Three-way catalyst for preparing carbon nano tube as well as preparation method and application of three-way catalyst

Abstract

The invention discloses a three-way catalyst for preparing a carbon nano tube as well as a preparation method and application thereof, and belongs to the technical field of catalysts. The catalyst comprises a carrier and active components Ni, Fe and Pd, the loading capacity of Ni is 55-70% of the weight of the carrier, the molar ratio of Ni to Fe is (10: 7)-(10: 6), and the molar ratio of Ni to Pd is (10: 2)-(10: 1). The second active component Fe and the third active component Pd with specific contents are introduced into the catalyst to form a ternary alloy structure, so that the service life of the catalyst is prolonged, and the activity of the catalyst and the selectivity of the carbon nanotubes are improved.

Description

Technical Field

[0001] The invention relates to the technical field of catalysts, and in particular to a ternary catalyst for preparing carbon nanotubes, a preparation method and an application thereof. Background Art

[0002] Carbon nanotubes are a one-dimensional quantum material with a special structure. Their radial dimensions are in the nanometer range, their axial dimensions are in the micrometer range, and both ends of the tube are basically sealed. Carbon nanotubes have unique mechanical, electrical and chemical properties and a unique quasi-one-dimensional tubular molecular structure. They have shown many potential application values ​​in many fields such as microelectronics, energy, national defense, and aerospace, and have become the research frontier and hotspot in the field of international new materials.

[0003] At present, the main methods for preparing carbon nanotubes are: arc discharge method, chemical vapor deposition method, and laser ablation method. Among them, chemical vapor deposition method, also known as hydrocarbon gas pyrolysis method, has the advantages of simple equipment, easy operation, and efficient preparation of carbon nanotubes. It is an ideal method for large-scale production of carbon nanotubes. Catalyst is the core technology of hydrocarbon gas pyrolysis method, and nickel-based catalyst is the main catalyst for preparing carbon nanotubes by hydrocarbon gas pyrolysis method.

[0004] Although existing nickel-based catalysts show excellent performance, they have the problem of decreased activity, which seriously affects the service life of the catalyst. One of the main factors for the decrease in the activity of nickel-based catalysts is catalyst carbon deposition, the mechanism of which can be described as the generation rate of carbon on the active metal-gas phase side is greater than the diffusion and dissolution rate of the active metal-carrier, resulting in the active sites being covered by a large amount of carbon deposition; the second main factor for the decrease in catalyst activity is the agglomeration of Ni metal particles in the active center of the catalyst caused by excessively high reaction temperature. In order to improve the service life and reduce the deactivation of the catalyst at the reaction temperature, different metals and metal oxides have been introduced into Ni-based catalysts. For example, Chinese patent CN100358802C discloses a Ni / Re / Cu catalyst that is contacted with methane or acetylene at a suitable temperature to prepare carbon nanotubes, but the preparation cost of the catalyst is high and is not suitable for large-scale production of carbon nanotubes. Chinese patent CN100368080C discloses a method for preparing carbon nanotubes using Ni / Al catalyst chemical vapor deposition, but the yield of carbon nanotubes prepared by the catalyst needs to be further improved. Summary of the invention

[0005] In view of the deficiencies of the prior art, the object of the present invention is to provide a ternary catalyst for preparing carbon nanotubes, wherein a specific content of a second active component Fe and a third active component Pd are introduced into the catalyst, thereby extending the service life of the catalyst and improving the activity of the catalyst.

[0006] In order to achieve the above object, according to one aspect of the present invention, a ternary catalyst for preparing carbon nanotubes is provided, the catalyst comprising a carrier and active components Ni, Fe and Pd, wherein the loading amount of Ni is 55-70% of the weight of the carrier, the molar ratio of Ni to Fe is 10:7-10:6, and the molar ratio of Ni to Pd is 10:2-10:1.

[0007] In some embodiments, the carrier is at least one of Al2O3, SiO2, MCM-41, and porous carbon materials.

[0008] In some embodiments, the catalyst has a particle size of 12-20 nm and a specific surface area of ​​260-320 m 2 / g.

[0009] According to another aspect of the present invention, there is also provided a method for preparing the ternary catalyst for preparing carbon nanotubes as described above, comprising the following steps: (1) Weighing soluble Ni salt, soluble Fe salt, and soluble Pd salt respectively, dissolving them in deionized water, heating them in a water bath, and preparing a mixed salt solution; (2) Impregnating the mixed salt solution and the carrier in equal volumes, drying, and calcining to obtain the three-way catalyst.

[0010] In some embodiments, in step (1), the soluble Ni salt includes one or more of nickel nitrate, nickel oxalate, and nickel acetate; the soluble Fe salt includes one or more of ferric nitrate, ferric oxalate, and ferric acetate; and the soluble Pd salt is palladium nitrate.

[0011] In some embodiments, in step (1), the molar ratio of nickel ions to iron ions in the mixed salt solution is 10:7-10:6, and the molar ratio of nickel ions to palladium ions is 10:2-10:1.

[0012] In some embodiments, in step (2), the drying temperature is 100-120° C. and the drying time is 12-24 hours.

[0013] In some embodiments, in step (2), the calcination conditions are: increasing the temperature to 650-750°C at a rate of 4-10°C / min and calcining for 3-6h.

[0014] According to another aspect of the present invention, the present invention also provides the use of the above-mentioned three-way catalyst or the three-way catalyst prepared by the above-mentioned preparation method in the preparation of carbon nanotubes by cracking low-carbon hydrocarbons.

[0015] In some embodiments, after the ternary catalyst is reduced, a carbon nanotube growth reaction is carried out at 700-850° C. for 3-6 hours in a low-carbon hydrocarbon atmosphere, and then purged with N 2 for 1-3 hours to prepare carbon nanotubes.

[0016] Compared with the prior art, the beneficial technical effects of the present invention are: (1) The catalyst described in the present invention introduces a second active component Fe with higher carbon dissolution efficiency and a third active component Pd with higher carbon dissolution efficiency. Pd can form a bridge for carbon transfer between metal Fe and Ni, which is beneficial to carbon transfer and reduces the coverage of carbon on the Ni metal surface. A ternary alloy structure that maintains carbon balance and limits Ni grain agglomeration is constructed, which promotes the diffusion and dissolution rate of carbon on the metal-carrier side, effectively maintains the carbon balance on both sides of the metal, thereby reducing carbon deposition on the catalyst surface and improving the service life of the catalyst. In addition, the formed ternary alloy structure effectively limits the agglomeration of Ni grains and improves the activity of the catalyst.

[0017] (2) In the process of preparing carbon nanotubes using the catalyst described in the present invention, due to the introduction of specific Fe and Pd into the catalyst, a "Fe-Pd carbon filter" is constructed on the metal Ni-gas phase side surface, and carbon preferentially passes through the "Fe-Pd carbon filter", so that the formed carbon nanotubes have a specific branching structure and a higher degree of graphitization, thereby improving the morphology of the carbon nanotubes. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to make the content of the present invention more clearly understood, the present invention is further described in detail below according to specific embodiments of the present invention in conjunction with the accompanying drawings, wherein: Figure 1 The XRD diagrams of the catalysts prepared in Example 1 and Comparative Examples 1-4 of the present invention.

[0019] Figure 2 (a) and (b) are TEM images of the carbon nanotubes prepared in Example 1 of the present invention and the carbon nanotubes prepared in Comparative Example 6, respectively. DETAILED DESCRIPTION

[0020] In order to enable those skilled in the art to understand the characteristics and effects of the present invention, the following is a general description and definition of the terms and expressions mentioned in the specification and claims. Unless otherwise specified, all technical and scientific terms used in the text are the common meanings understood by those skilled in the art for the present invention. In the event of a conflict, the definition in this specification shall prevail.

[0021] The theories or mechanisms described and disclosed herein, whether correct or incorrect, should not limit the scope of the present invention in any way, that is, the present invention can be implemented without being limited by any specific theory or mechanism.

[0022] Herein, when describing embodiments or examples, it should be understood that they are not used to limit the present invention to these embodiments or examples. On the contrary, all substitutes, improvements and equivalents of the methods and materials described in the present invention can be included in the scope limited by the claims.

[0023] In this document, in order to make the description concise, not all possible combinations of various technical features in various embodiments or examples are described. Therefore, as long as there is no contradiction in the combination of these technical features, the various technical features in various embodiments or examples can be combined arbitrarily, and all possible combinations should be considered to be within the scope of this specification.

[0024] The invention provides a ternary catalyst for preparing carbon nanotubes. The catalyst comprises a carrier and active components Ni, Fe and Pd.

[0025] In some embodiments, in the catalyst, the loading amount of Ni is 55-70% of the weight of the carrier. The loading amount used in the present invention can not only ensure the catalytic activity of the catalyst, but also provide sufficient carrier phase for the active metal particles, thereby improving the strength of the catalyst.

[0026] In some embodiments, in the catalyst, the molar ratio of Ni to Fe is 10:7-10:6.

[0027] In some embodiments, in the catalyst, the molar ratio of Ni to Pd is 10:2-10:1.

[0028] The present invention controls the molar ratio of Ni to Fe and the molar ratio of Ni to Pd in ​​the catalyst, thereby ensuring that Pd can form a certain amount of bridges for carbon transfer between metal Fe and Ni, which is beneficial to the transfer of carbon, reduces the coverage of carbon on the Ni metal surface, limits the agglomeration of Ni crystal grains, prolongs the service life of the catalyst, and improves the catalytic activity; at the same time, a specific content of Fe and Pd is introduced into the catalyst, and a "Fe-Pd carbon filter" is constructed on the metal Ni-gas phase side surface. Carbon preferentially passes through the "Fe-Pd carbon filter", so that the formed carbon nanotubes have a specific branching structure and a higher degree of graphitization, thereby improving the morphology of the carbon nanotubes.

[0029] In some embodiments, the carrier is at least one of Al2O3, SiO2, MCM-41, and porous carbon materials. These carriers have good structural stability, high specific surface area, and good dispersion of active centers.

[0030] In some embodiments, the particle size of the carrier is 2-10 nm. The carrier used in the present application has a relatively uniform particle size, a high degree of particle size uniformity, and a regular shape, thereby ensuring the uniformity of the particle size of the catalyst.

[0031] In some embodiments, the catalyst has a particle size of 12-20 nm and a specific surface area of ​​260-320 m 2 The catalyst of the present application has a relatively uniform particle size and a large specific surface area, which is beneficial to improving the growth stability and yield of carbon nanotubes.

[0032] The present invention also provides a method for preparing the ternary catalyst for preparing carbon nanotubes as described above, comprising the following steps: (1) Weighing soluble Ni salt, soluble Fe salt, and soluble Pd salt respectively, dissolving them in deionized water, heating them in a water bath, and preparing a mixed salt solution; (2) Impregnating the mixed salt solution and the carrier in equal volumes, drying, and calcining to obtain the three-way catalyst.

[0033] In some embodiments, in step (1), the soluble Ni salt includes one or more of nickel nitrate, nickel oxalate, and nickel acetate; the soluble Fe salt includes one or more of ferric nitrate, ferric oxalate, and ferric acetate; and the soluble Pd salt is palladium nitrate.

[0034] In some embodiments, in step (1), the molar ratio of nickel ions to iron ions in the mixed salt solution is 10:7-10:6.

[0035] In some embodiments, in step (1), the molar ratio of nickel ions to palladium ions in the mixed salt solution is 10:2-10:1.

[0036] In some embodiments, in step (1), the water bath heating temperature is 50-60°C. It is understood that the water bath heating temperature can be any specific value of 50°C, 51°C, 52°C, 53°C, 54°C, 55°C, 56°C, 57°C, 58°C, 59°C, 60°C or any value within the range of 50-60°C. The present invention has no specific restrictions on the specific method and equipment for water bath heating, and the water bath heating method and equipment commonly used in the art can be used.

[0037] In some embodiments, in step (2), the drying temperature is 100-120°C, and the drying time is 12-24h. It is understood that the drying temperature can be any specific value of 100°C, 105°C, 110°C, 115°C, 120°C, or any value within the range of 100-120°C; the drying time can be any specific value of 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h, 20h, 21h, 22h, 23h, 24h, or any value within the range of 12-24h.

[0038] In some embodiments, in step (2), the calcination conditions are: increasing the temperature to 650-750°C at a rate of 4-10°C / min and calcining for 3-6h. It can be understood that the heating rate can be any specific value of 4°C / min, 4.5°C / min, 5°C / min, 5.5°C / min, 6°C / min, 6.5°C / min, 7°C / min, 7.5°C / min, 8°C / min, 8.5°C / min, 9°C / min, 9.5°C / min, 10°C / min, or any value in the range of 4-10°C / min; the calcination temperature can be any specific value of 650°C, 660°C, 670°C, 680°C, 690°C, 700°C, 710°C, 720°C, 730°C, 740°C, 750°C, or any value in the range of 650-750°C; the calcination time can be any specific value of 3h, 4h, 5h, 6h, or any value in the range of 3-6h. The present invention can stably combine metal particles by controlling the roasting conditions to obtain a ternary alloy structure catalyst with uniform alloy particle size and high mechanical strength. Since the catalyst has a ternary alloy structure, it is suitable for the process of preparing carbon nanotubes by cracking low-carbon hydrocarbons, especially for gas operations with a large flux, thereby improving the yield of carbon nanotubes.

[0039] According to another aspect of the present invention, the present invention also provides the use of the above-mentioned three-way catalyst or the three-way catalyst prepared by the above-mentioned preparation method in the preparation of carbon nanotubes by cracking low-carbon hydrocarbons.

[0040] In the present invention, the low-carbon hydrocarbons refer to hydrocarbon gases with 1-3 carbon atoms.

[0041] In some embodiments, the low-carbon hydrocarbons include but are not limited to methane, ethane, propylene, ethylene, acetylene, etc. The low-carbon hydrocarbons described in the present application can be rapidly cracked to produce carbon under appropriate temperature conditions, providing a material basis for the subsequent efficient growth of carbon nanotubes. Preferably, the low-carbon hydrocarbon is methane.

[0042] In some specific embodiments, the specific method for preparing carbon nanotubes using the ternary catalyst is as follows: after the ternary catalyst is reduced, the carbon nanotube growth reaction is carried out at 700-850°C in a low-carbon hydrocarbon atmosphere for 3-6 hours, and then purged with N2 for 1-3 hours to prepare carbon nanotubes.

[0043] In the present invention, the three-way catalyst reduction treatment can adopt conventional reduction methods in the art, including but not limited to using hydrogen or a mixed gas for reduction for 1-2 hours. Furthermore, the mixed gas can be 95% N2 and 5% H2 by volume; the reduction treatment can be carried out in a tubular furnace.

[0044] In some embodiments, the step of carbon nanotube growth reaction includes: introducing low-carbon hydrocarbon gas into the reactor at a flow rate of 15-30mL / min, and reacting at a temperature of 700-850°C for 3-6h. Under the reaction conditions, the active metal in the ternary alloy structure catalyst is heated and melted; at the same time, the low-carbon hydrocarbon gas is thermally decomposed to produce carbon, and the carbon preferentially passes through the "Fe-Pd carbon filter" on the surface of the catalyst metal Ni-gas phase side. The mechanism of metal Fe and Ni forming carbon nanotubes is different. The carbon nanotubes formed by metal Fe can be used as branches of carbon nanotubes formed on the rear side of metal Ni, thereby forming a carbon nanotube with a specific branch structure, forming carbon nanotubes.

[0045] In some embodiments, after the carbon nanotube growth reaction, N2 is purged for 1-3 hours to increase the graphitization degree of the carbon nanotubes and improve the morphology of the carbon nanotubes.

[0046] The present invention will be described in detail below by way of examples. It should be understood that the following examples are only used to further explain and illustrate the content of the present invention by way of example, and are not intended to limit the present invention.

[0047] In the examples and comparative examples of the present invention, unless otherwise specified, the raw materials used are common commercial products that can be directly purchased or prepared according to conventional methods in the art. The specific information is as follows: Carrier MCM-41: water absorption rate 2-2.5g / g (water / carrier), particle size 2-10nm, manufacturer: Shanghai Juna Technology Co., Ltd.; Carrier SiO2: water absorption rate 2-2.5g / g (water / carrier), particle size 200-300 mesh, manufacturer: Sinopharm Chemical Reagent Co., Ltd.; Pd(NO3)2·2H2O was purchased from Shanghai MacLean Biochemical Technology Co., Ltd., and Ni(NO3)2·6H2O and Fe(NO3)3·9H2O were purchased from Sinopharm Chemical Reagent Co., Ltd.

[0048] Example 1 Take 60gNi(NO3)2·6H2O, 54gFe(NO3)3·9H2O and 10gPd(NO3)2·2H2O respectively, add 45g deionized water, heat to 60℃ in a water bath to dissolve and prepare a mixed brine solution; impregnate an equal volume of the above mixed brine solution on 20g carrier MCM-41, dry at 120℃ for 24h, calcine at 750℃ for 5h, and keep the heating rate at 4℃ / min. The obtained catalyst is named Cat-1.

[0049] 3 g of the catalyst Cat-1 was reduced with hydrogen at 750° C. for 2 h in a tubular furnace, and then methane gas was introduced to react at 750° C. for 3 h, and finally N2 was purged at 750° C. for 1 h to prepare product carbon nanotubes.

[0050] Example 2 Take 60gNi(NO3)2·6H2O, 54gFe(NO3)3·9H2O and 10gPd(NO3)2·2H2O respectively, add 45g deionized water, heat to 60℃ in a water bath to dissolve and prepare a mixed brine solution; impregnate an equal volume of the mixed brine solution on 20g carrier MCM-41, dry at 120℃ for 24h, calcine at 650℃ for 5h, and keep the heating rate at 10℃ / min. The obtained catalyst is named Cat-2.

[0051] 3 g of catalyst Cat-2 was reduced in a tube furnace at 750°C with a mixed gas (95% N2 and 5% H2 by volume) for 2 h, then reacted at 750°C for 3 h, and finally purged with N2 at 750°C for 1 h to prepare the product carbon nanotubes.

[0052] Example 3 Take 60gNi(NO3)2·6H2O, 54gFe(NO3)3·9H2O and 5.5gPd(NO3)2·2H2O respectively, add 45g deionized water, heat to 60℃ in a water bath to dissolve and prepare a mixed brine solution; impregnate an equal volume of the above mixed brine solution on 20g carrier MCM-41, dry at 120℃ for 24h, calcine at 700℃ for 5h, and maintain the heating rate at 10℃ / min. The obtained catalyst is named Cat-3.

[0053] 3 g of catalyst Cat-3 was reduced with hydrogen at 750°C for 3 h in a tube furnace, then reacted at 750°C for 3 h, and finally purged with N2 at 750°C for 1 h to prepare product carbon nanotubes.

[0054] Example 4 Take 54gNi(NO3)2·6H2O, 42gFe(NO3)3·9H2O and 10gPd(NO3)2·2H2O respectively, add 45g deionized water, heat to 60℃ in a water bath to dissolve and prepare a mixed brine solution; impregnate an equal volume of the above mixed salt solution on 20g carrier MCM-41, dry at 120℃ for 24h, calcine at 750℃ for 5h, and keep the heating rate at 10℃ / min. The obtained catalyst is named Cat-4.

[0055] 3 g of catalyst Cat-4 was reduced with hydrogen at 750°C for 3 h in a tube furnace, then reacted at 750°C for 3 h, and finally purged with N2 at 750°C for 2 h to prepare product carbon nanotubes.

[0056] Example 5 Take 70gNi(NO3)2·6H2O, 54gFe(NO3)3·9H2O and 6gPd(NO3)2·2H2O respectively, add 45g deionized water, heat to 60℃ in a water bath to dissolve and prepare a mixed brine solution; impregnate an equal volume of the mixed brine solution on 20g carrier SiO2, dry at 120℃ for 24h, calcine at 750℃ for 5h, and maintain the heating rate at 4℃ / min. The obtained catalyst is named Cat-5.

[0057] 3 g of catalyst Cat-5 was reduced with hydrogen at 750°C for 2 h in a tube furnace, then reacted at 800°C for 3 h, and finally purged with N2 at 750°C for 2 h to prepare product carbon nanotubes.

[0058] Comparative Example 1 The preparation method of the catalyst described in this comparative example is different from that in Example 1 in that Pd is not introduced. The specific preparation method is as follows: Take 60gNi(NO3)2·6H2O and 54gFe(NO3)3·9H2O respectively, add 47g deionized water, heat to 60℃ in a water bath to dissolve and prepare a mixed solution. Impregnate equal volumes of the above solutions on 20g carrier MCM-41, dry at 120℃ for 24h, calcine at 750℃ for 5h, and maintain the heating rate at 4℃ / min. The obtained catalyst is named D-Cat-1.

[0059] 3 g of catalyst D-Cat-1 was reduced with hydrogen at 750°C for 2 h in a tube furnace, then reacted at 750°C for 3 h, and finally purged with N2 at 750°C for 1 h to prepare product carbon nanotubes.

[0060] Comparative Example 2 The preparation method of the catalyst described in this comparative example is different from that in Example 1 in that Fe is not introduced. The specific preparation method is as follows: Take 60g Ni(NO3)2·6H2O and 10g Pd(NO3)2·2H2O respectively, add 68g deionized water, heat to 60℃ in a water bath to dissolve and prepare a mixed brine solution. Impregnate an equal volume of the mixed brine solution on 20g carrier MCM-41, dry at 120℃ for 24h, calcine at 750℃ for 5h, and maintain the heating rate at 4℃ / min. The obtained catalyst is named D-Cat-2.

[0061] 3 g of catalyst D-Cat-2 was reduced with hydrogen at 750°C for 2 h in a tube furnace, then reacted at 750°C for 3 h, and finally purged with N2 at 750°C for 1 h to prepare product carbon nanotubes.

[0062] Comparative Example 3 The preparation method of the catalyst described in this comparative example is different from that in Example 1 in that Ni is not introduced. The specific preparation method is as follows: Take 54g Fe(NO3)3·9H2O and 10g Pd(NO3)2·2H2O respectively, add 65g deionized water, heat to 60℃ in a water bath to dissolve and prepare a mixed brine solution; impregnate an equal volume of the above mixed brine solution on 20g carrier MCM-41, dry at 120℃ for 24h, calcine at 750℃ for 5h, and maintain the heating rate at 4℃ / min. The obtained catalyst is named D-Cat-3.

[0063] 3 g of catalyst D-Cat-3 was reduced with hydrogen at 750°C for 2 h in a tube furnace, then reacted at 750°C for 3 h, and finally purged with N2 at 750°C for 1 h to prepare product carbon nanotubes.

[0064] Comparative Example 4 The preparation method of the ternary catalyst described in this comparative example is the same as that of Example 1, except that the calcination conditions of the catalyst are: calcination at 450° C. for 5 h, with a heating rate of 4° C. / min. The obtained catalyst is named D-Cat-4.

[0065] 3 g of catalyst D-Cat-4 was reduced with hydrogen at 750°C for 2 h in a tube furnace, then reacted at 750°C for 3 h, and finally purged with N2 at 750°C for 1 h to prepare product carbon nanotubes.

[0066] Comparative Example 5 The preparation method of the three-way catalyst described in this comparative example is the same as that of Example 1, except that 60g of Ni(NO3)2·6H2O, 22g of Fe(NO3)3·9H2O and 2g of Pd(NO3)2·2H2O are taken, 45g of deionized water is added, and the mixture is dissolved and prepared into a mixed salt solution by heating to 60°C in a water bath. The obtained catalyst is named D-Cat-5.

[0067] 3 g of catalyst D-Cat-5 was reduced with hydrogen at 750°C for 2 h in a tubular furnace, and then methane gas was introduced to react at 750°C for 3 h. Finally, N2 was purged at 750°C for 1 h to prepare the product carbon nanotubes.

[0068] Comparative Example 6 The preparation method of the three-way catalyst described in this comparative example is the same as that of Example 1, except that 60g of Ni(NO3)2·6H2O, 69g of Fe(NO3)3·9H2O and 10g of Pd(NO3)2·2H2O are taken, 45g of deionized water is added, and the mixture is dissolved and prepared into a mixed salt solution by heating to 60°C in a water bath. The obtained catalyst is named D-Cat-6.

[0069] 3 g of catalyst D-Cat-6 was reduced with hydrogen at 750°C for 2 h in a tubular furnace, and then methane gas was introduced and reacted at 750°C for 3 h. Finally, N2 was purged at 750°C for 1 h to prepare the product carbon nanotubes.

[0070] Performance Testing The catalysts prepared in Examples 1-5 and Comparative Examples 1-6 were subjected to performance tests according to the corresponding test methods. The specific test methods are as follows: Contents of Ni, Fe and Pd in ​​the catalyst: Loading analysis was performed by using a ZSXPrimusⅡ X-ray fluorescence spectrometer (XRF); Particle size: XRD characterization was first performed on an X'Perts Power diffractometer using a CuKα target line (incident wavelength 1.54056Å), a scanning range of 0-90°, and a scanning speed of 10° / min, and then the particle size was calculated using the Scherrer formula.

[0071] Carbon nanotube yield: The mass before and after the reaction was weighed using a precision balance. The yield was the mass of carbon nanotubes generated by 1 g of catalyst per unit time.

[0072] Catalyst specific surface area BET: Micromeritics TriStarⅡ3020 physical adsorption instrument was used for testing. First, 100 mg of sample was degassed at 200℃ for 6 hours, and then adsorption and desorption experiments were carried out in liquid nitrogen at -196℃. The data were automatically recorded by computer. When the pressure was between 0.05-0.3, the specific surface area BET was calculated using adsorption data.

[0073] Table 1 Performance evaluation results of the catalysts in Examples 1-5 and Comparative Examples 1-6 .

[0074] It can be seen from the data in Table 1 that the yield of carbon nanotubes prepared using the catalysts prepared in Examples 1-5 is significantly higher than that in Comparative Examples 1-6, indicating that the catalyst of the present application has a higher yield of carbon nanotubes; it can be seen from Example 1 and Comparative Examples 1-2 that the catalytic activity and service life of the resulting binary catalyst are both low when Fe or Pd is introduced alone in the nickel-based catalyst system. It can be seen from Example 1 and Comparative Example 3 that, in the absence of Ni, the catalytic activity and service life of the binary catalyst containing only Fe and Pd are also low. It can be seen from Example 1 and Comparative Examples 5-6 that the molar ratio of Ni / Fe and the molar ratio of Ni / Pd in ​​the catalyst are very critical to the catalytic activity and service life of the catalyst. Therefore, the present application introduces a specific content of the second active component Fe and the third active component Pd into the nickel-based catalyst, and through the synergistic effect of Ni / Fe / Pd, the service life of the catalyst is extended and the activity of the catalyst is improved.

[0075] Figure 1 is the XRD diagram of the catalysts prepared in Example 1 and Comparative Examples 1-4 of the present invention. Figure 1 It can be seen that the catalyst prepared by the preparation method in the examples of the present application is a ternary NiFePd alloy structure, while the catalysts obtained in Comparative Examples 1-4 do not have a ternary structure.

[0076] Figure 2 (a) is a TEM image of the carbon nanotubes prepared in Example 1. Figure 2 (b) is a TEM image of the carbon nanotubes prepared in Comparative Example 6. Figure 2 (a) and (b) show that the carbon nanotubes prepared using the catalyst prepared in Example 1 of the present application have a specific branching structure and a higher degree of graphitization, and the morphology of the carbon nanotubes is improved, indicating that the molar ratio of the metal elements in the ternary catalyst is very critical.

[0077] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not limitations on the implementation methods of the present invention. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is impossible to list all the implementation methods here. All obvious changes or modifications derived from the technical solution of the present invention are still within the protection scope of the present invention.

Claims

1. A three-way catalyst for preparing carbon nanotubes, characterized in that: The catalyst comprises a carrier and active components Ni, Fe and Pd, wherein the loading amount of Ni is 55-65% of the weight of the carrier, the molar ratio of Ni to Fe is 10:7-10:6, and the molar ratio of Ni to Pd is 10:2-10:

1.

2. The ternary catalyst for preparing carbon nanotubes according to claim 1, characterized in that: The carrier is at least one of Al2O3, SiO2, MCM-41 and porous carbon material.

3. The ternary catalyst for preparing carbon nanotubes according to claim 1, characterized in that: The particle size of the catalyst is 12-20 nm, and the specific surface area is 260-320 m 2 / g.

4. A method for preparing a three-way catalyst for preparing carbon nanotubes according to any one of claims 1 to 3, characterized in that: The steps include: (1) Weighing soluble Ni salt, soluble Fe salt, and soluble Pd salt respectively, dissolving them in deionized water, heating them in a water bath, and preparing a mixed salt solution; (2) Impregnating the mixed salt solution and the carrier in equal volumes, drying, and calcining to obtain the three-way catalyst.

5. The method for preparing a three-way catalyst for preparing carbon nanotubes according to claim 4, characterized in that: In step (1), the soluble Ni salt includes one or more of nickel nitrate, nickel oxalate, and nickel acetate; the soluble Fe salt includes one or more of ferric nitrate, ferric oxalate, and ferric acetate; and the soluble Pd salt is palladium nitrate.

6. The method for preparing a ternary catalyst for preparing carbon nanotubes according to claim 4, characterized in that: In step (1), the molar ratio of nickel ions to iron ions in the mixed salt solution is 10:7-10:6, and the molar ratio of nickel ions to palladium ions is 10:2-10:

1.

7. The method for preparing a ternary catalyst for preparing carbon nanotubes according to claim 4, characterized in that: In step (2), the drying temperature is 100-120°C and the drying time is 12-24h.

8. The method for preparing a ternary catalyst for preparing carbon nanotubes according to claim 4, characterized in that: In step (2), the calcination conditions are: increasing the temperature to 650-750°C at a rate of 4-10°C / min and calcining for 3-6h.

9. Use of the ternary catalyst according to any one of claims 1 to 3 or the ternary catalyst prepared by the preparation method according to any one of claims 4 to 8 in the preparation of carbon nanotubes by cracking low-carbon hydrocarbons.

10. The use according to claim 9, characterized in that: After the ternary catalyst is reduced, a carbon nanotube growth reaction is carried out at 700-850° C. for 3-6 hours in a low-carbon hydrocarbon atmosphere, and then purged with N 2 for 1-3 hours to prepare carbon nanotubes.

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