A novel Ru-Co catalyst, its preparation method and application

Abstract

This invention discloses a novel Ru-Co catalyst, its preparation method, and its application, belonging to the technical field of catalysts for the electrochemical reduction of nitrate to ammonia. The invention involves mixing carbon black powder with ruthenium and cobalt salts in a solvent at a certain ratio, heating and stirring until the solvent evaporates, grinding and mixing until homogeneous, and then calcining in argon. The sample is collected after cooling to room temperature. The resulting powder is then dispersed in an acid solution at a constant temperature for acid etching. After acid etching, the catalyst is washed until the pH is neutral, then collected by centrifugation and vacuum dried. Finally, the obtained powder sample is calcined in a H2 / Ar mixed gas to obtain the Ru-Co catalyst. The preparation method of this invention is simple and can be mass-produced. The Ru-Co catalyst, used for electrochemical nitrate reduction, can achieve a near 100% Faraday efficiency in ammonia synthesis, and at an applied voltage of -0.8 V, the yield can reach 40 mg / h. ‑1 cm ‑2 It maintained good stability under 100 hours of cyclic testing.

Description

Technical Field

[0001] This invention belongs to the field of catalyst technology for the electrochemical reduction of nitrate to ammonia, specifically relating to a novel Ru-Co catalyst, its preparation method, and its application. Background Technology

[0002] Ammonia (NH3) is a colorless gas with a strong, pungent odor at room temperature and pressure. As one of the world's largest-produced and most widely used basic chemical products, it is not only an indispensable core raw material for the synthesis of nitrogen fertilizers, nitric acid, fibers, and pharmaceuticals, but also, due to its unique physicochemical properties, has been given new strategic significance in the modern energy transition. Currently, the mainstream industrial-scale production method is the Haber-Bosch process, which heavily relies on fossil fuels and requires harsh conditions of high temperature (400~600°C) and high pressure (20~40 MPa). Its annual energy consumption accounts for approximately 1~2% of global energy consumption, accompanied by massive carbon dioxide emissions. With the selection of suitable electrocatalysts, electrochemical nitrate reduction technology can effectively synthesize ammonia, potentially replacing current industrial ammonia synthesis technologies and achieving low-cost, high-efficiency, sustainable, and zero-carbon emission ammonia synthesis.

[0003] Ruthenium-based nanomaterials exhibit outstanding potential due to their unique electronic structure: the d orbital energy level of Ru is suitable for hybridization with the p orbital of nitrogen in nitrate, forming a stable coordination, thereby efficiently adsorbing and activating nitrate. Studies have shown that by constructing a bimetallic system, the electronic structure of Ru active sites and its adsorption energy for reaction intermediates can be finely tuned, thereby optimizing the reaction pathway, suppressing hydrogen evolution side reactions, and ultimately achieving a simultaneous improvement in the activity and selectivity of ammonia synthesis (Gao W, Xie K, Xie J, et al. Alloying of Cu with Ru Enabling the Relay Catalysis for Reduction of Nitrate to Ammonia[J]. Advanced Materials, 2023, 35(19): 2202952.). However, the noble metal Ru faces significant cost issues as a catalyst. To address this, numerous studies have attempted to modify Ru catalysts using other transition metals (such as Fe, Co, and Ni), which can not only improve the catalytic activity of the catalyst but also significantly reduce the amount of Ru metal used, thus lowering costs. However, transition metal atoms (such as Fe, Co, and Ni) often face problems such as surface reconstruction or dissolution in the electroreduction reaction of nitrate, resulting in insufficient catalyst stability. Therefore, there is an urgent need to develop novel Ru-based electrocatalysts that are low-cost, highly active, highly selective, and highly stable. Summary of the Invention

[0004] This invention provides a novel Ru-Co catalyst, its preparation method, and its application. The Ru-Co catalyst employs a structure in which Ru metal is coated with transition metal oxides, thus avoiding the problems of transition metal dissolution and surface reconstruction. The prepared Ru-Co catalyst exhibits high activity, high selectivity, and good stability in the electrocatalytic reduction of nitrate to ammonia.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing a Ru-Co catalyst includes the following steps: S1: Mix carbon black powder with ruthenium salt and cobalt salt in a solvent, heat and stir until the solvent evaporates, then grind and mix evenly. S2: After the mixture is thoroughly mixed, it is calcined in argon gas. After calcination, the sample is collected after cooling to room temperature. S3: The obtained powder is etched in sulfuric acid solution. After acid etching, the powder is washed with ultrapure water until the pH value is neutral. Then, it is collected by centrifugation and vacuum dried. S4: The obtained powder sample was calcined in a H2 / Ar mixed gas to obtain the Ru-Co catalyst.

[0006] In the steps described above, in step S1, carbon black powder, ruthenium salt, and cobalt salt are mixed in a solvent at a mass ratio of C, Ru, and Co atoms of 16:4:3; the carbon black is Ketjenblack EC-600J, Ketjenblack EC-300J, or Ketjenblack XC-72R; the ruthenium salt is ruthenium acetylacetonate or ruthenium chloride; the cobalt salt is cobalt acetylacetonate, cobalt nitrate, cobalt chloride, or cobalt sulfate; and the solvent is acetone. The calcination temperature in S2 is 250~600℃, and the calcination time is 1~10 hours.

[0007] The acid etching process in S3 is carried out at a temperature of 50~100℃ for 12~72 hours. The acid solution is either sulfuric acid or hydrochloric acid, and the concentration of the acid solution is 0.05~5 M.

[0008] The calcination temperature in S4 is 150~600℃, and the calcination time is 1~5 hours.

[0009] The Ru-Co catalyst prepared above is a core-shell structure Ru-Co supported on an amorphous carbon substrate, with the core-shell structure consisting of internal mixed-valence CoO. x The spatial configuration consists of a core and an outer continuous metallic Ru shell; the elemental contents of Ru and Co are 10% and 0.2%, respectively, and it possesses an internal mixed valence state of CoO. xThe spatial configuration of the core and the outer continuous metallic Ru shell. The core-shell structure with oxide embedding suppresses Ru atom dissolution and Ostwald ripening, improving catalytic stability. The internal CoO... x The nucleus modulates the electronic structure of the Ru shell, thereby altering the reaction pathway and improving the selectivity of the reaction.

[0010] The Ru-Co catalyst described above can be used in the electrochemical reduction of nitrates to prepare ammonia; the Ru-Co catalyst can also be used as a catalyst for the cathode reaction.

[0011] Beneficial effects: This invention provides a Ru-Co catalyst, its preparation method, and its application, which have the following advantages compared with the prior art: (1) The preparation method of the Ru-Co catalyst of the present invention is simple and can be used for large-scale production.

[0012] (2) The Ru-Co catalyst of the present invention has very high selectivity for ammonia synthesis in electrochemical nitrate reduction applications, with a Faraday efficiency close to 100%.

[0013] (3) The Ru-Co catalyst of this invention exhibits very high stability in the electrochemical reduction of nitrates to synthesize ammonia, and the yield can reach 40 mg / h when the applied voltage is -0.8 V. -1 cm -2 It maintained good stability even after 100 hours of cyclic testing. Attached Figure Description

[0014] Figure 1 It consists of carbon black powder, the Ru-Co catalyst in Example 1, and the CoO in Comparative Example 1. x / Ru / C catalyst and CoO in Comparative Example 3 x Powder X-ray diffraction pattern of / C catalyst.

[0015] Figure 2 CoO in Comparative Example 1 x Scanning and aberration-corrected electron microscopy images of the Ru / C catalyst and the Ru-Co catalyst in Example 1, wherein (a) is a TEM image of the Ru-Co catalyst, (b) is an aberration-corrected electron microscopy image of the Ru-Co catalyst, (c) is the particle size distribution of the Ru-Co catalyst, and (d) is the CoO... x TEM image of the / Ru / C catalyst, (e)CoO x Aberration-corrected electron microscopy image of the Ru / C catalyst, (f) CoO x Particle size distribution of the Ru / C catalyst; Figure 3The X-ray photoelectron spectra of the Ru-Co catalyst in Example 1 are shown; (a) Ru 3p spectrum; (b) Co 2p spectrum before and after Ar ion etching.

[0016] Figure 4 CoO in Comparative Example 1 x Electrochemical nitrate reduction to ammonia production performance of the Ru / C catalyst and the Ru-Co catalyst in Example 1, and stability test results of the catalytic performance of the Ru-Co catalyst in Example 1.

[0017] Figure 5 This is a comparison chart of the electrochemical nitrate reduction to ammonia production performance of the Ru-Co catalysts in Examples 1-4 and the corresponding catalysts in Comparative Examples 1-3 at -0.7 V (relative to the reversible hydrogen electrode). Detailed Implementation

[0018] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments: Electrochemical nitrate reduction test conditions: The electrochemical nitrate reduction performance of all catalysts was tested using the Wuhan Koster electrochemical workstation. The tests were conducted in an H-type electrolytic cell. The anolyte was a 1 mol / L KOH aqueous solution, and the catholyte was a mixed aqueous solution of KOH and KNO3 with concentrations of 1 M and 0.5 M, respectively.

[0019] In a typical test, 6 mg of catalyst was added to a mixture containing 1.584 mL of ethanol and 16 μL of Nafion-117 solution (5%, Sigma-Aldrich), and sonicated for half an hour to obtain a well-dispersed catalyst coating solution. Then, the catalyst was coated with a solution at 1 mg / cm³. 2 The catalyst loading was achieved by coating a carbon paper electrode with the catalyst and then drying it to serve as the working electrode. All tests were performed at room temperature, with a platinum mesh electrode and a saturated calomel electrode used as the counter electrode and reference electrode, respectively. Example 1

[0020] Catalyst preparation: 160 mg of carbon black powder, 160 mg of ruthenium acetylacetone, and 140 mg of cobalt acetylacetone were mixed in a pure acetone solution and stirred and evaporated in a water bath at 75°C. After the solvent was completely evaporated, the resulting solid powder was ground and mixed evenly, and then calcined in argon at 450°C for 8 hours. The powder sample obtained after calcination in argon was then dispersed in a 0.1 M H₂SO₄ solution and acid-etched by stirring at 80°C for 14 hours. After acid etching, the resulting powder sample was centrifuged, washed, and dried, and finally calcined in an H₂ / Ar mixed gas at 300°C for 3 hours. After natural cooling, it was ground to obtain the Ru-Co catalyst. Example 2

[0021] Catalyst preparation: 160 mg of carbon black powder, 130 mg of ruthenium acetylacetone, and 140 mg of cobalt acetylacetone were mixed in a pure acetone solution and evaporated by stirring in a water bath at 75°C. After the solvent was completely evaporated, the resulting solid powder was ground and mixed evenly, and then calcined in argon at 450°C for 8 hours. The powder sample obtained after calcination in argon was then dispersed in a 0.1 M H₂SO₄ solution and acid-etched by stirring at 80°C for 14 hours. After acid etching, the resulting powder sample was centrifuged, washed, and dried, and finally calcined in an H₂ / Ar mixed gas at 300°C for 3 hours. After natural cooling, it was ground to obtain the Ru-Co catalyst. Example 3

[0022] 160 mg of carbon black powder, 160 mg of ruthenium acetylacetone, and 160 mg of cobalt acetylacetone were mixed in a pure acetone solution and stirred and evaporated in a water bath at 75°C. After the solvent was completely evaporated, the resulting solid powder was ground and mixed evenly, and then calcined in argon at 450°C for 8 hours. The powder sample obtained after calcination in argon was then dispersed in a 0.1 M H₂SO₄ solution and acid-etched by stirring at 80°C for 14 hours. After acid etching, the resulting powder sample was centrifuged, washed, and dried, and finally calcined in an H₂ / Ar mixed gas at 300°C for 3 hours. After natural cooling, it was ground to obtain the Ru-Co catalyst. Example 4

[0023] 160 mg of carbon black powder, 130 mg of ruthenium acetylacetone, and 160 mg of cobalt acetylacetone were mixed in a pure acetone solution and evaporated by stirring in a 75°C water bath. After the solvent was completely evaporated, the resulting solid powder was ground and mixed evenly, and then calcined in argon at 450°C for 8 hours. The powder sample obtained after calcination in argon was then dispersed in a 0.1 M H₂SO₄ solution and acid-etched by stirring at 80°C for 14 hours. After acid etching, the resulting powder sample was centrifuged, washed, and dried, and finally calcined in an H₂ / Ar mixed gas at 300°C for 3 hours. After natural cooling, it was ground to obtain the Ru-Co catalyst.

[0024] Comparative Example 1 160 mg of carbon black powder, 160 mg of ruthenium acetylacetone, and 150 mg of cobalt acetylacetone were mixed in a pure acetone solution and stirred and evaporated in a 75°C water bath. After the solvent was completely evaporated, the resulting solid powder was ground and mixed evenly, and then calcined in argon at 450°C for 8 hours. The powder sample obtained after calcination in argon was then calcined in an H2 / Ar mixed gas at 300°C for 3 hours. After natural cooling, it was ground to obtain CoO. x / Ru / C catalyst.

[0025] Comparative Example 2 160 mg of carbon black powder and 160 mg of ruthenium acetylacetone were mixed in a pure acetone solution and evaporated by stirring in a 75°C water bath. After the solvent was completely evaporated, the resulting solid powder was ground and mixed evenly, and then calcined in argon at 450°C for 8 hours. The powder sample obtained after calcination in argon was then dispersed in a 0.1 M H₂SO₄ solution and acid-etched by stirring at 80°C for 14 hours. After acid etching, the resulting powder sample was centrifuged, washed, and dried. Finally, it was calcined in an H₂ / Ar mixed gas at 300°C for 3 hours. After natural cooling, it was ground to obtain the Ru / C catalyst.

[0026] Comparative Example 3 160 mg of carbon black powder and 140 mg of cobalt acetylacetonate were mixed in a pure acetone solution and evaporated by stirring in a 75°C water bath. After the solvent was completely evaporated, the resulting solid powder was ground and mixed evenly, and then calcined in argon at 450°C for 8 hours. The powder sample obtained after calcination in argon was then calcined in an H2 / Ar mixed gas at 300°C for 3 hours. After natural cooling, it was ground to obtain CoO. x / C catalyst.

[0027] Figure 1 It consists of carbon black powder, the Ru-Co catalyst in Example 1, and the CoO in Comparative Example 1. x / Ru / C catalyst and CoO in Comparative Example 3 x Powder X-ray diffraction pattern of the / C catalyst. The figure shows that the Ru-Co catalyst only exhibits the diffraction pattern of C, possibly because the loadings of Ru and Co are below the detection limit of powder X-ray diffraction.

[0028] Figure 2 CoO in Comparative Example 1 x Scanning electron microscope (SEM) images and aberration-corrected transmission electron microscope (TEM) images of the Ru / C catalyst and the Ru-Co catalyst in Example 1. Figure 2a and b show the microstructure of the Ru-Co catalyst, and it can be seen that the active nanoparticles are uniformly loaded on the carbon support surface without obvious agglomerates. Figure 2 c shows that the Ru-Co catalyst has an extremely narrow metal particle size distribution, exhibiting the characteristics of ultrafine nanoclusters, with an average particle size of only 1.0±0.3 nm. Figure 2 d shows CoO x The microstructure of the Ru / C catalyst reveals huge black spot-like aggregates with sizes far exceeding 50 nm, and some regions even form continuous bulk structures. Figure 2 e showcased CoO x The aberration-corrected electron microscopy image of Ru / C contrasts sharply with the ultrafine clusters (~1.0 nm) formed by the Ru-Co catalyst after acid etching, showing low dispersion and obvious tendency for particle aggregation. Figure 2 f displays CoO x The average particle size of / Ru / C is 2.21 ± 0.4 nm.

[0029] Figure 3 The following are X-ray photoelectron spectra of the Ru-Co catalyst in Example 1: (a) Ru 3p spectrum; (b) Co 2p spectrum before and after Ar ion etching. The Ru 3p spectrum results confirm that Ru in the Ru-Co catalyst mainly exists in the metallic state, but there is also partial oxidation on the surface. Before Ar ion etching, no XPS signal of Co was detected, and after Ar ion etching, a weak Co signal was detected, indicating that Co is distributed inside the Ru metal clusters, confirming the existence of the Ru metal-coated Co structure.

[0030] Figure 4 CoO in Comparative Example 1 x The graphs show the performance of the Ru / C catalyst and the Ru-Co catalyst in Example 1 for electrochemical nitrate reduction to ammonia, and the stability of the Ru-Co catalyst in Example 1. As can be seen from the graphs, the Ru-Co catalyst exhibits a near 100% Faraday efficiency for ammonia synthesis over a wide potential range. When a voltage of -0.2 V (relative to the reversible hydrogen electrode) is applied, the ammonia yield (blue bars) remains highly stable over 100 hours of cycling, without significant decline. Simultaneously, the ammonia production Faraday efficiency (red line) consistently fluctuates within the high range of 90%–95%.

[0031] Figure 5This is a comparison of the electrochemical nitrate reduction to ammonia production performance of the Ru-Co catalysts in Examples 1-4 and the corresponding catalysts in Comparative Examples 1-3 at -0.7 V (relative to the reversible hydrogen electrode). The graph shows that the Ru-Co catalyst in Example 1 has the highest ammonia selectivity, approaching 100%, while the Ru-Co catalysts in Example 2 and Example 4, with slightly lower Ru content, exhibit slightly lower ammonia selectivity. Comparing the performance of the Ru-Co catalysts in Example 1 and Example 3, it can be seen that the highest ammonia selectivity is achieved when the Ru loading is around 10 wt%. A comparison of the Ru-Co catalyst in Example 1 and the CoO catalyst in Comparative Example 1 further demonstrates this. x The performance of the Ru / C catalyst shows that acid etching is particularly important for improving catalytic performance. The catalytic performance of Comparative Examples 2 and 3, which did not introduce Co and Ru, is significantly lower than that of the Ru-Co catalyst in Example 1, indicating that the superior performance of the Ru-Co catalyst in Example 1 is a result of the synergistic effect of the two metals. During the reaction, the Ru shell continuously provides adsorbed hydrogen (H*) required for the reaction through the cracking of water molecules; while the internal CoO... x By adjusting the d-band center of the Ru shell, the core optimized the adsorption configuration of key intermediates (*NO, *HNO), significantly suppressing side reactions that are prone to occur on the pure Ru surface. The reaction was confirmed to follow an active hydrogen-mediated "deoxygenation-hydrogenation" cascade pathway (NO3⁻→*NO→*NH2OH→NH3), thus achieving high selectivity for the target product ammonia while ensuring a high reaction rate.

[0032] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a novel Ru-Co catalyst, characterized in that, Includes the following steps: S1: Mix carbon black powder with ruthenium salt and cobalt salt in a solvent, heat and stir until the solvent evaporates, then grind and mix evenly. S2: After the mixture is thoroughly mixed, it is calcined in argon gas. After calcination, the sample is collected after cooling to room temperature. S3: The obtained powder is etched in sulfuric acid solution. After acid etching, the powder is washed with ultrapure water until the pH value is neutral. Then, it is collected by centrifugation and vacuum dried. S4: The obtained powder sample was calcined in a H2 / Ar mixed gas to obtain the Ru-Co catalyst.

2. The method for preparing the novel Ru-Co catalyst according to claim 1, characterized in that, In S1, carbon black powder, ruthenium salt, and cobalt salt are mixed in a solvent at a mass ratio of C, Ru, and Co atoms of 16:4:

3.

3. The method for preparing the novel Ru-Co catalyst according to claim 1 or 2, characterized in that, The carbon black is Ketjenblack EC-600J, Ketjenblack EC-300J, or Ketjenblack XC-72R; the ruthenium salt is ruthenium acetylacetonate or ruthenium chloride; the cobalt salt is cobalt acetylacetonate, cobalt nitrate, cobalt chloride, or cobalt sulfate.

4. The method for preparing the novel Ru-Co catalyst according to claim 1, characterized in that, The calcination temperature of S2 is 250~600℃, and the calcination time is 1~10 hours.

5. The method for preparing the novel Ru-Co catalyst according to claim 1, characterized in that, The acid etching process in S3 is carried out at a temperature of 50~100℃ for 12~72 hours, with an acid solution concentration of 0.05~5 M.

6. The method for preparing the novel Ru-Co catalyst according to claim 1 or 5, characterized in that, The acid solution is either sulfuric acid or hydrochloric acid.

7. The method for preparing the novel Ru-Co catalyst according to claim 1, characterized in that, The calcination temperature in S4 is 150~600℃, and the calcination time is 1~5 hours.

8. The novel Ru-Co catalyst prepared by the method according to any one of claims 1-7, characterized in that, The catalyst is a core-shell Ru-Co structure supported on an amorphous carbon substrate, with the core-shell structure consisting of internally mixed-valence CoO. x The spatial configuration of a core and an outer continuous metallic Ru shell; The elemental contents of Ru and Co are 10% and 0.2%, respectively.

9. The application of the novel Ru-Co catalyst according to claim 8, characterized in that, The catalyst is used for the electrochemical reduction of nitrates to produce ammonia.

10. The application of the novel Ru-Co catalyst according to claim 9, characterized in that, Ru-Co catalysts are used as catalysts for cathode reactions.

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