Metallic single-atom composite catalyst, preparation method and application thereof

Abstract

The application discloses a metal single-atom composite catalyst and a preparation method and application thereof. The metal single-atom composite catalyst comprises a core-shell molecular sieve and an active component; wherein the core-shell molecular sieve is a ZSM-23 molecular sieve as a core and a mesoporous silica as a shell; and the active component is a Fe-N-C species. The metal single-atom composite catalyst provided by the application is applied to a reaction of preparing C1 liquid products by low-temperature oxidation of methane, and can realize direct oxidation of methane to prepare C1 liquid products under low-temperature conditions below 80 DEG C, and has outstanding catalytic activity, 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 metal single-atom composite catalyst and its preparation method, as well as its application in the low-temperature direct oxidation of methane to produce C1 liquid products. Background Technology

[0002] With the continuous increase in oil resource extraction and the continuous decrease in reserves, exploring alternatives to oil as raw materials for the production of high-value-added oxygenated compounds such as formic acid, methanol, and ethanol is of great significance. Natural gas is a clean, efficient, and high-quality low-carbon energy source, mainly composed of light alkanes, including 70-90% methane and 1-10% ethane. Effectively converting methane reserves into oxygenated C1 liquid products has been considered an effective strategy to replace petroleum-based chemical production methods. Meanwhile, methane, as the world's second largest greenhouse gas, although its content is less than carbon dioxide, has a greenhouse effect more than 20 times greater, thus exacerbating global warming. Therefore, research on the selective activation and directed conversion of methane has become particularly urgent in both energy utilization and environmental protection fields. However, compared to other organic molecules, methane's unique structure makes it very stable, requiring relatively harsh reaction conditions to activate methane molecules. Therefore, researching how to selectively activate and directionally convert methane is one of the major scientific challenges currently facing us, and it is also an urgent need to effectively alleviate the energy crisis and achieve sustainable development. At the same time, designing and researching catalysts that can selectively oxidize methane has always been a major scientific challenge for future industrial production.

[0003] Currently, the main industrial method for converting methane into liquid hydrocarbons is the indirect method. This involves first reforming methane into syngas (H2 + CO) via steam reforming, and then using Fischer-Tropsch synthesis (FT) at temperatures exceeding 600°C to convert the methane into the target product. This process has high equipment operation and maintenance costs, low catalyst atom utilization, and poor selectivity for the target product. With the urgent need to reduce energy consumption and equipment maintenance costs, directly preparing C1 liquid products (methanol, formic acid, etc.) from methane in a single step at low temperatures (<150°C) is very attractive. This eliminates the intermediate step of syngas preparation, significantly reducing energy consumption and making it more economical and environmentally friendly. Furthermore, the C1 main product is liquid at room temperature and pressure, making storage and transportation convenient, and is considered an ideal method for methane conversion. The direct, directed conversion of methane using inexpensive and environmentally friendly oxygen at low temperatures has been a major research focus. For example, CN111195514A discloses a single-atom-dispersed rhodium-based catalyst for the low-temperature oxidation of methane, in which CH4, CO, and O2 can be converted into acetic acid, formic acid, and methanol with high activity and selectivity. CN112892588A discloses a method for preparing and applying an atomically dispersed transition metal catalyst for the low-temperature catalytic oxidation of methane to acetic acid. However, oxygen molecules are extremely difficult to continuously form reactive oxygen species that can activate the CH bonds of methane under mild conditions, making the direct catalytic conversion of methane and oxygen at low temperatures extremely challenging. Summary of the Invention

[0004] To address the above-mentioned technical problems, the present invention aims to provide a metal single-atom composite catalyst, its preparation method, and its application. The metal single-atom composite catalyst provided by the present invention is applied to the low-temperature oxidation of methane to C1 liquid products. It can achieve the direct oxidation of methane to C1 liquid products at low 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 metal single-atom composite catalyst, comprising a core-shell molecular sieve and an active component;

[0006] The core-shell molecular sieve is a core-shell molecular sieve with ZSM-23 molecular sieve as the core and mesoporous silica as the shell; the active component is an Fe-NC species.

[0007] Furthermore, the Fe metal in the Fe-NC species exists in single-atom form.

[0008] Furthermore, the Fe metal exists in single-atom form by being dispersed on the core-shell molecular sieve as isolated single-atom sites.

[0009] Furthermore, in the catalyst, based on the mass of the catalyst, the mass content of iron is 1% to 1.5%, and the mass content of the core-shell molecular sieve is 92% to 98%.

[0010] Furthermore, in the Fe-NC species, the molar ratio of Fe, N and C is 1:(3-5):(10-12).

[0011] Furthermore, the ratio of the core particle size to the shell thickness of the core-shell molecular sieve is 6 to 18.

[0012] Furthermore, the total Brønsted acid content of pyridine in the core-shell molecular sieve is 0.08–0.32 mmol / g, preferably 0.11–0.29 mmol / g, more preferably 0.13–0.27 mmol / g; and the total Brønsted acid content of 2,6-dimethylpyridine in the infrared is 0.05–0.31 mmol / g, preferably 0.08–0.28 mmol / g, more preferably 0.10–0.25 mmol / g.

[0013] Furthermore, 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 (63-99):100, preferably (73-97):100, and even more preferably (76-93):100.

[0014] 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 0.07–0.29 mmol / g, preferably 0.09–0.27 mmol / g, and more preferably 0.11–0.26 mmol / g.

[0015] 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 (67-95):100, preferably (69-93):100, and even more preferably (73-92):100.

[0016] Furthermore, the SiO2 / Al2O3 molar ratio in the core-shell molecular sieve is 85–550, preferably 90–400.

[0017] A second aspect of the present invention provides a method for preparing the above-mentioned metal single-atom composite catalyst, comprising the following steps:

[0018] Iron source, complex, and organic solvent are mixed, and then a core-shell molecular sieve is added for heating and reflux reaction. After drying and calcination, a metal single-atom composite catalyst is obtained.

[0019] Furthermore, in the preparation method of the metal single-atom composite catalyst, the iron source is selected from at least one of ferric acetate and ferric acetylacetone.

[0020] Furthermore, in the preparation method of the metal single-atom composite catalyst, the complex is selected from 1,10-o-phenanthroline.

[0021] Furthermore, in the preparation method of the metal single-atom composite catalyst, the organic solvent is selected from at least one of ethanol and acetone.

[0022] Furthermore, in the preparation method of metal single-atom composite catalyst, the mass ratio of iron source, complex, organic solvent and core-shell molecular sieve is 1:(3-5):(350-550):(25-40).

[0023] Furthermore, in the preparation method of the metal single-atom composite catalyst, after adding the core-shell molecular sieve, it is preferable to first subject it to ultrasonic treatment, and then carry out a heating reflux reaction. The ultrasonic frequency is 20-30 kHz, and the treatment time is 10-50 min.

[0024] Furthermore, in the preparation method of the metal single-atom composite catalyst, the temperature of the heating reflux reaction is 40-90℃, the reflux time is 10-12h, and the rotation speed during the reflux process is 400-800rpm.

[0025] Furthermore, in the preparation method of the metal single-atom composite catalyst, the drying is preferably carried out by rotary evaporation at a temperature of 50-60°C for 1-2 hours.

[0026] Furthermore, in the preparation method of the metal single-atom composite catalyst, the calcination is carried out under an inert atmosphere, which includes at least one of argon and helium, the calcination temperature is 400-800℃, and the calcination time is 2-4h.

[0027] Furthermore, the preparation method of the core-shell molecular sieve includes the following steps:

[0028] (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;

[0029] (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;

[0030] (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;

[0031] (4) The ZSM-23 molecular sieve is subjected to ion exchange, drying and calcination to obtain HZSM-23 molecular sieve;

[0032] (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.

[0033] 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.

[0034] Further, in step (1), the template agent a is at least one of hexamethylenediamine, ethanol and n-hexamethylenediamine, preferably hexamethylenediamine and / or ethanol.

[0035] 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.

[0036] 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.

[0037] Furthermore, in step (1), the crystallization reaction is preferably carried out in a reactor with a polytetrafluoroethylene liner.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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%.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] Further, in step (5), the mass ratio of HZSM-23 molecular sieve to structure directing agent is 0.001 to 0.08, preferably 0.005 to 0.05; the volume ratio of expanding agent, silicon source and organic solvent is 1:(0.5 to 8):(20 to 100), preferably 1:(1 to 5):(30 to 80); the mass ratio of silicon source and HZSM-23 molecular sieve is 1:(1 to 10), preferably 1:(3 to 8).

[0053] 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.

[0054] The third aspect of this invention provides the application of the above-mentioned metal single-atom composite catalyst in the low-temperature oxidation of methane to C1 liquid products.

[0055] Furthermore, the C1 liquid product includes at least CH3OH, HCOOH, CH3OOH and HOCH2OOH.

[0056] Furthermore, the low-temperature oxidation reaction of methane to produce C1 liquid products 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.

[0057] Furthermore, the volume ratio of methane to hydrogen peroxide is 1:(1 to 1.5).

[0058] 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.

[0059] The present invention has the following advantages:

[0060] (1) The composite catalyst provided by the present invention can directly obtain C1 liquid products (including CH3OH, HCOOH, CH3OOH and HOCH2OOH) by catalyzing the methane oxidation reaction under low temperature conditions. The reaction temperature can be as low as below 80℃, which is different from the reaction temperature of more than 150℃ required in other methods, and can greatly reduce energy consumption.

[0061] (2) The metal single-atom core-shell composite molecular sieve catalyst provided by the present invention uses non-precious metal Fe-NC species as the active component, and the catalyst cost is low.

[0062] (3) The core-shell molecular sieve provided by the present invention has a gradient of pores on its surface, which is particularly suitable as a catalyst support component. It exhibits excellent activity, selectivity and stability in the reaction of methane oxidation to C1 liquid product at low temperature.

[0063] (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.

[0064] (5) The composite catalyst provided by this invention exhibits a high reaction rate in its catalytic process, wherein the C1 generation turnover frequency (TOF) can be greater than 22 mmol. C1 / g cat / h -1 Furthermore, the catalyst exhibits good stability, and the C1 yield remains essentially unchanged after multiple cycles of use. Attached Figure Description

[0065] Figure 1 The XRD pattern of the core-shell molecular sieve prepared in Example 1;

[0066] Figure 2 STEM image of the catalyst prepared in Example 2;

[0067] Figure 3 This is a stability test of the catalyst in Example 2. Detailed Implementation

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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 acid 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.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] Example 1: Preparation of Core-Shell Molecular Sieves

[0077] 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.

[0078] Add 0.67g Al2(SO4)3·18H2O and 0.40g pyrrolidine to 20mL of deionized water to obtain a clear solution C;

[0079] 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.

[0080] 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.

[0081] 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 molar ratio of SiO2 / Al2O3 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.

[0082] The XRD patterns of the prepared core-shell molecular sieves are shown in the figure. Figure 1 It has the structure of ZSM-23 molecular sieve.

[0083] Example 2: Preparation of the metal single-atom composite catalyst Fe-NC@ZSM-23-hk

[0084] 106 mg of ferric acetate and 330 mg of 1,10-o-phenanthroline were weighed and poured into a 150 mL round-bottom flask. 50 mL of ethanol was added, and the mixture was stirred at room temperature for 30 min. Then, 3 g of the core-shell molecular sieve powder prepared in Example 1 was slowly added, and the mixture was sonicated at a frequency of 25 kHz at room temperature for 30 min. After sonication, the mixture was placed in a water bath and heated to 60 °C for reflux with stirring at 600 rpm for 12 h. After reflux, the sample was transferred to a rotary evaporator for rotary evaporation at 55 °C for 1.5 h to obtain the precursor. The precursor was then transferred to a tube furnace and calcined under an argon atmosphere at 800 °C for 2 h. The resulting sample was labeled Fe-NC@ZSM-23-hk.

[0085] The mass content of iron and the molar ratio of Fe, N, and C are shown in Table 1. Additionally, STEM data... Figure 2 As can be seen, observation of the catalyst by aberration-corrected scanning transmission electron microscopy revealed that Fe in the active component Fe-NC species of this embodiment mainly exists in a highly dispersed single-atom form.

[0086] Example 3: Preparation of the metal single-atom composite catalyst Fe-NC@ZSM-23-hk

[0087] 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.

[0088] Add 0.67g Al2(SO4)3·18H2O and 0.40g pyrrolidine to 20mL of deionized water to obtain a clear solution C;

[0089] 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.

[0090] 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.

[0091] 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.

[0092] The preparation of the Fe-NC@ZSM-23-hk catalyst was the same as in Example 2, except that the core-shell molecular sieve prepared in Example 3 was used. The mass content of iron and the molar ratio of Fe, N, and C are shown in Table 1.

[0093] Example 4: Preparation of the metal single-atom composite catalyst Fe-NC@ZSM-23-hk

[0094] 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.

[0095] Add 0.67g Al2(SO4)3·18H2O and 0.40g pyrrolidine to 20mL of deionized water to obtain a clear solution C;

[0096] 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.

[0097] 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.

[0098] 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.

[0099] The preparation of the Fe-NC@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 mass content of iron and the molar ratio of Fe, N, and C are shown in Table 1.

[0100] Example 5: Preparation of the metal single-atom composite catalyst Fe-NC@ZSM-23-hk

[0101] 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.

[0102] Add 0.67g Al2(SO4)3·18H2O and 0.40g pyrrolidine to 20mL of deionized water to obtain a clear solution C;

[0103] 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.

[0104] 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.

[0105] 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.

[0106] The preparation of Fe-NC@ZSM-23-hk was the same as in Example 2, except that the core-shell molecular sieve prepared in Example 5 was used, and the amount of solid ferric acetate weighed was 76 mg. The mass content of iron and the molar ratio of Fe, N, and C are shown in Table 1. Comparative Example 1: Preparation of Fe-NC@ZSM-23

[0107] 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 mass content of iron and the molar ratio of Fe, N, and C are shown in Table 1.

[0108] Comparative Example 2: Preparation of the single-atom composite catalyst Fe-NC@ZSM-5-hk

[0109] 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.

[0110] 106 mg of ferric acetate and 330 mg of 1,10-o-phenanthroline were weighed and poured into a 150 mL round-bottom flask. 50 mL of ethanol was added, and the mixture was stirred at room temperature for 30 min. Then, 3 g of the core-shell molecular sieve powder ZSM-5-hk prepared in Comparative Example 2 was slowly added. The mixture was sonicated at room temperature for 30 min, and then placed in a water bath and heated to 60 °C for reflux with stirring at 600 rpm for 12 h. After reflux, the sample was transferred to a rotary evaporator for rotary evaporation to obtain the precursor. The precursor was then transferred to a tube furnace and calcined under an argon atmosphere at 800 °C for 2 h. The resulting sample was labeled Fe-NC@ZSM-5-hk. The mass content of iron and the molar ratio of Fe, N, and C are shown in Table 1.

[0111] Comparative Example 3: Single-Atom Composite Catalyst

[0112] The catalyst 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. The resulting ZSM-23 molecular sieve does not have a core-shell structure. The mass content of iron and the molar ratio of Fe, N and C are shown in Table 1.

[0113] Test 1: Catalytic Performance Test

[0114] The low-temperature direct oxidation reaction of methane is carried out in a high-pressure reactor equipped with a heating mantle.

[0115] First, 0.3 g of the catalyst prepared in the examples and comparative examples and 80 ml of hydrogen peroxide solution (0.5 mol / L) were added to a 160 ml reactor at room temperature. Nitrogen gas was introduced twice for purging, followed by methane gas purging three times. The reactor was then purged with methane gas to 3 MPa and stirred at 200 rpm while simultaneously heating 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. Nuclear magnetic resonance (NMR) analysis was performed to quantitatively analyze the C1 products (including CH3OH, HCOOH, CH3OOH, and HOCH2OOH) in the filtrate. The conversion frequency and yield of C1 liquid products generated on the composite catalyst at 50°C are shown in Table 1. The conversion frequency of C1 liquid product generation was calculated as (molar amount of C1 liquid product) / (catalyst amount × reaction time).

[0116] Table 1. Composition and catalytic performance of the examples and comparative examples.

[0117]

[0118] Test 2: Cyclic Activity Test

[0119] The Fe-NC@ZSM-23-hk composite catalyst 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 yield of C1 liquid products remained basically unchanged after multiple cycles of catalyst use, indicating that the catalyst is very stable.

[0120] 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 metal single-atom composite catalyst, comprising a core-shell molecular sieve and an active component; in, The core-shell molecular sieve has a ZSM-23 molecular sieve core and a mesoporous silica shell; the active component is an Fe-NC species.

2. The metal single-atom composite catalyst according to claim 1, characterized in that, The Fe metal in the Fe-NC species exists in single-atom form.

3. The metal single-atom composite catalyst according to claim 1, characterized in that, In the catalyst, based on the mass of the catalyst, the mass content of iron is 1% to 1.5%, and the mass content of the core-shell molecular sieve is 92-98%. And / or, in the Fe-NC species, the molar ratio of Fe, N and C is 1:(3-5):(10-12); And / or, the ratio of the core particle size to the shell thickness of the core-shell molecular sieve is 6 to 18.

4. The metal single-atom composite catalyst according to claim 1, characterized in that, The SiO2 / Al2O3 molar ratio in the core-shell molecular sieve is 85–550, preferably 90–400.

5. The metal single-atom composite catalyst according to claim 1, characterized in that, The total Brønsted acid content of pyridine in the core-shell molecular sieve is 0.08–0.32 mmol / g; the total Brønsted acid content of 2,6-dimethylpyridine in the core-shell molecular sieve is 0.05–0.31 mmol / g; and the amount of weak Brønsted acid with a desorption temperature <250℃ in the 2,6-dimethylpyridine in the core-shell molecular sieve is 0.07–0.29 mmol / g. And / or, the ratio of the total 2,6-dimethylpyridine infrared Brønsted acid content of the core-shell molecular sieve to the total Brønsted acid content of pyridine infrared Brønsted acid is (63-99):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 (67-95):

100.

6. A method for preparing the metal single-atom composite catalyst according to any one of claims 1-5, comprising the following steps: The iron source, complex, and organic solvent are mixed, and then a core-shell molecular sieve is added for heating and reflux reaction. After drying and calcination, a metal single-atom composite catalyst is obtained.

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 complex is selected from 1,10-o-phenanthroline; And / or, the organic solvent is selected from at least one of ethanol and acetone; And / or, in the preparation method of metal single-atom composite catalyst, the mass ratio of iron source, complex, organic solvent and core-shell molecular sieve is 1:(3-5):(350-550):(25-40).

14. The preparation method according to claim 6, characterized in that, The temperature of the heating and reflux reaction is 40-90℃, the reflux time is 10-12h, and the rotation speed during the reflux process is 400-800rpm. And / or, the drying is preferably carried out by rotary evaporation at a temperature of 50-60°C for 1-2 hours. And / or, the calcination is carried out under an inert atmosphere, the inert atmosphere including at least one of argon and helium, the calcination temperature is 400-800°C, and the calcination time is 2-4 hours.

15. The application of the metal single-atom composite catalyst according to any one of claims 1-5 in the low-temperature oxidation of methane to C1 liquid products.

16. The application according to claim 15, characterized in that, The C1 liquid products include at least CH3OH, HCOOH, CH3OOH, and HOCH2OOH.

17. 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.

Images