CN1673073A - Single-wall carbon nanotube synthesizing process - Google Patents

Abstract

The invention discloses a method for synthesizing single-walled carbon nanotubes. In a reactor, under the action of a catalyst containing transition metal or its alloy particles, the carbon-containing raw material gas is decomposed by high-temperature catalysis, and the carbon-containing raw material gas is Add 0.01 to 3% of water vapor by volume. The technical scheme of the present invention can prevent the formation of amorphous carbon and multi-walled carbon nanotubes, and obtain high-purity single-walled carbon nanotubes because water gas is added to the carbon-containing raw material gas.

Description

A method for synthesizing single-walled carbon nanotubes

technical field

The invention belongs to the field of nanotechnology, and in particular relates to a method for efficiently preparing high-purity single-wall carbon nanotubes.

Background technique

Since the discovery of carbon nanotubes by Iijima in 1991, the research on carbon nanotubes has developed rapidly. Due to the discovery that carbon nanotubes have many unique and superior properties, carbon nanotube research has become one of the hottest fields in material science in recent years. The application potential of carbon nanotubes is great, and its possible application areas include: conductive and high-strength composite materials, energy storage and conversion devices (fuel cells), sensors, field emission displays and emission sources, hydrogen storage materials, nano-semiconductor devices, micro-detectors Needles and microwires and more.

Carbon nanotubes are divided into multi-walled and single-walled. In many applications, single-walled carbon nanotubes have more superior properties than multi-walled carbon nanotubes. For example, single-walled carbon nanotubes have smaller diameters and fewer defects. Higher strength and better electrical conductivity.

Multi-walled carbon nanotubes with high purity are currently made of carbon-containing raw materials such as methane, C ₂ -C ₈ hydrocarbons, methanol, ethanol, and carbon monoxide, and in the presence of transition metal catalysts such as iron, cobalt, nickel, and molybdenum. High-temperature (600-1200°C) catalytic decomposition can be produced on a relatively large scale, and the cost is not too high. However, the preparation of single-walled carbon nanotubes is much more difficult than that of multi-walled carbon nanotubes. Up to now, there is still a lack of efficient and cheap methods for large-scale production of single-walled carbon nanotubes, which limits its popularization and application.

It has been reported in the literature that single-walled carbon nanotubes can be prepared by laser evaporation of carbon (Thoss, A., etc., Science, 273:483, 1996) and graphite electrode arc discharge (Journet, etc., Nature, 388:756, 1997), but often There are other forms of carbon products coexisting, and the energy consumption is very high and the output is very low, so it cannot be prepared continuously.

Catalytic cracking is a relatively promising method for large-scale and low-cost production of single-walled carbon nanotubes. Dai et al. (Chemical Physics Letter, 1996, 260: 471) first reported that single-walled carbon nanotubes were prepared by catalytic decomposition at 1200°C using CO as raw material gas through a fixed bed of molybdenum catalyst supported by Al ₂ O ₃ . However, the preparation conditions are harsh, the product purity is not high, and the yield is very low. Cheng et al. (Applied Physics Letters, 1998, 72{25}3282) reported that a horizontal floating bed iron catalyst plus sulfide additives was used to crack benzene at 1100-1200°C to obtain single-walled carbon nanotubes, but the yield and purity were also low. not tall.

Smalley et al reported in U.S. Patent No. 6,692,717 that CO and ethylene, etc., are used as raw material gases, and in a Kan _reactor in which a quartz _boat is loaded with transition metal catalysts such as Fe and Mo, the reaction can be carried out at 800-850°C. Single-walled carbon nanotubes were obtained, but the purity was not high and the yield was very low. Smalley et al reported in U.S. Patent No. 6,761,870 that high-pressure (about 30 atmospheric pressure) CO was used as a raw material, and Fe(CO) ₅ , Ni(CO) ₄ , Fe(C ₅ H ₅ ) ₂ were used as catalyst precursors in a horizontal suspended bed, Thermal decomposition of unsupported metal nanoparticles is used as a catalyst, and single-walled carbon nanotubes are catalytically decomposed at about 1000 ° C, but the purity and yield are also very low.

David Moy et al. reported in U.S. Patent US 6827919 that a molecule containing 1-6 carbon atoms was used as a raw material gas, and a gas containing a transition element compound was decomposed to obtain an unsupported transition metal aerosol particle as a catalyst, and the catalytic decomposition could obtain a single-walled Carbon nanotubes, but with a purity of less than 50%, there is a large amount of amorphous carbon and multi-walled carbon nanotubes.

Lesak etc. reported in Chinese patent CN1360558 that carbon-containing gases such as CO are used as raw materials, _SiO2 , etc. are used as carriers, and VIII metals other than iron such as Co and Ni and VIB metals such as Mo are loaded as catalysts, and catalytic decomposition can be obtained Single-walled carbon nanotubes, but the yield is very low, and the purity is mostly less than 90%.

Zheng Guobin et al. reported in Chinese patent CN1403371 that carrying orthosilicate and ferrocene into the reactor with a hydrogen-containing carrier gas and reacting at 900-1200 ° C can obtain single-walled carbon nanotubes, but the carbon-containing raw material gas used is expensive. And the _SiO2 content in the product is close to half, and it needs to be removed by hydrofluoric acid to obtain single-walled carbon nanotubes, and the highest yield is only 8%.

Zhao Shetao etc. reported in the Chinese patent CN1530321 a tubular reactor with molybdenum boat loading catalyst, using magnesia or alumina to load cobalt, molybdenum plus rare earth and alkaline earth element additives as catalyst, using methane and hydrogen gas mixture as raw material, The catalytic decomposition reaction at 700-1000 ° C for about 1 hour can obtain single-walled carbon nanotubes, but the space-time yield is not high, and the product contains multi-walled tubes.

Zhu Hongwei etc. report in Chinese patent CN1176014, use vertical bed floating catalytic cracking method, take n-hexane as carbon source, ferrocene as catalyst, thiophene as additive to make reaction solution, introduce reactor with hydrogen in vapor form, in 1000 Catalytic decomposition at -1200°C can obtain ultra-long single-wall carbon nanotube bundles up to 20 cm long, but the purity is very low, and the single-wall tubes only account for about 5% of the total carbon products.

It is known from the above literature and patent reports that the current preparation of single-walled carbon nanotubes has problems such as low yield, low product purity, and high manufacturing costs, making it difficult to mass-produce and apply cheaply.

Contents of the invention

The purpose of the invention is to provide a method for easily synthesizing high-purity single-wall carbon nanotubes.

Technical scheme of the present invention is as follows:

A method for synthesizing single-walled carbon nanotubes. In a reactor, under the action of a catalyst containing transition metals or alloy particles thereof, carbon-containing raw material gas is catalytically decomposed at high temperature, and the carbon-containing raw material gas is added to account for its volume 0.01-3% moisture.

In the above method for synthesizing single-walled carbon nanotubes, the carbon-containing raw material gas is selected from molecules containing 1 to 8 carbon atoms, or a mixture thereof. A preferred carbonaceous feedstock gas is methane. The carbon-containing raw material gas may also contain nitrogen, argon or hydrogen as diluent gas, and sulfur-containing compounds as additives.

In the above method for synthesizing single-walled carbon nanotubes, the reaction temperature of the catalytic decomposition is 600-1200°C.

In the above-mentioned method for synthesizing single-walled carbon nanotubes, the catalyst containing transition metal or alloy particles thereof is a catalyst of iron, cobalt, nickel, molybdenum and tungsten or alloy particles thereof supported by an oxide carrier, or unsupported Negative catalysts of iron, cobalt, nickel, molybdenum or tungsten or their alloy particles. The iron, cobalt, nickel, molybdenum or tungsten catalyst supported by the carrier is based on MgO or Al ₂ O ₃ or SiO ₂ or a combination thereof with a high specific surface area, and is loaded with iron, cobalt, nickel, molybdenum or tungsten The compound can be obtained by thermal decomposition and reduction. The unsupported iron, cobalt, nickel, molybdenum or tungsten or alloy particles thereof are obtained by thermally decomposing or reducing the compound vapor of iron, cobalt, nickel, molybdenum or tungsten in a reactor. The iron, cobalt, nickel, molybdenum or tungsten compounds refer to their oxides, chlorides, nitrates, sulfates, organic acid salts, carbonyl compounds, cyclocene compounds or acetylacetonates.

In the above method for synthesizing single-walled carbon nanotubes, the reactor is a fluidized bed reactor, a suspended bed reactor or a fixed bed reactor.

By adopting the technical solution of the present invention, a trace amount of water is added to the carbon-containing raw material gas, and when the carbon-containing raw material gas is decomposed into carbon products by the catalyst, the trace amount of water can prevent the formation of amorphous carbon and multi-walled carbon nanotubes, and promote the generation of single-walled carbon nanotubes. The tube is generated.

The mechanism of the present invention is analyzed in detail below.

Most of the previous methods for preparing single-walled carbon nanotubes by catalytic cracking produced a considerable amount of amorphous carbon and multi-walled carbon nanotubes at the same time.

Among the allotropes of carbon, the graphite structure is the most stable. Amorphous carbon can be regarded as a random connection of extremely small graphite crystallites. Multi-walled carbon nanotubes are cylinders with a diameter of several nanometers to tens of nanometers of multilayer graphitic carbon six-ring structure curled up, and the top is a multilayer cap similar to a fullerene structure. Single-walled carbon nanotubes are usually coiled cylinders of single-layer graphitic carbon six-ring structure with a diameter of 0.7-3nm, with a fullerene-like cap on the top.

The conditions and mechanism for the formation of single-walled carbon nanotubes are transition metals (Fe, Co, Ni, Mo, W) or their alloy particles that can catalyze the decomposition of carbon-containing raw materials, the size of which is about 1-3nm, or metal particles Larger but affected by additives (such as sulfide), the particle surface is segmented into a metal surface area of about 1-3nm. The carbon-containing raw material gas is catalyzed and decomposed on the surface of the transition metal particles at high temperature to produce carbon. The carbon diffuses and dissolves into the metal particles to reach saturation and then precipitates on the surface, forming a cap with a lower energy fullerene-like structure. In order to reduce energy, the surrounding of the cap will be A metal-carbon bond is formed. When the supply of carbon continues to increase, in order to reduce energy, carbon grows upward along the periphery according to the graphite layer structure, forming single-walled carbon nanotubes. On the surface of transition metal or their alloy particles less than about 3nm, as long as the decomposition rate of carbon-containing raw material gas does not exceed the growth rate of single-walled carbon nanotubes, only single-walled carbon nanotubes can be grown without graphite , nor generate amorphous carbon and multi-walled carbon nanotubes. Although the graphite structure is the most stable, the surrounding bonds are not saturated, and there are dangling bonds with high bond energy. Only when a sufficiently large graphite sheet is formed and the energy increase caused by the surrounding dangling bonds can be ignored, can it exist stably. Carbon-containing raw materials It is difficult to generate graphite with a stable structure by decomposing and desorbing carbon on the surface of very small nano-transition metal particles, because when the graphite sheet grows beyond the size of the metal nano-particles, it is impossible to generate metal-carbon bonds around the periphery, so that the surrounding dangling bonds are eliminated. Reduce energy. When the transition metal particles in the catalyst are more than 3nm but less than tens of nanometers, the high-temperature catalytic decomposition of carbon-containing raw material gas can produce multi-walled carbon nanotubes without generating graphite. When the transition metal particles in the catalyst are too large (more than tens of nanometers), the carbon-containing raw material gas is catalyzed and decomposed on the surface at high temperature, and amorphous carbon is easily formed. Amorphous carbon can also be generated when the carbon-containing raw material gas is thermally decomposed at high temperature or decomposed on the surface of the catalyst support and the surface of the reactor to produce carbon faster than the generation speed of multi-walled carbon nanotubes and single-walled carbon nanotubes.

From the above analysis, it can be seen that single-walled carbon nanotubes are a metastable state in carbon allotropes, and their formation is a process that combines kinetic control and structural control. Properly controlling the size of catalyst transition metal nanoparticles, selecting It is possible to synthesize selectively and efficiently under suitable process conditions.

The present invention finds that high-purity single-wall carbon nanotubes can be obtained by adding trace amounts of water to the carbon-containing raw material gas and decomposing it under the action of a catalyst containing transition metals such as iron, cobalt, nickel, molybdenum, and tungsten at high temperature. In contrast, with dry raw material gas without adding water, the products are amorphous carbon and multi-walled carbon nanotubes under the same conditions, and very few single-walled tubes are formed. It was also found in the experiment that if the amount of water added was too large, no carbon product would be generated. In order to generate single-walled carbon nanotubes, the amount of water needed to be added is very small, and calculated by chemical equivalent, it is far from enough to react the amorphous carbon produced when using dry raw material gas by water gas ( ) removed, indicating that the effect of trace water is to inhibit the formation of amorphous carbon and multi-walled carbon nanotubes on the surface of the catalyst, and promote the formation of single-walled carbon nanotubes. This may be related to the hydrolysis reaction between water and the surface of transition metal particles, and the strong interaction between water and the surface of the catalyst support.

Description of drawings

Fig. 1 (a) is the electron microscope observation figure of reaction product when not adding water in the carbon-containing raw material gas in embodiment 1;

Fig. 1 (b) is the electron microscope observation figure of reaction product when adding water in the carbon-containing raw material gas in embodiment 1;

Fig. 1 (c) is the electron microscope observation figure of reaction product when adding water in the carbon-containing raw material gas in embodiment 2;

Fig. 1 (d) is the electron microscope observation figure of reaction product when adding water in the carbon-containing raw material gas in embodiment 3;

Fig. 2 (a) is the electron microscope observation figure of reaction product when not adding water in the carbon-containing feedstock gas in embodiment 7;

Fig. 2 (b) is the electron microscope observation figure of reaction product when adding water in the carbon-containing raw material gas in embodiment 7;

Detailed ways

The obvious promotion effect of adding a trace amount of water on the formation of single-walled carbon nanotubes in the present invention will be illustrated through specific examples below.

Example 1:

Mix ammonium molybdate, ferric nitrate, magnesium nitrate and citric acid solution, evaporate to dryness, and roast in the air at 550°C to obtain a composite oxide powder with an atomic ratio of Mo:Fe:Mg of 3:10:100 as Mo-Fe- Take 100 mg of the precursor of the MgO catalyst and put it into a micro fluidized bed reactor with a diameter of 30 mm, feed 150 ml/min of argon gas, heat up to 1000 ° C, and then feed 45 ml/ min of methane gas, and react for 30 minutes. After cooling to room temperature, the crude product was washed with hydrochloric acid to remove MgO and most of the metals, washed with water and dried to obtain 99 mg of black powder. Figure 1(a) was observed with an electron microscope. The product was mainly amorphous carbon and multi-walled carbon nanotubes. Under the same conditions, water with a partial pressure of 0.67kPa was added to the reaction raw material gas to obtain 52 mg of a black product. From its electron microscope figure 1 (b), it can be seen that the product is a single-walled carbon with a high purity and a diameter of 1-3 nm. Nanotubes, almost no amorphous carbon and multi-walled carbon nanotubes occur.

Example 2:

Same example 1 catalyst and reaction condition, in reaction feed gas, add the water that partial pressure is 1.4kPa, obtain black product 41mg, by its electron microscope Fig. 1 (c) as can be seen, product is the very high single-walled carbon nanotube of purity, Very little amorphous carbon and multi-walled carbon nanotubes occur.

Example 3:

With example 1 catalyst and reaction condition, add the water that partial pressure is 2.0kPa in reaction raw material gas, obtain black product 40mg, by its electron microscope Fig. 1 (d) as can be seen, product is the very high single-walled carbon nanotube of purity, Very little amorphous carbon and multi-walled carbon nanotubes occur.

Example 4:

With the same catalyst and reaction conditions as in Example 1, the water pressure added to the reaction feed gas was increased to 3.5kPa, and no carbon product could be obtained.

Example 5:

Use ammonium molybdate, ferric nitrate, magnesium nitrate and citric acid solution to mix and evaporate to dryness, and bake in air at 550°C. The composite oxide powder with an atomic ratio of Mo:Fe:Mg of 2:10:100 is used as W-Fe-MgO For the precursor of the catalyst, take 100 mg and put it into a microfluidized bed with a diameter of 30 mm, feed 150 ml/min of argon, heat up to 1000, then feed 45 ml/min of methane gas, react for 30 minutes, and cool to room temperature. The crude product is washed with hydrochloric acid to remove MgO and most of the metals, washed with water and dried to obtain a black powder. Observation with an electron microscope shows that the product is mainly amorphous carbon and multi-walled carbon nanotubes. Under the same conditions, adding water with a partial pressure of 1.4kPa into the reaction raw material gas gives a black powder. According to its electron micrograph, the product is a single-walled carbon nanotube with a high purity and a diameter of 1-3nm, almost No amorphous carbon and multi-walled carbon nanotubes are present.

Embodiment 6:

Use ammonium molybdate, ferric nitrate, magnesium nitrate and citric acid solution to mix and evaporate to dryness, and bake in air at 550°C. The composite oxide powder with an atomic ratio of Mo:Fe:Mg of 2:10:100 is used as W-Fe-MgO For the precursor of the catalyst, take 100mg and put it into a microfluidized bed with a diameter of 30mm, pass in 150ml/min of argon, heat up to 850°C, and then pass in 45ml/min of methane gas, react for 30 minutes, and cool to room temperature , the crude product was washed with hydrochloric acid to remove MgO and most of the metals, washed with water and dried to obtain a black powder, and observed with an electron microscope, it was found that the product was mainly amorphous carbon and multi-walled carbon nanotubes. Under the same conditions, adding water with a partial pressure of 1.4kPa into the reaction raw material gas gives a black powder. According to its electron micrograph, the product is a single-walled carbon nanotube with a high purity and a diameter of 1-3nm, almost No amorphous carbon and multi-walled carbon nanotubes are present.

Embodiment 7:

Mix ammonium tungstate, ferric nitrate, magnesium nitrate and citric acid solution, evaporate to dryness, and bake in air at 550°C. The atomic ratio of W:Fe:Mg is 4:15:100 composite oxide powder, as W-Fe- For the precursor of MgO catalyst, take 100 mg and put it into a microfluidized bed with a diameter of 30 mm, feed 150 ml/min of argon gas, heat up to 1000 ° C, and then feed 45 ml/ min of methane gas, react for 30 minutes, and cool to At room temperature, the crude product was washed with hydrochloric acid to remove MgO and most of the metals, washed with water and dried to obtain a black powder. According to electron microscope Figure 2(a), the product is mainly amorphous carbon and multi-walled carbon nanotubes. Under the same conditions, add water with a partial pressure of 1.4KPa to the reaction raw material gas to obtain a black powder. According to its electron microscope figure 2(b), the product is a single-walled carbon with a high purity and a diameter of 1-3nm. Nanotubes, almost no amorphous carbon and multi-walled carbon nanotubes occur.

Embodiment 8:

Impregnated silica gel with a mixed solution of ammonium molybdate and cobalt nitrate, evaporated to dryness, and roasted and decomposed in air at 550°C to obtain a composite oxide powder with a weight ratio of MoO ₃ : Co ₂ O ₃ : SiO ₂ of 5:5:100. Take 100 mg Put it into a quartz boat, put it into a tube furnace with a diameter of 30mm as raw material gas, and react to obtain single-walled carbon nanotubes, pass in 150ml/min of argon gas, raise the temperature to 850°C, and then pass in hydrogen gas at 100ml/min Ethylene gas 50ml/min, reacted for 60 minutes, cooled to room temperature, the crude product was washed with HF acid to remove _SiO2 and metal, washed with water and dried to obtain a black powder, observed with an electron microscope, the product is mainly amorphous carbon and polycarbonate walled carbon nanotubes. Under the same conditions, adding water with a partial pressure of 1.0kPa into the reaction raw material gas gives a black powder. According to its electron micrograph, the product is a single-walled carbon nanotube with a high purity and a diameter of 1-3nm, almost No amorphous carbon and multi-walled carbon nanotubes are present.

Embodiment 9:

Impregnated silica gel with a mixed solution of ammonium molybdate and ferric nitrate, evaporated to dryness, and roasted and decomposed in air at 550°C to obtain a composite oxide powder with a weight ratio of MoO ₃ : Fe ₂ O ₃ : SiO ₂ of 3:10:100. Take 100 mg Put it into a quartz boat, put it into a quartz tube furnace with a diameter of 30mm, pass in 150ml/min of argon gas, raise the temperature to 850°C, then pass in 50ml/min of hydrogen gas and 60ml/min of ethylene, and react for 60 minutes. After cooling to room temperature, the crude product was washed with HF acid to remove _SiO2 and metals, washed with water and dried to obtain a black powder. Observation with an electron microscope showed that the product was mainly amorphous carbon and multi-walled carbon nanotubes. Under the same conditions, adding water with a partial pressure of 1.0kPa into the reaction raw material gas gives a black powder. According to its electron micrograph, the product is a single-walled carbon nanotube with a high purity and a diameter of 1-3nm, almost No amorphous carbon and multi-walled carbon nanotubes are present.

Example 10:

After impregnating alumina with a mixed solution of nickel nitrate and ferric nitrate, evaporate to dryness, roast and decompose in air at 550°C to obtain a composite oxide powder with a weight ratio of NiO _{: Fe2O3} :SiO2 of ₂ :8:100, take 100mg and put Put it into a quartz boat, put it into a quartz reaction tube with a diameter of 30mm, pass in 150ml/min of nitrogen gas, raise the temperature to 850°C, then switch to 100ml/min of hydrogen gas and 100ml/min of CO gas, react for 60 minutes, and cool to room temperature , the crude product was first washed with sodium hydroxide and then hydrochloric acid to remove Al ₂ O ₃ and metals, washed with water and dried to obtain a black powder. Observation with an electron microscope showed that the product was mainly amorphous carbon and multi-walled carbon nanotubes. Under the same conditions, adding water with a partial pressure of 1.0kPa into the reaction raw material gas gives a black powder. According to its electron micrograph, the product is a single-walled carbon nanotube with a high purity and a diameter of 1-3nm, almost No amorphous carbon and multi-walled carbon nanotubes are present.

Example 11:

In a vertical quartz reaction tube with a diameter of 40m, 500ml/min of nitrogen gas is purged from top to bottom, the temperature is raised to about 950°C, and about 10ml/min of normal temperature containing about 1Vol% Fe(CO) ₅ Fe(CO) ₅ is heated and decomposed into iron aerosol particles floating in the reactor. At the same time, 300ml/min of methane preheated to about 950°C is introduced into the reactor. The methane decomposes on the surface of the iron catalyst. When about 1Vol % water vapor, high-purity single-walled carbon nanotubes of 1 to 3 nm can be obtained. If there is no water in the feed gas, the product contains a large amount of amorphous carbon and multi-walled carbon nanotubes under the same conditions.

Example 12:

In a vertical quartz reaction tube with a diameter of 40m, 500ml/min of nitrogen is purged from top to bottom, the temperature is raised to about 1050°C, and about 10ml/min of normal temperature containing about 1Vol% cyclopentadienyl iron The methane, cyclopentadiene iron is decomposed into iron aerosol particles floating in the reactor, while passing 300ml/min of methane preheated to about 1050°C, the methane decomposes on the surface of the iron catalyst, and the product is collected by filtration. When about 0.03 Vol% water vapor is added to the raw material gas, high-purity single-walled carbon nanotubes of 1-3 nm can be obtained. If there is no water in the feed gas, the product contains a large amount of amorphous carbon and multi-walled carbon nanotubes under the same conditions.

Example 13:

In a vertical quartz reaction tube with a diameter of 40m, 500ml/min of nitrogen is purged from top to bottom, the temperature is raised to about 1050°C, and about 10ml/min of normal temperature hydrogen containing about 1Vol% iron acetylacetonate is introduced , iron acetylacetonate is decomposed by heat and reduced to iron aerosol particles floating in the reactor, and at the same time, 500ml/min of methane preheated to about 1050°C is introduced into the reactor. The methane decomposes on the surface of the iron catalyst, and the product is collected through the filter. When about 0.05 vol% water vapor is added to the raw material gas, high-purity single-wall carbon nanotubes of 1-3 nm can be obtained. If there is no water in the feed gas, the product contains a large amount of amorphous carbon and multi-walled carbon nanotubes under the same conditions.

Example 14:

In a vertical quartz reaction tube with a diameter of 40 m, 500 ml/min of nitrogen gas is passed from top to bottom for purging, the temperature is raised to about 1050° C., and methane containing about 1 Vol% FeCl is fed into about ₁₀ ml/min of normal temperature, FeCl ₃ is decomposed by heat and reduced to iron aerosol particles floating in the reactor. At the same time, 500ml/min of methane preheated to about 1050°C is introduced into the reactor. The methane decomposes on the surface of the iron catalyst and the product is collected by filtering. When about 0.01Vol% water vapor is added to the raw material gas, high-purity single-wall carbon nanotubes of 1-3nm can be obtained. If there is no water in the feed gas, the product contains a large amount of amorphous carbon and multi-walled carbon nanotubes under the same conditions.

Example 15:

In a vertical quartz reaction tube with a diameter of 40 m, 500 ml/min of nitrogen gas is passed from top to bottom for purging, the temperature is raised to about 800° C., and methane containing about ₁ Vol% FeCl is fed into about 10 ml/min of normal temperature, FeCl ₃ is decomposed by heat and reduced to iron aerosol particles floating in the reactor. At the same time, 500ml/min of methane preheated to about 50°C is introduced into the reactor. The methane decomposes on the surface of the iron catalyst, and the product is collected through the filter. When about 0.02 vol% water vapor is added to the raw material gas, high-purity single-walled carbon nanotubes of 1-3 nm can be obtained. If there is no water in the feed gas, the product contains a large amount of amorphous carbon and multi-walled carbon nanotubes under the same conditions.

Claims (10)

1. A method for synthesizing single-walled carbon nanotubes comprises the step of decomposing a carbon-containing raw material gas at high temperature in a reactor under the action of a catalyst containing transition metal or alloy particles thereof, wherein the carbon-containing raw material gas is added with water vapor accounting for 0.01-3% of the volume of the carbon-containing raw material gas.

2. The method of synthesizing single-walled carbon nanotubes of claim 1, wherein the carbon-containing feed gas is selected from molecules containing 1 to 8 carbon atoms, or mixtures thereof.

3. The method of synthesizing single-walled carbon nanotubes of claim 2, wherein the carbon-containing feed gas is methane.

4. The method of synthesizing single-walled carbon nanotubes of claim 3 wherein the carbon-containing feed gas further comprises nitrogen, argon or hydrogen as a diluent gas and a sulfur-containing compound as an adjuvant.

5. The method for synthesizing single-walled carbon nanotubes of claim 1, wherein the reaction temperature of said catalytic decomposition is 600-1200 ℃.

6. The method of synthesizing single-walled carbon nanotubes of claim 1, wherein the transition metal is selected from the group consisting of iron, cobalt, nickel, molybdenum, and tungsten.

7. The method for synthesizing single-walled carbon nanotubes of claim 6, wherein the catalyst is MgO or Al with high specific surface area₂O₃Or SiO₂Or the combination of the two is used as a carrier, and the compound loaded with the transition metal is obtained by heating, decomposing and reducing.

8. The method for synthesizing single-walled carbon nanotubes as claimed in claim 6, wherein the catalyst is obtained by decomposition or reduction of a vapor of a compound of a transition metal by heating in a reactor.

9. The method for synthesizing single-walled carbon nanotubes as claimed in claim 7 or 8, wherein said compound of transition metal is selected from the group consisting of oxides, chlorides, nitrates, sulfates, organic acid salts, carbonyl compounds, cyclopentadienyl compounds and acetylacetone compounds of transition metal.

10. The method for synthesizing single-walled carbon nanotubes of claim 1, wherein the reactor is a fluidized bed reactor, a suspended bed reactor or a fixed bed reactor.

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