Metallic θ-iron carbide compound, preparation method therefor, and use thereof

Abstract

The present invention relates to a metallic θ-iron carbide compound, a preparation method therefor, and a use thereof. The method comprises: S1, carrying out reduction and surface purification treatment on a precursor at a temperature of 300-500°C under the action of hydrogen to obtain an intermediate product; and S2, carrying out carbide preparation treatment on the intermediate product at a temperature of 300-470°C in a mixed gas atmosphere. The metallic θ-iron carbide compound according to one embodiment of the present invention is used as a catalyst for a syngas conversion reaction, so that the reaction has extremely low overall CO2 selectivity.

Description

A metallic θ-iron carbide composite and its preparation method and application Technical Field

[0001] The present invention relates to the conversion of synthesis gas, and in particular to a θ-iron carbide composite capable of being used for the conversion of synthesis gas and a preparation method thereof. Background Art

[0002] my country's primary energy structure is characterized by an abundance of coal, a shortage of oil, and limited natural gas. With the development of my country's economy, its dependence on foreign oil has continued to rise. Syngas, a mixture of CO and H₂ obtained by gasifying coal, natural gas, and biomass, has become increasingly important in recent years. Syngas conversion technology can be used to gasify carbon-containing materials such as coal, natural gas, and biomass to generate syngas, which can then be converted into liquid fuels and high-value chemicals.

[0003] The reaction equation for syngas conversion is 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 most affordable and readily available catalysts for syngas conversion. They offer advantages such as high activity, a wide window of applicable conditions, strong sulfur tolerance, simple online catalyst replacement, and suitability for continuous industrial production. However, one of the bottlenecks of conventional syngas conversion technology using iron-based catalysts is their excessively high CO2 selectivity (typically 35-45% of the raw CO converted).

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

[0010] The prior art discloses a high-purity iron carbide catalyst that can reduce primary CO2 in the Fischer-Tropsch synthesis reaction to near zero while achieving a high space-time conversion rate of CO, thereby reducing the overall CO2 selectivity to less than 5% at low CO conversions (typically below 35%). However, as CO conversion increases, the WGS reaction becomes more intense as the H2O content in the reaction environment rises, leading to an increase in secondary CO2 and ultimately increasing the overall CO2 selectivity at high CO conversions.

[0011] In addition, reducing CO2 selectivity will significantly increase carbon atom utilization efficiency, essentially improving the economic and environmental friendliness of syngas conversion technology. Therefore, how to suppress the water-gas shift side reaction at high CO conversion rates, reduce CO2 selectivity, and improve carbon atom utilization efficiency has become one of the common key issues in the field of syngas conversion. On the other hand, in addition to CO2, another major by-product in the field of syngas conversion is methane. In the reaction, higher CH4 selectivity will jointly reduce the effective product selectivity of the reaction with higher CO2 selectivity.

[0012] Summary of the Invention

[0013] To overcome at least one of the above-mentioned defects of the prior art, in a first aspect, an embodiment of the present invention provides a method for preparing a metallic θ-iron carbide composite, comprising the following steps:

[0014] S0: Providing a precursor, wherein the precursor is nano-iron and / or a nano-iron compound or the nano-iron and / or nano-iron compound containing bromide ions and / or iodide ions; the nano-iron compound can be prepared into nano-iron by a reduction reaction;

[0015] S1: reducing and surface-purifying the precursor at 300-500° C. under the action of hydrogen to obtain an intermediate product;

[0016] S2: preparing carbide from the intermediate product at 300-470° C. in a mixed gas atmosphere;

[0017] Wherein, the mixed gas comprises hydrogen and carbon monoxide in a molar ratio of (5:1 to 110):1;

[0018] The nano-iron and / or nano-iron compound is subjected to a first impregnation treatment with an impregnation liquid to obtain the nano-iron and / or nano-iron compound containing bromide ions and / or iodide ions; wherein, when the precursor is the nano-iron and / or the nano-iron compound, the product of step S2 is subjected to a second impregnation treatment with the impregnation liquid.

[0019] In a second aspect, an embodiment of the present invention provides a θ-iron carbide composite prepared by the above preparation method.

[0020] In a third aspect, an embodiment of the present invention provides a θ-iron carbide composite, comprising θ-iron carbide and a halogen element, wherein the molar ratio of the θ-iron carbide to the halogen element is 100:(0.1-40); wherein the halogen element is bromine and / or iodine; and the molar number of the θ-iron carbide is calculated based on the molar number of iron contained therein.

[0021] In a fourth aspect, an embodiment of the present invention provides a catalyst, comprising the θ-iron carbide composite prepared by the above preparation method or the above θ-iron carbide composite.

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

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

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

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

[0026] The accompanying drawings are only used to illustrate specific embodiments and are not to be considered as limiting the present invention.

[0027] FIG1 is an XRD pattern of the θ-iron carbide composite CX1 prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0028] Typical embodiments that embody 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 is capable of various variations in different embodiments without departing from the scope of the present invention, and the descriptions herein are intended to be illustrative rather than limiting.

[0029] One embodiment of the present invention provides a θ-iron carbide composite, comprising θ-iron carbide and a halogen element, wherein the molar ratio of θ-iron carbide to the halogen element is 100:(0.1-40);

[0030] The halogen element is bromine and / or iodine; the composite has an orthorhombic crystal structure, and its average grain diameter is 7 to 42 nm, and further can be 9 to 35 nm; herein, the molar number of θ-iron carbide is calculated based on the molar number of iron element it contains.

[0031] In one embodiment, the halogen element exists in the form of a halide ion, which may be a bromide ion and / or an iodide ion. The molar ratio of θ-iron carbide to the halogen element (or halide ion) may be 100:(0.1-40), further 100:(0.35-32), and further 100:(7-20), for example, 100:0.5, 100:1, 100:5, 100:10, 100:15, 100:20, 100:25, 100:30, or 100:40.

[0032] In one embodiment, the theta-iron carbide complex includes halide cations that are capable of maintaining charge balance with the halide ions, i.e., the total number of negative charges (or the total number of valences exhibited) of the halide ions is equal to the total number of positive charges of the halide cations.

[0033] In one embodiment, the θ-iron carbide composite further includes other cationic elements, and the other cationic elements exist in the form of other cations. The molar ratio of θ-iron carbide to the other cationic elements (or other cations) can be 100:(0.1-22), further can be 100:(0.1-18), and further can be 100:(0.1-10), for example, 100:0.5, 100:1, 100:3, 100:5, 100:7, 100:10, 100:15, and 100:20.

[0034] In one embodiment, the other cation is a halide cation, or the θ-iron carbide complex includes both halide cations and other cations.

[0035] In one embodiment, the θ-iron carbide complex further includes other anions that can maintain charge balance with the other cations when the complex includes both halide cations and other cations.

[0036] In one embodiment, the other cationic elements may be selected from one or more of manganese, copper, cobalt, molybdenum, chromium, rare earth elements, alkali metal elements, and alkaline earth metal elements; preferably, the other cationic elements are selected from one or more of manganese, copper, cobalt, molybdenum, chromium, lanthanum, cerium, neodymium, sodium, potassium, calcium, and barium. Accordingly, the other cations may be selected from one or more of manganese ions, copper ions, cobalt ions, platinum ions, chromium ions, rare earth ions, alkali metal ions, and alkaline earth metal ions; for example, the other cations may be manganese ions (e.g., divalent, trivalent, or tetravalent manganese ions), copper ions (e.g., monovalent or divalent copper ions), cobalt ions (e.g., divalent cobalt ions), platinum ions (e.g., divalent, trivalent, or tetravalent platinum ions), chromium ions (e.g., trivalent chromium ions), lanthanum ions (e.g., trivalent or tetravalent lanthanum ions), cerium ions (e.g., trivalent or tetravalent cerium ions), neodymium ions (e.g., trivalent or tetravalent neodymium ions), sodium ions, potassium ions, calcium ions, and barium ions.

[0037] In one embodiment, the halide cations include 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 (e.g., a divalent or trivalent iron ion), a manganese ion (e.g., a divalent manganese ion), a copper ion (e.g., a monovalent or divalent copper ion), a cobalt ion (e.g., a divalent cobalt ion), a platinum ion (e.g., a divalent, trivalent or tetravalent platinum ion), a lanthanum ion (e.g., a trivalent or tetravalent lanthanum ion), a cerium ion (e.g., a trivalent or tetravalent cerium ion), and a neodymium ion (e.g., a trivalent or tetravalent neodymium ion); and the complex cations include one or more of a hexaamminemanganese ion, a hexaammineferric ion, and a hexaamminecopper ion.

[0038] In one embodiment, the other anions include one or more of oxygen ions, complex ions, and acid ions, such as oxygen ions, nitrate, citrate, and gluconate.

[0039] One embodiment of the present invention provides a method for preparing the above-mentioned θ-iron carbide composite, comprising the following steps:

[0040] S1: Under the action of hydrogen, the precursor is reduced and surface purified at 300-500°C to obtain an intermediate product;

[0041] S2: Carbide preparation treatment of the intermediate product at 300-470° C. in a mixed gas atmosphere;

[0042] The mixed gas includes hydrogen and carbon monoxide, and the molar ratio of hydrogen to carbon monoxide is 5:1 to 110:1;

[0043] The precursor is nano-iron and / or nano-iron compound subjected to a first impregnation treatment with an impregnation solution, the nano-iron compound can be prepared into nano-iron by a reduction reaction, and the impregnation solution includes bromide ions and / or iodide ions; or,

[0044] The precursor is nano-iron and / or the nano-iron compound, and the product of step S2 is subjected to a second impregnation treatment using an impregnation solution.

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

[0046] In one embodiment, the nano-iron or nano-iron compound may 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, and can further be 9 to 28 nm, for example, 10 nm, 12 nm, 15 nm, 18 nm, 20 nm, 22 nm, 25 nm, 30 nm, or 32 nm.

[0048] In one embodiment, the impregnation solution is prepared by dissolving an impregnation compound in a solvent. The impregnation compound may include a water-soluble halide, wherein the halide includes a bromide and / or an iodide. Further, the halide includes one or more bromides and iodides containing manganese, molybdenum, cobalt, a rare earth metal element, iron, or copper. For example, the halide may 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, hexaamminemanganese bromide, hexaammineferric bromide, hexaamminecopper bromide, hexaamminemanganese iodide, hexaammineferric iodide, and hexaamminecopper iodide.

[0049] In one embodiment, the concentration of the halide in the impregnation solution may be 0.7 to 7 mol / L, for example, 1 mol / L, 2 mol / L, 3 mol / L, 5 mol / L, or 6 mol / L.

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

[0051] In one embodiment, the solute of the impregnation solution further includes other compounds, and the other compounds include one or more 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, the solute components of the impregnation solution do not chemically react with each other, for example, the solute does not include potassium carbonate and calcium nitrate at the same time.

[0053] In one embodiment, the amount of the halide or other compound can be appropriately selected based on the content of each ion in the complex to be prepared. Furthermore, the concentration of the halide or other compound can be 0.7 to 7 mol / L, for example, 1 mol / L, 2 mol / L, 3 mol / L, 5 mol / L, or 6 mol / L.

[0054] In one embodiment, the precursor is nano-iron or a nano-iron compound that is subjected to a first impregnation treatment with an impregnation liquid, and the temperature of the first impregnation treatment or the second impregnation treatment is 0 to 50°C, and can further be 20 to 30°C, for example, 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C; the time of the first impregnation treatment or the second impregnation treatment can be 0.1 to 12h, and can further be 0.2 to 10h, and further can be 0.3 to 9h, for example, 0.5h, 1h, 2h, 3h, 5h, 6h, 8h.

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

[0056] In one embodiment, the first impregnation treatment or the second impregnation treatment may be performed by a slurry impregnation method, a saturation impregnation method, a supersaturation impregnation method, or other feasible impregnation methods.

[0057] In one embodiment, the temperature of the reduction and surface purification treatment in step S1 can be 300-500°C, for example, 350°C, 400°C, 420°C, 450°C, 460°C, 480°C, and 500°C; the treatment pressure can be 0.13-9.5atm, and further can be 0.22-2.5atm, for example, 0.15atm, 0.2atm, 0.5atm, 0.8atm, 1atm, 1.5atm, 2atm, 5atm, 8atm, and 9atm; the treatment time can be 1.2-26h, and further can be 2-12h, for example, 5h, 8h, 10h, 15h, 20h, and 25h.

[0058] In one embodiment, the gas flow rate of H2 in step S1 can be 600-21000 mL / h / g, and can further be 1200-16000 mL / h / g, for example, 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, and 15000 mL / h / g.

[0059] In one embodiment, the mixed gas in step S2 includes hydrogen and carbon monoxide, and the molar ratio of hydrogen to carbon monoxide can be 5:1 to 110:1, for example, 10:1, 20:1, 30:1, 36:1, 40:1, 50:1, 60:1, 80:1, or 100:1. The mixed gas can be a mixture of hydrogen and carbon monoxide.

[0060] In one embodiment, the pretreatment temperature of step S2 can be 300-470°C, for example, 300°C, 320°C, 330°C, 350°C, 380°C, 400°C, and 420°C; the treatment pressure can be 0-21atm, and can further be 0.01-17atm, for example, 0.1atm, 0.2atm, 0.5atm, 0.8atm, 1atm, 1.5atm, 2atm, 3atm, 5atm, 8atm, 10atm, 12atm, 15atm, 18atm, and 20atm; the treatment time can be 3-72h, and can further be 5-48h, for example, 10h, 20h, 25h, 30h, 40h, 45h, 50h, 55h, 60h, and 70h.

[0061] In one embodiment, the gas flow rate of the mixed gas in step S2 can be 500-31000 mL / h / g, and can further be 1500-17000 mL / h / g, for example, 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, and 30000 mL / h / g.

[0062] In one embodiment, in step S2, the temperature of the system is increased or decreased from 300 to 500°C to 300 to 470°C at a heating rate of 0.2 to 5°C / min, and further, the temperature of the system is increased or decreased from 300 to 500°C to 300 to 400°C at a heating rate of 0.2 to 2.5°C / min; the heating rate of step S2 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, or 4°C / min.

[0063] In one embodiment, preferably, steps S1, S2 and the first or second immersion treatment are all performed under light-proof conditions.

[0064] In one embodiment, the preparation method of the metallic θ-iron carbide composite comprises the following steps:

[0065] S0: performing a first impregnation treatment on the nano-iron and / or nano-iron compound using an impregnation solution to obtain a precursor to be treated;

[0066] S1: Under the action of hydrogen, the precursor is reduced and surface purified at 300-500°C to obtain an intermediate product;

[0067] S2: treating the intermediate product at 300-470° C. in a mixed gas atmosphere to obtain a θ-iron carbide composite containing halogen elements.

[0068] In another embodiment, the preparation method of the metallic θ-iron carbide composite comprises the following steps:

[0069] S1: Under the action of hydrogen, the precursor (nano-iron and / or nano-iron compound) is reduced and surface-purified at 300-500° C. to obtain an intermediate product;

[0070] S2: treating the intermediate product at 300-470° C. in a mixed gas atmosphere;

[0071] S21: performing a second impregnation treatment on the product of step S2 to obtain a θ-iron carbide composite containing halogen elements.

[0072] One embodiment of the present invention provides a catalyst comprising the above-mentioned θ-iron carbide composite.

[0073] One embodiment of the present invention provides use of the aforementioned θ-iron carbide composite or catalyst in a synthesis gas conversion reaction.

[0074] In one embodiment, the synthesis gas conversion reaction may be a Fischer-Tropsch synthesis reaction, or other reactions based on the Fischer-Tropsch synthesis principle, such as a reaction using synthesis gas as a starting material and an alcohol as a final product.

[0075] In one embodiment, the syngas comprises CO and H2.

[0076] One embodiment of the present invention provides the use of the aforementioned θ-iron carbide composite or catalyst in a reaction based on the Fischer-Tropsch synthesis principle for synthesizing C and H fuels and / or chemicals. The Fischer-Tropsch synthesis principle refers to a reaction in which syngas (a mixture of CO and H₂) is used as a feedstock, and chain hydrocarbons and / or their oxygenated derivatives are produced through CO hydrogenation and carbon chain growth reactions in the presence of a catalyst and appropriate conditions.

[0077] In one embodiment, the above reaction is a Fischer-Tropsch synthesis reaction, the reaction temperature can be 280-340°C, for example, 290°C, 300°C, 310°C, 320°C; the reaction pressure can be 2-3.5 MPa, and the molar ratio of H2 / CO can be 1.7-2.15.

[0078] One embodiment of the present invention provides a synthesis gas conversion process, comprising contacting the above-mentioned catalyst with synthesis gas under synthesis gas conversion reaction conditions to react.

[0079] In one embodiment, syngas conversion may be performed in a high temperature and high pressure continuous reactor.

[0080] A θ-iron carbide composite according to one embodiment of the present invention can be used as a catalyst for syngas conversion reactions. By introducing halide ions into the θ-iron carbide, the reaction exhibits high CO conversion, extremely low overall CO selectivity, and low CH selectivity. Furthermore, the θ-iron carbide composite catalyst exhibits considerable activity, benefiting from its high space-time CO conversion rate.

[0081] The θ-iron carbide composite of one embodiment of the present invention can be used as a catalyst for synthesis gas conversion reactions, enabling the reaction to maintain extremely low CO2 selectivity while having a high CO conversion rate, while maintaining low CH4 selectivity and high reaction stability. This greatly improves the utilization efficiency of carbon atoms and the selectivity of effective products, breaks through key technical bottlenecks, and can promote the high-end, diversified and low-carbonization of clean synthesis gas conversion, indicating new trends and directions for the development of modern synthesis gas chemical industry.

[0082] The θ-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 hours using a high-pressure continuous reactor under industrial Fischer-Tropsch synthesis reaction conditions, with its CO2 selectivity below 5%, further below 3%; its by-product CH4 selectivity can be maintained below 8.5%, further below 5.5%; the carbon atom utilization efficiency is maintained above 95%, further above 97%; and the effective product selectivity can reach above 86.5%, further above 92%.

[0083] In one embodiment, the Fischer-Tropsch synthesis reaction catalyzed by the θ-iron carbide composite can achieve a CO2 selectivity of <5%, a carbon atom utilization efficiency of >95%, and an effective product selectivity of >90% at a CO conversion rate of more than 70%.

[0084] In this article, the "ions" contained in the complex include all particles that are bound to other particles by covalent bonds and / or ionic bonds. For example, the bromide ion in the complex includes both the bromide ion and the K + Interacting Br - , also including Br atoms that interact with H atoms through covalent bonds.

[0085] The pressure values ​​mentioned in this article are gauge pressure.

[0086] The following further describes the θ-iron carbide composite and its application according to one embodiment of the present invention in conjunction with the accompanying drawings and specific examples. The test methods involved are as follows:

[0087] 1. During the reaction process of the Examples or Comparative Examples, an in-situ XRD detection X-ray diffractometer (Rigaku, model D / max-2600 / PC) was used to monitor the crystal phase change of the material. The crystal structure of the θ-iron carbide composite was measured by the X-ray diffractometer.

[0088] 2. The average grain size of θ-iron carbide composite was obtained by XRD test.

[0089] 3. Using Mössbauer spectrometer (Transmission 57 Fe, 57The θ-iron carbide complex was detected by Mössbauer spectroscopy using a Co(Rh) source sinusoidal velocity spectrometer to obtain the composition of the complex.

[0090] 4. The elements of θ-iron carbide composite were detected using an inductively coupled plasma emission spectrometer (ICP).

[0091] 5. During the synthesis gas conversion reaction, the reaction products are subjected to gas chromatography analysis (Agilent 7890 gas chromatograph) to calculate the conversion rate, selectivity, etc. The products refer to the tail gas collected from the tail end of the reactor, including the generated hydrocarbon compounds, alcohol compounds, CO2, etc.

[0092] 6.CO conversion %, CO2 selectivity %, CH4 selectivity %, carbon atom utilization efficiency %, and effective product selectivity % are calculated using the following formulas:

[0093] CO conversion rate % = [(CO moles in feed - CO moles in discharge) / CO moles in feed] × 100%;

[0094] CO2 selectivity % = [CO2 moles in the discharge / (CO moles in the feed - CO moles in the discharge)] × 100%;

[0095] CH4 selectivity % = [mole number of CH4 in the discharge / (mole number of CO in the feed - mole number of CO in the discharge)] × 100%;

[0096] Carbon atom utilization efficiency % = (1-CO2 selectivity %) × 100%;

[0097] Effective product selectivity % = (1-CO2 selectivity %-CH4 selectivity %) × 100%.

[0098] Example 1

[0099] S1: At 430°C and a pressure of 2.0 atm, 5.6 g of nano-iron particles with an average grain diameter of 20 nm were taken and kept in H2 at a flow rate of 12000 mL / h / g for 2 hours for reduction and surface purification to obtain an intermediate product.

[0100] S2: Cooling the intermediate product to 420°C and contacting it with a mixed gas at this temperature to prepare a precarbide; wherein the system pressure is 2.0 atm, the flow rate of the mixed gas is 10,000 mL / h / g, and the treatment time is 6 hours; the mixed gas is a mixture of H2 and CO, and the molar ratio of H2 to CO is 30:1.

[0101] S21: Manganese bromide and potassium nitrate are dissolved in 50 ml of water to prepare an impregnation solution; the impregnation solution is mixed with the product of step S2 and impregnated by a slurry impregnation method with an impregnation ratio (molar ratio) of Fe:Br:K=100:7.0:2.0, an impregnation temperature of 32°C, and an impregnation time of 2 h; the impregnated solid material is dried at 35°C for 7 h. After the treatment, a θ-iron carbide composite is obtained, which is labeled CX1.

[0102] Examples 1-1 to 3-8 all used the same raw materials and processes as Example 1 to prepare metallic θ-iron carbide composites, differing only in the amount or type of halide ions or other cations in the impregnation solution. The resulting composites are numbered CX1-1 to CX3-8, using the same numbers as Example 1. Because material loss is minimal during the preparation process, the content of each substance in the resulting composites is essentially the same as the amount of the corresponding raw materials used. Specific content values ​​are shown in Table 1.

[0103] Example 4

[0104] S0: 0.035 mol manganese bromide, 0.03 mol potassium citrate, and 0.05 mol copper nitrate were dissolved in 50 ml of water to prepare an impregnation solution; 8.0 g of nano-iron oxide particles with an average grain diameter of 16 nm were taken, the impregnation solution was mixed with the nano-iron oxide particles, and impregnation treatment was performed by a slurry impregnation method. The impregnation ratio (molar ratio) was Fe:Br:K:Cu=100:7.0:3.0:5.0, the impregnation temperature was 37°C, and the impregnation time was 3 h; the solid material after impregnation was dried at 25°C for 8 h to obtain a precursor.

[0105] S1: The precursor prepared in step S0 was kept in H2 at a flow rate of 15000 mL / h / g for 2 h at 430° C. and a pressure of 3.0 atm to perform reduction and surface purification treatment to obtain an intermediate product.

[0106] S2: The intermediate product is cooled to 350°C and exposed to a mixed gas at this temperature to prepare a precarbide. The system pressure is 3.0 atm, the mixed gas flow rate is 12,000 mL / h / g, and the treatment time is 6 hours. The mixed gas is a mixture of hydrogen and carbon monoxide with a molar ratio of hydrogen to carbon monoxide of 30:1. After the treatment, a θ-iron carbide composite is obtained, labeled CX4.

[0107] Example 4-1

[0108] This example uses substantially the same raw materials and process as Example 1 to prepare a θ-iron carbide composite, with the only difference being that the H2 flow rate in step S1 is 1200 mL / h / g. The resulting θ-iron carbide composite is labeled CX4-1.

[0109] Example 4-2

[0110] This example uses substantially the same raw materials and process as Example 1 to prepare a θ-iron carbide composite, with the only difference being that the H2 flow rate in step S1 is 16000 mL / h / g. The resulting θ-iron carbide composite is labeled CX4-2.

[0111] Example 4-3

[0112] This example uses substantially the same raw materials and process as Example 1 to prepare a θ-iron carbide composite, with the only difference being that the H2 flow rate in step S1 is 10,000 mL / h / g. The resulting θ-iron carbide composite is labeled CX4-3.

[0113] Example 4-4

[0114] This embodiment uses substantially the same raw materials and processes as in embodiment 1 to prepare a θ-iron carbide composite, with the only difference being that the carbonization temperature in step S2 is 300° C. The resulting θ-iron carbide composite is labeled CX4-4.

[0115] Examples 4-5

[0116] This embodiment uses substantially the same raw materials and processes as in embodiment 1 to prepare a θ-iron carbide composite, with the only difference being that the carbonization temperature in step S2 is 470° C. The resulting θ-iron carbide composite is labeled CX4-5.

[0117] Examples 4-6

[0118] This embodiment uses substantially the same raw materials and processes as in embodiment 1 to prepare a θ-iron carbide composite, with the only difference being that the carbonization temperature in step S2 is 400° C. The resulting θ-iron carbide composite is labeled CX4-6.

[0119] Examples 4-7

[0120] This embodiment uses substantially the same raw materials and processes as in embodiment 1 to prepare a θ-iron carbide composite, with the only difference being that the reduction temperature in step S1 is 500° C. The resulting θ-iron carbide composite is labeled CX4-7.

[0121] Examples 4-8

[0122] This embodiment uses substantially the same raw materials and processes as in embodiment 1 to prepare a θ-iron carbide composite, with the only difference being that the carbonization pressure in step S2 is 17 atm. The resulting θ-iron carbide composite is labeled CX4-8.

[0123] Examples 4-9

[0124] This example uses substantially the same raw materials and process as Example 1 to prepare a θ-iron carbide composite, with the only difference being that the reduction time in step S1 is 12 hours. The resulting θ-iron carbide composite is labeled CX4-9.

[0125] Examples 4-10

[0126] This example uses substantially the same raw materials and process as Example 1 to prepare a θ-iron carbide composite, with the only difference being that the carbonization time in step S2 is 48 hours. The resulting θ-iron carbide composite is labeled CX4-10.

[0127] Example 5

[0128] S0: 0.035 mol manganese bromide and 0.02 mol potassium gluconate were dissolved in 50 ml of water to prepare an impregnation solution; 8.0 g of nano-iron oxide particles with an average grain diameter of 20 nm were taken, the impregnation solution and the nano-iron oxide particles were mixed, and impregnation treatment was performed by a slurry impregnation method. The impregnation ratio (molar ratio) was Fe:Br:K=100:7.0:2.0, the impregnation temperature was 37°C, and the impregnation time was 2 h; the solid material after impregnation was dried at 25°C for 6 h to obtain a precursor.

[0129] S1: The precursor prepared in step S0 was kept in H2 at a flow rate of 12000 mL / h / g for 2 h at 430° C. and a pressure of 2.0 atm to perform reduction and surface purification treatment to obtain an intermediate product.

[0130] S2: The intermediate product is cooled to 350°C and exposed to a mixed gas at this temperature to prepare a precarbide. The system pressure is 2.0 atm, the mixed gas flow rate is 10,000 mL / h / g, and the treatment time is 6 hours. The mixed gas is a mixture of H2 and CO with a molar ratio of H2 to CO of 30:1. After the treatment, a θ-iron carbide composite is obtained, labeled CX5.

[0131] Comparative Example 1

[0132] This example uses substantially the same raw materials and process as Example 1 to prepare a θ-iron carbide composite, with the only difference being that in step S21, the impregnation ratio is Fe:Br:K=100:50:2. The resulting θ-iron carbide composite is labeled DX1.

[0133] Comparative Example 2

[0134] This example uses essentially the same raw materials and process as Example 1 to prepare a θ-iron carbide composite. The only difference is that in step S21, when preparing the impregnation solution, only potassium nitrate is added, not manganese bromide. The resulting θ-iron carbide composite is labeled D2.

[0135] Comparative Example 3

[0136] This example used essentially the same raw materials and process as Example 1 to prepare a θ-iron carbide composite. The only difference was that in step S21, an equal amount of manganese chloride was used instead of manganese bromide to prepare an impregnation solution, which was then used to impregnate the nano-iron particles. The resulting θ-iron carbide composite was labeled DX3.

[0137] Comparative Example 4

[0138] The same raw materials and steps as those in steps S1 to S2 of Example 1 were used, but the impregnation step S21 was omitted to obtain θ-iron carbide, which was labeled D4.

[0139] Comparative Example 5

[0140] This example uses substantially the same raw materials and processes as Example 1 to prepare a θ-iron carbide composite, with the only difference being that in step S2, the temperature is lowered to 270° C. The resulting θ-iron carbide composite is labeled DX5.

[0141] The θ-iron carbide composites and θ-iron carbide prepared in each example and comparative example were subjected to XRD, Mössbauer spectroscopy and ICP determination, wherein the content of θ-iron carbide is calculated based on 100 mol, and the relevant content refers to the number of moles. Specific results are shown in Table 1.

[0142] The catalytic performance of the θ-iron carbide composites and θ-iron carbide 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 = 283°C, P = 2.70 MPa, H2:CO = 2.1:1, total (H2 + CO) = 15000 mL / h / g- Fe The reaction was carried out and the reaction products were analyzed by gas chromatography. The reaction performance evaluation data after 24 h and 300 h of reaction are shown in Tables 2 and 3.

[0143] Table 1

[0144] Table 2

[0145] Table 3

[0146] Combining the results of the Examples, Comparative Examples, and Tables 1-3, it can be seen that compared to Example 1, the impregnation 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 40.6% is much higher than the CO2 selectivity of 3.0% in Example 1, and its carbon atom utilization (59.4%) and effective product selectivity (55.8%) are much lower than the carbon atom utilization (97.0%) and effective product selectivity (92.4%) in Example 1. Therefore, the composite of Example 1 can improve the overall efficiency of the reaction compared to the composite of Comparative Example 2, achieving optimized comprehensive reaction results.

[0147] Furthermore, Example 1-1 differs from Example 1 in that a different halide, ferrous bromide, is used. The results in Table 2 show that the reaction performance data of Example 1-1 and Example 1 are not much different, indicating that the improvement in performance of Example 1 over Comparative Example 2 is primarily due to the addition of bromide ions rather than manganese ions.

[0148] 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 are not much different from those of Examples 1-2, indicating that the introduction of iodide ions into iron carbide can also improve the overall performance of the reaction. 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 overall results of the reaction cannot be optimized.

[0149] Furthermore, while bromide ions were also introduced into the iron carbide of Comparative Example 1, the bromide ion content was relatively high, exceeding the range of a θ-iron carbide to halide ion molar ratio of 100:(0.1-40) specified in one embodiment of the present invention. The results in Table 2 indicate that the CO conversion rate in Comparative Example 1 was only 35.2%, significantly lower than the 82.7% CO conversion rate in Example 1. Furthermore, the carbon atom utilization and effective product selectivity in Comparative Example 1 were significantly lower than those in Example 1. Therefore, when the bromide ion content in the iron carbide composite exceeds a certain range, comprehensive optimization of the reaction results cannot be achieved.

[0150] Furthermore, the difference between Examples 1 to 1-7 mainly lies in the different contents of bromide ions. Combining the results in 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).

[0151] Furthermore, the difference between Examples 3 to 3-8 mainly lies in the different contents of other cations. Combining the results in Tables 2 and 3, the molar ratio of iron carbide (or iron element) to other cations in the prepared composite is preferably 100:(0.1-10).

[0152] Furthermore, the results in Table 3 indicate that the reactions catalyzed by the composites of various embodiments of the present invention can maintain stable CO conversion rates and product selectivity over a prolonged period. Thus, by including halide ions such as bromine or iodine in the θ-iron carbide composite and limiting the halide ion content to a specific range, using it as a catalyst for the Fischer-Tropsch synthesis reaction can improve the overall efficiency of the reaction and optimize the overall reaction results.

[0153] In summary, the θ-iron carbide composite containing halide ions such as bromine or iodine, prepared according to the present invention, when used as a catalyst for syngas conversion reactions under industrial conditions, can exhibit ultra-low CO2 selectivity, low CH4 selectivity, and extremely high carbon atom utilization efficiency and selectivity for effective products, while maintaining a high CO conversion rate (>60%). Further long-term experiments, as shown in Table 3 after 300 hours of reaction, show that the CO conversion rate, product selectivity, carbon atom utilization efficiency, and effective product selectivity of the θ-iron carbide composite according to the present invention remain stable after long-term continuous operation in a stirred tank, demonstrating good operational stability. Therefore, by using the θ-iron carbide composite according to the present invention as a catalyst for syngas conversion reactions, comprehensive optimization of reaction results can be achieved.

[0154] Unless otherwise defined, the terms used in the present invention have the same meanings as those commonly understood by those skilled in the art.

[0155] 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 may make various other substitutions, changes and improvements within the scope of the present invention. Therefore, the present invention is not limited to the above-mentioned embodiments, but is only limited by the claims.

Claims

1. A preparation method for a metallic O-iron-carbide composite, comprising the following steps:S0: providing a precursor, the precursor is nanoiron and / or a nano iron compound or nanoiron and / or a nano iron compound comprising bromide ions and / or iodide ions; and the nano iron compound is capable of preparing nanoiron by a reduction reaction;S1: performing reduction and surface purification treatment on the precursor at 300-500 °C under the action of hydrogen to obtain an intermediate product; andS2: performing carbide preparation treatment on the intermediate product at 300-470 °C in a mixed gas atmosphere;wherein the mixed gas comprises hydrogen and carbon monoxide in a molar ratio of 5:1 to 110:1;a first impregnation treatment is performed on said nanoiron and / or nano iron compound by an impregnation solution to obtain said nanoiron and / or nano iron compound comprising bromide ions and / or iodide ions; when the precursor is said nanoiron and / or nano iron compound, a second impregnation treatment is performed on the product in step S2 by the impregnation solution.

2. The preparation method according to claim 1, wherein the impregnation solution comprises bromide ions and / or iodide ions; and / orthe nano iron compound comprises one or more of nano iron oxide, nanomagnetite, nano goethite, and nano iron hydrous oxide; and / orthe nanoiron or the nano iron compound has an average crystal grain diameter of 6 nm to 35 nm.

3. The preparation method according to claim 1 or 2, wherein starting materials for preparing the impregnation solution comprise an impregnation compound, and the impregnation compound comprises a water-soluble bromide and / or iodide; further, the impregnation compound comprises one or more of a bromide and an iodide containing manganese, molybdenum, cobalt, a rare earth metal element, iron, and copper; and / orthe first impregnation treatment or the second impregnation treatment is performed by a slurry impregnation method, a saturated impregnation method, or a supersaturated impregnation method.

4. The preparation method according to claim 3, wherein the impregnation compound further comprises an additional compound selected from one or more of salts of copper, molybdenum, an alkali metal, manganese, a rare earth metal, an alkaline earth metal, and cobalt.

5. The preparation method according to any one of claims 1 to 4, wherein the treatment in step S1 is performed under a pressure of 0.13-9.5 atm for 1.2-26 h, and the gas flow rate of hydrogen is 600-21000 mL / h / g; and / orthe treatment in step S2 is performed under a pressure of 0-21 atm for 3-72 h, and the gas flow rate of the mixed gas is 500-31000 mL / h / g.

6. A 0-iron-carbide composite prepared by the preparation method according to any one of claims 1 to 5.

7. A 0-iron-carbide composite, comprising 0-iron-carbide and a halogen element, the 0-iron-carbide and the halogen element are in a molar ratio of 100:(0.1-40); the halogen element is a bromine element and / or an iodine element; and the number of moles of the 0-iron-carbide is based on the number of moles of an iron element contained therein.

8. The 0-iron-carbide composite according to claim 7, wherein the 0-iron-carbide and the halogen element are in a molar ratio of 100:(0.35-32); and / orthe composite has an average crystal grain diameter of 7-42 nm; and / orthe halogen element is present in the form of a halide ion, the 0-iron-carbide composite comprises a halide cation, the halide cation is capable of maintaining charge balance with the halide ion, and the halide cation comprises one or more of a first metal ion and a complex cation; and / orthe 0-iron-carbide composite comprises an additional cation, and the 0-iron-carbide and the additional cation are in a molar ratio of 100:(0.1-22), and further 100:(0.1-18);the additional cation is selected from one or more of a molybdenum ion, a rare earth ion, a chromium ion, an alkali metal ion, an alkaline earth metal ion, a cobalt ion, a manganese ion, and a copper ion.

9. The 0-iron-carbide composite according to claim 8, wherein the first metal ion comprises one or more of an iron ion, a manganese ion, a copper ion, a cobalt ion, a molybdenum ion, a lanthanum ion, a cerium ion, and a neodymium ion; the complex cation comprises one or more of a hexaammine manganese ion, a hexaammine iron ion, and a hexaammine copper ion.

10. A catalyst, comprising the 0-iron-carbide composite according to any one of claims 6 to 9.

11. Use of the 0-iron-carbide composite according to any one of claims 6 to 9 or the catalyst according to claim 10 in a syngas conversion reaction.

12. Use of the 0-iron-carbide composite according to any one of claims 6 to 9 or the catalyst according to claim 10 in a reaction for the synthesis of C and H fuels and / or chemicals on the basis of the Fischer-Tropsch synthesis principle.

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

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