A preparation method of a high-entropy alloy nano catalyst for growing carbon nanotubes

Abstract

The application discloses a preparation method of a high-entropy alloy nanoparticle catalyst for growing carbon nanotubes, which comprises a multi-element active metal component and a carrier; the oxide carrier is MgO, SiO2, Al2O3 and a composite oxide thereof; the active metal component is composed of four or more than four metal elements selected from Fe, Co, Ni, Cu, Mo, W, Mn, Zn and Ce; the molar ratio of each metal element is (1-5):1; the total mass of the active metal elements is 10-60% of the total mass of the carrier; the active metal and the carrier are synthesized into a gel through a sol-gel method, foamed into a porous material in an oven, calcined in an inert atmosphere at 600-900 DEG C, and then calcined in air at 300-700 DEG C, so as to obtain the high-entropy alloy nanoparticle catalyst for growing carbon nanotubes; the catalyst has the advantages of high yield, good quality and simple preparation process for growing carbon nanotubes.

Description

Technical Field

[0001] This invention relates to a method for preparing a high-entropy alloy nanocatalyst for growing carbon nanotubes. Background Technology

[0002] With the development of science and technology, traditional alloys can no longer meet the demand for high-performance materials in people's lives. Against this backdrop, Professor Ye Junwei and others broke through traditional alloying theories to design a high-entropy alloy, also known as a multi-component alloy (principal element number ≥ 5), and defined it as an alloy composed of five or more metallic elements in equimolar or near-equimolar ratios. In recent years, with the exploration of research on high-entropy alloys, its definition has become increasingly broad. It is initially defined as a novel alloy containing four or more constituent elements in equimolar or near-equimolar ratios, with no single element comprising more than 50% of the total composition. Compared to binary alloys, high-entropy alloys are composed of more components. In binary alloys, the two elements often exhibit a large immiscibility gap when forming more stable phase-separated materials or intermetallic compounds, which limits the continuous adjustment of the composition ratio and catalytic activity. Therefore, high-entropy alloys not only significantly regulate electronic and geometric structures but can also serve as a platform for constructing catalysts with excellent performance.

[0003] High-entropy alloys typically exhibit simple face-centered cubic (FCC), body-centered cubic (BCC), and hexagonal close-packed (HCP) crystal structures, with different atoms randomly occupying lattice positions to form a single-phase solid solution state. Their wide range of compositional modulation and inherently complex surfaces make it possible to obtain a near-continuously distributed adsorption energy curve. This means that we can potentially achieve optimal adsorption strength through multi-element alloying, thereby maximizing activity. As a novel alloy with a novel design concept, high-entropy alloys possess unique characteristics in many aspects that differ from traditional alloy materials, such as the thermodynamic high-entropy effect, the kinetic delayed diffusion effect, the lattice distortion effect of the crystal structure, and the cocktail effect. Among these, the high-entropy effect and the delayed diffusion effect enable the catalyst to maintain thermodynamic and kinetic stability, giving high-entropy alloys excellent high-temperature stability. They can still exhibit a single-phase solid solution state at high temperatures and remain relatively stable in harsh service environments (high temperature, corrosion, and high electrochemical potential). In the chemical vapor deposition (CVD) process for preparing single-walled carbon nanotubes, the reaction temperature needs to reach about 1000℃, and the catalyst for synthesizing carbon nanotubes needs to have high temperature stability. High-entropy alloy nanocatalysts have higher thermodynamic and kinetic stability than traditional alloys. Therefore, this study intends to use high-entropy alloy nanocatalysts to synthesize carbon nanotubes.

[0004] Carbon nanotubes (CNTs) are nanoscale tubular structures composed of only a single layer of graphene. They possess a unique coaxial hollow structure, excellent electrical conductivity, large specific surface area, pores suitable for electrolyte ion migration, and the ability to form nanoscale network structures through intertwining. They are ideal electrode materials for supercapacitors, especially high-power supercapacitors, offering greater economic benefits. However, due to limitations in high-yield carbon nanotube fabrication techniques, the electronic applications built with carbon nanotubes are currently limited to laboratory-level prototype devices. Structure determines properties, and fabrication determines the future. Therefore, to fully leverage the superior properties and leading role of carbon nanotubes in applications, controlled fabrication of carbon nanotubes is a crucial step. Since their discovery 30 years ago, dozens of fabrication techniques exist, including arc discharge, laser evaporation, and chemical vapor deposition (CVD). Among these, CVD is widely used due to its lower reaction temperature, easily controllable parameters, and ability to produce large quantities of discrete, high-quality carbon nanotubes. Here, we report a method using high-entropy alloy nanoparticles synthesized by the sol-gel method as catalysts, calcined under different process conditions, and grown carbon nanotubes by chemical vapor deposition (CVD). Compared with traditional methods, this method is lower in cost and simpler to operate. Only one program needs to be set up to achieve catalyst preparation and high-yield, high-quality, discretely distributed carbon nanotubes on the catalyst in a single CVD furnace. Summary of the Invention

[0005] The technical problem this invention aims to solve is to provide a high-entropy alloy nanocatalyst for carbon nanotube growth that is simple to fabricate and exhibits good high-temperature stability. Compared to traditional methods for preparing carbon nanotubes, this method has lower preparation costs, is simpler to operate, and can yield high-yield high-entropy alloy nanocatalysts with high temperature stability for carbon nanotube growth. A sol-gel with a support mass of 1g is used, with the mass of Fe metal fixed at 5-10wt% of the total support mass, and the molar ratio of each active metal being 1:1. A single-phase solid solution FeMoWCo / MgO high-entropy alloy nanocatalyst is obtained under inert atmosphere and air calcination conditions (as shown in the figure). Carbon nanotubes are then grown at a certain temperature (as shown in the figure), yielding carbon nanotubes with relatively uniform diameter. This method can synthesize single-walled and oligo-walled carbon nanotubes of approximately 1-4nm, as well as multi-walled carbon nanotubes of approximately 7-9nm, with fine diameter and high yield. This meets the requirements for high-quality and high-yield carbon nanotubes.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] This invention provides a high-entropy alloy nanoparticle catalyst for growing carbon nanotubes. The catalyst is composed of a metal active component and a support. The metal active component is a combination of four or more metal elements selected from Fe, Co, Ni, Cu, Mo, W, Mn, Zn, and Ce. The molar ratio of each metal element in the active metal is (1-5):1. The support is selected from MgO, Al2O3, SiO2, or their composite oxides. The total mass of the active metal elements is 10-60 wt% of the total mass of the support.

[0008] Furthermore, in the above technical solution, the active metal component includes Fe, Mo, W, and also one or more of Co, Ni, Cu, Mn, Zn, and Ce.

[0009] Furthermore, in the above technical solution, the molar mass of Fe, Mo, W, and Co is 5-10 wt% of the carrier, and the molar ratio of Fe, Mo, W, and Co is 1:1:1:1.

[0010] The invention also provides a method for preparing the above-mentioned high-entropy alloy nanoparticle catalyst, which consists of two parts: an active component and a support. The preparation steps are as follows:

[0011] (1) Dissolve the active multimetal components in water to obtain a mixed solvent;

[0012] (2) Add a carrier metal salt, select a suitable oxide carrier, and fix the mass of the carrier metal salt;

[0013] (3) Add a metal complexing agent, stir in a water bath to make a homogeneous solution, form a sol, and finally form a gel;

[0014] (4) Place the gel obtained in (3) into a 100°C oven and foam it to form a porous material.

[0015] (5) Grind the porous material obtained in (4) into powder and calcine it in an inert atmosphere at 600-900℃ for 2 hours;

[0016] (6)(5) After cooling to room temperature, place it in the air, heat it to 300-700℃ and calcine for 4 hours, then cool it to room temperature to obtain a high-entropy alloy nanoparticle catalyst for growing carbon nanotubes.

[0017] Furthermore, in the above technical solution, (3) the metal ion complexing agent ensures that the amount of the complexing agent is greater than or equal to the mass of the active metal component and the carrier. The metal complexing agent is one or more of the organic acids such as citric acid, oxalic acid, and tartaric acid. The amount of metal complexing agent added should satisfy the function of completely dispersing metal ions.

[0018] Furthermore, in the above technical solution, the temperature mentioned in (5) is 600-900℃, and the inert atmosphere is one or more of argon, helium, nitrogen, etc.

[0019] Furthermore, in the above technical solution, the temperature mentioned in (6) is 300 to 700°C. Different calcination temperatures can affect the particle size of the metal active components in the catalyst and the specific surface area of ​​the support.

[0020] This invention discloses a method for preparing high-entropy alloy nanocatalysts for synthesizing carbon nanotubes. The method involves mixing solutions of four or more metal salts and preparing high-entropy alloy nanoparticle catalysts via a sol-gel method, exhibiting excellent high-temperature stability. The high-entropy alloy nanoparticle catalyst remains in a single-phase solid solution state at high temperatures and maintains relative stability under harsh service environments (high temperature, corrosion, and high electrochemical potential). Its wide range of composition modulation and inherently complex surface provide the possibility of obtaining a near-continuously distributed adsorption energy curve. This means that we can potentially obtain optimized adsorption strength through multi-element alloying, thereby maximizing activity. The catalyst preparation and calcination process are simple, simplifying the carbon nanotube preparation process. It yields relatively uniform carbon nanotubes, capable of synthesizing single-walled and oligowalled carbon nanotubes of approximately 1-4 nm, as well as multi-walled carbon nanotubes of approximately 7-9 nm, with fine diameter and high yield. Attached Figure Description

[0021] Figure 1 TEM image of carbon nanotubes provided for this invention;

[0022] Figure 2 SEM images and diameter distribution diagrams of carbon nanotubes provided for this invention. Detailed Implementation

[0023] The present invention will be further described in detail below with reference to the embodiments. However, the specific scope of implementation is not limited to the examples given.

[0024] Example 1:

[0025] A method for preparing a high-entropy alloy nanoparticle catalyst is provided. The catalyst consists of two parts: an active component and a support. The preparation steps are as follows:

[0026] (1) Dissolution of metal salts: Dissolve 0.3607g of Fe(NO3)3·9H2O and 0.1564g of (NH4)6Mo7O in 50ml of water. 24 0.2276g (NH4) 10 H2(W2O7)6 and 0.2599g of four metal salts, Co(NO3)2·6H2O;

[0027] (2) Add 6.41g of the carrier metal salt magnesium nitrate;

[0028] (3) Add metal ion complexing agent, heat and stir in an 80°C water bath to make a homogeneous solution, then form a sol, and finally form a gel; weigh out the mass of the complexing agent citric acid to be greater than the total mass of the active metal salt and the carrier.

[0029] (4) The gel obtained in (3) is placed in a 100°C oven to foam and form a porous material;

[0030] (5) The porous material obtained in (4) was ground with an agate mortar to obtain a yellow powder, which was used to grow a high-entropy alloy nanocatalyst for carbon nanotubes. The nanocatalyst was placed in an inert atmosphere at 800°C for 2 hours and the molar ratio of active metal ions of the catalyst was 1:1:1:1.

[0031] (6) After (5) is cooled to room temperature, it is placed in air, heated to 500℃ and calcined for 4 hours, and then cooled to room temperature. The black powder sample obtained is the carbon nanotube product mixed with the catalyst. Carbon nanotubes with relatively uniform diameter are obtained, with fine diameter and high yield.

[0032] (7) Catalyst used for carbon nanotube growth yield testing:

[0033] The catalyst was used to grow carbon nanotubes in a reaction tube with an inner diameter of 48 mm. 0.2 g of catalyst was weighed and evenly spread in a quartz boat, then purged with Ar at 80 mL / min. -1 Purge the reaction tube at a flow rate of 0.5 h to remove all air, then purge at 5 °C for 0 min. -1 Heat to 500℃, at a flow rate of 80 mL / min -1 The catalyst was reduced with pure hydrogen for 2 hours; then the temperature was raised to 800℃, and the reaction gas was a mixture of CH4 and H2 (V). CH4 :V H2 =40:80), total flow rate is 120 mL / min -1 The reaction was carried out for 2 hours to grow carbon nanotubes. It was then allowed to cool naturally to room temperature under an Ar atmosphere. The yield of carbon nanotubes was calculated, expressed in g·g⁻¹. cat -1 ·h -1 Let's calculate it. The calculation formula is: m before m represents the catalyst mass before carbon nanotube growth. after The mass of the catalyst after carbon nanotube growth is denoted as t, and the reaction time for carbon nanotube growth is t. The yield of the catalyst for carbon nanotube growth in this technical scheme is shown in Table 1.

[0034] Example 2:

[0035] (1) Dissolution of metal salts: Dissolve 0.3607g of Fe(NO3)3·9H2O and 0.1564g of (NH4)6Mo7O in 50ml of water. 24 0.2276g (NH4) 10 Five metal salts: H2(W2O7)6, 0.2599g Co(NO3)2·6H2O, and 0.2157g Cu(NO3)2·6H2O;

[0036] (2) Same as in Example 1;

[0037] (3) Add metal ion complexing agent, stir in an 80°C water bath to make a homogeneous solution, then form a sol, and finally form a gel; weigh out the mass of the complexing agent citric acid to be greater than the total mass of the active metal salt and the carrier.

[0038] (4) Place the gel obtained in (3) into a 100°C oven and foam it to form a porous material.

[0039] (5) The porous material obtained in (4) is ground into powder and placed in an inert atmosphere at 800℃ for 2 hours to obtain a high-entropy alloy nanoparticle catalyst for growing carbon nanotubes. The resulting catalyst has a metal ion molar ratio of 1:1:1:1:1;

[0040] (6) After (5) is cooled to room temperature, it is placed in air, heated to 500℃ and calcined for 4 hours, and then cooled to room temperature. The black powder sample obtained is the carbon nanotube product mixed with the catalyst. Carbon nanotubes with relatively uniform diameter are obtained, with fine diameter and high yield.

[0041] (7) The catalyst was used to grow carbon nanotubes. The yield test was the same as in Example 1. The yield of carbon nanotubes grown by the catalyst is shown in Table 1. The yield was relatively high.

[0042] Example 3:

[0043] (1) Dissolution of metal salts: Dissolve 0.3607g of Fe(NO3)3·9H2O and 0.1564g of (NH4)6Mo7O in 50ml of water. 24 0.2276g (NH4) 10 Five metal salts: H2(W2O7)6, 0.2599g Co(NO3)2·6H2O, and 0.2597g Ni(NO3)2·6H2O;

[0044] (2) Same as in Example 1;

[0045] (3) Add metal ion complexing agent, stir in an 80°C water bath to make a homogeneous solution, then form a sol, and finally form a gel; weigh out the mass of the complexing agent citric acid to be greater than the total mass of the active metal salt and the carrier.

[0046] (4) Place the gel obtained in (3) into a 100°C oven and foam it to form a porous material.

[0047] (5) The porous material obtained in (4) is ground into powder and placed in an inert atmosphere at 800℃ for 2 hours to obtain a high-entropy alloy nanoparticle catalyst for growing carbon nanotubes. The resulting catalyst has a metal ion molar ratio of 1:1:1:1:1;

[0048] (6) After (5) is cooled to room temperature, it is placed in air, heated to 500℃ and calcined for 4 hours, and then cooled to room temperature. The black powder sample obtained is the carbon nanotube product mixed with the catalyst. Carbon nanotubes with relatively uniform diameter are obtained, with fine diameter and high yield.

[0049] (7) The catalyst was used to grow carbon nanotubes. The yield test was the same as in Example 1. The yield of carbon nanotubes grown by the catalyst is shown in Table 1. The yield was relatively high.

[0050] Example 4:

[0051] (1) Dissolution of metal salts: Dissolve 0.3607g of Fe(NO3)3·9H2O and 0.1564g of (NH4)6Mo7O in 50ml of water. 24 0.2276g (NH4) 10 Four metal salts: H2(W2O7)6 and 0.2597g Ni(NO3)2·6H2O;

[0052] (2) Same as in Example 1;

[0053] (3) Add metal ion complexing agent, stir in an 80°C water bath to make a homogeneous solution, then form a sol, and finally form a gel; weigh out the mass of the complexing agent citric acid to be greater than the total mass of the active metal salt and the carrier.

[0054] (4) Place the gel obtained in (3) into a 100°C oven and foam it to form a porous material.

[0055] (5) The porous material obtained in (4) is ground into powder and placed in an inert atmosphere at 800℃ for 2 hours to obtain a high-entropy alloy nanoparticle catalyst for growing carbon nanotubes. The resulting catalyst has a metal ion molar ratio of 1:1:1:1;

[0056] (6) After (5) is cooled to room temperature, it is placed in air, heated to 500℃ and calcined for 4 hours, and then cooled to room temperature. The black powder sample obtained is the carbon nanotube product mixed with the catalyst. Carbon nanotubes with relatively uniform diameter are obtained, with fine diameter and high yield.

[0057] (7) The catalyst was used to grow carbon nanotubes. The yield test was the same as in Example 1. The yield of carbon nanotubes grown by the catalyst is shown in Table 1. The yield was relatively high.

[0058] Comparative Example 1:

[0059] (1) Dissolution of metal salts: Dissolve 0.3607g of Fe(NO3)3·9H2O and 0.1564g of (NH4)6Mo7O in 50ml of water. 24 0.2276g (NH4) 10 Three metal salts of H2(W2O7)6;

[0060] (2) Same as in Example 1;

[0061] (3) Add metal ion complexing agent, stir in an 80°C water bath to make a homogeneous solution, then form a sol, and finally form a gel; weigh out the mass of the complexing agent citric acid to be greater than the total mass of the active metal salt and the carrier.

[0062] (4) Place the gel obtained in (3) into a 100°C oven and foam it to form a porous material.

[0063] (5) The porous material obtained in (4) is ground into powder and placed in an inert atmosphere at 800℃ for 2 hours to obtain a high-entropy alloy nanoparticle catalyst for growing carbon nanotubes. The resulting catalyst has a metal ion molar ratio of 1:1:1:1;

[0064] (6) After (5) is cooled to room temperature, it is placed in air, heated to 500°C and calcined for 4 hours, and then cooled to room temperature. The black powder sample obtained is the carbon nanotube product mixed with the catalyst.

[0065] (7) The catalyst was used to grow carbon nanotubes. The yield test was the same as in Example 1. The yield of carbon nanotubes grown by the catalyst is shown in Table 1.

[0066] Comparative Example 2:

[0067] (1) Dissolution of metal salts: Dissolve 0.3607g of Fe(NO3)3·9H2O and 0.1564g of (NH4)6Mo7O in 50ml of water. 24 0.2276g (NH4) 10 H2(W2O7)6 and 0.3866g of four metal salts, LaN3O9·6H2O;

[0068] (2) Same as in Example 1;

[0069] (3) Add metal ion complexing agent, stir in an 80°C water bath to make a homogeneous solution, then form a sol, and finally form a gel; weigh out the mass of the complexing agent citric acid to be greater than the total mass of the active metal salt and the carrier.

[0070] (4) Place the gel obtained in (3) into a 100°C oven and foam it to form a porous material.

[0071] (5) The porous material obtained in (4) is ground into powder and placed in an inert atmosphere at 800℃ for 2 hours to obtain a high-entropy alloy nanoparticle catalyst for growing carbon nanotubes. The resulting catalyst has a metal ion molar ratio of 1:1:1:1;

[0072] (6) After (5) is cooled to room temperature, it is placed in air, heated to 500°C and calcined for 4 hours, and then cooled to room temperature. The black powder sample obtained is the carbon nanotube product mixed with the catalyst.

[0073] (7) The catalyst was used to grow carbon nanotubes. The yield test was the same as in Example 1. The yield of carbon nanotubes grown by the catalyst is shown in Table 1.

[0074] Table 1: Yield of carbon nanotubes grown at 1000℃ in Examples 1-4

[0075]

[0076] As shown in Table 1, the high-entropy alloy nanoparticle catalyst exhibits high carbon nanotube yield, good activity, and high-temperature stability, which is beneficial for carbon nanotube growth. The catalysts in Examples 1-4 all demonstrated good activity and high-temperature stability, with the catalyst in Example 1 producing the highest yield of carbon nanotubes at 5.4 g·g⁻¹. cat -1 ·h -1 .

[0077] from Figure 1 and Figure 2 It is evident that carbon nanotubes synthesized using high-entropy alloy nanoparticle catalysts exhibit relatively uniform diameters. They can synthesize single-walled and oligo-walled carbon nanotubes of 1-4 nm, as well as multi-walled carbon nanotubes with finer diameters, resulting in both fine diameters and high yields.

Claims

1. A method for preparing a high-entropy alloy nanoparticle catalyst for growing carbon nanotubes, characterized in that, The catalyst is composed of a metal active component and a support. The molar ratio of any two metal elements in the metal active component is (1-5):

1. The support is selected from MgO, Al2O3 or their composite oxides. The total mass of the metal elements in the metal active component is 10-60 wt% of the total mass of the support. The active metal components include Fe, Mo and W, and also one or more of Co, Ni, Cu, Mn, Zn and Ce; The method for preparing the catalyst includes the following steps: (1) Dissolve the active multimetal components in water to obtain a mixed solution; (2) Add metal salts to metal oxide carriers; (3) Add a metal complexing agent, stir in a water bath to make a homogeneous solution, form a sol, and finally form a gel; (4) Place the gel obtained in (3) into an oven at 50-150℃ and foam it to form a porous material. (5) Grind the porous material obtained in (4) into powder and calcine it in an inert atmosphere at 600-900℃ for 1-10 hours; (6) After the material obtained in (5) is cooled to room temperature, it is placed in air and heated to 300-700℃ for 1-10 hours. Then it is cooled to room temperature to obtain a high-entropy alloy nanoparticle catalyst for growing carbon nanotubes.

2. The preparation method according to claim 1, characterized in that, In step (3), the metal complexing agent is one or more of citric acid, oxalic acid, and tartaric acid, and the amount of metal complexing agent added should be sufficient to completely disperse the metal ions.

3. The preparation method according to claim 1, characterized in that, The inert atmosphere is one or more of argon, helium, and nitrogen.

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