Fe-zn bimetallic catalyst, preparation method and application thereof

Abstract

The application discloses an Fe-Zn bimetallic catalyst, a preparation method and application thereof. The Fe-Zn bimetallic catalyst according to the application comprises Fe3O4, Fe x C, ZnO and a catalytic aid, wherein Fe x C represents a mixture of Fe5C2 and Fe7C3, the mass ratio of Fe3O4:Fe5C2:Fe7C3 is 8:(1-4):(2-6), the catalytic aid is SiO2 and / or Al2O3, and the molar ratio of Fe elements:Zn elements:silicon elements and / or aluminum elements in the Fe-Zn bimetallic catalyst is 5:(0.7-3.5):(0.4-2.5). The Fe-Zn bimetallic catalyst has significantly improved catalytic activity, high carbon olefin and / or ethanol product selectivity, and improved carbon dioxide conversion.

Description

Technical Field

[0001] This invention relates to an Fe-Zn bimetallic catalyst, its preparation method, and its applications. The Fe-Zn bimetallic catalyst of this invention exhibits significantly improved catalytic activity, selectivity for high-carbon olefins and / or ethanol products, and increased carbon dioxide conversion rate. It provides 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] To mitigate global warming, it is necessary to curb the significant increase in atmospheric carbon dioxide levels. This can be achieved by reducing carbon dioxide emissions, and by converting carbon dioxide, a carbon-containing compound, into usable resources, thereby consuming atmospheric carbon dioxide. Several methods for converting and utilizing carbon dioxide have already been reported.

[0003] CN109675573A relates to a catalyst for the production of higher-carbon α-olefins via carbon dioxide hydrogenation. 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 via hydrogenation and showing good industrialization prospects.

[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 production of methanol from carbon dioxide via hydrogenation, 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.

[0006] However, no catalyst or method is disclosed in the prior art for the highly selective acquisition of high-carbon olefins and / or ethanol products by carbon dioxide hydrogenation reaction. Summary of the Invention

[0007] The purpose of this invention is to provide an Fe-Zn bimetallic catalyst for the hydrogenation reaction of carbon dioxide, its preparation method, and its application.

[0008] According to a first aspect of the present invention, an Fe-Zn bimetallic catalyst for the selective hydrogenation reaction of carbon dioxide is provided, wherein,

[0009] The Fe-Zn bimetallic catalyst contains Fe3O4 and Fe x C, ZnO, and catalyst promoters, of which Fe x C represents a mixture of Fe5C2 and Fe7C3, and the catalyst is SiO2 and / or Al2O3;

[0010] The molar ratio of Fe to Zn to silicon and / or aluminum in the Fe-Zn bimetallic catalyst is 5:(0.7-3.5):(0.4-2.5), preferably 5:(0.9-3.1):(0.5-1.5).

[0011] The mass ratio of Fe3O4:Fe5C2:Fe7C3 is 8:(1-4):(2-6).

[0012] Preferably, the Fe-Zn bimetallic catalyst is used to prepare high-carbon olefins and / or to prepare ethanol.

[0013] Preferably, the Fe-Zn 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.

[0014] According to a second aspect of the present invention, a method for preparing an Fe-Zn bimetallic catalyst for selective hydrogenation of carbon dioxide according to the present invention is provided, comprising the following steps:

[0015] 1) Prepare an aqueous solution by mixing the precursor salts of iron and zinc, and then mix the prepared aqueous solution with a grain dispersing agent, wherein the molar ratio of Fe to Zn is 5:(1-4).

[0016] 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;

[0017] 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), preferably 5:(0.5-1.2).

[0018] 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°C to obtain the Fe-Zn bimetallic catalyst.

[0019] Preferably, the iron precursor salt is one or more selected from ferric chloride, ferric nitrate, ferric carbonate, ferric sulfate, and ferric ammonium citrate.

[0020] Preferably, the zinc precursor salt is one or more of zinc nitrate, zinc acetate, and zinc sulfate.

[0021] 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 zinc precursor salts to prepare an aqueous solution is 0.5 to 2:1.

[0022] Preferably, the pH adjuster is one or more selected from sodium carbonate, potassium carbonate, ammonia, sodium bicarbonate, urea, and sodium hydroxide.

[0023] Preferably, the pH of the mixed system undergoing the precipitation reaction in step 2) is 7-10, and more preferably 8.

[0024] Preferably, the aging process in step 2) is carried out at room temperature for 6 to 24 hours.

[0025] Preferably, the cleaning in step 2) involves first cleaning with deionized water and then cleaning with ethanol.

[0026] Preferably, the roasting temperature in step 3) is 350–450 degrees Celsius.

[0027] Preferably, the molar ratio of H2 to CO in the synthesis gas in step 4) is 1 to 2.

[0028] 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. -1 5000h is preferred -1 The time is 4 to 24 hours, more preferably 12 to 24 hours.

[0029] According to a third aspect of the present invention, a method for preparing ethanol by selective hydrogenation of carbon dioxide is provided, comprising the following steps:

[0030] Ethanol is obtained by reducing CO2 and H2 in the presence of the Fe-Zn bimetallic catalyst according to the present invention.

[0031] Preferably, the molar ratio of H2 to CO2 is 3.

[0032] Preferably, the reaction is carried out in a fixed bed, and the reaction conditions are: temperature 260–340°C, pressure 1.5–4.0 MPa, and space velocity 2000–15000 h⁻¹. -1 .

[0033] Preferably, the CO2 conversion rate is 40% or more, more preferably 45% or more, and the ethanol selectivity is 18 c-mol% or more, more preferably 20 c-mol% or more.

[0034] According to a fourth aspect of the present invention, a method for preparing higher olefins by selective hydrogenation of carbon dioxide is provided, comprising the following steps:

[0035] In the presence of the Fe-Zn bimetallic catalyst according to the present invention, CO2 and H2 are reduced to obtain higher carbon olefins.

[0036] The high-carbon olefins are straight-chain or branched olefins having 4 to 18 carbon atoms.

[0037] Preferably, the molar ratio of H2 to CO2 is 3.

[0038] Preferably, the reaction is carried out in a fixed bed, and the reaction conditions are: temperature 280–340°C, pressure 0.5–1.5 MPa, and space velocity 2500–12000 h⁻¹. -1 .

[0039] The selectivity of the high carbon olefins is 45 c-mol% or more, preferably 50 c-mol% or more, and the CO2 conversion rate is 40% or more, preferably 45% or more.

[0040] The Fe-Zn bimetallic catalyst of this invention exhibits significantly enhanced catalytic activity (significantly improved carbon dioxide conversion rate) and selectivity for high-carbon olefins and / or ethanol 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

[0041] Figure 1 HAADF-STEM image of the Fe-Zn bimetallic catalyst prepared according to Example 1;

[0042] Figure 2 The image shows the XRD pattern of the Fe-Zn bimetallic catalyst prepared according to Example 1. Detailed Implementation

[0043] 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 used to illustrate the present invention and are not intended to limit the scope of the present invention.

[0044] Example 1

[0045] 1. Preparation of Fe-Zn bimetallic catalysts:

[0046] 1) Accurately weigh 40.4g Fe(NO3)3·9H2O (0.1mol) and 9.47g Zn(NO3)2 (0.05mol), add deionized water to make up to 100ml, and after complete dissolution, continue to add glycerol as a crystal dispersion aid, and make up to 200ml.

[0047] 2) Prepare 200 ml of 2 mol / L ammonia solution for later use.

[0048] 3) Add 200 ml of deionized water to a 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 keep the pH of the mixed solution in the four-necked flask stable at 8 ± 0.5.

[0049] 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.

[0050] 5) The precursor obtained in step 4) is mixed with a 20 wt% silica sol solution (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 400 °C for 4 h.

[0051] 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-Zn bimetallic catalyst.

[0052] The HAADF-STEM and XRD patterns of the prepared Fe-Zn bimetallic catalyst are shown below. Figure 1 and Figure 2 As shown.

[0053] like Figure 1 The image shown is a HAADF-STEM / EDX image of the Fe-Zn bimetallic catalyst, revealing the distribution of elements such as Fe, Zn, O, and Si within the catalyst. Furthermore, a unique Fe-Zn boundary structure is observed, indicating phase separation due to the phase transformation during activation.

[0054] like Figure 2 The XRD pattern of the Fe-Zn bimetallic catalyst is shown. The diffraction peaks of the following phases can be observed in the catalyst: Fe3O4 (PDF 82-1533), ZnO (PDF 36-1451), Fe7C3 (PDF 89-7273) and Fe5C2 (PDF 89-8968).

[0055] In the prepared Fe-Zn bimetallic catalyst, the element content was measured by ICP-OES experiment, and the molar ratio of Fe, Zn, and Si was calculated as Fe∶Zn∶Si=5∶1.94∶1.28. The mass ratio of Fe3O4, Fe7C3, and Fe5C2 was obtained by XRD fitting and was Fe3O4∶Fe5C2∶Fe7C3=1∶0.35∶0.56.

[0056] Example 2

[0057] 1. Preparation of Fe-Zn bimetallic catalysts:

[0058] 1) Accurately weigh 40.4g Fe(NO3)3·9H2O (0.1mol) and 14.85g Zn(NO3)2 (0.078mol), add deionized water to make up to 200ml, and after complete dissolution, continue to add glycerol and make up to 300ml.

[0059] 2) Prepare 200 ml of 2 mol / L ammonia solution for later use.

[0060] 3) Add 200 ml of deionized water to the four-necked flask and fix it in a water bath at 30°C with a stirring speed of 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 keep the pH of the mixed solution in the three-necked flask stable at 7.5 ± 0.5.

[0061] 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 300 ml of deionized water. Finally, wash with 40 ml of ethanol. Dry the washed precipitate in an oven at 110°C for 12 hours.

[0062] 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.

[0063] 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). This yields the Fe-Zn bimetallic catalyst, where the molar ratio obtained through testing is: Fe∶Zn∶Al=5∶3.07∶0.89, and the mass ratio is Fe3O4∶Fe5C2∶Fe7C3=1∶0.27∶0.25.

[0064] Example 3

[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 0.02 mol of ZnSO4, the Fe-Zn bimetallic catalyst was prepared in the same manner as in Example 1, wherein the molar ratio was found to be Fe∶Zn∶Si=5∶0.928∶1.08 and the mass ratio was Fe3O4∶Fe5C2∶Fe7C3=1∶0.20∶0.26.

[0066] Example 4

[0067] 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 0.06 mol of ZnSO4, the Fe-Zn bimetallic catalyst was prepared in the same manner as in Example 1, wherein the molar ratio was found to be Fe∶Zn∶Si=5∶2.152∶1.1057 and the mass ratio was Fe3O4∶Fe5C2∶Fe7C3=1∶0.23∶0.29.

[0068] Example 5

[0069] Except for the 0.04 mol of silica sol used in step 5), the Fe-Zn bimetallic catalyst was prepared in the same manner as in Example 1, wherein the molar ratio was found to be Fe∶Zn∶Si=5∶2.074∶2.162 and the mass ratio was Fe3O4∶Fe5C2∶Fe7C3=1∶0.16∶0.37.

[0070] Example 6

[0071] Except for the 0.01 mol of silica sol used in step 5), the Fe-Zn bimetallic catalyst was prepared in the same manner as in Example 1, wherein the molar ratio was found to be Fe∶Zn∶Si=5∶1.87∶0.544 and the mass ratio was Fe3O4∶Fe5C2∶Fe7C3=1∶0.22∶0.28.

[0072] Comparative Example 1

[0073] 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 ZnSO4, the Fe-Zn bimetallic catalyst was prepared in the same manner as in Example 1, wherein the molar ratio was found to be Fe∶Zn∶Si=5∶4.077∶0.983 and the mass ratio was Fe3O4∶Fe5C2∶Fe7C3=1∶0.28∶0.

[0074] Comparative Example 2

[0075] 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 0.1 mol of ZnSO4 was not used.

[0076] Comparative Example 3

[0077] Except for the silica sol not used in step 5), the Fe-Zn bimetallic catalyst was prepared in the same manner as in Example 1.

[0078] Comparative Example 4

[0079] 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-Zn bimetallic catalyst was prepared in the same manner as in Example 2.

[0080] Comparative Example 5

[0081] Except for the use of 0.2 mol silica sol in step 5), the Fe-Zn bimetallic catalyst was prepared in the same manner as in Example 1.

[0082] Hydrogenation reaction examples

[0083] 1. The hydrogenation of CO2 produces higher olefins.

[0084] 1 g of the Fe-Zn bimetallic catalyst prepared in Examples 1-6 and Comparative Examples 1-4 was used to initiate a CO2 hydrogenation reaction in a fixed bed with a reaction gas (H2 / CO2 = 3); the reaction conditions were 320 °C, 0.5 MPa, and 5000 h. -1 (V / V), the reaction results are shown in Table 1 below.

[0085] Table 1: Results using the catalysts prepared in Examples 1–6 and Comparative Examples 1–4

[0086]

[0087] 2. CO2 is hydrogenated to produce ethanol.

[0088] Take 1g of the Fe-Zn bimetallic catalyst prepared above and start the CO2 hydrogenation reaction in a fixed bed with reaction gas (H2 / CO2 = 3); the reaction conditions are 280℃, 3.5MPa, 2500h. -1 (V / V), the reaction results are shown in Table 2 below.

[0089] Table 2: Results using the catalysts prepared in Examples 1–6 and Comparative Examples 1–4

[0090]

Claims

1. A Fe-Zn bimetallic catalyst for the selective hydrogenation of carbon dioxide, wherein, The Fe-Zn bimetallic catalyst contains Fe3O4 and Fe x C, ZnO, and catalyst promoters, of which Fe x C represents a mixture of Fe5C2 and Fe7C3, and the catalyst is SiO2 and / or Al2O3; The molar ratio of Fe to Zn to silicon and / or aluminum in the Fe-Zn bimetallic catalyst is 5:(0.7~3.5):(0.4~2.5). The mass ratio of Fe3O4:Fe5C2:Fe7C3 is 8:(1~4):(2~6).

2. The Fe-Zn bimetallic catalyst according to claim 1, wherein, The molar ratio of Fe to Zn to silicon and / or aluminum in the Fe-Zn bimetallic catalyst is 5:(0.9~3.1):(0.5~1.5).

3. The Fe-Zn bimetallic catalyst according to claim 1, wherein, The Fe-Zn bimetallic catalyst is used to prepare high-carbon olefins and / or to prepare ethanol.

4. A method for preparing an Fe-Zn bimetallic catalyst for selective hydrogenation of carbon dioxide according to any one of claims 1 to 3, comprising the following steps: 1) Prepare an aqueous solution by mixing iron precursor salt and zinc precursor salt, then mix the prepared aqueous solution with a grain dispersing agent, wherein, The molar ratio of Fe to Zn 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-Zn bimetallic catalyst.

5. The preparation method according to claim 4, wherein, The molar ratio of Fe to silicon and / or aluminum in the catalyst precursor is 5: (0.5~1.2).

6. The preparation method according to claim 4, wherein, The iron precursor salt is selected from ferric chloride, ferric nitrate, ferric carbonate, ferric sulfate, and ferric ammonium citrate. And / or, the zinc precursor salt is one or more selected from zinc nitrate, zinc acetate and zinc 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 precursor salt and zinc precursor salt prepared into an aqueous solution is 0.5 to 2:

1.

7. The preparation method according to any one of claims 4 to 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 pH of the mixed system in step 2) where the precipitation reaction takes place is 7-10; 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 7, wherein, The pH of the mixed system in step 2) where the precipitation reaction takes place is 8.

9. The preparation method according to any one of claims 4 to 6, wherein, The roasting temperature in step 3) is 350~450 degrees Celsius; And / or, in step 4), the molar ratio of H2 to CO in the syngas is 1 to 2; And / or, 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. A method for preparing ethanol by selective hydrogenation of carbon dioxide, comprising the following steps: Ethanol is obtained by reducing CO2 and H2 in the presence of the Fe-Zn bimetallic catalyst according to any one of claims 1 to 3.

11. The method for preparing ethanol by selective hydrogenation of carbon dioxide according to claim 10, wherein, The molar ratio of H2 to CO2 is 3.

12. The method for preparing ethanol by selective hydrogenation of carbon dioxide according to claim 10, wherein, The reaction was carried out in a fixed bed under the following conditions: temperature 260–340 °C, pressure 1.5–4.0 MPa, and space velocity 2000–15000 h⁻¹. -1 ; And / or, the CO2 conversion rate is above 40%, and the ethanol selectivity is above 18 c-mol%.

13. The method for preparing ethanol by selective hydrogenation of carbon dioxide according to claim 12, wherein, The selectivity for ethanol is above 20 c-mol%.

14. A method for preparing higher olefins by selective hydrogenation of carbon dioxide, comprising the following steps: CO2 and H2 are reduced in the presence of the Fe-Zn bimetallic catalyst according to any one of claims 1 to 3 to obtain high carbon olefins; the high carbon olefins are straight-chain or branched olefins having 4 to 18 carbon atoms.

15. The method for preparing higher olefins by selective hydrogenation of carbon dioxide according to claim 14, wherein, The molar ratio of H2 to CO2 is 3.

16. The method for preparing higher olefins by selective hydrogenation of carbon dioxide according to claim 14, wherein, The reaction was carried out in a fixed bed under the following conditions: temperature 280–340℃, pressure 0.5–1.5 MPa, and space velocity 2500–12000 h⁻¹. -1 ; And / or, the selectivity of the higher carbon olefins is 45 c-mol% or more, and the CO2 conversion rate is 40% or more.

17. The method for preparing higher olefins by selective hydrogenation of carbon dioxide according to claim 16, wherein, The selectivity of the high-carbon olefins is above 50 c-mol%.

Images