Nitrogen and phosphorus co-doped carbon catalyst and preparation method thereof

Abstract

The invention relates to the technical field of catalysts, in particular to a nitrogen-phosphorus co-doped carbon catalyst and a preparation method thereof. The invention relates to a preparation method of a nitrogen and phosphorus co-doped carbon catalyst, which comprises the following steps: by taking porous organic polyvinyl benzene as a carbon source, adding a metal source, a nitrogen source and a phosphorus source into the porous organic polyvinyl benzene, mixing, sintering and pyrolyzing to generate the nitrogen and phosphorus co-doped carbon catalyst. According to the preparation method disclosed by the invention, the nitrogen-phosphorus co-doped carbon catalyst with high catalytic activity is successfully prepared through simple operation steps and low-cost raw materials. The catalyst shows excellent catalytic performance in the reaction of converting benzyl alcohol into benzaldehyde through catalytic oxidation, and the yield reaches up to 93% or above.

Description

Technical Field

[0001] The present application relates to the field of catalyst technology, and in particular to a nitrogen-phosphorus co-doped carbon catalyst and a preparation method thereof. Background Art

[0002] Benzaldehyde (BAD) is an important organic intermediate and has been widely used in medicine, fragrance, dye and food industries. The traditional production methods of benzaldehyde include toluene chlorination and benzyl chloride hydrolysis. Both processes will produce a large amount of harmful acidic waste. Selecting a suitable catalyst to selectively catalytically oxidize benzyl alcohol (BA) to prepare BAD can reduce harmful acidic waste. The catalyst for catalytic oxidation of benzyl alcohol is generally based on precious metals or transition metals. Some alkalis and other chemical reagents such as TEMPO are added during the catalytic reaction, which makes this method subject to certain limitations in practical applications. From the perspective of "green chemistry", the selective oxidation of benzyl alcohol to generate benzaldehyde using green oxidants is a feasible and more environmentally friendly method. Based on this, it is of great research significance to design a highly selective, low-cost, environmentally friendly and highly active catalyst to catalytically oxidize benzyl alcohol to benzaldehyde. Summary of the invention

[0003] In order to solve the above technical problems, the present application provides a nitrogen-phosphorus co-doped carbon catalyst and a preparation method thereof. The preparation method of the present application is simple, easy, low-cost and environmentally friendly. The prepared nitrogen-phosphorus co-doped carbon catalyst has a large average pore size, can provide more active sites and a larger reaction space; at the same time, it has a very large specific surface area and pore volume. Therefore, the nitrogen-phosphorus co-doped carbon catalyst has good catalytic activity. It is applied to the catalytic oxidation of benzyl alcohol into benzaldehyde. The reaction is carried out at 120°C for 12 hours, and the yield of benzaldehyde reaches more than 93%.

[0004] In a first aspect, the present application provides a method for preparing a nitrogen-phosphorus co-doped carbon catalyst, using the following technical solution: A method for preparing a nitrogen-phosphorus co-doped carbon catalyst comprises the following steps: S1, preparing porous organic polyvinylbenzene; S2, dissolving a metal source, a nitrogen source, and a phosphorus source in a solvent, then adding porous organic polyvinylbenzene, stirring at room temperature for 40-60 minutes, and then performing vacuum freeze drying to obtain a mixture; S3, calcining the mixture obtained in step S2 in a nitrogen atmosphere to obtain a calcined product; S4. Wash the calcined product obtained in step S3 with deionized water, and then dry it at a temperature of 80-100° C. for 12-20 hours to obtain a nitrogen-phosphorus co-doped carbon catalyst.

[0005] By adopting the above technical scheme, the porous organic polyvinylbenzene prepared in step S1 provides a basis for subsequent doping, and its porous structure is conducive to increasing the specific surface area and pore volume of the catalyst. In step S2, the addition of metal source, nitrogen source and phosphorus source forms a uniform doping layer on the surface of porous organic polyvinylbenzene, which is conducive to increasing the number of active sites and reaction space of the catalyst. In step S3, the calcination process under a nitrogen atmosphere causes the metal source, nitrogen source and phosphorus source in the mixture to undergo a chemical reaction to generate a nitrogen-phosphorus co-doped carbon catalyst. In this process, the synergistic effect of the metal source, nitrogen atoms and phosphorus atoms significantly improves the performance of the catalyst. In step S4, the deionized water washing and drying process helps to remove impurities in the calcined product, and gives the catalyst a certain degree of crystallinity and specific surface area, further improving the catalytic activity. In summary, the preparation method of the present application successfully prepares a nitrogen-phosphorus co-doped carbon catalyst with high catalytic activity through simple operating steps and low-cost raw materials. The catalyst exhibits excellent performance in the reaction of catalytic oxidation of benzyl alcohol to benzaldehyde, with a yield of more than 93%.

[0006] Preferably, in step S1, the method for preparing the porous organic polyvinylbenzene comprises the following steps: S21. According to the mass fractions, 10 parts of divinylbenzene were placed in a pear-shaped separatory bucket, and washed three times with 5% potassium hydroxide solution and saturated ammonium chloride solution respectively, and the upper layer of yellow liquid was retained for later use; S22. According to the mass fractions, put 3 parts of yellow liquid into a hydrothermal reactor, add 0.075 parts of azobisisobutyronitrile, stir at room temperature for 5-10 minutes, and then put it into a 100°C oven to react for 24 hours. After the reaction is completed, wait for it to cool to room temperature, then wash it with ethanol 3 times, and vacuum dry it at 80°C for 8-10 hours to obtain porous organic polyvinylbenzene.

[0007] By adopting the above technical scheme, first, by using divinylbenzene as a raw material and washing with potassium hydroxide solution and saturated ammonium chloride solution, impurities can be effectively removed and the purity of the product can be improved. Secondly, azobisisobutyronitrile in the hydrothermal reactor is used as an initiator to promote the polymerization of divinylbenzene to form an organic polyvinylbenzene with a porous structure. This porous structure not only helps to increase the specific surface area and pore volume of the catalyst, but also provides more active sites and a larger reaction space, thereby improving the catalytic performance. In addition, the porous organic polyvinylbenzene also plays a synergistic role in the subsequent steps. In the S2 step, it is used as a carrier material, which can effectively carry metal sources, nitrogen sources and phosphorus sources, and maintain a stable structure during the calcination process. This makes the final nitrogen-phosphorus co-doped carbon catalyst have better catalytic activity and stability.

[0008] Preferably, in step S2, the metal source is composed of nickel oxalate and cobalt phthalocyanine in a mass ratio of 3:4.

[0009] By adopting the above technical scheme, the metal source is composed of nickel oxalate and cobalt phthalocyanine in a mass fraction ratio of 3: 4. The role in this application is to utilize the synergistic catalytic effect of nickel and cobalt to further significantly improve the catalytic activity. Nickel oxalate, it can decompose to produce nickel oxide (NiO) at high temperature, and then be reduced to metallic nickel (Ni) in a reducing atmosphere. Metallic nickel has good catalytic performance, especially in reactions such as hydrogenation, dehydrogenation, and oxidation. Cobalt phthalocyanine is a macrocyclic compound containing cobalt atoms and has a planar structure. Cobalt phthalocyanine can decompose to produce cobalt oxide (CoO) at high temperature, and then be reduced to metallic cobalt (Co) in a reducing atmosphere. Metallic cobalt also has good catalytic performance, especially in oxidation reactions. The synergistic effect between nickel oxalate and cobalt phthalocyanine is mainly reflected in the following aspects: bimetallic effect: nickel oxalate and cobalt phthalocyanine generate nickel oxide and cobalt oxide respectively at high temperature, and these two oxides can be reduced to metallic nickel and metallic cobalt in a reducing atmosphere. There may be interaction between metallic nickel and metallic cobalt to form a bimetallic catalyst, thereby improving catalytic activity. Electronic regulation: The doping of nickel and cobalt can adjust the electronic properties of carbon materials, causing the electron density on the surface of carbon materials to change, which is beneficial to the adsorption and activation of reactant molecules, thereby improving the catalytic activity. Increased active sites: The doping of nickel oxalate and cobalt phthalocyanine can increase the number of active sites on the surface of carbon materials, provide more reaction space, and is beneficial to the adsorption and activation of reactant molecules, thereby improving the catalytic activity. In summary, the metal source composed of nickel oxalate and cobalt phthalocyanine in a mass ratio of 3:4 played a key role in the preparation of nitrogen-phosphorus co-doped carbon catalysts, and the synergistic catalytic effect of nickel and cobalt further significantly improved the catalytic activity.

[0010] Preferably, in step S2, the nitrogen source consists of melamine and urea in a mass ratio of 3:5.

[0011] Preferably, in step S2, the solvent consists of tetrahydrofuran and deionized water in a mass ratio of 6:1.

[0012] Preferably, in step S2, the phosphorus source consists of diammonium hydrogen phosphate and ammonium phosphate in a mass ratio of 5:2.

[0013] By adopting the above technical scheme, phosphorus element is provided: diammonium hydrogen phosphate and ammonium phosphate are both compounds rich in phosphorus element, which can release phosphorus ions in the solution, and these phosphorus ions can form chemical bonds with carbon atoms in porous organic polyvinyl benzene, thereby realizing phosphorus doping. Adjusting pH value: diammonium hydrogen phosphate and ammonium phosphate are both alkaline substances, which can adjust the pH value of the solution to keep it within a suitable range, which is conducive to the reaction of metal source, nitrogen source, phosphorus source and porous organic polyvinyl benzene. Promoting reaction: During the sintering pyrolysis process, the ammonia released by diammonium hydrogen phosphate and ammonium phosphate plays a pore-forming role, which increases the pore size of porous organic polyvinyl benzene, thereby increasing the specific surface area and pore volume of the catalyst. At the same time, ammonia can also react with metal source, nitrogen source and phosphorus source to promote their doping process. The synergistic effect between diammonium hydrogen phosphate and ammonium phosphate is mainly reflected in the fact that they jointly provide phosphorus element and adjust pH value for the system, as well as promote the reaction process. The ratio of these two substances is 5:2, indicating that their roles in the system are complementary and mutually reinforcing. By adjusting their ratio, the optimization of catalyst performance can be achieved. In summary, diammonium hydrogen phosphate and ammonium phosphate, as phosphorus sources in this application, not only provide phosphorus elements, but also play multiple functions such as adjusting pH value, promoting reaction and synergistic effect, thereby effectively improving the performance of nitrogen-phosphorus co-doped carbon catalysts.

[0014] Preferably, in step S2, the mass ratio of the metal source, the nitrogen source, the phosphorus source, the porous organic polyvinylbenzene and the solvent is 3:4.8:0.6:7:50-55.

[0015] Preferably, in step S2, the process conditions of vacuum freeze drying are: drying time is 18-24h, temperature is 40°C, and vacuum degree is 20Pa.

[0016] Preferably, in step S3, the calcination process conditions are: heating at a heating rate of 2.5-3°C / min to 400°C, maintaining for 120 minutes, and then heating to 800-850°C at the same heating rate, maintaining for 2-3 hours.

[0017] By adopting the above technical solution, by controlling the heating rate, it is possible to ensure that the organic polyvinylbenzene gradually decomposes during the calcination process, and avoid excessive heating to cause the material structure to be destroyed. At the same time, the slow heating rate helps the nitrogen source and phosphorus source to fully react with the carbon material to form a uniform doping structure. Keeping the temperature: Keeping it at 400°C for 120 minutes can fully decompose the organic polyvinylbenzene to generate a carbon material with a porous structure. At the same time, this temperature range is conducive to the chemical reaction of the nitrogen source and phosphorus source with the carbon material to form a stable doping structure. Further heating: Raising the temperature to 800-850°C and maintaining it for 2-3h can further improve the graphitization degree of the carbon material and enhance its conductivity and thermal stability. At the same time, high temperature conditions help the nitrogen source and phosphorus source to be more deeply doped into the carbon material, thereby improving the doping effect. During the entire calcination process, the nitrogen source, phosphorus source and metal source (such as nickel and cobalt) act together on the carbon material to form a nitrogen-phosphorus co-doped carbon catalyst with excellent catalytic performance. Nitrogen atom doping can adjust the electronic properties of carbon materials and provide a large number of catalytic active sites; phosphorus atom doping can increase the number of heteroatoms and improve catalytic performance; metal source doping utilizes the synergistic catalytic effect of metals to further enhance catalytic activity. In summary, the calcination process conditions in step S3 are crucial for the preparation of nitrogen-phosphorus co-doped carbon catalysts with high catalytic activity. By controlling the heating rate, maintaining the temperature and further heating the temperature, the full decomposition of organic polyvinylbenzene, the effective doping of nitrogen and phosphorus sources, and the synergistic catalytic effect of the metal source can be achieved, thereby obtaining a nitrogen-phosphorus co-doped carbon catalyst with excellent catalytic performance.

[0018] In a second aspect, the present application provides a nitrogen-phosphorus co-doped carbon catalyst, which adopts the following technical solution: As a general technical concept, the present application also provides the above-mentioned nitrogen-phosphorus co-doped carbon catalyst, which is prepared by the above-mentioned preparation method of the nitrogen-phosphorus co-doped carbon catalyst, wherein the average pore size of the nitrogen-phosphorus co-doped carbon catalyst is 3.85-4.65nm and the specific surface area is 1288-1425m 2 / g, pore volume is 1.85-2.16cm 3 / g.

[0019] In summary, the beneficial technical effects of this application are: 1. Highly efficient catalytic performance: The catalytic performance of the carbon catalyst is significantly improved by co-doping with nitrogen and phosphorus. Nitrogen atoms can adjust the electronic properties of carbon materials and provide a large number of catalytic active sites; phosphorus atoms can further improve the structural characteristics of the catalyst. In addition, the doping of metal sources (such as nickel and cobalt) utilizes their synergistic catalytic effect, making the catalyst show extremely high efficiency in catalytic oxidation of benzyl alcohol to benzaldehyde.

[0020] 2. Large pore size and high specific surface area: The porous organic polyvinylbenzene used in the preparation process is used as a precursor, combined with the sintering pyrolysis process control, so that the final nitrogen-phosphorus co-doped carbon catalyst has a large average pore size and a very high specific surface area. These structural characteristics provide the catalyst with more active sites and a larger reaction space, which is conducive to improving the catalytic efficiency.

[0021] 3. Green and environmentally friendly: The entire preparation method is simple and easy, and the raw materials are easy to obtain, the cost is low, and it does not involve the use of toxic and harmful chemicals, which meets the requirements of green environmental protection.

[0022] 4. Broad application prospects: Due to its excellent catalytic performance, the nitrogen-phosphorus co-doped carbon catalyst is not only suitable for the catalytic oxidation of benzyl alcohol into benzaldehyde, but may also be suitable for many other types of chemical reactions and has broad industrial application prospects.

[0023] 5. During the sintering and pyrolysis process, the ammonia released by the phosphorus source plays a pore-forming role and also acts as a doping agent for the phosphorus source. By controlling the sintering process, a nitrogen-phosphorus co-doped carbon catalyst with large pore size, very large specific surface area and pore volume is obtained, further improving the catalytic activity. DETAILED DESCRIPTION

[0024] The embodiments of the present application will be described in detail below in conjunction with the examples, but it will be appreciated by those skilled in the art that the following examples are only used to illustrate the present application and should not be considered as limiting the scope of the present application. In the examples, if specific conditions are not specified, they are carried out according to normal conditions or the conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0025] In the following embodiments and preparation examples, 1 portion is 1 kg.

[0026] Preparation Example 1 Preparation of porous organic polyvinylbenzene The method for preparing porous organic polyvinylbenzene comprises the following steps: S21. According to the mass fractions, 10 parts of divinylbenzene were placed in a pear-shaped separatory bucket, and washed three times with 5% potassium hydroxide solution and saturated ammonium chloride solution respectively, and the upper layer of yellow liquid was retained for later use; S22. According to the mass fractions, put 3 parts of yellow liquid into a hydrothermal reactor, add 0.075 parts of azobisisobutyronitrile, stir at room temperature for 8 minutes, and then put it into a 100°C oven to react for 24 hours. After the reaction is completed, wait for it to cool to room temperature, then wash it with ethanol 3 times, and vacuum dry it at 80°C for 9 hours to obtain porous organic polyvinylbenzene.

[0027] Example 1 S1. Dissolve 3 parts of a metal source, 4.8 parts of a nitrogen source, and 0.6 parts of a phosphorus source in 50 parts of a solvent, then add 7 parts of porous organic polyvinylbenzene, and stir at room temperature for 40 minutes, and then perform vacuum freeze drying. The process conditions of the vacuum freeze drying are: drying time is 18 hours, temperature is 40°C, and vacuum degree is 20Pa, to obtain a mixture, wherein the metal source consists of nickel oxalate and cobalt phthalocyanine in a mass ratio of 3:4; the nitrogen source consists of melamine and urea in a mass ratio of 3:5; the phosphorus source consists of diammonium hydrogen phosphate and ammonium phosphate in a mass ratio of 5:2; and the solvent consists of tetrahydrofuran and deionized water in a mass ratio of 6:1.

[0028] S2, calcining the mixture obtained in step S1 in a nitrogen atmosphere, wherein the calcination process conditions are: heating to 400° C. at a heating rate of 2.5° C. / min, maintaining for 120 min, and then heating to 800° C. at the same heating rate, maintaining for 3 h; obtaining a calcined product; S3. Wash the calcined product obtained in step S2 with deionized water, and then dry it at 80° C. for 20 hours to obtain a nitrogen-phosphorus co-doped carbon catalyst.

[0029] Example 2 S1. Dissolve 3 parts of a metal source, 4.8 parts of a nitrogen source, and 0.6 parts of a phosphorus source in 55 parts of a solvent, then add 7 parts of porous organic polyvinylbenzene, and stir at room temperature for 60 minutes, and then perform vacuum freeze drying. The process conditions of the vacuum freeze drying are: drying time is 24 hours, temperature is 40°C, and vacuum degree is 20Pa, to obtain a mixture, wherein the metal source consists of nickel oxalate and cobalt phthalocyanine in a mass ratio of 3:4; the nitrogen source consists of melamine and urea in a mass ratio of 3:5; the phosphorus source consists of diammonium hydrogen phosphate and ammonium phosphate in a mass ratio of 5:2; and the solvent consists of tetrahydrofuran and deionized water in a mass ratio of 6:1.

[0030] S2, calcining the mixture obtained in step S1 in a nitrogen atmosphere, wherein the calcination process conditions are: heating to 400° C. at a heating rate of 3° C. / min, maintaining for 120 min, and then heating to 850° C. at the same heating rate, maintaining for 2 h; obtaining a calcined product; S3. Wash the calcined product obtained in step S2 with deionized water, and then dry it at 100° C. for 12 hours to obtain a nitrogen and phosphorus co-doped carbon catalyst.

[0031] Example 3 S1. Dissolve 3 parts of a metal source, 4.8 parts of a nitrogen source, and 0.6 parts of a phosphorus source in 53 parts of a solvent, then add 7 parts of porous organic polyvinylbenzene, and stir at room temperature for 50 minutes, and then perform vacuum freeze drying. The process conditions of the vacuum freeze drying are: drying time is 21 hours, temperature is 40°C, and vacuum degree is 20Pa, to obtain a mixture, wherein the metal source consists of nickel oxalate and cobalt phthalocyanine in a mass ratio of 3:4; the nitrogen source consists of melamine and urea in a mass ratio of 3:5; the phosphorus source consists of diammonium hydrogen phosphate and ammonium phosphate in a mass ratio of 5:2; and the solvent consists of tetrahydrofuran and deionized water in a mass ratio of 6:1.

[0032] S2, calcining the mixture obtained in step S1 in a nitrogen atmosphere, wherein the calcination process conditions are: heating to 400° C. at a heating rate of 2.8° C. / min, maintaining for 120 min, and then heating to 830° C. at the same heating rate, maintaining for 2.5 h; obtaining a calcined product; S3. Wash the calcined product obtained in step S2 with deionized water, and then dry it at 90° C. for 16 hours to obtain a nitrogen-phosphorus co-doped carbon catalyst.

[0033] Comparative Example 1 The same as Example 3, except that the metal source is nickel oxalate.

[0034] Comparative Example 2 The same as Example 3, except that the metal source is cobalt phthalocyanine.

[0035] Comparative Example 3 The same as Example 3, except that the amount of metal source added is 0.

[0036] Comparative Example 4 The same as Example 3, except that the phosphorus source is diammonium hydrogen phosphate.

[0037] Comparative Example 5 Same as Example 3, except that the phosphorus source is ammonium phosphate.

[0038] Comparative Example 6 The porous organic polyvinylbenzene was calcined in a nitrogen atmosphere. The calcination process conditions were: heating at a heating rate of 2.8°C / min to 400°C, maintaining for 120 minutes, and then heating to 830°C at the same heating rate, maintaining for 2.5 hours, to obtain a porous carbon material.

[0039] Performance Testing The nitrogen and phosphorus co-doped carbon catalysts prepared in Examples 1 to 3 and Comparative Examples 1 to 5 and the porous carbon material of Comparative Example 6 were sampled and subjected to the following tests. The test results are shown in Table 1. Using N 2 The specific surface area, pore size and pore capacity of the prepared samples were tested by adsorption and desorption; Catalytic activity test: 0.5 g of benzyl alcohol, 0.05 g of nitrogen and phosphorus co-doped carbon catalyst (or porous carbon material of comparative example 6) and 5 mL of acetonitrile were placed in a high pressure reactor, and the reaction was carried out for 3 times. Finally, 0.5 MPa of oxygen was added, and the reaction was carried out in a 120°C oil bath for 12 hours. After the reaction was completed, the gas chromatography yield was measured.

[0040] Table 1 Performance test project Yield / % Average pore size / nm <![CDATA[Specific surface area (m 2 / g)]]> <![CDATA[Pore volume (cm 3 / g)]]> Example 1 93.1 3.85 1288 1.85 Example 2 93.7 4.27 1367 1.97 Example 3 94.2 4.65 1425 2.16 Comparative Example 1 83.4 3.54 1106 1.73 Comparative Example 2 88.6 3.67 1089 1.69 Comparative Example 3 65.6 3.79 1321 1.67 Comparative Example 4 89.7 3.57 1078 1.45 Comparative Example 5 86.3 3.12 923 1.36 Comparative Example 6 0.35 - - - Analyzing the data in Table 1, we can see that: 1) The nitrogen-phosphorus co-doped carbon catalysts prepared in Examples 1 to 3 have a large average pore size, which can provide more active sites and a larger reaction space; at the same time, they have a very large specific surface area and pore volume, so the nitrogen-phosphorus co-doped carbon catalyst has good catalytic activity, and is applied to the catalytic oxidation of benzyl alcohol into benzaldehyde. The reaction is carried out at 120°C for 12 hours, and the yield of benzaldehyde reaches more than 93%.

[0041] 2) The performance comparison analysis of the nitrogen-phosphorus co-doped carbon catalyst prepared in combination with Example 3 and Comparative Examples 1-2 shows that the metal source is composed of nickel oxalate and cobalt phthalocyanine in a mass ratio of 3:4. Nickel oxalate can be decomposed at high temperature to produce nickel oxide (NiO), and then reduced to metallic nickel (Ni) in a reducing atmosphere. Metallic nickel has good catalytic properties, especially in reactions such as hydrogenation, dehydrogenation, and oxidation. Cobalt phthalocyanine is a macrocyclic compound containing cobalt atoms and has a planar structure. Cobalt phthalocyanine can be decomposed at high temperature to produce cobalt oxide (CoO), and then reduced to metallic cobalt (Co) in a reducing atmosphere. Metallic cobalt also has good catalytic properties, especially in oxidation reactions. The synergistic effect between nickel oxalate and cobalt phthalocyanine is mainly reflected in the following aspects: Bimetallic effect: Nickel oxalate and cobalt phthalocyanine generate nickel oxide and cobalt oxide respectively at high temperature, and these two oxides can be reduced to metallic nickel and metallic cobalt in a reducing atmosphere. There may be an interaction between metallic nickel and metallic cobalt to form a bimetallic catalyst, thereby improving the catalytic activity. Electronic regulation: The doping of nickel and cobalt can adjust the electronic properties of carbon materials, causing the electron density on the surface of carbon materials to change, which is beneficial to the adsorption and activation of reactant molecules, thereby improving the catalytic activity. Increased active sites: The doping of nickel oxalate and cobalt phthalocyanine can increase the number of active sites on the surface of carbon materials, provide more reaction space, and is beneficial to the adsorption and activation of reactant molecules, thereby improving the catalytic activity. In summary, the metal source composed of nickel oxalate and cobalt phthalocyanine in a mass ratio of 3:4 played a key role in the preparation of nitrogen-phosphorus co-doped carbon catalysts, and the synergistic catalytic effect of nickel and cobalt further significantly improved the catalytic activity.

[0042] 3) The comparative analysis of the performance of the nitrogen-phosphorus co-doped carbon catalysts prepared in Example 3 and Comparative Example 3 shows that adding a metal source to the nitrogen-phosphorus co-doped carbon catalyst can significantly improve the catalytic activity of the nitrogen-phosphorus co-doped carbon catalyst.

[0043] 4) The performance comparison analysis of the nitrogen-phosphorus co-doped carbon catalysts prepared in combination with Example 3 and Comparative Examples 4-5 shows that the phosphorus source consists of diammonium hydrogen phosphate and ammonium phosphate in a mass ratio of 5:2. The synergistic effect between them is utilized to jointly provide phosphorus elements and adjust the pH value for the system, as well as to promote the reaction. During the sintering and pyrolysis process, the ammonia released by diammonium hydrogen phosphate and ammonium phosphate plays a pore-forming role, thereby increasing the pore size of the porous organic polyvinylbenzene, thereby increasing the specific surface area and pore volume of the catalyst, thereby effectively improving the performance of the nitrogen-phosphorus co-doped carbon catalyst.

[0044] The above embodiments are only used to explain the technical solutions of the present application rather than to limit them. Although the above embodiments provide a specific description of the present application, relevant technical personnel should understand that the specific implementation methods of the present application can still be modified or replaced by equivalents, and any modifications and equivalent replacements that do not depart from the spirit and scope of the present application should be included in the protection scope of the present application.

Claims

1. A method for preparing a nitrogen-phosphorus co-doped carbon catalyst, characterized in that: The following steps are involved: S1, preparing porous organic polyvinylbenzene; S2, dissolving a metal source, a nitrogen source, and a phosphorus source in a solvent, then adding porous organic polyvinylbenzene, stirring at room temperature for 40-60 minutes, and then performing vacuum freeze drying to obtain a mixture; S3, calcining the mixture obtained in step S2 in a nitrogen atmosphere to obtain a calcined product; S4. Wash the calcined product obtained in step S3 with deionized water, and then dry it at a temperature of 80-100° C. for 12-20 hours to obtain a nitrogen-phosphorus co-doped carbon catalyst.

2. The method for preparing a nitrogen-phosphorus co-doped carbon catalyst according to claim 1, characterized in that: In step S1, the method for preparing porous organic polyvinylbenzene comprises the following steps: S21. According to the mass fractions, 10 parts of divinylbenzene were placed in a pear-shaped separatory bucket, and washed three times with 5% potassium hydroxide solution and saturated ammonium chloride solution respectively, and the upper layer of yellow liquid was retained for later use; S22. According to the mass fractions, 3 parts of yellow liquid were put into a hydrothermal reactor, 0.075 parts of azobisisobutyronitrile were added, stirred at room temperature for 5-10 minutes, and then put into a 100°C oven to react for 24 hours. After the reaction was completed, it was cooled to room temperature, washed with ethanol 3 times, and vacuum dried at 80°C for 8-10 hours to obtain porous organic polyvinylbenzene.

3. The method for preparing a nitrogen-phosphorus co-doped carbon catalyst according to claim 1, characterized in that: In step S2, the metal source is composed of nickel oxalate and cobalt phthalocyanine in a mass ratio of 3:

4.

4. The method for preparing a nitrogen-phosphorus co-doped carbon catalyst according to claim 1, characterized in that: In step S2, the nitrogen source is composed of melamine and urea in a mass ratio of 3:

5.

5. The method for preparing a nitrogen-phosphorus co-doped carbon catalyst according to claim 1, characterized in that: In step S2, the solvent consists of tetrahydrofuran and deionized water in a mass ratio of 6:1, and the phosphorus source consists of diammonium hydrogen phosphate and ammonium phosphate in a mass ratio of 5:

2.

6. The method for preparing a nitrogen-phosphorus co-doped carbon catalyst according to claim 1, characterized in that: In step S2, the mass ratio of the metal source, the nitrogen source, the phosphorus source, the porous organic polyvinylbenzene and the solvent is 3:4.8:0.6:7:50-55.

7. The method for preparing a nitrogen-phosphorus co-doped carbon catalyst according to claim 1, characterized in that: In step S2, the process conditions of vacuum freeze drying are: drying time is 18-24h, temperature is 40°C, and vacuum degree is 20Pa.

8. The method for preparing a nitrogen and phosphorus co-doped carbon catalyst according to claim 1, characterized in that: In step S3, the calcination process conditions are: heating to 400°C at a heating rate of 2.5-3°C / min, maintaining for 120 minutes, and then heating to 800-850°C at the same heating rate, maintaining for 2-3 hours.

9. A nitrogen-phosphorus co-doped carbon catalyst, characterized in that: The nitrogen and phosphorus co-doped carbon catalyst is prepared by the preparation method of the nitrogen and phosphorus co-doped carbon catalyst according to any one of claims 1 to 8.

10. The nitrogen-phosphorus co-doped carbon catalyst according to claim 9, characterized in that: The nitrogen and phosphorus co-doped carbon catalyst has an average pore size of 3.85-4.65 nm and a specific surface area of ​​1288-1425 m 2 / g, pore volume is 1.85-2.16cm 3 / g.