Method for manufacturing catalyst for carbon nanotube production, catalyst for carbon nanotube production, and carbon nanotube

Abstract

The present invention relates to a method for manufacturing a catalyst for carbon nanotube production, a catalyst for carbon nanotube production manufactured by said manufacturing method, a method for manufacturing carbon nanotubes using said catalyst, and carbon nanotubes manufactured by said manufacturing method, wherein the catalyst can be readily manufactured for use in producing thin-walled carbon nanotubes by precipitating an active metal in a hydroxide form even under relatively mild conditions by using ammonium hydroxide as a co-precipitating agent.

Description

Method for producing a catalyst for producing carbon nanotubes, catalyst for producing carbon nanotubes, and carbon nanotubes

[0001] Cross-citation with related applications

[0002] This application claims the benefit of priority to Korean Patent Application No. 10-2023-0148157, filed October 31, 2023, the entire contents of which are incorporated herein by reference.

[0003] Technology field

[0004] The present invention relates to a method for producing a catalyst for producing carbon nanotubes capable of producing thin-walled carbon nanotubes with high crystallinity and electrical conductivity at a high yield, a catalyst for producing carbon nanotubes produced using the method, a method for producing carbon nanotubes using the catalyst, and carbon nanotubes produced therefrom.

[0005] Carbon nanomaterials include fullerene, carbon nanotube (CNT), graphene, and graphite nanoplate, depending on the shape of the material. Among these, carbon nanotubes are large molecules in which a hexagonal honeycomb-shaped graphite sheet, in which one carbon atom is bonded to three other carbon atoms, is rolled up to a nano-sized diameter.

[0006] Carbon nanotubes are hollow, lightweight, and boast electrical conductivity comparable to copper, thermal conductivity comparable to diamond, and tensile strength comparable to steel. Depending on their coiled form, they are classified as single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs), and rope-shaped carbon nanotubes (RCNTs).

[0007] Among the above types of carbon nanotubes, single-walled carbon nanotubes (SWCNTs) have the advantage of excellent conductivity, and have recently been attracting attention as a material to replace carbon black in the field of conductive materials. However, unlike multi-walled carbon nanotubes (MWCNTs), single-walled carbon nanotubes have the limitation that they are not easy to mass-produce. Therefore, various studies are underway to produce MWCNTs with properties similar to single-walled carbon nanotubes, and synthetic research on thin-walled carbon nanotubes, which are known to exhibit similar performance to single-walled carbon nanotubes, is also active.

[0008] Multi-walled carbon nanotubes are typically manufactured using supported catalysts, which involve supporting metal species on a support. While supported catalysts offer the advantage of ease of preparation, their ability to increase the dispersion of metal species exposed on the support surface is limited, making them disadvantageous for the synthesis of thin-walled carbon nanotubes with a small number of walls. On the other hand, when a catalyst is manufactured via a co-precipitation method, the metal species can be more uniformly distributed within the catalyst compared to supported catalysts, making it advantageous for the production of thin-walled carbon nanotubes.

[0009] When manufacturing a catalyst using a coprecipitation method, the physical properties and shape of the catalyst will vary depending on the type of coprecipitant used, or the pH, temperature, or pressure conditions during the manufacturing process. Conventionally known coprecipitation catalysts used in the manufacture of carbon nanotubes are manufactured through a hydrothermal synthesis method that uses a component such as urea as a coprecipitant and performs a reaction under high temperature and pressure conditions. In this method, carbonate ions generated by the thermal decomposition of urea during the reaction combine with metal cations to form a precipitate in the form of a metal carbonate. However, when precipitation occurs in the form of a metal carbonate, it is difficult to control the particle size or shape of the active metal as desired because the precipitation occurs even when the pH is not the desired condition. In addition, the hydrothermal synthesis method has the disadvantage of increasing the manufacturing cost of the catalyst because it requires high temperature and pressure conditions.

[0010] Therefore, further research is needed on a new catalyst preparation method that can produce a catalyst for producing thin-walled carbon nanotubes under milder conditions.

[0011]

[0012] Prior art literature

[0013] (Patent Document 1) KR 10-2016-0107524 A (Published on September 19, 2016)

[0014] The present invention provides a method for producing a catalyst capable of producing thin-walled carbon nanotubes with high crystallinity at a high yield by producing a catalyst using a co-precipitation method in which an active metal is precipitated in the form of a metal hydroxide, a catalyst produced from the method for producing the catalyst, a method for producing carbon nanotubes using the catalyst, and carbon nanotubes produced therefrom.

[0015] In order to solve the above-mentioned problem, the present invention provides a method for producing a catalyst for producing carbon nanotubes, a catalyst for producing carbon nanotubes, a method for producing carbon nanotubes, and carbon nanotubes.

[0016] Specifically, (1) the present invention provides a method for producing a catalyst for producing carbon nanotubes, including a step (S1) of preparing a precursor aqueous solution by dissolving an iron precursor, a molybdenum precursor, and a magnesium precursor in water, a step (S2) of preparing a slurry by adding ammonium hydroxide (NH4OH) to the precursor aqueous solution and co-precipitating the solution, a step (S3) of recovering a solid from the slurry, and a step (S4) of drying and calcining the solid.

[0017] (2) The present invention provides a method for producing a catalyst for producing carbon nanotubes, wherein the molar ratio between iron, molybdenum and magnesium in (1) above is 0.5 to 8:0.05 to 10:88.

[0018] (3) The present invention provides a method for producing a catalyst for producing carbon nanotubes, wherein the molar ratio between iron and molybdenum in (1) or (2) is 20:1 to 5:1.

[0019] (4) The present invention provides a method for producing a catalyst for producing carbon nanotubes, wherein the S2 step is performed under normal pressure and room temperature conditions in any one of the above (1) to (3).

[0020] (5) The present invention provides a method for producing a catalyst for producing carbon nanotubes, wherein, in any one of (1) to (4), the ammonium hydroxide is added in a molar ratio of 0.1 to 5.0 relative to the combined content of iron, molybdenum, and magnesium in the precursor aqueous solution.

[0021] (6) The present invention provides a method for producing a catalyst for producing carbon nanotubes, wherein the step S3 comprises a step of maturing a slurry (S3-1) and a step of recovering and washing a solid from the matured slurry (S3-2).

[0022] (7) The present invention provides a method for producing a catalyst for producing carbon nanotubes, wherein the step S3-1 is performed at 25 to 120°C for 6 to 48 hours in any one of the above (1) to (6).

[0023] (8) The present invention provides a method for producing a catalyst for producing carbon nanotubes, wherein in any one of the above (1) to (7), the iron precursor is at least one selected from the group consisting of iron nitrate, iron chloride, iron acetate, iron sulfate, and hydrates thereof, the molybdenum precursor is at least one selected from the group consisting of ammonium molybdate, sodium molybdate, phosphomolybdic acid, and hydrates thereof, and the magnesium precursor is at least one selected from the group consisting of magnesium nitrate, magnesium chloride, magnesium acetate, and hydrates thereof.

[0024] (9) The present invention provides a method for producing a catalyst for producing carbon nanotubes, wherein the drying is performed at 50 to 150°C and the calcination is performed at 300 to 900°C in any one of the above (1) to (8).

[0025] (10) The present invention provides a catalyst for producing carbon nanotubes, which comprises iron, molybdenum and magnesium, and wherein when the molar ratio between the iron, molybdenum and magnesium is a:b:c, a is 0.5 to 8, b is 0.05 to 10 and c is 88, and the ratio (D / a) of the maximum size D (nm) of active metal particles obtained by TEM analysis of the catalyst to the value a is 4 or less.

[0026] (11) The present invention provides a catalyst for producing carbon nanotubes, wherein, when the minimum size of the active metal particles obtained by TEM analysis of the catalyst in (10) is d (nm), d / a is 3 or less.

[0027] (12) The present invention provides a catalyst for producing carbon nanotubes, wherein the difference between D and d in (10) or (11) above is 2 or less.

[0028] (13) The present invention provides a method for producing carbon nanotubes, including the step of producing carbon nanotubes by introducing a catalyst according to any one of the above (10) to (12) into a reactor and heating the reactor while injecting a carbon source gas into the reactor.

[0029] (14) The present invention provides a carbon nanotube characterized in that a mass change rate graph per unit temperature obtained by TGA-DTG analysis has a maximum value at 500 to 700°C.

[0030] (15) In the present invention, in the above (14), the carbon nanotube has a crystallinity (I) obtained by Raman spectrum. G / I D ) provides carbon nanotubes having a molecular weight of 10 or more.

[0031] According to the method for producing a catalyst for producing carbon nanotubes of the present invention, by using ammonium hydroxide as a co-precipitant, an active metal can be precipitated in the form of a hydroxide even under relatively mild conditions, thereby more easily producing a catalyst that can be used for producing thin-walled carbon nanotubes.

[0032] In addition, the catalyst for producing carbon nanotubes of the present invention has metal active species uniformly distributed inside the catalyst particles, so that thin-walled carbon nanotubes with high crystallinity can be produced at a high yield.

[0033] In addition, the carbon nanotube of the present invention has a high degree of crystallinity and excellent thermal stability by being manufactured from the catalyst.

[0034] FIG. 1 is a diagram showing the Raman spectrum of carbon nanotubes manufactured from the catalyst of Example 1 of the present invention.

[0035] Figure 2 is a SEM image (x1,000K) observed after purification of carbon nanotubes manufactured from the catalyst of Example 1 of the present invention.

[0036] Figure 3 is a SEM image (x5,000K) observed after purification of carbon nanotubes manufactured from the catalyst of Example 1 of the present invention.

[0037] Figure 4 is a graph showing the results of TGA-DTG analysis of carbon nanotubes manufactured from catalysts of Examples 1, 6, 8, and 9 of the present invention.

[0038] Hereinafter, the present invention will be described in more detail.

[0039] Terms or words used in this specification and claims should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted as meanings and concepts that conform to the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concept of the term to explain his or her own invention in the best way.

[0040]

[0041] The term 'carbon nanotube' used in the present invention refers to a secondary structure formed by the assembly of carbon nanotube units in whole or in part, wherein the carbon nanotube units have a graphite sheet in the shape of a cylinder with a nano-sized diameter and an sp2 bonding structure. At this time, depending on the angle and structure at which the graphite sheets are rolled, they can exhibit the properties of a conductor or a semiconductor. Carbon nanotube units can be classified into single-walled carbon nanotubes (SWCNTs, single-walled carbon nanotubes), double-walled carbon nanotubes (DWCNTs, double-walled carbon nanotubes), and multi-walled carbon nanotubes (MWCNTs, multi-walled carbon nanotubes) depending on the number of bonds forming the wall, and the thinner the wall thickness, the lower the resistance.

[0042] In particular, the carbon nanotube of the present invention may be a thin-walled carbon nanotube having a wall thickness of approximately 1 to 5 nm and a wall number of 1 to 3.

[0043]

[0044] Method for producing a catalyst for producing carbon nanotubes

[0045] Many catalysts used in the mass production of carbon nanotubes are manufactured using the impregnation method. This method involves immersing a support in a solution containing dissolved active metal components, followed by drying and calcination. However, during this process, the active metals do not readily penetrate the internal spaces of the support. Therefore, the active metal components of the supported catalyst are mostly distributed on the surface region of the catalyst particles. This means that it is difficult to grow carbon nanotubes with a small number of walls from the catalyst.

[0046] A catalyst manufacturing method known to overcome the shortcomings of these support methods is the co-precipitation method. Co-precipitation involves adding a co-precipitant to a solution containing both the active metal and the support metal, causing them to precipitate together. Catalysts manufactured using the co-precipitation method have the advantage of uniformly distributing the active metal throughout the internal space of the catalyst, compared to catalysts manufactured using the support method. Among these co-precipitation methods, the most representative method known to be used in the production of carbon nanotube catalysts is hydrothermal synthesis. Hydrothermal synthesis is performed under high pressure and temperature conditions, and a method for manufacturing a catalyst for carbon nanotubes using this method is disclosed in the aforementioned prior art document 1. However, this method also has drawbacks. The high pressure and temperature required increase the energy cost of the catalyst manufacturing process, and the scale-up of hydrothermal synthesis is difficult, making it difficult to mass-produce catalysts with properties identical to those observed in laboratory settings. In addition, in the hydrothermal synthesis method, the properties of the catalyst easily change depending on the pressure and temperature conditions, so it is not easy to ensure the reproducibility of the catalyst.

[0047] In view of these points, the present invention provides a method for producing a catalyst that is relatively low in cost and capable of producing thin-walled carbon nanotubes with high crystallinity by using a coprecipitation method under mild conditions of room temperature and pressure, and using ammonium hydroxide as a coprecipitant to precipitate an active metal in the form of a hydroxide rather than a carbonate.

[0048]

[0049] More specifically, the present invention provides a method for producing a catalyst for producing carbon nanotubes, comprising the steps of (S1) preparing a precursor aqueous solution by dissolving an iron precursor, a molybdenum precursor, and a magnesium precursor in water, (S2) preparing a slurry by adding ammonium hydroxide (NH4OH) to the precursor aqueous solution and co-precipitating the solution, (S3) recovering a solid from the slurry, and (S4) drying and calcining the solid.

[0050]

[0051] Hereinafter, each step included in the method for manufacturing a catalyst for manufacturing carbon nanotubes provided by the present invention is described in detail.

[0052]

[0053] Precursor solution preparation step (S1)

[0054] In the above step S1, a precursor aqueous solution is prepared by dissolving precursors of iron and molybdenum, which are active metals of the catalyst, and precursors of magnesium, which is a support, in water.

[0055]

[0056] The molar ratio between iron, molybdenum and magnesium, which are metal components derived from the iron precursor, molybdenum precursor and magnesium precursor dissolved in this step, may be 0.5 to 8:0.05 to 10:88, and preferably 0.5 to 8:0.05 to 1:88. When iron and molybdenum are included in the molar ratio described above with respect to magnesium, sufficient durability of the manufactured catalyst can be ensured, while also providing sufficient catalytic activity.

[0057] Furthermore, the molar ratio between the iron and molybdenum may be 20:1 to 5:1, and preferably 15:1 to 7:1. The molybdenum is a kind of cocatalyst component that further enhances the catalytic activity of iron, and when the molar ratio between iron and molybdenum satisfies the above-described conditions, the synergistic effect between the two components is maximized, so that the catalytic activity can be particularly high.

[0058] The above iron precursor, molybdenum precursor, and magnesium precursor may be preferably those that can sufficiently dissolve in water under room temperature and pressure conditions. More specifically, the iron precursor may be at least one selected from the group consisting of iron nitrate, iron chloride, iron acetate, iron sulfate, and hydrates thereof. The molybdenum precursor may be at least one selected from the group consisting of ammonium molybdate, sodium molybdate, phosphomolybdic acid, and hydrates thereof. The magnesium precursor may be at least one selected from the group consisting of magnesium nitrate, magnesium chloride, magnesium acetate, and hydrates thereof.

[0059]

[0060] Co-precipitation stage (S2)

[0061] By adding a co-precipitant to the precursor solution manufactured through the previous step, the dissolved metal components can be precipitated together.

[0062] In catalyst synthesis by coprecipitation, the type of coprecipitant used determines the form in which the metal components are precipitated. Typically, a compound containing carbonate ions is used as a coprecipitant to precipitate the metal components in the form of metal carbonates. However, when precipitation occurs in the form of metal carbonates, precipitation occurs even when the desired pH conditions are not met, making it difficult to control the particle size and shape of the active metal as desired. Furthermore, even when ammonium bicarbonate, known as a coprecipitant, is used, the crystallinity of the carbon nanotubes produced from the resulting catalyst may be reduced, or the production yield of the carbon nanotubes may be reduced.

[0063] On the other hand, in the present invention, ammonium hydroxide is used as a co-precipitant to precipitate metal components in the form of metal hydroxides. These metal hydroxides can cause precipitation at relatively desired pH conditions, and accordingly, the size of the active metal particles can also be controlled within an appropriate range. In addition, the S2 step may be performed under atmospheric pressure and temperature conditions, thereby overcoming the shortcomings of the hydrothermal synthesis method described above.

[0064]

[0065] In addition, ammonium hydroxide introduced as a co-precipitant in this step may be introduced at a molar ratio of 0.1 to 5.0 relative to the combined content of iron, molybdenum, and magnesium in the precursor aqueous solution, and preferably may be introduced at a molar ratio of 0.5 to 3. Only when an appropriate amount of the co-precipitant is introduced can the yield of the catalyst be increased without loss of metal components.

[0066]

[0067] Solids recovery stage (S3)

[0068] The solid content can be recovered from the slurry manufactured through the previous steps and used as a catalyst.

[0069] In this step, a method commonly used to recover solids from a slurry can be applied, and for example, the solids can be recovered using a pressure reducing filter or centrifuge.

[0070] Meanwhile, the S3 step may include a step of maturing the slurry (S3-1) and a step of recovering and washing the solid content from the matured slurry (S3-2).

[0071] This slurry maturation step offers the technical advantage of ensuring that iron, the active metal within the catalyst, is uniformly distributed during the maturation process, and further converting any components that were not previously converted to hydroxide form. This maturation process may be performed at 25 to 120°C for 6 to 48 hours.

[0072] Additionally, impurities remaining in the solid content can be removed through the washing process in S3-2. If the washing process is not performed, the remaining impurities may have a negative effect on the carbon nanotube synthesis reaction.

[0073]

[0074] Drying and firing stage (S4)

[0075] The solid produced through the preceding steps can be finally dried and calcined to obtain a catalyst. The drying process removes any remaining moisture within the solid, and the calcination process converts the metal hydroxide into a stable metal oxide.

[0076] In this step, the drying may be performed at 50 to 150°C, preferably 80 to 105°C, and the calcination may be performed at 300 to 900°C, preferably 400 to 800°C. If the drying and calcination temperatures are too low, sufficient drying and calcination efficiency may not be achieved, and if they are higher, the cost of the manufacturing process may increase, and at the same time, the manufactured catalyst may undergo thermal decomposition.

[0077]

[0078] Catalysts for carbon nanotube production

[0079] The present invention provides, in addition to the method for producing a catalyst for producing carbon nanotubes described above, a catalyst for producing carbon nanotubes produced through the above-described method.

[0080]

[0081] More specifically, the present invention provides a catalyst for producing carbon nanotubes, which comprises iron, molybdenum and magnesium, and wherein when the molar ratio between the iron, molybdenum and magnesium is a:b:c, a is 0.5 to 8, b is 0.05 to 10 and c is 88, and the ratio (D / a) of the maximum size D (nm) of active metal particles obtained by TEM analysis of the catalyst to the value a is 4 or less. Meanwhile, the active metal means iron.

[0082]

[0083] The catalyst for producing carbon nanotubes of the present invention is characterized by having smaller active metal particles since it is produced using ammonium hydroxide as a co-precipitant. The smaller the size of the active metal particles, the more advantageous it is for synthesizing thin-walled carbon nanotubes with a small diameter. However, the size of the active metal particles is affected by the composition of the catalyst, more specifically, the composition of iron, which is the active metal in the catalyst. In the catalyst produced in the present invention, the ratio of the maximum size D (nm) of the active metal particles to the composition ratio a of the iron, which is a D / a value, is characterized by being 4 or less, preferably 2 to 3.5. Meanwhile, D refers to a number when the maximum size of the active metal particles is expressed in nm.

[0084]

[0085] In addition, in the catalyst for manufacturing carbon nanotubes of the present invention, when the minimum size of the active metal particles obtained by TEM analysis of the catalyst is d (nm), d / a may be 3 or less, preferably 1 to 2.5. In addition, the difference between D and d may be 2 or less, preferably 1.5 or less.

[0086]

[0087] Meanwhile, the above D and d can be directly measured by TEM analysis of the catalyst.

[0088]

[0089] Method for manufacturing carbon nanotubes

[0090] The present invention provides a method for producing carbon nanotubes using the catalyst for producing carbon nanotubes described above.

[0091]

[0092] More specifically, the present invention provides a method for producing carbon nanotubes, including the step of producing carbon nanotubes by introducing the above-described catalyst into a reactor and heating the reactor while injecting a carbon source gas into the reactor.

[0093]

[0094] The above reactor may be a chemical vapor deposition reactor or a fluidized bed reactor.

[0095] In addition, the carbon source gas is a carbon-containing gas that can be decomposed at high temperatures to form carbon nanotubes, and specific examples thereof include various carbon-containing compounds such as aliphatic alkanes, aliphatic alkenes, aliphatic alkynes, and aromatic compounds, and more specifically, compounds such as methane, ethane, ethylene, acetylene, ethanol, methanol, acetone, carbon monoxide, propane, butane, benzene, cyclohexane, propylene, butene, isobutene, toluene, xylene, cumene, ethylbenzene, naphthalene, phenanthrene, anthracene, acetylene, formaldehyde, and acetaldehyde.

[0096] To increase the fluidity of the catalyst, a fluidizing gas may be injected together with the above carbon source gas. The fluidizing gas may be a non-reactive inert gas or nitrogen gas, and more specifically, argon or nitrogen gas.

[0097] When the carbon source gas and the fluidizing gas are injected together, the flow rate ratio of the carbon source gas and the fluidizing gas may be 1:2 to 1:8 based on volume, and preferably 1:3 to 1:7.

[0098] Additionally, the carbon nanotube synthesis reaction can be performed at a temperature of 750 to 900°C.

[0099]

[0100] carbon nanotubes

[0101] The present invention provides a carbon nanotube manufactured from the above-described catalyst.

[0102] More specifically, the carbon nanotube provided by the present invention may be a carbon nanotube characterized in that the mass change rate graph per unit temperature obtained by TGA-DTG analysis has a maximum value at 500 to 700°C.

[0103] In addition, the above carbon nanotubes have a crystallinity (I) obtained by Raman spectrum G / I D ) may be 10 or more, preferably 10 to 20.

[0104] Additionally, the carbon nanotube may have a diameter of 0.8 to 2 nm as determined by Raman analysis.

[0105] In addition, the carbon nanotube has a BET surface area of ​​900 m 2 / g or more. Preferably, the BET surface area of ​​the carbon nanotube is 900 m 2 / g or more, 1300m 2 / g can be less.

[0106] Additionally, the number of walls of the carbon nanotube may be 1 to 3.

[0107] Carbon nanotubes manufactured from the catalyst of the present invention have excellent thermal stability and high crystallinity, resulting in excellent electrical conductivity.

[0108] Meanwhile, the above TGA-DTG analysis may be performed using TGA2 equipment (manufacturer: Mettler Toledo).

[0109] Also, the above I G / I D The ratio can be measured for the obtained carbon nanotubes, more specifically, the G peak (1550-1650 cm) of the Raman spectrum obtained at a laser wavelength of 532 nm using a DXR Raman Microscope (manufactured by Thermo Electron Scientific Instruments LLC). -1 ) and D peak (1250-1400cm -1 ) can be calculated by measuring the century ratio.

[0110] In addition, the BET specific surface area can be calculated by specifically obtaining the nitrogen gas adsorption amount at liquid nitrogen temperature (77K) using BELSORP-mini II of BEL Japan.

[0111] In addition, the wall number of the above carbon nanotubes can be confirmed through TEM analysis, and the 400 cm of Raman spectrum -1 This can also be indirectly confirmed through the RBM (Radial breathing mode) that appears in the following areas.

[0112]

[0113] Hereinafter, the present invention will be described in more detail with examples and experimental examples to specifically explain the present invention. However, the present invention is not limited to these examples and experimental examples. The examples according to the present invention can be modified in various different forms, and the scope of the present invention should not be construed as being limited to the examples described below. The examples of the present invention are provided to more completely explain the present invention to those of average skill in the art.

[0114]

[0115] Examples and Comparative Examples

[0116] Iron nitrate nonahydrate was used as the iron precursor, ammonium molybdate was used as the molybdenum precursor, and magnesium nitrate hexahydrate was used as the magnesium precursor. The iron precursor, molybdenum precursor, and magnesium precursor were all dissolved in distilled water to prepare a precursor aqueous solution.

[0117] Thereafter, a co-precipitant was added to the precursor solution prepared under room temperature and pressure conditions to prepare a slurry solution. The prepared slurry solution was aged at a temperature of 40 to 120°C for 6 to 48 hours, and the solid content was recovered using a vacuum filter, followed by washing with distilled water.

[0118] The washed solid was dried at 50 to 200°C for 6 to 24 hours and calcined at 300 to 900°C for 2 to 6 hours to finally obtain a catalyst for producing carbon nanotubes.

[0119]

[0120] The composition (by mole) of iron, molybdenum, and magnesium used in each example and comparative example, as well as the type and amount of the co-precipitant used, are summarized in Table 1 below.

[0121] Catalyst composition (by molar ratio)Coprecipitant typeCoprecipitant / metal molar ratioFeMoMgExample 110.188NH4OH1.8Example 20.50.0588NH4OH1.8Example 320.288NH4OH1.8Example 440.488NH4OH1.8Example 580.888NH4OH1.8Example 610.0588NH4OH1.8Example 710.388NH4OH1.8Example 810.588NH4OH1.8Example 91188NH4OH1.8Comparative example 110.188NaOH1.8Comparative example 210.188Na2CO31.8Comparative example 310.188(NH4)2CO31.8Comparative example 480.888(NH4)2CO31.8Comparative example 510.188NH4HCO31.8Comparative example 680.888NH4HCO31.8

[0122] * The above metal molar ratio refers to the combined molar ratio of iron, molybdenum, and magnesium.

[0123] Experimental Example 1. Confirmation of carbon nanotube production yield and crystallinity.

[0124] After filling 0.5 g of the catalysts manufactured in the above examples and comparative examples into a chemical vapor deposition reactor, the reaction was performed for 15 to 60 minutes under an argon / methane gas atmosphere at 850°C to obtain carbon nanotubes. The input flow rates of argon and methane gases were 540 sccm and 105 sccm, respectively.

[0125] The yield and crystallinity of the obtained carbon nanotubes were measured using the following method and summarized in Table 2.

[0126] 1) Yield (carbon nanotube yield per unit metal mass):

[0127] Yield = (mass of obtained carbon nanotubes / mass of active metal (iron)) * 100%

[0128] 2) Crystallinity (I) G / I D ): The G peak (1550-1650 cm) of the Raman spectrum obtained at a laser wavelength of 532 nm using a DXR Raman Microscope (manufactured by Thermo Electron Scientific Instruments LLC) for the obtained carbon nanotubes -1 ) and D peak (1250-1400cm -1 ) was calculated by measuring the century ratio.

[0129]

[0130] Yield (%) Crystallinity Example 1 1580 16.7 Example 2 1130 15.4 Example 3884 15.5 Example 4531 12.3 Example 5348 10.4 Example 6 596 12.8 Example 7 2230 15.3 Example 8 2418 12.1 Example 9 2302 11.0 Comparative Example 1 1163.7 Comparative Example 28904.5 Comparative Example 39798.1 Comparative Example 43518.4 Comparative Example 5682 11.7 Comparative Example 63147.4

[0131] As summarized in Table 2 above, it was confirmed that the catalyst of the present invention can synthesize carbon nanotubes at a high yield compared to the comparative example, and at the same time, the crystallinity of the obtained carbon nanotubes is very high, at 10 or higher.

[0132] On the other hand, the catalysts of Comparative Examples 1 to 6, which used a different type of co-precipitant from the examples of the present invention, showed results in which at least one of yield and crystallinity was inferior, and even in Comparative Examples 2 and 3, which showed relatively high yields among the Comparative Examples, it was confirmed that both yield and crystallinity were inferior compared to Example 1 of the present invention, which used ammonium hydroxide as a co-precipitant in the same composition.

[0133] From this, it was confirmed that when the catalyst of the present invention is used, carbon nanotubes with high crystallinity and excellent electrical conductivity can be manufactured at a high yield.

[0134]

[0135] Experimental Example 2. Measurement of the active metal particle size of the catalyst

[0136] The active metal particle sizes of the catalysts prepared in Example 1 and Comparative Example 3 were measured. Specifically, the obtained catalysts were observed using a TEM, and the sizes of the active metal particles were directly measured. A Titan G2 (manufacturer: FEI) was used as the TEM equipment.

[0137]

[0138] Catalyst composition a value Minimum active metal particle size (d, nm) Maximum active metal particle size (D, nm) Example 1 12.1 3.0 Comparative example 3 13.7 4.9

[0139] As can be seen from Table 3 above, the catalyst of the present invention using ammonium hydroxide as a co-precipitant has a smaller active metal particle size than the catalyst of Comparative Example 3. Since the active metal particle size of the catalyst is small, the catalyst of the present invention can produce carbon nanotubes with high yield and high crystallinity.

[0140]

[0141] Experimental Example 3. Confirmation of the Shape of Manufactured Carbon Nanotubes

[0142] The Raman spectrum obtained for the carbon nanotubes manufactured from the catalyst of Example 1 is shown in Fig. 1. In the Raman spectrum of Fig. 1, an RBM region was observed, which means that the carbon nanotubes manufactured from the catalyst of Example 1 are thin-walled carbon nanotubes.

[0143] Furthermore, the carbon nanotubes manufactured from the catalyst of Example 1 were purified and their morphology observed using a SEM. Specifically, the manufactured carbon nanotubes were treated in air at a temperature of 350°C or higher for at least 30 minutes, and the catalyst contained therein was removed using acid. The results are shown in Figures 2 and 3.

[0144] As can be seen from FIGS. 2 and 3, the shape of the carbon nanotubes produced from the catalyst of the present invention is a form in which thin-walled carbon nanotubes are aggregated.

[0145]

[0146] Experimental Example 4. TGA-DTG Analysis of Manufactured Carbon Nanotubes

[0147] TGA-DTG analysis was performed on carbon nanotubes manufactured using the catalysts of Examples 1, 6, 8, and 9. A TGA2 (manufacturer: Mettler Toledo) was used as the analysis equipment. The resulting graph is shown in Figure 4.

[0148] As can be confirmed through the above Figure 4, the carbon nanotube of the present invention shows a maximum value of the TGA-DTG graph in the range of 500 to 700°C, which means that the carbon nanotube of the present invention has excellent thermal stability.

Claims

1. A step (S1) of preparing a precursor solution by dissolving an iron precursor, a molybdenum precursor, and a magnesium precursor in water; Step (S2) of adding ammonium hydroxide (NH4OH) to the above precursor aqueous solution and co-precipitating to prepare a slurry; A step (S3) of recovering solids from the above slurry; and A method for producing a catalyst for producing carbon nanotubes, comprising a step (S4) of drying and calcining the above-mentioned solid content.

2. In paragraph 1, A method for producing a catalyst for producing carbon nanotubes, wherein the molar ratio between the iron, molybdenum and magnesium is 0.5 to 8:0.05 to 10:

88.

3. In paragraph 1, A method for producing a catalyst for producing carbon nanotubes, wherein the molar ratio between iron and molybdenum is 20:1 to 5:

1.

4. In paragraph 1, A method for producing a catalyst for producing carbon nanotubes, wherein the above step S2 is performed under normal pressure and temperature conditions.

5. In paragraph 1, A method for producing a catalyst for producing carbon nanotubes, wherein the ammonium hydroxide is added in a molar ratio of 0.1 to 5.0 relative to the combined content of iron, molybdenum, and magnesium in the precursor aqueous solution.

6. In paragraph 1, The above S3 step is a step of maturing the slurry (S3-1); and A method for producing a catalyst for producing carbon nanotubes, comprising a step (S3-2) of recovering and washing a solid from a matured slurry.

7. In paragraph 6, A method for producing a catalyst for producing carbon nanotubes, wherein the above step S3-1 is performed at 25 to 120°C for 6 to 48 hours.

8. In paragraph 1, The above iron precursor is at least one selected from the group consisting of iron nitrate, iron chloride, iron acetate, iron sulfate and hydrates thereof, The above molybdenum precursor is at least one selected from the group consisting of ammonium molybdate, sodium molybdate, phosphomolybdic acid and hydrates thereof. A method for producing a catalyst for producing carbon nanotubes, wherein the magnesium precursor is at least one selected from the group consisting of magnesium nitrate, magnesium chloride, magnesium acetate, and hydrates thereof.

9. In paragraph 1, The above drying is performed at 50 to 150°C, A method for producing a catalyst for producing carbon nanotubes, wherein the above calcination is performed at 300 to 900°C.

10. Contains iron, molybdenum and magnesium; When the molar ratio between the above iron, molybdenum and magnesium is a:b:c, a is a catalyst having a value of 0.5 to 8, b is a catalyst having a value of 0.05 to 10, and c is a catalyst having a value of 88. A catalyst for producing carbon nanotubes, wherein the ratio (D / a) of the maximum size D (nm) of active metal particles obtained by TEM analysis of the above catalyst to the above value a is 4 or less.

11. In paragraph 10, When the minimum size of the active metal particles obtained by TEM analysis of the above catalyst is d (nm), A catalyst for producing carbon nanotubes with a d / a of 3 or less.

12. In paragraph 10, A catalyst for producing carbon nanotubes, wherein the difference between D and d is 2 or less.

13. A method for producing carbon nanotubes, comprising the step of producing carbon nanotubes by introducing the catalyst of clause 10 into a reactor and heating the reactor while injecting a carbon source gas into the reactor.

14. A carbon nanotube characterized in that the mass change rate graph per unit temperature obtained by TGA-DTG analysis has a maximum value at 500 to 700°C.

15. In paragraph 14, The above carbon nanotubes have a crystallinity (I) obtained by Raman spectrum G / I D ) carbon nanotubes having a molecular weight of 10 or more.

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