Trace molybdenum-doped iron-based catalyst and preparation method and application thereof
阅读说明：本技术 一种微量钼掺杂的铁基催化剂及其制备方法和应用 (Trace molybdenum-doped iron-based catalyst and preparation method and application thereof ) 是由 胡丹丹 陈秉辉 郑进保 吴钊男 于 2021-08-30 设计创作，主要内容包括：本发明提供一种微量钼掺杂的铁基催化剂及其制备方法和应用,将可溶性钼盐和引发剂混合溶于水中,得到前驱体溶液后加入可溶性铁盐、可溶性镁盐和助剂,搅拌溶解,加入氧化硅、氧化铝载体,搅拌均匀,得到均匀黏稠的浆料,并进行干燥、研磨、焙烧得到所述钼掺杂的铁基催化剂。本发明制备得到的催化剂具有疏松多孔泡沫状结构,并且采用低温焙烧,微量Mo掺杂,形成特殊的钼酸铁结构,进一步采用水进行刻蚀,避免破坏该结构,可以实现高品质SWNTs的规模化制备。(The invention provides a trace molybdenum-doped iron-based catalyst and a preparation method and application thereof. The catalyst prepared by the invention has a loose porous foam structure, a special iron molybdate structure is formed by adopting low-temperature roasting and trace Mo doping, the structure is further etched by adopting water, the structure is prevented from being damaged, and the large-scale preparation of high-quality SWNTs can be realized.)
1. A preparation method of a trace molybdenum-doped iron-based catalyst is characterized by comprising the following steps:
s1: mixing soluble molybdenum salt and an initiator, and dissolving the mixture in water to obtain a precursor solution;
s2: adding soluble iron salt, soluble magnesium salt and an auxiliary agent into the precursor solution obtained in the step S1, stirring and dissolving, adding silicon oxide and an alumina carrier, and stirring uniformly to obtain uniform and viscous slurry;
s3: and (4) drying, grinding and roasting the uniform and viscous slurry obtained in the step (S2) at 300-400 ℃ to obtain the molybdenum-doped iron-based catalyst.
2. The method of claim 1, wherein the molar ratio of iron atoms in the soluble iron salt to molybdenum atoms in the soluble molybdenum salt is (25-60): 1.
3. The method of claim 2, wherein the molar ratio of iron atoms in the soluble iron salt to magnesium atoms in the soluble magnesium salt is (20-30): 1.
4. The preparation method according to claim 1, wherein the soluble iron salt is selected from at least one of ferric chloride, ferric nitrate and ferric sulfate, the soluble molybdenum salt is selected from at least one of ammonium molybdate and sodium molybdate, and the soluble magnesium salt is selected from at least one of magnesium chloride, magnesium nitrate and magnesium sulfate; the initiator is selected from urea; the auxiliary agent is at least one of citric acid and sodium citrate.
5. The preparation method according to claim 1, wherein the mass ratio of the silica to the alumina carrier is 3-9: 1, preferably 4: 1.
6. The method as claimed in claim 1, wherein the calcination temperature is 300-400 ℃ and the calcination time is 2-6 h.
7. A molybdenum-doped iron-based catalyst, which comprises an active component and a carrier, wherein the active component comprises a main active component and an auxiliary active component, the main active component is iron, the auxiliary active component is molybdenum, the iron content in the catalyst is 2-10 wt%, preferably 4-6 wt%, and the molar ratio of iron atoms to molybdenum atoms in the catalyst is (25-60):1, the carrier is silicon oxide and aluminum oxide.
8. The catalyst according to claim 7, wherein the particle size of the active component FeMo in the catalyst is 15-25 nm.
9. The catalyst according to claim 7, wherein the mass ratio of the carrier silica to alumina is 3 to 9: 1.
10. A method for preparing single-walled carbon nanotubes, comprising the steps of:
s1: placing the catalyst prepared by the preparation method of any one of claims 1 to 6 or the catalyst of any one of claims 7 to 9 in a reaction device, and raising the temperature;
s2: and adding methane containing water vapor and inert gas for reaction, and purifying to obtain the single-walled carbon nanotube.
Technical Field
The invention relates to the technical field of single-walled carbon nanotube preparation, in particular to a trace molybdenum-doped iron-based catalyst and a preparation method and application thereof.
Background
As a novel carbon material, carbon nanotubes have many excellent properties such as mechanical properties, electrical conductivity, and thermal conductivity due to their specific structure. 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 the wall layers, the single-walled carbon nanotubes have a one-dimensional carbon nanotube hollow tubular structure composed of carbon atoms and can be regarded as seamless carbon tubes formed by winding single-layer graphene, and carbon nanotube tubular structures similar to the structure thereof include double-walled carbon nanotubes and multi-walled carbon nanotubes and are regarded as concentric tubular structures formed by winding double-layer graphene and multi-layer graphene, respectively.
Among them, single-walled carbon nanotubes (SWNTs) have a high aspect ratio, are typical one-dimensional nanomaterials, and their special tubular structures determine the excellent physical, chemical, electrical and mechanical properties of carbon nanotubes, thereby having very important application values in many fields, especially in the fields of energy storage, environmental protection, electronics, composites, and medical care. At present, methods for growing single-walled carbon nanotubes mainly include an arc discharge method, a laser evaporation catalytic precipitation technology, a Chemical Vapor Deposition (CVD) method and the like, the first two methods are very complicated in operation, and a solid carbon source needs to be evaporated into carbon atoms at a high temperature of more than 3000 ℃, which severely limits the number of carbon nanotubes that can be synthesized, and in addition, the carbon nanotubes grown by evaporating the carbon atoms are highly entangled in shape and are mutually mixed with other carbon impurities and metal catalysts, so that the application range of the carbon nanotubes is severely limited. The chemical vapor deposition method for preparing the single-walled carbon nanotube has the advantages of convenient control, large yield, low impurity content of a product and the like, so that the method is the most main method for preparing the single-walled carbon nanotube, but the chemical vapor deposition method for preparing the SWNTs in a large scale still has very serious problems, such as low yield of the SWNTs, high preparation cost of the catalyst and the like.
The Fe group metal has high SWNTs growth activity and is widely used for industrially producing the carbon nano tube, but the service life of the catalyst is short, and the satisfactory SWNTs yield is difficult to obtain. To increase the yield of SWNTs, other metals may be added to achieve the requirement of high activity, long life of the catalyst. The metal Mo does not have the high activity characteristic of SWNTs growth, but the Mo and C have large binding force and high carbon dissolving capacity, and can improve the carbon yield of the catalyst, so that the single-walled carbon nanotube can be prepared on a large scale by adopting the CVD growth of the single-walled carbon nanotube based on the Fe-Mo bimetallic catalyst. However, based on the action of Mo, the amount of Mo in the prior art is high, and the atomic ratio of Fe to Mo is usually about 0.5 to 10, for example, the beijing university application CN201911006484 discloses a CVD preparation method of a single-walled carbon nanotube, which can realize the macro-quantitative preparation of the carbon nanotube by optimizing the catalyst formulation, reducing the Mg content in the catalyst, and optimizing the flux of carbon-containing gas, hydrogen and inert gas, and the carbon yield in the growth product is close to 2 times, wherein the molar ratio of Mo to Fe in the catalyst formulation is 0.1, the amount of Mo is high, and few researchers recognize that the low Mo addition amount can not only maintain the activity of the catalyst, but also significantly improve the stability of the catalyst.
Disclosure of Invention
In order to solve the problems, the invention provides a molybdenum-doped iron-based catalyst and a preparation method and application thereof. Can realize the large-scale preparation of SWNTs and simultaneously has trace H2O can regulate and control the quality and the property of SWNTs, and effectively improves the quality of products.
In a first aspect, the present invention provides a method for preparing a molybdenum-doped iron-based catalyst, the method comprising the steps of:
s1: mixing soluble molybdenum salt and an initiator, and dissolving the mixture in water to obtain a precursor solution;
s2: adding soluble iron salt, soluble magnesium salt and an auxiliary agent into the precursor solution obtained in the step S1, stirring and dissolving, then adding silicon oxide and an alumina carrier under vigorous stirring, and stirring uniformly to obtain uniform and viscous slurry;
s3: and (4) drying the uniform and sticky slurry obtained in the step (S2), then grinding, and finally roasting at low temperature to obtain the molybdenum-doped iron-based catalyst.
Further, 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 molar ratio of iron atoms in the soluble iron salt to magnesium atoms in the soluble magnesium salt is (20-30): 1.
Furthermore, weighing the carrier according to 2-10 wt% of the iron content in the catalyst.
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 selected from at least one of ammonium molybdate and sodium molybdate.
Further, the soluble magnesium salt is selected from at least one of magnesium chloride, magnesium nitrate and magnesium sulfate.
Further, the initiator is selected from urea.
Further, the auxiliary agent is at least one selected from citric acid and sodium citrate.
Further, the mass ratio of the silicon oxide to the alumina carrier is 3-9: 1, preferably 4: 1.
Furthermore, the drying temperature is 80-160 ℃, and the drying time is 6-48 h.
Further, the roasting temperature is 300-400 ℃, and the roasting time is 2-6 h.
The invention provides a molybdenum-doped iron-based catalyst, which comprises an active component and a carrier, wherein the active component comprises a main active component and an auxiliary active component, the main active component is iron, the auxiliary active component is molybdenum, and the carrier is silicon oxide and aluminum oxide.
Further, the content of iron in the catalyst is 2-10 wt%, preferably 4-6 wt%.
Further, the molar ratio of the iron atoms to the molybdenum atoms in the catalyst is (25-60):1, preferably 30: 1.
Furthermore, the particle size of the active component FeMo in the catalyst is 15-25 nm.
Further, the mass ratio of the carrier silicon oxide to the carrier aluminum oxide is 3-9: 1, and preferably 4: 1.
Further, the iron and molybdenum form iron molybdate.
In a third aspect, the present invention provides a method for preparing single-walled carbon nanotubes, comprising the steps of:
s1: placing the catalyst provided by the invention or the catalyst prepared by the preparation method provided by the invention in a reaction device, and heating to a reaction temperature;
s2: introducing methane containing water vapor and inert gas for reaction;
s3: and purifying the product obtained in the step S2 to obtain the single-wall carbon nanotube.
Further, the reaction temperature is 600-900 ℃, preferably 700-800 ℃.
Further, the concentration of the water vapor is 100-1000 ppm.
Further, the inert gas is one of helium and argon.
Further, the concentration of the methane is 20-50%.
Compared with the prior art, the invention at least has the following technical effects:
(1) the invention adopts low-concentration Mo doping and low-temperature roasting to form FeMo alloy, effectively improves the carbon yield and the purity of SWNTs, and simultaneously selects a proper amount of H2O is used as an etchant, the microstructure of FeMo is not damaged, the catalyst has better sintering resistance, the service life of the catalyst is prolonged, and trace H is added2O can regulate and control the quality and the property of SWNTs, and effectively improves the quality of products.
(2) The FeMo in the catalyst prepared by the method has small particle size, the average particle size is 15-25nm, and the catalyst prepared by the method has a porous foam structure, has the advantages of high porosity (micro mesopores are concentrated to form a mesopore-macropore loose structure), high metal dispersion degree and high activity, improves sufficient active sites and growth space for the mass growth of SWNTs, and can realize the large-scale preparation of the SWNTs.
(3) The invention adopts the silicon oxide and the alumina carrier, overcomes the defect that the magnesium oxide carrier is difficult to form, effectively improves the fluidity of the catalyst in a fluidized bed, and optimizes the proper reaction conditions of the obtained Fe-Mo catalyst. The catalyst used is at a higher CH4When the concentration is reacted with a lower reaction temperature, the growth of high-quality and high-yield SWNTs is facilitated. I of SWNTs prepared by the method of the inventionG/IDAll exceed 13, the specific surface area is as high as 1053.3m2The carbon yield can reach 33.5 percent and the purity of SWNTs is as high as 98.7 percent.
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 embodiments of the invention and together with the description serve to explain the principles of the invention and not to limit the invention.
FIG. 1 is an SEM photograph of catalyst Cat-1 prepared in example 1;
FIG. 2 is a TEM image of catalyst Cat-1 prepared in example 1;
FIG. 3 is an SEM photograph of the product SWNTs-1 of example 1;
FIG. 4 is an SEM photograph of product SWNTs-7 of comparative example 4;
FIG. 5 is an SEM photograph of SWNTs-10 as a product of comparative example 7.
Detailed Description
The invention provides a preparation method of a molybdenum-doped iron-based catalyst, which comprises the following steps:
s1: mixing soluble molybdenum salt and an initiator, and dissolving the mixture in water to obtain a precursor solution; according to an embodiment of the present invention, the soluble molybdenum salt is selected from at least one of ammonium molybdate and sodium molybdate, and the initiator is selected from urea.
S2: adding soluble iron salt, soluble magnesium salt and an auxiliary agent into the obtained precursor solution, stirring and dissolving, then adding silicon oxide and an alumina carrier under vigorous stirring, and stirring uniformly to obtain uniform and viscous slurry; according to the embodiment of the invention, the soluble ferric salt is at least one selected from ferric chloride, ferric nitrate and ferric sulfate, the soluble magnesium salt is at least one selected from magnesium chloride, magnesium nitrate and magnesium sulfate, the auxiliary agent is at least one selected from citric acid and sodium citrate, and the mass ratio of the silica alumina is 3-9: 1.
s3: and drying the obtained uniform and viscous slurry, grinding, and finally roasting at the low temperature of 300-400 ℃ to obtain the molybdenum-doped iron-based catalyst.
According to the embodiment of the invention, 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. And the low-concentration Mo is adopted for doping, so that the carbon yield and the SWNTs purity are effectively improved.
According to the embodiment of the invention, the molar ratio of the iron atoms in the soluble iron salt to the magnesium atoms in the soluble magnesium salt is (20-30): 1.
According to the examples of the present invention, the carrier was weighed in an amount of 2 to 10 wt% of the iron content in the catalyst.
According to the embodiment of the invention, the drying temperature is 80-160 ℃, and the drying time is 6-48 h.
According to the embodiment of the invention, the roasting temperature is 300-400 ℃, and the roasting time is 2-6 h.
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 in a reaction device, and heating to a reaction temperature; the reaction temperature according to the embodiment of the invention is 600-900 ℃, and preferably 700-800 ℃.
S2: methane containing water vapor and inert gas is added for reaction.
S3: and purifying the product obtained in the step S2 to obtain the single-wall carbon nanotube.
According to the embodiment of the invention, the concentration of the water vapor is 100-1000ppm, the concentration of the methane is 20-50%, and the inert gas is preferably argon. The invention utilizes H2O is used as an etchant, does not damage the microstructure of FeMo, and can ensure that the catalyst has better sintering resistance and ductilityThe service life of the catalyst is prolonged, and trace amount of H2O can regulate and control the quality and the property of SWNTs, and effectively improves the quality of products.
The detailed preparation process and conditions of the preparation method provided by the present invention are illustrated by the following examples.
Example 1
(1) Preparation of the catalyst: weighing 0.196g of ammonium molybdate and 1g of urea, mixing, dissolving in 20mL of deionized water, and uniformly stirring; then 8.2g of ferric nitrate, 0.148g of magnesium nitrate and 2g of citric acid are added, stirred and dissolved, after the mixture is stirred until the mixture is completely dissolved, 43.2g of fumed silica and 10.8g of gamma-alumina (more than 200 meshes) are further added under vigorous stirring, and the mixture is stirred until uniform and viscous slurry is formed; drying in a 120 deg.C oven overnight, grinding into powder after completely drying, heating to 350 deg.C at 2 deg.C/min, and calcining for 240min to obtain catalyst Fe30Mo1MgO, denoted Cat-1, with a Fe content of about 3 wt.%.
(2) Preparation of SWNTs: placing 0.5g of Cat-1 catalyst in a quartz reaction tube with the inner diameter of 16mm, introducing 100sccm argon, and heating to the reaction temperature of 800 ℃ for 60 min; introducing a mixed gas of 500sccm methane, water vapor and argon, wherein the concentration of the methane is 30 percent, and the concentration of the water vapor is 200ppm, and starting the SWNTs growth reaction; closing the reaction gas after 60min, stopping heating, keeping 100sccm Ar, and cooling to room temperature; the product was removed and then purified to yield single-walled carbon nanotubes, designated SWNTs-1.
Fig. 1 is an SEM image of the catalyst prepared in example 1, and it can be seen that the catalyst prepared in the present invention has a porous foam-like structure, which provides growth support and a wide space for SWNTs, so that the growth direction of the SWNTs is expanded from two dimensions to three dimensions, and the catalyst can satisfy the requirements of high metal loading and high dispersion, and form a barrier space, reduce the mutual influence between tubes, and facilitate the mass growth of the SWNTs due to the formation of a loose foam-like space structure composed of macropores and mesopores.
FIG. 2 is a TEM image of the catalyst prepared in example 1, and it can be seen that the FFT conversion shows that MgO (200) and Fe are excluded3C (301) crystal plane, and also Fe2MoO4(211), (432)And (223), indicating that Fe and Mo form a specific structure.
Example 2
The procedure for preparing the catalyst and the selection of the materials were the same as in example 1, except that the amount of ammonium molybdate used in this example was 0.098g, and the procedure for preparing the catalyst and the selection of the materials were the same as in example 1. The catalyst prepared in this example was Fe60Mo1MgO, referred to as Cat-2.
Preparation of SWNTs: the procedure and materials for preparing SWNTs in this example were the same as those in example 1, except that Cat-2 was used as the catalyst in this example, and the procedure and materials for preparing SWNTs were the same as those in example 1. The SWNTs prepared in this example were referred to as SWNTs-2.
Example 3
The procedure for preparing the catalyst and the selection of the materials in this example were the same as in example 1 except that the amount of ammonium molybdate used in this example was 0.0235g, and the procedure for preparing the catalyst and the selection of the materials in the remaining procedure were the same as in example 1. The catalyst prepared in this example was Fe25Mo1MgO, denoted Cat-3.
Preparation of SWNTs: the procedure and materials for preparing SWNTs in this example were the same as those used in example 1, except that Cat-3 was used as the catalyst in this example, and the remaining procedure and materials for preparing SWNTs were the same as those used in example 1. SWNTs prepared in this example were designated as SWNTs-3.
Performance test was performed on SWNTs-1, SWNTs-2 and SWNTs-3 prepared in examples 1 to 3 to determine IG/IDThe specific results are shown in table 1:
TABLE 1 SWNTs obtained in examples 1 to 3 are IG/IDValue of
Sample (I)
SWNTs
IG/ID
Example 1
SWNTs-1
15.5
Example 2
SWNTs-2
14.3
Example 3
SWNTs-3
14.7
As can be seen from the above table, the catalyst prepared by the present invention has the following characteristicsG/IDAll exceed 13, have very good graphitization degree, and the more complete the tube wall structure of the obtained SWNTs.
Comparative example 1
Comparative example 1 the catalyst preparation procedure and materials were as in example 1 except that the amount of ammonium molybdate in comparative example 1 was 0.588g and the remaining catalyst preparation procedures and materials were as in example 1. The catalyst prepared in comparative example 1 was Fe10Mo1MgO, denoted Cat-4.
Preparation of SWNTs: comparative example 1 the procedure for the preparation of SWNTs and the selection of materials were the same as in example 1, except that Cat-4 was used as the catalyst in comparative example 1 and the remaining procedures and materials for the preparation of SWNTs were the same as in example 1. The SWNTs prepared in comparative example 1 were designated as SWNTs-4.
Comparative example 2
Comparative example 2 the catalyst preparation procedure and materials were the same as in example 1 except that the amount of ammonium molybdate used in comparative example 2 was 2.94g, and the remaining catalyst preparation procedures and materials were the same as in example 1. The catalyst prepared in the comparative example is prepared into Fe2Mo1MgO, denoted Cat-5.
Preparation of SWNTs: comparative example 2 the procedure for preparing SWNTs and the selection of materials were the same as in example 1, except that Cat-5 was used as the catalyst in comparative example 2 and the remaining procedure for preparing SWNTs and the selection of materials were the same as in example 1. SWNTs prepared in comparative example 2 were designated as SWNTs-5.
Comparative example 3
Weighing 8.2g of ferric nitrate and 0.196g of ammonium molybdate, dissolving the ferric nitrate and the ammonium molybdate in a proper amount of absolute ethyl alcohol, then adding 54g of light MgO while stirring, putting the mixture into a 100 ℃ oven for drying overnight after uniformly stirring, grinding the mixture into powder after completely drying, heating the powder to 450 ℃ at a speed of 2 ℃/min, and roasting the powder for 180min, wherein the ethanol amount is 1.0-1.2 times of the saturated adsorption amount of the light MgO, and the obtained catalyst is 3 wt% of Fe30Mo1The term,/MgO-IM, is denoted as Cat-6.
Preparation of SWNTs: comparative example 3 the procedure for the preparation of SWNTs and the selection of materials were the same as in example 1, except that comparative example 3 used Cat-6 as the catalyst and the remaining procedure for the preparation of SWNTs and the selection of materials were the same as in example 1. SWNTs prepared in comparative example 3 were designated as SWNTs-6.
The structural data of the catalysts obtained in example 1 and comparative example 3 are shown in Table 2
Table 2 desorption standard data for N2 for the catalyst obtained in example 1
BET(m2g)
Hole valley (cm)3/g)
Average pore diameter (nm)
Cat-1
93.1
0.39
17.2
Cat-6
62.9
0.208
13.9
As can be seen from Table 2, compared with the conventional impregnation method, the catalyst prepared by the preparation method of the invention has higher specific surface area and better pore structure, and can provide more growth sites for the preparation of single carbon nanotubes.
Comparative example 4
Preparation of SWNTs: placing 0.5g of Cat-1 catalyst in a quartz reaction tube with the inner diameter of 16mm, introducing 100sccm argon, and heating to the reaction temperature of 800 ℃ for 60 min; introduction of H2Mixed with Ar, in which H2Keeping the concentration at 10% for 30min, introducing 500sccm methane and H2Argon gas mixture, wherein the concentration of methane is 30%, H2Starting the SWNTs growth reaction with the concentration of 10%; closing the reaction gas after 60min, stopping heating, keeping 100sccm Ar, and cooling to room temperature; the product was removed and then purified to yield single-walled carbon nanotubes, designated SWNTs-7.
Comparative example 5
Comparative example 5 catalyst preparation procedure and material selection the same as in example 1 except that the calcination temperature of the catalyst of comparative example 5 was 450 c, and the remaining catalyst preparation procedure and material selection were the same as in example 1. The catalyst prepared in comparative example 5 was designated Cat-8.
Preparation of SWNTs: comparative example 5 the procedure for preparing SWNTs and the selection of materials were the same as in example 1, except that comparative example 5 used Cat-8 as the catalyst and the remaining procedure for preparing SWNTs and the selection of materials were the same as in example 1. The SWNTs prepared in comparative example 5 were designated as SWNTs-8.
Comparative example 6
Comparative example 6 the catalyst preparation procedure and material selection were the same as in example 1, except that the calcination temperature in comparative example 6 was 500 deg.c, and the remaining catalyst preparation procedures and material selection were the same as in example 1. The catalyst prepared in comparative example 6 was designated Cat-9.
Preparation of SWNTs: comparative example 6 the procedure for preparing SWNTs and the selection of materials were the same as in example 1, except that comparative example 6 used Cat-9 as the catalyst and the remaining procedure for preparing SWNTs and the selection of materials were the same as in example 1. The SWNTs prepared in comparative example 6 were designated as SWNTs-9.
Comparative example 7
Preparation of SWNTs: comparative example 7 the procedure for preparing SWNTs and the selection of materials were the same as in example 1, except that the water vapor concentration was 2000ppm, and the remaining procedure for preparing SWNTs and the selection of materials were the same as in example 1. The SWNTs prepared in comparative example 7 were designated as SWNTs-10.
Comparative example 8
Preparation of SWNTs: placing 0.5g of Cat-1 catalyst in a quartz reaction tube with the inner diameter of 16mm, introducing 100sccm argon, and heating to the reaction temperature of 800 ℃ for 60 min; introducing a mixed gas of 500sccm methane and argon, wherein the concentration of the methane is 30%, and starting the SWNTs growth reaction; after 60min, closing the reaction gas, stopping heating, and keeping 100sccmAr to cool to room temperature; the product was removed and then purified to yield single-walled carbon nanotubes, designated SWNTs-11.
Performance tests were performed on SWNTs-1, SWNTs-2, SWNTs-3, SWNTs-4, SWNTs-5, SWNTs-6, SWNTs-7, SWNTs-8, SWNTs-9, SWNTs-10 and SWNTs-11 prepared in examples 1 to 3 and comparative examples 1 to 8 to obtain SWNTs carbon yield and SWNTs purity, respectively, and the specific results are shown in Table 3:
TABLE 3 results of SWNTs obtained in examples 1 to 3 and comparative examples 1 to 8
Sample (I)
SWNTs
SWNTs carbon yield (%)
SWNTs purity (%)
Example 1
SWNTs-1
33.5
98.7
Example 2
SWNTs-2
32.9
97.4
Example 3
SWNTs-3
31.2
95.5
Comparative example 1
SWNTs-4
30.5
89.1
Comparative example 2
SWNTs-5
28.8
80.6
Comparative example 3
SWNTs-6
20.8
85.7
Comparative example 4
SWNTs-7
9.8
59.7
Comparative example 5
SWNTs-8
25.9
91.3
Comparative example 6
SWNTs-9
12.6
84.6
Comparative example 7
SWNTs-10
17.1
76.6
Comparative example 8
SWNTs-11
29.4
63.4
As shown in table 3, the carbon yield of SWNTs prepared by the method of the present invention was up to 33.5%, and the purity of SWNTs was up to 98.7%, thus it was found that the method provided by the present invention is advantageous for growing high quality and high yield SWNTs. Meanwhile, comparing the product obtained from the catalyst obtained in example 1 with the test results of other examples or comparative examples, the following conclusions can be drawn: (1) comparing example 1 with comparative examples 1-2, it can be seen that trace Mo doping can result in better carbon yield and purity, because the low-concentration Mo and Fe form an iron molybdate structure, which is more stable under high temperature reaction, and become a structural assistant between Fe, thereby avoiding the growth and aggregation of Fe, and the obtained SWNTs have better quality, and when the Mo content is too high, Fe and Mo exist independently, and the high temperature exists separately, so that the high temperatureThe lower active component particles tend to become larger, producing more MWNTs. (2) Compared with the comparative example 3, the catalyst prepared by the method has a better microstructure, sufficient active sites and growth space are improved for the mass growth of the SWNTs, and the scale preparation of the SWNTs can be realized. (3) Comparative example 4 uses H2As an etchant, it can be seen from FIG. 4 that the obtained carbon nanotubes have less bundles and a low yield because of H2Not only can play a role in etching, but also can damage the original catalyst structure; comparative example 7 used 2000ppm of etchant H2O, it can be seen from FIG. 5 that the resulting carbon nanotubes are not uniform in morphology due to the low concentration of H2O acts on the catalytic interface to directly influence the growth of SWNTs, thereby being beneficial to etching disordered carbon. However, higher concentrations of H2O functionalizes SWNTs, preferentially etching small-diameter SWNTs, and gradually etching MWNTs, forming more defects and impurities. Comparative example 8 without addition of etchant, the presence of a large amount of amorphous carbon resulted in a significant decrease in purity. (4) It can be seen readily from the products obtained in comparative examples 5-6 that increasing the calcination temperature resulted in a catalyst with significantly reduced catalytic performance, which may be detrimental to the formation of iron molybdate structures upon high temperature calcination.
The foregoing embodiments are merely illustrative of the principles and utilities of the present invention and are not intended to limit the invention. Any person skilled in the art can modify the above-described embodiments without departing from the spirit and scope of the present invention. Therefore, the scope of the invention should be determined from the following claims.