Method for preparing high-purity carbon nanotubes by alloy catalytic methane cracking
Nickel-based alloy catalysts were prepared by electrospinning, which solved the problems of easy catalyst deactivation and low carbon nanotube purity, and achieved the synthesis of high-purity, highly graphitized carbon nanotubes suitable for lithium-ion battery electrodes.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-31
- Publication Date
- 2026-04-14
AI Technical Summary
Existing catalytic systems suffer from catalyst deactivation, low carbon nanotube purity, and difficulty in morphology control during methane cracking, which limits their application in fields requiring high consistency.
Nickel-based alloy precursor fibers were prepared by electrospinning and then heat-treated to form a nickel-based alloy catalyst with high specific surface area and porosity. This catalyst was used to catalyze the methane cracking reaction and to regulate the nucleation and growth process of carbon nanotubes.
The synthesis of carbon nanotubes with high graphitization degree, high purity, and consistent structure has been achieved, which improves catalytic activity and product selectivity, making them suitable as conductive additives for high-performance lithium-ion battery electrodes.
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Figure CN121849922A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a method for preparing high-purity carbon nanotubes. Background Technology
[0002] In recent years, carbon nanotubes (CNFs) have been extensively studied due to their unique hollow structure. They possess excellent electrical and thermal conductivity, mechanical properties, and biocompatibility, are easily functionalized, and are suitable for large-scale preparation and application in various technological fields, such as conductive agents for lithium-ion battery electrodes and reinforcements for composite materials. Especially in lithium-ion batteries, high-purity, highly graphitized carbon nanotubes, as conductive additives, can significantly improve the conductive network and structural stability of the electrode, thereby improving the rate performance and cycle life of the battery. However, existing carbon nanotube preparation methods are usually accompanied by high carbon emissions. For example, without considering purification and surface functionalization processes, the carbon footprint of carbon nanotube production can reach 21.1–47.1 tCO2 / t. Catalytic methane cracking (CMD) provides a feasible way to reduce the carbon footprint. Methane, as a typical hydrocarbon, decomposes to produce only hydrogen and solid carbon without direct CO2 emissions. Furthermore, by regulating the reaction system, the growth rate and nucleation site density of carbon nanotubes can be controlled; therefore, high-purity, structurally controllable carbon nanotubes can be produced using methane cracking.
[0003] Catalysts play a crucial role in the CMD reaction, but existing catalytic systems still have significant limitations. Traditional transition metal catalysts such as Ni and Co exhibit insufficient activity and stability in the high-temperature environment of the CMD reaction, and are prone to rapid deactivation due to carbon supersaturation deposition. Furthermore, the carbon products generated in the CMD reaction are closely related to the structure and properties of the catalyst; the generated carbon nanotubes often coexist with byproducts such as amorphous carbon, carbon fibers, and filamentous carbon, resulting in low product purity. This lack of purity and structural defects severely restricts the application of carbon nanotubes in fields with extremely high requirements for material consistency. Moreover, the performance of carbon nanotubes is highly dependent on their microstructure, and existing catalyst preparation techniques (such as impregnation methods) struggle to precisely control the size, dispersion, and alloying degree of active metal nanoparticles. Without forming a uniform and stable alloy phase, it is difficult to effectively regulate key structural features of carbon nanotubes, such as the degree of graphitization. Therefore, developing a novel alloy catalyst and preparation process with long-lasting catalytic stability, high selective growth capability, and precise control over product morphology is crucial for achieving the preparation of high-purity, high-quality carbon nanotubes via methane cracking. Summary of the Invention
[0004] The purpose of this invention is to solve the problems of easy catalyst deactivation, low purity of carbon nanotubes and difficulty in morphology control in existing catalytic systems for catalytic methane cracking, which seriously restricts their application in fields with extremely high requirements for carbon nanotube consistency. The invention provides a method for preparing high-purity carbon nanotubes by alloy-catalyzed methane cracking.
[0005] A method for preparing high-purity carbon nanotubes by alloy-catalyzed methane cracking, specifically comprising the following steps:
[0006] I. Preparation of nickel-based alloy precursor fibers by electrospinning:
[0007] ① Add polyvinylpyrrolidone to N,N-dimethylformamide and stir to obtain a polymer solution;
[0008] ② First, nickel nitrate hexahydrate is added to the polymer solution, followed by at least one metal nitrate from Cr, Co, Cu, In, and Al. The mixture is stirred at room temperature to obtain a precursor solution.
[0009] ③ The precursor solution is electrospun to obtain nickel-based alloy precursor fibers;
[0010] II. Heat treatment of nickel-based alloy precursor fibers:
[0011] The nickel-based alloy precursor fiber was vacuum dried and then placed in a vacuum tube furnace. It was heated to the heat treatment temperature in a hydrogen-argon mixture and held at that temperature until the temperature dropped to room temperature to obtain the nickel-based alloy catalyst.
[0012] III. Nickel-based alloy catalysts for methane cracking:
[0013] Nickel-based alloy catalysts were used as catalysts for methane cracking. The conditions for the methane cracking reaction were: under standard atmospheric pressure, the reaction temperature was 700℃~900℃, the CH4 gas flow rate was 6mL / min~60mL / min, and the protective gas Ar flow rate was 10mL / min~100mL / min, to obtain high-purity carbon nanotubes.
[0014] The principle of this invention:
[0015] This invention combines electrospinning technology to spin catalyst precursor solutions, forming nickel-based alloy precursor fibers with high specific surface area, high porosity, and controllable fiber arrangement. This preparation process not only enhances the catalytic activity of the catalyst in the CMD reaction but also effectively regulates the nucleation and growth process of carbon nanotubes, thereby achieving highly selective synthesis of carbon nanotubes with high graphitization, high purity, and consistent structure. This invention combines electrospinning-assisted catalyst preparation technology with the CMD reaction, providing a reliable method for the controllable preparation of high-quality carbon nanotubes.
[0016] The significant advantages of this invention compared to existing technologies are:
[0017] I. This invention synthesizes nickel-based alloy precursor fibers through electrospinning, which have high specific surface area, high porosity and regular and uniform fiber structure, effectively overcoming the structural defects of catalysts prepared by traditional coprecipitation method, such as wide particle size distribution and easy agglomeration, and providing more active sites for catalytic reactions.
[0018] Second, the synthesis method of the nickel-based alloy catalyst provided by this invention is simple, easy to mass-produce, and the operation process is safe;
[0019] III. This invention synthesizes a nickel-based alloy catalyst using electrospinning technology. When applied to the CMD reaction, it exhibits high activity at 800℃, with a methane conversion rate >85%.
[0020] IV. The nickel-based alloy catalyst prepared by electrospinning in this invention, when applied to the CMD reaction, yields carbon products with a high degree of graphitization and exhibits high Ig in the Raman spectrum. D / I G With a value of only 0.34, it exhibits good carbon structural order; it is particularly suitable as a conductive additive for high-performance lithium-ion battery electrodes, and is expected to significantly improve the overall performance of the battery.
[0021] V. The nickel-based alloy catalyst prepared by electrospinning technology in this invention, when applied to the CMD reaction, produces carbon products with a typical hollow tubular structure, which are carbon nanotubes with high purity and consistent morphology. Attached Figure Description
[0022] Figure 1 The methane conversion rate at 800°C in the CMD reaction is compared between the Ni-Co alloy catalyst prepared by co-precipitation method in Comparative Example 1 and the Ni-Co alloy catalyst prepared by electrospinning method in Example 1.
[0023] Figure 2 The image shows a SEM image of the Ni-Co alloy catalyst prepared by electrospinning in Example 1.
[0024] Figure 3 Raman spectra of the products after carbon separation and purification following CMD reaction of the Ni-Co alloy catalyst prepared by co-precipitation method in Comparative Example 1, the NiIn alloy catalyst prepared by co-precipitation method in Comparative Example 2, and the NiCo alloy catalyst prepared by electrospinning method in Example 1.
[0025] Figure 4 The left image is a SEM image of the product carbon separation and purification after CMD reaction of the Ni-Co alloy catalyst prepared by co-precipitation method in Example 1. The right image is a SEM image of the product carbon separation and purification after CMD reaction of the Ni-Co alloy catalyst prepared by electrospinning method in Example 1.
[0026] Figure 5This is a TEM image of the carbon separation and purification product of the Ni-Co alloy catalyst prepared by electrospinning in Example 1 after CMD reaction;
[0027] Figure 6 This is a mapping diagram of the carbon separation and purification of the Ni-Co alloy catalyst prepared by electrospinning in Example 1 after CMD reaction;
[0028] Figure 7 The images shown are HRTEM and SAED images of the carbon separation and purification products of the Ni-Co alloy catalyst prepared by electrospinning in Example 1 after CMD reaction. Detailed Implementation
[0029] Specific Implementation Method 1: This implementation method is a method for preparing high-purity carbon nanotubes by alloy-catalyzed methane cracking, specifically prepared according to the following steps:
[0030] I. Preparation of nickel-based alloy precursor fibers by electrospinning:
[0031] ① Add polyvinylpyrrolidone to N,N-dimethylformamide and stir to obtain a polymer solution;
[0032] ② First, nickel nitrate hexahydrate is added to the polymer solution, followed by at least one metal nitrate from Cr, Co, Cu, In, and Al. The mixture is stirred at room temperature to obtain a precursor solution.
[0033] ③ The precursor solution is electrospun to obtain nickel-based alloy precursor fibers;
[0034] II. Heat treatment of nickel-based alloy precursor fibers:
[0035] The nickel-based alloy precursor fiber was vacuum dried and then placed in a vacuum tube furnace. It was heated to the heat treatment temperature in a hydrogen-argon mixture and held at that temperature until the temperature dropped to room temperature to obtain the nickel-based alloy catalyst.
[0036] III. Nickel-based alloy catalysts for methane cracking:
[0037] Nickel-based alloy catalysts were used as catalysts for methane cracking. The conditions for the methane cracking reaction were: under standard atmospheric pressure, the reaction temperature was 700℃~900℃, the CH4 gas flow rate was 6mL / min~60mL / min, and the protective gas Ar flow rate was 10mL / min~100mL / min, to obtain high-purity carbon nanotubes.
[0038] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that: the mass ratio of polyvinylpyrrolidone to N,N-dimethylformamide in step one ① is (0.5g~10g):(1mL~200mL); the stirring speed in step one ① is 100r / min~600r / min, and the stirring time is 0.5h~2h. Other steps are the same as in Specific Implementation Method One.
[0039] Specific Implementation Method 3: This implementation method differs from Specific Implementation Method 1 or 2 in that the mass ratio of nickel nitrate hexahydrate mentioned in step 1 ② to the volume ratio of N,N-dimethylformamide mentioned in step 1 ① is (0.1g~50.0g):(1mL~200mL). The other steps are the same as in Specific Implementation Method 1 or 2.
[0040] Specific Implementation Method Four: The difference between this implementation method and Specific Implementation Methods One to Three is that the mass ratio of the metal nitrate mentioned in step one ② to the volume ratio of N,N-dimethylformamide mentioned in step one ① is (0.05g~10g):(1mL~200mL). The other steps are the same as in Specific Implementation Methods One to Three.
[0041] Specific Implementation Method Five: This implementation method differs from Specific Implementation Methods One to Four in that the stirring speed in step one, step two, is 100 r / min to 600 r / min, and the stirring time is 10 h to 20 h. The other steps are the same as in Specific Implementation Methods One to Four.
[0042] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in that the electrospinning process described in step one ③ is as follows: using a 24-gauge needle, a flow rate of 10μL / min to 30μL / min, a working voltage of 10kV to 20kV, a distance of 5cm to 30cm between the injection pump and the receiver, and a working time of 8h to 12h. The other steps are the same as in Specific Implementation Methods One to Five.
[0043] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods One to Six in that: the vacuum drying temperature in step two is 40℃~80℃, and the vacuum drying time is 10h~14h; the heating rate in step two is 1℃ / min~10℃ / min. Other steps are the same as in Specific Implementation Methods One to Six.
[0044] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Methods One to Seven in that the volume ratio of hydrogen to argon in the hydrogen-argon mixture described in step two is 5:95. The other steps are the same as in Specific Implementation Methods One to Seven.
[0045] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods One to Eight in that the heat treatment temperature in step two is 400℃~600℃. The other steps are the same as in Specific Implementation Methods One to Eight.
[0046] Specific Implementation Method Ten: The difference between this implementation method and Specific Implementation Methods One to Nine is that the heat preservation time in step two is 1 hour to 3 hours. The other steps are the same as in Specific Implementation Methods One to Nine.
[0047] The beneficial effects of the present invention are verified using the following embodiments:
[0048] Example 1: A method for preparing high-purity carbon nanotubes by alloy-catalyzed methane cracking, specifically comprising the following steps:
[0049] I. Preparation of nickel-based alloy precursor fibers by electrospinning:
[0050] ① Add 1.5g of polyvinylpyrrolidone (PVP) to 10mL of N,N-dimethylformamide (DMF) and stir at 400r / min for 1h to obtain a polymer solution;
[0051] ② First, add 1.5g of nickel nitrate hexahydrate (Ni(NO3)2·6H2O) to the polymer solution, then add 0.6g of cobalt nitrate hexahydrate (Co(NO3)2·6H2O), and then stir at 400r / min for 14h at room temperature to obtain the precursor solution;
[0052] ③ Pour the precursor solution into the electrospinning syringe, install the syringe into the electrospinning injection pump to perform electrospinning, and obtain nickel-based alloy precursor fibers.
[0053] The electrospinning process described in step 1③ is as follows: using a No. 24 needle, a flow rate of 20μL / min, a working voltage of 19.5kV, a distance of 15cm between the injection pump and the receiver, and a working time of 9h.
[0054] II. Heat treatment of nickel-based alloy precursor fibers:
[0055] The nickel-based alloy precursor fiber was vacuum dried at 60℃ for 12h, and then placed in a vacuum tube furnace. The temperature was increased from room temperature to 500℃ in a hydrogen-argon mixture at a heating rate of 1℃ / min, and held for 2h. After the temperature dropped to room temperature, the Ni-Co alloy catalyst (denoted as NiCo-f3) was obtained.
[0056] In step two, the volume ratio of hydrogen to argon in the hydrogen-argon mixture is 5:95.
[0057] III. Nickel-based alloy catalysts for methane cracking:
[0058] Under standard atmospheric pressure, the Ni-Co alloy catalyst was placed in a fixed-bed reactor with a catalyst bed height of 0.5 cm. After connecting the reactor, argon gas was introduced at a flow rate of 100 mL / min, and the temperature was raised to 800 °C. CH4 gas (feed gas) was introduced at a flow rate of 6 mL / min to initiate the catalytic methane cracking reaction for 1 hour. After the catalytic methane cracking reaction was completed, heating was stopped, and high-purity argon gas at a flow rate of 100 mL / min was used to replace the feed gas. The reactor was purged for 20 minutes, and then the Ar flow rate was reduced to 20 mL / min and maintained until the temperature dropped to 40 °C. The catalyst after the reaction was removed from the reaction tube and immersed in aqua regia to separate the catalyst from the carbon products. After thorough washing and drying, pure carbon products were obtained and characterized for analysis.
[0059] Comparing with Example 1: The method for preparing high-purity carbon nanotubes using a NiCo alloy catalyst prepared by co-precipitation is specifically prepared according to the following steps:
[0060] I. Preparation of NiCo alloy catalysts by co-precipitation method:
[0061] ① Dissolve 2.0g Ni(NO3)2·6H2O and 0.6g Co(NO3)2·6H2O in 30mL of deionized water, and denote this as solution A; dissolve 1.0g C2H2O4·2H2O in 30mL of deionized water, and denote this as solution B; titrate solution B into solution A using a constant pressure burette (tipping rate is 2mL / min), and stir magnetically for 60min during and after titration; transfer the suspension to a stainless steel autoclave lined with polytetrafluoroethylene, and maintain it at 120℃ for 12h. After cooling to room temperature, a dark red precipitate is obtained; centrifuge the obtained precipitate, wash it three times each with deionized water and ethanol, and place it in a vacuum drying oven at 60℃ for 24h. The resulting dark red powder is the Ni-Co alloy precursor;
[0062] ② The alloy particles were synthesized by heating the Ni-Co alloy precursor powder prepared in a CH4-Ar mixed flow (CH4 to Ar flow rate ratio of 1) at a total flow rate of 40 mL / min. The precursor was heated to 450℃ and maintained for 30 min to dehydrate and decompose the Ni-Co alloy precursor into a Ni-Co alloy catalyst. The product was named NiCo-1.
[0063] II. Catalytic methane cracking reaction:
[0064] Under standard atmospheric pressure, the Ni-Co alloy catalyst was placed in a fixed-bed reactor with a catalyst bed height of 0.5 cm. After connecting the reactor, argon gas was introduced at a flow rate of 100 mL / min, and the temperature was raised to 800 °C. CH4 gas (feed gas) was introduced at a flow rate of 6 mL / min to initiate the catalytic methane cracking reaction for 1 hour. After the catalytic methane cracking reaction was completed, heating was stopped, and high-purity argon gas at a flow rate of 100 mL / min was used to replace the feed gas. The reactor was purged for 20 minutes, and then the Ar flow rate was reduced to 20 mL / min and maintained until the temperature dropped to 40 °C. The catalyst after the reaction was removed from the reaction tube and immersed in aqua regia to separate the catalyst from the carbon products. After thorough washing and drying, pure carbon products were obtained and characterized for analysis.
[0065] Comparative Example 2: The method for preparing high-purity carbon nanotubes using NiIn alloy catalyst prepared by co-precipitation is specifically prepared according to the following steps:
[0066] I. Preparation of NiIn alloy catalysts by co-precipitation method:
[0067] ① Dissolve 2.0g Ni(NO3)2·6H2O and 0.6g In(NO3)3·H2O in 30mL of deionized water, and denote this as solution A; dissolve 1.2g C2H2O4·2H2O in 30mL of deionized water, and denote this as solution B; slowly titrate solution B into solution A using a constant pressure burette (tipping speed is 2mL / min), and magnetically stir for 60min during and after titration; transfer the suspension to a stainless steel autoclave lined with polytetrafluoroethylene, and maintain it at 120℃ for 12h. After cooling to room temperature, a light blue precipitate is obtained; centrifuge the obtained precipitate, wash it three times each with deionized water and ethanol, and place it in a vacuum drying oven at 60℃ for 24h. The resulting light blue powder is the Ni-In alloy precursor;
[0068] ② The alloy particles were synthesized by heating the Ni-In alloy precursor powder prepared in a CH4-Ar mixed flow (CH4 to Ar flow rate ratio of 1) at a total flow rate of 40 mL / min. The precursor was heated to 450℃ and maintained for 30 min to dehydrate and decompose the Ni-In alloy precursor into a Ni-In alloy catalyst. The product was named NiIn-2.
[0069] II. Catalytic methane cracking reaction:
[0070] Under standard atmospheric pressure, the Ni-In alloy catalyst was placed in a fixed-bed reactor with a catalyst bed height of 0.5 cm. After connecting the reactor, argon gas was introduced at a flow rate of 100 mL / min, and the temperature was raised to 800 °C. CH4 gas (feed gas) was introduced at a flow rate of 6 mL / min to initiate the catalytic methane cracking reaction for 1 hour. After the catalytic methane cracking reaction was completed, heating was stopped, and high-purity argon gas at a flow rate of 100 mL / min was used to replace the feed gas. The reactor was purged for 20 minutes, and then the Ar flow rate was reduced to 20 mL / min and maintained until the temperature dropped to 40 °C. The catalyst after the reaction was removed from the reaction tube and immersed in aqua regia to separate the catalyst from the carbon products. After thorough washing and drying, pure carbon products were obtained and characterized for analysis.
[0071] Figure 1 The methane conversion rate at 800°C in the CMD reaction is compared between the Ni-Co alloy catalyst prepared by co-precipitation method in Comparative Example 1 and the Ni-Co alloy catalyst prepared by electrospinning method in Example 1.
[0072] from Figure 1 It can be seen that the methane conversion rate of the Ni-Co alloy catalyst prepared by electrospinning under the same conditions is 81.42%, which is significantly higher than the 33.07% of the Ni-Co alloy catalyst prepared by coprecipitation in Control Example 1. This result shows that the advantages of electrospinning technology in controlling the microstructure and dispersibility of the catalyst effectively improve the catalytic activity of the Ni-Co alloy.
[0073] Figure 2 The image shows a SEM image of the Ni-Co alloy catalyst prepared by electrospinning in Example 1.
[0074] from Figure 2 It can be seen that the Ni-Co alloy catalyst prepared by electrospinning in Example 1 has a honeycomb structure.
[0075] Figure 3 Raman spectra of the products after carbon separation and purification following CMD reaction of the Ni-Co alloy catalyst prepared by co-precipitation method in Comparative Example 1, the NiIn alloy catalyst prepared by co-precipitation method in Comparative Example 2, and the NiCo alloy catalyst prepared by electrospinning method in Example 1.
[0076] from Figure 3 It can be seen that the product carbon corresponding to the NiCo alloy catalyst prepared by electrospinning in Example 1 has I D / I GThe value is the lowest, only 0.34, indicating that the carbon product has a high degree of structural order, few defects, and high graphitization. This result directly proves the advantages of electrospinning technology in controlling the microstructure of catalysts, effectively overcoming the limitations of traditional co-precipitation methods in preparing highly graphitized carbon nanotubes.
[0077] Figure 4 The left image is a SEM image of the product carbon separation and purification after CMD reaction of the Ni-Co alloy catalyst prepared by co-precipitation method in Example 1. The right image is a SEM image of the product carbon separation and purification after CMD reaction of the Ni-Co alloy catalyst prepared by electrospinning method in Example 1.
[0078] from Figure 4 It can be seen that the carbon product of the Ni-Co alloy catalyst prepared by the co-precipitation method in Example 1 is short and coarse, and has an intertwined filamentous structure. The carbon product of the Ni-Co alloy catalyst prepared by the electrospinning method in Example 1 has a curved, intertwined filamentous structure, which is thin and long, with a diameter distribution of approximately 55±0.5~95±0.5 nm and a length of approximately 4±0.5~18±0.5 μm, corresponding to an aspect ratio range of 45:1~180:1.
[0079] Figure 5 This is a TEM image of the carbon separation and purification product of the Ni-Co alloy catalyst prepared by electrospinning in Example 1 after CMD reaction;
[0080] from Figure 5 It can be seen that the carbon products exhibit a typical hollow tubular structure, which is a well-crystallized carbon nanotube. Statistical measurements show that its wall thickness is approximately 9.24±0.2 nm, and its inner diameter ranges from 50±0.5 to 80±0.5 nm.
[0081] EDS analysis was performed on the carbon products separated and purified in Example 1, see [see details]. Figure 6 As shown;
[0082] Figure 6 This is a mapping diagram of the carbon separation and purification of the Ni-Co alloy catalyst prepared by electrospinning in Example 1 after CMD reaction;
[0083] Mapping results showed that the purified sample had a uniform carbon distribution and no obvious alloy catalyst residue was observed. Table 1 shows the EDS elemental analysis results, indicating a carbon mass fraction as high as 99.98%, further confirming that this purification process can effectively remove catalyst impurities and obtain high-purity carbon nanotube products.
[0084] Figure 7The images shown are HRTEM and SAED images of the Ni-Co alloy catalyst prepared by electrospinning in Example 1 after carbon separation and purification of the product by CMD reaction.
[0085] Figure 7 The HRTEM images show that the product has clear lattice fringes with a lattice spacing of about 0.340 nm, which is basically consistent with the (002) interplanar spacing (0.339 nm) of ideal graphite. Figure 7 The SAED pattern shows diffraction rings corresponding to the (002) and (100) crystal planes of carbon, indicating that the carbon product has a polycrystalline structure.
[0086] Table 1
[0087]
Claims
1. A method for preparing high-purity carbon nanotubes by alloy-catalyzed methane cracking, characterized in that... The method specifically involves the following steps: I. Preparation of nickel-based alloy precursor fibers by electrospinning: ① Add polyvinylpyrrolidone to N,N-dimethylformamide and stir to obtain a polymer solution; ② First, nickel nitrate hexahydrate is added to the polymer solution, followed by at least one metal nitrate from Cr, Co, Cu, In, and Al. The mixture is stirred at room temperature to obtain a precursor solution. ③ The precursor solution is electrospun to obtain nickel-based alloy precursor fibers; II. Heat treatment of nickel-based alloy precursor fibers: The nickel-based alloy precursor fiber was vacuum dried and then placed in a vacuum tube furnace. It was heated to the heat treatment temperature in a hydrogen-argon mixture and held at that temperature until the temperature dropped to room temperature to obtain the nickel-based alloy catalyst. III. Nickel-based alloy catalysts for methane cracking: Nickel-based alloy catalysts were used as catalysts for methane cracking. The conditions for the methane cracking reaction were: under standard atmospheric pressure, the reaction temperature was 700℃~900℃, the CH4 gas flow rate was 6mL / min~60mL / min, and the protective gas Ar flow rate was 10mL / min~100mL / min, to obtain high-purity carbon nanotubes.
2. The method for preparing high-purity carbon nanotubes by alloy-catalyzed methane cracking according to claim 1, characterized in that... The mass ratio of polyvinylpyrrolidone to N,N-dimethylformamide in step 1① is (0.5g~10g):(1mL~200mL); the stirring speed in step 1① is 100r / min~600r / min, and the stirring time is 0.5h~2h.
3. The method for preparing high-purity carbon nanotubes by alloy-catalyzed methane cracking according to claim 1, characterized in that... The mass ratio of nickel nitrate hexahydrate mentioned in step 1② to the volume ratio of N,N-dimethylformamide mentioned in step 1① is (0.1g~50.0g):(1mL~200mL).
4. The method for preparing high-purity carbon nanotubes by alloy-catalyzed methane cracking according to claim 1, characterized in that... The mass ratio of the metal nitrate mentioned in step 1 ② to the volume ratio of N,N-dimethylformamide mentioned in step 1 ① is (0.05g~10g):(1mL~200mL).
5. The method for preparing high-purity carbon nanotubes by alloy-catalyzed methane cracking according to claim 1, characterized in that... The stirring speed mentioned in step 1② is 100r / min to 600r / min, and the stirring time is 10h to 20h.
6. The method for preparing high-purity carbon nanotubes by alloy-catalyzed methane cracking according to claim 1, characterized in that... The electrospinning process described in step 1③ is as follows: using a No. 24 needle, a flow rate of 10μL / min~30μL / min, a working voltage of 10kV~20kV, a distance of 5cm~30cm between the injection pump and the receiver, and a working time of 8h~12h.
7. The method for preparing high-purity carbon nanotubes by alloy-catalyzed methane cracking according to claim 1, characterized in that... The vacuum drying temperature in step two is 40℃~80℃, and the vacuum drying time is 10h~14h; the heating rate in step two is 1℃ / min~10℃ / min.
8. The method for preparing high-purity carbon nanotubes by alloy-catalyzed methane cracking according to claim 1, characterized in that... In step two, the volume ratio of hydrogen to argon in the hydrogen-argon mixture is 5:
95.
9. The method for preparing high-purity carbon nanotubes by alloy-catalyzed methane cracking according to claim 1, characterized in that... The heat treatment temperature mentioned in step two is 400℃~600℃.
10. The method for preparing high-purity carbon nanotubes by alloy-catalyzed methane cracking according to claim 1, characterized in that... The heat preservation time mentioned in step two is 1 to 3 hours.