Iron-based catalyst for carbon dioxide to olefin and preparation method and application thereof

Abstract

The application discloses a preparation method of an iron-based catalyst for carbon dioxide to olefin, which comprises the following steps: preparing a sodium hydroxide solution; weighing iron nitrate nonahydrate and dissolving the same into deionized water to obtain an iron nitrate solution; respectively weighing cobalt nitrate hexahydrate and zinc nitrate hexahydrate according to the molar ratio of iron nitrate nonahydrate to cobalt nitrate hexahydrate and zinc nitrate hexahydrate being (1-4):1, and adding the same into the iron nitrate solution to configure a mixed solution; slowly adding the mixed solution into the sodium hydroxide solution, stirring, and then transferring into a hydrothermal reaction kettle; adding propionaldehyde as a reducing agent; after hydrothermal reaction, cleaning the product with anhydrous ethanol and deionized water, and drying; reducing the dried catalyst in pure hydrogen, and thus the required iron-based catalyst is obtained. The catalyst can significantly improve the carbon dioxide conversion rate and the space-time yield of light olefins in carbon dioxide to olefin, and can significantly reduce the carbon monoxide selectivity.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of catalytic conversion of carbon dioxide, and particularly relates to an iron-based catalyst for preparing olefins from carbon dioxide as well as a preparation method and application thereof. BACKGROUND

[0002] Carbon capture is a feasible method for carbon emission reduction. At present, carbon dioxide capture technology is developing rapidly in China, and various traditional capture technologies are already in the engineering demonstration stage. New capture technologies such as chemical looping combustion and direct air capture are also under development. However, the method of directly installing a capture device on an existing device to achieve carbon emission reduction not only has the problem of high capture cost, but also faces the dilemma that the captured CO2 cannot be directly applied and additional storage and transportation costs need to be paid. Therefore, developing CO2 chemical production technology is the key to carbon emission reduction. Olefins are a basic chemical raw material and have a huge impact on downstream chemical products. Developing CO2 olefin production technology not only can achieve carbon emission reduction in the olefin production process, but also can reduce carbon emissions in the entire process using green and low-carbon olefins as raw materials. Furthermore, it can also absorb CO2 captured from other devices. In addition to environmental friendliness and market competitiveness, the technology can also promote the commercialization of CCUS (carbon capture, utilization and storage).

[0003] Directly using CO2 as a raw material to prepare olefins is the most ideal preparation process, but this technology started relatively late and is still in the basic research stage at home and abroad. The current research mainly has two different technical routes: one is the methanol-mediated preparation process using metal oxide and zeolite bifunctional catalysts. The methanol-mediated preparation process is developing rapidly, and researchers have developed many catalysts with excellent performance. However, these catalysts are mostly prepared using noble metals, which are high in cost, and have low CO2 conversion rates. The other is the modified Fischer-Tropsch synthesis preparation process using iron-based catalysts. Iron-based catalysts have much higher conversion rates than metal oxide and zeolite bifunctional catalysts at a lower cost, and the catalytic process has lower energy consumption, which is more conducive to the efficient conversion of CO2 to olefins. However, iron-based catalysts have the problem of unstable active phase, which is easily converted to other phases during the catalytic process, leading to a decrease in catalyst performance.

[0004] Therefore, developing iron-based catalysts with high activity and high stability is of great significance for promoting the commercialization of carbon dioxide to olefin technology. SUMMARY

[0005] To solve at least one of the above problems, the application provides an iron-based catalyst for preparing olefins from carbon dioxide as well as a preparation method and application thereof.

[0006] To achieve the above purpose, the application adopts the following technical means:

[0007] The first aspect of the present application provides a preparation method of an iron-based catalyst for carbon dioxide to olefin, comprising the following steps:

[0008] S1, preparing a precipitator sodium hydroxide solution;

[0009] S2, weighing 5-20 mmol of iron nitrate nonahydrate, dissolving it in deionized water to obtain an iron nitrate solution;

[0010] S3, according to the molar ratio (1-4):1 of iron nitrate nonahydrate to cobalt nitrate hexahydrate and iron nitrate nonahydrate to zinc nitrate hexahydrate, respectively weighing cobalt nitrate hexahydrate and zinc nitrate hexahydrate, and adding them to the iron nitrate solution obtained in S2 to configure a mixed solution;

[0011] S4, slowly adding the mixed solution to the sodium hydroxide solution obtained in S1, stirring for 25-35 minutes, and then transferring to a hydrothermal reaction kettle, and adding propyl aldehyde as a reducing agent in the hydrothermal reaction kettle;

[0012] S5, after hydrothermal reaction for 8-24 hours, washing the product with anhydrous ethanol and deionized water, and drying at 90-100℃;

[0013] S6, reducing the dried catalyst in pure hydrogen to obtain the desired iron-based catalyst.

[0014] In some embodiments of the present application, the propyl aldehyde is added in an amount of 1%-4% by volume.

[0015] In some embodiments of the present application, the hydrothermal reaction temperature is 150℃-200℃.

[0016] In some embodiments of the present application, the reduction temperature is 300-350℃, and the time is 3-5 hours.

[0017] The second aspect of the present application provides an iron-based catalyst prepared by the method of the first aspect.

[0018] The third aspect of the present application provides the use of the iron-based catalyst of the second aspect in carbon dioxide to olefin to improve carbon dioxide conversion and improve the space-time yield of light olefins.

[0019] Advantages of the present application

[0020] Compared with the prior art, the present application has the following advantages:

[0021] This invention modifies and optimizes iron catalysts by adding transition metal additives. Propanal is used as a reducing agent to promote the formation of a stable and uniform crystal structure during the catalyst preparation process. A complementary modification strategy of zinc and cobalt co-doping is adopted, which simultaneously leverages the role of Co additive in promoting the reduction and carburization of the Fe phase and the role of zinc additive in inhibiting the oxidation of the iron carbide phase. The synergistic modification effect of zinc and cobalt is utilized, taking advantage of the fact that zinc and cobalt are more likely to form co-oxides in the reaction than iron carbide, thereby inhibiting the oxidation and deactivation of the iron carbide phase. The raw materials used in this invention, such as iron, zinc, and cobalt, are widely available and inexpensive, making them suitable for large-scale industrial preparation. Attached Figure Description

[0022] Figure 1 The performance test results of the catalyst obtained in Example 1 of the present invention are shown;

[0023] Figure 2 The performance test results of the catalyst obtained in Example 2 of the present invention are shown;

[0024] Figure 3 The performance test results of the catalyst obtained in Example 5 of the present invention are shown;

[0025] Figure 4 The performance test results of the catalysts obtained in Examples 2 to 5 of this invention are shown.

[0026] Figure 5 The diagram shows a comparison of O / P, CO2 activity, and olefin yield of the catalysts obtained in Examples 2 to 5 of this invention.

[0027] Figure 6 The accompanying diagram shows a comparison between the catalysts obtained in Examples 3 to 5 of this invention and relevant studies at home and abroad;

[0028] Figure 7 The X-ray diffraction analysis diagrams of the four reduced catalysts and the catalysts after reaction for 36 hours in Examples 2-5 of the present invention are shown. Detailed Implementation

[0029] The following examples are used to illustrate preferred embodiments of the invention. Those skilled in the art will understand that the techniques disclosed in the examples represent techniques discovered by the inventors that can be used to implement the invention, and therefore can be considered preferred embodiments for implementing the invention. However, those skilled in the art should understand from this specification that many modifications can be made to the specific embodiments disclosed herein, still yielding the same or similar results, without departing from the spirit or scope of the invention.

[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs, and the materials described herein will be referred to by the names given in the references cited herein and throughout the specification. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the application described herein. Such equivalents are intended to be encompassed by the following claims.

[0031] A preparation method of an iron-based catalyst for carbon dioxide to olefin, comprising the following steps:

[0032] S1, preparing a precipitant sodium hydroxide solution;

[0033] S2, weighing 5-20 mmol of iron nitrate nonahydrate, dissolving it in deionized water to obtain an iron nitrate solution;

[0034] S3, according to the molar ratio (1-4):1 of iron nitrate nonahydrate to cobalt nitrate hexahydrate and iron nitrate nonahydrate to zinc nitrate hexahydrate, respectively weighing cobalt nitrate hexahydrate and zinc nitrate hexahydrate, and adding them to the iron nitrate solution obtained in S2 to configure a mixed solution;

[0035] S4, slowly adding the mixed solution to the sodium hydroxide solution obtained in S1, stirring for 25-35 minutes, and then transferring to a hydrothermal reaction kettle, the hydrothermal reaction temperature is 150-200°C; 1%-4% of propionaldehyde by volume is added to the hydrothermal reaction kettle as a reducing agent; the reduction temperature is 300-350°C, and the time is 3-5 hours;

[0036] S5, after hydrothermal reaction for 8-24 hours, the product is washed with anhydrous ethanol and deionized water, and dried at 90-100°C;

[0037] S6, reducing the dried catalyst in pure hydrogen to obtain the desired iron-based catalyst.

[0038] The technical solutions of the present application will be further described in detail below in conjunction with specific embodiments.

[0039] Example 1

[0040] (1) Prepare 40 mL of 5 mol / L sodium hydroxide solution as a precipitant;

[0041] (2) Weigh 15 mmol of iron nitrate nonahydrate, dissolve it in 40 mL of deionized water;

[0042] (3) Slowly add the iron nitrate solution to the sodium hydroxide solution, stir for 30 minutes, and then transfer to a hydrothermal reaction kettle with a polytetrafluoroethylene liner;

[0043] (4) After 24 hours of hydrothermal reaction at 180°C, the product was washed with anhydrous ethanol and deionized water respectively, and dried at 90°C;

[0044] (5) The dried catalyst was reduced in pure hydrogen at 350°C for 4 hours to obtain an unreduced iron-based catalyst.

[0045] Example 2

[0046] (1) A 40 mL 5 mol / L sodium hydroxide solution was prepared as a precipitant;

[0047] (2) 15 mmol of iron nitrate nonahydrate was weighed and dissolved in 40 mL of deionized water;

[0048] (3) The iron nitrate solution was slowly added to the sodium hydroxide solution, stirred for 30 minutes, and then transferred to a polytetrafluoroethylene-lined hydrothermal reactor, with 1 mL of propyl aldehyde added as a reducing agent;

[0049] (4) After 24 hours of hydrothermal reaction at 180°C, the product was washed with anhydrous ethanol and deionized water respectively, and dried at 90°C;

[0050] (5) The dried catalyst was reduced in pure hydrogen at 350°C for 4 hours to obtain a reduced iron-based catalyst, denoted as Fe catalyst.

[0051] Example 3

[0052] (1) A 40 mL 5 mol / L sodium hydroxide solution was prepared as a precipitant;

[0053] (2) 15 mmol of iron nitrate nonahydrate was weighed and dissolved in 40 mL of deionized water;

[0054] (3) Zinc nitrate hexahydrate was weighed according to a molar ratio of 3:1 of iron nitrate nonahydrate to zinc nitrate hexahydrate, and added to the iron nitrate solution to prepare a mixed solution;

[0055] (4) The mixed solution was slowly added to the sodium hydroxide solution, stirred for 30 minutes, and then transferred to a polytetrafluoroethylene-lined hydrothermal reactor, with 1 mL of propyl aldehyde added as a reducing agent;

[0056] (5) After 24 hours of hydrothermal reaction at 180°C, the product was washed with anhydrous ethanol and deionized water respectively, and dried at 90°C;

[0057] (6) The dried catalyst was reduced in pure hydrogen at 350°C for 4 hours to obtain an iron-based catalyst, denoted as FeZn catalyst.

[0058] Example 4

[0059] (1) Prepare 40 mL of 5 mol / L sodium hydroxide solution as precipitant;

[0060] (2) Take 15 mmol of iron nitrate nonahydrate and dissolve it in 40 mL of deionized water;

[0061] (3) Take cobalt nitrate hexahydrate according to the molar ratio of iron nitrate nonahydrate to cobalt nitrate hexahydrate of 3:1, and add it to the iron nitrate solution to configure a mixed solution;

[0062] (4) Slowly add the mixed solution to the sodium hydroxide solution, stir for 30 minutes, then transfer to a polytetrafluoroethylene-lined hydrothermal reactor, and add 1 mL of propyl aldehyde as a reducing agent;

[0063] (5) After hydrothermal reaction at 180°C for 24 hours, wash the product with anhydrous ethanol and deionized water respectively, and dry at 90°C;

[0064] (6) Reduce the dried catalyst in pure hydrogen at 350°C for 4 hours to obtain an iron-based catalyst, denoted as FeCo catalyst.

[0065] Example 5

[0066] (1) Prepare 40 mL of 5 mol / L sodium hydroxide solution as precipitant;

[0067] (2) Take 15 mmol of iron nitrate nonahydrate and dissolve it in 40 mL of deionized water;

[0068] (3) Take zinc nitrate hexahydrate and cobalt nitrate hexahydrate according to the molar ratio of iron nitrate nonahydrate to zinc nitrate hexahydrate and iron nitrate nonahydrate to cobalt nitrate hexahydrate of 3:1, respectively, and add them to the iron nitrate solution to configure a mixed solution;

[0069] (4) Slowly add the mixed solution to the sodium hydroxide solution, stir for 30 minutes, then transfer to a polytetrafluoroethylene-lined hydrothermal reactor, and add 1 mL of propyl aldehyde as a reducing agent;

[0070] (5) After hydrothermal reaction at 180°C for 24 hours, wash the product with anhydrous ethanol and deionized water respectively, and dry at 90°C;

[0071] (6) Reduce the dried catalyst in pure hydrogen at 350°C for 4 hours to obtain a zinc-cobalt co-doped iron-based catalyst, denoted as FeZeCo catalyst.

[0072] Test analysis:

[0073] (1) The performance of the catalysts obtained in Examples 1 to 5 was evaluated in a fixed bed reactor as follows: the reaction temperature was set to 340 ℃, the reaction pressure was 2 MPa, the carbon dioxide flow rate was 20 mL / min, the hydrogen flow rate was 60 mL / min, the nitrogen flow rate was 20 mL / min, and the catalyst dosage was 0.15 g.

[0074] The test results are shown in Table 1. Figures 1 to 5

[0075] Figure 1 The results show that the carbon dioxide conversion rate of the catalyst is less than 20% in the initial stage of the reaction, and the selectivity of the byproduct carbon monoxide is extremely high (about 30%), indicating that it is difficult to form active iron carbide phases, and the reverse water gas shift reaction and methanation reaction are intensified.

[0076] Figure 2 The results show that after adding propyl aldehyde as a reducing agent, the carbon dioxide conversion rate is significantly improved to a level close to 30%, and the selectivity of the byproduct carbon monoxide is also significantly reduced (less than 20%), indicating that the addition of propyl aldehyde is beneficial to promoting the formation of iron carbide phases in the initial stage of the reaction and improving the catalytic performance.

[0077] Figure 3 The results show that the iron-based catalyst obtained by zinc and cobalt co-doping under reduction conditions in this method has a CO2 conversion rate of 20%-40% and a CO selectivity of 10%-20% at different times, and remains stable, indicating that the catalyst activity does not significantly decay during the reaction, indicating that the catalyst has much higher catalytic performance and stability than ordinary iron-based catalysts.

[0078] As can be seen from Tables 1 and 2, Figure 4 and Figure 5 the undoped Fe-based catalyst has insufficient activity, with a C2-C4 olefin space-time yield of 16.4 mmol CO2 / (h·g cat ). After zinc doping, the carbon dioxide activation ability of the Fe-based catalyst is significantly improved, but the promotion effect on the space-time yield of the target product C2-C4 olefin is weak. After cobalt doping, both the carbon dioxide activation ability and the space-time yield of C2-C4 olefin are significantly improved. The combination of Fe and Co significantly improves the catalytic activity and selectivity, showing a synergistic effect. FeCoZn has obvious advantages in the amount of C2-C4 olefin generated per unit time and unit volume, and it combines high CO2 conversion rate and good olefin generation ability, which is more advantageous in industrial production.

[0079] ​Compared to single-doped FeZn and FeCo catalysts, the co-doped FeCoZn catalyst exhibits further improved catalytic performance due to the complementary nature of zinc and cobalt in the modification process. The co-doped FeCoZn catalyst significantly outperforms other catalysts in terms of CO2 conversion and C2-C4 olefin yield, indicating that the Fe-Co-Zn metal combination has a synergistic effect, effectively enhancing catalytic activity and selectivity. The zinc-cobalt co-doped iron-based catalyst achieves a CO2 conversion of 44.5%, a carbon monoxide selectivity of 3.6%, and a C... 2+ The olefin selectivity was 83.6%, the C2-C4 olefin selectivity was 27.2%, and the space-time yield of C2-C4 olefins was 41.7 mmol. CO2 / (h·g cat The carbon dioxide conversion rate and space-time yield of light olefins were significantly improved, while the carbon monoxide selectivity was significantly reduced.

[0080] (2) Comparison of the catalysts obtained in Examples 3 to 5 of this invention with relevant research at home and abroad. Figure 6 As shown.

[0081] The results show that, compared with relevant studies at home and abroad, the CO2 conversion rate and olefin yield of the FeCoZn catalyst prepared by the method of this application are far superior to those of traditional catalysts.

[0082] (3) X-ray diffraction (XRD) analysis was performed on the four reduced catalysts of Examples 2-5 and the catalysts after reaction for 36 h. The analysis results are shown in the figure. Figure 7 As shown.

[0083] The results showed that Co doping can form an FeCo alloy phase in the catalyst, which is beneficial to the reduction and carburization of the catalyst. A new phase was detected in the used FeCoZn catalyst. 0.85 Co 0.15 The presence of O and Fe5C2 indicates that metal oxidation and carbonization processes occurred during the reaction. These structural changes demonstrate the formation of catalytically active sites during the reaction. The FeCoZn catalyst forms a unique ZnCo co-oxide phase (Zn) during the reaction. x Co y This process (O) replaces the oxidation process of iron carbide, thereby improving the performance and stability of the catalyst.

[0084] All documents mentioned in this invention are incorporated herein by reference as if each document were individually incorporated by reference. Furthermore, it should be understood that after reading the foregoing teachings of this invention, those skilled in the art can make various alterations or modifications to this invention, and these equivalent forms also fall within the scope defined by this application.

Claims

1. A method for the preparation of an iron-based catalyst for the carbon dioxide to olefin process, characterized by, It comprises the following steps: S1, preparing a precipitant sodium hydroxide solution; S2, weighing 5-20 mmol of iron nitrate nonahydrate, dissolving it in deionized water to obtain an iron nitrate solution; S3, according to the molar ratio of iron nitrate nonahydrate to cobalt nitrate hexahydrate and iron nitrate nonahydrate to zinc nitrate hexahydrate (1-4):1, weighing cobalt nitrate hexahydrate and zinc nitrate hexahydrate respectively, and adding them to the iron nitrate solution obtained in S2 to prepare a mixed solution; S4, slowly adding the mixed solution to the sodium hydroxide solution obtained in S1, stirring for 25-35 minutes, and then transferring to a hydrothermal reaction kettle, and adding propyl aldehyde as a reducing agent in the hydrothermal reaction kettle; S5, after hydrothermal reaction for 8-24 hours, washing the product with anhydrous ethanol and deionized water, and drying at 90-100°C; S6, reducing the dried catalyst in pure hydrogen to obtain the desired iron-based catalyst; The amount of propyl aldehyde added is 1%-4% by volume.

2. The method of claim 1, wherein: The hydrothermal reaction temperature is 150-200°C.

3. The method of claim 1, wherein: The reduction temperature is 300-350°C, and the time is 3-5 hours.

4. An iron-based catalyst prepared by the method of any one of claims 1-3.

5. The use of the iron-based catalyst of claim 4 in the conversion of carbon dioxide to olefins to improve the carbon dioxide conversion rate and improve the space-time yield of light olefins.

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