A magnetically separable carbon-supported platinum cluster catalyst, its preparation method and application

Abstract

This invention relates to the field of catalysts for the hydrogenation of nitrobenzene to aniline, specifically disclosing a magnetically separable carbon-supported platinum cluster catalyst, its preparation method, and its applications. The magnetically separable carbon-supported platinum cluster catalyst comprises platinum nanoparticles as the active component and a nickel-coated nitrogen-doped graphene composite material as the support. The nickel-coated nitrogen-doped graphene composite material has a core-shell structure, with platinum nanoparticles uniformly loaded in clusters on the surface of the nitrogen-doped graphene, bonding with carbon and nitrogen atoms on graphene defects. The high utilization rate of platinum atoms enables efficient hydrogenation of nitrobenzene even at low loading levels, while also making the catalyst structure more stable. The support surface has abundant carbon defects and oxygen-containing functional groups, which facilitates the anchoring of platinum nanoparticles to the support surface through strong interactions between the metal and the support. The magnetic nickel nanoparticles impart a certain degree of magnetism to the catalyst, allowing for dispersion and recovery of the catalyst simply by removing and applying a magnetic field.

Description

Technical Field

[0001] This invention relates to the field of catalysts for the hydrogenation of nitrobenzene to aniline, and particularly to a magnetically separable carbon-supported platinum cluster catalyst, its preparation method, and its application. Background Technology

[0002] Aniline is an important chemical raw material with wide applications in rubber, textiles, and pharmaceuticals. As a raw material for various industries, the demand and growth rate of aniline are closely related to my country's economic development. In recent years, the aniline market has been highly competitive, with foreign companies possessing significant advantages in quality, technology, and brand, especially companies from Japan, South Korea, and the United States, which hold a certain market share in China. Therefore, improving cost reduction and efficiency is of positive significance for the aniline chemical industry. Currently, the main production processes for aniline include iron powder reduction, phenol reduction, nitrobenzene catalytic hydrogenation, and direct benzene amination. Among these, the nitrobenzene liquid-phase hydrogenation method has advantages such as low pollution, high capacity, and low investment costs, and is widely adopted by many companies. However, the liquid-phase hydrogenation method suffers from problems such as difficulty in separating the catalyst from the liquid phase, low catalytic selectivity, harsh catalytic hydrogenation reaction conditions, short catalyst cycle life, and high catalyst cost. Therefore, there is an urgent need to find a nitrobenzene hydrogenation catalyst that is easy to separate from the liquid phase, recyclable, has high catalytic selectivity, mild catalytic hydrogenation reaction conditions, and low cost. Summary of the Invention

[0003] To address the aforementioned problems, this invention provides a magnetically separable carbon-supported platinum cluster catalyst, its preparation method, and its application. The magnetically separable carbon-supported platinum cluster catalyst provided by this invention achieves magnetic separability through the use of the magnetic material nickel, allowing for multiple cycles and extended lifespan; it also features high catalytic selectivity, mild catalytic hydrogenation reaction conditions, and low cost.

[0004] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0005] In a first aspect, the present invention provides a magnetically separable carbon-supported platinum cluster catalyst, comprising an active component and a support; wherein the active component is platinum nanoparticles and the support is a nitrogen-doped graphene composite material coated with nickel;

[0006] The nickel-coated nitrogen-doped graphene composite material has a core-shell structure, with nitrogen-doped graphene as the shell and nickel nanoparticles as the metal core; the platinum nanoparticles are uniformly loaded on the surface of the nitrogen-doped graphene in the form of clusters and bonded to carbon and nitrogen atoms on graphene defects.

[0007] Compared to existing technologies, the magnetically separable carbon-supported platinum cluster catalyst provided by this invention has platinum nanoparticles as the active component, which are loaded onto the support surface in a cluster form. This increases the specific surface area of ​​the active component platinum and allows it to bond with carbon and nitrogen atoms on graphene defects, improving the utilization rate of platinum atoms. This enables the catalyst to achieve efficient hydrogenation of nitrobenzene even with low loading, while also making the structure of the magnetically separable carbon-supported platinum cluster catalyst more stable. The support is a nickel-coated nitrogen-doped graphene composite material with abundant carbon defects and oxygen-containing functional groups on its surface, which facilitates the anchoring of platinum nanoparticles to the support surface through strong interactions between the metal and the support. The presence of nitrogen not only bonds with the active component platinum but also increases the distance between graphene layers, making it less prone to aggregation. The magnetic nickel nanoparticles give the catalyst a certain degree of magnetism, allowing for dispersion and recovery of the catalyst simply by removing and applying a magnetic field. This simplifies the centrifugation and filtration processes of traditional catalysts, preventing aggregation during repeated use of the catalyst and simplifying the production process, thus saving costs. The support has a core-shell structure, in which nickel nanoparticles are encapsulated and protected by the shell, making them less prone to loss. Furthermore, there is a strong interaction between the core and the shell, which gives the support high stability. The magnetically separable carbon-supported platinum cluster catalyst still has high activity even after repeated use.

[0008] Furthermore, the magnetically separable carbon-supported platinum cluster catalyst provided by this invention can completely convert nitrobenzene into aniline at room temperature, with mild catalytic conditions and good catalytic activity; it is environmentally friendly and efficient, and the catalyst is easy and convenient to recover.

[0009] Preferably, the loading of the platinum nanoparticles is 0.1 wt% to 1 wt%.

[0010] Preferably, the nickel nanoparticles account for 20% to 40% of the mass of the carrier.

[0011] Preferably, the particle size of the platinum nanoparticle clusters is 1–5 nm.

[0012] Preferably, the nickel nanoparticles have a particle size of 2–20 nm.

[0013] Secondly, the present invention provides a method for preparing the above-mentioned magnetically separable carbon-supported platinum cluster catalyst, comprising the following steps:

[0014] S1, Add nickel salt and aminocarboxylic acid organic chelating agent to water, mix evenly, and carry out complexation reaction to obtain nickel complex;

[0015] S2, In an inert atmosphere, the nickel complex is calcined at 500-800°C to obtain a nickel-coated nitrogen-doped graphene composite material.

[0016] S3, add the nickel-coated nitrogen-doped graphene composite material to water, mix evenly, add a reducing agent and a platinum source to the resulting suspension, and react to obtain a catalyst precursor;

[0017] S4. Under a reducing atmosphere, the catalyst precursor is reduced and activated to obtain a magnetically separable carbon-supported platinum cluster catalyst.

[0018] Compared to existing technologies, the method for preparing magnetically separable carbon-supported platinum cluster catalyst provided by this invention uses an aminocarboxylic acid organic chelating agent as the carbon and nitrogen source. First, nickel ions are complexed onto the aminocarboxylic acid organic chelating agent. Then, through calcination, the nickel ions in the nickel complex are reduced to elemental nickel. Under the action of elemental nickel and specific high temperatures, the aminocarboxylic acid organic chelating agent is further carbonized to form a nitrogen-doped graphene-like structure, encapsulating elemental nickel within it, forming a unique structured nitrogen-doped graphene composite material (i.e., a support). Then, through deposition and precipitation... The method involves uniformly depositing a platinum source in the form of a precipitate onto the surface of a nickel-coated nitrogen-doped graphene composite material. Finally, under a reducing atmosphere, the catalyst precursor is reduced and activated, and platinum ions are reduced to elemental platinum, which then bonds with carbon and nitrogen atoms on graphene defects. This anchors the metallic platinum in the form of clusters on the support, increasing the specific surface area of ​​the active component platinum while making the structure of the magnetically separable carbon-supported platinum cluster catalyst more stable. Even with a small amount of active component platinum (0.1wt% to 1wt%), it can still exert a good catalytic effect.

[0019] Furthermore, the preparation method of the magnetically separable carbon-supported platinum cluster catalyst provided by this invention uses readily available and simple raw materials, is easy to operate, is suitable for large-scale production, and has significant economic benefits and market value.

[0020] Preferably, in step S1, the nickel salt is at least one of nickel hydroxide, nickel chloride, nickel nitrate, or nickel sulfate, and more preferably nickel hydroxide.

[0021] Preferably, in step S1, the aminocarboxylic acid organic chelating agent is at least one of ethylenediaminetetraacetic acid or propylenediaminetetraacetic acid.

[0022] Preferably, in step S1, the molar ratio of the nickel salt to the aminocarboxylic acid organic chelating agent is 1:(0.5-4).

[0023] This invention controls the nickel content in the support (nitrogen-doped graphene composite material coated with nickel) by limiting the molar ratio of nickel salt and aminocarboxylic acid organic chelating agent. This results in a magnetically separable carbon-supported platinum cluster catalyst with appropriate magnetic properties, allowing for separation of the catalyst from the reaction solution via an external magnetic field, thus enabling catalyst recovery and reuse. This invention does not specify the amount of water used; conventional amounts used in this field are sufficient.

[0024] Preferably, in step S1, the temperature of the complexation reaction is 50–100°C, and the reaction time is 50–80 min.

[0025] This invention allows the complexation reaction to proceed more fully and improves reaction efficiency by controlling the conditions of the complexation reaction.

[0026] For example, in step S1, after the complexation reaction is completed, the reaction product also needs to be dried and ground.

[0027] For example, in step S1, the particle size of the nickel complex is 200-500 mesh.

[0028] Preferably, in step S2, the gas flow rate of the inert atmosphere is 50-100 mL / min.

[0029] Preferably, in step S2, the calcination temperature is increased to 500-700°C at a rate of 2-10°C / min, and the holding time is 1-3 hours.

[0030] By controlling the calcination conditions, this invention facilitates the carbonization of aminocarboxylic acid organic chelating agents under the action of elemental nickel, forming a nitrogen-doped graphene-like structure, and encapsulating elemental nickel within it, thus forming a nitrogen-doped graphene composite material with a core-shell structure and coated nickel.

[0031] For example, in step S2, after calcination, the following steps are also included: acid washing the calcined product with excess hydrochloric acid at 20-60°C for 6-12 hours to remove excess elemental nickel; then washing with deionized water and anhydrous ethanol until neutral, and vacuum drying for 12-48 hours to obtain a nickel-coated nitrogen-doped graphene composite material.

[0032] Preferably, in step S3, the reducing agent is at least one of sodium formate or sodium carbonate.

[0033] Preferably, in step S3, the platinum source is at least one of chloroplatinic acid, sodium chloroplatinate, or platinum nitrate.

[0034] Preferably, in step S3, the mass-to-volume ratio of the nickel-coated nitrogen-doped graphene composite material, the water, the reducing agent, and the platinum source is 100 mg: (50-200) mL: (5-50) mg: (0.1-4) mg.

[0035] Preferably, in step S3, the reaction temperature is 80–100°C and the reaction time is 50–120 min.

[0036] For example, in step S3, after the reaction is complete, the reaction product also needs to be dried.

[0037] Preferably, in step S4, the reducing gas is hydrogen, and the flow rate of the reducing gas is 50-150 mL / min.

[0038] For example, in step S4, an inert gas is first introduced to replace the air, and then hydrogen is introduced.

[0039] For example, in steps S2 and S4, the inert atmosphere is helium, nitrogen, argon, or carbon dioxide.

[0040] Preferably, in step S4, the reduction and activation temperature is 200–300°C, and the time is 1–3 hours.

[0041] This invention, by controlling the conditions of reduction activation, facilitates the reduction of platinum ions to elemental platinum, which then bonds with carbon and nitrogen atoms on graphene defects, thereby making the structure of the magnetically separable carbon-supported platinum cluster catalyst more stable.

[0042] For example, in step S4, after the reduction and activation are completed, the reaction product needs to be cooled to room temperature under an inert atmosphere.

[0043] Thirdly, the present invention provides the application of the above-mentioned magnetically separable carbon-supported platinum cluster catalyst or the magnetically separable carbon-supported platinum cluster catalyst prepared by the above preparation method in the hydrogenation of nitrobenzene to aniline.

[0044] Preferably, the method for preparing aniline by hydrogenation of nitrobenzene includes the following steps:

[0045] A magnetically separable carbon-supported platinum cluster catalyst and nitrobenzene were added to a solvent and subjected to a hydrogenation reaction at 20–60 °C under a hydrogen atmosphere to obtain aniline.

[0046] More preferably, the solvent is ethanol.

[0047] More preferably, the mass molar volume ratio of the magnetically separable carbon-supported platinum cluster catalyst, the nitrobenzene, and the solvent is (5-20) mg: 1 mmol: (10-100) mL.

[0048] More preferably, the hydrogen pressure is 0.5–1 MPa; the hydrogenation reaction time is 5–120 min, more preferably 20–100 min.

[0049] The results of the examples show that when the magnetically separable carbon-supported platinum cluster catalyst provided by the present invention is applied to the hydrogenation of nitrobenzene to prepare aniline, the catalytic conditions are mild, and the conversion rate of nitrobenzene is above 90% and the selectivity of aniline is above 99%. Attached Figure Description

[0050] Figure 1 This is a transmission electron microscope (TEM) image of the nickel-coated nitrogen-doped graphene composite material in Example 1 of the present invention.

[0051] Figure 2 The image shown is a HAADF-STEM image of the magnetically separable carbon-supported platinum cluster catalyst of Example 1 of the present invention; the area enclosed by the dashed box represents the platinum cluster.

[0052] Figure 3 This is a stability test diagram of the magnetically separable carbon-supported platinum cluster catalyst of Example 1 of the present invention. Detailed Implementation

[0053] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0054] To better illustrate the present invention, further examples are provided below.

[0055] Example 1

[0056] This embodiment provides a magnetically separable carbon-supported platinum cluster catalyst Pt 0.5 / Ni 25 @NG (the loading of platinum nanoparticles is 0.5 wt%, and nickel nanoparticles account for 25% of the mass of the carrier).

[0057] The preparation method of the above-mentioned magnetically separable carbon-supported platinum cluster catalyst includes the following steps:

[0058] S1. Nickel hydroxide and ethylenediaminetetraacetic acid were added to deionized water in a 1:1 molar ratio, mixed evenly, and placed in an oil bath at 90°C for a complexation reaction for 60 min. After solid-liquid separation, drying, grinding, and passing through a 300-mesh sieve, a nickel complex was obtained.

[0059] S2, in a helium atmosphere with a flow rate of 80 mL / min, the nickel complex was calcined at 600 °C at a rate of 6 °C / min and held at that temperature for 2 h. The calcined product was then acid-washed at 40 °C with excess hydrochloric acid for 9 h to remove excess elemental nickel. It was then washed with deionized water and anhydrous ethanol until neutral, and vacuum-dried at 60 °C for 20 h to obtain a nickel-coated nitrogen-doped graphene composite material, denoted as Ni. 25 @NG.

[0060] Nitrogen-doped graphene composites coated with nickel 25 @NG performs transmission electron microscopy analysis, such as Figure 1 As shown, it can be seen that Ni 25 @NG is a core-shell structure, with nitrogen-doped graphene as the shell and nickel nanoparticles as the metal core. The nickel nanoparticles have a size of 5–10 nm, and the nitrogen-doped graphene has 2–5 layers.

[0061] S3, 100 mg of nickel-coated nitrogen-doped graphene composite material was added to 100 mL of deionized water and mixed evenly. 30 mg of sodium formate and 2 mg of chloroplatinic acid were added to the resulting suspension and reacted at 90 °C for 90 min. Solid-liquid separation was performed, and the mixture was dried to obtain the catalyst precursor.

[0062] S4. First, helium gas is introduced to replace the air in the quartz tube (helium purging for 30 min), then hydrogen gas is introduced at a flow rate of 100 mL / min. The catalyst precursor is placed in the quartz tube and reduced and activated at 250 °C for 2 h. After cooling to room temperature under a helium atmosphere, a magnetically separable carbon-supported platinum cluster catalyst is obtained, denoted as Pt. 0.5 / Ni 25 @NG.

[0063] For magnetically separable carbon-supported platinum cluster catalysts Pt 0.5 / Ni 25 @NG performs spherical aberration electron microscopy scanning, such as Figure 2 As shown, platinum nanoparticles are uniformly dispersed in Ni in the form of clusters. 25 The surface of the @NG carrier has a particle size of 1–3 nm after clustering.

[0064] Example 2

[0065] This embodiment provides a magnetically separable carbon-supported platinum cluster catalyst Pt 0.1 / Ni 20 @NG.

[0066] The preparation method of the above-mentioned magnetically separable carbon-supported platinum cluster catalyst includes the following steps:

[0067] S1. Nickel chloride and propylenediaminetetraacetic acid were added to deionized water at a molar ratio of 1:0.5, mixed evenly, and placed in an oil bath at 50°C for a complexation reaction for 80 min. The solid and liquid were separated, dried, ground, and passed through a 500-mesh sieve to obtain the nickel complex.

[0068] S2, under an argon atmosphere with a flow rate of 50 mL / min, the nickel complex was calcined at 500 °C at a rate of 2 °C / min and held at that temperature for 3 h. The calcined product was then acid-washed with excess hydrochloric acid at 20 °C for 12 h to remove excess elemental nickel. It was then washed with deionized water and anhydrous ethanol until neutral, and vacuum-dried at 60 °C for 12 h to obtain a nickel-coated nitrogen-doped graphene composite material, denoted as Ni. 20 @NG.

[0069] S3, 100 mg of nickel-coated nitrogen-doped graphene composite material was added to 50 mL of deionized water and mixed evenly. 5 mg of sodium carbonate and 0.1 mg of sodium chloroplatinate were added to the resulting suspension and reacted at 80 °C for 120 min. Solid-liquid separation was performed, and the mixture was dried to obtain the catalyst precursor.

[0070] S4. First, argon gas is introduced to replace the air in the quartz tube (argon purging for 30 min), then hydrogen gas is introduced at a flow rate of 50 mL / min. The catalyst precursor is placed in the quartz tube and reduced and activated at 200 °C for 3 h. After cooling to room temperature under an argon atmosphere, a magnetically separable carbon-supported platinum cluster catalyst is obtained, denoted as Pt. 0.1 / Ni 20 @NG.

[0071] Example 3

[0072] This embodiment provides a magnetically separable carbon-supported platinum cluster catalyst Pt 0.3 / Ni 30 @NG.

[0073] The preparation method of the above-mentioned magnetically separable carbon-supported platinum cluster catalyst includes the following steps:

[0074] S1. Nickel nitrate and ethylenediaminetetraacetic acid were added to deionized water at a molar ratio of 1:2, mixed evenly, and placed in an oil bath at 80°C for a complexation reaction for 70 min. The solid and liquid were separated, dried, ground, and passed through a 400-mesh sieve to obtain the nickel complex.

[0075] S2, in a helium atmosphere with a flow rate of 70 mL / min, the nickel complex was calcined at 700 °C at a rate of 8 °C / min and held at that temperature for 2 h. The calcined product was then acid-washed at 50 °C with excess hydrochloric acid for 8 h to remove excess elemental nickel. It was then washed with deionized water and anhydrous ethanol until neutral, and vacuum-dried at 60 °C for 25 h to obtain a nickel-coated nitrogen-doped graphene composite material, denoted as Ni. 30 @NG.

[0076] S3, 100 mg of nickel-coated nitrogen-doped graphene composite material was added to 150 mL of deionized water and mixed evenly. 20 mg of sodium formate and 1.2 mg of platinum nitrate were added to the resulting suspension and reacted at 90 °C for 80 min. Solid-liquid separation was performed, and the mixture was dried to obtain the catalyst precursor.

[0077] S4. First, helium gas is introduced to replace the air in the quartz tube (helium purging for 30 min), then hydrogen gas is introduced at a flow rate of 120 mL / min. The catalyst precursor is placed in the quartz tube and reduced and activated at 260 °C for 2 h. After cooling to room temperature under a helium atmosphere, a magnetically separable carbon-supported platinum cluster catalyst is obtained, denoted as Pt. 0.3 / Ni 30 @NG.

[0078] Example 4

[0079] This embodiment provides a magnetically separable carbon-supported platinum cluster catalyst Pt1 / Ni 40 @NG.

[0080] The preparation method of the above-mentioned magnetically separable carbon-supported platinum cluster catalyst includes the following steps:

[0081] S1. Nickel sulfate and propylenediaminetetraacetic acid were added to deionized water at a molar ratio of 1:4, mixed evenly, and placed in an oil bath at 100°C for a complexation reaction for 50 min. The solid and liquid were separated, dried, ground, and passed through a 200-mesh sieve to obtain the nickel complex.

[0082] S2, under a nitrogen atmosphere with a flow rate of 100 mL / min, the nickel complex was calcined at 760 °C at a rate of 10 °C / min and held at that temperature for 1 h. The calcined product was then acid-washed at 60 °C with excess hydrochloric acid for 6 h to remove excess elemental nickel. It was then washed with deionized water and anhydrous ethanol until neutral, and vacuum-dried at 60 °C for 40 h to obtain a nickel-coated nitrogen-doped graphene composite material, denoted as Ni. 40 @NG.

[0083] S3, 100 mg of nickel-coated nitrogen-doped graphene composite material was added to 200 mL of deionized water and mixed evenly. 50 mg of sodium formate and 4 mg of chloroplatinic acid were added to the resulting suspension and reacted at 100 °C for 50 min. Solid-liquid separation was performed, and the mixture was dried to obtain the catalyst precursor.

[0084] S4. First, nitrogen gas is introduced to replace the air in the quartz tube (nitrogen purging for 30 min), then hydrogen gas is introduced at a flow rate of 150 mL / min. The catalyst precursor is placed in the quartz tube and reduced and activated at 300 °C for 1.2 h. After cooling to room temperature under a nitrogen atmosphere, a magnetically separable carbon-supported platinum cluster catalyst is obtained, denoted as Pt1 / Ni. 40 @NG.

[0085] Example 5

[0086] This embodiment provides a method for preparing aniline by hydrogenation of nitrobenzene, including the following steps:

[0087] 10 mg of Pt from Example 1 0.5 / Ni 25 @NG, 1 mmol nitrobenzene, and 50 mL ethanol were added to a stainless steel batch reactor, sealed, and the air was purged with argon six times, followed by purging the argon with hydrogen five times at a pressure of 0.8 MPa. The hydrogenation reaction was carried out at 30 °C for 80 min to obtain aniline. Gas chromatography analysis of the reaction products showed that the conversion rate of nitrobenzene was 99.4%, and the selectivity of aniline was 99.7%.

[0088] Example 6

[0089] This embodiment provides a method for preparing aniline by hydrogenation of nitrobenzene, including the following steps:

[0090] 20 mg of Pt from Example 20.1 / Ni 20 @NG, 1 mmol nitrobenzene, and 100 mL ethanol were added to a stainless steel batch reactor, sealed, and the air was purged with argon six times, followed by purging the argon with hydrogen five times at a pressure of 1 MPa. The hydrogenation reaction was carried out at 60 °C for 50 min to obtain aniline. Gas chromatography analysis of the reaction products showed that the nitrobenzene conversion rate was 93.5% and the aniline selectivity was 95.8%.

[0091] Example 7

[0092] This embodiment provides a method for preparing aniline by hydrogenation of nitrobenzene, including the following steps:

[0093] 5mg of Pt from Example 3 0.3 / Ni 30 @NG, 1 mmol nitrobenzene, and 10 mL ethanol were added to a stainless steel batch reactor, sealed, and the air was purged with argon six times, followed by purging the argon with hydrogen five times at a pressure of 0.6 MPa. The hydrogenation reaction was carried out at 20 °C for 120 min to obtain aniline. Gas chromatography analysis of the reaction products showed that the conversion rate of nitrobenzene was 97.9% and the selectivity of aniline was 98.3%.

[0094] Example 8

[0095] This embodiment provides a method for preparing aniline by hydrogenation of nitrobenzene, including the following steps:

[0096] 15 mg of Pt1 / Ni from Example 4 was used. 40 @NG, 1 mmol nitrobenzene, and 30 mL ethanol were added to a stainless steel batch reactor, sealed, and the air was purged with argon six times, followed by purging the argon with hydrogen five times at a pressure of 0.5 MPa. The hydrogenation reaction was carried out at 20 °C for 20 min to obtain aniline. Gas chromatography analysis of the reaction products showed that the conversion rate of nitrobenzene was 99.7% and the selectivity of aniline was 99.9%.

[0097] Example 9

[0098] This embodiment provides a method for preparing a magnetically separable carbon-supported platinum cluster catalyst, which is similar to that of Example 1. The only difference is that in step S3, the reaction temperature is 50°C and the reaction time is 180 min. The other conditions are the same as those in Example 1 and will not be repeated here.

[0099] Testing revealed that due to the low reaction temperature, chloroplatinic acid could not be fully deposited onto the support via precipitation (platinum hydroxide), resulting in a final platinum loading of only about 0.1 wt% in the catalyst, leading to a significant waste of platinum source.

[0100] Comparative Example 1

[0101] This comparative example provides a method for preparing a carrier, which is similar to that of Example 1, except that in step S2, the calcination temperature is 1000℃. The remaining conditions of steps S1 and S2 are the same as those of Example 1, and will not be repeated here.

[0102] The results showed that the nickel ions in the nickel complex were reduced to nickel elemental particles at 1000℃, which were too large to be coated by nitrogen-doped graphene. The bonding between nickel and nitrogen-doped graphene was unstable, which would also have an adverse effect on the platinum loading in subsequent steps. Furthermore, nickel was easily lost during subsequent use, and the magnetism was correspondingly weakened.

[0103] Comparative Example 2

[0104] This comparative example provides a method for preparing a carrier, which is similar to that of Example 1, except that in step S2, the calcination temperature is 400°C. The remaining conditions of steps S1 and S2 are the same as those of Example 1, and will not be repeated here.

[0105] The results showed that the matrix ethylenediaminetetraacetic acid in the nickel complex could not be carbonized at 400°C to form a layered graphene structure, thus failing to coat nickel and affecting the platinum loading in subsequent steps; furthermore, nickel was easily lost during subsequent use, and the magnetism was correspondingly weakened.

[0106] Comparative Example 3

[0107] This comparative example provides a method for preparing aniline by hydrogenation of nitrobenzene, which is similar to Example 5, except that the catalyst is replaced with Ni1@NG of Example 1 (i.e. the catalyst is only the support of Example 1 and is not loaded with platinum). The other conditions are the same as those in Example 1 and will not be repeated.

[0108] Gas chromatography analysis of the reaction products revealed that the nitrobenzene conversion rate was 0, and no aniline or other byproducts were detected.

[0109] Comparative Example 4

[0110] This comparative example provides a method for preparing aniline by hydrogenation of nitrobenzene, which is similar to Example 5, except that the catalyst is replaced with a commercially available activated carbon supported platinum catalyst Pt / AC (purchased from Aladdin Biochemical Technology Co., Ltd., model P111328, with a platinum loading of 5.0 wt%). The other conditions are the same as in Example 1 and will not be repeated.

[0111] Gas chromatography analysis of the reaction products revealed a nitrobenzene conversion rate of 45.0% and an aniline selectivity of 71.2%. This indicates that commercially available Pt / AC exhibits poor low-temperature activity and can only effectively prepare aniline from nitrobenzene via hydrogenation at high temperatures.

[0112] Magnetic Cyclic Stability Test

[0113] To verify the magnetic cyclic stability of the magnetically separable carbon-supported platinum cluster catalysts in Examples 1-4, the following experiment was conducted: The liner containing the magnetically separable carbon-supported platinum cluster catalyst was removed from the reactor, allowed to stand, and then adsorbed using a magnetic stir bar. The clear reaction solution was poured off, and the catalyst was washed with excess water and anhydrous ethanol. After standing, the supernatant was poured off. This process was repeated three times. The recovered magnetically separable carbon-supported platinum cluster catalyst was then dried in a vacuum drying oven at 60°C for 6 hours. The nitrobenzene hydrogenation reaction was then repeated according to the steps in Example 5 for a cyclic test. This process was repeated multiple times, and the composition of the reaction products was analyzed by gas chromatography after each reaction to obtain the stability test chart of the magnetically separable carbon-supported platinum cluster catalyst.

[0114] Figure 3 Pt in Example 1 0.5 The stability test graph of / Ni1@NG after 10 cycles shows that after 10 cycles, Pt 0.5 / Ni1@NG maintains stable performance. Examples 2-4 achieve results comparable to Example 1.

[0115] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a magnetically separable carbon-supported platinum cluster catalyst, characterized in that, Includes the following steps: S1, Add nickel salt and aminocarboxylic acid organic chelating agent to water, mix evenly, and carry out complexation reaction to obtain nickel complex; S2, In an inert atmosphere, the nickel complex is calcined at 500~800℃ to obtain a nickel-coated nitrogen-doped graphene composite material. S3, add the nickel-coated nitrogen-doped graphene composite material to water, mix evenly, add a reducing agent and a platinum source to the resulting suspension, and react to obtain a catalyst precursor; S4, under a reducing atmosphere, the catalyst precursor is reduced and activated to obtain a magnetically separable carbon-supported platinum cluster catalyst. The magnetically separable carbon-supported platinum cluster catalyst includes an active component and a support; the active component is platinum nanoparticles, and the support is a nitrogen-doped graphene composite material coated with nickel. The nickel-coated nitrogen-doped graphene composite material has a core-shell structure, with nitrogen-doped graphene as the shell and nickel nanoparticles as the metal core; the platinum nanoparticles are uniformly loaded on the surface of the nitrogen-doped graphene in the form of clusters and bonded to carbon and nitrogen atoms on graphene defects.

2. The preparation method of the magnetically separable carbon-supported platinum cluster catalyst as described in claim 1, characterized in that, The loading of the platinum nanoparticles is 0.1wt%~1wt%; The nickel nanoparticles account for 20% to 40% of the mass of the carrier.

3. The preparation method of the magnetically separable carbon-supported platinum cluster catalyst as described in claim 1, characterized in that, The particle size of the platinum nanoparticles after clustering is 1~5nm; The nickel nanoparticles have a particle size of 2~20 nm.

4. The preparation method of the magnetically separable carbon-supported platinum cluster catalyst as described in claim 1, characterized in that, Includes the following steps: S1, add nickel salt and aminocarboxylic acid organic chelating agent to water, mix evenly, and complex at 50~100℃ for 50~80min to obtain nickel complex; S2, In an inert atmosphere, the nickel complex is heated to 500-700°C at a rate of 2-10°C / min and calcined for 1-3 hours to obtain a nickel-coated nitrogen-doped graphene composite material. S3, add the nickel-coated nitrogen-doped graphene composite material to water, mix evenly, add a reducing agent and a platinum source to the resulting suspension, and react at 80~100℃ for 50~120 min to obtain a catalyst precursor; S4. Under a reducing atmosphere, the catalyst precursor is reduced and activated at 200~300℃ for 1~3h to obtain a magnetically separable carbon-supported platinum cluster catalyst.

5. The method for preparing the magnetically separable carbon-supported platinum cluster catalyst as described in claim 1 or 4, characterized in that, In step S1, the nickel salt is at least one of nickel hydroxide, nickel chloride, nickel nitrate, or nickel sulfate; The aminocarboxylic acid organic chelating agent is at least one of ethylenediaminetetraacetic acid or propylenediaminetetraacetic acid; The molar ratio of the nickel salt to the aminocarboxylic acid organic chelating agent is 1:(0.5~4).

6. The method for preparing the magnetically separable carbon-supported platinum cluster catalyst as described in claim 1 or 4, characterized in that, In step S3, the reducing agent is at least one of sodium formate or sodium carbonate; The platinum source is at least one of chloroplatinic acid, sodium chloroplatinate, or platinum nitrate. The mass-to-volume ratio of the nickel-coated nitrogen-doped graphene composite material, the water, the reducing agent, and the platinum source is 100 mg: (50~200) mL: (5~50) mg: (0.1~4) mg.

7. The application of the magnetically separable carbon-supported platinum cluster catalyst prepared by the method of any one of claims 1 to 6 in the hydrogenation of nitrobenzene to aniline.

8. The application of the magnetically separable carbon-supported platinum cluster catalyst as described in claim 7 in the hydrogenation of nitrobenzene to aniline, characterized in that, The method for preparing aniline by hydrogenation of nitrobenzene includes the following steps: A magnetically separable carbon-supported platinum cluster catalyst and nitrobenzene were added to a solvent and subjected to a hydrogenation reaction at 20-60°C under a hydrogen atmosphere to obtain aniline.

9. The application of the magnetically separable carbon-supported platinum cluster catalyst as described in claim 8 in the hydrogenation of nitrobenzene to aniline, characterized in that, The solvent is ethanol; The magnetically separable carbon-supported platinum cluster catalyst, the nitrobenzene and the solvent have a mass molar volume ratio of (5~20) mg: 1 mmol: (10~100) mL; The hydrogen pressure is 0.5~1MPa; the hydrogenation reaction time is 5~120min.

Images