Catalyst taking artificial hydrotalcite as carrier, preparation method of catalyst, array type carbon nanotube and preparation method of array type carbon nanotube

Abstract

The invention provides a catalyst taking artificial hydrotalcite as a carrier, a preparation method of the catalyst, an array type carbon nanotube and a preparation method of the array type carbon nanotube, and relates to the technical field of the array type carbon nanotube. In the preparation method of the catalyst, the artificial hydrotalcite is adopted as the carrier, and catalytic metal is loaded on the surface layer of the artificial hydrotalcite; the obtained catalyst is a uniform sheet-shaped hexagon, the catalyst taking artificial hydrotalcite as a carrier is taken as a substrate, and the array type carbon nanotube which has BET capable of being regulated and controlled in a range of 170-370m < 2 > / g, is easy to purify and has high magnification is obtained through a substrate method; according to the method, the loading process and the CVD process are regulated and controlled, and the two processes cooperate with each other to control the thickness of the array, so that the BET of the product is accurately controlled.

Description

Technical Field

[0001] The present invention relates to the technical field of nanomaterials and their preparation, specifically to the technical field of array-type carbon nanotubes, and particularly to a catalyst supported by artificial hydrotalcite, its preparation method, array-type carbon nanotubes, and their preparation methods. Background Art

[0002] As the most representative one-dimensional nanomaterial, carbon nanotubes have many excellent mechanical, thermal, electrical, and chemical properties, and show broad application prospects in many fields such as electronic devices, composite materials, sensors, and catalyst carriers. Carbon nanotubes can be divided into agglomerated carbon nanotubes and array-type carbon nanotubes according to their microscopic morphology. Compared with agglomerated carbon nanotubes, array-type carbon nanotubes have a larger aspect ratio, more consistent orientation, and higher purity, which is conducive to exerting their excellent properties.

[0003] The BET of carbon nanotubes is an important performance index of carbon nanotubes, and the size of BET has a crucial impact on the dispersion and use at the application end. For example, the most widespread application of commercial carbon nanotubes is as a conductive agent in lithium batteries. Generally, carbon nanotubes are dispersed in a solvent to form a slurry for customers to use. In the pulping process, the BET of carbon nanotubes affects the maximum solid content, viscosity, and conductivity of the slurry. Different customers have different requirements for the slurry. Developing a carbon nanotube with controllable BET to meet the diverse needs of customers is a technical challenge in this field.

[0004] Hydrotalcite is a layered double hydroxide metal hydroxide, and its classical structure is that nanoscale two-dimensional lamellae are longitudinally arranged in an orderly manner to form a three-dimensional crystal structure, and the metal elements in its lamellae are mainly magnesium and aluminum. Due to its special structure and physical and chemical properties, such as microporous structure, thermal stability, adsorption performance, catalytic performance, etc., hydrotalcite has a wide range of applications in many fields such as catalysts and catalyst carriers.

[0005] CN109665512A discloses a preparation method of multi-walled carbon nanotubes, specifically discloses a method for preparing a hydrotalcite-like catalyst and carbon nanotubes by a one-step method, in which a mixed salt solution containing active component and carrier phase components is mixed with an alkaline solution containing an alkaline precipitant under stirring and then subjected to relevant reactions, filtered and washed, and the obtained solid is freeze-dried to obtain the catalyst; wherein, the catalyst is composed of a composite oxide of the active component and the carrier phase component, and the content of the active component is 10-20 wt%; the active component is at least two of Fe, Co, Ni, and Mo, and the carrier phase component is composed of Mg and Al. However, in this technical solution, the proportion of the active metal in the catalyst is relatively low. When the active metal is on the high side, the catalyst cannot maintain a complete flaky structure, thereby affecting the array morphology and even the rate performance of the carbon nanotubes, and it is also impossible to achieve the regulation of BET.

[0006] In summary, it is necessary to develop a new type of catalyst with artificial hydrotalcite as the carrier and its preparation method for preparing array-type carbon nanotubes with controllable BET, easy purification, and high magnification. SUMMARY OF THE INVENTION

[0007] To meet the customer's demand for product differentiation, the present invention provides a catalyst with artificial hydrotalcite as the carrier and its preparation method, an array-type carbon nanotube and its preparation method. In the preparation method of the catalyst, artificial hydrotalcite is used as the carrier, and the catalytic metal is loaded on the surface layer of the artificial hydrotalcite. The obtained catalyst is a uniform flaky hexagon. Using the catalyst with artificial hydrotalcite as the carrier as the substrate, the present invention obtains array-type carbon nanotubes with BET that can be regulated in the range of 170 - 370 m 2 / g, easy to purify, and high magnification through the substrate method; the present invention realizes the control of the thickness of the array by regulating the loading process and the CVD process, and the two-step process cooperates with each other to precisely control the BET of the product.

[0008] To achieve this purpose, the present invention adopts the following technical solutions:

[0009] One of the purposes of the present invention is to provide a preparation method of a catalyst with artificial hydrotalcite as the carrier, and the preparation method includes the following steps:

[0010] (1) Prepare a magnesium-aluminum salt solution by mixing soluble aluminum salt, soluble magnesium salt, urea, and water, control the molar ratio of magnesium to aluminum in the magnesium-aluminum salt solution to be 3:1, and successively carry out hydrothermal reaction and the first solid-liquid separation to obtain a Mg / Al LDH carrier;

[0011] (2) Prepare a suspension by mixing water and the Mg / Al LDH carrier obtained in step (1), and simultaneously add an alkali solution and a metal salt solution for metal precipitation adsorption, and successively carry out the second solid-liquid separation and calcination to obtain a catalyst with artificial hydrotalcite as the carrier;

[0012] Among them, the metal salt solution in step (2) includes a catalytic metal, and the molar ratio of the catalytic metal in the catalyst with artificial hydrotalcite as the carrier to all metals is 8.67 - 45.43%.

[0013] The preparation method of the present invention uses artificial hydrotalcite as the carrier, and this carrier has the following advantages: 1. The perfect lamellar structure can provide a better growth space for carbon nanotubes, reduce the steric hindrance during the carbon nanotube production process, and provide the possibility for the growth of high-magnification carbon nanotubes; 2. The surface flatness of the carrier is relatively high, which is conducive to the uniform loading of metals; 3. The elemental composition is relatively simple, and the treated carrier only contains two metals, Mg and Al, which is easy to purify by pickling; these advantages enable the grown carbon nanotubes to have the advantages of high magnification, easy purification, and maintaining the array morphology.

[0014] In the present invention, Mg and Al precursors are used to synthesize artificial hydrotalcite (binary layered double hydroxide), and its most typical chemical formula is Mg6Al2(OH) 16 CO3·4H2O; the microscopic morphology of the hydrotalcite is planar. By using the precipitation loading method, the impregnation loading method, and the spray drying method, catalytically active metals and promoter metals are loaded on the surface layer of the artificial hydrotalcite, and then calcined by programmed temperature rise. After the calcination reaction, the molar ratio of the sum of the moles of the catalytically active metals and the promoter metals to the total moles of all metals in the catalyst is 8.67-45.43%, such as 8.67%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45% or 45.43%, etc., but not limited to the listed values, and other unlisted values within the above value range are equally applicable.

[0015] It should be noted that in the preparation method of the present invention, for the metal precipitation adsorption, the alkali solution and the metal salt solution are required to be added simultaneously, and preferably added dropwise, which can ensure that the pH of the system is basically constant and near neutral, and the dropwise addition can ensure that the alkali solution and the metal salt solution react fully, and the reaction rate will not be too fast, ensuring that the catalytic metal can be uniformly and fully loaded on the surface of the carrier.

[0016] As a preferred technical solution of the present invention, the soluble aluminum salt in step (1) includes any one or a combination of at least two of aluminum nitrate, aluminum sulfate or aluminum chloride.

[0017] Preferably, the soluble magnesium salt in step (1) includes any one or a combination of at least two of magnesium nitrate, magnesium sulfate or magnesium chloride.

[0018] As a preferred technical solution of the present invention, the hydrothermal reaction in step (1) is carried out in a water bath, the temperature of the hydrothermal reaction is 90-100°C, such as 90°C, 91°C, 92°C, 93°C, 94°C, 95°C, 96°C, 97°C, 98°C, 99°C or 100°C, etc., and the time of the hydrothermal reaction is 20-30h, such as 20h, 21h, 22h, 23h, 24h, 25h, 26h, 27h, 28h, 29h or 30h, etc., but not limited to the listed values, and other unlisted values within the above value range are equally applicable.

[0019] Preferably, the Mg / Al LDH carrier in step (1) is flaky hexagonal.

[0020] As a preferred technical solution of the present invention, the solid content of the suspension in step (2) is 20-25wt%, such as 20wt%, 21wt%, 22wt%, 23wt%, 24wt% or 25wt%, etc., but not limited to the listed values, and other unlisted values within the above value range are equally applicable.

[0021] Preferably, the base in the base solution in step (2) includes ammonium carbonate and / or ammonium bicarbonate.

[0022] As a preferred technical solution of the present invention, the catalytic metal in step (2) includes a catalytically active metal and a promoter metal.

[0023] Preferably, the catalytically active metal includes Fe and / or Co.

[0024] Preferably, the promoter metal includes Mo.

[0025] As a preferred technical solution of the present invention, the second solid-liquid separation in step (2) includes any one of precipitation filtration, rotary evaporation or spray drying.

[0026] Preferably, the temperature of the rotary evaporation is 70 - 90 °C, such as 70 °C, 71 °C, 73 °C, 75 °C, 77 °C, 80 °C, 82 °C, 85 °C, 88 °C or 90 °C, etc., but not limited to the listed values, and other unlisted values within the above numerical range are equally applicable.

[0027] Preferably, the outlet temperature of the spray drying is 190 - 210 °C, such as 190 °C, 192 °C, 195 °C, 197 °C, 200 °C, 203 °C, 205 °C, 208 °C or 210 °C, etc., but not limited to the listed values, and other unlisted values within the above numerical range are equally applicable.

[0028] Preferably, the temperature of the calcination in step (2) is 400 - 600 °C, such as 400 °C, 450 °C, 500 °C, 550 °C or 600 °C, etc., and the time is 1 - 6 h, such as 1 h, 2 h, 3 h, 4 h, 5 h or 6 h, etc., but not limited to the listed values, and other unlisted values within the above numerical range are equally applicable.

[0029] The second object of the present invention is to provide a catalyst supported on artificial hydrotalcite, which is prepared by the preparation method described in the first object and presents a flaky hexagonal shape as a whole.

[0030] The third object of the present invention is to provide a preparation method of array-type carbon nanotubes. Prepare the catalyst supported on artificial hydrotalcite prepared by the preparation method described in the first object, or prepare the catalyst supported on artificial hydrotalcite described in the second object, and grow array-type carbon nanotubes thereon by chemical vapor deposition.

[0031] Through experimental design, the present invention statistically analyzes a large amount of experimental data, identifies significant factors affecting BET in the catalyst preparation process and chemical vapor deposition (CVD) through Pareto charts, and develops a method for preparing array-type carbon nanotubes with controllable BET, easy purification, and high magnification.

[0032] The present invention obtains array-type carbon nanotubes with a BET that can be regulated within the range of 170 - 370 m 2 / g, easy to purify, and high magnification through the substrate method. The catalyst supported by artificial hydrotalcite prepared in the present invention is used as the substrate. The catalyst substrate is a uniform flaky hexagon, which is conducive to the growth of straighter arrayed tube bundles. At the same time, such a structure provides sufficient growth space for the growth of carbon tubes, and carbon tubes with higher magnification can be obtained.

[0033] The control of BET is mainly achieved through the coordinated regulation of the loading process and the CVD process. By regulating the type and proportion of metals, lamellar catalysts with different metal components or contents can be obtained. In the CVD process, the reaction temperature is adjusted to control the cracking rate of the carbon source. The two-step process works together to control the thickness of the array and achieve precise control of the product BET. The final array-type carbon nanotube product has a high magnification, high array order, high yield, easy to purify, the substrate layer is clearly visible in the carbon tubes and has a single structure, and high-quality array carbon tubes can be grown. These properties greatly simplify the purification work, save resources, are environmentally friendly, and promote the wide application of carbon nanotubes.

[0034] To meet the customer's demand for product differentiation, the present invention provides a method for preparing array-type carbon nanotubes with controllable performance. By regulating the CVD reaction temperature and the active components (type / content), the BET of the carbon tubes can be controlled to prepare array-type carbon tubes that meet the customer's requirements. Specifically, it is a method for preparing array-type carbon nanotubes with controllable BET, easy purification, and high magnification based on artificial hydrotalcite loaded with active components as the catalyst, which solves the problem of precise regulation of the BET of array-type carbon tubes and promotes the applied research of array-type carbon nanotubes. The preparation method described in the present invention not only has controllable BET of carbon tubes, high purity, easy purification, high magnification, good conductivity of carbon tubes, and a powder resistivity of 10 - 25 mΩ·cm, but also has the advantages of simple process and easy implementation. Combining the above advantages, while obtaining differentiated carbon tubes, the production cost of carbon tubes is significantly reduced. The various catalyst precursors and carbon sources used in the present invention are cheap and easily available, facilitating batch production and convenient application.

[0035] As a preferred technical solution of the present invention, the conditions of the chemical vapor deposition include: the deposition temperature is 650 - 760 °C, first hydrogen is introduced for reduction, and then the carbon source gas is introduced, ensuring that the carrier gas is passed throughout the process.

[0036] Preferably, the carbon source gas includes any one or a combination of at least two of ethylene, propylene or propane.

[0037] Preferably, the carrier gas includes nitrogen and / or argon.

[0038] The fourth object of the present invention is to provide an array-type carbon nanotube, which is prepared by using the preparation method of the array-type carbon nanotube described in the third object. The BET of the array-type carbon nanotube is 170-370m 2 / g, the purity is ≥95%, the array length is 40-100μm, the average tube diameter is 8-12nm, and the powder resistivity is 10-25mΩ·cm.

[0039] Compared with the prior art solutions, the present invention has at least the following beneficial effects:

[0040] (1) The catalyst prepared in the present invention with artificial hydrotalcite as the carrier is used as the substrate. The catalyst substrate is a uniform sheet-shaped hexagon, which is beneficial to the growth of straighter array tubes. At the same time, such a structure provides sufficient growth space for the growth of carbon tubes, and carbon tubes with a higher magnification can be obtained;

[0041] (2) In the preparation method of the array-type carbon nanotube of the present invention, the BET control is mainly achieved by coordinating the loading process and the CVD process. By adjusting the type and proportion of metals, lamellar catalysts with different metal components or contents can be obtained. In the CVD process, the reaction temperature is adjusted to control the cracking rate of the carbon source. The two processes cooperate with each other to control the thickness of the array and achieve precise control of the product BET. Description of the Drawings

[0042] Figure 1 is the scanning electron microscope image of the Mg / Al LDH carrier prepared in Example 1 of the present invention;

[0043] Figure 2 is the scanning electron microscope image of the catalyst with artificial hydrotalcite as the carrier prepared in Example 1 of the present invention;

[0044] Figure 3 is the low-magnification scanning electron microscope image of the array-type carbon nanotube prepared in Example 1 of the present invention;

[0045] Figure 4 is the high-magnification scanning electron microscope image of the array-type carbon nanotube prepared in Example 1 of the present invention;

[0046] Figure 5 is the Raman spectrum of the array-type carbon nanotube prepared in Example 1 of the present invention;

[0047] Figure 6 is the scanning electron microscope image of the catalyst prepared in Comparative Example 1 of the present invention;

[0048] Figure 7 It is the scanning electron microscope image of the carbon nanotubes prepared in Comparative Example 1 of the present invention. Detailed implementation manners

[0049] The technical solution of the present invention will be further described below in conjunction with the accompanying drawings and through specific implementation manners.

[0050] To better illustrate the present invention and facilitate understanding of its technical solution, typical but non-limiting embodiments of the present invention are as follows:

[0051] Example 1

[0052] A preparation method of a catalyst using artificial hydrotalcite as a carrier, the preparation method comprising the following steps:

[0053] (1) Prepare a magnesium-aluminum salt solution by mixing 15 g of aluminum nitrate, 30.72 g of magnesium nitrate, 180 g of urea and 1000 g of water, control the molar ratio of magnesium to aluminum in the magnesium-aluminum salt solution to be 3:1, place it in a water bath at 95 °C for 24 h for hydrothermal reaction, and obtain a Mg / Al LDH carrier by filtration. The theoretical chemical formula is Mg6Al2(OH) 16 CO3·4H2O. The scanning electron microscope image of this carrier is as Figure 1 shown, and it can be seen that its main structure is a uniform sheet-like hexagon;

[0054] (2) Weigh 12 g of the Mg / Al LDH carrier prepared in step (1) and disperse it in 40 g of water to prepare a suspension. Under stirring, simultaneously dropwise add an alkali solution and a metal salt solution until neutral. The alkali solution is an aqueous ammonium carbonate solution with a mass concentration of 25 wt%, and the metal salt solution is prepared by mixing 12.15 g of iron(III) nitrate nonahydrate, 0.53 g of ammonium heptamolybdate tetrahydrate and 40 g of water, so that the catalytically active metal Fe and the promoter metal Mo are adsorbed by metal precipitation on the surface of the Mg / Al LDH carrier. After the precipitation is complete, filter the precipitate, and then carry out drying, calcination and grinding in sequence. The temperature of the calcination is 500 °C and the time is 2 h to obtain a catalyst using artificial hydrotalcite as a carrier. The atomic ratio of Mg / Al / Fe / Mo in this catalyst is about 3:1:0.75:0.08. The molar ratio of the catalytic metal to all the metals in the catalyst using artificial hydrotalcite as a carrier is 17.18%. The scanning electron microscope image of this catalyst is as Figure 2 shown, and it can be seen that its main structure is still a sheet-like hexagon.

[0055] A preparation method of an array-type carbon nanotube. The catalyst supported by artificial hydrotalcite prepared in this example is placed in a fixed-bed reactor. First, nitrogen is used as the carrier gas with a flow rate of 1000 sccm. Under this atmosphere, the temperature is raised to 670 °C at a heating rate of 10 °C / min. Then, 1000 sccm of hydrogen is introduced for pretreatment for 10 min, and the reaction temperature is maintained at 670 °C. Finally, propylene and nitrogen are introduced, where the volume ratio of nitrogen to propylene is 1:1. After chemical vapor deposition for 40 min, the reaction is shut down and cooled to room temperature. The array-type carbon nanotube is taken out under nitrogen protection. The low-magnification (×1000) scanning electron microscope image of the obtained array-type carbon nanotube is as shown in Figure 3 shown. It can be seen that the carbon nanotubes are arranged orderly, and the average tube diameter is about 8 - 12 nm. The high-magnification (×50000) scanning electron microscope image of the obtained array-type carbon nanotube is as shown in Figure 4 shown. It can be seen that the artificial hydrotalcite support is well-preserved, and the array carbon nanotubes grow perfectly on both sides of the artificial hydrotalcite support. The Raman spectrum of the obtained array-type carbon nanotube is as shown in Figure 5 shown. It can be obtained that IG / ID is 0.84, the purity is 96.43%, and BET is 277 m 2 / g.

[0056] Example 2

[0057] A preparation method of a catalyst supported by artificial hydrotalcite. The preparation method includes the following steps:

[0058] (1) Prepare a magnesium-aluminum salt solution by mixing 15 g of aluminum nitrate, 30.72 g of magnesium nitrate, 180 g of urea, and 1000 g of water. Control the molar ratio of magnesium to aluminum in the magnesium-aluminum salt solution to be 3:1. Place it in a water bath at 95 °C for 24 h for hydrothermal reaction. After filtration, obtain the Mg / Al LDH support. The theoretical chemical formula is Mg6Al2(OH) 16 CO3·4H2O. The scanning electron microscope image of this support refers to Figure 1 and the main structure is also a uniform flaky hexagon;

[0059] (2) Weigh 12 g of the Mg / Al LDH support described in step (1), disperse it in 40 g of water to prepare a suspension. While stirring, simultaneously add an alkali solution and a metal salt solution until neutral. The alkali solution is an aqueous ammonium carbonate solution with a mass concentration of 25 wt%, and the metal salt solution is prepared by dissolving 24.3 g of iron(III) nitrate nonahydrate, 1.06 g of ammonium heptamolybdate tetrahydrate, and 60 g of water, so that the catalytically active metal Fe and the promoter metal Mo are adsorbed by metal precipitation on the surface of the Mg / Al LDH support. After the precipitation is complete, filter the precipitate, and then perform drying, calcination, and grinding in sequence. The temperature of the calcination is 500 °C and the time is 2 h to obtain a catalyst supported on artificial hydrotalcite. The atomic ratio of Mg / Al / Fe / Mo in this catalyst is approximately 3:1:1.5:0.16, and the molar ratio of the catalytic metal in the catalyst supported on artificial hydrotalcite to all metals is 29.32%. The scanning electron micrograph of this catalyst refers to Figure 2 , and the main structure is still sheet-like hexagon.

[0060] A preparation method of an array-type carbon nanotube. Place the catalyst supported on artificial hydrotalcite prepared in this example in a fixed-bed reactor. The specific chemical vapor deposition operation is the same as that in Example 1. The obtained array-type carbon nanotubes have ordered carbon nanotube arrangements, an average tube diameter of about 9 - 13 nm, a purity of 96.97%, and a BET of 242 m 2 / g.

[0061] Example 3

[0062] A preparation method of a catalyst supported on artificial hydrotalcite, the preparation method comprising the following steps:

[0063] (1) Prepare a magnesium-aluminum salt solution by dissolving 15 g of aluminum nitrate, 30.72 g of magnesium nitrate, 180 g of urea, and 1000 g of water, control the molar ratio of magnesium to aluminum in the magnesium-aluminum salt solution to be 3:1, place it in a water bath at 95 °C for 24 h for hydrothermal reaction, and filter to obtain the Mg / Al LDH support. The theoretical chemical formula is Mg6Al2(OH) 16 CO3·4H2O. The scanning electron micrograph of this support refers to Figure 1 , and the main structure is also a uniform sheet-like hexagon;

[0064] (2) Weigh 12 g of the Mg / Al LDH support described in step (1), disperse it in 40 g of water to prepare a suspension. Under stirring, simultaneously add dropwise an alkali solution and a metal salt solution until neutral. The alkali solution is an aqueous ammonium carbonate solution with a mass concentration of 25 wt%, and the metal salt solution is prepared by dissolving 36.45 g of iron(III) nitrate nonahydrate, 1.59 g of ammonium heptamolybdate tetrahydrate, and 80 g of water, so that the catalytically active metal Fe and the promoter metal Mo are adsorbed by metal precipitation on the surface of the Mg / Al LDH support. After the precipitation is complete, perform precipitation filtration, followed by drying, calcination, and grinding. The temperature of the calcination is 500 °C and the time is 2 h to obtain a catalyst with artificial hydrotalcite as the support. The atomic ratio of Mg / Al / Fe / Mo in this catalyst is approximately 3:1:2.25:0.24. The molar ratio of the catalytic metal to all the metals in the catalyst with artificial hydrotalcite as the support is 38.36%. The scanning electron micrograph of this catalyst refers to Figure 2 , and the main structure is still sheet-like hexagons.

[0065] A preparation method of an array-type carbon nanotube. Place the catalyst with artificial hydrotalcite as the support prepared in this example in a fixed-bed reactor. The specific chemical vapor deposition operation is the same as that in Example 1. The carbon nanotubes of the obtained array-type carbon nanotubes are arranged in an orderly manner, with an average tube diameter of about 10 - 14 nm, a purity of 97.37%, and a BET of 215 m 2 / g.

[0066] Example 4

[0067] A preparation method of a catalyst with artificial hydrotalcite as the support, the preparation method comprising the following steps:

[0068] (1) Prepare a magnesium-aluminum salt solution by dissolving 15 g of aluminum nitrate, 30.72 g of magnesium nitrate, 180 g of urea, and 1000 g of water. Control the molar ratio of magnesium to aluminum in the magnesium-aluminum salt solution to be 3:1. Place it in a 95 °C water bath for 24 h for hydrothermal reaction. After filtration, obtain the Mg / Al LDH support. The theoretical chemical formula is Mg6Al2(OH) 16 CO3·4H2O. The scanning electron micrograph of this support refers to Figure 1 , and the main structure is also uniform sheet-like hexagons;

[0069] (2) Weigh 12 g of the Mg / Al LDH support described in step (1) and disperse it in 40 g of water to prepare a suspension. Under stirring, simultaneously add dropwise an alkali solution and a metal salt solution until neutral. The alkali solution is an aqueous ammonium carbonate solution with a mass concentration of 25 wt%, and the metal salt solution is prepared by dissolving 48.6 g of iron(III) nitrate nonahydrate, 2.12 g of ammonium heptamolybdate tetrahydrate, and 100 g of water, so that the catalytically active metal Fe and the promoter metal Mo are adsorbed by metal precipitation on the surface of the Mg / Al LDH support. After the precipitation is complete, perform precipitation filtration, followed by drying, calcination, and grinding. The temperature of the calcination is 500 °C and the time is 2 h to obtain a catalyst with artificial hydrotalcite as the support. The atomic ratio of Mg / Al / Fe / Mo in this catalyst is approximately 3:1:3:0.32. The molar ratio of the catalytic metal to all the metals in the catalyst with artificial hydrotalcite as the support is 45.43%. The scanning electron micrograph of this catalyst refers to Figure 2 , and the main structure is still sheet-like hexagons.

[0070] A preparation method of an array-type carbon nanotube. Place the catalyst with artificial hydrotalcite as the support prepared in this example in a fixed-bed reactor. The specific chemical vapor deposition operation is the same as that in Example 1. The carbon nanotubes of the obtained array-type carbon nanotubes are arranged orderly, the average tube diameter is about 11 - 20 nm, the purity is 97.56%, and the BET is 174 m 2 / g.

[0071] Example 5

[0072] A preparation method of a catalyst with artificial hydrotalcite as the support, the preparation method includes the following steps:

[0073] (1) Prepare a magnesium-aluminum salt solution by dissolving 15 g of aluminum nitrate, 30.72 g of magnesium nitrate, 180 g of urea, and 1000 g of water, control the molar ratio of magnesium to aluminum in the magnesium-aluminum salt solution to be 3:1, place it in a water bath at 95 °C for 24 h for hydrothermal reaction, and obtain a Mg / Al LDH support by filtration. The theoretical chemical formula is Mg6Al2(OH) 16 CO3·4H2O. The scanning electron micrograph of this support refers to Figure 1 , and its main structure is uniform sheet-like hexagons;

[0074] (2) Weigh 12 g of the Mg / Al LDH support described in step (1) and disperse it in 40 g of water to prepare a suspension. While stirring, simultaneously add dropwise an alkali solution and a metal salt solution until neutral. The alkali solution is an aqueous ammonium bicarbonate solution with a mass concentration of 25 wt%, and the metal salt solution is prepared by mixing 10.84 g of iron(III) nitrate nonahydrate, 0.786 g of cobalt(II) nitrate hexahydrate, 0.53 g of ammonium heptamolybdate tetrahydrate, and 40 g of water, so that the catalytically active metals Fe and Co and the promoter metal Mo are adsorbed by metal precipitation on the surface of the Mg / Al LDH support. After complete precipitation, transfer the solution to a rotary evaporator and evaporate the solvent at 80 °C to dryness. Take out the sample and conduct calcination and grinding in sequence. The temperature of the calcination is 500 °C and the time is 2 h to obtain a catalyst supported on artificial hydrotalcite. The atomic ratio of Mg / Al / Fe / Co / Mo in this catalyst is approximately 3:1:0.67:0.067:0.08. The molar ratio of the catalytic metals in the catalyst supported on artificial hydrotalcite to all the metals is 16.96%. The scanning electron micrograph of this catalyst refers to Figure 2 , and its main structure remains sheet-like hexagon.

[0075] A preparation method of an array-type carbon nanotube. Place the catalyst supported on artificial hydrotalcite prepared in this example in a fixed-bed reactor. First, use nitrogen as the carrier gas with a flow rate of 1000 sccm. Under this atmosphere, heat up to 680 °C at a heating rate of 10 °C / min, then introduce 1000 sccm of hydrogen for pretreatment for 10 min, maintain the reaction temperature at 680 °C, and finally introduce propylene and nitrogen, where the volume ratio of nitrogen to propylene is 1:1. After chemical vapor deposition for 40 min, stop the reaction and cool to room temperature. Take out the array-type carbon nanotube under nitrogen protection. The carbon nanotubes obtained have an ordered arrangement of carbon tubes, an average tube diameter of about 8 - 12 nm, a purity of 96.43%, and a BET of 302 m 2 / g.

[0076] Example 6

[0077] A preparation method of a catalyst supported on artificial hydrotalcite, the preparation method comprising the following steps:

[0078] (1) Prepare a magnesium-aluminum salt solution by mixing 15 g of aluminum nitrate, 30.72 g of magnesium nitrate, 180 g of urea, and 1000 g of water, control the molar ratio of magnesium to aluminum in the magnesium-aluminum salt solution to be 3:1, place it in a water bath at 95 °C for 24 h for hydrothermal reaction, and obtain a Mg / Al LDH support by filtration. The theoretical chemical formula is Mg6Al2(OH) 16 CO3·4H2O. The scanning electron micrograph of this support refers to Figure 1 , and its main structure is a uniform sheet-like hexagon;

[0079] (2) Weigh 12 g of the Mg / Al LDH support described in step (1), disperse it in 40 g of water to prepare a suspension. Under stirring, simultaneously add dropwise an alkali solution and a metal salt solution until neutral. The alkali solution is an aqueous ammonium bicarbonate solution with a mass concentration of 25 wt%, and the metal salt solution is prepared by dissolving 8.75 g of iron(III) nitrate nonahydrate, 0.629 g of cobalt(II) nitrate hexahydrate, 0.42 g of ammonium heptamolybdate tetrahydrate, and 40 g of water, so that the catalytically active metals Fe and Co and the promoter metal Mo are adsorbed by metal precipitation on the surface of the Mg / Al LDH support. After the precipitation is complete, transfer the solution to a rotary evaporator, evaporate the solvent at 80 °C until dry, take out the sample, and perform calcination and grinding in sequence. The temperature of the calcination is 500 °C and the time is 2 h to obtain a catalyst with artificial hydrotalcite as the support. The atomic ratio of Mg / Al / Fe / Co / Mo in this catalyst is approximately 3:1:0.54:0.054:0.06, and the molar ratio of the catalytic metals in the catalyst with artificial hydrotalcite as the support to all metals is 14.05%. The scanning electron micrograph of this catalyst refers to Figure 2 , and its main structure is still sheet-like hexagon.

[0080] A preparation method of an array-type carbon nanotube. Place the catalyst with artificial hydrotalcite as the support prepared in this example in a fixed-bed reactor. The specific chemical vapor deposition operation is the same as that in Example 5. The carbon nanotubes of the obtained array-type carbon nanotubes are arranged orderly, the average tube diameter is about 7 - 11 nm, the purity is 96.00%, and the BET is 327 m 2 / g.

[0081] Example 7

[0082] A preparation method of a catalyst with artificial hydrotalcite as the support, the preparation method includes the following steps:

[0083] (1) Prepare a magnesium-aluminum salt solution by mixing 15 g of aluminum nitrate, 30.72 g of magnesium nitrate, 180 g of urea, and 1000 g of water, control the molar ratio of magnesium to aluminum in the magnesium-aluminum salt solution to be 3:1, place it in a 95 °C water bath for 24 h for hydrothermal reaction, and filter to obtain the Mg / Al LDH support. The theoretical chemical formula is Mg6Al2(OH) 16 CO3·4H2O. The scanning electron micrograph of this support refers to Figure 1 , and its main structure is uniform sheet-like hexagon;

[0084] (2) Weigh 12 g of the Mg / Al LDH support described in step (1) and disperse it in 40 g of water to prepare a suspension. While stirring, simultaneously add an alkali solution and a metal salt solution until neutral. The alkali solution is an aqueous ammonium bicarbonate solution with a mass concentration of 25 wt%, and the metal salt solution is prepared by dissolving 2.75 g of iron(III) nitrate nonahydrate, 2 g of cobalt(II) nitrate hexahydrate, 0.265 g of ammonium heptamolybdate tetrahydrate, and 30 g of water, so that the catalytically active metals Fe and Co and the promoter metal Mo are adsorbed by metal precipitation on the surface of the Mg / Al LDH support. After the precipitation is complete, transfer the solution to a rotary evaporator and evaporate the solvent at 80 °C until dry. Take out the sample and perform calcination and grinding in sequence. The temperature of the calcination is 500 °C and the time is 2 h to obtain a catalyst with artificial hydrotalcite as the support. The atomic ratio of Mg / Al / Fe / Co / Mo in this catalyst is approximately 3:1:0.17:0.17:0.04. The molar ratio of the catalytic metals to all the metals in the catalyst with artificial hydrotalcite as the support is 8.67%. The scanning electron micrograph of this catalyst refers to Figure 2 , and its main structure remains sheet-like hexagon.

[0085] A preparation method of an array-type carbon nanotube. Place the catalyst with artificial hydrotalcite as the support prepared in this example in a fixed-bed reactor. The specific chemical vapor deposition operation is the same as that in Example 5. The carbon nanotubes of the obtained array-type carbon nanotube are arranged orderly, the average tube diameter is about 5 - 9 nm, the purity is 95.00%, and the BET is 371 m 2 / g.

[0086] Example 8

[0087] A preparation method of a catalyst with artificial hydrotalcite as the support, the preparation method includes the following steps:

[0088] (1) Prepare a magnesium-aluminum salt solution by dissolving 15 g of aluminum nitrate, 30.72 g of magnesium nitrate, 180 g of urea, and 1000 g of water. Control the molar ratio of magnesium to aluminum in the magnesium-aluminum salt solution to be 3:1. Place it in a water bath at 95 °C for 24 h for hydrothermal reaction, and filter to obtain the Mg / Al LDH support. The theoretical chemical formula is Mg6Al2(OH) 16 CO3·4H2O. The scanning electron micrograph of this support refers to Figure 1 , and its main structure is uniform sheet-like hexagon;

[0089] (2) Weigh 12 g of the Mg / Al LDH support described in step (1) and disperse it in 40 g of water to prepare a suspension. Under stirring, simultaneously add dropwise an alkali solution and a metal salt solution until neutral. The alkali solution is an aqueous ammonium bicarbonate solution with a mass concentration of 25 wt%, and the metal salt solution is prepared by mixing 10.84 g of iron(III) nitrate nonahydrate, 0.786 g of cobalt(II) nitrate hexahydrate, 0.53 g of ammonium heptamolybdate tetrahydrate, and 200 g of water, so that the catalytically active metals Fe and Co and the promoter metal Mo are adsorbed by metal precipitation on the surface of the Mg / Al LDH support. After the precipitation is complete, transfer the solution to a spray dryer, set the outlet temperature to 200 °C, take out the sample and calcine it. The calcination temperature is 500 °C and the time is 2 h to obtain a catalyst with artificial hydrotalcite as the support. The atomic ratio of Mg / Al / Fe / Co / Mo in this catalyst is approximately 3:1:0.67:0.067:0.08. The molar ratio of the catalytic metals in the catalyst with artificial hydrotalcite as the support to all the metals is 16.96%. The scanning electron micrograph of this catalyst refers to Figure 2 , and its main structure is still sheet-like hexagon.

[0090] A preparation method of an array-type carbon nanotube. Place the catalyst with artificial hydrotalcite as the support prepared in this example in a fixed-bed reactor. First, use nitrogen as the carrier gas with a flow rate of 1000 sccm. Under this atmosphere, heat it to 650 °C at a heating rate of 10 °C / min, then introduce 1000 sccm of hydrogen for pretreatment for 10 min, maintain the reaction temperature at 650 °C, and finally introduce propylene and nitrogen. The volume ratio of nitrogen to propylene is 1:1. After chemical vapor deposition for 40 min, stop the reaction and cool it to room temperature. Take out the array-type carbon nanotubes under nitrogen protection. The obtained array-type carbon nanotubes have ordered carbon tube arrangements, an average tube diameter of about 8 - 12 nm, a purity of 96.55%, and a BET of 328 m 2 / g.

[0091] Example 9

[0092] A preparation method of a catalyst with artificial hydrotalcite as the support. The preparation method is exactly the same as that described in Example 8 to obtain a catalyst with artificial hydrotalcite as the support. The atomic ratio of Mg / Al / Fe / Co / Mo in this catalyst is approximately 3:1:0.67:0.067:0.08. The molar ratio of the catalytic metals in the catalyst with artificial hydrotalcite as the support to all the metals is 16.96%, and its main structure is still sheet-like hexagon.

[0093] A method for preparing an array of carbon nanotubes. Place the catalyst supported on artificial hydrotalcite prepared in this example in a fixed-bed reactor. First, use nitrogen as the carrier gas with a flow rate of 1000 sccm. Under this atmosphere, heat it at a heating rate of 10 °C / min to 680 °C. Then, introduce 1000 sccm of hydrogen for pretreatment for 10 min, maintain the reaction temperature at 680 °C. Finally, introduce propylene and nitrogen, where the volume ratio of nitrogen to propylene is 1:1. After chemical vapor deposition for 40 min, turn off the reaction, cool it to room temperature, and take out the array of carbon nanotubes under nitrogen protection. The obtained array of carbon nanotubes has ordered carbon tube arrangement, with an average tube diameter of about 8 - 12 nm, a purity of 96.77%, and a BET of 317 m 2 / g.

[0094] Example 10

[0095] A method for preparing a catalyst supported on artificial hydrotalcite. The preparation method is exactly the same as that described in Example 8, obtaining a catalyst supported on artificial hydrotalcite. The atomic ratio of Mg / Al / Fe / Co / Mo in this catalyst is about 3:1:0.67:0.067:0.08. The molar ratio of the catalytic metal to all metals in the catalyst supported on artificial hydrotalcite is 16.96%, and its main structure remains sheet-like hexagon.

[0096] A method for preparing an array of carbon nanotubes. Place the catalyst supported on artificial hydrotalcite prepared in this example in a fixed-bed reactor. First, use nitrogen as the carrier gas with a flow rate of 1000 sccm. Under this atmosphere, heat it at a heating rate of 10 °C / min to 710 °C. Then, introduce 1000 sccm of hydrogen for pretreatment for 10 min, maintain the reaction temperature at 710 °C. Finally, introduce propylene and nitrogen, where the volume ratio of nitrogen to propylene is 1:1. After chemical vapor deposition for 40 min, turn off the reaction, cool it to room temperature, and take out the array of carbon nanotubes under nitrogen protection. The obtained array of carbon nanotubes has ordered carbon tube arrangement, with an average tube diameter of about 8 - 13 nm, a purity of 96.55%, and a BET of 301 m 2 / g.

[0097] Example 11

[0098] A method for preparing a catalyst supported on artificial hydrotalcite. The preparation method is exactly the same as that described in Example 8, obtaining a catalyst supported on artificial hydrotalcite. The atomic ratio of Mg / Al / Fe / Co / Mo in this catalyst is about 3:1:0.67:0.067:0.08. The molar ratio of the catalytic metal to all metals in the catalyst supported on artificial hydrotalcite is 16.96%, and its main structure remains sheet-like hexagon.

[0099] A preparation method of an array-type carbon nanotube. The catalyst supported on hydrotalcite prepared in this example is placed in a fixed-bed reactor. First, nitrogen is used as the carrier gas with a flow rate of 1000 sccm. Under this atmosphere, the temperature is raised to 740 °C at a heating rate of 10 °C / min. Then, 1000 sccm of hydrogen is introduced for pretreatment for 10 min, and the reaction temperature is maintained at 740 °C. Finally, propylene and nitrogen are introduced, where the volume ratio of nitrogen to propylene is 1:1. After chemical vapor deposition for 40 min, the reaction is turned off, cooled to room temperature, and the array-type carbon nanotube is taken out under nitrogen protection. The carbon nanotubes in the obtained array-type carbon nanotube are arranged orderly, with an average tube diameter of about 8 - 13 nm, a purity of 95.83%, and a BET of 274 m 2 / g.

[0100] Comparative Example 1

[0101] This comparative example provides a preparation method of a catalyst. Referring to the preparation method of the catalyst disclosed in CN109665512A, the preparation method uses a one-step method to prepare the catalyst, including the following steps:

[0102] Prepare ferric nitrate nonahydrate, ammonium heptamolybdate tetrahydrate, aluminum nitrate, magnesium nitrate, urea and water, and prepare a mixed salt solution with a concentration of 0.3 mol / L. Prepare an aqueous ammonium carbonate solution with a molar concentration of 10 mol / L as the base solution. The atomic ratio of Mg / Al / Fe / Mo in the mixed salt solution is 3:1:1.5:0.16, the molar amount of urea is 15 times that of the metal ions, and the content of the active component is 29.32 wt% of the total weight of the catalyst. Mix the above two solutions at room temperature, and slowly raise the temperature to 103 °C at a rate of 3 °C / min under stirring, continue to keep warm and stir for 12 h, and then stop the reaction. Place the obtained suspension in an oven at 95 °C for 12 h, then cool and filter, wash 3 times with deionized water, and freeze-dry. The scanning electron micrograph of the obtained catalyst refers to Figure 6 It can be seen that: due to the high content of active metals and the complex components in the catalyst, the morphology of the catalyst is damaged and it is no longer a lamellar structure.

[0103] A preparation method of a carbon nanotube. The catalyst prepared in this comparative example is placed in a fixed-bed reactor. First, nitrogen is used as the carrier gas with a flow rate of 1000 sccm. Under this atmosphere, the temperature is raised to 670 °C at a heating rate of 10 °C / min. Then, 1000 sccm of hydrogen is introduced for pretreatment for 10 min, and the reaction temperature is maintained at 670 °C. Finally, propylene and nitrogen are introduced, where the volume ratio of nitrogen to propylene is 1:1. After chemical vapor deposition for 40 min, the reaction is turned off, cooled to room temperature, and the carbon nanotube is taken out under nitrogen protection. The scanning electron micrograph of the carbon nanotube is as Figure 7As shown, it can be seen that the carbon nanotubes are no longer in an array form, and there is obvious smoke during the reaction process. This is because the catalyst has poor activity and side reactions occur; the purity of the carbon nanotubes is only 78.52%, and the BET is 214m 2 / g.

[0104] The key process parameters and characterization results in the above-mentioned examples and comparative examples are summarized in Table 1.

[0105] Table 1

[0106]

[0107] As can be seen from Table 1, the following points can be noted:

[0108] (1) Examples 1-4 of the present invention are Fe / Mo-based catalysts. Using the co-precipitation method, by adjusting the ratio of Fe / Mo to the total metal in the catalyst to 17.18-45.43%, the BET of the carbon nanotubes can be adjusted within a wide range of 174-277m 2 / g;

[0109] (2) Examples 5-7 of the present invention are Fe / Co / Mo-based catalysts. Using the precipitation-rotary evaporation method, by adjusting the ratio of Fe / Co / Mo to the total metal in the catalyst to 8.67-16.96%, the BET of the carbon nanotubes can be adjusted within a wide range of 302-371m 2 / g;

[0110] (3) Examples 8-11 of the present invention are Fe / Co / Mo-based catalysts. Using the precipitation-spray drying method, fixing the ratio of Fe / Co / Mo to the total metal in the catalyst at 16.96%, by adjusting the CVD temperature within the range of 650-740°C, the BET of the carbon nanotubes can be adjusted within the range of 274-328m 2 / g;

[0111] (4) By adjusting the molar ratio of the catalytically active metal and the promoter metal in the catalyst to the total metal, the BET of the carbon nanotubes can be adjusted within a relatively wide range; using the same catalyst, by adjusting the CVD temperature, the BET of the carbon nanotubes can be adjusted within a relatively narrow range; therefore, by combining the adjustment of the metal type and ratio in the catalyst and the CVD temperature, almost precise control of the BET of the carbon nanotubes can be achieved.

[0112] The present invention describes the detailed structural features of the present invention through the above embodiments. However, the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must rely on the above detailed structural features to be implemented. Those skilled in the art should understand that any improvement to the present invention, the equivalent replacement of the components selected for the present invention, the addition of auxiliary components, the selection of specific methods, etc. all fall within the protection scope and the disclosure scope of the present invention.

[0113] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0114] In addition, it should be noted that, among the various specific technical features described in the above specific embodiments, without conflict, they can be combined in any appropriate manner. To avoid unnecessary repetition, the present invention will not separately describe various possible combination methods.

[0115] In addition, any combination can be made between various different embodiments of the present invention, as long as it does not violate the idea of the present invention, it should also be regarded as the content disclosed by the present invention.

Claims

1. A method for preparing a catalyst with artificial hydrotalcite as a carrier, characterized in that, The preparation method includes the following steps: (1) Prepare a magnesium-aluminum salt solution by mixing soluble aluminum salt, soluble magnesium salt, urea and water, control the molar ratio of magnesium to aluminum in the magnesium-aluminum salt solution to be 3:1, and successively carry out hydrothermal reaction and the first solid-liquid separation to obtain a Mg / Al LDH support; (2) Prepare a suspension by mixing water and the Mg / Al LDH support obtained in step (1), and simultaneously add an alkali solution and a metal salt solution for metal precipitation adsorption, and successively carry out the second solid-liquid separation and calcination to obtain a catalyst with artificial hydrotalcite as the support; Among them, the metal salt solution in step (2) includes a catalytic metal, and the molar ratio of the catalytic metal to all metals in the catalyst with artificial hydrotalcite as the support is 8.67-45.43%.

2. The method for preparing a catalyst with artificial hydrotalcite as a carrier according to claim 1, characterized in that, The soluble aluminum salt in step (1) includes any one or a combination of at least two of aluminum nitrate, aluminum sulfate or aluminum chloride; Preferably, the soluble magnesium salt in step (1) includes any one or a combination of at least two of magnesium nitrate, magnesium sulfate or magnesium chloride.

3. The method for preparing a catalyst with artificial hydrotalcite as a carrier according to claim 1 or 2, characterized in that, The hydrothermal reaction in step (1) is carried out in a water bath, the temperature of the hydrothermal reaction is 90-100 °C, and the time of the hydrothermal reaction is 20-30 h; Preferably, the Mg / Al LDH support in step (1) is in the shape of a flaky hexagon.

4. The method for preparing a catalyst with artificial hydrotalcite as a carrier according to any one of claims 1 - 3, characterized in that, The solid content of the suspension in step (2) is 20-25 wt%; Preferably, the alkali in the alkali solution in step (2) includes ammonium carbonate and / or ammonium bicarbonate.

5. The method for preparing a catalyst with artificial hydrotalcite as a carrier according to any one of claims 1 - 4, characterized in that, The catalytic metal in step (2) includes a catalytically active metal and a promoter metal; Preferably, the catalytically active metal includes Fe and / or Co; Preferably, the promoter metal includes Mo.

6. The method for preparing a catalyst with artificial hydrotalcite as a carrier according to any one of claims 1 - 5, characterized in that, The second solid-liquid separation in step (2) includes any one of precipitation filtration, rotary evaporation or spray drying; Preferably, the temperature of the rotary evaporation is 70-90 °C; Preferably, the outlet temperature of the spray drying is 190-210 °C; Preferably, the temperature of the calcination in step (2) is 400-600 °C, and the time is 1-6 h.

7. A catalyst with artificial hydrotalcite as a carrier, characterized in that, Prepared by using the preparation method described in any one of claims 1-6, and the whole presents a flaky hexagon.

8. A method for preparing an array - type carbon nanotube, characterized in that, Prepare a catalyst with artificial hydrotalcite as the support prepared by using the preparation method described in any one of claims 1-6, or prepare the catalyst with artificial hydrotalcite as the support described in claim 7, and grow an array of carbon nanotubes on it by chemical vapor deposition.

9. The method for preparing an array - type carbon nanotube according to claim 8, characterized in that, The conditions of the chemical vapor deposition include: the deposition temperature is 650-760 °C; first introduce hydrogen for reduction, and then introduce a carbon source gas, and ensure that a carrier gas is introduced throughout the process; Preferably, the carbon source gas includes any one or a combination of at least two of ethylene, propylene or propane; Preferably, the carrier gas includes nitrogen and / or argon.

10. An array - type carbon nanotube, characterized in that, Prepared by the method for preparing an array-type carbon nanotube according to claim 8 or 9, the BET of the array-type carbon nanotube is 170-370m 2 / g, the purity is ≥95%, the array length is 40-100μm, the average tube diameter is 8-12nm, and the powder resistivity is 10-25mΩ·cm.

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