CN113663690B - Catalyst for preparing small-diameter single-wall carbon nano tube, preparation method and application - Google Patents

Catalyst for preparing small-diameter single-wall carbon nano tube, preparation method and application Download PDF

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CN113663690B
CN113663690B CN202111005249.8A CN202111005249A CN113663690B CN 113663690 B CN113663690 B CN 113663690B CN 202111005249 A CN202111005249 A CN 202111005249A CN 113663690 B CN113663690 B CN 113663690B
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CN113663690A (en
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胡丹丹
陈秉辉
郑进保
吴钊男
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Xiamen Huacarbon Technology Co ltd
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Fujian Haifan Pilot Technology Co ltd
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    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01JCHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/70Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper
    • B01J23/89Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with noble metals
    • B01J23/8933Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with noble metals also combined with metals, or metal oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
    • B01J23/8993Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with noble metals also combined with metals, or metal oxides or hydroxides provided for in groups B01J23/02 - B01J23/36 with chromium, molybdenum or tungsten
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01JCHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/002Mixed oxides other than spinels, e.g. perovskite
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01JCHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J35/00Catalysts, in general, characterised by their form or physical properties
    • B01J35/20Catalysts, in general, characterised by their form or physical properties characterised by their non-solid state
    • B01J35/23Catalysts, in general, characterised by their form or physical properties characterised by their non-solid state in a colloidal state
    • CCHEMISTRY; METALLURGY
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    • C01BNON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00Carbon; Compounds thereof
    • C01B32/15Nano-sized carbon materials
    • C01B32/158Carbon nanotubes
    • C01B32/159Carbon nanotubes single-walled
    • CCHEMISTRY; METALLURGY
    • C01INORGANIC CHEMISTRY
    • C01BNON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00Carbon; Compounds thereof
    • C01B32/15Nano-sized carbon materials
    • C01B32/158Carbon nanotubes
    • C01B32/16Preparation
    • C01B32/162Preparation characterised by catalysts
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01JCHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J2523/00Constitutive chemical elements of heterogeneous catalysts

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Abstract

The invention provides a catalyst for preparing small-diameter single-wall carbon nanotubes, a preparation method and application thereof, wherein the preparation method of the catalyst comprises the following steps: weighing soluble molybdenum salt and an auxiliary agent, mixing and dissolving in water, adding nitric acid, and uniformly stirring to obtain a solution A; weighing soluble ferric salt, soluble platinum salt and an initiator, adding the soluble ferric salt, the soluble platinum salt and the initiator into ethanol, and heating and stirring to obtain a solution B; mixing the solution A and the solution B, adding a carrier, stirring uniformly, and then continuously stirring, heating and evaporating to dryness to obtain a solid C; and drying, grinding and roasting the solid C to obtain the catalyst for preparing the small-diameter single-wall carbon nano tube. The invention mixes a very small amount of noble metal Pt into the Fe-Mo-based catalyst to form the Fe-Mo-Pt-based trimetallic catalyst, and the CH of Pt 4 The decomposition capacity is strong, a large number of carbon species can be obtained through decomposition, the carbon yield is improved, and in addition, the penetration of Pt can effectively reduce the pipe diameter of SWNTs and remarkably improve the overall quality of the SWNTs.

Description

Catalyst for preparing small-diameter single-wall carbon nano tube, preparation method and application
Technical Field
The invention relates to the technical field of single-walled carbon nanotube preparation, in particular to a catalyst for preparing small-caliber single-walled carbon nanotubes, a preparation method and application thereof.
Background
Carbon nanotubes, which are a novel carbon material, have many excellent properties such as mechanical properties, electrical conductivity, thermal conductivity, etc., due to their special structure. The carbon nanotubes can be roughly classified into single-walled carbon nanotubes, double-walled carbon nanotubes, multi-walled carbon nanotubes, and the like according to the number of layers of the wall, and single-walled carbon nanotubes are one-dimensional carbon nanotube hollow tubular structures composed of carbon atoms, and can be regarded as seamless carbon tubes formed by crimping single-layered graphene.
Among them, single-walled carbon nanotubes (SWNTs), which are typical one-dimensional nanomaterials, have a special tubular structure that determines that carbon nanotubes have excellent physical, chemical, electrical and mechanical properties, and thus have extremely important application values in many fields, especially in the fields of energy storage, environmental protection, electronics, composite materials, medical fields, etc., and are increasingly highlighted. At present, the methods for growing single-wall carbon nanotubes mainly comprise an arc discharge method, a laser evaporation catalytic precipitation technology, a Chemical Vapor Deposition (CVD) method and the like, the former two methods are very complex to operate, solid carbon sources are required to be evaporated into carbon atoms at a high temperature of more than 3000 ℃, the number of synthesizable carbon nanotubes is severely limited, and in addition, the carbon nanotubes grown by evaporating the carbon atoms are highly entangled in morphology, and are mixed with other carbon impurities and metal catalysts, so that the application range of the method is severely limited. The chemical vapor deposition process is simple, high in yield, low in impurity content and other advantages, and is one of the most important processes for preparing single-wall carbon nanotube.
Because of the thinning of the SWNTs pipe diameter, the lower the conduction threshold value is when the SWNTs pipe diameter is used for the conductive filler, the conduction threshold value can be as low as one ten thousandth, which is not reached by the conventional materials, and how to keep the preparation of the carbon nano-tube with the thin pipe diameter is an important difficulty in the preparation field. In recent years, many researchers have also focused on the controllable growth of the diameter of single-walled carbon nanotubes, for example, patent application CN201010234322.4 of Shanghai university discloses a method for preparing single-walled carbon nanotubes, which adopts a high-temperature arc ablation method to fill carbon powder and metal catalyst into a carbon electrode, and prepares the carbon nanotubes by direct arc ablation, but the method is mainly aimed at an arc catalysis method, and the method has high cost and is not easy for mass production.
Therefore, how to prepare small-diameter single-wall carbon nanotubes is still a problem to be solved.
Disclosure of Invention
In order to solve the problems, the invention provides a catalyst for preparing small-diameter single-wall carbon nanotubes, a preparation method and application thereof, which comprises the steps of doping a small amount of noble metal Pt into a Fe-Mo-based catalyst to form a Fe-Mo-Pt-based trimetallic catalyst, and doping a small amount of noble metal Pt into the Fe-Mo-based catalyst to form a small-diameter single-wall carbon nanotube catalyst 4 The decomposing capability is strong, a large number of carbon species can be obtained through decomposition, and the carbon yield is improved. In addition, pt penetration can effectively reduce the pipe diameter of the SWNTs and remarkably improve the overall quality of the SWNTs.
The invention provides a catalyst for preparing small-diameter single-walled carbon nanotubes, which comprises an active component and a carrier, wherein the active component comprises a main active component and a secondary active component, the main active component is iron and platinum, and the secondary active component is molybdenum.
Further, the iron content of the catalyst is 1-10wt%.
Further, the content of platinum in the catalyst is 0.03-0.5wt%.
Further, the molar ratio of iron atoms to molybdenum atoms in the catalyst is (25-60): 1, preferably 30:1.
Further, the carrier is at least one selected from silica, alumina and magnesia, preferably magnesia.
Further, the particle size of the catalyst active component is 8-15nm.
The second aspect of the present invention provides a method for preparing a catalyst for preparing small-diameter single-walled carbon nanotubes, the method comprising the steps of:
s1: weighing soluble molybdenum salt and an auxiliary agent, mixing and dissolving in water, adding nitric acid, and uniformly stirring to obtain a solution A;
s2: weighing soluble ferric salt, soluble platinum salt and an initiator, adding the soluble ferric salt, the soluble platinum salt and the initiator into ethanol, and heating and stirring to obtain a solution B;
s3: mixing the solution A and the solution B, adding a carrier under intense stirring, stirring uniformly, continuing stirring, heating and evaporating to dryness to obtain a solid C;
s4: and drying the solid C, grinding, and finally roasting to obtain the catalyst for preparing the small-diameter single-wall carbon nano tube.
The molar ratio of the iron atoms in the soluble iron salt to the molybdenum atoms in the soluble molybdenum salt is (25-60): 1.
Further, the carrier is weighed according to the content of iron in the catalyst of 1-10wt%.
Further, the soluble platinum salt is weighed according to the content of platinum in the catalyst of 0.03-0.5wt%.
Further, the soluble ferric salt is selected from at least one of ferric chloride, ferric nitrate and ferric sulfate.
Further, the soluble molybdenum salt is at least one selected from ammonium molybdate and sodium molybdate.
Further, the soluble platinum salt is at least one selected from chloroplatinic acid and sodium chloroplatinate.
Further, the initiator is selected from urea.
Further, the auxiliary agent is at least one selected from citric acid and sodium citrate.
Further, the carrier is at least one selected from silica, alumina and magnesia, preferably magnesia.
Further, the evaporating temperature is 120-180 ℃, and the evaporating time is 2-6h.
Further, the drying temperature is 60-100 ℃ and the drying time is 6-48h.
Further, the roasting temperature is 300-400 ℃ and the roasting time is 2-6h.
The third aspect of the present invention provides a method for preparing single-walled carbon nanotubes, the method comprising the steps of:
s1: placing the catalyst provided by the invention or the catalyst prepared by the preparation method provided by the invention into a reaction device, and heating to the reaction temperature;
s2: introducing methane containing water vapor and inert gas for reaction;
s3: purifying the product obtained in the step S2 to obtain the single-walled carbon nanotube.
Further, the reaction temperature is 600 to 900 ℃, preferably 700 to 800 ℃.
Further, the concentration of the water vapor is 100-1000ppm.
Further, the inert gas is one of helium and argon.
Further, the concentration of methane is 20-50%.
Compared with the prior art, the invention has at least the following technical effects:
(1) The invention adopts low-temperature roasting, trace Mo and Fe form a special ferric molybdate structure, effectively improves the carbon yield and the purity of SWNTs, and simultaneously utilizes H 2 O is used as an etchant, does not damage the microstructure of FeMo, can ensure that the catalyst has better anti-sintering performance, prolongs the service life of the catalyst, and simultaneously has trace H 2 The quality and the property of SWNTs can be regulated and controlled by O, so that the quality of the product is effectively improved.
(2) The invention mixes a very small amount of noble metal Pt into the Fe-Mo-based catalyst to form the Fe-Mo-Pt-based trimetallic catalyst, and the CH of Pt 4 The decomposition capacity is strong, a large number of carbon species can be obtained through decomposition, the carbon yield is remarkably improved, and in addition, the penetration of Pt can effectively reduce the pipe diameter of SWNTs and remarkably provide the overall quality of the SWNTs.
(3) The growth of the SWNTs of the invention follows a tangential growth mode, and the particle size of the Fe-Mo-Pt-based catalyst prepared by the invention is concentrated at 8-15nm and is close to the average pipe diameter value of the SWNTs further prepared by using the catalyst.
(4) The preparation method has the advantages of simple process, low cost, low energy consumption, small pipe diameter of the prepared SWNTs and high quality, and is suitable for mass industrialized production.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate and together with the embodiments of the invention serve to explain the invention and do not limit the invention.
FIG. 1 is a graph showing particle size distribution of catalysts Cat-1 to Cat-4 prepared in examples 1 to 4;
FIG. 2 shows the carbon yields and SWNTs I for examples 1 to 4 G /I D
FIG. 3 is an SEM image of the catalysts Cat-1 to Cat-4 prepared in examples 1 to 4;
FIG. 4 is XRD patterns of catalysts Cat-1 to Cat-4 prepared in examples 1 to 4;
FIG. 5 is an SEM image of SWNTs-1 through SWNTs-4 prepared in examples 1 through 4;
FIG. 6 is a graph showing the pipe diameter distribution of SWNTs-1 to SWNTs-4 obtained in examples 1 to 4;
FIG. 7 is a TEM image and pipe diameter distribution diagram of SWNTs-5 prepared in comparative example 1;
FIG. 8 is a graph showing the pipe diameter distribution of SWNTs-6 produced in comparative example 2.
Detailed Description
In one aspect, the present invention provides a method for preparing a catalyst for preparing small-diameter single-walled carbon nanotubes, the method comprising the steps of:
s1: weighing soluble molybdenum salt and an auxiliary agent, mixing and dissolving in water, adding nitric acid, and uniformly stirring to obtain a solution A; according to the embodiment of the invention, the soluble molybdenum salt is at least one selected from ammonium molybdate and sodium molybdate, and the auxiliary agent is at least one selected from citric acid and sodium citrate.
S2: weighing soluble ferric salt, soluble platinum salt and an initiator, adding the soluble ferric salt, the soluble platinum salt and the initiator into ethanol, and heating and stirring to obtain a solution B; according to the embodiment of the invention, the soluble ferric salt is selected from at least one of ferric chloride, ferric nitrate and ferric sulfate, the soluble platinum salt is selected from at least one of chloroplatinic acid and sodium chloroplatinate, and the initiator is selected from urea.
S3: mixing the solution A and the solution B, adding a carrier under intense stirring, stirring uniformly, continuing stirring, heating and evaporating to dryness to obtain a solid C; according to the embodiment of the invention, the evaporating temperature is 120-180 ℃, the evaporating time is 2-6h, and the carrier is at least one of silicon dioxide, aluminum oxide and magnesium oxide, preferably magnesium oxide.
S4: drying the solid C, grinding, and finally roasting to obtain the Fe-Mo-Pt-based catalyst; according to the embodiment of the invention, the drying temperature is 60-100 ℃, the drying time is 6-48h, the roasting temperature is 300-400 ℃, and the roasting time is 2-6h.
The molar ratio of the iron atoms in the soluble iron salt to the molybdenum atoms in the soluble molybdenum salt is (25-60): 1.
According to an embodiment of the invention, the carrier is weighed according to the iron content of the catalyst of 1-10wt%.
According to an embodiment of the present invention, the soluble platinum salt is weighed according to the content of platinum in the catalyst being 0.03-0.5wt%.
The invention also provides a preparation method of the single-walled carbon nanotube, which comprises the following steps:
s1: placing the catalyst prepared by the preparation method or the catalyst provided by the invention into a reaction device, and heating to the reaction temperature; the reaction temperature according to the embodiments of the present invention is 600 to 900 c, preferably 700 to 800 c.
S2: introducing methane containing water vapor and inert gas for reaction
S3: purifying the product obtained in the step S2 to obtain the single-walled carbon nanotube SWNTs.
The following examples illustrate the detailed preparation procedures and conditions of the preparation methods provided by the present invention.
Example 1
(1) Preparation of the catalyst: 0.131g of ammonium molybdate and 2g of citric acid are weighed and mixed and dissolved in 20mL of deionized water, 5mL of 10% HNO is added 3 Stirring uniformly to obtain a solution A; 5.47g of ferric nitrate, 4.461g of chloroplatinic acid and 1g of urea are weighed and added into 50mL of ethanol, and the temperature is raised to 80 ℃ and the mixture is stirred uniformly to obtain a solution B; adding the solution A into the solution B, further adding 54g of light MgO (commercially available) under intense stirring, continuously stirring after uniform stirring, raising the temperature to 150 ℃, and continuously stirring for 160min to obtain a solid C; drying the solid C in a baking oven at 120 ℃ overnight, grinding the dried solid C into powder, and roasting the powder at the temperature of 2 ℃/min to 400 ℃ for 180min to obtain the catalyst Fe 30 Mo 1 0.01Pt/MgO, designated Cat-1, wherein the content of Fe is about 2wt%, the content of Pt is about0.03wt%。
(2) SWNTs preparation: placing 0.3g Cat-1 catalyst in a quartz reaction tube with an inner diameter of 12mm, introducing 100sccm argon, heating to a reaction temperature of 800 ℃ for 45 min; introducing 500sccm methane, water vapor and argon gas mixture, wherein the concentration of methane is 30%, the concentration of water vapor is 200ppm, and starting SWNTs growth reaction; after 60min, the reaction gas is closed, heating is stopped, and 100sccm Ar is kept to be cooled to room temperature; the product was removed and then purified to give single walled carbon nanotubes, designated SWNTs-1.
Example 2
The procedure and materials used in the preparation of the catalyst in this example were the same as those in example 1, except that the chloroplatinic acid amount in this example was 7.435g, and the procedure and materials used in the preparation of the remaining catalyst were the same as those in example 1. The catalyst prepared in this example was designated Cat-2.
SWNTs preparation: the steps and materials for preparing SWNTs in this example are the same as those in example 1, except that Cat-2 is used as the catalyst in this example, and the steps and materials for preparing SWNTs are the same as those in example 1. SWNTs prepared in this example were designated SWNTs-2.
Example 3
The catalyst preparation step and materials used in this example were the same as those used in example 1, except that chloroplatinic acid was used in an amount of 14.87g, and the catalyst preparation steps and materials used in the other example were the same as those used in example 1. The catalyst prepared in this example was designated Cat-3.
SWNTs preparation: the steps and materials for preparing SWNTs in this example are the same as those in example 1, except that Cat-3 is used as the catalyst in this example, and the steps and materials for preparing SWNTs are the same as those in example 1. SWNTs prepared in this example were designated SWNTs-3.
Example 4
The catalyst preparation step and materials used in this example were the same as those used in example 1, except that the chloroplatinic acid amount used in this example was 74.35g, and the remaining catalyst preparation steps and materials were the same as those used in example 1. The catalyst prepared in this example was designated Cat-4.
SWNTs preparation: the steps and materials for preparing SWNTs in this example are the same as those in example 1, except that Cat-4 is used as the catalyst in this example, and the steps and materials for preparing SWNTs are the same as those in example 1. SWNTs prepared in this example were designated SWNTs-4.
The catalysts prepared in examples 1 to 4 and the corresponding SWNTs were tested for performance, and the specific results are shown in table 1:
TABLE 1 carbon yields of the catalysts obtained in examples 1 to 4 and I of SWNTs G /I D Value of
Sample of Catalyst Content of Pt Carbon yield (%) I G /I D
Example 1 Cat-1 0.03 22.40 21.2
Example 2 Cat-2 0.05 26.20 21.3
Example 3 Cat-3 0.1 28.62 23.0
Example 4 Cat-4 0.5 35.12 21.9
As can be seen from the above table, when the Pt loading was increased to 0.5wt%, the carbon yield of catalyst Cat-4 could reach 35.12%, which is due to the strong CH of Pt 4 The cracking capacity so as to significantly increase the carbon yield of the catalyst.
According to the Scherrer formula, the particle size distribution diagram of the Fe-Mo-Pt-based catalyst is obtained, the result is shown in figure 1, the particle size of the Fe-Mo-Pt-based catalyst is concentrated to 8-15nm as shown in figure 1, the particle size is close to the value of the average pipe diameter of corresponding SWNTs, the growth of the SWNTs in the system provided by the invention follows a tangential growth mode, and the influence of Pt load on the particle size of the catalyst and the pipe diameter of the SWNTs is small.
FIG. 2 shows the carbon yield and SWNTs I of the Fe-Mo-Pt-based catalyst prepared according to the present invention G /I D As can be seen from FIG. 2, the carbon yield of the Fe-Mo-Pt-based catalyst gradually increases with increasing Pt loading, while the IG/ID of the SWNTs remains high. I of SWNTs grown on Fe-Mo-Pt based catalyst after Pt addition G /I D The phase difference is smaller, and the phase difference is mainly concentrated between 20.0 and 23.0, so that the incorporation of Pt effectively improves the overall quality of SWNTs.
As shown in fig. 3 to 6, fig. 3 (a) to (d) are SEM images of the catalysts Cat-1 to Cat-4 prepared in examples 1 to 4, respectively, and it is understood from fig. 3 that Pt incorporation does not change the morphology of the "porous foam" of the catalyst, and the catalyst pore sizes are substantially uniform. It can be seen that the incorporation of a small amount of Pt has less effect on the morphology of the catalyst.
FIG. 4 (a) shows XRD patterns of catalysts Cat-1 to Cat-4 prepared in examples 1 to 4, and it is understood from FIG. 4 (a) that the diffraction peak of MgO is dominant, and other metal diffraction peaks or oxide diffraction peaks thereof are substantially covered with MgO diffraction peaks. Further, catalyst Cat-4 was selected for detailed analysis, and as shown in FIG. 4 (b), a comparison analysis with FIG. 4 (a) revealed that catalyst Cat-4 still exhibited an unconventionally whole MgO peak after calcination, and no Fe-Mo-Pt alloy was formed.
Fig. 5 (a) to (d) are SEM images of SWNTs-1 to SWNTs-4 prepared in examples 1 to 4, respectively, and as can be seen from fig. 5, the pipe diameters of SWNTs prepared by the Fe-Mo-Pt-based catalyst provided by the present invention are fine and uniform. Further, the pipe diameters were counted, and as shown in FIG. 6, the average pipe diameters of SWNTs were mainly concentrated around 13.6 nm.
Comparative example 1
(1) Preparation of the catalyst: 0.131g of ammonium molybdate and 2g of citric acid are weighed and mixed and dissolved in 20mL of deionized water, 5mL of 10% HNO is added 3 Stirring uniformly to obtain a solution A; weighing 5.47g of ferric nitrate and 1g of urea, adding the mixture into 50mL of ethanol, heating to 80 ℃ and uniformly stirring to obtain a solution B; adding the solution A into the solution B, further adding 54g of light MgO (commercially available) under intense stirring, continuously stirring after uniform stirring, raising the temperature to 150 ℃, and continuously stirring for 160min to obtain a solid C; drying the solid C in a baking oven at 120 ℃ overnight, grinding the dried solid C into powder, and roasting the powder at the temperature of 2 ℃/min to 400 ℃ for 180min to obtain the catalyst Fe 30 Mo 1 MgO, designated Cat-5, wherein the content of Fe is about 2wt%.
(2) SWNTs preparation: comparative example 1 the SWNTs preparation procedure and materials were the same as in example 1 except that Cat-5 was used as catalyst in comparative example 1 and the remaining SWNTs preparation procedure and materials were the same as in example 1. SWNTs prepared in comparative example 1 were designated SWNTs-5.
Further performance testing of Cat-5, measured a carbon yield of 20.5%, and although the carbon yield of the FeMo catalyst was not significantly reduced compared to Cat-1, the tube diameter of the resulting SWNTs was increased, as shown in fig. 7, and fig. 7 is a TEM image and tube diameter profile of the SWNTs prepared in comparative example 1, showing that when the FeMo catalyst was not doped with Pt, the average particle size of the catalyst was significantly increased to 19.9nm, while no Pt added resulted in more MWNTs (fig. 7 black arrow is short MWNTs).
Comparative example 2
(1) Preparation of the catalyst: 0.131g of ammonium molybdate and 2g of citric acid are weighed and mixed and dissolved in 20mL of deionized water, 5mL of 10% HNO is added 3 Stirring uniformly to obtain a solution A; 5.47g of ferric nitrate, 148.7g of chloroplatinic acid and 1g of urea are weighed and added into 50mL of ethanol, and the temperature is raised to 80 ℃ and the mixture is stirred uniformly to obtain a solution B; adding the solution A into the solution B, further adding 54g of light MgO (commercially available) under intense stirring, continuously stirring after uniform stirring, raising the temperature to 150 ℃, and continuously stirring for 160min to obtain a solid C; the solid C was dried overnight in an oven at 120deg.C, completely dried, ground into powder, and calcined at 400deg.C for 180min at 2deg.C/min to give a catalyst called Cat-6, wherein the content of Fe was about 2wt% and the content of Pt was about 1wt%.
(2) SWNTs preparation: comparative example 2 the SWNTs preparation procedure and materials were the same as in example 1 except that comparative example 2 used Cat-6 as the catalyst and the remaining SWNTs preparation procedure and materials were the same as in example 1. SWNTs prepared in comparative example 2 were designated SWNTs-6.
According to calculation, when the loading amount of Pt reaches 1wt%, the carbon yield reaches 38.2%, and the yield is still improved, but as shown in FIG. 8, the average pipe diameter of the prepared carbon nano-tube is 22.5nm, and the pipe diameters of most SWNTs are smaller, but the pipe diameters of the prepared SWNTs are distributed unevenly in general, because excessive concentration of Pt can generate a large amount of carbon species, more SWNTs with larger pipe diameters are formed, and the quality of the SWNTs is reduced.
The above embodiments are merely illustrative of the principles of the present invention and its effectiveness, and are not intended to limit the invention. Modifications to the above would be obvious to those of ordinary skill in the art, without departing from the spirit and scope of the present invention. The scope of the invention is therefore intended to be indicated by the appended claims.

Claims (9)

1. The catalyst for preparing the small-diameter single-wall carbon nano tube is characterized by comprising an active component and a carrier, wherein the active component comprises a main active component and a secondary active component, the main active component is iron and platinum, the secondary active component is molybdenum, wherein the content of iron in the catalyst is 1-10wt%, the content of platinum is 0.03-0.5wt%, and the molar ratio of iron atoms to molybdenum atoms in the catalyst is (25-60): 1.
2. the catalyst of claim 1, wherein the support is selected from at least one of silica, alumina, magnesia.
3. The catalyst of claim 2 wherein the support is selected from the group consisting of magnesium oxide.
4. The catalyst according to claim 1, wherein the particle size of the catalyst active component is 8-15nm.
5. A method for preparing the catalyst for preparing the small-diameter single-walled carbon nanotubes according to claim 1, comprising the following steps:
s1: weighing soluble molybdenum salt and an auxiliary agent, mixing and dissolving in water, adding nitric acid, and uniformly stirring to obtain a solution A;
s2: weighing soluble ferric salt, soluble platinum salt and an initiator, adding the soluble ferric salt, the soluble platinum salt and the initiator into ethanol, and heating and stirring to obtain a solution B;
s3: mixing the solution A and the solution B, adding a carrier, stirring uniformly, and then continuously stirring, heating and evaporating to dryness to obtain a solid C;
s4: drying, grinding and roasting the solid C to obtain the catalyst for preparing the small-diameter single-wall carbon nano tube;
the roasting temperature is 300-400 ℃ and the roasting time is 2-6h.
6. The method according to claim 5, wherein the molar ratio of the iron atoms in the soluble iron salt to the molybdenum atoms in the soluble molybdenum salt is (25-60): 1.
7. The method according to claim 5, wherein the soluble platinum salt is weighed according to the content of platinum in the catalyst of 0.03 to 0.5wt%.
8. The preparation method according to claim 5, wherein the soluble iron salt is at least one selected from the group consisting of ferric chloride, ferric nitrate and ferric sulfate, the soluble molybdenum salt is at least one selected from the group consisting of ammonium molybdate and sodium molybdate, and the soluble platinum salt is at least one selected from the group consisting of chloroplatinic acid and sodium chloroplatinate; the initiator is selected from urea; the auxiliary agent is at least one selected from citric acid and sodium citrate.
9. A method for preparing single-walled carbon nanotubes, the method comprising the steps of:
s1: placing the catalyst according to any one of claims 1 to 4 or the catalyst prepared by the preparation method according to any one of claims 5 to 8 in a reaction device, and heating;
s2: introducing methane containing water vapor and inert gas for reaction, and purifying to obtain the single-walled carbon nanotube.
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