Ruthenium-based green ammonia synthesis catalyst as well as preparation method and application thereof

Abstract

The invention relates to a ruthenium-based green ammonia synthesis catalyst and a preparation method and application thereof, and the preparation method comprises the following steps: dissolving iron salt, a carbon source and a surfactant in deionized water, uniformly stirring, drying and calcining to obtain an iron-carbon precursor; and carrying out ball milling on the iron-carbon precursor and a ruthenium source, and calcining in a reducing atmosphere to obtain a ruthenium-loaded iron-carbon catalyst, namely the ruthenium-based green ammonia synthesis catalyst. The surfactant can reduce the surface tension of a solution, effectively disperse the iron source and the carbon source, prevent the iron source and the carbon source from agglomeration, maintain the dispersibility of the iron source and the carbon source, improve the interfacial compatibility between the iron source and the carbon source, enhance the contact between the iron source and the carbon source and promote the reaction uniformity; the number of active centers is increased; meanwhile, the surfactant is adsorbed on the surfaces of the particles, a limiting layer can be formed on the surfaces of the particles, particle sintering is delayed during calcination, and the size and form of a final product are controlled.

Description

Technical Field

[0001] The present invention relates to the technical field of thermal catalysis, and in particular to a ruthenium-based green ammonia synthesis catalyst, a preparation method thereof, and an application thereof. Background Art

[0002] Green ammonia is the ammonia synthesis and production without carbonization. Green hydrogen produced by green electricity and nitrogen separated from air are synthesized into green ammonia through a certain synthesis process; green ammonia has great application potential in new application scenarios and markets such as clean power fuels, clean electricity fuels (co-firing in thermal power plants), and hydrogen storage carriers, and its penetration is expected to continue to rise rapidly. Determined by the carbon footprint of hydrogen, the preparation of ammonia can be divided into three categories: gray ammonia, blue ammonia, and green ammonia; green ammonia - the production of green ammonia by coupling green hydrogen produced by green electricity, realizing a highly efficient ammonia synthesis process with clean zero carbon emissions. The technical process has not been finalized yet. Comparatively speaking, the flexible low-temperature and low-pressure method is more suitable for the production conditions of green ammonia and is expected to become the mainstream technical path for large-scale production of green ammonia. At present, the outlet pressure of some electrolytic water hydrogen production can reach 3 MPa. If it can be directly used as a hydrogen source and input into the ammonia synthesis tower, it will greatly reduce energy consumption, reduce equipment requirements, eliminate the need to use compressors, and reduce the floor area. Thus, it is expected to achieve the goal of distributed ammonia production and continuously produce ammonia for small-scale ammonia demand scenarios.

[0003] Based on the demand and feasibility of green ammonia, the most important thing at present is to seek a catalyst that exhibits excellent catalytic ammonia synthesis yield at relatively low temperatures and pressures. Ruthenium-based catalysts can significantly reduce the temperature and pressure required for the ammonia synthesis reaction. However, ruthenium is prone to combine with the generated active hydrogen during the reaction, resulting in hydrogen poisoning, which affects the stability and service life of the catalyst. Summary of the Invention

[0004] Based on this, the object of the present invention is to provide a ruthenium-based green ammonia synthesis catalyst, a preparation method thereof, and an application thereof. The ruthenium-based green ammonia synthesis catalyst uses an iron-carbon material as a carrier, provides a good hydrogen dispersion environment for ruthenium, can timely transfer the formed active H during the reaction, avoid ruthenium poisoning, and thus ensure that the prepared catalyst has good activity and can operate stably for a long time.

[0005] To achieve the above object, the present invention adopts the following technical solutions: The present invention first provides a preparation method of a ruthenium-based green ammonia synthesis catalyst, which includes the following steps: S1. Dissolve an iron salt, a carbon source, and a surfactant in deionized water, stir evenly, dry, and calcine to obtain an iron-carbon precursor; S2. Ball-mill the iron-carbon precursor and a ruthenium source, and then calcine in a reducing atmosphere to obtain a ruthenium-loaded iron-carbon catalyst, which is the ruthenium-based green ammonia synthesis catalyst.

[0006] As a further improvement of the above solution of the present invention, in step S1, the iron salt is at least one of iron nitrate, iron sulfate, iron oxalate, ferrocene, and iron hydroxide; And / or, in step S1, the carbon source is at least one of glucose, sucrose, starch, and cellulose; And / or, in step S1, the surfactant is at least one of sodium dodecyl sulfonate, cetyltrimethylammonium bromide, polyvinylpyrrolidone, and polyvinyl alcohol.

[0007] As a further improvement of the above solution of the present invention, in step S1, the mass ratio of the surfactant to the iron salt is (0.01~0.5):1; and / or, in the iron-carbon precursor, the mass ratio of iron element to carbon element is 1:(0.1~1).

[0008] As a further improvement of the above solution of the present invention, in step S1, the stirring is magnetic stirring, the stirring speed is 300 rpm to 700 rpm, and the time is 10 to 24 h; And / or, in step S1, the drying temperature is 50~100 °C, and the time is 5~20 h; And / or, in step S1, the calcination is carried out in an air atmosphere, the temperature is 300~500 °C, and the time is 5~20 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 acetate, ruthenium nitrosyl nitrate, and dodecacarbonyltriruthenium.

[0010] As a further improvement of the above solution of the present invention, in step S2, the mass ratio of ruthenium element in the ruthenium source to the iron-carbon precursor is (0.01~0.1):1.

[0011] As a further improvement of the above solution of the present invention, in step S2, the ball milling speed is 300~600 rpm, and the time is 2~10 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 300~500 °C for 2~10 h; in the mixed gas of hydrogen and argon, the volume percentage of H 2 is 5%~10%.

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

[0013] The present invention also provides an application of a ruthenium-based green ammonia synthesis 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: loading the ruthenium-based green ammonia synthesis catalyst into the reaction tube of the ammonia synthesis fixed reaction bed, and introducing N 2 and H 2 mixed gas, and heating for catalytic reaction; in the N 2 and H 2 mixed gas, the molar ratio of N 2 and H 2 is 1:3, and the flow rate of the N 2 and H 2 mixed gas is 10-300 mL / min; the temperature of the heating catalytic reaction is 100-400 °C, and the pressure is 0.1-3 MPa.

[0015] Compared with the prior art, the present invention has the following beneficial effects: 1. In the present invention, an iron-carbon precursor is prepared from an iron source and a carbon source under the action of a surfactant. The surfactant can reduce the surface tension of the solution, effectively disperse the iron source and the carbon source, prevent the iron source and the carbon source from agglomerating, maintain the dispersibility of the iron source and the carbon source, improve the interfacial compatibility between the iron source and the carbon source, enhance their contact, promote the uniformity of the reaction, and increase the number of active centers; at the same time, the surfactant adsorbs on the particle surface, and can form a limiting layer on the particle surface, delaying particle sintering during calcination and controlling the size and morphology of the final product.

[0016] 2. The ruthenium-based green ammonia synthesis catalyst prepared by the present invention uses an iron-carbon material as a carrier. The iron-carbon material has excellent electrical conductivity, thermal stability and chemical stability, provides a good hydrogen dispersion environment for ruthenium, and can transfer the formed active H in time during the reaction to prevent the aggregation of H 2 on the ruthenium surface and loss of active sites, resulting in ruthenium poisoning, so as to ensure that the prepared catalyst has good activity and can operate stably for a long time. Description of the Drawings

[0017] Figure 1 is the XRD image of Ru / Fe-C-1 prepared in Example 1; Figure 2 is the SEM and Mapping images of Ru / Fe-C-1 prepared in Example 1; Figure 3 is the ammonia synthesis reaction result diagram of Ru / Fe-C-1 and Fe-C-1 at different pressures at 400 °C; Figure 4 is the ammonia synthesis stability test result diagram of the Ru / Fe-C-1 catalyst prepared in Example 1 at 400 °C and 2 MPa. Detailed 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 provides a ruthenium-based green ammonia synthesis catalyst, and its preparation includes the following steps: S1. Weigh 12.12 g of iron(III) nitrate nonahydrate, 2 g of glucose, and 2.42 g of polyvinylpyrrolidone and dissolve them in 50 mL of deionized water. Stir magnetically at 500 rpm for 12 h, and then dry the solution in an oven at 100 °C for 12 h. Scrape the dried product and place it in a muffle furnace. Heat it to 400 °C and keep it at 400 °C for 6 h to obtain an iron-carbon precursor.

[0021] S2. Put 5 g of the iron-carbon precursor obtained in step S1 and 0.1 g of ruthenium acetylacetonate into a zirconia grinding jar, set the ball milling speed at 600 rpm, and the ball milling time at 6 h. After ball milling is completed, take out the material and place it in a tube furnace. Pass a mixed gas of hydrogen and argon (the volume percentage of H 2 is 10%), heat it to 400 °C at a heating rate of 2 °C / min, and keep it at this temperature for 5 h to obtain a ruthenium-based green ammonia synthesis catalyst, denoted as Ru / Fe-C-1.

[0022] Figure 1 The X-ray diffraction pattern obtained by XRD characterization (XRD, Cu-Kα, λ = 1.5406 Å) of Ru / Fe-C-1 prepared in this example is shown. It can be seen that Figure 1 Ru / Fe-C-1 prepared in this example has good crystallinity, corresponding to the standard cards (Fe: PDF#06-0696) and (C: PDF#46-0944) respectively. Since the content of single-atom Ru is very low and cannot be detected by the instrument, the characteristic peak of Ru does not appear in the X-ray diffraction pattern.

[0023] Figure 2 The imaging diagram of the scanning electron microscope and the Mapping diagram of the surface scan of Ru / Fe-C-1 prepared in Example 1 are shown. It can be found that the overall morphology is a flaky structure, and Ru, Fe, and C are evenly distributed.

[0024] 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, ruthenium acetylacetonate was not added, and finally an iron-carbon catalyst without ruthenium was prepared, denoted as Fe-C-1.

[0025] Test Example 1 Take 1 g of Ru / Fe-C-1 prepared in Example 1 and 1 g of Fe-C-1 prepared in Comparative Example 1 and load them into the quartz reaction tube of the ammonia synthesis fixed-bed reactor respectively. A mixed gas of nitrogen and hydrogen (by molar ratio, N 2 :H 2 =1:3) was introduced into the quartz reaction tube at a flow rate of 90 mL / min. The reaction temperature was fixed at 400 °C, the reaction pressure was adjusted, and the generated ammonia was detected. The ammonia yield was calculated to obtain the ammonia synthesis reaction rate at different pressures at 400 °C as shown in Figure 3 the following figure.

[0026] From Figure 3 the figure, it can be seen that compared with Comparative Example 1, after loading Ru in Example 1, the activity of catalytic ammonia synthesis has been significantly improved.

[0027] Take 1 g of Ru / Fe-C-1 prepared in Example 1 and load it into the quartz reaction tube of the ammonia synthesis fixed-bed reactor. A mixed gas of nitrogen and hydrogen (by molar ratio, N 2 :H 2 =1:3) was introduced into the quartz reaction tube at a flow rate of 90 mL / min. The reaction temperature was fixed at 400 °C and the reaction pressure was 2 MPa. 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 1 at 400 °C and 2 MPa as shown in Figure 4 the following figure. From Figure 4 the figure, it can be seen that the Ru / Fe-C-1 catalyst prepared in Example 1 was still relatively stable after reacting at 400 °C and 2 MPa for 120 h, without obvious deactivation, indicating that it has good thermal stability.

[0028] Example 2 This example proposes a ruthenium-based green ammonia synthesis catalyst, and its preparation includes the following steps: S1. Weigh 8 g of ferric sulfate, 1.5 g of starch and 2 g of cetyltrimethylammonium bromide and dissolve them in 50 mL of deionized water. Stir magnetically at 500 rpm for 10 h, and then dry the solution in an oven at 80 °C for 20 h. Scrape the dried product and place it in a muffle furnace. Heat it to 300 °C and keep it warm for 8 h to obtain an iron-carbon precursor.

[0029] S2. Place 5 g of the iron-carbon precursor obtained in step S1 and 0.2 g of ruthenium nitrosyl nitrate in a zirconia grinding jar, set the ball milling speed to 400 rpm, and the ball milling time to 12 h. After ball milling is completed, take out the material and place it in a tubular furnace, and introduce a mixed gas of hydrogen and argon (the volume percentage of H 2 is 10%), heat it to 300 °C at a heating rate of 2 °C / min and hold it at 300 °C for 8 h to obtain a ruthenium-based green ammonia synthesis catalyst, denoted as Ru / Fe-C-2.

[0030] Comparative Example 2 This comparative example uses the same implementation method as Example 2. The difference from Example 2 is that: ruthenium nitrosyl nitrate was not added in step S2 of this comparative example, and finally an iron-carbon catalyst without ruthenium was prepared, denoted as Fe-C-2.

[0031] Test Example 2 Take 1 g of Ru / Fe-C-2 prepared in Example 2 and 1 g of Fe-C-2 prepared in Comparative Example 2 and load them into the quartz reaction tube of a synthetic ammonia fixed-bed reactor respectively. Introduce a mixed gas of nitrogen and hydrogen (by molar ratio, N 2 : H 2 = 1:3) into the quartz reaction tube at a flow rate of 120 mL / min, fix the reaction temperature at 300 °C and the reaction pressure at 3 MPa, detect the generated ammonia, and calculate the ammonia yield. The results are shown in Table 1.

[0032] Table 1

[0033] It can be seen from the results in Table 1 that the Ru / Fe-C-2 catalyst prepared in Example 2 has a very high synthetic ammonia reaction rate and has a relatively obvious activity improvement compared with pure Fe-C-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 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 described in this specification.

[0035] The above-described embodiments only represent several implementation manners of the present invention. Their descriptions are relatively specific and detailed, but they should not be construed as limiting 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 deformations 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 should be subject to the appended claims.

Claims

1. A method for preparing a ruthenium-based green ammonia synthesis catalyst, characterized in that: It includes the following steps: S1. The iron salt, the carbon source and the surfactant are dissolved in deionized water, stirred evenly, dried, and calcined to obtain an iron-carbon precursor; S2. After ball-milling the iron-carbon precursor and the ruthenium source, calcining under a reducing atmosphere to obtain a ruthenium-loaded iron-carbon catalyst, which is a ruthenium-based green ammonia synthesis catalyst.

2. The method for preparing a ruthenium-based green ammonia synthesis catalyst according to claim 1, characterized in that: In step S1, the iron salt is at least one of ferric nitrate, ferric sulfate, ferric oxalate, ferrocene, and hydroxyferric; And / or, in step S1, the carbon source is at least one of glucose, sucrose, starch, and cellulose; And / or, in step S1, the surfactant is at least one of sodium dodecyl sulfate, hexadecyltrimethylammonium bromide, polyvinyl pyrrolidone, and polyvinyl alcohol.

3. The method for preparing a ruthenium-based green ammonia synthesis catalyst according to claim 1, characterized in that: In step S1, the mass ratio of the surfactant to the iron salt is (0.01-0.5):1; and / or, in the iron-carbon precursor, the mass ratio of the iron element to the carbon element is 1:(0.1-1).

4. The method for preparing a ruthenium-based green ammonia synthesis catalyst according to claim 1, characterized in that: In step S1, the stirring is magnetic stirring, the stirring speed is 300 rpm to 700 rpm, and the time is 10 to 24 hours; And / or, in step S1, the drying temperature is 50-100°C and the time is 5-20h; And / or, in step S1, the calcination is carried out in an air atmosphere at a temperature of 300-500° C. for a time of 5-20 hours.

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

6. The method for preparing a ruthenium-based green ammonia synthesis catalyst according to claim 1, characterized in that: In step S2, the mass ratio of the ruthenium element in the ruthenium source to the iron-carbon precursor is (0.01-0.1):

1.

7. The method for preparing a ruthenium-based green ammonia synthesis catalyst according to claim 1, characterized in that: In step S2, the ball milling speed is 300-600 rpm, and the time is 2-10 hours; And / or, in step S2, the calcination is carried out in a tubular furnace in a mixed atmosphere of hydrogen and argon at a temperature of 300-500°C for 2-10 hours; the volume percentage of H2 in the mixed atmosphere of hydrogen and argon is 5%-10%.

8. A ruthenium-based green ammonia synthesis 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-based green ammonia synthesis 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-based green ammonia synthesis 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 10-300 mL / min; the temperature of the heated catalytic reaction is 100-400° C., and the pressure is 0.1-3 MPa.

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