A catalyst for preparing carbon nanotubes and a method for preparing the same

Abstract

The application discloses a catalyst for preparing carbon nanotubes and a preparation method thereof, and comprises the following steps: mixing a catalytically active gel with expanded vermiculite and performing ball milling treatment to obtain a catalyst precursor; and performing calcination treatment on the catalyst precursor and performing screening to obtain the catalyst for preparing carbon nanotubes; the catalyst is a laminar material with metal oxides as active components and expanded vermiculite as a carrier. The gel-assisted physical peeling method is adopted, the catalytically active gel in the form of gel can serve as a buffer layer to weaken the damage of the ball milling treatment process to the expanded vermiculite, and can also serve as a peeling agent to open the laminar structure of the expanded vermiculite and uniformly adhere to the two-dimensional layer surface of the expanded vermiculite, so that the uniformity of the active components in the catalyst for preparing high-aspect-ratio carbon nanotubes on the surface of the vermiculite is improved, the process is simple, the preparation is efficient, the prepared catalyst has good catalytic performance, and the catalyst can effectively improve the synthesis quality of the carbon nanotubes when applied to the carbon nanotube synthesis process.

Description

Technical Field

[0001] This invention relates to the field of carbon nanomaterials technology, and in particular to a catalyst for preparing carbon nanotubes and a method thereof. Background Technology

[0002] The aspect ratio and carbon purity of carbon nanotubes are key indicators for measuring their electrical conductivity, directly affecting the overall performance of carbon nanotube products. Theoretically, the smaller the diameter and the longer the length of the carbon nanotube, the better its electrical conductivity. Arrayed carbon nanotubes possess high axial thermal conductivity, low electrical resistance, and combine efficient heat dissipation with low-energy-consumption conductivity, making them widely used in electronic chemicals and related fields.

[0003] Currently, most metal catalysts used to prepare arrayed carbon nanotubes use alumina, vermiculite, and other materials as supports. However, the porosity and surface physicochemical properties of these supports greatly affect the permeability of active metal ions, resulting in low active metal loading and uneven distribution. The prepared arrayed carbon nanotubes typically exhibit shorter tube lengths and lower bundle densities, which not only affects the conductivity of carbon nanotubes but also limits their application in fields such as antistatic plastics and lithium-ion batteries.

[0004] Metal catalysts for the synthesis of arrayed carbon nanotubes are typically prepared using co-precipitation or impregnation methods. However, both methods have certain limitations. Co-precipitation requires stringent processing techniques, and the distribution of active catalytic sites is difficult to control precisely, resulting in low catalyst utilization and affecting product quality. Conventional impregnation methods, on the other hand, are limited by the adsorption efficiency of the support for the active component, making it difficult to increase the loading of the active material. Furthermore, during the calcination process, the interaction between the active component and the support is weak, making it prone to aggregation due to high temperatures.

[0005] For example, some existing technologies employ high-temperature and high-pressure impregnation, utilizing the pressure of high-temperature water vapor for pressurized impregnation. This accelerates the diffusion rate of catalytically active components, increases the driving force for these components to enter the pores of the layered support material, and enhances the adsorption capacity and ion exchange capacity of the catalytically active components on the support. This improves the catalyst loading effect, thereby reducing the production cost and cycle time of carbon nanotubes and reducing wastewater discharge. Although this technology can obtain array-type carbon nanotubes, the preparation process requires impregnation under high-temperature and high-pressure conditions, which is not conducive to cost control. Furthermore, in terms of results, the length distribution of the obtained array carbon nanotubes is only 10-20 μm, and the quality does not reach the ideal state.

[0006] Some existing technologies involve impregnating and mixing an active metal salt solution with a catalyst support, then introducing an alkaline gas into the resulting mixture to deposit and age the active metal, thus preparing a catalyst precursor. The catalyst precursor is then calcined, sieved, and reduced. Although this technology can achieve continuous production, it relies on specific equipment, has high costs, and is not conducive to large-scale production. Summary of the Invention

[0007] To address the problems existing in the prior art, this invention provides a catalyst for preparing carbon nanotubes and a method for preparing the same. The technical solution is as follows:

[0008] This invention provides a method for preparing a catalyst for preparing carbon nanotubes, comprising:

[0009] The first metal salt and the complexing agent are dissolved in deionized water and mixed with an alkaline solution to obtain a mixed solution; the complexing agent is a small organic molecule.

[0010] A second metal salt is mixed with the mixed solution to obtain a catalytically active gel; the second metal salt includes a cobalt salt; the catalytically active gel is a gel formed by adding small organic molecules with high functional group content;

[0011] The catalytically active gel was mixed with expanded vermiculite and ball-milled to obtain a catalyst precursor.

[0012] The catalyst precursor is calcined and sieved to obtain the catalyst for preparing carbon nanotubes; the catalyst for preparing carbon nanotubes is a layered material with metal oxide as active component and expanded vermiculite as support.

[0013] Furthermore, the preparation steps of the mixed solution satisfy at least one of the following characteristics:

[0014] The first metal salt includes molybdenum salts;

[0015] The organic small molecules include at least one of citric acid, ethylenediaminetetraacetic acid, terephthalic acid, and 2,5-dihydroxyterephthalic acid;

[0016] The alkaline solution includes a mixed aqueous solution of one or more of sodium hydroxide, sodium carbonate, ammonia, ammonium carbonate, and ammonium bicarbonate.

[0017] Furthermore, the second metal salt includes at least one of nitrate, hydrochloride and sulfate.

[0018] Furthermore, the second metal salt also includes at least one or more of aluminum salts, magnesium salts, and iron salts.

[0019] Further, the second metal salt includes aluminum salt, magnesium salt, cobalt salt and iron salt; in the second metal salt, the molar ratio between the aluminum salt, the magnesium salt, the cobalt salt and the iron salt is (1~4):(0.2~1):(0.2~1.5):(0.2~1).

[0020] Furthermore, the amount of the second metal salt used satisfies at least one of the following characteristics:

[0021] When the second metal salt includes a cobalt salt, the molar ratio of the cobalt salt to the first metal salt is 5:1 to 10:1;

[0022] The molar ratio of the second metal salt to the complexing agent is 2:1 to 3:1;

[0023] The concentration of the second metal salt in the catalytically active gel is 5 mol / L to 8 mol / L.

[0024] Furthermore, the ball milling process satisfies at least one of the following characteristics:

[0025] The expanded vermiculite has a mesh size of 10 to 40 mesh;

[0026] The mass ratio between the expanded vermiculite and the cobalt salt in the catalytically active gel is 1:1 to 2:1;

[0027] The ball milling media for the ball milling process includes zirconium balls, and the mass ratio of the zirconium balls to the expanded vermiculite is 2:1 to 4:1.

[0028] The stirring time for the ball milling process is 2 to 3 hours.

[0029] Furthermore, the calcination treatment is carried out at a temperature of 450℃ to 550℃ for a time of 1 hour to 2 hours.

[0030] On the other hand, the present invention also provides a catalyst for preparing carbon nanotubes, which is prepared based on the preparation method of the catalyst for preparing carbon nanotubes as described in any of the preceding claims.

[0031] Implementing this invention has the following beneficial effects:

[0032] This invention employs a gel-assisted physical exfoliation method. A gel-like catalytically active gel is mixed with expanded vermiculite and then ball-milled, followed by calcination and sieving. This gel-like catalytically active gel acts as a buffer layer to reduce damage to the expanded vermiculite during ball milling, and also as an exfoliant to open the lamellar structure of the expanded vermiculite, allowing it to adhere uniformly to the two-dimensional surface of the expanded vermiculite. After calcination, a uniform load of metal oxide active components is placed on the surface of the expanded vermiculite, improving the loading and distribution uniformity of the final active components on the expanded vermiculite carrier surface. This preparation method offers high controllability, a wide range of raw material sources, a simple process, high efficiency, and low cost. The resulting catalyst for carbon nanotube preparation exhibits excellent catalytic performance and can effectively improve the synthesis quality of carbon nanotubes in high aspect ratio carbon nanotube synthesis processes, thus facilitating the large-scale industrial production of carbon nanotubes. Attached Figure Description

[0033] To more clearly illustrate the technical solutions of the present invention, the accompanying drawings used in the embodiments will be briefly described below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.

[0034] Figure 1 A logical structure diagram of a method for preparing a catalyst for preparing carbon nanotubes provided in an embodiment of the present invention;

[0035] Figure 2 A logical structure diagram of a method for preparing a catalytically active gel provided in an embodiment of the present invention;

[0036] Figure 3 The image shows a scanning electron microscope (SEM) image of array-type carbon nanotubes synthesized based on the catalyst for preparing carbon nanotubes provided in Example 2 of this invention.

[0037] Figure 4 This is a scanning electron microscope image of array-type carbon nanotubes synthesized using the catalyst provided in Comparative Example 6 of the present invention. Detailed Implementation

[0038] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments, and therefore should not be construed as limiting the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0039] It should be noted that, in the description of this invention, the following definitions of terms shall apply unless a different definition is given elsewhere in the claims or this specification. All numerical values, whether explicitly indicated or not, are defined herein as being modified by the term "about." The term "about" generally refers to a range of numerical values ​​that a person skilled in the art would consider equivalent to the stated values ​​to produce substantially the same properties, functions, results, etc. A range of numerical values ​​indicated by a low value and a high value is defined as including all numerical values ​​within that range and all subranges included within that range.

[0040] It should be noted that the terms "first," "second," etc., in the specification, claims, and drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such objects can be used interchangeably where appropriate so that embodiments of the invention can be implemented in orders other than those illustrated or described below. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, or product comprising a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to these processes, methods, or products.

[0041] To address the technical problems of existing catalysts for synthesizing carbon nanotubes, such as the need for high-temperature, high-pressure, and high-energy-consumption preparation, excessively long preparation time, unsatisfactory catalyst performance, and over-reliance on specific equipment hindering large-scale production, this invention provides a catalyst for preparing carbon nanotubes and its preparation method. The high aspect ratio carbon nanotubes are prepared using this catalyst. The preparation method involves first mixing a catalytically active gel with expanded vermiculite and ball-milling it to obtain a catalyst precursor. Then, the catalyst precursor is calcined and sieved to obtain the catalyst for preparing carbon nanotubes. This catalyst for preparing carbon nanotubes uses a metal oxide as the active component and expanded vermiculite as the active component. This invention relates to a layered material using vermiculite as a carrier. The preparation method employs a gel-assisted physical exfoliation technique. The gel-like catalytically active gel acts as a buffer layer to mitigate damage to the expanded vermiculite during ball milling, and also as an exfoliating agent to open the layered structure of the expanded vermiculite, allowing it to adhere uniformly to the two-dimensional surface of the expanded vermiculite. After calcination, a uniform load of metal oxide active components is applied to the surface of the expanded vermiculite, improving the loading and uniformity of the final active components on the expanded vermiculite carrier surface. This preparation method offers high controllability, a wide range of raw material sources, a simple process, high efficiency, and low cost. The resulting catalyst for carbon nanotube preparation exhibits excellent catalytic performance and does not require specialized equipment. Its application in the synthesis of high aspect ratio carbon nanotubes can effectively improve the synthesis quality of carbon nanotubes, facilitating their large-scale industrial production.

[0042] Please refer to the appendix of the instruction manual below. Figure 1-2 This invention provides a detailed method for preparing the catalyst for carbon nanotubes.

[0043] First, such as Figure 1 As shown, in step S1, the catalytically active gel is mixed with expanded vermiculite and ball-milled to obtain the catalyst precursor.

[0044] The catalytically active gel contains metal ions and is a metal ion / organic gel. The metal ions eventually form metal oxides, which serve as the active component of the catalyst used to prepare carbon nanotubes. Expanded vermiculite serves as the main support in the catalyst used to prepare carbon nanotubes, loading the metal oxides to ensure that the catalyst used to prepare carbon nanotubes has good overall catalytic performance.

[0045] Specifically, such as Figure 2 As shown, the catalytically active gel is prepared through the following steps:

[0046] S11, dissolve the first metal salt and complexing agent in deionized water and mix with alkaline solution to obtain a mixed solution;

[0047] S12, the second metal salt is mixed with the mixed solution to obtain the catalytically active gel; the second metal salt includes cobalt salt.

[0048] In step S11, the first metal salt and the complexing agent are dissolved in deionized water to form a solution of a certain concentration. Then, an alkaline solution is added and stirred for 5 to 10 minutes. Next, the second metal salt is added and the mixture is stirred for 10 to 30 minutes until a uniform gel-like product is formed, thus obtaining the catalytically active gel. The first metal salt can react with the complexing agent to facilitate the subsequent gelation process and form a stable gel structure. The addition of the alkaline solution can adjust the pH of the mixed solution, thereby controlling the reaction of the first and second metal salts. Based on coordination chemistry and condensation reaction, a gel structure with a three-dimensional network structure is generated, improving the structural stability and preparation efficiency of the catalytically active gel.

[0049] Specifically, in step S11, during the preparation of the mixed solution, the first metal salt includes a molybdenum salt. The molybdenum salt can react with a complexing agent to generate molybdic acid or its complex ion (i.e., molybdenum salt / complexing agent). In the final catalyst used to prepare carbon nanotubes, metallic molybdenum can enhance the catalyst activity, promote the conversion of carbon source into carbon nanotubes, and improve the synthesis efficiency and quality of carbon nanotubes. In step S12, the second metal salt can coordinate with the molybdenum salt / complexing agent to form a metal-molybdenum-complexing agent complex. Under alkaline catalytic conditions, the mixed solution further undergoes hydrolysis or condensation reaction to generate a gel-like structure with a three-dimensional network structure, further improving the stability of the active catalyst precursor. It also facilitates the opening of the lamellar structure of expanded vermiculite and its uniform adhesion to the two-dimensional layer surface of expanded vermiculite during subsequent ball milling, thereby improving the loading and uniformity of the active ingredient. In some preferred embodiments, the molybdenum salt includes ammonium molybdate.

[0050] Specifically, the complexing agent includes an oxygen-containing functional group containing hydrogen. In some exemplary embodiments, the oxygen-containing functional group containing hydrogen includes at least one of carboxyl and hydroxyl groups. Thus, the oxygen-containing functional group containing hydrogen can promote the formation of a gel-like structure. It should be noted that by adjusting the pH with an alkaline solution, the complexing agent can be fully ionized, promoting coordination and condensation reactions between it and metal salts (including the first metal salt and the second metal salt), thereby effectively forming a gel and improving the activity of the final catalyst used to prepare carbon nanotubes.

[0051] Specifically, in some exemplary embodiments, the complexing agent is an organic small molecule, specifically a small molecule acid, including at least one of citric acid, ethylenediaminetetraacetic acid, terephthalic acid, and 2,5-dihydroxyterephthalic acid. This organic small molecule can react with molybdenum salt to generate molybdic acid or its complex ion, which is beneficial to the subsequent gelation process. Moreover, this organic small molecule is rich in oxygen-containing functional groups, especially oxygen-containing functional groups containing hydrogen, providing sufficient complexing sites to uniformly disperse the active metal, thereby effectively promoting the improvement of the catalyst activity used to prepare carbon nanotubes.

[0052] Specifically, the alkaline solution includes a mixed aqueous solution of one or more of sodium hydroxide, sodium carbonate, ammonia, ammonium carbonate, and ammonium bicarbonate. This alkaline solution can effectively regulate the pH of the mixed solution, promote the coordination and hydrolysis of metal ions in molybdenum, complexing agents, and second metal salts, and accelerate the gelation process.

[0053] Specifically, the concentration of the solute in the alkaline solution in the mixed solution is 0.1 mol / L to 2 mol / L; understandably, the concentration of the solute in the alkaline solution in the mixed solution can be any value within the range of 0.1 mol / L to 2 mol / L; for example, the concentration of the solute in the alkaline solution in the mixed solution can be 0.1 mol / L, 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, etc.; within this concentration range, a good alkaline environment can be maintained in the mixed solution, effectively accelerating the gelation process and improving the stability of the gel structure of the catalytically active gel.

[0054] Specifically, the cobalt salt in the second metal salt is the main catalytically active component in the catalyst ultimately used to prepare carbon nanotubes. The metal oxide in the catalyst used to prepare carbon nanotubes includes cobalt-based metal oxides, so as to play a highly efficient catalytic role in the process of synthesizing carbon nanotubes and improve the quality of the finished carbon nanotubes.

[0055] Specifically, in some exemplary embodiments, based on the metal cation classification, the second metal salt also includes at least one or more of aluminum salts, magnesium salts, and iron salts; wherein, aluminum salts and magnesium salts can serve as auxiliary supports, which is beneficial to increasing the loading of the active component of the final cobalt-based metal oxide. At the same time, aluminum salts and magnesium salts can also act as barrier agents in the subsequent sintering process, effectively preventing the cobalt-based metal oxide from sintering and agglomerating, which is beneficial to improving the dispersion and uniformity of the cobalt-based metal oxide loading in the final catalyst used to prepare carbon nanotubes, thereby improving the catalytic activity and catalytic uniformity of the catalyst used to prepare carbon nanotubes; while iron salts can form heterostructures with cobalt salts in the catalyst, playing an auxiliary catalytic role and improving the catalytic activity of the catalyst used to prepare carbon nanotubes; in some preferred embodiments, the second metal salt includes aluminum salts, magnesium salts, cobalt salts, and iron salts.

[0056] Specifically, in some exemplary embodiments, based on anion, the second metal salt includes at least one of nitrate, hydrochloride, and sulfate, which is beneficial for the metal cation in solution to undergo coordination reaction with molybdenum salt / complexing agent to form a metal-molybdenum-complexing agent complex. It is also beneficial for the metal cation to combine with molybdenum salt / complexing agent through hydrolysis or condensation reaction to finally generate a gel-like catalytically active gel with a three-dimensional network structure. In some preferred embodiments, the second metal salt includes nitrate, and correspondingly the first metal salt includes ammonium molybdate.

[0057] Specifically, in some exemplary embodiments, the second metal salt includes aluminum salt, magnesium salt, cobalt salt, and iron salt; in the second metal salt, the molar ratio between aluminum salt, magnesium salt, cobalt salt, and iron salt is (1-4):(0.2-1):(0.2-1.5):(0.2-1); it is understood that the molar ratio between aluminum salt, magnesium salt, cobalt salt, and iron salt can be any value within (1-4):(0.2-1):(0.2-1.5):(0.2-1), which will not be enumerated here; within this molar ratio range, the second metal salt... Metal ions can effectively coordinate with molybdenum salts / complexing agents to form metal-molybdenum-complexing agent complexes. Under alkaline catalysis, these complexes further undergo hydrolysis or condensation reactions to form a three-dimensional mesh-like gel structure, greatly improving the structural stability of the catalytically active gel. This also prevents the agglomeration of cobalt-based metal oxides, which are the main catalytically active components, during subsequent sintering. This is beneficial for improving the catalytic activity, catalytic uniformity, and catalytic effect of the catalyst ultimately used to prepare carbon nanotubes, thereby improving the synthesis quality of the corresponding carbon nanotube products and facilitating mass production.

[0058] Specifically, when the second metal salt includes cobalt salt, the molar ratio of cobalt salt to the first metal salt is 5:1 to 10:1; understandably, the molar ratio of cobalt salt to the first metal salt can be any value from 5:1 to 10:1; for example, the molar ratio of cobalt salt to the first metal salt can be 5:1, 6:1, 7:1, 7.5:1, 8:1, 9:1, 10:1, etc.; on the one hand, it provides sufficient raw materials for catalytic active ingredients, so that the catalyst finally used to prepare carbon nanotubes can have high activity; on the other hand, it also improves the effectiveness of gel structure formation, which is conducive to the active ingredients being loaded in large quantities and uniformly on the two-dimensional layer surface of expanded vermiculite during the preparation process, further improving the catalytic activity and the uniformity of catalytic performance.

[0059] Specifically, the molar ratio of the second metal salt to the complexing agent is 2:1 to 3:1; it can be understood that the molar ratio of the second metal salt to the complexing agent can be any value from 2:1 to 3:1; for example, the molar ratio of the second metal salt to the complexing agent can be 2:1, 2.1:1, 2.2:1, 2.5:1, 2.8:1, 3:1, etc.

[0060] Specifically, the concentration of the second metal salt in the catalytically active gel is 5 mol / L to 8 mol / L; it can be understood that the concentration of the second metal salt in the catalytically active gel can be any value from 5 mol / L to 8 mol / L; for example, the concentration of the second metal salt in the catalytically active gel can be 5 mol / L, 5.5 mol / L, 6 mol / L, 7 mol / L, 7.5 mol / L, 8 mol / L, etc.

[0061] Thus, the proportions of various raw materials (first metal salt, complexing agent, alkaline solution, and second metal salt) used to prepare the catalyst for carbon nanotubes are determined. Under these proportions, molybdenum salt can effectively react with small organic molecules to generate molybdic acid or its complex ions. In the alkaline environment created by the alkaline solution, the metal ions in the second metal salt can undergo hydrolysis or condensation reactions with the molybdenum salt / complexing agent to form a three-dimensional network gel. This allows the catalytically active gel to act as a buffer to reduce the damage of the milling media to the expanded vermiculite during subsequent ball milling, and also as a stripping agent to open the lamellar structure of the expanded vermiculite and carry the cobalt salt used to form the active ingredient to adhere to the two-dimensional layer surface of the expanded vermiculite. After calcination, a cobalt-based metal oxide with a large loading, uniform distribution, and low agglomeration is formed, which serves as the main catalytically active ingredient, greatly improving the catalytic performance of the catalyst finally used to prepare carbon nanotubes.

[0062] Specifically, in the ball milling process of step S1, the mesh size of the expanded vermiculite is 10 to 40 mesh; it can be understood that the mesh size of the expanded vermiculite can be any value from 10 to 40 mesh; for example, the mesh size of the expanded vermiculite can be 10 mesh, 15 mesh, 20 mesh, 25 mesh, 30 mesh, 40 mesh, etc.

[0063] Specifically, the mass ratio between expanded vermiculite and cobalt salt in the catalytically active gel is 1:1 to 2:1; understandably, the mass ratio between expanded vermiculite and cobalt salt in the catalytically active gel can be any value between 1:1 and 2:1; for example, the mass ratio between expanded vermiculite and cobalt salt in the catalytically active gel can be 1:1, 1.1:1, 1.3:1, 1.5:1, 1.8:1, 2:1, etc.

[0064] Specifically, the milling media used in the ball milling process includes zirconium balls, and the mass ratio of zirconium balls to expanded vermiculite is 2:1 to 4:1. Understandably, the mass ratio of zirconium balls to expanded vermiculite can be any value from 2:1 to 4:1. For example, the mass ratio of zirconium balls to expanded vermiculite can be 2:1, 2.5:1, 3:1, 3.2:1, 3.5:1, 4:1, etc.

[0065] Specifically, the mixing time for ball milling is 2h to 3h; understandably, the mixing time for ball milling can be any value between 2h and 3h; for example, the mixing time for ball milling can be 2h, 2.2h, 2.5h, 2.7h, 3h, etc.

[0066] Thus, by adding expanded vermiculite and zircon balls within the above mesh size range to the catalytic active gel and performing ball milling with mechanical rolling stirring, the physical exfoliation of the expanded vermiculite and the effective adhesion of the active components in the catalyst precursor to the surface of the expanded vermiculite can be effectively achieved, thereby improving the dispersion effectiveness and uniformity of the catalytic active gel and expanded vermiculite, which in turn helps to increase the loading amount and loading uniformity of the active components on the surface of the expanded vermiculite.

[0067] Next, as Figure 1 As shown, in step S2, the catalyst precursor is calcined and sieved to obtain the catalyst for preparing carbon nanotubes; the catalyst for preparing carbon nanotubes is a sheet-like material with metal oxide as active component and expanded vermiculite as support.

[0068] During the calcination process, metal ions in the catalyst precursor react to form metal oxides. Cobalt-based metal ions form cobalt-based metal oxides, which are the main active components of the catalyst used to prepare carbon nanotubes. In addition, the ball milling media are co-calcined with the catalyst precursor during the calcination process. Finally, the zirconium balls of the ball milling media are removed by sieving. Specifically, the separation can be carried out by a vibrating screen. This reduces the step of removing the ball milling media in advance, simplifies the preparation process, and can also improve the separation efficiency by using the ball milling media during the sieving process, thereby further improving the overall preparation efficiency of the preparation method.

[0069] Specifically, the calcination temperature is 450℃~550℃, and the time is 1h~2h; understandably, the calcination temperature can be any value within 450℃~550℃, and the time can be any value within 1h~2h; for example, the calcination temperature can be 450℃, 470℃, 480℃, 500℃, 525℃, 550℃, etc.; the time can be 1h, 1.2h, 1.5h, 1.8h, 2h, etc. Under these calcination conditions, metal ions can react with oxygen to generate corresponding metal oxides, which serve as the active components of the catalyst used to prepare carbon nanotubes. The calcination is thorough and can also remove impurities attached to the surface of the catalyst precursor to a certain extent, reducing the coverage of active sites, which is also beneficial to improving the catalytic activity of the catalyst used to prepare carbon nanotubes.

[0070] On the other hand, the present invention also provides a catalyst for preparing carbon nanotubes, which is prepared based on the preparation method of the catalyst for preparing carbon nanotubes as described above. Specifically, the catalyst for preparing carbon nanotubes is a layered metal oxide catalyst with a large loading of active components on the support surface, high catalytic activity, and good loading uniformity. The catalyst for preparing carbon nanotubes is used to synthesize carbon nanotubes. Further, the catalyst for preparing carbon nanotubes is used to synthesize array-type carbon nanotubes. More specifically, the catalyst is used to synthesize carbon nanotubes by chemical vapor deposition. When applied to the carbon nanotube synthesis process, the catalyst for preparing carbon nanotubes can effectively improve the synthesis efficiency and synthesis rate, improve the performance of the obtained carbon nanotubes, and can be widely used in the industrial production of array-type carbon nanotubes with high aspect ratio.

[0071] On the other hand, the present invention also provides a carbon nanotube, which is prepared using the catalyst for preparing carbon nanotubes as described above. The carbon nanotube can be an array-type carbon nanotube, specifically an array-type carbon nanotube synthesized by chemical vapor deposition. In some optional embodiments, the powdered catalyst can be placed in a tubular furnace reactor, and the temperature can be gradually increased to the reaction temperature under inert gas protection. After the temperature stabilizes, a carbon source gas is introduced. After reacting for a period of time, the introduction of the carbon source gas is stopped, and the product is collected after cooling to room temperature under inert gas protection to obtain carbon nanotubes.

[0072] The following describes specific embodiments of the present invention in conjunction with the above technical solutions.

[0073] Example 1

[0074] The layered metal oxide / expanded vermiculite catalyst of this embodiment is prepared by the following steps:

[0075] 1) Dissolve 0.7g of the first metal salt (ammonium molybdate) and 5.6g of the complexing agent (citric acid) in 10ml of deionized water, then mix with 7.3g of 15wt% ammonia solution as the alkali solution, and continue stirring for 10min to obtain a mixed solution;

[0076] 2) Mix 15g of aluminum salt (aluminum nitrate nonahydrate), 2.5g of magnesium salt (magnesium nitrate hexahydrate), 9g of cobalt salt (cobalt nitrate hexahydrate), and 5g of iron salt (ferric nitrate nonahydrate) with the mixed solution and stir continuously for 15 minutes until a uniformly colored jelly-like gel is formed, which is the catalytically active gel.

[0077] 3) Mix 12g of expanded vermiculite with a size of 20 mesh and 36g of zirconium balls with a diameter of 1 cm with the catalytic active gel, and perform physical ball milling for 2 hours using a double helical belt stirrer to obtain the catalyst precursor;

[0078] 4) The catalyst precursor was transferred to a tray and calcined at 530°C for 3 hours. It was then sieved through a 30-mesh sieve to separate the catalyst and zirconium spheres used for preparing carbon nanotubes. The resulting catalyst for preparing carbon nanotubes was named ICA-1.

[0079] Example 2

[0080] The difference between this embodiment and Example 1 is that in step 1, 0.7g of the first metal salt (ammonium molybdate) and 7.8g of the complexing agent (tetraethylamine oxalate) were dissolved in 8ml of deionized water, and then mixed with 10g of 15wt% ammonia water as an alkaline solution; the resulting catalyst for preparing carbon nanotubes was named ICA-2; the rest is the same as in Example 1.

[0081] Example 3

[0082] The difference between this embodiment and Example 1 is that in step 1, 0.7g of ammonium molybdate and 4.5g of complexing agent (terephthalic acid) were dissolved in 13ml of deionized water, and then mixed with 10g of 15wt% ammonia water as an alkaline solution; the resulting catalyst for preparing carbon nanotubes was named ICA-3; the rest is the same as in Example 1.

[0083] Example 4

[0084] The difference between this embodiment and Example 1 is that in step 1, 0.7g of ammonium molybdate and 5.5g of complexing agent (2,5-dihydroxyterephthalic acid) were dissolved in 13ml of deionized water, and then mixed with 5.6g of 15wt% ammonia water as an alkaline solution; the resulting catalyst for preparing carbon nanotubes was named ICA-4; the rest is the same as in Example 1.

[0085] Comparative Example 1

[0086] The difference between this embodiment and Example 2 is that in step 1, the amount of complexing agent ethylenediaminetetraacetic acid is 9g, the amount of ammonia is 11.5g, and the amount of deionized water is 6.5g, in order to investigate the effect of increasing the amount of complexing agent on the catalyst performance; the resulting catalyst is named ICA-D1; the rest is the same as in Example 2.

[0087] Comparative Example 2

[0088] The difference between this embodiment and Example 2 is that, in step 1, the amount of complexing agent ethylenediaminetetraacetic acid is 6.6g, the amount of ammonia is 8.5g, and the amount of deionized water is 9.5g, in order to investigate the effect of reducing the amount of complexing agent on the catalyst performance; the resulting catalyst is named ICA-D2; the rest is the same as in Example 2.

[0089] Comparative Example 3

[0090] The difference between this embodiment and Embodiment 2 is that, in step 1, no complexing agent or ammonia is added, and the amount of deionized water is 18g, in order to investigate the effect of not adding a complexing agent and not forming a gel on the catalyst performance; the resulting catalyst is named ICA-D3; the rest is the same as in Embodiment 2.

[0091] Comparative Example 4

[0092] The difference between this embodiment and Example 2 is that, in step 2, the amount of cobalt salt (cobalt nitrate hexahydrate) is 11g and the amount of iron salt (ferric nitrate nonahydrate) is 6g, in order to investigate the effect of increasing the amount of active metal ions on the catalyst performance; the resulting catalyst is named ICA-D4; the rest is the same as in Example 2.

[0093] Comparative Example 5

[0094] The difference between this embodiment and Example 2 is that, in step 2, the amount of cobalt salt (cobalt nitrate hexahydrate) is 7g and the amount of iron salt (ferric nitrate nonahydrate) is 3.5g, in order to investigate the effect of reducing the amount of active metal ions on the catalyst performance; the resulting catalyst is named ICA-D5; the rest is the same as in Example 2.

[0095] Comparative Example 6

[0096] The difference between this embodiment and Example 2 is that, in step 1, no ammonia was added, and the amount of deionized water was 18g, in order to investigate the effect of not forming a gel on the catalyst performance; the resulting catalyst was named ICA-D6; the rest is the same as in Example 2.

[0097] The catalysts prepared in Examples 1-4 and Comparative Examples 1-6 were applied to the synthesis process of carbon nanotubes, and the performance of the obtained carbon nanotubes was tested. The specific steps of the carbon nanotube synthesis process include: taking 2g of catalyst and adding it to a tubular furnace reactor, heating it to 660℃ at 15℃ / min under nitrogen protection (flow rate: 2L / min), and after the temperature stabilizes, introducing propylene gas (flow rate: 1L / min), reacting for 60min, stopping the introduction of propylene gas, cooling it to room temperature under nitrogen protection, and collecting the product to obtain carbon nanotubes.

[0098] The performance test results of carbon nanotubes are shown in Table 1 below.

[0099] Table 1. Performance test results of carbon nanotubes prepared using the catalysts of Examples 1-4 and Comparative Examples 1-6

[0100]

[0101] As shown in Table 1, the catalysts prepared in Examples 1-4 for the preparation of carbon nanotubes all exhibit good catalytic activity. Among them, the ICA-2 catalyst prepared in Example 2 has the highest activity and the largest specific surface area, reaching 293.6 m². 2 The powder exhibited the lowest resistivity, and the synthesized carbon nanotubes reached a bundle length of 68 μm; while the ICA-3 catalyst prepared in Example 3 had the lowest activity and, even with the smallest specific surface area, still achieved 243.2 m². 2 / g, the powder has the highest resistivity.

[0102] As can be seen from the structural formula of the complexing agent organic small molecules, under the same molar mass, ethylenediaminetetraacetic acid provides the most functional groups, followed by citric acid, then 2,5-dihydroxyterephthalic acid, and finally terephthalic acid. Combined with the data in Table 1, it can be concluded without a doubt that adding organic small molecules with high functional group content and forming a gel is more conducive to preparing highly active catalysts for the preparation of carbon nanotubes.

[0103] In addition, such as Figure 3 and Figure 4 As shown in the electron microscope images of the carbon nanotubes prepared in Comparative Example 2 and Comparative Example 6, it can be seen that the present invention can effectively increase the bundle length of arrayed carbon nanotubes, and after forming a gel, it can effectively alleviate the damage to the expanded vermiculite structure caused by physical peeling, thereby making the morphology of carbon nanotubes more regular and improving the performance of carbon nanotubes.

[0104] It should be noted that the various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0105] The above description is merely some embodiments of the present invention and is not intended to limit the present invention. Those skilled in the art should understand that the present invention can have various changes and improvements, and any modifications, equivalent substitutions and improvements made in accordance with the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A method for producing a catalyst for producing carbon nanotubes, characterized by, The application relates to a preparation method of a catalyst for preparing carbon nanotubes. The first metal salt and a complexing agent are dissolved in deionized water, and mixed with an alkali solution to obtain a mixed solution; the first metal salt comprises a molybdenum salt; the complexing agent is an organic small molecule, and the organic small molecule comprises at least one of citric acid, ethylenediaminetetraacetic acid and 2,5-dihydroxyterephthalic acid; A second metal salt is mixed with the mixed solution to obtain a catalytically active gel; the second metal salt comprises a cobalt salt; The catalytically active gel is mixed with expanded vermiculite and subjected to ball milling treatment to obtain a catalyst precursor; The catalyst precursor is subjected to calcination treatment, and is sieved to obtain the catalyst for preparing carbon nanotubes; the catalyst for preparing carbon nanotubes is a sheet-like material with a metal oxide as an active component and expanded vermiculite as a carrier.

2. The method for producing a catalyst for producing carbon nanotubes according to claim 1, wherein The preparation step of the mixed solution satisfies the following characteristics: The alkali solution comprises an aqueous solution of one or more of sodium hydroxide, sodium carbonate, ammonia water, ammonium carbonate and ammonium bicarbonate.

3. The method for producing a catalyst for producing carbon nanotubes according to claim 1, wherein The second metal salt comprises at least one of a nitrate, a hydrochloride and a sulfate.

4. The method for producing a catalyst for producing carbon nanotubes according to claim 1, wherein The second metal salt further comprises at least one of an aluminum salt, a magnesium salt and an iron salt.

5. The method for producing a catalyst for producing carbon nanotubes according to claim 4, wherein The second metal salt comprises an aluminum salt, a magnesium salt, a cobalt salt and an iron salt; in the second metal salt, the molar ratio of the aluminum salt, the magnesium salt, the cobalt salt and the iron salt is (1-4):(0.2-1):(0.2-1.5):(0.2-1).

6. The method for preparing a catalyst for preparing carbon nanotubes according to claim 1, wherein The amount of the second metal salt satisfies at least one of the following characteristics: The molar ratio of the cobalt salt to the first metal salt is 5:1-10:1; The molar ratio of the second metal salt to the complexing agent is 2:1-3:1; The concentration of the second metal salt in the catalytically active gel is 5 mol / L-8 mol / L.

7. The method for producing a catalyst for producing carbon nanotubes according to any one of claims 1 to 6, characterized by, The ball milling treatment satisfies at least one of the following characteristics: The expanded vermiculite has a mesh size of 10 mesh-40 mesh; The mass ratio of the expanded vermiculite to the cobalt salt in the catalytically active gel is 1:1-2:1; The ball milling medium of the ball milling treatment comprises zirconium balls, and the mass ratio of the zirconium balls to the expanded vermiculite is 2:1-4:1; The stirring time of the ball milling treatment is 2 h-3 h.

8. The method for producing a catalyst for producing carbon nanotubes according to any one of claims 1 to 6, characterized by, The calcination temperature of the calcination treatment is 450 DEG C-550 DEG C, and the time is 1 h-2 h.

9. A catalyst for producing carbon nanotubes, characterized by, The catalyst for preparing carbon nanotubes is prepared based on the preparation method of claim 1-8.

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