Composition containing metal type theta-iron carbide and epsilon / epsilon '-iron carbide as well as preparation method and application of composition

Abstract

The invention provides a composition containing metal type theta-iron carbide and epsilon / epsilon '-iron carbide as well as a preparation method and application of the composition. The method comprises the following steps: preparing a metal type theta-iron carbide compound; preparing a metal type epsilon / epsilon '-iron carbide compound; and mixing the metal type theta-iron carbide compound and the metal type epsilon / epsilon '-iron carbide compound to obtain the metal type iron carbide composition containing theta-iron carbide and epsilon / epsilon'-iron carbide, or mixing the metal type theta-iron carbide and the metal type epsilon / epsilon '-iron carbide to obtain a metal type iron carbide mixture; and carrying out dipping treatment on the metal type iron carbide mixture to enable the metal type iron carbide mixture to contain bromide ions and / or iodide ions. According to the composition disclosed by the invention, halide ions such as bromine or iodine are introduced into the components of the composition to serve as a catalyst for a synthesis gas conversion reaction, so that the reaction has a relatively high CO conversion rate and the like, and comprehensive optimization of a reaction result is realized.

Description

Technical Field

[0001] The present invention belongs to the field of syngas conversion, and relates to an iron carbide composition of a catalyst capable of being used for syngas conversion. Background Art

[0002] Syngas conversion technology is to convert syngas (H2 + CO) generated from non-petroleum carbon resources (such as coal, natural gas, biomass, etc.) into liquid fuels and high-value chemicals, which can effectively alleviate problems such as the increasingly depleted and uneven distribution of petroleum resources.

[0003] Among them, the reaction equations for syngas conversion 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 syngas conversion. Iron-based catalysts have the advantages of high activity, a wide applicable condition window, strong sulfur resistance, simple on-line catalyst replacement, and being suitable for industrial continuous production. However, one of the bottleneck problems existing 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), resulting in a significant reduction in the carbon atom utilization rate and being environmentally unfriendly.

[0009] Therefore, it is imperative to develop new applicable catalysts. Summary of the Invention

[0010] To overcome at least one defect of the above-mentioned prior art, in a first aspect, an embodiment of the present invention provides a preparation method of a metallic iron carbide composition containing θ-iron carbide and ε / ε’-iron carbide, including:

[0011] Preparing a metallic θ-iron carbide complex;

[0012] Preparing a metallic ε / ε’-iron carbide complex; and

[0013] Mix the metal θ-iron carbide composite and the metal ε / ε’-iron carbide composite to obtain a metal iron carbide composition containing θ-iron carbide and ε / ε’-iron carbide; or,

[0014] Mix the metal θ-iron carbide and the metal ε / ε’-iron carbide to obtain a metal iron carbide mixture; and

[0015] Impregnate the metal iron carbide mixture to make it contain bromide ions and / or iodide ions to obtain a metal iron carbide composition containing θ-iron carbide and ε / ε’-iron carbide;

[0016] Among them, the preparation process of the metal θ-iron carbide composite or the metal θ-iron carbide includes the following steps:

[0017] S11: Reduce the θ-precursor with hydrogen at 310-490 °C;

[0018] S12: Treat the product of step S11 with a first gas for carbide preparation, and the treatment temperature is 280-450 °C; the first gas includes hydrogen and carbon monoxide, and the molar ratio of hydrogen to carbon monoxide is 5.5:1-110:1;

[0019] Among them, the θ-precursor is nano-iron and / or nano-iron compound impregnated with bromide ions and / or iodide ions, and the product obtained in step S12 is the metal θ-iron carbide composite; or, the θ-precursor is nano-iron and / or nano-iron compound, and the product obtained in step S12 is the metal θ-iron carbide; or, the θ-precursor is nano-iron and / or nano-iron compound, and the product obtained in step S12 is impregnated to make it contain bromide ions and / or iodide ions to obtain the metal θ-iron carbide composite; among them, the nano-iron compound can be reduced to obtain nano-iron;

[0020] The preparation process of the metal ε / ε’-iron carbide composite or the metal ε / ε’-iron carbide includes the following steps:

[0021] S21: Reduce the ε / ε’-precursor with hydrogen at 260-510 °C;

[0022] S22: Treat the product of step S21 with a second gas, and the treatment temperature is 75-170 °C;

[0023] S23: Treat the product of step S22 with a third gas, and the treatment temperature is 180-270 °C;

[0024] Among them, the second gas includes hydrogen and carbon monoxide with a molar ratio of 1.2:1 to 2.8:1, and the third gas includes hydrogen and carbon monoxide with a molar ratio of 1:1 to 3:1;

[0025] The ε / ε’-precursor is nano-iron and / or nano-iron compound containing bromide ions and / or iodide ions through impregnation treatment, and the product obtained in step S23 is the metallic ε / ε’-iron carbide composite; or, the ε / ε’-precursor is the nano-iron and / or the nano-iron compound, and the product obtained in step S23 is the metallic ε / ε’-iron carbide; or, the ε / ε’-precursor is the nano-iron and / or the nano-iron compound, and the product obtained in step S23 is subjected to impregnation treatment to make it contain bromide ions and / or iodide ions, thereby obtaining the metallic ε / ε’-iron carbide composite.

[0026] In a second aspect, an embodiment of the present invention provides a metallic iron carbide composition prepared by the above-mentioned preparation method.

[0027] In a third aspect, an embodiment of the present invention provides a catalyst, which includes the iron carbide composition prepared by the above-mentioned preparation method or the above-mentioned iron carbide composition.

[0028] In a fourth aspect, an embodiment of the present invention provides the application of the iron carbide composition prepared by the above-mentioned preparation method, the above-mentioned iron carbide composition or the above-mentioned catalyst in the reaction of synthesizing C, H fuels and / or chemicals based on the Fischer-Tropsch synthesis principle.

[0029] In a fifth aspect, an embodiment of the present invention provides a syngas conversion process, which includes contacting the above-mentioned catalyst with syngas under reaction conditions for reaction.

[0030] The iron carbide composition of an embodiment of the present invention can be used as a catalyst for syngas conversion reaction, especially Fischer-Tropsch synthesis reaction. By introducing halide ions such as bromine or iodine into iron carbide, the reaction has a high CO conversion rate, an extremely low total CO2 selectivity and a low CH4 selectivity, realizing the comprehensive optimization of the reaction results. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] 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:

[0032] Figure 1 is the XRD pattern of the θ-iron carbide composite of Example 5 of the present invention;

[0033] Figure 2 is the XRD pattern of the ε / ε’-iron carbide composite of Example 5 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0034] 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.

[0035] An embodiment of the present invention provides a iron carbide composition, comprising iron carbide and halide ions, wherein the halide ions are bromide ions and / or iodide ions; wherein, the molar ratio of iron carbide to halide ions is 100:(0.11 - 46), and the molar number of iron carbide is calculated based on the molar number of iron element contained in the metallic iron carbide composition.

[0036] In one embodiment, the iron carbide in the composition comprises metallic θ-iron carbide and metallic ε / ε’-iron carbide.

[0037] In one embodiment, the grain diameter of θ-iron carbide or θ-iron carbide complex is 7 - 42 nm, further preferably 9 - 35 nm; the grain diameter of ε / ε’-iron carbide or ε / ε’-iron carbide complex is 5 - 30 nm, further preferably 8 - 26 nm.

[0038] In one embodiment, the iron carbide composition is formed by mixing metallic θ-iron carbide complex and metallic ε / ε’-iron carbide complex.

[0039] In one embodiment, the metallic θ-iron carbide (or metallic θ-iron carbide complex) has an orthorhombic crystal structure, and the metallic ε / ε’-iron carbide (or metallic ε / ε’-iron carbide complex) has a hexagonal, pseudo-hexagonal or trigonal crystal structure.

[0040] In one embodiment, based on the molar number (100%) of iron carbide in the iron carbide composition, the molar content of metallic θ-iron carbide is a, and the molar content of metallic ε / ε’-iron carbide is b, wherein, 0 < a ≤ 85%, 0 < b ≤ 85%, preferably, 0 < a ≤ 70%, 0 < b ≤ 70%, for example, a or b can be 1%, 5%, 10%, 15%, 20%, 30%, 50%, 80%. Alternatively, in the iron carbide composition, the molar content of the metallic θ-iron carbide composition is a, and the molar content of the metallic ε / ε’-iron carbide composition is b, wherein, 0 < a ≤ 85%, 0 < b ≤ 85%, preferably, 0 < a ≤ 70%, 0 < b ≤ 70%, for example, a or b can be 1%, 5%, 10%, 15%, 20%, 30%, 50%, 80%. Wherein, the molar numbers of the metallic θ-iron carbide, metallic ε / ε’-iron carbide, metallic θ-iron carbide complex, and metallic ε / ε’-iron carbide complex are calculated based on the molar numbers of the iron elements contained therein.

[0041] In one embodiment, the molar ratio of iron carbide to halide ions can be 100:(0.11 - 46), further can be 100:(0.35 - 32), still further can be 100:(7 - 20), such as 100:0.5, 100:1, 100:5, 100:10, 100:15, 100:20, 100:25, 100:30, 100:40.

[0042] In one embodiment, the iron carbide composition further includes promoter cations, and the molar ratio of iron carbide to promoter cations can be 100:(0.1 - 22), further can be 100:(0.1 - 18), still further can be 100:(0.1 - 10), even further can be 100:(3 - 7), such as 100:0.5, 100:1, 100:5, 100:10, 100:15, 100:20.

[0043] In one embodiment, the iron carbide composition includes halide cations, and the halide cations can maintain charge balance with the halide ions, that is, the total negative charge (or the total valence shown) carried by the halide ions is equal to the total positive charge carried by the halide cations.

[0044] In one embodiment, the iron carbide composition includes promoter anions, and the promoter cations can maintain charge balance with the promoter anions.

[0045] In one embodiment, the halide cations include one or more of first metal ions and complex cations. Further, the first metal ions include one or more of iron ions (such as divalent and trivalent iron ions), manganese ions (such as divalent manganese ions), copper ions (such as monovalent and divalent copper ions), cobalt ions (such as divalent cobalt ions), molybdenum ions (such as divalent, trivalent, and tetravalent molybdenum ions), lanthanum ions (such as trivalent and tetravalent lanthanum ions), cerium ions (such as trivalent and tetravalent cerium ions), and neodymium ions (such as trivalent and tetravalent neodymium ions); the complex cations include one or more of hexaammine manganese ions, hexaammine iron ions, and hexaammine copper ions.

[0046] In one embodiment, the promoter cations include one or more of the second metal ions. The second metal ions may 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; for example, the second metal ions may be manganese ions (such as divalent, trivalent, and tetravalent manganese ions), copper ions (such as monovalent and divalent copper ions), cobalt ions (such as divalent cobalt ions), molybdenum ions (such as divalent, trivalent, and tetravalent molybdenum ions), chromium ions (such as trivalent chromium ions), lanthanum ions (such as trivalent and tetravalent lanthanum ions), cerium ions (such as trivalent and tetravalent cerium ions), neodymium ions (such as trivalent and tetravalent neodymium ions), sodium ions, potassium ions, calcium ions, and barium ions.

[0047] In one embodiment, the promoter anions include one or more of oxygen ions, complex ions, and acid radical ions, such as nitrate, citrate, and gluconate.

[0048] One embodiment of the present invention provides a method for preparing the above iron carbide composition, comprising:

[0049] Preparing a metallic θ-iron carbide complex;

[0050] Preparing a metallic ε / ε'-iron carbide complex; and

[0051] Mixing the metallic θ-iron carbide complex and the metallic ε / ε'-iron carbide complex to obtain a metallic iron carbide composition containing θ-iron carbide and ε / ε'-iron carbide; or,

[0052] Mixing the metallic θ-iron carbide and the metallic ε / ε'-iron carbide to obtain a metallic iron carbide mixture; and

[0053] Performing an impregnation treatment on the metallic iron carbide mixture to make it contain bromide ions and / or iodide ions, thereby obtaining a metallic iron carbide composition containing θ-iron carbide and ε / ε'-iron carbide;

[0054] wherein the preparation process of the metallic θ-iron carbide complex or the metallic θ-iron carbide comprises the following steps:

[0055] S11: Reducing the θ-precursor with hydrogen at 310 - 490 °C;

[0056] S12: Preparing a carbide from the product of step S11 by using a first gas at a treatment temperature of 280 - 450 °C; the first gas includes hydrogen and carbon monoxide, and the molar ratio of hydrogen to carbon monoxide is 5.5:1 - 110:1;

[0057] Among them, the θ-precursor is obtained by impregnating nano-iron and / or nano-iron compounds containing bromide ions and / or iodide ions, and the product obtained in step S12 is a metallic θ-iron carbide composite; or, the θ-precursor is nano-iron and / or nano-iron compounds, and the product obtained in step S12 is metallic θ-iron carbide; or, the θ-precursor is nano-iron and / or nano-iron compounds, and the product obtained in step S12 is impregnated to contain bromide ions and / or iodide ions to obtain a metallic θ-iron carbide composite; among them, nano-iron compounds can be obtained by reduction reaction to obtain nano-iron;

[0058] The preparation process of the metallic ε / ε’-iron carbide composite or metallic ε / ε’-iron carbide includes the following steps:

[0059] S21: Reducing the ε / ε’-precursor with hydrogen at 260-510 °C;

[0060] S22: Treating the product of step S21 with a second gas at a treatment temperature of 75-170 °C;

[0061] S23: Treating the product of step S22 with a third gas at a treatment temperature of 180-270 °C;

[0062] Among them, the second gas includes hydrogen and carbon monoxide with a molar ratio of 1.2:1 to 2.8:1, and the third gas includes hydrogen and carbon monoxide with a molar ratio of 1:1 to 3:1;

[0063] The ε / ε’-precursor is obtained by impregnating nano-iron and / or nano-iron compounds containing bromide ions and / or iodide ions, and the product obtained in step S23 is a metallic ε / ε’-iron carbide composite; or, the ε / ε’-precursor is nano-iron and / or nano-iron compounds, and the product obtained in step S23 is metallic ε / ε’-iron carbide; or, the ε / ε’-precursor is nano-iron and / or the nano-iron compounds, and the product obtained in step S23 is impregnated to contain bromide ions and / or iodide ions to obtain a metallic ε / ε’-iron carbide composite.

[0064] In one embodiment, the nano-iron compounds include one or more of nano-iron oxide, nano-magnetite, nano-goethite, and nano-iron hydroxide oxide.

[0065] In one embodiment, the nano-iron or nano-iron compounds can be nano-iron powder and / or nano-iron particles.

[0066] In one embodiment, the average grain diameter of the nano-iron or nano-iron compound is 6 to 35 nm, further may 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.

[0067] In one embodiment, a first aqueous solution is used to perform a first impregnation treatment on the nano-iron and / or nano-iron compound to obtain a θ-precursor; alternatively, the product obtained in step S12 is impregnated with the first aqueous solution. Wherein, the first aqueous solution includes iodide ions and / or bromide ions and optional first auxiliary ions. The first auxiliary ions include one or more of copper ions, cobalt ions, rare earth ions, chromium ions, molybdenum ions, alkali metal ions, alkaline earth metal ions, and manganese ions.

[0068] In one embodiment, a second aqueous solution is used to perform a second impregnation treatment on the nano-iron and / or nano-iron compound to obtain an ε / ε'-precursor; alternatively, the product obtained in step S23 is impregnated with the second aqueous solution. Wherein, the second aqueous solution includes iodide ions and / or bromide ions and optional second auxiliary ions. The second auxiliary ions include one or more of copper ions, cobalt ions, rare earth ions, chromium ions, molybdenum ions, alkali metal ions, alkaline earth metal ions, and manganese ions.

[0069] In one embodiment, a third aqueous solution is used to perform a third impregnation treatment on the iron carbide mixture of the metal type. Wherein, the third aqueous solution includes iodide ions and / or bromide ions and optional third auxiliary ions. The third auxiliary ions include one or more of copper ions, cobalt ions, rare earth ions, chromium ions, molybdenum ions, alkali metal ions, alkaline earth metal ions, and manganese ions.

[0070] In one embodiment, the raw materials for preparing the first aqueous solution include a first halide and a first solvent, the raw materials for preparing the second aqueous solution include a second halide and a second solvent, and the raw materials for preparing the third aqueous solution include a third halide and a third solvent; the first halide, the second halide, and the third halide are all water-soluble bromides and / or iodides.

[0071] In one embodiment, the first halide, the second halide, and the third halide each independently include one or more of bromides and iodides containing molybdenum, iron, rare earth metal elements, cobalt, copper, and manganese. Further, the first halide, the second halide, and the third halide each independently include one or more of manganese bromide, ferrous bromide, copper bromide, cobalt bromide, molybdenum bromide, manganese iodide, ferrous iodide, copper iodide, rare earth bromides, rare earth iodides, hexaammine manganese bromide, hexaammine iron bromide, hexaammine copper bromide, hexaammine manganese iodide, hexaammine iron iodide, and hexaammine copper iodide.

[0072] In one embodiment, the raw materials for preparing the first aqueous solution further include a first auxiliary agent, and the first auxiliary agent is used to provide first auxiliary agent ions; the raw materials for preparing the second aqueous solution further include a second auxiliary agent, and the second auxiliary agent is used to provide second auxiliary agent ions; the raw materials for preparing the third aqueous solution further include a third auxiliary agent, and the third auxiliary agent is used to provide third auxiliary agent ions.

[0073] In one embodiment, the first auxiliary agent, the second auxiliary agent, and the third auxiliary agent are each independently selected from 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 first auxiliary agent, the second auxiliary agent, and the third auxiliary agent are each independently selected from 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.

[0074] In one embodiment, no chemical reaction occurs between the solute components of the same solution. For example, the solute of the first aqueous solution does not simultaneously include potassium carbonate and calcium nitrate.

[0075] In one embodiment, the first solvent, the second solvent, and the third solvent each independently include water and / or ethanol. For example, the first solvent, the second solvent, and the third solvent can all be water or a mixture of ethanol and water.

[0076] In one embodiment, the dosages of the first halide, the second halide, the third halide, the first auxiliary agent, the second auxiliary agent, and the third auxiliary agent can be appropriately selected according to the contents of the various ions in the composite to be prepared. Further, the concentrations of the first halide, the second halide, the third halide, the first auxiliary agent, the second auxiliary agent, and the third auxiliary agent can all be 0.7 - 7 mol / L, such as 1 mol / L, 2 mol / L, 3 mol / L, 5 mol / L, 6 mol / L.

[0077] In one embodiment, 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, 5 h, 6 h, 8 h.

[0078] In one embodiment, any impregnated material can be dried at 15 - 40°C, and further dried under light - proof 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 process can be carried out under normal pressure or reduced pressure conditions.

[0079] In one embodiment, any of the above impregnation treatments can adopt one of slurry impregnation method, saturated impregnation method, supersaturated impregnation method or other feasible impregnation methods.

[0080] In one embodiment, in the preparation of the metal - type θ - iron carbide composite or metal - type θ - iron carbide, the temperature of the reduction and surface purification treatment in step S11 can be 310 - 490°C, such as 400°C, 420°C, 450°C, 460°C, 480°C; the treatment pressure can be 0 - 12 atm, further can be 0.01 - 3 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 can be 1 - 40 h, further can be 2 - 18 h, such as 5 h, 8 h, 10 h, 12 h, 15 h, 20 h, 25 h, 30 h, 35 h.

[0081] In one embodiment, in the preparation of the metal - type θ - iron carbide composite or metal - type θ - iron carbide, the gas flow rate of H2 in step S11 can be 400 - 22000 mL / h / g, further can be 1000 - 18000 mL / h / g, such as 1200 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, 20000 mL / h / g.

[0082] In one embodiment, in the preparation of the metal - type θ - iron carbide composite or metal - type θ - iron carbide, the first gas in step S12 includes hydrogen and carbon monoxide, and the molar ratio of hydrogen to carbon monoxide can be 5.5:1 - 110:1, such as 10:1, 20:1, 30:1, 36:1, 40:1, 50:1, 60:1, 80:1, 100:1. The first gas can be a mixture of hydrogen and carbon monoxide.

[0083] In one embodiment, in the preparation of the metal-type θ-iron carbide composite or the metal-type θ-iron carbide, the treatment temperature in step S12 can be 280 to 450 °C, such as 300 °C, 320 °C, 330 °C, 350 °C, 380 °C, 400 °C, 420 °C; the treatment pressure can be 0 to 17 atm, further can be 0.01 to 13 atm, such as 0.1 atm, 0.2 atm, 0.5 atm, 0.8 atm, 1 atm, 1.5 atm, 2 atm, 3 atm, 5 atm, 8 atm, 10 atm, 12 atm, 15 atm; the treatment time can be 3 to 72 h, further can be 5 to 48 h, such as 10 h, 15 h, 20 h, 25 h, 30 h, 40 h, 45 h, 50 h, 55 h, 60 h, 70 h.

[0084] In one embodiment, in the preparation of the metal-type θ-iron carbide composite or the metal-type θ-iron carbide, the gas flow rate of the first gas in step S12 can be 200 to 35000 mL / h / g, further can be 1200 to 20000 mL / h / g, such as 1000 mL / h / g, 3000 mL / h / g, 5000 mL / h / g, 6000 mL / h / g, 7000 mL / h / g, 8000 mL / h / g, 10000 mL / h / g, 12000 mL / h / g, 15000 mL / h / g, 18000 mL / h / g, 25000 mL / h / g, 30000 mL / h / g.

[0085] In one embodiment, in the preparation of the metal-type θ-iron carbide composite or the metal-type θ-iron carbide, in step S12, the temperature of the system is cooled or heated from 310 to 490 °C to 280 to 450 °C at a temperature change rate (heating rate or cooling rate) of 0.2 to 5 °C / min. Further, the temperature of the system is cooled or heated from 310 to 490 °C to 300 to 400 °C at a temperature change rate of 0.2 to 2.5 °C / min; the cooling or heating rate in step S12 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.

[0086] In one embodiment, in the preparation of the metallic ε / ε'-iron carbide composite or metallic ε / ε'-iron carbide, the treatment temperature in step S21 can be 260 to 510 °C, such as 280 °C, 300 °C, 310 °C, 320 °C, 350 °C, 370 °C, 400 °C, 420 °C, 450 °C, 480 °C, 500 °C; the treatment pressure can be 0.1 to 12 atm, further can be 0.2 to 3.5 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 can be 0.5 to 8 h, further can be 1 to 7 h, such as 2 h, 3 h, 4 h, 5 h, 6 h.

[0087] In one embodiment, in the preparation of the metallic ε / ε'-iron carbide composite or metallic ε / ε'-iron carbide, the gas flow rate of H2 in step S21 can be 500 to 20000 mL / h / g, further can be 2500 to 15000 mL / h / g, such as 800 mL / h / g, 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.

[0088] In one embodiment, in the preparation of the metallic ε / ε'-iron carbide composite or metallic ε / ε'-iron carbide, the second gas in step S22 includes hydrogen and carbon monoxide, and the molar ratio of hydrogen to carbon monoxide can be 1.2:1 to 2.8:1, such as 1.5:1, 1.8:1, 2:1, 2.2:1, 2.5:1. The second gas can be a mixture of hydrogen and carbon monoxide.

[0089] In one embodiment, in the preparation of the metallic ε / ε'-iron carbide composite or metallic ε / ε'-iron carbide, the treatment temperature in step S22 can be 75 to 170 °C, such as 80 °C, 100 °C, 110 °C, 120 °C, 130 °C, 150 °C, 160 °C; the treatment pressure can be 0.05 to 5 atm, further can be 0.05 to 2.5 atm, such as 0.06 atm, 0.08 atm, 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, 5 atm; the treatment time can be 15 to 90 min, further can be 25 to 70 min, such as 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, 60 min, 80 min.

[0090] In one embodiment, in the preparation of the metallic ε / ε'-iron carbide composite or metallic ε / ε'-iron carbide, the gas flow rate of the second gas in step S22 may be 200 to 8000 mL / h / g, further may be 1000 to 6500 mL / h / g, such as 500 mL / h / g, 1200 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.

[0091] In one embodiment, in the preparation of the metallic ε / ε'-iron carbide composite or metallic ε / ε'-iron carbide, the molar ratio of hydrogen to carbon monoxide in the third gas in step S23 may be 1.2:1, 1.5:1, 1.8:1, 2:1, 2.2:1, 2.5:1, 2.8:1. The third gas may be a mixture of hydrogen and carbon monoxide.

[0092] In one embodiment, in the preparation of the metallic ε / ε'-iron carbide composite or metallic ε / ε'-iron carbide, the treatment temperature in step S23 may be 180 to 270 °C, such as 200 °C, 210 °C, 230 °C, 250 °C, 260 °C, 270 °C; the treatment pressure may be 0.09 to 8 atm, further may be 0.15 to 5 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, 2.8 atm, 5 atm, 8 atm; the treatment time may be 0.5 to 10 h, further may be 1.5 to 8 h, such as 1 h, 1.8 h, 2 h, 2.5 h, 3 h, 4 h, 5 h, 6 h, 9 h.

[0093] In one embodiment, in the preparation of the metallic ε / ε'-iron carbide composite or metallic ε / ε'-iron carbide, the gas flow rate of the third gas in step S23 may be 200 to 20000 mL / h / g, further may be 4000 to 15000 mL / h / g, such as 1000 mL / h / g, 3000 mL / h / g, 5000 mL / h / g, 6000 mL / h / g, 7000 mL / h / g, 8000 mL / h / g, 10000 mL / h / g, 12000 mL / h / g.

[0094] In one embodiment, in the preparation of the metallic ε / ε'-iron carbide composite or metallic ε / ε'-iron carbide, in step S23, the temperature of the system is raised from 75 to 170 °C to 180 to 270 °C at a heating rate of 0.2 to 5 °C / min. Further, the temperature of the system is raised from 75 to 170 °C to 200 to 270 °C at a heating rate of 0.2 to 2.5 °C / min. The heating rate of step S23 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.

[0095] In one embodiment, preferably, the above steps and the above impregnation treatment are all carried out under light-shielded conditions.

[0096] In one embodiment, the preparation method of the metallic θ-iron carbide composite includes the following steps:

[0097] S10: The nano iron and / or nano iron compound are subjected to a first impregnation treatment through a first aqueous solution to obtain a θ-precursor to be treated;

[0098] S11: The θ-precursor is subjected to a reduction treatment at 310 to 490 °C through hydrogen;

[0099] S12: The product of step S11 is subjected to a carbide preparation treatment through a first gas at a treatment temperature of 280 to 450 °C to obtain a metallic θ-iron carbide composite.

[0100] In one embodiment, the preparation method of the metallic θ-iron carbide includes the following steps:

[0101] S11: The θ-precursor (nano iron and / or nano iron compound) is subjected to a reduction treatment at 310 to 490 °C through hydrogen;

[0102] S12: The product of step S11 is subjected to a carbide preparation treatment through a first gas at a treatment temperature of 280 to 450 °C to obtain a metallic θ-iron carbide.

[0103] In one embodiment, the preparation process of the metallic ε / ε'-iron carbide composite includes the following steps:

[0104] S20: The nano iron and / or nano iron compound are subjected to a second impregnation treatment through a second aqueous solution to obtain an ε / ε'-precursor to be treated;

[0105] S21: The ε / ε'-precursor is subjected to a reduction treatment at 260 to 510 °C through hydrogen;

[0106] S22: Treat the product of step S21 with a second gas at a treatment temperature of 75 - 170 °C;

[0107] S23: Treat the product of step S22 with a third gas at a treatment temperature of 180 - 270 °C to obtain a metallic ε / ε'-iron carbide composite.

[0108] In one embodiment, the method for preparing metallic ε / ε'-iron carbide comprises the following steps:

[0109] S21: Reduce the ε / ε'-precursor (nano-iron and / or nano-iron compound) with hydrogen at 260 - 510 °C;

[0110] S22: Treat the product of step S21 with a second gas at a treatment temperature of 75 - 170 °C;

[0111] S23: Treat the product of step S22 with a third gas at a treatment temperature of 180 - 270 °C to obtain metallic ε / ε'-iron carbide.

[0112] One embodiment of the present invention provides a catalyst comprising the above-mentioned iron carbide composition.

[0113] One embodiment of the present invention provides the application of the above-mentioned iron carbide composition or catalyst in the synthesis gas conversion reaction.

[0114] 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.

[0115] In one embodiment, the synthesis gas comprises CO and H2.

[0116] One embodiment of the present invention provides the application of the above-mentioned iron carbide composition 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 in which a synthesis gas (a mixture of CO and H2) is used as a raw material, and through CO hydrogenation and carbon chain growth reactions under the action of a catalyst and appropriate conditions, chain hydrocarbons and / or their oxygen-containing derivatives are generated.

[0117] In one embodiment, the above reaction is a Fischer-Tropsch synthesis reaction, the reaction temperature can be 245 - 305 °C, such as 250 °C, 260 °C, 280 °C, 300 °C; the reaction pressure can be 2 - 3.5 MPa, and the molar ratio of H2 / CO can be 1.7 - 2.15.

[0118] One embodiment of the present invention provides a syngas conversion process, which includes contacting the above-mentioned catalyst with syngas under syngas conversion reaction conditions for reaction.

[0119] In one embodiment, the syngas conversion can be carried out in a high-temperature and high-pressure continuous reactor.

[0120] The iron carbide composition of one embodiment of the present invention can be used as a catalyst for syngas conversion reaction. By introducing halogen ions into 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 iron carbide composition catalyst, it shows considerable activity.

[0121] The iron carbide composition of one embodiment of the present invention can be used as a catalyst for 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 bottleneck, and being able to promote the high-end, diversification, and low-carbonization of clean syngas conversion, indicating new trends and directions for the development of modern syngas chemical industry.

[0122] The iron carbide composition of one embodiment of the present invention, as a catalyst for Fischer-Tropsch synthesis reaction, can maintain 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%.

[0123] In one embodiment, through the Fischer-Tropsch synthesis reaction catalyzed by the iron carbide composition, a CO2 selectivity of <5%, a carbon atom utilization efficiency of >95%, and an effective product selectivity of >90% can be achieved at a CO conversion rate of 70% or more.

[0124] In this article, the "ions" contained in the complex include all particles that are combined with other particles by covalent bonds and / or ionic bonds. For example, the bromide ions in the complex include both Br that interacts with K by ionic bonds + and Br atoms that interact with H atoms by covalent bonds. -

[0125] The pressure values involved in this article are all gauge pressures.

[0126] The following further describes a ferric carbide composition and its application according to an embodiment of the present invention in conjunction with the accompanying drawings and specific embodiments. Among them, the test methods involved are as follows:

[0127] 1. During the reaction process of the examples or comparative examples, in-situ XRD was used to detect the X-ray diffractometer (Rigaku Corporation, model D / max-2600 / PC) to monitor the phase changes of the materials, and the crystal system structures of the ferric carbide complexes were measured by the X-ray diffractometer.

[0128] 2. The average grain diameter of each ferric carbide or its complex was obtained through XRD testing.

[0129] 3. A Mössbauer spectrometer (Transmission 57 Fe, 57 Co(Rh) source sinusoidal velocity spectrometer) was used to perform Mössbauer spectroscopy detection on the ferric carbide composition to obtain the corresponding composition.

[0130] 4. An inductively coupled plasma emission spectrometer (ICP) was used to detect the elements of the ferric carbide composition.

[0131] 5. During the synthesis gas conversion reaction process, the products obtained from the reaction were subjected to gas chromatography analysis (Agilent 7890 gas chromatography) to calculate the conversion rate, selectivity, etc. The products refer to the tail gas collected from the reactor end, including the generated hydrocarbon compounds, alcohol compounds, CO2, etc.

[0132] 6. The CO conversion rate %, CO2 selectivity %, CH4 selectivity %, carbon atom utilization efficiency %, and effective product selectivity % were calculated through the following formulas:

[0133] CO conversion rate % = [(moles of CO in the feed - moles of CO in the product) / moles of CO in the feed] × 100%;

[0134] CO2 selectivity % = [moles of CO2 in the product / (moles of CO in the feed - moles of CO in the product)] × 100%;

[0135] CH4 selectivity % = [moles of CH4 in the product / (moles of CO in the feed - moles of CO in the product)] × 100%;

[0136] Carbon atom utilization efficiency % = (1 - CO2 selectivity %) × 100%;

[0137] Effective product selectivity % = (1 - CO2 selectivity % - CH4 selectivity %) × 100%.

[0138] Example 1

[0139] Preparation of metallic θ - iron carbide

[0140] S11: Take 5.6 g of nano - iron particles with an average grain diameter of 20 nm as the θ - precursor; at a temperature of 430 °C and a pressure of 3.0 atm, keep the θ - precursor in H₂ with a flow rate of 12000 mL / h / g for 2 h to carry out reduction and surface purification treatment.

[0141] S12: Contact the product obtained in step S11 with the first gas to prepare carbide at 410 °C; wherein, the pressure of the system is 2.5 atm, the flow rate of the first gas is 12000 mL / h / g, and the treatment time is 5.5 h; the first gas is a mixture of H₂ and CO, and the molar ratio of H₂ to CO is 20:1. After the treatment is completed, metallic θ - iron carbide is prepared and marked as θ - C1.

[0142] Preparation of metallic ε / ε’ - iron carbide

[0143] S21: Take 5.6 g of nano - iron particles with an average grain diameter of 20 nm as the ε / ε’ - precursor; at a temperature of 420 °C and a pressure of 3.0 atm, keep the ε / ε’ - precursor in H₂ with a flow rate of 8000 mL / h / g for 3 h to carry out reduction and surface purification treatment.

[0144] S22: Cool the product obtained in step S21 to 170 °C and contact it with the second gas at this temperature for pre - treatment; wherein, the pressure of the system is 2.0 atm, the flow rate of the second gas is 5000 mL / h / g, and the treatment time is 1 h; the second gas is a mixture of H₂ and CO, and the molar ratio of H₂ to CO is 2:1.

[0145] S23: Contact the product obtained in step S22 with the third gas. The pressure of the system is 3.0 atm, the total gas flow rate is 10000 mL / h / g, and under this condition, the system is heated to 250 °C at a heating rate of 1 °C / min to prepare carbide; wherein, the third gas is a mixture of H₂ and CO, and the molar ratio of H₂ to CO is 1.5:1. The treatment time of the material at 250 °C is 6 h, and metallic ε / ε’ - iron carbide is prepared and marked as ε / ε’ - C1.

[0146] Preparation of the composition

[0147] The as-prepared metallic θ-iron carbide and metallic ε / ε’-iron carbide were mixed in a molar ratio of 3:2 (based on the molar amount of iron contained in each) to obtain an iron carbide mixture. Manganese bromide and potassium nitrate were dissolved in 50 ml of water to prepare a third aqueous solution. The iron carbide mixture was impregnated with the third aqueous solution as the impregnating liquid. The impregnation ratio was Fe:Br:K = 100:7.0:2.0, the impregnation temperature was 33 °C, and the impregnation time was 3.2 h. The impregnated solid material was dried at 28 °C and 0.1 atm for 5 h to obtain an iron carbide composition, labeled as CX1.

[0148] Examples 1-1 to 3-8 were all prepared with substantially the same raw materials and processes as in Example 1, except that: the content or type of halide ions or promoter cations in each impregnating liquid was different, and the prepared compositions were sequentially labeled as CX1-1 to CX3-8 using the same numbering as in Example 1. Since the loss of materials during the preparation process was extremely small, the content of each substance in the obtained composition was basically the same as the amount of the corresponding raw material used. For specific content values, see Table 1.

[0149] Example 4

[0150] Preparation of Metallic θ-Iron Carbide Composite

[0151] S10: Manganese bromide, potassium citrate, and calcium nitrate were dissolved in 50 ml of water to prepare a first aqueous solution; 8.0 g of nano-iron oxide particles with an average grain diameter of 15 nm were taken, and the first aqueous solution was mixed with the nano-iron oxide particles, and impregnation treatment was carried out by the slurry impregnation method. The impregnation ratio (molar ratio) was Fe:Br:K:Ca = 100:15.0:3.0:3.0, the impregnation temperature was 37 °C, and the impregnation time was 3 h; the impregnated solid material was dried at 25 °C and 0.05 atm for 5 h to obtain a θ-precursor.

[0152] S11: At a pressure of 430 °C and 3.0 atm, the θ-precursor prepared in step S10 was maintained in H2 with a flow rate of 14000 mL / h / g for 3 h for reduction and surface purification treatment.

[0153] S12: The product obtained in step S11 was contacted with the first gas to prepare a carbide at 350 °C; wherein, the pressure of the system was 2.5 atm, the flow rate of the first gas was 10000 mL / h / g, and the treatment time was 5 h; the first gas was a mixture of H2 and CO, and the molar ratio of H2 to CO was 30:1. After the treatment was completed, a metallic θ-iron carbide composite was prepared.

[0154] Preparation of Metallic ε / ε’-Iron Carbide Composite

[0155] S20: Prepare the ε / ε’-precursor using exactly the same raw materials and method as in step S10.

[0156] S21: At a pressure of 430 °C and 2.0 atm, keep the ε / ε’-precursor prepared in step S20 in H2 with a flow rate of 12000 mL / h / g for 3 h to carry out reduction and surface purification treatment.

[0157] S22: Cool the product obtained in step S21 to 170 °C and contact it with a second gas at this temperature for pretreatment; wherein, the pressure of the system is 2.0 atm, the flow rate of the second gas is 8000 mL / h / g, and the treatment time is 1 h; the second gas is a mixture of H2 and CO, and the molar ratio of H2 to CO is 2:1.

[0158] S23: Contact the product obtained in step S22 with a third gas. The pressure of the system is 3.0 atm, and the total gas flow rate is 14000 mL / h / g. Under this condition, heat the system to 250 °C at a heating rate of 1 °C / min to prepare the carbide; wherein, the third gas is a mixture of H2 and CO, the molar ratio of H2 to CO is 1.5:1, the treatment time of the material at 250 °C is 8 h. After the treatment is completed, a metallic ε / ε’-iron carbide composite is prepared.

[0159] Preparation of the composition

[0160] Mix the above-prepared metallic θ-iron carbide composite and metallic ε / ε’-iron carbide composite in a molar ratio of 3:2 (based on the number of moles of iron contained in each) to obtain an iron carbide composition, labeled as CX4.

[0161] Example 4-1

[0162] This example prepares the iron carbide composition using substantially the same raw materials and process as in Example 1, with the only differences being: the H2 flow rate in step S11 is 18000 mL / h / g; the H2 flow rate in step S21 is 15000 mL / h / g. Label the finally obtained iron carbide composition as CX4-1.

[0163] Example 4-2

[0164] This example prepares the iron carbide composition using substantially the same raw materials and process as in Example 1, with the only differences being: the H2 flow rate in step S11 is 1000 mL / h / g; the H2 flow rate in step S21 is 2500 mL / h / g. Label the finally obtained iron carbide composition as CX4-2.

[0165] Example 4-3

[0166] This example uses substantially the same raw materials and processes as in Example 1 to prepare the iron carbide composition, with the only differences being that: in step S11, the H2 flow rate is 10,000 mL / h / g; in step S21, the H2 flow rate is 10,000 mL / h / g. The finally prepared iron carbide composition is labeled as CX4-3.

[0167] Example 4-4

[0168] This example uses substantially the same raw materials and processes as in Example 1 to prepare the iron carbide composition, with the only differences being that: in step S12, the carbonization temperature is 450 °C; in step S23, the carbonization temperature is 270 °C. The finally prepared iron carbide composition is labeled as CX4-4.

[0169] Example 4-5

[0170] This example uses substantially the same raw materials and processes as in Example 1 to prepare the iron carbide composition, with the only differences being that: in step S12, the carbonization temperature is 280 °C; in step S23, the carbonization temperature is 180 °C. The finally prepared iron carbide composition is labeled as CX4-5.

[0171] Example 4-6

[0172] This example uses substantially the same raw materials and processes as in Example 1 to prepare the iron carbide composition, with the only differences being that: in step S12, the carbonization temperature is 345 °C; in step S23, the carbonization temperature is 245 °C. The finally prepared iron carbide composition is labeled as CX4-6.

[0173] Example 4-7

[0174] This example uses substantially the same raw materials and processes as in Example 1 to prepare the iron carbide composition, with the only differences being that: in step S11, the reduction temperature is 390 °C; in step S21, the reduction temperature is 260 °C. The finally prepared iron carbide composition is labeled as CX4-7.

[0175] Example 4-8

[0176] This example uses substantially the same raw materials and processes as in Example 1 to prepare the iron carbide composition, with the only differences being that: in step S12, the carbonization pressure is 13 atm; in step S23, the carbonization pressure is 5 atm. The finally prepared iron carbide composition is labeled as CX4-8.

[0177] Example 4-9

[0178] This example uses substantially the same raw materials and processes as in Example 1 to prepare the iron carbide composition, with the only differences being that: in step S11, the reduction time is 18 h; in step S21, the reduction time is 7 h. The finally prepared iron carbide composition is labeled as CX4-9.

[0179] Examples 4 - 10

[0180] This example uses substantially the same raw materials and process as Example 1 to prepare an iron carbide composition, with the only differences being that: in step S12, the carbonization time is 48 h; in step S23, the carbonization time is 8 h. The finally obtained iron carbide composition is labeled as CX4 - 10.

[0181] Examples 4 - 11

[0182] This example uses substantially the same raw materials and process as Example 1 to prepare an iron carbide composition, with the only differences being that: in step S11, the reduction pressure is 3 atm; in step S21, the reduction pressure is 3.5 atm. The finally obtained iron carbide composition is labeled as CX4 - 11.

[0183] Example 5

[0184] Preparation of Metallic θ - Iron Carbide Composite

[0185] S10: Take manganese bromide and potassium gluconate and dissolve them in 50 ml of water to obtain a first aqueous solution; take 5.6 g of nano - iron particles with an average grain diameter of 20 nm, mix the first aqueous solution with the nano - iron particles, and perform an impregnation treatment by the slurry impregnation method. The impregnation ratio is Fe:Br:K = 100:7.0:2.0, the impregnation temperature is 40 °C, and the impregnation time is 6 h; dry the impregnated solid material at 25 °C and 0.05 atm pressure for 5 h to obtain a θ - precursor.

[0186] Process the θ - precursor using the same process as steps S11 to S12 of Example 1 to obtain a metallic θ - iron carbide composite.

[0187] Preparation of Metallic ε / ε’ - Iron Carbide Composite

[0188] S20: Use exactly the same raw materials and method as in step S10 to obtain an ε / ε’ - precursor.

[0189] Process the ε / ε’ - precursor using the same process as steps S21 to S23 of Example 1 to obtain a metallic ε / ε’ - iron carbide composite.

[0190] Preparation of Composition

[0191] Mix the above - prepared metallic θ - iron carbide composite and metallic ε / ε’ - iron carbide composite in a molar ratio of 3:2 (based on the molar number of iron contained in each) to obtain an iron carbide composition, labeled as CX5.

[0192] Comparative Example 1

[0193] In this example, an iron carbide composition was prepared using substantially the same raw materials and process as in Example 1, except that: in the preparation of the composition, the impregnation ratio was Fe:Br:K = 100:50:2. The finally prepared iron carbide composition was labeled as DX1.

[0194] Comparative Example 2

[0195] In this example, an iron carbide composition was prepared using substantially the same raw materials and process as in Example 1, except that: in the preparation of the composition, manganese bromide was not added to the third aqueous solution of the impregnating solution, and only potassium nitrate was added. The finally prepared iron carbide composition was labeled as D2.

[0196] Comparative Example 3

[0197] In this example, an iron carbide composition was prepared using substantially the same raw materials and process as in Example 1, except that: in the preparation of the composition, an equimolar amount of manganese chloride was used instead of manganese bromide to prepare the third aqueous solution of the impregnating solution. The finally prepared iron carbide composition was labeled as DX3.

[0198] Comparative Example 4

[0199] In this example, metallic θ-iron carbide and metallic ε / ε’-iron carbide were prepared using the same raw materials and process as in Example 1. The metallic θ-iron carbide and metallic ε / ε’-iron carbide were mixed in a molar ratio of 3:2 (based on the molar number of iron contained in each), and an iron carbide composition was prepared and labeled as D4.

[0200] Comparative Example 5

[0201] In this example, an iron carbide composition was prepared using substantially the same raw materials and process as in Example 1, except that: in step S23, the temperature was lowered to 100 °C for operation. The finally prepared iron carbide composition was labeled as DX5.

[0202] The iron carbide composites, iron carbides, iron carbide compositions, etc. prepared in each example and comparative example were measured by XRD, Mössbauer spectroscopy and ICP in the aforementioned manner. The total content of the target iron carbide (i.e., the total content of ε / ε’-iron carbide and θ-iron carbide) was calculated based on 100 mol, and the relevant contents all refer to the molar number. For specific results, see Table 1.

[0203] The catalytic reaction performance of the iron carbide compositions prepared in each example and comparative example was evaluated in a slurry bed continuous reactor. 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 = 15000 mL / h / g- Fe(Standard state flow rate, relative to Fe element), with a circulation ratio of 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 of the reaction are shown in Tables 2 and 3.

[0204] Table 1

[0205]

[0206]

[0207] Table 2

[0208]

[0209]

[0210] Table 3

[0211]

[0212]

[0213] Based on the above results, when the iron carbide composition containing halogen ions such as bromine or iodine prepared in the examples of the present invention is used as a catalyst for the syngas conversion reaction under industrial conditions, it 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 long-term experiments were carried out. From the data of the reaction at 300 h in Table 3, it can be seen that after the long-term continuous operation of the iron carbide composition of the examples 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. Therefore, by using the iron carbide composition of the examples of the present invention as a catalyst for the syngas conversion reaction, the comprehensive optimization of the reaction results can be achieved.

[0214] Unless otherwise specified, the terms used in the present invention have the meanings commonly understood by those skilled in the art.

[0215] The embodiments described in the present invention are only for illustrative purposes and are not intended to limit the protection scope 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 method for preparing a metallic iron carbide composition containing θ-iron carbide and ε / ε’-iron carbide, comprising: Preparation of metallic θ-iron carbide composite; Preparation of metallic ε / ε’-iron carbide composite; and mixing the metallic θ-iron carbide composite and the metallic ε / ε’-iron carbide composite to obtain a metallic iron carbide composition containing θ-iron carbide and ε / ε’-iron carbide; or, mixing metallic θ-iron carbide and metallic ε / ε’-iron carbide to obtain a metallic iron carbide mixture; and performing an impregnation treatment on the metallic iron carbide mixture to make it contain bromide ions and / or iodide ions, thereby obtaining a metallic iron carbide composition containing θ-iron carbide and ε / ε’-iron carbide; wherein the preparation process of the metallic θ-iron carbide composite or the metallic θ-iron carbide includes the following steps: S11: Reducing a θ-precursor with hydrogen at 310-490 °C; S12: Preparing a carbide from the product of step S11 by using a first gas at a treatment temperature of 280-450 °C; the first gas includes hydrogen and carbon monoxide, and the molar ratio of hydrogen to carbon monoxide is 5.5:1-110:1; wherein the θ-precursor is nano-iron and / or a nano-iron compound impregnated with bromide ions and / or iodide ions, and the product obtained in step S12 is the metallic θ-iron carbide composite; or, the θ-precursor is nano-iron and / or a nano-iron compound, and the product obtained in step S12 is the metallic θ-iron carbide; or, the θ-precursor is nano-iron and / or a nano-iron compound, and the product obtained in step S12 is impregnated to contain bromide ions and / or iodide ions to obtain the metallic θ-iron carbide composite; wherein the nano-iron compound can be reduced to obtain nano-iron; The preparation process of the metallic ε / ε’-iron carbide composite or the metallic ε / ε’-iron carbide includes the following steps: S21: Reducing an ε / ε’-precursor with hydrogen at 260-510 °C; S22: Treating the product of step S21 with a second gas at a treatment temperature of 75-170 °C; S23: Treating the product of step S22 with a third gas at a treatment temperature of 180-270 °C; wherein the second gas includes hydrogen and carbon monoxide with a molar ratio of 1.2:1 to 2.8:1, and the third gas includes hydrogen and carbon monoxide with a molar ratio of 1:1 to 3:1; The ε / ε’-precursor is nano-iron and / or a nano-iron compound impregnated with bromide ions and / or iodide ions, and the product obtained in step S23 is the metallic ε / ε’-iron carbide composite; or, the ε / ε’-precursor is the nano-iron and / or the nano-iron compound, and the product obtained in step S23 is the metallic ε / ε’-iron carbide; or, the ε / ε’-precursor is the nano-iron and / or the nano-iron compound, and the product obtained in step S23 is impregnated to contain bromide ions and / or iodide ions to obtain the metallic ε / ε’-iron carbide composite.

2. The preparation method according to claim 1, wherein, The nano iron and / or nano iron compound is impregnated with a first aqueous solution to obtain the θ-precursor; alternatively, the product obtained in step S12 is impregnated with the first aqueous solution; the first aqueous solution includes iodide ions and / or bromide ions and optional first auxiliary ions; the first auxiliary ions include one or more of copper ions, cobalt ions, rare earth ions, chromium ions, molybdenum ions, alkali metal ions, alkaline earth metal ions, and manganese ions; and / or The nano iron compound includes one or more of nano magnetite, nano iron oxide, nano iron hydroxide oxide, and nano goethite.

3. The preparation method according to claim 1, wherein, The nano iron and / or nano iron compound is impregnated with a second aqueous solution to obtain the ε / ε'-precursor; alternatively, the product obtained in step S23 is impregnated with the second aqueous solution; the second aqueous solution includes iodide ions and / or bromide ions and optional second auxiliary ions; the second auxiliary ions include one or more of copper ions, cobalt ions, rare earth ions, chromium ions, molybdenum ions, alkali metal ions, alkaline earth metal ions, and manganese ions; The metal-type iron carbide mixture is impregnated with a third aqueous solution; the third aqueous solution includes iodide ions and / or bromide ions and optional third auxiliary ions, and the third auxiliary ions include one or more of copper ions, cobalt ions, rare earth ions, chromium ions, molybdenum ions, alkali metal ions, alkaline earth metal ions, and manganese ions; and / or The average grain diameter of the nano iron or the nano iron compound is 6 - 35 nm, preferably 9 - 28 nm.

4. The preparation method according to claim 1, wherein, In step S11, the treatment pressure is 0 - 12 atm, the treatment time is 1 - 40 h, and the gas flow rate of H2 is 400 - 22000 mL / h / g; in step S12, the treatment pressure is 0 - 17 atm, the treatment time is 3 - 72 h, and the gas flow rate of the first gas is 200 - 35000 mL / h / g; and / or In step S21, the treatment pressure is 0.1 - 12 atm, the treatment time is 0.5 - 8 h, and the gas flow rate of H2 is 500 - 20000 mL / h / g; in step S22, the treatment pressure is 0.05 - 5 atm, the treatment time is 15 - 90 min, and the gas flow rate of the second gas is 200 - 8000 mL / h / g; in step S23, the treatment pressure is 0.09 - 8 atm, the treatment time is 0.5 - 10 h, and the gas flow rate of the third gas is 200 - 20000 mL / h / g.

5. A metallic iron carbide composition prepared by the preparation method according to any one of claims 1 to 4.

6. The composition according to claim 5, comprising iron carbide and halide ions, wherein the halide ions are bromide ions and / or iodide ions; wherein, The molar ratio of the iron carbide to the halide ion is 100:(0.11 - 46), further 100:(0.35 - 42), and the molar number of the iron carbide is calculated based on the molar number of the iron element contained in the composition.

7. The composition according to claim 6, wherein, The composition further comprises promoter cations, which include one or more of manganese ions, molybdenum ions, rare earth ions, alkali metal ions, copper ions, cobalt ions, chromium ions, alkaline earth metal ions; the molar ratio of the iron carbide to the promoter cations is 100:(0.1 to 22), further 100:(0.1 to 18).

8. A catalyst comprising an iron carbide composition prepared by the preparation method according to any one of claims 1 to 4 or an iron carbide composition according to any one of claims 5 to 7.

9. Use of the iron carbide composition prepared by the preparation method according to any one of claims 1 to 4, the iron carbide composition according to any one of claims 5 to 7, or the catalyst according to claim 8 in a reaction for synthesizing C and H fuels and / or chemicals based on the Fischer-Tropsch synthesis principle.

10. A syngas conversion process, comprising contacting the catalyst according to claim 8 with syngas under reaction conditions for reaction.

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