Process for the preparation of catalysts for growing single-walled carbon nanotubes with sub-nanometer diameters

Abstract

This invention provides a method for preparing and applying a catalyst for growing sub-nanometer diameter single-walled carbon nanotubes: A solution A is obtained by mixing soluble aluminum salt, soluble inorganic salt, urea, and deionized water. A solution B is obtained by mixing a soluble metal salt, a complexing agent, and a solvent. Solution A is subjected to hydrothermal treatment to form a solid suspension, which is then filtered, washed, dried, and calcined to form a nanosheet self-assembled alumina support. Solution B is mixed with the alumina support, dried, and calcined to form Al₂O₃-supported Fe sub-nano particles. This catalyst is used to catalyze the cracking of carbon source gas and grow sub-nanometer diameter single-walled carbon nanotubes. This invention utilizes the open, isolating cavity structure formed by the interwoven nanosheets on the alumina support surface to improve the dispersion and stability of Fe. Simultaneously, high-temperature calcination promotes the phase transition of alumina from γ-Al₂O₃ to θ-Al₂O₃, forming abundant nanoparticle grain boundaries and oxygen vacancies, further anchoring the Fe particles. This material can be used for the growth of sub-nanometer diameter single-walled carbon nanotubes at high temperatures.

Description

Technical Field

[0001] This invention belongs to the field of catalyst technology, specifically relating to a preparation method and application of a catalyst for growing sub-nanometer diameter single-walled carbon nanotubes. Background Technology

[0002] Single-walled carbon nanotubes (SWCNTs) can be structurally viewed as seamless, hollow, tubular, one-dimensional nanomaterials formed by rolling up a single layer of graphene along a specific direction. SWCNTs typically range in diameter from 0.4 nm to 3 nm and can reach lengths of tens of micrometers. The structural characteristics of SWCNTs endow them with exceptional physicochemical properties. Their theoretical tensile strength is approximately 100 times that of steel, the electronic conductivity of metallic SWCNTs is 1000 times that of copper, the carrier mobility of semiconductor SWCNTs is far higher than that of silicon, and the axial thermal conductivity of SWCNTs is more than 8 times that of copper. Simultaneously, SWCNTs possess extremely high specific surface areas, providing abundant active sites for ion adsorption and chemical reactions. Their superior performance demonstrates enormous application potential in fields such as energy storage and conversion, post-Moore's Law carbon-based integrated circuits, quantum computing, flexible electronic wearable devices, sensor technology, targeted drug delivery systems, neural repair, and advanced composite materials.

[0003] Achieving efficient and controllable preparation of SWCNTs is key to their application. Chemical vapor deposition (CVD) has become the mainstream production technology due to its mature equipment and strong parameter controllability, and its core lies in catalyst design and process optimization.

[0004] Commercially, catalysts for preparing SWCNTs via CVD mainly employ supported metal nanoparticle catalysts. These catalysts disperse active metal component particles onto a support, where the active metal component particles can be one or more transition metals such as iron, nickel, cobalt, and platinum. The support can be oxide materials such as alumina, silica, and magnesium oxide.

[0005] The process of preparing SWCNTs by supported catalysts via CVD is based on the following facts: at a specific temperature (600℃~1000℃), carbon source molecules (alkanes, alkenes, aromatics, carbon monoxide, alcohols, etc.) undergo catalytic cracking at the active sites of active metal component particles to generate carbon atoms. The carbon atoms form six-membered rings through carbon-carbon bonds to construct the carbon nanotube wall. As carbon source molecules continue to crack on the active component particles to generate carbon atoms, the carbon atoms are continuously assembled into the carbon nanotube wall, thus realizing the growth of carbon nanotubes.

[0006] Despite significant progress in single-walled carbon nanotube (SWCNT) preparation technology, the preparation of catalysts for the controllable growth of SWCNTs still faces many challenges. The most critical challenge lies in controlling the uniformity of the particle size of the active metal component in the catalyst. This includes two aspects: first, the uniformity of the dispersion of the active metal component on the support surface during catalyst preparation; and second, how to effectively suppress the migration and aggregation of the active metal component particles on the support under the high-temperature environment (600℃~1000℃) of catalytic carbon source molecule cleavage.

[0007] The diameter of SWCNTs (d SWCNTs ) and the diameter of the loaded active metal component particles (d CAT The relationship between ) is usually d SWCNTs = (0.6~0.9)d CAT Therefore, the size and distribution uniformity of the loaded active metal component particles can directly affect the diameter and size uniformity of the prepared SWCNTs.

[0008] The diameter of SWCNTs typically ranges from 0.4 nm to 3 nm. Theoretically, the minimum diameter of SWCNTs is limited by carbon-carbon bond length and curvature stress, with the smallest stable SWCNT diameter approaching 0.4 nm. In the laboratory, SWCNTs with diameters as small as approximately 0.43 nm have been successfully synthesized, approaching the theoretical limit. There is no strict theoretical upper limit to the maximum diameter of SWCNTs, but as the diameter increases, the tube wall becomes increasingly unstable, prone to collapse or the formation of multi-walled structures. Beyond 3 nm, the likelihood of forming multi-walled carbon nanotubes increases significantly. Therefore, the size of the corresponding supported active metal component particles is generally between 0.4 nm and 4 nm to efficiently prepare high-quality SWCNTs.

[0009] For supported catalysts, the active metal components are mainly iron, nickel, and cobalt. Their melting points decrease rapidly as the particle size decreases. When the size of the metal particles is reduced to below 10 nm, within the temperature range of carbon nanotube growth (600℃~1000℃), the metal particles have already melted and exist on the support surface in the form of metal droplets. For metal droplets with a diameter of 0.4 nm to 4 nm, their surface energy is very high, and they are very easy to migrate and aggregate on the support surface to form larger metal droplets. When the size exceeds 4 nm, the probability and quality of preparing SWCNTs will be greatly reduced.

[0010] Therefore, how to effectively control the uniformity of the dispersion of active metal components on the support surface during catalyst preparation, and how to effectively suppress the migration and aggregation of active metal component particles on the support in the high-temperature environment of carbon nanotube growth, are among the keys to solving the problem of efficient and controllable preparation of SWCNTs.

[0011] Patent CN 114797864 A discloses a method for preparing a catalyst for the growth of small-diameter bulk single-walled carbon nanotubes (SWCNTs). The method employs an oxide support impregnation method with an aqueous solution of a metal salt to achieve loading of the active component onto the support: solutions of iron, cobalt, and nickel are dissolved in water to form a metal salt solution; solid powders such as magnesium oxide, Y-type molecular sieves, and silicon oxide are dispersed in water to form a support suspension; the metal salt solution and support suspension are mixed and stirred; a complexing agent such as ethylenediaminetetraacetic acid (EDTA) is added; and the mixture is heated to boiling, filtered, washed, dried, calcined, and reduced to obtain the catalyst. The addition of the complexing agent coordinates with metal ions such as iron and cobalt, thereby inhibiting hydrolysis, reducing agglomeration, and limiting the catalyst particle size, resulting in small and uniform metal catalyst particles. This catalyst can prepare SWCNTs with a diameter of 0.9 nm to 1.2 nm.

[0012] Patent CN 115672345 A discloses a method for preparing single-walled carbon nanotube (SWCNT) catalysts. The method employs a layered magnesium-aluminum hydrotalcite (MgA) impregnation solution with a metal salt to achieve loading of the active component onto a support. Three active metal salts (lanthanum nitrate, cobalt nitrate, and iron nitrate) and auxiliary metal salts (chromium nitrate and copper nitrate) are added to an alcohol solvent and stirred until dissolved. Organic matter (phthalic acid and polyoxyethylene) is added and stirred, followed by the addition of MgA and MgA. The mixture is reacted at 200°C–250°C for 6–24 hours. After cooling to room temperature, a layered support compound loaded with the active metal component is obtained. This compound is then carbonized in an inert gas atmosphere at 600°C–650°C to finally obtain the desired catalyst. During carbonization, the organic matter forms carbon material on the surface and between the layers of the layered MgA and MgA. hydrotalcite, which can isolate the active metal particles and inhibit their sintering at high temperatures. This catalyst can prepare SWCNTs with diameters ranging from 1 nm to 2 nm.

[0013] Patent CN 116159566 A discloses a catalyst for preparing single-walled carbon nanotubes and its preparation method. The catalyst consists of active metal components iron, cobalt, and nickel distributed on the bulk and outer surface of porous silica. A layer of nano-rare earth oxides is then coated on the outer surface of the porous silica. The uniformly dispersed rare earth oxides on the porous silica surface effectively disperse the active metal components, preventing their aggregation and detachment at high temperatures. The active metal particles prepared by this method have a size between 1.5 nm and 3.8 nm, which can be used to prepare SWCNTs with a diameter of 1 nm to 3 nm.

[0014] Patent CN 116618053 A discloses a supported composite catalyst, its preparation method, and a method for preparing single-walled carbon nanotubes. The method involves dropwise adding a solution of various transition metal organic compounds (iron carbonyl, nickel acetate, molybdenum naphthenate) and / or organosilicon compounds (ethyl silicate) to an alkaline solution of magnesium oxide or silicon oxide. Through a co-precipitation reaction, the active metal components (iron, nickel, and / or molybdenum) are loaded onto the surface of the magnesium oxide or silicon oxide support. The catalyst is then separated, dried, and reduced by heating to obtain the supported composite catalyst. The catalytic performance is improved through the synergistic effect between the various transition metal organic compounds, and the particle size of the active components is 1 nm to 2 nm.

[0015] CN 117181246 A discloses a single-walled carbon nanotube growth catalyst and its preparation method. The method involves preparing a precursor solution by combining an active metal component precursor (at least one of iron, cobalt, nickel, and copper), a support precursor (at least one of Al and Mg), an auxiliary metal precursor (at least one of Mn, Mo, and W), and a sulfur-containing precursor (sodium thiosulfate, sulfuric acid, or sodium hydroxyethyl sulfonate). The pH of the precursor solution is adjusted with a weak alkaline solution. A complexing agent (at least one of citric acid and ethylenediaminetetraacetate) is then added to the precursor solution. The solution is then dried and calcined to obtain the final catalyst product. The auxiliary metal elements (Mn, Mo, W) are non-reactive and have high melting points, which can physically block and disperse the active component particles (such as iron, cobalt, and nickel). The addition of complexing agents can coordinate with metal ions such as iron and cobalt, thereby inhibiting their hydrolysis, reducing agglomeration, and improving their dispersion on the support surface. The addition of sulfur-containing precursors can form metal sulfides with active metal components to change the catalytic activity of active components and further regulate the growth of single-walled carbon nanotubes.

[0016] Currently, in order to control the size of supported metal nanoparticles (0.4nm~4nm) and inhibit the migration and aggregation of active metal component particles at high temperatures, the active metal component is usually composed of two or more alloy metal particles (Fe, Co, Ni, Pt, etc.), or inert, high-melting-point auxiliary metals (Mn, Mo, W, La, etc.) are added to the active metal component to space the auxiliary metal particles between the active metal component particles to inhibit the aggregation of the active metal component particles. Alternatively, organic matter is added for carbonization treatment to form a layer of carbon material on the surface of the support, forming carbon material spacers between the supported active metal particles to inhibit the sintering of the supported metal particles. Or, an inert oxide material, such as rare earth oxides, is coated on the surface of the support to inhibit the sintering of the active metal particles by utilizing the inertness and physical spacer effect of the oxides. However, the aforementioned methods have many shortcomings. For forming binary or higher alloy particles to suppress sintering, the effect of simply forming alloys to resist sintering is limited. Furthermore, the stoichiometric ratio of each element in the alloy particles is difficult to control, and different stoichiometric ratios result in different catalytic activities, increasing the difficulty of catalyst synthesis and preparation. Similarly, adding inert, high-melting-point auxiliary metals to inhibit the aggregation of active metal particles using the physical spacing of inert high-melting-point metal particles also presents the aforementioned preparation problems. That is, inert metal particles and active metal particles must be interleaved to achieve a good aggregation-suppressing effect, which poses a significant challenge to catalyst synthesis and preparation. Adding organic matter for carbonization of the support surface or covering the support surface with an inert oxide material easily covers the active metal component particles on the support surface, causing the catalyst to lose some activity. Summary of the Invention

[0017] The technical problem this invention aims to solve is to address the shortcomings of the prior art by providing a method for preparing and applying catalysts for growing sub-nanometer diameter single-walled carbon nanotubes. This method improves the dispersion and high-temperature stability of the supported active metal particles by directly constructing an interwoven, open, isolating cavity morphology on the support surface. Simultaneously, it utilizes the nanoparticle grain boundary defects and oxygen vacancies formed by the crystal phase transformation of the support at different temperatures to enhance the interaction between the support and metal particles, further anchoring the active metal particles and effectively inhibiting the migration and aggregation of active metal particles on the support surface at high temperatures. This preparation method is simple and reproducible. By modifying the morphology and surface physicochemical properties of the support itself, it achieves uniform dispersion of active component particles and inhibits the sintering of active metal component particles at high temperatures without the need for additional additives or surface post-treatment. The supported active metal component can be a single element, eliminating the need for a second element to form an alloy to achieve anti-sintering, and also eliminating the need for adding inert, high-melting-point additive metal elements to inhibit sintering. It also avoids the problem of surface active metal component particles being covered and losing activity when using organic materials for surface carbonization or additional deposition of inert metal oxides.

[0018] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a method for preparing catalysts for growing sub-nanometer diameter single-walled carbon nanotubes, the method being as follows: S1. Mix soluble aluminum salt, soluble inorganic salt, urea and deionized water evenly to obtain solution A; S2. Mix the soluble metal salt, complexing agent, and solvent to obtain solution B; S3. The solution A obtained in S1 is hydrothermally treated at a temperature of 160℃~180℃ for 2h~10h to obtain a solid suspension. S4. The solid suspension obtained in S3 is filtered and washed with deionized water. The solid precipitate is dried at 60℃~80℃ for 10h~12h, then calcined in air at 450℃~600℃ for 0.5h~5h, and naturally cooled to room temperature to obtain air-calcined nanosheet self-assembled alumina solid powder. S5. Add the air-calcined nanosheet self-assembled alumina solid powder obtained in S4 to the solution B obtained in S2, stir and mix evenly to obtain a wetted solid powder. S6. The wetted solid powder obtained in S5 is calcined at a temperature of 900℃~1100℃ for 0.5h~3h and then naturally cooled to room temperature to form metal sub-nano particles supported on alumina microspheres formed by nanosheet self-assembly, which are used to grow sub-nano-scale single-walled carbon nanotube catalysts.

[0019] Preferably, the soluble aluminum salt in S1 is one or more of aluminum nitrate, sodium aluminate, aluminum sulfate, and aluminum chloride; the soluble inorganic salt in S1 is one or more of potassium sulfate, potassium chloride, potassium nitrate, sodium sulfate, sodium chloride, and sodium nitrate.

[0020] Preferably, the molar ratio of Al, soluble inorganic salt, urea and deionized water in the soluble aluminum salt in S1 is 1.0:(0.8~1.2):(1.2~3.2):(500~1500).

[0021] Preferably, the soluble metal salt in S2 is ferric nitrate, nickel nitrate, cobalt nitrate, ferric sulfate, nickel sulfate, cobalt sulfate, ferric chloride, nickel chloride, or cobalt chloride; the complexing agent in S2 is ethylenediamine, ethylenediaminetetraacetic acid, potassium ethylenediaminetetraacetic acid, sodium ethylenediaminetetraacetic acid, hydroxylamine, citric acid, potassium citrate, sodium citrate, sodium tripolyphosphate, sodium pyrophosphate, aminotriacetic acid, potassium aminotriacetic acid, sodium aminotriacetic acid, or 10,10'-[(5-nitro-1,3-phenyl)bis(methylene)]bis[1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid] hydrochloride; the solvent in S2 is ethylene glycol, methanol, ethanol, glycerol, or deionized water.

[0022] Preferably, the molar ratio of the metal element, complexing agent, and solvent in the soluble metal salt in S2 is 1.0:(0.8-10.0):(500-1000).

[0023] Preferably, the ratio of the self-assembled alumina solid powder after air calcination to solution B in S5 is 100 mg: (0.16-0.32) mL.

[0024] Preferably, the gas atmosphere during calcination in S6 is one or more of argon, hydrogen, helium, and nitrogen.

[0025] The present invention also provides the application of the catalyst prepared by the above preparation method for growing sub-nanometer diameter single-walled carbon nanotubes, wherein the catalyst for growing sub-nanometer diameter single-walled carbon nanotubes is used to catalytically crack carbon source gas and grow sub-nanometer diameter single-walled carbon nanotubes.

[0026] Preferably, the catalytic cracking method is as follows: under a flowing gaseous atmosphere, the temperature is increased to 500℃ to 1100℃ at a heating rate of 2 to 10℃ / min, then a flowing gaseous atmosphere and a carbon source gas are introduced and the gas is kept flowing for 20 min to 60 min, and then the temperature is naturally cooled to room temperature. The flowing gaseous atmosphere is one or more of argon, hydrogen, nitrogen, helium, carbon dioxide, and water vapor; the carbon source gas is one or more of methane, ethane, propane, ethylene, propylene, carbon monoxide, carbon dioxide, and methanol.

[0027] Preferably, the sub-nanometer-scale single-walled carbon nanotubes have an average outer diameter of 0.5 nm to 0.8 nm and grow in a bundle-like manner.

[0028] Compared with the prior art, the present invention has the following advantages: 1. This invention improves the dispersion and high-temperature stability of loaded active metal particles by directly constructing an interwoven open isolation cavity morphology on the carrier surface. Simultaneously, it utilizes the nanoparticle grain boundary defects and oxygen vacancies formed by the crystal phase structure transformation of the carrier at different temperatures to enhance the interaction between the carrier and metal particles, further anchoring the active metal particles and effectively inhibiting the migration and aggregation of active metal particles on the carrier surface at high temperatures. This preparation method is simple and reproducible. By modifying the morphology and surface physicochemical properties of the carrier itself, it achieves uniform dispersion of active component particles and inhibits the sintering of active metal component particles at high temperatures without the need for additional additives or surface post-treatment. The loaded active metal component can be a single element, eliminating the need for a second element to form an alloy to achieve anti-sintering, and also eliminating the need to add inert, high-melting-point additive metal elements to inhibit sintering. It also avoids the problem of surface active metal component particles being covered and losing activity when using organic materials for surface carbonization treatment or additional deposition of inert metal oxides on the surface.

[0029] 2. The preparation method of this invention is simple and has good reproducibility. The size of the single metal particles supported in the prepared catalyst is about 1 nm, and the particle size can remain stable at temperatures up to 1000°C. Compared with other preparation methods, the diameter of the supported metal particles is generally reduced by 30% to 75%, and the average outer diameter of the grown carbon nanotubes is 0.5 nm to 0.8 nm, which is generally reduced by 33% to 80% compared with other preparation methods.

[0030] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. Attached Figure Description

[0031] Figure 1 These are SEM images of the catalysts for growing sub-nanometer diameter single-walled carbon nanotubes prepared in Example 1 and Comparative Examples 1-4 of this invention. (The second row consists of enlarged views of the images in the first row.)

[0032] Figure 2 These are performance test diagrams for Embodiment 1 and Comparative Examples 1-3 of the present invention; (a) XRD patterns of the catalysts for growing sub-nanometer diameter single-walled carbon nanotubes prepared in Example 1 and Comparative Examples 1-3; (b) to (e) are TEM results of the catalyst prepared in Example 1 for growing sub-nanometer diameter single-walled carbon nanotubes: (b) is a TEM image of the catalyst prepared in Example 1 for growing sub-nanometer diameter single-walled carbon nanotubes; (c) is a SAED image of the catalyst prepared in Example 1 for growing sub-nanometer diameter single-walled carbon nanotubes; (d) to (e) are TEM images of the catalyst prepared in Example 1 for growing sub-nanometer diameter single-walled carbon nanotubes. (f) to (h) are HR-TEM images of the catalyst prepared in Example 1 for growing sub-nanometer diameter single-walled carbon nanotubes; (i) is the FFT result of (h); (j) to (l) are EDS prepared in Example 1 for growing sub-nanometer diameter single-walled carbon nanotube catalysts.

[0033] Figure 3 These are XPS images of O1s and Fe2p on the catalysts prepared in Example 1 and Comparative Example 2 for growing sub-nanometer diameter single-walled carbon nanotubes. (a) is the XPS image of O1s on the surface of the 1000°C-Al2O3-Fe-C catalyst in Comparative Example 2; (b) is the XPS image of O1s on the surface of the 1000°C-Al2O3-Fe-R catalyst in Example 1; and (c) is the XPS image of Fe2p on the surface of the 1000°C-Al2O3-Fe-R catalyst in Example 1.

[0034] Figure 4 These are performance test diagrams of the catalysts prepared in Example 1 and Comparative Example 4 of this invention for growing sub-nanometer diameter single-walled carbon nanotubes after carbon nanotube growth. (a) to (b) are HR-TEM images of carbon nanotubes grown from the catalyst for growing sub-nanometer diameter single-walled carbon nanotubes prepared in Example 1 of this invention. (c) is the Raman spectrum of carbon nanotubes grown by the catalyst for growing sub-nanometer diameter single-walled carbon nanotubes prepared in Example 1 of the present invention; (d) to (e) are SEM images of the catalyst prepared for growing sub-nanometer diameter single-walled carbon nanotubes prepared in Comparative Example 4 of the present invention after growing carbon nanotubes. (f) is the Raman spectrum of carbon nanotubes grown by the catalyst prepared for growing sub-nanometer diameter single-walled carbon nanotubes in Comparative Example 4 of this invention. Detailed Implementation

[0035] Example 1 The preparation method of the catalyst for growing sub-nanometer diameter single-walled carbon nanotubes in this embodiment is as follows: S1. Mix soluble aluminum salt (Al(NO3)3·9H2O), soluble inorganic salt (K2SO4), urea and deionized water evenly to obtain solution A; The molar ratio of Al, soluble inorganic salt, urea and deionized water in the soluble aluminum salt is 1.0:1.0:2.1:1106, and the volume of deionized water is 120 mL. S2. Mix the soluble metal salt (ferric nitrate), complexing agent (ethylenediamine), and solvent (ethylene glycol) to obtain solution B; The molar ratio of the metal element, complexing agent, and solvent in the soluble metal salt is 1.0:2.0:800, wherein the volume of the solvent is 0.8 mL; S3. The solution A obtained in S1 is hydrothermally treated at 180℃ for 3 hours to obtain a solid suspension. S4. The solid suspension obtained in S3 is filtered and washed with deionized water. The solid precipitate is dried at 80°C for 12 hours and then calcined at 500°C in air for 2 hours. After cooling naturally to room temperature, the air-calcined nanosheet self-assembled alumina solid powder is obtained. S5. Add the air-calcined nanosheet self-assembled alumina solid powder obtained in S4 to the solution B obtained in S2, and stir to mix evenly to obtain a wetted solid powder; the ratio of the air-calcined nanosheet self-assembled alumina solid powder to solution B is 100mg: 0.26mL. S6. The wetted solid powder obtained in S5 is calcined in a gaseous atmosphere (200 mL / min argon and 200 mL / min hydrogen) at a temperature of 1000℃ for 1 h, and then naturally cooled to room temperature to obtain metal sub-nano particles supported on alumina microspheres formed by the self-assembly of nanosheets. This is used to grow single-walled carbon nanotube catalysts with sub-nano diameters, denoted as 1000℃-Fe-Al2O3-R.

[0036] Comparative Example 1 The preparation method of the catalyst for growing single-walled carbon nanotubes in this comparative example is the same as steps S1 to S5 of the example, except for step S6: S6. The wetted solid powder obtained in S5 is calcined in air at 500℃ for 1 hour and then naturally cooled to room temperature to obtain metal sub-nano particles supported on alumina microspheres formed by the self-assembly of nanosheets. This is the catalyst for growing single-walled carbon nanotubes in this comparative example, denoted as 500℃-Fe-Al2O3-C.

[0037] Comparative Example 2 The preparation method of the catalyst for growing single-walled carbon nanotubes in this comparative example is the same as steps S1 to S5 of the example, except for step S6: S6. The wetted solid powder obtained in S5 is calcined in air at 1000℃ for 1 hour and then naturally cooled to room temperature to obtain metal sub-nano particles supported on alumina microspheres formed by the self-assembly of nanosheets. This is the catalyst for growing single-walled carbon nanotubes in this comparative example, denoted as 1000℃-Fe-Al2O3-C.

[0038] Comparative Example 3 The preparation method of the catalyst for growing single-walled carbon nanotubes in this comparative example is the same as steps S1 to S5 of the example, except for step S6: S6. The wetted solid powder obtained in S5 is calcined at 1000℃ for 1 hour under an argon atmosphere of 200 ml / min and naturally cooled to room temperature to obtain metal sub-nano particles supported on alumina microspheres formed by the self-assembly of nanosheets, denoted as 1000℃-Fe-Al2O3-Ar.

[0039] Comparative Example 4 The comparative example illustrates a method for preparing catalysts for growing single-walled carbon nanotubes. The method is as follows: S1. Mix a soluble metal salt (ferric nitrate), a complexing agent (ethylenediamine), and a solvent (ethylene glycol) to obtain solution A; The molar ratio of the metal element, complexing agent, and solvent in the soluble metal salt is 1.0:2.0:800, wherein the volume of the solvent is 0.8 mL. S2. Add 0.3g of purchased commercial alumina solid powder to solution A in S1 and stir to mix evenly to obtain a moistened solid powder. S3. The wetted solid powder obtained in S2 is dried at 80°C for 12 hours, then calcined in air at 500°C for 2 hours, and naturally cooled to room temperature to obtain the air-calcined solid powder. S4. The solid powder obtained in S3 after air calcination is calcined in a gaseous atmosphere (200 mL / min argon and 200 mL / min hydrogen) at a temperature of 1000℃ for 1 h to form iron particles supported on alumina, which is the catalyst for growing single-walled carbon nanotubes in this comparative example, denoted as 1000℃-Fe-Al2O3-N.

[0040] The catalysts prepared in Example 1 and Comparative Example 4 were used for the growth of carbon nanotubes. The growth conditions were as follows: Catalyst performance was evaluated using a high-temperature tubular furnace. The prepared catalyst powder was placed in a ceramic boat, which was then placed in the heating zone of the tubular furnace. Argon gas was first introduced into the furnace at a rate of 200 mL / min for 40 min to purge the air. The furnace temperature was then increased from room temperature to 1000 °C at a rate of 10 °C / min. Hydrogen gas was then introduced at a rate of 100 mL / min and methane at a rate of 80 mL / min to begin carbon nanotube growth. After maintaining the gas flow for 40 min, the temperature was allowed to cool naturally to room temperature. The catalyst was then removed from the ceramic boat for further analysis.

[0041] The size of the single metal particles supported in the 1000℃-Fe-Al2O3-R prepared in Example 1 of this invention is about 1 nm, such as... Figure 2 (h) can maintain stable particle size at temperatures up to 1000℃.

[0042] like Figure 1 As shown, 1000℃-Fe-Al2O3-R, 500℃-Fe-Al2O3-C, 1000℃-Fe-Al2O3-C, and 1000℃-Fe-Al2O3-Ar are SEM images of metal sub-nanoparticle catalysts supported on alumina microspheres formed by the self-assembly of nanosheets prepared under different preparation conditions in Examples 1 and Comparative Examples 1-3, respectively. The catalyst support surface forms a very dense open isolation cavity morphology, which can significantly promote the dispersion of metal components on it. In contrast, the 1000℃-Fe-Al2O3-N prepared in Comparative Example 4 uses commercial alumina nanospheres as a support, and its surface is very smooth. The loaded Fe component exhibits obvious agglomeration on its surface.

[0043] like Figure 2 As shown in (a), the diffraction peaks of 500℃-Fe-Al2O3-C prepared in Comparative Example 1 at 37.6°, 39.4°, and 45.7° correspond to the (311), (222), and (400) crystal planes of γ-Al2O3, respectively. In addition to the diffraction peaks of γ-Al2O3, new diffraction peaks appeared at 31.5°, 32.7°, 36.7°, and 46.4° in 1000℃-Fe-Al2O3-R from Example 1 and 1000℃-Fe-Al2O3-C / Ar from Comparative Examples 2 / 3, corresponding to the (-401), (002), (111), and (-601) crystal planes of θ-Al2O3, respectively. This result indicates that when the calcination temperature is increased from 500℃ to 1000℃, the nanosheet portion of the hollow microspheres begins to transform from the γ phase to the θ phase. The corresponding SEM results show ( Figure 1(Columns 1-4) When the calcination temperature was increased from 500℃ to 1000℃, the Al2O3 microspheres maintained the nanosheet cross-linked structure, confirming that the prepared Al2O3 support has good thermal stability.

[0044] Figure 2 (b) to (i) show the performance tests of the 1000℃ Fe-Al2O3-R prepared in Example 1. Figure 2 (b) shows a TEM image of the 1000℃ Fe-Al2O3-R prepared in Example 1, which indicates that the catalyst particles have a hollow structure. Figure 2 (c) Its SAED image shows a large number of high-brightness concentric ring-shaped spots, which correspond to the (311), (400) and (440) crystal planes of γ-Al2O3 and the (203) and (111) crystal planes of θ-Al2O3, respectively, indicating that it has a distinct polycrystalline structure. Figure 2 (de) shows that the microstructure of the 1000℃-Fe-Al2O3-R nanosheets after heat treatment at 1000°C is actually composed of many small grains with a size distribution of about 1-7 nm. Figure 2 (fg)HR-TEM further revealed that the grains constituting the nanosheets have different crystal phases, with lattice spacings of 0.24 nm and 0.25 nm corresponding to the (311) plane of γ-Al2O3 and the (111) plane of θ-Al2O3, respectively. This is consistent with... Figure 2 The XRD results in (a) are consistent. The phase transition from γ-Al₂O₃ to θ-Al₂O₃ occurs in a dispersed, point-like manner at different locations on the Al₂O₃ nanosheets, resulting in numerous interphase grain boundaries. The irregular grain boundary and defect structures between grains can further suppress the aggregation of Fe nanoparticles at high temperatures. Furthermore, Figure 2 As shown by HR-TEM and FFT of (hi), Fe clusters with a diameter of about 1 nm are distributed on the Al2O3 surface. The results show that its 0.2 nm lattice spacing corresponds to the Fe (110) crystal plane, indicating that even at a high temperature of 1000 °C, Fe maintains excellent dispersion and small size on the alumina surface. Figure 2 The EDS analysis of (jl) shows that there is no obvious local aggregation of Fe on the Al2O3 surface, indicating that Fe is very stable on the alumina surface at a high temperature of 1000℃.

[0045] like Figure 3 The figures shown are XPS spectra of O 1s and Fe 2p on the catalyst surfaces of Comparative Example 2 and Example 1, where O1 represents lattice oxygen, O2 represents oxygen at vacancies, and O3 represents adsorbed oxygen before the catalyst is reduced. Figure 3(a) In Comparative Example 2 (1000℃-Fe-Al2O3-C), the peak area ratio of O1 / O2 is 0.69, indicating that there are a large number of vacancy sites on the catalyst surface. When the catalyst is reduced with hydrogen ( Figure 3 (b) In Example 1, the peak area ratio of O1 / O2 in the 1000℃-Fe-Al2O3-R region changed to 6.82, indicating that the proportion of vacancy sites was significantly reduced. Figure 3 (c) XPS shows that metallic Fe appeared on the 1000℃-Fe-Al2O3-R surface in the example, indicating that after the Fe in the oxidized state on the alumina surface was reduced to metallic Fe, the Fe nanoparticles continued to migrate at high temperature. When the Fe nanoparticles migrated to the hole sites, the hole sites had a stronger force on the Fe particles, thus anchoring the Fe nanoparticles, and the hole sites were covered.

[0046] like Figure 4 As shown in (ab), these are HR-TEM images of the 1000℃-Fe-Al2O3-R catalyst used in Example 1 for the growth of single-walled carbon nanotubes. Due to the difference in the interfacial forces between the supported Fe particles and the alumina support, the single-walled carbon nanotubes (SWCNTs) on the 1000℃-Fe-Al2O3-R exhibit both base-growth (a) and tip-growth (b) modes. Furthermore, the outer diameter of the SWCNTs reaches 0.54 nm, and they grow in a bundle-like manner under the influence of van der Waals forces. This indicates that Fe clusters, confined by oxygen vacancies and grain boundary defects, are gradually being used to catalyze the growth of SWCNTs. Figure 4 (c) is the Raman spectrum of carbon nanotubes grown at 1000℃-Fe-Al2O3-R in Example 1. The results show the radial breathing pattern of single-walled carbon nanotubes (RBMs=100-250 cm⁻¹). -1 ), while I D / I G =0.14, indicating that high-quality SWCNTs were synthesized on the 1000℃-Fe-Al2O3-R catalyst prepared in Example 1. Figure 4 (d)-(e) are SEM images at different scales of carbon nanotubes grown by the Fe-Al2O3-N catalyst at 1000℃ in Comparative Example 4. The results show that due to the smooth surface and lack of defect sites of commercial Al2O3-N, the size of the supported Fe nanoparticles increases rapidly at 1000℃, exceeding the size suitable for SWCNTs growth. Figure 4 (f) shows the Raman spectrum of carbon nanotubes grown by the 1000℃ Fe-Al2O3-N catalyst in Comparative Example 4. The results show that no radial breathing peaks were observed in the prepared carbon nanotubes, indicating that no SWCNTs were grown.

[0047] The catalyst prepared in Example 1 was used to catalytically crack carbon source gas and grow sub-nanometer single-walled carbon nanotubes. The average outer diameter of the sub-nanometer single-walled carbon nanotubes was 0.54 nm, and they grew in bundles.

[0048] Example 2 The preparation method of the catalyst for growing sub-nanometer diameter single-walled carbon nanotubes in this embodiment is as follows: S1. Mix soluble aluminum salt (sodium aluminate), soluble inorganic salt (potassium chloride), urea and deionized water evenly to obtain solution A; The molar ratio of Al, soluble inorganic salt, urea and deionized water in the soluble aluminum salt is 1.0:0.8:3.2:500, and the volume of deionized water is 54 mL. S2. Mix the soluble metal salt (nickel nitrate), complexing agent (potassium citrate), and solvent (methanol) to obtain solution B; The molar ratio of the metal element, complexing agent, and solvent in the soluble metal salt is 1.0:0.8:1000, wherein the volume of the solvent is 0.96 mL. S3. The solution A obtained in S1 is hydrothermally treated at 160℃ for 10 hours to obtain a solid suspension. S4. The solid suspension obtained in S3 is filtered and washed with deionized water. The solid precipitate is dried at 60°C for 10 hours and then calcined at 600°C in air for 0.5 hours. After cooling naturally to room temperature, the air-calcined nanosheet self-assembled alumina solid powder is obtained. S5. Add the air-calcined nanosheet self-assembled alumina solid powder obtained in S4 to the solution B obtained in S2, and stir to mix evenly to obtain a wetted solid powder; the ratio of the air-calcined nanosheet self-assembled alumina solid powder to solution B is 100mg: 0.32mL. S6. The wetted solid powder obtained in S5 is calcined in a gas atmosphere (200 mL / min helium) at a temperature of 900 °C for 3 h, and then naturally cooled to room temperature to obtain metal sub-nano particles supported on alumina microspheres formed by the self-assembly of nanosheets, which are used to grow single-walled carbon nanotube catalysts with sub-nano diameters.

[0049] This embodiment also provides the application of the catalyst for growing sub-nanometer diameter single-walled carbon nanotubes prepared by the above preparation method. The catalyst for growing sub-nanometer diameter single-walled carbon nanotubes is used to catalytically crack carbon source gas and grow sub-nanometer diameter single-walled carbon nanotubes. The average outer diameter of the sub-nanometer diameter single-walled carbon nanotubes is 0.5 nm, and they grow in bundles.

[0050] The catalytic cracking method is as follows: under a flowing gaseous atmosphere (helium) of 200 mL / min, the temperature is increased to 1100°C at a heating rate of 10°C / min, and then a flowing gaseous atmosphere (hydrogen) of 100 mL / min and a carbon source gas (carbon dioxide) of 80 mL / min are introduced. The gas is kept flowing for 20 min, and then the gas is naturally cooled to room temperature.

[0051] Example 3 The preparation method of the catalyst for growing sub-nanometer diameter single-walled carbon nanotubes in this embodiment is as follows: S1. Mix soluble aluminum salt (aluminum chloride), soluble inorganic salt (sodium nitrate), urea and deionized water evenly to obtain solution A; The molar ratio of Al, soluble inorganic salt, urea and deionized water in the soluble aluminum salt is 1.0:1.2:1.2:1500, and the volume of deionized water is 162 mL. The soluble aluminum salt in this step may also be one or more of aluminum nitrate, sodium aluminate, aluminum sulfate, and aluminum chloride; the soluble inorganic salt may also be one or more of potassium sulfate, potassium chloride, potassium nitrate, sodium sulfate, sodium chloride, and sodium nitrate. S2. Mix the soluble metal salt (cobalt nitrate), complexing agent (sodium tripolyphosphate), and solvent (glycerol) to obtain solution B; The molar ratio of the metal element, complexing agent, and solvent in the soluble metal salt is 1.0:10.0:500, wherein the volume of the solvent is 0.5 mL. The soluble metal salt in this step can also be ferric sulfate, nickel sulfate, cobalt sulfate, ferric chloride, nickel chloride, or cobalt chloride; The complexing agent in this step can also be ethylenediaminetetraacetic acid, potassium ethylenediaminetetraacetic acid, sodium ethylenediaminetetraacetic acid, hydroxylamine, citric acid, sodium citrate, sodium pyrophosphate, aminotriacetic acid, potassium aminotriacetic acid, sodium aminotriacetic acid, or 10,10'-[(5-nitro-1,3-phenyl)bis(methylene)]bis[1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid] hydrochloride; The solvent used in this step can also be ethanol or deionized water; S3. The solution A obtained in S1 is hydrothermally treated at 170℃ for 2 hours to obtain a solid suspension. S4. The solid suspension obtained in S3 is filtered and washed with deionized water. The solid precipitate is dried at 70°C for 12 hours and then calcined in air at 450°C for 5 hours. After cooling naturally to room temperature, the air-calcined nanosheet self-assembled alumina solid powder is obtained. S5. Add the air-calcined nanosheet self-assembled alumina solid powder obtained in S4 to the solution B obtained in S2, and stir to mix evenly to obtain a wetted solid powder; the ratio of the air-calcined nanosheet self-assembled alumina solid powder to solution B is 100mg: 0.16mL. S6. The wetted solid powder obtained in S5 is calcined in a gas atmosphere (200 mL / min nitrogen) at a temperature of 1100 °C for 0.5 h, and then naturally cooled to room temperature to obtain metal sub-nano particles supported on alumina microspheres formed by the self-assembly of nanosheets, which are used to grow single-walled carbon nanotube catalysts with sub-nano diameters.

[0052] The gas atmosphere in this step can also be one or more of argon, hydrogen, helium and nitrogen; This embodiment also provides the application of the catalyst for growing sub-nanometer diameter single-walled carbon nanotubes prepared by the above preparation method. The catalyst for growing sub-nanometer diameter single-walled carbon nanotubes is used to catalytically crack carbon source gas and grow sub-nanometer diameter single-walled carbon nanotubes. The average outer diameter of the sub-nanometer diameter single-walled carbon nanotubes is 0.8 nm, and they grow in bundles.

[0053] The catalytic cracking method is as follows: under a flowing gaseous atmosphere (nitrogen) of 200 mL / min, the temperature is increased to 500°C at a heating rate of 2°C / min, and then a flowing gaseous atmosphere (hydrogen) of 50 mL / min and a carbon source gas (carbon monoxide) of 80 mL / min are introduced and the gas is kept flowing for 60 min, and then the gas is naturally cooled to room temperature.

[0054] The flowing gaseous atmosphere in this step can also be one or more of argon, hydrogen, helium, carbon dioxide, and water vapor; The carbon source gas in this step can also be one or more of methane, ethane, propane, ethylene, propylene, carbon monoxide, and methanol.

[0055] This invention utilizes the open, isolating cavity structure formed by interwoven nanosheets on the surface of an alumina support to improve the dispersion and stability of Fe. Simultaneously, high-temperature calcination drives the alumina to undergo a phase transformation from γ-Al₂O₃ to θ-Al₂O₃, forming abundant nanoparticle grain boundaries and oxygen vacancies, further anchoring the Fe particles. The catalyst prepared by this invention can be used for the growth of sub-nanotube diameter single-walled carbon nanotubes at high temperatures.

[0056] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any way. Any simple modifications, alterations, and equivalent changes made to the above embodiments based on the inventive essence shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing a catalyst for growing sub-nanometer diameter single-walled carbon nanotubes, characterized in that, The method is as follows: S1. Mix soluble aluminum salt, soluble inorganic salt, urea and deionized water evenly to obtain solution A; S2. Mix the soluble metal salt, complexing agent, and solvent to obtain solution B; S3. The solution A obtained in S1 is hydrothermally treated at a temperature of 160℃~180℃ for 2h~10h to obtain a solid suspension. S4. The solid suspension obtained in S3 is filtered and washed with deionized water. The solid precipitate is dried at 60℃~80℃ for 10h~12h, then calcined in air at 450℃~600℃ for 0.5h~5h, and naturally cooled to room temperature to obtain air-calcined nanosheet self-assembled alumina solid powder. S5. Add the air-calcined nanosheet self-assembled alumina solid powder obtained in S4 to the solution B obtained in S2, stir and mix evenly to obtain a wetted solid powder. S6. The wetted solid powder obtained in S5 is calcined at a temperature of 900℃~1100℃ for 0.5h~3h and then naturally cooled to room temperature to form metal sub-nano particles supported on alumina microspheres formed by nanosheet self-assembly, which are used to grow sub-nano-scale single-walled carbon nanotube catalysts.

2. The method for preparing a catalyst for growing sub-nanometer diameter single-walled carbon nanotubes according to claim 1, characterized in that, The soluble aluminum salt mentioned in S1 is one or more of aluminum nitrate, sodium aluminate, aluminum sulfate, and aluminum chloride; the soluble inorganic salt mentioned in S1 is one or more of potassium sulfate, potassium chloride, potassium nitrate, sodium sulfate, sodium chloride, and sodium nitrate.

3. The method for preparing a catalyst for growing sub-nanometer diameter single-walled carbon nanotubes according to claim 1, characterized in that, The molar ratio of Al, soluble inorganic salt, urea and deionized water in the soluble aluminum salt described in S1 is 1.0:(0.8~1.2):(1.2~3.2):(500~1500).

4. The method for preparing a catalyst for growing sub-nanometer diameter single-walled carbon nanotubes according to claim 1, characterized in that, The soluble metal salt mentioned in S2 is ferric nitrate, nickel nitrate, cobalt nitrate, ferric sulfate, nickel sulfate, cobalt sulfate, ferric chloride, nickel chloride, or cobalt chloride; the complexing agent mentioned in S2 is ethylenediamine, ethylenediaminetetraacetic acid, potassium ethylenediaminetetraacetic acid, sodium ethylenediaminetetraacetic acid, hydroxylamine, citric acid, potassium citrate, sodium citrate, sodium tripolyphosphate, sodium pyrophosphate, aminotriacetic acid, potassium aminotriacetic acid, sodium aminotriacetic acid, or 10,10'-[(5-nitro-1,3-phenyl)bis(methylene)]bis[1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid] hydrochloride; the solvent mentioned in S2 is ethylene glycol, methanol, ethanol, glycerol, or deionized water.

5. The method for preparing a catalyst for growing sub-nanometer diameter single-walled carbon nanotubes according to claim 1, characterized in that, The molar ratio of the metal element, complexing agent, and solvent in the soluble metal salt described in S2 is 1.0:(0.8-10.0):(500-1000).

6. The method for preparing a catalyst for growing sub-nanometer diameter single-walled carbon nanotubes according to claim 1, characterized in that, The ratio of the self-assembled alumina solid powder after air calcination to solution B in S5 is 100 mg: (0.16–0.32) mL.

7. The method for preparing a catalyst for growing sub-nanometer diameter single-walled carbon nanotubes according to claim 1, characterized in that, The gas atmosphere during calcination in S6 is one or more of argon, hydrogen, helium, and nitrogen.

8. An application of a catalyst prepared by the method described in any one of claims 1-7 for growing sub-nanometer diameter single-walled carbon nanotubes, characterized in that, The catalyst used to grow sub-nanometer diameter single-walled carbon nanotubes is used to catalytically crack carbon source gas and grow sub-nanometer diameter single-walled carbon nanotubes.

9. The application according to claim 8, characterized in that, The catalytic cracking method is as follows: under the condition of a flowing gaseous atmosphere, the temperature is raised to 500℃ to 1100℃ at a heating rate of 2 to 10℃ / min, then a flowing gaseous atmosphere and carbon source gas are introduced and the gas is kept vented for 20 min to 60 min, and then the temperature is naturally cooled to room temperature. The flowing gaseous atmosphere is one or more of argon, hydrogen, nitrogen, helium, carbon dioxide, and water vapor; the carbon source gas is one or more of methane, ethane, propane, ethylene, propylene, carbon monoxide, carbon dioxide, and methanol.

10. The application according to claim 8, characterized in that, The sub-nanometer-scale single-walled carbon nanotubes have an average outer diameter of 0.5 nm to 0.8 nm and grow in bundles.

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