Rare earth catalyst, method of preparation and carbon nanotubes prepared thereby

Abstract

The application provides a rare earth catalyst, a preparation method and prepared carbon nanotubes, and relates to the technical field of rare earth catalysts.The preparation method provided by the application comprises the following steps: after a carbon source and a rare earth nitrate are mixed in an ethanol-water system and a mesoporous template agent is added, a rare earth gel is prepared through hydrothermal reaction; the rare earth gel is carbonized in an inert gas atmosphere to obtain a carbonized carrier; the carbonized carrier is used as a working electrode, and electrochemical deposition is carried out in an electrolyte containing iron ions and cobalt ions to obtain a composite carrier; and after a carbon coating layer is deposited on the surface of the composite carrier, the rare earth catalyst is prepared through reduction in a hydrogen atmosphere. Through carrier-metal-carbon coating multistage interface coupling, the metal active component can be well protected, the oxidation peeling of the active metal can be inhibited, the service life of the catalyst in the recycling process can be effectively improved, and the growth rate and orientation consistency of the carbon nanotubes can be improved.

Description

Technical Field

[0001] This invention relates to the field of rare earth catalyst technology, and more particularly to a rare earth catalyst, a preparation method, and the prepared carbon nanotubes. Background Technology

[0002] Arrayed carbon nanotubes exhibit unique performance advantages in fields such as electronic devices, energy storage materials, and composite materials due to their highly ordered one-dimensional structure. The characteristics of the catalyst used to prepare arrayed carbon nanotubes directly determine the growth quality and structural controllability of the arrayed carbon nanotubes, including key parameters such as carbon nanotube diameter, wall number, arrangement density, and defect degree. Therefore, by controlling the composition, morphology, and distribution of active sites of the catalyst, a dynamic balance between nucleation and extension during the growth of carbon nanotubes can be achieved, thereby optimizing the uniformity and functionality of the array structure.

[0003] Currently, mainstream catalyst systems for preparing arrayed carbon nanotubes typically use transition metals (such as iron, cobalt, and nickel) or their alloys as active components, and porous materials such as alumina and silica as supports. Typical catalyst structures include core-shell, multilayer stacked, or supported nanoparticles, constructing periodically distributed catalyst arrays to achieve directional growth of carbon nanotubes. However, the metal active components are prone to migration or sintering during high-temperature reactions, leading to uneven particle size distribution and problems such as large diameter dispersion and disordered array arrangement of carbon nanotubes. Secondly, insufficient interfacial bonding between the support and the active component can easily lead to component delamination during long-term reactions, causing catalyst deactivation. Therefore, there is an urgent need to provide a solution to improve these problems. Summary of the Invention

[0004] The purpose of this invention is to provide a rare earth catalyst, a preparation method, and a prepared carbon nanotube. Through multi-level interface coupling of support-metal-carbon coating, the active metal components can be well protected, the active metal oxidation and stripping can be inhibited, the service life of the catalyst during recycling can be effectively improved, and the growth rate and orientation consistency of the carbon nanotube can be improved.

[0005] In a first aspect, the present invention provides a method for preparing a rare earth catalyst, comprising: mixing a carbon source and a rare earth nitrate in an ethanol-water system, adding a mesoporous template agent, and then reacting the mixture hydrothermally to obtain a rare earth gel; carbonizing the rare earth gel in an inert gas atmosphere to obtain a carbonized support; using the carbonized support as a working electrode, electrochemically depositing it in an electrolyte containing iron and cobalt ions to obtain a composite support; and depositing a carbon coating layer on the surface of the composite support and then reducing it in a hydrogen atmosphere to obtain a rare earth catalyst.

[0006] The preparation method provided by this invention involves hydrothermal crosslinking of a carbon source and a rare earth catalyst in a mesoporous template agent within an ethanol-water solvent system to form a three-dimensional network of rare earth-doped gel. After carbonization, the rare earth elements are in situ embedded within the pore walls of the carbon framework, resulting in a carbonized support with high specific surface area, conductivity, and rare earth anchoring points. Electrochemical deposition enables the directional reduction of metal ions within the mesoporous channels of the carbonized support, preferentially adsorbing iron and cobalt ions with rare earth as anchoring points to induce heterogeneous nucleation and form highly dispersed alloy nanoparticles. This allows the strong bonding between rare earth oxides and the carbon framework to inhibit the migration and aggregation of metal particles. Furthermore, by depositing a carbon layer on the surface of the composite support, a triple-interface coupling structure can be constructed by rebonding with rare earth elements, effectively protecting the active metal components within the catalyst.

[0007] Optionally, the carbon source includes at least one of glucose and phenolic resin.

[0008] Optionally, the rare earth nitrate includes one of yttrium nitrate and gadolinium nitrate.

[0009] Optionally, the mass ratio of the carbon source to the rare earth nitrate is 1:(0.1-1).

[0010] Optionally, a hydrothermal reaction can be carried out at 160℃-200℃.

[0011] Optionally, rare earth gels can be prepared by hydrothermal reaction for 12-24 hours.

[0012] Optionally, the gas used in the inert gas atmosphere includes at least one of argon and nitrogen.

[0013] Optionally, the rare earth gel is carbonized at 700℃-900℃.

[0014] Optionally, the rare earth gel is carbonized for 1-2 hours.

[0015] Optionally, the carbonized support can be used as the working electrode and Ag / AgCl as the reference electrode.

[0016] Optionally, a pulse voltage of -0.5V to 1.2V is applied during electrochemical deposition.

[0017] Optionally, the electrolyte contains 2 mol / L to 5 mol / L of dissolved potassium chloride.

[0018] Optionally, the molar ratio of iron ions to cobalt ions in the electrolyte is (1-3):1.

[0019] Optionally, the electrolyte contains at least one of iron nitrate, iron sulfate, and iron chloride.

[0020] Optionally, the electrolyte contains at least one of cobalt sulfate, cobalt nitrate, and cobalt chloride.

[0021] Optionally, the volume fraction of ethanol in the ethanol-water system is 10%-70%.

[0022] Optionally, the mesoporous template agent includes one of F127 and CTAB.

[0023] Optionally, after depositing on the surface of the composite support for 5 min to 10 min in a mixed atmosphere of ethylene and hydrogen at 550℃-650℃, the rare earth catalyst is obtained by reduction in a hydrogen atmosphere.

[0024] Optionally, the volume ratio of ethylene to hydrogen in the mixed atmosphere is 1:(3-5).

[0025] Optionally, the pressure of the mixed atmosphere is 0.1 MPa to 0.5 MPa.

[0026] Optionally, after depositing on the surface of the composite carrier for 5-10 minutes, the substrate is kept at an inert gas atmosphere of 800℃-850℃ for 1-2 hours.

[0027] Secondly, the present invention also provides a rare earth catalyst prepared by any of the above-mentioned optional preparation methods.

[0028] Thirdly, the present invention also provides carbon nanotubes prepared using a rare earth catalyst prepared by any of the above-mentioned optional preparation methods.

[0029] The method for preparing a rare earth catalyst provided by this invention has at least one of the following beneficial technical effects compared with the prior art:

[0030] 1. The preparation method provided by this invention does not require the use of complex mechanical equipment, and the raw materials used are inexpensive and readily available. It has high batch production capacity in the preparation of rare earth catalysts and can be carried out on a large scale for industrial production, which is beneficial for the production and application of array-type carbon nanotubes. At the same time, the solvent system used in this invention is safe and non-toxic, which helps to reduce the release of toxic and harmful substances during the production process and has high environmental protection.

[0031] 2. The rare earth catalyst prepared by the present invention has a stable carbon skeleton structure, which can form a stable rare earth-carbon skeleton on the surface of the support. Furthermore, the carbon coating on the surface is beneficial to improving the stability of rare earth elements during catalytic use and avoiding stripping. Detailed Implementation

[0032] 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 clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. 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. Unless otherwise defined, the technical or scientific terms used herein should have the ordinary meaning understood by those skilled in the art to which this invention pertains.

[0033] This invention provides a method for preparing a rare earth catalyst, comprising the following steps:

[0034] S1. After mixing carbon source and rare earth nitrate in an ethanol-water system, a mesoporous template agent is added, and a rare earth gel is obtained after hydrothermal reaction.

[0035] S2. Carbonization of rare earth gel in an inert gas atmosphere yields a carbonized support.

[0036] S3. Using a carbonized support as the working electrode, a composite support is obtained by electrochemical deposition in an electrolyte of iron and cobalt ions.

[0037] S4. A rare earth catalyst is prepared by depositing a carbon coating layer on the surface of a composite support and then reducing it under a hydrogen atmosphere.

[0038] In fact, in step S1 of this invention, carbon source and rare earth nitrate are used as raw materials to undergo hydrothermal crosslinking under the guidance of mesoporous template agent, thereby forming a three-dimensional network of rare earth doped gel-rare earth gel. During this hydrothermal reaction, rare earth ions combine with carbon source through coordination, thereby being uniformly dispersed in the rare earth gel skeleton. In the subsequent carbonization process, the carbon source is decomposed into a conductive carbon skeleton, and rare earth ions and carbon skeleton are sintered to form a rare earth-carbon bonded structure.

[0039] In some embodiments, the carbon source used in step S1 includes at least one of glucose and phenolic resin. In fact, using different carbon sources can form carbon framework structures with different structures in rare earth gels. For example, carbonization with glucose can generate amorphous carbon with a higher density of surface active sites, while carbonization with phenolic resin results in better conductivity. In the ethanol-water system, the ethanol volume fraction is 10%-70%, and the mesoporous template agent includes one of F127 and CTAB.

[0040] In some embodiments, the rare earth nitrates used in step S1 include one of yttrium nitrate and gadolinium nitrate. In fact, yttrium nitrate and gadolinium nitrate are carbonized to generate Y2O3 and Gd2O3, respectively. Both are cubic rare earth oxides with high thermal stability and chemical inertness. They can serve as anchoring points to fix transition metal particles and avoid excessive adsorption of carbon sources that could clog active sites. They can work together with the carbon framework to construct a highly stable and highly active carbonized support.

[0041] In some embodiments, the mass ratio of carbon source to rare earth nitrate is 1:(0.1-1) during step S1. In practice, when the amount of rare earth nitrate is higher, cross-linked rare earth nanowires can be formed within the carbon framework, effectively improving the structural properties of the carbonized support through their interweaving with the carbon framework. Conversely, when the amount of rare earth nitrate is lower, rare earth oxides are embedded in the carbon framework as isolated nanoclusters, providing sufficient metal anchoring points and avoiding blockage of mesoporous channels.

[0042] In some embodiments, during step S1, the carbon source, rare earth nitrate, and mesoporous template agent are mixed and then subjected to a hydrothermal reaction at 160°C-200°C for 12-24 hours to obtain a rare earth gel. In practice, in an ethanol-water mixed solvent, the mesoporous template agent undergoes hydrophilic-hydrophobic rearrangement at high temperature to form micelles or a liquid crystal phase template. Carbon source molecules are adsorbed onto the surface of the template agent micelles, while rare earth ions coordinate with the carbon source to form a ternary composite system.

[0043] In some embodiments, the inert gas atmosphere used during the carbonization process in step S2 includes at least one of argon and nitrogen. Furthermore, the rare earth gel is carbonized at 700℃-900℃ for 1-2 hours. In fact, carbonizing the aforementioned ternary composite system transforms the rare earth gel into a carbonization carrier possessing high conductivity, high specific surface area, and strong interfacial bonding, enabling precise control of the graphitization degree of the carbon framework, the rare earth dispersion state, and the mesoporous structure.

[0044] In some embodiments, during step S3, the carbonized support is used as the working electrode, Ag / AgCl is used as the reference electrode, and a pulse voltage of -0.5V to 1.2V is applied. In some embodiments, during step S3, the electrolyte used for electrochemical deposition contains 2 mol / L to 5 mol / L potassium chloride, and also contains at least one of ferric nitrate, ferric sulfate, and ferric chloride, and at least one of cobalt sulfate, cobalt nitrate, and cobalt chloride. Furthermore, the molar ratio of iron ions to cobalt ions in the electrolyte is (1-3):1.

[0045] In some embodiments, during step S4, after depositing the rare earth catalyst on the surface of the composite support for 5 min to 10 min in a mixed atmosphere of ethylene and hydrogen at 550°C to 650°C, the catalyst is reduced in a hydrogen atmosphere to obtain the rare earth catalyst.

[0046] In some embodiments, during step S4, the volume ratio of ethylene to hydrogen in the mixed atmosphere is 1:(3-5), and the pressure of the mixed atmosphere is 0.1 MPa-0.5 MPa. Furthermore, after deposition on the composite support surface for 5-10 minutes, the mixture is held at an inert gas atmosphere at 800-850°C for 1-2 hours.

[0047] Example 1

[0048] This embodiment 1 provides a method for preparing a rare earth catalyst, including the following steps:

[0049] S1. Glucose and yttrium nitrate were mixed at a mass ratio of 1:0.5 and then added to an ethanol-water system (50% ethanol by volume) at a solid-liquid ratio of 0.08 g / mL. After mixing and dissolving, 20% of glucose by mass of mesoporous template agent F127 was added and stirred. The mixture was then subjected to hydrothermal reaction at 180°C for 18 h and then separated to obtain rare earth gel.

[0050] S2. The rare earth gel was placed in a tube furnace, and after gas replacement with argon, the tube furnace was heated to 800°C at a rate of 10°C / min and then held at that temperature for h. After cooling to room temperature with the furnace, the carbonized support was obtained.

[0051] S3. A composite support was prepared by electrochemical deposition for 1 hour using a carbonized support as the working electrode, Ag / AgCl as the reference electrode, and 3 mol / L potassium chloride as the electrolyte (which also contained 2 mol / L ferric chloride and 1 mol / L cobalt chloride).

[0052] S4. The composite support is transferred to the furnace chamber of a tube furnace, and a mixed atmosphere of 0.3 MPa (the volume ratio of ethylene to hydrogen is 1:4) is introduced. After surface deposition at 600°C for 8 min, it is kept at 800°C under an argon atmosphere for 2 h, and then reduced under a hydrogen atmosphere to obtain a rare earth catalyst.

[0053] Example 2

[0054] This embodiment 2 provides a method for preparing a rare earth catalyst. The difference from embodiment 1 is that in step S1, phenolic resin is used as a carbon source to replace glucose, and the mass ratio of phenolic resin to yttrium nitrate is 1:0.5.

[0055] Example 3

[0056] This embodiment 3 provides a method for preparing a rare earth catalyst. The difference from embodiment 1 is that in step S3, a constant DC voltage of 1.0V is used for electrochemical deposition for 1 hour.

[0057] Comparative Example 1

[0058] Comparative Example 1 provides a method for preparing a rare earth catalyst. The difference from Example 1 is that in step S3, the carbonized support is added to a mixed aqueous solution containing ferric chloride and cobalt chloride (the molar ratio of iron ions to cobalt ions is 2:1, and the mass ratio of carbonized support to iron ions is 1:0.2) at a solid-liquid ratio of 0.05 g / mL, and then sintered to obtain a composite support.

[0059] Comparative Example 2

[0060] Comparative Example 2 provides a method for preparing a rare earth catalyst. The difference from Example 1 is that in step S3, 3 mol / L potassium chloride is used as the electrolyte, and 2 mol / L ferric chloride is dissolved in the electrolyte.

[0061] Comparative Example 3

[0062] Comparative Example 3 provides a method for preparing a rare earth catalyst. The difference from Example 1 is that in step S3, 3 mol / L potassium chloride is used as the electrolyte, and 2 mol / L ferric chloride and 1 mol / L nickel chloride are dissolved in the electrolyte.

[0063] Comparative Example 4

[0064] Comparative Example 4 provides a method for preparing a rare earth catalyst. The difference from Example 1 is that in step S3, 3 mol / L potassium chloride is used as the electrolyte, and 2 mol / L ferric chloride and 1 mol / L zinc chloride are dissolved in the electrolyte.

[0065] Performance testing

[0066] The rare earth catalysts prepared in Examples 1 to 3 and Comparative Examples 1 to 4 were used to synthesize array-type carbon nanotubes. The process included: spreading the catalyst in a quartz boat and placing it in a tube furnace, heating it to 650°C under nitrogen protection, and introducing propylene at a flow rate of 500 sccm for 30 min. The reaction yield was then measured and is shown in Table 1 below. The rare earth catalysts prepared in Examples 1 and Comparative Examples 1 to 2 were used in a long-term cycle for 100 h. The retention rate of the reaction yield compared to the first cycle was measured and is shown in Table 1 below.

[0067] Table 1 Catalytic performance and long-term performance of rare earth catalysts

[0068] Reaction yield / % Retention rate after 100 hours / % Example 1 54.82 97.62 Example 2 51.39 98.13 Example 3 45.22 94.67 Comparative Example 1 34.58 72.18 Comparative Example 2 21.87 73.52 Comparative Example 3 36.75 83.41 Comparative Example 4 33.68 79.52

[0069] As shown in Table 1, the rare earth catalyst prepared in Example 1 of this invention exhibits good catalytic activity in the preparation of arrayed carbon nanotubes, effectively regulating the orientation of the carbon nanotubes and maintaining good catalytic activity during long-term use. In Example 2, using phenolic resin as a carbon source helps improve the structural stability of the catalyst, thereby increasing the retention rate of catalytic performance. In Example 3, using a DC power supply for deposition negatively impacts the loading of active metals on the catalyst surface and its structural stability. In Comparative Example 1, the catalyst prepared by the impregnation method shows a significant decrease in loading and stability. In Comparative Example 2, the presence of only iron ions in the electrolyte has a significant impact on the catalytic activity of the catalyst. From Examples 1, 3, and 4, it can be seen that loading iron and cobalt active components onto rare earth catalysts has a positive effect on the catalytic activity and structural stability of the catalyst.

[0070] While embodiments of the present invention have been described in detail above, it will be apparent to those skilled in the art that various modifications and variations can be made to these embodiments. However, it should be understood that such modifications and variations fall within the scope and spirit of the invention as set forth in the claims. Furthermore, the invention described herein may have other embodiments and can be implemented or carried out in various ways.

Claims

1. A method for preparing a rare earth catalyst, characterized in that, include: A rare earth gel was prepared by mixing a carbon source and a rare earth nitrate in an ethanol-water system, adding a mesoporous template agent, and then reacting the mixture hydrothermally. The rare earth gel was then carbonized in an inert gas atmosphere to obtain a carbonized support. The carbonized support was used as a working electrode and electrochemically deposited in an electrolyte of iron and cobalt ions to obtain a composite support. A rare earth catalyst was prepared by depositing a carbon coating layer on the surface of the composite support and then reducing it in a hydrogen atmosphere.

2. The preparation method according to claim 1, characterized in that, The carbon source includes at least one of glucose and phenolic resin; and / or, the rare earth nitrate includes one of yttrium nitrate and gadolinium nitrate; and / or, the mass ratio of the carbon source to the rare earth nitrate is 1:(0.1-1).

3. The preparation method according to claim 1, characterized in that, A rare earth gel is prepared by hydrothermal reaction at 160℃-200℃; and / or by hydrothermal reaction for 12h-24h; and / or by the inert gas atmosphere including at least one of argon and nitrogen; and / or by carbonization of the rare earth gel at 700℃-900℃; and / or by carbonization treatment of the rare earth gel for 1h-2h.

4. The preparation method according to claim 1, characterized in that, The carbonized support is used as the working electrode, and Ag / AgCl is used as the reference electrode; and / or, a pulse voltage of -0.5V to 1.2V is applied during electrochemical deposition; and / or, the electrolyte contains 2mol / L to 5mol / L potassium chloride.

5. The preparation method according to claim 1, characterized in that, The electrolyte contains an iron ion to cobalt ion molar ratio of (1-3):1; and / or, the electrolyte contains at least one of iron nitrate, iron sulfate, and iron chloride; and / or, the electrolyte contains at least one of cobalt sulfate, cobalt nitrate, and cobalt chloride.

6. The preparation method according to claim 1, characterized in that, The ethanol-water system has an ethanol volume fraction of 10%-70%; and / or the mesoporous template agent includes one of F127 and CTAB.

7. The preparation method according to claim 1, characterized in that, Rare earth catalysts are obtained by deposition on the surface of a composite support for 5-10 minutes in a mixed atmosphere of ethylene and hydrogen at 550℃-650℃, followed by reduction in a hydrogen atmosphere.

8. The preparation method according to claim 7, 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 0.1MPa-0.5MPa; and / or, after deposition on the surface of the composite carrier for 5min-10min, it is kept at an inert gas atmosphere of 800℃-850℃ for 1h-2h.

9. A rare earth catalyst prepared by the preparation method according to any one of claims 1 to 8.