Preparation method of metal monatomic catalyst

Abstract

The invention discloses a preparation method of a metal monatomic catalyst, which comprises the following steps: dispersing metal salt, PVC (polyvinyl chloride), melamine and hydrochloric acid in a solvent, removing the solvent, and calcining in a protective atmosphere to obtain the metal monatomic catalyst. The preparation method of the metal monatomic catalyst can be used for preparing various carbon-loaded metal monatomic catalysts, can be used for carrying out high-valued treatment on waste PVC (Polyvinyl Chloride), is simple to operate and low in cost, and has a wide practical application prospect.

Description

Technical Field

[0001] The invention relates to the technical field of catalyst preparation, and in particular to a method for preparing a metal single-atom catalyst. Background Art

[0002] Polyvinyl chloride (PVC) is one of the five major engineering plastics (PVC, PE, PP, PS and ABS), accounting for more than 16% of the total demand for plastics. Statistics show that the global consumption of PVC in 2021 exceeded 40 million tons, and it is expected to reach 56.2 million tons by 2026. However, this has also led to a large amount of PVC waste. Since PVC contains up to 56% chlorine, its recycling process will not only cause serious environmental pollution problems, but also cause chlorine pollution to the recycled products, thereby reducing the recycling efficiency of PVC. Therefore, it is of great significance to find a simple method to achieve high-value recycling of PVC.

[0003] PVC pyrolysis is an effective method for converting PVC into carbon materials. This method can effectively treat PVC waste and has attracted much attention in recent years. CN 107381532 A discloses a method for synthesizing polyvinyl chloride carbon spheres, wherein PVC is used as a raw material for catalytic dechlorination under the action of an alkaline solvent, then heated in an oxidizing atmosphere for cross-linking and curing, and then carbonized at high temperature to obtain carbon spheres. CN 108658055 A discloses a method for recycling waste polyvinyl chloride products to prepare porous carbon, wherein magnesium oxide formed by the decomposition of magnesium hydroxide during the carbonization process and hydrogen chloride released by the pyrolysis of PVC are used as templates to obtain a preliminary carbon material, and then the template is removed by acid washing to convert PVC into a porous carbon material. However, although the above methods can obtain carbon materials, complex acid washing and template removal operations are required, and the process is relatively complicated. CN 114715881 A discloses a waste plastic derived nanoporous carbon material and a preparation method and application thereof. Melamine is used as a dechlorinating agent and a cross-linking agent, and is ball-milled with PVC in N,N-dimethylformamide to dechlorinate, and then pyrolyzed and carbonized to obtain nitrogen-doped carbon nanosheets. The nanoporous carbon material exhibits excellent performance as a catalyst in acetylene hydrochlorination reaction. However, the method requires N,N-dimethylformamide as a solvent, and the added value of the prepared carbon material is not high, and the efficiency of PVC recycling is low.

[0004] Single-atom catalysis (the concept of single-atom catalysis was first proposed by Academician Zhang Tao of Dalian Institute of Chemical Physics, Chinese Academy of Sciences in 2011) not only has the advantages of homogeneous catalysts, but also has the characteristics of heterogeneous catalysts, showing many advantages such as high activity, high selectivity, stable and recyclable, and has shown good application prospects in many fields such as electrocatalysis, photocatalysis, thermal catalysis, and electrochemical energy storage. At present, the typical synthesis strategy of carbon-supported metal single-atom catalysts is to use soluble metal salts or metal complexes as precursors of metal atoms, nitrogen / carbon-containing organic matter as precursors of nitrogen-doped carbon, dissolve and mix them in water or organic solvents to achieve uniform dispersion of metal ions in the system, and then dry and calcine to obtain single-atom catalysts (metal salts are converted into metal atoms under thermal reduction). However, under high temperature conditions, especially when the metal loading is high, metal atoms will inevitably agglomerate to form clusters or particles, which usually need to be removed by acid washing. The whole process requires cumbersome process steps, which increases the production cycle. In addition, the process conditions are harsh and a large amount of waste liquid will be generated, resulting in this method being unsuitable for mass production of single-atom catalysts.

[0005] Therefore, it is of great significance to develop a method for preparing metal single atom catalysts with simple operation and low cost. Summary of the invention

[0006] The purpose of the present invention is to provide a method for preparing a metal single atom catalyst.

[0007] The technical solution adopted by the present invention is:

[0008] A preparation method of a metal single atom catalyst comprises the following steps: dispersing metal salt, PVC, melamine and hydrochloric acid in a solvent, removing the solvent, and calcining in a protective atmosphere to obtain the metal single atom catalyst.

[0009] Preferably, the mass ratio of the metal salt, PVC, melamine and hydrochloric acid is 0.0015-0.0255:1:0.25-4:0.14-2.38.

[0010] Preferably, the metal salt is at least one of a soluble Fe salt, a soluble Co salt, a soluble Ni salt, a soluble Cu salt, a soluble Mn salt, a soluble Mg salt, a soluble Bi salt, and a soluble Pd salt.

[0011] Further preferably, the metal salt is at least one of ferrous chloride tetrahydrate, cobalt chloride hexahydrate, cobalt nitrate hexahydrate, cobalt sulfate heptahydrate, cobalt acetate tetrahydrate, nickel chloride hexahydrate, nickel nitrate hexahydrate, cupric chloride dihydrate, manganese nitrate tetrahydrate, magnesium chloride, bismuth nitrate pentahydrate, and palladium chloride.

[0012] Preferably, the mass fraction of the hydrochloric acid is 30% to 40%.

[0013] Preferably, the solvent is at least one of ethanol and methanol.

[0014] Preferably, the protective atmosphere is one of a nitrogen atmosphere, an argon atmosphere, and a nitrogen-argon mixed atmosphere.

[0015] Preferably, the flow rate of the protective atmosphere is 10 mL / min to 100 mL / min.

[0016] Preferably, the calcination includes the following process: first control the heating rate to be 5℃ / min~15℃ / min to heat from room temperature to 450℃~600℃, then keep warm for 0.5h~1.5h, then control the heating rate to be 2℃ / min~10℃ / min to continue heating to 700℃~1000℃, and then keep warm for 1h~5h.

[0017] A metal single atom catalyst is prepared by the above preparation method.

[0018] Preferably, the metal loading of the metal single atom catalyst is 0.29 wt% to 3.19 wt%.

[0019] A method for preparing aniline by hydrogenating nitrobenzene, the catalyst used is the above-mentioned metal single-atom catalyst.

[0020] The beneficial effects of the present invention are as follows: the preparation method of the metal single atom catalyst of the present invention can prepare a variety of carbon-loaded metal single atom catalysts, and can perform high-value treatment on waste PVC, has simple operation, low cost, and has broad practical application prospects.

[0021] Specifically:

[0022] 1) The present invention directly mixes the metal precursor and the nitrogen-doped carbon precursor in one pot, and then calcines at high temperature to simultaneously realize the formation of the precursor and the anchoring of the metal, which is simple to operate;

[0023] 2) The present invention uses cheap melamine as a nitrogen source, so that the nitrogen content of the catalyst can reach 12wt%, which is beneficial to the anchoring of single atoms, and the prepared catalyst does not require an acid washing process, thus avoiding problems such as waste acid treatment and equipment loss, and reducing production costs;

[0024] 3) The present invention can turn waste PVC into valuable materials, and the treatment process is simple. The specific surface area of ​​the prepared metal single-atom catalyst can reach up to 460 m 2 / g, the maximum metal loading can reach 3.19wt%. The catalyst is used in the reaction of hydrogenating nitrobenzene to prepare aniline, which can make the conversion rate of nitrobenzene reach more than 99% and the selectivity of aniline reach more than 99%. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 These are the SEM image, TEM image and element distribution map of the metal single atom catalyst in Example 1.

[0026] Figure 2 This is the XRD pattern of the metal single atom catalyst in Example 1.

[0027] Figure 3 This is the HAADF-STEM image of the metal single atom catalyst in Example 1.

[0028] Figure 4 This is a graph showing the test results of the catalytic performance of the metal single atom catalyst in Example 1 for the hydrogenation of nitrobenzene to produce aniline.

[0029] Figure 5 TEM image of the metal catalyst in the comparative example. DETAILED DESCRIPTION

[0030] The present invention will be further explained and illustrated below in conjunction with specific embodiments.

[0031] Embodiment 1:

[0032] A method for preparing a metal single atom catalyst, comprising the following steps:

[0033] Dissolve 45 mg of cobalt chloride hexahydrate in 2 mL of water to prepare a metal precursor solution, then add the metal precursor solution, 2 g of PVC, 4 g of melamine and 2 mL of 38% concentrated hydrochloric acid into 400 mL of anhydrous ethanol, stir for 1 hour, then place in an oil bath and stir at 90°C until the solvent is evaporated, then place in a vacuum dryer for drying, then place in a tubular furnace, fill with argon, control the argon flow rate to 40 mL / min, control the heating rate to 5°C / min from room temperature to 550°C, then keep warm for 0.5 hour, then control the heating rate to continue to heat to 900°C at 5°C / min, keep warm for 3 hours, and naturally cool to room temperature to obtain a metal single atom catalyst.

[0034] Performance Testing:

[0035] 1) The scanning electron microscope (SEM) image, transmission electron microscope (TEM) image and element distribution map of the metal single atom catalyst in this embodiment are as follows: Figure 1 (a is the SEM image, b is the TEM image, and c is the element distribution image).

[0036] Depend on Figure 1 It can be seen that the metal single atom catalyst in this embodiment presents a uniform layered structure, no Co particles exist, and the Co element is uniformly dispersed in the carbon layer.

[0037] 2) The X-ray diffraction (XRD) pattern of the metal single atom catalyst in this embodiment is as follows: Figure 2 shown.

[0038] Depend on Figure 2 It can be seen that there is no metallic phase of Co in the metal single atom catalyst in this example.

[0039] 3) The spherical aberration corrected dark field scanning transmission microscopy (HAADF-STEM) image of the metal single atom catalyst in this embodiment is as follows: Figure 3 shown.

[0040] Depend on Figure 3 It can be seen that there are no Co particles in the metal single atom catalyst in this embodiment, and the Co element is dispersed in the carbon layer at the atomic level.

[0041] 4) 50 mg of the metal single atom catalyst in this embodiment, 2 mmol of nitrobenzene and 15 mL of ethanol were added to a stainless steel autoclave with a volume of 50 mL. The autoclave was purged with H2 for 5 times and finally pressurized to 1 MPa. The stirring speed was adjusted to 1100 rpm and the temperature was raised to 110°C for constant temperature reaction. After the reaction was completed, the reactor was placed in ice water and quickly cooled to room temperature. The exhaust gas was exhausted, the reactor was opened and internal standard biphenyl was added. After stirring evenly, sampling and analysis were performed. The catalytic performance test results of the obtained metal single atom catalyst for the hydrogenation of nitrobenzene to prepare aniline are shown as follows: Figure 4 shown.

[0042] Depend on Figure 4 It can be seen that the metal single atom catalyst in this embodiment shows excellent catalytic performance in the hydrogenation of nitrobenzene to prepare aniline. The conversion rate of nitrobenzene can reach more than 99% within 2 hours, and the selectivity of aniline can reach more than 99%.

[0043] 5) The metal loading of the metal single atom catalyst in this example was determined to be 3.19 wt % by inductively coupled plasma optical emission spectrometry (ICP-OES).

[0044] Embodiment 2:

[0045] A method for preparing a metal single atom catalyst, comprising the following steps:

[0046] Dissolve 45 mg of cobalt chloride hexahydrate in 2 mL of water to prepare a metal precursor solution, then add the metal precursor solution, 2 g of PVC, 4 g of melamine and 2 mL of 38% concentrated hydrochloric acid into 400 mL of methanol, stir for 1 hour, place in an oil bath and stir at 90°C until the solvent is evaporated, then place in a vacuum dryer for drying, then place in a tubular furnace, fill with argon, control the argon flow rate to 40 mL / min, control the heating rate to 5°C / min from room temperature to 550°C, then keep warm for 0.5 hour, then control the heating rate to continue to heat to 900°C at 5°C / min, keep warm for 3 hours, and naturally cool to room temperature to obtain a metal single atom catalyst.

[0047] After testing (the testing method is the same as that of Example 1), the metal loading of the metal single atom catalyst in this example is 2.21wt%, and it exhibits excellent catalytic performance when used for the hydrogenation of nitrobenzene to prepare aniline. The conversion rate of nitrobenzene can reach more than 99% within 2 hours, and the selectivity of aniline can reach more than 99%.

[0048] Embodiment 3:

[0049] A method for preparing a metal single atom catalyst, comprising the following steps:

[0050] 45 mg of cobalt chloride hexahydrate was dissolved in 2 mL of water to prepare a metal precursor solution, and the metal precursor solution, 2 g of PVC, 4 g of melamine and 0.25 mL of concentrated hydrochloric acid with a mass fraction of 38% were added to 400 mL of anhydrous ethanol, stirred for 1 hour, and then placed in an oil bath pot and stirred at 90°C until the solvent was evaporated, and then placed in a vacuum dryer for drying, and then placed in a tubular furnace, filled with argon, and the argon flow rate was controlled to be 40 mL / min. The temperature was raised from room temperature to 550°C at a rate of 5°C / min, and then kept warm for 0.5 h. The temperature was then raised to 900°C at a rate of 5°C / min, and then kept warm for 3 h. The solution was naturally cooled to room temperature to obtain a metal single atom catalyst.

[0051] After testing (the testing method is the same as that of Example 1), the metal loading of the metal single atom catalyst in this example is 2.03wt%, and it exhibits excellent catalytic performance when used for the hydrogenation of nitrobenzene to prepare aniline. The conversion rate of nitrobenzene can reach 78% within 2 hours, and the selectivity of aniline can reach more than 99%.

[0052] Embodiment 4:

[0053] A method for preparing a metal single atom catalyst, comprising the following steps:

[0054] Dissolve 45 mg of cobalt chloride hexahydrate in 2 mL of water to prepare a metal precursor solution, then add the metal precursor solution, 2 g of PVC, 4 g of melamine and 4 mL of 38% concentrated hydrochloric acid into 400 mL of anhydrous ethanol, stir for 1 hour, then place in an oil bath and stir at 90°C until the solvent is evaporated, then place in a vacuum dryer for drying, then place in a tubular furnace, fill with argon, control the argon flow rate to 40 mL / min, control the heating rate to 5°C / min from room temperature to 550°C, then keep warm for 0.5 hour, then control the heating rate to 5°C / min and continue to heat to 900°C, then keep warm for 3 hours, and naturally cool to room temperature to obtain a metal single atom catalyst.

[0055] After testing (the testing method is the same as that of Example 1), the metal loading of the metal single atom catalyst in this example is 2.32wt%, and it exhibits excellent catalytic performance when used for the hydrogenation of nitrobenzene to prepare aniline. The conversion rate of nitrobenzene can reach more than 99% within 2 hours, and the selectivity of aniline can reach more than 99%.

[0056] Embodiment 5:

[0057] A method for preparing a metal single atom catalyst, comprising the following steps:

[0058] 45 mg of cobalt chloride hexahydrate was dissolved in 2 mL of water to prepare a metal precursor solution, and the metal precursor solution, 2 g of PVC, 0.5 g of melamine and 2 mL of concentrated hydrochloric acid with a mass fraction of 38% were added to 400 mL of anhydrous ethanol, stirred for 1 hour, and then placed in an oil bath pot and stirred at 90°C until the solvent was evaporated, and then placed in a vacuum dryer for drying, and then placed in a tubular furnace, filled with argon, and the argon flow rate was controlled to be 40 mL / min. The temperature was raised from room temperature to 550°C at a rate of 5°C / min, and then kept warm for 0.5 h. The temperature was then raised to 900°C at a rate of 5°C / min, and then kept warm for 3 h. The solution was naturally cooled to room temperature to obtain a metal single atom catalyst.

[0059] After testing (the testing method is the same as that of Example 1), the metal loading of the metal single atom catalyst in this example is 2.35wt%, and it exhibits excellent catalytic performance when used for the hydrogenation of nitrobenzene to prepare aniline. The conversion rate of nitrobenzene can reach 81% within 2 hours, and the selectivity of aniline can reach more than 99%.

[0060] Embodiment 6:

[0061] A method for preparing a metal single atom catalyst, comprising the following steps:

[0062] 45 mg of cobalt chloride hexahydrate was dissolved in 2 mL of water to prepare a metal precursor solution, and the metal precursor solution, 2 g of PVC, 6 g of melamine and 2 mL of concentrated hydrochloric acid with a mass fraction of 38% were added to 400 mL of anhydrous ethanol, stirred for 1 hour, and then placed in an oil bath pot and stirred at 90°C until the solvent was evaporated, and then placed in a vacuum dryer for drying, and then placed in a tubular furnace, filled with argon, and the argon flow rate was controlled to be 40 mL / min. The temperature was raised from room temperature to 550°C at a rate of 5°C / min, and then kept warm for 0.5 h. The temperature was then raised to 900°C at a rate of 5°C / min, and then kept warm for 3 h. The solution was naturally cooled to room temperature to obtain a metal single atom catalyst.

[0063] After testing (the testing method is the same as that of Example 1), the metal loading of the metal single atom catalyst in this example is 2.19wt%, and it exhibits excellent catalytic performance when used for the hydrogenation of nitrobenzene to prepare aniline. The conversion rate of nitrobenzene can reach 85% within 2 hours, and the selectivity of aniline can reach more than 99%.

[0064] Embodiment 7:

[0065] A method for preparing a metal single atom catalyst, comprising the following steps:

[0066] 45 mg of cobalt chloride hexahydrate was dissolved in 2 mL of water to prepare a metal precursor solution, and the metal precursor solution, 2 g of PVC, 4 g of melamine and 2 mL of concentrated hydrochloric acid with a mass fraction of 38% were added to 400 mL of anhydrous ethanol, stirred for 1 hour, and then placed in an oil bath pot and stirred at 90°C until the solvent was evaporated, and then placed in a vacuum dryer for drying, and then placed in a tubular furnace, filled with argon, and the argon flow rate was controlled to be 40 mL / min. The temperature was raised from room temperature to 550°C at a rate of 5°C / min, and then kept warm for 0.5 h. The temperature was then raised to 700°C at a rate of 5°C / min, and then kept warm for 3 h. The solution was naturally cooled to room temperature to obtain a metal single atom catalyst.

[0067] After testing (the testing method is the same as that of Example 1), the metal loading of the metal single atom catalyst in this example is 2.75wt%, and it exhibits excellent catalytic performance when used for the hydrogenation of nitrobenzene to prepare aniline. The conversion rate of nitrobenzene can reach 84% within 2 hours, and the selectivity of aniline can reach more than 99%.

[0068] Embodiment 8:

[0069] A method for preparing a metal single atom catalyst, comprising the following steps:

[0070] Dissolve 45 mg of cobalt chloride hexahydrate in 2 mL of water to prepare a metal precursor solution, then add the metal precursor solution, 2 g of PVC, 4 g of melamine and 2 mL of 38% concentrated hydrochloric acid into 400 mL of anhydrous ethanol, stir for 1 hour, then place in an oil bath and stir at 90°C until the solvent is evaporated, then place in a vacuum dryer for drying, then place in a tubular furnace, fill with argon, control the argon flow rate to 40 mL / min, control the heating rate to 5°C / min from room temperature to 550°C, then keep warm for 0.5 hour, then control the heating rate to 5°C / min and continue to heat to 800°C, then keep warm for 3 hours, and naturally cool to room temperature to obtain a metal single atom catalyst.

[0071] After testing (the testing method is the same as that of Example 1), the metal loading of the metal single atom catalyst in this example is 2.39wt%, and it exhibits excellent catalytic performance when used for the hydrogenation of nitrobenzene to prepare aniline. The conversion rate of nitrobenzene can reach 83% within 2 hours, and the selectivity of aniline can reach more than 99%.

[0072] Embodiment 9:

[0073] A method for preparing a metal single atom catalyst, comprising the following steps:

[0074] Dissolve 45 mg of cobalt chloride hexahydrate in 2 mL of water to prepare a metal precursor solution, then add the metal precursor solution, 2 g of PVC, 4 g of melamine and 2 mL of 38% concentrated hydrochloric acid into 400 mL of anhydrous ethanol, stir for 1 hour, then place in an oil bath and stir at 90°C until the solvent is evaporated, then place in a vacuum dryer for drying, then place in a tubular furnace, fill with argon, control the argon flow rate to 40 mL / min, control the heating rate to 5°C / min from room temperature to 550°C, then keep warm for 0.5 hour, then control the heating rate to continue to heat to 1000°C at 5°C / min, keep warm for 3 hours, and naturally cool to room temperature to obtain a metal single atom catalyst.

[0075] After testing (the testing method is the same as that of Example 1), the metal loading of the metal single atom catalyst in this example is 2.35wt%, and it exhibits excellent catalytic performance when used for the hydrogenation of nitrobenzene to prepare aniline. The conversion rate of nitrobenzene can reach 42% within 2 hours, and the selectivity of aniline can reach more than 99%.

[0076] Embodiment 10:

[0077] A method for preparing a metal single atom catalyst, comprising the following steps:

[0078] 3 mg of cobalt chloride hexahydrate was dissolved in 2 mL of water to prepare a metal precursor solution, and the metal precursor solution, 2 g of PVC, 4 g of melamine and 2 mL of concentrated hydrochloric acid with a mass fraction of 38% were added to 400 mL of anhydrous ethanol, stirred for 1 hour, and then placed in an oil bath pot and stirred at 90°C until the solvent was evaporated, and then placed in a vacuum dryer for drying, and then placed in a tubular furnace, filled with argon, and the argon flow rate was controlled to be 40 mL / min. The temperature was raised from room temperature to 550°C at a rate of 5°C / min, and then kept warm for 0.5 h. The temperature was then raised to 900°C at a rate of 5°C / min, and then kept warm for 3 h. The solution was naturally cooled to room temperature to obtain a metal single atom catalyst.

[0079] After testing (the testing method is the same as that of Example 1), the metal loading of the metal single atom catalyst in this example is 0.29wt%, and it exhibits excellent catalytic performance when used for the hydrogenation of nitrobenzene to prepare aniline. The conversion rate of nitrobenzene can reach 30% within 2 hours, and the selectivity of aniline can reach more than 99%.

[0080] Embodiment 11:

[0081] A method for preparing a metal single atom catalyst, comprising the following steps:

[0082] 33 mg of cobalt nitrate hexahydrate was dissolved in 2 mL of water to prepare a metal precursor solution, and the metal precursor solution, 2 g of PVC, 4 g of melamine and 2 mL of concentrated hydrochloric acid with a mass fraction of 38% were added to 400 mL of anhydrous ethanol, stirred for 1 hour, and then placed in an oil bath pot and stirred at 90°C until the solvent was evaporated, and then placed in a vacuum dryer for drying, and then placed in a tubular furnace, filled with argon, and the argon flow rate was controlled to be 40 mL / min. The temperature was raised from room temperature to 550°C at a rate of 5°C / min, and then kept warm for 0.5 h. The temperature was then raised to 900°C at a rate of 5°C / min, and then kept warm for 3 h. The solution was naturally cooled to room temperature to obtain a metal single atom catalyst.

[0083] After testing (the testing method is the same as that of Example 1), the metal loading of the metal single atom catalyst in this example is 2.67wt%, and it exhibits excellent catalytic performance when used for the hydrogenation of nitrobenzene to prepare aniline. The conversion rate of nitrobenzene can reach 97% within 2 hours, and the selectivity of aniline can reach more than 99%.

[0084] Embodiment 12:

[0085] A method for preparing a metal single atom catalyst, comprising the following steps:

[0086] Dissolve 50 mg of cobalt sulfate heptahydrate in 2 mL of water to prepare a metal precursor solution, then add the metal precursor solution, 2 g of PVC, 4 g of melamine and 2 mL of 38% concentrated hydrochloric acid into 400 mL of anhydrous ethanol, stir for 1 hour, then place in an oil bath and stir at 90°C until the solvent is evaporated, then place in a vacuum dryer for drying, then place in a tubular furnace, fill with argon, control the argon flow rate to 40 mL / min, control the heating rate to 5°C / min from room temperature to 550°C, then keep warm for 0.5 hour, then control the heating rate to continue to heat to 900°C at 5°C / min, keep warm for 3 hours, and naturally cool to room temperature to obtain a metal single atom catalyst.

[0087] After testing (the testing method is the same as that of Example 1), the metal loading of the metal single atom catalyst in this example is 2.56wt%, and it exhibits excellent catalytic performance when used for the hydrogenation of nitrobenzene to prepare aniline. The conversion rate of nitrobenzene can reach 95% within 2 hours, and the selectivity of aniline can reach more than 99%.

[0088] Embodiment 13:

[0089] A method for preparing a metal single atom catalyst, comprising the following steps:

[0090] 46 mg of cobalt acetate tetrahydrate was dissolved in 2 mL of water to prepare a metal precursor solution, and the metal precursor solution, 2 g of PVC, 4 g of melamine and 2 mL of concentrated hydrochloric acid with a mass fraction of 38% were added to 400 mL of anhydrous ethanol, stirred for 1 hour, and then placed in an oil bath pot and stirred at 90°C until the solvent was evaporated, and then placed in a vacuum dryer for drying, and then placed in a tubular furnace, filled with argon, and the argon flow rate was controlled to be 40 mL / min. The temperature was raised from room temperature to 550°C at a rate of 5°C / min, and then kept warm for 0.5 h. The temperature was then raised to 900°C at a rate of 5°C / min, and then kept warm for 3 h. The solution was naturally cooled to room temperature to obtain a metal single atom catalyst.

[0091] After testing (the testing method is the same as that of Example 1), the metal loading of the metal single atom catalyst in this example is 2.71 wt %, and it exhibits excellent catalytic performance when used for the hydrogenation of nitrobenzene to prepare aniline. The conversion rate of nitrobenzene can reach more than 99% within 2 hours, and the selectivity of aniline can reach more than 99%.

[0092] Embodiment 14:

[0093] A method for preparing a metal single atom catalyst, comprising the following steps:

[0094] 45 mg of nickel chloride hexahydrate was dissolved in 2 mL of water to prepare a metal precursor solution, and then the metal precursor solution, 2 g of PVC, 4 g of melamine and 2 mL of concentrated hydrochloric acid with a mass fraction of 38% were added to 400 mL of anhydrous ethanol, stirred for 1 hour, and then placed in an oil bath pot and stirred at 90°C until the solvent was evaporated, and then placed in a vacuum dryer for drying, and then placed in a tubular furnace, filled with argon, and the argon flow rate was controlled to be 40 mL / min. The temperature was raised from room temperature to 550°C at a rate of 5°C / min, and then kept warm for 0.5 h. The temperature was then raised to 900°C at a rate of 5°C / min, and then kept warm for 3 h. The solution was naturally cooled to room temperature to obtain a metal single atom catalyst.

[0095] After testing (the testing method is the same as that of Example 1), the metal loading of the metal single atom catalyst in this example is 2.35wt%, and it exhibits excellent catalytic performance when used for the hydrogenation of nitrobenzene to prepare aniline. The conversion rate of nitrobenzene can reach 76% within 2 hours, and the selectivity of aniline can reach more than 99%.

[0096] Embodiment 15:

[0097] A method for preparing a metal single atom catalyst, comprising the following steps:

[0098] Dissolve 50 mg of nickel nitrate hexahydrate in 2 mL of water to prepare a metal precursor solution, then add the metal precursor solution, 2 g of PVC, 4 g of melamine and 2 mL of 38% concentrated hydrochloric acid into 400 mL of anhydrous ethanol, stir for 1 hour, then place in an oil bath and stir at 90°C until the solvent is evaporated, then place in a vacuum dryer for drying, then place in a tubular furnace, fill with argon, control the argon flow rate to 40 mL / min, control the heating rate to 5°C / min from room temperature to 550°C, then keep warm for 0.5 hour, then control the heating rate to continue to heat to 900°C at 5°C / min, keep warm for 3 hours, and naturally cool to room temperature to obtain a metal single atom catalyst.

[0099] After testing (the testing method is the same as that of Example 1), the metal loading of the metal single atom catalyst in this example is 2.14wt%, and it exhibits excellent catalytic performance when used for the hydrogenation of nitrobenzene to prepare aniline. The conversion rate of nitrobenzene can reach 60% within 2 hours, and the selectivity of aniline can reach more than 99%.

[0100] Embodiment 16:

[0101] A method for preparing a metal single atom catalyst, comprising the following steps:

[0102] Dissolve 30 mg of cupric chloride dihydrate in 2 mL of water to prepare a metal precursor solution, then add the metal precursor solution, 2 g of PVC, 4 g of melamine and 2 mL of 38% concentrated hydrochloric acid into 400 mL of anhydrous ethanol, stir for 1 hour, then place in an oil bath and stir at 90°C until the solvent is evaporated, then place in a vacuum dryer for drying, then place in a tubular furnace, fill with argon, control the argon flow rate to 40 mL / min, control the heating rate to 5°C / min from room temperature to 550°C, then keep warm for 0.5 hour, then control the heating rate to continue to heat to 900°C at 5°C / min, keep warm for 3 hours, and naturally cool to room temperature to obtain a metal single atom catalyst.

[0103] After testing (the testing method is the same as that of Example 1), the metal loading of the metal single atom catalyst in this example is 2.53wt%, and it exhibits excellent catalytic performance when used for the hydrogenation of nitrobenzene to prepare aniline. The conversion rate of nitrobenzene can reach 60% within 2 hours, and the selectivity of aniline can reach more than 99%.

[0104] Embodiment 17:

[0105] A method for preparing a metal single atom catalyst, comprising the following steps:

[0106] Dissolve 40 mg of ferrous chloride tetrahydrate in 2 mL of water to prepare a metal precursor solution, then add the metal precursor solution, 2 g of PVC, 4 g of melamine and 2 mL of 38% concentrated hydrochloric acid into 400 mL of anhydrous ethanol, stir for 1 hour, then place in an oil bath and stir at 90°C until the solvent is evaporated, then place in a vacuum dryer for drying, then place in a tubular furnace, fill with argon, control the argon flow rate to 40 mL / min, control the heating rate to 5°C / min from room temperature to 550°C, then keep warm for 0.5 hour, then control the heating rate to 5°C / min and continue to heat to 900°C, then keep warm for 3 hours, and naturally cool to room temperature to obtain a metal single atom catalyst.

[0107] After testing (the testing method is the same as that of Example 1), the metal loading of the metal single atom catalyst in this example is 2.54wt%, and it exhibits excellent catalytic performance when used for the hydrogenation of nitrobenzene to prepare aniline. The conversion rate of nitrobenzene can reach 78% within 2 hours, and the selectivity of aniline can reach 95%.

[0108] Embodiment 18:

[0109] A method for preparing a metal single atom catalyst, comprising the following steps:

[0110] Dissolve 26 mg of bismuth nitrate pentahydrate in 2 mL of water to prepare a metal precursor solution, then add the metal precursor solution, 2 g of PVC, 4 g of melamine and 2 mL of concentrated hydrochloric acid with a mass fraction of 38% to 400 mL of anhydrous ethanol, stir for 1 hour, then place in an oil bath and stir at 90°C until the solvent is evaporated, then place in a vacuum dryer for drying, then place in a tubular furnace, fill with argon, control the argon flow rate to 40 mL / min, control the heating rate to 5°C / min from room temperature to 550°C, then keep warm for 0.5 hour, then control the heating rate to continue to heat to 900°C at 5°C / min, keep warm for 3 hours, and naturally cool to room temperature to obtain a metal single atom catalyst.

[0111] After testing (the testing method is the same as that of Example 1), the metal loading of the metal single atom catalyst in this example is 2.74wt%, and it exhibits excellent catalytic performance when used for the hydrogenation of nitrobenzene to prepare aniline. The conversion rate of nitrobenzene can reach 49% within 2 hours, and the selectivity of aniline can reach 99%.

[0112] Embodiment 19:

[0113] A method for preparing a metal single atom catalyst, comprising the following steps:

[0114] Dissolve 50 mg of manganese nitrate tetrahydrate in 2 mL of water to prepare a metal precursor solution, then add the metal precursor solution, 2 g of PVC, 4 g of melamine and 2 mL of 38% concentrated hydrochloric acid to 400 mL of anhydrous ethanol, stir for 1 hour, then place in an oil bath and stir at 90°C until the solvent is evaporated, then place in a vacuum dryer for drying, then place in a tubular furnace, fill with argon, control the argon flow rate to 40 mL / min, control the heating rate to 5°C / min from room temperature to 550°C, then keep warm for 0.5 hour, then control the heating rate to continue to heat to 900°C at 5°C / min, keep warm for 3 hours, and naturally cool to room temperature to obtain a metal single atom catalyst.

[0115] After testing (the testing method is the same as that of Example 1), the metal loading of the metal single atom catalyst in this example is 2.35wt%, and it exhibits excellent catalytic performance when used for the hydrogenation of nitrobenzene to prepare aniline. The conversion rate of nitrobenzene can reach 50% within 2 hours, and the selectivity of aniline can reach 89%.

[0116] Embodiment 20:

[0117] A method for preparing a metal single atom catalyst, comprising the following steps:

[0118] Dissolve 43 mg of magnesium chloride in 2 mL of water to prepare a metal precursor solution, then add the metal precursor solution, 2 g of PVC, 4 g of melamine and 2 mL of 38% concentrated hydrochloric acid into 400 mL of anhydrous ethanol, stir for 1 hour, then place in an oil bath and stir at 90°C until the solvent is evaporated, then place in a vacuum dryer for drying, then place in a tubular furnace, fill with argon, control the argon flow rate to 40 mL / min, control the heating rate to 5°C / min from room temperature to 550°C, then keep warm for 0.5 hour, then control the heating rate to 5°C / min and continue to heat to 900°C, then keep warm for 3 hours, and naturally cool to room temperature to obtain a metal single atom catalyst.

[0119] After testing (the testing method is the same as that of Example 1), the metal loading of the metal single atom catalyst in this example is 2.21wt%, and it exhibits excellent catalytic performance when used for the hydrogenation of nitrobenzene to prepare aniline. The conversion rate of nitrobenzene can reach 19% within 2 hours, and the selectivity of aniline can reach 89%.

[0120] Embodiment 21:

[0121] A method for preparing a metal single atom catalyst, comprising the following steps:

[0122] 12 mg of palladium chloride was dissolved in 2 mL of water to prepare a metal precursor solution, and the metal precursor solution, 2 g of PVC, 4 g of melamine and 2 mL of 38% concentrated hydrochloric acid were added to 400 mL of anhydrous ethanol and stirred for 1 hour. The solution was placed in an oil bath and stirred at 90°C until the solvent was evaporated. The solution was then placed in a vacuum dryer for drying, and then placed in a tubular furnace, filled with argon gas, and the argon flow rate was controlled to be 40 mL / min. The temperature was raised from room temperature to 550°C at a rate of 5°C / min, and the solution was kept warm for 0.5 hour. The temperature was then raised to 900°C at a rate of 5°C / min, and the solution was kept warm for 3 hours. The solution was naturally cooled to room temperature to obtain a metal single atom catalyst.

[0123] After testing (the testing method is the same as that of Example 1), the metal loading of the metal single atom catalyst in this example is 1.32wt%, and it exhibits excellent catalytic performance when used for the hydrogenation of nitrobenzene to prepare aniline. The conversion rate of nitrobenzene can reach 76% within 2 hours, and the selectivity of aniline can reach 99%.

[0124] Comparative Example:

[0125] A method for preparing a metal catalyst comprises the following steps:

[0126] Dissolve 45 mg of cobalt chloride hexahydrate in 2 mL of water to prepare a metal precursor solution, then add the metal precursor solution, 2 g of PVC and 4 g of melamine into 400 mL of anhydrous ethanol, stir for 1 hour, then place in an oil bath and stir at 90°C until the solvent is evaporated, then place in a vacuum dryer for drying, then place in a tubular furnace, fill with argon, control the argon flow rate to 40 mL / min, control the heating rate to 5°C / min from room temperature to 550°C, then keep warm for 0.5 hour, then control the heating rate to continue to heat to 900°C at 5°C / min, then keep warm for 3 hours, and naturally cool to room temperature to obtain a metal catalyst.

[0127] Performance Testing:

[0128] 1) The TEM image of the metal catalyst in this comparative example is as follows Figure 5 shown.

[0129] Depend on Figure 5 It can be seen that the metal catalyst in this comparative example is a nanoparticle catalyst.

[0130] 2) After testing (the testing method is the same as that of Example 1), the metal catalyst in this comparative example showed very poor catalytic performance in the hydrogenation of nitrobenzene to prepare aniline, and the conversion rate of nitrobenzene within 2 hours was only 4%.

[0131] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A method for preparing a metal single atom catalyst, characterized in that: The following steps are involved: The metal salt, PVC, melamine and hydrochloric acid are dispersed in a solvent, the solvent is removed, and then the mixture is placed in a protective atmosphere for calcination to obtain a metal single atom catalyst.

2. The method for preparing a metal single atom catalyst according to claim 1, characterized in that: The mass ratio of the metal salt, PVC, melamine and hydrochloric acid is 0.0015-0.0255:1:0.25-4:0.14-2.

38.

3. The method for preparing a metal single atom catalyst according to claim 1 or 2, characterized in that: The metal salt is at least one of a soluble Fe salt, a soluble Co salt, a soluble Ni salt, a soluble Cu salt, a soluble Mn salt, a soluble Mg salt, a soluble Bi salt, and a soluble Pd salt.

4. The method for preparing a metal single atom catalyst according to claim 1 or 2, characterized in that: The mass fraction of the hydrochloric acid is 30% to 40%.

5. The method for preparing a metal single atom catalyst according to claim 1 or 2, characterized in that: The solvent is at least one of ethanol and methanol.

6. The method for preparing a metal single atom catalyst according to claim 1 or 2, characterized in that: The protective atmosphere is one of a nitrogen atmosphere, an argon atmosphere, and a nitrogen-argon mixed atmosphere.

7. The method for preparing a metal single atom catalyst according to claim 1 or 2, characterized in that: The flow rate of the protective atmosphere is 10 mL / min to 100 mL / min.

8. The method for preparing a metal single atom catalyst according to claim 1 or 2, characterized in that: The calcination process includes the following steps: firstly controlling the heating rate to be 5°C / min-15°C / min to heat from room temperature to 450°C-600°C, then keeping the temperature for 0.5h-1.5h, then controlling the heating rate to be 2°C / min-10°C / min to continue heating to 700°C-1000°C, and then keeping the temperature for 1h-5h.

9. A metal single atom catalyst, characterized in that: Prepared by the preparation method described in any one of claims 1 to 8.

10. A method for preparing aniline by hydrogenating nitrobenzene, characterized in that: The catalyst used is the metal single atom catalyst described in claim 9.

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