A method for preparing a catalyst and a method for preparing ultrafine array carbon nanotubes

Abstract

The present invention belongs to the fields of advanced carbon material preparation technology and industrial catalysis technology, and specifically is a method for preparing a catalyst, wherein a carrier is immersed in a mixed solution consisting of an active metal salt, an auxiliary metal salt and a complexing agent, and the mixture is dried after stirring, and then calcined to obtain a catalyst, which can conveniently produce the catalyst required for preparing carbon nanotubes. At the same time, the present invention also provides a method for preparing ultrafine array carbon nanotubes, which can improve the yield and quality of the prepared carbon nanotubes and obtain array carbon nanotubes with higher commercial value.

Description

Technical Field

[0001] The invention belongs to the fields of advanced carbon material preparation technology and industrial catalysis technology, and specifically relates to a method for preparing a catalyst and a method for preparing ultrafine array carbon nanotubes. Background Art

[0002] Carbon nanotubes are a new type of multifunctional nanomaterial with a one-dimensional tubular structure. Microscopically, carbon nanotubes are formed by curling graphite sheets and have a single-layer or multi-layer structure. Their special structure exhibits good electrical conductivity, thermal conductivity, extremely high tensile strength and stable chemical properties.

[0003] Carbon nanotubes have very broad application prospects in many fields such as catalysis, energy storage materials, composite materials and microelectronic devices. Taking advantage of the high specific surface area, excellent electron transmission performance and extremely high aspect ratio of ultra-fine carbon nanotubes, it can be used as a battery electrode material to effectively form a conductive network, greatly improve the electron transmission efficiency of the electrode, and provide new development space for the field of chemical energy storage. Specifically, it has large battery capacity and long cycle life, which is suitable for high-end digital batteries and new energy vehicle batteries. Carbon nanotubes have achieved widespread commercial applications in battery conductive additives.

[0004] At present, there are many methods for preparing carbon nanotubes, such as chemical vapor deposition (CVD), arc discharge, laser evaporation, and thermal decomposition polymerization. Different methods are suitable for different scenarios. Among them, CVD is the most widely used method. It has the characteristics of easy availability of raw materials, low cost, strong controllability, and high yield. It is suitable for the development and large-scale production of carbon nanotubes and is the main method for preparing carbon nanotubes.

[0005] Carbon nanotubes are classified into single-walled carbon nanotubes, few-walled carbon nanotubes and multi-walled carbon nanotubes according to the number of tube walls. According to the morphology of carbon nanotubes, they are divided into wound carbon nanotubes and array carbon nanotubes, referred to as wound tubes and array tubes. It is generally believed that array tubes with neatly arranged carbon nanotubes have better conductivity and higher commercial value. Therefore, the development of large-scale production of array tubes is very necessary. Summary of the invention

[0006] In order to solve the above technical problems, the present invention provides a method for preparing a carbon nanotube catalyst, which can conveniently produce the catalyst required for preparing carbon nanotubes. At the same time, the present invention also provides a method for preparing ultrafine array carbon nanotubes, which can improve the yield and quality of the prepared carbon nanotubes and obtain array carbon nanotubes with higher commercial value.

[0007] The technical scheme is as follows: a method for preparing a carbon nanotube catalyst, characterized in that the carrier is immersed in a mixed solution consisting of an active metal salt, an auxiliary metal salt and a complexing agent, and then dried after stirring, and then calcined to obtain the catalyst.

[0008] It is further characterized in that the active metal salt is one or more of iron nitrate, cobalt nitrate, and nickel nitrate; The auxiliary metal salt is one or more of aluminum nitrate, magnesium nitrate, manganese nitrate, ammonium metavanadate, chromium acetate, calcium acetate, zinc acetate, ammonium molybdate, lanthanum nitrate, cerium nitrate, and cerium ammonium nitrate; The complexing agent is one or more of citric acid, ammonium citrate, EDTA, glycine, alanine, serine, threonine, glutamine, and asparagine; The carrier is one of alumina, diaspore, pseudo-boehmite, magnesia, silica, and vermiculite; Based on the carrier mass, the total loading mass of active metal elements and auxiliary metal elements accounts for 0.5% to 40%, and the mass ratio of active metal salt to auxiliary metal salt is 1:(0.00-0.10). The total concentration of metal salts in the solution is 1 to 800 g / L.

[0009] Drying process: Use an oven to evaporate the water at normal pressure, and the oven temperature range is 60℃~120℃; The pressurization operation is performed before drying, including but not limited to first pressurizing the impregnation process in a hydrothermal autoclave and then taking out the carrier to dry; Drying operation is performed while pressurizing, including but not limited to immersing in a pressure cooker and then evaporating water in a high-temperature pressure cooker; Calcination process: The dried product is placed in a porcelain boat and calcined in a muffle furnace at 450-650°C for 2-8h; The calcined product is usually screened.

[0010] A method for preparing ultrafine array carbon nanotubes, characterized in that the catalyst is weighed and placed in a quartz boat, the quartz boat is placed in a moving bed, nitrogen is passed into the moving bed to raise the temperature to the reaction temperature; nitrogen, hydrogen and carbon source gas are passed through the moving bed to grow carbon nanotubes on the surface of the catalyst by a CVD method; and the catalyst is taken out after the temperature is cooled to room temperature through nitrogen.

[0011] It is further characterized in that the carbon source gas is one or more of methane, ethane, propane, ethylene, propylene, acetylene, butane, butene, butyne, and carbon dioxide; The reaction temperature for growing carbon nanotubes is 600-900° C., and the flow ratio of the carbon source gas to the nitrogen gas and the hydrogen gas is 1:(0-5):(0-0.4).

[0012] After adopting the present invention, the alumina carrier is treated by the impregnation method, the catalyst is easy to prepare, the output is large, it is suitable for large-scale production, the cost is low, and the metal loading is relatively low. The catalyst is then used to produce carbon nanotubes, and finally ultrafine array carbon nanotubes are obtained, which have high commercial value. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is a high-magnification TEM image of Example 1; Figure 2 This is the SEM high magnification image of Example 2; Figure 3 This is a low-magnification SEM image of Example 2. DETAILED DESCRIPTION

[0014] A method for preparing a carbon nanotube catalyst comprises the following steps: immersing a carrier in a mixed solution consisting of an active metal salt, an auxiliary metal salt and a complexing agent and stirring the mixture, wherein the carrier is one of aluminum oxide, diaspore, pseudo-boehmite, magnesium oxide, silicon dioxide and vermiculite; the active metal salt is one or more of iron nitrate, cobalt nitrate and nickel nitrate; the auxiliary metal salt is one or more of aluminum nitrate, magnesium nitrate, manganese nitrate, ammonium metavanadate, chromium acetate, calcium acetate, zinc acetate, ammonium molybdate, lanthanum nitrate, cerium nitrate and ammonium cerium nitrate; and the complexing agent is one or more of citric acid, ammonium citrate, EDTA, glycine, alanine, serine, threonine, glutamine and asparagine.

[0015] Assume that the mass of active metal element is A, the mass of auxiliary metal element is B, and the mass of carrier metal element is C, all in grams or kilograms; (A+B) / C is 0.5%~40%, A:B is 1:(0.00-0.10), and the total concentration of metal salt in the mixed solution is 1~800g / L.

[0016] After the stirring is completed, it is dried. The drying process is usually carried out by evaporating the water at normal pressure in an oven, and the oven temperature range is 60°C to 120°C. In addition, it can be pressurized and then dried, including but not limited to first pressurizing the impregnation process in a hydrothermal kettle, and then taking out the carrier to dry; in addition, it can be dried while pressurizing it, including but not limited to immersing it in a pressure cooker, and then evaporating the water in a high-temperature pressure cooker, preferably evaporating it in an oven at 80°C-100°C.

[0017] After drying, the catalyst is calcined. The calcination process is as follows: the dried product is placed in a porcelain boat and calcined in a muffle furnace at a temperature of 450-650°C for 2-8h, preferably 500°C-600°C for 4-6h. The calcined product is usually sieved, preferably using the portion larger than 120 mesh.

[0018] A method for preparing ultrafine array carbon nanotubes comprises the following steps: weighing a prepared catalyst and putting it into a quartz boat, placing the quartz boat into a moving bed, introducing nitrogen into the moving bed to raise the temperature to a reaction temperature; introducing nitrogen, hydrogen and a carbon source gas, and using a CVD method to grow carbon nanotubes on the surface of the catalyst; and introducing nitrogen to cool the temperature to room temperature before taking out the catalyst.

[0019] The carbon source gas is one or more of methane, ethane, propane, ethylene, propylene, acetylene, butane, butene, butyne, and carbon dioxide; the reaction temperature for growing carbon nanotubes is 600-900°C, and the flow ratio of the carbon source gas to nitrogen and hydrogen is 1:(0-5):(0-0.4).

[0020] The following is a detailed description using three specific embodiments.

[0021] Example 1 First, 19.7 g of ferric nitrate nonahydrate and 2.0 g of anhydrous citric acid were mixed and dissolved in 50 ml of deionized water; 0.43 g of ammonium heptamolybdate tetrahydrate was dissolved in 20 ml of deionized water and then added to prepare a solution; 19.9 g of aluminum oxide was added and stirred at 600 rpm using a magnetic stirrer for 15 min.

[0022] The solid-liquid mixture was poured into a porcelain boat, placed in an oven at 85°C for 18 hours to evaporate to dryness, and calcined in a muffle furnace at 500°C for 4 hours. After cooling, the catalyst FeMo-t1 was obtained. It was sieved before use, preferably the part with a mesh size larger than 120.

[0023] 1g of catalyst FeMo-t1 was placed in a 660℃ fluidized bed, and 12L / min hydrogen, 40L / min propylene, and 100L / min nitrogen were introduced. After 1h of reaction, the temperature was lowered to room temperature, and the carbon tube was taken out and weighed to 10g. The conversion rate was 15.6%. After testing, the multi-point BET specific surface area was 198m 2 / g. The average diameter is 8.5nm, which is ultra-fine carbon nanotubes, such as Figure 1 shown.

[0024] Comparative Example 1 The anhydrous citric acid in Example 1 was omitted, and the rest remained unchanged. The carbon tube was taken out and weighed to be 2.7 g, and the conversion rate was 4.2%.

[0025] Example 2 First, mix and dissolve 11.4 g of ferric nitrate nonahydrate, 18.4 g of cobalt nitrate hexahydrate and 3.0 g of anhydrous citric acid in 50 ml of deionized water; dissolve 0.62 g of ammonium heptamolybdate tetrahydrate in 20 ml of deionized water and then add it to form a solution FeCoMo-t2; add 9.6 g of alumina and stir at 600 rpm using a magnetic stirrer for 15 minutes.

[0026] The solid-liquid mixture was poured into a porcelain boat, left to stand in an oven at 85°C for 18 hours to evaporate to dryness, and calcined in a muffle furnace at 500°C for 4 hours. After cooling, the catalyst FeCoMo-t2 was obtained. It was sieved before use, preferably the part with a mesh size larger than 120.

[0027] 1g of FeCoMo-t2 catalyst was placed in a 660℃ fluidized bed, and 24L / min hydrogen and 150L / min propane were introduced. After 1h of reaction, the temperature was cooled to room temperature, and the carbon tube was taken out and weighed to be 12.7g, with a conversion rate of 8.7%. After testing, the multi-point BET specific surface area was 184m 2 / g. The average diameter is 9.9nm, which is an ultra-fine carbon nanotube. Figure 2 and Figure 3 . Comparative Example 2 The cobalt nitrate hexahydrate in Example 2 was replaced by nickel nitrate hexahydrate, and the rest remained unchanged. The carbon tube was taken out and weighed to be 6.9 g, and the conversion rate was 4.4%.

[0028] Example 3 First, mix and dissolve 7.7g of ferric nitrate nonahydrate, 12.5g of cobalt nitrate hexahydrate and 2.0g of anhydrous citric acid in 50ml of deionized water; dissolve 0.42g of ammonium heptamolybdate tetrahydrate in 20ml of deionized water and then add it to form a solution FeCoMo-t3; add 19.4g of alumina and stir at 600rpm using a magnetic stirrer for 15min.

[0029] The solid-liquid mixture was poured into a porcelain boat, left to stand at 85°C for 18 hours to evaporate to dryness, and calcined in a muffle furnace at 500°C for 4 hours. After cooling, the catalyst FeCoMo-t3 was obtained. It was sieved before use, preferably the part with a mesh size larger than 120.

[0030] 2g of FeCoMo-t3 catalyst was placed in a 660℃ fluidized bed, and 24L / min hydrogen and 150L / min propane were introduced. After 1h of reaction, the temperature was lowered to room temperature, and the carbon tube was taken out and weighed to 21.8g, with a conversion rate of 15.0%. After testing, the multi-point BET specific surface area was 200m 2 / g. The average tube diameter is 9.4nm, which is an ultra-fine carbon nanotube.

[0031] The carbon nanotube catalyst is quickly prepared by refining the metal particles with a complexing agent and crystallizing them on the surface of alumina during evaporation.

[0032] According to Example 1 and Comparative Example 1, the diameter of carbon nanotubes prepared with iron as the active metal is thinner, the propylene conversion rate catalyzed by the catalyst is higher, and the carbon nanotube rate is significantly improved after the addition of citric acid.

[0033] By using an iron-cobalt bimetallic combination, the metal loading on the surface of alumina is increased, thereby increasing the carbon nanotube rate.

[0034] According to Example 2 and Comparative Example 2, the catalytic effect of bimetallic iron-cobalt as active metal is better than that of monometallic iron or bimetallic iron-nickel. The catalyst has a good catalytic effect on propane, and the carbon tube rate and conversion rate increase with the increase of loading.

[0035] According to Example 3, by appropriately increasing the cobalt content, appropriately reducing the active metal loading rate and increasing the amount of catalyst, the performance and cost of the carbon tubes are improved, and a larger specific surface area and conversion rate are obtained.

[0036] According to the SEM images ( Figure 2 and Figure 3 ), it can be seen that the carbon nanotubes are arranged in an array, and the growth direction is highly consistent. In the macroscopic state, it is observed to be a strip with a diameter of 0.4-1mm and a length of varying lengths. In the microscopic state, the surface is shaped like waves. The carbon nanotubes are in good growth state and have a high distribution density. It is a unique array of carbon nanotubes.

[0037] The present invention adopts an impregnation method to prepare a carbon nanotube catalyst, which has the advantages of simple steps, easy availability of raw materials, high yield, low cost and is suitable for large-scale production.

[0038] The present invention synthesizes an ultrafine carbon nanotube by using a CVD method in a moving bed and using a catalyst loaded with an active metal to produce the carbon nanotube. TEM shows that the diameter of the prepared carbon nanotube is less than 10nm, belonging to an ultrafine carbon nanotube. At the same time, SEM shows that this type of carbon nanotube is an array carbon nanotube, which has a high growth rate and good commercial application prospects.

Claims

1. A method for preparing a carbon nanotube catalyst, characterized in that: The carrier is immersed in a mixed solution consisting of an active metal salt, an auxiliary metal salt and a complexing agent, and then dried after stirring, and then calcined to obtain a catalyst.

2. The method for preparing a carbon nanotube catalyst according to claim 1, characterized in that: The active metal salt is one or more of ferric nitrate, cobalt nitrate and nickel nitrate; the auxiliary metal salt is one or more of aluminum nitrate, magnesium nitrate, manganese nitrate, ammonium metavanadate, chromium acetate, calcium acetate, zinc acetate, ammonium molybdate, lanthanum nitrate, cerium nitrate and ammonium cerium nitrate; the complexing agent is one or more of citric acid, ammonium citrate, EDTA, glycine, alanine, serine, threonine, glutamine and asparagine; the carrier is one of alumina, diaspore, pseudo-boehmite, magnesium oxide, silicon dioxide and vermiculite.

3. The method for preparing a carbon nanotube catalyst according to claim 1, characterized in that: Based on the carrier mass, the total loading mass of active metal elements and auxiliary metal elements accounts for 0.5% to 40%, the mass ratio of active metal salt to auxiliary metal salt is 1:(0.00-0.10), and the total concentration of metal salt in the solution is 1 to 800 g / L.

4. The method for preparing a carbon nanotube catalyst according to claim 1, characterized in that: Drying process: Use an oven to evaporate the water at normal pressure, and the oven temperature range is 60℃~120℃.

5. The method for preparing a carbon nanotube catalyst according to claim 1, characterized in that: The pressurization operation is performed before drying, including but not limited to first pressurizing the impregnation process in a hydrothermal kettle, and then taking out the carrier to dry.

6. The method for preparing a carbon nanotube catalyst according to claim 1, characterized in that: The drying operation is performed while pressurizing, including but not limited to immersing in a pressure cooker and then evaporating the water in a high-temperature pressure cooker.

7. The method for preparing a carbon nanotube catalyst according to claim 1, characterized in that: Calcination process: The dried product is placed in a porcelain boat and calcined in a muffle furnace at a temperature of 450-650°C for 2-8 hours. The calcined product is sieved.

8. A method for preparing ultrafine array carbon nanotubes, characterized in that: The catalyst prepared in claim 1 is weighed and placed in a quartz boat, the quartz boat is placed in a moving bed, nitrogen is introduced into the moving bed to raise the temperature to the reaction temperature; nitrogen, hydrogen and carbon source gas are introduced to grow carbon nanotubes on the surface of the catalyst by CVD method; the temperature is lowered to room temperature after nitrogen is introduced and then taken out.

9. The method for preparing ultrafine array carbon nanotubes according to claim 8, characterized in that: The carbon source gas is one or more of methane, ethane, propane, ethylene, propylene, acetylene, butane, butene, butyne, and carbon dioxide.

10. The method for preparing ultrafine array carbon nanotubes according to claim 8, characterized in that: The reaction temperature for growing carbon nanotubes is 600-900° C., and the flow ratio of the carbon source gas to the nitrogen gas and the hydrogen gas is 1:(0-5):(0-0.4).

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