Rare earth catalyst for preparing array type carbon nanotubes and preparation method thereof

Abstract

The invention provides a rare earth catalyst for preparing array type carbon nanotubes and a preparation method of the rare earth catalyst, and relates to the technical field of rare earth catalysts. The preparation method provided by the invention comprises the following steps: mixing tetraethoxysilane and diaspore, and hydrolyzing to form composite gel; calcining the composite gel to obtain a porous carrier; dipping the porous carrier in the ligand solution, adding the cerium-containing feed liquid, stirring and mixing, and separating to obtain a catalytic precursor; dipping the catalytic precursor in the complexing solution, adding the iron-containing material liquid, stirring and mixing, and separating to obtain a catalytic intermediate; and depositing a carbon coating layer on the surface of the catalytic intermediate, and reducing in a hydrogen atmosphere to prepare the rare earth catalyst. According to the catalyst provided by the invention, in the growth process of the array type carbon nano tube, the diameter distribution of the carbon tube is concentrated by virtue of a confinement structure, and a Fe-Ce-O interface induces directional assembly of carbon atoms, so that the defect density of the tube wall is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of rare earth catalysts, and particularly to a rare earth catalyst for preparing array-type carbon nanotubes and a preparation method thereof. Background Art

[0002] Due to their highly oriented nature, large aspect ratio, and regular topological structure, array-type carbon nanotubes have become a research hotspot in the field of nanomaterials. Chemical vapor deposition (CVD) is the mainstream process for preparing array-type carbon nanotubes, and the catalyst plays a dual role in this process: on the one hand, it serves as the active center for the cracking of carbon sources (such as methane and ethylene), regulating the dynamic adsorption and dissociation efficiency of carbon atoms; on the other hand, through the size, morphology, and crystal plane orientation of the catalyst particles, it precisely controls the nucleation sites, growth directions, and tube wall structures of the carbon nanotubes. Therefore, the dispersion, thermal stability, and interfacial properties of the catalyst directly determine the orientation consistency, defect density, and macroscopic properties of the array.

[0003] Currently, the catalyst systems for preparing array-type carbon nanotubes mainly include supported catalysts and composite catalysts. The active components are anchored on the surface of high-melting-point oxide supports through physical vapor deposition, sol-gel, or impregnation methods to inhibit particle migration at high temperatures. In recent years, rare earth elements (such as lanthanum, cerium, and yttrium) have been introduced into the catalytic system due to their unique electronic structures and oxygen defect regulation capabilities, forming transition metal-rare earth oxide composite structures. Such designs capture carbon atom clusters through the oxygen vacancies of rare earth oxides or improve the dispersion of active components through strong metal-support interactions.

[0004] Although certain progress has been made in the existing catalyst systems, multiple technical defects have emerged during large-scale preparation. Firstly, under high-temperature reaction conditions, transition metal nanoparticles are prone to Ostwald ripening and sintering due to their high surface energy, resulting in a discrete particle size distribution, which in turn leads to uneven carbon nanotube diameters, disordered array orientations, and a sharp increase in tube wall defects; secondly, although the introduction of rare earth additives can inhibit particle agglomeration through electron doping, traditional co-precipitation or impregnation methods are difficult to achieve single-atom-level dispersion of rare earth oxides on the surface of the support, and micron-sized aggregates are easily formed, which not only weakens the catalytic activity but also causes the collapse of the support structure due to local stress concentration. Therefore, a solution is needed to improve the above problems. Summary of the Invention

[0005] The purpose of the present invention is to provide a rare earth catalyst for preparing array-type carbon nanotubes and a preparation method thereof, which can effectively improve the structural stability of the obtained rare earth catalyst during use, and at the same time induce the directional assembly of carbon atoms to form array-type carbon nanotubes with a high degree of orientation during the preparation process of carbon nanotubes, and help reduce the tube wall defects of carbon nanotubes.

[0006] In a first aspect, a preparation method of a rare earth catalyst for preparing array-type carbon nanotubes provided by the present invention includes: mixing and hydrolyzing tetraethyl orthosilicate and boehmite to form a composite gel; calcining the composite gel to obtain a porous support; impregnating the porous support in a ligand solution and then adding a cerium-containing feed solution and stirring and mixing, and separating to obtain a catalytic precursor; impregnating the catalytic precursor in a complexing solution and then adding an iron-containing feed solution and stirring and mixing, and separating to obtain a catalytic intermediate; depositing a carbon coating layer on the surface of the catalytic intermediate and then reducing in a hydrogen atmosphere to obtain a rare earth catalyst.

[0007] The preparation method provided by the present invention suppresses metal migration through the spatial confinement of the porous support, realizes the uniform dispersion of rare earth single atoms by ligand competitive adsorption, enhances the metal-support interaction at the Fe-Ce-O interface, and the carbon coating layer provides thermal stability. In the catalyst, Ce is uniformly distributed on the surface of the support in a single atomic state. Therefore, during the growth process of array-type carbon nanotubes, the confinement structure makes the diameter distribution of the carbon tubes concentrated, and the Fe-Ce-O interface induces the directional assembly of carbon atoms, reducing the defect density of the tube wall.

[0008] Optionally, tetraethyl orthosilicate and boehmite are mixed in a molar ratio of (2-5):1, and then a mesoporous template agent is added and mixed and hydrolyzed to form a composite gel; the mesoporous template agent includes block copolymer F127.

[0009] Optionally, the composite gel is pretreated at 400°C - 500°C for 1h - 3h, and then calcined at 650°C - 750°C for 1h - 2h to obtain a porous support.

[0010] Optionally, the ligand solution includes an ethanol solution of ethylenediaminetetraacetic acid.

[0011] Optionally, after impregnating the porous support in the ligand solution, it is ultrasonically dispersed.

[0012] Optionally, the cerium concentration in the cerium-containing feed solution is 0.01mol / L - 0.05mol / L.

[0013] Optionally, the cerium-containing feed solution includes an ethanol solution of cerium nitrate.

[0014] Optionally, after adding the cerium-containing feed solution and stirring and mixing, it is filtered and separated by suction and dried at 70°C - 90°C to obtain a catalytic precursor.

[0015] Optionally, the complexing solution includes a sodium citrate solution.

[0016] Optionally, after impregnating the catalytic precursor in the complexing solution, it is ultrasonically dispersed.

[0017] Optionally, the iron concentration in the iron-containing feed solution is 0.01mol / L - 0.1mol / L.

[0018] Optionally, the iron-containing feed solution includes a ferrous sulfate solution.

[0019] Optionally, the iron-containing feed liquid further includes cobalt ions with a concentration of 0.01 mol / L - 0.05 mol / L.

[0020] Optionally, after adding the iron-containing feed liquid and stirring for mixing, adjust the pH to 7 - 8, mix in a microwave environment for 1 h - 2 h, and then separate to obtain a catalytic intermediate.

[0021] Optionally, in a mixed atmosphere of ethylene and hydrogen and an environment of 550°C - 650°C, deposit on the surface of the catalytic intermediate for 5 min - 10 min, and then perform reduction in a hydrogen atmosphere to obtain a rare earth catalyst.

[0022] Optionally, the volume ratio of ethylene to hydrogen in the mixed atmosphere is 1:(3 - 5).

[0023] Optionally, the pressure of the mixed atmosphere is 0.1 Mpa - 0.5 Mpa.

[0024] Optionally, after depositing on the surface of the catalytic intermediate for 5 min - 10 min, keep it at a constant temperature for 1 h - 2 h in an inert atmosphere of 800°C - 850°C.

[0025] In a second aspect, the present invention also provides a rare earth catalyst prepared by using any one of the above optional preparation methods, and the rare earth catalyst is used for preparing array-type carbon nanotubes.

[0026] The preparation method of a rare earth catalyst for preparing array-type carbon nanotubes provided by the present invention has at least one of the following beneficial technical effects compared with the prior art:

[0027] 1. The preparation method provided by the present invention does not need to use complex mechanical equipment, can effectively improve the production convenience of the rare earth catalyst, and at the same time, the raw materials used are simple and easy to obtain, which is beneficial to reducing the production cost and is conducive to large-scale industrial production;

[0028] 2. The preparation method provided by the present invention inhibits the migration of metal active components through spatial confinement, and at the same time can make the metal active elements uniformly distributed on the carrier, which is not only beneficial to improving the catalytic activity and catalytic efficiency, but also can improve the structural stability of the metal active components on the carrier during long-term use;

[0029] 3. The preparation method provided by the present invention can protect the metal active components on the surface of the catalytic intermediate by depositing a carbon coating layer on the surface of the catalytic intermediate, avoid the peeling of the metal active components during the process of generating array-type carbon nanotubes, and at the same time is beneficial to adjusting the orientation of the rare earth catalyst for preparing array-type carbon nanotubes. Detailed Embodiments

[0030] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be described clearly and completely below. Apparently, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention. Unless otherwise defined, the technical terms or scientific terms used herein shall have the ordinary meanings understood by those of ordinary skill in the art belonging to the field of the present invention.

[0031] The present invention provides a preparation method for a rare earth catalyst for preparing array-type carbon nanotubes, comprising the following steps:

[0032] S1. Mix tetraethyl orthosilicate and boehmite and hydrolyze them to form a composite gel;

[0033] S2. Calcinate the composite gel to obtain a porous support;

[0034] S3. Immerse the porous support in a ligand solution, add a cerium-containing feed solution, stir and mix, and separate to obtain a catalytic precursor;

[0035] S4. Immerse the catalytic precursor in a complexing solution, add an iron-containing feed solution, stir and mix, and separate to obtain a catalytic intermediate;

[0036] S5. Deposit a carbon coating layer on the surface of the catalytic intermediate and reduce it in a hydrogen atmosphere to obtain a rare earth catalyst.

[0037] Actually, in the preparation method provided by the present invention, a composite gel with a Si-O-Al network structure is formed by using tetraethyl orthosilicate and boehmite to carry out a hydrolysis and polycondensation reaction, and a SiO2-Al2O3 porous support with a high specific surface area is formed by calcination. Then, the porous support is immersed in a ligand solution. Through the competitive adsorption of the ligand and the hydroxyl groups on the surface of the porous support, the high-energy active sites can be preferentially occupied. After introducing the cerium-containing feed solution, the free cerium ions are adsorbed at the defect positions of the support, thereby forming an atomically dispersed Ce-O-Si / Al bonding structure.

[0038] In addition, through treatment in the complexing solution and the iron-containing feed solution, Fe 2+ / Fe 3+ can form a stable complex with the complexing agent, and gradually replace the weakly bound Ce on the surface of the support through ion exchange 3+At the site, by utilizing the strong stability of the rare earth-support bond, the Fe species are forced to preferentially deposit in the region adjacent to the Ce atoms, forming an Fe-Ce-O ternary interface, enhancing the electron coupling effect between the active component and the support. Finally, by forming a carbon-coated structure on the surface to physically block, the surface energy of the Fe nanoparticles is reduced. At the same time, an Fe-C chemical bond is formed between the carbon layer and the metal, further fixing the particle position. Finally, the surface oxide layer is removed by hydrogen reduction, exposing the highly active metal crystal plane, while the carbon layer remains intact.

[0039] In some embodiments, when performing step S1, tetraethyl orthosilicate and boehmite are mixed at a molar ratio of (2-5):1 and then added with a mesoporous template agent for mixed hydrolysis to form a composite gel. Specifically, the mesoporous template agent includes the block copolymer F127. In fact, by adjusting the Si / Al ratio, the chemical properties of the support are optimized. For example, when the Si content is increased, the thermal stability and surface hydroxyl density of the support can be improved, providing more active sites. When the Al content is increased, the mechanical strength of the support can be enhanced and the electrostatic adsorption of metal ions on the support surface can be promoted.

[0040] In some embodiments, when performing step S2, the composite gel is pretreated at 400°C - 500°C for 1h - 3h and then calcined at 650°C - 750°C for 1h - 2h to obtain a porous support. In fact, through the low-temperature pretreatment process, the template agent and the unhydrolyzed tetraethyl orthosilicate can be removed. At the same time, the gradient heating is beneficial to slowing down the gas generation rate and avoiding pore defects and collapses caused by the rapid removal of gas.

[0041] In some embodiments, the ligand solution used in step S3 includes an ethanol solution of ethylenediaminetetraacetic acid, and when performing step S3, the porous support is impregnated in the ligand solution and then ultrasonically dispersed. In fact, by impregnating the porous support, it is beneficial to improve the uniformity of the ligand on the surface of the porous support. At the same time, the ultrasonic cavitation effect generates microjets and local high pressure, driving the ligand molecules to penetrate deep into the micropores of the support, thus ensuring that the inner wall of the pores is completely covered by the ligand modification.

[0042] In some embodiments, the cerium concentration in the cerium-containing feed solution in step S3 is 0.01 mol / L - 0.05 mol / L. In fact, by adjusting the cerium concentration in the cerium-containing feed solution, the cerium content modified on the surface of the porous support can be adjusted, thereby ensuring the uniformity of cerium modification on the porous surface. At the same time, avoiding the formation of polymerization sites due to oversaturation of loading is beneficial to forming a strong bonding structure of single-atom cerium-support on the porous support surface, providing a basis for the subsequent directional anchoring of Fe on the support and the generation of array-type carbon nanotubes.

[0043] In some embodiments, the cerium-containing feed solution in step S3 includes an ethanol solution of cerium nitrate. In fact, the cerium-containing feed solution can also be other cerium salts, such as sulfates, chlorides, etc. Thus,

[0044] In some embodiments, in step S3, a cerium-containing feed solution is added and stirred and mixed, then filtered by suction and separated, and dried at 70 °C - 90 °C to obtain a catalytic precursor. In fact, instead of using a traditional aqueous phase system, a cerium nitrate ethanol solution is adopted. Through the regulation of multiple interactions between the solvent, solute, and carrier, the cerium loading process is changed from "rapid hydrolysis - random deposition" to "slow-release adsorption - fixed-point anchoring". This is beneficial to maintaining the pore structure and surface hydroxyl activity, providing an ideal interfacial environment for the subsequent confined loading of Fe.

[0045] In some embodiments, in step S4, the complexing solution includes a sodium citrate solution. In fact, the sodium citrate complexing system upgrades the transition metal loading from "random deposition" to "directed assembly" through the cooperation of chemical coordination and physical confinement, can improve the problem of out-of-control particle size, and improve the growth orientation guiding performance of carbon nanotubes on the catalyst surface through the regulation of the interfacial electronic structure.

[0046] In some embodiments, in step S4, the catalytic precursor is impregnated in the complexing solution and then ultrasonically dispersed. In fact, during the ultrasonic impregnation process, sodium citrate in the complexing solution undergoes competitive coordination with the rare earth single atoms (such as Ce - O - Al / Si) pre-loaded on the surface of the catalytic precursor, and can preferentially bind to the weakly anchored Ce 3+ , displace it from the low-stability sites, and release high-energy anchoring sites for Fe 2+ to provide high-quality adsorption sites.

[0047] In some embodiments, in step S4, the iron-containing feed solution includes ferrous sulfate with a concentration of 0.01 mol / L - 0.1 mol / L, and also includes cobalt ions with a concentration of 0.01 mol / L - 0.05 mol / L. In fact, through dual-metal adsorption, an Fe - Co dual-active phase system can be constructed. The formed metal nanoparticles have both high catalytic activity and anti-sintering characteristics, improve the problem of high-temperature deactivation of the catalyst, and improve the orientation consistency of carbon nanotube generation through the dual-metal synergistic catalytic mechanism.

[0048] In some embodiments, in step S4, an iron-containing feed solution is added and stirred and mixed, then the pH is adjusted to 7 - 8, and after mixing in a microwave environment for 1 h - 2 h, a catalytic intermediate is separated. In fact, in a weakly alkaline environment, the oxidation potential of ferrous ions can be reduced, and a complex is formed by complexing with citrate ions, thus avoiding the formation of ferrous precipitates. In addition, through interfacial assembly in the microwave field, the dispersion uniformity of iron nanoclusters can be improved.

[0049] In some embodiments, when performing step S5, in a mixed atmosphere of ethylene and hydrogen and at an environment temperature of 550°C - 650°C, after depositing on the surface of the catalytic intermediate for 5 min - 10 min, reduction is carried out in a hydrogen atmosphere to obtain the rare earth catalyst. In fact, through carbon-confined deposition in the ethylene / hydrogen mixed atmosphere and hydrogen reduction activation, the problems of high-temperature sintering and disordered growth of carbon nanotubes can be improved, and through the synergy of the carbon layer pores and the rare earth electron effect, the ultra-long-range ordered growth of array-type carbon nanotubes is achieved.

[0050] In some embodiments, the volume ratio of ethylene to hydrogen in the mixed atmosphere is 1:(3 - 5), and the air pressure is 0.1 Mpa - 0.5 Mpa. In addition, after depositing on the surface of the catalytic intermediate for 5 min - 10 min, it is kept warm in an inert atmosphere at 800°C - 850°C for 1 h - 2 h.

[0051] Example 1

[0052] This Example 1 provides a preparation method of a rare earth catalyst for preparing array-type carbon nanotubes, including the following steps:

[0053] S1. Mix tetraethyl orthosilicate and boehmite at a molar ratio of 3:1 to obtain a preliminary mixture. After adding an F127 mesoporous template agent with a mass fraction of 10% of the preliminary mixture and mixing, add it to deionized water at a solid-liquid ratio of 0.08 g / mL for hydrolysis and polycondensation to form a composite gel;

[0054] S2. Calcinate the composite gel at 450°C for 2 h, then transfer it to 700°C for calcination treatment for 1 h, and naturally cool it to room temperature to obtain a porous support;

[0055] S3. Immerse the porous support in an ethylenediaminetetraacetic acid ethanol solution at a solid-liquid ratio of 0.05 g / mL, perform ultrasonic treatment for 15 min at an ultrasonic power of 200 W, then filter and separate. Add it to a 0.03 mol / L cerium nitrate ethanol solution, stir and mix at a rotation speed of 300 rpm for 2 h, then filter and separate, and dry it to constant weight in an oven at 80°C to obtain a catalytic precursor; wherein, the molar ratio of the porous support to ethylenediaminetetraacetic acid and cerium nitrate is 5:1.2:1;

[0056] S4. Immerse the catalytic precursor in a sodium citrate aqueous solution at a solid-liquid ratio of 0.05 g / mL, perform ultrasonic treatment for 15 min at an ultrasonic power of 200 W, then filter and separate. Add it to an iron-containing feed solution (with water as the solvent) containing 0.05 mol / L ferrous sulfate and 0.03 mol / L cobalt chloride, mix, adjust the pH to 8, and mix in a microwave environment (2.45 GHz, 500 W) for 2 h, then separate to obtain a catalytic intermediate; wherein, the mass ratio of the catalytic precursor to sodium citrate and iron ions is 1:0.2:0.2;

[0057] S5. Transfer the catalytic intermediate into a tubular furnace, introduce a mixed atmosphere of 0.3 Mpa (the volume ratio of ethylene to hydrogen is 1:4), deposit on the surface for 8 min in an environment of 600 °C, keep warm for 2 h in an argon atmosphere of 800 °C, and then carry out reduction in a hydrogen atmosphere to obtain a rare earth catalyst.

[0058] Example 2

[0059] This Example 2 provides a preparation method of a rare earth catalyst for preparing array-type carbon nanotubes. The difference from Example 1 is that the iron-containing feed liquid in step S4 does not contain cobalt chloride at 0.03 mol / L.

[0060] Example 3

[0061] This Example 3 provides a preparation method of a rare earth catalyst for preparing array-type carbon nanotubes. The difference from Example 1 is that in step S4, instead of mixing in a microwave environment, after ultrasonic treatment at a power of 200 W for 10 min, stirring is carried out at a rotation speed of 300 rpm for 20 min, and the ultrasonic treatment-stirring treatment is repeated for a total of 120 min (a total of four cycles of treatment), and then the catalytic intermediate is separated.

[0062] Comparative Example 1

[0063] This Comparative Example 1 provides a preparation method of a rare earth catalyst for preparing array-type carbon nanotubes. The difference from Example 1 is that step S5 is not carried out, and the rare earth catalyst is obtained in step S4.

[0064] Comparative Example 2

[0065] This Comparative Example 2 provides a preparation method of a rare earth catalyst for preparing array-type carbon nanotubes. The difference from Example 1 is that steps S3 and S4 are not carried out. In step S4, the porous carrier is added to a mixed solution containing cerium nitrate at 0.03 mol / L and ferrous sulfate at 0.05 mol / L at a solid-liquid ratio of 0.05 g / mL for impregnation and then calcined to obtain a catalytic intermediate; wherein, the mass ratio of the porous carrier to cerium nitrate is 1:0.2.

[0066] Performance detection

[0067] Synthesize array-type carbon nanotubes with the rare earth catalysts prepared in Examples 1 to 3 and Comparative Examples 1 to 2, including: lay the catalyst flat in a quartz boat and place it in a tubular furnace, heat up to 650 °C under nitrogen protection and introduce propylene with a flow rate of 500 sccm to react for 30 min, and then detect the reaction yield as shown in Table 1 below. After the rare earth catalysts prepared in Example 1, Comparative Examples 1 to 2 are used in long-term circulation for 100 h, detect the retention rate of the reaction yield compared with the first time as shown in Table 1 below.

[0068] Table 1 Catalytic performance and long-term service performance of rare earth catalysts

[0069] Reaction yield / % Retention rate after 100 h / % Example 1 43.5 95.47 Example 2 38.6 86.72 Example 3 35.3 79.54 Comparative Example 1 21.7 64.28 Comparative Example 2 36.8 76.52

[0070] As can be seen from Table 1, by combining Example 1 and Comparative Example 2, it can be seen that the rare earth catalyst prepared in Example 1 of the present invention has a good reaction yield in the preparation of array-type carbon nanotubes, and can maintain good catalytic activity during long-term use, which is beneficial to the industrial production of array-type carbon nanotubes. In addition, by combining Example 1 and Example 2, it can be seen that introducing Co element into the catalyst can effectively improve the catalytic activity and at the same time improve the structural stability of the metal active component on the carrier. And from Example 1 and Example 3, it can be seen that the method of microwave treatment helps to improve the dispersion uniformity and stability of the metal active component on the surface of the carrier. At the same time, from Example 1 and Comparative Example 1, it can be seen that the lack of carbon coating layer and reduction treatment on the surface will lead to a sharp drop in the reaction yield of the catalyst, and at the same time, the stability of the active component will be significantly reduced, and it is easy to fall off during the catalytic process.

[0071] Although the embodiments of the present invention have been described in detail above, it is obvious to those skilled in the art that various modifications and changes can be made to these embodiments. However, it should be understood that such modifications and changes are all within the scope and spirit of the present invention described in the claims. Moreover, the present invention described herein may have other embodiments, and can be implemented or realized in various ways.

Claims

1. A preparation method of a rare earth catalyst for preparing array-type carbon nanotubes, characterized in that, Including: Mix tetraethyl orthosilicate with boehmite for hydrolysis to form a composite gel; calcine the composite gel to obtain a porous support; impregnate the porous support in a ligand solution, then add a cerium-containing feed solution and stir to mix, and separate to obtain a catalytic precursor; impregnate the catalytic precursor in a complexing solution, then add an iron-containing feed solution and stir to mix, and separate to obtain a catalytic intermediate; deposit a carbon coating layer on the surface of the catalytic intermediate and then reduce it in a hydrogen atmosphere to obtain a rare earth catalyst.

2. The preparation method according to claim 1, wherein Mix tetraethyl orthosilicate with boehmite at a molar ratio of (2 - 5):1, then add a mesoporous template agent and mix for hydrolysis to form a composite gel; the mesoporous template agent includes block copolymer F127.

3. The preparation method according to claim 1, wherein, After pretreating the composite gel at 400°C - 500°C for 1h - 3h, then place it in a calcination at 650°C - 750°C for 1h - 2h to obtain a porous support.

4. The preparation method according to claim 1, characterized in that, The ligand solution includes an ethanol solution of ethylenediaminetetraacetic acid; and / or, after impregnating the porous support in the ligand solution, perform ultrasonic dispersion. And / or, the cerium concentration in the cerium-containing feed solution is 0.01 mol / L - 0.05 mol / L.

5. The preparation method according to claim 1, characterized in that The cerium-containing feed solution includes an ethanol solution of cerium nitrate; and / or, after adding the cerium-containing feed solution and stirring to mix, perform suction filtration and separation, and dry at 70°C - 90°C to obtain a catalytic precursor.

6. The preparation method according to claim 1, characterized in that, The complexing solution includes a sodium citrate solution; and / or, after impregnating the catalytic precursor in the complexing solution, perform ultrasonic dispersion. And / or, the iron concentration in the iron-containing feed solution is 0.01 mol / L - 0.1 mol / L.

7. The preparation method according to claim 1, characterized in that, The iron-containing feed solution includes a ferrous sulfate solution; and / or, the iron-containing feed solution further includes cobalt ions with a concentration of 0.01 mol / L - 0.05 mol / L; and / or, after adding the iron-containing feed solution and stirring to mix, adjust the pH to 7 - 8, mix in a microwave environment for 1h - 2h, and then separate to obtain a catalytic intermediate.

8. The preparation method according to claim 1, wherein In a mixed atmosphere of ethylene and hydrogen, at an environment of 550°C - 650°C, after depositing for 5min - 10min on the surface of the catalytic intermediate, perform reduction in a hydrogen atmosphere to obtain a rare earth catalyst.

9. The preparation method according to claim 8, characterized in that, The volume ratio of ethylene to hydrogen in the mixed atmosphere is 1:(3 - 5); and / or, the pressure of the mixed atmosphere is 0.1 Mpa - 0.5 Mpa; and / or, after depositing for 5min - 10min on the surface of the catalytic intermediate, keep it warm at 800°C - 850°C in an inert atmosphere for 1h - 2h.

10. A rare earth catalyst prepared by the preparation method according to any one of claims 1 to 9, and the rare earth catalyst is used for preparing array-type carbon nanotubes.