A catalyst for synthesizing ammonia, and its preparation method and application

Abstract

A catalyst for ammonia synthesis, its preparation method, and its application, belonging to the field of thermal catalytic ammonia synthesis, comprises the following steps: 1) using an alloy powder primarily composed of metallic iron as a raw material, printing an iron-based catalyst precursor using selective laser melting technology, washing, and drying to obtain a fresh iron-based catalyst; and 2) soaking the fresh iron-based catalyst in a chloride solution, followed by drying and calcining to obtain the catalyst for ammonia synthesis. The preparation process is simple and easy to operate, environmentally friendly, with low energy consumption and cost. The catalyst exhibits excellent mass and heat transfer during the reaction, resulting in strong catalytic performance and high practical value and application prospects.

Description

Technical Field

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

[0002] Ammonia (NH3) is a key raw material for the production of fertilizers, chemicals, and pharmaceuticals, and is also a promising carbon-free energy carrier. Currently, the traditional Haber-Bosch process is used to synthesize NH3 industrially. However, this method requires high temperature and high pressure, consumes fossil fuels, and releases large amounts of greenhouse gases, causing environmental pollution. Consequently, with the continuous advancement of technology, chemists are applying various new methods and technologies to the traditional ammonia synthesis industry. This improves the yield and energy efficiency of the ammonia synthesis reaction, reduces reaction energy consumption, maximizes the use of clean energy, and reduces pollutant emissions.

[0003] Commonly used metal-based catalysts in ammonia synthesis reactions are mainly iron-based and ruthenium-based. While newer ruthenium-based catalysts offer higher catalytic performance, their high price prevents large-scale industrialization. Iron-based catalysts are widely used in the thermal catalytic ammonia synthesis industry due to their excellent catalytic efficiency, high 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 solutions:

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

[0007] 1) Using metallic iron-based alloy powder as raw material, the iron-based catalyst precursor is printed using selective laser melting technology, and 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 thermal catalytic synthesis of ammonia.

[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 calcines 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 ionic radius, it can easily penetrate weak points on the surface of iron-based catalysts (inclusions, dislocation outcrops, alloy phases, holes, etc.). These weak points will become nucleation centers for pitting, destroying the density and integrity of the alloy protective film, thereby exposing the active centers; 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 increasing the activity of ammonia synthesis. Therefore, using KCl to soak iron-based catalysts provides a new research method for combining 3D printing technology with ammonia synthesis 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 nitrogen synthesis is increased by two orders of magnitude.

[0020] 3. The present invention creatively applies 3D printing technology to thermal catalytic ammonia synthesis. By designing different structures, the mass transfer and heat transfer of the catalytic system can be enhanced, 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 Graph showing the ammonia synthesis performance of the catalysts of Comparative Example 1 and Example 1;

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

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

[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 a performance diagram of ammonia synthesis 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 with reference to 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, the sample was vacuum dried at 60°C for 12 hours to obtain a fresh sample. 50ml of 1.5mol / L KCl solution was prepared, and 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 3 MPa, and the gas flow rate was 200 mL / min. The NH4 in the solution after the reaction was analyzed by ion chromatography. + The concentration was used to determine the activity of the catalyst.

[0032] Examples 2 to 4

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

[0034] Examples 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, 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).

[0038] Comparative Example 1

[0039] Using 316L stainless steel powder as raw material, the 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 vacuum dried at 60 ° C for 12 h to obtain the unsoaked and uncalcined catalyst (in Figures 2-4 (marked as Fresh).

[0040] Comparative Example 2

[0041] On the basis of Comparative Example 1, the catalyst which was not soaked and not calcined was calcined at 700°C for 24h to obtain a catalyst with a soaking concentration of 0 mol / L (in Figure 4 (marked as C700-24).

[0042] Figure 1 The performance graphs for ammonia synthesis of the catalysts obtained in Examples 1 to 4 show that at a reaction temperature of 400°C, the catalyst soaked in KCl solution exhibited better performance, while the catalysts soaked in AlCl3 and NaCl solutions exhibited significantly lower performance than the other two additives. At a reaction temperature of 500°C, the catalyst soaked in KCl solution exhibited the best performance, achieving a yield of 1463 μmol m -2 s -1 .

[0043] Figure 2 The results of the ammonia synthesis performance of the catalysts prepared in Comparative Example 1 and Example 1 at 500°C are shown. 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 These are the appearances of the catalysts of Example 1, Examples 5 to 8, and Comparative Example 1. After the catalysts were immersed in KCl solutions of different concentrations for 2 hours, varying degrees of shedding occurred on the catalyst surfaces as the concentration increased.

[0045] Figure 4The XRD patterns of the catalysts of Example 1, Examples 5 to 8, and Comparative Examples 1 to 2 are shown. It can be seen from the figure that the catalyst of Comparative Example 2, which has not been soaked, has no obvious iron oxide peak on its surface after calcination. However, after the catalysts of Example 1 and Examples 5 to 8 are soaked in KCl solution, iron oxide is more easily generated by calcination, indicating that soaking 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 soaking in KCl solution is conducive to the formation of active sites on the catalyst surface.

[0046] Figure 5 The results of ammonia synthesis performance of catalysts at different soaking concentrations in Example 1, Examples 5 to 8, and Comparative Example 2 are shown. At temperatures of 400°C and 500°C, the catalyst soaked 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. However, if the concentration is too high, the active sites of the catalyst for synthesizing ammonia may be destroyed, 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 are shown. The results 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 best.

Claims

1. A method for preparing a catalyst for synthesizing ammonia, characterized by comprising the following steps: 1) Using metallic iron-based alloy powder as raw material, the iron-based catalyst precursor is printed using selective laser melting technology, and then washed and dried to obtain a fresh iron-based catalyst; 2) soaking the fresh iron-based catalyst in a potassium chloride solution with a concentration of 0.5 to 4 mol / L, followed by drying and calcining to obtain the catalyst for synthesizing ammonia; wherein the soaking time is not less than 2 hours.

2. The method for preparing a catalyst for synthesizing ammonia according to claim 1, wherein: The concentration of the potassium chloride solution is 1.5 mol / L.

3. The method for preparing a catalyst for synthesizing ammonia according to claim 1, wherein: In step 2), the soaking time is 2 hours.

4. A catalyst for synthesizing ammonia, characterized in that: Prepared by the preparation method according to any one of claims 1 to 3.

5. The use of a catalyst for synthesizing ammonia according to claim 4, characterized in that: Used for thermal catalytic synthesis of ammonia.

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