CN119406408A

CN119406408A - An iron-based oxide catalyst and its preparation method and application

Info

Publication number: CN119406408A
Application number: CN202411609535.9A
Authority: CN
Inventors: 黄珏欣; 漆斌; 杨劲松; 石少华; 程光浩; 周维; 洪辉辉
Original assignee: Jiangxi Copper Technology Research Institute Co ltd
Current assignee: Jiangxi Copper Technology Research Institute Co ltd
Priority date: 2024-11-12
Filing date: 2024-11-12
Publication date: 2025-02-11
Anticipated expiration: 2044-11-12
Also published as: CN119406408B

Abstract

The invention discloses an iron-based oxide catalyst and a preparation method and application thereof. The iron-based oxide catalyst comprises a main catalyst body and cocatalysts distributed on the main catalyst body, wherein the main catalyst body comprises iron powder, and the cocatalysts comprise iron oxide. The preparation method comprises the steps of oxidizing iron powder in a reaction chamber in the presence of steam and oxygen to generate iron oxide in situ on the surface of the iron powder, so as to prepare the iron-based oxide catalyst. The iron-based oxide catalyst provided by the invention has the advantages of good stability, controllable particle size, strong interaction between the promoter component and the main catalyst body, capability of effectively preventing the promoter from agglomerating and falling off, and high yield and uniform tube diameter when being applied to the catalysis preparation of the carbon nano tube.

Description

Iron-based oxide catalyst and preparation method and application thereof

Technical Field

The invention belongs to the technical field of nano material preparation, and particularly relates to an iron-based oxide catalyst, a preparation method and application thereof.

Background

The carbon nano tube is divided into a single-wall carbon nano tube and a multi-wall carbon nano tube, is an allotrope of carbon, has a one-dimensional cylindrical hollow structure, adopts sp ² hybridization form among C atoms, and is widely applied due to excellent electric, mechanical and thermal properties. The existing carbon nano tube preparation method mainly comprises an electric arc method, a chemical vapor deposition method and a laser ablation method. Among them, chemical Vapor Deposition (CVD) is the most widely used and studied preparation method for growing carbon nanotubes. The catalyst plays roles of promoting cracking of organic matters to generate carbon atoms, adsorbing and dissolving active carbon and separating out the carbon atoms to grow the carbon nanotubes on the surface in the process of growing the carbon nanotubes by the CVD method. The preparation of the catalysts used in the CVD process is therefore at the position of the technical core. The existing grown carbon nano tube catalyst generally loads active components on the surface of a carrier, but the active components and the carrier have insufficient binding force and are easy to agglomerate together at high temperature, so that the catalyst is deactivated and the yield of the carbon nano tube is affected. Accordingly, a new catalyst for preparing carbon nanotubes is needed to solve the above problems.

Disclosure of Invention

The invention mainly aims to provide an iron-based oxide catalyst, and a preparation method and application thereof, so as to overcome the defects in the prior art.

In order to achieve the purpose of the invention, the technical scheme adopted by the invention comprises the following steps:

one aspect of the present invention provides an iron-based oxide catalyst comprising a main catalyst body, and a promoter distributed on the main catalyst body, the main catalyst body comprising iron powder, the promoter comprising iron oxide.

The invention also provides a preparation method of the iron-based oxide catalyst, which comprises the steps of oxidizing iron powder in a reaction chamber in the presence of water vapor and oxygen to generate iron oxide on the surface of the iron powder in situ, so as to prepare the iron-based oxide catalyst.

In another aspect, the present invention also provides an iron-based oxide catalyst prepared by the aforementioned preparation method.

In another aspect, the invention also provides an application of the iron-based oxide catalyst in preparing carbon nanotubes.

Compared with the prior art, the technical scheme of the invention has at least the following advantages:

1) The iron-based oxide catalyst provided by the invention has a special structure, and the promoter (iron oxide) component grows in situ and is distributed on the surface of the main catalyst (nano iron) body, so that on one hand, the binding force between the metal oxide promoter and the metal main catalyst is improved, and on the other hand, the existence of the metal oxide can prevent coarsening of iron-based catalyst particles at high temperature;

2) The preparation method provided by the invention is simple and convenient, is easy to expand, is suitable for industrial application, can control the structure and the composition of the finally generated catalyst according to the steam inlet amount, the reaction temperature and the reaction time during the reaction, and can regulate and control the content of the cocatalyst on the surface of the body through the preparation method, particularly can effectively prevent the cocatalyst from agglomerating and falling off in a high-temperature environment;

3) The iron-based oxide catalyst provided by the invention is used for preparing the carbon nano tube, and has the advantages of good stability, high yield and uniform tube diameter of the obtained carbon nano tube.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are required to be used in the embodiments or the description of the prior art will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments described in the present invention, and other drawings may be obtained according to the drawings without inventive effort to those skilled in the art.

FIG. 1 is a schematic diagram of an apparatus for use in preparing an iron-based oxide catalyst in accordance with an exemplary embodiment of the present invention;

FIG. 2 is an optical micrograph of an iron-based oxide catalyst prepared according to example 1 of the present invention;

FIG. 3 is an SEM image of single-walled carbon nanotubes prepared in example 1 of the present invention;

FIG. 4 is a TEM image of single-walled carbon nanotubes prepared in example 1 of the present invention;

FIG. 5a is an XRD pattern of the iron-based oxide catalyst prepared in example 1 of the present invention;

FIG. 5b is an XRD pattern of the iron-based oxide catalyst prepared in example 2 of the present invention;

fig. 5c is an XRD pattern of the catalyst prepared in comparative example 1 of the present invention.

Detailed Description

The invention will be more fully understood upon reading the following detailed description. However, it is to be understood that the following detailed description is merely exemplary of the invention, which may be embodied in various forms. Therefore, specific functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed embodiment.

As one aspect of the technical scheme of the invention, the iron-based oxide catalyst comprises a main catalyst body and a cocatalyst distributed on the main catalyst body, wherein the main catalyst body comprises iron powder, and the cocatalyst comprises iron oxide.

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

In another aspect of the technical scheme, the preparation method of the iron-based oxide catalyst comprises the steps of oxidizing iron powder in a reaction chamber in the presence of steam and oxygen to generate iron oxide on the surface of the iron powder in situ, so as to prepare the iron-based oxide catalyst.

In some embodiments, the oxidation reaction is at a temperature of 200 to 800 ℃ for a time of 0.5 to 6 hours. Fe is completely oxidized due to excessive reaction time, so the reaction time is controlled in this range according to the present invention.

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

In some embodiments, the particle size of the iron powder is 50nm to 50 μm. The carbonyl iron powder with the particle size being too small has higher cost and unstable performance, and the particle size of more than 50nm is more suitable. The particle size of the prepared catalyst is determined according to the particle size of the added pure iron powder, and the promoter iron oxide is generated on the surface of the pure iron powder in situ.

In some embodiments, the method of making comprises:

providing an air compression device, a heating device and a tube furnace which are communicated with each other;

placing iron powder into a reaction chamber of a tube furnace, heating to the temperature required by oxidation reaction, and heating selected liquid on a heating device to boiling;

and starting an air compression device to enable steam above the boiling liquid to be continuously introduced into a reaction cavity of the tube furnace to perform the oxidation reaction.

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

In some preferred embodiments, the temperature of the heating is 105 to 150 ℃.

In some preferred embodiments, one end of the reaction chamber of the tube furnace is fed with vapor of a selected liquid and the other end is placed with an alumina insulation assembly.

In some preferred embodiments, the working pressure of the air compression device is 0.4-1.0 MPa. The amount of steam fed into the tubular furnace is controlled by the pressure value of the air compressor, the total range is 0.4 to 1.0 Mpa (the upper limit of the working pressure of the common commercial air compressor is 1.0 Mpa), and the type of the iron oxide generated on the surface of the pure iron powder in situ can be controlled by the amount of the steam fed or the reaction temperature and time of the tubular furnace.

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

In some preferred embodiments, the heating means includes, but is not limited to, an electric jacket.

In some more specific embodiments, the method of making comprises:

And step one, assembling reaction equipment by using an air compressor, an electric heating sleeve and a tubular furnace, and ensuring the smoothness of air flow in the equipment.

And secondly, pouring pure iron powder (such as carbonyl iron powder) with the required particle size into a flat corundum boat, and spreading the boat bottom. And (3) moving the corundum boat into the tubular furnace in the first step, heating the tubular furnace, and heating the solution in the spherical flask.

And thirdly, when the tubular furnace in the equipment in the second step reaches the specified temperature and the solution in the electric heating sleeve boils, starting an air compressor to enable steam above the boiling liquid to be continuously introduced into the tubular furnace. And after the reaction time is over, waiting for the furnace body to cool to room temperature, closing the equipment, taking out the corundum boat, weighing to obtain the weight of the catalyst after the reaction, and carrying out XRD test on the catalyst powder.

Wherein, a three-neck round bottom flask is used in the electric heating sleeve to be filled with heating solution, the heating solution is pure water or oxygen-enriched water, and the heating temperature is 105-150 ℃. The three sockets of the three-neck round bottom flask are respectively connected with an air compressor, a temperature measuring probe and a tube furnace.

The air compressor is an oil-free mobile air compressor, the ventilation rate can be adjusted through a pressure switch, and the working pressure range is 0.4-1.0 MPa.

Wherein, the constant temperature of the tube furnace can be a fixed value of 200-800 ℃, the constant temperature keeping time is related to the constant temperature, the higher the temperature is, the shorter the reaction time is needed, and the total reaction time is 0.5-6 hours.

When the tubular furnace reaches the constant temperature and heat preservation stage, the air compressor is turned on, and steam in the round bottom flask is introduced into the tubular furnace through air flow to perform reaction. In the reaction process, an alumina porous heat-insulating furnace door plug is arranged at the air outlet of the tubular furnace.

Wherein the particle size of the selected pure iron powder is selected from 50 nm to 50 mu m. Because the tube furnace is in-situ reaction, the particle size of the catalyst obtained after the reaction is close to that of the original pure iron powder.

Wherein the selected corundum boat has a volume range of 10-200 mL and a boat body depth of less than 20 mm. The pure iron powder is flatly paved on the bottom of the boat, the weight range of the pure iron powder is 10 to 200 g, and the corundum boat containing the iron powder is placed in the middle section of the tubular furnace.

Wherein, the operation of the air compressor and the electric heating sleeve is stopped when the tube furnace reaches the cooling program section. And cooling the corundum boat to room temperature, taking out the corundum boat, weighing to obtain the oxidized weight of the iron powder, and detecting the type of the iron oxide in the powder by using XRD.

As another aspect of the technical scheme of the invention, the invention also relates to the iron-based oxide catalyst prepared by the preparation method.

The iron-based oxide catalyst provided by the invention has a special structure, the promoter (iron oxide) component grows in situ and is distributed on the surface of the main catalyst (nano iron) body, so that on one hand, the binding force between the metal oxide promoter and the metal main catalyst is improved, on the other hand, the existence of the metal oxide can prevent coarsening of iron-based catalyst particles at high temperature, and the promoter component and the main catalyst body have strong interaction, so that the promoter component is uniformly dispersed and is not easy to agglomerate.

As another aspect of the technical scheme of the present invention, it also relates to the application of the iron-based oxide catalyst in preparing carbon nanotubes.

In some embodiments, the use includes the use of the foregoing iron-based oxide catalysts in Chemical Vapor Deposition (CVD) processes for the preparation of carbon nanotubes.

Specifically, the iron-based oxide catalyst provided by the invention has good stability, high yield and uniform tube diameter of the obtained carbon nanotubes in the preparation of the carbon nanotubes, and the catalyst obtained by taking carbonyl iron powder with the initial particle diameter of 200 nm as a raw material can obtain uniform tube diameter with the diameter of 1-2 nm when used for producing the carbon nanotubes by a CVD method.

In summary, the invention combines the air compressor, the electric heating sleeve and the tubular furnace, the air compressor is used for leading the steam generated by heating the solution by the electric heating sleeve into the tubular furnace, and the oxidation reaction of the steam and oxygen at high temperature on the iron powder is utilized to form the iron oxide on the surface of the iron powder in situ to prepare the iron oxide-iron composite catalyst. Wherein the iron oxide is gradually converted into Fe ₃ C in the growth reaction of the carbon nanotubes and then decomposed into Fe and graphite, which promotes the growth of the carbon nanotubes, and the presence of the metal oxide can enhance the chemical stability of the metal nanoparticles and prevent coarsening thereof so that the catalyst maintains a small particle state. The preparation method of the invention is simple and convenient, can expand production and is convenient for realizing mass preparation of the carbon nano tube.

The invention is further illustrated by means of the following examples, which are not intended to limit the scope of the invention. The reagents and starting materials used in the following examples were all commercially available, and the test methods in which the specific conditions were not specified were generally conducted under conventional conditions or under the conditions recommended by the respective manufacturers.

Example 1

The embodiment provides a preparation method of an iron-based oxide catalyst, which comprises the following preparation steps:

S1, taking a 500 mL three-neck round-bottom flask, filling the flask with an aqueous solution, and putting the flask into an electrothermal sleeve. The air compressor, the electric heating sleeve and the tubular furnace are assembled to obtain the reaction equipment shown in the figure 1, so that the smoothness of air flow in the equipment is ensured.

S2, 1 part of carbonyl iron powder with the grain diameter of 200 nm and 50 g parts is weighed and poured into a flat corundum boat with the length, width and height of 80 multiplied by 30 multiplied by 10mm, and the boat bottom is fully paved. And (3) moving the corundum boat into the tubular furnace in the step (S1), heating the tubular furnace for 1 hour, heating from the room temperature of 25 ℃ to 200 ℃, preserving heat at 200 ℃ for 2 hours, and then cooling to the room temperature. While the target temperature of the electric jacket was set at 120 degrees celsius and heating of the solution in the round bottom flask was started.

And S3, when the temperature of the tubular furnace in the equipment in the step S2 reaches 200 ℃, the solution in the electric heating sleeve is in a boiling state, and an air compressor pressure gauge is started to display 0.6 MPa, so that steam above the boiling liquid is continuously introduced into the tubular furnace. After the reaction time is over, the furnace body is cooled to room temperature, the equipment is closed, the corundum boat is taken out, and the weight of the iron-based oxide catalyst (recorded as catalyst 1) obtained after the reaction is obtained by weighing is 54.24 g. The optical micrograph of catalyst 1 is shown in figure 2. XRD testing of the catalyst 1 powder, see FIG. 5a, found that Fe oxidized to Fe ₃O₄ in situ on the catalyst surface.

Adding a catalyst 1 into a reactor, introducing argon into the reactor to exhaust air, then bubbling ethanol with 4200 sccm hydrogen, introducing steam into the reactor, regulating the central temperature of the reactor to 1200 ℃ by a temperature programming mode, growing 60 min, stopping bubbling, and cooling the device to room temperature under the protection of 2000 sccm argon to obtain the carbon nano tube with the yield of 0.59 g/h.

And observing the morphology of the carbon nanotube sample by adopting a scanning electron microscope and a transmission electron microscope, wherein the obtained carbon nanotubes are longer and are larger than 1 mu m, and the tube diameters are uniform and are 1-2 nm as shown in a drawing (SEM drawing) and a drawing (TEM drawing) of FIG. 3.

Example 2

S2, 1 part of carbonyl iron powder with the grain diameter of 200 nm and 50 g parts is weighed and poured into a flat corundum boat with the length, width and height of 80 multiplied by 30 multiplied by 10 mm, and the boat bottom is fully paved. And (3) moving the corundum boat into the tubular furnace in the step (S1), heating the tubular furnace for 2 hours, heating from the room temperature of 25 ℃ to 600 ℃, preserving heat at 600 ℃ for 1 hour, and then cooling to the room temperature. And simultaneously setting the heating target temperature of the electric heating sleeve to 120 ℃ and starting to heat the solution in the round-bottomed flask.

And S3, when the temperature of the tubular furnace in the equipment in the step S2 reaches 600 ℃, the solution in the electric heating sleeve is in a boiling state, and an air compressor pressure gauge is started to display 0.8 MPa, so that steam above the boiling liquid is continuously introduced into the tubular furnace. After the reaction time is over, the furnace body is cooled to room temperature, the equipment is closed, the corundum boat is taken out, and the weight of the iron-based oxide catalyst (marked as catalyst 2) obtained after the reaction is obtained by weighing is 60.28 g. XRD testing of the catalyst 2 powder, see FIG. 5b, found that the surface of the catalyst was oxidized in situ to Fe ₂O₃ and Fe ₃O₄.

Adding a catalyst 2 into a reactor, introducing argon into the reactor to exhaust air, then bubbling ethanol with 4200 sccm hydrogen, introducing steam into the reactor, regulating the central temperature of the reactor to 1200 ℃ by a temperature programming mode, growing 60 min, stopping bubbling, and cooling the device to room temperature under the protection of 2000 sccm argon to obtain the carbon nano tube with the yield of 0.89 g/h.

Example 3

S2, 1 part of carbonyl iron powder with the grain diameter of 200 nm and 50 g parts is weighed and poured into a flat corundum boat with the length, width and height of 80 multiplied by 30 multiplied by 10 mm, and the boat bottom is fully paved. And (3) moving the corundum boat into the tubular furnace in the step (S1), heating the tubular furnace for 2 hours, heating from the room temperature of 25 ℃ to 800 ℃, preserving heat at the temperature of 800 ℃ for 1 hour, and then cooling to the room temperature. And simultaneously setting the heating target temperature of the electric heating sleeve to 120 ℃ and starting to heat the solution in the round-bottomed flask.

S3, when the temperature of the tube furnace in the equipment in the step S2 reaches 800 ℃, the solution in the electric heating sleeve is in a boiling state, and an air compressor pressure gauge is started to display 0.8 MPa, so that steam above boiling liquid is continuously introduced into the tube furnace. After the reaction time is over, the furnace body is cooled to room temperature, the equipment is closed, the corundum boat is taken out, and the weight of the iron-based oxide catalyst (marked as catalyst 3) obtained after the reaction is obtained by weighing is 61.97 g. XRD testing of the catalyst 3 powder revealed that Fe on the catalyst surface was oxidized to Fe ₂O₃ in situ.

Adding a catalyst 3 into a reactor, introducing argon into the reactor to exhaust air, then bubbling ethanol with 4200 sccm hydrogen, introducing steam into the reactor, regulating the central temperature of the reactor to 1200 ℃ by a temperature programming mode, growing 60 min, stopping bubbling, and cooling the device to room temperature under the protection of 2000 sccm argon to obtain the carbon nano tube with the yield of 0.75 g/h.

Example 4

S2, 1 part of carbonyl iron powder with the particle size of 50 g and the particle size of 50nm is weighed and poured into a flat corundum boat with the length, the width and the height of 80 multiplied by 30 multiplied by 10 mm, and the boat bottom is fully paved. And (3) moving the corundum boat into the tubular furnace in the step (S1), heating the tubular furnace for 1 hour, heating from the room temperature of 25 ℃ to 200 ℃, preserving heat at 200 ℃ for 6 hours, and then cooling to the room temperature. While the target temperature of the electric jacket was set at 120 degrees celsius and heating of the solution in the round bottom flask was started.

And S3, when the temperature of the tubular furnace in the equipment in the step S2 reaches 200 ℃, the solution in the electric heating sleeve is in a boiling state, and an air compressor pressure gauge is started to display 0.4 MPa, so that steam above the boiling liquid is continuously introduced into the tubular furnace. And after the reaction time is over, waiting for the furnace body to cool to room temperature, closing the equipment, and taking out the corundum boat to obtain the iron-based oxide catalyst after the reaction.

Adding the obtained iron-based oxide catalyst into a reactor, introducing argon into the reactor to exhaust air, then bubbling ethanol with 4200 sccm hydrogen, introducing steam into the reactor, regulating the central temperature of the reactor to 1200 ℃ in a temperature programming mode, growing at 60 min, stopping bubbling, and cooling the equipment to room temperature under the protection of 2000 sccm argon to obtain the carbon nano tube.

Example 5

S2, 1 part of carbonyl iron powder with the particle size of 50 mu m and the particle size of 50 g is weighed and poured into a flat corundum boat with the length, the width and the height of 80 multiplied by 30 multiplied by 10 mm, and the boat bottom is fully paved. And (3) moving the corundum boat into the tubular furnace in the step (S1), heating the tubular furnace for 2 hours, heating from the room temperature of 25 ℃ to 800 ℃, preserving heat at the temperature of 800 ℃ for 0.5 hour, and then cooling to the room temperature. And simultaneously setting the heating target temperature of the electric heating sleeve to 120 ℃ and starting to heat the solution in the round-bottomed flask.

S3, when the temperature of the tube furnace in the equipment in the step S2 reaches 800 ℃, the solution in the electric heating sleeve is in a boiling state, and an air compressor pressure gauge is started to display 1.0 MPa, so that steam above boiling liquid is continuously introduced into the tube furnace. And after the reaction time is over, waiting for the furnace body to cool to room temperature, closing the equipment, and taking out the corundum boat to obtain the iron-based oxide catalyst after the reaction.

Comparative example 1

1 Part of carbonyl iron powder with the grain diameter of 200 nm of 50 g is weighed and poured into a flat corundum boat with the length, the width and the height of 80 multiplied by 30 multiplied by 10 mm, the boat bottom is paved, and pure water is sprayed into the corundum boat for 5 mL. The corundum boat is moved into a constant temperature oven, the temperature is raised to 200 ℃, the heat is preserved for 2 hours, and the corundum boat is sprayed with water 5mL times every 30 minutes. After the reaction time was ended, the oven was waited for cooling to room temperature, the apparatus was turned off, the corundum boat was taken out, and the weight of the catalyst (denoted as catalyst D1) obtained after the reaction was weighed to be 50.89 g. XRD measurements were performed on catalyst D1 powder, with reference to FIG. 5c, and it was found that a small amount of Fe on the catalyst surface was oxidized to Fe ₃O₄ in situ. Adding a catalyst D1 into a reactor, introducing argon into the reactor to exhaust air, bubbling ethanol with 4200 sccm hydrogen, introducing steam into the reactor, regulating the temperature of the center of the reactor to 1200 ℃ by a temperature programming mode, growing at 60min, stopping bubbling, and cooling the device to room temperature under the protection of 2000 sccm argon to obtain the carbon nano tube with the yield of 0.09 g/h.

Comparative example 2

In comparison to example 2, the difference was that the tube furnace in the apparatus reached 600 degrees celsius, and the air compressor pressure gauge was turned on to display 0.3 MPa, allowing the vapor above the boiling liquid to continue to pass into the tube furnace. After the reaction time was over, the furnace was cooled to room temperature, the equipment was turned off, the corundum boat was taken out, and the weight of the catalyst (denoted as catalyst D2) obtained after the reaction was weighed to be 56.11 g. XRD measurements were performed on the catalyst D2 powder, and it was found that Fe was oxidized in situ to Fe ₂O₃ and Fe ₃O₄ on the catalyst surface, but the iron oxide content was reduced as compared to example 2. Catalyst D2 was added to the reactor for the preparation of carbon nanotubes, and the yield of comparative example 2 was reduced to 0.56 g/h.

Comparative example 3

Compared with example 1, the temperature of the tube furnace was increased from 25 degrees celsius to 150 degrees celsius for 1 hour, and the tube furnace was kept at 150 degrees celsius for 2 hours. When the temperature of the tube furnace in the equipment reaches 150 ℃, the air compressor is started, so that the steam above the boiling liquid is continuously introduced into the tube furnace. After the reaction time was ended, the furnace was cooled to room temperature, the equipment was turned off, the corundum boat was taken out, and the weight of the catalyst (denoted as catalyst D3) obtained after the reaction was weighed to be 51.59 g. XRD measurements of catalyst D3 powder revealed a decrease in iron oxide content compared to the catalyst of example 1. Catalyst D3 was added to the reactor for the preparation of carbon nanotubes, and the yield of comparative example 1 was reduced to 0.19 g/h.

Comparative example 4

Compared with example 3, the difference is that the temperature of the tube furnace is raised from 25 ℃ to 900 ℃ at room temperature for 2 hours, and the tube furnace is kept at 900 ℃ for 1 hour. When the temperature of the tube furnace in the equipment reaches 900 ℃, the air compressor is started, so that the steam above the boiling liquid is continuously introduced into the tube furnace. After the reaction time is over, the furnace body is cooled to room temperature, the equipment is closed, the corundum boat is taken out, and the weight of the catalyst (marked as catalyst D4) obtained after the reaction is obtained by weighing is 62.57 g. XRD testing of catalyst D4 powder showed an increase in iron oxide content compared to the catalyst of example 3. Catalyst D4 was added to the reactor for the preparation of carbon nanotubes, and the yield of comparative example 3 was reduced to 0.49 g/h.

Comparative example 5

Compared with example 1, the difference is that when the tube furnace in the equipment reaches 200 ℃ and keeps warm for 0.3 hour, the air compressor is started, so that the steam above the boiling liquid is continuously introduced into the tube furnace. After the reaction time was over, the furnace was cooled to room temperature, the equipment was turned off, the corundum boat was taken out, and the weight of the catalyst (denoted as catalyst D5) obtained after the reaction was weighed to be 50.33 g. XRD testing of catalyst D5 powder revealed a decrease in iron oxide content compared to the catalyst of example 1. Catalyst D5 was added to the reactor for the preparation of carbon nanotubes, and the yield of comparative example 1 was reduced to 0.12 g/h.

Comparative example 6

Compared with example 3, the difference is that when the tube furnace in the equipment reaches 800 ℃ and keeps warm for 6.5 hours, the air compressor is started, so that the steam above the boiling liquid is continuously introduced into the tube furnace. After the reaction time is over, the furnace body is cooled to room temperature, the equipment is closed, the corundum boat is taken out, and the weight of the catalyst (marked as catalyst D6) obtained after the reaction is obtained by weighing is 63.91 g. XRD test was conducted on the powder of catalyst D6, and it was found that the content of iron oxide in the catalyst was greatly increased as compared with that in example 3, and the characteristic peak of the elemental Fe completely disappeared. Catalyst D6 was added to the reactor for the preparation of carbon nanotubes, and the yield of comparative example 1 was reduced to 0.32 g/h.

In conclusion, the carbon nano tube prepared by the CVD method by adopting the iron-based oxide catalyst has uniform tube diameter and high yield, which indicates that the iron-based oxide catalyst has higher activity and excellent performance.

In addition, the inventors have conducted experiments with other materials, process operations, and process conditions as described in this specification with reference to the foregoing examples, and have all obtained desirable results.

The above examples illustrate only a few embodiments of the invention, which are described in detail and are not to be construed as limiting the scope of the invention. It should be noted that it will be apparent to those skilled in the art that several variations and modifications can be made without departing from the spirit of the invention, which are all within the scope of the invention. Accordingly, the scope of protection of the present invention is to be determined by the appended claims.

Claims

1. An iron-based oxide catalyst, characterized in that it comprises a main catalyst body and a co-catalyst distributed on the main catalyst body, wherein the main catalyst body comprises iron powder and the co-catalyst comprises iron oxide.

2. The iron-based oxide catalyst according to claim 1, characterized in that 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%.

3. A method for preparing an iron-based oxide catalyst, characterized in that it includes: in the presence of water vapor and oxygen, allowing iron powder to undergo an oxidation reaction in a reaction chamber to generate iron oxide in situ on the surface of the iron powder to obtain an iron-based oxide catalyst.

4. The preparation method according to claim 3, characterized in that the temperature of the oxidation reaction is 200-800°C and the time is 0.5-6 hours.

5. The preparation method according to claim 3, characterized in that the iron powder comprises carbonyl iron powder; and/or the particle size of the iron powder is 50 nm~50 µm.

6. The preparation method according to claim 3, characterized in that it comprises:

Provide an air compression device, a heating device, and a tube furnace that are interconnected;

The iron powder is placed in the reaction chamber of the tube furnace, and the temperature is raised to the temperature required for the oxidation reaction, while the selected liquid on the heating device is heated to boiling;

The air compression device is turned on to allow the steam above the boiling liquid to continuously flow into the reaction chamber of the tubular furnace to carry out the oxidation reaction.

7. The preparation method according to claim 6, characterized in that the selected liquid comprises pure water or oxygen-enriched water; and/or the heating temperature is 105-150°C.

8. The preparation method according to claim 6, characterized in that the vapor of the selected liquid is introduced into one end of the reaction chamber of the tube furnace, and an alumina heat insulation component is placed at the other end;

And/or, the working pressure of the air compression device is 0.4~1.0 MPa;

and/or, the air compression device comprises an oil-free portable air compressor;

And/or, the heating device comprises an electric heating jacket.

9. An iron-based oxide catalyst prepared by the preparation method according to any one of claims 3 to 8.

10. Use of the iron-based oxide catalyst according to any one of claims 1, 2 and 9 in the preparation of carbon nanotubes.