Monatomic alloy catalyst as well as preparation method and application thereof

Abstract

The invention relates to the technical field of catalytic materials, in particular to a monatomic alloy catalyst and a preparation method and application thereof.The preparation method comprises the steps that a first solution obtained by mixing cobalt salt, silver salt and a solvent is mixed with a second solution obtained by mixing 2-methylimidazole and a solvent, stirring treatment is conducted, and a first precursor solution is obtained; and carrying out first heat treatment on the obtained precipitate in an inert atmosphere to obtain the fcc Ag1Co / C monatomic alloy catalyst. A first solution and a second solution are mixed to obtain an Ag / ZIF-67 precipitate which is a Co-based zeolite imidazate framework structure composite material, an organic framework of the Co-based zeolite imidazate framework structure composite material is decomposed and carbonized through high-temperature heat treatment, meanwhile, Ag and Co species are reduced and converted into nanoparticles, and the Ag / ZIF-67 precipitate is obtained. And finally, the composite material catalyst with the Ag1Co monatomic alloy nanoparticles embedded into the nitrogen-doped carbon matrix is formed. The catalyst shows the most excellent activity and selectivity, the removal rate of 4-NP reaches 100% within 6 min, and high catalytic activity can be achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of catalytic materials, in particular to a single-atom alloy catalyst and a preparation method and application thereof. BACKGROUND

[0002] Functional aniline is an important aromatic amine compound, and the amino group and the substituent group in the molecular structure of the functional aniline endow the functional aniline with rich chemical properties, so that the functional aniline becomes an indispensable intermediate in the pharmaceutical synthesis, dye manufacturing and pigment industry. For many years, the reduction of aromatic nitro compounds has been one of the main ways to prepare aromatic amine compounds, and is widely used in the fine chemical industry. However, the traditional industrial production method usually relies on a stoichiometric reducing agent such as sodium dithionite or iron hydroxide, and these methods still have problems such as too much waste, difficult post-treatment, high cost, high risk coefficient and the like in actual production, which need to be solved urgently. Therefore, it is urgent to find an environmentally friendly and efficient production method of functional aniline.

[0003] In recent years, metal-organic frameworks (MOFs), especially zeolitic imidazolate frameworks (ZIFs) (such as ZIF-67), a new and rapidly developing porous material, are formed by the assembly of metal ions or clusters and organic linkers. It has attracted extensive attention and research due to its high specific surface area, controllable structure and adjustable pore size. In the high-temperature pyrolysis process, the ZIF-67 precursor can be converted into a catalytic material containing transition metal Co, thereby catalyzing chemical reactions. Co-based catalysts are expected to be a strong candidate to replace Pt group noble metals due to their abundant reserves, low price and unique electronic structure. However, there are still some problems to be solved in Co-based catalysts. When Co-based catalysts are used to reduce nitroaromatic compounds, there is a risk of excessive hydrogenation and C-C bond rupture, which greatly reduces the selectivity.

[0004] In recent research work, alloying and crystal phase engineering of Co-based catalysts are used to improve the catalytic activity of Co-based catalysts. However, due to high surface energy and complex phase transformation kinetics, the crystal phase engineering of single-atom alloys is still challenging, and there are still problems of poor stability, low activity and poor selectivity in the alloying engineering of Co-based catalysts.

[0005] Therefore, the prior art still needs to be improved and developed. SUMMARY

[0006] In view of the deficiencies of the prior art, the purpose of the present application is to provide a single-atom alloy catalyst and a preparation method and application thereof, aiming to solve the problems of low activity and poor selectivity of the single-atom alloy catalyst prepared by the prior method.

[0007] The technical scheme of the present application is as follows: A preparation method of a single-atom alloy catalyst, comprising the steps of: mixing a cobalt salt, a silver salt and a solvent to obtain a first solution; mixing 2-methylimidazole and a solvent to obtain a second solution; mixing the first solution and the second solution and stirring to obtain a precipitate; performing first heat treatment on the precipitate under an inert atmosphere to obtain an fcc Ag1Co / C single-atom alloy catalyst.

[0008] The preparation method of the single-atom alloy catalyst, wherein the cobalt salt is at least one selected from cobalt nitrate, cobalt acetate, cobalt acetylacetonate and cobalt chloride; and the silver salt is at least one selected from silver nitrate, silver fluoride and silver perchlorate.

[0009] The preparation method of the single-atom alloy catalyst, wherein the mass ratio of the cobalt salt to the silver salt is (3-100):1; and the concentration of the first solution is 0.16 mol / L-0.2 mol / L.

[0010] The preparation method of the single-atom alloy catalyst, wherein the concentration of the second solution is 0.4 mol / L-0.8 mol / L; and the volume ratio of the first solution to the second solution is 1:(0.5-1).

[0011] The preparation method of the single-atom alloy catalyst, wherein the temperature rising rate of the first heat treatment is 2℃ / min-10℃ / min, the temperature of the first heat treatment is 600℃-1000℃, and the time of the first heat treatment is 0.5h-3h.

[0012] The preparation method of the single-atom alloy catalyst, further comprising the steps of: performing second heat treatment on the precipitate under an air atmosphere to obtain an Ag-Co3O4 / C precursor; performing third heat treatment on the Ag-Co3O4 / C precursor under a reducing atmosphere to obtain an hcp Ag1Co / C single-atom alloy catalyst.

[0013] The preparation method of the single-atom alloy catalyst, wherein the temperature rising rate of the second heat treatment is 2℃ / min-10℃ / min, the temperature of the second heat treatment is 250℃-350℃, and the time of the second heat treatment is 0.5h-3h.

[0014] The preparation method of the monatomic alloy catalyst, wherein the third heat treatment is carried out under an argon and hydrogen mixed atmosphere; the temperature rising rate of the third heat treatment is 2-10 DEG C / min; the temperature of the third heat treatment is 300-400 DEG C; and the time of the third heat treatment is 0.5-3 h.

[0015] A monatomic alloy catalyst prepared by the preparation method of the monatomic alloy catalyst.

[0016] Application of a monatomic alloy catalyst in a nitroaromatic reduction reaction.

[0017] Beneficial effects: the present application provides a monatomic alloy catalyst, a preparation method and application thereof, the preparation method comprising the steps of: mixing a cobalt salt, a silver salt and a solvent to obtain a first solution; mixing 2-methylimidazole and a solvent to obtain a second solution; mixing the first solution and the second solution and stirring to obtain a precipitate; and performing first heat treatment on the precipitate under an inert atmosphere to obtain an fcc Ag1Co / C monatomic alloy catalyst. The Ag / ZIF-67 precipitate obtained by mixing the first solution and the second solution is a Co-based zeolite imidazole framework composite material, and through high-temperature heat treatment, the organic framework is decomposed and carbonized, and at the same time, Ag and Co species are reduced and converted into nanoparticles, and finally, an Ag1Co monatomic alloy nanoparticle embedded in a nitrogen-doped carbon matrix composite catalyst is formed. The catalyst exhibits optimal activity and selectivity, and the removal rate of 4-NP (p-nitrophenol) reaches 100% within 6 min; and the charge transfer between Ag and Co produces electron-rich Ag sites and electron-deficient Co sites, which can effectively promote the dissociation of active H from BH4 and the adsorption and reduction of 4-NP on the catalyst surface, realizing high catalytic activity. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 It is a process flow diagram of the preparation method of the monatomic alloy catalyst of the present application; Figure 2 It is an XRD pattern of fcc Co / C, Ag NP / C, hcp Co / C, hcp Ag1Co / C and fcc Ag1Co / C; Figure 3 It is an SEM image of the fcc Ag1Co / C catalyst material; Figure 4 It is a TEM image of the fcc Ag1Co / C catalyst material; Figure 5 It is an HR-TEM image of the fcc Ag1Co / C catalyst material; Figure 6HAADF-STEM image of fcc Ag1Co / C catalyst material; Figure 7 Enlarged HAADF-STEM images of the fcc Ag1Co catalyst material and their corresponding atomic intensity distribution curves; Figure 8 HAADF-STEM images and associated EDX spectra of fcc Ag1Co / C catalyst materials; Figure 9 The UV-Vis absorption spectra before and after adding NaBH4 to 4-NP; Figure 10 The image shows the UV-Vis absorption spectra of 4-NP catalyzed by fcc Ag1Co / C at specific time intervals. Figure 11 When fcc Ag1Co / C, fcc Co / C, hcp Ag1Co / C, Ag NP / C, and hcp Co / C catalyze the 4-NP reduction reaction, C t / C0 change curve with reaction time; Figure 12 Plots showing the apparent rate constant values ​​for fcc Ag1Co / C, fcc Co / C, hcp Ag1Co / C, Ag NP / C, and hcp Co / C; Figure 13 The graph shows the repeatability test results for fcc Ag1Co / C. Figure 14 The figure shows the toxicity test results of the fcc Ag1Co / C active site. Detailed Implementation

[0019] This invention provides a single-atom alloy catalyst, its preparation method, and its application. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0020] It will be understood by those skilled in the art that, unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. It should also be understood that terms such as those defined in general dictionaries should be understood to have the same meaning as in the context of the prior art, and should not be interpreted in an idealized or overly formal sense unless specifically defined as herein.

[0021] Sodium borohydride reduction is a common and effective strategy for the green preparation of functionalized aniline compounds. This strategy requires the design of highly efficient heterogeneous selective hydrogenation catalysts to reduce nitro aromatic compounds to the corresponding aniline derivatives. To achieve this, the designed catalyst must preferentially interact with the nitro group in the substrate molecule and promote its hydrogenation, while maximally suppressing the conversion of other sensitive functional groups (such as C=C, C=O, or C≡N). Although platinum group metal catalysts are considered promising candidates in nitro hydrogenation due to their excellent hydrogen activation capabilities, their surfaces often readily promote the hydrogenolysis of carbon-halogen (CX) bonds, leading to undesirable side reactions. Therefore, the selectivity of these catalysts in complex molecular transformations is often insufficient. Developing catalysts that can precisely control the nitro hydrogenation process without inducing the conversion of other functional groups remains a major challenge in this field.

[0022] Compared to solid solution alloys, single-atom alloys possess the highest atomic efficiency and uniform active sites, showing broad application prospects in heterogeneous catalysis. Therefore, the selection of guest metal atoms to embed into the host metal Co to form single-atom alloys is particularly important. Introducing noble metals (such as Ag, Ru, and Pt) into the host metal Co can regulate the d-band electronic structure of the Co active sites through local charge transfer. However, while metals such as Ru and Pt exhibit excellent hydrogen evolution reaction capabilities, their excessively strong hydrogen adsorption energy and the cleavage of CX can trigger intense competitive side reactions, severely reducing the selectivity of amino compounds. Furthermore, current Co-based catalyst alloying engineering still suffers from poor stability, low activity, and poor selectivity.

[0023] Based on this, such as Figure 1 As shown, this invention provides a method for preparing a single-atom alloy catalyst, comprising the following steps: Step S10: Mix cobalt salt, silver salt and solvent to obtain the first solution; Step S20: Mix 2-methylimidazole with a solvent to obtain a second solution; Step S30: Mix the first solution and the second solution, and stir to obtain a precipitate; Step S40: The precipitate is subjected to a first heat treatment under an inert atmosphere to obtain the fcc Ag1Co / C single-atom alloy catalyst.

[0024] In this embodiment, Ag / ZIF-67 precipitate is obtained by mixing the first and second solutions. This precipitate is a Co-based zeolite imidazole ester framework composite material. Through high-temperature heat treatment, its organic framework is decomposed and carbonized, while Ag and Co species are reduced and transformed into nanoparticles, ultimately forming a composite catalyst with Ag1Co single-atom alloy nanoparticles embedded in a nitrogen-doped carbon matrix. This catalyst exhibits superior activity and selectivity, achieving 100% removal of 4-NP (p-nitrophenol) within 6 minutes. Furthermore, charge transfer between Ag and Co generates electron-rich Ag sites and electron-deficient Co sites, effectively promoting the dissociation of BH4 to release active H and the adsorption and reduction of 4-NP on the catalyst surface, achieving high catalytic activity. Moreover, the entire preparation process is completed in a single solid-phase reaction, requiring no complex equipment or multi-step synthesis steps. The raw materials are inexpensive and readily available, the operation is simple, and the reproducibility is good, making it potential for large-scale production.

[0025] Specifically, Ag, due to its moderate hydrogen adsorption free energy and catalytic activity, provides a crucial reaction window for the multi-step reduction process of nitro compounds. Charge transfer between Ag and Co generates electron-rich Ag sites and electron-deficient Co sites, synergistically optimizing the intermediate adsorption energy. Furthermore, the single-atom dispersion strategy of Ag maximizes the utilization of active sites and enhances local electronic coupling, thereby constructing a highly active and selective catalytic system. Meanwhile, kinetic studies show that the catalytic reaction of p-nitrophenol (4-NP) follows a first-order kinetic model. The main principle of this reaction is the reduction of 4-NP to p-nitroaniline (4-AP) by active hydrogen ions generated from sodium borohydride catalyzed by the catalyst. Compared to fcc Co and hcp Co, the fcc Ag1Co / C single-atom alloy catalyst of this invention exhibits the best activity and selectivity, achieving 100% removal of 4-NP within 6 minutes. The rate constant k of fccAg1Co / C is... app 1.01 min -1 After 10 cycles of testing, the catalyst still achieved a substrate conversion rate of over 98%.

[0026] It should be noted that fcc refers to face-centered cubic structure, while hcp refers to hexagonal close-packed structure.

[0027] In some embodiments, the cobalt salt is selected from, but is not limited to, at least one of cobalt nitrate, cobalt acetate, cobalt acetylacetonate, and cobalt chloride; the silver salt is selected from, but is not limited to, at least one of silver nitrate, silver fluoride, and silver perchlorate. The above-mentioned cobalt and silver salts are used to provide cobalt and silver elements for single-atom alloy catalysts.

[0028] In some embodiments, the mass ratio of the cobalt salt to the silver salt is (3-100):1; the concentration of the first solution is 0.16 mol / L-0.2 mol / L. Controlling the mass ratio of the cobalt salt to the silver salt within the above range allows for the preparation of a composite catalyst in which Ag1Co single-atom alloy nanoparticles are embedded in a nitrogen-doped carbon matrix. This process enables charge transfer between Ag and Co, generating electron-rich Ag sites and electron-deficient Co sites, synergistically optimizing the intermediate adsorption energy. Maintaining the concentration of the first solution between 0.16 mol / L and 0.2 mol / L facilitates the dissolution of the cobalt and silver salts by the solvent, thus aiding in subsequent reactions with the ligand solution.

[0029] In some embodiments, the solvent is selected from, but not limited to, one or more of methanol, water, ethanol, and N,N-dimethylformamide (DMF).

[0030] In some embodiments, the concentration of the second solution is 0.4 mol / L-0.8 mol / L; the volume ratio of the first solution to the second solution is 1:(0.5-1). Mixing the first and second solutions at this volume ratio forms an Ag / ZIF-67 precipitate, which is a Co-based zeolite imidazole ester framework composite material. Specifically, both cobalt and silver salts react with 2-methylimidazole (C4H6N2), and Ag atoms are embedded in the ZIF-67 framework, generating Ag / ZIF-67 in situ. This process provides a precursor for subsequent catalyst synthesis.

[0031] In some embodiments, the heating rate of the first heat treatment is 2℃ / min-10℃ / min, the temperature of the first heat treatment is 600℃-1000℃, and the time of the first heat treatment is 0.5h-3h. Through high-temperature heat treatment, the organic framework is decomposed and carbonized, while Ag and Co species are reduced and transformed into nanoparticles, ultimately forming a composite catalyst of Ag1Co single-atom alloy nanoparticles embedded in a nitrogen-doped carbon matrix.

[0032] In a preferred embodiment, the heating rate of the first heat treatment is 5°C / min, the temperature of the first heat treatment is 800°C, and the time of the first heat treatment is 2 hours. By treating the Ag / ZIF-67 precipitate at high temperature, the Ag / ZIF-67 will be thermally reduced in situ to an Ag1Co / C single-atom alloy catalyst.

[0033] In some embodiments, the inert gas in the inert atmosphere includes, but is not limited to, at least one of nitrogen, argon, and helium.

[0034] In some embodiments, the preparation method further includes the step of: Step S50: The precipitate is subjected to a second heat treatment in air atmosphere to obtain Ag-Co3O4 / C precursor; Step S60: The Ag-Co3O4 / C precursor is subjected to a third heat treatment under a reducing atmosphere to obtain the hcpAg1Co / C single-atom alloy catalyst.

[0035] In this embodiment, the hcp phase Ag1Co / C single-atom alloy catalyst was prepared by using different heat treatment processes. It has the same effect as the fcc phase Ag1Co / C single-atom alloy catalyst. The charge transfer between Ag and Co generates electron-rich Ag sites and electron-deficient Co sites, which can effectively promote the dissociation of BH4 into active H and the adsorption and reduction of 4-NP on the catalyst surface, thus achieving high catalytic activity; and achieving an extremely high removal rate of 4-NP.

[0036] In some embodiments, the heating rate of the second heat treatment is 2℃ / min-10℃ / min, the temperature of the second heat treatment is 250℃-350℃, and the time of the second heat treatment is 0.5h-3h.

[0037] In a preferred embodiment, the heating rate of the second heat treatment is 5°C / min, the temperature of the second heat treatment is 300°C, and the time of the second heat treatment is 2 hours.

[0038] In some embodiments, the third heat treatment is carried out in a mixed atmosphere of argon and hydrogen; the heating rate of the third heat treatment is 2℃ / min-10℃ / min; the temperature of the third heat treatment is 300℃-400℃; and the time of the third heat treatment is 0.5h-3h.

[0039] In a preferred embodiment, the heating rate of the third heat treatment is 5°C / min, the temperature of the third heat treatment is 350°C, and the time of the third heat treatment is 2 hours.

[0040] In some embodiments, the silver salt can also be formed into a single-atom alloy with Co using other metal salts (such as Pt-based noble metals).

[0041] In addition, the present invention also provides a single-atom alloy catalyst, which is prepared using the same method as the single-atom alloy catalyst.

[0042] In this embodiment, the single-atom alloy catalyst prepared by the above method exhibits high catalytic activity, selectivity and stability by embedding atomically dispersed Ag into a metal Co host. It achieves a 100% removal rate of 4-NP (p-nitrophenol) within 6 minutes. Furthermore, the charge transfer between Ag and Co generates electron-rich Ag sites and electron-deficient Co sites, which can effectively promote the dissociation of BH4 into active H and the adsorption and reduction of 4-NP on the catalyst surface, thus achieving high catalytic activity.

[0043] In addition, the present invention also provides the application of a single-atom alloy catalyst in the reduction reaction of nitroaromatics.

[0044] In this embodiment, Ag1Co single-atom alloys with different crystal phases are prepared using a MOF-derived strategy and applied to the reduction reaction of nitroaromatics. The process is simple and easily industrialized. This catalyst reduces 4-NP to p-nitroaniline (4-AP) via active hydrogen ions generated by sodium borohydride. Compared to fcc Co and hcp Co, the fcc Ag1Co / C single-atom alloy catalyst of this invention exhibits superior activity and selectivity, achieving 100% removal of 4-NP within 6 minutes. Furthermore, charge transfer between Ag and Co in the catalyst generates electron-rich Ag sites and electron-deficient Co sites, which effectively promotes the dissociation of BH4- to active H and the adsorption and reduction of 4-NP on the catalyst surface.

[0045] The following examples further illustrate the present invention in detail. It should also be understood that the following examples are only for further explanation of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention are within the scope of protection of the present invention.

[0046] Example 1 This embodiment provides a single-atom alloy catalyst, the specific preparation steps of which are as follows: 1) Dissolve 3g of Co(NO3)2·6H2O and 100mg of AgNO3 in 100mL of CH3OH to prepare solution A; separately dissolve 6.6g of C4H6N2 in 100mL of CH3OH to prepare solution B. Then add solution B to solution A with continuous stirring, stir at room temperature for 24h, collect the product by centrifugation and dry it to obtain Ag / ZIF-67.

[0047] 2) Place Ag / ZIF-67 in a tube furnace and heat it at 5℃·min under an Ar atmosphere. -1 The temperature was increased to 800°C and maintained for 2 hours. After cooling to room temperature, the fcc Ag1Co / C catalyst material was obtained.

[0048] Ag / ZIF-67 was placed in a muffle furnace and heated at 5°C / min in air atmosphere. -1 The temperature was increased to 300°C and maintained for 2 hours. After cooling to room temperature, the Ag-Co3O4 / C precursor was obtained. Then, the Ag-Co3O4 / C was placed in a tube furnace and heated at 5°C / min under an Ar / H2 atmosphere. -1 The temperature was increased to 350°C and maintained for 2 hours. After cooling to room temperature, the hcp Ag1Co / C catalyst material was obtained.

[0049] The fcc Ag1Co / C catalyst and hcp Ag1Co / C catalyst prepared in this embodiment were characterized as follows: The XRD patterns of fcc Co / C, Ag NP / C, hcp Co / C, hcp Ag1Co / C, and fcc Ag1Co / C are as follows: Figure 2 As shown, the fcc Ag1Co / C sample exhibits distinct diffraction peaks at 44.2°, 51.5°, and 75.8°, which are characteristic metallic peaks belonging to fcc Co. No Ag diffraction peaks are observed, indicating that Ag exists in an atomically dispersed form within the fcc Ag1Co / C sample. Similarly, the hcp Ag1Co / C sample shows distinct diffraction peaks at 41.6°, 44.7°, 47.5°, 62.7°, 75.9°, and 84.2°, which are characteristic metallic peaks belonging to hcp Co. No Ag diffraction peaks are observed, indicating that Ag exists in an atomically dispersed form within the hcp Ag1Co / C sample. This also demonstrates the successful preparation of both hcp Ag1Co / C and fcc Ag1Co / C samples.

[0050] SEM images of the fcc Ag1Co / C catalyst material are shown below. Figure 3 As shown, the fcc Ag1Co / C catalyst material can be observed to exist in a dodecahedral form and has good dispersion.

[0051] TEM image of fcc Ag1Co / C catalyst material as shown below Figure 4 As shown, the nanoparticles in the fcc Ag1Co / C catalyst material are uniformly embedded in the graphitized carbon.

[0052] HR-TEM image of fcc Ag1Co / C catalyst material as shown in Figure 5 As shown, distinct lattice fringes can be observed, with a lattice spacing of 2.1 Å corresponding to the (111) crystal plane of metallic Co.

[0053] HAADF-STEM image of fcc Ag1Co / C catalyst material as shown in Figure 1 Figure 6As shown in the figure, the atoms with brighter contrast are Ag atoms, and they exist in an atomically dispersed form.

[0054] Figure 7 The enlarged HAADF-STEM image of the fcc Ag1Co catalyst material and its corresponding atomic intensity distribution curve further illustrate that Ag exists in the metal host Co in an atomically dispersed form.

[0055] HAADF-STEM images and related EDX spectra of fcc Ag1Co / C catalyst materials are as follows: Figure 8 As shown, the nanoparticles are composed of Ag and Co elements, which also indicates that Ag exists in the metal host Co in an atomically dispersed form.

[0056] The UV-Vis absorption spectra of 4-NP before and after the addition of NaBH4 are shown below. Figure 9 As shown, it can be observed that the absorption peak shifts after the addition of NaBH4 to the 4-NP solution.

[0057] The UV-Vis absorption spectra of 4-NP catalyzed by fcc Ag1Co / C at specific time intervals are shown below. Figure 10 As shown, after adding the fcc Ag1Co / C catalyst to the mixture of 4-NP and NaBH4, the absorption peak at 400 nm gradually weakened after 6 min. Simultaneously, a new absorption peak appeared at 300 nm, indicating that 4-NP was reduced to form 4-AP.

[0058] When fcc Ag1Co / C, fcc Co / C, hcp Ag1Co / C, Ag NP / C, and hcp Co / C catalyze the 4-NP reduction reaction, C t The curve of C0 changing with reaction time is shown in the figure below. Figure 11 As shown, when fcc Co / C, hcp Ag1Co / C, Ag NP / C and hcpCo / C are used as catalysts, there is almost no decrease in activity at 6 minutes, which means that fcc Ag1Co / C has the highest catalytic activity.

[0059] The apparent rate constants (k) of fcc Ag1Co / C, fcc Co / C, hcp Ag1Co / C, Ag NP / C, and hcp Co / C. app Value data graph as follows Figure 12 As shown, the rate constant k of fcc Ag1Co / C is found to be 1.01 min. -1 The activity of fcc Ag1Co / C is approximately 100 times that of hcp Ag1Co / C, indicating that fcc Ag1Co / C has high catalytic activity.

[0060] The repeatability test results of fcc Ag1Co / C are as follows:Figure 13 As shown, after 10 reaction cycles, its catalytic activity hardly decreased, highlighting the great potential for industrial application of this catalyst.

[0061] The toxicity test results of the fcc Ag1Co / C active site are as follows: Figure 14 As shown, the chloride and thiocyanate ion poisoning experiments revealed that after 24 hours of NaCl treatment, the catalytic activity of fcc Ag1Co / C plummeted from 99% to 63%. This indicates that the single-atom Ag site dominates the catalytic efficiency of the 4-NP reduction reaction. Simultaneously, after 24 hours of KSCN treatment, the catalytic activity of fcc Ag1Co / C plummeted from 99% to 53%, indicating that the single-atom Ag and metallic Co dual sites jointly dominate the catalytic efficiency of the 4-NP reduction reaction.

[0062] In summary, the present invention provides a single-atom alloy catalyst, its preparation method, and its application. The preparation method includes the following steps: mixing cobalt salt, silver salt, and solvent to obtain a first solution; mixing 2-methylimidazole with solvent to obtain a second solution; mixing the first solution and the second solution and stirring to obtain a precipitate; and subjecting the precipitate to a first heat treatment under an inert atmosphere to obtain the fcc Ag1Co / C single-atom alloy catalyst. This invention utilizes a mixture of a first solution and a second solution to obtain an Ag / ZIF-67 precipitate, which is a Co-based zeolite imidazole ester framework composite material. Through high-temperature heat treatment, its organic framework is decomposed and carbonized, while Ag and Co species are reduced and transformed into nanoparticles, ultimately forming a composite catalyst in which Ag1Co single-atom alloy nanoparticles are embedded in a nitrogen-doped carbon matrix. This catalyst exhibits superior activity and selectivity, achieving a 100% removal rate of 4-NP (p-nitrophenol) within 6 minutes. Furthermore, charge transfer between Ag and Co generates electron-rich Ag sites and electron-deficient Co sites, which can effectively promote the dissociation of BH4 to release active H and the adsorption and reduction of 4-NP on the catalyst surface, achieving high catalytic activity.

[0063] It should be understood that the application of the present invention is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A method for preparing a single-atom alloy catalyst, characterized by, The method comprises the steps of: mixing a cobalt salt, a silver salt and a solvent to obtain a first solution; mixing 2-methylimidazole and a solvent to obtain a second solution; mixing the first solution and the second solution and stirring to obtain a precipitate; performing a first heat treatment on the precipitate in an inert atmosphere to obtain an fcc Ag1Co / C monatomic alloy catalyst.

2. The method of claim 1, wherein the monolayer alloy catalyst is prepared by a method comprising: The cobalt salt is at least one selected from the group consisting of cobalt nitrate, cobalt acetate, cobalt acetylacetonate and cobalt chloride; and the silver salt is at least one selected from the group consisting of silver nitrate, silver fluoride and silver perchlorate.

3. The method of claim 1, wherein the monolayer alloy catalyst is prepared by a process comprising: The mass ratio of the cobalt salt to the silver salt is (3-100):1; and the concentration of the first solution is 0.16-0.2 mol / L.

4. The method of claim 1, wherein the monolayer alloy catalyst is prepared by a process comprising: The concentration of the second solution is 0.4-0.8 mol / L; and the volume ratio of the first solution to the second solution is 1:(0.5-1).

5. The method of claim 1, wherein the monolayer alloy catalyst is prepared by the steps of: The temperature increasing rate of the first heat treatment is 2-10 ℃ / min, the temperature of the first heat treatment is 600-1000 ℃, and the time of the first heat treatment is 0.5-3 h.

6. The method of claim 1, wherein the monolayer alloy catalyst is prepared by a method comprising: The method further comprises the steps of: performing a second heat treatment on the precipitate in an air atmosphere to obtain an Ag-Co3O4 / C precursor; performing a third heat treatment on the Ag-Co3O4 / C precursor in a reducing atmosphere to obtain an hcp Ag1Co / C monatomic alloy catalyst.

7. The method of claim 6, wherein the single-atom alloy catalyst is prepared by a method comprising: The temperature increasing rate of the second heat treatment is 2-10 ℃ / min, the temperature of the second heat treatment is 250-350 ℃, and the time of the second heat treatment is 0.5-3 h.

8. The method of claim 6, wherein the single-atom alloy catalyst is prepared by a method comprising: The third heat treatment is performed in an atmosphere of mixed argon and hydrogen; the temperature increasing rate of the third heat treatment is 2-10 ℃ / min, the temperature of the third heat treatment is 300-400 ℃, and the time of the third heat treatment is 0.5-3 h.

9. A single-atom alloy catalyst characterized by, The method is used to prepare the monatomic alloy catalyst as claimed in any one of claims 1-8.

10. Use of the monatomic alloy catalyst as claimed in claim 9 in a nitroarene reduction reaction.

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