Preparation method and application of nitrogen-doped carbon-coated platinum catalyst

Abstract

The invention discloses a preparation method and application of a nitrogen-doped carbon-coated platinum catalyst, and the preparation method comprises the following steps: 1, respectively weighing a soluble carbon source compound solution and a soluble nitrogen source compound solution, uniformly mixing, then adjusting the pH value of the whole solution to 5, and stirring at room temperature for 1-3 hours to obtain a mixed solution; 2, weighing a supported metal platinum catalyst, and uniformly stirring and mixing the supported metal platinum catalyst with a solvent; 3, slowly dropwise adding the mixed solution into the mixture obtained in the step 2, uniformly dispersing the mixed solution, and dipping at room temperature for 1-5 hours; 4, heating and stirring the mixture obtained in the step 3 in a water bath, or carrying out a hydrothermal reaction, and then carrying out vacuum drying; and 5, roasting the obtained product at a high temperature in an inert protective atmosphere to obtain the nitrogen-doped carbon-coated platinum catalyst. The invention provides the application of the prepared nitrogen-doped carbon-coated platinum catalyst in preparation of p-aminophenol through nitrobenzene hydrogenation rearrangement, and the nitrogen-doped carbon-coated platinum catalyst shows high stability and selectivity and is high in reaction rate.

Description

Technical Field

[0001] The invention relates to a preparation method of a nitrogen-doped carbon-wrapped platinum catalyst and application of the catalyst in preparing p-aminophenol by hydrogenation and rearrangement of nitrobenzene. Technical Background

[0002] Para-aminophenol is an amphoteric compound that is both weakly acidic and weakly alkaline, with relatively active chemical properties. It is an important organic synthesis intermediate and chemical raw material, and is widely used in the rubber, pharmaceutical, dye and other industries.

[0003] Nitrobenzene is catalytically hydrogenated to generate hydroxyaniline, and then a Bamberger rearrangement reaction occurs 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, less pollution, low energy consumption, and high yield. However, the disadvantage is that there is selectivity for the target product p-aminophenol.

[0004] At present, the industry mainly uses precious metals, such as palladium, platinum and other metal catalysts for nitrobenzene hydrogenation system, catalyzing nitrobenzene hydrogenation in 15% to 20% sulfuric acid solution to synthesize p-aminophenol. However, under acidic conditions, the main active component of the catalyst, the precious metal, is easily lost in the strongly acidic reaction environment, resulting in irreversible deactivation of the catalyst, serious equipment corrosion, industrial wastewater pollution, high product recovery costs and other problems. In addition, the intermediate product phenylhydroxylamine may also be further hydrogenated to produce a by-product aniline, which reduces the selectivity of p-aminophenol.

[0005] Preparing a carbon coating layer on the metal catalyst to cover the catalytically active substances can effectively prevent the loss of the active components of the catalyst. The appropriate thickness of the carbon layer is one of the key factors to ensure that the carbon layer can effectively play a stabilizing role while also having the protected active sites to effectively play a catalytic role. Summary of the invention

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

[0007] In order to achieve the above purpose, 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 preparing aminophenol by hydrogenation rearrangement of nitrobenzene, wherein the method comprises:

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

[0010] Step 2: weighing a supported metal platinum catalyst, wherein the supported platinum catalyst comprises a carrier and a metal active component supported on the carrier, wherein the metal active component is Pt, and stirring and mixing the supported metal platinum catalyst with a solvent;

[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 to 5 hours, ultrasonicate for 1 to 3 hours to make it evenly dispersed, and then immerse at room temperature for 1 to 5 hours;

[0012] Step 4: heating and stirring the mixture obtained in step 3 in a water bath at a temperature of 30 to 90° C. for 3 to 10 hours, or pouring the mixture obtained in step 3 into a hydrothermal kettle for hydrothermal reaction at a temperature of 90 to 150° C. for 10 to 20 hours; and then vacuum drying;

[0013] Step 5: The product obtained by vacuum drying in step 4 is calcined at 400-800° C. 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 at least one of hydrochloric acid, sulfuric acid, oxalic acid and acetic acid.

[0017] The supported metal platinum catalyst of the present invention can be prepared by oneself or selected from commercial catalysts. Preferably, the support of the supported platinum catalyst is activated carbon, TiO2, SiO2 or Al2O3. Preferably, the loading amount of platinum in the supported platinum catalyst relative to the support is 0.5-5wt%.

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

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

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

[0021] In a second aspect, the present invention provides the use of a nitrogen-doped carbon-wrapped platinum catalyst prepared according to the preparation method in the preparation of p-aminophenol by hydrogenation rearrangement of nitrobenzene.

[0022] The specific application method is: adding distilled water, 98wt% concentrated sulfuric acid, nitrobenzene, a surfactant, and a nitrogen-doped carbon-wrapped platinum catalyst in an acid-resistant high-pressure reactor in a mass ratio of 200-500:10-50:20-50:0.2-1:1, introducing hydrogen gas and performing a hydrogenation rearrangement reaction 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] The present invention provides a preparation method of a nitrogen-doped carbon-wrapped platinum catalyst and its application in the preparation of p-aminophenol by hydrogenation of nitrobenzene. It is well known that when a catalytic hydrogenation reaction needs to be carried out in a strongly acidic solvent, the active metal components of the catalyst are prone to dissolution and loss, resulting in catalyst deactivation. The catalyst prepared by the present invention has a nitrogen-containing carbon layer wrapping a noble metal-loaded catalyst, and is a shell-core structure at a microscopic level. The wrapping of the nitrogen-containing carbon layer makes it insoluble in a strongly acidic solution, thereby achieving the effect of protecting the active metal during the catalytic reaction in the strongly acidic solution medium. The shell layer spatially isolates the metal nanoparticles, avoiding the agglomeration, sintering and loss of the nanoparticles. At the same time, the nitrogen-doped carbon coating layer can improve the overall conductivity and active sites of the material. In the structure of the nitrogen-doped carbon coating, the doping of the nitrogen element can not only increase the defects of the carbon layer, but also because the nitrogen atom has one more extranuclear electron than the carbon atom and has a very high electron affinity, the carbon atoms near the nitrogen atom have a higher positive charge density, and also change the electron density of the carbon layer, enhance the electron transfer ability between the systems, thereby regulating the catalytic activity and stability of the catalyst, and is 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-wrapped platinum catalyst prepared by the present invention is covered by a nitrogen-doped carbon layer, has good stability in a hydrogenation reaction in a strong acid environment, has mild preparation conditions and low cost. In addition, the nitrogen-doped carbon layer has a suitable structure and thickness, and can maintain catalytic performance through the quantum tunneling effect.

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

[0029] (3) The present invention adds different amounts of acidic substances during the preparation process. The addition of acid will affect the solubility of the carbon source and nitrogen source substances, produce a solvation effect, change the stacking of the carbon layer after the catalyst is calcined, and thus adjust the crystallinity of the carbon and affect the activity of the catalyst. However, the amount of acid added is not necessarily the more the better. Excessive acid may destroy the structure of the carbon-nitrogen shell, resulting in reduced catalytic activity. Therefore, there is an optimal amount of acid added, which can enable the carbon-nitrogen shell of the catalyst to achieve the best crystallinity and thus affect the catalytic activity.

[0030] (4) The catalytic hydrogenation rearrangement of nitrobenzene to prepare p-aminophenol under the action of nitrogen-doped carbon-coated platinum catalyst used in the present invention has a faster reaction rate, better stability and target product selectivity than the platinum catalyst not coated with carbon. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a transmission electron microscope photograph of the nitrogen-doped carbon-wrapped platinum catalyst prepared in Example 5. DETAILED DESCRIPTION

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

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

[0034] Embodiment 1

[0035] 15g of 20wt% glucose aqueous solution and 8g of 10wt% urea aqueous solution were prepared and mixed evenly, and then a 25% mass fraction of hydrochloric acid aqueous solution was added to adjust the overall solution pH to 5 and stirred at room temperature for 1h for acid treatment. Weigh 10g of commercial 3wt% Pt / C (Shaanxi Ruike New Materials Co., Ltd. T3H3X-2 type), add it to 50ml water and mix evenly. The above-mentioned soluble carbon source and nitrogen source compound mixed solution was added drop by drop to the metal catalyst dispersion, stirred at room temperature for 2h, ultrasonicated for 1h to disperse it, and immersed at room temperature for 2h. After heating and stirring in a water bath at 80℃ for 7h, it was vacuum dried at 70℃ for 16h, and then heated to 600℃ under nitrogen atmosphere for high-temperature calcination for 7h, and finally a nitrogen-doped carbon-wrapped platinum catalyst was obtained.

[0036] Embodiment 2

[0037] Prepare 20g of 15wt% xylose aqueous solution and 10g of 10wt% glucosamine hydrochloride aqueous solution respectively and mix them evenly, then add 20% mass fraction of oxalic acid aqueous solution to adjust the overall solution pH to 5 and stir for 2h at room temperature for acid treatment. Weigh 10g of commercial 1wt% Pt / Al2O3 and add it to 50ml water and mix evenly. Add the above-mentioned soluble carbon source and nitrogen source compound mixed solution drop by drop into the metal catalyst dispersion, stir for 3h at room temperature, ultrasonicate for 1.5h to disperse it, and immerse it at room temperature for 1.5h. After heating and stirring in a 70℃ water bath for 9h, vacuum dry it at 90℃ for 10h, then heat it to 500℃ under nitrogen atmosphere for high-temperature calcination for 8h, and finally obtain nitrogen-doped carbon-wrapped platinum catalyst.

[0038] Embodiment 3

[0039] 15g of 30wt% fructose aqueous solution and 4g of 10wt% glycine aqueous solution were prepared and mixed evenly, and then 27% oxalic acid aqueous solution was used to adjust the pH of the overall solution to 5 and stirred at room temperature for 1.5h for acid treatment. Weigh 10g of commercial 3wt% Pt / C (Shaanxi Ruike New Materials Co., Ltd. T3H3X-2 type), add it to 50ml water and mix evenly. The above-mentioned soluble carbon source and nitrogen source compound mixed solution was added drop by drop to the metal catalyst dispersion and stirred at room temperature for 1.5h, ultrasonicated for 2.5h to disperse it, and immersed at room temperature for 5h. After heating and stirring in a 60℃ water bath for 10h, it was vacuum dried at 90℃ for 8h, and then heated to 700℃ under nitrogen atmosphere for high-temperature calcination for 5h, and finally a nitrogen-doped carbon-wrapped platinum catalyst was obtained.

[0040] Embodiment 4

[0041] Prepare 20g of 25wt% sucrose ethanol solution and 10g of 8wt% melamine ethanol solution respectively and mix them evenly, then add 30% hydrochloric acid aqueous solution to adjust the overall solution pH to 5 and stir at room temperature for 3h for acid treatment. Weigh 10g of commercial 5wt% Pt / Al2O3 and add it to 50ml water and mix evenly. Add the above-mentioned soluble carbon source and nitrogen source compound mixed solution drop by drop into the metal catalyst dispersion, stir at room temperature for 5h, ultrasonicate for 2h to disperse it, and immerse it at room temperature for 2h. Pour the mixed solution into a hydrothermal kettle and hydroheat at 100℃ for 12h, then wash it with ethanol and deionized water, dry it in vacuum at 60℃ for 17h, and then heat it to 450℃ under nitrogen atmosphere for high-temperature calcination for 10h to finally obtain nitrogen-doped carbon-wrapped platinum catalyst.

[0042] Embodiment 5

[0043] 10g of 20wt% glucose aqueous solution and 15g of 6wt% glucosamine hydrochloride aqueous solution were prepared and mixed evenly, and then 30% sulfuric acid aqueous solution was added to adjust the overall solution pH to 5 and stirred at room temperature for 2h for acid treatment. Weigh 10g of commercial 3wt% Pt / C (Shaanxi Ruike New Materials Co., Ltd. T3H3X-2 type), add it to 50ml water and mix evenly. The above-mentioned soluble carbon source and nitrogen source compound mixed solution was added drop by drop to the metal catalyst dispersion, stirred at room temperature for 3h, ultrasonicated for 3h to disperse it, and immersed at room temperature for 4h. Pour the mixed solution into a hydrothermal kettle and hydrotherm at 120℃ for 10h, then wash it with ethanol and deionized water, vacuum dry it at 80℃ for 15h, and then heat it to 500℃ under nitrogen atmosphere for high temperature calcination for 8h, and finally obtain nitrogen-doped carbon-wrapped platinum catalyst.

[0044] Embodiment 6

[0045] Prepare 25g of 20wt% sucrose aqueous solution and 5g of 5wt% glycine aqueous solution respectively and mix them evenly, then add 20% oxalic acid aqueous solution to adjust the overall solution pH to 5 and stir for 2.5h at room temperature for acid treatment. Weigh 10g of commercial 3wt% Pt / Al2O3 and add it to 50ml water and mix evenly. Add the above-mentioned soluble carbon source and nitrogen source compound mixed solution drop by drop into the metal catalyst dispersion, stir at room temperature for 4h, ultrasonicate for 1.5h to disperse it, and immerse it at room temperature for 4h. Pour the mixed solution into a hydrothermal kettle and hydroheat at 90℃ for 15h, then wash it with ethanol and deionized water, vacuum dry it at 40℃ for 25h, and then heat it to 400℃ under nitrogen atmosphere for high-temperature calcination for 10h to finally obtain a nitrogen-doped carbon-wrapped platinum catalyst.

[0046] Embodiment 7

[0047] 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 the nitrogen-doped carbon-wrapped platinum catalyst prepared in Example 1 were added, the reactor was closed, and the air in the reactor was replaced with nitrogen three times, and then replaced with hydrogen three times; the temperature was raised to 80° C. and the hydrogen pressure was 1.0 MPa, stirring was started, the stirring rate was 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 taken out, the catalyst was filtered and recovered, and the filtrate was analyzed by liquid chromatography, the nitrobenzene conversion rate was 100 wt %, and the p-aminophenol selectivity was 84.8 wt %.

[0048] Embodiment 8

[0049] In an acid-resistant high-pressure reactor, 200 g of distilled water, 30 g of 98 wt % concentrated sulfuric acid, 25 g of nitrobenzene, 0.3 g of hexadecyltrimethylammonium chloride, and 1.0 g of the nitrogen-doped carbon-wrapped platinum catalyst prepared in Example 2 were added, the reactor was closed, and the air in the reactor was replaced with nitrogen three times, and then replaced with hydrogen three times; the temperature was raised to 60° C. and the hydrogen pressure was 1.2 MPa, stirring was started, the stirring rate was 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 taken out, the catalyst was filtered and recovered, and the filtrate was analyzed by liquid chromatography, the nitrobenzene conversion rate was 100 wt %, and the p-aminophenol selectivity was 84.5 wt %.

[0050] Embodiment 9

[0051] 300g distilled water, 25g98wt% concentrated sulfuric acid, 20g nitrobenzene, 0.6g hexadecyltrimethylammonium chloride, 1.0g nitrogen-doped carbon-wrapped platinum catalyst prepared in Example 3 were added to an acid-resistant autoclave, the autoclave was closed, the air in the autoclave was replaced with nitrogen three times, and then replaced with hydrogen three times; the temperature was raised to 70°C, the hydrogen pressure was 1.0MPa, stirring was started, the stirring rate was 1000r / min, and the reaction time was 80min; the reaction was stopped, and after the temperature was reduced to room temperature, the reaction solution was taken out, the catalyst was filtered and recovered, and the filtrate was analyzed by liquid chromatography, and the nitrobenzene conversion rate was 100wt%, and the p-aminophenol selectivity was 84.2wt%. The recovered catalyst was continued to be applied (the catalyst addition method was the same as Table 1), and the reaction conditions were the same as above. After 10 times of catalyst application, the nitrobenzene conversion rate was 100wt%, and the p-aminophenol selectivity was 84.4wt%.

[0052] Embodiment 10

[0053] 240g distilled water, 20g98wt% concentrated sulfuric acid, 35g nitrobenzene, 0.4g hexadecyltrimethylammonium chloride, 1.0g nitrogen-doped carbon-wrapped platinum catalyst prepared in the fourth embodiment were added to an acid-resistant autoclave, the reactor was closed, the air in the reactor was replaced with nitrogen three times, and then replaced with hydrogen three times; the temperature was raised to 90°C, the hydrogen pressure was 0.8MPa, stirring was started, the stirring rate was 1000r / min, and the reaction time was 80min; the reaction was stopped, and after the temperature was reduced to room temperature, the reaction solution was taken out, the catalyst was filtered and recovered, and the filtrate was analyzed by liquid chromatography, and the nitrobenzene conversion rate was 100wt%, and the p-aminophenol selectivity was 84.4wt%. The recovered catalyst was continued to be applied to the experiment (the catalyst addition method was the same as Table 1), and the reaction conditions were the same as above. After 10 times of catalyst application, the nitrobenzene conversion rate was 100wt%, and the p-aminophenol selectivity was 83.9wt%.

[0054] Embodiment 11

[0055] 220g distilled water, 15g98wt% concentrated sulfuric acid, 20g nitrobenzene, 0.6g hexadecyltrimethylammonium chloride, 1.0g nitrogen-doped carbon-wrapped platinum catalyst prepared in Example 5 were added to an acid-resistant autoclave, the autoclave was closed, the air in the autoclave was replaced with nitrogen three times, and then replaced with hydrogen three times; the temperature was raised to 80°C, the hydrogen pressure was 0.7MPa, stirring was started, the stirring rate was 1000r / min, and the reaction time was 80min; the reaction was stopped, and after the temperature was lowered to room temperature, the reaction solution was taken out, the catalyst was filtered and recovered, and the filtrate was analyzed by liquid chromatography, and the nitrobenzene conversion rate was 100wt%, and the p-aminophenol selectivity was 83.6wt%. The recovered catalyst was continued to be applied to the experiment (the catalyst addition method was the same as Table 1), and the reaction conditions were the same as above. After 10 times of catalyst application, the nitrobenzene conversion rate was 100wt%, and the p-aminophenol selectivity was 83.4wt%.

[0056] Embodiment 12

[0057] In an acid-resistant high-pressure reactor, 250 g of distilled water, 20 g of 98 wt% concentrated sulfuric acid, 30 g of nitrobenzene, 0.3 g of hexadecyltrimethylammonium chloride, and 1.0 g of the nitrogen-doped carbon-encapsulated platinum catalyst prepared in Example VI were added, the reactor was closed, and the air in the reactor was replaced with nitrogen three times, and then replaced with hydrogen three times; the temperature was raised to 65° C. and the hydrogen pressure was 1.1 MPa, stirring was started, the stirring rate was 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 taken out, the catalyst was filtered and recovered, the filtrate was analyzed by liquid chromatography, and the recovered catalyst was continued to be applied to the experiment, the reaction conditions were the same as above, and the results are shown in Table 1.

[0058] Table 1 Application results of Example 12 Preparation of catalyst

[0059]

[0060]

[0061] Comparative Example 1

[0062] Comparative Example 1 examines the performance of the non-nitrogen-doped carbon-wrapped platinum catalyst. Compared with Example 1, the conversion rate and selectivity are greatly reduced.

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

[0064] 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 the carbon-encapsulated platinum catalyst prepared above were added, the reactor was closed, and the air in the reactor was replaced with nitrogen three times, and then replaced with hydrogen three times; the temperature was raised to 80° C. and the hydrogen pressure was 1.0 MPa, and stirring was started at a stirring 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 taken out, the catalyst was filtered and recovered, and the filtrate was analyzed by liquid chromatography, the nitrobenzene conversion rate was 79.38 wt %, and the p-aminophenol selectivity was 66.5 wt %.

[0065] Comparative Example 2

[0066] Comparative Example 2 investigates the effect of adding different amounts of acid for acid treatment on the catalyst activity. The amount of acid added is not necessarily the more the better. Excessive acid may destroy the structure of the carbonitride, resulting in reduced catalytic activity.

[0067] 15g of 20wt% glucose aqueous solution and 8g of 10wt% urea aqueous solution were prepared and mixed evenly. Five portions of the same solution were prepared, and then acid-treated with 25% hydrochloric acid aqueous solution, and the pH of the overall solution was adjusted to 7, 6, 5, 3, and 1, respectively. Mix evenly and stir at room temperature for 1h. Weigh 10g of commercially available 3wt% Pt / C, add it to 50ml of water and mix evenly. The above-mentioned soluble carbon source and nitrogen source compound mixed solution was added drop by drop to the metal catalyst dispersion, stirred at room temperature for 2h, ultrasonicated for 1h to disperse it, and immersed at room temperature for 2h. After heating and stirring in a water bath at 80℃ for 7h, it was vacuum dried at 70℃ for 16h, and then heated to 600℃ under nitrogen atmosphere for high-temperature calcination for 7h, and finally nitrogen-doped carbon-wrapped platinum catalysts with different amounts of acid treatment were obtained.

[0068] 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 the nitrogen-doped carbon-wrapped platinum catalyst prepared in Comparative Example 2 were added, the reactor was closed, and the air in the reactor was replaced with nitrogen three times, and then replaced with hydrogen three times; the temperature was raised to 80°C, the hydrogen pressure was maintained at 1.0 MPa, stirring was started, and the stirring rate was 1000 r / min until the reaction stopped, the reaction time was recorded, and after the temperature dropped to room temperature, the reaction solution was taken out, the catalyst was filtered and recovered, and the filtrate was analyzed by liquid chromatography. The results are shown in Table 2.

[0069] Table 2 Comparative Example 2 Catalyst Reaction Results

[0070] Adjust pH Reaction time / min Nitrobenzene conversion rate / % Selectivity for aminophenol / % 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 the nitrogen-doped carbon-wrapped platinum catalyst prepared by adding alkaline substances. Compared with Example 1, the catalyst had almost no activity.

[0073] Prepare 15g of 20wt% glucose aqueous solution and 8g of 10wt% urea aqueous solution respectively and mix them evenly, then add 50wt% NaOH to adjust the pH to 12, and stir at room temperature for 1h. Weigh 10g of commercially available 3wt% Pt / C, add it to 50ml water and mix evenly. Add the above-mentioned soluble carbon source and nitrogen source compound mixed solution drop by drop into the metal catalyst dispersion, stir at room temperature for 2h, ultrasonicate for 1h to disperse it, and immerse it at room temperature for 2h. After heating and stirring in an 80℃ water bath for 7h, vacuum dry it at 70℃ for 16h, then heat it to 600℃ under nitrogen atmosphere for high-temperature calcination for 7h to finally obtain a nitrogen-doped carbon-encapsulated platinum catalyst.

[0074] 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 the catalyst prepared above were added to an acid-resistant high-pressure reactor, the reactor was closed, and the air in the reactor was replaced with nitrogen three times, and then replaced with hydrogen three times; the temperature was raised to 80° C., the hydrogen pressure was maintained at 1.0 MPa, stirring was started, the stirring rate was 1000 r / min, and the reaction was carried out for 2 h; the reaction was stopped, and after the temperature dropped to room temperature, the reaction liquid was taken out, the catalyst was filtered and recovered, and the filtrate was analyzed by liquid chromatography. The nitrobenzene conversion rate was only 3 wt %, indicating that the catalyst was almost inactive.

[0075] Comparative Example 4

[0076] Comparative Example 4 investigated the performance of the nitrogen-doped carbon-encapsulated catalyst prepared at a lower calcination temperature. Compared with Example 1, the nitrogen-doped carbon-encapsulated catalyst was calcined at a lower temperature, the catalyst was not fully carbonized, and the conversion rate and selectivity were significantly reduced.

[0077] Prepare 15g of 20wt% glucose aqueous solution and 8g of 10wt% urea aqueous solution respectively and mix them evenly, then add 25% hydrochloric acid aqueous solution to adjust the overall solution pH to 5, and stir at room temperature for 1h for acid treatment. Weigh 10g of commercially available 3wt% Pt / C, add it to 50ml water and mix evenly. Add to the above-mentioned soluble carbon source and nitrogen source compound mixed solution and stir at room temperature for 2h, ultrasonic for 1h to disperse it, and immerse at room temperature for 2h. After stirring at 80℃ for 7h, vacuum dry at 70℃ for 16h, then heat to 200℃ under nitrogen atmosphere for high-temperature calcination for 7h to finally obtain nitrogen-doped carbon-wrapped platinum catalyst.

[0078] 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 the nitrogen-doped carbon-wrapped platinum catalyst prepared above were added, the reactor was closed, and the air in the reactor was replaced with nitrogen three times, and then replaced with hydrogen three times; the temperature was raised to 80° C. and the hydrogen pressure was 1.0 MPa, and stirring was started at a stirring 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 taken out, the catalyst was filtered and recovered, and the filtrate was analyzed by liquid chromatography, the nitrobenzene conversion rate was 77.5 wt %, and the p-aminophenol selectivity was 47.3 wt %.

[0079] Comparative Example 5

[0080] Comparative Example 5 investigated the performance of a supported platinum catalyst without carbon coating. Compared with Example 1, both the conversion rate and the selectivity decreased significantly.

[0081] Add 250g of distilled water, 20g of 98wt% concentrated sulfuric acid, 30g of nitrobenzene, 0.5g of hexadecyltrimethylammonium chloride, and 1.0g of 1% commercial Pt / C catalyst to an acid-resistant high-pressure reactor, close the reactor, replace the air in the reactor with nitrogen three times, and then replace it with hydrogen three times; raise the temperature to 80°C, the hydrogen pressure to 1.0MPa, start stirring, the stirring rate is 1000r / min, and the reaction is 80min; stop the reaction, wait until the temperature drops to room temperature, take out the reaction liquid, filter and recover the catalyst, and analyze the filtrate by liquid chromatography. The recovered catalyst continues to be used in the experiment, the reaction conditions are the same as above, and the results are shown in Table 2.

[0082] Table 3 Commercial Pt / C catalysts

[0083] Number of applications Catalyst addition amount Nitrobenzene conversion rate / % Selectivity for aminophenol / % 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] Add 250g distilled water, 20g 98wt% concentrated sulfuric acid, 30g nitrobenzene, 0.5g hexadecyltrimethylammonium chloride, 1.0g 3% commercial Pt / SiO2 catalyst into an acid-resistant high-pressure reactor, close the reactor, replace the air in the reactor with nitrogen three times, and then replace it with hydrogen three times; raise the temperature to 80°C, the hydrogen pressure to 1.0MPa, start stirring, the stirring rate is 1000r / min, and the reaction is 80min; stop the reaction, wait until the temperature drops to room temperature, take out the reaction liquid, filter and recover the catalyst, and analyze the filtrate by liquid chromatography. The recovered catalyst continues to be used in the experiment, the reaction conditions are the same as above, and the results are shown in Table 3.

[0085] Table 4 Commercial Pt / SiO2 catalysts

[0086]

[0087]

[0088] Add 250g distilled water, 20g 98wt% concentrated sulfuric acid, 30g nitrobenzene, 0.5g hexadecyltrimethylammonium chloride, 1.0g 5% commercial Pt / TiO2 catalyst into an acid-resistant high-pressure reactor, close the reactor, replace the air in the reactor with nitrogen three times, and then replace it with hydrogen three times; raise the temperature to 80°C, the hydrogen pressure to 1.0MPa, start stirring, the stirring rate is 1000r / min, and the reaction is 80min; stop the reaction, wait until the temperature drops to room temperature, take out the reaction liquid, filter and recover the catalyst, and analyze the filtrate by liquid chromatography. The recovered catalyst continues to be used in the experiment, the reaction conditions are the same as above, and the results are shown in Table 4.

[0089] Table 5 Commercial Pt / TiO2 catalysts

[0090] Number of applications Catalyst addition amount Nitrobenzene conversion rate / % Selectivity for aminophenol / % 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-coated platinum catalyst for preparing aminophenol by hydrogenation rearrangement of nitrobenzene, characterized in that: The preparation method is: Step 1: Weigh a soluble carbon source compound solution with a concentration of 15-30wt% and a soluble nitrogen source compound solution with a concentration of 5-10wt% respectively, mix them evenly in a mass ratio of 5-20:1-10, then add an acidic substance aqueous solution with a mass fraction of 20%-35% to adjust the overall solution pH to 5, and stir at room temperature for 1-3h to obtain a mixed solution; Step 2: weighing a supported metal platinum catalyst, wherein the supported platinum catalyst comprises a carrier and a metal active component supported on the carrier, wherein the metal active component is Pt, and stirring and mixing the supported metal platinum catalyst with a solvent; 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 to 5 hours, ultrasonicate for 1 to 3 hours to make it evenly dispersed, and then immerse at room temperature for 1 to 5 hours; Step 4: heating and stirring the mixture obtained in step 3 in a water bath at a temperature of 30 to 90° C. for 3 to 10 hours, or pouring the mixture obtained in step 3 into a hydrothermal kettle for hydrothermal reaction at a temperature of 90 to 150° C. for 10 to 20 hours; and then vacuum drying; Step 5: The product obtained by vacuum drying in step 4 is calcined at 400-800° C. 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 carrier of the supported platinum catalyst is activated carbon, TiO2, SiO2 or Al2O3, and the loading amount of platinum in the supported platinum catalyst relative to the carrier is 0.5-5wt%.

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

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

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

8. The use according to claim 7, characterized in that: The specific application method is: adding distilled water, 98wt% concentrated sulfuric acid, nitrobenzene, a surfactant, and a nitrogen-doped carbon-wrapped platinum catalyst in an acid-resistant high-pressure reactor in a mass ratio of 200-500:10-50:20-50:0.2-1:1, introducing hydrogen gas and performing a hydrogenation rearrangement reaction under stirring conditions to obtain the target product, p-aminophenol.

9. The use according to claim 8, characterized in that: The surfactant is hexadecyltrimethylammonium chloride.

10. The use according to 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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