Homonuclear diatomic ruthenium catalysts for the electroreduction of nitrate to ammonia and methods of making and using the same

Abstract

The application discloses a homonuclear diatomic ruthenium catalyst for nitrate electro-reduction to prepare ammonia and a preparation method and application thereof. The method is characterized in that carbon nanotube dispersion liquid is uniformly mixed with dichloro(p-methylisopropylbenzene) ruthenium (II) dimer, and after washing and freeze-drying, a catalyst precursor powder is obtained, and then high-temperature pyrolysis treatment is carried out on the catalyst precursor powder to prepare a Ru2-CNT catalyst. The preparation method is simple, and the prepared Ru2-CNT catalyst shows excellent electrochemical activity and stability in electrocatalytic reduction of nitrate to synthesize ammonia, and the faradaic efficiency of NH3 synthesis can reach 98.03%, so that the Ru2-CNT catalyst has a wide application prospect in the reduction electro-catalysis of nitrate to prepare ammonia.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical nitrate reduction technology, and relates to a homonuclear diatomic ruthenium catalyst for the electroreduction of nitrate to ammonia, its preparation method and application. Background Technology

[0002] The continued expansion of industrial production and agricultural activities has led to the discharge of large amounts of nitrogenous pollutants (especially nitrates), causing a series of environmental and health problems, including severe eutrophication of water bodies, ecosystem destruction, and drinking water source pollution. At the same time, the widespread presence of nitrates (NO3) has also contributed to the pollution. - The efficient and selective electrocatalytic reduction of nitrate to ammonia (NH3) is not only a promising water remediation technology, but also provides a new alternative to the traditional high-energy-consuming Haber process for achieving "green ammonia synthesis" under mild conditions. Therefore, the development of efficient and stable electrocatalytic nitrate reduction to ammonia (NO3RR) technology is of great strategic significance for environmental protection and sustainable chemical industry.

[0003] Among numerous NO3RR catalysts, platinum group metal-based materials (such as Pd, Pt, and Ru) exhibit high catalytic activity due to their strong adsorption and activation capabilities for nitrate ions. However, these noble metal-based catalysts generally suffer from high costs, insufficient selectivity for the target product ammonia, and susceptibility to deactivation under long-term operation or complex water quality conditions, severely limiting their large-scale practical application. To overcome these bottlenecks, research focus has gradually shifted to developing non-noble metal catalysts (such as Fe, Co, Ni, and Cu-based materials) and improving the atom utilization of noble metals through nanostructure engineering. In recent years, single-atom catalysts (SACs) have shown great potential in NO3RR due to their highest atom utilization and well-defined tunable active centers. However, single-atom sites sometimes exhibit insufficient intrinsic activity or excessively strong / weak adsorption energies for key intermediates when catalyzing multi-step reduction reactions (involving multiple electron-proton transfer steps), leading to limited reaction efficiency or selectivity.

[0004] Recent studies have shown that diatomic catalysts (DACs), especially homonuclear diatomic pair catalysts with precise structures, can optimize the adsorption behavior of various reaction intermediates through the synergistic effect between adjacent metal atoms and promote key steps (such as NO bond breaking, NO hydrogenation, or NH2 desorption), thus potentially improving the activity, selectivity, and stability of NO3RR. Ruthenium (Ru) has attracted attention in nitrogen fixation and nitrate reduction due to its moderate adsorption strength for nitrogen species. However, the synthesis of catalysts with well-defined and stable homonuclear ruthenium diatomic structures still faces significant challenges. Existing preparation methods (such as high-temperature pyrolysis, wet chemical anchoring, and electrochemical displacement) often have extremely stringent requirements for precursor design and synthesis condition control, are complex processes, and struggle to precisely control the local coordination environment and interatomic spacing of the diatomic sites. This results in a low proportion of diatomic sites in the product, structural heterogeneity, poor reproducibility, and hinders in-depth mechanistic research and large-scale preparation. For example, Wu et al. successfully synthesized a ruthenium diatomic catalyst by controlling the Ru-Ru spacing using a ruthenium di-complex precursor. However, the ruthenium loading of this catalyst was high (4.1 wt%), and the synthesis steps were complex ([1] Wu, Chuang; Gao, Bo; Hu, Wending; Xu, Song; Wu, Wenzhuo; Xu, Qun. Dual-Atomic Ruthenium Interdistance Mediated by Metal–Metal Multiple Bonds for Electrocatalytic Nitrate Reduction Optimization. Inorg. Chem. 2026, 65, 9559-9567.). Therefore, developing a method that is simple in steps, mild in conditions, low in loading, and can accurately and controllably synthesize a well-defined homonuclear diatomic ruthenium catalyst is crucial for promoting the basic research and application development of NO3RR catalysts. Summary of the Invention

[0005] To address the problems of excessively high overpotential, insufficient Faraday efficiency, complex preparation of catalytic materials, and high cost in the current electrocatalytic reduction of nitrate to ammonia, this invention provides a homonuclear diatomic ruthenium catalyst (Ru2-CNT) for the electroreduction of nitrate to ammonia, along with its preparation method and applications. In this invention, Ru in the homonuclear diatomic ruthenium catalyst mainly exists in the form of diatomic pairs, exhibiting an atomically dispersed structure and extremely low metal atom loading, thus demonstrating excellent nitrate electrocatalytic activity and stability.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] The preparation method of the homonuclear diatomic ruthenium catalyst for the electroreduction of nitrate to ammonia includes the following steps:

[0008] (1) Carbon nanotubes (CNTs) were pretreated in hydrochloric acid solution to remove any metallic impurities, then filtered, washed with water and freeze-dried;

[0009] (2) The dried carbon nanotubes were ultrasonically dispersed in N,N-dimethylformamide (DMF), and dichloro(p-methylisopropylbenzene)ruthenium(II) dimer was added. The mixture was ultrasonically dispersed and stirred until it was uniformly mixed. After centrifugation, the resulting solid was washed and freeze-dried to obtain catalyst precursor powder.

[0010] (3) The catalyst precursor powder is placed in a tube furnace and subjected to high-temperature pyrolysis treatment at 300~500℃ in an inert gas atmosphere to obtain Ru2-CNT catalyst with Ru2 loading of 0.02 wt%~0.1 wt%.

[0011] Furthermore, in step (1), the concentration of the hydrochloric acid solution is 1~6 mol L. -1 The pretreatment time is 6 to 24 hours.

[0012] Furthermore, in step (2), the ultrasonic time is 10 to 120 minutes, and the stirring time is 6 to 24 hours.

[0013] Furthermore, in step (2), the mass ratio of carbon nanotubes to dichloro(p-methylisopropylbenzene)ruthenium(II) dimer is 1:0.01 to 0.05.

[0014] Further, in step (2), the washing method is to wash with DMF, ethanol and deionized water in sequence.

[0015] Furthermore, in step (3), the inert gas is nitrogen or argon.

[0016] Furthermore, in step (3), the pyrolysis treatment temperature is 400℃, the heating rate is 10℃ / min, and the temperature holding time is 0.5~2 hours.

[0017] Furthermore, in step (3), the Ru2 loading in the Ru2-CNT catalyst is 0.04 wt%.

[0018] This invention provides a homonuclear diatomic ruthenium catalyst prepared by the above-described method.

[0019] The present invention also provides the application of the above-mentioned homonuclear diatomic ruthenium catalyst in the electrochemical catalytic reduction of nitrate to ammonia.

[0020] Furthermore, the specific application method is as follows: an electrode coated with a homonuclear diatomic ruthenium catalyst is used as the cathode, a platinum mesh electrode is used as the counter electrode, a saturated calomel electrode is used as the reference electrode, and the electrolyte is an aqueous solution of 1 mol / L KOH and 0.1 mol / L KNO3.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] (1) The Ru in the Ru2-CNT catalyst prepared by the present invention mainly exists in the form of two atomic pairs, presenting a uniform nanotube morphology with a nanotube diameter of 10~20nm. There are no metal nanoparticles or alloy nanoparticle structures, and it has an extremely low Ru loading, which greatly reduces the cost.

[0023] (2) The preparation process of the present invention is simple, easy to expand, and has a wide range of applications, and can be used for large-scale preparation;

[0024] (3) In the electrocatalytic performance test of nitrate reduction, the Ru2-CNT catalyst prepared in this invention has a Faraday efficiency of 98.03% for electrochemical reduction to ammonia (at -0.7 V vs. RHE potential), and the Faraday efficiency does not decrease after 100 cycles, showing excellent electrocatalytic performance and cycle stability. Attached Figure Description

[0025] Figure 1 These are transmission electron microscope (TEM) images and atomic resolution high-angle annular dark-field-scanning transmission electron microscope (HAADF-STEM) images of the Ru2-CNT catalyst prepared in Example 1.

[0026] Figure 2 The image shows the X-ray diffraction (XRD) pattern of the Ru2-CNT catalyst prepared in Example 1.

[0027] Figure 3 This is a comparison of the linear sweep voltammetry (LSV) curves of the Ru2-CNT catalyst prepared in Example 1 and the Ru1-CNT catalyst prepared in Comparative Example 2 in the electrolyte.

[0028] Figure 4 This is a comparison diagram of the activity of the Ru2-CNT catalyst prepared in Example 1 and the Ru1-CNT catalyst prepared in Comparative Example 2 for nitrate reduction to ammonia synthesis.

[0029] Figure 5 This is a comparison chart of the yields of nitrate reduction for ammonia synthesis between the Ru2-CNT catalyst prepared in Example 1 and the Ru1-CNT catalyst prepared in Comparative Example 2.

[0030] Figure 6This is a stability test diagram of the Ru2-CNT catalyst prepared in Example 1. Detailed Implementation

[0031] The present invention will be further described in detail below with reference to specific embodiments and accompanying drawings. Unless otherwise specified, the experimental methods in the following embodiments are conventional methods. Unless otherwise specified, the experimental materials used in the following embodiments are commercially available.

[0032] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0033] In the following examples and comparative examples, the electrochemical nitrate reduction test method is as follows:

[0034] The electrochemical nitrate reduction performance of the catalyst was tested using the Wuhan Koster electrochemical workstation. The tests were conducted in an H-type cell, with KOH + KNO3 aqueous solutions at concentrations of 1 mol / L and 0.1 mol / L, respectively.

[0035] In typical tests, a catalyst-coated electrode was used as the working electrode, while a platinum mesh electrode and a saturated calomel electrode were used as the counter and reference electrodes, respectively. All tests were performed at room temperature with an Ar gas flow rate of 20 mL / min.

[0036] Example 1

[0037] (1) Weigh 1g of commercial carbon nanotubes into a 250ml beaker and add 6.0 mol L -1 A suspension was formed in an HCl solution and sonicated for 30 minutes to ensure thorough dispersion and a homogeneous suspension. The suspension was then continuously stirred for 12 hours to remove any metallic impurities. Afterward, the suspension was transferred to centrifuge tubes and centrifuged at 10,000 rpm for 5 minutes. The supernatant was removed, and deionized water was added. This centrifugation and washing process was repeated three times. Finally, the solution was freeze-dried overnight to obtain purified carbon nanotubes.

[0038] (2) Weigh 20 mg of purified carbon nanotubes and disperse them in 20 ml of DMF. Separately weigh 1.5 mg of dichloro(p-methylisopropylbenzene)ruthenium(II) dimer, dissolve it in 5 ml of DMF, and slowly add it to the above carbon nanotube dispersion after complete dissolution. Sonicate the mixture for 30 minutes to ensure thorough mixing, and then stir continuously at room temperature for 24 hours. Afterward, transfer the mixture to a centrifuge tube, centrifuge at 10,000 rpm for 5 minutes, and collect the precipitate. Repeat the above centrifugation and washing operation twice each with DMF, ethanol, and deionized water to thoroughly remove impurities. Finally, freeze-dry the washed product overnight to obtain the catalyst precursor powder.

[0039] (3) The catalyst precursor was placed in a quartz boat and placed in the center of a tube furnace. The temperature was raised to 300°C at a rate of 10°C / min in an argon atmosphere with a flow rate of 50 mL / min. The high-temperature pyrolysis treatment was carried out for 2 h, and then the temperature was naturally cooled to room temperature to obtain the Ru2-CNT catalyst.

[0040] Comparative Example 1

[0041] This comparative example is roughly the same as Example 1, except that only step (1) is performed, and steps (2) and (3) are not performed, to obtain purified carbon nanotubes.

[0042] Comparative Example 2

[0043] This comparative example is roughly the same as Example 1, except that the dichloro(p-methylisopropylbenzene)ruthenium(II) dimer in step (2) is replaced with ruthenium trichloride. The final single-atom ruthenium catalyst is denoted as Ru1-CNT catalyst.

[0044] The Ru2-CNT catalyst obtained in Example 1 was characterized by TEM to observe its morphological characteristics. Figure 1 As shown in Figure a, the Ru2-CNT catalyst exhibits a uniform nanotube morphology with a nanotube diameter of 10~20 nm. Figure 1 The HAADF-STEM image of b shows homonuclear ruthenium diatomic sites uniformly distributed on the carbon nanotubes.

[0045] The Ru2-CNT catalyst obtained in Example 1 was characterized by XRD. Figure 2 As shown, the XRD spectra of both the Ru2-CNT catalyst and the purified carbon nanotubes have two broad peaks at around 23° and 44°, which correspond to the (002) and (100) crystal planes of graphite carbon, respectively. Moreover, the Ru2-CNT catalyst does not have the peaks shown in the standard card of Ru metal particles (PDF#01-089-4903). This indicates that the Ru metal element exists in the catalyst in an atomically dispersed form.

[0046] The Ru2-CNT catalyst prepared in Example 1 was tested by inductively coupled plasma mass spectrometry (ICP-MS), and the Ru content was found to be only 0.04 wt%.

[0047] Figure 3 A comparison of linear sweep voltammetry (LSV) curves obtained by the Ru2-CNT catalyst prepared in Example 1 and the Ru1-CNT catalyst prepared in Comparative Example 2 in a 1.0 M KOH electrolyte containing 0.1 MKNO3. A standard three-electrode system was used for the test, where the working electrode was a carbon paper electrode coated with catalyst slurry (the catalyst slurry was prepared by mixing the catalyst with ethanol, water, and Nafion solution, with a catalyst content of 10 mg / mL), the reference electrode was a saturated calomel electrode (SCE), and the counter electrode was a platinum mesh electrode. Figure 3 It can be seen that, compared with the Ru1-CNT catalyst, the Ru2-CNT catalyst exhibits a higher current density throughout the entire test potential range, indicating that it has superior electrocatalytic nitrate reduction activity.

[0048] Figure 4 The results of the Faradaic efficiency test of the Ru2-CNT catalyst prepared in Example 1 and the Ru1-CNT catalyst prepared in Comparative Example 2 are compared. As shown in the figure, the Faradaic efficiency of the Ru2-CNT catalyst for NH3 products is as high as 98.03% at -0.7 V vs. RHE potential, and the Faradaic efficiency of the Ru2-CNT catalyst is significantly better than that of the Ru1-CNT catalyst throughout the entire test potential range.

[0049] Figure 5 The ammonia yield test results of the Ru2-CNT catalyst prepared in Example 1 and the Ru1-CNT catalyst prepared in Comparative Example 2 are compared. As shown in the figure, the Ru2-CNT catalyst achieved the highest ammonia yield at -0.7 V vs. RHE potential, and the ammonia yield of the Ru2-CNT catalyst was significantly better than that of the Ru1-CNT catalyst throughout the entire test potential range.

[0050] Figure 6 The results show the stability test of the Ru2-CNT catalyst prepared in Example 1 in the electrocatalytic nitrate reduction reaction. As shown in the figure, after 100 cycles, the catalyst's Faraday efficiency did not decrease significantly, exhibiting excellent electrochemical stability.

[0051] Table 1 compares the NO3RR performance of the Ru2-CNT catalyst with that of the most advanced reported catalysts.

[0052]

[0053]

[0054] Table 1 compares the NO3RR performance of the Ru2-CNT catalyst prepared in Example 1 with that of the most advanced reported catalysts. The Ru2-CNT catalyst exhibits excellent NO3RR performance, with a Faraday efficiency of up to 98.03% and a TOF of 327.2 s⁻¹. -1 The quality activity reached 198.4 gh. -1 mg Ru -1 These values ​​are the highest reported for catalysts, while the Ru loading is only 0.04 wt%. These results fully demonstrate the significant advantages of the homonuclear ruthenium diatomic structure in improving catalytic activity and atom utilization efficiency.

[0055] literature:

[0056] [1] Wu, Chuang; Gao, Bo; Hu, Wending; et al., Dual-Atomic RutheniumInterdistance Mediated by Metal–Metal Multiple Bonds for ElectrocatalyticNitrate Reduction Optimization. Inorg. Chem. 2026, 65, 9559-9567.

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[0060] [5] Xu, Jingwen; Liu, Hengjie; Zhang, Shengbo; et al., IntegratedCascade Catalysts for Electrochemical Nitrate Reduction to Ammonia. J. Am.Chem. Soc. 2026, 148 (1), 148-161.

[0061] [6] Hong, Seongin; Jeong, Jaewoo; Yoo, Euichan; et al., Operando CuAggregation-Induced Spin State Modulation in Fe–Cu Single Atom Catalyst forEnhanced Tandem Electrochemical Nitrate Reduction Reaction. J. Am. Chem. Soc.2026, 148 (14), 15114-15124.

[0062] [7] Chen, Dechao; Li, Yong; Wei, Zengxi; et al., Inside-out-engineered CuO x / Ru sites for efficient electrochemical nitrate reduction toammonia. Proc Natl Acad Sci U S A 2026, 123 (20), e2537982123.

[0063] [8] Li, Di; Chai, Yani; Xiao, Qian; et al., Confinement-InducedEnrichment in Hollow Multishelled Structure for High-Efficiency AmmoniaElectrosynthesis. J. Am. Chem. Soc. 2026, 148 (17), 17910-17919.

[0064] [9] Tian, Yiqi; Shen, Chenyang; Han, Mingchen; et al., Elevating theEfficiency of Ammonia Synthesis by Dredging the Migration Hinges of ReactiveSpecies. J. Am. Chem. Soc. 2026, 148 (15), 16204-16210.

[0065]

[10] Li, Ruonan; Ma, Rrunlin; Zhang, Li. Li; et al., Sulfur-BridgeEngineering Enables Reverse Hydrogen Spillover to Atomic Cu for Nitrate-to-Ammonia Electrocatalysis. Angew Chem Int Ed 2026, 65, e7688164.

[0066]

[11] Zuo, Yunpeng; Sun, Mingzi; Li, Tingting; et al., CapturingCopper Single Atom in Proton Donor Stimulated O-End Nitrate Reduction. Adv.Mater. 2025, 37 (12), e2415632.

[0067]

[12] Guo, Jiangyi; Zhang, Lu. Hua.; Guo, Yabo.; et al., Oxygen-Incorporation-Engineered Interfacial Water Modulation on Single-Atom Cu Sitesfor Enhanced Dilute Nitrate Electroreduction. Angew Chem Int Ed 2026, 65 (2),e16401.

[0068]

[13] Zhu, Xiaojuan; Wang, Yi. Chi; Qu, Kaiyu; et al., Modulating Ru-Co bond lengths in Ru1Co single-atom alloys through crystal phase engineeringfor electrocatalytic nitrate-to-ammonia conversion. Nat. Commun. 2025, 16(1), 5742.

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[0072]

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Claims

1. A method for preparing a homonuclear diatomic ruthenium catalyst for the electroreduction of nitrate to ammonia, characterized in that, Includes the following steps: (1) Carbon nanotubes were pretreated in hydrochloric acid solution to remove any metallic impurities, then filtered, washed with water and freeze-dried; (2) The dried carbon nanotubes were ultrasonically dispersed in DMF, and dichloro(p-methylisopropylbenzene)ruthenium(II) dimer was added. The mixture was ultrasonically dispersed and stirred until it was uniformly mixed. After centrifugation, the resulting solid was washed and freeze-dried to obtain catalyst precursor powder. (3) The catalyst precursor powder is placed in a tube furnace and subjected to high-temperature pyrolysis treatment at 300~500℃ in an inert gas atmosphere to obtain Ru2-CNT catalyst with Ru2 loading of 0.02 wt%~0.1 wt%.

2. The preparation method according to claim 1, characterized in that, In step (1), the concentration of hydrochloric acid solution is 1~6 mol / L. -1 The pretreatment time is 6 to 24 hours.

3. The preparation method according to claim 1, characterized in that, In step (2), the ultrasonic time is 10 to 120 minutes and the stirring time is 6 to 24 hours.

4. The preparation method according to claim 1, characterized in that, In step (2), the mass ratio of carbon nanotubes to dichloro(p-methylisopropylbenzene)ruthenium(II) dimer is 1:0.01 to 0.

05.

5. The preparation method according to claim 1, characterized in that, In step (2), the washing method is to wash with DMF, ethanol and deionized water in sequence.

6. The preparation method according to claim 1, characterized in that, In step (3), the inert gas is nitrogen or argon.

7. The preparation method according to claim 1, characterized in that, In step (3), the pyrolysis temperature is 400℃, the heating rate is 10℃ / min, and the temperature holding time is 0.5~2 hours; the Ru2 loading in the Ru2-CNT catalyst is 0.04wt%.

8. The homonuclear diatomic ruthenium catalyst prepared by the preparation method according to any one of claims 1 to 7.

9. The application of the homonuclear diatomic ruthenium catalyst according to claim 8 in the electrochemical catalytic reduction of nitrate to ammonia.

10. The application according to claim 9, characterized in that, The specific application method is as follows: an electrode coated with a homonuclear diatomic ruthenium catalyst is used as the cathode, a platinum mesh electrode is used as the counter electrode, a saturated calomel electrode is used as the reference electrode, and the electrolyte is an aqueous solution of 1.0 mol / L KOH and 0.1 mol / L KNO3.

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