Nitrogen-doped carbon-loaded tin monatomic catalyst as well as preparation method and application thereof

Abstract

The invention relates to a nitrogen-doped carbon-loaded tin monatomic catalyst as well as a preparation method and application thereof. The catalyst comprises a nitrogen-doped carbon carrier and a tin metal single atom loaded on the nitrogen-doped carbon carrier, the tin metal single atoms are anchored on the carbon substrate in an atomic-scale dispersion form, and mutually connected metal-metal bonds do not exist; the loading capacity of the metal single atoms is 1-5wt%. The preparation method comprises the following steps: dispersing metal salt, a nitrogen source and a carbon source in a solvent, uniformly mixing, removing the solvent, and drying to obtain a precursor mixture; and carrying out high-temperature pyrolysis on the precursor mixture in an inert atmosphere, cooling, grinding, carrying out acid etching, removing undispersed metal particles, washing and drying to obtain the nitrogen-doped carbon-loaded tin metal monatomic catalyst. The catalyst is used for synthesizing hydrogen peroxide through an electro-catalysis two-electron oxygen reduction path, and the hydrogen peroxide selectivity is higher than 80%. The preparation method is simple in process and low in equipment cost, and meets actual production requirements.

Description

Technical Field

[0001] This invention relates to the field of materials chemistry, and in particular to a nitrogen-doped carbon-supported tin single-atom catalyst, its preparation method, and its application. Background Technology

[0002] Hydrogen peroxide (H2O2), as a green and strong oxidant and energy carrier, plays an irreplaceable role in paper bleaching, medical disinfection, wastewater treatment, and semiconductor cleaning. Currently, industrial production of hydrogen peroxide mainly relies on the traditional anthraquinone process. However, this process suffers from problems such as cumbersome procedures, high energy consumption, organic solvent pollution, and the need for centralized large-scale production. Furthermore, high-concentration hydrogen peroxide poses significant safety hazards during transportation and storage, while practical applications often require only low-concentration solutions, increasing on-site dilution costs. Therefore, utilizing renewable electricity to produce hydrogen peroxide via the two-electron oxygen reduction reaction (2e...)... - ORR (Organic Hydrogen Peroxide) is considered a promising alternative for the dispersed, in-situ preparation of hydrogen peroxide at ambient temperature and pressure. It offers advantages such as low cost, high sustainability, and high safety.

[0003] The key to achieving efficient electrochemical synthesis of hydrogen peroxide lies in developing high-performance electrocatalysts. Early research mainly focused on noble metals such as Pd, Pt, and Au and their alloys, but their scarce reserves and high costs severely limit their large-scale commercial application. In recent years, carbon-supported metal single-atom catalysts (SACs) have become a research hotspot in the field of catalysts due to their near 100% atom utilization and unique electronic structure. However, currently widely studied transition metal single-atom catalysts such as Fe, Co, and Ni typically have strong O / O bond dissociation capabilities and tend to undergo four-electron (4e) reactions. - The reaction produces water, resulting in low selectivity for hydrogen peroxide. In contrast, p-block metals (such as Sn and In), due to their electronic structure and Lewis acidity characteristics, have been reported to promote the adsorption of 2e⁻ by modulating the adsorption strength of key intermediates such as *OOH. - The pathway can suppress the breaking of OO bonds, thus possessing the potential for high H2O2 selectivity. However, there is still a lack of systematic solutions and engineeringable pathways for the stable construction of p-block metal single-atom sites and the introduction of high-density active sites. At the same time, p-block metal single-atom catalysts also face the problem of low stability. There is an urgent need to develop an N-coordinated p-block single-atom carbon-based catalytic material and its application system that combines high selectivity, high activity and high stability. Summary of the Invention

[0004] The technical problem to be solved by this invention is to overcome the high cost of noble metal catalysts in existing electrochemical synthesis of hydrogen peroxide technology, and the low selectivity of hydrogen peroxide caused by the strong OO bond dissociation ability of transition metal single-atom catalysts. At the same time, it solves the problems of difficult stable construction of p-block metal single-atom sites, insufficient number of active sites and low stability, and provides a nitrogen-doped carbon-supported tin single-atom catalyst, its preparation method and application.

[0005] The technical solution of the present invention is as follows:

[0006] A nitrogen-doped carbon-supported tin single-atom catalyst, comprising a nitrogen-doped carbon support and tin metal single atoms supported on the nitrogen-doped carbon support; the tin metal single atoms are anchored on the carbon substrate in an atomically dispersed manner and there are no interconnected metal-metal bonds; the loading amount of the metal single atoms is 1~5 wt%.

[0007] The loading of the metal single atom is 3 wt% to 4 wt%.

[0008] The preparation method of the nitrogen-doped carbon-supported tin single-atom catalyst of the present invention includes the following steps:

[0009] A) Disperse the metal salt, nitrogen source and carbon source in a solvent, mix them evenly, remove the solvent and dry to obtain a precursor mixture;

[0010] B) The precursor mixture obtained in step A) was subjected to high-temperature pyrolysis under an inert atmosphere, cooled, ground and acid etched to remove undispersed metal particles, and washed and dried to obtain nitrogen-doped carbon-supported tin metal single-atom catalyst (Sn-NC).

[0011] In step A), the metal salt is stannous chloride or stannous chloride; the nitrogen source is selected from melamine or dicyandiamide or a mixture of two of them; the carbon source is trimesic acid; and the solvent is ethanol.

[0012] In step A), the ratio of metal salt:total nitrogen source:carbon source is 1:(20~100):(2~10).

[0013] In step A), the solvent-removed part is continuously stirred at 60~90℃ until the solvent evaporates and then ground, with a stirring speed of 50~200rpm.

[0014] In step B), the high-temperature pyrolysis temperature is 700~800℃; the heating rate is 3~8℃ per minute; and the pyrolysis time is 2~4 hours.

[0015] In step B), the acid etching uses a 2-4 mol / L hydrochloric acid solution and is stirred at 80-95°C for 6-10 hours.

[0016] The application of the nitrogen-doped carbon-supported tin single-atom catalyst of the present invention in the electrocatalytic oxygen reduction to prepare hydrogen peroxide.

[0017] The nitrogen-doped carbon-supported tin single-atom catalyst of the present invention is used for the electrocatalytic synthesis of hydrogen peroxide via the two-electron oxygen reduction pathway, with a hydrogen peroxide selectivity of over 80%.

[0018] The specific process is as follows: Nitrogen-doped carbon-supported tin single-atom catalyst material is uniformly dispersed in a mixed solution of Nafion and ethanol, wherein the volume ratio of Nafion to ethanol is 2-5:95-98, preferably 2.5:97.5, to obtain a slurry with a concentration of 3-6 mg / mL, preferably 5 mg / mL. 10 μL of the slurry is drop-coated onto a glassy carbon electrode and dried at room temperature to obtain a glassy carbon electrode with the nitrogen-doped carbon-supported tin single-atom catalyst material loaded on its surface. Using a 0.1 mol / L KOH aqueous solution as the electrolyte, the glassy carbon electrode as the working electrode, a graphite carbon rod as the counter electrode, and Hg / HgO as the reference electrode, its electrocatalytic oxygen reduction reaction performance is tested. Within a wide potential range of 0.2 V to 0.7 V (relative to the reversible hydrogen electrode), its hydrogen peroxide selectivity consistently remains above 80%, reaching a maximum of 94.4%.

[0019] The above slurry was drop-coated onto hydrophobic carbon paper and dried at 60°C to obtain hydrophobic carbon paper with nitrogen-doped carbon-supported tin single-atom catalyst material on its surface. The loading was controlled at 0.2 mg / cm². Using 200 mL of 1 mol / L KOH aqueous solution as the electrolyte, the catalyst-supported hydrophobic carbon paper as the working electrode, an iridium dioxide-supported titanium mesh as the counter electrode, and Hg / HgO as the reference electrode, the yield and stability of actual hydrogen peroxide production were tested. In a 12-hour constant voltage test, the average growth rate of hydrogen peroxide concentration in the electrolyte was 449.8 mg / L per hour, indicating that the nitrogen-doped carbon-supported tin single-atom catalyst material proposed in this invention can be used for economical, efficient, and small-scale hydrogen peroxide production.

[0020] Advantages and excellent effects

[0021] 1. The nitrogen-doped carbon-supported tin single atom catalyst of the present invention has a greater atom utilization rate than clusters, metal particles and compound catalysts, and shows great potential in the rational utilization of metal resources and atom economy.

[0022] 2. The nitrogen-doped carbon-supported tin single-atom catalyst and its preparation method provided by this invention can achieve single-atom dispersion of tin on nitrogen-doped carbon materials. It features high utilization rate of non-precious metal single atoms, high selectivity, and good stability; the obtained material is easy to apply and conducive to its promotion and application in industrial production.

[0023] 3. This invention utilizes a precursor mixing pyrolysis method to obtain nitrogen-doped carbon-supported tin single-atom catalyst materials. The preparation method of this invention is simple, has low equipment cost, and meets the needs of actual production. Attached Figure Description

[0024] Figure 1 Transmission electron microscope image of nitrogen-doped carbon-supported tin single atoms prepared in Example 1.

[0025] Figure 2 Example 1: High-angle annular dark-field image and elemental image of tin, nitrogen and carbon prepared by nitrogen-doped carbon-loaded tin single atoms using scanning transmission electron microscopy.

[0026] Figure 3 X-ray diffraction pattern of nitrogen-doped carbon-supported tin single atoms prepared in Example 1.

[0027] Figure 4 : Graph showing the change of oxygen reduction current as a function of potential on the ring disk electrode of the catalyst prepared in Example 1.

[0028] Figure 5 Example 1 shows the selectivity of hydrogen peroxide at different potentials of the catalyst prepared.

[0029] Figure 6 Example 1: Current variation over time at constant potential of the catalyst prepared in Example 1 and the trend of hydrogen peroxide selectivity at corresponding time.

[0030] Figure 7 : The reduction current versus potential variation of the catalyst prepared in Example 1 during hydrogen peroxide production test.

[0031] Figure 8 : The current change over time of the catalyst prepared in Example 1 at a constant potential during hydrogen peroxide production test. Detailed Implementation

[0032] To further illustrate the present invention, the nitrogen-doped carbon-supported tin single-atom catalyst, its preparation method, and its application are described in detail below with reference to embodiments. However, it should be understood that these descriptions are merely for further illustrating the features and advantages of the present invention and are not intended to limit the scope of the claims.

[0033] This invention provides a nitrogen-doped carbon-supported tin single-atom catalyst, characterized in that: the catalyst comprises a nitrogen-doped carbon support and tin metal single atoms supported on the nitrogen-doped carbon support; the tin metal single atoms are anchored on the carbon substrate in an atomically dispersed manner and there are no interconnected metal-metal bonds; the loading amount (mass fraction) of the metal single atoms is 1 wt% to 5 wt%, preferably 3 wt% to 4 wt%.

[0034] This invention provides a method for preparing the above-mentioned nitrogen-doped carbon-supported tin single-atom catalyst, comprising the following steps:

[0035] A) Disperse the metal salt, nitrogen source and carbon source in a solvent, mix them evenly, remove the solvent and dry to obtain a precursor mixture;

[0036] The metal salt is stannous chloride or stannous chloride, preferably stannous chloride;

[0037] The nitrogen source is selected from a mixture of melamine and dicyandiamide, and the preferred mass ratio of the two is 1:1;

[0038] The preferred carbon source is pyromellitic acid;

[0039] The solvent is preferably ethanol;

[0040] The preferred feed mass ratio is: metal salt: total nitrogen source: carbon source = 1:(20~100):(2~10); more preferably 1:50:5;

[0041] The solvent removal process is preferably carried out by continuous stirring at 60~90℃ (more preferably 80℃) until the solvent evaporates and the mixture is ground. The stirring speed is preferably 50~200rpm, more preferably 100rpm.

[0042] B) The precursor mixture obtained in step A) was subjected to high-temperature pyrolysis under an inert atmosphere, cooled, ground and acid etched to remove undispersed metal particles, and washed and dried to obtain a nitrogen-doped carbon-supported tin metal single-atom catalyst.

[0043] The temperature of the high-temperature pyrolysis is 700~800℃, preferably 750℃;

[0044] The heating rate is 3~8℃ per minute, preferably 5℃ per minute;

[0045] The pyrolysis time is 2 to 4 hours, preferably 3 hours;

[0046] The acid etching is performed using a 2-4 mol / L (preferably 3 mol / L) hydrochloric acid solution, with stirring at 80-95℃ (preferably 90℃) for 6-10 hours (preferably 8 hours).

[0047] There are no particular restrictions on the source of any raw materials used in this invention; they can be purchased from the market or prepared using conventional methods known to those skilled in the art.

[0048] Example 1

[0049] This embodiment prepared a nitrogen-doped carbon-supported tin single-atom catalyst. The specific steps are as follows: 20 mg of stannous chloride, 1000 mg of a mixed nitrogen source (melamine and dicyandiamide in a mass ratio of 1:1), and 100 mg of trimesic acid were dispersed in 20 mL of anhydrous ethanol. After ultrasonic mixing for 15 minutes, the mixture was continuously stirred at 100 rpm at 80 °C until the solvent was completely evaporated. The resulting powder was then ground to obtain a white precursor powder.

[0050] The precursor powder was placed in a tube furnace and heated to 750°C at a heating rate of 5°C / min under a flowing nitrogen atmosphere, and held at that temperature for 3 hours. After naturally cooling to room temperature, the resulting black powder was ground and dispersed in a 3 mol / L hydrochloric acid solution, and etched by stirring at 90°C for 8 hours to remove unreacted metal particles and impurities. After the reaction was completed, the solid was collected by centrifugation, washed three times with water and ethanol respectively, and dried overnight in a vacuum oven at 60°C to obtain a nitrogen-doped carbon-supported tin single-atom catalyst.

[0051] Characterization tests: The mass loading of tin single atoms in the Sn-NC catalyst obtained in this example was determined to be approximately 3.45 wt% by inductively coupled plasma atomic emission spectrometry. The transmission electron microscope image of the catalyst obtained in Example 1 is shown below. Figure 1 As shown. Figure 1 No obvious metal particles were observed on the Sn-NC catalyst. Figure 2 The high-angle annular dark-field image and tin-nitrogen-carbon elemental image of the Sn-NC catalyst prepared in Example 1 clearly show that tin atoms are atomically dispersed bright spots on the carbon substrate, and the tin, nitrogen, and carbon elements are uniformly distributed. Figure 3 The X-ray diffraction pattern of the Sn-NC catalyst prepared in Example 1 shows no signals other than the broad diffraction peaks of the carbon material, indicating the absence of metal particles in the material. These test results demonstrate that the experimental method provided by this invention can stably construct nitrogen-doped carbon-supported tin catalysts dispersed in single-atom form while achieving high metal loading.

[0052] Example 2

[0053] The catalytic performance of the Sn-NC catalyst prepared in Example 1 was tested. The specific test method was as follows: the Sn-NC catalyst was dispersed in a mixed solution of Nafion and ethanol with a volume ratio of 2.5:97.5, and ultrasonically sonicated to obtain a uniform black slurry with a concentration of 5 mg / mL. The slurry was drop-coated onto the glassy carbon electrode surface of a rotating ring electrode and allowed to stand and dry to obtain the working electrode. A 0.1 mol / L KOH aqueous solution was prepared as the electrolyte for the catalytic performance test. A graphite carbon rod was used as the counter electrode and Hg / HgO was used as the reference electrode to test its electrocatalytic oxygen reduction reaction performance. Figure 4The graph shows the variation of oxygen reduction current as a function of potential on the ring disk electrode of the Sn-NC catalyst prepared in Example 1. Figure 5 The hydrogen peroxide selectivity of the Sn-NC catalyst prepared in Example 1 at different potentials is demonstrated. The test results show that the Sn-NC catalyst exhibits excellent two-electron oxygen reduction performance, maintaining a hydrogen peroxide selectivity above 80% and reaching a maximum of 94.4% across a wide potential range of 0.2 V to 0.7 V (relative to the reversible hydrogen electrode). These results prove that the nitrogen-doped carbon-supported tin single-atom catalyst provided by this invention can achieve high hydrogen peroxide selectivity. Furthermore, the stability of the nitrogen-doped carbon-supported tin single-atom catalyst prepared in Example 1 was characterized by chronoamperometry. Figure 6 The results showed that it maintained a high hydrogen peroxide selectivity of over 90% in a 30,000-second stability test, demonstrating its excellent stability. The above slurry was drop-coated onto hydrophobic carbon paper and dried at 60°C to obtain hydrophobic carbon paper with Sn-NC catalyst loaded on its surface, with the loading controlled at 0.2 mg / cm³. 2 Using 200 mL of 1 mol / L KOH aqueous solution as the electrolyte, hydrophobic carbon paper loaded with catalyst as the working electrode, titanium mesh loaded with iridium dioxide as the counter electrode, and Hg / HgO as the reference electrode, the yield and stability of hydrogen peroxide in actual production were tested. Figure 7 The graph shows the reduction current versus potential variation of the Sn-NC catalyst prepared in Example 1 during hydrogen peroxide production testing. Figure 8 The graph shows the current change over time of the Sn-NC catalyst prepared in Example 1 at a constant potential for hydrogen peroxide production. In the 12-hour constant potential (0.4 V (relative to the reversible hydrogen electrode) test, the average increase rate of hydrogen peroxide concentration in the electrolyte was 449.8 mg / L per hour, and the cumulative hydrogen peroxide concentration reached 5.397 g / L over 12 hours, indicating that the Sn-NC catalyst has a high yield of hydrogen peroxide produced by electrocatalytic oxygen reduction and good stability.

[0054] Example 3

[0055] 20 mg stannous chloride, 400 mg dicyandiamide, and 40 mg trimesic acid were dispersed in 20 mL ethanol, sonicated for 15 minutes, and evaporated to dryness by continuous stirring at 50 rpm at 60 °C. The resulting powder was then ground to obtain a white precursor powder. This precursor powder was placed in a tube furnace and heated to 700 °C at a heating rate of 3 °C / min under a flowing nitrogen atmosphere, and held at that temperature for 4 hours. After natural cooling to room temperature, the resulting black powder was ground and dispersed in a 2 mol / L hydrochloric acid solution, and etched by stirring at 95 °C for 6 hours to remove unreacted metal particles and impurities. After the reaction, the solid was collected by centrifugation, washed three times with water and ethanol, and dried overnight in a vacuum oven at 60 °C to obtain a nitrogen-doped carbon-supported tin single-atom catalyst. The tin loading of the catalyst prepared in this example was approximately 5 wt%.

[0056] Example 4

[0057] 20 mg tin chloride, 2 g melamine, and 200 mg trimellitic acid were dispersed in 20 mL ethanol, sonicated for 15 minutes, and evaporated to dryness by continuous stirring at 200 rpm at 90 °C. The resulting powder was then ground to obtain a white precursor powder. This precursor powder was placed in a tube furnace and heated to 800 °C at a heating rate of 8 °C / min under a flowing nitrogen atmosphere, and held at that temperature for 2 hours. After natural cooling to room temperature, the resulting black powder was ground and dispersed in a 4 mol / L hydrochloric acid solution, and etched by stirring at 80 °C for 10 hours to remove unreacted metal particles and impurities. After the reaction, the solid was collected by centrifugation, washed three times with water and ethanol, and dried overnight in a vacuum oven at 60 °C to obtain a nitrogen-doped carbon-supported tin single-atom catalyst. The tin loading of the catalyst prepared in this example was approximately 1 wt%.

[0058] Comparative Example 1

[0059] Patent CN115786962A reports a metal- and non-metal-doped amorphous carbon material, its preparation method, and its application. Electrochemical test results show that the reported single-atom dispersed Mo-FC catalyst maintains a hydrogen peroxide selectivity of about 80% in 0.1 mol / L KOH over a wide potential range. In 1 mol / L KOH, at a constant potential of -0.023 V (relative to the reversible hydrogen electrode), the average hydrogen peroxide concentration increase rate is 207.4 mg / L per hour after continuous operation for 12 hours.

[0060] The technical solutions disclosed and proposed in this invention can be implemented by those skilled in the art by appropriately modifying the conditions and routes, etc. Although the methods and preparation techniques of this invention have been described through preferred embodiments, those skilled in the art can obviously modify or recombine the methods and technical routes described herein without departing from the content, spirit, and scope of this invention to achieve the final preparation technique. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included within the spirit, scope, and content of this invention.

Claims

1. A nitrogen-doped carbon-supported tin single-atom catalyst, characterized in that the catalyst... It includes a nitrogen-doped carbon support and tin metal single atoms loaded on the nitrogen-doped carbon support; the tin metal single atoms are anchored on the carbon substrate in an atomically dispersed manner and there are no interconnected metal-metal bonds; the loading amount of the metal single atoms is 1~5 wt%.

2. The nitrogen-doped carbon-supported tin single-atom catalyst as described in claim 1, characterized in that, The loading of the metal single atom is 3 wt% to 4 wt%.

3. The method for preparing the nitrogen-doped carbon-supported tin single-atom catalyst of claim 1, characterized in that, Includes the following steps: A) Disperse the metal salt, nitrogen source and carbon source in a solvent, mix them evenly, remove the solvent and dry to obtain a precursor mixture; B) The precursor mixture obtained in step A) was subjected to high-temperature pyrolysis under an inert atmosphere, cooled, ground and acid etched to remove undispersed metal particles, and washed and dried to obtain a nitrogen-doped carbon-supported tin metal single-atom catalyst.

4. The preparation method according to claim 3, characterized in that, In step A), the metal salt is stannous chloride or stannous chloride; the nitrogen source is selected from melamine or dicyandiamide or a mixture of two of them; the carbon source is pyromellitic acid; and the solvent is ethanol.

5. The preparation method according to claim 3, characterized in that, In step A), the ratio of metal salt:total nitrogen source:carbon source = 1:(20~100):(2~10).

6. The preparation method according to claim 3, characterized in that, In step A), the solvent-removed part is continuously stirred at 60~90℃ until the solvent evaporates and then ground, with a stirring speed of 50~200rpm.

7. The preparation method according to claim 3, characterized in that, In step B), the high-temperature pyrolysis temperature is 700~800℃; the heating rate is 3~8℃ per minute; and the pyrolysis time is 2~4 hours.

8. The preparation method according to claim 3, characterized in that, In step B), acid etching is performed using a 2-4 mol / L hydrochloric acid solution, with stirring at 80-95°C for 6-10 hours.

9. The application of the nitrogen-doped carbon-supported tin single-atom catalyst of claim 1 in the electrocatalytic oxygen reduction to prepare hydrogen peroxide.

10. The nitrogen-doped carbon-supported tin single-atom catalyst of claim 1 is used for the electrocatalytic synthesis of hydrogen peroxide via the two-electron oxygen reduction pathway, with a hydrogen peroxide selectivity of over 80%.

Images