An iron-based oxide catalyst, its preparation method and application

Abstract

The present invention discloses an iron-based oxide catalyst, a preparation method thereof and an application thereof. The iron-based oxide catalyst includes a main catalyst body and a promoter distributed on the main catalyst body. The main catalyst body includes iron powder, and the promoter includes iron oxide. The preparation method includes: under the conditions of the presence of water vapor and oxygen, subjecting the iron powder to an oxidation reaction in a reaction chamber to in-situ generate iron oxide on the surface of the iron powder, thereby obtaining the iron-based oxide catalyst. The iron-based oxide catalyst provided by the present invention has good stability, controllable particle size, and strong interaction between the promoter component and the main catalyst body, which can effectively prevent the agglomeration and shedding of the promoter; when it is applied to the catalytic preparation of carbon nanotubes, the yield is high and the tube diameter is uniform.

Description

Technical Field

[0001] The present invention belongs to the technical field of the preparation of nanomaterials, and particularly relates to an iron-based oxide catalyst, a preparation method thereof and an application thereof. Background Art

[0002] Carbon nanotubes are divided into single-walled carbon nanotubes and multi-walled carbon nanotubes, which are an allotrope of carbon. Their shape is a one-dimensional cylindrical hollow structure, and the C atoms adopt sp 2 hybridization form. Due to their excellent electrical, mechanical and thermal properties, they have been widely used. The existing preparation methods of carbon nanotubes mainly include arc method, chemical vapor deposition and laser ablation method. Among them, chemical vapor deposition (CVD) is the most widely used and the most studied preparation method for the growth of carbon nanotubes at present. In the process of growing carbon nanotubes by CVD method, the catalyst plays the role of promoting the cracking of organic matter to generate carbon atoms, adsorbing and dissolving active carbon and precipitating carbon atoms on the surface to grow carbon nanotubes. Therefore, the preparation of the catalyst used in the CVD method is at the core of the technology. The existing catalysts for growing carbon nanotubes generally load the active components on the surface of the carrier, but the binding force between these active components and the carrier is insufficient and they are easily agglomerated together at high temperature, resulting in the inactivation of the catalyst and affecting the yield of carbon nanotubes. Therefore, a new catalyst for the preparation of carbon nanotubes is needed to solve the above problems. Summary of the Invention

[0003] The main purpose of the present invention is to provide an iron-based oxide catalyst, a preparation method thereof and an application thereof to overcome the deficiencies in the prior art.

[0004] To achieve the foregoing invention purpose, the technical solutions adopted by the present invention include:

[0005] One aspect of the present invention provides an iron-based oxide catalyst, which includes a main catalyst body and a promoter distributed on the main catalyst body. The main catalyst body includes iron powder, and the promoter includes iron oxide.

[0006] Another aspect of the present invention provides a preparation method of an iron-based oxide catalyst, which includes: under the conditions of the presence of water vapor and oxygen, carrying out an oxidation reaction on iron powder in a reaction chamber to in-situ generate iron oxide on the surface of the iron powder to obtain an iron-based oxide catalyst.

[0007] Another aspect of the present invention also provides an iron-based oxide catalyst prepared by the foregoing preparation method.

[0008] Another aspect of the present invention also provides an application of the foregoing iron-based oxide catalyst in the preparation of carbon nanotubes.

[0009] Compared with the prior art, the technical solutions of the present invention have at least the following advantages:

[0010] 1) The iron-based oxide catalyst provided by the present invention has a special structure. The promoter (iron oxide) component grows and distributes in-situ on the surface of the main catalyst (nano-iron). On the one hand, it improves the binding force between the metal oxide promoter and the metal main catalyst. On the other hand, the presence of the metal oxide can prevent the coarsening of the iron-based catalyst particles at high temperatures; and the promoter component has a strong interaction with the main catalyst body, making the promoter component evenly dispersed and not easily agglomerated;

[0011] 2) The preparation method provided by the present invention is simple, easy to scale up, and suitable for industrial applications. The structure and composition of the final catalyst can be controlled according to the steam input amount, reaction temperature, and reaction time during the reaction. The content of the promoter on the surface of the main body can be regulated by the preparation method. Especially in a high-temperature environment, it can effectively prevent the agglomeration and shedding of the promoter; and the catalyst particle size can be controlled by the particle size of the added pure iron powder;

[0012] 3) The iron-based oxide catalyst provided by the present invention has good stability and high yield in the preparation of carbon nanotubes, and the obtained carbon nanotubes have uniform diameters. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments recorded in the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0014] Figure 1 It is a schematic diagram of the equipment used in the preparation of the iron-based oxide catalyst in a typical embodiment of the present invention;

[0015] Figure 2 It is an optical microscope photograph of the iron-based oxide catalyst prepared in Example 1 of the present invention;

[0016] Figure 3 It is an SEM image of the single-walled carbon nanotubes prepared in Example 1 of the present invention;

[0017] Figure 4 It is a TEM image of the single-walled carbon nanotubes prepared in Example 1 of the present invention;

[0018] Figure 5a It is an XRD pattern of the iron-based oxide catalyst prepared in Example 1 of the present invention;

[0019] Figure 5b It is an XRD pattern of the iron-based oxide catalyst prepared in Example 2 of the present invention;

[0020] Figure 5c XRD pattern of the catalyst prepared in Comparative Example 1 of the present invention. Detailed implementation manners

[0021] The present invention will be more fully understood by reading the following detailed implementation manners. However, it should be understood that the specific implementation manners disclosed below are only exemplary of the present invention, and the present invention can be embodied in various forms. Therefore, the specific functional details disclosed herein should not be construed as restrictive, but only as the basis of the claims and as a representative basis for teaching those skilled in the art to adopt the present invention in any appropriate detailed embodiment in fact in different ways.

[0022] As an aspect of the technical solution of the present invention, an iron-based oxide catalyst involved therein includes a main catalyst body and a promoter distributed on the main catalyst body. The main catalyst body includes iron powder, and the promoter includes iron oxide.

[0023] In some embodiments, the content of iron powder in the iron-based oxide catalyst is 23.9 - 89.7 wt%, and the content of iron oxide is 10.3 - 76.1 wt%.

[0024] As another aspect of the technical solution of the present invention, a preparation method of an iron-based oxide catalyst involved therein includes: under the presence of water vapor and oxygen, subjecting iron powder to an oxidation reaction in a reaction chamber to in-situ generate iron oxide on the surface of the iron powder, thereby obtaining the iron-based oxide catalyst.

[0025] In some embodiments, the temperature of the oxidation reaction is 200 - 800 °C, and the time is 0.5 - 6 hours. If the reaction time is too long, Fe will be completely oxidized, so the reaction time of the present invention is controlled within this range.

[0026] In some embodiments, the iron powder includes but is not limited to carbonyl iron powder.

[0027] In some embodiments, the particle size of the iron powder is 50 nm - 50 µm. The raw material cost of carbonyl iron powder with too small particle size is relatively high and its performance is unstable. The present invention selects a particle size above 50 nm to be more suitable. The particle size of the prepared catalyst is determined according to the particle size of the pure iron powder added, and the promoter iron oxide is in-situ generated on the surface of the pure iron powder.

[0028] In some embodiments, the preparation method includes:

[0029] Providing an air compression device, a heating device, and a tube furnace that are interconnected;

[0030] Place iron powder in the reaction chamber of a tubular furnace, heat it to the temperature required for the oxidation reaction, and simultaneously heat the selected liquid on the heating device to boiling.

[0031] Turn on the air compression device so that the steam above the boiling liquid is continuously introduced into the reaction chamber of the tubular furnace to carry out the oxidation reaction.

[0032] In some preferred embodiments, the selected liquid includes, but is not limited to, pure water or oxygen-rich water.

[0033] In some preferred embodiments, the heating temperature is 105 - 150 °C.

[0034] In some preferred embodiments, steam of the selected liquid is introduced into one end of the reaction chamber of the tubular furnace, and an alumina heat insulation component is placed at the other end.

[0035] In some preferred embodiments, the working pressure of the air compression device is 0.4 - 1.0 MPa. The amount of steam introduced into the tubular furnace is controlled by the air compressor pressure value, with an overall range of 0.4 to 1.0 Mpa (the upper limit of the working pressure of a commercially available air compressor is usually 1.0 Mpa). The type of iron oxide formed in-situ on the surface of pure iron powder can be controlled by the amount of steam introduced or the reaction temperature and time in the tubular furnace.

[0036] In some preferred embodiments, the air compression device includes, but is not limited to, an oil-free mobile air compressor.

[0037] In some preferred embodiments, the heating device includes, but is not limited to, an electric heating mantle.

[0038] In some more specific embodiments, the preparation method includes:

[0039] Step 1: Assemble the reaction equipment using an air compressor, an electric heating mantle, and a tubular furnace to ensure smooth air flow inside the equipment.

[0040] Step 2: Pour pure iron powder of the required particle size (such as carbonyl iron powder) into a flat corundum boat, covering the bottom of the boat. Move the corundum boat into the tubular furnace in Step 1, set the temperature of the tubular furnace, and simultaneously heat the solution in the spherical flask on the electric heating mantle.

[0041] Step 3: When the tubular furnace in the equipment in Step 2 reaches the specified temperature and the solution in the electric heating mantle boils, turn on the air compressor so that the steam above the boiling liquid is continuously introduced into the tubular furnace. After the reaction time ends, wait for the furnace body to cool to room temperature, turn off the equipment, take out the corundum boat, weigh the catalyst after the reaction to obtain its weight, and perform XRD testing on the catalyst powder.

[0042] Among them, a three-neck round-bottom flask is used in the heating mantle to hold the heating solution, which is pure water or oxygen-rich water, and the heating temperature is 105 - 150 degrees Celsius. The three sockets of the three-neck round-bottom flask are respectively connected to an air compressor, a temperature measuring probe, and a tube furnace.

[0043] Among them, the air compressor is an oil-free mobile air compressor, and the ventilation rate can be adjusted through a pressure switch, and the working pressure range is selected from 0.4 to 1.0 MPa.

[0044] Among them, the constant temperature of the tube furnace can be selected as a certain fixed value between 200 and 800 degrees Celsius, and its constant temperature and heat preservation time are related to the constant temperature. The higher the temperature, the shorter the required reaction time, and the overall reaction time is 0.5 to 6 hours.

[0045] Among them, when the tube furnace reaches the constant temperature and heat preservation stage, turn on the air compressor, and pass the steam in the round-bottom flask into the tube furnace through the air flow for reaction. During the reaction process, an alumina porous heat-insulating furnace door plug is placed at the outlet of the tube furnace.

[0046] Among them, the selected range of the particle size of pure iron powder is from 50 nm to 50 µm. Because it is an in-situ reaction in the tube furnace, the particle size of the obtained catalyst after the reaction is close to that of the initial pure iron powder.

[0047] Among them, the selected range of the volume of the corundum boat is 10 to 200 mL, and the depth of the boat body is less than 20 mm. The pure iron powder is spread flat on the bottom of the boat, and its weight range is 10 to 200 g. The corundum boat containing the iron powder is placed in the middle section of the tube furnace.

[0048] Among them, when the tube furnace reaches the cooling program section, stop the operation of the air compressor and the heating mantle. Wait until the corundum boat cools to room temperature, take it out, weigh the weight of the iron powder after oxidation, and use XRD to detect the type of iron oxide in the powder.

[0049] As another aspect of the technical solution of the present invention, it also relates to the iron-based oxide catalyst prepared by the aforementioned preparation method.

[0050] The iron-based oxide catalyst provided by the present invention has a special structure. The promoter (iron oxide) component grows and distributes in-situ on the surface of the main catalyst (nano-iron) body. On the one hand, it improves the binding force between the metal oxide promoter and the metal main catalyst. On the other hand, the presence of the metal oxide can prevent the coarsening of the iron-based catalyst particles at high temperatures; and the promoter component has a strong interaction with the main catalyst body, making the promoter component evenly dispersed and not easy to agglomerate.

[0051] As another aspect of the technical solution of the present invention, it also relates to the application of the aforementioned iron-based oxide catalyst in the preparation of carbon nanotubes.

[0052] In some embodiments, the application includes: the application of the aforementioned iron-based oxide catalyst in the preparation of carbon nanotubes by chemical vapor deposition (CVD).

[0053] Specifically, the iron-based oxide catalyst provided by the present invention has good stability and high yield in the preparation of carbon nanotubes, and the obtained carbon nanotubes have uniform diameters; taking the catalyst obtained from carbonyl iron powder with an initial particle size of 200 nm as an example, when used in the CVD method for producing carbon nanotubes, carbon nanotubes with a uniform diameter of 1-2 nm can be obtained.

[0054] In summary, the present invention combines an air compressor, an electric heating mantle, and a tubular furnace. The steam generated by heating the solution in the electric heating mantle by the air compressor is introduced into the tubular furnace, and an iron oxide-iron composite catalyst is prepared in situ on the surface of iron powder by the oxidation reaction of water vapor and oxygen on iron powder at high temperature. Among them, iron oxide is gradually converted into Fe3C during the carbon nanotube growth reaction and then decomposed into Fe and graphite. This process can promote the growth of carbon nanotubes. In addition, the presence of metal oxides can enhance the chemical stability of metal nanoparticles and prevent their coarsening, keeping the catalyst in a small particle state. The preparation method of the present invention is simple, can be scaled up, and is convenient for realizing the large-scale preparation of carbon nanotubes.

[0055] The present invention will be further illustrated by the following examples, but the present invention is not limited to the scope of the described examples. The reagents and raw materials used in the following examples are all commercially available, and the test methods without specific conditions are usually carried out under conventional conditions or according to the conditions recommended by each manufacturer.

[0056] Example 1

[0057] This example provides a preparation method of an iron-based oxide catalyst, which includes the following preparation steps:

[0058] S1: Take a 500 mL three-necked round-bottom flask, fill it with an aqueous solution, and place it in an electric heating mantle. Assemble an air compressor, an electric heating mantle, and a tubular furnace to obtain a reaction device as shown in Figure 1 to ensure the smooth flow of the gas inside the device.

[0059] S2: Weigh 1 portion of 50 g of carbonyl iron powder with a particle size of 200 nm and pour it into a flat corundum boat with a length, width, and height of 80×30×10 mm, covering the bottom of the boat. Transfer the corundum boat into the tubular furnace in S1, and set the temperature of the tubular furnace to rise from room temperature of 25 °C to 200 °C in 1 hour, keep it at 200 °C for 2 hours, and then cool it down to room temperature. At the same time, set the target temperature of the electric heating mantle to 120 °C and start heating the solution in the round-bottom flask.

[0060] S3: Wait until the tube furnace in the equipment in step S2 reaches 200 °C. At this time, the solution in the heating mantle has been in a boiling state. Turn on the air compressor, and the pressure gauge shows 0.6 MPa. Continuously introduce the steam above the boiling liquid into the tube furnace. After the reaction time ends, wait for the furnace body to cool down to room temperature, turn off the equipment, take out the corundum boat, and weigh to obtain the weight of the iron-based oxide catalyst (denoted as catalyst 1) obtained after the reaction, which is 54.24 g. See the optical micrograph of catalyst 1 in Figure 2 for details. Conduct XRD tests on the catalyst 1 powder. The test results are shown in Figure 5a , and it is found that Fe on the surface of the catalyst is in-situ oxidized to Fe3O4.

[0061] Add catalyst 1 to the reactor. First, introduce argon into the reactor to exhaust the air, then bubble ethanol with 4200 sccm of hydrogen, and introduce the steam into the reactor. By means of programmed temperature rise, adjust the central temperature of the reactor to 1200 °C and grow for 60 min; stop bubbling, and cool the equipment to room temperature under the protection of 2000 sccm of argon to obtain carbon nanotubes, and the yield is 0.59 g / h.

[0062] Use a scanning electron microscope and a transmission electron microscope to observe the morphology of the carbon nanotube sample, as shown in Figure 3 (SEM image) and Figure 4 (TEM image). The obtained carbon nanotubes have a relatively long tube length, all greater than 1 μm, and the tube diameters are uniform, all in the range of 1 - 2 nm.

[0063] Example 2

[0064] This example provides a preparation method of an iron-based oxide catalyst, which includes the following preparation steps:

[0065] S1: Take a 500 mL three-necked round-bottom flask, fill it with an aqueous solution, and place it in a heating mantle. Assemble an air compressor, a heating mantle, and a tube furnace to obtain a reaction equipment as shown in Figure 1 to ensure the smooth flow of the internal air of the equipment.

[0066] S2: Weigh 1 portion of 50 g of carbonyl iron powder with a particle size of 200 nm and pour it into a flat corundum boat with a length, width, and height of 80×30×10 mm, covering the bottom of the boat. Transfer the corundum boat into the tube furnace in S1, and set the temperature of the tube furnace to rise from room temperature of 25 °C to 600 °C in 2 hours, hold at 600 °C for 1 hour, and then cool down to room temperature. At the same time, set the target temperature of the heating mantle to 120 °C and start heating the solution in the round-bottom flask.

[0067] S3: Wait until the tubular furnace in the equipment in step S2 reaches 600 °C. At this time, the solution in the heating mantle has been in a boiling state. Turn on the air compressor, and the pressure gauge shows 0.8 MPa. Continuously introduce the steam above the boiling liquid into the tubular furnace. After the reaction time ends, wait for the furnace body to cool down to room temperature, turn off the equipment, take out the corundum boat, and weigh it to obtain the weight of the iron-based oxide catalyst (denoted as catalyst 2) obtained after the reaction, which is 60.28 g. Conduct XRD testing on the catalyst 2 powder, and the test results are shown in Figure 5b , and it is found that Fe on the catalyst surface is in-situ oxidized to Fe2O3 and Fe3O4.

[0068] Add catalyst 2 to the reactor. First, introduce argon into the reactor to exhaust the air, and then bubble ethanol with 4200 sccm of hydrogen and introduce steam into the reactor. By means of programmed temperature rise, adjust the central temperature of the reactor to 1200 °C and grow for 60 min; stop bubbling, and cool the equipment to room temperature under the protection of 2000 sccm of argon to obtain carbon nanotubes, and the yield is 0.89 g / h.

[0069] Example 3

[0070] This example provides a preparation method of an iron-based oxide catalyst, which includes the following preparation steps:

[0071] S1: Take a 500 mL three-necked round-bottom flask, fill it with an aqueous solution, and place it in a heating mantle. Assemble an air compressor, a heating mantle, and a tubular furnace to obtain the reaction equipment as shown in Figure 1 , and ensure the smooth flow of the internal gas of the equipment.

[0072] S2: Weigh 1 portion of 50 g of carbonyl iron powder with a particle size of 200 nm and pour it into a flat corundum boat with a length, width, and height of 80×30×10 mm, covering the bottom of the boat. Transfer the corundum boat into the tubular furnace in S1, and set the temperature rise of the tubular furnace to increase from room temperature of 25 °C to 800 °C in 2 hours, keep it at 800 °C for 1 hour, and then cool it down to room temperature. At the same time, set the heating target temperature of the heating mantle to 120 °C and start heating the solution in the round-bottom flask.

[0073] S3: Wait until the tubular furnace in the equipment in step S2 reaches 800 °C. At this time, the solution in the heating mantle has been in a boiling state. Turn on the air compressor, and the pressure gauge shows 0.8 MPa. Continuously introduce the steam above the boiling liquid into the tubular furnace. After the reaction time ends, wait for the furnace body to cool down to room temperature, turn off the equipment, take out the corundum boat, and weigh it to obtain the weight of the iron-based oxide catalyst (denoted as catalyst 3) obtained after the reaction, which is 61.97 g. Conduct XRD testing on the catalyst 3 powder, and it is found that Fe on the catalyst surface is in-situ oxidized to Fe2O3.

[0074] Add catalyst 3 to the reactor. First, purge the air in the reactor with argon, then bubble ethanol with 4200 sccm of hydrogen, and introduce the vapor into the reactor. By means of programmed temperature increase, adjust the central temperature of the reactor to 1200 °C and grow for 60 min. Stop bubbling, and cool the equipment to room temperature under the protection of 2000 sccm of argon to obtain carbon nanotubes with a yield of 0.75 g / h.

[0075] Example 4

[0076] This example provides a preparation method of an iron-based oxide catalyst, which includes the following preparation steps:

[0077] S1: Take a 500 mL three-necked round-bottom flask, fill it with an aqueous solution, and place it in an electric heating mantle. Assemble an air compressor, an electric heating mantle, and a tube furnace to obtain the reaction equipment as shown in Figure 1 to ensure the smooth flow of the internal gas of the equipment.

[0078] S2: Weigh 1 portion of 50 g of carbonyl iron powder with a particle size of 50 nm and pour it into a flat corundum boat with a length, width, and height of 80×30×10 mm, covering the bottom of the boat. Move the corundum boat into the tube furnace in S1, and set the temperature increase of the tube furnace to rise from room temperature of 25 °C to 200 °C in 1 hour, hold at 200 °C for 6 hours, and then cool down to room temperature. At the same time, set the target temperature of the electric heating mantle to 120 °C and start heating the solution in the round-bottom flask.

[0079] S3: When the tube furnace in the equipment in step S2 reaches 200 °C, at this time the solution in the electric heating mantle has been in a boiling state. Turn on the air compressor, and the pressure gauge shows 0.4 MPa, so that the vapor above the boiling liquid is continuously introduced into the tube furnace. After the reaction time ends, wait for the furnace body to cool down to room temperature, turn off the equipment, take out the corundum boat, and obtain the iron-based oxide catalyst obtained after the reaction.

[0080] Add the obtained iron-based oxide catalyst to the reactor. First, purge the air in the reactor with argon, then bubble ethanol with 4200 sccm of hydrogen, and introduce the vapor into the reactor. By means of programmed temperature increase, adjust the central temperature of the reactor to 1200 °C and grow for 60 min. Stop bubbling, and cool the equipment to room temperature under the protection of 2000 sccm of argon to obtain carbon nanotubes.

[0081] Example 5

[0082] This example provides a preparation method of an iron-based oxide catalyst, which includes the following preparation steps:

[0083] S1: Take a 500 mL three-necked round-bottom flask, fill it with an aqueous solution, and place it in an electric heating mantle. Assemble an air compressor, an electric heating mantle, and a tube furnace to obtain the reaction equipment as shown inFigure 1 The reaction equipment shown ensures the smooth flow of the gas inside the equipment.

[0084] S2: Weigh 1 portion of 50 g of carbonyl iron powder with a particle size of 50 µm and pour it into a flat corundum boat with a length, width, and height of 80×30×10 mm, covering the bottom of the boat. Transfer the corundum boat into the tube furnace in S1, and set the temperature increase of the tube furnace to rise from room temperature of 25 °C to 800 °C in 2 hours, hold at 800 °C for 0.5 hours, and then cool down to room temperature. At the same time, set the target temperature of the heating mantle to 120 °C and start heating the solution in the round-bottom flask.

[0085] S3: When the tube furnace in the equipment in step S2 reaches 800 °C, at this time the solution in the heating mantle has been in a boiling state, turn on the air compressor, and the pressure gauge shows 1.0 MPa, so that the steam above the boiling liquid is continuously introduced into the tube furnace. After the reaction time ends, wait for the furnace body to cool down to room temperature, turn off the equipment, take out the corundum boat, and obtain the iron-based oxide catalyst obtained after the reaction.

[0086] Add the obtained iron-based oxide catalyst into the reactor. First, introduce argon into the reactor to exhaust the air, then bubble ethanol with 4200 sccm of hydrogen, and introduce steam into the reactor. By means of programmed temperature increase, adjust the central temperature of the reactor to 1200 °C and grow for 60 min; stop bubbling, and cool the equipment to room temperature under the protection of 2000 sccm of argon to obtain carbon nanotubes.

[0087] Comparative Example 1

[0088] Weigh 1 portion of 50 g of carbonyl iron powder with a particle size of 200 nm and pour it into a flat corundum boat with a length, width, and height of 80×30×10 mm, covering the bottom of the boat. Spray 5 mL of pure water into the corundum boat. Transfer the corundum boat into a constant-temperature oven and set the temperature to rise to 200 °C, hold for 2 hours, and keep spraying 5 mL of water into the corundum boat every 30 minutes. After the reaction time ends, wait for the oven to cool down to room temperature, turn off the equipment, take out the corundum boat, and weigh the weight of the catalyst (denoted as catalyst D1) obtained after the reaction, which is 50.89 g. Conduct XRD testing on the catalyst D1 powder, and the test results are shown in Figure 5c It is found that a small amount of Fe on the surface of the catalyst is in-situ oxidized to Fe3O4. Add catalyst D1 into the reactor. First, introduce argon into the reactor to exhaust the air, then bubble ethanol with 4200 sccm of hydrogen, and introduce steam into the reactor. By means of programmed temperature increase, adjust the central temperature of the reactor to 1200 °C and grow for 60 min; stop bubbling, and cool the equipment to room temperature under the protection of 2000 sccm of argon to obtain carbon nanotubes, and its yield is 0.09 g / h.

[0089] Comparative Example 2

[0090] Compared with Example 2, the difference is that when the tube furnace in the equipment reaches 600 °C, the air compressor is turned on and the pressure gauge shows 0.3 MPa, and the steam above the boiling liquid is continuously introduced into the tube furnace. After the reaction time ends, wait for the furnace body to cool down to room temperature, turn off the equipment, take out the corundum boat, and weigh to obtain the weight of the catalyst (denoted as catalyst D2) obtained after the reaction, which is 56.11 g. The XRD test was carried out on the catalyst D2 powder, and it was found that compared with Example 2, Fe on the catalyst surface was in-situ oxidized to Fe2O3 and Fe3O4, but the content of iron oxides decreased. Catalyst D2 was added to the reactor for the preparation of carbon nanotubes, and its yield decreased to 0.56 g / h compared with Example 2.

[0091] Comparative Example 3

[0092] Compared with Example 1, the difference is that the temperature of the tube furnace is set to rise from room temperature of 25 °C to 150 °C in 1 hour and keep it at 150 °C for 2 hours. When the tube furnace in the equipment reaches 150 °C, turn on the air compressor, and the steam above the boiling liquid is continuously introduced into the tube furnace. After the reaction time ends, wait for the furnace body to cool down to room temperature, turn off the equipment, take out the corundum boat, and weigh to obtain the weight of the catalyst (denoted as catalyst D3) obtained after the reaction, which is 51.59 g. The XRD test was carried out on the catalyst D3 powder, and it was found that the content of iron oxides in the catalyst decreased compared with Example 1. Catalyst D3 was added to the reactor for the preparation of carbon nanotubes, and its yield decreased to 0.19 g / h compared with Example 1.

[0093] Comparative Example 4

[0094] Compared with Example 3, the difference is that the temperature of the tube furnace is set to rise from room temperature of 25 °C to 900 °C in 2 hours and keep it at 900 °C for 1 hour. When the tube furnace in the equipment reaches 900 °C, turn on the air compressor, and the steam above the boiling liquid is continuously introduced into the tube furnace. After the reaction time ends, wait for the furnace body to cool down to room temperature, turn off the equipment, take out the corundum boat, and weigh to obtain the weight of the catalyst (denoted as catalyst D4) obtained after the reaction, which is 62.57 g. The XRD test was carried out on the catalyst D4 powder, and it was found that the content of iron oxides in the catalyst increased compared with Example 3. Catalyst D4 was added to the reactor for the preparation of carbon nanotubes, and its yield decreased to 0.49 g / h compared with Example 3.

[0095] Comparative Example 5

[0096] Compared with Example 1, the difference is that when the tubular furnace in the equipment reaches 200 °C, it is kept warm for 0.3 hours, and then the air compressor is turned on to continuously introduce the steam above the boiling liquid into the tubular furnace. After the reaction time ends, wait for the furnace body to cool down to room temperature, turn off the equipment, take out the corundum boat, and weigh to obtain the weight of the catalyst (denoted as Catalyst D5) obtained after the reaction, which is 50.33 g. Perform XRD test on the Catalyst D5 powder, and it is found that the content of iron oxide in the catalyst decreases compared with Example 1. Add Catalyst D5 to the reactor for the preparation of carbon nanotubes, and its yield decreases to 0.12 g / h compared with Example 1.

[0097] Comparative Example 6

[0098] Compared with Example 3, the difference is that when the tubular furnace in the equipment reaches 800 °C, it is kept warm for 6.5 hours, and then the air compressor is turned on to continuously introduce the steam above the boiling liquid into the tubular furnace. After the reaction time ends, wait for the furnace body to cool down to room temperature, turn off the equipment, take out the corundum boat, and weigh to obtain the weight of the catalyst (denoted as Catalyst D6) obtained after the reaction, which is 63.91 g. Perform XRD test on the Catalyst D6 powder, and it is found that the content of iron oxide in the catalyst increases significantly compared with Example 3, and the characteristic peak of Fe element completely disappears. Add Catalyst D6 to the reactor for the preparation of carbon nanotubes, and its yield decreases to 0.32 g / h compared with Example 1.

[0099] In summary, the carbon nanotubes prepared by using the iron-based oxide catalyst of the present invention by CVD method have uniform tube diameters and high yields, indicating that the iron-based oxide catalyst of the present invention has high activity and excellent performance.

[0100] In addition, the inventor of this case also referred to the foregoing examples and conducted experiments with other raw materials, process operations, and process conditions described in this specification, and all obtained relatively ideal results.

[0101] The above-described embodiments only represent several implementation manners of the present invention, and their descriptions are relatively specific and detailed, but should not be construed as limiting the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the invention patent shall be subject to the appended claims.

Claims

1. A preparation method of an iron-based oxide catalyst, characterized in that, Comprising: Providing a mutually connected air compression device, a heating device and a tubular furnace; Placing iron powder in the reaction chamber of the tubular furnace, heating it to the temperature required for the oxidation reaction, and simultaneously heating the selected liquid on the heating device to boiling; the selected liquid includes pure water or oxygen-rich water; Starting the air compression device to continuously introduce the steam above the boiling liquid into the reaction chamber of the tubular furnace to carry out the oxidation reaction; the working pressure of the air compression device is 0.4 - 1.0 MPa, one end of the reaction chamber of the tubular furnace is introduced with the steam of the selected liquid, and an alumina heat insulation component is placed at the other end; Under the conditions of the presence of water vapor and oxygen, enabling the iron powder to carry out the oxidation reaction in the reaction chamber, and in-situ generating iron oxide on the surface of the iron powder to prepare an iron-based oxide catalyst; The temperature of the oxidation reaction is 600 - 800 °C, and the time of the oxidation reaction is 0.5 - 6 hours; The iron powder is carbonyl iron powder, and the particle size is 50 nm - 50 µm; In the iron-based oxide catalyst, the content of iron powder is 23.9 - 89.7 wt%, and the content of iron oxide is 10.3 - 76.1 wt%.

2. The preparation method according to claim 1, characterized in that, The heating temperature is 105 - 150 °C.

3. The preparation method according to claim 1, wherein The air compression device includes an oil-free mobile air compressor.

4. The preparation method according to claim 1, wherein The heating device includes an electric heating mantle.

5. The iron-based oxide catalyst prepared by the preparation method according to any one of claims 1-4, wherein the iron-based oxide catalyst comprises a main catalyst body and a promoter distributed on the main catalyst body, the main catalyst body is iron powder, and the promoter is iron oxide; wherein, The content of iron powder is 23.9 - 89.7 wt%, and the content of iron oxide is 10.3 - 76.1 wt%.

6. Use of the iron-based oxide catalyst according to claim 5 in the preparation of carbon nanotubes by chemical vapor deposition method.

Images