Preparation method and application of Fe-Cu catalyst

Abstract

The invention relates to the technical field of catalysts, and discloses a preparation method and application of a Fe-Cu catalyst. The preparation method comprises the following steps: mixing an iron metal salt or a hydrate of the iron metal salt, a copper salt or a hydrate of the copper salt and a solvent to obtain a metal salt solution, adding an alkali liquor to obtain a precipitate, and crystallizing to obtain the Fe-Cu catalyst. The metal catalyst is obtained through a simple metal coprecipitation treatment process and crystallization reaction, the catalyst is low in raw material price, the preparation method is simple, large-scale production is easy, industrial application is facilitated, and the catalyst has high selectivity, is convenient to recycle and is suitable for industrial production. The multi-metal synergistic effect can reduce the activation energy and improve the catalytic activity, and the catalyst has wide application prospects in the fields of catalytic hydrogenation, oxidation, electrochemistry and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of catalysts, and particularly relates to a preparation method and application of an Fe-Cu catalyst. Background Art

[0002] Fossil fuels are being burned on an unprecedented scale to meet the energy needs of the growing world population, and a total of more than 30 billion tons of carbon dioxide are released into the environment every year. Such huge carbon dioxide emissions are related to environmental challenges such as climate change and ocean acidification. The emerging process of converting carbon dioxide into important bulk chemicals by heterogeneous catalytic hydrogenation provides an alternative strategy for sustainable and low-cost production of valuable chemicals and brings important opportunities for reducing carbon dioxide emissions. Hydrogenation of carbon dioxide to olefins is a promising green synthesis route, which not only reduces greenhouse gas emissions, improves environmental and ecological problems, but also realizes the resource utilization of carbon dioxide and promotes the green and low-carbon transformation of the energy structure.

[0003] The principle of hydrogenation of carbon dioxide to olefins can be mainly divided into two categories: the first category is the methanol intermediate pathway, the first step of which is the production of methanol from carbon dioxide, and the second step is the catalytic conversion of methanol to olefins (MTO). The second category is the CO intermediate pathway. The first step is that carbon dioxide first obtains CO through the reverse water gas shift reaction (RWGS), and the second step is to generate hydrocarbons through the Fischer-Tropsch synthesis reaction (FTS). At present, iron-based catalysts show good catalytic performance in the reaction of hydrogenation of carbon dioxide to olefins, but there are still problems of low olefin selectivity and high CO selectivity. Chinese Patent (CN117563605 A) reported a preparation method of a non-noble metal catalyst for hydrogenation of carbon dioxide to olefins. The developed Fe-Zn-Mg catalyst has a low olefin selectivity of only 35.3% in the reaction of hydrogenation of carbon dioxide at atmospheric pressure. On the other hand, the carbon monoxide selectivity reported in a large number of literatures is 10-50%. Therefore, from the perspective of improving the reaction efficiency, improving olefin selectivity, the O / P value (the O / P value is the ratio of olefins to alkanes), and reducing CO selectivity are urgent challenges to be solved in the reaction of hydrogenation of carbon dioxide. Summary of the Invention

[0004] The present invention aims to solve at least one of the above technical problems existing in the prior art. For this reason, the purpose of the present invention is to provide a preparation method and application of an Fe-Cu catalyst.

[0005] In order to achieve the above purpose, the technical solutions adopted by the present invention are as follows:

[0006] In the first aspect of the present invention, a preparation method of an Fe-Cu catalyst is provided, including the following steps:

[0007] Mix an iron metal salt or a hydrate of an iron metal salt, a copper salt or a hydrate of a copper salt, and a solvent to obtain a metal salt solution, then add an alkali solution to obtain a precipitate, and after crystallization, prepare the described Fe-Cu catalyst.

[0008] In the present invention, Cu is a mild hydrogenation catalyst, which can inhibit the over-hydrogenation of products to form alkanes in the reaction of hydrogenating carbon dioxide to olefins; the iron-based active phase is the best choice for producing olefins. Therefore, the present invention proposes a preparation method of an Fe-Cu catalyst. By introducing Fe elements to form Fe3O4, FeC3 and Fe5C2, the RWGS and FTS reactions are promoted, and the carbon dioxide conversion rate of the Fe-based catalyst is improved; through the formation of Cu metal and its oxides, the RWGS reaction is promoted while suppressing the over-hydrogenation of olefins to alkanes by the Fe-based catalyst. Introducing alkali metal Na can regulate the surface CH x * species ratio, which is beneficial to improving the C-C coupling ability. At the same time, it will also cause an increase in the electron cloud density of Fe5C2, inhibiting the secondary hydrogenation reaction of olefins and increasing the ratio of olefins to alkanes (O / P); using ethylene glycol as a solvent, the Fe3O4 active phase can be obtained after the catalyst is hydrothermally treated. Introducing copper acetate can effectively disperse the metal particles in the system evenly. Subsequently, the solution with the precipitate is further crystallized, making the precipitate in it become an oxide, which is more conducive to the subsequent catalytic performance; on the other hand, the introduction of copper acetate can cause the Cu in the freshly prepared catalyst to appear in the Cu +1 valence state, thus promoting the formation of the heterojunction of Cu2O, CuFeO2, Fe3O4 and Cu-Fe2O3. At the same time, Cu +1 through the electron transfer with FeC X makes the catalyst of the reaction gradually form a Fe5C2 phase with high FTS activity, reducing the formation of the Fe3C phase with low FTS activity, and realizing the rapid conversion of the CO by-product intermediate to CH x , and generating olefins through carbon-carbon coupling. When copper acetate and sodium acetate are added simultaneously, the content of the Fe5C2 phase is the highest. Therefore, the selectivity of olefins and the ratio of olefins to alkanes (O / P) are greatly improved, and the selectivity of CO and CH4 by-products is also reduced.

[0009] In some embodiments of the present invention, the molar ratio of Fe ions to Cu ions in the metal salt solution is (0.9 - 2.0):1.

[0010] In some embodiments of the present invention, the copper salt includes copper acetate, copper nitrate or their hydrates.

[0011] In some embodiments of the present invention, the molar ratio of Fe ions to Cu ions in the metal salt solution is (1.0 - 1.2):1.

[0012] In some embodiments of the present invention, the alkali solution includes an alkali metal salt of acetic acid and / or sodium hydroxide.

[0013] In some embodiments of the present invention, the alkali metal salt of acetic acid includes at least one of sodium acetate, potassium acetate, and lithium acetate.

[0014] In some embodiments of the present invention, the alkali solution contains acetate ions.

[0015] In some embodiments of the present invention, the Fe ions include Fe 3+ ; the Cu ions include Cu 2+ .

[0016] In some embodiments of the present invention, the alkali solution further includes ethylene glycol and / or deionized water.

[0017] In some embodiments of the present invention, the solvent includes ethylene glycol.

[0018] In some embodiments of the present invention, the alkali solution includes an aqueous ethylene glycol solution of at least one of sodium acetate and sodium hydroxide. In the present invention, compared with strong bases such as sodium hydroxide, sodium acetate can provide acetate ions. When ethylene glycol combines with acetate ions, through the deprotonation reaction of acetate ions, ethylene glycol dissociates to form a monoanionic valence state, thereby suppressing the excessive precipitation and hydrolysis of Fe and Cu, and forming more complexes of iron acetate and copper acetate, promoting the subsequent reduction reaction, making it easier to crystallize to form CuFeO2, Fe3O4, and Cu-Fe2O3 heterojunctions in the crystallization kettle, improving the conversion rate of the catalyst, and promoting the formation of Fe5C2 species in the reaction system, thereby improving the selectivity of olefins.

[0019] In some embodiments of the present invention, the volume ratio of ethylene glycol to water in the aqueous ethylene glycol solution is 2-8:1, such as 3-6:1, 4:1, etc.

[0020] In some embodiments of the present invention, the molar ratio of the alkali metal salt of acetic acid and / or sodium hydroxide in the alkali solution to Fe is 20-1:1. For example, it can also be 10-5:1.

[0021] In some embodiments of the present invention, the iron metal salt or the hydrate of the iron metal salt includes at least one of iron nitrate, iron chloride, iron sulfate, iron acetate, or their hydrates.

[0022] In some embodiments of the present invention, the crystallization temperature is 80-240°C, such as 150-240°C, 160-200°C, 180°C, etc.

[0023] In some embodiments of the present invention, the crystallization time is 8 to 12 h, such as 9 to 11 h, 10 h.

[0024] In a second aspect of the present invention, there is provided an Fe-Cu catalyst prepared by the method for preparing an Fe-Cu catalyst described above.

[0025] In a third aspect of the present invention, there is provided the use of the Fe-Cu catalyst prepared by the above method in the hydrogenation of carbon dioxide to prepare olefins.

[0026] In a fourth aspect of the present invention, there is provided a method for hydrogenating carbon dioxide to prepare olefins, comprising the following steps: under the condition of the presence of the Fe-Cu catalyst described above, introducing a mixed gas of H2 and CO2, and carrying out a hydrogenation reaction to obtain olefins.

[0027] In some embodiments of the present invention, the hydrogenation reaction is carried out at 280 to 350 °C and 0.1 to 3.0 MPa (such as 0.05 to 1.0 MPa).

[0028] In some embodiments of the present invention, in the mixed gas of H2 and CO2, the volume ratio of H2:CO2 is 3 to 1:1, such as the volume ratio of H2:CO2 is 3:1.

[0029] In some embodiments of the present invention, the space velocity of the mixed gas is 2000 to 15000 mL / (h·g cat ) such as 2000 to 12000 mL / (h·g cat ), within this space velocity range, when using the catalyst of the present invention to carry out the reaction of hydrogenating carbon dioxide to prepare olefins, a relatively high olefin yield can finally be obtained, and at the same time, the carbon dioxide conversion rate is also good.

[0030] In some embodiments of the present invention, the carbon dioxide conversion rate of the hydrogenation reaction is above 20%.

[0031] In some embodiments of the present invention, after the hydrogenation reaction is completed, the total olefin selectivity is greater than 36%, even greater than 50%.

[0032] In some embodiments of the present invention, the olefins are olefins having 2 to 10 carbon atoms, such as olefins such as ethylene, propylene and butene.

[0033] The beneficial effects of the present invention are as follows:

[0034] (1) The present invention uses a simple metal co-precipitation treatment process and a crystallization reaction to obtain a metal catalyst. The catalyst raw materials in the present invention are cheap and the preparation method is simple, which is easy to scale up production and facilitate industrial application;

[0035] (2) The catalyst in the present invention does not add harmful substances such as sulfur elements, reducing environmental pollution and harm to the human body;

[0036] (3) The catalyst prepared in the present invention can catalyze the hydrogenation reaction of carbon dioxide under the reaction conditions of 300 °C and 1 bar (0.1 MPa), that is, under low temperature and normal pressure conditions. Moreover, the total selectivity of the finally prepared olefins is greater than 60%, the carbon dioxide conversion rate can reach more than 20%, and the O / P value can be greater than 8, which can greatly reduce the industrial manufacturing cost and is conducive to industrial production. The technical effect is significantly better than that of the existing carbon dioxide hydrogenation catalysts (which require a pressurized environment to have good effects);

[0037] (4) The catalyst described in the present invention has high selectivity and convenient recyclability. The multi-metal synergistic effect can reduce the activation energy and improve the catalytic activity, and has broad application prospects in the fields of catalytic hydrogenation, oxidation, electrochemistry, etc. Detailed implementation mode

[0038] The content of the present invention will be further described in detail through specific examples below. Unless otherwise specified, the raw materials, reagents or devices used in the examples and comparative examples can be obtained from conventional commercial channels or can be obtained by existing technical methods. Unless otherwise specified, the test or testing methods are conventional methods in the art.

[0039] Example 1

[0040] In this example, an Fe-Cu catalyst was prepared. The specific process was as follows:

[0041] Weighed 4.0412 g of ferric nitrate nonahydrate (Fe(NO3)3·9H2O) and 1.9965 g of copper acetate monohydrate (Cu(CH3COO)2·H2O) and dissolved them in 100 mL of diglycol. Stirred for 30 min to obtain a metal salt mixture (molar ratio Fe:Cu = 1:1). Then, 3.2812 g of NaAc was added to 20 mL of ethylene glycol and 5 mL of deionized water to prepare an alkaline solution. The alkaline solution was dropped into the continuously stirred metal salt mixture at a speed of 60 rpm through a peristaltic pump to precipitate the metal ions in the solution. Then, the solution with the precipitate was transferred to a crystallization kettle and kept at 180 °C for 10 hours for crystallization. Subsequently, the crystallized precipitate was centrifuged at 5000 rpm for 5 min and washed with deionized water, and then dried in an oven at 80 °C to finally obtain a catalyst for the hydrogenation of carbon dioxide to olefins, labeled as FeCu(Ac)NaAc.

[0042] Example 2

[0043] In this example, an Fe-Cu catalyst was prepared. The specific process was as follows:

[0044] Weigh 1.652 g of ferric chloride (FeCl3) and 1.9965 g of copper acetate monohydrate (Cu(CH3COO)2·H2O), dissolve them in 100 mL of ethylene glycol monomethyl ether, stir for 30 min to obtain a metal salt mixture (molar ratio Fe:Cu = 1:1). Then, dissolve 3.2812 g of NaAc in 20 mL of ethylene glycol and 5 mL of deionized water to prepare an alkaline solution. Drop the alkaline solution into the continuously stirred metal salt mixture at a speed of 60 rpm through a peristaltic pump to precipitate the metal ions in the solution. Then, transfer the solution with the precipitate to a crystallization kettle, keep it at 180 °C for 10 hours for crystallization. Subsequently, centrifuge the crystallized precipitate at 5000 rpm for 5 min and wash it with deionized water, and then dry it in an oven at 80 °C. Finally, obtain a catalyst for hydrogenation of carbon dioxide to olefins, labeled as FeClCu(Ac)NaAc.

[0045] Example 3

[0046] In this example, a catalyst for hydrogenation of carbon dioxide to olefins was prepared. The difference from Example 1 was only that 2.4156 g of copper nitrate hexahydrate (Cu(NO3)2·6H2O) was used instead of 1.9965 g of copper acetate monohydrate (Cu(CH3COO)2·H2O), and the rest of the experimental steps were the same as those in Example 1.

[0047] The prepared catalyst for hydrogenation of carbon dioxide to olefins was labeled as FeCu(Ac)Na.

[0048] Example 4

[0049] In this example, a catalyst for hydrogenation of carbon dioxide to olefins was prepared. The difference from Example 1 was only that 3.2 g of NaOH was used instead of 3.2812 g of NaAc, and the rest of the experimental steps were the same as those in Example 1.

[0050] The prepared catalyst for hydrogenation of carbon dioxide to olefins was labeled as FeCuNaAc.

[0051] Comparative Example 1

[0052] In this comparative example, a catalyst for hydrogenation of carbon dioxide to olefins was prepared. The difference from Example 1 was only that 2.4156 g of copper nitrate hexahydrate (Cu(NO3)2·6H2O) was used instead of 1.9965 g of copper acetate monohydrate (Cu(CH3COO)2·H2O), and 3.2 g of NaOH was used instead of 3.2812 g of NaAC, and the rest of the experimental steps were the same as those in Example 1.

[0053] The prepared catalyst for hydrogenation of carbon dioxide to olefins was labeled as FeCuNa.

[0054] Comparative Example 2

[0055] In this comparative example, a catalyst for hydrogenating carbon dioxide to olefins was prepared. The difference from Example 1 was only that 0.04 mol of NH3·H2O was used instead of 3.2812 g of NaAc, and the rest of the experimental steps were the same.

[0056] The prepared catalyst for hydrogenating carbon dioxide to olefins was labeled as FeCu(Ac)NH3.

[0057] Example 5

[0058] In this example, 0.25 g of the catalysts of Examples 1 to 4 and Comparative Examples 1 to 2 were respectively weighed and confined in the middle of a fixed-bed reactor with quartz sand. Subsequently, a mixed gas of H2 and CO2 (total gas flow rate was 50 mL / min) was introduced, and the reaction was carried out at 300 °C and 1 bar (0.1 MPa) for 6 h (space velocity was 12000 mL / (h·g cat ))). By volume, H2:CO2 = 3:1; during the reaction, the product composition was analyzed online by gas chromatography at regular intervals.

[0059] According to the foregoing method, 0.625 g of the catalyst of Example 1 was weighed, that is, the performance of the catalyst of Example 1 was further tested under a space velocity of 4800 mL / (h·g cat ).

[0060] The performance effects of the catalysts prepared in Examples 1 to 4 and Comparative Examples 1 to 2 are shown in Table 1. It can be seen from Table 1 that the total selectivity of the olefins corresponding to the catalysts prepared in the examples of the present invention is significantly higher than that of the comparative examples. Among them, the catalyst of Comparative Example 2 hardly produced olefins under atmospheric pressure hydrogenation. Although the catalyst prepared in Comparative Example 1 could produce olefins, its carbon dioxide conversion rate was only 10.2%. For the catalyst prepared in Example 1 of the present invention, the carbon dioxide conversion rate was as high as 21.6%. At the same time, the total selectivity of olefins was as high as 60.15% (an increase of 52.22% compared with Comparative Example 4), and even reached 73.1%, proving that the performance effects of the catalysts prepared in the examples of the present invention are remarkable.

[0061] Table 1

[0062]

[0063]

[0064] Note: a is the space velocity of 12000 mL / (h·g cat ); b is the space velocity of 4800 mL / (h·g cat ); C2 ＝ -C3 ＝is an olefin product with 2 to 3 carbon atoms; C4 ＝ -C6 ＝ is an olefin product with 4 to 6 carbon atoms; the total selectivity of olefins is C2 ＝ -C3 ＝ 、C4 ＝ -C6 ＝ the sum of the percentage contents.

[0065] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. A preparation method of a Fe-Cu catalyst, characterized in that: It includes the following steps: Mix an iron metal salt or a hydrate of an iron metal salt, a copper salt or a hydrate of a copper salt, and a solvent to obtain a metal salt solution, then add an alkali solution to obtain a precipitate, and after crystallization, prepare the Fe-Cu catalyst.

2. The preparation method of the Fe-Cu catalyst according to claim 1, characterized in that: The molar ratio of Fe ions to Cu ions in the metal salt solution is (0.9 to 2.0):1; and / or, the alkali solution includes an alkali metal salt of acetic acid and / or sodium hydroxide.

3. The preparation method of the Fe-Cu catalyst according to claim 2, wherein: The molar ratio of sodium acetate and / or sodium hydroxide in the alkali solution to Fe is 20 to 1:1; and / or, the alkali metal salt of acetic acid includes at least one of sodium acetate, potassium acetate, and lithium acetate.

4. The preparation method of the Fe-Cu catalyst according to claim 1, characterized in that: The iron metal salt or the hydrate of the iron metal salt includes at least one of iron nitrate, iron chloride, iron sulfate, iron acetate, or their hydrates; and / or, the alkali solution further includes ethylene glycol and / or deionized water.

5. The preparation method of the Fe-Cu catalyst according to claim 1, characterized in that: The copper salt includes copper acetate, copper nitrate, or their hydrates; and / or, the temperature of the crystallization is 80 to 240 °C.

6. An Fe-Cu catalyst prepared by the preparation method of the Fe-Cu catalyst according to any one of claims 1 to 5.

7. Use of the Fe-Cu catalyst according to claim 6 in the hydrogenation of carbon dioxide to prepare olefins.

8. A method for preparing olefins by hydrogenating carbon dioxide, characterized in that: It includes the following steps: Under the condition of the presence of the Fe-Cu catalyst prepared by the preparation method according to any one of claims 1 to 5 or the Fe-Cu catalyst according to claim 6, introduce a mixed gas of H2 and CO2, and carry out a hydrogenation reaction to prepare olefins.

9. The method for preparing olefins by hydrogenating carbon dioxide according to claim 8, wherein: The hydrogenation reaction is carried out under the conditions of 280 to 350 °C and 0.1 to 3.0 MPa.

10. The method for preparing olefins by hydrogenating carbon dioxide according to claim 8, wherein: After the hydrogenation reaction is completed, the total selectivity of olefins is greater than 36%.

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