Preparation method and application of single-atom and atomically precise cluster co-supported catalyst

Abstract

The application discloses a preparation method and application of a single-atom and atom-accurate cluster co-supported catalyst. Before a metal source of a metal cluster source is introduced, a stable metal molecular cluster is formed by strong coupling of 2-Methyl-1H-benzimidazole-1-methanol organic ligand and a metal center. The strong coupling of the organic ligand to the metal center effectively avoids aggregation in a subsequent pyrolysis process, so that the metal cluster exists in an orderly arrangement and in a controllable atom number. The application prepares a series of atom-accurate cluster and single-atom supported carbon carrier catalysts and applies the catalysts to an electrocatalytic nitrate reduction field, so that efficient and directional conversion of nitrate is realized.

Description

Technical Field

[0001] This invention relates to a method for preparing nitrogen-doped carbon-supported metal cluster materials with precisely defined atoms (M4 / Cu-NC, where M can be metals such as Fe, Co, and Cu) and their application in the field of electrocatalysis. Specifically, the loading of different metal clusters on a single-atom carbon-nitrogen substrate enables a stronger synergistic effect at the interface of the M4 / Cu-NC catalyst, and the method for regulating the catalytic activity of the catalyst and its application in the electrocatalytic reduction of nitrate. Background Technology

[0002] Electrocatalysis plays a crucial role in the transition from fossil fuels to renewable energy. Therefore, it is essential to design electrocatalysts with high activity, selectivity, and stability for specific reaction pathways, guided by theoretical principles. Early research focused primarily on polycrystalline monometallic catalysts due to their simple structure, ease of manipulation, and suitability for study. In addition, surface-modified metals, nanoscale monometallic, bimetallic, and even nonmetallic materials are widely used in electrocatalysis. Compared to traditional materials, nanomaterials exhibit different catalytic properties due to the size effect of their smaller size, exposing more active sites.

[0003] Similar to homogeneous catalysts, single-atom catalysts (SACs) have attracted widespread attention from researchers due to their high atom utilization and excellent activity and selectivity for various catalytic reactions. The strong interaction between a single metal atom and the support can significantly improve electrocatalytic performance.

[0004] Although single-atom catalysts possess advantages such as well-defined active sites, high atom utilization, and clear reaction mechanisms, they also face challenges such as a limited number of active sites and insufficient activity per site. Yu et al. achieved highly efficient electrocatalytic carbon dioxide reduction by introducing adjacent copper clusters onto a copper single-atom substrate. However, because copper was directly introduced onto the carbon-nitrogen substrate during synthesis followed by pyrolysis, the inevitable aggregation of metal atoms during pyrolysis resulted in copper atoms being doped into clusters with uneven atomic numbers on the carbon-nitrogen substrate. This uneven size of the metal clusters hinders further exploration of the synergistic relationship between single atoms and clusters, as well as the reaction mechanism. [Angew.Chem.Int.Ed.2021,60,24022.]

[0005] Therefore, how to develop a controllable and simple preparation method to achieve precise control of metal cluster size and atomic level, precise positioning of catalyst active sites, further optimize the binding energy between active metal atoms and reaction intermediates, and realize the directional and efficient conversion of reactants are urgent problems to be solved. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of current technologies by providing a method for preparing catalysts co-supported with single atoms and atomically precise clusters, and their applications. This method involves first forming stable metal molecular clusters with the metal center through the strong coupling effect of the organic ligand 2-Methyl-1H-benzimidazole-1-methanol (Hmbm) before introducing the metal source. The strong coupling effect of the organic ligand with the metal center effectively avoids aggregation during subsequent pyrolysis, ensuring that the metal clusters exist in an ordered arrangement with a controllable number of atoms. This invention prepares a series of atomically precise cluster and single-atom supported carbon-supported catalysts for application in the field of electrocatalytic nitrate reduction, achieving efficient and directional conversion of nitrate.

[0007] The technical solution of the present invention:

[0008] A method for preparing a catalyst co-supported with single atoms and atomically precise clusters, the method comprising the following steps:

[0009] (1) Add M salt, 2-Methyl-1H-benzimidazole-1-methanol (Hmbm) and triethylamine to anhydrous methanol to obtain a solution. After stirring for 30-60 min, transfer the solution to a stainless steel Teflon reactor for hydrothermal reaction and maintain at 140-160℃ for 12-24 h. Then cool at room temperature for 24-48 h and obtain the product M4 molecular cluster by suction filtration.

[0010] Among them, the M salt is FeCl2·4H2O, CoCl2·6H2O or CuCl2·2H2O;

[0011] The mass ratio is Hmbm:triethylamine:M salt = 2.0-3.0:1-1.3:1; add 150-300 mg of M salt per 8 mL of anhydrous methanol;

[0012] (2) Subsequently, the prepared M4 molecular cluster, copper acetylacetonate and Zn(NO3)2·6H2O were dissolved in methanol to obtain solution A. Then, 2-methylimidazole was dissolved in methanol and labeled as solution B. A and B were then mixed at room temperature and stirred for 1 to 1.5 h. The mixture was then transferred to a reaction vessel and kept at 120-140 °C for 4 to 6 h. After the solution cooled to room temperature, the product M4 / Cu1-ZIF-8 was obtained by centrifugation and dried overnight in a vacuum drying oven.

[0013] The mass ratio of M4 molecular cluster to copper acetylacetone is 0.95 to 2:1, the mass ratio of Fe4 molecular cluster to Zn(NO3)2·6H2O is 0.042 to 0.05:1, and the mass ratio of 2-methylimidazole to Zn(NO3)2·6H2O is 1.1 to 1.5:1.

[0014] The volume ratio of solution A to solution B is 2 to 3:1.

[0015] The centrifugation conditions are 10000-12000 rpm for 5-10 min; the vacuum drying conditions are 60-80℃ and a vacuum degree of 0.8-1 MPa.

[0016] (3) The obtained Fe4 / Cu1-ZIF-8 was carbonized to obtain the final product Fe4 / Cu1-NC, which is a catalyst co-supported with atomically precise metal clusters and copper single atoms.

[0017] The carbonization conditions are maintained at 900-1000℃ for 1-2 hours, with a heating rate of 1-8℃ / min.

[0018] The catalyst prepared by the method, with atomically precise metal clusters co-supported with copper single atoms, is used as a catalyst for the electrocatalytic reduction of nitrate.

[0019] The essential features of this invention are:

[0020] This invention utilizes the strong coupling ability of organic ligands to stabilize metal centers and form ordered, uniformly sized, and precisely numbered metal clusters. Experiments have demonstrated that, in the subsequent pyrolysis step, the strong coupling effect of the organic ligands on the metal centers effectively avoids the inevitable aggregation during pyrolysis, allowing metal atoms to be doped onto the carbon-nitrogen substrate in the form of uniformly sized and precisely numbered clusters.

[0021] The size and number of metal clusters in the catalyst co-supported with copper single atoms prepared by this invention are controllable, and this invention extends to different metal elements (Fe, Co, Cu). It precisely controls the number of atoms in the clusters in the catalyst M4 / Cu-NC, and prevents aggregation during pyrolysis, thus avoiding the complex and uncontrollable coordination effect between the metal and the support caused by high-temperature carbonization. It can also maintain stability during the reaction.

[0022] The beneficial effects of this invention are:

[0023] (1) This invention provides a method for preparing metal clusters with controllable atomic numbers by stabilizing metal clusters through strong coupling between organic ligands and metal centers. Compared with traditional methods of mixing metal sources with carbon-nitrogen substrates and then calcining, this invention effectively avoids the random arrangement of metals and aggregation during the calcination process, such as... Figure 1 As shown, the metal clusters of the present invention are arranged in an orderly manner of four atoms, which avoids the phenomena of size inhomogeneity and uncontrollable number of atoms.

[0024] (2) The Fe4 / Cu1-NC obtained in this invention exhibits excellent electrochemical activity and selectivity in the electrocatalytic reduction of nitrate. Traditional copper single-atom catalysts achieve a Faradaic efficiency of only 87.5% in the electrocatalytic reduction of nitrate to ammonia. The catalyst obtained in this invention, by introducing clusters, significantly improves the selectivity, achieving a Faradaic efficiency of 97.5% for ammonia, while simultaneously reaching ampere-level current, demonstrating broad industrial application prospects. Furthermore, the single-atom and metal clusters of the catalyst obtained in this invention are coated with a carbon shell. It is precisely this carbon shell constraint effect that ensures the current density of the catalyst remains constant for 40 hours under constant voltage. NH3 >90%, exhibiting excellent electrocatalytic stability. Attached Figure Description

[0025] Figure 1 This is a transmission electron microscope (TEM) image of the Fe4 / Cu1-NC prepared in Example 1.

[0026] Figure 2 This is the X-ray photoelectron spectrum of Fe4 / Cu1-NC prepared in Example 1.

[0027] Figure 3 This is a graph showing the electrocatalytic nitrate reduction performance of the Fe4 / Cu1-NC catalyst prepared in Example 1.

[0028] Figure 4 This is a schematic diagram of the catalyst co-supported by copper single atoms and atomically precise metal clusters obtained in Example 1. The iron clusters can be replaced with cobalt clusters or copper clusters. Detailed Implementation

[0029] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and technical solutions.

[0030] The 2-Methyl-1H-benzimidazole-1-methanol (Hmbm) involved in this invention is a known substance, specifically from bidepharm. However, it is not limited thereto.

[0031] Example 1

[0032] (1) Dissolve 486 mg of Hmbm and 198 mg of FeCl2·4H2O in 8 mL of anhydrous methanol. Stir for 30 min to ensure complete dissolution, then add 197.8 mg of triethylamine and stir for another 30 min. Finally, place the mixture into a 15 mL polytetrafluoroethylene-lined reactor and perform a hydrothermal reaction at 140 °C in a sealed container for 24 h. Then cool at room temperature for 24 h. Filter and wash with anhydrous methanol, allow to stand and dry to obtain Fe4 molecular clusters.

[0033] (2) Dissolve 50 mg of Fe4 molecular clusters, 52 mg of copper acetylacetonate, and 1.19 g of Zn(NO3)2·6H2O obtained in the previous step in 30 mL of anhydrous methanol to obtain solution A. Simultaneously, dissolve 1.314 g of 2-methylimidazole in 10 mL of anhydrous methanol to obtain solution B. Quickly pour solution B into solution A and stir for 1 h. Transfer the solution to a 150 mL polytetrafluoroethylene-lined reactor and maintain at 120 °C for 4 h. After cooling to room temperature, wash repeatedly with N,N-dimethylformamide and anhydrous methanol, and finally dry overnight in a vacuum drying oven at 60 °C and a vacuum degree of 1 kPa. Fe4 / Cu1-ZIF-8 is obtained.

[0034] (3) The obtained Fe4 / Cu1-ZIF-8 was heated in a tube furnace at a heating rate of 5℃ / min and held at 1000℃ for 1.5h under Ar atmosphere. The final catalyst Fe4 / Cu1-NC was obtained.

[0035] Example 2

[0036] The remaining steps are the same as in Example 1, except that FeCl2·4H2O in (1) of Example 1 is replaced with CoCl2·4H2O, and the final product is Co4 molecular cluster.

[0037] (2) Dissolve 50 mg of Co4 molecular clusters, 52 mg of copper acetylacetonate, and 1.19 g of Zn(NO3)2·6H2O obtained in the previous step in 30 mL of anhydrous methanol to obtain solution A. Simultaneously, dissolve 1.314 g of 2-methylimidazole in 10 mL of anhydrous methanol to obtain solution B. Quickly pour solution B into solution A and stir for 1 h. Transfer the solution to a 150 mL polytetrafluoroethylene-lined reactor and maintain at 120 °C for 4 h. After cooling to room temperature, wash repeatedly with N,N-dimethylformamide and anhydrous methanol, and finally dry overnight in a vacuum oven at 60 °C and a vacuum degree of 1 kPa. Co4 / Cu1-ZIF-8 is obtained.

[0038] (3) The obtained Co4 / Cu1-ZIF-8 was heated in a tube furnace at a heating rate of 5℃ / min and held at 1000℃ for 1.5h under Ar atmosphere. The final catalyst Co4 / Cu1-NC was obtained.

[0039] Example 3

[0040] Replacing FeCl2·4H2O in Example 1(1) with an equal amount of CuCl2·2H2O yields Cu4 molecular clusters.

[0041] (2) Dissolve 50 mg of Cu4 molecular clusters, 52 mg of copper acetylacetonate, and 1.19 g of Zn(NO3)2·6H2O obtained in the previous step in 30 mL of anhydrous methanol to obtain solution A. Simultaneously, dissolve 1.314 g of 2-methylimidazole in 10 mL of anhydrous methanol to obtain solution B. Quickly pour solution B into solution A and stir for 1 h. Transfer the solution to a 150 mL polytetrafluoroethylene-lined reactor and maintain at 120 °C for 4 h. After cooling to room temperature, wash repeatedly with N,N-dimethylformamide and anhydrous methanol, and finally dry overnight in a vacuum drying oven at 60 °C and a vacuum degree of 1 kPa. This yields Cu4 / Cu1-ZIF-8.

[0042] (3) The obtained Co4 / Cu1-ZIF-8 was heated in a tube furnace at a heating rate of 5℃ / min and held at 1000℃ for 1.5h under Ar atmosphere. The final catalyst Cu4 / Cu1-NC was obtained.

[0043] Example 4

[0044] Without adding the Fe4 molecular cluster from (2) in Example 1, the remaining steps are the same as in Example 1, and the resulting product is Cu1-NC.

[0045] Example 5

[0046] Without adding copper acetylacetone from (2) in Example 1, the remaining steps are the same as in Example 1, and the product obtained is Fe4-NC.

[0047] Example 6

[0048] Without adding copper acetylacetone from (2) in Example 2, the remaining steps are the same as in Example 2, and the product obtained is Co4-NC.

[0049] Example 7

[0050] Without adding copper acetylacetone from (2) in Example 3, the remaining steps are the same as in Example 3, and the product obtained is Cu4-NC.

[0051] Figure 1 The image shows a transmission electron microscope (TEM) image of Fe4 / Cu1-NC obtained in Example 1. It can be clearly seen from the image that the prepared Fe4 / Cu1-NC did not exhibit any agglomeration. The metal clusters are uniformly dispersed on the nitrogen-doped carbon substrate, and the average number of atoms in the clusters is 4 or 5, which are respectively attributed to the tight coupling of iron clusters and copper single-atom iron clusters.

[0052] Figure 2The X-ray photoelectron spectra of Fe4 / Cu1-NC, Cu1-NC, and Fe4-NC prepared in Examples 1, 4, and 5 are shown. The figures reveal that the nitrogen configuration in the catalysts is mainly pyridine nitrogen and graphitic nitrogen, with obvious metal-nitrogen bonds, indicating coordination between metal and nitrogen.

[0053] Figure 3 The image shows the performance test results of the Fe4 / Cu1-NC catalyst prepared in Example 1 for the electrocatalytic reduction of nitrate. It can be seen that this catalyst, with both single atoms and clusters, exhibits excellent electrocatalytic nitrate reduction performance, high selectivity for ammonia, and a Faradaic efficiency of over 90% for the generated ammonia over a wide potential range, reaching a maximum of 97.5%.

[0054] Weigh 10 mg of Fe4 / Cu1-NC and add 475 μL of anhydrous ethanol, 475 μL of deionized water, and 50 μL of 0.5 wt.% Nafion solution. Disperse by sonication for 1 h to form a homogeneous dispersion. Drop 50 μL of the resulting dispersion onto carbon paper (0.25 cm²). 2 Let it air dry at room temperature.

[0055] All electrochemical tests in this invention were performed using a conventional three-electrode battery on a CHI760E electrochemical workstation, with a mixed solution of 0.1M NaNO3 and 1M NaOH as the electrolyte. Hg / HgO was used as the reference electrode, platinum wire as the counter electrode, and carbon paper coated with catalyst ink as the working electrode. The conversion formula between electrode potential and RHE is: E(vs.RHE)=E(vs.Hg / HgO)+0.095+0.059×pH. The test procedure involved electroreduction of nitrate in a 0.1M NaNO3 and 1M NaOH electrolyte after Ar purging. The ammonia product was detected by UV-Vis colorimetry. The maximum Faradaic efficiency for ammonia production using Fe4 / Cu1-NC reached 97.5%.

[0056] Figure 4 This is a schematic diagram of the catalyst co-supported by copper single atoms and atomically precise metal clusters obtained in Example 1. The diagram shows that the copper single atoms and metal clusters are tightly bonded, forming a system where single atoms and clusters coexist.

[0057] Through experimental comparison, it was found that Fe4 / Cu1-NC has the highest Faradaic efficiency and the highest partial current density in the field of electrocatalytic reduction of nitrate. This is due to the strong hydrolysis ability of the iron cluster and the strong adsorption ability of copper single atoms for nitrate molecules. The electrocatalytic reduction of nitrate to ammonia is a complex process of transferring eight electrons and nine protons. Water at the interface of the iron cluster electrolytic catalyst provides the necessary active hydrogen for the nitrate reduction reaction. However, the poor hydrolysis ability and competitive hydrogen evolution reaction of the other Co4 / Cu1-NC and Cu4 / Cu1-NC lead to a decrease in the Faradaic efficiency of the ammonia product.

[0058] Example 8

[0059] The other steps are the same as in Example 1, except that the mass ratio of Fe4 molecular clusters and copper acetylacetonate is changed from 0.95:1 to 1.92:1, the amount of Fe4 molecular clusters added is changed from 50mg to 100mg, and the amount of copper acetylacetonate remains unchanged. The resulting catalyst is Fe4 / Cu1-NC*2. The electrocatalytic nitrate reduction performance test is carried out in 0.1M NaNO3 and 1M NaOH electrolyte after Ar atmosphere purging. The maximum Faradaic efficiency is 60.02%.

[0060] Example 9

[0061] The other steps are the same as in Example 1, except that the mass ratio of 2-methylimidazole to Zn(NO3)2·6H2O is changed by... 1.1 The catalyst obtained by replacing 1 with 1.5~1 is Fe4 / Cu1-NC-Zn*1.5. The electrocatalytic nitrate reduction performance test was carried out in 0.1M NaNO3 and 1M NaOH electrolyte after Ar atmosphere purging. The maximum Faraday efficiency was 43.02%.

[0062] Example 10

[0063] The other steps are the same as in Example 1, except that the centrifugation speed in step (2) of Example 1 is replaced with 10 min instead of 5 min, and the resulting catalyst is Fe4 / Cu1-NC at 12000 rpm. The electrocatalytic nitrate reduction performance test was carried out in an electrolyte of 0.1 M NaNO3 and 1 M NaOH after Ar atmosphere purging, and the maximum Faraday efficiency was 67.98%.

[0064] Example 11

[0065] The other steps are the same as in Example 1, except that the calcination temperature in step (3) of Example 1 is replaced by 900℃ instead of 1000℃. The resulting catalyst is Fe4 / Cu1-NC-900℃. The electrocatalytic nitrate reduction performance test is carried out in 0.1M NaNO3 and 1M NaOH electrolyte after Ar atmosphere purging. The maximum Faraday efficiency is 87.06%.

[0066] The obtained material properties show that the highest Faradaic efficiency in the electrocatalytic reduction of nitrate in Fe4 / Cu1-NC reaches 97.5% at -0.38 V vs. RHE, and the partial current density of ammonia products reaches 86.05 mA·cm⁻¹. -2 It has good prospects for industrial application. In contrast, the Faraday efficiency of Cu1-NC is only 74.9%, and the partial current density of ammonia is 26.92 mA·cm⁻¹. -2 The Faraday efficiency of Fe4-NC is 75.2%, and the partial current density of ammonia is 22.38 mA·cm⁻¹. -2 After replacing the clusters with Co4 and Cu4 molecular clusters, the Faraday efficiency of Co4 / Cu1-NC was 54.13%, and the partial current density of ammonia was 4.83 mA·cm⁻¹. -2 The Faraday efficiency of Cu4 / Cu1-NC is 79.49%, and the partial current density of ammonia is 60.75 mA·cm⁻¹. -2 .

[0067] As can be seen from the above examples, the M4 / Cu1-NC prepared by the present invention forms an ordered metal cluster on a nitrogen-doped carbon substrate through the strong coupling effect of organic ligands. Different metal cluster properties lead to different electrocatalytic nitrate reduction performance.

[0068] Matters not covered in this invention are common knowledge.

Claims

1. A method for preparing a catalyst co-supported with single atoms and atomically precise clusters, characterized in that the method comprises the following steps: (1) Add M salt, 2-Methyl-1H-benzimidazole-1-methanol and triethylamine to anhydrous methanol to obtain a solution. After stirring for 30-60 min, transfer the solution to a reaction vessel and maintain it at 140-160℃ for 12-24 h. Then cool it at room temperature for 24-48 h and obtain the product M4 molecular cluster by suction filtration. in, The M salt is FeCl2·4H2O, CoCl2·6H2O or CuCl2·2H2O; The mass ratio is Hmbm:triethylamine:M salt = 2.0-3.0:1-1.3:1; add 150-300 mg of M salt per 8 mL of anhydrous methanol; (2) Subsequently, the prepared M4 molecular cluster, copper acetylacetonate and Zn(NO3)2·6H2O were dissolved in methanol to obtain solution A. Then, 2-methylimidazole was dissolved in methanol and labeled as solution B. A and B were then mixed at room temperature and stirred for 1 to 1.5 h. The mixture was then transferred to a reaction vessel and kept at 120-140 °C for 4 to 6 h. After the solution cooled to room temperature, it was centrifuged and vacuum dried to obtain product M4 / Cu1-ZIF-8. The mass ratio of M4 molecular cluster to copper acetylacetone is 1–2:1, the mass ratio of Fe4 molecular cluster to Zn(NO3)2·6H2O is 0.042–0.05:1, and the mass ratio of 2-methylimidazole to Zn(NO3)2·6H2O is 1.1–1.5:

1. (3) The obtained Fe4 / Cu1-ZIF-8 was carbonized to obtain a catalyst with atomically precise metal clusters and copper single atoms co-supported.

2. The method for preparing the catalyst co-supported with single atoms and atomically precise clusters as described in claim 1, characterized in that, The centrifugation conditions in step (2) are 10000-12000 rpm for 5-10 min; the vacuum drying conditions are 60-80℃ and a vacuum degree of 0.8-1 MPa.

3. The method for preparing the catalyst co-supported with single atoms and atomically precise clusters as described in claim 1, characterized in that, The volume ratio of solution A to solution B is 2 to 3:

1.

4. The method for preparing the catalyst co-supported with single atoms and atomically precise clusters as described in claim 1, characterized in that, The carbonization conditions are maintained at 900-1000℃ for 1-2 hours, with a heating rate of 1-8℃ / min.

5. The application of the catalyst co-supported with atomically precise metal clusters and copper single atoms prepared by the method described in claim 1, characterized in that, As a catalyst for the electrocatalytic reduction of nitrate.

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