X-iron carbide compound as well as preparation method and application thereof

Abstract

The invention relates to a chi-iron carbide compound and a preparation method and application thereof, the compound comprises iron carbide and halide ions, the iron carbide comprises chi-iron carbide, and the halide ions are bromide ions and / or iodide ions; the mole ratio of the x-iron carbide to the halide ions is 100: (0.1-45), and the mole number of the x-iron carbide is based on the mole number of the contained iron element; wherein the compound has a monoclinic system structure. The x-iron carbide compound can be used as a catalyst for a synthesis gas conversion reaction, and halogen ions such as bromine or iodine are introduced into the x-iron carbide compound, so that the reaction has relatively high CO conversion rate and extremely low total CO2 selectivity, and comprehensive optimization of a reaction result is realized.

Description

Technical Field

[0001] The present invention relates to the conversion of syngas, and particularly to a χ-iron carbide composite capable of being used for the conversion of syngas and a preparation method thereof. Background Art

[0002] Syngas is a mixed gas obtained by gasifying coal, natural gas, and biomass (its composition is CO and H2). The syngas conversion technology is an increasingly important energy conversion route in recent years. After carbon-containing substances such as coal, natural gas, and biomass are gasified to obtain syngas, it can be further converted into liquid fuels and high-value chemicals.

[0003] Among them, the reaction equations for the conversion of syngas are as follows:

[0004] (2n + 1)H2 + nCO → C n H 2n+2 + nH2O (a)

[0005] 2nH2 + nCO → C n H 2n + nH2O (b)

[0006] (n + 1)H2 + 2nCO → C n H 2n+2 + nCO2 (c)

[0007] nH2 + 2nCO → C n H 2n + nCO2 (d)

[0008] Iron-based catalysts are the cheapest and most readily available catalysts for the conversion of syngas. Iron-based catalysts have the advantages of high activity, a wide applicable condition window, strong sulfur resistance, simple online catalyst replacement, and being suitable for industrial continuous production. However, one of the bottleneck problems in the traditional iron-based catalyst syngas conversion technology is the excessively high CO2 selectivity (usually accounting for 35 - 45% of the converted raw material CO).

[0009] The paper published by Professor Enrique Iglesia, "Pathways for CO2 Formation and Conversion During Fischer-Tropsch Synthesis on Iron-Based Catalysts" (Catalysis Letters volume 80, pages 77-86 (2002)), elaborates that in the reaction of syngas conversion achieved by the Fischer-Tropsch synthesis principle, there are two sources of CO2 generation: (1) primary CO2 directly from the primary Fischer-Tropsch synthesis reaction (see the above equations (c) and (d)); and (2) secondary CO2 generated by the water-gas-shift reaction (WGS reaction, CO + H2O → CO2 + H2) between H2O and CO at a higher CO conversion rate.

[0010] The prior art discloses a high-purity iron carbide catalyst that can reduce the primary CO2 of the Fischer-Tropsch synthesis reaction to nearly zero, and at the same time can achieve a high CO space-time conversion rate, thereby reducing the total CO2 selectivity to <5% at a low CO conversion rate (usually lower than 35%). However, when the CO conversion rate increases, as the H2O content in the reaction environment increases, the WGS reaction becomes intense, resulting in an increase in secondary CO2, and ultimately leading to an increase in the total CO2 selectivity at a high CO conversion rate.

[0011] In addition, reducing the CO2 selectivity will significantly improve the carbon atom utilization efficiency and essentially enhance the economic efficiency and environmental friendliness of the syngas conversion technology. Therefore, how to suppress the water-gas-shift side reaction, reduce the CO2 selectivity, and improve the carbon atom utilization efficiency at a high CO conversion rate has become one of the common key problems in the field of syngas conversion. On the other hand, in addition to CO2, another main by-product in the field of syngas conversion is methane. In the reaction, a high CH4 selectivity and a high CO2 selectivity will jointly reduce the selectivity of the effective products of the reaction. Summary of the Invention

[0012] To overcome at least one defect of the above prior art, on the first aspect, an embodiment of the present invention provides a χ-iron carbide composite, including iron carbide and halide ions, the iron carbide includes χ-iron carbide, and the halide ions are bromide ions and / or iodide ions; the molar ratio of the χ-iron carbide to the halide ions is 100: (0.1-45), and the molar number of the χ-iron carbide is calculated based on the molar number of the iron element contained therein; wherein, the composite has a monoclinic crystal system structure.

[0013] On the second aspect, an embodiment of the present invention provides a preparation method of the above χ-iron carbide composite, including the following steps:

[0014] S1: Under the action of hydrogen, the precursor is subjected to reduction and surface purification treatment at a temperature of 260°C to 470°C to obtain a reduction product;

[0015] S2: The reduction product is subjected to surface passivation treatment at a temperature of 0°C to 40°C in a first gas atmosphere to obtain a passivation product; and

[0016] S3: The passivation product is treated at a temperature of 250°C to 430°C in a second gas atmosphere to form a product containing iron carbide;

[0017] Wherein, the first gas includes 1% to 3% by volume of oxygen; the second gas includes hydrogen and carbon monoxide, and the molar ratio of hydrogen to carbon monoxide is (8 - 90):1;

[0018] The precursor is nano-iron and / or nano-iron compound subjected to a first impregnation treatment with an impregnating solution, and the nano-iron compound can be prepared into nano-iron through a reduction reaction; or,

[0019] The precursor is nano-iron and / or the nano-iron compound, and after the passivation product is subjected to a second impregnation treatment in the impregnating solution, the treatment of step S3 is carried out; or,

[0020] The precursor is nano-iron and / or the nano-iron compound, and the product containing iron carbide is subjected to a third impregnation treatment with the impregnating solution; the impregnating solution includes bromide ions and / or iodide ions.

[0021] In a third aspect, an embodiment of the present invention provides a catalyst, including the above-mentioned χ-iron carbide composite or the χ-iron carbide composite prepared by the above-mentioned preparation method.

[0022] In a fourth aspect, an embodiment of the present invention provides the application of the above-mentioned χ-iron carbide composite, the χ-iron carbide composite prepared by the above-mentioned preparation method or the above-mentioned catalyst in the synthesis gas conversion reaction.

[0023] In a fifth aspect, an embodiment of the present invention provides the application of the above-mentioned χ-iron carbide composite, the χ-iron carbide composite prepared by the above-mentioned preparation method or the above-mentioned catalyst in the reaction of synthesizing C, H fuels and / or chemicals based on the Fischer-Tropsch synthesis principle.

[0024] In a sixth aspect, an embodiment of the present invention provides a synthesis gas conversion process, including contacting the above-mentioned catalyst with synthesis gas under reaction conditions for reaction.

[0025] A χ-iron carbide composite of an embodiment of the present invention can be used as a catalyst for the synthesis gas conversion reaction, especially the Fischer-Tropsch synthesis reaction. By introducing halide ions such as bromine or iodine into the χ-iron carbide composite, the reaction has a high CO conversion rate, an extremely low total CO2 selectivity, and a low CH4 selectivity, achieving a comprehensive optimization of the reaction results. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The drawings are only for the purpose of showing specific embodiments and are not considered to be a limitation of the present invention. Among them:

[0027] Figure 1 It is the Mössbauer spectrum of the χ-iron carbide composite CX1 prepared in Example 1 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0028] Typical embodiments embodying the features and advantages of the present invention will be described in detail in the following description. It should be understood that the present invention can have various variations in different embodiments, all of which do not depart from the scope of the present invention, and the descriptions therein are for illustrative purposes in nature and not intended to limit the present invention.

[0029] An embodiment of the present invention provides a χ-iron carbide composite, which includes iron carbide and halide ions. The iron carbide includes χ-iron carbide, and the halide ions are bromide ions and / or iodide ions; the molar ratio of χ-iron carbide to halide ions is 100:(0.1 - 45); herein, the molar number of χ-iron carbide is counted based on the molar number of the iron element contained therein; wherein, the composite has a monoclinic crystal system structure.

[0030] In one embodiment, the average grain diameter of the composite is 6 - 35 nm, and further can be 9 - 28 nm.

[0031] In one embodiment, the molar ratio of χ-iron carbide to halide ions can be 100:(0.1 - 45), further can be 100:(0.5 - 27), and still further can be 100:(7 - 20), such as 100:0.5, 100:1, 100:5, 100:7, 100:10, 100:15, 100:20, 100:25, 100:30, 100:40.

[0032] In one embodiment, the χ-iron carbide composite includes a first cation, and the first cation includes a halide cation. The halide cation can maintain charge balance with the halide ions, that is, the total negative charge (or the total valence shown) of the halide ions is equal to the total positive charge of the halide cation.

[0033] In one embodiment, the first cation includes other cations, and the molar ratio of χ-iron carbide to other cations can be 100:(0.1 to 23), further can be 100:(0.1 to 17), still further can be 100:(0.1 to 12), such as 100:0.5, 100:1, 100:3, 100:5, 100:10, 100:15, 100:20.

[0034] In one embodiment, the χ-iron carbide complex further includes other anions, and the other cations can maintain charge balance with the other anions.

[0035] In one embodiment, the halide cation includes one or more of a first metal ion and a complex cation. Further, the first metal ion includes one or more of an iron ion (such as divalent and trivalent iron ions), a manganese ion (such as divalent manganese ion), a copper ion (such as monovalent and divalent copper ions), a cobalt ion (such as divalent cobalt ion), a molybdenum ion (such as divalent, trivalent, and tetravalent molybdenum ions), a lanthanum ion (such as trivalent and tetravalent lanthanum ions), a cerium ion (such as trivalent and tetravalent cerium ions), and a neodymium ion (such as trivalent and tetravalent neodymium ions); the complex cation includes one or more of a hexaammine manganese ion, a hexaammine iron ion, and a hexaammine copper ion.

[0036] In one embodiment, the other cations include one or more of second metal ions. The second metal ion can include one or more of a manganese ion, a copper ion, a cobalt ion, a molybdenum ion, a chromium ion, a rare earth ion, an alkali metal ion, and an alkaline earth metal ion; for example, the second metal ion can be a manganese ion (such as divalent, trivalent, and tetravalent manganese ions), a copper ion (such as monovalent and divalent copper ions), a cobalt ion (such as divalent cobalt ion), a molybdenum ion (such as divalent, trivalent, and tetravalent molybdenum ions), a chromium ion (such as trivalent chromium ion), a lanthanum ion (such as trivalent and tetravalent lanthanum ions), a cerium ion (such as trivalent and tetravalent cerium ions), a neodymium ion (such as trivalent and tetravalent neodymium ions), a sodium ion, a potassium ion, a calcium ion, and a barium ion.

[0037] In one embodiment, the other anions include one or more of an oxygen ion, a complex ion, and an acid radical ion, such as an oxygen ion, a nitrate radical, a citrate radical, and a gluconate radical.

[0038] One embodiment of the present invention provides a preparation method of the above χ-iron carbide complex, including the following steps:

[0039] S1: Under the action of hydrogen, the precursor is subjected to high-temperature treatment at a temperature of 260 to 470 °C for reduction and surface purification to obtain a reduction product;

[0040] S2: Subject the reduction product to high-temperature treatment at a temperature of 0 to 40 °C in a first gas atmosphere for surface passivation to obtain a passivated product; and

[0041] S3: Subject the passivated product to high-temperature treatment at a temperature of 250 to 430 °C in a second gas atmosphere to form iron carbide and obtain a product containing iron carbide;

[0042] Wherein, the first gas includes 1 to 3 vol% of oxygen; the second gas includes hydrogen and carbon monoxide, and the molar ratio of hydrogen to carbon monoxide is (8 to 90):1;

[0043] The precursor is nano-iron and / or nano-iron compound obtained by first impregnation treatment with an impregnating solution, and the nano-iron compound can be prepared into nano-iron through a reduction reaction; or,

[0044] The precursor is nano-iron and / or nano-iron compound. After subjecting the passivated product to second impregnation treatment in the impregnating solution, then perform the treatment of step S3; or the precursor is nano-iron and / or nano-iron compound, and subject the product containing iron carbide to third impregnation treatment with the impregnating solution; the impregnating solution includes bromide ions and / or iodide ions.

[0045] In one embodiment, the nano-iron compound includes one or more of nano-iron oxide, nano-magnetite, nano-goethite, and nano-iron hydroxide.

[0046] In one embodiment, the nano-iron or nano-iron compound can be nano-iron powder and / or nano-iron particles.

[0047] In one embodiment, the average grain diameter of the nano-iron or nano-iron compound is 6 to 35 nm, further can be 9 to 28 nm, such as 10 nm, 12 nm, 15 nm, 18 nm, 20 nm, 22 nm, 25 nm, 30 nm, 32 nm.

[0048] In one embodiment, the impregnating solution is prepared by dissolving a solute in a solvent. The solute may include water-soluble halides, and the halides include bromides and / or iodides. Further, the halides include one or more of bromides and iodides containing manganese, iron, copper, cobalt, molybdenum, rare earth metal elements. For example, the halide can be one or more of manganese bromide, ferrous bromide, copper bromide, cobalt bromide, molybdenum bromide, manganese iodide, ferrous iodide, copper iodide, rare earth bromide, rare earth iodide, hexaammine manganese bromide, hexaammine iron bromide, hexaammine copper bromide, hexaammine manganese iodide, hexaammine iron iodide, hexaammine copper iodide.

[0049] In one embodiment, the concentration of the halide in the impregnating solution can be 0.7 - 7 mol / L, such as 1 mol / L, 2 mol / L, 3 mol / L, 5 mol / L, 6 mol / L.

[0050] In one embodiment, the solvent of the impregnating solution includes water and / or ethanol. For example, the solvent can be water or a mixture of ethanol and water.

[0051] In one embodiment, the solute of the impregnating solution further includes other compounds, and the other compounds include one or more of salts (organic salts and / or inorganic salts) of manganese, copper, cobalt, molybdenum, rare earth metals, alkali metals, and alkaline earth metals. For example, the other compounds can be one or more of potassium nitrate, sodium nitrate, manganese nitrate, copper nitrate, cobalt nitrate, molybdenum nitrate, calcium nitrate, barium nitrate, rare earth nitrates, potassium carbonate, sodium carbonate, potassium citrate, sodium citrate, manganese citrate, copper citrate, cobalt citrate, molybdenum citrate, calcium citrate, barium citrate, potassium gluconate, sodium gluconate, lithium gluconate, rubidium gluconate, cesium gluconate, manganese gluconate, copper gluconate, and calcium gluconate.

[0052] In one embodiment, no chemical reaction occurs between the solute components of the impregnating solution. For example, the solute does not include potassium carbonate and calcium nitrate at the same time.

[0053] In one embodiment, the concentration of the other compounds in the impregnating solution can be 0.7 - 7 mol / L, such as 1 mol / L, 2 mol / L, 3 mol / L, 5 mol / L, 6 mol / L.

[0054] In one embodiment, the precursor is nano-iron or nano-iron compound subjected to the first impregnation treatment with the impregnating solution. The temperature of the first impregnation treatment, the second impregnation treatment, or the third impregnation treatment is 0 - 50 °C, further can be 20 - 30 °C, such as 10 °C, 15 °C, 20 °C, 25 °C, 30 °C, 35 °C, 40 °C, 45 °C; the time of the first impregnation treatment, the second impregnation treatment, or the third impregnation treatment can be 0.1 - 12 h, further can be 0.2 - 10 h, still further can be 0.3 - 9 h, such as 0.5 h, 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h.

[0055] In one embodiment, the material after the first impregnation treatment, the second impregnation treatment, or the third impregnation treatment can be dried at 15 - 40 °C, and further dried under light-shielded conditions. The drying temperature can be, for example, 20 °C, 25 °C, 30 °C, 35 °C; the drying time can be 0.5 - 12 h. The drying treatment can be carried out under normal pressure or reduced pressure.

[0056] In one embodiment, the first impregnation treatment, the second impregnation treatment, or the third impregnation treatment may adopt one of slurry impregnation method, saturated impregnation method, supersaturated impregnation method, or other implementable impregnation methods.

[0057] In one embodiment, the temperature of the reduction and surface purification treatment in step S1 may be 260 to 470 °C, such as 300 °C, 310 °C, 320 °C, 350 °C, 370 °C, 400 °C, 420 °C, 450 °C; the treatment pressure may be 0.12 to 10 atm, further may be 0.15 to 7 atm, such as 0.15 atm, 0.2 atm, 0.5 atm, 0.8 atm, 1 atm, 1.5 atm, 2 atm, 5 atm, 8 atm, 10 atm; the treatment time may be 1.2 to 25 h, further may be 2 to 12 h, such as 5 h, 8 h, 10 h, 15 h, 20 h, 25 h.

[0058] In one embodiment, the gas flow rate of H2 in step S1 may be 600 to 22000 mL / h / g, further may be 1200 to 15000 mL / h / g, such as 1000 mL / h / g, 1500 mL / h / g, 2000 mL / h / g, 3000 mL / h / g, 5000 mL / h / g, 6000 mL / h / g, 8000 mL / h / g, 10000 mL / h / g, 12000 mL / h / g, 15000 mL / h / g.

[0059] In one embodiment, the first gas in step S2 includes 1 to 3 vol% of oxygen and 97 to 99 vol% of nitrogen, and the content of oxygen may be, for example, 1.5 vol%, 2 vol%, 2.5 vol%, 3 vol%.

[0060] In one embodiment, the temperature of the surface passivation treatment in step S2 may be 0 to 40 °C, such as 1 °C, 5 °C, 10 °C, 15 °C, 20 °C, 25 °C, 30 °C, 35 °C, 40 °C; the treatment pressure may be 0 to 1.5 atm, further may be 0 to 0.09 atm, such as 0.01 atm, 0.02 atm, 0.05 atm, 0.06 atm, 0.08 atm, 1 atm, 1.5 atm; the treatment time may be 2 to 60 h, further may be 3 to 45 h, such as 8 h, 12 h, 15 h, 20 h, 25 h, 30 h, 35 h, 40 h, 45 h, 50 h, 55 h, 60 h.

[0061] In one embodiment, the gas flow rate of the first gas in step S2 can be 500 - 20000 mL / h / g, and further can be 1200 - 12500 mL / h / g, such as 500 mL / h / g, 1000 mL / h / g, 1500 mL / h / g, 2000 mL / h / g, 3000 mL / h / g, 4000 mL / h / g, 5000 mL / h / g, 6000 mL / h / g, 7000 mL / h / g, 10000 mL / h / g, 15000 mL / h / g.

[0062] In one embodiment, the molar ratio of hydrogen to carbon monoxide in the second gas in step S3 can be 10:1, 20:1, 30:1, 36:1, 40:1, 50:1, 60:1, 80:1. The second gas can be a mixture of hydrogen and carbon monoxide.

[0063] In one embodiment, the treatment temperature in step S3 can be 250 - 430 °C, such as 280 °C, 300 °C, 320 °C, 330 °C, 350 °C, 380 °C, 400 °C; the treatment pressure can be 0.08 - 17 atm, and further can be 0.15 - 7 atm, such as 0.1 atm, 0.2 atm, 0.5 atm, 0.8 atm, 1 atm, 1.2 atm, 1.5 atm, 1.8 atm, 2 atm, 2.2 atm, 5 atm, 8 atm, 10 atm, 15 atm; the treatment time can be 0.3 - 24 h, and further can be 0.5 - 6 h, such as 1 h, 1.5 h, 1.8 h, 2 h, 2.2 h, 5 h, 10 h, 15 h, 20 h.

[0064] In one embodiment, the gas flow rate of the second gas in step S3 can be 250 - 21000 mL / h / g, and further can be 2000 - 17000 mL / h / g, such as 1000 mL / h / g, 3000 mL / h / g, 5000 mL / h / g, 6000 mL / h / g, 7700 mL / h / g, 8000 mL / h / g, 10000 mL / h / g, 12000 mL / h / g, 15000 mL / h / g, 16000 mL / h / g.

[0065] In one embodiment, in step S3, the temperature of the system is raised from 0 to 40 °C to 250 to 430 °C at a heating rate of 0.1 to 5 °C / min. Further, the temperature of the system is raised from 0 to 40 °C to 260 to 400 °C at a heating rate of 0.2 to 2.5 °C / min. The heating rate of step S3 can be, for example, 0.5 °C / min, 0.8 °C / min, 1 °C / min, 1.2 °C / min, 1.5 °C / min, 1.8 °C / min, 2 °C / min, 2.2 °C / min, 3 °C / min, 4 °C / min.

[0066] In one embodiment, preferably, steps S1, S2, S3 and the first, second, and third impregnation treatments can all be carried out under light-shielded conditions.

[0067] In one embodiment, the preparation method of the χ-iron carbide composite includes the following steps:

[0068] S0: The nanoiron and / or nanoiron compound are subjected to a first impregnation treatment with an impregnating solution to obtain a precursor to be treated.

[0069] S1: Under the action of hydrogen, the precursor is reduced and surface-purified at a temperature of 260 to 470 °C to obtain a reduction product.

[0070] S2: The reduction product is surface-passivated at a temperature of 0 to 40 °C in a first gas atmosphere to obtain a passivated product; and

[0071] S3: The passivated product is treated at a temperature of 250 to 430 °C in a second gas atmosphere to form iron carbide, obtaining a product containing iron carbide (i.e., the χ-iron carbide composite).

[0072] In another embodiment, the preparation method of the χ-iron carbide composite includes the following steps:

[0073] S1: Under the action of hydrogen, the precursor (nanoiron and / or nanoiron compound) is reduced and surface-purified at a temperature of 260 to 470 °C to obtain a reduction product.

[0074] S2: The reduction product is surface-passivated at a temperature of 0 to 40 °C in a first gas atmosphere to obtain a passivated product.

[0075] S21: The passivated product is subjected to a second impregnation treatment in the impregnating solution; and

[0076] S3: The material after the second impregnation treatment is treated at a temperature of 250 to 430 °C in a second gas atmosphere to form a product containing iron carbide (i.e., the χ-iron carbide composite).

[0077] In another embodiment, the method for preparing the χ-iron carbide composite includes the following steps:

[0078] S1: Under the action of hydrogen, the precursor (nano iron and / or nano iron compound) is reduced and surface-purified at a temperature of 260 - 470 °C to obtain a reduction product;

[0079] S2: The reduction product is surface-passivated at a temperature of 0 - 40 °C in a first gas atmosphere to obtain a passivation product; and

[0080] S3: The passivation product is treated at a temperature of 250 - 430 °C in a second gas atmosphere to form iron carbide, obtaining a product containing iron carbide;

[0081] S31: The product containing iron carbide is subjected to a third impregnation treatment to obtain the χ-iron carbide composite.

[0082] One embodiment of the present invention provides a catalyst comprising the above-mentioned χ-iron carbide composite.

[0083] One embodiment of the present invention provides the application of the above-mentioned χ-iron carbide composite or catalyst in the synthesis gas conversion reaction.

[0084] In one embodiment, the synthesis gas conversion reaction can be a Fischer-Tropsch synthesis reaction or other reactions based on the Fischer-Tropsch synthesis principle, such as a reaction starting from synthesis gas and having an alcohol as the final product.

[0085] In one embodiment, the synthesis gas comprises CO and H2.

[0086] One embodiment of the present invention provides the application of the above-mentioned χ-iron carbide composite or catalyst in the reaction for synthesizing C, H fuels and / or chemicals based on the Fischer-Tropsch synthesis principle. Among them, the reaction based on the Fischer-Tropsch synthesis principle refers to a reaction using synthesis gas (a mixture of CO and H2) as the raw material, and through CO hydrogenation and carbon chain growth reactions under the action of a catalyst and appropriate conditions, to generate chain hydrocarbons and / or their oxygen-containing derivatives.

[0087] In one embodiment, the above reaction is a Fischer-Tropsch synthesis reaction, the reaction temperature can be 230 - 280 °C, such as 240 °C, 250 °C, 260 °C, 270 °C, 275 °C, 277 °C; the reaction pressure can be 2 - 3.5 MPa, and the molar ratio of H2 / CO can be 1.7 - 2.15.

[0088] One embodiment of the present invention provides a synthesis gas conversion process, which includes contacting the above-mentioned catalyst with synthesis gas under synthesis gas conversion reaction conditions for reaction.

[0089] In one embodiment, the syngas conversion can be carried out in a high-temperature and high-pressure continuous reactor.

[0090] The χ-iron carbide composite of one embodiment of the present invention can be used as a catalyst for the syngas conversion reaction. By introducing halogen ions into χ-iron carbide, the reaction has a high CO conversion rate, an extremely low total CO2 selectivity, and a low CH4 selectivity. At the same time, benefiting from the very high CO space-time conversion rate of the χ-iron carbide composite catalyst, it exhibits considerable activity.

[0091] The χ-iron carbide composite of one embodiment of the present invention can be used as a catalyst for the syngas conversion reaction, enabling the reaction to maintain an extremely low CO2 selectivity at a high CO conversion rate, while maintaining a low CH4 selectivity and a high reaction stability, greatly improving the utilization efficiency of carbon atoms and the selectivity of effective products, breaking through the key technical bottlenecks, and promoting the high-end, diversification, and low-carbonization of clean syngas conversion, indicating new trends and directions for the development of modern syngas chemistry.

[0092] The χ-iron carbide composite of one embodiment of the present invention, as a catalyst for the Fischer-Tropsch synthesis reaction, can maintain a continuous and stable reaction for more than 300 h using a high-pressure continuous reactor under industrial Fischer-Tropsch synthesis reaction conditions. Its CO2 selectivity is below 5%, further below 3%; the selectivity of its by-product CH4 can be maintained below 8.5%, further below 5.5%; the utilization efficiency of carbon atoms is maintained above 95%, further above 97%; the selectivity of effective products can reach above 86.5%, further above 92%.

[0093] In one embodiment, through the Fischer-Tropsch synthesis reaction catalyzed by the χ-iron carbide composite, a CO2 selectivity of <5%, a carbon atom utilization efficiency of >95%, and an effective product selectivity of >88% can be achieved at a CO conversion rate of more than 70%.

[0094] In this article, the "ions" contained in the composite include all particles that are combined with other particles by covalent bonds and / or ionic bonds. For example, the bromide ions in the composite include both Br that interacts with K by ionic bonds + interacting Br - , and also Br atoms that interact with H atoms by covalent bonds.

[0095] The pressure values involved in this article are all gauge pressures.

[0096] Hereinafter, in combination with the accompanying drawings and specific examples, the χ-iron carbide composite of one embodiment of the present invention and its application will be further described. Among them, the test methods involved are as follows:

[0097] 1. The crystal structure and corresponding composition of the χ-iron carbide composite were measured by a Mössbauer spectrometer (Transmission 57 Fe, 57 Co(Rh) source sinusoidal velocity spectrometer).

[0098] 2. The average grain diameter of the χ-iron carbide composite was obtained by XRD testing.

[0099] 3. The χ-iron carbide composite was subjected to elemental detection using an Inductively Coupled Plasma Emission Spectrometer (ICP).

[0100] 4. During the syngas conversion reaction process, the products obtained from the reaction were subjected to gas chromatography analysis (Agilent 7890 gas chromatography) for calculating reaction performance such as conversion rate and selectivity; the products refer to the tail gas collected from the reactor outlet, including hydrocarbon compounds, alcohol compounds, CO2, etc.

[0101] 5. The CO conversion rate %, CO2 selectivity %, CH4 selectivity %, carbon atom utilization efficiency %, and effective product selectivity % were calculated using the following formulas:

[0102] CO conversion rate % = [(moles of CO in feed - moles of CO in product) / moles of CO in feed] × 100%;

[0103] CO2 selectivity % = [moles of CO2 in product / (moles of CO in feed - moles of CO in product)] × 100%;

[0104] CH4 selectivity % = [moles of CH4 in product / (moles of CO in feed - moles of CO in product)] × 100%;

[0105] Carbon atom utilization efficiency % = (1 - CO2 selectivity %) × 100%;

[0106] Effective product selectivity % = (1 - CO2 selectivity % - CH4 selectivity %) × 100%.

[0107] Example 1

[0108] S1: Take 5.6 g of nano-iron particles with an average grain diameter of 20 nm. At a pressure of 370 °C and 2.0 atm, keep the nano-iron particles in H2 with a flow rate of 12000 mL / h / g for 2 h for reduction and surface purification treatment to obtain a reduced product.

[0109] S2: Cool down the reduction product to 30 °C and carry out surface passivation treatment by contacting it with the first gas at this temperature to obtain a passivated product; wherein, the pressure of the system is 0.1 atm, the gas flow rate is 7500 mL / h / g, and the treatment time is 12 h; the first gas includes 2 vol% of oxygen and 98 vol% of nitrogen.

[0110] S21: Dissolve manganese bromide and potassium nitrate in water to prepare an impregnating solution with a manganese bromide concentration of 6.7 mol / L; mix the prepared impregnating solution with the passivated product and carry out impregnation treatment by the slurry impregnation method with an impregnation ratio of Fe:Br:K = 100:7:2, an impregnation temperature of 32 °C, and an impregnation time of 2 h; dry the impregnated solid material at 25 °C for 6 h.

[0111] S3: Contact the material after impregnation treatment with the second gas atmosphere. The pressure of the system is 2.1 atm, and the total gas flow rate is 11000 mL / h / g. Under this condition, heat the system from 30 °C to 350 °C at a heating rate of 2.0 °C / min to carry out carbide preparation; wherein, the second gas is a mixture of H2 and CO with a molar ratio of H2 to CO of 50:1, and the treatment time of the material at 350 °C is 5 h. After the treatment is completed, χ-iron carbide composite is prepared and labeled as CX1.

[0112] Examples 1-1 to 3-8 all use basically the same raw materials and processes as Example 1 to prepare metal-type χ-iron carbide composites, with the only difference being that the content or type of halide ions or other cations in the impregnating solution is different. The prepared composites are sequentially labeled as CX1-1 to CX3-8 using the same numbers as Example 1. Since the loss of materials during the preparation process is extremely small, the content of each substance in the obtained composites is basically the same as the dosage of the corresponding raw materials. For specific content values, see Table 1.

[0113] Example 4

[0114] S1: Take 8.0 g of nano-iron oxide particles with an average grain diameter of 15 nm and keep the nano-iron oxide particles in H2 with a flow rate of 8000 mL / h / g at 420 °C and a pressure of 3.0 atm for 3 h to carry out reduction and surface purification treatment to obtain a reduction product.

[0115] S2: Cool down the reduction product to 35 °C and carry out surface passivation treatment by contacting it with the first gas at this temperature to obtain a passivated product; wherein, the pressure of the system is 0.5 atm, the gas flow rate is 9500 mL / h / g, and the treatment time is 9 h; the first gas includes 1.5 vol% of oxygen and 98.5 vol% of nitrogen.

[0116] S21: Dissolve manganese bromide, potassium citrate, and calcium nitrate in water to prepare an impregnation solution with a manganese bromide concentration of 5.5 mol / L. Mix the prepared impregnation solution with the passivation product and perform impregnation treatment by the slurry impregnation method. The impregnation ratio (molar ratio) is Fe:Br:K:Ca = 100:7:3:2.7, the impregnation temperature is 37 °C, and the impregnation time is 3 h. Dry the impregnated solid material at 25 °C for 5 h.

[0117] S3: Contact the impregnated material with a second gas atmosphere. The pressure of the system is 3.6 atm, and the total gas flow rate is 7700 mL / h / g. Under these conditions, heat the system from 35 °C to 330 °C at a heating rate of 2.0 °C / min to prepare the carbide; wherein, the second gas is a mixture of H2 and CO, and the molar ratio of H2 to CO is 36:1. The treatment time of the material at 330 °C is 5 h. After the treatment is completed, prepare the χ-iron carbide composite, labeled as CX4.

[0118] Example 4-1

[0119] This example uses substantially the same raw materials and process as Example 1 to prepare the χ-iron carbide composite, with the only difference being that the H2 flow rate in step S1 is 1200 mL / h / g. The finally prepared χ-iron carbide composite is labeled as CX4-1.

[0120] Example 4-2

[0121] This example uses substantially the same raw materials and process as Example 1 to prepare the χ-iron carbide composite, with the only difference being that the H2 flow rate in step S1 is 15000 mL / h / g. The finally prepared χ-iron carbide composite is labeled as CX4-2.

[0122] Example 4-3

[0123] This example uses substantially the same raw materials and process as Example 1 to prepare the χ-iron carbide composite, with the only difference being that the H2 flow rate in step S1 is 9000 mL / h / g. The finally prepared χ-iron carbide composite is labeled as CX4-3.

[0124] Example 4-4

[0125] This example uses substantially the same raw materials and process as Example 1 to prepare the χ-iron carbide composite, with the only difference being that the carbonization temperature in step S3 is 430 °C. The finally prepared χ-iron carbide composite is labeled as CX4-4.

[0126] Example 4-5

[0127] This example uses substantially the same raw materials and processes as Example 1 to prepare the χ-iron carbide composite, with the only difference being that the carbonization temperature in step S3 is 250 °C. The finally obtained χ-iron carbide composite is labeled CX4-5.

[0128] Examples 4-6

[0129] This example uses substantially the same raw materials and processes as Example 1 to prepare the χ-iron carbide composite, with the only difference being that the carbonization temperature in step S3 is 350 °C. The finally obtained χ-iron carbide composite is labeled CX4-6.

[0130] Examples 4-7

[0131] This example uses substantially the same raw materials and processes as Example 1 to prepare the χ-iron carbide composite, with the only difference being that the reduction temperature in step S1 is 470 °C. The finally obtained χ-iron carbide composite is labeled CX4-7.

[0132] Examples 4-8

[0133] This example uses substantially the same raw materials and processes as Example 1 to prepare the χ-iron carbide composite, with the only difference being that the carbonization pressure in step S3 is 7 atm. The finally obtained χ-iron carbide composite is labeled CX4-8.

[0134] Examples 4-9

[0135] This example uses substantially the same raw materials and processes as Example 1 to prepare the χ-iron carbide composite, with the only difference being that the reduction time in step S1 is 12 h. The finally obtained χ-iron carbide composite is labeled CX4-9.

[0136] Examples 4-10

[0137] This example uses substantially the same raw materials and processes as Example 1 to prepare the χ-iron carbide composite, with the only difference being that the carbonization time in step S3 is 6 h. The finally obtained χ-iron carbide composite is labeled CX4-10.

[0138] Examples 4-11

[0139] This example uses substantially the same raw materials and processes as Example 1 to prepare the χ-iron carbide composite, with the only difference being that the reduction pressure in step S1 is 7.0 atm. The finally obtained χ-iron carbide composite is labeled CX4-11.

[0140] Examples 4-12

[0141] This example uses substantially the same raw materials and process as Example 1 to prepare the χ-iron carbide composite, with the only difference being that the passivation time in step S2 is 45 h. The finally obtained χ-iron carbide composite is labeled as CX4-12.

[0142] Example 5

[0143] S0: Take 5.6 g of nano-iron particles with an average grain diameter of 20 nm, prepare an impregnating solution using the same raw materials and method as in Example 1, mix the impregnating solution with the nano-iron particles, and perform impregnation treatment by the slurry impregnation method. The impregnation ratio (molar ratio) is Fe:Br:K = 100:7:2, the impregnation temperature is 35 °C, and the impregnation time is 6 h; dry the impregnated solid material at 25 °C and a pressure of 0.05 atm for 5 h to obtain a precursor.

[0144] S1: At a temperature of 370 °C and a pressure of 2.0 atm, keep the precursor obtained in step S0 in H2 with a flow rate of 12000 mL / h / g for 2 h to perform reduction and surface purification treatment to obtain a reduction product.

[0145] S2: Cool the reduction product to 30 °C and contact it with the first gas at this temperature for surface passivation treatment to obtain a passivation product; where the pressure of the system is 0.1 atm, the gas flow rate is 7500 mL / h / g, and the treatment time is 12 h; the first gas includes 2 vol% oxygen and 98 vol% nitrogen.

[0146] S3: Contact the passivation product with the second gas atmosphere. The pressure of the system is 2.1 atm, the total gas flow rate is 11000 mL / h / g, and under this condition, heat the system from 30 °C to 350 °C at a heating rate of 2.0 °C / min to perform carbide preparation; where the second gas is a mixture of H2 and CO, the molar ratio of H2 to CO is 50:1, and the treatment time of the material at 350 °C is 5 h; after the treatment is completed, the χ-iron carbide composite is obtained and labeled as CX5.

[0147] Example 6

[0148] S1: Take 5.6 g of nano-iron particles with an average grain diameter of 20 nm. At a temperature of 370 °C and a pressure of 2.0 atm, keep the nano-iron particles in H2 with a flow rate of 12000 mL / h / g for 2 h to perform reduction and surface purification treatment to obtain a reduction product.

[0149] S2: Cool the reduction product to 30 °C and contact it with the first gas at this temperature for surface passivation treatment to obtain a passivation product; where the pressure of the system is 0.1 atm, the gas flow rate is 7500 mL / h / g, and the treatment time is 12 h; the first gas includes 2 vol% oxygen and 98 vol% nitrogen.

[0150] S3: Contact the passivation product with a second gas atmosphere. The pressure of the system is 2.1 atm, and the total gas flow rate is 11000 mL / h / g. Under this condition, heat the system from 30 °C to 350 °C at a heating rate of 2.0 °C / min to prepare carbides. Among them, the second gas is a mixture of H2 and CO, and the molar ratio of H2 to CO is 50:1. The treatment time of the material at 350 °C is 5 h. After the treatment is completed, a product containing iron carbide is obtained;

[0151] S31: Prepare an impregnating solution using the same raw materials and method as in Example 1. Mix the impregnating solution with the product containing iron carbide and perform impregnation treatment by the slurry impregnation method. The impregnation ratio (molar ratio) is Fe:Br:K = 100:7.0:2.0. The impregnation temperature is 32 °C, and the impregnation time is 2 h. Dry the impregnated solid material at 25 °C for 9 h. An χ-iron carbide composite is obtained and labeled as CX6.

[0152] Comparative Example 1

[0153] In this example, an χ-iron carbide composite is prepared using substantially the same raw materials and process as in Example 1, except that: in step S21, the impregnation ratio (molar ratio) is Fe:Br:K = 100:50.0:2.0. The finally obtained χ-iron carbide composite is labeled as DX1.

[0154] Comparative Example 2

[0155] In this example, an χ-iron carbide composite is prepared using substantially the same raw materials and process as in Example 1, except that: in the preparation of the impregnating solution in step S21, manganese bromide is not added. Use this impregnating solution to impregnate the nano-iron particles. The finally obtained χ-iron carbide composite is labeled as D2.

[0156] Comparative Example 3

[0157] In this example, an χ-iron carbide composite is prepared using substantially the same raw materials and process as in Example 1, except that: in the preparation of the impregnating solution in step S21, manganese chloride is used instead of manganese bromide in an equal amount. The finally obtained χ-iron carbide composite is labeled as DX3.

[0158] Comparative Example 4

[0159] Use exactly the same raw materials and steps as in steps S1 to S3 of Example 1, but do not perform the S21 impregnation step to obtain χ-iron carbide. Labeled as D4.

[0160] Comparative Example 5

[0161] In this example, the χ-iron carbide composite was prepared using substantially the same raw materials and process as in Example 1, except that: in step S3, the mixing ratio of the second gas atmosphere, the mixture of H2 and CO, was 120:1. The finally prepared χ-iron carbide composite was labeled DX5.

[0162] The χ-iron carbide composites and χ-iron carbide prepared in each example and comparative example were subjected to XRD, Mössbauer spectroscopy, and ICP measurements. The content of χ-iron carbide was calculated based on 100 mol, and the relevant contents refer to the number of moles. The specific results are shown in Table 1.

[0163] In a slurry bed continuous reactor, the catalytic reaction performance of the χ-iron carbide composites and χ-iron carbide prepared in each example and comparative example was evaluated respectively. The catalyst loading was 9.0 g. Evaluation conditions: T = 277 °C, P = 2.75 MPa, H2:CO = 2.1:1, (H2+CO) total amount = 14500 mL / h / g- Fe (standard state flow rate, relative to Fe element), and the circulation ratio was 1.2. The reaction was carried out, and the reaction products were analyzed by gas chromatography. The reaction performance evaluation data at 24 h and 300 h are shown in Tables 2 and 3.

[0164] Table 1

[0165]

[0166]

[0167] Table 2

[0168]

[0169]

[0170] Table 3

[0171]

[0172] Combining the results of each example, comparative example, and Tables 1-3, it can be seen that compared with Example 1, the impregnating solution of Comparative Example 2 does not contain manganese bromide, indicating that the composite prepared in Comparative Example 2 does not contain manganese ions and bromide ions. The results in Table 2 show that although the CO conversion rate of Comparative Example 2 is higher than that of Example 1, its CO2 selectivity of 38.7% is much higher than the CO2 selectivity of 2.3% in Example 1, and the carbon atom utilization rate (61.3%) and effective product selectivity (57.4%) are much lower than the carbon atom utilization rate (97.7%) and effective product selectivity (93.5%) in Example 1. Therefore, the composite in Example 1 can improve the overall efficiency of the reaction and optimize the comprehensive results of the reaction compared with the composite in Comparative Example 2.

[0173] Furthermore, the difference between Example 1-1 and Example 1 lies in the different halides used, which is ferrous bromide. The results in Table 2 show that the reaction performance data of Example 1-1 and Example 1 are not very different, indicating that the improvement in performance of Example 1 compared to Comparative Example 2 is mainly brought about by the addition of bromide ions rather than manganese ions.

[0174] Furthermore, the main difference between Example 2 and Example 1-2 is that iodide ions are introduced into the prepared composite, rather than bromide ions. The results in Table 2 show that the reaction performance data of Example 2 and Example 1-2 are not very different, indicating that introducing iodide ions into iron carbide can also play a role in improving the comprehensive reaction performance. In addition, the difference between Comparative Example 3 and Example 1 is that chloride ions are introduced into the prepared composite, rather than bromide ions. The results in Table 2 show that all the reaction performances of Comparative Example 3 are significantly lower than those of Example 1, and the optimization of the comprehensive reaction results cannot be achieved.

[0175] Furthermore, bromide ions are also introduced into the iron carbide of Comparative Example 1, but the content of bromide ions is too high, exceeding the range of the molar ratio of χ-iron carbide to halide ions of 100:(0.1 - 45) defined in an embodiment of the present invention. According to the results in Table 2, the CO conversion rate of Comparative Example 1 is only 38.6%, far lower than the 81.8% CO conversion rate of Example 1, and the carbon atom utilization rate and effective product selectivity of Comparative Example 1 are also significantly lower than those of Example 1. Thus, when the bromide ions in the iron carbide composite exceed a certain range, the comprehensive optimization of the reaction results cannot be achieved either.

[0176] Furthermore, the main difference between Examples 1 to 1-7 lies mainly in the different contents of bromide ions. Combining the results of Tables 2 and 3, the molar ratio of iron carbide (or iron element) to bromide ions in the prepared composite is preferably 100:(7 - 20).

[0177] Furthermore, the main difference between Examples 3 to 3-8 lies mainly in the different contents of other cations. Combining the results of Tables 2 and 3, the molar ratio of iron carbide (or iron element) to other cations in the prepared composite is preferably 100:(0.1 - 12).

[0178] In addition, according to the results in Table 3, it can be seen that the reactions catalyzed by the composites of each embodiment of the present invention can keep the CO conversion rate, product selectivity, etc. stable for a long time. Thus, by making the χ-iron carbide composite contain halide ions such as bromine or iodine and limiting the halide ion content within a specific range, and using it as a catalyst for the Fischer-Tropsch synthesis reaction, the overall efficiency of the reaction can be improved, and the optimization of the comprehensive reaction results can be achieved.

[0179] Based on the above description, using the χ-iron carbide composite containing halogen ions such as bromine or iodine prepared in the embodiments of the present invention as a catalyst for the syngas conversion reaction under industrial conditions can exhibit ultra-low CO2 selectivity, relatively low CH4 selectivity, extremely high carbon atom utilization efficiency, and effective product selectivity while maintaining a high CO conversion rate (>60%). Further, a long-term experiment was carried out. From the data of the reaction for 300 h in Table 3, it can be seen that after the long-term continuous operation of the χ-iron carbide composite of the embodiments of the present invention as a catalyst in a stirred tank, its CO conversion rate, product selectivity, carbon atom utilization efficiency, and effective product selectivity all remain stable without obvious changes, showing good operation stability. Thus, by using the χ-iron carbide composite of the embodiments of the present invention as a catalyst for the syngas conversion reaction, comprehensive optimization of the reaction results can be achieved.

[0180] Unless otherwise specified, the terms used in the present invention have the meanings commonly understood by those skilled in the art.

[0181] The embodiments described in the present invention are for illustrative purposes only and are not intended to limit the scope of protection of the present invention. Those skilled in the art can make various other substitutions, changes, and improvements within the scope of the present invention. Therefore, the present invention is not limited to the above embodiments but is only defined by the claims.

Claims

1. A χ-iron carbide composite, comprising iron carbide and halide ions, wherein the iron carbide comprises χ-iron carbide, and the halide ions are bromide ions and / or iodide ions; the molar ratio of the χ-iron carbide to the halide ions is 100: (0.1 - 45), and the molar number of the χ-iron carbide is based on the molar number of the iron element contained therein; wherein, The complex has a monoclinic crystal structure.

2. The composite according to claim 1, comprising a first cation, wherein the first cation comprises other cations, and the molar ratio of the χ-iron carbide to the other cations is 100: (0.1 - 23), and further can be 100: (0.1 - 17); and / or, the average grain diameter of the composite is 6 - 35 nm.

3. The composite according to claim 2, wherein, The first cation includes a halide cation, and the halide cation can maintain charge balance with the halide ion; and / or, The molar ratio of the χ-iron carbide to the halide ion is 100:(0.5 - 27); and / or, The complex further includes other anions, and the other cation can maintain charge balance with the other anion.

4. The composite according to claim 3, wherein, The halide cation includes one or more of a first metal ion and a complex cation; and / or, The other cation includes one or more of second metal ions, and the second metal ions include one or more of manganese ions, copper ions, cobalt ions, molybdenum ions, chromium ions, rare earth ions, alkali metal ions, and alkaline earth metal ions; and / or, The other anion includes one or more of an oxygen ion, a complex ion, and an acid radical ion.

5. The composite according to claim 4, wherein, The first metal ion includes one or more of iron ions, manganese ions, copper ions, cobalt ions, molybdenum ions, and rare earth ions; the complex cation includes one or more of hexaammine manganese ions, hexaammine iron ions, and hexaammine copper ions; and / or, The other cation includes one or more of manganese ions, copper ions, cobalt ions, molybdenum ions, chromium ions, lanthanum ions, cerium ions, neodymium ions, sodium ions, potassium ions, calcium ions, and barium ions; and / or, The other anion includes one or more of an oxygen ion, nitrate, citrate, and gluconate.

6. A method for preparing the χ-iron carbide composite according to any one of claims 1 to 5, comprising the following steps: S1: Under the action of hydrogen, reducing and surface purifying a precursor at a temperature of 260°C to 470°C to obtain a reduction product; S2: Subjecting the reduction product to surface passivation treatment in a first gas atmosphere at a temperature of 0°C to 40°C to obtain a passivation product; and S3: Treating the passivation product in a second gas atmosphere at a temperature of 250°C to 430°C to form a product containing iron carbide; wherein, The first gas includes 1 vol% to 3 vol% of oxygen; the second gas includes hydrogen and carbon monoxide, and the molar ratio of hydrogen to carbon monoxide is (8 - 90):1; The precursor is nano-iron and / or a nano-iron compound obtained by a first impregnation treatment with an impregnating solution, and the nano-iron compound can be used to prepare nano-iron through a reduction reaction; or, The precursor is nano-iron and / or the nano-iron compound, and after the passivation product is subjected to a second impregnation treatment in the impregnating solution, the treatment of step S3 is carried out; or, The precursor is nano-iron and / or the nano-iron compound, and the product containing iron carbide is subjected to a third impregnation treatment with the impregnating solution; the impregnating solution includes bromide ions and / or iodide ions.

7. The preparation method according to claim 6, wherein, The nano-iron compound includes one or more of nano-iron oxide, nano-magnetite, nano-goethite, and nano-iron hydroxide; and / or, The impregnating solution is prepared by dissolving a solute in a solvent, and the solute includes a halide, and the halide includes bromide and / or iodide; and / or, The material after the first impregnation treatment, the second impregnation treatment, or the third impregnation treatment is dried at 15 - 40 °C.

8. The preparation method according to claim 7, wherein, The halide includes one or more of bromides and iodides containing manganese, iron, copper, cobalt, molybdenum, and rare earth metal elements; and / or, The solvent includes water and / or ethanol; and / or, The concentration of the halide in the impregnating solution is 0.7 - 7 mol / L; and / or, The solute further includes other compounds, and the other compounds include one or more of salts of molybdenum, manganese, copper, alkaline earth metals, cobalt, rare earth metals, and alkali metals; wherein, no chemical reaction occurs between the components of the solute.

9. The preparation method according to claim 6, wherein, The temperature of the first impregnation treatment, the second impregnation treatment, or the third impregnation treatment is 0 to 50 °C, further preferably 20 to 30 °C; the time of the first impregnation treatment is 0.1 to 12 h, further preferably 0.2 to 10 h, and still further preferably 0.3 to 9 h.

10. The preparation method according to claim 6, wherein, The treatment pressure in step S1 is 0.12 to 10 atm, further preferably 0.15 to 7 atm; the treatment time is 1.2 to 25 h, further preferably 2 to 12 h; and / or The treatment pressure in step S2 is 0 to 1.5 atm, further preferably 0 to 0.09 atm; the treatment time is 2 to 60 h, further preferably 3 to 45 h; and / or The treatment pressure in step S3 is 0.08 to 17 atm, further preferably 0.15 to 7 atm; the treatment time is 0.3 to 24 h, further preferably 0.5 to 6 h.

11. A catalyst, comprising the χ-iron carbide complex according to any one of claims 1 to 5 or the χ-iron carbide complex prepared by the preparation method according to any one of claims 6 to 10.

12. Use of the χ-iron carbide complex according to any one of claims 1 to 5, the χ-iron carbide complex prepared by the preparation method according to any one of claims 6 to 10, or the catalyst according to claim 11 in a syngas conversion reaction.

13. Use of the χ-iron carbide complex according to any one of claims 1 to 5, the χ-iron carbide complex prepared by the preparation method according to any one of claims 6 to 10, or the catalyst according to claim 11 in a reaction for synthesizing C, H fuels and / or chemicals based on the Fischer-Tropsch synthesis principle.

14. A syngas conversion process, comprising contacting the catalyst according to claim 11 with syngas under reaction conditions for reaction.

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