Catalyst for preparing small-diameter single-walled carbon nanotube and preparation method

Abstract

The invention provides a catalyst for preparing small-diameter single-walled carbon nanotubes and a preparation method thereof.The preparation method of the catalyst comprises the steps that soluble ferric salt, soluble platinum salt and auxiliaries are weighed, mixed and dissolved in water, the mixture is stirred to be uniform, and a solution A is obtained; adding a pretreated carrier into the solution A, uniformly stirring, continuing to heat and evaporate to dryness, and grinding to obtain a solid B; finally, the solid B is subjected to in-situ reduction with hydrogen at 500 DEG C for 1 h and then purged with nitrogen, and the catalyst for preparing the small-pipe-diameter single-wall carbon nanotube is obtained. The Fe-Pt alloy is used as a catalyst, Fe is used as a main active metal, and carbon source cracking and carbon tube nucleation are driven; the synergistic effect of Fe-Pt can improve the carbon deposition resistance of the catalyst, prolong the service life of the catalyst, further effectively reduce the pipe diameter of the SWCNTs and significantly improve the overall quality of the SWCNTs.

Description

Technical Field

[0001] The present invention relates to the technical field of single-walled carbon nanotube preparation, and in particular to a catalyst for preparing single-walled carbon nanotubes with a small tube diameter and a preparation method thereof. Background Art

[0002] Single-walled carbon nanotubes (SWCNTs), as a typical representative of one-dimensional nanomaterials, are famous for their unique tubular structure. This structure endows carbon nanotubes with excellent physical, chemical, electrical and mechanical properties, making them show great application potential in many fields. Especially in the fields of energy storage, environmental protection, electronic appliances, composite materials and medical treatment, the importance of single-walled carbon nanotubes is gradually emerging.

[0003] Chemical vapor deposition (CVD) method is the main method for preparing single-walled carbon nanotubes, which has the advantages of simple operation, high yield and high product purity. However, this method requires extremely high reaction temperatures (700 - 1200 °C), and common single-metal catalysts such as iron (Fe), cobalt (Co), nickel (Ni) and their conventional alloys have problems such as limited catalytic performance, difficulty in efficiently controlling the structure and growth of carbon nanotubes, easy sintering and aggregation resulting in a reduction of active sites, and uneven tube diameters. Therefore, developing efficient multi-component catalysts and realizing the preparation of single-walled carbon nanotubes with a small tube diameter are still problems to be solved urgently.

[0004] In recent years, researchers have been committed to developing high-performance multi-component catalysts. Some researchers prepared FePt nanoparticles on a MgO substrate by alternating sputtering deposition method, and used Pt as a dispersion aid to grow single-walled carbon nanotubes. (O. S. Syn. Carbon, 2015, 87: 453-461.) However, the performance improvement of the Fe-based catalyst by the additive Pt is limited. Intermetallic alloy catalysts have gradually come into people's view in recent years. It forms isolated active Pt single atoms and constructs a special intermetallic structure with another metal, changing the geometric structure (such as lattice parameters) and electronic effects (such as d-band hole density) of Pt, so as to obtain a high-activity and high-stability high-temperature catalyst. In this application, an FePt intermetallic alloy catalyst was constructed during the process of preparing single-walled carbon nanotubes by the fixed substrate method, and relatively good results were obtained. Summary of the Invention

[0005] To solve the above problems, the present invention provides a catalyst for preparing single-walled carbon nanotubes with a small tube diameter and a preparation method thereof. After co-impregnating Fe and Pt and reducing them with hydrogen, an Fe-Pt intermetallic alloy catalyst is formed. The synergistic effect of the Fe-Pt alloy can effectively reduce the tube diameter of SWCNTs and significantly improve the overall quality of SWCNTs.

[0006] In the first aspect of the present invention, a catalyst for preparing small-diameter single-walled carbon nanotubes is provided. The catalyst comprises an active component and a support, and the active component is an iron-platinum alloy.

[0007] Furthermore, the content of iron in the catalyst is 1 to 10 wt%.

[0008] Furthermore, the content of platinum in the catalyst is 1 to 5 wt%, preferably 3 wt%.

[0009] In the second aspect of the present invention, a method for preparing a catalyst for preparing small-diameter single-walled carbon nanotubes is provided. The method comprises the following steps: S1: Weigh soluble iron salts, soluble platinum salts and an auxiliary agent, dissolve them in water, and mix them evenly to obtain solution A, wherein the mass ratio of iron and platinum elements is 2:(1 to 5), and the mass ratio of the soluble salts to the auxiliary agent is 10:1; S2: First, pretreat the support in air at a certain temperature, and then add solution A, wherein the mass ratio of the support to solution A is 10:1. Stir evenly, heat to evaporate to dryness, and obtain solid B after grinding; S3: In-situ reduce solid B with hydrogen at a certain temperature, and then purge with nitrogen to obtain the catalyst for preparing small-diameter single-walled carbon nanotubes.

[0010] Furthermore, the soluble iron salt in step S1 is selected from at least one of ferric chloride, ferric nitrate and ferric sulfate.

[0011] Furthermore, the soluble platinum salt in step S1 is selected from at least one of chloroplatinic acid and sodium chloroplatinate.

[0012] Furthermore, the auxiliary agent in step S1 is selected from at least one of citric acid and sodium citrate.

[0013] Furthermore, the support in step S2 is selected from at least one of silica, alumina and magnesia, preferably silica.

[0014] Furthermore, the temperature for pretreating the support in step S2 is 400 to 600 °C, and the treatment time is 2 to 4 h.

[0015] Furthermore, the stirring rate in step S2 is 500 to 800 r / min, and the stirring time is 12 to 72 h.

[0016] Furthermore, the evaporation temperature in step S2 is 80 to 105 °C, and the evaporation time is 2 to 6 h.

[0017] Furthermore, the temperature for in-situ reduction in step S3 is 400 to 600 °C, and the reduction time is 1 to 2 h.

[0018] Further, in step S3, the hydrogen concentration is 50 sccm and the nitrogen concentration is 100 sccm.

[0019] The third aspect of the present invention provides a method for preparing single-walled carbon nanotubes, the method comprising the following steps: Place the catalyst provided by the present invention or the catalyst prepared by the preparation method provided by the present invention in a quartz boat in a reaction device, introduce an inert gas, and heat up to the reaction temperature; introduce hydrogen, inject a carbon source into the tube, and obtain the single-walled carbon nanotubes after the reaction.

[0020] Further, the reaction temperature is 800 - 1000 °C, preferably 900 °C.

[0021] Further, the concentration of hydrogen is 30 sccm and the inert gas is 300 sccm.

[0022] Further, the inert gas is one of helium and argon.

[0023] Compared with the prior art, the present invention has at least the following technical effects: (1) The synergistic effect of the Fe-Pt alloy can significantly improve the activity of the catalyst and promote the cracking of the carbon source. This synergistic effect makes it easier for carbon atoms to precipitate on the catalyst surface, thus promoting the growth of carbon nanotubes. The Fe-Pt intermetallic alloy catalyst can form more active sites, increasing the adsorption and diffusion ability of carbon atoms. These active sites contribute to the uniform distribution of carbon atoms on the catalyst surface, thereby improving the growth efficiency of carbon nanotubes.

[0024] (2) In the present invention, Fe and Pt are mutually doped to form an Fe-Pt intermetallic alloy catalyst, and its synergistic effect can effectively reduce the tube diameter of SWCNTs and significantly improve the overall quality of SWCNTs. Fe, as the main active metal, drives the cracking of the carbon source and the nucleation of carbon tubes; Pt can inhibit the sintering of Fe particles, enhance its dispersion, and extend the catalyst life.

[0025] (3) The preparation process of the present invention is simple, has low energy consumption, and the prepared SWCNTs have a small tube diameter and high quality, and are suitable for large-scale industrial production. Description of the Drawings

[0026] Figure 1 XRD pattern of the catalyst prepared in Example 3; Figure 2 Raman pattern of the SWCNTs prepared in Examples 1 to 3; Figure 3 Raman pattern of the SWCNTs prepared in Comparative Examples 1 to 2. Detailed implementation mode

[0027] On the one hand, the present invention provides a preparation method of a catalyst for preparing single-walled carbon nanotubes with a small tube diameter, and the method comprises the following steps: S1: Weigh soluble iron salt, soluble platinum salt and an auxiliary agent, dissolve them in water, and mix them evenly to obtain solution A; According to the embodiments of the present invention, the soluble iron salt is selected from at least one of ferric chloride, ferric nitrate, and ferric sulfate, and the soluble platinum salt is selected from at least one of chloroplatinic acid and sodium chloroplatinate; The auxiliary agent is selected from at least one of citric acid and sodium citrate. According to the embodiments of the present invention, the content of the soluble iron salt is 1 to 10 wt%, and the content of the soluble platinum salt is 1 to 5 wt%, preferably 3 wt%.

[0028] S2: First, pretreat the carrier in air at a certain temperature, then add solution A, stir evenly, heat to evaporate to dryness, and obtain solid B after grinding; According to the embodiments of the present invention, the carrier is selected from at least one of silica, alumina, and magnesia, preferably silica; Weigh the carrier according to the mass of the soluble iron salt and platinum salt. The temperature for pretreating the carrier is 400 to 600 °C, and the treatment time is 2 to 4 h. The stirring rate is 500 to 800 r / min, and the stirring time is 12 to 72 h. The evaporation temperature is 80 to 105 °C, and the evaporation time is 2 to 6 h.

[0029] S3: In-situ reduce solid B with hydrogen at a certain temperature, and then purge with nitrogen to obtain the catalyst for preparing single-walled carbon nanotubes with a small tube diameter; According to the examples of the present invention, the temperature for in-situ reduction is 400 to 600 °C, and the reduction time is 1 to 2 h. The hydrogen concentration is 50 sccm, and the nitrogen concentration is 100 sccm.

[0030] The present invention also provides a preparation method of single-walled carbon nanotubes, comprising the following steps: S1: Place the catalyst prepared by the preparation method provided by the present invention or the catalyst provided by the present invention on a quartz boat in a reaction device, introduce an inert gas, and heat to the reaction temperature; According to the embodiments of the present invention, the inert gas is helium, and the flow rate is 300 sccm; The reaction temperature is 800 to 1000 °C, preferably 800 °C.

[0031] SS2: Introduce hydrogen, inject a carbon source into the tube, and obtain single-walled carbon nanotubes SWCNTs after the reaction. According to the embodiments of the present invention, the flow rate of the hydrogen gas is 30 sccm, the carbon source is ethanol, and the injection amount is 0.45 mL.

[0032] Example 1 The following illustrates the detailed preparation process and conditions of the preparation method provided by the present invention through examples.

[0033] (1) Preparation of catalyst: Weigh 0.3077 g of ferric sulfate, 0.0720 g of sodium chloroplatinate, and 0.1 g of citric acid, mix and dissolve them in 30 mL of deionized water, stir evenly to obtain solution A; Treat 1 g of SiO2 in air at 500 °C for 2 h, add the support to solution A and stir vigorously, raise the temperature to 100 °C, and continuously stir for 24 h to obtain solid B; Place solid B in an 80 °C oven and dry it overnight, and grind it into powder after complete drying. Reduce it in situ with hydrogen at 500 °C for 1 h, and then purge it with nitrogen to obtain the catalyst FePt / SiO2, denoted as Cat-1, where the content of Fe is about 2 wt%. The content of Pt is about 1 wt%.

[0034] (2) Preparation of SWCNTs: Take 0.01 g of Cat-1 catalyst and place it in a quartz reaction tube with an inner diameter of 12 mm, introduce 300 sccm of argon, and heat it to the reaction temperature of 800 °C in 80 min; Introduce 30 sccm of hydrogen, and at the same time inject 0.45 mL of ethanol into the tube to start the reaction; After 60 min, turn off the reaction gas, stop heating, and keep 100 sccm of argon to cool to room temperature; Collect the product to obtain single-walled carbon nanotubes, denoted as SWCNTs-1.

[0035] Example 2 The steps and material selection for preparing the catalyst in this example are the same as those in Example 1. The difference is that the amount of sodium chloroplatinate used in this example is 0.2280 g, and the remaining steps and material selection for preparing the catalyst are the same as those in Example 1. The catalyst prepared in this example is denoted as Cat-2, where the content of Pt is about 3 wt%.

[0036] Preparation of SWCNTs: The steps and material selection for preparing SWCNTs in this example are the same as those in Example 1. The difference is that Cat-2 is used as the catalyst in this example, and the remaining steps and material selection for preparing SWCNTs are the same as those in Example 1. The SWCNTs prepared in this example are denoted as SWCNTs-2.

[0037] Example 3 The steps and material selection for preparing the catalyst in this example are the same as those in Example 1. The difference is that the amount of sodium chloroplatinate used in this example is 0.3800 g, and the remaining steps and material selection for preparing the catalyst are the same as those in Example 1. The catalyst prepared in this example is denoted as Cat-3, where the content of Pt is about 5 wt%.

[0038] Preparation of SWCNTs: The steps for preparing SWCNTs in this example are the same as those in Example 1, and the materials used are also the same. The difference is that Cat-3 is used as the catalyst in this example, and the remaining steps for preparing SWCNTs and the materials used are the same as those in Example 1. The SWCNTs prepared in this example are denoted as SWCNTs-3.

[0039] Figure 1 Figure 4 is the XRD pattern of SWCNTs-1 prepared in Example 1. The phase structure in the figure is that of the Fe-Pt intermetallic alloy. The catalyst provided by the present invention forms an Fe3Pt alloy, and the two exhibit a synergistic effect.

[0040] Figure 2 Figure 5 shows the IG / ID of SWCNTs prepared from the Fe Pt-based catalyst of the present invention. It can be seen from the figure that the I G / I D of SWCNTs all remain at relatively high values. With the change of the Pt loading amount, the I G / I D of SWCNTs grown on the Fe, Pt-based series catalysts will change but the difference is small, mainly concentrated between 20.0 and 25.0. It can be seen that the synergistic effect of the FePt alloy can effectively improve the overall quality of SWCNTs. Using the formula ω RBM =234 / d + 10 to further estimate the tube diameter, the result shows that the average tube diameter of SWCNTs is mainly concentrated around 13 nm.

[0041] Comparative Example 1 (1) Preparation of the catalyst: Weigh 0.3077 g of ferric sulfate and dissolve it in 30 mL of deionized water, stir evenly to obtain Solution A; treat 1 g of SiO2 in air at 500 °C for 2 h, then add the carrier to Solution A and stir vigorously. Raise the temperature to 100 °C and continue stirring for 24 h to obtain Solid B; place Solid B in an 80 °C oven and dry it overnight. After complete drying, grind it into powder. Reduce it in situ with hydrogen at 500 °C for 1 h, and then purge it with nitrogen to obtain the catalyst Fe / SiO2, denoted as Cat-4, where the content of Fe is the same as that in Example 1.

[0042] (2) Preparation of SWCNTs: The steps for preparing SWCNTs in Comparative Example 1 are the same as those in Example 1, and the materials used are also the same. The difference is that Cat 4 is used as the catalyst in Comparative Example 1, and the remaining steps for preparing SWCNTs and the materials used are the same as those in Example 1. The SWCNTs prepared in Comparative Example 1 are denoted as SWCNTs 4.

[0043] Comparative Example 2 (1) Preparation of catalyst: Weigh 0.2280 g of sodium chloroplatinate and dissolve it in 30 mL of deionized water, stir evenly to obtain solution A; treat 1 g of SiO2 in air at 500 °C for 2 h, then add the support to solution A and stir vigorously, raise the temperature to 100 °C, and continuously stir for 24 h to obtain solid B; place solid B in an 80 °C oven and dry overnight, and grind it into powder after complete drying. Reduce it in situ with hydrogen at 500 °C for 1 h, and then purge it with nitrogen to obtain the catalyst Pt / SiO2, denoted as Cat-5, where the Pt content is the same as in Example 3.

[0044] (2) Preparation of SWCNTs: The steps and material selection for preparing SWCNTs in Comparative Example 2 are the same as those in Example 1, except that Comparative Example 2 uses Cat-5 as the catalyst, and the remaining steps and material selection for preparing SWCNTs are the same as those in Example 1. The SWCNTs prepared in Comparative Example 2 are denoted as SWCNTs-5.

[0045] Further, Raman tests were performed on SWCNTs-4 and SWCNTs-5, and their I G / I D ratio is significantly smaller, indicating that the synergistic effect generated by the Fe-Pt alloy can significantly improve the quality of SWCNTs.

[0046] The above embodiments are only used to illustrate the principle and its effects of the present invention by way of example, rather than to limit the present invention. Any person skilled in this art can modify the above embodiments without departing from the spirit and scope of the present invention. Therefore, the scope of the protection of the rights of the present invention shall be as shown in the claims.

Claims

1. A catalyst for preparing single-walled carbon nanotubes with small tube diameters, characterized in that, The catalyst includes an active component and a support, and the active component is an alloy between iron and platinum; wherein, the content of iron in the catalyst is 1-10 wt%, and the content of platinum is 1-5 wt%.

2. The catalyst according to claim 1, characterized in that, The support is selected from at least one of silica, alumina, and magnesia.

3. The catalyst according to claim 2, wherein The support is silica.

4. The preparation method of the catalyst for preparing single-walled carbon nanotubes with a small tube diameter according to claim 1, characterized in that, Specifically, it includes the following steps: S1: Weigh soluble iron salts, soluble platinum salts, and additives, dissolve them in water, and mix evenly to obtain solution A, where the mass ratio of iron and platinum elements is 2:(1-5), and the mass ratio of the soluble salts to the additives is 10:1; S2: First, pretreat the support in air at a certain temperature, then add solution A, where the mass ratio of the support to solution A is 10:1, stir evenly, heat to evaporate to dryness, and grind to obtain solid B; S3: In-situ reduce solid B with hydrogen at a certain temperature, and then purge with nitrogen to obtain the catalyst for preparing small-diameter single-walled carbon nanotubes.

5. The preparation method according to claim 4, characterized in that, In step S1, the soluble iron salts are selected from at least one of ferric chloride, ferric nitrate, and ferric sulfate, and the soluble platinum salts are selected from at least one of chloroplatinic acid and sodium chloroplatinate; the additives are selected from at least one of citric acid and sodium citrate.

6. The preparation method according to claim 4, characterized in that, In step S2, the temperature for the support pretreatment is 400-600 °C, the treatment time is 2-4 h; the stirring rate is 500-800 r / min, and the stirring time is 12-72 h; the evaporation temperature is 80-105 °C, and the evaporation time is 2-6 h.

7. The preparation method according to claim 4, characterized in that, In step S3, the temperature for in-situ reduction is 400-600 °C, the reduction time is 1-2 h; the hydrogen concentration is 50 sccm, and the nitrogen concentration is 100 sccm.

8. Use of the catalyst according to claim 1 in the preparation of single-walled carbon nanotubes, characterized in that, It includes the following steps: Weigh and place the catalyst in a quartz boat in the reaction device, introduce an inert gas, heat to the reaction temperature; introduce hydrogen, inject a carbon source into the tube, and obtain the single-walled carbon nanotubes after the reaction.

9. The application according to claim 8, wherein The inert gas is one of helium and argon.

10. The application according to claim 8, wherein, The reaction temperature is 800-1000 °C.

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