Cerium oxide loaded metal monatomic catalyst as well as preparation method and application thereof

Abstract

The invention discloses a preparation method of a cerium oxide loaded metal monatomic catalyst, which comprises the following steps: a, adding a CeO2 carrier into a soluble metal salt solution, mixing, and evaporating a solvent to dryness to obtain solid powder; b, the solid powder obtained in the step a is subjected to first roasting treatment, the temperature of the first roasting treatment is lower than the decomposition temperature of the soluble metal salt, and a first roasting product is obtained after washing, filtering and drying; c, the first roasting product obtained in the step b is subjected to second roasting treatment, the temperature of the second roasting treatment is higher than that of the first roasting treatment, and the cerium oxide loaded metal monatomic catalyst is obtained. According to the catalyst, the loading capacity of active metal single atoms is effectively improved, meanwhile, the carrier is prevented from being oxidized and damaged in the reaction process when the catalyst is used for persulfate catalytic activation, and the stability of the catalyst is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalysts, and in particular relates to a cerium oxide-supported metal single-atom catalyst and a preparation method thereof, and further relates to the application of the single-atom catalyst. Background Art

[0002] Persulfate (PMS) exists in solid form, is easily soluble in water, and is a strong oxidant. However, persulfate is relatively stable at room temperature, and its effect on the degradation of organic pollutants is not obvious when used alone. It requires the introduction of catalysts or external energy to activate it. The principle of persulfate activation is to activate the peroxide OO bond, causing electron transfer between the catalyst and the persulfate. The persulfate activation mechanism varies greatly depending on the activation method. There are free radical pathways based on sulfate radicals, hydroxyl radicals and superoxide anions, and non-free radical pathways based on singlet oxygen and electron transfer. Compared with the traditional Fenton oxidation method, the sulfate radicals unique to the persulfate oxidation method have higher oxidation potential, stronger oxidation ability, longer half-life, and wider pH application range than hydroxyl radicals; at the same time, compared with hydrogen peroxide, the storage and transportation of persulfate is safer, more convenient, and cheaper. The activation methods of persulfate mainly include: thermal activation, ultraviolet light activation, alkali activation, zero-valent iron activation, transition metal catalyst activation, etc. Oxidation technology based on persulfate activation has been widely studied.

[0003] Compared with other activation methods, transition metal catalytic activation has the advantages of low energy consumption, high activation efficiency, small amount of catalyst, and adjustable active oxidizing species. According to the state of transition metal catalysts, it can be divided into homogeneous catalysis and heterogeneous catalysis. 2+ 、Co 2+ , Mn 2+ etc.) are the most commonly used homogeneous catalysts, which can efficiently catalyze PMS activation and produce sulfate radicals, hydroxyl radicals, etc.; however, transition metal ions are easily lost during the reaction and are difficult to reuse, causing secondary pollution. Supported heterogeneous catalysts catalyze persulfate activation by loading transition metal or transition metal oxide nanoparticles onto high specific surface carriers to produce active sites at the edges, corners, faces, steps, defects, etc. of the nanoparticles. However, only a few special parts of the nanoparticles have catalytic activity, and most of the transition metal atoms encapsulated in the nanoparticles cannot be used; in addition, the activity of the catalyst is closely related to the size and morphology of the nanoparticles, but it is difficult to control the transition metal or transition metal oxide to form a uniform size and morphology during the catalytic synthesis process, resulting in low catalyst selectivity.

[0004] Compared with traditional nanocatalysts, single-atom catalysts have significant advantages such as high intrinsic activity, uniform structure, high atomic utilization efficiency, and good stability. At present, transition metal single-atom catalysts (denoted as M-N-C, where M = Fe, Co, Ni, Mn, Cu, etc.) prepared using carbon-based materials such as nitrogen-doped activated carbon, nitrogen-doped graphene, and nitrogen-doped ordered mesoporous carbon as carriers are the most commonly used single-atom catalysts for activating persulfate. However, the highly reactive oxygen species (sulfate radicals, hydroxyl radicals, singlet oxygen, etc.) generated in-situ during the persulfate catalytic activation process will attack the carbon carrier of the catalyst. On the one hand, this will lead to the destruction of the catalyst structure and reduce the catalyst stability; on the other hand, it will reduce the utilization efficiency of the reactive oxygen species and increase material and energy consumption.

[0005] Therefore, the development of single-atom catalysts supported on non-carbon-based carriers is of great significance for enhancing the catalyst stability and improving the utilization rate of persulfate. Summary of the Invention

[0006] This invention is based on the inventors' discovery and understanding of the following facts and problems: Since the highly reactive oxygen species (sulfate radicals, hydroxyl radicals, singlet oxygen, etc.) generated in-situ during the persulfate catalytic activation process will attack the carbon carrier of the catalyst, it will not only lead to the destruction of the catalyst structure and reduce the catalyst stability, but also reduce the utilization efficiency of the reactive oxygen species. Therefore, it is necessary to study a brand-new catalyst to achieve the efficient catalytic activation of persulfate.

[0007] This invention aims to solve at least one of the technical problems in the related art to some extent. For this purpose, an embodiment of this invention provides a cerium oxide-supported metal single-atom catalyst and its preparation method. Using CeO2 as the carrier, a two-step calcination method is adopted to stably load the active metal on the carrier, effectively improving the loading amount of the active metal single atoms, and at the same time avoiding the oxidation and destruction of the carrier during the reaction when the catalyst is used for persulfate catalytic activation, thus improving the stability of the catalyst.

[0008] The preparation method of the cerium oxide-supported metal single-atom catalyst according to the embodiment of this invention includes the following steps:

[0009] a. Add the CeO2 carrier to the soluble metal salt solution, mix and then evaporate the solvent to obtain a solid powder;

[0010] b. Perform a first calcination treatment on the solid powder obtained in step a. The temperature of the first calcination treatment is lower than the decomposition temperature of the soluble metal salt. After washing, filtering, and drying, a first calcination product is obtained;

[0011] c. Subject the first calcination product obtained in step b to a second calcination treatment at a temperature higher than that of the first calcination treatment to obtain a cerium oxide-supported single-atom metal catalyst.

[0012] Advantages and technical effects brought by the preparation method of the cerium oxide-supported single-atom metal catalyst according to the embodiments of the present invention: 1. In the method of the embodiments of the present invention, cerium oxide is used as a catalyst support. O vacancies and Ce vacancies are easily formed on the surface of the cerium oxide support, and these vacancies can be used as riveting sites for metal ions. After high-temperature calcination, the metal ions are firmly adsorbed on the surface of the CeO2 support, playing a role in stabilizing metal atoms and inhibiting the migration and aggregation of metal atoms, and enabling single-atom loading of metal elements on the CeO2 support; 2. In the method of the embodiments of the present invention, a "two-step calcination method" is adopted, that is, first, the metal salt precursor physically adsorbed on the surface of the CeO2 support is subjected to a first calcination treatment. Low-temperature calcination promotes the reaction of metal ions with O on the surface layer of the CeO2 support to form M-O bonds, playing a role in stabilizing metal atoms and inhibiting the migration and aggregation of metal atoms; then the metal precursor that has not formed stable M-O bonds is removed by washing; finally, a second calcination treatment is carried out, and the coordinated atoms remaining in the metal precursor are removed by high-temperature calcination to obtain a CeO2-supported single-atom metal catalyst; 3. In the embodiments of the present invention, CeO2 is used as a support, which is a relatively stable metal oxide support. Compared with carbon-based supports, it has better tolerance to the attack of highly active oxidation species in-situ generated during the PMS activation process, thus avoiding the oxidation and damage of the catalyst support during the reaction process, improving the stability of the catalyst and the selectivity for the degradation of organic pollutants in organic wastewater, and further improving the utilization efficiency of PMS.

[0013] In some embodiments, in step a, the soluble metal salt includes at least one of acetates, nitrates, sulfates, chlorides, acetylacetonates, and organic complexes of Fe, Co, Ni, Mn, Cu, Zn, Au, Ru, or Pt; and / or, the soluble metal salt solution includes at least one of an aqueous solution, a methanol solution, an ethanol solution, an isopropanol solution, an acetone solution, a DMF solution, and a pyrrolidone solution of the soluble metal salt.

[0014] In some embodiments, in step a, the preparation method of the CeO2 support includes: calcining an inorganic compound precursor containing Ce to obtain a CeO2 support; preferably, the inorganic compound precursor containing Ce includes at least one of cerium acetate, cerium nitrate, cerium sulfate, ammonium cerium nitrate, ammonium cerium sulfate, cerium oxalate, cerium acetylacetonate, and cerium hydroxide.

[0015] In some embodiments, in step a, the mass ratio of the metal element in the metal salt solution to the CeO2 support is (0.1 - 5):100.

[0016] In some embodiments, in step b, the atmosphere for the first calcination treatment includes at least one of nitrogen, argon, helium, hydrogen, ammonia, air, and oxygen; the temperature of the first calcination treatment is higher than the melting point of the soluble metal salt; the temperature of the first calcination treatment is 200 - 600 °C, and the calcination time is 1 - 5 h; the washing liquid used for washing includes at least one of water, methanol, ethanol, isopropanol, acetone, DMF, and pyrrolidone.

[0017] In some embodiments, in step c, the atmosphere for the second calcination treatment includes at least one of nitrogen, argon, helium, hydrogen, ammonia, air, and oxygen; the temperature of the second calcination treatment is 200 - 900 °C, and the calcination time is 2 - 12 h.

[0018] The embodiment of the present invention also provides a cerium oxide supported metal single - atom catalyst prepared by the method of the embodiment of the present invention. The cerium oxide supported metal single - atom catalyst of the embodiment of the present invention, prepared by the method of the embodiment of the present invention, has all the advantages that the method of the present invention can bring, which will not be elaborated here.

[0019] In some embodiments, the catalyst includes a CeO2 support and an active metal distributed on the support in a single - atom form, and the active metal includes at least one of Fe, Co, Ni, Mn, Cu, Zn, Au, Ru, or Pt; preferably, the active metal is 0.2 - 3% of the mass of the CeO2 support.

[0020] The embodiment of the present invention also provides an application of the cerium oxide supported metal single - atom catalyst in the treatment of organic wastewater. The catalyst of the embodiment of the present invention has excellent stability and selectivity, can efficiently treat organic pollutants in organic wastewater, and improves the utilization rate of persulfate and the removal rate of pollutants.

[0021] In some embodiments, the metal element in the cerium oxide supported metal single - atom catalyst is selected from at least one of Co, Mn, Cu, Au, and Fe; preferably, the pollutant in the organic wastewater is Rhodamine B. Description of the Drawings

[0022] Figure 1 is the X - ray diffraction pattern of the catalyst Co - CeO2 sample prepared in Example 2;

[0023] Figure 2 is the aberration - corrected transmission electron microscopy image of the catalyst Co - CeO2 sample prepared in Example 2;

[0024] Figure 3 is the synchrotron radiation X - ray absorption spectrum of the catalyst Co - CeO2 sample prepared in Example 2;

[0025] Figure 4 are the X-ray diffraction patterns of the Fe-CeO2, Ni-CeO2, Mn-CeO2, and Cu-CeO2 samples in Examples 8 to 11;

[0026] Figure 5 are the X-ray diffraction patterns of the Zn-CeO2, Au-CeO2, Ru-CeO2, and Pt-CeO2 samples in Examples 12 to 15;

[0027] Figure 6 is the X-ray diffraction pattern of the Co3O4 / CeO2 sample of the catalyst prepared in Comparative Example 1. Specific Embodiments

[0028] The embodiments of the present invention will be described in detail below. The examples are shown in the accompanying drawings. The embodiments described below by referring to the drawings are exemplary and are intended to explain the present invention and should not be construed as limiting the present invention.

[0029] The preparation method of the ceria-supported metal single-atom catalyst according to the embodiments of the present invention includes the following steps:

[0030] a. Add a CeO2 support to a soluble metal salt solution, mix and then evaporate the solvent to obtain a solid powder;

[0031] b. Perform a first calcination treatment on the solid powder obtained in step a. The temperature of the first calcination treatment is lower than the decomposition temperature of the soluble metal salt. After washing, filtering, and drying, a first calcination product is obtained;

[0032] c. Perform a second calcination treatment on the first calcination product obtained in step b. The temperature of the second calcination treatment is higher than the temperature of the first calcination treatment to obtain a ceria-supported metal single-atom catalyst.

[0033] In the preparation method of the cerium oxide supported metal single-atom catalyst according to the embodiments of the present invention, cerium oxide is used as the catalyst support. O vacancies and Ce vacancies are easily formed on the surface of the cerium oxide support. These vacancies can be used as riveting sites for metal ions. After high-temperature calcination, the metal ions are firmly adsorbed on the surface of the CeO2 support, which plays a role in stabilizing metal atoms and inhibiting the migration and aggregation of metal atoms, enabling single-atom loading of metal elements on the CeO2 support. In the method of the embodiments of the present invention, a "two-step calcination method" is adopted, that is, first, the metal salt precursor physically adsorbed on the surface of the CeO2 support is subjected to the first calcination treatment. The low-temperature calcination promotes the reaction of metal ions with O on the surface layer of the CeO2 support to form M-O bonds, which plays a role in stabilizing metal atoms and inhibiting the migration and aggregation of metal atoms. Then, the metal precursor that has not formed stable M-O bonds is removed by washing. Finally, the second calcination treatment is carried out, and the residual coordination atoms in the metal precursor are removed by high-temperature calcination to obtain the CeO2 supported metal single-atom catalyst. In the embodiments of the present invention, CeO2 is used as the support, which is a relatively stable metal oxide support. Compared with the carbon-based support, it has better tolerance to the attack of highly active oxidation species in-situ generated during the PMS activation process, thus avoiding the oxidation and damage of the catalyst support during the reaction process, improving the stability of the catalyst and the selectivity for the degradation of organic pollutants in organic wastewater, and further improving the utilization efficiency of PMS.

[0034] In some embodiments, in step a, the soluble metal salt includes at least one of acetates, nitrates, sulfates, chlorides, acetylacetonates, and organic complexes of Fe, Co, Ni, Mn, Cu, Zn, Au, Ru, or Pt; the soluble metal salt solution includes at least one of an aqueous solution, a methanol solution, an ethanol solution, an isopropanol solution, an acetone solution, a DMF solution, and a pyrrolidone solution of the soluble metal salt.

[0035] In some embodiments, in step a, the preparation method of the CeO2 support includes: calcining an inorganic compound precursor containing Ce to obtain the CeO2 support; preferably, the inorganic compound precursor containing Ce includes at least one of cerium acetate, cerium nitrate, cerium sulfate, ammonium cerium nitrate, ammonium cerium sulfate, cerium oxalate, cerium acetylacetonate, and cerium hydroxide.

[0036] In some embodiments, in step a, the mass ratio of the metal element in the metal salt solution to the CeO2 support is (0.1-5):100. In the embodiments of the present invention, the ratio of the metal element in the metal salt solution to the CeO2 support is further preferably selected, which is beneficial to the sufficient adsorption of metal elements on the support surface, increasing the loading amount of metal single atoms in the catalyst and improving the activity of the catalyst.

[0037] In some embodiments, in step b, the atmosphere for the first calcination treatment includes at least one of nitrogen, argon, helium, hydrogen, ammonia, air, and oxygen.

[0038] In some embodiments, in step b, the temperature of the first calcination treatment is higher than the melting point of the soluble metal salt. In the embodiments of the present invention, it is preferred that the temperature of the first calcination treatment is higher than the melting point of the soluble metal salt, which is beneficial to promoting the formation of M-O bonds and reducing the dosage of the soluble metal salt. However, the temperature of the first calcination treatment should be controlled below the decomposition temperature of the soluble metal salt to avoid the decomposition of the metal salt and the generation of nanoparticles. When the melting point of the soluble metal salt used is lower than the decomposition temperature, the preferred temperature of the first calcination treatment is higher than the melting point of the soluble metal salt and lower than the decomposition temperature of the soluble metal salt. When the melting point of the soluble metal salt is higher than the decomposition temperature, the temperature of the first calcination treatment needs to be controlled below the decomposition temperature of the soluble metal salt.

[0039] In some embodiments, in step b, the temperature of the first calcination treatment is 200 - 600 °C, and the calcination time is 1 - 5 h. In the embodiments of the present invention, the process conditions of the first calcination treatment are optimized, which is beneficial to promoting the reaction between metal ions and O on the surface layer of the CeO2 support to form M-O bonds, effectively stabilizing metal atoms, and inhibiting the migration and aggregation of metal atoms. If the calcination temperature is too low, it will be unfavorable for the formation of M-O bonds. If the calcination temperature is too high, it will cause the decomposition of the metal salt precursor and the generation of nanoparticles, which is unfavorable for the formation of M-O bonds. If the calcination time is too short, the amount of metal forming M-O bonds is too small, resulting in too low a loading amount. If the calcination time is too long, the already formed M-O bonds will be further oxidized to generate nanoparticles, reducing the single-atom site loading amount.

[0040] In some embodiments, in step b, the washing liquid used for washing includes at least one of water, methanol, ethanol, isopropanol, acetone, DMF, and pyrrolidone. In the embodiments of the present invention, after the first calcination treatment, the metal precursor that has not formed a stable M-O bond is removed through the washing treatment.

[0041] In some embodiments, in step c, the atmosphere for the second calcination treatment includes at least one of nitrogen, argon, helium, hydrogen, ammonia, air, and oxygen; the temperature of the second calcination treatment is 200 - 900 °C, and the calcination time is 2 - 12 h. In the embodiments of the present invention, the process conditions for the second calcination treatment are optimized, which is beneficial to removing the residual coordination atoms in the metal precursor on the catalyst and preparing a metal single-atom catalyst. If the calcination temperature is too low, it will be unfavorable for the removal of residual coordination atoms, resulting in a decrease in the activity of the catalyst. If the calcination temperature is too high, the formed M - O bonds will break, causing the metal atoms to migrate and agglomerate on the surface of the support, forming nanoparticles, destroying the single-atom structure, and reducing the single-atom loading. If the calcination time is too short, it is not conducive to the complete removal of the residual coordination atoms of the metal salt precursor, resulting in a decrease in the activity of the catalyst. If the calcination time is too long, the formed M - O bonds will be further oxidized to generate nanoparticles, reducing the single-atom site loading.

[0042] The embodiments of the present invention also provide a cerium oxide-supported metal single-atom catalyst prepared by the method of the embodiments of the present invention. The cerium oxide-supported metal single-atom catalyst of the embodiments of the present invention, prepared by the method of the embodiments of the present invention, has all the advantages that the method of the present invention can bring, which will not be elaborated here.

[0043] In some embodiments, the catalyst includes a CeO₂ support and active metals distributed as single atoms on the support, and the active metals include at least one of Fe, Co, Ni, Mn, Cu, Zn, Au, Ru, or Pt; preferably, the active metals are 0.2 - 3% of the mass of the CeO₂ support. The catalyst of the embodiments of the present invention effectively improves the loading of metal single atoms.

[0044] The embodiments of the present invention also provide an application of the cerium oxide-supported metal single-atom catalyst in the treatment of organic wastewater. The catalyst of the embodiments of the present invention has excellent stability and selectivity, can efficiently treat organic pollutants in organic wastewater, and improves the utilization rate of persulfate and the removal rate of pollutants.

[0045] In some embodiments, the metal element in the cerium oxide-supported metal single-atom catalyst is selected from at least one of Co, Mn, Cu, Au, and Fe, and preferably, the pollutant in the organic wastewater is Rhodamine B.

[0046] The present invention will be described in detail below with reference to the embodiments and the drawings.

[0047] Example 1

[0048] Put 10.0 g of cerium acetate hydrate into a muffle furnace. Under an air atmosphere, first at 2 °C / min -1Raise the temperature to 650 °C and maintain for 2 h; then at a rate of 1 °C / min -1 Raise the temperature to 800 °C and maintain for 2 h; after natural cooling to room temperature, obtain the CeO2 support.

[0049] Mix 0.1 g of cobalt acetate and 15 mL of ethanol, and stir for 30 min; after cobalt acetate is completely dissolved, obtain an ethanol solution of cobalt acetate. Add 2 g of CeO2 support to the solution and ultrasonically disperse for 10 min. Transfer the above suspension into a round-bottom flask, use a rotary evaporator to evaporate the ethanol solvent, and place the remaining solid powder in an oven at 80 °C for drying for 12 h to obtain the solid powder.

[0050] Put the dried solid powder into a muffle furnace and at a rate of 2 °C / min -1 Raise the temperature to 200 °C and maintain for 2 h for the first calcination treatment; after natural cooling to room temperature, obtain the sample. Transfer the sample into a beaker, add 200 mL of ethanol-water mixed solvent (volume ratio of ethanol to water is 15:1), stir at room temperature for 2 h; filter by suction, collect the filter cake; wash the filter cake successively with 200 mL of water, 200 mL of ethanol-water mixed solvent, and 200 mL of ethanol; after suction drying, place it in an oven at 60 °C for drying for 12 h to obtain the first calcination product.

[0051] Put the first calcination product into a muffle furnace and at a rate of 5 °C / min -1 Raise the temperature to 600 °C and maintain for 3 h for the second calcination treatment, and naturally cool to room temperature to obtain the Co-CeO2-0.3 single-atom catalyst. Using ICP-MS, it is measured that in the catalyst of this example, the Co element is 0.28% of the mass of the CeO2 support.

[0052] Example 2

[0053] Obtain the CeO2 support by the same method as in Example 1.

[0054] Mix 0.32 g of cobalt chloride and 60 mL of methanol, and stir for 20 min; after cobalt chloride is completely dissolved, obtain a methanol solution of cobalt chloride. Add 1 g of CeO2 support to the solution and ultrasonically disperse for 30 min. Transfer the above suspension into a round-bottom flask, use a rotary evaporator to evaporate the methanol solvent, and place the remaining solid powder in an oven at 100 °C for drying for 2 h to obtain the solid powder.

[0055] Put the dried solid powder into a muffle furnace and at a rate of 2 °C / min -1Heat to 300 °C, maintain for 5 h, and perform the first calcination treatment; after natural cooling to room temperature, obtain the sample. Transfer the sample into a beaker, add 100 mL of a methanol-water mixed solvent (the volume ratio of methanol to water is 5:1), stir at room temperature for 0.5 h; perform suction filtration and collect the filter cake; wash the filter cake successively with 200 mL of water, 100 mL of the methanol-water mixed solvent, and 200 mL of methanol; after suction drying, place it in an oven at 120 °C and dry for 24 h to obtain the first calcination product.

[0056] Put the first calcination product into a tubular furnace, introduce nitrogen, and heat at a rate of 5 °C / min -1 Heat to 700 °C, maintain for 10 h, and perform the second calcination treatment; after natural cooling to room temperature, obtain the Co-CeO2-2 single-atom catalyst. Using ICP-MS, it is measured that in the catalyst of this example, the Co element is 2.12% of the mass of the CeO2 support.

[0057] Figure 1 is the X-ray diffraction pattern of the Co-CeO2-2 single-atom catalyst prepared in this example. From Figure 1 it can be seen that only the diffraction peaks of the CeO2 support are detected in the CeO2 support and the Co-CeO2-2 single-atom catalyst, and no diffraction peaks of Co-containing species (including CoO, Co2O3, Co3O4, metallic cobalt, etc.) are detected, indicating that the Co species are atomically dispersed on the CeO2 support.

[0058] Figure 2 is the aberration-corrected scanning transmission electron microscopy image of the Co-CeO2-2 single-atom catalyst prepared in this example. Figure 2 No nanoparticles or nanocluster structures are seen in it. Since the atomic number of Co is less than that of Ce, dark spots of atomically dispersed Co atoms are seen under the aberration-corrected scanning transmission electron microscope, proving that the Co-CeO2-2 prepared in this example is a single-atom catalyst.

[0059] Figure 3 is the synchrotron radiation X-ray absorption spectrum of the Co-CeO2-2 single-atom catalyst prepared in this example. Figure 3 It can be seen from it that the absorption peak of Co foil at is attributed to the Co-Co bond in metallic Co, and the absorption peak of CoO at is attributed to the Co-O bond. In the absorption spectrum of the Co-CeO2-2 single-atom catalyst, the Co-Co bond at disappears, indicating that there is no Co-Co bond in the Co-CeO2-2 single-atom catalyst, and a single-atom catalyst is formed.

[0060] Example 3

[0061] The CeO2 support was prepared by the same method as in Example 1.

[0062] 0.16 g of cobalt acetylacetonate was mixed with 20 mL of ethanol and stirred for 60 min. After the cobalt acetylacetonate was completely dissolved, an ethanol solution of cobalt acetylacetonate was obtained. 3 g of the CeO2 support was added to the solution and ultrasonically dispersed for 80 min. The above suspension was transferred to a round-bottom flask, and the ethanol solvent was evaporated to dryness using a rotary evaporator. The remaining solid powder was placed in an oven at 100 °C and dried for 2 h to obtain a solid powder.

[0063] The dried solid powder was placed in a muffle furnace and heated to 260 °C at a rate of 1 °C / min, maintained for 2 h for the first calcination treatment; after natural cooling to room temperature, a sample was obtained. The sample was transferred to a beaker, 100 mL of an ethanol-water mixed solvent (the volume ratio of ethanol to water was 5:1) was added, and stirred at room temperature for 2 h; filtered by suction, and the filter cake was collected; the filter cake was successively washed with 500 mL of water, 500 mL of the ethanol-water mixed solvent, and 500 mL of ethanol; after suction drying, it was placed in an oven at 80 °C and dried for 12 h to obtain the first calcination product. -1 The first calcination product was placed in a muffle furnace and heated to 750 °C at a rate of 5 °C / min, maintained for 8 h; after natural cooling to room temperature, the Co-CeO2-0.8 single-atom catalyst was obtained. By ICP-MS measurement, in the catalyst of this example, the Co element was 0.83% of the mass of the CeO2 support.

[0064] -1

[0065] Example 4

[0066]

[0067] The CeO2 support was prepared by the same method as in Example 1.

[0067] 0.4 g of cobalt nitrate was mixed with 20 mL of DMF and stirred for 40 min. After the cobalt nitrate was completely dissolved, a DMF solution of cobalt nitrate was obtained. 2 g of the CeO2 support was added to the solution and ultrasonically dispersed for 10 min. The above suspension was transferred to a round-bottom flask, and the DMF solvent was evaporated to dryness using a rotary evaporator. The remaining solid powder was placed in an oven at 120 °C and dried for 24 h to obtain a solid powder.

[0068] -1 The dried solid powder was placed in a muffle furnace and heated to 200 °C at a rate of 1 °C / min, maintained for 2 h for the first calcination treatment; after natural cooling to room temperature, a sample was obtained. The sample was transferred to a beaker, 300 mL of a DMF-water mixed solvent (the volume ratio of DMF to water was 10:1) was added, and stirred at room temperature for 12 h; filtered by suction, and the filter cake was collected; the filter cake was successively washed with 200 mL of DMF, 100 mL of the DMF-water mixed solvent, and 100 mL of water; after suction drying, it was placed in an oven at 120 °C and dried for 24 h to obtain the first calcination product.

[0069] Put the first calcination product into a muffle furnace and heat it at 10 °C / min -1 to 750 °C and maintain for 2.5 h for the second calcination treatment; after natural cooling to room temperature, the Co-CeO₂-1.9 single-atom catalyst is obtained. Using ICP-MS, it is measured that in the catalyst of this example, the Co element is 1.89% of the mass of the CeO₂ support.

[0070] Example 5

[0071] The CeO₂ support was prepared by the same method as in Example 1.

[0072] Mix 0.24 g of cobalt sulfate and 20 mL of pyrrolidone, and stir for 30 min; after the cobalt sulfate is completely dissolved, a pyrrolidone solution of cobalt sulfate is obtained. Add 1.5 g of CeO₂ support to the solution and ultrasonically disperse for 10 min. Transfer the above suspension into a round-bottom flask, use a rotary evaporator to evaporate the pyrrolidone solvent to dryness, and put the remaining solid powder into an oven at 130 °C for drying for 15 h to obtain a solid powder.

[0073] Put the dried solid powder into a muffle furnace and heat it at 5 °C / min -1 to 400 °C and maintain for 1 h for the first calcination treatment; after natural cooling to room temperature, the sample is obtained. Transfer the sample into a beaker, add 200 mL of a pyrrolidone-water mixed solvent (the volume ratio of pyrrolidone to water is 3:1), stir at room temperature for 3 h; filter by suction and collect the filter cake; wash the filter cake successively with 150 mL of pyrrolidone, 100 mL of pyrrolidone-water mixed solvent, and 100 mL of water; after suction drying, put it into an oven at 130 °C for drying for 24 h to obtain the first calcination product.

[0074] Put the first calcination product into a muffle furnace and heat it at 5 °C / min -1 to 750 °C and maintain for 3 h for the second calcination treatment; cool naturally to room temperature to obtain the Co-CeO₂-1.5 single-atom catalyst. Using ICP-MS, it is measured that in the catalyst of this example, the Co element is 1.51% of the mass of the CeO₂ support.

[0075] Example 6

[0076] The CeO₂ support was prepared by the same method as in Example 1.

[0077] Mix 0.082 g of cobalt acetate and 10 mL of isopropanol, and stir for 30 min; after the cobalt acetate is completely dissolved, an isopropanol solution of cobalt acetate is obtained. Add 0.5 g of CeO₂ support to the solution and ultrasonically disperse for 20 min. Transfer the above suspension into a round-bottom flask, use a rotary evaporator to evaporate the isopropanol solvent to dryness, and put the remaining solid powder into an oven at 80 °C for drying for 6 h to obtain a solid powder.

[0078] Put the dried solid powder into a muffle furnace and heat it at 2 °C / min -1 to 200 °C, hold for 5 h, and conduct the first calcination treatment; after natural cooling to room temperature, obtain the sample. Transfer the sample into a beaker, add 100 mL of isopropanol-water mixed solvent (the volume ratio of isopropanol to water is 4:1), stir at room temperature for 3 h; filter by suction and collect the filter cake; wash the filter cake successively with 100 mL of water, 100 mL of isopropanol-water mixed solvent, and 100 mL of isopropanol; after suction drying, put it into an oven at 80 °C and dry for 8 h to obtain the first calcination product.

[0079] Put the first calcination product into a muffle furnace and heat it at 2 °C / min -1 to 650 °C, hold for 10 h, and conduct the second calcination treatment; after natural cooling to room temperature, obtain the Co-CeO2-2.5 single-atom catalyst. By ICP-MS measurement, in the catalyst of this example, the Co element is 2.51% of the mass of the CeO2 support.

[0080] Example 7

[0081] Prepare the CeO2 support by the same method as in Example 1.

[0082] Mix 0.2 g of cobalt sulfate and 20 mL of water, and stir for 30 min; after the cobalt sulfate is completely dissolved, obtain an aqueous solution of cobalt sulfate. Add 1.8 g of CeO2 support to the solution and ultrasonically disperse for 20 min. Under normal pressure, heat to evaporate the solvent, and put the remaining solid powder into an oven at 100 °C and dry for 12 h to obtain the solid powder.

[0083] Put the dried solid powder into a muffle furnace and heat it at 5 °C / min -1 to 400 °C, hold for 1 h, and conduct the first calcination treatment; after natural cooling to room temperature, obtain the sample. Transfer the sample into a beaker, add 100 mL of water, stir at room temperature for 2 h; filter by suction and collect the filter cake; wash the filter cake with 300 mL of water; after suction drying, put it into an oven at 100 °C and dry for 6 h to obtain the first calcination product.

[0084] Put the first calcination product into a muffle furnace and heat it at 5 °C / min -1 to 700 °C, hold for 8 h, and conduct the second calcination treatment; after natural cooling to room temperature, obtain the Co-CeO2-1 single-atom catalyst. By ICP-MS measurement, in the catalyst of this example, the Co element is 1.02% of the mass of the CeO2 support.

[0085] Example 8

[0086] Prepare the CeO2 support by the same method as in Example 1.

[0087] Mix 0.45 g of ferric chloride with 35 mL of isopropanol and stir for 10 min. After the ferric chloride is completely dissolved, an isopropanol solution of ferric chloride is obtained. Add 1.1 g of CeO₂ support to the solution and ultrasonically disperse for 10 min. Transfer the above suspension into a round-bottom flask, evaporate the isopropanol solvent using a rotary evaporator, and place the remaining solid powder in an oven at 105 °C for drying for 2.5 h to obtain a solid powder.

[0088] Place the dried solid powder in a muffle furnace and heat it at 3 °C / min -1 to 280 °C and maintain for 1.5 h for the first calcination treatment. After natural cooling to room temperature, a sample is obtained. Transfer the sample into a beaker, add 150 mL of an isopropanol-water mixed solvent (the volume ratio of isopropanol to water is 7:1), stir at room temperature for 2.5 h, filter by suction, and collect the filter cake. Wash the filter cake successively with 120 mL of water, 120 mL of the isopropanol-water mixed solvent, and 220 mL of isopropanol. After suction drying, place it in an oven at 100 °C for drying for 20 h to obtain the first calcination product.

[0089] Place the first calcination product in a tubular furnace, introduce argon, and heat it at 2 °C / min -1 to 450 °C and maintain for 8 h for the second calcination treatment. After natural cooling to room temperature, an Fe-CeO₂-1.8 single-atom catalyst is obtained. Using ICP-MS, it is measured that in the catalyst of this example, the Fe element in the catalyst is 1.81% of the mass of the CeO₂ support.

[0090] Figure 4 The X-ray diffraction pattern of the Fe-CeO₂ single-atom catalyst prepared in this example is shown. From Figure 4 it can be seen that only the diffraction peaks of the CeO₂ support are detected in the Fe-CeO₂ single-atom catalyst, and no diffraction peaks of Fe-containing species (including FeO, Fe₂O₃, Fe₃O₄, metallic iron, etc.) are detected, indicating that the Fe species are atomically dispersed on the CeO₂ support.

[0091] Example 9

[0092] Prepare the CeO₂ support using the same method as in Example 1.

[0093] Mix 0.48 g of nickel sulfate with 60 mL of ethanol and stir for 20 min. After the nickel sulfate is completely dissolved, an ethanol solution of nickel sulfate is obtained. Add 1.4 g of CeO₂ support to the solution and ultrasonically disperse for 50 min. Transfer the above suspension into a round-bottom flask, evaporate the ethanol solvent using a rotary evaporator, and place the remaining solid powder in an oven at 80 °C for drying for 6 h to obtain a solid powder.

[0094] Place the dried solid powder in a muffle furnace and heat it at 4 °C / min -1Raise the temperature to 500 °C, maintain for 1.5 h, and perform the first calcination treatment; after natural cooling to room temperature, obtain the sample. Transfer the sample into a beaker, add 100 mL of a methanol-water mixed solvent (the volume ratio of methanol to water is 5:1), stir at room temperature for 1.5 h; perform suction filtration and collect the filter cake; wash the filter cake successively with 200 mL of water, 150 mL of the methanol-water mixed solvent, and 100 mL of methanol; after suction drying, place it in an oven at 100 °C and dry for 9 h to obtain the first calcination product.

[0095] Put the first calcination product into a muffle furnace, at a rate of 1 °C / min -1 Raise the temperature to 850 °C, maintain for 9 h, and perform the second calcination treatment; naturally cool to room temperature to obtain the Ni-CeO2-2 single-atom catalyst. Using ICP-MS, it is measured that in the catalyst of this example, the Ni element in the catalyst is 2.02% of the mass of the CeO2 support.

[0096] Figure 4 The X-ray diffraction pattern of the Ni-CeO2 single-atom catalyst prepared in this example is shown. From Figure 5 it can be seen that only the diffraction peaks of the CeO2 support are detected in the Ni-CeO2 single-atom catalyst, and no diffraction peaks of Ni-containing species (including NiO, metallic nickel, etc.) are detected, indicating that the Ni species are atomically dispersed on the CeO2 support.

[0097] Example 10

[0098] The CeO2 support was prepared by the same method as in Example 1.

[0099] Mix 0.51 g of manganese oxalate with 60 mL of methanol and stir for 20 min; after the manganese oxalate is completely dissolved, obtain a methanol solution of manganese oxalate. Add 1.2 g of the CeO2 support to the solution and ultrasonically disperse for 30 min. Transfer the above suspension into a round-bottom flask, use a rotary evaporator to evaporate the methanol solvent, and place the remaining solid powder in an oven at 60 °C and dry for 8 h to obtain the solid powder.

[0100] Put the dried solid powder into a muffle furnace, at a rate of 5 °C / min -1 Raise the temperature to 200 °C, maintain for 1.5 h, and perform the first calcination treatment; after natural cooling to room temperature, obtain the sample. Transfer the sample into a beaker, add 180 mL of a methanol-water mixed solvent (the volume ratio of methanol to water is 10:1), stir at room temperature for 4.5 h; perform suction filtration and collect the filter cake; wash the filter cake successively with 400 mL of water, 500 mL of the methanol-water mixed solvent, and 600 mL of methanol; after suction drying, place it in an oven at 110 °C and dry for 18 h to obtain the first calcination product.

[0101] Put the first calcination product into a tube furnace, introduce helium gas, at a rate of 2 °C / min -1Raise the temperature to 550 °C, maintain for 10 h, and perform the second calcination treatment; cool naturally to room temperature to obtain the Mn-CeO₂-1.7 single-atom catalyst. Using ICP-MS, it is measured that in the catalyst of this example, the Mn element in the catalyst is 1.73% of the mass of the CeO₂ support.

[0102] Figure 4 shows the X-ray diffraction pattern of the Mn-CeO₂ single-atom catalyst prepared in this example. From Figure 4 it can be seen that only the diffraction peaks of the CeO₂ support are detected in the Mn-CeO₂ single-atom catalyst, and no diffraction peaks of Mn-containing species (including MnO, Mn₂O₃, Mn₃O₄, metallic manganese, etc.) are detected, indicating that the Mn species are atomically dispersed on the CeO₂ support.

[0103] Example 11

[0104] The CeO₂ support was prepared by the same method as in Example 1.

[0105] Mix 0.56 g of copper sulfate and 100 mL of methanol, and stir for 20 min; after the copper sulfate is completely dissolved, a methanol solution of copper sulfate is obtained. Add 1.3 g of the CeO₂ support to the solution and ultrasonically disperse for 30 min. Transfer the above suspension into a round-bottom flask, use a rotary evaporator to evaporate the methanol solvent, and put the remaining solid powder into an oven at 100 °C to dry for 6 h to obtain a solid powder.

[0106] Put the dried solid powder into a muffle furnace and raise the temperature to 600 °C at a rate of 5 °C / min -1 maintain for 1 h, and perform the first calcination treatment; cool naturally to room temperature to obtain a sample. Transfer the sample into a beaker, add 300 mL of a methanol-water mixed solvent (the volume ratio of methanol to water is 2:1), stir at room temperature for 8.5 h; filter, collect the filter cake; wash the filter cake successively with 100 mL of water, 300 mL of the methanol-water mixed solvent, and 500 mL of methanol; after drying, put it into an oven at 105 °C to dry for 14 h to obtain the first calcination product.

[0107] Put the first calcination product into a tubular furnace, introduce argon, and raise the temperature to 800 °C at a rate of 3 °C / min -1 maintain for 12 h, and perform the second calcination treatment; cool naturally to room temperature to obtain the Cu-CeO₂-2 single-atom catalyst. Using ICP-MS, it is measured that in the catalyst of this example, the Cu element in the catalyst is 1.96% of the mass of the CeO₂ support.

[0108] Figure 4 shows the X-ray diffraction pattern of the Cu-CeO₂ single-atom catalyst prepared in this example. From Figure 4It can be seen that only the diffraction peaks of the CeO2 support were detected in the Cu-CeO2 single-atom catalyst, and no diffraction peaks of Cu-containing species (including CuO, Cu2O, metallic copper, etc.) were detected, indicating that the Cu species achieved atomic-level dispersion on the CeO2 support.

[0109] Example 12

[0110] The CeO2 support was prepared by the same method as in Example 1.

[0111] 0.41 g of zinc sulfate and 60 mL of DMF were mixed and stirred for 60 min; after the zinc sulfate was completely dissolved, a DMF solution of zinc sulfate was obtained. 1.2 g of the CeO2 support was added to the solution and ultrasonically dispersed for 30 min. The above suspension was transferred to a round-bottom flask, and the DMF solvent was evaporated to dryness using a rotary evaporator. The remaining solid powder was placed in an oven at 80 °C and dried for 2.5 h to obtain a solid powder.

[0112] The dried solid powder was placed in a muffle furnace and heated to 450 °C at a rate of 3 °C / min -1 and maintained for 4 h for the first calcination treatment; after natural cooling to room temperature, a sample was obtained. The sample was transferred to a beaker, 500 mL of a methanol-water mixed solvent (the volume ratio of methanol to water was 3:1) was added, and stirred at room temperature for 6.5 h; filtered, and the filter cake was collected; the filter cake was successively washed with 100 mL of water, 500 mL of the methanol-water mixed solvent, and 100 mL of methanol; after drying, it was placed in an oven at 70 °C and dried for 18 h to obtain the first calcination product.

[0113] The first calcination product was placed in a tubular furnace, nitrogen was introduced, and heated to 750 °C at a rate of 1 °C / min -1 and maintained for 12 h for the second calcination treatment; after natural cooling to room temperature, a Zn-CeO2-1.8 single-atom catalyst was obtained. By ICP-MS measurement of the catalyst in this example, the Zn element in the catalyst was 1.84% of the mass of the CeO2 support.

[0114] Figure 5 The X-ray diffraction pattern of the Zn-CeO2 single-atom catalyst prepared in this example is shown. From Figure 5 it can be seen that only the diffraction peaks of the CeO2 support were detected in the Zn-CeO2 single-atom catalyst, and no diffraction peaks of Zn-containing species (including ZnO, metallic zinc, etc.) were detected, indicating that the Zn species achieved atomic-level dispersion on the CeO2 support.

[0115] Example 13

[0116] The CeO2 support was prepared by the same method as in Example 1.

[0117] Mix 0.12 g of gold-phenanthroline with 30 mL of water and stir for 20 min. After the gold-phenanthroline is completely dissolved, an aqueous solution of gold-phenanthroline is obtained. Add 1.2 g of CeO2 support to the solution and disperse it by ultrasonic wave for 60 min. Transfer the above suspension into a round-bottom flask, evaporate the solvent to dryness using a rotary evaporator, and put the remaining solid powder into an oven at 90 °C for drying for 7 h to obtain the solid powder.

[0118] Put the dried solid powder into a muffle furnace and raise the temperature to 200 °C at a rate of 6 °C / min, -1 maintain for 4.5 h for the first calcination treatment; after natural cooling to room temperature, obtain the sample. Transfer the sample into a beaker, add 400 mL of methanol-water mixed solvent (the volume ratio of methanol to water is 6:1), stir at room temperature for 8.5 h; filter by suction and collect the filter cake; wash the filter cake successively with 500 mL of water, 800 mL of methanol-water mixed solvent, and 400 mL of methanol; after suction drying, put it into an oven at 100 °C for drying for 10 h to obtain the first calcination product.

[0119] Put the first calcination product into a tubular furnace, introduce argon, and raise the temperature to 450 °C at a rate of 10 °C / min -1 maintain for 3 h for the second calcination treatment; after natural cooling to room temperature, obtain the Au-CeO2-0.15 single-atom catalyst. Using ICP-MS, it is measured that in the catalyst of this example, the Au element in the catalyst is 0.15% of the mass of the CeO2 support.

[0120] Figure 5 The X-ray diffraction pattern of the Au-CeO2 single-atom catalyst prepared in this example is shown. It can be seen from the figure that only the diffraction peaks of the CeO2 support are detected in the Au-CeO2 single-atom catalyst, and the diffraction peaks of Au-containing species (including Au2O3, Au, etc.) are not detected, indicating that the Au species are atomically dispersed on the CeO2 support.

[0121] Example 14

[0122] The CeO2 support is prepared by the same method as in Example 1.

[0123] Mix 0.15 g of ruthenium chloride with 30 mL of water and stir for 50 min. After the ruthenium chloride is completely dissolved, an aqueous solution of ruthenium chloride is obtained. Add 1.8 g of CeO2 support to the solution and disperse it by ultrasonic wave for 80 min. Transfer the above suspension into a round-bottom flask, evaporate the solvent to dryness using a rotary evaporator, and put the remaining solid powder into an oven at 110 °C for drying for 22 h to obtain the solid powder.

[0124] Put the dried solid powder into a muffle furnace and raise the temperature at a rate of 10 °C / min -1Heat to 500 °C, maintain for 5 h, and conduct the first calcination treatment; after natural cooling to room temperature, obtain the sample. Transfer the sample into a beaker, add 900 mL of DMF-water mixed solvent (the volume ratio of DMF to water is 9:1), stir at room temperature for 9.5 h; perform suction filtration and collect the filter cake; wash the filter cake successively with 200 mL of DMF, 100 mL of DMF-water mixed solvent, and 300 mL of water; after suction drying, place it in an oven at 100 °C and dry for 21 h to obtain the first calcination product.

[0125] Put the first calcination product into a tube furnace, introduce nitrogen, and at a rate of 2 °C / min -1 Heat to 650 °C, maintain for 8 h, and conduct the second calcination treatment; after natural cooling to room temperature, obtain the Ru-CeO2-1 single-atom catalyst. Using ICP-MS, it is measured that in the catalyst of this example, the Ru element in the catalyst is 1.03% of the mass of the CeO2 support.

[0126] Figure 5 is the X-ray diffraction pattern of the Ru-CeO2 single-atom catalyst prepared in this example. It can be seen from the figure that only the diffraction peaks of the CeO2 support are detected in the Ru-CeO2 single-atom catalyst, and no diffraction peaks of Ru-containing species (including RuO2, metallic ruthenium, etc.) are detected, indicating that the Ru species are atomically dispersed on the CeO2 support.

[0127] Example 15

[0128] Prepare the CeO2 support by the same method as in Example 1.

[0129] Mix 0.11 g of chloroplatinic acid with 70 mL of water and stir for 90 min; after the chloroplatinic acid is completely dissolved, obtain an aqueous solution of chloroplatinic acid. Add 1.5 g of CeO2 support to the solution and ultrasonically disperse for 20 min. Transfer the above suspension into a round-bottom flask, use a rotary evaporator to evaporate the solvent to dryness, and place the remaining solid powder in an oven at 60 °C and dry for 12 h to obtain the solid powder.

[0130] Put the dried solid powder into a muffle furnace and at a rate of 10 °C / min -1 Heat to 300 °C, maintain for 1.5 h, and conduct the first calcination treatment; after natural cooling to room temperature, obtain the sample. Transfer the sample into a beaker, add 500 mL of isopropanol-water mixed solvent (the volume ratio of isopropanol to water is 8:1), stir at room temperature for 4.5 h; perform suction filtration and collect the filter cake; wash the filter cake successively with 100 mL of water, 100 mL of isopropanol-water mixed solvent, and 600 mL of isopropanol; after suction drying, place it in an oven at 60 °C and dry for 20 h to obtain the first calcination product.

[0131] Put the first calcination product into a tube furnace, introduce helium, and at a rate of 4 °C / min -1Raise the temperature to 500 °C and maintain for 9 h; naturally cool to room temperature to obtain the Pt-CeO₂-0.9 single-atom catalyst. Using ICP-MS, it is measured that in the catalyst of this example, the Pt element in the catalyst is 0.87% of the mass of the CeO₂ support.

[0132] Figure 5 Figure 4 is the X-ray diffraction pattern of the Pt-CeO₂ single-atom catalyst prepared in this example. It can be seen from the figure that only the diffraction peaks of the CeO₂ support are detected in the Pt-CeO₂ single-atom catalyst, and no diffraction peaks of Pt-containing species (including PtO, PtO₂, metallic platinum, etc.) are detected, indicating that the Pt species are atomically dispersed on the CeO₂ support.

[0133] Comparative Example 1

[0134] The method is the same as that of Example 2, except that the first calcination treatment is cancelled and only one calcination treatment is carried out. The calcination step is as follows: put the dried solid powder into a muffle furnace and raise the temperature to 700 °C at a rate of 5 °C / min, maintain for 10 h; naturally cool to room temperature to obtain the Co₃O₄ / CeO₂ catalyst. -1 Raise the temperature to 700 °C and maintain for 10 h; naturally cool to room temperature to obtain the Co₃O₄ / CeO₂ catalyst.

[0135] Figure 6 Figure 5 is the X-ray diffraction pattern of the Co₃O₄ / CeO₂ catalyst prepared in Comparative Example 1. From Figure 6 it can be seen that obvious Co₃O₄ diffraction peaks are detected in the catalyst obtained by the direct one-step calcination method, indicating that Co species migrate and agglomerate on the CeO₂ support during the direct one-step calcination process of Comparative Example 1, forming Co₃O₄ nanoparticles and unable to obtain a single-atom catalyst.

[0136] Comparative Example 2

[0137] The method is the same as that of Example 2, except that the second calcination treatment is cancelled.

[0138] Comparative Example 3

[0139] The method is the same as that of Example 2, except that the time of the first calcination treatment is 0.4 h.

[0140] Comparative Example 4

[0141] The method is the same as that of Example 2, except that the temperature of the first calcination treatment is 700 °C.

[0142] Perform application tests on the catalysts prepared in each example and comparative example.

[0143] The catalyst samples prepared in each example and comparative example were used for the study of activating persulfate (PMS) to degrade rhodamine B (RhB). The experimental process was as follows: 10 mg of the catalyst sample was added to a 250 mL conical flask, and 200 mL of the rhodamine B stock solution (20 mg L -1 ) was added. The mixture was stirred in the dark for 40 min until adsorption equilibrium was reached; persulfate (PMS) was added to the above mixed system, and the reaction was started with timing. Every 5 min, 1 mL of the reaction solution was taken, filtered to remove the catalyst powder, and the active oxygen species were quenched with sodium thiosulfate solution. Then, the conversion rate of rhodamine B was separated and detected by high performance liquid chromatography. The results are shown in Table 1.

[0144] Table 1

[0145]

[0146]

[0147] Note: The metal content refers to the ratio of the mass of the metal element to the mass of the catalyst support.

[0148] As can be seen from Table 1, the catalysts prepared using cobalt salts, iron salts, manganese salts, copper salts, and gold salts showed excellent catalytic performance in removing rhodamine B from wastewater, and the conversion rate could reach over 60% within 10 min. In particular, the Co-CeO2 catalyst with a loading of 2.51% prepared in Example 6 had a conversion rate as high as 97.7%.

[0149] In Comparative Example 1, although the Co loading could reach 5.89%, since the Co element was not loaded in the form of single atoms but in the form of oxide nanoparticles on CeO2, the conversion rate could only reach 55.1%.

[0150] In Comparative Example 2, the first calcined product after the first calcination treatment, washing, and drying was directly used as the catalyst without the second calcination treatment. A large amount of coordinated anions remained on the catalyst, resulting in a significant decrease in the activity of the catalyst, and the removal rate of rhodamine B could only reach 46.6%.

[0151] In Comparative Example 3, due to the short first calcination treatment time, it was impossible to fully form Co-O bonds between the Co salt and the cerium oxide support to stabilize the Co salt precursor. Most of the Co salt was washed away after the washing treatment after the first calcination treatment. Although a Co single-atom catalyst could also be obtained after the second calcination treatment, the Co content in the catalyst decreased severely, only being 0.23%, resulting in the removal rate of rhodamine B being only 59.1%.

[0152] In Comparative Example 4, since the temperature of the first calcination treatment was relatively high and reached the decomposition temperature of cobalt chloride, cobalt chloride decomposed on the surface of the cerium oxide support to form Co3O4 particles. This process is irreversible. Therefore, cobalt chloride cannot form Co-O bonds with the cerium oxide support, resulting in the inability to obtain a single-atom Co catalyst ultimately. Instead, it is loaded on CeO2 in the form of Co3O4 nanoparticles. Although the cobalt loading of the catalyst prepared in Comparative Example 4 can reach 5.22%, the removal rate of rhodamine B can only reach 48.9%.

[0153] In the present invention, the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples", etc. mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0154] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

Claims

1. A preparation method of a cerium oxide-supported metal single-atom catalyst, characterized in that, It includes the following steps: a. Add a CeO2 support to a soluble metal salt solution, mix and then evaporate the solvent to dryness to obtain a solid powder; b. Perform a first calcination treatment on the solid powder obtained in step a. The temperature of the first calcination treatment is lower than the decomposition temperature of the soluble metal salt. After washing, filtering, and drying, a first calcined product is obtained; c. Perform a second calcination treatment on the first calcined product obtained in step b. The temperature of the second calcination treatment is higher than that of the first calcination treatment to obtain a cerium oxide-supported single-atom metal catalyst.

2. The preparation method of the cerium oxide supported metal single-atom catalyst according to claim 1, wherein In step a, the soluble metal salt includes at least one of acetates, nitrates, sulfates, chlorides, acetylacetonates, and organic complexes of Fe, Co, Ni, Mn, Cu, Zn, Au, Ru, or Pt; and / or, the soluble metal salt solution includes at least one of an aqueous solution, methanol solution, ethanol solution, isopropanol solution, acetone solution, DMF solution, and pyrrolidone solution of the soluble metal salt.

3. The preparation method of the cerium oxide-supported metal single-atom catalyst according to claim 1, characterized in that, In step a, the preparation method of the CeO2 support includes: calcining an inorganic compound precursor containing Ce to obtain a CeO2 support; preferably, the inorganic compound precursor containing Ce includes at least one of cerium acetate, cerium nitrate, cerium sulfate, ammonium cerium nitrate, ammonium cerium sulfate, cerium oxalate, acetylacetone cerium, and cerium hydroxide.

4. The preparation method of the cerium oxide supported metal single-atom catalyst according to claim 1, wherein, In step a, the mass ratio of the metal element in the metal salt solution to the CeO2 support is (0.1-5):

100.

5. The preparation method of the cerium oxide-supported metal single-atom catalyst according to claim 1, characterized in that, In step b, the atmosphere of the first calcination treatment includes at least one of nitrogen, argon, helium, hydrogen, ammonia, air, and oxygen; and / or, the temperature of the first calcination treatment is higher than the melting point of the soluble metal salt; and / or, the temperature of the first calcination treatment is 200-600 °C, and the calcination time is 1-5 h; and / or, the washing liquid used for washing includes at least one of water, methanol, ethanol, isopropanol, acetone, DMF, and pyrrolidone.

6. The preparation method of the cerium oxide supported metal single-atom catalyst according to claim 1, wherein, In step c, the atmosphere of the second calcination treatment includes at least one of nitrogen, argon, helium, hydrogen, ammonia, air, and oxygen; and / or, the temperature of the second calcination treatment is 200-900 °C, and the calcination time is 2-12 h.

7. A cerium oxide supported metal single-atom catalyst, characterized in that, Prepared by the method according to any one of claims 1-6.

8. The cerium oxide-supported single-atom metal catalyst according to claim 7, wherein The catalyst includes a CeO2 support and an active metal distributed as single atoms on the support. The active metal includes at least one of Fe, Co, Ni, Mn, Cu, Zn, Au, Ru, or Pt; preferably, the active metal is 0.2-3% of the mass of the CeO2 support.

9. Use of a cerium oxide-supported single-atom metal catalyst prepared by the method according to any one of claims 1-6 or a cerium oxide-supported single-atom metal catalyst according to any one of claims 7-8 in the treatment of organic wastewater.

10. Use of the cerium oxide supported metal single-atom catalyst according to claim 9 in sewage treatment, characterized in that, The metal element in the cerium oxide-supported single-atom metal catalyst is selected from at least one of Co, Mn, Cu, Au, and Fe. Preferably, the pollutant in the organic wastewater is Rhodamine B.

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