Method for producing a catalyst for carbon nanotube production, catalyst for carbon nanotube production, and carbon nanotube

Abstract

The present invention relates to a method for producing a catalyst for carbon nanotube production, which allows for the easy production of a catalyst usable for the production of thin-walled carbon nanotubes by precipitating active metals in the form of hydroxides even under relatively mild conditions using ammonium hydroxide as a coprecipitant; a catalyst for carbon nanotube production produced by the method described above; a method for producing carbon nanotubes using the catalyst described above; and carbon nanotubes produced by the method described above.

Description

[Technical Field]

[0001] This application claims priority under Korean Patent Application No. 10-2023-0148157 dated October 31, 2023, and all content disclosed in the said Korean Patent Application is incorporated herein by reference.

[0002] The present invention relates to a method for producing a catalyst for carbon nanotube production that can produce thin-walled carbon nanotubes with high crystallinity and electrical conductivity in high yield, a catalyst for carbon nanotube production produced using the method, a method for producing carbon nanotubes using the catalyst, and carbon nanotubes produced therefrom. [Background technology]

[0003] Carbon nanomaterials include fullerenes, carbon nanotubes (CNTs), graphenes, and graphite nanoplates, depending on their shape. Of these, carbon nanotubes are giant molecules in which hexagonal honeycomb-shaped graphite surfaces, each consisting of one carbon atom bonded to three different carbon atoms, are rolled up to a nanoscale diameter.

[0004] Carbon nanotubes are hollow and lightweight, possess electrical conductivity comparable to copper, thermal conductivity as excellent as diamond, and tensile strength comparable to steel. Depending on their coiled form, they can be classified into single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs), and rope carbon nanotubes.

[0005] Among the aforementioned types of carbon nanotubes, single-walled carbon nanotubes have the advantage of particularly excellent conductivity and have recently attracted attention in the field of conductive materials as a material to be used as a substitute for carbon black. However, unlike multi-walled carbon nanotubes, single-walled carbon nanotubes have the limitation that they are not easy to mass-produce. For this reason, various studies are being conducted to produce multi-walled carbon nanotubes that have similar physical properties to single-walled carbon nanotubes, and synthesis research on thin-walled carbon nanotubes that are known to exhibit similar performance to single-walled carbon nanotubes is also being actively pursued.

[0006] Generally, multi-walled carbon nanotubes are manufactured using supported catalysts, which are produced by supporting metal-active species on a support. While supported catalysts have the advantage of being easy to manufacture, they have limitations in increasing the dispersion of metal-active species exposed on the surface of the support, making them unsuitable for synthesizing thin-walled carbon nanotubes with a small number of walls. On the other hand, when catalysts are manufactured by coprecipitation, metal-active species can be distributed more uniformly within the catalyst compared to supported catalysts, which is advantageous for the production of thin-walled carbon nanotubes.

[0007] When producing catalysts using the coprecipitation method, the physical properties and shape of the catalyst change depending on the type of coprecipitant used and the pH, temperature, or pressure conditions during the manufacturing process. Conventional coprecipitating catalysts used in the production of carbon nanotubes are produced by hydrothermal synthesis, which involves using a component such as urea as the coprecipitant and carrying out the reaction under high temperature and pressure conditions. In this method, during the reaction process, carbonate ions generated by the thermal decomposition of urea combine with metal cations, resulting in the formation of a precipitate in the form of metal carbonates. However, when precipitates are formed in the form of metal carbonates in this way, precipitation occurs even if the pH conditions are not as desired, making it difficult to adjust the size and shape of the active metal particles as desired. Furthermore, hydrothermal synthesis requires high temperature and pressure conditions, which increases the cost of catalyst production.

[0008] Therefore, further research is needed on novel catalyst manufacturing methods that can produce catalysts for thin-walled carbon nanotube production under milder conditions. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] KR10-2016-0107524 A (released on September 19, 2016) [Overview of the project] [Problems that the invention aims to solve]

[0010] The present invention provides a method for producing a catalyst that can produce thin-walled carbon nanotubes with high crystallinity in high yield by using a coprecipitation method to precipitate the active metal in the form of a metal hydroxide, a catalyst produced by the method for producing the catalyst, a method for producing carbon nanotubes using the catalyst, and carbon nanotubes produced therefrom. [Means for solving the problem]

[0011] To solve the above problems, the present invention provides a method for producing a catalyst for carbon nanotube production, a catalyst for carbon nanotube production, a method for producing carbon nanotubes, and carbon nanotubes.

[0012] Specifically, (1) the present invention provides a method for producing a catalyst for carbon nanotube production, comprising the steps of: (S1) dissolving an iron precursor, a molybdenum precursor, and a magnesium precursor in water to produce an aqueous precursor solution; (S2) adding ammonium hydroxide (NH4OH) to the aqueous precursor solution and coprecipitation to produce a slurry; (S3) recovering solids from the slurry; and (S4) drying and calcining the solids.

[0013] (2) The present invention provides a method for producing a catalyst for carbon nanotube production, wherein, in (1) above, the molar ratio of iron, molybdenum, and magnesium is 0.5 to 8:0.05 to 10:88.

[0014] (3) The present invention provides a method for producing a catalyst for carbon nanotube production, wherein, in (1) or (2) above, the molar ratio of iron to molybdenum is 20:1 to 5:1.

[0015] (4) The present invention provides a method for producing a catalyst for carbon nanotubes, in any one of (1) to (3) above, wherein step S2 is carried out under normal pressure and room temperature conditions.

[0016] (5) The present invention provides a method for producing a catalyst for carbon nanotube production in any one of (1) to (4) above, wherein the ammonium hydroxide is added in a molar ratio of 0.1 to 5.0 with respect to the combined content of iron, molybdenum, and magnesium in the precursor aqueous solution.

[0017] (6) The present invention provides, in any one of (1) to (5) above, a method for producing a catalyst for carbon nanotube production, wherein the step S3 comprises a step of aging a slurry (S3-1) and a step of recovering a solid content from the aged slurry and washing the solid content (S3-2).

[0018] (7) The present invention provides, in any one of (1) to (6) above, a method for producing a catalyst for carbon nanotube production, wherein the step S3-1 is performed at 25 to 120°C for 6 to 48 hours.

[0019] (8) The present invention provides, in any one of (1) to (7) above, a method for producing a catalyst for carbon nanotube production, wherein: the iron precursor is one or more selected from the group consisting of iron nitrate, iron chloride, iron acetate, iron sulfate, and hydrates thereof; the molybdenum precursor is one or more selected from the group consisting of ammonium molybdate, sodium molybdate, phosphomolybdic acid, and hydrates thereof; and the magnesium precursor is one or more selected from the group consisting of magnesium nitrate, magnesium chloride, magnesium acetate, and hydrates thereof.

[0020] (9) The present invention provides, in any one of (1) to (8) above, a method for producing a catalyst for carbon nanotube production, wherein the drying is performed at 50 to 150°C, and the calcination is performed at 300 to 900°C.

[0021] (10) The present invention provides a catalyst for carbon nanotube production, which comprises iron, molybdenum and magnesium, wherein when the molar ratio of iron, molybdenum and magnesium is defined as a:b:c, a is 0.5 to 8, b is 0.05 to 1, and c is 88 to 99, and a ratio (D / a) of a maximum size D (nm) of active metal particles obtained by TEM analysis of the catalyst to a is 4 or less.

[0022] (11) The present invention provides a catalyst for manufacturing carbon nanotubes in which, when the minimum size of the active metal particles obtained by TEM analysis of the catalyst is d (nm), d / a is 3 or less.

[0023] (12) The present invention provides a catalyst for manufacturing carbon nanotubes in which, in (10) or (11), the difference between D and d is 2 or less.

[0024] (13) The present invention provides a method for producing carbon nanotubes, which includes the step of introducing a catalyst according to any one of (10) to (12) into a reactor and heating the reactor while injecting a carbon source gas into the reactor.

[0025] (14) The present invention provides carbon nanotubes 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.

[0026] (15) In the present invention, in (14) above, the carbon nanotube is the degree of crystallinity (I) obtained by Raman spectroscopy. G / I D The present invention provides carbon nanotubes in which the ratio is 10 or greater. [Effects of the Invention]

[0027] According to the method for producing a carbon nanotube catalyst of the present invention, by using ammonium hydroxide as a coprecipitant, the active metal can be precipitated in the form of a hydroxide even under relatively mild conditions, making it easier to produce a catalyst that can be used for the production of thin-walled carbon nanotubes.

[0028] Furthermore, the carbon nanotube production catalyst of the present invention has metal-active species uniformly distributed inside the catalyst particles, enabling the production of thin-walled carbon nanotubes with high crystallinity in high yield.

[0029] Furthermore, the carbon nanotubes of the present invention, being manufactured from the catalyst, exhibit high crystallinity and excellent thermal stability. [Brief explanation of the drawing]

[0030] [Figure 1] This figure shows the Raman spectrum of carbon nanotubes produced from the catalyst of Example 1 of the present invention. [Figure 2] This is an SEM image (×1,000K) of carbon nanotubes produced from the catalyst of Example 1 of the present invention, after purification. [Figure 3] This is an SEM image (×5,000K) of carbon nanotubes produced from the catalyst of Example 1 of the present invention, after purification. [Figure 4] This graph shows the TGA-DTG analysis results of carbon nanotubes produced from the catalysts of Examples 1, 6, 8, and 9 of the present invention. [Modes for carrying out the invention]

[0031] The present invention will be described in more detail below.

[0032] The terms and words used in this specification and in the claims should not be interpreted in a manner limited to their ordinary or dictionary meanings, but rather should be interpreted in a manner consistent with the technical idea of ​​the present invention, in accordance with the principle that inventors may appropriately define the concepts of terms in order to best describe their invention.

[0033] In this invention, the term "carbon nanotube" refers to a secondary structure formed by the whole or partial assembly of carbon nanotube units. Each carbon nanotube unit is a graphite sheet with a cylindrical shape having a nanoscale diameter and an sp2 bond structure. Depending on the angle and structure in which the graphite sheet is wound, it can exhibit conductive or semiconductor properties. Carbon nanotube units are classified into single-walled carbon nanotubes (SWCNTs), double-walled carbon nanotubes (DWCNTs), and multi-walled carbon nanotubes (MWCNTs) according to the number of bonds forming the walls, with lower resistance occurring as the wall thickness decreases.

[0034] 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.

[0035] Method for manufacturing catalysts for carbon nanotube production Various catalysts used in the mass production of carbon nanotubes are manufactured using the supported method. In the supported method, catalysts are produced by immersing a support in a solution containing dissolved active metal components, followed by drying and calcination. However, in this process, it is not easy for the active metal to penetrate into the internal space of the support. As a result, most of the active metal components in supported catalysts are distributed on the surface of the catalyst particles, which means that it is not easy to grow carbon nanotubes with a small number of walls from the catalyst.

[0036] One known catalyst manufacturing method that can overcome the disadvantages of the supported material method is the coprecipitation method. In the coprecipitation method, a coprecipitating agent is added to a solution in which both the active metal and the support metal are dissolved, and the catalyst is produced by causing both the active metal and the support metal to precipitate. Catalysts produced using the coprecipitation method have the advantage of having the active metal uniformly distributed even within the internal space of the catalyst, compared to catalysts produced using the supported material method. Among such coprecipitation methods, a representative method known to be used for catalysts for carbon nanotube production is the hydrothermal synthesis method. Hydrothermal synthesis is carried out under high pressure and temperature conditions, and a method for producing catalysts for carbon nanotube production using such a hydrothermal synthesis method is disclosed in the aforementioned prior art document 1. However, even in the method of producing catalysts using hydrothermal synthesis, there are disadvantages. The requirement of high pressure and temperature means that the energy costs used in the catalyst manufacturing process are high, and hydrothermal synthesis is difficult to scale up, making it difficult to actually mass-produce catalysts with the same physical properties as catalysts confirmed on a wrap scale. In addition, in hydrothermal synthesis, the physical properties of the catalyst tend to change depending on the pressure and temperature conditions, making it difficult to ensure the reproducibility of the catalyst.

[0037] Focusing on these points, the present invention provides a method for producing a catalyst that uses a coprecipitation method under mild conditions of room temperature and atmospheric pressure, but uses ammonium hydroxide as a coprecipitation agent to precipitate the active metal in the form of a hydroxide rather than a carbonate, thereby enabling the production of thin-walled carbon nanotubes with a relatively low catalyst production cost.

[0038] More specifically, the present invention provides a method for producing a catalyst for carbon nanotube production, comprising the steps of: dissolving an iron precursor, a molybdenum precursor, and a magnesium precursor in water to produce an aqueous precursor solution (S1); adding ammonium hydroxide (NH4OH) to the aqueous precursor solution and coprecipitation to produce a slurry (S2); recovering solids from the slurry (S3); and drying and calcining the solids (S4).

[0039] The following describes in detail each step included in the method for producing a carbon nanotube catalyst provided by the present invention.

[0040] Precursor aqueous solution preparation step (S1) In step S1, an aqueous precursor solution is produced by dissolving precursors of iron and molybdenum, which are the active metals of the catalyst, and a precursor of magnesium, which is the support, in water.

[0041] In this step, the molar ratio of iron, molybdenum, and magnesium, which are metal components derived from the dissolved iron precursor, molybdenum precursor, and magnesium precursor, 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 present in the above molar ratios relative to magnesium, sufficient durability of the manufactured catalyst can be ensured, and sufficient catalytic activity can be provided.

[0042] Furthermore, the molar ratio of iron to molybdenum may be 20:1 to 5:1, and preferably 15:1 to 7:1. Molybdenum is a co-catalyst component that enhances the catalytic activity of iron, and when the molar ratio of iron to molybdenum satisfies the above conditions, the synergistic effect between the two components is maximized, resulting in particularly high catalytic activity.

[0043] The iron precursor, molybdenum precursor, and magnesium precursor are preferably those that are sufficiently soluble in water under normal temperature and pressure conditions. More specifically, the iron precursor may be one or more selected from the group consisting of iron nitrate, iron chloride, iron acetate, iron sulfate, and their hydrates. The molybdenum precursor may be one or more selected from the group consisting of ammonium molybdate, sodium molybdate, phosphomolybdic acid, and their hydrates. The magnesium precursor may be one or more selected from the group consisting of magnesium nitrate, magnesium chloride, magnesium acetate, and their hydrates.

[0044] Co-settling step (S2) By adding a co-precipitant to the precursor aqueous solution produced in the previous step, the dissolved metal components can be precipitated together.

[0045] In catalyst synthesis by coprecipitation, the form in which the metal component precipitates depends on the type of coprecipitant added. Generally, by adding a compound containing carbonate ions as a coprecipitant, the metal component precipitates in the form of metal carbonate. However, when precipitation occurs in the form of metal carbonate, it occurs even under non-desirable pH conditions, making it difficult to control the size and morphology of the active metal particles as desired. Furthermore, when using ammonium bicarbonate, a known coprecipitant, the crystallinity of the carbon nanotubes produced from the catalyst may decrease, or the carbon nanotube production yield may decrease.

[0046] On the other hand, in the present invention, ammonium hydroxide is used as a coprecipitant to precipitate the metal component in the form of a metal hydroxide. Such a metal hydroxide can precipitate under relatively desired pH conditions, and the size of the active metal particles can be controlled within an appropriate range. Furthermore, step S2 may be carried out under atmospheric pressure and room temperature conditions, thereby overcoming the disadvantages of the aforementioned hydrothermal synthesis method.

[0047] Furthermore, in this step, the ammonium hydroxide added as a coprecipitant may be 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, preferably in a molar ratio of 0.5 to 3. When an appropriate amount of coprecipitant is added, the amount of catalyst obtained can be increased without loss of metal components.

[0048] Solids recovery step (S3) The solid component can be recovered from the slurry produced in the previous step and used as a catalyst.

[0049] In this step, methods typically used to recover solids from a slurry can be applied, such as using a vacuum filter or a centrifuge to recover the solids.

[0050] On the other hand, step S3 may include a step of maturing the slurry (S3-1) and a step of recovering solids from the matured slurry and washing it (S3-2).

[0051] Thus, when the slurry undergoes a maturation step, there is a technical advantage in that the iron, which is the active metal in the catalyst, can be uniformly distributed during the maturation process, and all components that have not yet been converted to the form of hydroxide can be converted to the form of hydroxide. Such a maturation process may be carried out at 25-120°C for 6-48 hours.

[0052] Furthermore, the washing process in S3-2 removes impurities remaining in the solid content. If the washing process is not followed, the remaining impurities may adversely affect the carbon nanotube synthesis reaction.

[0053] Drying and firing step (S4) The catalyst can be obtained by finally drying and calcining the solid produced in the previous step. The drying process removes any remaining moisture from the solid, and the calcination process converts the metal hydroxide into a stable metal oxide.

[0054] In this step, the drying may be carried out at 50 to 150°C, preferably 80 to 105°C, and the calcination may be carried out at 300 to 900°C, preferably 400 to 800°C. If the temperatures for drying and calcination are too low, sufficient drying and calcination efficiency may not be achieved, and if they are too high, the cost of the manufacturing process will increase, and phenomena such as thermal decomposition of the manufactured catalyst may occur.

[0055] Catalyst for carbon nanotube production In addition to the method for producing a carbon nanotube catalyst as described above, the present invention provides a carbon nanotube catalyst produced by the above method.

[0056] More specifically, the present invention provides a catalyst for carbon nanotube production comprising iron, molybdenum, and magnesium, wherein the molar ratio of iron, molybdenum, and magnesium is a:b:c, where a is 0.5 to 8, b is 0.05 to 10, and c is 88, and the ratio of the maximum size D (nm) of the active metal particles obtained by TEM analysis of the catalyst to the value a (D / a) is 4 or less. On the other hand, the active metal refers to iron.

[0057] The carbon nanotube production catalyst of the present invention is characterized by smaller active metal particle size due to being manufactured using ammonium hydroxide as a coprecipitant. Smaller active metal particle size offers a technical advantage in the synthesis of thin-walled carbon nanotubes with smaller diameters. However, the size of the active metal particles is affected by the catalyst composition, more specifically, the composition of iron, which is the active metal in the catalyst. Therefore, the catalyst manufactured in the present invention is characterized by a D / a value, which is the ratio of the maximum size D (nm) of the active metal particles to the iron composition ratio a, being 4 or less, preferably 2 to 3.5. On the other hand, D represents the number when the maximum size of the active metal particles is expressed in nm.

[0058] Furthermore, in the carbon nanotube manufacturing catalyst of the present invention, when the minimum size of the active metal particles obtained by TEM analysis of the catalyst is denoted as d (nm), d / a may be 3 or less, preferably 1 to 2.5. Also, the difference between D and d may be 2 or less, preferably 1.5 or less.

[0059] On the other hand, D and d may be directly measured by TEM analysis of the catalyst.

[0060] Method for manufacturing carbon nanotubes The present invention provides a method for producing carbon nanotubes using the above-mentioned catalyst for carbon nanotube production.

[0061] More specifically, the present invention provides a method for producing carbon nanotubes, which includes the step of introducing the above-mentioned catalyst into a reactor and heating the reactor while injecting a carbon source gas into the reactor.

[0062] As the reactor, a chemical vapor deposition reactor or a fluidized bed reactor can be used.

[0063] Furthermore, the carbon source gas is a carbon-containing gas that can decompose at high temperatures to form carbon nanotubes. Specific examples include various carbon-containing compounds such as aliphatic alkanes, aliphatic alkenes, aliphatic alkynes, and aromatic compounds. 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 can be used.

[0064] Along with the carbon source gas, a fluidized gas may be injected to increase the fluidity of the catalyst. The fluidized gas may be an inert gas or nitrogen gas, and more specifically, argon or nitrogen gas.

[0065] When both a carbon source gas and a fluidized gas are injected, the flow rate ratio of the carbon source gas to the fluidized gas may be 1:2 to 1:8 based on volume, and preferably 1:3 to 1:7.

[0066] Furthermore, the carbon nanotube synthesis reaction can be carried out at a temperature of 750 to 900°C.

[0067] carbon nanotubes The present invention provides carbon nanotubes produced from the catalyst described above.

[0068] More specifically, the carbon nanotubes provided by the present invention may be carbon nanotubes characterized in that a graph of mass change rate per unit temperature obtained by TGA-DTG analysis has a maximum value at 500 to 700°C.

[0069] Further, the carbon nanotubes may have a crystallinity obtained by Raman spectrum (I G / I D ) of 10 or more, preferably 10 to 20.

[0070] Further, the carbon nanotubes may have a diameter obtained by Raman analysis of 0.8 to 2 nm.

[0071] Further, the carbon nanotubes may have a BET specific surface area of 900 m 2 / g or more. Preferably, the BET specific surface area of the carbon nanotubes is 900 m 2 / g or more and 1300 m 2 / g or less.

[0072] Further, the number of walls of the carbon nanotubes may be 1 to 3.

[0073] Carbon nanotubes produced from the catalyst of the present invention are characterized by excellent thermal stability, high crystallinity, and excellent electrical conductivity.

[0074] On the other hand, the TGA-DTG analysis may be performed using a TGA2 apparatus (manufactured by Mettler Toledo).

[0075] Further, the I G / I DThe ratio can be measured for the acquired carbon nanotubes, more specifically, using a DXR Raman Microscope (Thermo Electron Scientific Instruments LLC) to obtain the Raman spectrum at a laser wavelength of 532 nm, specifically at the G peak (1550-1650 cm⁻¹). -1 ) and D peak (1250~1400cm) -1 The intensity ratio of ) can be measured and calculated.

[0076] Furthermore, the BET specific surface area may be specifically calculated by determining the amount of nitrogen gas adsorbed under liquid nitrogen temperature (77K) using BELSORP-mini II manufactured by BEL Japan.

[0077] Furthermore, the number of walls in the carbon nanotubes can be confirmed by TEM analysis, and the Raman spectrum at 400 cm² can be determined. -1 This can be indirectly confirmed by RBM (Radial Breathing Mode) in the following areas.

[0078] The present invention will be described in detail below with reference to examples and experimental examples in order to specifically illustrate it. However, the present invention is not limited to these examples and experimental examples. The examples of the present invention can be modified in various other forms, and the scope of the present invention should not be construed as being limited to the examples detailed below. The examples of the present invention are provided to give a more complete explanation of the present invention to a person of average skill in the art.

[0079] Examples and Comparative Examples Iron nitrate notahydrate was used as the iron precursor, ammonium molybdate as the molybdenum precursor, and magnesium nitrate hexahydrate as the magnesium precursor. All of the iron precursor, molybdenum precursor, and magnesium precursor were dissolved in distilled water to prepare aqueous precursor solutions.

[0080] Subsequently, a coprecipitant was added to the precursor aqueous solution prepared under normal temperature and pressure conditions to produce a slurry solution. The prepared slurry solution was aged at a temperature of 40-120°C for 6-48 hours, and after recovering the solids using a vacuum filter, it was washed with distilled water.

[0081] The washed solids were dried at 50-200°C for 6-24 hours, then calcined at 300-900°C for 2-6 hours to obtain a catalyst for carbon nanotube production.

[0082] The composition (molar basis) of iron, molybdenum, and magnesium used in each example and comparative example, along with the type and amount of co-precipitant used, are summarized in Table 1 below.

[0083] [Table 1]

[0084] Experimental Example 1. Confirmation of carbon nanotube production yield and crystallinity. 0.5G of the catalyst produced in the above examples and comparative examples was packed into a chemical vapor deposition reactor and reacted at 850°C in an argon / methane gas atmosphere for 15 to 60 minutes to obtain carbon nanotubes. The flow rates of argon and methane gas were 540 sccm and 105 sccm, respectively.

[0085] The yield and crystallinity of the acquired carbon nanotubes were measured using the method described below and summarized in Table 2.

[0086] 1) Yield (carbon nanotube yield per unit mass of metal): Yield = (Mass of carbon nanotubes obtained / Mass of active metal (iron)) * 100%

[0087] 2) Crystallinity (I G / I D): The acquired carbon nanotubes were analyzed using a DXR Raman Microscope (Thermo Electron Scientific Instruments LLC) to obtain the Raman spectrum at a laser wavelength of 532 nm, and the G peak (1550-1650 cm⁻¹) was observed. -1 ) and D peak (1250~1400cm) -1 The intensity ratio was measured and calculated.

[0088] [Table 2]

[0089] As summarized in Table 2 above, the catalyst of the present invention was found to be able to synthesize carbon nanotubes in a higher yield compared to the comparative example, and the crystallinity of the obtained carbon nanotubes was confirmed to be very high, at 10 or higher.

[0090] On the other hand, the catalysts of Comparative Examples 1 to 6, which used a different type of coprecipitant than that of the Examples of the present invention, showed results that were inferior in one or more of the following: yield and crystallinity. Even in the case of Comparative Examples 2 and 3, which still obtained high yields, it was confirmed that both the yield and crystallinity were inferior to those of Example 1 of the present invention, which used ammonium hydroxide as the coprecipitant with the same composition.

[0091] This confirmed that, when using the catalyst of the present invention, highly crystallinity carbon nanotubes with excellent electrical conductivity can be produced in high yield.

[0092] Experimental Example 2. Measurement of the size of activated metal particles in a catalyst. The size of the active metal particles was measured for the catalysts of Example 1 and Comparative Example 3 prepared as described above. Specifically, the size of the active metal particles was measured directly after observing the acquired catalysts with a TEM. A Titan G2 (manufactured by FEI) was used as the TEM equipment.

[0093] [Table 3]

[0094] As can be confirmed by referring to Table 3 above, the catalyst in the example of the present invention using ammonium hydroxide as a coprecipitant has a smaller active metal particle size compared to the catalyst in Comparative Example 3. Due to the smaller size of the active metal particles in the catalyst, the catalyst of the present invention can produce carbon nanotubes with high yield and high crystalline properties.

[0095] Experimental Example 3. Confirmation of the morphology of the fabricated carbon nanotubes. Figure 1 shows the Raman spectrum obtained for carbon nanotubes produced from the catalyst of Example 1. The RBM region is observed in the Raman spectrum of Figure 1, which means that the carbon nanotubes produced from the catalyst of Example 1 are thin-walled carbon nanotubes.

[0096] Furthermore, after purifying the carbon nanotubes produced from the catalyst of Example 1, their morphology was observed using a scanning electron microscope (SEM). Specifically, the produced carbon nanotubes were treated in air at a temperature of 350°C or higher for 30 minutes or more, and the catalyst contained therein was removed using an acid. The results are shown in Figures 2 and 3.

[0097] Referring to Figures 2 and 3, it can be seen that the carbon nanotubes produced from the catalyst of the present invention have a form in which thin-walled carbon nanotubes are aggregated.

[0098] Experimental Example 4. TGA-DTG analysis of fabricated carbon nanotubes TGA-DTG analysis was performed on carbon nanotubes produced using the catalysts of Examples 1, 6, 8, and 9. A TGA2 (Mettler Toledo) was used as the analytical instrument. The resulting graph is shown in Figure 4.

[0099] As can be confirmed by referring to Figure 4, the carbon nanotubes of the present invention exhibit the maximum value of the TGA-DTG graph in the range of 500 to 700°C, which means that the carbon nanotubes of the present invention have excellent thermal stability.

Claims

1. Step (S1) involves dissolving an iron precursor, a molybdenum precursor, and a magnesium precursor in water to produce an aqueous precursor solution. Ammonium hydroxide (NH₄) in the aqueous precursor solution ４ Step (S2) involves adding OH) and allowing it to co-precipitate to produce a slurry. The steps include recovering solid matter from the slurry (S3), A method for producing a catalyst for carbon nanotubes, comprising the step (S4) of drying and calcining the solid component.

2. The method for producing a catalyst for carbon nanotubes according to claim 1, wherein the molar ratio of iron, molybdenum, and magnesium is 0.5 to 8:0.05 to 10:

88.

3. The method for producing a catalyst for carbon nanotubes according to claim 1, wherein the molar ratio of iron to molybdenum is 20:1 to 5:

1.

4. The method for producing a catalyst for carbon nanotubes according to claim 1, wherein step S2 is carried out under normal pressure and room temperature conditions.

5. The method for producing a catalyst for carbon nanotubes according to claim 1, wherein the ammonium hydroxide is added in a molar ratio of 0.1 or more and 5.0 or less relative to the combined content of iron, molybdenum, and magnesium in the precursor aqueous solution.

6. The aforementioned S3 step is a step of maturing the slurry (S3-1), A method for producing a catalyst for carbon nanotube production according to any one of claims 1 to 5, comprising the step of recovering solid matter from the matured slurry and washing it (S3-2).

7. The method for producing a catalyst for carbon nanotubes according to claim 6, wherein step S3-1 is performed at a temperature of 25°C or higher and 120°C or lower for 6 hours or more and 48 hours or less.

8. The iron precursor is one or more selected from the group consisting of iron nitrate, iron chloride, iron acetate, iron sulfate, and their hydrates. The molybdenum precursor is one or more selected from the group consisting of ammonium molybdate, sodium molybdate, phosphomolybdic acid, and hydrates thereof. The method for producing a catalyst for carbon nanotubes according to claim 1, wherein the magnesium precursor is one or more selected from the group consisting of magnesium nitrate, magnesium chloride, magnesium acetate, and hydrates thereof.

9. The drying is carried out at a temperature of 50°C or higher and 150°C or lower. The method for producing a catalyst for carbon nanotubes according to claim 1, wherein the calcination is carried out at a temperature of 300°C or higher and 900°C or lower.

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

11. When the minimum size of the active metal particles obtained by TEM analysis of the catalyst is denoted as d (nm), The catalyst for producing carbon nanotubes according to claim 10, wherein d / a is 3 or less.

12. The catalyst for producing carbon nanotubes according to claim 10, wherein the difference between D and d is 2 or less.

13. A method for producing carbon nanotubes, comprising the step of introducing the catalyst described in claim 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 between 500°C and 700°C.

15. The carbon nanotube has a degree of crystallinity (I) obtained by Raman spectroscopy. Ｇ / I Ｄ The carbon nanotube according to claim 14, wherein the ratio is 10 or more.

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