A nanoscale multi-metallic catalyst, single-walled carbon nanotubes and a method for preparing the same

Abstract

The application discloses a preparation method of a nanoscale multi-metal catalyst, which comprises the following steps: mixing ferric nitrate, magnesium nitrate, lanthanum nitrate, gadolinium nitrate, ammonium heptamolybdate and citric acid with water to obtain a concentrated solution by heating and concentrating; mixing ethylenediaminetetraacetic acid, ammonia water and urea to obtain an ethylenediaminetetraacetic acid solution; mixing the concentrated solution and the ethylenediaminetetraacetic acid solution to obtain a mixed solution by stirring, adding a surfactant into the mixed solution and calcining, and finally roasting. The ferric nitrate, the magnesium nitrate, the lanthanum nitrate and the gadolinium nitrate are mixed, a complexing agent is added, a solution is prepared by using a complexing method, the solution is concentrated, calcined and sieved, and finally the nanoscale multi-metal catalyst is formed. The catalyst prepared by the method has a uniform particle size. The catalyst prepared by the method is combined with a plasma technology to prepare a single-walled carbon nanotube, and the single-walled carbon nanotube (without treatment) has a high ratio, a large IG / ID and a small powder resistance.

Description

A nanoscale multi-metal catalyst, single-walled carbon nanotubes and their preparation method Technical Field

[0001] This invention relates to a nanoscale multi-metal catalyst, a single-walled carbon nanotube and its preparation method, belonging to the field of materials technology. Background Technology

[0002] Single-walled carbon nanotubes (SWCNTs or SWNTs) are composed entirely of carbon atoms. Their geometry can be considered as a single layer of graphene rolled up. The structure determines the properties, thus SWCNTs possess excellent electronic, mechanical, and other properties. They have wide applications in supercapacitors, catalyst supports, hydrogen storage, carbide-ion batteries, and functional coatings.

[0003] The main methods for preparing single-walled carbon nanotubes include arc ablation, laser evaporation, and chemical vapor deposition. The currently accepted growth mechanism is as follows: at high temperatures, the carbon source decomposes on the surface of a transition metal catalyst, and the resulting carbon dissolves in the catalyst particles. As the carbon continues to dissolve, when supersaturation is reached, it precipitates from the metal to form carbon nanotubes.

[0004] To achieve high yield, high purity, high quality, and structural control in the growth of single-walled carbon nanotubes (SHU), catalysts should possess high catalytic activity, high-temperature thermal stability, high carbon solubility, and high carbon diffusivity. While single catalyst systems each have their own characteristics, they often fail to simultaneously meet these requirements, necessitating the development of multi-component catalyst systems. Firstly, multi-component catalysts exhibit high catalytic decomposition activity for hydrocarbon molecules, enabling the growth of SHU at lower temperatures and showcasing the energy differences between different chiralities. Secondly, the higher melting point and thermal stability of multi-component catalysts facilitate the nucleation of specific chiral carbon nanotubes through lattice matching and maintain a stable growth front interface during the growth process. Simultaneously, the high carbon solubility and high carbon diffusivity of multi-component catalysts allow for the acquisition of carbon nanotubes in high yields.

[0005] Since multi-metal catalysts are typically prepared by impregnation, they inevitably agglomerate and grow under high-temperature conditions. Larger catalyst particles cannot achieve carbon supersaturation in the reaction zone, thus hindering carbon nanotube growth. Smaller catalyst particles, on the other hand, easily achieve carbon supersaturation. Therefore, on these smaller particles, carbon source precipitates through carbon saturation, leading to the growth of single-walled carbon nanotubes. However, even smaller catalyst particles may be coated with carbon from the decomposition of the carbon source before the carbon is fully incorporated, resulting in catalyst deactivation and preventing carbon nanotube growth. This leads to low yields and low efficiency of the grown single-walled carbon nanotubes. G / I D Low.

[0006] In summary, the goal is to develop a nanoscale multi-metal catalyst and apply it to the preparation of single-walled carbon nanotubes to achieve high yield and high Ig content. G / I D Single-walled carbon nanotubes are essential. Summary of the Invention

[0007] To address the aforementioned problems, the present invention aims to provide a nanoscale multi-metal catalyst and its preparation method. This involves preparing a multi-metal composite solution using a complexation method, followed by concentration, calcination, and sieving to form the nanoscale multi-metal catalyst. The present invention also provides a method for preparing single-walled carbon nanotubes. Using the nanoscale multi-metal catalyst prepared in this invention as the catalyst, single-walled carbon nanotubes are prepared using plasma arc technology to improve the yield and Ig of single-walled carbon nanotubes. G / I D value.

[0008] This invention first provides a method for preparing nanoscale multi-metal catalysts, comprising the following steps:

[0009] (1) Take ferric nitrate, magnesium nitrate, lanthanum nitrate, gadolinium nitrate, ammonium heptamolybdate and citric acid, mix them evenly with water, heat and concentrate to obtain concentrated solution;

[0010] (2) Mix ethylenediaminetetraacetic acid, ammonia and urea evenly to obtain an ethylenediaminetetraacetic acid solution;

[0011] (3) Mix the concentrated solution from step (1) and the ethylenediaminetetraacetic acid solution from step (2), and stir to make them evenly mixed to obtain a mixture;

[0012] (4) Add surfactant to the mixture obtained in step (3), stir and mix evenly, and then place the mixture in a muffle furnace for calcination to obtain powder;

[0013] (5) The powder obtained in step (4) is placed in a tube furnace and calcined under an inert atmosphere to obtain a nano-scale multi-metal catalyst.

[0014] In one embodiment of the present invention, in step (1), the mass ratio of ferric nitrate, magnesium nitrate, lanthanum nitrate, and gadolinium nitrate is 90-97:1-5:1-3:1-2.

[0015] In one embodiment of the present invention, in step (1), the mass ratio of the mixture of ferric nitrate, magnesium nitrate, lanthanum nitrate, and gadolinium nitrate to ammonium heptamolybdate is 85-99:1-15.

[0016] In one embodiment of the present invention, in step (1), the mass ratio of the mixture of ferric nitrate, magnesium nitrate, lanthanum nitrate, gadolinium nitrate, and ammonium heptamolybdate to citric acid is 60-50:40-50.

[0017] In one embodiment of the present invention, in step (1), the mass ratio of the mixture of ferric nitrate, magnesium nitrate, lanthanum nitrate, gadolinium nitrate, ammonium heptamolybdate and citric acid to water is 80-40:20-60.

[0018] In one embodiment of the present invention, in step (1), water bath heating is used for heating concentration, the heating temperature is 60 to 120°C, the heating time is 1 to 10 hours, and stirring is performed during heating, with a stirring speed of 200 to 800 rpm.

[0019] In one embodiment of the present invention, in step (2), the mass ratio of ethylenediaminetetraacetic acid to ammonia is 5-20:95-80, and the mass fraction of the ammonia is 10-25%.

[0020] In one embodiment of the present invention, in step (2), the mass ratio of ethylenediaminetetraacetic acid to urea is 60-20:40-80.

[0021] In one embodiment of the present invention, in step (3), the volume ratio of the concentrate to the ethylenediaminetetraacetic acid solution is 1-5:5-1, the stirring speed is 400 rpm, and the stirring time is 30 min.

[0022] In one embodiment of the present invention, in step (4), the surfactant is a mixed solution of surfactant and water, wherein the concentration of surfactant in the mixed solution is 4.4%, and the surfactant includes at least one of sodium oleate, octadecylamine, sodium dodecyl sulfate, dodecylamine, and sodium dodecylbenzenesulfonate.

[0023] In one embodiment of the present invention, in step (4), the volume ratio of the surfactant to the mixture is 40-70:60-30, the stirring speed is 200-800 rpm, and the stirring time is 0.5-2 hours.

[0024] In one embodiment of the present invention, in step (4), calcination is carried out in an air atmosphere, the calcination temperature is 200-900°C, and the calcination time is 1-10h.

[0025] In one embodiment of the present invention, in step (4), the powder obtained is a sieved powder, and the sieve used during sieving is 50 to 200 mesh.

[0026] In one embodiment of the present invention, in step (5), the roasting is carried out in three stages. The first stage of roasting is the heating stage, which is carried out in a nitrogen atmosphere, with the temperature rising from 0°C to 200-500°C for 20-50 minutes. In the second stage of roasting, the temperature rises from 200-500°C to 600-900°C for 20-30 minutes. The atmosphere in the second stage is a mixture of nitrogen and hydrogen, wherein the flow ratio of nitrogen to hydrogen is 3:1 to 1:3. The third stage of roasting is the cooling stage, which is carried out in a nitrogen atmosphere.

[0027] In one embodiment of the present invention, in step (5), the nitrogen flow rate in the first roasting stage is 100-1000 sccm; the nitrogen flow rate in the second roasting stage is 300-900 sccm, and the hydrogen flow rate is 100-300 sccm; the nitrogen flow rate in the third roasting stage is 100-1000 sccm.

[0028] The present invention also provides a nanoscale multi-metal catalyst prepared according to the above method.

[0029] The present invention also provides a method for preparing single-walled carbon nanotubes using the above-mentioned nanoscale multi-metal catalyst, comprising the following steps: weighing the above-mentioned catalyst, graphite powder and sulfur, grinding and dispersing them evenly to obtain a mixed powder, loading the powder into a hollow graphite rod, placing the graphite rod at the anode of an electric arc furnace, introducing a mixed gas of argon and hydrogen, and reacting to prepare single-walled carbon nanotubes.

[0030] In one embodiment of the present invention, the mass ratio of catalyst, graphite powder and sulfur is 80-40:15-59:5-1.

[0031] In one embodiment of the present invention, the flow ratio of argon to hydrogen is 3:2. After the mixed gas of argon and hydrogen is introduced, the pressure inside the electric arc furnace is maintained at 20-60 kPa, the reaction current is 50-150 A, the reaction time is 1-5 min, and after the reaction, an inert gas is introduced to atmospheric pressure, and the sample is taken out to obtain single-walled carbon nanotubes.

[0032] Beneficial effects of the present invention

[0033] (1) The present invention mixes ferric nitrate, magnesium nitrate, lanthanum nitrate and gadolinium nitrate, adds a complexing agent, and uses the complexation method to prepare a solution. The solution is then concentrated, calcined and sieved to form a nanoscale multi-metal catalyst. The catalyst prepared by the method of the present invention has a relatively uniform particle size.

[0034] (2) By adding surfactants to suppress the increase in catalyst particle size, and by optimizing the influencing factors such as different metal types and their ratios, foaming agents, pyrolysis temperature, and reduction conditions, the particle size of the prepared nanoscale multi-metal catalyst is controlled within the range of 10nm-100nm.

[0035] (3) Using the catalyst prepared in this invention, combined with plasma technology, single-walled carbon nanotubes are prepared. The resulting single-walled carbon nanotubes (untreated) have a high yield. G / I D Large, powder resistance is small. Attached Figure Description

[0036] Figure 1 shows the SEM image (500 nm) of the nanoscale multi-metal catalyst prepared in Example 1 before reduction.

[0037] Figure 2 shows the SEM spectrum (100 nm) of the nanoscale multi-metal catalyst prepared in Example 1 before reduction.

[0038] Figure 3 shows the SEM spectrum (500 nm) of the nanoscale multi-metal catalyst prepared in Example 1 after reduction.

[0039] Figure 4 shows the SEM spectrum (100 nm) of the nanoscale multi-metal catalyst prepared in Example 1 after reduction.

[0040] Figure 5 shows the SEM image (500 nm) of the single-walled carbon nanotubes prepared in Example 1.

[0041] Figure 6 shows the SEM image (100 nm) of the single-walled carbon nanotubes prepared in Example 1.

[0042] Figure 7 shows the Raman spectrum of the single-walled carbon nanotubes prepared in Example 1.

[0043] Figure 8 shows the SEM image (500 nm) of the nanoscale multi-metal catalyst prepared in Comparative Example 1 before reduction.

[0044] Figure 9 shows the SEM spectrum (200 nm) of the nanoscale multi-metal catalyst prepared in Comparative Example 1 before reduction.

[0045] Figure 10 shows the SEM image (500 nm) of the single-walled carbon nanotubes prepared in Comparative Example 1.

[0046] Figure 11 shows the SEM image (200 nm) of the single-walled carbon nanotubes prepared in Comparative Example 1.

[0047] Figure 12 shows the Raman spectra of single-walled carbon nanotubes prepared in Comparative Example 1. Detailed Implementation

[0048] Example 1

[0049] A method for preparing a nanoscale multi-metal catalyst includes the following steps:

[0050] (1) Weigh out 24.6g of ferric nitrate nonahydrate, 0.78g of magnesium nitrate hexahydrate, 24.69g of anhydrous citric acid, 0.28g of ammonium heptamolybdate, 0.31g of lanthanum nitrate, 0.27g of gadolinium nitrate, and 70.58g of water in sequence, place them in a 250mL beaker and stir to dissolve them, to obtain a solution of the mixture; place the above solution in a 90℃ water bath and heat it with a rotor speed of 400rpm for 2 hours to concentrate it, to obtain a concentrated solution;

[0051] (2) Weigh 18.78g of ethylenediaminetetraacetic acid, 18.78g of ammonia (25wt.%) and 25.06g of urea in sequence, place them in a 250mL beaker, seal and stir at room temperature to dissolve them, and obtain an ethylenediaminetetraacetic acid solution; mix the concentrated solution from step (1) with the ethylenediaminetetraacetic acid solution, set the rotor speed to 400rpm, seal and stir at room temperature for 30min to make them fully mixed and uniform, and obtain a mixed solution;

[0052] (3) Weigh 0.22g of surfactant and 5g of water in sequence, place them in a 50ml beaker and mix them evenly. Pour the mixture into the mixture from step (2) above, set the rotor speed to 400rpm, and stir at room temperature for 30min to mix them evenly and obtain a mixed solution.

[0053] (4) Pour the mixed solution from step (3) into a crucible, place the crucible in a muffle furnace, and calcine at 450°C for 1 hour in an air atmosphere; after cooling, sieve the powder through a 200-mesh sieve for later use.

[0054] (5) Weigh 5g of the sieved powder obtained in step (4), place it in a quartz boat, and place the quartz boat in the middle of an 80mm quartz tube furnace to calcine the powder. The calcine is divided into three stages: the first stage: under a nitrogen atmosphere, the tube furnace is heated from 0℃ to 300℃ for 20 minutes, and the nitrogen flow rate is 300sccm; the second stage: the temperature is increased from 300℃ to 700℃ for 22 minutes, and the gas introduced is a mixture of nitrogen and hydrogen, with a nitrogen flow rate of 300sccm and a hydrogen flow rate of 100sccm; the third stage is the cooling stage, with a nitrogen flow rate of 300sccm. Open the tube furnace lid and allow it to cool naturally to room temperature. After cooling, take it out for use.

[0055] A method for preparing single-walled carbon nanotubes using electric arc furnace plasma technology includes the following steps:

[0056] 2.0g of nanoscale multi-metal catalyst, 3.0g of graphite powder, and 0.05g of sulfur were weighed in a mortar and ground for 5 minutes to disperse evenly. The powder was then loaded into a hollow graphite rod, which was placed at the anode of an electric arc furnace. A mixture of argon and hydrogen was introduced to replace the gas in the electric arc furnace, with a flow ratio of argon to hydrogen of 3:2. The furnace pressure was maintained at 39 kPa, and the current was adjusted to 90 A. The reaction was carried out for 2 minutes, and then an inert gas was introduced to bring the pressure to atmospheric pressure. The sample was then removed to obtain single-walled carbon nanotubes.

[0057] Figures 1-4 show the SEM images of the prepared nanoscale multi-metal catalyst before and after reduction (reduction refers to the reaction in step (5)). As can be seen from the images shown in Figures 1-4, the catalyst particles are uniform in size before and after reduction.

[0058] Figure 7 shows the Raman spectra of the prepared carbon nanotubes, and Table 1 shows the Ig spectra of the carbon nanotubes prepared in Example 2. G / I D Data such as yield and ratio, as shown in Table 1 and Figure 7, indicate that the carbon nanotubes prepared using the method in Example 2 have a higher yield, reaching 15.9 g / h. G / I D The value can reach 60, and the powder resistivity is as low as 15mΩ·cm.

[0059] Example 2

[0060] The difference between Example 2 and Example 1 is that the preparation methods of the nanoscale multi-metal catalyst are different.

[0061] A method for preparing a nanoscale multi-metal catalyst includes the following steps:

[0062] (1) Weigh out 24.6g of ferric nitrate nonahydrate, 0.25g of magnesium nitrate hexahydrate, 24.69g of anhydrous citric acid, 0.28g of ammonium heptamolybdate, 0.253g of lanthanum nitrate, 0.253g of gadolinium nitrate, and 70.58g of water in sequence, place them in a 250mL beaker and stir to dissolve, to obtain a solution of the mixture; place the above solution in a 90℃ water bath and heat it with a rotor speed of 400rpm for 2 hours to concentrate it, to obtain a concentrated solution;

[0063] (2) Weigh 18.78g of ethylenediaminetetraacetic acid, 18.78g of ammonia (25wt.%) and 25.06g of urea in sequence, place them in a 250mL beaker, seal and stir at room temperature to dissolve them, and obtain an ethylenediaminetetraacetic acid solution; mix the concentrated solution from step (1) with the ethylenediaminetetraacetic acid solution, set the rotor speed to 400rpm, seal and stir at room temperature for 30min to make them fully mixed and uniform, and obtain a mixed solution;

[0064] (3) Weigh 0.22g of surfactant and 5g of water in sequence, place them in a 50ml beaker and mix them evenly. Pour the mixture into the mixture from step (2) above, set the rotor speed to 400rpm, and stir at room temperature for 30min to mix them evenly and obtain a mixed solution.

[0065] (4) Pour the mixed solution from step (3) into a crucible, place the crucible in a muffle furnace, and calcine at 450°C for 1 hour in an air atmosphere; after cooling, sieve the powder through a 200-mesh sieve for later use.

[0066] (5) Weigh 5g of the sieved powder obtained in step (4), place it in a quartz boat, and place the quartz boat in the middle of an 80mm quartz tube furnace to calcine the powder. The calcine is divided into three stages: the first stage: under a nitrogen atmosphere, the tube furnace is heated from 0℃ to 300℃ for 20 minutes, and the nitrogen flow rate is 300sccm; the second stage: the temperature is increased from 300℃ to 700℃ for 22 minutes, and the gas introduced is a mixture of nitrogen and hydrogen, with a nitrogen flow rate of 300sccm and a hydrogen flow rate of 100sccm; the third stage is the cooling stage, with a nitrogen flow rate of 300sccm. Open the tube furnace lid and allow it to cool naturally to room temperature. After cooling, take it out for use.

[0067] As can be seen from Table 1, the carbon nanotubes prepared using the method in Example 2 have a high yield, reaching 14.3 g / h. G / I D The value can reach 58, and the powder resistivity is as low as 20mΩ·cm.

[0068] Example 3

[0069] The difference between Example 3 and Example 1 lies in the different preparation methods of the nanoscale multi-metal catalyst.

[0070] A method for preparing a nanoscale multi-metal catalyst includes the following steps:

[0071] (1) Weigh out 24.6g of ferric nitrate nonahydrate, 1.37g of magnesium nitrate hexahydrate, 24.69g of anhydrous citric acid, 0.28g of ammonium heptamolybdate, 0.82g of lanthanum nitrate, 0.545g of gadolinium nitrate, and 70.58g of water in sequence, place them in a 250mL beaker and stir to dissolve them, to obtain a solution of the mixture; place the above solution in a 90℃ water bath and heat it with a rotor speed of 400rpm for 2 hours to concentrate it, to obtain a concentrated solution;

[0072] (2) Weigh 18.78g of ethylenediaminetetraacetic acid, 18.78g of ammonia (25wt.%) and 25.06g of urea in sequence, place them in a 250mL beaker, seal and stir at room temperature to dissolve them, and obtain an ethylenediaminetetraacetic acid solution; mix the concentrated solution from step (1) with the ethylenediaminetetraacetic acid solution, set the rotor speed to 400rpm, seal and stir at room temperature for 30min to make them fully mixed and uniform, and obtain a mixed solution;

[0073] (3) Weigh 0.22g of surfactant and 5g of water in sequence, place them in a 50ml beaker and mix them evenly. Pour the mixture into the mixture from step (2) above, set the rotor speed to 400rpm, and stir at room temperature for 30min to mix them evenly and obtain a mixed solution.

[0074] (4) Pour the mixed solution from step (3) into a crucible, place the crucible in a muffle furnace, and calcine at 450°C for 1 hour in an air atmosphere; after cooling, sieve the powder through a 200-mesh sieve for later use.

[0075] (5) Weigh 5g of the sieved powder obtained in step (4), place it in a quartz boat, and place the quartz boat in the middle of an 80mm quartz tube furnace to calcine the powder. The calcine is divided into three stages: the first stage: under a nitrogen atmosphere, the tube furnace is heated from 0℃ to 300℃ for 20 minutes, and the nitrogen flow rate is 300sccm; the second stage: the temperature is increased from 300℃ to 700℃ for 22 minutes, and the gas introduced is a mixture of nitrogen and hydrogen, with a nitrogen flow rate of 300sccm and a hydrogen flow rate of 100sccm; the third stage is the cooling stage, with a nitrogen flow rate of 300sccm. Open the tube furnace lid and allow it to cool naturally to room temperature. After cooling, take it out for use.

[0076] As can be seen from Table 1, the carbon nanotubes prepared using the method in Example 3 have a high yield, reaching 15.6 g / h. G / I D The value can reach 52, and the powder resistivity is as low as 26mΩ·cm.

[0077] Example 4

[0078] The difference between Example 4 and Example 1 lies in the different preparation methods of the nanoscale multi-metal catalyst.

[0079] A method for preparing a nanoscale multi-metal catalyst includes the following steps:

[0080] (1) Weigh out 24.6g of ferric nitrate nonahydrate, 0.78g of magnesium nitrate hexahydrate, 24.69g of anhydrous citric acid, 1.31g of ammonium heptamolybdate, 0.31g of lanthanum nitrate, 0.27g of gadolinium nitrate, and 70.58g of water in sequence, place them in a 250mL beaker and stir to dissolve them, to obtain a solution of the mixture; place the above solution in a 90℃ water bath and heat it with a rotor speed of 400rpm for 2 hours to concentrate it, to obtain a concentrated solution;

[0081] (2) Weigh 18.78g of ethylenediaminetetraacetic acid, 18.78g of ammonia (25wt.%) and 25.06g of urea in sequence, place them in a 250mL beaker, seal and stir at room temperature to dissolve them, and obtain an ethylenediaminetetraacetic acid solution; mix the concentrated solution from step (1) with the ethylenediaminetetraacetic acid solution, set the rotor speed to 400rpm, seal and stir at room temperature for 30min to make them fully mixed and uniform, and obtain a mixed solution;

[0082] (3) Weigh 0.22g of surfactant and 5g of water in sequence, place them in a 50ml beaker and mix them evenly. Pour the mixture into the mixture from step (2) above, set the rotor speed to 400rpm, and stir at room temperature for 30min to mix them evenly and obtain a mixed solution.

[0083] (4) Pour the mixed solution from step (3) into a crucible, place the crucible in a muffle furnace, and calcine at 450°C for 1 hour in an air atmosphere; after cooling, sieve the powder through a 200-mesh sieve for later use.

[0084] (5) Weigh 5g of the sieved powder obtained in step (4), place it in a quartz boat, and place the quartz boat in the middle of an 80mm quartz tube furnace to calcine the powder. The calcine is divided into three stages: the first stage: under a nitrogen atmosphere, the tube furnace is heated from 0℃ to 300℃ for 20 minutes, and the nitrogen flow rate is 300sccm; the second stage: the temperature is increased from 300℃ to 700℃ for 22 minutes, and the gas introduced is a mixture of nitrogen and hydrogen, with a nitrogen flow rate of 300sccm and a hydrogen flow rate of 100sccm; the third stage is the cooling stage, with a nitrogen flow rate of 300sccm. Open the tube furnace lid and allow it to cool naturally to room temperature. After cooling, take it out for use.

[0085] As can be seen from Table 1, the carbon nanotubes prepared using the method in Example 4 have a high yield, reaching 13.8 g / h. G / I D The value can reach 54, and the powder resistivity is as low as 31mΩ·cm.

[0086] Example 5

[0087] The difference between Example 5 and Example 1 lies in the different preparation methods of the nanoscale multi-metal catalyst.

[0088] A method for preparing a nanoscale multi-metal catalyst includes the following steps:

[0089] (1) Weigh 24.6g of ferric nitrate nonahydrate, 0.78g of magnesium nitrate hexahydrate, 24.69g of anhydrous citric acid, 4.58g of ammonium heptamolybdate, 0.31g of lanthanum nitrate, 0.27g of gadolinium nitrate, and 70.58g of water in sequence, place them in a 250mL beaker and stir to dissolve them, to obtain a solution of the mixture; place the above solution in a 90℃ water bath and heat it with a rotor speed of 400rpm for 2 hours to concentrate it, to obtain a concentrated solution;

[0090] (2) Weigh 18.78g of ethylenediaminetetraacetic acid, 18.78g of ammonia (25wt.%) and 25.06g of urea in sequence, place them in a 250mL beaker, seal and stir at room temperature to dissolve them, and obtain an ethylenediaminetetraacetic acid solution; mix the concentrated solution from step (1) with the ethylenediaminetetraacetic acid solution, set the rotor speed to 400rpm, seal and stir at room temperature for 30min to make them fully mixed and uniform, and obtain a mixed solution;

[0091] (3) Weigh 0.22g of surfactant and 5g of water in sequence, place them in a 50ml beaker and mix them evenly. Pour the mixture into the mixture from step (2) above, set the rotor speed to 400rpm, and stir at room temperature for 30min to mix them evenly and obtain a mixed solution.

[0092] (4) Pour the mixed solution from step (3) into a crucible, place the crucible in a muffle furnace, and calcine at 450°C for 1 hour in an air atmosphere; after cooling, sieve the powder through a 200-mesh sieve for later use.

[0093] (5) Weigh 5g of the sieved powder obtained in step (4), place it in a quartz boat, and place the quartz boat in the middle of an 80mm quartz tube furnace to calcine the powder. The calcine is divided into three stages: the first stage: under a nitrogen atmosphere, the tube furnace is heated from 0℃ to 300℃ for 20 minutes, and the nitrogen flow rate is 300sccm; the second stage: the temperature is increased from 300℃ to 700℃ for 22 minutes, and the gas introduced is a mixture of nitrogen and hydrogen, with a nitrogen flow rate of 300sccm and a hydrogen flow rate of 100sccm; the third stage is the cooling stage, with a nitrogen flow rate of 300sccm. Open the tube furnace lid and allow it to cool naturally to room temperature. After cooling, take it out for use.

[0094] As can be seen from Table 1, the carbon nanotubes prepared using the method in Example 5 have a high yield, reaching 13.1 g / h. G / I D The value can reach 49, and the powder resistivity is as low as 29mΩ·cm.

[0095] Comparative Example 1

[0096] The difference between Comparative Example 1 and Example 1 lies in the different preparation methods of the nanoscale multi-metal catalyst.

[0097] A method for preparing a nanoscale multi-metal catalyst includes the following steps:

[0098] (1) Weigh 24.6g of ferric nitrate nonahydrate, 0.78g of magnesium nitrate hexahydrate, 24.69g of anhydrous citric acid, 0.28g of ammonium heptamolybdate, and 70.58g of water in sequence, place them in a 250mL beaker and stir to dissolve them to obtain a solution of the mixture; place the above solution in a 90℃ water bath and heat it with a rotor speed of 400rpm for stirring and concentration for 2 hours to obtain a concentrated solution;

[0099] (2) Weigh 18.78g of ethylenediaminetetraacetic acid, 18.78g of ammonia (25wt.%) and 25.06g of urea in sequence, place them in a 250mL beaker, seal and stir at room temperature to dissolve them, and obtain an ethylenediaminetetraacetic acid solution; mix the concentrated solution from step (1) with the ethylenediaminetetraacetic acid solution, set the rotor speed to 400rpm, seal and stir at room temperature for 30min to make them fully mixed and uniform, and obtain a mixed solution;

[0100] (3) Weigh 0.22g of surfactant and 5g of water in sequence, place them in a 50ml beaker and mix them evenly. Pour the mixture into the mixture from step (2) above, set the rotor speed to 400rpm, and stir at room temperature for 30min to mix them evenly and obtain a mixed solution.

[0101] (4) Pour the mixed solution from step (3) into a crucible, place the crucible in a muffle furnace, and calcine at 450°C for 1 hour in an air atmosphere; after cooling, sieve the powder through a 200-mesh sieve for later use.

[0102] (5) Weigh 5g of the sieved powder obtained in step (4), place it in a quartz boat, and place the quartz boat in the middle of an 80mm quartz tube furnace to calcine the powder. The calcine is divided into three stages: the first stage: under a nitrogen atmosphere, the tube furnace is heated from 0℃ to 300℃ for 20 minutes, and the nitrogen flow rate is 300sccm; the second stage: the temperature is increased from 300℃ to 700℃ for 22 minutes, and the gas introduced is a mixture of nitrogen and hydrogen, with a nitrogen flow rate of 300sccm and a hydrogen flow rate of 100sccm; the third stage is the cooling stage, with a nitrogen flow rate of 300sccm. Open the tube furnace lid and allow it to cool naturally to room temperature. After cooling, take it out for use.

[0103] Figures 8-9 show the SEM images of the prepared nanoscale multi-metal catalyst before reduction (reduction refers to the reaction after step (5)). As can be seen from the images shown in Figures 8-9, the catalyst particles are not uniform in size and are relatively large before reduction.

[0104] As can be seen from Table 1 and Figure 12, the yield of carbon nanotubes prepared using the method of Comparative Example 1 is not high, only 12.4 g / h. G / I D The value can only reach 47, and the powder resistivity is relatively high, at 40 mΩ·cm.

[0105] Comparative Example 2

[0106] The difference between Comparative Example 2 and Example 1 lies in the different preparation methods of the nanoscale multi-metal catalyst.

[0107] A method for preparing a nanoscale multi-metal catalyst includes the following steps:

[0108] (1) Weigh out 24.6g of ferric nitrate nonahydrate, 0.78g of magnesium nitrate hexahydrate, 24.69g of anhydrous citric acid, 0.28g of ammonium heptamolybdate, 0.31g of lanthanum nitrate, 0.27g of gadolinium nitrate, and 70.58g of water in sequence, place them in a 250mL beaker and stir to dissolve them, to obtain a solution of the mixture; place the above solution in a 90℃ water bath and heat it with a rotor speed of 400rpm for 2 hours to concentrate it, to obtain a concentrated solution;

[0109] (2) Weigh 18.78g of ethylenediaminetetraacetic acid, 18.78g of ammonia (25wt.%) and 25.06g of urea in sequence, place them in a 250mL beaker, seal and stir at room temperature to dissolve them, and obtain an ethylenediaminetetraacetic acid solution; mix the concentrated solution from step (1) with the ethylenediaminetetraacetic acid solution, set the rotor speed to 400rpm, seal and stir at room temperature for 30min to make them fully mixed and uniform, and obtain a mixed solution;

[0110] (3) Pour the mixed solution from step (2) into a crucible, place the crucible in a muffle furnace, and calcine at 450°C for 1 hour in an air atmosphere; after cooling, sieve the powder through a 200-mesh sieve for later use.

[0111] (4) Weigh 5g of the sieved powder obtained in step (3), place it in a quartz boat, and place the quartz boat in the middle of an 80mm quartz tube furnace to calcine the powder. The calcine is divided into three stages: the first stage: under a nitrogen atmosphere, the tube furnace is heated from 0℃ to 300℃ for 20 minutes, and the nitrogen flow rate is 300sccm; the second stage: the temperature is increased from 300℃ to 700℃ for 22 minutes, and the gas introduced is a mixture of nitrogen and hydrogen, with a nitrogen flow rate of 300sccm and a hydrogen flow rate of 100sccm; the third stage is the cooling stage, with a nitrogen flow rate of 300sccm. Open the tube furnace lid and allow it to cool naturally to room temperature. After cooling, take it out for use.

[0112] As can be seen from Table 1, the carbon nanotubes prepared by the method of Comparative Example 2 have a high yield of 13.2 g / h, an IG / ID value of only 32, and a very high powder resistivity of about 100 mΩ·cm.

[0113] Comparative Example 3

[0114] A method for preparing single-walled carbon nanotubes using a tube furnace includes the following steps:

[0115] Weigh 2.0 g of catalyst and load it into a quartz boat, which is then placed in the center of an 80 mm quartz tube furnace. First, under a nitrogen atmosphere, heat the tube furnace from 0 °C to 300 °C over 20 min at a nitrogen flow rate of 500 sccm. Then, raise the temperature from 300 °C to 660 °C over 22 min, introducing a mixture of nitrogen and hydrogen at a flow rate of 300 sccm and 500 sccm. At 660 °C, introduce a mixture of nitrogen and ethylene at a flow rate of 400 sccm and 200 sccm, and maintain this temperature for 60 min. After the reaction, cool the furnace under argon protection at a flow rate of 1000 sccm. The catalyst preparation method is the same as in Example 1.

[0116] The experimental results of Comparative Example 3 show that carbon nanotubes cannot be grown using the tube furnace deposition method.

[0117] Table 1 Test results of carbon nanotube properties

[0118] Example I G / I D Production (g / h) Raw Powder Powder Resistance (mΩ·cm) Example 1 60 15.9 15 Example 2 58 14.3 20 Example 3 52 15.6 26 Example 4 54 13.8 31 Example 5 49 13.1 29 Comparative Example 1 47 12.4 40 Comparative Example 2 32 13.2 100 Comparative Example 3 000 surface

[0119] The embodiments provided above are not intended to limit the scope of the invention, nor are the described steps intended to limit the order of execution. Any obvious modifications made to the invention by those skilled in the art based on existing common knowledge also fall within the scope of protection defined by the claims.

Claims

1. A nanoscale multi-metal catalyst, characterized in that, The catalyst is prepared according to the following steps: (1) Take ferric nitrate, magnesium nitrate, lanthanum nitrate, gadolinium nitrate, ammonium heptamolybdate and citric acid, mix them evenly with water, heat and concentrate to obtain a concentrated solution; the mass ratio of ferric nitrate, magnesium nitrate, lanthanum nitrate and gadolinium nitrate is 90~97:1~5:1~3:1~2, the mass ratio of the mixture of ferric nitrate, magnesium nitrate, lanthanum nitrate and gadolinium nitrate to ammonium heptamolybdate is 85~99:1~15, and the mass ratio of the mixture of ferric nitrate, magnesium nitrate, lanthanum nitrate and gadolinium nitrate to citric acid is 60~50:40~50; (2) Mix ethylenediaminetetraacetic acid, ammonia water and urea evenly to obtain an ethylenediaminetetraacetic acid solution; (3) Mix the concentrated solution from step (1) and The ethylenediaminetetraacetic acid solution from step (2) is mixed and stirred to make it uniform, resulting in a mixed solution; (4) a surfactant is added to the mixed solution obtained in step (3), and after stirring and mixing, the mixed solution is placed in a muffle furnace and calcined at 200~900℃ for 1~10h. After cooling, it is taken out to obtain powder; the volume ratio of the surfactant to the mixed solution is 40~70:60~30; the surfactant is selected from at least one of sodium oleate, octadecylamine, sodium dodecyl sulfate, dodecylamine, and sodium dodecylbenzenesulfonate; (5) the powder obtained in step (4) is passed through a 50~200 mesh sieve and placed in a tube furnace for calcination under an inert atmosphere to obtain a nano-scale multi-metal catalyst.

2. The nanoscale multi-metal catalyst according to claim 1, characterized in that, In step (1), the mass ratio of the mixture of ferric nitrate, magnesium nitrate, lanthanum nitrate, gadolinium nitrate, ammonium heptamolybdate and citric acid to water is 80~40:20~60. Water bath heating is used for heating and concentration. The heating temperature is 60~120℃ and the heating time is 1h~10h. Stirring is carried out during heating. The stirring speed is 200rpm~800rpm.

3. The nanoscale multi-metal catalyst according to claim 1, characterized in that, In step (2), the mass ratio of ethylenediaminetetraacetic acid to ammonia is 5~20:95~80, the mass fraction of ammonia is 10~25%, and the mass ratio of ethylenediaminetetraacetic acid to urea is 60~20:40~80.

4. The nanoscale multi-metal catalyst according to claim 1, characterized in that, In step (3), the volume ratio of the concentrate to the ethylenediaminetetraacetic acid solution is 1~5:5~1, the stirring speed is 400 rpm, and the stirring time is 30 min.

5. The nanoscale multi-metal catalyst according to claim 1, characterized in that, In step (4), the surfactant is a mixed solution of surfactant and water, the concentration of surfactant in the mixed solution is 4.4%, the stirring speed is 200 rpm to 800 rpm, and the stirring time is 0.5 h to 2 h.

6. The nanoscale multi-metal catalyst according to claim 1, characterized in that, The roasting process is carried out in three stages. The first stage is the heating stage, which is conducted under a nitrogen atmosphere with a nitrogen flow rate of 100-1000 sccm. The temperature rises from 0℃ to 200-500℃ over a period of 20-50 minutes. In the second stage, the temperature rises from 200-500℃ to 600-900℃ over a period of 20-30 minutes. The atmosphere in the second stage is a mixture of nitrogen and hydrogen, with a nitrogen flow rate of 300-900 sccm and a hydrogen flow rate of 100-300 sccm. The third stage is the cooling stage, which is also conducted under a nitrogen atmosphere with a nitrogen flow rate of 100-1000 sccm.

7. A method for preparing single-walled carbon nanotubes using any one of the nanoscale multi-metal catalysts according to claims 1 to 6, characterized in that, The process includes the following steps: weighing the catalyst, graphite powder, and sulfur, grinding and dispersing them evenly to obtain a mixed powder, loading the powder into a hollow graphite rod, placing the graphite rod at the anode of an electric arc furnace, introducing a mixed gas of argon and hydrogen, and reacting to prepare single-walled carbon nanotubes.

8. The method according to claim 7, characterized in that, The mass ratio of catalyst, graphite powder and sulfur is 80~40:15~59:5~1, the flow ratio of argon and hydrogen is 3:2, after the mixed gas of argon and hydrogen is introduced, the pressure inside the electric arc furnace is maintained at 20~60 kPa, the reaction current is 50~150 A, the reaction time is 1~5 min, after the reaction, inert gas is introduced to atmospheric pressure, and the sample is taken out to obtain single-walled carbon nanotubes.

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