and an active component supported on the ZSM-5 molecular sieve; the active component comprises Fe species and In species, and the loading of Fe in the catalyst is 0.1~1.0 wt%, and the loading of In is 0.25~1.5 wt%.

[0012] The ZSM-5 molecular sieve contains Brønsted acid.

[0013] The Fe species is one or more of mononuclear Fe, oligomeric Fe, and Fe2O3 nanoparticles; the In species is one or more of mononuclear In, oligomeric In, and In2O3 nanoparticles.

[0014] The catalyst has a total specific surface area of ​​300~400 m². 2 / g, total pore volume is 0.15~0.35 cm³ 3 / g.

[0015] The preparation method of the (FeIn) / ZSM-5 catalyst as described above includes the following steps: S1 is used to prepare a composite solution of iron and indium: Iron source is dissolved in anhydrous ethanol to obtain an iron source solution with a concentration of 0.1~1 g / L; indium source is dissolved in water to obtain an indium source solution with a concentration of 0.25~1.5 g / L; the iron source solution and indium source solution are mixed evenly at a volume ratio of 1:0.8~5 to obtain a composite solution. S2 The composite solution and NH4–ZSM-5 molecular sieve are mixed and vacuum impregnated. After impregnation, rotary evaporation, drying and grinding are performed to obtain (FeIn) / ZSM-5 catalyst precursor. S3 reduces and calcines the (FeIn) / ZSM-5 catalyst precursor to obtain the bimetallic supported catalyst (FeIn) / ZSM-5.

[0016] In step S1, the iron source includes one or more of Fe(NO3)3, Fe2(SO4)3, FeCl3, ferric acetate, and ferric acetylacetonate; the indium source includes one or more of In2(SO4)3, In(NO3)3, InCl3, and indium acetate.

[0017] The conditions for vacuum impregnation in step S2 are as follows: the solid-liquid ratio is 1 g: 8~12 mL, the process is carried out at room temperature with stirring, the stirring speed is 750~850 rpm, the stirring time is 22~26 h; the rotary evaporation temperature is 65~75℃; the drying temperature is 75~85℃, and the time is 10~14 h.

[0018] The conditions for reduction calcination in step S3 are as follows: temperature is 350~550 ℃, heating rate is 2.8~3.2 ℃ / min, time is 2~6 h; the reducing atmosphere is a mixture of hydrogen and nitrogen, and the volume percentage of hydrogen in the mixture is 4.8~5.2%.

[0019] The application of the (FeIn) / ZSM-5 catalyst as described above is characterized in that: the catalyst is used in the catalytic oxidative carbonylation reaction of methane to prepare acetic acid.

[0020] The acetic acid is prepared by the following method: Methane and carbon monoxide with a partial pressure of 1–4 MPa are introduced into a mixed system containing a catalyst and an aqueous solution of hydrogen peroxide with a concentration of 0.1–0.75 mol / L. A catalytic oxidative carbonylation reaction is carried out at 25–75 °C and a total pressure of 3–8 MPa for 0.5–6 h.

[0021] Compared with the prior art, the present invention has the following advantages: 1. This invention adopts a "molecular anchor" strategy, introducing a second metal, indium (In). By utilizing the stronger electronic interaction between In and Al in the molecular sieve framework, and the weaker electronic interaction between In and Fe, a "molecular anchor" effect is formed, anchoring iron (Fe) species to the support surface. This effectively inhibits the migration and aggregation of iron during preparation and reaction, and significantly increases the proportion of highly active mononuclear Fe active sites in the catalyst.

[0022] 2. Because the bimetallic synergistic effect (Fe-In) stabilizes the mononuclear iron active center in this invention, a higher acetic acid yield is achieved in the methane oxidative carbonylation reaction, which is a significant improvement over traditional catalysts.

[0023] 3. Using the catalyst described in this invention, the yield of acetic acid can reach 27.1 mmol g. cat -1 h -1 The selectivity for acetic acid reached 81.2%, which is significantly better than that of single-metal Fe catalysts. Attached Figure Description

[0024] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0025] Figure 1 The nitrogen adsorption-desorption isotherms of the catalysts in Examples 1 and 1-2 of this invention and the NH4–ZSM-5 molecular sieve are shown.

[0026] Figure 2 The PXRD spectra of the catalysts in Example 1 and Comparative Examples 1-2 of this invention and the NH4–ZSM-5 molecular sieve are shown.

[0027] Figure 3 The images show the UV-Vis diffuse reflectance spectra of the catalysts in Example 1 and Comparative Examples 1-2 of this invention.

[0028] Figure 4 The images show the TEM and EDX images of the catalyst in Example 1 of this invention.

[0029] Figure 5 This is a graph showing the ToF-SIMS analysis results of Embodiment 1 of the present invention.

[0030] Figure 6 These are ToF-SIMS images of the catalysts in Example 1 and Comparative Examples 1-2 of the present invention.

[0031] Figure 7 The above are H2-TPR diagrams of the catalysts in Example 1 and Comparative Example 2 of this invention.

[0032] Figure 8 The images show the pyridine infrared spectra of the catalysts in Examples 1 and 1-2 of this invention, as well as the H–ZSM-5 molecular sieve.

[0033] Figure 9 The images show the Raman spectra of the catalysts in Examples 1 and 1-2 of this invention, as well as the NH4–ZSM-5 molecular sieve.

[0034] Figure 10 These are XPS spectra of Al 2p in the catalysts of Example 1, Comparative Examples 1 and 2, and NH4–ZSM-5 molecular sieve of the present invention. Wherein: a is the fine Al 2p spectrum of NH4–ZSM-5 molecular sieve; b is the fine Al 2p spectrum of catalyst of Comparative Example 1; c is the fine Al 2p spectrum of catalyst of Comparative Example 2; and d is the fine Al 2p spectrum of catalyst of Example 1.

[0035] Figure 11 The above are XPS spectra of Fe 2p in the catalysts of Example 1 and Comparative Example 2 of this invention.

[0036] Figure 12 The above are XPS spectra of In 3d in the catalysts of Example 1 and Comparative Example 1 of this invention.

[0037] Figure 13 This is a comparison chart of the catalytic performance of methane oxidative carbonylation of Examples 1, 1-2, and the mixed catalyst of Comparative Examples 1 and 2 of the present invention.

[0038] Figure 14 This is a comparison chart of the catalytic performance of the catalysts in Examples 1-5 of this invention for the oxidative carbonylation of methane.

[0039] Figure 15 This is a comparison chart of the catalytic performance of the catalysts in Examples 1, 6-9 of this invention for the oxidative carbonylation of methane.

[0040] Figure 16 This is a comparison chart showing the catalytic performance of the catalyst in Example 1 of the present invention for the oxidative carbonylation of methane under different partial pressure ratios of methane and carbon monoxide.

[0041] Figure 17 This is a comparison chart showing the catalytic performance of the catalyst in Example 1 of the present invention for the oxidative carbonylation of methane under different total pressures.

[0042] Figure 18 This is a comparison chart showing the catalytic performance of the catalyst in Example 1 of the present invention for the oxidative carbonylation of methane at different reaction temperatures.

[0043] Figure 19 This is a comparison chart showing the catalytic performance of the catalyst in Example 1 of the present invention for the oxidative carbonylation of methane at different reaction times.

[0044] Figure 20 This is a comparison chart showing the catalytic performance of the catalyst in Example 1 of the present invention for the oxidative carbonylation of methane under different hydrogen peroxide solution concentrations. Detailed Implementation

[0045] A (FeIn) / ZSM-5 catalyst comprising a ZSM-5 molecular sieve support and an active component supported on the ZSM-5 molecular sieve.

[0046] The active components are Fe and In species, and the loading of Fe in the catalyst is 0.1~1.0 wt%, preferably 0.4~0.6 wt%, and can also be 0.2~0.8 wt%, specifically 0.1 wt%, 0.25 wt%, 0.5 wt%, 0.75 wt%, or 1.0 wt%. The loading of In is 0.25~1.5 wt%, preferably 0.5~0.8 wt%, and can also be 0.3~1.2 wt%, specifically 0.25 wt%, 0.5 wt%, 0.75 wt%, 1.0 wt%, or 1.5 wt%.

[0047] Among them, ZSM-5 molecular sieve contains Brønsted acid, and iron and indium can replace the Brønsted acid sites in the molecular sieve to form a catalyst with good catalytic performance.

[0048] The Fe species are one or more of mononuclear Fe, oligomeric Fe, and Fe2O3 nanoparticles; the In species are one or more of mononuclear In, oligomeric In, and In2O3 nanoparticles.

[0049] The total specific surface area of ​​the catalyst is 300~400 m² 2 / g, which can be specifically 320 m 2 / g、350 m 2 / g, 374.15 m 2 / g or 390 m 2 / g; total pore volume is 0.15~0.35 cm³. 3 / g, which can be specifically 0.18 cm 3 / g, 0.22 cm 3 / g, 0.25 cm 3 / g or 0.30 cm 3 / g.

[0050] A method for preparing a (FeIn) / ZSM-5 catalyst includes the following steps: S1 is used to prepare a composite solution of iron and indium: Iron source solution is dissolved in anhydrous ethanol to obtain iron source solution with concentration of 0.1~1 g / L; indium source solution is dissolved in water to obtain indium source solution with concentration of 0.25~1.5 g / L; iron source solution and indium source solution are mixed evenly at a volume ratio of 1:0.8~5 to obtain composite solution.

[0051] The iron source includes one or more of Fe(NO3)3, Fe2(SO4)3, FeCl3, ferric acetate, and ferric acetylacetonate; the indium source includes one or more of In2(SO4)3, In(NO3)3, InCl3, and indium acetate.

[0052] S2 involves vacuum impregnation of a composite solution with NH4–ZSM-5 molecular sieve at a solid-liquid ratio of 1 g: 8–12 mL, carried out at room temperature with stirring at 750–850 rpm for 22–26 h. After impregnation, the mixture is first rotary evaporated at 65–75 °C, then dried at 75–85 °C for 10–14 h to remove the solvent. The resulting (FeIn) / ZSM-5 catalyst precursor is obtained after grinding.

[0053] For vacuum impregnation, the preferred solid-liquid ratio is 1 g: 10 mL, the stirring speed is 800 rpm, and the stirring time is 24 h. The preferred rotary evaporation temperature is 70 °C, and the evaporation time is not particularly limited, as long as most of the water in the system is removed. Drying is preferably performed at 80 °C for 12 h.

[0054] The present invention may further include, before vacuum impregnation, subjecting the ZSM-5 molecular sieve to vacuum treatment. The vacuum degree of the vacuum treatment can be 0.05~0.10 MPa, specifically 0.08 MPa; the vacuum treatment time can be 0.3~2.0 h, specifically 1 h. The vacuum treatment of the present invention can remove the adsorbed gas from the pores of the ZSM-5 molecular sieve, which is beneficial for the subsequent thorough impregnation of the ZSM-5 molecular sieve with the composite aqueous solution.

[0055] The average particle size after grinding is <65 mesh. The grinding process facilitates thorough reduction and calcination in this invention.

[0056] S3 reduces and calcines the (FeIn) / ZSM-5 catalyst precursor at a temperature of 350~550 ℃, a heating rate of 2.8~3.2 ℃ / min, and a time of 2~6 h; the reducing atmosphere is a mixture of hydrogen and nitrogen, and the volume percentage of hydrogen in the mixture is 4.8~5.2%, thus obtaining the bimetallic supported catalyst (FeIn) / ZSM-5.

[0057] The reduction calcination is preferably carried out at 450 °C, with a heating rate of 3 °C / min and a time of 3 h; the volume percentage of hydrogen in the mixed gas is 5%.

[0058] The present invention may further include, before reduction calcination, replacing the reducing atmosphere in the apparatus for reduction calcination. During the replacement process, the flow rate of the reducing atmosphere can be 40-100 mL / min, specifically 80 mL / min; the product of the replacement time and the flow rate of the reducing atmosphere is more than twice the volume of the apparatus for reduction calcination. The present invention removes air from the apparatus through reducing atmosphere replacement.

[0059] The present invention may further include, after reduction and calcination, cooling the product to room temperature. There are no special requirements for the cooling method, as long as it achieves the desired temperature.

[0060] An application of a (FeIn) / ZSM-5 catalyst in the catalytic oxidative carbonylation of methane to prepare acetic acid is described. Acetic acid is specifically prepared by introducing methane and carbon monoxide at a partial pressure of 1–4 MPa into a mixed system containing the catalyst and an aqueous hydrogen peroxide solution at a concentration of 0.1–0.75 mol / L. The catalytic oxidative carbonylation reaction is carried out at 25–75 °C and a total pressure of 3–8 MPa for 0.5–6 h.

[0061] Wherein: the concentration of hydrogen peroxide solution can be specifically 0.1 mol / L, 0.25 mol / L, 0.5 mol / L, or 0.75 mol / L; the total pressure of the catalytic oxidative carbonylation reaction can be specifically 3 MPa, 4 MPa, 5 MPa, 6 MPa, 7 MPa, or 8 MPa; the partial pressure of methane can be specifically 1 MPa, 2 MPa, 2.5 MPa, 3 MPa, or 4 MPa; the partial pressure of carbon monoxide can be specifically 1 MPa, 2 MPa, 2.5 MPa, 3 MPa, or 4 MPa; the temperature of the catalytic oxidative carbonylation can be specifically 25 ℃, 50 ℃, or 75 ℃; and the time of catalytic oxidation can be specifically 0.5 h, 1 h, 2 h, 3 h, or 6 h.

[0062] To further illustrate the present invention, the technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0063] In the examples, the subscript values ​​of the catalyst abbreviation represent the theoretical mass percentage content of the supported element, such as (Fe). 0.5 In 0.75 ) / ZSM-5 indicates simultaneous (one-step impregnation) loading of Fe and In, with theoretical loadings of Fe and In (mass percentages of the bimetallic supported catalyst) of 0.5 wt% and 0.75 wt%, respectively.

[0064] Example 1 Weigh 0.032 g of ferric acetylacetonate and dissolve it in 1.5 mL of anhydrous ethanol. Weigh 0.373 g of In(NO3)3•4H2O and dissolve it in 100 mL of deionized water to obtain a 0.01 mol / L In(NO3)3 solution. Then, use a pipette to transfer 6.6 mL of the 0.01 mol / L In(NO3)3 solution and mix it with the ethanol solution of ferric acetylacetonate to obtain a composite solution of iron and indium.

[0065] Weigh 1 g of NH4–ZSM-5 molecular sieve and place it in a 100 mL pear-shaped flask. After adding a magnetic stir bar, seal the flask with a rubber stopper and perform vacuum treatment (vacuum degree of 0.08 MPa) for 1 h. Use a syringe to transfer the iron and indium composite solution into the vacuum-treated pear-shaped flask. Wash the container containing the iron and indium composite solution and the syringe 2-3 times with 1 mL of deionized water each time and transfer them to the pear-shaped flask. Then continue vacuum treatment for 10 minutes. Vacuum impregnation was completed by stirring at 800 rpm for 24 h at room temperature (25 ℃). The impregnated system was then rotary evaporated at 70 ℃ to remove most of the water, and then dried in an 80 ℃ oven for 12 h. The dried product was ground to an average particle size <65 mesh and transferred to a corundum boat. The boat was placed in a 4 L tube furnace, sealed, and purged with a 80 mL / min H2 / N2 (5% hydrogen by volume) mixture for 2 h to replace the air in the furnace and prevent a dangerous reaction between air and hydrogen under heating conditions. After replacement, the H2 / N2 (5%) mixture flow rate was adjusted to 40 mL / min, and the temperature was increased to 450 ℃ at a rate of 3 ℃ / min. The mixture was then calcined at 450 ℃ for 3 h and naturally cooled to room temperature (25 ℃) to obtain the bimetallic supported catalyst (Fe). 0.5 In 0.75 ) / ZSM-5.

[0066] Example 2 A bimetallic supported catalyst was prepared according to the method of Example 1, except that the loading amount of Fe was adjusted. The mass of ferric acetylacetonate used in the catalyst preparation was 0.0064 g. The resulting bimetallic supported catalyst is denoted as (Fe 0.1 In 0.75 ) / ZSM-5.

[0067] Example 3 A bimetallic supported catalyst was prepared according to the method of Example 1, except that the loading amount of Fe was adjusted. The mass of ferric acetylacetonate used in the catalyst preparation was 0.016 g. The resulting bimetallic supported catalyst is denoted as (Fe 0.25 In 0.75 ) / ZSM-5.

[0068] Example 4 A bimetallic supported catalyst was prepared according to the method of Example 1, except that the loading of Fe was adjusted. The mass of ferric acetylacetonate used in the catalyst preparation was 0.048 g. The resulting bimetallic supported catalyst is denoted as (Fe 0.75 In 0.75 ) / ZSM-5.

[0069] Example 5 A bimetallic supported catalyst was prepared according to the method of Example 1, except that the loading amount of Fe was adjusted. The mass of 0.064 g of acetylacetone iron used in the catalyst preparation was used. The resulting bimetallic supported catalyst is denoted as (Fe 1.0 In 0.75 ) / ZSM-5.

[0070] Example 6 The bimetallic supported catalyst was prepared according to the method in Example 1, except that the loading amount of In was adjusted, and 2.2 mL of 0.01 mol / L In(NO3)3 solution was used for catalyst preparation. The resulting bimetallic supported catalyst is denoted as (Fe 0.5 In 0.25 ) / ZSM-5.

[0071] Example 7 The bimetallic supported catalyst was prepared according to the method in Example 1, except that the loading of In was adjusted and 4.4 mL of 0.01 mol / L In(NO3)3 solution was used for catalyst preparation. The resulting bimetallic supported catalyst is denoted as (Fe 0.5 In 0.5 ) / ZSM-5.

[0072] Example 8 The bimetallic supported catalyst was prepared according to the method of Example 1, except that the loading of In was adjusted. 8.8 mL of 0.01 mol / L In(NO3)3 solution was used for catalyst preparation. The resulting bimetallic supported catalyst is denoted as (Fe... 0.5 In 1.0 ) / ZSM-5.

[0073] Example 9 A bimetallic supported catalyst was prepared according to the method in Example 1, except that the loading of In was adjusted. The amount of 0.01 mol / L In(NO3)3 solution used in the catalyst preparation was 13.2 mL. The resulting bimetallic supported catalyst is denoted as (Fe... 0.5 In 1.5 ) / ZSM-5.

[0074] Comparative Example 1 Weigh 1 g of NH4–ZSM-5 molecular sieve and place it in a 100 mL pear-shaped flask. After adding a magnetic stir bar, seal the flask with a rubber stopper and perform vacuum treatment (vacuum degree of 0.08 MPa) for 1 h. Weigh 0.373 g of In(NO3)3•4H2O and dissolve it in 100 mL of deionized water to obtain a 0.01 mol / L In(NO3)3 solution. Use a pipette to transfer 6.6 mL of the 0.01 mol / L In(NO3)3 solution into a glass bottle. Use a syringe to transfer the In(NO3)3 solution from the glass bottle to the vacuum-treated pear-shaped flask. Wash the glass bottle containing the In(NO3)3 solution and the syringe 2-3 times with 1 mL of deionized water each time and transfer them to the pear-shaped flask. Then continue vacuum treatment for 10 minutes. Vacuum impregnation was completed by stirring at 800 rpm for 24 h at room temperature (25 ℃). The impregnated system was then rotary evaporated at 70 ℃ to remove most of the water, and then dried in an 80 ℃ oven for 12 h. The dried product was ground to an average particle size <65 mesh and transferred to a corundum boat. The boat was placed in a 4 L tube furnace, sealed, and purged with a 5% H2 / N2 mixture at a flow rate of 80 mL / min for 2 h to replace the air in the furnace and prevent a dangerous reaction between air and hydrogen under heating conditions. After replacement, the H2 / N2 (5%) mixture flow rate was adjusted to 40 mL / min, and the temperature was increased to 450 ℃ at a rate of 3 ℃ / min. The mixture was then calcined at 450 ℃ for 3 h and naturally cooled to room temperature (25 ℃) to obtain the catalyst In. 0.75 / ZSM-5.

[0075] Comparative Example 2 Weigh 1 g of NH4–ZSM-5 molecular sieve and place it in a 100 mL pear-shaped flask. After adding a magnetic stir bar, seal the flask with a rubber stopper and perform vacuum treatment (vacuum degree of 0.08 MPa) for 1 h. Weigh 0.032 g of ferric acetylacetonate and dissolve it in a glass bottle containing 5 mL of anhydrous ethanol. Use a syringe to transfer the ferric acetylacetonate solution from the glass bottle to the pear-shaped flask after vacuum treatment. Wash the glass bottle containing the ferric acetylacetonate solution and the syringe 2-3 times with 1 mL of deionized water each time and transfer them to the pear-shaped flask. Then continue vacuum treatment for 10 minutes. Vacuum impregnation was completed by stirring at 800 rpm for 24 h at room temperature (25 ℃). The impregnated system was then rotary evaporated at 70 ℃ to remove most of the water, and then dried in an 80 ℃ oven for 12 h. The dried product was ground to an average particle size <65 mesh and transferred to a corundum boat. The boat was placed in a 4 L tube furnace, sealed, and purged with a 5% H2 / N2 mixture at a flow rate of 80 mL / min for 2 h to replace the air in the furnace and prevent a dangerous reaction between air and hydrogen under heating conditions. After replacement, the H2 / N2 (5%) mixture flow rate was adjusted to 40 mL / min, and the temperature was increased to 450 ℃ at a rate of 3 ℃ / min. The furnace was then calcined at 450 ℃ for 3 h and naturally cooled to room temperature (25 ℃) to obtain the catalyst Fe. 0.5 / ZSM-5.

[0076] The specific surface area, pore volume, and metal element content of the catalysts prepared in Example 1 and Comparative Examples 1-2 and NH4–ZSM-5 molecular sieves were tested, and the results are listed in Table 1.

[0077] Table 1. Physicochemical properties of the catalysts prepared in Examples 1 and 1-2 and the NH4–ZSM-5 molecular sieves. a S BET = BET specific surface area; b Calculations are performed using the t-plot method; c Total pore volume, P / P The value when 0 = 0.99; d The elemental content in the catalyst sample determined by ICP-OES.

[0078] Figure 1 The nitrogen adsorption-desorption isotherms of the catalysts prepared in Examples 1 and 1-2, and the NH4–ZSM-5 molecular sieve. Figure 1As shown in Table 1, the specific surface area of ​​the metal-loaded catalyst did not change significantly compared to the NH4–ZSM-5 molecular sieve support, indicating that the introduction of metal did not disrupt the pore structure of the molecular sieve. Quantitative analysis of Fe and In elements in the catalyst was performed using inductively coupled plasma atomic emission spectrometry (ICP-AES). The results showed that NH4–ZSM-5 without any metal loading contained trace amounts of Fe (0.05 wt%), which is an impurity introduced during the synthesis process. 0.75 The actual loading of metallic In in the ZSM-5 catalyst is 0.81 wt%, Fe 0.5 The actual loading of metallic Fe in the ZSM-5 catalyst is 0.56 wt%, (Fe 0.5 In 0.75 The actual loading of Fe in the ZSM-5 catalyst was 0.54 wt%, and the actual loading of In was 0.82 wt%, indicating that Fe and In elements were successfully loaded.

[0079] Powder X-ray diffraction (PXRD) was performed on the catalysts prepared in Example 1 and Comparative Examples 1-2, and the PXRD spectra were obtained as follows: Figure 2 As shown. By Figure 2 It can be seen that only the characteristic peaks of the MFI topology of the NH4–ZSM-5 molecular sieve itself were observed in the catalyst, and no signals were generated from any phase containing Fe or In elements, indicating that the Fe and In elements are well dispersed or the crystal size formed is lower than the instrument detection limit.

[0080] The catalysts prepared in Example 1 and Comparative Examples 1-2 were subjected to UV-Vis diffuse reflectance spectroscopy (DR UV-Vis) in the range of 200-800 nm to analyze the coordination environment and aggregation state of the metal species. The resulting UV-Vis diffuse reflectance spectra are shown below. Figure 3 As shown. By Figure 3 It can be seen that the absorption peak appearing at 277 nm belongs to the isolated six-coordinate octahedral Fe. 3+ The broad absorption band of 300–500 nm originates from oligomeric Fe. x O y The clusters, with absorption wavelengths greater than 500 nm, are attributed to the signal from large-sized Fe₂O₃ nanoparticles. (Compared to Fe...) 0.5 / ZSM-5、In 0.75 / ZSM-5 and bimetallic (Fe) 0.5 In 0.75 In the ZSM-5 sample, the introduction of indium was found to suppress oligomeric Fe. x O y The formation of Fe2O3 clusters and nanoparticles significantly increases the proportion of isolated mononuclear iron species.

[0081] For (Fe)0.5 In 0.75 Transmission electron microscopy (TEM) analysis was performed on the ZSM-5 catalyst, and the results are as follows: Figure 4 As shown, Fe and In are well dispersed, and a large number of uniformly dispersed, spatially adjacent mononuclear FeIn species are visible.

[0082] For (Fe) 0.5 In 0.75 The ZSM-5 catalyst was analyzed by time-of-flight secondary ion mass spectrometry (ToF-SIMS) to investigate the atomic bonding mode and the form of metal presence in the catalyst. The results are as follows: Figure 5 As shown in the figure, * indicates that one Fe atom in the fragment is replaced by two Si atoms (1Fe m / z = 55.935; 2Si m / z = 55.965). FeO - and FeO2 - The fragments indicate the presence of mononuclear Fe species in the catalyst, while Fe2O3... - The presence of Fe indicates that some Fe species exist in the catalyst as Fe. x O y It exists in the form of clusters. InO − The presence of fragments indicates the presence of mononuclear In on the catalyst, and In3O3 was observed. - The fragments indicate that In agglomeration occurred on the catalyst. In addition, SiOAlFe was also detected. - SiOAlIn - The fragmentation indicates that monodisperse Fe and In species are anchored to the molecular sieve framework and interact with it. Notably, (Fe... 0.5 In 0.75 FeInO was also detected in the ZSM-5 catalyst. - FeInO2 - The fragmentation indicates that some Fe and In species are spatially close to each other on the support. ToF-SIMS imaging analysis more intuitively demonstrates the changes in metal dispersion, as shown in the results... Figure 6 As shown, Fe2O3 - Signal strength relative to Si − After normalization, it was found that compared to Fe 0.5 / ZSM-5, (Fe 0.5 In 0.75 Fe2O3 in ZSM-5 catalyst - The signal strength decreased significantly, indicating that the addition of In can improve the dispersion of Fe. In3O3 - Signal strength relative to Si - After normalization, it was found that compared to In 0.75 / ZSM-5, (Fe 0.5 In 0.75 In3O3 in ZSM-5 catalyst - The signal strength is significantly weakened, indicating that (Fe) 0.5 In 0.75 The In dispersion in the ZSM-5 catalyst is higher.

[0083] The catalysts prepared in Example 1 and Comparative Example 2 were characterized by H2-TPR to analyze their reduction properties. The results are as follows: Figure 7 As shown, the peak at a reduction temperature of 400 °C belongs to the reduction of mononuclear Fe species, while the peak at a reduction temperature of 443 °C belongs to oligomeric Fe species. x O y Reduction of clustered species. Fe 0.5 / ZSM-5 and (Fe 0.5 In 0.75 Both Fe and ZSM-5 showed reduction peaks at 400℃, indicating that the electronic interaction between Fe and In is weak; while (Fe) 0.5 In 0.75 The reduction peak intensity of (Fe) / ZSM-5 decreases significantly at higher temperatures, indicating that (Fe) 0.5 In 0.75 The dispersion of metallic Fe in the ZSM-5 catalyst is better.

[0084] The catalysts prepared in Example 1 and Comparative Examples 1-2, as well as H−ZSM-5, were characterized by pyridine infrared spectroscopy to analyze the acidic sites of the catalysts. The results are shown in Table 2. Figure 8 As shown, 1544 cm -1 and 1453 cm -1 The peaks at 1489 cm⁻¹ are attributed to Brønsted acid centers (BAS) and Lewis acid centers (LAS), respectively. -1 The signal at that location corresponds to the overlapping peaks of Brønsted and Lewis acids. Quantitative data show that, relative to H−ZSM-5 (BAS: 196 μmol / g), metal modification significantly reduced the amount of BAS, and Fe... 0.5 The most significant decrease in BAS in ZSM-5 was 72 μmol / g, indicating that Fe mainly settled at the Brønsted acid sites of the molecular sieve. Furthermore, compared to H−ZSM-5 (LAS: 38 μmol / g), metal modification significantly increased the amount of LAS, suggesting that the introduction of metal created new Lewis acid sites in the ZSM-5 molecular sieve.

[0085] Table 2. Concentration of acidic sites of the catalysts prepared in Examples 1 and Comparative Examples 1-2 and H–ZSM-5 molecular sieves. a The concentrations of Brønsted acid and Lewis acid were calculated using the formula. , ε B = 1.67 cm / μmol, ε L = 2.22 cm / μmol.

[0086] Raman spectroscopy was performed on the catalysts prepared in Example 1 and Comparative Examples 1-2, as well as the NH4–ZSM-5 molecular sieve, to analyze the metal placement in the catalysts. The results are as follows: Figure 9 As shown, 292cm -1 378 cm -1 and 465 cm -1 The peaks at 807 cm⁻¹ correspond to the six-membered, five-membered, and four-membered rings of the NH₄–ZSM-5 molecular sieve, respectively. -1 The peaks at that location are attributed to the –Si–OH group of the NH4–ZSM-5 molecular sieve. The intensities of these peaks significantly decreased after the introduction of the metal, indicating that the metal falls within the six-membered, five-membered, four-membered rings and the –Si–OH group of the molecular sieve.

[0087] X-ray photoelectron spectroscopy (XPS) was performed on the catalysts prepared in Example 1 and Comparative Examples 1-2, as well as the NH4–ZSM-5 molecular sieve, to analyze their electronic structures. First, the Al 2p fine spectrum was analyzed, and the results are as follows: Figure 10 As shown, 74.3 eV is attributed to the Al–O–Si signal in NH4–ZSM-5 molecular sieve, In 0.75 The signal shift for Al–O–Si in the / ZSM-5 catalyst reached 74.8 eV, and for Fe... 0.5 / ZSM-5 and (Fe 0.5 In 0.75 The Al–O–Si signals of the ) / ZSM-5 catalyst are all at 74.6 eV, indicating that In 0.75 The larger Al–O–Si signal shift in the / ZSM-5 catalyst indicates a stronger interaction between In and Al in the NH4–ZSM-5 molecular sieve framework. Then, the fine spectrum of Fe 2p was analyzed, and the results are as follows... Figure 11 As shown, 711.2 eV belongs to Fe 3+ The signal indicates that Fe 0.5 / ZSM-5 and (Fe 0.5 In 0.75 In the ZSM-5 catalyst, Fe exists in the +3 oxidation state; additionally, Fe... 0.5 / ZSM-5 and (Fe 0.5 In 0.75 Fe ) / ZSM-5 catalyst3+ The signal showed no significant change, indicating a weak electronic interaction between Fe and In. Furthermore, analysis of the fine spectrum of In 3d yielded the following results: Figure 12 As shown, In 0.75 / ZSM-5 and (Fe 0.5 In 0.75 The ) / ZSM-5 catalysts exhibited In at 446.4 eV and 446.1 eV, respectively. 3+ Signal, Explanation In 0.75 / ZSM-5 and (Fe 0.5 In 0.75 In the ZSM-5 catalyst, In exists in the +3 oxidation state, (Fe) 0.5 In 0.75 ) / ZSM-5 compared to In 0.75 / ZSM-5, In 3+ The signal shifted by 0.3 eV, which is due to the strong electronic interaction between In and Al in the molecular sieve framework, consistent with the conclusions of the Al 2p fine spectrum.

[0088] Application Example 1 30 mg of the catalysts prepared in each example and comparative example were weighed and placed in a high-pressure reactor with a glass liner. A magnetic stir bar and 10 mL of 0.5 mol / L H2O2 solution were added, and the reactor was tightened and sealed with a wrench. Methane gas was introduced into the reactor to 2.0 MPa, and then purged to replace the air in the reactor. This purging operation was repeated twice. Methane (2.5 MPa) and carbon monoxide (2.5 MPa) were introduced at the required pressure, and the stirring was turned on (1000 rpm). The temperature was raised to the target reaction temperature (50 °C), and the timer was started after the temperature was reached to carry out the catalytic oxidative carbonylation reaction for 0.5 h. After the reaction was completed, the reactor was removed from the heating jacket and placed in an ice-water bath to cool it for 30 minutes. After cooling, the gas after the reaction was collected using a gas bag and quantitatively analyzed using a gas chromatograph. The chromatographic column used was a TDX-01 packed column. The solid-liquid mixture after the reaction was collected and centrifuged. 0.4 mL of the supernatant was accurately transferred to an NMR tube using a pipette, and 0.1 mL of D₂O (containing 0.02 wt% DSS) was added. The mixture was then analyzed using a liquid NMR spectrometer. 1 Quantitative analysis was performed using H-spectrum.

[0089] Figure 13 Example 1 ((Fe) 0.5 In 0.75 ) / ZSM-5), Comparative Example 1 (In 0.75 / ZSM-5), Comparative Example 2 (Fe 0.5 / ZSM-5) and the mixed catalyst of Comparative Example 1 and Comparative Example 2 (In 0.75 / ZSM-5 + Fe 0.5 A comparison of the yields and selectivity of CH3OH, HCOOH, CH3COOH, and CH3OOH obtained by the / ZSM-5 catalytic reaction; wherein the total mass of the mixed catalyst is 60 mg, including 30 mg In 0.75 / ZSM-5 and 30 mg Fe 0.5 / ZSM-5. By Figure 13 It can be seen that In 0.75 Following the reaction catalyzed by ZSM-5, four liquid products were detected: CH3OH, HCOOH, CH3COOH, and CH3OOH, with yields of 0.08, 0.13, 0.96, and 0.34 mmol g, respectively. cat -1 h -1 It can be seen that In 0.75 / ZSM-5 has very low catalytic performance. Using Fe 0.5 The ZSM-5 catalyst, under the same reaction conditions, was used for the oxidative carbonylation of methane, and the liquid products were still CH3OH, HCOOH, CH3COOH, and CH3OOH, with yields of 1.02, 6.18, 9.30, and 0.21 mmol g, respectively. cat -1 h -1 The selectivity of CH3COOH was 55.7%. (Fe 0.5 In 0.75 Using ZSM-5 as a catalyst, under the same reaction conditions, the yields of CH3OH, HCOOH, CH3COOH, and CH3OOH were 1.74, 9.13, 15.43, and 0.16 mmol g, respectively. cat -1 h -1 Of which, the selectivity for CH3COOH was 58.3%. (Fe 0.5 In 0.75 The excellent catalytic performance of the ) / ZSM-5 catalyst indicates that the addition of In can significantly improve the yield of acetic acid. 0.75 / ZSM-5 + Fe 0.5 The / ZSM-5 composite catalyst, when used under the same reaction conditions, still yielded a lower acetic acid yield than (Fe) 0.5 In 0.75 The result of ) / ZSM-5 indicates that even if Fe and In species coexist in the reaction system, the yield of acetic acid cannot be significantly improved because the proportion of mononuclear Fe in the catalyst cannot be increased.

[0090] The yields of the products and the selectivity of acetic acid for the catalytic carbonylation of methane were obtained by using bimetallic supported catalysts with different Fe loadings (Examples 1-5). Table 3 shows the results.

[0091] Table 3 Catalytic performance of catalysts in Examples 1-5 for the catalytic reaction of methane oxidative carbonylation Figure 14 This is a comparison of the catalytic performance of the catalysts prepared in Examples 1-5 for the catalytic oxidative carbonylation reaction. (See Table 3 and...) Figure 14 It can be seen that as the Fe loading increases from 0.1 wt% to 1.0 wt%, the acetic acid yield exhibits a volcano-like trend, reaching its maximum at a Fe loading of 0.5 wt%. The formic acid yield, however, gradually increases with increasing Fe loading. This is because the increased Fe loading leads to a higher proportion of oligomeric Fe clusters and Fe₂O₃ nanoparticles, resulting in an increased yield of the deeply oxidized product, formic acid.

[0092] The catalytic oxidative carbonylation reaction was carried out using bimetallic supported catalysts with different In loadings (Example 1, Examples 6-9), and the yields of the products and the selectivity for acetic acid are listed in Table 4.

[0093] Table 4 shows the catalytic performance of the catalysts in Examples 6-9 for the catalytic oxidative carbonylation of methane. Figure 15 A comparison of the catalytic performance of the catalysts prepared in Examples 1 and 6-9 for the catalytic oxidative carbonylation reaction. (See Table 4 and...) Figure 15 It can be seen that as the In loading increases from 0.25 wt% to 1.5 wt%, the yields of formic acid and acetic acid exhibit a volcanic-like trend, (Fe 0.5 In 0.75 The highest acetic acid yield was achieved with the () / ZSM-5 catalyst. Further increasing the In loading to 1.5 wt% resulted in a gradual decrease in the yields of formic acid and acetic acid, possibly due to excess In covering some Fe active sites, leading to the yield reduction. Therefore, the optimal catalyst loading ratio is (Fe) / ZSM-5. 0.5 In 0.75 ) / ZSM-5.

[0094] Application Example 2 The (Fe) prepared in Example 1 was selected. 0.5 In 0.75The methane catalytic oxidative carbonylation reaction was carried out using ZSM-5 as a catalyst according to the method of Application Example 1. The difference was that different partial pressure ratios of the reactant gases were used in the reaction process. Under the premise of keeping the total pressure at 5.0 MPa, the partial pressure ratios of methane and carbon monoxide were adjusted to 4 / 1, 3 / 2, 2.5 / 2.5, 2 / 3, and 1 / 4, respectively. The product yields and acetic acid selectivity results are listed in Table 5.

[0095] Table 5. Catalytic performance of the catalyst in Example 1 for the oxidative carbonylation of methane under different partial pressure ratios of methane and carbon monoxide. Figure 16 This is a comparison of the catalytic performance of the catalyst in Example 1 for the catalytic oxidative carbonylation reaction under different methane and carbon monoxide partial pressure ratios. (See Table 5 and...) Figure 16 It can be seen that the yield of acetic acid exhibits a volcanic pattern, with the highest yield achieved at a methane / carbon monoxide partial pressure ratio of 3 / 2. As the methane / carbon monoxide partial pressure ratio decreases from 4 / 1 to 1 / 4, the yields of HCOOH, CH3OH, and CH3OOH decrease accordingly, which may be related to the decrease in methane partial pressure.

[0096] Application Example 3 The (Fe) prepared in Example 1 was selected. 0.5 In 0.75 The methane catalytic oxidative carbonylation reaction was carried out using ZSM-5 as a catalyst according to the method of Application Example 1, except that different total reaction pressures were used during the reaction. The partial pressure ratio of methane / carbon monoxide was fixed at 1 / 1, and the total reaction pressures were adjusted to 3 MPa, 4 MPa, 5 MPa, 6 MPa, 7 MPa and 8 MPa. The yield of the product and the selectivity of acetic acid are listed in Table 6.

[0097] Table 6. Catalytic performance of the catalyst in Example 1 for the oxidative carbonylation of methane under different total pressures. Figure 17 This is a comparison of the catalytic performance of the catalyst in Example 1 under different total reaction pressures for the catalytic oxidative carbonylation reaction. (See Table 6 and...) Figure 17 It can be seen that the yield and selectivity of acetic acid increase with the increase of total reaction pressure.

[0098] Application Example 4 The (Fe) prepared in Example 1 was selected. 0.5 In 0.75The catalytic oxidative carbonylation of methane was carried out using ZSM-5 as a catalyst according to the method of Application Example 1, except that different reaction temperatures were used during the reaction process. The reaction temperatures were adjusted to 25 °C, 50 °C, and 75 °C, and the yield of the product and the selectivity of acetic acid are listed in Table 7.

[0099] Table 7. Catalytic performance of the catalyst in Example 1 for the oxidative carbonylation of methane at different reaction temperatures. Figure 18 This is a comparison of the catalytic performance of the catalyst in Example 1 for the catalytic oxidative carbonylation reaction at different reaction temperatures. (See Table 7 and...) Figure 18 It can be seen that the yield of acetic acid gradually increases with the increase of reaction temperature, and the temperature at which acetic acid is generated is as low as 25 °C; the yield of formic acid increases sharply with the increase of reaction temperature, which is due to excessive oxidation that occurs with the increase of temperature.

[0100] Application Example 5 The (Fe) prepared in Example 1 was selected. 0.5 In 0.75 The catalytic oxidative carbonylation of methane was carried out using ZSM-5 as a catalyst according to the method of Application Example 1, except that different reaction times were used during the reaction process. The reaction times were adjusted to 0.5 h, 1 h, 2 h, 3 h and 6 h, and the yield of the product and the selectivity of acetic acid are listed in Table 8.

[0101] Table 8. Catalytic performance of the catalyst in Example 1 for the oxidative carbonylation of methane at different reaction temperatures. Figure 19 This is a comparison of the catalytic performance of the catalyst in Example 1 for the catalytic oxidative carbonylation reaction at different reaction times. (See Table 8 and...) Figure 19 It can be seen that the yields of formic acid and acetic acid gradually increase with the extension of reaction time.

[0102] Application Example 6 The (Fe) prepared in Example 1 was selected. 0.5 In 0.75 The catalytic oxidative carbonylation of methane was carried out using ZSM-5 as a catalyst according to the method in Application Example 1, except that different concentrations of hydrogen peroxide solution were used during the reaction. The concentrations of hydrogen peroxide solution were adjusted to 0.1 mol / L, 0.25 mol / L, 0.5 mol / L, and 0.75 mol / L, and the yield of the product and the selectivity of acetic acid are listed in Table 9.

[0103] Table 9. Catalytic performance of the catalyst in Example 1 for the oxidative carbonylation of methane at different reaction temperatures. Figure 20 This is a comparison of the catalytic performance of the catalyst in Example 1 for the catalytic oxidative carbonylation reaction under different hydrogen peroxide solution concentrations. (See Table 9 and...) Figure 20 It can be seen that the yields of formic acid and acetic acid increase with the increase of hydrogen peroxide solution concentration. However, when the hydrogen peroxide solution concentration increases to 0.75 mol / L, the yield of acetic acid decreases. This may be because the concentration of •OH in the solution is too high at this point, which promotes deep oxidation of the reaction.

[0104] Application Example 7 The (Fe) prepared in Example 1 was selected. 0.5 In 0.75 The catalytic oxidative carbonylation of methane was carried out using ZSM-5 as a catalyst according to the method of Application Example 1, except that some reaction conditions were adjusted to obtain higher acetic acid yield and selectivity. The yield and selectivity of the products are listed in Table 10.

[0105] Table 10. Yields and selectivity of the catalyst in Example 1 for catalytic oxidation at different reaction temperatures. As shown in Table 10, under the reaction conditions of 4.0 MPa CH4, 4.0 MPa CO, 20 mL 0.5 M H2O2, 50 ℃, and 0.5 h, the yield of acetic acid was 27.1 mmol g. cat -1 h -1 The selectivity was 62.2%. Under the reaction conditions of 4.0 MPa CH4, 4.0 MPa CO, 20 mL 0.1 M H2O2, 50 ℃, and 0.5 h, the yield of acetic acid was 9.2 mmol g. cat -1 h -1 The selectivity rate was 81.2%.

Claims

1. A (FeIn) / ZSM-5 catalyst, characterized in that: The catalyst comprises a ZSM-5 molecular sieve support and an active component supported on the ZSM-5 molecular sieve; the active component is an Fe species and an In species, and the loading of Fe in the catalyst is 0.1~1.0 wt%, and the loading of In is 0.25~1.5 wt%.

2. The (FeIn) / ZSM-5 catalyst as described in claim 1, characterized in that: The ZSM-5 molecular sieve contains Brønsted acid.

3. The (FeIn) / ZSM-5 catalyst as described in claim 1, characterized in that: The Fe species is one or more of mononuclear Fe, oligomeric Fe, and Fe2O3 nanoparticles; the In species is one or more of mononuclear In, oligomeric In, and In2O3 nanoparticles.

4. The (FeIn) / ZSM-5 catalyst as described in claim 1, characterized in that: The catalyst has a total specific surface area of ​​300~400 m². 2 / g, total pore volume is 0.15~0.35 cm³ 3 / g.

5. A method for preparing a (FeIn) / ZSM-5 catalyst according to any one of claims 1 to 4, comprising the following steps: S1 is used to prepare a composite solution of iron and indium: Iron source solution is obtained by dissolving iron source in anhydrous ethanol, with a concentration of 0.1~1 g / L; indium source solution is obtained by dissolving in water, with a concentration of 0.25~1.5 g / L. The composite solution is obtained by mixing the iron source solution and the indium source solution at a volume ratio of 1:0.8~5. S2 The composite solution and NH4–ZSM-5 molecular sieve are mixed and vacuum impregnated. After impregnation, rotary evaporation, drying and grinding are performed to obtain (FeIn) / ZSM-5 catalyst precursor. S3 reduces and calcines the (FeIn) / ZSM-5 catalyst precursor to obtain the bimetallic supported catalyst (FeIn) / ZSM-5.

6. The method for preparing a (FeIn) / ZSM-5 catalyst as described in claim 5, characterized in that: In step S1, the iron source includes one or more of Fe(NO3)3, Fe2(SO4)3, FeCl3, ferric acetate, and ferric acetylacetonate; the indium source includes one or more of In2(SO4)3, In(NO3)3, InCl3, and indium acetate.

7. The method for preparing a (FeIn) / ZSM-5 catalyst as described in claim 5, characterized in that: The conditions for vacuum impregnation in step S2 are as follows: the solid-liquid ratio is 1 g: 8~12 mL, the process is carried out at room temperature with stirring, the stirring speed is 750~850 rpm, the stirring time is 22~26 h; the rotary evaporation temperature is 65~75 ℃; the drying temperature is 75~85 ℃, and the time is 10~14 h.

8. The method for preparing a (FeIn) / ZSM-5 catalyst as described in claim 5, characterized in that: The conditions for reduction calcination in step S3 are as follows: temperature is 350~550 ℃, heating rate is 2.8~3.2 ℃ / min, time is 2~6 h; the reducing atmosphere is a mixture of hydrogen and nitrogen, and the volume percentage of hydrogen in the mixture is 4.8~5.2%.

9. The application of the (FeIn) / ZSM-5 catalyst according to any one of claims 1 to 4, characterized in that: This catalyst is used in the catalytic oxidative carbonylation of methane to produce acetic acid.

10. The application of the (FeIn) / ZSM-5 catalyst as described in claim 9, characterized in that: The acetic acid is prepared by the following method: Methane and carbon monoxide with a partial pressure of 1–4 MPa are introduced into a mixed system containing a catalyst and an aqueous solution of hydrogen peroxide with a concentration of 0.1–0.75 mol / L. A catalytic oxidative carbonylation reaction is carried out at 25–75 °C and a total pressure of 3–8 MPa for 0.5–6 h.

Images