Catalyst for synthesizing ammonia as well as preparation method and application of catalyst

Abstract

The invention relates to a catalyst for ammonia synthesis and a preparation method and application thereof, and belongs to the field of thermocatalytic ammonia synthesis, and the preparation method of the catalyst comprises the following steps: 1) taking alloy powder mainly containing metal iron as a raw material, printing by using a selective laser melting technology to obtain an iron-based catalyst precursor, cleaning and drying to obtain a fresh iron-based catalyst; and 2) soaking the fresh iron-based catalyst in a chlorate solution, and then drying and roasting to obtain the catalyst for ammonia synthesis. The preparation process is simple and easy to operate, green and environment-friendly, low in energy consumption and low in cost, and the catalyst is good in mass and heat transfer effect in the reaction process and high in catalytic performance and has high practical value and application prospects.

Description

Technical Field

[0001] The invention relates to the field of thermal catalytic synthesis of ammonia, and in particular to a catalyst for synthesizing ammonia and a preparation method and application thereof. Background Art

[0002] Ammonia (NH3) is an important raw material for the production of fertilizers, chemicals and medicines, and is also a promising carbon-free energy carrier. The current means of synthesizing NH3 in industry is the traditional Haber-Bosch method. However, this method requires high temperature and high pressure conditions, and while consuming fossil fuels, it will release a large amount of greenhouse gases, causing environmental pollution. Therefore, with the continuous innovation of technology, chemists have applied various new methods and technologies to the traditional synthetic ammonia industry. Thereby improving the yield and energy utilization rate of the synthetic ammonia reaction, reducing the energy consumption required for the reaction, making full use of clean energy, and reducing pollutant emissions.

[0003] The metal-based catalysts commonly used in the ammonia synthesis reaction are mainly divided into iron-based catalysts and ruthenium-based catalysts. Although the new ruthenium-based catalysts have higher catalytic performance, they are too expensive to be industrialized on a large scale. Iron-based catalysts are widely used in the thermal catalytic ammonia synthesis industry because of their excellent catalytic efficiency, good reusability and economical price. Summary of the invention

[0004] The purpose of the present invention is to solve the above problems in the prior art and to provide a catalyst for synthesizing ammonia and a preparation method and application thereof.

[0005] In order to achieve the above object, the present invention adopts the following technical scheme:

[0006] A method for preparing a catalyst for synthesizing ammonia comprises the following steps:

[0007] 1) Using alloy powder mainly composed of metallic iron as raw material, selective laser melting technology is used to print an iron-based catalyst precursor, which is then washed and dried to obtain a fresh iron-based catalyst;

[0008] 2) Soaking the fresh iron-based catalyst in a chloride salt solution, and then drying and calcining to obtain the catalyst for synthesizing ammonia.

[0009] The chloride salt includes at least one of potassium chloride, sodium chloride, calcium chloride and aluminum chloride.

[0010] The chloride salt is potassium chloride.

[0011] The concentration of the chloride salt solution is 0.5-4 mol / L.

[0012] The concentration of the chloride salt solution is 1.5 mol / L.

[0013] In step 2), the soaking time is not less than 2 hours.

[0014] In step 2), the soaking time is 2 hours.

[0015] A catalyst for synthesizing ammonia is prepared by the above preparation method.

[0016] The catalyst for synthesizing ammonia is used for synthesizing ammonia by thermal catalysis.

[0017] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0018] 1. The present invention soaks the fresh iron-based catalyst printed by 3D printing in a chloride solution and then roasts it to destroy the alloy structure and promote the formation of iron oxides, thereby improving the catalytic performance; the corrosive anion Cl - Due to its small ion radius, it is easy to penetrate from the weak points on the surface of the iron-based catalyst (inclusions, dislocation outcrops, alloy phases, holes, etc.). These weak points will become the nucleation centers of pitting corrosion, destroying the density and integrity of the alloy protective film, thereby exposing the active center; in addition, potassium ions can reduce the surface electron work function. When N2 molecules are adsorbed onto the iron surface, a dipole is formed, and the iron electrons tend to the N2 molecules, thereby weakening the triple bond of the nitrogen molecule, making nitrogen easier to dissociate and improving the activity of synthetic ammonia. Therefore, soaking the iron-based catalyst in KCl provides a new research method for combining 3D printing technology with synthetic ammonia reaction.

[0019] 2. The catalyst prepared by the present invention has excellent ability to adsorb and activate nitrogen and hydrogen. Compared with untreated fresh catalyst, the activity of thermal catalytic synthesis of nitrogen is increased by two orders of magnitude.

[0020] 3. The present invention creatively applies 3D printing technology to thermal catalytic ammonia synthesis, and can enhance the mass transfer and heat transfer of the catalytic system by designing different structures, thereby further improving the catalytic efficiency.

[0021] 4. The entire process of the present invention is simple and easy to control, the production process is green and environmentally friendly, has low energy consumption, high yield, low cost, meets actual production needs, and is conducive to large-scale promotion. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The ammonia synthesis performance diagram of the catalysts of Examples 1 to 4;

[0023] Figure 2 It is the performance diagram of synthetic ammonia of the catalyst of comparative example 1 and embodiment 1;

[0024] Figure 3 The catalyst diagrams of Example 1, Examples 5 to 8 and Comparative Example 1;

[0025] Figure 4 The XRD diagrams of the catalysts of Example 1, Examples 5 to 8, and Comparative Examples 1 to 2;

[0026] Figure 5 The ammonia synthesis performance diagram of the catalysts of Example 1, Examples 5 to 8, and Comparative Example 2;

[0027] Figure 6 It is the synthetic ammonia performance diagram of the catalysts of Example 1 and Examples 9 to 12. DETAILED DESCRIPTION

[0028] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention clearer and more understandable, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0029] Example 1

[0030] Using 316L stainless steel powder as raw material, the required target structure was printed using selective laser melting technology. The printed object was removed from the substrate by wire cutting, and then the powder residue and soap oil produced by cutting were cleaned with kerosene. After cleaning, it was vacuum dried at 60°C for 12 hours to obtain a fresh sample. 50ml of 1.5mol / L KCl solution was prepared, the fresh sample was immersed in the KCl solution for 2 hours, vacuum dried at 60°C for 12 hours, and then calcined at 700°C for 24 hours to obtain the catalyst.

[0031] The catalyst was loaded into a transparent quartz tube with an inner diameter of 12 mm. The quartz tube was placed inside the reactor and fixed in a heating furnace for ammonia synthesis reaction test. A hydrogen-nitrogen mixture with a volume ratio of 3:1 was introduced, and the program was set to rise from room temperature to 500°C at a rate of 3°C / min, reduce for 3 hours, stabilize for 2 hours, and then set to the required experimental temperature for activity test. The test temperature range was 400°C to 500°C, the pressure was 3MPa, and the gas flow rate was 200mL / min. NH4 in the solution after the reaction was analyzed by ion chromatography + The concentration is used to determine the activity of the catalyst.

[0032] Embodiments 2 to 4

[0033] Different from Example 1, Examples 2 to 4 respectively use different chloride salts for soaking, specifically 50 ml of 1.5 mol / L CaCl2 solution, 50 ml of 1.5 mol / L AlCl3 solution, and 50 ml of 1.5 mol / L NaCl solution.

[0034] Embodiments 5 to 8

[0035] Different from Example 1, Examples 5 to 8 respectively use KCl solutions of different concentrations (0.5 mol / L, 1 mol / L, 2 mol / L, and 4 mol / L) for immersion treatment.

[0036] Examples 9 to 12

[0037] Different from Example 1, Examples 9 to 12 were treated with different soaking times (0.5 h, 1 h, 3 h, 4 h), respectively.

[0038] Comparative Example 1

[0039] The 316L stainless steel powder was used as the raw material and the desired target structure was printed by selective laser melting technology. The printed object was removed from the substrate by wire cutting, and then the powder residue and soap oil produced by cutting were cleaned with kerosene. After cleaning, the catalyst was dried at 60 °C in vacuum for 12 h to obtain the unsoaked and uncalcined catalyst ( Figures 2 to 4 Indicated as Fresh).

[0040] Comparative Example 2

[0041] Based on Comparative Example 1, the unsoaked and uncalcined catalyst was calcined at 700°C for 24h to obtain a catalyst with an impregnation concentration of 0 mol / L ( Figure 4 (marked as C700-24).

[0042] Figure 1 The performance diagram of the catalyst obtained in Examples 1 to 4 shows the performance of the catalyst for synthesizing ammonia. It can be seen from the performance diagram that at a reaction temperature of 400°C, the catalyst soaked in KCl solution has better performance, while the catalyst soaked in AlCl3 solution and NaCl solution has much lower performance than the other two additives. At a reaction temperature of 500°C, the catalyst soaked in KCl solution has the best performance, with a yield of 1463 μmol m -2 s -1 .

[0043] Figure 2 The results of the synthetic ammonia performance of the catalysts prepared in Comparative Example 1 and Example 1 at 500° C. show that compared with the catalyst in Comparative Example 1, the activity of the catalyst is increased by two orders of magnitude after being soaked in potassium chloride and calcined.

[0044] Figure 3 The appearance diagrams of the catalysts of Example 1, Examples 5 to 8 and Comparative Example 1 show that after the catalysts were immersed in KCl solutions of different concentrations for 2 hours, the catalyst surfaces showed different degrees of shedding as the concentration increased.

[0045] Figure 4The XRD diagrams of the catalysts of Example 1, Examples 5 to 8 and Comparative Examples 1 to 2 show that the catalyst of Comparative Example 2 which has not been immersed has no obvious iron oxide peak on its surface after calcination; while the catalysts of Example 1 and Examples 5 to 8 are more easily formed into iron oxide by calcination after being immersed in KCl solution, indicating that immersion in KCl solution can promote the formation of iron oxide; in addition, as the concentration of KCl solution increases, the iron alloy powder peak gradually weakens, while the iron oxide peak gradually strengthens, further indicating that immersion in KCl solution is conducive to the formation of active sites on the catalyst surface.

[0046] Figure 5 The results of the synthetic ammonia performance of the catalysts at different immersion concentrations in Example 1, Examples 5 to 8, and Comparative Example 2 are shown. At 400°C and 500°C, the catalysts immersed in 1.5 mol / L KCl solution showed the best performance, with a yield of 1463 μmol m -2 s -1 This shows that as the concentration of KCl solution increases, more active sites are exposed, thereby promoting the reaction activity, while too high a concentration may destroy the active sites of the catalyst for synthesizing ammonia, thereby reducing the activity.

[0047] Figure 6 The results of ammonia synthesis performance of the catalysts of Examples 1 and 9 to 12 with different immersion times show that if the immersion time is too short, the active sites will be insufficiently exposed. When the immersion time reaches 2 hours, the catalyst performance reaches the optimum.

Claims

1. A method for preparing a catalyst for synthesizing ammonia, characterized by comprising the following steps: 1) Using alloy powder mainly composed of metallic iron as raw material, the iron-based catalyst precursor is printed by selective laser melting technology, and then cleaned and dried to obtain a fresh iron-based catalyst; 2) Soaking the fresh iron-based catalyst in a chloride salt solution, and then drying and calcining to obtain the catalyst for synthesizing ammonia.

2. The method for preparing a catalyst for synthesizing ammonia according to claim 1, characterized in that: The chloride salt includes at least one of potassium chloride, sodium chloride, calcium chloride and aluminum chloride.

3. The method for preparing a catalyst for synthesizing ammonia according to claim 2, characterized in that: The chloride salt is potassium chloride.

4. The method for preparing a catalyst for synthesizing ammonia according to claim 1, characterized in that: The concentration of the chloride salt solution is 0.5-4 mol / L.

5. The method for preparing a catalyst for synthesizing ammonia according to claim 4, characterized in that: The concentration of the chloride salt solution is 1.5 mol / L.

6. The method for preparing a catalyst for synthesizing ammonia according to claim 1, characterized in that: In step 2), the soaking time is not less than 2 hours.

7. The method for preparing a catalyst for synthesizing ammonia according to claim 6, characterized in that: In step 2), the soaking time is 2 hours.

8. A catalyst for synthesizing ammonia, characterized in that: Prepared by any one of the preparation methods of claims 1 to 7.

9. The use of a catalyst for synthesizing ammonia according to claim 8, characterized in that: Used for thermal catalytic synthesis of ammonia.

Images