A method for preparing a single-atom catalyst

Abstract

The application provides a preparation method of a single-atom catalyst, and comprises the following steps: (1) heat treating nitrogen-doped carbon material in an inert atmosphere to obtain a graphene-like carrier material; (2) mixing the graphene-like carrier material with a solvent, preparing a graphene-like dispersion liquid through ultrasonic treatment, and drying the graphene-like dispersion liquid in a protective atmosphere through low-temperature staged drying to obtain a foam metal-graphene-like material; and (3) performing liquid-phase ultrasonic stripping on the foam metal-graphene-like material to obtain a single-atom catalyst. Compared with the prior art, the application eliminates the high-temperature treatment of the foam transition metal in a reducing atmosphere, and compared with the traditional high-energy-consumption high-temperature (above 500 DEG C) treatment method, the method is more moderate and has lower production cost.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of nanomaterials, and particularly relates to a preparation method of a single-atom catalyst. BACKGROUND

[0002] With the development of nanocatalysis and the progress of characterization technology, researchers have found that unsaturated coordination atoms on the surface are often active sites for catalysis, so researchers control the size, morphology and crystal plane of nanocrystals to regulate the distribution and structure of atoms on the surface of the catalyst to improve the catalytic performance. When the size of the nanocrystal is reduced to a cluster or a single atom, the energy level structure and electronic structure will change fundamentally. Due to this unique structural feature, single-atom catalysts often exhibit different activity, selectivity and stability from traditional nanocatalysts. Single-atom materials not only provide an ideal model and research platform for understanding the mechanism of catalytic reactions at the molecular level, but also have the potential to become a new type of catalyst with industrial catalytic applications and biological and medical potential.

[0003] At present, various methods for preparing carbon-supported nitrogen-coordinated single-atom catalysts have been reported in the literature, such as impregnation pyrolysis, wet chemical synthesis, physical and chemical vapor deposition, electrochemical deposition, and ball milling.

[0004] In the invention patent with publication number CN110801838A, a preparation method of a single-atom catalyst is disclosed, which is to mix foam transition metal with graphene oxide dispersion after high-temperature treatment in a reducing atmosphere. The temperature of the high-temperature treatment is 500-900℃, and the time of the high-temperature treatment is 1-3h.

[0005] In the above preparation method, the foam transition metal needs to be subjected to high-temperature treatment (above 500℃) in a reducing atmosphere, which consumes a large amount of energy and has high production cost, hindering the practical application of single-atom catalysts. Therefore, there is an urgent need for a preparation method with milder conditions to obtain single-atom catalysts with uniform atomic distribution. SUMMARY

[0006] Therefore, the technical problem to be solved by the present application is to provide a preparation method of a single-atom catalyst, which eliminates the high-temperature treatment (above 500℃) of foam transition metal in a reducing atmosphere. Compared with the traditional high-temperature treatment method with high energy consumption, the present method is milder and has lower production cost.

[0007] To achieve the above-mentioned purpose, the technical solution adopted by the present application is as follows: a preparation method of a single-atom catalyst, comprising the following steps:

[0008] (1) heat-treating a nitrogen-doped carbon material in an inert atmosphere to obtain a graphene-like support material;

[0009] (2) mixing the graphene-like carrier material with solvent, preparing graphene-like dispersion liquid by ultrasonic, mixing the graphene-like dispersion liquid with the foam transition metal, drying in a protective atmosphere to obtain the foam metal-graphene-like material;

[0010] (3) liquid phase ultrasonic peeling the foam metal-graphene-like material to obtain single-atom catalyst;

[0011] In step (2), the graphene-like dispersion liquid obtained in step (1) is uniformly coated on the foam metal net with a reticular structure, first treated at room temperature for a period of time in an inert atmosphere to remove the surface ethanol and prevent the oxidation of the foam metal, and then heated below 100 DEG C for a period of time in an inert atmosphere to obtain the foam metal-graphene-like material.

[0012] Preferably, the solvent of the graphene-like carrier material in step (2) is ethanol.

[0013] Preferably, after mixing the graphene-like dispersion liquid with the foam transition metal in step (2), the drying in a protective atmosphere is segmented drying, first dried at room temperature for 10-12 hours, and then dried at a temperature of 85-90 DEG C for 10-12 hours.

[0014] Preferably, the foam transition metal is one of cobalt, nickel and copper.

[0015] Preferably, the power of the ultrasonic in step (3) is 800-1000 W.

[0016] Preferably, the flow rate of the protective atmosphere gas in step (2) is 50-80 mL / min.

[0017] Compared with the prior art, the present application eliminates the high-temperature treatment of the foam transition metal in a reducing atmosphere, adopts low-temperature segmented drying, first dried at room temperature for 10-12 hours, and then dried at a temperature of 85-90 DEG C for 10-12 hours. First, the room temperature treatment for 12 hours slowly removes the ethanol to avoid the oxidation of the foam copper, and then the low-temperature (85-90 DEG C) treatment captures the metal atoms on the surface of the foam metal by the surface dangling bonds of the graphene-like material and forms metal-oxygen coordination to realize the preparation of single-atom catalyst. It can be seen from the characterization by spherical aberration-corrected transmission electron microscopy that the prepared single-atom catalyst has uniform metal single-atom distribution and good dispersibility. Compared with the traditional high-temperature (above 500 DEG C) treatment method with high energy consumption, the method is more moderate and has lower production cost. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 The synthesis schematic diagram of the single-atom catalyst provided by the present application;

[0019] Figure 2 This is a spherical aberration corrected transmission electron microscope image of a copper single atom in Example 1 of the present invention;

[0020] Figure 3 This is a spherical aberration corrected transmission electron microscope image of a cobalt single atom in Example 2 of the present invention;

[0021] Figure 4 This is a transmission electron microscope image of a nickel single atom with spherical aberration correction in Example 3 of the present invention. Detailed Implementation

[0022] The following detailed description, in conjunction with the accompanying drawings, outlines specific embodiments. However, it should be understood that the scope of protection of this invention is not limited to these specific embodiments. Unless otherwise specified, all raw materials and reagents used in the examples are commercially available.

[0023] like Figure 1 As shown, the present invention provides a method for preparing a single-atom catalyst, comprising the following steps:

[0024] (1) The nitrogen-doped carbon material is heat-treated in an inert atmosphere to obtain a graphene-like carrier material;

[0025] (2) The graphene-like carrier material is mixed with a solvent and ultrasonically prepared to obtain a graphene-like dispersion. The prepared graphene-like dispersion is mixed with a foam transition metal and dried in a protective atmosphere to obtain a foam metal-graphene-like material.

[0026] (3) The foamed metal-graphene-like material is subjected to liquid-phase ultrasonic exfoliation to obtain a single-atom catalyst;

[0027] The solvent for the graphene-like carrier material in step (2) is ethanol.

[0028] In step (2), after the graphene-like dispersion is mixed with the foam transition metal, it is dried in a protective atmosphere in stages. First, it is dried at room temperature for 10-12 hours, and then dried at 85-90℃ for 10-12 hours. During this process, the surface dangling bonds of the graphene-like material are used to capture metal atoms on the surface of the foam metal at low temperature (90℃) and form metal-oxygen coordination.

[0029] The foam transition metal is one of cobalt, nickel, and copper.

[0030] The foamed metal-graphene oxide material is subjected to liquid-phase ultrasonic exfoliation to obtain a single-atom catalyst. The ultrasonic power during liquid-phase ultrasonic exfoliation in step (3) is 800-1000W.

[0031] During the drying process in step (2), the flow rate of the protective atmosphere gas is 50 mL / min to 80 mL / min.

[0032] Example 1: Preparation of Cu single-atom catalyst

[0033] (1) 2 g of melamine was heated at 600 °C under argon atmosphere for 3 h to obtain a block of carbon nitride material, which was then heated at 500 °C under argon atmosphere for 2 h to obtain about 100 mg of graphene-like powder.

[0034] (2) The above 20 mg of graphene-like powder was mixed with 5 ml of ethanol and ultrasonicated (800 w) for 30 min to obtain a graphene-like dispersion.

[0035] (3) The above dispersion was uniformly dropped onto a foam copper mesh (area of 16 cm 2 , thickness of 3 mm) (the ratio of graphene-like dispersion to foam copper was 1 ml: 10 g), dried under argon atmosphere at a flow rate of 50 mL / min, and treated at room temperature for 10 h to slowly remove ethanol and avoid oxidation of the foam copper.

[0036] (4) The above material was further treated under argon atmosphere at a flow rate of 80 mL / min at 90 °C for 10 h to obtain a foam copper-graphene-like material.

[0037] (5) The foam copper-graphene-like material was dispersed in 100 mL of ethanol and ultrasonicated (1000 w) for 3 h, and the suspension was separated by centrifugation (2000 rpm, 10 min), washed with deionized water for 3 times, washed with ethanol for 1 time, and vacuum dried at 40 °C for 24 h to obtain a copper single-atom catalyst.

[0038] (6) The copper single-atom catalyst obtained in Example 1 was characterized by spherical aberration-corrected transmission electron microscopy, and the results are shown in Figure 2 , from which it can be seen that the copper single atoms are uniformly dispersed on the surface of the graphene-like material. Figure 2

[0039] Example 2: Preparation of Co single-atom catalyst

[0040] (1) 2 g of melamine was heated at 600 °C under argon atmosphere for 3 h to obtain a block of carbon nitride material, which was then heated at 500 °C under argon atmosphere for 2 h to obtain about 100 mg of graphene-like powder.

[0041] (2) The above 20 mg of graphene-like powder was mixed with 5 ml of ethanol and ultrasonicated (800 w) for 30 min to obtain a graphene-like dispersion.

[0042] (3) The above dispersion was uniformly dropped onto a foam cobalt mesh (area of 16 cm 2 ​, thickness of 3 mm) at a ratio of 1 ml: 10 g, dried under an argon atmosphere, argon flow rate of 50 mL / min, room temperature treatment for 11 h, slow removal of ethanol to avoid oxidation of the foam cobalt.

[0043] (4) The above material was continuously placed under an argon atmosphere, argon flow rate of 80 mL / min, 90°C treatment for 11 h, to obtain a foam cobalt-graphene material.

[0044] (5) The foam cobalt-graphene material was dispersed in 100 mL of ethanol under ultrasonic treatment (power of 1000 w) for 3 h, the suspension was separated by centrifugation (2000 rpm, 10 min), washed with deionized water for 3 times, washed with ethanol for 1 time, and vacuum dried at 40°C for 24 h to obtain a cobalt monatomic catalyst.

[0045] (6) The cobalt monatomic catalyst obtained in Example 2 was subjected to spherical aberration-corrected transmission electron microscopy characterization, and the results are shown in Figure 3 , and it can be seen from Figure 3 that the cobalt monatomic atoms are uniformly dispersed on the surface of the graphene.

[0046] Example 3: Preparation of a Ni monatomic catalyst

[0047] (1) 2 g of melamine was heated at 600°C under an argon atmosphere for 3 h to obtain a blocky carbon nitride material, and then heated at 500°C under an argon atmosphere for 2 h to obtain about 100 mg of graphene powder.

[0048] (2) The above 20 mg of graphene was mixed with 5 ml of ethanol, and ultrasonic treatment (power of 800 w) was performed for 30 min to obtain a graphene dispersion.

[0049] (3) The above dispersion was uniformly dropped on a foam nickel mesh (area of 16 cm 2 , thickness of 3 mm) at a ratio of 1 ml: 10 g, dried under an argon atmosphere, argon flow rate of 50 mL / min, room temperature treatment for 12 h, slow removal of ethanol to avoid oxidation of the foam nickel.

[0050] (4) The above material was continuously placed under an argon atmosphere, argon flow rate of 80 mL / min, 85°C treatment for 12 h, to obtain a foam nickel-graphene material.

[0051] (5) The foam cobalt-graphene material was dispersed in 100 mL of ethanol under ultrasonic treatment (power of 1000 w) for 3 h, the suspension was separated by centrifugation (2000 rpm, 10 min), washed with deionized water for 3 times, washed with ethanol for 1 time, and vacuum dried at 40°C for 24 h to obtain a cobalt monatomic catalyst.

[0052] (6) The nickel monatomic catalyst obtained in Example 3 was subjected to spherical aberration correction transmission electron microscopy characterization, and the results are shown in Figure 4 As shown in Figure 4 It can be seen that the nickel monatomic atoms are uniformly dispersed on the graphenelike surface.

[0053] The innovation of the present application is that high-temperature treatment of the foam transition metal in a reducing atmosphere is omitted, and low-temperature staged drying is adopted, that is, first drying for 10-12 h at room temperature, and then drying for 10-12 h at a temperature of 85-90 DEG C. First, the room temperature treatment for 12 h slowly removes ethanol, avoiding oxidation of the foam copper, and then after low-temperature (85-90 DEG C) treatment, the surface dangling bonds of the graphenelike surface are used to capture metal atoms on the surface of the foam metal at low temperature (90 DEG C), and metal-oxygen coordination is formed, realizing preparation of a monatomic catalyst. It can be seen from spherical aberration correction transmission electron microscopy characterization that the prepared monatomic catalyst has uniform metal monatomic atom distribution and good dispersibility. Compared with the traditional high-temperature (above 500 DEG C) treatment method with high energy consumption, the prepared catalyst has the same effect, but the method is more moderate, and the production cost is lower.

Claims

1. A process for the preparation of a single-atom catalyst, characterized in that, It comprises the following steps: (1) heating 2g melamine at 600 DEG C under argon atmosphere for 3h to obtain blocky carbon nitride material, and then heating at 500 DEG C under argon atmosphere for 2h to obtain 100mg graphene-like powder; (2) mixing the graphene-like carrier material with ethanol to prepare graphene-like dispersion liquid by ultrasonic treatment, mixing the graphene-like dispersion liquid with foam transition metal, and drying in stages in a protective atmosphere to obtain foam metal-graphene-like material; (3) performing liquid-phase ultrasonic stripping on the foam metal-graphene-like material to obtain single-atom catalyst; In step (2), the graphene-like dispersion liquid obtained in step (1) is uniformly spread on a foam metal net with a reticular structure, and first dried at room temperature for 10-12h in an inert atmosphere to remove surface ethanol and prevent the foam metal from being oxidized; then dried at a temperature of 85-90 DEG C for 10-12h in an inert atmosphere to obtain foam metal-graphene-like material.

2. The method for preparing a single-atom catalyst according to claim 1, characterized in that, The foam transition metal is one of cobalt, nickel and copper.

3. The method for preparing a single-atom catalyst according to claim 1, characterized in that, In step (3), the power of ultrasonic stripping is 800-1000W.

4. The method for preparing a single-atom catalyst according to claim 1, characterized in that, In step (2), the flow rate of the protective atmosphere gas is 50-80mL / min.

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