A bimetallic supported composite catalyst, a preparation method and application thereof

Abstract

The application discloses a bimetallic supported composite catalyst and a preparation method thereof. The bimetallic supported composite catalyst comprises a core-shell molecular sieve, a modified metal component and an active metal component; the modified metal component is copper oxide; the active metal component is iron oxide species; the core-shell molecular sieve takes ZSM-23 molecular sieve as a core and takes mesoporous silica as a shell; and the ratio of the particle size of the core of the core-shell molecular sieve to the thickness of the shell layer is 6-18. The bimetallic supported composite catalyst provided by the application is applied to a reaction of low-temperature oxidation of methane to prepare methanol, and can realize direct oxidation of methane to prepare methanol under a low-temperature condition below 80 DEG C, and has outstanding catalytic activity and selectivity and good stability.

Description

Technical Field

[0001] This invention belongs to the technical field of direct methane conversion and utilization, specifically relating to a bimetallic supported composite catalyst and its preparation method, as well as its application in the low-temperature direct oxidation of methane to methanol. Background Technology

[0002] Methane, a major component of natural gas, is not only one of the cleanest fossil fuels due to its abundant reserves and relatively low price, but also an important C1 feedstock for the production of bulk chemicals. In recent years, the proportion of natural gas production in fossil energy (coal, oil, and natural gas) has generally shown an upward trend. With the development and progress of extraction technologies for natural energy sources such as combustible ice, shale gas, and coalbed methane, the utilization of abundant and inexpensive methane is no longer limited to its use as fuel. Meanwhile, as the world's second largest greenhouse gas, although its content is less than that of carbon dioxide, its greenhouse effect is more than 20 times that of carbon dioxide, thus exacerbating global warming. Therefore, the rational use of natural gas resources plays a crucial role in both the economy and the environment. However, methane's unique symmetrical structure makes it one of the most stable small energy molecules in nature, requiring relatively stringent reaction conditions to activate the methane molecule. Therefore, researching how to selectively activate and directionally convert methane is one of the major scientific challenges currently facing the field, among which the oxidation of methane to methanol is considered a significant research area.

[0003] Traditionally, methanol is synthesized from methane indirectly using a process where methane is first reformed into syngas (CO + H2), and then methanol is synthesized at temperatures exceeding 600°C. This process incurs high operating and maintenance costs for the equipment, and its utilization rate of methane and selectivity for methanol are both low. Currently, the conversion of methane into methanol under mild conditions is considered the most ideal route. Methanol, as a basic chemical raw material, can be easily converted into important chemical raw materials and fuels such as olefins and aromatics. Furthermore, methanol is liquid at room temperature and pressure, making storage and transportation relatively convenient. If this reaction can be scaled up for industrial production, it will greatly help humanity reduce its dependence on petroleum. The direct oxidation of methane to methanol has been studied for decades, including homogeneous gas-phase oxidation (Applied Catalysis A:General, 2001, 205:51-59; Applied Catalysis A:General, 2002, 224:201-207; Catalysis Today, 2009, 142:2-8.), gas-solid multiphase oxidation (Chemical Engineering and Processing, 2009, 48:1333-1340; Journal of Catalysis, 2003, 217:457-467; Applied Catalysis A:General, 2011, 400:122-130.), and liquid-phase catalytic oxidation (Journal of the American Chemical Society, 2006, 128:16028-16029; Applied Catalysis Today, 2009, 142:2-8.), The methods include photocatalytic oxidation (Catalysis Today, 2003, 84: 9-15; Applied Catalysis A:General, 2003, 243: 165-174, Journal of the American Chemical Society, 2011, 133: 17257–17261.) and enzyme-catalyzed oxidation (Bioresource Technology, 2011, 102: 7349-7353.). Each of these methods has its advantages, but the high reaction temperatures, harsh reaction conditions, and the use of expensive precious metal catalysts limit their industrialization. Therefore, developing catalysts capable of selectively oxidizing methane is crucial. Summary of the Invention

[0004] To address the above-mentioned technical problems, the present invention aims to provide a bimetallic supported composite catalyst and its preparation method. The bimetallic supported composite catalyst provided by the present invention, when applied to the low-temperature oxidation of methane to methanol, enables the direct oxidation of methane to methanol at temperatures below 80°C, and exhibits outstanding catalytic activity, selectivity, and good stability.

[0005] To achieve the above objectives, the first aspect of the present invention provides a bimetallic supported composite catalyst, comprising a core-shell molecular sieve, a modified metal component, and an active metal component;

[0006] The modified metal component is copper oxide; the active metal component is an iron oxide species.

[0007] Among them, the core-shell molecular sieve uses ZSM-23 molecular sieve as the core and mesoporous silica as the shell; the ratio of the core particle size to the shell thickness of the core-shell molecular sieve is 6 to 18.

[0008] Furthermore, the catalyst contains 0.01% to 5% copper by mass and 0.01% to 0.2% iron by mass.

[0009] Furthermore, the catalyst contains 89.5 wt% to 99.5% core-shell molecular sieve by mass.

[0010] Furthermore, the total Brønsted acid content of pyridine in the core-shell molecular sieve is 0.10–0.37 mmol / g, preferably 0.13–0.35 mmol / g, more preferably 0.15–0.33 mmol / g; and the total Brønsted acid content of 2,6-dimethylpyridine in the infrared is 0.07–0.35 mmol / g, preferably 0.09–0.33 mmol / g, more preferably 0.12–0.30 mmol / g.

[0011] Further, the ratio of the total 2,6-dimethylpyridine infrared Brønsted acid content to the total pyridine infrared Brønsted acid content of the core-shell molecular sieve is (65-99):100, preferably (70-97):100, and even more preferably (74-95):100.

[0012] Furthermore, in the 2,6-dimethylpyridine infrared acid of the core-shell molecular sieve, the amount of weak Brønsted acid with a desorption temperature <250°C is 0.09–0.31 mmol / g, preferably 0.11–0.29 mmol / g, and more preferably 0.13–0.28 mmol / g.

[0013] Furthermore, in the 2,6-dimethylpyridine infrared acid of the core-shell molecular sieve, the ratio of the amount of weak Brønsted acid with a desorption temperature <250°C to the total amount of Brønsted acid in the 2,6-dimethylpyridine infrared sieve is (64-95):100, preferably (67-93):100, and even more preferably (70-92):100.

[0014] Furthermore, the SiO2 / Al2O3 (molar ratio) of the core layer in the core-shell molecular sieve is 85–550, preferably 90–400.

[0015] A second aspect of the present invention provides a method for preparing the above-mentioned bimetallic supported composite catalyst, comprising the following steps:

[0016] An iron source is impregnated onto a core-shell molecular sieve, dried, and calcined to obtain a molecular sieve catalyst precursor; then, a copper-soluble salt is impregnated into the molecular sieve catalyst precursor, dried, and calcined to obtain the bimetallic supported composite catalyst.

[0017] Furthermore, in the preparation method of the bimetallic supported composite catalyst, the iron source is selected from at least one of ferric nitrate and ferric chloride.

[0018] Furthermore, in the preparation method of the bimetallic supported composite catalyst, the amount of iron source is such that the mass fraction of iron in the final catalyst is 0.05wt% to 0.2wt%.

[0019] Furthermore, in the preparation method of the bimetallic supported composite catalyst, the copper soluble salt is selected from at least one of copper nitrate and copper chloride.

[0020] Furthermore, in the preparation method of the bimetallic supported composite catalyst, the mass ratio of iron source, core-shell molecular sieve and copper soluble salt is 1:(150-400):(5-50), preferably 1:(170-350):(5-35).

[0021] Furthermore, in the preparation method of the bimetallic supported composite catalyst, the copper-soluble salt is dissolved in water to prepare a modified copper salt solution. The amount of water added is selected according to the requirement of equal volume impregnation.

[0022] Furthermore, in the preparation method of the bimetallic supported composite catalyst, the impregnation method employs equal-volume impregnation. After impregnation, the catalyst is allowed to stand for 12–24 hours, followed by drying at a temperature of 80–140°C for 6–24 hours.

[0023] Furthermore, in the preparation method of the bimetallic supported composite catalyst, the calcination adopts programmed temperature calcination with a heating rate of 2-10℃ / min, a calcination temperature of 450-650℃, and a calcination time of 4-10h.

[0024] Furthermore, the preparation method of the core-shell molecular sieve includes the following steps:

[0025] (1) A mixture of silicon source, template agent a and water is subjected to a crystallization reaction, and solid material A is separated from the reacted material;

[0026] (2) The solid material A is mixed with fatty amine and inorganic base and subjected to a first low-temperature reaction, then ZSM-23 seed crystals are added and subjected to a second low-temperature reaction to obtain a mixed material;

[0027] (3) The template agent b and the aluminum source are mixed with the mixture, and then crystallization, filtration, washing, drying and calcination are carried out in sequence to obtain ZSM-23 molecular sieve;

[0028] (4) The ZSM-23 molecular sieve is subjected to ion exchange to obtain HZSM-23 molecular sieve;

[0029] (5) The HZSM-23 molecular sieve, structure guiding agent, and expansion agent are mixed, and then an organic solvent and silicon source are added. The solid material is separated and then filtered, washed, dried and calcined to obtain a core-shell molecular sieve.

[0030] Further, in step (1), the silicon source is one or more of silica, silica sol, water glass, fumed silica and tetraethyl orthosilicate, preferably silica and / or fumed silica.

[0031] Further, in step (1), the template agent a is at least one of hexamethylenediamine, ethanol and n-hexamethylenediamine, preferably hexamethylenediamine and / or ethanol.

[0032] Further, in step (1), the molar ratio of the template agent a to the silicon source (calculated as SiO2) is 0.1 to 1.0, preferably 0.15 to 0.8; the molar ratio of water to the silicon source (calculated as SiO2) is 20 to 80, preferably 30 to 70.

[0033] Further, in step (1), the operating conditions of the crystallization reaction are as follows: the crystallization temperature is 120-220℃, the crystallization time is 8-48h, preferably the crystallization temperature is 140-200℃, and the crystallization time is 12-30h.

[0034] Furthermore, in step (1), the crystallization reaction is preferably carried out in a reactor with a polytetrafluoroethylene liner.

[0035] Furthermore, in step (1), the solid-liquid separation can be achieved by any of the existing technologies in the art, such as gravity sedimentation, filtration separation and centrifugal separation, preferably centrifugal separation.

[0036] Furthermore, in step (1), the process of separating solid material A from the reacted material is called solid-liquid separation. The solid-liquid separation method can be selected from, but is not limited to, gravity sedimentation, filtration separation, and centrifugal separation, with centrifugal separation being preferred.

[0037] Further, in step (2), the fatty amine is a C12-C18 fatty amine, preferably one or more of oleylamine (9-octadeceneamine), octadecylamine, and dodecylamine, preferably oleylamine.

[0038] Further, in step (2), the liquid-to-solid ratio of the fatty amine to the solid material A is 0.3 to 3 mL / g, preferably 0.5 to 2.0 mL / g.

[0039] Further, in step (2), the inorganic alkali is used in the form of an alkaline solution, the concentration of which is 0.003 to 0.015 mol / L, preferably 0.005 to 0.010 mol / L; the liquid-to-solid ratio of the alkaline solution to the solid material A is 2 to 20 mL / g, preferably 5 to 15 mL / g; and the inorganic alkali is at least one of sodium hydroxide, potassium hydroxide, and ammonia water.

[0040] Further, in step (2), the temperature of the first low-temperature reaction is 20-40°C and the time is 3-15h; preferably, the temperature is 25-30°C and the time is 6-12h; the first low-temperature reaction is preferably carried out under stirring conditions, with a stirring rate of 100-300rpm.

[0041] Further, in step (2), the ZSM-23 seed crystals are added in the form of a seed solution. The specific operation process of the seed solution is as follows: the ZSM-23 seed crystals are uniformly dispersed in water (preferably deionized water) to form a seed solution; wherein, the liquid-solid ratio of water to ZSM-23 seed crystals is 5 to 70 mL / g, preferably 10 to 60 mL / g.

[0042] Further, in step (2), based on the weight of the solid material A, the amount of ZSM-23 seed crystals added is 0.1 to 8.0 wt%, preferably 0.5 to 5.0 wt%.

[0043] Further, in step (2), the temperature of the secondary low-temperature reaction is 60-120°C and the time is 6-30 hours; preferably, the temperature is 80-100°C and the time is 12-24 hours; the secondary low-temperature reaction is preferably carried out under stirring conditions, with a stirring rate of 100-300 rpm.

[0044] Further, in step (3), the template agent b is one or more of pyrrolidine, isopropylamine and N,N-dimethylformamide, preferably pyrrolidine; the aluminum source is one or more of aluminum sulfate, aluminum isopropoxide, sodium aluminate and aluminum hydroxide, preferably aluminum sulfate.

[0045] Further, in step (3), the molar ratio of template agent b to the solid material A (calculated as SiO2) is 0.01 to 0.1, preferably 0.02 to 0.08; the molar ratio of aluminum source (calculated as Al2O3) to the solid material A (calculated as SiO2) is 0.002 to 0.015, preferably 0.005 to 0.01.

[0046] Further, in step (3), the crystallization temperature is 180-220℃ and the crystallization time is 24-72h; the drying temperature is 80-120℃ and the drying time is 6-12h; the calcination temperature is 540-560℃ and the calcination time is 3-8h.

[0047] Further, in step (4), the ion exchange treatment can be carried out using conventional methods in the prior art. Specifically, in this invention, the ZSM-23 molecular sieve is placed in an ammonium salt solution with a concentration of 1-2 mol / L, wherein the liquid-to-solid ratio is 10-20, and stirred continuously in a water bath at 70-90°C for 2-4 hours. The above process can be repeated multiple times until the Na2O content in the ZSM-23 molecular sieve after ammonium exchange is less than 0.1 wt%. Then, washing, drying, and calcination are performed, wherein the drying temperature is 80-120°C and the time is 6-12 hours; the calcination temperature is 500-550°C and the time is 3-8 hours. The ammonium salt solution is selected from one or more of ammonium chloride solution or ammonium nitrate solution, preferably ammonium chloride.

[0048] Further, in step (5), the structure directing agent is one or more of hexadecyltrimethylammonium bromide, hexadecyltrimethylammonium chloride, and octadecyltrimethylammonium chloride, preferably hexadecyltrimethylammonium bromide; the swelling agent is one or more of glycerol, triethanolamine, and butanediol, preferably triethanolamine; the organic solvent is one or more of cyclopentane and cyclohexane, preferably cyclopentane; and the silicon source is one or more of tetraethyl orthosilicate, silica sol, and sodium silicate, preferably silica sol.

[0049] Further, in step (5), the mass ratio of HZSM-23 molecular sieve to structure directing agent is 0.001–0.08, preferably 0.005–0.05; the volume ratio of expanding agent, silicon source, and organic solvent is 1:(0.5–8):(20–100), preferably 1:

[0050] (1~5):(30~80); the mass ratio of silicon source to HZSM-23 molecular sieve is 1:(1~10), preferably 1:(3~8).

[0051] Further, in step (5), the stirring temperature is 30-80℃, the stirring speed is 100-300rpm, the drying temperature is 80-120℃, and the drying time is 6-12h; the calcination temperature is 540-560℃, and the calcination time is 3-8h.

[0052] The third aspect of this invention provides the application of the above-mentioned bimetallic supported composite catalyst in the low-temperature oxidation of methane to methanol reaction.

[0053] Furthermore, the low-temperature oxidation reaction of methane to methanol uses pure methane as the reaction gas and low-concentration hydrogen peroxide as the oxidant, wherein the concentration of hydrogen peroxide in the hydrogen peroxide is 0.5–1 mol / L.

[0054] Furthermore, the volume ratio of methane to hydrogen peroxide is 1:(1 to 1.5).

[0055] Furthermore, the reaction temperature is 30–80°C, preferably 30–50°C, the reaction time is 15–60 min, the reaction pressure is 1–3 MPa, and the catalyst dosage is 2.5–12.5 g per liter of hydrogen peroxide.

[0056] The present invention has the following advantages:

[0057] (1) The bimetallic supported composite catalyst of the present invention can directly produce methanol by catalyzing the oxidation reaction of methane at low temperature. The reaction temperature can be lower than 80°C, while other methods, including high-temperature reforming or gas-solid multiphase oxidation in a fixed bed, require a reaction temperature greater than 200°C to activate methane. In comparison, the present invention can greatly reduce energy consumption.

[0058] (2) The bimetallic supported composite catalyst provided by the present invention uses copper as the modifying component and iron as the active component. Both are non-precious metals and have low cost. The two work together synergistically to significantly improve the catalytic activity.

[0059] (3) The core-shell molecular sieve provided by the present invention has a gradient divergence of surface pores and a large specific surface area, making it particularly suitable as a catalyst support component for the direct production of methanol from methane oxidation reaction. It exhibits excellent activity, selectivity and stability in the direct production of methanol from methane oxidation reaction.

[0060] (4) When the catalyst of the present invention is used to catalyze the methane oxidation reaction, the reaction system is simple (including methane, hydrogen peroxide solution and catalyst), and a low concentration of hydrogen peroxide solution is used as the oxidant, which is safer than using oxygen or air directly.

[0061] (5) The bimetallic supported composite catalytic process provided by this invention has a very high reaction rate, wherein the methanol production turnover frequency (TOF) can be greater than 640 mol. CH3OH / mol Fe / h -1 Furthermore, the catalyst exhibits good stability, and the methanol production remains unchanged after multiple cycles. Attached Figure Description

[0062] Figure 1 The XRD pattern of the core-shell molecular sieve prepared in Example 1;

[0063] Figure 2 STEM image of the catalyst prepared in Example 2;

[0064] Figure 3 This is a stability test of the catalyst in Example 2. Detailed Implementation

[0065] The catalyst of the present invention, its preparation method, and its effects are further illustrated below through examples. These examples are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operating procedures; however, the scope of protection of the present invention is not limited to the following examples.

[0066] Unless otherwise specified, the experimental methods used in the following examples are conventional methods in the art. Unless otherwise specified, the experimental materials used in the following examples were purchased from conventional biochemical reagent stores.

[0067] In this invention, the infrared acidity of pyridine is determined by pyridine adsorption infrared spectroscopy; the infrared acidity of 2,6-dimethylpyridine is determined by 2,6-dimethylpyridine adsorption infrared spectroscopy.

[0068] In this invention, "total Brønsted acid content in pyridine infrared spectroscopy" is used to represent the total Brønsted acid content in the molecular sieve, including Brønsted acid on the surface, at the pore openings, and within the pores. It is determined by pyridine adsorption infrared spectroscopy. The specific process is as follows: the molecular sieve sample is prepared into a self-supporting wafer (5-6 mg / cm³). 2 The sample was placed in an in-situ cell and treated under vacuum at 400℃ for 4 hours, then cooled to 50℃, and spectra were collected. After adsorbing pyridine for 10 minutes, the sample was heated to 150℃ for desorption for 1 hour, cooled to room temperature, and spectra were collected. The total Brønsted acid content of pyridine was calculated. The Brønsted acid content was calculated according to the Lambert-Beer law, using a 1540 cm⁻¹ spectral depth. -1 The acidity of Brønsted acid is calculated using the area of ​​the absorption peak. The acidity is calculated according to the Lambert-Beer law, using a peak area of ​​1540 cm⁻¹. -1 The acidity of Brønsted acid is calculated from the area of ​​the absorption peak.

[0069] In this invention, the acid content of different intensities at the pore openings and outer surface of molecular sieves is determined by 2,6-dimethylpyridine adsorption infrared spectroscopy. The specific process is as follows: the molecular sieve sample is prepared into a self-supporting wafer (5-6 mg / cm²). 2 The sample was placed in an in-situ cell and treated under vacuum at 400℃ for 4 hours, then cooled to 50℃, and the spectrum was collected. After adsorbing 2,6-dimethylpyridine for 10 minutes, the sample was heated to 150℃ for desorption for 1 hour, cooled to room temperature, and the spectrum was collected again. At this point, the total infrared acid content of 2,6-dimethylpyridine could be calculated. After further desorption at 250℃ for 1 hour, the sample was cooled to room temperature, and the spectrum was collected again to calculate the acid content of weak acids with a desorption temperature <250℃ for 2,6-dimethylpyridine. The acid content of Brønsted acids was calculated according to the Lambert-Beer law, using a 1630 cm⁻¹ spectral density. -1 1650cm -1 The amount of Brønsted acid is calculated by measuring the area of ​​the absorption peak.

[0070] In this invention, "the amount of Brønsted acid with a desorption temperature < 250°C" is used to represent the amount of weak Brønsted acid. "The amount of Brønsted acid with a desorption temperature < 250°C in 2,6-dimethylpyridine infrared Brønsted acid" is used to represent the amount of weak Brønsted acid distributed in the pores and surface of ZSM-23 molecular sieve.

[0071] In this invention, the SiO2 / Al2O3 (molar ratio) in the molecular sieve core layer was obtained by X-ray fluorescence spectroscopy (XRF) analysis. A ZSX100e X-ray fluorescence spectrometer was used, with the spectral line being Kα, the crystal being LiF1, the target material being Rh, the detector being SC scintillation, the timing being 20s, and the optical path atmosphere being vacuum.

[0072] In this invention, the analysis of metallic iron species was performed using an aberration-corrected scanning transmission electron microscope (AC-STEM) with a JEOL JEM ARM200F electron microscope. A trace amount of powder sample was ultrasonically dispersed in anhydrous ethanol, and a few drops of suspension were added to the microgrid supporting the carbon film. After the sample dried, its microstructure was observed under a transmission electron microscope.

[0073] Example 1: Preparation of Core-Shell Molecular Sieves

[0074] 4.68 g of hexamethylenediamine was dissolved in 54 g of deionized water, and then 6 g of fumed silica was added. After stirring at room temperature (25°C) for 1 h, the mixture was transferred to a 100 mL reactor lined with polytetrafluoroethylene (PTFE). The mixture was crystallized at 150°C for 24 h, then quenched and centrifuged. 10 mL of oleylamine was added to the resulting solid, and the mixture was thoroughly mixed in a shaker. The mixture was stirred at room temperature (25°C) for 0.5 h at a stirring rate of 200 rpm. 42 mL of 0.008 mol / L NaOH solution was added to the mixture, and the mixture was stirred at 25°C for 6 h at a stirring rate of 200 rpm to obtain mixture A. 0.18 g of ZSM-23 seed crystals were added to deionized water, and 10 mL of ZSM-23 seed solution was added to mixture A. The mixture was stirred at 80°C for 16 h at a stirring rate of 300 rpm to obtain mixture B.

[0075] Add 0.67g Al2(SO4)3·18H2O and 0.40g pyrrolidine to 20mL of deionized water to obtain a clear solution C;

[0076] Solution C was added to mixture B and mixed thoroughly. The final mixture was then transferred to a 150 mL reactor lined with polytetrafluoroethylene and crystallized at 180 °C for 48 h. After crystallization, the mixture was filtered, washed, dried at 100 °C for 12 h, and then calcined at 550 °C for 4 h to obtain the product ZSM-23 molecular sieve.

[0077] Ion exchange was performed on ZSM-23 molecular sieve: 4g of ZSM-23 molecular sieve was weighed and added to 60mL of 1.5mol / L ammonium chloride solution. The temperature was raised to 80℃ for ion exchange. After 3 hours, the solution was filtered, washed, and dried at 100℃ for 6 hours. This process was repeated three times. Finally, the solution was calcined at 500℃ for 4 hours to obtain HZSM-23 molecular sieve.

[0078] Weigh 0.2g of the above HZSM-23 molecular sieve and add it to 150ml of deionized water. Then add 15g of hexadecyltrimethylammonium bromide and 1ml of triethanolamine. Stir well at 50℃, then add 50ml of cyclopentane and continue stirring for 2h. Add 2ml of silica sol and continue stirring for 24h. Centrifuge and wash and filter the separated solid material. Finally, dry at 110℃ for 6h and calcine at 550℃ for 4h to obtain the core-shell molecular sieve, labeled as ZSM-23-hk. Analysis using pyridine adsorption infrared spectroscopy and 2,6-dimethylpyridine adsorption infrared spectroscopy revealed that the total Brønsted acid content of pyridine in the core-shell molecular sieve was 0.181 mmol / g, and the total Brønsted acid content of 2,6-dimethylpyridine was 0.159 mmol / g. The ratio of the total Brønsted acid content of 2,6-dimethylpyridine to the total Brønsted acid content of pyridine was 87.8:100. Among the Brønsted acid content of 2,6-dimethylpyridine in the core-shell molecular sieve, the amount of weak Brønsted acid below 250℃ was 0.145 mmol / g, and the ratio of the amount of weak Brønsted acid below 250℃ to the total Brønsted acid content of 2,6-dimethylpyridine was 91.2:100. The SiO2 / Al2O3 molar ratio in the ZSM-23 core layer was 96. The ratio of the core particle size to the shell thickness of the obtained core-shell molecular sieve was 6.4. The XRD pattern of the prepared core-shell molecular sieve is shown in [Figure number missing]. Figure 1 It has the structure of ZSM-23 molecular sieve.

[0079] Example 2: Preparation of bimetallic supported composite catalyst FeCu / ZSM-23-hk

[0080] Weigh 5.8 mg of ferric chloride solid and dissolve it in 5.1 ml of water according to the water absorption capacity of 2 g of core-shell molecular sieve. Sonicate for 10 min. Then weigh 2 g of the core-shell molecular sieve prepared in Example 1 and mix the above solution and molecular sieve using an equal-volume impregnation method. Stir until homogeneous and let stand overnight. Next, place the sample in an oven at 110 °C for 12 h. After drying, calcine the sample in a muffle furnace at a heating rate of 5 °C / min, a calcination temperature of 550 °C, and a calcination time of 4 h. The resulting sample is labeled Fe / ZSM-23-hk.

[0081] 144.2 mg of copper nitrate solid was weighed at room temperature and dissolved in water according to an equal volume impregnation amount. The solution was then sonicated for 10 min at a frequency of 25 kHz. The solution was then mixed with the Fe / ZSM-5-hk sample using an equal volume impregnation method, stirred thoroughly, and allowed to stand overnight. The sample was then placed in an oven at 110 °C for 8 h. Subsequently, the dried precursor was calcined in a muffle furnace at a heating rate of 5 °C / min, a calcination temperature of 550 °C, and a calcination time of 4 h. The resulting sample was labeled FeCu / ZSM-23-hk. The specific composition is shown in Table 1.

[0082] Example 3: Preparation of the bimetallic supported composite catalyst FeCu / ZSM-23-hk

[0083] 4.68 g of hexamethylenediamine was dissolved in 54 g of deionized water, and then 6 g of fumed silica was added. After stirring at room temperature (25°C) for 1 h, the mixture was transferred to a 100 mL reactor lined with polytetrafluoroethylene (PTFE). The mixture was crystallized at 150°C for 24 h, then quenched and centrifuged. 10 mL of oleylamine was added to the resulting solid, and the mixture was thoroughly mixed in a shaker. The mixture was stirred at room temperature (25°C) for 0.5 h at a stirring rate of 200 rpm. 42 mL of 0.008 mol / L NaOH solution was added to the mixture, and the mixture was stirred at 25°C for 6 h at a stirring rate of 200 rpm to obtain mixture A. 0.18 g of ZSM-23 seed crystals were added to deionized water, and 10 mL of ZSM-23 seed solution was added to mixture A. The mixture was stirred at 80°C for 16 h at a stirring rate of 300 rpm to obtain mixture B.

[0084] Add 0.67g Al2(SO4)3·18H2O and 0.40g pyrrolidine to 20mL of deionized water to obtain a clear solution C;

[0085] Solution C was added to mixture B and mixed thoroughly. The final mixture was then transferred to a 150 mL reactor lined with polytetrafluoroethylene and crystallized at 180 °C for 48 h. After crystallization, the mixture was filtered, washed, dried at 100 °C for 12 h, and then calcined at 550 °C for 4 h to obtain the product ZSM-23 molecular sieve.

[0086] Ion exchange was performed on ZSM-23 molecular sieve: 4g of ZSM-23 molecular sieve was weighed and added to 60mL of 1.5mol / L ammonium chloride solution. The temperature was raised to 80℃ for ion exchange. After 3 hours, the solution was filtered, washed, and dried at 100℃ for 6 hours. This process was repeated three times. Finally, the solution was calcined at 500℃ for 4 hours to obtain HZSM-23 molecular sieve.

[0087] Weigh 0.2g of the above HZSM-23 molecular sieve and add it to 150ml of deionized water. Then add 15g of octadecyltrimethylammonium chloride and 1ml of triethanolamine. Stir well at 50℃, then add 50ml of cyclopentane and continue stirring for 2h. Add 2ml of silica sol and continue stirring for 24h. Centrifuge and wash and filter the separated solid material. Finally, dry at 110℃ for 6h and calcine at 550℃ for 4h to obtain the core-shell molecular sieve, labeled as ZSM-23-hk. Analysis using pyridine adsorption infrared spectroscopy and 2,6-dimethylpyridine adsorption infrared spectroscopy revealed that the total Brønsted acid content of pyridine in the core-shell molecular sieve was 0.180 mmol / g, and the total Brønsted acid content of 2,6-dimethylpyridine was 0.157 mmol / g. The ratio of the total Brønsted acid content of 2,6-dimethylpyridine to the total Brønsted acid content of pyridine was 87.2:100. Among the Brønsted acid content of 2,6-dimethylpyridine in the core-shell molecular sieve, the amount of weak Brønsted acid below 250℃ was 0.142 mmol / g, and the ratio of the weak Brønsted acid content below 250℃ to the total Brønsted acid content of 2,6-dimethylpyridine was 90.4:100. The SiO2 / Al2O3 molar ratio in the ZSM-23 core layer was 95. The XRD pattern of the prepared core-shell molecular sieve was similar to... Figure 1 Similarly, it is a ZSM-23 molecular sieve. The ratio of the core particle size to the shell thickness of the obtained core-shell molecular sieve is 8.5.

[0088] The preparation of the FeCu / ZSM-23-hk catalyst was the same as in Example 2, except that the core-shell molecular sieve prepared in Example 3 was used, and the amount of ferric chloride solid weighed was 11.6 mg. The specific composition is shown in Table 1.

[0089] Example 4: Preparation of the bimetallic supported composite catalyst FeCu / ZSM-23-hk

[0090] 4.68 g of hexamethylenediamine was dissolved in 54 g of deionized water, and then 6 g of fumed silica was added. After stirring at room temperature (25°C) for 1 h, the mixture was transferred to a 100 mL reactor lined with polytetrafluoroethylene (PTFE). The mixture was crystallized at 150°C for 24 h, then quenched and centrifuged. 10 mL of oleylamine was added to the resulting solid, and the mixture was thoroughly mixed in a shaker. The mixture was stirred at room temperature (25°C) for 0.5 h at a stirring rate of 200 rpm. 42 mL of 0.008 mol / L NaOH solution was added to the mixture, and the mixture was stirred at 25°C for 6 h at a stirring rate of 200 rpm to obtain mixture A. 0.18 g of ZSM-23 seed crystals were added to deionized water, and 10 mL of ZSM-23 seed solution was added to mixture A. The mixture was stirred at 80°C for 16 h at a stirring rate of 300 rpm to obtain mixture B.

[0091] Add 0.67g Al2(SO4)3·18H2O and 0.40g pyrrolidine to 20mL of deionized water to obtain a clear solution C;

[0092] Solution C was added to mixture B and mixed thoroughly. The final mixture was then transferred to a 150 mL reactor lined with polytetrafluoroethylene and crystallized at 180 °C for 48 h. After crystallization, the mixture was filtered, washed, dried at 100 °C for 12 h, and then calcined at 550 °C for 4 h to obtain the product ZSM-23 molecular sieve.

[0093] Ion exchange was performed on ZSM-23 molecular sieve: 4g of ZSM-23 molecular sieve was weighed and added to 60mL of 1.5mol / L ammonium chloride solution. The temperature was raised to 80℃ for ion exchange. After 3 hours, the solution was filtered, washed, and dried at 100℃ for 6 hours. This process was repeated three times. Finally, the solution was calcined at 500℃ for 4 hours to obtain HZSM-23 molecular sieve.

[0094] Weigh 0.2g of the above HZSM-23 molecular sieve and add it to 150ml of deionized water. Then add 15g of hexadecyltrimethylammonium bromide and 1ml of glycerol. Stir well at 50℃, then add 50ml of cyclopentane and continue stirring for 2h. Add 2ml of silica sol and continue stirring for 24h. Centrifuge and wash and filter the separated solid material. Finally, dry at 110℃ for 6h and calcine at 550℃ for 4h to obtain the core-shell molecular sieve, labeled as ZSM-23-hk. Analysis using pyridine adsorption infrared spectroscopy and 2,6-dimethylpyridine adsorption infrared spectroscopy revealed that the total Brønsted acid content of pyridine in the core-shell molecular sieve was 0.179 mmol / g, and the total Brønsted acid content of 2,6-dimethylpyridine was 0.163 mmol / g. The ratio of the total Brønsted acid content of 2,6-dimethylpyridine to the total Brønsted acid content of pyridine was 91.1:100. Among the Brønsted acid content of 2,6-dimethylpyridine in the core-shell molecular sieve, the amount of weak Brønsted acid below 250℃ was 0.141 mmol / g, and the ratio of the weak Brønsted acid content below 250℃ to the total Brønsted acid content of 2,6-dimethylpyridine was 86.5:100. The SiO2 / Al2O3 molar ratio in the ZSM-23 core layer was 94. The XRD pattern of the prepared core-shell molecular sieve was similar to... Figure 1 Similarly, it is a ZSM-23 molecular sieve. The ratio of the core particle size to the shell thickness of the obtained core-shell molecular sieve is 7.4.

[0095] The preparation of the FeCu / ZSM-23-hk catalyst was the same as in Example 2, except that the core-shell molecular sieve prepared in Example 4 was used. The specific composition is shown in Table 1.

[0096] Example 5: Preparation of the bimetallic supported composite catalyst FeCu / ZSM-23-hk

[0097] 4.68 g of hexamethylenediamine was dissolved in 54 g of deionized water, and then 6 g of fumed silica was added. After stirring at room temperature (25°C) for 1 h, the mixture was transferred to a 100 mL reactor lined with polytetrafluoroethylene (PTFE). The mixture was crystallized at 150°C for 24 h, then quenched and centrifuged. 10 mL of oleylamine was added to the resulting solid, and the mixture was thoroughly mixed in a shaker. The mixture was stirred at room temperature (25°C) for 0.5 h at a stirring rate of 200 rpm. 42 mL of 0.008 mol / L NaOH solution was added to the mixture, and the mixture was stirred at 25°C for 6 h at a stirring rate of 200 rpm to obtain mixture A. 0.18 g of ZSM-23 seed crystals were added to deionized water, and 10 mL of ZSM-23 seed solution was added to mixture A. The mixture was stirred at 80°C for 16 h at a stirring rate of 300 rpm to obtain mixture B.

[0098] Add 0.67g Al2(SO4)3·18H2O and 0.40g pyrrolidine to 20mL of deionized water to obtain a clear solution C;

[0099] Solution C was added to mixture B and mixed thoroughly. The final mixture was then transferred to a 150 mL reactor lined with polytetrafluoroethylene and crystallized at 180 °C for 48 h. After crystallization, the mixture was filtered, washed, dried at 100 °C for 12 h, and then calcined at 550 °C for 4 h to obtain the product ZSM-23 molecular sieve.

[0100] Ion exchange was performed on ZSM-23 molecular sieve: 4g of ZSM-23 molecular sieve was weighed and added to 60mL of 1.5mol / L ammonium chloride solution. The temperature was raised to 80℃ for ion exchange. After 3 hours, the solution was filtered, washed, and dried at 100℃ for 6 hours. This process was repeated three times. Finally, the solution was calcined at 500℃ for 4 hours to obtain HZSM-23 molecular sieve.

[0101] Weigh 0.2g of the above HZSM-23 molecular sieve and add it to 150ml of deionized water. Then add 15g of hexadecyltrimethylammonium bromide and 1ml of triethanolamine. Stir well at 50℃, then add 50ml of cyclopentane and continue stirring for 2h. Add 2ml of silica sol and continue stirring for 24h. Centrifuge and wash and filter the separated solid material. Finally, dry at 110℃ for 6h and calcine at 550℃ for 4h to obtain the core-shell molecular sieve, labeled as ZSM-23-hk. Analysis using pyridine adsorption infrared spectroscopy and 2,6-dimethylpyridine adsorption infrared spectroscopy revealed that the total Brønsted acid content of pyridine in the core-shell molecular sieve was 0.181 mmol / g, and the total Brønsted acid content of 2,6-dimethylpyridine was 0.159 mmol / g. The ratio of the total Brønsted acid content of 2,6-dimethylpyridine to the total Brønsted acid content of pyridine was 87.8:100. Among the Brønsted acid content of 2,6-dimethylpyridine in the core-shell molecular sieve, the amount of weak Brønsted acid below 250℃ was 0.145 mmol / g, and the ratio of the amount of weak Brønsted acid below 250℃ to the total Brønsted acid content of 2,6-dimethylpyridine was 91.2:100. The SiO2 / Al2O3 molar ratio in the ZSM-23 core layer was 96. The ratio of the core particle size to the shell thickness of the obtained core-shell molecular sieve was 6.4. The XRD pattern of the prepared core-shell molecular sieve is shown in [Figure number missing]. Figure 1 It is ZSM-23 molecular sieve.

[0102] The preparation of the FeCu / ZSM-23-hk catalyst was the same as in Example 2, except that the core-shell molecular sieve prepared in Example 5 was used. The specific composition is shown in Table 1.

[0103] Comparative Example 1

[0104] 144.2 mg of copper nitrate solid was weighed at room temperature and dissolved in water according to an equal volume impregnation amount. The solution was then sonicated for 10 min at a frequency of 25 kHz. The solution was then mixed with the ZSM-23-hk sample obtained in Example 1 using an equal volume impregnation method. After stirring thoroughly, the mixture was allowed to stand overnight. The sample was then placed in an oven at 110 °C for 8 h. Subsequently, the dried precursor was calcined in a muffle furnace at a heating rate of 5 °C / min, a calcination temperature of 550 °C, and a calcination time of 4 h. The resulting sample was labeled Cu / ZSM-23-hk. The specific composition is shown in Table 1.

[0105] Comparative Example 2

[0106] The catalyst preparation process was the same as in Example 2, except that the core-shell molecular sieve was replaced with the HZSM-23 molecular sieve prepared in Example 1. The obtained sample was labeled FeCu / ZSM-23. The specific composition is shown in Table 1.

[0107] Comparative Example 3

[0108] Weigh 5.8 mg of ferric chloride solid and dissolve it in 5.1 ml of water according to the water absorption capacity of 2 g of core-shell molecular sieve. Sonicate for 10 min. Then weigh 2 g of core-shell molecular sieve and mix the above solution and molecular sieve using an equal-volume impregnation method. Stir thoroughly and let stand overnight. Next, place the sample in an oven at 110℃ for 12 h. After drying, calcine the sample in a muffle furnace at a heating rate of 5℃ / min, a calcination temperature of 550℃, and a calcination time of 4 hours. The resulting sample is labeled Fe / ZSM-23-hk.

[0109] 140.4 mg of nickel nitrate solid was weighed at room temperature and dissolved in water according to an equal volume impregnation amount. The solution was then sonicated for 10 min at a frequency of 25 kHz. The solution and the Fe / ZSM-5-hk sample were then mixed using an equal volume impregnation method, stirred thoroughly, and allowed to stand overnight. The sample was then placed in an oven at 110 °C for 8 h. Subsequently, the dried precursor was calcined in a muffle furnace at a heating rate of 5 °C / min, a calcination temperature of 550 °C, and a calcination time of 4 h. The resulting sample was labeled FeNi / ZSM-23-hk. The specific composition is shown in Table 1.

[0110] Comparative Example 4

[0111] The preparation process is the same as in Example 3, except that no expanding agent is added during the synthesis of the core-shell molecular sieve, and the resulting ZSM-23 molecular sieve does not have a core-shell structure. The specific composition is shown in Table 1.

[0112] Comparative Example 5

[0113] Weigh 0.2g of ZSM-5 molecular sieve and add it to 150ml of deionized water. Then add 15g of hexadecyltrimethylammonium bromide and 1ml of triethanolamine. Stir well at 50℃, then add 50ml of cyclopentane and continue stirring for 2h. Add 2ml of silica sol and continue stirring for 24h. Centrifuge the mixture and wash and filter the separated solid material. Finally, dry it at 110℃ for 6h and calcine it at 550℃ for 4h to obtain the core-shell molecular sieve, labeled as ZSM-5-hk.

[0114] The catalyst was prepared in the same manner as in Example 2, except that the core-shell molecular sieve ZSM-5-hk prepared in Comparative Example 5 was used, denoted as Fe-Cu@ZSM-5-hk.

[0115] Test 1: Catalytic Performance Test

[0116] The direct oxidation of methane to methanol at low temperature is carried out in a high-pressure reactor equipped with a heating mantle.

[0117] First, at room temperature, 0.3 g of the catalyst prepared in the examples and the comparative examples, along with 80 ml of hydrogen peroxide solution (0.5 mol / L), were added to a 160 ml reactor. The reactor was purged twice with nitrogen gas, then three times with methane gas. The pressure was then increased to 3 MPa with methane gas, and the mixture was stirred at 200 rpm while simultaneously heated to 50°C. The stirring speed was then adjusted to 1500 rpm, and the reaction was allowed to proceed for 30 min. After the reaction, stirring was stopped, and the temperature was lowered to below 20°C. The liquid was then collected and filtered. NMR spectroscopy was used to quantitatively analyze the methanol in the filtrate. The conversion frequency of methanol formation at 50°C was calculated as (methanol formation) / (amount of iron × reaction time), and the results are shown in Table 1.

[0118] Table 1. Composition and catalytic performance of the examples and comparative examples.

[0119]

[0120]

[0121] Test 2: Cyclic Activity Test

[0122] The composite catalyst FeCu / ZSM-23-hk prepared in Example 2 was subjected to cyclic activity testing. The catalyst preparation and activity evaluation conditions were the same as in Example 1, except that the catalyst from the previous reaction was used in each test, and multiple parallel tests were performed for each test to ensure consistent catalyst quality for subsequent tests. The results are shown below. Figure 3 As can be seen, the methanol production remained essentially unchanged after the catalyst was used multiple times, indicating that the catalyst is very stable.

[0123] The specific embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including combining the various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A bimetallic supported composite catalyst, comprising a core-shell molecular sieve, a modified metal component, and an active metal component; in, The modified metal component is copper oxide; the active metal component is an iron oxide species. Among them, the core-shell molecular sieve uses ZSM-23 molecular sieve as the core and mesoporous silica as the shell; the ratio of the core particle size to the shell thickness of the core-shell molecular sieve is 6 to 18.

2. The bimetallic supported composite catalyst according to claim 1, characterized in that, The catalyst contains 0.01% to 5% copper by mass and 0.01% to 0.2% iron by mass. And / or, in the catalyst, the mass content of the core-shell molecular sieve is 89.5 wt% to 99.5%.

3. The bimetallic supported composite catalyst according to claim 1, characterized in that, The total Brønsted acid content of pyridine in infrared spectroscopy of the core-shell molecular sieve is 0.10–0.37 mmol / g; the total Brønsted acid content of 2,6-dimethylpyridine in infrared spectroscopy is 0.07–0.35 mmol / g. And / or, in the 2,6-dimethylpyridine infrared acid of the core-shell molecular sieve, the amount of weak Brønsted acid with a desorption temperature <250°C is 0.09–0.31 mmol / g.

4. The bimetallic supported composite catalyst according to claim 1, characterized in that, The ratio of the total Brønsted acid content of 2,6-dimethylpyridine in infrared to the total Brønsted acid content of pyridine in infrared is (65-99):

100. And / or, in the 2,6-dimethylpyridine infrared acid of the core-shell molecular sieve, the ratio of the amount of weak Brønsted acid with a desorption temperature <250°C to the total amount of Brønsted acid in the 2,6-dimethylpyridine infrared sieve is (64-95):

100.

5. The bimetallic supported composite catalyst according to claim 1, characterized in that, The SiO2 / Al2O3 (molar ratio) of the core layer in the core-shell molecular sieve is 85–550, preferably 90–400.

6. A method for preparing the bimetallic supported composite catalyst according to any one of claims 1-5, comprising the following steps: An iron source is impregnated onto a core-shell molecular sieve, dried, and calcined to obtain a molecular sieve catalyst precursor; then, a copper-soluble salt is impregnated into the molecular sieve catalyst precursor, dried, and calcined to obtain the bimetallic supported composite catalyst.

7. The preparation method according to claim 6, characterized in that, The preparation method of the core-shell molecular sieve includes the following steps: (1) A mixture of silicon source, template agent a and water is subjected to a crystallization reaction, and solid material A is separated from the reacted material; (2) The solid material A is mixed with fatty amine and inorganic base and subjected to a first low-temperature reaction, then ZSM-23 seed crystals are added and subjected to a second low-temperature reaction to obtain a mixed material; (3) The template agent b and the aluminum source are mixed with the mixture, and then crystallization, filtration, washing, drying and calcination are carried out in sequence to obtain ZSM-23 molecular sieve; (4) The ZSM-23 molecular sieve is subjected to ion exchange, drying and calcination to obtain HZSM-23 molecular sieve; (5) The HZSM-23 molecular sieve, structure guiding agent, and expansion agent are mixed, and then an organic solvent and silicon source are added. The solid material is separated and then filtered, washed, dried and calcined to obtain a core-shell molecular sieve.

8. The preparation method according to claim 7, characterized in that, In step (1), the silicon source is one or more of silica, silica sol, water glass, fumed silica and tetraethyl orthosilicate; And / or, in step (1), the template agent a is at least one of hexamethylenediamine, ethanol and n-hexamethyleneamine; And / or, in step (1), the molar ratio of the template agent a to the silicon source, calculated as SiO2, is 0.1 to 1.0; the molar ratio of water to the silicon source, calculated as SiO2, is 20 to 80. And / or, in step (1), the operating conditions of the crystallization reaction are as follows: the crystallization temperature is 120 to 220°C, and the crystallization time is 8 to 48 hours.

9. The preparation method according to claim 7, characterized in that, In step (2), the fatty amine is a C12-C18 fatty amine, preferably one or more of oleylamine (9-octadeceneamine), octadecylamine, and dodecylamine; And / or, in step (2), the liquid-to-solid ratio of the fatty amine to the solid material A is 0.3 to 3 mL / g; And / or, in step (2), the inorganic base is used in the form of an alkaline solution, the concentration of which is 0.003 to 0.015 mol / L; the liquid-to-solid ratio of the alkaline solution to the solid material A is 2 to 20 mL / g; the inorganic base is at least one of sodium hydroxide, potassium hydroxide, and ammonia water; And / or, in step (2), the temperature of the first low-temperature reaction is 20-40°C and the time is 3-15h.

10. The preparation method according to claim 7, characterized in that, In step (2), the ZSM-23 seed crystals are added in the form of seed crystal solution. The specific operation process of the seed crystal solution is as follows: the ZSM-23 seed crystals are uniformly dispersed in water to form seed crystal solution; wherein, the liquid-solid ratio of water to ZSM-23 seed crystals is 5 to 70 mL / g. And / or, in step (2), the amount of ZSM-23 seed crystals added is 0.1 to 8.0 wt%, based on the weight of the solid material A; And / or, in step (2), the temperature of the secondary low-temperature reaction is 60 to 120°C and the time is 6 to 30 hours.

11. The preparation method according to claim 7, characterized in that, In step (3), the template agent b is one or more of pyrrolidine, isopropylamine and N,N-dimethylformamide; the aluminum source is one or more of aluminum sulfate, aluminum isopropoxide, sodium aluminate and aluminum hydroxide. And / or, in step (3), the molar ratio of template agent b to the solid material A, calculated as SiO2, is 0.01 to 0.1; the molar ratio of aluminum source, calculated as Al2O3, to the solid material A, calculated as SiO2, is 0.002 to 0.

015. And / or, in step (3), the crystallization temperature is 180-220℃, the crystallization time is 24-72h; the drying temperature is 80-120℃, the drying time is 6-12h; the calcination temperature is 540-560℃, and the calcination time is 3-8h.

12. The preparation method according to claim 7, characterized in that, In step (5), the structure directing agent is one or more of hexadecyltrimethylammonium bromide, hexadecyltrimethylammonium chloride, and octadecyltrimethylammonium chloride; the swelling agent is one or more of glycerol, triethanolamine, and butanediol; the organic solvent is one or more of cyclopentane and cyclohexane; and the silicon source is one or more of tetraethyl orthosilicate, silica sol, and sodium silicate. And / or, in step (5), the mass ratio of HZSM-23 molecular sieve to structure directing agent is 0.001 to 0.08; the volume ratio of expansion agent, silicon source and organic solvent is 1:(0.5 to 8):(20 to 100); and the mass ratio of silicon source and HZSM-23 molecular sieve is 1:(1 to 10).

13. The preparation method according to claim 6, characterized in that, The iron source is selected from at least one of ferric nitrate and ferric chloride; And / or, the copper-soluble salt is selected from at least one of copper nitrate and copper chloride; And / or, the mass ratio of iron source, core-shell molecular sieve, and copper soluble salt is 1:(150-400):(5-50).

14. The preparation method according to claim 6, characterized in that, The impregnation method employs equal-volume impregnation. And / or, after impregnation, let stand for 12 to 24 hours, then dry at a temperature of 80 to 140°C for 6 to 24 hours; And / or, the calcination is carried out using programmed temperature rise calcination, with a heating rate of 2 to 10 °C / min, a calcination temperature of 450 to 650 °C, and a calcination time of 4 to 10 h.

15. The application of the bimetallic supported composite catalyst according to any one of claims 1-5 in the low-temperature oxidation of methane to methanol.

16. The application according to claim 15, characterized in that, The reaction uses pure methane as the reaction gas and low-concentration hydrogen peroxide as the oxidant. And / or, the concentration of hydrogen peroxide in the hydrogen peroxide solution is 0.5–1 mol / L; And / or, the volume ratio of methane to hydrogen peroxide is 1:(1 to 1.5); And / or, the reaction temperature is 30-80℃, the reaction time is 15-60min, the reaction pressure is 1-3MPa, and the catalyst dosage is 2.5-12.5g per liter of hydrogen peroxide.

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