Iron-based bimetallic catalysts, methods of making and using the same

Abstract

The present application discloses an iron-based bimetallic catalyst, a preparation method and a use method thereof. The iron-based bimetallic catalyst comprises an active metal; and a composite carrier, the composite carrier comprises zirconium oxide, a zirconium-based organic framework and an iron-based organic framework, wherein the iron-based organic framework is coated on the zirconium-based organic framework, and iron and the active metal are loaded on the zirconium oxide. The preparation method comprises: mixing zirconium nitrate pentahydrate and a first organic ligand to react, obtaining a zirconium-based organic framework material; mixing the zirconium-based organic framework material, a second organic ligand and a metal salt to react, preparing a composite organic framework material; calcining the composite organic framework material, then soaking the calcined composite organic framework material in a auxiliary metal salt solution; and after drying treatment, obtaining the iron-based bimetallic catalyst. The iron-based bimetallic catalyst is used for catalytic reaction of carbon dioxide hydrogenation to generate low-carbon olefins.

Description

TECHNICAL FIELD

[0001] The present application relates to an iron-based bimetallic catalyst and a preparation method and use method thereof, in particular to an iron-based bimetallic catalyst for carbon dioxide hydrogenation reaction, a preparation method of the iron-based bimetallic catalyst and a use method of the iron-based bimetallic catalyst for carbon dioxide hydrogenation reaction. BACKGROUND

[0002] With the accelerated development of industrial process, the burning of a large amount of fossil fuels leads to a sharp increase in carbon dioxide (CO2) emissions, causing environmental problems such as greenhouse effect and ocean acidification. Carbon dioxide is currently considered to be the main anthropogenic greenhouse gas, so carbon is often used as a proxy for greenhouse gases in the target of net zero emissions or net zero emissions determined by each country. The conversion of carbon dioxide into useful chemicals such as olefins, aromatics and methanol through catalytic hydrogenation has been considered as a frontier direction to solve these problems. This way not only effectively reduces the emission of carbon dioxide, but also provides new economic value for carbon dioxide. Among them, low-carbon olefins (C2 ＝ -C4 ＝ ) are particularly attractive due to their important role in the synthesis of plastic, polymer and other chemical products.

[0003] Due to the limitations of single active metals such as iron (Fe) on CO2 hydrogenation activity, the CO2 conversion rate is not ideal. Similar to Fe, active metals such as cobalt (Co) and nickel (Ni) are often used for CO2 hydrogenation because of their activity on CO2 hydrogenation. In recent years, in the research of Fe-based bimetallic catalysts, impregnation or coprecipitation method is mostly used in the preparation method, which has certain limitations in adjusting the interaction between Fe and the second active metal, metal distribution and composition control, etc. Therefore, it is of great significance to design a reasonable and easy-to-control Fe-based bimetallic catalyst to further improve its catalytic performance.

[0004] Therefore, it is necessary to provide an iron-based bimetallic catalyst and a preparation method and use method thereof, which can be used for synthesizing low-carbon olefins from carbon dioxide through hydrogenation reaction to solve the problems existing in the prior art. SUMMARY

[0005] The main purpose of the present application is to provide an iron-based bimetallic catalyst. The iron-based bimetallic catalyst embeds two different metal ions in its skeleton structure, thereby generating more catalytically active sites and adsorption sites, so that the structural adjustability can be further improved, and the physical and chemical properties are more superior. At the same time, the iron-based bimetallic catalyst is uniformly distributed on zirconia (ZrO2), and the surface morphology of the iron-based bimetallic catalyst is regular and uniform in size under TEM observation.

[0006] Another object of the present application is to provide a preparation method and a use method of the iron-based bimetallic catalyst. The preparation method of the iron-based bimetallic catalyst is simple, does not contain noble metals, is suitable for mass production, has low cost and is environmentally friendly. The iron-based bimetallic catalyst has high reaction activity and good stability in the reaction of catalytically preparing low-carbon olefins from carbon dioxide hydrogenation, and the carbon dioxide conversion rate can reach 44.6%, and the low-carbon olefin selectivity can reach 45%.

[0007] To achieve the above object, an embodiment of the present application provides an iron-based bimetallic catalyst, which comprises: an active metal; and a composite carrier, the composite carrier comprising zirconium oxide (ZrO2), a zirconium-based organic framework and an iron-based organic framework; wherein: the iron-based organic framework is coated on the zirconium-based organic framework, and iron of the iron-based organic framework and the active metal are loaded on the zirconium oxide.

[0008] In an embodiment of the present application, the zirconium-based organic framework comprises a first organic ligand part, and the first organic ligand part is selected from at least one of terephthalic acid, fumaric acid, trimesic acid and tetra-carboxyphenyl porphyrin.

[0009] In an embodiment of the present application, the iron-based organic framework comprises a second organic ligand part, and the second organic ligand part is selected from at least one of 2-amino terephthalic acid, fumaric acid and trimesic acid.

[0010] In an embodiment of the present application, the active metal is selected from at least one of cobalt (Co), nickel (Ni), manganese (Mn) and molybdenum (Mo).

[0011] In an embodiment of the present application, the molar ratio of iron to the active metal is 10:1 to 1:2.

[0012] Another embodiment of the present application provides a preparation method of an iron-based bimetallic catalyst, the preparation method comprising the following steps:

[0013] Step (S1): mixing zirconium nitrate pentahydrate and a first organic ligand in a first solvent to react, to obtain a zirconium-based organic framework material;

[0014] Step (S2): mixing the zirconium-based organic framework material, a second organic ligand and a metal salt in a second solvent, the metal salt comprising an iron salt and an active metal salt, to prepare a composite organic framework material;

[0015] Step (S3): calcining the composite organic framework material;

[0016] Step (S4): soaking the calcined composite organic framework material in a co-metal salt solution; and

[0017] Step (S5): drying the solid part of step (S4) to obtain the iron-based bimetallic catalyst as described above.

[0018] In an embodiment of the present application, the first organic ligand is selected from at least one of terephthalic acid, fumaric acid, trimesic acid, and tetra-carboxyphenyl porphyrin, and the second organic ligand is selected from at least one of 2-amino terephthalic acid, fumaric acid, and trimesic acid.

[0019] In an embodiment of the present application, in step (S1), the molar ratio of the zirconium nitrate pentahydrate and the first organic ligand is 1:1.

[0020] In an embodiment of the present application, in step (S1), the temperature for reaction is 80-120°C, and the time for reaction is 10-48 hours.

[0021] In an embodiment of the present application, in step (S2), the mass ratio of the zirconium-based organic framework material, the second organic ligand, and the metal salt is 2.1-3.3:0.8-1.2:2.7-3.5.

[0022] In an embodiment of the present application, in step (S2), the iron salt is at least one of ferric nitrate, ferric acetate, ferric oxalate, ferric chloride, and ferrous chloride; and the active metal salt is at least one of nickel nitrate, cobalt nitrate, manganese nitrate, and ammonium molybdate.

[0023] In an embodiment of the present application, in step (S2), the molar ratio of the iron salt and the active metal salt is 10:1-1:2.

[0024] In an embodiment of the present application, in step (S3), the temperature for calcination is 400-900°C, and the time for calcination is 1-10 hours.

[0025] In an embodiment of the present application, in step (S4), the co-metal salt solution is formed by dissolving a co-metal salt in deionized water, the co-metal salt is at least one of sodium nitrate, sodium carbonate, sodium bicarbonate, potassium nitrate, potassium carbonate, and potassium bicarbonate, the mass ratio of the co-metal salt and deionized water is (1.1-4.1):120, the temperature for soaking is 20-80°C, and the time for soaking is 2-6 hours.

[0026] In an embodiment of the present application, in step (S5), the temperature for drying is 80-120°C, and the time is 7-9 hours.

[0027] Yet another embodiment of the present application provides a method for using the iron-based bimetallic catalyst, which comprises using the above-mentioned iron-based bimetallic catalyst to perform a catalytic reaction of carbon dioxide hydrogenation in a fixed bed micro-reactor to generate low-carbon olefins; the catalytic reaction of carbon dioxide hydrogenation is performed under the following conditions:

[0028] The temperature is 200-500°C, the pressure is 3 MPa, the reaction raw material comprises hydrogen / carbon dioxide in a volume ratio of 2-4, and the space velocity is 2000-15000 milliliters per gram per hour.

[0029] The present application has the following beneficial effects:

[0030] (1) The present application first synthesizes a zirconium-based organic framework material, then grows an iron-based organic framework material inside to prepare a composite structure containing the zirconium-based organic framework material and the iron-based organic framework material, and finally prepares a hybrid structure of iron-based bimetallic oxide supported on ZrO2 through calcination. The iron-based bimetallic catalyst prepared by the method of the present application has the advantages of regular morphology, uniform size, and uniform distribution of iron-based bimetallic particles supported on ZrO2.

[0031] (2) The bimetallic catalyst used in the present application has a synergistic effect, the active metal can enhance CO2 adsorption, and at the same time improve the dispersion of the iron active metal, thereby improving the reaction activity and service life of the catalyst.

[0032] (3) The material structure of the iron-based bimetallic catalyst supported on ZrO2 designed in the present application has a CO2 conversion rate of up to 44.6% and a low-carbon olefin selectivity of up to 45% for the CO2 hydrogenation reaction. At the same time, the preparation method is simple, the preparation conditions are relatively easy to control, no noble metal is involved, and the catalyst has potential industrial application value. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 is a flowchart of a preparation method of an iron-based bimetallic catalyst according to an embodiment of the present application.

[0034] Figure 2 is an X-ray diffractometer (XRD) pattern of an iron-based bimetallic catalyst FeCo@ZrO2 prepared in Example 1 of the present application.

[0035] Figure 3 is a transmission electron microscope (TEM) pattern of an iron-based bimetallic catalyst FeCo@1.5ZrO2 prepared in Example 2 of the present application. DETAILED DESCRIPTION

[0036] To make the above and other objects, features, and advantages of the present invention more apparent and understandable, preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Furthermore, the singular forms “a,” “an,” and “described” used in this invention include plural references unless the context clearly specifies otherwise. Numerical ranges (e.g., 10% to 11% of A) include upper and lower limits unless specifically stated otherwise (i.e., 10% ≤ A ≤ 11%); if a numerical range does not define a lower limit (e.g., less than 0.2% of B, or B below 0.2%), it means that the lower limit may be 0 (i.e., 0% ≤ B ≤ 0.2%). The above terms are used to illustrate and understand the present invention, and not to limit the present invention.

[0037] In this invention, "room temperature" refers to 15 to 30°C, preferably 20 to 25°C.

[0038] In this invention, "atmospheric pressure" refers to 0.1 MPa.

[0039] Unless otherwise specified, the solvent used for impregnation or soaking in this invention is generally deionized water.

[0040] Unless otherwise specified, all reagents or solvents used in the embodiments of this invention are of analytical grade (AR).

[0041] Unless otherwise defined, all technical and scientific terms used in the context of this invention have the same meaning as those familiar to those skilled in the art. Furthermore, any methods and materials similar to or equivalent to those described herein may be applied to the methods of this invention.

[0042] An embodiment of the present invention provides an iron-based bimetallic catalyst, which mainly comprises an active metal and a composite support, wherein the composite support comprises zirconium oxide (ZrO2), a zirconium-based organic framework and an iron-based organic framework, wherein the iron-based organic framework coats the zirconium-based organic framework, and the iron in the iron-based organic framework and the active metal are both supported on the zirconium oxide.

[0043] In one embodiment, the zirconium-based organic framework includes a first organic ligand portion. The first organic ligand portion is derived from a first organic ligand, which may be at least one selected from terephthalic acid, fumaric acid, triterephthalic acid, and tetracarboxyphenylporphyrin. Preferably, the first organic ligand is terephthalic acid.

[0044] In one embodiment, the iron-based organic framework includes a second organic ligand portion derived from a second organic ligand, which may be at least one selected from 2-aminoterephthalic acid, fumaric acid, and triterephthalic acid. Preferably, the second organic ligand is 2-aminoterephthalic acid.

[0045] In an embodiment, the active metal can be at least one of cobalt (Co), nickel (Ni), manganese (Mn), and molybdenum (Mo), and the active metal can exist in the form of metal oxide. In an embodiment of the present application, the molar ratio of iron in the iron-based organic framework to the active metal is 10:1 to 1:2, which can be, for example, 10:1, 5:1, 2:1, 1:2, but is not limited thereto, and can also be any integer or non-integer value between 10:1 and 1:2. Preferably, the molar ratio of iron to the active metal is 10:1 or 5:1.

[0046] Another embodiment of the present application provides a method for preparing an iron-based bimetallic catalyst, which mainly comprises the following steps: (S1) mixing zirconium nitrate pentahydrate and a first organic ligand in a first solvent to react, to obtain a zirconium-based organic framework material; (S2) mixing the zirconium-based organic framework material, a second organic ligand, and a metal salt in a second solvent to prepare a composite organic framework material; (S3) calcining the composite organic framework material; (S4) soaking the calcined composite organic framework material in a co-metal salt solution; and (S5) drying the solid part of step (S4) to obtain the iron-based bimetallic catalyst as described above.

[0047] The implementation details and principles of each of the above steps will be described in detail below.

[0048] Please refer to Figure 1 The method for preparing an iron-based bimetallic catalyst according to an embodiment of the present application first comprises the following step: (S1) mixing zirconium nitrate pentahydrate and a first organic ligand in a first solvent to react, to obtain a zirconium-based organic framework material. In this step, the molar ratio of the zirconium nitrate pentahydrate to the first organic ligand can be 1:1, that is, equimolar. In an embodiment, the first solvent can be, for example, a mixed solvent of N,N-dimethylformamide (DMF) and formic acid in a volume ratio of 5:1, and the zirconium nitrate pentahydrate and the first organic ligand have a concentration of 0.1 mol / L in the first solvent. In an embodiment, the first organic ligand can be at least one of terephthalic acid, fumaric acid, trimesic acid, and tetra-carboxyphenyl porphyrin. Preferably, the first organic ligand is terephthalic acid, because the zirconium-based organic framework material (UiO-66) synthesized from terephthalic acid and zirconium nitrate pentahydrate has simple preparation conditions and stable chemical properties.

[0049] In an embodiment, the temperature for the reaction in this step is 80 to 120°C, and the reaction time is 10 to 48 hours.

[0050] In this step, after the reaction is completed, centrifugation, washing, drying, and the like can also be included.

[0051] Please continue to refer to Figure 1 The preparation method of the iron-based bimetallic catalyst of an embodiment of the present application is as follows: (S2) mixing the zirconium-based organic framework material, a second organic ligand, and a metal salt in a second solvent to react, to prepare a composite organic framework material. In this step, the metal salt comprises an iron salt and an active metal salt. In an embodiment, the molar ratio of the iron salt to the active metal salt is 10:1 to 1:2, which may, for example, be 10:1, 5:1, 2:1, 1:2, but is not limited thereto, and can also be any integer or non-integer value between 10:1 and 1:2. Preferably, the molar ratio of the iron salt to the active metal salt is 10:1 or 5:1. In an embodiment, the iron salt is at least one of ferric nitrate, ferric acetate, ferric oxalate, ferric chloride, and ferrous chloride, which may, for example, be ferric nitrate or ferric chloride. In an embodiment, the active metal salt is at least one of nickel nitrate, cobalt nitrate, manganese nitrate, and ammonium molybdate, which may, for example, be cobalt nitrate and ammonium molybdate.

[0052] In an embodiment, the second solvent may, for example, be DMF, and the zirconium-based organic framework material and the second organic ligand have a concentration of 0.1 mol / L in the second solvent. In addition, the concentration of the metal salt in the second solvent can also be 0.1 mol / L. The second organic ligand is at least one of 2-amino terephthalic acid, fumaric acid, and trimesic acid. Preferably, the second organic ligand is 2-amino terephthalic acid, because the composite organic framework material (NH2-MIL-88B) synthesized from 2-amino terephthalic acid and the metal salt has a uniform surface morphology and stable chemical properties.

[0053] In an embodiment, the mass ratio of the zirconium-based organic framework material, the second organic ligand, and the metal salt is 2.1-3.3:0.8-1.2:2.7-3.5, preferably 2.5-3.1:1.0:2.9-3.6, and more preferably 3.0:1.0:3.5. Under this ratio, the morphology and size of the composite organic framework material formed by internal growth can ensure that it can support and wrap the zirconium-based organic framework material, thereby forming a hybrid structure.

[0054] In this step, after mixing and reaction are completed, centrifugation, washing, drying, and the like can also be included to obtain the composite organic framework material.

[0055] In one embodiment, the temperature for the reaction is 80 to 120°C, and the reaction time is 10 to 48 hours. Preferably, the reaction time is 15 to 30 hours, because the heating temperature and time affect the morphology and size of the MOFs, so that the final NH2-MIL-88B@UiO-66 has regular morphology and uniform size.

[0056] Please continue to refer to Figure 1 The preparation method of the iron-based bimetallic catalyst of one embodiment of the present application is followed by (S3) calcining the composite organic framework material. In this step, the temperature for the calcination is 400 to 900°C, and the calcination time is 1 to 10 hours. Because the calcination temperature and time affect the morphology and particle size of the catalyst after calcination, it is preferred to calcine at 450 to 600°C for 3 to 8 hours, so that the final iron-based bimetallic catalyst loaded on ZrO2 has regular shape and uniform particle size.

[0057] Please continue to refer to Figure 1 The preparation method of the iron-based bimetallic catalyst of one embodiment of the present application is followed by (S4) soaking the calcined composite organic framework material in a co-metal salt solution. In this step, the co-metal salt solution is formed by dissolving a co-metal salt in deionized water. In one embodiment, the co-metal salt is at least one of sodium nitrate, sodium carbonate, sodium bicarbonate, potassium nitrate, potassium carbonate, and potassium bicarbonate, and the mass ratio of the co-metal salt to deionized water is (1.1-4.1):120; the soaking temperature is 20 to 80°C, and the soaking time is 2 to 6 hours.

[0058] Please continue to refer to Figure 1 The preparation method of the iron-based bimetallic catalyst of one embodiment of the present application is followed by (S5) drying the solid part of step (S4) to obtain the above-mentioned iron-based bimetallic catalyst. In one embodiment, the drying temperature is 80 to 120°C, and the time is 7 to 9 hours.

[0059] Another embodiment of the present application provides a method for using an iron-based bimetallic catalyst, which comprises using the above-mentioned iron-based bimetallic catalyst to perform a catalytic reaction of carbon dioxide hydrogenation in a fixed-bed microreactor to generate low-carbon olefins; the conditions of the catalytic reaction of carbon dioxide hydrogenation are as follows:

[0060] The temperature is 200 to 500°C, the pressure is 3 MPa, the reaction raw material comprises hydrogen / carbon dioxide in a volume ratio of 2 to 4, and the space velocity is 2000 to 15000 milliliters per gram per hour.

[0061] Other details and conditions regarding the use of the catalyst can be appropriately adjusted according to actual needs, except for the iron-based bimetallic catalyst of the present application.

[0062] In order to make the iron-based bimetallic catalyst and the preparation method thereof of the present application clearer, and meanwhile verify the effect of the iron-based bimetallic catalyst for catalytically preparing low-carbon olefins from carbon dioxide and hydrogen, the following experiments were carried out.

[0063] Example 1:

[0064] (1) Preparation of Zr-based MOFs: 1 g of Zr(NO3)4·5H2O, 0.4 g of H2BDC (terephthalic acid) and 15 mL of formic acid were uniformly mixed in 60 mL of N,N-dimethylformamide (DMF), and after ultrasonic dispersion for 1 h, they were transferred into a polytetrafluoroethylene-lined reaction kettle, and then placed into an oven at 120°C for heating for 20 h. After cooling to room temperature, they were washed with methanol and DMF three times respectively, and then centrifuged and collected, and then dried in an oven at 100°C overnight to collect white solid UiO-66.

[0065] (2) Preparation of composite MOFs: 3 g of UiO-66 and 1 g of NH2-BDC were uniformly mixed in 40 mL of DMF. 3.3 g of Fe(NO3)3·9H2O and 0.24 g of Co(NO3)2·6H2O were uniformly mixed in 80 mL of DMF. Then the two solutions were uniformly mixed under stirring. Finally, the mixed solution was transferred into a polytetrafluoroethylene-lined reaction kettle, and then placed into an oven at 100°C for heating for 20 h. After cooling to room temperature, they were washed with methanol and DMF three times respectively, and then centrifuged and collected, and then dried in an oven at 100°C for 12 h to collect the composite MOFs.

[0066] (3) Preparation of iron-based bimetallic catalyst supported on ZrO2: the composite MOFs were heated from room temperature to 500°C at a rate of 2°C / min in a muffle furnace under air atmosphere, and kept for 5 h. 0.1 g of potassium carbonate was dissolved in 10 g of deionized water to prepare a potassium carbonate aqueous solution, and the product obtained in the above muffle furnace was immersed in the above potassium carbonate aqueous solution in an equal volume, and the immersion was ultrasonic for 1 h at 60°C. Then, after heating and drying at 100°C, the catalyst was obtained and was recorded as FeCo@ZrO2.

[0067] Referring to Figure 2 , the X-ray diffractometer (XRD) pattern of FeCo@ZrO2 is presented. The XRD characterization can preliminarily detect the composition of the FeCo@ZrO2 catalyst. It can be seen that the composition in FeCo@ZrO2 is Fe2O3, CoFe2O4 and ZrO2.

[0068] Example 2:

[0069] With 2.5g UiO-66, and 2.8g Fe(N03)3*9H20 and 0.15g Co(N03)2*6H20 instead of 3g UiO-66, and 3.3g Fe(N03)3*9H20 and 0.24g Co(N03)2*6H20 in step (2) of Example 1, and the rest is the same as Example 1, the catalyst is recorded as FeCo@1.5Zr02.

[0070] Referring to Figure 3 The transmission electron microscopy (TEM) image of FeCo@1.5Zr02is shown. TEM characterization can observe the morphology structure and particle dispersion of FeCo@1.5Zr02catalyst. It can be seen that the FeCo@1.5Zr02catalyst is mainly based on a honeycomb-shaped uniform solid sphere Zr02, and the black Fe, Co formed metal oxide is uniformly dispersed on the Zr02.

[0071] Example 3:

[0072] With 2.5g FeCl3*9H20 instead of 3.3g Fe(N03)3*9H20 in step (2) of Example 1, and the rest is the same as Example 1, the catalyst is recorded as C-FeCo@Zr02.

[0073] Example 4:

[0074] With 1g (NH4)6Mo7O 24 4H20 instead of 0.24g Co(N03)2*6H20 in step (2) of Example 1, and the rest is the same as Example 1, the catalyst is recorded as FeMo@Zr02.

[0075] Example 5:

[0076] With 0.48g Co(N03)2*6H20 instead of 0.24g Co(N03)2*6H20 in step (2) of Example 1, and the rest is the same as Example 1, the catalyst is recorded as Fe2Co@Zr02.

[0077] Example 6:

[0078] With heating temperature of 80℃ and time of 24h instead of 100℃ and 20h in step (2) of Example 1, and the rest is the same as Example 1, the catalyst is recorded as 80-FeCo@Zr02.

[0079] Example 7:

[0080] With calcination temperature of 600℃ and time of 6h instead of 500℃ and 5h in step (3) of Example 1, and the rest is the same as Example 1, the catalyst is recorded as FeCo@Zr02-600.

[0081] Example 8:

[0082] Replace 0.1g of potassium carbonate in step (3) of Example 1 with 0.08g of sodium nitrate, and keep the rest the same as in Example 1 to obtain a catalyst denoted as FeCo@ZrO2-Na.

[0083] Comparative Example 1:

[0084] By replacing 3.3g Fe(NO3)3·9H2O and 0.24g Co(NO3)2·6H2O in Example 1 with 3.64g Fe(NO3)3·9H2O, and keeping the rest the same as in Example 1, a single iron-based catalyst without a second active metal can be obtained, denoted as Fe@ZrO2.

[0085] Comparative Example 2:

[0086] Weigh 3.3g of Fe(NO3)3·9H2O and 0.24g of Co(NO3)2·6H2O, add them to 80mL of DMF and mix thoroughly. Then, mix the two solutions thoroughly with stirring. Finally, transfer the mixture to a polytetrafluoroethylene-lined reactor and heat it in an oven at 100℃ for 20h. After cooling to room temperature, wash three times with methanol and DMF respectively, centrifuge and collect the product, then dry it in an oven at 100℃ for 12h to collect the bimetallic MOFs. The MOFs were then heated from room temperature to 500℃ at a rate of 2℃ / min in an air atmosphere in a muffle furnace and held for 5h. Dissolve 0.1g of potassium carbonate in 10g of deionized water to prepare a potassium carbonate aqueous solution. Impregnate an equal volume of the product obtained in the muffle furnace in the above potassium carbonate aqueous solution, and sonicate at 60℃ for 1h. Then, after heating and drying at 100℃, a ZrO2-free bimetallic catalyst, denoted as FeCo, is obtained.

[0087] Example 9:

[0088] The catalysts prepared in Examples 1-8 and Comparative Examples 1-2 were packed into a fixed-bed microreactor with an inner diameter of 8 mm. Before the reaction, the air was purged with N2, followed by in-situ reduction for 5 hours at a temperature of 400 °C, a pressure of 0.1 MPa, and an H2 flow rate of 20 mL / min. The reduced catalyst was then used to catalyze the hydrogenation reaction of the feed gas. The gaseous products of the reaction were analyzed online using gas chromatography and a thermal conductivity detector (TCD).

[0089] The composition of the feed gas and the catalytic reaction conditions are as follows:

[0090] Raw material gas composition: CO2: 23%, H2: 69%, N2: 8%.

[0091] Catalyst loading: 0.25g.

[0092] Reaction temperature: 250-350℃.

[0093] Reaction pressure: 3 MPa.

[0094] Reaction space velocity: 5000 mL / g / h.

[0095] The CO2 conversion and the selectivity to lower olefins were measured and calculated according to the following methods, and the results are shown in Table 1.

[0096] CO2 conversion: (1 - amount of CO2 contained in the product / amount of CO2 contained in the raw material gas) x 100%

[0097] Selectivity to lower olefins: (amount of CO2 converted to lower olefins / amount of CO2 converted) x 100%

[0098] Table 1:

[0099]

[0100]

[0101] The present application has been described by the above-mentioned related examples, however, the above-mentioned examples are only examples for implementing the present application. It must be pointed out that the disclosed examples do not limit the scope of the present application. On the contrary, modifications and equivalents included in the spirit and scope of the claims are included in the scope of the present application.

Claims

1. An iron-based bimetallic catalyst, characterized in that: The iron-based bimetallic catalyst is prepared by the following steps: Step (S1): Zirconium nitrate pentahydrate and a first organic ligand are mixed in a first solvent to carry out a reaction to obtain a zirconium-based organic framework material; Step (S2): The zirconium-based organic framework material, a second organic ligand, and a metal salt are mixed in a second solvent to carry out a reaction, wherein the metal salt comprises an iron salt and an active metal salt, to prepare a composite organic framework material. Step (S3): Calcination of the composite organic framework material; Step (S4): Immerse the calcined composite organic framework material in a metal salt solution; as well as Step (S5): The solid portion from step (S4) is dried to obtain the iron-based bimetallic catalyst; The active metal includes cobalt. The iron-based bimetallic catalyst uses honeycomb-shaped uniform solid spheres ZrO2 as a substrate, and the metal oxides formed by Fe and Co are uniformly dispersed on ZrO2 to form Fe2O3, CoFe2O4 and ZrO2.

2. The iron-based bimetallic catalyst as described in claim 1, characterized in that: The first organic ligand is selected from at least one of terephthalic acid, fumaric acid, triterpenoid, and tetracarboxyphenylporphyrin.

3. The iron-based bimetallic catalyst as described in claim 1, characterized in that: The second organic ligand is selected from at least one of 2-aminoterephthalic acid, fumaric acid, and triterephthalic acid.

4. The iron-based bimetallic catalyst as described in claim 1, characterized in that: The molar ratio of the iron salt to the active metal salt is 10:1 to 1:

2.

5. A method for preparing an iron-based bimetallic catalyst, characterized in that: The preparation method includes the following steps: Step (S1): Zirconium nitrate pentahydrate and a first organic ligand are mixed in a first solvent to carry out a reaction to obtain a zirconium-based organic framework material; Step (S2): The zirconium-based organic framework material, a second organic ligand, and a metal salt are mixed in a second solvent to carry out a reaction, wherein the metal salt comprises an iron salt and an active metal salt, to prepare a composite organic framework material. Step (S3): Calcination of the composite organic framework material; Step (S4): Immerse the calcined composite organic framework material in a metal salt solution; as well as Step (S5): The solid portion from step (S4) is dried to obtain the iron-based bimetallic catalyst as described in claim 1; The iron salt includes ferric nitrate, the active metal salt includes cobalt nitrate, the second solvent includes N,N-dimethylformamide, and the second organic ligand includes 2-aminoterephthalic acid. In step (S2), the mixing of the zirconium-based organic framework material, the second organic ligand, and the metal salt in a second solvent specifically includes: adding the zirconium-based organic framework material and 2-aminoterephthalic acid to N,N-dimethylformamide and mixing them evenly; adding Fe(NO3)3·9H2O and Co(NO3)2·6H2O to N,N-dimethylformamide and mixing them evenly; and then mixing the two solutions evenly under stirring.

6. The method for preparing the iron-based bimetallic catalyst as described in claim 5, characterized in that: The first organic ligand is selected from at least one of terephthalic acid, fumaric acid, triterpenoid, and tetracarboxyphenylporphyrin.

7. The method for preparing the iron-based bimetallic catalyst as described in claim 5, characterized in that: In step (S1), the molar ratio of zirconium nitrate pentahydrate to the first organic ligand is 1:

1.

8. The method for preparing the iron-based bimetallic catalyst as described in claim 5, characterized in that: In step (S1), the reaction is carried out at a temperature of 80 to 120°C for a time of 10 to 48 hours.

9. The method for preparing the iron-based bimetallic catalyst as described in claim 5, characterized in that: In step (S2), the mass ratio of the zirconium-based organic framework material, the second organic ligand, and the metal salt is 2.1-3.3:0.8-1.2:2.7-3.

5.

10. The method for preparing the iron-based bimetallic catalyst as described in claim 5, characterized in that: In step (S2), the molar ratio of the iron salt to the active metal salt is 10:1 to 1:

2.

11. The method for preparing the iron-based bimetallic catalyst as described in claim 5, characterized in that: In step (S3), the calcination temperature is 400 to 900°C and the calcination time is 1 to 10 hours.

12. The method for preparing the iron-based bimetallic catalyst as described in claim 5, characterized in that: In step (S4), the auxiliary metal salt solution is formed by dissolving an auxiliary metal salt in deionized water. The auxiliary metal salt is selected from at least one of sodium nitrate, sodium carbonate, sodium bicarbonate, potassium nitrate, potassium carbonate, and potassium bicarbonate. The mass ratio of the auxiliary metal salt to deionized water is (1.1-4.1):

120. The soaking temperature is 20 to 80°C, and the soaking time is 2 to 6 hours.

13. The method for preparing the iron-based bimetallic catalyst as described in claim 5, characterized in that: In step (S5), the drying process is carried out at a temperature of 80 to 120°C for 7 to 9 hours.

14. A method of using an iron-based bimetallic catalyst, characterized in that: The catalytic reaction of carbon dioxide hydrogenation is carried out in a fixed-bed microreactor using the iron-based bimetallic catalyst as described in claim 1 to produce low-carbon olefins; the conditions for the catalytic reaction of carbon dioxide hydrogenation are as follows: The temperature is 200 to 500°C, the pressure is 3 MPa, the reactants contain hydrogen / carbon dioxide in a volume ratio of 2 to 4, and the space velocity is 2000 to 15000 ml / g per hour.

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