A catalyst for preparing single-walled carbon nanotubes and a preparation method thereof

Abstract

The present invention provides a catalyst for preparing single-walled carbon nanotubes and a preparation method thereof, the preparation method comprising the following steps: (1) mixing a metal salt solution containing a first metal salt and a second metal salt with a precipitant to obtain a coprecipitation liquid; (2) subjecting the coprecipitation liquid to a first heat treatment under a first atmosphere and a second heat treatment under a second atmosphere in sequence to obtain the catalyst. The carbon nanotube catalyst prepared by the preparation method has the advantages of easy storage, uniform particle size distribution, high mechanical strength, and not easy to be deactivated and agglomerated during use, and is suitable for a fluidized bed preparation process for continuous production, and has extremely high industrial application value.

Description

Technical Field

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

[0002] More than 90% of the carbon nanotubes currently on the market are used to prepare lithium battery conductive agents. The aspect ratio of carbon nanotubes is directly related to their conductivity. The larger the aspect ratio, the better the conductivity. In lithium batteries, only a very small amount of carbon nanotubes is needed as a conductive agent to achieve excellent results. The remaining amount can allow the positive and negative electrodes of the battery to load more active substances, thereby increasing the battery capacity and cycle life.

[0003] The vast majority of carbon nanotubes sold in the domestic market are multi-walled carbon nanotubes prepared by the CVD method, with diameters ranging from 5 to 40 nm. Currently, the industry generally believes that the diameter of carbon nanotubes is consistent with the size of the catalyst, so how to reduce the size of the catalyst and maintain the uniformity of the catalyst size has become a difficult problem in the industry.

[0004] CN 111495380 A provides a method for preparing a carbon nanotube catalyst and a carbon nanotube with a diameter of 2-14 nm. The technical scheme is to prepare a mixed solution containing Mg2+, Al3+, Co2+ and a catalyst promoter containing metal ions, then add a weak base solution, and then calcine at high temperature to prepare a catalyst with a spinel structure, which can improve the yield of carbon nanotubes, and the prepared carbon nanotubes have a small diameter distribution, a large specific surface area, and good electrical conductivity. However, they are still multi-walled carbon nanotubes, and there is still much room for improvement. Summary of the invention

[0005] In order to solve the technical problems existing in the prior art, the present invention provides a catalyst for preparing single-walled carbon nanotubes and a preparation method thereof. The carbon nanotube catalyst prepared by the preparation method has the advantages of easy storage, uniform particle size distribution, high mechanical strength, and not easy to deactivate and agglomerate during use. It is suitable for a fluidized bed preparation process for continuous production and has extremely high industrial application value.

[0006] In order to achieve the above technical effects, the present invention adopts the following technical solutions:

[0007] One of the purposes of the present invention is to provide a method for preparing a catalyst for preparing single-walled carbon nanotubes, the preparation method comprising the following steps:

[0008] (1) mixing a metal salt solution containing a first metal salt and a second metal salt with a precipitant to obtain a coprecipitation solution;

[0009] (2) The coprecipitation liquid is subjected to a first heat treatment in a first atmosphere and a second heat treatment in a second atmosphere to obtain the catalyst.

[0010] In the present invention, the catalyst prepared by the preparation method can be used for the preparation of single-walled carbon nanotubes because the particle size distribution of the catalyst is between 1-5 nm.

[0011] In the present invention, the catalyst prepared by the preparation method has the advantages of easy storage, uniform particle size distribution, high mechanical strength, and not easy to be deactivated and agglomerated during use. The main reason is that the catalyst is oxide particles with a particle size distribution of 100-600nm when stored, and is split into metal single substance particles with a particle size distribution between 1-5nm through hydrogen reduction during use.

[0012] As a preferred technical solution of the present invention, in step (1), the first metal salt comprises a combination of at least two of an iron salt, a cobalt salt, a nickel salt, a cerium salt, an indium salt or a zirconium salt. Typical but non-limiting examples of the combination include: a combination of an iron salt and a cobalt salt, a combination of a cobalt salt and a nickel salt, a combination of a nickel salt and a cerium salt, a combination of a cerium salt and an indium salt, a combination of an indium salt and a zirconium salt, a combination of a zirconium salt and an iron salt, or a combination of an iron salt, a cobalt salt and a nickel salt, etc.

[0013] Preferably, the second metal salt in step (1) comprises any one of silver salt, gold salt, ruthenium salt, manganese salt, tin salt or lead salt, or a combination of at least two thereof. Typical but non-limiting examples of the combination include: a combination of silver salt and gold salt, a combination of gold salt and ruthenium salt, a combination of ruthenium salt and manganese salt, a combination of manganese salt and tin salt, a combination of tin salt and lead salt, a combination of lead salt and silver salt, or a combination of silver salt, gold salt and ruthenium salt, etc.

[0014] Preferably, in step (1), the first metal salt and the second metal salt each independently comprise nitrate.

[0015] As a preferred technical solution of the present invention, the concentration of the first metal salt in the metal salt solution in step (1) is 0.1 to 15 wt%, such as 0.1 wt%, 0.5 wt%, 1 wt%, 2 wt%, 5 wt%, 8 wt%, 10 wt%, 12 wt% or 15 wt%, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0016] Preferably, the concentration of the second metal salt in the metal salt solution in step (1) is 0.01-1wt%, such as 0.02wt%, 0.05wt%, 0.1wt%, 0.2wt%, 0.5wt%, 0.8wt% or 1wt%, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0017] As a preferred technical solution of the present invention, the precipitant in step (1) includes aqueous ammonia.

[0018] Preferably, the concentration of the ammonia water is 1 to 5 mol / L, such as 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, 4 mol / L, 4.5 mol / L or 5 mol / L, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0019] As a preferred technical solution of the present invention, in step (2), the first atmosphere is a mixed atmosphere of hydrogen and nitrogen.

[0020] Preferably, the volume concentration of hydrogen in the first atmosphere is 1 to 50%, such as 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45% or 50%, etc., but is not limited to the listed values. Other unlisted values ​​within the numerical range are also applicable, and more preferably 1 to 20%.

[0021] Preferably, the gas flow rate of the first atmosphere in step (2) is 0.5 to 1.0 m / s, such as 0.5 m / s, 0.6 m / s, 0.7 m / s, 0.8 m / s, 0.9 m / s or 1.0 m / s, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0022] As a preferred technical solution of the present invention, the temperature of the first heat treatment in step (2) is 1000-1500°C, such as 1000°C, 1100°C, 1200°C, 1300°C, 1400°C or 1500°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0023] Preferably, the time of the first heat treatment in step (2) is 1 to 3 h, such as 1 h, 1.2 h, 1.5 h, 1.8 h, 2 h, 2.2 h, 2.5 h, 2.8 h or 3 h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0024] As a preferred technical solution of the present invention, in step (2), nitrogen is continuously introduced for 10 to 30 minutes after the first heat treatment, such as 10 minutes, 12 minutes, 15 minutes, 18 minutes, 20 minutes, 22 minutes, 25 minutes, 28 minutes or 30 minutes, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0025] Preferably, the flow rate of the nitrogen is 0.5-1.0 m / s, such as 0.5 m / s, 0.6 m / s, 0.7 m / s, 0.8 m / s, 0.9 m / s or 1.0 m / s, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0026] As a preferred technical solution of the present invention, in step (2), the second atmosphere is a mixed gas of nitrogen and oxygen.

[0027] Preferably, the volume concentration of oxygen in the second atmosphere is 0.5-5%, such as 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5% or 5%, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0028] Preferably, the gas flow rate of the second atmosphere in step (2) is 0.5 to 1.0 m / s, such as 0.5 m / s, 0.6 m / s, 0.7 m / s, 0.8 m / s, 0.9 m / s or 1.0 m / s, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0029] As a preferred technical solution of the present invention, the temperature of the second heat treatment in step (2) is 600-1200°C, such as 600°C, 700°C, 800°C, 900°C, 1000°C, 1100°C or 1200°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0030] Preferably, the time for the second heat treatment in step (2) is 1 to 3 h, such as 1 h, 1.2 h, 1.5 h, 1.8 h, 2 h, 2.2 h, 2.5 h, 2.8 h or 3 h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0031] In the present invention, the role of the first heat treatment is to first use hydrogen to reduce the catalyst into small particles of metal elements, and the role of the second heat treatment is to re-oxidize the metal elements into metal oxides so that the catalyst particle size can be further reduced to 1-5nm when hydrogen is used for secondary reduction during use.

[0032] A second object of the present invention is to provide a catalyst, which is prepared by the above-mentioned preparation method and is used to prepare single-walled carbon nanotubes.

[0033] Compared with the prior art, the present invention has at least the following beneficial effects:

[0034] (1) The present invention provides a catalyst for preparing single-walled carbon nanotubes and a preparation method thereof. The carbon nanotube catalyst prepared by the preparation method has the advantages of easy storage, uniform particle size distribution, high mechanical strength, and not easy to be deactivated and agglomerated during use;

[0035] (2) The present invention provides a catalyst for preparing single-walled carbon nanotubes and a preparation method thereof. The carbon nanotube catalyst prepared by the preparation method is suitable for a fluidized bed preparation process for continuous production and has extremely high industrial application value;

[0036] (3) The present invention provides a catalyst for preparing single-walled carbon nanotubes and a preparation method thereof. The carbon nanotube catalyst prepared by the preparation method can prepare single-walled carbon nanotubes with a tube diameter mainly of 1-2 nm, and the tube diameter distribution range is 1-5 nm. DETAILED DESCRIPTION

[0037] For the convenience of understanding the present invention, the present invention lists the following embodiments. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0038] Example 1

[0039] This embodiment provides a method for preparing a catalyst for preparing single-walled carbon nanotubes, the preparation method comprising the following steps:

[0040] (1) mixing a metal salt solution containing ferric nitrate (0.05 wt%), cobalt nitrate (0.05 wt%) and silver nitrate (0.01 wt%) with 1 mol / L ammonia water to obtain a coprecipitation solution;

[0041] (2) subjecting the coprecipitation liquid to a first heat treatment in a mixed atmosphere of hydrogen (volume concentration 1%) and nitrogen, wherein the gas flow rate of the first atmosphere is 0.5 m / s, the temperature of the first heat treatment is 1000° C., and the time is 3 h;

[0042] After the first heat treatment, nitrogen is continuously introduced for 10 minutes, and the flow rate of the nitrogen is 1.0 m / s;

[0043] The second heat treatment is carried out in a mixed atmosphere of nitrogen and oxygen (volume concentration is 0.5%), the gas flow rate of the second atmosphere is 0.5 m / s, the temperature of the second heat treatment is 600° C., and the time is 3 hours to obtain the catalyst.

[0044] Example 2

[0045] This embodiment provides a method for preparing a catalyst for preparing single-walled carbon nanotubes, the preparation method comprising the following steps:

[0046] (1) mixing a metal salt solution containing ferric nitrate (7.5 wt%), cobalt nitrate (7.5 wt%) and silver nitrate (1 wt%) with 5 mol / L ammonia water to obtain a coprecipitation solution;

[0047] (2) subjecting the coprecipitation liquid to a first heat treatment in a mixed atmosphere of hydrogen (volume concentration 50%) and nitrogen, wherein the gas flow rate of the first atmosphere is 1.0 m / s, the temperature of the first heat treatment is 1500° C., and the time is 1 h;

[0048] After the first heat treatment, nitrogen is continuously introduced for 30 minutes, and the flow rate of the nitrogen is 0.5 m / s;

[0049] The catalyst is obtained by performing a second heat treatment in a mixed atmosphere of nitrogen and oxygen (volume concentration is 5%), the gas flow rate of the second atmosphere is 1.0 m / s, the temperature of the second heat treatment is 1200° C., and the time is 1 h.

[0050] Example 3

[0051] This embodiment provides a method for preparing a catalyst for preparing single-walled carbon nanotubes, the preparation method comprising the following steps:

[0052] (1) mixing a metal salt solution containing ferric nitrate (5 wt %), cobalt nitrate (5 wt %) and silver nitrate (0.5 wt %) with 2 mol / L ammonia water to obtain a coprecipitation solution;

[0053] (2) subjecting the coprecipitation liquid to a first heat treatment in a mixed atmosphere of hydrogen (volume concentration 25%) and nitrogen, wherein the gas flow rate of the first atmosphere is 0.8 m / s, the temperature of the first heat treatment is 1200° C., and the time is 2 h;

[0054] After the first heat treatment, nitrogen is continuously introduced for 20 minutes, and the flow rate of the nitrogen is 0.75 m / s;

[0055] The second heat treatment is carried out in a mixed atmosphere of nitrogen and oxygen (volume concentration is 2.5%), the gas flow rate of the second atmosphere is 0.8 m / s, the temperature of the second heat treatment is 1000° C., and the time is 2 h to obtain the catalyst.

[0056] Example 4

[0057] Except that the metal salt solution contains nickel nitrate (5 wt %), cerium nitrate (5 wt %) and lead nitrate (0.5 wt %), the other conditions of this embodiment are the same as those of embodiment 3.

[0058] Example 5

[0059] In this embodiment, except that the metal salt solution contains indium nitrate (5 wt %), zirconium nitrate (5 wt %) and manganese nitrate (0.5 wt %), the other conditions are the same as those in embodiment 3.

[0060] Example 6

[0061] Except that the metal salt solution contains iron nitrate (5wt%), nickel nitrate (5wt%) and ruthenium nitrate (0.5wt%), the other conditions of this embodiment are the same as those of Example 3.

[0062] Comparative Example 1

[0063] Except that silver nitrate was not added, the other conditions in this comparative example were the same as those in Example 3.

[0064] Comparative Example 2

[0065] This comparative example is the same as Example 3 except that silver nitrate is replaced by ferric nitrate.

[0066] Single-walled carbon nanotubes were prepared using the catalysts provided in Examples 1-6 and Comparative Examples 1 and 2. The specific method is as follows: the catalyst was placed in a quartz tube fluidized bed with a diameter of 60 mm, nitrogen was introduced at a flow rate of 1.0 m / s, the furnace temperature was maintained at 800°C, methane was introduced at a flow rate consistent with the nitrogen flow rate, and single-walled carbon nanotubes were obtained after the reaction.

[0067] The diameter and length of the prepared single-walled carbon nanotubes were tested by SEM, and the results are shown in Table 1.

[0068] Table 1

[0069] Experiment number Diameter distribution / nm Tube length distribution / μm Example 1 1-3 3 Example 2 1-3 3.1 Example 3 1-5 4 Example 4 1-2 2.9 Example 5 1-4 3.5 Example 6 1-2 3.1 Comparative Example 1 5-12 4 Comparative Example 2 1-12 4

[0070] It can be seen from the test results in Table 1 that the single-walled carbon nanotubes prepared by the catalysts prepared in Examples 1-6 have a diameter of only 1-5 nm, a uniform diameter distribution, and can even reach 1-2 nm, and a tube length distribution of up to 4 μm. The catalyst prepared in Comparative Example 1, without adding silver nitrate, has a tube diameter distribution of 5-12 nm, and the catalyst prepared in Comparative Example replaces silver nitrate with iron nitrate, and has a tube diameter distribution of 1-12 nm, both of which are inferior to those in Example 3.

[0071] The applicant declares that the present invention illustrates the detailed process equipment and process flow of the present invention through the above-mentioned embodiments, but the present invention is not limited to the above-mentioned detailed process equipment and process flow, that is, it does not mean that the present invention must rely on the above-mentioned detailed process equipment and process flow to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of various raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing a catalyst for preparing single-walled carbon nanotubes, characterized in that: The preparation method comprises the following steps: (1) mixing a metal salt solution containing a first metal salt and a second metal salt with a precipitant to obtain a coprecipitation solution; The first metal salt comprises a combination of at least two of an iron salt, a cobalt salt, a nickel salt, a cerium salt, an indium salt or a zirconium salt; The second metal salt includes any one of silver salt, ruthenium salt, manganese salt or lead salt, or a combination of at least two thereof; The first metal salt and the second metal salt each independently comprise a nitrate; The precipitant includes aqueous ammonia; (2) subjecting the coprecipitation liquid to a first heat treatment in a first atmosphere and a second heat treatment in a second atmosphere to obtain the catalyst; The first atmosphere is a mixed atmosphere of hydrogen and nitrogen; The second atmosphere is a mixed gas of nitrogen and oxygen.

2. The preparation method according to claim 1, characterized in that: The concentration of the first metal salt in the metal salt solution in step (1) is 0.1 to 15 wt %.

3. The preparation method according to claim 1, characterized in that: The concentration of the second metal salt in the metal salt solution in step (1) is 0.01 to 1 wt %.

4. The preparation method according to claim 1, characterized in that: The concentration of the ammonia water is 1-5 mol / L.

5. The preparation method according to claim 1, characterized in that: The volume concentration of hydrogen in the first atmosphere is 1 to 50%.

6. The preparation method according to claim 5, characterized in that: The volume concentration of hydrogen in the first atmosphere is 1-20%.

7. The preparation method according to claim 1, characterized in that: In step (2), the gas flow rate of the first atmosphere is 0.5 to 1.0 m / s.

8. The preparation method according to claim 1, characterized in that: Step (2) The temperature of the first heat treatment is 1000-1500°C.

9. The preparation method according to claim 1, characterized in that: The time of the first heat treatment in step (2) is 1 to 3 hours.

10. The preparation method according to claim 1, characterized in that: Step (2) After the first heat treatment, nitrogen is continuously introduced for 10 to 30 minutes.

11. The preparation method according to claim 10, characterized in that: The flow rate of the nitrogen is 0.5-1.0 m / s.

12. The preparation method according to claim 1, characterized in that: The volume concentration of oxygen in the second atmosphere is 0.5-5%.

13. The preparation method according to claim 1, characterized in that: In step (2), the gas flow rate of the second atmosphere is 0.5 to 1.0 m / s.

14. The preparation method according to claim 1, characterized in that: Step (2) The temperature of the second heat treatment is 600-1200°C.

15. The preparation method according to claim 1, characterized in that: The time of the second heat treatment in step (2) is 1 to 3 hours.

16. A catalyst, characterized in that The catalyst is prepared by the preparation method according to any one of claims 1 to 15, and the catalyst is used to prepare single-walled carbon nanotubes.