Low-temperature and low-pressure ammonia synthesis catalyst as well as preparation method and application thereof
By adding rare earth metal oxides to the iron-carbon catalyst to adjust its electron density and oxygen vacancies, the problems of high energy consumption and hydrogen poisoning of existing iron-carbon catalysts operating under high temperature and high pressure are solved, and the effect of efficient ammonia synthesis under low temperature and low pressure is achieved.
Patent Information
- Application Number
- CN202510077858.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-01-17
- Publication Date
- 2025-04-04
AI Technical Summary
The existing iron-carbon catalysts for thermally catalyzing ammonia synthesized by thermally catalyzing ammonia operate under high temperature and high pressure conditions, resulting in high energy consumption, expensive equipment costs, and prone to hydrogen poisoning, reducing catalytic activity.
The low-temperature and low-pressure ammonia catalyst is used to synthesize the low-temperature and low-pressure rare earth metal oxides, and the electron density and oxygen vacancies of the iron carbon body are adjusted through rare earth elements to improve catalytic activity and prevent hydrogen poisoning.
The efficient synthesis of ammonia at lower temperatures (≤400°C) and lower pressures (≤3MPa) is achieved, reducing energy consumption and equipment costs, and improving the activity, selectivity and stability of the catalyst.
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Figure CN119746897A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of thermal catalytic ammonia synthesis, and in particular to a low-temperature and low-pressure ammonia synthesis catalyst and a preparation method and application thereof. Background Art
[0002] Ammonia is an important basic chemical raw material, widely used in fertilizer, chemical industry, energy storage and clean fuel. 2 ) triple bond has a high bond energy barrier (945 kJ / mol), which enables hydrogen (H 2 ) and nitrogen for effective activation and reaction, so it needs to be carried out under high temperature (400-500℃) and high pressure (15-30 MPa). The entire synthetic ammonia process consumes a lot of coal and natural gas, with high energy consumption, expensive equipment costs, and significant carbon emissions. With the advancement of the global energy crisis and carbon neutrality goals, the development of catalysts and processes for efficient synthesis of ammonia under low temperature and low pressure conditions has become a research hotspot.
[0003] At present, the iron-carbon catalyst used for thermal catalytic synthesis of ammonia is mainly based on graphene / fullerene modified iron-based catalysts, which have high carbon cost and complex preparation. Studies have shown that although simple iron-carbon catalysts can reduce some reaction conditions, the reaction pressure needs to be around 7MPa, which still requires high energy consumption and equipment costs. At the same time, conventional iron-carbon catalysts are prone to hydrogen poisoning during the reaction, resulting in a decrease in catalyst activity. In order to maintain activity, the catalyst needs to be regenerated frequently, which increases operational complexity and cost. On this basis, it is necessary to improve the existing iron-carbon catalyst with a low-cost, easy-to-operate method. Summary of the invention
[0004] Based on this, the purpose of the present invention is to provide a low-temperature and low-pressure ammonia synthesis catalyst and a preparation method and application thereof. By optimizing the structure and composition of the catalyst, using cheap and readily available Fe source and C source, and without complicated operation, the prepared catalyst can enable the ammonia synthesis reaction to be carried out at a lower temperature (≤400°C) and lower pressure (≤3MPa), thereby further reducing energy consumption and equipment costs.
[0005] To achieve the above object, the present invention adopts the following technical solutions: The present invention first provides a low-temperature and low-pressure ammonia synthesis catalyst, which comprises a main body and a support, wherein the main body is composed of Fe and C, and the support is a rare earth metal oxide.
[0006] The low-temperature and low-pressure ammonia synthesis catalyst provided by the present invention is composed of iron and carbon as the main body and loaded with rare earth metal oxides. The rare earth elements can adjust the electron density of the iron-carbon main body through electronic effect and spatial effect, improve the adsorption capacity of the iron-carbon main body to the target reactant, and thus enhance the catalytic activity of the iron-carbon main body; the rare earth elements can also promote the formation of oxygen vacancies on the surface of the iron-carbon main body, optimize the redox characteristics and improve the anti-poisoning ability of the iron-carbon main body, and can effectively prevent the hydrogen poisoning phenomenon of the iron-carbon main body during the catalytic process; the iron-carbon catalyst modified by the rare earth elements of the present invention can significantly improve the catalytic activity, selectivity and stability of the iron-carbon catalyst.
[0007] As a further improvement of the above solution of the present invention, in the main body, the mass ratio of Fe to C is 1:(0.01~0.2).
[0008] As a further improvement of the above scheme of the present invention, in the low-temperature and low-pressure ammonia synthesis catalyst, the mass percentage of the rare earth metal is 1% to 10%.
[0009] As a further improvement of the above-mentioned scheme of the present invention, the rare earth metal oxide is at least one of the oxides of lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), and yttrium (Y).
[0010] The present invention also provides a method for preparing the low-temperature and low-pressure ammonia synthesis catalyst as described above, which comprises the following steps: ball-milling an iron source, a carbon source, and a rare earth metal oxide together to obtain a catalyst precursor; and calcining the catalyst precursor to obtain a low-temperature and low-pressure ammonia synthesis catalyst.
[0011] As a further improvement of the above solution of the present invention, the iron source is iron powder; And / or, the carbon source is one of glucose, sucrose, starch and cellulose.
[0012] As a further improvement of the above scheme of the present invention, the ball-to-material ratio of the ball mill is 1-50:1, the ball mill speed is 200-800 rpm, and the ball mill time is 1-24 hours.
[0013] As a further improvement of the above scheme of the present invention, the calcination is carried out in a tubular furnace under H 2 and Ar mixed atmosphere, calcined at 200-500°C for 2-10h, the heating rate of the calcination is 1-5°C / min; in the mixed gas, H 2 The volume percentage is 5%~10%.
[0014] The present invention also provides an application of the low-temperature and low-pressure ammonia synthesis catalyst as described above in low-temperature and low-pressure thermal catalytic ammonia synthesis, which comprises the following steps: loading the low-temperature and low-pressure ammonia synthesis catalyst into a reaction tube of a fixed ammonia synthesis reaction bed, introducing N 2 and H 2 The mixed gas is heated and catalytically reacted.
[0015] As a further improvement of the above solution of the present invention, in the mixed gas, N 2 and H 2 The molar ratio is 1:0.5~5, the flow rate of the mixed gas is 10~300mL / min; the temperature of the heating catalytic reaction is 100~400℃, and the pressure is 0.1~3MPa.
[0016] Compared with the prior art, the present invention has the following beneficial effects: 1. The low-temperature and low-pressure ammonia synthesis catalyst provided by the present invention is composed of iron and carbon as the main body and loaded with rare earth metal oxides. The rare earth elements can adjust the electron density of the iron-carbon main body through electronic effect and spatial effect, improve the adsorption capacity of the iron-carbon main body to the target reactant, thereby enhancing the catalytic activity of the iron-carbon main body; the rare earth elements can also promote the formation of oxygen vacancies on the surface of the iron-carbon main body, optimize the redox characteristics and improve the anti-poisoning ability of the iron-carbon main body, and can effectively prevent the hydrogen poisoning phenomenon of the iron-carbon main body during the catalytic process; the iron-carbon catalyst modified by the rare earth elements of the present invention can significantly improve the catalytic activity, selectivity and stability of the iron-carbon catalyst.
[0017] 2. Compared with traditional Fe-based catalysts, the low-temperature and low-pressure ammonia synthesis catalyst provided by the present invention can exhibit excellent ammonia synthesis reaction rate under milder reaction conditions (temperature ≤ 400°C, pressure ≤ 3MPa), and has better thermal stability, which can effectively reduce the problems of large volume, high equipment requirements, energy consumption and environmental pollution caused by high temperature and high pressure reaction conditions in traditional ammonia synthesis processes.
[0018] 3. The present invention adopts a simple ball milling and high-temperature calcination method, which can simply and quickly synthesize a large amount of catalysts. Fe powder, carbon source and rare earth metal oxide are directly dry-milled and then calcined in a reducing atmosphere to obtain an iron-carbon catalyst modified with a rare earth element. The grinding medium and the material to be synthesized in the ball mill are caused to collide and rub against each other through rotation and vibration, thereby significantly reducing the size of the material particles and increasing the surface area of the particles, which is beneficial to improving the activity and availability of the catalyst; the high-energy impact and local high temperature during the ball milling process can promote solid-state reactions, causing the raw materials to undergo chemical reactions to form new compounds; through appropriate ball milling conditions, a catalyst with nanometer size, high surface area and unique physical and chemical properties can be obtained; the method of the present invention is simple to operate, has a high raw material utilization rate, and can be prepared in large quantities. BRIEF DESCRIPTION OF THE DRAWINGS
[0019] Figure 1 This is a scanning electron microscope photograph of the low-temperature and low-pressure ammonia synthesis catalyst Ce / Fe-C prepared in Example 1; Figure 2 This is a scanning electron microscope photograph of the low-temperature and low-pressure ammonia synthesis catalyst La / Fe-C prepared in Example 2. DETAILED DESCRIPTION
[0020] For ease of understanding of the present invention, the present invention will be described more fully 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 thoroughly understood.
[0021] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. 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.
[0022] Example 1 This embodiment provides a low-temperature and low-pressure ammonia synthesis catalyst, and the preparation method thereof comprises the following steps: weighing 10g iron powder, 5g glucose and 0.74g CeO 2 The material was placed in a grinding jar for ball milling, with a grinding ball to material mass ratio of 30:1, a ball milling speed of 600 rpm, and a ball milling time of 10 h. After ball milling, a catalyst precursor was obtained, which was placed in a tubular furnace, and a mixture of hydrogen and argon (the volume percentage of hydrogen was 10%) was introduced at a rate of 20 mL / min, and the temperature was raised to 400 ° C at a rate of 3 ° C / min, and kept at 400 ° C for 4 h to obtain a low-temperature and low-pressure ammonia synthesis catalyst Ce / Fe-C.
[0023] Figure 1 The low-temperature and low-pressure ammonia synthesis catalyst Ce / Fe-C prepared in this example was characterized by transmission electron microscopy to obtain scanning electron microscope photos. Figure 1 It can be seen that the main body of the Ce / Fe-C prepared in this embodiment presents a flaky structure, and the Ce, Fe and C elements are evenly distributed.
[0024] Comparative Example 1 This comparative example adopts the same implementation method as Example 1, and the difference from Example 1 is that CeO is not added in this comparative example. 2 , to obtain the synthetic ammonia catalyst Fe-C.
[0025] Test Example 1 This test example tests the catalytic activity of the catalysts prepared in Example 1 and Comparative Example 1 as thermal catalytic synthesis of ammonia, wherein the thermal catalytic synthesis of ammonia is as follows: 500 mg of the catalyst is loaded into a quartz reaction tube of a fixed bed reactor for synthesis of ammonia, the reaction temperature is fixed at 400°C, the reaction pressure is 3 MPa, N 2 :H 2 The molar ratio was 1:3, the flow rate was 90 mL / min, the generated ammonia was collected and the ammonia yield was calculated. The results are shown in Table 1.
[0026] The ammonia yield is calculated by passing the collected ammonia into H 2 SO 4 solution (0.1mol / L), in acid solution NH 3 Transformed to NH 4 + , using UV spectrophotometer to calculate H 2 SO 4 NH in solution 4 + The specific method is salicylic acid-hypochlorite spectrophotometry. The specific principle is that in the presence of alkaline medium (pH = 11.7) and sodium nitrosoferricyanide, ammonia and ammonium ions in water react with salicylate and hypochlorite ions to generate a blue compound with a maximum absorption peak at 697 nm. The absorbance can be measured by a spectrophotometer to quantitatively analyze the concentration of ammonia. 4 Cl as NH 4 + Standard substances with different concentrations of NH 4 Cl solution, according to the above salicylic acid-hypochlorite spectrophotometry, a NH 4 + Concentration-absorbance standard curve; H 2 SO 4 The solution is tested with the same test method as the standard curve and substituted into the standard curve to obtain H 2 SO 4 NH in solution 4 + Concentration. Then calculate the ammonia yield according to the following formula:
[0027] Where: Represents NH 4 + The concentration difference, represents the mass of the catalyst, t Represents reaction time.
[0028] Table 1
[0029] It can be seen from the results in Table 1 that, compared with Fe-C prepared in Comparative Example 1, the low-temperature and low-pressure ammonia synthesis catalyst Ce / Fe-C prepared in Example 1 has a very high ammonia synthesis reaction rate and a significant improvement in activity.
[0030] Example 2 This embodiment provides a low-temperature and low-pressure ammonia synthesis catalyst, and the preparation method thereof comprises the following steps: weighing 10g iron powder, 4.55g starch and 1.4g La 2 O 3 The mixture was placed in a grinding jar for ball milling, with a grinding ball to material mass ratio of 40:1, a ball milling speed of 400 rpm, and a ball milling time of 15 h. After ball milling, a catalyst precursor was obtained, which was placed in a tubular furnace, and a mixture of hydrogen and argon (the volume percentage of hydrogen was 10%) was introduced at a rate of 20 mL / min, and the temperature was raised to 500 ° C at a rate of 2 ° C / min, and kept warm for 2 h to obtain a low-temperature and low-pressure ammonia synthesis catalyst La / Fe-C.
[0031] Figure 2 The La / Fe-C prepared in this example is characterized by a transmission electron microscope and a scanning electron microscope photograph. Figure 2 It can be seen that the La / Fe-C prepared in this embodiment has a flaky structure, and the La, Fe and C elements are evenly distributed.
[0032] Comparative Example 2 This comparative example adopts the same implementation method as Example 2, and the difference from Example 2 is that La is not added in this comparative example. 2 O 3 , to obtain the synthetic ammonia catalyst Fe-C.
[0033] Test Example 2 This test example tests the catalytic activity of the catalysts prepared in Example 2 and Comparative Example 2 as thermal catalytic synthesis of ammonia, wherein the thermal catalytic synthesis of ammonia is as follows: 500 mg of the catalyst is loaded into a quartz reaction tube of a fixed bed reactor for synthesis of ammonia, the reaction temperature is fixed at 300°C, the reaction pressure is 3 MPa, N 2 :H 2 The molar ratio of is 2:3, the flow rate is 120 mL / min, and the ammonia yield is calculated (the ammonia yield calculation method is the same as that of Test Example 1). The results are shown in Table 2.
[0034] Table 2
[0035] It can be seen from the results in Table 2 that, compared with Fe-C prepared in Comparative Example 2, the low-temperature and low-pressure ammonia synthesis catalyst La / Fe-C prepared in Example 2 has a very high ammonia synthesis reaction rate and a significant improvement in activity.
[0036] Example 3 This embodiment provides a low-temperature and low-pressure ammonia synthesis catalyst, and the preparation method thereof comprises the following steps: weighing 10g of iron powder, 5g of starch and 1.16g of Sm 2 O 3 The mixture was placed in a grinding jar for ball milling, with a grinding ball to material mass ratio of 30:1, a ball milling speed of 400 rpm, and a ball milling time of 12 h. After ball milling, a catalyst precursor was obtained, which was placed in a tubular furnace, and a mixture of hydrogen and argon (hydrogen volume percentage of 5%) was introduced at a rate of 20 mL / min, and the temperature was raised to 300 ° C at a rate of 5 ° C / min, and kept warm for 6 h to obtain a Sm / Fe-C catalyst.
[0037] Comparative Example 3 This comparative example adopts the same implementation method as Example 3, and the difference from Example 3 is that Sm is not added in this comparative example. 2 O 3 , to obtain the synthetic ammonia catalyst Fe-C.
[0038] Test Example 3 This test example tests the catalytic activity of the catalysts prepared in Example 3 and Comparative Example 3 as thermal catalytic synthesis of ammonia, wherein the thermal catalytic synthesis of ammonia is as follows: 500 mg of the catalyst is loaded into a quartz reaction tube of a fixed bed reactor for synthesis of ammonia, the reaction temperature is fixed at 400°C, the reaction pressure is 2 MPa, N 2 :H 2 The molar ratio of is 1:4, the flow rate is 40 mL / min, and the ammonia yield is calculated (the ammonia yield calculation method is the same as that of Test Example 1). The results are shown in Table 3.
[0039] Table 3
[0040] It can be seen from the results in Table 3 that, compared with the Fe-C prepared in Comparative Example 3, the low-temperature and low-pressure ammonia synthesis catalyst Sm / Fe-C prepared in Example 3 has a very high ammonia synthesis reaction rate and a significant improvement in activity.
[0041] Example 4 This embodiment provides a low-temperature and low-pressure ammonia synthesis catalyst, and the preparation method thereof comprises the following steps: weighing 10 g of iron powder, 8 g of cellulose and 1.28 g of Er 2 O 3The mixture was placed in a grinding jar for ball milling, with a grinding ball to material mass ratio of 40:1, a ball milling speed of 500 rpm, and a ball milling time of 6 hours. After ball milling, a catalyst precursor was obtained, which was placed in a tubular furnace, and a mixture of hydrogen and argon (the volume percentage of hydrogen was 5%) was introduced at a rate of 20 mL / min, and the temperature was raised to 400°C at a rate of 3°C / min, and kept warm for 8 hours to obtain an Er / Fe-C catalyst.
[0042] Comparative Example 4 This comparative example adopts the same implementation method as Example 4, and the difference from Example 4 is that Er is not added in this comparative example. 2 O 3 , to obtain the synthetic ammonia catalyst Fe-C.
[0043] Test Example 4 This test example tests the catalytic activity of the catalysts prepared in Example 4 and Comparative Example 4 as thermal catalytic synthesis of ammonia, wherein the thermal catalytic synthesis of ammonia is as follows: 500 mg of the catalyst is loaded into a quartz reaction tube of a fixed bed reactor for synthesis of ammonia, the reaction temperature is fixed at 300°C, the reaction pressure is 3 MPa, N 2 :H 2 The molar ratio of is 1:3, the flow rate is 160 mL / min, and the ammonia yield is calculated (the ammonia yield calculation method is the same as that of Test Example 1). The results are shown in Table 4.
[0044] Table 4
[0045] It can be seen from the results in Table 4 that, compared with Fe-C prepared in Comparative Example 4, the low-temperature and low-pressure ammonia synthesis catalyst Er / Fe-C prepared in Example 4 has a very high ammonia synthesis reaction rate and a significant improvement in activity.
[0046] Example 5 This embodiment provides a low-temperature and low-pressure ammonia synthesis catalyst, and the preparation method thereof comprises the following steps: weighing 10g iron powder, 6g glucose and 0.75g Y 2 O 3 The material was placed in a grinding jar for ball milling, with a grinding ball to material mass ratio of 40:1, a ball milling speed of 300 rpm, and a ball milling time of 20 h. After the ball milling was completed, the material was taken out and placed in a tubular furnace, and a mixture of hydrogen and argon (the volume percentage of hydrogen was 10%) was introduced at a rate of 20 mL / min, and the temperature was raised to 400 °C at a heating rate of 2 °C / min, and kept warm for 4 h to obtain a Y / Fe-C catalyst.
[0047] Comparative Example 5 This comparative example adopts the same implementation method as Example 5, and the difference from Example 5 is that Y is not added in this comparative example. 2 O3 , to obtain the synthetic ammonia catalyst Fe-C.
[0048] Test Example 5 This test example tests the catalytic activity of the catalysts prepared in Example 5 and Comparative Example 5 as thermal catalytic synthesis of ammonia, wherein the thermal catalytic synthesis of ammonia is as follows: 500 mg of the catalyst is loaded into a quartz reaction tube of a fixed bed reactor for synthesis of ammonia, the reaction temperature is fixed at 300°C, the reaction pressure is 3 MPa, N 2 :H 2 The molar ratio of is 2:3, the flow rate is 80 mL / min, and the ammonia yield is calculated (the ammonia yield calculation method is the same as that of Test Example 1). The results are shown in Table 5.
[0049] Table 5
[0050] It can be seen from the results in Table 5 that, compared with the Fe-C prepared in Comparative Example 5, the low-temperature and low-pressure ammonia synthesis catalyst Y / Fe-C prepared in Example 5 has a very high ammonia synthesis reaction rate and a significant improvement in activity.
[0051] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, 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, they should be considered to be within the scope of this specification.
[0052] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.
Claims
1. A low-temperature and low-pressure ammonia synthesis catalyst, characterized in that: The low-temperature and low-pressure ammonia synthesis catalyst comprises a main body and a support supported on the main body, wherein the main body is composed of Fe and C, and the support is a rare earth metal oxide.
2. The low-temperature and low-pressure ammonia synthesis catalyst according to claim 1, characterized in that: In the main body, the mass ratio of Fe to C is 1:(0.01~0.2).
3. The low-temperature and low-pressure ammonia synthesis catalyst according to claim 1, characterized in that: In the low-temperature and low-pressure ammonia synthesis catalyst, the mass percentage of the rare earth metal is 1% to 10%.
4. The low-temperature and low-pressure ammonia synthesis catalyst according to claim 1, characterized in that: The rare earth metal oxide is at least one of oxides of lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium and yttrium.
5. A method for preparing the low-temperature and low-pressure ammonia synthesis catalyst according to any one of claims 1 to 4, characterized in that: It includes the following steps: The iron source, the carbon source and the rare earth metal oxide are ball-milled together to obtain a catalyst precursor; the catalyst precursor is calcined to obtain a low-temperature and low-pressure ammonia synthesis catalyst.
6. The method for preparing a low-temperature and low-pressure ammonia synthesis catalyst according to claim 5, characterized in that: The iron source is iron powder; And / or, the carbon source is one of glucose, sucrose, starch and cellulose.
7. The method for preparing a low-temperature and low-pressure ammonia synthesis catalyst according to claim 5, characterized in that: The ball-to-material ratio of the ball mill is 1-50:1, the ball mill speed is 200-800 rpm, and the ball mill time is 1-24 hours.
8. The method for preparing a low-temperature and low-pressure ammonia synthesis catalyst according to claim 5, characterized in that: The calcination is carried out in a tubular furnace in a mixed atmosphere of H2 and Ar at 200-500°C for 2-10 hours, and the heating rate of the calcination is 1-5°C / min; the volume percentage of H2 in the mixed gas is 5%-10%.
9. Use of the low-temperature and low-pressure ammonia synthesis catalyst according to any one of claims 1 to 4 in low-temperature and low-pressure thermal catalytic ammonia synthesis, characterized in that: It includes the following steps: The low-temperature and low-pressure ammonia synthesis catalyst is loaded into the reaction tube of the fixed ammonia synthesis bed, and a mixed gas of N2 and H2 is introduced to heat and perform a catalytic reaction.
10. The use according to claim 9, characterized in that: In the mixed gas, the molar ratio of N2 to H2 is 1:0.5~5, and the flow rate of the mixed gas is 10~300mL / min; the temperature of the heating catalytic reaction is 100~400℃, and the pressure is 0.1~3MPa.