Iron-based catalyst, method for preparing the same, and method for producing low-carbon olefins by hydrogenation of co2

Abstract

The application provides an iron-based catalyst, a preparation method thereof, and a method for preparing low-carbon olefins by CO2 hydrogenation. The preparation method of the iron-based catalyst comprises the following steps: crushing iron rust and performing first calcination treatment to obtain an iron-based catalyst precursor; impregnating the iron-based catalyst precursor in an alkali metal salt solution; and performing second calcination treatment on the impregnated iron-based catalyst precursor to obtain the iron-based catalyst. The iron rust simultaneously satisfies the following characteristics: (1) the content of Cl element in the iron rust is less than 0.3 wt%; (2) the content of S element in the iron rust is less than 1.2 wt%; (3) the iron rust does not contain Ni element; and (4) the content of P element in the iron rust is less than 2 wt%. The iron-based catalyst prepared by using the iron rust as a raw material can be used for catalyzing the reaction of preparing low-carbon olefins by CO2 hydrogenation, and realizes high-value utilization of the waste iron rust and resource conversion of carbon dioxide.

Description

Technical Field

[0001] This application relates to the fields of catalysts and carbon dioxide resource utilization technology, and in particular to an iron-based catalyst and its preparation method, and a method for producing low-carbon olefins by CO2 hydrogenation. Background Technology

[0002] With the rapid development of the global steel industry, steel corrosion has become an increasingly serious problem. Every year, a large amount of steel is replaced due to corrosion failure, generating a large amount of waste rust. Traditional methods for recycling rust and scrap steel mainly rely on high-temperature smelting, a process that is not only energy-intensive but also produces large amounts of carbon dioxide emissions, further exacerbating the greenhouse effect and environmental pollution. Current research has explored the use of rust in photocatalysis, electrochemical energy storage, and nanomaterial preparation, but its direct utilization in industrial catalytic reactions remains limited.

[0003] Iron-based catalysts are widely used in important industrial reactions such as Fischer-Tropsch synthesis, ammonia synthesis, and carbon dioxide hydrogenation. Among them, Fe2O3 is a common catalyst precursor in carbon dioxide hydrogenation, which can form active phases such as Fe3O4 and Fe5C2 in situ during the reaction, realizing the conversion of CO2 into high-value-added chemicals such as low-carbon olefins.

[0004] The main component of natural rust is also Fe2O3, but there are currently no reports on the technology of directly preparing iron-based catalysts from waste rust and using them for the hydrogenation of carbon dioxide to produce low-carbon olefins. Summary of the Invention

[0005] The purpose of this application is to provide an iron-based catalyst and its preparation method, as well as a method for CO2 hydrogenation to produce low-carbon olefins, so as to achieve high-value utilization of waste rust and resource conversion of carbon dioxide. The specific technical solution is as follows:

[0006] The first aspect of this application provides a method for preparing an iron-based catalyst, which includes the following steps: pulverizing rust and then subjecting it to a first calcination treatment to obtain an iron-based catalyst precursor; impregnating the iron-based catalyst precursor in an alkali metal salt solution; subjecting the impregnated iron-based catalyst precursor to a second calcination treatment to obtain an iron-based catalyst; wherein the rust simultaneously satisfies the following characteristics: (1) the content of Cl element in the rust is less than 0.3 wt%, (2) the content of S element in the rust is less than 1.2 wt%, (3) the rust does not contain Ni element, and (4) the content of P element in the rust is less than 2 wt%.

[0007] In one embodiment of this application, the first roasting treatment and / or the second roasting treatment includes: roasting at a temperature of 500°C to 600°C for 3 to 6 hours in an air atmosphere.

[0008] In one embodiment of this application, the alkali metal salt of the alkali metal salt solution is selected from at least one of K2CO3, Na2CO3 and Li2CO3.

[0009] The second aspect of this application provides an iron-based catalyst prepared using the preparation method provided in the first aspect of this application, wherein the alkali metal loading in the iron-based catalyst is 0.1 wt% to 5 wt%.

[0010] The third aspect of this application provides a method for producing low-carbon olefins by CO2 hydrogenation, using an iron-based catalyst prepared by the method provided in the first aspect of this application as the catalyst for the CO2 hydrogenation reaction to produce low-carbon olefins.

[0011] In some embodiments of this application, the method for producing low-carbon olefins by CO2 hydrogenation includes the following steps: reducing an iron-based catalyst in a hydrogen atmosphere at 350°C to 450°C for 4 to 10 hours; adding the reduced iron-based catalyst to a CO2 hydrogenation reactor for producing low-carbon olefins, and introducing a reaction gas to carry out the CO2 hydrogenation reaction for producing low-carbon olefins.

[0012] In some embodiments of this application, the reaction gas includes CO2, H2 and an inert gas, and the molar ratio of CO2, H2 and the inert gas is 1:(2~5):(0.1~0.3).

[0013] In some embodiments of this application, the reaction conditions for CO2 hydrogenation to produce low-carbon olefins are: temperature of 280℃~350℃, pressure of 1MPa~5MPa, and gas hourly space velocity of 2000 ml·g. -1 ·h -1 ~10000ml·g -1 ·h -1 .

[0014] In some embodiments of this application, the low-carbon olefin includes at least one of ethylene, propylene, and butene.

[0015] The beneficial effects of this application are:

[0016] This application provides an iron-based catalyst and its preparation method, as well as a method for CO2 hydrogenation to produce low-carbon olefins. The preparation method of the iron-based catalyst includes the following steps: pulverizing rust and then subjecting it to a first calcination treatment to obtain an iron-based catalyst precursor; impregnating the iron-based catalyst precursor in an alkali metal salt solution; subjecting the impregnated iron-based catalyst precursor to a second calcination treatment to obtain the iron-based catalyst; wherein the rust simultaneously meets the following characteristics: (1) the content of Cl element in the rust is less than 0.3 wt%, (2) the content of S element in the rust is less than 1.2 wt%, (3) the rust does not contain Ni element, and (4) the content of P element in the rust is less than 2 wt%. The iron-based catalyst of this application has a wide range of raw material sources and low cost, which is conducive to avoiding the high energy consumption and high carbon emissions in the traditional high-temperature smelting process of steel recycling. It has the advantages of being green and environmentally friendly, having a simple process, and high resource recycling value. When the iron-based catalyst of this application is used to catalyze the reaction of carbon dioxide hydrogenation to produce low-carbon olefins, the carbon dioxide conversion rate is high and the low-carbon olefin selectivity is high, which has important application prospects in the fields of carbon dioxide resource utilization and high-value utilization of solid waste.

[0017] Of course, implementing any product or method of this application does not necessarily require achieving all of the advantages described above at the same time. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other embodiments can be obtained based on these accompanying drawings.

[0019] Figure 1 XRD patterns of rust samples from different sources;

[0020] Figure 2 'a' represents the H2-TPR curves of rust samples from different sources;

[0021] Figure 2 b represents the N2 adsorption-desorption curves of rust samples from different sources;

[0022] Figure 3 Evaluation results of CO2 hydrogenation performance of rust samples from different sources and Fe2O3 as catalyst;

[0023] Figure 4 The results of CO2 hydrogenation performance evaluation of the iron-based catalysts and K-modified Fe2O3 prepared in Examples 1 to 5 and Comparative Examples 1 to 2 of this application are as follows;

[0024] Figure 5 XPS images of #1 rust and the iron-based catalyst prepared in Example 1 after the reaction. Detailed Implementation

[0025] The technical solutions of this application will be clearly and completely described below with reference to the embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0026] The first aspect of this application provides a method for preparing an iron-based catalyst, which includes the following steps: pulverizing rust and then subjecting it to a first calcination treatment to obtain an iron-based catalyst precursor; impregnating the iron-based catalyst precursor in an alkali metal salt solution; subjecting the impregnated iron-based catalyst precursor to a second calcination treatment to obtain an iron-based catalyst; wherein the rust simultaneously satisfies the following characteristics: (1) the content of Cl element in the rust is less than 0.3 wt%, (2) the content of S element in the rust is less than 1.2 wt%, (3) the rust does not contain Ni element, and (4) the content of P element in the rust is less than 2 wt%. For example, the Cl content in rust can be 0 wt%, 0.05 wt%, 0.1 wt%, 0.2 wt%, 0.29 wt%, or any range of two of these values; the S content can be 0 wt%, 0.1 wt%, 0.3 wt%, 0.5 wt%, 1 wt%, 1.15 wt%, or any range of two of these values; and the P content can be 0.1 wt%, 0.5 wt%, 1 wt%, 1.99 wt%, or any range of two of these values. The main component of rust is Fe2O3, which is a common catalyst precursor in the hydrogenation reaction of carbon dioxide. During the reaction, it can form active phases such as Fe3O4 and Fe5C2 in situ, achieving efficient conversion of CO2 to low-carbon olefins. The iron-based catalyst of this application has widely available and low-cost raw materials. Rust, after being crushed and calcined, can be directly used for catalyst preparation without complex chemical synthesis steps. After impregnation with alkali metal salts and calcination, the iron-based catalyst can be obtained, exhibiting high activity and good stability. It can be used to catalyze the hydrogenation of CO2 to produce low-carbon olefins, where CO2 has a high conversion rate and low-carbon olefins have high selectivity.

[0027] This application does not impose any particular restrictions on the source of rust, as long as it achieves the purpose of this application. For example, rust can originate from everyday steel corrosion environments, marine environments, underground environments, chemical environments, scrap steel dumping environments, or natural environments such as grasslands and deserts.

[0028] This application does not impose any particular limitation on the particle size of the shredded rust, as long as the purpose of this application can be achieved. For example, the rust can be shredded to 20-40 mesh.

[0029] In some embodiments of this application, the first calcination treatment includes calcining at a temperature of 500℃~600℃ for 3h~6h in an air atmosphere. In some embodiments of this application, the second calcination treatment includes calcining at a temperature of 500℃~600℃ for 3h~6h in an air atmosphere. For example, the temperatures of the first and second calcination treatments can be 500℃, 520℃, 550℃, 580℃, 600℃, or any combination of two of these values; the calcination time can be 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h, or any combination of two of these values. Adjusting the parameters of the first calcination treatment within the above ranges is beneficial for removing adsorbed water, crystal water, and volatile impurities from rust, transforming the rust into relatively homogeneous iron oxide. Simultaneously, the dehydration process can further expand pores and retain the mesoporous structure and high specific surface area of ​​the iron-based catalyst precursor, providing more permeation channels and adsorption sites for subsequent alkali metal salt solutions. Adjusting the parameters of the second roasting treatment within the above range is beneficial for the conversion of alkali metal salts into alkali metal oxides, and promotes the synthesis of olefins in the product.

[0030] In some embodiments of this application, the alkali metal salt in the alkali metal salt solution is selected from at least one of K2CO3, Na2CO3, and Li2CO3. Controlling the type of alkali metal salt within the above range is beneficial for promoting CO2 adsorption and activation, while simultaneously promoting olefin desorption and inhibiting secondary hydrogenation and the formation of byproduct alkanes.

[0031] The second aspect of this application provides an iron-based catalyst prepared using the preparation method provided in the first aspect of this application.

[0032] In iron-based catalysts, the loading of alkali metals ranges from 0.1 wt% to 5 wt%. For example, the loading of alkali metals can be 0.1 wt%, 0.5 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, or any combination of two of these values. By controlling the loading of alkali metals within this range, the iron-based catalyst surface has more basic sites, which is beneficial for carbon dioxide adsorption. Simultaneously, excessive loading avoids masking the active iron sites, thereby improving the conversion rate of carbon dioxide and the selectivity for low-carbon olefins.

[0033] The third aspect of this application provides a method for producing low-carbon olefins by CO2 hydrogenation, using an iron-based catalyst prepared by the method provided in the first aspect of this application as the catalyst for the CO2 hydrogenation reaction to produce low-carbon olefins.

[0034] In some embodiments of this application, the method for CO2 hydrogenation to produce low-carbon olefins includes the following steps: reducing an iron-based catalyst in a hydrogen atmosphere at 350°C to 450°C for 4 to 10 hours; adding the reduced iron-based catalyst to a CO2 hydrogenation reactor for producing low-carbon olefins, and introducing a reaction gas to carry out the CO2 hydrogenation reaction. For example, the reduction temperature of the iron-based catalyst can be 350°C, 400°C, 450°C, or a range of any two of these values; the reduction time can be 4 hours, 6 hours, 8 hours, 10 hours, or a range of any two of these values. By reducing the catalyst in a hydrogen atmosphere and controlling the reduction temperature and time within the above ranges, it is beneficial to improve the reactivity of the iron-based catalyst.

[0035] In some embodiments of this application, the reaction gas includes CO2, H2, and an inert gas, with a molar ratio of CO2, H2, and inert gas of 1:(2~5):(0.1~0.3). For example, the molar ratio of CO2, H2, and inert gas can be 1:2:0.1, 1:2:0.3, 1:3:0.167, 1:5:0.2, or a range consisting of any two of these values. Adjusting the molar ratio of CO2, H2, and inert gas within the above range is beneficial for improving the conversion rate of carbon dioxide hydrogenation and the selectivity of low-carbon olefins.

[0036] In this application, the inert gas includes, but is not limited to, at least one of nitrogen and argon. The inert gas does not participate in the CO2 hydrogenation reaction to produce low-carbon olefins; it is only used as an internal standard and equilibrium gas for auxiliary analysis.

[0037] In some embodiments of this application, the reaction conditions for CO2 hydrogenation to produce low-carbon olefins are: temperature of 280℃~350℃, pressure of 1MPa~5MPa, and gas hourly space velocity of 2000 ml·g. -1 ·h -1 ~10000ml·g -1 ·h -1 For example, the reaction temperature can be 280℃, 300℃, 320℃, 350℃, or a range of any two of these values; the pressure can be 1MPa, 2MPa, 3MPa, 4MPa, 5MPa, or a range of any two of these values; and the gas hourly space velocity (GHSV) is 2000 ml·g. -1 ·h -1 3000ml·g -1 ·h -1 5000ml·g -1 ·h -1 6000ml·g -1 ·h -1 8000ml·g -1 ·h -1 10000ml·g -1·h -1 This could be a range consisting of any two of these values. Adjusting the reaction conditions for CO2 hydrogenation to produce lower olefins within this range can improve the CO2 hydrogenation conversion rate and the selectivity of lower olefins.

[0038] In some embodiments of this application, the low-carbon olefin includes at least one of ethylene, propylene, and butene.

[0039] In this application, low-carbon olefins refer to olefins with 4 or fewer carbon atoms, including ethylene, propylene, butene, etc.

[0040] Example

[0041] The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below. Furthermore, unless otherwise specified, "parts" and "%" are quality standards.

[0042] Test methods and equipment:

[0043] X-ray fluorescence spectroscopy (XRF):

[0044] The content of various elements in rust was determined using an X-ray fluorescence spectrometer, model Rigaku ZSX primus IV.

[0045] X-ray diffraction (XRD):

[0046] An X-ray diffractometer, model D8 powder diffractometer (manufactured by Bruker GmbH, Germany), was used. The parameters were set to 35 kV 40 mA, continuous mode, scan step size of 0.04°, integration time of 0.4 s, and scan range of 20-100°. A Co target was used for testing. Crystal phase analysis was performed based on the JCPDS database.

[0047] Temperature-programmed hydrogen reduction (H2-TPR) test:

[0048] H2 temperature-programmed reduction (H2-TPR) was performed using a BELCAT-II-T-SP analyzer with either a thermal conductivity detector (TCD) or a mass spectrometer. A 50 mg sample was pretreated with helium at 200 °C for 1 hour. Subsequently, after cooling to 50 °C, a gas mixture (5% H2 / Ar) was injected into the reactor at a rate of 30 mL / min. H2-TPR curves were then measured at a heating rate of 10 °C / min, ranging from 50 to 900 °C.

[0049] N2 adsorption-desorption test:

[0050] Specific surface area, pore volume, and pore size were determined using an N2 adsorption-desorption experiment (ASAP 2460 3.00) at -196°C. Prior to testing, the samples were degassed under vacuum at 240°C for 8 hours.

[0051] X-ray photoelectron spectroscopy (XPS):

[0052] X-ray photoelectron spectroscopy analysis was performed using a Thermo Scientific K-Alpha X-ray photoelectron spectrometer. The excitation source was Al Kα rays, hv = 1486.6 eV.

[0053] <Preliminary screening of rust>

[0054] XRD was used to test rust samples from different sources, such as Figure 1 As shown in the figure, similar to Fe2O3 prepared by co-precipitation, the Fe2O3 phase was observed in all 12 rust samples from different sources (#1 to #12). The SiO2 phase was also observed in rust samples #3 and #10, which is attributed to impurities in the environment. Subsequently, the content of each element in the rust samples was determined by X-ray fluorescence spectrometry, and the results are shown in Table 1. Reducing ability is a key performance characteristic of iron-based catalysts in the carbon dioxide hydrogenation reaction. Figure 2 'a' represents the H2-TPR curves of rust samples from different sources. Figure 2 Figure b shows the N2 adsorption-desorption curves of rust samples from different sources. As can be seen from the figure, most rust can be reduced to elemental iron phase, facilitating the subsequent carbonization process. Simultaneously, most rust exhibits favorable physical properties, such as specific surface area and pore volume.

[0055] Rust samples from different sources were also used directly as catalysts to test their carbon dioxide hydrogenation performance. The test method is as shown in Example 1 below, "Catalytic Performance Test of Iron-Based Catalysts," where the iron-based catalyst is replaced with rust. The results are as follows. Figure 3 As shown, from Figure 3 It can be seen that rust #1 to #7 exhibits a high CO2 conversion rate when used as a catalyst for CO2 hydrogenation, comparable to that of Fe2O3. However, rust #8 to #12 only achieves a CO2 conversion rate of approximately 5%. Combined with the data in Table 1, it can be seen that excessively high Cl and / or S content in the rust leads to a decrease in CO2 conversion rate. Based on preliminary screening, rust #8 to #12 cannot be used as raw materials for preparing the iron-based catalyst of this application.

[0056] Table 1

[0057] In Table 1, a content of 0 indicates that the content of each element in the rust sample could not be detected by X-ray fluorescence spectroscopy.

[0058] The sources of rust #1~#12 are as follows: #1 comes from a processing plant in Shenyang, #2 comes from molds in Dalian, #3 comes from rural areas in Hulunbuir, #4 comes from rooftops in Toyama, Japan, #5~#8 come from rural areas in Chaoyang City, #9 and #10 come from fishing boats in Huludao, #11 comes from a scrap yard in Jinchang City, and #12 comes from a chemical plant in Zhenjiang.

[0059] Example 1

[0060] <Preparation of Iron-Based Catalysts>

[0061] Rust (#1) from the Shenyang processing plant was collected, pulverized into powder, and calcined at 550°C for 5 hours in air to obtain an iron-based catalyst precursor. The iron-based catalyst precursor was loaded with 1wt% K2CO3 (based on the mass of rust) using an equal-volume impregnation method and calcined again at 550°C for 5 hours in air to obtain the iron-based catalyst.

[0062] <Catalytic Performance Testing of Iron-Based Catalysts>

[0063] The iron-based catalyst prepared above was reduced at 400°C for 8 hours under a hydrogen atmosphere.

[0064] The reduced iron-based catalyst was packed into a fixed-bed reactor, and a reaction gas with a molar ratio of CO2, H2, and Ar of 24:72:4 was introduced. The reactor was subjected to reaction at a temperature of 320℃, a pressure of 3 MPa, and a gas hourly space velocity of 6000 ml·g. -1 ·h -1 The reaction was carried out under the specified reaction conditions. C5 was collected using a cold trap. + Heavy hydrocarbons are removed and the water produced in the reaction is eliminated. Octane is then added to the cold trap to absorb C5 hydrocarbons. + Heavy hydrocarbons. At the end of the reaction, the product was collected in the cold trap, and dodecane was added to the oil phase as an internal standard. The oil and aqueous phase products were analyzed using an offline gas chromatograph (Shimadzu GC-2014) equipped with a flame ionization detector (FID) and a DB-1 capillary column. Two online gas chromatograph systems (Jier GC 320 and Shimadzu GC-2014) were used to analyze the gas phase products. One system was equipped with a thermal conductivity detector (TCD) and an activated carbon column for analyzing argon, carbon monoxide, methane, and carbon dioxide; the other system was equipped with a flame ionization detector (FID) and a GS-alumina capillary column for analyzing light hydrocarbons.

[0065] Examples 2 to 5

[0066] Except for adjusting the source of rust according to Table 1, everything else is the same as in Example 1.

[0067] Comparative Examples 1 to 2

[0068] Except for adjusting the source of rust according to Table 1, everything else is the same as in Example 1.

[0069] The performance parameters of each embodiment and comparative example are shown in Table 2.

[0070] Table 2

[0071] In Table 2, C 2-4 = This refers to alkenes with 2 to 4 carbon atoms, C 2-4 o C5 represents unsaturated hydrocarbons with 2 to 4 carbon atoms. + This refers to hydrocarbons with 5 or more carbon atoms.

[0072] Figure 4 The figures show the CO2 hydrogenation performance evaluation results of the iron-based catalysts and K-modified Fe2O3 prepared in Examples 1 to 5 and Comparative Examples 1 to 2 of this application. As can be seen from the figures, the iron-based catalyst prepared from #1 rust has the highest CO2 conversion rate and the highest low-carbon olefin selectivity, both of which are higher than those of K-modified Fe2O3. The iron-based catalysts prepared from #2 and #3 rust have lower low-carbon olefin selectivity. Based on the data in Table 1, #2 and #3 rust contain Ni, which is commonly used in methanation reactions and has a strong hydrogenation capacity, thus resulting in lower low-carbon olefin selectivity. The low-carbon olefin selectivity of the iron-based catalysts prepared from #6 and #7 rust is lower than that of the iron-based catalyst prepared from #1. This is attributed to the higher P content in #6 and #7 rust. P in rust usually exists as phosphorus pentoxide, which neutralizes the alkali metals in the catalyst, thereby reducing the low-carbon olefin selectivity. Figure 5 The XPS spectra of the rust from #1 after the reaction and the iron-based catalyst prepared in Example 1 are shown. It can be seen from the figures that in the Fe 2p spectrum, the binding peaks at 707.5, 710.7, and 713.9 eV are attributed to the Fe-C bond, Fe... 2+ Fe 2+ After the reaction, the proportion of Fe-C phase in the iron-based catalyst prepared in Example 1 (8.1%) was higher than that in the rust of #1 (7.1%), indicating that the iron-based catalyst generated more iron carbide active phase during the reaction.

[0073] The preparation process of the above-mentioned K-modified Fe2O3 is as follows: Fe2O3 is loaded with 1wt% K2CO3 by equal volume impregnation method and calcined at 550℃ for 5h in air atmosphere to obtain iron-based catalyst.

[0074] As can be seen from Examples 1 to 5 and Comparative Examples 1 to 2, the iron-based catalyst prepared by the preparation method of this application using rust as raw material that meets the requirements of this application has a high CO2 conversion rate and low carbon olefin selectivity.

[0075] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A method for preparing an iron-based catalyst, comprising the following steps: The rust was crushed and then subjected to a first calcination treatment to obtain an iron-based catalyst precursor. The iron-based catalyst precursor was impregnated in an alkali metal salt solution; The impregnated iron-based catalyst precursor is subjected to a second calcination treatment to obtain the iron-based catalyst. The rust described therein simultaneously satisfies the following characteristics: (1) The content of Cl in the rust is less than 0.3wt%, (2) The content of S in the rust is less than 1.2wt%, (3) The rust does not contain Ni, and (4) The content of P in the rust is less than 2wt%.

2. The preparation method according to claim 1, wherein, The first roasting treatment and / or the second roasting treatment includes: roasting at a temperature of 500°C to 600°C for 3 to 6 hours in an air atmosphere.

3. The preparation method according to claim 1, wherein, The alkali metal salt in the alkali metal salt solution is selected from at least one of K2CO3, Na2CO3 and Li2CO3.

4. An iron-based catalyst prepared by the method according to any one of claims 1 to 3, wherein, In the iron-based catalyst, the alkali metal loading is 0.1wt%~5wt%.

5. A method for producing low-carbon olefins by CO2 hydrogenation, wherein, The iron-based catalyst prepared by any one of claims 1 to 3 is used as a catalyst for the reaction of CO2 hydrogenation to produce low-carbon olefins.

6. The method according to claim 5, comprising the following steps: The iron-based catalyst was reduced in a hydrogen atmosphere at 350℃~450℃ for 4h~10h; The reduced iron-based catalyst was added to the CO2 hydrogenation reactor for producing low-carbon olefins, and a reaction gas was introduced to carry out the CO2 hydrogenation reaction for producing low-carbon olefins.

7. The method according to claim 6, wherein, The reaction gas includes CO2, H2 and an inert gas, and the molar ratio of CO2, H2 and the inert gas is 1:(2~5):(0.1~0.3).

8. The method according to any one of claims 5 to 7, wherein, The reaction conditions for the CO2 hydrogenation to produce low-carbon olefins are: temperature 280℃~350℃, pressure 1MPa~5MPa, and gas hourly space velocity 2000 ml·g. -1 ·h -1 ~10000ml·g -1 ·h -1 .

9. The method according to claim 5, wherein, The low-carbon olefins include at least one of ethylene, propylene, and butene.

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