Ruthenium-modified iron-based catalyst as well as preparation method and application thereof

Abstract

The invention relates to a ruthenium-modified iron-based catalyst and a preparation method and application thereof, and the preparation method comprises the following steps: carrying out wet grinding on iron powder, a carbon and nitrogen source and a solvent to obtain slurry, and drying the slurry to obtain a precursor; and carrying out dry grinding on the precursor and a ruthenium source, and calcining in a reducing atmosphere to obtain the ruthenium-modified iron-based catalyst. According to the ruthenium-modified iron-based catalyst prepared by the invention, a carbon-nitrogen layer is formed on the surface of Fe, then Ru loading is carried out, active hydrogen generated in the reaction process can be timely transferred to the surface of the carbon-nitrogen layer to be combined with electrons to form H2 during thermocatalytic synthesis of ammonia, and the poisoning problem of the catalyst is effectively relieved.

Description

Technical Field

[0001] The present invention relates to the field of thermal catalysis technology, and in particular to a ruthenium-modified iron-based catalyst and a preparation method and application thereof. Background Art

[0002] Based on the current development of chemistry and people's high attention to environmental pollution and energy consumption, the use of fossil energy must be reduced to reduce carbon dioxide emissions and store necessary energy as reserves. In this case, hydrogen, as a clean energy, has gained more and more attention due to its advantages such as zero terminal carbon emissions and the use of renewable energy production. Many processes and technologies based on hydrogen utilization have been developed. However, the most important issue that plagues the use of hydrogen is the storage / transportation problem.

[0003] As a hydrogen storage carrier, ammonia has the advantages of high energy density, high safety, easy storage and transportation, etc. In addition, ammonia can replace fossil energy as a fuel for direct use, and plays a very important role in chemical industries such as raw materials for explosives and fertilizers. However, the current industrial synthesis of ammonia requires high temperature and high pressure reaction conditions, which is not conducive to the use of small-scale ammonia demand scenarios. Therefore, it is necessary to develop low-temperature and low-pressure synthetic ammonia, directly use the electricity generated by renewable energy to electrolyze water to produce hydrogen for ammonia synthesis, and realize ammonia-hydrogen conversion and comprehensive utilization. Summary of the invention

[0004] Based on this, the purpose of the present invention is to provide a ruthenium-modified iron-based catalyst and its preparation method and application, wherein a carbon-nitrogen layer is first formed on the Fe surface, and then Ru is loaded. During the thermal catalytic synthesis of ammonia, the active hydrogen generated during the reaction can be transferred to the surface of the carbon-nitrogen layer to combine with electrons to form H 2 , effectively alleviating the problem of catalyst poisoning.

[0005] To achieve the above object, the present invention adopts the following technical solutions: The present invention first provides a method for preparing a ruthenium-modified iron-based catalyst, which comprises the following steps: S1. Wet-grinding iron powder, a carbon and nitrogen source and a solvent to obtain a slurry, and drying the slurry to obtain a precursor; S2. dry-grind the precursor and the ruthenium source together, and then calcine under a reducing atmosphere to obtain a ruthenium-modified iron-based catalyst.

[0006] As a further improvement of the above solution of the present invention, in step S1, the purity of the iron powder is 99.99%; And / or, in step S1, the carbon and nitrogen source is at least one of urea, dicyandiamide and melamine; And / or, in step S1, the solvent is a mixture of ethanol and water, and the volume ratio of ethanol to water in the mixture is 1:(0.1~2).

[0007] As a further improvement of the above solution of the present invention, in step S1, the addition amounts of the iron powder and the carbon and nitrogen source satisfy that the molar ratio of Fe element to C element is 1:(0.1~1).

[0008] As a further improvement of the above solution of the present invention, in step S1, the rotation speed of the wet grinding is 400 rpm to 800 rpm, and the time is 10 to 24 h; And / or, in step S1, the drying is carried out at a temperature of 50 to 100 °C for 5 to 20 h.

[0009] As a further improvement of the above solution of the present invention, in step S2, the ruthenium source is at least one of ruthenium acetylacetonate, ruthenium nitrosyl nitrate, and dodecacarbonyltriruthenium.

[0010] As a further improvement of the above solution of the present invention, in the ruthenium-modified iron-based catalyst in step S2, the content of ruthenium element is 1 wt% to 10 wt%.

[0011] As a further improvement of the above solution of the present invention, in step S2, the rotation speed of the dry grinding is 400 rpm to 800 rpm, and the time is 10 to 24 h; And / or, in step S2, the calcination is carried out in a tubular furnace under a mixed atmosphere of hydrogen and argon at a temperature of 400 to 800 °C for 2 to 10 h; in the mixed gas of hydrogen and argon, the volume percentage of H 2 is 5% to 10%.

[0012] The present invention also provides a ruthenium-modified iron-based catalyst prepared by the preparation method as described above.

[0013] The present invention also provides an application of a ruthenium-modified iron-based catalyst prepared by the preparation method as described above in ammonia synthesis.

[0014] As a further improvement of the above solution of the present invention, it includes the following steps: filling the ruthenium-modified iron-based catalyst in the reaction tube of the ammonia synthesis fixed reaction bed, introducing a mixed gas of N 2 and H 2 , and heating for catalytic reaction; in the mixed gas of N 2 and H 2 , the molar ratio of N 2 and H 2 is 1:3, the flow rate of the mixed gas of N 2 and H 2 is 40 to 400 mL / min; the temperature of the heating catalytic reaction is 100 to 500 °C, and the pressure is 0.1 to 5 MPa.

[0015] Compared with the prior art, the present invention has the following beneficial effects: 1. When preparing the precursor of the present invention, iron powder, carbonitride source and solvent are wet-milled together. During the wet-milling process, the solvent acts as a liquid medium, wrapping the iron powder and carbonitride source particles. By the wetting effect, the adhesion force between the particles is reduced, agglomeration is avoided, and the particles are more easily ground, thereby improving the grinding efficiency and fineness, increasing the specific surface area of the material, which is crucial for improving its reactivity and adsorption capacity; and the dissolved carbonitride molecules are more likely to penetrate to the surface of the iron powder, promoting carbonitride doping or coating in the subsequent heat treatment; in addition, the liquid medium can effectively act as a coolant to prevent the carbon from gelatinizing and agglomerating due to excessive local temperature; and with the assistance of the solvent, the wet-milling can effectively crush the iron powder to the nanoscale, while the carbonitride source is uniformly coated on the surface of the iron powder, thus finally obtaining an iron-based carbonitride precursor with excellent performance. Then, after dry-milling the precursor with a ruthenium source and calcining, a ruthenium-modified iron-based catalyst can be obtained. The method of the present invention is simple in operation, high in raw material utilization rate, and can be prepared in large quantities.

[0016] 2. The ruthenium-modified iron-based catalyst prepared by the present invention forms a carbonitride layer on the surface of Fe, and then Ru is loaded. When thermally catalyzing ammonia synthesis, the active hydrogen generated during the reaction process can be timely transferred to the surface of the carbonitride layer to combine with electrons to form H 2 , effectively alleviating the problem of catalyst poisoning. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 SEM and Mapping images of Ru 1% / Fe-CN-1 prepared in Example 1; Figure 2 Reaction results of the iron-based catalysts prepared in Examples 1-4 and Comparative Example 1 for ammonia synthesis at 400 °C and 3 MPa; Figure 3 Thermal catalytic ammonia synthesis stability test results of Ru 8% / Fe-CN-1 prepared in Example 4 at 400 °C and 3 MPa. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0018] For the convenience of understanding the present invention, the present invention will be described more comprehensively below in conjunction with specific embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present invention more thorough and comprehensive.

[0019] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which the present invention belongs. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0020] Example 1 This example presents a ruthenium-modified iron-based catalyst, and its preparation includes the following steps: S1. Add 50 mL of ethanol-aqueous solution (the volume ratio of ethanol to water is 1:1) into a polytetrafluoroethylene ball milling tank, then add 5.58 g of Fe powder (purity is 99.99%) and 3 g of urea, and then ball mill at a speed of 400 rpm for 8 h to obtain a slurry. Dry the obtained slurry at 80 °C for 8 h to obtain Fe-CN precursor powder; S2. Take 2 g of the Fe-CN precursor powder obtained in step S1 and 0.0788 g of ruthenium acetylacetonate and place them in a polytetrafluoroethylene ball milling tank, ball mill at a speed of 400 rpm for 2 h. After the ball milling is completed, take out the material and place it in a tube furnace, and introduce a mixed gas of hydrogen and argon at a rate of 30 mL / min (in the mixed gas, the volume percentage of hydrogen is 10%), heat up to 400 °C at a heating rate of 2 °C / min and keep it at 400 °C for 4 h to prepare a ruthenium-modified iron-based catalyst, denoted as Ru 1% / Fe-CN-1.

[0021] Figure 1 The scanning electron microscope imaging diagram and Mapping image of Ru 1% / Fe-CN-1 prepared in Example 1. It can be seen from Figure 1 that the overall morphology of Ru 1% / Fe-CN-1 prepared in Example 1 is a flaky structure, and Ru, Fe, C, and N are evenly distributed.

[0022] Example 2 This example adopts the same implementation method as Example 1. The difference from Example 1 is that: in step S2 of this example, the addition amount of ruthenium acetylacetonate is 0.236 g, and the finally prepared ruthenium-modified iron-based catalyst is denoted as Ru 3% / Fe-CN-1.

[0023] Example 3 This example adopts the same implementation method as Example 1. The difference from Example 1 is that: in step S2 of this example, the addition amount of ruthenium acetylacetonate is 0.394 g, and the finally prepared ruthenium-modified iron-based catalyst is denoted as Ru 5% / Fe-CN-1.

[0024] Example 4 This example adopts the same implementation method as Example 1. The difference from Example 1 is that: in step S2 of this example, the addition amount of ruthenium acetylacetonate is 0.631 g, and the finally prepared ruthenium-modified iron-based catalyst is denoted as Ru 8% / Fe-CN-1.

[0025] Comparative Example 1 This comparative example uses the same implementation method as Example 1. The difference from Example 1 is that in step S2 of this comparative example, the addition amount of ruthenium acetylacetonate is 0, and the finally prepared iron-based catalyst is denoted as Fe-CN-1.

[0026] Test Example 1 Take 1 g of Ru prepared in Example 1 1% / Fe-CN-1, 1 g of Ru prepared in Example 2 3% / Fe-CN-1, 1 g of Ru prepared in Example 3 5% / Fe-CN-1, 1 g of Ru prepared in Example 4 8% / Fe-CN-1, 1 g of Fe-CN-1 prepared in Comparative Example 1 were respectively loaded into the quartz reaction tube of the ammonia synthesis fixed-bed reactor. A mixed gas of nitrogen and hydrogen was introduced into the quartz reaction tube at a flow rate of 90 mL / min (by molar ratio, N 2 :H 2 =1:3), the reaction temperature was fixed at 400 °C, the reaction pressure was adjusted, the generated ammonia was detected, and the ammonia yield was calculated to obtain the ammonia synthesis reaction rate at different pressures at 400 °C as shown in Figure 2 the following.

[0027] From Figure 2 it can be seen that compared with Comparative Example 1, after loading Ru in Examples 1-4, the activity of catalytic ammonia synthesis has been significantly improved. The optimal Ru loading amount is 8%, and the ammonia yield reaches 19.6 mmol NH3 ·g cat -1 ·h -1 .

[0028] Test Example 2 Take 1 g of Ru prepared in Example 4 8% / Fe-CN-1 and load it into the quartz reaction tube of the ammonia synthesis fixed-bed reactor. A mixed gas of nitrogen and hydrogen was introduced into the quartz reaction tube at a flow rate of 80 mL / min (by molar ratio, N 2 :H 2 =1:3), the reaction temperature was fixed at 400 °C, the reaction pressure was 3 MPa, and the reaction time was 120 h. The outlet tail gas was collected at different time periods and the change in ammonia concentration in it was measured to obtain the thermal stability test result curve of the catalyst obtained in Example 4 at 400 °C and 3 MPa as shown in Figure 3 the following. From Figure 3 it can be seen that the Ru 8% / Fe-CN-1 catalyst prepared in Example 4 is still relatively stable after reacting at 400 °C and 3 MPa for 120 h without obvious deactivation, indicating that it has good thermal stability.

[0029] Example 5 This example presents a ruthenium-modified iron-based catalyst, and its preparation includes the following steps: S1. Add 50 mL of ethanol-aqueous solution (volume ratio of ethanol to water is 1:1) into a polytetrafluoroethylene ball milling jar, then add 5.58 g of Fe powder (purity is 99.99%) and 3 g of melamine, and then ball mill at a speed of 500 rpm for 10 h to obtain a slurry. Dry the obtained slurry at 90 °C for 10 h to obtain Fe-CN precursor powder; S2. Take 2 g of the Fe-CN precursor powder obtained in step S1 and 0.064 g of ruthenium nitrosyl nitrate and place them in a polytetrafluoroethylene ball milling jar, ball mill at a speed of 500 rpm for 3 h. After the ball milling is completed, take out the material and place it in a tubular furnace, and introduce a mixture of hydrogen and argon at a rate of 30 mL / min (in the mixture, the volume percentage of hydrogen is 10%), heat up to 500 °C at a heating rate of 2 °C / min and keep it at 500 °C for 2 h to prepare a ruthenium-modified iron-based catalyst, denoted as Ru 1% / Fe-CN-2.

[0030] Comparative Example 2 This comparative example adopts the same implementation method as Example 5. The difference from Example 5 is that in step S2 of this comparative example, the addition amount of ruthenium nitrosyl nitrate is 0, and the finally prepared iron-based catalyst is denoted as Fe-CN-2.

[0031] Test Example 3 Take 1 g of Ru 1% / Fe-CN-2 prepared in Example 5 and 1 g of Fe-CN-2 prepared in Comparative Example 2 and load them into the quartz reaction tube of a synthetic ammonia fixed bed reactor respectively. Pass a mixture of nitrogen and hydrogen into the quartz reaction tube at a flow rate of 120 mL / min (by molar ratio, N 2 :H 2 =1:3), fix the reaction temperature at 400 °C and the reaction pressure at 3 MPa, detect the generated ammonia, calculate the ammonia yield, and the results are shown in Table 1.

[0032] Table 1

[0033] As can be seen from the results in Table 1, the Ru / Fe-CN-2 catalyst prepared in Example 5 has a very high ammonia synthesis reaction rate, and there is a relatively obvious improvement in activity compared with the pure Fe-CN-2.

[0034] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope recorded in this specification.

[0035] The above-described embodiments only express several implementation manners of the present invention. The description is relatively specific and detailed, but it cannot be understood as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the appended claims.

Claims

1. A method for preparing a ruthenium-modified iron-based catalyst, characterized in that: It includes the following steps: S1. Wet-grinding iron powder, a carbon and nitrogen source and a solvent to obtain a slurry, and drying the slurry to obtain a precursor; S2. dry-grind the precursor and the ruthenium source together, and then calcine under a reducing atmosphere to obtain a ruthenium-modified iron-based catalyst.

2. The method for preparing a ruthenium-modified iron-based catalyst according to claim 1, characterized in that: In step S1, the purity of the iron powder is 99.99%; And / or, in step S1, the carbon and nitrogen source is at least one of urea, dicyandiamide and melamine; And / or, in step S1, the solvent is a mixture of ethanol and water, and the volume ratio of ethanol to water in the mixture is 1:(0.1~2).

3. The method for preparing a ruthenium-modified iron-based catalyst according to claim 1, characterized in that: In step S1, the added amounts of the iron powder and the carbon-nitrogen source satisfy: the molar ratio of the Fe element to the C element is 1:(0.1~1).

4. The method for preparing a ruthenium-modified iron-based catalyst according to claim 1, characterized in that: In step S1, the wet grinding speed is 400 rpm to 800 rpm, and the time is 2 to 24 hours; And / or, in step S1, the drying is carried out at a temperature of 50-100° C. for 5-20 hours.

5. The method for preparing a ruthenium-modified iron-based catalyst according to claim 1, characterized in that: In step S2, the ruthenium source is at least one of ruthenium acetylacetonate, ruthenium nitrosyl nitrate, and triruthenium dodecacarbonyl.

6. The method for preparing a ruthenium-modified iron-based catalyst according to claim 1, characterized in that: In step S2, the content of ruthenium element in the ruthenium-modified iron-based catalyst is 1wt%~10wt%.

7. The method for preparing a ruthenium-modified iron-based catalyst according to claim 1, characterized in that: In step S2, the dry grinding is performed at a speed of 400 rpm to 800 rpm for 2 to 24 hours; And / or, in step S2, calcination is carried out in a tubular furnace in a mixed atmosphere of hydrogen and argon at a temperature of 400-800°C for 2-10 hours; the volume percentage of H2 in the mixed atmosphere of hydrogen and argon is 5%-10%.

8. A ruthenium-modified iron-based catalyst, characterized in that: The method is prepared by the method described in any one of claims 1 to 7.

9. Use of a ruthenium-modified iron-based catalyst prepared by the preparation method according to any one of claims 1 to 7 in ammonia synthesis.

10. The use according to claim 9, characterized in that: It includes the following steps: The ruthenium-modified iron-based catalyst is loaded into a reaction tube of a fixed reaction bed for synthetic ammonia, a mixed gas of N2 and H2 is introduced, and a catalytic reaction is carried out by heating; in the mixed gas of N2 and H2, the molar ratio of N2 to H2 is 1:3, and the flow rate of the mixed gas of N2 and H2 is 40-400 mL / min; the temperature of the heated catalytic reaction is 100-500° C., and the pressure is 0.1-5 MPa.

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