Nickel-cobalt-loaded nitrogen-sulfur-doped graphene aerogel microsphere as well as preparation method and application thereof

Abstract

The invention discloses a nickel-cobalt-loaded nitrogen-sulfur-doped graphene aerogel microsphere and a preparation method and application thereof.The preparation method comprises the following steps that S1, a graphene oxide water-phase dispersion liquid is prepared, L-cysteine is added into the graphene oxide water-phase dispersion liquid, the mixture is stirred to be uniform, and a first mixed dispersion liquid is obtained; s2, performing electrostatic spraying, obtaining ice microspheres by combining an ice template method, and performing freeze drying to obtain nitrogen and sulfur doped graphene oxide aerogel microspheres; s3, reduction is carried out, and nitrogen and sulfur doped reduced graphene oxide aerogel microspheres are obtained; s4, preparing a nickel-cobalt compound mixed dispersion liquid, adding nitrogen and sulfur doped reduced graphene oxide aerogel microspheres into the nickel-cobalt compound mixed dispersion liquid, and uniformly stirring to obtain a mixed dispersion liquid II; and S5, carrying out hydrothermal reduction, washing and freeze drying to obtain the nickel-cobalt-loaded nitrogen-sulfur-doped graphene aerogel microspheres. The nickel-cobalt-loaded nitrogen-sulfur-doped graphene aerogel microspheres with high catalytic activity can be provided, and technical support is provided for catalyzing propylene cracking to grow carbon nanotubes.

Description

Technical Field

[0001] The present invention relates to the field of catalyst technology, and in particular to nickel-cobalt-loaded nitrogen-sulfur-doped graphene aerogel microspheres, and a preparation method and application thereof. Background Art

[0002] Carbon nanotubes (CNTs) are made of sp 2 One-dimensional nanocarbon materials with tubular structures composed of hybrid carbon atoms. The unique structure of carbon nanotubes gives them excellent properties: tensile strength and Young's modulus are as high as 100GPa and 1TPa respectively; it has excellent fatigue resistance; thermal conductivity is as high as 3500Wm -1 K -1 , exceeding that of natural diamond; the electron and hole mobility is 10 5 cm 2 V -1 S -1 , which is more than 10 times the mobility of silicon and is considered to be one of the ideal materials for preparing integrated circuits.

[0003] Catalytic propylene cracking not only produces large amounts of hydrogen, but also enables the efficient production of carbon nanotubes. Since hydrogen and carbon materials are two promising research topics in environmentally friendly energy and materials science, respectively, the development of advanced catalysts and catalyst supports plays a crucial role in the synergistic hydrogen production from propylene catalytic cracking and the efficient propylene conversion to nanocarbons. Various carbon-based catalysts and catalyst supports have emerged in this field.

[0004] Catalysts for propylene cracking include transition metals such as nickel, cobalt, and iron. Nickel, however, has been widely studied due to its higher activity at low temperatures and its high carbon yield. However, during high-temperature propylene cracking reactions, carbon deposition occurs on the catalyst, resulting in carbon coating and deactivation of single-metal nickel catalysts. Consequently, their efficiency in catalyzing carbon nanotube growth during propylene cracking is low. While single-metal iron and nickel-cobalt alloy catalysts are relatively stable, their catalytic activity is poor, and the support cost of nickel-cobalt alloy catalysts is relatively high. Therefore, the development of new catalysts with high catalytic activity and relatively low cost is urgently needed. Summary of the Invention

[0005] In response to the above problems, the present invention aims to provide a nickel-cobalt loaded nitrogen-sulfur doped graphene aerogel microsphere and its preparation method and application.

[0006] The technical solutions of the present invention are as follows:

[0007] On the one hand, a method for preparing nickel-cobalt loaded nitrogen-sulfur doped graphene aerogel microspheres is provided, comprising the following steps:

[0008] S1: preparing a graphene oxide aqueous dispersion, adding L-cysteine ​​to the graphene oxide aqueous dispersion, and stirring uniformly to obtain a mixed dispersion 1;

[0009] S2: electrostatically spraying the mixed dispersion 1, combining with an ice template method to obtain ice microspheres, and freeze-drying to obtain nitrogen-sulfur-doped graphene oxide aerogel microspheres;

[0010] S3: reducing the nitrogen-sulfur doped graphene oxide aerogel microspheres to obtain nitrogen-sulfur doped reduced graphene oxide aerogel microspheres;

[0011] S4: preparing a nickel-cobalt compound mixed dispersion, adding the nitrogen-sulfur-doped reduced graphene oxide aerogel microspheres and a metal reducing agent to the nickel-cobalt compound mixed dispersion, and stirring uniformly to obtain a second mixed dispersion;

[0012] S5: performing hydrothermal reduction on the second mixed dispersion, washing, and freeze-drying to obtain the nickel-cobalt loaded nitrogen-sulfur doped graphene aerogel microspheres.

[0013] Preferably, in step S1, the concentration of the graphene oxide aqueous dispersion is 5-10 mg / mL, and the amount of L-cysteine ​​used is 5-15% of the mass of the graphene oxide.

[0014] Preferably, in step S2, when electrostatic spraying is performed, the electrostatic voltage is less than or equal to 15KV, the injection speed is less than or equal to 2.4mm / min, and the pressure is less than or equal to 0.4MPa.

[0015] Preferably, in step S2, after obtaining the ice microspheres, the step further includes filtering the ice microspheres through a sieve, and the mesh size of the sieve is 200-400 meshes.

[0016] Preferably, in step S3, when reduction is performed, the temperature is raised from room temperature to 800-1000° C. at a heating rate of 5° C. / min under a protective atmosphere, kept at this temperature for 2-4 hours, and then naturally cooled to room temperature.

[0017] Preferably, in step S4, the nickel-cobalt compound mixed dispersion comprises a water-soluble nickel source, a water-soluble cobalt source and a solvent, and the mass ratio of the water-soluble nickel source to the water-soluble cobalt source is 1:2-2:1.

[0018] Preferably, in step S4, the mass ratio of the nitrogen-sulfur doped reduced graphene oxide aerogel microspheres to the solute of the nickel-cobalt compound mixed dispersion is 1:3-8.

[0019] Preferably, in step S5, the temperature of the hydrothermal reduction is 140-160° C., and the time is 24-48 hours.

[0020] On the other hand, provided are nickel-cobalt loaded nitrogen-sulfur doped graphene aerogel microspheres prepared by any of the above methods for preparing nickel-cobalt loaded nitrogen-sulfur doped graphene aerogel microspheres and their use in catalyzing propylene cracking to grow carbon nanotubes.

[0021] The beneficial effects of the present invention are:

[0022] The present invention can provide nitrogen-sulfur-doped graphene aerogel microspheres loaded with nickel and cobalt with high catalytic activity, and provide technical support for catalyzing the cracking of propylene to grow carbon nanotubes. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0024] Figure 1 This is an SEM image of nitrogen-sulfur-doped graphene aerogel microspheres loaded with nickel and cobalt in Example 1;

[0025] Figure 2 is the SEM image (100 μm) of the microspheres of Comparative Example 1;

[0026] Figure 3 This is the SEM image (200 μm) of the microspheres of Comparative Example 1;

[0027] Figure 4 This is the SEM image (200 μm) of the microspheres of Comparative Example 5;

[0028] Figure 5 This is the SEM image (500 μm) of the microspheres of Comparative Example 5;

[0029] Figure 6 Schematic diagram of the catalytic performance comparison results of Example 1 and other comparative catalysts;

[0030] Figure 7 Schematic diagram of the diameter morphology of carbon nanotubes grown by catalytic cracking of propylene in Example 1 (4 μm);

[0031] Figure 8 Schematic diagram of the diameter morphology of carbon nanotubes grown by catalytic cracking of propylene in Example 1 (500 nm);

[0032] Figure 9 This is a schematic diagram of the size distribution of carbon nanotubes grown by catalytic cracking of propylene in Example 1. DETAILED DESCRIPTION

[0033] The present invention is further described below with reference to the accompanying drawings and examples. It should be noted that, in the absence of conflict, the embodiments in this application and the technical features in the embodiments can be combined with each other. It should be noted that, unless otherwise specified, all technical and scientific terms used in this application have the same meanings as those commonly understood by those of ordinary skill in the art to which this application belongs. The use of similar words such as "include" or "comprising" in the present invention means that the elements or objects appearing before the word cover the elements or objects listed after the word and their equivalents, without excluding other elements or objects.

[0034] In one aspect, the present invention provides a method for preparing nickel-cobalt loaded nitrogen-sulfur doped graphene aerogel microspheres, comprising the following steps:

[0035] S1: preparing a graphene oxide aqueous dispersion, adding L-cysteine ​​to the graphene oxide aqueous dispersion, and stirring uniformly to obtain a mixed dispersion 1.

[0036] In a specific embodiment, the concentration of the graphene oxide aqueous dispersion is 5-10 mg / mL, and the amount of L-cysteine ​​used is 5-15% of the mass of the graphene oxide.

[0037] S2: using the mixed dispersion liquid 1 for electrostatic spraying, combining with ice template method to obtain ice microspheres, freeze-drying, and obtaining nitrogen-sulfur doped graphene oxide aerogel microspheres.

[0038] In a specific embodiment, during electrostatic spraying, the electrostatic voltage is less than or equal to 15 kV, the injection speed is less than or equal to 2.4 mm / min, and the pressure is less than or equal to 0.4 MPa. Alternatively, the electrostatic voltage is 15 kV, the injection speed is 2 mm / min, and the pressure is 0.4 MPa.

[0039] It should be noted that the concentration of the graphene oxide aqueous dispersion and the parameters of the electrostatic spraying will affect the morphology of the microspheres. The parameters of the above embodiment are only preferred embodiment parameters of the present invention. As long as the obtained microspheres are spherical and the particle size of each microsphere is within the particle size threshold range, it will be sufficient.

[0040] In a specific embodiment, after obtaining the ice microspheres, the step of sieve filtration is further included, and the mesh size of the sieve filtration is 200-400. In this embodiment, by filtering the ice microspheres, ice microspheres with more uniform particle size can be obtained.

[0041] S3: reducing the nitrogen-sulfur doped graphene oxide aerogel microspheres to obtain nitrogen-sulfur doped reduced graphene oxide aerogel microspheres.

[0042] In a specific embodiment, during reduction, the temperature is raised from room temperature to 800-1000°C at a heating rate of 5°C / min under a protective atmosphere, maintained for 2-4 hours, and then naturally cooled to room temperature. It should be noted that the parameters of this embodiment are only preferred parameters of the present invention, and any method that can reduce graphene oxide to reduced graphene oxide is applicable to the present invention.

[0043] S4: preparing a nickel-cobalt compound mixed dispersion, adding the nitrogen-sulfur doped reduced graphene oxide aerogel microspheres and the metal reducing agent to the nickel-cobalt compound mixed dispersion, and stirring evenly to obtain a mixed dispersion second.

[0044] In a specific embodiment, the nickel-cobalt compound mixed dispersion comprises a water-soluble nickel source, a water-soluble cobalt source, and a solvent, and the mass ratio of the water-soluble nickel source to the water-soluble cobalt source is 1:2-2:1.

[0045] Optionally, the water-soluble nickel source is nickel acetate tetrahydrate and / or nickel nitrate hexahydrate, the water-soluble cobalt source is cobalt acetate tetrahydrate and / or cobalt nitrate hexahydrate, and the metal reducing agent is ethanol or ethylene glycol.

[0046] In a specific embodiment, the mass ratio of the nitrogen-sulfur doped reduced graphene oxide aerogel microspheres to the solute of the nickel-cobalt compound mixed dispersion is 1:3-8.

[0047] S5: performing hydrothermal reduction on the second mixed dispersion, washing, and freeze-drying to obtain the nickel-cobalt loaded nitrogen-sulfur doped graphene aerogel microspheres.

[0048] In a specific embodiment, the temperature of the hydrothermal reduction is 140-160°C and the time is 24-48h. It should be noted that the parameters of this embodiment are only preferred parameters of the present invention, and its purpose is to reduce the nickel-cobalt compound to metallic nickel and metallic cobalt so that it can be loaded on nitrogen-sulfur-doped graphene aerogel microspheres. In addition, it should be noted that step S4 can only use nickel-cobalt compounds, and then step S5 will reduce them, so that nickel-cobalt can be loaded on nitrogen-sulfur-doped graphene aerogel microspheres; if metallic nickel and metallic cobalt are directly used, they can be directly loaded on nitrogen-sulfur-doped graphene aerogel microspheres in the same way.

[0049] In the present invention, a highly active composite catalyst is obtained by combining a nickel-cobalt bimetallic catalyst, L-cysteine ​​(a nitrogen and sulfur source), and three-dimensional spherical graphene aerogel microspheres. The extremely high specific surface area of ​​the graphene aerogel microspheres provides a large number of active sites for loading the bimetallic catalyst. Furthermore, the nitrogen doping provided by the L-cysteine ​​modifies the electronegativity of the carbon material, increasing the positive charge of the carbon atoms surrounding the nitrogen atoms, thereby affecting the spin density of the carbon atoms and providing a large number of active sites, thereby improving catalytic reaction activity. The sulfur doping also facilitates the catalytic reaction by making it more likely to replace carbon at the jagged edges of the graphene, resulting in a high electron affinity and further boosting catalytic efficiency.

[0050] On the other hand, the present invention also provides nickel-cobalt loaded nitrogen-sulfur doped graphene aerogel microspheres prepared by any of the above-mentioned preparation methods for nickel-cobalt loaded nitrogen-sulfur doped graphene aerogel microspheres and their use in catalyzing propylene cracking to grow carbon nanotubes.

[0051] Example 1

[0052] Nitrogen-sulfur-doped graphene aerogel microspheres loaded with nickel and cobalt are prepared by the following steps:

[0053] (1) preparing a 6 mg / mL graphene oxide aqueous dispersion by ultrasound assistance, adding 10% L-cysteine ​​by weight of the graphene oxide thereto, and stirring ultrasonically until the system is dispersed to obtain a mixed dispersion 1;

[0054] (2) The mixed dispersion is injected into the syringe, and an air pump element is used as a pneumatic assisted electrostatic sprayer. The syringe is placed on the syringe pump and a needle with a specification of "19G outside and 27G inside" is installed (the needle specification can be adjusted according to the size of the prepared microspheres). At the same time, the height between the needle and the n-hexane liquid level is adjusted to 4-10 cm. A 15.0KV electrostatic voltage is applied through the electrode clamp. The dispersion is sprayed through the outer ring of the coaxial needle at an injection speed of 2mm / min, and compressed air is passed through the inner ring to assist the spraying at a pressure of 0.4MPa. At the same time, an ethyl acetate ice bath is used to cool the beaker containing n-hexane to -80℃ and then used as a collection device. After everything is ready, the ball spraying can be carried out. The liquid sprayed from the needle is split into fine water droplets under the action of static electricity. After the water droplets fall into the n-hexane collection device, the difference in surface tension between water and n-hexane causes the water droplets to quickly become spherical. At the same time, because the temperature of n-hexane is very low, the water droplets quickly freeze and fix their own morphology after becoming spherical, thereby obtaining ice microspheres. After the spraying is completed, the microspheres are filtered through a 400-mesh sieve, and the microspheres obtained by separating the ice microspheres from the liquid nitrogen are placed in a freeze dryer and freeze-dried for 72 hours to obtain nitrogen-sulfur doped graphene oxide aerogel microspheres, which are recorded as N,S-GOAMs.

[0055] (3) The obtained N,S-GOAMs were placed in a tube furnace and nitrogen was introduced as a protective gas. The temperature was raised from room temperature to 800°C at a heating rate of 5°C / min. After being kept at this temperature for 2 h, the temperature was naturally cooled to room temperature to obtain nitrogen-sulfur doped reduced graphene oxide aerogel microspheres, which were recorded as N,S-rGOAMs.

[0056] (4) Nickel acetate tetrahydrate and cobalt acetate tetrahydrate were dispersed in 32 mL of N,N-dimethylformamide (DMF) at a mass ratio of 1:1 by magnetic stirring (150 mg each), and 30 mg of N,S-rGOAMs were added to the system and slowly dispersed by magnetic stirring for 5 h. Then, 3.2 mL of ethanol was added to the system and dispersed for another 2 h to obtain a mixed dispersion solution II.

[0057] (5) The mixed dispersion liquid 2 is transferred to the inner lining of the reactor and placed in a sealed high-pressure reactor, which is placed in a vacuum oven at 140°C for reaction for 48 hours. After the reaction is completed, an 1800-mesh sieve is used as a receiver, and the solvent DMF is removed by repeated washing with deionized water and a small amount of ethanol. The product is placed on an 1800-mesh sieve; liquid nitrogen is poured into the sieve to freeze it while retaining a small amount of water. The obtained microspheres are placed in a freeze dryer for freeze-drying for 24 hours to obtain the nickel-cobalt-loaded nitrogen-sulfur-doped graphene aerogel microspheres, which are recorded as N,S-rGOAMs-M.

[0058] Example 2

[0059] The difference from Example 1 is that in step (1) of this example, L-cysteine ​​in an amount of 5% by weight of graphene oxide is added to the graphene oxide aqueous dispersion.

[0060] Example 3

[0061] The difference from Example 1 is that in step (1) of this example, L-cysteine ​​in an amount of 15% by mass of graphene oxide is added to the graphene oxide aqueous dispersion.

[0062] Example 4

[0063] Different from Example 1, nickel nitrate hexahydrate and cobalt nitrate hexahydrate are added in step (4) of this example.

[0064] Example 5

[0065] Different from Example 1, ethylene glycol is added in step (4) of this example.

[0066] Comparative Example 1

[0067] Different from Example 1, L-cysteine ​​was not added in step (1) of this comparative example (ie, nitrogen and sulfur were not doped in this comparative example), and nickel-cobalt loaded graphene aerogel microspheres were obtained, which were recorded as rGOAMs-M.

[0068] Comparative Example 2

[0069] Different from Example 1, in step (1) of this comparative example, DL-dithiothreitol is added instead of L-cysteine ​​(i.e., only sulfur is doped in this comparative example), which is recorded as S-rGOAMs-M.

[0070] Comparative Example 3

[0071] Different from Example 1, in step (1) of this comparative example, L-methionine is added instead of L-cysteine ​​(i.e., the nitrogen source and sulfur source in this comparative example are different), which is recorded as N,S-rGOAMs-M-1.

[0072] Comparative Example 4

[0073] Different from Example 1, in step (1) of this comparative example, L-alanine and DL-dithiothreitol are added instead of L-cysteine ​​(i.e., the nitrogen source and sulfur source in this comparative example are different), and the amount of both is 10%, recorded as N,S-rGOAMs-M-2.

[0074] Comparative Example 5

[0075] Different from Example 1, in step (1) of this comparative example, L-alanine is added instead of L-cysteine ​​(i.e., only nitrogen is doped in this comparative example), which is denoted as N-rGOAMs-M.

[0076] Test Example 1

[0077] The morphology of each embodiment and each comparative example was observed using a scanning electron microscope, and the morphology of Example 1 was as follows: Figure 1 As shown, the morphology results of Comparative Example 1 are as follows Figure 2-3 As shown, the morphology results of Comparative Example 5 are as follows Figure 4-5 As shown. Figure 1 It can be seen that the microspheres obtained in the present invention are round and regular, while the microspheres obtained in Comparative Examples 1 and 5 have uneven sizes and low sphericity. It should be noted that the microspheres obtained in other examples of the present invention are similar to the microspheres in Example 1, with high sphericity and uniform size distribution.

[0078] Test Example 2

[0079] The microspheres of Example 1 were tested by ICP-MS. The results are shown in Table 1:

[0080] Table 1 ICP-MS test results

[0081]

[0082]

[0083] As can be seen from Table 1, the mass ratio of the metal catalyst in Example 1 of the present invention is about 50%, of which the mass ratio of nickel metal is about 30% and the mass ratio of cobalt metal is about 23%, indicating that the present invention successfully loads nickel and cobalt on nitrogen-sulfur-doped graphene aerogel microspheres.

[0084] Test Example 3

[0085] The microspheres of each embodiment and comparative example, as well as commercial vermiculite and nickel metal, were used as catalysts to catalyze the cracking of propylene to grow carbon nanotubes (CNTs). Specifically: 3 mg of the catalyst was weighed and placed in a porcelain boat, which was then transferred to a tube furnace. By CVD, N2 was introduced at a flow rate of 34 L / h and vacuumed until the oxygen content in the furnace was less than 100 ppm. The temperature was then raised from room temperature to 660°C at a rate of 8.5°C / min. The N2 flow rate was changed to 24 L / min, and hydrogen was introduced at a flow rate of 3 L / h, and propylene was introduced at a flow rate of 34 L / h. After the reaction was continued at 660°C for 70 minutes, the introduction of propylene was stopped, and the tube furnace was naturally cooled to room temperature. At this point, CNTs grown by the cracking of propylene catalyzed by the catalyst were obtained.

[0086] The results of the growth of CNTs by catalytic propylene cracking by the catalyst of Example 1 and other comparative catalysts are as follows: Figure 6 As shown. Figure 6 It can be seen that the catalytic magnification of the microspheres of the commercial vermiculite catalyst purchased on the market for catalyzing the cracking of propylene to grow CNTs is about 15 times, the catalytic magnification of the microspheres of the nickel single metal catalyst is 23 times, the catalytic magnification of the microspheres of Comparative Example 1 is 53 times, the catalytic magnification of the microspheres of Comparative Example 2 is 62.4 times, the catalytic magnification of the microspheres of Comparative Example 3 is 70.03 times, the catalytic magnification of the microspheres of Comparative Example 4 is 92.71 times, the catalytic magnification of the microspheres of Comparative Example 5 is 105 times, and the catalytic magnification of the microspheres of Example 1 of the present invention is 196.4 times.

[0087] The microspheres of Example 1 of the present invention: compared with the microspheres doped with only nitrogen in Comparative Example 5, the catalytic propylene cracking activity is increased by 87%, compared with Comparative Example 4 using other nitrogen sources and sulfur sources, the catalytic propylene cracking activity is increased by 112%, compared with Comparative Example 3 using other nitrogen sources and sulfur sources, the catalytic propylene cracking activity is increased by 180%, compared with Comparative Example 2, the catalytic propylene cracking activity of the microspheres doped with only sulfur is increased by 215%, compared with Comparative Example 1, the catalytic propylene cracking activity of the microspheres not doped with nitrogen or sulfur is increased by 269%, compared with the nickel single metal catalyst, the catalytic propylene cracking activity is increased by 750%, and compared with the commercial vermiculite catalyst, the catalytic propylene cracking activity is increased by 1209%.

[0088] The ratios of Example 2 and Example 3 were 134 and 169. In addition, the catalytic effect of Example 1 was also measured at a reaction time of 30 min, and the ratio was 158.

[0089] In addition, the appearance and size of the CNTs obtained by catalysis of Example 1 and each comparative example were observed, and the results of Example 1 are as follows: Figure 7-Figure 9 As shown. By randomly selecting 100 valid samples for analysis based on the SEM image of local CNTs in Example 1, the average tube diameter size of the obtained multi-walled CNTs is about 37.027nm. The average tube diameter size of Comparative Example 1 is about 100.42nm, the average tube diameter size of Comparative Example 2 is about 84.2nm, the average tube diameter size of Comparative Example 3 is about 72.37nm, and the average tube diameter size of Comparative Example 5 is about 53.8nm. It can be seen that the CNTs obtained by the present invention have a smaller and more slender morphology. The smaller the size of the multi-walled CNTs, the stronger the improvement in the mechanical properties of the CNTs, the higher the improvement in strength and stiffness, and the significantly improved chemical activity.

[0090] It should be noted that the above test examples are only a subset of the present invention. Other embodiments of the present invention achieve similar results as Example 1, all effectively catalyzing the decomposition of propylene to produce carbon nanotubes. Furthermore, the above examples are only a subset of the present invention. Microspheres obtained by varying other parameters in the preparation method of the present invention, such as temperature, time, and reagents, exhibit similar performance.

[0091] In summary, the present invention can provide graphene aerogel microspheres with high catalytic activity and is much cheaper than other carriers. Compared with the existing technology, it is a significant improvement.

[0092] The above description is merely a representative embodiment of the present invention and does not constitute any form of limitation to the present invention. Any technical personnel familiar with the present invention who, without departing from the scope of the technical solution of the present invention, makes some changes or modifications to the embodiments disclosed above using the technical contents disclosed above are equivalent embodiments of the present invention. However, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A method for preparing nickel-cobalt loaded nitrogen-sulfur doped graphene aerogel microspheres, characterized in that: The following steps are involved: S1: preparing a graphene oxide aqueous dispersion, adding L-cysteine ​​to the graphene oxide aqueous dispersion, and stirring uniformly to obtain a mixed dispersion 1; S2: electrostatically spraying the mixed dispersion 1, combining with an ice template method to obtain ice microspheres, and freeze-drying to obtain nitrogen-sulfur-doped graphene oxide aerogel microspheres; S3: reducing the nitrogen-sulfur doped graphene oxide aerogel microspheres to obtain nitrogen-sulfur doped reduced graphene oxide aerogel microspheres; S4: preparing a nickel-cobalt compound mixed dispersion, adding the nitrogen-sulfur-doped reduced graphene oxide aerogel microspheres and a metal reducing agent to the nickel-cobalt compound mixed dispersion, and stirring uniformly to obtain a second mixed dispersion; S5: performing hydrothermal reduction on the second mixed dispersion, washing, and freeze-drying to obtain the nickel-cobalt loaded nitrogen-sulfur doped graphene aerogel microspheres.

2. The method for preparing nickel-cobalt loaded nitrogen-sulfur doped graphene aerogel microspheres according to claim 1, characterized in that: In step S1, the concentration of the graphene oxide aqueous dispersion is 5-10 mg / mL, and the amount of L-cysteine ​​used is 5-15% of the mass of the graphene oxide.

3. The method for preparing nickel-cobalt loaded nitrogen-sulfur doped graphene aerogel microspheres according to claim 1, characterized in that: In step S2, when electrostatic spraying is performed, the electrostatic voltage is less than or equal to 15KV, the injection speed is less than or equal to 2.4mm / min, and the pressure is less than or equal to 0.4MPa.

4. The method for preparing nickel-cobalt loaded nitrogen-sulfur doped graphene aerogel microspheres according to claim 1, characterized in that: In step S2, after obtaining the ice microspheres, the step of filtering the ice microspheres through a sieve is also included, and the mesh size of the sieve is 200-400 meshes.

5. The method for preparing nickel-cobalt loaded nitrogen-sulfur doped graphene aerogel microspheres according to claim 1, characterized in that: In step S3, during the reduction, the temperature is raised from room temperature to 800-1000° C. at a heating rate of 5° C. / min under a protective atmosphere, kept at this temperature for 2-4 hours, and then naturally cooled to room temperature.

6. The method for preparing nickel-cobalt loaded nitrogen-sulfur doped graphene aerogel microspheres according to claim 1, characterized in that: In step S4, the nickel-cobalt compound mixed dispersion includes a water-soluble nickel source, a water-soluble cobalt source, and a solvent, and the mass ratio of the water-soluble nickel source to the water-soluble cobalt source is 1:2-2:

1.

7. The method for preparing nickel-cobalt loaded nitrogen-sulfur doped graphene aerogel microspheres according to claim 1, characterized in that: In step S4, the mass ratio of the nitrogen-sulfur doped reduced graphene oxide aerogel microspheres to the solute of the nickel-cobalt compound mixed dispersion is 1:3-8.

8. The method for preparing nickel-cobalt loaded nitrogen-sulfur doped graphene aerogel microspheres according to any one of claims 1 to 7, characterized in that: In step S5, the temperature of the hydrothermal reduction is 140-160° C., and the time is 24-48 hours.

9. A nickel-cobalt loaded nitrogen-sulfur doped graphene aerogel microsphere, characterized in that: The aerogel microspheres are prepared by the method for preparing the nitrogen-sulfur-doped graphene aerogel microspheres loaded with nickel and cobalt according to any one of claims 1 to 8.

10. Use of the nickel-cobalt loaded nitrogen-sulfur doped graphene aerogel microspheres according to claim 9 in catalyzing propylene cracking to grow carbon nanotubes.

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