Preparation method and application of carbon-nitrogen-oxygen co-doped supported single-atom titanium-zinc catalyst

Abstract

The application provides a preparation method and application of a carbon-nitrogen-oxygen co-doped supported monatomic titanium-zinc catalyst. The application adopts a liquid-phase anhydrous ethanol assisted dispersion method to prepare a precursor emulsion containing a carbon source, a nitrogen source, a zinc salt, a titanium salt and uniform dispersion; and the precursor emulsion is heated under oil bath or water bath conditions, and then is ground and calcined to obtain the carbon-nitrogen-oxygen co-doped supported monatomic titanium-zinc catalyst. Through the above method, the carbon-nitrogen-oxygen co-doping can be realized, the unique TiZn-CNO structure formed can be constructed into monatomic titanium-zinc, and the monatomic titanium-zinc can be stably anchored by oxygen atoms without falling off, so that the catalytic stability and the number of Lewis acid sites in the catalyst are improved. The catalyst prepared by the application can maximize the utilization of titanium-zinc active sites, improve the utilization rate of metal atoms, and has a good application prospect in the reaction of forming a cyclic carbonate by the ring addition of an epoxide and carbon dioxide.

Description

Technical Field

[0001] This invention relates to the field of carbon dioxide fixation and addition catalyst preparation technology, and particularly to a method for preparing and applying a carbon-nitrogen-oxygen co-doped supported single-atom titanium-zinc catalyst. Background Technology

[0002] As a major component of greenhouse gases, the concentration of carbon dioxide in the atmosphere affects the Earth's thermal balance. Chemical conversion of carbon dioxide is a crucial pathway to mitigate its accumulation in the atmosphere and to obtain value-added chemicals. Among various methods of carbon dioxide chemical fixation, the carbon dioxide cycloaddition reaction has attracted significant attention due to its 100% carbon utilization rate and substantial economic benefits. For example, inserting carbon dioxide ($51 / ton) into styrene oxide (98%, $0.08 / gram) synthesizes styrene cyclic carbonates ($1180 / gram), representing a more than 14,700-fold increase in value. Simultaneously, the cyclic carbonates produced by the carbon dioxide cycloaddition reaction are widely used as electrolytes in secondary batteries, precursors for polycarbonates, and aprotic polar solvents. Therefore, research on carbon dioxide cycloaddition reactions is of great significance.

[0003] Currently, catalysts used for the carbon dioxide cycloaddition reaction mainly include semiconductor quantum dots, metal-organic framework-based catalysts, nanocluster catalysts, and single-atom catalysts. Among them, single-atom catalysts, with their unique electronic structure and unsaturated coordination environment, have the potential to exhibit high photothermal catalytic performance in the carbon dioxide cycloaddition reaction. In this process, the metal sites in single-atom catalysts have the advantage of acting as highly active Lewis acid sites. However, most of these catalysts require harsh conditions such as solvents, high temperature, and high pressure, leading to cumbersome post-processing, consuming additional energy, and causing environmental problems.

[0004] Patent CN114917892A discloses a method for preparing a carbon-based metal single-atom catalyst in the carbon dioxide cycloaddition reaction. The method includes mixing a carbon source, a nitrogen source, and a metal salt to obtain a mixture; ball milling the mixture to obtain a mixed intermediate; and heat-treating the mixed intermediate under an inert atmosphere using a high-temperature pyrolysis method. Based on this method, the carbon source in this patent serves as the support, and the nitrogen source serves as the ligand. Heat treatment allows the metal single atoms in the metal salt to be uniformly dispersed on the support through the ligand, resulting in a carbon-based metal single-atom catalyst. However, this method can only anchor a single type of metal single atom through conventional nitrogen coordination. Furthermore, for titanium precursors, the microliter-level solution makes conventional ball milling impossible, leading to relatively low catalyst activity. Even when adding different types of metal salts to prepare bimetallic single-atom catalysts, effective co-dispersion between different metal precursors is difficult, affecting the catalytic effect.

[0005] In view of this, it is necessary to design an improved catalyst preparation method to anchor two metals, including titanium, in a single-atom dispersion, making it suitable for converting carbon dioxide and capable of efficiently and persistently generating cyclic carbonates to solve the above problems. Summary of the Invention

[0006] To address the shortcomings of the existing technology, the present invention aims to provide a highly reactive catalyst applicable to the preparation of cyclic carbonates under photothermal conditions. This invention employs a method for preparing a carbon-nitrogen-oxygen co-doped supported single-atom titanium-zinc catalyst, resulting in a catalyst material with high reactivity and extremely high metal atom utilization. This catalyst can effectively convert epoxides into cyclic carbonates under photothermal conditions, showing promising application prospects in carbon fixation and the preparation of high-value-added chemicals.

[0007] To achieve the above objectives, the present invention provides a method for preparing a carbon-nitrogen-oxygen co-doped supported single-atom titanium-zinc catalyst, comprising the following steps:

[0008] S1. Prepare a precursor emulsion containing a carbon source, a nitrogen source, a zinc salt, and a titanium salt;

[0009] S2. The precursor emulsion is heated in an oil bath or water bath and then ground into powder.

[0010] S3. The powder obtained in step S2 is subjected to high-temperature calcination to obtain a carbon-nitrogen-oxygen co-doped supported single-atom titanium-zinc catalyst.

[0011] As a further improvement of the present invention, in step S1, the method for preparing the precursor emulsion includes the following steps:

[0012] S11. Disperse the carbon source in anhydrous ethanol to prepare emulsion A;

[0013] S12. Dissolve the nitrogen source and zinc salt in anhydrous ethanol to prepare solution B;

[0014] S13. Add titanium salt to solution B to form solution C; then add solution C to emulsion A and stir evenly to obtain precursor emulsion.

[0015] As a further improvement of the present invention, the mass ratio of carbon source, nitrogen source and zinc salt in the precursor emulsion is 20:1:(0.3-1.4).

[0016] As a further improvement of the present invention, the volume-to-mass ratio of titanium salt to carbon source in the precursor emulsion is 50-100 μL:1 g.

[0017] As a further improvement of the present invention, the carbon source is melamine, the nitrogen source is 1,10-phenanthroline, the zinc salt is zinc nitrate hexahydrate, and the titanium salt is titanium trichloride solution.

[0018] As a further improvement of the present invention, the titanium trichloride solution is obtained by dispersing titanium trichloride in hydrochloric acid solution; the volume fraction of titanium trichloride in the titanium trichloride solution is 15-20%.

[0019] As a further improvement of the present invention, in step S11, the dispersion concentration of the carbon source in the prepared emulsion A is 0.8–1.2 g·mL. -1 .

[0020] As a further improvement of the present invention, in step S2, the temperature of the oil bath or water bath is 80-100°C, the heating time is 3-5 hours, and the grinding time is 10-20 minutes.

[0021] As a further improvement of the present invention, in step S3, the atmosphere of the high-temperature calcination is argon, the temperature of the high-temperature calcination is 500-850°C, and the time is 2.5-10h.

[0022] The present invention also provides the application of the carbon-nitrogen-oxygen co-doped supported single-atom titanium-zinc catalyst prepared by the above preparation method in the reaction of epoxide with carbon dioxide cycloaddition to form cyclic carbonates.

[0023] The beneficial effects of this invention are:

[0024] 1. The method for preparing a carbon-nitrogen-oxygen co-doped supported single-atom titanium-zinc catalyst provided by this invention involves preparing a precursor emulsion containing a carbon source, a nitrogen source, a zinc salt, and a titanium salt, heating it in an oil bath or water bath, and then grinding and calcining it. This method achieves carbon-nitrogen-oxygen co-doping, anchoring titanium-zinc in single-atom form to form coordinate bonds with oxygen atoms. This results in uniform anchoring of titanium-zinc single atoms on a carbon-nitrogen-oxygen substrate, increasing the number of Lewis acid sites in the catalyst. Furthermore, the catalyst prepared based on the method provided by this invention has a large specific surface area, which promotes the exposure of active sites and provides significant structural advantages for catalysis.

[0025] 2. The method for preparing the carbon-nitrogen-oxygen co-doped supported single-atom titanium-zinc catalyst provided by the present invention employs a liquid-phase anhydrous ethanol-assisted dispersion method during the preparation of the precursor emulsion. First, the carbon source is dispersed in anhydrous ethanol to prepare emulsion A. Then, the nitrogen source and zinc salt are dissolved in anhydrous ethanol to prepare solution B. Next, the titanium salt is added to solution B to form solution C, which is then dropwise into emulsion A. This achieves co-doping of the liquid-phase precursor titanium and the solid-phase precursor zinc, and forms oxygen coordination, thereby improving the catalytic performance of the finally obtained carbon-nitrogen-oxygen co-doped supported single-atom titanium-zinc catalyst.

[0026] 3. The catalyst prepared by the method of preparing carbon, nitrogen and oxygen co-doped supported single-atom titanium-zinc catalyst provided by the present invention has high reactivity, recycling performance and extremely high metal atom utilization rate. It can be used as a catalytic material that can fix carbon dioxide and convert it into higher value-added chemicals. Under photothermal conditions, it can widely convert epoxides into cyclic carbonates, which provides important reference for the development of carbon fixation technology and the preparation of cyclic ester products in industry. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the preparation process of the carbon-nitrogen-oxygen co-doped supported single-atom titanium-zinc catalyst provided by the present invention.

[0028] Figure 2 The image shows an HRTEM image of the carbon-nitrogen-oxygen co-doped supported single-atom titanium-zinc catalyst prepared in Example 1.

[0029] Figure 3 AC-STEM image of the carbon-nitrogen-oxygen co-doped supported single-atom titanium-zinc catalyst prepared in Example 1.

[0030] Figure 4 The XRD patterns are of the catalysts provided in Example 1 and Comparative Examples 1-3.

[0031] Figure 5 XPS O 1s and Zn 2p plots for the catalysts provided in Example 1 and Comparative Examples 1-2, and synchrotron radiation fitting plot for Example 1.

[0032] Figure 6 This is a schematic diagram comparing the coordination environments of Example 1 and Comparative Example 2.

[0033] Figure 7 BET diagrams for the catalysts provided in Example 1 and Comparative Examples 1-3.

[0034] Figure 8 The graph shows a comparison of the yields of the target product in the cycloaddition reaction of styrene oxide and carbon dioxide provided by the catalysts provided in Example 1 and Comparative Examples 1-3.

[0035] Figure 9 The graph shows the cyclic regeneration performance of the carbon-nitrogen-oxygen co-doped supported single-atom titanium-zinc catalyst prepared in Example 1 for the cycloaddition reaction of styrene oxide and carbon dioxide.

[0036] Figure 10 The graph shows the performance of the catalysts provided in Example 1 and Comparative Examples 1-2 in the carbon dioxide cycloaddition of different epoxides. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0038] It should also be noted that, in order to avoid obscuring the present invention with unnecessary details, only the structures and / or processing steps closely related to the present invention are shown in the accompanying drawings, while other details that are not closely related to the present invention are omitted.

[0039] Additionally, it should be noted that the terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0040] This invention provides a method for preparing a carbon-nitrogen-oxygen co-doped supported single-atom titanium-zinc catalyst, comprising the following steps:

[0041] S1. Prepare a precursor emulsion containing a carbon source, a nitrogen source, a zinc salt, and a titanium salt;

[0042] S2. The precursor emulsion is heated in an oil bath or water bath and then ground into powder.

[0043] S3. The powder obtained in step S2 is subjected to high-temperature calcination to obtain a carbon-nitrogen-oxygen co-doped supported single-atom titanium-zinc catalyst.

[0044] Through the above methods, this invention enables carbon-nitrogen-oxygen co-doping, anchoring titanium-zinc in single-atom form to form coordinate bonds with oxygen atoms. This results in uniform anchoring of titanium-zinc single atoms onto the carbon-nitrogen-oxygen substrate, increasing the number of Lewis acid sites in the catalyst. Furthermore, the catalyst prepared based on the method provided by this invention has a large specific surface area, which promotes the exposure of active sites and provides significant structural advantages for catalysis.

[0045] Preferably, in step S1, the method for preparing the precursor emulsion includes the following steps:

[0046] S11. Disperse the carbon source in anhydrous ethanol to prepare emulsion A;

[0047] S12. Dissolve the nitrogen source and zinc salt in anhydrous ethanol to prepare solution B;

[0048] S13. Add titanium salt to solution B to form solution C; then add solution C to emulsion A and stir evenly to obtain precursor emulsion.

[0049] The above method enables the co-doping of liquid-phase precursor titanium and solid-phase precursor zinc, thereby improving the catalytic performance of the catalyst. Experiments have shown that without the use of ethanol for auxiliary dispersion, it is impossible to simultaneously anchor both titanium and zinc in single-atom form, thus failing to obtain the desired single-atom catalyst. Furthermore, the method provided by this invention, while anchoring titanium and zinc in a single-atom dispersed form, also alters their coordination relationship, forming oxygen coordination, thereby improving the catalytic performance of the final carbon-nitrogen-oxygen co-doped supported single-atom titanium-zinc catalyst.

[0050] Preferably, in the precursor emulsion, the mass ratio of carbon source, nitrogen source, and zinc salt is 20:1:(0.3-1.4), the volume-to-mass ratio of titanium salt to carbon source is 50-100 μL:1 g, and the volume-to-mass ratio of ethanol to carbon source is preferably 1-2 mL:1 g. The carbon source is preferably melamine, the nitrogen source is preferably 1,10-phenanthroline, the zinc salt is preferably zinc nitrate hexahydrate, and the titanium salt is preferably a titanium trichloride solution. The titanium trichloride solution is obtained by dispersing titanium trichloride in hydrochloric acid solution; the volume fraction of titanium trichloride in the titanium trichloride solution is 15-20%. More preferably, in the precursor emulsion, the molar ratio of titanium in the titanium salt to zinc in the zinc salt is 1:0.5-2.

[0051] In step S11, the carbon source in the prepared emulsion A has a dispersion concentration of 0.8–1.2 g·mL. -1 .

[0052] In step S13, it is preferable to first add the titanium salt to anhydrous ethanol and then add it to solution B. The preferred ratio of the amount of titanium in the titanium salt to the mass of the carbon source is 0.225 mmol: 2 g.

[0053] In step S2, the temperature of the oil bath or water bath is 80-100°C, and the heating time is 3-5 hours; the grinding time is 10-20 minutes.

[0054] In step S3, the atmosphere for high-temperature calcination is argon, the calcination temperature is 500–700°C, and the time is 2.5–10 hours. If the calcination temperature is too low, clusters or nanoparticles will form; the duration of calcination determines the catalytic activity and recyclability of the catalyst. This invention, by controlling the temperature and time of high-temperature calcination, ensures the formation of single-atom materials.

[0055] Using the above method, the carbon, nitrogen, and oxygen co-doped supported single-atom titanium-zinc catalyst prepared by the present invention can be applied to the reaction of epoxide and carbon dioxide cycloaddition to form cyclic carbonates, and the catalyst with the highest yield can achieve a yield of 93.6% in 3 hours.

[0056] The preparation method and application of the carbon-nitrogen-oxygen co-doped supported single-atom titanium-zinc catalyst provided by the present invention will be described in detail below with reference to specific embodiments.

[0057] Example 1

[0058] This embodiment provides a method for preparing a carbon-nitrogen-oxygen co-doped supported single-atom titanium-zinc catalyst, the process flow diagram of which is shown below. Figure 1 As shown, the specific steps include the following:

[0059] S1. Prepare a precursor emulsion containing a carbon source, a nitrogen source, a zinc salt, and a titanium salt according to the following steps:

[0060] Mix 2g of melamine with 2mL of anhydrous ethanol in a 50mL beaker and stir to disperse the emulsion at a uniform concentration to obtain emulsion A;

[0061] Dissolve 100 mg of 1,10-phenanthroline in 0.5 mL of anhydrous ethanol, then add 100 mg of zinc nitrate hexahydrate, and sonicate in a 2 mL centrifuge tube to obtain solution B;

[0062] 150 μL of a 15% (v / v) titanium trichloride solution was added dropwise to 0.5 mL of anhydrous ethanol, and then added to solution B (at which point the amount of titanium was 0.225 mmol). After mixing and sonicating until homogeneous, solution C was obtained. Solution C was then added to emulsion A and stirred until homogeneous to obtain the precursor emulsion. In this precursor emulsion, the molar ratio of titanium to zinc was approximately 1:1.5.

[0063] S2. Place the precursor emulsion in an oil bath and heat it at 80°C for 4 hours. Then grind it into powder to obtain the precursor powder.

[0064] S3. Place the precursor powder obtained in step S2 in a magnetic boat, place the magnetic boat in a tube furnace, and heat it to 600°C at a rate of 5°C / min under argon protection. Then, keep it at 600°C for 10 hours and then let it cool naturally to room temperature to obtain a carbon-nitrogen-oxygen co-doped supported single-atom titanium-zinc catalyst.

[0065] The HRTEM and AC-STEM images of the carbon-nitrogen-oxygen co-doped supported single-atom titanium-zinc catalyst prepared in this embodiment are shown below. Figure 2 , Figure 3 As shown. By Figure 2 It can be seen that the catalyst has a flat two-dimensional structure, with no particle clusters or crystal lattice present; Figure 3 It can be seen that the catalyst contains monodisperse titanium-zinc sites.

[0066] Comparative Examples 1-3

[0067] Comparative Examples 1-3 each provided a catalyst, which differed from Example 1 only in that the addition of titanium precursor and / or zinc precursor was omitted.

[0068] In Comparative Example 1, no zinc precursor zinc nitrate hexahydrate was added; in Comparative Example 2, no titanium precursor titanium trichloride was added; and in Comparative Example 3, neither zinc nor titanium precursors were added. The remaining preparation steps were the same as in Example 1 and will not be repeated here.

[0069] The XRD patterns of the catalysts provided in Example 1 and Comparative Examples 1-3 were analyzed as follows: Figure 4 As shown, TiZn1.5-CNO, Ti-CNO, Zn-CNO, and CN represent the catalysts in Example 1 and Comparative Examples 1-3, respectively. Figure 4 It can be seen that the XRD pattern of the catalyst prepared in Example 1 only has two broad peaks belonging to graphitized carbon, and no cluster peaks of titanium or zinc appear.

[0070] The catalysts provided in Example 1 and Comparative Examples 1-2 were further analyzed, and their XPS O1s and Zn 2p plots and synchrotron radiation fitting plots were obtained as follows: Figure 5 As shown. By Figure 5 It can be seen that in the TiZn1.5-CNO prepared in Example 1 and the Ti-CNO prepared in Comparative Example 1, Ti coordinates with O. Further investigation revealed that in Comparative Example 2, without the addition of the titanium precursor, Zn did not coordinate with O, but rather with N. A schematic diagram comparing the coordination environments in Example 1 and Comparative Example 1 is shown below. Figure 6 As shown. Therefore, the method provided in Example 1 can not only anchor both titanium and zinc in a single-atom dispersion form at the same time, but also change their coordination relationship so that they coordinate with O.

[0071] The BET diagrams of the catalysts provided in Example 1 and Comparative Examples 1-3 are as follows: Figure 7 As shown. By Figure 7It can be seen that, compared with the titanium single-atom catalyst in Comparative Example 1, the zinc single-atom catalyst in Comparative Example 2, and Comparative Example 3, the catalyst prepared in Example 1 has the highest specific surface area and is more suitable for the exposure of active sites.

[0072] To verify the effectiveness of the catalysts provided in Example 1 and Comparative Examples 1-3 in the cycloaddition reaction of epoxides with carbon dioxide to form cyclic carbonates, 5 mmol of styrene oxide was used as the reactant, and the reaction was carried out under light intensity of 2 W / cm². -2 Under a carbon dioxide pressure of 1 bar, the reactions were carried out using 10 mg of the catalysts provided in Example 1 and Comparative Examples 1-3, respectively. The yield comparison graphs are shown below. Figure 8 As shown.

[0073] The yield is calculated as: (yield) = (amount of cyclic carbonate substance (mmol)) / (amount of epoxide substance (mmol)).

[0074] Depend on Figure 8 It can be seen that the yield of the catalyst provided in Example 1 is significantly higher than that of the other comparative examples, indicating that the method provided in Example 1 is beneficial to improving the catalytic performance of the catalyst.

[0075] The cyclic regeneration performance of the catalyst provided in Example 1 was further tested, and the results are as follows: Figure 9 As shown. By Figure 9 It can be seen that the catalyst provided in Example 1 can still effectively convert and generate more than 80% of the target product after four cycles of regeneration. When the catalysts provided in Example 1 and Comparative Examples 1-2 are applied to the carbon dioxide cycloaddition reaction of different epoxides, the corresponding yields are as follows: Figure 10 As shown. By Figure 10 It can be seen that the catalyst provided in Example 1 exhibits high conversion and cycloaddition capabilities for a wide range of substrates, and its catalytic activity for each substrate is superior to that of Comparative Examples 1-2. Therefore, the carbon-nitrogen-oxygen co-doped supported single-atom titanium-zinc catalyst prepared in Example 1 possesses excellent recycling performance and a broader capacity for converting epoxides.

[0076] Examples 2-5

[0077] Examples 2-5 provide a method for preparing a carbon-nitrogen-oxygen co-doped supported single-atom titanium-zinc catalyst. Compared with Example 1, the only difference is that the molar ratio of titanium precursor and zinc precursor is changed. The other steps are the same as in Example 1 and will not be repeated here.

[0078] The catalysts prepared in each example were applied to the reaction of epoxide and carbon dioxide cycloaddition to form cyclic carbonates according to the application method in Example 1. The molar ratio of titanium-zinc precursors and the yield of catalysts in carbon dioxide cycloaddition reaction corresponding to each example are shown in Table 1.

[0079] Table 1. Molar ratio and yield of titanium and zinc precursors in Examples 1-5

[0080] Example 1 1:1.5 93.6 Example 2 1:0.5 71.5 Example 3 1:0.75 75.3 Example 4 1:1 82.1 Example 5 1:2 87.5

[0081] As shown in Table 1, the ratio of titanium-zinc precursors to carbon dioxide cycloaddition reaction exhibits a typical volcano-like relationship. The catalyst with a titanium-zinc precursor ratio of 1:1.5 shows the best performance under the same conditions, and the yield of the target product styrene cyclic carbonate reaches 93.6% after 3 hours of catalysis.

[0082] Comparative Example 4

[0083] This comparative example provides a method for preparing a catalyst. Compared with Example 1, the difference is that the process of preparing the zinc precursor emulsion in step S2 is placed after S5. That is, the Ti-CNO catalyst powder obtained after pyrolysis is impregnated in the zinc precursor solution, vacuum dried, and then pyrolyzed at high temperature under a hydrogen-argon mixed atmosphere at 500°C for 1 hour. The remaining steps are the same as in Example 1 and will not be repeated here.

[0084] The catalyst prepared in this comparative example was applied to the reaction of epoxide and carbon dioxide cycloaddition to form cyclic carbonates according to the application method in Example 1. The yield was measured to be 65.9%, which was lower than that in Example 1. This is mainly because the zinc in this example exists in the form of nanoparticles, and the synergistic promoting effect of titanium zinc single atoms as in Example 1 is not present.

[0085] Comparative Example 5

[0086] This comparative example provides a carbon-nitrogen-oxygen co-doped supported single-atom titanium and zinc catalyst, which is composed of 4 mg of Ti-CNO provided in Comparative Example 1 and 6 mg of Zn-CNO provided in Comparative Example 2.

[0087] The catalyst prepared in this comparative example was applied to the reaction of epoxide and carbon dioxide cycloaddition to form cyclic carbonates according to the application method in Example 1. The yield was measured to be 47.6%, which was lower than that in Example 1. This was mainly because the directly mixed Ti-CNO and Zn-CNO catalysts could not provide the synergistic effect of bimetallic titanium-zinc single atoms.

[0088] In summary, this invention provides a method for preparing and applying a carbon-nitrogen-oxygen co-doped supported single-atom titanium-zinc catalyst. This invention utilizes anhydrous ethanol in a liquid phase to assist dispersion, preparing a uniformly dispersed precursor emulsion containing a carbon source, nitrogen source, zinc salt, and titanium salt. This precursor emulsion is then heated in an oil bath or water bath, followed by grinding and calcination to obtain the carbon-nitrogen-oxygen co-doped supported single-atom titanium-zinc catalyst. Through this method, this invention achieves carbon-nitrogen-oxygen co-doping, forming a unique TiZn-CNO structure that can construct single-atom titanium-zinc atoms, stably anchoring them to oxygen atoms without detachment, thus improving catalytic stability and the number of Lewis acid sites in the catalyst. The catalyst prepared by this invention maximizes the utilization of titanium-zinc active sites, improving the utilization rate of metal atoms. It exhibits high activity and high yield in the cycloaddition of epoxides with carbon dioxide to form cyclic carbonates, making it a promising novel catalyst for the simultaneous carbon fixation and preparation of high-value-added chemicals.

[0089] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a carbon-nitrogen-oxygen co-doped supported single-atom titanium-zinc catalyst, characterized in that, Includes the following steps: S1. Prepare a precursor emulsion containing a carbon source, a nitrogen source, a zinc salt, and a titanium salt; wherein the carbon source is melamine, and the nitrogen source is 1,10-phenanthroline; S2. The precursor emulsion is heated in an oil bath or water bath and then ground into powder. S3. The powder obtained in step S2 is subjected to high-temperature calcination to obtain a carbon-nitrogen-oxygen co-doped supported single-atom titanium-zinc catalyst; the atmosphere of the high-temperature calcination is argon, the temperature of the high-temperature calcination is 500-850℃, and the time is 2.5-10h. In step S1, the method for preparing the precursor emulsion includes the following steps: S11. Disperse the carbon source in anhydrous ethanol to prepare emulsion A; S12. Dissolve the nitrogen source and zinc salt in anhydrous ethanol to prepare solution B; S13. Add titanium salt to solution B to form solution C; then add solution C to emulsion A and stir evenly to obtain precursor emulsion.

2. The method for preparing the carbon-nitrogen-oxygen co-doped supported single-atom titanium-zinc catalyst according to claim 1, characterized in that: In the precursor emulsion, the mass ratio of carbon source, nitrogen source and zinc salt is 20:1:(0.3-1.4).

3. The method for preparing the carbon-nitrogen-oxygen co-doped supported single-atom titanium-zinc catalyst according to claim 1, characterized in that: In the precursor emulsion, the volume-to-mass ratio of titanium salt to carbon source is 50–100 μL: 1 g.

4. The method for preparing the carbon-nitrogen-oxygen co-doped supported single-atom titanium-zinc catalyst according to claim 1, characterized in that: The zinc salt is zinc nitrate hexahydrate, and the titanium salt is titanium trichloride solution.

5. The method for preparing the carbon-nitrogen-oxygen co-doped supported single-atom titanium-zinc catalyst according to claim 4, characterized in that: The titanium trichloride solution is obtained by dispersing titanium trichloride in hydrochloric acid solution; the volume fraction of titanium trichloride in the titanium trichloride solution is 15-20%.

6. The method for preparing the carbon-nitrogen-oxygen co-doped supported single-atom titanium-zinc catalyst according to claim 1, characterized in that: In step S11, the carbon source in the prepared emulsion A has a dispersion concentration of 0.8–1.2 g·mL. -1 .

7. The method for preparing the carbon-nitrogen-oxygen co-doped supported single-atom titanium-zinc catalyst according to claim 1, characterized in that: In step S2, the temperature of the oil bath or water bath is 80-100°C, and the heating time is 3-5 hours; the grinding time is 10-20 minutes.

8. The application of a carbon-nitrogen-oxygen co-doped supported single-atom titanium-zinc catalyst prepared by any one of claims 1 to 7 in the reaction of epoxide with carbon dioxide cycloaddition to form cyclic carbonates.

Images