Oxygen-doped carbon nanosheet-supported palladium single-atom catalyst, preparation method, and application thereof

Abstract

The present invention relates to the field of nanomaterials. In view of the problem that it is difficult for electrocatalysts for H2O2 to simultaneously achieve high selectivity and high activity, the present invention provides an oxygen-doped carbon nanosheet-supported palladium single-atom catalyst, a preparation method thereof, and an application thereof. The catalyst has a lamellar structure, and Pd is anchored in the surface structure of the oxygen-doped carbon nanosheet in the form of a single atom. The preparation method of the catalyst comprises the following steps: (1) using anhydrous manganese acetate, sodium benzoate, and terephthalic acid to obtain a primary product through a hydrothermal reaction, filtering and drying the primary product, and then carbonizing, calcining, acid washing, and drying to obtain an oxygen-doped carbon nanosheet; (2) immersing the oxygen-doped carbon nanosheet obtained in step (1) in a metal palladium salt solution, and then drying and calcining to obtain an oxygen-doped carbon nanosheet-supported palladium single-atom catalyst. The catalyst is used in the electrocatalytic oxygen reduction reaction to produce H2O2, and has good electrocatalytic selectivity and activity.

Description

Technical Field

[0001] The present invention relates to the field of nanomaterials, and in particular to an oxygen-doped carbon nanosheet-supported palladium single-atom catalyst, a preparation method thereof, and applications thereof. Background Art

[0002] As a chemical product, hydrogen peroxide (H2O2) has a wide range of applications in wastewater treatment, industrial bleaching, chemical synthesis, and medical disinfection. Currently, the main method for industrial H2O2 production both domestically and internationally is the anthraquinone process. The anthraquinone process for H2O2 production is susceptible to poisoning and agglomeration of catalysts, and the organic solvents used in the production process can enter the H2O2 product, affecting its purity. Furthermore, the production process is energy-intensive. Furthermore, the transportation of H2O2 presents safety risks, which limit the large-scale application of the anthraquinone process for H2O2 production. Currently, the production of H2O2 via the electrocatalytic oxygen reduction reaction is considered an effective technical means to overcome these shortcomings and achieve green, low-energy, in-situ H2O2 production. Electrocatalytically synthesized H2O2 is highly pure and impurity-free, and has attracted widespread attention from researchers in recent years.

[0003] The development of highly active and selective electrocatalysts is key to electrocatalytic oxygen reduction to produce H2O2. Precious metal catalysts, such as Pd, exhibit excellent activity in oxygen reduction, but their reaction pathway is primarily a four-electron pathway. A small number of studies have shown that a two-electron pathway for oxygen reduction to produce H2O2 can be achieved through appropriate regulation of Pd-based catalysts. However, the high cost of Pd-based catalysts limits their large-scale application. Currently, most reported Pd-based catalysts are dispersed on the support surface in the form of nanoparticles, resulting in low atomic utilization and poor dispersion of active sites.

[0004] Research has shown that single-atom metal catalysts possess isolated, dispersed active sites. Their high atomic utilization efficiency and strong metal-support interactions contribute to their excellent catalytic activity and selectivity in catalytic reactions. For example, patent CN107008290A discloses a single-atom Pd@hydrotalcite catalyst. This invention prepares the hydrotalcite using a double-drop method, then photodeposits a Pd source onto the support surface using a photodeposition method to obtain the single-atom Pd@hydrotalcite catalyst. The specific method is as follows: (i) ZnCr-LDH hydrotalcite is prepared using the double-drop method; (ii) the zinc-chromium hydrotalcite support is dispersed in deionized water, a certain amount of chloropalladium solution is added, and the mixture is irradiated under a xenon lamp for a certain period of time to react. After the reaction, the mixture is centrifuged, washed, and vacuum-dried. Finally, the resulting powder is reduced in a hydrogen atmosphere for a certain period of time to obtain the single-atom Pd@hydrotalcite catalyst. Patent publication number CN110433798A discloses a single-atom Pd / SiO2-ZrO2 catalyst. This invention utilizes the long molecular chain of the silicon source loaded on ZrO2 to better disperse the impregnated metal Pd source. After calcination, the precious metal Pd forms a single-atom Pd.

[0005] Although single-atom catalysts have made some progress in the field of catalysis, little research has been conducted on how to manipulate the structure of single-atom electrocatalysts to achieve highly selective H2O2 production in oxygen reduction reactions. Furthermore, achieving both high selectivity and high activity remains challenging. Therefore, an oxygen-doped carbon nanosheet-supported Pd single-atom catalyst was prepared to achieve electrocatalytic oxygen reduction to produce H2O2. The oxygen atoms in the oxygen-doped carbon nanosheets can modulate the electronic structure of the single Pd atoms, and the oxygen-doped carbon nanosheet structure helps enhance catalytic reaction activity, thereby further improving the activity and selectivity of the electrocatalytic oxygen reduction to produce H2O2. This is of great significance for achieving electrocatalytic synthesis of H2O2 under industrial-scale conditions. Summary of the Invention

[0006] In order to overcome the problem that H2O2 electrocatalysts find it difficult to simultaneously achieve high selectivity and high activity, the present invention provides an oxygen-doped carbon nanosheet-loaded palladium single-atom catalyst and its preparation method and application, thereby obtaining a lamellar oxygen-doped nanocarbon structure. By loading Pd single atoms, the selectivity and catalytic activity of the catalyst are improved, and the catalyst is applied to the electrocatalytic oxygen reduction reaction to produce H2O2, exhibiting good electrocatalytic selectivity and activity.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] The invention discloses an oxygen-doped carbon nanosheet-supported palladium single-atom catalyst. The catalyst has a layered structure, and Pd is anchored in the surface structure of the oxygen-doped carbon nanosheet in the form of a single atom.

[0009] The present invention also provides a method for preparing the catalyst, comprising the following steps:

[0010] (1) anhydrous manganese acetate, sodium benzoate and terephthalic acid are subjected to a hydrothermal reaction to obtain a primary product, the primary product is filtered and dried, and then carbonized, calcined, acid-washed and dried to obtain oxygen-doped carbon nanosheets;

[0011] (2) Immersing the oxygen-doped carbon nanosheets obtained in step (1) in a metal palladium salt solution, and then drying and calcining to obtain an oxygen-doped carbon nanosheet-loaded palladium single-atom catalyst.

[0012] Preferably, step (1) comprises: adding anhydrous manganese acetate and sodium benzoate to an organic solvent, stirring until fully dissolved, then adding terephthalic acid, continuing to stir, and transferring the mixture to a hydrothermal reactor for hydrothermal reaction; after the hydrothermal reaction, centrifugally washing with dimethylformamide and ethanol for multiple times, vacuum drying and collecting the metal organic framework material of the manganese sample, and then carbonizing, calcining, acid washing, and drying to obtain oxygen-doped carbon nanosheets;

[0013] Step (2) is: dissolving a metal palladium salt in water, adding an oxygen-doped carbon nanosheet carrier, stirring and dispersing, adjusting the pH to alkaline using a sodium hydroxide solution, centrifugally drying, and calcining in an Ar atmosphere in a tubular furnace to finally obtain an oxygen-doped carbon nanosheet-supported palladium single-atom catalyst.

[0014] The present invention selects terephthalic acid, an organic substance containing oxygen elements, as the oxygen source and carbon source for the reaction, uses sodium benzoate that can form a nanosheet structure as a structure-directing agent for preparing the material, uses acid as an etchant for the metal manganese oxide, and etches the manganese oxide in its sheet structure after high-temperature carbonization to form an oxygen-doped carbon nanosheet structure with a high specific surface area, and uses a metal salt containing palladium (such as palladium chloride) as an atomically dispersed Pd metal precursor to provide metal atoms.

[0015] Preferably, the mass ratio of anhydrous manganese acetate, sodium benzoate and terephthalic acid in step (1) is (0.5-2.5):(0.2-1.0):(1.0-3.5).

[0016] Preferably, the solvent used in the hydrothermal reaction in step (1) is dimethylformamide, wherein the ratio of anhydrous manganese acetate to solvent dimethylformamide is 40-70 mL dimethylformamide per 1 g of anhydrous manganese acetate, the reaction temperature is 160-200° C., and the reaction time is 10-15 h.

[0017] Preferably, the carbonization calcination temperature in step (1) is 700-900°C, and the calcination time is 1-6 hours. During the calcination process, the manganese metal organic framework material provides a carbon source and an oxygen source. By controlling the calcination temperature, the degree of graphitization and the content of doped oxygen elements are adjusted, thereby regulating the electrocatalytic H2O2 selectivity of the oxygen-doped carbon nanosheets. As a further preference, the carbonization calcination temperature in step (1) is 680-730°C, and the calcination time is 2-4 hours; the calcination temperature can be 680°C, 685°C, 690°C, 700°C, 720°C, etc. Too low a temperature can easily lead to a low degree of graphitization and poor conductivity, while too high a temperature can lead to excessive oxidation of the sample carbon material, making it impossible to obtain a sample.

[0018] Preferably, the pickling in step (1) is carried out by etching with sulfuric acid having a molar concentration of 0.1 to 5 M for 5 to 20 hours. Further preferably, the pickling in step (1) is carried out by etching with sulfuric acid having a molar concentration of 0.5 M for 12 hours.

[0019] Preferably, the amount of the metal palladium salt added in step (2) is calculated as 0.1-1.0% of the mass of palladium relative to the mass of the oxygen-doped carbon nanosheets. Too little metal palladium salt results in fewer effective catalytic sites, while too much metal palladium salt easily forms palladium particles, resulting in reduced selectivity. The metal palladium salt is preferably palladium chloride.

[0020] Preferably, in step (2), the pH is adjusted to 9-11 using sodium hydroxide solution, and then stirred for 1-4 hours. Further preferably, in step (2), the impregnation is performed by first stirring for 1-4 hours, adjusting the pH to 9-11, and then stirring for 1-4 hours.

[0021] Preferably, the calcination temperature in step (2) is 100-400°C, and the calcination time is 1-3 hours. More preferably, the calcination temperature in step (2) is 300°C, and the calcination time is 2 hours.

[0022] The present invention also provides the use of the catalyst in the electrocatalytic oxygen reduction reaction to produce H2O2. The catalyst exhibits excellent electrocatalytic activity and selectivity. When used as a cathode material for electrocatalytic synthesis of H2O2, its onset potential is 0.84V and the H2O2 selectivity can reach 73%.

[0023] Therefore, the beneficial effects of the present invention are:

[0024] (1) Oxygen-doped carbon nanosheets loaded with Pd single-atom catalysts were obtained by high-temperature calcination, acid etching, and impregnation of metal-organic frameworks. The catalysts have a lamellar structure, abundant oxygen-containing functional groups, and single-atom dispersed Pd sites. They can be used for the electrocatalytic reduction of oxygen to produce H2O2 with good electrocatalytic activity and selectivity.

[0025] (2) The catalyst preparation method is simple, highly controllable, low-cost and reproducible, making it suitable for industrial production applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is a scanning electron microscope image of the catalyst prepared in Example 1;

[0027] Figure 2 is a transmission electron microscope image of the catalyst prepared in Example 1;

[0028] Figure 3 The XRD pattern of the catalyst prepared in Example 1;

[0029] Figure 4 This is the curve of the electrocatalytic reduction of O2 to H2O2 by the catalysts prepared in Example 1-2 and Comparative Example 1-2. DETAILED DESCRIPTION

[0030] The technical solution of the present invention is further described below through specific embodiments.

[0031] In the present invention, unless otherwise specified, the raw materials and equipment used can be purchased from the market or are commonly used in the art. The methods in the embodiments, unless otherwise specified, are all conventional methods in the art.

[0032] Overall embodiment

[0033] The invention discloses an oxygen-doped carbon nanosheet-supported palladium single-atom catalyst. The catalyst has a layered structure, and Pd is anchored in the surface structure of the oxygen-doped carbon nanosheet in the form of a single atom.

[0034] The preparation method of the catalyst comprises the following steps:

[0035] (1) Anhydrous manganese acetate and sodium benzoate are added to 50-80 mL of an organic solvent, dimethylformamide, and stirred until fully dissolved. Then, terephthalic acid is added, and the mass ratio of anhydrous manganese acetate, sodium benzoate and terephthalic acid is (0.5-2.5):(0.2-1.0):(1.0-3.5). After continuing to stir, the mixture is transferred to a hydrothermal reactor for hydrothermal reaction at a reaction temperature of 160-200°C and a reaction time of 10-15 hours. After the hydrothermal reaction is completed, the sample is washed with dimethylformamide and ethanol by centrifugation for multiple times, and the metal organic framework material of the manganese sample is collected by vacuum drying. The sample is then carbonized and calcined at a calcination temperature of 700-900°C and a calcination time of 1-6 hours. The sample is etched with sulfuric acid having a molar concentration of 0.1-5M for 5-20 hours, and dried to obtain oxygen-doped carbon nanosheets.

[0036] (2) dissolving a metal palladium salt in water, adding an oxygen-doped carbon nanosheet carrier, wherein the amount of the metal palladium salt added is calculated as 0.1-1.0% of the mass of palladium to the mass of the oxygen-doped carbon nanosheet, stirring and dispersing for 1-4 hours, adjusting the pH to 9-11 with a sodium hydroxide solution, stirring for another 1-4 hours, centrifuging and drying, and calcining at 100-400° C. in an Ar atmosphere in a tubular furnace for 1-3 hours to finally obtain an oxygen-doped carbon nanosheet-supported palladium single-atom catalyst.

[0037] The catalyst is used as a cathode material to electrocatalytically synthesize H2O2. The catalyst exhibits excellent electrocatalytic activity and selectivity, with an initial potential of 0.84V and an H2O2 selectivity of up to 73%.

[0038] Example 1

[0039] A method for preparing an oxygen-doped carbon nanosheet-supported palladium single-atom catalyst, comprising the following steps:

[0040] (1) 1.08 g of anhydrous manganese acetate and 0.674 g of sodium benzoate were added to 60 mL of dimethylformamide and stirred thoroughly for 12 h. 1.83 g of terephthalic acid was then added and stirred for 1 h. The mixture was transferred to a 100 mL hydrothermal reactor and reacted at 180 °C for 10 h. The mixture was washed several times by centrifugation with dimethylformamide and ethanol and finally dried under vacuum for 12 h. The manganese metal organic framework material obtained above was placed in an alumina porcelain boat and heated in a tube furnace under Ar conditions at 2.5 °C·min -1 The sample was heated to 700°C at a heating rate of 1000 ℃ for 120 minutes. After cooling, the obtained sample was added to 200 mL of 0.5 M H2SO4 and stirred for 12 hours. The sample was collected by filtration and vacuum dried to obtain an oxygen-doped carbon nanosheet substrate.

[0041] (2) PdCl2 solution (Pd content of 1 mg / mL) was dissolved in 20 mL of water, and then added to the oxygen-doped carbon nanosheet support obtained in step (1), wherein the mass of Pd in ​​the PdCl2 solution was 0.25% of the oxygen-doped carbon nanosheet, and stirred for 2 h. The pH value of the solution was adjusted to 10.5 with sodium hydroxide solution, and stirred for another 2 h. After centrifugal drying, the solution was placed in a tube furnace and heated at 5 ° C. min under Ar atmosphere. -1 The sample was heated to 300 °C at a heating rate of 100 °C and reacted for 2 h. After cooling, a sample of oxygen-doped carbon nanosheets loaded with Pd single atom catalyst was obtained.

[0042] The surface micromorphology of the catalyst was observed. Figure 1-3 As shown in the figure, the catalyst has a lamellar structure with pores in the lamellar layer. The lamellar layer is thin and well dispersed, with no obvious metal Pd particles.

[0043] Example 2

[0044] The difference from Example 1 is that the mass of Pd in ​​the PdCl2 solution in step (2) is 0.1% of the oxygen-doped carbon nanosheets.

[0045] Comparative Example 1

[0046] The catalyst of Comparative Example 1 is oxygen-doped carbon nanosheets, and its preparation steps are as follows:

[0047] 1.08g of anhydrous manganese acetate and 0.674g of sodium benzoate were added to 60mL of dimethylformamide and stirred thoroughly for 12h. Then 1.83g of terephthalic acid was added and stirred for 1h. After that, the mixture was transferred to a 100mL hydrothermal autoclave and reacted at 180℃ for 10h. The mixture was washed several times by centrifugation with dimethylformamide and ethanol and finally dried under vacuum for 12h. The manganese metal organic framework material obtained above was placed in an alumina porcelain boat and heated in a tube furnace under Ar conditions at 2.5℃·min -1 The sample was heated to 700°C at a heating rate of 1000 ℃ for 120 minutes. After cooling, the obtained sample was added to 200 mL of 0.5 M H2SO4 and stirred for 12 hours. The sample was collected by filtration and vacuum dried to obtain an oxygen-doped carbon nanosheet substrate.

[0048] Comparative Example 2

[0049] The difference from Example 1 is that the mass of Pd in ​​the PdCl2 solution in step (2) is 2% of the oxygen-doped carbon nanosheets.

[0050] Comparative Example 3

[0051] The catalyst of Comparative Example 3 is oxygen-doped carbon nanosheets, and its preparation steps are as follows:

[0052] 1.08g of anhydrous manganese acetate and 0.674g of sodium benzoate were added to 60mL of dimethylformamide and stirred thoroughly for 12h. Then 1.83g of terephthalic acid was added and stirred for 1h. After that, the mixture was transferred to a 100mL hydrothermal autoclave and reacted at 180℃ for 10h. The mixture was washed several times by centrifugation with dimethylformamide and ethanol and finally dried under vacuum for 12h. The manganese metal organic framework material obtained above was placed in an alumina porcelain boat and heated in a tube furnace under Ar conditions at 2.5℃·min -1 The sample was heated to 600°C at a heating rate of 1000 ℃ for 120 minutes. After cooling, the obtained sample was added to 200 mL of 0.5 M H2SO4 and stirred for 12 hours. The sample was collected by filtration and vacuum dried to obtain an oxygen-doped carbon nanosheet substrate.

[0053] Application example: Using the catalyst for electrocatalytic reduction of O2 to synthesize H2O2

[0054] The specific steps are as follows: First, prepare a catalyst dispersion: 5 mg of the catalyst is dispersed in a mixture of ethanol and 0.5 wt% Nafion solution in a 9:1 volume ratio. Then, 1 μL of the dispersion containing the catalysts prepared in Examples 1-3 and Comparative Example 1 is dropwise applied to a rotating disk electrode. After air drying, this serves as the working electrode. A silver / silver chloride electrode is used as the reference electrode, a platinum column is used as the counter electrode, and the electrolyte is 0.1 M KOH solution.

[0055] Cyclic voltammetry (CV) activation: A Shanghai Chenhua CHI 660E electrochemical workstation was used. Oxygen was continuously introduced into the electrolyte for 0.5 h before testing. The CV program was used with a test interval of 0–1.2 V (vs. RHE) and a scan rate of 50 mV·s. -1 , circulate and scan 40 times, activate the disk electrode and ring disk electrode respectively, and make the electrodes reach a stable state.

[0056] Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Catalyst onset potential V 0.84 0.84 0.84 0.84 0.80 <![CDATA[Selectivity of H2O2 (%)]]> 73 61 57 20 38

[0057] The results are as follows Figure 4 As shown in the table above, the catalysts prepared in each example exhibit excellent electrocatalytic oxygen reduction to H2O2 performance. The catalyst of Example 1 has an initial potential of 0.84V and an H2O2 selectivity of 73%; the catalyst of Example 2 has an initial potential of 0.84V and an H2O2 selectivity of 61%. The catalyst of Comparative Example 1 is not loaded with palladium, and its H2O2 selectivity is not as good as that of Example 1. Compared with Comparative Example 1, the carbonization and calcination temperature of Comparative Example 3 is not within the preferred range, and the selectivity is significantly reduced. The palladium mass of the catalyst in Comparative Example 2 is 2% of that of the oxygen-doped carbon nanosheets, and the palladium dosage exceeds the preferred range, and the H2O2 selectivity is reduced to 20%.

[0058] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as a preferred embodiment, it is not intended to limit the present invention. Any technician familiar with the present profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for preparing an oxygen-doped carbon nanosheet-supported palladium single-atom catalyst, characterized in that: The following steps are involved: (1) Anhydrous manganese acetate, sodium benzoate and terephthalic acid are hydrothermally reacted to obtain a primary product, which is filtered and dried, then carbonized, calcined, acid-washed and dried. The carbonization and calcination temperature is 700-900 °C and the calcination time is 1-6 h to obtain oxygen-doped carbon nanosheets. (2) The oxygen-doped carbon nanosheets are immersed in a metal palladium salt solution, where the amount of metal palladium salt added is calculated to be 0.1-1.0% of the mass of palladium to the mass of the oxygen-doped carbon nanosheets, and then dried and calcined to obtain the oxygen-doped carbon nanosheet-loaded palladium single-atom catalyst.

2. The method for preparing an oxygen-doped carbon nanosheet-supported palladium single-atom catalyst according to claim 1, wherein: The catalyst has a layered structure, and Pd is anchored in the surface structure of the oxygen-doped carbon nanosheet in the form of a single atom.

3. The method for preparing an oxygen-doped carbon nanosheet-supported palladium single-atom catalyst according to claim 1, wherein: The mass ratio of anhydrous manganese acetate, sodium benzoate and terephthalic acid in step (1) is (0.5~2.5):(0.2~1.0):(1.0~3.5).

4. The method for preparing an oxygen-doped carbon nanosheet-supported palladium single-atom catalyst according to claim 1 or 3, wherein: The solvent used in the hydrothermal reaction in step (1) is dimethylformamide, the reaction temperature is 160-200 °C, and the reaction time is 10-15 h.

5. The method for preparing an oxygen-doped carbon nanosheet-supported palladium single-atom catalyst according to claim 4, wherein: The ratio of anhydrous manganese acetate to dimethylformamide is 40-70 mL of dimethylformamide per 1 g of anhydrous manganese acetate.

6. The method for preparing an oxygen-doped carbon nanosheet-supported palladium single-atom catalyst according to claim 1, wherein: The carbonization calcination temperature is 700-730° C., and the calcination time is 2-4 h.

7. The method for preparing an oxygen-doped carbon nanosheet-supported palladium single-atom catalyst according to claim 1, wherein: The pickling in step (1) is performed by etching with sulfuric acid having a molar concentration of 0.1 to 5 M for 5 to 20 hours.

8. The method for preparing an oxygen-doped carbon nanosheet-supported palladium single-atom catalyst according to claim 1, wherein: The soaking in step (2) is as follows: first stirring for 1-4 hours, adjusting the pH to 9-11, and then stirring for 1-4 hours.

9. The method for preparing an oxygen-doped carbon nanosheet-supported palladium single-atom catalyst according to claim 1 or 8, wherein: The calcination temperature in step (2) is 100-400°C, and the calcination time is 1-3 h.

10. Use of the oxygen-doped carbon nanosheet-supported palladium single-atom catalyst prepared by the preparation method according to claim 1 in the electrocatalytic oxygen reduction reaction to produce H2O2.

Images