A method for preparing and applying a nitrogen-doped carbon-encapsulated platinum catalyst

Abstract

This invention discloses a method for preparing and applying a nitrogen-doped carbon-encapsulated platinum catalyst. The preparation method comprises: Step 1: Weighing and mixing a soluble carbon source compound solution and a soluble nitrogen source compound solution, then adjusting the pH of the overall solution to 5 and stirring at room temperature for 1-3 hours to obtain a mixed solution; Step 2: Weighing a supported platinum catalyst and mixing it with a solvent; Step 3: Slowly adding the mixed solution dropwise to the mixture obtained in Step 2, dispersing it evenly, and then impregnating it at room temperature for 1-5 hours; Step 4: Heating and stirring the mixture obtained in Step 3 in a water bath, or performing a hydrothermal reaction, followed by vacuum drying; Step 5: Calcining the obtained product at high temperature under an inert protective atmosphere to obtain a nitrogen-doped carbon-encapsulated platinum catalyst. This invention provides the application of the prepared nitrogen-doped carbon-encapsulated platinum catalyst in the hydrogenation rearrangement of nitrobenzene to prepare p-aminophenol, exhibiting high stability, selectivity, and a fast reaction rate.

Description

Technical Field

[0001] This invention relates to a method for preparing a nitrogen-doped carbon-encapsulated platinum catalyst and its application in the hydrogenation rearrangement of nitrobenzene to prepare p-aminophenol. Technical Background

[0002] p-Aminophenol is an amphoteric compound, exhibiting both weak acidity and weak basicity. It is chemically reactive and is an important organic synthesis intermediate and chemical raw material, with wide applications in industries such as rubber, pharmaceuticals, and dyes.

[0003] Nitrobenzene undergoes catalytic hydrogenation to produce hydroxyaniline, which then undergoes a Bamberger rearrangement reaction in an acidic medium to generate p-aminophenol in one step. This process has broad industrial application prospects due to its advantages such as short process, low pollution, low energy consumption, and high yield. However, a drawback is the selectivity of the target product, p-aminophenol.

[0004] Currently, precious metal catalysts, such as palladium and platinum, are mainly used in industry for the hydrogenation of nitrobenzene to synthesize p-aminophenol in a 15%–20% sulfuric acid solution. However, under acidic conditions, the main active component of the catalyst, the precious metal, is easily lost in the strongly acidic reaction environment, leading to irreversible catalyst deactivation, severe equipment corrosion, industrial wastewater pollution, and high product recovery costs. Furthermore, the intermediate product phenylhydroxylamine may undergo further hydrogenation to generate the byproduct aniline, reducing the selectivity of p-aminophenol.

[0005] Preparing a carbon coating layer around a metal catalyst to encapsulate the catalytically active material can effectively prevent the loss of the active components. The appropriate carbon layer thickness is one of the key factors ensuring that the carbon layer can effectively exert its stabilizing effect while also protecting the active sites to effectively perform their catalytic function. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing a platinum-based catalyst with a nitrogen-doped carbon layer and its application in the hydrogenation rearrangement of nitrobenzene to prepare p-aminophenol. This catalyst exhibits high stability and selectivity and a fast reaction rate in the hydrogenation rearrangement of nitrobenzene to prepare p-aminophenol.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a method for preparing a nitrogen-doped carbon-encapsulated platinum catalyst for the hydrogenation rearrangement of nitrobenzene to prepare aminophenol, the method comprising:

[0009] Step 1: Weigh out a soluble carbon source compound solution with a concentration of 15-30 wt% and a soluble nitrogen source compound solution with a concentration of 5-10 wt% respectively, mix them evenly at a mass ratio of 5-20:1-10, then add an acidic aqueous solution with a mass fraction of 20%-35% to adjust the pH of the overall solution to 5, and stir at room temperature for 1-3 hours to obtain a mixed solution;

[0010] Step 2: Weigh the supported platinum catalyst, which includes a support and a metal active component supported on the support, wherein the metal active component is Pt, and mix it with the solvent until homogeneous.

[0011] Step 3: Slowly add the mixed solution obtained in Step 1 dropwise to the mixture obtained in Step 2, stir at room temperature for 1-5 hours, sonicate for 1-3 hours to disperse it evenly, and then soak at room temperature for 1-5 hours;

[0012] Step 4: Heat and stir the mixture obtained in Step 3 in a water bath at a temperature of 30–90°C for 3–10 hours; or pour the mixture obtained in Step 3 into a hydrothermal reactor for hydrothermal reaction at a temperature of 90–150°C for 10–20 hours; then dry under vacuum.

[0013] Step 5: The product obtained from vacuum drying in Step 4 is calcined at 400-800℃ for 2-10 hours under an inert protective atmosphere to obtain a nitrogen-doped carbon-encapsulated platinum catalyst.

[0014] Preferably, the soluble carbon source compound is at least one of glucose, sucrose, fructose, maltose, and xylose.

[0015] Preferably, the soluble nitrogen source compound is at least one of melamine, urea, glucosamine hydrochloride, and glycine.

[0016] Preferably, the acidic substance is selected from at least one of hydrochloric acid, sulfuric acid, oxalic acid, and acetic acid.

[0017] The supported platinum catalyst of this invention can be prepared in-house or a commercial catalyst can be selected. Preferably, the support for the supported platinum catalyst is activated carbon, TiO2, SiO2, or Al2O3. Preferably, the platinum loading relative to the support in the supported platinum catalyst is 0.5–5 wt%.

[0018] Preferably, in step 2, the solvent is water, and the feeding ratio of the supported platinum catalyst to water is 10g:40-60mL.

[0019] Preferably, the vacuum drying temperature in step 4 is 40–90°C, and the vacuum drying time is 2–30 hours.

[0020] Preferably, the inert protective atmosphere in step 5 is one or more of nitrogen, argon, and helium.

[0021] Secondly, the present invention provides the application of the nitrogen-doped carbon-encapsulated platinum catalyst prepared according to the preparation method in the preparation of p-aminophenol by hydrogenation rearrangement of nitrobenzene.

[0022] The specific method of the application is as follows: Distilled water, 98wt% concentrated sulfuric acid, nitrobenzene, surfactant, and nitrogen-doped carbon-coated platinum catalyst are added to an acid-resistant high-pressure reactor in a mass ratio of 200-500:10-50:20-50:0.2-1:1. Hydrogen gas is introduced and a hydrogenation rearrangement reaction is carried out under stirring conditions to obtain the target product p-aminophenol.

[0023] Preferably, the surfactant is hexadecyltrimethylammonium chloride.

[0024] Preferably, the reaction temperature is 60–90°C and the hydrogen pressure is 0.6–2.0 MPa.

[0025] This invention provides a method for preparing a nitrogen-doped carbon-coated platinum catalyst and its application in the hydrogenation of nitrobenzene to p-aminophenol. It is well known that when catalytic hydrogenation reactions are carried out in strongly acidic solvents, the active metal component of the catalyst is prone to dissolution and loss, leading to catalyst deactivation. The catalyst prepared by this invention is a nitrogen-doped carbon-coated noble metal supported catalyst with a core-shell structure at the microscopic level. The nitrogen-doped carbon layer makes it insoluble in strongly acidic solutions, thus protecting the active metal during catalytic reactions in strongly acidic media. The shell spatially isolates the metal nanoparticles, preventing their aggregation, sintering, and loss. Simultaneously, the nitrogen-doped carbon coating improves the overall conductivity and active sites of the material. In the nitrogen-doped carbon-coated structure, the doping of nitrogen not only increases the defects in the carbon layer, but also, because nitrogen atoms have one more electron than carbon atoms and have a high electron affinity, the carbon atoms near the nitrogen atom have a higher positive charge density. This also changes the electron density of the carbon layer, enhancing the electron transfer ability between systems, thereby regulating the catalytic activity and stability of the catalyst, making it particularly suitable for selective hydrogenation reactions.

[0026] Compared with the prior art, the present invention has the following advantages:

[0027] (1) The nitrogen-doped carbon-encapsulated platinum catalyst prepared in this invention has good stability in hydrogenation reactions in strong acid environments, and the preparation conditions are mild and the cost is low. Furthermore, the nitrogen-doped carbon layer has a suitable structure and thickness, which can maintain catalytic performance through the quantum tunneling effect.

[0028] (2) This invention uses a nitrogen-containing carbon source to form a nitrogen-doped carbon-coated structure, which increases the carbon layer defects and facilitates electron penetration and transport. At the same time, the carbon coating layer can improve the overall conductivity of the material and provide more active sites to maintain excellent catalytic performance.

[0029] (3) In the preparation process of this invention, different amounts of acidic substances are added. The addition of acid affects the solubility of carbon and nitrogen sources, producing a solvation effect that alters the stacking of the carbon layer after calcination, thereby controlling the crystallinity of carbon and thus affecting the activity of the catalyst. However, more acid is not necessarily better. Excessive acid may damage the structure of the carbon-nitrogen shell, leading to a decrease in catalytic activity. Therefore, there exists an optimal amount of acid added that can enable the carbon-nitrogen shell of the catalyst to achieve the best crystallinity and thus affect the catalytic activity.

[0030] (4) The reaction of nitrobenzene to prepare para-aminophenol by catalytic hydrogenation rearrangement under the action of nitrogen-doped carbon-encapsulated platinum catalyst has a faster reaction rate and better stability and target product selectivity compared with unencapsulated platinum catalyst. Attached Figure Description

[0031] Figure 1 This is a transmission electron microscope (TEM) image of the nitrogen-doped carbon-encapsulated platinum catalyst prepared in Example 5. Detailed Implementation

[0032] The technical solution of the present invention is illustrated below with specific embodiments, but the scope of protection of the present invention is not limited thereto:

[0033] The commercial catalysts used in the embodiments of this invention were all purchased from Shaanxi Ruike New Materials Co., Ltd.

[0034] Example 1

[0035] 15g of a 20wt% glucose aqueous solution and 8g of a 10wt% urea aqueous solution were prepared and mixed thoroughly. Then, a 25% hydrochloric acid aqueous solution was added to adjust the overall solution pH to 5, and the mixture was stirred at room temperature for 1 hour for acid treatment. 10g of commercial 3wt% Pt / C (Shaanxi Ruike New Material Co., Ltd. T3H3X-2 type) was weighed and added to 50ml of water and mixed thoroughly. The above mixed solution of soluble carbon and nitrogen sources was added dropwise to the metal catalyst dispersion, stirred at room temperature for 2 hours, sonicated for 1 hour to disperse, and then impregnated at room temperature for 2 hours. After heating and stirring in an 80℃ water bath for 7 hours, it was then vacuum dried at 70℃ for 16 hours, and finally calcined at 600℃ for 7 hours under a nitrogen atmosphere to obtain the nitrogen-doped carbon-encapsulated platinum catalyst.

[0036] Example 2

[0037] 20g of a 15wt% xylose aqueous solution and 10g of a 10wt% glucosamine hydrochloride aqueous solution were prepared and mixed thoroughly. Then, a 20% oxalic acid aqueous solution was added to adjust the overall solution pH to 5, and the mixture was stirred at room temperature for 2 hours for acid treatment. 10g of commercially available 1wt% Pt / Al₂O₃ was weighed and added to 50ml of water and mixed thoroughly. The above mixed solution of soluble carbon and nitrogen sources was added dropwise to the metal catalyst dispersion, stirred at room temperature for 3 hours, sonicated for 1.5 hours to disperse, and then impregnated at room temperature for 1.5 hours. After heating and stirring in a 70℃ water bath for 9 hours, it was then vacuum dried at 90℃ for 10 hours, and finally calcined at 500℃ for 8 hours under a nitrogen atmosphere to obtain a nitrogen-doped carbon-coated platinum catalyst.

[0038] Example 3

[0039] 15g of a 30wt% fructose aqueous solution and 4g of a 10wt% glycine aqueous solution were prepared and mixed thoroughly. The pH of the overall solution was then adjusted to 5 with a 27% oxalic acid aqueous solution and stirred at room temperature for 1.5 hours for acid treatment. 10g of commercially available 3wt% Pt / C (T3H3X-2 type, Shaanxi Ruike New Material Co., Ltd.) was weighed and added to 50ml of water and mixed thoroughly. The above mixed solution of soluble carbon and nitrogen sources was added dropwise to the metal catalyst dispersion and stirred at room temperature for 1.5 hours, then sonicated for 2.5 hours to disperse it, and impregnated at room temperature for 5 hours. After heating and stirring in a 60℃ water bath for 10 hours, it was vacuum dried at 90℃ for 8 hours, and then calcined at 700℃ for 5 hours under a nitrogen atmosphere to finally obtain a nitrogen-doped carbon-encapsulated platinum catalyst.

[0040] Example 4

[0041] 20g of a 25wt% sucrose ethanol solution and 10g of an 8wt% melamine ethanol solution were prepared and mixed thoroughly. Then, a 30% hydrochloric acid aqueous solution was added to adjust the overall solution pH to 5, and the mixture was stirred at room temperature for 3 hours for acid treatment. 10g of commercially available 5wt% Pt / Al₂O₃ was weighed and added to 50ml of water and mixed thoroughly. The above mixed solution of soluble carbon and nitrogen sources was added dropwise to the metal catalyst dispersion, stirred at room temperature for 5 hours, sonicated for 2 hours to disperse, and then impregnated at room temperature for 2 hours. The mixed solution was poured into a hydrothermal reactor and hydrothermally heated at 100℃ for 12 hours, then washed with ethanol and deionized water, vacuum dried at 60℃ for 17 hours, and then calcined at 450℃ for 10 hours under a nitrogen atmosphere to finally obtain the nitrogen-doped carbon-encapsulated platinum catalyst.

[0042] Example 5

[0043] 10g of a 20wt% glucose aqueous solution and 15g of a 6wt% glucosamine hydrochloride aqueous solution were prepared and mixed thoroughly. Then, a 30% sulfuric acid aqueous solution was added to adjust the overall solution pH to 5, and the mixture was stirred at room temperature for 2 hours for acid treatment. 10g of commercially available 3wt% Pt / C (T3H3X-2 type, Shaanxi Ruike New Material Co., Ltd.) was weighed and added to 50ml of water and mixed thoroughly. The above mixed solution of soluble carbon and nitrogen sources was added dropwise to the metal catalyst dispersion, stirred at room temperature for 3 hours, sonicated for 3 hours to disperse, and then impregnated at room temperature for 4 hours. The mixed solution was poured into a hydrothermal reactor and hydrothermally heated at 120℃ for 10 hours, then washed with ethanol and deionized water, vacuum dried at 80℃ for 15 hours, and then calcined at 500℃ for 8 hours under a nitrogen atmosphere to finally obtain a nitrogen-doped carbon-encapsulated platinum catalyst.

[0044] Example 6

[0045] 25g of a 20wt% sucrose aqueous solution and 5g of a 5wt% glycine aqueous solution were prepared and mixed thoroughly. Then, a 20% oxalic acid aqueous solution was added to adjust the overall solution pH to 5, and the mixture was stirred at room temperature for 2.5 hours for acid treatment. 10g of commercial 3wt% Pt / Al₂O₃ was weighed and added to 50ml of water and mixed thoroughly. The above mixed solution of soluble carbon and nitrogen sources was added dropwise to the metal catalyst dispersion, stirred at room temperature for 4 hours, sonicated for 1.5 hours to disperse, and then impregnated at room temperature for 4 hours. The mixed solution was poured into a hydrothermal reactor and hydrothermally heated at 90℃ for 15 hours. It was then washed with ethanol and deionized water, vacuum dried at 40℃ for 25 hours, and then calcined at 400℃ for 10 hours under a nitrogen atmosphere to finally obtain the nitrogen-doped carbon-encapsulated platinum catalyst.

[0046] Example 7

[0047] 250g distilled water, 20g 98wt% concentrated sulfuric acid, 30g nitrobenzene, 0.5g hexadecyltrimethylammonium chloride, and 1.0g nitrogen-doped carbon-coated platinum catalyst prepared in Example 1 were added to an acid-resistant high-pressure reactor. The reactor was then closed, and the air inside the reactor was replaced three times with nitrogen and then three times with hydrogen. The temperature was raised to 80℃ and the hydrogen pressure was 1.0MPa. Stirring was started at a speed of 1000r / min and the reaction was carried out for 80min. The reaction was stopped, and after the temperature dropped to room temperature, the reaction solution was removed, the catalyst was recovered by filtration, and the filtrate was analyzed by liquid chromatography. The conversion rate of nitrobenzene was 100wt%, and the selectivity for p-aminophenol was 84.8wt%.

[0048] Example 8

[0049] 200g distilled water, 30g 98wt% concentrated sulfuric acid, 25g nitrobenzene, 0.3g hexadecyltrimethylammonium chloride, and 1.0g nitrogen-doped carbon-coated platinum catalyst prepared in Example 2 were added to an acid-resistant high-pressure reactor. The reactor was then closed, and the air inside the reactor was replaced three times with nitrogen and then three times with hydrogen. The temperature was raised to 60℃ and the hydrogen pressure was 1.2MPa. Stirring was started at a speed of 1000r / min and the reaction was carried out for 80min. The reaction was stopped, and after the temperature dropped to room temperature, the reaction solution was removed, the catalyst was recovered by filtration, and the filtrate was analyzed by liquid chromatography. The conversion rate of nitrobenzene was 100wt%, and the selectivity for p-aminophenol was 84.5wt%.

[0050] Example 9

[0051] In an acid-resistant high-pressure reactor, 300g of distilled water, 25g of 98wt% concentrated sulfuric acid, 20g of nitrobenzene, 0.6g of hexadecyltrimethylammonium chloride, and 1.0g of the nitrogen-doped carbon-coated platinum catalyst prepared in Example 3 were added. The reactor was closed, and the air inside was replaced three times with nitrogen, followed by three times with hydrogen. The temperature was raised to 70℃ and the hydrogen pressure to 1.0MPa. Stirring was started at a rate of 1000r / min for 80min. The reaction was stopped, and after the temperature dropped to room temperature, the reaction solution was removed, and the catalyst was recovered by filtration. The filtrate was analyzed by liquid chromatography, showing a nitrobenzene conversion of 100wt% and a p-aminophenol selectivity of 84.2wt%. The recovered catalyst was reused in the experiment (catalyst replenishment method as in Table 1), under the same reaction conditions. After 10 catalyst reuses, the nitrobenzene conversion was 100wt%, and the p-aminophenol selectivity was 84.4wt%.

[0052] Example 10

[0053] In an acid-resistant high-pressure reactor, 240 g of distilled water, 20 g of 98 wt% concentrated sulfuric acid, 35 g of nitrobenzene, 0.4 g of hexadecyltrimethylammonium chloride, and 1.0 g of nitrogen-doped carbon-coated platinum catalyst prepared according to the above method were added. The reactor was then closed, and the air inside was replaced three times with nitrogen, followed by three times with hydrogen. The temperature was raised to 90 °C and the hydrogen pressure to 0.8 MPa. Stirring was started at a rate of 1000 r / min, and the reaction was allowed to proceed for 80 min. The reaction was then stopped, and after the temperature dropped to room temperature, the reaction solution was removed, and the catalyst was recovered by filtration. The filtrate was analyzed by liquid chromatography, showing a nitrobenzene conversion of 100 wt% and a p-aminophenol selectivity of 84.4 wt%. The recovered catalyst was reused in a repeated experiment (catalyst replenishment method as in Table 1), under the same reaction conditions. After 10 catalyst reuses, the nitrobenzene conversion reached 100 wt%, and the p-aminophenol selectivity was 83.9 wt%.

[0054] Example 11

[0055] In an acid-resistant high-pressure reactor, 220 g of distilled water, 15 g of 98 wt% concentrated sulfuric acid, 20 g of nitrobenzene, 0.6 g of hexadecyltrimethylammonium chloride, and 1.0 g of the nitrogen-doped carbon-coated platinum catalyst prepared in Example 5 were added. The reactor was closed, and the air inside was replaced three times with nitrogen, followed by three times with hydrogen. The temperature was raised to 80 °C and the hydrogen pressure to 0.7 MPa. Stirring was started at a rate of 1000 r / min, and the reaction was carried out for 80 min. The reaction was stopped, and after the temperature dropped to room temperature, the reaction solution was removed, and the catalyst was recovered by filtration. The filtrate was analyzed by liquid chromatography, and the conversion rate of nitrobenzene was 100 wt%, with a selectivity of 83.6 wt% for p-aminophenol. The recovered catalyst was reused in the experiment (catalyst replenishment method is the same as in Table 1), and the reaction conditions were the same as above. After 10 catalyst reuses, the conversion rate of nitrobenzene was 100 wt%, and the selectivity of p-aminophenol was 83.4 wt%.

[0056] Example 12

[0057] 250g distilled water, 20g 98wt% concentrated sulfuric acid, 30g nitrobenzene, 0.3g hexadecyltrimethylammonium chloride, and 1.0g nitrogen-doped carbon-coated platinum catalyst prepared in Example 6 were added to an acid-resistant high-pressure reactor. The reactor was then closed, and the air inside was replaced with nitrogen three times, followed by hydrogen three times. The temperature was raised to 65℃ and the hydrogen pressure to 1.1MPa. Stirring was started at a rate of 1000r / min, and the reaction was carried out for 80min. The reaction was stopped, and after the temperature dropped to room temperature, the reaction solution was removed, and the catalyst was recovered by filtration. The filtrate was analyzed by liquid chromatography. The recovered catalyst was reused in experiments under the same reaction conditions. The results are shown in Table 1.

[0058] Table 1. Application results of the catalyst prepared in Example 12

[0059]

[0060]

[0061] Comparative Example 1

[0062] Comparative Example 1 examined the performance of a carbon-coated platinum catalyst without nitrogen doping. Compared with Example 1, the conversion rate and selectivity were significantly reduced.

[0063] Prepare 15g of a 20wt% glucose aqueous solution, add 25% hydrochloric acid aqueous solution to adjust the overall solution pH to 5, mix thoroughly, and stir at room temperature for one hour. Weigh 10g of commercially available 3wt% Pt / C and add it to 50ml of water and mix thoroughly. Add the above soluble carbon source compound mixture to the solution and stir at room temperature for 2 hours, sonicate for 1 hour to disperse, and impregnate at room temperature for 2 hours. After stirring at 80℃ for 7 hours, dry under vacuum at 70℃ for 16 hours, and then calcine at 600℃ for 7 hours under nitrogen atmosphere to finally obtain the carbon-coated platinum catalyst.

[0064] 250g distilled water, 20g 98wt% concentrated sulfuric acid, 30g nitrobenzene, 0.5g hexadecyltrimethylammonium chloride, and 1.0g of the carbon-coated platinum catalyst prepared above were added to an acid-resistant high-pressure reactor. The reactor was closed, and the air inside the reactor was replaced three times with nitrogen and then three times with hydrogen. The temperature was raised to 80℃ and the hydrogen pressure was 1.0MPa. Stirring was started at a speed of 1000r / min and the reaction was carried out for 80min. The reaction was stopped, and after the temperature dropped to room temperature, the reaction solution was removed, the catalyst was recovered by filtration, and the filtrate was analyzed by liquid chromatography. The conversion rate of nitrobenzene was 79.38wt%, and the selectivity for p-aminophenol was 66.5wt%.

[0065] Comparative Example 2

[0066] Comparative Example 2 investigated the effect of acid treatment with different amounts of acid on catalyst activity. More acid is not necessarily better. Excessive acid may damage the structure of carbonitrides, leading to a decrease in catalytic activity.

[0067] Five aliquots of the same solution were prepared, each containing 15g of a 20wt% glucose aqueous solution and 8g of a 10wt% urea aqueous solution. Each aliquot was then treated with 25% hydrochloric acid to adjust the pH of the solutions to 7, 6, 5, 3, and 1, respectively. The aliquots were then thoroughly mixed and stirred at room temperature for 1 hour. 10g of commercially available 3wt% Pt / C was added to 50ml of water and mixed thoroughly. The mixture of the soluble carbon and nitrogen source compounds was added dropwise to the metal catalyst dispersion. The mixture was stirred at room temperature for 2 hours, sonicated for 1 hour to disperse the catalyst, and then impregnated at room temperature for 2 hours. After heating and stirring in an 80℃ water bath for 7 hours, the catalyst was vacuum dried at 70℃ for 16 hours, and then calcined at 600℃ for 7 hours under a nitrogen atmosphere. This yielded nitrogen-doped carbon-encapsulated platinum catalysts with different amounts of acid treatment.

[0068] 250g distilled water, 20g 98wt% concentrated sulfuric acid, 30g nitrobenzene, 0.5g hexadecyltrimethylammonium chloride, and 1.0g nitrogen-doped carbon-coated platinum catalyst prepared in Comparative Example 2 were added to an acid-resistant high-pressure reactor. The reactor was closed, and the air inside the reactor was replaced with nitrogen three times, followed by hydrogen three times. The temperature was raised to 80℃, and the hydrogen pressure was maintained at 1.0MPa. Stirring was started at a rate of 1000r / min until the reaction stopped. The reaction time was recorded. After the temperature dropped to room temperature, the reaction solution was removed, the catalyst was recovered by filtration, and the filtrate was analyzed by liquid chromatography. The results are shown in Table 2.

[0069] Table 2. Results of catalyst reaction in Comparative Example 2

[0070] Adjust pH Reaction time / min Nitrobenzene conversion rate / % p-Aminophenol selectivity / % 7 130 100 84.0 6 100 100 84.3 5 80 100 84.8 3 120 100 83.9 1 210 100 83.6

[0071] Comparative Example 3

[0072] Comparative Example 3 investigated the performance of a nitrogen-doped carbon-encapsulated platinum catalyst prepared by adding alkaline substances. Compared with Example 1, the catalyst had almost no activity.

[0073] 15g of a 20wt% glucose aqueous solution and 8g of a 10wt% urea aqueous solution were prepared and mixed thoroughly. Then, 50wt% NaOH was added to adjust the pH to 12, and the mixture was stirred at room temperature for 1 hour. 10g of commercially available 3wt% Pt / C was weighed and added to 50ml of water and mixed thoroughly. The above mixed solution of soluble carbon and nitrogen sources was added dropwise to the metal catalyst dispersion, stirred at room temperature for 2 hours, sonicated for 1 hour to disperse, and then impregnated at room temperature for 2 hours. After heating and stirring in an 80℃ water bath for 7 hours, it was then vacuum dried at 70℃ for 16 hours, and finally calcined at 600℃ for 7 hours under a nitrogen atmosphere to obtain the nitrogen-doped carbon-encapsulated platinum catalyst.

[0074] 250g of distilled water, 20g of 98wt% concentrated sulfuric acid, 30g of nitrobenzene, 0.5g of hexadecyltrimethylammonium chloride, and 1.0g of the catalyst prepared above were added to an acid-resistant high-pressure reactor. The reactor was then closed, and the air inside was replaced three times with nitrogen and then three times with hydrogen. The temperature was raised to 80℃, and the hydrogen pressure was maintained at 1.0MPa. Stirring was started at a speed of 1000r / min, and the reaction was carried out for 2 hours. The reaction was stopped, and after the temperature dropped to room temperature, the reaction solution was removed, and the catalyst was recovered by filtration. The filtrate was analyzed by liquid chromatography, and the conversion rate of nitrobenzene was only 3wt%, indicating that the catalyst had almost no activity.

[0075] Comparative Example 4

[0076] Comparative Example 4 investigated the performance of nitrogen-doped carbon-encapsulated catalysts prepared at lower calcination temperatures. Compared with Example 1, the catalysts prepared by calcining at lower temperatures were not fully carbonized, and both the conversion rate and selectivity decreased significantly.

[0077] 15g of a 20wt% glucose aqueous solution and 8g of a 10wt% urea aqueous solution were prepared and mixed evenly. Then, a 25% hydrochloric acid aqueous solution was added to adjust the overall solution pH to 5, and the mixture was stirred at room temperature for 1 hour for acid treatment. 10g of commercially available 3wt% Pt / C was weighed and added to 50ml of water and mixed evenly. This mixture was then added to the above-mentioned soluble carbon and nitrogen source compound mixture and stirred at room temperature for 2 hours, ultrasonicated for 1 hour to disperse it, and impregnated at room temperature for 2 hours. After stirring at 80℃ for 7 hours, it was vacuum dried at 70℃ for 16 hours, and then calcined at 200℃ for 7 hours under a nitrogen atmosphere to finally obtain a nitrogen-doped carbon-encapsulated platinum catalyst.

[0078] 250g distilled water, 20g 98wt% concentrated sulfuric acid, 30g nitrobenzene, 0.5g hexadecyltrimethylammonium chloride, and 1.0g of the nitrogen-doped carbon-coated platinum catalyst prepared above were added to an acid-resistant high-pressure reactor. The reactor was closed, and the air inside the reactor was replaced three times with nitrogen and then three times with hydrogen. The temperature was raised to 80℃ and the hydrogen pressure was 1.0MPa. Stirring was started at a speed of 1000r / min and the reaction was carried out for 80min. The reaction was stopped, and after the temperature dropped to room temperature, the reaction solution was removed, the catalyst was recovered by filtration, and the filtrate was analyzed by liquid chromatography. The conversion rate of nitrobenzene was 77.5wt%, and the selectivity for p-aminophenol was 47.3wt%.

[0079] Comparative Example 5

[0080] Comparative Example 5 investigated the performance of the uncoated carbon-supported platinum catalyst. Compared to Example 1, both conversion and selectivity decreased significantly.

[0081] In an acid-resistant high-pressure reactor, 250 g of distilled water, 20 g of 98 wt% concentrated sulfuric acid, 30 g of nitrobenzene, 0.5 g of hexadecyltrimethylammonium chloride, and 1.0 g of 1% commercial Pt / C catalyst were added. The reactor was then closed, and the air inside was replaced three times with nitrogen, followed by three times with hydrogen. The temperature was raised to 80 °C and the hydrogen pressure to 1.0 MPa. Stirring was started at a rate of 1000 r / min, and the reaction was allowed to proceed for 80 min. The reaction was then stopped, and the reaction solution was allowed to cool to room temperature. The reaction solution was removed, and the catalyst was recovered by filtration. The filtrate was analyzed by liquid chromatography. The recovered catalyst was reused in experiments under the same conditions, and the results are shown in Table 2.

[0082] Table 3 Commercial Pt / C Catalysts

[0083] Number of times to apply Catalyst replenishment Nitrobenzene conversion rate / % p-Aminophenol selectivity / % 1 1.0 93.5 42.7 2 0 91.4 42.0 3 0 84.6 41.3 4 0.05 78.7 42.1 5 0 69.9 41.5

[0084] 250g distilled water, 20g 98wt% concentrated sulfuric acid, 30g nitrobenzene, 0.5g hexadecyltrimethylammonium chloride, and 1.0g 3% commercial Pt / SiO2 catalyst were added to an acid-resistant high-pressure reactor. The reactor was then closed, and the air inside was replaced three times with nitrogen, followed by three times with hydrogen. The temperature was raised to 80℃ and the hydrogen pressure to 1.0MPa. Stirring was started at a rate of 1000 r / min, and the reaction was carried out for 80 min. The reaction was stopped, and after the temperature dropped to room temperature, the reaction solution was removed, and the catalyst was recovered by filtration. The filtrate was analyzed by liquid chromatography. The recovered catalyst was reused in experiments under the same conditions, and the results are shown in Table 3.

[0085] Table 4 Commercial Pt / SiO2 catalysts

[0086]

[0087]

[0088] 250g distilled water, 20g 98wt% concentrated sulfuric acid, 30g nitrobenzene, 0.5g hexadecyltrimethylammonium chloride, and 1.0g 5% commercial Pt / TiO2 catalyst were added to an acid-resistant high-pressure reactor. The reactor was then closed, and the air inside was replaced three times with nitrogen, followed by three times with hydrogen. The temperature was raised to 80℃ and the hydrogen pressure to 1.0MPa. Stirring was started at a rate of 1000 r / min, and the reaction was carried out for 80 min. The reaction was stopped, and after the temperature dropped to room temperature, the reaction solution was removed, and the catalyst was recovered by filtration. The filtrate was analyzed by liquid chromatography. The recovered catalyst was reused in experiments under the same conditions, and the results are shown in Table 4.

[0089] Table 5 Commercial Pt / TiO2 Catalysts

[0090] Number of times to apply Catalyst replenishment Nitrobenzene conversion rate / % p-Aminophenol selectivity / % 1 1.0 95.1 42.7 2 0 91.8 42.5 3 0 83.4 42.1 4 0.05 75.5 42.9 5 0 68.8 42.3

Claims

1. A method for preparing a nitrogen-doped carbon-encapsulated platinum catalyst for the hydrogenation rearrangement of nitrobenzene to aminophenol, characterized in that: The preparation method is as follows: Step 1: Weigh out a soluble carbon source compound solution with a concentration of 15-30 wt% and a soluble nitrogen source compound solution with a concentration of 5-10 wt% respectively, mix them evenly at a mass ratio of 5-20:1-10, then add an acidic aqueous solution with a mass fraction of 20%-35% to adjust the pH of the overall solution to 5, and stir at room temperature for 1-3 hours to obtain a mixed solution; Step 2: Weigh the supported platinum catalyst, which includes a support and a metal active component supported on the support, wherein the metal active component is Pt, and mix it with the solvent until homogeneous. Step 3: Slowly add the mixed solution obtained in Step 1 dropwise to the mixture obtained in Step 2, stir at room temperature for 1-5 hours, sonicate for 1-3 hours to disperse it evenly, and then soak at room temperature for 1-5 hours; Step 4: Heat and stir the mixture obtained in Step 3 in a water bath at a temperature of 30–90°C for 3–10 hours; or pour the mixture obtained in Step 3 into a hydrothermal reactor for hydrothermal reaction at a temperature of 90–150°C for 10–20 hours; then dry under vacuum. Step 5: The product obtained from vacuum drying in Step 4 is calcined at 400-800℃ for 2-10 hours under an inert protective atmosphere to obtain a nitrogen-doped carbon-encapsulated platinum catalyst.

2. The preparation method according to claim 1, characterized in that: The soluble carbon source compound is at least one of glucose, sucrose, fructose, maltose, and xylose; the soluble nitrogen source compound is at least one of melamine, urea, glucosamine hydrochloride, and glycine.

3. The preparation method according to claim 1, characterized in that: The acidic substance is selected from at least one of hydrochloric acid, sulfuric acid, oxalic acid, and acetic acid.

4. The preparation method according to claim 1, characterized in that: The supported platinum catalyst is supported on activated carbon, TiO2, SiO2 or Al2O3, and the loading of platinum relative to the support in the supported platinum catalyst is 0.5 to 5 wt%.

5. The preparation method according to claim 1, characterized in that: In step 2, the solvent is water, and the feeding ratio of the supported platinum catalyst to water is 10g:40-60mL.

6. The preparation method according to claim 1, characterized in that: The vacuum drying temperature in step 4 is 40–90°C, and the vacuum drying time is 2–30 hours.

7. The application of the nitrogen-doped carbon-encapsulated platinum catalyst prepared by the method according to any one of claims 1-6 in the preparation of p-aminophenol by hydrogenation rearrangement of nitrobenzene.

8. The application as described in claim 7, characterized in that: The specific method of the application is as follows: Distilled water, 98wt% concentrated sulfuric acid, nitrobenzene, surfactant, and nitrogen-doped carbon-coated platinum catalyst are added to an acid-resistant high-pressure reactor in a mass ratio of 200-500:10-50:20-50:0.2-1:

1. Hydrogen gas is introduced and a hydrogenation rearrangement reaction is carried out under stirring conditions to obtain the target product p-aminophenol.

9. The application as described in claim 8, characterized in that: The surfactant is hexadecyltrimethylammonium chloride.

10. The application as described in claim 8, characterized in that: The reaction temperature is 60–90°C, and the hydrogen pressure is 0.6–2.0 MPa.

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