JP2003313018A - Method for producing carbon nanotube - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for efficiently producing diameter-controlled carbon nanotubes, particularly diameter-controlled single layer carbon nanotubes by thermal decomposition of a hydrocarbon compound using a catalyst. <P>SOLUTION: A hydrocarbon compound is thermally decomposed using a catalyst obtained by highly dispersing and carrying metal iron or a metal iron- containing substance on a porous silica-base carrier having mesopores. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing carbon nanotubes. More specifically, the present invention provides
The present invention relates to a method for efficiently producing diameter-controlled carbon nanotubes, particularly diameter-controlled single-wall carbon nanotubes, which are useful as functional materials, by a thermal decomposition method of a hydrocarbon compound using a catalyst.

[0002]

2. Description of the Related Art In recent years, carbon nanotubes, which are tubular carbon materials having a diameter of several nanometers to several tens of nanometers, are, for example, molecular elements capable of ultra-high integration, storage materials for various gases such as hydrogen, Field emission display (FE
D) has attracted attention as a functional material such as a member and an additive for a resin molded product. This carbon nanotube has 19
It was found by Iijima et al. In a mass of carbon deposited on the cathode of the arc discharge method in 1991 ["Nature", vol. 354, pp. 56-58 (1991)]. , Has been actively researched since then, and has been synthesized by various methods such as a laser irradiation method and a vapor phase synthesis method by thermal decomposition.

There are multi-layered carbon nanotubes and single-walled carbon nanotubes. In particular, single-walled carbon nanotubes are expected to be used as a storage material for various gases such as hydrogen. However, the reality is that no technology has been found so far that can produce such single-walled carbon nanotubes inexpensively, in large quantities, efficiently, and easily. For example, as a method for producing single-walled carbon nanotubes, an arc discharge method (Japanese Patent Laid-Open No. 6-322616) is used.
Although a laser beam irradiation method (Japanese Patent Laid-Open No. 10-273308) and the like are disclosed, these methods require high manufacturing costs and are difficult to mass produce. Further, the diameter of the carbon nanotube is controlled by the particle diameter of the catalyst metal, but it is difficult to control the particle diameter of the catalyst metal to be used by the arc discharge method or the laser light irradiation method described above. In order to obtain the single-walled carbon nanotubes possessed, it is necessary to set the reaction conditions and the catalytic metal species in detail.

On the other hand, in the usual gas phase synthesis method using a catalyst, acetylene having high reactivity (Japanese Patent Laid-Open No. 2000-8621) is used.
No. 7) and carbon monoxide [“Chemical Physics Letters (Chemical Physics Letters
ers), vol. 317, pp. 497-503 (2
000 years)] is used as a raw material, but these raw materials have problems in terms of safety and harmfulness. Further, in the same vapor phase synthesis method using a catalyst, since the growth of carbon nanotubes proceeds outside the pores of the catalyst support, the diameter of the carbon nanotubes is not controlled, and the problem that multilayering is likely to proceed There is.

[0005]

Under such circumstances, the present invention aims to carbonize carbon nanotubes having a controlled diameter useful as a functional material, particularly single-walled carbon nanotubes having a controlled diameter, using a catalyst. It is an object of the present invention to provide a method for efficiently producing a hydrogen compound by a thermal decomposition method.

[0006]

Means for Solving the Problems As a result of intensive studies conducted by the present inventors to achieve the above object,
Using a catalyst using a silica-based material having mesopores,
It has been found that the object can be achieved by thermally decomposing a hydrocarbon compound in the mesopores of the catalyst. The present invention has been completed based on such findings. That is, the present invention is characterized in that (1) a hydrocarbon compound is thermally decomposed by using a catalyst in which iron metal or an iron metal-containing material is highly dispersed and supported on a porous silica-based carrier having mesopores. Method for producing carbon nanotubes, (2) Method for producing carbon nanotubes according to the above (1) having a thermal decomposition temperature of 500 to 1100 ° C., (3) Porous silica-based carrier having mesopores has a pore diameter of 1 to 10 nm. , Pore volume 0.1 to 1.5 cm ³ / g and specific surface area 100 to 200
The method for producing carbon nanotubes according to (1), which has 0 m ² / g, and (4) the hydrocarbon compound is at least one selected from alkanes having 1 to 4 carbon atoms and alkenes having 2 to 4 carbon atoms. And (5) the method for producing a carbon nanotube according to (1), wherein the carbon nanotube is a single-wall carbon nanotube.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION In the method for producing carbon nanotubes of the present invention, a hydrocarbon compound is used as a raw material. Examples of the hydrocarbon compound include alkanes having 1 to 4 carbon atoms, specifically methane, ethane, propane, butane, and alkenes having 2 to 4 carbon atoms, specifically ethylene, propylene, butene, and the like. These may be used alone or in combination of two or more. In the present invention, as the raw material gas,
An inert gas such as nitrogen, helium or argon, or a mixture of the above hydrocarbon compounds diluted with hydrogen at an arbitrary ratio can be used.

On the other hand, as the catalyst, there is used a porous silica-based carrier having mesopores on which iron metal or an iron metal-containing material is highly dispersed and supported. The properties of the porous silica-based carrier having mesopores used in the present invention include a pore size of 1 to
Preferable ones are those having a diameter of 10 nm, a pore volume of 0.1 to 1.5 cm ³ / g and a specific surface area of 100 to 2000 m ² / g, and particularly made of silica and having a pore diameter of 2 to 5 nm. , The pore volume is 0.5 to 1.0 cm ^3.
/ G and specific surface area in the range of 500-1500 m < ² > / g are suitable. Examples of the porous silica-based carrier having such mesopores include [C. T. Kres
ge et al., Nature, 359 (1992), 710].
"MCM-41" and the like described in.

In the above catalyst, the method of supporting the iron metal or the iron metal-containing material on the porous silica-based carrier having mesopores is not particularly limited, and various methods can be used. A method in which an inorganic salt or an organic salt of iron is impregnated and supported, or the like can be preferably used.

The amount of supported iron metal in the catalyst thus obtained is not particularly limited, but is usually 0.1% by mass or more in terms of Fe ₂ O ₃ . The upper limit is not particularly limited as long as the iron metal is supported in a highly dispersed state, but is generally about 2% by mass from the viewpoint of the dispersibility and supportability of the iron metal and the preparation of the catalyst. . The shape of this catalyst is not particularly limited, but it is usually used in the form of powder or particles. Next, a preferred embodiment of the reaction method will be described. First, the catalyst is set in a cylindrical reactor, and then the reactor is heated to a predetermined temperature while circulating an inert gas such as nitrogen, helium, or argon, or hydrogen. When the temperature reaches a predetermined temperature, the flow gas is switched to the raw material gas, the flow rate of the gas is adjusted to a predetermined value, and then the reaction is started. The reaction temperature is usually selected in the range of 500 to 1100 ° C. This temperature is 5
If the temperature is lower than 00 ° C., the thermal decomposition of the hydrocarbon compound is difficult to proceed, and if the temperature exceeds 1100 ° C., the amount of graphitic carbon produced increases, so that the target single-walled carbon nanotube cannot be efficiently obtained. Therefore, the preferred reaction temperature is in the range of 700 to 900 ° C.

The gas flow rate is preferably 10 to 10,000 cm ³ / min, more preferably 10 per 1 g of the catalyst.
It is 0 to 1000 cm ³ / min. This flow rate is 10 cm ³ /
If it is less than a minute, it is difficult to obtain the target single-walled carbon nanotubes in a high yield, and 10000 cm ³
When it exceeds / min, it is difficult to secure a sufficient amount of contact and retention time between the catalyst and the raw material gas for the production and growth of the target single-walled carbon nanotube. Reaction time is usually 5
It is about 120 minutes, preferably 15 to 60 minutes. If the reaction time is less than 5 minutes, the growth of the target single-walled carbon nanotubes may not proceed sufficiently, and if it exceeds 120 minutes, the amount of graphitic carbon produced increases, and the target single-walled carbon nanotubes. Is difficult to obtain efficiently. After completion of the reaction, after cooling to room temperature while circulating an inert gas such as nitrogen, helium or argon,
The catalyst is taken out of the reactor and the target single-walled carbon nanotube is separated from the catalyst. The means for separating the single-walled carbon nanotubes from the catalyst is not particularly limited, but for example, a method in which only the catalyst is dissolved with hydrofluoric acid, hydrochloric acid, nitric acid or an aqueous sodium hydroxide solution and separated can be used. The single-walled carbon nanotubes are chemically extremely stable against these acids and aqueous sodium hydroxide solution, and therefore can be separated from the catalyst. Thus, by thermally decomposing the hydrocarbon compound, single-walled carbon nanotubes having a diameter not larger than the mesopore diameter can be selectively and efficiently obtained.

[0012]

EXAMPLES The present invention will now be described in more detail with reference to examples, but the present invention is not limited to these examples. Preparation Example 1 Preparation of Catalyst As a porous silica-based carrier having mesopores, “MCM-41” having a pore diameter of 2.5 to 4.0 nm, a pore volume of 0.95 cm ³ / g and a specific surface area of 720 m ² / g. Was used as described below to prepare a powdery catalyst on which iron metal was selectively supported. The iron metal content in this catalyst is F
It was 1.4% by mass in terms of e ₂ O ₃ . An aqueous iron solution having a concentration of 0.35 mol / liter prepared using iron (III) nitrate nonahydrate was impregnated under vacuum in the water-equivalent amount of the porous silica-based carrier, and at 80 ° C. for 2 hours. 120 ° C
After drying for 2 hours at 550 ° C., the catalyst was prepared by baking at 550 ° C. for 6 hours. Preparation Example 2 Preparation of catalyst By the same impregnation method as in Preparation Example 1, the iron metal content was Fe ₂
A 0.4% by mass powdery catalyst in terms of O ₃ was prepared.

Example 1 As a reactor, a gas introduction pipe was connected to the inlet side and a gas discharge pipe was connected to the outlet side, and the entire reactor can be heated by an electric heater,
In addition, an alumina horizontal cylindrical reactor having a structure capable of being cooled by circulating water was used. First, 0.5 g of the powdery catalyst obtained in Preparation Example 1 was set on an alumina dish in an alumina cylindrical horizontal reactor, and the reactor was evacuated to start the flow of hydrogen gas. . 100 g of hydrogen gas was put in the reactor.
While circulating at m ³ / min, the temperature was raised at a rate of 15 ° C / min to 550 ° C, and finally, at a rate of 10 ° C / min, the reaction initiation temperature was raised to 750 ° C. . 75
Immediately after reaching 0 ° C, the raw material gas consisting of 10% by volume of ethylene and 90% by volume of nitrogen was switched to, and the reaction was carried out by keeping the temperature at 750 ° C and flowing at 100 cm ³ / min for 30 minutes. After the completion of the reaction, the flow rate was switched to 100 cm ³ / min of nitrogen gas, the temperature was cooled to room temperature at a rate of 100 ° C./min, and the reacted catalyst was taken out with the inside of the reactor open to the atmosphere. Next, this reacted catalyst is dissolved with hydrofluoric acid and hydrochloric acid, and after filtering, the residue on the filter paper is observed with a transmission electron microscope (TEM) to obtain about 3n.
It was confirmed that single-walled carbon nanotubes having a uniform diameter of m were produced. FIG. 1 is a TEM photograph of the obtained carbon nanotubes, and the diameter is MCM.
It can be seen that it is controlled to be equal to or less than the mesopore diameter of −41 or less.

Example 2 0.5 g of the powdery catalyst obtained in Preparation Example 2 was placed on an alumina dish in the cylindrical horizontal alumina reactor shown in Example 1, and the inside of the reactor was vacuumed. After exhausting, circulation of hydrogen gas was started. 100 cm ^{3 of} hydrogen gas in the reactor
The temperature is raised at a rate of 15 ° C./min while circulating for 65 min.
After reaching 0 ° C., the temperature was finally raised to 850 ° C. which is a reaction start temperature at a rate of 10 ° C./min. Immediately after reaching 850 ° C., switching to the same raw material gas as in Example 1,
³ at 100 cm ³ / min while maintaining the temperature at 850 ° C
The reaction was allowed to proceed for 0 minutes. Flow rate after reaction is 1
After switching to nitrogen gas at 00 cm ³ / min and cooling and cooling to room temperature at a rate of 100 ° C./min, the reacted catalyst was taken out with the inside of the reactor open to the atmosphere. Next, this reacted catalyst was dissolved by heating in an aqueous solution of sodium hydroxide having a concentration of 10 mol / liter, and after filtration, the residue on the filter paper was observed with a transmission electron microscope (TEM) to obtain a uniform particle of about 1.5 nm. It was confirmed that single-walled carbon nanotubes having a diameter were produced. FIG. 2 is a TEM photograph of the obtained carbon nanotube, the diameter of which is MCM-4.
It can be seen that the diameter is controlled to be equal to or smaller than the mesopore diameter of 1.

[0015]

EFFECTS OF THE INVENTION According to the method of the present invention, single-walled carbon nanotubes having a diameter equal to or smaller than the mesopores and having a well-controlled diameter can be obtained regardless of the reaction time and reaction temperature during production. It can be selectively and efficiently obtained. The single-walled carbon nanotubes obtained by the method of the present invention are expected to be used as various functional materials, especially as various gas storage materials including hydrogen.

[Brief description of drawings]

FIG. 1 is a transmission electron microscope (TEM) photograph of the single-walled carbon nanotube obtained in Example 1.

FIG. 2 is a transmission electron microscope (TEM) photograph of the single-walled carbon nanotube obtained in Example 2.

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Claims (5)

[Claims] 1. Production of carbon nanotubes, characterized in that a hydrocarbon compound is thermally decomposed by using a catalyst in which iron metal or an iron metal-containing material is highly dispersed and supported on a porous silica-based carrier having mesopores. Method. 2. The method for producing carbon nanotubes according to claim 1, wherein the thermal decomposition temperature is 500 to 1100 ° C. 3. A porous silica-based carrier having mesopores,
Pore diameter 1-10 nm, pore volume 0.1-1.5 cm ³ /
The method for producing carbon nanotubes according to claim 1, which has g and a specific surface area of 100 to 2000 m ² / g. 4. The method for producing carbon nanotubes according to claim 1, wherein the hydrocarbon compound is at least one selected from alkanes having 1 to 4 carbon atoms and alkenes having 2 to 4 carbon atoms. 5. The method for producing a carbon nanotube according to claim 1, wherein the carbon nanotube is a single-wall carbon nanotube.