Fe-mn bimetallic catalyst, preparation method and application thereof

Abstract

The application discloses a Fe-Mn bimetallic catalyst, a preparation method and application thereof. The Fe-Mn bimetallic catalyst according to the application comprises Fe3O4, Fe x C, MnCO3 and a catalytic aid, wherein the catalytic aid is SiO2 and / or Al2O3, the molar ratio of Fe elements:Mn elements:silicon elements and / or aluminum elements in the Fe-Mn bimetallic catalyst is 5:(1.2-4.5):(0.5-2.0), Fe x C represents a mixture of Fe5C2 and Fe7C3, the mass ratio of Fe3O4:Fe5C2:Fe7C3 is 8:(1.8-4.0):(1.8-3.8). The Fe-Mn bimetallic catalyst has significantly improved catalytic activity and olefin selectivity.

Description

Technical Field

[0001] This invention relates to catalysts for the selective hydrogenation of carbon dioxide, and more specifically, to an Fe-Mn bimetallic catalyst, its preparation method, and its applications. The catalyst of this invention exhibits significantly high activity and selectivity for olefin products, providing a new approach for the selective hydrogenation of carbon dioxide to produce high-value-added chemicals, and has promising prospects for industrial application. Background Technology

[0002] With global industrialization, the amount of carbon dioxide in the atmosphere is increasing. This increase leads to the greenhouse effect and a series of other problems. To reduce carbon dioxide emissions, one approach is to reduce emissions and achieve carbon neutrality; another is to utilize carbon dioxide and convert it into useful substances, turning waste into treasure. Several methods for converting carbon dioxide into useful substances have already been reported.

[0003] CN109675573A relates to a catalyst for the hydrogenation of carbon dioxide to produce higher-carbon α-olefins. The catalyst is a composite metal oxide catalyst containing Fe, an alkali metal, and other metals, wherein the molar ratio of Fe to other metals is 1:1 to 1:0.05, and the mass fraction of the alkali metal in the catalyst is 0.01% to 15%. The alkali metal includes one or more of Na, K, and Rb, and the other metals include one or more of Mn, Zn, Cu, and Co. This catalyst significantly improves catalytic activity, selectivity for higher-carbon α-olefins, and catalyst stability, providing a new approach for the efficient conversion of carbon dioxide into hydrogen and showing good prospects for industrial application.

[0004] CN112973702B describes a method for producing high-carbon olefins from a mixture of carbon dioxide and hydrogen. This invention utilizes a composite of ferrous oxalate, alkali metals, other metals, and carbon. The iron-to-carbon ratio is 0.7:10 to 6:10, and the molar ratio of iron to other metals is 10:0.01 to 10:5. The alkali metal in the catalyst comprises 1%-10% by mass; the alkali metal is one or more of Na, K, and Rb, and the other metals are one or more of Mn, Zn, Cu, and Co. This catalyst significantly improves catalyst activity and the selectivity of high-carbon olefin products, providing a new approach for the selective hydrogenation of carbon dioxide to produce high-value-added chemicals, and has good prospects for industrial application.

[0005] CN113976126A discloses a catalyst for the hydrogenation of carbon dioxide to methanol, its preparation method, and its application. The catalyst is a non-supported or supported spinel-phase catalyst with a composition that can be denoted as AB₂O₄, Cu / AB₂O₄, or Pd / AB₂O₄, where A is Zn / Mg / Co, B is Al / Ga / Cr / Fe / In, the Cu loading in Cu / AB₂O₄ is 0.001%–0.5%, and the Pd loading in Pd / AB₂O₄ is 0.1%–1%. The non-supported spinel-phase catalyst is prepared using a co-precipitation method. The spinel-phase catalyst is used as a support to increase the copper component via ion exchange, and the supported spinel catalyst is prepared by impregnation with palladium. The preparation method is simple and inexpensive. It has advantages such as high carbon dioxide conversion rate and methanol selectivity, and good stability. Summary of the Invention

[0006] The purpose of this invention is to provide a Fe-Mn bimetallic catalyst for carbon dioxide hydrogenation reaction, its preparation method, and its application.

[0007] According to a first aspect of the present invention, an Fe-Mn bimetallic catalyst for the selective hydrogenation reaction of carbon dioxide is provided, wherein,

[0008] The Fe-Mn bimetallic catalyst contains Fe3O4 and Fe. x C, MnCO3 and catalyst promoters, of which, Fe x C represents a mixture of Fe5C2 and Fe7C3, and the catalyst is SiO2 and / or Al2O3;

[0009] The molar ratio of Fe to Mn to silicon and / or aluminum in the Fe-Mn bimetallic catalyst is 5:(1.2-4.5):(0.5-2.0), preferably 5:(1.3-4.2):(0.6-1.8), and the mass ratio of Fe3O4 to Fe5C2 to Fe7C3 is 8:(1.8-4.0):(1.8-3.8), preferably 8:(2.1-3.8):(2.0-3.5).

[0010] Preferably, the Fe-Mn bimetallic catalyst is used to prepare olefins, and more preferably to prepare straight-chain or branched olefins having two or more carbon atoms.

[0011] Preferably, the Fe-Mn bimetallic catalyst is substantially free of sodium. It should be noted that the absence of sodium does not exclude the presence of sodium as an impurity.

[0012] According to a second aspect of the present invention, a method for preparing the catalyst according to the present invention is provided, comprising the following steps:

[0013] 1) Prepare an aqueous solution by mixing the precursor salts of iron and manganese, and then mix the aqueous solution with a grain dispersing agent, wherein the molar ratio of Fe to Mn is 5:(1-4);

[0014] 2) The solution obtained in step 1) is subjected to precipitation reaction with an aqueous solution of pH adjuster using a co-precipitation method, followed by aging, separation, washing and drying to obtain the precipitate;

[0015] 3) The precipitate obtained in step 2) is mixed with the catalyst precursor, and dried and calcined to obtain the catalyst precursor. The catalyst precursor is one or more selected from Si sol, Al sol, SiO2 powder, and Al2O3 powder. The molar ratio of Fe element to silicon element and / or aluminum element in the catalyst precursor is 5: (0.5-3).

[0016] 4) The catalyst precursor obtained in step 3) is placed in a tube furnace and subjected to high-temperature treatment with syngas at 250-450℃ to obtain the Fe-Mn bimetallic catalyst.

[0017] Preferably, the iron precursor salt is one or more selected from ferric chloride, ferric nitrate, ferric carbonate, ferric sulfate, and ferric ammonium citrate.

[0018] Preferably, the precursor salt of manganese is one or more selected from manganese nitrate, manganese acetate, manganese dichloride, and manganese sulfate.

[0019] Preferably, the grain dispersion aid is one or more selected from glycerol, ethylene glycol and acetic acid, and the volume ratio of the grain dispersion aid to the iron and manganese precursor salts to prepare an aqueous solution is 0.3 to 2:1.

[0020] Preferably, the pH adjuster is one or more selected from sodium carbonate, potassium carbonate, ammonia, sodium bicarbonate, urea, and sodium hydroxide.

[0021] Preferably, the aging process in step 2) is carried out at room temperature for 6 to 24 hours.

[0022] Preferably, the cleaning in step 2) involves first cleaning with deionized water and then cleaning with ethanol.

[0023] Preferably, the roasting temperature in step 3) is 350–450 degrees Celsius.

[0024] Preferably, the molar ratio of H2 to CO in the synthesis gas in step 4) is 1 to 2.

[0025] Preferably, the high-temperature treatment conditions in step 4) are: temperature 250–450°C; pressure 0.1–0.5 MPa, more preferably 0.2 MPa; and space velocity 1250–10000 h⁻¹. -15000h is preferred -1 The time is 4 to 24 hours, more preferably 12 to 24 hours.

[0026] According to a third aspect of the present invention, a method for preparing olefins by selective hydrogenation of carbon dioxide is provided, comprising the following steps:

[0027] In the presence of the Fe-Mn bimetallic catalyst according to the present invention, CO2 and H2 are reduced to obtain olefins.

[0028] Preferably, the molar ratio of H2 to CO2 is 3.

[0029] Preferably, the reaction is carried out in a fixed bed, and the reaction conditions are: temperature 260–340°C, pressure 0.1–2.0 MPa, and space velocity 2000–15000 h⁻¹. -1 .

[0030] Preferably, the CO2 conversion rate is 40% or more, more preferably 45% or more, and the olefin selectivity is 65 c-mol% or more, more preferably 70 c-mol% or more.

[0031] Preferably, the olefin is a straight-chain or branched olefin having two or more carbon atoms.

[0032] The Fe-Mn bimetallic catalyst described in this invention significantly improves the catalyst activity (significantly increasing carbon dioxide conversion rate) and the selectivity of olefin products, providing a new approach for the selective hydrogenation of carbon dioxide to produce high-value-added chemicals, and has good prospects for industrial application. Attached Figure Description

[0033] Figure 1 HAADF-STEM image of the Fe-Mn bimetallic catalyst prepared according to Example 1;

[0034] Figure 2 The image shows the XRD pattern of the Fe-Mn bimetallic catalyst prepared according to Example 1. Detailed Implementation

[0035] The present invention will be further described below with reference to specific embodiments. Those skilled in the art should understand that the following embodiments are only for illustrating the present invention and are not intended to limit the scope of the present invention.

[0036] Example 1

[0037] 1. Preparation of Fe-Mn bimetallic catalysts:

[0038] 1) Accurately weigh 40.4g Fe(NO3)3·9H2O (0.1mol) and 8.95g Mn(NO3)2 (0.05mol), add deionized water to make up to 150ml, dissolve completely and set aside. Then add glycerol, a crystal dispersant, and make up to 200ml.

[0039] 2) Prepare 200 ml of 2 mol / L ammonia solution for later use.

[0040] 3) Add 200 ml of deionized water to the four-necked flask and fix it in a water bath at 30°C and 300 rpm. Then, add the solutions prepared in steps 1) and 2) dropwise to the four-necked flask using a peristaltic pump, controlling the dropping rate to stabilize the pH of the mixed solution in the four-necked flask at 8 ± 0.5.

[0041] 4) After the solution has been added dropwise, continue stirring for 30 minutes, then let it stand overnight at room temperature for aging. Afterwards, separate the filtrate and slurry using a vacuum filtration pump, using 1000 ml of deionized water. Finally, wash with 40 ml of ethanol. Dry the washed precipitate in an oven at 110°C for 12 hours.

[0042] 5) The precursor obtained in step 4) is mixed with 20 wt% silica sol (the silica sol solution contains 0.02 mol of silica sol) and dried at 120 °C for 12 h; finally, the resulting solid is transferred to a muffle furnace and calcined at 450 °C for 4 h.

[0043] 6) The catalyst precursor obtained in step 5) was treated in syngas (H2 / CO = 1) for 12 h at 340 °C, 0.2 MPa, for 5000 h. -1 (V / V) yields the Fe-Mn bimetallic catalyst.

[0044] The HAADF-STEM and XRD patterns of the prepared Fe-Mn bimetallic catalyst are shown below. Figure 1 and Figure 2 As shown.

[0045] Figure 1 The image shows a HAADF-STEM / EDX image of the Fe-Mn bimetallic catalyst, which reveals the distribution of elements such as Fe, Mn, O, and Si within the catalyst.

[0046] Figure 2 The XRD pattern of the Fe-Mn bimetallic catalyst shows the diffraction peaks of the following phases: Fe3O4 (PDF 82-1533), MnCO3 (PDF 83-1763), Fe7C3 (PDF 89-7273), and Fe5C2 (PDF 89-8968).

[0047] In the prepared Fe-Mn bimetallic catalyst, the element content was measured by ICP-OES experiment, and the molar ratio of Fe, Mn and Si was calculated. The ratio of Fe:Mn:Si was 5:2.3:1.2. The mass ratio of Fe3O4, Fe7C3 and Fe5C2 was obtained by XRD fitting and was 8:2.8:3.5.

[0048] Example 2

[0049] 1. Preparation of Fe-Mn bimetallic catalysts:

[0050] 1) Accurately weigh 40.4g Fe(NO3)3·9H2O (0.1mol) and 13.96g Mn(NO3)2 (0.078mol), add deionized water to make up to 150ml, and after complete dissolution, continue to add glycerol and make up to 300ml.

[0051] 2) Prepare 200 ml of 2 mol / L ammonia solution for later use.

[0052] 3) Add 200 ml of deionized water to the four-necked flask, fix it in a water bath at 30°C, and stir at 300 rpm. Then, add the solutions prepared in steps 1) and 2) dropwise to the four-necked flask using a peristaltic pump, controlling the dropping rate to stabilize the pH of the mixed solution in the four-necked flask at 7.5 ± 0.5.

[0053] 4) After the solution has been added dropwise, continue stirring for 30 minutes, then let it stand overnight at room temperature for aging. Afterwards, separate the filtrate and slurry using a vacuum filtration pump, using 1000 ml of deionized water. Finally, wash with 40 ml of ethanol. Dry the washed precipitate in an oven at 110°C for 12 hours.

[0054] 5) The precursor obtained in step 4) was mixed with 15 wt% aluminum sol (the aluminum sol solution contained 0.01 mol of aluminum sol) and dried at 120 °C for 12 h; finally, the resulting solid was transferred to a muffle furnace and calcined at 450 °C for 4 h.

[0055] 6) The catalyst precursor obtained in step 5) was treated in syngas (H2 / CO = 2) for 12 h at 300 °C, 0.2 MPa, for 5000 h. -1 (V / V) yields the Fe-Mn bimetallic catalyst, where the molar ratio obtained by testing is: Fe∶Mn∶Al=5∶3.5∶1.1, and the mass ratio is Fe3O4∶Fe5C2∶Fe7C3=8∶2.1∶2.

[0056] Example 3

[0057] Except for the use of 0.1 mol of ferric chloride hexahydrate instead of Fe(NO3)3·9H2O in step 1) and the use of 0.02 mol of manganese acetate, the Fe-Mn bimetallic catalyst was prepared in the same manner as in Example 1, wherein the molar ratio was found to be Fe∶Mn∶Si=5∶1.3∶0.9 and the mass ratio was Fe3O4∶Fe5C2∶Fe7C3=8∶3.8∶2.1.

[0058] Example 4

[0059] Except for the use of 0.1 mol of ferric chloride hexahydrate instead of Fe(NO3)3·9H2O in step 1) and the use of 0.08 mol of manganese dichloride, the Fe-Mn bimetallic catalyst was prepared in the same manner as in Example 1, wherein the molar ratio was found to be Fe∶Mn∶Si=5∶4.2∶1.1 and the mass ratio was found to be Fe3O4∶Fe5C2∶Fe7C3=8∶2.5∶3.0.

[0060] Example 5

[0061] Except for the 0.04 mol of silica sol used in step 5), the Fe-Mn bimetallic catalyst was prepared in the same manner as in Example 1, wherein the molar ratio was found to be Fe∶Mn∶Si=5∶2.6∶1.8 and the mass ratio was Fe3O4∶Fe5C2∶Fe7C3=8∶3∶3.1.

[0062] Example 6

[0063] Except for the 0.01 mol silica sol used in step 5), the Fe-Mn bimetallic catalyst was prepared in the same manner as in Example 1, wherein the molar ratio was found to be Fe∶Mn∶Si=5∶2.3∶0.6 and the mass ratio was Fe3O4∶Fe5C2∶Fe7C3=8∶3.4∶2.9.

[0064] Comparative Example 1

[0065] Except for the use of 0.1 mol of ferric chloride hexahydrate instead of Fe(NO3)3·9H2O in step 1) and the use of 0.1 mol of manganese dichloride, the Fe-Mn bimetallic catalyst was prepared in the same manner as in Example 1, wherein the molar ratio was found to be Fe∶Mn∶Si=5∶5.1∶0.9 and the mass ratio was Fe3O4∶Fe5C2∶Fe7C3=8∶3∶0.5.

[0066] Comparative Example 2

[0067] The Fe catalyst was prepared in the same manner as in Example 1, except that in step 1) only 0.1 mol of ferric chloride hexahydrate was used instead of Fe(NO3)3·9H2O, and manganese nitrate was not used.

[0068] Comparative Example 3

[0069] Except for the silica sol not used in step 5), the Fe-Mn bimetallic catalyst was prepared in the same manner as in Example 1.

[0070] Comparative Example 4

[0071] Except for the conditions in step 6), where the catalyst precursor is treated in H2 for 12 h at 300 °C, 0.2 MPa, and 5000 h. -1 (V / V). In addition, the Fe-Mn bimetallic catalyst was prepared in the same manner as in Example 2.

[0072] Hydrogenation reaction examples

[0073] 1. CO2 hydrogenation reaction produces alkenes

[0074] 1 g of the Fe-Mn bimetallic catalysts prepared in Examples 1 to 6 and the catalysts prepared in Comparative Examples 1 to 4 were respectively used to initiate CO2 hydrogenation reactions in a fixed bed with reaction gas (H2 / CO2 = 3); the reaction conditions were 300 °C, 0.5 MPa, and 2500 h. -1 (V / V), the reaction results are shown in Table 1 below.

[0075] Table 1: Raw material conversion rate and product selectivity

[0076]

Claims

1. A Fe-Mn bimetallic catalyst for the selective hydrogenation of carbon dioxide, wherein, The Fe-Mn bimetallic catalyst comprises Fe3O4, Fe x C, MnCO3and a catalytic aid, wherein Fe x C represents a mixture of Fe5C2and Fe7C3, and the catalytic aid is SiO2and / or Al2O3; The molar ratio of Fe to Mn to silicon and / or aluminum in the Fe-Mn bimetallic catalyst is 5:(1.2~4.5):(0.5~2.0), and the mass ratio of Fe3O4:Fe5C2:Fe7C3 is 8:(1.8~4.0):(1.8~3.8).

2. The Fe-Mn bimetallic catalyst for selective hydrogenation of carbon dioxide according to claim 1, wherein, The molar ratio of Fe to Mn to silicon and / or aluminum in the Fe-Mn bimetallic catalyst is 5:(1.3~4.2):(0.6~1.8). And / or, the mass ratio of Fe3O4:Fe5C2:Fe7C3 is 8:(2.1~3.8):(2.0~3.5).

3. The Fe-Mn bimetallic catalyst for selective hydrogenation of carbon dioxide according to claim 1 or 2, wherein, The Fe-Mn bimetallic catalyst is used to prepare olefins.

4. The Fe-Mn bimetallic catalyst for selective hydrogenation of carbon dioxide according to claim 1 or 2, wherein, The Fe-Mn bimetallic catalyst is used to prepare straight-chain or branched olefins with two or more carbon atoms.

5. A method for preparing an Fe-Mn bimetallic catalyst for selective hydrogenation of carbon dioxide according to any one of claims 1 to 4, comprising the following steps: 1) Prepare an aqueous solution by mixing iron precursor salt and manganese precursor salt, then mix the aqueous solution with a grain dispersing agent, wherein, The molar ratio of Fe to Mn is 5: (1~4). 2) The solution obtained in step 1) is subjected to precipitation reaction with an aqueous solution of pH adjuster using a co-precipitation method, followed by aging, separation, washing and drying to obtain the precipitate; 3) The precipitate obtained in step 2) is mixed with the catalyst precursor, and then dried and calcined to obtain the catalyst precursor. The catalyst precursor is one or more selected from Si sol, Al sol, SiO2 powder, and Al2O3 powder. The molar ratio of Fe element to silicon element and / or aluminum element in the catalyst precursor is 5: (0.5~3). 4) The catalyst precursor obtained in step 3) is placed in a tube furnace and subjected to high-temperature treatment with syngas at 250~450℃ to obtain the Fe-Mn bimetallic catalyst.

6. The preparation method according to claim 5, wherein, The iron precursor salt is selected from one or more of ferric chloride, ferric nitrate, ferric sulfate, and ferric ammonium citrate; And / or, the precursor salt of manganese is one or more of manganese nitrate, manganese acetate, manganese dichloride and manganese sulfate; And / or, the grain dispersion aid is one or more selected from glycerol, ethylene glycol and acetic acid, and the volume ratio of the grain dispersion aid to the iron and manganese precursor salts to prepare an aqueous solution is 0.3 to 2:

1.

7. The preparation method according to claim 5 or 6, wherein, The pH adjuster is selected from one or more of sodium carbonate, potassium carbonate, ammonia, sodium bicarbonate, urea, and sodium hydroxide. And / or, the aging in step 2) is carried out at room temperature for 6 to 24 hours; And / or, the cleaning in step 2) is to first clean with deionized water and then with ethanol.

8. The preparation method according to claim 5 or 6, wherein, The roasting temperature in step 3) is 350~450 degrees Celsius; And / or, the molar ratio of H2 to CO in the synthesis gas in step 4) is 1~2.

9. The preparation method according to claim 5 or 6, wherein, The high-temperature treatment conditions in step 4) are: temperature 250~450℃; pressure 0.1~0.5MPa; space velocity 1250~10000h. -1 The time is 4~24 hours.

10. The preparation method according to claim 9, wherein, The high-temperature treatment conditions in step 4) are as follows: The pressure is 0.2 MPa; And / or, airspeed of 5000 h -1 ; And / or, the time is 12~24h.

11. A method for preparing olefins by selective hydrogenation of carbon dioxide, comprising the following steps: In the presence of the Fe-Mn bimetallic catalyst according to any one of claims 1 to 4, CO2 and H2 are reduced to obtain olefins.

12. The method for preparing olefins by selective hydrogenation of carbon dioxide according to claim 11, wherein, The molar ratio of H2 to CO2 is 3.

13. The method for preparing olefins by selective hydrogenation of carbon dioxide according to claim 11, wherein, The reaction was carried out in a fixed bed under the following conditions: temperature 260–340 °C, pressure 0.1–2.0 MPa, and space velocity 2000–15000 h⁻¹. -1 ; And / or, the CO2 conversion rate is above 40%, and the olefin selectivity is above 65 c-mol%.

14. The method for preparing olefins by selective hydrogenation of carbon dioxide according to claim 13, The CO2 conversion rate is over 45%. And / or, the selectivity for olefins is above 70 c-mol%.

15. The method for preparing olefins by selective hydrogenation of carbon dioxide according to claim 13, wherein, The olefin is a straight-chain or branched olefin having two or more carbon atoms.

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