Bimetal alloy catalyst with fragmented morphology and preparation method and application thereof

Abstract

The invention discloses a bimetallic alloy catalyst with fragmented morphology and a preparation method and application thereof, and belongs to the technical field of catalysts. According to the invention, the preparation process of the bimetallic alloy catalyst is optimized, and the sintering phenomenon of nanoparticles can be effectively avoided, so that the obtained bimetallic alloy catalyst has smaller particle size and larger specific surface area, exposes more active sites, and has excellent electro-catalytic performance. The prepared bimetallic alloy catalyst can provide more abundant active sites under the condition that intrinsic performance is not lost, the electrocatalytic activity is obviously improved, and the bimetallic alloy catalyst can be applied to the reaction of synthesizing ammonia through electrocatalytic reduction of nitrate.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalysts, and in particular relates to a bimetallic alloy catalyst with a fragmented morphology, a preparation method and an application thereof. Background Art

[0002] Large-scale synthesis technology solves the food and medicine problems for billions of people on Earth. Haber-Bosch technology is currently the most important technology for synthesizing ammonia, and its development spans over a century. However, the traditional Haber-Bosch process is energy-intensive, requiring reactions to be carried out at temperatures exceeding 400°C and pressures exceeding 200 atm. This results in annual energy consumption exceeding 2% of global energy consumption and annual carbon dioxide emissions exceeding 1.6% of total emissions, creating significant energy and environmental challenges.

[0003] In recent years, electrocatalytic ammonia synthesis has attracted widespread attention due to its mild reaction conditions, low energy input, and direct use of nitrogen as a nitrogen source. However, in practice, the efficiency of electrocatalytic ammonia synthesis is low due to nitrogen's low solubility and difficulty in activating the nitrogen-nitrogen triple bond. Therefore, the use of nitrate pollutants concentrated in water or nitrogen oxides in the air to synthesize ammonia has gained widespread attention.

[0004] Nitrate electroreduction to ammonia exhibits excellent performance because its catalytic reaction rate is less hindered by mass transfer during the reaction. Nitrate electroreduction is a multi-step electron-proton synergistic catalytic reaction, which is typically catalyzed by bimetallic alloy catalysts. However, the performance of currently reported bimetallic alloy catalysts for nitrate electroreduction to ammonia falls short of actual industrial needs. This is because the active sites of existing bimetallic alloy catalysts are insufficiently exposed, resulting in poor catalytic performance.

[0005] Electrocatalysts with highly exposed active sites need to be small in size. However, the bimetallic alloy nanoparticles reported so far inevitably encounter sintering during the synthesis process, which causes the nanoparticle size to increase further, thus inhibiting the improvement of catalyst performance. Summary of the Invention

[0006] In response to the above-mentioned prior art, the present invention provides a bimetallic alloy catalyst with a fragmented morphology, a preparation method and application thereof, to solve the technical problem that the existing bimetallic catalysts have poor catalytic performance due to fewer active sites.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is to provide a method for preparing a bimetallic alloy catalyst having a fragmented morphology, comprising the following steps:

[0008] S1: pretreating the nickel substrate to obtain a base material;

[0009] S2: dissolving nickel salt, cobalt salt, ammonium fluoride and urea in water to obtain a hydrothermal reaction solution;

[0010] S3: immersing the substrate in a hydrothermal reaction solution for hydrothermal reaction, and then vacuum drying to obtain a precursor;

[0011] S4: placing the precursor in a reducing atmosphere, calcining at 300-500° C. for 1-5 hours; then cooling to room temperature in a nitrogen atmosphere to obtain the product; the reducing atmosphere is ammonia or a mixed gas of ammonia and nitrogen.

[0012] On the basis of the above technical solution, the present invention can also be improved as follows.

[0013] Furthermore, the nickel substrate is foam nickel, and its size is 2 cm×3 cm×1 mm.

[0014] Furthermore, the nickel foam is pretreated by first placing it in an acidic solution for ultrasonic soaking for 2 to 10 minutes, then placing it in an organic solvent for ultrasonic soaking for 2 to 10 minutes, and finally placing it in deionized water for ultrasonic soaking for 2 to 10 minutes.

[0015] Furthermore, the acidic solution is a hydrochloric acid solution with a concentration of 3 mol / L; and the organic solvent is acetone.

[0016] Furthermore, the nickel salt is nickel nitrate, and the cobalt salt is cobalt nitrate.

[0017] Furthermore, the material-liquid ratio of nickel nitrate, cobalt nitrate, ammonium fluoride, urea and water is 1-3 mol:1-3 mol:5-8 mol:10-15 mol:30L.

[0018] Furthermore, in S3, the hydrothermal reaction temperature is 100-160° C., and the hydrothermal reaction time is 4-12 h; the vacuum drying temperature is 40-75° C., and the vacuum drying time is 8-12 h.

[0019] Furthermore, the volume percentage of ammonia in the mixed gas is 75%.

[0020] The invention also discloses a bimetallic alloy catalyst with a fragmented morphology, which is prepared by the above preparation method.

[0021] The present invention also discloses the application of the bimetallic alloy catalyst with fragmented morphology in electrocatalytic nitrate reduction to synthesize ammonia.

[0022] The beneficial effects of the present invention are:

[0023] 1. The present invention adopts a two-step method to prepare a bimetallic alloy catalyst NiCo with a fragmented morphology, and the catalytic activity of the obtained catalyst is better than that of a conventional NiCo alloy catalyst. The surface roughness factor of the NiCo alloy electrocatalyst with a fragmented morphology provided by the present invention is higher than 28, which is significantly higher than that of conventional NiCo alloy catalysts and metal electrode sheets. The higher roughness factor exposes more active sites, thereby improving the catalytic activity of the catalyst. The bimetallic alloy catalyst prepared by the present invention can provide a richer number of active sites without losing intrinsic performance, and the electrocatalytic activity is significantly improved. It can be used in the reaction of electrocatalytic reduction of nitrate to synthesize ammonia.

[0024] 2. The present invention optimizes the preparation process of the bimetallic alloy catalyst NiCo, which can effectively avoid the sintering of nanoparticles, so that the obtained bimetallic alloy catalyst has a smaller particle size, a larger specific surface area, and exposes more active sites, thus having excellent electrocatalytic performance.

[0025] 3. The present invention does not require the addition of other chemical reagents during the preparation of the bimetallic alloy catalyst with a fragmented morphology, nor does it require complex post-processing. The preparation method is simple and the conditions are mild. While reducing production costs, it can simplify the production process and enable it to be applied on a large scale in industrial applications.

[0026] 4. The bimetallic alloy catalyst with fragmented morphology prepared by the present invention can obtain about 7 mmol·h -1 cm -2 The rate of ammonia synthesis by electrocatalytic nitrate reduction was greatly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is an X-ray diffraction pattern of a bimetallic alloy catalyst having a fragmented morphology prepared in Example;

[0028] Figure 2 A transmission electron micrograph of a bimetallic alloy catalyst having a fragmented morphology prepared in Example;

[0029] Figure 3 This is a transmission electron microscope image of the bimetallic alloy catalyst prepared in Comparative Example 1;

[0030] Figure 4 Graph showing the roughness factor test results of the bimetallic alloy catalysts prepared in Examples and Comparative Examples. DETAILED DESCRIPTION

[0031] The specific implementation methods of the present invention are described in detail below with reference to the embodiments.

[0032] Example 1

[0033] A bimetallic alloy catalyst with a fragmented morphology is prepared by the following steps:

[0034] S1: A nickel foam with a size of 2 cm × 3 cm × 1 mm was first placed in a 0.2 mmol / L hydrochloric acid solution and ultrasonically soaked for 5 minutes, then placed in acetone and ultrasonically soaked for 5 minutes, and finally placed in deionized water and ultrasonically soaked for 5 minutes to obtain a substrate; the frequency of ultrasonic soaking was 20 kHz;

[0035] S2: Dissolve 1 mmol of nickel nitrate, 2 mmol of cobalt nitrate, 6 mmol of ammonium fluoride, and 12 mmol of urea in 30 mL of deionized water and stir well to obtain a hydrothermal reaction solution;

[0036] S3: Immerse the substrate in the hydrothermal reaction solution, heat the system to 120°C, and keep the temperature to react for 8 hours; then remove the nickel foam and vacuum dry it at 60°C for 10 hours to obtain a precursor;

[0037] S4: Place the precursor in a tubular furnace, and then introduce a mixed gas of ammonia and nitrogen, with the system fraction of ammonia being 75%; heat the precursor to 400°C, keep it warm for 2 hours, then introduce nitrogen, and cool it to room temperature in a nitrogen atmosphere to obtain a bimetallic alloy catalyst with a fragmented morphology.

[0038] Example 2

[0039] A bimetallic alloy catalyst with a fragmented morphology is prepared by the following steps:

[0040] S1: A nickel foam with a size of 2 cm × 3 cm × 1 mm was first placed in a 0.2 mmol / L hydrochloric acid solution and ultrasonically soaked for 5 minutes, then placed in acetone and ultrasonically soaked for 5 minutes, and finally placed in deionized water and ultrasonically soaked for 5 minutes to obtain a substrate; the frequency of ultrasonic soaking was 20 kHz;

[0041] S2: Dissolve 1 mmol of nickel nitrate, 2 mmol of cobalt nitrate, 6 mmol of ammonium fluoride, and 12 mmol of urea in 30 mL of deionized water and stir well to obtain a hydrothermal reaction solution;

[0042] S3: Immerse the substrate in the hydrothermal reaction solution, heat the system to 120°C, and keep the temperature to react for 8 hours; then remove the nickel foam and vacuum dry it at 60°C for 10 hours to obtain a precursor;

[0043] S4: Place the precursor in a tubular furnace and then introduce ammonia; heat the precursor to 400°C, keep it warm for 2 hours, then introduce nitrogen, and cool it to room temperature in a nitrogen atmosphere to obtain a bimetallic alloy catalyst with a fragmented morphology.

[0044] Comparative Example 1

[0045] A bimetallic alloy catalyst is prepared by the following steps:

[0046] S1: A nickel foam with a size of 2 cm × 3 cm × 1 mm was first placed in a 0.2 mmol / L hydrochloric acid solution and ultrasonically soaked for 5 minutes, then placed in acetone and ultrasonically soaked for 5 minutes, and finally placed in deionized water and ultrasonically soaked for 5 minutes to obtain a substrate; the frequency of ultrasonic soaking was 20 kHz;

[0047] S2: Dissolve 1 mmol of nickel nitrate, 2 mmol of cobalt nitrate, 6 mmol of ammonium fluoride, and 12 mmol of urea in 30 mL of deionized water and stir well to obtain a hydrothermal reaction solution;

[0048] S3: Immerse the substrate in the hydrothermal reaction solution, heat the system to 120°C, and keep the temperature to react for 8 hours; then remove the nickel foam and vacuum dry it at 60°C for 10 hours to obtain a precursor;

[0049] S4: Place the precursor in a tube furnace, and then introduce a mixed atmosphere of hydrogen and nitrogen, with a hydrogen volume fraction of 5%; heat the precursor to 400° C. and keep it warm for 2 hours to obtain a bimetallic alloy catalyst.

[0050] Since the bimetallic alloy catalysts prepared in Example 1 and Example 2 have similar performances, the bimetallic alloy catalyst prepared in Example 1 is taken as an example to analyze the performance of the bimetallic alloy catalyst.

[0051] Experimental example

[0052] 1. Morphology and composition analysis of bimetallic alloy catalysts

[0053] The surface X-ray diffraction pattern of the bimetallic alloy catalyst prepared in the embodiment of the present invention is as follows: Figure 1 As shown. Figure 1 It can be seen that the X-ray characteristic diffraction peak position of the prepared bimetallic alloy catalyst corresponds to that of face-centered cubic cobalt (PDF#15-0806) and face-centered cubic nickel (PDF#04-0850), indicating that the final catalyst is composed of cobalt mixed with nickel. The transmission electron microscopy image of the bimetallic alloy catalyst prepared in the example of the present application is as follows Figure 2 As shown, from Figure 2It can be seen that the bimetallic alloy catalyst prepared by the preparation process of the present invention has a particle size of about 20nm and has a distinct fragmented structure, with more active sites exposed to the outside and a higher catalytic activity on the surface. The scanning electron microscope image of the bimetallic alloy catalyst prepared in Comparative Example 1 is as follows: Figure 3 As shown, from Figure 3 As can be seen in the figure, the bimetallic alloy catalyst nanoparticles prepared using the preparation process in the comparative example agglomerated, with a particle size of approximately 60 nm. This is because in Comparative Example 1, the reducing atmosphere was hydrogen, resulting in a faster reduction rate. Furthermore, after calcination, the catalyst was not cooled in a nitrogen atmosphere, resulting in intense Oswald heating during the heating and cooling process, which caused the nanoparticles to agglomerate, thereby obtaining an agglomerated catalyst product. Furthermore, the roughness factor of the bimetallic alloy catalysts prepared in the present invention and the comparative example was tested using Ni foil as a reference. The results are shown in FIG. Figure 4 shown; from Figure 4 It can be seen that the roughness of the bimetallic alloy catalyst prepared in Comparative Example 1 is greatly improved compared with that of metallic nickel, but the roughness factor is still lower than 20, and the active sites cannot be fully exposed, resulting in insufficient catalytic performance; the roughness factor of the bimetallic alloy catalyst prepared in Example can reach more than 28, and the roughness has a greater increase compared with the catalyst in Comparative Example 1. The larger roughness factor can expose more active sites, thereby producing a good catalytic effect.

[0054] 2. Electrical Performance Test of Bimetallic Alloy Catalyst

[0055] Electrochemical performance testing: Electrolysis experiments were conducted in a two-chamber electrolytic cell with a cathode and an anion membrane separating the two chambers. A 1 mol / L KOH solution was used as the anolyte, a 1 mol / L KOH and 0.2 mol / L KNO3 solution was used as the catholyte, a Pt sheet electrode was used as the anode, Hg / HgO electrolysis was used as the reference electrode, and the bimetallic alloy catalysts prepared in the examples and comparative examples of the present invention were used as the working electrode. During the electrolysis, argon gas was introduced into the cathode chamber at a flow rate of 25 mL / min, and the cathode was tested at a potential of -0.1 to -0.7 V (vs RHE). The electrolysis reaction was carried out for one hour. After the reaction, the concentration of the produced ammonia product was determined by cation chromatography. In addition, the electrochemically active area (ECSA) of the bimetallic alloy catalyst prepared in the present invention was tested using a single-cell electrolytic cell. The electrolyte was a 0.1 M KOH solution, a platinum sheet was used as the anode, a Hg / HgO electrode was used as the reference electrode, and the bimetallic alloy catalyst was used as the working electrode. The experiment was conducted at room temperature using cyclic voltammetry (CV) at different scan rates (10, 20, 30, 40, 50, and 60 mV / s) in the non-faradaic range. The current response was recorded, and the electric double layer capacitance (Cdl) was calculated by analyzing the relationship between the current and the scan rate at different scan rates. The experimental results are shown in Table 1.

[0056] Table 1 Electrical performance test results of bimetallic alloy catalysts

[0057]

[0058] As can be seen from Table 1, the bimetallic alloy catalysts prepared in the Examples exhibited excellent catalytic performance in the electroreduction of nitrate to ammonia, with Faradaic efficiencies exceeding 92%. In contrast, the bimetallic alloy catalyst prepared in Comparative Example 1 achieved a Faradaic efficiency of only approximately 81%. This is because, during the preparation of the bimetallic alloy catalyst in Comparative Example 1, the solid material sintered, resulting in aggregation of the nanoparticles. The surface roughness factor of the agglomerated nanoparticles decreased, reducing the number of active sites and suppressing the catalytic performance.

[0059] By comparing the embodiment with comparative example 1, it can be seen that the bimetallic alloy catalyst prepared by the process of the present invention has the characteristic of highly exposed active sites, exposes abundant active sites, and exhibits excellent catalytic effect in the electroreduction of nitrate to synthesize ammonia.

[0060] Although the specific embodiments of the present invention have been described in detail in conjunction with the embodiments, this should not be construed as limiting the scope of protection of this patent. Within the scope described by the claims, various modifications and variations that can be made by those skilled in the art without creative work still fall within the scope of protection of this patent.

Claims

1. A method for preparing a bimetallic alloy catalyst having a fragmented morphology, characterized in that: The following steps are involved: S1: pretreating the nickel substrate to obtain a base material; S2: dissolving nickel salt, cobalt salt, ammonium fluoride and urea in water to obtain a hydrothermal reaction solution; S3: immersing the substrate in a hydrothermal reaction solution for hydrothermal reaction, and then vacuum drying to obtain a precursor; S4: placing the precursor in a reducing atmosphere, calcining at 300-500° C. for 1-5 hours; then cooling to room temperature in a nitrogen atmosphere to obtain the product; the reducing atmosphere is ammonia or a mixed gas of ammonia and nitrogen.

2. The preparation method according to claim 1, wherein: The nickel substrate is foam nickel, and its size is 2 cm×3 cm×1 mm.

3. The preparation method according to claim 2, wherein: The nickel foam is pretreated by firstly placing it in an acidic solution for ultrasonic soaking for 2 to 10 minutes, then placing it in an organic solvent for ultrasonic soaking for 2 to 10 minutes, and finally placing it in deionized water for ultrasonic soaking for 2 to 10 minutes.

4. The preparation method according to claim 3, wherein: The acidic solution is a hydrochloric acid solution with a concentration of 0.2 mmol / L; and the organic solvent is acetone.

5. The preparation method according to claim 1, wherein: The nickel salt is nickel nitrate, and the cobalt salt is cobalt nitrate.

6. The preparation method according to claim 5, characterized in that: The material-liquid ratio of the nickel nitrate, cobalt nitrate, ammonium fluoride, urea and water is 1-3 mol: 1-3 mol: 5-8 mol: 10-15 mol: 30L.

7. The preparation method according to claim 1, wherein: In S3, the hydrothermal reaction temperature is 100-160° C., and the hydrothermal reaction time is 4-12 h; the vacuum drying temperature is 40-75° C., and the vacuum drying time is 8-12 h.

8. The preparation method according to claim 1, wherein: The volume percentage of ammonia in the mixed gas is 75%.

9. A bimetallic alloy catalyst having a fragmented morphology obtained by the preparation method according to any one of claims 1 to 8.

10. Use of the bimetallic alloy catalyst with fragmented morphology according to claim 9 in electrocatalytic nitrate reduction to synthesize ammonia.

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