A noble metal core-shell structure catalyst, a preparation method thereof and application thereof
By preparing a core-shell catalyst Ru@RuO2/C with ruthenium as the core and ruthenium dioxide as the shell on a carbon support, the problem of unsatisfactory activity and selectivity of noble metal catalysts in the nitric acid reduction reaction was solved, achieving efficient electroreduction of nitrate to NH3 with high Faraday efficiency and good stability.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SOUTHERN UNIVERSITY OF SCIENCE AND TECHNOLOGY
- Filing Date
- 2026-01-19
- Publication Date
- 2026-06-05
AI Technical Summary
Existing noble metal catalysts exhibit unsatisfactory activity and selectivity in nitric acid reduction reactions, mainly because the high coverage of active hydrogen on the surface of noble metals results in insufficient electron adsorption and injection into the π* antibonding orbitals of NO3 ions, leading to low efficiency in NH3 generation.
A core-shell catalyst Ru@RuO2/C with ruthenium as the core and ruthenium dioxide as the shell on a carbon support was prepared by impregnation-thermal reduction and low-temperature oxidation. By controlling the thermal reduction and annealing oxidation conditions, a uniform core-shell structure was formed, which inhibited the hydrogen evolution reaction and promoted the electroreduction of nitrate to NH3.
It achieves efficient electroreduction of nitrate to NH3 with a Faraday efficiency of 90-100%, and inhibits the hydrogen evolution reaction. It has good catalytic performance and stability, and is suitable for large-scale commercial production.
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Figure CN122147434A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the fields of nitrate-contaminated wastewater treatment and energy catalysis, and particularly to a noble metal core-shell structure catalyst, its preparation method, and its application. Background Technology
[0002] Ammonia (NH3) plays a vital role in human production and daily life, and is widely used in chemical, fertilizer, pharmaceutical, synthetic textile, and dye industries. Currently, the industrial production of NH3 mainly relies on the Haber-Bosch (HB) process, in which nitrogen and hydrogen are reacted at 200 atmospheres and 400°C with an iron compound catalyst (Fe). 3+ This method produces NH3. However, it is inefficient, energy-intensive (consuming approximately 2% of global energy consumption), and causes significant carbon emissions (300 million tons of carbon emissions annually). Therefore, there is an urgent need to develop a new, efficient, low-energy-consumption, and carbon-free method for synthesizing NH3. Nitrate nitrogen (NO3) Converting NO3 to NH3 is an effective way to solve the problems of low efficiency, high energy consumption, and large carbon emissions associated with nitrate nitrogen. Meanwhile, nitrates can originate from domestic sewage, fertilizers, and industrial wastewater. Therefore, the use of NO3... As a nitrogen source, NH3 electrosynthesis is made sustainable, opening up an economical way to remediate environmental pollution.
[0003] Although electrocatalysts for several noble metals such as Ru, Ir, Pd, and Pt and their compounds have been developed towards the reduction of nitric acid (NO3) However, its catalytic performance is still greatly limited by problems such as the accumulation of byproducts due to the mismatch of multi-electron transition kinetics in the nitric acid reduction reaction. Due to the high coverage of active hydrogen (*H) on the noble metal surface, the adsorbed *H strongly competes for the active sites of the noble metal, leading to NO3-... The lack of sufficient electron adsorption and injection in the π* antibonding orbitals of ions leads to unsatisfactory activity and selectivity in NH3 generation.
[0004] Therefore, existing technologies need to be improved. Summary of the Invention
[0005] In view of the shortcomings of the prior art, the purpose of this invention is to provide a noble metal core-shell structure catalyst, its preparation method and its application, aiming to solve the problem of unsatisfactory activity and selectivity of existing noble metal catalysts for NH3 generation.
[0006] The technical solution of the present invention is as follows: In a first aspect, the present invention provides a method for preparing a noble metal core-shell structured catalyst, wherein the noble metal core-shell structured catalyst mainly comprises a carbon support and core-shell structured nanoparticles supported on the carbon support, with ruthenium as the core and ruthenium dioxide as the shell, and the preparation method includes the following steps: S1. Add ruthenium salt to the solvent, mix well, add carbon support, and perform pretreatment to obtain precursor powder; S2. The precursor powder is thermally reduced to obtain carbon-supported ruthenium nanoparticles; S3. Anneal and oxidize the carbon-supported ruthenium nanoparticles to obtain core-shell structured nanoparticles with ruthenium as the core and ruthenium dioxide as the shell, which are the noble metal core-shell structured catalysts.
[0007] Optionally, the pretreatment includes ultrasonication, stirring and dispersing to achieve uniform dispersion, and then removing the solvent.
[0008] Optionally, the ruthenium salt is one or more selected from anhydrous ruthenium chloride, ruthenium acetate, ruthenium carbonyl, ruthenium acetylacetonate, and ammonium hexachlororuthenate.
[0009] Optionally, the solvent is a 0.5-2 mol / L HCl solution.
[0010] Optionally, the carbon support is carbon black Black Pearl 2000, carbon black Ketjenblack EC-600JD, or carbon black Ketjenblack EC-300J.
[0011] Alternatively, the solvent can be removed by rotary evaporation.
[0012] Optionally, the conditions for thermal reduction are: heating to 600-1000℃ at a rate of 5-10℃ / min under a reducing atmosphere, and holding at that temperature for 1-5 hours.
[0013] Optionally, the annealing oxidation conditions are as follows: heating to 200-350°C at a rate of 5-10°C / min in air, and holding at that temperature for 1-6 hours.
[0014] Secondly, the present invention provides a noble metal core-shell structured catalyst prepared by the method described above.
[0015] Optionally, the particle size of the noble metal core-shell structure catalyst is 2-6 nm.
[0016] Thirdly, this invention provides the application of a noble metal core-shell structure catalyst in the electroreduction of nitrate to prepare ammonia.
[0017] Beneficial Effects: This invention provides a noble metal core-shell structured catalyst, its preparation method, and its applications. This invention prepares a core-shell structured catalyst (Ru@RuO2 / C) with a ruthenium core and a ruthenium dioxide shell on a carbon support through impregnation-thermal reduction and oxidative annealing. This invention proposes a simple impregnation-thermal reduction and low-temperature oxidation technique for preparing carbon-supported core-shell structures. This method is simple and suitable for large-scale commercial production. The Ru@RuO2 / C catalyst obtained by this invention has the characteristics of small size and uniform particle distribution. The core-shell structured catalyst can effectively promote the electroreduction of nitrate to ammonia while inhibiting the hydrogen evolution reaction, thus improving the Faradaic efficiency of ammonia synthesis. The Ru@RuO2 / C catalyst exhibits excellent catalytic performance, achieving a Faradaic efficiency of 90-100% in electrocatalytic nitrate or nitrite reduction systems for ammonia production, enabling the conversion of nitrate or nitrite-containing wastewater into valuable ammonia. Attached Figure Description
[0018] Figure 1 This is a flowchart illustrating the preparation of the catalyst for this invention.
[0019] Figure 2 X-ray diffraction patterns of the catalysts Ru@RuO2 / C and Ru / C prepared in Example 1.
[0020] Figure 3 This is a high-resolution transmission electron microscope image of the catalyst Ru@RuO2 / C prepared in Example 1.
[0021] Figure 4 Dark-field high-resolution transmission electron microscopy image of the catalyst Ru@RuO2 / C prepared in Example 1.
[0022] Figure 5 The elemental distribution diagram of the catalyst Ru@RuO2 / C prepared in Example 1.
[0023] Figure 6 This is a high-resolution transmission electron microscope image of the Ru / C catalyst prepared in Example 1.
[0024] Figure 7 A comparison of the Faraday efficiency of the catalyst Ru@RuO2 / C prepared in Example 1 for reducing nitrate to ammonia at different potentials, Ru / C and pure carbon C.
[0025] Figure 8 The graph shows the cycle stability test results of the catalyst Ru@RuO2 / C prepared in Example 1 for the reduction of nitrate to ammonia at the optimal Faraday efficiency of 0V vs RHE potential. Detailed Implementation
[0026] This invention provides a noble metal core-shell structured catalyst, its preparation method, and its applications. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
[0027] Currently, although electrocatalysts for several noble metals and their compounds such as Ru, Ir, Pd, and Pt have been developed towards the reduction of nitric acid (NO3)... However, its catalytic performance is still greatly limited by problems such as the accumulation of byproducts due to the mismatch of multi-electron transition kinetics in the nitric acid reduction reaction. Due to the high coverage of active hydrogen (*H) on the noble metal surface, the adsorbed *H strongly competes for the active sites of the noble metal, leading to NO3-... The lack of sufficient electron adsorption and injection into the π* antibonding orbitals of ions leads to unsatisfactory activity and selectivity in NH3 formation. Therefore, a simple and reasonable method is employed to design catalysts that suppress HER and promote NO3 formation. RR is crucial.
[0028] Based on this, this embodiment provides a method for preparing a noble metal core-shell structured catalyst, such as... Figure 1 As shown, it includes the following steps: S1. Add ruthenium salt to the solvent, mix well, add carbon support, and perform pretreatment to obtain precursor powder; S2. The precursor powder is thermally reduced to obtain carbon-supported ruthenium nanoparticles; S3. Anneal and oxidize the carbon-supported ruthenium nanoparticles to obtain core-shell structured nanoparticles with ruthenium as the core and ruthenium dioxide as the shell, which are the noble metal core-shell structured catalysts.
[0029] It should be noted that this embodiment mainly comprises a carbon support and core-shell structured nanoparticles with ruthenium as the core and ruthenium dioxide as the shell supported on the carbon support. In this embodiment, the raw material is first impregnated to obtain a precursor powder. Then, the ruthenium precursor is completely converted into metallic Ru nanocrystals using high-temperature reduction, the size of which is controlled by the support and reduction conditions. Subsequently, annealing oxidation (low-temperature selective oxidation) utilizes the high activity of the surface atoms of the Ru nanoparticles, preferentially oxidizing them to form a thin and dense RuO2 shell layer. The internal Ru core is retained due to oxygen diffusion restriction, thus spontaneously forming a Ru@RuO2 / C core-shell structure. This invention uses impregnation-thermal reduction and low-temperature oxidation to prepare a core-shell structured catalyst Ru@RuO2 / C with ruthenium as the core and ruthenium dioxide as the shell. The carbon support of this catalyst not only helps to suppress the agglomeration and growth of catalyst particles during high-temperature alloying but also provides good conductivity during electrocatalysis and significantly reduces costs. The synthesis method provided by this invention is simple and convenient for large-scale commercial production. The obtained catalyst Ru@RuO2 / C exhibits characteristics such as small size and uniform particle distribution. The core-shell structure of the catalyst effectively promotes the electroreduction of nitrate to ammonia while inhibiting the hydrogen evolution reaction, thus improving the Faradaic efficiency of ammonia synthesis. In electrocatalytic nitrate or nitrite reduction systems for ammonia production, a Faradaic efficiency of 90-100% can be achieved, enabling the conversion of nitrate- or nitrite-containing wastewater into valuable ammonia.
[0030] In some embodiments, the pretreatment includes ultrasonication, stirring to disperse the material evenly, and then removing the solvent. This pretreatment ensures a highly uniform dispersion of the raw materials.
[0031] In some embodiments, the ruthenium salt is one or more selected from anhydrous ruthenium chloride, ruthenium acetate, ruthenium carbonyl, ruthenium acetylacetone, and ammonium hexachlororuthenate.
[0032] The ruthenium salts used in this embodiment are all soluble compounds that can dissociate or disperse in a solvent (HCl solution), providing a uniform ruthenium source. Their thermal decomposition or reduction temperature range matches the process of this invention (high-temperature reduction followed by low-temperature oxidation), ensuring complete conversion to metallic ruthenium in the reduction step and preventing residual impurities from affecting the purity of the core or the formation of the shell. Using these specific salts ensures that the precursor fully and uniformly combines with the carbon support in the impregnation step, which is the material basis for achieving uniform size and distribution of the final catalyst nanoparticles. Their wide range of options also provides flexibility for adjusting costs, solubility, and process adaptability.
[0033] In some embodiments, the solvent is a 0.5-2 mol / L HCl solution, which can be selected from 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1.0 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.5 mol / L, 1.6 mol / L, 1.7 mol / L, 1.8 mol / L, 1.9 mol / L, and 2 mol / L.
[0034] It should be noted that HCl solution serves two purposes: firstly, it acts as a solvent to dissolve ruthenium salts (especially chlorides), and secondly, its acidic environment inhibits the hydrolysis of ruthenium salts to prevent precipitation, ensuring the formation of a stable and uniform impregnation solution. This allows for the initial atomic or nanoscale dispersion of ruthenium species on the carbon support. Only by using a solvent of appropriate concentration can a good impregnation effect be achieved. Too high a concentration will etch the carbon support, while too low a concentration will cause the metal to hydrolyze and precipitate.
[0035] In some embodiments, the carbon support is Black Pearl 2000, Ketjenblack EC-600JD, or Ketjenblack EC-300J.
[0036] It should be noted that, in the application of the carbon support in this embodiment, the high conductivity of carbon black ensures efficient electron transport between the catalyst particles and the electrode, reducing the reaction overpotential. Its porous structure facilitates electrolyte wetting and reactant / product diffusion, thereby improving the overall catalytic rate (yield).
[0037] In some implementations, rotary evaporation is used to remove the solvent.
[0038] In some embodiments, the conditions for thermal reduction are as follows: under a reducing atmosphere, the temperature is increased to 600-1000℃ (which can be selected as 600℃, 700℃, 800℃, 900℃, 1000℃, etc.) at a rate of 5-10℃ / min (which can be selected as 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, 10℃ / min, etc.), and the holding time is 1-5h (which can be selected as 1h, 2h, 3h, 4h, 5h, etc.).
[0039] It should be noted that in this embodiment, the precursor powder is completely converted into well-crystallized Ru nanoparticles. This temperature range ensures sufficient reduction kinetics and atomic lattice rearrangement, forming a stable metal core. Controlling the heating rate (e.g., 10°C / min) helps to ensure a smooth and controllable reduction reaction, avoiding particle sintering caused by local overheating. The holding time ensures complete reaction. Impact on core-shell structure: The size and crystallinity of the Ru core formed in this step directly determine the shell formation mode and the quality of the final core-shell structure in subsequent oxidation steps. Appropriately sized, well-crystallized Ru cores are beneficial for forming a complete and uniform RuO2 shell. The reducing atmosphere can be a mixture of hydrogen and argon (containing 2-5% H2 by volume).
[0040] In some embodiments, the annealing oxidation conditions are as follows: heating to 200-350°C at a rate of 5-10°C / min in air, and holding at that temperature for 1-6 hours.
[0041] It should be noted that the annealing oxidation conditions in this embodiment are the core step in forming the core-shell structure. Choosing a low-temperature oxidation of 200-350℃ is crucial. At this temperature, oxygen atoms have sufficient activity to oxidize the surface of metallic Ru, but their diffusion rate into the particle interior is slow, thus achieving selective surface oxidation. The metal core is preserved, forming a Ru@RuO2 shell structure. By controlling the oxidation temperature and time, the thickness and density of the RuO2 shell can be precisely controlled. For example, oxidation at 250℃ for 4 hours yields the optimal shell, which effectively modulates the surface electronic structure to suppress the hydrogen evolution reaction (HER) without hindering the reaction of NO3- due to excessive shell thickness. - It contacts the active sites in the core, thereby achieving a perfect balance between activity and selectivity.
[0042] In some embodiments, the particle size of the noble metal core-shell structure catalyst is 2-6 nm.
[0043] Thirdly, this invention provides the application of a noble metal core-shell structure catalyst as an electrocatalyst in the reduction of nitrate to prepare ammonia.
[0044] The catalyst in this embodiment exhibits a Faradaic efficiency greater than 90% in the catalytic reduction of nitrate to ammonia within a potential range of -0.4 to 0.2 V (vs. RHE). In an alkaline (KOH) electrolyte, OH... - High concentrations promote water decomposition to generate *H (NO3). -Reduction provides an ample hydrogen source. Simultaneously, alkaline conditions suppress the competing hydrogen evolution reaction (HER), as the kinetics of HER are inherently slower under alkaline conditions. This catalyst achieves a Faraday efficiency of >99% near zero potential (0 V vs. RHE), meaning that almost all the input electrical energy is used to generate the target product, ammonia, and side reactions (especially HER) are significantly suppressed.
[0045] The present invention will be further described below through specific embodiments.
[0046] Example 1 Preparation of a noble metal core-shell structured catalyst: 0.145 g of ruthenium trichloride was dissolved in 200 mL of 1 mol / L hydrochloric acid solution and sonicated for 0.5 h. Then, 0.45 g of Black Pearl 2000 was added and sonicated for another 2 h. The mixture was stirred for 24 h to ensure that the precursor and carbon black carrier were fully mixed. The solution was then removed by vacuum rotary evaporation and dried to obtain the precursor powder.
[0047] The precursor powder was placed in a corundum crucible and then placed in a tube furnace. Under a hydrogen-argon reducing atmosphere, the temperature was increased to 900°C at a rate of 10°C / min and held for 2 hours. After natural cooling, carbon-supported ruthenium nanoparticles (Ru / C) were obtained.
[0048] The Ru / C was then placed in a tube furnace and heated to 250°C at a rate of 10°C / min under air conditions. The temperature was then maintained for 4 hours and allowed to cool naturally to obtain a noble metal core-shell structure catalyst, which was denoted as Ru@RuO2 / C.
[0049] Figure 2 X-ray diffraction patterns of the catalysts Ru@RuO2 / C and Ru / C prepared in Example 1. Figure 3 The image shows a high-resolution transmission electron microscope (TEM) image of the catalyst Ru@RuO2 / C prepared in Example 1, with the inset showing the particle size distribution of Ru@RuO2 / C. Figure 4 Dark-field high-resolution transmission electron microscopy image of the catalyst Ru@RuO2 / C prepared in Example 1. Figure 5 The elemental distribution diagram of the catalyst Ru@RuO2 / C prepared in Example 1. Figure 6 This is a high-resolution transmission electron microscope image of the Ru / C catalyst prepared in Example 1. Figure 7 A comparison of the Faraday efficiency of the catalyst Ru@RuO2 / C prepared in Example 1 for reducing nitrate to ammonia at different potentials, Ru / C and pure carbon C. Figure 8 The graph shows the cycle stability test results of the catalyst Ru@RuO2 / C prepared in Example 1 for the reduction of nitrate to ammonia at the optimal Faraday efficiency of 0 V vs RHE potential.
[0050] from Figure 2 It can be seen that the catalyst Ru@RuO2 / C possesses the crystal forms of both Ru and RuO2, while Ru / C possesses the crystal form of Ru, proving the success of the material's crystal structure. From Figure 3 It can be seen that Ru@RuO2 / C is uniformly dispersed on the BP2000 surface, with an average particle size of about 4 nm, and no obvious agglomeration. Figure 4 , Figure 5 It can be seen that the catalyst (Ru@RuO2 / C) in this embodiment exhibits a core-shell structure, with RuO2 as the shell and Ru as the core. From Figure 6 It can be seen that Ru / C is uniformly dispersed on the BP2000 surface, with an average particle size of about 3 nm and no obvious agglomeration, which provides a basis for subsequent annealing and oxidation to Ru@RuO2 / C. Figure 7 As can be seen, the performance of the catalyst in a 1 mol / L potassium hydroxide solution containing 2000 ppm nitrate is demonstrated. The ammonia Faradaic efficiency of the catalyst (Ru@RuO2 / C) in this embodiment is 99.7%, which is significantly higher than that of the comparative samples Ru / C and C. From Figure 8 As can be seen, the cyclic stability test performance of the catalyst (Ru@RuO2 / C) in a 1 mol / L potassium hydroxide solution containing 2000 ppm nitrate is demonstrated. The cyclic stability of the catalyst in this embodiment is 50 cycles, and both the ammonia faradaic ratio and ammonia yield are at a stable level without significant decay.
[0051] In summary, this invention provides a noble metal core-shell structured catalyst, its preparation method, and its applications. This invention uses carbon black as a support and employs an impregnation-thermal reduction and low-temperature oxidation method to prepare a core-shell structured catalyst Ru@RuO2 / C with a ruthenium core and a ruthenium dioxide shell. This invention proposes a simple impregnation-thermal reduction and low-temperature oxidation technique for preparing carbon-supported core-shell structures. This method is simple and suitable for large-scale commercial production. The Ru@RuO2 / C catalyst obtained by this invention has the characteristics of small size and uniform particle distribution. The core-shell structured catalyst can effectively promote the electroreduction of nitrate to ammonia while inhibiting the hydrogen evolution reaction, thus improving the Faradaic efficiency of ammonia synthesis. The Ru@RuO2 / C catalyst exhibits excellent catalytic performance, with a high Faradaic efficiency (FE) (reaching 90-100%) for the reduction of nitrate to ammonia at 0V versus RHE, and also possesses excellent stability.
[0052] It should be understood that the application of the present invention is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.
Claims
1. A method for preparing a noble metal core-shell structured catalyst, characterized in that, The noble metal core-shell structured catalyst mainly comprises a carbon support and core-shell structured nanoparticles supported on the carbon support, with ruthenium as the core and ruthenium dioxide as the shell. The preparation method includes the following steps: S1. Add ruthenium salt to the solvent, mix well, add carbon support, and perform pretreatment to obtain precursor powder; S2. The precursor powder is thermally reduced to obtain carbon-supported ruthenium nanoparticles; S3. Anneal and oxidize the carbon-supported ruthenium nanoparticles to obtain core-shell structured nanoparticles with ruthenium as the core and ruthenium dioxide as the shell, which are the noble metal core-shell structured catalysts.
2. The method for preparing a noble metal core-shell structured catalyst according to claim 1, characterized in that, The ruthenium salt is one or more of anhydrous ruthenium chloride, ruthenium acetate, ruthenium carbonyl, ruthenium acetylacetone, and ammonium hexachlororuthenate.
3. The method for preparing a noble metal core-shell structured catalyst according to claim 1, characterized in that, The solvent is a 0.5-2 mol / L HCl solution.
4. The method for preparing a noble metal core-shell structured catalyst according to claim 1, characterized in that, The carbon support is Black Pearl 2000, Ketjenblack EC-600JD, or Ketjenblack EC-300J.
5. The method for preparing a noble metal core-shell structured catalyst according to claim 1, characterized in that, The solvent is removed by rotary evaporation.
6. The method for preparing a noble metal core-shell structured catalyst according to claim 1, characterized in that, The conditions for thermal reduction are as follows: under a reducing atmosphere, the temperature is increased to 600-1000℃ at a rate of 5-10℃ / min, and the holding time is 1-5h.
7. The method for preparing a noble metal core-shell structured catalyst according to claim 1, characterized in that, The annealing and oxidation conditions are as follows: under air, the temperature is increased to 200-350℃ at a rate of 5-10℃ / min, and the holding time is 1-6h.
8. A noble metal core-shell structured catalyst, characterized in that, Prepared by the method of any one of claims 1-7, or mainly comprising a carbon support and core-shell structured nanoparticles with ruthenium as the core and ruthenium dioxide as the shell loaded on the carbon support.
9. A noble metal core-shell structured catalyst according to claim 8, characterized in that, The particle size of the noble metal core-shell structure catalyst is 2-6 nm.
10. The application of a noble metal core-shell structure catalyst as described in claim 8 or 9 in the electroreduction of nitrate to prepare ammonia.