FeMo-based metal oxide / MgO catalyst, preparation method and preparation method of carbon nanotube

Abstract

The invention discloses a FeMo-based metal oxide / MgO catalyst, a preparation method thereof and a preparation method of a carbon nano tube, the catalyst takes MgO as a carrier, the catalyst provided by the invention is applied to catalytic synthesis of the carbon nano tube, and by optimizing the proportion of FeMo-based metal oxide and the relative content of Mo metal element, the content of the metal element in the carbon nano tube is increased, and the content of the metal element in the carbon nano tube is increased. High yield and high IG / ID ratio of the carbon nanotubes in the method for catalytically synthesizing the carbon nanotubes by using the catalyst are realized; meanwhile, before the alkane gas is catalyzed to decompose and grow the carbon nano tube, the catalyst is pretreated to activate the catalyst, the pretreatment condition of the catalyst is optimized, slow reduction is carried out under the condition of lower reduction temperature, and a mixture of FeO and metal Fe is formed; the blend enables the FeMo-based catalyst to be beneficial to stabilizing the catalytic effect of metal iron and accelerating the decomposition rate of alkane, especially methane, in the reaction process, and finally the high-yield and high-quality carbon nanotubes are obtained.

Description

Technical Field

[0001] The invention belongs to the field of catalysts, and in particular relates to an FeMo-based metal oxide / MgO catalyst, a preparation method and a preparation method of carbon nanotubes. Background Art

[0002] Carbon nanotubes (CNTs) are nanomaterials with a layered, hollow structure. The carbon atoms in CNTs are known to adopt sp2 hybridization, forming a delocalized, large π bond throughout the molecule. This unique structure gives them excellent properties in electrical, mechanical, thermal, and magnetic fields, leading to their widespread application in energy, catalytic materials, composite materials, and electronics. CNTs are classified as single-walled (SWCNTs) or multi-walled (MWCNTs) based on the number of layers they contain. SWCNTs are composed of a single, coiled graphite sheet; MWCNTs are composed of carbon tubes of varying diameters arranged in layers along a common axis.

[0003] Currently, the main methods for growing carbon nanotubes include arc discharge, laser ablation, and chemical vapor deposition (CVD). The first two methods are very complex to operate, requiring the evaporation of a solid carbon source into carbon atoms at temperatures above 3000°C, and the yield is very low. In addition, the carbon nanotubes produced by laser ablation are of low purity and tend to tangle together. Chemical vapor deposition, on the other hand, has the advantages of high yield, low product impurity content, simple process, and controllable carbon nanotube diameter and length. Therefore, it is the most important method for producing carbon nanotubes.

[0004] As understanding of the growth principles and preparation methods of carbon nanotubes continues to deepen, their industrial application has also developed. The ideal path to carbon nanotube production is to combine fine structural control with large-scale production. Currently, the market is in urgent need of a carbon nanotube preparation method that can achieve both high quality and high yield. Summary of the Invention

[0005] To solve the above technical problems, the first aspect of the present invention is to provide an FeMo-based metal oxide / MgO catalyst, wherein the catalyst is MgO-supported FeMo-based metal oxide, the FeMo-based metal oxide includes Fe2O3 and MoO2, and the MgO carrier is a foamy porous carrier; the FeMo-based metal oxide is supported on the MgO carrier, wherein the a value is the ratio of the mass of the FeMo-based metal oxide to the mass of MgO, a=40-60%, and x:y represents the molar ratio of iron and molybdenum metals, x:y=(5-45):1.

[0006] Preferably, the x:y=(25-45):1.

[0007] The second aspect of the present invention is to provide a method for preparing the FeMo-based metal oxide / MgO catalyst of the first aspect of the present invention, comprising:

[0008] S1: Weigh a soluble iron salt, a soluble molybdenum salt and a foaming agent, and dissolve them in water to form a solution;

[0009] S2: adding solid magnesium oxide to the solution under stirring, and continuing to stir and evaporate to dryness until the sample becomes gel-like;

[0010] S3: placing the gel in an oven to dry, and then grinding it into powder;

[0011] S4: Calcination in air to obtain a foamy porous catalyst.

[0012] Preferably, the foaming agent is at least one of citric acid and urea.

[0013] Preferably, the drying temperature in step S3 is 100-150° C., and the drying time is 12-24 hours. The calcination environment in step S4 is an oxygen-containing environment, and the calcination temperature is 300-500° C., and the calcination time is 2-4 hours.

[0014] Preferably, step S1 further comprises weighing magnesium nitrate.

[0015] The third aspect of the present invention is to provide a method for preparing carbon nanotubes, which comprises: using the catalyst of the first aspect of the present invention or the catalyst obtained by the preparation method of the second aspect of the present invention to perform high-temperature catalytic conversion of alkane gas to produce carbon nanotubes.

[0016] Preferably, the catalyst is first reduced by introducing a hydrogen atmosphere at a reduction temperature and then used for high-temperature catalytic alkane gas reaction. The hydrogen reduction condition is 450-750° C., and the hydrogen reduction time is 30 min-120 min.

[0017] Preferably, the high temperature is 750-850° C.; the high temperature catalytic alkane gas reaction is pure methane gas condition.

[0018] Beneficial effects

[0019] Compared with the prior art, the present invention has at least one of the following beneficial effects:

[0020] The present invention provides an FeMo-based metal oxide / MgO catalyst for catalyzing the decomposition of alkane gas to grow carbon nanotubes. By adding a foaming agent to the raw materials used to synthesize the catalyst, the foaming agent undergoes oxidative decomposition during the calcination process, releasing a large amount of gas and heat, resulting in a foamy, porous structure on the MgO carrier. The MgO carrier has numerous attachment sites, providing ample space for loading the FeMo-based metal oxide, allowing for uniform dispersion of the FeMo-based metal oxide, facilitating the efficient decomposition of alkane gas to grow high-quality carbon nanotubes.

[0021] Before catalyzing the decomposition of alkane gas to grow carbon nanotubes, the present invention pre-treats the catalyst to activate the catalyst and optimizes the catalyst pre-treatment conditions. Specifically, by optimizing the reduction temperature, Fe2O3 is slowly reduced under relatively low reduction temperature conditions, forming a blend of FeO and metallic Fe. The presence of this blend, on the one hand, allows the metallic Fe to act as the primary catalyst, achieving sustainable metallic Fe generation during the catalytic carbon nanotube formation process under high-temperature conditions, preventing the metallic Fe from agglomerating due to excessively rapid generation of metallic Fe under high-temperature reducing conditions, which reduces the catalytic efficiency of the metallic Fe. Therefore, its effect on the decomposition of alkanes, especially methane, to produce carbon nanotubes can maintain a stable and efficient catalytic effect over the long term during the reaction. On the other hand, the metallic Mo formed after the MoO2 reduction has a stabilizing effect on the metallic Fe, also preventing the metallic Fe formed in the reducing environment from agglomerating. Furthermore, the metallic Mo also has a certain co-catalytic effect, promoting the decomposition and production of carbon nanotubes. Therefore, the FeMo-based catalyst helps stabilize the catalytic effect of metallic Fe and accelerates the decomposition rate of alkanes, especially methane, during the reaction, ultimately producing high-yield, high-quality carbon nanotubes.

[0022] The catalyst provided by the present invention is used for catalytic synthesis of carbon nanotubes, wherein a is the mass percentage of FeMo-based metal oxide in MgO, a=40-60%, and x:y represents the molar ratio of iron and molybdenum metal elements, x:y=(5-45):1. The high a value and the appropriate ratio of x:y achieve a high yield of carbon nanotubes and high yield of carbon nanotubes in the method for synthesizing carbon nanotubes using the catalyst. G / I D The catalyst of the present invention can be used for large-scale and efficient production of high-quality carbon nanotubes.

[0023] Terminology

[0024] Certain embodiments of the present invention will now be described in detail, and the present invention is intended to encompass all substitutions, modifications, and equivalent technical solutions, which are all included within the scope of the invention as defined in the claims. It will be appreciated by those skilled in the art that many methods and materials similar or equivalent to those described herein can be used to practice the present invention. The present invention is in no way limited to the methods and materials described herein. In the event that one or more of the combined documents, patents, and similar materials differ from or contradict the present application (including but not limited to defined terms, term applications, described technologies, etc.), the present application shall prevail.

[0025] It will be further appreciated that certain features of the invention, which, for clarity, are described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention, which, for brevity, are described in the context of a single embodiment, may also be provided separately or in any suitable subcombination.

[0026] Unless otherwise specified, all technical terms used in the present invention have the same meaning as commonly understood by those skilled in the art to which the present invention belongs. All patents and publications related to the present invention are incorporated herein by reference in their entirety.

[0027] In the description of this specification, the reference terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 AC are SEM images of three catalysts numbered Cat1, Cat3 and Cat5, respectively.

[0029] Figure 2 Figures ac are the SEM images of three products numbered CNTs-1, CNTs-3 and CNTs-5, respectively.

[0030] Figure 3 Figures ac are the statistical diagrams of the diameter distribution of carbon nanotubes of three products numbered CNTs-1, CNTs-3 and CNTs-5. DETAILED DESCRIPTION

[0031] To make the objectives, technical solutions, and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the following examples. The specific embodiments described herein are intended only to illustrate the present invention and are not intended to limit the present invention in any way. In addition, in the following description, descriptions of known structures and technologies are omitted to avoid unnecessary confusion about the concepts of the present disclosure. Such structures and technologies are also described in many publications.

[0032] The present invention provides an FeMo-based metal oxide / MgO catalyst. The catalyst is MgO-supported FeMo-based metal oxide. MgO is used as a catalyst carrier for producing carbon nanotubes. It not only provides a good carrier for active metal components but can also be removed from the carbon nanotubes by a simple method after the carbon nanotubes are synthesized, such as acid washing.

[0033] The MgO support is a porous foam with three-dimensional pores dispersed throughout the support, with pore sizes ranging from micrometers to nanometers. The porous MgO foam has a large specific surface area, providing a good dispersion base for metal-based oxides, facilitating the loading of high catalyst loadings. This improves the catalytic performance of carbon nanotube synthesis, resulting in high-quality carbon nanotubes.

[0034] FeMo-based metal oxides are catalyst precursors for catalytically preparing carbon nanotubes. The FeMo-based metal oxides are specifically Fe2O3 and MoO2 oxides, and the Fe2O3 and MoO2 are mixed and dispersed on a MgO carrier. a is used to represent the mass percentage of the FeMo-based metal oxide in MgO, a=40-60%, that is, the ratio of the total mass of Fe2O3 and MoO2 to the mass of MgO. x:y represents the molar ratio of iron and molybdenum metal elements, x:y=(5-45):1.

[0035] More preferably, the x:y=(25-45):1.

[0036] A second aspect of the present invention is to provide a method for preparing a FeMo-based metal oxide / MgO catalyst, comprising:

[0037] S1: Weigh a soluble iron salt, a soluble molybdenum salt and a foaming agent, and dissolve them in water to form a solution;

[0038] S2: adding solid magnesium oxide to the solution under stirring, and continuing to stir and evaporate to dryness until the sample becomes gel-like;

[0039] S3: placing the gel in an oven to dry, and then grinding it into powder;

[0040] S4: calcining in air to obtain a foamed porous catalyst;

[0041] The catalyst is MgO-supported FeMo-based metal oxide, the FeMo-based metal oxide includes Fe2O3 and MoO2, and the MgO carrier is foamy and porous; the FeMo-based metal oxide is supported on the MgO carrier, wherein the value a is the ratio of the mass of the FeMo-based metal oxide to the mass of MgO, a=40-60%, and x:y represents the molar ratio of iron and molybdenum metals, x:y=(5-45):1.

[0042] Preferably, the evaporation temperature in step S2 is 90-110° C., and the evaporation time is 6-8 hours to obtain a gel.

[0043] Preferably, the drying temperature in step S3 is 100-150° C. and the drying time is 12-24 hours to remove moisture from the gel.

[0044] Preferably, the calcination environment in step S4 is an oxygen-containing environment, the calcination temperature is 300-500° C., and the calcination time is 2-4 hours.

[0045] During the roasting process, the magnesium oxide powder is transformed into a foamed porous magnesium oxide carrier through the reaction between the foaming agent and oxygen; the soluble iron salt and the soluble molybdenum salt are converted into Fe2O3 and MoO2 oxides during the calcination process, and are synchronously and evenly dispersed on the MgO carrier during the synthesis process of the foamed porous MgO carrier.

[0046] Preferably, the foaming agent is at least one of citric acid and urea, for example, citric acid or urea, or more preferably a combination of the two.

[0047] Preferably, the step S1 further comprises weighing magnesium nitrate and adding it into water to form the solution.

[0048] The present invention also provides a method for preparing carbon nanotubes, which comprises: using the catalyst of the present invention to perform high-temperature catalytic conversion of alkane gas to generate carbon nanotubes.

[0049] Preferably, the catalyst is first reduced in a hydrogen atmosphere at a reduction temperature between 450 and 750°C, and then used for high-temperature catalytic reaction of alkane gas to prepare carbon nanotubes after hydrogen reduction. The hydrogen reduction time is 30-120 minutes; preferably, the high temperature is 750-850°C, and more preferably 800°C.

[0050] The present invention optimizes the catalyst pretreatment conditions, specifically by adjusting the temperature of the reducing gas, to allow Fe2O3 to undergo slow reduction at low temperatures, thereby forming a blend of FeO and metallic Fe. The presence of this blend, on the one hand, allows Fe, acting as the primary catalyst, to catalyze the decomposition of alkane compounds during the carbon nanotube formation process under high temperature conditions. The hydrogen generated by the decomposition of FeO decomposes FeO to form metallic Fe, thereby achieving sustainable metallic Fe generation and preventing metallic Fe from agglomerating due to excessively rapid generation, which would otherwise reduce catalytic efficiency. Consequently, the blend maintains a long-term, stable, and highly efficient catalytic effect on the decomposition of alkanes, particularly methane, to produce carbon nanotubes. On the other hand, the metallic Mo formed by the reduction of MoO2 stabilizes the metallic Fe, preventing the metallic Fe formed in the reducing environment from agglomerating. Furthermore, the metallic Mo also has a certain co-catalytic effect, promoting the decomposition and production of carbon nanotubes. Therefore, the FeMo-based catalyst helps stabilize the catalytic effect of metallic Fe and accelerates the decomposition rate of alkanes during the reaction, ultimately yielding high-quality carbon nanotubes.

[0051] Preferably, the high temperature catalytic alkane gas reaction is carried out under pure methane gas conditions.

[0052] Used for high temperature catalytic reaction of alkane gas.

[0053] Preferably, a method for preparing carbon nanotubes is as follows: placing the catalyst prepared by the preparation method provided by the present invention or the catalyst provided by the present invention into a quartz tube of a fluidized bed reactor / fixed bed reactor; then introducing hydrogen and heating the temperature at 6°C / min to 450-650°C, for example, 450°C, 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, preferably 450-650°C; preferably, maintaining the temperature at the reduction temperature for 30min-120min, for example, 30min, 60min, 90min or 120min. Too long a time or too high a temperature will cause excessive reduction and agglomeration of metallic Fe, thereby reducing the catalytic performance of the product; after the reduction process is completed, continuing to heat the temperature at 6°C / min to 750-850°C, preferably 800°C, switching the gas to 80-150sccm of pure methane, catalytic reaction to prepare carbon nanotubes, and cooling to room temperature under an argon atmosphere after the reaction is completed.

[0054] The catalyst, preparation method and method for preparing carbon nanotubes using the catalyst of the present invention will be described below with reference to specific examples.

[0055] Example 1

[0056] Preparation methods of catalysts 1 to 5 (numbered Cat1-Cat5):

[0057] Weigh ferric nitrate, ammonium molybdate, magnesium nitrate, citric acid and urea, and dissolve them together in 50 ml of water, wherein the amount of magnesium nitrate, the amount of magnesium oxide and the amount of urea are 15.9063 g, 2.5 g and 0.5 g, and heat and stir to evaporate to dryness at 90°C for 8 hours to obtain a gel-like object. The gel-like object is dried at 150°C for 12 hours, ground into powder after complete drying, and then heated to 500°C at 2°C / min and calcined for 3 hours. The amount of ferric nitrate and ammonium molybdate is calculated based on the finally formed magnesium oxide, a value and x:y value.

[0058] Method for preparing carbon nanotubes using Cat1-Cat5 catalysts:

[0059] S1: 0.15 g of each of the obtained catalysts Cat1-Cat5 was placed in a quartz tube of a fluidized bed reactor / fixed bed reactor;

[0060] S2: introduce 100 sccm of hydrogen, increase the temperature to 550°C at 6°C / min, and maintain at the reduction temperature for 60 min;

[0061] S3: Continue to raise the temperature to 800°C at 6°C / min, switch the gas to 100 sccm pure methane, and react at 800°C for 90 min. After the reaction, maintain 100 sccm Ar and cool to room temperature to obtain carbon nanotubes. The products are numbered CNTs-1 to CNTs-5.

[0062] Table 1 shows the effects of different X:Y ratios on carbon yield and I G / I D The impact of (a = 50%)

[0063] Catalyst No. carbon nanotubes Catalyst expression x:y Carbon yield (%) <![CDATA[I G / I D ]]> Cat-1 CNTs-1 <![CDATA[50Fe5Mo1 / MgO]]> 5:1 236.37 6.23 Cat-2 CNTs-2 <![CDATA[50Fe 15 Mo1 / MgO]]> 15:1 228.06 7.56 Cat-3 CNTs-3 <![CDATA[50Fe 25 Mo1 / MgO]]> 25:1 216.29 12.27 Cat-4 CNTs-4 <![CDATA[50Fe 35 Mo1 / MgO]]> 35:1 202.08 16.35 Cat-5 CNTs-5 <![CDATA[50Fe 45 Mo1 / MgO]]> 45:1 197.31 14.66

[0064] The carbon yield %=(mass of carbon nanotubes in the crude product / mass of catalyst in the crude product)*100%.

[0065] At the same time, the product was tested by Raman spectroscopy, and the typical peak of carbon nanotubes appeared at a wavelength of 1350 cm -1 and 1580cm -1 Of which 1350cm -1 The peak is called D peak, and its intensity corresponds to the degree of defects in carbon nanotubes; 1580 cm -1 The peak is called G peak, and its intensity corresponds to the integrity of carbon nanotubes; G / I D To characterize the graphitization degree of carbon nanotubes.

[0066] like Figure 1 As shown, Figure 1(a) to (c) are SEM images of catalysts Cat-1, Cat-3, and Cat-5, respectively. The catalysts exhibit a "porous foam" morphology, which provides support and ample space for the growth of carbon nanotubes.

[0067] Figure 2 as well as Figure 3 The SEM images and tube diameter distribution diagrams of the corresponding carbon nanotubes show that: when Fe / Mo=5:1, although carbon nanotubes are generated, a lot of amorphous carbon is generated, and the average tube diameter is about 17.49nm; when Fe / Mo=25:1, the quality of the carbon nanotubes of CNTs-3 is good, the amorphous carbon is relatively less, and the average tube diameter is about 14.31nm; when Fe / Mo=45:1, CNTs-5 presents uniform and small-diameter carbon nanotubes, relatively less amorphous carbon, and the average tube diameter is about 12.64nm.

[0068] It can be seen from Table 1 that with the increase of the molar ratio of metal Fe to metal Mo, the I G / I D The carbon yield of catalysts Cat-1 to Cat-5 showed an overall downward trend. Although the carbon yield reached 236.37% when Fe / Mo=5:1, the I G / I D Only 6.23, but combined with I G / I D as well as Figure 2 The SEM image of the product shows that most of the carbon grown at this time is amorphous carbon and the quality of carbon nanotubes is poor; when Fe / Mo=25:1, the carbon yield of the catalyst decreases, but I G / I D The value increased significantly, reaching 12.27, and the overall quality of carbon nanotubes was preferred; when Fe / Mo=35:1, the catalyst carbon yield was 202.08% and the I G / I D When Fe / Mo=45:1, the catalyst carbon yield was 197.31% and the I G / I D Reaching 14.66, the overall quality of the carbon nanotubes is good.

[0069] Example 2

[0070] The catalyst numbered Cat-4 in Example 1 was used in the preparation method of carbon nanotubes:

[0071] S1: 0.15 g of catalyst was placed in a quartz tube of a fluidized bed reactor / fixed bed reactor;

[0072] S2: 100 sccm of hydrogen was introduced, the temperature was raised to different reduction temperatures at 6°C / min, and the reduction temperature was maintained for 60 min;

[0073] S3: Continue to raise the temperature to 800°C at 6°C / min, switch the gas to 120 sccm pure methane, and react at 800°C for 90 min. After the reaction, maintain 100 sccm Ar and cool to room temperature to obtain carbon nanotubes. The products are numbered CNTs-6 to CNTs-10.

[0074] Table 2 shows the effect of different reduction temperatures on carbon yield and IG / ID (a = 50%)

[0075]

[0076]

[0077] From the data in Table 2, it can be seen that the carbon yield of carbon nanotube products varies with the reduction temperature. G / I D With the increase of reduction temperature, carbon yield first increases and then decreases. G / I D The value also increases first and then decreases, indicating that at a reduction temperature of 450-650 °C, the quality of the obtained carbon nanotubes is optimal and the reduction performance of the catalyst is better.

[0078] In summary, the present invention provides an FeMo-based metal oxide / MgO catalyst for catalyzing the decomposition of alkane gas to grow carbon nanotubes. By adding a blowing agent to the raw materials used to synthesize the catalyst, the blowing agent undergoes oxidative decomposition during the calcination process, releasing a large amount of gas and heat, resulting in a foamy, porous structure in the MgO carrier. The porous MgO carrier has numerous attachment sites, providing ample space for loading the FeMo-based metal oxide, allowing for uniform dispersion of the FeMo-based metal oxide, facilitating the efficient decomposition of alkane gas to grow high-quality carbon nanotubes.

[0079] Before catalyzing the decomposition of alkane gas to grow carbon nanotubes, the present invention pre-treats the catalyst to activate the catalyst and optimizes the catalyst pre-treatment conditions. Specifically, by optimizing the reduction temperature, Fe2O3 is slowly reduced under relatively low reduction temperature conditions, forming a blend of FeO and metallic Fe. The presence of this blend, on the one hand, allows the metallic Fe to act as the primary catalyst, achieving sustainable metallic Fe generation during the catalytic carbon nanotube formation process under high-temperature conditions, preventing the metallic Fe from agglomerating due to excessively rapid generation of metallic Fe under high-temperature reducing conditions, which reduces the catalytic efficiency of the metallic Fe. Therefore, its effect on the decomposition of alkanes, particularly methane, to produce carbon nanotubes can maintain a stable and efficient catalytic effect over the long term during the reaction. On the other hand, the metallic Mo formed after the MoO2 reduction has a stabilizing effect on the metallic Fe, also preventing the metallic Fe formed in the reducing environment from agglomerating. Furthermore, the metallic Mo also has a certain co-catalytic effect, promoting the decomposition and production of carbon nanotubes. Therefore, the FeMo-based catalyst helps stabilize the catalytic effect of metallic Fe and accelerates the decomposition rate of alkanes, particularly methane, during the reaction, ultimately yielding high-quality carbon nanotubes.

[0080] The catalyst provided by the present invention is used for catalytic synthesis of carbon nanotubes, wherein a is the mass percentage of FeMo-based metal oxide in MgO, a=40-60%, and x:y represents the molar ratio of iron and molybdenum metal elements, x:y=(5-45):1. The high a value and the appropriate ratio of x:y achieve a high yield of carbon nanotubes and high yield of carbon nanotubes in the method for catalytic synthesis of carbon nanotubes. G / I D The catalyst of the present invention can be used for large-scale and efficient production of high-quality carbon nanotubes.

[0081] The reagents used in the present invention can be purchased from the market or prepared by the method described in the present invention.

[0082] The methods of the present invention have been described through preferred embodiments. It is apparent that those skilled in the art will be able to modify or appropriately alter and combine the methods and applications described herein within the scope, spirit, and spirit of the present invention to implement and apply the technology of the present invention. Those skilled in the art may refer to the disclosure herein and appropriately modify the process parameters to achieve the desired effect. It is particularly important to note that all similar substitutions and modifications apparent to those skilled in the art are considered encompassed by the present invention.

Claims

1. An FeMo-based metal oxide / MgO catalyst, characterized in that: The catalyst is MgO-supported FeMo-based metal oxide, the FeMo-based metal oxide includes Fe2O3 and MoO2, and the MgO carrier is foamy and porous; the FeMo-based metal oxide is supported on the MgO carrier, wherein the value a is the ratio of the mass of the FeMo-based metal oxide to the mass of MgO, a=40-60%, and x:y represents the molar ratio of iron and molybdenum metals, x:y=(5-45):

1.

2. The FeMo-based metal oxide / MgO catalyst according to claim 1, wherein: The x:y=(25-45):

1.

3. A method for preparing the FeMo-based metal oxide / MgO catalyst according to any one of claims 1 to 2, characterized in that: The method comprises the following steps: S1: Weigh a soluble iron salt, a soluble molybdenum salt and a foaming agent, and dissolve them in water to form a solution; S2: adding solid magnesium oxide to the solution under stirring, and continuing to stir and evaporate to dryness until the sample becomes gel-like; S3: drying the gel in an oven and grinding it into powder; S4: Calcination in air to obtain a foamy porous catalyst.

4. The method for preparing the FeMo-based metal oxide / MgO catalyst according to claim 3, wherein: The foaming agent is at least one of citric acid and urea.

5. The method for preparing the FeMo-based metal oxide / MgO catalyst according to claim 3, wherein: The drying temperature in step S3 is 100-150° C., and the drying time is 12-24 hours. The calcination environment in step S4 is an oxygen-containing environment, and the calcination temperature is 300-500° C., and the calcination time is 2-4 hours.

6. The method for preparing the FeMo-based metal oxide / Mg catalyst according to claim 3, wherein: The step S1 further includes weighing magnesium nitrate.

7. A method for preparing carbon nanotubes, comprising: The catalyst according to any one of claims 1 to 2 or the catalyst obtained by the preparation method according to any one of claims 3 to 6 is used to carry out high-temperature catalytic reaction of alkane gas to produce carbon nanotubes.

8. The method for preparing carbon nanotubes according to claim 7, wherein: The catalyst is first reduced by introducing a hydrogen atmosphere at a reduction temperature and then used in the high-temperature catalytic alkane gas reaction. The hydrogen reduction condition is 450-750° C. and the hydrogen reduction time is 30-120 minutes.

9. The method for preparing carbon nanotubes according to claim 8, wherein: The high temperature is 750-850°C.

10. The method for preparing carbon nanotubes according to claim 8, wherein: The high temperature catalytic alkane gas reaction condition is pure methane gas condition.

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