Iron-based composite material catalyst capable of being used for low-temperature methane oxidation as well as preparation method and application of iron-based composite material catalyst
By preparing Fe3O4-WO3 composite material catalysts, using their active species to activate the CH bonds of methane molecules at low temperatures, and combining them with hydrogen peroxide solution to catalyze the reaction, the problem that existing catalysts are difficult to convert methane into high-value-added liquid products under mild conditions was solved, and high selectivity and stability were achieved.
Patent Information
- Application Number
- CN202510843892.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-06-23
- Publication Date
- 2025-09-19
AI Technical Summary
Existing catalysts find it difficult to quickly convert methane into high-value-added liquid products under mild conditions. Traditional oxidation processes are environmentally unfriendly, and precious metal catalysts are expensive and lack selectivity.
The Fe-SiW precursor was solvothermally synthesized by silicotungstic acid and ferric nitrate in an organic solvent. The Fe3O4-WO3 composite material was prepared by hydrogen treatment. The active species of the Fe3O4-WO3 composite material activated the CH bond of the methane molecule and catalyzed the reaction at low temperature in combination with hydrogen peroxide solution.
The highly efficient activation of methane at low temperature is achieved to generate highly selective C1 oxygenated compounds. The catalyst has good stability, low cost, low hydrogen peroxide consumption rate, and no significant decrease in recycling.
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Figure CN120662324A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of low-temperature methane direct conversion and utilization, and in particular relates to an iron-based composite material catalyst that can be used for low-temperature methane oxidation, and a preparation method and application thereof. Background Art
[0002] Methane is an important carrier of the earth's carbon resources, and the research on its direct catalytic conversion technology is of great strategic significance. The traditional industrial conversion path requires the preparation of synthesis gas intermediates. In recent years, the non-indirect path of direct partial oxidation to methanol has attracted much attention due to its high efficiency. However, this process faces two challenges. On the one hand, the methane molecule has a highly symmetrical tetrahedral structure, and its C-H bond has a carbonyl content of 439.3 kJ·mol -1 The high dissociation energy and low polarization of methane make it difficult to activate under mild conditions. On the other hand, the target product, methanol, is more susceptible to deep oxidation than methane, producing CO2 as a byproduct with lower economic value.
[0003] In existing technology systems, traditional oxidation processes generally use strong oxidants with poor environmental friendliness. For example, fuming sulfuric acid reacts with mercury or platinum catalysts to produce methyl sulfate, but this process is accompanied by the formation of SO2 as a byproduct, posing significant environmental risks. Although precious metal-based catalysts (such as Au and Pt systems) exhibit certain catalytic activity, their industrial application is limited by the high costs caused by the scarcity of precious metals and the technical bottleneck of insufficient product selectivity.
[0004] Based on the concept of green chemistry, hydrogen peroxide (H2O2) shows unique advantages as an environmentally friendly oxidant. Current research focuses on the development of efficient catalytic systems, among which breakthroughs in non-precious metal catalysts are particularly critical. Polyacid-based composite materials have shown great application potential in liquid-phase catalytic systems due to their excellent hydrothermal stability and corrosion resistance. At the same time, metal oxides also show significant advantages in the field of catalysis. Their unique physical and chemical properties make them efficient and stable catalyst materials. Their rich surface active sites and controllable crystal structure can enhance the adsorption and activation capabilities of reactants through oxygen vacancies, defect sites or exposed crystal planes. These comprehensive characteristics enable metal oxides to continue to play a core role in thermal catalysis, electrocatalysis and photocatalysis systems.
[0005] Composite nanomaterials often exhibit excellent catalyst regeneration properties, which not only extends the catalyst's lifespan but also enables reuse through simple regeneration operations, significantly reducing catalyst costs and resource consumption. By manipulating the electronic structure and spatial configuration of the active sites, these materials are expected to achieve selective activation of methane C-H bonds and targeted conversion of intermediates, providing a new strategy for developing efficient and green direct methane oxidation technologies.
[0006] In summary, it is very meaningful to provide a method for preparing a self-stable composite catalyst with catalytic activity and its application in catalytic methane oxidation to methanol. Summary of the Invention
[0007] In view of this, the present invention discloses an iron-based composite catalyst for low-temperature methane oxidation, its preparation method, and its application, overcoming the problem that traditional catalysts have poor cyclic stability and are difficult to quickly convert methane into high-value-added liquid products under mild conditions.
[0008] The technical solution provided by the present invention is specifically as follows: first, the present invention provides a method for preparing an iron-based composite material catalyst that can be used for low-temperature methane oxidation, comprising:
[0009] Step 1: In an organic solvent, silicotungstic acid hydrate and ferric nitrate are solvothermally synthesized into a Fe-SiW precursor;
[0010] Step 2: Treat the Fe-SiW precursor Fe3O4-WO3 composite material through hydrogen process.
[0011] Preferably, step 1 comprises:
[0012] Dissolving silicotungstic acid hydrate in Fe(NO3)3 ethanol solution to obtain a mixed system;
[0013] Oleylamine and n-hexane are added to the mixed system, and after heating in a sealed state for reaction, the temperature is lowered to room temperature. The obtained product is washed, centrifuged, and dried to obtain a Fe-SiW precursor.
[0014] Preferably, the solvent thermal reaction in step 1 is carried out in a high-pressure reactor, the heating reaction temperature is 140° C., and the reaction time is 4 h.
[0015] Preferably, the obtained product is washed with ethanol, centrifuged twice at 9000 rpm, each time for 5 minutes, and dried under vacuum at 60° C. for 8 hours.
[0016] Preferably, step 2 includes:
[0017] The Fe-SiW precursor was ground and placed in a porcelain boat and tube furnace;
[0018] The ground Fe-SiW precursor was calcined in a hydrogen-argon mixed atmosphere, and the sample was taken out after natural cooling to obtain a Fe3O4-WO3 composite material.
[0019] Preferably, the calcination conditions are: calcination at a temperature of 550° C., at a heating rate of 10° C. / min, and calcination for 2 hours.
[0020] Preferably, during calcination, the ratio of hydrogen and argon mixed gas introduced is 5% H2 / 95% Ar, and the gas flow rate is 50 mL / min.
[0021] In addition, the present invention also provides a composite material catalyst prepared by the above preparation method, wherein the catalyst is an iron-based polyacid composite material.
[0022] Preferably, the composite material is used for low-temperature oxidation of methane to produce C1 oxygen-containing compounds.
[0023] Finally, the present invention provides an application of the above catalyst, wherein the composite catalyst and hydrogen peroxide solution are added to a high-temperature and high-pressure reactor, the gas in the reactor is replaced with methane, 3 MPa of methane is introduced, the reactor is heated to 40-100°C, and stirring is started. After the catalytic reaction, a liquid C1 oxygen-containing product is obtained; the hydrogen peroxide concentration is 0.75-1.5 mol / L, and the catalytic reaction time is 5 min-1 h among the controlled variables;
[0024] The present invention provides an iron-based composite material catalyst that can be used for low-temperature methane oxidation, as well as its preparation method and application. The catalyst is a stable polyacid-based composite material catalyst, has a simple preparation method, uses cheap and readily available raw materials, is green and pollution-free, has strong stability after synthesis, requires no subsequent treatment, is extremely stable in water, and maintains its structure even after long-term immersion in water.
[0025] The catalyst of the present invention has a strong ability to activate methane. The yield of liquid phase C1 oxygen-containing product obtained by catalyzing methane with the catalyst is as high as 6.70 mmol·g cat -1 ·h -1 , with only a small amount of over-oxidation product CO2 generated, the selectivity of C1 oxygenated products was 92.65%, and the hydrogen peroxide consumption rate was 49.83%. After five cycles of testing, the yield remained essentially unchanged, showing excellent cyclic stability.
[0026] It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the disclosure of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS
[0027] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.
[0028] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.
[0029] Figure 1 XRD of the Fe3O4-WO3 composite material provided in the embodiment disclosed in the present invention;
[0030] Figure 2 FT-IR of the Fe3O4-WO3 composite material provided in the disclosed embodiment of the present invention;
[0031] Figure 3 TEM+EDS of the Fe3O4-WO3 series composite materials provided in the disclosed embodiments of the present invention.
[0032] Figure 4 This is a diagram of the catalytic mechanism of the Fe3O4-WO3 composite material provided in the disclosed embodiments of the present invention. DETAILED DESCRIPTION
[0033] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. In the following description, when referring to the drawings, like numbers in different figures represent the same or similar elements unless otherwise indicated. The embodiments described in the following exemplary embodiments are not intended to represent all possible embodiments consistent with the present invention. Rather, they are merely examples of systems consistent with certain aspects of the present invention, as detailed in the appended claims.
[0034] To address the difficulty of existing catalysts in rapidly converting methane into high-value-added liquid products under mild conditions, this embodiment provides a hydrophobic composite catalyst and preparation method for low-temperature oxidation of methane to produce C1 oxygenated products. The catalyst is prepared by solvothermal synthesis of a precursor of silicotungstic acid and ferric nitrate in an organic solvent, followed by temperature-programmed heating with hydrogen. The active species is an unsaturated iron species.
[0035] The specific preparation method includes:
[0036] Step 1: Solvothermally synthesizing ferric nitrate and silicotungstic acid in an organic solvent and then centrifugally drying the mixture to prepare a Fe-SiW precursor;
[0037] Preferably, silicotungstic acid hydrate is weighed and dissolved in a Fe(NO3)3 ethanol solution in a 25ml polytetrafluoroethylene autoclave. Oleylamine and n-hexane are then added to the above system. After all these steps are completed, the autoclave is sealed and placed in an oven for reaction at 140°C for 4 hours. After the reaction is completed and the temperature is lowered to room temperature, the product is washed with ethanol, centrifuged twice at 9000rpm for 5 minutes each time, and dried in a vacuum drying oven at 60°C for 8 hours to obtain a Fe-SiW precursor.
[0038] Step 2: Prepare Fe3O4-WO3 composite material by hydrogen temperature-programmed reduction.
[0039] Preferably, the Fe-SiW precursor is ground and placed in a porcelain boat and a tube furnace. It is calcined in a hydrogen-argon mixed atmosphere at 550°C for 2 hours at a heating rate of 10°C / min in the tube furnace. The sample is removed after natural cooling, thereby producing a Fe3O4-WO3 composite material.
[0040] Preferably, the ratio of the hydrogen-argon mixed gas introduced is (5% H2 / 95% Ar), and the gas flow rate is 50 mL / min.
[0041] In this embodiment, hydrogen is introduced and the temperature is programmed to convert the catalyst into a more stable composite metal oxide at room temperature. Part of the trivalent iron is reduced to form divalent iron. The Fe(II)-O unsaturated bond in the resulting Fe3O4-WO3 catalyst can activate the O-O bond of H2O2, thereby generating two ·OH radicals, one of which bonds with the Fe atom to form an Fe(II)-O active site, and the other ·OH bonds with the hydrogen atom to generate a water molecule. At the same time, the generated Fe(II)-O active species, due to its high spin density, can effectively activate the C-H bond of the methane molecule, generating a ·CH3 radical, and stabilizing the transition state at room temperature through electron transfer from the Fe atom to the O atom.
[0042] The catalyst material obtained by the above method is an extremely stable iron-based composite material. The composite catalyst, with iron as the active component, exhibits exceptional stability in hydrogen peroxide solution without any further treatment. It also features a well-defined structure and highly dispersed active species, effectively reducing the activation energy of methane and enabling rapid catalytic methane oxidation under mild conditions to produce a large amount of C1 oxygenated liquid products.
[0043] The composite material can be used for low-temperature oxidation of methane to prepare C1 oxygen-containing compounds: The low-temperature rapid oxidation of methane to methanol is carried out in a closed high-temperature and high-pressure reactor through heating, stirring, reaction, and cooling. Pure methane is introduced three times to replace the air in the high-pressure reactor. The reactants are pure methane and a prepared hydrogen peroxide solution with a certain concentration. The material obtained in this embodiment is used as a catalyst.
[0044] Specifically, the composite catalyst and hydrogen peroxide solution were added to a high-temperature and high-pressure reactor. After replacing the gas in the reactor with methane, 3MPa of methane was added, and the reactor was heated to 40-100°C and stirred. The hydrogen peroxide concentration was 0.75-1.5 mol / L, and the reaction time was 5 minutes. -1 h.
[0045] Before filling methane to 3MPa, nitrogen and methane were introduced into the high-pressure reactor in sequence for replacement.
[0046] The catalyst in this embodiment can catalyze the direct oxidation of methane to produce C1 products such as methanol at relatively low temperatures and low H2O2 concentrations. The composite catalyst provided by the present invention is low in cost and has good stability. The optimal catalyst can produce a yield of liquid oxygen-containing compounds as high as 6.70 mmol·g at 80°C and 1 M H2O2 for 30 minutes. cat -1 ·h -1 The total selectivity of C1 oxygen-containing compounds reached 92.65%, the hydrogen peroxide consumption rate was 49.83%, and after multiple cycles, the output of C1 oxygen-containing compounds did not decrease significantly.
[0047] The following non-limiting examples may enable those skilled in the art to more fully understand the present invention, but are not intended to limit the present invention in any way.
[0048] Example 1
[0049] Step 1: Fe-SiW Precursor: Weigh 0.056g of silicotungstic acid hydrate and dissolve it in 2ml of 0.1M Fe(NO3)3 ethanol solution in a 25ml polytetrafluoroethylene autoclave. Then, add 1.9ml of oleylamine and 6ml of n-hexane to the above system, stirring ultrasonically for 10 minutes. After all these steps are completed, the autoclave is sealed and placed in an oven at 140°C for 4 hours. After the reaction is completed and the temperature is cooled to room temperature, the product is washed with anhydrous ethanol and centrifuged twice at 9000rpm for 5 minutes each time. Then, dry it in a vacuum oven at 60°C for 8 hours, and collect the sample.
[0050] Figure 3 (a) is a transmission electron micrograph of the Fe-SiW precursor. From the figure, it can be seen that the catalyst has a nanosheet structure with a width of about 800nm and a length of several microns.
[0051] Step 2: Preparation of Fe3O4-WO3 composite material: 0.1g Fe-SiW precursor was ground and placed in a porcelain boat and tube furnace, and hydrogen-argon mixture (5% H2 / 95% Ar) was introduced at 550℃ and heated at 10℃·min -1 The mixture was calcined at a heating rate of 2 h to obtain Fe3O4-WO3 composite material.
[0052] Figure 3 (b) is a transmission electron microscopy image of the Fe3O4-WO3 composite material. From the image, it can be seen that the catalyst presents a nanoparticle cluster structure with a width of about 80nm and a length of about 300nm. Figure 3 (c) is a high-resolution transmission electron microscopy image of the Fe3O4-WO3 composite material, showing that the lattice spacing of the Fe3O4 (220) crystal plane is 0.29 nm and the lattice spacing of the WO3 (201) crystal plane is 0.22 nm. Figure 3 (dg) are the EDS spectra of Fe3O4-WO3 composite materials. It can be observed that Fe, O, Si, and W elements are evenly distributed on the catalyst surface, proving that the catalyst is well prepared.
[0053] Example 2
[0054] Low-temperature direct oxidation of methane to produce C1 oxygenates
[0055] The low-temperature direct oxidation of methane to produce C1 oxygenates is carried out in an integrated high-pressure reactor. The reactant used is pure gaseous methane.
[0056] The specific reaction steps are as follows: first, weigh 10 mg of catalyst and place it in the reactor lining, then place a rotor, add a certain concentration of hydrogen peroxide solution, and repeat the process three times to fill with methane gas to displace the residual air in the reactor lining.
[0057] A final injection of 3 MPa methane gas was performed. The reactor was set to 80°C, stirring was turned on, the speed was set to 600 rpm, and the reaction time was set to 30 minutes. After the reaction, the reactor was quickly placed in an ice-water bath. When the temperature was cooled to below 10°C, the gaseous product was collected using an air bag. The rotor was removed and the liquid product was centrifuged (9000 rpm, 5 minutes). The supernatant was extracted and the liquid product was filtered using a needle filter.
[0058] The recovered catalyst was washed with water several times and then dried in a vacuum drying oven at 60°C for 8 h.
[0059] The gaseous products after the reaction were quantitatively detected by gas chromatography, and the liquid products were quantitatively detected by liquid hydrogen nuclear magnetic resonance spectrometer ( 1 H-NMR) was used for quantitative analysis, and the remaining hydrogen peroxide concentration was quantitatively calculated using liquid ultraviolet characterization.
[0060] The performance of the catalysts Fe-SiW (precursor) and Fe3O4-WO3 for the low-temperature direct oxidation of methane to C1 oxygenates is compared, as shown in Table 1. The reaction conditions are the same as in Example 1.
[0061] As can be seen from Table 1, although Fe-SiW has a higher yield, its selectivity is low, only 72.42%. The total value of methane activation product C1 of Fe3O4-WO3 is 6.70mmol·g cat -1 ·h -1 , the selectivity increased to 92.65%.
[0062] Table 1 Comparison of catalytic performance of different catalysts
[0063]
[0064] Note: Yield unit is mmol·g cat -1 ·h -1 , refers to the millimole amount of product that can be catalyzed by 1 gram of catalyst to produce methane in 1 hour.
[0065] The tungsten trioxide in the catalyst of this invention, by virtue of its layered structure, influences the dynamic characteristics of oxygen vacancies, thereby accelerating the migration of active oxygen and forming a heterojunction with the iron-based component to indirectly optimize the electron transfer path, thereby reducing the reaction energy barrier. This also improves catalyst stability and enhances product selectivity.
[0066] Stability testing of the Fe3O4-WO3 catalyst was conducted: The catalyst preparation and activity evaluation test conditions were identical to those in Examples 1 and 2, with the difference being that recovered catalyst from the previous catalytic cycle was used each time. Multiple parallel tests were conducted for each test to ensure the same catalyst dosage. The results are shown in Table 2. As can be seen from Table 2, the total yield of C1 oxygenates did not decrease significantly after five cycles of use, demonstrating the high stability of the Fe3O4-WO3 catalyst.
[0067] Table 2 Stability test results of Fe3O4-WO3 catalyst
[0068]
[0069] Figure 1 This is the XRD diagram of the Fe3O4-WO3 composite material. From the figure, it can be seen that the XRD characteristic peaks do not change before and after catalysis. Figure 2 This is the FT-IR graph of the Fe3O4-WO3 composite material. From the figure, it can be seen that the FT-IR characteristic peaks before and after catalysis have not changed.
[0070] Other embodiments of the present invention will readily occur to those skilled in the art after considering the specification and practicing the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of the present invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein. The description and examples are to be considered as exemplary only, with the true scope and spirit of the invention being indicated by the claims.
Claims
1. A method for preparing an iron-based composite catalyst for low-temperature methane oxidation, characterized in that: include: Step 1: In an organic solvent, silicotungstic acid hydrate and ferric nitrate are solvothermally synthesized into a Fe-SiW precursor; Step 2: Treat the Fe-SiW precursor Fe3O4-WO3 composite material through hydrogen process.
2. The method for preparing an iron-based composite material catalyst for low-temperature methane oxidation according to claim 1, characterized in that: Step 1 includes: Dissolving silicotungstic acid hydrate in Fe(NO3)3 ethanol solution to obtain a mixed system; Oleylamine and n-hexane are added to the mixed system, and after heating in a sealed state for reaction, the temperature is lowered to room temperature. The obtained product is washed, centrifuged, and dried to obtain a Fe-SiW precursor.
3. The method for preparing an iron-based composite material catalyst for low-temperature methane oxidation according to claim 2, characterized in that: The solvent thermal reaction in step 1 is carried out in a high-pressure reactor, the heating reaction temperature is 140° C., and the reaction time is 4 h.
4. The method for preparing an iron-based composite material catalyst for low-temperature methane oxidation according to claim 2, characterized in that: The obtained product was washed with ethanol, centrifuged twice at 9000 rpm, each time for 5 min, and dried in vacuum at 60° C. for 8 h.
5. The method for preparing an iron-based composite material catalyst for low-temperature methane oxidation according to claim 1, characterized in that: Step 2 includes: The Fe-SiW precursor was ground and placed in a porcelain boat and tube furnace; The ground Fe-SiW precursor was calcined in a hydrogen-argon mixed atmosphere, and the sample was taken out after natural cooling to obtain a Fe3O4-WO3 composite material.
6. The method for preparing an iron-based composite material catalyst for low-temperature methane oxidation according to claim 5, characterized in that: The calcination conditions are: calcination at a temperature of 550° C., a heating rate of 10° C. / min, and calcination for 2 hours.
7. The method for preparing an iron-based composite material catalyst for low-temperature methane oxidation according to claim 5, characterized in that: During calcination, the ratio of hydrogen and argon mixed gas introduced was 5% H2 / 95% Ar, and the gas flow rate was 50 mL / min.
8. The composite material catalyst prepared by the preparation method according to any one of claims 1 to 7, characterized in that: The catalyst is an iron-based polyacid composite material.
9. The use of the catalyst according to claim 8, characterized in that The composite material is used for low-temperature oxidation of methane to prepare C1 oxygen-containing compounds.
10. The use according to claim 9, characterized in that: The composite catalyst and hydrogen peroxide solution are added to a high-temperature and high-pressure reactor. After replacing the gas in the reactor with methane, 3MPa of methane is filled in. After heating to 40-100°C, stirring is started. After catalytic reaction, a liquid C1 oxygen-containing product is obtained. The hydrogen peroxide concentration is 0.75-1.5 mol / L, and the catalytic reaction time is 5 minutes to 1 hour among the controlled variables.