Fe-based catalyst and its preparation method and application

Abstract

The present invention relates to the field of catalysts and discloses an Fe-based catalyst and its preparation method and application. The method comprises the following steps: (1) providing a mixed solution containing an Fe salt, a Mn salt and a carbon-containing compound; (2) mixing the mixed solution with supercritical water for reaction; and (3) heat-treating the product obtained by the reaction. A simple and efficient supercritical fluid deposition technology is used to adjust the temperature and pressure so that the Fe and Mn precursors in the supercritical solution instantly reach an oversaturated state, forming a large number of crystal nuclei, and further growing C-FeMnO with adjustable particle size and morphology. x The preparation method is simple, low-cost, and easy to industrially apply. The prepared Fe-based catalyst has high activity and olefin selectivity.

Description

Technical Field

[0001] The present invention relates to the field of catalysts, and in particular to an Fe-based catalyst and a preparation method and application thereof. Background Art

[0002] Reacting CO2 with H2 from renewable energy to produce chemicals is not only an effective way to control greenhouse gases but also an effective way to replace fossil fuels.

[0003] CO2 hydrogenation to hydrocarbons is one of the most important pathways for CO2 catalytic conversion. From a technological perspective, its research and development holds strategic importance. Optimizing the CO2 conversion reaction process and improving the selectivity of target products are key challenges in this field. The design of novel catalytic materials and catalysts, along with the development of catalytic systems based on novel research strategies, are key to achieving efficient conversion.

[0004] CN106031871B discloses an Fe-based catalyst for producing light olefins by CO2 hydrogenation and its preparation method. The main active component is Fe3O4, which can effectively produce light olefins (C2-C4=), but the methane selectivity is high and the selectivity for higher olefins is unknown. CN108262055B discloses a composite catalyst for producing light olefins by CO2 hydrogenation in one step with high selectivity and its preparation method. The catalyst contains nano-oxides and hierarchical pore zeolite molecular sieves, and has good selectivity, but the catalyst composition is complex, the overall conversion efficiency is low, and the deactivation rate is fast.

[0005] Therefore, in response to the needs of industrial development, there is an urgent need to develop a CO2 hydrogenation catalyst with simple preparation method, low cost, easy industrial application, high activity and olefin selectivity. Summary of the Invention

[0006] The purpose of the present invention is to overcome the problems of the existing technology of CO2 hydrogenation to prepare light olefins reaction catalyst, such as complex preparation process, poor high olefin selectivity and poor stability, and to provide an Fe-based catalyst and its preparation method and application.

[0007] In order to achieve the above object, the present invention provides a method for preparing an Fe-based catalyst, which comprises the following steps:

[0008] (1) providing a mixed solution containing an Fe salt, a Mn salt, and a carbon-containing compound;

[0009] (2) mixing the mixed solution with supercritical water to react;

[0010] (3) The product obtained by the reaction is subjected to heat treatment.

[0011] The second aspect of the present invention provides an Fe-based catalyst prepared by the first aspect.

[0012] The third aspect of the present invention provides use of the Fe-based catalyst described in the second aspect in the reaction of hydrogenating carbon dioxide to produce olefins.

[0013] Through the above technical solution, the beneficial technical effects achieved by the present invention are as follows:

[0014] (1) The present invention adopts a simple and efficient supercritical fluid deposition technology. By adjusting the temperature and pressure, the Fe and Mn precursors are instantly supersaturated in the supercritical solution, forming a large number of crystal nuclei, and further growing C-FeMnO with adjustable particle size and morphology. x .

[0015] (2) The active components formed by the supercritical fluid deposition technology of the present invention have a fast nucleation speed, uniform dispersion, high nucleation rate and low energy consumption.

[0016] (3) The Fe-based catalyst of the present invention is low-cost and has a simple catalyst regeneration process. Compared with precious metal catalysts, it is a most competitive non-precious metal catalyst in the market and can achieve a higher CO2 conversion rate and olefin selectivity in the CO2 preparation of light olefins reaction. DETAILED DESCRIPTION

[0017] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0018] A first aspect of the present invention provides a method for preparing an Fe-based catalyst, the method comprising the following steps:

[0019] (1) providing a mixed solution containing an Fe salt, a Mn salt, and a carbon-containing compound;

[0020] (2) mixing the mixed solution with supercritical water to react;

[0021] (3) The product obtained by the reaction is subjected to heat treatment.

[0022] According to the present invention, supercritical water has strong reactivity and wide solubility, which is conducive to accelerating mass transfer and improving reaction rate. In a supercritical water environment, the solubility of metal oxides is low, so the nucleation rate is high, which is conducive to the synthesis of nanoparticles. By adjusting the temperature and pressure, the Fe and Mn precursors are instantly supersaturated in the supercritical solution, which is conducive to the formation of a large number of crystal nuclei. Furthermore, the C-FeMnO prepared by this method xThe particle size and morphology are adjustable.

[0023] According to the present invention, the Mn element is introduced and the Fe and Mn are coordinated. Compared with the conventional iron-based catalysts in the prior art, the catalyst has the characteristics of uniform and small size and high reaction activity, which is conducive to improving the reaction activity.

[0024] According to a preferred embodiment of the present invention, the molar ratio of Fe salt to Mn salt is 8:1-12:1. x The Fe and Mn contents in the mixture are appropriate, which is beneficial to improving the CO2 conversion rate and olefin selectivity.

[0025] According to a preferred embodiment of the present invention, the mixed liquid further contains a solvent. The type of the solvent is not specifically limited, as long as it can dissolve and disperse the Fe salt, Mn salt and carbon-containing compound. Preferably, the solvent is water.

[0026] According to a preferred embodiment of the present invention, the total concentration of Fe salt and Mn salt in the mixed solution is 0.1-3 mol / L, preferably 1-2 mol / L. Under the above preferred conditions, the catalyst performance is improved.

[0027] In the present invention, the selection range for the specific types of the Fe salt and the Mn salt is relatively wide, and they can be independently selected from any soluble salt of a metal. Preferably, the soluble salt is an inorganic salt and / or an organic substance.

[0028] According to a preferred embodiment of the present invention, the inorganic salt is selected from one or more of chlorides, nitrates, acetates and sulfates, preferably metal chlorides; and the organic matter is a metal alkoxide.

[0029] According to a preferred embodiment of the present invention, the mass ratio of the total amount of the Fe salt and the Mn salt to the carbon-containing compound is 1-2:1, preferably 1.2-1.5:1. By preferably adjusting the mass ratio of the total amount of the Fe salt and the Mn salt to the carbon-containing compound, it helps to enhance the active sites of the catalyst.

[0030] In the present invention, the carbon-containing compound has a wide range of choices, as long as it can provide a carbon source. Preferably, the carbon-containing compound is selected from at least one of sucrose, sodium polyacryloyl, sodium formate, sodium acetate, sodium oxalate, sodium citrate, sodium succinate, starch, glucose, maltose, cellulose, citric acid, maleic acid, fumaric acid, succinic acid, tartaric acid, malic acid, gluconic acid, terephthalic acid, ethylenediaminetetraacetic acid, dipicolinic acid, and trimesic acid, and more preferably at least one of sucrose, sodium polyacrylate, sodium citrate, succinic acid, starch, and gluconic acid.

[0031] According to a preferred embodiment of the present invention, the mass of the supercritical water is greater than the mass of the mixed liquid. Further preferably, the mass ratio of the mixed liquid to the supercritical water is 1:1.2-2, more preferably 1:1.6-2. The above preferred conditions help the Fe and Mn precursors in the mixed liquid to quickly reach a supersaturated state, further facilitating the formation of crystal nuclei.

[0032] According to a preferred embodiment of the present invention, the reaction in step (2) is a supercritical reaction, which is carried out rapidly under high temperature and high pressure conditions. Preferably, the reaction conditions include: reaction temperature of 400-650°C, reaction pressure of 23-40MPa; reaction time of 30-600s; more preferably, the reaction conditions in step (2) include: reaction temperature of 400-500°C, reaction pressure of 23-35MPa; reaction time of 50-100s.

[0033] In the present invention, there is no particular limitation on the specific manner of the mixing reaction of the mixed solution and supercritical water in step (2), as long as the above-mentioned reaction can be achieved.

[0034] According to a preferred embodiment of the present invention, the reaction of mixing the mixed solution with supercritical water in step (2) comprises:

[0035] The mixed liquid and heated water are respectively fed into reactors for reaction.

[0036] In the present invention, the mixed reaction of the mixed solution and supercritical water in step (2) can be carried out in any conventional reactor as long as the above reaction can be achieved. Preferably, the reactor is a tubular split flow reactor. When a tubular split flow reactor is used, the flow rates of the mixed solution and water can be further controlled, which helps to control the reaction rate and the amount of material input.

[0037] According to a preferred embodiment of the present invention, the step of mixing and reacting supercritical water and a mixed liquid comprises: using a pump to pump the mixed liquid into a reactor; another pump pumps water into the reactor, passing through a heater in the middle to heat it to a supercritical state.

[0038] Preferably, the flow rate of the mixed liquid is 5-20 ml / min, and the flow rate of the heated water is 15-35 ml / min.

[0039] According to a preferred embodiment of the present invention, in step (2), the water is heated to 400-650°C, preferably 400-500°C, and then fed into the reactor; preferably, the heating device is a three-stage furnace heating, and the internal pressure can be 23-40 MPa.

[0040] According to a preferred embodiment of the present invention, the method further comprises cooling and / or filtering the reaction product obtained in step (2). Specifically, the fluid after the reaction is passed through a cooling system and a filtering system.

[0041] According to a preferred embodiment of the present invention, the method further comprises washing and drying the cooled sample to obtain catalyst powder. In the present invention, the washing and drying method is not specifically limited and can be performed using any conventional method and conditions.

[0042] According to the present invention, the heat treatment can be carried out using conventional heat treatment methods and conditions. Preferably, the heat treatment conditions include: in an inert atmosphere, a temperature of 300-500°C, and a time of 1-5h; preferably, a temperature of 350-450°C, and a time of 1-3h.

[0043] According to a preferred embodiment of the present invention, the inert atmosphere is a nitrogen atmosphere and / or an argon atmosphere.

[0044] According to a preferred embodiment of the present invention, providing the mixed solution in step (1) comprises: dissolving Fe salt and Mn salt in water to obtain a metal salt solution, and then adding a carbon-containing compound to obtain the mixed solution.

[0045] According to a preferred embodiment of the present invention, the method further comprises introducing an oxidant into the mixed solution. Specifically, the oxidant may be introduced into the metal salt solution and then the carbon-containing compound is added, or the oxidant may be introduced after the mixed solution is obtained; preferably, the oxidant is introduced after the mixed solution is obtained.

[0046] According to a preferred embodiment of the present invention, the oxidant is H2O2, and the oxidant is preferably provided in the form of a solution. By introducing the oxidant, the oxidizing property of supercritical water can be improved.

[0047] According to a preferred embodiment of the present invention, based on the total mass of the mixed solution, the amount of the oxidant is 0.1-1% by mass, preferably 0.15-0.25% by mass.

[0048] A second aspect of the present invention provides an Fe-based catalyst prepared by the first aspect. The Fe-based catalyst has low preparation cost and a simple catalyst regeneration process. Compared with precious metal catalysts, it can achieve higher CO2 conversion rate and olefin selectivity in the CO2 to light olefin reaction, and has good market competitiveness as a non-precious metal catalyst.

[0049] The third aspect of the present invention provides the use of the Fe-based catalyst described in the second aspect in the reaction of hydrogenating carbon dioxide to produce olefins. Preferably, the conditions of the reaction of hydrogenating carbon dioxide to produce olefins include: a reaction pressure of 0.1 MPa-6 MPa, a reaction temperature of 200°C-400°C, a volume space velocity of 1000 h -1 -50000h -1 , the H2 / CO2 molar ratio is 1-6; further preferably, the reaction pressure is 1MPa-5MPa, the reaction temperature is 250℃-400℃, and the volume space velocity is 8000h -1 -20000h -1 , the H2 / CO2 molar ratio is 4 to 6. Under the above preferred conditions, it is beneficial to improve the CO2 conversion rate and olefin selectivity.

[0050] The present invention will be described in detail below through examples.

[0051] The raw materials used in the following examples are all commercially available.

[0052] Example 1

[0053] (1) 97.2 g of FeCl3·6H2O and 5.02 g of MnCl2 were added to 200 mL of deionized water, followed by 80 g of sucrose. The mixture was stirred at 50°C for 1 h, followed by 3 g of 30% H2O2 solution, and continued stirring for 30 min. The mixed solution was pumped into the reactor at a flow rate of 10 ml / min. Simultaneously, another pump heated the deionized water to 480°C through a heater, causing it to reach a supercritical state. The deionized water was then pumped into the reactor at a flow rate of 20 ml / min. The reactor was a tubular split-flow reactor with a temperature of 480°C and a pressure of 30 MPa. The reaction was carried out for 60 s. After the reaction, the mixture was cooled and filtered. The cooled sample was washed and dried to obtain a catalyst powder. The catalyst powder was placed in a tubular furnace and calcined at 350°C in a N2 atmosphere for 3 h to obtain an Fe-based catalyst.

[0054] (2) The carbon dioxide hydrogenation reaction to produce olefins was carried out in a stainless steel reactor with an inner diameter of 8 mm. The reaction conditions were as follows: 3.0 MPa, 280°C, 10,000 h -1 , n(H2) / n(CO2)=4, the liquid product was collected in an ice-water bath, and the product composition was analyzed by gas chromatography. The evaluation results are shown in Table 1.

[0055] Comparative Example 1

[0056] (1) Add 97.2 g of FeCl₃·6H₂O and 5.02 g of MnCl₂ to 200 mL of deionized water and stir to dissolve. Weigh 150 g of sodium carbonate and add it to 400 mL of deionized water and stir to dissolve. Titrate the salt solution and sodium carbonate solution in parallel, controlling the pH to be around 9.0. Continue stirring for 1 h after the titration. Let it stand overnight, then pour off the supernatant and centrifuge. Wash four times with 60°C deionized water. After centrifugation, dry the solid at 60°C for 15 h and 120°C for 1 h.

[0057] (2) The activity of the prepared Fe-based catalyst was evaluated in a fixed-bed reactor. The reaction conditions were the same as in Example 1. The test results are shown in Table 1.

[0058] Example 2

[0059] (1) 108.12 g of FeCl3·6H2O and 6.29 g of MnCl2 were added to 400 mL of deionized water, followed by 90 g of sodium polyacryloyl acrylate. The mixture was stirred at 50°C for 1 h, followed by 5 g of 30% H2O2 solution, and continued stirring for 30 min. The mixed solution was pumped into the reactor at a flow rate of 12 ml / min. Simultaneously, another pump heated the deionized water to 400°C through a heater, bringing it to a supercritical state. The mixture was then pumped into the reactor at a flow rate of 23 ml / min. The reactor was a tubular split-flow reactor with a temperature of 400°C and a pressure of 25 MPa. The reaction was carried out for 70 s. After the reaction, the mixture was cooled and filtered. The cooled sample was washed and dried to obtain a catalyst powder. The catalyst powder was placed in a tubular furnace and calcined at 380°C in a N2 atmosphere for 2 h to obtain an Fe-based catalyst.

[0060] (2) The carbon dioxide hydrogenation reaction to produce olefins was carried out in a stainless steel reactor with an inner diameter of 8 mm. The reaction conditions were as follows: 5.0 MPa, 200 °C, 8000 h -1 , n(H2) / n(CO2)=6, the liquid product was collected in an ice-water bath, and the product composition was analyzed by gas chromatography. The evaluation results are shown in Table 1.

[0061] Example 3

[0062] (1) 50.34 g of FeCl3·6H2O and 2.33 g of MnCl2 were added to 100 mL of deionized water, followed by 40 g of sodium citrate. The mixture was stirred at 50°C for 1 h, followed by 1 g of 30% H2O2 solution, and continued stirring for 30 min. The mixed solution was pumped into the reactor at a flow rate of 6 ml / min. Simultaneously, another pump heated the deionized water to 500°C through a heater, bringing it to a supercritical state. The deionized water was then pumped into the reactor at a flow rate of 10 ml / min. The reactor was a tubular split-flow reactor with a temperature of 500°C and a pressure of 24 MPa. The reaction was carried out for 100 s. After the reaction, the mixture was cooled and filtered. The cooled sample was washed and dried to obtain a catalyst powder. The catalyst powder was placed in a tubular furnace and calcined at 400°C in a N2 atmosphere for 2 h to obtain an Fe-based catalyst.

[0063] (2) The carbon dioxide hydrogenation reaction to produce olefins was carried out in a stainless steel reactor with an inner diameter of 8 mm. The reaction conditions were as follows: 5.0 MPa, 340°C, 15000 h -1 , n(H2) / n(CO2)=4, the liquid product was collected in an ice-water bath, and the product composition was analyzed by gas chromatography. The evaluation results are shown in Table 1.

[0064] Example 4

[0065] (1) 74.21 g of FeCl3·6H2O and 3.15 g of MnCl2 were added to 150 mL of deionized water, and 55 g of succinic acid was added. The mixture was stirred at 50°C for 1 h, and then 2 g of 30% H2O2 solution was added and stirred for 30 min. The mixed solution was pumped into the reactor at a flow rate of 18 ml / min. At the same time, another pump heated the deionized water to 420°C through a heater, causing the deionized water to reach a supercritical state, and then pumped into the reactor at a flow rate of 29 ml / min. The reactor was a tubular split-flow reactor with a temperature of 420°C and a pressure of 30 MPa. The reaction was carried out for 70 s. After the reaction was completed, the sample was cooled and filtered. The cooled sample was washed and dried to obtain a catalyst powder. The catalyst powder was placed in a tubular furnace and calcined at 420°C in a N2 atmosphere for 1.5 h to obtain an Fe-based catalyst.

[0066] (2) The carbon dioxide hydrogenation reaction to produce olefins was carried out in a stainless steel reactor with an inner diameter of 8 mm. The reaction conditions were as follows: 1.0 MPa, 400 °C, 10,000 h -1 , n(H2) / n(CO2)=5, the liquid product was collected in an ice-water bath, and the product composition was analyzed by gas chromatography. The evaluation results are shown in Table 1.

[0067] Example 5

[0068] (1) 35.67 g of FeCl3·6H2O and 1.39 g of MnCl2 were added to 80 mL of deionized water, followed by 20 g of starch and 10 g of gluconic acid. The mixture was stirred at 50°C for 1 h, followed by 1 g of a 30% H2O2 solution and continued stirring for 30 min. The mixed solution was pumped into the reactor at a flow rate of 8 ml / min. Simultaneously, another pump passed the deionized water through a heater, heated it to 450°C, and supercritically pumped it into the reactor at a flow rate of 18 ml / min. The reactor was a tubular split-flow reactor with a temperature of 450°C and a pressure of 35 MPa. The reaction was carried out for 100 s. After the reaction, the mixture was cooled and filtered. The cooled sample was washed and dried to obtain a catalyst powder. The catalyst powder was placed in a tubular furnace and calcined at 360°C for 3 h in a N2 atmosphere to obtain an Fe-based catalyst.

[0069] (2) The carbon dioxide hydrogenation reaction to produce olefins was carried out in a stainless steel reactor with an inner diameter of 8 mm. The reaction conditions were as follows: 4.0 MPa, 250°C, 20,000 h -1 , n(H2) / n(CO2)=6, the liquid product was collected in an ice-water bath, and the product composition was analyzed by gas chromatography. The evaluation results are shown in Table 1.

[0070] Example 6

[0071] The method of Example 1 was followed, except that no H2O2 solution was added.

[0072] Table 1

[0073]

[0074] It can be seen from the data in Table 1 that the Fe-based catalyst obtained by the preparation method provided in the present invention has excellent catalytic performance, high reaction activity, high CO2 conversion rate, and high selectivity for olefins.

[0075] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A method for preparing an Fe-based catalyst for improving the selectivity of C2-C16 olefins in a carbon dioxide hydrogenation reaction to produce olefins, the method comprising the following steps: (1) providing a mixture of an Fe salt, a Mn salt, and a carbon-containing compound; the molar ratio of the Fe salt to the Mn salt, calculated as elements, is 8:1-12:1; and the mass ratio of the total amount of the Fe salt and the Mn salt to the carbon-containing compound is 1-2:1; (2) mixing the mixed solution with supercritical water to react; (3) The product obtained by the reaction is subjected to heat treatment.

2. The method according to claim 1, wherein In the mixed solution, the total concentration of Fe salt and Mn salt is 0.1-3 mol / L.

3. The method according to claim 1, wherein The Fe salt and the Mn salt are each independently selected from soluble salts of metals, and the soluble salts are selected from inorganic salts and / or organic substances.

4. The method according to claim 3, wherein: The inorganic salt is selected from one or more of chloride, nitrate, acetate and sulfate, and the organic matter is metal alkoxide.

5. The method according to claim 1, wherein The mass ratio of the total amount of the Fe salt and the Mn salt to the carbon-containing compound is 1.2-1.5:

1.

6. The method according to claim 1, wherein The carbon-containing compound is selected from at least one of sucrose, sodium polyacrylamide, sodium formate, sodium acetate, sodium oxalate, sodium citrate, sodium succinate, starch, glucose, maltose, cellulose, citric acid, maleic acid, fumaric acid, succinic acid, tartaric acid, malic acid, gluconic acid, terephthalic acid, ethylenediaminetetraacetic acid, dipicolinic acid and trimesic acid.

7. The method according to claim 6, wherein: The carbon-containing compound is selected from at least one of sucrose, sodium polyacrylate, sodium citrate, succinic acid, starch and gluconic acid.

8. The method according to claim 1, wherein The mass ratio of the mixed liquid to supercritical water is 1:1.2-2.

9. The method according to claim 8, wherein The mass ratio of the mixed liquid to supercritical water is 1:1.6-2.

10. The method according to claim 1, wherein The reaction conditions of step (2) include: reaction temperature of 400-650° C., reaction pressure of 23-40 MPa; and reaction time of 30-600 s.

11. The method according to claim 10, wherein: The reaction conditions of step (2) include: reaction temperature of 400-500°C, reaction pressure of 23-35 MPa; and reaction time of 50-100 s.

12. The method according to claim 1, wherein Step (2) mixing the mixed solution with supercritical water to react comprises: The mixed liquid and water heated to a supercritical state are respectively fed into reactors for reaction.

13. The method according to claim 12, wherein: The reactor is a tubular split flow reactor.

14. The method according to claim 12, wherein: The flow rate of the mixed liquid is 5-20 ml / min, and the flow rate of the water heated to a supercritical state is 15-35 ml / min.

15. The method according to claim 12, wherein: The water is heated to 400-650°C and then fed into the reactor.

16. The method according to claim 1, wherein The heat treatment conditions include: in an inert atmosphere, a temperature of 300-500° C., and a time of 1-5 hours.

17. The method according to claim 16, wherein: The heat treatment conditions include: temperature of 350-450° C. and time of 1-3 hours.

18. The method according to claim 1, wherein Providing the mixed solution in step (1) includes: dissolving Fe salt and Mn salt in water to obtain a metal salt solution, and then adding a carbon-containing compound to obtain the mixed solution.

19. The method according to claim 1, wherein The method further includes introducing an oxidant into the mixed liquor.

20. The method according to claim 19, wherein The oxidant is H2O2.

21. The method according to claim 19, wherein The oxidizing agent is provided in the form of a solution.

22. The method according to claim 19, wherein Based on the total mass of the mixed solution, the amount of the oxidant is 0.1-1% by mass.

23. An Fe-based catalyst obtained by the preparation method according to any one of claims 1 to 22.

24. Use of the Fe-based catalyst according to claim 23 in the reaction of preparing olefins by hydrogenation of carbon dioxide.

25. The use according to claim 24, wherein The conditions for the carbon dioxide hydrogenation reaction to prepare olefins include: reaction pressure of 0.1MPa-6MPa, reaction temperature of 200℃-400℃, volume space velocity of 1000h -1 -50000h -1 , the H2 / CO2 molar ratio is 1-6.

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